Gear tooth wear and micropitting is a very difficult phenomenon to predict analytically. The failure mode of
micropitting is closely correlated to the lambda ratio [1][2]. Micro pitting can be the limiting design parameter
for long-term durability. Also, the failure mode of micropitting can progress to wear or macropitting, then
manifest into 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
Testing was designed using an existing aerospace two stage gearbox with a low lambda ratio. All gears were
carburized, ground and shot peened. Two populations were then created and tested. One population was
finish honed and the second was shot peened and isotropic super finished.
A standard qualification test was conducted for 1 50hrs at maximum continuous load. The honed gears
experienced micro and macro pitting during the test. The Isotropic Super Finishing (ISF) gears were also
tested for 1 50hrs under the same loading. The ISF gears were absent of any surface distress. The ISF gears
were further subjected to a 2000hr endurance test. The ISF gears had less surface distress after 2000hrs
than the baseline honed gears after 150hrs.
AGMA 11FTM20-2011 pdf download
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