Ultrasonic phased array inspection of the fully-automated multi-pass weld with an intentionally embedded tungsten rod

Y Javadi, E Mohseni, M Vasilev, D Lines, C MacLeod, R Vithanage, Z Qiu, R Zimermann, C Loukas, E Foster, G Pierce and A Gachagan
Centre for Ultrasonic Engineering (CUE), Department of Electronic & Electrical Engineering, University of Strathclyde, Glasgow G1 1RD, UK 

In this study, a multi-pass weld is deposited by a six-axis KUKA robot equipped by the tungsten inert gas (TIG) welding torch. The specimen is a 10 mm-thick structural steel (S275) plate that is 300 mm in length. In total, seven weld passes are deposited in four layers inside a 60° degree V-groove. Using CompactRIO (National Instruments, USA) and LabVIEW, an integration system is employed to connect the welder machine and robot. A number of trial specimens are first manufactured to develop the welding parameters as well as the horizontal and vertical offset for the robot positioning in each pass. Two main specimens are then manufactured while the welding parameters are consistent in both samples. The first specimen is for recording the temperature over the weld, using thermocouples, to ensure the interpass temperature requirements, 150-200°C, is achieved and then the interval pause required after each pass is determined too. Once the welding parameters, the interpass pause and the robot offset for each pass are all determined, the welder robot can be safely left in the auto-mode to work independently for around 40 minutes with an outcome of the fully-automated multi-pass weld. This system also includes two automated tack welds as well as two bead-on-plate passes, without wire, for preheating before the root pass. The only interruption of this automated manufacturing system is the process of embedding a tungsten rod in the weld, known as the intentional weld defect process. Since a known size defect, ø2.6 mm tungsten rod in this study, is intentionally embedded in the weld, the calibration procedure for non-destructive testing (NDT) of unknown size defects (for example, lack of fusion, cracks, etc) will be achieved. The specimen is then inspected by the ultrasonic phased array system in order to detect the tungsten rod and the other possible defects. The ultrasonic array is a 5 MHz Olympus array (contact mode) with 64 elements and the phased array controller is LTPA (PEAK Ltd, UK). The Olympus high-temperature wedge, manufactured with an amorphous thermoplastic polyetherimide resin called ULTEM™, is also employed to deploy the sectorial scanning approach. The ray tracing is determined by the CIVA simulation in order to decide the best inspection methodology (ie the position of the array with respect to the weld centre). It has been shown that the tungsten rod can be successfully detected in the weld centre. Because the fully-automated welding system is quite flexible, it is feasible to use the NDT feedback in order to improve the weld integrity.

Keywords: automation, ultrasonic phased array, robotic welding, intentional weld defects.