Figure error correction of ultra-precision optical surfaces by dual-rotation magnetorheological finishing

Due to the great demand of modern optical systems, many researches on magnetorheological finishing (MRF) technology have been carried out. In this paper, the common MRF was discussed. To reduce the figure error of optical surfaces, dual-rotation magnetorheological finishing (DRMRF) technology was studied. A DRMRF setup was designed and built. Customised magnetorheological polishing fluid was developed and rheological properties were tested. Experiments of removal functions and micro-topography of common MRF and DRMRF were conducted. An experiment of figure error correction was conducted on a Fused Silica workpiece by DRMRF. The figure error was corrected from initial 110.549 nm PV (peak to valley) and 18.201 nm RMS (root mean square) of the whole surface (φ100 mm) to 21.474 nm PV and 2.513 nm RMS within optical aperture (φ96 mm). Results indicate that dual-rotation magnetorheological finishing is an effective method of the figure error correction for ultra-precision optical surfaces.