Ultrasonic phased array inspection of wire plus arc additive manufacture (WAAM) samples using conventional and total focusing method (TFM) imaging approaches

In this study, three aluminium samples produced by wire + arc additive manufacture (WAAM) are inspected using ultrasonic phased array technology. Artificial defects are machined using a centre drill, ø3 mm, and electro-discharge machining (EDM), ø0.5-1 mm, in a cylindrical through hole topology. The sample was first inspected by a single element wheel probe mounted on a KUKA robot in order to investigate the feasibility of using a conventional ultrasonic transducer approach. Unfortunately, the wheel probe was found to be unsuitable for scanning of the WAAM specimens and ultrasonic phased arrays were employed next. The setup included 5 MHz and 10 MHz arrays (128 elements) in direct contact with the sample surface using both conventional and total focusing method (TFM) imaging techniques. Using FIToolbox (Diagnostic Sonar, UK) as the controller, a phased array aperture of 32 elements was used to perform a focussed B-scan with a range of settings for the transmit focal depth. All the reflectors (including those located near the WAAM top surface) were successfully detected by a combination of conventional phased array and TFM, using a range of settings and setups including bottom surface inspection, application through a Plexiglas wedge and variation of the scanning frequency.