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New thermo-mechanical approach to overcome hot cracking in laser welding

: Göbel, G.; Brenner, B.

Vollertsen, F. ; Wissenschaftliche Gesellschaft Lasertechnik -WLT-:
Lasers in manufacturing 2007 : Proceedings of the Fourth International WLT-Conference Lasers in Manufacturing, LIM 2007, Munich, Germany, June 18th - 22nd, 2007
Stuttgart: AT-Fachverlag, 2007
ISBN: 978-3-00-021449-3
International Conference on Lasers in Manufacturing (LIM) <4, 2007, München>
Conference Paper
Fraunhofer IWS ()
laser welding; hot cracking; solidification; induction; free cutting steel; Warmriss; Laserschweißen; Schnellstahl; Aluminiumlegierung; austenitischer Stahl; thermomechanische Eigenschaft; Zugbeanspruchung; Temperaturfeld; induktives Erwärmen; experimentelles Ergebnis

Hot cracking in welding is still an unresolved problem for a wide range of materials that restricts their use in production. Although free cutting steels are a prominent example of hot cracking sensitivity, other industrially important materials like high strength aluminium alloys, many austenitic steel grades and several high-temperature alloys are also prone to hot cracking. In all cases the actual forming of a hot crack is not only the consequence of metallurgical reasons but also of special thermomechanical conditions, namely too much tensile strain on the not fully solidified regions. Therefore it is not only possible to avoid the cracks by avoiding the mentioned metallurgical reasons, but also by reducing or counteracting any stress / strain on the hot-cracking critical zones. As the latter approach is much less discussed in the literature and only seldom pursued industrial application research, this article wants to emphasize its importance by introducing a new technique against hot cracks on this basis. A new process technique is presented which aims at reducing or avoiding hot cracking during laser welding. It is based on a tailored temperature field around the molten pool that changes the thermomechanical conditions of the material during the solidification of the weld. The required additional volumetric heat input is realized by inductive heating. The technique was tested successfully on strongly hot cracking sensitive heat treatable free cutting steels. The results of these tests show not only the relation between possible thermal and mechanical influences on the cracking intensity but also give important information about the possibilities and limits of the technique. Typical application areas are presented.
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