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- Herausgeber: John Wiley & Sons
- Kategorie: Fachliteratur
- Sprache: Englisch
WELDING ENGINEERING
The new edition of the popular welding engineering textbook includes brand-new topics, assignments, and review questions
Welding Engineering: An Introduction provides a clear and accessible overview of the concepts, tools, materials, and methods of modern welding and joining technology. With emphasis on fundamental engineering principles, this comprehensive textbook offers easy-to-understand coverage of a wide range of key topics in welding engineering, from the basics of arc welding processes to welding metallurgy, design, and safety. Concise chapters offer numerous figures, tables, images, and recommended readings to promote reader comprehension of the material.
Now in its second edition, the text contains fully revised content throughout, including entirely new sections on additive manufacturing and computational modeling of welds. Updated and expanded chapters address modern arc welding power supply technology, resistance, solid-state, and high energy density welding processes, weld inspection methods, codes and standards, welding of high strength steels, and more. This edition features simple yet effective end-of-chapter assignments that enhance students’ learning and assist instructors in developing assessment questions for their course.
The second edition of Welding Engineering:
- Provides up-to-date coverage of rapidly growing techniques and technologies within the field
- Features new assignments and true/false questions at the end of each chapter
- Explains the essential concepts and principles necessary for more in-depth courses in welding, metallurgy, and design
- Covers all the major welding processes used in manufacturing and fabrication
Welding Engineering: An Introduction, Second Edition is an excellent textbook for undergraduate and graduate welding engineering courses taught within four-year engineering degree programs, and a valuable guide for engineers and professionals in the manufacturing industry who need to learn fundamental welding engineering concepts for their job roles.
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Welding Engineering
An Introduction
David H. Phillips
The Ohio State UniversityOH, USA
Second Edition
Copyright © 2023 by John Wiley & Sons, Inc. All rights reserved.
Published by John Wiley & Sons, Inc., Hoboken, New Jersey.
Published simultaneously in Canada.
No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, scanning, or otherwise, except as permitted under Section 107 or 108 of the 1976 United States Copyright Act, without either the prior written permission of the Publisher, or authorization through payment of the appropriate per-copy fee to the Copyright Clearance Center, Inc., 222 Rosewood Drive, Danvers, MA 01923, (978) 750-8400, fax (978) 750-4470, or on the web at www.copyright.com. Requests to the Publisher for permission should be addressed to the Permissions Department, John Wiley & Sons, Inc., 111 River Street, Hoboken, NJ 07030, (201) 748-6011, fax (201) 748-6008, or online at http://www.wiley.com/go/permission.
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Set in 9.5/12.5pt STIXTwoText by Integra Software Services Pvt. Ltd, Pondicherry, India
“To my dad, David M. Phillips, a perpetual source of encouragement who loved everything about The Ohio State University, and would have been so proud to know that his son became a professor there.”
Contents
Cover
Title page
Copyright
Dedication
Preface
About the Companion Website
1 What Is Welding Engineering?
1.1 Introduction to Welding Processes
2 Arc Welding Processes
2.1 Fundamentals and Principles of Arc Welding
2.1.1 Fundamentals of an Electric Arc
2.1.2 Arc Voltage
2.1.3 Polarity
2.1.4 Heat Input
2.1.5 Welding Position
2.1.6 Filler Metals and Electrodes
2.1.7 Shielding
2.1.7.1 Gas Shielding
2.1.7.2 Flux Shielding
2.1.8 Weld Joints and Weld Types for Arc Welding
2.1.9 Primary Operating Variables in Arc Welding
2.1.9.1 Voltage
2.1.9.2 Current
2.1.9.3 Electrode Feed Rate/Wire Feed Speed
2.1.9.4 Welding Travel Speed
2.1.10 Metal Transfer Mode
2.1.11 Arc Blow
2.1.12 Common Arc Welding Defects and Discontinuities
2.2 Arc Welding Power Supplies
2.2.1 Transformers
2.2.2 Generators
2.2.3 Important Electrical Elements in Arc Welding Power Supplies
2.2.4 Volt-Ampere Characteristic of Arc Welding Power Supplies
2.2.5 Duty Cycle
2.2.6 Modern Advanced Arc Welding Power Supplies
2.3 Shielded Metal Arc Welding
2.4 Gas Tungsten Arc Welding
2.5 Plasma Arc Welding
2.6 Gas Metal Arc Welding
2.7 Flux Cored Arc Welding
2.8 Submerged Arc Welding
2.9 Other Arc Welding Processes
2.9.1 Electrogas Welding
2.9.2 Electroslag Welding
2.9.3 Arc Stud Welding
2.10 Test Your Knowledge
3 Resistance Welding Processes
3.1 Fundamentals and Principles of Resistance Welding Processes
3.1.1 Resistance and Resistivity
3.1.2 Current Range and Lobe Curves
3.1.3 Modern Equipment and Power Supplies
3.2 Resistance Spot Welding
3.3 Resistance Seam Welding
3.4 Resistance Projection Welding
3.5 High Frequency Welding
3.6 Flash Welding
3.7 Test Your Knowledge
4 Solid-State Welding Processes
4.1 Fundamentals and Principles of Solid-State Welding
4.1.1 Solid-State Welding Theory
4.1.2 Roll Bonding Theory
4.2 Friction Welding Processes
4.2.1 Inertia Friction Welding
4.2.2 Continuous Drive Friction Welding
4.2.3 Linear Friction Welding
4.2.4 Friction Stir Welding
4.3 Other Solid-State Welding Processes
4.3.1 Diffusion Welding
4.3.2 Explosion Welding
4.3.3 Ultrasonic Welding
4.4 Test Your Knowledge
5 High-Energy Density Welding Processes
5.1 Fundamentals and Principles of High-Energy Density Welding
5.1.1 Power Density
5.1.2 Keyhole Mode Welding
5.2 Laser Beam Welding
5.3 Electron Beam Welding
5.4 Test Your Knowledge
6 Other Approaches to Welding and Joining
6.1 Brazing and Soldering
6.2 Welding of Plastics
6.2.1 Hot Tool (Plate) Welding
6.2.2 Hot Gas Welding
6.2.3 Implant Induction Welding
6.2.4 Ultrasonic Welding
6.2.5 Vibration Welding
6.3 Adhesive Bonding
6.4 Novel and Hybrid Welding Processes
6.5 Additive Manufacturing
6.6 Oxyfuel Welding and Cutting
6.7 Other Cutting Processes
6.7.1 Plasma Cutting
6.7.2 Laser Beam Cutting
6.7.3 Air Carbon Arc Gouging
6.8 Test Your Knowledge
7 Design Considerations for Welding
7.1 Introduction to Welding Design
7.2 Mechanical Properties
7.2.1 Yield Strength
7.2.2 Tensile Strength
7.2.3 Ductility
7.2.4 Fatigue Strength
7.2.5 Toughness
7.2.6 Mechanical Properties—Effect of Temperature
7.3 Physical Properties
7.3.1 Thermal Conductivity
7.3.2 Melting Temperature
7.3.3 Coefficient of Thermal Expansion
7.3.4 Electrical Conductivity
7.4 Design Elements for Welded Connections
7.4.1 Joint and Weld Types
7.4.2 Joint and Weld Type Selection Considerations
7.4.3 Weld Joint Nomenclature—Groove Welds
7.4.4 Weld Joint Nomenclature—Fillet Welds
7.4.5 Welding Positions
7.5 Welding Symbols
7.6 Weld Sizing
7.7 Computational Modeling of Welds
7.8 Test Your Knowledge
8 Heat Flow, Residual Stress, and Distortion
8.1 Heat Flow
8.2 Fundamentals and Principles of Residual Stress and Distortion
8.3 Approaches to Minimizing or Eliminating Distortion
8.4 Test Your Knowledge
9 Welding Metallurgy
9.1 Introduction to Welding Metallurgy
9.2 The Fusion Zone
9.3 The Partially Melted Zone
9.4 The Heat-Affected Zone (HAZ)
9.5 Introduction to Phase Diagrams
9.6 Test Your Knowledge
10 Welding Metallurgy of Carbon Steels
10.1 Introduction to Steels
10.2 Steel Microstructures and the Iron-Iron Carbide Diagram
10.3 Continuous Cooling Transformation (CCT) Diagrams
10.4 Hardness and Hardenability
10.5 Hydrogen Cracking
10.6 Heat-Affected Zone Microstructures in Steel
10.7 Advanced High-Strength Steels
10.8 Test Your Knowledge
11 Welding Metallurgy of Stainless Steels
11.1 Introduction to Stainless Steels
11.2 Constitution Diagrams
11.3 Martensitic Stainless Steels
11.4 Ferritic Stainless Steels
11.5 Austenitic Stainless Steels
11.6 Duplex Stainless Steels
11.7 Precipitation-Hardening Stainless Steels
11.8 Test Your Knowledge
12 Welding Metallurgy of Nonferrous Alloys
12.1 Aluminum Alloys
12.2 Nickel-Based Alloys
12.3 Titanium Alloys
12.4 Copper Alloys
12.5 Magnesium Alloys
12.6 Test Your Knowledge
13 Weld Quality
13.1 Weld Discontinuities and Defects
13.2 Mechanical Testing of Weldments
13.2.1 Tensile Testing
13.2.2 Ductility Testing
13.2.3 Toughness Testing
13.2.4 Fatigue Testing
13.3 Nondestructive Testing
13.3.1 Visual Examination
13.3.2 Liquid Penetrant Testing
13.3.3 Magnetic Particle Testing
13.3.4 Radiographic Testing
13.3.5 Ultrasonic Testing
13.4 Introduction to Fractography
13.5 Test Your Knowledge
14 Codes, Standards, and Welding Qualification
14.1 Introduction to Standards
14.2 AWS D1.1—“Structural Welding Code—Steel”
14.2.1 Welding and Welder Qualification
14.2.2 Fabrication and Inspection
14.3 Test Your Knowledge
15 Safe Practices in Welding
15.1 Electrical Shock
15.2 Radiation
15.3 Burns
15.4 Smoke and Fumes
15.5 Welding in Confined Space
15.6 Fire and Explosion Danger
15.7 Compressed Gasses
15.8 Hazardous Materials
15.9 Test Your Knowledge
Index
End User License Agreement
List of Tables
CHAPTER 02
Table 2.1 Welding flux ingredients...
Table 2.2 Typical shielded metal...
Table 2.3 Electrode specification...
Table 2.4 Electrode specification...
Table 2.5 AWS specifications...
Table 2.6 AWS specifications...
Table 2.7 Current ranges as...
CHAPTER 07
Table 7.1 Designation for...
Table 7.2 Minimum fillet...
Table 7.3 Equations for...
CHAPTER 12
Table 12.1 The eight families...
Table 12.2 Comparison of selected...
CHAPTER 13
Table 13.1 A summary of common...
CHAPTER 14
Table 14.1 Examples of the wide...
Table 14.2 Example of prequalified...
List of Illustrations
CHAPTER 01
Figure 1.1 A sampling of welding...
CHAPTER 02
Figure 2.1 Common arc welding...
Figure 2.2 Arc welding circuit...
Figure 2.3 Ionization of a gas...
Figure 2.4 Thermal diagram...
Figure 2.5 Voltage across ...
Figure 2.6 DCEN—common...
Figure 2.7 DCEP—common...
Figure 2.8 Heat input during...
Figure 2.9 Arc efficiency...
Figure 2.10 Forms of shielding...
Figure 2.11 Typical arc welding...
Figure 2.12 Gas metal arc welding...
Figure 2.13 Spray transfer...
Figure 2.14 Arc blow. Reproduced...
Figure 2.15 Undercut and overlap...
Figure 2.16 Transformer construction...
Figure 2.17 Modern engine-driven...
Figure 2.18 Simple DC...
Figure 2.19 Typical elements...
Figure 2.20 A typical rectifier...
Figure 2.21 Phase control of...
Figure 2.22 Basic electrical...
Figure 2.23 DC pulsed current...
Figure 2.24 Volt-ampere characteristic...
Figure 2.25 Volt-ampere characteristic...
Figure 2.26 Power supply output...
Figure 2.27 Class I machines...
Figure 2.28 RMD short circuit...
Figure 2.29 Advanced multiple...
Figure 2.30 Advanced multiple...
Figure 2.31 Lincoln Electric's Power...
Figure 2.32 Shielded metal arc...
Figure 2.33 Typical effects of amperage, arc...
Figure 2.34 Electrode orientation...
Figure 2.35 Examples of shielded...
Figure 2.36 Gas tungsten arc...
Figure 2.37 Gas tungsten arc...
Figure 2.38 Gas tungsten arc...
Figure 2.39 Effect of polarity...
Figure 2.40 Typical customized...
Figure 2.41 Effect of electrode...
Figure 2.42 GTAW pulsing schedule...
Figure 2.43 Typical gas tungsten...
Figure 2.44 High frequency starting...
Figure 2.45 Plasma arc welding. (Source: Reproduced...
Figure 2.46 Comparison of gas tungsten...
Figure 2.47 Effect of arc...
Figure 2.48 Keyhole mode...
Figure 2.49 The two modes...
Figure 2.50 Gas metal arc...
Figure 2.51 Typical equipment...
Figure 2.52 Gas metal arc...
Figure 2.53 Common gas metal...
Figure 2.54 Effect of wire...
Figure 2.55 Metal transfer...
Figure 2.56 Gas metal arc...
Figure 2.57 Electromagnetic...
Figure 2.58 Globular transfer...
Figure 2.59 Effect of welding...
Figure 2.60 Typical AWS A5.18...
Figure 2.61 Flux cored arc...
Figure 2.62 Gas-shielded version...
Figure 2.63 Flux cored arc welding...
Figure 2.64 Typical AWS A5.20...
Figure 2.65 Typical mechanized...
Figure 2.66 Multiple wire submerged...
Figure 2.67 Submerged arc welding...
Figure 2.68 Dual head submerged...
Figure 2.69 Submerged arc welding...
Figure 2.70 Effect of slope...
Figure 2.71 Electrogas welding...
Figure 2.72 Electrogas welding...
Figure 2.73 Electroslag welding...
Figure 2.74 Arc stud welding...
Figure 2.75 Arc stud welding...
Figure 2.76 Arc stud welding...
Figure 2.77 A wide variety...
CHAPTER 03
Figure 3.1 Resistance spot welding.
Figure 3.2 Resistances associated...
Figure 3.3 Resistivity of steel...
Figure 3.4 Dynamic resistance...
Figure 3.5 Resistance spot...
Figure 3.6 Resistance Spot...
Figure 3.7 A modern resistance...
Figure 3.8 The Peltier effect...
Figure 3.9 Resistance spot...
Figure 3.10 A resistance spot...
Figure 3.11 A typical resistance...
Figure 3.12 Typical resistance...
Figure 3.13 Annealing temperatures...
Figure 3.14 Over time, electrode...
Figure 3.15 Resistance seam...
Figure 3.16 Resistance seam...
Figure 3.17 Mash seam welding produces...
Figure 3.18 Typical resistance projection...
Figure 3.19 Resistance projection welding...
Figure 3.20 Two common projection designs...
Figure 3.21 Typical projection weld...
Figure 3.22 High frequency resistance...
Figure 3.23 High frequency induction...
Figure 3.24 Current path through...
Figure 3.25 Current penetration...
Figure 3.26 The shape of the “V” where...
Figure 3.27 The primary steps of flash...
Figure 3.28 Flash welding of railroad...
Figure 3.29 A complete flash welding...
Figure 3.30 A complete flash welding...
CHAPTER 04
Figure 4.1 In order to achieve...
Figure 4.2 Roll bonding theory...
Figure 4.3 Basic steps of both...
Figure 4.4 Initial heating is due...
Figure 4.5 Excessive pressure...
Figure 4.6 Inertia friction...
Figure 4.7 Typical inertia...
Figure 4.8 Inertia welded...
Figure 4.9 Continuous drive...
Figure 4.10 Typical continuous...
Figure 4.11 Automotive strut...
Figure 4.12 Linear friction...
Figure 4.13 Large-scale linear...
Figure 4.14 Friction stir welding.
Figure 4.15 Typical friction...
Figure 4.16 Regions of a friction...
Figure 4.17 Flow stress at high...
Figure 4.18 Diffusion welding.
Figure 4.19 Vacuum hot...
Figure 4.20 Pressure combined...
Figure 4.21 The stages of diffusion...
Figure 4.22 Typical arrangement...
Figure 4.23 Explosion welding...
Figure 4.24 The six steps of...
Figure 4.25 Ultrasonic welding.
Figure 4.26 Ultrasonic welding...
Figure 4.27 Typical ultrasonic...
Figure 4.28 Typical ultrasonically...
Figure 4.29 Closed-loop control...
CHAPTER 06
Figure 6.1 Approach to verifying...
Figure 6.2 Typical furnace brazing...
Figure 6.3 Polyethylene.(Source: Dr. Avi...
Figure 6.4 Classification of...
Figure 6.5 Semicrystalline and...
Figure 6.6 There are many methods...
Figure 6.7 Hot tool...
Figure 6.8 Hot gas welding...
Figure 6.9 An energy director...
Figure 6.10 Vibration...
Figure 6.11 Hybrid laser...
Figure 6.12 Hybrid laser...
Figure 6.13 “TiP TiG” welding...
Figure 6.14 “DeltaSpot” welding...
Figure 6.15 “LightWELD” handheld...
Figure 6.16 Laser powder bed fusion...
Figure 6.17 Laser direct energy...
Figure 6.18 Oxyacetylene flame...
Figure 6.19 Steps to achieve...
Figure 6.20 Oxyfuel cutting.(Source: Reproduced...
Figure 6.21 Oxyacetylene cutting...
Figure 6.22 Common cutting...
Figure 6.23 Kerf and...
Figure 6.24 Cutting surfaces...
Figure 6.25 Plasma cutting.(Source: Reproduced...
Figure 6.26 Mechanized plasma...
Figure 6.27 Laser beam cutting...
Figure 6.28 Air carbon arc...
Figure 6.29 Typical air carbon...
CHAPTER 07
Figure 7.1 Typical location...
Figure 7.2 Impact test machine...
Figure 7.3 Weld distortion...
Figure 7.4 The five basic...
Figure 7.5 Typical approaches ...
Figure 7.6 Examples of single-sided...
Figure 7.7 Examples double-sided...
Figure 7.8 (a) Single and (b) double...
Figure 7.9 Three options for...
Figure 7.10 Effect of weld type...
Figure 7.11 Joint design...
Figure 7.12 A proper root...
Figure 7.13 Groove weld...
Figure 7.14 Fillet weld...
Figure 7.15 Weld positions...
Figure 7.16 Weld positions...
Figure 7.17 Welding symbols...
Figure 7.18 Weld symbols and...
Figure 7.19 Other and arrow...
Figure 7.20 Examples of groove...
Figure 7.21 A break in the arrow...
Figure 7.22 The vertical member...
Figure 7.23 Supplementary...
Figure 7.24 Examples of the...
Figure 7.25 A few examples...
Figure 7.26 Approaches...
Figure 7.27 Sample calculation...
Figure 7.28 Simulated resistance...
Figure 7.29 Simulated resistance...
CHAPTER 08
Figure 8.1 The three types...
Figure 8.2 Fourier’s...
Figure 8.3 2‐D versus...
Figure 8.4 Peak temperatures, time...
Figure 8.5 Cooling rate comparison...
Figure 8.6 Three‐bar...
Figure 8.7 Stress level of...
Figure 8.9 Typical residual...
Figure 8.10 Cause of...
Figure 8.11 Typical examples...
Figure 8.12 Methods of distortion...
Figure 8.13 Typical joint restraint...
Figure 8.14 Welding on both sides...
Figure 8.15 Intermittent fillet...
Figure 8.16 Distortion control...
CHAPTER 09
Figure 9.1 Dendritic solidification....
Figure 9.2 The mechanical properties...
Figure 9.3 Terminology describing the...
Figure 9.4 Fusion zone microstructures ...
Figure 9.5 Segregation of alloying...
Figure 9.6 Simple binary eutectic...
Figure 9.7 Two examples of actual...
CHAPTER 10
Figure 10.1 The allotropic behavior...
Figure 10.2 The iron-iron carbide...
Figure 10.3 Typical carbon steel...
Figure 10.4 Modification and...
Figure 10.5 The 1060 steel...
Figure 10.6 When cooling rates...
Figure 10.7 When cooling rates...
Figure 10.8 Simple time temperature...
Figure 10.9 CCT diagram for...
Figure 10.10 Plot of hardness...
Figure 10.11 Due to 3-D heat flow, weld...
Figure 10.12 Hydrogen cracks...
Figure 10.13 Typical variation...
Figure 10.14 Typical carbon steel...
Figure 10.16 Controlled cooling...
Figure 10.17 TRIP 780 microstructure...
CHAPTER 11
Figure 11.1 Fe‐Cr binary phase...
Figure 11.2 The Schaeffler diagram...
Figure 11.3 Different heat treatment...
Figure 11.4 High frequency resistance...
Figure 11.5 Ferritic stainless steel...
Figure 11.6 Alloy 409 microstructure...
Figure 11.7 Austenitic stainless steels...
Figure 11.8 Solidification cracking...
Figure 11.9 Solidification as 100% austenite...
Figure 11.10 WRC‐1992 diagram...
Figure 11.11 Chromium depletion along...
Figure 11.12 HAZ grain boundary...
Figure 11.13 Duplex stainless...
CHAPTER 12
Figure 12.1 All aluminum alloys...
Figure 12.2 Porosity in the weld...
Figure 12.3 The rapid increase...
Figure 12.4 Aluminum weld metal...
Figure 12.5 Aluminum weld filler...
Figure 12.6 Classes of alloys...
Figure 12.7 The gas turbine engine...
Figure 12.8 During a postweld heat...
Figure 12.9 The susceptibility...
Figure 12.10 Nickel-based alloys...
Figure 12.11 Medical devices and...
Figure 12.12 Titanium is used...
Figure 12.13 Colored oxide...
Figure 12.14 Typical preheat...
Figure 12.15 Effect of shielding...
Figure 12.16 Alloy designation...
CHAPTER 13
Figure 13.1 A sampling of common...
Figure 13.2 Weld metal and reduced...
Figure 13.3 The stress–strain...
Figure 13.4 Guided bend testing...
Figure 13.5 Transverse bend testing...
Figure 13.6 The area under the...
Figure 13.7 Charpy V-Notch impact...
Figure 13.8 Typical ductile-to-brittle...
Figure 13.9 Compact tension fracture...
Figure 13.10 Fatigue cycles may be...
Figure 13.11 Typical S-N curve compares...
Figure 13.12 Weld discontinuities...
Figure 13.13 Two typical joint...
Figure 13.14 AWS D1.1 fatigue...
Figure 13.15 Ultrasonic testing...
Figure 13.16 Typical gauges used...
Figure 13.18 Basic principles of...
Figure 13.19 With magnetic particle...
Figure 13.20 The yoke method works...
Figure 13.21 Radiographic testing...
Figure 13.22 The slag inclusion seen...
Figure 13.23 A basic principle...
Figure 13.24 Two approaches to...
Figure 13.25 Ductile dimple fracture...
Figure 13.26 Fatigue failures produce...
Figure 13.27 Chevron markings...
CHAPTER 14
Figure 14.1 AWS D1.1, a very common...
Figure 14.2 ISO (International...
Figure 14.3 The various products...
Figure 14.4 The AISC manual...
Figure 14.5 The ASME “Boiler...
Figure 14.6 The Bridge Welding...
Figure 14.7 Example of a prequalified...
Figure 14.8 Typical PQR...
Figure 14.9 Typical test...
Figure 14.10 Typical format...
Figure 14.11 Example of a welder...
Guide
Cover
Title page
Copyright
Dedication
Table of Contents
Preface
About the Companion Website
Begin Reading
Index
End User License Agreement
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Preface
The Welding Engineering program at The Ohio State University is well known for its long history of graduating students who serve critical roles in industry. This textbook was written for use in an undergraduate course in Welding Engineering that I have taught at Ohio State for the past 12 years. The course serves as an introduction to the Welding Engineering curriculum at Ohio State, and is intended to prepare sophomore students for more in‐depth Welding Engineering courses in welding processes, metallurgy, design, and NDE, which are required courses they take during their junior and senior years. Much of what is included in this book comes from my class lectures. Since both the course and this book represent “An Introduction” to all the important topics associated with the field of Welding Engineering, the coverage of each of the topics is intended to be relatively brief and concise. Fundamentals and basic concepts are emphasized, while many of the details are intentionally omitted. So, while it is not intended to serve as a handbook, recommended reading for further information and greater detail is provided at the end of each chapter.
This second edition includes many new sections and updates. All chapters (except the first introductory chapter) now end with a self-assessment titled “Test Your Knowledge.” The self-assessment consists of several simple True/False questions covering important topics in the chapter, as well as a more involved “solve a welding engineering problem” question. This question asks the student to apply knowledge gained from that chapter toward solving a typical welding engineering challenge. In addition to the numerous chapter updates and revisions, many new topics have been added, including additive manufacturing, computational modeling of welds, advanced high strength steels, and precipitation-hardening stainless steels. Although this book is intended for sophomore-level Welding Engineering students, it should also serve as a useful guide to other engineers, technicians, and specialists who are working in the field of welding and are seeking a more fundamental understanding of the important concepts. Universities offering Welding Engineering Technology programs may want to consider it as well.
About the Companion Website
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Answer Key
1 What Is Welding Engineering?
Welding Engineering is a complex field that requires proficiency in a broad range of engineering disciplines. Students who pursue a degree in Welding Engineering engage in a curriculum that is more diverse than other engineering disciplines (Figure 1.1). They take advanced courses in welding metallurgy and materials science that cover materials ranging from carbon steels and stainless steels, to nonferrous alloys such as nickel, aluminum, and titanium, as well as polymers. Welding process courses emphasize theory, principles, and fundamental concepts pertaining to the multitude of important industrial welding processes.
Figure 1.1 A sampling of welding engineering topics—design (top left), processes (top right), and welding metallurgy (bottom). Adapted from AWS Handbook.
While many associate welding with arc welding processes, a Welding Engineer may be responsible for many other processes throughout their career. Therefore, in addition to arc welding, the Welding Engineering curriculum includes thorough coverage of high-energy density processes such as Laser and Electron Beam Welding, solid‐state welding processes such as Friction Welding and Explosion Welding, and resistance welding processes including Spot and Projection Welding. Students are trained in many important electrical concepts associated with welding such as process control and transformer theory and operation. Welding design courses cover the principles of important subjects such as heat flow, residual stress, fatigue and fracture, weld sizing, and weld design for various loading conditions. Analysis through computational modeling is included in many of the courses. Nondestructive testing techniques including x‐ray, ultrasonics, eddy current, magnetic particle, and dye penetrant are emphasized as well.
The diverse Welding Engineering curriculum prepares its graduates for a wide range of possible career paths and industrial fields. Working environments include automation and high-speed production, fabrication, manufacturing, and research. Welding Engineering graduates are typically in high demand and choose jobs from a variety of industry sectors including nuclear, petrochemical, automotive, medical, shipbuilding, aerospace, power generation, and heavy equipment sectors.
1.1 Introduction to Welding Processes
Considering the recent developments in hybrid approaches to welding, there are probably now more than 75 types of welding processes available for the manufacturer or fabricator to choose from. The reason that there are so many processes is that each process has its own unique advantages and disadvantages that make them ideal for some applications and a poor choice for others. Arc welding processes offer advantages such as portability and low cost but are relatively slow and rely on a considerable amount of heating to produce the weld. High‐energy density processes such as Laser Welding produce low heat inputs and fast welding speeds, but the equipment is very expensive and joint fit‐up needs to be nearly perfect. Solid‐state welding processes avoid many of the weld discontinuities associated with melting and solidification, but are also very expensive and often are restricted to limited joint designs. Resistance welding processes are typically very fast and require no additional filler materials, but are often limited to thin sheet applications or very high production applications such as the seams in welded pipe.
Each of these processes produces a weld (metallic bond) using some combination of heat, time, and/or pressure. Those that rely on extreme heat at the source such as arc and high-energy density processes generally need no pressure. A process such as Diffusion Welding relies on some heating and some pressure, but with a considerable amount of time. Explosion Welding relies on a tremendous amount of pressure, with minimal heating and time to produce the weld.
When choosing an optimum process for a given application, the Welding Engineer must consider all the above, including much more that will be covered in the next few chapters on welding processes.
2 Arc Welding Processes
2.1 Fundamentals and Principles of Arc Welding
This section serves as a general introduction to all the arc welding processes. The common features, important concepts, and terminology of this family of welding processes are reviewed, with more process‐specific details provided in the sections that follow. Arc welding refers to a family of processes that rely on the extreme heat of an electric arc to create a weld. They usually, but not always, involve the use of additional filler metal to produce the weld. As one of the first welding processes, arc welding continues to be very popular primarily due to its low equipment cost, portability, and flexibility. Some of the key developments that led to modern arc welding include the discovery of the electric arc in the 1820s (Davies), the first welding patent using a carbon electrode in 1886, the first covered electrode in 1900 (Kjellberg), and the first process using a continuously fed electrode in the 1940s.
The most common arc welding processes today are charted in Figure 2.1. The abbreviations refer to the American Welding Society (AWS) terminology as follows: SMAW—Shielded Metal Arc Welding, GMAW—Gas Metal Arc Welding, GTAW—Gas Tungsten Arc Welding, PAW—Plasma Arc Welding, SAW—Submerged Arc Welding, FCAW—Flux Cored Arc Welding, SW—Arc Stud Welding, and EGW—Electrogas Welding. Although technically not an arc welding process, ESW—Electroslag Welding is very similar to EGW and as such, is often included with arc welding. In practice, older designations and trade names of processes are often used, some of which are given in italics in the figure. Examples are Stick or Covered Electrode welding for SMAW, MIG meaning Metal Inert Gas for GMAW, and TIG meaning Tungsten Inert Gas for GTAW. One key generalization in the modern terms is the substitution of “G” for “IG” denoting inert gas since these processes no longer rely solely on inert gasses for shielding.
Figure 2.1 Common arc welding processes.
With all arc welding processes, the initiation of an arc basically completes (or closes) an electrical circuit. As shown in Figure 2.2, the most basic arc welding arrangement consists of an arc welding power supply, electrode, work cables (or leads), means to connect to the electrode (electrode holder with SMAW as shown), and the work piece or parts to be welded. A range of typical currents and voltages are shown. Open circuit voltages provided by traditional power supplies are in the range of 60–80 volts although they are sometimes lower. The open circuit voltage is the voltage between the electrode and ground clamp after the power supply is turned on, but before the arc is initiated. This voltage range is high enough to establish and maintain an arc, but low enough to minimize the risk of electrical shock. Once the arc is established, the voltage across the arc typically ranges between 10 volts and 40 volts, depending on the process.
Figure 2.2 Arc welding circuit depicting SMAW.
Welding power supplies are usually designed to deliver direct current electricity referred to as DC. A pulsing output called pulsed direct current has become a prominent feature in many advanced welding power supplies. Programmable pulsing parameters or preprogrammed pulsing schedules can be used to optimize welding performance, primarily for GMAW. Alternating current (AC) is sometimes used. One benefit is that AC machines are simple and inexpensive. Welding with AC is also a very effective way to weld aluminum, which will be discussed later in the section on GTAW. A form of pulsing known as variable polarity is another advanced capability of many modern power supplies. Variable polarity capability allows for the customization of pulsing frequency and waveform to optimize welding performance.
Arc welding processes can be divided into three categories: manual, semiautomatic, and automatic. Manual processes such as SMAW and GTAW require the welder to control travel speed, arc length, and electrode (or filler metal) feed rate. As a result, these processes require the most welder skill. Semiautomatic processes such as GMAW use a continuous motorized wire feed mechanism. The power supply controls the arc length through a concept known as “self‐regulation” to be discussed later. Since the welder only needs to control the position and travel speed of the gun, GMAW is relatively easy to learn, and for the same reasons is also an ideal process for robotic welding. SAW is an example of an automatic arc welding process because all the variables of travel speed, arc length, and electrode feed are controlled by the machine. Therefore, there is no welding skill required to operate automatic processes, only the knowledge needed to set up the machine and select the proper variables. Any arc welding process may be referred to as mechanized or automated if it is attached to a travel mechanism or robotic arm.
2.1.1 Fundamentals of an Electric Arc
An electric arc is a type of electrical discharge that occurs between electrodes when a sufficient voltage is applied across a gap causing the gas to break down or ionize (Figure 2.3). Gas is normally an insulator, but once ionized it becomes a conductor of electricity. Ionization occurs when the gas atoms lose bound electrons that are then free to travel independently in the gas to produce an electric current. These free electrons pick up energy from the electric field produced by the applied voltage and collide with other gas atoms. This allows the ionization process to grow resulting in an “avalanche” effect. Once the gas is highly ionized, it becomes relatively easy for electrons to flow, and under the right conditions a stable electric arc can be formed.
Figure 2.3 Ionization of a gas and current flow in an arc.
An ionized gas consists of free electrons that flow in one direction and positive ions that flow in the other direction. Collisions with mostly neutral atoms produce a tremendous resistive heating of the gas, so, in a sense, the arc is a large resistor. The extreme heat also maintains the ionization process. Electromagnetic radiation is given off due to the high temperatures resulting in the characteristic glow of the arc. In addition to the observable visible wavelengths, large amounts of invisible infrared and ultraviolet wavelengths are emitted. The ionized glowing gas that makes up the arc is often referred to as plasma. For the arc to be maintained, the power supply must be able to supply the high current and low voltage demanded by the arc.
The utility of the electric arc to welding is the extreme heat that is produced under stable arc conditions which can melt most metals and form what is known as a weld pool or puddle. Arc temperatures are known to range from 5000 up to 30,000 C. As Figure 2.4 indicates, the temperature of an arc is hottest at its center since the outer portions of the arc lose heat to the surroundings due to convection, conduction, and radiation. A major contribution of heat to the welding and work electrodes is actually not just the extremely high arc temperatures, but the intense energy dissipative processes at the arc attachment points to the welding and work electrodes. This will be discussed later.
Figure 2.4 Thermal diagram of gas tungsten arc. (Source: Reproduced by permission of American Welding Society, ©Welding Handbook).
For consumable electrode processes such as SMAW and GMAW, the arc contains molten droplets of filler metal, which melt from the electrode and travel through the arc to the weld pool. As will be discussed later, the size, shape, and way the molten metal travels from the electrode to the puddle are known as the modes of metal transfer. This is of particular interest with the GMAW process but is not an important consideration for the other arc welding processes. Filler metal transfer through the arc inevitably results in some molten drops being ejected from the arc or weld pool that may stick to the part. This is called spatter and is often a quality concern. GTAW and PAW processes deliver the filler metal directly to the weld puddle (not through the arc) and are therefore not susceptible to spatter.
2.1.2 Arc Voltage
It was mentioned previously that operating arc voltages typically fall in the range of 10–40 volts. Arc voltages are primarily related to arc lengths. Longer arc lengths produce higher arc voltages and shorter arcs produce lower voltages. Figure 2.5 shows how voltage (potential) varies through the arc. As the figure indicates, a significant amount of the voltage distribution or drop across the arc is close to the anode and the cathode. These regions are known as the anode drop or fall at the positive electrode (the work piece in the figure) and the cathode drop or fall at the negative electrode (the welding electrode in the figure). The primary change in arc voltage as a function of arc length is known to be associated with the region between the anode and cathode drops called the plasma column. Voltages at the anode and cathode drop regions are not significantly affected by arc length. As a result, even extremely short arc lengths will exhibit voltages much greater than zero. This provides evidence that most of the arc voltage exists at the two voltage drop regions at the electrodes. For a typical welding arc length, these voltages may represent as much as 80–90% of the total arc voltage. Since heat generation and power dissipation are functions of voltage and current, and the level of current is uniform through the arc, the amount of power dissipation must therefore be greatest at the electrode drop regions and not in the plasma column. These anode and cathode drop regions are extremely narrow, and, therefore, their effect is not revealed on thermal diagrams of arcs such as that shown in Figure 2.4. Nevertheless, they play a critical role in the melting at the anode and cathode, which is why the arc temperature alone is not the key to explaining the arc as an effective heat source for welding.
Figure 2.5 Voltage across a welding arc. (Source: Reproduced by permission of American Welding Society, ©Welding Handbook).
Higher voltages are required to ionize a gas across a given gap and gas pressure. The latter is usually atmospheric pressure for a welding arc; however, arc welding can be conducted at other pressure conditions as well such as under water or in a chamber. Since the open circuit voltage typical of power supplies (60–80 volts) is relatively low, it is not sufficient to simply break down a gap. With manual arc welding processes, it is usually necessary to touch, or so‐called scratch or drag the electrode on the work piece. This produces an instantaneous short circuit current from the power supply and is referred to as “striking” or “drawing” an arc. Once the ionization process has been initiated, the gap can be increased to achieve a stable arc. With semiautomatic processes, the wire is driven into the work piece by the wire feed mechanism producing a short circuit. The power supply reacts by producing a very high short circuit current that rapidly melts the wire forming a gap. The differences between arc welding power supplies for manual and semiautomatic processes will be explained later in this chapter. With GTAW, special arc starting systems that produce high voltages at a high frequency may be integrated with the power supply so the welder can initiate the arc without touching the tungsten electrode to the part. Touching the tungsten electrode can produce contamination in the weld or on the electrode tip altering its performance.
2.1.3 Polarity
The electrical polarity applied to the arc via the power supply is very important for the operation of an arc process. The direction of current flow in the arc produces the main effects of polarity on welding. There is potential for confusion regarding the direction of current flow since in welding literature current is commonly described as being in the direction of electron flow, or from the negative to the positive electrode. However, according to standard electrical convention, current is described as flowing from the positive to the negative electrode, or in the direction of the positively charged ions. In any case, in a welding arc, electrons flow from the negative electrode (cathode) to the positive electrode (anode), but this has different effects with different processes. In arc welding, a negative electrode and positive work polarity is referred to as DCEN (DC electrode negative) or historically DCSP (DC straight polarity). The electrons flow out of the welding electrode, through the arc and into the work piece. When the electrode is positive relative to the work the polarity is called DCEP (DC electrode positive) or historically DCRP (DC reverse polarity). Other polarity options are AC (simple alternating current) and VP (variable polarity) which refers to voltage waveforms and frequencies that are more complex and controllable than simple AC. In both cases, the polarity and direction of electron flow alternate during welding.
The effect of polarity on heat input and arc behavior differs with the process and the characteristics of the material being welded. For GTAW, DCEN produces the predominance of heat into the work, and is the most common polarity (Figure 2.6). This is because the tungsten electrode can be heated to extremely high temperatures without melting. At these extremely high temperatures, electrons are easily emitted or “boiled off” from the tungsten electrode (cathode) by a process known as thermionic emission. This produces a stable arc with most of the arc heat concentrating at the work piece where the electrons are deposited. When operating with DCEP polarity, most of the arc heat goes into the electrode which greatly accelerates electrode wear. But DCEP can be beneficial when welding aluminum since the electron emission process can help remove the tenacious aluminum oxide from the surface, a process known as cleaning action. This is where AC current can be advantageous since it delivers a half cycle of DCEN which heats the work piece, and a half cycle of DCEP which removes the oxide but doesn’t excessively heat the electrode.
Figure 2.6 DCEN—common with GTAW.
With GMAW, DCEN is generally not usable since the much lower temperature of the melting bare electrode wire cannot easily achieve thermionic emission, resulting in an arc that is very erratic and difficult to control. The unstable and erratic arc is the primary reason DCEN will generate minimal heat into the work piece in the rare cases when it might be used, and in those cases special wire that promotes thermionic emission will be required. On the other hand, DCEP produces a stable arc, and therefore, can sufficiently heat the work piece for welding. The arc stability with DCEP polarity when welding with the GMAW (Figure 2.7) process is due in part to the metal oxides on the work surface which facilitate the electron emission process. In addition to these surface oxides, thermionic emission becomes easier because electrons have a larger surface area when exiting the work piece as compared to the end of an electrode.
Figure 2.7 DCEP—common with GMAW.
Processes where fluxes are used such as SMAW, FCAW, and SAW can use DCEP, DCEN, or AC polarities, depending on the type of flux and the application. Flux additions that are in contact with the welding electrode can promote electron emission when the electrode is the cathode (DCEN). This allows the DCEN polarity to be an effective process choice. In some cases, DCEN may be selected to produce higher deposition rates due to greater electrode heating, with less heat input to the part. Because of the reduced heating at the part, with the proper electrode, the DCEN polarity works very well for welding thinner materials.
2.1.4 Heat Input
The energy or heat input that occurs in the making of an arc weld is an important consideration. It is expressed as energy per unit length, and is primarily a function of voltage, current, and weld travel speed as indicated in Figure 2.8. Although voltage plays a prominent role in the equation, it is a variable that is chosen primarily to create a stable arc and not for affecting heat input. Arc efficiency, f1, refers to what percentage of the total heat produced by the arc is delivered to the weld. Weld heat input is an important consideration because it affects the amount of distortion and residual stress in the part, and the mechanical properties of the welded part that are a function of the metallurgical transformations that take place during welding. In general, arc welding processes produce higher heat inputs than many other welding processes because arc heating is not very concentrated and tends to heat large areas of the work piece.
Figure 2.8 Heat input during welding.
Figure 2.9 compares some measured efficiencies (f1) for different processes. Less efficient processes such as GTAW may lose 50% or more of the arc heat to the surrounding atmosphere. On the other extreme, efficiencies of 90% or greater can be achieved with SAW because the flux and molten slag blanket act as an insulator surrounding the electrode and the arc. Arc efficiencies for other processes lie somewhere between. Although the efficiency of a given arc welding process directly affects heat input, it is typically not a reason affecting the choice of processes. This is because there are usually other much more important reasons driving the selection of the proper welding process for a given application.
Figure 2.9 Arc efficiency comparisons. (Source: Reproduced by permission of American Welding Society, ©Welding Handbook).
2.1.5 Welding Position
A significant factor in arc welding is the position of welding. Welding position refers to the way the weld joint is oriented in space relative to the welder. A flat position is the most common position in which the weld joint lays flat (such as on a table) and the molten weld pool is held in the joint by gravity. This is usually the easiest position for making a weld. But the flat position may not be an option, so welds often must be made in other positions. The most extreme is an overhead position that is directly opposite to a flat position. In this case, the molten metal is held solely by its surface tension. Overhead position welding is very difficult and requires significant welder skill. Therefore, welder qualifications include the important factor of position since some positions are much more difficult to master than others. Consideration of welding positions may also affect the choice of processes since not all arc welding processes work in all positions. AWS provides specific designations for all the possible welding positions which are described in Chapter 7.
2.1.6 Filler Metals and Electrodes
All arc welding processes except for GTAW and PAW use a consumable electrode. It is considered consumable because it melts from arc heating and mixes with the molten base metal to create the weld metal. It is called an electrode because it is part of the electrical circuit carrying the current to the arc. The filler metal used for GTAW and PAW is not called an electrode since it does not carry the current. There are numerous varieties of filler metals and electrodes available for different materials, arc welding processes, and applications. AWS provides specifications for filler metals which govern their production, but they are also subject to much proprietary protection regarding exact constituents and formulas.
2.1.7 Shielding
When metals are heated to high temperatures approaching or exceeding their melting point, reactions with the surrounding atmosphere are accelerated and the metals become very susceptible to contamination. Elements that can be most damaging are oxygen, nitrogen, and hydrogen. Contamination from these elements can result in the formation of embrittling phases such as oxides and nitrides, as well as porosity due to entrapment of gasses that form bubbles in the solidifying weld metal. To avoid this contamination, the metal must be shielded as it solidifies and begins to cool. The arc welding processes all rely on either a gas or a flux, or a combination of both for shielding. The way these processes utilize shielding is one of their main distinguishing features. Shielding is important to not only protect the molten metal, but the surrounding heated metal as well. Some metals such as titanium are especially sensitive to contamination from the atmosphere, and often require more thorough shielding techniques.
2.1.7.1 Gas Shielding
Processes such as GMAW, GTAW, and PAW rely solely on externally delivered gas for shielding. Gasses protect by purging atmospheric gasses away from the susceptible metal. The welding gun (or torch for GTAW) is designed so that a coaxial shielding gas flow emanates from the gun, which surrounds the electrode and blankets the weld area. In the case of GTAW and PAW, inert gasses are used with argon being the most common. Helium and blends of helium and argon can also be used. Helium is more expensive than argon, but it transfers more heat from the plasma column to the part due to the higher thermal conductivity of its ionized gas. In some cases, small amounts of hydrogen are added to argon to improve heating by transferring energies of molecular dissociation of the hydrogen in the plasma column to the work.
The GMAW process commonly uses argon for nonferrous metals, particularly aluminum. CO2 or blends of argon and O2 or CO2 are used for ferrous materials such as steels. CO2 gas produces more spatter and a rougher weld bead appearance, but can produce fast welding speeds, is readily available, and is inexpensive (because it is common and widely used commercially in products such as carbonated beverages). In some cases, additions of CO2 or small amounts of O2 to argon can improve electron emission from the negative electrode (or work piece) and enhance weld metal flow by affecting the surface tension of the molten puddle. Helium or blends of argon and helium are sometimes used for nonferrous metals. The choice of shielding gas for GMAW also plays a major role in the mode of molten metal transfer from the electrode to the weld pool.
2.1.7.2 Flux Shielding
The processes of SMAW, SAW, and FCAW use flux for shielding. A welding flux is a material used to prevent or minimize the molten and heated solid metal from forming potentially detrimental constituents such as oxides and nitrides, and to facilitate the removal of such substances if they form or are present prior to welding. Fluxes are used in arc welding processes in three different ways. They are: (1) applied in a granular form to the surface ahead of the weld (SAW), (2) bound with a binding agent to bare electrode wire (SMAW), and (3) contained in the core of a tubular wire (FCAW). Welding fluxes easily absorb moisture and therefore can be a major source of hydrogen to the weld puddle. As a result, when using processes that rely on flux, special care must often be taken when welding certain steels known to be susceptible to hydrogen cracking, a topic that is covered in Chapter 10.
Fluxes provide shielding in two primary ways. With SMAW and FCAW, the fluxes decompose when exposed to the heat of the arc to form CO2 gas to displace air from the arc. In the case of SAW, the flux melts to form a liquid that reacts with impurities in or on the weld metal to form a slag that floats on the top of the weld pool and later solidifies. SMAW and FCAW also typically form slag in addition to gas, with some electrodes forming more slag than others. Slags are removed at the end of welding and between welding passes with wire brushing or grinding. With some versions of FCAW, shielding gas is delivered through the nozzle as it is with GMAW. Figure 2.10 shows the various ways shielding is implemented with most common arc welding processes.
Figure 2.10 Forms of shielding for arc welding.
Welding fluxes serve other roles as well, including the very important function of stabilizing the arc by improving electron emission at the negative electrode. Elements that are referred to as deoxidizers or scavengers are added to remove undesirable materials such as oxides before they affect the weld. For example, such elements can make it possible to weld on steel with surface rust or mill scale. Other elements may be added to affect surface tension and improve the fluidity of the puddle. Iron powder is sometimes added to increase deposition rates, and alloying elements may be added to improve mechanical properties and form certain desirable metallurgical phases. Slag-forming elements produce molten slags that not only protect as described above but can also help shape the weld and assist in out‐of‐position welding. In the case of SAW, the flux that melts and floats to the top of the weld puddle plays a major role in the final shape of the weld bead. Table 2.1 shows some of the common elements that are added to create the various fluxes, and the roles that these elements play.
Table 2.1
