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Friction Stir Welding

During the last ten years Sapa has invested heavily in Friction Stir Welding (FSW) – a friction welding technique developed and patented by the Welding Institute from Great Britain.

Image: Friction Stir Welding

In 1996, as the first company in the world, we started production on an industrial scale using FSW as a jointing method. Today we are a world leader as regards industrial use of FSW and we can offer our customers panels that are up to 14.5 metres long and 3 metres wide.

Some advantages of Friction Stir Welding:

  • A simple process which results in completely pore-free, tight joints with a high strength.
  • Minimum heat influence on the material. Only small heat stress occurs in the material and flat surfaces.
  • Good mechanical properties. The production process involves few, easily controlled variables which allows tight tolerances.
  • Ensures a good working environment.

FSW is a method that makes it possible to weld components with high compression strength and tightness requirements. The method allows the production of wide panels, such as roofs or walls of trains, which are difficult or impossible to extrude.

The jointing of elements takes place in solid state. A rotating tool creates pressure and friction heat on the jointed surfaces so that the metal is mixed together and forms a top quality joint. The temperature of the material next to the joint reaches a maximum of 500 °C during some fractions of a second and then falls quickly. The low temperature makes that the melting point is not exceeded, which is the case in conventional friction welding. FSW significantly improves the working environment. The welding light, smoke and ozone formation are completely eliminated. Steel brushing, grinding and intermediate bead cleaning are not required either.

The FSW method has proved to give high strength joints without inclusions of impurities.  Tensile tests have shown that the welded joints are almost completely free from stress. Det Norske Veritas has performed, among other things, bending and X-ray tests of the joints and approved the process for demanding solutions in railway and marine applications.

Jointing of aluminium by FSW is based on a quickly rotating tool which is inserted into the joint and moved along it. The rotating tool generates high friction heat and causes a heavy plastic deformation of aluminium. The strong mechanical influence under high pressure from the tool presses together the weld surfaces forming a homogenous structure.