Evaluation of Isotropic Superfinishing on a Bell Helicopter Model 427 Main Rotor Gearbox

The surface finish of a gear tooth is a critical factor in the wear, durability, noise generation, and efficiency of modern helicopter transmissions. Currently, optimized grinding and honing processes are used to improve the surface finish of both gear teeth and roller bearing races. With the promise of reduced manufacturing cost, reduced scrap, reduced noise, and improved gearbox efficiency, a new surface refinement process known as isotropic superfinishing is making its way into the aerospace industry. Isotropic superfinishing (ISF) is able to produce 2-4 pin Ra surface finishes using a combination of vibratory media and surface conversion chemicals without modifying the profiles of aerospace quality ground gear teeth. This paper will outline NRTC-CRI funded testing of a Bell Model 427 main rotor gearbox with ISF processed gears. Testing performed includes thermal efficiency, gear tooth bending fatigue, acoustic, and extreme conditions.