Effect of ultrasonic vibration on oxide layer properties in ultrasonic-assisted ELID internal cylinder grinding

The oxide film on the surface of the grinding wheel plays a very important role in ultrasonic-assisted electrolytic in-process dressing (UA-ELID) grinding. In order to investigate the influence of ultrasonic vibration on the characteristics of oxide film on the surface of grinding wheel in compound grinding, the formation mechanism of oxide film on the surface of grinding wheel under ultrasonic action was analyzed theoretically from two aspects: the change of single grain trajectory caused by ultrasonic vibration and the effect of ultrasonic cavitation. The pre-dressing tests were conducted with different pre-dressing times to observe the oxide layer properties at different pre-dressing stages. The grinding tests were conducted after pre-dressing to verify the grinding performance of oxide layer under different pre-dressing methods. The results show that after the ultrasonic vibration of the grinding wheel is added during electrolytic in-process dressing (ELID) process, the holes and cracks of the oxide film on the surface of the grinding wheel are greatly reduced during the whole pre-dressing process. In addition, the pre-dressing current decreases more stably and the current is smaller when it reaches stability. After the pre-dressing, the thickness of the oxide film is reduced by about 35 % and the hardness is increased by about 70 % compared with the ordinary pre-dressing process. The grinding test results show that the oxide film obtained by ultrasonic vibration of the additional grinding wheel is more conducive to improving the surface quality of the grinding process. Therefore, compared with the ordinary pre-dressing process, the density and uniformity of oxide film on the surface of grinding wheel is better and the hardness is higher after the additional ultrasonic vibration of grinding wheel. It is beneficial to improve the surface quality of workpiece.