With the widespread use of plastic products, such as daily necessities and beverage packaging containers, the appearance of the need to often require the plastic mold cavity surface to achieve the degree of mirror polishing. The production of optical lenses, CD-ROM and other mold surface roughness requirements are extremely high, so the requirements of the polishing is also very high.
Polishing not only increases the appearance of the workpiece, but also to improve the corrosion of the surface of the material, wear resistance, but also can make the mold has other advantages, such as plastic products easy to mold, reduce the production of injection cycle. So polishing in the plastic mold making process is a very important process.
Plastic mold working conditions and cold stamping die, generally in the 150 degrees Celsius to two hundred degrees Celsius to work, in addition to a certain pressure, but also to withstand the temperature. Is based on the use of plastic molding mold conditions, different processing methods will be the basic performance of plastic mold with steel generally summarized as follows:
First, excellent cutting workability
Most of the plastic molding die, in addition to EMD processing outside the need for a certain degree of cutting and fitter repair. To extend the life of cutting tools, enhance the cutting performance, reduce surface roughness, plastic mold steel hardness must be appropriate.
Second, good thermal stability
Plastic injection mold parts of the shape is often more complex, difficult to process after quenching, it should try to use a good thermal stability, when the two-color mold forming heat treatment after the small coefficient of linear expansion, heat treatment deformation, temperature differences caused by the size The rate of change is small, the microstructure and mold size is stable, can be reduced or no longer processing, you can ensure that the mold size and surface roughness requirements.
Third, good polishing performance
High-quality two-color injection molding plastic products, requiring cavity surface roughness value is small. For example, the surface roughness value of the injection mold cavity is less than the level of Ra0.1 ~ 0.25, the optical surface requires Ra <0.01nm, the cavity must be polished to reduce the surface roughness value. The steel used for this purpose requires less material impurities, the organization of fine uniform, no fiber direction, polishing should not appear pitting or orange peel-like defects.
Fourth, enough surface hardness and wear resistance
The hardness of the plastic mold is usually below 50-60 HRC. The heat treated mold should have sufficient surface hardness to ensure that the mold has sufficient rigidity. Mold in the work due to the filling and flow of plastic to withstand greater compressive stress and friction, the mold to maintain the shape of the accuracy and dimensional accuracy of the stability, to ensure that the mold has sufficient service life. Mold wear resistance depends on the chemical composition of steel and heat treatment hardness, so enhance the hardness of the mold is conducive to enhancing its wear resistance.
Five, 50 grades of carbon steel has a certain strength and wear resistance, after quenching and tempering treatment for the mold material. High-carbon tool steel, low-alloy tool steel after heat treatment has a high strength and wear resistance, and more for forming parts. However, high-carbon tool steel due to its heat treatment deformation, only for the manufacture of small size, simple shape of the molding parts.
With the development of the plastics industry, the complexity of plastic products, precision and other requirements are getting higher and higher, the two-color injection mold material also put forward higher requirements. For the manufacture of complex, precision and corrosion resistance of the plastic mold, can be used hard steel (such as PMS), corrosion-resistant steel (such as PCR) and low-carbon martensitic aging steel (such as 18Ni-250), have a good Cutting, heat treatment and polishing performance and high strength.
In addition, the choice of materials must also be considered to prevent abrasion and gluing, such as the existence of relative movement of the two surfaces, then try to avoid the choice of the same structure of the material, under special circumstances can be coated or nitrided, so that both sides have different The surface structure.