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Green lasers to optimise underwater laser cutting

Underwater laser

A short-wavelength green laser cutting steel and metals in the sea (Image: Fraunhofer IWS)

A new energy-efficient underwater laser-cutting process has been developed using kilowatt-level green lasers.

The process could be used to safely decommission old nuclear power plant structures, or cut steel frames surrounding off-shore wind turbines when increasing their size to up their power output.

Traditional laser metal cutting typically occurs in dry environments using infrared or other long-wave laser radiation, which requires auxiliary gases delivered coaxially to the beam via intricate piping systems in order to expel the molten metal produced. If such wavelengths are used underwater, however, the light is scattered in all directions, causing substantial power loss over short distances.

A new process developed Fraunhofer IWS researchers instead uses short-wavelength green lasers exceeding 1kW of power (which have only become available in recent years) that can penetrate water with minimal power loss. The researchers believe that shorter-wavelength blue lasers also show promise for such underwater cutting.

Underwater laser cutting offers several advantages over alternative mechanical sawing and plasma cutting methods. 

“The process requires comparatively little energy, and the power transmission is more efficient,” said project leader Dr Patrick Herwig, who heads the Laser Cutting Group at 
Fraunhofer IWS.

In nuclear decommissioning applications, the technique could be used to cut structures without releasing hazardous particles into the atmosphere. Melted residue could also be removed more efficiently underwater during cutting without the need for auxilary gases, eliminating the need for complex piping. In addition, the process is non-contact, removing the need for continuous blade replacement, as would be the case with sawing.

Herwig added that the new approach could also enable the creation of compact, efficient underwater robots with laser attachments, which could access difficult-to-access areas of underwater structures more easily than automatic sawing machines used today.

Professor Christoph Leyens, Director of Fraunhofer IWS, adds: “70% of the earth consists of water. In the future, humanity must increasingly use these offshore reserves to develop and expand environmentally friendly energy sources. We need new underwater manufacturing technologies like our laser cutting solutions. Until now, water has been seen as the ‘enemy’. We are reversing that and understanding it as a ‘friend’.” 

The researchers have so far proven the method in the laboratory, and plan to unveil it at the Schweißen & Schneiden trade show in Essen, Germany in September 2023. In the next steps, they want to further develop their lab-scale concept into practically applicable systems.

The scientists are also currently looking for industrial partners to outline concrete application scenarios, experiences, and challenges as well as to accompany the substantial technology development.

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