Numerical analysis of metal transfer in gas metal arc welding
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Numerical Analysis of Metal Transfer in Gas Metal Arc Welding G. WANG, P.G. HUANG, and Y.M. ZHANG The present article describes a numerical procedure to simulate metal transfer and the model will be used to analyze the transport processes involved in gas metal arc welding (GMAW). Advanced Computational fluid dynamics (CFD) techniques used in this model include a two-step projection method for solving the incompressible fluid flow; a volume of fluid (VOF) method for capturing free surface; and a continuum surface force (CSF) model for calculating surface tension. The electromagnetic force due to the welding current is estimated by assuming several different types of current density distribution on the free surface of the drop. The simulations based on the assumption of Gaussian current density distribution show that the transition from globular to spray transfer mode occurs over a narrow current range and the size of detached drops is nonuniform in this transition zone. The analysis of the calculation results gives a better understanding of this physical procedure. Comparisons between calculated results and experimental results are presented. It is found that the results computed from the Gaussian assumption agree well with those observed in experiments.
I. INTRODUCTION
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 consi
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