Abstract: Residual stress of the injection molded polymers is a key factor of quality control on precision injection molded part and has important effect on the mechanical and optical properties of the molding. To investigate the development of this residual stress, the in-cavity creep experiment of acrylonitrile butadiene styrene(ABS) is carried out and its in-cavity creep behavior is studied. In-cavity creep is defined as the variance of shrinkage which is calculated by thermal elastic model with measured in the experiments. General rules are learnt that injection processing conditions affect in-cavity creep of the molding. Based on the experimental results, a creep model for calculating residual stress of the molding is built. The elastic module of material is calculated with Tait equation and the viscous factor calculates with inversion method. The residual stress of injection molded plate made by ABS with this model integrated thin shell finite element method is calculated, and calculation result is verified by the experiments and compared with stress relaxation. The results show that the new model is more accurate than general relaxation model and that is a new effective way to predict the residual stress of precision injection moldings.

Key words: Creep model, Precision injection, Residual stress