Meaning
Piezoelectric transducers monitor force transfer within the mold cavity during filling, packing, and cooling phases. Measuring in-cavity pressure provides direct feedback on melt viscosity shifts and part density formation during injection. Standard hydraulic pressure readings fail to account for runner friction drops or nozzle resistance variations.
Molders use cavity sensor signals to trigger melt decoupling switches, transferring control from velocity to pressure control modes at precise cavity fill thresholds.
Cavity Mechanism
Transducers installed behind ejector pins convert mechanical force into electrical charge proportional to local melt pressure. Pressure peaks at the end of fill indicate cavity packing level and wall contact quality. Dropping pressure curves during the cooling stage signal volumetric shrinkage and solidification of the gate region.
Signal variations between cavities identify unbalanced runner channels or uneven cooling channel performance.
Process Control
Decoupled molding strategies use peak pressure thresholds to freeze hydraulic hold pressure, eliminating flash formation caused by overpacking. Variations in resin viscosity, such as those introduced by regrind blending, shift hydraulic pressure without altering actual force delivered to the polymer inside the cavity. Real-time cavity monitoring automatically compensates for viscosity changes by adjusting holding pressure duration.
Machine operators set pressure limits to ensure consistent wall density across production batches.
Quality Assurance
Part weight stability correlates directly with peak pressure values recorded during the holding phase. Maintaining consistent pressure profiles prevents sink mark formation and dimensional warpage in thick-walled parts. Integrated pressure sensors eliminate manual weight checks and guarantee part reproducibility.
