A model of the dynamic variation of geometry in the resistance spot weld is presented. Due to the complexities arising from the complex flow paths of the electric current, the material property variation during welding and the phase change problem between the nugget and solid region, an approximate method based upon the integral method that is one of the Weighted Residual Methods is employed, accompanying the divergence theorem along the boundary concerned. Through thus obtained model, the nugget growth pattern varied with heat input, weld cycle and the other parameters can be examined.
The patterns are compared with the experimentally obtained ones by observation of the macro-photographs of the prepared specimens made of mild steel. Despite of many assumptions in the analysis, the comparison result shows that the nugget radius growth and penetration are well predictable by the proposed model.
