Ultrasonic flow front, thickness and cure monitoring of liquid composite molding processes

Abstract

Liquid composite molding processes (LCM) can reduce production costs of composite parts due to low material costs and the high lay-up rates of dry fabrics. But LCM are very sensitive to deviations in raw materials, lay-up or processing parameters. Small variations can have a high effect on the fill patterns which can lead to incomplete impregnation and gas inclusions. In order to monitor, thus analyze and control the ongoing infusion process, there is a high demand for suitable sensor systems. Ultrasound is particularly well suited for process monitoring of LCM. The most crucial parameters of the filling as well as the resin cure can be monitored with ultrasound. Furthermore no direct contact to the part is required, thus the part surface and the mold vacuum integrity are not affected. The DLR has developed small and low cost ultrasound sensors allowing the integration of a dense sensor network. The developed method allows monitoring arrival time, shape and velocity of the flow front as well as the laminate thickness evolution. Also the cure, gelation and vitrification can be monitored with the same sensors. Due to the acquired information the process parameters can be adapted to correct deviations and reduce process duration.