Prediction of Metal-flake Pigmented Polymer Appearance Using Smoothed Particle Hydrodynamics

Injection molding of metal-flake pigmented polymers is an energy-efficient manufacturing process for metallic polymer products as it eliminates the need for painting and/or coating processes. The appearance of the product is primarily influenced by the orientation of the flakes in the surface layer. Regions with a disturbed flake orientation exhibit a metallic effect that differs from that in regions with an ordered flake orientation (this appearance defect is herein referred to as flowlines). Therefore, predicting the surface flake orientation is crucial for designing metallic polymer products without flowlines. This study examines the applicability of Smoothed Particle Hydrodynamics (SPH), a fully Lagrangian particle method, to the prediction of surface flake orientation (i.e., appearance) in injection-molded metallic polymer products. We employed a fully implicit SPH scheme to handle a highly viscous flow and implemented the evolution of temperature and flake orientation within the SPH framework to simulate the formation of surface flake orientation. The developed SPH was applied to simulate injection molding of a plate with a thin-walled region. The simulation predicted the formation of a long flowline behind the thin-walled region, with its width increasing and visibility decreasing downstream. These predicted trends agreed with experimental observations, although the simulation tended to overpredict them. The results indicate that the developed SPH framework is capable of predicting flowlines in metallic polymer products.