Development of tornado nozzle for reduction in porosity during laser welding of aluminum alloy

Porosity is one of the most serious problems in a keyhole-type of deep penetration weld beads produced with a high power CO2 or YAG laser. It was revealed that many bubbles were generated from the bottom tip of the keyhole, leading to the formation of porosity. Especially, Ar or He inert shielding gas was chiefly included in the porosity, and therefore a tornado welding nozzle was newly devised as one of the procedures for the decrease or the prevention of an inert gas invasion into a keyhole. In this study, a feasibility of porosity reduction was investigated by using the newly-devised tornado welding nozzle, where the He or Ar shielding gas was flowed as a vortex gas to prevent the keyhole from the invasion of the inert gas or ambient gas. It was confirmed that the tornado welding nozzle could generate negative pressure over the keyhole. It was consequently revealed that the new nozzle was especially effective to the reduction of porosity at slower speeds in CO2 and YAG laser welding of aluminum alloys.