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

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 advanctment during the cavity-filling stage.

Elastic flow-front fingering instability in flowing polymer solutions

“…Finally, we wish to mention that most of the numerical modeling studies in injection molding are based on the lubrication approximation to formulate the mold filling problems (see, e.g., Williams and Lord 1975;Hieber and Shen 1980;Dupret and Vanderschuren 1988;Chiang et al 1991;Dupret et al 1999), although a number of recent papers use a fully three-dimensional approach (see, e.g., Pichelin and Coupez 1999;Ilinca and He´tu 2001;Michaeli et al 2001) to address specific problems that need to solve the full Navier-Stokes equations. Nevertheless, all published theoretical studies and simulations are far from predicting flow-front finger-like instabilities described in this study due to the lack of physics in the models used.…”

A 3‐D finite element model for gas‐assisted injection molding: Simulations and experiments

“…The pvT -behavior of the polystyrene can be described by a so-called double-domain Tait equation [23]: …”

Principles of polymer processing modelling

“…Measuring and modeling rheology around the Glass transition temperature for amorphous polymer and in the crystallization range for semi-crystalline polymers remains a challenge and this explains using a mysterious "no flow temperature" in commercial software which is just a fitting parameter. The early models have been applied to simple plaque or disk geometries (Kamal and Kenig [21]; Huilier et al [22]; Titomanlio et al [23]) then generalized to Hele-Shaw models (Chiang et al [24]) and to 3D models (Silva et al [11]). x…”