Computer simulation of the injection molding of viscoelastic crystalline thermoplastics

The thermomechanical history experienced by plastics melts and solids during processing leads to the development of microstructure, which directly influences the ultimate properties of the plastic articles. Therefore, besides the predictions of thermomechanical history, the prediction of microstructure represents an important aspect of the modeling of plastics processing.A comprehensive model has been developed to describe the behaviour of thermoplastic polymer melts during the injection molding process. The model, which deals with the three stages of the process (filling, packing and cooling), employs a viscoelastic constitutive equation and incorporates crystallization kinetics. All the properties of the material employed are based on experimental data. The model predicts fill times, velocity, temperature and pressure distributions, the distribution of shear and normal stresses, and stress relaxation. The predictions of the model are compared to experimental data relating to pressure distributions and variation with time, fill times, and the distributions of crystallinity, orientation and tensile modulus