Meaning
Control triggers in the injection cycle switch the machine from velocity control to pressure control at a specific point in the stroke. The switchover pressure is the hydraulic or cavity pressure measured at the moment the screw stops moving at a constant speed and begins the packing phase. This transition is a primary variable for controlling the weight and dimensions of the part.
Phase Transition
Moving from filling to packing requires a precise handover between the different control logics of the machine. If the switchover pressure is reached too early, the part will be under-filled, resulting in a short shot. A delay in the transition can cause a pressure spike that leads to flash or damage to the mould.
Hydraulic Change
Monitoring the force required to maintain the injection speed provides a way to detect changes in material viscosity. When the switchover pressure fluctuates between cycles, it suggests that the resin flow is inconsistent or that the check ring is failing. Stable hydraulic performance is necessary for a repeatable process.
The use of cavity pressure for this trigger removes the influence of barrel friction.
Pack Logic
Establishing the correct point for this transition ensures that the cavity is filled with the optimal amount of material. The switchover pressure must be set based on the specific geometry of the part and the flow characteristics of the resin.
