Projects to advance underwater welding and brass joining

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Laser-assisted metal flux-cored welding will increase underwater joining efficiency and quality. (Image: LZH)

The Laser Zentrum Hannover (LZH) is currently undertaking two projects to advance underwater welding, as well as brass joining.

The first project aims to develop a laser-assisted metal flux-cored welding process for use underwater

Whether for wind farms, coastal protection structures, or harbours: when technical constructions have to be welded underwater, divers usually do it by manual electrode welding. While this process is relatively simple and inexpensive, it has a major disadvantage in that the diver must frequently replace the burnt electrodes. This means that the process has to be interrupted repeatedly, especially for longer welds.

In the BMBF-funded LaMeer project, LZH scientists are therefore now developing an alternative process together with its industry partner AMT from Aachen. The new process, called laser-assisted metal flux-cored underwater welding, aims to make welding underwater easier and produce better weld seams.

In standard flux-cored welding, a wire is continuously taken from a wire reel and melted. This allows significantly longer weld seams to be produced, thus increasing deposition rates and production rates. With the help of laser radiation the LZH scientists now want to optimise flux-cored welding further as a more efficient underwater welding alternative. To this end, they want to develop and test a welding torch prototype with integrated laser optics. The laser beam will insert energy into the workpiece in a targeted manner to improve arc ignition and stability. 

The work is based on research into laser beam-arc hybrid welding in an atmosphere, which has shown that the targeted combination of laser beam and arc in a common process zone allows the arc to be guided precisely, resulting in higher process stability and geometric accuracy of the weld seam. In addition, higher welding speeds and the over-welding of existing weld seams are possible. 

Bettering brass joining

The LZH is also looking to improve the welding of brass in another project with LMB Automation from Iserlohn. 

Brass’ high electrical conductivity, high corrosion resistance and attractive appearance make it suited to many applications ranging from fittings, machinery, and apparatus engineering to power plants, vehicles, and shipbuilding. 

However, welding the copper alloy is challenging due to process instabilities. The alloyed zinc evaporates below the melting temperature of copper. For this reason, pore formation and a high hot cracking tendency of the seams occur.

Spectroscopic measurement data and adaptable beam profiles will be combined to control and stabilise laser brass welding in one manufacturing system. (Credit: LZH)

Therefore, in the project LaserMessing, the LZH and its industry partner are developing a laser-based manufacturing system for the automated series production of brass components such as fittings, bearings, valves, turbines or heat exchangers.

The partners are combining laser-based deep welding using adaptable beam profiles, with cored wire processes, to produce a stable, automatable process that produces weld seams free of pores, weld spatters and underfill. Thermography and spectroscopy data will be used to monitor the process and develop a process control system. In doing so, energy can be directed into the workpieces to reduce vapour capillary fluctuations. The use of core and ring spots will provide additional process stabilisation. The subsequent laser cored wire process then smooths the seam surface of the previously created deep welds.

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