The injection moulds of plastic products made by injection moulding machines usually need to be 150 to 200 degrees Celsius in high temperature environment. Therefore, in the process of selecting raw materials, the injection moulds should be made with great attention. It will be late for the production and quality of life of the whole injection moulds and plastics products, so it plays an important role in choosing the injection moulding steel. Do materials need to meet performance requirements?
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Material Selection Principle of Injection Mold
Sufficient surface hardness and wear resistance
The hardness of injection moulds is generally below 50-60HRC. The heat treated moulds should have enough surface hardness to ensure that the moulds have enough rigidity. Because filling and flow injection moulding have to bear large compressive stress and friction in the work of the die, the die needs to maintain the stability of shape accuracy and dimension accuracy to ensure that the die has sufficient service life. The wear resistance of the die depends on the chemical composition of the steel and the hardness of the heat treatment.
Most injection moulds require cutting and fitter repairs in addition to EMD processing. In order to prolong tool life, improve cutting performance and reduce surface roughness, the hardness of injection steel must be appropriate.
Grade 50 carbon steel has a certain strength and wear resistance, and is often used as quenched and tempered die base material. High carbon tool steels and low alloy tool steels have high strength and wear resistance after heat treatment, which are mainly used for forming parts. However, high carbon tool steels have large deformation during heat treatment, and are only suitable for manufacturing small size and simple shape parts.
Good thermal stability
Injection mold parts are more complex in shape and difficult to quench, so it should be chosen to have good thermal stability as far as possible. After two-color forming, heat treatment can reduce or stop processing because of linear expansion coefficient, small heat treatment deformation, small temperature difference caused by change rate, stable microstructure and die size. The requirement of dimension accuracy and surface roughness of die is verified.
Good polishing performance
High quality two-color injection moulding products require small surface roughness of the cavity. For example, the surface roughness of injection mould cavity is less than ra0.1-0.25, and the optical surface is less than 0.01 nm. Cavity must be polished to reduce surface roughness. For this reason, the steel selected has few impurities, uniform structure, no fiber direction, and should not appear pitting or orange peel defects when polishing.
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