UNIVERSITI TEKNIKAL MALAYSIA MELAKA

THE EFFECT OF PROCESS PARAMETERS ON SPOT WELDS

STRENGTH OF 6061 ALUMINIUM ALLOY

This report submitted in accordance with requirement of the Universiti Teknikal

Malaysia Melaka (UTeM) for the Bachelor Degree of Manufacturing Engineering

(Manufacturing Process)

by

SHAHDAN AJIB BIN OMAR

B050710221

FACULTY OF MANUFACTURING ENGINEERING

2011

UNIVERSITI TEKNIKAL MALAYSIA MELAKA

BORANG PENGESAHAN STATUS LAPORAN PROJEK SARJANA MUDA

TAJUK: The Effect of Process Parameters on Spot Welds Strength of 6061 Aluminium Alloy

SESI PENGAJIAN: 2010/11 Semester 2 Saya SHAHDAN AJIB BIN OMAR

mengaku membenarkan Laporan PSM ini disimpan di Perpustakaan Universiti Teknikal Malaysia Melaka (UTeM) dengan syarat-syarat kegunaan seperti berikut:

1. Laporan PSM adalah hak milik Universiti Teknikal Malaysia Melaka dan penulis. 2. Perpustakaan Universiti Teknikal Malaysia Melaka dibenarkan membuat salinan

untuk tujuan pengajian sahaja dengan izin penulis. 3. Perpustakaan dibenarkan membuat salinan laporan PSM ini sebagai bahan

pertukaran antara institusi pengajian tinggi. 4. **Sila tandakan (√)

SULIT

TERHAD

TIDAK TERHAD

(Mengandungi maklumat yang berdarjah keselamatan atau kepentingan Malaysia yang termaktub di dalam AKTA RAHSIA RASMI 1972)

(Mengandungi maklumat TERHAD yang telah ditentukan oleh organisasi/badan di mana penyelidikan dijalankan)

Alamat Tetap:

165-W, Jalan Balai Besar,

Dungun, 23000

Dungun, Terengganu. Tarikh: 19 Mei 2011

Disahkan oleh:

PENYELIA PSM

(Tandatangan dan Cop Rasmi) Tarikh: 19 Mei 2011

** Jika Laporan PSM ini SULIT atau TERHAD, sila lampirkan surat daripada pihak berkuasa/organisasi berkenaan dengan menyatakan sekali sebab dan tempoh laporan PSM ini perlu dikelaskan sebagai SULIT atau TERHAD.

DECLARATION

I hereby, declared this report entitled “The effect of process parameters on spot welds

strength of 6061 aluminium alloy” is the results of my own research except as cited in

references

Signature : …………………………………………….

Author’s Name : …………………………………………….

Date : …………………………………………….

SHAHDAN AJIB BIN OMAR

19 MEI 2011

APPROVAL

This report is submitted to the Faculty of Manufacturing Engineering of UTeM as a

partial fulfillment of the requirements for the degree of Bachelor of Manufacturing

Engineering (Manufacturing Process) with Honours. The member of the supervisory

committee is as follow:

……..………………………………

Supervisor

(Signature & Official Stamp of Supervisor)

i

ABSTRAK

Rintangan pengimpalan titik (RSW) ialah satu proses kimpalan logam kepingan bersama

itu menyelesaikan dengan menggunakan tekanan dan lalu satu semasa besar melalui

kawasan setempat manakala kepingan tetap bersama. Tujuan projek ini ialah untuk

menyiasat contoh-contoh microstructural dan ciri-ciri rintangan kimpal bintik pada

aluminium logam kepingan. Kepingan logam Aluminium akan digunakan. Pertindihan

bersama yang berketebalan 1 mm akan dikimpal menggunakan (SSW-2040) dengan

berbeza daya electrik, arus kimpalan, dan masa kimpalan. Analisa struktur micro akan

dilaksanakan. Sifat-sifat mekanikal akan dinilai dalam ujian-kekuatan tarikan dan ujian

kekerasan. Semua data akan dikumpul dan dianalisis. Kekerasan mungkin akan

menunjukkan nilai tinggi pada hasil kimpal kawasan. Ujian terikan pula menunujukkan

logam yg mempunyai ketebalan 1.0mm adalah lebih baik daripada logam 1.5mm kerana

ketebalannya. Penentuan pengelasan untuk rintangan pengimpalan titik mesti sesuai bagi

mendapat keputusan yang lebih baik. Kesalahan dalam pengelasan secara tak langsung

akan menjejaskan dapatan keseluruhan sama sekali.

ii

ABSTRACT

Resistance spot welding (RSW) is a welding process that joint sheet metal pieces

together by applying pressure and passing a large current through localized area while

the sheets are fixed together. The aim of this project is to investigate the microstructural

samples and characteristics of resistance spot welds on aluminum sheet metal and

examine the mechanical behavior at different welding parameters. It also evaluates the

hardness of the samples in order to determine the influence of welding parameters.

Aluminium 6061 will be used. Lap joining of plates 1mm and 1.5mm in thickness will

be weld by using (SSW-2040) with different electrode force, welding current and

welding time. Microstructure analysis will carried out. Mechanical properties will be

evaluated in tensile tests and hardness test. All the data will be collected and analyzed.

Hardness will probably show high value at weldment area. Base on the finding, tensile

test show at 1.0mm strength was better than 1.5mm thickness. The parameter of

resistance spot welding must be proper decided in order to get the better result. Improper

control the parameter of welding will be affected on the result entirely.

iii

DEDICATION

Dedicated to my beloved father, En Omar bin Hj. Mohd Shah and my lovely mother, Pn

Mahani bt Abdul Rahman who are very concern, patient and supporting. Last but not least,

to all my brothers, sisters and friends. The work and success will never be achieved without

all of you.

iv

ACKNOWLEDGEMENT

Alhamdulillah and thank to Allah S.W.T. with all His Gracious and His Merciful for

giving me strength and ability to accomplish this project research successfully. I

would like to take the utmost opportunity to express my sincere and gratitude to my

supervisor, Mr. Mohd Shukor bin Salleh who is always giving me supports and

guidance throughout the year in completing this final year project. Besides, thanks a

lot to all lecturers and staffs of Faculty of Manufacturing Engineering.

Finally, to all my fellow friends who involves direct or indirectly that always stand

strong beside me in giving opinions and supports throughout our relationship, I really

thankful and appreciate it.

v

TABLE OF CONTENT

Abstrak i

Abstract ii

Dedication iii

Acknowledgement iv

Table of Content v

List of Tables ix

List of Figures x

List of Abbreviations xii

1. INTRODUCTION 1.1 Introduction 1

1.2 Problem Statement 2

1.3 Objective 3

1.4 Scope of Project 3 1.5 Gantt chart 8

2. LITERATURE REVIEW 2.1 Introduction 4

2.2 Resistance Welding 6

2.2.1 Types of Resistance Welds 6

2.2.1.1 Lap Welding 6

2.2.2 Resistance Welding Processes 8

2.2.2.1 Spot Welds 8

2.2.3 Weld Inspection 11

2.2.4 Spot Welding Parameter 12

2.2.4.1 Current 12

2.2.4.2 Pressure 12

vi

2.2.4.3 Time 13

2.3 6061 Aluminum Alloy 13

2.3.1 Suitability of Aluminum and its Alloys for Spot Welding 14

2.3.2 Comparison of Physical Properties of Aluminum and Unalloyed Steel 16

2.3.3 Resistances during Spot Welding of Steel and Aluminium 17

2.4 Mechanical Properties 18

2.4.1 Tensile Test 18

2.4.2 Stress Strain Curves 19

2.4.3 Basic Calculation 19

2.4.4 Ductility 20

2.5 Hardness Test 22

2.5.1 Brinell Hardness Test 22

2.5.2 Rockwell Hardness Test 23

2.6 Impact Test 23

2.7 Toughness 24

2.8 Weldment Microstructure 24

2.9 Factors Influencing the Life of Electrodes 26

2.9.1 Influence of Storage Time on Life of Electrodes 26

2.10 The Process of Resistance Spot Welding 28

2.10.1 Current-Force Diagram For Spot Welding Aluminium 28

2.10.2 Recommended Values For Spot Welding With Direct Current 29

2.10.3 Example Of A Field Of Suitable Welding Parameters 30

2.10.4 Effect of Weld Spot Diameter on the Shear Strength 31

2.10.5 Correlations between Surface Pretreatment, Weld Strength and Electrode

Life 31

3. METHODOLOGY

3.1 Introduction 33

3.2 Process Flow Chart 33

3.3 Experimental 35

vii

3.4 Materials preparation 36

3.5 Equipment preparation 36

3.6 Specimens Preparation 39

3.6.1 Tensile Test Specimen 39

3.6.2 Hardness Test Specimen 40

3.7 Experimentation 41

3.7.1 Microstructure Measurement 41

3.7.2 Optical Microscope Measurement 41

3.7.3 Hardness Test Measurement 42

3.7.4 Tensile Test Measurement 43

4. RESULT AND DISCUSSION 4.1 Introduction 45

4.2 Microstructure Result 46

4.2.1 Microstructure for 1.0mm and 1.5mm thickness 46

4.3 Optical Measurement Result 47

4.3.1 Relationship between 1.0mm and 1.5mm Thickness and Optical

Measurement 48

4.4 Hardness Result 50

4.4.1 Hardness of 1.5mm thickness 51

4.4.2 Hardness of 1.0mm thickness 52

4.5 Tensile Test Result 53

4.5.1 Result of 1.0 mm thickness 54

4.5.1.2 Stress versus Strain Analysis for 1.0mm thickness 55

4.5.2 Result of 1.5 mm thickness 56

4.5.1.2 Stress versus Strain Analysis for 1.5mm thickness 57

4.5.3 Different of maximum forces for 1.0mm and 1.5mm thickness 58

viii

5. CONCLUSION AND RECOMMENDATION

5.1 Conclusion 59

5.2 Recommendation For Further Research 60

REFERENCES 61

APPENDICES A Gantt Chart

B Measurement Result Data C Conducting Experiment

ix

LIST OF TABLES

2.1 Chemical composition of Al 6061 13

2.2 Comparisons of Physical Properties of Aluminum and Unalloyed Steel

(0.15%C) at RT 16

3.1 Control parameter for spot welding process 38

3.2 Standard specimen size for tensile experiment 39

3.3 Minimum thickness requirement for Brinell hardness test 40

x

LIST OF FIGURES

2.1 How an overlapped spot weld is made 6

2.2 Cross Section of Completed Spot Weld 7

2.3 Cross Section of Completed Spot Weld 8

2.4 Principle of Stationary Spot Welding With Close-up of Operation 9

2.5 Pictorial sequence of the making of a spot weld 10

2.6 (A) Visual inspection, (B) Peel test, (C) Chisel test 11

2.7 Suitability of Aluminium and its Alloys for Spot Welding 15

2.8 Resistance during Spot Welding of steel and aluminum 18

2.9 Diagram of tensile test machine 18

2.10 Typical stress-strain curve from tensile test 19

2.11 Standard plate specimen size 21

2.12 Brinell hardness testing technique 23

2.13 Rockwell hardness testing technique 23

2.14 Charpy-V notch impact apparatus 24

2.15 Optical microstructure of parent metal Austenite 304 stainless steel 25

2.16 Optical microstructure of parent metal plain mild steel 25

2.17 Heat affected zone microstructure Austenitic steel side 25

2.18 Factors Influencing the Life of Electrodes 26

2.19 Influence of Storage Time on Life of Electrodes 27

2.20 Influence of Machine Design and Current Type on Life of Electrodes 28

2.21 Current-Force Diagram for Spot Welding Aluminium 29

2.22 Guide Values For Spot Welding With Direct Current 30

2.23 Example Of A Field Of Suitable Welding Parameters 30

2.24 Effect of Weld Spot Diameter on the Shear Strength 31

2.25 Correlations between Surface Pretreatment, Weld Strength and Electrode

Life 32

xi

3.1 Process Flow Chart 34

3.2 Flow chart of the experiment 35

3.3 Aluminum Alloy plate 35

3.4 Laser Cutting Machine (Helius 2513).37

3.5 Spot Welding Machine 38

3.6 Standard specimen for tensile test (Dog bone) 39

3.7 Example of hardness test specimen 40

3.8 Image Analyzer (Buehler Omniment). 41

3.9 Optical Microscope 42

3.10 Rockwell hardness machine (MITUTOYO Model: HR-523). 42

3.11 Universal Testing Machine (AG-1/100 kN). 43

3.12 Tensile works 44

4.1 Sample 1(1.0mm thickness) 47

4.2 Sample 5 (1.0mm thickness) 47

4.3 Sample 1(1.5mm thickness) 47

4.4 Sample 8(1.5mm thickness) 47

4.5 Result of optical measurement for 1.0mm and 1.5mm thickness 49

4.6 1.0mm thickness 49

4.7 1.5mm thickness 49

4.8 Point for Taken Measurement 50

4.9 Hardness Result for 1.5mm thickness 51

4.10 Hardness Result for 1.0mm thickness 52

4.11 Maximum Force of 1.0mm thickness 54

4.12 Result tension test for specimen 6 55

4.13 Maximum Force of 1.5mm thickness 56

4.14 Result tension test for specimen 8 57

4.15 Maximum Force for 1.0mm and 1.5mm thickness 58

xii

LIST OF ABBREVIATIONS

AISI - American Iron and Steel Institute

AMCs - Aluminum Matrix Composites

ASTM - American Society for Testing Materials

AWS - American Welding Society

BHN - Brinell Hardness Number

CV - Constant Voltage

FEM - Finite Element Method

HP - Horse power

MMCs - Metal Matrix Composites

RSW - Resistance Spot Welding

UTeM - Universiti Teknikal Malaysia Melaka

UTS - Ultimate Tensile Strength

1

CHAPTER 1 INTRODUCTION

Spot welding is a technique in welding field. It is the most commonly used joining

technique for parts made of steel sheets. The main advantages of the spot welding

process are its relatively low capital cost, ease of maintenance, and high tolerance to

poor part fit up compared with other fusion welding technologies.

1.1 Introduction

In the spot welding process, two or three overlapped or stacked stamped components are

welded together due to the heat created by electrical resistance. This can be done by the

work pieces as they are held together under pressure between two electrodes. Spot

welding may be performed manually, using robots, or by a dedicated spot welding

machine and the process takes only few seconds.

Spot welds are discrete weld locations that look like small circles on the assembled

components. They are not continuous, linear welds. Low volumes of components are

usually done manually, whereas high volumes can be achieved the best by using robots

or dedicated weld equipment. In spot welding, there are number of variables involved

such as current, pressure, time, human element, type of condition of welder, condition of

electrodes and condition of surface. Some of the weld parameters are difficult to control

and may cause weld problems. Others are easy to control such as the current, time and

2

electrode pressure. Achieving good weld quality starts with a good process design that

minimizes the variables during welding.

1.2 Problem Statement

The spot welding process is fast, flexible, and easy to maintain. Moreover, it is a well-

established process in the automotive industry. As a result, there is a strong preference to

using spot welding in joining aluminum sheet metal parts. However, a serious concern

exists on the quality of aluminum spot welds due to the difference between the spot

welding of steel and aluminum.

The advantages of spot welding are high speed and suitability for automation and

inclusion in high production assembly lines with other fabricating operations. Spot

welding is a very fast process and there are many factors that affect the quality of welds.

Compared to steel, aluminum has higher electrical and thermal conductivities, a

narrower range between the solidus and liquidus temperatures (about 30°C), and a lower

melting temperature around 670°C. Aluminum also forms nonconductive films on its

surfaces when exposed to air. All these properties make the spot welding process of

aluminum harder to control. Consequently, detailed studies are need on the effect of

process parameters of 6061 aluminum alloy to achieve spot welds strength.

3

1.3 Objectives

The objectives of this project are:-

a) To investigate the microstructural samples and characteristics of resistance spot

welds on aluminum sheet metal.

b) To examine the mechanical behavior at different welding parameters.

c) To evaluate the hardness of the samples in order to determine the influence of

welding parameters.

1.4 Scope of Project

Here, scope act as the guidance that limits this research is doing without loss the

focusing. It is capable to bring the project to their objective without run out by doing

work that not relate to the objective. Welding process has done using Miller Spot

Welding machine (SSW-2040ATT). Material used is 6061 Aluminum Alloy sheets with

thickness 1.0mm and 1.5mm. The joint design was lab joining.

4

CHAPTER 2 LITERATURE REVIEW

2.1 Introduction

A lot research has been done on joining dissimilar metal through various purpose and

application. The famous is about study the resistance and parameter because it had

related to the most application requirement. Several finding that has been gathering are

as follow:

Research has been done by Bowers, Sorensen and Eagar (1990) about mathematical

model predicts current distribution as a function of electrode geometry. His finding

about the research is it important to note that the mathematical model developed herein

is a first level approach to understand the trends produced in current distribution as

affected by electrode geometry. It is most interesting that the experimental results

support the predictions derived from the model, despite the model not incorporating such

factors as contact resistance, alloying and deformation of the electrode tips and the

temperature dependence of electrical conductivity of the electrode material. Yet, the

experimental results support the predictions derived from the modeling effort. The

shifted lobe position and longer electrode life obtained merely by changing the electrode

geometry indicate that geometry is a controlling process for a given set of welding

parameters.

Sun and Khaleel (2004) was research about whether spot welding between aluminum

and steel can be achieved using a transition material. Both experimental welding trials

5

and finite element simulations were used in determining the optimal electrode

combinations and welding parameters. The nugget formation process was then examined

using consecutive metallurgical cross-sectioning and finite element analyses. The

finding show that two distinct fusion zones formed during the spot welding process of

aluminum to steel using a transition aluminum-clad steel strip. The nugget on the steel

side is a regular, elliptical weld with dendrite grain structure inside the nugget region.

The nugget on the aluminum side is the top half of the elliptical shape.

Son and Kim (2006) was study the numerical analysis of the resistance spot welding

process. This research is used 2D axisymmetric Finite Element Method (FEM) model

that has been developed to analyze the transient thermal behaviors of Resistance Spot

Welding (RSW) process. In this model, the temperature dependent material properties,

phase change and convectional boundary conditions were taken account for the

improvement of the calculated accuracy, but the determination of the contact resistance

at the surface is moderately simplified in order to reduce the calculating time through the

analysis. The finding show the developed model has been employed the thermal history

of the whole process (including cooling) and temperature distributions for any position

in the weldment.

Shamsul and Hisyam (2007) was study the Spot Welding of Austenitic Stainless Steel

Type 304. In this study, austenitic stainless steel types 304 were welded by resistance

spot welding. The research is about the relationship of nugget diameter, welding current

and hardness distribution along welding zone. The finding shows Austenitic stainless

steel AISI-304 is an extremely important commercial alloy due to its excellent corrosion

resistance, high strength, good ductility and toughness. In this study, two plates of these

steel were placed as a lap joint and spot welded using varied welding current.

6

2.2 Resistance Welding

Resistance welding is the science of welding two or more metal plates together in a

localized area by application of heat and pressure. The heat being produced a by

resistance set up to the passage of heavy ampere current, predetermined as to density and

time interval, through the metal parts held under predetermined pressure. Both pressure

and electrical current transfer provided by opposite electrodes. No need materials such

as rods, fluxes, inert gases, oxygen, or acetylene are required.

2.2.1 Types of Resistance Welds

All resistance welds are either overlap welds or butt welds, according to how they are

physically joined together and regardless of whether the welds are made by the spot,

projection or seam process.

2.2.1.1 Lap Welding

In Figure 2.1 is shown a lap weld, in which the two parts are overlapped sufficiently to

provide an sample area for the application of tile tips or electrodes used in making the

weld. When current is passed through the pieces of metal, their resistance to the current

flow causes the temperature to rise rapidly to the welding point and the two parts “fuse”

together. If the welding current is shut off at this stage and pressure is maintained on the

electrodes until the parts have chilled or rehardened, a resistance spot weld will have

taken place. The result is shown in Figure 2.1 two pieces of metal so completely fused

together that a perfect weld “nugget” is formed.

7

Figure 2.1 How an overlapped spot weld is made (Hafizi Lukman, 2007)

The resistance between the interfaces of the overlapping parts (Figure 2.1) causes a rise

in temperature in much the same manner as the filament wires in a tungsten lamp heat

up from the passage of current. After the carefully timed and controlled welding current

has passed from the electrodes through the parts, the metal reaches welding temperature

in both parts or throughout the nugget area. Nothing has been added to this joint at the

weld except the passage of electrical current and an application of pressure. When the

two pieces completely coalesce in a permanent bond, they are as strong and of the same

material throughout the weld area as the original two pieces, provided, of course, that the

two pieces were of the same metallurgical characteristics.

Figure 2.2: Cross Section of Completed Spot Weld (Vural and Akkus,2004)

2.2.1.2 Butt Welding

In Figure 2.3 the parts are butted together physically, end to end, to make a butt weld,

and the welding current is conducted through the pieces by means of copper clamps or

dies. In the butt weld (Figure 2.3), while clamps apply pressure to the parts, welding

current is passed from one piece into the other, thereby causing the ends of the two

pieces to become heated. When the heat is sufficient to weld the two pieces together

Resistance to flow of electric current generated heat quickly causing a weld.

Homogenous metal

completely welded

all the way through

8

completely, current is shut off and butts weld results. In Figure 2.3, the passage of

sufficient current through the two parts has resulted in a complete weld at the abutting

ends, and the molecular structure of the weld area is of the same composition and will

have strength equal to that of the parent metals.

Figure 2.3 Cross Section of Completed Spot Weld (Hafizi Lukman, 2007)

2.2.2 Resistance Welding Processes

There are four major classifications, according to process, of resistance welds. They are

spot, seam, projection, and butt welds of either the upset-butt or flash-butt types.

2.2.2.1 Spot Welds

Spot welding, the most widely known form of resistance welding, is so named because

the weld is in the form of a “spot,” averaging about 1.47 to 6.35 mm in diameter, made

by the application of two copper-alloy welding electrodes called “tips.” To produce a

spot weld, electrodes, or tips, are applied to an overlapping portion of two or more

pieces of metal as illustrated in Figure 2.4 (B). The welding current passes through the