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Material Types

Selecting the right materials to build a mold depends on features such as the base, cavity and core plates, ejector pins, ejector sleeves, gate blocks, and cavity blocks.

For the base, there are many options available. Each falls into one of three main categories: hardened steel, pre-hardened steel or aluminum.

Hardened steels are typically used for higher volume, corrosive plastics or more complicated designs and are more expensive. Pre-hardened is used for lower volume and less complex mold designs and have a lower price point. The least expensive option is aluminum, which is typically only recommended for prototype or short-run tooling.

Mold material selection has a dramatic impact on result of the project. Having the proper materials improves the design, build and repair processes for specialty injection mold making and timely product delivery. If done correctly, these choices can save time and money.
When choosing the best materials, consider not only the part, but also things like wear resistance, part geometry, cooling, part stability and desired cycle times. The chart below outlines different material characteristics and uses.



Category of Steel

Type of Steel



Typical Use in a Mold



High luster

Relatively tough, easy to weld

Cavity plates, core plates & laminates as well as thin wall sections



Diamond polish

High hardness, toughness and high temperature strength

Cavity plates and core plates



High polish

Corrosion and wear resistant, easy to weld

Cavity blocks, ejector pins, sleeves, etc.


NAK 55

High polish

Easy to weld

Ejector pins, ejector sleeves and ejector blades


NAK 80

High luster

Tougher than NAK 55,

Gate blocks, gib plates to prevent galling, gate blocks to prevent wear



Not recommended for polish

Easy to weld and polish, may rust

Mold bases, ejector plates & some cavities


Many grades available

High luster

Easy to weld

Mold bases


In addition to the options above, there are many specialty options that can fit the needs of unique projects.

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