The cooling rate dependence of the specific volume in amorphous plastic injection molding

In numerical simulation of injection molding, the specific volume is important for the cavity pressure prediction, which governs the part properties, such as shrinkage and warpage. The specific volume is often considered as a function of pressure and temperature only. This neglects its cooling rate dependence. The related degradation of the cavity pressure prediction usually remains unknown. In this work, the cooling rate effect is modeled and the discrepancy is quantified for amorphous polystyrene. A rate equation is used to model the specific volume relaxation within the scope of three-dimensional computational fluid dynamics. The model incorporates the mold compliance to allow a comparison to the experimental results. The cavity pressure evolution and the final residual stresses are calculated for both the modeled and the neglected cooling rate effects. This provides argumentation for either neglecting or modeling the phenomenon.