Optimal control of accelerator concentration for resin transfer molding process Sun K. Kim, Dae-Hwan Kim 1 , Isaac M. Daniel * Robert R. McCormick School of Engineering and Applied Science, Center for Intelligent Processing of Composites, Northwestern University, 2137 North Sheridan Road, Evanston, IL 60208-3020, USA Received 13 September 2002; received in revised form 11 April 2003 Abstract Resin cure following mold filling is an essential element in resin transfer molding. To fabricate a composite part with high dimensional stability and minimize residual stress, uniform resin cure should be achieved. This study considers a three-part resin system composed of epoxy, hardener and accelerator. The cure kinetics can be controlled by the ac- celerator concentration at the injection gate. A numerical method that can predict degree of cure distribution based on accelerator concentration at the gate was proposed. The degree of cure distribution is obtained by solving the resin flow, heat transfer, accelerator concentration and cure problems sequentially. Utilizing this numerical method, an optimal variation of accelerator concentration during mold filling was sought by solving a constrained optimization problem. The effect of accelerator control on degree of cure distribution was investigated and its validity was examined for two different geometries. Ó 2003 Elsevier Ltd. All rights reserved. Keywords: Resin transfer molding; Degree of cure; Accelerator concentration 1. Introduction The resin transfer molding (RTM) is one of the most studied manufacturing processes of thermoset polymer composite materials because of its wide applicability. The process consists of preform placement, resin injec- tion and mold filling and curing. One of the most im- portant issues in RTM is what is optimization of processing conditions. In order to estimate the optimum processing window and curing conditions, it is necessary to predict the filling pattern of the resin and degree of cure distribution of the composite part throughout the entire process. To date many researchers have investi- gated numerical techniques for mold filling simulation [1–5]. In order to determine the optimum processing cycle, however, it is essential to establish a combined model, which describes not only the mold filling stage but also the curing process. A comprehensive review of filling and cure phenomena in RTM can be found in [6]. When manufacturing large composite structures or high fiber volume ratio composites, the mold filling time can be very long and nonuniform curing can occur. The filling and curing times could be shortened by heating the mold moderately. Preheating the mold, however, there are differences in degree of cure. The degree of cure near the vents is higher than that near the injection gate. This difference can introduce residual stresses and de- formation of the final part [7–9]. Recently, Antonucci et al. proposed varying the mold wall temperature to control the cure reaction [10]. In this study, cure reaction is controlled in order to achieve uniform cure by changing the cure kinetics. Some RTM machines allow resin injection with varying accelerator concentration. This approach in manufacturing requires a model to analyze the distribution of accelerator concentration * Corresponding author. Tel.: +1-847-491-5649; fax: +1-847- 491-5227. E-mail address: imdaniel@northwestern.edu (I.M. Daniel). 1 Current address: Samsung Electronics, Soowon, Republic of Korea. 0017-9310/03/$ - see front matter Ó 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S0017-9310(03)00214-X International Journal of Heat and Mass Transfer 46 (2003) 3747–3754 www.elsevier.com/locate/ijhmt