Study On Techniques For Polishing Processing Aspheric Surfaces Of Single-crystal Silicon

Today, the optical element has been widely used in various fields for its good performance, and each requirements of the modern optical system on the optical element are gradually toward diversification and high quality. Aspherical element has advantage of eliminating aberrations, reducing dispersion, simplifing the structure and reducing costs. In the infrared optical system, the demands for aspherical lens maded of singlecrystal silicon are growing, with higher requirements of surface roughness and surface shape. The conventional processing of silicon lens can’t meet extremely high demand of optical system on precision machining and surface roughness of the silicon lens both from productivity or precision. Thus, a highly efficient and high-precision optical aspheric technology is important.This paper focuses on a new form of polishing techniques: chemical mechanical wheel polishing, that make use of flexibility of self-developed polishing wheel for the force of alumina particles exert in polishing liquid, and use the grinding effect on the aspheric surface to accurately remove material to improve the surface roughness by computer control. So this paper mainly research the contents as follows:As to exert positive pressure to the surface of aspherical lens, we set up wheel polishing system based on the B-axis platform. In order to avoid the problem that the installation errors offset of polishing spindles in the center of the B-axis will make the polishing pressure changes, we analyze the influence of the installation offset error, and propose three kinds of measurements on bias error and adjuste installation errors offset through three-dimensional micro-displacement adjustment stage. And then performed experiments about corrugated surface machining, and the machining error is about 3μm.Using the knowledge of Hertz contact theory to get the size of contact area and pressure distribution between the polishing wheel and the workpiece. On this basis, build a semi-empirical chemical mechanical polishing wheel removal function model on combination of kinematic and Preston assumed knowledge. And then work on the Simulation analysis of the polishing technology for flat workpiece.Based on the theoretical model, we designed fixed point single factor experiment about the polishing pressure, polishing time and polishing wheel speed to obtained polishing removal volume and shape, and then according to the asymmetry of pit contour machined, the ratio of ellipse minor of pressure model is corrected to 0.726. By fitting the data to calculate the coefficient of generalized Preston equation, and then we get removal function is 4.6299×10-14m2/N. Design orthogonal experiment about ring polishing process to analyze the law about how the polishing process parameters have effect on the polishing wheel polishing process removal efficiency of monocrystalline silicon surface and surface roughness. Finally, summed up the polish the best features of the preferred polishing process parameters, polishing wheel speed of 897 rpm, the polishing liquid particle size of 1μm, buffing wheel pressed into the workpiece depth of 120μm.Finally, use the removal function to calculate the dwell time by discrete matrix algorithm, and then machined the single crystal silicon flat of the diameter of 30 mm, r300 mm convex spherical and aspheric. This return the result of a surface roughness of about 4nm, and face shape improved. And it verified good processability of wheeled chemical mechanical polishing technique.