[4A1] Inspection of laser welds in titanium using electromagnetic acoustic transducers
C Peyton¹,², S Dixon¹, B Dutton², W Vesga² and R S Edwards¹
¹University of Warwick, UK
²The Manufacturing Technology Centre, UK
Performing inspections inline with the welding process can result in more time- and economically efficient manufacturing. The in-process inspection of laser welds requires a technique to detect small defects, with a minimum target length of
0.5 mm specified in this project. The approach in this work uses electromagnetic acoustic transducers (EMATs) to generate and receive ultrasonic signals. The fundamental shear horizontal mode (SH0) is used because it offers particular benefits, such as being non-dispersive, and is easily generated using EMATs. Our previous work has shown that EMATs can be used to generate shear horizontal guided waves in titanium with sufficient signal-to-noise ratio (SNR), contradicting conventional wisdom, which considers EMATs challenging to use on this material due to its relatively low electrical conductivity and high ultrasonic attenuation and density.
The minimum target defect size requires the capability to recover signals scattered from the defect, with a low SNR in the time domain A-scan. Therefore, simulations and experimental work investigated the interactions between the incident SH0 guided wave mode and different sized defects to identify different approaches and mechanisms for the detection of defects. This work showed that the defect width affects the defect length-to-wavelength ratio at which maximum SH0 reflection occurs. As well as the direct reflections, mode conversions at the defect have been investigated, demonstrating how the defect width impacts the angle at which maximum reflection occurs. This work brings together these findings, developing an inline EMAT-based inspection set-up for laser-manufactured welds in thin titanium sheets. Multiple receiver transducers allow for detecting the different wave modes scattered in the forward and reverse direction of the SH0 wave incident on the defect. By having additional receivers, data fusion can be applied to the small amplitude reflections, improving the probability of detection. The results focus on using a 6 mm wavelength guided SH0 mode, interacting with defects present in the weld bead.
The minimum target defect size requires the capability to recover signals scattered from the defect, with a low SNR in the time domain A-scan. Therefore, simulations and experimental work investigated the interactions between the incident SH0 guided wave mode and different sized defects to identify different approaches and mechanisms for the detection of defects. This work showed that the defect width affects the defect length-to-wavelength ratio at which maximum SH0 reflection occurs. As well as the direct reflections, mode conversions at the defect have been investigated, demonstrating how the defect width impacts the angle at which maximum reflection occurs. This work brings together these findings, developing an inline EMAT-based inspection set-up for laser-manufactured welds in thin titanium sheets. Multiple receiver transducers allow for detecting the different wave modes scattered in the forward and reverse direction of the SH0 wave incident on the defect. By having additional receivers, data fusion can be applied to the small amplitude reflections, improving the probability of detection. The results focus on using a 6 mm wavelength guided SH0 mode, interacting with defects present in the weld bead.
