Optimization of processing parameters for minimizing warpage of large thin-walled parts in whole stages of injection molding

This study investigated total warpage of a type of motorcycle seat support made of polypropylene (PP) during the entire process of injection molding and free-cooling after demolding. Finite element modeling (FEM) analysis for injection molding and its associated thermal deformation was carried out in the study. The effects of processing parameters on warpage occurring in different stages were analyzed by Taguchi optimization method. It was found that packing pressure is the major factor that affects warpage in the injection stage, whereas cooling time is the major factor in free-cooling stage. From an overall evaluation, melt temperature affects the total warpage most, followed by cooling time, packing pressure, packing time and mold temperature. The result proved that optimum parameters for minimizing final warpage of the injected parts can be obtained only when the deformation in the entire manufacturing process is addressed in both molding and demolding stages.