iii effect of material structure
TRANSCRIPT
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
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APPENDIX A
Figure A.1: Type of engine parts was produced by A390 alloy. (Source by SEIL CO. LTD)
APPLICATION OF ALUMINUM SILICON ALLOYS