| Beryllium-aluminium alloy appeared in the 1970 s.It fully inherits the high stiffness of beryllium and the easy-to-process characteristics of aluminium.ESA classifies beryllium-aluminium alloy as a material of grade I.After the advent of beryllium-aluminium alloy,with its excellent light weight and high stiffness characteristics and good processing performance,it is mainly used in aviation,aerospace,national defense and other areas with strict requirements on weight and stiffness.Early applications of beryllium-aluminium alloys mainly focused on key structural components,excluding optical mirrors.Around 2000,the United States took the lead in exploring the application of beryllium-aluminium alloy in mirror manufacturing.At present,it has initially realized industrialization.However,due to its sensitive application background,there are very few published literatures and reports.China is the only country with a complete beryllium industry chain besides the United States,but the preparation of beryllium-aluminium alloy materials was gradually broken through after 2000.Because the processing of beryllium-aluminium alloy requires special protective conditions,the application of materials is still in the exploratory stage,and the design and manufacturing technology of berylliumaluminium alloy mirrors for optical applications is still in the blank stage.In this paper,beryllium-aluminium mirror is taken as the research object.The key technologies related to beryllium-aluminium mirror are studied from two aspects of design and manufacture.The specific contents include:Firstly,the basic concept of stability and the influence of material micro-structure on the stability of mirror are elaborated in detail.By analyzing the factors affecting the stability of material,the materials used in mirror manufacturing should have the characteristics of uniform and compact microstructure,few internal defects,small residual stress and high yield strength.According to the two forming processes of beryllium-aluminium alloy,the forming process of beryllium-aluminium alloy reflector material based on powder metallurgy is determined.During the preparation process,the powder size is strictly controlled,and the microstructure of the material after forming is tested and verified.Then,the design technology of reflective metal mirrors is studied from two aspects of lightweight and integration,and the lightweight structural parameters of the reflective mirror are optimized by using the method of analysis and driving design,taking the 200 mm coaxial composite mirror for infrared application and 320 mm 120mm off-axis strip mirror for visible light application as objects.A double-layer lateral lightweight aperture suitable for long strip off-axis mirror is proposed.The twolayer lightweight aperture is arranged orthogonally,which can improve the lightweight ratio of the mirror and ensure the stiffness of two orthogonal directions.A design of offaxis mirror assembly which integrates mirror body,flexible connection and support backplane is proposed,and a special structural datum is designed to realize the assembly from processing to assembly.The benchmark transfer of tuning can effectively improve the efficiency of processing and adjusting.Furthermore,the structure of single point diamond lathe and various processing methods which can be realized by different combination of moving axes are introduced.The single point diamond turning of off-axis mirror with diameter of 280 mm×100 mm is carried out by means of disc turning.The influence process of centrifugal deformation on mirror machining accuracy in high speed turning of off-axis mirror is analyzed.A method of analyzing centrifugal deformation by finite element method is established.A supporting scheme and a design method of tooling for off-axis mirror turning are proposed.Finally,the centrifugal deformation can be effectively restrained by optimizing the process parameters and auxiliary support,so that the surface accuracy of the mirror after turning can be improved from RMS 0.786 ?@0.6328 ?m before optimization to RMS 0.112 ?@0.6328 ?m.Then,the reason why the surface of beryllium-aluminium alloy needs to be modified is explained from the point of view of the micro-structure of berylliumaluminium alloy.Based on the analysis of the micro-structure,material hardness and the coincidence with the thermal expansion coefficient of beryllium-aluminium alloy,electroless nickel plating is selected as the modified layer material The electroless nickel plating process of beryllium-aluminium alloy was formed.The bonding force between the modified layer and beryllium-aluminium alloy matrix was effectively improved by improving the modification process.The properties of the modified layer were tested.The bimetallic effect of 110mm×50mm planar mirror is analyzed by finite element analysis technology.The method of bimetallic effect analysis by finite element technology is established and verified by experiments.The experimental results also show that the bimetallic effect of beryllium-aluminium mirror is much smaller than that of aluminium mirror under the same conditions.Finally,the basic concepts and evaluation methods of optical surface full-band error are introduced,as well as MCP501 polishing equipment,which can achieve a variety of polishing and figuring methods.Partial pitch polishing is used to suppress the high frequency error of mirror surface,effectively remove the turning tool marks in the single point turning process,and the surface roughness is close to 2 nm.Active jet polishing is used to correct the low frequency surface error of the mirror.The surface shape of the off-axis mirror after polishing is close to RMS 1/30?@0.6328 ?m.An offaxis TMA camera with beryllium-aluminium primary mirror has been completed.The wavefront aberration of the optical system is RMS 1/8A@0.6328 ?m after adjustment.The static MTF(@77lp/mm)of the camera is better than 0.15.The system-level verification of the beryllium-aluminium mirror has been realized.In this paper,the design and manufacturing technology of beryllium-aluminium mirror is studied.The new beryllium-aluminium alloy material is taken as the research object.The whole process of material preparation,optical-mechanical integration design and optical processing are comprehensively considered.The key technology is broken through,the design and manufacture of beryllium-aluminium alloy off-axis mirror is completed,and an off-axis TMA imaging The system verifies the optical performance of the mirror.These studies have played a role in paving the way for the follow-up development of beryllium-aluminium alloy mirrors toward large aperture,free-form surface and optical-mechanical integration design. |
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