Investigate On Mild Steel Spot Welding Strength Effect By Using Design Of Experiment(DOE).

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INVESTIGATE ON MILD STEEL SPOT WELDING STRENGTH EFFECT BY USING DESIGN OF EXPERIMENT (DOE)

SYED MOHD AFIQ BIN SYED HASSAN

This report is submitted in partial fulfillment of the requirements for the award Bachelor of Mechanical Engineering (Design and Innovation)

Faculty of Mechanical Engineering Universiti Teknikal Malaysia Melaka

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SUPERVISOR DECLARATION

“I hereby declare that I have read this thesis and in my opinion this report is sufficient in terms of scope and quality for the award of the degree of Bachelor of Mechanical

Engineering (Design and Innovation)”

Signature : ... Supervisor : Dr. Hady Efendy

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DECLARATION

“I declare that this report entitled “Investigate on Mild Steel Spot Welding Strength Effect by using Design of Experiment (DOE)” is the result of my own research except as

cited in the references”

Signature : ……….

Author’s Name : Syed Mohd Afiq Bin Syed Hassan

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iii

DEDICATION

Highest Special Thankful Wishes to Both My Lovely Father and Mother

Syed Hassan Bin Syed Mohamaad &

Zaliha Bt. Anang

Also

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ACKNOWLEDGEMENT

Firstly, thousands of thankful wishes to ALLAH S.W.T because with His permissions, I am able to complete my Final Year Project report (BMCU 4974) without many problems and difficulties.

Next, I would like to thank my supervisor, Dr. Hady Efendi, who has willing to offer his support throughout my final year project and until this report is completed. He has never stop to support me in the best way through finding the information about my project and also on the problem solving methods. He is also very kind to contribute his time and patience to guide me to complete my project. His experience in this related topic is so valuable in my case study. Also thanks to Dr. Zulkefli and for willing to help me on using Minitab Statistical Software as this is the first time I am using the software. Lot of thanks to UiTM master student Mr. Mohammad Ridzwan Bin Abdul Rahim that were help me to teach me how to analyze the result using Minitab Statistical Software and give an idea on this study topics as I need to complete my final year project task.

Apart from that, thankful wish also to all lecturers, classmates, all my friends no matter in UTeM or other places, and also them who has contributed in helping me to finish my PSM project and report. A lot of thanks also to UTeM librarian staffs for their guidance and advices when I went to library to complete my research

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Not to forget, thankful wishes to my family who kept supporting me in giving advices and moral support so I became stronger and more determined to finish this project. All the useful experiences that I had gained and learned really give me many experiences which will be useful when I am in working fields in future.

Lastly, I once again want to thank those who had given their cooperation directly or indirectly in helping me to finish this final year project and the report of Investigate on Mild Steel Spot Welding Strength Effect by using Design of Experiment (DOE). Thank You.

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vi ABSTRAK

Proses kimpalan rintangan titik adalah salah satu proses penyambungan logam yang penting terutamanya di industri automotif. Proses kimpalan rintangan titik memerlukan parameter yang telah ditentukan oleh pengguna kimpalan titik seperti arus elektrik atau kuasa elektrik, kitaran masa dan tekanan. Dalam kajian ini, parameter-parameter kimpalan rintangan titik akan dianggarkan menggunakan perisian statistik Minitab melalui kaedah rekabentuk eksperimen (DOE). Parameter-parameter tersebut perlu ditetapkan nilai atas dan bawahnya. Dengan menggunakan kaedah rekabentuk eksperimen (DOE), parameter-parameter tersebut dapat dioptimasikan dan mempunyai gabungan parameter yang mencapai kualiti sasaran. Analisis dari rekabentuk eksperimen (DOE) boleh menunjukkan kepentingan parameter-parameter yang digunakan sama ada ia memberi kesan ataupun tidak dalam perubahan kualiti dan kekuatan pada produk tertentu.

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vii ABSTRACT

Spot welding is one of the metal joining processes that mainly use in the automotive industries. Spot welding process needed parameters that been define by the user such as power or current, time cycle, and pressure. In this study, parameters of the welding will be estimated using Minitab Statistical Software by Design of Experiment (DOE) method. The parameters will be set to high and lower value. By using DOE method, the parameters can be optimize and having the best parameters combination for target quality. The analysis from DOE method can give the significance of the parameters as it give effect to change of the quality and strength of product or does not.

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viii

TABLE OF CONTENT

CHAPTER TITLE PAGE

SUPERVISOR DECLARATION i

DECLARATION ii

DEDICATION iii

ACKNOWLEDGEMENT iv

ABSTRAK vi

ABSTRACT vii

TABLE OF CONTENT viii

LIST OF FIGURES xi

LIST OF TABLES xiii

LIST OF ABBREVIATIONS xiv

CHAPTER 1 INTRODUCTION

1.1 Background of the project 1

1.2 Objectives of the project 3

1.3 Problem Statement 3

1.4 Scope of the project 4

CHAPTER 2 LITERATURE REVIEW

2.1 Welding viii

2.1.1 Selection of Welding Process 9 2.1.2 Welding Quality and Performance 10 2.3 Design of Experiment (DOE) 12

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CHAPTER TITLE PAGE

2.3.1 Fractional Factorial Design 13 2.3.2 Response Methodology Surface (RSM) 15 2.3.3 Path of Steepest Ascent (POA) 20

CHAPTER 3 METHODOLOGY

3.1 Introduction 23

3.2 The Study 24

3.2.1 Methodology 26

CHAPTER 4 DATA AQUISITION

4.1 Introduction 27

4.2 Operational Framework 28

4.3 Specimen Selection 29

4.4 Specimen Preparation 29

4.4.1 Procedure for Specimen Preparation 31

4.5 Spot Welding Process 33

4.5.1 Resistance Spot Welding Machine 33 4.5.2 Machine Operation 34

4.6 Experiment Procedure 35

CHAPTER 5 RESULT

5.1 Introduction 36

5.2 Observation Data 36

5.3 Tensile Sheat Test 38

5.3.1 Tensile Shear Test Data Collection 38

CHAPTER 6 DISCUSSION

6.0 Introduction 41

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CHAPTER TITLE PAGE

6.1.1 Factorial Design 43

6.2 Mathematical Modeling 51

6.3 Response Optimizer 51

6.4 Main Effects 53

CHAPTER 7 CONCLUSION AND RECOMMENDATION

7.1 Introduction 58

7.2 Conclusion 58

7.3 Recommendation 60

REFERENCES 61

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LIST OF FIGURES

NO. TITLE PAGE

Figure 1 Master Chart of Welding and Applied Processes 6 Figure 2.1 Half fractional and full factorial design 14 Figure 2.2 Response Surface Methodology 18

Figure 2.3 Contour plot 19

Figure 2.4 Path of Steepest Ascent 20

Figure 3.1 Basic module of design process 25 Figure 3.2 Methodology flow chart of the project 25

Figure 4.1 The operational framework 28

Figure 4.2 Shape of the specimen 30

Figure 4.3 Procedure for specimen preparation flow chart 31 Figure 4.4a Resistance spot welding machine control panel 33 Figure 4.4b Resistance spot welding machine specification 33 Figure 4.5 Machine Operation Flow Chart 34 Figure 4.6 Experiment Procedure Flow Chart 35

Figure 5.1 Align specimen 38

Figure 5.2 Tensile stress versus time graph 40 Figure 6.1 Tensile stress versus extension at max load graph 42 Figure 6.2a Effect plot for top spot welding diameter 44 Figure 6.2b Effects Pareto for top spot welding diameter 44 Figure 6.3a Effect plot for bottom spot welding diameter 45 Figure 6.3b Effects Pareto for bottom spot welding diameter 46 Figure 6.4a Effects plot for overlapped thickness 47

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xii

NO. TITLE PAGE

Figure 6.4b Effects Pareto for overlapped thickness 47 Figure 6.5a Effects plot for tensile stress at max load 48 Figure 6.5b Effects Pareto for tensile stress at max load 49 Figure 6.6a Effects plot for tensile stress at yield load 50 Figure 6.6b Effects Pareto for tensile stress at yield load 50 Figure 6.7 Main effects plot for top spot welding diameter 53 Figure 6.8 Main effects plot for bottom spot welding diameter 54 Figure 6.9 Main effects plot for overlapped thickness 54 Figure 6.10 Main effects plot for max load 55 Figure 6.11 Main effects plot for extension at max load 56 Figure 6.12 Main effects plot for tensile stress at max load 56 Figure 6.13 Main effects plot for tensile stress at yield load 57

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xiii

LIST OF TABLES

NO. TITLE PAGE

Table 1 Shielding Gas Selection Chart 11 Table 4.1 Dimension for test specimen 30

Table 4.2 Experiment parameters 32

Table 5.1 Variables Data 37

Table 5.2 Observation Result 37

Table 5.3 Tensile Shear Test Result 39

Table 6.1 Variable and response set 42

Table 6.2 ANOVA table for top spot welding diameter 43 Table 6.3 ANOVA table for bottom spot welding diameter 45 Table 6.4 ANOVA table for overlapped thickness 46 Table 6.5 ANOVA table for tensile stress at max load 48 Table 6.6 ANOVA table for tensile stress at yield load 49 Table 6.7 Response optimization parameters 52

Table 6.8 Global solution 52

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xiv

LIST OF ABBREVIATIONS

DOE - Design of Experiment JIS - Japanese Industrial Standard BS - British Standard

twd - Top Spot Welding Diameter bwd - Bottom Spot Welding Diameter lt - Overlapped Thickness

ML - Max Load YL - Yield Load

Seq SS - Sequence Sum of Square Adj SS - Adjusted Sum of Square Adj MS - Adjusted Mean of Square

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1 CHAPTER 1

INTRODUCTION

1.1 Background of The Project

Nowadays, development of technologies provides us an extra change and awareness in technology which lead to specific changes in economic and socio-cultural values. Along with the change in values, the society becomes more focus from production to information and creativity. As the result, the consumer of this era has started to access creativity and innovation.

Welding technology is one of the joining processes that are widely used in the modern manufacturing technology such as shipbuilding, automotive industry, bridges and more. It is also well-known that the welding distortions defects are always occur during the welding process due to the non-uniform expansion and contraction of the weld and the surrounding base material. The welding distortion and defects not only degraded the welding quality but also increasing the production cost. Therefore, the prediction and control of welding distortion and defects have become of critical importance in industries producing welded structures.

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components that are weld together due to heat created by electrical resistance. This process may be performed manually, robotic or by dedicated spot welding machine. The spot welding process take the shortest time comparing to the other type of welding process.

Weld that was done by spot welding process is discrete wed locations that look like small circles on the assembled components. This weld process is not continuous. In spot welding there are several variables involve in the process such as current, pressure, human element, type of material, material thickness, welders condition, material surface and electrode tip surface. Some of the spot welding machines were use power instead current. To achieve to good quality of spot welding start with a good process design that minimize the variables during the process.

Up to now, there a lot of study on the statistical method of getting the best parameters for welders, such as (Casalino, Curcio et al.) were investigates laser welding by using statistical and Taguchi approaches.

Design of Experiment (DOE) can be defined as a systematic problem-solving approach to engineering that applies principles and technique at the data collection stage to ensure the generation of valid defensible and supportable engineering conclusions. All of this carried out can reduce expenditure of engineering runs, time and money.

By understanding this scenario of the current needed. This project were pointed on investigating on spot welding strength effect in getting the optimize parameters as the one part to improve the parameters selection to get the best strength by using Design of Experiment (DOE) method.

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This study aims to explore the role of the statistical modeling methods such as ANOVA, Taguchi approaches and Design of Experiment (DOE) on analyzing the parameters as the parameters that will affect spot welding quality. The primary interest is the parameters that give main effect to the welding quality and strength. The objectives of this project are:

i. To study the spot welding and the factors affecting the good spot welding quality.

ii. To analyze the spot welding parameters as the main effect of the welding strength by using statistical modeling.

iii. Using Design on Experiment to estimate good parameter of the spot welding variables.

1.3 Problem Statement

Spot welding is the major bonding technique that were widely use in automotive industry. 30% of the total amount of the joining part of the car was use spot welding as the joining technique due to difficulties to estimate welding parameters. The advantages of the resistance spot welding are high speed and suitability for automation and inclusion in high production assembly lines with other fabricating operations. Spot welding is a fast process that does not need any welding skill. Spot welding also have less probability on human error affect to the welding quality.

Several variables to control resistance spot welding in order to produce good quality welding are weld current, welding pressure and time. Current, timing and electrode force were control automatically. This type of control can produces a very fast

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labor cost as it can be operate by unskilled operators.

1.4 Scope of The Project

This study is base on the statistical experiment modeling by combining various welding parameters. Scope of this project will be covering the case study through the literature review, journal finding and experimental for new combination of welding parameters.

By study the literature review and journal, the effect to the strength and quality of the welding in understood. These can give some information during develop a new combination of spot welding parameters. The output data is collected by a method as the mathematical model is produce during the end of this study. The method going to be use is Design of Experimental (DOE). Scopes of this project are:

1. Study will base on the best combination of parameters on mild steel by using spot welding machine as tool for welding.

2. By using Design of Experiment (DOE) method to get the combination of parameters and the number of experiment.

3. Study on power usage for spot welding, time cycle needed, and pressure use to get the best quality ant toughest strength.

4. Observe welding quality that occurs from the experiment as the reference to comparing with the welding strength to get the best quality

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5 CHAPTER 2

LITERATURE REVIEW

2.1 Welding

Today, it is clearly shows that the status of welding has now changed from skill to science. A scientific understanding of the material and service requirement of the joints is necessary produce successful welds which will meet the challenge of hostile service requirements.

Welding is a process of permanent joining between two materials through localized coalescence resulting from a suitable combination of temperature, pressure and metallurgical. It also depending on the combination of temperature and pressure, a wide range processes has been developed. American Welding Society has classified the welding process as shown in Figure 1.

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7 i. Gas Welding

• Oxyacetylene • Oxy hydrogen ii. Arc Welding

• Carbon arc • Metal arc • Submerged arc

• Inert gas welding (MIG and TIG) • Plasma arc

• Electro-slag

iii. Resistance Welding • Spot welding • Seam welding • Projection welding • Butt welding • Induction welding iv. Solid State Welding

• Friction welding • Ultrasonic welding • Explosive welding

• Forge and diffusion welding v. Thermo-chemical Welding

• Thermit welding • Atomic H2 welding

vi. Radiant Energy Welding • Electron beam welding • Laser beam welding

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proximity and activity between the molecules of the pieces being joined, sufficient to cause the formation of common metallic crystals. Proximity and activity can be increase by plastic deformation or by the melting the two surfaces so that the fusion occurs.

Solid state welding, surfaces are joined by mechanically or chemically cleaned to welding. Fusion welding, the contaminants are removed from the molten pool by the use of fluxes and in vacuum or in outer space the removal of contaminant layer is quite easy and welds are formed under light pressure.

Surfaces contaminants may be organic film, absorbed gases and chemical compounds of the base metal. Heat when used as a source of energy, effectively removes organic films and adsorbed gases and only oxide film remains to be cleaned. Fluxes are used to clean the oxide film and other contaminants to form slag which floats and solidifies above the weld bead protecting the weld from further oxidation.

To protect the molten weld pool and filler metal from atmospheric contaminants such as oxygen and nitrogen, shielding gas need to be used. This shielding gas would be argon, helium, carbon dioxide or combination of argon and helium with carbon dioxide supplied externally. Carbon dioxide can also be produced by the burning of flux coating on the consumable electrode which supplies the molten filler metal to the weld pool.

When the molten metal solidified, the microstructures formed in the weld and the heat affected zone (HAZ) region determines the mechanical properties of the joint produced. The cooling rate in the weld and HAZ regions can be control by post welding heat-treatment and pre-heating and thus control the microstructure and properties of the

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9 weld-metal properties.

2.1.1 Selection of Welding Process

A weld should achieve a complete continuity between the parts being joined such that the joint is indistinguishable from the metal in which the joint is made. An ideal situation is unachievable but welds giving satisfactory service can be made in several ways. The choice of the particular welding will depends on several factors, that is:

i. Type of metal and its metallurgical characteristics ii. Type of joint, its location and welding position iii. End use of the joint

iv. Cost production v. Structural size

vi. Desired performance

vii. Experience and abilities of man power viii. Joint accessibility

ix. Joint design

x. Accuracy of assemblies required xi. Welding equipment available xii. Work sequence

xiii. Welder skill

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process with high quality of welding and strength at high production rates and low unit labor cost as it can be operate by unskilled operators.

1.4 Scope of The Project

1. Study will base on the best combination of parameters on mild steel by using spot welding machine as tool for welding.

2. By using Design of Experiment (DOE) method to get the combination of parameters and the number of experiment.

3. Study on power usage for spot welding, time cycle needed, and pressure use to get the best quality ant toughest strength.

4. Observe welding quality that occurs from the experiment as the reference to comparing with the welding strength to get the best quality

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5 CHAPTER 2

LITERATURE REVIEW

2.1 Welding

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Figure 1: Master Chart of Welding and Applied Processes (http://www.newagepublishers.com/samplechapter/001469.pdf)

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7 Type of welding processes:

i. Gas Welding • Oxyacetylene • Oxy hydrogen ii. Arc Welding

• Carbon arc • Metal arc • Submerged arc

• Inert gas welding (MIG and TIG) • Plasma arc

• Electro-slag

iii. Resistance Welding • Spot welding • Seam welding • Projection welding • Butt welding • Induction welding iv. Solid State Welding

• Friction welding • Ultrasonic welding • Explosive welding

• Forge and diffusion welding v. Thermo-chemical Welding

• Thermit welding • Atomic H2 welding

vi. Radiant Energy Welding • Electron beam welding • Laser beam welding

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To obtain coalescence between two materials there must be a combination of proximity and activity between the molecules of the pieces being joined, sufficient to cause the formation of common metallic crystals. Proximity and activity can be increase by plastic deformation or by the melting the two surfaces so that the fusion occurs.

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welds produced. Deoxidants and alloying elements are added as in foundry to control the weld-metal properties.

2.1.1 Selection of Welding Process

i. Type of metal and its metallurgical characteristics ii. Type of joint, its location and welding position iii. End use of the joint

iv. Cost production v. Structural size

vi. Desired performance

vii. Experience and abilities of man power viii. Joint accessibility

ix. Joint design

x. Accuracy of assemblies required xi. Welding equipment available xii. Work sequence

xiii. Welder skill

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