Mold or Die are the common terms used to describe the tooling used to produce injection molded plastic parts.
Traditionally injection molds have been expensive to manufacture. They were usually only used in mass production where thousands of parts were being produced. Molds are typically constructed from hardened steel, pre-hardened steel, aluminum, and/or beryllium-copper alloy. The choice of material to build an injection molded part is primarily one of economics. Steel molds generally cost more to construct, but their longer lifespan will offset the higher initial cost over a higher number of parts made before wearing out. Pre-hardened steel injection molds are less wear resistant and are used for lower volume requirements or larger components. The steel hardness is typically 38-45 on the Rockwell-C scale. Hardened steel molds are heat treated after machining. These are by far the superior in terms of wear resistance and lifespan. Typical hardness ranges between 50 and 60 Rockwell-C (HRC).
Today, aluminum molds cost substantially less than steel injection molded parts. When higher grade aluminum such as QC-7 and QC-10 aircraft aluminum is used and machined with modern computerized equipment, they can be economical for molding hundreds of thousands of parts. Aluminum molds also offer quick turnaround and faster cycles because of better heat dissipation. It can also be coated for wear resistance to fiberglass reinforced materials. Beryllium copper is used in areas of the injection molds which require fast heat removal or areas that see the most shear heat generated. Today's Mold companies use CNC machining and Electrical Discharge Machining (EDM) in the manufacturing processes.