HANNOVER MESSE 2021

•••6••• Innovationen Magnetic pulse welding Optimized joining technology is opening the door to the safe use of hydrogen in the aviation industry An innovative newwelding process has been developed to help: mag- netic pulse welding. Researchers at the Fraunhofer Institute forMaterial and Beam Technology IWS in Dres- den have now demonstrated that this joining technology can produce extremely resilient, metallic mixed joints for cryogenic applications. They successfully achieved these outstanding joint properties in coop- erationwith the Technical University ofMunich. Scientists at Fraunhofer IWS pro- vided the research neutron source Heinz Maier-Leibnitz (FRM II) at the Technical University of Munich with a special component made of cop- per, high-grade steel and aluminum for its cryostats – cooling systems that are able to maintain extremely low temperatures. Until now, this assembly had to be produced by a complex process involving multiple laser beamwelded seams, addition- al joining elements and a brazed or electron beam welded seam. “But then there were problems with sta- bility and tightness,” explains Dr. Markus Wagner, Group Manager Design and Special Processes at the Fraunhofer Fraunhofer Institute for Material and BeamTechnology IWS. Themagnetic pulsemethod creates tighter jointswithin just a fewmicro- seconds. These joints function relia- bly both at very lowtemperatures of down to minus 270 degrees Celsius and alsowherever extreme temper- ature differences prevail. Overlaps, which provide even more stability, are also created at the joints. The technologies previously applied by the researchers at the Technical University of Munich are among the group of fusion welding processes. Metals are fused to create a joint be- tween them. However, these meth- ods rely on themetals having similar fusion points. This is the tempera- ture at which a substance begins to fuse. As Dr. Jürgen Peters, Head of Sample Environment at the research neutron sourceHeinzMaier-Leibnitz (FRM II) of the Technical University of Munich explains: “The problem comes when we try to create joints between metals that have highly dissimilar fusion temperatures or be- come extremely brittle whenmixed together – aluminumwith copper or high-grade steel, for example. The samples welded by the magnetic pulse method provided by our part- ners at Fraunhofer IWS passed the tightness tests.” Fast, cost-efficient joining Scientists in Dresden have been researching a new process for several years now. The materials do not need to be fused. “Mag- netic pulse welding is not based on a high heat input. The process relies mainly on a high pressure between the joining partners,” explains Jörg Bellmann, expert in magnetic pulse welding in Markus Wagner’s group. When the pro- cess starts, there is a distance of one to one-and-a-half millimeters between the joining partners. A magnetic field causes one of the two partners to accelerate. In the rest of the process, the metals collide with a bright flash at high speeds – 200 to 300 meters per second. A high pressure is then generated on the joining surface and this ultimately welds the two metals together. A measuring sys- tem, likewise developed at Fraun- hofer IWS, guarantees throughout all this that the components are correctly positioned, collide at the right angle and that the entire pro- cess consumes the smallest possi- ble amount of energy. Process scores highly with liquid hydrogen The great advantage of mag- netic pulse welding: It can join combinations of metals which, until now have been impossi- ble or difficult to weld together – especially important when it comes to liquid hydrogen ap- plications. Materials with poor thermal conductivity, high-grade steel for example, have to be joined to lightweight construc- tion materials such as aluminum. The new process now makes this possible. “The temperature only really gets hot at the boundary surface itself,” reports Wagner. The process is said to be fast and cost-efficient and is able to pro- duce joints of a consistently high quality. “We can also employ this method to combine extremely thin-walled components,” adds Bellmann. This is made possible by introducing special supporting elements that can be removed again when the process is com- plete. And the new process holds po- tential for more than just aircraft construction. Its good electrical conductivity in the joining zones also makes it an attractive propo- sition for the electromobility sec- tor and for processes in the elec- tronics manufacturing industry. “This welding technology will also create new possibilities for space travel,” of that Bellmann is con- vinced. Magnetic pulse welding is able to create solid state joints between dissimilar materials like copper, alumi- num and steel. The method fulfills the tightness requi- rements even at very low temperatures, in systems for storing and distributing liquid hydrogen for example. Foto: ronaldbonss.com With magnetic pulse welding, the magnetic pressure of a tool coil ensures a high-speed collision and the formation of a solid state joint of several millimeters in width, as well as high stability and leak tightness, even under extreme application conditions. Foto: ronaldbonss.com Continued from Page 1