Aerospace gears require post case-hardening grinding of the gearteeth to achieve their necessary accuracy. Tempering of the casehardened surface, commonly known as grinding burn, occurs in themanufacturing process when control of the heat generation at thesurface is lost. A gearbox with minimal service time was removed inservice from an aircraft, disassembled, and visual inspectionperformed. Linear cracks along the dedendum of the working geartooth face were found in three adjacent teeth. A detailedinspection of the gearbox found no other components with distress.AGMA 2007-C00 provides details of the temper etch process andexclusively uses a Nitric acid etch process, which is typicallyused in production quality inspections. The incident gear wasprocessed for grinding burn using an Ammonium Persulfate etchsolution. Quality records documented variation in chemicalconcentration levels during the time the failed gear wasmanufactured. A design of experiments was conducted to understandthe effects of the factors and interactions that impact thecapability of the Ammonium Persulfate process used in production todetect griding burn. Presented are the metallurgical findings, loaddistribution analysis of actual geometry, crack propagationanalysis, and design of experiment results of the AmmoniumPersulfate etch process.
- Edition:
- 08
- Published:
- 10/01/2008
- Number of Pages:
- 10
- File Size:
- 1 file , 810 KB
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