Numerical Analysis of Metal Transfer in Gas Metal Arc Welding

METAL transfer describes the process of the molten metal movement from the electrode tip to the workpiece in gas metal arc welding (GMAW). A better understanding of the metal transfer process is important for improvements in the quality and productivity of welding. While several distinct modes of the metal transfer have been classified,[1] the globular and spray transfer modes have received attention from many investigations.[1–16] In the globular transfer, the diameter of the drop is much greater than that of the electrode. Spray transfer can be further classified as drop (projected) spray or streaming spray, depending on the diameter of the drop in relation to that of the electrode: approximately the same in drop spray or much smaller in streaming spray. It is found experimentally that a sharp transition in the drop detachment frequency and size occurs when the mode changes between the globular and spray transfer modes. A bifurcation in the drop detachment frequency and the drop size has been observed in the middle of the transition current range.[2,3,4] A theoretical description of droplet formation in GMAW is complicated by the following effects: the dynamic nature of droplet growth, thermal phenomena in the wire, and heat transfer from the arc. Because of the complexities associated with these effects, models in the literature for prediction of metal transfer in GMAW are typically based on simplified descriptions of the effects influencing the process of droplet formation. The two most well-known models of metal transfer are the static force balance theory (SFBT)[5,6] and the magnetic pinch instability theory (PIT).[7,8] The SFBT considers the balance between gravity, electromagnetic force, plasma drag force, and surface tension. The PIT considers perturbation due to the radial magnetic force acting on an infinite cylindrical column of liquid metal. Nemchinsky[9] Numerical Analysis of Metal Transfer in Gas Metal Arc Welding