ii

EFFECT OF DIFFERENT MACHINING PARAMETERS ON SURFACE

ROUGHNESS OF ALUMINUM ALLOYS BASED ON Si AND Mg CONTENT

ABDUL HAMEED BALOCH

UNIVERSITI TEKNOLOGI MALAYSIA

iii

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

iii

To

My beloved family

iv

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.

v

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.

vi

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.

vii

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

viii

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

ix

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

xi

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

xii

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

xiii

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

xiv

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

xvi

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

xvii

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

74

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

2

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.

3

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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