Ultrasound Sensors for Process Monitoring in Injection Moulding

Abstract

Injection moulding is an extremely important industrial process, being one of the most commonly-used plastic formation techniques. However, the industry faces many current challenges associated with demands for greater product customisation, higher precision and, most urgently, a shift towards more sustainable materials and processing. Accurate real-time sensing of the material and part properties during processing is key to achieving rapid process optimisation and set-up, reducing down-times, and reducing waste material and energy in the production of defective products. While most commercial processes rely on point measurements of pressure and temperature, ultrasound transducers represent a non-invasive and non-destructive source of rich information on the mould, the cavity and the polymer melt, and its morphology, which affect critical quality parameters such as shrinkage and warpage. In this paper the relationship between polymer properties and the propagation of ultrasonic waves is described and the application of ultrasound measurements in injection moulding is evaluated. The principles and operation of both conventional and high temperature ultrasound transducers (HTUTs) are reviewed together with their impact on improving the efficiency of the injection moulding process. The benefits and challenges associated with the recent development of sol-gel methods for HTUT fabrication are described together with a synopsis of further research and development needed to ensure a greater industrial uptake of ultrasonic sensing in injection moulding.

State Estimators in Soft Sensing and Sensor Fusion for Sustainable Manufacturing

“…It is one of the most used industrial processes for the formation of polymer products. Improvements in monitoring and control of the process can reduce energy consumption and waste generation as well as enable the processing of more complex, sustainable raw material streams [57].…”

In-Line Near-Infrared Spectral Monitoring of Dissolved Nitrogen in Molten Polymers during Foam Injection Molding

“…Because polymer production processes, such as injection molding and extrusion, include molten polymers at elevated temperatures and pressures, the development of inline sensors for chemical composition analysis has been delayed by concerns related to equipment durability under such harsh operating conditions. Several inline monitoring methods have been proposed thus far, including visual window observation, − inline ultrasonic sensors, − and various inline spectroscopic methods such as near-infrared (NIR) spectroscopy, Raman spectroscopy, − and visible spectroscopy. , Among these methods, inline NIR spectroscopy has gained widespread acceptance due to its affordability, rapid data acquisition, nondestructive nature, and ability to analyze millimeter-thickness samples and provide valuable chemical insights.…”

In-Line Monitoring of the Physical Blowing Agent Concentration by Transmission Near-Infrared Spectroscopy with High-Pressure Resistance Fiber Optic Probes for Foam Injection Molding Processes

“…This is because the parts of the measurement device in contact with the molten polymer must have high heat and pressure resistances under the process’s repetitive, nonsteady-state operation. Scientists have proposed ultrasonic sensors − and near-infrared spectroscopic (NIR) sensors − for in-line measurements of process variables that are not easy to measure with conventional sensors. Ultrasonic sensors have attracted attention because they can be attached directly to the outer surface of molds or barrels without the need to modify the equipment.…”