Abstract: Compare to argon arc welding, helium can provide deeper penetration, much more efficient and high-quality weld when it serves as shielding gas, and it performed well in aerospace products welding. In order to compare the characters of these two different arcs, use high-speed camera to observe the shapes of argon and helium arc, while pressure sensors and two divided anodes are used to measure the distribution of arc pressure and anode current density. The results show that, helium arc is obviously compressed near the anode, and it turns to pear-shape with the arc length increasing, while the shape is spherical when the arc length is small. Both helium and argon arc pressure increase with the increasing of welding current, and the arc pressure of helium is much smaller than that of argon under the same welding current. The anode current density of helium arc is much more concentrated than that of argon arc, with larger maximum current density at the same time. The more concentrated anode current density and higher arc volt provide helium arc greater energy with concentrated anode power density, which is beneficial to increase the weld penetration and the depth-to-width ratio, make thicker workpiece welded.

Key words: anode power density, arc pressure, arc shapes, argon arc, helium arc