Ultrasonic surface rolling strengthening and its parameter optimization on bearing raceway

Abstract

For the first time, the ultrasonic surface rolling processing (USRP) technology was applied to a real bearing raceway, and a finite element simulation model for USRP on a bearing raceway was established. Practical tests were conducted to evaluate the surface integrity of the bearing raceway before and after USRP treatment. The USRP parameters were optimized using Taguchi-gray correlation analysis. The results show that the optimal process parameters for the 7224 bearing raceway are: an amplitude of 10 μm, a static pressure of 2400 N, a spindle speed of 45 rad/min, and rolling times of 7. In the process of USRP, residual compressive stress results from inhomogeneous elastic and plastic deformation. Adjacent tempered martensitic laths merge and deflect at a certain angle along the rolling direction to form directional grain stacks, resulting in a flocculent plastic deformation layer. The USRP based on the finishing mechanism of “peak-cutting and valley-filling” can improve the surface micro-morphology, reduce roughness value Ra to approximately 0.16 μm, and effectively eliminate microscopic cracks caused by grinding. The micro-hardness of the bearing raceway surface increased from 760 HV to 840 HV under the dual action of surface grain refinement and work hardening effect.