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.