Abstract: In the light of viscoelastic theories of polymer and relevant experimental results, a creep model for calculating the internal stress of injection molded parts is constructed. Based on the creep experimental results and theoretical analysis on the non-linear viscoelastic response of polymer, the formulas are presented to evaluate elastic modulus and viscosity of injection molding polymer. Furthermore, the internal stresses of an injection molded ABS plate are predicted by finite element method. To verify the reliability of the model, the results are compared with relevant experimental data and the data simulated by Moldflow. The results show that the calculating precision with new model is improved. And the calculating steps are simplified. It is tested that the model is an effective approach to predict the internal stresses of injection molded parts.

Key words: Creep, Injection, Internal stress, Non-linearity