What is the principle of material selection for injection molding molds?

Author: MULAN - Plastic Molding Manufacturer

Due to the combined action of force and heat, the working conditions of injection molds are different from those of cold stamping molds. These forces are the pressure when the mold is closed, the pressure of the melt in the cavity and the tension when the mold is opened, and the pressure of the melt is the main factor. Injection molds generally work at a certain temperature, and the temperature fluctuates.

In addition, the injection mold will be rubbed by the plastic during operation, and may be corroded by corrosive gases. The working conditions of injection molds are quite harsh. In order to ensure that the mold has a certain life, the material of the injection mold, especially the material of the molded parts, must meet certain requirements.

1. Excellent machining performance. Choose steel grades that are easy to cut and can obtain high precision after processing. Medium carbon steel and medium carbon alloy steel are the most commonly used, which is especially important for large molds. For parts that require EDM, it is also required that the burn hardened layer of this steel type is thinner.

2. Excellent polishing performance. Most of the working surfaces of molded injection parts need to be polished to reach the mirror surface. Ra<0.05um, the hardness is more than 40HRC, but the hard surface will make polishing difficult. The microstructure of the steel should be uniform and dense, less impurities, no flaws and pinpoints! 3. Good wear resistance and fatigue resistance. The cavity is not only washed by high-pressure plastic melt, but also affected by the temperature stress of alternating cold and heat. The selected steel type should enable the injection mold to reduce the number of polishing and repairing molds, maintain the dimensional accuracy of the cavity for a long time, and meet the service life requirements of mass production.

It is especially important for the injection molding production of more than 300,000 injection molding times and fiber-reinforced plastics. 4. Corrosion-resistant For some plastic varieties, such as polyvinyl chloride and flame-retardant plastics, it is necessary to consider the selection of steel with corrosion resistance.