Mathematical modeling of the dynamic behavior of gas tungsten arc weld pools
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I. INTRODUCTION
WELD pool size, shape, and motion are intimately connected to melt convection, which is determined mainly by electromagnetic forces and surface tension gradients for arc welding processes. This article describes modeling efforts carried out to understand the influence of process parameters and material properties on weld pool convection, bulk melt motion, and the resulting final weld shape. The fluid dynamic behavior of weld pools is of interest because it is fundamental in at least two significant welding research and development areas. One of these is concerned with the effects of material characteristics and process parameters on the shape and size of the completed weld. Early work in this area was mainly concerned with the effects of heat conduction. It was later demonstrated[1] that minor element compositions can significantly influence weld pool surface tension gradients, which, in turn, dramatically affect fluid convection and, ultimately, the shape and size of the completed weld. Numerous subsequent studies of weld pool dynamics followed this seminal work and some are discussed in more detail subsequently. A second development area that is intimately related to weld pool dynamics is pool oscillation-based process sensing and control. Early work[2] suggested that weld pool size and penetration could be measured by analysis of pool oscillation characteristics, detectable in “real-time” by their effect on the arc voltage signal. Subsequently, there have been a number of efforts to develop and refine pool oscillation-based monitoring and control algorithms. Weld pool behavior has been studied extensively through numerical simulations and laboratory experiments.[3–11] The SUNG H. KO, Graduate Associate, and CHOONG D. YOO, Associate Professor, are with the Department of Mechanical Engineering, KAIST, Taejon, Korea. DAVE F. FARSON, Assistant Professor, is with the Department of Industrial, Welding and Systems Engineering, Ohio State University, Columbus, OH 43210. SANG K. CHOI, Research Professor, is with the School of Mechanical Engineering, Kyungpook National University, Taegu, Korea. Manuscript submitted December 13, 1999. METALLURGICAL AND MATERIALS TRANSACTIONS B
numerical approach has some advantages since it can provide detailed predictions of pool convection patterns that are practically impossible to measure experimentally. A major limitation of many of the previous numerical analyses of molten weld pools stems from the modeling of the free surfaces and of the liquid-solid boundaries. In many reported works,[7,8,9] the free surface was assumed to be flat or some specified, fixed profile. Recently, dynamic fluctuation of the free surface has been included in the analysis of metal transfer and molten pool behavior by the volume of fluid (VOF) numerical method.[10–13] Since the fully penetrated pool is supported only by surface tension on the free surfaces, surface effects become more prominent and need to be considered for fluid dynamics analysis. For example, in fully penetrated pools, th
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