Arc pressure and fluid flow during alternating shielding gases. Part 2: arc force determination

The transient variation of the shielding gas present in the alternating shielding gas process produces a dynamic action within the liquid weld metal. Flow vectors opposite in direction have been reported due to the various forces acting on the weld metal when argon and helium are present; however, no data have been provided to substantiate this claim. This part of the study evaluates the various forces acting on the liquid weld metal when using argon and helium, and their effects are discussed. It was determined that argon produces a greater vertically downward force in the central region than does helium for both the arc force and Lorentz force. However, helium produces a greater radially outward force at the pool surface than does argon due to plasma shear stress and Marangoni convection. In addition, the buoyancy force, i.e. the vertically upward force in the central portion of the weld metal, was greater for helium.