Before talking about mold materials, we must first understand some basic things about injection molds. The first is the classification of molds. Generally, molds are divided into five levels according to the length of service life. The first level is more than one million times, and the second level is 500,000- — 1 million times, the third level is between 300,000 and 500,000 times, the fourth level is between 100,000 and 300,000 times, and the fifth level is below 100,000 times. Both the first and second molds are required to be used Heat treatment of steel with a hardness of about HRC50, otherwise it is easy to wear, and the injection molded product is easy to be out of tolerance. Therefore, the selected steel must have good heat treatment performance and good cutting performance under high hardness. Of course, it is also There are other considerations. Because I rarely come into contact with domestic plastic mold steel, I can only introduce imported materials commonly used in the Pearl River Delta. Usually choose 8407, S136 in Sweden, 420, H13 in the United States, 2316, 2344, 083 in Europe, or SKD61, DC53 in Japan (formerly metal mold materials, used under special circumstances). In addition, the raw materials for injection molding and the added fillers have a great influence on the selection, especially the glass fiber wears a lot to the mold.
Some plastic materials are acid corrosive, and some are added with reinforcing agents or other modifiers. For example, glass fiber can cause great damage to the mold. Therefore, comprehensive consideration should be given to the selection of materials. For the highly corrosive plastics, generally choose S136, 2316, 420-type steel, and for the weakly corrosive plastics, in addition to S136, 2316, 420, there are SKD61, NAK80, PAK90, 718M. Strongly acidic plastic materials include: PVC, POM, PBT. Weakly acidic plastic materials include: PC, PP, PMMA, PA,
The appearance requirements of the product also have a great influence on the selection of mold materials. For transparent parts and products with mirror-like surfaces, the available materials are s136, 2316, 718S, NAK80, PAK90, 420, and molds with extremely high transparency should be selected. S136, followed by 420.
The above is in terms of meeting product requirements, but as a designer, if you only consider these, you will not only be unable to become a good designer, you may have problems with your job, and the cost of the molds you involve is important. The most important thing is that you have to consider the price. Compare s136 with 2316. The difference is 55-60 yuan per kilogram. If you choose improperly, your boss will either fail to receive the order or go bankrupt.
There are many pre-hardened materials for the third-level molds, the grades are: S136H, 2316H, 718H, 083H, the hardness is HB270—-340, the fourth and fifth-level molds use P20, 718, 738, 618, 2311, 2711, for the very low requirements For the mold, it is possible to use S50C, 45# steel, that is, to make the cavity directly on the mold base. Bulletproof glass glue)