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.
Thermal Fatigue Crazing
Meaning
Network-like cracks forming on the surface of a die or mould result from repeated cycles of heating and cooling during the production run. Frequent thermal fatigue crazing typically appears in high-temperature applications where the surface expands and contracts rapidly. They are often referred to as heat checking in the die casting and high-performance polymer industries.
Cyclic Loading
Repetitive expansion and contraction create internal stresses that eventually exceed the fatigue limit of the steel surface. Small micro-cracks from thermal fatigue crazing initiate at points of highest thermal gradient and grow into a visible web.
Surface Failure
Roughness caused by these cracks is transferred to the surface of the moulded part, resulting in poor aesthetic quality. If the cracks are deep, they can act as stress risers that lead to catastrophic failure of the entire tool. This defect is particularly problematic in parts that require a high-gloss finish or transparent properties.
Material Stress
Resistance to this type of degradation depends on the thermal conductivity and hot-yield strength of the tool steel. Using conformal cooling or advanced hot-work steels can mitigate the temperature spikes that drive the cracking process. Regular stress-relieving heat treatments during the life of the tool can also help in managing the accumulation of these thermal stresses.