Estimation of lobe curve with material strength in resistance projection welding

This study aims at estimating lobe curve in resistance projection welding (RPW) according to material strength. A three-dimensional (3D) fully coupled electrical-thermal-mechanical finite element (FE) model was developed by considering temperature-dependent material properties and projection forming process. Residual stress within the projection after stamping process, which affects the initial contact resistance, increases as projection height and material strength increase. For DP780 steel, an average error of nugget size between welding experiments and FE analyses is less than 10 %. A method for estimating lobe curves with material strength including welding parameters such as electrode force, current, welding time and projection height is proposed based on systematic FE analyses. Lobe curve moves towards a lower current region as the material strength increases.