Project shows laser joining of steel-aluminum mixed connections

The LaserLeichter project has developed a laser welding process for quick and safe joining of 3D structures made of steel and aluminum.

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Within the Development of Laser-Based Joining Technologies for Similar Lightweight Constructions (LaserLeichter) project, non-profit research institute Laser Zentrum Hannover (LZH; Hannover, Germany) has developed a laser welding process for quick and safe joining of three-dimensional (3D) structures made of steel and aluminum. Scientists at LZH have developed processes for joining two- and three-sheet metal joints with high welding speeds of up to 7 m/min. The basis for the remote laser beam welding process is a 3D scanner optic newly developed by TRUMPF (Ditzingen, Germany). With this, complex 3D seam geometries are possible, even with large structures. Thus, the process is particularly interesting for car body construction and can replace complex robot movements.

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The weld joint achieves a shear tensile strength of approximately 67% of the aluminum alloy. Because of the parallel arrangement of three welds, this can even be increased to about 95%. The process was developed for battery cases of electric cars, seat structures, and car body parts. Volkswagen (VW) has quasistatically and dynamically tested the validation components for car body applications. The joined mixed compounds have an advantageous crash behavior, since the joining partners remain safely connected.

One of the challenges in welding steel and aluminum is to avoid hard and brittle intermetallic phases in the welding seam, which cannot be completely avoided. During laser welding, a low amount of heat is introduced into the workpiece in a well targeted manner. Therefore, these phases are formed to a reduced extent and the dissimilar materials are melted as defined. Thus, it is possible to control the mixing of the joint.

LaserLeichter project partners include VW, INPRO, Precitec, MATFEM Partnerschaft, LUNOVU, Scherdel Marienberg, InfraTec, Brandenburgische Technische Universität Cottbus-Senftenberg, and the Fraunhofer Institute for Material and Beam Technology (Fraunhofer IWS), which all worked together under the coordination of Robert Bosch. Associated partners were TRUMPF, ASTOR Schneidwerkzeuge, ThyssenKrupp Steel Europe, Bond-Laminates, and Hydro Extrusion Offenburg (formerly SAPA Aluminium Profile).

LaserLeichter was funded by the Federal Ministry of Education and Research (BMBF) within the scope of the Photonic Processes and Tools for Resource-Efficient Lightweight Construction funding initiative.The project group was coordinated by LZH.

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