iii

EFFECT OF MATERIAL STRUCTURE MACHININGCHARACTERISTICS OF

HYPEREUTECTIC AL-SI ALLOY

FAREG SAEID MOFTAH SAEID

A project report submitted in the fulfillment

of the requirements for the award of the degree of Master of Engineering

(Mechanical - Advanced Manufacturing Technology)

Faculty of Mechanical Engineering

Universiti Teknologi Malaysia

NOVEMBER 2007

v

To My Beloved Mother, Father, Brothers and Sisters

.

vi

ACKNOWLEDGMENTS

In the name of Allah, Most Gracious, and Most Merciful I would like to

thank the many people who have made my master project possible. In particular I

wish to express my sincere appreciate to my supervisors, Assoc. Professor Dr. Ali

Ourdjini, Assoc. Professor Dr. Izman Sudin for encouragement, guidance, critics and

friendship.

I would never have been able to make accomplishment without my loving

support of my family.

I would like to thank all, technicians and fellow researchers in the Production

and materials science laboratories especially to Mr. Aidid. Assistance given by my

fellow postgraduate colleagues especially Mr. Denni Kurniawan and Mr.Kamely and

Mr. Ayob.

My sincere appreciation extends to all my friends and others who have

provide assistance. Their views and tips are useful indeed. Unfortunately, it’s not

possible to list all of them in this limited space. I am grateful having all of you beside

me. Thank you very much.

vii

ABSTRACT

In the present research, experimental results of an investigation of dry turning

of hypereutectic aluminium silicon alloy using polycrystalline diamond (PCD) tools

are presented. Attention is focused on the effect of workpiece microstructure on the

performance of the cutting tools in terms of tool wear, surface roughness and chip

formation. The experimental study involves turning operations at three different

cutting speeds: 500, 600 and 700 m/min and constant depth of cuts and feed rates.

The results obtained showed that PCD tools are important in cutting this hard Al-Si

alloy of reduced machinibility. The lowest cutting speed provides good

machinibility and surface finish. The change of workpiece structure was induced by

modifying the primary Si phase in Al-Si alloy with strontium (Sr). This attempt

found that Sr alone does not lead to a significant reduction in the size of primary Si

phase. However, the results indicated that if the structure is modified the tool wear

improves compared to the unmodified alloy.

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ABSTRAK

Penyelidikan ini membentangkan keputusan hasil ujikaji terhadap pemesinan

bahan aloi aluminium silicon hipereutektik tanpa menggunakan bahan penyejuk

dengan menggunakan mata alat intan polikristal (PCD). Fokus utama adalah untuk

melihat kesan mikrostruktur bendakerja terhadap mata alat dari segi kadar kehausan

mata alat, kekasaran permukaan dan pembentukkan tatal. Kajian eksperimen

melibatkan proses melarik dengan menggunakan tiga tahap kelajuan pemotongan

yang berbeza iaitu 500, 600 dan 700 m/min. Kedalaman pemotongan dan kadar

uluran adalah tetap. Hasil kajian menunjukkan bahawa mata alat PCD sangat

penting kerana ia dapat memudahkan pemesinan aloi AI-Si yang keras ini. Halaju

pemotongan yang paling rendah didapati memberikan kadar pemesinan yang paling

baik dan hasil permukaan yang licin. pembahan mikrostuktur bendakerja adalah

dihasilkan melalui pengubahsuaian fasa utama Si di dalam aloi Al-Si dengan

strontium (Sr). Kajian ini mendapati bahawa Sr sahaja tidak memberi kesan yang

nyata dalam pengurangan saiz fasa utama Si. Walau bagaimanapun hasil kajian ini

menunjukkan bahawa sekiranya struktur ini diubahsuai, maka kadar kehausan mata

alat dapat dikurangkan berbanding dengan aloi yang tidak diubahsuai.

ix

TABLE OF CONTENTS

CHAPTER

TITLE PAGE

DECLARATION ii

DEDICATION iii

ACKNOWLEDGEMENTS iv

ABSTRACT vi

ABSTRAK vii

TABLE OF CONTENTS viii

LIST OF TABLES xii

LIST OF FIGURES xiii

LIST OF APPENDENCES xvii

1 INTRODUCTION 1

1.1 Background 1

1.2 Problem Statement 2

1.3 Objective of the Project 2

1.4 Scope of the Project 2

2 LITERATURE REVIEW 4

2.1 Aluminium and its alloys 4

2.1.1 Classification of Aluminium Alloys 5

2.1.1.1 Casting Alloys 5

2.1.1.2. Wrought Alloys 6

2.1.2 Applications of Aluminium Alloys 7

2.1.3 Casting processes 7

2.2 Al-Si Casting alloys 8

x

2.2.1 Solidification of Al-Si Alloys 9

2.2.2 Aluminum- silicon – magnesium alloys 10

2.2.3 Hypereutectic Al-Si Alloys 13

2.2.4 Grain Refinement of hypereutectic Al-Si

Alloys 14

2.2.5. Modification of Al-Si Alloys 15

2.3 Machining 16

2.3.1 Theory of metal cutting and hard turning 17

2.3.1.1 Hard turning 19

2.3.2 Cutting force 20

2.3.3 Cutting temperature and heat generated 20

2.3.4 Chip Formation 21

2.3.4.1 Chip formation during hard

turning 24

2.3.5 Tool life criteria 25

2.3.6 Tool failure modes 25

2.3.6.1 Flank wear 25

2.3.6.2 Crater wear 28

2.3.6.3 Brittle fracture 29

2.3.6.4 Plastic deformation 30

2.3.7 Tool wear mechanism 30

2.3.7.1 Abrasion (abrasive) wear 30

2.3.7.2 Attrition (adhesion) wears 31

2.3.7.3 Diffusion wear 32

2.3.7.4 Oxidation wear 32

2.4 Cutting tools 32

2.4.1 Single point tools 33

2.4.2 Cutting tool material 34

2.4.2.1 High speed steel 34

2.4.2.2 Carbides 34

2.4.2.3 Coated carbides 36

2.4.2.4 Ceramic 36

2.4.2.5 Cubic boron nitride 37

xi

2.4.2.6 Diamond 37

2.4.2.6.1 Single-crystal diamond 37

2.4.2.6.2 Polycrystalline diamond 38

2.4.2.6.3 Chemical vapor

deposition 38

3 RESEARCH METHODOLOGY 39

3.1 Introduction 39

3.2 Research Design Variables 41

3.2.1 Response Parameters 41

3.3 Workpiece Material 41

3.3.1 CO2 Sand Casting 42

3.3.1.1 Modification of aluminium-silicon

casting alloys 43

3.3.1.2 Impurity Modification on Al-Si

Alloys 43

3.3.2 Preliminary machining 45

3.4 Machines and Equipments 45

3.5 Tool Material 48

3.6 Experimental Set Up 49

3.7 Measurement of Tool Wear 49

3.8 Tool Life Criteria 50

3.9 Chip Morphology 51

4 RESULTS AND DISCUSSION 53

4.1 Introduction 53

4.2 Microstructure analysis of workpiece material 57

4.3 Wear and Tool Life curves 59

4.3 Surface Roughness 64

4.4 chip Morphology 56

5 CONCLUSIONS AND FUTURE WORK 73

5.1 Conclusions 73

xii

5.2 Recommendations for future work. 74

REFERENCES 75

APPENDIX A 79

xiii

LIST OF TABLES

TABLE NO. TITLE PAGE

2.1 The general characteristics of aluminium 4

2.2 Cast aluminum alloy groups 6

2.3 Wrought aluminum alloy groups 7

3.1 Chemical compositions of A390 44

3.2 Mechanical Properties of A390 44

4.1.1 Test results for the unmodified alloy for cutting speed of

500 m/min 53

4.1.2 Test results for the unmodified alloy for cutting speed of

600 m/min 54

4.1.3 Test results for the unmodified alloy for cutting speed of

700 m/min 55

4.2.1 Test results for the Sr-modified alloy for cutting speed of

500 m/min 55

4.2.2 Test results for the Sr-modified alloy for cutting speed of

600 m/min 56

4.2.3 Test results for the Sr-modified alloy for cutting speed of

700 m/min 57

xiv

LIST OF FIGURES

FIGURE NO. TITLE PAGE

2.1 Phase diagram of Al-Si alloy 9

2.2 Types of microstructures that may form during

solidification of a casting 10

2.3 Aluminum – silicon phase diagram and microstructures 11

2.4 Cooling curve of a cooled metal and the effect of grain

refinement 12

2.5 Orthogonal and oblique cutting, a) orthogonal cutting,

b) oblique cutting 16

2.6 Terms used in metal cutting a) Positive rake angle, b)

negative rake angle 17

2.7 Merchant force diagram 18

2.8 Turning operation 18

2.9 Force in turning 19

2.10 Heat generation zone 20

2.11 Formation of chip during metal cutting 21

2.12 continuous chip formations during machining 22

2.13 Continuous chips with BUE formation during

machining 23

2.14 Discontinuous chip formation 23

2.15 Chip morphology according to hardness and cutting

speed 24

2.16 Types of wear observed in cutting tool 25

2.17 Tool life criteria 26

2.18 The effect of cutting speed and the progress of flank

wear 27

xv

2.19 Common properties of cutting tool materials 28

2.20 Turning tool geometry showing all angles 33

2.21 Tool designations for single point cutting tool 34

3.1 Summary of the methodology used in the study 40

3.2 Condition of workpiece material 42

3.3 Comparison of the solidification modes in aluminium

silicon alloys 44

3.4 Condition of workpiece material (a) as cast, (b) after

skinning process 45

3.5 ALPHA 1350S, 2-axis CNC lathe 46

3.6 Tool Maker’s Microscope Nikon 46

3.7 Portable Surface Profilometer, Taylor Hobson

Surtronic 3+. 47

3.8 Optical Nikon Microscope c/w Image Analyzing Software 47

3.9 Polycrystalline diamond (PCD) tool 48

3.10 Measurements of tool wear in turning according 50

3.11 Metallurgical and specimen preparation equipments, (a)

Mounting machine, (b) Polishing machine and (c)

Manual sanding machine 52

4.1 Microstructures of a) unmodified and b) Sr-modified

AlSi18 alloy (X100) 58

4.2 Wear curves for PCD insert in turning the unmodified

alloy versus cutting time at cutting speeds of 500, 600

and 700 m/min 60

4.3 Wear curves for PCD insert in turning Sr-modified alloys

versus cutting time at different cutting speeds of 500, 600

and 700 m/min 60

4.4 Image of flank wears of PCD tool when machining

unmodified AlSi18 alloy at different cutting speeds:

500, 600, and 700 (m/min). 62

4.5 Image of flank wear of PCD tool when machining Sr-

modified AlSi18 alloy at different cutting speeds: 500,

600, 700 (m/min). 63

xvi

4.6 Surface roughness obtained when machine unmodified

AlSi18 alloy with PCD at different cutting speeds 64

4.7

Surface roughness obtained when machining Sr-

modified AlSi18 with PCD at different cutting speeds 65

4.8 Types of chip produced by PCD tool in turning the

unmodified AlSi18 alloy at different cutting speeds and

cutting time 67

4.9 Types of chip produced by PCD tool in turning Sr-

modified AlSi18 alloy at different cutting speeds and

cutting time 68

4.10 Image of chip root when cutting unmodified alloy at

500m/min using PCD cutting tool. 69

4.11 Image of chip root when cutting unmodified alloy at

600m/min using PCD cutting tool. 70

4.12 Image of chip root when cutting unmodified alloy at

700m/min using PCD cutting tool. 70

4.13 Image of chip root when cutting Sr-modified alloy at

500m/min using PCD cutting tool. 71

4.14 Image of chip root when cutting Sr-modified alloy at

600m/min using PCD cutting tool. 71

4.15 Image of chip root when cutting Sr-modified alloy at

700m/min using PCD cutting tool. 72

A.1 Type of engine parts was produced by A390 alloy.

(Source by SEIL CO. LTD) 79

xvii

LIST OF APPENDICES

APPENDIX TITLE PAGE

A application of aluminum silicon alloys 79

CHAPTER 1

INTRODUCTION

1.1 Background

Hypereutectic aluminum–silicon (Al–Si) alloys have been used for many

lightweight, high-strength applications. A390 is one of hypereutectic Al–Si alloys,

with 18wt% Si, and has been used for internal combustion engine parts, cylinder

bodies of compressors and pumps, and brake systems, etc., because of its low

thermal expansion coefficient, high hardness, and good wear resistance. In

hypereutectic Al–Si alloys, the high silicon content, exceeding the eutectic

composition (about 12 wt%), is purposely introduced to enhance the wear resistance

at high temperatures, however, the excess silicon, in the form of proeutectic silicon

grains (order of 10 mm), is hard, highly abrasive, and significantly impact the

machinability.

Tool wear in machining of high-Si aluminum alloys has been characterized as

abrasion due to scratching of crushed primary Si particles and adhesion/abrasion

induced micro-chipping of the cutting edge due to periodic removals of the built-up

workpiece material at the tool surface.

The wear mechanisms of PCD are various in machining different materials.

Nowadays, the development of construction industry accelerates the increase of man-

made boards. Much attention has been focused on the machining of wood based

materials by diamond tools.

2

1.2 Problem statement

The properties of Al- Si alloy are controlled by the reinforcement and the

interface. In particular, many of the considerations arising due to fabrication,

processing and considerations performance of Al- Si alloy are related to process that

take place in the interfacial region between matrix and reinforcement.

A continuing problem with Al- Si alloy is that they are difficult to machine,

tool wear is rapid due to the hardness and abrasive nature of the Si and other

reinforcing particles. Polycrystalline diamond (PCD) is an exception, as its hardness

is approximately three or four times that of the silicon (Si). This is the reason why

PCD is recommended by many researchers, who studied the turning of these

materials.

Evaluate the performance of Diamond tool become important depends to

application of Al- Si alloy to improve their machinability and to obtain economical

tool life in machining Al- Si alloy.

1.3 Objective

The main objective of this thesis is to evaluate the influence of work-piece

material structure on machining characteristics of hypereutectic Al-Si cast alloy and

to examine the type of chips formed during turning of hypereutectic Al-Si cast alloy.

1.4 Scope of the Project

a) Work-piece materials preparation

• Unmodified hypereutectic Al-Si cast alloy.

• Sr-Modified hypereutectic Al-Si cast alloy

b) Microstructure Analysis.

3

c) Evaluate effect of material structure on machining characteristics during

turning using diamond tools.

d) Performances the tools are evaluated based on wear and tool life criteria.

4

CHAPTER 2

LITERATURE REVIEW

2.1 Aluminium and Its Alloys

Aluminum is the third most abundant element in the Earth's crust and

constitutes 7.3% by mass. In nature, however it only exists in very stable

combinations with other materials (particularly as silicates and oxides) and it was not

until 1808 that its existence was first established.

The metal originally obtained its name from the Latin word for alum, alumen. The name alumina was proposed by L.B.G de Moreveau, in 1761 for the base in

alum, which was positively shown in 1787 to be the oxide of a yet to be discovered

metal. Finally, in 1807, Sir Humphrey Davy proposed that of aluminum so to agree

with the “ium” spelling that ended most of the elements.

Table2.1: The general characteristics of aluminium.

Characteristics of aluminium

Symbol Al

atomic number 13

atomic weight 26.98

Density 2698 kg

melting point 660.37

boiling point 2467 ºc

electrical resistively 26.548 · 10-3 µ · m (to 25ºC)

Thermal Conductivity 237 W/m · K (to 27 ºC)

5

2.1.1 Classification of Aluminium Alloys

Aside from steel and cast iron, aluminium is one of the most widely used

metals owing to its characteristics of lightweight, good thermal and electrical

conductivities. Despite these characteristics, however, pure aluminium is rarely used

because it lacks strength. Thus, in industrial applications, most aluminium is used in

the form of alloys.

There are a number of elements that are added to aluminium in order to

produce alloys with increased strength and improved foundry or working properties.

In addition to alloying aluminum with other elements, the mechanical properties can

also be enhanced by heat treatment. Generally, aluminium alloys can be classified

into two main categories: cast alloys and wrought alloys.

2.1.1.1 Casting Alloys

Aside from their lightweight, cast aluminium alloys have relatively low

melting temperatures when compared to steel and cast iron; have negligible solubility

for gases except hydrogen, good fluidity and good surface finish. However, these

alloys suffer from higher shrinkage (up to 7%) which occurs during cooling or

solidification. Higher mechanical properties in these alloys can be achieved by

controlling the level of impurities, grain size, and solidification parameters such as

the cooling rate.

A system of four-digit numerical designation is used to identify aluminum

and aluminum alloys in the form of castings and foundry ingots. The first digit

indicates the alloy group as shown in Table 2. The second and third digits identify

the aluminum alloy or indicate the minimum aluminum percentage. The last digit,

which is to the right of the decimal point, indicates the product form: XXX.0

indicates castings, and XXX.1 and XXX.2 indicate ingots.

6

Table 2.2: Cast aluminum alloy groups [1].

Aluminum 99.00 percent minimum and greater 1xx.x

Aluminum alloys grouped by major alloying elements: copper 2xx.x

Manganese 3xx.x

Silicon 4xx.x

Magnesium 5xx.x

Magnesium 6xx.x

Zinc 7xx.x

Other element 8xx.x

Unused 9xx.x

2.1.1.2 Wrought Alloys

In wrought aluminium alloys means that the alloys have undergone certain

working processes. The use of aluminium alloys is dominated by this group of alloys,

in products such as rolled plates, sheet metal, foil, extrusion tubes, rods, bars and

wire. Table 3 shows the main classes of wrought aluminium alloys. Like cast alloys,

wrought alloys are also designated by a four digit system. Both wrought and cast

aluminium alloys are divided into alloys which can be heat treated (in order to

increase the mechanical properties) and alloys which cannot be heat treated.

7

Table 2.3: Wrought aluminum alloy groups [1].

Aluminum,99.00 percent minimum and greater 1xxx

Aluminum alloys grouped by major alloying elements copper 2xxx

Silicon, with added copper and / or magnesium 3xxx

Silicon 4xxx

Magnesium 5xxx

Zinc 7xxx

Tin 8xxx

Other element 9xxx

Unused series 6xxx

2.1.2 Applications of Aluminium Alloys

Table 2.4: some typical applications of cast aluminium alloys include the following:

Alloy Type Typical Applications

319.0

332.0

356.0

A356.0

A380.0

383.0

B390.0

Manifolds, cylinder heads, blocks, internal engine parts.

Pistons.

Cylinder heads manifolds.

Wheels.

Blocks, transmission housings/parts, fuel metering devices.

Brackets, housings, internal engine parts, steering gears.

High-wear applications such as ring gears & internal transmission Parts.

2.1.3 Casting processes

In general, aluminum castings can be produced by more than one process.

Quality requirements, technical limitations and economic considerations dictate the

8

choice of a casting process. The common casting processes used for aluminium

alloys include the following:

1. Sand casting: large castings (up to several tons), produced in quantities of

from one to several thousand castings.

2. Permanent mold casting (gravity and low pressure): medium size casting (up

to 100kg) in quantities of form 1000 to 100,000;

3. High pressure dies casting: small castings (up to 50 kg): in large quantities

(10,000 to 100,000)

There are several reasons why castings should be made from aluminium

alloys. These include properties like: Ductility, high deformation, weight reduction,

shape stability, wear resistance, and stress distribution [2]

2.2 Al-Si Casting Alloys

Over the last 50 years, there has been a growing trend towards lightweight

materials because of environmental concerns and for producing components and

structures at low cost with increased performance. Al-Si casting alloys are the most

widely used alloys due to the following characteristics [3]:

• Low density

• Excellent fluidity (due to addition of silicon)

• Good weldability

• High corrosion resistance

• Low coefficient of thermal expansion (CTE)

9

2.2.1 Solidification of Al-Si Alloys:

Al-Si alloys differ from the "standard" phase diagram in that aluminium has

zero solid solubility in silicon at any temperature. This means that there is no β phase

and so this phase is "replaced" by pure silicon. So, for Al-Si alloys, the eutectic

composition is a structure of α + Si rather than α +β. Figure 1 shows the Al-Si phase

diagram.

Figure 2.1:Phase diagram of Al-Si alloy

The solidification of Al-Si alloys is an important aspect because it controls

final microstructure which in turn controls the mechanical properties. Therefore, it is

necessary to understand the basic principle of solidification and how the

microstructure form. In general, solidification of an alloy occurs in two stages:

nucleation and growth. In the nucleation stage, stable nuclei are formed into the

liquid metal and the subsequent growth of these nuclei into crystals and the

formation of the final grain structure.

There are two types of grain structures that may be formed upon

solidification of a metal alloy: columnar and equiaxed grains. Equiaxed grains form

as a result of equal growth in all directions of the crystal (prevalent in grain refined

alloy due to the presence of large number of nucleation sites) while columnar grains

are present as thin, long structures which grow under a temperature gradient during

slow solidification. These columnar grains grow in a direction normal to the mould

wall and in a direction opposite the heat flow.

10

The preferred structure of a casting is one that has small equiaxed grains

(Figure2.2), since this type of structure improves feeding, resistance to hot tearing

and enhances the mechanical properties. Improvements in the mechanical properties

are the result of sound casting that can be produced during casting. Producing a

structure with equiaxed grains can be achieved through control of the solidification

conditions or by the use of inoculants or grain refiners.

Figure 2.2: Types of microstructures that may form during

solidification of a casting [4].

2.2.2 Aluminum – silicon - magnesium alloys

Aluminum–silicon alloys are widely used for shape casting due to their high

fluidity, ease of casting, low density and controllable mechanical properties.

Commercial Al-Si alloys are available in alloys with silicon additions of up to 11 %(

hypoeutectic), 11 to 13% (eutectic) or over 13% (hypereutectic). Various other

elements such as Fe, Cu, Mg, Ni, and Zn are added to achieve the optimum casting

or mechanical properties.

11

Figure 2.3: Aluminum – silicon phase diagram and microstructures [2].

According to Figure 3, upon solidification of aluminum–silicon alloys of

composition generally less than 12% silicon (hypoeutectic) the first phase to form is

aluminum. Considering an alloy containing 7% silicon on cooling form the liquid

phase (Ts) the aluminum forms as small dendrites when the solidification

temperature (Tl) is reached. The temperature difference Ts-Tl is the melt "superheat"

or undercooling, which represents the driving force for solidification. Solidification

does not occur at a single temperature but rather over a temperature range and will be

completed at the eutectic temperature (Te). The exception is the case of alloys of

eutectic composition (~12% Si) where solidification occurs at the eutectic

temperature. As the temperature falls below the liquids point (TI), aluminum

dendrites grow and more are nucleated until the eutectic temperature is reached. The

dendrites formed are seen as the aluminum grains in the final microstructure. At the

12

eutectic temperature all of the remaining liquid will freeze as aluminum–silicon

eutectic in simple binary alloys. However, various other intermetallic phases such as

CuAl2, Mg2Si will form at lower temperatures in commercial alloys depending on the

actual alloy composition.

Figure 2.4: Cooling curve of a cooled metal and the effect of grain refinement.

Because solidification liberates heat, we would expect to see a plateau in the

melt temperature on a thermal analysis trace when it occurs. In practice, cooling

below the equilibrium point is required in order to nucleate the first dendrites. As

those dendrites grow, heat is liberated and the temperature will rise (Figure 2.4).

The temperature drop required "undercooling", and is a measure of the

difficulty in nucleation of the first aluminum dendrites. Grain refined alloys have

very low undercooling compared to non-grain refined alloys because the action of

the refiner is to aid nucleation. Following the temperature rise it will fall again as

heat is extracted, until the eutectic temperature is reached when it stabilizes while

solidification of aluminum-silicon is completed. Further arrests in the temperature

trace may also be seen as intermetallic phases during cooling.

Accompanying solidification is a change in density of the alloy from typically

2.3g/cm3 in the liquid to 2.7 g/cm3 in the solid. If this shrinkage is not controlled it

13

may lead to voids forming in the solid as macro or micro-porosity. The structure of

the alloy will thus be comprised of a mixture of dendritic grains surrounded by

aluminium-silicon eutectic with isolated pockets of intermetallics and shrinkage

porosity.

2.2.3 Hypereutectic Al-Si Alloys

Hypereutectic Al-Si casting alloys (> 13%Si) are widely used in the

automotive industry. Components such as engine blocks, pistons, cylinders, and

pump components are made from this category of alloys. The hypereutectic Al-Si

alloys contain hard primary particles of non-metallic silicon embedded in an Al-Si

eutectic matrix. Hypereutectic alloys possess outstanding wear resistance and good

elevated temperature strength, lower thermal expansion coefficient (CTE), very good

casting characteristics and excellent strength to weight ratio. One of the most widely

used hypereutectic Al-Si alloys is the 390 alloy, which possesses excellent fluidity

and has good resistance to hot cracking during casting.

However, these alloys have serious machinability problems due to the

presence of the hard primary silicon phase which acts as abrasives. In order to obtain

the best machinability, enhanced mechanical properties and higher performance of

cast parts, the size of silicon phase must be controlled through melt treatment. This is

usually achieved by treating the melt with additions of phosphorous.

Since the eutectic in Al-Si alloy system occurs at about 13% Si, it is expected

that all alloys containing more than this amount of silicon should exhibit a normal

hypereutectic structure consisting of primary silicon in a binary Al-Si eutectic

matrix. Depending on the situation, however, three types of structures may form in

cast hypereutectic alloys:

i) primary aluminum dendrites may form in alloys which are just

slightly hypereutectic

14

ii) completely eutectic structure in hypereutectic alloys modified with

strontium

iii) Hypereutectic alloys often contain primary aluminium in addition to

primary silicon.

The existence of these structures reflects the complexity of the solidification

process of a casting, as they are often due to melt treatment or casting conditions.

Primary silicon in hypereutectic Al-Si alloys may appear in several different

morphologies, and it is not uncommon to find many of these in the same casting. The

morphology of silicon in hypereutectic alloys is highly dependent on the

solidification parameters such as: cooling rate, temperature gradient in the liquid and

presence of inoculants.

Hypereutectic Al-Si alloys also suffer from macro-segregation, particularly

under slow solidifications conditions as in sand casting for example. Additions of

phosphorous as well as strontium to these alloys may reduce silicon segregation in

casting by providing longer flotation time or short primary solidification temperature

range. Cooling the casting at higher solidification rate in excess of 15 oC/s, was

found to reduce segregation of primary silicon.

2.2.4 Grain Refinement of hypereutectic Al-Si Alloys

The benefits of a fine and uniform grain size are many. Improved mechanical

properties can be achieved such as higher tensile strength, increased ductility and

fatigue resistance. Physical properties may also be affected. Grain refiners are

materials added ton alloys to aid in nucleation, and lead to the production of fine and

uniform grain size. There are several types of grain refiner available for aluminum–

silicon alloys, based on aluminum-titanium or aluminum-titanium-boron master

alloys, and titanium or titanium-boron containing salt tablets for hypoeutectic alloys.

15

In hypereutectic alloys, grain refinement is achieved through the addition of

phosphorous. The phosphorous has a marked effect on the size, shape and

distribution of the primary silicon. The addition of phosphorous into hypereutectic

alloys reduces the size of silicon by a factor of 5 to 10, increases their number and

provides for their even distribution throughout the structure.

The result of grain refinement is reduced or better dispersed porosity in the

casting which will also lead to improved mechanical properties.

2.2.5 Modification of Al-Si Alloys

Modification has become a common and sometimes an essential foundry

practice when it comes to casting the aluminium-silicon alloys. Modification is a

process that changes the microstructure of cast alloys either through quenching or by

adding some alkaline elements. The main objective of modification in a casting is to

achieve a different microstructure that can yield better mechanical properties and

characteristics. . Modification is mainly associated with the alteration of the silicon

phase in aluminium-silicon casting alloys since there is no evidence that the

aluminium phase is directly influenced by modifiers addition.

Basically modification can be divided into impurity modification and quench

modification. Modification through the additions of a small amount of modifiers is

termed impurity modification while the latter is due to rapid solidification rate.

Although there are many elements, which are found to have modification ability,

only sodium and strontium appear to be stronger modifiers at low concentration and

now they are widely used for commercial applications. In hypoeutectic Al-Si alloys,

silicon is present as a constituent of the eutectic phase, so sodium and strontium

transform the flake eutectic silicon into fibrous form, hence increasing the ultimate

tensile strength, ductility, hardness and machinability. Modification is affected by

several variables and reversion of the modified structure back to the unmodified state

16

is possible when there is higher silicon content, higher temperature and longer

holding times.

Figure 2.5: Optical micrographs showing the various phases observed.

In hypereutectic alloys, however, silicon is present both as a eutectic

constituent and as primary phase. Thus modification induces another transition,

which is a transition of the primary silicon involving three apparent possibilities:

irregular to dendritic, irregular to spheroidal, and dendritic to spheroidal [5].

2.3 Machining

Traditional machining operations such as turning, milling, boring, tapping,

sawing etc. are easily performed on aluminum and its alloys. The machines that are

used can be the same as for use with steel, however optimum machining conditions

such as rotational speeds and feed rates can only be achieved on machines designed

for machining aluminum alloys.

17

2.3.1 Theory of metal cutting and hard turning

Machining is changing the geometry of work piece to produce desire shape

by removing several materials. Generally, metal cutting operation is classified into

two types operation model; orthogonal cutting and oblique cutting, Figure 2.6 shows

both orthogonal cutting and oblique cutting. Orthogonal cutting is an idealized case,

where the cutting edge is straight and perpendicular with direction of tool travel

(Figure 2.6.a). On other hand, when the cutting edge is not perpendicular with

direction of tool travel is termed oblique cutting (Figure 2.6.b). The orthogonal

cutting is simpler where it represents in two dimensional rather than three

dimensional and widely used in the cutting process analysis. Figure 2.7 shown terms

are used in metal cutting.

Figure 2.6: Orthogonal and oblique cutting, a) orthogonal cutting,

b) oblique cutting [8].

18

Figure 2.7: Terms used in metal cutting a) Positive rake angle,

b) negative rake angle [10].

The first complete analysis of the cutting process problem was proposed by

Ernst and Merchant [8]. Their analysis was successfully and more accurate than

other analysis were carried out by various researchers. Ernst and Merchant analysis

represent in Merchant force diagram (Figure 2.8), while their analysis assumptions

using orthogonal cutting.

Figure 2.8: Merchant force diagram [8]

Turning is one type of metal cutting process that used to produce cylindrical

surface. During turning operation workpiece is rotated and tool will travel along

workpiece rotation. The combination between workpiece rotation and tool motion

19

will result reducing workpiece size or diameter of workpiece. Figure 2.9 shown

turning operations.

Figure 2.9: Turning operation [9].

2.3.1.1 Hard turning

Hard turning is one type of turning operation. Hard turning referrer as turning

the workpiece with hardness value above 45 HRC. Typical workpiece materials

suitable for hard turning operations include heat-treatment materials e.g., quenched

and tempered case hardening among other heat-treatments [10].

Hard turning mostly need high hardness tools while negative rake angle is

required besides, lower both feed rate and depth of cut also applied to generated

better performance. However, large nose radius (generally 0.8 mm) is selected to

achieve better surface finish

Hard turning is one alternative for replace grinding operation, hard turning

has significant growth due to improving productivity and low production cost

associated rather than grinding. Generally, applications grinding process present low

material removal rate, and requires large quantities of coolants that impact both

operator health and environmental pollution. However, hard turning offer several

20

advantages than grinding such as reduce machining time, high geometry flexibility,

less energy required, environmental friendly, and better surface finish quality.

2.3.2 Cutting force

Cutting force is an important aspect in turning operation. There are three

types force action on cutting tool during turning operation (Figure 2.10)

• Cutting force Fc, also known as tangential force and the largest force of

the three forces, acts in the direction of the cutting velocity. This force is

used to determine the power requirement.

• Thrust force Ft, also known as feed force, this force acts in longitudinal of

feed motion.

• Radial force Fr, is the smallest of the force components and inmost case it

is usually ignored.

Figure 2.10: Force in turning [11].

2.3.3 Cutting temperature and heat generated

The mechanical action during machining produce heat, heat generate will

increase the cutting temperature and accelerate tool wear than the life of tool is

shorted excessively. There are three main regions that heat generated during

21

machining, these are primary shear zone, secondary shear zone, and flank surface.

Heat generate in primary shear zone because plastic deformation of workpiece to

form the chip. In secondary shear zone heat generate between the chip and tool, heat

from chip will transfer to the tool surface. The third region is flank surface where

heat is generated by forming of new surface. Besides, cutting speed and hardness

value will effect to cutting temperature, where as in the cutting speed increase the

temperature is increasing. Figure 2.11 shown heat generation zone

Figure2.11: Heat generation zone [8].

Carried out the experiment of hard turning steel AISI 4340 which hardness

value above 50 HRC. It showed increase the cutting speed will increase the

temperature [12]. However, the cutting temperature is increased with increase of

work material hardness. Additionally, increase the hardness value at high feed rate

significantly increases the cutting temperature [13].

2.3.4 Chip Formation

Cutting process remove material from the surface of a workpiece by

producing chips [14]. The formation of chip for metal cutting involves the shearing

(plastic flow process) of the workpiece from the tool edge to the position where the

chip leaves the workpiece surface [15].

22

This process occurs at shear plane at the angle φ with the cutting tool. This is

known as shear angle. Figure 2.12 illustrate the mechanism of chip formation during

metal cutting.

Figure 2.12: Formation of chip during metal cutting [14].

The chips formation under different metal cutting conditions can be classified

into few categories. Workpiece material and cutting condition will influence the type

of chips form during machining. The surface finish and overall cutting operation are

significantly influenced by chips produced. The types of chips produced during metal

cutting are continuous chips, continuous chips with built up edge, discontinuous

chips and serrated chips [14, 15, 16]

Continuous chips are usually formed when cutting ductile materials under a

steady state condition at high cutting speeds and high rake angles Even though

continuous chips produce good surface finish, but they are not always desirable

particularly in automated machine tools as being widely used nowadays. This is

because they tend to get entangled around the tool holder, fixturing and workpiece.

It is also a problem to dispose these chips as the automated machines need to be

stops and handling these chips need high safety awareness. Figure 2.13 shows

formation of continuous chips [17, 18].

23

Figure 2.13: continuous chip formations during machining [18].

Continuous chips with built up edge is formed at the tip of the tool due to

excessive frictional resistance at the cutting edge and at tool rake face at normally

high cutting speeds. This built-up-edge consists of layers of material from the

workpiece that are gradually deposited on the tool and as it becomes larger, the BUE

becomes unstable and eventually breaks up. Part of the BUE material is carried

away by the tool side of the chip while the rest is deposited randomly on the

workpiece surface. The tendency for the formation of BUE is reduced by decreasing

the depth of cut and increasing the rake angle. These chips give undesirable surface

finish, but a thin and stable layer protects the surface of the tool from wear [14, 19].

Figure 2.14 shows continuous chips with built up edge.

Figure 2.14: Continuous chips with BUE formation during machining [18].

24

Discontinuous chips consist of segments that may be firmly or loosely

attached to each other. It is normally formed at brittle workpiece materials,

workpiece materials that contains hard inclusion and impurities or have structures

such as graphite flakes in grey cast iron. It is also common to see discontinuous chips

at very low or very high cutting speeds. The depth of cut, machine and tool stiffness

and lack of effective cutting fluid also may lead to this category chips formation [14].

Figure 2.15 illustrates discontinuous chips.

Figure 2.15: Discontinuous chip formation [18]

Serrated chips are also called as segmented or nonhomogeneous chips which

are semi continuous chips with zones of low and high shear strain. The chips have

saw teeth appearance. During hard turning process this type of chip will be formed.

2.3.4.1 Chip formation during hard turning

One of common chip formation during hard turning is serrated chip or saw

tooth. Poulachon et al. (2001) reported when turning 100Cr (AISI 52100) with

hardness 38-60 HRC using PCBN tool, the chip formed is saw tooth. Their

concluded that, during turning steel with hardness range 10-50 HRC continuous

chips was produced. However, when the hardness excess 50 HRC, saw tooth

appears. Figure 2.16 shown the chip morphology during machining with different

hardness and cutting speed

25

Figure 2.16: Chip morphology according to hardness and cutting speed [19].

2.3.5 Tool life criteria

Tool life is defined as cutting time required to reach a tool life criterion [8].

The factors affecting tool life criteria are workpiece material, tool material, and

cutting condition. According to the criteria recommended by ISO to define the tool

life criteria for diamond tools [20], it also reported that at high temperature caused by

high cutting speeds and feed rate, catastrophic failure often lead to destructive the

tool. In such case, catastrophic failure can be used as the tool life criterion.

2.3.6 Tool failure modes

In the process machining, tool wear occurs in cutting tool. Tool wear is one

of most important and complex aspects of machining operation [11]. Generally, tool

life can be determined by tool failure modes. The various regions of tool wear are

identified as flank wear, crater wear, nose wear, chipping of the cutting edge, plastic

26

deformation, and catastrophic failure [11]. Figure 2.17; shown types of wear

observed in cutting tool.

Figure 2.17: Types of wear observed in cutting tool [11].

2.3.6.1 Flank wear

Flank wear occurs due to rubbing action on both major and minor cutting

edges during cutting. Flank wear is often used to define the end of effective tool life

(Arsecularate et al., 2006). Flank wear has been studied extensively and generally

attribute to [11].

• Sliding of the tool along machined surface, causing adhesive and abrasive

wear depending on the material involved.

• Temperature rise, because of its influence on the properties of the tool

material.

Figure 2.18 shown recommends the tool life criteria by ISO while it’s divided

into three zones:

27

• Tool nose region (Zone C) designated by VC

• Center part of the active cutting edge or flank wear land (Zone B)

designated by VB and maximum wear land is designated by VB max

• Groove or notch (Zone N) designated by VN

Figure 2.18: Tool life criteria [20].

Development of flank wear land (VB) increases proportionally with increases

the cutting speed. Figure 2.18, shown the effect of cutting speed and the progress of

flank wear, the wear rate increase rapidly as the cutting speed is increase and

subsequently tends to increase gradually at a uniform rate (zone BC) to a critical

point C. At (zone CD) rapid develop of flank wear leading to fracture of the tool.

Flank wear will affect on surface finish, excessive flank wear will cause poor surface

finish increase both cutting force and temperature. In practical, tool is replaced

before pass from flank wear rapid breakdown limit.

28

Figure 2.19: The effect of cutting speed and the progress of flank wear [10].

In finish hard turning with low depth off cut and feed rates groves are often

found in minor flank wear (Zone C). Tang (2006) was observed that flank wear is

mainly concentrated on the nose region Zone C due to low depth of cut value,

opposite of these flank wear Zone B and Zone N do not exist.

The flank wear increase rapidly by the formation of severe abrasive and,

flank wear was very rapid with increases both cutting time and cutting speed. [21].

indicated that flank wear of carbide tool increase with increasing the turning speed.

At higher cutting speeds and feed rate, the effect of abrasion has the overall wear

mechanism on the flank face of TiN coated carbide tool reported by [22].

2.3.6.2 Crater wear

Crater wear occurs on the rake face, the most significant factor in crater wear

is temperature and degree of chemical affinity between the tool and work piece. The

rake face of the tool is subjected to high level of stress and temperature, in addition

to sliding at relative high speed [11].

The wear process in the crater wear of carbide tool is one of diffusion; the

occurrence of crater wear by diffusion is a function of cutting speed (Trent, 2000).

Excessive crater wear lead to weakness the cutting edge and consequently

deformation and fracture the tool. Crater wear is one of the factors to determine the

29

tool life at high cutting speed condition. Maximum depth of cut crater wear

designated by (KT) and the width from the cutting edge to wear edge designated by

(KB) .

Experimental evidence by [24] indicates crater wear form when turning EN

24 steel at high cutting speed. The temperature at the tool-chip interface increase and

the transfer of material between the workiece material and the tool occurs.

2.3.6.3 Brittle fracture

Brittle fracture element such as cracks, chipping, and catastrophic failure are

resulted from occurrence of cracks in the cutting tool which can cause loss of tool

material. Brittle fracture is often thermal-mechanical phenomenon, where the tool

surface repeatedly subjected to loading force especially in milling process. In

turning, catastrophic tool failure is to be avoided since it can result in the breakage

off cutting edge, too high depth of cut or cutting feed and sharp cutting edge are

several factors that causes catastrophic failure in turning process.

Investigated chipping and catastrophic failure of both conventional and

wiper TiA1N coated carbide tool increase rapidly at high cutting speed that can be

attributing to crack formation [15]. discussed at high cutting speed with high

hardness of workpiece material which causes high cutting force and high cutting

temperature leads the carbide tool to suffer rapid wear, chipping or fracture. By

increasing cutting speed wear both chipping and catastrophic failure on TiN coated

carbide tool was often occurring due to high cutting force and sharp edge chipping, it

reported by [24].

Application of coolant is the other factor to led brittle fracture, better

performance thermal shock of carbide tool is attainable under dry cutting during

cutting at high speed. Concluded that chipping occurs on coated carbide tools

probably because of thermal shock occurring when the coolant is being applied [25].

30

2.3.6.4 Plastic deformation

Plastic deformation is the distortion of cutting part of a tool from its original

shape without the initial loss of tool material. Plastic deformation is not considered

as a wear process because there is no material being removed from the tool during

machining. However, the geometry of the tool will change and this will affect the

ability of the tool to perform as expected under severe cutting condition. This will

affect the outcome of the machining process.

2.3.7 Tool wear mechanism

Tool wear is a phenomenon that results of mechanical and chemical process

which changes of the tool from its original shape during cutting resulting from

gradual loss of tool material. The fundamental of wear mechanism can be

differenced under different condition, it depend on various factors such as cutting

parameters (cutting speed, feed rate, and depth of cut), material types, and type of

tool used. The four main wear mechanisms which occur during metal cutting are

abrasion (abrasive), attrition (adhesion), diffusion, and oxidation wear.

2.3.7.1 Abrasion (abrasive) wear

Abrasion is a wear mechanism where hard particles abrade and remove some

of the tool material [18, 19]. Hard particles that could cause this wear mechanism

could be carbides, oxides and nitrides that could present in the tools or workpiece.

Abrasion rate will increase if the speed and feed during machining increased.

Increasing the hardness of the tool can overcome abrasion.

Abrasive wear is mainly caused by hard particles or impurities within the

workpiece such as carbide nitride and oxide compounds. The hard particles may be

containing underside of the chip Passover the tool face and remove some of tool

31

material. This is mechanical wear with causes wear on flank wear, rake face, and

notch wear, abrasive wear increase with increase in cutting speed [26].

In hard turning using coated carbide insert abrasion takes place particularly at

rake face and flank wear. Abrasion is also an important wear mechanism when using

PCBN tool during cutting hard turning which give significant contribution to flank

wear, probably owning to the presence of hard carbide particle [26].

2.3.7.2 Attrition (adhesion) wears

Attrition wear or adhesion wear is a mechanism which caused by fracture of

welding between the tool and work material due to friction and small fragment of

tool material are carried away by chips or on the new workpiece surface. When

cutting at relative low speeds attrition result in formation of build up edge and its

takes as dominant wear and pulls out the tool surface material. Attrition is not

accelerated by high temperature and tends to disappear at high cutting speed as the

flow becomes laminar however, fine grain size carbide cutting tool will reduce

attrition wear [23].

found that adhesion wear occurring at low machining temperature is also

investigated as a wear mechanism causing the TiA1N coated carbide inserts to fail

besides, adhesion is more common at low and medium cutting speeds when unstable

BUE is likely to form during cutting Stavax ESR stainless tool [21].

At low cutting speed adhesion wear and BUE occurs, where adhered and

fragment of BUE due to broken flank edge area. In additionally, carried out

experiment during turning steel AISI 1045 using TiC coated carbide tools that BUE

presence at low cutting speed, forms of BUE on cutting tool is very unstable and it

break off and reform over and over again than fragments of BUE would tear away

the coating material. Besides, his also discussed the cracking of TiC coated tool

occurs at the rake face leading to high crater wear and facilitates removal of the

coating by attrition wear [22].

32

2.3.7.3 Diffusion wear

Diffusion wear is a mechanism where a constituent of a tool material diffuses

into or forms a solid solution with the chip materials. Diffusion wear depends

primarily on the solubility of the tool material in the work material and the contact

time between the tool and chip at elevated temperature, and increases exponentially

as the cutting temperature increases. The metallurgical relationship between the tool

and work material will influence the rate of diffusion wear.

2.3.7.4 Oxidation wears (Chemical wear)

At very high cutting speed, the presence of air and high temperature produce

oxidation wear. Chemical reaction can take place between tool and workpiece hence

weakened the tool.

2.4 Cutting tools

Cutting tool materials in various ranges has been used in the industry for

different kind of applications. A large variety of cutting tool materials has been

developed to cater for various programmes such as nuclear and aerospace industry.

According to, important characteristics expected in cutting tool materials are;

i) Hardness of higher than the workpiece material.

ii) Hot hardness where the tool should be able to retain hardness at

elevated temperature

iii) Wear resistance with high abrasion resistance to improve the effective

life of the tool

iv) Toughness to withstand the impact loads at beginning of the cut and

force fluctuation due to imperfection of workpiece material.

v) Low friction would allow lower wear rates and improved chip flow.

33

vi) Thermal characteristic where the tool material should have higher

thermal conductivity to dissipate heat in shortest time.

These characteristics will give a better cutting performance. The continuous

development in the cutting tool will help to achieve this characteristic.

Figure 2.20: Common properties of cutting tool materials [14].

2.4.1 Single point tools

Single point tools are tools having one cutting part (chip producing element)

and one shank. They are commonly used in lathes. Figure 2.21 shows turning tool

geometry. There are various angles in single cutting tool and each angle has its

importance during turning operation.

34

Figure 2.21: Turning tool geometry showing all angles [27].

Rake angle will determine the direction of chip flow and the strength of the

tool tips. Cutting force can be reduced with positive rake angle but the problem is it

will produce a small included angle of the tool tip [14].

Relief angle will control the interference and rubbing of tool and workpiece.

The tool may chip off if the relief angle is large while excessive flank wear will

happen in the angle is small [17].

Chip formation, tool strength and cutting forces are influenced by cutting

edge angles. The surface finish is influenced by nose radius. Small value of nose

radius is will reduce surface roughness and strength of the tool while large nose

radius will cause tool to chatter [17]. The tool angles and nose radius are specified as

in Figure 2.22

Figure 2.22: Tool designations for single point cutting tool [27]

35

2.4.2 Cutting tool material

The various cutting tool materials commercially today have ability to satisfy

the demand of cutting tool properties such as high hot hardness, toughness, and

chemical stability. Several cutting tool materials are developed for different

applications and have different properties for these applications.

2.4.2.1 High speed steel

The first produced of HSS was in 1900, HSS has good wear resistance,

toughness resistance to fracture, suitable for positive rake angle, and less expensive.

These tools will loss the strength when temperature reach above 650 0C but, the

coating development especially TiN coatings have several beneficial effects to

minimize their weakness. HSS tool is often used for interrupted cutting, drilling, and

taps.

2.4.2.2 Carbides

Carbide tool is compounds the hard carbide particle, nitrides, borides, and

silicides, these compounds are bonded together with binder such as cobalt.

Performances of carbide tools are depended on the composition and grain size; these

tools have sufficient toughness, impact strength, and high thermal resistance but have

limitation with hardness properties. The hardness of carbide tool drops rapidly in

high temperature consequently; it cannot be used in high cutting speed hence high

temperature involved. Nowadays, development of technology coated tools can

improve the tool life of uncoated carbide tools.

36

2.4.2.3 Coated carbides

Coating is believed can improve the tool life and productivity where it can be

used at higher cutting speeds and feed rates. The high hardness, wear resistance,

toughness, and chemical stability of the coating tools offer benefit in term machining

performance. The development coating technology on carbide tools have become

more variant and sophisticated to improve the performance of carbide tools in metal

cutting.

In addition, PVD has three basic types of process; these are arc evaporation,

sputtering, and ion plating. These process are carried out in a high vacuum and

temperature between 200 0C- 500 0C, in PVD process the particles to be deposited

are carried physically to the workpiece rather than by chemical reactions as in CVD

process (Kalpakjian and Schmid, 2001). PVD has coated thickness range of 2-4 µm.

2.4.2.4 Ceramic

Ceramic tools have better properties with high abrasion resistance, strength to

higher temperature, and chemical stability but, their toughness and strength in

tension are lower besides, ceramic tools are expensive compare with carbide tools.

Ceramic tools are not suitable for interrupted cutting because their lower toughness

but, this tools give potential advantages during turning at high cutting speed as a

result good surface finish is obtained in turning steel and cast iron. Generally,

ceramic tools use negative rake angle to avoid chipping since reduce their poor

tensile strength.

37

2.4.2.5 Cubic boron nitride

CBN has been developed for machining of hard material because CBN tools

provide high hot hardness, wear resistance, and chemical stability at high cutting

speed but more brittle. Therefore, CBN tools particularly suitable for cutting

hardened material of steels or cast irons with hardness value above 45 HRC.

Because CBN tools are brittle these requiring suitable stiffness machine tool for

avoid vibration.

2.4.2.6 Diamond

Diamond tools have higher wear resistance, low friction coefficient that gives

ability to maintenance a sharp cutting edge. Diamond tools can be used in high

cutting speed, provide good surface finish and dimensional accuracy. Diamond tools

present excellent result during machining of soft non ferrous alloys such as

aluminum alloy but presenting lower performance when machining ferrous material

such as steel.

2.4.2.6.1 Single-crystal diamond

Single-crystal diamond of various carats is used for special applications, such

as machining copper-front precision optical mirrors for the Strategic Defense

Initiative (SDI) program. Because diamond is brittle, tool shape and sharpness are

important. Low rake angles (large included angles) are generally used to provide a

strong cutting edge. Special attention should have been given to proper mounting and

crystal orientation in order to obtain optimum tool life. Wear may occur through

micro chipping (cause by thermal stresses and oxidation) and through transformation

to carbon (caused by the heat generated during cutting). In order to minimize tool

fracture, the single-crystal diamond must be resharpened as soon as it becomes dull.

Single-crystal diamond is very expensive and is not widely available.

38

2.4.2.6.2 Polycrystalline diamond (PCD)

Polycrystalline diamond has replaced use of single-crystal diamond and these

materials consist of very small synthetic crystals, fused by a high-pressure, high-

temperature process to a thickness of about 0.5 to 1 mm (0.02 to 0.04 in) and bonded

to a carbide substrate. The random orientation of the diamond crystals prevents the

propagation of cracks through the structure, significantly improving its toughness.

2.4.2.6.3 Chemical vapor deposition (CVD)

CVD coated tools are a much newer product and consist of a pure diamond

coating over a general purpose carbide substrate. Thin-film diamond coated inserts

are deposited on substrates with PVD and CVD technique. Thick films are obtained

by growing a large sheet of pure diamond, which is then laser cut to shape and

brazed to a carbide shank. Diamond coated tools are particularly affective in

machining nonferrous and abrasive material, such as aluminum alloys containing

silicon, fiber-reinforced and metal-matrix composite material, and graphite. As much

a tenfold improvements in tool life have been obtained other coated tool.

39

CHAPTER 3

RESEARCH METHODOLOGY

3.1 Introduction

Proper experimental plan is necessary to achieve good results in

conducting research. This chapter describes the experimental setup, measurement

techniques and measurement equipment used in this study. Figure 3.1 shows the

summary of the overall methodology.

In experimental test, the major factor whose influence the cutting condition

was chosen and be variables for diamond tool performance measurement.

The measurement was divided in three; tool life criteria, surface roughness

and type of chips. Tool life criteria are the measurement for cutting tool performance

and surface roughness is the measurement of Ra. Type of chips will be shows the

effect of cutting terminology. After that, each of the measurement was analyzed and

written in report.

40

Literature Review Input: Cutting speeds, feed rate, Depth of cut

Output: Type of wear, Tool life, Surface roughness, Type of chip formation. Preparation of Material

CO2 Sand Casting

Manual Lathe Machine Conduct Experiment

and Data Recorded ALPHA 1350S 2-Axis CNC Lathe Measurement and Analyze of Results

Carl Zeiss Stemi 2000-C Optical microscope KS 300 version 3.0

Report Writing

Figure 3.1: Summary of the methodology used in the study.

41

3.2 Research Design Variables

In turning process there are two kinds of variables is described into two main

groups. They are dependent variables or response parameters and independent

variables or machining parameters. Response parameters are used to determine the

machining characteristic of workpiece material and machining parameters are used to

design the experiment.

3.2.1 Response Parameters

There are 4 response parameters are concerned in this research for measure the

performance of diamond tool, there are;

1. Type of wear and wear mechanism, VB max (mm)

2. Tool life, T (min)

3. Surface roughness, Ra (μm)

4. Chip deformed

3.3 Workpiece Material

The material used is A390 (Al-Si-alloy). The size of the material used in this

investigation was decided based on experimental design. The preparation has been

by CO2 Sand Casting.

42

3.3.1 CO2 Sand Casting

The selected workpiece material was A390 (Al-Si-alloy)foundry cast

produced by EPS Sand Casting Mould and Enterprise with CO2

Sand Casting, which

contain 16-18 % wt silicon particles. This workpiece has been used for internal

combustion engine parts, cylinder bodies of compressors and pumps, and brake

systems. Other suitable applications are found in engine and gearbox parts. Example

of the product produced by this material can be seen in Appendix 1.

(c) (d)

Figure 3.2: Condition of workpiece material (a) mould design (b) cast the

material (c) pouring metal (d) as cast,

(a) (b)

43

3.3.1.1 Modification of aluminium-silicon casting alloys

Modification has become a common and sometimes an essential foundry

practice when it comes to casting the aluminium-silicon alloys. Modification is a

process that changes the microstructure of cast alloys either through quenching or by

adding some alkaline elements. The main objective of modification in a casting is to

achieve a different microstructure that can yield better mechanical properties and

characteristics. Modification is mainly associated with the alteration of the silicon

phase in aluminium-silicon casting alloys since there is no evidence that the

alumin

3.3.1.2 Impurity Modification on Hypoeutectic Al-Si Alloys

Basically modification can be divided into impurity modification and quench

ount of modifiers is

termed impurity modification while the latter is due to rapid solidification rate.

Althou

purity or chemical modification renders a change in morphology of silicon

om anisotropic to isotropic shape. Under this modification, the modifiers inhibit

ensity [26].

ium phase is directly influenced by modifiers addition.

modification. Modification through the additions of a small am

gh there are many elements, which are found to have modification ability,

only sodium and strontium appear to be stronger modifiers at low concentration and

now they are widely used for commercial applications. Both sodium and strontium

transform the flake eutectic silicon into fibrous form, hence increasing the ultimate

tensile strength, ductility, hardness and machinability. Modification is affected by

several variables and reversion of the modified structure back to the unmodified state

is possible when there is higher silicon content, higher temperature and longer

holding times (Neff, 1987).

Im

fr

the preferred growth (poisoning effect), which leads to generation of higher twin

d

The material for conducting the experiment was supplied by supplier in

hardened state. The workpiece was solid bar with 140 mm diameter and 200 mm

44

length. The chemical and mechanical properties of the material are shown in Table

3.1 and Table 3.2 respectively.

Figure3.3: Comparison of the solidification modes in aluminium silicon alloys

(a) A micrograph of an unmodified alloy (unetched), the fine structure is quenched

liquid; (b) macrograph of an alloy modified by 100 ppm strontium and etched

Table 3.1: Chemical compositions of A390

Table 3.2: Mechanical Properties of A390.

Tensile Strength

MPa

Compressive Yield Strength

MPa

Impact Strength

J

Hardness

BHN

240 414 58 85

Component Si Fe Cu Mn Mg Zn Ti other Al

Wt% 16-18 0.5 4.5 0.1 0.45-0.65 0.1 0.1 0.2 Balanced

45

3

Preliminary machining (skinning process) of this research was performed on

Manu l lathe machine. The workpiece was firstly prepared by skinning a certain

rial to remove the oxidized skin on the

sin rbid ert tti eed 300 m/min. mf g a nd of

pact e the tool to

aterial was turning into solid bar

ith 140 mm diameter and 200 mm length.

ents were used throughout the study:

)

- Serial number; S9 D133

- Spindle speed range; 156 to 3250 rpm

- Feed rate; 0.03 to 0.6 mm/rev

- Spindle motor; 5.5 KW (75hp)

.3.2 Preliminary machining

a a

thickness of the outer layer of supplied mate

layer by u g ca e ins at cu ng sp Cha erin t the e

the workpiece was done to avoid high im load during the first tim

engage the workpiece as show in Figure 3.3. The m

w

Figure 3.4: Condition of workpiece material (a) as cast, (b) after skinning process.

3.4 Machines and Equipments

The following equipm

1 ALPHA 1350S 2-Axis CNC Lathe (figure 3.3)

46

- Purpose: To conducted the experiments when measuring the progression of

tool wear

1350S, 2-axis CNC lathe.

2) r Microscope Nikon. (Figure 3.5)

- Brand and Model: Nikon

Figure 3.5: ALPHA

Tool Make

- Magnification: 30 X

- Measuring Device: Incorporated Micrometer

- Purpose: To measure of tool flank wear.

Figure 3.6: Tool Maker’s Microscope Nikon

47

3) Portable Surface Profilometer (Figure 3.6)

- Brand/Model: Taylor Hobson Surtronic 3+

a

- Range: 0.05 μm–10 μm

- Accuracy: ±0.01μm

- Purpose: To measure surface roughness, R

Figure 3.7: Portable Surface Profilometer, Taylor Hobson Surtronic 3+.

4) Optical Microscope (Figure 3.7)

- Brand/mod

lor Video Camera.

mage of tool wear.

el: Carl Zeis Stemi 2000-c

- Magnification: 6.5X-50X

- Incorporated device: SONY ExwaveHAD co

- Purpose: To capture the i

Figure 3.8: Optical Nikon Microsc

ope c/w Image Analyzing Software.

48

5)

on 3.0

3.5 Tool Material.

Commercially Polycrystalline diamond (PCD) tool from Kennam

been selected for conduct the machining test. The tool grade was KD100 (PCD). The

PCD tool was triangular shape having diamond tip brazed on carbide substrate the

ISO code for this insert was: TPGN 160308; and tool holders was CTGPL 2020K16.

The cutting tool geometry used in the experiment as follows:

ake rake angle α = 0 0

Side ra

Side re

ose radius r = 0.8 mm

e 3.9 Polycrystalline diamond (PCD) tool

Image analyzing software

- Brand/Model: KS 300 versi

- Purpose: To analyze the image of tool flank wear.

etal® have

B

ke angle γ = -50

End relief = 5 0

lief =50

Side cutting edge (SCEA) = 50 (PCD)

N

Figur

49

3.6 Experimental Set Up

his study is to evaluate the performance of diamond tools

hen machining Al-Si alloy. Workpiece material was an Unmodified 390 alloy

r-modified 390 alloys with contain 16-18% wt silicon. The experiment was

erformed with various cutting speeds while feed rate and depth of cut were kept

onstant. Machining test was carried out under dry cutting condition as this is the

quirement in today machining industries. The outputs of the experiment were

of tool wear, surface roughness and chips

eformed.

The progression of the tool wear was monitored at fixed interval time using

ol maker’s microscope. The optical microscope incorporated with charge couple

iode (CCD) camera was used to capture the image of worn tools and to analyze the

worn

ere conducted on ALPHA 1350S CNC 2-axis lathe to

easure the progression of tool wear. The surface roughness was recorded at every

stop of tool wear measurement using Taylor’s Hobson stylus portable surface

profilo

tool’s maker microscope with magnification of 30X was used to measure

e flank wear while optical microscope of 50X magnification integrated with CCD

camera

The purpose of t

w

S

p

c

re

tabulated accordingly. The output consists

d

to

d

The experiments w

m

meter

3.7 Measurement of Tool Wear

The tool wear was expected to occur on the flank face as well as on the rake

face. Nikon

th

was used to capture the image of worn tools. The tool wear measurement has

been conducted at a reasonable time interval until the tools reach the tool life criteria.

50

3.8

3685-1977(E) and ANSI/ASME B94.55M-1985. The selection of tool

fe criteria gave direct impact on the product controlled features and geometry as

llows:

e the control value.

2. The surface finish of product in controlled value.

3. The

. Average VC =0.2mm (Minor flank) or

. VCM

= 0.3mm, when non-uniform wear occurs

Tool Life Criteria

The results of experiment were collected and analysis of tool life criteria were

based on ISO

li

fo

1. Th geometry accuracy of product in

product is not damage by catastrophic failure of the tool.

From the listed control feature of the product and ISO guide lines, the tool life

criteria proposed are listed as below:

1. Average VB =0.2 mm (Major flank) or

2. VB Max

= 0.3 mm, when non-uniform wear occurs or

3

4ax.

Figure 3.10: Measurements of tool wear in turning according [4].

51

3.9 Chip Morphology

The Chip morphology study is an important element in metal cutting

research. The study will reveal the phenomena that will take place while the metal is

being cut. Study by Elbestawi et al. (1996) found that for a hard material, the chip

formed a cyclic saw tooth due to the crack of chip when the stress reaches the

ltimate shear strength of the material. The effect of tool-chip interface during

achining can be evaluated. Gekonde (2001) was suggested that the tool-chip

interface was a m

ere collected from each cutting condition The microstructure of the chips were

ongitudinal section mounted on the epoxy

ounting, ground, polished and etched in mixture of nitric and hydrochloric acid in

tio of 1:3. Figure 3.10 shows the metallurgical and specimen preparation

quipments.

u

m

ain cause of tool wear during hard turning. In this study, the chips

w

investigated by preparing the chip l

m

ra

e

(a)

(b)

52

(c)

Figure 3.11: Metallurgical and specimen preparation equipments, (a) Mounting

machine, (b) Polishing machine and (c) Manual sanding m chine.

a

53

CHAPTER 4

RESULTS AND DISCUSSION

4.1 Introduction

This chapter describes all the findings from this research. The results of

turning tests allowed the evaluation d comparison of the diamond tools

performance with unmodified hypereutectic and Sr-modified hypereutectic Al-Si cast

alloys. All results were obtained according to the cutting condition and cutting time.

The results of experiment trials are summ

unmodified alloy and Table 4.2.1 to Table 4.2.3 for the Sr-modified alloy.

Table 4.1.1: Test results for the unmodified alloy for cutting speed of 500 m/min

Vc =500 m/min m

an

arized in Table 4.1.1 to Table 4.1.3 for the

ƒ = 0.1 mm/rev doc = 1m

Ra (μm) Test Time

(min)

Σ Time (min) 1 2 3 Average

VB max

(mm)

1 2 2 0.82 0.85 0.80 0.823 0.01

2 2 4 0.79 0.82 0.82 0.810 0.03

3 2 6 0.85 0.80 0.81 0.820 0.04

4 2 8 0.84 0.84 0.85 0.843 0.06

5 2 10 0.80 0.81 0.81 0.806 0.08

6 2 12 0.79 0.80 0.81 0.800 0.10

7 2 14 0.79 0.80 0.83 0.806 0.11

8 2 16 0.80 0.81 0.80 0.803 0.13

54

9 2 18 0.82 0,81 0.82 0.816 0.15

10 2 20 0.76 0.79 0.78 0.770 0.16

11 2 22 0.80 81 0.81 0.806 0.18 0.

12 2 24 0.79 0.78 0.80 0.790 0.20

13 2 26 0.80 0.76 0.773 0.76 0.21

14 2 0.84 0.80 0.85 28 0.830 0.23

15 2 30 0.76 0.79 0.78 0.776 0.25

16 2 32 0.84 0.80 0.82 0.820 0.26

17 2 34 0.79 0.81 0.81 0.803 0.28

18 2 36 0.77 0.79 0.79 0.783 0.29

19 2 38 0.80 0.84 0.85 0.830 0.30

Table 4.1.2: Test results for the unmodified alloy for cutting s 600 m/

Vc =600 m/m ƒ = 0.1 mm/ = 1m

peed of min

in rev doc m

Ra (μm) Test Time

(m )

Σ Time

( Average

VB max

in min) 1 2 3 (mm)

1 2 2 0.92 0.89 0.90 0.903 0.02

2 2 4 0.86 0.89 0.89 0.883 0.03

3 2 6 0.94 0.92 0.92 0.926 0.05

4 2 8 0.95 0.93 0.94 0.940 0.07

5 2 10 0.90 0.90 0.88 0.893 0.09

6 2 12 0.92 0.94 0.95 0.936 0.12

7 2 14 0.94 0.90 0.91 0.916 0.14

8 2 16 0.90 0.94 0.93 0.923 0.16

9 2 18 0.86 .89 0.88 0.876 0.18 0

10 2 20 0.85 0.88 0.87 0.866 0.19

11 2 22 0.86 0.92 0.890 0.21 0.89

12 2 24 0.89 0.92 0.93 0.913 0.23

13 2 26 0.88 0.86 0.880 0.90 0.25

14 0.85 0.88 0 2 28 .90 0.873 0.27

15 2 30 0.86 0.88 0.91 0.883 0.29

55

16 1 31 0.95 0.92 0.92 0.930 0.30

Table 4.1.3: Test results for the unmodified alloy for cutting s 700 m/

Vc =700 m/m ƒ = 0.1 mm/ = 1m

peed of min

in rev doc m

Ra (μm) Test Time

(m )

Σ Time

( Average

VB max

in min) 1 2 3 (mm)

1 2 2 1.02 1.04 1.04 1.033 0.04

2 2 4 1.00 1.04 1.05 1.030 0.09

3 2 6 1.07 1.05 1.06 1.060 0.13

4 2 8 1.01 0.98 0.99 0.993 0.17

5 2 10 1.02 1.04 1.04 1.033 0.19

6 2 12 1.06 1.01 0.99 1.020 0.22

7 2 14 1.03 1.07 1.00 1.030 0.27

8 1 15 1.02 0.98 1.00 1.000 0.30

Table 4.2.1: Test results for the Sr-modified alloy for cutting speed of 500 m/min

Vc =500 m/min ƒ = 0.1 mm/rev doc = 1mm

Ra (μm) Test Time

(min)

Σ Time

(min) 1 2 3 Average

VB max

(mm)

1 2 2 0.80 0.81 0.80 0.803 0.01

2 2 4 0.82 0.78 0.80 0.800 0.02

3 2 6 0.78 0.80 0.80 0.793 0.04

4 2 8 0.81 0.82 0.80 0.810 0.05

5 2 10 0.80 0.80 0.77 0.790 0.07

6 2 12 0.82 0.77 0.78 0.790 0.08

7 2 14 0.79 0.75 0.77 0.770 0.10

8 2 16 0.77 0.82 0.82 0.803 0.12

9 2 18 0.79 0,80 0.84 0.806 0.14

10 2 20 0.80 0.82 0.83 0.813 0.15

11 2 22 0.78 0.76 0.83 0.790 0.16

56

12 2 24 0.79 0.76 0.76 0.770 0.17

13 2 26 0.80 0.77 0.776 0.76 0.19

14 0.77 0.79 0 2 28 .78 0.780 0.20

15 2 30 0.83 0.82 0.82 0.823 0.21

16 2 32 0.81 0.83 0.83 0.826 0.22

17 2 34 0.83 0.78 0.78 0.810 0.24

18 2 36 0.76 0.77 0.77 0.766 0.26

19 2 38 0.78 0.80 0.78 0.786 0.28

20 2 40 0.80 0.79 0.81 0.800 0.30

Table 4.2.2: Test results for the Sr-modified alloy for cutting s f 600 m

Vc 0 m/m ƒ = 0.1 mm/ = 1m

peed o /min

=60 in rev doc m

Ra (μm) Test Time

(m )

Σ Time

( Average

VB max

in min) 1 2 3 (mm)

1 2 2 0.90 0.88 0.90 0.893 0.02

2 2 4 0.92 0.92 0.90 0.913 0.03

3 2 6 0.88 0.89 0.90 0.890 0.05

4 2 8 0.89 0.92 0.92 0.910 0.07

5 2 10 0.94 0.92 0.90 0.920 0.08

6 2 12 0.90 0.91 0.87 0.893 0.10

7 2 14 0.94 0.93 0.95 0.930 0.12

8 2 16 0.92 0.93 0.92 0.923 0.14

9 2 18 0.90 0.86 0.85 0.870 0.15

10 2 20 0.90 0.89 0.88 0.890 0.17

11 2 22 0.92 0.92 0.92 0.920 0.19

12 2 24 0.89 0.89 0.89 0.886 0.20

13 2 26 0.89 0.89 0.920 0.93 0.22

14 0.88 0.88 0 2 28 .86 0.870 0.24

15 2 30 0.90 0.90 0.91 0.900 0.26

16 2 32 0.86 0.986 0.88 0.873 0.28

17 2 34 0.90 0.89 0.91 0.900 0.30

57

Table 4.2.3: Test results for the Sr-modified alloy for cutting s f 700 m

Vc =700 m/mi ƒ = 0.1 mm/rev = 1mm

peed o /min

n doc

Ra (μm) Test Time

(m )

Σ Time

( Average

VB max

in min) 1 2 3 (mm)

1 2 2 1.01 0.99 0.99 0.996 0.03

2 2 4 0.98 0.97 0.98 0.976 0.06

3 2 6 0.96 0.99 0.99 0.980 0.19

4 2 8 1.03 1.02 1.02 1.023 0.12

5 2 10 1.00 1.02 1.01 1.010 0.16

6 2 12 1.03 1.00 1.01 1.013 0.20

7 2 14 0.97 0.99 1.00 0.986 0.23

8 2 16 0.95 0.99 0.98 0.973 0.27

9 2 18 1.00 0.99 1.01 1.000 0.30

4.2 Microstructure analysis of workpiece material

The truc f bo unmo ied and Sr-modified AlSi18 alloy are

shown in Figure 4.1a and Figure 4.1b respectiv The truct onsist

mainly of prim y Si ph in an i e c p It is sho at the

addition of Sr has induced a cha n t e stribution of the primary Si

phase. It is w establis d tha g a utec i ca y will

� achin the pr ry Si p whi pro ts nabil wev is not

good a modifi to the p ry Si ar ho ous, usua ded to

mo y the h oeutect l-Si s. pt to

inv igate its ect on the primary Si and ultimately the ma be using

PCD tools.

micros tures o th dif

ely. micros ures c

ar ase Al-S utecti hase. clearly wn th

nge i he siz and di

ell he t addin Sr to hypere tic Al-S st allo

ima hase ch im ves i machi ity. Ho er, Sr

er rima comp ed to p sphor as it is lly ad

dif yp ic A alloy Nevertheless, this was an attem

est eff chining havior

58

(a)

Figure 4.1: Microstructures of a) unmodified and b) Sr-modified AlSi18 alloy

(b)

(X100)

59

4.3 Wear and Tool Life curves

After identifying the kind of predominant wear in the tools- the flank wear-

nd the way of quantifying it (VB (max) flank wear according ISO 3685), wear

urves were obtained.

Figures 4.2 and Figure 4.3 show the charts for flank wear versus cutting time

at the three different cutting speeds inves gated in turning the unmodified and Sr-

modified hypereutectic Al-Si alloy using PCD tools. In the best situation represented,

500 m/min cutting speed, it is possible to perform the turning in 38 min for the

unm nd

40 min for the Sr-modified alloy: 20 of approximately 2 min cutting time

each) for an flank wear VB(max) = 0.3 mm. In the worst represented situation, 700

m/min cutting speed, it was possible only to machine for 15 min: 8 passes for and 18

min: 9 passes (of approximately 2 min cutting time each) for flank wear VB(max) =

0.3 mm for the unmodified and modified alloys respectively.

From the present results, it is quite clear that at lower cutting speed higher

tool life is achieved in turning the hypereutectic Al-Si alloys. Also edge chipping

was found to be the main mode of failure of PCD tools and abrasion was the main

wear mechanism limiting tool life due to abrasion with the silicon phase, particularly

the silicon primary phase.

a

c

ti

odified alloy, that is 19 passes (of approximately 2 min cutting time each) , a

passes (

60

flank wear for Unmodified 390 alloy

0.2

0.35

(mic

ron)

Vc = 500 m/minVc = 600 m/minVc = 700 m/min

0.25

0.3

0

0.05

0.1

0.15

0 5 10 15 20 25 30 35 40

Cutting TIme, T (min)

Flan

k w

ear

Figure 4.2: Wear curves for PCD insert in turning the unmodified alloy versus

cutting time at cutting speeds of 500, 600 and 700 m/min.

flank wear for Sr-modified 390 alloy

0

0.05

0.1

0.15

0.2

0.25

0.3

n)

0.35

0 5 10 15 20 25 30 35 40 45

Cutting Time, t (min)

Flan

k w

ear (

mic

ro

Vc = 500 m/minVc = 600 m/minVc = 700 m/min

Figure 4.3: Wear curves for PCD insert in turning Sr-modified alloys versus cutting

time at different cutting speeds of 500, 600 and 700 m/min.

61

In order to obtain life curves, reasonable flank wear values must be

established for the cutting inserts. In the present study a flank wear VB(max) = 0.3

mm was considered as tool life criteria for PCD inserts based on previous researchers

and mainly, in a way to get a dimensional and geometrical precision, as well as the

required surface roughness of the investigated Al-Si alloy.

Figures 4.4 and 4.5 show the micrographs of flank wear at different cutting

speeds early in the turning experiments until when it reached VB (max) = 0.3 mm. It

can be seen that the tool life of PCD inserts is longer when turning the Sr-modified

alloy compared with when turning the unmodified alloy. As discussed in the section

on microstructure analysis of workpiece material, this is attributed to the effect of Sr

which reduced the size of primary silicon phase making it smaller in size and quite

homogenous in terms of its distribution. The results, however, did not show a

significant increase in tool life when turning the Sr-modified alloy since Sr is only an

effe se.

Nevertheless, d by adding

phosphorous, it is expected that the tool life will be longer than observed in this

study.

The wear on the PCD tool flank is most likely caused by the abrasive nature

of the hard primary Si phase present in the material microstructure. However, no

attempt was made in the present study to analyze the mechanism of wear in details.

ctive modifier for the eutectic Si phase rather than the primary pha

should a modified primary Si phase, for example achieve

62

5minutes(Vc=500m/min) 22minutes(Vc=500m/min) 38minutes(Vc=500m/min)

5minutes(Vc=600m/min) 18minutes(Vc=600m/min) 32minutes(Vc=600m/min)

3minutes(Vc=700m/min) 9minutes(Vc=700m/min) 15minutes(Vc=700m/min)

Figure 4.4: Image of flank wears of PCD tool when machining unmodified AlSi18

alloy at different cutting speeds: 500, 600, and 700 (m/min).

63

6minutes(Vc=500m/min) 24minutes(Vc=500m/min) 40 minute(Vc=500m/min)

5minutes(Vc=600m/min) 18minutes(Vc=600m/min) 34minutes(Vc=600m/min)

4minutes(Vc=700m/min) 11minutes(Vc=700m/min) 18minutes(Vc=700m/min)

Figure 4.5: Image of flank wear of PCD tool when machining Sr-modified AlSi18

alloy at different cutting speeds: 500, 600, 700 (m/min).

64

4.3 Surface Roughness

Figures 4.6 and 4.7 show the surface roughness (Ra) obtained when

machining the AlSi18 alloy both in the unmodified and Sr-modified conditions at

different cutting speeds. The Ra varies approximately between 0.8 to 1.05 μm. The

lowest cutting speed gives the lowest surface roughness at an average of Ra = 0.85

μm and the higher cutting speed gives higher surface roughness at an average of Ra =

1.00 μm. It is also noted that the Ra value increases when cutting speed increases.

s ind sh t

results, cutting AlSi18 alloy at lower speed (500 m/min) gives better surface finish

compared when cutting at 600 or 700 m/min.

Lower surface roughnes icates better surface fini and based on the curren

Surface Roughness for unmodified 390 alloy

0.7

0.75

0.8

0.85

0.9

0.95

1

1.1

0 5 10 15 20 25 30 35 40

Cutting Time, T (min)

Ra

(mic

ron)

Vc = 500 m/minVc = 600 m/minVc = 700 m/min

1.05

Figure 4.6: Surface roughness obtained when machining unmodified AlSi18 alloy

with PCD at different cutting speeds. Both feed rate and depth of cut were kept

constant for all tests at 0.1mm/rev and 1mm respectively (failed at VB=0.3mm).

65

surface roughness for modified 390 alloy

0.7

0.75

0.8

0.85

0.9

0.95

1

Ra

(mic

ron)

1.05

0 5 10 15 20 25 30 35 40 45

Cutting Time, T (min)

Vc = 500 m/minVc = 600 m/minVc = 700 m/min

Figure 4.7: Surface roughness obtained when machining Sr-modified AlSi18 with

PCD at different cutting speeds. Both feed rate and depth of cut were kept constant

for all test at 0.1mm/rev and 1mm respectively (failed at VB=0.3mm).

4.4 chip Morphology

Generally, less attention is given to chip control, the occurrence of acceptable

chip forms in the working zone, or the chip formation and chip breaking aspects.

However, they have strong effects on the surface finish, force, workpiece accuracy,

and tool life. The psychical appearance or chip form of the chips collected during the

machining test performed using PCD cutting tool is observed using digital camera

an f

the

The types of chips produced by the PCD inserts in turning the unmodified

and Sr-modified alloys are shown in Figure 4.8 and Figure 4.9 at different cutting

d microscope. The chips are being studied for their form and the mechanism o

ir formation.

66

speeds. The chips form is a snarled chip but both cutting speed and condition of tool

flank is the main factor controlling the length of chips. It is clear from the photos that

with increasing cutting speed the length of chips increases indicating that better

machining and better surface finish. When the cutting time increases the chips

become short. This situation is caused by the condition of the tool flank, meaning

that when the tool flank is still sharp long chips will be produced and whereas when

the tool flank becomes dull, after long cutting time, short chips will be produced. The

chips become thin when built up edge (BUE) is observed at the cutting edge of the

PCD insert but the surface finish tends to be poor. These situations also affect the

surface roughness of workpiece because of rubbing between chips and machine

surface when dry cutting is applied.

67

T = 1 min T = 22 min T = 36 min

Vc = 500 m/min, f = 0.1 mm/rev , doc =1mm

T = 18 min

T = 1 min T = 30 min

Vc = 600 m/min, f = 0.1 mm/rev , doc =1mm

T = 8 min

T = 1 min T = 15 min

Vc = 700 m/min, f = 0.1 mm/rev , doc =1mm

Figure 4.8: Types of chip produced by PCD tool in turning the unmodified

AlSi18 alloy at different cutting speeds and cutting time.

68

T = 24 min T = 1 min T = 38 min

Vc = 500 m/min, f = 0.1 mm/rev, doc =1mm

T = 1 min T = 18 min T = 34 min

Vc = 600 m/min, f = 0.1 mm/rev, doc =1mm

T = 1 min T = 10 min T = 18 min

Vc = 700 m/min, /rev, doc =1m f = 0.1 mm m

Figure 4.9: Types of chip produced by PCD tool in turning Sr-modified

Further chip analysis was provided by examining the chips at higher

magnification using the optical microscope. As discussed in Chapter 3, the chip

pecimens were prepared according to metallographic procedures by mounting,

AlSi18 alloy at different cutting speeds and cutting time.

s

69

grinding, and polishing the chip specimens. The structure obtained is used to

evaluate the flow of the chip grain structures and also to determine the shape of the

chips under microscopic view.

As shown in Figure 4.10 – 4.15, the chips have a segmented shape and as the

cutting speed increases, the primary Si particles become aligned along the maximum

shear bands as shown in Figure 4.11 and Figure 4.12 when the cutting speed is 600

and 700 ectively. High c results in higher which

induces excessive de e primary Si

particles is quite clearly seen in the microstructures, and which may have started as

voids at these brittle Si particles, then cracking, and ultimately fractures. This

situation results in the formation of segmented chips. The above observation was

found in both unmodified and Sr-modified alloy. This is evidence that although Sr

was added to the AlSi18 alloy its effect on the primary Si phase was as effective as

its effect on the Si in the eutectic phase.

100 tion 200 tion 500 ion

m/min resp utting speed temperature,

formation in the ductile Al-Si matrix. Fracture of th

X magnifica X magnifica X magnificat

Figure 4.10: Image of chip root when cutting unmodified alloy at

500m/min using PCD cutting tool.

70

100X magnification 200X magnification 500X magnification

Figure 4.11: Image of chip root when cutting unmodified alloy at

600m/min using PCD cutting tool.

100X magnification 200X magnification 500X magnification

Figure 4.12: Image of chip root when cutting unmodified alloy at

700m/min using PCD cutting tool.

71

100X magnification 200X magnification 500X magnification

Figure 4.13: Image of chip root when cutting Sr-modified alloy at

500m/min using PCD cutting tool.

100X magnification 200X magnification 500X magnification

Figure 4.14: Im dified alloy at

600m/min using PCD cutting tool.

age of chip root when cutting Sr-mo

72

100X magnification 200X magnification 500X magnification

Figure 4.15: Im dified alloy at

700m/min using PCD cutting tool.

age of chip root when cutting Sr-mo

73

CHAPTER 5

CONCLUSIONS AND FUTURE WORK

5.1 Conclusions

The objective of this research was to evaluate the performance of diamond tool

hen machining Al-Si hypereutectic alloy in two conditions: unmodified and Sr-

odified. Tool wear, tool life, and surface roughness on turned surface are used as

e performance measures. The experiments were conducted using an ALPHA 1350S

-Axis CNC Lathe machine. Based on this research, the following conclusions were

rawn:

1. Addition of Sr to the Hypereutectic AlSi18 alloy induced modification in they

microstructure by reducing the size of primary Si particles. However, the use

of Sr was found not to be effective in modifying the primary Si compared to

the well established modification induced by the addition of phosphorous.

2. Lower cutting speed (500 m/min) gives higher tool life in both unmodified and

Sr-modified alloys.

2. Higher tool life is observed when cutting Sr-modified alloys compared to the

unmodified alloys under similar tool geometry and cutting conditions.

3. The lowest cutting condition (500 m/min) also provide short snarled chips and

give better surface finish compared to 600 and 700 m/min.

w

m

th

2

d

74

4. Surface roughness, Ra value increases when cutting speed increases when

turning hypereutectic Al-Si alloy.

.2 Recommendations for future work.

Based on the fi ommendations are

roposed for future research work:

ge weight of silicon particles around 18 to 25% in

Al- Si alloy suitable for aerospace and automotive industries application.

5

ndings from the research, the following rec

p

1. Increases content percenta

2. Investigate the effect of feed rate change in machining Al-Si alloys and

workpiece surface integrity.

75

REFERENCES

1.

23.

2.

3. nts%20and%20Settings/HomePc/Desktop/3.htm.

15th, September 2007.

. Timothy Godowsky, Web side:

http://web.mit.edu/lienhard/www/ahtt.html,casting since about 4000BC.

12th , September, 2007

ffect of metallurgical parameters on the

machinability of heat-treated 356 and 319 aluminum alloys, 2006, pp207-

217.

. J. Paulo Davim, A. Monteiro, Relationship between cutting force and PCD

cutting tool wear in machining silicon carbide reinforced aluminium, 2000,

417-423.

. Stuart D. McDonald, Eutectic nucleation in Al–Si alloys, 2004, pp 4273–

4280.

Practices for the repair of automotive sheet aluminum, Copyright 1998 the

Aluminum Association, pp 1-

Grain Refinement of Aluminium-Silicon Foundry Alloys. London&

Scandinavian Metallurgical Co. Limited, 1998, pp1-29.

Web side: file:///C:/Docume

4

5. M. Tash, F.H.Samuel, E

6

7

76

8. Bothered, G. 1975. Fundamentals of Metal Machining and Machine Tools.

Washington DC Mc Graw Hill.

. Ghosh, A. and Mallik, A.K ring Science. 2nd ed. Chichester:

Ellis Horword Limited

0. Galoppi, G.d.S., Filho, M.S. and Batalha, G.F. 2006. Hard turning of

chnology.

el by ceramic and CBN tools. Elsevier Journal of

Materials Processing Technology. 88: 114-121.

13.

5. Effect feed rate, workpiece hardness and cutting

edge on subsurface residual stress in the hard turning of bearing steel using

4. Kalpakjian and Schmid, Manufacturing Processes for Engineering Materials,

15. 2003. Analyses of Tool Life and Surface Roughness during Hard

Turning of AISI H13 Hot Work Tool Steel using Mixed Ceramic Tools.

9 . 1986 Manufactu

1

tempered DIN 100Cr6 steel with coated and no coated CBN inserts. Elsevier

Journal of Material Processing Te

11. Kalpakjian, S. and Schmid, S.R. 2001. Manufacturing Engineering and

Technology.4th Ed. New Jersey: Prientice Hall.

12. Luo, S.Y., Liao, Y.S. and Tsai, Y.Y. 1999. Wear characteristic in turning

high hardness alloy ste

Hua, J., Shivpuri, R., Cheng, X., Bedekar, V., Matsumoto, Y., Hashimoto, F.

and Watkins, T.R. 200

chamfer + hone cutting edge geometry. Elsevier Material Science and

Engineering. A 394: 238-248.

1

Fourth Edition, Prientice Hall, 2003, pp 464, 527.

Tan, P. L.

Universiti Teknologi Malaysia: Master Thesis.

77

16. Noordiii Yusof 2004, Performance Evaluation of Coated Carbide and Coated

gi

206.

9 Poulachon, G., Bandyopadhyay, B.P., Jawahir, I.S., Pheulpin, S. and

ened

1. Yang, L.J. 2001. Determination of the wear coefficient of tungsten carbide by

22.

25-229: 354-367

ard Materials. 21: 109-117.

Cermet Tools When Turning Hardened Tool Steel. Universiti Teknolo

Malaysia. Doctorate Thesis.

17. A. Ghosh and A.K. Mallik, Manufacturing Science, Ellis Horword Limited,

1986, pp 191,193, 205,

18. E.J.A Armarego and R.H.Brown, The machining of metals, Prentice Hall,

1969, pp5.

1

Seguin, E. 2004. Wear behavior of CBN tools while turning various hard

steels.Elsevier Wear. 256: 302-310

20. International Organization for Standardization 1977. Tool-life testing with

single Point turning tools. ISO 3685.

2

a turning operation. Elsevier Wear. 250: 336-375

Lim, C.Y.H., Lim, S.C. and Lee, K.S. 1999. Wear of TiC coated carbide tools

in dry turning. Elsevier wear. 2

23. Trent, E.M. and Wright, P.K. 2000. Metal Cutting. 4th ed. Woburn:

Butterworth Heinamann.

24. Kumar, S.A., Durai, R.A. and Sornakumar, T. 2003. Machinability of

hardened steel using alumina based ceramic cutting tools. Elsevier

International Journal of Refractory Metals & H

78

25. Che haron, C.H., Ginting A. and Goh, J.H. 2001. Wear of coated and

uncoated carbides in turning tool steel. Elsevier Journal of Material

Processing Technology. 116: 49-54.

26. ao, A.M., Faustino, M. and Davim, J.P. 2005.

Hard turning: AISI 4340 high strength low alloy steel and AISI D2 cold work

5

Lima, J.G., Avila, R.F., Abr

tool steel. Elsevier Journal of Materials Processing Technology.

169: 385-39

27. J.Wang, The effect of the multi-layer surface coating of carbide inserts on the

cutting forces in turning operations, Journal of Material Processing

Technology, 2000, pp. 114-119.

79

APPENDIX A

Figure A.1: Type of engine parts was produced by A390 alloy. (Source by SEIL CO. LTD)

APPLICATION OF ALUMINUM SILICON ALLOYS