Effective Local, Crystallization Degree and Microstructure Dependent Thermo‐Elastic Properties of an Injection Molded i‐ <scp>PP</scp> Component via a Multiscale Approach and Their Impact on Warpage Simulations

ABSTRACT In injection molding processes of semi‐crystalline polymers, different cooling rates occur at the mold walls and in the part center leading to an inhomogeneous melt solidification and the formation of locally different spherulitic microstructures. To determine their effect on the local thermo‐elastic properties and their impact on the part warpage, a multi‐scale simulation scheme is used here to investigate the injection molding of an α‐iPP stepped plate. After modeling the melt flow during the injection phase, the residual packing pressure is determined in the cooling phases. Then, the formation of the spherulite microstructure is calculated over a plate section with an athermal nucleation model. Based on the predicted effective lamella properties, the radial spherulite model is extended here. It permits deriving more accurate and less anisotropic effective thermo‐elastic properties. The local mechanical properties vary strongly in accordance with the local crystallization degree. A generalized plane strain model is used to predict the warpage and shrinkage of the plate section during the in‐mold cooling phase and after ejection. Simulations with either constant, mean properties or local ones show clearly that crystallization‐dependent properties predict more accurately the warpage and shrinkage behavior compared to constant properties over the plate section.