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Smooth operator…FSW leading the way with 'impossible' joints

Tee and corner joints, previously considered impossible-to-weld using friction stir welding, now look likely to be just the opposite using a radical, and extremely attractive refinement of the stationary shoulder friction stir welding technique.

The process uses a skid shaped internal corner shoulder which contains the stirred material and forms it into a pre-determined profile, usually a tangentially curved fillet.

Not only does it broaden the scope of FSW but it also gives welded fabrications the appearance of extrusions. In other words, they are perfectly smooth.

Completed welded fabrications may comprise two or more different materials, but visually they resemble one-piece extrusions. So they demand minimal post weld dressing because they emerge from the process with a perfectly smooth weld top. A desirable consequence of this is that rapid geometric changes in the joint's section, stress raisers in other words, are eliminated.

It has also been demonstrated that a filler material can be added into the corner weld during the FSW process to increase its volume.

As a direct consequence of the success of AdStir, as it has been dubbed,   TWI will be launching a group sponsored project in May 2010 to develop and exploit the technique.   

Numbered among its benefits are:

  • Good component surface finish
  • Low distortion
  • Small heat affected zone
  • No ‘undercutting’ of the top surface.
  • Wrought materials are used, not extrusions
  • Structures can be fabricated where size and thickness ratios prohibit use extrusion
  • Components can be fabricated with tailored properties using dissimilar materials
  • Third body materials can be added
  • Increased tolerance to component set up

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