A unified simulation of the filling and postfilling stages in injection molding. Part I: Formulation

Abstract

Abstract This study employs a unified theoretical model to simulate the filling and postfilling stages of the injection‐molding process. Implementation of such a model is based on a hybrid finite‐element/finite‐difference numerical solution of the generalized Hele‐Shaw flow of a compressible viscous fluid under nonisothermal conditions. The shear viscosity of the polymeric material is represented by a Cross model for the shear‐rate dependence and a WLF‐type functional form for the temperature and pressure dependence, whereas the specific volume is modeled in terms of a double‐domain Tait equation. The analysis also handles variable specific heat and thermal conductivity of the polymer as a function of temperature. Complex thin parts of variable thickness can be modeled and discretized by flat, triangular finite elements which may have arbitrary orientation in three‐dimensional space, whereas runners and possible round pins or bosses in the part are represented as one‐dimensional circular‐tube elements. A control‐volume scheme is employed that leads to automatic melt‐front advancement during the cavity‐filling stage.