Effects of magnetorheological processing parameters on the mid-spatial frequency errors of optics

By virtue of the characteristics of high machining certainty, fast surface shape convergence and less subsurface damage, magnetorheological finishing (MRF) has been widely applied in ultra-precision machining for optics. However, the convolution of tool influence function (TIF) and the regular movement track make it difficult to avoid the deterioration of mid-spatial frequency (MSF) errors in the MRF process, which will affect the optical properties of optics. In this paper, the main factors affecting the MSF errors in grating path processing are theoretically analyzed. Under the condition of determinate polishing spot, the main influencing factors are the removal depth and processing spacing of a single scan. Through experimental research, the influence of removal depth and processing spacing of a single scan on the MSF errors in the MRF process is acquired. On this basis, the preferred parameters of removal depth and processing spacing of a single scan under specific processing conditions in the MRF process are obtained with the MSF errors of 1 nm as the evaluation index. It provides a theoretical basis and reference value for suppressing the deterioration of MSF errors of optics during MRF process and obtaining high quality optical surfaces.