Case Study Involving Surface Durability and Improved Surface Finish


Gear tooth wear and micro-pitting is a very difficult phenomenon to predict analytically. The failure mode of micro-pitting 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 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 150hrs 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 150hr 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 2000hr than the baseline honed gears after 150hrs.
ISBN: 1-978-61481-019-3 Pages: 18
Authors: G. Blake and J. Reynolds
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