Mechanical polishing is a polishing method that obtains a smooth surface by removing the convex parts after polishing through cutting and plastic deformation of the material surface. It generally uses oilstone strips, wool wheels, sandpaper, etc., and is mainly manually operated. Special parts such as the surface of the rotating body can use auxiliary tools such as a turntable. For high surface quality requirements, ultra precision polishing can be used. Ultra precision polishing is the use of specially designed grinding tools, which are tightly pressed onto the machined surface of the workpiece in a polishing fluid containing abrasives and perform high-speed rotational motion.
Chemical polishing is the process of allowing materials to preferentially dissolve the micro protruding parts of the surface in a chemical medium, resulting in a smooth surface. The main advantage of this method is that it does not require complex equipment and can polish workpieces with complex shapes. It can simultaneously polish many workpieces with high efficiency.
The basic principle of Electropolishing is the same as that of chemical polishing, that is, by selectively dissolving the small protruding parts on the surface of the material, the surface is smooth. Compared with chemical polishing, it can eliminate the influence of cathodic reaction and achieve better results.
Place the workpiece in an abrasive suspension and place it together in an ultrasonic field, relying on the oscillation effect of the ultrasonic wave to grind and polish the abrasive on the surface of the workpiece. Ultrasonic machining has low macroscopic force and will not cause deformation of the workpiece, but it is difficult to make and install 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 uniform; The cavitation effect of ultrasound in liquids can also suppress the corrosion process, which is conducive to surface brightening.
It relies on the high-speed flow of liquid and its carried abrasive particles to wash the surface of the workpiece to achieve polishing. Common methods include abrasive jet machining, liquid jet machining, Fluid power grinding, etc. Fluid power grinding is driven by hydraulic pressure, which makes the liquid medium carrying abrasive particles flow back and forth across the workpiece surface at a high speed. The medium is mainly made of special compounds (usually polymer like substances) with good flowability under low pressure and mixed with abrasives, which can be silicon carbide powder.
Magnetic abrasive polishing is the use of magnetic abrasives to form abrasive brushes under the action of a magnetic field, which grind and process workpieces. This method has high processing efficiency, good quality, easy control of processing conditions, and good working conditions.
2 The basic method of mechanical polishing in plastic mold processing differs greatly from the surface polishing required in other industries. To be precise, mold polishing should be referred to as mirror processing. 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 obtaining a bright surface.
2.1 In order to achieve high-quality polishing results in the basic mechanical polishing program, the most important thing is to have high-quality polishing tools and accessories such as oilstones, sandpaper, and diamond grinding paste. The selection of polishing program depends on the surface condition after the initial processing, such as machining, Electrical discharge machining, grinding, etc. The general process of mechanical polishing is as follows:
（1）The surface after rough polishing, milling, electric discharge, grinding, and other processes can be polished using a rotating surface polishing machine or ultrasonic grinding machine at a rotational speed. Afterwards, manual oilstone grinding was carried out, and strip shaped oilstones were added with kerosene as a lubricant or coolant.
（2）Semi precision polishing mainly uses sandpaper and kerosene.
（3）Fine polishing mainly uses diamond grinding paste.
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