Modeling and Optimization of Two-Stage Composite Cure with the Use Open-Mold Tooling

The paper presents an optimal control synthesis for curing shell-like composite structures using open dies in an autoclave. The control synthesis is a multi-objective optimization problem where minimization objectives are deviations of temperature and degree of cure within a cured part, considering constraints imposed by thermo-kinetic properties of prepreg and manufacturing requirements. The control should eliminate the formation of early hard skin, resin-rich or resin-dry areas, insufficient consolidation, and uneven cure. Such a purpose can be achieved through uniform distribution of temperature and degree of cure within the cured structure. The optimization procedure, including the formulation of the cure problem and the finite element implementation where correct timing of heating-up and maintaining isothermal, is illustrated by an example of the shell-like composite structure manufactured by means of two-stage curing in an autoclave. The technique developed allows estimating the best achievable quality indicators of composite parts, finding key parameters of the control law, and considering all imposed constraints for decision-making.