TY - CONF A1 - Stankevich, S. A1 - Gumenyuk, Andrey A1 - Straße, Anne A1 - Rethmeier, Michael ED - Reisgen, U. ED - Schmidt, M. ED - Zaeh, M. ED - Rethmeier, Michael T1 - Measurement of thermal cycle at multi-pass layer build-up with different travel path strategies during DLMD process N2 - The shape of the parts, created by the technology of direct laser metal deposition (DLMD), is influenced by various parameters, for example, the power and diameter of the laser source spot. The contribution of energy from the laser affects the temperature distribution in the formed layers. The changing temperature in the working area entails a Change in the geometry of the layers and affects the stability of the process. In this paper, experiments on the measurement of temperature cycles in the DLMD process with different directions of the filling track are carried out. An infrared camera was used to measure thermal cycles. The calibration of the acquired data (i.e. correspondence table between the intensity of thermal radiation of the material and the absolute temperature) was done with help of two-color pyrometer ex situ and in situ measurements. The experiments are carried out on two materials 316L and Inconel 718. The effect of the maximum temperature on the layer height is shown, and thermal cycles in the formation of layers for different filling strategies are presented. T2 - Laser in Manufacturing Conference 2019 CY - Munich, Germany DA - 24.06.2019 KW - Thermography KW - Direct Laser Metal Deposition PY - 2019 SP - 1 EP - 9 AN - OPUS4-48716 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Frei, J. A1 - Biegler, M. A1 - Rethmeier, Michael A1 - Böhne, Ch. A1 - Meschut, G. T1 - Investigation of liquid metal embrittlement of dual phase steel joints by electro-thermomechanical spot-welding simulation N2 - A 3D electro-thermomechanical model is established in order to investigate liquid metal embrittlement. After calibration to a dual phase steel of the 1000 MPa tensile strength class, it is used to analyse the thermo-mechanical system of an experimental procedure to enforce liquid metal embrittlement during resistance spot welding. In this procedure, a tensile stress level is applied to zinc coated advanced high strength steel samples during welding. Thereby, liquid metal embrittlement formation is enforced, depending on the applied stress level and the selected material. The model is suitable to determine and visualise the corresponding underlying stresses and strains responsible for the occurrence of liquid metal embrittlement. Simulated local stresses and strains show good conformity with experimentally observed surface crack locations. KW - RSW KW - LME KW - Advanced high strength steel KW - Zinc coated steel KW - Testing method KW - Dual phase steel KW - Cracking KW - Electro-thermomechnical model PY - 2019 DO - https://doi.org/10.1080/13621718.2019.1582203 SN - 1362-1718 SN - 1743-2936 VL - 24 IS - 7 SP - 624 EP - 633 PB - Taylor & Francis AN - OPUS4-47747 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Brunner-Schwer, C. A1 - Graf, B. A1 - Rethmeier, Michael T1 - Laser-Plasma-Hybrid-Cladding: Possibilities in the combination 2 of arc and laser for deposition welding N2 - Plasma-Transferred-Arc (PTA) welding is a process that enables high deposition rates, but also causes increased thermal load on the component. Laser based Direct Energy Deposition (DED) welding, on the other hand, achieves a high level of precision and thus comparatively low deposition rates, which can lead to high processing costs. Combining laser and arc energy aims to exploit the respective advantages of both technologies. In this study, different possibilities of this process combination are presented using a PTA system and a 2 kW disk laser. This includes the combination in a common process zone as a highspeed plasma laser cladding technology (HPLC), which achieves process speeds of 10 m/min. Besides that it is being examined whether a pre-running plasma arc can be used to coat difficult-to-weld rail steel with a carbon content of 0.8 % due to a preheating effect. Furthermore, a smoothing of the coating by a plasma arc following the laser is investigated. T2 - Lasers in Manufacturing 2019 CY - Munich, Germany DA - 24.06.2019 KW - Plasma-Transferred-Arc KW - Direct Energy Deposition KW - highspeed plasma laser cladding KW - deposition welding PY - 2019 SP - 1 EP - 9 AN - OPUS4-48724 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Bakir, Nasim A1 - Biltgen, J. A1 - Gumenyuk, Andrey A1 - Rethmeier, Michael T1 - Influence of Partial Penetration Laser Hybrid Welding Parameters on the Solidification Cracking for Thick-Walled Structures N2 - In this study, the influence of the welding speed and the arc power on the solidification crack formation for partial penetration laser hybrid welded Thick-Walled plates were investigated. Experimentally, a linear correlation between the welding velocity and the crack number was observed. That is by reducing the welding velocity the crack number was reduced. The reduced welding velocity showed a strong impact on stress, as the model demonstrated a very lower stress amount in comparison to the reference case. The reduction of the welding speed could be a helpful technique to reduce the hot cracking. The wire feed speed showed a very slight influence on the crack formation. That can be returned to the large distance between the critical region for cracking and the arc region. T2 - Lasers in Manufacturing Conference 2019 CY - Munich, Germany DA - 24.06.2019 KW - Hybrid laser-arc welding KW - Solidification cracking KW - Thick-walled steel KW - Numerical simulation PY - 2019 SP - 1 EP - 7 PB - WLT Wissenschaftliche Gesellschaft Lasertechnik e.V AN - OPUS4-48733 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Spranger, Felix A1 - Hilgenberg, Kai A1 - Rethmeier, Michael T1 - Laserimplantation von TiB2-Partikeln in X153CrMoV12 Kaltarbeitsstahl und Ihr Einfluss auf die Materialeigenschaften N2 - Die Laserimplantation erlaubt die Herstellung verschleißbeständiger, erhabener Mikrostrukturen (Implants) auf Stahloberflächen durch ein diskontinuierliches Dispergieren von keramischen Partikeln mittels gepulster Laserstrahlung. Durch die flexible Anordnung separierter Implants zu komplexen Mustern erlaubt das Verfahren eine gezielte Oberflächenstrukturierung zur Beeinflussung des Reibungs- und Verschleißverhaltens. Insbesondere erwies sich Titandiborid (TiB2) als Implantationsmaterial für geeig-net, da eine Manipulation der Implantgeometrie in einem breiten Bereich vorgenommen werden konnte, ohne dass Materialdefekte wie Risse oder Poren auftraten. Ziel der Untersuchungen war es, den Einfluss implantierter TiB2-Partikel auf die Materialeigenschaften von X153CrMoV12 zu ermitteln. Hierfür wurden im Rahmen der Arbeit die Laserparameter (Pulsleistung und -dauer) in einem breiten Parameterfeld variiert und vergleichende Untersuchungen an TiB2 implan-tierten Zonen sowie an punktuell umschmelzstrukturierten Zonen durchgeführt. Die Ergebnisse zeigen, dass eine reine Umschmelzstrukturierung zu einer deutlichen Reduktion der Oberflächenhärte aufgrund erhöhter Restaustenitgehalte (γR) führt. Im Gegensatz dazu führt das Laserimplantieren von TiB2-Partikeln zu einer deutlichen Härtesteigerung in den kuppel- oder ringförmigen Implants. Härtewerte von bis zu 1800 HV1 resultieren aus dispergierten TiB2-Primärpartikeln sowie in-situ ausgeschiedenen Se-kundärphasen, durch die der Restaustenitanteil zudem deutlich reduziert wird. T2 - 39. Assistentenseminar Füge- und Schweißtechnik CY - Eupen, Belgium DA - 12.09.2018 KW - Laserimplantation KW - TiB2 KW - AISI D2 KW - Laserdispergieren PY - 2019 SN - 978-3-96144-070-2 VL - Band 356 SP - 51 EP - 59 PB - DVS Media GmbH CY - Düsseldorf AN - OPUS4-48751 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Artinov, Antoni A1 - Bachmann, Marcel A1 - Karkhin, Victor A1 - Rethmeier, Michael ED - Sommertisch, C. ED - Enzinger, N. ED - Mayr, P. T1 - A novel approach for calculating the thermal cycle of a laser beam welding process using a stationary CFD model N2 - This work aims to find the thermal cycles during and after fusion welding through simulation by first calculating the resulting local temperature field in the quasi-stationary part of the process. Here complete-penetration keyhole laser beam welding with a laser power of 18 kW on a 15 mm thick slab of a low-alloyed steel at a welding speed of 2 m/min is considered. In order to physically depict the laser material interaction a multi-physics numerical model including the effects of phase transformation, thermo-capillary convection, natural convection and temperature-dependent material properties up to evaporation temperature is developed. It uses a fixed keyhole geometry with a right truncated circular cone shape to introduce the laser beam energy to the workpiece. In a subsequent study, the resulting local temperature field is then used as an equivalent heat source in order to predict the unsteady thermal cycle during and after fusion welding. The translational movement of the laser beam through the workpiece is represented by a moving mesh approach. For the simulation, stationary heat transfer and fluid dynamics are described by a system of strongly coupled partial differential equations. These are solved with the commercial finite element software COMSOL Multiphysics 5.0. The results of the numerical simulation are validated by experiments, where the weld bead shapes and the thermal cycles show good correlation. T2 - 12th International Seminar "Numerical Analysis of Weldability" CY - Graz, Austria DA - 24.09.2018 KW - Equivalent heat source KW - Process simulation KW - Laser beam welding KW - Transient heat transfer KW - Moving mesh PY - 2019 SN - 978-3-85125-616-1 VL - 12 SP - Chapt. VI, 694 EP - 710 PB - Verlag der Technischen Universität Graz AN - OPUS4-48817 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - RPRT A1 - Bachmann, Marcel A1 - Rethmeier, Michael T1 - Gekoppelte numerische Untersuchung der Bildung von Mittelrippendefekten beim Hochleistungslaserstrahlschweißen N2 - Die Entstehung von Erstarrungsrissen stellt ein in der Schweißtechnik lange bekanntes Problem dar. Diese prozessseitige Herausforderung ist selbst nach dem heutigen Wissenstand schwer zu beherrschen und gefährdet die Sicherheit der gefügten Bauteile. Dieses Problem erweist sich als besonders schwierig beim einlagigen Hochleistungslaserstrahlschweißen von Metallteilen hoher Blechstärke, welche eine essentielle Rolle in vielerlei industriellen Anwendungen spielen. Gegenstand des hier bearbeiteten Forschungsprojekts war die numerische Untersuchung der Entstehungsmechanismen des Mittelrippendefekts beim Laserstrahlschweißen niedriglegierter Stähle. Mittels mehrerer gekoppelter Simulationen, für welche sowohl kommerziellen Softwares, wie COMSOL Multiphysics und ANSYS, als auch in-house entwickelte Programme eingesetzt worden sind, wurden die am stärksten ausgeprägten Mechanismen der Erstarrungsrissbildung und deren Zusammenspiel aufgeklärt. Begleitend zur Simulation wurden mehrere experimentelle Untersuchungen für den niedriglegierten Baustahl S355 an den Blechdicken 12 mm und 15 mm zu deren Validierung durchgeführt. Die Ergebnisse der Simulation des Kristallwachstums, der Diffusion und der Makroseigerung von Schwefel zeigen, dass die Risse für bestimmte Werkstoffe mit einer hohen Konzentration an Verunreinigungen hauptsächlich metallurgisch bedingt entstehen können. Allerdings zeigte die Untersuchung des Einflusses der Ausbauchung (Bulging) im Mittenbereich der Schweißnaht auf das transiente Temperaturfeld und die transienten Transversalspannungen im risskritischen Bereich auch, dass die Rissbildung nicht nur metallurgisch bedingt und insbesondere auch für aus metallurgischer Sicht eigentlich rissunkritische Materialien auftreten kann. Der Bulging-Bereich hat sich in der Untersuchung als besonders kritisch in allen Teilen der Simulationskette gezeigt. Die Einflüsse dieser geometrischen Besonderheit konnten bei allen physikalischen Teilaspekten der Problematik als heißrissinduzierend identifiziert werden. Von besonderer Bedeutung wird an dieser Stelle das erkannte Zusammenspiel dieser Einflüsse hervorgehoben. Bisher wurde die Bildung der Erstarrungsrisse hauptsächlich durch einen einzelnen physikalischen Aspekt, wie z.B. rein metallurgisch oder rein thermomechanisch bedingt, isoliert betrachtet. Die gewonnen Erkenntnisse über die Einflüsse des Bulgings auf die unterschiedlichen Teilaspekte zeigen deutlich, dass alle Entstehungsmechanismen auch die Schmelzbadgeometrie als Ursprung haben. Von dieser hängen die transienten Temperatur- und Spannungsfelder, die Kristallwachsrichtung, die Erstarrungsgeschwindigkeit und die Konzentration von Verunreinigungen, welche zur Entstehung von niedrigschmelzenden Phasen führt, ab. Die Ergebnisse des Forschungsvorhabens sind vielfach in referierten Zeitschriften und auf Fachtagungen veröffentlicht worden. Hervorzuheben dabei ist der „Best Presentation Award“ auf der LANE Conference 2018 in Fürth, wodurch die Thematik einem breiten Publikum bekannt gemacht werden konnte. KW - Laserstrahlschweißen KW - Mittelrippendefekt KW - Simulation PY - 2019 SP - 1 EP - 14 AN - OPUS4-49516 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Uhlmann, E. A1 - Düchting, J. A1 - Petrat, T. A1 - Graf, B. A1 - Rethmeier, Michael T1 - Heat treatment of SLM-LMD hybrid components N2 - Additive manufacturing is no longer just used for the production of prototypes but already found its way into the industrial production. However, the fabrication of massive metallic parts with high geometrical complexity is still too time-consuming to be economically viable. The combination of the powder bed-based selective laser melting process (SLM), known for its geometrical freedom and accuracy, and the nozzle-based laser metal deposition process (LMD), known for its high build-up rates, has great potential to reduce the process duration. For the industrial application of the SLM-LMD hybrid process chain it is necessary to investigate the interaction of the processes and its effect on the material properties to guarantee part quality and prevent component failure. Therefore, hybrid components are manufactured and examined before and after the heat treatment regarding the microstructure and the hardness in the SLM-LMD transition zone. The experiments are conducted using the nickel-based alloy Inconel 718. T2 - LiM 2019 CY - München, Germany DA - 23.06.2019 KW - Additive Manufacturing KW - Selective Laser Melting KW - Hybrid components KW - Inconel 718 KW - Laser Metal Deposition PY - 2019 SP - 1 EP - 9 AN - OPUS4-48410 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Meng, Xiangmeng A1 - Bachmann, Marcel A1 - Artinov, Antoni A1 - Rethmeier, Michael T1 - Experimental and numerical assessment of weld pool behavior and final microstructure in wire feed laser beam welding with electromagnetic stirring N2 - Advantages such as element homogenization and grain refinement can be realized by introducing electromagnetic stirring into laser beam welding. However, the involved weld pool behavior and its direct role on determining the final microstructure have not been revealed quantitatively. In this paper, a 3D transient heat transfer and fluid flow model coupled with element transport and magnetic induction is developed for wire feed laser beam welding with electromagnetic stirring. The magnetohydrodynamics, temperature profile, velocity field, keyhole evolution and element distribution are calculated and analyzed. The model is well tested against the experimental results. It is suggested that a significant electromagnetic stirring can be produced in the weld pool by the induced Lorentz force under suitable electromagnetic parameters, and it shows important influences on the thermal fluid flow and the solidification parameter. The forward and downward flow along the longitudinal plane of the weld pool is enhanced, which can bring the additional filler wire material to the root of the weld pool. The integrated thermal and mechanical impacts of electromagnetic stirring on grain refinement which is confirmed experimentally by electron backscatter diffraction analysis are decoupled using the calculated solidification parameters and a criterion of dendrite fragmentation. KW - Magnetohydrodynamics KW - Weld pool behavior KW - Grain structure KW - Laser beam welding KW - Numerical simulation PY - 2019 DO - https://doi.org/10.1016/j.jmapro.2019.07.021 SN - 1526-6125 VL - 45 SP - 408 EP - 418 PB - Elsevier AN - OPUS4-48611 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Artinov, Antoni A1 - Karkhin, V. A1 - Khomich, P. A1 - Bachmann, Marcel A1 - Rethmeier, Michael T1 - Assessment of thermal cycles by combining thermo-fluid dynamics and heat conduction in keyhole mode welding processes N2 - A numerical framework for simulation of the steady-state thermal behaviour in keyhole mode welding has been developed. It is based on the equivalent heat source concept and consists of two parts: computational thermo-fluid dynamics and heat conduction. The solution of the thermo-fluid dynamics problem by the finite element method for a bounded domain results in a weld pool interface geometry being the input data for a subsequent heat conduction problem solved for a workpiece by a proposed boundary element method. The main physical phenomena, such as keyhole shape, thermo-capillary and natural convection and temperature-dependent material properties are taken into consideration. The developed technique is applied to complete-penetration keyhole laser beam welding of a 15 mm thick low-alloyed steel plate at a welding speed of 33 mm/s and a laser power of 18 kW. The fluid flow of the molten metal has a strong influence on the weld pool geometry. The thermo-capillary convection is responsible for an increase of the weld pool size near the plate surfaces and a bulge formation near the plate middle plane. The numerical and experimental molten pools, cross-sectional weld dimensions and thermal cycles of the heat affected zone are in close agreement. KW - Welding process simulation KW - Thermo-fluid dynamics KW - Heat conduction KW - High power laser beam welding KW - Finite element method KW - Boundary element method PY - 2019 DO - https://doi.org/10.1016/j.ijthermalsci.2019.105981 SN - 1290-0729 VL - 145 SP - 105981, 1 EP - 10 PB - Elsevier Ltd. CY - Amsterdam [u.a.] AN - OPUS4-48652 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Jokisch, T. A1 - Marko, A. A1 - Gook, S. A1 - Üstündag, Ö. A1 - Gumenyuk, Andrey A1 - Rethmeier, Michael T1 - Laser Welding of SLM-Manufactured Tubes Made of IN625 and IN718 N2 - The advantage of selective laser melting (SLM) is its high accuracy and geometrical flexibility. Because the maximum size of the components is limited by the process chamber, possibilities must be found to combine several parts manufactured by SLM. An application where this is necessary, is, for example, the components of gas turbines, such as burners or oil return pipes, and inserts, which can be joined by circumferential welds. However, only a few investigations to date have been carried out for the welding of components produced by SLM. The object of this paper is, therefore, to investigate the feasibility of laser beam welding for joining SLM tube connections made of nickel-based alloys. For this purpose, SLM-manufactured Inconel 625 and Inconel 718 tubes were welded with a Yb:YAG disk laser and subsequently examined for residual stresses and defects. The results showed that the welds had no significant influence on the residual stresses. A good weld quality could be achieved in the seam circumference. However, pores and pore nests were found in the final overlap area, which meant that no continuous good welding quality could be accomplished. Pore formation was presumably caused by capillary instabilities when the laser power was ramped out. KW - Inconel 718 KW - Laser welding KW - Selective Laser Melting KW - Laser Powder Bed Fusion PY - 2019 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-489679 DO - https://doi.org/10.3390/ma12182967 SN - 1996-1944 VL - 12 IS - 18 SP - 2967, 1 EP - 15 PB - Multidisciplinary Digital Publishing Institute CY - Basel AN - OPUS4-48967 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -