Piezoelectric Cavity Pressure Sensor Setup in Micro Injection Moulding
Direct piezoelectric cavity pressure sensing in micro injection moulding requires sub-micron bore tolerances, rigid preloading, and active thermal drift compensation.
VP Switchover
Meaning
Transition point during the injection moulding cycle where the machine shifts from velocity-controlled filling to pressure-controlled packing governs the final density of the part. Determining the correct vp switchover prevents overfilling the cavity and protects the mould from excess stress. This setting is typically determined by screw position, cavity pressure, or injection time.
Process Transition
The injection stroke must fill the cavity to ninety-five percent of its volume before the shift. If the vp switchover is executed too early, the machine struggles to pack the part. Conversely, a delayed transition causes high pressure spikes.
Control Strategies
Moulders select the switchover method based on part geometry and quality requirements. Position-based switchover is the most common method, using the screw position to trigger the change. Cavity-pressure-based switchover offers the highest repeatability, as it directly measures the pressure of the melt front, compensating for variations in resin viscosity between virgin and regrind batches.
Defect Mitigation
Consistency in the switchover point is critical to maintaining a stable part weight across a production run. By switching to pressure control at the same instant in each cycle, the internal stresses in the polymer are kept uniform, which reduces part warpage. Modern machines monitor the switchover pressure to detect process drift and adjust the screw speed dynamically to keep the process stable.