Repair of High-Value/High-Demand Spiral Bevel Gears by Superfinishing

摘要

Following is a report on the R&D findings regarding remediation of high-value, high-demand spiral bevel gears for the UH-60 helicopter tail rotor drivetrain. As spiral bevel gears for the UH-60 helicopter are in generally High-Demand due to the needs of new aircraft production and the overhaul and repair of aircraft returning from service, acquisition of new spiral bevel gears in support of R&D activities is very challenging. To compensate, an assessment was done of a then-emerging superfinishing method - i.e., the micromachining process (MPP) - as a potential repairtechnique for spiral bevel gears, as well as a way to enhance their performance and durability. The results are described in this paper. Spiral bevel gears are high-precision, high-cost components that are used in the main powertrain of nearly all modern rotorcraft. Production of these gears is a complex process, beginning with a forged shape of high-quality aerospace steel, such as AMS 6265. The shape is rough-machined into a precise 3-D geometry and heat-treated to achieve the desired strength characteristics that provide the desired combination of surface durability and bending fatigue resistance. The final geometry and surface finish are achieved by finish-grinding and shot peening. The complete processing cycle can take from six to nine months, creating a significant lead time for the acquisition of new production parts. Production of new aircraft - coupled with the overhaul of aircraft returning from service in both Iraq and Afghanistan - has created a situation where the demand for new-production spiral bevel gears is very high. Available gear assets are closely monitored by both the OEM and the government to ensure that an adequate supply is available for new-production and overhaul purposes. This situation creates significant challenges in acquiring spiral bevel gear assets with which to conduct research and development programs.