Surface quality in ultrasonic-electrolytic internal grinding of GCr15 steel

To tackle the issues of poor surface quality, grinding burn, microcrack and deformation in conventional grinding, in this paper, combined the merits of ultrasonic vibration and electrolytic grinding, the material removal characteristics of GCr15 steel in longitudinal torsional ultrasonic electrolytic internal grinding were revealed based on the kinematic analysis of single abrasive particle. Additionally, a theoretical analysis of the heights of material removed by electrolytic action and mechanical grinding was conducted. The single factor experiments were completed for conventional grinding (CG), longitudinal torsional ultrasonic grinding (LTUG), electrolytic grinding (EG) and longitudinal torsional ultrasonic electrolytic grinding (LTUEG). The results demonstrated the superiority of LTUEG processing through comparisons with CG, LTUG and EG. LTUEG shows significant advantages in reducing grinding force, improving surface roughness and quality, and achieving ideal microhardness and residual stress. The formation and removal mechanism of the passivation film were elucidated. The passivation film was primarily composed of iron oxides, hydroxides, and precipitates of the C element. Increasing the voltage helped to increase the thickness of the passive film and reduce the actual grinding depth; however, excessively high voltages could easily lead to residual passive film coverage and electrolytic burn phenomena. The influence of different processing parameters on surface quality was investigated. Within a certain range, increasing the ultrasonic amplitude, voltage, and grinding wheel speed, while decreasing the feed speed, had a beneficial effect on enhancing the surface quality. Therefore, LTUEG is an effective processing method to improve the quality of GCr15 steel.