Studying the Effects of Lapping Process on Hypoid Gears Surface Finish and Transmission Errors

There are several geometric and working parameters, besides offset, that have minor effects on hypoid gears efficiency (i.e. spiral angle, pressure angle, lubricant type & temperature, surface finish, etc.). Some theoretical analyses of mechanical efficiency of hypoid gears show that surface finish has considerable effect on hypoid gear efficiency. This is due to a high sliding to rolling ratio in these types of gears. In this paper, a study on measuring of surface finish of both ring gear and pinion will be presented. Moreover, the effects of lapping on surface finish will be discussed. Using an accurate form-measuring machine, surface finish measurements were done on several experimentally produced hypoid gear pairs¹. Despite the fact that lapping is expected to improve the surface finish, measurement results show that ring gear's surface finish becomes worse (roughness increased) after lapping while no consistent results for pinion surface finish were observed. However, it will be shown that lapping decreases transmission errors for both sides (drive and coast). Utilizing a Gleason single flank tester 600HTT it will be shown experimentally that transmission errors up to the third harmonics for both sides will be decreased. In addition, it can be seen that lapping decreases surface finish variation among gear sets.