Development Of An Activating Flux For TIG Of Stainless Steel And Effect Of Activating Flux On Plasma During CO₂ Laser Welding

During high power CO₂ laser beam welding, laser-induced plasma over the keyhole has important influence on the transmission of incident laser. Laser-induced plasma would reflect, refract, absorb and scatter the incident laser. The negative effects such as shadow effect, negative lens effect are displayed macroscopically. So it is very important to be depressed as far as possibly. Now in A-TIG welding, the coefficient of arc shrinking and the weld pool surface tension result in penetration increased. For arc shrinking in A-TIG welding, it is thought that atoms evaporated trap electrons external plasma and finally make arc plasma shrank. Whereas decreasing electron density is one of controlling plasma principles during laser beam welding.In this paper, for stainless steel (0Crl8Ni9Ti), several common oxides and halides, namely SiO₂, Cr₂O₃, CaF₂, TiO₂ B₂O₃, etc, are taken as basic activating flux. On this basis, the composition uniform design method is employed to develop A-TIG activating flux. By this way, the experiments times decrease remarkably and the weld penetration increase more than 2.5 times compared with the conventional TIG welding.And then the effect of activating flux on plasma during laser welding is studied. The stainless steel (0Cr18Ni9Ti) is respectively welded by using activating flux and by not using activating flux. And the shape variation of plasma during laser welding is recorded directly by using three-dimension synchrony high-speed photography separately. After analyzing the weld penetration, plasma shape change and plasma area change curves, it is found that the penetration increases, plasma area becomes smaller and the area change range of laser-induced plasma is also smaller.