SHAPE ADJUSTMENT PROCESS FOR EPOXY COMPOSITES DURING POST CURE

Abstract

There is an increasing request for high precision composite parts for aeronautic natural laminar flow and low radar cross section applications. The allowed geometrical deviations for such applications are an order of magnitude lower than todays accepted tolerances. The implementation of established measures like tool compensation for spring-in or thermal expansion prior to the manufacturing process significantly reduces the occurring geometrical tolerances. But there are also variations during the manufacturing process that cannot be compensated in advance such as deviations during ply application or varying fiber angles. This publication shows a way how to adapt the manufacturing procedure to achieve high precision composite parts despite of process deviations. The curing characteristics of epoxy resins enable a two-stage curing process. In the initial step the resin is cured to about 65 % chemical interlacing. The viscoelastic properties of partially interlaced epoxides close to their current glass transition temperature allow an adjustment of the components geometry during the following post cure. This can be achieved using a closed loop temperature control combined with a cure monitoring and a geometry measurement system. This means that process induced deviations of composite components made from thermoset matrix systems can be adjusted during the post cure process.