The working conditions of plastic molds are different from cold stamping molds . Generally, they must work at 150 ° C-200 ° C. In addition to being subjected to a certain pressure effect, they must also be affected by temperature. The basic performance requirements of steel for plastic molds are roughly summarized as follows according to the different conditions and processing methods of plastic molding molds:
1. Sufficient appearance hardness and wear resistance
The hardness of plastic molds is usually below 50-60HRC. The heat-treated molds should have a satisfactory external hardness to ensure that the molds have sufficient rigidity. Due to the large compressive stress and friction of the plastic during the filling and movement of the mold, the mold is required to maintain the stability of the accuracy of the shape and the accuracy of the scale 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 the heat treatment. Therefore, increasing the hardness of the mold is conducive to improving its wear resistance.
In addition to EMD processing, most plastic molding molds also need to be cut and machined. In order to extend the service life of cutting tools, improve the cutting function, and reduce the appearance roughness, the hardness of steel for plastic molds must be appropriate.
3. Outstanding polishing function
High-quality plastic products require a small surface roughness value. For example, the surface roughness value of the injection mold 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="">0.01> The steel selected for this purpose requires less material impurities, fine and uniform arrangements, no fiber orientation, and no pitting or orange peel defects should occur during polishing.
4. Outstanding thermal stability
Plastic injection mold parts often have complex shapes and are difficult to process after quenching. Therefore, Dongguan plastic mold manufacturers have suggested that we should use materials with outstanding thermal stability as much as possible. When the mold forming process is heat treated, the linear expansion coefficient is small and the heat treatment deforms. Small, small scale change rate caused by temperature difference, metallographic arrangement and mold size are stable, can be reduced or no longer processed, can ensure the mold scale accuracy and appearance roughness requirements.
With the development of the plastics industry, the requirements for the complexity and accuracy of plastic products have become higher and higher, and higher requirements have been placed on mold materials. For the production of complex, fine 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) are available. Cutting, heat treatment and polishing functions and high strength.
In addition, remind us that we must also consider preventing scratches and gluing when selecting materials. If there is relative movement between the two surfaces, try to avoid choosing materials with the same structure. In special circumstances, one side can be plated or nitrided to make Both sides have different appearance structures.