Hot Runner
Cavity pressure is the pressure the melt actually reaches inside the mold cavity; it is not the same as the injection pressure on the machine screen. Gate wear, a dirty runner, viscosity differences and mold temperature create losses in between. A piezoelectric sensor placed in the cavity records the pressure curve of every cycle; the integral of the curve correlates with part weight, and good/bad part separation can be automated.
The pressure curve is read in five regions: rise (filling), knee point (switchover), peak, plateau (holding) and decline (gate freeze). A high peak means flash, a short plateau means the gate is freezing early, and a curve that shifts from cycle to cycle means the process is unstable.
The sensor can be placed near the gate or at the end of flow; direct placement in the cavity or indirect placement behind an ejector pin is chosen. Measurement does not correct, it shows: the source of an unstable curve is usually drying, dosing or mold temperature.
It is an expected capability in medical, automotive safety parts and zero-defect production; in low-volume general production it may be a premature investment.