What are the common polishing methods for plastic molds?

2019-11-19

There are two main intentions for polishing the mold: one is to increase the gloss and aesthetics of the plastic mold; the other is to make the mold easier to demold.

When polishing, generally use rough whetstone to roughen the surface of the machined mold cavity, and then remove the marks of the machine tool, and then use fine whetstone to remove the rough whetstone marks, and then use Fine sandpaper is used to polish the surface of the fine oil stone, and finally the polishing cavity or polishing paste is used to polish the external appearance of the cavity of the mold to achieve the effect of shining like a mirror.

In daily life, there are six common ways of polishing plastic molds:

Mechanical polishing

Mechanical polishing is a polishing method that obtains a smooth surface by cutting and plastic deformation of the material's surface to remove the convex parts after polishing. Generally, you use whetstone strips, wool wheels, sandpaper, etc., mainly manual operations, and special parts such as rotating external surfaces can be used. The use of turntables and other auxiliary tools, the appearance of high quality requirements can choose the ultra-refined polishing method.

The ultra-precise grinding polishing is made of a specially-made grinding tool. In the grinding polishing liquid containing abrasives, it is pressed against the surface of the workpiece to be processed for high-speed rotation. Using this technology can reach Ra0.008μm surface roughness, which is higher among various polishing methods. Optical lens mold often chooses this method.

2. Chemical polishing

Chemical polishing is to allow the microscopic convex part of the material in the chemical medium to dissolve preferentially than the concave part, and then obtain a smooth surface. The first advantage of this method is that it does not require complex equipment, can polish workpieces with complex shapes, and can polish many workpieces together, with high efficiency. The core problem of chemical polishing is the manufacture of polishing liquid. The surface roughness obtained by chemical polishing is generally several tens of μm.

3. Electrolytic polishing

Electrolytic polishing is basically the same as chemical polishing, that is, by selectively dissolving the small protruding parts of the material surface 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 is reduced, Ra & gt; 1 μm;

(2) Low light leveling. Anodic polarization, appearance brightness improvement, Ra & lt; 1 μm.

4. Ultrasonic polishing

The workpiece is placed in the abrasive suspension and placed in an ultrasonic field together, and the abrasive is ground and polished on the surface of the workpiece depending on the ultrasonic vibration effect. Ultrasonic machining has a small macro force and does not cause workpiece deformation, but tooling production and installation are difficult.

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 to dissolve the surface of the workpiece. The corrosion or electrolyte near the surface is uniform; the cavitation effect of the ultrasonic wave in the liquid can also suppress the corrosion process, which is conducive to the brightening of the surface.

5. Fluid polishing

Fluid polishing is based on the intention of the high-speed flowing liquid and the abrasive particles carried by it to scour the surface of the workpiece to polish. Common methods are: abrasive eruption processing, liquid eruption processing, hydrodynamic grinding, etc.

Hydrodynamic grinding is driven by hydraulic pressure, which causes the liquid medium with abrasive particles to flow back and forth through the surface of the workpiece at high speed. The medium is mainly made of special compounds (polymer-like substances) that flow through under low pressure and mixed with abrasives. The abrasives can be silicon carbide powder.

6. Magnetic grinding and polishing

Magnetic grinding and polishing is the use of magnetic abrasives to form an abrasive brush under the effect of a magnetic field to grind the workpiece. This method has high processing efficiency, good quality, simple processing conditions and good working conditions. With suitable abrasives, the surface roughness can reach Ra0.1μm.

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