Ultrasonic phased array inspection of wire plus arc additive manufacture samples using conventional and total focusing method 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, ø 3 mm, and electrical discharge machining (EDM), ø 0.5-1 mm, in a cylindrical through-hole topology. The samples are first inspected using 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 is found to be unsuitable for scanning the WAAM specimens and ultrasonic phased arrays are employed next. The set-up includes 5 MHz and 10 MHz arrays (128 elements) in direct contact with the sample surface using both the conventional and total focusing method (TFM) imaging techniques. Using an FIToolbox (Diagnostic Sonar, UK) as the controller, a phased array aperture of 32 elements is used to perform a focused B-scan with a range of settings for the transmit focal depth. All of the reflectors (including those located near the WAAM top surface) are successfully detected with a combination of conventional phased array and TFM, using a range of settings and set-ups, including bottom surface inspection, application through a plexiglass wedge and variation of the scanning frequency.