New technology to magnetorheological finishing aspheric cylindrical mirror

Cylindrical mirror is a high-precision optical element, which requires not only very low surface roughness, no surface/subsurface damage and low residual stress, but also parallelism and verticality of cylindrical generatrix. By analyzing the influence of traditional grinding and polishing technology and computer controlled optical surfacing (CCOS) on surface roughness, surface profile accuracy and generatrix error of cylindrical mirror after machining, the advantages and disadvantages of two methods are summarized. Aiming at the low efficiency, high roughness and surface/subsurface damages of the existing machining methods,a new magnetorheological finishing process with symmetrical structure for aspheric cylindrical mirror is proposed, and the feasibility of the new process is verified by the experiment of time parameters. The surface roughness and profile accuracy of the cylindrical mirror are effectively reduced. At the polishing time of 40 min, the surface roughnessR_adecreases from 1.84 to 0.36 μm, the local profile accuracyRMS₁decreases from 1.91 to 0.24 μm, and the generatrix section profile accuracyRMS₂decreases from 4.1 to 0.68 μm.