WELDING ALUMINUM Friction stir technique now operational for topside structures

Esab Welding Equipment has completed the first delivery and installation of its ESAB SuperStir welding system. The customer, Haugesund-based Marine Aluminium, which makes products such as helidecks, gangways, sections and panels in aluminium for the offshore and shipbuilding industries, received the system in August. Full production was achieved in November, with complete approval for applications in DNV classed vessels.

Mar 1st, 1997

Esab Welding Equipment has completed the first delivery and installation of its ESAB SuperStir welding system. The customer, Haugesund-based Marine Aluminium, which makes products such as helidecks, gangways, sections and panels in aluminium for the offshore and shipbuilding industries, received the system in August. Full production was achieved in November, with complete approval for applications in DNV classed vessels.

This is the first customized set of equipment in the world to use the new Friction Stir Welding (FSW) method developed and patented by TWI in the UK. Marine Aluminum's steel-constructed SuperStir system weighs 63 tonnes and measures 20 x 11 metres. Esab has one smaller system at its Laxaa plant which is used for testing and further development of the FSW technique.

Homogeneous joint

The principle of friction stir welding is based on obtaining a sufficiently high temperature to `forge' two aluminium components together using a rotating tool that moves along the joint. The temperature is kept below the melting point for aluminium, resulting in distortion-free welds.

Components to be joined are clamped to a backing plate using a powerful fixture and, as the distance between the rotating tool and backing plate needs to be exact, the machine has to be extremely accurate. Furthermore, the process for lifting the panels into place has been automated and the beam has been filled with concrete for added strength.

Divisional manager Lars Goran Eriksson states that design implications of using this welding method are great. "We believe that where applicable, friction stir welding will eventually replace existing methods for welding aluminium. Designers have more freedom to make the design much simpler since the technique can also be used to weld through one piece of aluminium to another piece without actually using a joint."

A significant benefit of friction stir welding is that, since the finished weld is extremely strong, there is no need to compensate for weak welds by using thicker aluminium. With FSW, thinner aluminium plate can be employed, resulting in weight savings of up to 30%.

When welding materials over 15mm thick, welding is performed from both sides. Maximum thickness is around 30mm at 100% penetration. Welding speed of up to 750mm/min can be achieved on 5mm thick 6082-T6 alloyed aluminium.

For more information contact Lars Goran Eriksson, Esab Welding Equipment: telephone +46 584 81000 or fax +46 584 411721.

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