A methodology to obtain a desired filling pattern during resin transfer molding

In Resin Transfer Molding (RTM), dry spot formation and air entrapment during the filling stage often lead to defective parts and high scrap rate. These problems are usually caused by improper design of inlet conditions and vent locations that prevent the Last Point to Fill (LPF) location from coinciding with the preset vent location. Use of direct filling simulation as a design tool for the RTM process often involves trial-and-error procedures in order to find the appropriate inlet conditions and locations as well as exit vent locations. This design procedure becomes complex when a design involving multiple inlet gates is being considered, especially in large parts. There may also be uncertainty as to whether the Final design (obtained using trial-and-error simulation procedures) is indeed the optimum design. This paper presents a methodology to design the RTM process with a desired filling pattern free of dry spots and knitlines. Unlike the traditional filling simulation that predicts the filling pattern using prescribed inlet conditions and the specification of the preform permeability field, this methodology calculates the optimum inlet conditions based on the specification of the desired filling pattern and the prescription of preform permeability. The use of this algorithm greatly enhances the process design capability by reducing trial-and-error procedures that use traditional direct filling simulation as a primary process design tool. The numerical algorithm is described along with several RTM design examples showing that use of the proposed methodology results in the LPF location coinciding with the predetermined exit vent location.