Effect of crystallization and packing pressure on the development of residual stresses on injection molded polypropylene samples

Thermoplastics processing usually involves the non-uniform cooling of molten polymer, which results in the presence of residual stresses in the final product. The magnitude of these stresses can be high enough to induce severe shape changes in the product, as well as changes in the overall material performance. Because of this, it is important to be able to accurately predict and measure them. In this study, the effect of coupling a kinetic model of crystallization on the prediction of thermal and pressure-induced residual stresses using the residual temperature field and formation pressure concepts is investigated. In addition, the effect of packing pressure on the deflection of injection molded polymer plates after ejection is reported. Simulation results were compared with experimental data, and it was found that considering crystallization in the prediction of residual stresses decreased the % error between predicted deflection and experimental results, from 0.52–7.34 to 3.0–56.3%. Also, good agreement between experimental results and the simulations performed using the residual temperature and pressure fields concepts in 2D while including a kinetic model of crystallization with different packing pressures.