Effect of abrasive grit shape on polishing of β-Ga2O3(100) substrate

β-Ga₂O₃ can be cleaved easily, where the (100) surface is the main cleavage surface. This surface encounters local stress concentration during ultra-precision machining and is prone to local fragmentation, resulting in formation of micro-cleavage pits. The effects of different abrasive grit shapes on polishing are studied in order to ensure smooth processing of β-Ga₂O₃(100). First, a contact mechanics model for different shapes of abrasive grits and crystal surfaces is established in accordance with the theory of elasticity. Then, the contact mechanism between the abrasive grits and the crystal surfaces is analyzed using a theoretical model. Finally, the feasibility of the theoretical model is verified in experiments. The results show that blunt spherical abrasive grits are more suitable for polishing of β-Ga₂O₃(100) than sharp diamond-shaped abrasive grits. Compared to sharp abrasive grits, the crystal surfaces processed using blunt abrasive grits are smoother, with surface roughness (Ra) of approximately 14 nm. During polishing, the sharp and blunt abrasive grits remove brittle and plastic material, respectively. Therefore, blunt abrasive grits are more suitable for the polishing of β-Ga₂O₃ than sharp abrasive grits.     

Magnetic field-assisted polishing — application to a curved surface

Magnetic field-assisted polishing using a magnetic fluid was applied to a curved surface. As a polishing test material, a single crystal of LiNBO₃, a hard and brittle material, was examined; it was previously machined to a spherical surface by diamond turning. The results of polishing experiments show that surface roughness of 0.01 μm R_max can be easily obtained by this method. It is also clarified that the magnetic field intensity is closely related to the polishing pressure and the removal rate. Therefore, to finish curved surfaces precisely, the magnetic field distribution must be kept uniform.     

Morphology of Co–Cr–Mo dental alloy surfaces polished by three different mechanical procedures

The present study aims at characterizing the three‐dimensional (3‐D) morphology of a Co–Cr–Mo dental alloy surface as a result of three different procedures used for polishing it. The sample surface morphology of the sampled surface was examined employing atomic force microscopy (AFM), statistical surface roughness parameters, and fractal analysis. An extra‐hard dental alloy of cobalt–chromium–molybdenum (Co–Cr–Mo) (Wironit^®, from BEGO, Bremen, Germany) was prepared and moulded. Different polishing treatments were carried out on three groups of six samples each—a total of 18 samples. The first group contained six electropolished (EP) samples. The second group containing six samples went through a mechanical polishing process employing green rubber discs and a high shine polishing paste applied by a rotating black brush (BB). The third group comprising six samples as well went through a mechanical polishing process by means of green rubber discs, high shine polishing paste, and a rotating deer leather brush (DL). Fractal analysis on the basis of a computational algorithm applied to the AFM data was employed for the 3‐D quantitative characterization of the morphology of the sampled surfaces. The fractal dimension D (average ± standard deviation) of 3‐D surfaces for BB samples (2.19 ± 0.07) is lower than that of the DL samples (2.24 ± 0.08), which is still lower than that of the EP samples (2.27 ± 0.09). The results indicated the BB samples as presenting the lowest values of statistical surface roughness parameters, thus the best surface finish, while the EP samples yielded the highest values. Microsc. Res. Tech. 78:831–839, 2015. © 2015 Wiley Periodicals, Inc.     

Study on the manufacturing process controlling for aspheric surface ballonet polishing

Ballonet polishing tools, soft gasbags filled with compressed gas, have already been one of the most reliable tools in curved surface polishing due to their adaptability to change their shape to fit the worked surfaces with the same contact stress everywhere. When the internal pressure of the gasbag is adjusted on-line, the contact stress could be controlled as you want. But, because of the tensile stress of the gasbag's material, the internal pressure could not identify the real contact condition anymore. In this paper, the contact force is used to identify the real contact condition for workpieces of aspheric surfaces which is indispensable to the polishing process control. Based on the measured internal pressure of the gasbag and the on-line-controlled contact force in the normal direction, this paper studies the arithmetic of the contact area for aspheric surfaces, finds a way to eliminate the great difference of machining speed, and advances an arithmetic of the machining time for material removal controlling in the process of aspheric surface ballonet polishing. A real ballonet polishing system is developed for aspheric surfaces, and experiments show that it is a better way by controlling the contact force rather than by controlling the internal pressure in the process of aspheric surface ballonet polishing.     

光学脆性材料的金刚石切削加工

重点对脆性材料的超精密研磨、抛光加工技术及超精密磨削加工技术和超精密切削加工技术进行了分析研究。分析表明,硬脆材料光学元件主要应进行超精密研磨、抛光及超精密磨削加工;软脆材料光学元件主要应进行金刚石切削加工。对软脆材料金刚石切削进行了试验设计,指出了光学脆性材料的金刚石切削加工过程不同于金属加工过程,通过控制切削条件可以实现脆性材料塑性域加工,提高光学脆性材料的表面加工质量。     

Theoretical and experimental investigation of surface generation in swing precess bonnet polishing of complex three-dimensional structured surfaces

Three-dimensional structured surfaces (3D-structured surfaces) possessing specially designed functional textures are widely used in the development of advanced products. This paper presents a novel swing precess bonnet polishing (SPBP) method for generating complex 3D-structured surfaces which is accomplished by the combination of specific polishing tool orientation and tool path. The SPBP method is a sub-aperture finishing process in which the polishing spindle is swung around the normal direction of the target surface within the scope of swing angle while moving around the center of the bonnet. This is quite different from the ‘single precess’ and ‘continuous precessing’ polishing regime, in which the precess angle is constant. The technological merits of the SPBP were realized through a series of polishing experiments. The results show that the generation of complex 3D-structured surfaces is affected by many factors which include point spacing, track spacing, swing speed, swing angle, head speed, tool pressure, tool radius, feed rate, polishing depth, polishing cloth, polishing strategies, polishing slurry, etc. To better understand and determine the surface generation of complex 3D-structured surfaces by the SPBP method, a multi-scale material removal model and hence a surface generation model have been built for characterizing the tool influence function and predicting the 3D-structured surface generation in SPBP based on the study of contact mechanics, kinematics theory, abrasive wear mechanism, and the convolution of the tool influence function and dwell time map along the swing precess polishing tool path. The predicted results agree reasonably well with the experimental results.     

评价机械加工表面形貌的小波变换方法

提出了用小波变换计算粗糙表面分形维数的新方法 ,并基于Weierstrass -Mandelbrot函数 (W -M函数Majumdar-Bhushan函数 (M -B函数 )对该方法进行了验证 ,结果表明该方法具有很高的计算精度。应用小波变换方法对核态池沸腾试验板表面形貌的分形特征进行了评价 ,包括铜和不锈钢材料 ,轧制、砂纸打磨和表面机械抛光等 3种加工方法生成 5个粗糙度级别的试验板 ,研究结果表明该方法能有效评价表面形貌的分形特征。     

<Emphasis Type="Bold">Ductile or Partial Ductile Mode Machining of Brittle Materials</Emphasis>

This paper reports ductile or partial ductile mode machining of silicon, glass and some advanced ceramics. Results are presented using scanning electron micrographs of the machined surfaces. Grinding and lapping operations using inexpensive machine tools could produce ductile streaks on surfaces of these brittle materials under good conditions. Manufacture of spherical glass lenses by the fracture mode or partial ductile mode grinding followed by partial ductile mode lapping and ductile mode polishing is fast and economical. Using partial ductile mode grinding and ductile mode polishing has also been very successful for manufacturing aspherical glass lenses. Reduced polishing time and improved surface quality are due to the presence of ductile streaks. Ground silicon, ZrO2 and Al2O3 also showed ductile streaks. Toroidal SiC surfaces ground with flat-face cup wheels indicated 100% ductile machining, and did not require polishing.     

Corrective polishing of complex ceramics geometries

High quality surfaces in terms of low roughness and high form accuracy are achieved by polishing as the essential finishing step. Polishing of brittle materials is an established process in science and industry. However, the machining is limited to planar or spherical geometries. The objective of this paper is to present first results to overcome this limitations indicated by processing advanced ceramics.In order to finish complex surfaces, a technological transfer of known parameters and conditions of 2-dimensional to zonal polishing is undertaken. To shorten the development of stable and reproducible processes the knowledge and understanding of the complex interactions of the 2-dimensional process is used. The applicability of these conditions is evaluated by extensive research on the zonal polishing setup. The used machine tool is capable of adjusting significant process factors, such as free controlled force and heterodyne velocity profiles. By use of a small tool the material removal is only affecting a zonal area of a complex surface. Based on preliminary investigations concerning the material removal function the scientific insight on zonal processes is extended. This first approach will be used for corrective polishing of zonal form deviations.     

双面抛光机气动加载的建模与仿真

双面抛光机广泛用于硅片、蓝宝石、陶瓷、磁性材料、电子器材的表面超光滑无损伤的平整加工。气动加载系统是双面抛光机实现精密抛光非常关键的部分。抛光压力加载精度的高低直接决定了抛光机性能的好坏。本文利用法国AMESim软件对气动加载系统进行建模,通过仿真得出了一组最佳PID参数,满足了系统要求,并使系统性能得到提高。     

Failure Mechanisms of CVD Diamond Wafers and Thin Films During Polishing

This article investigates the failure mechanisms of CVD diamond wafers and thin films during a fast dynamic friction polishing process. To explore the evolution of temperature and stress fields, a comprehensive finite element analysis was systematically carried out, with the aid of experimental examination. It was found that the discontinuity and sharp change of the stresses across the film-substrate interface causes debonding failure of a CVD diamond thin film specimen. In the case of a CVD diamond wafer, however, the high surface tensile stress and bulk bending is responsible for the cracking. It was concluded that specimen cracking is sensitive to the polishing pressure, and that the polishing window for the CVD thin films is smaller. Polishing time is a critical factor, because a longer time corresponds to a higher thermal stress. This article points out that using the combination of a smaller polishing load and a greater sliding speed is a good option in selecting polishing parameters. To minimize cracking, a stepwise polishing process can be used. With the proper parameters obtained in this study, very smooth, high-quality surfaces of CVD diamond wafers and thin films can be produced in a short polishing duration of minutes.     

单晶硅同质互抛实验研究

以材料的去除率和表面粗糙度为评价指标设计对比实验,验证了硬脆材料互抛抛光的可行性,得到了抛光盘转速对硬脆材料互抛的影响趋势和大小。实验结果表明：当抛光压力为48 265 Pa（7 psi）、抛光盘转速为70 r/min时,自配抛光液互抛的材料去除率为672.1 nm/min,表面粗糙度为4.9 nm,与传统化学机械抛光方式的抛光效果相近,验证了硬脆材料同质互抛方式是完全可行的;互抛抛光液中可不添加磨料,这改进了传统抛光液的成分;采用抛光液互抛时,材料去除率随着抛光盘转速的增大呈现先增大后减小的趋势,硅片的表面粗糙度随着抛光盘转速的增大呈先减小后增大的趋势。     

纳米胶体自激脉冲空化射流抛光技术

为了满足光学复杂曲面的精密、高效加工,提出一种利用空化效应促进射流加工效率的光学表面加工方法——纳米胶体自激脉冲空化射流抛光,并研制了加工系统。采用流体动力学对纳米胶体自激脉冲空化射流抛光中的喷射过程进行了仿真,获得了周期为0.3s的自激脉冲射流典型时刻下加工流场的流体动、静压力、速度、空化效应分布规律。进行了纳米胶体自激脉冲空化射流抛光试验,结果表明该系统能够产生效果良好的自激脉冲空化射流。采用该方法对单晶硅表面进行加工可以得到表面粗糙度为Ra0.904nm(Rms1.225nm)的超光滑表面,此加工表面粗糙度质量与相同加工条件下的普通纳米胶体射流抛光相当,但其加工效率较普通纳米胶体射流抛光能够提升20%左右,能够满足光学表面高效精密加工的需要。     

化学机械抛光工艺中的抛光垫

抛光垫是晶片化学机械抛光中决定表面质量的重要辅料。研究了抛光垫对光电子晶体材料抛光质量的影响：硬的抛光垫可提高晶片的平面度;软的抛光垫可改善晶片的表面粗糙度;表面开槽和表面粗糙的抛光垫可提高抛光效率;对抛光垫进行适当的修整可使抛光垫表面粗糙。     

Predicting the Material Removal in Polishing: The Applicability of Two Types of Statistical Models

This article develops two statistical rough surface models to investigate the material removal rate in surface polishing. Model I implies that the contact between two surfaces is equivalent to that between a composite surface and a plane; but Model II is without the equivalent surface concept. The prediction differences of the two models were first investigated with the aid of contact mechanics. The analysis shows that the relative error of the predictions by the two models could be minimized by considering the interactions between asperities, and that this error increases with the separation of the mean planes, but decreases with the asperity density, asperity radius and standard deviation of the asperity height. By extending the models to study the material removal rate in polishing, it was found that asperity interaction is an important factor in a statistical modelling of polishing, and that with a given separation of the reference planes of the pad and workpiece surfaces, the material removal rate increases with the volume concentration of abrasive particles and varies with the pad roughness. The study also showed that the microstructure of a polishing pad has a significant effect on the material removal rate of a polishing.     

A review on ductile mode cutting of brittle materials

Brittle materials have been widely employed for industrial applications due to their excellent mechanical, optical, physical and chemical properties. But obtaining smooth and damage-free surface on brittle materials by traditional machining methods like grinding, lapping and polishing is very costly and extremely time consuming. Ductile mode cutting is a very promising way to achieve high quality and crack-free surfaces of brittle materials. Thus the study of ductile mode cutting of brittle materials has been attracting more and more efforts. This paper provides an overview of ductile mode cutting of brittle materials including ductile nature and plasticity of brittle materials, cutting mechanism, cutting characteristics, molecular dynamic simulation, critical undeformed chip thickness, brittle-ductile transition, subsurface damage, as well as a detailed discussion of ductile mode cutting enhancement. It is believed that ductile mode cutting of brittle materials could be achieved when both crack-free and no subsurface damage are obtained simultaneously.     

单晶SiC基片的集群磁流变平面抛光加工

基于集群磁流变效应超光滑平面抛光理论及研制的试验装置,对单晶SiC基片进行了平面抛光试验研究。研究结果表明,金刚石磨料对单晶SiC基片具有较好的抛光效果;加工间隙在1.4mm以内抛光效果较好,30min抛光能使表面粗糙度值减小87%以上;随着加工时间的延长,表面粗糙度越来越小,加工30min时粗糙度减小率达到86.54%,继续延长加工时间,加工表面粗糙度趋向稳定。通过优化工艺参数对直径为50.8mm(2英寸)6H单晶SiC进行了集群磁流变平面抛光,并用原子力显微镜观察了试件加工前后的三维形貌和表面粗糙度,发现经过30min加工,表面粗糙度Ra从72.89nm减小至1.9nm,说明集群磁流变效应超光滑平面抛光用于抛光单晶SiC基片可行有效且效果显著。     

超声研磨硬脆材料的去除模型研究

从理论上分析了脆性材料在超声研磨过程中影响表面质量的各种主要因素，对影响加工表面粗糙度的主要因素进行了试验。研究结果表明，超声工具头与被加工工件的间隙对表面质量影响很大。试验表明，当超声工具头与被加工工件的间隙在一定的范围内，能在超声研磨条件下加工出高质量的超光滑表面。     

基于分形几何的表面微观形貌模拟及粘着弹性接触计算研究

基于Ausloos和Berman提出的推广的W-M函数对具有分形特征的粗糙表面进行仿真模拟,分析了函数中与尺度无关的特征参数对表面微观形貌的物理意义。同时,基于Yan和Maugis的理论研究,用模拟的分形表面建立了考虑表面效应的弹性接触模型,通过数值方法对整个过程进行迭代求解,得到了两接触面在不同的接触条件下各个接触斑点上的载荷分布和真实接触面积以及接触斑点的数量和尺寸。由于真实接触面积的尺寸敏感地反应表面微观几何形貌的变化,因此该方法为研究粘着机制和减小微尺度粘着效应提供了思路。     

Electrochemical mechanical polishing technology: recent developments and future research and industrial needs

Electrochemical mechanical (ECM) polishing processes are widely used in various industries such as die and mould manufacturing, turbine blades, and components with complex surfaces. They are used to improve the surface quality and get glossy surfaces with enhanced mechanical properties. In this paper, the authors first look into the fundamental principles of the ECM polishing technology. Then the main parameters that affect the ECM polishing process such as applied voltage, electrolyte concentration, rotational speed and polishing pressure are discussed, and the related research issues are raised. Studying these parameters will enhance the performance, increase the efficiency of ECM polishing technology and provide a useful reference for further developments. Up to date, automatic ECM polishing is limited for planarization process and surfaces with simple geometry such as hole-wall and rotary surfaces. In addition, in some of ECM finishing technologies, the limited available working space usually forces the manufacture to machine one part in multiple stages. Because robots have some advantages over conventional machines such as flexibility, low price and mechanical reconfigurability, they are an effective and economical solution for ECM polishing of geometrically complex workpieces. In order to advance the ECM technology for the next competitive stage where a promising quantitative and qualitative processing is required, the authors proposed that the future researches on ECM polishing should also include ECM polishing using robots. In addition, the authors propose several configurations and setups of robotic ECM polishing systems. The research topics in this area should include designing of new ECM polishing tools, investigating the synergistic effects of additional sources of energies such as magnetic field and ultrasonic vibrations besides the normal effect of ECM tools and developing models and control methods of the processes.