Ultrasound Based Monitoring of Flow Front and Laminate Thickness without Contact to Part

Kurzfassung

As liquid composite molding processes are very sensitive to deviations in raw materials and pro-cess parameters, sensing systems providing information about the flow propagation inside the preform are highly demanded. For monitoring LCM processes ultrasonic sensors are particularly well suited, as they offer a wide range of the most crucial information about the process. Furthermore they do not require direct contact to the part, thus the part surface and the mould vacuum integrity are not affected. The sensors are applied on the outer side of the mould, from where the sound waves propagate through the wall and then interact with the part. A large fraction of the sound waves are reflected back to the sender while the remaining sound waves or pass through the part. By analyzing this signal the arrival of the flow front can be obtained in a very robust way. Not only the arrival time, also the flow speed and even its direction can be derived by enhanced signal processing. The DLR has developed small and low cost ultrasound sensors which allow the integration of a dense sensor network. These sensors require less effort in order to integrate them and provide broader information in comparison to conventional transducers. Besides the flow front the laminate thickness can be derived from the time of flight through the part, which then can be for thickness control by pressure and infusion time adaption, where the cure influence on the sound velocity needs to be compensated. Lastly the cure progress as well as gelation and vitrification can be monitored with the same sensors. The developed sensor system, a short theoretical overview, experimental validation and first near industrial applications including autoclave based infusion will be presented.