Abstract
Main causes that associate streaming in a weld pool are the electromagnetic, buoyancy, surface-tension and aerodynamic drag force. In this work, numerical calculations of heat and mass transfer in a stationary TIG arc weld pool were conducted considering the above four forces and their results were compared with actual penetration shapes of mild steel and steels containing active elements which were spot welded by a stationary TIG arc.
The surface tension driven flow was the major factor to determine the penetration shape in a short arc process in the calculation. However, there is no experimental evidence that surface tension plays the dominant role in actual welding of various steels. The actual penetration shape is rather well fitted to the calculated shape without surface tension term. It has been thus concluded that the electromagnetic force is the major factor to determine the penetration shape and the aerodynamic drag force plays the secondary role in short arc welding. The results suggest that the value of surface tension measured in vacuum or inert atmosphere may not be the same with that of liquid exposed to plasma. While, in case of long arc welding, the aerodynamic drag force of arc plasma is the predominant force which leads to the "shallow center and deep peripheral penetration".
