Quality Assurance of Vacuum Assisted Resin Infusion (VARI) Manufacturing Processes via Acoustic Monitoring with polyCMUTs

The increasing complexity and use of composite structures demand robust quality assurance during manufacturing. Vacuum-Assisted Resin Infusion (VARI) is a widely used process in which sheets of composite fibers are placed over forms, encased in vacuum bags, and infused with resin drawn by a vacuum. A critical challenge in VARI is controlling and monitoring the resin flow front to avoid voids or dry spots and overseeing the curing process to prevent warping and residual stress.

Current solutions, such as sensors that measure electrical resistance via embedded wires or capacitive sensors that detect changes in electric fields, are costly and require access to both sides of the part, limiting their practicality. We propose an alternative approach using a sensor network of active polymer-based capacitive micromachined ultrasonic transducers (polyCMUTs). These flexible, thin, and lightweight transducers are applied on top of the vacuum bag. They transmit and receive ultrasonic signals, allowing precise monitoring of resin flow and curing. Their small and flexible size, ease of application, and low cost enable the use of more sensors with minimal impact on the workpiece and more complex geometries, compared to traditional piezoelectric sensors.

By analyzing changes in ultrasonic signal parameters, such as time-of-flight and attenuation, we can accurately track the resin flow front and curing progress. This work presents results from initial prototyping and system development, demonstrating successful flow front and room temperature curing measurements on a small-scale (8 plies, 200 x 200 mm) demonstrator.