Ultrasonic phased array inspection of a Wire + Arc Additive Manufactured (WAAM) sample with intentionally embedded defects

Abstract

In this study, Wire + Arc Additive Manufacture (WAAM) was employed to manufacture a steel specimen with intentionally embedded defects which were subsequently used for calibration of an ultrasonic phased array system and defect sizing. An ABB robot was combined with the Cold Metal Transfer (CMT) Gas Metal Arc (GMA) process to deposit 20 layers of mild steel. Tungsten-carbide balls (ø1-3 mm) were intentionally embedded inside the additive structure after the 4th, 8th, 12th and 18th layers to serve as ultrasonic reflectors, simulating defects within the WAAM sample. An ultrasonic phased array system, consisting of a 5 MHz 64 Element phased array transducer, was used to inspect the WAAM sample non-destructively. The majority of the reflectors were detected successfully using Total Focusing Method (TFM), proving that the tungsten carbide balls were successfully embedded during the WAAM process and also that these are good ultrasonic reflectors. Owing to a lack of standards and codes for the ultrasonic inspection of WAAM samples (Lopez et al., 2018), a calibration method and step-by-step inspection strategy were introduced and then used to estimate the size and shape of an unknown lack of fusion (LoF) indication. This was then validated by destructive analysis, showing a good correlation with the phased array results.