What is Friction Stir Welding?
Friction stir welding (FSW) is a solid-state joining process that uses frictional heat generated by a rotating tool to join materials.
The non-consumable tool with a central probe is rotated and inserted into the interface between two workpieces before traversing along the weld line. Most of the heat generation occurs under the tool shoulder as it moves along the interface, causing the material to heat and soften. The shoulder also acts to contain the softened material, which is mechanically mixed to create a solid phase weld.
What are the Advantages of Friction Stir Welding?
The process is primarily used in industry to join aluminum alloys of all grades, whether cast, rolled or extruded. FSW has been shown to weld aluminum alloy butt joints with a thickness of between 0.3mm and 75mm in a single pass, depending on the parent material used, the machine power and the structural stiffness of the workpiece.
- As a solid-state welding process, FSW is a largely defect-free joining method with no hot cracking, porosity or solidification cracks
- Due to the lower temperatures, there is a reduction in shrinkage and distortion in the material being joined
- No filler materials, flux or shielding gas requirement for aluminum alloys
- FSW is environmentally friendly as it produces no fume, spatter, or UV radiation
- Uses machine tool technology, making the process easy to automate, highly repeatable and reducing need for skilled welders
- Good mechanical properties, which for aluminum alloys typically equals or exceeds those obtainable by competing processes
- Able to join many ‘non-weldable’ aluminum alloys, such as those from the 1xxx, 2xxx and 7xxx series
What are the Disadvantages of Friction Stir Welding?
While friction stir welding provides many advantages, there are a few limitations associated with the process.
- Exit hole left after withdrawing tool from the materials to be joined
Generally 4mm in diameter and 4mm deep
- The need for significant down force and traversing forces means that clamping is more substantial than for tig or arc welds
- Lacks the flexibility of manual and arc processes, for example, FSW cannot be used where metal deposition is required
- Holes and Machined features need a setback from the weld line unlike in brazing.
- Setback generally needs to be 3 – 5mm from the weld center line.
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