Study On Flexible Polishing Technology Of Infrared Polycrystalline Materials Based On Analysis Of Optical Characteristics

Infrared polycrystalline materials play an important role in the infrared imaging terminal guidance,and have great military and commercial applications.Flexible polishing of infrared polycrystalline materials doesn't cause sub-surface damage,but can form grain morphology due to uneven grain properties,which affects the surface quality of the workpiece.At present,there is no effective method to control grain morphology at home and abroad.As an infrared polycrystalline material,spinel has excellent comprehensive performance.It is a good infrared window and dome material,and has become one of the research hotspots in polycrystalline material field.Spinel has high hardness and brittleness,thus there are many problems in ultra precision machining.Electron beam modification technology can make the material achieve grain refinement,and provide the idea for flexible polishing of spinel.Therefore,the modification of spinel by electron beam and polishing with magnetorheological machine tool are carried out.The infrared transmittance of spinel is detected at different stages.The research work mainly includes the following parts:1)Based on the principle of electron beam modification,the physical model of electron beam modified spinel is established.Combined with the physical and chemical properties of spinel,the temperature field of the modification process is simulated by using finite element software.The modification process of electron beam and its characteristics are analyzed and the modification parameters are optimized.According to the numerical simulation results,the reason of grain refinement is analyzed in the modified layer,which lays the foundation for the realization of uniform grain properties.2)In order to eliminate the influence of surface topography on the effect of electron beam modification,spinel specimens are polished with single pendulum plane polishing machine to obtain a smooth surface before the electron beam modification.Then the electron beam irradiation experiment of spinel is carried out on the electron beam modification equipment,and the experimental results are tested and analyzed.The surface morphology of spinel is observed before and after modification,and its change rule is analyzed.The depth of modified layer of spinel is measured,and the relationship between the depth of modified layer and the depth of electron incident is analyzed.3)The magnetorheological finishing experiments of modified spinel are carried out by using the optimized machining parameters of magnetorheological polishing.The roughness value is Ra 4.8nm in the polishing surface,which is visibly lower than that of the polished surface when the electron beam modification parameters are not optimized.4)The infrared transmittances of spinel are measured before and after modification and polishing.It is found that the infrared transmittance decreased with the increase of the modified voltage or the times of modification.By controlling the depth of the magnetorheological polishing layer,the infrared transmittance of the spinel basically restores to the level before the electron beam modification,which meets the requirements of infrared windows.