Techniques in Welding Practices

Techniques in Welding Practices

Techniques in Welding Practices

Gopal Devar

Techniques in Welding Practices

Gopal Devar

ISBN - 9789361529245

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Preface

Welding is a crucial manufacturing technique in creating countless numbers of commonly used items. From buildings to bridges and cars to computers, many of these items would be virtually impossible to produce without the use of welding. This text is a concise, explanatory guide to commonly used and commercially significant welding processes. It describes processes and equipment applicable to all instruction levels and takes the novice or student through the individual steps involved in each process in a clear and comprehensible way.

Topics such as welded joint design, quality assurance, and costing are all covered in detail. The handbook provides an up-to-date reference on the significant welding applications as they are used in the industry. It is poised to become the leading guide to basic welding technologies for those new to the industry.

This book contains information obtained from authentic and highly regarded sources. Reprinted material is quoted with permission, and sources are indicated. Reasonable efforts have been made to publish reliable data and information. In writing the book, there has been a conscious effort to ensure that both text and illustrative material is clear, concentrating particularly on interesting and important aspects. My thanks are due to all those who have been involved in the work and helped in its successful completion.

Table of Contents

1 Arc Welding- an Overview 1

1.1 History of Welding 1

1.2 Terminology 5

1.2.1 Welding Methods 5

1.2.2 Basic Terms 5

1.2.3 Joint Types 6

1.2.4 Welding Positions 7

1.3 Distortion 7

1.4 The Welding Arc 8

1.4.1 Spray Arc 9

1.4.2 Short Arc 9

1.4.3 Magnetic Arc Blow 10

1.4.4 Possible Causes 10

1.5 Shielding Gases 12

1.5.1 Argon (Ar) 12

1.5.2 Helium (He) 12

1.5.3 Carbon Dioxide (CO2) 13

1.5.4 Hydrogen (H2) 13

1.5.5 Nitrogen (N2) 13

1.6 Power Sources 13

1.6.1 The Importance of the Power Source for

the Welding Process 13

1.6.2 Straight Characteristic (constant-voltage characteristic) 14

1.6.3 Self-regulation of the Arc 14

1.6.4 Setting the Current and Voltage 15

1.6.5 Dynamic Characteristic 16

1.6.6 Welding with Alternating Current 17

1.6.7 Different Types of Welding Power Units 18

1.6.8 Motor-generator Sets 18

1.6.9 The Welding Transformer 18

1.6.10 Welding Rectifier 19

1.6.11 Welding Inverters 20

1.6.12 Development Trends 20

1.6.13 Inverter Control 21

1.6.14 Electric and Welding Characteristics 21

1.6.15 Controllable Welding Characteristics 22

1.6.16 Computer Controls 22

1.6.17 Rating Data for Power Sources 23

1.6.18 The Standard for Welding Power Sources 24

1.6.19 Efficiency and Power Factor 25

1.6.20 Electrical Safety Requirements 25

1.6.21 Fire Risks 26

1.7 Exercise 27

2 Glass Welding 28

2.1 Equipment 28

2.1.1 Acetylene 29

2.1.2 Oxygen 29

2.1.3 Pressure Regulators 29

2.1.4 Gas Hoses 30

2.1.5 Flashback Arrester 30

2.1.6 Welding Torches 30

2.1.7 Gas Flames 31

2.1.8 Neutral Flame 31

2.1.9 Forehand and Backhand Welding 33

2.1.10 The Benefits of Gas Welding 34

2.2 Exercise 35

3 Tig Welding 36

3.1 A Description of the Method 36

3.2 Equipment 37

3.2.1 The Welding Gun 37

3.2.2 Striking the Arc 38

3.2.3 The Power Source 38

3.2.4 Square Wave Ac 39

3.2.5 Thermal Pulsing 39

3.2.6 Control Equipment 39

3.2.7 The Electrode 40

3.3 Consumables 41

3.3.1 Shielding Gases for Different Workpiece Materials 41

3.4 Exercise 43

4 Plasma Welding 44

4.1 A Description of the Method 44

4.1.1 Classification of Plasma Welding Methods 45

4.2 Equipment 47

4.2.1 Welding Torch 47

4.2.2 Power Source 47

4.2.3 HF Generator 47

4.2.4 Control Equipment 48

4.3 Gases for Plasma Welding 48

4.4 The Advantages of the Plasma Method 49

4.5 Exercise 50

5 Mlglmag Welding 51

5.1 Equipment 51

5.1.1 Wire Feed Unit 53

5.1.2 Welding Gun and Feeding Properties 53

5.1.3 Power Source 54

5.1.4 Cooling Units 54

5.2 Setting of Welding Parameters 55

5.2.1 Electrode Diameter 55

5.2.2 Voltage 55

5.2.3 Wire Feed Speed and Current 56

5.2.4 Welding Speed 56

5.2.5 Inductance 56

5.2.6 Electrode Extension 56

5.2.7 Choice of Shielding Gas 57

5.2.8 Gas Flow Rate 57

5.3 Consumables 59

5.3.1 Filler Wires 59

5.3.2 Solid or Cored Wires? 59

5.3.3 Welding Technology 60

5.3.4 Spray Arc Welding 61

5.3.5 Short Arc Welding 61

5.3.6 Globular Transfer 62

5.3.7 Pulsed MIG Welding 62

5.3.8 Cored Wire Welding 64

5.3.9 Equipment 65

5.3.10 Structure and Characteristics of Cored Wires 65

5.3.11 Applications 68

5.3.12 Single-wire Methods 69

5.3.13 Tandem and Twin-wire Welding 70

5.3.14 Arc Spot Welding 70

5.3.15 The Welding Environment 71

5.3.16 Fumes and Gases 72

5.3.17 Noise 73

5.3.18 Arc Radiation 73

5.3.19 Ergonomics 73

5.3.20 Spatter 74

5.3.21 Weld Quality 74

5.3.22 Joint Preparation 75

5.3.23 Striking the Arc 75

5.3.24 Pores 76

5.3.25 Lack of Fusion 77

5.3.26 End Craters 77

5.3.27 Post Weld Treatment 78

5.4 Exercise 78

6 Submerged Arc Welding 79

6.1 Description 79

6.2 Equipment 81

6.2.1 Power Sources 81

6.2.2 Arc Striking Methods 82

6.2.3 Mechanization Aids 82

6.3 Filler Material 84

6.3.1 Filler Wires 84

6.3.2 Flux 85

6.4 The Effect of the Welding Parameters 87

6.4.1 Welding Speed 87

6.4.2 Polarity 88

6.4.3 High Arc Voltage 88

6.4.4 Welding Current 89

6.4.5 Wire Size 90

6.4.6 Wire Angle 90

6.5 Productivity Improvements 91

6.5.1 Tandem Welding 91

6.5.2 Twin Arc Welding 91

6.5.3 Long Stick Out 92

6.5.4 Cold Wire 93

6.5.5 Hotwire 94

6.5.6 Metal Powder Additive 94

6.6 Joint Preparation 95

6.7 Risks of Weld Defects 96

6.7.1 Hydrogen Embrittlement 96

6.8 Exercise 101

7 Welding Methods 102

7.1 Pressure Welding Methods 102

7.2 Resistance Welding 102

7.2.1 Spot Welding 103

7.2.2 Important Parameters of Spot Welding 106

7.2.3 Seam Welding 108

7.2.4 Projection Welding 109

7.2.5 Resistance Butt Welding 110

7.2.6 Flash Welding 111

7.3 Friction Welding 112

7.3.1 Friction Welding by Rotation of One Part

of the Workpiece 113

7.3.2 Friction Surfacing 114

7.3.3 Friction Stir Welding 115

7.4 High-frequency Welding 117

7.4.1 Induction Welding 118

7.5 Ultrasonic Welding 118

7.5.1 Equipment 119

7.6 Explosion Welding 120

7.7 Magnetic Pulse Welding 121

7.8 Cold Pressure Welding 123

7.9 Diffusion Welding 124

7.10 Other Methods Of Welding 125

7.10.1 Electroslag Welding 125

7.11 Electrogas Welding 126

7.12 Stud Welding 128

7.12.1 Equipment 128

7.13 Laser Welding 129

7.13.1 Description 130

7.13.2 Equipment 132

7.13.3 The Co2 Laser 133

7.13.4 The Nd: YAG Laser 134

7.13.5 Diode Lasers 136

7.13.6 Protection 136

7.13.7 Cladding 137

7.13.8 Hybrid Welding 138

7.14 Electron Beam Welding 139

7.14.1 Description 139

7.14.2 Equipment 140

7.14.3 The Welding Method 141

7.15 Thermite Welding 142

7.16 Exercise 143

8 Soldering and Brazing 144

8.1 General 144

8.1.1 Description 144

8.1.2 Types of Joints 146

8.1.3 Definitions 147

8.1.4 Different Types of Methods 148

8.2 Soft Soldering 153

8.3 Brazing 155

8.3.1 Braze Welding 158

8.3.2 Arc Brazing 159

8.3.3 Laser Beam Brazing 162

8.4 Exercise 162

9 The Weldability of Steel 163

9.1 Carbon Steels 164

9.1.1 Risks of Cracking 165

9.2 High-strength and Extra High-strength Steels 167

9.2.1 Stainless Steels 168

9.3 Austenitic Steels 170

9.3.1 Alloying Elements 171

9.3.2 Ferrite Formation 172

9.3.3 Intercrystalline Corrosion 173

9.3.4 Stress Corrosion 175

9.3.5 Tool Steels 175

9.3.6 Welding Stresses 176

9.3.7 Ferritic Steels 177

9.3.8 Martensitic Steels 180

9.3.9 Ferritic-austenitic Steels 182

9.3.10 Martensitic-austenitic Steels 183

9.3.11 Welding of Dissimilar Materials 184

9.4 Exercise 185

10 Welding Costs 186

10.1 Welding Cost Calculations 186

10.2 Some Welding Cost Concepts 187

10.3 Cost Calculation 189

10.3.1 Computer Programs for Welding

Cost Calculations 190

10.4 Mechanisation, Automation, Robot Welding 192

10.5 Exercise 192

Appendix 193

Glossary 194

Index 212

Chapter

1 Arc Welding- an Overview

1.1 History of welding

Methods for joining metals have been known for thousands of years, but most of this period, the only form of welding was forge welding by a blacksmith. Some totally new welding principles emerged at the end of the 19th century; sufficient electrical current could then be generated for resistance welding and arc welding. Arc welding was initially carried out using carbon electrodes, developed by Bemados, and was shortly followed by the use of steel rods. The Swede Oskar Kjellberg made an important advance when he developed and patented the coated electrode. The welding result was amazing and formed the foundation of the ESAB welding company.

Fig 1.1: Principle of Manual Metal Arc (MM) welding

Source: https://www.theweldingmaster.com/what-is-arc-welding-how-arc-welding-works/

Another early method of welding, which was also developed at that time, was gas welding. The use of acetylene and oxygen made it possible to produce a comparatively high flame temperature, 3100°C, which is higher than that of other hydrocarbon-based gas.

The intensity of all these heat sources enables heat to be generated in or applied to the workpiece quicker than it is conducted away into the surrounding metal. Consequently, it is possible to generate a molten pool, which solidifies to form the unifying bond between the parts being joined.

Fig 1.2 Submerged arc welding.

Source: https://www.google.com/search?q=Submerged+arc+welding.&rlz=1C1CHBD_enIN858IN858&sxsrf=ACYBGNTMWsfv_f0jeElWUiJNctmeHdmO-w:1578491935115&source=lnms&tbm=isch&sa=X&ved=2ahUKEwiQ2crYlPTmAhXvxzgGHbNdDf0Q_AUoAXoECBIQAw&biw=1163&bih=488#imgrc=3mEcDAxgZiCpLM:

Later, in the 1930s, new methods were developed. Up until then, all metal-arc welding had been carried out manually. Attempts were made to automate the process using a continuous wire. The most successful process was submerged arc welding (SAW), where the arc is submerged in a blanket of granular fusible flux. During the Second World War, the aircraft industry required a new method for the welding of magnesium and aluminum. In 1940 experiments began in the USA with the shielding of the arc by inert gases. By using an electrode of tungsten, the arc could be struck without melting the electrode, which made it possible to weld with or without filler material. The method is called TIG welding (Tungsten Inert Gas).

Fig 1.3 The TIG welding method.

Source: http://www.advantagefabricatedmetals.com/tig-welding.html

Some years later, the MIG welding process (Metal Inert Gas) was also developed using a continuously fed metal wire as the electrode. Initially, the shielding gases were inert such as helium or argon. Zaruba and Potapevski tried to use C02 as this was much easier to obtain and by using the dip transfer method, they did manage to reduce some of the problems caused by the intense generation of spattering; however, when using a relatively reactive gas such as C02 or mixed gases such as argon/C02, the process is generally called MAG welding (Metal Active Gas).

Fig 1.4 The MIG/MAG welding method.

Source: https://www.open.edu/openlearn/science-maths-technology/engineering-technology/manupedia/gas-shielded-arc-welding-processes-tig/mig/mag

The power-beam processes electron beam (EB) welding and laser welding have the most intensive of heat sources. The breakthrough of EB-welding came in 1958. The aircraft and nuclear power industries were the first to utilize the method. The main characteristics of EB-welding are its deep and narrow penetration. It is one limitation is the need for a vacuum chamber to contain the electron beam gun and the workpiece.

In some respects, Laser welding (and cutting) have ideal characteristics. The laser beam is a concentrated heat source, which permits high speed and very low distortion of the workpiece; unfortunately, a high power laser is large and expensive. The beam must also be conducted to the joint in some way. The light from a C02 laser must be transmitted by mirrors, while that from an Nd: YAG-laser can be carried by a thin glass fiber, which makes it attractive for use with robotic welding.

In the future, it should be possible to utilize lightweight diode lasers with sufficient power for welding. The diode laser has a higher efficiency in converting electrical energy into the light beam. Although it has not yet been possible to produce diode lasers with the same power output and beam quality as present welding laser sources, these are already being used for welding metal up to about 1 mm thick. The low weight and size make them an interesting power source for use with robotic welding.

1.2 Terminology

1.2.1 Welding Methods

Definitions of welding processes are given in IS0 857. Reference numbers for the processes are defined in IS0 4063. These numbers are then used on drawings (IS0 2553) or in welding procedure specifications (EN 288) as references.

1.2.2 Basic Terms

Pressure welding. Welding in which sufficient outer force is applied to cause more or less plastic deformation of both the facing surfaces, generally without the addition of filler metal. Usually, but not necessarily, the facing surfaces are heated to permit or to facilitate bonding.

Fusion welding. Welding without application of outer force in which