【作者】 李平；

【导师】 金滩；

【作者基本信息】 湖南大学 ， 机械工程， 2017， 博士

【摘要】 大中型光学元件在天文观测系统、激光核聚变装置、精密光学测量仪器及其它国防与民用领域具有重要应用。然而,大中型光学元件在产品加工精度、表面/亚表面质量及加工效率等方面的严苛要求对现阶段的光学制造能力提出了极大的挑战。磨削作为大中型光学元件整个生产工艺链中的关键工序,其加工质量的好坏与加工效率的高低对产品成本与产量的控制起着决定性作用。目前,国内外对于脆性光学材料磨削加工机理、加工工艺以及工程化应用等方面尚未有系统的研究,在很大程度上限制了磨削加工技术在光学元件加工领域的发展,从而影响着大型天文望远镜项目以及大型激光核聚变项目的开展和实施。本文以两种典型脆性光学材料BK7光学玻璃和Fused Silica光学玻璃为研究对象,提出了基于多工步磨削工艺链的脆性光学材料高效精密低损伤磨削加工技术,系统地开展了磨削加工机理、加工工艺及工程化应用方面的理论分析和试验研究。论文的主要内容包括:(1)脆性光学材料动态磨削加工理论建模与分析。建立了计及应变率效应和温度效应的压缩断裂强度模型、显微硬度模型、断裂韧性模型、横向裂纹深度模型、中位裂纹深度模型、亚表面损伤深度模型及临界磨削深度模型,给出了磨削模式转变的临界条件。研究结果表明:磨削区的应变率效应和温度效应会对脆性光学材料的力学性能产生影响,进而影响其磨削机制。所提出的模型可为深入分析磨削加工试验结果提供理论支持。(2)脆性光学材料压痕断裂力学试验研究。采用能谱分析及压痕断裂力学试验方法,对两种脆性光学材料的化学元素成分、微观结构以及不同压头载荷和不同加载温度条件下的材料力学性能、脆性和延塑性等进行了研究。阐明了 Fused Silica光学玻璃的断裂韧性取值;验证了计及温度效应的材料显微硬度和断裂韧性模型的合理性;分析了两种脆性光学材料的脆性和延塑性参数的差异性。(3)脆性光学材料磨削加工试验研究。揭示了两种脆性光学材料多工步磨削(粗磨、半精磨及精磨)过程中砂轮线速度与材料去除率(工件进给速度或砂轮磨削深度)对磨削力、磨削温度、表面粗糙度、表面形貌、亚表面形貌及亚表面损伤深度等输出参数的影响规律。验证了脆性光学材料磨削理论分析的合理性;并重点论述了磨削区的应变率效应和温度效应的作用机制。详细地分析了比材料去除率相同情况下工件进给速度与砂轮磨削深度各输出参数的差异性;提出了多工步磨削工艺链技术中磨削工艺参数的优选策略。(4)大中型光学镜面高效精密低损伤磨削加工技术的工程化应用研究。在工业环境下,对口径为φ300mm的平面镜和口径为φ300mm、曲率半径为R1500mm的球面镜进行了磨削。提出了一种定向射流斜坡抛光方法来检测大中型光学元件的亚表面损伤深度。平面光学镜面与球面光学镜面的面形精度和表面粗糙度参数指标在粗磨、半精磨及精磨各阶段的补偿加工效果明显;最终平面光学镜面和球面光学镜面的面形精度分别达到了 1.56μm PV和0.65μm PV,表面粗糙度分别达到了23.7nm Ra和37nm Ra,亚表面损伤深度分别达到了18.2μm和17.5μm,平均材料去除率分别达到了 383.24mm~3/s和467.19mm~3/s。与当今世界上其它磨削技术及国内外相关机构的研究结果进行对比,结果表明本文所提出的高效精密低损伤磨削加工技术实现了加工品质与加工效率的全面提升,其工程化应用达到了较高水平。更多还原

【Abstract】 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 φ300mm and a sphere optic with diameter φ300mm 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 1.56μm PV and 23.7nm Ra,0.65μm PV and 37nm Ra,18.2μm and 17.5μm,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.更多还原