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 ii 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:……………………………………………….….. iii 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. iv 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. v 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. vi DEDICATIONS I dedicate this to my father, you made this all possible. vii 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 viii 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 ix 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 x
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