Abstract: Formation of residual stresses during hot plate welding and other plastic welding processes can have detrimental effects on the joint quality under static and dynamic loading as well as reduce the corrosion resistance of the joints. Therefore, it is important to measure and predict residual stress level to prevent premature failures. Uncoupled finite element thermal analysis and viscoelastic stress-strain analysis were used to calculate the temperature distribution and history in the parts and thermal and residual stress formation during welding. Thermal properties and viscoelastic relaxation modulus of polycarbonate were compiled from the literature to build the material model for the finite element simulation. Residual stress levels in hot plate polycarbonate welds were computed for different hot plate temperatures and heating times. It was found that shorter heating times resulted in faster cooling rates and higher residual stress. The model was also used to calculate residual stresses in through transmission infrared and vibration welding of polycarbonate. The predicted residual stress levels and distributions were in good agreement with published experimental results for hot plate and through transmission infrared welding. Thus, finite element modeling is an effective way for predicting residual stress for a wide range of plastic welding method.