Dynamic Viscosity Curve Generation and Transfer Point Calibration in Technical Molding
Calibrating transfer points via press-side viscosity curves optimizes fill pressure, cuts part mass variation, and locks in DIN 16742 tolerance bands.
Pressure Transfer Point
Meaning
Screw position thresholds or cavity pressure readings trigger the machine transition from velocity-controlled filling to pressure-controlled packing during injection moulding. Machine setup relies on the pressure transfer point to prevent overpacking of the mould cavity while ensuring adequate volumetric filling. Setting this transition accurately governs peak cavity pressure, part weight consistency and flash formation, stopping the primary injection phase when ninety-five to ninety-eight percent of cavity volume is filled.
A datasheet value for material viscosity offers initial estimates, but actual production stability requires real-time position or cavity transducer feedback.
Switchover Control
Machine control systems execute velocity-to-pressure switchover using screw position sensors, hydraulic line transducers or piezoresistive cavity sensors. Precise timing of the pressure transfer point prevents sudden pressure spikes that cause tool wear and parting line flash. Switching too early on screw position causes premature pressure drop, resulting in short shots and sink marks in thick sections.
Modern electric injection machines hold switchover position within hundredths of a millimeter, maintaining uniform part weights across extended production runs despite minor lot-to-lot resin viscosity variations.
Pressure Propagation
Pressure propagation within the cavity changes instantly upon reaching the transition threshold. Screw forward speed decreases while cavity pressure stabilizes to pack out remaining volumetric shrinkage during cooling. Proper timing matches melt front arrival near the cavity end-of-fill zone.
Quality Tolerance
Drift in material viscosity or oil temperature shifts effective cavity pressure if switchover relies solely on screw position. Implementing hydraulic or in-cavity pressure triggers fixes the pressure transfer point to actual melt conditions, reducing part weight variance below zero point two percent across consecutive moulding cycles.