Analysis of Mold Filling in RTM Process

Abstract

A simplified RTM process analysis is presented which is based on the one-dimensional resin flow model by using Darcy's law for flow through porous media. Closed form solutions for the wet length, mold filling time, and pressure distributions are derived for different simplified mold shapes such as rectangular, trapezoidal, and circular sections. These results are then applied to the mold design and vent arrangement in RTM process. Two design principles are proposed from these derivations and confirmed by nu merical application examples. One is to arrange the vents to assure that flow takes the shorter path whenever possible. The other is to use line gates and to inject the fluid from the larger side to the smaller side, or with rapid reduction of the filling volume. Illustration examples show that these arrangements can cut down the mold filling time or reduce the required applied pressure. Especially in the case of RTM with high volume fraction of fibrous preforms, where the process usually involves applying a constant inlet pressure to squeeze the resin into the preform, the mold filling time or the applied pressure require ment is lowered substantially by these arrangements.