Three-dimensional transient model for arc welding process
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I.
INTRODUCTION
IT has
long been known that the solidification structure of the weld metal depends on the heat transfer conditions that exist in the material during welding. The factors that are o f paramount importance are the thermal cycle, the peak temperature, the temperature gradient at the solid/ liquid interface, and the cooling rate through certain critical temperature ranges, t~l Molten metal, due to its capability of movement, can transport heat within the puddle, thereby influencing all these factors. Fluid flow in the weld pool can significantly influence the fusion zone geometry 12] and alter the metallurgical characteristics of the weld joint, t3] Experimental determination of temperature and flow conditions in the weld pool is extremely difficult, owing to the size of the weld pool, the extreme temperatures involved, and the presence o f the welding arc. Theoretical investigation by mathematically modeling the process provides an opportunity to understand the complex phenomena that occur during welding. The solution of moving boundary problems such as weld pool fluid flow and heat transfer that involve melting and/or solidification is inherently difficult, because the location of the solid/liquid interface is not known a p r i o r i and must be obtained as a part of the solution. Because of the nonlinearity of the governing equations, exact analytical solutions can be obtained only for a limited number of idealized cases, and these are documented in the literature, t4-TJ Therefore, considerable interest has been directed toward the use of numerical T. ZACHARIA, Research Staff, and S.A. DAVID, Leader, Materials Joining Group, are with the Metals and Ceramics Division, Oak Ridge National Laboratory, Building 4508, P.O. Box 2008, Oak Ridge, TN 37831-6096. A.H. ERASLAN is with AHE Associates, UTSI Research Park, Tullahoma, TN 37384. D.K. AIDUN, Associate Professor, is with the Department of Mechanical Engineering, Clarkson University, Potsdam, NY 13676. Manuscript submitted September 6, 1988. METALLURGICAL TRANSACTIONS B
methods to obtain time-dependent solutions for theoretical models that describe the welding process, t8-141 Numerical methods can be employed to predict the transient development of the weld pool as an integral part of the overall heat transfer conditions. The structure of the model allows each phenomenon to be addressed individually, t~31 thereby gaining more insight into their competing interactions. In addition, numerical models provide the potential of taking into account the geometrical variations in the workpiece. Table I summarizes theoretical developments for the fluid flow and the heat transfer in the weld pool. Consideration of these studies of the fluid flow and the heat transfer shows that they are limited to two-dimensional (2-D) transient or three-dimensional (3-D) steady-state, flat weld pool surface, infinite plate, simple geometry, etc. Traughatt uSl notes: "It would seem advisable, to explore such two-dimensional approaches only as a preliminary to more realistic fu
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