Multi-criteria thermal optimization in liquid composite molding to reduce processing stresses and cycle time

Liquid Composite Molding (LCM) regroups a number of increasingly used composite manufacturing processes. A proper selection of process parameters is crucial to yield successful molding results and obtain an appropriately cured part with minimum defects. In the case of thermosetting resins, the polymerization shrinkage increases the complexity of the thermo-mechanical problem. Numerical analysis of the internal stresses developed during resin cure and subsequent part cooling does not only help to understand the process, but it is also necessary to make thermal optimization reliable. The scope of this work concerns the optimization of resin cure, cycle time and residual stresses during LCM composite processing. A multi-criteria optimization algorithm called Logical Evolutionary Curing Optimization and Quenching (LeCoq) based on evolutionary algorithms was developed to optimize a multi-dimensional objective function that incorporates the following conflicting goals: minimization of residual stresses, maximization of the final degree of cure and reduction of cycle time. An optimized temperature profile obtained with this approach minimizes cycle time and processing stresses, while avoiding at the same time thermal degradation of the matrix and composite delamination. Process optimization with two different objective functions is conducted for a thick composite part. Two optimized temperature cycles are obtained and numerical results are compared and discussed.