Arc welding control

Preface ix List of symbols xii Part I Dynamic behaviour of arc welding 1 Theoretical analysis 3 1.1 Introduction 3 1.2 Welding with constant wire-feed rate 4 1.3 Welding with regulated wire-feed rate 12 1.4 Welding with both regulated wire-feed rate and self-regulation 15 2 Dynamic characteristics of power sources 19 2.1 Status of research 19 2.2 Description of dynamic characteristics 25 2.3 Transfer functions of power sources 26 2.4 Measurement of the transfer function 41 2.5 Influence of the transfer function on technological properties 48 2.6 Summary 50 3 Experimental study 52 3.1 Introduction 52 3.2 CO2 welding 53 3.3 DC MIG welding 68 3.4 Pulsed MIG welding 75 3.5 Summary 81 v Part II Welding arc control 4 Control method QH-ARC 101 85 4.1 Status of research on welding arc control 85 4.2 Principle of control method QH-ARC 101 88 4.3 Realisation of double-step characteristic 92 4.4 Circuit for alternating between two double-step output characteristics 100 4.5 Static accuracy and dynamic characteristics 103 4.6 Circuit diagram of the power source 115 4.7 Technological behaviour 117 5 Control method QH-ARC 102 and 103 126 5.1 Introduction 126 5.2 Control method QH-ARC 102 129 5.3 Control method QH-ARC 103 134 5.4 Mathematical analysis of arc operating-point movement 148 5.5 Closed-loop control of weld penetration 168 6 Arc control of CO2 welding and AC MIG welding 179 6.1 CO2 welding 179 6.2 AC MIG welding 194 Part III Arc sensors and seam tracking 7 Sensors for weld-seam tracking 235 7.1 Status of research and development 235 7.2 Status of the application of arc sensors in industry 240 7.3 Principles of seam tracking with arc sensors 243 7.4 Scanning arc-welding torches 248 8 Mathematical models of arc sensors 261 8.1 Introduction 261 8.2 Static model 261 8.3 Dynamic model 271 9 Processing of arc-sensor signals 296 9.1 Introduction 296 9.2 Signal processing of an ideal welding arc 296 9.3 Analysis of signal characteristics 313 vi Contents 9.4 Filtering of signals 327 9.5 Signal processing in a practical welding process 343 10 An automatic seam-tracking machine with an arc sensor 360 10.1 Introduction 360 10.2 Conventional automatic seam-tracking machine 360 10.3 Crawling type of tractor 374 Part IV Real time measurement of welding temperature-field 11 Principles of the colorimetric imaging method 411 11.1 Introduction 411 11.2 Fundamentals of the colorimetric imaging method 417 12 Study of the colorimetric imaging method 429 12.1 Introduction 429 12.2 Facilities for acquisition of the infrared image 429 12.3 Sensor for experimental use 432 12.4 The colorimetric imaging system 435 12.5 Calibration of the system using a mathematical method 439 12.6 Experimental results and verification 440 12.7 Calibration procedure 444 12.8 Effects of measurement conditions 445 13 Design of a colorimetric imaging apparatus 450 13.1 Introduction 450 13.2 Formation of the thermal-radiation image 450 13.3 Theoretical analysis of the colorimetric imaging method 453 13.4 Division of the temperature field 457 13.5 Wavelength of the filter 462 13.6 Design of the sensor 470 13.7 Effects of measuring conditions 477 13.8 Calibration of the system 484 14 Practical measurement and application 488 14.1 Experimental apparatus 488 14.2 Measurement of the welding temperature field 488 Contents vii 14.3 Mathematical model of the temperature field in welding based on measurement 492 14.4 Theoretical results and measured data for different welding parameters 503 14.5 Extraction of the thermal-cycle parameters 505 14.6 Three-dimensional welding temperature field 507 14.7 Closed-loop control of weld penetration 511 14.8 Summary 525 Part V Automatic path programming of robot 15 Vision systems and automatic path programming 531 15.1 Recognition of the groove path 531 15.2 A robot with automatic path programming 548 References 582 Index 601