Fraunhofer-Institut für Produktionsanlagen und Konstruktionstechnik IPK

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  • Publication
    Kombination des Laserhybridschweißens und UP-Engspaltschweißens für dickwandige Bauteile zur Erhöhung der Wirtschaftlichkeit
    ( 2024)
    Gook, Sergej
    ;
    El-Sari, Bassel
    ;
    Üstündag, Ömer
    ;
    Gumenyuk, Andrey
    ;
    Biegler, Max
    ;
    Rethmeier, Michael
    Dieser Beitrag befasst sich mit der Entwicklung eines wirtschaftlichen und robusten Verfahrens zum Schweißen dicker Stahlbleche. Es werden Ergebnisse für das Fügen von Blechen im Dickenbereich von 25 mm bis 80 mm vorgestellt. Die 30 mm dicken Schweißnähte konnten im Stumpfstoß in zwei Durchgängen unter Verwendung des Laserhybridschweißens und des Unterpulverschweißens (UP) geschweißt werden. Das Laserhybridschweißen wird als Einschweißung mit einer Tiefe von ca. 25 mm ausgeführt. Die UP-Lagen werden auf der gegenüberliegenden Seite des Blechs aufgebracht. Bei richtiger Wahl der Schweißparameter wird der Nahtquerschnitt durch eine sichere Überlappung beider Lagen geschlossen. Bei Blechdicken über 30 mm ist eine Kantenvorbereitung erforderlich, die eine Ausführung der UP-Fülllagen in Engspalttechnik ermöglicht. Die Vorteile der vorgeschlagenen Prozesskombination liegen darin, dass die Nahtwurzel der Laserhybridnaht nicht geformt werden muss. Defekte in der Wurzel der Laserhybrideinschweißung können durch die UP-Lagen effektiv beseitigt werden. Das Verfahren bietet eine hohe Stabilität des Schweißprozes-ses in Bezug auf die Qualität der Blechkanten. Plasmageschnittene Kanten konnten ohne Bindefehler geschweißt werden. Die erreichte Nahtqualität wurde durch zerstörende und zerstörungsfreie Prüfungen bestätigt.
  • Publication
    Process advantages of laser hybrid welding compared to conventional arc-based welding processes for joining thick steel structures of wind tower
    ( 2023-12-22)
    Brunner-Schwer, Christian
    ;
    Üstündag, Ömer
    ;
    Bakir, Nasim
    ;
    Gumenyuk, Andrey
    ;
    Rethmeier, Michael
    The most common welding processes when joining thick-walled steels in the industry are arc-based welding processes such as GMAW or SAW. For this purpose, the sheets are joined in multi-layer technique, which can lead to productivity losses due to high welding times. The process-specific challenges in welding thick steels using multi-layer technique relate to the high heat input from the process. Therefore, alternative welding processes are being actively sought. A suitable alternative is provided by beam-based welding processes such as the laser hybrid welding processes, which are characterized by deep penetration welds and lower heat input. With implementation of the laser hybrid welding process in the heavy industry, such as the wind tower industry, economic benefits can be reached such as the increase in productivity by reducing the layer number, and the lower consumption of filler material and energy. When comparing SAW welded 25 mm thick steels in five to six layers and single-pass laser hybrid welding, the welding time can be reduced more than 80 % and the costs of filler material, flux and energy can be saved up to 90 %. However, the industrial use of the laser hybrid welding process is still limited to applications, where the material thickness does not exceed 15 mm due to some process-specific challenges such as the sagging, sensitivity to manufacturing tolerances such as gaps and misalignment, limited filler wire mixing, and deteriorated mechanical properties resulting from high cooling rates. To overcome these challenges, a contactless electromagnetic backing based on an externally applied AC magnetic field was used. Eddy currents are induced due to the oscillating magnetic field, and an upward-oriented Lorentz force is generated to counteract the droplets formed due to gravitational forces. It allows to weld up to 30 mm thick structural steels in a single-pass with a 20-kW fiber laser system. Additionally, the gap bridgeability and the misalignment of edges were increased to 2 mm when welding 20 mm thick steels. With the aid of the AC magnetic field, a vortex was formed in the weld root, which had a positive effect on the filler wire mixing.
  • Publication
    Laserstrahlhybridschweissen von Türmen für Windkraftanlagen - Ökonomische und ökologische Vorteile
    ( 2023-12-19)
    Üstündag, Ömer
    ;
    Bakir, Nasim
    ;
    Brunner-Schwer, Christian
    ;
    Knöfel, Frieder
    ;
    Gook, Sergej
    ;
    Gumenyuk, Andrey
    ;
    Rethmeier, Michael
    Das Laserstrahlhybridschweißen ist beim Schweißen von Türmen für Windkraftanlagen eine Alternative zum Unterpulver schweißen von Dickblechen in Mehrlagentechnik und bietet hier ökonomische und ökologische Vorteile. Der industrielle Einsatz des Verfahrens ist jedoch durch prozessspezifische Herausforderungen eingeschränkt. Die im Beitrag beschriebene kontaktlose elektromagnetische Badstütze dient zur Erweiterung des Verfahrenspotenzials im Dickblechbereich >15 mm.
  • Publication
    Retaining Mechanical Properties of GMA-Welded Joints of 9%Ni Steel Using Experimentally Produced Matching Ferritic Filler Metal
    ( 2022-11-30)
    El-batahgy, Abdel-monem
    ;
    Elkousy, Mohamed Raafat
    ;
    Al-Rahman, Ahmed Abd
    ;
    Gumenyuk, Andrey
    ;
    Rethmeier, Michael
    ;
    Gook, Sergej
    Motivated by the loss of tensile strength in 9%Ni steel arc-welded joints performed using commercially available Ni-based austenitic filler metals, the viability of retaining tensile strength using an experimentally produced matching ferritic filler metal was confirmed. Compared to the austenitic Ni-based filler metal (685 MPa), higher tensile strength in gas metal arc (GMA) welded joints was achieved using a ferritic filler metal (749 MPa) due to its microstructure being similar to the base metal (645 MPa). The microstructure of hard martensite resulted in an impact energy of 71 J (−196 °C), which was two times higher than the specified minimum value of ≥34 J. The tensile and impact strength of the welded joint is affected not only by its microstructure, but also by the degree of its mechanical mismatch depending on the type of filler metal. Welds with a harder microstructure and less mechanical mismatch are important for achieving an adequate combination of tensile strength and notched impact strength. This is achievable with the cost-effective ferritic filler metal. A more desirable combination of mechanical properties is guaranteed by applying low preheating temperature (200 °C), which is a more practicable and economical solution compared to the high post-weld heat treatment (PWHT) temperature (580 °C) suggested by other research.
  • Publication
    Laserstrahlhybridschweißen von Türmen für Windkraftanlagen
    ( 2022-08-29)
    Üstündag, Ömer
    ;
    Bakir, Nasim
    ;
    Brunner-Schwer, Christian
    ;
    Knöfel, Frieder
    ;
    Gook, Sergej
    ;
    Rethmeier, Michael
    ;
    Gumenyuk, Andrey
    Das Laserstrahlhybridschweißen ist beim Schweißen von Türmen für Windkraftanlagen eine Alternative zum Unterpulverschweißen von Dickblechen in Mehrlagentechnik und bietet hier ökonomische und ökologische Vorteile. Der industrielle Einsatz des Verfahrens ist jedoch durch prozessspezifische Herausforderungen eingeschränkt. Die im Beitrag beschriebene kontaktlose elektromagnetische Badstütze dient zur Erweiterung des Verfahrenspotenzials im Dickblechbereich >15 mm.
  • Publication
    Joining 30 mm Thick Shipbuilding Steel Plates EH36 Using a Process Combination of Hybrid Laser Arc Welding and Submerged Arc Welding
    ( 2022-08-04)
    Gook, Sergej
    ;
    Midik, Ahmet
    ;
    Biegler, Max
    ;
    Gumenyuk, Andrey
    ;
    Rethmeier, Michael
    This article presents a cost-effective and reliable method for welding 30 mm thick sheets of shipbuilding steel EH36. The method proposes to perform butt welding in a two-run technique using hybrid laser arc welding (HLAW) and submerged arc welding (SAW). The HLAW is performed as a partial penetration weld with a penetration depth of approximately 25 mm. The SAW is carried out as a second run on the opposite side. With a SAW penetration depth of 8 mm, the weld cross-section is closed with the reliable intersection of both passes. The advantages of the proposed welding method are: no need for forming of the HLAW root; the SAW pass can effectively eliminate pores in the HLAW root; the high stability of the welding process regarding the preparation quality of the weld edges. Plasma cut edges can be welded without lack of fusion defects. The weld quality achieved is confirmed by destructive tests.
  • Publication
    Improvement of Charpy impact toughness by using an AC magnet backing system for laser hybrid welding of thick S690QL steels
    ( 2022)
    Üstündağ, Ömer
    ;
    Bakir, Nasim
    ;
    Gumenyuk, Andrey
    ;
    Rethmeier, Michael
    The study deals with the influence of the heat input and the resulting cooling times on the microstructure and Charpy impact toughness of single-pass laser hybrid welded 20-mm thick high-strength steel S690QL. The main focus is on the change of the mechanical properties over the entire seam thickness. The cooling times were measured in-situ using a pyrometer and an optical fibre in three different depths of the seam where Charpy impact test specimens were also later taken. Thereby, three different heat inputs from 1.3 kJ/mm to 2 kJ/mm were investigated. Despite the observed decreased values of both t8/5-cooling time and the Charpy impact toughness in the root part of the seam, the required impact toughness of 38 J/cm2 could be reached in dependance on applied heat input, especially at the heat input of 1.6 kJ/mm.
  • Publication
    Hybrid laser-arc welding of laser- and plasma-cut 20-mm-thick structural steels
    ( 2022)
    Üstündag, Ömer
    ;
    Bakir, Nasim
    ;
    Gook, Sergej
    ;
    Gumenyuk, Andrey
    ;
    Rethmeier, Michael
    It is already known that the laser beam welding (LBW) or hybrid laser-arc welding (HLAW) processes are sensitive to manufacturing tolerances such as gaps and misalignment of the edges, especially at welding of thick-walled steels due to its narrow beam diameter. Therefore, the joining parts preferably have to be milled. The study deals with the influence of the edge quality, the gap and the misalignment of edges on the weld seam quality of hybrid laser-arc welded 20-mm-thick structural steel plates which were prepared by laser and plasma cutting. Single-pass welds were conducted in butt joint configuration. An AC magnet was used as a contactless backing. It was positioned under the workpiece during the welding process to prevent sagging. The profile of the edges and the gap between the workpieces were measured before welding by a profile scanner or a digital camera, respectively. With a laser beam power of just 13.7 kW, the single-pass welds could be performed. A gap bridgeability up to 1 mm at laser-cut and 2 mm at plasma-cut samples could be reached respectively. Furthermore, a misalignment of the edges up to 2 mm could be welded in a single pass. The new findings may eliminate the need for cost and time-consuming preparation of the edges.
  • Publication
    Preliminary study to investigate the applicability of optical strain measurement technique for the detection of hot cracks in laser metal deposited layers
    ( 2022)
    Straße, Anne
    ;
    Bakir, Nasim
    ;
    Gumenyuk, Andrey
    ;
    Rethmeier, Michael
    Laser metal deposition (LMD) as an additive manufacturing technique became increasingly important in recent years and thus the demand for component safety. This is the reason, for the need for reliable in-situ defect detection techniques. For laser beam weld seams an optical measurement technique based on an optical flow algorithm was successfully used to define the critical straining conditions that lead to hot cracking. This algorithm was adapted for bead-on-plate weld seams on LMD deposited layers of IN718 alloy while performing external strain on the specimen in an externally loaded hot cacking test facility. The resulting transversal hot cracks along the weld seam were localized via X-Ray inspection and the type of cracking confirmed by Scanning Electron Microscopy (SEM). The strain distribution was measured in the vicinity of the solidification front and correlated to the detected hot cracks. Based on the results this technique could be adopted for LMD experiments.
  • Publication
    Influence of the weld pool geometry on solidification cracking in partial penetration high power laser beam welding
    ( 2022)
    Bakir, Nasim
    ;
    Üstündağ, Ömer
    ;
    Gumenyuk, Andrey
    ;
    Rethmeier, Michael
    Solidification cracking is still a serious problem in laser beam welding, especially in the welding of thick-walled plates. The influence of weld pool geometry on solidification cracking in partial penetration welding of thick plates is investigated within scope of this study. Therefore, a specific experimental setup of steel and quartz glass in butt configuration and on the side with high-speed camera were used to record the weld pool shape. In addition, the influence of laser inclination angle on the weld pool geometry and on solidification crack formation was investigated. The results show a bulge in the weld pool root, which is separated from an upper region by a necking region. This leads to a case where there are three different longitudinal region lengths with different solidification zones. This temporal sequence of solidification strongly promotes the formation of solidification cracks in the weld root.