• 2023-05-09
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Material selection for injection mold

In the manufacturing of injection mold, the choice of materials is very important, the following we give some suggestions for reference.

Injection mold material

The injection molding process begins with a metal mold. Injection molds may be made of steel, aluminum, or beryllium copper. High strength steel is the material we use most in tooling.

The type of steel selected for the mold can be one of the key choices when entering an injection molding project. The correct injection mold material is critical to the success of plastic applications, just as the correct plastic resin is critical to the performance of the final product.

Steel: The best choice of die material

Steel has considerable advantages over other die materials such as aluminum and beryllium copper. Steel molds last longer, ensuring greater durability and even, in some cases, repairability.

Steel can also be used in alloys, allowing mold materials to be customized to meet the exact specifications of the project. Steel is alloyed to meet the specific performance requirements of the project in much the same way that resin is formulated to meet the performance requirements of the final plastic component. Some applications may require steel dies with high hardness and wear resistance to achieve parting line durability, while other applications require steel dies with higher toughness to resist mechanical fatigue.

In general, injection mold materials that provide higher hardness and wear resistance tend to be more brittle. In almost all cases, steels with higher toughness will reduce to some extent the resistance of steel to steel wear (adhesive wear) and to resins containing fiberglass or mineral fillers. We have the knowledge and experience to select the right injection molding materials for your project.

For example, parting line integrity is usually better for higher hardness steels (Rockwell 55 or higher) and for points where cutting between steels produces coring. The hardness range of one or both steel faces shall be between Rockwell 55 and Rockwell 58. Consideration should be given to using A-2 steel, D-2 steel, or M-2 steel gate inserts and the die core inserted into them opposite the gate of wear-resistant steel mold material to prevent abrasion of glass or mineral filled resins.

P-20 steel

P-20 steel is regarded as the main force of injection molding die material industry. P-20 steel supplied in the pre-hardened state is very tough but fairly easy to work with. This is a good steel to consider in applications where cavity sizes exceed 12 "x 12" x 12 "(303.6 mm x 303.6 mm x 303.6 mm), as the cost and associated risks of a heat-treated block of this size can be prohibitive. P-20 steel is also selected for a die with a smaller cavity size to eliminate the time and expense of heat treatment when the die is not expected to exceed 500,000 cycles.

Sliders, lifts, cams or other moving parts in P-20 steel dies shall be made of steels with different alloys and hardness. This is to reduce wear or high adhesion wear. H-13 steel sliders or tappets that have been heat-treated to reach Rockwell 50-52 are usually used in P-20 steel dies. Rockwell 55 to Rockwell 58 series steels with locally worn surfaces are another option.

H-13 and S-7 steel

H-13 steel and S-7 steel have excellent durability and resistance to mechanical fatigue. H-13 steel has higher toughness at Rockwell 50-52, while S-7 has better durability because it has a higher hardness rating at Rockwell 55-57. H-13 and S-7 steels do not exhibit the special wear resistance of glass or mineral resin fillers.

H-13 is a common mold material for cavities larger than 8 "x 8" x 8 "(202.4 mm x 202.4 mm x 202.4 mm) and requires higher hardness and toughness than P-20.

The smaller cavity and core are usually made of S-7 steel. S-7 steel can be air quenched for small cross sections 2.5 inches (63.25 mm) or smaller and provides very good dimensional stability through this process. The large cross sections of H-13 and S-7 are usually quenched in oil.

Corrosion protection

When forming in a high humidity environment, nickel or stainless steel plating may be required to help prevent mold corrosion. Corrosion is most likely to occur in cold plastic injection moulds, where condensation may occur and then oxidation may occur, or when using materials that may release gases that are corrosive to most steel.

GE resin molding usually does not require nickel-plated or stainless steel plastic injection moulds because mold temperatures should not fall below 140°F (60°C) and only a few grades of GELOY resin (such as PVC) have corrosive components.

Nickel plating of die materials is typical for long-term die storage or may require corrosion protection other than preventive spraying. Electroless nickel plating provides excellent chemical protection and is relatively inexpensive compared to chrome or other protection techniques for die materials. The benefits of nickel plating include higher mechanical properties such as toughness, hardness, wear resistance or resistance to adhesive wear, and better thermal conductivity than stainless steel.