Finite element modelling of shielded metal arc welding

127 Pages·2006·1.78 MB·English

Finite Element Modelling of Shielded Metal Arc
Welding
By

M Cronje

Thesis presented at the University of Stellenbosch in
partial fulfilment of the requirements for the degree of

Master of Science in Mechanical Engineering

Department of Mechanical Engineering
Stellenbosch University
Private Bag X1, 7602 Matieland, South Africa

Study leader: Mr K. van der Westhuizen
Dr A.B. Taylor

December 2005
Copyright © 2005 University of Stellenbosch
All rights reserved
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DECLARATION

I, the undersigned, hereby declare that the work contained in this thesis is my
own work and that I have not previously in its entirety or in part submitted it at
any university for a degree.

Signature:……………………………………………..
M. Cronje

Date:……………………………………………….…..
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ABSTRACT

Finite Element Modelling of Shielded Metal Arc Welding
M. Cronje
Department of Mechanical Engineering
Stellenbosch University
Private Bag X1, 7602 Matieland, South Africa
Thesis: MScEng (Mech) December 2005

This study involved the modelling and verification of the Shielded Metal
Arc Welding of mild steel with the focus on displacement and temperature
distribution prediction of welded plates.
The project was divided into three phases namely; the literature survey
into finite element modelling of welding processes, the modelling of a welding
process and verification of the modelling with experimental results.
A working welding model was created using a commercial finite element
software package with the capabilities to model welding processes. The welding
model was systematically developed from a two-dimensional model into a three-
dimensional full physics process model. Experimental measured welding heat
input parameters were applied in the model, temperature dependent material
properties were applied and actual structural restraints from the experiments
were modelled.
Displacement and temperature distributions were measured on mild steel
plates welded with the Shielded Metal Arc Welding process. The plate
temperature was measured at various locations with K-type thermocouples spot
welded onto the plates. Plate deformation was measured at various stages of the
manufacturing process. Tendencies in plate displacement were investigated with
a change in certain welding parameters. The finite element model was verified
and good correlations were found, especially for the temperature distribution in
the welded plates.
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UITREKSEL

Eindige Element Modellering van Geskermde Metaal Vonk Sweis
M. Cronje
Departement Meganiese Ingenieurswese
Universiteit van Stellenbosch
Privaatsak X1, 7602 Matieland, Suid-Afrika
Tesis: MScIng (Meg) Desember 2005

Hierdie studie behels die modellering en verifiëring van Geskermde
Metaal Vonk Sweis van sagte staal met die fokus gemik op die verplasing en
temperatuur verspreiding van gesweiste plate.
Die projek was opgedeel in drie fases naamlik; die literatuurstudie van die
eindige element modellering van sweisprosesse, die modellering van ‘n
sweisproses en die verifiëring van die model met eksperimentele resultate.
’n Werkende model was geskep met die gebruik van ‘n kommersiële
eindige element pakket met die vermoë om sweisprosesse te modelleer. Die
sweis model was sistematies ontwikkel vanaf ’n twee-dimensionele model na ’n
volledige-proses drie-dimensionele model. Eksperimentele gemete sweis hitte-
inset parameters was toegepas in die model, temperatuur afhanklike materiaal
eienskappe en die strukturele beperkings van die eksperiment was gemodelleer.
Verplasing en temperatuur verspreiding van sagte staal plate, gesweis
met die Geskermde Metaal Vonk Sweisproses, was gemeet. Die plaat
temperatuur was gemeet by verskeie liggings met K-tipe termokoppels wat
gepuntsweis is op die plaat. Plaat verplasing was gemeet by verskillende
stadiums van die vervaardigingsproses. Tendense in plaat verplasing was
ondersoek met verandering in sekere sweis veranderlikes. Die resultate van die
eindige element metode was geverifieer en goeie korrelasie was gevind, veral vir
die temperatuur verspreiding in gesweiste plate.
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ACKNOWLEDGEMENTS

First of all, I would like to thank Dr Taylor and Mr Van der Westhuizen for
their persistent motivation, visionary guidance and continual support. You
believed in this project where others doubted. Your inspiration made this project
possible.
Many thanks to the modelling teams of Stellenbosch Automotive
Engineering (CAE) and IMEC (Belgium) who were always nearby and willing to
assist in the many challenges faced in this project. The free advice and support
you have given cannot be valued and I will always be in your debt.
The staff and artisans at SMD for all the mechanical services and
performing of the experiments, especially Mr Van der Vinne and Van der Berg for
their patience, support and advise which were unmistakably the backbone of the
project. Mr Cobus Zietsman who made everything possible and was never to
busy to give a helping hand.
Many friends, co-students and colleagues for their support and
understanding.
Lastly, my family who provided continuous support, love and motivation
and a very special lady friend, Hannelie, for the support and motivation during the
project.

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DEDICATIONS

I dedicate this to my father, you made this all possible.

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TABLE OF CONTENTS

DECLARATION...................................................................................................iii
ABSTRACT..........................................................................................................iv
UITREKSEL..........................................................................................................v
ACKNOWLEDGEMENTS....................................................................................vi
DEDICATIONS................................................................................................... vii
TABLE OF CONTENTS......................................................................................viii
LIST OF FIGURES..............................................................................................xi
LIST OF TABLES............................................................................................... xiv
NOMENCLATURE..............................................................................................xv
LIST OF ABBREVIATIONS ...............................................................................xvii
1 INTRODUCTION...........................................................................................1
2 WELDING......................................................................................................3
2.1 Background of Welding...........................................................................3
2.2 Physics of Welding.................................................................................4
2.2.1 Heat Transfer ..................................................................................4
2.3 Welding Processes.................................................................................5
2.3.1 Shielded Metal Arc Welding ............................................................6
2.3.2 Gas Metal Arc Welding....................................................................6
2.3.3 Gas Tungsten Arc Welding..............................................................7
2.4 Welding Distortions.................................................................................8
2.4.1 Control of Welding Distortions.........................................................9
2.4.2 Calculation of Welding Distortions.................................................13
2.5 Metallurgy of Welding...........................................................................14
2.5.1 Low Carbon Steels........................................................................14
2.6 Conclusion............................................................................................16
3 FINITE ELEMENT METHOD: APPLICATION TO WELDING......................17
3.1 Introduction...........................................................................................17
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3.2 Finite Element Analysis of Welding ......................................................17
3.2.1 Two-dimensional vs. Three-dimensional Modelling.......................18
3.2.2 Thermal and Structural Analysis....................................................21
3.2.3 Prediction of Welding Distortion ....................................................21
3.2.4 Modelling Assumptions..................................................................22
3.2.5 Applied Heat Source......................................................................23
3.2.6 Time Step Estimate.......................................................................27
3.2.7 Boundary Heat Loss Conditions....................................................29
3.3 Material Properties ...............................................................................30
3.3.1 Conductivity...................................................................................30
3.3.2 Specific Heat.................................................................................31
3.3.3 Yield Strength................................................................................33
3.3.4 Alternative Material Property Methods...........................................34
3.4 Conclusion............................................................................................35
4 EXPERIMENTS...........................................................................................37
4.1 Introduction...........................................................................................37
4.2 Experimental Set Up.............................................................................38
4.3 Effect of Restraints...............................................................................40
4.3.1 Introduction....................................................................................40
4.3.2 Results..........................................................................................42
4.4 Effect of Plate Thickness......................................................................44
4.4.1 Introduction....................................................................................44
4.4.2 Results..........................................................................................46
4.5 Effect of Current Setting.......................................................................54
4.5.1 Introduction....................................................................................54
4.5.2 Results..........................................................................................54
4.6 Temperature Measurement..................................................................58
4.6.1 Introduction....................................................................................58
4.6.2 Results..........................................................................................60
4.7 Conclusion on Experiments..................................................................64
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5 MODELLING OF WELDING EXPERIMENTS.............................................66
5.1 Introduction...........................................................................................66
5.2 Weld Modelling in MSC.Marc ...............................................................67
5.3 Weld Model Preparation.......................................................................67
5.3.1 Geometry and Element Meshing...................................................67
5.3.2 Material Properties........................................................................68
5.3.3 Boundary Conditions.....................................................................69
5.3.4 Element Activation/De-Activation ..................................................71
5.3.5 Coupled and Uncoupled Analysis..................................................72
5.4 Numerical Results ................................................................................73
5.4.1 Thermal Results............................................................................73
5.4.2 Structural Results..........................................................................75
5.4.3 Experiment vs. FEM......................................................................81
6 CONCLUSION.............................................................................................83
6.1 Recommendations................................................................................85
REFERENCES...................................................................................................86
APPENDIX A......................................................................................................91
A.1 Calculation of Natural Convection ........................................................91
APPENDIX B EXPERIMENTAL RESULTS........................................................95
B.1 Effect of Restraints...............................................................................95
B.2 Effects of Plate Thickness....................................................................99
B.3 Effect of Heat Input.............................................................................103
APPENDIX C EXPERIMENTAL TEMPERATURE RESULTS..........................107

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