Today’s conventional friction stir welding tools offer a range of design features that improve welded joints.

The original welding tool developed by The Welding Institute (TWI, Cambridge, UK) in 1992 made sound welds in aluminum alloys. Many improvements have been developed since then, leading to improved joint quality and weldability, increased joint thickness, and other operating advantages.

Evolution of welding tools

Scrolled shoulder tools eliminate the need for a tilted tool axis while welding. A flat shoulder face with spiral-shaped grooves that pull softened workpiece material toward the pin prevents the escape of material without needing welding tool tilt.

Flat pin tips produce better weld penetration beyond the tip of the pin. Improved heat generation and plastic deformation at the bottom of the weld reduce the likelihood of incomplete weld penetration.

Reentrant features, such as flutes or flats, interrupt the flow of workpiece material within the pin threads. This increases heat generation from plastic work, rather than depending solely on sliding friction.

Multi-piece tools have a separate pin and shoulder that rotate together. This makes it possible to adjust the pin length (set and lock), which fine tunes the pin length to the workpiece thickness. It also allows selection of a pin material that is specific for the given application.

Tapered shoulder tools embed the shoulder into the workpiece surface during welding. Instead of having a flat, scrolled shoulder that rides on the surface, a tapered (or convex) shoulder profile with scrolls can be used with the shoulder partially embedded into the workpiece. This design improves the tolerance to joint mismatch, reduces flash and makes possible variable depth welds. It also makes possible fixed-gap bobbin-style tools.

Retractable pin tools extend and retract the pin using a mechanical means during welding. This action makes possible variable weld penetration and welds with no terminal keyhole. These tools require special enhancements to the welding machine spindle.

Bond Technologies produces all types of friction stir welding tools, based on customer designs or from designs produced by Bond welding specialists.

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