Optimization of Tool Wear in End Milling

7/15/2019 Optimization of Tool Wear in End Milling

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OPTIMISATION OF TOOL WEAR IN END MILLING

DEPARTMENT OF MECHANICAL ENGINEERING ,CMRCET Page 1

CONTENTS

Chapter name page no

Chapter-1........................................................................................................

1.1 Introduction..............................................................................................

1.2 Types of milling machines.......................................................................

1.3 Types of milling cutters...........................................................................

1.4 End milling cutter.....................................................................................

1.5 Adjustable cutting factors in milling......................................................

1.6 Tool geometry of milling cutters..............................................................

Chapter-2........................................................................................................

2. Literature review.......................................................................................

Chapter-3.........................................................................................................

3.1 Classification of tool materials.................................................................

3.2 Types of tool failure...................................................................................

3.3 Basic wear mechanisms..............................................................................

3.4 Factors involved in tool life.......................................................................

3.5 Tool deformations.....................................................................................

Chapter-4..........................................................................................................

4 .1 Introduction to dampers................................................................................

4.1.1 Use cutters with few inserts......................................................................

4.1.2 Optimize inserts geometry.........................................................................





4.1.3 Choose inserts coatings carefully..............................................................

4.2 End mill cutter damper geometry..................................................................

Chapter-5.............................................................................................................

5.1 Equipment used............................................................................................

5.1.1Vertical milling machine............................................................................

5.2 Cutting tools used..........................................................................................

5.2.1Cutting tool material...................................................................................

5.3.1 Collet..........................................................................................................

5.4. Work piece material....................................................................................

5.4.1Aluminum....................................................................................................

5.5Work piece holding device.............................................................................

5.5.1Bench vice...................................................................................................

5.6 Measuring instruments..................................................................................

5.6.1 Tool maker microscope...............................................................................

5.6.2 Stop watch..................................................................................................

Chapter-6..............................................................................................................

6.1 Defination of anova.........................................................................................

6.2 Purpose............................................................................................................

6.3 Types of anova................................................................................................

6.4 Taguchi design................................................................................................

6.5 Introduction to Taguchi design......................................................................

6.5.1 Trail and error method.................................................................................

6.5.2 Design of experiment................................................................................





6.6 Taguchi design..............................................................................................

6.7 Taguchi method treats optimization problems in two categories…………

6.7.1 Static problem………………………………………………………….

6.7.2 Dynamic problem......................................................................................

6.8 Types of static problem s/n ratio’s................................................................

6.9 Types of dynamic problem s/n ratio’s...........................................................

6.10 8 – Steps of Taguchi methodology...............................................................

6.11 Signal to Noise s/n ratio.............................................................................

6.12 Static v/s dynamic s/n ratio........................................................................

Chapter-7 design of experiments..................................................................

7.1 Taguchi design method................................................................................

7.2 Experimental setup and conditions...............................................................

7.3 Experimental design.....................................................................................

7.3.1Orthogonal arry and experimental factors.................................................

7.3.2 Experimental set up and procedure...........................................................

7.4 Results and discussions................................................................................

7.5 Regression analysis.......................................................................................

Conclusion..........................................................................................................

References............................................................................................................





ABSTRACT

Milling is one of the machining process and one of the most widely used metal

removal processes in industry. Cutting action in milling operation is different from other

operation. With the cutting tool rotating, work piece moves in feed direction. In milling

multipoint cutting tool used. Milled surfaces are largely used to mate with other parts in die,

aero space, automotive, and machinery design as well as in manufacturing industries. Long

end mills, the most widely used tool in high speed machining operations, undergo a bending

vibration similar to a cantilevered structure during machining. Sensing of tool wear and

breaking in machining is important for the manufacturing processes.

In this project, the tool wear area was considered as the criterion that would affect the

result of cutting process. Tool wear and breakage detection systems are typically based on

force acoustic emission and temperature in milling process. In the present project, an attempt

is made to understand the influence of cutting speed, feed and depth of cut on tool wear of the

end milling cutter. This project studies the application of Taguchi design to optimize tool

wear in end milling. ANOVA analysis is carried out to identify the significant characters

affecting tool wear





Chapter-1

INTRODUCTION

Milling machines were first invented and developed by Eli Whitney to mass produce

interchangeable musket parts. Although crude, these machines assisted man in maintaining

accuracy and uniformity while duplicating parts that could not be manufactured with the use

of a file.Development and improvements of the milling machine and components

Continued, which resulted in the manufacturing of heavier Arbors and high speed steel and

carbide cutters. These components allowed the operator to remove metal faster, and with

more accuracy, than previous machines. Variations of milling machines were also developed

to perform special milling operations. During this era, computerized machines have been

developed to alleviate errors and provide better quality in the finished product

Milling is the most common form of machining, a material removal process, which

can create a variety of features on a part by cutting away the unwanted material. The milling

process requires a milling machine, work piece, fixture, and cutter. The work piece is a piece

of pre-shaped material that is secured to the fixture, which itself is attached to a platform

inside the milling machine. The cutter is a cutting tool with sharp teeth that is also secured in

the milling machine and rotates at high speeds. By feeding the work piece into the rotating

cutter, material is cut away from this work piece in the form of small chips to create the

desiredshape.

Milling is typically used to produce parts that are not axially symmetric and have

many features, such as holes, slots, pockets, and even three dimensional surface contours.

Parts that are fabricated completely through milling often include components that are used in

limited quantities, perhaps for prototypes, such as custom designed fasteners or brackets.

Another application of milling is the fabrication of tooling for other processes. For example,

three-dimensional molds are typically milled. Milling is also commonly used as a secondary





process to add or refine features on parts that were manufactured using a different process.

Due to the high tolerances and surface finishes that milling can offer, it is ideal for adding

precision features to a part whose basic shape has already been formed.

1.1 Types of Milling Machine

1.1.1 Vertical milling machine

Fig 1.1Vertical milling machine

This study guide will cover the major working parts, functions, and machining

techniques that can be found used on most vertical milling machines. This study guide has

been designed to directly represent the questions that will be found on the open book written

assessment and as an aid for the hands-on usability assessment. Both assessments will also

include questions related to standard machine shop safety and APS internal user safety

guidelines. Answering the questions found at the end of the study guide will enable the user to successfully pass the hands-on usability and open book written assessments. Study guide





practice test and answers can be found at the end of the guide. The Milling Machine uses a

rotating milling cutter to produce machined surfaces by progressively removing material

from a work piece. The vertical milling machine also can function like a drill press because

the spindle is perpendicular to the table and can be lowered into the work piece

1.1.2 Horizontal milling machine

Fig1.2 Horizontal milling machine

Horizontal milling machine is provided with horizontal spindle, parallel to the work

piece or job .this machine comprises a vertical column in corporate with an over arm, to

support arbour free end which carries a cutting tool. Operating the horizontal milling machine

is not much different than operating the vertical milling machine until you begin using the

over-arm supports and arbor driven cutters. When we use the horizontal milling machine in

this way, a new set of operating principles need to be addressed. In the information that

follows please pay close attention to the details. The information will help you not only make

better parts and keep the machine running in proper order, but it may also keep you from

getting seriously injured.





1.2 Types of milling cutter

1. Plain milling cutter

2. Side milling cutter

3. Metal slitting saw

4. Angle milling cutters

5. End milling cutters

6. T-slot milling cutters

7. Slot drill

8. Fly cutter

9. Woodruff key slot miller cutter

10. Form milling cutter

1.3 End milling cutter:

Fig 1.3 End mill cutters





These milling cutters have teeth on the periphery as well as on the end face. It is used

for machining both horizontal and vertical surfaces. It is employed for milling slots, key

ways, grooves and irregular shaped surfaces. They are sub divided into,

a) Shank type milling cutter:

It may be taper shank or straight shank. Taper shank confirm to the morse taper and is

directly secured in the spindle nose whereas, straight shanks are held in a spring collets

b) Shell end milling cutters:

It has a central hole for mounting on arbour and made without shank. They are large

and heavier compared to other types of end mills. It carries teeth on its periphery and on end

face. They are available for the diameter ranging from 50 to 160 mm and width from 32 to 63

mm. The teeth may be straight or helical.

1.4 Adjustable cutting factors in milling:

The three primary factors in any basic turning operation are speed, feed, and depth of

cut. Other factors such as kind of material and type of tool have a large influence, of course,

but these three are the ones the operator can change by adjusting the controls, right at themachine.

Speed:

Speed always refers to the spindle and the work piece. When it is stated in revolutions

per minute (rpm) it tells their rotating speed. But the important feature for a particular turning

operation is the surface speed, or the speed at which the work piece material is moving past

the cutting tool. It is simply the product of the rotating speed times the circumference of the

work piece before the cut is started. It is expressed in meter per minute (m/min), and it refers

only to the work piece. Every different diameter on a work piece will have a different cutting

speed, even though the rotating speed remains the same. Min 1 1000

V DN m π − = Here, v is the cutting speed in turning, Dis the initial diameter of the work

piece in mm, and N is the spindle speed in RPM.





Feed:

Feed always refers to the cutting tool, and it is the rate at which the tool advances

along its cutting path. On most power-fed lathes, the feed rate is directly related to the spindle

speed and is expressed in mm (of tool advance) per revolution (of the spindle), or mm/rev. .

.min 1 m F = f N mm − Here, m F is the feed in mm per minute, f is the feed in mm/rev and

N is the spindle speed in RPM.3

Depth of Cut

Depth of cut is practically self explanatory. It is the thickness of the layer being

removed (in a single pass) from the work piece or the distance from the uncut surface of the

work to the cut surface, expressed in mm. It is important to note, though, that the diameter of

the work piece is reduced by two times the depth of cut because this layer is being removed

from both sides of the work. Cut 2 d D d mm −=Here, Dand d represent initial and final

diameter (in mm) of the job respectively.

1.5 Tool geometry of milling cutters:





Fig 1.4 Tool geometry of end mill cutter

The geometry of milling cutters includes four angles such as radial rake angle, angle,

radial relief angle and axial relief angle. Generally, these angles are considered for three typesof milling cutters like face mills, end mills, side and slot mills.

When angles of milling cutter are compared with the angles of single pont

tool, axial rake angle of milling cutter becomes similar to back rake angle of single point tool

whereas, radial rake angle of milling cutter becomes similar to side rake angle of single point

tool.





Radial rake angle:

The angle measured between the slide face and the radial plane passing through the

cutter axis is reffered as radial rake angle. Radial rake angle can be positive or negative.

Angle makes the cutting edge more stronger.

Axial rake angle:

Axial rake angle is the cutting edge inclination with respect to cutter axis. It also gives

the direction of chips flow. Axial rake angle can positive or negative.

Positive axial rake angle removes the chips away from the cut when rake nose of

cutter contacts with the workpiece while negative axial rake angle traverse the chips along thedirection of work piece. It also makes the cutting edge morestronger

Mostly negative axial rake angle is applied in carbide cutters.

Approach angle:

The angle measured between the plane normal to axial cutter and the plane tangent to

the surface of revolution of thecutting edge is reffered as approach angle.

The value of approach angle is different for different types of milling cutters.

Side clearance angle:

The angle measured between the cut surface and the clearance flank on the cutter is

reffered as side clearance angle. The cutting edges becomes weak at higher clearance, but less

wear and tear occurs. Its value rely on the end mill diameter.





Chapter-2

Literature review

B. S. Patel [ 1 ] investigated about influence of various machining parameters like tool speed,

tool feed, depth of cut and tool diameter. In the present study, experiments are conducted on

al 6351 – t6 material with four factors and five levels and try to find out optimum surface

roughness by using Taguchi method. This paper attempts to introduce how Taguchi

parameter design could be used in identifying the significant processing parameters and

optimizing the surface roughness of end-milling operations.

In this study, the analysis of confirmation experiments has shown that Taguchi

parameter design can successfully verify the optimum cutting parameters, which are a1 > b4

> c4 > d1 (tool feed (a), tool speed(b), tool diameter(c), depth of cut(d) ). The work piece

material used was al 6351 – t6. The average value of surface roughness [mean (= - 4.44 μm)

and s/n ratio (= 16.1115 db.)] Were calculated and were found to be within the range.

Taguchi parameter design can provide a systematic procedure that can effectively and

efficiently identify the optimum surface roughness in the process control of individual end

milling machines. It also allows industry to reduce process or product variability and

minimize product defects by using a relatively small number of experimental runs and costs

to achieve superior-quality products. This research only demonstrates how to use Taguchi

parameter design for optimizing machining performance with minimum cost. Further study

could consider more factors (e.g. Forces, materials, lubricant, etc.) In the research to see how

the factors would affect surface roughness. Also, further study could consider the outcomes

of Taguchi parameter design when it is implemented as a part of management decision-

making processes.

1. P.S. SIVASAKTHIVEL

Department of mechanical engineering, kumaraguru college of technology

Prediction of tool wear from machining parameters by response surfacemethodology in end milling





Tool wear increases cutting force, vibration, temperature, etc in end milling and

reduces surface finish of the Machined work piece. Mathematical model has been developed

to predict the tool wear in terms of machining Parameters such as helix angle of cutting tool,

spindle speed, feed rate, axial and radial depth of cut. Central Composite rotatable second

order response surface methodology was employed to create a mathematical model and the

adequacy of the model was verified using analysis of variance. The experiments were

conducted on aluminium Al 6063 by high speed steel end mill cutter and tool wear was

measured using tool maker’s microscope. The direct and interaction effect of the machining

parameter with tool wear were analyzed, which helped to select process Parameter in order to

reduce tool wear which ensures quality of milling.

The following conclusions were arrived from the results of the present investigation.

The investigation presented a central composite rotatable second order response

surface methodology to develop a mathematical model to predict tool wear in terms of helix

angle, spindle speed, feed rate, axial and radial depth of cut. The helix angle is the most

significant parameter which reduces tool wear. The tool wear is minimal in between 400 –

450 helix angles. The increase in spindle speed and axial depth of cut reduces the tool wear.

The decrease in radial depth of cut reduces tool wear. The interactions between the process

parameters were analyzed and strong interactions were observe between helix angle and axial

depth of cut; spindle speed and feed rate; helix angle and feed rate; and spindle speed and

radial depth of cut

3. K. SUNDARA MURTHYI; DR. I. RAJENDRAN

II Jayam College of Engineering and

Technology, Department of Mechanical Engineering, 636 813 Dharmapuri, Tamil Nadu,

India, [email protected]

Optimization of end milling parameters under minimum quantity lubrication using

principal component analysis and grey relational analysis

In his paper, genetic algorithm based artificial neural network hybrid prediction

model is proposed to foretell surface roughness and tool wear. A multiple objective

optimization methodology, by using principal component analysis, grey relational analysis

and Taguchi method is also proposed to optimize the machining parameters of Al 6063 under

maximum quantity lubrication. The following conclusions are made:





The optimum machining parameters for minimum surface roughness and tool wear

are cutting speed of 88 m/min, feed velocity of 180 mm/min, depth of cut of 1.4 mm and

coolant flow rate of 600 ml/hr. Among the machining parameters: cutting speed, feed

velocity, depth of cut and lubricant flow rate, the cutting speed is the most significant with

percentage contribution of 48.75%, followed by feed velocity with 22.12%, liquid flow rate

with 18.86% and at last depth of cut with 10.26%.

The proposed GA based ANN hybrid prediction model has excellent agreement with

experimental values, with errors of only 3.3%.The validity tests demonstrated that the

proposed multiple objective optimization methodology is able in determining the optimum

machining parameters in end milling

4. J.PRADEEP KUMAR1 K.THIRUMURUGAN2

Address for Correspondence

1Assistant Professor, 2PG Student, Department of Production Engineering, PSG college of

Technology,Coimbatore-641 004

Optimization of machining parameters for Milling titanium using Taguchi method

Titanium alloys have been widely used in industries, especially aerospace industries,

due to their good mechanical and chemical properties. However, machining of titanium alloys

involves expensive tooling cost at the expense of getting good surface roughness. This paper

describes a comprehensive study of end milling of titanium alloys. The study investigated the

optimum parameters that could produce significant good surface roughness whereby reducing

tooling cost. The quality of design can be improved by improving quality and productivity in

company-wide activities. It employed the Taguchi design method to optimize the surface

roughness quality in a computer numerical control end mills. Taguchi’s parameter design is

an important tool for robust design, which offers a simple and systematic approach to

optimize a design for performance, quality and cost. The control parameters were spindle

speed, feed rate, depth of cut and type of end milling tool. Then, an orthogonal array of L27

(313) and analysis of variance (ANOVA) were carried out to identify the significant factors

affecting the surface roughness. The best parameters were chosen based on the signal-to-

noise ratio (SNR).The experimental results indicated that the most significant factors

affecting the surface roughness of titanium alloy during end milling process were primarily





the spindle speed used, secondly, the type of cutting tool used, thirdly, the feed rate chosen

and lastly, the depth of cut chosen.

From the findings of the following can be concluded;

Taguchi’s robust design method is suitable to optimize the surface roughness in

milling CP Ti Grade 2. The significant factors for the surface roughness in milling CP Ti

Grade 2 were the spindle speed and the tool grade, with contribution of 30.347 and 29.933

respectively.

The optimal condition for surface roughness in milling CP Ti Grade 2 was resulted

at spindle speed of 2500 rpm, feed rate of 300, depth of cut 0.3 and solid carbide end mill

cutter.

The optimal interaction parameter was between the spindle speed and feed rate at level 3.

Chapter-3

TOOL MATERIALS AND WEAR OF CUTTING TOOLS

3.1 Classification of tool materials

The several tool materials in use today may be classified as follows:

1. Carbon steels

2. Medium alloy steels





3. High speed steels

4. Cast tool alloys

5. Cemented carbides

6. Minerals

a. Silicon carbide

b. Aluminum oxide

c. Diamond

While the first three groups of materials are really steels in as much as their major

constituents iron, the latter three groups contain iron as an impurity.

3.1.1 Carbon tool steels:

Tools in use before 1900 were all of this type. Their chief characteristics are low hot

hardeners and poor hard-enability. They are usually quenched into brine and even then only a

thin layer can be fully hardened with the attendant risk of developing quenching cracks. The

carbon steels are limited in use to tools of small section which operate at relatively low speed

(and hence low temperature)

plain carbon steel would have the following range of analysis:

C,% Si,% Mn,%

0.8-1.3 0.1-0.4 0.1-0.4

The higher the carbon content, the greater will be the wear resistance of the tool.

3.1.2 Medium alloy steels:

These steels differ from the plain carbon steels by the presence of the elements

designed to improve hardenability. Small amounts of chromium and molybdenum are

frequently used for this purpose. Representative compositions of some of medium alloy steels

are given below:

C S Mn Cr Mo W Fe

1.2 0.3 0.6 0.5 -- -- bal.

1.2 0.3 0.7 0.5 0.5 --

1.2 0.3 0.3 0.7 0.3 1.5





1.3 0.3 0.3 0.7 -- 4.0

Upto about 4% of tungsten is sometimes added to these steels in order to improve

their wear resistance. While these steels are widely used for drills,taps and reamers,their hot

hardness is about the same as that of carbon steels, and they are not satisfactory for high

speed turning or milling.

3.1.3 High speed steels:

This material was first used for tuning tools by taylor and white about the turn of the

century. Its introduction made possible a significant increase in machining speeds,which

accounts for its name. However, today high speed steel is misnamed since it is now the

general purpose material for use in machining operations performed at low or moderate

speeds. The chief characteristic of these steels is superior hot hardness and wear resistance.

The compositions of three popular high speed steels are given below:

Designation Type W Cr V Mo C Fe

T-1 W 18 4 1 -- 0.7 Bal.

M-1 Mo 1.5 4 1 8.5 0.8

M-2 W-Mo 6 4 2 5 0.8

High speed steels have wide applications but in many operations(particularly single

point) they have been superseded by carbides.

3.1.4 Cast alloy tools:

A number of nonferrous alloys high in cobalt have been developed for use as cutting

tools.These materials which are taken known as satellites cannot be heat treated and are used

as cast from a temperature of about 2300. A representative range of analyses for materials of

this sort is as follows:

Co,% Cr,% W,% C,%

40 to 50 27 to 32 14 to 29 2 to 4s

Cast alloys are not quite as hard as tool steels at room temperature, but retain their

hardness to higher temperatures. They are not in wide use. This is due to their fragile nature.





Like all cast materials these alloys are relatively weak in tension and hence tend to shatter

when subjected to a shock load or if not properly supported.

3.1.5 Cemented carbides:

Carbides can be classified into two types:

1. The C grade (straight carbides) consisting of tungsten carbide with cobalt as a

binder for use in machining cast iron and nonferrous metals.

2. The S grade (steel cutting carbides) consisting of tungsten, titanium and

tanlabim carbides with a cobalt binder for using machining steels.

Cemented carbides are unusual in several respects:

1. They have high hardness over a wide range of temperatures.

2. They are very stiff (young’s modulus is nearly three times that for steel).

3. They exhibit no plastic flow (yield point) even to stresses as high as

Psi.

4. They have low thermal expansion compared with steel.

5. They have relatively high thermal conductivity.

6. They have strong tendency to form pressure welds at low cutting speeds.

3.1.6 Diamond tools:

Diamond tipped tools are sometimes used for special applications such as production

of surfaces of high finish on soft materials that are normally difficult to machine.

The general properties of diamond may be summarized as follows:

1. Hardest known substance (brinell hardness=7000).

2. Lowest thermal expansion of any pure substances (about 12% that for steel).

3. High heat conductivity (twice that for steel).

4. Poor electrical conductor.

5. Burns to when heated to about 1500 in air.

6. Very low coefficient of friction against metals.

Since very high hardness is always accompanied by brittleness, a diamond tool must be cautiously used to avoid rupturing the point . This usually limits the use of diamond





tools to light continuous cuts in relatively soft metals, and low values of rake angle are

normally used to provide a cutting edge.

3.2 Types of tool failure

The failure of cutting tools may be classified in three general types

3.2.1. Temperature failure:

The hardness (and strength) of a tool varies with temperature. When the rate of energy

input to the tip of a tool becomes too large, the tool becomes too soft to function properly and

failure ensues. This type of failure occurs quite rapidly, is frequently accompanied by

sparking, and is easily recognized.

3 .2.2.Rupture of tool point:

Because of high hardness required, the tip of a cutting tool is mechanically weak and

brittle. This is particularly true of carbide and diamond tipped tools. Whenever the cutting

forces exceed a critical value for a given tool, small portions of the cutting edge begin to chip

off, or the entire tip may break away in one piece. The high forces which produce this type of

failure are not generally associated with steady state cutting, but rather with variations in the

cutting process such as might obtain in milling operation or when cutting with excessive

vibration(chatter). For a given tool material, the tendency toward a rupture failure can be

diminished either by reducing the casual forces, redirecting them, or redesigning the tool to

withstand them. The forces can frequently be diminished by increasing the rigidity of the tool

and work holders.

3.2.3 .Gradual wear at the tool point:

When a tool has been in use for some time, wear may become evident in two regions

as indicated in fig. 2-1 (i.e. On the flank and faces of the cutting tool). In some cases the flank

wear is by no means uniform as indicated in fig. 2-1(b). Nose grooving is a common form of

during wear high speed finishing operations, while notching occurs when machining high

strength material, particularly heavily work hardening material such as stainless steel, Ni and

Co base alloys. Both crater and flank wear (including nose grooving and notch) are

progressive with time as indicated in fig.2-2(a) and 2-2(b). At high metal removal rates nose

grooving and notch wear may be severely modified due to oxidation.





3.3 Basic wear mechanisms:

Several mechanisms of tool wear have been proposed. Under certain conditions all

these mechanisms may act simultaneously as indicated in fig.2-3, after

A brief description of the various mechanisms is given below:

3.3.1 Adhesion wear mechanism:

When surfaces rub together, particularly in the absence of lubricant films, some

adhesion occurs at the rubbing contact. The friction is primarily the force required to shear

the junction so formed. The simple mechanism of friction and wear proposed by Bowden and

Is based on the concept of the formation of welded junctions and the subsequent

destruction of these. When the destruction is by sharing below the interface, a wear particle is

transferred. The plucked fragments may initially be attached to one surface but may

subsequently be back transferred onto the other. However, in machining operations this

process is probably of very minor importance since fragments plucked either from the tool or

rapidly carried away from the rubbing region.

For this reason, adhesive wear in machining operations is a relatively straightforward

concept. The tool is invariablely chosen to be harder than work. If a junction is formed at the

metal/work interface it will generally pluck out a fragment from the work. The process of

plucking-out will have the fragment in a very work-hardened condition and it may well be

hard enough to score or groove the work. The accumulation of the transferred material from

the work to tip of the tool is, of course, the origin of the built-up-edge. This nose act as an

extension of the tool, and to some extent protects the tool from water. However, the built-up-

edge may occasionally break away with a small portion of the tool itself. This is particularly

likely if the tool is heterogeneous in structure so that local regions may be appreciablyweaker in tension or shear than the overall strength. Adhesive wear of the tool is therefore

likely to be most marked if the tool is of non-uniform strength

Clearly the best way of minimizing adhesive wear is by reducing the amount of

adhesion. The commonest method is by using a lubricant. However, it is still not clear

whether the lubricant acts mainly as a coolant or as a means of reducing friction and

adhesion. If it acts as a true lubricant it is highly desirable to know how the lubricant gets into

the work/tool interface and how quickly it can interact to be effective.





Another approach is to allow adhesion to occur but to ensure that transferred film is

very easy to shear. The easiest way of doing this is to incorporate suitable materials on small

quantities in the work material itself. It may be that free-machining steel, which contains

small quantities of lead, function, to some extent, in this way. Another idea is to make the

work relatively brittle so that the removed chip easily fragments and breaks away from the

tool face. Silicates in the work probably function in this way, although at higher speeds it is

possible that a smeared glass-like film acts, in some measure, as a lubricant between work

and tool.

This mechanism cannot be the complete explanation of the wear process, since it

implies that one surface will become covered with a layer of metal from the other surface and

it does nor explain how loose wear particles are produced.

3.3.2 Abrasive wear mechanism:

Probably the earliest concept of wear was one of abrasion of high spots on one surface

through material of the other surface. The abrasion process involves cutting and, as such, it

depends on the hardness, the elastic properties and the geometry of mating surfaces.

Abrasive wear occurs if a hard particle cuts or grooves one of the rubbing surfaces.

The first criterion for appreciable abrasive wear is that the particle should be harder than the

surface being abraded. If the Vickers hardness of the particle is, say, 1.5 times that of the

surface, abrasion can occur fairly readily. If the particle is smooth, most of the abrasion will

be in the form of plastic grooves (with very little material removed) or in the form of chips

and flakes if the surface is brittle. If the particle has sharp corners or edges and it is

appropriately oriented, it will cut the surface. Abrasion then resembles micro cutting and the

abrasion rates are relatively high.

Tool wear by abrasion is most likely to occur with work materials containing hard

inclusions. According to D. If the inclusions are spherical they are more likely to

groove the face and flank and the rate of removal of material will be very small. If on the

other hand, the high rates of abrasion. Clearly the best way of avoiding such wear is to use

work materials that do not contain hard inclusions or at least to arrange for the inclusions to

be smooth. Another approach is to use a tool material that is harder than the inclusions.

Alternatively, a softer tool material may be used provided it work hardens under repeated

abrasion to give a hard surface layer capable of resisting further deformation or cutting by





coating the tool with a very hard skin either by plating or by chemical treatment, e.g.

Nitriding.

3.3.3 Diffusion wear mechanisms:

Thought of wear as a process of atomic transfer at contacting asperities, i.e.,

wear purely by diffusion. More recent concepts of wear consider diffusion to be an integral

pert of other wear processes. As pointed out by Bowden and Tabor Some diffusion must

occur in the adhesion of contacting asperities. The diffusion and alloying processes at the

interface junctions will control the size and nature of the wear particles.

Diffusion may be classified as part of the abrasion wear mechanism under certain

circumstances. One of the well known examples of this is in the wear of tungsten carbide

tools used in cutting steels. The chemical affinity between the steel of the work material and

the cobalt binder in the tungsten carbide leads to diffusion of the cobalt out of the tool. This,

in turn , causes the formation of a weakened surface layer on the tool, which is manifested by

severe cratering of tungsten carbide when cutting steels. It can be controlled by addition of

titanium and tantalum alloying elements.

The diffusion rate is a temperature dependent phenomenon, i.e., a direct function of

the rubbing speed. However, the amount of material transferred by diffusion is dependent on

the time of contact of the mating surfaces an inverse function of speed. The relationship

between sliding speed and wear rate as influenced by diffusion is thus a complex one.

This type of wear may be reduced in three ways:

a. By running at lower speeds so that the surface temperatures are lower.

b. By cooling the system so that the interfacial temperatures are diminished.

c. By using tools that are not soluble in the work even at elevated temperatures, e.g.,

by the use of titanium carbide with ferrous materials.

3.3.4 Chemical wear mechanism:

There is another kind of wear which may involve both adhesion and abrasion. It

occurs if the rubbing surfaces are attacked by the environment to form a removable surface

film. For e.g., in the presence of a sulphurized lubricant a sulphide film may be formed on the

metal surface, in the presence of a fatty acid o soap film. More generally oxide or hydroxide

films will be formed in the presence of air. These films may be removed by the sliding





processes to expose fresh underlying metal which is highly labile and can readily react with

the environment to reform the surface film. This type of wear is often slow and generally is to

be preferred to the wear that would occur if no surface films were present. However, if

extremely reactive lubricants are used, chemical wear are even direct corrosion may become

significant.

3.3.5 Fatigues wear mechanism:

Although fatigue wear can always occur between sliding surfaces it is usually

swamped by adhesive or abrasive wear. Consequently, fatigue wear becomes important only

when adhesive and abrasive wear are relatively small. For e.g.in well lubricated systems

adhesive wear may be negligible. If hard particles are excluded from the system this may be

difficult because dust can often act in this way) abrasive wear may be small. If then the

surfaces are continuously subjected to loading or unloading they may gradually fatigue and

pieces of the surface may easily be detached. This occurs in sliding systems where asperities

on one surface continuously transmit stresses onto the other, even though they are completely

separated by a lubricant film. A similar effect may occur in rolling bearings. Fatigue failure is

often initiated at a surface flaw or crack. According to D. An applied stress may

open the crack a little; in the presence of a contaminating atmosphere the crack does not heal

on moval of the stress. Repeated cycling of a fragment out of the surface. Sometimes fatigue

cracks can be initiated at defects which lie below the surface.

In this case repeated stressing gradually work hardens the sub-surface material. This

may be followed by shear or tensile failure.

Fatigue does not usually occur if the applied stress is below a certain limit. To

minimize fatigue wear in tools it is desirable to use tools that are considerably harder than

work. The contact pressures which are determined by the yield properties of the work may

then be below the limit at which rapid fatigue occurs. It is also desirable to avoid flaws in the

surface of the tool and homogeneities in its structures.

3.4 Factors involved in tool life





Fig 3.1 Factors influencing the tool wear

Although the shapes of metal-cutting tools used in turning, milling, drilling, etc., varywidely, The basic form is that of a wedge forced asymmetrically into the work material. It is

now accepted that in general the work piece material is deformed as indicated in fig.2-4

The secondary deformation zone is caused by the total contact length between chip

and tool. This form is dictated by the objective of the operation, which is to remove a thin

layer from a more rigid body. The layer moved in the form of fragment or a continuous bears

on the rake face of the tool and passes over it, while the more rigid body of the work material

bears against the passes over the flank or clearance face of the tool. To avoid excessive

friction between the tools and work piece a clearance angle (which may be from about 1 to

20 ) on the flank of the tool ensures that the work surface is in contact with only a narrow

band very close to the tool edge. Because of the rigidity of the work this normally remains

narrow until a new surface, more or less parallel to the work surface, is formed by wear. Such

a worn surface is called the flank wear or land is the most typical form of tool wear.

The layer removed from the work surface (the swarf or chip), being thinner and more

flexible, can conform more readily to the tool shape and normally makes contact with the





rake face of the tool along a considerably longer path, a distance several times the thickness

of the under formed chip. Wear also takes place on the rake face of the tool although not so

universally as on the flank.

Fig 3.2 Tool wear

3.4.1 Flank wear:

This often takes the form of an even band of wear (fig.1-2), the width of which can be

measured with reasonable accuracy. Wear-land formation is not always uniform along the

side and end cutting edges of the tool. Often localized wear at one or more positions along the

edge is several times greater than the average. Two positions at which accelerated wear commonly occurs are where the work surface intersects the cutting edge of the tool and near

the nose of the tool. At the former position the surface condition of the work and the

atmosphere may influence the wear process.

Flank wear occurs under almost all conditions of cutting, but metallographic evidence

shows that more than one wear process is involved so that simple laws relating the rate of

wear to variables such as speed, feed, tool geometry, etc., can be expected only under

conditions where the wear process remains substantially unaltered. Cutting tools are generally

used most efficiently when the only form of wear is an even land on the tool flank, but factors

other than flank wear influence the life of carbide tools in practice.

The surface finish produced in a machining operation usually deteriorates as the

flank-land wear increases although there are circumstances in which a wear land may burnish

the work piece and produce a good finish. Cutting forces are normally increased by flank

wear of the tool. Flank wear also influence the plan geometry of o tool. This may affect the

workpiece

tool

crater wear

flank wear

chip

workpiece

tool

crater wear

flank wear

chip





dimensions of components produced in a machine with set cutting tool positions, or it may

influence the shape of components produced in an operation utilizing a form tool.

Vibration or chatter is another aspect of the cutting process which may be influenced

by tool wear. A wear land increases the tendency of a tool to dynamic instability. A cutting

operation which is quite free of vibration when the tool is sharp may be subjected to an

unacceptable chatter mode when the tool wears.

Fig 3.3 flank wear (width of flank wear land of the tool)

3.4.2 Crater wear:





Fig 3.4 crater wear

On the rake face a cavity or crater frequently forms a short distance from the cuttingedge, as shown in fig.1-2. Once the crater is established, its depth KT grows more rapidly

than its top width KB. The edge of the crater approaches the cutting edge, both by wear of the

crater and by clearance-face wear. This weakens the tool close to the cutting edge and a

major failure may occur by fracture from the crater through to the clearance face. This is

more likely under discontinuous cutting conditions. Cutting forces are normally increased

by wear of the tool. Crater wear may, however, under certain circumstances, reduce forces by





effectively increasing the rake angle of the tool.

Fig 3.5 various stages of tool wear

3.4.3 Built-up edge:

According to E.M. Trent In steel cutting, the pressure locally on the rake face

may be greater than 100,000. The surface temperatures may be several hundred

degrees C, and clean metal surfaces are constantly being generated. It is not surprising

therefore, that when the tool is withdrawn from the cut a fragment of the work material is

often found firmly adhering at the edge. The built-up-edge is not formed during the act of

disengaging the tool, but represents a body of metal present throughout the cutting process.

Size and shape of the built-up-edge vary with the cutting speed and feed. Fig.2-5 shows an

idealized picture of built-up-edge. As cutting speed increases, the shape often changes from a

large wedge to a flattened lump and then with further increase in speed it disappears almost

entirely leaving only smears of metal on the tool surfaces.

The presence of built-up-edge is important in relation to tool life and surface finish. It

may either be harmful or beneficial to the tool, depending on the conditions E.M.

has suggested that when cutting cast iron B.U.E. is usually beneficial and cast iron is

frequently cut under conditions where built-up-edge is formed. This largely protects the rake

surface of the tool from wear and the rate of flank wear is low.

When cutting steel with carbide tools, the built-up-edge is most frequently harmful.(9)

not only does surface finish of the work become poor, but the built-up-edge is often broken





away, bringing with its small fragments of the tool edge and leading to rapid breakdown of

the tool. Without dissolving the metal adhering to the tool, the cause of breakdown may not

be obvious and failure may appear to be due to rapid flank wear.

Unlike flank wear, which occurs under almost all conditions of cutting, the built-up-

edge is a factor affecting tool life mainly at low cutting speeds and feeds. To predict tool life,

surface finish, etc., it is important to know and work material concerned.

3.5 Tool deformation:

There is a constant trend in metal cutting to increase metal removal rate by increasing

cutting speed and feed rate. With increased speed the temperature at the edge of the tool is

raised, while both temperature and the stress near the cutting edge are increased with

increments of feed rate. A limit is eventually reached at which the tool material can no longer

resist the combination of stress and temperature, and begins to deform permanently. The

resistance of the tool to deformation may be the property on which depends the upper limit to

the cutting speed and feed which can be used. The development of tool materials from carbon

steel through high-speed steel and cast co-based alloys to cemented carbides represents a

series with increasing resistance to deformation under compressive stress at high temperature.

Deformation is a factor in tool life quite distinct from normal flank wear. Where the

tool tip is not stressed above its elastic limit the wear rate is not related to the resistance to

deformation. As cutting speed and feed are raised, the elastic limit is exceeded and the tool

begins to deform. At first this may have no effect on the wear rate then, rather suddenly, the

limit may be reached of the strain which the tool a withstand, and it may fail suddenly as a

result of local fracture. Such failure may be attributed to flank wear or to mechanical

chipping, unless the tool is carefully examined under the microscope, but it is necessary to

diagnose the failure correctly in order to apply the correct remedy. Tool failure by

mechanical chipping may require the use of a tougher tool material, while to overcome

deformation a harder though less tough tool may be needed. Deformation occurs most

frequently at the nose radius of a tool and may be minimized by attention to tool design. A

tool with a small nose radius will deform at much lower speed and feed then one with a large

radius.

It is useful to know under what conditions deformation of the tool occurs. To

calculate this would require knowledge of the temperature and stress distribution near the





cutting edge of the tool, knowledge not at present available. Fortunately, much useful

information can be obtained at relatively simple laboratory tests. The flank surface of a tool

tip is lapped optically flat and the tip is then clamped in a tool holder and used for cutting

under controlled conditions. After cutting, any deformation of the tool tip can be observed

and measured by placing the flank surface of the tip on a flat glass plate and examining it

under monochromatic light.

By testing different tool and work material in this way, with varying tool geometry, it

is possible to build-up a body of knowledge concerning conditions under which deformation

of the tool is a factor of importance in tool life, and the relative resistance of a tool material to

deformation

3.5.1 Mechanical chipping:

Chipping of the tool, as the name implies, involves removal of relatively large

discrete particles of tool material. Tools subjected to discontinuous cutting conditions are

particularly prone to chipping. Built – up-edge formation also has a tendency to promote tool

chipping. A built up edge is never completely stable, but it periodically breaks off. Each time

some of the built up material is removed it may take with it a lump of tool edge, to which it

has adhered. This leaves a chipped cutting edge.

Chipping results most frequently from impact of the swarf on part of the cutting edge

not engaged in the cutting, or when starting or stopping the cut, or from careless handling. (9)

it can be greatly reduced by measures taken to control the formation of swarf by chip curlers,

etc ., and by efficient methods of swarf disposal. In many cases honing, or the formation of

small radius or chamfer on the cutting edge of the tool, will prevent this form of damage, or it

may be necessary to use a tougher grade of cemented carbide. In such ways mechanical

chipping can be minimized but its general effect is to cause scatter in the data for tool life,

and often so much scatter as to render work shop test results meaningless.

Again it is important to be able to distinguish correctly between failure due to

mechanical chipping and other causes. To do this with certainty usually requires

microscopical examination of tools treated in acid to remove adhering metal.

3.5.2 Thermal cracking:





At the cutting edge of the tool very steep temperature gradients exist, and in

interrupted cutting frequent and rapid changes of temperature occur. It is therefore, not

surprising to find, particularly in milling operations, that cracks may be formed across the

cutting edge which can be attributed to the stresses associated with local thermal expansion

and contraction. They may shorten tool life in two ways. If many cracks from close together,

fragments of the tool edge may break away between them. If the tool is subjected to major

stresses in service, the stress concentration at the root of the thermal cracks may result in

failure of the tool by larger scale fracture, but a small number of short thermal cracks does

not appreciably affect the tool life.

There are other factors and causes of wear involved in particular metal cutting

processes but most of these, e.g., oxidation of the tip, or failure due to brazing and grinding

stresses,are avoided by taking reasonable precautions well known to those skilled in the art of

metal cutting or are rarely encountered.

3.6. Methods to reduce Tool Wear

Speed is too fast Decrease spindle speed, use another coolant

Hard work material Use Coatings (TiN, TiCN, TiAlN)

Improper speed and feed

(too slow) Increase feed and speed Improper helix angle Change tool to correct helix angle

Primary relief angle is toolarge

Change to smaller relief angle

Recutting chips Change feed and speed, Change chip size or clear chips withmore coolant or air pressure





Chapter-4

Introduction to dampers

4.1 Introduction to dampers:

A mechanical damper has been introduced to reduce tool vibration during the high-

speed milling process. The mechanical damper is composed of multi-fingered cylindrical

inserts placed in a matching cylindrical hole in the center of a standard end-milling cutter.

Centrifugal forces during high-speed rotation press the flexible fingers against the inner

surface of the tool. Bending of the tool/damper assembly due to cutting forces or chatter

vibration causes relative axial sliding between the tool inner surface and the damper fingers,

and dissipates energy in the form of friction work.

Damper consists of a multi-fingered cylindrical insert placed inside a matching

axial hole along the center line of the milling cutter. During high speed rotation, centrifugal

forces press the outer surface of the insert fingers against the inner surface of the tool. During

lateral vibrations of the tool, relative sliding occurs at the interface between the damper and

tool inner surface, and the resulting frictional work in the contact interface dissipates energyand reduces vibration amplitude. They developed a simplified analytical model for the multi

fingered cylindrical damper and performed experiments. In this paper, non-linear finite

element analysis with frictional contact is used to study the mechanical damper, and calculate

the amount of friction work during lateral bending of the tool. Although chatter vibration is a

dynamic

Phenomenon, the amount of damping in the proposed system is directly

dependent on the energy dissipated during lateral vibrations. If we assume that the contact

pressure between the damping elements inside the tool is primarily due to centrifugal forces,

i.e. The bending stiffness of the damping elements is small, then static finite element analysis

is sufficient to predict frictional work during static bending.

4.1.1 Use cutters with fewer inserts:

Although it may seem counterintuitive, the first step to reducing chatter in milling

operations is to switch to a cutter with fewer teeth. In general, the coarser the cutter pitch, the

lesser the chance of harmonic vibration. Sometimes, replacing a 16-tooth cutter with a 12-





tooth tool ends chatter altogether. A differential-pitch cutter may be required in more difficult

cases to eliminate troublesome harmonics.

The larger the cutter, the better the performance will be. Conditions permitting,

larger cutters provide more choices about how to approach the work piece. Varying the

relative position often helps damp vibration. Manufacturing engineers should try to keep the

cutter diameter 20 to 50 percent larger than the width of the cut. The cutter should be sized so

that no more than two-thirds of the inserts are engaged in the cut at any time. These

guidelines help produce an ideal entry angle, thereby reducing cutting forces and vibration.

4.1.2 Optimize insert geometry:

The shape of the cutting inserts often determines their vibration tendency. Round

inserts are most vibration prone, while those with 45-degree lead angles are the least prone to

chatter. The smaller the entry angles of the cutting edge to the work, the lower the tendency

to vibrate.

Cutting tool specifies can reduce overall cutting force and resulting vibration by using

positive rake insert geometry. The shearing action of positive rake cutters reduces cutting

pressure by more than 20 percent versus zero- or negative-rake milling tools. The sharper

edge and angle of entry of this type of insert also helps to reduce the power needed to

penetrate the surface of the work piece.

4.1.3 Choose inserts coatings carefully:

Coatings on inserts perform many functions, but their primary jobs are protecting

against heat, maintaining lubricity and preventing build-up on the insert. To reduce edge

rounding and chatter, you should look to replace inserts protected by thick CVD coatings

with those wearing thinner PVD coatings. Though CVD treatments are formulated for wear

resistance, PVD coatings provide a sharper insert edge and a more positive rake angle to help

minimize vibration.

4.2 End mill cutter damper geometry

The cutting tool (end mill) used in conventional end mills have a solid

cylindrical cross section, the proposed mechanical damper requires an axial hole along the

tool center line . When the multi-fingered cylindrical damper is inserted into the hollow tool,centrifugal forces from the high-speed spindle rotation cause high contact pressures between





the damper fingers and the inner surface of the tool. When lateral bending of the system

occurs, it causes a Relative sliding motion between the damper and the tool due to their

differences in neutral axis locations. This relative motion in conjunction with the contact

pressure causes a friction stress at the interface, which dissipates the vibration energy. In this

paper, this damping mechanism will be referred to as a mechanical damper. While the

geometry of the cutting edges of the tool is very important for cutting performance, it does

not affect damper performance. Therefore, the tool can be simplified as End mill . Geometry

of end mill and four-fingered mechanical damper.

The simplified ‘damper’ is also modelled as a hollow cylinder, slit along its

length to form individual ‘fingers’. The inner diameter of the tool shank is set to 9.525 mm

and it cannot be made larger because enough material must be left on the shank to allow

cutting teeth to be formed. Thus, although a larger inner diameter of the tool might provide

better damper performance; this is not considered as a design variable since these dimensions

could not be used to produce the actual cutting tool. The damper has an outer diameter of

9.525 mm. The inner diameter of the damper can be changed to maximize the frictional

energy dissipation. The number of fingers can also be altered to improve damping

performance. The parameter study detailed in Section 4 will examine the effect of varying the

number of fingers as well as the damper inner diameter. Because a damper with one finger will not work in the manner described above, this case will not be considered.

.





CHAPTER-5

EXPERMENTATION

Equipments Used

5.1 Vertical milling machine

Fig 5.1 vertical milling machine

This study guide will cover the major working parts, functions, and machining

techniques that can be found/used on most vertical milling machines. This study guide has

been designed to directly represent the questions that will be found on the open book written

assessment and as an aid for the hands-on usability assessment. Both assessments will also

include questions related to standard machine shop safety and APS internal user safety





guidelines. Answering the questions found at the end of the study guide will enable the user

to successfully pass the hands-on usability and open book written assessments. Study guide

practice test and answers can be found at the end of the guide. The Milling Machine uses a

rotating milling cutter to produce machined surfaces by progressively removing material

from a work piece. The vertical milling machine also can function like a drill press because

the spindle is perpendicular to the table and can be lowered into the work piece.

5.2 Cutting tools used

1. Solid end mill

Fig5.2 Solid end mill cutter





2. Hollow with one damper

Fig 5.3 hollow end mill cutter with two dampers

3. Hollow with two damper

1 damper 3600 2 dampers 1800 3 dampers 1200

Fig 5.4 cross section of end mill cutter with dampers

4. Hollow with three damper





Fig 5.5 hollow end mill cutter with three ampers5. Hollow with four damper

6. Hollow with five damper

5.2.1 Cutting tool material used:

High speed steel:

High speed steel is so called because, its speed of cutting is very high compared to the

high carbon steel.

High speed steel can withstand higher temperature without loosing its hardness, but it

becomes soften rapidly at higher temperatures. It also has high wear resistance.

High speed steel are classified into the following types

1. High tungsten steel (T-type)

2. High molybdenum (M-type)

3. Cobalt type

1. High tungsten steel (T-type)

High tungsten type are also known as (18-4-1)tool steel because it contains,

18% of tungsten





4% of chromium

1% of vanadium

0.7% of carbon

2. High molybdenum (M-type)

High tungsten type are replaced with high molybdenum type because small portion of

molybdenum can substitute tungsten which is more economical and also have better

absorption resistance it contains

6% of molybdenum

6% of tungsten

4% of chromium

2% of vanadium

3.Cobalt type

Cobalt has the ability to retain surface hardness of high speed steel tools when

quenched or scratched. Hot hardness and wear resistance increases when 2-15% cobalt is

added to high speed steel

5.3 Tool holding device used:

Fig 5.6 Collet





Collet is a cone-shaped sleeve used for holding circular or rodlike pieces in milling or

other machine.

A collet is a metal band placed around a cutting tool to prevent it from splitting. In

manufacturing, a collet is a type of chuck used to hold cylindrical objects in milling. This

type of chuck is a metal cone-like device that surrounds the work piece and applies an equal

amount of holding pressure to the entire circumference of the piece.

Typically found on milling, grinders and lathe machines, the collet is know for its

extreme accuracy. Much more accurate than a multi-jaw type chuck, the collet holds the work

piece to exacting tolerances. Its downside is that it typically fits only one size of work piece.

The chuck is, however, very easily changed when the need to work on a different size of

stock arises.

While the collet is designed to primarily work with round stock, octagonal, square and

even hexagonal work pieces can be used in the chuck. Many manufacturers utilize this type

of chuck when completing very precise operations and doing very detailed work. Special

emergency-type collets can be machined to hold different shapes of stock as well as different

sizes.

Collet chucks





Fig 5.7 Collet chucks

Chucks are made of special hardened steel to withstand many use cycles, as would be

typical in a high-volume manufacturing environment. There are, however, collets made of

brass and even nylon that can be custom made to hold special work pieces. These chucks can

also be made in step models that are machined to hold shorter pieces that have a larger

diameter than the standard size chuck.

There are several advantages to using a collet chuck over a self-centering or multi-jaw

type chuck. To decipher which type of chuck to use there are some key points to consider.

Spindle speed is crucial to chuck choice. A high-speed tooling requires the lower mass chuck

over the higher mass and weight of a self-centering chuck. The lighter weight and less massallows the chuck to accelerate in a much faster manner.

When working on a large run order or creating many identical pieces, the collet

allows for easy stock changing and precise holding. Also, when the parts are of a diameter of

less than three inches, this type of chuck is preferred due to its holding power and easy

operating tendencies. When making multiple operation cuts on a work piece, the collet

provides a much tighter clamping tolerance, thereby ensuring that the outcome of the

different steps will be precise.





5.4 Work piece material used:

Fig 5.8 Aluminium:

Aluminium alloys require relatively high speeds and feeds. They respond best to

cutters with few teeth and correspondingly wide chip spaces, and can be worked very

effectively by using two flute end mills, which have the advantage of fewer teeth engaged in

the cut. In many cases coolant may not be needed to cool the cutter although it is of benefit in

lubricating and particularly in removing chips. Climb milling gives definite advantages and

shows significant benefits where a good quality surface finish is needed. These materials can

be worked quite effectively with regular tooling, although benefits would be obtained from

custom tools in the event of large volume production being the norm

5.5 Work piece holding device

Vises:

These are the commonly used work holding devices in work shapes because of their

quick loading and un loading of work pieces. Generally, there are three types of vises used in

milling machines for holding work. They are plain vise, swivel vise and tool makers universal

vise. The plain vise can directly be clamped on the milling machine table slots. The swivel

vise consist of a circular bottom plate on which the body can be rotated to obtained angular

milling surface without removing the work from the vise. The universal vise has one or more

degree of freedom of rotation. I.e, it can be swivelled in a horizontal position and can be





tilted for angular cuts in any vertical position. It is not so rigid and hence used only for light

and precision work.

Fig 5.9 Plain vise

5.6 Measuring instrument used:

5.6.1 Tool makers microscope

A tool maker microscope is a type of a multi functional device that is primarily used

for measuring tools and apparatus. These microscopes are widely used and commonly seen

inside machine and tools manufacturing industries and factories. These microscopes are also

inside electronics production houses and in aeronautic parts factories. A tool maker

microscope is an indispensable tool in the different measurement tasks performed throughout

the engineering industry.

The main use of a tool maker microscope is to measure the shape, size, angle, and the

position of the small components that falls under the microscope’s measuring range. Moreoften than not, a tool maker microscope is outfitted with a CCD camera that has the ability to

capture, collect, and store images into specialized computer software. Certain computer aided

design software is commonly used for such applications. The image produced by the camera

and processed by the software is normally a two dimensional image.

But what makes a tool maker microscope fully functional are its glass grading and

optics system. Since what are being viewed under these microscopes are metals and precision

instruments, it is important that the objectives and the eye piece lenses are made of fine





quality glasses only. These essential parts are what makes the device very durable and gives it

the ability to withstand the wear and tear associated with the everyday stress of factory usage.

And much because of this, it is also important that the body, structure, and

mechanisms of a tool maker microscope are created with highly durable materials, most

preferably good quality metals. Because the conditions inside an industrial laboratory are not

as good as a home or office laboratory setup, the microscope’s body should be capable of low

heat production. It should also be able to resist corrosion, oscillation, and pollution – because

all of these elements are present inside an industrial laboratories and production plants.

There are tool maker microscopes that are equipped with a cross hair reticle on the

eye piece, coupled with a protractor on the tube. These are good instruments used toaccurately measure the distance or the diameter of the tool under observation. The

microscope’s stage is also built with a millimeter measuring system that also allows for the

measurement of the specimen. The stage when moved, produce the distance traveled with

which the microscope effectively measures.

Right now, quality tool maker microscopes are using semiconductor laser devices as

directors. Instead of the cross hairs, a red point is virtually marked on the microscope’s

working surface in order to locate the parts that have to be measured by the microscope. The

CCD imaging system can also be used as a measurement system as well. This is another

advanced feature of the newer versions of a tool maker microscope models. A CCD camera

that has the ability to measure diameters and distances is a lot more convenient to use,

especially to beginners.

But aside from all of these, a tool maker microscope should also have a good

illumination system. It is the lights that allows for the superior viewing of tools andspecimens. The higher the luminance value of the light provided by the microscope, the better

its performance is. If necessary, an incandescent lamp should not be used for these

applications. The light that is ideal is the one that produces a nice level of brightness with less

heat. Lamps have life spans too. And because most of a tool maker microscope uses a built-in

lighting system, the light to be used should last for an extended period of time, if and when

possible.





A tool maker microscope is primarily used for measuring the shape of different

components like the template, formed cutter, milling cutter, punching die, and cam. The

pitch, external, and internal diameters are specifically measured as well. The thread gauge,

guide worm, and guide screw are conveniently handled as well. As far angles are concerned,

the thread and pitch angle are of chief concern.

These are what make a good tool maker microscope. If you are not familiar with these

devices, it pays to know more about their specifications. The magnification power of tool

maker microscope is nothing better than a regular compound microscope. In fact, it has a

total magnification power of only 80x. This is due to the fact that these microscopes require

good working distances of around 100 millimeters.

Fig 5.10 Tool maker microscope

Measuring principle:

The work piece to be checked is arranged in the path of the rays of the lighting

equipment. It produces a shadow image, which is viewed with the microscope eyepiece

having either a suitable mark for aiming at the next points of the objects or in case of often





occurring profiles. E.g. Threads or rounding – standard line pattern for comparison with the

shadow image of the text object is projected to a ground glass screen. The text object is

shifted or turned on the measuring in addition to the comparison of shapes. The addition to

this method (shadow image method), measuring operations are also possible by use of the

axial reaction method, which can be recommended especially for thread measuring. This

involves approached measuring knife edges and measurement in axial section of thread

according to definition. This method permits higher precision than shadow image method for

special measuring operations.

5.6.2 Stop watch:

Fig 5.11 stop watch

A stopwatch is a handheld timer used in sporting events such as track meets, swim

meets, triathlons and other time-lapse games. It is designed to be manually started, for example at the beginning of an event, then stopped with the press of a button at the exact

moment a runner crosses a finish line, a swimmer reaches the end lap or a skier sails past the

final gate. Aside from officials, coaches use stopwatches for training and practices.

A stopwatch can be mechanical, resembling a pocket watch with an analog face, or

digital. Digital stopwatches are more accurate, though some people prefer the traditional look

of a silver-cased analog stopwatch. Winning team members or students often choose this type

of stopwatch to engrave as a gift to a coach or trainer.

http://www.wisegeek.com/what-are-the-different-types-of-coaches.htm

http://www.wisegeek.com/what-is-a-pocket-watch.htm

http://www.wisegeek.com/what-is-a-pocket-watch.htm

http://www.wisegeek.com/what-are-the-different-types-of-coaches.htm





A stopwatch can have many functions or modes, depending on the model. Even a

basic stopwatch will keep a running time and "split" or lap time, which allows the user to

keep track of individual laps or events and cumulative time. Some models only store up to 10

lap times, while other models will be able to store 50 laps or more. If the distance of a track

or lane is known, some stopwatches will also calculate speed based on the time it takes for

the competitor to cover the distance.





Chapter-6

Introduction to ANOVA analysis and Taguchi design

6.1 Definition of 'Analysis Of Variance - ANOVA'

A statistical analysis tool that separates the total variability found within a data set

into two components: random and systematic factors. The random factors do not have any

statistical influence on the given data set, while the systematic factors do. The ANOVA test is

used to determine the impact independent variables have on the dependent variable in a

sregression analysis.

6.2 Analysis of variance (ANOVA):Purpose:

The reason for doing an ANOVA is to see if there is any difference between groups

on some variable. For example, you might have data on student performance in non-assessed

tutorial exercises as well as their final grading. You are interested in seeing if tutorial

performance is related to final grade. Anova allows you to break up the group according to

the grade and then see if performance is different across these grades. Anova is available for

both parametric (score data) and non-parametric (ranking/ordering) data.

6.3 Types of anova:

One-way between groups:

The example given above is called a one-way between groups model. You are looking

at the differences between the groups. There is only one grouping (final grade) which you areusing to define the groups. This is the simplest version of anova. This type of anova can also

be used to compare variables between different groups - tutorial performance from different

intakes.

One-way repeated measures:

A one way repeated measures anova is used when you have a single group on which

you have measured something a few times. For example, you may have a test of





understanding of classes. You give this test at the beginning of the topic, at the end of the

topic and then at the end of the subject. You would use a one-way repeated measures anova

to see if student performance on the test changed over time.

Two-way between groups:

A two-way between groups anova is used to look at complex groupings. For example,

the grades by tutorial analysis could be extended to see if overseas students performed

differently to local students what you would have from this form of anova is: the effect of

final grade the effect of overseas versus local the interaction between final grade and

overseas/local each of the main effects are one-way tests the interaction effect is simply

asking "is there any significant difference in performance when you take. Final grade andoverseas/local acting together"

Two-way repeated measures:

This version of anova simple uses the repeated measures structure includes an

interaction effect. In the example given for one-way between groups, you could add gender

and see if there was any joint effect of gender and time of testing - i.e. Do males and females

differ in the amount they remember absorb over time. Nonparametric and parametric anova is

available for score or interval data as parametric anova. This is the type of anova you do from

the standard menu options in a statistical package. The non-parametric version is usually

found under the heading "nonparametric test". It is used when you have rank or ordered data.

You cannot use parametric anova when you data is below interval measurement. Where you

have categorical data you do not have an anova method – you would have to use chi-square

which is about

6.4 Taguchi designs

Quality was the watchword of 1980s, and Genichi Taguchi was a leader in the

growth of quality consciousness. One of Taguchi’s technical contributions to the field of

quality control was a new approach to industrial experimentation. The purpose of the Taguchi

method was to develop products that worked well in spite of natural variation in materials,

operators, suppliers, and environmental change. This is robust engineering.





Much of the Taguchi method is traditional. His orthogonal arrays are two-level, three-

level, and mixed-level fractional factorial designs. The unique aspects of his approach are the

use of signal and noise factors, inner and outer arrays, and signal-to-noise ratios.

The goal of the Taguchi method is to find control factor settings that generate

acceptable responses despite natural environmental and process variability. In each

experiment, Taguchi’s design approach employs two designs called the inner and outer array.

The Taguchi experiment is the cross product of these two arrays. The control factors, used to

tweak the process, form the inner array. The noise factors, associated with process or

environmental variability, form the outer array. Taguchi’s signal-to-noise ratios are functions

of the observed responses over an outer array. The Taguchi designer supports all these

features of the Taguchi method. You choose from inner and outer array designs, which use

the traditional Taguchi orthogonal arrays, such as L4, L8, and L16.

Dividing system variables according to their signal and noise factors is a key

ingredient in robust engineering. Signal factors are system control inputs. Noise factors are

variables that are typically difficult or expensive to control.

The inner array is a design in the signal factors and the outer array is a design in the

noise factors. A signal-to-noise ratio is a statistic calculated over an entire outer array. Its

formula depends on whether the experimental goal is to maximize, minimize or match a

target value of the quality characteristic of interest.

A Taguchi experiment repeats the outer array design for each run of the inner array.

The response variable in the data analysis is not the raw response or quality characteristic; it

is the signal-to-noise ratio.

The Taguchi designer in JMP supports signal and noise factors, inner and outer

arrays, and signal-to-noise ratios as Taguchi specifies.

6.5 Introduction to Taguchi method

Every experimenter has to plan and conduct experiments to obtain enough and

relevant data so that he can infer the science behind the observed phenomenon. He can do so

by,

1.Trial and error method:





Performing a series of experiments each of which gives some understanding. This

requires making measurements after every experiment so that analysis of observed data will

allow him to decide what to do next - "which parameters should be varied and by how much".

Many a times such series does not progress much as negative results may discourage or will

not allow a selection of parameters which ought to be changed in the next experiment.

Therefore, such experimentation usually ends well before the number of experiment reach a

double digit! The data is insufficient to draw any significant conclusions and the main

problem (of understanding the science) still remains unsolved.

2. Design of experiments:

A well planned set of experiments, in which all parameters of interest are varied over

a specified range, is a much better approach to obtain systematic data. Mathematically

speaking, such a complete set of experiments ought to give desired results. Usually the

number of experiments and resources (materials and time) required are prohibitively large.

Often the experimenter decides to perform a subset of the complete set of experiments to save

on time and money! However, it does not easily lend itself to understanding of science behind

the phenomenon. The analysis is not very easy (though it may be easy for themathematician/statistician) and thus effects of various parameters on the observed data are

not readily apparent. In many cases, particularly those in which some optimization is

required, the method does not point to the best settings of parameters. A classic example

illustrating the drawback of design of experiments is found in the planning of a world cup

event, say football. While all matches are well arranged with respect to the different teams

and different venues on differ rent dates and yet the planning does not care about the result of

any match (win or lose)!!!! Obviously, such a strategy is not desirable for conducting

scientific experiments

6.6 Taguchi method

Dr. Taguchi of Nippon telephones and telegraph company, Japan has developed a

method based on “orthogonal array" experiments which gives much reduced " variance " for

the experiment with " optimum settings " of control parameters. Thus the marriage of design

of experiments with optimization of control parameters to obtain best results is achieved in

the Taguchi method. "orthogonal arrays" (oa) provide a set of well balanced (minimum)





experiments and Dr. Taguchi signal-to-noise ratios (s/n), which are log functions of desired

output, serve as objective functions for optimization, help in data analysis and prediction of

optimum results.

6.7 Taguchi method treats optimization problems in two categories,

6.7.1 Static problems:

Generally, a process to be optimized has several control factors which directly decide the

target or desired value of the output. The optimization then involves determining the best control

factor levels so that the output is at the target value. Such a problem is called as a "static problem".

This is best explained using a p-diagram ("p" stands for process or product). Noise is

shown to be present in the process but should have no effect on the output! This is the

primary aim of the Taguchi experiments - to minimize variations in output even though noise

is present in the process. The process is then said to have become robust.

6.7.2 Dynamic problems:

If the product to be optimized has a signal input that directly decides the output, the

optimization involves determining the best control factor levels so that the "input signal / output" ratio

is closest to the desired relationship. Such a problem is called as a "Dynamic problem".

This is best explained by a p-diagram which is shown below. Again, the primary aim of the

Taguchi experiments - to minimize variations in output even though noise is present in the process- is

achieved by getting improved linearity in the input/output relationship.

6.8 Types of static problem s/n ratio’s: (batch process optimization)

There are 3 signal-to-noise ratios of common interest for optimization of static problems;

(a). Smaller-the-better:

N = -10 log10 [mean of sum of squares of measured data]





This is usually the chosen s/n ratio for all undesirable characteristics like "defects"

etc. For which the ideal value is zero. Also, when an ideal value is finite and its maximum or

minimum value is defined (like maximum purity is 100% or maximum tc is 92k or minimum

time for making a telephone connection is 1 sec) then the difference between measured data

and ideal value is expected to be as small as possible. The generic form of s/n ratio then

becomes,

N = -10 log10 [mean of sum of squares of {measured - ideal}]

(b). Larger-the-better:

N = -10 log10 [mean of sum squares of reciprocal of measured data]

This case has been converted to smaller-the-better by taking the reciprocals of

measured data and then taking the s/n ratio as in the smaller-the-better case.

(c). Nominal-the-best:

Square of mean

n = 10 log10 -----------------

variance

This case arises when a specified value is most desired, meaning that neither a smaller

nor a larger value is desirable.

Examples are;

(i) Most parts in mechanical fittings have dimensions which are nominal-the-best type.

(ii) Ratios of chemicals or mixtures are nominally the best type.

E.g. Aqua regia 1:3 of hno3:hcl

ratio of sulphur, kno3 and carbon in gun powder





(iii) Thickness should be uniform in deposition /growth /plating /etching..

6.9 Types of dynamic problem s/n ratio’s (technology development) :

In dynamic problems, we come across many applications where the output is supposed to

follow input signal in a predetermined manner. Generally, a linear relationship between "input"

"output" is desirable.

For example: accelerator peddle in cars,

volume control in audio amplifiers,

document copier (with magnification or reduction)

various types of moldings

etc.

There are 2 characteristics of common interest in "follow-the-leader" or

"transformations" type of applications,

(i) Slope of the i/o characteristics

And

(ii)Linearity of the i/o characteristics

(minimum deviation from the best-fit straight line)

The signal-to-noise ratio for these 2 characteristics have been defined as;

(a).Sensitivity (slope):

The slope of i/o characteristics should be at the specified value (usually 1).

It is often treated as larger-the-better when the output is a desirable characteristics (as

in the case of sensors, where the slope indicates the sensitivity).

N = 10 log10 [square of slope or beta of the i/o characteristics]

On the other hand, when the output is an undesired characteristics it can be treated as

smaller-the-better.

N = -10 log10 [square of slope or beta of the i/o characteristics]





(b). Linearity (larger-the-better)

Most dynamic characteristics are required to have direct proportionality between the

input and output. These applications are therefore called as "transformations". The straight

line relationship between i/o must be truly linear i.e. With as little deviations from the straight

line as possible.

Square of slope or beta

n = 10 log10 ----------------------------

variance

Variance in this case is the mean of the sum of squares of deviations of measured data

points from the best-fit straight line (linear regression).

6.10 8-Steps in Taguchi methodology:

Taguchi method is a scientifically disciplined mechanism for evaluating and implementing

improvements in products, processes, materials, equipment, and facilities. These

improvements are aimed at improving the desired characteristics and simultaneously reducing

the number of defects by studying the key variables controlling the process and optimizing

the procedures or design to yield the best results.

The method is applicable over a wide range of engineering fields that include

processes that manufacture raw materials, sub systems, products for professional and

consumer markets. In fact, the method can be applied to any process be it engineering

fabrication, computer-aided-design, banking and service sectors etc. Taguchi method is

useful for 'tuning' a given process for 'best' results.

Taguchi proposed a standard 8-step procedure for applying his method for optimizing

any process

Step-1: identify the main function, side effects, and failure mode

Step-2: identify the noise factors, testing conditions, and quality characteristics

Step-3: identify the objective function to be optimized

Step-4: identify the control factors and their levels





Step-5: select the orthogonal array matrix experiment

Step-6: conduct the matrix experiment

Step-7: analyze the data predict the optimum levels and performance

Step-8: perform the verification experiment an plan the future action

A technique for designing and performing experiments to investigate processes where

the output depends on many factors (variables; inputs) without having to tediously and

uneconomically run the process using all possible combinations of values of those variables.

By systematically choosing certain combinations of variables it is possible to separate their

individual effects.

A special variant of design of experiments (doe) that distinguishes itself from classic

doe in the focus on optimizing design parameters to minimize variation before optimizing

design to hit mean target values for output parameters.

6.11 Signal to Noise (S/N) Ratios:

The product/process/system design phase involves deciding the best values/levels for the control factors. The signal to noise (S/N) ratio is an ideal metric for that purpose.

The equation for average quality loss, Q, says that the customer’s average quality loss

depends on the deviation of the mean from the target and also on the variance. An important

class of design optimization problem requires minimization of the variance while keeping the

mean on target.

Between the mean and standard deviation, it is typically easy to adjust the mean on

target, but reducing the variance is difficult. Therefore, the designer should minimize the

variance first and then adjust the mean on target.Among the available control factors most of

them should be used to reduce variance. Only one or two control factors are adequate for

adjusting the mean on target.

The design optimization problem can be solved in two steps:

1. Maximize the S/N ratio, h, defined as

H = 10 log10 ( h2~ / sigma2 )





This is the step of variance reduction.

2. Adjust the mean on target using a control factor that has no effect on h. Such a factor is

called a scaling factor. This is the step of adjusting the mean on target.

One typically looks for one scaling factor to adjust the mean on target during design

and another for adjusting the mean to compensate for process variation during manufacturing

6.12 Static versus Dynamic S/N Ratios:

In some engineering problems, the signal factor is absent or it takes a fixed value.

These problems are called Static problems and the corresponding S/N ratios are called static

S/N ratios. The S/N ratio described in the preceding section is a static S/N ratio.

In other problems, the signal and response must follow a function called the ideal

function. In the cooling system example described earlier, the response (room temperature)

and signal (set point) must follow a linear relationship. Such problems are called dynamic

problems and the corresponding S/N ratios are called dynamic S/N ratios.

The dynamic S/N ratio will be illustrated in a later section using a turbine design

example.

Dynamic S/N ratios are very useful for technology development, which is the process

of generating flexible solutions that can be used in many products.





Chapter 7

Design of experiments

7.1 Taguchi design method

To better understand Taguchi design, the procedure of the Taguchi design is described in fig.

1. The complete procedure in Taguchi design method can be divided into three stages: system

design, parameter design, and tolerance design (shown in fig. 1).of the three design stages,

the second stage – the parameter design – is the most important stage it has been widely

applied in the US and Japan with great success for optimizing industrial/production

processes. The stage of Taguchi parameter design requires that the factors affecting quality

characteristics in the manufacturing process have been determined. The major goal of this

stage is to identify the optimal cutting conditions that yield the lowest tool wear value (V b).

Fig.7.1. Taguchi design procedure

The steps included in the Taguchi parameter design are:

Selecting the proper orthogonal array (OR) according to the numbers of

controllable factors (parameters)





Running experiments based on the OA

Analyzing data

Identifying the optimum condition;

Conducting confirmation runs with the optimal levels of all the parameters.

The details regarding these steps will be described in the section of experimental

design.

7.2 Experimental setup and conditions

The experiments were carried out into two stages. Initially the Aluminum material parts are

machined using milling machine with end mill cutter. Then the surface roughness profile was

investigated. The surface roughness values were recorded for at different cutting speeds,

feeds and depth of cut using tool maker microscope.

Tests were performed at different spindle speeds. Three cutting speeds were selected and the

results obtained where chatter was initiated and observed. The details of these experimental

conditions are shown in table 6.1.

Table 7.1 Experimental details for tool wear analysis

Speed in rpm 385 685 960

Feed in mm/min 18 29 41

Depth of cut in mm 0.25 0.35 0.5

Type of cutting

tool

Solid

end

mill

cutter

Solid end

mill

cutter

with one

damper

Solid

end mill

cutter

with

two

dampers

Solid

end mill

cutter

with

three

dampers

Solid

end mill

cutter

with

four

dampers

Solid

end mill

cutter

with

five

dampers

After machining with the different cutting conditions, the tool wear is measured using tool

makers microscope





The experiments were carried out on vertical milling machine. Each experiment was repeated

using a new cutting edge every time to obtain accurate reading of tool wear. The physical and

mechanical properties of work piece are 50mm in length, 50mm in width, 10mm in depth.

The work piece material is Aluminum. The end milling cutter is of high speed steel (HSS).

7.3 Experimental design

7.3.1. Orthogonal array and experimental factors

Following the procedure described in fig. 1, the first step in the Taguchi method is to select a

proper orthogonal array. The standardized Taguchi-based experimental design, a l18 (3^4)

orthogonal array was used in this study and is shown in table 1. This basic design makes use

of up to four control factors, with three levels each. A total of nine experimental runs must be

conducted, using the combination of levels for each control factor as indicated in table 2. The

control factors are the basic controlled parameters used in a milling operation. The spindle

speeds and type of tools were selected from within the range of parameters for milling of

Aluminum. The feed and depth of cut used for milling Aluminum work pieces are constant.

7.3.2. Experimental set-up and procedure

After the orthogonal array has been selected, the second step in Taguchi parameter design(see fig.1) is running the experiment. This experiment was conducted using the hardware

listed as follows:

• Milling machine: vertical milling machine

• Tool wear measurement device: tool makers microscope

• Cutting tools: solid end mill cutter, hollow tool with one damper, hollow tool with two

damper, hollow tool with three damper, hollow tool with four damper, hollow tool with five

damper.





Table 7.2Factors and level values used for orthogonal array l18

Levels(3) /

Factors(4)

Level 1 Level 2 Level 3

Speed (rpm) 385 685 960

Type of tool Solid

end

mill

cutter

Solid end

mill cutter

with one

damper

Solid end

mill cutter

with two

dampers

Solid end

mill cutter

with three

dampers

Solid end

mill cutter

with four

dampers

Solid end

mill cutter

with five

dampers

Feed

(mm/min)

18 29 41

Depth of cut

(mm)

0.25 0.35 0.5

Orthogonal array L18 is shown in following table





Table 7.3 orthogonal array

Trail

No

1 2 3 4

1 1 1 1 1

2 2 2 2 2

3 3 3 3 3

4 1 1 1 2

5 2 2 2 3

6 3 3 3 1

7 1 1 2 1

8 2 2 3 2

9 3 3 1 3

10 1 1 3 3

11 2 2 1 1

12 3 3 2 2

13 1 1 2 3

14 2 2 3 1

15 3 3 1 2

16 1 1 3 2

17 2 2 1 3

18 3 3 2 1





7.4 Results and discussions

Aluminum work piece of 50mm x 50mm x 10mm is machined on vertical milling machine

Table 7.4

Trail

no type of tool

Speed in

rpm

Feed in

mm/min

Depth of cut

in mm

1 Solid end mill 385 18 0.25



4 Hollow with one damper 385 18 0.35



7 Hollow with two damper 385 29 0.25



10 Hollow with three damper 385 41 0.5



13 Hollow with four damper 385 29 0.5



16 Hollow with five damper 385 41 0.35







With various cutting tools, speeds, feeds and depth of cuts shown in above table .then tool wear is

measured using is measured on tool makers microscope and values are given in table7.1.

In the Taguchi method, the term ‘signal’ represents the desirable value (mean) for the

output characteristic and the term ‘noise’ represents the undesirable value for the output characteristic.Taguchi uses the s/n ratio to measure the quality characteristic deviating from the desired value. There

are several s/n ratios available depending on type of characteristic: lower is better (lb), nominal is best

(nb), or higher is better (hb) .smaller is better s/n ratio was used in this study because less tool wear

was desirable.

Quality characteristic of the smaller is better is calculated in the following equation

Experiments are conducted in the order given by Taguchi method and tool wear values are measured

and tabulated Table 7.5

Trail

no type of tool

Speed in

rpm

Feed in

mm/min

Depth of

cut in mm

Tool wear in

mm























6.5 Regression analysis:

Mathematical models for cutting parameters such as cutting speed, feed rate, depth of cut and cutting

fluids were obtained from regression analysis using qualitek software to predict tool wear

The following notation is used in mathematical models:

N: cutting speed

V b: flank wear

The tool wear model equation is as follows:

The tool wear is depends on speed, feed, depth of cut. The relation is given by

For solid end milling cutter

R a= 2.93 - 0.00178 n.

R 2

= 89.2 % r 2

(adj) = 78.5%

For hollow end milling cutter

R a= 2.84-0.00176 n.

R 2= 98.1 % r

2(adj) = 96.2 %

For hollow end milling cutter with one damper

R a= 2.42-0.00148 n.





R 2= 86.7% r 2 (adj) = 73.5%

Where n is speed in rpm.

In multiple linear regression analysis, r 2

is value of the correlation coefficient and should be between

0.8 and 1. In this study, results obtained from surface roughness were in good agreement with

regression models (r 2>0.80) i.e surface roughness measurements matched very well with the

experimental data.

300 400 500 600 700 800 900 1000

1.7

1.8

1.9

2.0

2.1

2.2

S U R F A C E

R O U G H N E S S

SPEED

Fig. 6.2.variation of surface roughness with speed for solid end milling cutter





300 400 500 600 700 800 900 1000

1.50

1.55

1.60

1.65

1.70

1.75

1.80

1.85

1.90

1.95

S U R F A C E

R O U G H N E S

S

SPEED

Fig. 6.3.variation of surface roughness with speed for hollow end milling cutter

300 400 500 600 700 800 900 1000

0.90

0.95

1.00

1.05

1.10

1.15

1.20

S U R F A C E

R O U G H N E S S

SPEED

Fig.6.4. Variation of surface roughness with speed for hollow end milling cutter with one damper





300 400 500 600 700 800 900 1000

0.9

1.0

1.1

1.2

1.3

1.4

1.5

1.6

1.7

1.8

1.9

2.0

2.1

2.2

SOLID CUTTER

HOLLOW CUTTER

HOLLOW CUTTER WITH ONE DAMPER

S U R F A C E

R O U G H N E S S

SPEED

Fig. 6.5. Variation of tool wear with speed

3

1.0

2

1.5

2.0

400600 1

8001000

Surface roughness

Type of tool

speed

Fig.6.6. 3-d graph showing variation of tool wear with speed and type of tool

After calculating s/n ratios, the effect of control parameters on s/n ratio is shown below.





Fig.6.7. Effect of speed on s/n ratio

There is large variation in s/n ratio due to variation in speed.

Fig.6.8. Effect of type of tool on s/n ratio

There is considerable variation in s/n ratio because of type of tool.





Fig. 6.9.effect of feed on s/n ratio

There is slight variation in s/n ratio because of feed.

Fig.6.10. Effect of depth of cut on s/n ratio

There is slight variation in s/n ratio because of depth of cut

.





Fig.6.11 Effect of control factors on s/n ratio




Table 6.5 Summary of anova results

Col#/factor Dof Sum of

squares (s)

Variance(v) Pure sum(s’) Percent

P(%)

Speed 2 50.101 25.005 50.011 86.892

Type of tool 2 5.029 2.514 5.029 8.738

Feed 2 1.163 0.581 1.163 2.021

Doc 2 1.35 0.675 1.35 2.346

Table 6.6.Optimum conditions and performance:

Column#/factor Level description Level Contribution

1.speed 960 3 3.2

2.typpe of tool Hollow tool with one

damper

3 1.034

3.feed 29 mm 3 0.493

4.doc 0.5 mm 1 0.546

Total contribution from all factors 5.273

Current grand average of performance -3.727

Expected result at optimum condition 1.546

P di t d ti l / l f 1 546

Documents

Optimization of Tool Wear in End Milling