Abstract: A permanent magnetic yoke with a straight air gap is proposed to form a stiffened magnetorheological polishing tool of large area for magnetorheological planarization of ultra-smooth surface. A finite element analysis is conducted to optimize the permanent magnetic yoke, combining an orthogonal method, thus to further improve the efficiency of the magnetorheological polishing process. To examine the effectiveness of the optimization，magnetorheological planarization experiment is carried out using permanent magnetic yokes prior to and after optimization. The external magnetic flux density of the permanent magnetic yoke is measured. The performances of magnetic field，the stiffened magnetorheological fluid and the polishing areas are compared. Final tests are performed on optical glasses to evaluate the polishing performances of the modified yoke. The results show that the magnetic flux density and the area of the gradient magnetic field above the permanent magnetic yoke are increased through the optimization. Therefore, the stiffened magnetorheological polishing tool is expanded. The polishing area and the volumetric removal rate are enhanced. The efficiency of the magnetorheological planarization process is well improved.

Key words: high efficiency removal, magnetorheological planarization, optimization, permanent magnetic yoke