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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