Injection Moulding Core and Cavity Steel Guide

Common Steel Types Used for Injection Mold Cavities and Cores

Choosing the right tool steel directly impacts part precision, cycle efficiency, and overall mold lifespan. As a professional injection molding manufacturer and supplier, we select core and cavity materials based on production volume, resin aggressiveness, and surface finish targets. Building durable, long-lasting tooling also limits scrap and reduces material waste—a core reason clients ask is injection moulding environmentally friendly when optimizing high-volume production. Pairing high-performance steel tooling with a reliable 販売用の注塑成形機を探すことは ensures consistent output and maximum operational efficiency.

Pre-Hardened Mold Steels (P20 and 718)

Pre-hardened steel supplies ready-to-machine hardness without requiring post-machining heat treatment, eliminating distortion risks.

• • P20ツール鋼: Delivered at 29–34 HRC. It offers great machinability and uniform hardness, making it the industry workhorse for medium-volume runs (up to 500,000 shots) and large structural parts.
  • 718 Steel: An upgraded version of P20 with enhanced core strength and a finer grain structure, making it easier to polish for smooth automotive and consumer plastic components.

Hardened Tool Steels (H13 and S7)

When high-volume production or abrasive resins threaten tool integrity, fully hardened steel grades provide extreme wear resistance and structural stability.

Corrosion-Resistant Stainless Steels (S136 and 420)

Processing corrosive polymers like PVC or flame-retardant resins causes rapid rust and pitting on standard steels. Using a stainless mold steel prevents surface degradation and extends tool life in high-humidity facilities.

• • 420ステンレス鋼: Hardens to 48–52 HRC, balancing strong corrosion protection with good wear resistance for general-purpose applications.
  • S136 Stainless Steel: An ultra-clean, electro-slag remelted (ESR) grade. It resists chemical attack and accepts an optics-grade mirror polish, making it essential for medical devices, lenses, and transparent housings.

High-Precision Mold Steels (NAK80)

NAK80 is a precipitation-hardened steel delivered at 37–41 HRC that requires zero stress-relieving heat treatment after machining.

• • High-Gloss Polishability: Easily achieves an SPI A1 optical finish with minimal polishing labor.
  • Tight Dimensional Control: Maintains stable dimensions during EDM and fine machining, perfect for intricate electronic connectors.
  • Uniform Hardness: Consistent structural density prevents uneven wear across deep cavity features.

Key Factors in Selecting Cavity and Core Steel Types

Selecting the right mold steel directly impacts production efficiency, part quality, and long-term costs. A frequent question from manufacturers is whether injection moulding is environmentally friendly—the answer largely depends on choosing durable tool steel that maximizes mold lifespan and minimizes scrap waste. As our facility 成形生産能力を拡大する, we carefully align core and cavity steel properties with specific operational demands.

Production Volume and SPI Mold Class Requirements

Production volume dictates the appropriate SPI (Society of the Plastics Industry) mold class and structural hardness required for the tool steel:

Selecting the right cavity and core steel directly impacts tool performance, part quality, and unit cost. Choosing durable materials also touches on sustainability—many clients ask, is injection moulding environmentally friendly? Maximizing steel durability reduces scrap rates, minimizes tooling waste, and optimizes energy consumption over long production runs. As a professional injection molding manufacturer and supplier, we evaluate four key criteria when selecting core and cavity steels.

Production Volume and SPI Mold Class Requirements

Expected production volume determines whether you need a pre-hardened steel or fully hardened steel to maximize mold lifespan.

As our facility expands moulding production capacity, we match these SPI standards to ensure long-term tooling stability without over-engineering lower-volume molds.

Plastic Resin Properties and Wear Potential

The raw plastic resin dictates the chemistry required for cavity and core steels:

• • Abrasive Resins (Glass/Mineral Filled): Resins with glass fiber reinforcement cause fast physical wear. We specify H13鋼 or S7 steel hardened above 50 HRC to prevent erosion along high-velocity flow paths.
  • Corrosive Resins (PVC, POM, Flame Retardants): These materials release acidic off-gases during processing. We use stainless mold steel いいね 420ステンレス鋼 or S136 to prevent pitting and rusting inside the core and cavity.
  • Standard Resins (PP, ABS, PS): Non-abrasive commodities run efficiently in standard P20 ツール鋼.

Surface Finish and Polishability Standards

High-gloss parts, optical lenses, and clear enclosures require specialized steel microstructures without voids or impurities.

• • Mirror Polish (SPI A-1 / A-2): Requires super-clean ESR (Electro-Slag Remelted) steels such as NAK80 or polished 420ステンレス鋼.
  • Textured/Grain Finish (Mold-Tech): P20 ツール鋼 provides uniform chemical etching performance for standard automotive and consumer electronic textures.
  • Standard Matte Finish: Pre-hardened grades handle standard EDM or machined finishes without requiring costly polishing steps.

Budget and Machinability Constraints

Tooling budgets must balance initial mold-making costs against long-term maintenance.

• • Pre-Hardened Steels (P20, NAK80): Delivered pre-treated (28–40 HRC). They require no post-machining heat treatment, reducing lead times and risk of thermal distortion.
  • Through-Hardened Steels (H13, S7): Machined in an annealed state, heat-treated to high hardness, and final-ground. While initial machining costs are higher, they offer lower cost-per-part on high-volume runs by preventing premature tool failure.

Heat Treatment and Maintenance Best Practices for Mold Steel

Proper heat treatment and routine care maximize mold lifespan and efficiency. When asking is injection moulding environmentally friendly, extending tool durability plays a vital role by reducing material waste, conserving energy, and lowering overall resource consumption over high-volume production cycles. As a professional injection molding manufacturer and supplier, we implement strict thermal and maintenance protocols to ensure every tool steel component performs reliably.

Heat Treatment and Surface Modification Techniques

Correct thermal processing optimizes core and cavity strength without compromising dimensional stability:

• • Vacuum Heat Treatment: Provides uniform hardening for tool steel types like H13 and S7 while eliminating surface oxidation.
  • Nitriding Treatment: Creates a high-hardness surface layer that protects against wear when running abrasive bulk plastic pellets for injection molding.
  • PVD Coating: Applies a thin, ultra-hard coating to enhance wear resistance and improve plastic part release during cycling.

Maintenance and Care for Prolonged Steel Life

Maintaining hardened steel and stainless mold steel tooling requires a proactive preventive routine: