Process research of magnetorheological finishing with a small permanent magnet ball-end tool

A magnetorheological finishing (MRF) technology with a small permanent magnet ball-end tool (Φ4 mm) was developed to solve the problem that it is difficult for hemispherical resonator to be processed by traditional wheel-type MRF machine, for the reason that the minimum curvature radius of hemispherical resonator is 2 mm. The removal function and polishing process of this new polishing method was studied. Based on the analysis method of hydrodynamic lubrication sliding bearing, a three-dimensional removal model of MRF process with a small permanent magnet ball-end tool was established. After solving the removal model by using two-dimensional finite difference numerical method and relaxation iteration method, it is indicated that the morphology of polished spot is similar to the distribution of the product of shear and velocity, while different from the distribution of the product of velocity and pressure, which proves that the surface material of workpiece was mainly removed by shear, rather than by positive pressure. Therefore, the removal function was established based on the shear stress and the relative polishing velocity. And the mean value of K in Preston equation is 8.93×10^-13 m²/N in center region. Combining the simulation result with the single factor experiments, it is indicated that the smaller the minimum machining gap and the larger the spindle speed, the larger the removal rate. It provides a theoretical basis for the selection of optimum process parameters under different conditions.