The paper summarizes the latest developments in numerical simulation and optimization of resistance welding as well as new developments in 3D simulation. Resistance welding simulation can be applied for the prediction of weld nugget sizes in various material combinations, and for the optimization and planning of welding process parameters. Weld quality can be modelled in terms of microstructural phase changes, resulting hardness distribution and strength under specified loading conditions. New developments for 3D simulation of complex joints allow for modelling strength testing and special effects such as shunting. Furthermore, projection welding often needs 3D simulation. 3D simulation of a new, lightweight, sandwich material is presented in the paper.