Final Exam

Exam 1: - The NAE Grand Challenges describe 14 topics of national importance in engineering, including

topics such as: “make solar energy more economical,” “provide access to clean water” … etc. true

- The price of a Ford “model T” was $850 when it rolled out of the assembly line in 1918. False - High speed steel tools (including tungsten, molybdenum, and molybdenum-cobalt, invented in

the 1950’s, can sustain temperatures up to 1000. False - Stainless steel, as an alloy of iron, have more than 12% of chromium, especially, the famous 18-8

stainless steel has a composition of 18% chromium and 8% nickel. True - The 400 series ferritic stainless steel has a high chromium content (up to 27%), is magnetic, and

is the cheapest among stainless steels: True - The so-called “eutectic solder” in electronic soldering is a tin-lead alloy with about 62% of time

and 38% of lead in the alloy, so as to create the co-existence of solid and liquid phase in soldering applications when heat is applied with a soldering iron. False

- The two G-codes G02 and G03 for circular interpolation and cutting are modal because once the code is issued in a CNC program, the function remains active until canceled by another modal G code. True

- In machine design, we typically consider materials within elastic range. However, in the manufacturing processes presented in this class, we often consider materials and processes in the plastic range, not the linear range. True

- The van der waals force is a primary bond between atoms and molecules and is stronger than a covalent bond. False

- Alumina (Al2O3) is a? ceramic metal - Orthogonal cutting is a manufacturing process model for? Ductile materials - Which of the following statements is not true about passivation of stainless steel? Common

passivation treatment uses alkaline solution - The EDM machine in lab OE-137 is a? wire EDM - What is the average share of manufacturing industry in US GDP from 1950 to 2000? It is always

between 15% and 20% - The American National Standards defines GD&T vocabulary and provide its grammatical rules.

Which document defines the most updated “Dimensioning and Tolerancing”? ASME Y14.5M-1994

- Name the three basic categories of engineering materials: metals, ceramics, polymers - What is the carbon content in 1040 steel? 0.4% - Crystalline structures: BCC (Iron (Fe) and Chromium (Cr))

FCC (Aluminum (Al), Nickel (Ni), and Copper (Cu)) HCP (Titanium (Ti))

Exam 2: - The two steps of parameter design in Taguchi method to enhance the robustness of design are:

step 1: reduce variation Step 2: move to target

- 6 and 9 are the best shape of a chip, they are small and can be removed easily from work piece. - Which mode of wear is the Taylor’s tool life equation based on? Flank wear - Center drill: makes a primary hole that shows the location of the hole. Without it, a drill may not

be able to place the hole at the intended precise location - Binder material for cemented carbides: cobalt

Cements: aluminum - Hardness strongest to weakest: diamond, cubic boron nitride, boron carbide, silicon carbide,

aluminum oxide

- Coated carbide insert tools: The thin film coating are typically done by the following two deposition processes: chemical vapor deposition, physical vapor deposition

Exam 3:

- What is the main factor that distinguishes between the “bulk deformation” and “sheet metal-working” processes? Volume-to-surface-area-ratio

- Explain the reason(s) why a forged connecting rod is better, as far as strength is concerned, than a machined (with material removal) one: forged: continuous grain flow

Machined: interrupted grain flow - The aluminum beverage can is manufactured by a deep drawing process:

a. The manufacturing cost of each can: 4 cents b. The cost of the 12 oz beverage you drink: less than 1 cent c. Why is the lid shaped with a neck area: save material cost of lid (more expensive alloy)

- HONDA’s humanoid robot ASIMO was introduced in 2000. When asked why HONDA invested in such humanoid robot, the CEO of HONDA responded with this answer: Mobility

Quiz 1:

- It is estimated that cutting tools are always used correctly: false - High speed steel tools are stronger than carbide tools: false - Work piece composition and hardness will determine tool shape: true - Only conductive work pieces can be EDM’ed: true - The single piece dies are stronger than those built from segments: true. - Cutting tool selection should be based on safety, time, and quality - Two-thirds of carbide tools are coated, which gives more life time and more cutting speed - Ceramic tools are excellent in chemical resistance but do not withstand high heat - EDM is a thermo erosion process. - Wire cut EDM machine use traveling wire electrode to cut

Quiz 2:

- Stamping dies are the tools that shape and cut sheet metal parts: true - The two principal types of die casting machines are Hot chamber machine and cold chamber

machine: true - Die casting is a high precision rapid part production process involving the high pressure injection

of a molten metal into a die having a cavity of the desired part shape: true - The most common die casting metals are steel and Magnesium alloys: False - Forgibility depends on Metal’s/alloy’s composition, crystal structure, and mechanical properties:

True - Die cast machines are often rated by clamping-force capacity or shot weight capacity. - The die halves are attached to platens of the die cast machine, including stationary platen and

removable platen. - Close-die forging performing may include, edging, blocking and finish-forging - Two most common types of dies are cutting and forming dies - Dies refers to only female part of the tooling.

Quiz 3: - The Knee Mill is used for tool making, prototyping, and mass-volume production: false - Power required for milling operations varies with cutter geometry and speed: true - Process accuracy is an important process and/or property of workholding: true - There are a total of 3 degrees-of-freedom (dof) to be constrained for locating: false - Hole making including holemaking and hole finishing operations: true - Milling process uses the relative motion between the rotating multiple edge cutters and the

workpiece to generate flat and curved surfaces. - Most machining centers have 20-40 tools installed - Workholding includes any device used to grip and present the work piece. - The engine lathe requires means to hold and rotating the workpiece, and hold and move the

cutting tool - Operating parameters and process variables of Lathe are cutting speed, feed rate, and depth of

cut. Quiz 4:

- All injection molding machines are a combination of an injection system and clamping system: true

- Vents are used to heat the thermoplastic material to its appropriate viscosity: false - Thermal expansion of plastics is ten times greater than metals: true - Friction heat easily dissipates through a plastic workpiece: false - Vacuum metallizer is a physical process of depositing a plastic layer on the metal part: false - Injection molding is the most common method of produce part out of plastic material - The speed of the injection molding machine is determined by the mold cooling system - Snap fits are integral fasteners that are molded into plastic parts which lock into place when

assembled. - Welding provides exceptional joints that are as strong as the surrounding plastics - The finishing includes degating, deflashing, cleaning, and decorating.

Homework 2: Chapter 1

- The three basic categories of engineering materials are: metals, ceramics, polymers - Inventions of the Industrial Revolution include which of the following? Steam engine - Ferrous Metals include which of the following? Copper, steel - Which one of the following engineering materials is defined as a compound containing metallic

and nonmetallic elements? Ceramic Chapter 2:

- The basic structure unit of matter is which of the following? Atom - Which of the following bond types are classified as primary bonds? Covalent, ionic bonding,

metallic bonding - How many atoms are there in the face-centered cubic (FCC) unit cell? 14 - Which of the following are not point defects in a crystal lattice structure? Edge dislocations,

grain boundaries, screw dislocation - Polymers are characterized by which of the following bonding types? Covalent, Van der Waals

Chapter 3:

- Which of the following is the correct definition of ultimate tensile strength, as derived from the results of a tensile test on a metal specimen? The maximum load divided by the original area of the specimen

- If stress values were measured during a tensile test, which of the following would have the higher value? True stress

- If strain measurements were made during a tensile test, which would have the higher value? Engineering strain

- The plastic region of the stress-strain curve for a metal is characterized by a proportional relationship between stress and strain? False

- Which of the following types of stress-strain relationships best describes the behavior of brittle materials such as ceramics and thermosetting plastics? Perfectly elastic

- Most hardness tests involve pressing a hard object into the surface of a test specimen and measuring the indentation (or its effect) that result? true

- Which of the following materials had highest hardness? Alumina ceramic Chapter 4:

- In the heating of most metal alloys, melting begins at a certain temperature and concludes at a higher temperature. In these cases, which of the following marks the beginning of melting? Solidus

- Which of the following pure metals is the best conductor of electricity? Silver - A super conductor is characterized by which of the following? Zero resistivity

Chapter 5:

- A tolerance is which of the following? Total permissible variation from a specified dimension - Which one of the following manufacturing processes will likely result in the best surface finish?

Grinding - Which one of the following manufacturing processes will likely result in the worst surface finish?

Sand casting, sawing

Equations

Chapter 3 (hw 2)

- Flow curve: pg 46: 𝜎 = 𝐾𝜀𝑛

- Brinell Hardness Test: pg 53: HB = 2𝐹

𝜋𝐷𝑏 (𝐷𝑏− 𝐷𝑏2−𝐷𝑖

2

Chapter 4 (hw 2)

- Thermal expansion: pg 68: 𝐿2 − 𝐿1 = 𝛼𝐿1(𝑇2 − 𝑇1)

Chapter 5 (hw 2)

- Average roughness: pg 90: 𝑅𝑎 = 𝑦𝑖

𝑛𝑛𝑖=1

- Root-mean square average roughness: 90: 𝑅𝑅𝑀𝑆 =1

𝑛 |𝑦𝑖|2𝑛𝑖=1

Chapter 6: (hw 4)

- Inverse lever rule: pg 102:

L phase proportion: 𝐶𝑆

𝐶𝑆+𝐶𝐿

S phase proportion: 𝐶𝐿

𝐶𝑆+𝐶𝐿

Chapter 21: (hw 5)

- Material Removal Rate: pg 487: 𝑅𝑀𝑅 = 𝑣𝑓𝑑

- Orthogonal cutting operation:

Chip thickness ratio: pg 489: r = 𝑡𝑜

𝑡𝑐

Shear plane angle: pg 489: tan(𝜑) = 𝑟𝑐𝑜𝑠 𝛼

1−𝑟𝑠𝑖𝑛 𝛼

Shear strain: pg 490: 𝛾 = tan 𝜑 − 𝛼 + cot 𝜑

- Forces in metal cutting:

Coefficient of friction: pg 493: 𝜇 = 𝐹

𝑁 = tan(β)

Shear stress: pg 493: 𝜏 = 𝑆 =𝐹𝑠

𝐴𝑠

Area of shear plane: pg 493: 𝐴𝑠 =𝑡0𝑤

sin 𝜑

Pg. 494: F = 𝐹𝑐 sin 𝛼 + 𝐹𝑡cos(𝛼)

N = 𝐹𝑐 cos 𝛼 − 𝐹𝑡sin(𝛼)

𝐹𝑠 = 𝐹𝑐 cos 𝜑 − 𝐹𝑡sin(𝜑)

𝐹𝑛 = 𝐹𝑐 sin 𝜑 + 𝐹𝑡cos(𝜑)

Cutting force: pg 495: 𝐹𝑐 =𝐹𝑠 cos 𝛽−𝛼

cos 𝜑+𝛽−𝛼

Thrust force: pg 495: 𝐹𝑡 =𝐹𝑠 sin 𝛽−𝛼

cos 𝜑+𝛽−𝛼

- Merchant equation: pg 495: 𝜑 =𝛼

2−

𝛽

2

- Cutting power: pg 497: 𝑃𝑐 = 𝐹𝑐𝑣 = U𝑅𝑀𝑅

- Specific energy: pg 498: U =𝑃𝑢

Chapter 22 (hw 6)

- Turning

Rotational speed: pg 511: N = 𝑣

𝜋𝐷0

Feed rate: pg 511: 𝐹𝑟 = 𝑁𝑓

Machining time: pg 511: 𝑇𝑚 =𝐿

𝑓𝑟=

𝜋𝐷0𝐿

𝑓𝑣

- Drilling


𝜋𝐷

Feed rate: pg 520: 𝐹𝑟 = 𝑁𝑓

Machining time for through hole: pg 520: 𝑇𝑚 =𝑡+𝐴

𝑓𝑟

Machining time for blind hole: pg 521: 𝑇𝑚 =𝑑+𝐴

𝑓𝑟

Approach allowance: pg 520: A = 0.5Dtan(90-𝜃

2))

Material Removal Rate: pg 521: 𝑅𝑀𝑅 = 𝜋𝐷2𝑓𝑟/4

- Milling


𝜋𝐷

Feed rate: pg 526: 𝐹𝑟 = 𝑁𝑛𝑡𝑓

Material Removal Rate: pg 527: 𝑅𝑀𝑅 = 𝑤𝑓𝑟𝑑

Slab milling:

Approach allowance: pg 527 A = 𝑑(𝐷 − 𝑑)

Machining time: pg 527: 𝑇𝑚 =𝐿+𝐴

𝑓𝑟

Face milling:

Center over work piece: Approach allowance: pg 527 A = 0.5(𝐷 − 𝐷2 −𝑤2)

Offset: Approach allowance: pg 528: A = 𝑤 𝐷 − 𝑤

Machining time: pg 528: 𝑇𝑚 =𝐿+𝐴

𝑓𝑟

Chapter 23 (hw 6)

- Taylor tool life equation: pg556: 𝑣𝑇𝑛 = 𝐶

- MR = 𝑇

𝑇𝑟𝑒𝑓

Chapter 25: (hw 7)

- Grinding

Average length of chip: pg 610: 𝑙𝑐 = 𝐷𝑑

Material Removal rate: pg 610: 𝑅𝑀𝑅 = 𝑀𝑅𝑅 = 𝑣𝑤𝑤𝑑

Number of chips formed per time: pg 611: 𝑛𝑐 = 𝑣𝑤𝐶

Power: P =Fv = T𝜔

T = 𝐹𝑐𝐷

2

Surface wheel speed: v = 𝜋𝐷𝑁 (N = spindle speed)

Specific energy: u =𝑃

𝑅𝑀𝑅

Chapter 18 (hw 10)

- Strain: 𝜀 =𝐿

𝐿0

- Flow stress: pg 386: 𝑌𝑓 = 𝐾𝜀𝑛

- Average Flow stress: pg 387: 𝑌𝑓 =𝐾𝜀𝑛

1+𝑛

Chapter 19 (hw 10)

- Flat rolling:

Draft: pg397: d = 𝑡0 − 𝑡𝑓

Maximum draft: pg 398: 𝑑𝑚𝑎𝑥 𝜇2𝑅

- forging

Volume: pg 408: V = 𝜋𝐷2𝐿

4

Area: A = 𝑉

𝑕

Forging shape factor: 𝑝𝑔 408: 𝐾𝑓 = 1 +0.4𝜇𝐷

𝑕

Force: pg 408: F =𝐾𝑓𝑌𝑓𝐴

- extrusion:

reduction ratio: pg 423: 𝑟𝑥 =𝐴0

𝐴𝑓

strain: pg 423: 𝜀 = ln(𝑟𝑥)

extrusion strain: pg 424: 𝜀 = 𝑎 + 𝑏ln(𝑟𝑥)

ram pressure for direct extrusion: pg 424: p = 𝑌𝑓 𝜀𝑥 +2𝐿

𝐷0

- Drawing:

Reduction: pg 431: 𝑟 =𝐴0−𝐴𝑓

𝐴0

Strain: pg 431: 𝜀 = ln𝐴0

𝐴𝑓= ln

1

1−𝑟

Draw stress: pg 431: 𝜎𝑑 = 𝑌𝑓 (1 +𝜇

tan 𝛼 )𝜑𝑙𝑛

𝐴0

𝐴𝑓

Pg 432: 𝜑 = 0.88 +0.12𝐷

𝐿𝑐

Contact length: pg 432: 𝐿𝑐 =𝐷0−𝐷𝑓

2 sin ∝

Draw force: pg 432: F = 𝐴𝑓𝜎𝑑

Chapter 20 (hw 10):

- Sheet metal cutting

Clearance: pg 446: c = 𝐴𝑐𝑡

Blanking Punch Diameter: pg 447:𝐷𝑏 − 2𝑐

Blanking die diameter: pg 447:𝐷𝑏

Hole Punch Diameter: pg 447:𝐷𝑕

Hole die diameter: pg 447: 𝐷𝑕 + 2𝑐

- Bending: pg 452-453

- Drawing:

Drawing ratio: pg 457

Reduction: pg 458

Thickness to diameter ratio: pg 458

Chapter 10 (hw 11):

- Solidification time: chvorinov’s rule: 𝑝𝑔 216:

Chapter 38:

- Open loop positioning system:

Speed of motor shaft rotation: pg 899

Angle of rotation: pg 900

Number of pulses: pg 900

Rotational speed of lead screw: pg 900

Pulse train frequency: pg 900

- Closed loop positioning system:

Control resolution: pg 903

KINEMATICS AND WORKSPACE OF SERIAL ROBOT ARM

MEC325/580, Spring 2010 I. Kao

This handout explains the kinematics and workspace of a two-link planar serial manipulator, or robot arm.Analysis of a two-link arm, shown in Figure 1, is the most basic kinematic analysis for serial robots. TheIBM 7545 SCARA robot in the lab has a similar kinematics. Here, we will discuss the forward kinematicsand workspace of such robot arm.

P(x, y)

L2

X

Y

θ1

L1

θ2

O

Figure 1: A 2-link planar manip-ulator.

Kinematics: As shown in Figure 1, the Cartesian coordinates of the end-effector point

can be obtained as follows !"

(1) $#&%' ()$#&% !"(2)

Note that the angle*

is measured from the + axis and

is measuredfrom the extension line of the base link

, . With equations (1) and (2),

we can define the Jacobian matrix which relates the infinitesimal dis-placement in the Cartesian space ( -. ) to that in the joint space ( - ) asfollows

/01-.- 32454 076 454 0984:4 0 6 4$:4 0 8; =<?>' $#&%' > 7#&%@ !A > B$#&% !"' !A B !"C (3)

where -. ED - - GFIH is the vector of the Cartesian coordinates, and - JED "K!7FIH is the vectorcontaining the joint coordinates. The Jacobian matrix relates the infinitesimal displacement - (in radians)to the resulting infinitesimal displacement -. in the Cartesian space by the following equation

-. L/B0 - M@N < - - OC P/0Q< - - !RC (4)

An important note is in order here. Note that any time when the angles are involved in direct algebra, suchas that in equation (4) with

/0 - , you have to use angles in “radians” instead of “degrees.”

Example of forward kinematics and Jacobian: Two configurations of the 2-link arm are given atS $ TUWVYXZ![\]Z

andXZ!$XZ^

, with _XO`bac

and LXO`bVc

.

From equations (1) and (2), the coordinates of the end-effector and the Jacobian matrices are:

At A$!ATUWVYX Z [\ Z ed < C < XO`b\]fgYVXO`b\]h]f]h C /0 <?> XO`b\]h]f]h > XO`bi]h]f]hXO`b\]fgYV XO`jXg]gYa CAt A$ATUX Z $X Z ed < C < XO`bfYXX C /0 < X XXO`bfYX XO`bVYX C

Note that the Jacobian matrix for the second configuration is singular. This is because the two-link arm atthat configuration cannot move along

,direction instantaneously. When this happens, we call the robot

being at a singular configuration. In fact, you should be able to prove that the Jacobian matrix is always

1

singular (i.e., the robot is at a singular configuration) whenever the distal link is aligned with the base link,with

! _X.

With infinitesimal angular displacement of - D XO`jX XO`jX FH - (note the angles are in “radi-ans”), the displacement of the end-effector in the Cartesian coordinates for the two configurations can beobtained from equation (4), and are

-. < - - C <9> XO`jX]XhgYf]aXO`jX]Xag[f C c and -. < - - C < XXO`jX iYXC c (5)

respectively. Again, we find that the two-link manipulator can not move in the

-direction instantaneouslyat configuration 2 because - is identically zero.

Workspace: Workspace of a robot (or called the work envelope) represents the space within which the robotcan reach without singularity. The boundary of the workspace represents the singular configuration of therobot. The workspace depends on the angular range of the two angles of the arms,

and!

. The typicalworkspace for a two-link arm is illustrated in Figure 2 by the shaded region.

X

Y

L2L1

θ2

θ1

O

L1

L2

Figure 2: The workspace of a two-link manipulator with link lengths

and

and the range ofX G

[h]ZandX ! hYXZ

.

2

Taguchi Methods

Parameter Design:Definition of S/N Ratios

Professor Imin Kao, Manufacturing Automation Laboratory, SUNY at Stony Brook; [email protected]

Topics of Exam #3 •  Metal forming & sheet metal working

–  Feasibility of processes –  Analysis and synthesis

•  Casting & molding –  Chvorinov equation & riser design –  Processes of expendable/permanent casting

•  Manufacturing automation & robotics –  Kinematics of robotics: analysis & workspace –  Motion control: accuracy and repeatability –  Design for X –  PLC

Exam #3 Arrangement of Problems •  5 fill-in-blank questions

•  5 Problems

•  Extra credit problems (more difficult; may not necessarily be in textbook; may need additional derivation or work)

MEC325/580 HANDOUT: AN EXAMPLE OF THE TAGUCHI METHOD


This handout explains the application of the non-dynamic Taguchi method using an example of experimentaldesign withL4 orthogonal array on a practical manufacturing process withexperimental measurements.

Problem Statement: Experiments were conducted for a tile making process using the Taguchi method.Three control factors are identified as crucial to the strength of the tiles, as described in the following.

A: ingredient #1,B: ingredient #2, andC: temperature of the curing process

with each control factor having two levels. The experimentswere conducted with the results tabulated inTable 1. Note that in Table 1, the orthogonal array employed is theL4 array. (cf. the handout on variousorthogonal arrays) The data measured (or thereadings) in Table 1 are the strength of the tiles, inMPa.

ResultsNo. A B C N1 N2

1 1 1 1 100 2502 1 2 2 160 1853 2 1 2 495 2954 2 2 1 360 313

Table 1: AL4 array and experimental results

1. Since the strength of the tile is considered here as the measure to evaluate the tile making process,which criterion should you use:larger-the-better, smaller-the-better, or nominal-the-best?

2. Determine the optimal condition of each control factor, based on the parameter design with the S/Nratios to maximize the strength.

Solution: The experimental design has 4 experiments, each with 2 readings. The terms “experiment” and“reading” are explained in theRemarks at the end of this handout.

1. Because the strength of the tile is to be maximized, we willuselarger-the-better criterion.

2. Once thelarger-the-better criterion is chosen, the following equations for calculating the S/N ratiosare employed.

σ2 =1

2

(

1

y21

+1

y22

)

(1)

η = −10 log σ2 (2)

wherey1 andy2 are the data under the 2 columnsN1 andN2. Substituting the readings in Table 1 intoequations (1) and (2), we obtain theL4 orthogonal array with the calculated data ofσ2 andη listed inTable 2.

Once the S/N ratios,η, are calculated, as listed in the last column in Table 2, we can calculate theaverage S/N ratios associated with each level of the three control factors. For example, the average

1

Results S/N RatiosNo. A B C N1 N2 σ2 η

1 1 1 1 100 250 0.00005800 42.372 1 2 2 160 185 0.00003414 44.673 2 1 2 495 295 0.00000779 51.094 2 2 1 360 313 0.00000896 50.48

Table 2: Calculating the S/N ratios based on the measurements and readings

A B C

level 1 43.52 46.73 46.42level 2 50.78 47.57 47.88

Table 3: The response table

S/N ratio forA1 (first level of control parameterA) is the average of experiment No. 1 and 2 (row 1and 2) by virtue of the designation of levels under the columnfor the control factorA. Similarly, theaverage S/N ratio forB2 is the average of experiment No. 2 and 4. The entries of the response tablesare calculated and listed in Table 3.

The response table can be used to plot the following responsechart for the signal-to-noise ratios, asshown in Figure 1.

38

40

42

44

46

48

50

52

A1 A2 B1 B2 C1 C2

Figure 1: The plot of response chart based on the values obtained in the response table.

Optimal Levels of Control Factors:

From the response chart (or the response table), the optimaldesign corresponding to the choice ofthe combination of one of the two levels of the three control factors is found to beA2 B2 C2 (i.e.,level 2 of parameterA, level 2 of parameterB, and level 2 of parameterC) which corresponds to thecombination of highest S/N ratios from each parameter.

For example, if the first and second levels of the curing temperatures (C1 andC2) are150F and200F , respectively, we will choose level 2 with a curing temperature at200F as our design basedon the results of Taguchi method.

Remarks:

2

(i) Each row of the orthogonal array is call an “experiment” which represents a set of experimental setupusing the designated levels of the control factors. For example, in theL4 array in Table 1, each of the4 rows represents one experiment.

(ii) In each experiment, there are “readings”—typically two readings if two compound noise levels areused, as in the case of the example here withN1 andN2.

(iii) Note that the largest S/N ratio is always chosen for optimal design levels regardless of the criterionused. This applies to both positive and negative S/N ratios.

(iv) For other orthogonal arrays, the number of experimentswill change and the combination of the levelsof the control factors will also change. For example, aL9 array has 9 experiments and each controlfactor has 3 levels. Yet, the methodology of finding the S/N ratios and the response table/chart remainsthe same.

3

Taguchi Methods!

Case Study of Taguchi Methods: Canon Example

Professor Imin Kao!Department of Mechanical Engineering!

SUNY at Stony Brook!631-632-8308; email: [email protected]!

Taguchi Methods!

Cannon Example

Distance ! !y= (F!t/m)2 /g sin2" = k F2 sin2" !Ball weight & !!t !m = 0.2 kg, !t=0.1sec!Constant (k) ! !k = 0.02549 m/N2!Range of " ! !0 < " " 45º!Range of F ! !0 < F " 170 N!

Taguchi Methods!

Traditional Approach

Starts with F=130N and apply the !projectile equation!

y = y(F, ") = k F2 sin2"!150 = (0.02549)1302 sin(2 ")!

Solve for " = 10.19º!

Taguchi Methods!

Parameter Design

!  Control factors!

!  Noise factors!

!  Compound factor!

F1 = 30 N "1 = 5°!F2 = 90 N "2 = 23°!F3 = 150 N "3 = 42°!

Fi+ = nominal + 10% Fi

= nominal!Fi- = nominal -10% "i

+ = nominal + 3°! "i = nominal "i

- = nominal - 3°!

N1 = y(Fi+ , "i

+)!N2 = y(Fi

- , "i- ) for i=1,2,3!

Calculations of Flying Distance N1=y(F1’!1’)

F1 = 30 N !1=5º !2=23º !3=42º

F1 = 33 != 8º != 26º != 45º

F2 = 90 N !1=5º !2=23º !3=42ºF2 = 150 N !1=5º !2=23º !3=42º

F2 = 99 != 8º != 26º != 45º

F3 = 165 != 8º != 26º != 45º

y

7.6521.8827.76

68.87196.88249.85

191.30546.89694.02

N2=y(F3’!3’)

F1 = 27 != 2º != 20º != 39º

F2 = 81 != 2º != 20º != 39º

F3 = 135 != 2º != 20º != 39º

y

1.3011.9518.18

11.67107.51163.60

32.41298.63454.44

nominal

Taguchi Methods!

Calculation of S/N Ratio and Mean

Taguchi Methods!

Response Tables

Response table (#)! Response table (mean)!

Optimum Condition: " = 42º! (within chosen range) F = 76.9 N!

F avg@30N 6.06 (!=5º)-0.0386

1st

!

2nd 3rdavg@90N 6.06(!=23º) 7.63

avg@150N 6.06(!=42º) 10.60

Taguchi Methods!

Plot of Response

Taguchi Methods!

Comparison of Variability

Traditional Solution!(F=130 N, "=10.19º) !=45!

Parameter Design!(F=76.9 N, " = 42º) !=26!

Taguchi Methods!

Conclusions of First Iteration

" Conclusions From Response Table (#)!–  The parameter " is more sensitive to parameter

variation so we pick one with largest S/N!–  F has constant S/N ratio so it is insensitive to

parameter variations!" Conclusions From Response Table (mean)!

–  The mean values increase with F!–  The mean values increase with " for the range of

values in the first iteration!

Taguchi Methods!

Graphical Interpretations

Increase S/N ratio !Output variations are much!smaller at "=42o than those!at 5o, for input variation!of ±3o!

Move mean to target!The slope at F=30N!is about 88o so the output is nearly linear when F>30N!

Taguchi Methods!

Summary

•  Quality and Loss Function!•  Two Steps to Increase Robustness and

to Enhance Quality!•  Use Signal-to-Noise Ratio (S/N) in

Parameter Design for Robust Technology!

•  More Robust Results are obtained by Using Parameter Design!

MEC325/580 HANDOUT: VOLUMETRIC CHANGES AND

DEFECTS INMETAL CASTING

Spring 2010 I. Kao

The following lecturing materials are adapted from the textbook [1].

Shrinkage in metal casting: Metals shrink or contract during solidification and coolingprocesses. Shrink-age, which causes dimensional changes in casting, is the result of the following three factors:

1. Contraction of the molten metal as it cools prior to solidification;

2. Contraction of the metal during phase change from liquid to solid (latent heat of fusion); and

3. Contraction of the solidified metal (the casting) as its temperature drops to ambient temperature.

The largest amount of shrinkage occurs during the cooling ofthe casting in factor 2 above. In thefollowing table, the percentages of contraction for several metals during solidification are listed. Note,however, some metals expand during cooling, including graycast iron.

Table 1: Volumetric contraction or expansion percentage for various metals in casting during solidification

metal volumetric contractionAluminum 7.1%Zinc 6.5%Al, 4.5% Cu 6.3%Gold 5.5%White iron 4–5.5%Copper 4.9%Brass (70-30%) 4.5%Magnesium 4.2%90% Cu, 10% Al 4%Carbon steels 2.5–4%Al, 12% Si 3.8%Lead 3.2%

metal volumetricexpansionBismuth 3.3%Silicon 2.9%Gray cast iron 2.5%

Defects in Casting: Defects are important in casting. Different names have beenused to associate the sameor similar defects. As a result, theInternational Committee of Foundry Technical Associations has developedstandardized nomenclature, consisting of seven basic categories of casting defects, as follows.

1. Metallic projections: This category consists of fins, flash, or massive projectionssuch as swells andrough surfaces.

1

2. Cavities: This category consists of rounded or rough internal or exposed cavities, including blow-holes, pinholes, and shrinkage cavities.

3. Discontinuities: Examples are such as cracks, cold or hot tearing, and cold shuts. If the solidifyingmetal is constrained from shrinking freely, cracking and tearing can occur. Although many factorsare involved in tearing, coarse grain size and the presence of low-melting segregates along the grainboundaries (intergranular) increase the tendency for hot tearing. Incomplete castings result from themolten metal being at too low a temperature or from the metal being poured too slowly. Cold shut isan interface in a casting that lacks complete fusion becauseof the meeting of two streams of partiallysolidified metal.

4. Defective surface: This includes defects such as surface folds, laps, scars, adhering sand layers (insand casting), and oxide scale.

5. Incomplete casting: This category includes defects such as misruns (due to premature solidification),insufficient volume of metal poured, and runout (due to loss of metal from the mold after pouring).

6. Incorrect dimension or shape: Such defects are owing to factors such as improper shrinkageal-lowance, pattern-mounting error, irregular contraction,deformed pattern, or warped casting.

7. Inclusions: Inclusions usually form during melting, solidification, and molding. Generally nonmetal-lic, they are regarded as harmful because they act like stress raisers and reduce the strength of thecasting. Hard inclusions (spots) also tend to chip or break tools in machining. They can be filteredout during processing of the molten metal with the environment (usually with oxygen) or the cruciblematerial. Chemical reactions among components in the molten metal may produce inclusions; slugsand other foreign materials entrapped in the molten metal also become inclusions. Reactions betweenthe metal and the mold material may produce inclusions as well. In addition, spalling of the moldand core surfaces produces inclusions, suggesting the importance of maintaining melt quality andmonitoring the conditions of the molds.

References

[1] S. Kalpakjian and S. R. SchmidManufacturing Processes for Engineering Materials Prentice Hall,fourth ed., 2003

2

1

Metal CastingIntroduction

Manufacturing Processes –– Podcast Series

Imin Kao, ProfessorDept. of Mechanical EngineeringCollege of Engineering and App. Sci.SUNY at Stony Brook

An Introduction of Casting• Process in which molten metal/materials

flows by gravity or other force into a moldwhere it solidifies in the shape of the moldcavity

• Solidification processes can be classifiedaccording to engineering material processed:– Metals– Ceramics, specifically glasses– Polymers and polymer matrix composites (PMCs)

2

Metal Casting

Open mold Closed mold

Two Categories of Casting Processes

1. Expendable mold processes – uses anexpendable mold which must be destroyedto remove casting

– Mold materials: sand, plaster, and similarmaterials, plus binders

2. Permanent mold processes – uses apermanent mold which can be used overand over to produce many castings

– Made of metal (or, less commonly, a ceramicrefractory material

3

Solidification Time• Heat content ∝ volume & heat transfer ∝ surface area• Solidification time depends on size and shape of

casting by relationship known as Chvorinov's Rule

where TST = total solidification time; V = volume ofthe casting; A = surface area of casting; n = exponentwith typical value = 2; and Cm is mold constant.

!

TST = Cm

V

A

"

# $

%

& '

n

Mold Constant in Chvorinov's Rule• Mold constant Cm depends on:

– Mold material– Thermal properties of casting metal– Pouring temperature relative to melting point

• Value of Cm for a given casting operationcan be based on experimental data fromprevious operations carried out using samemold material, metal, and pouringtemperature, even though the shape of thepart may be quite different

4

Chvorinov’s Rule & Cast Design

• A casting with a higher V/A ratio cools andsolidifies more slowly than one with lower ratio– To feed molten metal to main cavity, TST for riser

must greater than TST for main casting

• Since mold constants of riser and casting will beequal, design the riser to have a larger V/A ratioso that the main casting solidifies first– Riser acts as heat & cast reservoir– This minimizes the effects of shrinkage

Furnaces for Casting Processes

Furnaces most commonly used in foundries:• Cupolas• Direct fuel‑fired furnaces• Crucible furnaces• Electric‑arc furnaces• Induction furnaces

5

Metals for Casting• Most commercial castings are made of

alloys rather than pure metals– Alloys are generally easier to cast, and

properties of product are better• Casting alloys can be classified as:

– Ferrous: (1) gray cast iron, (2) nodular iron, (3)white cast iron, (4) malleable iron, and (5) alloycast irons (∼ 1400°C or 2500°F) & (6) steel (1650°C or 3000°F)

– Nonferrous: (1) Aluminum (660°C or 1220°F), (2)Copper Alloys (1083°C or 1981°F), (3) Zinc Alloys(419°C or 786°F), (4) others

Post-Solidification Processes• Trimming• Removing the core• Surface cleaning• Inspection• Repair, if required• Heat treatment

6

Casting Quality• There are numerous opportunities for things to

go wrong in a casting operation, resulting inquality defects in the product

• The defects can be classified as follows:– Common defects to all casting processes: (a)

misrun, (b) cold shut, (c) cold shots, (d) shrinkagecavity, (e) microporosity, (f) hot tearing

– Defects related to sand casting process: (a) sandblow, (b) pinholes, (c) sand wash, (d) scabs, (e)penetration, (f) mold shift, (g) core shift, (h) moldcrack

Misrun: A casting that hassolidified before completelyfilling mold cavity

Cold shot: Two portions ofmetal flow together but thereis a lack of fusion due topremature freezing

Common Casting Defects (a) & (b)

7

Common Casting Defects (c) & (d)Cold shots: Metal splattersduring pouring and solidglobules form and becomeentrapped in casting

Shrinkage cavity: Depression in surfaceor internal void caused by solidificationshrinkage that restricts amount ofmolten metal available in last region tofreeze

Common Casting Defects (e) & (f)Microporosity: network ofsmall voids due to localshrinkage in the dendriticstructure

Hot tearing: hot crackingcaused by unyielding mold incontraction during cooling,with separation of metal cast

MEC325/580 HANDOUT: METAL CASTING AND RISER DESIGN

Spring 2010 I. Kao

An important aspect of design for metal casting using sand mold is the consideration of solidification time,and the inclusion of riser design to elongate the time to solidification in order to reduce defects or otherfailures in the casting process.

The solidification time in metal casting is governed by the following empirical equation called theChvorinov’s rule

TST = Cm

(

V

A

)n

(1)

whereTST is the total solidification time,Cm is the mold constant,VA

is the volume-to-surface-area ratio,andn is the exponent, usually taken as 2. The mold constant,Cm depends on the particular conditions ofthe cast operation, including mold material, thermal properties of case metal, and pouring temperature. Themold constant can be obtained based on experimental data with the same mold, metal, pouring temperature,... etc, even though the part may be very different. The Chvorinov’s rule suggests that a casting with highervolume-to-surface-area ratio will cool and solidify more slowly than one with a lower ratio.

The riser design can be used to prevent part of the metal cast from prematurely solidified which causescasting defects. Risers by its relative position can beside riser or top riser, or by its configuration can beopen riser or blind riser. The following figure shows a closed mold with a complex mold geometry whichrequires a riser design. Note the different terminology of the parts of the cast and mold, as illustrated inFigure 1.

Figure 1: A closed mold in which the mold geometry is more complex and requires a passageway systemleading into the cavity, with a riser design.

Example: Riser design using the Chvorinov’s rule.A cylindrical riser must be designed for the sand casting mold shown in Figure 1. The passageway leadingto the cavity casting is a steel rectangular plate with dimension of3′′ × 5′′ × 1′′. Previous observations haveindicated that the total solidification time (TST ) for this casting is1.6 min. The cylindrical riser will havea diameter-to-height ratio of 1.0. Determine the dimensions of the riser so that theTST is 2.0 minutes toallow more time for the flow of metal to cavity for a successfulcasting.

Solution: First, we need to determineCm for the casting:

1

The volume isV = 3 × 5 × 1 = 15 in3; the surface area isA = 2(3 × 5 + 3 × 1 + 5 × 1) = 46 in2.GivenTST = 1.6 min, we taken = 2 and apply the Chvorinov’s rule,

1.6 = Cm

(

15

46

)2

=⇒ Cm = 15.05 min/in2 (2)

Therefore, the mold constant for the riser is alsoCm = 15.05 min/in2.

For the cylindrical riser, the volume isV = πD2

4h = πD3

4since D

h= 1 (given); the surface area is

A = πDh + 2(

πD2

4

)

= 1.5πD2. Thus, the ratio is

V

A=

(1

4)

1.5D =

D

6(3)

Substituting into the Chvorinov’s equation, we have

2.0 = 15.05

(

D

6

)2

=⇒ D = h = 2.187′′ (4)

Therefore, the cylindrical riser with a diamter-to-heightratio of 1.0 should have a diamter ofD = 2.187′′.

Remarks: For the riser and cast, the following comparison can be made.

volume surface area

riser Vr = 8.216 in3 Ar = 22.54 in2

cast Vc = 15 in3 Ac = 46 in2

Based on the table, we haveVr

Vc

= 55%. That is, the volume of the cast is increased by 55% due to theriser if only the rectangular part is concerned. However, the gain in time is 25% that allows the cavity to befilled more completely.

References

[1] M. P. GrooverFundamentals of Modern Manufacturing: materials, processes, and systems Wiley, thirded., 2006

2

©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

INTRODUCTION AND OVERVIEW OF MANUFACTURING

1. What is Manufacturing?2. Materials in Manufacturing3. Manufacturing Processes4. Production Systems5. Organization of the Book


Manufacturing is Important

Technologically Economically Historically


Manufacturing - Technologically Important

Technology - the application of science to provide society and its members with those things that are needed or desired

Technology provides the products that help our society and its members live better

What do these products have in common? They are all manufactured

Manufacturing is the essential factor that makes technology possible


Manufacturing - Economically Important

Manufacturing is one way by which nations create material wealth

U.S. economy:

Sector% of

GNP

Manufacturing 20%

Agriculture, minerals, etc. 5%

Construction & utilities 5%

Service sector – retail, transportation, banking, communication, education, and government

70%


Manufacturing - Historically Important

Throughout history, human cultures that were better at making things were more successful

Making better tools meant better crafts & weapons Better crafts allowed people to live better Better weapons allowed them to conquer

other cultures in times of conflict To a significant degree, the history of

civilization is the history of humans' ability to make things


What is Manufacturing?

The word manufacture is derived from two Latin words manus (hand) and factus (make); the combination means “made by hand”

“Made by hand” accurately described the

fabrication methods that were used when the English word “manufacture” was first coined

around 1567 A.D. Most modern manufacturing operations are

accomplished by mechanized and automated equipment that is supervised by human workers


Manufacturing - Technologically

Figure 1.1 (a) Manufacturing as a technical process

Application of physical and chemical processes to alter the geometry, properties, and/or appearance of a starting material to make parts or products Manufacturing also includes assembly Almost always carried out as a sequence of operations


Manufacturing - Economically

Figure 1.1 (b) Manufacturing as an economic process

Transformation of materials into items of greater value by means of one or more processing and/or assembly operations Manufacturing adds value to the material by changing its shape or properties, or by combining it with other materials


Manufacturing Industries

Industry consists of enterprises and organizations that produce or supply goods and services

Industries can be classified as:1. Primary industries - those that cultivate

and exploit natural resources, e.g., farming, mining

2. Secondary industries - take the outputs of primary industries and convert them into consumer and capital goods -manufacturing is the principal activity

3. Tertiary industries - service sector


Manufacturing Industries - continued

Secondary industries include manufacturing, construction, and electric power generation

Manufacturing includes several industries whose products are not covered in this book; e.g., apparel, beverages, chemicals, and food processing

For our purposes, manufacturing means production of hardware Nuts and bolts, forgings, cars, airplanes,

digital computers, plastic parts, and ceramic products


Production Quantity Q

The quantity of products Q made by a factory has an important influence on the way its people, facilities, and procedures are organized

Annual production quantities can be classified into three ranges: Production range Annual Quantity QLow production 1 to 100 units Medium production 100 to 10,000 unitsHigh production 10,000 to millions of


Product Variety P

Product variety P refers to different product types or models produced in the plant

Different products have different features They are intended for different markets Some have more parts than others

The number of different product types made each year in a factory can be counted

When the number of product types made in

the factory is high, this indicates high

product variety


P versus Q in Factory Operations

Figure 1.2 P-Q Relationship


More About Product VarietyAlthough P is a quantitative parameter, it is

much less exact than Q because details on how much the designs differ is not captured simply by the number of different designs

Soft product variety - small differences between products, e.g., between car models made on the same production line, with many common parts among models

Hard product variety - products differ substantially, e.g., between a small car and a large truck, with few common parts (if any)


Manufacturing Capability

A manufacturing plant consists of processes and systems (and people, of course) designed to transform a certain limited range of materials

into products of increased value The three building blocks - materials,

processes, and systems - are the subject of modern manufacturing

Manufacturing capability includes:1. Technological processing capability

2. Physical product limitations

3. Production capacity


1. Technological Processing Capability

The available set of manufacturing processes in the plant (or company)

Certain manufacturing processes are suited to certain materials By specializing in certain processes, the

plant is also specializing in certain materials

Includes not only the physical processes, but also the expertise of the plant personnel

Examples: A machine shop cannot roll steel A steel mill cannot build cars


2. Physical Product Limitations

Given a plant with a certain set of processes, there are size and weight limitations on the parts or products that can be made in the plant

Product size and weight affect: Production equipment Material handling equipment

Production, material handling equipment, and plant size must be planned for products that lie within a certain size and weight range


3. Production CapacityDefined as the maximum quantity that a plant

can produce in a given time period (e.g., month or year) under assumed operating conditions

Operating conditions refer to number of shifts per week, hours per shift, direct labor manning levels in the plant, and so on

Usually measured in terms of output units, such as tons of steel or number of cars produced by the plant

Also called plant capacity


Materials in Manufacturing

Most engineering materials can be classified into one of three basic categories: 1. Metals2. Ceramics3. Polymers

Their chemistries are different Their mechanical and physical properties

are dissimilar These differences affect the manufacturing

processes that can be used to produce products from them


In Addition: Composites

Figure 1.3 Venn diagram of three basic material types plus composites

Nonhomogeneous mixtures of the other three basic types rather than a unique category


1. Metals

Usually alloys, which are composed of two or more elements, at least one of which is metallic

Two basic groups: 1. Ferrous metals - based on iron, comprises

about 75% of metal tonnage in the world:

Steel = Fe-C alloy (0.02 to 2.11% C)

Cast iron = Fe-C alloy (2% to 4% C)

2. Nonferrous metals - all other metallic elements and their alloys: aluminum, copper, magnesium, nickel, silver, tin, titanium, etc.


2. Ceramics

Compounds containing metallic (or semi-metallic) and nonmetallic elements.

Typical nonmetallic elements are oxygen, nitrogen, and carbon

For processing, ceramics divide into:1. Crystalline ceramics – includes:

Traditional ceramics, such as clay (hydrous aluminum silicates)

Modern ceramics, such as alumina (Al2O3)

2. Glasses – mostly based on silica (SiO2)


3. Polymers

Compound formed of repeating structural units called mers, whose atoms share electrons to form very large molecules

Three categories: 1. Thermoplastic polymers - can be

subjected to multiple heating and cooling cycles without altering molecular structure

2. Thermosetting polymers - molecules chemically transform (cure) into a rigid structure – cannot be reheated

3. Elastomers - shows significant elastic behavior


4. CompositesMaterial consisting of two or more phases that

are processed separately and then bonded together to achieve properties superior to its constituents

Phase - homogeneous mass of material, such as grains of identical unit cell structure in a solid metal

Usual structure consists of particles or fibers of one phase mixed in a second phase

Properties depend on components, physical shapes of components, and the way they are combined to form the final material


Manufacturing Processes

Two basic types: 1. Processing operations - transform a work

material from one state of completion to a more advanced state Operations that change the geometry,

properties, or appearance of the starting material

2. Assembly operations - join two or more components to create a new entity


Figure 1.4 Classification of manufacturing processes


Processing Operations

Alters a material’s shape, physical properties,

or appearance in order to add value Three categories of processing

operations: 1. Shaping operations - alter the geometry

of the starting work material 2. Property-enhancing operations -

improve physical properties without changing shape

3. Surface processing operations - to clean, treat, coat, or deposit material on exterior surface of the work


Shaping Processes – Four Categories

1. Solidification processes - starting material is a heated liquid or semifluid

2. Particulate processing - starting material consists of powders

3. Deformation processes - starting material is a ductile solid (commonly metal)

4. Material removal processes - starting material is a ductile or brittle solid


Solidification Processes

Starting material is heated sufficiently to transform it into a liquid or highly plastic state

Examples: metal casting, plastic molding


Particulate Processing

Starting materials are powders of metals or ceramics

Usually involves pressing and sintering, in which powders are first compressed and then heated to bond the individual particles


Deformation Processes

Starting workpart is shaped by application of forces that exceed the yield strength of the material

Examples: (a) forging, (b) extrusion


Material Removal Processes

Excess material removed from the starting piece so what remains is the desired geometry

Examples: machining such as turning, drilling, and milling; also grinding and nontraditional processes


Waste in Shaping ProcessesDesirable to minimize waste in part shaping Material removal processes are wasteful in

unit operations, simply by the way they work Most casting, molding, and particulate

processing operations waste little material Terminology for minimum waste processes:

Net shape processes - when most of the starting material is used and no subsequent machining is required

Near net shape processes - when minimum amount of machining is required


Property-Enhancing Processes

Performed to improve mechanical or physical properties of work material

Part shape is not altered, except unintentionally Example: unintentional warping of a heat

treated part Examples:

Heat treatment of metals and glasses Sintering of powdered metals and ceramics


Surface Processing Operations Cleaning - chemical and mechanical

processes to remove dirt, oil, and other contaminants from the surface

Surface treatments - mechanical working such as sand blasting, and physical processes like diffusion

Coating and thin film deposition - coating exterior surface of the workpart


Assembly Operations

Two or more separate parts are joined to form a new entity

Types of assembly operations:1. Joining processes – create a permanent

joint Welding, brazing, soldering, and

adhesive bonding2. Mechanical assembly – fastening by

mechanical methods Threaded fasteners (screws, bolts and

nuts); press fitting, expansion fits


Production Systems

People, equipment, and procedures used for the combination of materials and processes that constitute a firm's manufacturing operations

A manufacturing firm must have systems and procedures to efficiently accomplish its type of production

Two categories of production systems: Production facilities Manufacturing support systems

Both categories include people (people make the systems work)


Production Facilities

The factory, production equipment, and material handling systems

Production facilities "touch" the product Includes the way the equipment is arranged

in the factory - the plant layout

Equipment usually organized into logical groupings, called manufacturing systems

Examples: Automated production line Machine cell consisting of an industrial

robot and two machine tools


Facilities versus Product QuantitiesA company designs its manufacturing systems

and organizes its factories to serve the particular mission of each plant

Certain types of production facilities are recognized as the most appropriate for a given type of manufacturing:1. Low production – 1 to 1002. Medium production – 100 to 10,0003. High production – 10,000 to >1,000,000

Different facilities are required for each of the three quantity ranges


Low ProductionJob shop is the term used for this type of

production facility A job shop makes low quantities of

specialized and customized products Products are typically complex, e.g.,

space capsules, prototype aircraft, special machinery

Equipment in a job shop is general purpose Labor force is highly skilled Designed for maximum flexibility


Medium Production

Two different types of facility, depending on product variety:

Batch production

Suited to hard product variety Setups required between batches

Cellular manufacturing

Suited to soft product variety Worker cells organized to process parts

without setups between different part styles


High Production

Often referred to as mass production

High demand for product Manufacturing system dedicated to the

production of that product Two categories of mass production:

1. Quantity production2. Flow line production


Quantity Production

Mass production of single parts on single machine or small numbers of machines

Typically involves standard machines equipped with special tooling

Equipment is dedicated full-time to the production of one part or product type

Typical layouts used in quantity production are process layout and cellular layout


Flow Line Production

Multiple machines or workstations arranged in sequence, e.g., production lines

Product is complex Requires multiple processing and/or

assembly operations Work units are physically moved through the

sequence to complete the product Workstations and equipment are designed

specifically for the product to maximize efficiency


Manufacturing Support Systems

A company must organize itself to design the processes and equipment, plan and control production, and satisfy product quality requirements

Accomplished by manufacturing support systems - people and procedures by which a company manages its production operations

Typical departments: 1. Manufacturing engineering 2. Production planning and control3. Quality control


Overview of Major Topics

Figure 1.10 Overview of production system and major topics in Fundamentals of Modern Manufacturing.


A spectacular scene in steelmaking is charging of a basic oxygen furnace, in which molten pig iron produced in a blast furnace is poured into the BOF. Temperatures are around 1650°C (3000 ° F).


A machining cell consisting of two horizontal machining centers supplied by an in-line pallet shuttle (photo courtesy of Cincinnati Milacron).


A robotic arm performs unloading and loading operation in a turning center using a dual gripper (photo courtesy of Cincinnati Milacron).


Metal chips fly in a high speed turning operation performed on a computer numerical control turning center (photo courtesy of Cincinnati Milacron).


Photomicrograph of the cross section of multiple coatings of titanium nitride and aluminum oxide on a cemented carbide substrate (photo courtesy of Kennametal Inc.).


A batch of silicon wafers enters a furnace heated to 1000°C (1800°F) during fabrication of integrated circuits under clean room conditions (photo courtesy of Intel Corporation).


Two welders perform arc welding on a large steel pipe section (photo courtesy of Lincoln Electric Company).


Automated dispensing of adhesive onto component parts prior to assembly (photo courtesy of EFD, Inc.).


Assembly workers on an engine assembly line (photo courtesy of Ford Motor Company).


Assembly operations on the Boeing 777 (photo courtesy of Boeing Commercial Airplane Co.).


DIMENSIONS, TOLERANCES, AND SURFACES

1. Dimensions, Tolerances, and Related Attributes

2. Surfaces 3. Effect of Manufacturing Processes


Dimensions and Tolerances

Factors that determine the performance of a manufactured product, other than mechanical and physical properties, include : Dimensions - linear or angular sizes of a

component specified on the part drawing Tolerances - allowable variations from the

specified part dimensions that are permitted in manufacturing


Dimensions (ANSI Y14.5M-1982):

A dimension is "a numerical value expressed in appropriate units of measure and indicated on a drawing and in other documents along with lines, symbols, and notes to define the size or geometric characteristic, or both, of a part or part feature"

Dimensions on part drawings represent nominal or basic sizes of the part and its features

The dimension indicates the part size desired by the designer, if the part could be made with no errors or variations in the fabrication process


Tolerances (ANSI Y14.5M-1982):

A tolerance is "the total amount by which a specific dimension is permitted to vary. The tolerance is the difference between the maximum and minimum limits"

Variations occur in any manufacturing process, which are manifested as variations in part size

Tolerances are used to define the limits of the allowed variation


Bilateral Tolerance

Variation is permitted in both positive and negative directions from the nominal dimension Possible for a bilateral tolerance to be unbalanced; for example, 2.500 +0.010, -0.005 Figure 5.1 Ways to specify

tolerance limits for a nominal dimension of 2.500: (a) bilateral


Unilateral Tolerance

Variation from the specified dimension is permitted in only one direction Either positive or negative, but not both

Figure 5.1 Ways to specify tolerance limits for a nominal dimension of 2.500:(b) unilateral


Limit Dimensions

Permissible variation in a part feature size consists of the maximum and minimum dimensions allowed

Figure 5.1 - Ways to specify tolerance limits for a nominal dimension of 2.500:(c) limit dimensions


SurfacesNominal surface – designer’s intended surface

contour of part, defined by lines in the engineering drawing The nominal surfaces appear as

absolutely straight lines, ideal circles, round holes, and other edges and surfaces that are geometrically perfect

Actual surfaces of a part are determined by the manufacturing processes used to make it Variety of processes result in wide

variations in surface characteristics


Why Surfaces are Important

Aesthetic reasons Surfaces affect safety Friction and wear depend on surface

characteristics Surfaces affect mechanical and physical

properties Assembly of parts is affected by their surfaces Smooth surfaces make better electrical

contacts


Surface Technology

Concerned with: Defining the characteristics of a surface Surface texture Surface integrity Relationship between manufacturing

processes and characteristics of resulting surface


Metallic Part Surface

Figure 5.2 A magnified cross-section of a typical metallic part surface.


Surface Texture

The topography and geometric features of the surface

When highly magnified, the surface is anything but straight and smooth It has roughness, waviness, and flaws

It also possesses a pattern and/or direction resulting from the mechanical process that produced it


Surface TextureRepetitive and/or random deviations from the

nominal surface of an object

Figure 5.3 Surface texture features.


Four Elements of Surface Texture

1. Roughness - small, finely-spaced deviations from nominal surface Determined by material characteristics and

processes that formed the surface 2. Waviness - deviations of much larger spacing

Waviness deviations occur due to work deflection, vibration, heat treatment, and similar factors

Roughness is superimposed on waviness



3. Lay - predominant direction or pattern of the surface texture

Figure 5.4 Possible lays of a surface.



4. Flaws - irregularities that occur occasionally on the surface Includes cracks, scratches, inclusions, and

similar defects in the surface Although some flaws relate to surface

texture, they also affect surface integrity


Surface Roughness and Surface Finish

Surface roughness - a measurable characteristic based on roughness deviations

Surface finish - a more subjective term denoting smoothness and general quality of a surface In popular usage, surface finish is often

used as a synonym for surface roughness Both terms are within the scope of surface

texture


Surface RoughnessAverage of vertical deviations from nominal

surface over a specified surface length

Figure 5.5 Deviations from nominal surface used in the two definitions of surface roughness.


Surface Roughness Equation

Arithmetic average (AA) based on absolute values of deviations, and is referred to as average roughness

where Ra = average roughness; y = vertical deviation from nominal surface (absolute value); and Lm = specified distance over which the surface deviations are measured

dxL

yR

mL

ma ∫

0

=


Alternative Surface Roughness Equation

Approximation of previous equation is perhaps easier to comprehend

where Ra has the same meaning as above; yi = vertical deviations (absolute value) identified by subscript i; and n = number of deviations included in Lm

n

i

ia

n

yR

1


Cutoff Length

A problem with the Ra computation is that waviness may get included

To deal with this problem, a parameter called the cutoff length is used as a filter to separate waviness from roughness deviations

Cutoff length is a sampling distance along the surface A sampling distance shorter than the

waviness eliminates waviness deviations and only includes roughness deviations


Surface Roughness Specification

Figure 5.6 Surface texture symbols in engineering drawings: (a) the symbol, and (b) symbol with identification labels.


Surface Integrity

Surface texture alone does not completely describe a surface

There may be metallurgical changes in the altered layer beneath the surface that can have a significant effect on a material's mechanical properties

Surface integrity is the study and control of this subsurface layer and the changes in it that occur during processing which may influence the performance of the finished part or product


Surface Changes Caused by Processing

Surface changes are caused by the application of various forms of energy during processing Example: Mechanical energy is the most

common form in manufacturing Processes include forging, extrusion,

and machining Although its primary function is to change

geometry of workpart, mechanical energy can also cause residual stresses, work hardening, and cracks in the surface layers


Energy Forms in Surface Integrity

Mechanical energy Thermal energy Chemical energy Electrical energy

Trumpf-machines.com


Surface Changes by Mechanical Energy

Residual stresses in subsurface layer Example: bending of sheet metal

Cracks - microscopic and macroscopic Example: tearing of ductile metals in

machining Voids or inclusions introduced mechanically

Example: center-bursting in extrusion Hardness variations (e.g., work hardening)

Example: strain hardening of new surface in machining


Surface Changes by Thermal Energy

Metallurgical changes (recrystallization, grain size changes, phase changes at surface)

Redeposited or resolidified material (e.g., welding or casting)

Heat-affected zone in welding (includes some of the metallurgical changes listed above)

Hardness changes

Wikipedia.org – root weld


Surface Changes by Chemical Energy

Intergranular attack Chemical contamination Absorption of certain elements such as H and

Cl in metal surface Corrosion, pitting, and etching Dissolving of microconstituents Alloy depletion and resulting hardness changes


Surface Changes by Electrical Energy

Changes in conductivity and/or magnetism Craters resulting from short circuits during

certain electrical processing techniques such as arc welding


Effect of Manufacturing Processes

•Let’s Look at Table 5.4

•and Table 5.5


Tolerances and Manufacturing Processes

Some manufacturing processes are inherently more accurate than others

Examples: Most machining processes are quite

accurate, capable of tolerances = 0.05 mm ( 0.002 in.) or better

Sand castings are generally inaccurate, and tolerances of 10 to 20 times those used for machined parts must be specified


Surfaces and Manufacturing Processes

Some processes are inherently capable of producing better surfaces than others In general, processing cost increases with

improvement in surface finish because additional operations and more time are usually required to obtain increasingly better surfaces

Processes noted for providing superior finishes include honing, lapping, polishing, and superfinishing


FUNDAMENTALS OF METAL CASTING

1. Overview of Casting Technology2. Heating and Pouring3. Solidification and Cooling


Solidification Processes

Starting work material is either a liquid or is in a highly plastic condition, and a part is created through solidification of the material

Solidification processes can be classified according to engineering material processed: Metals Ceramics, specifically glasses Polymers and polymer matrix composites

(PMCs)


Figure 10.1 Classification of solidification processes.


Casting

Process in which molten metal flows by gravity or other force into a mold where it solidifies in the shape of the mold cavity

The term casting also applies to the part made in the process

Steps in casting seem simple: 1. Melt the metal2. Pour it into a mold3. Let it freeze


Capabilities and Advantages of Casting

Can create complex part geometries Can create both external and internal shapes Some casting processes are net shape; others

are near net shape

Can produce very large parts Some casting methods are suited to mass

production


Disadvantages of Casting

Different disadvantages for different casting processes: Limitations on mechanical properties Poor dimensional accuracy and surface

finish for some processes; e.g., sand casting

Safety hazards to workers due to hot molten metals

Environmental problems


Parts Made by Casting

Big parts Engine blocks and heads for automotive

vehicles, wood burning stoves, machine frames, railway wheels, pipes, church bells, big statues, pump housings

Small parts Dental crowns, jewelry, small statues, frying

pans All varieties of metals can be cast, ferrous and

nonferrous


Overview of Casting Technology

Casting is usually performed in a foundry Foundry = factory equipped for making molds,

melting and handling molten metal, performing the casting process, and cleaning the finished casting

Workers who perform casting are called foundrymen


The Mold in Casting

Contains cavity whose geometry determines part shape Actual size and shape of cavity must be

slightly oversized to allow for shrinkage of metal during solidification and cooling

Molds are made of a variety of materials, including sand, plaster, ceramic, and metal


Open Molds and Closed Molds

Figure 10.2 Two forms of mold: (a) open mold, simply a container in the shape of the desired part; and (b) closed mold, in which the mold geometry is more complex and requires a gating system (passageway) leading into the cavity.



1. Expendable mold processes – uses an expendable mold which must be destroyed to remove casting Mold materials: sand, plaster, and similar

materials, plus binders2. Permanent mold processes – uses a

permanent mold which can be used over and over to produce many castings Made of metal (or, less commonly, a

ceramic refractory material


Advantages and Disadvantages

More intricate geometries are possible with expendable mold processes

Part shapes in permanent mold processes are limited by the need to open the mold

Permanent mold processes are more economic in high production operations


Sand Casting Mold

Figure 10.2 (b) Sand casting mold.


Sand Casting Mold Terms

Mold consists of two halves: Cope = upper half of mold Drag = bottom half

Mold halves are contained in a box, called a flask

The two halves separate at the parting line


Forming the Mold Cavity

Mold cavity is formed by packing sand around a pattern, which has the shape of the part

When the pattern is removed, the remaining cavity of the packed sand has desired shape of cast part

The pattern is usually oversized to allow for shrinkage of metal during solidification and cooling

Sand for the mold is moist and contains a binder to maintain its shape


Use of a Core in the Mold Cavity

The mold cavity provides the external surfaces of the cast part

In addition, a casting may have internal surfaces, determined by a core, placed inside the mold cavity to define the interior geometry of part

In sand casting, cores are generally made of sand


Gating System

Channel through which molten metal flows into cavity from outside of mold

Consists of a downsprue, through which metal enters a runner leading to the main cavity

At the top of downsprue, a pouring cup is often used to minimize splash and turbulence as the metal flows into downsprue


Riser

Reservoir in the mold which is a source of liquid metal to compensate for shrinkage of the part during solidification

The riser must be designed to freeze after the main casting in order to satisfy its function


Heating the Metal

Heating furnaces are used to heat the metal to molten temperature sufficient for casting

The heat required is the sum of: 1. Heat to raise temperature to melting point 2. Heat of fusion to convert from solid to

liquid 3. Heat to raise molten metal to desired

temperature for pouring


Pouring the Molten Metal

For this step to be successful, metal must flow into all regions of the mold, most importantly the main cavity, before solidifying

Factors that determine success Pouring temperature Pouring rate Turbulence


Solidification of Metals

Transformation of molten metal back into solid state

Solidification differs depending on whether the metal is A pure element or An alloy


Cooling Curve for a Pure Metal

A pure metal solidifies at a constant temperature equal to its freezing point (same as melting point)

Figure 10.4 Cooling curve for a pure metal during casting.


Solidification of Pure Metals

Due to chilling action of mold wall, a thin skin of solid metal is formed at the interface immediately after pouring

Skin thickness increases to form a shell around the molten metal as solidification progresses

Rate of freezing depends on heat transfer into mold, as well as thermal properties of the metal


Figure 10.5 Characteristic grain structure in a casting of a pure metal, showing randomly oriented grains of small size near the mold wall, and large columnar grains oriented toward the center of the casting.


Solidification of Alloys Most alloys freeze over a temperature range

rather than at a single temperature

Figure 10.6 (a) Phase diagram for a copper-nickel alloy system and (b) associated cooling curve for a 50%Ni-50%Cu composition during casting.


Figure 10.7 Characteristic grain structure in an alloy casting, showing segregation of alloying components in center of casting.


Solidification Time

Solidification takes time Total solidification time TTS = time required for

casting to solidify after pouring TTS depends on size and shape of casting by

relationship known as Chvorinov's Rule

where TST = total solidification time; V = volume of the casting; A = surface area of casting; n = exponent with typical value = 2; and Cm is mold constant.

n

mA

VCTST


Mold Constant in Chvorinov's Rule

Mold constant Cm depends on: Mold material Thermal properties of casting metal Pouring temperature relative to melting point

Value of Cm for a given casting operation can be based on experimental data from previous operations carried out using same mold material, metal, and pouring temperature, even though the shape of the part may be quite different


What Chvorinov's Rule Tells Us

A casting with a higher volume-to-surface area ratio cools and solidifies more slowly than one with a lower ratio To feed molten metal to main cavity, TST for

riser must greater than TST for main casting Since mold constants of riser and casting will

be equal, design the riser to have a larger volume-to-area ratio so that the main casting solidifies first This minimizes the effects of shrinkage


Shrinkage in Solidification and Cooling

Figure 10.8 Shrinkage of a cylindrical casting during solidification and cooling: (0) starting level of molten metal immediately after pouring; (1) reduction in level caused by liquid contraction during cooling (dimensional reductions are exaggerated for clarity).


Shrinkage in Solidification and Cooling

Figure 10.8 (2) reduction in height and formation of shrinkage cavity caused by solidification shrinkage; (3) further reduction in height and diameter due to thermal contraction during cooling of solid metal (dimensional reductions are exaggerated for clarity).


Solidification Shrinkage

Occurs in nearly all metals because the solid phase has a higher density than the liquid phase

Thus, solidification causes a reduction in volume per unit weight of metal

Exception: cast iron with high C content Graphitization during final stages of freezing

causes expansion that counteracts volumetric decrease associated with phase change


Shrinkage Allowance

Patternmakers account for solidification shrinkage and thermal contraction by making mold cavity oversized

Amount by which mold is made larger relative to final casting size is called pattern shrinkage

allowance

Casting dimensions are expressed linearly, so allowances are applied accordingly


Directional Solidification

To minimize damaging effects of shrinkage, it is desirable for regions of the casting most distant from the liquid metal supply to freeze first and for solidification to progress from these remote regions toward the riser(s) Thus, molten metal is continually available

from risers to prevent shrinkage voids The term directional solidification describes

this aspect of freezing and methods by which it is controlled


Achieving Directional Solidification

Desired directional solidification is achieved using Chvorinov's Rule to design the casting itself, its orientation in the mold, and the riser system that feeds it

Locate sections of the casting with lower V/Aratios away from riser, so freezing occurs first in these regions, and the liquid metal supply for the rest of the casting remains open

Chills - internal or external heat sinks that cause rapid freezing in certain regions of the casting


External Chills

Figure 10.9 (a) External chill to encourage rapid freezing of the molten metal in a thin section of the casting; and (b) the likely result if the external chill were not used.


Riser Design

Riser is waste metal that is separated from the casting and remelted to make more castings

To minimize waste in the unit operation, it is desirable for the volume of metal in the riser to be a minimum

Since the geometry of the riser is normally selected to maximize the V/A ratio, this allows riser volume to be reduced to the minimum possible value


METAL CASTING PROCESSES

1. Sand Casting2. Other Expendable Mold Casting Processes3. Permanent Mold Casting Processes4. Foundry Practice5. Casting Quality6. Metals for Casting7. Product Design Considerations



1. Expendable mold processes - mold is sacrificed to remove part Advantage: more complex shapes possible Disadvantage: production rates often limited by

time to make mold rather than casting itself2. Permanent mold processes - mold is made of metal

and can be used to make many castings Advantage: higher production rates Disadvantage: geometries limited by need to

open mold


Overview of Sand Casting

Most widely used casting process, accounting for a significant majority of total tonnage cast

Nearly all alloys can be sand casted, including metals with high melting temperatures, such as steel, nickel, and titanium

Castings range in size from small to very large Production quantities from one to millions

Figure 11.1 A large sand casting weighing over 680 kg (1500 lb) for an air compressor frame (photo courtesy of Elkhart Foundry).


Making the Sand Mold

The cavity in the sand mold is formed by packing sand around a pattern, then separating the mold into two halves and removing the pattern

The mold must also contain gating and riser system

If casting is to have internal surfaces, a core must be included in mold

A new sand mold must be made for each part produced


Steps in Sand Casting1. Pour the molten metal into sand mold2. Allow time for metal to solidify3. Break up the mold to remove casting 4. Clean and inspect casting

Separate gating and riser system5. Heat treatment of casting is sometimes required to

improve metallurgical properties

Figure is from

www.themetalcasting.com


The Pattern A full-sized model of the part, slightly enlarged to account for

shrinkage and machining allowances in the casting Pattern materials:

Wood - common material because it is easy to work, but it warps

Metal - more expensive to make, but lasts much longer Plastic - compromise between wood and metal

Top center is the clay original, then the two part

plaster mold used for casting the lead at above, and

wax cast from mold, sprued for better brass casting,

not yet cast. 2008-01-12.

homepages.waymark.net/mikefirth/tapper6881b.jpg


Types of Patterns

Figure 11.3 Types of patterns used in sand casting: (a) solid pattern(b) split pattern(c) match-plate pattern(d) cope and drag pattern


CoreFull-scale model of interior surfaces of part It is inserted into the mold cavity prior to pouring The molten metal flows and solidifies between the mold

cavity and the core to form the casting's external and internal surfaces

May require supports to hold it in position in the mold cavity during pouring, called chaplets

Figure 11.4 (a) Core held in place in the mold cavity by chaplets, (b) possible chaplet design, (c) casting with internal cavity.


Desirable Mold Properties

Strength - to maintain shape and resist erosion Permeability - to allow hot air and gases to pass

through voids in sand Thermal stability - to resist cracking on contact with

molten metal Collapsibility - ability to give way and allow casting

to shrink without cracking the casting Reusability - can sand from broken mold be reused

to make other molds?


Foundry Sands

Silica (SiO2) or silica mixed with other minerals Good refractory properties - capacity to endure high temperatures Small grain size yields better surface finish on the cast part Large grain size is more permeable, allowing gases to escape

during pouring Irregular grain shapes strengthen molds due to interlocking,

compared to round grains Disadvantage: interlocking tends to reduce permeability

Binders

Sand is held together by a mixture of water and bonding clay Typical mix: 90% sand, 3% water, and 7% clay

Other bonding agents also used in sand molds: Organic resins (e g , phenolic resins) Inorganic binders (e g , sodium silicate and phosphate)

Additives are sometimes combined with the mixture to increase strength and/or permeability


Types of Sand Mold

Green-sand molds - mixture of sand, clay, and water; “Green" means mold contains moisture at time of

pouring Dry-sand mold - organic binders rather than clay

And mold is baked to improve strength Skin-dried mold - drying mold cavity surface of a

green-sand mold to a depth of 10 to 25 mm, using torches or heating lamps


Buoyancy in Sand Casting Operation

During pouring, buoyancy of the molten metal tends to displace the core, which can cause casting to be defective

Force tending to lift core = weight of displaced liquid less the weight of core itself

Fb = Wm - Wc

where Fb = buoyancy force; Wm = weight of molten metal displaced; and Wc = weight of core


Other Expendable Mold Processes

Shell Molding Vacuum Molding Expanded Polystyrene Process Investment Casting Plaster Mold and Ceramic Mold CastingHere is a good reference web site:http://www.custompartnet.com/wu/SandCasting

http://www.custompartnet.com/wu/SandCasting


Shell Molding Casting process in which the mold is a thin shell of

sand held together by thermosetting resin binder

Figure 11.5 Steps in shell-molding: (1) a match-plate or cope-and-drag metal pattern is heated and placed over a box containing sand mixed with thermosetting resin.


Shell Molding

Figure 11.5 Steps in shell-molding: (2) box is inverted so that sand and resin fall onto the hot pattern, causing a layer of the mixture to partially cure on the surface to form a hard shell; (3) box is repositioned so that loose uncured particles drop away;


Shell Molding

Figure 11.5 Steps in shell-molding: (4) sand shell is heated in oven for several minutes to complete curing; (5) shell mold is stripped from the pattern;


Shell Molding

Figure 11.5 Steps in shell-molding: (6) two halves of the shell mold are assembled, supported by sand or metal shot in a box, and pouring is accomplished; (7) the finished casting with sprue removed.

From www.janfa.com



Advantages of shell molding: Smoother cavity surface permits easier flow of

molten metal and better surface finish Good dimensional accuracy - machining often

not required Mold collapsibility minimizes cracks in casting Can be mechanized for mass production

Disadvantages: More expensive metal pattern Difficult to justify for small quantities


Expanded Polystyrene Process

Figure 11.7 Expanded polystyrene casting process: pattern of polystyrene is coated with refractory compound;

Uses a mold of sand packed around a polystyrene foam pattern which vaporizes when molten metal is poured into mold

Other names: lost-foam process, lost pattern process, evaporative-foam process, and full-mold process

Polystyrene foam pattern includes sprue, risers, gating system, and internal cores (if needed)

Mold does not have to be opened into cope and drag sectionsFrom www.wtec.org/loyola/casting/fh05_20.jpg



Figure 11.7 Expanded polystyrene casting process: (2) foam pattern is placed in mold box, and sand is compacted around the pattern;

Figure 11.7 Expanded polystyrene casting process: (3) molten metal is poured into the portion of the pattern that forms the pouring cup and sprue. As the metal enters the mold, the polystyrene foam is vaporized ahead of the advancing liquid, thus the resulting mold cavity is filled.



Advantages of expanded polystyrene process: Pattern need not be removed from the mold Simplifies and speeds mold-making, because two

mold halves are not required as in a conventional green-sand mold

Disadvantages: A new pattern is needed for every casting Economic justification of the process is highly

dependent on cost of producing patterns



Applications: Mass production of castings for automobile

engines Automated and integrated manufacturing

systems are used to 1. Mold the polystyrene foam patterns and then2. Feed them to the downstream casting

operation


Investment Casting (Lost Wax Process)

A pattern made of wax is coated with a refractory material to make mold, after which wax is melted away prior to pouring molten metal

"Investment" comes from a less familiar definition of "invest" - "to cover completely," which refers to coating of refractory material around wax pattern

It is a precision casting process - capable of producing castings of high accuracy and intricate detail


Investment Casting

Figure 11.8 Steps in investment casting: (1) wax patterns are produced, (2) several patterns are attached to a sprue to form a pattern tree


Investment Casting

Figure 11.8 Steps in investment casting: (3) the pattern tree is coated with a thin layer of refractory material, (4) the full mold is formed by covering the coated tree with sufficient refractory material to make it rigid


Investment Casting

Figure 11.8 Steps in investment casting: (5) the mold is held in an inverted position and heated to melt the wax and permit it to drip out of the cavity, (6) the mold is preheated to a high temperature, the molten metal is poured, and it solidifies


Investment Casting

Figure 11.8 Steps in investment casting: (7) the mold is broken away from the finished casting and the parts are separated from the sprue


Investment Casting

Figure 11 9 A one-piece compressor stator with 108 separate airfoils made by investment casting (photo courtesy of Howmet Corp.).



Advantages of investment casting: Parts of great complexity and intricacy can be

cast Close dimensional control and good surface

finish Wax can usually be recovered for reuse Additional machining is not normally

required - this is a net shape process Disadvantages

Many processing steps are required Relatively expensive process


Plaster Mold Casting

Similar to sand casting except mold is made of plaster of Paris (gypsum - CaSO4-2H2O)

In mold-making, plaster and water mixture is poured over plastic or metal pattern and allowed to set Wood patterns not generally used due to

extended contact with water Plaster mixture readily flows around pattern,

capturing its fine details and good surface finish



Advantages of plaster mold casting: Good accuracy and surface finish Capability to make thin cross-sections

Disadvantages: Mold must be baked to remove moisture,

which can cause problems in casting Mold strength is lost if over-baked Plaster molds cannot stand high

temperatures, so limited to lower melting point alloys


Ceramic Mold Casting

Similar to plaster mold casting except that mold is made of refractory ceramic material that can withstand higher temperatures than plaster

Can be used to cast steels, cast irons, and other high-temperature alloys

Applications similar to those of plaster mold casting except for the metals cast

Advantages (good accuracy and finish) also similar


Permanent Mold Casting Processes

Economic disadvantage of expendable mold casting: a new mold is required for every casting

In permanent mold casting, the mold is reused many times

The processes include: Basic permanent mold casting Die casting Centrifugal casting


The Basic Permanent Mold Process

Uses a metal mold constructed of two sections designed for easy, precise opening and closing

Molds used for casting lower melting point alloys are commonly made of steel or cast iron

Molds used for casting steel must be made of refractory material, due to the very high pouring temperatures


Permanent Mold Casting

Figure 11.10 Steps in permanent mold casting: (1) mold is preheated and coated



Figure 11.10 Steps in permanent mold casting: (2) cores (if used) are inserted and mold is closed, (3) molten metal is poured into the mold, where it solidifies.


Advantages and Limitations

Advantages of permanent mold casting: Good dimensional control and surface finish More rapid solidification caused by the cold

metal mold results in a finer grain structure, so castings are stronger

Limitations: Generally limited to metals of lower melting

point Simpler part geometries compared to sand

casting because of need to open the mold High cost of mold


Applications of Permanent Mold Casting

Due to high mold cost, process is best suited to high volume production and can be automated accordingly

Typical parts: automotive pistons, pump bodies, and certain castings for aircraft and missiles

Metals commonly cast: aluminum, magnesium, copper-base alloys, and cast iron


Die Casting

A permanent mold casting process in which molten metal is injected into mold cavity under high pressure

Pressure is maintained during solidification, then mold is opened and part is removed

Molds in this casting operation are called dies; hence the name die casting

Use of high pressure to force metal into die cavity is what distinguishes this from other permanent mold processes


Die Casting Machines

Designed to hold and accurately close two mold halves and keep them closed while liquid metal is forced into cavity

Two main types: 1. Hot-chamber machine2. Cold-chamber machine


Hot-Chamber Die Casting

Metal is melted in a container, and a piston injects liquid metal under high pressure into the die

High production rates - 500 parts per hour not uncommon

Applications limited to low melting-point metals that do not chemically attack plunger and other mechanical components

Casting metals: zinc, tin, lead, and magnesium



Figure 11.13 Cycle in hot-chamber casting: (1) with die closed and plunger withdrawn, molten metal flows into the chamber (2) plunger forces metal in chamber to flow into die, maintaining pressure during cooling and solidification.


Cold-Chamber Die Casting Machine

Molten metal is poured into unheated chamber from external melting container, and a piston injects metal under high pressure into die cavity

High production but not usually as fast as hot-chamber machines because of pouring step

Casting metals: aluminum, brass, and magnesium alloys

Advantages of hot-chamber process favor its use on low melting-point alloys (zinc, tin, lead)


Cold-Chamber Die Casting

Figure 11.14 Cycle in cold-chamber casting: (1) with die closed and ram withdrawn, molten metal is poured into the chamber


Cold-Chamber Die Casting

Figure 11.14 Cycle in cold-chamber casting: (2) ram forces metal to flow into die, maintaining pressure during cooling and solidification.


Molds for Die Casting

Usually made of tool steel, mold steel, or maraging steel

Tungsten and molybdenum (good refractory qualities) used to die cast steel and cast iron

Ejector pins required to remove part from die when it opens

Lubricants must be sprayed into cavities to prevent sticking


Advantages and Limitations

Advantages of die casting: Economical for large production quantities Good accuracy and surface finish Thin sections are possible Rapid cooling provides small grain size and

good strength to casting Disadvantages:

Generally limited to metals with low metal points

Part geometry must allow removal from die


Centrifugal Casting

A family of casting processes in which the mold is rotated at high speed so centrifugal force distributes molten metal to outer regions of die cavity

The group includes: True centrifugal casting Semicentrifugal casting Centrifuge casting


True Centrifugal Casting

Molten metal is poured into rotating mold to produce a tubular part

In some operations, mold rotation commences after pouring rather than before

Parts: pipes, tubes, bushings, and rings Outside shape of casting can be round, octagonal,

hexagonal, etc , but inside shape is (theoretically) perfectly round, due to radially symmetric forces


True Centrifugal Casting

Figure 11.15 Setup for true centrifugal casting.


Semicentrifugal Casting

Centrifugal force is used to produce solid castings rather than tubular parts

Molds are designed with risers at center to supply feed metal

Density of metal in final casting is greater in outer sections than at center of rotation

Often used on parts in which center of casting is machined away, thus eliminating the portion where quality is lowest

Examples: wheels and pulleys


Centrifuge Casting

Mold is designed with part cavities located away from axis of rotation, so that molten metal poured into mold is distributed to these cavities by centrifugal force

Used for smaller parts Radial symmetry of part is not required as in other

centrifugal casting methods


Furnaces for Casting Processes

Furnaces most commonly used in foundries: Cupolas Direct fuel-fired furnaces Crucible furnaces Electric-arc furnaces Induction furnaces


Cupolas

Vertical cylindrical furnace equipped with tapping spout near base

Used only for cast irons Although other furnaces are also used, the

largest tonnage of cast iron is melted in cupolas The "charge," consisting of iron, coke, flux, and

possible alloying elements, is loaded through a charging door located less than halfway up height of cupola


Direct Fuel-Fired Furnaces

Small open-hearth in which charge is heated by natural gas fuel burners located on side of furnace

Furnace roof assists heating action by reflecting flame down against charge

At bottom of hearth is a tap hole to release molten metal

Generally used for nonferrous metals such as copper-base alloys and aluminum


Crucible Furnaces

Metal is melted without direct contact with burning fuel mixture

Sometimes called indirect fuel-fired furnaces

Container (crucible) is made of refractory material or high-temperature steel alloy

Used for nonferrous metals such as bronze, brass, and alloys of zinc and aluminum

Three types used in foundries: (a) lift-out type, (b) stationary, (c) tilting


Crucible Furnaces

Figure 11.19 Three types of crucible furnaces: (a) lift-out crucible, (b) stationary pot, from which molten metal must be ladled, and (c) tilting-pot furnace.


Electric-Arc Furnaces

Charge is melted by heat generated from an electric arc High power consumption, but electric-arc furnaces can be

designed for high melting capacity Used primarily for melting steel


Induction FurnacesUses alternating current passing through a coil to develop magnetic

field in metal Induced current causes rapid heating and melting Electromagnetic force field also causes mixing action in liquid metal Since metal does not contact heating elements, environment can

be closely controlled to produce molten metals of high quality and purity

Melting steel, cast iron, and aluminum alloys are common applications in foundry work


Ladles

Moving molten metal from melting furnace to mold is sometimes done using crucibles

More often, transfer is accomplished by ladles

Figure 11.21 Two common types of ladles: (a) crane ladle, and (b) two-man ladle.


Additional Steps After Solidification

Trimming Removing the core Surface cleaning Inspection Repair, if required Heat treatment


Trimming

Removal of sprues, runners, risers, parting-line flash, fins, chaplets, and any other excess metal from the cast part

For brittle casting alloys and when cross sections are relatively small, appendages can be broken off

Otherwise, hammering, shearing, hack-sawing, band-sawing, abrasive wheel cutting, or various torch cutting methods are used


Removing the Core

If cores have been used, they must be removed Most cores are bonded, and they often fall out of

casting as the binder deteriorates In some cases, they are removed by shaking

casting, either manually or mechanically In rare cases, cores are removed by chemically

dissolving bonding agent Solid cores must be hammered or pressed out


Surface Cleaning

Removal of sand from casting surface and otherwise enhancing appearance of surface

Cleaning methods: tumbling, air-blasting with coarse sand grit or metal shot, wire brushing, buffing, and chemical pickling

Surface cleaning is most important for sand casting In many permanent mold processes, this step

can be avoided Defects are possible in casting, and inspection is

needed to detect their presence


Heat Treatment

Castings are often heat treated to enhance properties

Reasons for heat treating a casting: For subsequent processing operations such as

machining To bring out the desired properties for the

application of the part in service


Casting Quality

There are numerous opportunities for things to go wrong in a casting operation, resulting in quality defects in the product

The defects can be classified as follows: General defects common to all casting processes Defects related to sand casting process


A casting that has solidified before completely filling mold cavity

Figure 11.22 Some common defects in castings: (a) misrun

General Defects: Misrun


Two portions of metal flow together but there is a lack of fusion due to premature freezing

Figure 11.22 Some common defects in castings: (b) cold shut

General Defects: Cold Shut


Metal splatters during pouring and solid globules form and become entrapped in casting

Figure 11.22 Some common defects in castings: (c) cold shot

General Defects: Cold Shot


Depression in surface or internal void caused by solidification shrinkage that restricts amount of molten metal available in last region to freeze

Figure 11.22 Some common defects in castings: (d) shrinkage cavity

General Defects: Shrinkage Cavity


Balloon-shaped gas cavity caused by release of mold gases during pouring

Figure 11.23 Common defects in sand castings: (a) sand blow

Sand Casting Defects: Sand Blow


Formation of many small gas cavities at or slightly below surface of casting

Figure 11.23 Common defects in sand castings: (b) pin holes

Sand Casting Defects: Pin Holes


When fluidity of liquid metal is high, it may penetrate into sand mold or core, causing casting surface to consist of a mixture of sand grains and metal

Figure 11.23 Common defects in sand castings: (e) penetration

Sand Casting Defects: Penetration


A step in cast product at parting line caused by sidewise relative displacement of cope and drag

Figure 11.23 Common defects in sand castings: (f) mold shift

Sand Casting Defects: Mold Shift


Foundry Inspection Methods

Visual inspection to detect obvious defects such as misruns, cold shuts, and severe surface flaws

Dimensional measurements to insure that tolerances have been met

Metallurgical, chemical, physical, and other tests concerned with quality of cast metal


Metals for Casting

Most commercial castings are made of alloys rather than pure metals Alloys are generally easier to cast, and properties

of product are better Casting alloys can be classified as:

Ferrous Nonferrous


Ferrous Casting Alloys: Cast Iron

Most important of all casting alloys Tonnage of cast iron castings is several times that

of all other metals combined Several types: (1) gray cast iron, (2) nodular iron, (3)

white cast iron, (4) malleable iron, and (5) alloy cast irons

Typical pouring temperatures 1400C (2500F), depending on composition


Ferrous Casting Alloys: Steel

The mechanical properties of steel make it an attractive engineering material

The capability to create complex geometries makes casting an attractive shaping process

Difficulties when casting steel: Pouring temperature of steel is higher than for

most other casting metals 1650C (3000F) At such temperatures, steel readily oxidizes, so

molten metal must be isolated from air Molten steel has relatively poor fluidity


Nonferrous Casting Alloys: Aluminum

Generally considered to be very castable Pouring temperatures low due to low melting

temperature of aluminum Tm = 660C (1220F)

Properties: Light weight Range of strength properties by heat treatment Easy to machine


Nonferrous Casting Alloys: Copper Alloys

Includes bronze, brass, and aluminum bronze Properties:

Corrosion resistance Attractive appearance Good bearing qualities

Limitation: high cost of copper Applications: pipe fittings, marine propeller blades,

pump components, ornamental jewelry


Nonferrous Casting Alloys: Zinc Alloys

Highly castable, commonly used in die casting Low melting point – melting point of zinc Tm = 419C

(786F) Good fluidity for ease of casting Properties:

Low creep strength, so castings cannot be subjected to prolonged high stresses


Product Design Considerations

Geometric simplicity: Although casting can be used to produce

complex part geometries, simplifying the part design usually improves castability

Avoiding unnecessary complexities: Simplifies mold-making Reduces the need for cores Improves the strength of the casting



Corners on the casting: Sharp corners and angles should be avoided,

since they are sources of stress concentrations and may cause hot tearing and cracks

Generous fillets should be designed on inside corners and sharp edges should be blended



Draft Guidelines: In expendable mold casting, draft facilitates

removal of pattern from mold Draft = 1 for sand casting

In permanent mold casting, purpose is to aid in removal of the part from the mold Draft = 2 to 3 for permanent mold processes

Similar tapers should be allowed if solid cores are used


Draft

Minor changes in part design can reduce need for coring

Figure 11.25 Design change to eliminate the need for using a core: (a) original design, and (b) redesign.


Product Design Considerations Dimensional Tolerances and Surface Finish:

Significant differences in dimensional accuracies and finishes can be achieved in castings, depending on process: Poor dimensional accuracies and finish for

sand casting Good dimensional accuracies and finish for

die casting and investment casting



Machining Allowances: Almost all sand castings must be machined to

achieve the required dimensions and part features

Additional material, called the machining

allowance, is left on the casting in those surfaces where machining is necessary

Typical machining allowances for sand castings are around 1.5 and 3 mm (1/16 and 1/4 in)


SHAPING PROCESSES FOR PLASTICS

1. Properties of Polymer Melts2. Extrusion3. Production of Sheet, Film, and Filaments4. Coating Processes5. Injection Molding6. Other Molding Processes7. Thermoforming8. Casting9. Polymer Foam Processing and Forming10.Product Design Considerations


Plastic Products

Plastics can be shaped into a wide variety of products: Molded parts Extruded sections Films Sheets Insulation coatings on electrical wires Fibers for textiles


More Plastic Products

In addition, plastics are often the principal ingredient in other materials, such as Paints and varnishes Adhesives Various polymer matrix composites

Many plastic shaping processes can be adapted to produce items made of rubbers and polymer matrix composites


Trends in Polymer Processing

Applications of plastics have increased at a much faster rate than either metals or ceramics during the last 50 years Many parts previously made of metals are

now being made of plastics Plastic containers have been largely

substituted for glass bottles and jars Total volume of polymers (plastics and

rubbers) now exceeds that of metals


Plastic Shaping Processes are Important

Almost unlimited variety of part geometries Plastic molding is a net shape process

Further shaping is not needed Less energy is required than for metals due to much

lower processing temperatures Handling of product is simplified during production

because of lower temperatures Painting or plating is usually not required


Two Types of Plastics

1. Thermoplastics Chemical structure remains unchanged during

heating and shaping More important commercially, comprising more

than 70% of total plastics tonnage 2. Thermosets

Undergo a curing process during heating and shaping, causing a permanent change (cross-linking) in molecular structure

Once cured, they cannot be remelted


Classification of Shaping Processes

Extruded products with constant cross-section Continuous sheets and films Continuous filaments (fibers) Molded parts that are mostly solid Hollow molded parts with relatively thin walls Discrete parts made of formed sheets and films Castings Foamed products


Polymer Melts

To shape a thermoplastic polymer it must be heated so that it softens to the consistency of a liquid

In this form, it is called a polymer melt

Important properties of polymer melts: Viscosity Viscoelasticity


Viscosity of Polymer Melts

Fluid property that relates shear stress to shear rate during flow

Due to its high molecular weight, a polymer melt is a thick fluid with high viscosity

Most polymer shaping processes involve flow through small channels or die openings Flow rates are often large, leading to high shear

rates and shear stresses, so significant pressures are required to accomplish the processes


Viscosity and Shear Rate

Viscosity of a polymer melt decreases with shear rate, thus the fluid becomes thinner at higher shear rates

Figure 13.1 Viscosity relationships for Newtonian fluid and typical polymer melt.


Viscosity and TemperatureViscosity decreases with temperature, thus the

fluid becomes thinner at higher temperatures

Figure 13.2 Viscosity as a function of temperature for selected polymers at a shear rate of 103 s-1.


Viscoelasticity

Combination of viscosity and elasticity Possessed by both polymer solids and polymer

melts Example: die swell in extrusion, in which the hot

plastic expands when exiting the die opening


Extruded polymer "remembers" its previous shape when in the larger cross section of the extruder, tries to return to it after leaving the die orifice

Figure 13.3 Die swell, a manifestation of viscoelasticity in polymer melts, as depicted here on exiting an extrusion die.

Die Swell


Extrusion

Compression process in which material is forced to flow through a die orifice to provide long continuous product whose cross-sectional shape is determined by the shape of the orifice

Widely used for thermoplastics and elastomers to mass produce items such as tubing, pipes, hose, structural shapes, sheet and film, continuous filaments, and coated electrical wire

Carried out as a continuous process; extrudate is then cut into desired lengths


Extruder

Figure 13.4 Components and features of a (single-screw) extruder for plastics and elastomers


Two Main Components of an Extruder

1. Barrel2. Screw Die - not an extruder component

Special tool that must be fabricated for particular profile to be produced


Extruder Barrel

Internal diameter typically ranges from 25 to 150 mm (1.0 to 6.0 in.)

L/D ratios usually between 10 and 30: higher ratios for thermoplastics, lower ratios for elastomers

Feedstock fed by gravity onto screw whose rotation moves material through barrel

Electric heaters melt feedstock; subsequent mixing and mechanical working adds heat which maintains the melt


Extruder Screw

Divided into sections to serve several functions: Feed section - feedstock is moved from

hopper and preheated Compression section - polymer is

transformed into fluid, air mixed with pellets is extracted from melt, and material is compressed

Metering section - melt is homogenized and sufficient pressure developed to pump it through die opening


Extruder Screw

Figure 13.5 Details of an extruder screw inside the barrel.


Die End of Extruder

Progress of polymer melt through barrel leads ultimately to the die zone

Before reaching die, the melt passes through a screen pack - series of wire meshes supported by a stiff plate containing small axial holes

Functions of screen pack: Filter out contaminants and hard lumps Build pressure in metering section Straighten flow of polymer melt and remove its

"memory" of circular motion from screw


Melt Flow in Extruder

As screw rotates inside barrel, polymer melt is forced to move forward toward die; as in an Archimedian screw

Principal transport mechanism is drag flow, Qd, resulting from friction between the viscous liquid and the rotating screw

Compressing the polymer melt through the die creates a back pressure that reduces drag flow transport (called back pressure

flow, Qb ) Resulting flow in extruder is Qx = Qd – Qb


Die Configurations and Extruded Products

The shape of the die orifice determines the cross-sectional shape of the extrudate

Common die profiles and corresponding extruded shapes: Solid profiles Hollow profiles, such as tubes Wire and cable coating Sheet and film Filaments


Extrusion of Solid Profiles

Regular shapes such as Rounds Squares

Irregular cross sections such as Structural shapes Door and window moldings Automobile trim House siding


Extrusion Die for Solid Cross Section

Figure 13.8 (a) Side view cross-section of an extrusion die for solid regular shapes, such as round stock; (b) front view of die, with profile of extrudate. Die swell is evident in both views.


Hollow Profiles

Examples: tubes, pipes, hoses, and other cross-sections containing holes

Hollow profiles require mandrel to form the shape Mandrel held in place using a spider

Polymer melt flows around legs supporting the mandrel to reunite into a monolithic tube wall

Mandrel often includes an air channel through which air is blown to maintain hollow form of extrudate during hardening


Extrusion Die for Hollow Shapes

Figure 13.10 Side view cross-section of extrusion die for shaping hollow cross-sections such as tubes and pipes; Section A-A is a front view cross-section showing how the mandrel is held in place; Section B-B shows the tubular cross-section just prior to exiting the die; die swell causes an enlargement of the diameter.


Wire and Cable Coating

Polymer melt is applied to bare wire as it is pulled at high speed through a die A slight vacuum is drawn between wire and

polymer to promote adhesion of coating Wire provides rigidity during cooling - usually

aided by passing coated wire through a water trough

Product is wound onto large spools at speeds up to 50 m/s (10,000 ft/min)


Extrusion Die for Coating Wire

Figure 13.11 Side view cross-section of die for coating of electrical wire by extrusion.


Polymer Sheet and Film Film - thickness below 0.5 mm (0.020 in.)

Packaging - product wrapping material, grocery bags, garbage bags

Stock for photographic film

Pool covers and liners for irrigation ditches

Sheet - thickness from 0.5 mm (0.020 in.) to about 12.5 mm (0.5 in.)

Flat window glazing

Thermoforming stock

Materials

All thermoplastic polymers

Polyethylene, mostly low density PE

Polypropylene

Polyvinylchloride

Cellophane


Sheet and Film Production Processes

Most widely used processes are continuous, high production operations

Processes include: Slit-Die Extrusion of Sheet and Film Blown-Film Extrusion Process Calendering


Slit-Die Extrusion of Sheet and FilmProduction of sheet and film by conventional extrusion, using a narrow slit as

the die opening

Slit may be up to 3 m (10 ft) wide and as narrow as around 0.4 mm (0.015

in)

A problem is uniformity of thickness throughout width of stock, due to

drastic shape change of polymer melt as it flows through die

Edges of film usually must be trimmed because of thickening at edges

Figure 13.14 A die configurations for extruding sheet & film.


Blown-Film Extrusion Process

Combines extrusion and blowing to produce a tube of thin film

Process sequence:

Extrusion of tube

Tube is drawn upward while still molten and simultaneously

expanded by air inflated into it through die

Air is blown into tube to maintain uniform film thickness and

tube diameter

Figure 13.16 Blown-film process for high production of thin tubular film.


Calendering

Figure 13.17 A typical roll

configuration in calendering

Feedstock is passed through a series of rolls to reduce thickness to desired gage

Expensive equipment, high production rates

Process is noted for good surface finish and high gage accuracy

Typical materials: rubber or rubbery thermoplastics such as plasticized PVC

Products: PVC floor covering, shower curtains, vinyl table cloths, pool liners, and inflatable boats and toys


Fiber and Filament Products

Definitions: Fiber - a long, thin strand whose length is at

least 100 times its cross-section Filament - a fiber of continuous length

Applications: Fibers and filaments for textiles

Most important application Reinforcing materials in polymer composites

Growing application, but still small compared to textiles


Materials for Fibers and Filaments

Fibers can be natural or synthetic Natural fibers constitute ~ 25% of total market

Cotton is by far the most important staple Wool production is significantly less than cotton

Synthetic fibers constitute ~ 75% of total fiber market Polyester is the most important Others: nylon, acrylics, and rayon


Fiber and Filament Production - Spinning

For synthetic fibers, spinning = extrusion of polymer melt or solution through a spinneret, then drawing and winding onto a bobbin

Spinneret = die with multiple small holes The term is a holdover from methods used to

draw and twist natural fibers into yarn or thread

Three variations, depending on polymer : 1. Melt spinning 2. Dry spinning 3. Wet spinning


Melt Spinning Starting polymer is heated to molten state and

pumped through spinneret Typical spinneret is 6 mm (0.25 in) thick and

contains approximately 50 holes of diameter 0.25 mm (0.010 in)

Filaments are drawn and air cooled before being spooled onto bobbin

Significant extension and thinning of filaments occur while polymer is still molten, so final diameter wound onto bobbin may be only 1/10 of extruded size

Used for polyester and nylon filaments


Figure 13.18 Melt spinning of continuous filaments

Melt Spinning


Dry Spinning

Similar to melt spinning, but starting polymer is in solution and solvent can be separated by evaporation

First step is extrusion through spinneret Extrudate is pulled through a heated chamber which

removes the solvent, leaving the polymer Used for filaments of cellulose acetate and acrylics


Wet Spinning

Similar to melt spinning, but polymer is again in solution, only solvent is non-volatile

To separate polymer, extrudate is passed through a liquid chemical that coagulates or precipitates the polymer into coherent strands which are then collected onto bobbins

Used to produce filaments of rayon (regenerated cellulose)


Subsequent Processing of Filaments

Filaments produced by any of the three processes are usually subjected to further cold drawing to align crystal structure along direction of filament axis Extensions of 2 to 8 are typical Effect is to significantly increase tensile strength Drawing is done by pulling filament between two

spools, where winding spool is driven at a faster speed than unwinding spool


Injection Molding

Polymer is heated to a highly plastic state and forced to flow under high pressure into a mold cavity where it solidifies and the molding is then removed from cavity

Produces discrete components almost always to net shape

Typical cycle time 10 to 30 sec, but cycles of one minute or more are not uncommon

Mold may contain multiple cavities, so multiple moldings are produced each cycle


Injection Molded Parts

Complex and intricate shapes are possible Shape limitations:

Capability to fabricate a mold whose cavity is the same geometry as part

Shape must allow for part removal from mold Part size from 50 g (2 oz) up to 25 kg (more than

50 lb), e.g., automobile bumpers Injection molding is economical only for large

production quantities due to high cost of mold


Polymers for Injection Molding

Injection molding is the most widely used molding process for thermoplastics

Some thermosets and elastomers are injection molded Modifications in equipment and operating

parameters must be made to avoid premature cross-linking of these materials before injection


Injection Molding Machine

Two principal components:1. Injection unit

Melts and delivers polymer melt Operates much like an extruder

2. Clamping unit Opens and closes mold each injection cycle



Figure 13.20 A large (3000 ton capacity) injection molding machine (Photo courtesy of Cincinnati Milacron).



Figure 13.21 Diagram of an injection molding machine, reciprocating screw type (some mechanical details are simplified).


Injection Unit of Molding Machine

Consists of barrel fed from one end by a hopper containing supply of plastic pellets

Inside the barrel is a screw which:1. Rotates for mixing and heating polymer2. Acts as a ram (i.e., plunger) to inject

molten plastic into mold Non-return valve near tip of screw

prevents melt flowing backward along screw threads

Later in molding cycle ram retracts to its former position


Clamping Unit of Molding Machine

Functions: 1. Holds two halves of mold in proper alignment

with each other2. Keeps mold closed during injection by applying

a clamping force sufficient to resist injection force

3. Opens and closes mold at the appropriate times in molding cycle


Figure 13.22 Typical molding cycle: (1) mold is closed

Injection Molding Cycle


Figure 13.22 Typical molding cycle: (2) melt is injected into cavity.



Figure 13.22 Typical molding cycle: (3) screw is retracted.



Figure 13.22 Typical molding cycle: (4) mold opens and part is ejected.



The Mold

The special tool in injection molding Custom-designed and fabricated for the part to be

produced When production run is finished, the mold is

replaced with a new mold for the next part Various types of mold for injection molding:

Two-plate mold Three-plate mold Hot-runner mold


Figure 13.23 Details of a two-plate mold for thermoplastic injection molding: (a) closed. Mold has two cavities to produce two cup-shaped parts with each injection shot.

Two-Plate Mold


Figure 13.23 Details of a two-plate mold for thermoplastic injection molding: (b) open

Two-Plate Mold


Two-Plate Mold Features

Cavity – geometry of part but slightly oversized to allow for shrinkage Created by machining of mating surfaces of two

mold halves Distribution channel through which polymer melt

flows from nozzle into mold cavity Sprue - leads from nozzle into mold Runners - lead from sprue to cavity (or cavities) Gates - constrict flow of plastic into cavity


More Two-Plate Mold Features

Ejection system – to eject molded part from cavity at end of molding cycle Ejector pins built into moving half of mold usually

accomplish this function Cooling system - consists of external pump

connected to passageways in mold, through which water is circulated to remove heat from the hot plastic

Air vents – to permit evacuation of air from cavity as polymer melt rushes in


Three-Plate Mold

Uses three plates to separate parts from sprue and runner when mold opens

Advantages over two-plate mold: As mold opens, runner and parts disconnect and

drop into two containers under mold Allows automatic operation of molding machine


Hot-Runner Mold

Eliminates solidification of sprue and runner by locating heaters around the corresponding runner channels

While plastic in mold cavity solidifies, material in sprue and runner channels remains molten, ready to be injected into cavity in next cycle

Advantage: Saves material that otherwise would be scrap in

the unit operation


Injection Molding Machines

Injection molding machines differ in both injection unit and clamping unit

Name of injection molding machine is based on the type of injection unit used Reciprocating-screw injection molding machine Plunger-type injection molding machine

Several clamping designs Mechanical (toggle) Hydraulic


Shrinkage

Reduction in linear size during cooling from molding to room temperature

Polymers have high thermal expansion coefficients, so significant shrinkage occurs during solidification and cooling in mold

Typical shrinkage values: Plastic Shrinkage, mm/mm (in/in)Nylon-6,6 0.020Polyethylene 0.025Polystyrene 0.004PVC 0.005


Compensation for Shrinkage

Dimensions of mold cavity must be larger than specified part dimensions:

Dc = Dp + DpS + DpS2

where Dc = dimension of cavity; Dp = molded part dimension, and S = shrinkage value Third term on right hand side corrects for

shrinkage in the shrinkage


Shrinkage Factors

Fillers in the plastic tend to reduce shrinkage Injection pressure – higher pressures force more

material into mold cavity to reduce shrinkage Compaction time - similar effect – longer time forces

more material into cavity to reduce shrinkage Molding temperature - higher temperatures lower

polymer melt viscosity, allowing more material to be packed into mold to reduce shrinkage


Thermoplastic Foam Injection MoldingMolding of thermoplastic parts that possess dense outer skin

surrounding lightweight foam center Part has high stiffness-to-weight ratio suited to structural

applications Produced either by introducing a gas into molten plastic in

injection unit or by mixing a gas-producing ingredient with starting pellets

A small amount of melt is injected into mold cavity, where it expands to fill cavity

Foam in contact with cold mold surface collapses to form dense skin, while core retains cellular structure

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Injection Molding of Thermosets

Equipment and operating procedure must be modified to avoid premature cross-linking of TS polymer Reciprocating-screw injection unit with shorter

barrel length Temperatures in barrel are relatively low Melt is injected into a heated mold, where

cross-linking occurs to cure the plastic Curing in the mold is the most time-consuming

step in the cycle Mold is then opened and part is removed


Reaction Injection Molding

Two highly reactive liquid ingredients are mixed and immediately injected into a mold cavity where chemical reactions leading to solidification occur

RIM was developed with polyurethane to produce large automotive parts such as bumpers and fenders RIM polyurethane parts possess a foam internal

structure surrounded by a dense outer skin Other materials used in RIM: epoxies, and

urea-formaldehyde


Compression Molding

A widely used molding process for thermosetting plastics

Also used for rubber tires and polymer matrix composite parts

Molding compound available in several forms: powders or pellets, liquid, or preform

Amount of charge must be precisely controlled to obtain repeatable consistency in the molded product


Compression Molding

Figure 13.28 Compression molding for thermosetting plastics: (1) charge is loaded, (2) and (3) charge is compressed and cured, and (4) part is ejected and removed.


Molds for Compression Molding

Simpler than injection molds No sprue and runner system in a compression mold Process itself generally limited to simpler part

geometries due to lower flow capabilities of TS materials

Mold must be heated, usually by electric resistance, steam, or hot oil circulation


Compression Molding

Molding materials: Phenolics, melamine, urea-formaldehyde, epoxies, urethanes,

and elastomers Typical compression-molded products:

Electric plugs, sockets, and housings; pot handles, and dinnerware plates

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Transfer Molding

TS charge is loaded into a chamber immediately ahead of mold cavity, where it is heated; pressure is then applied to force soft polymer to flow into heated mold where it cures

Two variants: Pot transfer molding - charge is injected from a

"pot" through a vertical sprue channel into cavity Plunger transfer molding – plunger injects charge

from a heated well through channels into cavity


Figure 13.29 (a) Pot transfer molding: (1) charge is loaded into pot, (2) softened polymer is pressed into mold cavity and cured, and (3) part is ejected.

Pot Transfer Molding


Figure 13.29 (b) plunger transfer molding: (1) charge is loaded into pot, (2) softened polymer is pressed into mold cavity and cured, and (3) part is ejected.

Plunger Transfer Molding


Compression vs. Transfer Molding

In both processes, scrap is produced each cycle as leftover material, called the cull

The TS scrap cannot be recovered Transfer molding is capable of molding more

intricate part shapes than compression molding but not as intricate as injection molding

Transfer molding lends itself to molding with inserts, in which a metal or ceramic insert is placed into cavity prior to injection, and the plastic bonds to insert during molding


Blow Molding

Molding process in which air pressure is used to inflate soft plastic into a mold cavity

Important for making one-piece hollow plastic parts with thin walls, such as bottles

Because these items are used for consumer beverages in mass markets, production is typically organized for very high quantities

Accomplished in two steps:1. Fabrication of a starting tube, called a parison

2. Inflation of the tube to desired final shape Forming the parison is accomplished by either

Extrusion or Injection molding


Figure 13.30 Extrusion blow molding: (1) extrusion of parison; (2) parison is pinched at the top and sealed at the bottom around a metal blow pin as the two halves of the mold come together; (3) the tube is inflated so that it takes the shape of the mold cavity; and (4) mold is opened to remove the solidified part.

Extrusion Blow Molding


Figure 13.32 Injection blow molding: (1) parison is injected molded around a blowing rod; (2) injection mold is opened and parison is transferred to a blow mold; (3) soft polymer is inflated to conform to the blow mold; and (4) blow mold is opened and blown product is removed.

Injection Blow Molding


Stretch Blow Molding

Variation of injection blow molding in which blowing rod stretches the soft parison for a more favorable stressing of polymer than conventional blow molding

Resulting structure is more rigid, more transparent, and more impact resistant

Most widely used material is polyethylene terephthalate (PET) which has very low permeability and is strengthened by stretch blow molding Combination of properties makes it ideal as

container for carbonated beverages


Figure 13.33 Stretch blow molding: (1) injection molding of parison; (2) stretching; and (3) blowing.

Stretch Blow Molding


Materials and Products in Blow Molding

Blow molding is limited to thermoplastics Materials: high density polyethylene, polypropylene

(PP), polyvinylchloride (PVC), and polyethylene terephthalate

Products: disposable containers for beverages and other liquid consumer goods, large shipping drums (55 gallon) for liquids and powders, large storage tanks (2000 gallon), gasoline tanks, toys, and hulls for sail boards and small boats


Thermoforming

Flat thermoplastic sheet or film is heated and deformed into desired shape using a mold

Heating usually accomplished by radiant electric heaters located on one or both sides of starting plastic sheet or film

Widely used in packaging of products and to fabricate large items such as bathtubs, contoured skylights, and internal door liners for refrigerators


Figure 13.35 Vacuum thermoforming: (1) a flat plastic sheet is softened by heating

Figure 13.35 Vacuum thermoforming: (2) the softened sheet is placed over a concave mold cavity

Vacuum Thermoforming


Figure 13.35 Vacuum thermoforming: (3) a vacuum draws the sheet into the cavity

Figure 13.35 (4) plastic hardens on contact with the cold mold surface, and the part is removed and subsequently trimmed from the web.



Negative Molds vs. Positive Molds

Negative mold has concave cavity Positive mold has convex shape Both types are used in thermoforming For positive mold, heated sheet is draped over

convex form and negative or positive pressure forces plastic against mold surface


Figure 13.37 Use of a positive mold in vacuum thermoforming: (1) the heated plastic sheet is positioned above the convex mold

Figure 13.37 Use of a positive mold in vacuum thermoforming: (2) the clamp is lowered into position, draping the sheet over the mold as a vacuum forces the sheet against the mold surface



Materials for Thermoforming

Only thermoplastics can be thermoformed, Extruded sheets of thermosetting or elastomeric

polymers have already been cross-linked and cannot be softened by reheating

Common TP polymers: polystyrene, cellulose acetate, cellulose acetate butyrate, ABS, PVC, acrylic (polymethylmethacrylate), polyethylene, and polypropylene


Applications of Thermoforming

Thin films: blister packs and skin packs for packaging commodity products such as cosmetics, toiletries, small tools, and fasteners (nails, screws, etc.) For best efficiency, filling process to containerize

item(s) is immediately downstream from thermoforming

Thicker sheet stock: boat hulls, shower stalls, advertising displays and signs, bathtubs, certain toys, contoured skylights, internal door liners for refrigerators


Casting

Pouring liquid resin into a mold, using gravity to fill cavity, where polymer hardens

Both thermoplastics and thermosets are cast Thermoplastics: acrylics, polystyrene, polyamides

(nylons) and PVC Thermosetting polymers: polyurethane,

unsaturated polyesters, phenolics, and epoxies Simpler mold Suited to low quantities


Polymer Foam

A polymer-and-gas mixture that gives the material a porous or cellular structure

Most common polymer foams: polystyrene (Styrofoam, a trademark), polyurethane

Other polymers: natural rubber ("foamed rubber") and polyvinylchloride (PVC)

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Properties of a Foamed Polymer

Low density High strength per unit weight Good thermal insulation Good energy absorbing qualities Classification Elastomeric - matrix polymer is a rubber, capable of

large elastic deformation Flexible - matrix is a highly plasticized polymer such

as soft PVC Rigid - polymer is a stiff thermoplastic such as

polystyrene or a thermoset such as a phenolic


Applications of Polymer Foams

Characteristic properties of polymer foams, and the ability to control elastic behavior by selection of base polymer, make these materials suitable for certain applications

Applications: hot beverage cups, heat insulating structural materials, cores for structural panels, packaging materials, cushion materials for furniture and bedding, padding for automobile dashboards, and products requiring buoyancy

Figure 13.40 Two polymer foam structures: (a) closed cell and (b) open cell.


Figure 13.40 Two polymer foam structures: (a) closed cell and (b) open cell.

Polymer Foam Structures


Extrusion of Polystyrene Foams

Polystyrene (PS) is a thermoplastic polymer A physical or chemical blowing agent is fed into polymer melt

near die end of extruder barrel; thus, extrudate consists of expanded polymer

Products: large sheets and boards that are subsequently cut to size for heat insulation panels and sections

Expandable foam molding Molding material consists of prefoamed polystyrene

beads Beads are fed into mold cavity where they are

further expanded and fused together to form the molded product

Products: hot beverage cups, www.8linx.com/cnc/eps_foam.htm


Shaping of Polyurethane Foams

Polyurethane can be thermosetting, elastomer or thermoplastic (less common)

Polyurethane foam products are made in a one-step process in which the two liquid ingredients are mixed and immediately fed into a mold or other form Polymer is synthesized and part

geometry is created at the same time Shaping processes for polyurethane foam:

Spraying Pouring Cutting

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Product Design Guidelines: General

Strength and stiffness Plastics are not as strong or stiff as metals Avoid applications where high stresses will be

encountered Creep resistance is also a limitation Strength-to-weight ratios for some plastics are

competitive with metals in certain applications


Product Design Guidelines: General

Impact Resistance Capacity of plastics to absorb impact is generally good;

plastics compare favorably with most metals Service temperatures

Limited relative to metals and ceramics Thermal expansion

Dimensional changes due to temperature changes much more significant than for metals

Many plastics are subject to degradation from sunlight and other forms of radiation

Some plastics degrade in oxygen and ozone atmospheres Plastics are soluble in many common solvents Plastics are resistant to conventional corrosion mechanisms that

afflict many metals


Product Design Guidelines: Extrusion Wall thickness

Uniform wall thickness is desirable in an extruded cross section

Variations in wall thickness result in non-uniform plastic flow and uneven cooling which tend to warp extrudate

Hollow sections Hollow sections complicate die design and plastic flow Desirable to use extruded cross-sections that are not

hollow yet satisfy functional requirements Corners

Sharp corners, inside and outside, should be avoided in extruded cross sections

They result in uneven flow during processing and stress concentrations in the final product


Product Design Guidelines: Moldings

Economic production quantities Each part requires a unique mold, and the mold

for any molding process can be costly, particularly for injection molding

Minimum production quantities for injection molding are usually around 10,000 pieces

For compression molding, minimum quantities are 1000 parts, due to simpler mold designs

Transfer molding lies between injection molding and compression molding



Part complexity An advantage of plastic molding is that it allows multiple functional

features to be combined into one part Although more complex part geometries mean more costly molds,

it may nevertheless be economical to design a complex molding if the alternative involves many individual components that must be assembled.

Wall thickness Thick cross sections are wasteful of material, more likely to cause

warping due to shrinkage, and take longer to harden Reinforcing ribs

Achieves increased stiffness without excessive wall thickness Ribs should be made thinner than the walls they reinforce to

minimize sink marks on outside wall


Product Design Guidelines: Moldings Corner radii and fillets

Sharp corners, both external and internal, are undesirable in molded parts

They interrupt smooth flow of the melt, tend to create surface defects, and cause stress concentrations in the part

Holes Holes are quite feasible in plastic moldings, but they complicate

mold design and part removal Draft

A molded part should be designed with a draft on its sides to facilitate removal from mold

Especially important on inside wall of a cup-shaped part because plastic contracts against positive mold shape

Recommended draft: For thermosets, ~ 1/2 to 1

For thermoplastics, ~ 1/8 to 1/2



Tolerances Although shrinkage is predictable under closely

controlled conditions, generous tolerances are desirable for injection moldings because of Variations in process parameters that affect

shrinkage Diversity of part geometries encountered


RUBBER PROCESSING TECHNOLOGY

1. Rubber Processing and Shaping2. Manufacture of Tires and Other Rubber

Products3. Product Design Considerations


Overview of Rubber Processing

Many of the production methods used for plastics are also applicable to rubbers

However, rubber processing technology is different in certain respects, and the rubber industry is largely separate from the plastics industry

The rubber industry and goods made of rubber are dominated by one product: tires Tires are used in large numbers on

automobiles, trucks, aircraft, and bicycles


Rubber Processing and Shaping

Two basic steps in rubber goods production:1. Production of the rubber itself

Natural rubber (NR) is an agricultural crop

Synthetic rubbers is based on petroleum

2. Processing into finished goods: Compounding Mixing Shaping Vulcanizing


The Rubber Industries

Production of raw NR is an agricultural industry because latex, the starting ingredient, is grown on plantations in tropical climates

By contrast, synthetic rubbers are produced by the petrochemical industry

Finally, processing into tires and other products occurs at processor (fabricator) plants, commonly known as the rubber industry The company names include Goodyear, B.

F. Goodrich, and Michelin, all reflecting the importance of the tire


Production of Natural Rubber

Natural rubber is tapped from rubber trees (Hevea brasiliensis) as latex The trees are grown on plantations in

Southeast Asia and other parts of the world Latex is a colloidal dispersion of solid particles

of the polymer polyisoprene in water Polyisoprene (C5H8)n is the chemical

substance that comprises NR, and its content in the emulsion is about 30%

The latex is collected in large tanks, thus blending the yield of many trees together


Recovering the Rubber

Preferred method to recover rubber from latex involves coagulation - adding an acid such as formic acid (HCOOH) Coagulation takes about 12 hours

The coagulum, now soft solid slabs, is then squeezed through a series of rolls which drive out most of the water and reduce thickness to about 3 mm (1/8 in)

The sheets are then draped over wooden frames and dried in smokehouses Several days are normally required to

complete the drying process


Grades of Natural Rubber

The resulting rubber, now in a form called ribbed smoked sheet, is folded into large bales for shipment to the processor It has a characteristic dark brown color

In some cases, the sheets are dried in hot air rather than smokehouses, and the term air-dried sheet is used; this is considered to be a better grade of rubber

A still better grade, called pale crepe rubber, involves two coagulation steps, followed by warm air drying Its color is light tan


Synthetic Rubber

Most synthetic rubbers are produced from petroleum by the same polymerization techniques used to synthesize other polymers

Unlike thermoplastic and thermosetting polymers, which are normally supplied to the fabricator as pellets or liquid resins, synthetic rubbers are supplied to rubber processors in the form of large bales The rubber industry has a long tradition of

handling NR in these unit loads


Compounding

Rubber is always compounded with additives Compounding adds chemicals for

vulcanization, such as sulfur Additives include fillers which act either to

enhance the rubber's mechanical properties (reinforcing fillers) or to extend the rubber to reduce cost (non-reinforcing fillers)

It is through compounding that the specific rubber is designed to satisfy a given application in terms of properties, cost, and processability


Carbon Black in Rubber

The single most important reinforcing filler in rubber is carbon black, a colloidal form of carbon obtained by thermal decomposition of hydrocarbons (soot) Its effect is to increase tensile strength and

resistance to abrasion and tearing of the final rubber product

Carbon black also provides protection from ultraviolet radiation

Most rubber parts are black in color because of their carbon black content


Other Fillers and Additives in Rubber

China clays - hydrous aluminum silicates (Al2Si2O5(OH)4) reinforce less than carbon black but are used when black is not acceptable

Other polymers, such as styrene, PVC, and phenolics

Recycled rubber added in some rubber products, but usually 10% or less

Antioxidants; fatigue- and ozone-protective chemicals; coloring pigments; plasticizers and softening oils; blowing agents in the production of foamed rubber; mold release compounds


Mixing

The additives must be thoroughly mixed with the base rubber to achieve uniform dispersion of ingredients

Uncured rubbers have high viscosity so mechanical working of the rubber can increase its temperature up to 150C (300F)

If vulcanizing agents were present from the start of mixing, premature vulcanization would result - the “rubber processor's nightmare”


Two-Stage Mixing

To avoid premature vulcanization, a two-stage mixing process is usually employed

Stage 1 - carbon black and other non-vulcanizing additives are combined with the raw rubber The term master batch is used for this

first-stage mixture Stage 2 - after stage 1 mixing is completed,

and cooling time has been allowed, stage 2 mixing is carried out in which vulcanizing agents are added


Filament Reinforcement in Rubber

Many products require filament reinforcement to reduce extensibility but retain the other desirable properties of rubber Examples: tires, conveyor belts Filaments used for this purpose include

cellulose, nylon, and polyester Fiber-glass and steel are also used (e.g.,

steel-belted radial tires) Continuous fiber materials must be added

during shaping; they are not mixed like the other additives


Shaping and Related Processes

Shaping processes for rubber products can be divided into four basic categories: 1. Extrusion2. Calendering3. Coating4. Molding and casting

Some products require several basic processes plus assembly work Example: tires


Extrusion

Screw extruders are generally used for extrusion of rubber

The L/D ratio of the extruder barrel is less than for thermoplastics, typically in the range 10 to 15, to reduce risk of premature cross-linking

Die swell occurs in rubber extrudates, since the polymer is in a highly plastic condition and exhibits the “memory” property

The rubber has not yet been vulcanized


Stock is passed through a series of gaps of decreasing size made by a stand of rotating rolls

Rubber sheet thickness is determined by final roll gap

Figure 13.17 Calendering

Calendering


Combination of extrusion and calendering that results in better quality product than either extrusion or calendering alone

Figure 14.2 Roller die process - rubber extrusion followed by rolling

Roller Die Process


An important industrial process for producing automobile tires, conveyor belts, inflatable rafts, and waterproof cloth tents and rain coats

Figure 14.3 Coating of fabric with rubber using a calendering process

Coating or Impregnating Fabrics with Rubber


Molded Rubber Products

Molded rubber products include shoe soles and heals, gaskets and seals, suction cups, and bottle stops

Also, many foamed rubber parts are produced by molding

In addition, molding is an important process in tire production


Molding Processes for Rubber

Principal molding processes for rubber are 1. Compression molding 2. Transfer molding 3. Injection molding

Compression molding is the most important because of its use in tire manufacture

Curing (vulcanizing) is accomplished in the mold in all three processes, this representing a departure from previous shaping methods, all of which use a separate vulcanizing step


What is Vulcanization?Treatment that accomplishes cross-linking of

elastomer molecules, to make the rubber stiffer and stronger but retain extensibility

On a submicroscopic scale, the long-chain molecules of rubber become joined at certain tie points, the effect of which is to reduce the ability of the elastomer to flow A typical soft rubber has 1 or 2

cross-links per 1000 units (mers) As the number of cross-links increases,

the polymer becomes stiffer and behaves more and more like a thermosetting plastic (e.g., hard rubber)


Figure 14.4 Effect of vulcanization on rubber molecules: (1) raw rubber, and (2) vulcanized (cross-linked) rubber. Variations of (2) include: (a) soft rubber, low degree of cross-linking; and (b) hard rubber, high degree of cross-linking.

Effect of Vulcanization


Vulcanization Chemicals and Times

When first invented by Goodyear in 1839, vulcanization used sulfur (about 8 parts by weight of S mixed with 100 parts of NR) at 140C (280F) for about 5 hours Vulcanization with sulfur alone is no longer

used today, due to long curing times Various other chemicals (e.g., zinc oxide, stearic

acid) are combined with smaller doses of sulfur to accelerate and strengthen the treatment Resulting cure time is 15-20 minutes


Tires and Other Rubber Products

Tires are about 75% of total rubber tonnage Other important products:

Footwear Seals Shock-absorbing parts Conveyor belts Hose Foamed rubber products Sports equipment


Pneumatic Tires

Functions of pneumatic tires on vehicle : Support the weight of the vehicle,

passengers, and cargo Transmit the motor torque to propel the

vehicle Absorb road vibrations and shock to provide

a comfortable ride Tires are used on automobiles, trucks, buses,

farm tractors, earth moving equipment, military vehicles, bicycles, motorcycles, and aircraft


Tire Construction

A tire is an assembly of many parts Passenger car tire has about 50 individual

components Large earthmover tire has as many as 175

The internal structure of the tire, known as the carcass, consists of multiple layers of rubber coated cords, called plies

The cords are strands of nylon, polyester, fiber glass, or steel, which provide inextensibility to reinforce the rubber in the carcass


Figure 14.5 Three tire constructions: (a) diagonal ply, (b) belted bias, and (c) radial ply.

Three Tire Constructions


Tire Production Sequence

Tire production is summarized in three steps: 1. Preforming of components2. Building the carcass and adding rubber

strips to form the sidewalls and treads3. Molding and curing the components into one

integral piece Following descriptions of these steps are typical

Variations exist in processing depending on construction, tire size, and type of vehicle on which the tire will be used


Preforming of Components

Carcass consists of multiple components, most of which are rubber or reinforced rubber

These components and others are produced by continuous processes Then pre-cut to size and shape for

subsequent assembly Other components include: bead coil, plies,

inner lining, belts, tread, and sidewall


Carcass is traditionally assembled using a machine known as a building drum, whose main element is a cylindrical arbor that rotates

Figure 14.6 Tire just before removal from building drum, but prior to molding and curing.

Building the Carcass


Tire molds are usually split molds and contain the tread pattern to be impressed on the tire

Figure 14.7 Tire molding: (1) uncured tire is placed over expandable diaphragm; (2) mold is closed and diaphragm is expanded to force uncured rubber against mold cavity, impressing tread pattern into rubber; mold & diaphragm are heated to cure rubber

Molding and Curing


Other Rubber Products: Rubber Belts

Widely used in conveyors and mechanical power transmission systems (pulleys)

Rubber is an ideal material for these products because if its flexibility, but the belt must have little or no extensibility in order to function Accordingly, it is reinforced with fibers,

commonly polyester or nylon Fabrics of these polymers are usually coated

by calendering, assembled together to obtain required number of plies and thickness, and subsequently vulcanized by continuous or batch heating processes


Other Rubber Products: Hose

Two basic types:1. Plain hose (no reinforcement) is extruded

tubing 2. Reinforced tube, which consists of:

Inner tube - extruded of a rubber compounded for particular liquid that will flow through it

Reinforcement layer - applied to inner tube as fabric, or by spiraling, knitting, braiding

Outer layer – compounded for environment and applied by extrusion


Other Rubber Products: Footwear

Rubber components in footwear: soles, heels, rubber overshoes, and certain upper parts

Molded parts are produced by injection molding, compression molding, and certain special molding techniques developed by the shoe industry

The rubbers include both solid and foamed For low volume production, manual methods

are sometimes used to cut rubber from flat stock


Processing of Thermoplastic Elastomers

A thermoplastic elastomer (TPE) is a thermoplastic polymer that possesses the properties of a rubber

TPEs are processed like thermoplastics, but their applications are those of an elastomer

Most common shaping processes are injection molding and extrusion Generally more economical and faster than

the traditional processes used for rubbers that must be vulcanized


TPE Products

Molded products: shoe soles, athletic footwear, and automotive components such as fender extensions and corner panels

Extruded items: insulation coating for electrical wire, tubing for medical applications, conveyor belts, sheet and film stock

No tires of TPE



Economic Production Quantities: Rubber parts produced by compression

molding (the traditional process) can often be produced in quantities of 1000 or less The mold cost is relatively low compared to

other molding methods As with plastic parts, injection molding of

rubber parts requires higher production quantities to justify the more expensive mold



Draft: Draft is usually unnecessary for molded parts

of rubber, because its flexibility allows it to deform for removal from the mold

Shallow undercuts, although undesirable, are possible with rubber molded parts for the same reason

The low stiffness and high elasticity of the material permits removal from the mold


SHAPING PROCESSES FOR POLYMER MATRIX COMPOSITES

1. Starting Materials for PMCs2. Open Mold Processes3. Closed Mold Processes4. Filament Winding5. Pultrusion Processes6. Other PMC Shaping Processes


Overview of PMC Technology

A polymer matrix composite (PMC) is a composite material consisting of a polymer imbedded with a reinforcing phase such as fibers or powders

The importance of PMC processes derive from the growing use of this class of material, especially fiber-reinforced polymers (FRPs) FRP composites can be designed with very

high strength-to-weight and modulus-to-weight ratios

These features make them attractive in aircraft, cars, trucks, boats, and sports equipment


PMC Shape Processing

Many PMC shaping processes are slow and labor intensive

In general, techniques for shaping composites are less efficient than for other materials - Why? Composites are more complex than other

materials, consisting of two or more phases For FRPs, there is the need to orient the

reinforcing phase Many new composites fabrication processes in

last 7 years. – SCRIMP, VARTM, automated

open-mold, etc.


Categories of FRP Shape Processes

Open mold processes - some of the original FRP manual procedures for laying resins and fibers onto forms

Closed mold processes - much the same as those used in plastic molding

Filament winding - continuous filaments are dipped in liquid resin and wrapped around a rotating mandrel, producing a rigid, hollow, cylindrical shape

Pultrusion - similar to extrusion only adapted to include continuous fiber reinforcement

Other - operations not in previous categories


Figure 15.1 Classification of manufacturing processes for fiber reinforced polymer (FRP) composites

Classification of FRP Processes


Polymer Matrix

Thermosetting (TS) polymers are the most common matrix materials Principal TS polymers are:

Phenolics – used with particulate reinforcing phases

Polyesters and epoxies - most closely associated with FRPs

Thermoplastic molding compounds include fillers or reinforcing agents

Nearly all rubbers are reinforced with carbon black


Reinforcing Agent

Possible geometries - fibers, particles, and flakes Possible materials - ceramics, metals, other

polymers, or elements such as carbon or boron Particles and flakes are used in many plastic

molding compounds Of most engineering interest is the use of fibers as

the reinforcing phase in FRPs


Fibers as the Reinforcing Phase

Common fiber materials: glass, carbon, and Kevlar (a polymer)

In some fabrication processes, the filaments are continuous, while in others, they are chopped into short lengths In continuous form, individual filaments are

usually available as rovings - collections of untwisted continuous strands, convenient form for handling

By contrast, a yarn is a twisted collection of filaments


Fibers as the Reinforcing Phase

The most familiar form of continuous fiber is a cloth - a fabric of woven yarns

Similar to a cloth is a woven roving, a fabric consisting of untwisted filaments rather than yarns Woven rovings can be produced with unequal

numbers of strands in the two directions so that they possess greater strength in one direction

Such unidirectional woven rovings are often preferred in laminated FRP composites


Mats and Preforms as Reinforcements

Fibers can also be in a mat form - a felt consisting of randomly oriented short fibers held loosely together with a binder Mats are commercially available as blankets of

various weights, thicknesses, and widths Mats can be cut and shaped for use as preforms

in some of the closed mold processes During molding, the resin impregnates the preform

and then cures, thus yielding a fiber-reinforced molding


Combining Matrix and Reinforcement

1. The starting materials arrive at the fabrication operation as separate entities and are combined into the composite during shaping Filament winding and pultrusion, in which

reinforcing phase = continuous fibers 2. The two component materials are combined into

some starting form that is convenient for use in the shaping process Molding compounds Prepregs


Molding Compounds

FRP composite molding compounds consist of the resin matrix with short randomly dispersed fibers, similar to those used in plastic molding

Most molding compounds for composite processing are thermosetting polymers

Since they are designed for molding, they must be capable of flowing Accordingly, they have not been cured prior to

shape processing Curing is done during and/or after final shaping


Prepregs

Fibers impregnated with partially cured TS resins to facilitate shape processing

Available as tapes or cross-plied sheets or fabrics Curing is completed during and/or after shaping Advantage: prepregs are fabricated with continuous

filaments rather than chopped random fibers, thus increasing strength and modulus


Open Mold Processes

Family of FRP shaping processes that use a single positive or negative mold surface to produce laminated FRP structures

The starting materials (resins, fibers, mats, and woven rovings) are applied to the mold in layers, building up to the desired thickness

This is followed by curing and part removal Common resins are unsaturated polyesters and

epoxies, using fiberglass as the reinforcement


Open Mold FRP Processes

1. Hand lay-up 2. Spray-up3. Vacuum Bagging – uses hand-lay-up, uses

atmospheric pressure to compact laminate.4. Automated tape-laying machines The differences are in the methods of applying the

laminations to the mold, alternative curing techniques, and other differences


Hand Lay-Up Method

Open mold shaping method in which successive layers of resin and reinforcement are manually applied to an open mold to build the laminated FRP composite structure

Labor-intensive Finished molding must usually be trimmed with a

power saw to size outside edges Oldest open mold method for FRP laminates, dating

to the 1940s when it was first used for boat hulls


Figure 15.4 Hand lay-up : (1) mold is treated with mold release agent; (2) thin gel coat (resin) is applied, to the outside surface of molding; (3) when gel coat has partially set, layers of resin and fiber are applied, the fiber is in the form of mat or cloth; each layer is rolled to impregnate the fiber with resin and remove air; (4) part is cured; (5) fully hardened part is removed from mold.

Hand Lay-Up Method


Products Made by Hand Lay-Up

Generally large in size but low in production quantity - not economical for high production

Applications: Boat hulls Swimming pools Large container tanks Movie and stage props Other formed sheets

The largest molding ever made was ship hulls for the British Royal Navy: 85 m (280 ft) long


Spray-Up Method

Liquid resin and chopped fibers are sprayed onto an open mold to build successive FRP laminations

Attempt to mechanize application of resin-fiber layers and reduce lay-up time

Alternative for step (3) in the hand lay-up procedure


Figure 15.5 Spray-up method

Spray-Up Method


Products Made by Spray-Up

Boat hulls, bathtubs, shower stalls, automobile and truck body parts, recreational vehicle components, furniture, large structural panels, and containers

Movie and stage props are sometimes made by this method

Since products made by spray-up have randomly oriented short fibers, they are not as strong as those made by lay-up, in which the fibers are continuous and directed


Vacuum Bagging

Use atmospheric pressure to suck air from under vacuum bag, to compact composite layers down and make a high quality laminate (image from cgi.ebay.com).

Layers from bottom include: mold, mold release, composite, peel-ply, breather cloth, vacuum bag, also need vacuum valve, sealing tape.


Automated Tape-Laying Machines

Automated tape-laying machines operate by dispensing a prepreg tape onto an open mold following a programmed path

Typical machine consists of overhead gantry to which the dispensing head is attached

The gantry permits x-y-z travel of the head, for positioning and following a defined continuous path


Figure 15.6 Automated tape-laying machine (photo courtesy of Cincinnati Milacron).


Curing in Open Mold Processes

Curing is required of all thermosetting resins used in FRP laminated composites

Curing cross-links the polymer, transforming it from its liquid or highly plastic condition into a hardened product

Three principal process parameters in curing: 1. Time 2. Temperature 3. Pressure


Curing at Room Temperature

Curing normally occurs at room temperature for the TS resins used in hand lay-up and spray-up procedures Moldings made by these processes are often

large (e.g., boat hulls), and heating would be difficult due to product size

In some cases, days are required before room temperature curing is sufficiently complete to remove the part


Curing Methods Based on Heating

Oven curing provides heat at closely controlled temperatures; some curing ovens are equipped to draw a partial vacuum

Infrared heating - used in applications where it is impractical to place molding in oven

Curing in an autoclave, an enclosed chamber equipped to apply heat and/or pressure at controlled levels In FRP composites processing, it is usually a

large horizontal cylinder with doors at either end


Closed Mold Processes

Performed in molds consisting of two sections that open and close each molding cycle

Tooling cost is more than twice the cost of a comparable open mold due to the more complex equipment required in these processes

Advantages of a closed mold are: (1) good finish on all part surfaces, (2) higher production rates, (3) closer control over tolerances, and (4) more complex three-dimensional shapes are possible


Classification of Closed Mold Processes

Three classes based on their counterparts in conventional plastic molding: 1. Compression molding2. Transfer molding3. Injection molding

The terminology is often different when polymer matrix composites are molded


Compression Molding PMC Processes

A charge is placed in lower mold section, and the sections are brought together under pressure, causing charge to take the shape of the cavity

Mold halves are heated to cure TS polymer When molding is sufficiently cured, the mold is

opened and part is removed Several shaping processes for PMCs based on

compression molding The differences are mostly in the form of the

starting materials


Transfer Molding PMC Processes

A charge of thermosetting resin with short fibers is placed in a pot or chamber, heated, and squeezed by ram action into one or more mold cavities

The mold is heated to cure the resin Name of the process derives from the fact that the

fluid polymer is transferred from a pot into a mold


Injection Molding PMC Processes

Injection molding is noted for low cost production of plastic parts in large quantities

Although most closely associated with thermoplastics, the process can also be adapted to thermosets

Processes of interest in the context of PMCs: Conventional injection molding Reinforced reaction injection molding


Conventional Injection Molding

Used for both TP and TS type FRPs Virtually all TPs can be reinforced with fibers Chopped fibers must be used

Continuous fibers would be reduced by the action of the rotating screw in the barrel

During injection into the mold cavity, fibers tend to become aligned as they pass the nozzle Part designers can sometimes exploit this feature

to optimize directional properties in the part


Reinforced Reaction Injection Molding

Reaction injection molding (RIM) - two reactive ingredients are mixed and injected into a mold cavity where curing and solidification occur due to chemical reaction

Reinforced reaction injection molding (RRIM) -similar to RIM but includes reinforcing fibers, typically glass fibers, in the mixture

Advantages: similar to RIM (e.g., no heat energy required, lower cost mold), with the added benefit of fiber-reinforcement

Products: auto body, truck cab applications for bumpers, fenders, and other body parts


Filament Winding

Resin-impregnated continuous fibers are wrapped around a rotating mandrel that has the internal shape of the desired FRP product; the resin is then cured and the mandrel removed

The fiber rovings are pulled through a resin bath immediately before being wound in a helical pattern onto the mandrel

The operation is repeated to form additional layers, each having a criss-cross pattern with the previous, until the desired part thickness has been obtained


Figure 15.8 Filament winding.

Filament Winding


Figure 15.10 Filament winding machine (photo courtesy of Cincinnati Milacron).

Filament Winding Machine


Pultrusion Processes

Similar to extrusion (hence the name similarity) but workpiece is pulled through die (so prefix "pul-" in place of "ex-")

Like extrusion, pultrusion produces continuous straight sections of constant cross section

Developed around 1950 for making fishing rods of glass fiber reinforced polymer (GFRP)

A related process, called pulforming, is used to make parts that are curved and which may have variations in cross section throughout their lengths


Pultrusion

Continuous fiber rovings are dipped into a resin bath and pulled through a shaping die where the impregnated resin cures

The sections produced are reinforced throughout their length by continuous fibers

Like extrusion, the pieces have a constant cross section, whose profile is determined by the shape of the die opening

The cured product is cut into long straight sections


Figure 15.11 Pultrusion process

Pultrusion Process


Materials and Products in Pultrusion

Common resins: unsaturated polyesters, epoxies, and silicones, all thermosetting polymers

Reinforcing phase: E-glass is most widely, in proportions from 30% to 70%

Products: solid rods, tubing, long flat sheets, structural sections (such as channels, angled and flanged beams), tool handles for high voltage work, and third rail covers for subways.


Pulforming

Pultrusion with additional steps to form the length into a semicircular contour and alter the cross section at one or more locations along the length

Pultrusion is limited to straight sections of constant cross section

There is also a need for long parts with continuous fiber reinforcement that are curved rather than straight and whose cross sections may vary throughout length Pulforming is suited to these less regular shapes


Figure 15.12 Pulforming process (not shown in the sketch is the cut-off of the pulformed part).

Pulforming Process


Other PMC Shaping Processes

Centrifugal casting Tube rolling Continuous laminating Cutting of FRPs In addition, many traditional thermoplastic shaping

processes are applicable to FRPs with short fibers based on TP polymers Blow molding Thermoforming Extrusion


Cutting Methods

Cutting of FRP laminated composites is required in both uncured and cured states

Uncured materials (prepregs, preforms, SMCs, and other starting forms) must be cut to size for lay-up, molding, etc. Typical cutting tools: knives, scissors, power

shears, and steel-rule blanking dies Nontraditional methods are also used, such as

laser beam cutting and water jet cutting


Cutting Methods

Cured FRPs are hard, tough, abrasive, and difficult-to-cut Cutting of FRPs is required to trim excess

material, cut holes and outlines, and so on For glass FRPs, cemented carbide cutting tools

and high speed steel saw blades can be used For some advanced composites (e.g.,

boron-epoxy), diamond cutting tools cut best Water jet cutting is also used, to reduce dust and

noise problems with conventional sawing methods


FUNDAMENTALS OF METAL FORMING

1. Overview of Metal Forming2. Material Behavior in Metal Forming3. Temperature in Metal Forming4. Strain Rate Sensitivity5. Friction and Lubrication in Metal Forming


Metal Forming

Large group of manufacturing processes in which plastic deformation is used to change the shape of metal workpieces

The tool, usually called a die, applies stresses that exceed the yield strength of the metal

The metal takes a shape determined by the geometry of the die


Stresses in Metal Forming

Stresses to plastically deform the metal are usually compressive Examples: rolling, forging, extrusion

However, some forming processes Stretch the metal (tensile stresses) Others bend the metal (tensile and

compressive) Still others apply shear stresses


Material Properties in Metal Forming

Desirable material properties: Low yield strength High ductility

These properties are affected by temperature: Ductility increases and yield strength

decreases when work temperature is raised Other factors:

Strain rate and friction


Basic Types of Deformation Processes

1. Bulk deformation Rolling Forging Extrusion Wire and bar drawing

2. Sheet metalworking Bending Deep drawing Cutting Miscellaneous processes


Bulk Deformation Processes

Characterized by significant deformations and massive shape changes

"Bulk" refers to workparts with relatively low surface area-to-volume ratios

Starting work shapes include cylindrical billets and rectangular bars


Figure 18.2 Basic bulk deformation processes: (a) rolling

Rolling


Figure 18.2 Basic bulk deformation processes: (b) forging

Forging


Figure 18.2 Basic bulk deformation processes: (c) extrusion

Extrusion


Figure 18.2 Basic bulk deformation processes: (d) drawing

Wire and Bar Drawing


Sheet Metalworking

Forming and related operations performed on metal sheets, strips, and coils

High surface area-to-volume ratio of starting metal, which distinguishes these from bulk deformation

Often called pressworking because presses perform these operations Parts are called stampings

Usual tooling: punch and die


Figure 18.3 Basic sheet metalworking operations: (a) bending

Sheet Metal Bending


Figure 18.3 Basic sheet metalworking operations: (b) drawing

Deep Drawing


Figure 18.3 Basic sheet metalworking operations: (c) shearing

Shearing of Sheet Metal


Material Behavior in Metal Forming

Plastic region of stress-strain curve is primary interest because material is plastically deformed

In plastic region, metal's behavior is expressed by the flow curve:

nK

where K = strength coefficient; and n = strain hardening exponent

Flow curve based on true stress and true strain


Flow Stress

For most metals at room temperature, strength increases when deformed due to strain hardening

Flow stress = instantaneous value of stress required to continue deforming the material

where Yf = flow stress, that is, the yield strength as a function of strain

nf KY


Average Flow Stress

Determined by integrating the flow curve equation between zero and the final strain value defining the range of interest

where = average flow stress; and = maximum strain during deformation process

n

KY

n

f

1

_

_fY


Temperature in Metal Forming

For any metal, K and n in the flow curve depend on temperature Both strength (K) and strain hardening (n)

are reduced at higher temperatures In addition, ductility is increased at higher

temperatures


Temperature in Metal Forming

Any deformation operation can be accomplished with lower forces and power at elevated temperature

Three temperature ranges in metal forming: Cold working Warm working Hot working


Cold Working

Performed at room temperature or slightly above

Many cold forming processes are important mass production operations

Minimum or no machining usually required These operations are near net shape or net

shape processes


Advantages of Cold Forming

Better accuracy, closer tolerances Better surface finish Strain hardening increases strength and

hardness Grain flow during deformation can cause

desirable directional properties in product No heating of work required


Disadvantages of Cold Forming

Higher forces and power required in the deformation operation

Surfaces of starting workpiece must be free of scale and dirt

Ductility and strain hardening limit the amount of forming that can be done In some cases, metal must be annealed to

allow further deformation In other cases, metal is simply not ductile

enough to be cold worked


Warm Working

Performed at temperatures above room temperature but below recrystallization temperature

Dividing line between cold working and warm working often expressed in terms of melting point: 0.3Tm, where Tm = melting point (absolute

temperature) for metal


Advantages of Warm Working

Lower forces and power than in cold working More intricate work geometries possible Need for annealing may be reduced or

eliminated


Hot Working

Deformation at temperatures above therecrystallization temperature

Recrystallization temperature = about one-half of melting point on absolute scale In practice, hot working usually performed

somewhat above 0.5Tm

Metal continues to soften as temperature increases above 0.5Tm, enhancing advantage of hot working above this level


Why Hot Working?

Capability for substantial plastic deformation of the metal - far more than possible with cold working or warm working

Why? Strength coefficient (K) is substantially less

than at room temperature Strain hardening exponent (n) is zero

(theoretically) Ductility is significantly increased


Advantages of Hot Working

Workpart shape can be significantly altered Lower forces and power required Metals that usually fracture in cold working can

be hot formed Strength properties of product are generally

isotropic No strengthening of part occurs from work

hardening Advantageous in cases when part is to be

subsequently processed by cold forming


Disadvantages of Hot Working

Lower dimensional accuracy Higher total energy required (due to the

thermal energy to heat the workpiece) Work surface oxidation (scale), poorer surface

finish Shorter tool life


Strain Rate Sensitivity

Theoretically, a metal in hot working behaves like a perfectly plastic material, with strain hardening exponent n = 0 The metal should continue to flow at the

same flow stress, once that stress is reached

However, an additional phenomenon occurs during deformation, especially at elevated temperatures: Strain rate sensitivity


What is Strain Rate?

Strain rate in forming is directly related to speed of deformation v

Deformation speed v = velocity of the ram or other movement of the equipment

Strain rate is defined:

where = true strain rate; and h = instantaneous height of workpiece being deformed

h

v

.

.


Evaluation of Strain Rate

In most practical operations, valuation of strain rate is complicated by Workpart geometry Variations in strain rate in different regions

of the part Strain rate can reach 1000 s-1 or more for

some metal forming operations


Effect of Strain Rate on Flow Stress

Flow stress is a function of temperature At hot working temperatures, flow stress also

depends on strain rate As strain rate increases, resistance to

deformation increases This effect is known as strain-rate sensitivity


Figure 18.5 (a) Effect of strain rate on flow stress at an elevated work temperature. (b) Same relationship plotted on log-log coordinates.

Strain Rate Sensitivity


Strain Rate Sensitivity Equation

where C = strength constant (similar but not equal to strength coefficient in flow curve equation), and m = strain-rate sensitivity exponent

m

f CY ε=


Figure 18.6 Effect of temperature on flow stress for a typical metal. The constant C, as indicated by the intersection of each plot with the vertical dashed line at strain rate = 1.0, decreases, and m (slope of each plot) increases with increasing temperature.

Effect of Temperature on Flow Stress


Observations about Strain Rate Sensitivity

Increasing temperature decreases C and increases m At room temperature, effect of strain rate is

almost negligible Flow curve is a good representation of

material behavior As temperature increases, strain rate

becomes increasingly important in determining flow stress


Friction in Metal Forming

In most metal forming processes, friction is undesirable: Metal flow is retarded Forces and power are increased Tooling wears faster

Friction and tool wear are more severe in hot working


Lubrication in Metal Forming

Metalworking lubricants are applied to tool-work interface in many forming operations to reduce harmful effects of friction

Benefits: Reduced sticking, forces, power, tool wear Better surface finish Removes heat from the tooling


Considerations in Choosing a Lubricant

Type of forming process (rolling, forging, sheet metal drawing, etc.)

Hot working or cold working Work material Chemical reactivity with tool and work metals Ease of application Cost

BULK DEFORMATION PROCESSES IN METALWORKING Rolling Other Deformation Processes Related

to Rolling Forging Other Deformation Processes Related

to Forging Extrusion Wire and Bar Drawing

Bulk DeformationMetal forming operations which cause

significant shape change by deformation in metal parts whose initial form is bulk rather than sheet

Starting forms: cylindrical bars and billets, rectangular billets and slabs, and similar shapes

These processes work by stressing metal sufficiently to cause plastic flow into desired shape

Performed as cold, warm, and hot working operations

Importance of Bulk Deformation In hot working, significant shape

change can be accomplished In cold working, strength can be

increased during shape change Little or no waste - some operations

are near net shape or net shape

processes The parts require little or no

subsequent machining

Four Basic Bulk Deformation Processes

1. Rolling – slab or plate is squeezed between opposing rolls

2. Forging – work is squeezed and shaped between between opposing dies

3. Extrusion – work is squeezed through a die opening, thereby taking the shape of the opening

4. Wire and bar drawing – diameter of wire or bar is reduced by pulling it through a die opening

RollingDeformation process in which work

thickness is reduced by compressive forces exerted by two opposing rolls

Figure 19.1 - The rolling process (specifically, flat rolling)

The Rolls

The rotating rolls perform two main functions:

Pull the work into the gap between them by friction between workpart and rolls

Simultaneously squeeze the work to reduce cross section

Types of Rolling

By geometry of work: Flat rolling - used to reduce thickness of a

rectangular cross-section Shape rolling - a square cross-section is

formed into a shape such as an I-beam By temperature of work: Hot Rolling – most common due to the

large amount of deformation required Cold rolling – produces finished sheet and

plate stock

Figure 19.2 - Some of the steel products made in a rolling mill

Figure 19.3 - Side view of flat rolling, indicating before and after thicknesses,

work velocities, angle of contact with rolls, and other features

Flat Rolling – Terminology

Draft = amount of thickness reduction

fo ttd

where d = draft; to = starting thickness; and tf = final thickness

Flat Rolling – Terminology

Reduction = draft expressed as a fraction of starting stock thickness:

ot

dr

where r = reduction

Shape Rolling

Work is deformed into a contoured cross-section rather than flat (rectangular)

Accomplished by passing work through rolls that have the reverse of desired shape

Products include: Construction shapes such as I-beams, L-beams,

and U-channels Rails for railroad tracks Round and square bars and rods

Figure 19.5 - A rolling mill for hot flat rolling; the steel plate is seen as the glowing strip extending diagonally from the lower left corner (photo courtesy of Bethlehem Steel Company)

Rolling Mills Equipment is massive and expensive Rolling mill configurations: Two-high – two opposing large diameter rolls Three-high – work passes through both

directions Four-high – backing rolls support smaller work

rolls Cluster mill – multiple backing rolls on smaller

rolls Tandem rolling mill – sequence of two-high mills

Figure 19.6 - Various configurations of rolling mills:

(a) 2-high rolling mill


(b) 3-high rolling mill


(c) four-high rolling mill

Cluster MillMultiple backing rolls allow even smaller roll

diameters

Figure 19 6 - Various configurations of rolling mills: (d) cluster mill

Tandem Rolling MillA series of rolling stands in sequence


(e) tandem rolling mill

Thread Rolling

Bulk deformation process used to form threads on cylindrical parts by rolling them between two dies

Most important commercial process for mass producing bolts and screws

Performed by cold working in thread rolling machines Advantages over thread cutting (machining):

Higher production rates Better material utilization Stronger threads due to work hardening Better fatigue resistance due to compressive stresses

introduced by rolling

Figure 19.7 - Thread rolling with flat dies: (1) start of cycle, and (2) end of cycle

Ring Rolling

Deformation process in which a thick-walled ring of smaller diameter is rolled into a thin-walled ring of larger diameter

As thick-walled ring is compressed, deformed metal elongates, causing diameter of ring to be enlarged

Hot working process for large rings and cold working process for smaller rings

Applications: ball and roller bearing races, steel tires for railroad wheels, and rings for pipes, pressure vessels, and rotating machinery

Advantages: material savings, ideal grain orientation, strengthening through cold working

Figure 19.8 - Ring rolling used to reduce the wall thickness and increase the diameter of a ring:

(1) start, and (2) completion of process

Forging

Deformation process in which work is compressed between two dies

Oldest of the metal forming operations, dating from about5000 B C

Components: engine crankshafts, connecting rods, gears, aircraft structural components, jet engine turbine parts

In addition, basic metals industries use forging to establish basic form of large components that are subsequently machined to final shape and size

Classification of Forging Operations

Cold vs. hot forging: Hot or warm forging – most common, due

to the significant deformation and the need to reduce strength and increase ductility of work metal

Cold forging - advantage is increased strength that results from strain hardening

Impact vs. press forging: Forge hammer - applies an impact load Forge press - applies gradual pressure

Types of Forging Dies

Open-die forging - work is compressed between two flat dies, allowing metal to flow laterally without constraint

Impression-die forging - die surfaces contain a cavity or impression that is imparted to workpart, thus constraining metal flow - flash is created

Flashless forging - workpart is completely constrained in die and no excess flash is produced

Figure 19.10 - Three types of forging: (a) open-die forging

Figure 19.10 - Three types of forging (b) impression-die forging

Figure 19.10 - Three types of forging (c) flashless forging

Open-Die Forging

Compression of workpart with cylindrical cross-section between two flat dies

Similar to compression test Deformation operation reduces height

and increases diameter of work Common names include upsetting or

upset forging

Open-Die Forging with No Friction

If no friction occurs between work and die surfaces, then homogeneous deformation occurs, so that radial flow is uniform throughout workpart height and true strain is given by:

where ho= starting height; and h = height at some point during compression

At h = final value hf, true strain is maximum value

h

holn

Figure 19.11 - Homogeneous deformation of a cylindrical workpart under ideal conditions in an open-die forging

operation: (1) start of process with workpiece at its original length and

diameter, (2) partial compression, and (3) final size

Open-Die Forging with Friction Friction between work and die

surfaces constrains lateral flow of work, resulting in barreling effect

In hot open-die forging, effect is even more pronounced due to heat transfer at and near die surfaces, which cools the metal and increases its resistance to deformation

Figure 19.12 - Actual deformation of a cylindrical workpart in open-die forging,

showing pronounced barreling: (1) start of process, (2) partial deformation,

and (3) final shape

Impression-Die Forging

Compression of workpart by dies with inverse of desired part shape

Flash is formed by metal that flows beyond die cavity into small gap between die plates

Flash must be later trimmed from part, but it serves an important function during compression: As flash forms, friction resists continued metal flow

into gap, constraining material to fill die cavity In hot forging, metal flow is further restricted by

cooling against die plates

Figure 19.15 - Sequence in impression-die forging: (1) just prior to initial contact with raw workpiece, (2) partial compression, and (3) final die closure, causing flash to form in gap

between die plates

Impression-Die Forging Practice

Several forming steps often required, with separate die cavities for each step Beginning steps redistribute metal for more

uniform deformation and desired metallurgical structure in subsequent steps

Final steps bring the part to its final geometry Impression-die forging is often performed

manually by skilled operator under adverse conditions

Impression-Die Forging Advantages and Limitations

Advantages compared to machining from solid stock: Higher production rates Conservation of metal (less waste) Greater strength Favorable grain orientation in the metal

Limitations: Not capable of close tolerances Machining often required to achieve accuracies

and features needed, such as holes, threads, and mating surfaces that fit with other components

Flashless ForgingCompression of work in punch and die tooling

whose cavity does allow for flash Starting workpart volume must equal die

cavity volume within very close tolerance Process control more demanding than

impression-die forging Best suited to part geometries that are simple

and symmetrical Often classified as a precision forging process

Figure 19.18 - Flashless forging: (1) just before initial contact with

workpiece, (2) partial compression, and (3) final punch and die closure

Forging Hammers (Drop Hammers)

Apply an impact load against workpart - two types: Gravity drop hammers - impact energy from

falling weight of a heavy ram Power drop hammers - accelerate the ram by

pressurized air or steam Disadvantage: impact energy transmitted

through anvil into floor of building Most commonly used for impression-die forging

Figure 19.20 - Drop forging hammer, fed by conveyor and heating units at the right of

the scene (photo courtesy of Chambersburg Engineering

Company)

Figure 19.21 - Diagram showing details of a drop hammer for impression-die forging

Forging Presses

Apply gradual pressure to accomplish compression operation - types: Mechanical presses - converts

rotation of drive motor into linear motion of ram

Hydraulic presses - hydraulic piston actuates ram

Screw presses - screw mechanism drives ram

ExtrusionCompression forming process in which the work

metal is forced to flow through a die opening to produce a desired cross-sectional shape

Process is similar to squeezing toothpaste out of a toothpaste tube

In general, extrusion is used to produce long parts of uniform cross-sections

Two basic types of extrusion: Direct extrusion Indirect extrusion

Figure 19.31 - Direct extrusion

Comments on Direct Extrusion

Also called forward extrusion

As ram approaches die opening, a small portion of billet remains that cannot be forced through die opening

This extra portion, called the butt, must be separated from extruded product by cutting it just beyond the die exit

Starting billet cross section usually round, but final shape is determined by die opening

Figure 19.32 - (a) Direct extrusion to produce a hollow or semi-hollow cross-section; (b) hollow and (c) semi-hollow cross- sections

Figure 19.33 - Indirect extrusion to produce

(a) a solid cross-section and (b) a hollow cross-section

Comments on Indirect Extrusion Also called backward extrusion and

reverse extrusion

Limitations of indirect extrusion are imposed by the lower rigidity of hollow ram and difficulty in supporting extruded product as it exits die

General Advantages of Extrusion

Variety of shapes possible, especially in hot extrusion Limitation: part cross-section must be uniform

throughout length Grain structure and strength enhanced in

cold and warm extrusion Close tolerances possible, especially in cold

extrusion In some operations, little or no waste of

material

Hot vs. Cold Extrusion

Hot extrusion - prior heating of billet to above its recrystallization temperature This reduces strength and increases

ductility of the metal, permitting more size reductions and more complex shapes

Cold extrusion - generally used to produce discrete parts The term impact extrusion is used to

indicate high speed cold extrusion

Extrusion Ratio

Also called the reduction ratio, it is defined as

where rx = extrusion ratio; Ao = cross-sectional area of the starting billet; and Af = final cross-sectional area of the extruded section

Applies to both direct and indirect extrusion

f

ox

A

Ar

Comments on Orifice Shape of Extrusion Die Simplest cross section shape =

circular die orifice Shape of die orifice affects ram

pressure As cross-section becomes more

complex, higher pressure and greater force are required

Figure 19.37 - A complex extruded cross-section for a heat sink (photo

courtesy of Aluminum Company of America)

Extrusion Presses

Either horizontal or vertical Horizontal more common

Extrusion presses - usually hydraulically driven, which is especially suited to semi-continuous direct extrusion of long sections

Mechanical drives - often used for cold extrusion of individual parts

Wire and Bar Drawing

Cross-section of a bar, rod, or wire is reduced by pulling it through a die opening

Similar to extrusion except work is pulled

through die in drawing (it is pushed through in extrusion)

Although drawing applies tensile stress, compression also plays a significant role since metal is squeezed as it passes through die opening

Figure 19.41 - Drawing of bar, rod, or wire

Area Reduction in Drawing

Change in size of work is usually given by area reduction:

where r = area reduction in drawing; Ao

= original area of work; and Ar = final work

o

fo

A

AAr

Wire Drawing vs. Bar Drawing Difference between bar drawing and

wire drawing is stock size Bar drawing - large diameter bar and

rod stock Wire drawing - small diameter stock -

wire sizes down to 0.03 mm (0.001 in.) are possible

Although the mechanics are the same, the methods, equipment, and even terminology are different

Drawing Practice and Products

Drawing practice: Usually performed as cold working Most frequently used for round cross-sections

Products: Wire: electrical wire; wire stock for fences, coat

hangers, and shopping carts Rod stock for nails, screws, rivets, and springs Bar stock: metal bars for machining, forging,

and other processes

Bar Drawing

Accomplished as a single-draft

operation - the stock is pulled through one die opening

Beginning stock has large diameter and is a straight cylinder

This necessitates a batch type operation

Figure 19.42 - Hydraulically operated draw bench

for drawing metal bars

Wire Drawing

Continuous drawing machines consisting of multiple draw dies (typically 4 to 12) separated by accumulating drums Each drum (capstan) provides proper force to

draw wire stock through upstream die Each die provides a small reduction, so desired

total reduction is achieved by the series Annealing sometimes required between dies

Figure 19.43 - Continuous drawing of wire

Figure 19.44 - Draw die for drawing of round rod or wire

Preparation of the Work for Wire or Bar Drawing Annealing – to increase ductility of

stock Cleaning - to prevent damage to work

surface and draw die Pointing – to reduce diameter of

starting end to allow insertion through draw die

SHEET METALWORKING

• Cutting Operations

• Bending Operations

• Drawing

• Other Sheet Metal Forming

Operations

• Dies and Presses for Sheet Metal

Processes

• Sheet Metal Operations Not

Performed on Presses

• Bending of Tube Stock

Sheet Metalworking Defined

Cutting and forming operations

performed on relatively thin sheets of

metal

• Thickness of sheet metal = 0.4 mm

(1/64 in) to 6 mm (1/4 in)

• Thickness of plate stock > 6 mm

• Operations usually performed as

cold working

Sheet and Plate Metal Products

• Sheet and plate metal parts for

consumer and industrial products

such as

• Automobiles and trucks

• Airplanes

• Railway cars and locomotives

• Farm and construction equipment

• Small and large appliances

• Office furniture

• Computers and office equipment

Advantages of Sheet Metal Parts

• High strength

• Good dimensional accuracy

• Good surface finish

• Relatively low cost

• For large quantities, economical

mass production operations are

available

Sheet Metalworking Terminology

1. “Punch-and-die”

• Tooling to perform cutting, bending,

and drawing

2. “Stamping press”

• Machine tool that performs most sheet

metal operations

3. “Stampings”

• Sheet metal products

Three Major Categories of

Sheet Metal Processes

1. Cutting

• Shearing to separate large sheets; or

cut part perimeters or make holes in

sheets

2. Bending

• Straining sheet around a straight axis

3. Drawing

• Forming of sheet into convex or

concave shapes

Figure

20.1 - Shearing

of sheet metal

between two

cutting edges:

(1) just before the

punch contacts

work

CuttingShearing between two sharp cutting edges

Figure 20.1 - Shearing of sheet metal between two cutting edges:

(2) punch begins to push into work, causing plastic deformation

Figure

20.1 - Shearing

of sheet metal

between two

cutting edges:

(3) punch

compresses and

penetrates into

work causing a

smooth cut

surface

Figure

20.1 - Shearing of

sheet metal

between two

cutting edges:

(4) fracture is

initiated at the

opposing cutting

edges which

separates the sheet

Shearing, Blanking, and Punching

Three principal operations in

pressworking that cut sheet metal:

• Shearing

• Blanking

• Punching

Shearing

Sheet metal cutting operation along a

straight line between two cutting

edges

• Typically used to cut large sheets

into smaller sections for subsequent

operations

Figure 20.3 - Shearing operation:

(a) side view of the shearing operation

(b) front view of power shears equipped with inclined upper cutting blade Symbol v indicates motion

Blanking and Punching

Blanking - sheet metal cutting to

separate piece from surrounding

stock

• Cut piece is the desired part, called a

blank

Punching - sheet metal cutting similar

to blanking except cut piece is scrap,

called a slug

• Remaining stock is the desired part

Figure 20.4 - (a) Blanking and (b) punching

Figure 20.6 - Die size determines blank size

Db; punch size determines hole size Dh.; c

= clearance

Angular Clearance

Purpose: allows slug or blank to drop

through die

• Typical values: 0.25 to 1.5 on each

side

Figure 20.7 - Angular clearance

Cutting Forces

Important for determining press size

(tonnage)

F = S t L

where S = shear strength of metal;

t = stock thickness, and L = length of

cut edge

BendingStraining sheetmetal around a straight

axis to take a permanent bend

Figure 20.11 - (a) Bending of sheet metal

Metal on inside of neutral plane is

compressed, while metal on outside

of neutral plane is stretched

Figure 20.11 - (b) both compression and tensile elongation of the metal occur in bending

Types of Sheetmetal Bending

• V-bending - performed with a

V-shaped die

• Edge bending - performed with a

wiping die

V-Bending

• For low production

• Performed on a press brake

• V-dies are simple and inexpensive

Figure 20.12 -(a) V-bending

Edge Bending

• For high production

• Pressure pad required

• Dies are more complicated and costly

Figure 20.12 - (b) edge bending

Stretching during Bending

• If bend radius is small relative to

stock thickness, metal tends to

stretch during bending

• Important to estimate amount of

stretching, so that final part length =

specified dimension

• Problem: to determine the length of

neutral axis of the part before

bending

Bend Allowance Formula

where BA = bend allowance; A = bend

angle; R= bend radius; t = stock

thickness; and Kba is factor to

estimate stretching

• If R < 2t, Kba = 0.33

• If R 2t, Kba = 0.50

)( tKRA

BA ba360

2

Springback in Bending

Springback = increase in included

angle of bent part relative to included

angle of forming tool after tool is

removed

• Reason for springback:

• When bending pressure is removed,

elastic energy remains in bent part,

causing it to recover partially toward its

original shape

Figure 20.13 - Springback in bending shows itself as a decrease in bend angle and an increase in bend radius: (1) during bending, the work is forced to take the radius Rb and included angle Ab' of the bending tool (punch in V-bending), (2) after punch is removed, the work springs back to radius R and angle A'

Bending Force

Maximum bending force estimated as

follows:

where F = bending force; TS = tensile strength of sheet metal; w = part width in direction of bend axis; and t = stock thickness. For V- bending, Kbf = 1.33; for edge bending, Kbf = 0.33

D

TSwtKF bf

2

Figure 20.14 - Die opening dimension D: (a)

V-die, (b) wiping die

Drawing

Sheet metal forming to make

cup-shaped, box-shaped, or other

complex-curved, hollow-shaped

parts

• Sheet metal blank is positioned over

die cavity and then punch pushes

metal into opening

• Products: beverage cans,

ammunition shells, automobile body

panels

Figure 20.19 -

(a) Drawing of a

cup-shaped

part:

(1) start of

operation

before punch

contacts work

(2) near end of

stroke

(b) Corresponding

workpart:

(1) starting blank

(2) drawn part

Drawing Ratio DR

where Db = blank diameter; and Dp =

punch diameter

• Indicates severity of a given drawing

operation

• Upper limit = 2.0

Most easily defined for cylindrical shape:

p

b

D

DDR

Reduction r

• Again, defined for cylindrical shape:

b

pb

D

DDr

• Value of r should be less than 0.50

Thickness-to-Diameter Ratio

Thickness of starting blank divided by

blank diameter

Thickness-to-diameter ratio = t/Db

• Desirable for t/Db ratio to be greater

than 1%

• As t/Db decreases, tendency for

wrinkling increases

Blank Size Determination

• For final dimensions of drawn shape

to be correct, starting blank diameter

Db must be right

• Solve for Db by setting starting sheet

metal blank volume = final product

volume

• To facilitate calculation, assume

negligible thinning of part wall

Shapes other than Cylindrical Cups

• Square or rectangular boxes (as in

sinks),

• Stepped cups,

• Cones,

• Cups with spherical rather than flat

bases,

• Irregular curved forms (as in

automobile body panels)

• Each of these shapes presents its

own unique technical problems in

drawing

Other Sheet Metal Forming on Presses

Other sheet metal forming operations

performed on conventional presses

• Operations performed with metal

tooling

• Operations performed with flexible

rubber tooling

Ironing

• Makes wall thickness of cylindrical cup more uniform

• Examples: beverage cans and artillery shells

Figure 20.25 - Ironing to achieve a more uniform wall thickness in a drawn cup: (1) start of process; (2) during process

Note thinning and elongation of walls

Embossing

• Used to create indentations in sheet,

such as raised (or indented) lettering

or strengthening ribs

Figure 20.26 - Embossing: (a) cross-section of punch and die configuration during pressing; (b) finished part with embossed ribs

Figure 20.28 - Guerin process: (1) before and (2) after

Symbols v and F indicate motion and applied force

respectively

Guerin Process

Advantages of Guerin Process

• Low tooling cost

• Form block can be made of wood,

plastic, or other materials that are

easy to shape

• Rubber pad can be used with

different form blocks

• Process attractive in small quantity

production

Dies for Sheet Metal Processes

Most pressworking operations

performed with conventional

punch-and-die tooling

• Custom-designed for particular part

• The term stamping die sometimes

used for high production dies

Figure 20.30 - Components of a punch and die

for a blanking operation

Figure

20.31 -

(a)Progressi

ve die;

(b)associate

d strip

developm

ent

Figure 20.32 - Components of a

typical mechanical drive

stamping press

Figure

20.33 - Gap

frame press for

sheet

metalworking

(photo courtesy

of E. W. Bliss

Company)

Capacity = 1350

kN (150 tons)

Figure 20.34 -

Press brake with

bed width of

9.15 m (30 ft)

and capacity

of 11,200 kN

(1250 tons);

two workers

are

positioning

plate stock for

bending

(photo courtesy

of Niagara

Machine &

Tool Works)

Figure 20.35 - Several sheet metal parts

produced on a turret press, showing

variety of hole shapes possible

(photo courtesy of Strippet, Inc.)

Figure 20.36 - Computer numerical control

turret press

(photo courtesy of Strippet, Inc.)

Figure 20.37 -

Straight-sided

frame press

(photo courtesy

Greenerd Press

& Machine

Company, Inc.)

Power and Drive Systems

• Hydraulic presses - use a large

piston and cylinder to drive the ram

• Longer ram stroke than mechanical

types

• Suited to deep drawing

• Slower than mechanical drives

• Mechanical presses – convert

rotation of motor to linear motion of

ram

• High forces at bottom of stroke

• Suited to blanking and punching

Sheet Metal Operations

Not Performed on Presses

• Stretch forming

• Roll bending and forming

• Spinning

• High-energy-rate forming processes.

Stretch FormingSheet metal is stretched and

simultaneously bent to achieve shape change

Figure 20.39 - Stretch forming: (1) start of process; (2) form die is pressed into the work with force Fdie, causing it to be stretched and

bent over the form. F = stretching force

Force Required in Stretch Forming

where F = stretching force; L = length

of sheet in direction perpendicular to

stretching; t = instantaneous stock

thickness; and Yf = flow stress of

work metal

• Die force Fdie can be determined by

balancing vertical force components

fLtYF

Roll Bending

Large metal sheets and plates are

formed into curved sections using

rolls

Figure 20.40 - Roll bending

Roll Forming

Continuous bending process in which

opposing rolls produce long sections

of formed shapes from coil or strip

stock

Figure 20.41 - Roll forming of a continuous channel section:

(1) straight rolls(2) partial form (3) final form

Spinning

Metal forming process in which an

axially symmetric part is gradually

shaped over a rotating mandrel

using a rounded tool or roller

• Three types:

1. Conventional spinning

2. Shear spinning

3. Tube spinning

Figure 20.42 - Conventional spinning: (1)

setup at start of process; (2) during

spinning; and (3) completion of process

High-Energy-Rate Forming (HERF)

Processes to form metals using large

amounts of energy over a very short

time

• HERF processes include:

• Explosive forming

• Electrohydraulic forming

• Electromagnetic forming

Explosive Forming

Use of explosive charge to form sheet

(or plate) metal into a die cavity

• Explosive charge causes a shock

wave whose energy is transmitted to

force part into cavity

• Applications: large parts, typical of

aerospace industry

Figure 20.45 - Explosive forming:

(1) setup, (2) explosive is detonated, and

(3) shock wave forms part and plume escapes water surface

Electromagnetic Forming

Sheet metal is deformed by

mechanical force of an

electromagnetic field induced in

workpart by an energized coil

• Presently the most widely used

HERF process

• Applications: tubular parts

Figure 20.47 - Electromagnetic forming: (1)

setup in which coil is inserted into tubular

workpart surrounded by die; (2) formed

part


THEORY OF METAL MACHINING

1. Overview of Machining Technology2. Theory of Chip Formation in Metal Machining3. Force Relationships and the Merchant

Equation4. Power and Energy Relationships in Machining5. Cutting Temperature


Material Removal Processes

A family of shaping operations, the common feature of which is removal of material from a starting workpart so the remaining part has the desired geometry

Machining – material removal by a sharp cutting tool, e.g., turning, milling, drilling

Abrasive processes – material removal by hard, abrasive particles, e.g., grinding

Nontraditional processes - various energy forms other than sharp cutting tool to remove material


Cutting action involves shear deformation of work material to form a chip As chip is removed, new surface is exposed

Figure 21.2 (a) A cross-sectional view of the machining process, (b) tool with negative rake angle; compare with positive rake angle in (a).

Machining


Why Machining is Important

Variety of work materials can be machined Most frequently used to cut metals

Variety of part shapes and special geometric features possible, such as: Screw threads Accurate round holes Very straight edges and surfaces

Good dimensional accuracy and surface finish


Disadvantages with Machining

Wasteful of material Chips generated in machining are wasted

material, at least in the unit operation Time consuming

A machining operation generally takes more time to shape a given part than alternative shaping processes, such as casting, powder metallurgy, or forming


Machining in Manufacturing Sequence

Generally performed after other manufacturing processes, such as casting, forging, and bar drawing Other processes create the general shape

of the starting workpart Machining provides the final shape,

dimensions, finish, and special geometric details that other processes cannot create


Machining Operations

Most important machining operations: Turning Drilling Milling

Other machining operations: Shaping and planing Broaching Sawing


Single point cutting tool removes material from a rotating workpiece to form a cylindrical shape

Figure 21.3 Three most common machining processes: (a) turning,

Turning


Used to create a round hole, usually by means of a rotating tool (drill bit) with two cutting edges

Figure 21.3 (b) drilling,

Drilling


Rotating multiple-cutting-edge tool is moved across work to cut a plane or straight surface

Two forms: peripheral milling and face milling

Figure 21.3 (c) peripheral milling, and (d) face milling.

Milling


Cutting Tool Classification

1. Single-Point Tools One dominant cutting edge Point is usually rounded to form a nose

radius Turning uses single point tools

2. Multiple Cutting Edge Tools More than one cutting edge Motion relative to work achieved by rotating Drilling and milling use rotating multiple

cutting edge tools


Figure 21.4 (a) A single-point tool showing rake face, flank, and tool point; and (b) a helical milling cutter, representative of tools with multiple cutting edges.

Cutting Tools


Cutting Conditions in Machining

Three dimensions of a machining process: Cutting speed v – primary motion Feed f – secondary motion Depth of cut d – penetration of tool

below original work surface For certain operations, material removal

rate can be computed as RMR = v f d

where v = cutting speed; f = feed; d = depth of cut


Cutting Conditions for Turning

Figure 21.5 Speed, feed, and depth of cut in turning.


Roughing vs. Finishing

In production, several roughing cuts are usually taken on the part, followed by one or two finishing cuts

Roughing - removes large amounts of material from starting workpart Creates shape close to desired geometry,

but leaves some material for finish cutting High feeds and depths, low speeds

Finishing - completes part geometry Final dimensions, tolerances, and finish Low feeds and depths, high cutting speeds


Machine Tools

A power-driven machine that performs a machining operation, including grinding

Functions in machining: Holds workpart Positions tool relative to work Provides power at speed, feed, and depth

that have been set The term is also applied to machines that

perform metal forming operations


Simplified 2-D model of machining that describes the mechanics of machining fairly accurately

Figure 21.6 Orthogonal cutting: (a) as a three-dimensional process.

Orthogonal Cutting Model


Chip Thickness Ratio

where r = chip thickness ratio; to = thickness of the chip prior to chip formation; and tc = chip thickness after separation

Chip thickness after cut always greater than before, so chip ratio always less than 1.0

c

o

t

tr


Determining Shear Plane Angle

Based on the geometric parameters of the orthogonal model, the shear plane angle can be determined as:

where r = chip ratio, and = rake angle

sincostanr

r

1


Figure 21.7 Shear strain during chip formation: (a) chip formation depicted as a series of parallel plates sliding relative to each other, (b) one of the plates isolated to show shear strain, and (c) shear strain triangle used to derive strain equation.

Shear Strain in Chip Formation


Shear Strain

Shear strain in machining can be computed from the following equation, based on the preceding parallel plate model:

= tan( - ) + cot

where = shear strain, = shear plane angle, and = rake angle of cutting tool


Figure 21.8 More realistic view of chip formation, showing shear zone rather than shear plane. Also shown is the secondary shear zone resulting from tool-chip friction.

Chip Formation


Four Basic Types of Chip in Machining

1. Discontinuous chip2. Continuous chip3. Continuous chip with Built-up Edge (BUE)4. Serrated chip


Brittle work materials Low cutting speeds Large feed and depth

of cut High tool-chip friction

Figure 21.9 Four types of chip formation in metal cutting: (a) discontinuous

Discontinuous Chip


Ductile work materials

High cutting speeds

Small feeds and depths

Sharp cutting edge

Low tool-chip friction

Figure 21.9 (b) continuous

Continuous Chip


Ductile materials Low-to-medium cutting

speeds Tool-chip friction

causes portions of chip to adhere to rake face

BUE forms, then breaks off, cyclically

Figure 21.9 (c) continuous with built-up edge

Continuous with BUE


Semicontinuous -saw-tooth appearance

Cyclical chip forms with alternating high shear strain then low shear strain

Associated with difficult-to-machine metals at high cutting speeds

Serrated Chip

Figure 21.9 (d) serrated.


Friction force F and Normal force to friction N Shear force Fs and Normal force to shear Fn

Figure 21.10 Forces in metal cutting: (a) forces acting on the chip in orthogonal cutting

Forces Acting on Chip


Resultant Forces

Vector addition of F and N = resultant R Vector addition of Fs and Fn = resultant R' Forces acting on the chip must be in balance:

R' must be equal in magnitude to R R’ must be opposite in direction to R R’ must be collinear with R


Coefficient of Friction

Coefficient of friction between tool and chip:

Friction angle related to coefficient of friction as follows:

N

F

tan


Shear Stress

Shear stress acting along the shear plane:

sinwt

A os

where As = area of the shear plane

Shear stress = shear strength of work material during cutting

s

s

A

FS


F, N, Fs, and Fn cannot be directly measured Forces acting on the tool that can be measured:

Cutting force Fc and Thrust force Ft

Figure 21.10 Forces in metal cutting: (b) forces acting on the tool that can be measured

Cutting Force and Thrust Force


Forces in Metal Cutting

Equations can be derived to relate the forces that cannot be measured to the forces that can be measured:

F = Fc sin + Ft cos

N = Fc cos - Ft sin

Fs = Fc cos - Ft sin

Fn = Fc sin + Ft cos

Based on these calculated force, shear stress and coefficient of friction can be determined


The Merchant Equation

Of all the possible angles at which shear deformation can occur, the work material will select a shear plane angle that minimizes energy, given by

Derived by Eugene Merchant Based on orthogonal cutting, but validity

extends to 3-D machining

2245


What the Merchant Equation Tells Us

To increase shear plane angle Increase the rake angle Reduce the friction angle (or coefficient of

friction)

2245


Higher shear plane angle means smaller shear plane which means lower shear force, cutting forces, power, and temperature

Figure 21.12 Effect of shear plane angle : (a) higher with a resulting lower shear plane area; (b) smaller with a corresponding larger shear plane area. Note that the rake angle is larger in (a), which tends to increase shear angle according to the Merchant equation

Effect of Higher Shear Plane Angle


Power and Energy Relationships

A machining operation requires power The power to perform machining can be

computed from: Pc = Fc v

where Pc = cutting power; Fc = cutting force; and v = cutting speed



In U.S. customary units, power is traditional expressed as horsepower (dividing ft-lb/min by 33,000)

where HPc = cutting horsepower, hp

00033,vF

HP cc



Gross power to operate the machine tool Pg or HPg is given by

or

where E = mechanical efficiency of machine tool Typical E for machine tools 90%

E

PP c

g E

HPHP c

g


Unit Power in Machining

Useful to convert power into power per unit volume rate of metal cut

Called unit power, Pu or unit horsepower, HPu

or

where RMR = material removal rate

MR

c

U R

PP =

MR

c

u R

HPHP =


Specific Energy in Machining

Unit power is also known as the specific energy U

Units for specific energy are typically N-m/mm3 or J/mm3 (in-lb/in3)

wvt

vF

R

PPU

o

c

MR

c

u ===


Cutting Temperature

Approximately 98% of the energy in machining is converted into heat

This can cause temperatures to be very high at the tool-chip

The remaining energy (about 2%) is retained as elastic energy in the chip


Cutting Temperatures are Important

High cutting temperatures 1. Reduce tool life2. Produce hot chips that pose safety hazards to

the machine operator3. Can cause inaccuracies in part dimensions

due to thermal expansion of work material


Cutting Temperature

Analytical method derived by Nathan Cook from dimensional analysis using experimental data for various work materials

where T = temperature rise at tool-chip interface; U = specific energy; v = cutting speed; to = chip thickness before cut; C = volumetric specific heat of work material; K = thermal diffusivity of work material

333040

..

K

vt

C

UT o


Cutting Temperature

Experimental methods can be used to measure temperatures in machining Most frequently used technique is the

tool-chip thermocouple

Using this method, Ken Trigger determined the speed-temperature relationship to be of the form:

T = K vm

where T = measured tool-chip interface temperature, and v = cutting speed

©2002 John Wiley & Sons, Inc. M. P. Groover, “Fundamentals of Modern Manufacturing 2/e”

MACHINING OPERATIONS ANDMACHINE TOOLS

•Turning and Related Operations•Drilling and Related Operations•Milling•Machining Centers and Turning Centers•Other Machining Operations•High Speed Machining


Machining

A material removal process in which a sharp cutting toolis used to mechanically cut away material so that thedesired part geometry remains

•Most common application: to shape metal parts•Machining is the most versatile and accurate of all

manufacturing processes in its capability to producea diversity of part geometries and geometric featuresCasting can also produce a variety of shapes, but

it lacks the precision and accuracy of machining


Classification of Machined Parts1. Rotational - cylindrical or disk-like shape2. Nonrotational (also called prismatic) - block-like or

plate-like

Figure 22.1 - Machined parts are classified as: (a) rotational, or (b)nonrotational, shown here by block and flat parts


Machining Operations and Part Geometry

Each machining operation produces a characteristic partgeometry due to two factors:1. Relative motions between the tool and the

workpart• Generating –part geometry is determined by

the feed trajectory of the cutting tool

2. Shape of the cutting tool• Forming –part geometry is created by the

shape of the cutting tool


Figure 22.2 - Generating shape: (a) straight turning, (b) taperturning, (c) contour turning, (d) plain milling, (e) profile milling


Figure 22.3 - Forming to create shape: (a) form turning, (b) drilling,and (c) broaching


Figure 22.4 - Combination of forming and generating to createshape: (a) thread cutting on a lathe, and (b) slot milling


Turning

A single point cutting tool removes material from arotating workpiece to generate a cylindrical shape

•Performed on a machine tool called a lathe•Variations of turning that are performed on a lathe:

FacingContour turningChamferingCutoffThreading


Figure 22.5 - Turning operation


Figure 22.6 (a) facing

FacingTool is fedradially inward


Contour TurningInstead of feeding the tool parallel to the axis of rotation,

tool follows a contour that is other than straight, thuscreating a contoured form

Figure 22.6 (c) contour turning


ChamferingCutting edge cuts an angle on the corner of the cylinder,

forming a "chamfer"

Figure 22.6 (e) chamfering


CutoffTool is fed radially into rotating work at some location to

cut off end of part

Figure 22.6 (f) cutoff


ThreadingPointed form tool is fed linearly across surface of

rotating workpart parallel to axis of rotation at a largefeed rate, thus creating threads

Figure 22.6 (g) threading


Figure 22.7Diagram ofan enginelathe,showing itsprincipalcomponents


Methods of Holding the Work in a Lathe

•Holding the work between centers•Chuck•Collet•Face plate


Holding the Work Between Centers

Figure 22.8 (a) mounting the work between centers using a "dog”


Chuck

Figure 22.8 (b) three-jaw chuck


Collet

Figure 22.8 (c) collet


Face Plate

Figure 22.8 (d) face plate for non-cylindrical workparts


Turret Lathe

Tailstock replaced by “turret”that holds up to six tools•Tools rapidly brought into action by indexing the

turret•Tool post replaced by four-sided turret to index four

tools•Applications: high production work that requires a

sequence of cuts on the part


Chucking Machine

•Uses chuck in its spindle to hold workpart•No tailstock, so parts cannot be mounted between

centers•Cutting tool actions controlled automatically•Operator’s job: to load and unload parts•Applications: short, light-weight parts


Bar Machine

•Similar to chucking machine except collet replaceschuck, permitting long bar stock to be fed throughheadstock

•At the end of the machining cycle, a cutoff operationseparates the new part

•Highly automated (the term automatic bar machine isoften used)

•Applications: high production of rotational parts


Automatic Screw Machine

•Same as automatic bar machine but smaller•Applications: high production of screws and similar

small hardware items; hence, its name


Multiple Spindle Bar Machines

•More than one spindle, so multiple parts machinedsimultaneously by multiple toolsExample: six spindle automatic bar machine works

on six parts at a time•After each machining cycle, spindles (including

collets and workbars) are indexed (rotated) to nextposition


Figure 22.9 - (a) Part produced on a six-spindle automatic barmachine; and (b) sequence of operations to produce the part: (1)

feed stock to stop, (2) turn main diameter, (3) form seconddiameter and spotface, (4) drill, (5) chamfer, and (6) cutoff


Boring

•Difference between boring and turning:Boring is performed on the inside diameter of an

existing holeTurning is performed on the outside diameter of

an existing cylinder• In effect, boring is an internal turning operation•Boring machines

Horizontal or vertical - refers to the orientation ofthe axis of rotation of machine spindle


Figure 22.12 - A vertical boring mill –for large, heavy workparts


Drilling•Creates a round hole in

a workpart•Contrasts with boring

which can only enlargean existing hole

•Cutting tool called a drillor drill bit

•Customarily performedon a drill press Figure 21.3 (b) drilling


Through Holes vs. Blind HolesThrough-holes - drill exits the opposite side of workBlind-holes –drill does not exit work on opposite side

Figure 22.13 - Two hole types: (a) through-hole, and (b) blind hole


ReamingUsed to slightly

enlarge a hole,provide bettertolerance ondiameter, andimprove surfacefinish

Figure 22.14 -Machining operationsrelated to drilling:(a) reaming


TappingUsed to provide

internal screwthreads on anexisting hole

Tool called a tap

Figure 22.14 (b) tapping


CounterboringProvides a stepped

hole, in which alarger diameterfollows a smallerdiameter partiallyinto the hole

Figure 22.14 (c) counterboring


Upright DrillStands on the floor

Bench DrillSimilar but smaller

and mounted ona table or bench

Figure 22.15 - Upright drill press


Radial DrillLarge drill press

designed forlarge parts

Figure 22.16 - Radial drill press (Willis Machinery and Tools)


Work Holding for Drill Presses

•Workpart can be clamped in a vise, fixture, or jigVise - general purpose workholder with two jawsFixture - workholding device that is usually

custom-designed for the particular workpartDrill jig –similar to fixture but also provides a

means of guiding the tool during drilling


Milling

Machining operation in which work is fed past a rotatingtool with multiple cutting edges

•Axis of tool rotation is perpendicular to feed direction•Creates a planar surface; other geometries possible

either by cutter path or shape•Other factors and terms:

Milling is an interrupted cutting operationCutting tool called a milling cutter, cutting edges

called "teeth"Machine tool called a milling machine


Figure 21.3 - Two forms of milling:(a) peripheral milling, and (b) face milling


Peripheral Milling vs. Face Milling

•Peripheral millingCutter axis is parallel to surface being machinedCutting edges on outside periphery of cutter

•Face millingCutter axis is perpendicular to surface being milledCutting edges on both the end and outside

periphery of the cutter


Slab MillingThe basic form of peripheral milling in which the cutter

width extends beyond the workpiece on both sides

Figure 22.18(a) slab milling


Slotting•Width of cutter is less than workpiece width, creating

a slot in the work

Figure 22.18(b) slotting


ConventionalFace Milling

Cutter overhangs workon both sides

Figure 22.20(a) conventional face milling


End MillingCutter diameter is less

than work width, soa slot is cut into part

Figure 22.20 - (c) end milling


Profile MillingForm of end milling

in which theoutside peripheryof a flat part iscut

Figure 22.20 (d) profile milling


Pocket MillingAnother form of

end milling usedto mill shallowpockets into flatparts

Figure 22.20 (e) pocket milling


Surface ContouringBall-nose cutter is fed

back and forth acrossthe work along acurvilinear path at closeintervals to create athree dimensionalsurface form

Figure 22.20 (f) surface contouring


Figure 22.23 (a) horizontal knee-and-column milling machine


Figure 22.23 (b) vertical knee-and-column milling machine


Figure 22.24 (b) ram type knee-and-column machine; ram canbe adjusted in and out, and toolhead can be swiveled


Machining Centers

Highly automated machine tool capable of performingmultiple machining operations under CNC control inone setup with minimal human attentionTypical operations are milling and drillingThree, four, or five axes

•Other features:Automatic tool-changingPallet shuttlesAutomatic workpart positioning


Figure 22.26 - Universal machining center (Cincinnati Milacron);highly automated, capable of multiple machining operations under

computer control in one setup with minimal human attention


Figure 22.27 - CNC 4-axis turning center (Cincinnati Milacron);capable of turning and related operations, contour turning, and

automatic tool indexing, all under computer control.


Mill-Turn Centers

Highly automated machine tool that can perform turning,milling, and drilling operations on a workpart

•General configuration of a turning center•Can position a cylindrical workpart at a specified

angle so a rotating cutting tool (e.g., milling cutter)can machine features into outside surface of partA conventional turning center cannot stop

workpart at a defined angular position and doesnot possess rotating tool spindles


Figure 22.28 - Operation of a mill-turn center: (a) example part withturned, milled, and drilled surfaces; and (b) sequence of

operations on a mill-turn center: (1) turn second diameter,(2) mill flat with part in programmed angular position, (3) drill hole

with part in same programmed position, and (4) cutoff


Shaping and Planing•Similar operations•Both use a single point cutting tool moved linearly

relative to the workpart

Figure 22.29 - (a) Shaping, and (b) planing


Shaping and Planing

•A straight, flat surface is created in both operations• Interrupted cutting

Subjects tool to impact loading when enteringwork

•Low cutting speeds due to start-and-stop motion•Usual tooling: single point high speed steel tools


Figure 22.30 - Components of a shaper


Figure 22.31 - Open side planer


Broaching•Moves a multiple tooth cutting tool linearly relative to

work in direction of tool axis

Figure 22.33 - The broaching operation


Broaching

Advantages:•Good surface finish•Close tolerances•Variety of work shapes possibleCutting tool called a broach•Owing to complicated and often custom-shaped

geometry, tooling is expensive


Internal Broaching•Performed on internal surface of a hole•A starting hole must be present in the part to insert

broach at beginning of stroke

Figure 22.34 - Work shapes that can be cut by internal broaching;cross-hatching indicates the surfaces broached


Sawing

•Cuts narrow slit in work by a tool consisting of aseries of narrowly spaced teeth

•Tool called a saw blade•Typical functions:

Separate a workpart into two piecesCut off unwanted portions of part


Figure 22.35 (a) power hacksaw –linear reciprocating motionof hacksaw blade against work


Figure 22.35 (b) bandsaw(vertical) –linearcontinuous motion ofbandsaw blade, which is inthe form of an endlessflexible loop with teeth onone edge


Figure 22.35 (c) circular saw –rotating saw blade providescontinuous motion of tool past workpart


High Speed Machining (HSM)

Cutting at speeds significantly higher than those used inconventional machining operations

•A persistent trend throughout history of machining ishigher and higher cutting speeds

•At present there is a renewed interest in HSM due topotential for faster production rates, shorter leadtimes, and reduced costs


High Speed Machining

Comparison of conventional vs. high speed machining

ft/minm/minft/minm/min

Source: Kennametal Inc.

1200360700210Steel, alloy

3000900800250Cast iron, ductile

400012001200360Cast iron, soft

12,000+3600+2000+600+Aluminum

High speedConventional speedWork material

Indexable tools (face mills)


Other HSM Definitions –DN Ratio

DN ratio = bearing bore diameter (mm) multiplied bymaximum spindle speed (rev/min)

•For high speed machining, typical DN ratio isbetween 500,000 and 1,000,000

•Allows larger diameter bearings to fall within HSMrange, even though they operate at lower rotationalspeeds than smaller bearings


Other HSM Definitions –HP/RPM Ratio

hp/rpm ratio = ratio of horsepower to maximum spindlespeed

•Conventional machine tools usually have a higherhp/rpm ratio than those equipped for HSM

•Dividing line between conventional machining andHSM is around 0.005 hp/rpm

•Thus, HSM includes 15 hp spindles that can rotate at30,000 rpm (0.0005 hp/rpm)


Other HSM Definitions

•Emphasize:Higher production ratesShorter lead timesRather than functions of spindle speed

• Important non-cutting factors:Rapid traverse speedsAutomatic tool changes


Requirements for High Speed Machining

•Special bearings designed for high rpm•High feed rate capability (e.g., 50 m/min)•CNC motion controls with “look-ahead”features to

avoid “undershooting”or “overshooting”tool path•Balanced cutting tools, toolholders, and spindles to

minimize vibration•Coolant delivery systems that provide higher

pressures than conventional machining•Chip control and removal systems to cope with much

larger metal removal rates


High Speed Machining Applications

•Aircraft industry, machining of large airframecomponents from large aluminum blocksMuch metal removal, mostly by milling

•Multiple machining operations on aluminum toproduce automotive, computer, and medicalcomponentsQuick tool changes and tool path control important

•Die and mold industryFabricating complex geometries from hard

materials


CUTTING TOOL TECHNOLOGY

•Tool Life•Tool Materials•Tool Geometry•Cutting Fluids


Cutting Tool Technology

Two principal aspects:1. Tool material2. Tool geometry


Three Modes of Tool Failure

•Fracture failureCutting force becomes excessive and/or dynamic,

leading to brittle fracture•Temperature failure

Cutting temperature is too high for the toolmaterial

•Gradual wearGradual wearing of the cutting tool


Preferred Mode of Tool Failure:Gradual Wear

•Fracture and temperature failures are prematurefailures

•Gradual wear is preferred because it leads to thelongest possible use of the tool

•Gradual wear occurs at two locations on a tool:Crater wear –occurs on top rake faceFlank wear –occurs on flank (side of tool)


Figure 23.1 - Diagram of worn cutting tool, showing the principallocations and types of wear that occur


Figure 23.2 -

(a) Crater wear, and

(b) flank wear on a cementedcarbide tool, as seenthrough a toolmaker'smicroscope

(Courtesy ManufacturingTechnology Laboratory,Lehigh University, photoby J. C. Keefe)


Figure 23.3 - Tool wear as a function of cutting timeFlank wear (FW) is used here as the measure of tool wear

Crater wear follows a similar growth curve


Figure 23.4 - Effect of cutting speed on tool flank wear (FW) for threecutting speeds, using a tool life criterion of 0.50 mm flank wear


Figure 23.5 - Natural log-log plot of cutting speed vs tool life


Taylor Tool Life Equation

This relationship is credited to F. W. Taylor (~1900)

CvT n where v = cutting speed; T = tool life; and n and Care parameters that depend on feed, depth of cut,work material, tooling material, and the tool lifecriterion used

•n is the slope of the plot•C is the intercept on the speed axis


Tool Life Criteria in Production

1. Complete failure of cutting edge2. Visual inspection of flank wear (or crater wear) by the

machine operator3. Fingernail test across cutting edge4. Changes in sound emitted from operation5. Chips become ribbony, stringy, and difficult to dispose of6. Degradation of surface finish7. Increased power8. Workpiece count9. Cumulative cutting time


Tool Materials

•Tool failure modes identify the important propertiesthat a tool material should possess:Toughness - to avoid fracture failureHot hardness - ability to retain hardness at high

temperaturesWear resistance - hardness is the most important

property to resist abrasive wear


Figure 23.6 - Typical hot hardness relationships for selected toolmaterials. Plain carbon steel shows a rapid loss of hardness astemperature increases. High speed steel is substantially better,while cemented carbides and ceramics are significantly harderat elevated temperatures.


Typical Values of n and C inTaylor Tool Life Equation

Tool material n C (m/min) C (ft/min)

High speed steel:Non-steel work 0.125 120 350Steel work 0.125 70 200

Cemented carbideNon-steel work 0.25 900 2700Steel work 0.25 500 1500

CeramicSteel work 0.6 3000 10,000


High Speed Steel (HSS)

Highly alloyed tool steel capable of maintaininghardness at elevated temperatures better than highcarbon and low alloy steels

• One of the most important cutting tool materials• Especially suited to applications involving

complicated tool geometries, such as drills, taps,milling cutters, and broaches

• Two basic types (AISI)1. Tungsten-type, designated T- grades2. Molybdenum-type, designated M-grades


High Speed Steel Composition

•Typical alloying ingredients:Tungsten and/or MolybdenumChromium and VanadiumCarbon, of courseCobalt in some grades

•Typical composition:Grade T1: 18% W, 4% Cr, 1% V, and 0.9% C


Cemented Carbides

Class of hard tool material based on tungsten carbide(WC) using powder metallurgy techniques withcobalt (Co) as the binder

• Two basic types:1. Non-steel cutting grades - only WC-Co2. Steel cutting grades - TiC and TaC added to

WC-Co


Cemented Carbides –General Properties

•High compressive strength but low-to-moderatetensile strength

•High hardness (90 to 95 HRA)•Good hot hardness•Good wear resistance•High thermal conductivity•High elastic modulus - 600 x 103 MPa (90 x 106 lb/in2)•Toughness lower than high speed steel


Non-steel Cutting Carbide Grades

•Used for nonferrous metals and gray cast iron•Properties determined by grain size and cobalt

contentAs grain size increases, hardness and hot

hardness decrease, but toughness increasesAs cobalt content increases, toughness improves

at the expense of hardness and wear resistance


Steel Cutting Carbide Grades

•Used for low carbon, stainless, and other alloy steelsFor these grades, TiC and/or TaC are substituted

for some of the WCThis composition increases crater wear resistance

for steel cutting, but adversely affects flank wearresistance for non-steel cutting applications


Cermets

Combinations of TiC, TiN, and titanium carbonitride(TiCN), with nickel and/or molybdenum as binders.

•Some chemistries are more complex•Applications: high speed finishing and semifinishing

of steels, stainless steels, and cast ironsHigher speeds and lower feeds than steel-cutting

carbide gradesBetter finish achieved, often eliminating need for

grinding


Coated Carbides

Cemented carbide insert coated with one or more thinlayers of wear resistant materials, such as TiC, TiN,and/orAl2O3

•Coating applied by chemical vapor deposition orphysical vapor deposition

•Coating thickness = 2.5 - 13 m (0.0001 to 0.0005 in)•Applications: cast irons and steels in turning and

milling operations•Best applied at high speeds where dynamic force and

thermal shock are minimal


Ceramics

Primarily fine-grained Al2O3, pressed and sintered athigh pressures and temperatures into insert form withno binder

•Applications: high speed turning of cast iron and steel•Not recommended for heavy interrupted cuts (e.g.

rough milling) due to low toughness•Al2O3 also widely used as an abrasive in grinding


Synthetic Diamonds

Sintered polycrystalline diamond (SPD) - fabricated bysintering very fine-grained diamond crystals underhigh temperatures and pressures into desired shapewith little or no binder

•Usually applied as coating (0.5 mm thick) on WC-Coinsert

•Applications: high speed machining of nonferrousmetals and abrasive nonmetals such as fiberglass,graphite, and woodNot for steel cutting


Cubic Boron Nitride

•Next to diamond, cubic boron nitride (cBN) is hardestmaterial known

•Fabrication into cutting tool inserts same as SPD:coatings on WC-Co inserts

•Applications: machining steel and nickel-based alloys•SPD and cBN tools are expensive


Tool Geometry

Two categories:•Single point tools

Used for turning, boring, shaping, and planing•Multiple cutting edge tools

Used for drilling, reaming, tapping, milling,broaching, and sawing


Figure 23.7 - (a)Seven elements ofsingle-point toolgeometry; and (b) thetool signatureconvention thatdefines the sevenelements

Single-PointToolGeometry


Figure 23.9 - Three ways of holding and presenting the cutting edge for asingle-point tool:

(a) solid tool, typical of HSS;(b) brazed insert, one way of holding a cemented carbide insert; and(c) mechanically clamped insert, used for cemented carbides, ceramics,

and other very hard tool materials


Figure 23.10 - Common insert shapes: (a) round, (b) square, (c)rhombus with two 80point angles, (d) hexagon with three 80point angles, (e) triangle (equilateral), (f) rhombus with two 55point angles, (g) rhombus with two 35point angles. Also shownare typical features of the geometry.


Twist Drills•By far the most common cutting tools for hole-making•Usually made of high speed steel

Figure 23.12 - Standard geometry of a twist drill


Twist Drill Operation

•Rotation and feeding of drill bit result in relativemotion between cutting edges and workpiece to formthe chipsCutting speed varies along cutting edges as a

function of distance from axis of rotationRelative velocity at drill point is zero, so no cutting

takes placeA large thrust force is required to drive the drill

forward into hole


Twist Drill Operation - Problems

•Chip removalFlutes must provide sufficient clearance to allow

chips to be extracted from bottom of hole•Friction makes matters worse

Rubbing between outside diameter of drill bit andnewly formed hole

Delivery of cutting fluid to drill point to reducefriction and heat is difficult because chips areflowing in the opposite direction


Milling Cutters

•Principal types:Plain milling cutterForm milling cutterFace milling cutterEnd milling cutter


Plain Milling Cutter•Used for peripheral or slab milling

Figure 23.13 -Tool geometry elementsof an 18-tooth plainmilling cutter


Form Milling Cutter

Peripheral milling cutter in which cutting edges havespecial profile to be imparted to work

• Important applicationGear-making, in which the form milling cutter is

shaped to cut the slots between adjacent gearteeth, thereby leaving the geometry of the gearteeth


Face Milling Cutter•Teeth cut on side and periphery of the cutter

Figure 23.14 - Tool geometry elements of a four-tooth facemilling cutter: (a) side view and (b) bottom view


End Milling Cutter

•Looks like a drill bit but designed for primary cuttingwith its peripheral teeth

•Applications:Face millingProfile milling and pocketingCutting slotsEngravingSurface contouringDie sinking


Cutting Fluids

Any liquid or gas applied directly to machining operationto improve cutting performance

• Two main problems addressed by cutting fluids:1. Heat generation at shear zone and friction zone2. Friction at the tool-chip and tool-work interfaces

• Other functions and benefits: Wash away chips (e.g., grinding and milling) Reduce temperature of workpart for easier

handling Improve dimensional stability of workpart


Cutting Fluid Functions

•Cutting fluids can be classified according to function:Coolants - designed to reduce effects of heat in

machiningLubricants - designed to reduce tool-chip and

tool-work friction


Coolants

•Water used as base in coolant-type cutting fluids•Most effective at high cutting speeds where heat

generation and high temperatures are problems•Most effective on tool materials that are most

susceptible to temperature failures (e.g., HSS)


Lubricants

•Usually oil-based fluids•Most effective at lower cutting speeds•Also reduces temperature in the operation


Cutting Fluid Contamination

•Tramp oil (machine oil, hydraulic fluid, etc.)•Garbage (cigarette butts, food, etc.)•Small chips•Molds, fungi, and bacteria


Dealing with Cutting Fluid Contamination

•Replace cutting fluid at regular and frequent intervals•Use filtration system to continuously or periodically

clean the fluid•Dry machining


Cutting Fluid Filtration

Advantages:•Prolong cutting fluid life between changes•Reduce fluid disposal cost•Cleaner fluids reduce health hazards•Lower machine tool maintenance•Longer tool life


Dry Machining

•No cutting fluid is used•Avoids problems of cutting fluid contamination,

disposal, and filtration•Problems with dry machining:

Overheating of the toolOperating at lower cutting speeds and production

rates to prolong tool lifeAbsence of chip removal benefits of cutting fluids

in grinding and milling


GRINDING ANDOTHER ABRASIVE PROCESSES

•Grinding•Related Abrasive Process


Abrasive Machining

Material removal by action of hard, abrasive particlesusually in the form of a bonded wheel

•Generally used as finishing operations after partgeometry has been established y conventionalmachining

•Grinding is most important abrasive processes•Other abrasive processes: honing, lapping,

superfinishing, polishing, and buffing


Why Abrasive Processes are Important

•Can be used on all types of materials•Some can produce extremely fine surface finishes, to

0.025 m (1 -in)•Some can hold dimensions to extremely close

tolerances


Grinding

Material removal process in which abrasive particles arecontained in a bonded grinding wheel that operatesat very high surface speeds

•Grinding wheel usually disk-shaped and preciselybalanced for high rotational speeds


The Grinding Wheel

•Consists of abrasive particles and bonding materialAbrasive particles accomplish cuttingBonding material holds particles in place and

establishes shape and structure of wheel


Grinding Wheel Parameters

•Abrasive material•Grain size•Bonding material•Wheel grade•Wheel structure


Abrasive Material Properties

•High hardness•Wear resistance•Toughness•Friability - capacity to fracture when cutting edge

dulls, so a new sharp edge is exposed


Traditional Abrasive Materials

•Aluminum oxide (Al2O3) - most common abrasiveUsed to grind steel and other ferrous high-strength

alloys•Silicon carbide (SiC) - harder than Al2O3 but not as

toughUsed on aluminum, brass, stainless steel, some

cast irons and certain ceramics


Newer Abrasive Materials

•Cubic boron nitride (cBN) –very hard, very expensiveSuitable for steelsUsed for hard materials such as hardened tool

steels and aerospace alloys (e.g., Ni-based alloys)•Diamond –Even harder, very expensive

Occur naturally and also made syntheticallyNot suitable for grinding steelsUsed on hard, abrasive materials such as

ceramics, cemented carbides, and glass


Hardness of Abrasive Materials

Abrasive material Knoop hardnessAluminum oxide 2100Silicon carbide 2500Cubic boron nitride 5000Diamond (synthetic) 7000


Grain Size

•Small grit sizes produce better finishes•Larger grit sizes permit larger material removal rates•Harder work materials require smaller grain sizes to

cut effectively•Softer materials require larger grit sizes


Measurement of Grain Size

•Grit size is measured using a screen mesh procedureSmaller grit sizes indicated by larger numbers in

the screen mesh procedure and vice versaGrain sizes in grinding wheels typically range

between 8 (very coarse) and 250 (very fine)


Bonding Material Properties

•Must withstand centrifugal forces and hightemperatures

•Must resist shattering during shock loading of wheel•Must hold abrasive grains rigidly in place for cutting

yet allow worn grains to be dislodged so new sharpgrains are exposed


Wheel Structure

Refers to the relative spacing of abrasive grains inwheel

• In addition to abrasive grains and bond material,grinding wheels contain air gaps or pores

•Volumetric proportions of grains, bond material, andpores can be expressed as:

01 . pbg PPP


Figure 25.1 - Typical structure of a grinding wheel


Wheel Structure

•Measured on a scale that ranges between "open"and "dense."Open structure means Pp is relatively large and Pg

is relatively small - recommended when clearancefor chips must be provided

Dense structure means Pp is relatively small andPg is larger - recommended to obtain bettersurface finish and dimensional control


Wheel Grade

Indicates bond strength in retaining abrasive grits duringcutting

•Depends on amount of bonding material in wheelstructure (Pb)

•Measured on a scale ranging between soft and hardSoft" wheels lose grains readily - used for low

material removal rates and hard work materialsHard wheels retain grains - used for high stock

removal rates and soft work materials


Grinding Wheel Specification

•Standard grinding wheel marking system used todesignate abrasive type, grit size, grade, structure,and bond materialExample: A-46-H-6-V

•Also provides for additional identifications for use bygrinding wheel manufacturers


Figure 25.2 - Some of the standard grinding wheel shapes:(a) straight, (b) recessed two sides, (c) metal wheel frame with abrasive

bonded to outside circumference, (d) abrasive cutoff wheel


Surface Finish

•Most grinding is performed to achieve good surfacefinish

•Best surface finish is achieved by:Small grain sizesHigher wheel speedsDenser wheel structure = more grits per wheel

area


Why Specific Energy in Grinding is High

•Size effect - small chip size causes energy to removeeach unit volume of material to be significantlyhigher - roughly 10 times higher

• Individual grains have extremely negative rakeangles, resulting in low shear plane angles and highshear strains

•Not all grits are engaged in actual cutting


Three Types of Grain Action

•Cutting - grit projects far enough into surface to forma chip - material is removed

•Plowing - grit projects into work, but not far enough tocut - instead, surface is deformed and energy isconsumed, but no material is removed

•Rubbing - grit contacts surface but only rubbingfriction occurs, thus consuming energy, but nomaterial is removed


Figure 25.4 - Three types of grain action in grinding:(a) cutting, (b) plowing, and (c) rubbing


Temperatures at the Work Surface

•Grinding is characterized by high temperatures andhigh friction, and most of the energy remains in theground surface, resulting in high work surfacetemperatures

•Damaging effects include:Surface burns and cracksMetallurgical damage immediately beneath the

surfaceSoftening of the work surface if heat treatedResidual stresses in the work surface


How to Reduce Work Surface Temperatures

•Decrease infeed (depth of cut) d•Reduce wheel speed v•Reduce number of active grits per square inch on the

grinding wheel C• Increasing work speed vw

•Use a cutting fluid


Causes of Wheel Wear - 1

Grain fracture - when a portion of the grain breaks off,but the rest remains bonded in the wheel

• Edges of the fractured area become new cuttingedges

• Tendency to fracture is called friability



Attritious wear - dulling of individual grains, resulting inflat spots and rounded edges

• Analogous to tool wear in conventional cutting tool• Caused by similar mechanisms including friction,

diffusion, and chemical reactions



Bond fracture - the individual grains are pulled out of thebonding material

•Depends on wheel grade, among other factors•Usually occurs because grain has become dull due to

attritious wear, and resulting cutting force becomesexcessive


Figure 25.5 - Typical wear curve of a grinding wheel. Wearis conveniently plotted as a function of volume of

material removed, rather than as a function of time(based on [13])


Grinding Ratio

Indicates slope of the wheel wear curve

where GR = grinding ratio; Vw = volume of work materialremoved; and Vg = corresponding volume of grindingwheel worn

gV

VGR

W


Dressing the WheelDressing - accomplished by rotating disk, abrasive stick,

or another grinding wheel held against the wheelbeing dressed as it rotates

•Functions:Breaks off dulled grits to expose new sharp grainsRemoves chips clogged in the wheel

•Accomplished by a rotating disk, an abrasive stick, oranother grinding wheel operating at high speed, heldagainst the wheel being dressed as it rotates

•Required when wheel is in third region of wear curve


Truing the Wheel

Truing - use of a diamond-pointed tool fed slowly andprecisely across wheel as it rotates

•Very light depth is taken (0.025 mm or less) againstthe wheel

•Not only sharpens wheel, but restores cylindricalshape and insures straightness across outsideperimeterAlthough dressing sharpens, it does not guarantee

the shape of the wheel


Application Guidelines - I

•To optimize surface finish, selectSmall grit size and dense wheel structureUse higher wheel speeds (v) and lower work

speeds (vw)Smaller depths of cut (d) and larger wheel

diameters (D) will also help•To maximize material removal rate, select

Large grit sizeMore open wheel structureVitrified bond


Application Guidelines - II

•For grinding steel and most cast irons, selectAluminum oxide as the abrasive

•For grinding most nonferrous metals, selectSilicon carbide as the abrasive

•For grinding hardened tool steels and certainaerospace alloys, chooseCubic boron nitride as the abrasive

•For grinding hard abrasive materials such asceramics, cemented carbides, and glass, chooseDiamond as the abrasive


Application Guidelines - III

•For soft metals, chooseLarge grit size and harder grade wheel

•For hard metals, chooseSmall grit size and softer grade wheel


Figure 25.7 - Four types of surface grinding: (a) horizontal spindle withreciprocating worktable, (b) horizontal spindle with rotating worktable,

(c) vertical spindle with reciprocating worktable,and (d) vertical spindle with rotating worktable


Figure 25.8 - Surface grinder with horizontal spindle andreciprocating worktable (most common grinder type)


Figure 25.9 - Two types of cylindrical grinding:(a) external, and (b) internal


Figure 25.11 - External centerless grinding

Centerless Grinding


Figure 25.13 - Comparison of (a) conventional surfacegrinding and (b) creep feed grinding

Creep Feed Grinding


Creep Feed Grinding

•Depths of cut 1000 to 10,000 times greater than inconventional surface grinding

•Feed rates reduced by about the same proportion•Material removal rate and productivity are increased

in creep feed grinding because the wheel iscontinuously cutting

• In conventional surface grinding, wheel is engaged incutting for only a portion of the stroke length


Honing

Abrasive process performed by a set of bondedabrasive sticks using a combination of rotational andoscillatory motions

•Common application is to finish the bores of internalcombustion engines

•Grit sizes range between 30 and 600•Surface finishes of 0.12 m (5 -in) or better•Creates a characteristic cross-hatched surface that

retains lubrication


Figure 25.16 - The honing process: (a) the honing tool used forinternal bore surface, and (b) cross-hatched surface pattern

created by the action of the honing tool


Lapping

Uses a fluid suspension of very small abrasive particlesbetween workpiece and lap (tool)

•Lapping compound - fluid with abrasives, generalappearance of a chalky paste

•Typical grit sizes between 300 to 600•Applications: optical lenses, metallic bearing surfaces,

gages


Figure 25.17 - The lapping process in lens-making


Superfinishing

Similar to honing - uses bonded abrasive stick pressedagainst surface and reciprocating motion

•Differences with honing:Shorter strokesHigher frequenciesLower pressures between tool and surfaceSmaller grit sizes


Figure 25.18 - Superfinishing on anexternal cylindrical surface


RAPID PROTOTYPING

1. Fundamentals of Rapid Prototyping

2. Rapid Prototyping Technologies

3. Applications and Benefits of Rapid Prototyping

news.thomasnet.com/fullstory/451186


Rapid Prototyping (RP)

A family of fabrication processes developed to make engineering prototypes in minimum lead time based on a CAD model of the item

Traditional method is machining Can require significant lead-times – several

weeks, depending on part complexity and difficulty in ordering materials

RP allows a part to be made in hours or days, given that a computer model of the part has been generated on a CAD system


Why is Rapid Prototyping Important?

Product designers want to have a physical model of a new part or product design rather than just a computer model or line drawing Creating a prototype is an integral step in design A virtual prototype (a CAD model of the part) may

not be sufficient for the designer to visualize the part adequately

Using RP to make the prototype, the designer can see and feel the part and assess its merits and shortcomings


RP – Two Basic Categories:

1. Material removal RP - machining, using a dedicated CNC machine that is available to the design department on short notice Starting material is often wax

Easy to machine Can be melted and resolidified

The CNC machines are often small - called desktop machining

2. Material addition RP - adds layers of material one at a time to build the solid part from bottom to top


Starting Materials in Material Addition RP

1. Liquid monomers that are cured layer by layer into solid

polymers

2. Powders that are aggregated and bonded layer by layer

3. Solid sheets that are laminated to create the solid part

Additional Methods

In addition to starting material, the various material addition RP technologies use different methods of building and adding layers to create the solid part There is a correlation between starting material

and part building techniques


Steps to Prepare Control Instructions

1. Geometric modeling - model the component on a CAD system to define its enclosed volume

2. Tessellation of the geometric model - the CAD model is converted into a computerized format that approximates its surfaces by facets (triangles or polygons)

3. Slicing of the model into layers - computerized model is sliced into closely-spaced parallel horizontal layers


Figure 34.1 Conversion of a solid model of an object into layers (only one layer is shown).

Solid Model to Layers


More About Rapid Prototyping

Alternative names for RP:

Layer manufacturing

Direct CAD manufacturing

Solid freeform fabrication

Rapid prototyping and manufacturing (RPM)

RP technologies are being used increasingly to make production parts and production tooling, not just prototypes


Classification of RP Technologies

There are various ways to classify the RP techniques that have currently been developed

The RP classification used here is based on the form of the starting material:

1. Liquid-based

2. Solid-based

3. Powder-based


Liquid-Based Rapid Prototyping Systems

Starting material is a liquid

About a dozen RP technologies are in this category

Includes the following processes:

Stereolithography

Solid ground curing

Droplet deposition manufacturing


Stereolithography (STL)

RP process for fabricating a solid plastic part out of a photosensitive liquid polymer using a directed laser beam to solidify the polymer

Part fabrication is accomplished as a series of layers - each layer is added onto the previous layer to gradually build the 3-D geometry

The first addition RP technology - introduced 1988 by 3D Systems Inc. based on the work of Charles Hull

More installations than any other RP method


Figure 34.2 Stereolithography: (1) at the start of the process, in which the initial layer is added to the platform; and (2) after several layers have been added so that the part geometry gradually takes form.

Stereolithography


Figure 34.3 A part produced by stereolithography (photo courtesy of 3D Systems, Inc.).


Facts about STL

Each layer is 0.076 mm to 0.50 mm (0.003 in to 0.020 in.) thick

Thinner layers provide better resolution and more intricate shapes; but processing time is longer

Starting materials are liquid monomers

Polymerization occurs on exposure to UV light produced by laser scanning beam

Scanning speeds ~ 500 to 2500 mm/s


Part Build Time in STL

Time to complete a single layer :

where Ti = time to complete layer i; Ai = area of layer i; v = average scanning speed of the laser beam at the surface; D = diameter of the “spot

size,” assumed circular; and Td = delay time between layers to reposition the worktable

di

i TvD

AT


Part Build Time in STL - continued

Once the Ti values have been determined for all layers, then the build cycle time is:

where Tc = STL build cycle time; and nl = number of layers used to approximate the part

Time to build a part ranges from one hour for small parts of simple geometry up to several dozen hours for complex parts

in

iic TT

1


Solid Ground Curing (SGC)

Like stereolithography, SGC works by curing a photosensitive polymer layer by layer to create a solid model based on CAD geometric data

Instead of using a scanning laser beam to cure a given layer, the entire layer is exposed to a UV source through a mask above the liquid polymer

Hardening takes 2 to 3 s for each layer


Figure 34.4 SGC steps for each layer: (1) mask preparation, (2) applying liquid photopolymer layer,(3) mask positioning and exposure of layer, (4) uncured polymer removed from surface, (5) wax filling, (6) milling for flatness and thickness.

Solid Ground Curing


Facts about SGC

Sequence for each layer takes about 90 seconds Time to produce a part by SGC is claimed to be

about eight times faster than other RP systems The solid cubic form created in SGC consists of solid

polymer and wax The wax provides support for fragile and

overhanging features of the part during fabrication, but can be melted away later to leave the free-standing part


Droplet Deposition Manufacturing (DDM)

Starting material is melted and small droplets are shot by a nozzle onto previously formed layer

Droplets cold weld to surface to form a new layer Deposition for each layer controlled by a moving x-y

nozzle whose path is based on a cross section of a CAD geometric model that is sliced into layers

Work materials include wax and thermoplastics


Solid-Based Rapid Prototyping Systems

Starting material is a solid

Solid-based RP systems include the following processes:

Laminated object manufacturing

Fused deposition modeling


Laminated Object Manufacturing (LOM)

Solid physical model made by stacking layers of sheet stock, each an outline of the cross-sectional shape of a CAD model that is sliced into layers

Starting sheet stock includes paper, plastic, cellulose, metals, or fiber-reinforced materials

The sheet is usually supplied with adhesive backing as rolls that are spooled between two reels

After cutting, excess material in the layer remains in place to support the part during building


Figure 34.5 Laminated object manufacturing.

Laminated Object Manufacturing


Fused Deposition Modeling (FDM)

RP process in which a long filament of wax or polymer is extruded onto existing part surface from a workhead to complete each new layer

Workhead is controlled in the x-y plane during each layer and then moves up by a distance equal to one layer in the z-direction

Extrudate is solidified and cold welded to the cooler part surface in about 0.1 s

Part is fabricated from the base up, using a layer-by-layer procedure


Powder-Based RP Systems

Starting material is a powder

Powder-based RP systems include the following: Selective laser sintering Three dimensional printing


Selective Laser Sintering (SLS)

Moving laser beam sinters heat-fusible powders in areas corresponding to the CAD geometry model one layer at a time to build the solid part

After each layer is completed, a new layer of loose powders is spread across the surface

Layer by layer, the powders are gradually bonded by the laser beam into a solid mass that forms the 3-D part geometry

In areas not sintered, the powders are loose and can be poured out of completed part


Three Dimensional Printing (3DP)

Part is built layer-by-layer using an ink-jet printer to eject adhesive bonding material onto successive layers of powders

Binder is deposited in areas corresponding to the cross sections of part, as determined by slicing the CAD geometric model into layers

The binder holds the powders together to form the solid part, while the unbonded powders remain loose to be removed later

To further strengthen the part, a sintering step can be applied to bond the individual powders


Figure 34.6 Three dimensional printing: (1) powder layer is deposited, (2) ink-jet printing of areas that will become the part, and (3) piston is lowered for next layer (key: v = motion).

Three Dimensional Printing


RP Applications

Applications of rapid prototyping can be classified into three categories: 1. Design 2. Engineering analysis and planning 3. Tooling and manufacturing


Design Applications

Designers are able to confirm their design by building a real physical model in minimum time using RP

Design benefits of RP:

Reduced lead times to produce prototypes

Improved ability to visualize part geometry

Early detection of design errors

Increased capability to compute mass properties


Engineering Analysis and Planning

Existence of part allows certain engineering analysis and planning activities to be accomplished that would be more difficult without the physical entity

Comparison of different shapes and styles to determine aesthetic appeal

Wind tunnel testing of streamline shapes

Stress analysis of physical model

Fabrication of pre-production parts for process planning and tool design


Tooling Applications

Called rapid tool making (RTM) when RP is used to fabricate production tooling

Two approaches for tool-making: 1. Indirect RTM method 2. Direct RTM method


Indirect RTM Method

Pattern is created by RP and the pattern is used to fabricate the tool

Examples: Patterns for sand casting and investment

casting Electrodes for EDM


Direct RTM Method

RP is used to make the tool itself Example:

3DP to create a die of metal powders followed by sintering and infiltration to complete the die


Manufacturing Applications

Small batches of plastic parts that could not be economically molded by injection molding because of the high mold cost

Parts with intricate internal geometries that could not be made using conventional technologies without assembly

One-of-a-kind parts such as bone replacements that must be made to correct size for each user


Problems with Rapid Prototyping

Part accuracy: Staircase appearance for a sloping part surface

due to layering Shrinkage and distortion of RP parts

Limited variety of materials in RP Mechanical performance of the fabricated parts is

limited by the materials that must be used in the RP process


MICROFABRICATION TECHNOLOGIES

1. Microsystem Products2. Microfabrication Processes


Relative Sizes in Microtechnology


Design Trend and Terminology

Miniaturization of products and parts, with features sizes measured in microns (10-6 m)

Some of the terms: Microelectromechanical systems (MEMS) -

miniature systems consisting of both electronic and mechanical components

Microsystem technology (MST) - refers to the products as well as the fabrication technologies

Nanotechnology - even smaller entities whose dimensions are measured in nanometers (10-9 m)


Advantages of Microsystem Products

Less material usage Lower power requirements Greater functionality per unit space Accessibility to regions that are forbidden to

larger products In most cases, smaller products should mean

lower prices because less material is used


Types of Microsystem Devices

Microsensors Microactuators Microstructures and microcomponents Microsystems and micro-instruments


Microsensors

A sensor is a device that detects or measures some physical phenomenon such as heat or pressure

Most microsensors are fabricated on a silicon substrate using same processing technologies as those used for integrated circuits

Microsensors have been developed to measure force, pressure, position, speed, acceleration, temperature, flow, and various optical, chemical, environmental, and biological variables


Microactuators

An actuator converts a physical variable of one type into another type, and the converted variable usually involves some mechanical action

An actuator causes a change in position or the application of force

Examples of microactuators: valves, positioners, switches, pumps, and rotational and linear motors


Microstructures and Microcomponents

Micro-sized parts that are not sensors or actuators

Examples: microscopic lenses, mirrors, nozzles, gears, and beams

These items must be combined with other components in order to provide a useful function


Microscopic Gear and Human Hair

Figure 37.3 A microscopic gear and a human hair. Image created by scanning electron microscope. The gear is high-density polyethylene molded by a process similar to LIGA except that the mold cavity was fabricated using a focused ion beam (photo courtesy of W. Hung, Texas A&M U., and M. Ali, Nanyang Tech. U).


Microsystems and micro-instruments

Integration of several of the preceding components with the appropriate electronics package into a miniature system or instrument

They tend to be very application-specific Examples: microlasers, optical chemical

analyzers, and microspectrometers The economics of manufacturing these kinds

of systems have tended to make commercialization difficult


Industrial Applications of Microsystems

Ink-jet printing heads Thin-film magnetic heads Compact disks Automotive components Medical applications Chemical and environmental applications Other applications


Ink-Jet Printing Heads

Currently one of the largest applications of MST

A typical ink-jet printer uses up several cartridges each year

Today’s ink-jet printers have resolutions of 1200 dots per inch (dpi) This resolution converts to a nozzle

separation of only about 21 m, certainly in the microsystem range


Figure 37.3 Diagram of an ink-jet printing head.

Ink-Jet Printer Head


Thin-Film Magnetic Heads

Read-write heads are key components in magnetic storage devices

Reading and writing of magnetic media with higher bit densities limited by the size of the read-write head

Development of thin-film magnetic heads was an important breakthrough not only in digital storage technology but microfabrication technologies as well

Thin-film read-write heads are produced annually in hundreds of millions of units, with a market of several billion dollars per year


Figure 37.4 Thin-film magnetic read-write head (simplified).

Thin-Film Magnetic Read-Write Head


Compact Disks (CDs) and DVDs

Important commercial products, as storage media for audio, video, and computer software

Molded of polycarbonate (ideal optical and mechanical properties for the application)

Diameter D = 120 mm and thickness = 1.2 mm Data consists of small pits (depressions) in a

helical track that begins at D = 46 mm and ends at D = 117 mm Tracks separated by 1.6 m Each pit is 0.5 m wide and about 0.8 m to

3.5 m long


Molds for CDs

A master for the mold is made from a smooth thin layer of photoresist on a glass plate (300 mm diameter)

Photoresist is exposed to a laser beam that writes data into surface while the glass plate is rotated and moved slowly to create spiral track

Exposed regions are removed; they will correspond to pits in the CD track

A thin layer of nickel is deposited onto surface by sputtering

Electroforming used to build up Ni thickness


Molds for CDs (continued)

This negative impression of the master is called the father

Several impressions of the father are made (called mothers), whose surfaces are identical to the original master

Finally, the mothers are used to create the actual mold impressions (called stampers)

The stampers will be used to mass-produce the CDs


Molding and Further Processing of CD

Once molded, the pitted side of the polycarbonate disk is coated with aluminum by sputtering to create a mirror surface

To protect this layer, a thin coating of polymer is deposited on the metal

Thus, the final CD is a sandwich Thick polycarbonate substrate on one side Thin polymer layer on the other side Very thin layer of Aluminum in between


Reading the Compact Disk

In operation, the laser beam of a CD player reads through the polycarbonate substrate onto the reflective surface The reflected beam is interpreted as a

sequence o binary digits


Automotive Components

Micro-sensors and other micro-devices are widely used in modern automobiles

Between 20 and 100 sensors installed in a modern automobile Functions include cruise control, anti-lock

braking systems, air bag deployment, automatic transmission control, power steering, all-wheel drive, automatic stability control, and remote locking and unlocking

In 1970 there were virtually no on-board sensors


Medical Applications

A driving force for microscopic devices is the principle of minimal-invasive therapy Small incisions or even available body

orifices to access the medical problem Standard medical practice today is to use

endoscopic examination accompanied by laparoscopic surgery for hernia repair and removal of gall bladder and appendix

Growing use of similar procedures is expected in brain surgery, operating through one or more small holes drilled through the skull


Microfabrication Processes

Many MST products are based on silicon Reasons why silicon is a desirable material:

Microdevices often include electronic circuits, so both the circuit and the device can be made on the same substrate

Silicon has good mechanical properties: High strength and elasticity, good

hardness, and relatively low density Techniques to process silicon are well-

established


Other Materials and MST Processing

MST often requires other materials in addition to silicon to obtain a particular microdevice Example: microactuators often consist of

several components made of different materials

Thus, microfabrication techniques consist of more than just silicon processing: LIGA process Other conventional and nontraditional

processes performed on microscopic scale


Silicon Layer Processes

First application of silicon in MST was in the fabrication of piezoresistive sensors to measure stress, strain, and pressure in the early 1960s

Silicon is now widely used in MST to produce sensors, actuators, and other microdevices

The basic processing technologies are those used to produce integrated circuits

However, there are certain differences between the processing of ICs and the fabrication of microdevices


Microfabrication vs. IC Fabrication

Aspect ratios (height-to-width ratio of the features) in microfabrication are generally much greater than in IC fabrication

The device sizes in microfabrication are often much larger than in IC processing

The structures produced in microfabrication often include cantilevers and bridges and other shapes requiring gaps between layers These features are not found in integrated

circuits


Figure 37.5 Aspect ratio (height-to-width ratio) typical in (a) fabrication of integrated circuits and (b) microfabricated components.

Aspect Ratio


3D Features in Microfabrication

Chemical wet etching of polycrystalline silicon is isotropic, with the formation of cavities under the edges of the resist

However, in single-crystal Si, etching rate depends on the orientation of the lattice structure

3-D features can be produced in single-crystal silicon by wet etching, provided the crystal structure is oriented to allow the etching process to proceed anisotropically


Figure 37.6 Three crystal faces in the silicon cubic lattice structure: (a) (100) crystal face, (b) (110) crystal face, and (c) (111) crystal face.

Crystal Faces in Cubic Lattice Structure


Bulk Micromachining

Certain etching solutions, such as potassium hydroxide (KOH), have a very low etching rate in the direction of the (111) crystal face This permits formation of distinct geometric

structures with sharp edges in single-crystal Si if the lattice is oriented favorably

Bulk micromachining - relatively deep wet etching process on single-crystal silicon substrate

Surface micromachining - planar structuring of the substrate surface, using much more shallow etching


Figure 37.7 Several structures that can be formed in single-crystal silicon substrate by bulk micromachining: (a) (110) silicon and (b) (100) silicon.

Bulk Micromachining


Figure 37.7 Formation of a thin membrane in a silicon substrate: (1) silicon substrate is doped with boron, (2) a thick layer of silicon is applied on top of the doped layer by epitaxial deposition, (3) both sides are thermally oxidized to form a SiO2 resist on the surfaces, (4) the resist is patterned by lithography, and (5) anisotropic etching is used to remove the silicon except in the boron doped layer.

Bulk Micromachining of Thin Membrane


Cantilevers and Similar Structures

Surface micromachining can be used to construct cantilevers, overhangs, and similar structures on a silicon substrate The cantilevered beams are parallel to

but separated by a gap from the silicon surface

Gap size and beam thickness are in the micron range


Figure 37.9 Surface micromachining to form a cantilever: (1) on the silicon substrate is formed a silicon dioxide layer, whose thickness will determine the gap size for the cantilevered member; (2) portions of the SiO2 layer are etched using lithography; (3) a polysilicon layer is applied; (4) portions of the polysilicon layer are etched using lithography; and (5) the SiO2 layer beneath the cantilevers is selectively etched.

Micromachining to Form Cantilever


Lift-Off Technique in Microfabrication

A procedure to pattern metals such as platinum on a substrate

These structures are used in certain chemical sensors, but are difficult to produce by wet etching


Figure 37.10 Lift-off technique: (1) resist is applied to substrate and structured by lithography, (2) platinum is deposited onto surfaces, and (3) resist is removed, taking with it the platinum on its surface but leaving the desired platinum microstructure.

Lift-Off Technique


LIGA Process

An important technology of MST Developed in Germany in the early 1980s LIGA stands for the German words

LIthographie (in particular X-ray lithography) Galvanoformung (translated

electrodeposition or electroforming) Abformtechnik (plastic molding)

The letters also indicate the LIGA process sequence


Figure 37.10 LIGA processing steps: (1) thick layer of resist applied and X-ray exposure through mask, (2) exposed portions of resist removed, (3) electrodeposition to fill openings in resist, (4) resist stripped to provide (a) a mold or (b) a metal part.

Processing Steps in LIGA


Advantages of LIGA

LIGA is a versatile process – it can produce parts by several different methods

High aspect ratios are possible (large height-to-width ratios in the fabricated part)

Wide range of part sizes is feasible - heights ranging from micrometers to centimeters

Close tolerances are possible


Disadvantages of LIGA

LIGA is a very expensive process Large quantities of parts are usually

required to justify its application LIGA uses X-ray exposure

Human health hazard


Ultra-High Precision Machining

Trends in conventional machining include taking smaller and smaller cut sizes

Enabling technologies include: Single-crystal diamond cutting tools Position control systems with resolutions

as fine as 0.01 m Applications: computer hard discs,

photocopier drums, mold inserts for compact disk reader heads, high-definition TV projection lenses, and VCR scanning heads



One reported application: milling of grooves in aluminum foil using a single-point diamond fly-cutter The aluminum foil is 100 m thick The grooves are 85 m wide and 70 m

deep


Figure 37.11 Ultra-high precision milling of grooves in aluminum foil.



Microstereolithography (MSTL)

MSTL layer thickness t = 10 to 20 m typically, with even thinner layers possible In conventional STL, t = 75 m to 500 m

MSTL spot size is as small as 1 or 2 m Laser spot size diameter in STL ~ 250 m

Work material in MSTL not limited to photosensitive polymer Researchers report fabricating 3-D ceramic

and metallic microstructures Starting material is a powder rather than a

liquid


NUMERICAL CONTROL ANDINDUSTRIAL ROBOTICS

•Numerical Control• Industrial Robotics•Programmable Logic Controllers


Numerical Control

A form of programmable automation in which themechanical actions of a piece of equipment arecontrolled by a program containing codedalphanumeric data

•The data represent relative positions between aworkhead and a workpartWorkhead = tool or other processing elementWorkpart = object being processed

•NC operating principle is to control the motion of theworkhead relative to the workpart and to control thesequence in which the motions are carried out


Components of a Numerical Control System

•Part program - the detailed set of commands to befollowed by the processing equipment

•Machine control unit (MCU) - microcomputer thatstores and executes the program by converting eachcommand into actions by the processing equipment,one command at a time

•Processing equipment - accomplishes the sequenceof processing steps to transform starting workpartinto completed part


NC Coordinate System

•Consists of three linear axes (x, y, z) of Cartesiancoordinate system, plus three rotational axes (a, b, c)Rotational axes are used to orient workpart or

workhead to access different surfaces formachining

Most NC systems do not require all six axes


Figure 38.2 - Coordinate systems used in numerical control: (a)for flat and prismatic work


Figure 38.2 - Coordinate systems used in numerical control:(b) for rotational work


NC Motion Control Systems

• Two types:1. Point-to-point2. Continuous path


Point-to-Point (PTP) System

Workhead (or workpiece) is moved to a programmedlocation with no regard for path taken to get to thatlocation

•Once the move is completed, some processing actionis accomplished by the workheadExamples: drilling or punching a hole

•Thus, the part program consists of a series of pointlocations at which operations are performed

•Also called positioning systems


Continuous Path (CP) System

Continuous simultaneous control of more than one axis,thus controlling path followed by tool relative to part

•Permits tool to perform a process while axes aremoving, enabling the system to generate angularsurfaces, two-dimensional curves, or 3-D contours inthe workpartExamples: many milling and turning operations,

flame cutting•Also called contouring in machining operations


Two Types of Positioning

•Absolute positioningLocations are always defined with respect to origin

of axis system• Incremental positioning

Next location is defined relative to present location


Figure 38.3 - Absolute vs. incremental positioning. The workhead ispresently at point (2,3) and is to be moved to point (6,8). Inabsolute positioning, the move is specified by x = 6, y = 8; while inincremental positioning, the move is specified by x = 4, y = 5


Figure 38.4 - Motor and leadscrew arrangement in a NCpositioning system

NC Positioning System


NC Positioning System

Converts the coordinates specified in the NC partprogram into relative positions and velocities betweentool and workpart during processingLeadscrew pitch p - table is moved a distance

equal to the pitch for each revolutionTable velocity (e.g., feed rate in machining) is set

by the RPM of leadscrew•To provide x-y capability, a single-axis system is

piggybacked on top of a second perpendicular axis


Two Basic Types of Control in NC

•Open loop systemOperates without verifying that the actual position

is equal to the specified position•Closed loop control system

Uses feedback measurement to verify that theactual position is equal to the specified location


Precision in Positioning

• Three critical measures of precision in positioning:1. Control resolution2. Accuracy3. Repeatability


Control Resolution (CR)

Defined as the distance separating two adjacent controlpoints in the axis movement

•Control points are sometimes called addressablepoints because they are locations along the axis towhich the worktable can be directed to go

•CR depends on:Electromechanical components of positioning

systemNumber of bits used by controller to define axis

coordinate location


Figure 38.7 - A portion of a linear positioning system axis, withshowing control resolution, accuracy, and repeatability


Statistical Distribution of Mechanical Errors

•When a positioning system is directed to move to agiven control point, the capability to move to thatpoint is limited by mechanical errorsErrors are due to a variety of inaccuracies and

imperfections, such as play between leadscrewand worktable, gear backlash, and deflection ofmachine components

• It is assumed that the errors form an unbiased normaldistribution with mean = 0 and that the standarddeviation is constant over axis range


Accuracy in a Positioning System

Maximum possible error that can occur between desiredtarget point and actual position taken by system

•For one axis:Accuracy = 0.5 CR + 3

where CR = control resolution; and = standarddeviation of the error distribution


Repeatability

Capability of a positioning system to return to a givencontrol point that has been previously programmed

•Repeatability of any given axis of a positioningsystem can be defined as the range of mechanicalerrors associated with the axis

Repeatability = 3


NC Part Programming Techniques

1. Manual part programming2. Computer-assisted part programming3. CAD/CAM- assisted part programming4. Manual data input• Common features:

Points, lines, and surfaces of the workpart mustbe defined relative to NC axis system

Movement of the cutting tool must be definedrelative to these part features


Manual Part Programming

Uses basic numerical data and special alphanumericcodes to define the steps in the process

•Suited to simple point-to-point machining jobs, suchas drilling operations


Manual Part Programming: Example

•Example command for drilling operation:n010 x70.0 y85.5 f175 s500

where n-word (n010) = a sequence number; x- andy-words = x and y coordinate positions (x = 70.0mm and y = 85.5 mm), and f-word and s-word =feed rate and spindle speed (feed rate = 175mm/min, spindle speed = 500 rev/min)

•Complete part program consists of a sequence ofcommands


Computer-Assisted Part Programming

• Uses a high-level programming language Suited to programming of more complex jobs First NC part programming language was APT =

Automatically Programmed Tooling In APT, part programming is divided into two

basic steps:1. Definition of part geometry

2. Specification of tool path and operationsequence


APT Geometry Statements

•Part programmer defines geometry of workpart byconstructing it of basic geometric elements such aspoints, lines, planes, circles, and cylindersExamples:

P1 = POINT/25.0, 150.0L1 = LINE/P1, P2

where P1 is a point located at x = 25 and y = 150,and L1 is a line through points P1 and P2

•Similar statements are used to define circles,cylinders, and other geometry elements


APT Motion Statements:Point-to-Point (PTP)

•Specification of tool path accomplished with APTmotion statementsExample statement for point-to-point operation:

GOTO/P1

•Directs tool to move from current location to P1P1 has been defined by a previous APT geometry

statement


APT Motion Statements (CP)

•Use previously defined geometry elements such aslines, circles, and planes.Example command:

GORGT/L3, PAST, L4

•Directs tool to go right (GORGT) along line L3 until itis positioned just past line L4L4 must be a line that intersects L3


CAD/CAM-Assisted Part Programming

Takes computer-assisted part programming further byusing a CAD/CAM system to interact withprogrammer as part program is being prepared

• In conventional use of APT, program is written andthen entered into the computer for processingProgramming errors may not be detected until

computer processing•With CAD/CAM, programmer receives immediate

visual verification as each statement is enteredErrors can be corrected immediately rather than

after entire program has been written


Manual Data Input (MDI)

Machine operator enters part program at the machine• Involves use of a CRT display with graphics

capability at machine tool controlsNC part programming statements are entered

using a menu-driven procedure that requiresminimum training of machine tool operator

•Because MDI does not require a staff of NC partprogrammers, MDI is a way for small machine shopsto economically implement NC


Applications of Numerical Control

• Operating principle of NC applies to manyoperations There are many industrial operations in which the

position of a workhead must be controlledrelative to the part or product being processed

• Two categories of NC applications:1. Machine tool applications2. Non- machine tool applications


Machine Tool Applications

•NC is widely used for machining operations such asturning, drilling, and milling

•NC has motivated the development of machiningcenters, which change their own cutting tools toperform a variety of machining operations under NC

•Other NC machine tools:Grinding machinesSheet metal pressworking machinesTube bending machinesThermal cutting processes


Non-Machine Tool Applications

•Tape laying machines and filament winding machinesfor composites

•Welding machines, both arc welding and resistancewelding

•Component insertion machines in electronicsassembly

•Drafting machines•Coordinate measuring machines for inspection


Benefits of NC Relative to ManuallyOperated Equipment

•Reduced non-productive time which results in shortercycle times

•Lower manufacturing lead times•Simpler fixtures•Greater manufacturing flexibility• Improved accuracy•Reduced human error


Industrial Robotics

An industrial robot is a general purpose programmablemachine that possesses certain anthropomorphicfeatures

•The most apparent anthropomorphic feature of anindustrial robot is its mechanical arm, or manipulator

•Robots can perform a variety of tasks such asloading and unloading machine tools, spot weldingautomobile bodies, and spray painting

•Robots are typically used as substitutes for humanworkers in these tasks


Robot Anatomy

•An industrial robot consists of a mechanicalmanipulator and a controller to move it and performother related functionsThe mechanical manipulator consists of joints and

links to position and orient the end of themanipulator relative to its base

The controller operates the joints in a coordinatedfashion to execute a programmed work cycle


Figure 38.8 -The manipulator of a

modern industrialrobot

(photo courtesy ofAdept Technology,Inc.)


Manipulator Joints and Links

•A robot joint is similar to a human body jointIt provides relative movement between two parts

of the body•Typical industrial robots have five or six joints

Manipulator joints: classified as linear or rotatingEach joint moves its output link relative to its input

linkCoordinated movement of joints gives the robot its

ability to move, position, and orient objects


Manipulator Design

• Robot manipulators can usually be divided into twosections: Arm-and-body assembly - function is to position

an object or tool Wrist assembly - function is to properly orient the

object or tool• There are typically three joints associated with the

arm-and-body assembly, and two or three jointsassociated with the wrist


Manipulator Wrist

•The wrist is assembled to the last link in any of thesearm-and-body configurations

•The SCARA is sometimes an exception because it isalmost always used for simple handling andassembly tasks involving vertical motionsA wrist is not usually present at the end of its

manipulatorSubstituting for the wrist on the SCARA is usually

a gripper to grasp components for movementand/or assembly


End Effectors

The special tooling that connects to the robot's wrist toperform the specific task

• Two general types:1. Tools - used for a processing operation Applications: spot welding guns, spray

painting nozzles, rotating spindles, heatingtorches, assembly tools

2. Grippers - designed to grasp and move objects Applications: part placement, machine

loading and unloading, and palletizing


Figure 38.10 - A robot gripper:(a) open and (b) closed to grasp a workpart


Robot Programming

•Robots execute a stored program of instructionswhich define the sequence of motions and positionsin the work cycleMuch like a NC part program

• In addition to motion instructions, the program mayinclude commands for other functions such as:Interacting with external equipmentResponding to sensorsProcessing data


Two Basic Teach Methods inRobot Programming

1. Leadthrough programming - "teach-by-showing" inwhich manipulator is moved through the sequenceof positions in the work cycle and the controllerrecords each position in memory for subsequentplayback

2. Computer programming languages –robot programis prepared at least partially off-line for subsequentdownloading to computer


Where Should Robots beUsed in the Workplace?

•Work environment is hazardous for humans•Work cycle is repetitive•The work is performed at a stationary location•Part or tool handling is difficult for humans•Multi-shift operation•Long production runs and infrequent changeovers•Part positioning and orientation are established at the

beginning of work cycle, since most robots cannotsee


Applications of Industrial Robots

• Three basic categories:1. Material handling2. Processing operations3. Assembly and inspection


Programmable Logic Controller (PLC)

Microcomputer-based device that uses storedinstructions in programmable memory to implementlogic, sequencing, timing, counting, and arithmeticcontrol functions, through digital or analoginput/output modules, for controlling variousmachines and processes

• Introduced around 1969 in response to specificationsproposed by General Motors CorporationControls manufacturers saw a commercial

opportunity, and today PLCs are an importantindustrial controls technology


Why PLCs are Important

•Many automated systems operate by turning on andoff motors, switches, and other devices to respond toconditions and as a function of time

•These devices use binary variables that have twopossible values, 1 or 0, which means ON or OFF,object present or not present, high or low voltage

•Common binary devices used in industrial control:limit switches, photodetectors, timers, control relays,motors, solenoids, valves, clutches, and lights

•Some devices send a signal in response to a physicalstimulus, while others respond to an electrical signal


Figure 38.12 - Major components of a programmable logic controller


PLC Programming

•Most common control instructions include logicaloperations, sequencing, counting, and timing

•Many control applications require additionalinstructions for analog control, data processing, andcomputations

•A variety of PLC programming languages have beendeveloped, ranging from ladder logic diagrams tostructured text

What is Manufacturing?

Manufacture is derived from two Latin words manus

(hand) and factus (make); the combination means “made by hand”

• “Made by hand” accurately described the manual

methods used when the English word “manufacture”

was first coined around 1567 A.D. • Most modern manufacturing is accomplished by

automated and computer-controlled machinery that is manually supervised

Manufacturing is the application of physical and chemical processes to alter the geometry, properties, and/or appearance of a given starting material to make parts or products; manufacturing also includes assembly of multiple parts to make products

• Manufacturing is almost always carried out as a sequence of operations

Manufacturing

as a technical

definition

Manufacturing is the transformation of materials into items of greater value by means of one or more processing and/or assembly operations

• Manufacturing adds value to the material by changing its shape or properties, or by combining it with other materials that have been similarly altered

Manufacturing

as an economic

definition

Manufacturing Industries (Table 1.2)

Industry consists of enterprises and organizations that produce or supply goods and services

• Industries can be classified as:1. Primary industries - those that cultivate and

exploit natural resources, e.g., agriculture, mining 2. Secondary industries - take the outputs of

primary industries and convert them into consumer and capital goods - manufacturing is the principal activity

3. Tertiary industries -service sector of the economy

Manufacturing Industries - continued

• Most secondary industries are companies that do manufacturing; others are construction and power generation

• However, manufacturing includes several industries whose production technologies are not covered in this course; e.g., apparel, beverages, chemicals, and food processing

• For our purposes, manufacturing means production of hardware, which ranges from nuts and bolts to digital computers and military weapons, as well as plastic and ceramic products

Manufactured Products (Table1.3)

• Consumer Goods: Products purchased directly by consumers, such as cars, personal computers, TV’s

and tennis rackets.

• Capital Goods: Products purchased by other companies to produce goods and supply services. Examples include aircraft, mainframe computers, railroad equipment, machine tools and construction equipment.

Manufactured Products (continued..)

• Other manufactured products include materials, components and supplies.

• Examples of these items include sheet steel, bar stock, metal stampings, machined parts, plastic moldings, and extrusions, cutting tools, dies, molds and lubricants..

Production Quantity

The quantity of products Q made by a factory has an important influence on the way its people, facilities, and procedures are organized

Annual production quantities can be classified into three ranges: Production range Annual Quantity QLow production 1 to 100 units Medium production 100 to 10,000 unitsHigh production 10,000 to millions of units

The ranges provided are arbitrary. Depending on the kind of product these boundaries may shift.

Product Variety

Product variety P refers to different product types produced in the plant

• Product variety is distinct from production quantity • Different products have different shapes and sizes;

they are intended for different markets; some have more parts than others

• The number of different product types made each year in a factory can be counted

• When the number of product types made in the factory is high, this indicates high product variety

• An inverse correlation exists between product variety P and production quantity Q in factory operations

• If a factory's P is high, then Q is likely to be low; and if Q is high, then P is likely to be low

Figure 1.2 -P-Q Relationship

Production Quantity and Product Variety

Although P is a quantitative parameter, it is much less exact than Q because details on how much the designs differ is not captured simply by the number of different designs

• Soft product variety - small differences between products, e.g., differences between car models made on the same production line, in which there is a high proportion of common parts among models

• Hard product variety - products differ substantially, and there are few, if any, common parts, e.g., the difference between a small car and a large truck

Manufacturing Capability

A manufacturing plant consists of a set of processes

and systems (and people, of course) designed to transform a certain limited range of materials into products of increased value

• The three building blocks - materials, processes, and systems - are the subject of modern manufacturing

• Manufacturing capability includes: Technological processing capability Physical product limitations Production capacity

Technological Processing Capability

The available set of manufacturing processes in the plant (or company)

• Certain manufacturing processes are suited to certain materials By specializing in certain processes, the plant is

also specializing in certain material types• Includes not only the physical processes, but also the

expertise of the plant personnel

Physical Product Limitations

Given a plant with a certain set of processes, there are size and weight limitations on the parts or products that can be made in the plant

• Product size and weight affect: Production equipment Material handling equipment

• The production and material handling equipment, and plant size must be planned for products that lie within a certain size and weight range

Production Capacity

The production quantity that can be produced in a given time period (e.g., month or year)

• Commonly called plant capacity, or production

capacity, it is defined as the maximum rate of production that a plant can achieve under assumed operating conditions Operating conditions refer to number of shifts per

week, hours per shift, direct labor manning levels in the plant, and so on

• Usually measured in terms of output units, such as tons of steel or number of cars produced by the plant

Materials in Manufacturing

• Most engineering materials can be classified into one of three basic categories: 1. Metals2. Ceramics3. Polymers

• Their chemistries are different, their mechanical and physical properties are dissimilar, and these differences affect the manufacturing processes that can be used to produce products from them

• In addition to the three basic categories, there are: 4. Composites - nonhomogeneous mixtures of the

other three basic types rather than a unique category

Figure 1.3 –Venn diagramof three basicMaterial types plus composites

MetalsUsually alloys, which are composed of two or more

elements, at least one of which is metallic• Two basic groups:

1. Ferrous metals - based on iron, comprise 75% of metal tonnage in the world: Steel = iron-carbon alloy with 0.02 to 2.11% C

Cast iron = alloy with 2% to 4% C

2. Nonferrous metals - all other metallic elements and their alloys: aluminum, copper, gold, magnesium, nickel, silver, tin, titanium, etc.

Ceramics

A compound containing metallic (or semi-metallic) and nonmetallic elements. Typical nonmetallic elements are oxygen, nitrogen, and carbon

• For processing purposes, ceramics divide into:1. Crystalline ceramics – includes:

Traditional ceramics, such as clay (hydrous aluminum silicates)

Modern ceramics, such as alumina (Al2O3)

2. Glasses – mostly based on silica (SiO2)

Polymers

A compound formed of repeating structural units called mers, whose atoms share electrons to form very large molecules. Polymers usually consist of carbon plus other elements like hydrogen, oxygen, chlorine.

• Three categories:

1. Thermoplastic polymers - can be subjected to multiple heating and cooling cycles without altering their molecular structure. Common thermoplastics include polyethylene, polystyrene, polyvinyl chloride, and nylon.

Polymers (continued..)

2. Thermosetting polymers - molecules chemically transform (cure) into a rigid structure upon cooling from a heated plastic condition. Members include, phenolics, amino resins and epoxies.

3. Elastomers - exhibit significant elastic behavior. Members include natural rubber, neoprene, silicone and polyurethane.

Composites

A material consisting of two or more phases that are processed separately and then bonded together to achieve properties superior to its constituents

• A phase = a homogeneous mass of material, such as grains of identical unit cell structure in a solid metal

• Usual structure consists of particles or fibers of one phase mixed in a second phase

• Properties depend on components, physical shapes of components, and the way they are combined to form the final material

Manufacturing Processes (Figure 1.4)

Two basic types: 1. Processing operations - transform a work material

from one state of completion to a more advanced state. It adds value by

Operations that change the geometry, properties, or appearance of the starting material.

2. Assembly operations - join two or more components in order to create a new entity called assembly, subassembly or joining.

Processing OperationsAlters a part's shape, physical properties, or

appearance in order to add value to the material. • Three categories of processing operations:

1. Shaping operations - alter the geometry of the starting work material

2. Property-enhancing operations - improve physical properties of the material without changing its shape (Heat Treatment)

3. Surface processing operations - performed to clean, treat, coat, or deposit material onto the exterior surface of the work (Finishing Operations)

Shaping Processes – Four Categories

1. Solidification processes - starting material is a heated liquid or semifluid that solidifies to form part geometry

2. Particulate processing - starting material is a powder, and the powders are formed into desired geometry and then sintered to harden

3. Deformation processes - starting material is a ductile solid (commonly metal) that is deformed

4. Material removal processes - starting material is a solid (ductile or brittle), from which material is removed so resulting part has desired geometry

Solidification Processes• Starting material is heated sufficiently to transform it

into a liquid or highly plastic state • Examples: Casting for metals, molding for plastics

Particulate Processing• Starting materials are powders of metals or ceramics• Usually involves pressing and sintering, in which

powders are first squeezed in a die cavity and then heated to bond the individual particles

Deformation ProcessesStarting workpart is shaped by application of forces that

exceed the yield strength of the material• Examples: (a) forging, (b) extrusion

Material Removal ProcessesExcess material removed from the starting workpiece so

what remains is the desired geometry • Examples: machining such as turning, drilling, and

milling; also grinding and nontraditional processes

Waste in Shaping ProcessesIt is desirable to minimize waste and scrap in part

shaping• Material removal processes tend to be wasteful in the

unit operation, simply by the way they work • Casting and molding usually waste little material• Terminology:

Net shape processes - when most of the starting material is used and no subsequent machining is required to achieve final part geometry

Near net shape processes - when minimum amount of machining is required

Property-Enhancing Processes

• Performed to improve mechanical or physical properties of the work material

• Part shape is not altered, except unintentionally• Examples:

Heat treatment of metals and glasses Sintering of powdered metals and ceramics

Surface Processing Operations

1. Cleaning - chemical and mechanical processes to remove dirt, oil, and other contaminants from the surface

2. Surface treatments - mechanical working such as sand blasting, and physical processes like diffusion

3. Coating and thin film deposition - coating exterior surface of the workpart

• Several surface processing operations used to fabricate integrated circuits

Assembly OperationsTwo or more separate parts are joined to form a new

entity• Types of assembly operations:

1. Joining processes – create a permanent joint. • Examples: welding, brazing, soldering, and

adhesive bonding

2. Mechanical assembly – fastening by mechanical methods

Examples: use of screws, bolts, nuts, other threaded fasteners; press fitting, expansion fits

Production SystemsProductions systems consist of people, equipment, and

procedures designed for the combination of materials and processes that constitute a firm's manufacturing operations

• A manufacturing firm must have systems to efficiently accomplish its type of production

• Two categories of production systems: 1. Production facilities

2. Manufacturing support systems

• Both categories include people (people make these systems work)

Production FacilitiesThe factory, production equipment, and material

handling equipment• The facilities "touch" the product• Also includes the way the equipment is arranged in

the factory - the plant layout

• Equipment usually organized into logical groupings, called manufacturing systems

Examples: automated production line, machine cell consisting of an industrial robot and two machine tools

Production Facilities and Product Quantities

• A company designs its manufacturing systems and organizes its factories to serve the particular mission of each plant

• Certain types of production facilities are recognized as the most appropriate for a given type of manufacturing (combination of product variety and production quantity)

• Different facilities are required for each of the three quantity ranges

Low Quantity Production

Job shop is the term used for this production facility• Low quantity range = 1 to 100 units/year• A job shop makes low quantities of specialized and

customized products• Products are typically complex, e.g., space capsules,

prototype aircraft, special machinery • Equipment in a job shop is general purpose• Labor force is highly skilled• Designed for maximum flexibility

Medium Quantity Production

• Medium quantity range = 100 to 10,000 units annually

• Two different types of facility, depending on product variety: Hard product variety: batch production

Soft product variety: cellular manufacturing

High Production

• High quantity range = 10,000 to millions of units per year

• Referred to as mass production

High demand for product Manufacturing system dedicated to the

production of that product • Two categories of mass production:

1. Quantity production2. Flow line production

Quantity Production

Mass production of single parts on single machine or small numbers of machines

• Typically involves standard machines equipped with special tooling

• Equipment is dedicated full-time to the production of one part type

• Typical layouts used in quantity production = process layout and cellular layout

Flow Line Production

Multiple machines or workstations arranged in sequence, e.g., production lines

• Product is complex and requires multiple processing and/or assembly operations

• Work units are physically moved through the sequence to complete the product

• Workstations and equipment are designed specifically for the product to maximize efficiency

Manufacturing Support Systems

• A company must organize itself to design the processes and equipment, plan and control the production orders, and satisfy product quality requirements

• These functions are accomplished by manufacturing support systems - people and procedures by which a company manages its production operations

• Typical departments: 1. Manufacturing engineering 2. Production planning and control3. Quality control

Figure 1.10 – Overview of production system and major topics in Fundamentals of Modern Manufacturing

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CNC Programming Example (Lecture, Spring 2010)

CNC Programming Sheet

Part Name: Programmed by: Machine: Date: Page:


Setup information: N

Seq G/M Code

X Pos

Y Pos

Z Pos

IJK Loc

F Feed

R Rad/ret

S Speed

T Tool

Others

5 (start) 10 G20 15 G00 20 G17 25 G40 30 G49 35 G80 40 G90 45 M06 T30 50 G00 55 G00 X3.0 Y-0.5 Z0.5 60 M03 S2000 65 M08 70 G01 Z-0.25 F5.0 75 G03 X3.0 Y-3.5 I0 J-1.5 F4.0 80 G01 X7.0 F5.0 85 G00 Z0.2 90 G00 X3.0 Y-0.5 95 G01 Z-0.25 F5.0

100 G01 X7.0 105 G02 X7.0 Y-3.5 I0 J-1.5 F4.5 110 G00 Z0.5 115 X4.0 Y-2.0 120 G81 Z-0.5 F8.0 R0.1 125 X6.0 130 G00 Z0.5

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N Seq

G/M Code

X Pos

Y Pos

Z Pos

IJK Loc

F Feed

R Rad/ret

S Speed

T Tool

Others

135 M05 140 G28 Z0 145 M09 150 M30

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ME325/580 Handout: CNC Machining

Spring 2010 I. Kao Introduction Computer numerical control (CNC) is the process of manufacturing machined parts in a production environment, as controlled and allocated by a computerized controller that used motors to drive each axis. The CNC technology has been one of manufacturing’s major development in the 20th century. The controller is designed to control the direction, speed, and length of time each motor rotates. The operator downloads programmed path to the computer connected to the machine and then executes the code. The idea of Numerical Control (NC) was conceived by John Parsons, taken up by USAF, in 1948. This term is used interchangeably with CNC. The CNC technology not only has facilitated the development of new techniques and achievement of higher production levels but also has helped to increase product quality. The CNC technology was developed to:

1. increase production 2. improve the quality and accuracy of manufactured parts 3. stabilize manufacturing costs 4. manufacture complex or otherwise impossible jobs

Numerical control was also designed to help produce parts with the following characteristics: • similar in terms of raw material • various sizes and geometry • small- to medium-sized batches • a sequence of similar steps was used to complete each workpiece

CNC is now a well-established process, especially with the information and computer technology, compared to the NC technology first demonstrated in 1952. The CNC technology has the following advantages over the NC technology:

1. Programs can be entered at the machine and stored into memory. 2. Programs are easier to edit, so part programming process design time is reduced. 3. There is greater flexibility in the complexity of parts that can be produced. 4. Three-dimensional geometric models of parts, stored in the computer, can be used to

generate CNC part programs with tool path almost automatically, thus saving manual programming labor. This is referred to as CAD/CAM integration.

5. Computers can be connected to other computers worldwide through network, thereby allowing part programs to be transmitted directly to remote CNC machines.

Training is required for the operator of a CNC machine. The CNC machine also requires maintenance for smooth operations and extended life.

Two very similar standards are generally followed worldwide: the ISO 6983 and the EIA RS274. ISO (International Standardization Organization) and EIA (Electronic Industries Association) developed the main standard for CNC, which used simple programming instructions to enable a machine tool to carry out a particular operation. The flow charts of CNC processing, with and without computer aided process, are shown below.

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CNC Programming A CNC program is a sequential list of machining instructions for the CNC machine to execute. CNC code consists of blocks (also called lines), each of which contains an individual command for a movement or specific action. There are two major types of CNC codes, or letter addresses, in any program. The major CNC codes are G-codes and M-codes.

• G-code are preparatory functions, which involve actual tool moves (for example, control of the machine). These include rapid moves, feed moves, radial feed moves, dwells, and roughing and profiling cycles.

• M-codes are miscellaneous functions, which include actions necessary for machining, but not those that are an actual tool movement (for example, auxiliary functions). These

develop part drawing

Flow of CNC Processing

decide machine for the part

choose the required tooling

design machining sequence

calculate the coordinates

calculate spindle speed and feedrate

write the CNC program

preapre setup sheets and tool lists

verify/edit: simulator/machine tool

verify/edit on actual machine

Run the program to produce part

3D geometric CAD model

Flow of Computer-Aided CNC Processing

decide machining ops for the part

choose the required tooling

use CAM to generate CNC program

download the part program

verify/edit via simulator

verify/edit on actual machine

Run the program to produce part

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include spindle on and off, tool changes, coolant on and off, program stops, and other similar related functions.

Other letter addresses or variable are used in the G- and M-codes to make words. Most G-codes contain a variable, defined by the programmer, for each specific function. Each designation used in CNC programming is called a letter address. The letters used for programming are as follows:

N Block number – specifies the start of a block G Preparatory function, as previously explained X X-axis coordinate Y Y-axis coordinate Z Z-axis coordinate I X-axis location of arc center J Y-axis location of arc center K Z-axis location of arc center S Set the spindle speed F Assign a feed rate T Specify tool to be used M Miscellaneous function, as previously explained

The Three Major Phases of a CNC Program The three phases of a CNC program can be illustrated with the following sample code.

Phase CNC program Descriptions % Program start flag (syntax & format are machine-dependent) :1001 Four digit program number; up to four digits, 0-9999 N5 G90 G20 Use absolute units, and inch programming N10 M06 T2 Stop for tool change, use Tool #2 Pr

ogra

m

setu

p

N15 M03 S1200 Turn the spindle on CW to 1200 rpm N20 G00 X1 Y1 Rapid to (X1, Y1) from the origin N25 Z0.125 Rapid down to Z0.125 N30 G01 Z-0.125 F5 Feed down to Z-0.125 at 5 in./min N35 G01 X2 Y2 Feed diagonally to (X2, Y2) N40 G00 Z1 Rapid up to Z1 M

ater

ial

rem

oval

N45 X0 Y0 Rapid to (X0, Y0) N50 M05 Turn the spindle off N55 M30 End of program Sy

s sh

ut

(1) Program setup: This phase is virtually identical in every program. It always begins with the program start flag (% sign). Note: The actual setup for each CNC machine may differ. For example, the CNC in our machine shop uses “0100” to start the CNC code. Line two always has a program number from 0 to 9999. Line three is the first actually numbered. G90 tells the controller that all distances (X and Z) are absolute, that is, measured from the origin. G20 instructs the controller that all coordinates are measured in inch units.

(2) Material removal: This phase deals exclusively with the actual cutting feed moves. It contains all the commands that designate linear or circular feed moves, rapid moves,

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canned cycles such as grooving or profiling, or any other function required for that particular part.

(3) System shutdown: It contains all those G-codes and M-codes that turn off all options that were turned on in the setup phase. Functions such as coolant and spindle rotation must be shut off prior to removal of the part from the machine. The shutdown phase also is virtually identical in every program.

Using A Programming Sheet Each row in the following program sheet contains all the data required to write one CNC block.




Seq G/M Code

X Pos

Y Pos

Z Pos

IJK Loc

F Feed

R Rad/ret

S Speed

T Tool

Others

5 G90,G20 10 M6 2 15 M3 1200 20 G00 0 0 25 0.1 30 G01 -0.1 2 35 G01 1.5 Block Format Each block of CNC code needs to be entered correctly. The block comprises of different components which can produce tool moves on the machine. Here is a sample:

N105 G01 X1.0 Y1.0 Z0.125 F5 N105 Block number Shows the current CNC block number G01 G-code Tells the machine what to do. In this case, a linear feed

move X1.0 Y1.0 Z0.125 Coordinate Gives the machine an end point for its move. X

designates an X-axis coordinates, Y/Z for Y/Z-axis. F5 Special function Contains any special function or related parameter. In

this case, a feed rate of 5 in/min is specified. There are some simple restrictions on CNC blocks, as follows:

• Each may contain only one tool move. • Each may contain any number of non-tool move G-codes (e.g., G90 G20 for absolute

system and inch system), provided that they do not conflict between each other (for example, G42 and G43).

• Each may contain only one feedrate per block. • Each may contain only one specified tool or spindle speed. • The block numbers should be sequential. • Both the program start flag and the program number must be independent of all other

commands. • The data within a block follow the sequence shown in the above sample block.

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Preparing to Program Before you start writing a CNC program, you must first prepare to write it. The steps include

(a) Develop an order of operations (b) Calculate coordinates and complete a coordinate sheet (c) Choose tooling with clamping devices, and calculate speeds and feeds

Program Zero Program zero allows the programmer to specify a position from which all other coordinates will be referenced. Program zero is also called “part zero” or “machine home.” “Program zero” is particularly important in absolute programming. In incremental programming (where coordinates are related incrementally), one has a floating program zero that changes all the time. Tool Motion There are three types of tool motions used in a CNC machine. They are:

(1) G00: rapid tool move (2) G01: straight line feed move (3) G02/03: circular interpolation or arc feed moves

All cycles such as G71 rough turning are either one of these types or a combination of these types of motion. These motion command are modal. That is, if you program one of these commands, you do not need to program the same code again until you want to change the type of tool motion. The command will be in effect until it is changed or turned off. Using Canned Cycles Canned cycles combine many standard programming operations and are designed to shorten the program length, minimize math calculations, and optimize cutting conditions to improve the production of the machine. Examples of canned cycles on a mill are drilling, boring, spot facing, tapping, … etc; on a lathe, threading and pattern repeating cycles. On the lathe, canned cycles are also referred to as multiple repetitive cycles. Canned cycles also facilitate programming. You should check out the canned cycles that your CNC control offers. Subroutines are also available on many CNC controllers. You can utilize these routines to make your own canned cycles. Tooling Separate tools are used for roughing and finishing, and tasks such as drilling, slotting, and thread cutting require specific tools. Feedrates, spindle speeds and Cutting Fluids A good surface finish and economical production rates require proper use of spindle speeds and feed rates, as well as cutting fluids.

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CNC Milling The following tables list G-codes and M-codes. The G-codes, which include preparatory functions, involve actual tool moves. The following table lists G-codes in CNC milling.

G-Code name Function Op* G00 Positioning in rapid Modal G01 Linear interpolation Modal G02 Circular interpolation (CW) Modal G03 Circular interpolation (CCW) Modal G04 Dwell G17 XY plane Modal G18 XZ plane Modal G19 YZ plane Modal G20/G70 Inch unit system Modal G21/G71 Metric unit system Modal G28 Automatic return to reference point G29 Automatic return from reference point G40 Cutter compensation cancel Modal G41 Cutter compensation left Modal G42 Cutter compensation right Modal G43 Tool length compensation (Plus) Modal G44 Tool length compensation (Minus) Modal G49 Tool length compensation cancel Modal G80 Cancel canned cycles Modal G81 Drilling cycle Modal G82 Counter boring cycle Modal G83 Deep hole (peck) drilling cycle Modal G90 Absolute positioning Modal G91 Incremental positioning Modal G92 Reposition origin point G98 Set initial plane default G99 Return to retract (rapid) plane

Op: When noted as “modal”, it means that the function remain active until cancelled by another G-code. * Check your CNC machine manuals for G-codes which are not listed here.

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The M-codes, miscellaneous functions, include actions necessary for machining, but not those that are actual tool movements. That is, they are auxiliary functions, such as spindle on and off, tool changes, coolant on and off, program stops, other similar related functions. The following table lists M-codes in CNC milling.

M-Code Function M00 Program stop M01 Optional program stop M02 Program end M03 Spindle on clockwise (CW) M04 Spindle on counterclockwise (CCW) M05 Spindle stop M06 Tool change M08 Coolant on M09 Coolant off M10 Clamps on M11 Clamps off M30 Program end, reset to start

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Letter Address Listing Letter addresses are variables used in the different G-codes and M-codes. Most G-codes contain a variable, defined by the programmer, for each specific function. Each letter used in conjunction with G-codes or M-codes is called words. The letter used for programming are as follows:

Letter address Function D Diameter offset register number H Height offset register number F Assigns a feed rate G Preparatory function I X-axis location of arc center J Y-axis location of arc center K Z-axis location of arc center M Miscellaneous function N Block number (specifies the start of a block) P Dwell time R Retract distance used with G81, 82, 83

Radius when used with G02 or G03 S Sets the spindle speed T Specifies the tool to be used X X-axis coordinates Y Y-axis coordinates Z Z-axis coordinates

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Appendix: CNC Programming Sheet




Seq G/M Code

X Pos

Y Pos

Z Pos

IJK Loc

F Feed

R Rad/ret

S Speed

T Tool

Others

5 10 15 20 25 30 35

MEC325/580 HANDOUT: CNC TURNING OPERATION AND LATHE


In this handout, CNC programming for turning operations will be presented. The coordinate references arediscussed with an example of code based on thediameter programming reference.

CNC lathe programming: Before writing CNC code for turning operation, it is important to first identifyand calculate the coordinates of points of transition in turning. The machining may include multiple passes.We will use a CNC lathe program with the finishing cut of the following lathe part, shown in Figure 1, as anexample to illustrate the concept of CNC programming in turning operations.

−2 −1 10

1

2

3

4

−3−4−5−6−7−8−91 +Z axis

+X axis

−ZProgram zero

345

67

89

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Figure 1: An example of CNC part for the illustration of CNC turning operation. All units are in inches.

First the coordinate frame with a right-hand coordinate system is shown in Figure 1. The conventionalcoordinates of parts in turning operation are in the second quadrant with+X and−Z coordinates. Since aturning operation is always axisymmetric with respect to the Z axis, the profile shown includes point 1 topoint 9, as shown in Figure 1. Note that the entire profile for programming consideration fits in the secondquadrant. The other half in the third quadrant is a mirror image of the profile shown in Figure 1. AllXvalues are positive, while allZ values are negative.

However, there are two types of programming references to theXZ dimension. The “diameter program-ming” relates theX-axis to the diameter of the workpiece. The “radius programming” relates theX-axis tothe radius of the workpiece. Although many controller can work in either mode,diameter programmingis the most common and is the default for most CNC lathe. To change the default, one can enable the radiusprogramming mode.

Based on Figure 1, the coordinates of the diameter programming for points 1 to 9 are identified and listedin Table 1, using thediameter programming reference. The workpiece is a cylindrical stock of diameterof8”; tool #1 is the regular right-hand turning tool, and the tool start position isX4, Z3. The CNC code withcomments is in the following for this turning operation of the finishing cut shown in Figure 1.

N5 ____ Code for program start (machine-dependent)N10 G90 G20 Absolute, inches systemN15 M06 T1 Tool change to Tool #1N20 M03 S500 spindle CW with speed 500 RPMN25 G00 X0 Z0.1 M08 Rapid to X0,Z0.1, coolant on (ready to start)

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Table 1: Coordinates of the points identified in Figure 1, under the diameter programming reference.Point # X Z

1 0 02 6 −3

3 6 −4

4 5 −4.5

5 5 −5.5

6 4 −5.5

7 4 −6

8 8 −7

9 8 −9

N30 G01 Z0 F0.02 Feed to point 1 at 0.02 in/revN35 G03 X6 Z-3 I0 K-3 CCW circular feed to point 2N40 G01 Z-4 Linear Feed to point 3N45 X5 Z-4.5 Feed to point 4N50 Z-5.5 Feed to point 5N55 X4 Feed to point 6N60 Z-6 Feed to point 7N65 X8 Z-7 Feed to point 8N70 Z-9 Feed to point 9N75 G00 Z2 M09 Rapid to Z2, coolant offN80 M05 Spindle offN85 M02 End program

Note that block 35 usesG03 to do a circular feed in CCW direction to arrive at the destination point (X6,Z−3), with center of the90 arc at (I0, K−3), using the notation of I,J,K to express theX,Y,Z coordinatesof the center. In block 40, the G-codeG01 is used to do linear interpolation. Since this is a “modal” code,it stays in effect from block 40 to 70 until it is turned off byG00, another modal code, in block 75. At theend, the M-code is used to turn off coolant, spindle, and to end the program.

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CNC Turning Machining Example: A part is to be finished using turning operation, as shown in thefollowing figure. The information about the workpiece and tool is in the following.

Workpiece size: 4" diameter by 5" lengthTool: Tool #1, right-hand turning toolTool start position: X4,Z3

1

234

567

8

9

0.60 1.002.00 2.40 4.00

0.201.10

1.50

2.30

5.00

0.30 radius

1. The coordinates of the finished part, as indicated in the v figure, are calculated using the diameterprogramming and listed in the following table.

Point # X Z

1 0 02 0.6 03 1 −0.24 1 −1.15 2 −1.16 2.4 −1.57 2.4 −28 3 −2.39 4 −2.3

2. The following CNC program is written for the finishing passof the lathe part.

N05____ Start of the programN10 G90 G20 Absolute, inches systemN15 M06 T1 Tool change to Tool #1N20 M03 Spindle on CWN25 G00 X0 Z0.1 M08 Rapid to X0,Z0.1, coolant on (ready to start)N30 G01 Z0 F0.012 Feed to point 1 at 0.012 in/revN35 X0.6 Feed to point 2N40 X1 Z-0.2 Feed to point 3N45 Z-1.1 Feed to point 4N50 X2 Feed to point 5N55 X2.4 Z-1.5 Feed to point 6N60 Z-2 Feed to point 7N65 G02 X3 Z-2.3 I0.3 K0 Cicular feed to point 8N70 G01 X4 Feed to point 9N75 G00 Z3 M09 Rapid to Z3, coolant offN80 M05 Spindle offN85 M02 End program

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ME325/580 SME Video: Cutting Tool Geometries

Spring 2010 I. Kao 1. The chip formation is influenced by

• Work materials • Tool materials • Tool geometry • Machine tool forces • Process conditions (e.g., heat and vibration)

2. Use wrong cutting tool materials may • Fail to cut • Accelerate tool wear • Cause tool breakage • Damage parts

3. The following process parameters • Workpiece composition and hardness • Workpiece shape and surface condition • Machine’s horsepower • Feed and speed ranges • Workholding rigidity will determine (a) tool shape (b) tool material (c) process parameters

Single-point cutting tools -- having only one chip producing edge Example: turning 4. Three important considerations

• Tool material/grade • Tool geometry • Tool holder design

5. Definitions and terminology • Angle of inclination • Rake angle • Lead/entry angle • Insert tool holder: shank, pocket, head

6. Tool holders are specified with • Shank size • Right/left/neutral • Clamping method • Insert shape • Insert size • Insert style • Insert angle

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7. Effective break of chips is important. Proper chip breaking results from • Feed rate • Depth of cut • Chipbreaker geometry

8. Shape of chips • 6 or 9 shape – ideal shape • helical – acceptable if it is short helical • long stringy (or hay chips) – not desirable • corrugated – will cause excessive cutting edge wear

Multiple-point cutting tools – having two or more chip producing edges Examples: milling, reaming, drilling, tabbing 9. Two different milling modes

• Climb milling mode (materials removed gradually reduce as the tool travels) • Conventional milling mode (materials removed gradually increase as the tool travels)

10. Major variables in design of miller body • Cutter’s diameter • Right/left hand (RH – CCW; LH – CW) • Cutter geometries (rake and lead angles) • Insert pocket design • Cutter pitch • Mounting method

Total time: 25:51 (22:30 without the Review)

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ME325/580 SME Video: Cutting Tool Materials

Spring 2010 I. Kao 1. Cutting tools can be broken into two categories, as shown in the following table.

Cutting Tools Single-Point Tools Multiple-Point Tools Example Turning Milling, drilling, reaming

2. It is estimated that at least 50% of cutting tools are used incorrectly. The number one error in

formulating tool selection is to lower cost on tools rather than optimize productivity and extend tool life.

3. Cutting tool selection should be based on the following triangular chart.

4. Workpiece information includes:

• Workpiece starting and finished shapes • Workpiece hardness • Workpiece tensile strength • Material abrasiveness

5. Changes in (1) workpiece materials, (2) part tolerance, (3) part geometries, and (4) required quantities will result in changes of (a) tool materials, and (b) tool geometry.

6. Cutting tool material are required to: • Be harder than workpiece • Retain hardness • Resist wear and thermal shock • Be impact resistant • Be chemically inert Trade-off always exists among different requirements. A good cutting tool should be optimized with respect to the specific cutting situation.

7. Ceramic cutting tools: properties for stability and shock

8. High speed steel tools: invented in the 1900’s, can sustain temperature up to 600°C. Include

three categories: • Tungsten • Molybdenum • Molybdenum-cobalt Titanium nitride coatings are usually used to enhance the performance and life.

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9. In the 1930’s, carbide tools were introduced in Germany. It can sustain a temperature as high as 1200°C, and has 3~5 times higher strength than the high speed steel tools. Typical carbide tools include: • tungsten carbide • titanium carbide • tantalum carbide • niobium carbide The binder material for carbide is usually cobalt.

10. The property variables for carbide tools include • Particle size • Binder • Metallurgy • Manufacturing technology

11. Contents of carbides and properties of wear and heat resistance versus strength

12. Carbide insert and fixture: considerations for selecting carbide grade cutting tools include

type of work materials, hardness, condition of outer skin of workpiece, heavy or light, rigid or loose machine tool holder … etc.

13. Though with the same ISO 513-1991 standard coating, the carbide insert tools may differ in • Compositions • Microstructures • Coatings • Properties • Performance

14. ANSI classification of carbide insert tools: example CNMG-432-MR7. The first 7 digits represent the following properties: • Insert shape • Insert relief angle (N=0°, A=3°, B=5°, C=7°, P=11°, D=15°, E=20°, F=25°, G=30°) • Insert tolerance class

Insert inscribed circle thickness C = ± 0.0005 ± 0.001 E = ± 0.001 ± 0.001 G = ± 0.001 ± 0.005 M = ± 0.002 ± 0.004

± 0.005

U = ± 0.005 ± 0.012

± 0.005

• Insert type: use a one-letter symbol • Insert size (inscribed circle or the IC size) • Insert thickness • Insert corner radius

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The manufacturers often provide additional chip breaker code such as MR7 in the above example.

15. Two-thirds of carbide tools are coated, which give rise to three times more tool life or 2~4 times more cutting speed. The coating are typically 1 mil thickness or smaller, with multiple layers. The carbide’s primary limitation is shown in the following figure.

16. Primary cutting tool coating materials are

• Titanium carbide • Titanium nitride • Aluminum oxide • Titanium carbonitride where the titanium nitride minimizes friction.

17. Primary coating methods • Chemical vapor deposition (CVD): at 1000°C, usually for multiple layers • Physical vapor deposition (PVD): at 500°C, usually for single or dual layers

18. Ceramic tools have high hardness but tend to be more brittle. Ceramic cutting tools materials can be categorized into two areas: • Alumina-based • Silicon nitride-based: (e.g., for high speed grey cast iron)

19. Cermet tools: excellent in chemical resistance but do not withstand high heat. 20. Super hard tools:

• Cubic boron nitride (CBN, which is the second hardest material after diamond) • Polycrystalline diamond (PCD, 50 times more hardness than carbides)

21. Diamond coated inserts are normally for non-ferrous materials. 22. Tool failure modes:

• Edge wear • Flank wear • Cratering (or top wear) • Chipping (of the tool edge) • Built-up edge • Deformation (normally occurs at high temperature, such as 1800-2000°F, need to use

microscope to detect) • Thermal cracking • Notching


Merchant Equation – Know how to derive it!

Shear Plane which minimize energy is 𝑑𝑡

𝑑∅= 0 ; ∅ = (45𝑜 +

𝛼

2−

𝛽

2)

Lathe

Unit Power/Specific Energy 𝑈 = 𝑃

𝑀𝑅𝑅=

𝐹𝑐𝑣

𝑣𝑡𝑜𝑤=

𝐹𝑐

𝑡𝑜𝑤

Milling

Materials with high strain hardening factor prefer down milling

High Strain produces “chattering” which is vibrations in cutting tool

Climb Milling aka Down Milling produces better surfaces

Drilling

One line makes contact and may wobble

Precision Drilling – Start with hole so drill is centered ~ known as Center Drill

**Taylor Tool Life Equation**

𝑣𝑇𝑛 = 𝑐 ; log 𝑣 + 𝑛𝑙𝑜𝑔 𝑇 = log 𝑐 Tool Life

Cemented Carbides – Cobalt can be a binder because of relative atomic size. Invented in the 1930s by Germanym Based on Tungsten Carbide

Cermet TiC, TiN, TiCN with Nickel as binder Typical Values

n c Steel .125 120-70

Carbide .25 900-500 Ceramic 0.6 3000

Cubic Boron Nitride – 2nd Hardest Material

material Hardness (1 being hardest) Cubic Boron Nitride 2

Boron Carbide 3 Diamond 1

Aluminum Oxide (alumina) 5 Silicon Carbide 4

Sintered Polycrystalline Diamond (SPD) – Fabricated by sintering very fine-grained

diamond crystals under high temperatures Usually 0.5mm thick (coating) High Speed Machining of Non-Ferrous Metals

Abrasive Machining (Grinding,etc.)

Grain Size measured using screen mesh Larger Number = smoother (smaller grain size) Bonding Materials

Vitrified Bond, Silicate Structure ~ Sodium Silicate, Rubber Bond, Shellac Bond, Metallic Bond

Grain Aspect Ratio = 𝑟𝑔 =𝑤

𝑇 ; w = width of cut, T = thickness of chip

Taguchi Methods

Always Pick Largest Signal to Noise Ratio Please reference chart for method

Bulk Deformation

B.D. = low Surface Area to Volume Ratio; Sheet Metal Working = high Surface Area to Volume Ratio

Recrystallization Temperature = 50% Melting Temperature Warm Working = 30% Recrystallization Temperature Cold Working Hot Working Strain Hardening Yes No Ductility Yes Yes/No Yield Strength Increased Same or Decreased Drasitically Change Shape No Yes At Plastic State Yes Yes Energy Required Large Amounts Small Amounts (excluding heat) Oxidation Less (~0) More Recrystallization Temperature

Increased Not Affected

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ME325/580 SME DVD Video: Die Casting

Spring 2010 I. Kao 1. Die casting is a high precision rapid part production process involving the high pressure

injection of molten metal into a die having a cavity of the desired part shape. 2. Die casting is extremely versatile technique allowing single part to be cast or multiple parts

to be cast simultaneously. 3. The most common die casting metals are

• Aluminum alloys (melting point 580 °C—600 °C) • Zinc alloys (387 °C) • Magnesium alloys (596 °C) In general, metals with low melting point can be die-cast. Copper and copper alloy like brass are also die-cast but less frequently because of the high melting temperature. Metal with high melting point can make casting more difficult. A metal with low melting temperature has high cast ability.

4. Castability is general term which refers to • Complexity of shape • Minimum wall thickness • Minimum wall draft/taper • Precision to which the metal can be cast

5. The two principal types of die casting machines are • Hot chamber machine • Cold chamber machine

6. Die cast machines are often rated by clamping-force capacity or shot weight capacity. 7. Maximum part weight are

• Aluminum and Zinc (75 lbs/34 kg) • Magnesium (45 lbs/20 kg) • The brass (10 lbs/4.5 kg)

8. The die halves are attached to platens of the die cast machine, including stationary platen and removable platen.

9. The die • determines the shape of the part, • acts as a heat exchanger, • vents trapped air/gas, and • ejects the solidified part.

10. The die must withstand a combination of • molten metal heat and erosion • thermal shock from repeated heating and cooling • metal injection and clamping pressure

11. Dies are usually produced by • Hot-work tool steels • Mold steel • Maraging steel

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• Refractory steel such as tungsten alloys and molybdenum alloys

12. Die casting is used in many industrial applications such as trucks, cars, computer, camera, toys, locks, agriculture, and many others.

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MEC325/580 SME Video: Electrical Discharge Machining Spring 2010 I. Kao EDM: Electrical Discharge Machining 1. EDM is a thermo erosion process, in which work material is removed through a series of

rapidly recurring electrical discharges between an electrode, or cutting tool, and an electrical conductive work piece, in the presence of dielectric fluids. These discharges occur over a voltage gap between the electrode and work piece. Heat from the spark vaporizes minute particles from work piece material which is then washed from the gap by the continuously flushing dielectric fluid.

2. Two main types of ED machines: RAM & WIRE 3. EDM is an exceptionally diverse process and examples of its products are:

• tiny electronic connectors • highly accurate medical parts • automatic stamping dies • aircraft body panels

4. EDM has replaced much of machining and grinding steps formerly needed in die making, which represent the largest single use of the EDM process. Die components cut with EDM can often be made in a single piece, no matter how complex their internal form is. The single piece dies are stronger than those built from segments.

5. Dies are cut from: • Hardened Steel • Heat-Treated Steel • Carbide

6. Other materials can be EDM’ed: • Polycrystalline diamond • Titanium • Hot-rolled steel • Cold-rolled steel • Copper • Brass • High temperature alloys

7. Benefits of EDM: • Work piece and electrode never touch No cutting force generated produce frail and

fragile parts (cannot be done by conventional machining) • Burr-free, intricate details, superior surfaces finishes are possible. • Allows heat treating before EDM eliminates risk of damaging expensive work pieces • Building process knowledge help reduce training

8. Limitations: • Low metal removal rate (MRR) • Electrode fabrication requires time • Electrodes are consumable • Work pieces must be conductive

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9. Basic Components of EDM: The electrode is attached to the ram, which is connected to one pole of pulse power supply. The work piece connects to the other pole of power supply. There is a small gap between the work and electrode. This gap is flooded with dielectric fluid, which acts as insulator until the power is turned down. The machine control delivers thousands of DC electrical pulses per second to the gap and erosion begins.

10. The sparks are generated one at a time, but it rates from tens of thousands to hundreds of thousands of times per second. Each spark has temperature from 14,000 to 21,000ºF. As erosion continues, the machine control advances the electrode through the work always maintaining a constant gap distance.

11. Single spark in erosion process: As a pulse of DC electricity reaches the electrode and part, an intense electrical field develops in the gap. Microscopy contaminants suspended in the dielectric fluid are attracted by the field and concentrate at the field strongest point. These contaminants build a high conductivity bridge cross the gap. As the field’s voltage increases, this material in the conductive bridge heat up. Some pieces ionized to form a sparkle channel between the electrode and work piece. At this point both temperature and pressure in the channel rapidly increase generating a spark. A small amount of material melts and vaporizes from the electrode and work piece at the points of spark contact. A bubble composed of gases by product vaporization rapidly expands outwards from the spark channel. Once the pulse ends, the sparking and heating actions stop collapsing the spark channel. Dielectric fluid then rushes into the gap, flushing molt material from both surfaces.

12. Three observable surface layers:

• Top layer, melt, easy to remove • Middle layer, recast, polishing • Third layer, heat affected zone, only heated not melt

13. Part surface condition is a function of EDM cycle, which has on-time and off-time expressed in micro-seconds. All work occurs during on-time. Metal removal is proportional to the amount of energy applied during on-time. That energy is controlled by two variables, peak amperage or intensity of the spark and the length of on-time. The longer the on-time, the more metal erodes.

14. Duty Cycle: percentage of on-time relative to the total cycle time. 15. Gap between work piece and electrode also impacts metal removal rate. Generally, the

smaller the gap, the better the accuracy and part finish are, and the slower the metal removal rate is.

16. Kerf / overcut RAM EDMING 17. Work piece mounts inside of a tank and is covered with dielectric fluid. An electrode then

lowers to within a few thousandths of an inch to the work piece to begin EDM. 18. Produce complex cavities out of a solid piece of metal. 19. Also refer to as die sinker and vertical EDM.

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20. Size and automation range from manually operated tabletop systems to large bed manual or CNC systems.

21. Subsystems: • Power supply

Provides… o Series of DC current electrical discharges

Controls… o Pulse voltage o Current o Pulse duration o Duty cycle o Pulse frequency o Electrode polarity

• Dielectric system Introduces clean dielectric Popular dielectric fluids are hydrocarbon and silicon-based oil Flushes away debris Cools work piece and electrode

• Electrode Shape is negative to generated cavity Usually has a “+” polarity Some EDM’s require multiply electrodes for roughing and finishing operations Electrode making is important Equipped with systems of dust control and evacuation

• Servo system WIRE EDMING 22. CNC WIRE cut EDM machine uses a traveling wire electrode to cut complex outlines and

fine details in stamping and binding dies of pretty hard steel. 23. Subsystems

• Power supply Similar to RAM

• Dielectric system • Wire feeding system

A large spool of wire Rollers that direct the wire through the machine A metal contact to conduct power to the wire Guides to keep the wire straight in the cut Pinch rolls which provide drive and wire tension A system to thread the wire from the upper to the lower guide An idle or balancing arm A sensor to detect when the wire runs out or breaks A place for wire to collect

• Positioning system

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Use CNC two axis table (X, Y) and provides a variety of multi-axis wire positioning capabilities

24. Wire diameter: 0.002” ~ 0.013” 25. Metal removal rate:

Inches traversed per hour × thickness of work in inches = square inches per hour 26. Top speed: 20 to 25 square inches per hour 27. The wire never touches the work piece while cutting, the servo system maintains at least one

thousandth of an inch gap between wire and work piece. 28. During spark erosion, each wire produces a kerf for overcutting the work surface that is

slightly larger than the wire’s diameter. For example, 0.012” wire can create 0.015” kerf. 29. The wire cuts along a programmed path, starting from the side of the work piece or through

drilled holes made with small EDM hole making machines designed for that purpose. 30. WIRE EDM machines can also process parts that are stacked. But flushing could be

problematic. Third type of EDM: drilling small deep holes and slots around or regular shapes 31. Size of electrode: up to 1 foot long with diameters of one hundredth to one eighth of an inch. 32. Rotation speed: up to 100 rev/min. 33. Accuracy: up to one thousandth of an inch. 34. Fire & Smoke Total time: 22:00 (19:30 without the Review)

ME325/580 Handout: Engineering Materials

Spring 2010 I. Kao Descriptions and comparisons of the three basic categories of engineering materials (metals, ceramics, and polymers) and their mechanical, physical, and other properties

Metals Ceramics Polymers

Description

Ferrous and non-ferrous metals

Compound containing metallic (or semi-metallic) and nonmetallic elements

Compound formed of repeating structural units called “mers” whose atoms share electrons to form very large structure

Structure Crystalline (solid state) Crystalline or non-crystalline (amorphous; e.g., glass, SiO2)

Glassy or Glassy + Crystalline

Mechanical Properties

Strong, hard, ductile (esp. FCC)

High hardness High stiffness High brittleness

Strength & stiffness vary

Physical Properties

High electrical conductivity High thermal conductivity

Electrical insulation Thermally resistant (refractoriness)

Low density High electric resistivity Low thermal conduction

Other Properties

Opaqueness Reflectivity

Chemical inertness Carbon +(H2,N2,O2,Cl2)

In addition to the basic three categories described above, the composite materials are typically combinations of two of the three engineering materials, as illustrated in the diagram (also called the Venn diagram).

PLC Logic Table: an example Logic States

X1 1 1 0 0

X2 1 0 1 0

C1 1 1 0 1

S1 1 1 0 1

T1 1 1 0 1

S2 1 1 0 1

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Expendable-MoldCasting



Metal Casting

Open mold Closed mold

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Riser Design for Casting• Riser is waste metal that is separated from

the casting and can be re-melted to makemore castings

• To minimize waste in the unit operation, itis desirable for the volume of metal in theriser to be a minimum

• Since the geometry of the riser is normallyselected to maximize the V/A ratio (why?),this allows riser volume to be reduced to theminimum possible value

Figure 11.1 (textbook) A large sand casting weighing over680 kg (1500 lb) for an air compressor frame (photocourtesy of Elkhart Foundry).

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Types of Patterns for Sand CastingFigure 11.3 (textbook) Types of patterns used in

sand casting:(a) solid pattern (b) split pattern(c) match‑plate pattern (d) cope and drag pattern

Sand Casting• Core:

– inserted into the mold cavity prior to pouring– May require supports to hold it in position in the mold cavity

during pouring, called chaplets

• Desirable Mold Properties:– Strength; Permeability; Thermal stability; Collapsibility;

Reusability

• Foundry Sands: Silica (SiO2) or silica mixed withother minerals– Good refractory properties; Small grain size yields better

surface finish on the cast part; Large grain size is morepermeable; Irregular grain shapes strengthen molds due tointerlocking

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Sand Casting Defects (a) & (b)Sand blow: Balloon‑shapedgas cavity caused by releaseof mold gases during pouring

Pinholes: Formation of manysmall gas cavities at or slightlybelow surface of casting

Sand Casting Defects (c) & (d)Sand wash: irregularity in thesurface resulting from erosionof sand mold during pouring

Scabs: rough area on the surfacedue to encrustations of sand andmetal, due to mold surfaceflaking off during solidification

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Sand Casting Defects (e) & (f)Penetration: When fluidity of liquidmetal is high, it may penetrate intosand mold or core, causing castingsurface to consist of a mixture ofsand grains and metal

Mold shift: A step in castproduct at parting linecaused by sidewiserelative displacement ofcope and drag

Sand Casting Defects (g) & (h)Core shift: the core beingdisplaced from its intendedposition, usually vertical, causedby buoyancy of the molten metal

Mold crack: a crack developsdue to insufficient mold strengthwith molten seeping into themold to form a ‘fin’

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Other Expendable Mold Processes

• Shell Molding

• Vacuum Molding• Expanded Polystyrene Process• Investment Casting• Plaster Mold and Ceramic Mold Casting

Investment Casting (Lost Wax Process)A pattern made of wax is coated with a refractory

material to make mold, after which wax is meltedaway prior to pouring molten metal

• “Investment” comes from a less familiardefinition of “invest” – “to cover completely,”which refers to coating of refractory materialaround wax pattern

• It is a precision casting process - capable ofproducing castings of high accuracy and intricatedetail

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Investment Casting

Figure 11.8 (textbook) Steps in investment casting: (1)wax patterns are produced, (2) several patterns areattached to a sprue to form a pattern tree

Investment Casting (cont.)

Figure 11.8 (textbook) Steps in investment casting: (3) the patterntree is coated with a thin layer of refractory material, (4) the fullmold is formed by covering the coated tree with sufficientrefractory material to make it rigid

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Figure 11.8 (textbook) Steps in investment casting: (5) the mold is heldin an inverted position and heated to melt the wax and permit it to dripout of the cavity, (6) the mold is preheated to a high temperature, themolten metal is poured, and it solidifies


Figure 11.8 (textbook) Steps in investment casting: (7) the mold isbroken away from the finished casting and the parts are separated fromthe sprue

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Investment Casting

Figure 11.9 (textbook) A one‑piece compressor stator with108 separate airfoils made by investment casting (photocourtesy of Howmet Corp.).






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SME Video Clip

• Next, let’s watch the SMEvideo clip about Castingwhich came with the textbookfor classroom use ONLY…

EXTRUSION AND ANALYSIS OF PRESSUREDURING PROCESS


Extrusion Problem: In an direct extrusion process, pressure needs to be appliedto extrude a billet of lengthL0 = 75mm and diameterD0 = 25mm with an extrusion ratio ofrx = 4.0. The die angle isα = 90.The billet material has the following parameters for the plastic flow stress equation:K = 415MPa andn = 0.18. Use the Johnson’s formula witha = 0.8 andb = 1.5.

1. Determine the ram pressures needed for the extrusion process at the following lengths:

L = 75, 50, 25, 0mm

2. Based on the results in Part (1), plot the pressure-strokecurve. What is your conclusion about suchcurve?

Solution : Use the Johnson’s formula with

p = Yf ǫx (1)

whereǫx = a + b ln rx, with a = 0.8 andb = 1.5. Thus,

ǫ = ln rx = ln 4.0 = 1.3893

ǫx = 0.8 + 1.5(ln rx) = 2.8795

Yf =415(1.3863)0.18

(1 + 0.18)= 373MPa

1. Use the die angle ofα = 90, the billet material is to be forced through the die opening almostimmediately. The ram pressures are calculated in the following at the respective lengths.

At L = 75mm the ram pressure is

p = 373

[

2.8795 +2(75)

25

]

= 3312MPa (2)

where the additional pressure due to friction was added in the term2(75)/25.

Repeat the calculation forL = 50, 25, 0mm, we find

p = 373

[

2.8795 +2(50)

25

]

= 2566MPa

p = 373

[

2.8795 +2(25)

25

]

= 1820MPa

p = 373

[

2.8795 +2(0)

25

]

= 1074MPa

2. The ram stroke is(L0 − L). The pressure-stroke curve is plotted in Figure 1.

It is noted that the pressure required for the indirect extrusion is constant, as shown in Figure 1, and itis equal to the pressure of the direct extrusion at the end when L = 0mm.

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0 10 20 30 40 50 60 700

500

1000

1500

2000

2500

3000

Ram stroke (mm)

Ram

pre

ssur

e (M

Pa)

Direct extrusion in solid line; Indirect in dashed line

Figure 1: The pressure-stroke curves of direct and indirectextrusion processes are in solid and dashed lines,respectively.

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ME325/580 SME DVD Video: Forging

Spring 2010 I. Kao 1. Forgibility is valued in

• Excellent • Good • Fair • Poor or low

2. Forgibility depends on • Metal’s/alloy’s composition • Crystal structure • Mechanical properties

3. Materials rank high in forgibility • Aluminum alloys • Copper alloys • Magnesium alloys • Carbon steel • Low and high alloy steel • Nickel alloys • Titanium alloys

4. There are two primary types of forging • Open die forging • Impression die forging or close die forging

5. In open die forging, flat, V-shaped and semi-round dies are commonly used. Other auxiliary tools are also used • Saddles • Blocks • Mandrels • Punches

6. Handling used for various purposes of open forging • Work piece transfer • Manipulating during forging • Off-handing of finished forgings

7. Close-die forging performing may include • Edging • Blocking • Finish-forging

8. Lubricant serves for • Minimize friction • Minimize abrasion • Minimize heat loss • Enhance metal flow • Permits the release of forging from dies

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9. Related forging processes include • Seamless ring rolling • Hot die forging • Isothermal forging

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MEC 325/580 Handout: Geometric Dimensioning and Tolerancing

Spring 2010 I. Kao Geometric Dimensioning and Tolerancing (GD&T) is a language for communicating engineering design specifications. GD&T includes all the symbols, definitions, mathematical formulae, and application rules necessary to embody a variable engineering language. It conveys both the nominal dimensions (ideal geometry), and the tolerance for a part. It is now the predominant language used worldwide as well as the standard language approved by the American Society of Mechanical Engineers (ASME), the American National Standards Institute (ANSI), and the United States Department of Defense (DoD). GD&T is the language that designers should use to translate design requirements into measurable specifications. The following American National Standards define GD&T’s vocabulary and provide its grammatical rules.

• ASME Y14.5M-1994, Dimensioning and Tolerancing • ASME Y14.5.1M-1994, Mathematical Definition of Dimensioning and Tolerancing

Principles • ASME Y14.41-2003, Digital Product Definition Data Practices

These are often referred to as the “Y14.5” and “the Math Standards,” respectively.

Usage of GD&T and why do we use GD&T The following drawing is an example for the identification of hole location.

Figure 1: Drawing showing distance to ideal hole location

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A drawing which does not use GD&T (Figure 2) can be potentially misunderstood and fabricated incorrectly (see Figure 3 for the illustration).

Figure 2: Drawing that does not use GD&T

Figure 3: Manufactured part that conforms to the drawing without GD&T in Figure 2

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GD&T provides unique, unambiguous meaning for each control, precluding each person’s having his own competing interpretation. GD&T is simply a means of controlling surfaces more precisely and unambiguously. See Figure 4 for an illustration.

Figure 4: Drawing that uses GD&T with unique and unambiguous interpretation

More information and a list of symbols of GD&T can be found in the reference [1].

ASME Y14.41-2003 Standard for CAD ASME Y14.41-2003 standard is an extension of the Y14.5 standard for 2-dimensional drawings to 3D computer-aided design (CAD) environments. The standard also provides a guide for CAD software developers working on improved modeling and annotation practices for the engineering community. ASME Y14.41 sets forth the requirements for tolerances, dimensional data, and other annotations, and advances the capabilities of Y14.5. Y14.41 defines the exceptions as well as additional requirements to existing ASME standards for using product definition data or drawings in 3-D digital format. [2] The standard is separated into 3 industrial practices: (i) Models Only: These portions cover the practices, requirements, and interpretation of the CAD data when there is no engineering drawing. While ASME Y14.41-2003 is commonly called the “solid model standard,” this is misleading. The standard was intentionally written for different user levels; (ii) Models and Drawing: These portions cover what is commonly called “reduced content drawings” or

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“minimally dimensioned drawings,” where an engineering drawing is available, but does not contain all the necessary information for producing the part or assembly; (iii) Drawings only: These portions of the standard allow the historical practices of using engineering drawings to define a product. However, this standard adds to the practices defined in ASME Y14.5 for Geometric Dimensioning and Tolerancing with some additional symbols, the use of axinometric views as dimensionable views, and the concept of supplemental geometry–all of which can help to clarify the drawing and its interpretation. [3]

Part of the materials in this handout have been taken from the following reference. Reference:

[1] Walter M. Stites and Paul Drake, Jr., “Dimensioning and Tolerancing Handbook,” Editor Paul J. Drake, Jr., Ch. 5, McGraw-Hill, 1999

[2] ASME Y14.41-2003 Standard on Digital Product Definition Data Practices, ISBN: 0791828107, 2003

[3] Wikipedia, http://en.wikipedia.org/wiki/ASME_Y14.41-2003

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MEC325/580 Handout: Introduction of Rapid Prototyping Spring 2010 I. Kao 1. What is Rapid Prototyping? The idea behind Rapid Prototyping (RP) is to have a machine or machines that can create a desired solid model directly from a computer-aided design (CAD) file without any human intervention. A 3-D model is decomposed into multiple 2-dimensional layers with the use of computer software, and a machine will then manufacture the model one layer at a time. When the layers are sequentially stacked up and connected, a 3D model will emerge at the end of the fabrication process.

Since its development in the mid 1980’s numerous Rapid Prototyping1 methods have been devised. One of the first machine that was devised to fabricate rapid prototypes was the stereo lithography which used laser to solidify 2D features of a solid model layer by layer in a polymer liquid bath. Many other methods have since come out. Some of the more common methods include:

• Stereo Lithography (SLA) • Selective Laser Sintering (SLS) • Laminated Object Modeling (LOM) • Fused Deposition Modeling (FDM)

The RP technique was initially designed to make prototypes quickly for the designers to

evaluate the design and to revise as needed. Owing to the typically high cost of making prototypes and discarding them after initial evaluation to render the final design, the RP methods feature the advantages of short time to fabricate and low cost for prototyping. Since then, some machines, especially those use the laser sintering approach, have been revised and designed to include metal powder metallurgy with bonder (e.g., resin) and baking process to cure metal solids with near shape and strength. Nevertheless, this type of efforts still cannot replace the conventional process of machining. From its inception, the RP technique was not meant to replace the conventional manufacturing, and it appears that it will not in the foreseeable future.

In many cases where actual parts are required for design consideration, RP is better than the “virtual” prototyping in which computer is used to view and manipulate solids from different angles to simulate the design. For example, in the design of ink refilling of an ink-jet printer cartridge in which the cartridge was decapitated and replaced by a new polymer cap, after replacing the sponges and inks inside the ink compartments, through ultrasonic welding process. The physical prototype of the cap design is crucial and needed to actually mesh with the ink cartridge for the inspection of the statistical range of the parameters of cartridges. A virtual prototype, no matter how sophisticated it may be, just will not do.

In the following, we briefly explain each of the methods for rapid prototyping.

1 In a broader context, sometimes the “free-form machining” (FFM) is used to refer to these types of forming processes, distinct from the conventional machining or forming processes.

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1.1 Stereo Lithography (SLA) The stereo lithography (SLA or STL) process is based on the principle of curing or hardening a liquid photo polymer into a specific shape. A laser is used to focus on spot-curing the polymer, providing the necessary energy to polymerization. Based on the Beer-Lambert law, the exposure decreases exponentially with depth according to the rule

€

E(z) = E0−z /Dp (1)

where E is the exposure in energy per area, E0 is the exposure at the resin surface (z=0), and Dp is the “penetration depth” at the laser wavelength and is a property of the resin. At the surface depth, the polymer is sufficiently exposed for it to gel, or

€

Ec = E0−Cd /Dp (2)

where Ec is the critical threshold exposure and Cd is the cure depth. Thus, the cure depth is given by the following equation

€

Cd = DpE0

Ec

⎛

⎝ ⎜

⎞

⎠ ⎟ (3)

The cure depth represents the thickness in which the resin has polymerized into a gel, but it does not have high strength at this state. Thus, the controlling software will slightly overlaps the cured volumes, but curing under fluorescent lamps is often necessary as a finishing operation.

Stereo lithography has a vat container with a platform on which the part to be fabricated can be raised or lowered vertically. This vat is filled with a photo-curable liquid acrylate polymer, a mixture of acrylic monomers, oligomers (polymer intermediates), and a phtoinitiator. A laser, generating an ultraviolet beam, is then focused along a selected surface area of photopolymer at surface to lay out the required feature. As these 2D features are laid, the platform is lowered to expose a fresh layer of liquid ready for the next layer of 2D features. Successive operations will render the final 3D solid.

Depending on the capacity of the machine, the cost ranges from $100,000 to $500,000, with cost of liquid polymer at $300 per gallon. The fume released by the liquid polymer during the fabrication process needs to be vented out for health consideration. One major area of application for stereo lithography is in the making of molds and dies for casting and injection molding.

1.2 Selective Laser Sintering (SLS) Selective laser sintering is a process based on the sintering of polymer and metallic powders selectively into an individual object. Two cylinders are used in the process chamber: (i) part-build cylinder which is lowered incrementally to where the sintered part is formed, and (ii) powder-feed cylinder which is raised incrementally to supply powder to the part-build cylinder through a roller mechanism. A thin layer is first deposited in the part-build cylinder. A laser beam, guided by the process-control computer is then focused on that layer, tracing and melting (or for metal, sintering) a particular cross-section, which then quickly solidifies into a solid mass. This is repeated for layers after layers of 2D slices of features of the solid. At the end, the loose particles are shaken off and the part recovered.

Typical cost of a SLS machine is about $500,000.

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1.3 Laminated Object Modeling (LOM) Lamination implies a laying down of layers that are adhesively bonded to one another. Laminated Object Modeling (LOM) uses layers of paper or plastic sheets with glue on one side to produce parts sheet by sheet. The adhesion process can be done by laser beam through heating, or simply by gluing. The excess materials are removed manually. LOM usually uses materials of thickness about 0.5 mm (0.02 in.) although materials as thin as 0.05mm (0.002 in.) have been used.

One example of such system is the SilverScreen+ JP 5 system which uses back-glue papers and a cutter on a printer setup to cut (or print onto) the papers into series of 2D features, to be glued together to make 3D solids. This type of systems can be very inexpensive.

1.4 Fused Deposition Modeling (FDM) In a Fused Deposition Modeling (FDM) process, a platform is used to move in the vertical (Z) direction to raise or lower the part to be made, and a nozzle assembly with both model and support materials controlled by a XY table is used to trace and lay out molten polymer filament through nozzles to make solid parts layer by layer. The support material is constructed as part of the slicing algorithm to ensure that overhanging features of the solid part is supported throughout the fabrication process. More details will follow in the next section.

2. Rapid Prototyping Using the FDM 3000 2.1 What is FDM? The FDM rapid prototyping machines use the Fused Deposition Modeling (FDM) method to create prototypes. Fused Deposition Modeling is a process whereby the layers of the model are created by forcing a special material filament through a heating system, causing the material to melt into a smooth hot molten paste, which is then forced through a delivery nozzle, and emerges as a thin ribbon of hot paste. The nozzle is guided along the XY plane, depositing the ribbon at desired positions to form a layer. After completing one layer, the entire model is lowered. The machine will then deposit another layer on top of the previous one.

Fused Deposition Modeling uses two different materials to manufacture a model; the first material is called the model material, and is what the final model will consist of, the second material is called the support material, this material is laid underneath any overhanging parts of the model so that the model will not collapse during fabrication. The temperature of the P-400 set includes P-400 ABS model material (Tm=270ºF) and P-400 water-soluble support material (Tm=235ºF) under an envelop temperature of 70ºF.

Each material is delivered through its own nozzle, which are both mounted on the underside of the of the FDM head. Apart from two nozzles, the head contains two heating elements, two thermocouples, two motors and one solenoid actuator. The two motors force the two materials into the two heating elements, and then through the delivery nozzles. The solenoid actuator lowers the support nozzle below the level of the model nozzle every time support material is needed.

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2.1.1 Motion, the Head and the Z-table The head can only move in the XY-plain. To accomplish this, the head is mounted on sliders for motion in the X-direction, while the sliders are mounted on rollers for motion in the Y-direction. Both X and Y motions are cable-driven.

Vertical or Z-directional motion is accomplished with the use of the z-table. The model is build directly onto the sponge insert in the z-table, thus when the z-table is lowered so will the model. The z-table is moved with the use of 4 lead screws.

2.1.2 Materials A range of plastics and waxes can be used to create models. Different materials display different physical properties, with each material having its own melting and envelope temperatures. The envelope temperature is the temperature of the air inside the FDM, and is set to the optimal solidification temperature of the materials. As a result of the required envelope temperature for a specific material, all model and support materials come as a couple and should not be mixed.

One particularly interesting model-support combination is that of the P400 ABS model and P400 water-soluble support. The P400 support material can be removed by means of submerging the finished part in an ultrasonic bath consisting of a heated-water-chemical solution. The ultrasound breaks down the support and dissolves it away until only the model remains. This enable very complicated models to be created, models that could not be created by conventional machinery.

2.1.3 Nozzles (Tips) The nozzles come in three different combinations pairs. They are classified according to the diameter of the outlet opening and are as follows, 0.010", 0.012" and 0.016". All the nozzles are coded with the use of rings around their lower surface. The codes can be found in the user manuals.

2.2 Steps Required to Create a Prototype on FDM 3000 The block diagram below shows the basic steps required to create a prototype.

Solid Modeling (I-DEAS or others)

• Create a Solid Model

InsightV34 • Position & Scale STL • Slice STL File • Add Support and Base • Edit Curves • Create Roads

FDM 3000 • Fabricate Model

SSL File

SML File

Model

STL File

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2.2.1 Computer Aided Design and the STL file First of all, a solid model of the prototype must be designed using any solid modeling package such as I-DEAS or AutoCAD or ProEngineer. Once this model is complete, it must undergo a process known as tessellation in order to become an STL file (STereoLithography File). Tessellation is an approximation of the solid model surface; it is accomplished by breaking the surface of the solid model into hundreds of small, interconnected triangles, each with a normal vector pointing outward from the solid. Most solid modeling software will automatically create an STL file if prompted by the user.

Note: Step by step instructions on how to create an STL file using I-DEAS can be found in the User Manual. 2.2.2 Procedures to fabricate the rapid prototype with your STL file Note: You are expected to do this part with the assistance of a staff or TA. You should NOT attempt the following procedures alone!

(a) Start the FDM3000 machine. Check if the temperatures of the Model and Support are set correct. Incase they are not, then wait till they reach the required temperature.

(b) In the selection display on the machine, select Model and try to load the model. Confirm that the Model is flowing smooth. Similarly confirm that the support is also flowing smooth.

(c) On the PC: Go to ‘Start’, then go to ‘Programs’ and then run the ‘InsightV34’ and select Insight.

(d) Go to ‘File’ menu option. Select ‘Open’ and select ‘STL’ option and open your STL file. You would see your model on the screen.

(e) Now go to ‘Orient STL’ option in the software menu. Then rotate the model so that you obtain the orientation in which you want to make the model. Select the orientation such that the support needed is minimum.

(f) Click (Slice icon). (g) Click (Support icon). (h) Click (Toolpath icon). (i) Click (Build icon). (j) Click Build icon one more time.

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(k) Next, on the FDM machine press the pause button so that the pause light will start blinking and the door will open. Now you can set the nozzle position at appropriate place so that your part is made on desired location on the supporting plate. You can set the X and Y positions it by pressing the appropriate buttons on the panel of the FDM machine. You can also set Z by first selected Z axis button. Set Z such that the model nozzle just touches the surface of the fixture plate.

(l) After setting the nozzle at appropriate position close the door of the machine and press the pause button. The door will get locked and the machine will start making the model.

(m) Wait near the machine till it finished making the part. (n) After the solid model is made, the door would get unlocked. Then open the door and

remove the model from the machine very carefully. Using the ultrasonic water bath and appropriate tools to remove the support material from the prototype. Apply proper post-fabrication processes, if necessary, such as polishing the model by sand paper or painting.

(o) Don’t forget to turn off the machine after you have finished your work. (p) Ask the TA to inspect and sign you off.

2.2.3 FDM 3000 The SML file can now be inputted into the FDM 3000. The FDM 3000 will follow the Roads created during the generation of the SML file.

Although a large part of the fabrication is autonomous, the FDM sill requires an operator, especially during the first layers of a model. Furthermore, the FDM 3000 requires constant maintenance and cleaning. Due to the nature of Fused Deposition Modeling, the nozzles, head and envelope of the FDM require thorough cleaning after every model. Calibration and general lubrication are also commonly required.

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ME325/580 SME Video: Turning & Lathe Basics

Spring 2010 I. Kao Turning is an operation where the work rotates with tool feeding. The size and work capacity are determined by:

• Swing • Distance between centers

I. The Engine Lathe – requires means to (1) hold and rotating the workpiece, and (2) hold and

move the cutting tool • Spindle, headstock • Speed & feed controls • Engine lathe workholding • Chucks • Collets • Between centers turning • Carriage, “Z” axis • Cross slide, “X” axis • Compound rest • Tool post • Tailstock

II. Lathe Operations External turning operations: • Straight turning • Taper turning • Contour turning • Forming • Chamfering • Grooving • Thread chasing • Facing Holemaking includes holemaking and hole finishing operations: • Holemaking • Reaming • Boring • Tapping Separating or cutting operations: • Parting off – or called cut-off • Picking off

2

III. Lathe Types • Engine Lathe • Electronic engine lathe • NC lathe • 2 axis, single turret CNC lathe – CNC lathe can achieve accurate and identical parts

except for tool wear and materials discrepancy • 2 turret, 4 axis CNC lathe • Turn mill CNC turning machine • Subspindle CNC lathe • Twin opposed CNC lathe • Automatic screw machine • CNC swiss type automatic lathe • Vertical turret lathe (VTL)

IV. Workholding in Turning

• Bar stock loader • Hand loading • Between centers workholding • Workholding for castings • Gantry loading systems

V. Tool Arrangement

• Turrets – typically holds 6-14 tools • Gang tooling – e.g., 4-10 tools in a slide

VI. Operating Parameters and Process Variables

• Cutting speed – the speed at which the surface of the work moves past the cutting tool; the speed changes as the tool moves (in or mm / min)

• Feed rate – the speed at which tool advances into the part longitudinally (in or mm / rev) • Depth of cut – the thickness of material removed from work surface

VII. Factors Affecting Process Variables • Machinability of work materials • Materials and geometry of cutting tool • The angle at which the cutting tool enters the work • The type of operation • The horsepower and conditions of the lathe All of which should be used for selecting the turning speed and feed.


Chapter 20

Sheet Metalworking

Part V: Metal Forming and Sheet Metal Working

Groover “Manufacturing Processes”



SHEET METALWORKING

!  Three Basic Processes 1.  Cutting Operations 2.  Bending Operations 3.  Drawing

!  Other Sheet Metal Forming Operations 1.  Dies and Presses for Sheet Metal Processes 2.  Sheet Metal Operations Not Performed on Presses 3.  Bending of Tube Stock


Sheet Metalworking Defined

Cutting and forming operations performed on relatively thin sheets of metal

!  Thickness of sheet metal = 0.4 mm (1/64 in) to 6 mm (1/4 in)

!  Thickness of plate stock > 6 mm !  Operations usually performed as cold working


Sheet and Plate Metal Products

!  Sheet and plate metal parts for consumer and industrial products such as !  Automobiles and trucks !  Airplanes !  Railway cars and locomotives !  Farm and construction equipment !  Small and large appliances !  Office furniture !  Computers and office equipment


Sheet Metalworking Terminology

!  Punch and die – tooling to perform cutting, bending, and drawing

!  Stamping press – machine tool that performs most sheet metal operations

!  Stampings – sheet metal products


Three Basic Types of Sheet Metal Processes

1.  Cutting !  Shearing to separate large sheets !  Blanking to cut part perimeters out of sheet metal !  Punching to make holes in sheet metal

2.  Bending !  Straining sheet around a straight axis

3.  Drawing !  Forming of sheet into convex or concave shapes


(1) Just before punch contacts work; (2) punch pushes into work, causing plastic deformation; (3) punch penetrates into work causing a smooth cut surface; and (4) fracture is initiated at opposing cutting edges to separate the sheet

Sheet Metal Cutting

Characteristics of Sheared Edge



Blanking and Punching

!  Blanking (a) - sheet metal cutting to separate piece (called a blank) from surrounding stock

!  Punching (b) - similar to blanking except cut piece is scrap, called a slug


Clearance in Sheet Metal Cutting

Distance between punch cutting edge and die cutting edge

!  Typical values range between 4% and 8% of stock thickness !  If too small, fracture lines pass each other,

causing double burnishing and larger force !  If too large, metal is pinched between cutting

edges and excessive burr results


Clearance in Sheet Metal Cutting

!  Recommended clearance is calculated by: c = at where c = clearance; a = allowance; and t = stock thickness

!  Allowance a is determined according to type of metal


Sheet Metal Groups Allowances

Metal group a 1100S and 5052S aluminum alloys, all tempers

0.045

2024ST and 6061ST aluminum alloys; brass, soft cold rolled steel, soft stainless steel

0.060

Cold rolled steel, half hard; stainless steel, half hard and full hard

0.075


Punch and Die Sizes

!  For a round blank of diameter Db: !  Blanking punch diameter = Db 2c !  Blanking die diameter = Db where c = clearance

!  For a round hole of diameter Dh: !  Hole punch diameter = Dh !  Hole die diameter = Dh + 2c where c = clearance


!  Die size determines blank size Db

!  Punch size determines hole size Dh

!  c = clearance

Punch and Die Sizes


!  Purpose: allows slug or blank to drop through die !  Typical values: 0.25° to 1.5° on each side

Angular Clearance


Cutting Forces

!  Important for determining press size (tonnage) F = S t L = (0.7) Sut t L

where S = shear strength of metal; Sut = ultimate tensile strength of metal; t = stock thickness, and L = length of cut edge

Example of Cutting

Problem: A sheet metal under cutting process has the following parameters: hole=1”-dia; thickness=!”; Sut=140,000 psi. Estimate the force required for cutting.

!  Solution: Fmax= (0.7)(140,000)(!) (" "1) = 38,500 lb = 19.25 tons = 170,000 Newtons




(a) Straining of sheet metal around a straight axis to take a permanent bend

(b) Metal on inside of neutral plane is compressed, while metal on outside of neutral plane is stretched

Sheet Metal Bending


Types of Sheet Metal Bending

!  V bending - performed with a V shaped die !  Edge bending - performed with a wiping die


(1) Before bending (2) After bending !  Application notes:

!  Low production !  Performed on a

press brake !  V-dies are simple

and inexpensive

V-Bending


(1) Before bending (2) After bending !  Application notes:

!  High production !  Pressure pad

required !  Dies are more

complicated and costly

Edge Bending


Stretching during Bending

!  If bend radius is small relative to stock thickness, metal tends to stretch during bending

!  Important to estimate amount of stretching, so final part length = specified dimension

!  Problem: to determine the length of neutral axis of the part before bending


Bend Allowance Formula

where Ab = bend allowance; ! = bend angle; R= bend radius; t = stock thickness; and Kba is factor to estimate stretching

!  If R < 2t, Kba = 0.33 !  If R ! 2t, Kba = 0.50

Handout & Example

!  (See Handout) !  Equations and example to calculate

!  the Bend Allowance !  the Bending Force !  the Springback




Drawing

Sheet metal forming to make cup shaped, box shaped, or other complex curved, hollow shaped parts

!  Sheet metal blank is positioned over die cavity and then punch pushes metal into opening

!  Products: beverage cans, ammunition shells, automobile body panels

!  Also known as deep drawing (to distinguish it from wire and bar drawing)

Deep Drawing of a Soda Can

!  (See the Soda Can Manufacture PPT)



Shapes other than Cylindrical Cups

!  Each of the following shapes presents its own unique technical problems in drawing !  Square or rectangular boxes (as in sinks) !  Stepped cups !  Cones !  Cups with spherical rather than flat bases !  Irregular curved forms (as in automobile body

panels)


Other Sheet Metal Forming on Presses

!  Other sheet metal forming operations performed on conventional presses can be classified as !  Operations performed with metal tooling !  Operations performed with flexible rubber tooling


Ironing

!  Achieves thinning and elongation of wall in a drawn cup: (1) start of process; (2) during process


!  Creates indentations in sheet, such as raised (or indented) lettering or strengthening ribs

!  (a) Punch and die configuration during pressing; (b) finished part with embossed ribs

Embossing


(1) before and (2) after

Guerin Process

Tools for the Sheet Metalworking Processes



!  Components of a punch and die for a blanking operation

Punch and Die Components


!  Components of a typical mechanical drive stamping press

Stamping Press


Gap Frame Press

!  Gap frame press for sheet metalworking (photo courtesy of E. W. Bliss Co.)

!  Capacity = 1350 kN (150 tons)


Press Brake

!  Press brake (photo courtesy of Niagara Machine & Tool Works)

!  Bed width = 9.15 m (30 ft)

!  Capacity = 11,200 kN (1250 tons)


CNC Turret Press

!  Computer numerical control turret press (photo courtesy of Strippet, Inc.)


CNC Turret Press Parts

!  Sheet metal parts produced on a turret press, showing variety of hole shapes possible (photo courtesy of Strippet Inc.)


Straight-Sided Frame Press

!  Straight sided frame press (photo courtesy of Greenerd Press & Machine Company, Inc.)


Power and Drive Systems

!  Hydraulic presses - use a large piston and cylinder to drive the ram !  Longer ram stroke than mechanical types !  Suited to deep drawing !  Slower than mechanical drives

!  Mechanical presses – convert rotation of motor to linear motion of ram !  High forces at bottom of stroke !  Suited to blanking and punching


Operations Not Performed on Presses

!  Stretch forming !  Roll bending and forming !  Spinning !  High energy rate forming processes

MEC580: HANDOUT ON THE LEAST-SQUARES BEST FIT ALGORITHM

MEC580 Spring 2010 I. Kao

1 Introduction

In engineering applications, experiments are often conducted with multiple sets of data points for best curvefitting. If the case when the governing equation between the two parameters is linear, the “linear regression”algorithm can be applied. However, such linear regression method can not be applied directly if the equationis in a power equation form, such as that in the Taylor’s equation for tool wear:

v T n = C (1)

Equation (1) is a standard nonlinear power equation. In the case of equation presented in equation (1), wecan take logarithmic relationship of the variables and makea linear equation in the log-log coordinates, asexpressed in the following equation

log v + n log T = log C (2)

Equation (2) represents a line in the(log T, log v) space.In the next section, a standard technique for determining the least-squares best fit solution is presented

as a matrix solution.

2 Algorithm of the Weighted Least-Squares Fit for Power Equations

Equation (2) is a result of taking logarithmic form of equation (1). It can be re-arranged in the followingform

log v = log C + ζ log T (3)

whereζ = −n.With a total ofi data sets of(v, T ) from experiments, we can re-arrange equation (3) in the following

matrix form for least-squares fity = Ax (4)

where

y =

log v1

log v2

...log vi

A =

1 log T1

1 log T2

......

1 log Ti

x =

[

log C

ζ

]

(5)

The least-squares solution ofx in equation (4) can be obtained using the Penrose-Moore generalized inversethat minimizes the norm of errors iny [3]. That is,

x = A∗ y (6)

where the superscript ‘*’ denotes the generalized inverse.The left inverse is used in equation (6);i.e.,A∗ = (ATA)−1AT .

Equation (6) minimizes the norm of the squared errors iny = log v instead ofv. In order to compensatefor such discrepancy, we utilize a weighted least-squares fit of the following form

x = (WA)∗ Wy (7)

where the weighting matrix isW = diag[ey1 . . . eyi ] = diag[v1 . . . vi] that corrects the logarithmic scaleof the norm of squared errors to be minimized.

The equation and derivation presented in this section can also be found in references [1, 2].

1

3 Example: Experimental Results and Curve Fitting

An example is used in this section to illustrate the application of the LS fit equations in (6) and (7). We willuse relationship between the tool speed and tool life, as characterized in the Taylor’s equation in (1). Theexperimental results are tabulated in the following:

exp data velocity,v tool life, T

set 1 400m/min 100min



When the three data sets are used to find the LS solution of the exponent,n, and constant,C, we canobtain the following terms based on the experimental data and equations (6) and (7). We have

A =

1 2.0000

1 2.3802

1 2.9138

y =

2.6021

2.4771

2.3010

W =

400.0 0 0

0 300.0 0

0 0 200.0

(8)

The generalized inverse ofA andWA are

A∗ =

[

2.8217 0.6283 −2.4500

−1.0235 −0.1213 1.1448

]

(WA)∗ =

[

8.8962 −2.1113 −9.6255

−3.3497 1.4018 4.5967

]

× 10−3 (9)

Substituting into equations (6) and (7), respectively, we obtain

without weighting: n = 0.3295;C = 1824.3 (10)

with weighting: n = 0.3293;C = 1822.7 (11)

It is noted that equations (10) and (11) differ only slightly. Thus, either solution is acceptable. We will adopt

v (T )0.3293 = 1823 (12)

wherev has a unit ofm/min andT is in minutes.If a fourth data set was added via experiments with

exp data velocity,v tool life, T




set 4 50m/min 54, 000min

Employing the same procedures above, by including the additional data, we obtain:

without weighting: n = 0.3306;C = 1836.1 (13)

with weighting: n = 0.3298;C = 1827.0 (14)

It is noted that the solution in equation (14) with the weighting matrix renders a result that is more consistentwith those in equations (10) and (11). This is because the addition of the weighting matrix will restore thescales ofv andT in the LS fitting, instead of using the logarithmic scales oflog v andlog T .

The results of equation (14) are plotted in Figure 1, to compare with the raw data points in a log-logplot.

2

100

101

102

103

104

105

101

102

103

104

Figure 1: Comparison between the raw data (indicated by ’o’)and the results of the weighted least-squaresbest fit using the power equation (1) and LS fit equation (7).

References

[1] N. Xydas and I. Kao, “Modeling of contact mechanics and friction limit surface for soft fingers withexperimental results,”International Journal of Robotic Research, vol. 18, no. 9, pp. 941–950, September1999.

[2] I. Kao and F. Yang,Stiffness and Contact Mechanics for Soft Fingers in Grasping and Manipulation toappear on the IEEE Transactions of Robotics and Automation, 2004

[3] G. Strang,Linear Algebra and Its Applications, Academic Press, 2nd edition, 1980.

3

Manufacturing Frontiers

National Science Foundation Directorate for Engineering

Adnan Akay

Manufacturing Contribution to US GDP

Source: National Association of Manufacturers, U.S. Department of Commerce

Manufacturing Contribution to US GDP and Employment

Data Source: US Dept of Labor, NAM GDP calculations using 1982 constant-weighted price index

Issues & Drivers

!  Competition – emerging economies !  Enabling technologies !  Environment, sustainability, resource issues !  Socio-economics !  Regulations

EU Manufuture!

Response

!  New products and service with high added values

!  New business models !  Emerging manufacturing sciences and

engineering

EU Manufuture!

Manufacturing Research: Example Directions

!  Improving decision making (tolerancing, fixturing, tool path optimization)

!  New processes (nanomanufacturing, lithography, solid freeform fabrication)

!  Metrology and process monitoring (nanometrology)

!  Predictive modeling (incorporation of uncertainty)

(J. Lee-Ohio State U)! (S. Girshik-U. Minnesota)!

(P.Gouma-SUNY SB)!

Challenge: Manufacturing Across Scales

Manufacturing Miniaturization Trends

Macro!Meso!Micro!!Nano-Manufacturing!

Manufacturing Automation

Imin Kao Professor Department of Mechanical Engineering SUNY at Stony Brook

Manufacturing Automation •  Manufacturing Automation

– Fixed automation – Flexible automation – Agile automation – …

•  Societal Impacts –  (name impacts …; See the next page)

•  Positioning System & Accuracy –  (See Handout)

Impacts of Automation •  Increased production rate •  Reduction of labor (economic impact on

society) •  Societal impact on labor force •  Technological innovation •  Precision & repeatability in production •  Hostile/hazardous environment •  24-hour operation •  …

Concurrent Engineering •  Concurrent Engineering

– History & perspectives – What is it? – Famous case studies

•  Design for X – Design for assembly – Design for manufacturing/manufacturability – Design for XXX

CE vs. Traditional Prod. Dev. (a) Traditional product development

(b) Product development using Concurrent Engineering

Programmable Automation Systems •  Numerical control (NC) and CNC

– Presented earlier …

•  Industrial robots – History – Kinematics – Robotic programming language (RPL) – Workspace or work envelope

•  Programmable login control (PLC) – Automation on manufacturing floors

Introduction to Robotics •  “Robot” – history and origin

–  1920 by Czech author K. !apek in his play R.U.R. (Rossum’s Universal robots); from Czech word “robota” meaning “worker”

– Webster Dictionary: “An automated apparatus or device that performs functions ordinarily ascribed to humans or operates with what appears to be almost human intelligence”

Robots: Fiction or Reality? •  Ahead of Its Time?

– Star Wars: C3-PO like humanoid? – The six-million dollar man?

•  Today – AIBO pet robot (a dog which can learn) – HONDA’s ASIMO humanoid robot

•  Speed: 2 km/h; hand load: 2~5kg/hand; weight: 130~210 kg; height: 160~182 cm

– Others

Robotics Research Today Robotics Research Today:

1.  Where are we now? 2.  Where is the robotics research heading

to? 3.  Different fields of robotics research

Classification of Robots •  By Coordinate System

1.  Cylindrical coordinate robots 2.  Spherical coordinate robots 3.  Jointed arm (articulated) robots 4.  Cartesian coordinate robots

•  By Mechanism Types 1.  Revolute 2.  Prismatic

Kinematics of a 2-link robot arm •  A 2-link SCARA (Selectively Compliant

Arm for Robotic Assembly) – Kinematics: forward and inverse kinematics –  Joint space and tool (Cartesian) space – Workspace consideration

(see handout: 2-link-robot.pdf )

Workspace of a SCARA Robot

Workspace Synthesis

Robot Programming Language •  Robot Programming Language (RPL)

– High-level macro language to control motions of a robot

•  Examples: – Adept: V++ –  IBM: AML (A manufacturing language) – RobotWorld: RAIL – …

RPL Example PL1:NEW 0; -- PAYLOAD SET TO DEFAULT PL2:NEW 15; -- PAYLOAD SET TO 50% LIN1:NEW 0; -- LINEAR OFF LIN2:NEW 20; -- LINEAR(20)

PT1:NEW PT(-132.95,490.45,0,-27); -- COORDINATE PT2:NEW PT(-161.55,521.20,0,-27); -- POSITIONS PT3:NEW PT(-187.05,553.90,0,-27); -- FOR PT4:NEW PT(-214.95,583.80,0,-27); -- POINTS PT5:NEW PT(-457.50,201.15,0,-27); -- 1 THROUGH 8 PT6:NEW PT(-483.85,236.10,0,-27); PT7:NEW PT(-512.70,264.50,0,-27); PT8:NEW PT(-541.35,297.75,0,-27); HOME:NEW PT(650,0,0,0); -- HOME POSITION

HGT1:NEW 0; HGT2:NEW -90; HGT3:NEW -184.0;

MAIN:SUBR; -- MANUFACTURING SUBROUTINE

FASTSPEED:SUBR; -- DEFAULT SPEEDS & LINEAR OFF

LINEAR(LIN1); PAYLOAD(PL1); END; -- END FASTSPEED SUBROUTINE

SLOWSPEED:SUBR; -- Z DOWN & SLOW SPEED ZMOVE(HGT2); PAYLOAD(PL2); ZMOVE(HGT3); END; -- END SLOWSPEED SUBROUTINE

PICKUP:SUBR; -- GRASP, Z UP & LINEAR ON GRASP; DELAY(1.0); ZMOVE(HGT2); PAYLOAD(PL1); ZMOVE(HGT1); LINEAR(LIN2); END; -- END PICKUP SUBROUTINE

DROPOFF:SUBR; -- RELEASE & Z UP RELEASE; DELAY(1.0); ZMOVE(HGT2); PAYLOAD(PL1); ZMOVE(HGT1); END; -- END DROPOFF SUBROUTINE

RPL Example (cont.) FASTSPEED; -- MOVES FROM POSITION 1 TO 5 PMOVE(PT1); SLOWSPEED; PICKUP; PMOVE(PT5); SLOWSPEED; DROPOFF;

FASTSPEED; -- MOVES FROM POSITION 2 TO 6 PMOVE(PT2); SLOWSPEED; PICKUP; PMOVE(PT6); SLOWSPEED; DROPOFF; …

1

ME325/580 SME Video: Milling & Machining Center

Spring 2010 I. Kao Milling is a highly versatile machining process that uses the relative motion between the rotating multiple edge cutters and the workpiece to generate flat and curved surfaces. It is an interrupted cutting process. The capabilities of a milling machine or machining center are measured by:

• Motor horsepower • Maximum spindle speed • Spindle taper size • Work table capacity • Travel capacity

I. The Knee Mill – for tool making, prototyping, low-volume production

• Knee & column • Vertical traverse crank • Saddle, cross traverse handle • Table, table traverse handle • Ram • Milling head • Quill, spindle, quill feed hand lever – quill is non-rotating; spindle rotates • Knee mill toolholding • Knee mill workholding • Power feed controls • Digital readouts • CNC knee mill

II. The Machining Center 1. Advantages of CNC over manual milling

• Consistency • Repeatability • Fast • Simulation can be used to verify the tool path before actual cut

2. Tool changing in machining centers • Most machining centers have 20 ~ 40 tools installed

3. The vertical machining centers (VMC) • Spindle in vertical position • Usually the work is done on single surface • 4-axis: x (table direction), y (in and out), z (vertical), and B axis (rotation)

4. The horizontal machining centers (HMC) • Spindle in horizontal orientation • Preferred in machining heavy boxy parts • 4-axis: x (table movement), y (head up and down), z (in and out), and B axis (rotation)

2

5. The universal machining centers (UMC)

• Spindle can tilt, swivel, assume horizontal and vertical orientations – in a compound angles

• Preferred in machining heavy boxy parts • 4-axis: x (table movement), y (head up and down), z (in and out), and B axis (rotation)

III. Milling Cutters and Operations – rotary tool with multiple cutting tools

1. Flat surface and square shoulders • Face milling – tool can be 3” to 2’ in diameter • Square shoulder milling

2. Edges, shoulders and grooves • Edges – one or two surfaces, or called edging • Shoulders – usually two surfaces • Grooves – closed at one end or open at both ends • Peripheral cutters – for long cutting or slots • End milling • Grooving cutters • Chamfering

3. Pockets and contours • Pocket milling • Contour milling – for die or mold making

IV. Workholding in CNC Milling

• T-slots – on the CNC table • Tombstones • Multi-vises

V. Workchanging

• Manual workchanging • Multiple fixturing on long bed • Pallet changer • Touch trigger probe – probes are stored in the tool magazine, used to inspect the part

before it is removed to ensure the dimension is right • Tool presetting

VI. Operating Parameters

• Cutting speed – speed at which the tool edge enters the cut, range 40-1000 surface/min • Feed rate – linear distance the tool travels in one cutter revolution; note it is different

from the table speed • Axial depth of cut – distance the tool is set under the uncut surface

3

• Radial depth of cut – distance of work surface engaged by the tool, the width of work surface involved. For steel 1 H.P. of power can remove 1 in3/min; for aluminum 4 in3/min.

VII. Horsepower factors and operating parameters

Power required for operations varies with the following parameters: • Amount of material removed • Chip thickness • Cutter geometry • Workpiece materials • Speed


Taguchi Methods!

Taguchi Methods Lecture (I)

•  “Taguchi Methods” refer to a collection of – Non-dynamic methods in product

design – Dynamic method – Newest: Mohalanobis-Taguchi

method

Taguchi Methods!

Taguchi Methods Lecture (II)

•  Non-Dynamic Taguchi Method (Handouts on bboard)!– ASME magazine: vol. 14, no. 8, December 1994!

– His visit to ASME after the one-day workshop at Stony Brook!

–  Introduction & parameter design!– Orthogonal arrays!– Case study 1: canon example!– Case study 2: RL circuit design!

– With Excel spreadsheet for calculation!– Handout for further details!

Taguchi Methods Myth? Or Good Engineering?


SUNY at Stony Brook!Phone: 631-632-8308 [email protected]!

Taguchi Methods!

Quality Engineering

“Quality Is The Loss A Product Causes To!Society After Being Shipped,!

Other Than Any Losses Caused By!Its Intrinsic Functions.”!

! ! ! !-- by Dr. Genichi Taguchi!

Taguchi Methods!

Loss Function

Products That Meet Tolerance Also Inflict A Loss!

where x is the value of the quality characteristic!! m is the target value!! k=A/!2 with A= cost to handle a defective; !=tolerance!

Taguchi Methods!

How to Reduce Loss: 2 steps

Starting ! ! Reduce ! ! Place on!

Conditions ! Variation ! Target!

Taguchi Methods!

R & D Activities

Robust!Technology!

Taguchi Methods!

Parameter Design

•  Control Factors!–  Factors you can and want to control during

manufacturing and during use!–  e.g., gun powder, angle of incline!

•  Noise Factors!–  Factors you cannot or do not want to

control during manufacturing or during use!–  e.g. temperature, wind, uncertainties!

Taguchi Methods!

Sources of Noises

! Inner Noise!–  Material or dimensional deterioration!–  A function of time or usage!

! Outer Noise!–  Conditions such as temperature, humility, voltage!

! Unit-to-Unit Variation!–  Variation in manufacturing under same conditions!–  Such as parts in different locations of an oven!

Taguchi Methods!

Comparison Between Traditional and Taguchi Methods

Traditional Methods:!Remove cause of defect!

Taguchi Methods:!Reduce effects of cause!

Traditional approaches may be expensive or impossible or may be more difficult to implement!

Taguchi Methods!

Case Studies

Parameter Design!1.  Canon Example!

–  A system with well-known mechanics model : to design for target distance!

2.  Circuit Design Example!–  A simple RL circuit: to maintain constant

level of current output!

Taguchi Methods!

Orthogonal Arrays in Experimental Design

" L4, L8, L9, L12, L16, L18, L27, and L36!" Recommended: L9 and L18!

–  Number of experiments: 9 and 18!–  Number of readings: product array!

" Product Array:!–  inner array: control factors!–  outer array: noise factors!

Taguchi Methods!

Parameter Design: Definition of S/N Ratios

Professor Imin Kao, Manufacturing Automation Laboratory, SUNY at Stony Brook; [email protected]!

Taguchi Methods!

Smaller-the-Better Criterion Definition of S/N Ratios


Taguchi Methods!

Larger-the-Better Criterion Definition of S/N Ratios


Taguchi Methods!

Nominal-the-Best Criterion Definition of S/N Ratios


Orthogonal Arrays forTaguchi Methods

Manufacturing Automation LaboratoryDepartment of Mechanical Engineering

SUNY at Stony BrookStony Brook, NY 11794-2300

Abstract

This article contains the orthogonal arrays that are listed in Appendix 3 of the “Taguchi Methods:Research and Development”. The book is Volume One of the Quality Engineering Series, published bythe ASI Press.

According to Dr. Taguchi, however, only

,

, and

are preferred for parameter design.

1 The

orthogonal array

The orthogonal array is for 3 control factors, each with two-level variations. This is denoted as .

No. 1 1 1 12 1 2 23 2 1 24 2 2 1

Table 1: orthogonal array

1

2 The

orthogonal array

The orthogonal array is for 7 control factors, each with two-level variations. This is denoted as .

No. 1 1 1 1 1 1 1 12 1 1 1 2 2 2 23 1 2 2 1 1 2 24 1 2 2 2 2 1 15 2 1 2 1 2 1 26 2 1 2 2 1 2 17 2 2 1 1 2 2 18 2 2 1 2 1 1 2


3 The

orthogonal array

The orthogonal array is for 4 control factors, with 4 three-level variations. This is denoted as .

No. 1 1 1 1 12 1 2 2 23 1 3 3 34 2 1 2 35 2 2 3 16 2 3 1 27 3 1 3 28 3 2 1 39 3 3 2 1


2

4 The

orthogonal array

The orthogonal array is for 11 control factors, with 11 two-level variations. This is denoted as .

No. 1 1 1 1 1 1 1 1 1 1 1 12 1 1 1 1 1 2 2 2 2 2 23 1 1 2 2 2 1 1 1 2 2 24 1 2 1 2 2 1 2 2 1 1 25 1 2 2 1 2 2 1 2 1 2 16 1 2 2 2 1 2 2 1 2 1 17 2 1 2 2 1 1 2 2 1 2 18 2 1 2 1 2 2 2 1 1 1 29 2 1 1 2 2 2 1 2 2 1 1

10 2 2 2 1 1 1 1 2 2 1 211 2 2 1 2 1 2 1 1 1 2 212 2 2 1 1 2 1 2 1 2 2 1


3

5 The

orthogonal array

The orthogonal array is for 15 control factors, with 15 two-level variations. This is denoted as .

No. 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 12 1 1 1 1 1 1 1 2 2 2 2 2 2 2 23 1 1 1 2 2 2 2 1 1 1 1 2 2 2 24 1 1 1 2 2 2 2 2 2 2 2 1 1 1 15 1 2 2 1 1 2 2 1 1 2 2 1 1 2 26 1 2 2 1 1 2 2 2 2 1 1 2 2 1 17 1 2 2 2 2 1 1 1 1 2 2 2 2 1 18 1 2 2 2 2 1 1 2 2 1 1 1 1 2 29 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2

10 2 1 2 1 2 1 2 1 2 1 2 1 2 1 211 2 1 2 2 1 2 1 1 2 1 2 2 1 2 112 2 1 2 2 1 2 1 2 1 2 1 1 2 1 213 2 2 1 1 2 2 1 1 2 2 1 1 2 2 114 2 2 1 1 2 2 1 2 1 1 2 2 1 1 215 2 2 1 2 1 1 2 1 2 2 1 2 1 1 216 2 2 1 2 1 1 2 2 1 1 2 1 2 2 1


4

6 The

orthogonal array

The orthogonal array is for 8 control factors, with 1 two-level and 7 three-level variations. This is denotedas .

No.

1 1 1 1 1 1 1 1 12 1 1 2 2 2 2 2 23 1 1 3 3 3 3 3 34 1 2 1 1 2 2 3 35 1 2 2 2 3 3 1 16 1 2 3 3 1 1 2 27 1 3 1 2 1 3 2 38 1 3 2 3 2 1 3 19 1 3 3 1 3 2 1 2

10 2 1 1 3 3 2 2 111 2 1 2 1 1 3 3 212 2 1 3 2 2 1 1 313 2 2 1 2 3 1 3 214 2 2 2 3 1 2 1 315 2 2 3 1 2 3 2 116 2 3 1 3 2 3 1 217 2 3 2 1 3 1 2 318 2 3 3 2 1 2 3 1


5

7 The

orthogonal array

The orthogognal array is for 13 contrl factors, with 13 three level variations. This is denoted as .

No. 1 1 1 1 1 1 1 1 1 1 1 1 1 12 1 1 1 1 2 2 2 2 2 2 2 2 23 1 1 1 1 3 3 3 3 3 3 3 3 34 1 2 2 2 1 1 1 2 2 2 3 3 35 1 2 2 2 2 2 2 3 3 3 1 1 16 1 2 2 2 3 3 3 1 1 1 2 2 27 1 3 3 3 1 1 1 3 3 3 2 2 28 1 3 3 3 2 2 2 1 1 1 3 3 39 1 3 3 3 3 3 3 2 2 2 1 1 1

10 2 1 2 3 1 2 3 1 2 3 1 2 311 2 1 2 3 2 3 1 2 3 1 2 3 112 2 1 2 3 3 1 2 3 1 2 3 1 213 2 2 3 1 1 2 3 2 3 1 3 1 214 2 2 3 1 2 3 1 3 1 2 1 2 315 2 2 3 1 3 1 2 1 2 3 2 3 116 2 3 1 2 1 2 3 3 1 2 2 3 117 2 3 1 2 2 3 1 1 2 3 3 1 218 2 3 1 2 3 1 2 2 3 1 1 2 319 3 1 3 2 1 3 2 1 3 2 1 3 220 3 1 3 2 2 1 3 2 1 3 2 1 321 3 1 3 2 3 2 1 3 2 1 3 2 122 3 2 1 3 1 3 2 2 1 3 3 2 123 3 2 1 3 2 1 3 3 2 1 1 3 224 3 2 1 3 3 2 1 1 3 2 2 1 325 3 3 2 1 1 3 2 3 2 1 2 1 326 3 3 2 1 2 1 3 1 3 2 3 2 127 3 3 2 1 3 2 1 2 1 3 1 3 2


6

8 The

orthogonal array

The orthogognal array is for 23 contrl factors, with 11 two level variations and 12 three level variations.This is denoted as .

No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 1’ 2’ 3’ 4’

1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 12 1 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 2 2 1 1 1 13 1 1 1 1 1 1 1 1 1 1 1 3 3 3 3 3 3 3 3 3 3 3 3 1 1 1 14 1 1 1 1 1 2 2 2 2 2 2 1 1 1 1 2 2 2 2 3 3 3 3 1 2 2 15 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3 3 3 1 1 1 1 1 2 2 16 1 1 1 1 1 2 2 2 2 2 2 3 3 3 3 1 1 1 1 2 2 2 2 1 2 2 17 1 1 2 2 2 1 1 1 2 2 2 1 1 2 3 1 2 3 3 1 2 2 3 2 1 2 18 1 1 2 2 2 1 1 1 2 2 2 2 2 3 1 2 3 1 1 2 3 3 1 2 1 2 19 1 1 2 2 2 1 1 1 2 2 2 3 3 1 2 3 1 2 2 3 1 1 2 2 1 2 1

10 1 2 1 2 2 1 2 2 1 1 2 1 1 3 2 1 3 2 3 2 1 3 2 2 2 1 111 1 2 1 2 2 1 2 2 1 1 2 2 2 1 3 2 1 3 1 3 2 1 3 2 2 1 112 1 2 1 2 2 1 2 2 1 1 2 3 3 2 1 3 2 1 2 1 3 2 1 2 2 1 113 1 2 2 1 2 2 1 2 1 2 1 1 2 3 1 3 2 1 3 3 2 1 2 1 1 1 214 1 2 2 1 2 2 1 2 1 2 1 2 3 1 2 1 3 2 1 1 3 2 3 1 1 1 215 1 2 2 1 2 2 1 2 1 2 1 3 1 2 3 2 1 3 2 2 1 3 1 1 1 1 216 1 2 2 2 1 2 2 1 2 1 1 1 2 3 2 1 1 3 2 3 3 2 1 1 2 2 217 1 2 2 2 1 2 2 1 2 1 1 2 3 1 3 2 2 1 3 1 1 3 2 1 2 2 218 1 2 2 2 1 2 2 1 2 1 1 3 1 2 1 3 3 2 1 2 2 1 3 1 2 2 219 2 1 2 2 1 1 2 2 1 2 1 1 2 1 3 3 3 1 2 2 1 2 3 2 1 2 220 2 1 2 2 1 1 2 2 1 2 1 2 3 2 1 1 1 2 3 3 2 3 1 2 1 2 221 2 1 2 2 1 1 2 2 1 2 1 3 1 3 2 2 2 3 1 1 3 1 2 2 1 2 222 2 1 2 1 2 2 2 1 1 1 2 1 2 2 3 3 1 2 1 1 3 3 2 2 2 1 223 2 1 2 1 2 2 2 1 1 1 2 2 3 3 1 1 2 3 2 2 1 1 3 2 2 1 224 2 1 2 1 2 2 2 1 1 1 2 3 1 1 2 2 3 1 3 3 2 2 1 2 2 1 225 2 1 1 2 2 2 1 2 2 1 1 1 3 2 1 2 3 3 1 3 1 2 2 1 1 1 326 2 1 1 2 2 2 1 2 2 1 1 2 1 3 2 3 1 1 2 1 2 3 3 1 1 1 327 2 1 1 2 2 2 1 2 2 1 1 3 2 1 3 1 2 2 3 2 3 1 1 1 1 1 328 2 2 2 1 1 1 1 2 2 1 2 1 3 2 2 2 1 1 3 2 3 1 3 1 2 2 329 2 2 2 1 1 1 1 2 2 1 2 2 1 3 3 3 2 2 1 3 1 2 1 1 2 2 330 2 2 2 1 1 1 1 2 2 1 2 3 2 1 1 1 3 3 2 1 2 3 2 1 2 2 331 2 2 1 2 1 2 1 1 1 2 2 1 3 3 3 2 3 2 2 1 2 1 1 2 1 2 332 2 2 1 2 1 2 1 1 1 2 2 2 1 1 1 3 1 3 3 2 3 2 2 2 1 2 333 2 2 1 2 1 2 1 1 1 2 2 3 2 2 2 1 2 1 1 3 1 3 3 2 1 2 334 2 2 1 1 2 1 2 1 2 2 1 1 3 1 2 3 2 3 1 2 2 3 1 2 2 1 335 2 2 1 1 2 1 2 1 2 2 1 2 1 2 3 1 3 1 2 3 3 1 2 2 2 1 336 2 2 1 1 2 1 2 1 2 2 1 3 2 3 1 2 1 2 3 1 1 2 3 2 2 1 3


References

[1] G. Taguchi System of Experimental Design, vols. 1 and 2 Quality Resources, Dearborn Michigan, vol. 1and 2, 1991

[2] G. Taguchi and S. Konishi Taguchi Methods – Research and Development ASI press, vol. 1 in QualityEngineering Series, 1992

7

t0

tc

chip

Tool

shear plane

: shear plane angle: rake angle: clearance angleor relief angle

t0: depth of cuttc: chip thicknessr= t0/tc: chip thickness ratio

chip

t0

tc

workpiece

cutting edge of toolshear deformationto form chips

VsVc

V

Tool

shear plane

MEC325/580 Orthogonal Cutting Model

B

C

A

B

C

A

D

thickness of plate

shear deformation approximatedby a series of parallel platessliding against one anotherto form the chips

(Idealized assumption)chips = parallel shear plates

AD+DCBD

ACBD

shear strain

I. Kao

chip

Tool

N

FR

Fn

Fs

R’

R = total force acting on chipR’= force imposed by the work on the chip

(R = R’)R”= force measured by the dynamometer

Fs: shear forceFn: normal force to shearF : friction forceN : normal force to frictionFc: cutting forceFt: thrust force

chip

Tool

Ft

R”

Fc

MEC325/580 Forces in the Orthogonal Cutting Model I. Kao

1

Permanent-MoldCasting



Metal Casting

2

Permanent Mold Casting Processes• Economic disadvantage of expendable mold

casting: a new mold is required for everycasting

• In permanent mold casting, the mold is reusedmany times

• The processes include:– Basic permanent mold casting– Die casting– Centrifugal casting


3


Figure 11.10 (textbook) Steps in permanent mold casting: (2) cores (ifused) are inserted and mold is closed, (3) molten metal is poured intothe mold, where it solidifies.

Advantages and Limitations• Advantages of permanent mold casting:

– Good dimensional control and surface finish– More rapid solidification caused by the cold metal

mold results in a finer grain structure, so castings arestronger

• Limitations:– Generally limited to metals of lower melting point– Simpler part geometries compared to sand casting

because of need to open the mold– High cost of mold

4

Die CastingA permanent mold casting process in which

molten metal is injected into mold cavity underhigh pressure

• Pressure is maintained during solidification,then mold is opened and part is removed

• Molds in this casting operation are called dies;hence the name die casting

• Use of high pressure to force metal into diecavity is what distinguishes this from otherpermanent mold processes

Die Casting Machines• Designed to hold and accurately close two

mold halves and keep them closed whileliquid metal is forced into cavity

• Two main types:1. Hot‑chamber machine: Metal is melted in a

container, and a piston injects liquid metal underhigh pressure into the die

2. Cold‑chamber machine: Molten metal is pouredinto unheated chamber from external meltingcontainer, and a piston injects metal under highpressure into die cavity

5


Cold‑Chamber Die Casting

(2)

6

Molds for Die Casting

• Usually made of tool steel, mold steel, ormaraging steel

• Tungsten and molybdenum (good refractoryqualities) used to die cast steel and cast iron

• Ejector pins required to remove part fromdie when it opens

• Lubricants must be sprayed into cavities toprevent sticking

Advantages and Limitations• Advantages of die casting:

– Economical for large production quantities– Good accuracy and surface finish– Thin sections are possible– Rapid cooling provides small grain size and good

strength to casting

• Disadvantages:– Generally limited to metals with low melting points– Part geometry must allow removal from die

7






SME Video Clip

• Next, let’s watch the SMEvideo clip about Die Castingwhich came with the textbookfor classroom use ONLY…

ME325/580 HANDOUT: IRON-CARBON PHASE DIAGRAM


Iron-Carbon or Fe-Fe3C phase diagram: Iron-Carbon phase diagram (also called the iron and iron carbidephase diagram), as shown in the following figure, is an equilibrium diagram of iron and carbon that is veryuseful in dealing with steel and heat treatment.

400

600

800

1000

Tem

pera

ture

, o C

727oC (1341oF)

1200

1400

1600

0 1 2 3 4 5 6 6.67

1800

1154oC (2109oF)

1252oC

912oC (1674oF)

1394oC (2541oF)

1539oC (2802oF)

4.30%

2.11%

0.77%

0.022%

γγ+liquid

Liquid

Liquid+graphite

γ+graphite

α+graphite

(solid)

(solid)

α+γα

δ

% Carbon (C)

steel cast iron

eutectic

eutectoid

Fe3C

Figure 1: The equilibrium phase diagram of iron and iron-carbon

As shown in Figure 1, at carbon composition of 2.11% the diagram is partitioned into regions of steel(%C < 2.11%) and cast iron (%C > 2.11%). Within the region of steel, it can be further broken into tworegions, divided by the eutectoid line with carbon composition of 0.77% (some use 0.80% or 0.83%): (i)hypo-eutectoid (%C < 0.77%), and (ii) hyper-eutectoid (%C > 0.77%).

The Fe-C phase diagram has oneeutectic state at1154C with 4.30% of carbon (some use1130C and4.0%) at which the alloy transforms from liquid toγ-austenite and Fe3C-graphite. In addition, it also hasoneeutectoid state at727C with 0.77% of carbon (some use723C and 0.80% or 0.83%) at which thealloy transitions from one solid (γ-austenite) to two solids (α-ferrite and Fe3C-graphite).

Remarks:

(i) Phasesα andδ are both ferrite (BCC). Theα-ferrite (or simply ferrite) is stable at room temperature;whereas theδ-ferrite is only stable at high temperature. Phaseγ is austenite (FCC).

1

(ii) α → γ: The transition for pure iron from BCC to FCC takes place at912C.

(iii) γ → δ: The transition for pure iron from FCC to BCC takes place at1394C.

(iv) Pure iron melts at1539C.

(v) Fe3C-graphite is cementite, also called carbide, and is hard and brittle.

Figure 2 illustrates the equilibrium cooling of a hypoeutectoid (which means “less than eutectoid” inGreek) steel alloy and the changes of phases as it cools to different regions of the phase diagram. The mi-crostructures of the hypoeutectoid alloy are illustrated at different temperatures, as shown in the figure. Thephase changes fromγ-austenite to (α-ferrite+γ-austenite) to (α-ferrite+Fe3C-graphite) as the temperature isdecreased. While at the state with co-existence ofα-ferrite andγ-austenite, the percentage of each can becalculated using the inverse lever rule. In the following, an example is used for illustration.

M

O

1000

900

800

700

600

500

400

Tem

pera

ture

(o C)

Composition (wt% C)0 1.0 2.0

γ

γγ

γ

γ

γ + Fe3C

γ

γ γ

γ

α

γ

γ γ

γ

α + Fe3C

Fe3C

Pearlite

Proeutectoid αEutectoid α

α

α+γ

Figure 2: Hypoeutectoid alloy in the equilibrium phase diagram and the phase change subject to equilibriumcooling.

Example: Given the Fe-Fe3C phase diagram in Figure 1, calculate the phases present fora 1020 steel at thefollowing temperatures:

(a) T = 1600C

(b) T = 1200C

(c) T = 728C

2

(d) T = 710C

(e) T = 400C

Solution: The 1020 steel has a carbon content of%C = 0.20% at the hypo-eutectoid region to the left ofthe eutectoid state. Figure 1 will be employed to perform thefollowing calculation.

(a) At T = 1600C, it is in liquid state.

(b) At T = 1200C, γ-austenite exists as a single-phase state.

(c) At T = 728C, just above the temperature at the eutectoid point (T = 727C, shown in the figure),two phases exist:α-ferrite andγ-austenite. The percentage can be determined by the inverseleverrule.

α-ferrite =0.77 − 0.20

0.77 − 0.022= 76.2% (1)

γ-austenite =0.20 − 0.022

0.77 − 0.022= 23.8% (2)

A zoom-in view of the eutectoid region is shown in Figure 2, and can be used for the application ofthe inverse lever rule as demonstrated in equations (1) and (2).

(d) At T = 710C, just below the temperature at the eutectoid point, a small amount of Fe3C-graphite(cementite) will precipitate following the solubility line from 0.022% carbon at727C to 0.022%carbon at room temperature. The percentage ofα-ferrite and Fe3C-graphite are:

α-ferrite =6.67 − 0.20

6.67 − 0.022= 97.3% (3)

Fe3C-graphite =0.20 − 0.022

6.67 − 0.022= 2.7% (4)

(e) At T = 400C: Similar to Part (d), the percentages are:

α-ferrite =6.67 − 0.20

6.67 − 0.0= 97.0% (5)

Fe3C-graphite =0.20 − 0.0

6.67 − 0.0= 3.0% (6)

The results are not very different from those in Part (d), showing a slight increase in the Fe3C precip-itation.

3

1

ME325/580 Handout: Copper-Nickel Phase Diagram

Spring 2010 I. Kao Phase diagram is an equilibrium diagram showing the way an alloy forms. The equilibrium diagram for the binary copper-nickel alloy is illustrated on the next page. For example, “Monel,” which resists saltwater corrosion, has 67% nickel and 33% copper shown in the diagram and is used in packaging beverages and foods. It has a range of working temperatures from –100° to 400°F (–75° to 205°C).

The Copper-Nickel phase diagram shown on the next page is the simplest phase diagram. The illustration of its usage will be presented in the following with an example. The temperature under consideration is at T=1260°C. Several states are considered and discussed in the following.

(I) At T=1260°C and under equilibrium condition, there are three possible states, as follows.

(1) When the percentage of Ni is smaller than 36% Liquid state (2) When the percentage of Ni is larger than 62% Solid state (3) When the percentage of Ni is between 36% and 62% co-existence of Liquid and

Solid (II) When liquid and solid co-exist, the following “inverse lever rule” should be applied to

determine the percentage of solid (and percentage of liquid) in the co-existing state. The Inverse Lever Rule is defined to determine the contents of solid and liquid when they co-exist within specific temperature range. Here, we use an example of 50% Ni and 50% Cu alloy at the temperature of 1260°C, as shown in the following diagram, for the illustration of this rule.

The % of solid at the state C is:

€

LCLS

=LC

(LC + CS)=(50 − 36)%(62 − 36)%

=1426

= 53.8% (1)

The % of liquid at the state C is:

€

CSLS

=CS

(LC + CS)=(62 − 50)%(62 − 36)%

=1226

= 46.2% (2)

Note the ratios formulated in equation (1) and (2). Based on the results in the equations, the percentage of solid at 1260°C with 50%Ni-50%Cu alloy is 53.8%, and with 46.2% liquid. For this alloy with 50%Ni-50%Cu, both liquid and solid co-exist from 1210°C to 1316°C, as shown in the figure. The percentage of solid and liquid can be determined by equations (1) and (2) at any given temperature within this range for the 50%Ni-50%Cu alloy. The verification of results is on the next page. In the preceding analysis, we consider different compositions of Cu and Ni at a constant given temperature (1260°C). Similarly, we can also consider a given alloying composition and vary the temperatures to acquire and analyze different states at different temperatures. For example, with the alloy composition of 67% nickel and 33% copper, as the temperature cools down from liquid state, it transitions to co-existence of liquid and solid at 2510°F and becomes complete solid as the temperature cools further to 2320°F. Thereafter, the alloy becomes entirely solid.

2

Verification of the results: Because the solid and liquid states at 1260°C have their own respective percentage of Ni and Cu, we can use the information to verify the answers obtained in equations (1) and (2). It can be obtained from the figure that at 1260°C

the solid state of this alloy has 62% of Ni and 38% of Cu (point S) the liquid state of this alloy has 36% of Ni and 64% of Cu (point L)

Thus, the total percentage of the Ni is the sum of the that in the solid and liquid states. That is,

total % of Ni = (53.8%) x 62% + (46.2%) x 36% = 50% This is as expected since the total weight percentage of the Ni element in the alloy remains 50% and cannot be changed. Similarly, the total percentage of Cu is

total % of Cu = (53.8%) x 38% + (46.2%) x 64% = 50% as expected.

1

ME325/580 Handout: Tin-Lead Phase Diagram

Spring 2010 I. Kao The equilibrium diagrams for binary alloys can assume different shapes. For example, the copper-nickel alloy is very simple with only three regions, as discussed earlier. The following is the phase diagram for tin-lead (Sn-Pb) alloy, which has α and β phases as well as combinations of them with liquid and solid phases. A few important observations are in order.

(1) The freezing point of pure tin (point C) is 232ºC. As the alloying element (or impurity) of lead is added, the freezing point is decreased (just like the way that salt lowers the freezing point of water). This trend of lowering freezing point is shown in CB curve. The same is true for pure lead (point A; 327ºC) and the curve AB with decreasing freezing point. The point of intersection between the curves AB and BC (i.e., point B) indicates the eutectic mixture at 61.9% tin (Sn) and 38.1% lead (Pb). The eutectic composition gives rise to the lowest possible temperature of solidification for the Sn-Pb binary alloy. The eutectic temperature of this binary alloy is 183ºC.

2

(2) In the two freezing zones ABD and CBF, the alloy is “pasty.” In other words, they contain both liquid and solid phases. Taking region ABD as an example, crystals of composition α will be forming whilst the rest of the alloy is still liquid. These crystals will grow into dendritic structure (similar to the formation of ice crystals in water with pointy tips) until such time as the alloy solidifies completely. Then the granular structure will consist of α dendrite cores in a β crystal mix. Because the β crystals form virtually instantaneously as the alloy temperature drops below 183ºC, they tend to be small. The resulting alloy is characterized by a coarse grained structure (large α, small β) and tends to be mechanically weaker and a poorer conductor. It does have its usage, however. A good example is plumber’s solder (34%Sn+66%Pb). In this case, electrical conductivity is not an issue, and the extended pasty stage is advantageous for making “wiped” joints.

(3) The tin-lead binary alloy diagram contains a eutectic point, unlike the Cu-Ni alloy which does not have one. Electronic solder made of 62%Sn and 38%Pb, or called the eutectic solder, not only has the lowest melting point and reverts from liquid to solid (and vice versa) virtually instantaneously (point B on the phase diagram). In addition, it has lowest melting point at 183ºC, which makes it ideal for electronic grade solder. The electronic grade solder alloys, or eutectic solder, fall in a narrow band ranging from 60%Sn+40%Pb to 65%Sn+35%Pb.

(4) The crystal structure of eutectic solder alloys consists of fine equally sized grains of α and β (because they have limited time to grow) with no evidence of potentially strength-reducing dendritic core. This fine grain structure also maintains a high degree of electrical conductivity—a characteristic that lends itself to becoming an ideal electronic solder.

(5) The inverse lever rule discussed previously also can be applied in the regions indicated above based on the same rules used in the Cu-Ni phase diagram.

1

ME325/580 SME DVD Video: Plastic Finishing

Spring 2010 I. Kao 1. Injected molded parts are produced from two types of plastics

• Thermoplastic • Thermoset

2. The finishing include • Degating • Deflashing • Cleaning • Decorating

3. Sprue bushing directs the molten material from the injection machine’s nozzle either directly into the mold cavity or into the mold’s runner system.

4. Degating is the process to move the parts from gate and runner system. 5. To remove the need for manual or automatic degating, Runner-less Injection Mold should be

designed. These molds include • Hot Sprue Gated Mold • Hot Runner Mold • Insulated Runner Mold

6. Flashing can occur both internally and externally. The primary flash removal or deflashing include: • Cutting and trimming • Media blasting • Cryogenic deflashing

7. Cleaning is the process to remove residues from the molding process by soaking or spraying parts in a mild detergent solution.

8. The method of decorating molded parts include: • Molded-in decorations • Applied decorations

9. The most common methods of applied decorations include: • Painting • Plating • Vacuum metallizing • Pad printing • Hot stamping • Silk Screening • Fill and Wipe

10. Variety of paints • Epoxies • Polyurethane • Enamels • Acrylics • Latexes

2

11. Painting methods • Conventional air spraying • High volume/low pressure spraying • Flow coating

12. Plating is the chemical or electro-chemical deposit of a thin metal layer to the surface or substrate of a plastic part.

13. Plastic parts are prepared for Electroless Plating operation by submersion in • a sulfured chromic acid bath • an activated bath • an accelerated bath

14. Vacuum metallizer is a physical process of depositing a metal layer on the plastic part surface.

15. In Pad Printing, ink core paint is pick it up by a silicon rubber transfer pad from a plate (Cliché) to the plastic part. Pad Printing is use extensively because of its ability to: • Print on a range of part surfaces and part geometry • Reproduce fine image detail • Wet-on-wet printing of multiple colors

16. Hot stamping uses heating silicon rubber dies to forcing from the foil film carrier into the surface of the plastic part.

1

ME325/580 SME DVD: Plastic Injection Molding

Spring 2010 I. Kao 1. Plastic – Any natural or synthetic polymer that has a high molecular weight 2. Injection molding is the most common method of produce part out of plastic material. 3. Injection molding is extremely versatile process that can produce parts with

• Holes • Springs • Threads • Hinges

4. Injection molded parts can be: • Simple vs. Complex • Solid vs. Foam • Reinforced vs. Filled • Small vs. Large • Thick vs. Thin • Flexible vs. Rigid

5. The process involves molten plastic injected at high pressure into the mold shaped into the form of the part. Once the plastic cools and solidifies, the mold opens and the part is ejected.

6. There are four primary elements that influence the plastic injection process: • Molder • Material • Injection machine • Mold

7. All injection molding machines are a combination of two systems: • An injection system • Clamping system

8. An injection system heats the thermoplastic material to its appropriate viscosity or flow ability and then forcefully injects it into the mold.

9. There are two types of injection mechanisms: • Reciprocating screw (most common) • Two stage screw

10. The main parts of the reciprocating screw injection system are • Hopper • Reciprocating screw • Injection barrel • Hydraulic motor • Injection cylinder

2

11. The reciprocating screw consists of three zones • Feed zone • Melt zone • Metering zone

12. The function of the injection molding machine-clamping system is to keep the plastic material from leaking out or flashing at the parting line of the mould cavity and core. The clamping system of some of the injection-molding machine has two configurations:

• Fully hydraulic system • Toggle system

13. Platens are thick blocks of tough steel which will not deflect significantly to affect the injection process. The platens include:

• Stationary platen • Movable platen • Rear stationary platen

14. Injection molding machines are designated by there clamp tonnage which is the amount of ceiling force a machine can produce against the high pressure generated during the injection process.

15. The injection mold both determines shape of the part, and acts as a heat exchanger. In addition, the injection mold vents the trapped air/gas and ejects the cooled parts.

16. The speed of the injection molding machine is determined by the mold cooling system. 17. Efficient cooling is one of the most significant factors of the injection molding process. 18. The mold design includes:

• Cold-runner two-plate mold • Cold runner three-plate mold • Hot-runner mold • Insulated runner mold.

19. Types of gates used in a runner system: • Edge gate • Submarine gate • Tap gate • Ring gate • Fan gate

20. Vents are used to remove air displaced by the incoming flow of material. The size and location of the vents are established by:

• Part geometry • Gate location • Type of injection material • Viscosity of material • Rate of injection

21. The type and location of machine controls are dependent on the injection molding machines. These controls can vary from electromagnetic relays and timers to computer driven solid-state devices.

3

22. These computers not only control the process but also perform several other function such as • Quality control • Real-time reject recognition • Fault analysis • Record keeping • Instant/accurate setup

23. Additionally computers are used for the design and generation of injection mold.

1

ME325/580 SME DVD: Plastic Machining and Assembly

Spring 2010 Imin Kao 1. Plastic parts are most commonly produced by:

• Injection molding • Thermo-forming • Blow molding

2. Machining and assembly operations can be performed on plastic parts for structural and aesthetic purposes. These operations are used on parts produced from two types of plastics:

• Thermoplastic • Thermosets

3. Thermoplastics undergo a reversible change from solids to liquids when heated and can be reused continuously

4. Thermosets undergo a chemical reaction between two reagents when heated and cannot be re-softened or reused

5. Key differences between machining plastics and metals: • Thermal expansion of plastics is ten times greater than metals. • The rate of heat loss for plastics is lower when compared to metals. • Plastics are more elastic and have lower melting temperatures than metals.

6. Due to the range of plastic materials responding differently to machining, plastic materials are typically divided into three categories:

• Soft plastic • Hard plastic • Reinforced plastic

7. The primary types of operations used to machine plastics include: • Sawing • Milling • Drilling • Turing • Water jet cutting • Laser cutting

8. Frictional heat does not dissipate easily through a plastic work-piece; the part surface finish may be affected if allowed to reach the softening point. Excessive heat buildup can also dull the cutting tool; therefore coolants are used to reduce heat.

9. Typical coolants used for machining plastics include: • Clean compressed air (aides with chip removal as well) • Mist sprays • Water soluble oils • Light cutting oils

2

10. Functions of coolant: • Lubricate the cut • Cool the drilling point • Flush the chips

11. Water-jet cutting employs the force of a high pressure water stream. Characteristics for water-jet cutting include:

• A pressure range between 20,000 to 60,000 psi • No heat or dust are generated • Can be used to cut abrasive material allowing the cutting of the most difficult plastics

12. Laser cutting is used when a fine polished, ultra smooth finish is required on a plastic part. The two most common types of lasers include:

• CO2 gas laser • YAG solid-state laser

13. The most common methods of assembling plastic components together include the use of: • Snap fits • Hinges • Mechanical fasteners • Bonding • Welding

14. Snap fits are integral fasteners that are molded into plastic parts which lock into place when assembled. Common types of snap fits include:

• Cantilever arm beam snap fits • Annual ring snap fits • Hinges

15. Hinges are used for assemblies requiring repeated opening and closing and divided into three categories:

• One piece integral hinges • Two piece integral hinges • Multi-part hinges

16. Two types of mechanical fastening: • Threaded fasteners • Non-threaded fasteners

17. Mechanical fasteners are frequently used because: • Low cost of assembling • They can hold similar or dissimilar plastic part components together

18. The use of bonding methods in joining plastic components together are widespread and include:

• Adhesive bonding • Solvent bonding

3

19. Welding is the joining of thermoplastic components together. Welding provides exceptional joints that are as strong as the surrounding plastics. The various types of welding include:

• Spin welding • Hot-gas • Ultrasonic • Vibration • Staking

20. Ultrasonic welding uses high frequency, longitudinal, and mechanical vibrations to weld thermoplastic components together. The primary elements of a ultrasonic welding system include:

• Power supply • Converter • Booster • Horn

21. Staking is the method of applying energy against a thermoplastic protrusion that is passed through a component ready to be assembled. Staking is performed using two primary methods:

• Heat Staking – the energy is applied using a heated probe that impacts and melts the protrusion and forms a head to assemble the components

• Ultrasonic Staking – the energy is applied using an ultrasonic tool or horn that causes friction and resultant melting of the protrusion for assembly

Manufacturing Automation: Programmable Logic Controller

(PLC)


Programmable Logic Controller •  History of PLC

– First introduced in 1970 – Used for automated factory which provide

system reliability, product quality, information flow, reduced costs, efficiency, and flexibility

– Today's PLC are designed using the latest in microprocessor design and electronic circuitry which provides reliable operation in industry applications

Advantages Over Other Devices •  PLC offers many advantages over other

control devices such as relay, electrical timers/counters. Advantages include –  Improved reliability –  Smaller space required –  Easier to maintain –  Reusable –  Reprogrammable if requirements change –  More flexible-performs more functions

Schematic of PLC

I/O CPU &Memory

Basic PLC Block DiagramUser SuppliedField Devices

Programmer

Nomenclature & Example

(See handout)

Ladder Logic Diagram

•  Example of programming PLC using a ladder login diagram

MEC326/580 HANDOUT: POSITIONING SYSTEMS AND ACCURACY


This handout discusses the positioning systems and accuracy [1]. Positioning systems, depending on theircontrol scheme, can be broken into two categories: (i) open-loop positioning systems, and (ii) closed-looppositioning systems. Furthermore, they can also be either linear positioning or rotational positioning. Mostelectromechanical motors are rotary, with some capable of delivering linear motion directly. For closed-looppositioning system, encoders (both rotary and linear) are typically used to provide the positions for feedbackcontrol. In the following, positioning and accuracy of motorized systems are discussed.

Open-Loop Positioning: Stepper motors are typically used for open-loop linear or rotary systems. Forexample, a XY table utilizing two leadscrews in orthogonal directions to index(x, y) position on a planecan be made an open-loop positioning system. The step angle is determined by the stepper motor—usuallycomes in1.8 or 0.9. For example, a0.9 stepper motor has a total of 400 steps per revolution. Thefollowing equation relates the step angle and number of steps of a stepper motor.

α =360

ns

(1)

whereα is the step angle in degrees andns is the total number of steps in one full revolution of the motor.In the previous example, we havens = 400 andα = 0.9.

Note that a open-loop positioning system counts on the motorto rotate without slip. If the motor slipsand misses counts (which can take place when the load is larger than the rated load and the torque generatedcannot consistently move from one step to another), the positioning error will accumulated.

The resolution (or the smallest linear displacement or control resolution) of the leadscrew driven by astepper motor can be determined by the following equation.

r = l p( α

360

)

=l p

ns

(2)

wherel is 1 for single-thread screw, 2 for double-thread screw,· · · etc, andp is the pitch of the leadscrewmeasuring the axial distance between two adjacent threads in the unit ofinch/rev or mm/rev. Equation(2) corresponds to one step of the stepper motor, and thus is the resolution of the linear positioning. Thetotal number of pulses,Np, (one pulse per step) needed for the required linear displacement,x, is

Np =x

r=

xns

l p(3)

The corresponding angle of rotation for the stepper motor is

θ = Np α = 360x

l p(4)

where the unit ofθ is degree. The total number of revolution is

Rev =x

l p(5)

When continuous motion is required, typically at a constantspeed, the following equation relates therequired linear speed with respect to the rotational speed of the stepper motor.

v =N

60(l p) (6)

1

wherev is the linear speed ininch/sec or mm/sec, andN is the rotational speed of the stepper motor inRPM. Conversely, the constant rotational speed of motor required to keep a constant linear motion is

N = 60v

l p(7)

Closed-Loop Positioning: All closed-loop positioning systems require sensory information for feedbackcontrol. Typical sensory information of angular or linear displacement is provided by optical encoders orpotentiometers. DC servo motors are often used with opticalencoders for the control of angular or linearposition and speed. Sometimes, tachometers are also used toprovide information of angular speed, basedon the fact thatback emf is proportional to the speed of rotation. Equations that describe the motion andanalysis are similar to those in equations (1) to (7).

Example: A 1.8-stepper motor is connected to a leadscrew via a coupler connection for motion control ofa platform mounted and carried by the leadscrew. The single-thread leadscrew has a pitch of5mm. Theplatform is to move a distance of70mm at a top speed of7mm/sec. Answer the following questions.

1. What is the smallest linear displacement that this motionsystem can realize?

2. Determine the total angle of revolution of the stepper motor, as well as the number of pulses, requiredto move the platform over the specified distance.

3. What is the required angular speed of the stepper motor in order to achieve the top speed of the linearmotion?

Solution: Note the leadscrew is single-thread; thus,l = 1 in equations (2) to (7). Since the step angle is1.8, equation (1) gives the total number of steps per a full revolution as

ns =360

1.8= 200 (8)

1. The smallest linear displacement that this motion systemcan realize is the resolution given by equation(2). That is,

r = p

(

1.8

360

)

= 5/200 = 0.025mm = 25µm or r =p

ns

=5

200= 0.025mm (9)

2. To move the entire distance of70mm, the total angle of revolution and number of pulses requiredare

Np =x

r=

70

0.025= 2, 800

θ = Np α = (2800)(1.8) = 5040 = 14 rev.

respectively.

3. The angular speed of the stepper motors is given by equation (7):

N = 60 ×

v

p= 60 ×

7

5= 84RPM (10)

2

Precision in Positioning: Three important measures of precision in positioning are (i) control resolution,(ii) accuracy, and (iii) repeatability.

Control resolution is defined as the distance separating two adjacent control points in the axis of move-ment. The control resolution is determined by the pitch of leadscrew, gear ratio, step angles (in the case ofstepper motor), and the angles between slots in an encoder disk. For a stepper motor system without gearreduction, the control resolution is the same asr given in equation (2). If digital encoders are used in acontrol system, the number of bits also affects the resolution–known as the quantization effect. IfB is thenumber of bits in the storage register (for example, the number of bits in the representation of encoder data,say a 12-bit encoder), then the number of control points intowhich the axis range can be divided is2B .For example, a 12-bit encoder has212 = 4096 control points and 4095 equal divisions. Assuming that thecontrol points are separated equally within the range, we have

s =L

2B− 1

(11)

wheres is the control resolution of the computer control system ininch or mm, andL is the range of axisin inch or mm. Similarly, if the range of consideration is angular displacement with a range of angle ofΘ(Θ ≤ 360), then the angular control resolution is

sΘ =Θ

2B− 1

(12)

The resulting control resolution of the positioning systemis the maximum of the two values; that is,

CR = Maxr, s (13)

wherer ands are calculated from equations (2) and (11), respectively. In general, it is desirable thats ≤ r.In modern sensor and computer technology, this is typicallythe case.

In an actual environment, many practical factors influence the performance of the control of systems.These factors include the backlash in the leadscrews or ballscrews, backlash in the gearing and transmission,and deflection and elasticity due to loading. If assuming a normal distribution with mean value beingzero, we can define the random nature of accuracy of positioning systems by the 3-σ principle with±3σencompassing 99.7% of the population.

Accuracy is thus defined in a worst-case scenario in which the desired target point lies exactly betweentwo adjacent control points. An illustration in Figure 1 helps to visualize the situation. If the target wascloser to one of the control points, then the control system can be moved to the closer control point and theerror would be smaller. The accuracy of any given axis of a positioning system is the maximum possibleerror that can occur between the desired target point and theactual position taken by the system, using the3σ range,

Accuracy = 0.5CR + 3σ (14)

whereCR is the control resolution given by equation (13), andσ is the standard deviation of the distributionof errors.

Repeatability is defined as the capability of a positioning system to returnto a given control point thathas been previously designated. Therefore, the repeatability is given by

Repeatability = ±3σ (15)

3

axisaccuracy=0.5(CR)+3σ repeatability= 3σ

control resolution= CR

controlpoint

controlpoint

Desired targetpoint

distribution of errors

Figure 1: Terminology for positioning and accuracy

Example: A closed-loop control system is assumed to have random errors which are normally distributed(Gaussian) with a standard deviation ofσ = 0.004mm. The range of the workspace is700mm with 16-bitstorage register. The single-thread ball screw has a pitch of 5mm, with a1.8-stepper motor. Determine (a)control resolution, (b) accuracy, and (c) repeatability ofthe positioning system.

Solution: Apply the equations formulated above. For single-thread ball screw,l = 1.

(a) The deterministic resolution defined in equation (2) andquantization in equation (11) are

r =p

ns

=5

200= 0.025mm

s =L

2B− 1

=700

216− 1

=700

65536 − 1= 0.0107mm

respectively. Sinces < r, the control resolution is

CR = Max0.025, 0.0107 = 0.025mm (16)

(b) The accuracy is given by equation (14),

Accuracy = 0.5(0.025) + 3(0.004) = 0.0245mm (17)

(c) The repeatability is given by equation (15),

Repeatability = ±3(0.004) = ±0.012mm (18)

References

[1] M. P. Groover Fundamentals of Modern Manufacturing: materials, processes, and systems Wiley,second ed., 2002

4

Using Taguchi Methods in Circuit Design1

Manufacturing Automation Laboratory (MAL)Department of Mechanical Engineering

SUNY at Stony Brook

1 Purpose

To design a simple circuit with a resistance,R, and self-inductance,L, so that the output current is at 10amperes. The loss function, in terms of dollars, is estimated at $200 if the current deviates more than 4amperes which will cause the circuit to cease functioning.

2 Theoretical Equations to Calculate Currenty and Sensitivity

The output current subject to theRL circuit is given by the following equation.

y =V

√

R2 + (2πfL)2(1)

whereV is the input voltage,R is the resistance,f is the frequency, andL is the inductance. The followingterms are also defined:

m =1

n(y1 + y2 + · · · + yn)

Sm =1

n(y1 + y2 + · · · + yn)2

Ve =1

n − 1(y2

1 + y2

2 + · · · + y2

n − Sm)

The sensitivity is defined in this case (nominal-the-better) to be

S =1

n(Sm − Ve) (2)

with the signal-to-noise ratio

η = 10 log1

n

Sm − Ve

Ve(3)

The loss function is defined as

L =A0

∆20

σ2 (4)

whereA0 is the loss due to malfunction of this circuit,∆0 is the function limit, andσ2 is the variance.

1The example was adapted from theTaguchi Methods – Research and Development.

1

Control factors Values selected for parameter designResistance (R) R1 = 0.5Ω R1 = 5.0Ω R1 = 9.5ΩInductance (L) L1 = 0.010H L1 = 0.020H L1 = 0.030H

Noise factors Values estimated for parameter designVoltage (V ) 90V 100V 110V

Frequency (f ) 50Hz 55Hz 60HzR′

−10% 0 10%L′

−10% 0 10%

Table 1: Values and estimated ranges of control and noise factors

Results S/N ratio SensitivityNo. R L N1 N2 η S

1 1 1 21.5 38.4 7.6 29.22 1 2 10.8 19.4 7.5 23.23 1 3 7.2 13.0 7.4 19.74 2 1 13.1 20.7 9.7 24.35 2 2 9.0 15.2 8.5 21.46 2 3 6.6 11.5 8.0 18.87 3 1 8.0 12.2 10.4 20.08 3 2 6.8 10.7 9.8 18.69 3 3 5.5 9.1 8.9 17.0

Table 2: Calculation of S/N ratios and sensitivities

3 Specification of Design Parameters

In the parameter design, we first need to identify the controland noise factors. Control factors are the factorsthat we can control or select freely. The noise factors are the ones that we can not or do not want to control,such as the actual voltage and frequency of input power and the variations in the actual values of resistanceand inductance (assume that the actual values vary within certain ranges).

The control factors are the resistance,R, and inductance,L. Each control parameter is chosen to havethree levels in our analysis. The noise factors include the voltage of power input,V , and frequency,f ,and the uncertainties of the resistor and inductor components which are assume to vary±10% from theirnominal values. Table 1 summarizes the factors.

4 Parameter Design

Using the parameter design, we can calculate the signal-to-noise ratios and sensitivities using equations (2)and (3). The results are tabulated in Table 2.

2

η S

R1 7.5 24.0R2 8.7 21.5R3 9.7 18.5

η S

L1 9.2 24.5L2 8.6 21.1L3 8.1 18.5

Table 3: Factorial effects

Table 3 of average values are computed in order to compare thecontrol factors of each level using theS/N ratios,η, and sensitivities,S. From Table 3, we conclude that the optimal design isR3L1 which hasthe highest S/N ratios inR andL, respectively. In order to determine the difference between average outputand the target value, a confirmation experiment is performed. The currents are found to bey1 = 8.0A andy2 = 12.2A with an average of 10.1. There is nearly no difference between the average and the target valuein this case and thus no further adjustment is needed. If, however, there is a large difference, the output willneed to be adjusted using a factor that has larger sensitivity but affects S/N less. Such a factor is called theadjustment factor.

5 Loss Calculation

Using the loss function defined in equation (4) as a basis, we employ the following equation to calculateLwith a similar definition in order to obtain figures of loss function for the purpose of comparison. The lossusing parameter design is

L =A0

∆20

1

10η/10=

200

42

1

101.04= $1.14

This value is much smaller than $200.

If traditional design is chosen,i.e. R2L2, we obtain

L =200

42

1

100.85= $1.76

The improvement by using the parameter design is $0.62 per each product – about 35% improvement.

6 Conclusion

The parameter design of the Taguchi Methods, when applied tothis electronic design problem, yields satis-factory results. The S/N ratio enhances the robustness of the product and reduces the loss. The quality ofdesign of this circuit is improved over the traditional solution.

References

[1] G. TaguchiSystem of Experimental Design, vols. 1 and 2Quality Resources, Dearborn Michigan, vol.1 and 2, 1991

3

[2] G. Taguchi and S. KonishiTaguchi Methods – Research and DevelopmentASI press, vol. 1 in QualityEngineering Series, 1992

4

Taguchi Methods!

Case Study of Taguchi Methods: RL circuit example


SUNY at Stony Brook!631-632-8308; email: [email protected]!

Taguchi Methods!

RL Circuit Design

! Design RL circuit such that the current, y, is at 10 A.!

! The loss function is estimated at $200 if current deviates more than 4A!

Taguchi Methods!

Control and Noise Factors

Taguchi Methods!

Calculating S/N Ratios

•  Apply Nominal-the-Best Criterion!•  S/N ratio equation for 2 data points!

Taguchi Methods!

Parameter Design Using Orthogonal Array

Taguchi Methods!

S/N Ratio: Factorial Effects

! The S/N ratios from the orthogonal array!

! The optimal design is R3L1 which has highest S/N ratios in R and L!

! Confirmation Run: y1=8.0A, y2=12.2A with average at 10.1A!

ME325/580 HANDOUT: SHEET-METAL BENDING


Sheet-Metal Bending: This handout concerns the sheet metal bending process and analysis. [The materialis from “Fundamentals of Modern Manufacturing: materials, processes, and systems” by M. P. Groover,Wiley, 2002; and other sources]

Bend Allowance: If the bend radius is small relative to stock thickness, the metal tends to stretch duringbending. It is important to be able to estimate the amount of stretching that occurs, if any, so that the finalpart length will match the specified dimension. The problem is to determine the length of the neutral axisbefore bending to account for stretching of the final bent section. This length is called the bend allowance,and it can be estimated as follows: (1)

where

= bend allowance (in or mm),! #" $ is the bend angle (in degrees), is the bend

radius (in or mm), is the stock thickness (in or mm), as shown in Figure 1(a), and % is a factor to estimatestretching. Note the term

'&($) *,+ is the bend angle in radians. The following design values are recommendedfor - . - 0/2131

if 54768- 0/29 if 5:768 (2)

This only applies when the bend radius is small relative to sheet thickness. An illustration is shown inFigure 1.

F

punch

AiRi

die

Rf

Af

(a) During punch (b) After punch: springback

t

Figure 1: Illustration of sheet-metal bending V-die. The included angle of the part is , which is the same

as that of the V-die, and becomes;

after the springback.

Bending Force: The force required to perform bending depends on the geometry of the punch and die andthe strength, thickness, and width of the sheet metal. The maximum bending force can be estimated by thefollowing equation, based on bending of a simple beam

<= ;?>A@3B DCE (3)

where<

is the bending force (in lb or N),>@

is the tensile strength of the sheet metal (in psi or MPs),B

isthe width of part in the direction of the bend axis (in or mm), is the stock thickness (in or mm), and

Eis

1

the die opening dimension as defined in Figure 2. The constant ! ; accounts for differences encountered inan actual bending process. Its value depends on type of bending, as defined in the following. - ; /2131

for "

- ; 0/29 for

(4)

die

punch

D

V-diewiping die

D

Figure 2: Illustration of die opening dimensions for V-bending and edge bending.

Example: A sheet-metal blank is to be bent as shown in Figure 3. The metal has a modulus of elasticity5 1 , yield strength ,33

, and tensile strength>@ ! 9,33

.

1.500

t=0.125 R=0.187120 o

1.000

w=1.750

Figure 3: Example of sheet-metal bending

1. Determine the starting blank size, and

2. Calculate the bending force if a V-die will be used with a die opening dimensionE / "$#

.

Solution: Refer to the dimensions in Figure 3.

1. The starting blank has a width ofB /&% 9'(#

. Its length is equal to /29 / 3

. For anincluded angle

6 , as shown, the bend angle is)

. The value of - in equation (2) is0.33 since 54768 . The bend allowance is obtained from equation (1) 0/ *% 0/2131+ 0/ 6 9 0/ 6 1,-(#Thus, the required length of the blank is

. 6 /29 3 0/ 6 1, 6 /&% 1,-(# /2. The required bending force is obtained from equation (3) using ! ; /2131

in equation (4) for V-die.Thus, < /2131 /&% 9 9,33 0/ 6 9 C / 6 1 -0/21 (5)

2

Springback: When the bending pressure is removed at the end of the deformation operation, elastic energyremains in the bent part, causing it to recover partially towards its original shape. This elastic recovery iscalled springback, as shown in Figure 1, defined as the increase in the included angle of the bent part relativeto the included angle of the forming tool after the tool is removed. That is,

> = #; " (6)

where>

is the springback, is the included angle of the bending die tool, and

;is the included angle

of the sheet-metal part after it is removed from the bending die, as shown in Figure 1.

Analysis of Spring Back in Bending of Sheet-Metal: The following empirical equation defines the amountof springback in a bending operation on a sheet metal with the geometry shown in Figure 4.

; " 1 (7)

where and ;are the bend radii before and after the spring back, is the yield strength,

is the Young’s

modulus, and is the thickness of the sheet metal.

t

Ri

Rf

θi

Ai

Figure 4: Springesback during the bending process of a sheet metal of thickness The springback defined in equation (6) is based on the included angle before and after the springback. It isuseful, however, to use the radii of curvature ( and ;

in Figure 4) to represent the amount of springback.To this end, we assume that the arc length of the curved bend is the same before and after springback, asshown in Figure 4; that is,

; ; 8; 8; ; (8)

Since " and

#; " ;, we can write

#; " ; " ; ; (9)

Since ; and 4 , the springback is

> #; " " ; " (10)

3

Equation (10) depends on the ratio of , which can be substituted by equation (7), and the included angleof the bending die tool

.In a design problem with synthesis, the radius of curvature of the bending die angle, , often needs to bedesigned in order to render the final radius at the desired value after springback. In this case, equation (7)needs to be solved using an equation solver (root finder) or by iteration.

Example: In a bending operation of a 1010 cold-drawn steel sheet metal of thickness () , with a yieldstrength of

9,33and the Young’s modulus of

1 , the radius of curvature of the bending die

tool is 6 .

1. When the bending operation on the die tool is finished, what will be the final radius of the bend basedon equation (7), as the sheet metal is removed from the die tool?

2. What is the springback as a function of the included angle of the bending die tool ? Plot the

springback as a function of the angle .

Solution: Several equations in this section are employed to solve this problem.

1. Applying equation (7), we find

6 ; 6 9,33 1 " 1 6 9,33 1 0/ , 6 0Solve for ; 6 / 939 .

2. Employing equation (10), we have

> " 0/ , 6 0 " If

& C , the springback is> 0/ % 6 % / 6 . If

& , the springback is> 0/ 6

6 / . The springback as a function of the bending die angle (included angle, ) is plotted in Figure 5.

4

40 60 80 100 120 140 160 1800

0.05

0.1

0.15

0.2

0.25

include angle in degrees, Ai

spin

gbac

k

Figure 5: Plot of springback as a function of the included angle

5

Shop Scheduling with Many Parts


Terminology •  Sequencing:

– The process of defining the order in which jobs are to be run on a machine

•  Scheduling: – The process of adding start and finish time

information to the job order dictated by the sequence

Sequence determines the schedule

Assumptions of Shop Scheduling •  Each job is started on a machine as

soon as the job has finished all predecessor operations and the machine has completed all earlier job in its sequence

•  All jobs are in the shop and ready for processing at time zero (t =0)

•  Flow time = completion time

Definitions •  Scheduling process variables:

– N : the number of jobs to be scheduled – M : the number of machines; each job is

assumed to visit each machine once – Pij : set up and processing time of job i on

machine j (elements in the time matrix)

Objectives ① Minimize average flow time ② Minimize the time required to complete

all jobs (Cmax = makespan)!③ Minimize average tardiness ④ Minimize maximum tardiness ⑤ Minimize the number of tardy jobs

Choice of “objective” depends on tasks and requirements

Permutation Schedule •  Assumptions:

– All machines process jobs in the same order – Nearly the optimal solution for flow shops

•  Given the sequence, scheduling is: ①  At time 0, the first job is started on machine 1 ②  As soon as this operation is completed, the

first job begins on machine 2 & the second job begins on machine 1

③  Repeat 1 & 2 until the last job finishes on machine M

Remarks •  Permutation Scheduling: Need to

consider (N!) total of job sequences, where N is the number of jobs

•  As N grows, (N!) grows even more!! •  The Permutation Scheduling is not

suitable for too many jobs (N < 7~10)

N! = N×(N-1)! … !2!1

Example: Shop Scheduling •  Consider the set of jobs (N=3) and

processing times in the following time matrix. The unit of time is in minutes.

M N

Lathe (m/c 1)

Milling (m/c 2)

Milling (m/c 3)

Job 1 2.0 3.5 1.5 Job 2 4.5 3.0 2.5 Job 3 1.5 1.5 5.0

Example (cont.) •  Process variables:

– N = 3 (number of jobs) – M = 3 (number of machines: lathe, milling,

milling machines) •  Gantt Chart is used to illustrate the

permutation scheduling of each job sequence

•  First example: use the job sequence of 1, 2, 3

Example: Job Seq=1,2,3 M N Lathe (m/c 1) Milling (m/c 2) Milling (m/c 3)

Job 1 2.0 3.5 1.5

Job 2 4.5 3.0 2.5

Job 3 1.5 1.5 5.0

Job Sequence = 1, 2, 3

m/c 1

m/c 2

m/c 3 0 2 4 6 8 10 12 14 16 18 time (minutes)

Job 1 Job 1

Job 1

Job 2 Job 2

Job 3

Job 2

Job 3

Job 3

Makespan = 17 17

Now, you do it … M N Lathe (m/c 1) Milling (m/c 2) Milling (m/c 3)

Job 1 2.0 3.5 1.5

Job 2 4.5 3.0 2.5

Job 3 1.5 1.5 5.0

Job Sequence = 3, 2, 1

m/c 1

m/c 2

m/c 3 0 2 4 6 8 10 12 14 16 18 time (minutes)

Job 3

Job 3

Job 3

Job 2

Job 2 Job 2

Job 1 Job 1

Job 1

Makespan = 14

About the Makespan •  The “makespan” must accommodate: ①  The delay before the machine j can begin

processing ②  The total processing time on the machine j ③  The remaining processing time for the last job

after it leaves the machine j •  Calculate the “theoretical” lower bound

(LB)j based on machine j!

Theoretical Lower Bound (LB) •  A lower bound (LBj) based on machine j is

•  where pij is the (setup+processing) time of job i on machine j, N is the number of jobs, and M is the number of machines. The largest lower bound amongst all (LBj) is the lower bound for reference. That is,

!

LB j =mini

pirr=1

j"1

#$ % &

' ( )

+ piji=1

N

# +mini

pirr= j+1

M

#$ % *

& *

' ( *

) *

!

LBref =max LB1, LB2, ! , LBM

Calculating Theoretical LB

Machine 1 to 3 (j= 1, 2, 3) (LB)1= 0+(2+4.5+1.5)+min(3.5+1.5),(3+2.5),(1.5+5)= 13 (LB)2= min2,4.5,1.5+(3.5+3+1.5)+min1.5,2.5,5= 11 (LB)3= min(2+3.5),(4.5+3),(1.5+1.5)+(1.5+2.5+5)+0= 12

LB = max13,11,12 = 13 minutes

M N Lathe (m/c 1) Milling (m/c 2) Milling (m/c 3)

Job 1 2.0 3.5 1.5

Job 2 4.5 3.0 2.5

Job 3 1.5 1.5 5.0

Remarks •  The theoretical lower bound is 13

minutes. Thus, job sequence 1,2,3, having makespan of 17 minutes, most likely is not optimal/minimum

•  There are a total of 6 (3!=3!2!1=6) permutations of job sequence.

•  The job sequence of 3,1,2 has a makespan of 13.5 minutes ! minimum makespan

Procedures of Permutation Scheduling ① Establish the time matrix based on data/

time of machining, including set-up time ② Determine (LB)1, (LB)2, … , (LB)M for the

M machines ③ Determine the theoretical lower bound

④ Draw the Gantt chart based on permutation scheduling (a total of N! Gantt charts)

Note: there may be zero in the time matrix

!

LBref =max LB1, LB2, ! , LBM

1

ME325/580 Handout: Shop Scheduling with Many Products

Spring 2010 I. Kao Consider the set of jobs and processing times shown in the following table for three jobs on three machines. Generate the schedule assuming jobs are processed in the order of 1, 2, 3. The unit of the time in the following time matrix table is in minutes.

Milling (machine 1) Lathe (machine 2) Milling (machine 3) Job 1 2.0 3.5 1.5 Job 2 4.5 3.0 2.5 Job 3 1.5 1.5 5.0

Solution: The solution of the processing order 1, 2, 3 is summarized in the Gantt chart below. We start by assigning job 1 to machine 1 at time 0. Since p11 =2.0, the operation lasts until 2.0 minutes. Since all jobs must go to machine 1 first, the other machines are idle and the other jobs are queued. At 2.0 minutes, job 1 is loaded onto machine 2 and machine 1 starts on job 2, the second job in the sequence. Machine 2 finishes job 1, p12 =3.5 minutes later (time is now 5.5 min.). Machine 1 is still busy with job 2; thus, while job 1 is begun on machine 3, machine 2 is idle, waiting for job 2. The remainder of the schedule is shown in the figure. Note that the schedule reflects the rule that machine j starts job i when job i is finished on machine (j−1) and all jobs with earlier locations in the schedule have finished with machine j.

Mach 1 Job 1 Job 2 job 3 Mach 2 Job 1 Job 2 job 3 Mach 3 job 1 Job 2 Job 3 0 2 4 6 8 10 12 14 16

A few observations are in order: • Machine utilization probably can be made higher with less idle time via change of job

sequence. • Makespan is 17 minutes for 1, 2, 3 job sequence: machine 1 takes 8 minutes; machine 2

takes 9 minutes; machine 3 takes 11.5 minutes. • Lower bounds of time span can be established for reference of process scheduling efficiency.

2

Improve the efficiency and reduce makespan The makespan must accommodate:

(1) the delay before the machine can begin processing (2) the total processing time on the machine (3) the remaining processing time for the last job after it leaves the machine

Thus, a lower bound (LBj) based on machine j is

LBj = mini

pirr=1

j−1

∑⎧ ⎨ ⎩

⎫ ⎬ ⎭

+ piji=1

N

∑ + mini

pirr= j+1

M

∑⎧ ⎨ ⎩

⎫ ⎬ ⎭

where pij is the (setup+processing) time of job i on machine j, N is the number of jobs, and M is the number of machines. The largest lower bound amongst all (LBj) is the lower bound for reference. That is,

€

LBref =max LB1, LB2, , LBM where the (LBj) terms are obtained from the equation above. This LBref is the lower bound that is used as a reference in your design. In this example, the lower bounds can be calculated as follows. Machines 1 to 3 (j=1, 2, 3):

LB1= 0 + (2.0+4.5+1.5) + min(3.5+1.5), (3.0+2.5), (1.5+5.0) = 0+8+5 = 13 LB2= min2.0, 4.5, 1.5 + (3.5+3.0+1.5) + min1.5, 2.5, 5.0 = 11 LB3= min(2.0+3.5), (4.5+3.0), (1.5+1.5) + 9 + 0 = 12

Therefore, the reference lower bound is LB=13 minutes. Since the makespan for the job order 1, 2, 3 is 17 minutes, we suspect that it can be improved though we may not necessarily be able to reduce the makespan to 13 minute – the lower bound. There are 6 (3!= 3x2x1) permutations of the job order. Employ the same method to the other 5 permutations, we find that the most efficient scheduling is 3, 1, 2 with a makespan of 13.5 minutes. Exercise: Try to follow the above procedure to confirm that the 3, 1, 2 is indeed the most efficient scheduling with a makespan of 13.5 minutes.

100

1000

10000

20000

0 1 2 3 4 5 6 7

2000

5000

200

500

Shear rate (1/s)

ratio=1.25

ratio=1.0ratio=0.5

ratio=0.75

Typical viscosity for slurry used in industrial processesThe slurry used here consists of glycol carrier with silicon carbide gritsat F400 grain size (average grain size is 17 microns). The mixing ratiois in kilogram of silicon carbide grits vs. liter of carrier fluid. Theviscosity as a function of temperature also resembles the shape of curveshown here.

MEC325/580 Handout: Viscosity for Industrial Slurry

I. Kao Spring 2010

MEC325/580: Food/Soda Cans Manufacturing

Facts and Manufacturing Processes

Imin Kao, Professor Dept. of Mechanical Engineering

College of Engineering and App. Sci. SUNY at Stony Brook

Prof. Imin Kao

Do You Know?

•  Formaldehyde is added to many food cans •  The formaldehyde flavor legacy in can-

making •  You should NEVER cook food with the can •  A single can-tooling machine spits out 400

cans per minute •  250 millions cans per day are consumed

(one can per person per day)

Prof. Imin Kao

Why Using Formaldehyde in Can?

•  To kill bacteria! –  Steel cans in 1940s use an emulsion (95% water

and 5% oil) for lubrication in mfg process –  Certain bacteria eats oil in the emulsion, so the

biocide is added –  Amount is not enough to cause health hazard, but

enough to taste –  This results in the famous preservative flavor (e.g.,

in Budweiser)

Prof. Imin Kao

Formaldehyde Flavor Legacy

•  Why not use biocides without flavor? –  Yes, mfg’ers do that in recent years (e.g., Miller

Genuine Draft and other similar brews)

•  Almost every new emulsion formula had to be made to taste like formaldehyde or else people aren’t going to accept it.

•  Are there any other things/additives in your food or beer/soda cans?

Prof. Imin Kao

Polymer in Your Food Can

•  Polymer (in solvent) is spray-coated inside to serve two functions: –  Plasters any microscopic debris (resulting from mfg proc) to

the can wall and away from the food –  Keeps the food from interacting with can material (e.g.,

tomato acid to corrode the can)

•  Don’t cook the food in the can when you go camping! –  Or else you will be eating polymer (since they degrade when

heated) –  Typical consequence of such a culinary blunder: headaches

and constipation

Prof. Imin Kao

Soda Can Manufacturing

•  Soda can manufacturers are competing with low-priced plastic and glass bottles

•  A single can-tooling machine can spit 400 cans a minute (i.e. 7 cans per second!!)

•  For one can per a person per day –  Need 250 million cans per day

•  Employ the “Deep Drawing” process

Prof. Imin Kao

Manufacture of Aluminum Can Starting Material:

Canstock from a roll

Cupper

Bodymaker (inkl.domer and trimmer)

Washer Printer Printerdrier oven

Insidecoating

Inside coatingdrier oven

Shipment ofcan to filler

Flanger

Necker

Prof. Imin Kao

Manufacturing Process (I)

Source: J. E. Wang, Texas A&M University

Prof. Imin Kao

Manufacturing Process (II)


Prof. Imin Kao

Finished Product of Can


Prof. Imin Kao

Can Top: material and design


Prof. Imin Kao

Video Clip (source: Discovery Channel)

Prof. Imin Kao

Process & Materials

•  Cost of mfg: $40 per 1,000 cans (4 cent @) •  Major cost is on the lid of the can

–  Body made of AA3004 aluminum (Al 97.8%; Mg 1.0%) with a yield strength 170 MPa and tensile strength 215 Mpa.

–  Lid made of a stronger aluminum alloy of AA5182 (Al 95.2%; Mg 4.5%) with a yield strength 395 MPa and tensile strength 420 Mpa.

•  The necking at the lid: to reduce cost of material

Prof. Imin Kao

What Are You Paying?

•  A typical breakdown of what you are paying in a can of soda: –  4 cents for making the can (major cost:

magnesium aluminum alloy with higher ductility) –  10 cents (or more) goes for advertising –  Less than 1 cent for the 12 ounces of beverage!

•  That’s why the no-name brand soda sells for much less in stores!

Prof. Imin Kao

Summary

•  Formaldehyde smell in food and beer cans •  Do not cook food with the can when go

camping •  Addition of polymer inside the can to

protect the can/food, and to enclose mfg remains

•  How much are you paying in a can of soda

HANDOUT ON STATISTICAL PROCESSCONTROL (SPC)


1 Statistical Process Control and Methodology

The “statistical process control” (SPC) uses various statistical methods to assess and analyze variations in aprocess. SPC keeps record of production data, histogram, process capability, and control charts. Two controlcharts are most widely used in SPC, which will be discussed inSection 2.

There are two types of variations considered in SPC: (1) random variations and (2) assignable variations.The former is present if the process is in statistical control; the latter indicates departure from statisticalcontrol. The control charts are used to identify when the process has gone out of statistical control, thussignaling that some corrective actions should be taken. A process is out of control if there are significantchanges in eitherprocess mean or process variability.

2 Control Charts of SPC

The use of control charts is a technique in which statistics computed from measured values of a certain processcharacteristics are plotted over time to determine if the process remains in statistical control. The chart consistsof three horizontal lines: a center, a lower control limit (LCL), and a upper control limit (UCL), as shown inFigure 1. The process is said to be out of statistical controlif sample is out of these limits.

Two types of control charts are commonly used in SPC. They arethe x-chart and theR-chart. Thex-chart plots the average measured value of a series of samples, with LCL and UCL bounds corresponding to3σ standard variation; whereas, theR-chart plots the range of each sample, with its corresponding LCL andUCL.

In SPC, samples are taken at every designated time period (e.g., every 15 minutes) and certain number ofmeasurements (or parts) are taken per each sample.The variablem denotes the number of samples, andnis the number of measurements (d1, d2, · · · , dn) per sample, or thesample size that is designated in Table 1.Therefore, for each sample, we can compute

x =

∑

ni=1 di

n(1)

R = maxd1, · · · dn − mind1, · · · dn (2)

The mean values ofx and the range are thus

¯x =

∑

mj=1 xj

m(3)

R =

∑

mj=1 Rj

m(4)

1

Table 1: Constants for thex andR charts. Note that the “Sample size” (n) is the number of measurement pereach sample.

Sample size x-chart R-chartn A2 D3 D4

3 1.023 0 2.5744 0.729 0 2.2825 0.577 0 2.1146 0.483 0 2.0047 0.419 0.076 1.9248 0.373 0.136 1.8649 0.337 0.184 1.816

10 0.308 0.223 1.77711 0.29 0.26 1.7412 0.27 0.28 1.7213 0.25 0.31 1.6914 0.24 0.33 1.6715 0.22 0.35 1.6516 0.21 0.36 1.6417 0.20 0.38 1.6218 0.19 0.39 1.6119 0.19 0.40 1.6020 0.18 0.41 1.59

The equations for computing the upper and lower bounds are:

x − chart:

LCL = x − 3σ = ¯x − A2RUCL = x + 3σ = ¯x + A2R

(5)

R − chart:

LCL = D3RUCL = D4R

(6)

where the constants:A2,D3, andD4 are listed in Table 1.Note that Table 1 is listed according to the samplesizen, or preferably called thenumber of measurement, not the number of samplesm.

The procedure for constructing the charts is in the following.

1. Compute the mean (x) out of n measurements, and the range (R) for each of them samples usingequations (1) and (2).

2. Compute the grand meanx, which is the mean of thex values for them samples using equation (3).This will be the center for thex-chart.

3. ComputeR, which is the mean of theR values for them samples using equation (4). This will be thecenter for theR-chart.

4. DetermineUCL andLCL, based on equations (5) and (6) and the constants listed in Table 1.

2

Sample number d1 d2 d3 d4

1 2.46 2.40 2.44 2.462 2.45 2.43 2.47 2.393 2.38 2.48 2.42 2.424 2.42 2.44 2.53 2.495 2.42 2.45 2.43 2.446 2.44 2.45 2.44 2.397 2.39 2.41 2.42 2.468 2.45 2.41 2.43 2.41

Table 2: SPC for 8 samples, each with 4 measurements

2.1 LCL and UCL with known mean and standard deviation

For some processes, the mean and standard deviation of the process may be known. Under such circumstances,the parameters of thex-chart can be obtained as follows:

x = µ (7)

LCL = µ −

3σ√

n(8)

UCL = µ +3σ√

n(9)

whereµ is the process mean,σ is the standard deviation of the process,n is the number of measurement (orsample size), andσ

√

nis the standard deviation of the sample mean.

Equations ofLCL andUCL this section and the previous section have control limits set at 99.73% of thesamples at 3-sigma range.

3 An Example

Samples are collected from an extrusion process that is in statistical process control, and the diameter of theextrudate is measured incm. Eight samples are taken with a time interval of 15 minutes between each samplefor a duration of 2 hours. Four measurements (d1 to d4) are performed in each sample. The quantityx is theaverage of four measurements in each sample, andR is the range of measurements. The measurements aretabulated in Table 2. Answer the following questions.

1. Find the grand average,¯x, and the control limits (LCL andUCL) of thex-chart.

2. Calculate the average ofR, and the control limits (LCL andUCL) of theR-chart.

3. Construct thex-chart andR-chart.

4. Another sample was taken with four measurements as follows: 2.41, 2.50, 2.49, 2.55. Determine ifthe process is out of (statistical) control, based on the previously established control charts.

Solution: We first identify that the number of measurement per each sample (or sample size) isn = 4 with atotal number of 8 sample batches,m = 8. The averagex and the rangeR are calculated and shown in Table 3.

3

x = (∑

di)/4 R

1 2.440 0.062 2.435 0.083 2.425 0.104 2.470 0.115 2.435 0.036 2.430 0.067 2.420 0.078 2.425 0.04

Table 3: The tabulated data forx andR

From Table 3, we find¯x = 2.435 R = 0.06875 (10)

1. From the above results, equations (5) and (6), and Table 1 with 4 measurements per sample (or thesample size), we haven = 4. Thus, we compute:

¯x = 2.435 (11)

LCL = 2.435 − (0.729) × 0.06875 = 2.3849 (12)

UCL = 2.435 + (0.729) × 0.06875 = 2.4851 (13)

Thex-chart is plotted in Figure 1.

2. Similarly, we can compute forR-chart:

R = 0.06875 (14)

LCL = D3R = 0 (15)

UCL = D4R = (2.282) × 0.06875 = 0.1569 (16)

TheR-chart is plotted in Figure 1.

3. See Figure 1.

4. For the next sample with four measurements: 2.41, 2.50, 2.49, 2.55, we find

x =

∑

4

i=1 di

4= 2.4875 R = 2.55 − 2.41 = 0.14 (17)

Hence, it is out of control (due to thex-chart).

4 Control Charts for Attributes

In addition to thex-chart andR-chart, two other charts are used for attributes. They are used to monitor thenumber of defects present in sample, or the fraction of defect rate, for example, the number of defects perautomobile, existence or absence of flash in a plastic molding. Two types of charts are used: thep-chart andthec-chart.

4

R-chart

0.000

0.020

0.040

0.060

0.080

0.100

0.120

1 2 3 4 5 6 7 8

0.06875

0.140

0.160

LCL= 0.0

UCL= 0.1569

x-chart

2.390

2.400

2.410

2.420

2.430

2.440

2.450

2.460

2.470

2.480

1 2 3 4 5 6 7 8

2.435

2.380

2.490

UCL= 2.4851

LCL= 2.3849

Figure 1: Thex-chart andR-chart

4.1 The p-chart

Thep-chart plots the fraction defect rate in successive samples. The “p” stands forproportion which is definedas

pi =di

n(18)

for m samples of equal sizen, wheredi is the number of defective items, andn is the number of parts in

sample. The parameters are calculated based on binomial distribution with standard deviationσ =√

p(1−p)

n.

Form samples of equal sizen, the center and control limits are

p =

∑

mi=1 pi

m(19)

LCL = p − 3

√

p(1 − p)

n(20)

UCL = p + 3

√

p(1 − p)

n(21)

If LCL < 0 then useLCL = 0 in equation (20).

5

4.2 The c-chart

The c-chart plots the number of defects or flaws per sample. Thec stands forcount. The parameters of thec-chart are based on the Poisson distribution. They are

c =

∑

mi=1 ci

m(22)

LCL = c − 3√

c (23)

UCL = c + 3√

c (24)

whereci is the number of imperfections or number of events occurringwithin a defined sample space (e.g.,defects per car). IfLCL < 0 then useLCL = 0 in equation (23).

References

[1] M. P. GrooverFundamentals of Modern Manufacturing: materials, processes, and systems Wiley, seconded., 2002

[2] S. Kalpakjian and S. R. SchmidManufacturing Processes for Engineering Materials Prentice Hall, fourthed., 2003

6

Statistical Process Control (SPC)


What is SPC? •  SPC

–  is based on the 3-! principle –  uses various statistical methods to assess and

analyze variations in a process –  keeps record of production data, histogram,

process capability, and control charts

•  Two Types of Variations Considered 1.  Random variations 2.  Assignable variations

SPC and Control Charts •  Control charts are used to identify when

the process has gone out of statistical control ! require corrective action

•  A process is “out of control”, if there are significant changes in – Process mean, or – Process variability

Control Charts •  Three horizontal lines

– Center – LCL: Lower control limit – UCL: Upper control limit

Control Chart: Types •  Two Types:

– The – The R-chart

!

x " chart

Variables for Control Charts •  SPC takes samples at designated time

interval (e.g., every 15 minutes) •  Variables:

– m: the number of samples –  n: the number of measurement per sample (or

the sample size) – Example: takes samples every 15 minutes for 8

hours, each time with 8 parts in the sample ! m = 32; n = 8

Computing the Parameters The n measurements are denoted as: d1, d2, … dn

Computing LCL and ULC •  The LCL and UCL for the two charts

Constants for the Charts

Note: The tables is based on the “Sample size” (n, or the number of measurement in each sample), not “m”

Procedures ① Compute the mean out of n

measurements, and the range R for each of the m samples

② Compute the grand mean for the m samples ! center of the x-chart

③ Compute the mean of range for the m samples ! center of the R-chart

④ Determine UCL and LCL to complete the charts

Example SPC for 8 samples, each with 4 measurements

Example (cont.)

Control Charts

UCL & LCL with known Std Dev

Control Charts for Attributes •  The p-Chart

The proportion is defined as:

with

Control Charts for Attributes •  The c-Chart

1

MEC325/580 Handout: Stainless Steel Spring 2010 I. Kao Supplementary Lecture about Stainless Steel The corrosion resistance is imparted by the formation of a strong adherent chromium oxide on the surface of metal. On the other hand, existence of carbon will form chromium carbide which takes away ability for chromium to form the shielding chromium oxide. When the amount of atomic chromium in solution exceeds 12%, improved corrosion resistance and outstanding appearance are achieved. This category forms what has been commonly called the true stainless steels. Several classification schemes have been devised to categorize the stainless steel alloys. The American Iron and Steel Institute (AISI) groups the metals by chemistry and assigns a three-digit number that identifies the basic family and the particular alloy within that family. The following table presents the AISI designation scheme for stainless steels and correlates it with the microstructural families.

Series Alloys Structure Magnetic? 200 chromium, nickel, manganese, or nitrogen austenitic No 300 chromium, nickel austenitic No 400 chromium only ferritic or martensitic Yes 500 low chromium (<12%) martensitic Yes

The material can also be grouped by microstructural families. In general, there are five main types as will be described in the following, although new stainless steel alloys have been developed to meet special needs. (1) Austenitic (200 and 300 series): These steels are generally composed of chromium, nickel,

and manganese in iron. Nickel is an austenite stabilizer, and with sufficient amounts of both chromium and nickel, it is possible to produce a stainless steel in which austenite is the stable structure at room temperature. Known as austenitic stainless steels, these alloys may cost twice as much as the ferritic variety, with the added expense being attributed to the cost of the alloying nickel and chromium. Manganese and nitrogen are also austenite stabilizers and may be substituted for some of the nickel to produce a lower-cost, somewhat lower-quality austenitic stainless steel. Austenitic stainless steels are nonmagnetic and are highly resistant to corrosion in almost all media except hydrochloric acid and other halide acids and salts. However, they are susceptible to stress-corrosion cracking. In addition, they may be polished to a mirror finish and thus combine attractive appearance and corrosion resistance. Formability is outstanding (characteristic of the FCC crystal structure), and these steel strengthen considerably when cold worked. The popular 304 alloy, suited for all types of dairy equipment, brewing industry, citrus and fruit juice industry, dye tanks, pipelines buckets, dippers, and food processing industry, is also known as the 18-8 because of the composition of 18% chromium and 8% nickel (18-8 also refers to 302, 303, 305, and 384). Austenitic stainless steels are hardened by cold-working. They are most ductile of all stainless steels, so they can be easily formed, although, with increasing cold work, their

2

formability is reduced. These steels are in a wide variety of applications, such as kitchenware, fittings, welded construction, lightweight transportation equipment, furnace and heat-exchanger parts, and components for severe chemical environment.

(2) Ferrite (400 series): These steels have a high chromium content—up to 27%. Chromium is a ferrite stabilizer, the addition of chromium tending to increase the temperature range over which ferrite is the stable structure. If sufficient chromium is added to the iron, and carbon is kept low, an alloy can be produced that is ferrite at all temperatures below solidification. These alloys are known as ferritic stainless steels. Such ferrite alloys are also the cheapest type among stainless steels. They are magnetic and have good corrosion resistance. Ferrite stainless steels possess rather poor ductility or formability because of the BCC crystal structure (they have lower ductility than austenitic stainless steels), but they are readily weldable. They are hardened by cold-working and are not heat-treatable. They are generally used for nonstructural applications such as kitchen equipment and automotive trim.

(3) Martensitic (400 and 500 series): Most martensitic stainless steels do not contain nickel and are hardenable by heat treatment. Their chromium content may be as much as 18%. If increased strength is needed, the martensitic stainless steels should be considered. However, caution should be taken to assure more than 12% chromium in solution. Slow cools may allow the carbon and chromium to react and form chromium carbides. When this occurs, the chromium is not available to react with oxygen and form the protective oxide. Thus the martensitic stainless steels may only be “stainless” when in the martensitic condition (when the chromium is trapped in atomic solution), and may be susceptible to red rust when annealed or normalized for machining or fabrication. The martensitic stainless steel cost about 1.5 times as much as the ferritic alloys, part of being due to the additional heat treatment, which generally consists of an austenitization, quench, stress relief, and temper. These stainless steels are magnetic. Martensitic stainless steels have high strength, hardness, and fatigue resistance, good ductility, and moderate corrosion resistance. They are typically used for cutlery, surgical tools, instruments, valves, and springs.

(4) Precipitation-hardening (PH): A fourth and special class of stainless steels is the precipitation-hardening variety. These steels contain chromium and nickel, along with copper, aluminum, titanium, or molybdenum. These alloys are basically martensitic or austenitic types, modified by the addition of alloying elements such as aluminum that permit age hardening at relatively low temperatures. By adding age hardening to the existing strengthening mechanisms, these materials are capable of attaining properties such as a 260-ksi (1790-MPa) yield strength and 265-ksi (1825-MPa) tensile strength with a 2% elongation.

They have good corrosion resistance and ductility, and they have high strength at elevated temperatures. Their main application is in aircraft and aerospace structural components.

(5) Duplex structure: Duplex stainless steels contain between 21 to 25% chromium and 5 to 7% nickel and are water quenched from a hot-working temperature that is between 1830 and 1920°F to produce a microstructure that is approximately half ferrite and half austenite. The structure offers a higher yield strength and greater resistance to stress corrosion cracking than either then austenitic or ferritic grades. These steels have a mixture of austenite and ferrite.

3

They have good strength, and they have higher resistance to both corrosion and stress-corrosion cracking than do the 300 series of austenite steels. Typical applications are in water-treatment plants and in heat-exchanger components.

(6) Other stainless steels: Still other stainless alloys have been developed to meet special needs.

Ordinary stainless steels are difficult to machine because of their work-hardening properties and their tendency to seize during cutting. Special free-machining alloys have been produced within each family, with addition of sulfur or selenium raising the machinability to approximately that of a medium-carbon steel.

The following tables shows typical alloy compositions, structure, and usage for the first three families of stainless steels.

TABLE: Typical Composition (in wt. %) of the ferritic, martensitic, and austenitic Stainless Steels

Element Ferritic Martensitic Austenitic Carbon 0.08-0.20 0.15-1.2 0.03-0.25 Chromium 11-27 11.5-18 16-26 Manganese 1-1.5 1 2 (5.5-10) Molybdenum some cases Nickel 3.5-22 Phosphorus and sulfur Normal (0) Silicon 1 1 1-2 (0) Titanium Some cases

TABLE: Popular alloys structures and AISI designation for three primary types of stainless steel

AISI Type Martensitic (Hardenable by heat treatment )

410, 420, 440C

Ferritic (More corrosion resistant than martensitic, but not hardenable by heat treatment)

405, 430, 446

Austenitic (best corrosion resistance, but hardenable only by cold working)

201, 202, 301, 302, 302B, 304L, 310, 316, 321

TABLE: Key purpose and usage for different stainless steel alloys

Purpose and Usage AISI Types General purpose 410, 430, 202, 302 Automobile parts 301, 409, 430, 434 Hardenable by heat treatment 410, 420, 440C Hardenable by cold working 201, 301 For elevated-temperature service 446, 302B, 310

4

Modified for welding 405, 304L, 321 Superior corrosion resistance 316 Catalytic converters 409

Remarks: (1) Sensitization: Problems with stainless steels are often due to the loss of corrosion resistance

(sensitization) when the amount of chromium in solution drops below 12%. Since chromium depletion is usually caused by the formation of chromium carbides along grain boundaries, and these carbides form at elevated temperatures, various means have been developed to prevent their formation. One approach is to keep the carbon content of stainless steels as low as possible, usually less than 0.10%. Another method is to tie up the carbon with small amounts of “stabilizing” elements, such as titanium or niobium, that have a stronger affinity for carbon than does chromium. Rapidly cooling of these metals through the carbide-forming range of 900 to 1500°F (480 to 820°C) also works to prevent carbide formation.

(2) Embrittlement: Another problem with high-chromium stainless steels is an embrittlement that occurs after long times at elevated temperatures. This is attributed to the formation of sigma phase, a brittle compound that forms at elevated temperatures and coats grain boundaries, thereby producing a brittle crack path through the metal. Stainless steels used in high-temperature service should be checked periodically to detect sigma-phase formation.

(3) Passivation & surface treatment: According to ASTM A380, passivation is “the removal of exogenous iron or iron compounds from the surface of stainless steel by means of a chemical dissolution, most typically by a treatment with an acid solution that will remove the surface contamination, it will not significantly affect the stainless itself.” In addition, it also describes passivation as “the chemical treatment of stainless steel with a mild oxidant, such as a nitric acid solution, for the purpose of enhancing the spontaneous formation of the protective passive film.” Passivation is recommended where the surface must be free of iron. Passivation can also aid in the rapid development of the passive surface layer on the steel, but usually does not result in a marked change in appearance of the steel surface. Passivation is performed with acid solutions (or pastes) to remove contaminants and promote the formation of the passive film on a freshly created surface (for example, via grinding, machining or mechanical damage). Common passivation treatments include nitric acid (HNO3) solutions or pastes which will clean the steel surface of free iron contaminants. Since dangerous acids are involved, only trained personnel can perform such process. In addition, stainless steel pickling acids are highly corrosive to carbon steel, and should be thoroughly removed by rinsing the component after completing the process, and/or neutralize with alkali before the rising. Residual hydrofluoric acid will initiate pitting corrosion.

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ME325/580 SME Video: Sheet Metal Stamping Dies & Processes

Spring 2010 I. Kao 1. Stamping dies are the tools that shape and cut sheet metal parts. The main manufacturing

requirement for most sheet metal applications is good formability. Sheet metal formability is metal’s ability to deform into intricate shapes without defects in the finished part.

2. Types of deformation include • Bending • Stretching • Drawing

3. Formability factors include • Metal’s ductility • Die design • Stamping press • Press speed • Lubrication • Sheet metal feeding mechanisms • Monitoring/control systems

4. Most sheet metals range from thickness of 20 to 80 thousands. Low carbon or mild steels are most commonly used in automotive industry. Aluminum and its alloys are most commonly used nonferrous sheet metals.

5. Definitions of dies used in sheet metal forming • As its generic term: Dies represent the entire press tooling used to cut and form metals. • Dies refers to only the female part of the tooling. In this reference, the tooling includes:

punch, die, and die set.

6. Basic die operations: • Cutting – shearing, blanking, hole punching, trimming • Bending • Forming – shape of punch and die is reproduced directly on the metal • Drawing • Squeezing

7. Two most common types of dies are cutting and forming dies.

8. Proper clearance needed for operation is determined by • Material type • Workpiece thickness • Material temper

9. Factors determining the blankholder pressures vary from part to part but depend on • draw reduction severity • metal properties • metal thickness • die lubrication and other factors

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10. Use of flanged edge for • part appearance • part rigidity • edge strengthening • metal thickness • die lubrication & other factors

11. Four basic types of hems in hemming processes • Flat hem • Tear drop hem • Open hem • Rope hem (open and rope hems are used to join metal parts.)

12. Single station dies include: (1) compound dies, and (2) combination dies. Multiple station dies include: (1) progressive dies, and (2) transfer dies.

13. Die lubrication’s main function is to minimize surface contact between the tolling and the workpiece.

14. Effective lubrication results in • controlled friction • reduced force • reduced power requirements • reduced tooling stresses

15. Proper lubrication (1) extends tooling life, and (2) eliminates surface damage.

16. Choice of lubrication determined by • operation type • tooling design • tooling materials • metal to be formed • press speed • lubrication application method

17. Types of lubricants • oil-based lubricants • water soluble lubricants • synthetic lubricants

18. Application methods for lubrication • manual • dip • roller • spraying • flooding

19. stamping analysis: circular grid analysis (CGA) are usually used for stamp analysis. Others: • metal flow • tool/workpiece friction • behavior properties of stamped materials

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MEC325/580 HANDOUT: TAYLOR ’ S TOOL WEAR EQUATION

Spring 2010 I. Kao

1 Introduction

The Taylor’s equation for tool wear is expressed in a power-law equation form, as follows

v T n = C (1)

Equation (1) is a standard nonlinear power equation. In the case of equation presented in equation (1), wecan take logarithmic relationship of the variables and makea linear equation in the log-log coordinates, asexpressed in the following equation

log v + n log T = log C (2)

Equation (2) represents a line in the(log T, log v) space.In the next sections, an example is given for finding the exponentn, and the coefficient,C, for a tool byapplying the Taylor equation for tool wear.

2 Finding Parameters of the Taylor’s Tool Wear Equation

Equation (2) is a result of taking logarithmic form of equation (1). At least two sets of experimental data oftool speed and life are required to find the exponentn and the coefficientC. If the two experimental datasets are given as(T1, v1) and(T2, v2), we can write equation (2) for the two data sets as

log v1 + n log T1 = log C (3)

log v2 + n log T2 = log C (4)

Equation (3) minus (4) renders the following

n =log v2 − log v1

log T1 − log T2

=log(v2/v1)

log(T1/T2)(5)

Once the exponentn is obtained from equation (5), the result can be substitutedinto equation (1) to find thecoefficientC = v1 T n

1.

3 Example: Experimental Results

Experiments were conducted to characterize the parametersof tool wear based on the Taylor’s equation.The experimental results of the relationship between the tool speed and tool life are tabulated in thefollowing. The points are corresponding to the following figure (the first two circled points).

exp data tool life, T velocity,vset 1 100min 400m/min

set 2 240min 300m/min

Applying the data of experiments in the table to equation (5), we obtain

n =log(300/400)

log(100/240)=

−0.1249

−0.3802= 0.3286 (6)

1

101

102

103

102

103

Tool life (min)

spee

d of

tool

(m

/min

)

Plot of Taylor’s tool life equation

Figure 1: The raw data of experiments are indicated by ’o’. The results of equation of tool wear is plottedas a line in the logarithmic space oflog T versuslog v.

Substituting into equation (1), we findC = 1817. Thus, the Taylor’s equation of tool wear is

v (T )0.3296 = 1817 (7)

where the tool speedv has a unit ofm/min and the tool lifeT is in minutes.The result of the tool life relationship in equation (7) is plotted in Figure 1, in logarithmic scale. The twocircles indicate the two sets of experimental measurementsgiven in the table.

2

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MEC325/580 Handout: Milling Process and Machines Spring 2010 I. Kao Milling—A machining operation in which a workpiece is fed past a rotating cylindrical tool with multiple cutting edges. Two (2) basic types of milling operations:

1. peripheral milling: the axis of tool is parallel to the surface being machined; the machining is performed by cutting edges on the outside peripheral of the cutter.

2. face milling: the axis of cutter is perpendicular to the surface being machined; common type of end mill found in machine shop.

An illustration of these two basic types of milling operations is shown in the following figure.

Classification of milling machines: Various classifications are used, as follows

1. Horizontal spindle (for peripheral milling) or Vertical spindle (for face milling, end mill, …) 2. Types including (i) knee and column (most common type), (ii) bed type, (iii) planer type, (iv) tracer

mills, and (v) CNC milling machines

Two forms of milling processes: up milling and down milling Milling is an interrupted cutting process wherein entering and leaving the cut subjects the tool to impact loading, cyclic heating, and cycle cutting forces. Two common types of milling configurations are: up milling (or conventional milling) and down milling (or climb milling). The former has the tool and workpiece moving in

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opposite directions; whereas in the latter, the tool moves in the same direction as the work feed. In up milling, the chip is very thin at the beginning, where the tooth contacts the work, and increases in thickness, becoming a maximum where the tooth leaves the work.

Advantages include: (1) The cutter tends to push the work along and lift it upward from the table. This action tends to

eliminate any effect of looseness in the feed screw and nut of the milling machine table and results in a smooth cut.

(2) Tooth engagement is not a function of workpiece surface characteristics, and contamination or scale on the surface does not affect tool life.

(3) There is a tendency for the tool to chatter.

Disadvantages include: (1) The action also tends to loosen the work from the clamping device; therefore, greater clamping

forces must be employed. (2) The smoothness of the generated surface depends greatly on the sharpness of the cutting edges. (3) The chips can be carried into the newly machined surface, causing the surface finish to be poorer

(rougher) than in down milling. In down milling, maximum chip thickness occurs close to the point at which the tooth contacts the work. Because the relative motion tends to pull the workpiece into the cutter, any possibility of looseness in the table feed screw must be eliminated if down milling is to be used. It should never be attempted on machines that are not designed for this type of milling. Virtually all modern milling machines are capable of doing down milling. Metals that readily work harden should be climb milled.

Advantages include: (1) Because the material yields in approximately a tangential direction at the end of the tooth

engagement, there is less tendency (than when up milling is used) for the machined surface to show toothmarks.

(2) The cutting process is smoother with less chatter. (3) The cutting force tends to hold the work against the machine table, permitting lower clamping

forces, particularly for slender parts. (4) Recommended for maximum cutter life when CNC machine tools are used. (5) Suitable for finishing cuts, e.g., on aluminum.

Disadvantages include: (1) The fact that the cutter teeth strike against the surface of the work at the beginning of each chip can

be a disadvantage if the workpiece has a hard surface, as casting sometimes does. (2) The teeth may dull more rapidly. (3) Because of the resulting high impact forces when the teeth engage the workpiece, this operation

must have a rigid setup, and backlash must be eliminated in the table feed mechanism. (4) It is not suitable for workpiece having surface scale, such as hot-worked metals, forgings, and

castings – because the scale is hard and abrasive and causes excessive wear and damage to cutter teeth, thus tool life can be short.

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Probable Cause of Milling Problems and Cures (cf. DeGarmo, et al. “Materials and Process in Manufacturing”)

Problem Probable Cause Cures Chatter (vibration)

1. Lack of rigidity in machine,

fixture, arbor, or workpiece 2. Cutting load too great 3. Dull cutter 4. Poor lubrication 5. Straight-tooth cutter 6. Radial relief too great 7. Rubbing, insufficient clearance

Use large arbors Decrease feed per tooth or number of teeth in contact Sharpen or replace inserts Flood coolant Use helical cutter Check tool angles

Loss of accuracy (cannot hold size)

1. High cutting load causing deflection

2. Chip packing, between teeth 3. Chips not cleaned away before

mounting new piece of work

Decrease number of teeth in contact with work or feed per tooth Adjust cutting fluid to wash chips out of teeth

Cutter rapidly dulls 1. Cutting load too great 2. Insufficient coolant

Decrease feed per tooth or number of teeth in contact Add blending oil or coolant

Poor surface finish 1. Feed too high 2. Tool dull 3. Speed too low 4. Not enough cutter teeth

Check to see if all teeth are set at same height

Cutter dig in (hogs into work)

1. Radial relief too great 2. Rake angle too large 3. Improper speed

Check to see that workpiece is not deflecting and is clamped securely

Work burns 1. Cut is too light 2. Tool edge worn 3. Insufficient radial relief 4. Land too wide

Enlarge feed per tooth Sharpen cutter

Cutter burns 1. Not enough lubricant 2. Speed too high

Add sulfur-based oil Reduce cutting speed Flood coolant

Teeth breaking 1. Feed too high

Decrease feed per tooth Use cutter with more teeth Reduce table feed rate

WIRE DRAWING PROCESS ANDANALYSIS


Extrusion Problem: In a wire drawing process to reduce the diameter of a plain carbon steel wire fromD0 = 220µm to Df = 175µm in a cold working process, the angle of the die isα = 15 and thecoefficient of friction isµ = 0.1. The plastic strength of the material isK = 500MPa with a strainhardening exponent ofn = 0.25. The tensile strength of the steel wire isSut = 390MPa.

1. Determine if the process is feasible?

2. If the drawing process is feasible, what is the force required for the wire drawing process?

3. Determine the safety margin of the drawing force versus the rupture force of the wire. Is this wiredrawing process safe?

Solution : First, we need to determine if the drawing process is feasible, based on the parameters given.

1. The maximum reduction per pass is

A0

Af

= e = 2.71828 =⇒ rmax = 63.2% (1)

Here, the reduction isr =A0−A

f

A0=

D2

0−D2

f

D2

0

= 36.7%. Thus, the drawing process is feasible.

2. The drawing force is

F = Af Yf

(

1 +µ

tan α

)

φ lnA0

Af

=π

4

(

175 × 10−6)2

× 3.29 × 108(

1 +0.1

tan 5

)

(0.9719)(0.4577)

= 7.54N

whereǫ = ln A0

Af

= 0.4577, Yf = 500×106(0.4577)0.25

(1+0.25) = 329MPa, D =D0+D

f

2 = 197.5µm,

Lc =(D0−D

f)

2 sinα= 258µm, andφ = 0.88 + 0.12 D

Lc

= 0.9719.

3. The force to rupture, depending on the tensile strength, is

Fr = Af · Sut =π

4D2

f · Sut =π

4(175 × 10−6)(390 × 106) = 9.38N (2)

Thus, the safety margin is

ns =Fr − F

Fr

=9.38 − 7.54

9.38= 20% (3)

ME325/580 SME Video: Workholding

Spring 2010 I. Kao Workholding includes any device used to grip and present the work piece to a cutting tool on a machine tool. It includes

• clamps • vises • fixtures • chucks • others

I. Principles of workholding 1. Important process and/or properties of workholding

• Reference surface/datums • Machinable surfaces • Process accuracy • Allowable cutting forces, feeds, and shapes • Tool path, size, and shape

2. There are a total of 12 degrees-of-freedom (dof) to be constrained for locating. They include three linear and three rotational dof each having two directions (+ and −).

3. 3-2-1 locational method: six points of contact • 3 primary locators (constrain 5 dof) • 2 secondary locators (constrain 3 dof) • 1 tertiary locator (constrain 1 dof) with additional clamping which takes care of the other 3 dof.

II. Milling and machining centers workholding • Manual clamps • Toggle clamps • Vises & vises types • Swivel bases • Multi-vises • Tombstones • Rotary tables • Indexing rotary tables • “Full” rotary tables • Modular fixturing • Pallets • Pallet changers • Manual pallet changing • Pre-fixtured pallets • Hydraulic clamping • Dedicated fixtures • Chucks on mills

• Chucks on tombstone

III. Lathe workholding • 3 & 6 jaw chucks • Master jaws • Top jaws • Soft jaws • Automatic chucks • 4 & 2 jaw chucks • Indexing chucks • Collets – round bars, cylindrical slugs • Multi-size collets • Bar feeding • Collet chucks • Between center turning • Steady rest • Face driving • Expanded mandrels • Magnetic chucks • Workholding on 2-spindle lathes


Final Exam

Documents

false stainless steel

false high speed steel

false high speed steel

passivation of stainless

thirds of carbide tools

cutting speed ceramic

high heat edm

high chromium content