Glass-fiber composite foam sandwiches are already used in aircraft manufacturing to help planes shed weight, and carbon composite sandwiches using foam or honeycomb cores are also on the rise in planes and trains. Now, a laser-welded metal sandwich with a metal foam core has been demonstrated for lightweighting ships.

Along with its project partners, the German Laser Zentrum Hannover research and development center laser welded a demonstrator for marine gear unit foundations made of steel and aluminum foam sandwich material. The demonstrator was on display at the Hannover Messe 2012 show.

Using metal foam sandwiches to make ships lighter isn't a new idea. The metal foams are highly porous materials, often made of aluminum, that can also more easily absorb noise because of their cellular structure. Noise reduction is a growing trend in car interiors, and both the inside and outside of planes, in those cases usually employing non-metal foam or metal or non-metal honeycomb cores.

Metal foams are not only light in weight and sound-absorbing, but also heat-resistant and provide good insulation against electromagnetic waves. In sandwich constructions, they have a much higher bending stiffness than solid sheets. Because of their lighter weight, they are also applicable for parts that undergo high amounts of stress, such as rudders or machine foundations. In those applications, large-scale metal foam sandwich constructions can reduce weight by as much as 20 percent.

The problem with this technology has been the difficulty in welding steel and aluminum. This is caused by different material thicknesses, and the inhomogeneity of the foam core. Aside from problems such as the distortion caused by the thermal effects of foaming the aluminum core in mixed sandwich materials, cracks in the welding seam can also occur, caused by intermetallic phases due to welding.