Research On Characteristics And Morphology Control Of Polished Surface Of Spinel Optical Elements

Due to its excellent optical and mechanical properties,spinel optical components have broad application prospects in the field of aviation and aerospace.As a multiphase hard and crisp material,the micro hardness of spinel is repugnant in different zones.The morphology with grain shape will appear on the machined surface when the spinel is polished by a soft carrier for inconsistent removal efficiency.The scratches will appear on the machined surface,and the curvature of polishing tool can't match with the aspherical surface of elements when the spinel is polished by a rigid carrier.According to the difficulty of manufacturing for spinel,the analysis and the control method of grain morphology on the polished surface are researched by using the electron beam modification and optimizing the polishing parameters in this paper,and the manufacture for spinel optical elements with high efficiency and high precision are achieved.The main contents and results are as follows:1)As spinel is a kind of multiphase material,the grain morphology will appear on the polished surface,this affects the machining accuracy and surface roughness,and the requirements can't be satisfied.The inherent relation is researched between the process conditions and grain morphology by using different types of polishing disc and polishing powder,and the variations of grain characteristics scale and edge slope are synthetically analyzed.Furthermore,the flexibility formula on polishing tool is presented,and this can provide guidance for the optimization of machining parameters in the polishing process of spinel optical elements.2)As a flexible polishing media,the magnetorheological fluid removes the surface materials by shearing way,the scratch is greatly reduced on the polished surface,but the grain morphology will clearly increase.Therefore,based on profile error and surface roughness,the magnetorheological polishing parameters are optimized by using the grey correlation method,and the grain effect is controlled with low subsurface damage.3)In order to overcome the inconsistent shortcomings of spinel's hardness,based on the principle of electron beam modification,non crystallization treatment of surface materials is implemented by energy conversion,and the temperature field and the thermal stress field are simulated and analyzed in the process of modification.According to the removing depth and the actual machining conditions,the reasonable depth of modified layer is designed,and the modified parameters of spinel are optimized in the process of electron beam modification by synthetically considering the material properties,the temperature gradient and the melting energy.4)Aiming at typical spinel specimens whose diameters are 30 mm,the polishing properties are compared before modified and after modified,the machining process is analyzed and the grain morphology is controlled by the polyurethane polishing and the magnetorheological finishing.The measuring results show that the peak of removal efficiency is increased by about 4 times on the modified layer by using the optimized magnetorheological finishing parameters,the value of surface roughness decreases into Ra 8.89 nm from unmodified Ra 13.28 nm,and the peak value of grains decreases into 9.4nm from unmodified 32.0nm.