Gear tooth wear and micropitting are very difficult phenomena to predict
analytically. The failure mode of micropitting is closely correlated to the lambda ratio. Micropitting can be the limiting design parameter
for long-term durability. Also, the failure mode of micropitting can progress to wear or macropitting, and then go on to manifest more severe failure modes, such as bending. The results of a gearbox test and manufacturing process development program will be presented to evaluate super-finishing and its impact on micropitting.
The objective of this paper is to demonstrate that transmission gears
of rotary-wing aircraft, which are typically scrapped due to minor foreign
object damage (FOD) and grey staining, can be repaired and re-used with
signifi cant cost avoidance. The isotropic superfinishing (ISF) process is used to repair the gear by removing surface damage. It has been demonstrated
in this project that this surface damage can be removed while maintaining
OEM specifications on gear size, geometry and metallurgy. Further, scrap
CH-46 mix box spur pinions, repaired by the ISF process, were subjected to
gear tooth strength and durability testing, and their performance compared
with or exceeded that of new spur pinions procured from an approved
Navy vendor. This clearly demonstrates the feasibility of the repair and
re-use of precision transmission gears.
Results from the Technical University
of Munich were presented in a previous technical article (see Ref. 4). This
paper presents the results of Ruhr University Bochum. Both research groups
concluded that superfinishing is one of the most powerful technologies for
significantly increasing the load-carrying capacity of gear flanks.