Presented in

Appl. Math. Modeling, 1994, Vol. 18, June

Page 347

THE CALCULATION OF SCALAR TRANSPORT DURING THE INJECTION MOLDING OF THERMOSET POLYMERS

Foluso Ladeinde

SUNY at Stony Book, Stony Brook, NY, USA

H. U. Akay

Technalysis Incorporated
Indianapolis, IN, USA

During the injection mold filling of thermoset polymers. A finite-element method is presented, with variations intended to cover a variety of processing conditions. Sample calculations are presented for the Garcia10 problem and the encapsulation of a Motorola computer chip. We also share our experience with some of the peculiar numerical difficulties associated with the simulation of injection molding for realistic systems. Some of these are related to mesh "quality," time step size selection, and (numerical) degeneracy that could result from some otherwise "physical" material models. The foregoing are issues that have not received a great deal of attention in the literature.

Keywords: transport, injection molding, thermoset polymers

Introduction

The process of injection molding of polymers seems to have benefited greatly from emerging computer technology. For example, with commercially available computer codes such as PLASTEC,1 the filling simulation could predict short shots, weld lines, air trapping, overheating, the number of gates and their locations for optimum design, balancing of runners, optimization of injection pressure and clamp force requirements, calculation of pressures, temperatures, shear rate, shear stress, velocity distribution, etc. Further, postfilling processes (packing, in the case of thermoplastics) can also be simulated to provide part shrinkage and the initial state of stress (needed for subsequent structural analysis of the part).

thin parts arbitrarily orientated in three-dimensional space which, sometimes, are combined with full three-dimensional parts, (c) moving fluid front, (d) fountain flow phenomenon at the front and, finally, (e) fiber orientation, as in Reifschneider, et al.1 Some examples of numerical simulation of injection molding include Broyer et al.,2 Hieber and Shen,3 Kamal et al.,4 Wang et al.,5 Ladeinde et al.,6 and Subbiah et al.7

Most of the computer simulation capabilities mentioned in the first paragraph have been applied to thermoplastics and, to a lesser extent, to thermosetting polymers.