We often say that stainless steel parts need to be polished. Why should stainless steel be polished? Stainless steel polishing technologies include mechanical polishing, chemical polishing, electrolytic polishing, ultrasonic polishing, fluid polishing and magnetic abrasive polishing.
1. Mechanical polishing
Mechanical polishing is a polishing method to obtain a smooth surface by cutting and removing the convex parts after polishing due to plastic deformation of the material surface. Generally, oilstone strips, wool wheels, sandpaper, etc. are used. Manual operation is the main method. For special parts such as rotary surfaces, turntables and other auxiliary tools can be used. For those with high surface quality requirements, ultra precision polishing can be used. Super precision polishing is to use special abrasive tools, which are pressed on the surface of the workpiece in the polishing fluid containing abrasives to rotate at a high speed. The surface roughness of Ra0.008um can be achieved by using this technology, which is the highest among various polishing methods. This method is often used for optical lens molds.
2. Chemical polishing
Chemical polishing is to make the material dissolve preferentially in the concave part of the surface micro convex 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, and can polish workpieces with complex shapes. It can also polish many workpieces at the same time, with high efficiency. The core problem of chemical polishing is the preparation of polishing solution. The surface roughness obtained by chemical polishing is generally 10 um.
3. Electrolytic polishing
The basic principle of electrolytic polishing is the same as that of chemical polishing, that is, by selectively dissolving the small protruding parts of the material surface, the surface is smooth. Compared with chemical polishing, it can eliminate the influence of cathodic reaction and has better effect. The electrochemical polishing process is divided into two steps:
(1) The macro leveling solution product diffuses into the electrolyte, and the geometric roughness of the material surface decreases, with Ra>1um.
(2) Low light level, anodized, surface brightness improved, Ra<1um.
4. Ultrasonic polishing
The workpiece is put into the abrasive suspension and placed together in the ultrasonic field, and the abrasive is ground and polished on the surface of the workpiece by the vibration of the ultrasonic. Ultrasonic machining has small macro 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 ultrasonic wave in liquid can also inhibit the corrosion process, which is conducive to surface brightening.
5. Fluid polishing
Fluid polishing is to achieve the purpose of polishing by washing the workpiece surface with high-speed flowing liquid and abrasive particles carried by it. Common methods include abrasive jet machining, liquid jet machining, hydrodynamic grinding, etc. Hydrodynamic lapping is driven by hydraulic pressure, which makes the liquid medium carrying abrasive particles flow back and forth across the workpiece surface at high speed. The medium is mainly made of special compounds (polymer like substances) with good flowability under low pressure and mixed with abrasives, which can be silicon carbide powder.
6. 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 high processing efficiency, good quality, easy control of processing conditions and good working conditions. With proper abrasive, the surface roughness can reach Ra0.1um.
The polishing in plastic mold processing is very different from the surface polishing required in other industries. Strictly speaking, mold polishing should be called mirror processing. It not only has high requirements for polishing itself, but also has high standards for surface flatness, smoothness and geometric accuracy. Generally, surface polishing only requires obtaining a bright surface. The standard of mirror processing is divided into four levels: AO=Ra0.008L m, A1=Ra0.016um, A3=Ra0.032um, A4=Ra0.063um. Since it is difficult to accurately control the geometric accuracy of parts by electrolytic polishing, fluid polishing and other methods, and the surface quality of chemical polishing, ultrasonic polishing, magnetic abrasive polishing and other methods cannot meet the requirements, the mirror processing of precision molds is mainly mechanical polishing.
