Taylor & Francis Taylor & Francis Croup Boca Raton London New York

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1 RESISTANCE WELDING Fundamentals and Applications Hongyan Zhang Jacek Senkara Taylor & Francis Taylor & Francis Croup Boca Raton London New York A CRC title, part of the Taylor & Francis imprint, a member of the Taylor & Francis Croup, the academic division of T&F Informa plc.

2 Contents Chapter 1 Welding Metallurgy 1.1 Solidification in Resistance Spot Welding Phase Transformations in RSW Transformations in Steels Continuous Cooling of Plain Carbon Steels Transformations in the HAZ of a Steel Weld Structures of a Steel Weld and an Aluminum Weld Cracking Solidification Cracking Liquation Cracking 15 References 16 Chapter 2 Electrothermal Processes of Welding 2.1 Introduction Electrical Characteristics of Resistance Welding Bulk Resistance Contact Resistance Total Resistance Shunting Thermal Characteristics of Resistance Welding Heat Balance The Law of Thermal Similarity Heat Balance Modified Heat Balance Theory Experimental Verification Electrode Life Experiment Rapid Electrode Life Determination Electrode Life Tests Relations between 60 Weld Electrodes and Electrode Life Lobe Diagrams Current Profiles Constant Current Half-Sine Current Profile Sinusoidal Current Profile Effects of the Current Profiles 56 References 59

3 Chapter 3 Weld Discontinuities 3.1 Classification of Discontinuities External Discontinuities Internal Discontinuities Void Formation in Weld Nuggets Gas Bubbles Effect of Volume Shrinkage Cracking in Welding AA6111 Alloys Cracking in Welding AA5754 Alloys Liquation Cracking in Aluminum Alloys Mechanisms of Cracking Metallurgical Effect Thermomechanical Effects Thermal Stress during Heating Thermal Stress during Cooling Influence of Other Factors Cracking Suppression Effect of Specimen Width and Electrode Geometry Effect of Welding Sequence Effect of Washer Clamping Effect of Current Shunting 98 References 103 Chapter 4 Mechanical Testing 4.1 Introduction Shop Floor Practices Chisel Test Peel (Roller) Test Bend Test Instrumented Tests 1ll Static Tests 1ll Tension Test Tension-Shear Test Dynamic Tests Fatigue Test Impact Test A New Impact Tester Torsion Test Twisting Torsional Shear Test 141 References 141 Chapter 5 Resistance Welding Process Monitoring and Control 5.1 Introduction 143

4 5.2 Data Acquisition Process Monitoring Signals Commonly Monitored during Welding Electric Voltage Electric Current Dynamic Resistance Electrode Displacement Electrode Force Acoustic Emission Pneumatic Pressure Fluctuation Adaptive Noise Cancellation Relationship between Monitored Signals and Welding Processes Effects of Process Conditions Fault Identification Expulsion Detection Preweld Fault Condition Determination Lobe Diagrams Constant-Power Density Hypothesis Algorithm Algorithm Implementation Gain Scheduling Experimental Results Artificial Neural Network Modeling A Case Study of Using ANN for RSW Quality Control 185 References 189 Chapter 6 Weld Quality and Inspection 6.1 Weld Quality Attributes Weld Attributes Weld Attributes Weld Performance Process Characteristics Weld Quality Requirements Relations between Weld Attributes and Strength Destructive Evaluation Peel Test Chisel Test Metallographic Test Nondestructive Evaluation Ultrasonic B-Scan Examining Various Welds Using the B-Scan System Identification of Cold Welds 218

5 6.3.4 Relationship between Weld Attributes and Weld Strength References 224 Chapter 7 Expulsion in Resistance Spot Welding 7.1 Influence of Expulsion on Spot Weld Quality Expulsion Process and Detection Expulsion Prediction and Prevention Geometry Comparison Model Force Balance Model The Principle Evaluation of Effective Electrode Force Pressures and Forces in the Liquid Nugget Statistical Modeling Modeling Procedure Statistical Analysis Summary Examples...' Application of the Force-Balance Model Calculation of Pressures and Forces Experimental Verification Perspective Applications Examples of the Use of the Statistical Model Experiments Discussion 266 References 279 Chapter 8 Influence of Mechanical Characteristics of Welding Machines 8.1 Introduction Mechanical Characteristics of Typical Spot Welders Influence of Machine Stiffness Effect on Electrode Force Effect on Electrode Displacement Effect on Electrode Touching Behavior Effect on Weld Formation Expulsion Weld Strength Effect on Electrode Alignment Stiffness and Damping Ratio Estimation Influence of Friction Effect on Electrode Force Effect on Electrode Displacement Effect on Microstructure Effect on Tensile-Shear Strength Influence of Moving Mass 305

6 8.5.1 A Dynamic Force Analysis Effect on Weld Quality Follow-Up in a Welding Cycle Thermal Expansion Effect of a Pneumatic Cylinder Theoretical Analysis Experiment Results Squeeze Time and Hold Time Measurement Other Factors Electrode Alignment and Workpiece Stack-Up Electrode Force Materials 327 References 330 Chapter 9 Numerical Simulation in Resistance Spot Welding 9.1 Introduction Comparison between the Finite Difference and Finite Element Methods Discretization Geometry Formulation Accuracy and Others Methods of RSW Process Simulation Coupled Electrical-Thermal-Mechanical Analysis A General (Three-Dimensional) Finite Element Model Formulation of Electric Process Formulation of Heat Transfer Process Boundary Conditions Formulation of Thermomechanical Analysis Simulation of Melting and Solidification Finite Element Formulation Two-Dimensional Finite Element Modeling Formulation for Electric Analysis Formulation of Thermal Analysis Finite Element Formulation Axisymmetric Problems Simulation of Contact Properties and Contact Area Simulation of Other Factors Effect of Zinc Coating Effect of Electric Current Profile Modeling of Microstructure Evolution Effect of Cooling Rate Microstructure Evolution in the Heat-Affected Zone Simulation of Microstructure of a Nugget An Example of Simulating Microstructure Evolution in a Spot Weldment 358

7 9.6 Examples of Numerical Simulation of RSW Processes Case Study I: Effect of Electrode Face Geometry Case Study II: Differences between Using Coupled and Uncoupled Algorithms Case Study III: Effect of Electrode Axial Misalignment Case Study IV: Effect of Angular Misalignment of Domed Electrodes 364 References 367 Chapter 10 Statistical Design, Analysis, and Inference in Resistance Welding Research 10.1 Introduction Basic Concepts and Procedures Data Collection Statistical Modeling and Data Analysis Inference and Decision Making Experiments with Continuous Response Statistical Design Factorial Designs Orthogonal Arrays Second-Order Designs Robust Parameter Designs The Use of Blocks Analysis and Modeling Use of Graphs Multiple Regression Model Residual Analysis Location-Dispersion Modeling for Variance Reduction Inference and Decision Making Factor Screening Treatment Comparison Combination of Experiments Response Surface Exploration Variance Reduction Two-Stage Sliding-Level Experiments Experiment Design Analysis and Modeling Analysis of Current Range Analysis of Button Size Inference and Decision Making Experiments with Categorical Responses Experiment Design Analysis and Modeling Inference and Decision Making 402

8 Statistical Analysis Coding System and Transformations Use of Pseudodata Analysis and Results Inference and Decision Making Computer Simulation Experiments Experiment Design Analysis and Modeling Planning of Numerical Experiments Results and Inference Summary 421 References 421 Index 425