TY - CONF A1 - Meng, Xiangmeng A1 - Putra, Stephen Nugraha A1 - Bachmann, Marcel A1 - Rethmier, Michael T1 - The influence of the spatial laser energy absorption on the molten pool dynamics in high power laser beam welding N2 - The spatial laser energy absorption inside the keyhole is decisive for the dynamic molten pool behaviors and the resultant weld properties in high-power laser beam welding (LBW). In this paper, a numerical simulation of the LBW process, considering the 3D transient heat transfer, fluid flow, and keyhole dynamics, is implemented, in which the free surface is tracked by the volume-of-fluid algorithm. The underlying laser-material interactions i.e., the multiple reflections and Fresnel absorption, are considered by an advanced ray-tracing method based on a localized Level-Set strategy and a temperature-dependent absorption coefficient. The laser energy absorption is analyzed from a time-averaged point of view for a better statistical representation. It is found for the first time that a noticeable drop of the time-averaged laser energy absorption occurs at the focus position of the laser beam, and the rest region of the keyhole has relatively homogenous absorbed energy. This unique absorption pattern may lead to a certain keyhole instability and have a strong correlation with the detrimental bulging and narrowing phenomena in the molten pool. The influence of the different focus positions of the laser beam on the keyhole dynamics and molten pool profile is also analyzed and compared. The obtained numerical results are compared with experimental measurements to assure the validity of the proposed model. T2 - International Congress of Applications of Lasers & Electro-Optics 2023 CY - Chicago, Illinois, USA DA - 16.10.2023 KW - Laser beam welding KW - Laser energy absorption KW - Molten pool KW - Keyhole dynamics KW - Numerical modeling PY - 2023 AN - OPUS4-58755 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Bachmann, Marcel A1 - Artinov, Antoni A1 - Meng, Xiangmeng A1 - Putra, Stephen Nugraha A1 - Rethmeier, Michael T1 - Challenges in dynamic heat source modeling in high-power laser beam welding N2 - The amount of absorbed energy in the keyhole as well as its spatial and temporal distribution is essential to model the laser beam welding process. The recoil pressure, which develops because of the evaporation process induced by the absorbed laser energy at the keyhole wall, is a key determining factor for the macroscopic flow of the molten metal in the weld pool during high-power laser beam welding. Consequently, a realistic implementation of the effect of laser radiation on the weld metal is crucial to obtain reliable and accurate simulation results. In this paper, we discuss manyfold different improvements on the laser-material interaction, namely, the ray tracing method, in the numerical simulation of the laser beam welding process. The first improvement relates to locating the exact reflection points in the ray tracing method using a so-called cosine condition in the determination algorithm for the intersection of reflected rays and the keyhole surface. A second correction refers to the numerical treatment of the Gaussian distribution of the laser beam, whose beam width is defined by a decay of the laser intensity by a factor of 1/e2, thus ignoring around 14% of the total laser beam energy. In the third step, the changes in the laser radiation distribution in the vertical direction were adapted by using different approximations for the converging and the diverging regions of the laser beam, thus mimicking the beam caustic. Finally, a virtual mesh refinement was adopted in the ray tracing routine. The obtained numerical results were validated with experimental measurements. T2 - International Congress of Applications of Lasers & Electro-Optics 2023 CY - Chicago, Illinois, USA DA - 16.10.2023 KW - Laser beam welding KW - Laser energy distribution KW - Ray tracing KW - Numerical modeling PY - 2023 AN - OPUS4-58759 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Putra, Stephen Nugraha A1 - Meng, Xiangmeng A1 - Yang, Fan A1 - Bachmann, Marcel A1 - Rethmeier, Michael T1 - Einfluss der Temperaturabhängigen Modellierung der Laserstrahlabsorption auf die Schmelzbadgeometrie beim Hochleistungslaserstrahlschweißen N2 - Der Absorptionsgrad metallischer Werkstoffe spielt bei Fügeprozessen mit einer Strahlungsquelle wie dem Hochleistungslaserstrahltiefschweißen eine bedeutende Rolle. Dieser beeinflusst die Menge der absorbierten Laserenergie, welche zum Aufschmelzen sowie zur lokalen Verdampfung des zu verbindenden Materials führt. Eine der wichtigsten Eigenschaften der Laserstrahlabsorption ist die Temperaturabhängigkeit. Dennoch wird sie in vielen Simulationsarbeiten häufig ignoriert und stattdessen ein angepasster Parameter zur Kalibrierung der Ergebnisse implementiert. Diese Vorgehensweise wirkt sich negativ auf die Zuverlässigkeit sowie die Genauigkeit des numerischen Modells sowie auf die Vorhersagbarkeit der Simulationsergebnisse aus. In der vorliegenden Arbeit wird die Temperaturabhängigkeit der Laserabsorption in ein selbstkonsistentes zweiphasiges Modell unter Berücksichtigung der gekoppelten 3D-Fluidströmung und Wärmeübertragung einbezogen. Die berechnete Laserstrahlabsorption wird durch die temperaturabhängigen Materialeigenschaften, die Lasercharakteristik und den Einfallswinkel des Laserstrahls bestimmt. Die freie Oberfläche jeder Phase wird mithilfe der volume-of-fluid Methode, kurz VOF, berechnet und die Laser-Material-Wechselwirkung wird durch ein neulich implementiertes Ray-Tracing-Verfahren modelliert, die auf einem lokalisierten Level-Set-Algorithmus basiert. Anschließend wird die transiente Wärmeeinbringung und die Geometrie der Schweißnaht analysiert und mit dem temperaturunabhängigen Absorptionsmodell verglichen. Es wurde festgestellt, dass die Temperaturabhängigkeit der Laserabsorption entscheidend für die genaue Bestimmung der Wärmeeinbringung und der Schmelzbadgeometrie ist. Das entwickelte Modell wurde anhand der experimentellen Untersuchungen validiert und die Bedeutung der Temperaturabhängigkeit bei der Laserstrahlabsorption wurde für die Simulation des Laserstrahltiefschweißens aufgeklärt. T2 - 44. Assistentenseminar CY - Päwesin, Germany DA - 20.09.2023 KW - Laser beam welding KW - Temperature dependent absorption KW - Weld pool dynamics KW - Numerical modeling PY - 2023 AN - OPUS4-58810 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Rethmeier, Michael A1 - Artinov, Antoni A1 - Meng, Xiangmeng A1 - Bakir, Nasim A1 - Üstündag, Ömer A1 - Bachmann, Marcel A1 - Gumenyuk, Andrey T1 - The bulging effect and its relevance in high power laser beam welding N2 - The present work deals with the recently confirmed widening of the weld pool interface, known as a bulging effect, and its relevance in high power laser beam welding. A combined experimental and numerical approach is utilized to study the influence of the bulge on the hot cracking formation and the transport of alloying elements in the molten pool. A technique using a quartz glass, a direct-diode laser illumination, a high-speed camera, and two thermal imaging cameras is applied to visualize the weld pool geometry in the longitudinal section. The study examines the relevance of the bulging effect on both, partial and complete penetration, as well as for different sheet thicknesses ranging from 8 mm to 25 mm. The numerical analysis shows that the formation of a bulge region is highly dependent on the penetration depth and occurs above 10 mm penetration depth. The location of the bulge correlates strongly with the cracking location. The obtained experimental and numerical results reveal that the bulging effect increases the hot cracking susceptibility and limits the transfer of alloying elements from the top of the weld pool to the weld root. T2 - 1st Annual Assembly and Conference of The Welding Federation of Africa (TWF-Africa) CY - Cairo, Egypt DA - 14.03.2023 KW - Laser beam welding KW - Melt pool dinamics PY - 2023 AN - OPUS4-58695 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Yang, Chunliang A1 - Yang, Fan A1 - Meng, Xiangmeng A1 - Bachmann, Marcel A1 - Putra, Stephen Nugraha A1 - Rethmeier, Michael T1 - Experimental and numerical study on grain refinement in electromagnetic assisted laser beam welding of 5754 al alloy N2 - Through experimental observation and auxiliary numerical simulation, this investigation studies the different types of grain refinement of 5754 aluminum alloy laser beam welding by applying a transverse oscillating magnetic field. Scanning electron microscope results have proved that the application of a magnetic field can reduce the average crystal branch width and increase its number. The interaction between the induced eddy current generated by the Seebeck effect and the applied external magnetic field produces a Lorentz force, which is important for the increase in the number of crystal branches. Based on the theory of dendrite fragmentation and the magnetic field-induced branches increment, the grain size reduction caused by the magnetic field is studied. Furthermore, the effects of the magnetic field are ana lyzed by combining a phase field method model and simulations of nucleation and grain growth. The grain distribution and average grain size after welding verify the reliability of the model. In addition, the introduction of a magnetic field can increase the number of periodic three-dimensional solidification patterns. In the intersection of two periods of solidification patterns, the metal can be re-melted and then re-solidified, which prevents the grains, that have been solidified and formed previously, from further growth and generates some small cel lular grains in the new fusion line. The magnetic field increases the building frequency of these solidification structures and thus promotes this kind of grain refinement. T2 - ICALEO 2023 CY - Chicago, IL, USA DA - 16.10.2023 KW - Laser beam welding KW - Magnetic field KW - Crystal branch development KW - Grain refinement KW - Periodic solidification pattern PY - 2023 AN - OPUS4-58493 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Simón Muzás, Juan A1 - Brunner-Schwer, C. A1 - Hilgenberg, Kai A1 - Rethmeier, Michael T1 - Weldability of PBF-LB/M Inconel 718 lattice structures by laser beam N2 - The present research focuses on the weldability of PBF-LB/M lattice structure parts of Inconel 718 by means of laser beam welding. The integration of complex and lightweight AM structures into assemblies employing conventional joining methods is challenging. During the welding process, dissipation of the laser heat input through thin-walled structures of these lightweight structures is strongly limited, resulting in heat accumulation, atypical cooling rates, and affecting weld geometry, quality of the joint and microstructure. PBF-LB/M parts have been manufactured in three characteristic build directions. They were all stress relieved, then a group of them were submitted to an additional solution annealing and the second group to a two-step aging treatment. Afterwards, these parts were welded to identical PBF-LB/M parts and to wrought ones in butt position. To gain insight into the welding temperature field and to explain segregation mechanisms, grain growth and asymmetries, thermocouples have been attached on the surface’s regions and struts nearby. Joining a lattice structure with a full material wrought sample results in clear asymmetric welds due to dissimilar heat dissipation on both sides of the seam. Selected pre-weld heat treatments have a crucial influence on the quality of the seam on the AM part. T2 - International Institute of Welding IIW 2023 Conference CY - Singapore DA - 16.07.2023 KW - Additive manufacturing (AM) KW - Laser-based powder bed fusion of metal (PBF-LB/M) KW - Laser beam welding KW - Lattice structure KW - Hybrid part KW - Heat treatment KW - Inconel 718 PY - 2023 AN - OPUS4-58017 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Heßmann, Jennifer A1 - Hilgenberg, Kai T1 - New approach for multi material design: combination of laser beam and electromagnetic melt pool displacement by induced lorentz forces N2 - Multi-material structures are a promising solution to reduce vehicle weight and save fuel or electric energy in automotive design. However, thermal joining of steel and aluminum alloys is a challenge to overcome due to different material properties and the formation of brittle intermetallic phases. In this study, a new joining approach for producing overlap line-shaped joints is presented. The lower joining partner (EN AW 5754) is melted by a laser beam and this melt is displaced into a line-shaped cavity of the upper joining partner (1.0330) by induced Lorentz forces. The melt solidifies in the cavity to a material and form-fitting joint. This approach needs no auxiliary joining elements or filler materials. Previous investigation to produce spot-shaped joints by using this approach showed that quality and reproducibility were limited by known melt pool dynamics of aluminum alloys (keyhole collapses). For line-shaped joints, the melt displacement can take place behind the keyhole. This allows the displacement process to be spatial uncoupled from the influence of the keyhole collapses. The study shows that this improved the process stability and the quality of the joint. The created line-shaped joints were microstructurally characterized by transversal sections. Intermetallic phases were identified by electron backscatter diffraction (EBSD) and EDX-Analysis. The detected intermetallic phases consist of a 5 µm - 6 µm compact phase seam of Al5.6Fe2 and a needle shaped phase of Al13Fe4. Tensile shear tests were carried out to quantify the load capacity. It was possible to create a joint with a load capacity of about 2 kN. T2 - ICALEO Orlando 2022 CY - Orlando, Florida, USA DA - 17.10.2022 KW - Electromagnetic forces KW - Joining dissimilar materials KW - Laser beam welding KW - Steel and aluminium PY - 2022 AN - OPUS4-56149 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Meng, Xiangmeng A1 - Putra, Stephen Nugraha A1 - Bachmann, Marcel A1 - Artinov, Antoni A1 - Rethmeier, Michael T1 - The influence of the free surface reconstruction on the spatial laser energy distribution in high power laser beam welding modeling N2 - An accurate and efficient description of the spatial distribution of laser energy is a crucial factor for the modeling of laser material processing, e.g., laser welding, laser cutting, or laser-based additive manufacturing. In this study, a 3D heat transfer and fluid flow model coupled with the volume-of-fluid algorithm for free surface tracking is developed for the simulation of molten pool dynamics in high-power laser beam welding. The underlying laser-material interactions, i.e., the multiple reflections and Fresnel absorption, are considered by a ray-tracing method. Two strategies of free surface reconstruction used in the ray-tracing method are investigated: a typical piecewise linear interface calculation (PLIC)-based method and a novel localized Level-Set method. The PLIC-based method is discrete, resulting in non-continuous free surface reconstruction. In the localized Level-Set method, a continuous free surface is reconstructed, and thus the exact reflection points can be determined. The calculated spatial laser energy distribution and the corresponding molten pool dynamics from the two methods are analyzed and compared. The obtained numerical results are evaluated with experimental measurements to assure the validity of the proposed model. It is found that distinct patterns of the beam multiple reflections are obtained with the different free surface reconstructions, which shows significant influence not only on the molten pool behaviors but also on the localized keyhole dynamics. T2 - The 41st annual International Congress on Applications of Lasers & Electro-Optics CY - Orlando, FL, USA DA - 17.10.2022 KW - Laser beam welding KW - Laser energy distribution KW - Weld pool dynamics KW - Ray-tracing PY - 2022 AN - OPUS4-56312 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Bakir, Nasim A1 - Üstündag, Ömer A1 - Gumenyuk, Andrey A1 - Rethmeier, Michael T1 - Influence of the weld pool geometry on solidification cracking in partial penetration high power laser beam welding N2 - 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. T2 - LANE 2022: 12th CIRP Conference on Photonic Technologies CY - Fürth, Germany DA - 04.09.2022 KW - Laser beam welding KW - Weld pool shape KW - Solidification craking PY - 2022 AN - OPUS4-56395 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Bachmann, Marcel A1 - Meng, Xiangmeng A1 - Artinov, Antoni A1 - Rethmeier, Michael T1 - Evaluation of narrowed weld pool shapes and their effect on resulting potential defects during deep penetration laser beam welding N2 - This study presents mechanisms of the evolution of a narrowed region in the weld pool center during deep penetration laser beam welding. In numerous numerical studies presented in this study, it was also found that the local reduction of the weld pool size can cause detrimental effects on the melt flow behavior and the resulting properties of the welds. A particularly large influence of this effect was identified in three aspects. First, the local variation of the solidification sequence of the weld pool causes an increase in the hotcracking susceptibility due to a locally delayed solidification. Second, it was proven that a change in the local length and width of the weld pool is associated with an adverse impact on the potential flow routes of the molten material that induces stronger local variations of its solidification. Thus, the element mixing, e.g., during the welding with filler materials, is blocked. This leads to a nonhomogeneous chemical composition of the final weld and can cause undesired effects on the final material properties. Finally, another observed effect is related to the reduced ability of process pores to reach the top surface. As this type of porosity is usually produced around the keyhole tip, the change of the fluid flow regime above this area plays a significant role in determining the final path of the pores until the premature solidification in the middle of the weld pool captures them. This study summarizes mainly numerical results that were supported by selected experimental validation results. T2 - International Congress of Applications of Lasers & Electro-Optics 2022 CY - Orlando, FL, USA DA - 17.10.2022 KW - Weld pool shape KW - Laser beam welding KW - Solidification KW - Porosity KW - Element distribution KW - Numerical process simulation PY - 2022 AN - OPUS4-56335 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -