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.
Gate Washing
Meaning
Erosion of the steel surface at the point of melt entry occurs when abrasive polymers or high injection velocities wear down the gate geometry. This phenomenon, known as gate washing, leads to dimensional instability and visual defects in the finished part. It effectively changes the pressure drop across the gate as the orifice enlarges.
Erosion Mechanism
Physical friction between the flowing resin and the tool wall strips away small amounts of material during every cycle. When glass-filled resins are used, gate washing proceeds rapidly because the hard fibres act like sandpaper against the steel.
Processing Variable
Injection speed and melt temperature influence the rate at which the gate geometry degrades over time. High shear rates increase the localized temperature and reduce the viscosity of the melt, which can accelerate the removal of surface material. Decreasing the fill speed often slows the degradation but may result in longer cycle times or aesthetic issues elsewhere on the part.
Quality Impact
Changes in gate dimensions alter the filling pattern and the degree of packing achieved inside the cavity. Once gate washing becomes advanced, the moulder may observe flash at the gate area or sinks in the final product. Regular inspection of the gate diameter allows the operator to predict when the tool will require refurbishment or a new gate insert.