Six common polishing methods for plastic molds

- Apr 17, 2018-

The purpose of polishing the mold is mainly two:          One is to increase the brightness and aesthetics of plastic molds;          The second is to make the mold easier to release.          In the polishing process, the rough surface of the cavity of the machined mold cavity is roughly roughened with a rough oilstone, and the tool marks are ground to add the tool marks, and then the fine oilstone is used to polish the traces of the rough stone and then used again. Fine sandpaper polishes the polished surface of the fine whetstone, and finally polishes the surface of the cavity of the mold with a polishing paste or an abrasive paste, and finally achieves a bright, mirror-like effect. In daily life, there are six common plastic mold polishing methods:1.Mechanical polishing             Mechanical polishing is a polishing method in which a smooth surface is obtained by removing a convex portion after being polished by plastic deformation of a cutting surface or a material surface. Generally, an oil stone bar, a wool wheel, and a sandpaper are used, and a manual operation is mainly used, and a special part such as a surface of a rotating body can be used. Using an auxiliary tool such as a turntable, a high-precision surface polishing method can be used. Ultra-precision polishing is the use of special grinding tools, in the grinding liquid containing abrasive, pressed on the workpiece surface is processed for high-speed rotary motion. The use of this technology can achieve a surface roughness of Ra0.008μm, which is the highest among various polishing methods. Optical lens molds often use this method.

2. Chemical polishing              Chemical polishing preferentially dissolves the relatively concave portions of the material microscopically protruding from the surface of the chemical medium, thereby obtaining a smooth surface. The main advantage of this method is that it does not require complicated equipment, it can polish workpieces with complex shapes, and can polish many workpieces at the same time with high efficiency. The core problem of chemical polishing is the preparation of a polishing liquid. The surface roughness obtained by chemical polishing is generally 10 μm.

3. Electropolishing            Electropolishing is basically the same as chemical polishing, that is, by selectively dissolving tiny protruding portions of the surface of the material to make the surface smooth. 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) Macro leveling. The dissolved product diffuses into the electrolyte and the surface roughness of the material decreases, Ra>1μm;             (2) Smooth glare. Anodic polarization, surface brightness, Ra <1μm.4. Ultrasonic polishing             The workpiece is placed in an abrasive suspension and placed in an ultrasonic field together, and the abrasive is ground and polished on the workpiece surface by virtue of the ultrasonic vibration. Ultrasonic machining has a low macroscopic force and does not cause deformation of the workpiece, but it is difficult to make and install tooling.             Ultrasonic processing can be combined with chemical or electrochemical methods. On the basis of solution corrosion and electrolysis, ultrasonic vibrating agitation solution is applied to remove the dissolved products on the surface of the workpiece and the corrosion or electrolyte near the surface is uniform. The cavitation effect of ultrasonic waves in the liquid can also inhibit the corrosion process and facilitate the surface brightening.

5. Fluid polishing            Fluid polishing relies on the high-speed flow of liquid and the abrasive particles it carries to flush the surface of the workpiece for polishing purposes. Common methods are: abrasive jet machining, liquid jet machining, fluid power grinding and so on.           Hydrodynamic grinding is driven by hydraulic pressure so that the liquid medium carrying the abrasive particles reciprocates across the surface of the workpiece at high speed. The medium is mainly made of a special compound (polymer-like material) that flows at a relatively low pressure and is made of an abrasive material. Silicon carbide powder may be used as the abrasive.6. Magnetic Abrasive Polishing             Magnetic abrasive polishing is the use of magnetic abrasives to form abrasive brushes under the action of a magnetic field, grinding workpieces. This method has high processing efficiency, good quality, easy control of processing conditions and good working conditions. With suitable abrasives, the surface roughness can reach Ra 0.1 μm.