Laser Zentrum Hannover (LZH) is developing a laser welding process for joining three-dimensional structures made of steel and aluminium in a hybrid design. The work is part of a project called Laser Leichter.
Steel-aluminium hybrid welds are of great interest for automotive production since they can be used for load-adapted, lightweight components. One of the challenges of welding steel with aluminium is to avoid hard and brittle intermetallic phases in the weld seam. These phases can occur easily, since iron and aluminium do not combine well.
The goal of the Laser Leichter project is to control the welding process. The engineers will be testing a spectroscopic method for control of the weld depth, which measures the emissions of the plasma. The composition of the plasma indicates the weld depth and allows the system to adapt the laser output accordingly. The control mechanism is being evaluated at LZH for flat welds, and as part of Laser Leichter will be expanded to three-dimensional structures.
Since the distance between the process zone and the measurement sensors inevitably changes during the process, detecting the plasma emissions accurately is difficult. For optimal measurements, the spectrometer will be integrated into an innovative, scanner-based processing head.
The scientists are also testing a sensor made by project partner Precitec, which can measure the depth of the keyhole weld (vapour capillary) directly. Additionally, they are examining a thermal imaging process from InfraTec, as well as a trailing non-destructive sample analysis using active thermal imaging from Inpro (Inpro Innovationsgesellschaft für fortgeschrittene Produktionssysteme in der Fahrzeugindustrie). The processes developed within the project are tested directly on demonstrators for the automotive industry, for example on a car body element or a battery case.
Apart from the LZH, Precitec, InfraTec and Inpro, the following companies are working together in the joint project ‘Development of a laser-based joining technology for dissimilar lightweight constructions’ (Laser Leichter): Volkswagen, Scherdel Marienberg, Matfem Partnerschaft Dr Gese and Oberhofer, Lunovu Integrated Laser Solutions, Brandenburg University of Technology, and Fraunhofer-Institut für Werkstoff- und Strahltechnik (Fraunhofer IWS).
Associated partners in the project are Trumpf Laser, Astor Schneidwerkzeuge, ThyssenKrupp Steel Europe, Bond-Laminates, and Sapa Aluminium Profile.
The joint project is coordinated by Robert Bosch, and the project management organisation is VDI Technologiezentrum. Laser Leichter is financed by the Federal Ministry of Education and Research (BMBF).