Meaning
Machine control transitions mark the operational change from volumetric velocity control to hydraulic pressure control during mold filling. Operating parameters governing v/p crossover set the precise stroke position, cavity pressure, or time where the press stops pushing melt at constant speed and begins maintaining holding pressure. Machine position sensors trigger this switchover before the mold cavity is completely filled with molten plastic.
Process engineers tune this transition point to prevent tool damage and avoid cosmetic defects on molded parts.
Switchover Mechanism
High-speed injection units fill approximately 95 to 98 percent of cavity volume under closed-loop velocity control. At the pre-set trigger point, control algorithms switch execution from screw speed control to pressure regulation. Switching too early causes short shots and sink marks due to insufficient volumetric filling before pressure transfer.
Switching too late causes severe pressure spikes when moving melt hits stationary mold boundaries, forcing mold plates apart and generating part flash across parting lines.
Cavity Protection
Timely pressure transfer prevents excessive hydraulic pressure spikes from damaging delicate cavity tooling. Precise v/p crossover tuning ensures consistent cavity packing without overstressing gate areas.
Process Repeatability
Consistent switchover execution stabilizes part weight and dimensional accuracy across continuous production runs. Variations in resin viscosity shift hydraulic pressure demands, making position-based switchover more reliable than pressure-based triggers for variable material lots. Incorporating regrind shifts melt compressibility, requiring minor adjustments to switchover position to maintain constant cushion size.
Precise transition timing ensures reliable packing density without overpacking gate areas.
