Surface roughness model of ultrasonic vibration-assisted grinding GCr15SiMn bearing steel and surface topography evaluation

It is necessary to improve the surface performance of bearing rings and extend the service life of bearings. In this study, ultrasonic vibration-assisted grinding (UVAG) was applied to process GCr15SiMn bearing steel, considering the effects of grinding-wheel wear, overlap of abrasive motion tracks under ultrasonic conditions, elastic yield of abrasives, and elastic recovery of the workpiece on the machined surface. In addition, a novel mathematical model was established to predict surface roughness (R_a). The proposed model was validated experimentally, and the predicted and experimental results showed similar trends under various processing parameters, with both within an error range of 12%–20%. The relationships between the machining parameters and R_a for the two grinding methods were further investigated. The results showed that increases in the grinding speed and ultrasonic amplitude resulted in a decrease in R_a, whereas increases in the grinding depth and workpiece speed resulted in an increase in R_a. Furthermore, the R_a values obtained using the UVAG method were lower than those of conventional grinding (CG). Finally, the influence of ultrasonic vibration on the surface topography was investigated. Severe tearing occurred on the CG surface, whereas no evident defects were observed on the ultrasonically machined surface. The surface quality was improved by increasing the ultrasonic amplitude such that it did not exceed 4 μm, and a further increase in ultrasonic amplitude deteriorated the surface topography. Nevertheless, this improvement was superior to that of the CG surface and was consistent with the variation in R_a.