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
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 Semest er 2
Saya SHAHDAN AJIB BIN OMAR
mengaku membenarkan Laporan PSM ini disimpan di Perpust akaan Universit i Teknikal Malaysia Melaka (UTeM) dengan syarat -syarat kegunaan sepert i berikut :
1. Laporan PSM adalah hak milik Universit i Teknikal Malaysia Melaka dan penulis. 2. Perpust akaan Universit i Teknikal Malaysia Melaka dibenarkan membuat salinan
unt uk t uj uan pengaj ian sahaj a dengan izin penulis.
3. Perpust akaan dibenarkan membuat salinan laporan PSM ini sebagai bahan pert ukaran ant ara inst it usi pengaj ian t inggi.
4. **Sila t andakan (√)
SULIT
TERHAD
TIDAK TERHAD
(Mengandungi maklumat yang berdarj ah keselamat an at au kepent ingan Malaysia yang t ermakt ub di dalam AKTA RAHSIA RASMI 1972)
(Mengandungi maklumat TERHAD yang t elah dit ent ukan oleh organisasi/ badan di mana penyelidikan dij alankan)
Alamat Tet ap:
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 : ……….
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
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ABSTRAK
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ABSTRACT
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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
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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.
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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
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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
2.5.2 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
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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
4.5.1.2 Stress versus Strain Analysis for 1.0mm thickness 55
4.5.2 Result of 1.5 mm thickness 56
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5. CONCLUSION AND RECOMMENDATION
5.1 Conclusion 59
5.2 Recommendation For Further Research 60
REFERENCES 61
APPENDICES A Gantt Chart
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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
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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
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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
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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
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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.
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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.
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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
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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.
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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.
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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.
2.2.1.1Lap Welding
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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)
2.2.1.2Butt Welding
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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.
2.2.2.1Spot Welds
