Basic principle and mechanical property of magnetorheological hydrodynamic compound polishing

The work aims to investigate the basic principle and mechanical properties of magnetorheological hydrodynamic compound (MRHC) polishing. Effects of structured element of the polishing disk on the mechanical properties of polishing were analyzed according to the mathematical model for hydrodynamic pressure of MRHC and the structure was optimized accordingly. Then, effects of working gap and rotating speed of polishing disk, workpiece and cam on the polishing force were studied. Furthermore, the orthogonal test was carried out to obtain the optimal polishing efficiency. The hydrodynamic pressure could be generated in the wedge region of structured element on the polishing disk and decreased with the increase of wedge angle and working gap and increased with the increase of width of wedge region. The reasonable geometrical parameters of structured element were wedge angle of 3°~5°, working gap of 0.2~1.0 mm and width of wedge region of 15~30 mm. The normal force Fn decreased with the increase of working gap and the decrease of rotating speed of workpiece, and increased first and then decreased with the increase of rotating speed of polishing disk and cam. The shear force Ft decreased as working gap increased, increased first and then decreased as the rotating speed of workpiece, polishing gap and cam increased. Finally, the optimal polishing parameters were obtained through orthogonal test: the rotating speed of polishing disk, workpiece and cam was 60, 600, and 150 r/min, respectively. After 2 in single-crystal silicon was polished for 4 h under the conditions of carbonyl iron powder (size 3 μm, mass fraction 35%), SiC abrasive (size 3 μm, mass fraction 5%), working gap of 0.4 mm and magnetic induction strength of 0.1 T, the surface roughness Ra decreased from 20.11 nm to 2.36 nm, the material removal rate was 5.1 mg/h, and the initial large-scale scratches were obviously removed. Hydrodynamic pressure can be induced according to the structured element on the polishing disk of MRHC to strengthen the polishing mechanical properties. In addition, the update and truing of flexible polishing head can be realized with the drive of moving magnetic field in radial direction, thus finally improving the polishing efficiency and quality. © 2020, Chongqing Wujiu Periodicals Press. All rights reserved.