Preliminary analysis on the design of plastic extrusion die

When polishing, it is generally used to roughen the surface of the machined mold cavity with coarse oil stone, polish the knife mark of the machine and add the tool, and then use the fine oil stone to polish the trace of the rough stone, and then use it. The fine sandpaper is used to polish the polished surface of the fine stone. Finally, the surface of the cavity of the mold is polished and polished by polishing paste or abrasive paste, and finally the effect of brightness is mirrored.

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

Mechanical polishing

Mechanical polishing is a polishing method that removes the polished convex portion by plastic deformation on the surface of the material to obtain a smooth surface. Generally, oil stone strips, wool wheels, sandpaper, etc. are used, which are mainly manual operations, and special parts such as the surface of the rotating body can be used. Using an auxiliary tool such as a turntable, the method of super-fine polishing can be used with high surface quality requirements.

Ultra-fine grinding and polishing is a special-purpose grinding tool. In the polishing liquid containing abrasive, it is pressed against the machined surface to perform high-speed rotary motion. With this technology, a surface roughness of Ra0.008 μm can be achieved, which is the highest among various polishing methods. This method is often used in optical lens molds.

2. Chemical polishing

Chemical polishing is a process in which a portion of a material that is microscopically convex in a chemical medium is preferentially dissolved in a concave portion to obtain a smooth surface. The main advantage of this method is that it can polish a workpiece with complex shapes without complicated equipment, and can polish many workpieces at the same time with high efficiency. The core issue of chemical polishing is the formulation of the polishing fluid. The surface roughness obtained by chemical polishing is generally several 10 μm.

3. Electropolishing

Electropolishing is basically the same as chemical polishing, that is, by selectively dissolving tiny projections on the surface of the material to make the surface smooth. Compared with chemical polishing, the effect of the 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 decreases, Ra>1 μm;

(2) Low light leveling. Anodic polarization, surface brightness increased, Ra < 1 μm.

4. Ultrasonic polishing

The workpiece is placed in the abrasive suspension and placed together in the ultrasonic field, and the abrasive is ground and polished on the surface of the workpiece by the vibration of the ultrasonic wave. Ultrasonic machining has a small macroscopic force and does not cause deformation of the workpiece, but it is difficult to manufacture and install the 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 to dissociate the dissolved products on the surface of the workpiece, and the corrosion or electrolyte near the surface is uniform. The cavitation of the ultrasonic wave in the liquid can also inhibit the corrosion process and facilitate surface illuminating.

5. Fluid polishing

Fluid polishing relies on high-speed flowing liquid and abrasive particles carried by it to wash the surface of the workpiece for polishing. Common methods include: abrasive jet processing, liquid jet processing, hydrodynamic grinding, and the like.

Hydrodynamic grinding is driven hydraulically to allow the liquid medium carrying the abrasive particles to flow back and forth across the surface of the workpiece at high speed. The medium is mainly made of a special compound (polymeric substance) which flows at a relatively low pressure and is doped with an abrasive, and the abrasive can be made of silicon carbide powder.

6. Magnetic grinding and polishing

Magnetic grinding and polishing is the use of magnetic abrasive to form an abrasive brush 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 a suitable abrasive, the surface roughness can reach Ra 0.1 μm.