Large And Medium-sized SiC Aspherical Mirrors Deterministic Efficient Processing Technology Research

Medium and large aspheric mirrors are widely used for the investigation of optical system in both ground telescope optical system and space optics. With the increasing of demands, the processing need be done efficiently and fast, not limited by the processing could be done. In the paper, we studied the efficient and certain processing method to aspherical mirrors in both grinding and polishing periods,based on the processing to the aspherical mirrors in medium or large size.Combining the national engineering task requirements with my own work, we studied the efficient and certain processing method to Si C aspherical mirrors in medium or large size.1. Research on the ultrasonic grinding deterministic efficient processing: the mechanism of ultrasonic grinding was analyzed, which proved the ultrasonic grinding was efficient. The diamond grinding wheels were analyzed and designed to determine the types of diamond grinding wheel for Si C mirror ultrasonic grinding of the three stages. The parameters of grinding process of Si C material ultrasonic grinding and optimization were determined through the grinding experiments. The process parameters database of ultrasonic grinding Si C material was established. The ultrasonic spindle and handle were analyzed; the efficiency of ultrasonic grinding was demonstrated by grinding process experiments.2. Study of ultrasonic combined deterministic grinding of large and medium Si C aspheric mirrors: coefficient method and reverse engineering method were adopted to establish the precise aspherical model. Simulation and cutter path planning were carried out according to the model. Online detection based on laser tracker in the process of ultrasonic grinding Si C mirror, not only reduced risk, but improved grinding efficiency and accuracy. Combined with engineering examples, a Si C aspherical mirror with the aperture of 800 mm had been manufactured by ultrasonic composite deterministic grinding and online testing, and the grinding efficiency had been improved more than 30%. After grinding, the surface error was PV 11.2μm and RMS 1.8μm.3. Study of magnetic media assisted polishing: the design of wheel type magnetic media assisted polishing module had been completed and optimized; it could be applied to the spindle for machining center BT40 taper shank directly. The process parameters of magnetic media assisted polishing were optimized, the optimum process parameters of magnetic media assisted polishing for coated Si C mirror were determined. For example, a Φ150 mm coated Si C flat mirror had been fabricated by magnetic media assisted polishing, the final result reaches PV:0.107λand RMS:0.23λ( λ =0.6328 μ m). Research on the magnetic media assisted polishing laid a good foundation for the research of Magnetorheological Finishing(MRF).4. The spherical wheel MRF system design and the analysis of machine tool design: with the help of the modular design concept, the polishing mechanism module and magnetorheological fluid circulation module of the MRF system were completed, and the spherical wheel was analyzed. The requirements for the performance of the machine tool parameters of MRF were determined. the vertical machining center was designed, reconstructed and analyzed according to the requirements. The precise position of spherical MRF removal function center was found by using a dial indicator alignment method, which improved the certainty of MRF. Combined with engineering examples, a Φ400 mm convex off-axis asphericcoated Si C mirror had been finished by IBF, after finishing a cycle of 12 hours, the surface error had been converged from PV:0.614λ, RMS:0.099λ to PV:0.201λ,RMS:0.025λ.The research work in this paper improved grinding efficiency and accuracy of the large and medium Si C aspheric mirror. It reduced the subsequent grinding time.High deterministic MRF improved efficiency of polishing large and medium coated Si C aspherical mirror obviously.