ii effect of different machining parameters on surface...
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EFFECT OF DIFFERENT MACHINING PARAMETERS ON SURFACE
ROUGHNESS OF ALUMINUM ALLOYS BASED ON Si AND Mg CONTENT
ABDUL HAMEED BALOCH
UNIVERSITI TEKNOLOGI MALAYSIA
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EFFECT OF DIFFERENT MACHINING PARAMETERS ON SURFACE
ROUGHNESS OF ALUMINUM ALLOYS BASED ON Si AND Mg CONTENT
ABDUL HAMEED BALOCH
A report submitted in fulfilment of the
requirements for Master’s Degree (Mechanical Engineering)
Faculty of Mechanical Engineering
Universiti Teknologi Malaysia
JUNE 2015
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To
My beloved family
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ACKNOWLEDGEMENT
First of all I would like to thank Allah for this valuable time given, where I
had the chance to understand about His wonders on materials.
I am deeply grateful to my supervisor, Prof Dr. Jamaliah Binti Idris for her
guidance, patience and support. I have been extremely lucky to have a supervisor
who cared so much about my work, and who responded to my questions and queries
so promptly.
My thanks are also due to the staff, faculty members, and technicians of the
Faculty of Mechanical Engineering, Universiti Teknologi Malaysia, who contributed
to my research.
I am most grateful to my wife, family and close friends for their infinite
support, patience and encouragements during these years.
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ABSTRACT
Aluminum alloys are being extensively used almost in all engineering fields
owing to their wide range of mechanical properties. Machining of the aluminum
alloys is one of the research area that focusses primarily on improved machining with
high production rate. In machining of aluminum alloys, some common problems are
faced, i.e. surface roughness, build-up edge on cutting edge, burr formation and
continuous chip formation. This research was carried on three different aluminum
alloys namely AA6061T6, AA5083 and LM6 to investigate the optimum drilling
parameters for improved chip morphology, surface roughness, build-up edge and
burr formation. The drills were performed by using a MAHO three axis CNC drilling
machine with a HSS drill bit at three different spindle speeds and feed rates. It was
found that the surface roughness was different for each aluminum alloy and it was
found to be decreasing with increased spindle speeds. The BUE was found to be
minimum for AA6061T6 and AA5083 but was quite high for LM6.
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ABSTRAK
Aloi aluminium sedang meluas digunakan hampir dalam semua bidang
kejuruteraan kerana pelbagai mereka sifat-sifat mekanik. Pemesinan daripada aloi
aluminium merupakan satu bidang kajian yang memberi tumpuan terutamanya
kepada pemesinan yang lebih baik dengan kadar pengeluaran yang tinggi. Dalam
pemesinan aloi aluminium, beberapa masalah yang dihadapi, iaitu kekasaran
permukaan, kelebihan membina-up pada hujung pemolongsan, pembentukan burr
dan pembentukan serpihan berterusan. Kajian ini telah dijalankan di tiga aloi
aluminium yang berbeza iaitu AA6061T6, AA5083 dan LM6 untuk menyiasat
parameter penggerudian optimum untuk morfologi cip bertambah baik, kekasaran
permukaan, BUE dan pembentukan duri. Latih tubi telah dijalankan dengan
menggunakan MAHO tiga paksi CNC mesin gerudi dengan gerudi bit HSS di tiga
kelajuan gelendong yang berbeza dan kadar snapan. Didapati bahawa kekasaran
permukaan adalah berbeza untuk setiap aloi aluminium tetapi ia telah didapati
berkurangan dengan peningkatan kelajuan gelendong. BUE didapati minimum untuk
AA6061T6 dan AA5083 tetapi ia adalah agak tinggi untuk LM6.
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TABLE OF CONTENT
CHAPTER TITLE PAGE
DECLARATION ii
ABSTRACT v
ABSTRAK vi
TABLE OF CONTENT vii
LIST OF TABLES x
LIST OF FIGURES xii
LIST OF SYMBOLS xvi
LIST OF APPENDICES xvii
1 INTRODUCTION 1
Introduction 1 1.1
Problem Background 2 1.2
Problem statement 3 1.3
Research Objectives 3 1.4
Scopes of the Study 4 1.5
2 LITERATURE REVIEW 5
Introduction 5 2.1
Aluminum 6 2.2
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Aluminum Alloys 6 2.3
Designation of Aluminum Alloys 7 2.4
Aluminum-Silicon system 8 2.5
Iron Intermetallics in Al-Si Alloys 10 2.6
Modification of Al-Si Eutectic 11 2.7
AA5083 Aluminum Alloy 12 2.8
A6061 Aluminum alloy 13 2.9
LM6 Aluminum Alloy 15 2.10
Heat Treatment 17 2.11
2.11.1 Solution Heat Treatment 18
2.11.2 Aging Treatment 20
2.11.3 T6 Heat treatment of AA6061 22
Machining 24 2.12
Drilling 25 2.13
Drill Nomenclature 26 2.14
Machinability 28 2.15
2.15.1 Good Quality Machining 29
2.15.1.1 Tool Wear 29
2.15.1.2 Chip Formation 30
2.15.1.3 Surface Roughness 36
2.15.1.4 Build-up Edge and Burr Formation 37
3 METHODOLOGY 45
Introduction 45 3.1
Casting Procedure 47 3.2
Preliminary machining 47 3.3
T6 Heat treatment 47 3.4
Metallography 48 3.5
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CNC Drilling 49 3.6
Surface roughness 51 3.7
3.8 Hardness Test 51
Chip Morphology 52 3.9
Burr Height 52 3.10
Build-up Edge 53 3.11
Impact Test 53 3.12
4 RESULTS & DISCUSSIONS 54
Introduction 54 4.1
Hardness Test Result 566 4.2
Impact Test Results 577 4.3
Surface Roughness 588 4.4
Burr Formation 599 4.5
Chip Morphology 60 4.6
Build-up Edge 644 4.7
5 CONCLUSIONS & FUTURE WORKS 688
Conclusions 688 5.1
Recommendations for Future Work 699 5.2
REFERENCES 70
APPENDIX A 755
x
LIST OF TABLES
TABLE NO. TITLE PAGE
2.1 Aluminum designation system 8
2.2 Typical chemical composition of A5083 12
2.3 Physical properties of A5083 aluminum alloy 13
2.4 Physical properties of A6061 aluminum alloy 14
2.5 Typical chemical composition of A6061 15
2.6 Typical chemical composition of LM6 16
2.7 Physical properties of LM6 16
2.8 Heat treatment procedures 18
3.1 Drilling parameters 49
3.2 Arrangement of experiments on each sample 50
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5.1 Optimum drilling spindle speeds and feed rates
values based on surface roughness 68
5.2 Optimum drilling spindle speeds and feed rates
values based on burr height 69
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LIST OF FIGURES
FIGURE NO. TITLE PAGE
2.1 Types of aluminum alloys 7
2.2 Al-Si phase diagram 9
2.3 Optical micrographs of
Al-12.6Si, Al-12.6Si-0.3Er 11
2.4 Optical microstructure of A5083 13
2.5 A6061 aluminum alloy ingot 14
2.6 Optical microstructure of A6061 15
2.7 Optical micrograph of LM6 17
2.8 Typical aging curve for aluminum alloys 21
2.9 Hardness values of the HST and SHTA 22
2.10 Hardness versus aging time for the aged A6061 23
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2.11 Cutting lip of drill bit 26
2.12 Nomenclature of a twist drill 27
2.13 Typical forms of chip 31
2.14 Different forms of chip of A6061 32
2.15 SEM images of chip obtained during the
drilling of aluminum alloys at different
spindle speeds and feed rates 35
2.16 Clean cutting edge and the build-up edge
cutting process 38
2.17 Build-up edge formation 39
2.18 Optical microscope photos of drill bits
for build-up edge 41
2.19 Burr model for drilling opertations 41
2.20 Burr size produced by HSS drill at
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spindle speed of 1320rpm and 0.036mm/rev 42
2.21 Effects of drilling parameters on burr height
drilling of hybrid MMC composites 43
3.1 Research methodology flow chart 46
3.2 Optical microscope 48
3.3 CNC drilling machine 50
3.4 Surface profilometer 51
3.5 Height gauge 52
3.6 Macroscope equipped with camera 53
4.1 Optical micrographs of A6061T6,
A5083 and LM6 55
4.2 Hardness test results 57
4.3 Energy absorbed during impact test 58
4.4 Surface roughness values for each experiment
xv
on each sample 59
4.5 Formation of burrs at each hole for each sample 60
4.6 Chips collected for each experiment
on A6061T6 61
4.7 Chips collected for each experiment
on A5083 62
4.8 Chips collected for each experiment
on LM6 63
4.9 BUE formation for A6061T6 65
4.10 BUE formation for A5083 66
4.11 BUE formation for LM6 67
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LIST OF SYMBOLS
AA - Aluminum alloy
wt% - Weight percent
% - Percentage
CNC - Computer numerical control
BUE - Build-up edge
rpm - Revolution per minute
BHN - Brinnel hardness number
VHN - Vickers hardness number
GP - Guinier Preston
SHT - Solution heat treated
SHTA - Solution heat treated and artificially aged
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LIST OF APPENDICES
APPENDIX TITLE PAGE
A Surface roughness values for each experiment on
each sample and Formation of burrs at each hole
for each sample
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CHAPTER 1
1 INTRODUCTION
Introduction 1.1
Aluminum alloys are being given a big attention by automotive, aerospace
and train companies because these aluminum alloys can replace the steel and cast
iron mechanical components as they are lighter and have high-strength. The weight
savings will lead to a reduction in the fuel consumption and environmental impact.
The 6xxx, 5xxx and LM6 aluminum alloys which possess a number of important
properties as medium strength, formability, weldability, corrosion resistance and low
cost, are being extensively studied. The A6061 aluminum alloy is a heat treatable
precipitation hardening alloy that contains magnesium and silicon as the major
alloying elements and has good mechanical properties and is one of the worth
aluminum alloys that is highly demanded by automotive and aerospace industries
(Demir and Gündüz, 2009). Current research has shown that the strength of
aluminum alloys in general can be improved significantly by the addition of alloying
elements such as Cu, Mg, Ti and Li. The Mg2Si intermetallic compound is reinforced
by in-situ in aluminum based composites that exhibit high melting temperature, low
density, high hardness, low thermal expansion coefficient and high elastic modulus.
Contrary to this, the presence of coarse primary and eutectic Mg2Si phases lead to
poor mechanical properties. For the present technological productions, efforts have
been made to develop near net shape from these aluminum alloys but some level of
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finishing is need to be done to complete the assembly process (Ramulu, Rao and
Kao, 2002). Therefore, it is important to establish optimum machining parameters for
different aluminum alloys based on silicon and magnesium content for different
hardness values for better production rates and good surface roughness, since very
little information is available about the optimum machining parameters for a better
surface roughness of A6061T6, LM6 and A5083 containing different weight percent
of Si and Mg. Therefore, this study is concerned to establish a comparison of very
basic optimized machining parameters for these alloys by performing drilling
operations for surface roughness.
Problem Background 1.2
It has been aforementioned that there is an increasing trend of using
aluminum alloys in automotive and aerospace industries as cost-effective,
environment-friendly lightweight materials and some of them are renowned
A6061T6, A5083 and LM6 aluminum alloys. For mass production of these
aluminum alloys, it becomes imperative to look at the mechanical properties,
machinability and the aftermaths of machining on surface roughness of these
aluminum alloys. The term machinability is a broad term and refers to either ease or
difficulty of machining a material. The machining of a material includes turning,
facing, cutting, lapping, honing, drilling, threading, milling and reaming etc. Among
all these machining operations, drilling is the most important machining operation
because it contributes 40% of machining operations almost on all the cast parts
produced from aluminum alloys in automotive and aerospace industry before final
assembly. While performing drilling operations, the chip form is often used to assess
the machinability of soft, ductile alloys, especially the aluminum alloys and the chip
control is an important issue especially in drilling operations involving ductile work
materials such as aluminum alloys. Chip control usually involves two tasks; that of
the breaking of chips to avoid the formation of long continuous chips which can
become entangled in the machinery, and that of the removal of chips from the cutting
zone to prevent damage to the machined surface.
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In this study it is aimed to discuss the optimized machining parameters for the
above mentioned aluminum alloys for the better surface roughness on the basis of
different weight percentages of Si and Mg.
Problem statement 1.3
The cast parts machining properties are of prime importance because these
machining operations are accomplished by removal of material from the machined
surface and easy machining results in cost effective products.
A6061T6, LM6 and A5083 aluminum alloys are being extensively used in
aerospace and automotive industry owing to their light weight and improved
mechanical properties and are environmental friendly.
It is found that the machinability of aluminum alloys is mostly defined in
terms of reinforced particles in aluminum matrix (metal matrix composites) or high
Si content, but there is very little information available about the machinability of
aluminum alloys based on Mg content. Therefore, there is the need to investigate for
the optimized machining parameters for aluminum alloys based on Si and Mg
content
Research Objectives 1.4
It is well known that Si is one of the crucial alloying elements necessary to
enhance the fluidity of molten metal for sound castings and also contributes for high
hardness and strength of aluminum alloys. Contrary to this it has been found from
research that increasing Si content increases the tool wear during material removal
4
for aluminum alloy castings. Similarly the presence of Mg in aluminum alloys also
improves the hardness and strength of aluminum alloys.
Hence, the purpose of this study is to find a comparison of surface roughness
between A6061T6, LM6 and A5083 by using different machining parameters based
on their different weight percentage of Si and Mg content to achieve acceptable chip
forms and improved drill holes in terms of surface roughness.
Scopes of the Study 1.5
The areas of focus of this study are as under:
1- Preparation of castings (A6061, A5083 and LM6) by using cast iron
permanent mold under similar casting conditions.
2- T6 heat treatment of A6061casting.
3- Microstructure examination of the A6061T6, LM6 and A5083
through optical microscope
4- Hardness test of the castings
5- CNC drilling of the castings at different spindle speed and feed rate.
6- Surface roughness test of the samples.
7- Chip morphology
8- Measurement of bur height
70
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