Injection Cavity Pressure

Process Control

Piezoelectric sensors mounted behind ejector pins or directly in the cavity wall capture the pressure curve as the melt fills the cavity. The peak of this curve determines the weight and density of the finished part, directly impacting the final dimensions and shrink rate. When the pressure falls below a predetermined limit, the moulding machine can automatically divert the short shot or sink-marked part to the scrap bin.

High pressure spikes indicate overpacking, which causes parts to stick to the mould or develop high molded-in stress that leads to cracking.

Quality Prediction

Measuring this parameter at the end of the flow path helps ensure that the polymer has reached the furthest sections of the mould before solidifying. Consistent pressure at the end of fill correlates with reliable weld line strength and uniform surface gloss across the entire batch. Sourcing departments can use this data to qualify recycled resin runs because it identifies when the viscosity of regrind batches deviates from the virgin baseline.

Resolving these viscosity shifts on the fly reduces setup scrap and avoids costly downtime during material changeovers.

Sensor Maintenance

Regular inspection of the sensor pocket and ejector pins is necessary to prevent polymer residue from build-up and causing incorrect readings. Mould release agents and polymer outgassing can deposit on the pin sides and restrict free movement, which dampens the recorded pressure signal. Technicians must clean the sensor channels during routine tool maintenance to maintain system accuracy.

Calibrating the signal amplifiers against known loads ensures that the recorded data remains comparable across different machines and production runs.