Heat Transfer and Fluid Flow during Gas-Metal-Arc Fillet Welding for Various Joint Configurations and Welding Positions
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ter modeling efforts to simulate and understand various welding processes through transport phenomena-based models have focused either on simple butt joints of rectangular workpiece or the symmetrical V-shaped fillet joints.[1,2,3] However, the fillet joint is not symmetrical in many practical situations. Depending on the structure, the welding is generally performed either by tilting the fillet joint or by lifting the workpiece. The inclinations of the workpiece and welding positions (i.e. downhill, flat, and uphill) affect the weld pool convective flow and hence the weld bead profile, thermal cycles, and cooling rates inside the workpiece. Furthermore, most of the previous models did not consider the effect of arc pressure on weld pool surface deformation.[4–11] Depending on the current and the voltage levels, the arc can exert significant pressure on the surface of the weld pool that deforms the free surface.[1–3,12–15] The deformation of the weld pool surface affects the heat transfer, fluid flow, and solidified weld bead geometry.[1,2,13–17] The purpose of this study is to investigate how the temperature distribution, velocity fields, free surface profile, and cooling rates change with uphill or downhill welding A. KUMAR, Graduate student and T. DEBROY, Professor, are with the Department of Materials Science and Engineering, The Pennsylvania State University, University Park, PA 16802, USA. A. KUMAR is currently working as Senior Research Engineer at ExxonMobil Upstream Research Company, Houston, TX, USA. Contact e-mail: [email protected] Manuscript submitted June 22, 2006. Article published online April 13, 2007. 506—VOLUME 38A, MARCH 2007
positions and workpiece orientation, i.e., V, L, and other configurations during GMA fillet welding. Such modeling of the GMA fillet welding process is important because an improved understanding of the underlying physics would lead to better welds. In this article, a numerical model is developed to consider the orientations of fillet joint; welding positions such as downhill, flat, and uphill welding; and the deformation of the weld pool free surface during GMA welding in spray mode. The weld pool surface profile is calculated by minimizing the total surface energy, which includes the surface tension energy, gravity potential, and work done by arc force. The impingement of droplets on the weld pool surface is considered via a volumetric heat source. This model is used to investigate the heat transfer and fluid flow during GMA fillet welding of A-36 mild steel. The calculated weld bead shape is compared with the corresponding experimental result. A dimensional analysis is performed to understand the role of various driving forces on convection in the liquid weld pool. The effects of various welding parameters, welding positions, and workpiece orientations on weld bead geometry and cooling rates are quantitatively studied using the numerical model.
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MATHEMATICAL FORMULATION
A. Assumptions and Salient Features Because of the complexity of the GMA fillet welding, the following simplifying assumption
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