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Assessment of bobbin FSW for joining aluminium alloys

Connect, no. 159, March/April 2009, p.6

Macrograph of 25mm thick 6082-T6
Macrograph of 25mm thick 6082-T6

The friction stir welding (FSW) process was invented by TWI and was originally developed for industrial exploitation via a TWI Group Sponsored Project (GSP), the Sponsors of which were amongst the first to benefit from the new technology. TWI has recently developed a novel enhancement to the FSW process, called floating bobbin FSW which offers the potential to produce improved full penetration welding performance using significantly simplified, and therefore cheaper, equipment.

Recent trials using this technique have clearly highlighted some of the benefits. Along with the complete elimination of root flaws and the need for a backing bar, lower distortion joints are produced compared to conventional FSW, due to a lower heat input and a balanced weld profile.

Process benefits are also realised through almost zero weld forging forces acting on the FSW machine and work holding fixture. The innovative floating action of the tool compensates for misalignment between the tool and work piece and also for work piece dimensional and geometrical tolerances without the need for sophisticated machine control systems.

Floating bobbin FSW has the potential to produce high quality, low distortion welds on simplified FSW equipment. Elimination of the backing bar also makes new joint designs possible and will extend the range of possible FSW applications.

Further development of this technique for joining component sections up to 12mm is being undertaken within a group sponsored project which began in January 2009. This technique has benefits across a wide range of industry sectors but should be of particular interest to transport industries such as train makers, automotive and shipbuilding.

Contact gec@twi.co.uk

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