Multi-objective optimization for minimizing weldline and cycle time in rapid heating cycle molding

Abstract

Weldline, which has an influence on the strength as well as the surface appearance of a plastic product, is one of the crucial defects in plastic injection molding (PIM). Process parameters such as melt temperature, injection time and so on should be adjusted and optimized for the weldline reduction. Rapid heating cycle molding (RHCM) that controls the mold temperature during the PIM is an effective approach for the weldline reduction, but the mold temperature profile is completely determined by an engineering experience or a trial and error method. In addition, some process parameters such as melt temperature, injection time and packing pressure also play an important role for the weldline and cycle time. In this paper, for weldline reduction and short cycle time, the mold temperature profile and several process parameters in the RHCM are determined by using sequential approximate optimization. The mold temperature during heating time is maximized for the weldline reduction, whereas the cycle time is minimized for the high productivity. Through the numerical result, the trade-off between the mold temperature and the cycle time is clarified. Also, it is found that the higher mold temperature is, the shorter weldline is.