Advanced magnetorheological finishing of polymethyl methacrylate under concentrated and uniform magnetic fields
摘要
Polymethyl methacrylate (PMMA) is widely used in optics, where superior surface quality is essential. This study compares multipole concentrated and uniformly distributed magnetic fields for magnetic-assisted surface finishing of PMMA, focusing on magnetic field distribution, shear stress generation, and material removal mechanisms. Finite element analysis was employed to simulate field behaviour, revealing that the concentrated configuration achieves a shorter decay time (0.9 s vs. 1.1 s), indicating better magnetic retention and enhanced finishing performance. A series of experiments was conducted to validate simulation results and assess surface quality improvements in PMMA finishing. Magnetorheological finishing is conducted for 90 min with an initial surface roughness of approximately Ra = 450 nm. The use of a concentrated magnetic field results in a surface with Ra = 6.451 nm that is significantly smoother than that achieved under the application of a uniformly distributed magnetic field (Ra = 11.438 nm). Compared to the study by DeGroote et al., using a Q22Y MRF system reduced the PMMA surface error from PV = 4.45 μm to 0.35 μm; however, it required 3.5 h of processing, whereas the proposed method achieved comparable nanometric smoothness in only 1.5 h, highlighting its strong potential for widespread application in precision finishing processes. Furthermore, this work analyses shear stress and process parameters, with shear stress estimated from a physical model of centrifugal forces on abrasive particles and surface morphology evaluated experimentally. The results confirm the effectiveness of the concentrated magnetic configuration in generating localised stress that enhances material removal, highlighting the scientific novelty and practical potential of multipole concentrated magnetic fields for high-precision PMMA surface finishing.