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.
Nitrogen Gas Quenching
Meaning
High-pressure gas cooling processes used in heat treatment rapidly cool heated steel parts to achieve the desired hardness and microstructure. By using nitrogen gas quenching, tool steel undergoes rapid and controlled cooling to transform the metal into martensite without the risk of cracking. This technique is commonly applied to complex injection moulds where liquid quenching would cause severe warping.
Process Mechanics
Pressurized gas streams are directed through the furnace chamber at pressures of up to twenty bar. During nitrogen gas quenching, the cold gas absorbs heat from the metal surfaces, creating a highly uniform cooling rate across the entire part. This controlled rate prevents the formation of soft spots and reduces residual stresses in the steel.
Mould Protection
Oxidation and scaling on the steel surface must be avoided to preserve the fine finish of the mould cavities. Utilizing nitrogen gas quenching in a vacuum furnace prevents oxygen from reacting with the hot metal. This ensures that the high-polish finish of the mould is preserved, reducing the need for extensive polishing after heat treatment.
Dimensional Stability
Distortion during heat treatment can ruin expensive mould components before they are even used. The thermal control of nitrogen gas quenching reduces the dimensional movement of the steel to a fraction of that seen with oil quenching. This precision allows toolmakers to machine components closer to their dimensions prior to heat treatment, saving machining time.
By minimizing the amount of post-hardening grinding required, this method also lowers the risk of micro-cracking caused by heavy abrasive wheels on hard steels.