The working conditions of plastic molds are different from those of cold stamping dies. Generally, they must work at 150°C-200°C. In addition to a certain pressure, they must also be affected by temperature. Jeward summarizes the basic performance requirements of plastic mold steel according to the use conditions and processing methods of plastic molding molds as follows.
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. Due to the filling and flow of plastic, the mold is required to bear large compressive stress and friction during work, and the mold is required to maintain the stability of shape accuracy and dimensional accuracy to ensure that the mold has a sufficient service life. The wear resistance of the mold depends on the chemical composition of the steel and the hardness of heat treatment, so increasing the hardness of the mold is beneficial to improve its wear resistance.
Most plastic molding molds require certain cutting processing and fitter repair in addition to EMD processing. In order to prolong the service life of cutting tools, improve cutting performance, and reduce surface roughness, the hardness of plastic mold steel must be appropriate.
High-quality plastic injection mold products require a small roughness value on the surface of the cavity. For example, the surface roughness value of the injection mold cavity is required to be less than Ra0.1~0.25, and the optical surface is required to be Ra<0.01nm. The cavity must be polished to reduce the surface roughness value. The steel selected for this purpose requires less material impurities, fine and uniform structure, no fiber orientation, and no pitting or orange peel defects during polishing.
The shape of the parts of plastic injection molds is often complex and difficult to process after quenching. Plastic mold manufacturers remind everyone that they should try to choose those with good thermal stability, the dimensional change rate caused by temperature difference is small, the metallographic structure and mold size are stable, and the processing can be reduced or no longer carried out, so as to ensure the mold dimensional accuracy and surface roughness requirements.
With the development of the plastics industry, the requirements for the complexity and precision of plastic products are getting higher and higher, and higher requirements are also put forward for plastic injection mold materials. For the manufacture of complex, precise and corrosion-resistant plastic molds, pre-hardened steel, corrosion-resistant steel and low-carbon maraging steel can be used, all of which have good machining, heat treatment and polishing properties and high strength.