Mold and die are used interchangeably to describe the tooling applied to produce plastic parts. They are typically constructed from pre-hardened steel, hardened steel, aluminum, and/or beryllium-copper alloy. Of these materials, hardened steel molds are the most expensive to make, but offer the user a long lifespan, which offsets the cost per part by spreading it over a larger quantity. For low volumes or large components, pre-hardened steel molds provide a less wear-resistant and less expensive option.
The most economical molds are produced out of aluminum. When designed and built using CNC machines or Electrical Discharge Machining processes, these molds can economically produce tens of thousands to hundreds of thousands of parts. Note that beryllium copper is often used in areas of the mold that require fast heat removal or places that see the most shear heat generated.