Selection of mold materials Before we talk about mold materials, we must first understand some basic things of injection molds. The first is the classification of molds. Generally, molds are divided into five grades according to the length of service life. Level 1 is more than one million times, and level two. It is 500,000---100 million times, the third level is 300,000-500,000, the fourth level is 100,000-300,000, the fifth level is less than 100,000, the first and second level. Molds are required to be able to heat-treated steel with a hardness of about HRC50, otherwise they are prone to wear, and the injection-molded products are easily out of tolerance. Therefore, the selected steel must have good heat treatment performance and good hardness under high hardness conditions. Cutting performance, of course, there are other considerations. Because I rarely contact domestic plastic mold steel, I can only introduce imported materials commonly used in the Pearl River Delta. Usually used are Swedish 8407, S136, American 420, H13, European 2316, 2344,083, or Japan's SKD61, DC53 (formerly metal mold materials, used under special circumstances). In addition, injection molding raw materials and their added fillers have a great influence on the selection just now, especially the glass fiber wears on the mold.
Some plastic materials have acid corrosion, and some have added to the reinforcing agent or other modification agents, such as glass fiber damage to the mold, should be comprehensive consideration when selecting materials. Corrosive plastics are generally selected S136,2316,420 a class of steel, weakly corrosive addition of S136,2316,420, there are SKD61, NAK80, PAK90, 718M. Strong acid plastic materials: PVC, POM, PBT Weakly acidic plastic materials: PC, PP, PMMA, PA,
Appearance requirements of the product also have a great influence on the choice of mold materials. Transparent parts and surface-required products with throwing mirrors are available. 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 from the satisfaction of product requirements, but as a designer, if you only consider these things, you will not only become a good designer, you may have problems with your rice bowl, and the cost of the molds you need is heavy. The top priority, you have to consider the price, take S136 and 2316 to compare, a difference of 55-60 yuan per kilogram, if you choose improperly, your boss is not a single, is to achieve bankruptcy.
There are many pre-hard materials for the third-level molds, and the grades are: S136H, 2316H, 718H, 083H, hardness HB270 ---340, four or five molds with P20, 718, 738, 618, 2311, 2711, for the requirements of ultra-low For the die, it is also possible to use S50C, 45# steel, ie, to make the cavity directly on the die. Bulletproof glass glue
Molding shrinkage of common plastics
Plastic Name Shrinkage (%)
HDPE (hard plastic) 1.5~3.5(2.0)*
LDPE (soft) 1.5~3.0(1.5)*
PP (100% soft rubber) 1.0~3.0(1.5)*
ABS (unbreakable glue) 0.4~0.7(0.5)*
PMMA (Acrylic) 0.5~0.7(0.5)*
PC (ballistic glass adhesive) 0.5~0.7(0.5)*