Introduction to several commonly used polishing methods

The currently used polishing methods are as follows:

1.1 Mechanical polishing

Mechanical polishing is a polishing method that removes the polished convex portion by plastic deformation on the surface of the material to obtain a smooth surface. Generally, oil stone strips, wool wheels, sandpaper, etc. are used, which are mainly manual operations, and special parts such as the surface of the rotating body can be used. Using an auxiliary tool such as a turntable, the method of super-fine polishing can be used with high surface quality requirements. Ultra-fine grinding and polishing is a special-purpose grinding tool. In the polishing liquid containing abrasive, it is pressed against the machined surface to perform high-speed rotary motion. With this technology, a surface roughness of Ra0.008 μm can be achieved, which is the highest among various polishing methods. This method is often used in optical lens molds.

1.2 Chemical polishing

Chemical polishing is a process in which a portion of a material that is microscopically convex in a chemical medium is preferentially dissolved in a concave portion to obtain a smooth surface. The main advantage of this method is that it can polish a workpiece with complex shapes without complicated equipment, and can polish many workpieces at the same time with high efficiency. The core issue of chemical polishing is the formulation of the polishing fluid. The surface roughness obtained by chemical polishing is generally several 10 μm.

1.3 Electropolishing

The basic principle of electropolishing is the same as chemical polishing, which is to selectively dissolve the surface of the material to make the surface smooth. Compared with chemical polishing, the effect of the cathode reaction can be eliminated, and the effect is better. The electrochemical polishing process is divided into two steps:

(1) The macro-leveling dissolved product diffuses into the electrolyte, and the surface roughness of the material decreases, Ra > 1 μ m.

(2) The low light leveling anodic polarization increases the surface brightness, Ra < 1 μ m.

1.4 Ultrasonic polishing

The workpiece is placed in an abrasive suspension and placed together in an ultrasonic field, and the abrasive is ground and polished on the surface of the workpiece by the action of ultrasonic waves. Ultrasonic machining has a small macroscopic force and does not cause deformation of the workpiece, but it is difficult to manufacture and install the tooling. 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 to dissociate the dissolved products on the surface of the workpiece, and the corrosion or electrolyte near the surface is uniform. The cavitation of the ultrasonic wave in the liquid can also inhibit the corrosion process and facilitate surface illuminating.

1.5 fluid polishing

Fluid polishing relies on high-speed flowing liquid and abrasive particles carried by it to wash the surface of the workpiece for polishing purposes. Common methods include: abrasive jet processing, liquid jet processing, hydrodynamic grinding, and the like. Hydrodynamic grinding is driven hydraulically to allow the liquid medium carrying the abrasive particles to flow back and forth across the surface of the workpiece at high speed. The medium is mainly made of a special compound (polymeric substance) which flows at a relatively low pressure and is doped with an abrasive, and the abrasive can be made of silicon carbide powder.

1.6 Magnetic Abrasive Polishing

Magnetic grinding and polishing is the use of magnetic abrasive to form an abrasive brush under the action of a magnetic field to grind the workpiece. This method has high processing efficiency, good quality, easy control of processing conditions and good working conditions. With a suitable abrasive, the surface roughness can reach Ra 0.1 μ m.

The polishing described in plastic mold processing is very different from the surface polishing required in other industries. Strictly speaking, the polishing of the mold should be called mirror processing. Not only does it have high requirements for polishing itself, but it also has a high standard for surface flatness, smoothness and geometric accuracy. Surface polishing generally requires only a shiny surface. The standard for mirror processing 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, due to electropolishing, fluid polishing, etc. It is difficult to accurately control the geometric accuracy of parts, and the surface quality of chemical polishing, ultrasonic polishing, magnetic polishing and other methods can not meet the requirements, so the mirror processing of precision molds is mainly based on mechanical polishing.

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