Research On Grinding Mechanism, Processing And Engineering Application Of The Precision And Low Damage Grinding Technology Oriented To Achieve High Process Efficiency For Brittle Optical Materials

The large and middle-scale optics are wildely used in the astronomical observation system,high power laser fusion devises,precision optical metrology instruments and other military and civilian fields.The grand challenge for providing the stringent requirements of the large and middle-scale optics of ultra-precision has been raised to pursue high processing precision and high surface/subsurface quality and high efficiency.Grinding technology,which plays a decisive role for the production costs and outputs,is an indispensable key process at the production chain of large and middle-scale optics.However,existing research lacks of comprehensive grasp in grinding mechanism,processing and engineering application of brittle optical materials,which largely limits the applications of grinding technology in the field of optical element machining.Therefore,it is extremely difficult to develop and implement the projects of large astronomical telescopes and high power laser fusion.Two typical brittle optical materials,such as BK7 optical glass and Fused silica optical glass,are selected as the research target in this paper.The precision and low damage grinding technology oriented to achieve high process efficiency is proposed based on multi-stages grinding process chain technology.A systematic theoretical analysis and experimental research are carried out in grinding mechanism,processing and engineering application of brittle optical materials of grinding.The main contents of this paper are as follows:Firstly,theory modeling and analyze of dynamic grinding for brittle optical materials.The compression fracture strength model,micro hardness model,fracture toughness model,lateral crack depth model,median crack depth model and critical cutting depth model are proposed considering the strain rate effect and temperature effect.The critical conditions of grinding mode transformation are provided.The results indicate that the mechanical properties are affected by the strain rate effect and temperature effect,and further influence the grinding mechanism.These models will provide reliable supports for in-depth analysis the experimental research results.Secondly,experimental research on the indentation fracture mechanics for brittle optical materials is investigated.Energy spectroscopy analysis and indentation fracture mechanics are used to study the element composition and micro structure,as well as the mechanical properties and the brittleness or ductility at different indenter loads and different loading temperatures.The fracture toughness value of Fused silica optical glass is obtained and made an explicit statement on grinding experiments.The micro hardness model and fracture toughness model considering the temperature effect are testified reasonable.The brittleness and ductility of the BK7 optical glass and Fused silica optical glass are analyzed.Thirdly,grinding experimental research of brittle optical materials is study.The grinding speed and materials removal rates at the multi-stages grinding(rough grinding,semi-finishing grinding and finishing grinding)on the effect of grinding forces,grinding temperatures,surface roughnesses,surface morphologies,subsurface morphologies and damage depth are revealed.The rationality of theory analysis is confirmed,and the active mechanism of the strain rate effect and temperature effect of the grinding zone are highlighted.The difference of various output parameters between workpiece feed rate and grinding depth is explicated.Optimization strategies of process parameters about the multi-stages grinding process chain technology are proposed.Fourthly,engineering application of the precision and low damage grinding techno logy oriented to achieve high process efficiency is study for large and middle-scale optics.A piano optic with diameter ?300mm and a sphere optic with diameter ?300mm and curvature radius R1500mm are ground in industrial environment.A novel FJP(fluid jet polishing)wedge technique is used to measure the depth of subsurface damage.The compensation effect of form error and surface roughness is very obvious before and after compensation at each grinding stages.The ultimate figure error,surface roughness,subsurface damage depth and average material removal rates of piano optic and sphere optic are 1.56?m PV and 23.7nm Ra,0.65?m PV and 37nm Ra,18.2?m and 17.5?m,383.24mm~3/s and 467.19mm~3/s,respectively.Compared with others grinding technology and institutions,it is found that the precision and low damage grinding technology oriented to achieve high process efficiency proposed by this paper realized the total improvement between the process quality and efficiency,and the engineering application has reached a high level.