Low Cost Fabrication Techniques for Propulsion Structures

Carbon fiber reinforced polymers have found wide use in aerospace structures, however currently used materials are costly and require extended cure times which greatly increases manufacturing cost and consequently part cost.  Most aerospace and defense structural composites are manufactured using slow hand layup and autoclave curing processes which are labor intensive and costly.  Cylindrical cross sections such as those used in pressure vessels and rocket motor cases utilize automated filament winding processes, however this method is slow in applying axial reinforcement due to the placement of a single roving at a time and the extended cure cycle required for current resin systems.  Since the aerospace field works with the highest performance materials, it is less cost sensitive than other industries and is therefore slow to incorporate new manufacturing methods that can yield cost savings.  With the growth of composite materials in consumer products, the manufacturing processes required to rapidly produce fiber reinforced polymer parts have also matured, enabling composites to find use in high volume applications, such as the automotive industry, where part-to-part times can be as low as 90 seconds.  Resins compatible with high volume manufacturing include polyesters, vinyl esters, snap cure epoxies and polyurethanes.  While each of these materials are low cost commodity resins that enable rapid manufacturing, they exhibit low glass transition temperature (Tg) and inferior mechanical properties compared to the 350° F autoclave cured epoxy resins typically found in the aerospace industry.  In order to implement low-cost manufacturing processes for aerospace structural applications, there exists a critical need for new resin technologies which are compatible with high rate industrial manufacturing approaches yet provide high Tg and equivalent mechanical properties of existing aerospace resins.  Trimer proposes to implement a hybrid filament winding approach that will reduce winding time by 85% and the use of our novel resin system that can cure in as little as 30 sec, is an order of magnitude less expensive than current aerospace resins and attains a Tg greater than 700° F.  The Phase I effort demonstrated our proposed hybrid winding approach could achieve the Army’s strength objective and that the use of our low-cost resin could reduce the total resin cost by an order of magnitude compared to BMI’s.  This combined with our sub two-minute cure time and hybrid winding would further reduce the manufacturing cost of by more than an order of magnitude.  Trimer will collaborate with Raytheon Missile Systems to design, characterize and test the structures.  The outcome of this Phase II will be a low-cost polymer specifically formulated to meet the needs of tactical rocket motor cases and missile structures and the demonstration of its performance on a representative element as well as the manufacturing processes needed to reduce production costs.