FSWShipConstruction.pdf - Friction Stir Welding For Ship...

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Abstract Aluminum alloys are relatively difficult to weld primarily due to aluminum’s high thermal conductivity and the formation of defects during welding including porosity and solidification cracking. In shipyards that perform aluminum construction, much of the welding is done manually using gas metal arc welding (GMAW), otherwise known as metal inert gas (MIG) welding. Friction stir welding (FSW) is a relatively new joining process that has been demonstrated in a variety of metals, such as steel, titanium, lead, copper, and aluminum. The process is especially advantageous for joining aluminum and has been exploited commercially around the world in several industries. The unique properties of friction stir welds make possible some completely new structural designs with significant impact to ship design and construction. Improvements in construction cost, durability, and welding distortion have been demonstrated in Europe and Japan and the process is now becoming more widely accepted in the United States. However, it is up to naval architects to incorporate this new method of construction into their designs to take advantage of the benefits of FSW. Friction Stir Welding For Ship Construction Background Friction stir welding (FSW) is a solid-state joining process that was invented in 1991 at The Welding Institute in the United Kingdom (Thomas, 1994). The process works by plunging a rotating, non-consumable welding tool into the joint, then traversing the rotating tool along the joint, as shown in Figure 1, and schematically in Figure 2. Most remarkably, friction and plastic work provide all of the heat for the process, which is sufficient to soften the workpiece to just below the melting point, allowing the tool to “stir in” the joint surfaces. The process is especially well suited to butt and lap joints in aluminum since aluminum is difficult to weld by arc processes, but is very simple to weld by FSW. The process is carried out in aluminum without filler metal or shielding gas, and full-penetration butt welds can be made in aluminum from 0.02” thick up to as thick as 3” in a single welding pass. Different alloys of a like base metal can be welded to each other, such as 6061 aluminum to 5083 aluminum, and welds can easily be made to join wrought plate, forgings and castings to each other. Enables Prefabricated, Stiffened Panels with Low Distortion Figure 1. Welding tool plunge (left) and traverse (right). Kevin J. Colligan Concurent Technologies Corporation
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The unique characteristics of FSW make fundamental changes in joining and processing methods possible. Since FSW operates at a much lower temperature than traditional arc processes, the residual stress and distortion are typically very low. This characteristic makes it possible to prefabricate stiffened panels that are dimensionally accurate, with implications for several industries. In addition, the FSW process produces an extremely fine grain structure, giving the stir zone unique deformation characteristics compared with other welding processes,
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  • Spring '18
  • Prof Lilly
  • friction stir

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