Laser welded multi-metal structures promise big weight reductions

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The laser welding of different metals into sandwich structures has been achieved promising 20 per cent reductions in the weight of large structures, such as ship rudders.

Steel and aluminium has been used to create a sandwich with the aluminium as the core material. Because these multi-metal structures are porous and lightweight, due to their cellular structure, they can absorb energy in the form of vibrations and knocks or noise. They are also heat resistant and provide insulation against electromagnetic waves.

Carried out by Laser Zentrum Hannover (LZH), butt and fillet welds for a steel, aluminium sandwich structure has been completed with a diode laser with a wavelength between 900 and 1030nm and an output of 5kW. The tests showed that continuous weld seams are possible and that material thicknesses up to 5mm can be processed at speeds of 0.2 to 1.5m per minute.

A problem that had existed with producing steel, aluminium sandwich structures was that the thermal effects on the aluminum core could distort the material. Because of the different metals' properties cracks could occur in the weld seam. The LZH team has been able to overcome this.

The work was undertaken for the Meschlas project, which aims at providing lightweight structures using sandwich technology. For Meschlas, LZH is working with the Fraunhofer Institute for Machine Tools and Forming Technology and the companies Blohm and Voss Naval, and Precitec Optronik. The project is funded by the Federal Ministry of Economics and Technology.