Super Abrasive Machining Process Benefits Complex Engines

  • Published
  • By Holly Jordan
  • Aerospace Systems
WRIGHT-PATTERSON AIR FORCE BASE, Ohio --  Air Force Research Laboratory engineers originated an Advanced Manufacturing Propulsion Initiative (AMPI) program that advances a high-speed grinding process for complex engine structures. The initiative leveraged internal efforts from Pratt & Whitney, providing the final risk reduction to accelerate implementation for use in F135 turbine engine production.

The process worked under AMPI focused on the F135 third-stage low-pressure turbine disc blade slot, and is now approved for four different turbine discs in the F119 and F135 engines. This advanced technology has demonstrated material removal rates greater than conventional milling, while retaining the surface finish capabilities of grinding. The process is able to machine intricate features while reducing machining-induced metallurgical damage to the base material, a factor important to the structural integrity of critical rotating components.

AMPI identified super-abrasive machining (SAM) as a rapid insertion technology to replace traditional broaching methods for F135 blade slots, enabling improved metallurgical integrity, reduced cost, and high performance turbine engine designs.

Broaching has been used to create complex profile turbine blade slots for decades. However, as next-generation higher strength nickel superalloys have emerged, conventional broaching processes have, in some cases, resulted in excessive tool wear and lower yield of surface-distress-free blade slots.

Pratt & Whitney performed extensive testing to determine the key process inputs required to meet all quality requirements. For example, extensive low-cycle fatigue testing has been performed on SAM-processed specimens to demonstrate full-life capability. SAM offers superior capabilities at reduced cost when machining today's harder, higher temperature disc materials, while at the same time preserving material fatigue life characteristics required for 5th generation gas turbine engines.