A process performance index and its application to optimization of the RTM process

Resin transfer molding (RTM) is a promising manufacturing process for high performance composite materials. However, the fact that RTM process design has traditionally been an expensive, time-consuming trial-and-error procedure has prohibited its wide application base. This paper proposes a solution to that problem-a simulation-based optimum process design scheme for RTM. This scheme enables engineers to determine the optimum locations of injection gates and vents so that both process efficiency and high part quality can be ensured. Essential to this optimum process design scheme is a process performance index, which is defined with respect to the major factors influencing RTM process efficiency and part quality. This index is then used as the objective function for the RTM process design optimization model. Gate and vent locations are the process design parameters to be optimized. All data is obtained by running an RTM simulation program, and the genetic algorithm (GA) is employed to carry out the optimization procedure for the design parameters. It is found that constant pressure optimization will yield a process with a short flow path, whereas constant flow optimization will yield a process with smooth and vent-oriented flow pattern. Although there is no dry spot factor in the objective function, it is interesting to note that both constant pressure and constant flow optimization procedures result in process designs with a minimum probability of dry spot formation. This study finds that, in general, constant flow optimization should be employed if injection pressure is not a major concern; otherwise, constant pressure optimization should be used. Two case studies are presented to illustrate the efficacy of this approach.