ABSTRACT
The spiral structure of seven-wire is the fundamental cause of arc rotation. The arc rotation frequency decreases with the radius of twisting circle and the helix angle, and increases with the welding current. The arc presents the reciprocating rotating upward motion when welding torch oscillates along the thickness of the plate. The sidewall penetration along the thickness direction of plates is approximately the same. The rotating arc promotes the stirring of melting metal, and the stirring effect intensifies the flow of melting metal and accelerates the heat transfer from the molten pool to the sidewall, which has a positive effect on increasing the penetration of sidewall and refining the grains of weld seams.