Cure and Consolidation Study of Cavity Molded Flex Beam Composite Parts

Preimpregnated fibers or prepregs are widely used to produce high quality composite parts. One process in particular, known as cavity molding, is frequently used to process high quality thick composite details with exceptionally precise dimensions by using a platen press to apply heat and pressure to rigid tooling and thereby entice the prepreg within to cure into the shape of the confines of an internal cavity. The objective of the research described here is to develop an mathematical model for glass/epoxy prepreg which simulates the resin flow, heat transfer, consolidation and curing of cavity-molded flex beams which varies significantly with location. An enhanced understanding of the mechanisms involved will help significantly improve the costeffectivity of molding processes development. The current work is focused on process modeling of composite flex beams which are manufactured by cavity molding. The curing kinetics of such parts is particularly difficult to model because tool/part geometries are complex. The combined effects of heat transferred by the tool and heat spontaneously generated by the reacting thermoset during cure results in significant gradients of resin advancement throughout the part that range from incomplete polymerization, in the thinnest cross-sections, to complete cure (and potential embrittlement) at the thickest cross sections. This causes formidable temperature spikes that result from internally-generated exothermic heat that cannot be quickly dissipated because of the low thermal conductivity of composite and tooling. Various governing equations are presented here that describe the resin cure kinetics, thermal energy balance and consolidation of this porous medium. A general-purpose, finite-element package with multiphysics capabilities is used for simulating the non-isothermal prepreg-press process, the degrees of cure and temperature field distribution at different cross-sections are also presented.