Fundamental Research On Ion Beam Figuring Of Aluminum Optics With Complex Geometric Form

Possessing advantanges of high design freedom,light weight,strong ability to correct aberration and capability of integrated opto-mechanical design,aluminum optics with complex forms have been widely used in the field of fabrication of aerospace optical systems.With increasing demands on the systems performance,the fabrication specification for surface accuracy,surface quality and shape complexity are becoming more stringent.Due to the lower fabrication precision and efficiency,conventional fabrication technologies cannot satisfy the manufacturing requirements.Therefore,it is urgent to explore new fabrication technologies.Owing to its atomic scale material removal capability by physical sputtering effects,ion beam figuring(IBF)attracts wide attention from researchers at home and abroad.IBF is considered to have the highest fabrication precision.With convenient adjustment for ion beam diameter,IBF is easy to implement for manufacturing of complex form surface.Belonging to the non-contact processing,the clean degree of IBF is significantly higher than other determistic optical fabrication technologies.Therefore,IBF is expeted to improve the fabrication precision and efficiency of aluminm optics with complex form.However,some critical scientific problems need further investigation to understand,including the optimization of IBF cleaning process for magnetorheological finishing(MRF)contamination layer,the evolution regularity and its regulation of surface quality of turning aluminum optics and constraints of high precision figuring of complex form surfaces.Consequently,fundamental researches need to be performed to address the basic theory and key technical problems,achieve breakthroughs in manufacturing theory and technology,and provide new methods and approaches for realizing the manufacture of aluminum optics with complex form,which is of great significance to promote the development aerospace optical systems.This thesis is mainly dedicated to the fabrication requirements of high precision and efficeiency of aluminum optics with complex forms.The related fundamental researches will be carried out to investigate the polishing theory and process,revealing the new phenomenon and mechanisms in the fabrication process and exploring new method and approaches for the manufacture of aluminum optics with complex forms.The specific research content includes the following aspects:(1)Researches are performed to investigate the mathematical models and action mechanism in ion sputtering process of aluminum.The multi-parameter model of material removal in ion polishing process was studied,and the key factors affecting material sputtering efficiency were analyzed;Based on the specific working conditions of manufacture of optics with complex forms,the influence of process conditions on the fabrication precision of IBF are discussed;The surface shaping behavior during ion sputtering was studied.Combined with the charateristics of aluminum alloy,the theory of multiple sputtering and special action mechanism were investigated;The ion beam sputtering process of aluminum was studied by molecular dynamics method,and the applicability of sputtering theory on new materials was verified.(2)Cleaning process for MRF contamination layer with IBF was explored and studied.The characteristics and formation mechanism of MRF contaminated layer were investigated,and its influence on fabrication process was analyzed;The IBF process was introduced to remove the contaminated layer,the removal effect and mechanism of the contaminated layer were revealed,and the combined processing technology was put forward;On this basis,the evolution law of surface shape error in the process of removing contaminated layer was studied,and the conformal machining strategy and precision improvement strategy were proposed to realize the improvement of machining accuracy and efficiency.(3)The surface quality evolution regularity of turning aluminum mirror during IBF and corresponding mechanism were studied,and an optimized manufacturing process for aluminum optics was proposed.Based on the principle of Computer Controlled Optical Surfacing(CCOS),the feasibility of IBF process for turning aluminum optics is verified;The evolution of surface quality and the microstructure of aluminum optics during IBF was studied,and the mechanism was further revealed by sputtering theory and molecular dynamics method;Smoothing polishing method was adopted to restore the surface quality of aluminum optics after IBF,and a new manufacturing process of aluminum optics was proposed.(4)Researches are performed to regulate the surface quality evolution of aluminum optics during IBF.Based on the molecular dynamics method,the formation process and the mechanism of turning metamorphic layer and its influence mechanism on ion beam machining were investigated;The multi-scale characterization of the turning metamorphic layer was realized.With turning parameters tuned,the control of surface quality of aluminum optics during IBF is realized.(5)IBF process suitable for free-form aluminum optics fabrication is proposed.Based on the requirement of improving the surface shape precision and controlling the surface quality during IBF machining of aluminum optics,the technological constraints of IBF were explored.An IBF accurate figuring method for free-form surfaces based on surface shape filtering was proposed to improve machining accuracy and control surface quality.