Intentional weld defect process: from manufacturing by robotic welding machine to inspection using TFM phased array

Specimens with intentionally embedded weld defects or flaws can be employed for training, ‎development and research into ‎procedures for mechanical property evaluation and ‎structural integrity assessment. It is critical that the artificial defects are ‎a realistic ‎representation of the flaws produced by welding. Cylindrical holes, which are usually ‎machined after welding, ‎are not realistic enough for our purposes as it is known that they ‎are easier to detect than the naturally occurring ‎imperfections and cracks. Furthermore, it is ‎usually impractical to machine a defect in a location similar to where the real ‎weld defects ‎are found. For example, electro-discharge machining can produce a through hole ‎‎(cylindrical reflector) which ‎neither represents the weld porosity (spherical voids) nor the ‎weld crack (planar thin voids).‎‏ ‏In this study, the aim is to ‎embed reflectors inside the weld intentionally, and then locate ‎them using ultrasonic phased array imaging. The specimen is ‎an 8 mm thick 080A15 ‎Bright Drawn Steel plate of length 300 mm. Tungsten rods (o2.4-3.2 mm & length 20-25 ‎mm) and ‎tungsten carbide balls (o4 mm) will be used to serve as reflectors simulating ‎defects within the weld itself. This study is ‎aligned to a larger research project investigating ‎multi-layer metal NDE found in many multi-pass welding and wire arc ‎additive ‎manufacturing (WAAM) applications and as such, there is no joint preparation as the first ‎layer is deposited over ‎the plate surface directly and subsequent layers contribute to the ‎specimen build profile, similar to the WAAM samples. A ‎tungsten inert gas welding torch ‎mounted on a KUKA robot is used to deposit four layers for each weld, with our process ‎‎using nine passes for the first layer, down to six passes for the last layer. During this procedure, ‎the tungsten artificial ‎reflectors are embedded in the weld, between the existing layers. The ‎sample is then inspected by a 10 MHz ultrasonic ‎phased array in direct contact with the ‎sample surface using both conventional and total focusing method (TFM) imaging ‎‎techniques. A phased array aperture of 32 elements has been used. The phased array ‎controller is FIToolbox (Diagnostic ‎Sonar, UK). Firstly, a focused B-scan has been ‎performed with a range of settings for the transmit focal depth. Secondly, a ‎full-aperture ‎TFM method has been processed. All the reflectors of interest were detected successfully ‎using this ‎combination of B-scan and TFM imaging approaches.‎