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Mechanical polishing is a polishing method to obtain a smooth surface by cutting and plastic deformation of the material surface to remove the convex part after polishing. Generally, oilstone strips, wool wheels, sandpaper, etc. are used. Manual operation is the main method. Auxiliary tools such as turntable can be used for special parts, and ultra precision polishing method can be used for surfaces with high quality requirements. Superfinishing is a kind of special grinding tool. In the polishing liquid containing abrasive, it is pressed on the machined surface of the workpiece to make high-speed rotation motion. The surface roughness of ra0.008 μ M can be achieved by using this technology, which is the highest among various polishing methods. This method is often used in optical lens mould.
Chemical polishing is to make the micro protruding part of the material surface dissolve preferentially than the concave part in the chemical medium, so as to obtain a smooth surface. The main advantage of this method is that it does not need complex equipment, can polish the workpiece with complex shape, can polish many workpieces at the same time, and has high efficiency. The key problem of chemical polishing is the preparation of polishing fluid. The surface roughness obtained by chemical polishing is usually 10 μ M.
The basic principle of electropolishing is the same as that of chemical polishing, that is, to make the surface smooth by selectively dissolving the tiny protruding part of the material surface. Compared with chemical polishing, it can eliminate the influence of cathode reaction and has better effect. The electrochemical polishing process can be divided into two steps: (1) the macro leveling solution diffuses into the electrolyte, the surface roughness of the material decreases, RA > 1 μ M. (2) low light level anodized, surface brightness increased, RA < 1 μ M.
The workpiece is put into the abrasive suspension and placed in the ultrasonic field together. The abrasive is grinded and polished on the workpiece surface by the action of ultrasonic vibration. The macro force of ultrasonic machining is small and will not cause workpiece deformation, but it is difficult to make and install the tooling. Ultrasonic machining can be combined with chemical or electrochemical methods. On the basis of solution corrosion and electrolysis, ultrasonic vibration is applied to stir the solution to separate the dissolved products on the surface of the workpiece, and the corrosion or electrolyte near the surface is even; the cavitation effect of ultrasonic in the liquid can also inhibit the corrosion process, which is conducive to the surface lightening.
The purpose of fluid polishing is to wash the surface of workpiece by the high-speed fluid and abrasive particles carried by it. Common methods include abrasive jet machining, liquid jet machining, hydrodynamic grinding, etc. Hydrodynamic grinding is driven by hydraulic pressure, which makes the liquid medium carrying abrasive particles flow through the workpiece surface at high speed. The medium is mainly made of special compound (polymer like substance) with good flowability under low pressure and mixed with abrasive. The abrasive can be silicon carbide powder.
Magnetic abrasive polishing
Magnetic abrasive polishing is to use magnetic abrasive to form abrasive brush under the action of magnetic field to grind the workpiece. This method has the advantages of high processing efficiency, good quality, easy control of processing conditions and good working conditions. The surface roughness can reach ra0.1 μ m with suitable abrasive. 2. Mechanical polishing base the polishing method in the processing of plastic mold is very different from the surface polishing required by other industries. Strictly speaking, the polishing of mold should be called mirror machining. It not only has high requirements for polishing itself, but also has high standards for surface flatness, smoothness and geometric accuracy. Surface polishing generally requires only obtaining a bright surface. The standard of mirror machining is divided into four levels: Ao = ra0.008 μ m, A1 = ra0.016 μ m, A3 = ra0.032 μ m, A4 = ra0.063 μ M. because of the difficulty in precisely controlling the geometric accuracy of parts by electrolytic polishing, fluid polishing and other methods, while the surface quality of chemical polishing, ultrasonic polishing, magnetic abrasive polishing and other methods does not meet the requirements, the mirror machining of precision molds is mainly mechanical polishing.