Study On Polishing Technology Using Spherical Tool

With the application of optical elements in many fields and the increasing requirements of performance in modern optical system, more optical elements with asphere, light and thin, large relative aperture are needed. Moreover, in order to solve the problem of fabrication and installation of super large optical mirror, the development of stitching optical system is more and more emphasized. In the machining process of this kind of large aperture optics, edge effect will influence the quality of stitched optical mirrors. The edge effect will also bring disadvantage into polishing efficiency and the consistency of surface error, and minish the effective optical diameter which can affect the performance of optical system,such as distinguishablity and light gathering power. Today,typical other polishing technologies such as Computer Controlled Optical Surfacing, Stressed-lap Polishing, Magnetorheological Finishing and Ion Beam Figuring Technology and so on,all of them have some disadvantages for controlling edge effect.The spherical polishing technology has high machining accuracy, simple process conditions, low cost.Because its removal function whose diameter is very small has nice stability and conforms to Gaussian distribution and don't bring effect to near area when figuring targeted area of a mirror,which make the technology possess good figuring capability specially for removing the edge effect and local surface error. This thesis is dedicated to study the theory and technology of spherical polishing process, in order to solve the edge effect appearing in the process of polishing large aperture optical mirror. The major research efforts include the following points:1. According to the Hertz theory, the contace area is mainly analyzed when the spherical polishing tool is used to machine the optical workpieces, including the shape, the size and the pressure distribution of contact area, and so on. Based on the kinematics theory and the Preston equation, the removal function of spherical polishing tool is modeled and the simulation analysis is carried out under different conditions.2. Based on the analysis of the removal function's theory model, the spherical polishing tool's structure is simplified and the theory model is validated by experients. The technological experiments are executed to study the influences of parameters such as sphrecial polishing tool's rotating speed, the polishing pressure on the material removal rate, the surface roughness and the workpiece's rotating speed on removal function. The influence of polishing time on the stability of removal function is correspondingly studied.3. Figuring capability and processing characteristics of spherical polishing technology are analyzed and studied in detail. The appropriate polishing method and feed way are chosen, the reason that it needs machining compensation is analyzed, and a new polishing route and a method for removing the small scale manufacturing errors are present.4. Finally, experiments using spherical polishing tool are performed on some typical optical surfaces, including a piece ofφ190mm crystallite spherical mirror and a piece ofφ290mm SiC parahboloidal mirror, and good results are obtained which prove its feasibility and good machining ability for removing edge effect and and local surface error.