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Innovative NDE for laser welding

: Dobmann, G.; Salzburger, H.-J.

Russian Welding Society:
Welding - Quality - Competitiveness. CD-ROM : Exposvarka 2002. International Conference, Moscow, Russia, October 22-25, 2002
Moskau: Spetselectrode JSK, 2002
International Conference "Welding - Quality - Competitiveness" <2002, Moskau>
Conference Paper
Fraunhofer IZFP ()
Laser; laser welding; nondestructive testing

The contribution reports to developments recently performed for the non-destructive evaluation of welds produced by Laser welding as well as for production monitoring as well as for quality inspection.
Laser welding shows some peculiarities compared with other types of welding procedures. This is on one hand the advantage to have a very small heat-affected zone and therefore not affecting the mechanical properties of the full product very much. On the other hand microstructure gradients combined with residual stresses are very steep and so also the gradients in the properties. Furthermore one type of nonconformity is also typical for Laser welding, i.e. the micro porosity.
During the last years Fraunhofer-IZFP has performed research for monitoring Laser welds in tailored blanks manufactured as half-finished products for car body fabrication. Ultrasonic inspection systems based on the transmitting and receiving of electro-magnetically excited ultrasonic waves have been developed and introduced in the industrial application. For classification of the different types of scattering geometries - linear-dimensional, crack-like nonconformities like lack of fusion or three-dimensional, globular-ones like pores - are separated by using a back reflected and a forward-scattered mode. Due to the higher specular reflection the findings of linear scatterers compared with the others, clearly can be classified by amplitude thresh-holding. The advantage of the technique is the contact-less working transducer, which is gliding on an air pillow avoiding scratches at the sensitive surfaces.