Abstract
This study aims to reveal the cause of different weld formation quality for varying welding position in the GTAW (Gas Tungsten Arc Welding) of a thick-sheet aluminum alloy structure. The fluid flow characteristics of weld pools are investigated by CFD (Computational Fluid Dynamic) modeling and high-speed imaging for the climbing and flat welding positions, which correspond to the start and finish ends of the welds of the structure, respectively. Results show that the directions of gravity relative to weld pools may notably affect the fluid flows in weld pools for different welding positions. For flat welding, gravity will accelerate the fluid flow in the direction of sheet thickness only and in turn result in a high velocity downwards, which implies a good penetrating capability. Welds of good formation with smooth surface and consistent width can be produced under flat welding position. In contrast, for climbing welding, gravity will act on the molten metal in both the direction of sheet thickness and the lateral direction of the weld pool. As a result, the velocity in sheet-thickness direction is decreased, which implies a decreased penetrating capability. Meanwhile, the velocity backwards is increased in the top portion of the weld pool, which makes the molten metal apt to flow out of the weld pool. Both the decreased penetrating capability and the accelerated molten metal outflow would render the climbing welding process unstable, and result in welds of poor formation with uneven weld surface and inconsistent weld width. Based on the study, possible methods are proposed that could be used to improve the weld formation quality when welding thick-sheet aluminum alloys structures using various welding positions.
Highlights
Aluminum alloys have been widely used in manufacturing aeronautical and aerospace structures thanks to their high specific strengths and moderate cost
When flat welding, the only weldin pool the sheet direction, thickness direction, component parallel to the sheet surface is zero. Such a difference in the gravity action direction has a while the component parallel to the sheet surface is zero. Such a difference in the gravity action notable influence on theinfluence flow of molten weld metal pool and weld formation quality revealed direction has a notable on themetal flowin ofthe molten in the weld pool and weldas formation in this study, which in is similar to those reported for the welding of steelfor and titanium alloys by laser quality as revealed this study, which is similar to those reported the welding of steel and and titanium alloys by laser and gas metal arc welding (GMAW) welding processes
Fluid flow characteristics and their relationship with the weld formation quality were studied for the Gas tungsten arc welding (GTAW) of a 9.5 mm thick-sheet 2219 aluminum alloy shell structure, during which various welding positions are used
Summary
Aluminum alloys have been widely used in manufacturing aeronautical and aerospace structures thanks to their high specific strengths and moderate cost. Sci. 2018, 8, 1215 welding torch is manipulated during welding according to the trajectory of a weld path while the structure is fixed and welded. Under such conditions, other welding positions, besides the flat welding position, are inevitable. Are more apt to occur for welding positions (e.g., vertical welding) other than the flat position This becomes even more serious when the aluminum alloy sheets are thick (with thickness greater than 5.0 mm) [3]. It is imperative to investigate the causes and possible solutions to the poor weld formation in the GTAW of a thick-sheet aluminum alloy structure using varying welding positions
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