Accelerated Machining Technology Transitions for CMC Engine Component Production

  • Published
  • By Heyward Burnette
  • AFRL/RX
WRIGHT-PATTERSON AIR FORCE BASE, Ohio --  AFRL collaborated with industry for an Advanced Manufacturing Propulsion Initiative (AMPI) to increase material removal rates for profile machining of ceramic matrix composites (CMC). The successful effort, which achieved removal rates increased by more than two orders of magnitude, prompted transition of the accelerated machining technology to Pratt & Whitney, General Electric, and Rolls Royce machining vendors. Lighter than conventional materials and capable of operating effectively in high-temperature environments, CMC components increase gas turbine engine fuel efficiency. Their accelerated machining can save hundreds of hours and tens of thousands of dollars. Applying this technology to a single set of F-35 aircraft engine parts would reduce related machining time by more than 100 hours and cut associated tooling costs in half. Potential applications include nozzles, blades, vanes, flame holders, and brakes.

The AFRL-industry engineering team--which included participants from TechSolve, General Dynamics Information Technology, General Electric, Rolls Royce, Pratt & Whitney, ATK-COIC, and Goodrich--conducted value stream analysis (VSA) of CMC-based vanes and exhaust nozzles proposed for use in F135 and F136 turbine engines. In every case, the team's VSA activity identified machining as a driver of high cost and lengthy cycle time in the delivery of high-performance CMC components. Accordingly, the AMPI team worked to develop a collaborative approach for addressing issues inherent to machining CMCs.

Very hard, brittle, and difficult to cut, ceramic materials are not conducive to machining via traditional methods. Finding cost-effective and efficient ways to machine these materials without damaging them, while crucial, poses a substantial challenge. The situation is further complicated by the nature of CMCs, which are a combination of two ceramic materials and are consequently even more difficult to cut. During this AMPI effort, the researchers validated that improvements made to various aspects of tooling (e.g., materials, geometry, cooling, fixturing) were key to reducing machining cycle time. They likewise demonstrated that such tooling advances reduced associated costs by 80%. The team investigated machining parameters as well, ultimately implementing advanced cutting parameters that increased both depth of cut (from .025 to .100 in.) and feed rate (from 3 to 200 in./min). The researchers used several CMCs in evaluating the effects of their various process improvements and, further, shared important outcomes with major engine contractors involved in F135 and F136 engine production.