A CAE simulation methodology was developed to predict the warpage and shape deviation from nominal in finished plastic sub-assemblies that are joined using Infra-Red (IR), hot-plate or vibration welding processes. An automotive glove box bin and door sub-assembly was used to develop the methodology. It was seen that part warpage from injection molding and welding causes warpage in final assembled product which results in gaps and the consequent loss in quality of appearance.The CAE simulation methodology included prediction of the part warpage with residual stress from the injection molding process, use the post-molded shape as an initial part condition for the welding process, and simulation of the welding process itself. The welding process simulation included fixturing of the parts in the welding process, localized heating in the case of an IR welding process, fusion of the parts at the weld locations and thermal creep resulting in long term stress and shape relaxation of the part.This simulation methodology was seen to correlate well with observed part warpage. Further refinements to the processes are being evaluated and a robust simulation based predictive methodology is being developed.