In-line quality control of laser welds of tailored blanks by couplant free ultrasonic inspection

In modern design of automobile car bodies reduction in weight and maximization of the structural stiffness and passive safety are the main challenge. The 'Tailored Blank' has contributed to achieve a significant weight reduction in recent years. The single flat sheets are joined by Laser Welding in butt configuration without filler wire. Usually the quality of the welds is assured by precise preparation of the plate edges as well by the suitable selection of process parameters. However due to unforeseen deviations typical defects occur, which make NDT necessary to detect defects as incomplete welding, lack of fusion, misalignment, pinholes, porosity ect. The contribution presents a new UT inspection technique designed for the in-line inspection of the laser welds of Tailored Blanks. Conventional UT is ruled out because of the necessary liquid coupling medium. The inspection is based on the application of guided ultrasonic (plate) waves with shear horizontal polarization excited and detected by couplant free Electromagnetic Acoustic Transducers (EMAT's).