Optimization of mold temperature profile and process parameters for weld line reduction and short cycle time in rapid heat cycle molding

Weld line reduction is one of the major concerns in plastic injection molding (PIM) that results in high surface appearance and high strength of a plastic product. To resolve this issue, rapid heat cycle molding (RHCM) has attracted attention as an innovative PIM technology. In the RHCM, the mold temperature profile plays a crucial role in weld line reduction. On the other hand, high productivity as well as high surface appearance is also required in the PIM, and the trade-off between them will be observed. To achieve weld line reduction and high productivity simultaneously, it is important to adjust both the mold temperature profile and other process parameters in RHCM. A trial and error method is so widely used to adjust them, but it is much time-consuming task. In this paper, the mold temperature profile and several process parameters are optimized for the weld line reduction and the short cycle time. Therefore, multi-objective design optimization is performed. Numerical simulation in PIM is so intensive that a sequential approximate optimization using radial basis function is adopted to identify the Pareto frontier with a small number of simulations. The trade-off between the weld line reduction and the cycle time is clarified through the numerical result. Based on the numerical result, the experiment using a PIM machine (GL100, Sodick) is carried out. It has been confirmed through the numerical and experimental result that the proposed approach in RHCM is valid for the weld line reduction and the short cycle time.