Air-coupled Ultrasonic Testing-Method, System and practical Applications

Abstract

Since more than 20 years the air-coupled ultrasonic technique already exists. Problems caused by the large acoustic mismatch between solids and air are solved with special transducers, a powerful excitation as well as a hard- software signal processing. Our USPC 4000 AirTech includes a powerful burst-pulser, an ultralow noise preamplifier and a band pass filter amplifier. The combination of hard- and software filters increases the signalto noise ratio up to 50 dB. The software imaging Hillgus for Windows enables an easy control of the system and of the different manipulators as well as evaluation and measuring functions of the C-scans. Air-coupled ultrasonic testing requires separate transducers as a sender and receiver on opposite sides of the component. Pitch and catch technique require only a single sided access. Because of critical adjustments this method is only preferable for laboratory applications. However, a robust inspection requires a two sided access. This paper presents details of automated scanning systems for tube-shaped- and flat CFRP- and CFRP honeycomb components. Usually ultrasonic testing of complex aerospace components is carried out with squirter technique. However, water coupling delivers disadvantages like pressure variations, air-bubbles, lime scales, algae and corrosion of the mechanics. Therefore a non-contact technique is preferable which avoids these disadvantages. Because of the coaxial alignment of the transducers on opposite sides of a complex component a ten axes robot scanning system is necessary. This paper presents first results and details of the automated air-coupled robot ultrasonic imaging system which is in operation by Airbus Helicopters in Donauworth/Germany since 2011. A larger device is currently installed in Zurich/Switzerland for sandwich space components. The 10 axes scanning system has a mass of 18 tons. These projects have been a co-operation between Robo-Technology, Dr. Hillger, and Eugen Ostertag. New developmens are focused on the one-sides access of air-coupled ultrasonic. The project is called BUC which means non-contact ultrasonic testing. We would like to thank the German Government (BMBF – KMU innovative) for their support.