Super sensors for moulding

Injection moulding cavity pressure sensors provide a means of knowing what is happening to the plastic within a mould as it forms a part.

Data from the cavity pressure sensor can help identify undesirable elements of the final part, such as sinks or short shots. A short shot cavity results in the production of an incomplete part. If a part short shots, the plastic does not fill the cavity. A sink mark is a depression such as a dimple caused by excessive shrinking of the material after the part has cooled.

Used as a means to detect part quality, cavity pressure sensors determine whether the cavity pressure in the process is repeatable. Too much pressure can result in the part becoming warped.

“Putting cavity pressure sensors in the mould can help identify sinks and shorts”

Identifying problems with the mould

Putting injection moulding cavity pressure sensors in the mould can help identify sinks and shorts but also voids, flashes and variations in dimensions. They can also assess component weight. But it is not just cavity pressure that is measured in the injection moulding process. Measuring temperature via sensors can also identify incorrect mould temperatures and variations in temperature in the cooling circuit. Cooling rates in the injection moulding process should be monitored because cooling rate variations will cause different rates of material shrinkage. Once the optimum cooling time has been determined, the goal should be to maintain a consistent cooling rate.

Sensor strategies

Injection moulding cavity pressure sensors include various types, capable of withstanding different forces and temperatures. For example, Michigan’s RJG Sensors provides sensors that can withstand forces from 50 to 4,000 pounds, and temperatures of 425ºF. It also makes piezoelectric force transducer and button-style cavity pressure sensors that provide accurate sensor-based statistical process control.

Essentra is a highly experienced and flexible producer of injection moulded parts using the latest sensing, hot runner and other injection moulding technologies. The company has more than 300 moulding machines worldwide, producing millions of parts a week.