Simulation of Multi-cavity Micro-injection System for Reducing Cavity Filling Deviation

Abstract

In micro-injection molding, it is important to make each cavity filled uniformly. However, there are several factors that cause deviation in cavity filling. These factors include the mold temperature differential between runners and the diameter differential of gates or runners caused by mold manufacturing tolerances. In this study, we conducted numerical analysis to identify the major factors that cause cavity filling deviation and suggest a considerably robust design for microinjection mold to minimize the deviation. In the numerical simulation, we used thermophysical property values of EP-7000, one of the polycarbonate series polymers used for injection molding. The Cross-Arrhenius model was adopted with regard to the viscosity of the polymer. To model the specific heat and the thermal conductivity, we used the piecewise-linear method. Further, the volume of fluid method and the piecewise-linear interface scheme were used to visualize the polymer flow. Sixteen-cavity injection mold was modeled, and simulations were done for four different variations (the mold temperature, the runner diameter, the gate thickness, and a combination of the mold temperature and the runner diameter). Numerical analysis indicated that the case of mold temperature exhibited a difference of up to 28 % in instant cavity filling rate and the case of combination showed a difference of up to 33 %. We suggested designs employing convergent runner and resin reservoir to reduce deviation. As a result, the convergent runner design could reduce the instant cavity filling rate deviation by 20 %, while the resin reservoir design reduced the deviation by 18 %. The combination of these two could reduce the deviation by up to 22 %.