The plastic injection mold material mainly depends upon the annual shot quantity requirement. But it also depends upon part design and part plastic material.
For shot quantity requirements of less than 500,000 prehardened tool steel (called P20) is most commonly used for cores and cavities and the mould base.
Although mild steel could also be used for the injection mould base as well.This steel is cheap.
Also, aluminium is growing in popularity in the automotive sector.Aluminium is much easier to machine and handle compared with tool steel so the cost of manufacture is less.Cycle times are also better but mold maintenance is critical to ensure part quality – anybuild up of residue will damage the shut off surface and cause part flashing.
Anything above 500,000 the use of thru hardened tool steels such as H13 or H11 should be considered for the cores and cavities. These materials will produce quality parts for much longer than P20 or aluminium because mould wear is less.
For corrosive environments such as when molding PVC plastic, stainless steel tool steels can also be used in mold construction. Stainless steels will minimize corrosion.
In addition to the above, part design & mould design play a role in material selection.. Some part designs will require moving or rotating components in the mould design. One option is to use nitriding steels so that “pick up” or damage does not occur when plastic mould components move relative to each other. Examples of nitriding steels are P20 & H13.