Monitoring the injection moulding process: direct sensorisation of the mould cavity

In-process monitoring techniques are of paramount importance for optimisation of the injection moulding process. Real-time measurements provide valuable information of the quality of the moulded parts and operating conditions which are required for the success of manufacturing finished plastic products of industrial or consumer applications.

Pressure transducers, rapid dynamic response cavity thermocouples and position sensors are among the most widely used in the plastic injection moulding industry and are thought to result from the ability of these to describe the whole process in detail.

The processes that take place inside the mould are widely acknowledged as being decisive for the quality of the finished product. For example, monitoring of cavity melt pressure data enable examination of the injection moulding, compression and holding processes (Figure 1). The profile of the cavity pressure curve provides detailed information concerning weight, shape, burrs, shrinkage cavity, cavitation, contraction and deformation. Correctly controlled, it guarantees a sustainable quality improvement and a reduction in scrap.

Image for blog3Figure 1: The Four Phases of Cavity Pressure*

Cavity melt pressure measurements are known to be highly affected by the correct positioning of the cavity pressure sensor. Compared to measurements near the gate, measurements far away from the gate have been reported to be more favourable when special quality problems must be monitored at the end of the flow path*.

In-process quality is concerned with the relationship between pressure and temperature profiles. Combined sensors for pressure and temperature are particularly suited to use for the monitoring of parts with a tendency to shrinking and deformation.

Therefore, the use of real-time monitoring techniques appears to be crucial for the analysis of the injection moulding process and examination of its efficiency, leading to manufacturing process improvements by direct sensorisation of the mould cavity.

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