AUTOMATED FABRICATION PROCESSES FOR LARGE COMPOSITE AEROSPACE STRUCTURES : A TRADE STUDY

A Phase I SBIR program called “Low Cost Processing of Large Composite Structures (1)” reviewed autoclave and candidate out-of-autoclave processes for fabricating very large composite parts like the RLV liquid hydrogen tanks. These highly loaded structures require very high quality microstructure to yield the ultimate in mechanical properties. Autoclave processing yields ultimate properties but carries large capital and operating expenses. Thermoset “all-atonce” E-Beam curing, thermoset/oven curing, Cure On The Fly (COTF), and Vacuum Assisted Resin Transfer Molding (VARTM) were all considered and discarded because none provided sufficient normal compaction force to the laminate during curing. This high compaction force is considered essential for creating adequate microstructure. Thermoplastic in situ fiber placement and the more embryonic layer-by-layer E-Beam fiber placement process were downselected because of both their promise in fabricating parts and the high normal force available to compact the microstructure as an integral step in consolidating or curing. Even these processes will not be effective without a proven conformable compaction system to allow complex geometry shapes to be placed. The phase II program will fabricate, assemble, develop, and prove out a number of innovative conformable compactors, then assemble them into deposition heads.