Couplant free UT of laser weld joints of thin sheets using guided waves and EMAT´s

For the quality assurance of laser butt welds of tailored blanks conventional UT is ruled out because of the necessary coupling medium. UT by EMAT´s using the dispersionless lowest mode of guided shear horizontal has big advantages for practical in-line inspections due to large distances between probe and weld, low influence of the thickness step and couplant free, contactless inspection. The investigations performed on a large set of test samples showed that all types of defects which may occur during laser welding are detected with signal-to-noise ratios > 20 dB