The development will be shown by the Fraunhofer Institute for Material and Beam Technology (IWS) at the Hannover Messe trade show starting in May.
Many technical structures feature some form of steel construction. Be it a container ship, railway vehicle, bridge or wind turbine tower, any one of these structures can have several hundred meters of welding seams. Conventional industrial processes such as metal active gas welding or submerged arc welding are usually used for this purpose. Here’s the problem: due to the low intensity of the arc, a large proportion of the energy expended 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 treatment is often of a similar magnitude to that required for the welding process itself.
“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,” emphasizes Dr. Dirk Dittrich, who heads up the Laser Beam Welding group at Fraunhofer IWS.
A team of researchers led by Dr. Dittrich has developed an energy-efficient alternative together with industrial partners as part of the “VE-MES – Energy-efficient and low-distortion laser multi-pass narrow-gap welding” project, which was publicly funded. Laser multi-pass narrow-gap welding uses a commercially available high-power laser and stands out from conventional methods thanks to its reduced number of layers and drastically reduced seam volume. These elements of the welding process are its key benefits. In the process, the laser is positioned at the joint between the two sheet edges to be welded while a filler metal is added. The energy of the laser beam melts the edges of the workpieces, as well as the filler metal from the wire, which then fills the void between the two pieces and creates a high-quality weld seam. The process can be used to weld typical joint configurations in steel construction. When welding either a web plate (T-joint) or a butt joint, the process ensures that the joint is complete, i.e., that the two parts are joined across the entire contact area.
For a one-meter weld seam, it was possible to reduce the costs for a sheet thickness of 30mm by 50% compared with submerged arc welding, including the subsequent straightening process. For sheet thicknesses of less than 20mm, where metal active gas welding processes are also commonly used, the potential cost savings are even higher, at up to 80%.
The cost savings in terms of welding filler materials alone can amount to more than 100,000 euros per year for larger companies. In addition, the laser beam sources used offer great potential for stemming rising energy costs due to their high efficiency (approximately 50%) and good process efficiency (reduction of energy input by 80%). With this evidence of practical suitability, the approach can now be extended to other applications.
