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Plastic mold material selection

update:16-11-2018
abstract:

The working condition of the plastic mold is different […]

The working condition of the plastic mold is different from that of the cold die. Generally, it must be operated at 150 °C-200 °C. In addition to being subjected to a certain pressure, it must also withstand the temperature influence. According to the different conditions and processing methods of plastic molding dies, the basic performance requirements of steel for plastic molds are roughly summarized as follows:

1. Sufficient surface hardness and wear resistance

The hardness of the plastic mold is usually below 50-60HRC, and the heat-treated mold should have sufficient surface hardness to ensure that the mold has sufficient rigidity. In the work, the mold is subjected to large compressive stress and friction due to the filling and flowing of the plastic, and the mold is required to maintain the accuracy of the shape and the stability of the dimensional accuracy. ** The mold has a sufficient service life. The wear resistance of the mold depends on the chemical composition of the steel and the heat treatment hardness, so increasing the hardness of the mold is beneficial to improve its wear resistance.

2, excellent machinability

Most plastic molding dies require a certain amount of cutting and fitter repair in addition to EMD processing. In order to prolong the service life of the cutting tool, improve the cutting performance, and reduce the surface roughness, the hardness of the steel for the plastic mold must be appropriate.

3, good polishing performance

High-quality plastic products require a small roughness value on the surface of the cavity. For example, the surface roughness value of the injection molding cavity is required to be less than Ra 0.1 to 0.25, and the optical surface is required to be Ra < 0.01 nm. The cavity must be polished to reduce the surface roughness value. The steel material selected for this purpose requires less material impurities, fine uniformity of the structure, no fiber orientation, and no pitting or orange peel defects during polishing.

4, good thermal stability

The shape of the parts of the plastic injection mold is often complicated, and it is difficult to process after quenching. Therefore, it should be selected with good thermal stability. When the mold is formed by heat treatment, the linear expansion coefficient is small, the heat treatment deformation is small, and the dimensional difference caused by the temperature difference The rate is small, the metallographic structure and mold dimensions are stable, and can be reduced or ** processed, which can be ** mold dimensional accuracy and surface roughness requirements.

45, 50 grade carbon steel has a certain strength and wear resistance, and is mostly used for formwork materials after quenching and tempering treatment. High carbon tool steel and low alloy tool steel have high strength and wear resistance after heat treatment, and are mostly used for forming parts. However, high carbon tool steel is only suitable for the manufacture of molded parts with small size and simple shape due to its large heat treatment deformation.

With the development of the plastics industry, the complexity and precision of plastic products are becoming more and more demanding, and higher requirements are also placed on the mold materials. For the production of complex, precise and corrosion-resistant plastic molds, pre-hardened steel (such as PMS), corrosion-resistant steel (such as PCR) and low-carbon maraging steel (such as 18Ni-250) can be used. Machining, heat treatment and polishing performance and high strength.