In-situ X-ray Observation of Molten Pool Depth

To clarify phenomena which cause strength decrease in the molten pool during laser welding processes, we have carried out X-ray imaging of inside materials using intense synchrotron radiation during laser welding.An air-cooled continuous wave fiber laser was used for welding.When the laser beam was irradiated on sample materials, molten pool shape were successfully observed using an X-ray absorption contrast technique.Moreover, bubbles in molten pool and cracks in weld metal were clearly observed.Butt welding for heat exchanger tubes was demonstrated by a specially designed probing system.The probing system consisted on a composite-type optical fiber, a laser processing head, air-cooled fiber laser and so on.Here, the surface of the weld bead was observed by fiber scope images.In such a repair welding, the observation of the inside material by X-ray imaging is very effective because it can inform us how the weld depth could grow and why the weld defect would be born.