Most commercial friction stir welding (FSW) applications use simple butt joint configurations; T-sections and corner welds are very rarely considered due to how difficult it is to weld them using conventional FSW tools. These joint configurations are used extensively in the transport industries for adding ribs and strengtheners to plates.
TWI has developed a technique based on the stationary shoulder FSW technique where a rotating pin running in a non-rotating shoulder is shaped to the angle of the plates to be welded. The shaped shoulder contains the stirred material and slides over the surface of the material during welding.
This technique has been further developed so that a filler wire can be added into the corner weld to produce a reinforced fillet weld. This offers the potential to produce filleted corner joints from wrought plates, the fillet material being provided by the filler in a similar manner to fusion welding processes.
Corner FSW brings the same benefits as using a stationary shoulder, including a very smooth, polished weld surface with no or minimal reduction in cross-section, and a consistent and almost linear heat input throughout the weld section. In addition to this, it also brings the potential to extend the range of applications where FSW can be applied and offers some unique attributes:
- Use of wrought plates instead of bespoke extrusions
- Structures fabricated where size and thickness ratios prohibit extrusion use
- Fabricated components with tailored properties by using dissimilar materials
- Addition of third-body filler materials.