Investigation on bubble morphological evolution and plastic part surface quality of microcellular injection molding process based on a multiphase-solid coupled heat transfer model

Abstract

The surface of plastic parts molded by Microcellular Injection Molding (MIM) process usually has silver marks, spiral lines, pits and other defects. Rapid Heat Cycle Molding (RHCM) technology has become an efficient technology to eliminate these defects by controlling the heat and mass transfer in the MIM mold. However, the influence of heat transfer on the evolution of multiphase composite (polymer, supercritical fluid, air) in the mold cavity is still not clarified. To understand it, a new non-isothermal transient multiphase model based on finite volume method was established, and the Implicit Domain Coupling Algorithm (IDCA) was used to synchronously calculate the temperature field of mold and cavity regions. A compound experiment of RHCM and MIM (RHCM/MIM) with mold temperature control realized by electrical heating and water cooling was performed. Based on the simulation and experiment results, the transient flow behavior of foam composite in mold cavity was analyzed. The effect of mold temperature on the deformation, bursting and collapsing process of bubbles in fountain flow field was revealed. The phenomena of bubble bursting delay in filling stage of RHCM/MIM process were discovered, and the formation mechanism of the surface defects of RHCM/MIM plastic part was also revealed.