Chips Formation

8/8/2019 Chips Formation

1/15

CONTENTS

Page No: Marks

Allocated

Marks

Obtained

PO Achievement Remarks

FRONT COVER

GRADING FORM

CONTENTS Page 1

1. Title Page 2

2. Objective(s) Page 2 5 PO1

(Total Marks:20)3. Introduction (background and

theory)

Page 2 -

5

10

4. Apparatus Page 6 5

5. Experimental Procedure Page 7 10 PO3

(Total Marks: 30)6. Results & Data Analysis Page 8 20

7. Discussion of Results Page 9 -

13

15 PO2

(Total Marks: 30)

8. Conclusion Page 14 8

9. Recommendation Page 14 5

10. References Page 15 2

11. Group Members

Contribution

Page 15 20 PO6

(Total Marks:20)


2/15

1.0 Title: Study of Chip Formation

2.0 Abstract:

This report is about the investigation or experiment of physical phenomena of chipformation during metal cutting process. Besides that, this experiment also done toexamine the effect of lubrication on chip formation. The study concerns themachining of work piece material which is mild steel with cutting tool of carbide.This study focuses on comparing multiple type of chip formation produced bydifferent of cutting speed, depth of cut, feed rate and the presence of coolant. Thepresent work deals with experimental investigation in the role of coolant on chipformation like chip shape and color in plain turning of medium mild steel rod atdifferent cutting velocities and feed rates.

3.0 Objective:

y To illustrate the various types of chips that can be produced during metal cuttingprocess.

y To examine the effect of lubrication on chip formation.

4.0 Introduction:

The chip formation process is the same for most machining processes, and it hasbeen researched in order to determine closed-form solutions for speeds, feeds, andother parameters which have in the past been determined by the "feel" of themachinist.

With CNC machine tools producing parts at ever-faster rates, it has becomeimportant to provide automatic algorithms for determining speeds and feeds. Theinformation presented in this section are some of the more important aspects ofchip formation. Reasons for machining being difficult to analyze and characterizecan 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.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 occureven with the same configuration.


3/15

4.1 Chip Formation Theory

Below is illustrated the basic geometry of two-dimensional chip formation. Themodel is two-dimensional for simplicity.

Figure 1 : Basic Geometryof2-D ChipFormation

The material immediately in front of the tool is bent upward and is compressed in anarrow 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 shearplane. If the material is ductile, fracture will not occur and the chip will be in the formof a continuous ribbon. If the material is brittle, the chip will periodically fracture andseparate chips will be formed. It is within the shear zone that gross deformation ofthe 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.


4/15

The figure below depicts the cutting area in terms of lines of flow. As the materialflows from the bulk of the work piece to the shear area, it is violently sheared, andthen continues into the chip section.

Figure 2 : The Cutting Area

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

piece by the action of the cutting tool. The piece of metal removed is referred to as

chips and the chips produced are in the different forms and sizes due to various

conditions. In practice, it is possible to produce three distinct types of chip namely

as:

a) Continuous chips

y It usually formed when machined at high cutting speedand high rake angle. Also in sharp cutting edge and lessfriction

y Typical for ductile material such as mill, steel, copper,aluminum and other.

y Chip disposal is a problem because at the large coils of chips. It can be solveusing chip breakers (to follow) or by changing parameters like cutting speed,feed, depth of cut and by using cutting fluids.


5/15

b) Discontinuous chips

y It usually formed by very low or very high cutting speed, largedepth of cut, low rate angles, lack of an effective cutting fluid and

low stiffness of the tool holders

y Typical for brittle material. Work piece materials that contain hardinclusions and impurities or have structured such as the graphite flakes ingray cast iron.

y The problem is machine tool may begin to vibrate and chatter. The stiffness ofthe cutting tool holder, the work holding device and the machine tool areimportant in cutting with serrated chip as well as discontinuous chips.

c) Continuous chip with buildupedge (BUE)

y As it grows larger, the BUE becomes unstable and eventually breaks apart.Cycle of BUE formation and destruction is repeatedcontinuously during the cutting operation until correctionmeasures are taken.

y Typical of ductile material such as cast iron.

In effect, BUE changes the geometry of the cutting edge and dulls it. It is majorfactor that adversely affects surface finish. It can solve by increase the cuttingspeed, decrease depth of cut, increase the rake angle and use the sharp tools.


6/15

5.0 Apparatus:

Equipments Function

1) Lathe machine - As a machine tool and equippedwith individual electric motors.

2) Work piece material- Use a rod of mild steel.

3) Cutting tool- Use carbide because their high

hardness, high elastic modulus,and low thermal expansion.

4) Cutting fluid- To reduce friction and wear, cool

the cutting zone, and flash awaythe chips from cutting zone.

5) Vernier caliper

- To use for measure the

dimensions of work piece.

Table 1 : Equipment andFunction


7/15

6.0 Procedure:

1. The lathe machine was set up by the instructor.

2. The demonstration of cutting was demonstrated by the instructor and the relevantparameters are been distinguish.

3. The relevant parameters in this demonstration are cutting speed, feed rate, andthe usage of cutting fluid.

4. First, the cutting machine was set up at 130 rpm speed, 3mm of depth of cutting,and 0.25 of feed rate and in the existence of coolant. After that, the experimentwith same parameters however in the absence of coolant.

5. Second, the cutting machine was set up at 130 rpm speed, 3mm of depth ofcutting, and 1.0 of feed rate and in the existence of coolant. After that, theexperiment with same parameters however in the absence of coolant.

6. Thirdly, the cutting machine was set up at 1200 rpm speed, 3mm of depth of

cutting, and 0.05 of feed rate and in the existence of coolant. After that, theexperiment with same parameters however in the absence of coolant.7. For every state of experiment, the shape and color of chip produced after the

cutting process recorded.


8/15

7.0 ResultObservation:

WithCoolant WithoutCoolant

Cutting Speed: 300 rpmFeed Rate: 0.2 mm/revDepth of Cut: 2mmColor: Silver

Cutting Speed: 300 rpmFeed Rate: 0.2 mm/revDepth of Cut: 2mmColor: Silver + Yellow

Cutting Speed: 1200 rpmFeed Rate: 0.05 mm/revDepth of Cut: 2mmColor: Yellow

Cutting Speed: 1200 rpmFeed Rate: 0.05 mm/revDepth of Cut: 2mmColor: Yellow + Purple

Cutting Speed: 130 rpmFeed Rate: 1.0 mm/revDepth of Cut: 2mmColor: Gold

Cutting Speed: 130 rpmFeed Rate : 1.0 mm/revDepth of Cut: 2mmColor: Burning Brown


9/15

8.0 Discussion:

1) Discuss theresultofthedemonstration.

From the formation of chips, it showed that chips produced at the existence of

coolant are silver color and the surface is smoother. However, in the absence ofcoolant, chips that produced are brown color. These showed that the use of lubricationcan affect surface finishing of the work piece.

2) Whythe knowledgeon thechipformation is veryimportantinmetalcutting.

The knowledge of chip formation is very important in metal cutting because it canhelps to understand the characteristics of chips and to attain favorable chip forms. Theform of the chips is an important index of machining because it directly or indirectlyindicates the nature and behavior of the work material under machining condition.

Besides that, it gave the specific energy requirement (amount of energy required toremove unit volume of work material) in the machining work. Other than that, nature anddegree of interaction at the chip-tool interfaces.

3) Thetrendinmachining now is drymachining. Explain andgivereason why.

Dry Machining term refers to machining process without the presence of coolantsfluids.There are the reasons to use dry machining:a) Nowadays, most technologies are high speed machining. So, no need to use

coolant.b) One of the main factors is that coolants usage consumes the cost of more than 5

times compared to the cost of cutting tools. In engineering field, this is atremendously expensive.

c) Dry machining would also result in more environmentally-friendly clean-up ofworkpieces, as no oil would have adhered to the workpiece.

d) Since there is no coolant being used in the process, the cutting tool must be able towithstand the high temperature. Thus, both ordinary tools and coated tools are usedin dry machining.

e) Lastly, it can eliminate production shutdown for machinery clean-up.

Figure 3 : Dry MachiningFigure 3ssFigure 4 : Ultra-high-speedinDry Machining


10/15

4)Commenton thevarious chuck used bythelathemachines.

Workholding devices are particularly important in machine tools and machining

operations. Chuck is one of the work holding devices in lathe machine. The function isto grip the job or workpiece. Chucks is located at the spindle axis of the lathe machine.

This arrangement provides convenience in that parts can be mounted and dismounted

quickly. There are many types of chucks being used in lathe machine, each has specific

purpose and method of clamping work piece.

a) Three-jaw universalchucks It used to hold round or hexagonal bar or other

symmetrical work. All jaws move together. The jaws may clamp outside or inside theworkpiece, depending on convenience and the operation to be performed. The job isheld in such a way that its axis coincides with that of lathe spindle.

b) Four-jaw independentchucks It used for square or octagonal work. The jawsmove independently of each other. This type of chuck is also useful for irregularwork wherein a hole is to be positioned off centre on the workpiece.

c) Combination chuck It combines the features of both the above mentionedchucks. It is a four jaw chuck in which the jaws may be moved separately ortogether.

d) Powerchucks It isactuated either hydraulically or pneumatically. It often is usedin automated manufacturing process, high production rates, and also robotic workpiece handling.

Figure 5 : Three-jaw Universal

Chucks

Figure 6 : Four-jaw Independent

Chucks

Figure 5 : Power Chucks


11/15

5) Givethreeimportantaccuracyaspects/procedures inmetalcuttingprocess.

1. Reducedvibrations

If the motion repeats itself after given interval of time, the motion is known as

vibration. Vibration, in general is a form of wasted energy and undesirable in

many cases. Uncontrolled vibration can result in the following;

a) Poor surface finish

b) Loss dimensional accuracy of the workpiece

c) Shorter tool life; premature wear, chipping and failure of the cutting

tool, a crucial possible damage to the machine tool components

from excessive vibration

d) Objectionable or unpleasant noise.

Because of that, vibrations should be reduced such us with minimize tool

overhang and improve the damping capacity of the machine tool to achieve the

good result on product and machine.

2. Accuracyandrepeatabilityofpart size

The big change in the last decade or so is that producers want to shift the

attainment of this accuracy as far up the line as possible, to the cutting stage.

This can often remove the need for subsequent processing. Putting more

accuracy into the cutting process is a trend that is likely to continue. However the

costs must be balanced against the benefit that greater and greater accuracy will

deliver. These benefits will peak at a certain point and thereafter, for every penny

spent on attaining more accuracy, the return on that investment will reduce.

3. Position ofthecuttingtool Obliquecutting.

Position of the cutting tool must in right position to get the good accuracy.

The good cutting process is oblique cutting. Oblique cutting is more advantages

than orthogonal cutting at same feed rate and depth of cut because the force of

oblique cutting acts larger area of the tool. This will result in longer tool life and

can remove more material. This in turn translates to better economy andproductivity.


12/15

6) Discuss/givethree ways foryoutomanagechips efficiently.

1. Collectingchips systematically

The chips produced during machining must be collected and dispose of properly.

The volume of chip produced can very high, particularly in high speed and high-removal-rate operation. The chip management is a process involves collecting

chips from their source in the machine tool in an efficient manner and removing

them from the work area. Chip can be collected by any of the following methods:

y Allowing gravity to drop them on a steel conveyor belt

y Dragging the chips from a settling tank

y Using augers, with feed screws similar to those in meat grinders

y Using magnetic conveyors (for ferrous chips)

y Employing vacuum methods of removal

The collected chips may be recycled or dumped (provided they are free ofharmful chemical component or fluids).

2. Cutting Fluid & Lubricant

The aims in metal cutting are to retain accuracy, to get a good surface finish on

the workpiece and at the same time to have a longer tool life. However during the

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

ahead of the tool and friction at the tool point Heat generated due to friction can

readily be reduced by using a lubricant. Heat caused by deformation cannot be

reduced and yet it can be carried away by a fluid. 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 canform a film at the sliding surfaces of the tool.


13/15

3. CuttingSpeed & Feed

The relative `speed' of work piece rotation and `feed' rates of the cutting tool

coupled to the material to be cut must be given your serious attention. This

relationship is of paramount importance if items are to be manufactured in a cost-

effective way in the minimum time, in accordance with the laid down

specifications for quality of surface finish and accuracy. We, as a potential

supervisory / management level engineer, must take particular note of these

important parameters and ensure that you gain a fundamental understanding of

factors involved. All materials have an optimum Cutting Speed and it is defined

as the speed at which a point on the surface of the work passes the cutting edge

or point of the tool and is normally given in meters/min. The term `feed' is used to

describe the distance the tool moves per revolution of the workpiece and

depends largely on the surface finish required. For roughing out a soft material a

feed of up to 0.25 mm per revolution may be used. With tougher materials this

should be reduced to a maximum of 0.10 mm/rev. Finishing requires a finer feed

then what is recommended


14/15

Conclusion:

From the observation which has been made during the demonstration, it can be

concluded that the formation of the chips were depends on the several parameters such

as; speed, feed rate, type of material, depth of cut, usage of cutting fluid and several

more. Basically there were 3 types of chips which have been obtained during thedemonstration; continuous chips, discontinuous chips and built-up-edge chips. From the

demonstration also, it was found that with the present of coolant, the chips produced

were softer compared with the process without coolant. The color of the chips been

produced were also different. Without coolant, the chips tend to become yellowish and

heat treated compared to the cutting process with coolant where the chips still

maintained it original color.

From the understanding which has been obtained during the demonstration, it can be

concluded that by knowing the chips formation we can determine the parameters shall

be used for machining selected materials.


15/15

Chips Formation

Documents

Transcript of Chips Formation