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FRICTION STIR WELDING TECHNOLOGY |
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FRICTION STIR WELDING TECHNOLOGY |
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Friction Stir Welding (FSW) Description Friction Stir Welding (FSW) is a patented welding process that was invented by the Welding Institute in Cambridge, UK in 1991. Friction Stir Welding (FSW) is a solid state welding process (no melting) where a machine rotates, plunges, and then traverses a special shaped FSW Tool along a joint to form a weld. The rotation action and the specific geometry of the FSW tool generates friction and mechanical working of the material which in turn generate the heat and the mixing necessary to transport material from one side of the joint line to the other. The process has numerous advantages over other joining technologies and can be used to weld numerous materials including, but not limited to aluminum, bronze, copper, titanium, steel, magnesium, and plastic.  Friction Stir Welding offers a variety of advantages over traditional welding processes. These advantages include improve static strength and fatigue properties. The process is also very robust, not being sensitive to environmental conditions, unlike many traditional welding processes. This is especially true for welding of lower melting point materials such as aluminum, magnesium, bronze, and copper. It also yields significantly less distortion than the fusion welding processes, allowing for dramatic cost reductions in many applications.  Friction Stir Welding can be used in a variety of joint configurations, including butt welds, dissimilar thickness butt welds, lap penetration, and lap fillet configurations (see figure of joint configurations below). However, it cannot be used for the traditional tee fillet joint configuration that is commonly used in many fusion welding applications. This can often require redesign of the product, to take full advantage of the FSW process.  The friction stir welding process has two significant variants that can be used for other applications. The first is Friction Stir Spot Welding (FSSW), where the tool is plunged and retracted, without traversing the tool. This particular variant has parallels with the resistance spot welding (RSW) process and has significant advantages over RSW, and avoids many of the difficulties of RSW of aluminum. In many applications, FSSW can be readily substituted for RSW with little or no design modifications. Another variant of FSW is friction stir processing (FSP), where the friction stir tool is simply traversed through the material. There is no joint in these applications. FSP can be used to significantly enhance the material properties of castings and wrought material. In castings, porosity can be eliminated (see image below - friction stir processed NiAlBronze propeller). Furthermore a significant improvement in material properties can be realized. In other applications, the material can be processed to improve the ductility of the material. This can be taken advantage of in forming or bending applications of material that typically exhibits lower ductility, such as aluminum.  Friction Stir Welding is a new process, but has been used in production applications since 1995 in Europe. The first applications involved welding of extrusions to form paneling for marine applications. Since then, the process has been commercialized in many other applications, including rail car, automotive, aerospace, heavy truck, medical applications, etc. Today, the process is being transitioned into fabrication of complex assemblies, yielding significant quality and cost improvements. As the process is maturing, designers are taking advantage of the process, by designing the product specifically for the FSW process. |
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