The basic procedure of plastic mold polishing In order to obtain high-quality polishing effect, the most important thing is to have
High-quality polishing tools and auxiliary products such as whetstone, sandpaper and diamond lapping paste.
The general process of plastic mold polishing is as follows:
Diamond polishing paste is mainly used for fine polishing. If the polishing cloth wheel is mixed with diamond abrasive powder or abrasive paste for polishing, the usual polishing order is 9μm (#1800) ~ 6μm (#3000) ~ 3μm (#8000). 9μm diamond abrasive paste and polishing cloth wheel can be used to remove the hair-like wear marks left by #1200 and #1500 sandpaper. Then use sticky felt and diamond polishing paste for polishing, the order is 1μm (#14000) ~ 1/2μm (#60000) ~ 1/4μm (#100000). The polishing process with an accuracy requirement of 1μm or more (including 1μm) can be carried out in a clean polishing room in the mold processing workshop. For more precise polishing, an absolutely clean space is necessary. Dust, smoke, dandruff and saliva can all scrap the high-precision polished surface obtained after hours of work.
After milling, EDM, grinding, etc., the surface can be polished with a rotating surface polisher or ultrasonic grinder with a speed of 35 000-40 000 rpm. The commonly used method is to remove the white EDM layer with wheels with diameter Φ3mm and WA # 400. Then there is manual whetstone grinding, and the strips of whetstone are added with kerosene as a lubricant or coolant. The general order of use is #180 ~ #240 ~ #320 ~ #400 ~ #600 ~ #800 ~ #1000. Many mold manufacturers choose to start with #400 in order to save time.
Semi-precision polishing mainly uses sandpaper and kerosene. The number of sandpaper is: #400 ~ #600 ~ #800 ~ #1000 ~ #1200 ~ #1500. In fact, #1500 sandpaper only uses die steel suitable for hardening (above 52HRC), not pre-hardened steel, because it may cause burns on the surface of pre-hardened steel parts.
Use abrasive paste for fine polishing, 8000, 10000 will reach the mirror surface
Plastic Mould Polishing Method
Mechanical polishing is a polishing method that relies on cutting and plastic deformation of the material surface to remove the polished convex parts 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 tightly on the processed surface of the workpiece in a polishing fluid containing abrasives for high-speed rotation. Using this technology, the surface roughness of Ra0.008μm can be achieved, which is the highest among various polishing methods. Optical lens molds often use this method.
Chemical polishing is to make the surface microscopic convex part of the material in the chemical medium dissolve preferentially than the concave part, 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 liquid. The surface roughness obtained by chemical polishing is generally several 10 μm.
The basic principle of electrolytic polishing is the same as that of 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) Macroscopic leveling The dissolved products diffuse into the electrolyte, and the geometric roughness of the material surface decreases, Ra>1μm.
- ⑵ Low-light leveling: Anode polarization, surface brightness is improved, Ra<1μm.
Put the workpiece in 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 products on the surface of the workpiece are 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.
Fluid polishing relies on high-speed flowing liquid and 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.
F.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. 2 Mechanical polishing based on this method The polishing mentioned in the processing of plastic molds is very different from the surface polishing required in other industries. Strictly speaking, the polishing of the mold should be called mirror finishing. It not only has high requirements for polishing itself, but also has high standards for surface flatness, smoothness and geometric accuracy. Surface polishing generally only requires a bright surface. The standard of mirror surface processing is divided into four levels: AO=Ra0.008μm, A1=Ra0.016μm, A3=Ra0.032μm, A4=Ra0.063μm. It is difficult to precisely control the geometric accuracy of parts due to methods such as electrolytic polishing and fluid polishing. However, the surface quality of chemical polishing, ultrasonic polishing, magnetic abrasive polishing and other methods are not up to the requirements, so the mirror processing of precision molds is still mainly mechanical polishing.
To obtain high-quality polishing results, the most important thing is to have high-quality polishing tools and auxiliary products such as oilstone, sandpaper and diamond paste. The choice of polishing procedure depends on the surface condition after pre-processing, such as machining, EDM, grinding and so on.