It is very important to ensure that the correct materials are specified in all new injection mold designs. Use of incorrect or inappropriate materials can lead to poor mold performance in production and to early failure of the tool.

In all plastic mold materials we are looking for certain characteristics for ease of tool making and good performance during production from the mold tool. Ideally we would prefer the material finally selected to have the following properties:

Good machining properties
Ease of heat treatment where hardening is required
Good toughness and strength
Polishes and accepts texturing well
Good resistance to heat and wear
Good fatigue resistance
High thermal conductivity for effective water cooling
Good corrosion resistance

Unfortunately, in practice no single material will exhibit all these characteristics and therefore a compromise has to be reached depending on the type of tool design being employed. Among the major governing factors that should be considered are:
The tool life in terms of the quantity of parts required to be produced from the tool
The molding material being used (e.g., abrasive or corrosive?)
Texturing and polishing requirements
Whether hardening is required (e.g., , for long running tools or for side cores and splits, etc)
Whether high thermal conductivity will be required
Exceptional requirements like the use of very high injection pressures or speeds

For most normal applications steel is used because it has most of the properties we require. There are several other applications, however, where alternative materials may be used.