Study on theory and finite element simulation of ultrasonic rolling extrusion process

Ultrasonic rolling extrusion process (UREP) is the newly arisen surface strengthening technology, which can effectively reduce the surface roughness of the workpiece and improve the residual compressive stress at the certain depth on the surface so that it has great adaptability to the enhancement of the surface properties of the bearing ring. Through theoretical analysis, finite element simulation, and experiment method, the surface mechanical properties and the surface roughness of UREP strengthening when applied to the material of the wind power bearing ring are studied. Firstly, the strengthening principle of UREP is illustrated. Secondly, according to the motion trajectory of the rolling ball during UREP, the kinematic model of UREP is established. The forming principle of the surface micromorphology during UREP is explored. Thirdly, based on the contact characteristics between the rolling ball and the surface of the workpiece, the contact mechanics model of UREP is established. Based on Hertz contact theory, elastoplastic mechanics theory, and contact mechanics theory, the mechanical properties of the contact area between the rolling ball and the surface of the workpiece during UREP are analyzed. Finally, the simulation and experiment of 42CrMo steel cylindrical workpiece during UREP are carried out, and the variation trends in the simulation values are found to be consistent with those observed in the experimental results. The results show that the residual compressive stress generated in the surface of 42CrMo cylindrical workpiece after UREP gradually increases with the increase of the layer depth and then decreases and transforms into the residual tensile stress. Moreover, the surface roughness first decreases and then increases with the rise of the amplitude and the static pressure. Similarly, it gradually improves when the feed rate and rotational speed rises. The established UREP simulation is useful for imitating the actual machining process of 42CrMo steel during UREP, which extends the effective way for UREP parameter optimization.