Cavity Pressure Measurement in Micro Injection Moulding Tooling
Cavity pressure measurement in micro-injection tooling decouples machine dynamics from cavity fill, eliminating part weight variance and micro-defects.
Velocity Pressure Switchover
Meaning
Transition control points switch injection moulding machine operation from volumetric speed control to dynamic pressure holding during cavity filling. Precise velocity pressure switchover prevents mould overfilling and flash while ensuring complete cavity packing before gate freeze occurs. The parameter governs part weight repeatability, flash prevention and structural density distribution throughout the molded component.
It ceases to apply once the machine completes the hold phase and transitions into screw rotation for cooling.
Switching Criteria
Machine controllers execute switchover based on screw position, hydraulic pressure, cavity pressure or optical sensor triggers. Initiating velocity pressure switchover when the cavity is approximately ninety five percent full allows controlled deceleration before complete mold filling. Switching too early creates short shots and surface sink marks, whereas switching late causes high pressure spikes that flash tool parting lines.
Process engineers adjust position setpoints based on real time sensor feedback to maintain volumetric stability.
Viscosity Variation
Melt viscosity changes alter hydraulic pressure demands during volumetric filling, shifting the ideal transfer point location.
Part Density
Controlling the transition timing establishes consistent molecular orientation and shrinkage behavior in semi crystalline polymers. Blending regrind resin into virgin stocks alters melt flow properties, making cavity pressure based velocity pressure switchover superior to simple position based transfer. Consistent switchover execution reduces internal stress and minimizes warping across thin wall geometries.
Holding accurate transition timing guarantees part weight stability and dimensional conformance across long production runs.