Cure cycle modification for efficient vacuum bag only prepreg process

Over the past decade, increasing use of continuous fiber-reinforced polymer composites has created a demand for manufacturing methods with lower costs, higher production rates, and improved processing efficiency. To meet the growing demands, vacuum bag only (VBO) prepreg processing has been proposed and implemented in industrial settings. However, in the absence of high consolidation pressure, VBO prepreg must undergo compaction for longer durations during cure and requires use of more elaborate processing schemes to conform to complex geometries. The main objective of our cure cycle modification was to reduce overall manufacturing time for more efficient processing, while maintaining robust part quality. This study demonstrates the effect of cure cycle on formability and part quality of three complex-shaped composite structures, a bulkhead, fuselage, and I section frame, featuring drop-offs, corners and sandwich areas consisting of less than 10 plies. Three different cure cycles were chosen: Reference cure cycle 1, Modified I and Modified II cure cycle. The reference was modified based on resin cure kinetics/viscosity modeling results and “effective flow number” to shorten the overall cure cycle time while maintaining robust part quality. To compare the quality of manufactured parts, destructive test and digestion method were used. For the bulkhead parts, Modified I was proven to be more effective in meeting the commercially acceptable part criteria (void content, ply wrinkle, resin ridge, and surface resin starvation), whereas Reference failed to meet the requirements, showing pervasive presence of porosity in drop-offs, corners and sandwich areas. The fuselage and I section frame parts produced with Modified I and Modified II were shown to meet the part quality requirements, with slight improvements in surface quality observed with the Modified II method.