Simultaneous optimization of variable injection velocity profile and process parameters in plastic injection molding for minimizing weldline and cycle time

Abstract

Weldline that is formed when two or more melt fronts meet is one of the major defects in plastic injection molding (PIM), which has an influence on not only the appearance but also the strength of a plastic product. Consequently, it is preferable to reduce it as much as possible for high product quality. On the other hand, high productivity is always required in the PIM. In other words, cycle time should be minimized. To achieve the high product quality and productivity, process parameters such as melt temperature, cooling time and so on plays an important role. In this paper, the process parameters in PIM are optimized for minimizing the weldline and the cycle time simultaneously. In particular, variable injection velocity that the injection velocity varies during the PIM process is adopted and optimized. A novel weldline evaluation is also proposed. Numerical simulation in PIM is so intensive that a sequential approximate optimization (SAO) using radial basis function (RBF) network is adopted for the design optimization. It is found from the numerical result that the trade-off between the weldline reduction and the cycle time is observed. Based on the numerical result, the experiment using the PIM machine (GL100, Sodick) is carried out. Through the numerical and experimental result, the validity of the proposed approach is examined.