There are two main purposes of polishing the mold, one is to increase the brightness and beauty of the plastic mold. The second is to make the mold easy to demould. When polishing, generally use a coarse oil stone to roughly grind the surface of the machined mold cavity to remove the knife marks of the machining tool, and then use a fine oil stone to polish the traces of the coarse oil stone, and then use a fine oil stone Sandpaper is used to polish the surface polished by fine oilstone, and finally use polishing paste or abrasive paste to perform final fine polishing on the cavity surface of the mold, and finally achieve the effect of being as bright as a mirror. horizontal honing machine.
In daily life, there are six polishing methods for our common plastic molds:
1. Mechanical polishing
Mechanical polishing is a method of polishing to obtain a smooth surface by cutting and plastically deforming the surface of the material to remove the polished convex part. Generally, oil stone strips, wool wheels, sandpaper, etc. are used. Using auxiliary tools such as turntables, ultra-fine grinding and polishing methods can be used for high surface quality requirements. Ultra-fine polishing is to use a special abrasive tool, which is pressed tightly on the surface of the workpiece to be processed in the polishing liquid containing abrasives, and performs high-speed rotating motion. Using 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 is to make the microscopic convex part of the surface of the material dissolve preferentially compared with the concave part in the chemical medium, so as to obtain a smooth surface. The main advantage of this method is that it does not require complex 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 fluid. The surface roughness obtained by chemical polishing is generally several 10 μm.
Electrolytic polishing is basically the same as chemical polishing, that is, to make the surface smooth by selectively dissolving the tiny protrusions on the surface of the material. Compared with chemical polishing, it can eliminate the influence of cathode reaction, and the effect is better. The electrochemical polishing process is divided into two steps:
(1) The dissolved product of macroscopic leveling diffuses into the electrolyte, and the geometric roughness of the surface of the material decreases, Ra>1μm.
(2) Twilight smooth anodic polarization, improved surface brightness, Ra<1μm.
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 relying on the oscillation of the ultrasonic wave. Ultrasonic machining has a small macroscopic 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, so that the dissolved products on the surface of the workpiece are separated, 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 surface brightening.
5. Fluid throwing
Fluid polishing relies on the high-speed flowing liquid and the abrasive particles carried to scour the surface of the workpiece to achieve the purpose of polishing. Commonly used methods are: abrasive jet processing, liquid jet processing, hydrodynamic grinding, etc. Hydrodynamic grinding is driven by hydraulic pressure, so that the liquid medium carrying abrasive particles flows back and forth across the surface of the workpiece at high speed. The medium is mainly made of a special compound (polymer-like substance) with good flowability under relatively low pressure and mixed with abrasives, and the abrasives can be silicon carbide powder.
6. Magnetic grinding and polishing
Magnetic grinding and 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. With suitable abrasives, the surface roughness can reach Ra0.1μm.