Keyhole gas tungsten arc welding

311 Pages·2012·6.8 MB·English

University of Wollongong
Research Online
University of Wollongong Thesis Collection University of Wollongong Thesis Collections
2001
Keyhole gas tungsten arc welding: a new process
variant
Brian Laurence Jarvis
University of Wollongong
Recommended Citation
Jarvis, Brian Laurence, Keyhole gas tungsten arc welding: a new process variant, Doctor of Philosophy thesis, Faculty of Engineering,
University of Wollongong, 2001. http://ro.uow.edu.au/theses/1833
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Keyhole Gas Tungsten Arc Welding:
a new process variant.
tSS!1'
This photograph is an end-on view of keyhole G T AW on 8mm wall-thickness
stainless steel pipe.
Certification
I, Brian Laurence (Laurie) Jarvis, declare that this thesis, submitted in fulfilment of
the requirements for the award of Doctor of Philosophy, in the Department of
Mechanical Engineering, University of Wollongong, is wholly my own work unless
otherwise referenced or acknowledged. The document has not been submitted for
qualifications at any other academic institution.
Brian Laurence Jarvis
15m July 2001.
Keyhole Gas Tungsten Arc Welding:
a new process variant
By
Brian Laurence Jarvis
B.Sc. (Hons) Flinders University, 1975
Thesis
Submitted in fulfilment of the requirements
for the degree of Doctor of Philosophy in Mechanical Engineering,
Faculty of Engineering, University of Wollongong
June 2001.
Wollongong, New South Wales
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Dedication
To my Mother and Father
Acknowledgements
I wish to thank my adviser and supervisor, Professor Michael West, for his support
and direction during this investigation.
Special thanks are also due to my co-supervisor, colleague and friend, Dr Nasir
Ahmed for laying the foundations for this work, and for his continued encouragement
and support. Particular thanks are also extended to Ken Barton, who has played such a
major role in the practical development of this process. Thanks are also extended to
my many colleagues who have contributed in numerous ways.
This work has been made possible through the support and generosity of the CSIRO
and the CRC for Welded Structures (formerly the CRC for Metals Welding and
Joining)
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Table of Contents
ACKNOWLEDGEMENTS HI
TABLE OF CONTENTS IV
TABLE OF TABLES X
TABLE OF FIGURES XII
NOMENCLATURE XVITI
ABSTRACT 1
1. THESIS 2
1.1. OBJECTIVES 2
/././. Introduction 2
1.1.2. Thesis 2
1.1.3. Implications 3
1.2. JUSTIFICATION STRATEGY 4
1.2.1. Justification criteria 4
1.2.2. Outline 4
1.2.3. Detailed research intentions 4
2. LITERATURE REVIEW - DEEP PENETRATION WELDING 7
2.1. INTRODUCTION 7
2.1.1. Power density infusion welding 7
2.1.2. Fluidf low in conventional arc welding. 9
2.2. KEYHOLE (DEEP PENETRATION) WELDING PROCESSES 11
2.2.1. Electron Beam 11
2.2.2. Plasma Arc 13
2.2.3. Laser Beam 13
2.3. BEAM-TO-WORK-PIECE COUPLING 15
2.3.1. Electron beam coupling 15
2.3.2. Laser beam coupling 16
2.3.3. Laser-matter interactions 19
2.4. KEYHOLE MODELS 21
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2.4.1. Conduction Models 22
2.4.2. Fundamental models 24
2.4.3. Dynamic behaviour 26
2.5. PLASMA ARC KEYHOLES 29
2.5.1. Process characteristics 29
2.5.2. Variable polarity plasma arc welding 30
2.5.3. Enhanced plasma arcs 31
2.5.4. Fluid flow in VPPA weldments 32
3. A PRACTICAL APPRAISAL OF KEYHOLE GTAW 34
3.1. INTRODUCTION 34
3.1.1. Background 34
3.1.2. Keyhole mode GTAW 37
3.2. EQUIPMENT 40
3.3. PROCESS PARAMETERS 42
3.3.1. Introduction 42
3.3.2. Threshold current 43
3.3.3. Experimental schedule 44
3.3.4. Travel speed 45
3.3.5. Voltage 45
3.3.6. Shielding gas 46
3.3.7. Electrode geometry 47
3.3.8. Combined effects of gas and electrode geometry: 5.6mm SAF 2205 48
3.3.9. Material 48
3.3.10. Other variables: wire feed, flow-rate and the influence of cross flow 49
3.4. PROCESS PERFORMANCE AND OPERATING WINDOWS 50
3.4.1. Joint qualification 50
3.4.2. Operational windows 56
3.4.3. Application to pipe 58
3.4.4. Process extensions 61
3.4.5. Competitiveness 62
4. THE ROLE OF SURFACE TENSION IN KEYHOLE BEHAVIOUR. 65
4.1. SURFACE TENSION IN RELATION TO KEYHOLE FAILURE 65
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4.1.1. 2-D verses 3-D geometries 65
4.1.2. Aspects of surface tension 69
4.1.3. Keyhole failure in thick plate 71
4.1.4. Travel speed 76
4.1.5. A first rule for keyhole stability. 77
4.1.6. Control limitations 78
4.1.7. Keyhole failure in thin plate 82
4.1.8. A secondrule for keyhole stability. 85
4.1.9. Failure characteristics 87
4.2. DISPLACEMENT OF METAL IN THE G T AW KEYHOLE 89
4.2.1. Deficit 89
4.2.2. Experimental method and results 91
4.2.3. Forces required maintaining a deficit 93
4.2.4. Discussion of displacement results 95
4.2.5. Characteristics of the transition 100
4.3. MATHEMATICAL CONSIDERATIONS FOR WELD POOL SURFACES 105
4.3.1. Introduction 105
4.3.2. The equation for weld pool surfaces 105
4.3.3. Equation for axi-symmetric weld pools 108
4.3.4. Solutions for axi-symmetric weld pools Ill
4.3.5. Numerical verification 115
4.3.6. Moving weld pools 120
4.3.7. The effects of flow on the surfaces 121
4.3.8. Numerical simulation of the process 124
4.4. KEYHOLES FROM A GEOMETRIC PERSPECTIVE 124
4.4.1. Surface types 124
4.4.2. Transitions and hysteresis 126
4.4.3. Hysteresis in the M-K transition 127
4.4.4. More surfaces and porosity. 128
4.4.5. Undercut. 129
5. DISPLACEMENT FORCES IN GTAW 131
5.1. A MATHEMATICAL MODEL FOR ARC FORCES 131
5.1.1. Arc force fundamentals 131
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