MODELING AND SIMULATION OF HIGH REYNOLDS-NUMBER FLOWS DURING REACTIONINJECTION MOLD FILLING

Reaction injection molding (RIM) involves the injection of low viscosi ty polymers into mold cavities at relatively high injection speeds. Th e short cycle times, coupled with low injection pressures and clamping forces make RIM well suited for the rapid production of complex parts . High injection speeds, low viscosities and narrow cavities lead to h igh Reynolds' number flows during mold filling. The presence of high R eynolds' number flows is a notable difference between RIM and conventi onal thermoplastic injection molding (TIM). Unfortunately, this type o f flow with significant inertia effects can lead to reduced part quali ty. The material properties and characteristics of RIM parts are influ enced by flow patterns, weld lines, air entrapment as bubbles or pocke ts, especially as the material flows around inserts. These defects and characteristics, coupled with a growing demand for high quality RIM p arts, is responsible for the increased interest in the flow during mol d filling. This paper presents the development and test of a model to stimulate high Reynolds' number flows in thin cavities present during reaction injection mold filling.