The change of the capillary shape during pore formation and its effect on process emissions

Detecting the formation of pores during laser beam welding is challenging as pores are not visible from the outside of the weld seam. However, during formation, pores inherently change the capillary shape, leading to a change in its emissions as well as a change in the back reflection of the laser beam. Monitoring of these emissions has already proven to be a suitable tool in order to determine the formation of defects in welds based on statistical methods and empirical evaluations. To clarify the effect of shape fluctuations of the capillary on its emissions during laser beam welding the capillary shape was recorded by means of synchrotron X-ray imaging and the process emissions were simultaneously measured in different spectroscopic ranges. The analysis of the data proves the connection between capillary fluctuations and characteristic changes of the signals and therefore enables the detection of pore formation.