3D FE Simulations of Resistance Spot Welding

Sammanfattning: Resistance spot welding (RSW) is thedominant joining technology in theautomotive industry. This is due to its lowcosts and high efficiency. Other advantageswith RSW is the high ability for automation,low consumption of energy, lack of need foradded materials and low degree of pollution,no expensive equipment or education ofpersonal compared to arc welding and laserwelding. A modern automobile containsapproximately 4000 resistance spot welds,which is why it is of great interest to be ableto predict the properties of the resistance spotwelds. The most important measurementused to ensure the quality of the weld is thenugget size, as it correlates to the weldsmechanical strength. This is usuallymeasured by destructive testing, and the mostcommon method is the coach peel test. Thistest is performed by manually peeling thespecimen and then measuring the largest andsmallest nugget diameter. It is also possibleto perform non-destructive testing onresistance spot welds with both ultrasonicandx-ray tests, however none of thesemethods have the same accuracy as thedestructive methods and they arecumbersome to use in large-scale. Toimprove the efficiency and lower the cost forthe optimization of the welding parameters,simulation tools have been developed. Thereare both 2D- and 3D-simulation software tomodel the RSW process. When the spotwelds are simulated with 2D or 2D axissymmetry,the number of elements is lowercompared to a full 3D model, which reducesthe computation times. The disadvantageswith the 2D model are the inabilities tomodel misalignments or other asymmetricalgeometries. In contrast, the 3D-simulationsare not limited by these factors, and they arealso capable of modeling the shunt effectsoccurring when a weld is placed close to aprevious weld.The aims of this thesis was to evaluate such a3D-simulation software, Sorpas 3D, and itspotential to be used in industrial processplanning, and to assess the software’susefulness for both simple and more complexcases.The results from this work show a goodcorrespondence between the simulations andthe physical tests. However, in order toachieve these results a number ofmodifications in the material properties wererequired. Another critical limitation in thesoftware is that no expulsion criterion isimplemented. Considering the possibility thatthe problems can be solved with a number ofupdates in the software, Sorpas 3D can be auseful tool in the process planning industry inorder to decrease process times and materialcosts and improve the weld quality in thefuture.