Tool Steel Selection Guidelines for High Volume Injection Moulding Tooling Baseline Fabrication
High-volume injection moulding baseline tooling demands martensitic stainless or pre-hardened steels matched to polymer abrasiveness and cycle volume.
Martensitic Stainless
Meaning
High-strength chromium steel alloys provide both corrosion resistance and high hardness through heat treatment. Because of these properties, martensitic stainless is widely used to manufacture injection mould cavities for corrosive resins. This material class prevents chemical wear from acidic outgassing while resisting mechanical deformation under high clamping forces.
Alloy Properties
Elevated carbon content combined with chromium allows these steels to be hardened by quenching and tempering. Utilizing martensitic stainless ensures that the mould faces maintain a high level of scratch resistance during operation. This prevents abrasive wear from mineral-filled resins, extending the time between mould maintenance cycles.
Corrosion Resistance
Corrosion of tooling surfaces is a major risk when processing polymers that release corrosive byproducts like hydrochloric acid. Opting for martensitic stainless prevents the development of rust in the cooling channels of the mould, which would otherwise reduce cooling efficiency. This protective property is particularly critical when using recycled resins that may contain unknown contaminants.
By preventing localized pitting, the alloy ensures that the heat transfer across the mould remains uniform, avoiding hot spots that cause part distortion during cooling.
Machinability Tradeoffs
Although the steel holds high hardness after treatment, it can be difficult to machine in its hardened state. Moulders must perform rough machining of martensitic stainless in the annealed condition before hardening it to the final specification. This sequence minimizes tooling wear during manufacture and secures the required final dimensions.