Papers by Keyword: Polishing

Abstract: Diamond is widely used in the fields of precise and ultraprecise machining because of its superlative characters. Due to high hardness and great brittleness of diamond, the grinding of diamond needs a kind of high effective and stable polishing method. Dynamic friction polishing (DFP) is deemed to be an innovative method by means of a synergistic reaction of mechanical effect and chemical change. The condition of high pressure and high temperature puts forward a high requirement for mechanical property of the grinding wheel in DFP, other than that, the graphitization of diamond catalyzed by catalytic metal is also a focus of research. In this paper, the transition metals with unpaired d electrons were selected as polishing materials, and powder metallurgy technique was used to prepare alloy grinding wheel for polishing diamond by dynamic friction polishing.

Abstract: Galvanic retroreflector moulds suffer from fabrication errors and considerable wear due to the manufacturing process and the subsequent use for injection moulding. To remove degradations like flaws and wear marks from the mould’s optical surfaces without tedious manual labour, a partially automated process chain using a 6-axis robot is being developed combining surface metrology and machining technology. The areal limitation of the structured surfaces excludes conventional rotatory polishing processes. Vibration polishing is applied instead to remove critical surface errors and to enhance surface roughness to a near optical value of Sa ≤ 50 nm. The work presented in this paper gives insights into experiments performed on a robot polishing system and illustrates and the suitability for an application in the aforementioned partially automated process chain.

Abstract: Understand the impact of new materials on the study of modern sculpture, stainless steel sculpture and its understanding, awareness and stainless steel sculpture to the current problems that exist through observation, induction and summary, stainless steel sculpture by recognizing the problems at the same time, given a reasonable solution. Such as the use of welding techniques, and how to be colored stainless steel polishing process.

Abstract: Reflecting lens is an important component of optical systems, such as high-resolution cameras, large space telescopes and meteorological satellites etc. Among the lens materials, Silicon Carbide (SiC) has attracted a lot of attention as an important optical material because of its excellent mechanical and physical properties. Apart from the form accuracy, the attainment of a consistently high optical quality in polishing SiC is still of a concern. There are advanced ultra-precision polishing machines that can correct geometrical errors and surface finish of the workpiece. These include surface roughness and waviness. However, the hardness of SiC material itself put an challenge for polishing process. In this paper, A computer controlled ultra-precision polishing (CCUP) method based on mechanical polishing is used to produce the SiC lens. Experiments are being designed on a 7-axis ultra precision polishing machine (Zeeko IRP200). As it is difficult to find out slurry which is harder than SiC so that the conventional polishing slurry is be used. It provides a nice consequence that it also efficient when the polish powder is softer than the machined materials. The tool pressure, polishing head speed and the feed rate are varied and optimized to obtain the best reflectivity of the lens being polished. A pilot experiment will be conducted for the corrective polishing for the form error of the optical surface made of SiC. The result from the study will provide an important means to optimize the process for machining SiC reflective lens using the CCUP process.

Abstract: 4H-SiC is considered as one of the most promising next-generation semiconductor power-device materials. An atomically flat 4H-SiC surface with a well-ordered step/terrace structure was essential for epitaxial growth or applications in electrical devices. Plasma assisted polishing (PAP), in which the irradiation of atmospheric-pressure water vapor plasma and ceria (CeO₂) abrasive polishing were combined, was successfully applied to the atomic-scale flattening of 4H-SiC. To clarify the atomic-scale flattening mechanism of 4H-SiC in PAP process, investigations of thermal oxidation of 4H-SiC were conducted. Cross-sectional transmission electron microscopy (XTEM) observations revealed that the interfaces between the thermal oxidized oxide layer and SiC were very flat regardless of the thickness of the oxide layer. Dipping in hydrofluoric acid for 10 min and CeO₂ abrasive polishing for 3 h were respectively conducted on a 4H-SiC surface which was thermally oxidized for 2 h. A flat surface was obtained after dipping in HF acid. However, no step/terrace structure, which corresponds to the inclination of the crystal plane, could be observed due to the residual of silicon oxycarbide. A well-ordered step/terrace structure was obtained on the surface polished by CeO₂ abrasive. The step height was about 0.25 nm, which corresponds to a one-bilayer structure of 4H-SiC. The different oxidation rates of Si atoms on the cubic face and Si atoms on the hexagonal face were considered the reason why two kinds of terraces with different width were generated.

Abstract: Single crystal sapphire is widely used as the material for precision equipments, due to its high hardness, chemical inertness and light transmission. However, it is difficult to obtain a scratch-free and damage-free sapphire surface with high-efficiency through traditional mechanical polishing or etching. We developed plasma assisted polishing (PAP) for the finishing of difficult-to-machine materials, such as silicon carbide, diamond, and sapphire. In this article, preliminary research results are showed about PAP applied to polishing of single crystal c-plane sapphire substrates. Combination of helium based atmospheric pressure water vapor plasma irradiation and silica abrasive polishing drastically increased removal rate of the sapphire c-plane. XPS measurements of the surfaces with and without irradiation of water vapor plasma revealed that alumina hydrate was formed by plasma irradiation at low temperature of less than 40°C. It is assumed that formation of alumina hydrate promoted the removal rate of sapphire.

Abstract: Reaction-sintered silicon carbide (RS-SiC) is a promising material for optical components used in space, or molds for precision glass lens because of its excellent properties. For processing of RS-SiC, diamond tools are utilized because RS-SiC is difficult-to-machine material due to its high hardness. In that case, subsurface damage (SSD) and scratches are inevitably introduced on the processed surface, and they deteriorate the qualities of products. To resolve these issues, we proposed a complex machining technique named anodic oxidation assisted process (AOAP), in which localized anodic oxidation and removal of the oxidation layer by grinding or polishing were combined, for figuring or polishing of RS-SiC without introducing any scratches and SSD. The grinding or polishing tool used in AOAP has a lower hardness than that of RS-SiC, but higher than that of the oxidation products. It is possible to figure the objective shape and polish the surface by changing the conditions including the oxidation time, the composition of electrolyte, the configuration of the cathode electrode, applied voltage, and so on. In our previous study, we found that RS-SiC was oxidized efficiently by anodic oxidation with various electrolytes such as phosphoric acid, ultrapure water, and a mixture of hydrochloric acid and hydrogen peroxide. In this research, we investigated the preliminary processing characteristics of AOAP for RS-SiC. We ascertained that irradiating UV light with photon energy higher than the band gap of processed materials is very effective for increasing the oxidation rate of anodic oxidation. And we proposed a novel polishing process of RS-SiC, which combining oxidation only SiC area in RS-SiC by anodic oxidation with the electrolyte of ceria slurry, with polishing by ceria slurry which removes both oxidized layer and unoxidized layer in RS-SiC. The results of investigation for the oxidation rate and the polishing rate of SiC, Si and SiO₂ with ceria slurry implies that we can remove SiC grain and Si grain in RS-SiC at the same MRR by combing the anodic oxidation and polishing with ceria slurry at the same time, and obtain the smooth surface.

Abstract: Behavior of both suspended micrometer-size magnetic particles and micrometer-size nonmagnetic abrasive particles in a micro-tube filled with a magnetic compound fluid is investigated by using discrete particles method based on the simplified Stokesian dynamics in order to reveal the polishing process of inner surface of the tube with an axial flow. Giving the axial flow of the appropriate velocity is effective on performing uniform polishing of the surface in the magnetic compound fluid polishing.

Abstract: Chemical mechanical polishing (CMP) is often employed to obtain a super smooth work-surface of a silicon wafer. However, as a conventional CMP is a loose abrasive process, it is hard to achieve the high profile accuracy and lots of slurry must be supplied during CMP operations. As an alternate solution, a fixed abrasive CMP process can offer better geometrical accuracy and discharges less waste disposal. In this paper, in order to enhance the polishing efficiency and improve the work-surface quality, a novel ultrasonic assisted fixed abrasive CMP (UF-CMP) is proposed and the fundamental machining characteristics of the UF-CMP of a silicon wafer is investigated experimentally. The results show that with the ultrasonic assistance, the material removal rate (MRR) is increased, and the surface quality is improved.

Abstract: Finishing process (Grinding and Polishing), is still manually performed, specially in free form surface parts. This involves a series of remaining problems, mainly related with the geometrical shape of the finished part. In traditional manually finishing task, the final quality aspect of the part is the only parameter to be controlled. This supposes a lack in the quality parameter control, mainly in high level parts, as in automotive, aeronautics or mould making parts. Manual finishing has not any control about the amount of material removed, during finishing process, affecting this way to the final geometrical shape of the product. This is the reason why this investigation proposes an exhaustive research of the parameter influencing the finishing tasks, and defining a finishing methodology adapted for an automatic process executed by a spherical robot. Making it an automatic way, and controlling paths, tool, abrasive, and defining a mathematical model for the finishing process, final quality of the part and product will be optimized, from a quality point of view, at the same time process time and cost is reduced.