Numerical simulation of plate-like particle orientation in injection molding

Abstract

This study developed a method for predicting the orientation of plate-like particles within an injection-molded product at low filler content. We derived a numerical model that describes the motion of a plate-like particle and combined it with a mold-filling simulation to calculate the motion of individual flakes during molding. To validate the simulation results, a plaque was injection-molded with polypropylene and 2 wt% glass flakes. X-ray micro-computed tomography analysis was then employed to obtain the orientation (the normal vector) for each flake. The simulation reproduced the through-thickness orientation within the plaque by using a corrected flake aspect ratio. Also, numerical investigation revealed that the orientation is little affected by the in-plane flake shape if the aspect ratio remains the same. A useful application of the simulation will be the prediction of appearance defects caused by the flake orientation misalignment that occur in metallic-looking products molded using thermoplastics containing metallic-flake pigments.