Experimental Analysis of Mold Filling in Compression Resin Transfer Molding

Over the years, several modifications of the more standard liquid molding processes such as SRIM and RTM have been proposed. Among them the Compression Resin Transfer Molding (CRTM) presents great interest. In that process, like in RTM, the fiber preform is preplaced in a mold and then a liquid resin is injected. In CRTM however, the mold is kept slightly open during the resin injection. Once the necessary amount of resin is injected, the final closing is done and the resin filled the entire cavity. The main advantage of this technique is to reduce the necessary injection pressure and to ease the molding of parts with high fiber. In this paper, results are reported for two series of plaque molding experiments. In all cases filling time and pressure distribution in the cavity were recorded. In the first series, vinyl ester resin was injected in a slightly open cavity where a thermoformed glass fiber preform had been placed. In this case, an open gap was present on the top of the preform which eased considerably the filling. The mold was then closed to final part thickness. In this case, the resin injection time was extremely short and most filling and wetting time was elevated to the final closing of the cavity. In the second set of experiments continuous strand glass fiber mat was used. Because of their nature, the layers of glass mat completely filled in partially closed cavity. As opposed to the previous experiments, in this case, the cavity was closed during the resin injection. The closing time was chosen in such a way that filling and closing occur simultaneously. Since the reinforcement permeability is reduced during injection, the filling rate was much slower at the end. The data gathered with these experiments could also be used to validate the modeling of foamed core parts molding when resin pressure crushes the core.