Fully Coupled Transient Heat Transfer and Melt Filling Simulations in Rapid Heat Cycle Molding with Steam Heating

Abstract

Rapid heat cycle molding (RHCM) is a novel injection molding technology, in which injection mold is rapidly heated to a high temperature, usually higher than the glass transition temperature of the polymer material, before melt-injection and rapidly cooled down to solidify the shaped polymer melt in mold cavity for ejection. Since the elevated mold temperature can eliminate the unwanted premature melt freezing during filling stage, the melt flow resistance is greatly reduced and the filling ability of the polymer melt is also significantly improved. As a result, plastic parts with excellent surface appearance can be obtained. In this study, a three-dimensional numerical model coupled with heat transfer analysis and melt-filling processes for RHCM with steam heating was established. The thermal response analysis for the heating stage of RHCM process was performed by solving heat conduction equations. The heat transfer analysis results right after the mold cavity surface is heated up to the required temperature are taken as initial temperature conditions of the mold cavity for the following melt filling simulation. The pressure implicit splitting of operations solution algorithm was used to solve the pressure-velocity coupled Navier-Stokes equation for melt filling process. The moving interface between melt and air was captured by using the volume of fluid method. The energy equations for melt filling process were solved in a coupled manner for the cavity and mold domain at the matrix level. The proposed fully-coupled numerical model was applied in simulation of the molding processes, including a two-dimensional rectangular cavity with different heating times and a three-dimensional large scale LCD panel with a stem-heated stationary mold. The results show that the fully coupled numerical method provides reliable temperature and flow field predictions with the thermal response analysis and melt flow estimation.