SBIR-STTR Award

The Army’s Rotorcraft Force Modernization Fleet requires a substantial increase in main gearbox power density, with minimal impact on the gearbox interface. Instead of increasing gearbox size and transmission weight, this project seeks to accommodate the higher power density requirements through designed material processing techniques, integrating several state-of-the-art manufacturing processes to specifically improve the gear material contact and bending fatigue strengths. In Phase I, a novel heat treating method called "Intensive Quenching", as well as superfinishing will be investigated to determine the feasibility of improving the bending fatigue life of the Pyrowear 53 steel by at least 25% over conventional processing.

Benefits:
The project will benefit the Army's commercial Original Equipment Manufacturers (OEM's) and the Army itself by achieving improved rotorcraft transmission power density while not increasing gearbox weight. In place of conventional oil quenching, the intensive quenching process will provide an environmental safety benefit by substitution of water for oil. Free quenching proposed in the innovation, as opposed to press quenching, will reduce heat treatment cost by at least 50%. While superfinishing may add to the existing machining cost, the increase will more be more than offset by the improved part life. Overall, the use of a low-cost, environmentally friendly heat treatment in combination with superfinishing of the gear tooth will increase transmission component life by at least 25%. The added use of Pyrowear 53 will provide helicopter safety and allow damaged transmissions to function for a longer time period.

Keywords:
Pyrowear 53, Fatigue Life, Helicopter Gear Material Performance Improvement, Heat Treatment, Superfinishing, Intensive Quenching, Residual Stress

The Army's Rotorcraft Force Modernization Fleet requires a substantial increase in main gear box power density, with minimal impact on the gearbox interface. Consequently the Army has specified the goal of achieving transmission gear tooth bending fatigue improvement of 25%. This project seeks to accommodate the higher power density requirements through enhanced and innovative material processing. The Phase I effort of this project has successfully demonstrated both the improvements in residual surface compressive stress and bending fatigue life possible for the gear steel Pyrowear 53 through an innovative heat treatment called "Intensive Quenching." Comparative evaluation of Pyrowear 53 notch bar specimens demonstrated a 2x increase in residual surface compression, and at least 20% improvement in bending fatigue performance with the use of intensive quench processing as opposed to standard oil quenching. Phase II will seek to expand the characterization of the innovative heat treatment, in conjunction with superfinishing, into full test gears. The Pryowear 53 gears will be fully processed, comparing the standard to the innovative heat treatment, with single tooth bending fatigue comparisons performed, along with full metallurgical, dimensional and residual stress characterization. With this assessment, technology transfer to the US Army OEM's will be facilitated.

Keywords:
Helicopter Transmission Gears, Pyrowear 53, Heat Treatment, Intensive Quenching, Bending Fatigue Life, Surface Residual Compressive Stress Enhancement