New laser process ramps up efficiency of high-strength steel welding

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Laser MPNG welding can achieve dramatic efficiency gains over conventional joining processes such as submerged arc welding and metal active gas welding. (Image: Fraunhofer ILT)

Fraunhofer IWS researchers have developed a new laser welding process that dramatically increases the efficiency of joining high-strength steels compared to submerged arc welding.

Called ‘laser multi-pass narrow-gap welding’ (laser MPNG welding), the new process consumes up to 80 per cent less energy, up to 85 per cent less filler material, and takes 50-70 per cent less time than arc welding. The process also removes any need for post-weld straightening.

Due to the low intensity of the arc in submerged arc welding, a large proportion of the expended energy can be lost to the component in the form of heat, rather than being used in the joining process.

‘These energy-intensive processes cause significant thermal damage to the material and result in severe distortion of the structure, which then demands very costly straightening work afterwards,’ explained Dr Dirk Dittrich, head of the Laser Beam Welding group at Fraunhofer IWS.

The team of researchers led by Dittrich has therefore developed laser MNPG welding as an energy-efficient alternative together with the industrial partners of the VE-MES (Energy-efficient and low-distortion laser multi-pass narrow-gap welding) project. The process uses a commercially available high-power laser and stands out from conventional methods thanks to its reduced number of layers and dramatically reduced seam volume. These elements of the welding process are its key benefits. The high intensity of the laser beam guarantees that the energy input is highly localised at the welding point, whereas the surrounding areas of the component remain comparatively cold. The new process also excels in terms of weld seam quality – the seams are significantly slimmer and the edges are virtually parallel, whereas in conventional welding processes the seams are V-shaped. 

‘Depending on the component, we can reduce the energy input for the component during welding by up to 80 per cent, and we can lower filler material consumption by up to 85 per cent compared to conventional arc processes,’ said Dittrich. ‘The welding time is also reduced by 50 to 70 per cent. What’s more, it is not necessary to carry out a straightening process on the component. As a result, we can cut production time and costs, process high-strength steel materials and significantly improve the CO2 balance of the entire production chain.’

If laser welding were used in steel construction processes, it would become a unique selling point for medium-sized businesses in Germany and strengthen its market position in the face of international competition, according to Dittrich. ‘We are providing the industry with an efficient form of joining technology that is set to revolutionise steel construction on account of its cost-effective application and resource-saving production process,’ he remarked.

The cross-sections of a butt joint and a T-joint produced using laser MPNG show the seam quality that can be produced with significantly reduced costs and resource consumption. (Image: Fraunhofer IWS)

The researchers demonstrated the performance of their new process using a practical example from indoor crane construction. They deployed the new welding technology using special system technology and an integrated beam protection concept. The design of the experimentally built, 4m-long rectangular profile of an indoor crane segment conformed to the design and manufacturing guidelines of comparable, conventionally produced components. Weld seams typical of the application were produced: a butt joint on 30mm plates and a fully joined T-joint (15mm plate). For a 1m weld seam, it was possible to reduce the costs for a sheet thickness of 30mm by 50 per cent compared with submerged arc welding, including the subsequent straightening process. For sheet thicknesses of less than 20mm, where metal active gas welding (another conventional joining process) is also commonly used, the potential cost savings are even higher at up to 80 per cent. 

The cost savings in terms of welding filler materials alone could amount to more than 100,000 euros per year for larger companies, according to the researchers. In addition, the laser beam sources used offer great potential for stemming rising energy costs due to their high efficiency (approximately 50 per cent) and good process efficiency (reduction of energy input by 80 per cent). 

With this evidence of practical suitability, the approach can now be extended to other applications.

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