Meaning
Injection velocity control during the secondary stage of the moulding cycle maintains pressure within the cavity as the polymer cools and contracts. This managed sequence is the dynamic packing profile, which compensates for volumetric contraction without overpacking the gate region. A tailored pressure profile reduces internal stress by gradually lowering the pressure before the gate freezes.
Shrinkage Control
Thick-walled parts require extended packing to prevent sink marks and internal voids. Utilizing a dynamic packing profile ensures that additional melt is pushed into the cavity only as needed during solidification. Controlled replenishment yields uniform density across the part and improves overall dimensional stability.
Stress Reduction
Constant high pressure during the holding phase creates molded-in stress near the gate. By transitionally reducing the pressure, the dynamic packing profile prevents the gate area from becoming brittle and failing under mechanical load. Pressure reduction also lowers the clamping force required to keep the mould closed during the cycle.
Process Optimization
Optimizing the pressure curve requires analyzing the part weight at different holding times. Developing a dynamic packing profile involves finding the exact point of gate freeze-off to avoid packing an already solidified gate. Running trials with progressive step-downs in pressure helps to establish the most efficient cycle time.
Process refinement ensures that the tool is not overpressurized and reduces mechanical wear on the parting line.
