Abstract: Based on the contact mechanics theory in ultrasonic rolling process, the evaluation index of impact contact rate per unit area is proposed, and the displacement and area of ball-workpiece contact under different process parameters are solved. The mechanism of surface finishing in ultrasonic rolling process is studied, and the featured structures of active plastic deformation zone, passive plastic deformation zone and passive elastic deformation zone of surface layer materials are proposed. The effect of ultrasonic rolling parameters on surface roughness is discussed through orthogonal test, which provides a theoretical basis for the active control of surface topography by optimizing ultrasonic rolling parameters. The results show that the displacement value of the contact point between the rolling ball and the workpiece is always higher than the ultrasonic amplitude value under the ultrasonic rolling process parameters selected, which indicates that the rolling head always keeps in contact with the workpiece surface during the ultrasonic rolling process. Ultrasonic rolling has the effect of “peak shaving and filling valley”, and the material flow in the active plastic deformation area of the surface is the fundamental reason for the improvement of surface finish. The feed speed of the rolling ball has the greatest influence on the surface roughness, followed by the static load and the minimum speed. If a better surface finish and higher machining efficiency are desired during the ultrasonic rolling process, higher speed, larger static load and smaller ball feed can be selected.

Key words: 300M steel, ultrasonic rolling, surface morphology, roughness, plastic flow