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

In modern design of automobile bodies reduction in weight and maximisation of the structural stiffness and passive safety are the main challenge. The `tailored blank´ has contributed to achieving a significant weight reduction in recent years. Single flat sheets are joined by laser welding into the desired configuration without filler wire. Usually the quality of the welds is assured by precise preparation of the plate edges and measurement of two of the process parameters. However, due to process deviations, defects occur, which makes NDT necessary. These defects include incomplete welding, lack of fusion, misalignment of the weld, holes and porosity. The paper presents a versatile ultrasonic inspection technique designed for in-line inspection of laser welds of tailored blanks. Conventional ultrasonic testing is ruled out because of the necessary liquid coupling medium. Therefore, the proposed inspection approach is based on the application of guided ultrasonic (plate) waves with shear horizontal polarisation excited and detected by couplant-free electromagnetic acoustic transducers