Đồ án tốt nghiệp Công nghệ kỹ thuật cơ khí: Research on the effects of MIG welding parameters on weld quality of C20 steel and SUS201 stainless steel

MINISTRY OF EDUCATION AND TRAININGHO CHI MINH CITY UNIVERSITY OF TECHNOLOGY AND EDUCATION GRADUATION THESIS MAJOR: MECHANICAL ENGINEERING TECHNOLOGY INSTRUCTOR: NGUYEN THANH TAN NGUYEN T

MINISTRY OF EDUCATION AND TRAINING

HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY AND EDUCATION

GRADUATION THESIS MAJOR: MECHANICAL ENGINEERING TECHNOLOGY

INSTRUCTOR: NGUYEN THANH TAN

NGUYEN THANH LICH NGUYEN VAN HIEN

RESEARCH ON THE EFFECTS OF MIG WELDING PARAMETERS ON WELD QUALITY OF C20 STEEL AND

SUS201 STAINLESS STEEL

MINISTRY OF EDUCATION AND TRAINING

HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY AND EDUCATION

FACULTY OF MECHANICAL ENGINEERING



BACHELOR THESIS

RESEARCH ON THE EFFECTS OF MIG WELDING PARAMETERS ON WELD QUALITY OF C20 STEEL AND

SUS201 STAINLESS STEEL

Ho Chi Minh City, July 2024

MINISTRY OF EDUCATION AND TRAINING

HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY AND EDUCATION

FACULTY OF MECHANICAL ENGINEERING



BACHELOR THESIS

RESEARCH ON THE EFFECTS OF MIG WELDING

PARAMETERS ON WELD QUALITY OF C20 STEEL AND SUS201

STAINLESS STEEL

HO CHI MINH CITY UNIVERSITY OF

TECHNOLOGY AND EDUCATION

THE SOCIALIST REPUBLIC OF VIETNAM FACULTY OF MECHANICAL ENGINEERING Independence – Freedom – Happiness

GRADUATION PROJECT ASSIGNMENT Semester II / School year 2023 – 2024

Student’s name:

1 Nguyen Tran Trung Kien ID Number: 20144114 Phone: 0906408184

1 Project code: CKM-78

Project title: Research on The Effects of MIG Welding Parameters on Weld Quality

of C20 Steel and SUS201 Stainless Steel

2 Initial materials provided by the advisor:

- Recent studies related to the topic

- Documents on welding techniques, materials science,

- MIG welding robot G2

- PROFI PRESS hydraulic press

- Universal Testing Machine – WE-1000B

- Micro polishing machine

- Materials: C20 steel, SUS201

3 Content of the project:

- Understand the theoretical basis, analyze and evaluate previous research works

- Experiment with influencing parameters

- Process the data

4 Final product:

- Explanation report

- Optimal parameter set

5 Project sending date: 15/01/2024

6 Project submission date: 06/07/2024

6 Presentation language: The report: English  Vietnamese 

Present thesis: English  Vietnamese 

CHAIR OF THE PROGRAM

(Sign with full name)

COMMITMENT

Project title: Research on The Effects of Mig Welding Mode on Weld Quality of C20 Steel and Sus201 Stainless Steel

Supervisor: ME NGUYEN THANH TAN

Student’s name : Nguyen Tran Trung Kien

ID Number: 20144114 Student’s name : Nguyen Thanh Lich

ID Number: 20144414 Student’s name: Nguyen Van Hien

ID Number: 20144387 Class: 201441C

Project submission date:

Commitment : “We hereby declare that this thesis was carried out by ourselves under the guidance and supervision of ME Nguyen Thanh Tan; and that the work contained and the results in it are true by authors and have not violated research ethics The data and figures presented in this thesis are for analysis, comments, and evaluations from various resources

by our own work and have been duly acknowledged in the reference part In addition, other comments, reviews and data used by other authors, and organizations have been acknowledged, and explicitly cited

We will take full responsibility for any fraud detected in my thesis.”

ACKNOWLEDGMENT

A bachelor’s thesis is the most important achievement for all students We don't know what to say other than express our deepest gratitude to the teachers who have always accompanied and supported us throughout the project

First of all, we would like to extend our sincere thanks to ME Nguyen Thanh Tan –

our main instructor this time, who wholeheartedly instructed, guided us throughout the project process

We would also like to thank sincerely ME Nguyen Thanh Tan, Ph.D Nguyen Van

Thuc and ME Hoang Van Huong, who together supported and taught us about the

knowledge of books, newspapers, and equipment in the school to help us gain a solid theoretical basis and how to operate the machine effectively

Besides, we are also thankful to my friends and teachers at Ho Chi Minh City

University of Technical Education for always caring, helping, and encouraging us

throughout the learning process so that we have the basic knowledge to prepare for the project

Finally, we would be remiss in not mentioning our families who silently stand behind

us, cheering, caring, and helping us throughout the study process and completing our bachelor thesis

With our limited conditions, time and experience, this project cannot avoid mistakes and shortcomings We look forward to receiving guidance and comments from the teachers

so that we can supplement and raise our awareness and better serve our practical work in the future

ABSTRACT

The topic “Research on The Effects of MIG Welding Parameters on Weld Quality of C20 Steel and SUS201 Stainless Steel”.In this study, the main objective is to investigate the impact of welding parameters when performing MIG welding on C20 steel and SUS201 stainless steel The goal is to determine the optimal parameters to enhance the tensile strength, flexural strength, and elongation of the welds using GM70S filler materials

The first chapter introduces the study, its motivation, and structure Chapter 2 reviews related research, highlighting gaps this study aims to address Chapter 3 covers MIG welding theory, experimental setup, and quality tests, detailing processing conditions and their effects Chapters 4 and 5 discuss experimental preparation, execution, and results Chapter 6 explores future research directions The thesis comprehensively presents the theoretical foundation of the MIG welding method using GM70S, C20 steel, and SUS201 stainless steel workpieces, welding conditions, and input parameters The parameters were optimized using the Taguchi method and ANOVA

For the experimental part, the study examines four main input parameters: welding current (I), welding voltage (U), electrode extension (d), and welding speed (v) By applying the Taguchi method and ANOVA, the research team obtained the following optimal parameter sets:

- Optimal parameters for improving tensile strength

- Optimal parameters for improving yield strength

- Optimal parameters for improving elongation

- Optimal parameters for improving modulus of elasticity

- Optimal parameters for improving flexural strength

All experiments in the thesis were conducted directly at the mechanical workshop and

the micro-lab of the Ho Chi Minh City University of Technology and Education The

project received support in terms of machinery, experimental equipment, and funding from

ME Nguyen Thanh Tan, Ph.D Nguyen Van Thuc, and ME Hoang Van Huong

Student group

Nguyen Tran Trung Kien Nguyen Thanh Lich Nguyen Van Hien

TABLE OF CONTENTS

GRADUATION PROJECT ASSIGNMENT i

COMMITMENT iii

ACKNOWLEDGMENT iv

ABSTRACT v

LIST OF TABLES ix

LIST OF FIGURES xi

LIST OF ABBREVIATIONS xiii

CHAPTER 1 INTRODUCTION 1

1.1 Urgency of the study 1

1.2 Scientific and practical significance of the study 5

1.2.1 Scientific significance of the study 5

1.2.2 Practical significance of the study 6

1.3 Aims of the study 6

1.4 Object and range of the study 6

1.4.1 Object of the study 6

1.4.2 Range of the study 6

1.5 Research methods 6

1.5.1 Methodology 7

1.5.2 Specific research methods 7

1.6 Structure of the study 7

CHAPTER 2 THEORETICAL BACKGROUND 8

2.1 Introduction to alloy steel material C20 8

2.1.1 Alloy steel C20 8

2.1.2 Characteristics of C20 alloy steel 8

2.1.3 Composition of C20 steel 8

2.1.4 Applications of C20 alloy steel 9

2.2 Introduction to stainless steel material SUS201 10

2.2.1 Stainless steel SUS201 10

2.2.2 Characteristics of stainless steel SUS201 10

2.2.3 Composition of stainless steel SUS201 11

2.2.4 Applications of stainless steel SUS201 11

2.2.5 Distinguishing stainless steel SUS201 from other steel types 12

2.3 MIG welding technology 12

2.3.1 Overview of MIG welding technology in mechanical engineering 12

2.3.2 Principles of MIG welding process 13

2.3.3 The welding arc 14

2.3.4 Shielding gas 15

2.3.5 Welding wire 16

2.3.6 Advantages, limitations, and applications of MIG welding technology 19

2.4 Experimental methods and planning 20

2.4.1 Orthogonal array 20

2.4.2 Signal-to-noise ratio 21

2.4.3 Analysis of variance 21

2.4.4 Taguchi method 21

2.5 Methods of checking and evaluating welding quality 24

2.5.1 Research on structural components of welded joints 24

2.5.2 Method for determining the durability of the weld bond with materials 24

CHAPTER 3 EXPERIMENTAL DESIGN 28

3.1 Experimental setup 28

3.2 Experimental equipment 28

3.2.1 Mig welding robot 28

3.2.2 Hydraulic press machine – PROFI PRESS 30

3.2.3 Universal testing machine 31

3.2.4 Technological jigs 32

3.3 Prepare test sample and welding process 33

3.4 Select welding parameters for MIG welding robots 36

3.5 Statistical analysis using the taguchi method to optimize process parameters 37

CHAPTER 4 RESULTS AND DISCUSSION 40

4.1 Effects of welding parameters on weld quality 40

4.1.1 Effects of welding parameters on weld quality by tensile test 40

4.1.2 Effects of welding parameters on weld quality by bending test 56

4.1.3 Microstructure of the weld 63

4.2 Experiment validation compared to prediction, base metal, and optimal results 67

4.3 Summary of the MIG welding process 72

CHAPTER 5 CONCLUSION AND DEVELOPMENT DIRECTIONS 75

5.1 Conclusion 75

5.2 Future Development of the Research 75

APPENDIX I PENETRATION DEPTH OF THE WELD 77

APPENDIX II MICROSTRUCTURE OF THE WELD 79

APPENDIX III WELD STRENGTH GRAPH 82

REFERENCES 89

LIST OF TABLES

Table 2.1: Composition of C20 Steel according to JIS G4051 Standard 8

Table 2.2: Application of Shielding Gas to Weld Metal 16

Table 2.3: Welding wire size with corresponding current 17

Table 2.4: Taguchi Experimental Plan for Array L9 (33) 23

Table 3.1: Chemical Composition and Mechanical Components of SUS 201 Stainless Steel according to ASTM 240/240M Standard 36

Table 3.2: Chemical Composition and Mechanical Components of C20 Steel according to JIS G4051 36

Table 3.3: Fixed MIG welding parameters with GM70S filler materials 37

Table 3.4: MIG Welding Parameters Performed with GM70S filler materials 37

Table 3.5: Taguchi Experimental Plan for Array L16 with GM70S filler material 38

Table 4.1: Table L16 of Taguchi and tensile test results 40

Table 4.2: Response table for S/N ratios (dB) 41

Table 4.3: Analysis of variance for tensile strength 43

Table 4.4: Table of optimal tensile strength parameters 47

Table 4.5: Response table for S/N ratios (dB) 47

Table 4.6: Analysis of variance for yield strength 48

Table 4.7: Table of optimal yield strength parameters 50

Table 4.8: Response table for S/N ratios (dB) 51

Table 4.9: Analysis of variance for elongation 52

Table 4.10: Table of optimal elongation parameters 53

Table 4.11: Response table for S/N ratios (dB) 54

Table 4.12: Analysis of variance for elastic modulus 55

Table 4.13: Table of optimal elastic modulus parameters 56

Table 4.14: Table L16 of Taguchi and bending test results 56

Table 4.15: Response table for S/N ratios (dB) 58

Table 4.16: Analysis of variance for Flexural strength 59

Table 4.17: Table of optimal flexural strength parameters 60

Table 4.18: Response table for S/N ratios (dB) 61

Table 4.19: Analysis of variance for elastic modulus 62

Table 4.20: Table of optimal elastic modulus parameters 63

Table 4.21: Comparison table of optimal parameters and experimental parameters results 67 Table 4.22: Tensile Test Results of Base Metal 68

Table 4.23: Rules of the Studied Parameters 73

LIST OF FIGURES

Figure 2.1: Some Examples of Applications of C20 Steel 9

Figure 2.2: Some Examples of Applications of SUS201 12

Figure 2.3: MIG Welding System 13

Figure 2.4: The principle of MIG welding 14

Figure 2.5: The voltage distribution in the arc 15

Figure 2.6: Relationship between wire speed and welding current 18

Figure 2.7: Stick-out outside the welding torch 19

Figure 2.8: Test Samples Include the Unprocessed Part of the Product 25

Figure 2.9: Dog-bone Sample Parameters according to ASTM E8/E8M Standards 25

Figure 2.10: Stress-Strain Curves For Mild Steel and Low And High Alloy Steel 26

Figure 3.1: Experimental Setup 28

Figure 3.2: Flowchart of The Experimental Work 28

Figure 3.3: PANASONIC TA-1400G2 MIG Welding Robot 29

Figure 3.4: MIG Welding process by G2 Welding Robot 29

Figure 3.5: Hydraulic Press Machine – PPCM 50 30

Figure 3.6: Stamping die for specimen testing 30

Figure 3.7: Universal Testing Machine – WE-1000B 31

Figure 3.8: Tensile - Bending test using WE-1000B tensile machine 31

Figure 3.9: Model of MIG Welding Jig for Robots 32

Figure 3.10: Jigs for Automatic Welding Robots 32

Figure 3.11: Laser Cutting Profile of Welded Workpiece 33

Figure 3.12: The Welding Sample Has Been Prepared 33

Figure 3.13: Joint square preparation for butt welds, welded from one side 34

Figure 3.14: Fix The Welding Workpiece on The Jig 34

Figure 3.15: Profile for Tensile Test Specimen According to ASTM E8 Standard 35

Figure 3.16: Profile for Bending Test Specimen According to ISO 15614-1 Standard 35

Figure 3.17: Experimental and Sample Processing Procedure 39

Figure 4.1: Average graph of output results during tensile testing 41

Figure 4.2: Main effects plot for ratios 42

Figure 4.3: The penetration depth of the sample was measured using ImageJ software 44

Figure 4.4: Penetration depends on the microstructure of the weld 45

Figure 4.5: Main effects plot for ratios 48

Figure 4.6: Main effects plot for ratios 51

Figure 4.7: Main effects plot for ratios 54

Figure 4.8: Average graph of output results during bending testing 57

Figure 4.9: Main effects plot for ratios 58

Figure 4.10: Main effects plot for ratios 61

Figure 4.11: The surveyed areas of the weld and the affected zones 63

Figure 4.12: Microstructure at 5x 64

Figure 4.13: Microstructure at 20x 65

Figure 4.14: Stress-Strain graph from the tensile test 68

Figure 4.15: Stress-Strain graph from the bending test 68

Figure 4.16: Fracture position of the tensile tests sample with optimal parameters 71

Figure 4.17: Tensile Test Bar and Force - Displacement Diagram 71

LIST OF ABBREVIATIONS

LASER Light Amplification by Stimulated Emission of Radiation

ATSM American Society for Testing and Materials

UTM Ultimate Tensile Machine

SUS Steel Use Stainless

CHAPTER 1 INTRODUCTION

1.1 Urgency of the study

In today’s world, metal welding is not only an important part of the metal industry but also plays a key role in creating complex products and structures One of the popular welding methods is the MIG (Metal Inert Gas) method, a modern process that offers flexibility and high performance The MIG method typically uses an electric current passing through a continuous welding wire, combined with an inactive shielding gas, creating a welding environment that does not include air from the surrounding environment This not only prevents contamination from forming during the welding process but also keeps the weld high quality MIG welding method is not only widely used in welding common carbon steels, but

is also suitable for welding metals such as stainless steel, aluminum, and many other alloys This creates a great diversity of applications from automobile manufacturing, and ship construction, to medical equipment manufacturing and the aerospace industry Thanks to the automation and adaptability of the MIG process, today’s MIG welders not only significantly reduce labor but also provide precision and uniformity in the welding process The flexibility and adaptability of MIG welding play an important role in responding quickly and accurately

to the increasingly diverse demands of the metal welding industry

The overall quality of a weld is often determined mainly by its specific geometrical characteristics, which in turn affect the mechanical properties of the weld The selection and control of special welding process parameters such as welding current, welding voltage, welding speed, electrode length, welding gas flow rate, wire feed speed, welding position, protective gas or welding angle is not only an important factor, but also essential to ensure weld quality and performance

What is especially important is the accuracy in adjusting and maintaining the above parameters, and this depends not only on technical factors such as equipment and welding technology, but also strongly on the technique, skills and experience of the machine operator

or engineer performing the welding process The accuracy of this process can even increase

or decrease depending on a deep understanding of the welding process and the ability to cope with unwanted fluctuations

Faced with this challenge, manufacturers today are making efforts to research and apply advances in the MIG welding process Recent studies have been carried out by many authors from many different angles, aiming to optimize the welding process and enhance the

ability to control the quality of welds This is an important area of research and contributes to the continuous development of welding technology in modern industry

In their study, P Sakthivel et al [32] examined the MIG welding process for joining

different materials, particularly aluminum alloys AA6063, AA7075, AA2014 with mild steel MIG welding of dissimilar materials is a novel approach for weight reduction in various industries Aluminum alloys are favored in aerospace and automotive sectors for their light weight Mechanical properties were tested through tensile, Rockwell hardness, Vickers hardness, macro, and micro tests, revealing good weld quality Results indicated that the AA6063 alloy and mild steel combination exhibited the best Rockwell and Vickers hardness and tensile strength

Aysha Sh Hasan et al [21] studied the impact of welding current during MIG and TIG

welding on the mechanical properties of medium carbon steel (0.58% C) and 304L stainless steel welds, using E309L welding wire They optimized welding current for butt and lap joints

to achieve optimal tensile strength and analyze heat generation Findings showed that increasing welding current raised welding temperature, with TIG welding being hotter than MIG Tensile strength was higher for butt joints than lap joints in TIG welding, and TIG welding generated more heat than MIG for both joint types

In their study, Bhuvan Bhardwaj et al [16] welded 8mm thick AISI 202 stainless steel

plates using SS-304L welding wire AISI 202 SS, though similar in mechanical properties to AISI 304 SS, is less corrosion-resistant in chloride environments but is cheaper and used in furniture, kitchen utensils, the food industry, oil and gas, and automobiles The research aimed

to optimize welding parameters such as current, CO2 gas flow rate, and speed to enhance weld quality Tests showed that low gas flow rates resulted in high tensile strength and low ductility, while high welding speeds increased defects and improper weld penetration The lowest hardness occurred at a speed of 4mm/min and current of 200A, and the highest hardness at the same speed but with 300A The lowest tensile strength was at a speed of 5mm/min, current of 100A, and gas flow of 1.5 liters/min, whereas the highest tensile strength was at 3mm/min, 300A, and 1 liter/min gas flow, with 5% elongation Saurabh Gandhe et

al.[40] utilized the Taguchi method with an L9 orthogonal array, preparing 9 samples to

optimize welding parameters for AISI 1040 steel plates, aiming to improve output quality parameters such as tensile strength and microhardness in the base metal area and heat-affected zone

In their study, Vijaya Sankar B et al [39] used AISI 310, known for its

high-temperature resistance, good surface finish, corrosion resistance, ductility, and weldability

AISI 310 is commonly used in plates, tubes, furnaces, and pressure vessels They employed the Gray-Taguchi method to optimize welding parameters for AISI 310 steel plates Key factors like welding current, voltage, speed, gas flow, and electrode material significantly influenced penetration depth, enhancing tensile strength, microstructure, and microhardness The L9 orthogonal array was used for test planning

R Sakthivel et al [35] also used the L9 Taguchi orthogonal array to study the effect

of welding current, voltage, and gas flow on penetration, bead height, and bead width when welding AA2014 plates (150 x 50 x 6 mm) with the MIG method Results indicated that increasing voltage and current boosts penetration, bead width, and height, whereas increasing gas flow increases penetration depth but decreases bead height and width

SD Ambekar et al [11] investigated the influence of process parameters on penetration

depth during gas metal arc welding of Martensitic stainless steel AISI 410 Using the Taguchi method, they conducted 16 experiments based on the L16 orthogonal array The study analyzed the effects of welding speed, current, and wire diameter on weld penetration, employing analysis of variance and signal-to-noise ratio to identify key factors and predict optimal parameters Experiments with these optimal settings yielded positive results, with validation tests closely matching the predicted outcomes, demonstrating the method’s

efficiency and reliability for welding AISI 410 stainless steel Tadele Tesfaw et al.[43]

optimized welding parameters for 2 mild carbon steel plates (0.08%-0.15% C, 60x60x5mm) using a semi-automatic welding machine They applied Taguchi’s method to adjust parameters such as current, voltage, gas flow rate, and wire feed speed to enhance weld hardness Using the Taguchi orthogonal array, signal-to-noise ratio, and ANOVA, the study provided insights into the variation of materials and plate thicknesses, particularly beneficial for the automobile industry in Ethiopia

Kapil B Pipavat et al [24] used the Taguchi technique to design an experiment with

9 samples, employing an orthogonal array and analysis of variance to investigate and optimize the welding properties of AISI 316 material The study reviewed methods to obtain optimal process parameters from experimental data, focusing on achieving good weld quality and high tensile strength The research identified significant factors influencing weld durability and examined how changes in welding angle and shielding gas ratio impact weld quality The goal was to find the best parameters to enhance ultimate tensile strength, yield strength, and elongation of the weld

Mehmet Şükrü Adin et al [10] varied the welding angle (60°, 75°, 90°), along with

voltage, current, speed, and gas flow rate, when welding cylindrical AISI 1040 medium

carbon steel, known for its strength, abrasion resistance, and ductility Results showed the highest tensile strength (597.963 MPa) and elongation (11.551%) at a 90° groove angle, 120A current, and 30V voltage The lowest tensile strength (395.125 MPa) and elongation (8.354%) were also recorded Changes in current and voltage significantly affected tensile strength and elongation ANOVA determined the groove angle as the most impactful parameter on average tensile strength (62.75%) and elongation (75.58%) Optimal parameters for ultimate tensile strength and elongation were identified using the S/N ratio

Diganta Kalita et al [23] aimed to enhance weld quality through tensile strength by

designing an experiment using Taguchi’s L9 orthogonal array They optimized welding current, voltage, and shielding gas flow rates for welding C20 steel (16mm diameter) with ER70S-4 material The results indicated that welding voltage significantly influenced both the mean value and variation of weld tensile strength, while welding current significantly affected only the mean value The shielding gas flow rate had a negligible effect on tensile strength

Nabendu Ghosh et al [18] used the Gray-Taguchi method to optimize welding

parameters such as current, gas flow rate, and nozzle-to-plate distance for welding 316L stainless steel with ER 316L filler rod Their study found that electric current greatly influenced joint quality, while gas flow rate and nozzle-to-plate distance had minimal impact

In addition to tensile tests, weld quality was assessed through visual inspection and microscopic analysis Some samples exhibited defects like dents, holes, blotches, poor penetration, low porosity, and lack of fusion, as revealed by visual and microscopic evaluations

With the same goal of optimizing the above parameters to improve the weld between AISI 409 and the same welding wire material, to achieve similar output values, Nabendu

Ghosh et al [19] welded AISI 409 plates (100x65x3mm) using Taguchi’s L9 orthogonal array

due to the material’s low cost and wide applications in household appliances Their experiments, evaluated through visual and x-ray observations, showed similar results to their previous study ANOVA results indicated that welding parameters did not significantly influence tensile strength and elongation The optimal conditions were the lowest levels of current, gas flow rate, and nozzle-to-plate distance Confirmation experiments validated these optimal results obtained using the Taguchi method This study highlights that many researchers have only experimentally investigated welding parameters such as voltage, current, speed, or angle

Kedir Beyene Behredin et al [15] optimized welding parameters for high-strength

steel EN 10149-2 S700MC, known for its unique physical properties and industrial applications, despite welding challenges Their study quantified the contributions of voltage, current, and speed to tensile strength as 83.24%, 13.14%, and 3.57%, respectively For weld zone hardness, the contributions were 62.27% (voltage), 30.52% (current), and 7.07% (speed) In the heat-affected zone, the current, voltage, and speed contributed 51.69%,

16.16%, and 16.10%, respectively SA Rizvi et al [37] researched 304H stainless steel welds,

changing parameters like shielding gas flow rate and wire feed speed to enhance weld quality They found that increasing welding current improved weld strength and initially increased ultimate tensile strength before it decreased Grain size increased with heat input, while

microhardness decreased sharply from low to high heat input Raja Subramanian et al [42]

also aimed to improve weld quality, finding that tensile strength increased with current, voltage, and speed up to a saturation point, beyond which further increases led to defects like excessive penetration, incomplete penetration, and incomplete fusion, reducing tensile strength

Many studies use the Taguchi method, analysis of variance, or the Grey-Taguchi method to optimize welding parameters such as current, voltage, shielding gas flow, and speed Some also optimize parameters like nozzle-to-plate distance and welding angle These parameters affect weld quality indicators like tensile strength, microhardness, microstructure, and elongation This research focuses on welding C20 steel and SUS201 stainless steel using robots, varying current, voltage, speed, and stick-out length while holding other factors constant The Taguchi L16 orthogonal array setup will be used to optimize these parameters for the best weld quality, with tests on tensile strength, flexural strength, elongation, elastic modulus

To solve that problem, our team chose the topic “Research on The Effects of Mig

Welding Mode on Weld Quality of C20 Steel and SUS 201 Stainless Steel” to conduct a

survey and make comments and practical applications

1.2 Scientific and practical significance of the study

1.2.1 Scientific significance of the study

- Research to investigate the basic factors affecting MIG welding mode on two different materials: C20 steel and SUS201

- Evaluate the strength, hardness, microstructure, etc of the weld, thereby drawing conclusions and applying it to production

1.2.2 Practical significance of the study

Currently, MIG welding technology has become increasingly popular and widely used

to weld materials However, welding two different materials is still difficult for many people, especially those new to the profession This research will help improve the selection of more effective MIG welding parameters when welding between two different materials, specifically C20 steel and SUS201 stainless steel At the same time, the research also helps

to better understand welding of two different materials and thereby helps reduce errors in the process of selecting welding parameters

1.3 Aims of the study

- Investigate the parameters affecting MIG welding mode with two different materials using the Taguchi method

- Compare experimental results with previous results, then make comments

- Provide effective solutions to save costs and time as well as simplify processes

- Understand the influence of parameters in the MIG welding process for research to improve the process more effectively

1.4 Object and range of the study

1.4.1 Object of the study

- MIG welding technology

- Steel materials C20 and SUS201

- MIG welding parameters

- Flexural strength, tensile strength, elongation and elastic modulus of the material

1.4.2 Range of the study

- Learn the operating principles of welding robots, tensile strength tester, bending tester, microstructure

- Learn about welding mode, MIG welding slag

- Calculate experimental layout for the project

- Analyze, evaluate and propose improvement plans after obtaining experimental results

1.5 Research methods

1.5.1 Methodology

- Based on the growing need to connect steel and stainless steel materials

- Based on MIG welding technology, which is being used very commonly today

- Inherit and expand previous experimental results

1.5.2 Specific research methods

- Read books and newspapers, collect data, determine sample size, and arrange experiments

- Research the experimental results of previous experiments

- Calculate and select welding parameters appropriate to laboratory conditions

- Conduct trial experiments

- Evaluate the results of trial experiments then conduct mass experiments

- Compare experimental results with previous studies, thereby making comments and improving experimental procedures to optimize

1.6 Structure of the study

- Chapter 1: Introduction

- Chapter 2: Theoretical Background

- Chapter 3: Experimental Design

- Chapter 4: Results and Discussion

- Chapter 5: Conclusion and Development Direction

CHAPTER 2 THEORETICAL BACKGROUND

2.1 Introduction to alloy steel material C20

2.1.1 Alloy steel C20

C20 steel is a type of alloy steel with a carbon content ranging from 0.18% to 0.23%

It is widely used in the mechanical engineering, construction, hot forging, seamless steel tube manufacturing, and other machinery components industries C20 steel conforms to the JIS G4051 – S20C standard, applied in the steel industry of Japan It is produced through various methods such as: the forging process, Blast Furnace Process, Heat Treatment Process (Basic Oxygen Process – BOP), Hot Rolling Process, Cold Rolling Process, and Casting Process With high strength, good ductility, and excellent machinability, C20 steel has become a

popular material choice in various industrial applications [50][17][8]

2.1.2 Characteristics of C20 alloy steel

Yield Strength: > 245 MPA The maximum stress S20C steel can endure without

permanently deforming Beyond this point, the steel will deform rapidly without an increase

in stress [50][17][8]

Tensile Strength: > 400 MPa The tensile stress C20 steel can withstand before

cracking or breaking, crucial for understanding its load-bearing capacity in practical

applications [50][17][8]

Elongation: > 28 % Measures the steel’s ability to stretch before breaking Important

for applications requiring flexibility and deformation, such as construction and mechanical

engineering [8]

Hardness: 116 – 174 HB Indicates resistance to impacts and scratches Determined

by measuring the indentation from a steel ball under a fixed force, crucial for evaluating the

steel’s durability in various applications [8]

2.1.3 Composition of C20 steel

Table 2.1: Composition of C20 Steel according to JIS G4051 Standard [50][8]

Chemical Composition Carbon (C) Silicon (Si) Manganese (Mn) Phosphorus (P) Sulfur (S)

0.18 - 0.23% 0.15 - 0.35% 0.3 - 0.6% < 0.03% < 0.035%

Copper (Cu) Chromium (Cr) Nickel (Ni) Iron (Fe) Ni + Cr

< 0.3% < 0.2 % < 0.2% Rest < 0.035%

2.1.4 Applications of C20 alloy steel

C20 alloy steel, also known as C20 steel, finds widespread applications in various fields due to its flexibility and excellent load-bearing capabilities Here are some common applications of C20 alloy steel:

Mechanical Engineering: Used in the production of machine components such as

shafts, gears, bearings, and load-bearing and wear-resistant parts in machinery and mechanical equipment

Construction and Building Industry: Utilized in structural elements such as columns,

beams, and framework, as well as in the manufacturing of construction accessories like pipes, steel plates, and structural materials

Hot Forging: Employed in the manufacturing and processing of hot-forged products

such as shafts and wear-resistant tool bits

Seamless Steel Tubes: Used to produce seamless steel tubes widely employed in the

oil and gas, energy, and chemical industries

Plastic Molding Dies: Used for making molds in the plastic production process Manufacturing Machine Components: Produced for a diverse range of parts and

components in various industries

These applications are just a few examples and not an exhaustive list The versatility and flexibility of C20 alloy steel make it a preferred material in many industrial sectors

Figure 2.1: Some Examples of Applications of C20 Steel [51]

2.1.5 Distinguishing C20 steel from other types of steel

To differentiate C20 steel from other types of steel, various criteria can be considered

[8]:

Chemical Composition: C20 steel is classified in the low carbon steel group, with a

carbon content higher than medium carbon steel (C: 0.23% – 0.6%) and high carbon steel (C

> 0.6%) Additionally, the content of alloying elements in C20 steel is generally lower than

in other alloy steels, such as chrome (Cr), nickel (Ni), manganese (Mn), molybdenum (Mo), titanium (Ti), copper (Cu), etc., which often have values exceeding 2.5%

Mechanical Properties: C20 steel typically exhibits a tensile strength greater than 402

MPa, hardness in the range of 116 to 174 HB, and good toughness Compared to low carbon steel, it shows higher strength and hardness, though still lower than high carbon steel and alloy steel This characteristic is coupled with better machinability compared to high carbon steel and alloy steel

Color and Form: C20 steel usually has a metallic gray color and is corrosion-resistant,

unlike stainless steel Produced through the hot rolling process, it may appear in the form of solid round bars or cast tubes

2.2 Introduction to stainless steel material SUS201

2.2.1 Stainless steel SUS201

SUS201 is a type of stainless steel (Inox) belonging to the Austenitic family, also known by other names such as AISI 201 It is characterized by its main components, Manganese (Mn) and Nitrogen (N), with a lower Nickel (Ni) content compared to many other types of stainless steel This results in stability and lower cost for SUS201 due to the flexible substitution of Manganese for Nickel

Although SUS201 has lower corrosion resistance compared to SUS304, this makes it more versatile in various applications Its characteristics of good ductility and excellent machinability contribute to its popularity in many industries, especially in the production of household appliances, automatic doors, and other mechanical components The diversity and flexibility of SUS201 make it a useful material for numerous applications, offering low cost and excellent processability

2.2.2 Characteristics of stainless steel SUS201

Tensile Strength: The minimum tensile strength of stainless steel SUS201 is 515 MPa,

depending on the manufacturing process and heat treatment This is the stress the material can

endure before cracking or fracturing [12][20]

Elongation: SUS201 typically has an elongation of 40%, indicating its ability to resist

cracking and its flexibility under tensile forces This makes it ideal for applications in mechanical engineering, household appliances, and machinery manufacturing, where

flexibility and ductility are crucial [12][20]

Hardness: The maximum hardness of SUS201 is 95 HRB or 217 HB, balancing

strength and scratch resistance This makes it suitable for various industrial and daily

applications [12][20]

Thermal Conductivity: SUS201 has moderate thermal conductivity, effectively

transmitting heat from high-temperature to low-temperature areas [12]

Machinability: SUS201 is easily processed into products like tubes, sheets, and wires

through methods such as cutting, welding, and grinding [12]

2.2.3 Composition of stainless steel SUS201

The primary chemical composition of stainless steel SUS201 includes:

Carbon (C): ≤ 0.15% , Silicon (Si): ≤ 1.00%, Manganese (Mn): From 5.50% to 7.50%, Phosphorus (P): ≤ 0.060%, Sulfur (S): ≤ 0.030%, Nickel (Ni): From 3.50% to 5.50%,

Chromium (Cr): From 16.00% to 18.00%, Nitrogen (N): ≤ 0.25% [12][20]

These components play a crucial role in conveying essential properties to SUS201, including strength, corrosion resistance, ductility, and other characteristics This favorable combination makes it suitable for various applications, from industrial use to daily life

2.2.4 Applications of stainless steel SUS201

Due to its combination of mechanical and chemical properties, stainless steel SUS201 has found widespread applications in various fields

Mechanical Engineering: SUS201 is used for manufacturing machine components like

bearings, shafts, and load-bearing parts It's also employed in producing aesthetically pleasing mechanical products, such as decorative materials for various applications

Household Appliances and Furniture: SUS201 is used in household products like

pans, pots, sinks, and stove control panels It is also utilized in furniture items, including door handles, decorative pipes, and accessories, creating high-quality, aesthetically pleasing products

Construction and Architecture: SUS201 stainless steel is used in constructing

structures like gates, railings, and signage It is integrated into both interior and exterior architectural designs, ensuring a blend of quality and design

Food and Medical Industry: SUS201 is used in food industry equipment such as ice

cream machines and steam tables, as well as food contact materials It is also employed in the production and installation of medical equipment and tools

Chemical Industry and Oil & Gas: SUS201 is crucial for making pipes and equipment

used in the chemical and oil & gas industries It is also used to manufacture parts resistant to abrasion and corrosion in challenging industrial environments

Electronics and Electrical Industry: SUS201 is used in producing electronic

components like water conduits, machine casings, and technical parts It is also common in electrical components such as LED lights and compact electronic devices

Figure 2.2: Some Examples of Applications of SUS201 [52]

2.2.5 Distinguishing stainless steel SUS201 from other steel types

Distinguishing SUS201 from other stainless steels can be based on the following factors:

Chemical Composition: Stainless steel SUS201 is primarily composed of Manganese

(Mn) and Nitrogen (Ni), with a lower Nickel (Ni) content compared to many other stainless steel

Color and Surface Shine: SUS201 stainless steel typically has a shiny metallic gray

color This can be used as a relative indicator, although this method is not entirely accurate

Magnetic Testing: SUS201 stainless steel exhibits non-magnetic properties A magnet

can be used to test whether it adheres to the material

Acid Testing: SUS201 is generally resistant to weak acids, such as acetic acid Testing

can be conducted by applying a small amount of acetic acid (found in vinegar) to the steel surface and observing the reaction

Density Testing: SUS201 has a relatively light density compared to some other steel

types

2.3 MIG welding technology

2.3.1 Overview of MIG welding technology in mechanical engineering

Figure 2.3: MIG Welding System [7]

Gas Metal Arc Welding (GMAW), also known as Metal Inert Gas (MIG) welding when using inert gases like argon, or Metal Active Gas (MAG) welding when using active gases like CO2, employs an electric arc to melt and fuse metal wires In Europe, it is

commonly referred to as MIG/MAG welding or simply MIG welding [44]

MIG welding is suitable for various metal sheet thicknesses, particularly thin sheets, due to its ease of starting and stopping, which enhances productivity Unlike Shielded Metal Arc Welding (SMAW) or Stick welding, MIG welding does not require frequent electrode

changes and produces no slag [44][4][6]

The main principle of MIG welding involves continuously feeding a metal wire into the welding area from the welding gun through a wire push mechanism This wire acts as both

a current-carrying electrode and an auxiliary material with the same composition as the welded metal The inert gas used for welding prevents the molten metal from reacting, effectively protecting the weld area For welding stainless steel, using Argon gas with 2% O2 stabilizes the weld For low alloy steel, an Argon-CO2 gas mixture is optimal, providing a well-shaped weld, deep penetration, and minimal metal splashing However, MIG welding

can be challenging in windy conditions as it affects the protective gas compound [44][4][6]

2.3.2 Principles of MIG welding process

Figure 2.4: The principle of MIG welding [44]

1 Electric arc; 2 Electrode; 3 Reel or drum; 4 Drive rollers;

5 Flexible conduit; 6 Hose package; 7 Welding gun; 8 Power source;

9 Contact tip; 10 Shielding gas; 11 Shielding gas nozzle; 12 Weld pool

Figure 2.4 illustrates the fundamental process of MIG welding The molten welding

wire is automatically fed continuously into the workpiece, while inert gases are supplied around the electrode to protect and shield the metal and heat-affected zone from the surrounding environment

The ionized supply gas creates an arc between the welding wire and the workpiece The wire is fed from a feeder at several meters per minute through driven rollers to the welding

gun [44][1]

The power source supplies current to the electrode via the contact tip in the gun, with the wire as the positive pole and the workpiece as the negative Typically, a DC electrode

with constant voltage allows arc length adjustment via the voltage setting [1][44]

Welding robots are now widely used, offering automated, flexible welding for any position and material They enhance productivity with continuous operation and diverse

movements, improving welding efficiency [1][44]

2.3.3 The welding arc

The welding arc consists of an anode, cathode, and arc column, formed by electric discharge between electrodes with current flowing through ionized plasma The arc's voltage drop and current determine power release, melting the electrode and joint surfaces Plasma ionization maintenance depends on the shielding gas, with different gases requiring varying temperatures Helium causes higher voltage drops and more heat input Heat is lost near

electrodes and workpiece surfaces due to conduction Figure 2.5 shows significant voltage

drops in the arc regions

Figure 2.5: The voltage distribution in the arc [44]

2.3.4 Shielding gas

A shielding gas serves the purpose of safeguarding the molten metal from detrimental effects caused by exposure to the air Even a small percentage of oxygen in the air can cause oxidation of the alloys in the welding area, leading to the formation of welding slag Nitrogen

as it solidifies, the solubility decreases and the gas evaporates which can lead to the formation

of pores Nitrogen can also contribute to brittleness Moreover, the shielding gas significantly influences welding properties, playing a crucial role in penetration and determining the

geometry of the weld bead [44][4][6][1]

• Argon (Ar)

Argon is a popular protective gas in welding due to its inert properties, making it suitable for materials like stainless steel and aluminum Argon can be combined with CO2 or O2 to enhance welding, especially in short arc welding It's also recommended for alloys such

as nickel, copper, aluminum, titanium, and magnesium, as it increases the transfer efficiency

of welding wire metal into the weld puddle[44][4][6][1]

• Helium (He)

Helium, similar to argon, is used in protective gas mixtures, particularly for steel and aluminum Its thermal conductivity provides higher heat input, resulting in wider but shallower welds Helium is often mixed with argon for welding thick-walled materials (over 25mm) like aluminum and copper, improving arc stability and preventing corrosion

However, helium is costly and has low density [44][4][6][1]

• Carbon Dioxide (CO 2 )

Pure CO2 is popular in short arc welding, especially galvanized steel welding, with good protection and cost savings The limitation is that higher sparks may occur and cannot

be used for spray arc welding [44][4][6][1]

Table 2.2: Application of Shielding Gas to Weld Metal [6]

Shielding gas

Welding metal Low alloy

steel

Stainless Steel

Aluminum (Alloy) Nickel Titanium

Copper alloy

MIG welding is often used for carbon and low alloy steel

Welding wire with diameter from 0.6 to 1.6 mm: 0.6; 0.8; 0.9; 1.1; 1.2; 1.4; 1.6 According to AWS standards, welding wire is denoted as follows:

ER 70 S – 3 [4]

E – Electrode conducts electricity

R – Rod adds metal to the weld

70 minimum tensile strength of the weld metal, measured in ksi –

ER70–S2: welding wire with high Si and Mn content In addition, it also contains some other deoxidizing elements such as Al, Zircon, and Titanium This type of welding wire can

be used for both single-layer welding and multi–layer welding

ER70–S3: has average Si and Mn content, used for single-layer or multi-layer welds This is the most commonly used type of welding wire

ER70–S4: has higher Si and Mn content than ER70-S3 Can be used for single–layer and multi–layer welds

ER70–S6: has high Si and Mn content, used for materials with high oxidation potential Can be used for single-layer and multi-layer welds

ER70–S7: has higher Mn content but lower Si content than ER70–S6, good for use with a mixture of Ar and CO2 protective gases

• Wire size

Wire size directly affects the quality of the weld, which determines the welding parameters Usually, the size of the welding wire is often determined by the current used during the welding process However, unlike stick electrodes, each wire can operate over a

fairly wide and possibly overlapping current range Table 2.3 shows the selection of welding wire with corresponding current [44]

Table 2.3: Welding wire size with corresponding current [4]

Wire diameter (mm) Welding current range (Amperes)

0.8 40 – 145 0.9 50 – 180 1.2 75 – 250

In general, using thinner wire will result in smoother material transfer When soldering with soft wire, wire feeding problems can easily occur when the wire is thin To overcome

the above disadvantage, using wires with larger diameters will be more optimal[44][1]

• Welding voltage

Welding voltage is crucial in MIG welding as it determines the type of metal transfer The appropriate voltage depends on factors like the thickness of the part, type of weld, electrode size and composition, protective gas, and welding position Higher arc voltage results in a longer arc and flatter welds, while lower voltage creates a shorter arc and

protruding welds Voltage affects arc stability and metal splatter [44][1]

For thin plates, short arc welding enables high speeds without burning Achieving the right voltage may require several test welds, starting with a calculated or reference value and

adjusting based on the weld line's appearance [44][4]

In positions that endure significant fatigue, like fillet welds, the weld should have a low profile with smooth edges or be multilayered A high bead profile can lead to insufficient

adhesion [44][4][1]

• Wire feed speed and current

As the welding current increases, the wire feed rate, flow rate, weld width, and weld penetration also increase For the same current, a smaller welding wire will melt more quickly The choice of welding current depends on the wire size, welding speed, and joint thickness With a power source with hard external characteristics (constant voltage), increasing the current will increase the wire feed speed, and vice versa Too low a current results in insufficient penetration and reduced weld strength, while too high a current causes metal

splashing, porosity, deformation, and uneven welds [43][6][4]

Figure 2.6: Relationship between wire speed and welding current [6]

• Welding speed

From a productivity standpoint, maximizing welding speed is advantageous There is

a general tendency that higher speed results in a narrower weld, and at excessively high

speeds, the tolerance for variations in all parameters will decrease [44][4]

• Gas flow rate

The gas flow must be tailored to the arc At low currents, 10 liters per minute may suffice, whereas higher welding currents may require up to 20 liters per minute Welding

aluminum typically requires more gas compared to steel [44][4]

• Wire stick-out length

The stick-out is the part of the welding wire extending outside the torch The contact tip-to-work distance affects current and penetration Increasing stick-out reduces current and heat input, decreasing penetration and risking lack of fusion Maintaining a constant stick-out

is crucial [4][6][44]

If the wire feed speed is constant, increasing the nozzle-to-weld distance heats the wire and reduces welding current Keep this distance between 10-20 mm during MIG welding to avoid issues Adjusting the wire stick-out length can affect welding current, especially for

stainless steel [1][4][6][44]

Too large a stick-out increases metal residue, reduces penetration, wastes weld metal, and lowers arc stability Too small a stick-out causes splashing, gas capture, obstructed gas

flow, pitting, and porosity [44][4]

Figure 2.7: Stick-out outside the welding torch (a) and welding current – electrode

extension relationship (b) [44]

2.3.6 Advantages, limitations, and applications of MIG welding technology

MIG welding technology offers significant benefits, notably enhancing productivity while minimizing heat input to the workpiece Its automation capabilities provide substantial convenience, leading to higher productivity compared to manual metal arc welding This is due to the seamless welding process without interruptions for filler rod replacement and the

reduction or elimination of slag chipping around the weld joint [4][44]

MIG welding is a particularly flexible method and covers a wide range of applications:

- MIG welding is ideal for plate thicknesses starting from 0.5 mm and beyond It manages low heat input well, preventing deformation in thin sheets and ensuring precise welds For thicker metals, MIG welding effectively applies filler passes with high productivity, maintaining quality Its adaptability across different thicknesses makes it

versatile for applications from intricate sheet metal work to heavy-duty fabrication projects

[4][6][44]

- MIG welding is compatible with all commonly encountered structural materials, including mild, low-alloy, and stainless steel, aluminum and its alloys, and several other non-

ferrous metals It is also effective for surface-coated metals, such as Zn-coated steel [4][44]

While MIG welding provides flexibility, it also presents numerous challenges, making

it a complex process to learn and apply Welding two thin metal pieces without specific quality demands can be user-friendly However, when high-quality standards are required—such as thorough welding, complete fusion, minimal porosity, and other factors—the MIG

welding process demands expertise and substantial experience [4][6]

2.4 Experimental methods and planning

Currently, there are many methods for setting conditions and conducting experiments for welding parameters These methods include level 1 and level 2 orthogonal planning, as well as the Taguchi experimental design method With the traditional orthogonal planning method, the number of experiments that need to be performed for research purposes is quite large For example, with a project including 3 welding parameters, each parameter has 3 – level design, even with experiments up to 33 = 27 Meanwhile, with the Taguchi method, only

9 experiments need to be performed, helping to save time and research costs Therefore, choosing the Taguchi method as a means to design experiments in this project is a reasonable choice [3][38]

2.4.1 Orthogonal array

An orthogonal array (more specifically a fixed-element orthogonal array) of s elements, denoted by OAN (sm) is an N × m matrix whose columns have the property that in every pair of columns each of the possible ordered pairs of elements appears the same number

of times The symbols used for the elements of an orthogonal array are arbitrary

Taguchi refers to OAN (sm) by the notation LN (sm) The letter L in this notation stands for latin square, and it indicates that orthogonal arrays are generalized latin squares Taguchi uses the symbols or numbers to denote the elements of an orthogonal array

An N × m matrix whose columns have the property that each possible ordered pair of elements occurs the same number of times is an orthogonal array (more precisely, a fixed-element orthogonal array) of s elements, denoted as OAN (sm) An orthogonal array’s elements are represented by arbitrary symbols

Taguchi uses the notation LN (sm) to refer to OAN (sm) Orthogonal arrays are generalized latin squares, as shown by the letter L in this notation, which stands for latin

square Taguchi indicates the elements of an orthogonal array with symbols or integers [3]

2.4.2 Signal-to-noise ratio

Signal-to-noise ratio is a measure of system quality and performance, usually calculated based on standard deviation In the Taguchi method, the S/N ratio is used to represent the system performance, and the optimal value of the S/N ratio usually corresponds

to the optimal values of the parameter changes The S/N ratio provides an effective way to evaluate the quality of the system during optimization, and the maximum value of the S/N

ratio is usually the optimal level of the parameter changes [3][5]

2.4.3 Analysis of variance

Analysis of Variance is a common statistical method used when it is necessary to compare the averages of at least three groups This method provides a clear view of the differences between groups and the importance of factors to the research objectives, helping

to assess the relative influence of factors and also assess their importance to research objectives This method analyzes the variance of an observation into two main components: variance between groups and variance within groups This helps understand how the variation

of the data is classified, with particular attention to differences between groups and variation

within each group [3][5][30]

s Number of levels in each column, maximum number of values that can be taken

on any single factor

m Number of columns in the array, which translates into a maximum number of

variables that can be handled

Each row of the orthogonal array represents a particular experiment in the research object, and each column represents an experimental factor and the levels of influence on it The orthogonal array is chosen so that all experimental configurations are balanced and statistically independent, helping to minimize the number of experiments that need to be

performed while still ensuring the reliability of the results [5][30]

The characteristics of orthogonal arrays are expressed as [3][5][30][38]:

Numbers in the array and levels of factors: Numbers in the array are often expressed

in the form Lk where L is the number of levels of each factor, and k is the number of factors

This number describes the total number of test conditions in the array

Rows and test conditions: Each row of the array represents a specific test condition,

with each cell in the row containing a value of the corresponding factor This defines the specific assumptions and conditions of each test

Columns containing elements: Each column of the array corresponds to an element

being studied The values in the column are the levels of that factor, and each level will appear

at least once in the array

The array’s columns are orthogonal: To ensure orthogonality, each pair of element

values must appear together at least once in the entire array This helps evaluate the impact

of each factor independently and synergistically

Arrays for a variety of experimental situations: An orthogonal array can be designed

to serve a variety of experimental purposes The specific test conditions can be varied by changing the values of the elements in each row

Results analysis: After collecting data from the test conditions, results analysis is

performed to determine the influence of each factor and their interactions

The columns in the array are designed to ensure orthogonality or balance, meaning that the number of levels of each element in a column is equivalent Similarly, there must be balance between any two columns, meaning each level of combination appears in equal numbers

In Taguchi, an orthogonal array N × m is formed from p (number of parameters) and l

(number of levels)

Example: A study that studies three welding parameters simultaneously: voltage, current and gas flow rate (with p = 3); each element has three levels (with l = 3), the suitable orthogonal array is the L9 (33) or L9 array as illustrated in Table 2.4

Table 2.4: Taguchi Experimental Plan for Array L9 (33)

Number of experiments Voltage Current Gas flow rate

Depending on the specific quality characteristics of the system, the S/N ratio is built

and converted to calculate for 3 main cases [5][30][38]:

- Smaller–the–better:

S/N = −10 log (1

n∑ yi2n

2.5 Methods of checking and evaluating welding quality

2.5.1 Research on structural components of welded joints

• Evaluation of appearance – weld shape

By using the naked eye, magnifying glasses and measuring tools, we can evaluate the weld coverage in detail after each advance in the work process At the same time, we can check the electrode marks, analyze cracks on the surface of the welding material and measure the exact size of the welded area This process helps ensure quality and uniformity during the

welding process [1]

• Evaluate the rough structure of the weld

To evaluate the deformation, size of the weld zone, heat affected zone, as well as check for defects such as cracks, pits, and uneven adhesion between the weld layer and the base layer, or between adjacent layers of auxiliary welding wire after each feed step, as well as between two adjacent areas after each welding electric pulse, rough inspection samples are collected from the welded structure Then, they are cut, ground and polished to eliminate the influence of heat and meet the technical requirements according to the standards of the test samples

This test sample processing process not only helps determine the quality of the welded

structure but also ensures full compliance with technical standards [1]

• Research on weld microstructure

Research focuses on the microstructure of the base metal, the weld metal, the interface between the weld metal and the base metal, as well as the heat-affected zone to observe the microscopic structure and evaluate the composition of the metal phases, the size of the phases, and their distribution in the weld and heat-affected zone

From the information obtained from the microstructure, research can evaluate the bonding ability and hardness of the weld layer At the same time, this process also helps detect defects such as cracks, pits, or other problems that exist in the structure of the weld and the heat-affected zone This provides important information to ensure quality and uniformity in the welding process, as well as to develop repair methods and improve the performance of

welded structures [1][7]

2.5.2 Method for determining the durability of the weld bond with materials