1. Define the Core Selection Criteria

• General Plastics: Such as PP, PE, ABS. They have low corrosiveness, offering the widest material selection.

• Corrosive Plastics: Such as PVC, flame-retardant grades, and some medical plastics. It is mandatory to use corrosion-resistant stainless steels, for example, S136 (1.2083).

• High-Abrasion Plastics: Such as engineering plastics filled with glass fibers or minerals. Priority should be given to high-wear-resistance steels.

• < 100,000 cycles: Economical pre-hardened steels like P20 or 718 can be used.

• 100,000 - 500,000 cycles: More wear-resistant hardened steels or high-grade pre-hardened steels like NAK80 or high-hardness 718 are required.

• > 500,000 cycles: High-performance hardened steels, such as hardened S136 or H13, are essential.

• For parts requiring high-gloss polish or high transparency, it is necessary to use steels with high purity and excellent polishability, like S136 or NAK80.

• Large Mold Bases: The hardenability of the material is crucial to ensure uniform properties throughout the cross-section. Commonly used are pre-hardened steels for large sections like 718H.

• Complex Structures: For designs with thin walls or deep cavities, materials with good toughness and low distortion should be selected.

2. Detailed Overview of Common Mold Base Materials

• Pre-Hardened Steels (e.g., P20 / 718)

  • Characteristics: Supplied with a hardness of approx. HRC 30-40. They can be machined directly without heat treatment, offering high cost-effectiveness and fast delivery.

  • Typical Applications: The most common and economical choice. Suitable for general plastics, medium to low production volumes, large mold base frames, and projects with tight deadlines.

• Corrosion-Resistant Mirror Polish Steels (e.g., S136 / 2083)

  • Characteristics: Excellent rust and corrosion resistance, superior polishability, capable of achieving a high-gloss mirror finish.

  • Typical Applications: Corrosive plastics, transparent parts, high-gloss surfaces, medical molds, and any application requiring rust prevention and a high-quality finish.

• Hardened Wear-Resistant Steels (e.g., NAK80, Hardened S136)

  • Characteristics: High hardness (typically HRC 40+), excellent wear resistance, and long service life.

  • Typical Applications: Medium to high-volume production, plastics containing abrasive fillers, molds requiring high longevity.

• Hot Work Tool Steels (e.g., H13)

  • Characteristics: Good strength at elevated temperatures, resistant to thermal fatigue, with good toughness.

  • Typical Applications: Often used for components near hot runner systems that endure cyclical heating, or for applications demanding both high wear resistance and toughness.

3. Quick Decision-Making Flow

1. First, consider the plastic: Is it corrosive? Yes → Choose S136-type steel.

2. Then, consider volume and abrasion: High volume or filled plastic? Yes → Choose high-hardness, wear-resistant steel.

3. Third, consider surface finish: Requires a high-gloss mirror finish? Yes → Choose mirror polish steel.

4. Fourth, consider size and structure: Very large or complex mold base? Yes → Prioritize high-toughness pre-hardened steel.

5. Finally, balance cost and lead time: Limited budget and tight deadline? → Opt for pre-hardened steel P20/718 first.