Friction Stir Welding
The comparatively young joining method friction stir welding is based on the special property of plastifiable materials, e.g. aluminium, magnesium, copper or steel, to be fluid without being in a liquid state at increased temperature and under mechanical load. In friction stir welding, a rotating tool with a so-called weld pin is used for the thermal and mechanical load on the joining point of a work-piece. This tool is positioned partly on the work-piece surface and partly in the work-piece during the joining process. The relative motion of the tool to the work-piece generates frictional heat which leads to process temperature increase and thus to the release of yield stress in the work-piece material. Through the simultaneous rotation and feed motion of the tool, welded joints along a definable line are the result. With a suitable parameter selection, the friction stir welded joints are characterised by a high reproducibility and excellent mechanical weld seam properties. Since the partners are joined in the solid state, friction stir welding is well suited for the joining of dissimilar material joints, for example, aluminium-copper and aluminium-steel as the formation of unwanted brittle intermetallic phases is to a great extent avoided by the low process temperature.