Study On Abrasive Jet Polishing Technology

With the ever-increasing demands on performances of modern optical system, more and more aspherical surfaces and freeform surfaces are required. In recent years, the development of modern optical system is multi-polar; the demands of large aperture, large relative aperture, steep aspherics and cavities with big ratio of length-diameter, micro-aperture aspherical surfaces are all increasing rapidly. Due to the restrictions of mechanical interferences and the size of the polishing head, there are still no effective methods for the finishing of steep aspherics, cavities with big ratio of length-diameter and micro-aperture aspherical surfaces, which seriously limits the applications and researches of the above optics. Very small removal spots will be produced in abrasive jet polishing owing to its slight fluid column. The length of the fluid column is changeable, which can't bring mechanical interferences to the workpiece. Abrasive jet polishing has many advantages such as wide application, no sub-surface damage, high machining accuracy, steady material removal and so on. It has become one of the most potential machining techniques in high accuracy optical mirrors process. This thesis is dedicated to solving key problems in the material removal mechanism, modeling and optimization of the removal function and the stability of the process parameters with the CCOS principle. Plentiful experiments are carried out on high accuracy mirrors with abrasive jet polishing technology to validate its particular machining ability.The major research efforts include the following points.1. Based on the CCOS principle and its demands for removal function, an abrasive jet polishing system is designed. According to the material removal characteristic of jet polishing, an oblique-rotary polishing system is introduced. The structure of the nozzle, which is the key components in jet polishing, is contrasted and optimal selected by simulation.2. The process of jet impingement is physically depicted, and whether the material removal in abrasive jet polishing belongs to brittle or plastic is estimated by theoretical computing. The velocity and pressure of the jet impingement area are researched. Material removal mechanism during polishing process is analyzed through elastic wave energy and its distributing, and the material removal amount in vertical and oblique impact mode is modeled. The material removal ability of pure water jet and abrasive jet is compared, which indicates that the collision and shearing stress between abrasives and workpiece are the main factors of material removal in abrasive jet polishing.3. The 3D model of material removal in vertical and oblique impact is derived and removal functions under different impact angles are obtained through multi-point experimental methods. Improved methods are proposed to conquer the problems appeared in the removal function obtaining process. Gaussian shaped removal function is acquired through theoretical analysis and experimental validation. Combined with a concrete optical mirror, the advantages of optimized removal function in form correction process are simulated. The stability and its influence factors are experimental researched, which shows that the removal function fluctuate errors can be controlled within±5%. The correcting ability of the removal function is studied. For different spatial frequency figure error, the smaller the removal functions is, generally the stronger the correcting ability will be, which further explains the advantages of the optimized removal function.4. The effect of some main parameters on the material removal efficiency and surface roughness in abrasive jet polishing process is researched through experiments. According to the experimental results, different process parameters are chosen based on different machining periods and different machining requirements, which is beneficial to polishing efficiency and results. An improved positioning method is proposed and error identification and compensation technology is researched. The distributing of fluid jet impact on different shaped work pieces is analyzed through CFD simulation.5. With the discussions above, application experiments for abrasive jet polishing technology are carried out. Single point diamond turning marks remove experiments are performed and high precision polishing experiments are also accomplished on stainless steel which is machined after grinding. The experimental results show the feasibility of polishing metals for abrasive jet polishing technology. In correcting figure machining, a rectangle plane mirror and a micro circular plane mirror with the diameter of 21mm is polished, and the experiments indicate that this polishing method has a high form error convergence ratio. The experiments reveal that abrasive jet polishing technology is a promising technique in high precision mirror correcting figure process.