There are two main purposes of polishing the mold. One is to increase the brightness and appearance of the plastic mold. The second is to make the mold easy to demold. When polishing, rough oilstone is generally used to roughen the surface of the machined mold cavity to remove the knife marks of the machine tool, and then use fine oilstone to polish to remove the coarse oilstone to reach the traces, and then use the finer Sandpaper polishes the surface polished by the fine oilstone, and then uses polishing paste or abrasive paste to polish and polish the surface of the mold cavity to achieve a mirror-like effect.
In daily life, our common plastic molds have six polishing methods:
1. Mechanical polishing
Mechanical polishing is a polishing method that relies on cutting and plastic deformation of the material surface to remove the polished protrusions to obtain a smooth surface. Generally, oil stone sticks, wool wheels, sandpaper, etc. are used, and manual operations are the main method. Special parts such as the surface of the rotating body can be used. Use the turntable and other auxiliary tools, and the ultra-precision polishing method can be used if the surface quality is high. Ultra-precision polishing is the use of special abrasive tools, which are pressed against the processed surface of the workpiece in a polishing liquid containing abrasives for high-speed rotation. The surface roughness of Ra0.008μm can be achieved by using this technology, which is among various polishing methods. Optical lens molds often use this method.
2. Chemical polishing
Chemical polishing is to make the surface microscopic convex part of the material in the chemical medium dissolve preferentially than the concave part, thereby obtaining a smooth surface. The main advantage of this method is that it does not require complicated equipment, 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 polishing liquid. The surface roughness obtained by chemical polishing is generally several 10 μm.
3. Electrolytic polishing
Electrolytic polishing is basically the same as chemical polishing, that is, by selectively dissolving tiny protrusions on 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) The macroscopic leveling dissolved product diffuses into the electrolyte, and the geometric roughness of the material surface decreases, Ra>1μm.
(2) Low-light leveling anode polarization, improved surface brightness, Ra<1μm.
4. Ultrasonic polishing
Put the workpiece into the abrasive suspension and put it together in the ultrasonic field, relying on the oscillation effect of the ultrasonic, so that the abrasive is ground and polished on the surface of the workpiece. Ultrasonic machining has a small macroscopic force and will not cause deformation of the workpiece, but it is difficult to manufacture and install 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, so that the dissolved product on the surface of the workpiece is separated, and the corrosion or electrolyte near the surface is uniform; the cavitation effect of ultrasonic in the liquid can also inhibit the corrosion process and facilitate surface brightening.
5. Fluid throw
Fluid polishing relies on high-speed flowing liquid and the abrasive particles carried by it to wash the surface of the workpiece to achieve the purpose of polishing. Commonly used methods are: abrasive jet processing, liquid jet processing, hydrodynamic grinding and so on. Hydrodynamic grinding is driven by hydraulic pressure to make the liquid medium carrying abrasive particles flow back and forth across the surface of the workpiece at high speed. The medium is mainly made of special compounds (polymer-like substances) with good flowability under lower pressure and mixed with abrasives. The abrasives can be made of silicon carbide powder.
6. Magnetic grinding and polishing
Magnetic abrasive polishing is to use magnetic abrasives to form abrasive brushes 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. Using suitable abrasives, the surface roughness can reach Ra0.1μm.