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  • Improvement of the fatigue life of welded structures in high strength steel grades

    The fatigue properties of welded components can be improved by means of post-weld treatments, like TIG dressing or hammering. This article describes the results obtained in the research project “DURIMPROVE”, in which the effects of post-weld treatments on welds in high strength steel were investigated.

  • Joining of additively and conventionally manufactured stainless steels by means of automated laser beam welding

    Die Notwendigkeit ressourcenschonend zu fertigen sowie Produktionsprozesse unter Berücksichtigung sich wandelnder Rahmenbedingungen effizient zu gestalten und somit flexibel agieren zu können, führt zu einer stetig steigenden Nachfrage nach additiven Fertigungsverfahren seitens der Industrie. Nachaktuellen Zahlen wird hierfür ein jährliches Umsatzwachstum von 22,1% bis zum Jahr 2030 prognostiziert. 

    Die additive Fertigung wird dabei häufig als Konkurrenz zu konventionellen Fertigungsverfahren betrachtet, wenngleich die Kombination der beiden Ansätze eine hohes Anwendungspotential aufweist. Im Bereich der pulverbettbasierten additiven Fertigung wird die begrenzte Bauraumgröße oft als limitierender Faktor angeführt. In diesem Zusammenhang bietet die Nutzung moderner automatisierter Schweißverfahren die Möglichkeit einzelne Bauteile zu größeren Baugruppen zu verbinden und dabei die technischen, funktionalen und geometrischen Anforderungen des Endproduktes zu berücksichtigen.

    Aufgrund der zum Teil anisotropen Materialeigenschaften additiv gefertigter Komponenten birgt das Verschweißen von AM-Bauteilen besondere Herausforderungen, die zum aktuellen Zeitpunkt nicht ausreichend erforscht sind. Infolgedessen wird in dieser Arbeit der Einfluss des Laserstrahlschweißens auf Schweißverbindungen zwischen additiv und konventionell gefertigten Bauteilen untersucht. Als Werkstoff wird der in vielen Industriebereichen verwendete austenitische Stahl 1.4404 verwendet. Dabei werden sowohl additive Bauteile miteinander als auch konventionelle Bauteile mit additiv gefertigten Bauteilen verschweißt. Die AM-Probekörper wurden sowohl unter Verwendung von selektivem Laserstrahlschmelzen als auch mittels Lichtbogenauftragsschweißen gefertigt, sodass auch mögliche Einflüsse des jeweiligen Herstellungsprozesses berücksichtigt werden können. Die hergestellten Schweißverbindungen werden zunächst zerstörungsfrei geprüft, bevor im Anschluss mechanisch-technologische Kennwerte ermittelt werden und die vorliegende Mikrostruktur untersucht wird.

  • A Review on the Weldability of Additively Manufactured Aluminium Parts by Fusion and Solid-StateWelding Processes

    Additive manufacturing (AM) processes are playing a significant role in several industrial sectors such as construction and machine building industries, involving a wide variety of metallic materials. Among these, the AM of aluminium alloys has developed significantly over the last decade, mainly through Powder Bed Fusion (PBF) and Directed Energy Deposition (DED) processes. 
    Despite the many advantages of AM technology, some large or complex products cannot be produced entirely without the use of conventional manufacturing and joining processes, generally for financial or operational reasons. In this way, the ability to join conventionally and additively manufactured components or parts represents a crucial step towards their future use and the consolidation of conventional and additive manufacturing technologies. Despite the growing interest in AM technologies, there is still a significant lack of information on the joining of conventionally and additively manufactured components. The present work proposes a first review of the literature evaluating the weldability of AM aluminium alloys. The focus is on the use of fusion and solid-state welding processes and analysing the achieved microstructural evolution and mechanical properties. A clear relationship is observed between the AM technology used to produce the part, and the physical principles of the joining process. In addition, the gaps in the literature are highlighted to enable focused future work.

  • Joining Of Metal-Plastic Composites With Advanced Welding Processes

    Due to the growing environmental concern and the increasing demand for more ecological methods of transportation, composite materials that combine low weight and high resistance have raised the interest of several industrial sectors. Among these materials, the metal-plastic composites (MPCs) can be highlighted, who combine a low weight and a relatively high mechanical resistance. Such materials are used in advertising signs, building panels, motor shielding, etc. Mechanical joining of MPC materials is to be avoided when protrusions are not allowed or because of aesthetical reasons. Welding is therefore considered as an interesting alternative. However, qualitative joining using welding of the MPC materials to other MPC materials or to metallic plates is a real challenge. Due to their special features (layer structure, material mix, etc.), conventional manufacturing processes are therefore only of limited or no use at all. In particular, the polymer core layer is a barrier for the use of conventional joining methods. This contribution presents a novel joining approach for MPCs. The basic approach is the local melting of the polymer layer by ultrasonic waves and displacement of the molten plastic material by pressure on the cover sheets. This work proposes the investigation of the use of non-conventional solid-state welding processes, such as ultrasonic welding (USW) and refill friction stir spot welding (RFSSW), for joining MPCs with aluminium sheets. Prior to the application of the joining processes, the intermediate plastic core of the MPC materials is displaced using ultrasonic vibrations, so that the materials can be joined as monolithical materials. These joining concepts are validated experimentally. The obtained weld quality is assessed based on destructive and non-destructive testing methods.

  • Development of Resistance Spot Welding Processes of Metal–Plastic Composites

    Metal–plastic composites (MPCs) are gaining importance mainly due to high strength to weight ratio. They consist of three layers, two outer metallic cover sheets, and a plastic core. The presence of that inner plastic layer makes them rather unsuitable for joining by means of any conventional welding processes, which significantly reduces the application range of MPC. In this work, three various resistance spot welding (RSW)-based concepts were developed to overcome that limitation and join Litecor to DP600 steel. In all cases, a dedicated initial stage was implemented to RSW, which was aimed at removing the non-conductive polymer layer from the welding zone and creating the proper electrical contact for the resistance welding. These were, namely: (i) shunt current-assisted RSW; (ii) induction heating-assisted RSW; and (iii) ultrasonic-assisted RSW. The development of each concept was supported by finite element modeling, which was focused on setting the proper process parameters for polymer layer removal. Finally, the macro- and microstructure of exemplary RSW joints are shown and the most common spot weld features as well as the further development possibilities are discussed. 

  • Manual, Cobot and Robot Welding? How to Make the Choice?

    There are several reasons why automation of welding production is gaining more and more importance. For example, skilled welders are nowadays scarce. Besides that, the weld quality obtained when using automatic welding processes has shown to significantly reduce the need for rework.

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