Meaning
Dynamic pressure transients occurring inside a mould cavity during the packing phase record the precise moment of gate freeze and melt compression. Piezoelectric sensors installed behind ejector pins capture cavity pressure pulses as molten polymer fills and packs the void. Monitoring these signal peaks provides continuous verification of viscosity changes between virgin resin batches and regrind blends.
Viscosity Monitoring
Rheological variation alters the peak amplitude recorded by internal pressure sensors. Fluctuations in cavity pressure pulses highlight lot-to-lot melt flow rate shifts before dimensional defects manifest in ejected parts.
Freeze Detection
Pressure attenuation curves define the duration of effective packing before resin solidifies in the gate channel. Monitoring cavity pressure pulses during cycle optimization shows the exact second when pressure transmission ceases. Maintaining packing pressure beyond gate freeze wastes energy and risks stressing the part, while releasing pressure early causes sink marks and unacceptably high volumetric shrinkage.
Automated press control systems use sensor feedback to trigger hydraulic holding pressure switchover based on real-time curve shapes.
Defect Prevention
Flash and short shots result from uncontrolled pressure variations during plastication and injection steps. Stable cavity pressure pulses confirm consistent melt volume delivery into every cavity of a multi-cavity tool. Adjusting hold pressure profiles based on sensor data eliminates part weight variance across long manufacturing runs.
