1.1 Mechanical Polishing

Mechanical polishing is by cutting, material surface plastic deformation removed after polishing convex and smooth surface polishing method, generally use the whetstone strip, wool wheel, sandpaper, etc., mainly manual operation, special parts such as the surface of the rotary body, can use the rotary table and other auxiliary tools, surface quality requirements can be high by super finishing polishing method. Super finishing polishing is the use of special grinding tools, containing abrasive polishing liquid, pressed on the workpiece is processed on the surface, for high-speed rotation. The surface roughness of Ra0.008μm can be achieved by this technique, which is the highest among various polishing methods. This method is often used in optical lens molds.

1.2 Chemical Polishing

Chemical polishing is to make the material in the chemical medium surface of the micro convex part of the dissolution of the concave part, so as to get 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 workpiece at the same time, high efficiency. The core problem of chemical polishing is the preparation of polishing fluid. The surface roughness obtained by chemical polishing is generally 10 μm.

1.3 Electrolytic Polishing

The basic principle of electrolytic polishing is the same as that of chemical polishing, that is, it makes the surface smooth by selectively dissolving small protruding parts on the surface of the material. Compared with chemical polishing, the effect of cathode reaction can be eliminated and the effect is better. The electrochemical polishing process is divided into two steps:

(1) The solution products of macroscopic leveling were diffused into the electrolyte, and the geometrical roughness of the material surface decreased, Ra > 1μm.

(2) The anode polarization of low level flat, surface brightness increased, Ra < 1μm.

1.4 Ultrasonic Polishing

The workpiece is put into the abrasive suspension and placed in the ultrasonic field. The abrasive is grinding and polishing on the workpiece surface depending on the oscillation of the ultrasonic wave. Ultrasonic machining macroscopic force is small, will not cause workpiece deformation, but tooling production and installation is more difficult. Ultrasonic processing can be combined with chemical or electrochemical methods. On the basis of solution corrosion and electrolysis, ultrasonic vibration is applied to stir the solution, so that the workpiece surface dissolves the product, and the corrosion or electrolyte near the surface is uniform; Ultrasonic cavitation in the liquid can also inhibit the corrosion process, conducive to surface lighting.

1.5 Fluid Polishing

Fluid polishing relies on the high speed flowing liquid and the abrasive particles it carries to wash the workpiece surface to achieve the purpose of polishing. Common methods are: abrasive jet machining, liquid jet machining, hydrodynamic grinding, etc. Hydrodynamic lapping is driven by hydraulic pressure to make the liquid medium carrying abrasive particles flow through the workpiece surface at high speed. The medium is mainly made of special compounds (polymer-like substances) with good flow under low pressure and mixed with abrasive, abrasive can be made of silicon carbide powder.

1.6 Magnetic grinding and polishing

Magnetic grinding polishing is the use of magnetic abrasives under the action of magnetic field formed abrasive brush, grinding workpiece. This method has high processing efficiency, good quality, easy to control processing conditions and good working conditions. With suitable abrasive, the surface roughness can reach Ra0.1μm.

The polishing said in the processing of plastic molds is very different from the surface polishing required in other industries. Strictly speaking, the polishing of molds should be called mirror processing. It not only has high requirements for polishing itself but also has high standards for surface smoothness, smoothness and geometric accuracy. Surface polishing generally requires only a polished surface. The standard of mirror processing is divided into four levels: AO= Ra0.008μm, A1= Ra0.016μm, A3= Ra0.032μm, A4= Ra0.063μm. Because electrolytic polishing, fluid polishing and other methods are difficult to accurately control the geometric accuracy of parts, The surface quality of chemical polishing, ultrasonic polishing, magnetic grinding polishing and other methods can not meet the requirements, so the mirror processing of precision mold is mainly mechanical polishing.