轻质碳化硅平面反射镜超光滑表面加工

介绍了对角线为110mm六边形反应烧结轻质碳化硅平面反射镜超光滑光学加工工艺流程。详细阐述了各个工序所使用的磨具、磨料和抛光机床工艺参数,对实际加工的轻质碳化硅平面反射镜超光滑表面进行检测,检测结果为:面形精度均方根值(RMS)为0.011λ(PV值为0.071,λ=632.8nm),表面粗糙度RMS达0.75nm。     

磁流变抛光光学曲面的两级插补算法

根据磁流变抛光的加工特点,本文提出一种加工光学曲面的粗、精两级插补算法。粗插补算法控制工件的面形,精插补算法采用PVT模式,可实现对磁流变抛光光学曲面复杂过程的控制。仿真结果表明,采用该插补算法加工R41.3mm、口径20mm的球面工件,插补误差小于0.45nm,磁流变抛光该尺寸的K9光学玻璃,获得PV57.911nm的面形精度。     

磁流变抛光驻留时间算法

针对磁流变抛光去除量与驻留时间呈线性关系特点,本文以Preston方程为依据,根据磁流变抛光专用机床的运动形式,提出了基于矩阵的磁流变抛光驻留时间算法,该算法通过调整各点驻留时间控制光学器件表面的去除量,达到面形误差修正的目的,适用于非球面等可用通用光学方程表示的回转对称曲面.仿真实验结果表明,采用该算法仿真加工可以使球形表面面形误差收敛至十几个纳米.通过对K9光学玻璃球面进行的磁流变抛光实验,获得了表面粗糙度Ra0.636 nm的球形表面,面形精度P-V值由抛光前的158.219nm减小到52.14 nm,验证了驻留时间算法的合理性.     

光刻物镜高精度挠性结构镜框设计及分析

光刻投影物镜的透镜支撑形式决定透镜的面形精度,进而影响光学系统的成像质量。本设计为实现透镜面形精度优于5 nm的RMS值,提出一种三点挠性主支撑和六点弹片辅助支撑的支撑形式。综合考虑透镜自重、夹持力和热载荷对透镜面形影响,对支撑结构进行优化设计,并进行了仿真分析。仿真后的面形结果为：上表面面形PV 21.7 nm,RMS 4.49 nm;下表面面形PV 81.3 nm,RMS 3.63 nm。仿真结果显示：该种透镜的支撑结构可以满足光刻投影物镜的高精度面形指标要求。     

大尺寸反射镜高精度光学镜面Ni-P过渡层的制备方法

为了解决高精度光学系统中铝合金、铍反射镜易钝化、难加工的问题,采用自催化镍-磷合金作为过渡层后进行抛光的方法得到了高精度光学镜面．采用该方法所得到的镍-磷合金过渡层厚度为85gm,磷质量分数为11．88％,镀层显微硬度为730MPa镍-磷合金过渡层与反射镜结合牢固、耐蚀性较好,可通过±200℃热震试验及96h中性盐雾试验检测,适用于进行古典法抛光．经抛光后反射镜面形精度均方根值（RMS）为0．049λ（面形检测波长λ为0．6328μm）,表面疵病等级为Ⅳ级,能够满足光学系统的要求．     

单晶硅镜面超光滑表面工艺技术研究

用古典的沥青盘抛光技术,通过对超光滑抛光时所使用磨料的选取、沥青抛光盘的软硬和 厚度的合理应用、抛光温度的控制等工艺参数的优化,以f220mm内的单晶硅进行了超光滑表面抛光工艺试验。试验结果,单晶硅表面粗糙度RMS值达0.37nm,平面面形误差PV小于l/15,且加工工艺技术稳定可靠。     

确定性光学加工中抑制边缘效应的一种方法(英文)

在确定性光学抛光过程中,当加工到工件边缘时由于工艺条件发生变化会产生边缘效应,导致加工效率降低和面形误差增大.针对这种情况,提出了一种可修正边缘现象的球形工具抛光技术,其去除函数稳定性较好,形状趋于高斯分布且束径也较小,对修正边缘现象以及局部面形误差具有较好的效果.同时规划了其抛光路径,采用一种伪ρ-θ光栅扫描运动方式的加工路径,简化了球形抛光工具的结构,并且由于使加工纹路有了变化,可使加工后的表面纹理呈现无序性和均匀性特征,相应可提高加工后工件的表面质量.最后通过对一块微晶球面镜的加工(面形误差峰谷值PV由加工前1.607λ(λ=632.8 nm)收敛到加工后0.365λ,均方根值RMS由0.195λ收敛到0.024λ),验证了球形抛光工具具有修正边缘翘边现象的能力.     

光学加工中抛光垫特征对工件面形的影响分析

抛光是光学加工中获得超精密表面的主要手段.为明确抛光垫特征对平面光学元件抛光面形的影响规律,分析了抛光垫与工件之间的界面接触形式,并建立接触力学分析模型,运用有限元方法分析了工件与抛光垫之间的接触压力分布情况,获得了抛光垫厚度及表面球半径等特征对抛光压力分布的影响规律.基于理论分析结果,提出了一种新的平面抛光面形控制技术.在实验中对一块尺寸为430 mm×430 mm×60 mm的熔石英元件进行了加工,通过将抛光垫表面修整为微凸面,同时对抛光转速比进行精确控制,实现了工件面形精度的快速收敛.     

长条形SiC空间反射镜轻量化结构优化设计

在保证空间光学遥感相机反射镜结构刚度、面形精度的同时,最大限度的降低反射镜质量,成为各国新兴的、重要的研究课题。本文从材料、支撑形式、相关几何参数以及轻量化结构形式等方面对反射镜进行详细设计。提出了通过拓扑优化确定反射镜背部轻量化形式的方案。采用有限元分析法对获得的优化结果进行分析。分析结果表明：重力载荷下面形精度达到 λ/10 PV,λ/50 RMS (λ=632.8 nm),PV值 7 nm,RMS值 1.68 nm,反射镜组件一阶固有频率 256 Hz,均优于传统结构形式的反射镜,能够满足应用要求。     

光学元件检测技术的研究

介绍了光学非球面加工精磨阶段和抛光阶段的检测技术、柱面镜面形的测量方法、超高精度球面面形的测量方法和光学元件参数的高精度测量技术。     

Removal rate model for magnetorheological finishing of glass

Magnetorheological finishing (MRF) is a deterministic subaperture polishing process. The process uses a magnetorheological (MR) fluid that consists of micrometer-sized, spherical, magnetic carbonyl iron (CI) particles, nonmagnetic polishing abrasives, water, and stabilizers. Material removal occurs when the CI and nonmagnetic polishing abrasives shear material off the surface being polished. We introduce a new MRF material removal rate model for glass. This model contains terms for the near surface mechanical properties of glass, drag force, polishing abrasive size and concentration, chemical durability of the glass, MR fluid pH, and the glass composition. We introduce quantitative chemical predictors for the first time, to the best of our knowledge, into an MRF removal rate model. We validate individual terms in our model separately and then combine all of the terms to show the whole MRF material removal model compared with experimental data. All of our experimental data were obtained using nanodiamond MR fluids and a set of six optical glasses.     

Minimizing artifact formation in magnetorheological finishing of chemical vapor deposition ZnS flats

The polishing performance of magnetorheological (MR) fluids prepared with a variety of magnetic and nonmagnetic ingredients was studied on four types of initial surface for chemical vapor deposition (CVD) ZnS flats from domestic and foreign sources. The results showed that it was possible to greatly improve smoothing performance of magnetorheological finishing (MRF) by altering the fluid composition, with the best results obtained for nanoalumina abrasive used with soft carbonyl iron and altered MR fluid chemistry. Surface roughness did not exceed 20 nm peak to valley and 2 nm rms after removal of 2 microm of material. The formation of orange peel and the exposure of a pebblelike structure inherent in ZnS from the CVD process were suppressed.     

磁流变抛光液的研制

磁流变抛光是近十年来新兴的一种先进光学制造技术。首先简要介绍了磁流变抛光的抛光机理，然后对在磁流变抛光中起重要作用的磁流变抛光液的组成，流变性和稳定性进行了研究。在外加磁场强度高于318kA/m时，磁流变抛光液的剪切应力大于20kPa，该应力足以完成磁流变抛光，最后给出一个磁流变抛光的实例，证明了磁流变抛光液的实用性，实验中磁流变抛光的最大材料去除率约为0.2μm/s.     

Manipulating mechanics and chemistry in precision optics finishing

Deterministic processing is critical to modern precision optics finishing. Put simply, determinism is the ability to predict an outcome before carrying out an activity. With the availability of computer numerically controlled (CNC) equipment and sophisticated software algorithms, it is now possible to grind and polish optics from a variety of materials to surface shape accuracies of ∼20 nm peak-to-valley (p-v), with surface roughness values (measured on white light interferometers over 250 μm×350 μm areas) to sub-nm root-mean-square (rms) levels. In the grinding phase the capability now exists to estimate removal rates, surface roughness, and the depth of subsurface damage (SSD) for a previously unprocessed material, knowing its Young's modulus, hardness, and fracture toughness. An understanding of how chemistry aids in the abrasive-driven removal of material from the surface during polishing is also critical. Recent polishing process research reveals the importance of chemistry, specifically slurry pH, for preventing particle agglomeration in order to achieve smooth surface finishes with conventional pad or pitch laps. New sub-aperture polishing processes like magnetorheological finishing (MRF) can smooth and shape flat, spherical, aspheric and free-form surfaces within a few process iterations. Difficult to finish optical materials like soft polymer polymethyl methacrylate, microstructured polycrystalline zinc sulfide, and water soluble single-crystal potassium dihydrogen phosphate (KDP) can be finished with MRF. The key is the systematic alteration of MR fluid chemistry and mechanics (i.e. the abrasive) to match the unique physical properties of each workpiece.     

Experiments and observations regarding the mechanisms of glass removal in magnetorheological finishing

Recent advances in the study of the magnetorheological finishing (MRF) have allowed for the characterization of the dynamic yield stress of the magnetorheological (MR) fluid, as well as the nanohardness (H(nano)) of the carbonyl iron (CI) used in MRF. Knowledge of these properties has allowed for a more complete study of the mechanisms of material removal in MRF. Material removal experiments show that the nanohardness of CI is important in MRF with nonaqueous MR fluids with no nonmagnetic abrasives, but is relatively unimportant in aqueous MR fluids or when nonmagnetic abrasives are present. The hydrated layer created by the chemical effects of water is shown to change the way material is removed by hard CI as the MR fluid transitions from a nonaqueous MR fluid to an aqueous MR fluid. Drag force measurements and atomic force microscope scans demonstrate that, when added to a MR fluid, nonmagnetic abrasives (cerium oxide, aluminum oxide, and diamond) are driven toward the workpiece surface because of the gradient in the magnetic field and hence become responsible for material removal. Removal rates increase with the addition of these polishing abrasives. The relative increase depends on the amount and type of abrasive used.     

油基磁流变液的开发及抛光性能研究

磁流变抛光技术可用于具有超光滑要求光学元件的超精密制造。在明确磁流变抛光机理的基础上,开发了油基磁流变抛光液,其体积比配方是:33.84%的羰基铁,57.34%的硅油,6%的氧化铈,2.82%的稳定剂。抛光液初始粘度达到0.5Pas,流变性具有较大范围的稳定性能。实验中,利用磁流变液在外磁场作用下形成的强剪切应力对一平面K9玻璃进行了可控抛光,结果证明其具有良好的抛光特性,抛光23分钟后工件表面粗糙度降低到0.6739nm。     

Analysis of particles in magnetorheological polishing fluid for finishing of ferromagnetic cylindrical workpiece

Magnetorheological honing process is developed for nanofinishing of internal surfaces of ferromagnetic and non-ferromagnetic cylindrical objects. The process makes use of smart fluid called magnetorheological (MR) polishing fluid for finishing which has a property to become stiff in the existence of magnetic field. The smart MR polishing fluid is made with the ingredients of carbonyl iron (CI) particles, abrasive particles, and base fluid. Direct current given to the electromagnet coil engenders magnetic field on finishing tool surface. Magnetic force acts on magnetic CI particles which further exert the repulsive force on nonmagnetic silicon carbide (SiC) abrasive particles and performs finishing when tool rotates as well as reciprocates inside the cylindrical workpiece. The CI and SiC particles present in MR polishing fluid are magnetically simulated and analyzed using finite element (FE) analysis. The distribution of magnetic flux density and magnitude of magnetic force acting on CI particles are analyzed through FE analysis. It is found that the CI particles which are available adjacent to the active abrasives are major responsible for indenting the active abrasive particles into workpiece surface. Also, the effect of finishing tool surface areas and particles size on the strength of chains of CI particles in MR polishing fluid have been analyzed.     

Research on error control and compensation in magnetorheological finishing

Although magnetorheological finishing (MRF) is a deterministic finishing technology, the machining results always fall short of simulation precision in the actual process, and it cannot meet the precision requirements just through a single treatment but after several iterations. We investigate the reasons for this problem through simulations and experiments. Through controlling and compensating the chief errors in the manufacturing procedure, such as removal function calculation error, positioning error of the removal function, and dynamic performance limitation of the CNC machine, the residual error convergence ratio (ratio of figure error before and after processing) in a single process is obviously increased, and higher figure precision is achieved. Finally, an improved technical process is presented based on these researches, and the verification experiment is accomplished on the experimental device we developed. The part is a circular plane mirror of fused silica material, and the surface figure error is improved from the initial λ/5 [peak-to-valley (PV) λ=632.8 nm], λ/30 [root-mean-square (rms)] to the final λ/40 (PV), λ/330 (rms) just through one iteration in 4.4 min. Results show that a higher convergence ratio and processing precision can be obtained by adopting error control and compensation techniques in MRF.     

Rheological Characterization of MR Polishing Fluid Used for Silicon Polishing in BEMRF Process

The finishing mechanism of the ball-end magnetorheological finishing (BEMRF) process mainly depends on the stiffened hemispheroid, which is formed at the tool tip. Magnetorheological (MR) polishing fluid imparts strength to the polishing spot because of the effect of magnetic field strength. Behavior of this polishing fluid mainly depends on the size and shape of its constituents, volume concentration, particle size distribution, and applied magnetic field strength. A detailed study was undertaken on the role of carbonyl iron particle (CIP) size on the rheological behavior of the MR polishing fluid under various magnetic flux densities. Evaluation of the behavior of MR polishing fluid for silicon polishing was attempted through designing and fabrication of a parallel-plate magnetorheometer. Rheological characterization study was carried out using the Casson fluid model and the MR polishing fluid rheological properties, namely field-induced yield stress and shear viscosity were evaluated.