There are two main purposes for polishing molds:

One is to increase the brightness and aesthetics of plastic molds;

The second is to make the mold easier to demould.

When polishing, a coarse oilstone is usually used to roughly polish the surface of the machined mold cavity, removing the tool marks from the machining tool. Then, a fine oilstone is used to polish the traces of the coarse oilstone. Then, a fine sandpaper is used to polish the surface after the fine oilstone has been polished. Finally, a polishing paste or grinding paste is used to perform the final fine polishing and polishing on the surface of the mold cavity, achieving a shiny mirror like effect.

In daily life, there are six common polishing methods for plastic molds:

1. Mechanical polishing

Mechanical polishing is a polishing method that obtains a smooth surface by removing the convex parts after polishing through cutting and plastic deformation of the material surface. It generally uses oilstone strips, wool wheels, sandpaper, etc., and is mainly manually operated. Special parts such as the surface of the rotating body can use auxiliary tools such as a turntable. For high surface quality requirements, ultra precision polishing can be used.

Ultra precision polishing is the use of specially designed grinding tools, which are tightly pressed onto the machined surface of the workpiece in a polishing fluid containing abrasives and perform high-speed rotational motion. By utilizing this technology, Ra0.008 can be achieved μ The surface roughness of m is the highest among various polishing methods. This method is often used in optical lens molds.

2. Chemical polishing

Chemical polishing is the process of allowing materials to preferentially dissolve the micro protruding parts of the surface in a chemical medium, resulting in a smooth surface. The main advantage of this method is that it does not require complex equipment and can polish workpieces with complex shapes. It can simultaneously polish many workpieces with high efficiency. The core issue of chemical polishing is the preparation of polishing solution. The surface roughness obtained by chemical polishing is generally in the order of 10 μ M.

3. Electropolishing

Electropolishing is basically the same as chemical polishing, that is, by selectively dissolving the small protruding parts on the surface of the material to make the surface smooth. Compared with chemical polishing, it can eliminate the influence of cathodic reaction and achieve better results. The electrochemical polishing process is divided into two steps:

(1) Macro leveling. Dissolved products diffuse into the electrolyte, resulting in a decrease in the geometric roughness of the material surface, with Ra>1 μ M;

(2) The shimmer is flat. Anodic polarization, increased surface brightness, Ra<1 μ M.

4. Ultrasonic polishing

Place the workpiece in an abrasive suspension and place it together in an ultrasonic field, relying on the vibration of the ultrasonic wave to grind and polish the abrasive on the surface of the workpiece. Ultrasonic machining has low 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 to separate the dissolved products on the surface of the workpiece, and the corrosion or electrolyte near the surface is uniform; The cavitation effect of ultrasound in liquids can also suppress the corrosion process, which is conducive to surface brightening.

5. Fluid polishing

Fluid polishing is achieved by flushing the surface of a workpiece with high-speed flowing liquid and its carried abrasive particles. Common methods include abrasive jet machining, liquid jet machining, Fluid power grinding, etc.

Fluid power grinding is driven by hydraulic pressure, which makes the liquid medium carrying abrasive particles flow back and forth across the workpiece surface at a high speed. The medium is mainly made of special compounds (polymer like substances) with good flowability under low pressure and mixed with abrasives, which can be silicon carbide powder.

6. Magnetic grinding and polishing

Magnetic abrasive polishing is the use of magnetic abrasives to form abrasive brushes under the action of a magnetic field to grind and process workpieces. 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 Ra0.1 μ M.