Simulation of filling pattern of multicomponent injection molding

The multicomponent injection-molding process is a sequential molding process in which one plastic material (overmold) is molded onto a previously filled and solidified plastic part (substrate). This innovative manufacturing process is gaining popularity among plastic manufacturers because of its flexibility and potential to produce multifunctional plastic parts. In contrast with increasing popularity, an integrated computer simulation software for this process is currently unavailable, partially because of the difficulty in mapping the boundary between the substrate and the overmold. As a matter of fact, multicomponent molders are still using the trial-and-error approach while the computer-aided engineering prevails in the conventional injection-molding practice. When the flow pattern of the overmold is of interest, it may be justifiable to use the conventional mold-filling simulation to predict the pattern. It is postulated that the influence of the interface boundary on the flow pattern of the overmold is insignificant due to the high filling rates normally encountered in the multicomponent injection-molding process. In this article, the flow patterns of the overmold of the handle of Gillette's shaving razor for ladies ate predicted based on an approach where an integrated filling-packing-cooling simulation is first run for the substrate; upon completion of the substrate cooling, the substrate surface temperature is used as the initial boundary condition for the overmold in the second-stage analysis. Boundary interface techniques are applied to map the boundary condition from the substrate to the overmold. The predicted flow pattern is found to be in reasonably good agreement with that obtained using the conventional injection-molding simulation as well as with the experimental results.