Simulation and experimental research on magnetorheological finishing under dynamic pressure with a gap-varying

Abstract

Magnetorheological finishing (MRF) is a novel machining method used to obtain ultra-smooth and even surfaces. To improve the material removal rate (MRR) while attaining smooth and undamaged surfaces, an MRF method with a varying machining gap between the polishing disks and workpieces is proposed to increase the polishing efficiency and improve the surface quality. According to the computational fluid dynamics (CFD) method, the behaviors of MRF fluids under the effect of magnetic fields are measured using a rheometer. Furthermore, a simulation model for fluids based on the gap-varying MRF is established to evaluate the influence of the varying machining gap on the behaviors of the flow field of MRF fluids. The results show that the flow field formed during gap-varying MRF presents a periodic dynamic change and formation of turbulence. Both the fluid pressure and velocity on the workpiece surface show a periodic change and the maximum fluid velocity on the workpiece surface in the x-direction is much greater than that in the z-direction; the transverse shear velocity contributes to the material removal and abrasive update. Under the same polishing time and rotational speed, the surface roughness is reduced from Ra 6.36 nm to Ra 0.155 nm after MRF without varying gaps for 5 h; in contrast, the surface roughness decreases from Ra 6.44 nm to Ra 0.104 nm after MRF with a varying gap, attaining an atomic step-structure. Properly increasing the frequency and amplitude of gap variations is conducive to achieving a better polishing effect. By conducting real-time force measurement and establishing a material removal function, it is shown that the simulation results match the test results. MRF with a varying gap can increase the polishing efficiency and surface quality by changing the behaviors of the flow field.