Mathematical modeling of three-dimensional heat and fluid flow in a moving gas metal arc weld pool
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I.
INTRODUCTION
GAS metal arc (GMA) welding is the most common method for arc welding steels and aluminum alloys. About 40 pct of the production welding in the United States is accomplished by this process in which the thermal phenomena and melting of the solid electrode are coupled to the plasma arc and the weld pool.[1] It is used widely both in mechanized welding and in robotic welding.[2] By selecting the correct electrode type and size, shielding gas, and welding parameters, high-quality welds can be made in all positions with this process. However, experimental determination of the correct welding procedure for each new application can be very time consuming and costly. In automated GMA welding applications, empirical relations that describe the interaction of process variables and their influence on average weld dimensions, such as weld pool width and depth and reinforcement bead height and width, are required for the development of process control algorithms.[3] Experimental studies to determine such relationships require substantial effort, and the results are usually limited to the range of parameters studied. Changes of materials, plate thickness, or other parameters would require repetition of the experiments to derive new equations.[4] Clearly, a flexible mathematical model for the process would be valuable for the rapid development of welding procedures and empirical equations for control algorithms in automated welding applications. Mathematical modeling has been found to be a powerful tool for understanding the heat transfer, fluid flow, and development of weld pool geometry.[5] Recently, considerable progress has been made in modeling the fluid flow and heat transfer condition of weld M. USHIO, Professor, is with the Joining and Welding Research Institute, Osaka University, Osaka 567, Japan. C.S. WU, Professor, is with the Shandong University of Technology, Institute for Joining Technology, Jinan 250061, People’s Republic of China. Manuscript submitted October 24, 1995. METALLURGICAL AND MATERIALS TRANSACTIONS B
pools, but mainly for gas tungsten arc (GTA) welding processes. There are fewer precedents of numerical modeling of GMA welding processes because of the additional difficulties posed by the deposition of filler metal and various metal transfer mechanisms occurring at different welding parameters.[6] Tsao and Wu[7] presented a two-dimensional stationary weld pool convection and heat transfer model for GMA welding process. Wu also set up a three-dimensional (3-D) model for convection and heat transfer in traveling GMA weld pools.[8] These two models took the heat content of filler metal droplets into consideration, but did not study the impact of filler metal droplets on the molten pool and adopted the assumption of flat weld pool surface. Using the finite-element program ABAQUS,* Tekriwal and Mazum*ABAQUS is a trademark of HKS Inc., Pawtucket, RI.
der[9] simulated the transient temperature distribution of the plate in GMA welding. The metal transfer from the consumable electrode was appr
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