Experimental Investigation of Material Removal and Surface Roughness during Optical Glass Polishing

It has been a challenge to finish optical glass surfaces due to their hard and brittle nature. Moreover, tight tolerances of surface figure and finish make polishing a more critical operation. This work reports the results of an experimental study performed for full aperture polishing of BK7 optical glass. Flat samples of borosilicate (BK7) glass are polished using an optical pitch polisher and cerium oxide (CeO₂) slurry. Taguchi's L9 orthogonal array is used for the design of experiments. Abrasive concentration, pressure and overarm speed are considered as variable process parameters. Polishing is performed for duration of 120 minutes for each combination of parameters. Material removal is measured using the precision weighing balance. Surface roughness was measured using a Form Talysurf PGI 120 profiler. Abrasive slurry concentration is observed to be one of the most significant parameters in the optical polishing process. It affects both the material removal rate (MRR) and the surface roughness. Pressure applied at the workpiece–polisher interface affects the MRR, but the variation of pressure is not found to affect the surface roughness significantly. Relative motion at the workpiece–polisher interface is also observed to be significant in defining the final polishing outputs.     

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.     

Partial-Ductile Grinding, Lapping, and Polishing of Aspheric and Spherical Surfaces on Glass

This paper discusses partial-ductile-mode grinding, lapping and polishing of aspheric and spherical surfaces on glass. Industrial manufacture of glass lenses usually involves three operations: grinding (known as milling in the optical industry), tapping, and polishing. The fracture mode of material removal is dominant in the grinding process. While these three operations have been successful for machining spherical lenses, aspheric lenses have been manufactured in the absence of the lapping process, because of the considerable amount of ductile mode of material removal in grinding. The parameters that helped identify and solve problems in manufacturing were surface roughness, micro-fractures and ductile streaks on glass surfaces, and interferometric fringes.     

光学元件聚氨酯抛光特性研究

本文研究了应用于平面光学元件的快速抛光技术,从材料去除率、元件面形和表面粗糙度出发,对快速抛光技术应用于平面大口径元件的加工效果进行了探讨。研究了在快速抛光技术中压力和主轴转速对材料去除率的影响,验证了Preston公式在快速抛光中的适用性,快速抛光技术的去除效率可达10μm/h;其次,研究了聚氨酯抛光元件面形的精度,对于330mm×330mm元件可达～1.0λ（λ=632.8nm）;最后,对快速抛光系统中抛光粉颗粒大小及形态随使用时间的变化进行了观测,并测量了使用300目和500目抛光粉时快速抛光元件表面粗糙度以及其随抛光粉使用时间的变化。     

Development of a compression molding process for three-dimensional tailored free-form glass optics

Because of the limitation of manufacturing capability, free-form glass optics cannot be produced in a large volume using traditional processes such as grinding, lapping, and polishing. Very recently compression molding of glass optics became a viable manufacturing process for the high-volume production of precision glass optical components. An ultraprecision diamond-turning machine retrofitted with a fast tool servo was used to fabricate a free-form optical mold on a nickel-plated surface. A nonuniform rational B-spline trajectory generator was developed to calculate the computer numerical control machine tool path. A specially formulated glass with low transition temperature (Tg) was used, since the nickel alloy mold cannot withstand the high temperatures required for regular optical glasses. We describe the details of this process, from optical surface geometry, mold making, molding experiment, to lens measurement.     

硼硅酸盐浮法玻璃的抛光温度

浮法工艺的优点之一是可以获得极佳的玻璃表面质量,硼硅酸盐浮法玻璃是近年来的研究热点。本文采用原子力显微镜(AFM)研究了温度和时间对硼硅酸盐玻璃浮法成形过程中抛光阶段的影响。研究结果表明:高温抛光过程中时间不是限制玻璃表面抛光质量的决定因素,温度是决定抛光质量的关键。硼硅酸盐浮法玻璃在大于1250℃以上的温度可以快速达到良好的抛光效果。     

抛光液组分对硬盘盘基片超光滑表面抛光的影响

在硬盘盘基片的最终抛光中,研究SiO2溶胶颗粒、氧化剂、络合剂和润滑剂对盘基片Ni—P材料抛光性能的变化规律,获得较高的材料去除速率（MRR）和原子级光滑表面,以满足下一代硬盘盘基片制造的更高要求．结果表明,采用平均粒径25nm的SiO2溶胶颗粒,易减少微划痕等缺陷;以过氧化氢为氧化剂,可大幅提高MRR;加入有机酸络合剂后,MRR显著增大,其中含有水杨酸的抛光液MRR最大,并讨论不同络舍剂对盘基片去除的影响机理;丙三醇润滑剂的引入,使抛光中摩擦系数减小,盘基片的表面粗糙度得到明显降低．采用原子力显微镜（AFM）、光学显微镜和ChapmanMP2000＋表面形貌仪来考察盘基片抛光后的表面质量,基于抛光液各组分的影响作用,最终获得表面粗糙度尺。为0．08nm的盘基片表面,且MRR达到0．132μm／min．     

Partial-Ductile Grinding and Reduced Polishing for Ophthalmic Glass Molds

Plastic lenses are manufactured by the classical replication technique where two glass molds are assembled in a jacket and liquid plastic is injected into it. The glass molds are fabricated conventionally by fracture mode grinding, followed by lapping, and Finally polishing. This paper presents an alternative fabrication process using partial-ductile grinding, followed by a short polishing in an industrial polishing machine. The partial-ductile surfaces were generated on a laboratory ultra-precision machine using Fine grit resinoid-bond diamond wheel and they were compared to the glass molds prepared by industry. The results showed that (i) as much as 100% ductile streaks (fully ductile grinding) can be obtained in the ultra-precision ground surface and (ii) a net saving of 55 seconds polishing time if only 60% of ductile streaks on the glass mold surface was used prior to polishing.     

Integrating grey sequencing with the genetic algorithm–immune algorithm to optimise touch panel cover glass polishing process parameter design

The touch panel cover glass is one of the important parts and components that determine touch panel quality. The quality requirement of touch panel cover glass emphasises the stability of glass thickness. As this factor directly influences the induction effect and touch of the touch panel, the parameter conditions for the cover glass polishing process have significant impact. This study integrated grey sequencing with the Genetic algorithm–Immune algorithm to optimise the parameter design for the touch panel cover glass polishing process. The experimental measurement value was the thickness value of the processed glass, and the uniformity of glass thickness after processing was discussed. The optimum processing combination influencing the process conditions is as follows: the ambient temperature is 22 (°C), the processing pressure is 0.04 (Mpa), the processing time is 30 (min), the machine speed is 70 (rpm), the polishing solution concentration is 1.4 (g/cm³), the central particle size of polishing powder is 1.4 (um) and the process capability C_pk is 1.75, which is better than the process capability of C_pk 1.41 of the response surface methodology and the process capability of C_pk 1.37 of the Taguchi experimental design.     

聚合物光波导端面磁流变抛光工艺(英文)

光波导端面的表面质量会严重影响光波导器件的光耦合封装性能,耦合封装前必须对波导器件端面进行抛光处理.目前聚合物光波导端面主要依靠传统研磨盘进行抛光处理,该工艺工序复杂、抛光效率低已成为制约聚合物波导器件应用的瓶颈.基于聚合物光波导材料优良的加工特性,通过对比实验提出了聚合物光波导的磁流变端面抛光工艺.采用5μm、0.5μm和1μm粒径的氧化铈抛光粉分别配制研磨盘抛光液及磁流变抛光液对3 mm×3 mm聚合物光波导端面进行抛光实验,发现磁流变加工对聚合物光波导端面进行一次2 m in光栅扫描抛光就具有比传统研磨盘约3 h精、粗抛光较好的端面质量.经过白光干涉仪测量,磁流变抛光后光波导端面表面粗糙度的均方根值达到了2.6 nm,传统端面抛光端面粗糙度均方根值为128.7 nm.通过自动对准耦合平台测试,结果显示通过磁流变端面抛光的光波导的插入损耗由抛光前的32.7 dB降低到了17.8 dB.磁流变抛光方法可以对聚合物光波导端面进行快速、高性能的抛光,在光波导应用领域具有非常广阔的应用前景.     

固结磨料化学机械研抛K9玻璃的材料去除机理

采用失重法对固结磨料研抛K9玻璃材料去除过程中的机械与化学作用进行了分离,采用显微硬度方法分析了研抛液对K9玻璃工件表层硬度的影响.研究结果表明:研抛液能与K9玻璃发生化学反应并在其表面形成一层较基质材料软的变质层,变质层厚度随浸泡时间的延长而增加；单纯研抛液的化学作用对K9玻璃的材料去除作用有限,固结磨料研抛垫对K9玻璃的机械去除作用主要以脆性去除为主,化学与机械的交互作用是K9玻璃影响材料去除的主要方式:当研抛盘转速为200r/min时,化学作用与机械作用达到平衡,交互作用最为强烈,材料去除率达到最大值.     

Some observations on the wear of single point diamond tools used for machining glass

The wear pattern on a single point diamond tool used for machining glass is studied. Possible wear mechanisms are proposed on the basis of additional sliding wear tests and observations by scanning electron and optical microscopy. The wear process is believed to take place in two stages, one involving a polishing mechanism and the other consisting of crack propagation which occurs after the accumulation of a certain amount of damage. The importance of the crystallographic orientation of the diamond single crystal, particularly for crack propagation along cleavage planes is pointed out. It is concluded that the likelihood of rapid deterioration of the diamond tool may be decreased by proper crystallographic orientation.     

Loose abrasive slurries for optical glass lapping

Loose abrasive lapping is widely used to prepare optical glass before its final polishing. We carried out a comparison of 20 different slurries from four different vendors. Slurry particle sizes and morphologies were measured. Fused silica samples were lapped with these different slurries on a single side polishing machine and characterized in terms of surface roughness and depth of subsurface damage (SSD). Effects of load, rotation speed, and slurry concentration during lapping on roughness, material removal rate, and SSD were investigated.     

LBO晶体的超精密加工工艺研究

采用Logitech PM5精密研抛机,通过机械抛光和化学机械抛光方法超精密加工LBO晶体;详细研究了LBO晶体的超精密加工工艺,并观察研磨和抛光等加工过程后的晶体表面形貌;研究抛光液和抛光垫在抛光中对LBO晶体表面微观形貌的影响.使用Wkyo激光干涉仪测量平面度,光学显微镜观察表面宏观损伤,原子力显微镜测量表面粗糙度和观察微观形貌.通过实验,实现高效率、高精度、高质量的LBO晶体的超精密加工,得到了LBO晶体的超精密加工工艺;超精密加工后晶体的表面粗糙度＜0.2nm RMS,表面平面度＜氇/10(氇=633nm),微观损伤少.     

Wet-etch figuring for precision optical contouring

Wet-etch figuring utilizes free surface flows driven by surface tension gradients (the Marangoni effect) to confine and stabilize the size and shape of an etchant droplet attached to the underside of a glass surface. This droplet, or wetted zone, is translated on the surface, etching where it contacts and leaving behind no residue, to facilitate an etching-based small-tool figuring process that is free of mechanical and thermal stresses. The optic needs no backing plate, and its back side is free for inspection by optical means. When transmissive optics is figured, the optical thickness between the front and the rear surfaces of the optic is measured interferometrically and used in real time to control the local dwell time of the etchant zone. This truly closed-loop figuring process is robust, environmentally insensitive, and fully automated. It is particularly suited for figuring patterns such as phase plates, corrective elements, and optical flats on very thin (< 1-mm) substrates that are difficult to figure with traditional abrasive polishing methods.     

无机材料超光滑表面的制备

随着光学、微电子、航天和激光技术的发展，在晶体或玻璃等无机材料上制备亚纳米级的超光滑无损伤表面已成为现代精密加工技术领域的重点研究课题。近年来，此项技术研究进展声速，不仅改进了传统的抛光技术，还出现了浮法抛光、离子束加工和弹性发射加工等新技术。系统介绍了超光滑表面的检测、制备技术及其发展，并讨论了抛光过程中的机械化学作用机理。     

P_2O_5-BaO-Al_2O_3-K_2O磷酸盐激光玻璃的表面处理

采用化学浸蚀与高温热处理相结合的方法来改善P2O5-BaO-Al2O3-K2O磷酸盐玻璃表面平整性、去除玻璃表面杂质,提高用管棒法制备光纤预制棒时纤芯和包层玻璃的表面质量,消除由于机械抛光工艺带来的表面缺陷和表面污染.实验研究了磷酸盐玻璃盐酸浸蚀的特性,分析了盐酸溶液与磷酸盐玻璃作用机制,并确定了浸蚀参数,9mol/L的盐酸溶液对此磷酸盐玻璃具有最大浸蚀速率,浸蚀30min后,可消除玻璃表面的划痕.盐酸溶液对玻璃的浸蚀反应使磷酸盐玻璃表面平整,但在玻璃表面产生了晶化覆盖层.通过进一步在拉丝温度下热处理,可使玻璃表面覆盖层重新非晶化,提高玻璃透过率.实验结果表明:化学浸蚀和高温热处理的复合方法是一种有效改善磷酸盐玻璃表面质量的途径.     

Preparation of ceria-based polishing powders from carbonates

The preparation of Ce(IV) oxide-based polishing powders by thermal decomposition of carbonates was studied and the effect of the calcination process conditions on the properties of product was examined. High-grade polishing powders can be produced at calcination temperatures 700–1200°C, the maximum polishing efficiency is achieved by calcining at 1000–1100°C. The observed dependences were interpreted from the standpoint of the present mechanochemical theory of glass polishing.     

Laser polishing and laser form correction of fused silica optics

With laser polishing, the roughness of ground glass surfaces can be significantly reduced. With process speeds up to 1 cm²/s independent of the processed surface shape, the resulting roughness is already sufficient for illumination optics. To further reduce the roughness, the polishing process itself will be optimized and moreover combined with a subsequent laser based form correction. Within this paper, results of laser polishing as well as laser form correction and combination of the two processes are presented and discussed.     

Single-mode D-shaped optical fiber sensor for the refractive index monitoring of liquid

A new fabrication method is introduced for the production of D-shaped optical fiber. A mechanical end and edge polishing system with aluminum oxide polishing film is utilized to perform sequential polishing on one side (lengthwise) of single-mode optical fiber in order to obtain a D-shaped cross section. Adjusting specific mechanical parameters allows for control of the volume of the D-shaped zone, while the fiber surface smoothness is governed by selection of polishing film grit size. To meet the accuracy and repeatability requirements, optical power loss is monitored during the entire polishing process in situ and in real time. This proposed technique possesses advantages of rapidity, safety, simplicity, repeatability and stability with high precision in comparison with contemporary methods for production. Sensor performance tests on the fiber reveal a linear response with linearity up to R² = 0.984 for surrounding refractive index in the range of 1.320–1.342 refractive index, which corresponds to different concentrations of the glucose solution test environment. The produced D-shaped optical fiber has potential sensing and monitoring applications in chemical, environmental, biological and biochemical fields.