An Integrated Capacitance-Pressure-Temperature Sensing Probe for Injection Molding Monitoring

Process monitoring is a valuable tool in the modern injection molding industry for assessing process health, maintaining safety, and improving product quality. However, to truly tap into the potential of process monitoring, new advancements in sensing technology must be made. Currently, the industry only has a way to monitor the cavity conditions (temperature and pressure) where the product is formed, lacking an online method to monitor in-mold material behaviors. This gap can be bridged by the innovative use of a capacitance sensor, which allows for the real-time characterization of the in-mold material’s dielectric properties and monitoring its status during the molding process. In this work, we develop a low-cost, highly integrated, compact sensing probe capable of simultaneously measuring pressure, temperature, and capacitance signals at the same location, providing comprehensive data for analysis. The sensor is designed, fabricated, and validated through real injection molding experiments. The analysis shows that the capacitance signal can monitor the in-mold material status throughout the cycle, with its endpoint signal strongly correlated with product shrinkage. Furthermore, excellent part weight and thickness prediction results using the machine learning models demonstrate the effectiveness of the sensor signals for injection molding quality monitoring.