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Evaluation of the Scuffing Resistance of Isotropic Superfinished Precision Gears

05FTM13

Authors: Paul W. Niskanen, Alion Science and Technology, Bruce Hansen, Sikorsky Aircraft
Corporation and Lane Winkelmann, REM Chemicals, Inc.
The high performance required from aerospace gears places stringent requirements upon the metallurgical
quality, geometry, and surface finish of mating parts. In an effort to meet their mission requirements,
2005 FTM 5
aerospace gears are often engineered to operate near the upper bounds of their theoretical design
allowables. Due to this, scuffing is a primary failure mode for aerospace gears.
It was previously shown that specimens having an isotropic superfinish using chemically accelerated
vibratory finishing had an improved performance inRolling/Sliding Contact Fatigue (R/SCF) testing. Isotropic
superfinishing improved R/SCF resistance up to nine times that of baseline test specimens. These tests also
demonstrated the ability to successfully carry 30 percent higher loads for at least three times the life of the
baseline samples.
A study was then conducted on actual gears having an isotropic superfinish. This study showed isotropic
superfinishing technology increased a gear's resistance to contact fatigue by a factor of three, and increased
bending fatigue resistance by at least 10 percent. This increase in gear performance translates to reduced
operation and sustainment costs, and also offers the potential for weight reduction in new transmission
designs.
The present paper will discuss an additional study which is underway to determine and compare the scuffing
resistance of isotropic superfinished aerospace gears to that of baseline ground gears. Sample gears were
made from case carburized SAE 9310. These tests were conducted using a method that progressively
increases lubricant temperature until scuffing occurs, rather than the traditional load increasingmethod used
in FZG testing rigs. The results of the current testing reveals that isotropic superfinished SAE 9310
specimens show at least a 40 F higher lubricant temperature at the point of scuffing compared to as--ground
baseline gears. Based on these results and the previous studies, it was concluded that this isotropic
superfinishing technology should be incorporated in all future aerospace gear designs. A later paper will
report on similar scuffing testing performed onAMS 6308 gears due to run--outs achieved by both the baseline
and isotropic superfinished samples during the current procedure.
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