The influence of shielding gas on process properties during laser welding

Many studies have shown that type and flow rate of shielding gas are important to weld depth and weld quality during laser welding. These results are attributed that different shielding gas can change the laser radiation into the workpiece. In this paper, high- speed camera and optical emissions monitoring and spectroscopic analysis were used to study the processes of laser welding of 304 stainless steel taking He and Ar as shielding gas. The research results show that shielding gas type has more effects on welding process features. First of all, shielding gases have great effect on the spectrum of optical emission. With Ar as a shielding gas, intense spectrum lines locate the range of 450nm ~ 850nm, mainly Ar lines and Fe lines. However, with He gas, intense spectrum lines are mainly ultraviolet. Next, the shielding gas types have obviously influence on size and fluctuation frequency of plasma/vapour. The use of He gas, maximum width of the plasma/vapour is about 36 percent of that with Ar, and the dominant fluctuation frequency band of 1000Hz ~ 1500Hz is much lower than the band of 1500Hz ~ 3500Hz with Ar shielding gas. Finally, the shielding gases influence apparently on geometry of melt pool. At the same heat input, the pool volume with Ar gas is larger than that with He, and this differences increase with larger input heat. And the length of surface pool with Ar gas is much longer than with He, and the differences increase with heat input. For the length of back pool these differences are quite little. Moreover, there is a more narrow surface with He gas than with Ar. All of these results can be from its different ionization potential and resistance to breakdown for He and Ar gas. And these differences bring great effects on laser radiation into workpiece.