Quality control of laser welds of tailored blanks using guided waves and EMATs

In modem design of automobile bodies reduction in weight and maximisation o f the structural stiffness and passive safety are the main challenge. ne 't ailored blank' has contributed to achieving a significant weight reduction in recent years. Single flat sheets are joined by laser welding into the de sired configuration without filler wire. Usually the quality of the welds i s assured by precise preparation of the plate edges and measurement of two of the process parameters. However, due to process deviations, defects occu r, which make non-destructive testing (NDT) necessary. These defects includ e incomplete welding, lack of fusion, misalignment of the weld, holes and p orosity. The paper presents a versatile ultrasonic (UT) inspection techniqu e designed for in-line inspection of laser welds of tailored blanks. Conven tional ultrasonic tetsing is ruled out because of the necessary liquid coup ling medium. Therefore, the proposed inspection approach is based on the ap plication of guided ultrasonic (plate) waves with shear horizontal polarisa tion excited and detected by couplant-free electromagnetic acoustic transdu cers (EMATs).