Numerical and experimental study on nugget formation in resistance spot welding for three pieces of high strength steel sheets

A resistance spot welding for three pieces of high strength steel sheets was selected as a research subject and the nugget formation processes at the various welding conditions were investigated by both experimental measurement and FEM simulation. The FEM program developed by the authors considered the coupling of the electrical field, thermal field and mechanical field. The interface elements were used to model the transient contact states between two worksheets or between a worksheet and an electrode. The electrical resistance and thermal–mechanical properties of the interface elements change with the contact state, and can have different values from the worksheets and electrodes. The nugget sizes and its formation process predicted by FEM agreed very well with experimental results. The welding conditions (current, cycles and force) to produce sound nuggets for both two pieces and three pieces of high strength steel sheets were accurately estimated by the simulation.