Influence of the Machining Process on the Service Life and Pitting Morphology of Gear-Tooth Surfaces

Abstract

Pitting, which results from contact fatigue, is a common failure mode in gear transmission systems and is influenced by the material strength and stress state of the contact area, which is further influenced by lubrication and roughness because of stress fluctuations. In this study, a comparative contact-fatigue test was conducted on two types of gears with different terminal machining processes. The contact stress of the tooth surface considering the microtopography was analyzed using the fractal method based on surface microtopography data measured from the surface formed by the two processes. Test results show that the average service life of gears machined using the barrel-finishing process was approximately 5–7 times that of gears machined using grinding. The pitting morphologies of gears fabricated using different processes exhibited evident differences. The maximum stress level of the gears machined with barrel finishing was approximately twice that of the gears machined through grinding. Different stress levels resulted in different micropitting load-bearing capacities, which could be attributed to the different service lives of gears manufactured through different machining processes. The different presence features of the pitting morphology were due to the different micromorphologies of the surface formed by the different finishing processes. In particular, the randomly distributed pitting morphology of the gear surface machined using the barrel-finishing process was due to its flattening and polishing effect. Optimization of the surface-microgeometry distribution via the finishing process is an effective method for prolonging the service life of gears.