Laser welding mode transition and influence of thermal focusing on mode transition

Abstract

In high-power CO 2 laser welding, in addition to well- known stable heat conduction welding (HCW) and stable deep penetration welding (DPW), the authors have found a third welding process: unstable-mode welding (UWM). UMW has the feature of the two welding modes (HCW and DPW) appearing intermittently. The physical characteristics of the three welding processes and the features of their weld formation have been described. By synthesizing the effects of laser power, focal position and travel speed on welding mode and welding process, the laser welding mode-transition curves which include three kinds of welding process have been obtained. The curves precisely indicate the welding- parameter ranges of three different welding processes. During laser welding, the thermal focusing of the lens will change the focal position and may cause transition of welding mode and fluctuation of penetration and weld width. The relationships between lens focal shift, laser power and beam irradiation time have been investigated. By using welding mode-transition curve, the influence of thermal focusing on welding mode and welding process has been studied, and measures for prevention of welding process instability induced by thermal focusing have also been suggested.