Prediction of shrinkage and warpage in consideration of residual stress inintegrated simulation of injection molding

The accurate prediction of shrinkage and warpage of injection molded parts is important to achieve successful mold design with high precision. III thi s study, the numerical analysis of shrinkage and warpage of injection molde d parts made of amorphous polymers was carried out in consideration of the residual stresses produced during the packing and cooling stages of injecti on molding. The temperature and pressure fields were obtained from the coup led analysis of the filling and post-filling stages. For residual stress an alysis, a thermo-rheologically simple viscoelastic material model was intro duced to consider the stress relaxation effect and to describe the mechanic al behavior according to the temperature change. The effect of the addition al material supply during the packing stage was modeled by assigning the re ference strain. The deformation of injection molded parts after ejection in duced by the residual stress and temperature change was analyzed using a li near elastic three-dimensional finite element approach. In order to verify the numerical predictions obtained from the developed program, the simulati on results were compared with the available experimental data in the litera ture. In the case of residual stress, it was found that the present simulat ion results overpredicted the tensile residual stresses at the surface of i njection molded parts. However, the predicted shrinkage was found to be: re asonable to describe the effects of processing conditions well. Finally, an analysis of the shrinkage and warpage was successfully extended for a part with a more complex curved shape. (C) 2000 Published by Elsevier Science L td.