Dynamics of keyhole and molten pool in high power CO2 laser welding

A deep cavity called keyhole is formed in the laser weld pool due to the intense recoil pressure of evaporation. The formation of keyhole leads to a deep penetration weld with high aspect ratio. However, a hole drilled in a liquid pool is primarily unstable by its nature and the instability of keyhole also causes the formation of porosity in the weld metal. The porosity formation is one of the serious problems in the very high power laser welding, but its mechanism has not been well understood. The authors have conducted systematic studies on observation of keyhole as well as weld pool dynamics and their related phenomena to reveal the mechanism of porosity formation and its suppression methods(1-7). The paper describes the real time observation of keyhole and laser plasma/plume behaviors in the high power CW CO2 laser welding by the high speed optical and X-ray transmission methods, cavity formation process and its suppression measures.