Optimal layering time control for stepped-concurrent radiative curing process

Abstract

This paper makes the following main proposals: (1) a stepped-concurrent curing (SCC) approach for making thick parts using ultraviolet (UV) radiative curing and (2) an optimal interlayer hold time control scheme to maximize the benefit of the SCC approach. The SCC approach seeks to reduce cure level deviations across a thick part by introducing new layers before earlier ones cure completely. A model of the UV curing process that includes the coupled cure kinetics and heat transfer is used to motivate the SCC scheme as well as the inherent optimization problem in this process. Then, the SCC process is cast as a hybrid system in which the addition of each layer switches the underlying state space to one with a higher dimension. Minimization of the overall cure deviation is set as the objective of the process and the necessary conditions for the optimal interlayer hold time control sequence are explicitly derived and solved via a steepest descent algorithm. Applications of the proposed scheme to a composite laminate curing process show that the so computed optimal layering time control sequence indeed gives the best performance in terms of closely tracking a target cure level distribution, compared to equal-time SCC or one-shot curing of the whole thick part.