1. Types of plastic materials
Ordinary plastics (PE, PP, ABS, etc.): Low corrosion resistance requirements for mold steel, priority should be given to pre hardened steel (such as P20, 718) or carbon tool steel (T8, T10A).
Fiberglass/mineral filled plastic: Strong abrasion resistance, requiring high wear resistant steel such as Cr12MoV, DC53 (hardness ≥ 60HRC after quenching), or surface hardening treatment (carburizing, nitriding).
Corrosive plastics (PVC, flame retardant containing plastics): Corrosion resistant steel must be selected, such as S136 (1Cr13Mo), 4Cr13, or chrome plated (Cr coating thickness ≥ 10 μ m).
High temperature plastics (PEEK, PI, etc.): require hot work mold steel (H13, 3Cr2W8V), with a temperature resistance of ≥ 500 ℃ and resistance to thermal fatigue.
2. Product accuracy and surface quality
High precision products (tolerance ≤± 0.05mm): Choose age hardened steel (such as P21, 18Ni steel) with a heat treatment deformation rate of ≤ 0.03% and good dimensional stability.
Mirror products (such as optical lenses and cosmetic packaging): The steel structure should be uniform and free of impurities, such as S136 and NAK80, with a polished roughness Ra ≤ 0.01 μ m.
Leather/corrosion pattern surface: Steel should be suitable for electrical discharge etching, such as 718H and S136, with clear and uniform patterns after etching.
3. Complexity of product structure
Complex thin-walled molds: require steel with good toughness (impact energy ≥ 40J), such as pre hardened steel 718H and H13 (toughness better than Cr12 series after quenching), to avoid cracking.
Large molds (size>500mm): require high hardenability steel, such as H13 (hardenable within 200mm diameter), P20+(improved high hardenability pre hardened steel).
