Research On Magnetorheological Finishing For Optical Mirror Materials Of SiC

In recent years the demand for complex optical systems has increased significantly, driven by growth in terrestrial and satellite-based astronomy, and defense and security applications. Proper optical material and fabrication technique is the key problem.Magnetorheological Finishing (MRF) can deterministically produce better, faster, and cheaper high-precision optics, and have gained broad acceptance by most of the world's leading optics fabricators. MRF can make surfaces: extremely flat, extremely spherical, aspherical, cylindrical or any other mathematically defined shape, and extremely uniform in thickness or optical thickness. MRF can also improve the surface integrity by: removing micro-cracks and subsurface damage, removing residual stresses, and improving glass resistance to laser damage.In this work we focus on building a better understanding of the MRF process for the next-generation optical material Silicon carbide (SiC). The main research includes:1. Material removal mechanism in MRF process for SiC. Combine several material-removed theories with structure of SiC, we analyze MR fluids, removal functions models and surface roughness theory. Then we discuss several influenced factors on mechanisms.2. Material removal rate and"polishing spot"in MRF process for SiC. We establish the evaluative targets on removal functions, and study the peak removal rate,volume removal rate,geometrical size.3. Proper polishing parameters in MRF process for SiC. We establish the evaluative targets on polishing parameters, and summarize the influenced degree of parameters on polishing.4. Active control method of surface quality in MRF process for SiC.Based on mechanisms in MRF process for SiC, we develop a high precision and more efficient fabrication technique for optical surface of SiC using MRF. By selecting proper MR fluids, establishing stable removal functions and choosing proper polishing parameters, we succeed in the fabrication of a SiC plane (202mm in diameter). The finial P-V value is 0.13μm and RMS value is 12nm.