UNIVERSITI TEKNIKAL MALAYSIA MELAKA

THE INFLUENCE OF WELDING PARAMETER ON BUTT

JOINT WELDING STRENGTH

This report submitted in accordance with requirement of the Universiti Teknikal

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

(Manufacturing Process)

by

LIM MING HAO

B050710146

FACULTY OF MANUFACTURING ENGINEERING

2011

DECLARATION

I hereby, declared this report entitled “The Influence of Welding Parameter on Butt

Joint Welding Strength” is the results of my own research except as cited in

references.

Signature : ………………………………………….

Author’s Name : LIM MING HAO

Date : 16 May 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). The member of the supervisory committee is

as follow:

………………………………

Supervisor

i

ABSTRAK

Penghasilan barangan kimpalan terus dicabar agar dapat meningkatkan lagi mutu

kimpalan terutama bagi kimpalan keluli lembut. Keluli lembut mempunyai sifat

kimpalan tersendiri berbanding dengan bahan lain. Oleh itu, satu kajian mengenai

mengoptimumkan kimpalan temu bagi keluli lembut dilakukan dengan menggunakan

pemodelan matematik, Response Surface Methodology (RSM). Response Surface

Methodology merupakan kaedah lanjutan pengoptimuman dan teknik sampel

statistik yang dapat membantu memahami interaksi parameter. Eksperimen

dilakukan untuk mengkaij pengaruhan tiga parameter iaitu voltan, arus dan kelajuan

kimpalan terhadap kekuatan kimpalan temu keluli lembut. Projek ini bermula dengan

mengkaji kimpalan parameter kemudian diikuti dengan proses kimpalan dengan

kombinasi parameter yang berbeza tahap. Ujian tarik dijalankan untuk mendapatkan

kekuatan tarik maing-masing. Kekuatan tarik seterusnya dianalisis bersama dengan

tiga kimpalan parameter dan bermodelan dengan Response Surface Methodology.

Kombinasi parameter terbaik akan dinilai. Dengan tetapan parameter yang tepat, ia

mampu menghasilkan kimpalan yang mempunyai kekuatan dinamik dan kualiti

kimpalan dapat dijaminkan.

ii

ABSTRACT

Producing good welded components are continually challenged in order to improve

the welding quality especially for mild steel welding. Mild steel has their unique

welding characteristic compare with other material. Therefore, a research on

optimizing the mild steel welded butt joints was carried out by using mathematically

modelling, Response Surface Methodology (RSM). Response Surface Methodology

is an advanced optimization methods and statistical sampling techniques which can

significantly help in understanding the interaction of parameter. Experiments were

carried out to study the influence of three MIG welding parameters that is welding

current, welding voltage and welding speed on the strength of welded mild steel butt

joints. This project is been started by study the welding parameter for mild steel then

follow with a welding process with different combination of parameter level. A

tensile test was done to find out the respectively tensile strength. This tensile strength

wills analysis together with three parameters and modelling by Response Surface

Methodology. A best combination of welding parameter will evaluate. With the right

welding parameters setting, it able to produce a sufficiently dynamic strength and the

best weld quality, was ensured.

iii

ACKNOWLEDGEMENT

I owe a debt of thanks to all whose time, concern and efforts were given during my

project period. Thus, I would like to extend my heartfelt gratitude to my beloved

supervisor that is Dr. Ahmad Kamely bin Mohamad for given me constructive advice

and encouragement. Besides that, I am also greatly indebted to my academic

supervisor, Mr. Ammar bin Abd. Rahman. He always gave me the inspiration on

this research.

iv

DEDICATION

For my family and friends as the endless concern, financial support, moral support,

understanding and inspired me to complete this project successfully.

v

TABLE OF CONTENT

Abstrak i

Abstract ii

Acknowledgement iii

Dedication iv

Table of Content v

List of Tables viii

List of Figures ix

List of Abbreviations xi

1. INTRODUCTION 1

1.1 Background 1

1.2 Problem Statement 2

1.3 Objective 2

1.4 Scopes 2

1.5 Organization 3

1.6 The Importance of Study 3

2. LITERATURE REVIEW 4

2.1 Introduction 4

2.2 Arc Welding 5

2.2.1 Gas Metal Arc Weld 5

2.2.2 Advantages of Gas Metal Arc Weld 6

2.2.3 Limitation of Gas Metal Arc Weld 7

2.2.4 Metal Transfer Modes 7

2.2.5 Welding Parameter 10

2.2.5.1 Welding Current 13

2.2.5.2 Welding Voltage 13

2.2.5.3 Welding Speed 13

2.2.5.4 Welding Shielding Gases 14

2.2.5.5 Electrode Orientation 16

vi

2.2.5.6 Consumable Electrode 17

2.3 Welding Material 18

2.3.1 Mild Steel 18

2.3.2 Designation of Steel 19

2.4 Tensile Test 19

2.5 Design of Experiment (DOE) 20

2.5.1 Response Surface Methodology (RSM) 20

2.5.2 Central Composite Design 22

3. METHODOLOGY 24

3.1 Response Surface Methodology (RSM) 24

3.2 Robot Welding 24

3.3 Flow Chart of Study 29

3.3.1 Define the Objective of the Experiments 30

3.3.2 Determine the Welding Parameter Level 30

3.3.3 Identify the Response Variable 30

3.3.4 Preparation for Welding Process 30

3.3.4.1 Workpiece Preparation 30

3.3.5 Running the Welding Process 31

3.3.5.1 Joint Geometries 32

3.3.5.2 Parameter Setting 34

3.3.6 Tensile Test 35

3.3.6.1 Standard Test Methods of Tension Testing Wrought Mild Steel 35

3.3.7 Develop Mathematical Model of Response Surface 36

3.3.8 Finding the Optimum Set of Parameter and Result Analysis 36

3.3.9 Conclusion 37

3.4 Welding Setup 37

3.5 Standard Operation Procedure (SOP) of Robot Welding 39

3.6 Tensile Test Setup 40

3.7 Designs-Expert Software Setup 41

4. RESULT AND DISCUSSION 43

4.1 Result and Discussion 43

4.2 Design Summary 45

vii

4.3 Evaluation Model Screen 46

4.3.1 Design Matrix Evaluation for Response Surface Quadratic Model 46

4.4 Fit Summary 49

4.4.1 Sequential Model Sum of Squares 49

4.4.2 Lack of Fit Tests 50

4.4.3 Model Summary Statistics 50

4.5 Analysis of Variance (ANOVA) 51

4.6 Diagnostics 52

4.7 Model Graphs 56

4.8 Optimization 60

4.8.1 Numerical Optimization 60

4.9 Confirmation Run 62

4.10 Average Deviation Percentage Value 63

4.11 Welding Bead 64

5. CONCLUSION AND RECOMMENDATIONS 67

5.1 Conclusion 67

5.2 Recommendation for Future Research 68

REFERENCES 69

APPENDICES

A Gantt Chart for Final Year Project 1

B Gantt Chart for Final Year Project 2

viii

LIST OF TABLES

2.1 Variation of Transfer Mode for GMAW Process 9

2.2 Important Parameters Affecting the Performance of GMAW-P 11

2.3 Effect of Change in Process Variables on Weld Attributes 12

2.4 Recommended Shielding Gas Selection for GMAW 15

2.5 Composition Requirement for GMAW Electrode 17

2.6 Mechanical Property Requirements for Weld Metal Deposit of GMAW 18

Electrode

2.7 Central Composite Design 23

3.1 Basic Specifications of the Manipulator 25

3.2 Model DR-4000 Basic Configuration 26

3.3 𝐶𝑂2/ MAG Welding Components 26

3.4 Dimensions of Rectangular Tension Test Specimen 31

3.5 Combination of Welding Parameters 24

3.6 Welding Parameters, Units and Level values 41

3.7 Replication Point and Alpha Value 42

4.1 Maximum Stress for Welding Parameter Combinations 43

4.2 Design Summary 45

4.3 Design Summary 45

4.4 Degree of Freedom for Evaluation 46

4.5 Result of Power Calculation 47

4.6 Sequential Model Sum of Squares 49

4.7 Lack of Fit Tests 50

4.8 Model Summary Statistics 50

4.9 Analysis of Variance 51

4.10 Summarize Value of Analysis of Variance 52

4.11 Prediction of Numerical Optimization 61

4.12 Maximum Stress Value for Random Trials 63

4.13 Average Deviation Percentage Value 63

ix

LIST OF FIGURES

2.1 GMAW Process 6

2.2 Schematic of Metal Transfer Process in GMAW 8

2.3a Different Modes of Metal Transfers in GMAW, Globular 9

2.3b Different Modes of Metal Transfers in GMAW, Spray 9

2.3c Different Modes of Metal Transfers in GMAW, Pulse 9

2.4 Central Composite Design 23

3.1 𝐶𝑂2/ MAG Welding Robot System Standard Configuration 28

3.2 Flow Chart of Conducting Experiments 29

3.3 Rectangular Tension Test Specimens 31

3.4 OTC DR 4000 Welding Robot 32

3.5 Typical Joint Geometries used for GMAW 33

3.6 Universal Tensile Machine 35

3.7 Flow Chart of Tensile Experiment Procedures 36

3.8 The Installment of Filler Metal 37

3.9 The Clamped Workpiece 38

3.10 The Control Unit (DR Control) 38

3.11 The Welding Process 39

4.1 Fraction of Design Space Graph 48

4.2 Normal Plot of Residuals 53

4.3 Studentized Residual versus Predicted Values 53

4.4 Externally Studentized Residuals 54

4.5 Box-Cox Plot for Power Transforms 56

4.6 One Factor Graph of Welding Current (A) versus Maximum Stress 57

4.7 One Factor Graph of Welding Voltage (B) versus Maximum Stress 57

4.8 One Factor Graph of Welding Speed (C) versus Maximum Stress 58

4.9 Cube Plot 59

4.10 3D Surface 59

4.11 Ramp Function Graph 60

4.12 The Penetration for Second Experiment Run 64

x

4.13 The Top View for Sixth Specimen 64

4.14 The Bottom View for Sixth Specimen 64

4.15 The Top View for Seventh Specimen 65

4.16 The Bottom View for Seventh Specimen 65

4.17 The Penetration for Seventh Experiment Run 66

4.18 The Penetration for Tenth Experiment Run 66

4.19 The Top View for Tenth Specimen 66

4.20 The Bottom View for Tenth Specimen 66

xi

LIST OF ABBREVIATIONS

A - Ampere

AC - Alternating Current

ANOVA - Analysis of Variance

Ar - Argon

ASTM - American Society for Testing and Materials

BDMS - Bright Drawn Mild Steel

CCD - Central Composite Design

𝐶𝑂2 - Carbon Dioxide

CV - Constant Voltage

dB - Decibel

df - Degree of Freedom

DCEN - Direct Current Electrode Negative

DCEP - Direct Current Electrode Position

DOE - Design of Experiments

FDS - Fraction of Design Space

GMAW - Gas Metal Arc Welding

HAZ - Heat Affected Zone

MAD - Mean Absolute Deviation

MAG - Metal Active Gas

MIG - Metal Inert Gas

𝑂2 - Oxygen

PRESS - Prediction Error Sum of Squares

RH - Relative Humidity

RSM - Response Surface Methodology

Std. Dev. - Standard Deviation

V - Voltage

VIF - Variance Inflation Factor

vs - Versus

W - Wat

1

CHAPTER 1

INTRODUCTION

This chapter describes the introduction to the title of the project and briefly explains

the problem faced for mild steel welding. In addition, the planning of completing

final year project was discussing. It also covers the scope and importance of this

project.

1.1 Background

The recent manufacturing technologies developments have enable the manufacturers

to make parts, components and products faster, better quality, and more complexity.

From car manufacturing to the production of niche products, industrial robotics was

widespread applied in welding industry. Robotics welding with high power density,

high degree of automation and high production rate are extremely advantageous in

automotive application and revolutionized the welding industrial workplace. Good

robotic welding system able to decrease the welding cost and production time for a

desired product.

According to Tewari et al., (2010) an investigation into the relationship between the

welding process parameters began in the mid 1900s and regression analysis was

applied to welding geometry and research by Lee and Raveendra. The selection of

the appropriate welding process parameters for robot welding is required in order to

obtain the desired welding quality. Rapid growths in the manufacturing industry

driven by the advances of computer and technologies have introduced a

mathematically modeling method, response surface methodology which can apply

into welding industry for welding optimizing. Response surface methodology is an

2

advanced statistical and mathematical technique which useful in modelling,

improving, and optimizing processes.

1.2 Problem Statement

Nowadays, producing good welded components are continually challenged in order

to improve the welding quality and maintain their competitiveness. Good welds are

essentially a result of optimization welding parameter (Holimchayachotikul et al.,

2007). Without an optimum welding condition, a good joint or perfect arc is

impossible to achieve. Traditionally, the welding parameters were optimize depend

on the welder experience and it is lack of precision.

1.3 Objective

The objectives of this research project are:

i. To study the effect of welding parameter on mild steel weldment physical

properties.

ii. To model the relationship of welding parameter and physical properties by using

RSM.

1.4 Scopes

For this research, the robot welding which is model OTC DR 4000 was selected to

perform the gas metal arc weld welding task. The welding parameters that selected

are welding current, welding voltage and welding speed. Material that selected for

welding parameter optimizing is mild steel. Type of joint was selected is butt joint.

Mathematically modeling, Response Surface Methodology (RSM) was applying to

get the optimum parameters. The factors that would not cover are torch angle,

shielding gas, wire feed rate and electrode diameter.

3

1.5 Organization

The report begins with a Chapter 1 Introduction and this chapter presents the

background, problem statement, introduction, scopes of this project. Then follow

with Chapter 2 Literature Review which presents literature research of researchers

and summarizing point of its. The Chapter 3 Methodology presents the methodology

that adopted to conduct the overall final year project, including the method and

sequence of process flow of this project. Then follow with Chapter 4 Result and

Discussion which presents a best optimizing welding parameter setting result and

discussion on the results. The last chapter is Chapter 5 Conclusion and

Recommendations which summarize the important points of overall report and

recommendations for future research.

1.6 The Importance of Study

Holimchayachotikul et al., (2007) concluded that when the process parameters are

not carefully controlled, the welding quality might be affected which results in low

tensile strength at the joint area or the damage of welding area. Therefore, this study

is important as a guideline to perform welding task in future.

4

CHAPTER 2

LITERATURE REVIEW

This literature review is discussing the points, ideas and knowledge that have been

previously studied by other researchers. The main objective of the literature review is

to summarize the important points of the related journal as the depth evaluation for

this project research.

2.1 Introduction

The robots can be classified depending on their function and the market needs. Two

major classes of robots were classified that is industrial robots and service robots.

According to the Robotic Industries Association, an industrial robot can define as an

automatically controlled, reprogrammable, multipurpose manipulator programmable

in three or more axes that may be either fixed in place or mobile for use in industrial

automation applications. The first industrial robot is manufactured by Unimate and

installed by General Motors in 1961. Nowadays, majority of robot were applying in

material handling or welding usage (Bekey and Yuh, 2008).

Moore, (1985) mention that welding robots have to be 'taught' how to do the job

either by leading them through the complete job or by the use of teaching points,

which can then be interpolated by the robot. The natural unpleasantness of the job

has made the arc welder an endangered species. However, the robots will possibly

alter this danger situation for the better by making the job more varied and, once

safety standards have been established, a lot less hazardous. Furthermore, robots can

certainly free workers from unpleasant, stressful and hazardous jobs, but in many

cases this implies the phasing out of semiskilled and unskilled jobs in some areas.

5

However, the skilled welder still required to teach and operate the arc-welding robot,

and to carry out repairs or alterations on robot welds.

Wang, (2009) highlighted the importance of welding in industry as one of the

material processing method. With the development of technology and the realization

of the welding process, the requirements of welding quality are getting higher and

higher. The application of welding robot seen as a revolutionary development, which

totally changes the typical mode of rigid atomization to the flexible mode .Welding

robot consists of few major components that is robot controller and welding power

and other equipments. Welding robots have high stability of function and can

enhance welding quality greatly, so it is an important application area for industrial

robots. In addition, Alfaro and Drews, (2006) state that the welding automation able

to guide the robot movements. Besides that, the automation in welding allowing the

welding torch to be always inside the welding joint and controlling the welding

parameters such as current, voltage, wire feed rate, heat input, and many.

2.2 Arc Welding

Arc welding is a materials joining technique whereby two or more surfaces are fuse

together by exposure to the intense heat of an electric arc created between an

electrode and the workpiece to be welded. The technique used and electrode type

vary, depending on the welding process chosen (Moore, 1985).

2.2.1 Gas Metal Arc Weld

Bowditch et al., (2005) highlighted gas metal arc welding (GMAW) is a welding

process in which metals are joined by heating them with a welding arc between a

continuous consumable electrode and the base metal. A shielding gas or gas mixture

is used to prevent the atmosphere from contaminating the weld. Furthermore, gas

metal arc welding using a wire as an electrode. A welding arc is struck between the

electrode and the base metal. The electrode melts as it is continuously fed to maintain

the welding arc.

6

Weglowski et al., (2008) indicate that the increasing of gas metal arc welding

(GMAW) employed for fabrication industries (Figure 2.1). This process is versatile,

since it can be applied for all position welding. It can easily be integrated into the

robotized production canters. Furthermore, this process is used an externally supplied

of shielding gas and without the application of a pressure. MIG welding refers to the

use of an inert gas while metal active gas welding (MAG) involves the use of an

active gas (i.e. carbon dioxide and oxygen). A variant of the GMAW process uses a

tubular electrode filled with metallic powders to make up the bulk of the core

materials (metal core electrode). Normally, the commercially important metals such

as carbon steel, high-strength low alloy steel, stainless steel, aluminium, copper,

titanium, and nickel alloys can be welded in all position with GMAW process by

choosing appropriate shielding gas, electrode, and welding variables.

Figure 2.1: GMAW process (Weglowski et al., 2008).

2.2.2 Advantages of Gas Metal Arc Weld

The MIG welding provides a controlled weld pool for welding thin material in any

position. It produces a smooth weld and minimum spatter and has become very

popular. The major advantages of gas metal arc welding are high operator factor,

high deposition rates, high use of filler metal, elimination of slag and flux removal,.

Moreover, other advantages are reduction in smoke and fumes, lower skill level in a

semiautomatic method of application than that required for manual shielded metal

arc welding and automation possible (Cary and Helzer, 2004).

7

2.2.3 Limitation of Gas Metal Arc Weld

The GMAW process, like any other welding process, has certain limitations that

restrict its use. First, the welding equipment is more complex, usually more costly,

and less. Then, GMAW process is more difficult to apply in hard-to-reach places

because the welding gun is larger than a small holder and must be held close to the

joint within 10 to 19 mm. Lastly, its shielding gas limits outdoor applications unless

protective (Ferjutz and Davis, 1993).

2.2.4 Metal Transfer Modes

Weglowski et al., (2008) defines the metal transfer in GMAW as a process of

transferring material of the welding wire in the form of molten liquid droplets to the

work-piece (Figure 2.2). According to Ferjutz and Davis, (1993) the optimum

transfer mode depends in part on the thickness of the base metal being welded. For

example, very thin sections (in all positions) require the short-circuiting mode (with

low current levels and appropriate settings of voltage and other operating parameters,

including shielding gas composition). Thicker sections show best results with spray

or streaming transfer. These transfer modes also produce high heat input, maximum

penetration, and a high deposition rate.

Metal transfer plays an important role in determining the process stability and weld

quality. Depending on the welding conditions, metal transfer can take place in few

principal modes: globular, spray, and short circuiting (Figure 2.3). Globular transfer,

where the droplet diameter is larger than the wire diameter, occurs at relatively low

currents. Since it is often accompanied by extensive spatters, globular transfer is

typically used in welding parts which has relatively loose quality requirements.

Spray transfer, where the droplet diameter is smaller than the wire diameter, occurs

at medium and high currents. It is a highly stable and efficient process, and is widely

used in welding thick steel plates and aluminium parts. Short – circuiting transfer is a

special transfer mode where the molten droplet on the wire tip makes direct contact

with the work-piece or the surface of the weld pool. It is characterized by repeated,

8

intermittent arc extinguishment and re-ignition. It requires low heat input hence it is

commonly used in welding thin sheets (Weglowski et al, 2008).

During the mid 1960s, an alternative transfer technique of metal transfer that is

pulse-spray metal transfer mode was invented. This mode of metal transfer able to

overcomes the drawbacks of globular mode while achieving the benefits of spray

transfer. This metal transfer mode is characterized by pulsing of current between

low-level background current and high-level peak current. It provides stability by

operates mostly in one drop per pulse to the arc. It also produces lesser distortions

and fumes. Pulse-spray metal transfer mode able reduces the heat input to the base

material and operates mostly in one drop per pulse which provides good stability to

the arc. Furthermore, it operates with large diameter electrode wire for wider

application ranges and reduces wire feeding problems in welding equipment and

porosity incidence because of smaller surface area to volume ratio (Praveen and

Yarlagadda, 2005). Variation of transfer mode for GMAW process was illustrated in

the Table 2.1.

Figure 2.2: Schematic of metal transfer process in GMAW (Weglowski et al., 2008).

9

Figure 2.3: Different modes of metal transfers in GMAW (a) globular, (b) spray, and (c) pulse

(Weglowski et al., 2008).

Table 2.1: Variation of transfer mode for GMAW process (Cary and Helzer, 2004).

Metal

Transfer

Globular Short-

Circuiting

Spray Pulsed-Spray

Shielding

gas

𝐶𝑂2 𝐶𝑂2 or 𝐶𝑂2 +

argon (C-25)

Argon + oxygen

and other

Argon +

oxygen and

other

Metals to

be welded

Low-carbon

and medium-

carbon steel,

low-alloy high-

strength steels

Low-carbon

and medium-

carbon steel,

low-alloy high-

strength steels,

some stainless

steels

Low-carbon and

medium-carbon

steel, low-alloy

high-strength

steels

All steels,

aluminium

and many

alloys

Metal

thickness

10 gauge

(0.140 in); up

to 0.5 in.

without bevel

preparation

20 gauge

(0.038 in); up

to 0.25 in. ;

economical in

heavier metals

for vertical and

overhead

welding

0.25 to 0.5 in.

with no

preparation;

maximum

thickness

practically

unlimited

Thin to

unlimited

thickness

Welding

positions

Flat and

horizontal

All position

(also pipe

welding)

Flat and

horizontal with

small electrode

All position