Injection Mold Tooling Materials

injection mold tooling materials

  • There are 5 classes of standard molds defined by the Plastics Industry Association, formerly known as the Society of Plastics Industry, or SPI.  See the table below for further details.

  • For higher volumes, it is recommended to use harder more expensive steels due to long production runs and high service life.

  • P-20 is a very common tool steel for non-abrasive and non-corrosive resins.

  • P-20 High Hard (HH) (approximately 20% harder than P-20) is also a common choice as it provides more compressive strength than standard P-20.  We typically spec this material for most new tools if using resins without abrasive additives.

  • Harder tool steels like H13 are a common choice for abrasive resins such as glass filled, or to prolong tool life and reduce maintenance.

  • Stainless steel is a common choice for corrosive resins such as PVC.

  • S-7 is typically used for small-tolerance and very high-volume applications.

  • Aluminum tools can be a good choice for low-volume tools, although they can produce many thousands of parts with proper design and meticulous care.

  • Hardening, plating, and surface treatments may also be required, depending on the resin and application.

  • Higher wear resistance and higher hardness tool generally equals a more brittle tool.  And likewise, greater toughness generally equals less wear and abrasion resistance.

  • Higher wear resistance and higher hardness tool generally equals a more brittle tool. And likewise, greater toughness generally equals less wear and abrasion resistance.

SPI Class or GradeCyclesGeneral Description & UseInvestment LevelMold Material Recommendation
101Over 1,000,000Extremely high production, fast cycle timesHighestCavity and core inserts: Stainless Steel or H-13 steel. Mold base: stainless steel pre-hardened.
102Up to 1,000,000Medium to high production, good for parts with abrasive materials and/or tight tolerancesMedium to highCavity and core inserts: H-13 steel. Mold base: P-20 steel.
103Up to 500,000Low to medium production, tends to be the most common requested.MediumCavity and core inserts: H-13 or P-20 or P-20HH steel. Mold base: S50C or 1050 steel.
104Up to 100,000Limited to low production with non-abrasive plastics.Low to mediumCavity and core inserts: P-20 or P-20HH steel, or aluminum. Mold base: S50C or 1050 steel.
105Up to 500Prototype only. No restriction on materials - non-metals or mild steel ok.LowestCavity and core inserts: None, cut into mold base. Mold base: P-20 steel.
CharacteristicAluminumP20 SteelH13 SteelStainless SteelS-7 Steel
Thermal Conductivity+N---


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