The Physics of Welding

Chapter 1: Symbols, Units and Dimensions

1.1 SI Units

1.2 EMU and ESU Systems

1.3 This Book

Chapter 2: The Physical Of Fluids at Elevated Temperatures

2.1 Introduction

2.2 Gases

2.2.1 Dissociation and Ionization

2.2.2 The Equation of State of a Gas at Elevated Temperature

2.2.3 The Equilibrium Constant

2.2.4 Evaluating the Degree of Dissociation and Ionization

2.2.5 Specific Heat

2.2.6 Transport Phenomena

2.2.7 Particle Encounters in a Slightly Ionized Gas

2.2.8 Particle Encounters in a Highly Ionized Plasma

2.2.9 Electrical Conductivity

2.2.10 Thermal Conductivity

2.2.11 Viscosity

2.2.12 Calculating the Transport Coefficients

2.3 Liquid Metals

2.3.1 Vapor Pressure

2.3.2 Surface Tension

2.3.3 Viscosity

Chapter 3: Electricity and Magnetism

3.1 Electrons and Ions

3.2 Electrostatics

3.3 Gauss's Law

3.4 The Magnetic Force

3.5 The Law of Biot and Savart

3.6 Electromagnetic Induction

3.7 The Maxwell Stress and the Force on a Conducting Body

3.7.1 The Force Acting on a Liquid Drop Carrying an Electric Current

3.8 The Current Density and Ohms Law

3.9 The Pinch Instability: an Approximate Solution

3.10 The Dynamics of Instability in Fluid Cylinder

3.11 Predicted Behavior of Perturbed Cylinder: Radial Pinch (m = 0)

3.12 The Higher Unstable Modes (m > 0)

3.13 The Effect of an Externally-Applied Magnetic Field

3.14 The Growth Rate Constant

3.15 The Effect of Viscosity on the Instability of a Fluid Cylinder

3.16 Instability of a Viscous Liquid Cylinder with a Surface Charge and Carrying an Axial Current

Chapter 4: Fluid and Magneto Fluid Dynamics

4.1 Introduction

4.2 The Continuity Equation

4.3 The Momentum Equation

4.4 Momentum

4.5 Pressure

4.6 Viscosity

4.7 Lorentz Force

4.8 Other Forces, and the Equilibrium Condition

4.9 The Stream Function

4.10 The Components of Stress

4.11 The Bernoulli Equation

4.12 Solutions of the Momentum Equation

4.13 Laminar Flow from a Point Source of Momentum with no Electric Current: the Steady Jet

4.14 The Fluid Pressure in the Jet

4.15 The Steady Jet with a Heat Source

4.16 Laminar Flow from a Point Source in a Semi-Infinite Fluid (No Electric Current)

4.17 Laminar Flow in a Semi-Infinite Fluid having a Point Source of Current in the Plane θ = ττ/2

4.18 Laminar Flow in a Semi-Infinite Fluid: the Linear Solution

4.19 The Time-Dependant Development of Flow due to a Point Source of Current in a Semi-Infinite Region

4.20 Breakdown of the Solution to the Non-Linear Problem

4.21 Other Limitations to Analytical Solutions of the Momentum Equation

4.22 Laminar Flow in a Liquid Drop Immersed in a Conducting Fluid Carrying an Electric Current

4.23 Distortion of the Liquid Drop

4.24 An Ellipsoid of Revolution in a Conducting Fluid: the Drag Coefficient

4.25 Laminar Flow in a Hemisphere having a Point Source of Current at the Origin

4.26 Flow in a Container Induced by a Distributed Current Source

4.27 Flow Induced by a Gradient of Surface Tension

Chapter 5: The Electric Arc

5.1 Introduction

5.2 General Description of Glow and Arc Discharges

5.3 Principal Characteristics of the Electrode Regions of Arcs

5.3.1 High Electric and Thermal Fields

5.3.2 Contraction

5.4 Classification based on Degree of Contraction: Range of Observed Current Density

5.5 Glow and Arc Cathode, Glow and Arc Plasma, Glow and Arc Cathode and Anode Falls

5.6 Distinction between Thermionic and Non-Thermionic Cathodes

5.7 The Low-Voltage Non-Thermionic Cathode

5.7.1 Surface Clean Up and Movement in Magnetic Field including Retrograde Motion

5.7.2 Vapor and Plasma Jets. Force on Cathode

5.7.3 Electrode Material and Surface State

5.7.4 Nature of Gas or Vapor

5.7.5 Value of Current

5.7.6 Gas Pressure, Vacuum Arcs

5.8 Theories of the Cathode Mechanism

5.8.1 The Glow Cathode: The Thermionic Cathode

5.8.2 Theories of the Non-Thermionic Cathode

5.9 The Arc Column

5.10 The Anode

5.10.1 Theory of Glow Anode

5.10.2 Anode Fall Voltage and Current Density

5.10.3 Energy Balance at the Anode

5.10.4 Plasma and Vapor Jets

Chapter 6: The Electric Arc in Welding

6.1 Introduction

6.2 Structural Features

6.2.1 Overall Electrical Characteristics

6.2.2 The Total Arc Characteristics at Various Pressures

6.2.3 Relationship between Power Source and Arc Characteristics

6.2.4 Arc Efficiency

6.3 Cathode Phenomena

6.3.1 Cathode Phenomena and Characteristics: Thermionic Cathodes

6.3.2 The Potential Drop Adjacent to a Thermionic Cathode

6.3.3 Cathode Phenomena and Characteristics: Non-Thermionic Cathodes

6.4 Anode Phenomena

6.4.1 Anode Characteristics

6.4.2 The Anode at the Tip of the Rod

6.4.3 The Heat Balance at the Anode

6.4.4 The Depth of the Anode Drop Zone

6.4.5 Gas Metal Reactions at the Anode

6.5 The Arc Column

6.5.1 The Energy Flux in the Arc Column

6.5.2 The Arc Column Temperature

6.5.3 Mass Flow in the Arc Column

6.5.4 The Effect of Pressure Variation on the Arc Column

6.5.5 Calculating Mass and Heat Flow in the Arc Column

6.5.6 Arc Stiffness and Arc Blow

6.5.7 Controlling Arc Stiffness and Arc Force

Chapter 7: Metal Transfer and Mass Flow in the Weld Pool

7.1 Metal Transfer

7.1.1 Introduction

7.1.2 The Effect of Static Forces in Drop Detachment

7.1.3 The Pinch Instability in GMA Welding

7.1.4 Other Unstable Modes

7.1.5 The Burnoff Rate

7.1.6 The Drop Temperature

7.1.7 The Drop Transfer Rate

7.1.8 The Pinch Model Applied to the Droplet Transfer Rate

7.1.9 Pulse Arc Welding

7.1.10 Transfer of Drops across the Arc

7.1.11 The Arc Force

7.2 The Weld Pool

7.2.1 Flow in the Weld Pool

7.2.2 The Weld Pool Temperature

7.2.3 The Shape of the Weld Pool and the Reinforcement Bead

Chapter 8: High Power Density Welding

8.1 Introduction

8.2 Keyholing

8.2.1 Range of Power Densities in Welding Processes

8.2.2 Threshold Power Density for Vaporisation

8.2.3 Size of the Keyhole

8.3 Discussion on Forces Acting Within the Keyhole

8.3.1 Forces Tending to Form and Maintain the Keyhole

8.3.2 Forces Tending to Close the Keyhole

8.3.3 Pressure Balances for a Generalized Keyhole

8.3.4 Moving Weld Pool

8.4 Heat Transfer Analysis

8.5 Plasma Welding

8.5.1 Principles of Operation

8.5.2 Applications and Advantages

8.5.3 Keyhole Stability for Plasma Welding

8.6 Electron Beam Welding

8.6.1 Principles of Operation

8.6.2 Applications and Advantages

8.6.3 Keyhole Stability for Electron Beam Welding

8.7 Laser Welding

8.7.1 Principles of Operation

8.7.2 Applications and Advantages

8.7.3 Keyhole Stability for Laser Welding

8.8 Glow Discharge Electron Beam Welding

8.8.1 Principle of Operation

8.8.2 Application and Advantages

8.8.3 Keyholing

Appendix A: Electrode Wire Heating in Terms of Welding Parameters

Index