The length is divided into five levels, the first level is more than one million times, the second level is 500,000----1 million times, the third level is 300,000----500,000 times, and the fourth level is between 100,000 and 300,000. Second, the fifth grade is below 100,000 times. Both the first and second molds are required to heat the steel with a hardness of about HRC50. Otherwise, it is easy to wear, and the molded product is easy to be out of tolerance. Therefore, the selected steel must have better quality. The heat treatment performance has good cutting performance under high hardness, and of course there are other considerations. Because I rarely touch domestic plastic mold steel, I can only introduce imported materials commonly used in the Pearl River Delta. Usually used in Sweden 8407, S136, the United States 420, H13, Europe 2316, 2344, 083, or Japan's SKD61, DC53 (formerly metal mold materials, used in special cases.). In addition, the injection molding materials and the added fillers have a great influence on the selection, especially the wear of the glass fibers on the mold.
     Some plastic materials are acid corrosive, and some are added with reinforcing agents or other modifying agents, such as glass fiber to damage the mold, and all materials should be considered. Strongly corrosive plastics are generally selected from S136, 2316, 420, and weakly corrosive except S136, 2316, 420, and SKD61, NAK80, PAK90, and 718M. Strong acid plastic materials are: PVC, POM, PBT weakly acidic plastic materials are: PC, PP, PMMA, PA,
     The appearance requirements of the product also have a great influence on the choice of mold materials. The transparent parts and surfaces require mirror-like products. The available materials are S136, 2316, 718S, NAK80, PAK90, 420. The mold with high transparency should be selected. S136, followed by 420.
     The above is from satisfying the product requirements, but as a designer, if you only consider these, you can not only become a good designer, maybe your rice bowl has problems, the cost of the mold you are involved is heavy. The weight of the middle, you have to consider the price, take S136 and 2316 to compare, the difference of 55-60 yuan per kilogram, if you choose improperly, your boss is not unable to receive the order, is to go bankrupt.
There are many pre-hard materials for the three-stage mold. The grades are: S136H, 2316H, 718H, 083H, hardness HB270----340, and the four-five-level molds are P20, 718, 738, 618, 2311, 2711. Mold, it is also possible to use S50C, 45# steel, that is, directly on the mold embryo. Bulletproof glass glue)
Molding shrinkage of common plastics
  
Plastic name shrinkage rate (%)
HDPE (hard soft rubber) 1.5~3.5(2.0)*

POM (Saigang) 1.8~2.6(2.0)*

LDPE (soft rubber) 1.5~3.0(1.5)*

PA6 0.7~1.5

PP ({bfb} soft rubber) 1.0~3.0(1.5)*

PA66 1.0~2.5

GPPS 0.4~0.8(0.5)*

SPVC 1.5~2.5(2.0)*

HIPS 0.4~0.6(0.5)*

TPU 1.2~2.0(1.6)*

ABS (Super Unbreakable) 0.4~0.7(0.5)*

PMMA (acrylic) 0.5~0.7(0.5)*

PC (bulletproof glass glue) 0.5~0.7(0.5)*

PBT