Plastic mould material requirements
Plastic mould working conditions and cold punching die is different, generally must be under 150 ° C to 200 ° C, except under certain pressure, and temperature effects.According to the different use conditions and processing methods of plastic mold, the basic performance requirements of steel for plastic mold are summarized as follows:
- Sufficient surface hardness and wear resistance
The hardness of the plastic mold is usually below 50-60hrc, and the molds after heat treatment should have enough surface hardness to ensure that the mold has enough stiffness.Due to the plastic filling and flow in the work of the mold to bear large compressive stress and friction, mold to maintain the shape of the accuracy and dimensional accuracy of the stability, ensure that the mold has enough life.The wear resistance of the mould depends on the chemical composition and heat treatment hardness of the steel.
2, excellent cutting processing
Most plastic molding molds, in addition to EMD processing, but also a certain amount of cutting and fitter repair.In order to extend the service life of cutting tools, improve cutting performance and reduce surface roughness, the hardness of steel used in plastic mold must be appropriate. - Good polishing performance
For high quality plastic products, the roughness of cavity surface is required to be small.For example, the injection mold cavity surface roughness value is required to be less than ra0.1-0.25 level, the optical surface is required to be Ra<0.01nm, the cavity must be polished to reduce the surface roughness value.For this selection of steel requires less impurities, microstructure uniform, no fiber direction, polishing should not appear pitting or orange peel defects. - Good thermal stability
Plastic injection mould parts shapes are more complex, difficult to process after quenching, so should choose as far as possible with good thermal stability, when the mould processing after the heat treatment for small linear expansion coefficient, heat treatment deformation is small, the size of the rate of change caused by the temperature difference is small, the microstructure and the mold size stability, can reduce or no longer carry on the processing, can guarantee the mold size accuracy and surface roughness requirements.
45, 50 grades of carbon steel has a certain strength and wear resistance, after the quenching and tempering treatment is mostly used for formwork materials.High carbon tool steels and low alloy tool steels have high strength and wear resistance after heat treatment.However, high carbon tool steels are only suitable for making small and simple shaped parts due to their large deformation during heat treatment.
With the development of the plastic industry, the requirements of the complexity and precision of the plastic products are higher and higher, and the requirements of the mould materials are also higher.For the manufacture of complex, precision and corrosion resistant plastic molds, prehardened steels (such as PMS), corrosion resistant steels (such as PCR) and low carbon martensitic aging steels (such as 18ni-250) can be used, with good cutting, heat treatment and polishing properties and high strength.
In addition, in the selection of materials should also be considered to prevent abrasion and gluing, such as the two surface there is relative movement, it is possible to avoid the choice of the same structure of the organization of the material, special conditions can be one side plating or nitriding, so that the two sides have a different surface structure.
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