Report Cip Formation

8/8/2019 Report Cip Formation

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Table of Contents

1.0 INTRODUCTION (BACKGROUND AND THEORY): ............ .............. ............. ............. ............. ............. ..... 2

2.0 OBJECTIVE .................................................................................................................................................... 9

3.0 EQUIPMENT................................................................................................................................................... 94.0 PROCEDURE ................................................................................................................................................ 11

5.0 RESULT ........................................................................................................................................................ 11

6.0 DISCUSSION ................................................................................................................................................ 13

7.0 CONCLUSION .............................................................................................................................................. 21

8.0 REFERENCE ................................................................................................................................................. 22

9.0 GROUP MEMBER CONTRIBUTION ........................................................................................................... 23


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TITLE: STUDY OF CHIP FORMATION.

1.0 INTRODUCTION (BACKGROUND AND THEORY):

In the metal cutting process, layers from metal are removed systematically from a work

piece by the action of the cutting tool. The metals removed referred to as chips and the

chip produced are in different formed sizes due to various conditions. In practice, it is

impossible to produce three distinct types of chip namely; a continuous chip, a

continuous chip with a built-up-age (BUE) and a discontinuous chip. The type of chips

produced depends on the work and tools materials, the geometry and the speed of the

cutting process and the existence or absence of lubrication. Knowing about chip

formation and control is very important because among others, it affect tool life, surface

finish of type product, disposal problem and cost. The basic mechanism of chip

formation is that of shear formation. The material is assumed to shear along a shear

plane extending from the tool tip to the surface.

The chip formation process is the same for most machining processes, and it has been

researched in order to determine closed-form solutions for speeds, feeds, and other

parameters which have in the past been determined by the "feel" of the machinist.

With CNC machine tools producing parts at ever-faster rates, it has become important

to provide automatic algorithms for determining speeds and feeds. The information

presented in this section are some of the more important aspects of chip formation.

Reasons for machining being difficult to analyze and characterize can be summarized as

follows:

y The strain rate is extremely high compared to that of other fabrication

processes.

y The process varies considerably depending on the part material, temperature,

cutting fluids, etc.


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y The process varies considerably depending on the tool material, temperature,

chatter and vibration, etc.

y The process is only constrained by the tool cutter. Unlike other processes such as

molding and cold forming which are contained, a lot of variation can occur even

with the same configuration.

For all types of machining, including grinding, honing, lapping, planning, turning, or

milling, the phenomenon of chip formation is similar at the point where the tool meets

the work.

Below is illustrated the basic geometry of two-dimensional chip formation. The model is

two-dimensional for simplicity.

Figure 3.1 : 2-d dimensional movements


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The material immediately in front of the tool is bent upward and is compressed in a

narrow zone of shear which is shaded on the drawing above. For most analyses, this

shear area can be simplified to a plane.

As the tool moves forward, the material ahead of the tool passes through this shear

plane. If the material is ductile, fracture will not occur and the chip will be in the form of

a continuous ribbon. If the material is brittle, the chip will periodically fracture and

separate chips will be formed. It is within the shear zone that gross deformation of the

material takes place which allows the chips to be removed. As on the stress-strain

diagram of a metal, the elastic deformation is followed by plastic deformation. The

material ultimately must yield in shear.

The figure below depicts the cutting area in terms of lines of flow. As the material flows

from the bulk of the work piece to the shear area, it is violently sheared, and then

continues into the chip section.

Figure 3.2 : cutting area in term of lines of flow


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a) Continuous chip

Continuous chip are usually formed when machining ductile material such as mild

steel, iron, cooper or aluminum. The formation of chip takes place in the zone

extending from the tool cutting edge to the junction between the surface of the chip

and the work piece known as primary deformation zone. The chip flows in a

continuous ribbon without breaking when it is compressed by the action of the

cutting tool and as the chip separates from the metal. Depending upon the cutting

conditions, a normal continuous chip or continuous chip with built-up-edge (BUE)

would be formed.

Continuous chip generally produce good surface finish but they are not always

desirable. They tend to become tangled around the tool holder, the fixture, and the

work piece, as well as chip-disposal systems and the operation has to be stopped to

clear away the chips. Long continuous chip may damage the machine tool, damage

the surface finish of the machined surface, may cause the inserts to break, or even

hurt the machinist. Usually a chip breaker is used to fracture the chip into small bits

so it does not get tangled in the machine and become a safety hazard.

Some of the conditions favorable for continuous chip formation can be summarized

as:

y Ductile work piece material.

y Small chip thickness.

y Fine feeds.

y Sharp cutting edge of the cutting tool.

y A large rake angle on the cutting tool.

y High cutting speeds.

y Using coolant.


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b) Discontinuous chip (segmented chip)

This is formed in small segments separately due to periodic rupture ahead of the

cutting tool due to high stress applied by the cutting action. The chip then separates

from the unmachined portion. As a result of this successive ruptures, a poor surface

is produces on the work piece. This is typical of brittle material such as cast iron, or

cast brass. This is due to brittle failure at the shear plane before any tangible plastics

flow occurs. Discontinuous may also be produced when machining ductile materials

at very low speeds and high feeds.

Conditions favorable for discontinuous chip formation are as listed below:

y Brittle work piece material.

y Small rake angle on the cutting tool

y Large depth of cut or uncut chip thickness.

y Low cutting speed.

y Work piece materials that contain hard inclusions and impurities, or have

microstructures such as the graphite flakes in gray cast iron.

y Lack of effective cutting fluid.

y Low stiffness of the machine tool.

c) Continuous chip with built-up-edge (BUE)

The continuous chip and built-up-edge (BUE) is similar to continuous chip but with

the additional molten metal material sticking to it. Under most cutting conditions,

some of the work piece material will form or attach to the face of the cutting tool.

This is the formation of layer after layer of molten material onto the rake face at the

tool nose due to high pressure and temperatures. This phenomenon is called the

built-up-edge (BUE). Due to work hardening and the deposition of the successive

layers of material, the BUE hardness increases significantly and sometimes


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exceeding the hardness of the parent metal. The molten metal would be welded

onto the rake face, grows larger and then would reach a critical size, becomes

unstable and breaks. Part of it would be welded onto the chip and partly onto the

machined surface. The one on the rake face tends to cause the cut to deeper then

the tip of the cutting tool and degrades surface finish. Often the BUE continuous to

grow and then breaks down when it becomes unstable, the broken pieces then

carried away by underside of the chip and the new work piece surface. The process

of BUE formation and destruction is repeated continuously during the cutting

operation, unless measures are taken to eliminate it.

At high speeds, the BUE gradually disappears and the chip once again makes full

contact with the tool. Periodically the BUE on the rake face of the cutting tool will

break off and remove some of the cutting tool and leaves the cavity. This crater

wear and thus, tool life is reduced. Decreasing the depth of cut, increasing rake

angle and using sharp cutting tool and an effective cutting fluid, reduces the

tendency for BUE to form.

Conditions for BUE formation while machining:y Mating metals must be mixable with each other.

y Metallic bonding.

y High temperature (do not use coolant/cutting fluid)

y High stresses

y Softer non-ferrous metals.

y Ductile materials and low carbon steels.

y Low cutting speed.

y BUE chip formation increases as the tool begins to dull.


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Some problems due to BUE can list as follows:

y A major factor that affects surface finish, bad surface finish.

y Loss of dimensional accuracy due to changing tool geometry during

operation.

y Cutting tool becomes dull.

y Low tool life.

In general, BUE can be reducing by:

y Increasing cutting speed.

y Decreasing feed rate.

y Decreasing depth of cut.

y Increasing ambient work piece temperature.

y Increasing rake angle.

y Using sharp cutting tool.

y Reducing friction.

y Using a tool that has lower chemical affinity for the work piece material.

Figure 3.3 : types of chip formation


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2.0 OBJECTIVETo purpose of experiment /demonstration is to illustrate various types of chip that can be

produce during metal cutting process and to examine the effect of lubrication on chip

formation. . We also want to know the uses of lathe machine and their part that involve for

metal cutting process. Other than that we want to identify the important of study chip

formation for applying in industry.

3.0 EQUIPMENT

1) LatheMachine

2) Work pieceM

aterial (mild steel)

3) Cutting Fluid (mineral oil base)

4) Cutting tools

LatheMachine Work pieceMaterial Cutting Fluids


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FIGURE 1: Lathe machine

DIGITAL READ OUT

MAIN SPINDLE HANDWHEEL

WAYS

LEA

SCR

FEED RODCLUCTH

BED

REDUCTION

GEAR BOX

TAILSTOC

THESPINDLE


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4.0 PROCEDURE1) The work piece material was securely clamped in a chuck. The work piece material

should not extend more than three times its diameter.

2) Then a cutting tool (Tungsten Carbide) been installed.

3) The cutting tool then been moved off the part by backing the carriage up with the

carriage hand wheel and then use the cross feed to set the desired depth of cut.

4) The machine was then been started so that the cutting tool cut the work piece material.

The different feed rates apply to produce different chip with cutting or without cutting

fluid.

5.0 RESULTTable 1 : Result of demonstration

Type of Chips With Coolant Without Coolant

Continuous Chips

Speed : 790 rpm

Feed rate : 0.05 mm/rev

( AEV3X )

Depth of Cut : 2 mm

Surface Finish : Fine

Chip Formation

> low temperature> curl

> silver colour /original

colour

> thick width

Chip Formation

> high temperature

> curl

> bright colour / burning

> thin width


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Built-Up-Edge (b.u.e)

Speed : 130 rpm


( BER7X )

Depth of Cut : 2 mm

Surface Finish : Course

Chip Formation

> low temperature

> curl> silver colour /original

colour

> thick width

Chip Formation

> high temperature

> curl

> bright colour / burning

> thin width

Discontinous Chips

Speed : 300 rpm


(AET8X)

Depth of Cut : 2 mm

Surface Finish : Too course

Chip Formation

> low temperature

> small curl

> dark colour

> thin width

Chip Formation

> high temperature

> small size

> bright+blue colour

> thin width


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6.0 DISCUSSION

I. Discuss the result of the demonstration.

Continous Chip B.U.E Chip Discontinous

Velocity Of Cutting High cutting speed Low cutting speedVery low or very high

cutting speed

Advantages

Very good surface

finish.

Reduce cost.

Reduce tool wear by

protecting its rake

face regarded the

condition.

Good surface finish.

Desirable for ease of

chip disposal.

Disadvantages

Stick at tool or

machine.

Chip disposal system.

Changes the

geometry of the

cutting edge and

dulls it.

Poor surface finish.

Can affect surface

finish and cause

vibration and

chatter.

Other Factor

Contributing.

High rake angles.

Steady cutting

forces.

Depth of cut is high.

Low rake angles.

Blank tools.

Low rake angles.

Large depth of cut.

Brittle material.


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II. Why the knowledge on chip formation is very important in metal cutting.

It is important to study the formation of chip during the machining processes as the

former affects the surface finish, cutting forces, temperature, tool life and dimensional

tolerance. Understanding the chip formation during the machining process for the specific

materials will allow us to determine the machining speeds, feed rates and depth of cuts for

efficient machining and increase tool life in the specific actual machining operation.

The chip formation is important because of the importance of machining for any

industrial economy, has been extensively studied. The chip formation process is the same for

most machining processes, and it has been researched in order to determine closed-form

solutions for speeds, feeds, and other parameters which have in the past been determined by

the feel of the machinist. It has become important to provide automatic algorithms for

determining speeds and feeds. The information presented in this section is some of the more

important aspects of chip formation.

The chip formation is important to observe whether the surface finish of the work piece is good

or not. From the observation of the chip can be a measurement that can be used to improve

and verify the accuracy of the work piece. From the formation, we could observe of the chips

colour and shape. From the colour we can be measured the temperature affected from the

friction is very high that change the colour of the work piece that might be change the strength.

There are several shapes that we can observed which are continuous, built-up edge and

discontinuous chip as function of experiment that determined the best machining operation.


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III. The trend in machining now is for dry machining. Explain and give reasons

why.

There are some reasons why the world has minimized or eliminated the use of

metalworking fluids, and switch to dry machining trend. Dry or near dry machining

major benefits are:

y Alleviating the environmental effect of using cutting fluids, improving air quality in

manufacturing plants, and reducing health hazards

y Reducing the cost of machining operations, including the cost of maintenance, recycling

and disposal of cutting fluids

y Further improving surface quality

Dry machining is also a viable alternative. With major advances in cutting tools, dry

machining has been shown to be effective in various machining operations especially

turning, milling, and gear cutting.

IV. Comment on the various chuck used by the lathe machine.

Lathe chuck is a relatively simple device. There are only a few major parts that go into

the construction of a lathe chuck. Each lathe chuck consists of a spindle and jaws. The jaws

are used to grip the item to be worked on with the lathe. A lot of lathe chuck models are

available with either two, three, four or six jaws depending on the manufacturer. A chuck is

usually equipped with three or four jaws. Three jaw chucks generally have a geared scroll

design that makes the jaws self centering. They are used for round work pieces (such as bar

stock, pipes, and tubing), which can be centered to within 0.025mm.

Four jaws (independent) chucks have jaws that can be moved and adjusted

independently of each other. Thus, they can be used for square, rectangular, or odd shaped

work pieces. Because they are constructed more ruggedly than three jaw chucks, four jaw

chucks are used for heavy work pieces or for work requiring multiple chucking where

concentricity is important.

Power chucks, actuated pneumatically or hydraulically, are used in automated

equipment for high production rates, including the loading of parts using industrial robots.


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1. Self Centring Lathe Chuck (True Chuck) (Three Jaws)These chucks are having 3 jaws & these types of chucks have maximum demand. These

chucks are suitable for gripping round or hexagonal jobs. One set of reverse jaws is

supplied with each chuck

2. Self Centring Lathe Chuck (True Chuck) (four Jaws)These chucks have 4 jaws & are suitable for gripping round or square jobs. These

chucks are available with extra set of reverse jaw.

An independent jaw chuck is designed with 4 jaws which may be moved independently

of another. A t-handle wrench is used to actuate a screw on each jaw

independently. When the t-wrench in inserted into the end of a jaw screw and turned

clockwise the jaw moves to the center of the chuck. These chucks may be used to

center an irregular shaped work part or to position a work part off center by


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choice. Independent chucks are available with solid one piece jaws or 2 piece jaws with

a removable top jaw.

Different types of lathe chucks command different prices. Lathe chucks are generally not

cheap. Lathe chuck systems can be bought assembled or disassembled. The cost of a

lathe chuck is heavily dependent on type and size.

V. Give three important accuracy aspects/procedures in metal cutting

process.

y Cutting speed.

Cutting speed play an important role to produce high quality of workpiece.

Selection of the suitable cutting speed is the main factor to be considered before

machining process start. The cutting speed can effect on the volume of metal removed.

When the volume of material removed is directly proportional to the distance the tool

has travel or the feed, we will be less likely to be over cutting the piece, thus making it

more accurate. It is also need to be understood that by decreasing the cutting speed,

the longer the time required to machine a part.

y Type of cutting tool that is being use.

In any metal cutting operation, to get the best product there must be a proper

selection of the cutting tool. The selection of various material of cutting tool depends

on the different application. The cutting tool materials commonly made by high speed

steels, uncoated or coated carbides, ceramic and diamond. The properties or quality of

the cutting tool material also differ from each other. The cutting tool which has a

thermal shock resistance can withstand the rapid change in temperature encountered in


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interrupted cutting. While the cutting tool with chemical stability can avoid or minimize

any adverse reaction and adhesion which can affect the cutting tool quality. Using the

right cutting tool will not just result in better precision but it will also ensure longer tool

life.

y The use of lubricant.

To retain accuracy, to get a good surface finish on the workpiece and at the same

time to have a longer tool life the use of good lubricants or coolant is needed. During

the metal cutting process heat is generated due to the deformation of the material and

friction at the tool tip. Heat generated due to the friction can be reduced by use of

lubricant. The heat from the friction will be carried away by the lubricants during the

machining process. Too much heat cause by the friction can affect the material which

will cause distortion, tool wear and accuracy. Thus the use of a cutting fluid will serve to

reduce the tool wear, give better surface finish and a tighter dimensional control. The

proper selection, mixing and application of cutting fluids is however often

misunderstood and frequently neglected in machining practice. In order that the cutting

fluid performs its functions properly it is necessary to ensure that the cutting fluid be

applied directly to the cutting zone so that it can form a film at the sliding surfaces of

the tool.

VI. Discuss three ways for you to manage chips efficiently

Lubricants

y The easiest way to manage chips from machining processes is to use lubricants or

coolant. Lubricants as we already know is use to reduce heat that occur from the friction

of tool tip and material surface. In addition to the heat reducing ability, lubricants can

also be use to flush away chips that is produce so that it wont be entangled during

machining process which is not preferable in CNC machining.


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y There are many types of lubricants such as:

a. Water

It has a high specific heat but is poor in lubrication and also encourages rusting. It is used

as a cooling agent during tool grinding

b. Soluble Oils

Oil will not dissolve in water but can be made to form an intimate mixture or emulsion by

adding emulsifying agents. The oil is then suspended in the water in the form of tiny

droplets. These fluids have average lubricating abilities and good cooling properties.

Soluble oils are suitable for light cutting operations on general purpose machines where

high rates of metal removal are often not of prime importance. There are many forms of

soluble oil in the market and the suppliers instruction should be followed regarding the

proportions of the mix'.

c.Mineral Oils

They are used for heavier cutting operations because of their good lubricating properties

and are commonly found in production machines where high rates of metal removal are

employed. Mineral oils are very suitable for steels but should not be used on copper or

its alloys since it has a corrosive effect.

d. Vegetable Oils

They are good lubricants but are of little used since they are liable to decompose and

smell badly.

Chip breakers

Chip breakers can be use to control chip flow during machining,

eliminating long chips and reducing vibration and heat generated. The

selection of chip breakers depends on the feed and depth of cut of the

operation, the work piece material, the type of chip produced during

cutting, and whether it is a roughing or finishing cut.


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Continuous and long chips are undesirable so chip-breakers are use in

this kind of situation. It is use to break the chip intermittently.

Traditionally chip breakers are a piece of metal clamp together with the

work piece to bend and break the chip. However, nowadays there are

chip breakers that have built in chip breakers features of various designs.

Chips also can be broken by changing the geometry of the tool to control

chip flow, in any machining processes. The ideal chip breakers are the

type that can break the chips into the shape of letter C or number 9 and

fits within a 25 mm square space.

Cutting in a small increment

Another method of removing the chips is by cutting it in a small

increment. Machinist usually will machine at small increment and

pausing, so that the chips can be removed. But, the chip breakers are not

efficient to be used for soft work piece material such as aluminum and

copper. Therefore, for this type of material, the method by cutting in a

small increment will be used.


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7.0 CONCLUSION

In conclusion, many types of chip that can be produced during metal cutting

process after our group did the experiment. Also we see that the lubrication effect on

the chip formation and from the experiment, we found that different color has different

of chip formation due to the lubrication hat we use. If without coolant, the chip

formation color is brown color and if with the coolant the chip color is silver color. The

color different also because of the different of the temperature during metal cutting

process occur the chip formation that produce without coolant during metal cutting is

more higher temperature than the chip formation that produce with coolant, it is

because the coolant make the temperature during metal cutting process much lower. It

also will make the different structure of the chip formation with the different cutting

speed, feed and depth cut, it also produce different shape of the chip formation. When

the depth of cut is decreases, the width of the chip that produce will decreases. And

when the feed rate is decreases, the chips that produce will not continuous. The high

speed will produces a smooth surface on the work piece, and the resulting surface will

be smoother and good.

Although continuous chip generally produce good surface finish, continuouschips are not always desirable, particularly with the computer-controlled machine tools

widely used today, as they tend to be tangled around the tool holder, the featuring, the

work piece, as well as the chip disposal system. This problem can be eliminated by chip

breakers, or by changing parameters such as cutting speed or depth of cut

A BUE consists of layers of material from the work piece that are gradually are

deposited on the tool tip. As it becomes larger, the BUE becomes unstable and

eventually breaks apart. Discontinuous chips consist of segments that may be firmly orloosely attached to each other. Discontinuous chip also produce a good surface but not

as good as continuous chip. Lastly, this experiment had given us a knowledge about the

process that effect the work piece if we not us a right method such use a suitable tool,

the speed of the cutting process and other factor.


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8.0 REFERENCE

i. Serope Kalpakjian, Steven Schmid (2005), Manufacturing Engineering &

Technology, Fifth Edition. Singapore: Pearson PrenticeHall.

ii. MEM 560 MANUFACTURING PROCESSES COURSE MANUAL, chapter 6:

traditional machining process, facilitator: Mohd Yusoff Bin Mohd al-Rangi (Assoc.

Prof.,Haji)

iii. http://www.efunda.com/processes/machining/chip.cfm

iv. http://machine-tools.netfirms.com/01_Chip_Formation.htm#continuous

v. http://www.cpmt.com/newsletter_related_docs/Part%203%20-

%20Basics%20of%20Metal%20Chip%20Formation.pdf

vi. http://web.mit.edu/2.670/www/Tutorials/Machining/physics/Description.html


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9.0 GROUP MEMBER CONTRIBUTION

Fauzany INTRODUCTION (BACKGROUND AND THEORY)

Azman

y OBJECTIVE

y CONCLUSION

Arez

y EQUIPMENT

y RESULT

Kamarul

y PROCEDURE

y DISCUSSION

Report Cip Formation

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