Booklet for Machining Process

Machining

2.810 Fall 2009

T. Gutowski

go to website below

http://electron.mit.edu/~gsteele/mirrors/www.nmis.org/EducationTraining/machineshop/mill/intro.html

Tools to cut and scrape goback at least 150,000 yrs

Stone work in Cuzco

http://electron.mit.edu/~gsteele/mirrors/www.nmis.org/EducationTraining/machineshop/mill/intro.html

Readings

Kalpakjian Ch 21-27

“Simplified Time Estimation Booklet

for Basic Machining Operations”

Design for Machining handout

Outline

1. Basics

2. Machine Configurations

3. Production Configurations

4. Processing Planning

5. Environment

Basics: Machining Process Single point machining

Turning, boring, trepanning, planing

Multiple point machining

Drilling, milling, reaming, sawing, broaching, grinding

Tool Stationary: turning, boring…

Tool moves: sawing, milling, drilling, broaching

Work Piece moves: milling, boring…

Both move: milling, 5 axis milling

Machining processes

Horizontal Slab milling Face milling End milling

Cutter Arbor

Arbor

Spindle

Spindle

End mill

Shank

Turning

Milling

* Source: Kalpakjian, “Manufacturing Engineering and Technology”

*

* Grinding

Grindingwheel

DGrains

Workpiecev

V

Horizontal-spindle surface grinderMachine Tools

Column

Base

Head

Table

Saddle

Knee

*

Spindlespeed

selector

Feed change

gearbox

Compound rest and slides (swivels) Apron

Bed

Lead screw

Feed rod

Headstock

Spindle

Cross slideWays

Carriage

Center

Tailstock quill

Tailstock

Basic Lathe

Vertical-Spindle Mill

*


*

Basic Mechanics Issues

Power, Forces

Heat, Tool materials, Rate limits

Temperature

Surface finish

See Video on Plastic Deformation

Basic Machining Mechanism

Shear takes place ina narrow zone nearthe tool tip at angle ,the tool has rake angle , the resulting shears is From geometry,

= cot( ) + tan ( - )

becomes large for small , and small or negative



Approximation

us ~ H (Hardness)

t0

tc

Shear plane Shear angle

Tool

V

Chip

Workpiece

+-

Rakeangle

)42(6

1 u

4 2 d u

u 80%) to(65 u u

u energy specific

vol

work

work dt

d(work) Power VF

p

p

friction workplasticS

S

H

Specific energy, uS

For comparison see Table 26.2 for grinding

Hence we have the approximation;

Power ≈ us X MRR

MRR is the Material Removal Rate or d(Vol)/dt

Since Power isP = F * V

and MRR can be written as,d(Vol)/dt = A * V

Where A is the cross-sectional area of the undeformed chip, we can get an estimate for the cutting force as,

F ≈ us A

Note that this approximation is the cutting force in the cutting direction.


Cutting Force Directions in Milling

Fp

Fcn

Fc

Fcn

Fp

Fc

Fcn

Fc

Fp

Fcn

Fp

Fc

Fc ~ H Ac

(Tangential Cutting Force ~

Chip Cross-section Hardness)

Feed per Tooth and MRR

f = feed per tooth (m)w = width of cut (m)

v (m/s)

= rotational rate (rpm)

Consider the workpiece moving into the cutter at rate “v”. In travel time t’ the feed is v t’. The time for one rotation is t’ = The travel for one tooth is

1/4 Hence the feed per tooth is f = v/4 . In general, a cutter may have “N”

teeth, so the feed per tooth is

f = v / NThe material removal rate (MRR) is,

MRR = v w d

where “d” is the depth of the tool into the workpiece.

Top view of face millingWith 4 tooth cutter

Side view

Ex) Face milling of Al Alloy

w

d D

vw

N = 4 (number of teeth)D = 2” (cutter diameter)

Let w = 1” (width of cut), d=0.1” (depth of cut)f = 0.007” (feed per tooth), vs = 2500 ft/min (surface speed; depends on cutting tool material; here, we must have a coated tool such as TiN or PCD)

The rotational rate for the spindle is= vs / D = 4775 rpm

Now, we can calculate vw, workpiece velocity,f = vw / N => vw= 134 [in/min]

Material removal rate, MRR = vw*w*d = 13.4 [in3/min] Power requirement, P = us*MRR = 5.36 [hp]Cutting force / tooth, F ~ us*d*f = 111 [lbf]

us from Table 21.2 (20.2 ed 4); Note 1 [hp min/in3] = 3.96*105 [psi]

Ex) Turning a stainless steel bar

f

D=1”

d

Tool

Recommended feed = 0.006” (Table 23.4 (22.4))Recommended surface speed = 1000 ft/min

= 1000 ft/min = 3820 rpm1” 1ft/12”

Material removal rate, MRR = 0.1 0.006 1 3820) = 7.2 [in3/min]

Power requirement, P = us*MRR = 1.9*7.2 = 13.7 [hp]

Cutting force / tooth, F ~ us*d*f = (1.9*3.96*105)*(0.1*0.006)

= 450 [lbf]

us from Table 21.2 (20.2 ed 4); Note 1 [hp min/in3] = 3.96*105 [psi]

Let d = 0.1”

Temperature Rise in Cutting

Adiabatic Temperature Rise: cp T = uS

Note : uS ~ H, HardnessTadiabatic > ½ Tmelt (Al & Steel)

Interface Temperature:

T = 0.4 (H / cp)(v f / )0.33

v = cutting speedf = feed

= thermal diffusivity of workpieceNote v f / = Pe = convection/conduction

Typical temperature distribution in the cutting zone

* Source: Kalpakjian, and Schmidt 5th ed

*

* Reference: N. Cook, “Material Removal Processes”

Cutting tool materials & process conditions

Temperature ( F)

Hard

ness

(H

RA)

HR

C

Feed (in/rev)

Cutt

ing s

peed (

ft/m

in)

m/m

in

Year

Mach

inin

g tim

e (

min

)


Cutting Speed (ft/min)

Tool lif

e (

min

)

Limits to MRR in Machining

Spindle Power – for rigid, well supported parts

Cutting Force – may distort part, break delicate tools

Vibration and Chatter – lack of sufficient rigidity in the machine, workpiece and cutting tool may result in self-excited vibration

Heat – heat build-up may produce “welding”, poor surface finish, excessive work hardening; can be reduced with cutting fluid

See Video on Rate Limits In Machining

Typical Material Removal Rate

10-4 10-3 10-2 10-1 1 10 102

EBM1 EDM1,2

Grinding3

Machining

Creep Feed2

Grinding

LASER3

Chem. Milling2

[cm3/sec]

25A, 6um RMS1

Rough milling of Al > 35hp

1m X 1m areaNote: 1cm3/sec = 3.67 in3/min

* References: 1. Advanced Methods of Machining, J.A.McGeough, Chapman and Hall, 1988

2. Manufacturing Engineering and Technology, S. Kalpakjian, Addison-Wesley, 1992

3. Laser Machining, G. Chryssolouris, Springer-Verlag, 1991

High speed Machining and AssemblyHigh Speed Machined aluminum parts are replacing built-up parts made by forming and assembly (riveting) in the aerospace industry. The part below was machined on a 5-axis Makino (A77) at Boeing using a 8-15k rpm spindle speed, and a feed of 240 ipm vs 60 ipm conventional machining. This part replaces a build up of 25 parts. A similar example exists for the F/A-18 bulkhead (Boeing, St. Louis) going from 90 pieces (sheetmetal build-up) to 1 piece. High speed machining is able to cut walls to 0.020” (0.51mm) without distortion. Part can be fixtured using “window frame” type fixture.

MRR = f d * N w

Variation Vs Part Size

Machine tool configurations

Machine tool

number of axes, spindles, serial and parallel configurations

Cutter geometry

Form tool, cutter radius, inserts, tool changers

Software

flexibility, geometrical compensation, “look ahead” dynamics compensation

Column

Base

Head

Table

Saddle

Knee

*



New developments

Diamond turning And grinding of optical parts

Micro machines

Hexapod Milling Machines

Tool

Linear actuator

Stewart Platform

*

* Source: http://macea.snu.ac.kr/eclipse/background/background.html

Hexapod machining center(Ingersoll, USA)

Schematics

http://macea.snu.ac.kr/eclipse/background/background.html

Institut für Werkzeugmaschinen und FertigungHexaglide from Zurich (ETH)

www.iwf.mavt.ethz.ch/

http://www.iwf.mavt.ethz.ch/

Fast Tool Serverhttp://web.mit.edu/pmc/www/index.html

* Source: Reintjes, “Numerical Control 1991”

NC machine tool developed at MIT mid 1950’s

Machining Part 2

System Configurations

Part Holding / Fixturing

Process Planning

Environment

Simple Classification Scheme for Part Geometry

Primary RotationalPrimary Rotational with secondary Primary Planar

Primary Planar with secondary

Primary Rotational and Planar

Primary Rotational and Planar with secondary

Secondary

Pop quiz; how would you make a gun stock?

See video

Machining Systems Classification

Ref J T. Black

Job shop

Flow Shop

L

M

D GL M

A A

L M G G

L D

Receiving

Shipping

Flexible Manufacturing System

Transfer line


VM

Machining Cell

S

L

L

HM

VM

G

Final inspection

Finished part cart

Raw materialcart

Worker position

Worker path

Part movement

Decoupler(Kanban square)

OUT

Part Fixturing for Prismatic Parts

Job Shop Vise Jaws / T-slot

Bolt clamps / T-slot

Direct bolt to plate / T-slot

Production Special work holding jaws and clamps

Soft jaws, custom jaws, stops, mechanical clamps, hydraulic clamps, pneumatic clamps, magnetic chuck

Multiple parts fixtures and indexing heads Tombstones, trunnion, indexing heads

Job shop fixturing

Vise Faceplate on lathe

T-slot & clamps on mill

Production

8-station Visehttp://www.te-co.com/toolex/html/10a.html

Quad-Vertical combination Chuckhttp://www.royalworkholding.com/RM3.html

Indexing Trunnionhttp://www.royalworkholding.com

Modular Fixtureshttp://www.royalworkholding.com/RM3.html

Hydraulic Pallet Fixturehttp://www.royalworkholding.com

Collet Index Fixturehttp://www.cuttingtoolmall.com/catalog/standard.cfm?FamilyID=225205

http://www.te-co.com/toolex/html/10a.html



http://www.royalworkholding.com/RM3.html

http://www.royalworkholding.com/

http://www.royalworkholding.com/RM3.html

http://www.royalworkholding.com/

http://www.cuttingtoolmall.com/catalog/standard.cfm?FamilyID=225205

SMED

Single-Minute-Exchange-Die Shigeo Shingo, “A Study of the Toyota

Production Systems”

Stage1: Separating Internal and External Setup

Stage2: Converting Internal to External Setup

Stage3: Streamlining all aspects of the setup operation

Standardized Fixtures

Process planningHow would you machine this part?

Assumption:1. We begin with a stock size of 2.5” X 2.25” X 12”2. This will be manufactured in a job shop for very low quantity

We will use:- A bandsaw to roughly cut the stock to size- A manual vertical mill to create the planar features and the holes- A belt sander to sand the radii ( assuming the tolerance is not

very high)

Machine Operation

Horizontal band saw Saw stock to ~4.125”

Manual vertical mill

Mill two ends to length 4”

Mill width to 2”

Mill out 2”X1.5”X4”

Drill hole 1” diameter

Bore 1” radius

Belt sender Sand 0.5 radii

* Source: http://www.jettools.com/Catalog/Metalworking/CatalogPages/HVBS56M.html

*

http://www.jettools.com/Catalog/Metalworking/CatalogPages/HVBS56M.html

Machine Operation



Mill two ends to length 4”Mill width to 2”



Bore 1” radius


*

* Source: http://www.hemsaw.com/Videolinkpages/x-vVideopg.htm

http://www.hemsaw.com/Videolinkpages/x-vVideopg.htm



Machine Operation




Mill width to 2”Mill out 2”X1.5”X4”


Bore 1” radius



*




Machine Operation




Mill width to 2”

Mill out 2”X1.5”X4”Drill hole 1” diameter

Bore 1” radius



*




Machine Operation




Mill width to 2”


Drill hole 1” diameterBore 1” radius



*




Machine Operation




Mill width to 2”



Bore 1” radiusBelt sender Sand 0.5 radii


*




Machine Operation




Mill width to 2”



Bore 1” radius


* Source: http://www.jettools.com/jet-index.html (WMH Tool Group)

*

http://www.jettools.com/jet-index.html



Process plan

Machine Operation




Mill width to 2”



Bore 1” radius


Time estimation (minutes)Machine Operation (V = Volume, A

= Area, P = Perimeter)Fixture Tool

ChangeRun (R=Rough, F=Finish)

Deburr/Inspect/

Measure

Horizontal band saw

Saw stock to ~4.125”

A = 5.6525 in2, P = 9 in0.23 - 2.02 0.30D, 0.05I



V = 0.703 in3

A = 11.25 in2, P = 19in

0.20

0.202

0.13R

0.75F

0.63D, 0.05I,

0.13M

Mill width to 2”

V = 2.5 in3

A = 10 in2, P = 13in

0.20 -0.46R

0.67F

0.43D, 0.05I,

0.13M


V = 12 in3

A = 14 in2, P = 15in

- -2.19R

0.93F

0.50D, 0.05I

0.13M, 0.13M


-Center drill

-Pilot drill ½”

-Pilot drill 63/64”

-Ream

0.20

2

2

2

2

0.03

0.05

0.04

0.01

0.21D, 0.05I

0.17M

Bore 1” radius

V = 0.79 in3

A = 1.57 in2, P = 7.28in

0.20 20.96R

0.01F

0.24D, 0.05I

0.06M

Belt sender

Sand 0.5 radii

V = 0.05 in3

A = 0.79 in2, P = 3.14in

0.08 -0.20R

0.21F

0.10D, 0.05I

0.06M, 0.06M

Summary Times (minutes)

Fixture Tool Change Run (R=Rough, F=Finish) Deburr/Inspect/Measure

1.31 12 6.08 2.58 3.63

Total Time 25.6 minutes

Environmental issues

Waste material

Energy

Machine, material (embodied energy), temperature controlled environment

Lubricants and hydraulic fluids

Cutting Fluids

Dry machining

The average power plant in the United States is 33% efficient.

A Machine Tool Vs A SUV

50% of the energy from the grid comes from coal

electricity from the US grid comes with

667 kg of CO2/MWh

2.75 kg of SO2/MWh

1.35 kg of NOx/MWh

12.3 g Hg/GWh

etc……..

Data from US Energy Information Administration, DOE 2002 & Klee & Graedel

annual SUV equivalents

the fine print

Assumptions:

Annual emissions resulting from the operation of a typical production machine tool

(22 kW spindle, cutting 57% of the time, 2 shifts, auxiliary equipment, electricity from US grid)

as measured in annual SUV equivalents (12,000 miles annually, 20.7 mpg)

CO2 – 61 SUV’s

SO2 – 248 SUV’s

NOx – 34 SUV’s

Production machining energy Vs production rate

Ref. Toyota

Electricity Breakdown

Constant start-up operations (idle)

Run-time operations (positioning, loading, etc)

Material removal operations (in cut)

Electricity Requirements




Machine Use Scenario

Arbitrary Number of work hours

Machine uptime

Machine hours (idle, positioning, or in cut)

Percentage of machine hours spent idle

Machine hours spent idle

Active machine hours per 1000 work hours

Machining Scenario

Percentage of machine hours spent positioning

Machine hours spent positioning

Percentage of machine hours spent in cut

Machine hours spent in cut

Electricity Use per 1000 work hours




Total electricity use per 1000 work hours

Electricity Used per Material Removed

Material Machined

Material Removal Rate 20.0 cm3/sec 4.7 cm

3/sec 5.0 cm

3/sec 1.2 cm

3/sec 5.0 cm

3/sec 1.2 cm

3/sec 1.5 cm

3/sec 0.35 cm

3/sec

Material removed per 1000 work hours 40824000 cm3

9593640 cm3

4212000 cm3

1010880 cm3

4212000 cm3

1010880 cm3

510300 cm3

119070 cm3

Electricity used/Material removed 14.2 kJ/cm3

60 kJ/cm3

2.3 kJ/cm3

10 kJ/cm3

4.7 kJ/cm3

20 kJ/cm3

4.9 kJ/cm3

21 kJ/cm3

kWh

35%

315 hours

351 hours

40%

Aluminum Steel

13.2%

20.2%

65.8%

1.2

100

Aluminum Steel Aluminum SteelAluminum Steel

kWh

160996 kWh 5553 kWh 700 kWh2744 kWh

6237 kWh 702 kWh

600kWh 3033 kWh

673 kWh

1033

kWh

5471 kWh 1818 kWh 0 kWh

1038 kWh149288

30%

567 hours 234 hours 94.5 hours234 hours

70% 40%

70%

243 hours 351 hours 221 hours

60%30% 60%

585 hours

810 hours 585 hours 315 hours585 hours

90 hours 315 hours

900 hours

10% 35% 65%

900 hours900 hours 900 hours

1000 hours

90% 90% 90%90%

1000 hours 1000 hours1000 hours

22 kW 6.0 kW5.8 kW

3.4 kW

2.1 kW

0.7 kW

0 kW3.1 kW

kW

1.8

166 kW

6.8 kW kW

11.3%

0% (manual)

48.1% 69.4%

24.9%3.5%

31.6%

Manual Milling Machine (1985)Production Machining Center (2000)

85.2% 27.0%

Automated Milling Machine (1998) Automated Milling Machine (1988)

eye chart for energy values

Electricity Breakdown




Electricity Requirements




Machine Use Scenario

Arbitrary Number of work hours

Machine uptime

Machine hours (idle, positioning, or in cut)

Percentage of machine hours spent idle

Machine hours spent idle

Active machine hours per 1000 work hours

Machining Scenario

Percentage of machine hours spent positioning

Machine hours spent positioning

Percentage of machine hours spent in cut

Machine hours spent in cut

Electricity Use per 1000 work hours




Total electricity use per 1000 work hours

Electricity Used per Material Removed

Material Machined

Material Removal Rate 20.0 cm3/sec 4.7 cm

3/sec 1.5 cm

3/sec 0.35 cm

3/sec

Material removed per 1000 work hours 40824000 cm3

9593640 cm3

510300 cm3

119070 cm3

Electricity used/Material removed 14.2 kJ/cm3

60 kJ/cm3

4.9 kJ/cm3

21 kJ/cm3

Aluminum Steel

100

Aluminum Steel

kWh

160996 kWh 700 kWh

6237 kWh

600kWh kWh

5471 kWh 0 kWh

149288

30%

567 hours 94.5 hours

70%

70%

243 hours 221 hours

30%

585 hours

810 hours 315 hours

90 hours

900 hours

10% 65%

900 hours

1000 hours

90% 90%

1000 hours

22 kW 2.1 kW

0.7 kW

0 kW

166 kW

6.8 kW

11.3%

0% (manual)

69.4%

3.5%

31.6%

Manual Milling Machine (1985)Production Machining Center (2000)

85.2%

Results are in terms of primary energy

Ref Smil

Sample calculation

1 kg part made from 2 kg of aluminum stock 2024

production machining 14.2 kJ/cm3

1000 g /2.7 g/cm3 = 370 cm3

(14.2 X 370 = 5.25 MJ) X 3 = 15.8 MJ

material production

(284.5 MJ/kg X 2 kg = 569 MJ)+15.8 = 585 MJ/ kg of part

Power plant efficiency

C. Smith 2001

emissions for the power station

585 MJ of primary energy (195 MJ of electricity / efficiency = .33), or .06 MWh. This gives:

33.35 kg of CO2

140 g of SO2

0.6 g of Hg

all for a 1 kg part

Home works

See webpage

Re-do “face milling of Al alloy” example with uncoated tools

estimate % of spindle power (7hp) used for “tool break video”

Booklet for Machining Process

Documents