Effect of preform non-uniformity on mold filling in RTM process

Abstract

A reinforcing fabric preform is placed in a mold, and thermoset resin is injected into the mold to form a composite part in the Resin Transfer Molding (RTM) process. As resin flows through a porous fabric preform, it races along less resistive sections of a non-uniform preform. Racetracking channels between preform and mold wall are a major reason for non-uniformity. As a secondary effect, the random variations in tow cross section and spacing between them, cause non-uniform preform. Mold filling simulations were performed for a simple mold shape to observe the effect of preform non-uniformity on the flow patterns and injection pressure under constant flow rate. The effect of random permeability variation of up to +/- 35% from the average value did not have a significant effect on the flow pattern if the resin was injected from a line source in a rectangular mold, and if the preform permeability variation was completely random. The same amount of permeability variation in a specific pattern, rather than random, resembling the effect of bending of mold lid, caused a more significant effect on the mold filling results than the effect of random variation.