Keyhole-induced porosity formation during laser welding

Through laser welding experiment with glass, the dynamics of keyhole and molten pool could be directly observed to reveal the mechanism of porosity formation using high speed camera. The high speed images showed that large fluctuation of keyhole was responsible for the increased bubble formation, and bubble merging resulted in the formation of large pore. The porosity of the welded samples was characterized qualitatively and quantitatively by combining super depth microscope and image processing. Porosity characteristics such as pore number, pore diameter (maximum and mean), porosity volume and porosity ratio varied with changes in welding speeds and laser powers. Increased energy density led to a decrease in the number but an increase in the other characteristics, indicating that the higher the energy density the more violent the bubble merging and giving rise to an increased possibility to form large pores.