(Dr. Colton, advisor)
"A Machine System for the Rapid Production of Composite Structures"
A rapid manufacturing process for thermosetting materials was developed to produce composite structures in a manner similar to rapid prototyping. The machine system builds the part layer by layer with continuous curing and consolidation, making traditional curing methods unnecessary. Each part layer, which has been prestaged to reduce thermal stresses and warpage during processing, moves under a heat gun and roller for curing and consolidation. The heat gun initiates the cure in the part layer, partially curing it and making it tacky enough for the next layer to stick to it when it goes through the consolidation process. The cure continues to advance as each layer is placed.
Testing was performed by fabricating three layer parts and performing tests on single strips of towpreg to determine how temperature and time affect degree of cure. The material was IM7 carbon fiber/977-3 epoxy towpreg, prestaged in a tunnel oven to an approximate 30% degree of cure. Hot air temperatures of 150 - 380ºC, roller pressures of 0.21 - 0.41 Mpa (30 - 60 psi), table speeds of 12.7 - 38.1 mm/sec (0.5 - 1.5 in/sec), and times of 5, 10, and 20 seconds were used. The results showed that the machine system can continuously cure and consolidate parts. The cure was advanced to any level up to 100% degree of cure with an air temperature of 380ºC. Parts were produced with layers well stuck together. Within the limitations of the experiments, temperature was determined to be the most significant factor affecting degree of cure. With the correct processing conditions, the machine system has the capability to produce well-consolidated, high quality parts without using traditional curing methods. The design of the machine system allows for the addition of components for the fabrication of arbitrarily shaped parts and for different curing methods.