Braided preforms meet phase-change tooling

In March 2020, the Air Force Research Laboratory (AFRL; Dayton, Ohio, U.S.) announced that its Manufacturing and Industrial Technologies Division had partnered with Cornerstone Research Group (Dayton), A&P Technology (Cincinnati, Ohio, U.S.) and Spintech LLC (Xenia, Ohio, U.S.) on research to quantify the benefits of replacing legacy manufacturing processes with novel processes for the fabrication of an 11-foot long, S-shaped engine inlet duct for unmanned aircraft systems. One of the stated goals of the program is to understand part cost and production time benefits from introducing the new tooling and processing solutions.

The inlet duct—a hollow tube-shaped part of the aircraft that ensures smooth airflow into the aircraft engine—was previously fabricated by applying a composite prepreg by hand to a multi-piece steel mandrel. The mandrel and material would then be cured in an autoclave.

In the new process, dry carbon fiber is applied, using A&P Technology’s automated overbraid process, to a mandrel made from Spintech’s Smart Tooling shape memory polymer (SMP) tooling. The resulting preform is infused with low-cost epoxy through vacuum-assisted resin transfer molding (RTM).

In the Smart Tooling process (see video below, or a demonstration of the product here), once the dry carbon fiber is applied to the rigid polymer tool, vacuum bags are placed around the outside and through the hollow center of the tool. The part is placed in an oven where heated resin is applied under pressure, and then cured. Post-cure, the Smart Tooling tool is brought to its elastic temperature, at which point it can be easily extracted from the finished composite part, reformed, and then cooled to solidify the material again for reuse.

Because of the inlet duct’s geometrical complexity, multiple iterations were expected for optimization of the overbraiding process settings to minimize composite material wrinkling, resulting in four inlet ducts total to be compared against the cost and production time of the legacy part. A&P’s QISO triaxial braid was the dominant architecture employed in the preform.

The overall program goal is delivery of the final inlet duct to the U.S. government for integration into the Aerospace System’s Directorate’s airframe design and manufacturing program, with further testing of the structure conducted by to the Aerospace Vehicles Division.