Non-destructive testing of laser welds in tailored blanks using electromagnetic transducers

An ultrasonic system using electromagnetic acoustic transducers has been developed at the Fraunhofer Institute for Non-Destructive Testing (IZFP), in order to test laser welds in tailored blanks. Shear horizontal modes are exploited to detect different types of defects in the laser welds, such as lack of penetration, lack of fusion, mismatch and cracks. In the present work, studies of the discontinuities of the laser weld that affect specularly reflected and non-specularly signals have been carried out on ferritic sheets. Geometric parameters of the laser weld, such as the fusion-zone width and the discontinuities at the weld root, were measured and compared with the amplitude of the reflected signals. Furthermore, X-ray radiographs and metallography were made to obtain additional information on the different defects, which affect the ultrasonic signal. From our results we conclude that under thickness and incomplete penetration at the root, together with the pores of the weld affect the reflected signal more than any other discontinuity.