EFFECT OF PARAMETERS ON PROPERTIES OF SHEET METAL …eprints.utem.edu.my/22182/1/Effect Of Parameters On Properties Of Sheet... · I hereby, declared this report entitled “Effect

EFFECT OF PARAMETERS ON PROPERTIES OF SHEET METAL WELDED BY ROCKER ARM SPOT

WELDING MACHINE

NADIA SYAHIDA BINTI MOHD AMIR B051310310

UNIVERSITI TEKNIKAL MALAYSIA MELAKA 2017

B051310310 BACHELOR OF MANUFACTURING ENGINEERING (MANUFACTURING PROCESS) (HONS.) 2017 UTeM

UNIVERSITI TEKNIKAL MALAYSIA MELAKA 2017

EFFECT OF PARAMETERS ON PROPERTIES OF SHEET METAL

WELDED BY ROCKER ARM SPOT WELDING MACHINE

This report is submitted in accordance with requirement of the Universiti Teknikal

Malaysia Melaka (UTeM) for Bachelor Degree of Manufacturing Engineering

(Manufacturing Process) (Hons.)

by

NADIA SYAHIDA BINTI MOHD AMIR

B051310310

941031-06-5240

FACULTY OF MANUFACTURING ENGINEERING

2017

UNIVERSITI TEKNIKAL MALAYSIA MELAKA

BORANG PENGESAHAN STATUS LAPORAN PROJEK SARJANA MUDA

Tajuk: EFFECT OF PARAMETERS ON PROPERTIES OF SHEET METAL WELDED BY ROCKER ARM SPOT WELDING MACHINE

Sesi Pengajian: 2016/2017 Semester 2

Saya NADIA SYAHIDA BINTI MOHD AMIR (941031-06-5240)

mengaku membenarkan Laporan Projek Sarjana Muda (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

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

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

TIDAK TERHAD

Disahkan oleh:

Alamat Tetap: Cop Rasmi:

Tarikh: Tarikh: *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 “Effect of Parameters on Properties of Sheet Metal

Welded by Rocker Arm Spot Welding Machine” is the result of my own research except as

cited in references. Signature : ……………………………………

Author’s Name : NADIA SYAHIDA BINTI MOHD AMIR

Date : 14th June 2017

APPROVAL

This report is submitted to the Faculty of Manufacturing Engineering of Universiti

Teknikal Malaysia Melaka as a partial fulfilment of the requirement for Degree of

Manufacturing Engineering (Manufacturing Process) (Hons). The member of the

supervisory committee are as follow:

…………………….................................

(Profesor Madya Dr Nur Izan Syahriah Binti Hussein)

i

ABSTRAK Kajian ini bertujuan untuk menyiasat kesan parameter terhadap ciri-ciri tegangan, kekuatan dan

diameter titik kimpalan dan mencadangkan parameter optimum untuk mengimpal kepingan

keluli dengan menggunakan mesin kimpalan spot “rocker arm”. Pada masa kini, industri boleh

menggunakan 30% sahaja dari jumlah titik kimpalan kerana kesukaran dalam menentukan

parameter kimpalan. Terdapat banyak faktor yang boleh menjejaskan kualiti kimpalan kerana

ia adalah satu proses yang sangat cepat. Kegagalan juga boleh berlaku atas sebab tempat

kimpalan mempunyai kekuatan ditolak dan boleh membawa kepada kemusnahan pada bahagian

badan kereta. Spesimen yang perlu dikimpal perlu menetapkan julat parameter pada mesin

kimpalan spot. Parameter kimpalan yang berbeza telah dihasilkan dengan menggunakan kaedah

Taguchi Minitab 17. Terdapat dua dimensi yang digunakan dalam kajian ini. Sifat-sifat mekanik

yang spot weld telah diuji dengan menggunakan ujian tegangan dan kekuatan mikro. Diameter

titik kimpalan diperhatikan dengan menggunakan mikroskop stereo untuk menentukan kualiti

dan kekuatan kimpalan. Ujian tegangan digunakan untuk menentukan kekuatan tegangan

terhadap arus elektrik dan masa kimpalan. Kemudian, ia telah terbukti tegangan kekuatan dan

kekerasan itu meningkat selari dengan peningkatan arus elektrik dan masa kimpalan. Titik

kimpalan juga diperluaskan apabila haba tinggi digunakan. Berdasarkan analisis ANOVA, masa

kimpalan sangat mempengaruhi kekuatan tegangan dan pengesahan ujian telah dijalankan untuk

membuktikan bahawa masa kimpalan ialah parameter paling optimum dalam kajian ini.Oleh

yang demikian, dapatlah disimpulkan bahawa apabila arus elektrik dan masak kimpalan

meningkat, kekuatan tegangan, kekerasan dan titik kimpalan juga meningkat. Parameter

optimum untuk mengimpal keluli yang ringan adalah masa kimpalan.

ii

ABSTRACT

The aim of this study is to investigate the effect of parameters on tensile properties,

hardness, and weld nugget diameter and to suggest optimum parameter to weld steel sheets by

using rocker arm spot welding machine. Nowadays, industries can only use 30% of the total

amount of spot weld due to difficulty in determine the welding parameter. There are many

factors that can affect the quality of spot welds as it is a very fast process. Failure also could

happen on spot welds cause the spot welds to have less strength and can lead into destruction of

joining parts of car bodies. The specimens were welded by setting range of parameters on spot

welding machine. The weld parameters were generated by using Taguchi method from Minitab

17. There were two dimensions used in the study. The mechanical properties of the spot weld

were tested by using tensile shear test and micro hardness test. The nugget diameter of spot weld

was observed by using stereo microscope to determine the quality and strength of a spot weld.

Tensile test was used to determine the tensile shear strength of a spot weld against weld current

and weld time. Then, it was proved that tensile shear strength and hardness value increase

parallel with the increase of weld current and weld time. Weld nugget diameter also extended

when high heat input was applied. Based on ANOVA analysis, weld time highly influenced

tensile shear strength as it came out in first rank. Confirmation test had been conducted to prove

that weld time is the optimum parameter in this research. Therefore, it can be concluded that

when weld current and weld time increase, tensile shear strength, hardness value and nugget

diameter also increase. The optimum parameter to weld mild steel was weld time.

iii

DEDICATION

Only

my beloved father, Mohd Amir

my appreciated mother, Siti Zuraini

my adored sisters and brothers, Nabila, Nazira, Nabil, Najmi and Najwan

for giving me moral; support, money, cooperation, encouragement and also understandings

Thank You So Much & Love You All Forever

iv

ACKNOWLEDGEMENT

In the name of ALLAH, the most gracious, the most merciful, with the highest praise to

Allah that I manage to complete this final year project successfully without difficulty.

Primarily, I would like to thank my supervisor, Associate Professor Dr. Nur Izan

Syahriah Binti Hussin who had taken a lot of efforts meticulously to give advices, constant

guidances and came out with helpful suggestions.

I also want to thank my family for giving me endless love, understanding and support.

Lastly, I would like to express thanks and gratitude to those who have helped me to make this

project success.

v

TABLE OF CONTENT Abstrak i

Abstract ii

Dedication iii

Acknowledgement iv

Table of Contents v

List of Tables viii

List of Figures ix

List of Abbreviation xi

List of Symbols xii

CHAPTER 1: INTRODUCTION

1.1 Background of Study 1

1.2 Problem Statement 3

1.3 Objective 4

1.4 Scope of Project 4

CHAPTER 2: LITERATURE REVIEW

2.1 Resistance Spot Welding 5

2.2 Operation Principle of Resistance Spot Welding 7

2.3 Parameters for Resistance Spot Welding 8

2.3.1 Weld Current 9

2.3.2 Weld Time 9

2.4 Materials 11

2.4.1 Type of Materials 11

2.4.2 Material Thickness 12

2.4.3 Applications 13

2.5 Mechanical Test 14

vi

2.5.1 Tensile Shear Test 14

2.5.2 Micro Hardness Test 17

CHAPTER 3: METHODOLOGY

3.1 Flowchart 20

3.2 Material Preparation 22

3.2.1 Substrate 22

3.3 Experimental Setup 23

3.3.1 Spot Welding Machine 23

3.3.2 Parameter Setup 24

3.3.3 Spot Welding Process 24

3.4 Design of Experiment 25

3.4.1 Parameter and Variable 25

3.4.2 Design Matrix 26

3.5 Mechanical Testing 26

3.5.1 Tensile Shear Test 27

3.5.2 Micro Hardness Test 28

3.5.3 Weld Nugget Diameter Measurement 29

CHAPTER 4: RESULTS AND DISCUSSION

4.1 Parameter Involve 30

4.2 Effect of Weld Current 31

4.2.1 Tensile Shear Strength 31

4.2.2 Micro hardness 32

4.2.3 Weld Nugget Diameter 33

4.3 Effect of Weld Time 35

4.3.1 Tensile Shear Strength 35

4.3.2 Micro hardness 36

4.4 Taguchi Analysis 36

4.4.1 Taguchi Orthogonal Array Design 37

4.4.2 Analysis of Tensile Shear Strength 37

vii

4.4.2.1 Analysis of Variance 39

4.4.2.2 Confirmation Test 40

4.4.3 Analysis of Micro Hardness 42

4.4.3.1 Analysis of Variance 43

CHAPTER 5: CONCLUSION AND RECOMMENDATION

5.1 Conclusion 44

5.2 Recommendations 45

REFERENCES 46

APPENDICES

A Gantt Chart of FYP 1 48

B Gantt Chart of FYP 2 49

C Tensile Shear Test Result 50

viii

LIST OF TABLE 2.1 Chemical Composition of S235JR (Cu) Steel Sheets 11

2.2 Mechanical Properties of S235JR (Cu) Steel Sheets 11

2.3 Chemical Composition of DP590 Steel Sheet 11

2.4 Mechanical Properties of DP590 Steel Sheet 12

2.5 Chemical Composition of AISI-1008 Steel Sheet 12

3.1 Factors used in Taguchi method 25

3.2 Design of Experiment 25

4.1 Experiment parameters 30

4.2 Setting of spot weld parameters 37

4.3 Experimental result for tensile shear strength 38

4.4 Ranking of parameters for tensile shear strength 38

4.5 Result of the ANOVA of tensile shear strength 40

4.6 Experimental result for micro hardness test 42

4.7 Ranking of parameters for micro hardness value 42

4.8 Results of the ANOVA of micro hardness test 45

ix

LIST OF FIGURES

1.1 Complete Circuit of Resistance Spot Welding 2

1.2 Lap joint of a mild steel (side view) 4

2.1

Illustration of a rocker arm spot welding machine

6

2.2 Cross-Section of Weld Nugget and Indentation of Electrode on Sheet Surfaces 7

2.3 The Occurrence of Resistances in Resistance Spot Welding 8

2.4 Spot Welding Application on the Automotive 14

2.5 Effect of welding current on tensile-shear strength 15

2.6 Effect of weld current on shear strength 16

2.7 Welding Time Effect on Tensile-Shear Force of Joints 17

2.8 Effect of weld current on hardness 18

2.9 Effect of weld time on hardness 1

3.1

Flow chart of the study

21

3.2 Mild Steel Plate 22

3.3 Rocker arm spot welding machine 24

3.4 Universal testing machine 27

3.5 Vickers hardness machine 28

3.6 Stereo Microscope 29

4.1

Result of tensile shear test on a specimen

31

4.2 Graph of tensile shear strength against weld current 32

4.3 Graph of micro hardness at 5 locations 33

4.4 Graph of nugget diameter against weld current 34

4.5 Samples of weld nugget diameter 34

4.6 Graph of tensile shear strength against weld time 35

4.7 Graph of micro hardness at 5 locations 36

x

4.8 Graph of main effect plot for S/N ratio of tensile shear strength 39

4.9 Calculation of percentage error 41

4.10 Graph of main effect plot for S/N ratio of micro hardness values 43

xi

LIST OF ABBREVIATIONS RSW - Resistance Spot Welding

C - Carbon

Si - Silicon

P Phosphorus

Fe - Iron

Cu - Copper

Mn - Manganese

Cr - Chromium

Al - Aluminum

Q - Amount of Heat Generated

I - Current

R - Resistance

t - time

DOE - Design of Experiment

S/N Signal noise

ANOVA Analysis of Variance

xii

LIST OF SYMBOLS mm - Mili Metre

s Second

kA - Kilo Ampere

MPa - Mega Pascal

kN - Kilo Newton

HVN Hardness Vickers

1

CHAPTER 1

INTRODUCTION

This chapter introduces the subject matter and the problems that are being studied. It

states the general idea on what is the study is all about. It should consist of background of study,

problem statement, objectives, and scope of project. 1.1 Background of Study

Resistance spot welding (RSW) is of the oldest welding processes. It is one type of

welding that weld at least two metal sheets together without utilizing any filler material. This is

because it can be applied pressure and heat to the area that is going to be welded by using

electrode. Spot welding is widely used as joining process for fabrication in automotive, home

appliances and many more because of the effectiveness and adaptability of the high-speed

automation. RSW joins the material by applied the pressure and pass on the welding current

through the workpieces. The material between the electrode will be pressed together. When the

current is turned off, the nugget will be formed. Figure 1.1 illustrates the complete spot welding

circuit (Ali et al., 2015).

2

Figure 1.1: Complete Circuit of Resistance Spot Welding (Ali et al., 2015)

Pandey et al. (2013) stated that RSW is a major metal sheet joining process in many

industries. It is so important especially in automobile industries. For example, there are 3000 to

6000 spot welds in any car, which shows the importance of spot welding. The advantages of the

RSW are low cost, high production rate and adaptability of the high-speed automation.

Aslanlar et al. (2007) also stated that RSW is a critical process in industry. In RSW, the

overlapped workpiece is situated between the water-cooled electrodes. Then the heat input will

be passed by a large electrical current for a brief timeframe. RSW also has been used widely as

a joining process to fabricate sheet metal assemblies because of its advantages in welding

efficiency and appropriateness for automation. For example, 7000 to 12 000 spots of welding

are needed for assembly according to the size of a car. That is why the spot welding process in

very important.

3

1.2 Problem Statement

Spot welding is a major joining process in automotive industries. Today, only 30% of

the total amount of spot weld to join a part of a car can be used. This is because there is difficulty

in determine the welding parameter. Even though RSW has advantages for high speed and

suitability for automation and other fabricating operations, it also has the limitation. There are

many factors that can affect the quality of spot welds as it is a very fast process (Lukman, 2007).

Pouranvari et al., (2013) stated that the failure that happen on spot welds cause the spot

welds to have less strength and can lead into destruction of joining parts of car bodies. So, the

failure characteristics and performance of the spot weld will affect the durability and safety of

the vehicles.

In today technology, resistance spot welding is an important form in manufacture

especially automotive. Automotive industries must meet the customers’ requirements to face

the global competition that are high strength values of used sheet, the stiffness of weld joint and

ability to absorb impacts. Several parameters influenced the quality of the weld joint (Aslanlar

et al., 2007) .

Resistance spot welding is a cheap and effective method to join the metal sheets. It has

good benefits in economy such as low cost, high speed, and suitability for automotive industries.

The order of sheets and the surface condition are the causes why each spot welding cannot be

implement in the same condition (Akkas et al., 2016).

Normally, 3000-6000 spot weld are weld in any car. That is how important the resistance

spot welding as it need low cost and can produce high production rate in automation assemblies.

The diameter of nugget determines the quality of weld joint (Pandey et al., 2013). The weld is

produce by heat, electrode force and time. It uses the resistance of the materials to flow the

current that will localized heating between the part to be joined. So, it is important to understand

the mechanisms that are needed to control the weld quality.

4

1.3 Objectives

Ojectives of the study are: -

i. To investigate the effect of parameters to the tensile properties, hardness, and nugget

diameter of spot weld.

ii. To suggest optimum parameter to weld steel sheets by using Rocker Arm spot welding

machine. 1.4 Scopes of Project

In this research, the mild steel will be used as a material. It will be cut by using shear

cutting machine into plate. There will be two dimensions which are for tensile shear test and

micro hardness test that are 100 mm x 40 mm and 60 mm x 30 mm respectively. The thickness

of the steel plate is 1 mm. The mild steel will be grinded first by using sand paper to remove

any contaminants on the surface of the mild steel. The mild steel plate then will be welded by

using rocker arm spot welding machine. The parameters that will be focus on is weld current

and weld time. The joining type for the spot welding process is lap joint as shown in Figure 1.2.

Taguchi method approach is used to create L9 orthogonal array design with two factors and

three levels. Then, the spot welds are tested by using tensile shear test, Vickers hardness test,

and nugget diameter measurement.

Figure 1.2: Lap joint of a mild steel (side view)

5

CHAPTER 2

LITERATURE REVIEW

This chapter reviews the important and extensive review of literature related to the topic

of this research. It is a base for the experimental and analytical sections of this study. It also an

important summary and synthesis of current study of the topic. 2.1 Resistance Spot Welding

Resistance spot welding (RSW) is often used for producing a vehicle body-in-white

(BIW). It is normally made of thin metal sheets. The sheets are connected by clamping with two

pincers and the force and current are applied to it. The nugget will develop and the interface will

disappear. The quality factor of resistance spot welding usually consists of fusion zone size,

weld mechanical performance and failure modes. During the spot weld process, the changes will

occur in mechanical and metallurgical properties of the spot weld area (Ghazali et al., 2015).

In the spot welding process, an electric current is passed through the parts that will be

welded together. Normally, high conductive electrode is used in this process. A pressure is

exerted during the process to hold the parts that will be welded. Sufficient heat must be applied

to the metal surface that will be welded together to obtain a good welding joint. Weld current

weld time must be properly related to produce a good weld (Aslanlar et al., 2008). Spot welding

may be performed manually, robotically or by a dedicated spot welding machine but this project

emphasizes on the in-house fabricated spot welding machine.

6

Figure 2.1: Illustration of Rocker Arm Spot Welding Machine (Kalpakjian and Shmid, 2006).

Figure 2.1 shows a schematic diagram for a spot welding machine. It is a rocker-arm

type spot welding machine that commonly used for small parts. In RSW, the spot weld is

produced from a resistance heating after electrodes touch the surface of two sheet metals as

shown in Figure 2.2.