| With the development of science and technology,the requirements for the optical systems,in such high-tech fields as space optics,astronomy optics,inertial confinement nuclear fusion and ultraviolet lithography,are becoming higher.The optical components are the key parts of the optical systems,and their surface errors in different frequency bands will affect the performance of the optical systems differently.To achieve the full-band error-controllable processing of the optical components,various optical processing methods based on different principles are proposed,and they are developed towards high efficiency,high precision and high surface quality.To combine the advantages of magnetorheological finishing(MRF)and small tool finishing technology,a novel magnetorheological finishing method is proposed,which is named Lap-MRF.Its key techniques are deeply studied to meet the processing requirements of the high-precision optical components.In this paper,the design and performance optimization of Lap-MRF device,the finishing mechanism and mathematic model,the optimization of processing parameters based on the objectives of high efficiency and high surface quality,the convergence of the optical surface error and the improvement of the optical surface quality are studied theoretically and experimentally.The research provides a new method and approach for the processing of the optical components with high efficiency and high surface quality.The main contents include the following aspects:(1)The design and performance optimization of Lap-MRF device.To improve material removal efficiency,simplify structure and reduce cost,the permanent magnet excitation device is designed based on the overall design of Lap-MRF system,which can produce high gradient magnetic field.The magnetic field around the excitation device is simulated using finite element method,and the structure parameters are optimized using multi-objective parameters method.Thus,the magnetic field distribution in the finishing area is optimized.(2)The research on the material removal efficiency of Lap-MRF.The material removal mechanism of Lap-MRF is analyzed.Based on the analysis of the normal and shear stresses between the MR fluid and the workpiece surface,a mathematical model of the Lap-MRF removal function is established.The effect of the key parameters on the material removal efficiency and its stability is studied,and the optimal key parameters to achieve high material removal efficiency processing are determined.The effect of the material removal efficiency stability on the convergence efficiency of the optical surface error is studied using MATLAB simulation method.(3)The research on the surface quality of Lap-MRF.The relative motion trajectory between the lap and the workpiece surface and the formation mechanism of the surface morphology are analyzed.A mathematical model for predicting surface roughness is established.Based on the model,the evolution process of the surface profile for a given optical surface is simulated.The effect of the key parameters on the surface roughness is studied,and the optimal key parameters to achieve high surface quality processing are determined.The finishing experiments of the K9 glass,single crystal silicon and fused silica are carried out under the optimal key parameters.The evolution of the roughness,surface element content and photo-thermal absorption level of the surface before and after Lap-MRF are studied.(4)The experimental verification of Lap-MRF.Based on the above research,the experiments of the rapid surface error convergence and the rapid surface quality improvement are carried out.The figuring ability of the removal function is analyzed.Based on the filtering technology,the iterative processing experiment of a ?350 mm K9 glass is carried out.The uniform finishing experiment of a ?100 mm single crystal silicon is carried out,and the surface morphology evolution law before and after Lap-MRF is studied.Through the finishing experiments,the conclusions of this paper are verified. |
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