Investigation of Isotropic Superfinishing Effects on Ground Hypoid Gears

Abstract Isotropic superfinishing has been demonstrated by many studies that it can have positive influence on friction/heat reduction and surface fatigue life improvement for sliding/rolling contact elements such as bearings and gears. However, superfinished gears are still not widely used in automotive transmissions and axles. The tradeoff between cost and benefit is certainly an important reason, but more importantly it is perhaps due to the lack of evidence in demonstrating the effect of isotropic superfinishing on several gear parameters and performances, such as process inherited micro-geometry, contact pattern and noise characteristics alteration. Published data are particularly limited on superfinishing effects on axle hypoid gears. On the other hand, over the past several years, superfinishing processes for gears have been evolved since decades ago. It could take up to a couple hours to process a typical hypoid gear set to a desired surface finish level in the past. With today’s latest technology, it can be done within a few minutes. In this paper, a study has been performed to investigate the effects of super finishing process on hypoid gears by using a vendor’s latest isotropic superfinishing technology. Experimental hypoid gears hard finished by grinding were used such that the tooth geometry was precisely controlled prior to superfinishing. The final surface finish processed with different cycle times were compared to its original ones. The amount of material removal and micro-geometry change were quantified through CMM measurements. Contact pattern and motion transmission error (MTE) before and after superfinishing were taken by using a Single Flank Tester (SFT). Finally, two samples were built into axles and tested on a noise and vibration (NV) dynamometer to evaluate and compare the NV performances with standard non-superfinished gears.