Underwater co nstruction on offshore wind farms, bridges or locks must presently be done by scuba divers. For main-tenance and repair of me tal constructions, a number of processes are available, but these are time co nsuming and difficult on the divers. For this reason, engineers at the Laser Zentrum Hannover e.V. (LZH) and the Leibniz Universität Hannover (LUH) are developing a process for automated, underwater laser cutting.

At the moment, mainly light arc oxygen cutting is being used for underwater cutting. The electrodes are hand-guided. Depending on the material thickness, divers need a workday to cut 20 me-ters in material. For a diving period of five hours this means a cutting speed of o nly 7 centimeter per minute.

Cutting seven times faster

With a laser-ba sed automated process, the cutting speed should be increased by a factor of seven. “During pilot tests, we have already achieved a cutting speed of 0.5 meters per minute for 10 millimeter thick steel” says Dr.-Ing. Jörg Hermsdorf, head of the Machines and Co ntrols Group at the LZH. “With this process, underwater me tal working could be co nsiderably faster and thus less expensive. Our goal is to make the work of the divers safer and more efficient.”

Efficient dismantling of sheet piling

The process is being developed for dismantling sheet pilingsin two to six meters deep water. For this, it is crucial that the piling-sincluding the interlocks are reliably cut, aspost processing is time-co nsuming and expensive. Since me tal part corrode under water and are subject to overgrowth, the process is supposed to function reliably, even for varying material thicknesses and pollution levels.

The finished process could also be used for the maintenance and repair of offshore structures and other hydraulic structures. Also, dismantling of nuclear power plants is a further field of application.

The project “Laser cutting under water for higher productivity – LuWaPro” is supported by the German Federation of Industrial Research Associations "Otto von Guericke" e.V. (AiF).

Captio nfigure 1: Underwater laser cutting is a fast and thus eco nomical alternative to co nventional processes. (Photo:LZH)