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Surfaces and sub-surfaces
Published in Roger M Wood, Laser-Induced Damage of Optical Materials, 2003
Some materials are hard, i.e. they can only be polished with another hard material (e.g. diamond or alumina). However, it must be realized that polishing with diamond paste removes material by scratching and that the material loosened from the surface does not always disappear from the scene but can form a polycrystalline layer on the surface of the material. This layer may not itself be easily removable but it may be weak in terms of its laser power/energy handling capability (because of the possibility of lowering the thermal conductivity of the material due to the presence of defects and grain boundaries). The imperfect surface layer may also add scatter or divergence to the transmitted beam. Polishing with hard compounds is therefore usually done by ‘polishing through the grades’. This entails performing a rough polish with a relatively large diameter material (e.g. lOjim diameter diamond powder). The polishing process is then transferred to a lap with a finer grade of powder (e.g. 3μm diameter) and so on until the surface is finally finished with a very fine powder (with diameter less than λ/10 of the wavelength of light to be used). Each lap must be kept completely free from the coarser grades of polishing compound. Stringent precautions must also be taken to clean the surfaces before changing grades so that the coarser grades of polishing material are not just simply transferred to the new polishing pad, thus negating the whole process.
Building from Proof of Concept Design
Published in Bahram Nassersharif, Engineering Capstone Design, 2022
The service requirements may lead to the choice of metals for manufacturing the working model of the design. Metals are typically solid at room temperature (Mercury being an exception). Metals have a reflective surface and can be polished. Metals are ductile and malleable so they can be formed into different shapes such as sheets, rods, tubes, and blocks. Metals are much harder materials than many alternatives and are typically good conductors of heat and electricity. Metals have high density and are heavy. The melting and boiling points of metals are high, and therefore, they are suitable for high-temperature applications.
Optical Fabrication
Published in Daniel Malacara-Hernández, Brian J. Thompson, Advanced Optical Instruments and Techniques, 2017
Metals, plastics, and crystals can be polished the same way as glass, but using different polishing pads and compounds. Metals are polished best with cloth polishers and polishing compound with very fine chrome oxide or diamond [29]. The quality of the finish depends on the hardness, porosity, and inclusions of the metal substrate. Plastic optics, such as acrylics, are polished with aluminum or tin oxide with soft synthetic polishing pads. Most crystals are polished using synthetic pads with a compound of colloidal silica, fine diamond, or alumina (aluminum oxide).
Investigation into the error compensation method of the surface form based on feed rate optimization in deterministic polishing
Published in Machining Science and Technology, 2020
Cheng Fan, Yucheng Xue, Lei Zhang, Qizhi Zhao, Yao Lu, Qian Wang
The amount of material removed during the polishing process is affected by polishing conditions, polishing parameters and physical and geometric characteristics of polished parts and polishing tools (Wang et al., 2018). Sun et al. (2000) developed an empirical equation to evaluate the material removal process in the optical polishing of spherical surfaces of hydrophilic materials, and the formula indicates that the polishing normal force directly affects the material removal. Tam and Cheng (2010) investigated how the tool path may affect the removal of material in polishing. A polishing process is defined as deterministic if the material removal behavior is predictable when the polishing parameters are set to fixed values. During the past decades, much research has been performed on the deterministic polishing, mainly focusing on the design of polishing machine tool (Yi et al., 2004; Cheng et al., 2005), planning of the tool path (Chen et al., 2002; Rososhansky and Xi, 2011), strategy of polishing force control (Zhan and Yu, 2011) and reduction of surface roughness ((Lien and Guu, 2008; Savio et al., 2009; Ji et al., 2019). The deterministic polishing is regarded as an error compensation method by Hung et al. (2012) and Fan et al. (2014) to correct the surface form error. Thus, the material removal during the deterministic polishing should be controllable and a local model of material removal is essential for the planning of the polishing process.
Empirical approach to develop a multilayer icebonded abrasive polishing tool for ultrafine finishing of Ti-6Al-4V alloy
Published in Materials and Manufacturing Processes, 2018
Recent attempts were made to study the feasibility of a two-layered IBAP tool, with each layer having different sizes of abrasives and concentrations, for polishing of the Ti-6Al-4V alloy and alumina ceramics in a single polishing step. Such a tool has produced a fine finish and quality on the titanium alloy surface in a short time [19, 20]. Similarly, a multilayered ice fixed abrasive polishing tool was employed to polish a single-crystal germanium wafer surface in a single step [21]. As the purpose of a multilayer IBAP tool is to accomplish multistage polishing, i.e., rough, fine and ultrafine polishing, in one setup, it is important to develop the tool by selecting the number of layers, the type of abrasive, its size and concentration in each layer and the thickness of each layer. In essence, the type of abrasive, its size and concentration can influence the performance of the polishing process such as material removal rate, finish and quality of the polished specimen [22232425]. Different types of abrasives such as diamond, boron carbide, silicon carbide and aluminum oxide are the most widely used abrasive materials with the diamond having the highest hardness and aluminum oxide having the least hardness. Therefore, it suggests that the choice of abrasive material depends on the hardness of the work material [22]. Furthermore, the choice of abrasives also depends on the initial roughness on the work surface. For polishing of rough surfaces, it is preferable to choose coarse abrasives that are harder than the work material. Apart from this, the concentration of abrasives can also influence the material removal rate and the finish achieved over the polished surface [24, 25]. However, there was no systematic effort for the selection of the number of layers, thickness of each layer, and the type, size and concentration of abrasives in each layer of a multilayered IBAP tool.