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Direct Laser Interference Patterning (DLIP) is used to generate textured stainless steel surfaces to control the wettability of a liquid nickel-based brazing alloy. The interference of two laser beams leads to periodic line-like structures with a spatial period of 6.0 µm. A maximum structure depth of 2.0 µm is reached by controlling the processing parameters. Moreover, the generation of laser induces periodic surface structures (LIPSS) with a period of ∼ 800 nm is observed on top of the DLIP structures. Depending on the produced texture depth, the contact angle of the molten metal is increased from 13° up to 96°. This allows adjusting the contact angle for various brazing and soldering applications and can also be used as a filler metal stop.

Laser-based joining is a potential key manufacturing process for realizing metal plastic hybrids. Therefore, surface preparation is essential to achieve a mechanical form fit. A new approach for surface preparation is based on a tungsten inert gas (TIG) arc process with anodic polarity. This TIG structure was characterized compared to fiber laser manufactured structures in cw and pw mode. The comparison of different preparations was based on pure ultimate tensile strength tests on spot joints. Finally, a transfer to overlap joints was successfully carried out and characterized by tensile shear tests using fiber reinforced plastics.

The high potential of Friction Stir Welding (FSW) is already widely used in industrial applications. In combination with a suitable machine concept, this technology is appropriate for small components and can be extended to applications on structures of several meters in length. Using a 3D-capable system that is stiff enough to handle the high process forces, machining and friction stir welding of complex geometries can be carried out directly in one set-up. In order to ensure reproducible, high quality welds, appropriate control strategies are needed. Furthermore the use of various tool types such as standard or bobbin tools can extend the range of weldable geometries tremendously. The aforementioned aspects have been part of process development work for FSW at Fraunhofer IWS Dresden in the last few years. Within the current paper interesting findings are discussed in detail. This includes the realization of a fully 3D-capable FSW machine based on a so-called Pentapod concept. This parallel-kinematic system is suitable for large and complex three-dimensional structures up to 7 meters in length. The FSW research is focused on the welding of aircraft structures and mixed-material joints; examples of research projects and their results are given. Selected welding examples of wrought and cast aluminum, high strength alloys and copper will be presented as well as experiences, which have been made in terms of process development and process control.

Aluminum alloys are widely used as technical lightweight materials. For industrial applications, these materials often have to be bonded, e. g. welded or brazed. To get a metallic connection by brazing, the natural oxide layer on Al-materials, which is dense and has a high melting point, has to be eliminated. This layer can be influenced by the temperature and humidity in the surrounding atmosphere. Due to the nm-thickness of the layer, the analysis of its thickness and composition is challenging. An applicable method is X-ray photoelectron spectroscopy (XPS). The present investigation shows the applicability of XPS to estimate the oxide layer thickness as well as to distinguish between Al-hydroxide and Al-oxide phases. Finally, reasons for the differences in brazeability depending on the previous storage conditions are studied. It is shown, that a storage under condensation for 9 days causes an increase of the oxide layer thickness and an aggregation of water inside the pores of the hydroxide layer. This lowers significantly the brazeability of the material.