Research On The Optimization Of The Process Parameters And Its Correlative Technology In Bonnet Polishing The Curved Optical Parts

There are more and more widespread applications of the precise curved optical parts especially aspheric and free curved optical parts in the aerospace, the universe detection, the military reconnaissance and many civil fields. To acquire the high quality optical parts with curved surface, some novel polishing methods have been developed. The bonnet tool polishing is a novel precise aspheric surface polishing method which has been developed for the decade years. In the process of the bonnet polishing, the semi-flexible bubble is used as the polishing tool and the precession movement is accomplished by the bonnet polishing tool, so the optical parts with the high precise and high quality can be obtained by this polishing method. Therefore, this bonnet polishing methods has a good applied prospect and it is worthwhile to be studied profoundly. In this paper, the key technology which relates to the application of the bonnet polishing is studied at length. The material removal characteristic of the optical parts with curved surface is analyzed, and the material removal function model is built; moreover, the processing parameters influencing the material removal rate and the surface roughness are optimized, and the polishing pathe is also optimized; based on the dwell time algorithm of the symmetric optical parts with curved surface, the experiments of the surface shape on the optical parts with curved surface are accomplished.The material removal characteristic of the curved optical parts is researched on the basis of the experimental analysis method. For acquiring the effective polishing spot, the sampling feature of the process parameters are researched and the best processing parameters span are determined. And the relationship between the material removal rate and the process parameters on the curved optical parts with the different curvature radius is be researched importantly. The researched process parameters, which correlate with the polishing pressure and the relative kinetic velocity between the bonnet polishing tool and the parts, include the precession angle, the bonnet decrement, the bonnet rotational speed, the bonnet inner pressure.According to the method of conversion coordinates and the Hertz Contact Theory, the expression of pressure distribution on the convex sphere, the plane and the concave sphere respectively are deduced and the velocity distribution are analyzed according to the motion feature of the bonnet polishing tool on the curved surface, and build the pressure distribution expression which relates the curvature radius of the optical parts. And for the curved surface, the semi-experimental material removal model of the bonnet polishing is established according to the Preston equation which is used in the polishing process generally.Based on the orthogonal experiments, the processing parameters influencing on the material removal rate are optimized synthetically. And then the process parameters (including the bonnet decrement, the curvature radius of the optical parts, the bonnet rotational speed, the bonnet inner pressure and the concentration of the polishing fluid) influencing on the surface roughness had been made process experiments; research the influencing regular of the process parameters on the surface roughness on curved optical parts and the chosen laws of parameters are given. Furthermore, the best process parameters combination are determined to acquire the best surface roughness, and the polishing experiments about the surface roughness are accomplished by the discrete precession polishing motion. Measured by the WYKO RST Plug, the best surface roughness results can achieve 3.02 nm (Ra).Furtherly, according to the material removal model of the bonnet polishing, the expressions of theoretical roughness on the optical parts with the convex sphere, the plane and the concave sphere are deduced respectively, and all which functions is related to the curvature radius of the optical parts and the bonnet. And discuss the synthetical influence of the distance and the dwell time on the surface roughness, the optimization selected scheme of the distance and the dwell time is given.Finally discuss the adaptability between the curvature radius of the work-piece and the polishing tool bonnet, and discuss the polishing path layout method of the rotational axisymmetric curved optical work-piece in the bonnet polshing. According to the previous research on material removal rate, the material removal quantitative is coherent to the dwell time. Through adjusting the dwell time, the material removal quantitative can be controlled and further the surface shape error can be corrected. On the basis of the theory of the surface shape in bonnet polishing and according to the material removal characteristic in the bonnet polishing, on the dwell time algorithm of the rotary symmetric curved optical parts, the experiments of the surface shape on the curved optical work-pieces are researched, the precision of the surface shape on the machined work-piece has been improved. The results could be helpful for further development of high precise optical aspheric surface using the bonnet polishing method.