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Low-force mobile welding for on-site marine fabrication

new low-force friction stir welding (FSW) technique has been developed to enable the mobile joining of aluminium alloy plates. The low-cost Mobi-Weld system is transportable and has has the potential to join panels of unlimited length.

The two-year Mobi-Weld project, funded by the European Union Seventh Framework Programme, was launched in January 2013. Its main aim was to develop a mobile FSW system for in-situ use in shipyards.

Overcoming long-standing challenges

One of the major limitations of FSW, which prevents its use on a mobile machine, is that the process requires relatively high levels of force to be applied, primarily to maintain the correct tool position, during welding. The challenge was therefore to develop a mobile FSW system incorporating a crawler system which would be low-cost, transportable and have no limit on panel and weld length. This system must be capable of resisting the welding forces and provide a precise, smooth FSW tool path movement.

 

Inventing a new technique

The Mobi-Weld project had to address some major technical challenges, including:

  • Development of low-force FSW tools suitable for welding the 6mm and 4mm AA5083-H111 and AA6082-T6
  • Integration of an automated joint tracking system to identify the weld path which is integrated with the positioning system to present the tool in the correct position and orientation to the component joint line, ensuring weld quality
  • Design of a crawler system which can transport the welding head across large section areas of panels and be deployed within a shipyard environment.

TWI undertook development of the welding process and selected a new welding technique called floating bobbin FSW.

This technique eliminates potential kissing bonds, uses much lower forge forces, requires no backing bar and is very simple to control. Within this project it was shown possible to make welds to ISO 25239 standard, with gaps in the joint between the components to be welded up to 5% of the component thickness. The process was also capable of welding components which varied in thickness up to 0.3mm.

The crawler was designed and built by VTT (Finland) and most of the mechanical parts were manufactured in-house. The control system was also developed by VTT, synchronising the crawler motion and seam tracker and providing continuous motion to the tool and aligning it to the joint. The device attaches itself to the aluminum plates using vacuum cups and moves along the plates following the joint line to produce the weld.

It is believed to be the first machine in the world of its type and represents a major breakthrough in its field.

For further information about the project, please visit the project website at www.mobiweld.eu or email contactus@twi.co.uk

The crawler created for the project
The crawler created for the project
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