Determination of the optimal coverage for heavy-duty-axle gears in shot peening

Abstract

Pitting and wear often appear on heavy-duty-axle gears due to their harsh working conditions, such as high torques, high loads and poor lubrication. Shot peening is a popular surface strengthening method for gears. In order to ensure complete coverage during shot peening, 100%~200% coverage is usually prescribed for most gears. However, it is difficult to effectively improve the contact fatigue and wear resistance of heavy-duty-axle gears. Generally, increasing shot peening coverage can heighten the compressive residual stress for prolonging the service lifetime of gears. Whereas, high coverage levels may cause the deterioration of surface roughness, thus increase the noise and vibration of gears. To address this issue, this paper deals with the determination of optimal coverage for heavy-duty-axle gears by experimental tests. The influence of shot peening coverage on the surface integrity of gears is analyzed in terms of residual stress, microhardness, surface morphology and dislocation density. The results show that the maximum compressive residual stress increases first and then keeps stable with the increase of coverage, and the maximum value is −1172.10 MPa. The microhardness peak increases obviously in the beginning and then slowly rises with the increase of coverage, and the maximum value is 747.5 HV1.0. The surface roughness (Ra) decreases initially and then enhances with the increase of coverage, and the minimum value is 0.99 μm under the coverage of 1000%. The dislocation density increases with the increase of coverage, and the maximum value is 3.70×10 16 m -2 . Numerous damages (microscalings, spallings) occur on the treated gear tooth flank affecting the residual stress distribution and roughness under high coverage levels. Taking into consideration of service lifetime, working noise and economic efficiency, the coverage of 1000% is the optimal coverage for heavy-duty-axle gears in shot peening.