LZH simulates undersea conditions to test laser machining

27 Jun 2018

Pressure chamber recreates deep-sea environment allowing assessment of laser performance.

Underwater laser cutting and welding operations are a key aspect of the construction of offshore wind farms, bridges or other civil engineering structures, but the nature of the environment can make optimizing the machining operation difficult.

Laser Zentrum Hannover (LZH), as part of its ongoing work on undersea machining operations and the key performance parameters involved, has now developed an instrument that might assist the development of optimized laser machining operations in this marine environment.

It includes a purpose-built pressure chamber, able to simulate a water depth of 6,500 meters and operating pressures of up to 650 bar. The chamber is suitable for use with both freshwater and saltwater, allowing it to represent a range of the application scenarios that undersea laser machining platforms may face.

According to LZH, the pressure chamber's design allows two different viewing windows, 25 mm and 80 mm in size, to be be used for introducing laser radiation and observing the machining process with a camera.

"Scientists can, for example, analyze the plasma formation on the surface of the sample," noted the LZH team. "This is interesting for the preparation of deep-sea work and measurements, as in the current Robust project at the LZH that focuses on the investigation of mineral resources on the seabed."

The chamber can also be used to examine the reaction of different materials to high pressures under water. Using high-speed camera technology, LZH can record full HD video material at over 12,000 images per second and synchronize it with the pressure curve in the chamber.

Undersea exploration

Robust—for Robotic Subsea Exploration Technologies—is a EU Horizon 2020 research project coordinated by the UK's Welding Institute, in collaboration with partners including LZH and neoLASE.

Its goal is to develop a means of identifying seabed material in situ, by combining laser-induced breakdown spectroscopy with current developments in autonomous underwater vehicles (AUVs), to produce a platform able to carry out 3D mapping of the seabed. For this, an understanding of how lasers can operate reliably in underwater platforms will be essential.

Once perfected, the system could be used to detect soil samples, such as manganese nodules, and analyze the material composition of the specimen directly on the deep sea ground.

LZH is also researching the effectiveness of underwater laser cutting for the decommissioning of marine constructions, a topic of significant importance for the offshore energy sector.

At a 2017 conference on maritime energy held at Hamburg University of Technology, a group from LZH presented a study in which a 4 kW Yb:YAG laser attached to an underwater arm could be used in a laser flame cutting process, with oxygen as the cutting gas. Trials showed that the LZH platform could successfully cut 10 mm thick steel plates, and with optimization of the cutting parameters this could be increased to 50 mm under certain conditions.