Effects of Different Shot Peening Treatments in Combination with a Superfinishing Process on the Surface Durability of Case-Hardened Gears
Modern gearbox designs set increasing requirements on the surface durability of gears in light of calls for downsizing and performance optimization. Using additional manufacturing processes is one way to tackle these challenges. The increase in the compressive residual stress state due to shot peening and the decrease in the roughness of the gear flank surface due to superfinishing processes are two possible measures. While there have been extensive scientific studies in the past on the positive effects of shot peening and superfinishing, a detailed quantification of a calculation model of these two effects has not been subject to in-depth investigation yet. To address this gap in knowledge, a study was carried out to examine and evaluate different peening processes and the resulting residual stress profiles in combination with a superfinishing process. Experimental investigations showed significant differences in the gear flank load-carrying capacity due to the different surface treatments. In addition, a significant reduction in micropitting appearance was observed due to the superfinishing process, while the increased compressive residual stresses due to shot peening showed no significant influence on the development of micropitting. By correlating the pitting durability from the experimental investigations with existing calculation methods, it was possible to extend the surface factor ZR from ISO 6336 to a wider range of roughness values as well as to introduce a new factor ZS for different shot peening treatments. Based on the results of this paper, the positive effects of different shot peening processes as well as superfinishing processes can be taken into account for gearbox design and rating processes.
Authors: Dominik Kratzer, Johannes König, Thomas Tobie, & Karsten Stahl
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