Thermoplastic injection molds. Choice of steels

The main factors influencing the longevity of plastic injection molding tools are design, mechanical engineering and choice of materials. The cost of tooling is often very high, consisting mainly of the manufacture of cavities. The cost of steel is proportionately low. This is why the choice of steels is based primarily on technical criteria, with the purchase price being secondary. A judicious choice enables effective action to be taken to considerably increase tool life.

Requirements in terms of material properties are specific to the carcass, cavities and moving parts of the mold. These include impact strength, yield strength, thermal conductivity, chemical resistance, wear resistance, and suitability for machining, heat treatment and polishing.

The properties of steels depend above all on their composition and heat treatment: knowledge of the influence of these parameters on the specific requirements of plastic injection molding helps to optimize tool life. However, the practice of heat treatment presents risks linked to the specificity of the steels generally chosen. By taking these phenomena into account, the risk of destroying cavities during heat treatment can be considerably reduced.

The steelmaking process also makes it possible to significantly optimize certain properties that are essential for specific applications in the plastics industry.

A number of situations require properties that cannot be obtained with steels. Other materials can be used to meet these sometimes conflicting needs.