Laser welding will revolutionise steel construction
Energy and resource efficiency are becoming increasingly important and recently the Fraunhofer Institute for Materials and Beam Technology IWS has been working with its partners to develop an alternative to conventional steel structures which also incorporates base hardware and laser safety.The solution facilitates gentler processing of high-strength materials and significantly reduces energy consumption and costs, while significantly increasing processing speed. Compared to conventional welding processes, the energy input required for components can be reduced by up to 80%. In addition, subsequent straightening of the component is completely eliminated from the process. The innovative welding process is expected to be presented at the Hannover Messe Preview 2022.
Many technical structures are constructed in some form of steel. Whether it is a container ship, a railway vehicle, a bridge or a wind turbine tower, there can be hundreds of metres of weld seams in these structures. Therefore, if conventional industrial processes such as metal activated gas welding or submerged arc welding are used, problems arise in one way or another: due to the low strength of the arc, most of the energy consumed is not actually used in the welding process but is lost to the component in the form of heat. The energy required for post-weld processing is usually similar to the energy required for the welding process itself. "These energy-intensive processes can cause severe thermal damage to the material and lead to severe deformation of the structure, which later requires very expensive straightening work." Dr Dirk Dittrich, head of the Fraunhofer IWS Laser Beam Welding Group, emphasises.
The laser beam is positioned at the joint between the two plate edges to be welded and the filler metal is inserted in front of it, a process that produces a high-quality weld.
Powerful laser welding process
A group of researchers led by Dr. Dittrich has developed an energy-efficient alternative together with industrial partners as part of the project "VE-MES - Energy Efficient and Low Distortion Laser Multipass Narrow Gap Welding". Laser multi-pass narrow gap welding uses a commercially available high power laser and stands out from conventional methods due to its reduced number of layers and significantly smaller weld seam volume.In his report, Dr. Dittrich refers to the main advantages of the welding process.
"Depending on the component, we can reduce the energy input to the component during welding by up to 80% and we can reduce filler material consumption by up to 85% compared to conventional arc processes," Dr Dittrich reported."In addition, there is no need to carry out a straightening process for the parts under study. As a result, we can reduce production times and costs, process high-strength steel and significantly improve the CO2 balance along the entire production chain. Given the large number of steel structures being built in Germany and around the world, this could prove to be very beneficial." This is because the high intensity of the laser beam ensures that the energy input is highly concentrated at the welding point, while the surrounding area of the component remains relatively cool. "The welding time is also reduced by 50 to 70 percent," says Dittrich.
The new process is also outstanding in terms of weld quality - the weld seam is significantly thinner and the edges are almost parallel, whereas in conventional welding processes the seam is V-shaped. "If laser welding is used in the steel construction process, it will become a unique selling point for the medium-sized German company and strengthen its market position in the face of international competition," says Dittrich confidently. "We are offering the industry an efficient form of welding technology that will revolutionise steel construction thanks to its cost-effective application and resource-efficient production processes.
Cross-sections of welded joints and T-joints produced with laser MPNG: superb welds guaranteed at significantly reduced cost and resource consumption.
Practical study: steel beams for indoor crane construction
The Fraunhofer IWS researchers demonstrated the performance of their new development using practical examples of indoor crane construction. They deployed the new welding technology using special system technology and an integrated beam protection concept. The experimental design of the four-metre-long rectangular profile of the indoor crane section complies with comparable design and manufacturing guidelines for conventional production components. Typical application welds were produced: butt joints on a 30 mm plate and fully joined T-joints (15 mm plate).
For a one-metre-long weld, the cost of a plate with a thickness of 30 mm can be reduced by up to 50% compared to submerged arc welding, including the subsequent straightening process. For thin plates less than 20 mm thick, the metal-activated gas welding process is also commonly used and the potential cost savings are even higher, up to 80%. For large companies, savings of more than €100,000 per year can be achieved by welding filler material alone. In addition, the laser beam source used offers great potential for stopping rising energy costs due to its high efficiency (approx. 50%) and good process efficiency (80% reduction in energy input). With this evidence of practical applicability, the method can now be extended to other applications.
IWS researchers used an indoor crane section made of S355J2 structural steel (4 x 0.75 x 0.5 m) to demonstrate that their developed laser MPNG welding process can reduce energy costs by up to 80% and filler material consumption by up to 85% compared to conventional welding processes.
The principle of laser multi-pass narrow gap welding (MPNG)
While the filler metal is being added, the laser is positioned at the joint between the edges of the two sheets to be welded. The energy of the laser beam melts the edges of the workpiece and the filler metal on the wire, which then fills the gap between the two pieces and creates a high-quality weld. This process can be used to weld typical joint configurations in steel construction. The edges of the plates are plasma cut and the joints sometimes have gaps of up to 2 mm wide which can be reliably bridged by the laser welding process. When welding webs (T-joints) or butt joints, the process ensures that the joint is complete, i.e. that the two parts are joined over the entire contact area. In conventional steel construction, this is a technical limitation, especially when using T-joints.
