Improving Wear Characteristics of a Rotorcraft Mast and Transmission Spline Interface with Laser Hardening

This study investigates an improved tribological relationship at the mast and transmission spline interface for extended wear life. Various techniques for increasing surface hardness are considered. Metallurgical results for induction hardening were unfavorable. A hardening method that is new to the rotorcraft transmission industry is evaluated; laser hardening. Metallurgical results are promising, finding sufficient case hardness and depth, repeatability of profile, and minimal heat affected zone (HAZ). Finite element analysis (FEA) and residual stress analyses are performed for a laser hardened mast spline. The stress analysis, laser hardening capabilities, manufacturing and processing tolerances, and metallurgical test results ultimately drive the detailed design of a laser hardened mast spline. Laser hardened masts will be subjected to fatigue testing. Also, a lead-the-fleet program will be implemented to monitor the wear characteristics and verify improvement with a laser hardened mast and transmission spline interface that is subjected to real helicopter flight conditions.