SHIPBUILDING


recently, his group developed a laser arc technological system intended for agglomeration of panels during ship building. Teir experimental studies test different joint geometries in high strength steels, in a portal system comprising a complete solution for welding panels. Tey demonstrated that the weld quality meets shipbuilding industry standards for panels of thicknesses 7mm to 45mm[4]


. Teir system uses a ytterbium fibre laser


with maximum power of 16kW. Te laser head and arc torch are fixed to a carriage that moves along the overhead crossrail of the portal at up to 10 metres per minute. All controls are automatic, and the system is capable of welding seams on panels 6 x 6m, but it ‘can be scaled to size’, added Kruznetsov. For some configurations, the welding


system yielded interior defects in the weld seam, but the researchers found that by minimising the distance between laser spot and arc, and using metal powder welding wire, they could achieve the mechanical properties required by the Russian Maritime Register of Shipping. ‘Using hybrid laser-arc welding in


working with the shipbuilding industry to develop new methods for joining different metals. In 2015, ten partners of the Laser Welding


of Steel to Aluminium for Applications in Shipbuilding (LaSAAS) research project began a collaboration with ship manufactures including Meyer Werſt and Lürssen Werſt to develop a laser process that would let them directly weld dissimilar joints of steel and aluminium. Te main benefit of laser welding for


joining steel with aluminium is the ability to control the mixing ratio of the two melted metals. To obtain a relatively high quality weld seam in terms of imperfections and joint strength, the mixing ratio must consist of more melted steel than aluminium. Led by Laser Zentrum Hannover (LZH),


hybrid laser- arc welding in shipyards is new


Using


shipyards is new. It has not yet made its way into the world practice of the shipyards industry,’ said Kuznetsov.


Different materials It’s not just welding thick sheets of steel that’s important in the maritime industry. A push toward reducing fuel consumption has led to the incorporation of weight-reducing materials such as aluminium in shipbuilding, particularly for deck structures on top of a steel hull. So far, different metals have been joined to


one another using a separate adapter component. Tis is done via an expensive and complicated joining process called explosive cladding. Now, scientists and engineers are


the LaSAAS industrial partners developed a laser processing head with which to control how deep the weld penetrates. Tat’s key to the process: with the steel sheet positioned on top of the aluminium, the operator can weld all the way through the steel and only a predetermined amount into the aluminium. Te optimised


penetration depth into the aluminium depends on the sheet thickness and laser spot diameter. Tey used a TruDisk 16002 disk laser with maximum beam power of 16kW. ‘Te adapter welded with optimised


welding parameters and a certain number of weld seams is able to exceed the yield strength of the aluminium by more than 152 per cent,’ said Rabi Lahdo, engineer at LZH. Te laser processing head controls the


penetration depth using two different measurement principles based on: firstly, a non-contact optical sensing technology called short coherence interferometry and secondly, spectral analysis of emissions from the weld plume during welding. Te operator can establish a clear relation between the characteristics of these spectral emissions and the penetration depth, as the intensity is indicative of the weld depth. During the welding process, the operator compares the spectral intensity with the intensity that has been determined to indicate optimal depth. Te laser power is adapted to ensure a constant penetration depth. ‘Using the depth-control laser processing


Cross-section of T-joint weld www.lasersystemseurope.com | @lasersystemsmag


head, a consistent and comparatively high weld seam quality can be achieved independently of the weld speed, different


Laser welded adapter of steel and aluminium for shipbuilding applications


material batches, [or other variations],’ added Lahdo. Te laser welding process has only been


developed under laboratory conditions, however. ‘Our project partners are intent on transferring the process to the field of ship manufacturers,’ Lahdo explained. Key challenges will be to weld very long seams of dissimilar materials. Laser welding dissimilar joints of steel and


aluminium for shipbuilding applications in this thickness range is very new. ‘It’s hard to know what will work and what won’t long term,’ said Lahdo. Te goal is to achieve the standards for dissimilar joints set by DNV GL, a Norway-based company that sets standards for ships and offshore structures. Shipbuilding has its roots in human beings’


earliest transportation, exploration, and commercial efforts. It will be interesting for mariners and scientists alike to see how laser technologies shape the industry’s future.


References [1]


S. T. Riches, J. Klaestrup Kristensen et al, Laser welding in ship construction phase 1 – feasibility study, TWI-UK/Force Institute-Denmark, June 1992.


[2] Guidelines for the approval of CO2 laser welding, Lloyd’s Register, March 1997.


[3]


Christoph H.J. Gerritsen (TWI), David J. Howarth (Lloyd’s Register), A Review of the development and application of laser and laser-arc hybrid welding in European shipbuilding; paper presented at the 11th CF/DRDC International Meeting on Naval Applications of Materials Technology, Halifax, Nova Scotia, Canada, 7-9 June 2005.


[4] Turichin et al., Physics Procedia 89, 156-163 (2017).


ISSUE 37 • WINTER 2017 LASER SYSTEMS EUROPE


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Turichin et al. 2017


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