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.‎