TY - CONF A1 - Heßmann, Jennifer T1 - Joining dissimilar materials a new approach based on laser beam welding and melt displacement by electromagnetic forces N2 - In order to reduce weight of vehicles, the interest in multi-material-design has been growing within the last few years. For vehicles the combination of steel and aluminium alloys offers the most promising compromise between weight, strength and formability. Thermal joining of these dissimilar materials is still a challenge to overcome. A possible approach is a new joining technology, whereby a combination of laser beam welding and contactless induced electromagnetic forces are used to displace the generated melt of one joining partner into a notch of the other. This paper presents the working principle and shows numerical analyses to improve the understanding of this joining process. The simulations help to calculate the thermal development of the joining partners, which is important for the formation of intermetallic phases. Furthermore, the calculation of the time required for a complete displacement is possible. The numerical results are validated by experimental results. T2 - LiM 2021 CY - Online meeting DA - 21.06.2021 KW - Joining dissimilar materials KW - Laser beam welding KW - Electromagnetic forces KW - Steel and aluminium PY - 2021 AN - OPUS4-52977 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Heßmann, Jennifer T1 - Meeting the challenge of thermal joining of steel and aluminum using a new approach based on melt displacement by electromagnetic forces N2 - Environmental protection, resource conservation and CO2 reduction require new joining concepts for effective multi-material design in automotive lightweight construction. The thermal joining of dissimilar materials, especially the combination of aluminum alloys and steel, is associated with difficulties. Different material properties, such as melting point and coefficient of thermal expansion, complicate joining processes. Furthermore, the insolubility between these materials results in the formation of intermetallic phases. These brittle phases reduce the load-bearing capacity and quality of the joints. The thickness of the intermetallic phases should not reach the critical value of 10 μm to ensure good mechanical properties of the joint. It is known that a two-phase reaction layer consisting of Al5Fe2 and Al3Fe (also known as Al13Fe4) forms at the interface between solid steel and liquid aluminum. Due to high cooling rates, as it is the case in laser beam welding, metastable intermetallic compounds can form different from the equilibrium state. The formation of the intermetallic reaction layer is a diffusion-controlled process. So, it is only possible to control the growth of these phases. This problem has led to use joining methods that do not require the melting of both joining partners. A promising joining method is laser beam welding-brazing, whereby only one joining partner is melted and wets the solid joining partner. Conventional laser beam welding-brazing only results in material-fit joints and often requires the use of expensive filler materials. An additional form-fit could optimize the mechanical performance of the joint. For this reason, a new joining method for overlap configurations of dissimilar materials was developed. A laser beam melts the lower joining partner through a cavity of the upper joining partner. The created melt pool is moved upwards into the cavity of the upper joining partner due to contactless induced Lorentz forces of an AC-magnetic system. The displaced melt creates a form- and material-fit joint after solidification. The advantage of this joining technology is the absence of filler materials, flux agents and expensive auxiliary joining elements. T2 - 5th International Conference Hybrid 2022 - Materials and Structures CY - Leoben, Austria DA - 20.07.2022 KW - Joining dissimilar materials KW - Laser beam welding KW - Electromagnetic forces KW - Steel and aluminium PY - 2022 AN - OPUS4-55534 LA - eng 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 - 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 - Heßmann, Jennifer 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 - Bakir, Nasim 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 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 - TY - CONF A1 - Bachmann, Marcel 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 - Bachmann, Marcel T1 - A parametric study of the laser energy absorption in high power laser beam welding N2 - Laser energy absorption on the keyhole wall is decisive for the thermodynamic behavior and the resultant weld properties in the high-power laser beam welding process. However, its highly transient nature on a microsecond scale makes the quantitative analysis challenging. In this paper, the influence of the relevant welding parameters on laser energy absorption is studied statistically by utilizing multiphysical modeling, in which the three-dimensional transient keyhole dynamics and thermo-fluid flow are calculated. A dynamic mesh adaption technique and a localized level-set-based ray-tracing method are employed to improve the model accuracy further. The results show that the focus position has a remarkable effect on the time-averaged laser absorption, and in contrast, the laser energy distribution regime is only slightly influenced by the welding speed in the studied parameter range (1.5–3.0 m/min). The absorption ratio of the laser energy on the keyhole front wall decreases with increasing welding speed and increases with upward-moving focus positions. The comparison between the calculated results and the experimental measurements ensures the validity of the proposed model. T2 - International Congress of Applications of Lasers & Electro-Optics 2024 CY - Los Angeles, CA, USA DA - 03.11.2024 KW - Laser beam welding KW - Laser energy absorption KW - Weld pool KW - Parametric study KW - Multiphysics modeling PY - 2024 AN - OPUS4-61619 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 - Marquardt, Raphael T1 - Influence of laser power on the melt pool shape of handheld laser beam welding of 1.5 mm thick micro alloyed steel N2 - Manual welding of structures requires highly skilled welders due to the large heat-affected zone of arc-based processes, that can negatively impact microstructure and cause distortion. Handheld laser beam welding is a promising alternative with high welding velocity and a concentrated heat input. However, its current use in industry is limited to parts with aesthetic requirements, often made of high-alloyed steel. To extend the use of handheld laser beam welding to low-cost steels with good mechanical properties, this study investigates the influence of laser power on the melt pool shape for micro-alloyed steel with a thickness of 1.5 mm. Tested joint geometries are T-joints welded with filler wire as well as butt joints and overlap joints without filler wire, which are typically found in assemblies under mechanical load. Weld quality is assessed by weld porosity analysis. The results show that the handheld laser beam welding with filler wire produces T-joints with a very good external appearance, but with porosity between level C and D in the cross sections according to DIN EN ISO 13919-1. By increasing the laser power, a deep penetration of the T-joint zone can be achieved without increasing the actual throat thickness. For handheld laser beam welding of butt joints a full penetration weld of the highest quality class can be reached. Overlap joints can be welded with full or partial penetration depending on the laser power selected, with quality classes between B and C in terms of porosity. T2 - 20th Nordic Laser Materials Processing Conference CY - Kongens Lyngby, Denmark DA - 26.08.2025 KW - Hand held laser welding KW - Laser beam welding KW - Low alloyed steel KW - Process parameter PY - 2025 AN - OPUS4-64169 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Artinov, Antoni T1 - On the relationship between the bulge effect and the hot cracking formation during deep penetration laser beam welding N2 - Recent studies have confirmed the widening of the weld pool interface, known as a bulge effect, during deep penetration high power laser beam welding. The link between such geometric particularities of the weld pool shape and the hot cracking phenomena is significant. The present work seeks to extend the level of understanding by investigating their relationship. A coupled multiphysics, multiscale numerical framework is developed, comprising a series of subsequent analyses. The study examines the influences of the bulge on the three most dominant effects causing hot cracking, namely the thermal cycles, the mechanical loading, and the local microstructure. The bulge in the weld pool shape forms approximately in the middle of the plate, thus correlating with the location of hot cracking. It increases the hot cracking susceptibility by enhancing the three dominant effects. The numerical results are backed up by experimental data. T2 - 11th CIRP Conference on Photonic Technologies [LANE 2020] CY - Online meeting DA - 07.09.2020 KW - Hot cracking KW - Bulge effect KW - Numerical modelling KW - Laser beam welding KW - Deep penetration PY - 2020 AN - OPUS4-51277 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Straße, Anne T1 - LMD coatings as filler material for laser beam welded 30 mm thick plates N2 - The development of high energy laser sources enables single-pass welds of thick plates up to 30 mm, but often additional materials are needed to influence the properties of the weld seams. However, the homogenous distribution of filler materials in form of e.g. electrodes is only possible up to 7 mm while the elements are only traceable up to a depth of 14 mm. To overcome this problem a two-step process is used where first the edges of the weld partners are coated with the filler material by laser metal deposition (LMD) and afterwards are welded by laser beam. Single-pass welds with electromagnetic weld pool support of 30 mm thick S355 J2+N-plates with austenitic AISI 316L-coatings were investigated as well as the influence of the coatings to the penetration depth of the laser beam without electromagnetic weld pool support in double-sided joints. The weld seams were tested by X-ray inspection and cross sections. T2 - 11th CIRP Conference on Photonic Technologies [LANE 2020] CY - Online meeting DA - 07.09.2020 KW - Penetration depth KW - Laser metal deposition (LMD) KW - Laser beam welding KW - Filler material distribution PY - 2020 AN - OPUS4-51276 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Gumenyuk, Andrey T1 - New developments in high power laser and hybrid welding of thick plates for application in modern ship building N2 - High power laser beam welding has been already introduced in ship building industry since last two decades and is characterized by higher performance as conventional arc welding technologies through its higher welding speed, penetration depth and therefore higher productivity. Moreover, high quality weld joints are achievable thanks to a stronger automatization degree and better repeatability of the process. A further advantage of the laser beam welding is a manufacturing of parts with very low distortion according to much lower heat input, so that rework amount can be reduced significantly. Nevertheless, there are still some unresolved problems limiting the range of application of the technology in part manufacturing within ship building industry, restricted by development and application of new materials or new design of ship vessels. The present contribution deals with some novel aspects of laser beam welding technology allowing to widen this range significantly. One of the possibilities is to increase the weld seam thickness for single pass laser or laser-hybrid welding is to apply contactless EM-support system based on generation of the Lorentz force counteracting the liquid metal drop out. Also, application of laser-hybrid welding technology for welding novel materials like cold resistant steel X8Ni9 used for construction of LNG tanks brings technological and design advantages comparing to conventional welding technologies by using of a similar alloyed filler wire instead of expensive Ni-based filler material. Finally, it is shown how the application of computational techniques can be used to helps to improve the quality of laser welded joints and avoid the critical weld failure by optimization of the welding process parameters. T2 - SHY Virtual Laserforum 2020 CY - Online meeting DA - 01.09.2020 KW - Ship building KW - Laser beam welding KW - Hybrid laser arc welding PY - 2020 UR - https://laserforum.mobieforum.fi/ AN - OPUS4-51221 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Bakir, Nasim T1 - In situ determination of the critical staining condition for solidification cracking during laser beam welding N2 - Using a novel optical measurement technique together with the OF algorithm, a two-dimensional deformation analysis during welding was conducted. The OF technique was the first of its kind to provide a measurement of the full strain field locally in the immediate vicinity of the solidification front. The local critical strain and strain rate in vicinity of the solidification front has observed 1.57%, 28 %/s, respectively. T2 - Lane 2020 CY - Online meeting DA - 07.09.2020 KW - Optical measurement technique KW - Laser beam welding KW - Solidification cracking PY - 2020 AN - OPUS4-51741 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Meng, Xiangmeng T1 - Numerical study of additional element transport in wire feed laser beam welding N2 - The distribution of the alloying elements from the filler wire in laser beam welding plays an important role on the property of the final weld. In this study, the transport phenomena in the wire feed laser beam welding are investigated numerically. A three-dimensional transient heat transfer and fluid flow model coupled with free surface tracing and element transport is developed. A ray-tracing method with local grid refinement algorithm is used to calculate the multiple reflections and Fresnel absorption on the keyhole wall. The filler material flows backward along the lateral side of the weld pool, and subsequently flows forward along the longitudinal plane to bring the additional alloying elements to the forepart of the weld pool. The occurrence of the bulging phenomenon may further prevent the downward transfer of the additional elements to the root of the weld pool. The numerical results show a good agreement with the experimental fusion line and element distribution. T2 - 11th CIRP Conference on Photonic Technologies [LANE 2020] CY - Online meeting DA - 07.09.2020 KW - Laser beam welding KW - Element transport KW - Filler material PY - 2020 AN - OPUS4-51568 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Bachmann, Marcel T1 - Numerical studies of keyhole dynamic behavior during the laser beam welding with an oscillating magnetic field N2 - The formation of keyhole induced porosity (Process porosity) during laser beam welding (LBW) is mainly associated with the dynamic keyhole behavior. Experimental studies have confirmed that the application of a magnetic field can effectively suppress process porosity. However, there is still no quantitative evidence supporting that this suppression mechanism involves a direct influence of the magnetic field on the keyhole dynamics. In this paper, a novel keyhole reconstruction algorithm is developed and incorporated into a three-dimensional transient multi-physics coupled numerical model to study the dynamic keyhole behavior under the influence of an oscillating magnetic field. This keyhole reconstruction algorithm accurately reproduces the 2D time-averaged keyhole shape, effectively capturing the keyhole tailing and the backward shift of its centroid on the keyhole top. The application of an oscillating magnetic field reduces the keyhole diameter and enhances its stability. The frequency of keyhole collapse is reduced under the influence of a magnetic field. Additionally, the occurrence of keyhole collapses with long duration is significantly reduced in the presence of a magnetic field. T2 - 78th IIW Annual Assembly and International Conference CY - Genua, Italy DA - 22.06.2025 KW - Laser beam welding KW - Magnetohydrodynamics KW - Porosity KW - Numerical simulation PY - 2025 AN - OPUS4-63645 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Rethmeier, Michael A1 - Gook, Sergej T1 - Notch impact toughness of laser beam welded thick sheets of cryogenic nickel alloyed steel X8Ni9 N2 - This research work deals with the investigations of the impact toughness of laser beam welded 14.5 mm thick sheets made of cryogenic steel X8Ni9 as a function of preheating. This 9% nickel alloyed steel is widely used in the liquefied natural gas (LNG) industry. An application of highly efficient welding processes such as high-power laser beam welding (LBW) in LNG sector requires an understanding of the interactions between the LBW process parameters and weld properties, in particular the impact toughness. The results show that the original fine-grained martensitic microstructure of the base metal (BM) is significantly changed by melting and crystallization during the LBW, what can lead to a decrease in the impact toughness of the weld metal (WM) below the required level. An optimal preheating temperature range leads to the favorable thermal welding cycle and is of remarkable importance for maintaining the notch impact toughness of laser beam welded joints of these thick steel sheets. A parameter window was identified in which V-notch impact toughness comparable to that of the BM at -196 °C was achieved. T2 - 11th CIRP Conference on Photonic Technologies LANE 2020 CY - Online meeting DA - 06.09.2020 KW - Cryogenic steel KW - Laser beam welding KW - Welding thermal cycle PY - 2020 AN - OPUS4-51750 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Rethmeier, Michael 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 - The 18th Nordic Laser Materials Processing Conference CY - Lulea, Sweden DA - 18.01.2022 KW - Laser beam welding KW - Melt pool dinamics PY - 2022 AN - OPUS4-54333 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Gumenyuk, Andrey T1 - Influence of an external applied AC magnetic field on the melt pool dynamics at high-power laser beam welding N2 - The study deals with the determination of the influence of an externally applied oscillating magnetic field on the melt pool dynamics in high power laser beam and hybrid laser arc welding processes. An AC magnet was positioned under the workpiece which is generating an upward directed electromagnetic force to counteract the formation of the droplets. To visualise the melt flow characteristics, several experiments were carried out using a special technique with mild steel from S355J2 with a wall thickness of up to 20 mm and a quartz glass in butt configuration. The profile of the keyhole and the melt flow were recorded with a high-speed camera from the glass side. Additionally, the influence of the magnetic field orientation to the welding direction on the filler material dilution on laser hybrid welding was studied with variating oscillation frequency. The element distribution over the whole seam thickness was measured with X-ray fluorescence (XRF). The oscillation frequency demonstrated a greater influence on the melt pool dynamics and the mixing of the elements of the filler wire. The high-speed recordings showed, under the influence of the magnetic field, that the melt is affected under strong vortex at the weld root, which also avoids the formation of droplets T2 - The 18th Nordic Laser Materials Processing Conference CY - Lulea, Sweden DA - 18.01.2022 KW - Laser beam welding KW - Melt pool dinamics PY - 2022 AN - OPUS4-54331 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Meng, Xiangmeng T1 - A numerical study on the suppression of a detrimental weld pool profile in wire feed laser beam welding by MHD technique N2 - The weld quality and the possible defect formation are directly determined by the weld pool shape and the thermo-fluid dynamics therein. In this paper, an untypical weld pool profile, i.e., elongated at its top and bottom but narrowed at the middle, is found experimentally and numerically in the wire feed laser beam welding. The detrimental influence of the weld pool narrowing on the element transport is analyzed and discussed. A magnetohydrodynamic technique is utilized to suppress the narrowing, aiming at a more homogenous element distribution. It is found that a low-temperature region is formed in the middle of the weld pool due to the interaction of the two dominant circulations from the top and bottom regions. The weld pool is significantly narrowed due to the untypical growth of the mushy zone in the low-temperature region, which results in a direct blocking effect on the downward flow and the premature solidification in the middle region. The Lorentz force produced by a transverse oscillating magnetic field shows the potential to change the flow pattern into a single-circulation type and the low-temperature-gradient region is mitigated. Therefore, the downward transfer channel is widened, and its premature solidification is prevented. The numerical results are well validated by experimental measurements of metal/glass observation and X-ray fluorescence element mapping. T2 - The 13th International Seminar "Numerical Analysis of Weldability" CY - Graz, Austria DA - 04.09.2022 KW - Thermo-fluid flow KW - Element transport KW - Laser beam welding KW - Magnetohydrodynamics KW - Multi-physical modeling PY - 2022 AN - OPUS4-55780 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Bachmann, Marcel T1 - Numerical analysis of the dependency of the weld pool shape on turbulence and thermodynamic activity of solutes in laser beam welding of unalloyed steels N2 - A three-dimensional numerical model was developed to accurately predict the steady-state weld pool shape in full penetration laser beam welding. The model accounts for the coupling between the heat transfer and the fluid dynamics by considering the effects of solid/liquid phase transition, thermo-capillary convection, natural convection, and phase-specific and temperature-dependent material properties up to the evaporation temperature. A fixed right circular cone was utilized as a keyhole geometry to consider the heat absorbed from the laser beam. The model was used to analyze the influence of the thermodynamic activity of solutes and turbulence on the weld pool shape. A mesh sensitivity analysis was performed on a hybrid mesh combining hexahedral and tetrahedral elements. For the case of full penetration laser beam welding of 8 mm thick unalloyed steel sheets, the dependence of the weld pool shape on the surface-active element sulfur was found to be negligible. The analysis of the results showed that a laminar formulation is sufficient for accurately predicting the weld pool shape since the turbulence has a minor impact on the flow dynamics in the weld pool. The validity of the numerical results was backed up by experimental measurements and observations, including weld pool length, local temperature history, and a range of metallographic cross-sections. T2 - 13th International Seminar Numerical Analysis of Weldability CY - Seggau, Austria DA - 04.09.2022 KW - Weld pool shape KW - Numerical modeling KW - Laser beam welding KW - Thermo-capillary convection KW - Turbulence PY - 2022 AN - OPUS4-55718 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Artinov, Antoni T1 - Numerical study on the formation of a bulging region in partial penetration laser beam welding N2 - A transient three-dimensional thermo-fluid dynamics numerical model was developed to study the formation of a bulging region in partial penetration laser beam welding. The model accounts for the coupling between the fluid flow, the heat transfer, and the keyhole dynamics by considering the effects of multiple reflections and Fresnel absorption of the laser beam in the keyhole, the phase transitions during melting and evaporating, the thermo-capillary convection, the natural convection, and the phase-specific and temperature-dependent material properties up to the evaporation temperature. The validity of the model was backed up by experimentally obtained data, including the drilling time, the weld pool length, the local temperature history outside the weld pool, the process efficiency, and a range of metallographic cross-sections. The model was applied for the cases of partial penetration laser beam welding of 8 mm and 12 mm thick unalloyed steel sheets. The obtained experimental and numerical results reveal that the bulging region forms transiently depending on the penetration depth of the weld, showing a tendency to transition from a slight bulging to a fully developed bulging region between penetration depths of 6 mm and 9 mm, respectively. T2 - The 13th International Seminar "Numerical Analysis of Weldability" CY - Graz - Castle Seggau, Austria DA - 04.09.2022 KW - Laser beam welding KW - Deep penetration KW - Bulge formation KW - Numerical modeling PY - 2022 AN - OPUS4-55719 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Meng, Xiangmeng 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 - Gumenyuk, Andrey T1 - Investigation of the gap bridgeability at high-power laser hybrid welding of plasma-cut thick mild steels with AC magnetic support N2 - One of the challenges of the high-power hybrid laser welding of thick steels is the sensitivity of the process of the process to manufacturing tolerances. This usually leads to a time-consuming preparation of the welding edges, such as milling. The study deals with the influence of the edge quality of milled and plasma-cut steel made of S355J2 with a wall thickness of 20 mm on the laser hybrid welded seam quality. Furthermore, the gap bridgeability and the tolerances towards edge misalignment was investigated. An AC magnet was used as backing support to prevent sagging and positioned under the workpiece, to generate an upwards directed electromagnetic pressure. The profiles of the edges and the gap on the top and root side were measured using a digital camera. Single-pass laser hybrid welds of plasma-cut edges could be welded using a laser beam power of just 13.7 kW. A gap bridgeability up to 2 mm and misalignment of edges up to 2 mm could be achieved successful. Additionally, the independence of the cutting side and the welding side was shown, so that samples were welded to the opposite side to their cutting. For evaluation of internal defects or irregularities, X-ray images were carried out. Charpy impact strength tests were performed to determine the toughness of the welds. T2 - X International Conference «Beam Technologies in Welding and Materials Processing» CY - Odessa, Ukraine DA - 7.09.2021 KW - Laser beam welding KW - Hybrid laser arc welding KW - Material transport PY - 2021 AN - OPUS4-53569 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Gumenyuk, Andrey T1 - Improvement of the mechanical properties and corrosion resistance of laser welds on thick duplex plates by laser cladded buttering N2 - Because of its excellent corrosion resistance, high tensile strength and high ductility, duplex stainless steel 2205 offers many areas of application. Though laser beam welding accompanied by high cooling rates, duplex steels tend to perform higher ferrite contents in weld metal as the base metal, which leads to a reduction of ductility and corrosion resistance of the weld joint. To overcome this problem, a solution, based on buttering the plate edges by laser metal deposition (LMD) with material containing higher Ni concentrations prior to laser welding was suggested. In this context different process parameters for LMD and different mixtures of duplex and nickel powder, were investigated. In a second step the possibility of welding those edges defect free while achieving balanced austenite-ferrite ratio was verified with metallographic analysis, Electron Backscatter Diffraction (EBSD) and impact testing according to Charpy. The improved corrosion resistance was observed with ASTM G48 standard test method. T2 - X International Conference «Beam Technologies in Welding and Materials Processing» CY - Odessa, Ukraine DA - 7.09.2021 KW - Laser beam welding KW - Laser metal deposition KW - Duplex steels PY - 2021 AN - OPUS4-53568 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Putra, Stephen Nugraha 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 - Putra, Stephen Nugraha T1 - Der Einfluss verschiedener räumlicher Diskretisierungsansätze des Ray-Tracing-Verfahrens bei der Simulation des Laserstrahltiefschweißen N2 - Die Wärmeverteilung des Lasers beim Laserstrahltiefschweißen ist für die Formgebung der Dampfkapillare und für die Schweißbaddynamik entscheidend. In dieser Arbeit werden die Laserwärmeverteilung und deren Einflüsse auf die Schweißbadtiefe sowie -breite numerisch anhand des Ray-Tracing-Verfahrens analysiert. Hierbei wird der La-serstrahl in mehreren Strahlenbündeln bzw. Subrays unterteilt. Diesbezüglich soll der Pfad der Subrays präzis berechnet werden, um die Dynamik der Dampfkapillare und des Schweißbades eines realen Schweißprozesses richtig abzubilden. Zu diesem Zweck beschäftigt sich die vorliegende Arbeit mit der Genauigkeitsverbesserung der Kontaktposition und der Reflexionsrichtung der Subrays auf der freien Oberfläche anhand der Level-Set-Methode. Um die Güte dieses Simulationsansatzes zu gewährleisten, wurde eine Gegenüberstellung mit den zwei klassi-schen Ray-Tracing-Verfahren mittels drei verschiedenen Benchmark-Testreihen durchgeführt. Anschließend wur-den die Versuchsergebnisse zur Validierung der implementierten numerischen Ansätze verwendet. Im Rahmen dieser Arbeit kann es gezeigt werden, dass unterschiedliche Wärmeverteilung aufgrund der verschiedenen Ray-Tracing-Verfahren deutlich zu erkennen ist, welche wiederum die Schweißbaddynamik sowie die lokalisierte Dampfkapillardynamik stark beeinflussen. Ferner wurde es bestätigt, dass die implementierte Level-Set-Methode zu einer genaueren Ermittlung der Kontaktposition und der Reflexionsrichtung der Subrays und somit zu einer Ver-besserung der simulierten Schmelzkontur führt. T2 - 43. Assistentenseminar CY - Schwarzenberg, Germany DA - 27.09.2022 KW - Laser beam welding KW - Ray tracing method KW - Weld pool dynamics KW - Numerical modeling PY - 2022 AN - OPUS4-58840 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Simón Muzás, Juan 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 - Gumenyuk, Andrey T1 - Determination of critical local straining conditions for solidification cracking at laser beam welding by experimental and numerical methods N2 - The phenomenon of solidification cracking has been the subject of numerous research projects over the years. Great efforts have been made to understand the fundamentals of hot cracking. It is generally agreed that solidification cracks form in the solidification range between the liquidus and solidus temperatures under the combination of thermal, metallurgical and mechanical factors. There is still a need to determine the time-resolved strain distribution in the cracksensitive region in order to analyse the local critical conditions for solidification cracking phenomena. This was a strong motivation for the development of a measurement system used in this study to estimate the local strains and strain rates in the zone where the solidification crack is expected to occur. The laser beam welding experiments were conducted using the Controlled-Tensile-Weldability test (CTW test) to apply an external strain condition during welding to generate solidification cracks. The CTW test is a test method for investigating the suscep�tibility of laser-welded joints to solidification cracking, in which the sample can be subjected to a defined strain at a defined strain rate during welding. In combination with experimental investigations, numerical simulations provide spatially detailed and time-dependent information about the strain development during the welding process, especially regarding the critical conditions for solidification cracking. Therefore, this tool was also used in the present study to evaluate the accuracy of measurement methods and to estimate experimentally derived values and their concrete influence on the formation of solidification cracks. By integrating experimental methods and numerical simulations, this study investigates the spatially resolved and temporally changing development of strain during welding, with a particular focus on the critical conditions that lead to the formation of solidification cracks. T2 - GAMM 94th Annual Meeting CY - Magdeburg, Germany DA - 18.03.2024 KW - Laser beam welding KW - Solidification cracking KW - FEM simulation PY - 2024 AN - OPUS4-62417 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Meng, Xiangmeng T1 - A statistical investigation of the laser energy absorption and keyhole stability in high-power laser beam welding N2 - The behaviour of the weld pool in high-power laser beam welding is significantly influenced by laser absorption and keyhole stability, which determines the final weld qualities. However, their dynamic features and multi-coupled interactions make in-depth analyses difficult. This study addresses the challenges by conducting a thorough statistical evaluation of the effects of welding parameters on laser absorption and keyhole fluctuations, using experimental investigations and a well-validated numerical model. From a statistical aspect, the laser energy distribution and the keyhole collapse, commonly considered highly time-varying, show clear regularities. Three distinct regions of the time-averaged energy distribution are identified. The possibility of the keyhole collapse positions obeys a universal normal distribution. The statistical data show greater potential in revealing some well-known, industry-related but unclearly explained findings, such as the saturation of the weld penetration with increasing heat input and the physical basis of the contributions of different welding parameters in the porosity reduction. T2 - The 14th International Seminar Numerical Analysis of Weldability CY - Graz, Austria DA - 21.09.2025 KW - Laser beam welding KW - Energy absorption KW - Keyhole stability KW - Multi-physics modelling PY - 2025 AN - OPUS4-64811 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Meng, Xiangmeng T1 - A statistical assessment of the laser energy absorption and keyhole stability in high-power laser welding N2 - The behavior of the weld pool in high-power laser beam welding is significantly influenced by laser absorption and keyhole stability, which determines the final weld qualities. However, their dynamic features and multi-coupled interactions make in-depth analyses difficult. This study addresses the challenges by conducting a thorough statistical evaluation of the effects of welding parameters on laser absorption and keyhole fluctuations, using experimental investigations and a well-validated numerical model. From a statistical aspect, the laser energy distribution and the keyhole collapse, commonly considered to be highly time-varying, show clear regularities. Three distinct regions of the time-averaged energy distribution are identified. The possibility of the keyhole collapse positions obeys a universal normal distribution. The statistical data show greater potential in revealing some well-known, industry-related but unclearly explained findings, such as the saturation of the weld penetration with increasing heat input and the physical basis of the contributions of different welding parameters in the porosity reduction. T2 - 78th IIW Annual Assembly CY - Genoa, Italy DA - 22.06.2025 KW - Laser beam welding KW - Energy absorption KW - Keyhole stability PY - 2025 AN - OPUS4-64810 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Gumenyuk, Andrey T1 - The effect of an AC magnetic field on flow dynamics and filler wire mixing in high power laser hybrid welding N2 - The use of the oscillating magnetic field as a backing support for the welding of thick components is already known. The influence of the magnetic field and the induced Lorentz forces in the melt on the melt pool geometry and the fluid flows is not yet fully investigated. The study deals with the determination of the influence of an externally applied oscillating magnetic field on the melt pool dynamics in high power laser hybrid welding process. An AC magnet was positioned under the specimen to create an electromagnetic force directed upwards to oppose dropping. To visualise the flow characteristics of the melt, several experiments were carried out using a technique specifically designed for this purpose with mild steel made of S355J2 with a wall thickness of 20 mm and a quartz glass in a butt configuration. A high-speed camera was used to monitor the geometry of the melt pool through the glass. The influence of the magnetic field orientation to the welding direction and the oscillation frequency on the molten pool was investigated for the case of the metal-glass configuration and for laser hybrid welding. The high-speed recordings were analysed with the Optical Flow Algorithm to characterise the flow within the melt pool. The element distribution over the whole seam thickness was evaluated by X-ray fluorescence (XRF). The high-speed analysis showed that in the melt pool two vortices are formed, one in the upper part and the other in the lower part. In the region where the two vortices come together, a narrow region (necking region) forms in the melt pool. The evaluation of the high-speed recordings shows that the depth of the region where the two vortices meet is strongly influenced by the oscillation frequency. Additionally, the oscillation frequency demonstrated a greater influence on the melt pool dynamics and the mixing of the elements of the filler wire. T2 - X International Conference «Beam Technologies & Laser Application» CY - Pushkin (St. Petersburg), Russia DA - 20.09.2021 KW - Hybrid laser arc welding KW - Laser beam welding KW - Material transport PY - 2021 AN - OPUS4-53573 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Bakir, Nasim T1 - Observation of the weld pool shape in partial penetration welding and its influence on solidification crack formation for high-power laser beam welding N2 - Solidification cracking is still a particular problem in laser beam welding, especially in the welding of thick-walled plates. In this study, the influence of weld pool geometry on solidification cracking in partial penetration welding of thick plates is a subject of discussion. For this purpose, a special experimental setup of steel and quartz glass in butt configuration and lateral with high speed camera was used to capture the weld pool shape. Additionally, laser beam welding experiments were carried out to compare the crack positions and the cross section with the high-speed camera observations. The results showed a bulge in the weld pool root separated from the upper region by a nick area. This leads to the fact that three different longitudinal lengths with different solidification areas are taking place. This temporal sequence of solidification strongly promotes the solidification cracks in the weld root. T2 - Lasers in Manufacturing Conference 2021 CY - Online meeting DA - 21.06.2021 KW - Solidification cracking KW - Laser beam welding KW - Partial penetration PY - 2021 AN - OPUS4-53586 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Bachmann, Marcel T1 - Challenges in Modelling Dynamic Heat Sources in High-Power Laser Beam Welding N2 - The amount of absorbed energy in the keyhole as well as its distribution is essential to model the laser beam welding process. The recoil pressure 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 laser radiation on the weld metal is crucial to obtain accurate simulation results. The following developments on the laser-material interaction are discussed for the numerical simulation of the laser beam welding process. The first implemented improvements relate to locating the exact reflection points in the ray tracing method in the determination algorithm for the intersection of the 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 a third step, the laser radiation distribution in vertical direction was approximated according to the beam caustics. Finally, a virtual mesh refinement was adopted in the ray tracing routine. The obtained numerical results were validated with experimental measurements. T2 - IIW Annual Assembly 2024 CY - Rhodes , Greece DA - 07.07.2024 KW - Laser beam welding KW - Numerical modeling KW - Ray tracing KW - Heat source modeling PY - 2024 AN - OPUS4-60634 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Gumenyuk, Andrey T1 - Two-colour thermography for measurement of temperature distribution in laser beam welding N2 - Solidification cracking is a frequently observed phenomenon in laser beam welding of austenitic stainless steels and other metallic alloys. Characterisation of cracking susceptibility requires knowledge of the precise and spatially resolved temperature distribution near the solidification front in the welding process. Thermography is a standard tool that provides a qualitative estimate of the 2D temperature field. The general disadvantage of this method is its dependence on the emission characteristics of the measured object. For welding applications, these can vary significantly in the temperature range above and below the melting temperature. For this purpose, we have developed a thermography-based measurement technique using a SWIR camera system in combination with two narrow bandpass filters that use the principle of two-wavelength pyrometry to estimate absolute temperature values. This technique was used to determine the temperature distributions and gradients near the solidification front of laser-welded austenitic steel. The results were validated by other measurements. T2 - 13th CIRP Conference on Photonic Technologies [LANE 2024] CY - Fürth, Germany DA - 16.09.2024 KW - Laser beam welding KW - Solidification cracking KW - FEM simulation PY - 2024 AN - OPUS4-62415 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Meng, Xiangmeng T1 - Prediction of porosity formation in high power laser beam welding using physics informed machine learning framework N2 - The applications of the high-power laser beam welding process are often hindered by the occurrence of the porosity defect. However, an accurate prediction and an insight of the porosity formation are still challenging due to the highly nonlinear physics involved in the dynamic weld pool and keyhole behaviours. In this paper, the effects of relevant physical variables related to the porosity defect are evaluated by utilizing mechanistic modelling and experimental data within a physics-informed machine learning (PIML) framework. With a proper selection of the physical variables (features) in the aspects of keyhole stability, liquid metal flow and weld pool geometry, which correspondingly describes the bubble formation, bubble movement and bubble capture by the solidification front, the PIML shows great superiority in predicting the porosity ratio in the laser welding of aluminium in comparison with conventional ML model using welding parameters. The Shapley Additive Explanations analysis is employed to provide a hierarchical importance of the variables on the defect formation. T2 - 77th IIW Annual Assembly and International Conference CY - Rhodes, Greece DA - 07.07.2024 KW - Laser beam welding KW - Machine learning KW - Porosity KW - Modelling PY - 2024 AN - OPUS4-61610 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Putra, Stephen Nugraha T1 - Numerical study on the temperature characteristic of material absorptivity and its significance in high-power laser beam welding N2 - The absorptivity of metallic materials plays an important role in high-power laser beam welding. It affects the amount of absorbed laser power leading to the heating and melting of the surfaces to be joined and is highly dependent on the temperature. Nonetheless, this key characteristic is often ignored in numerical simulations and an empirical parameter determined by trial-and-error approaches is rather implemented to calibrate the results. In the present work, the temperature dependence of laser absorption is included in a three-dimensional multiphase numerical model considering the coupled fluid flow and heat transfer. The calculated laser absorption is determined by the temperature-dependent material properties, laser characteristics, and incident angle of the laser beam. It is found that the temperature dependence of the laser absorption is crucial for accurately determining the keyhole and weld pool geometries, which is validated by experimental measurements using 304 austenitic steel. T2 - 13th CIRP Conference on Photonic Technologies [LANE 2024] CY - Fürth, Germany DA - 15.09.2024 KW - Laser beam welding KW - Temperature dependent absorption KW - Weld pool KW - Keyhole dynamics KW - Numerical modelling PY - 2024 AN - OPUS4-61612 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Yang, Fan A1 - Meng, Xiangmeng A1 - Putra, Stephen Nugraha A1 - Bachmann, Marcel A1 - Rethmeier, Michael T1 - Numerical studies of magnetohydrodynamic technology in suppressing process porosity during laser beam welding N2 - The magnetohydrodynamic (MHD) technology is employed to mitigate the porosity problem during partial penetration laser beam welding (LBW) of 10 mm thick aluminum alloy. The effectiveness and universal applicability of the MHD technology in reducing porosity during the LBW process are confirmed by a reduction in the porosity ratio of more than 89%. A transient 3D multi-physical model coupled with the MHD effect has been developed to investigate the suppression mechanism of process porosity. Due to the influence of Lorentz force, there is an obvious change in the weld pool length. This change widens the escaping channel of bubbles escaping from the weld pool. The application of an oscillating magnetic field changes the fluid flow pattern noticeably, whose influence on the formation of porosity defects is highly complicated and nonlinear. T2 - 13th CIRP Conference on Photonic Technologies CY - Nuremberg, Germany DA - 15.09.2024 KW - Laser beam welding KW - Aluminum alloy KW - Process Porosity KW - Porosity suppression KW - Magnetohydrodynamic technology PY - 2024 AN - OPUS4-61604 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Bachmann, Marcel T1 - Reconstruction of the time-averaged keyhole geometry in laser beam welding with electromagnetic support N2 - In laser beam welding (LBW), the time-averaged keyhole shape provides statistical insights into the process compared to its transient geometry, offering a deeper understanding of the overall keyhole behaviour. However, capturing the time-averaged keyhole shape through experimental methods remains challenging. In this paper, a reconstruction algorithm for the time-averaged keyhole is developed and integrated into a three-dimensional transient multi-physical coupled numerical model. The algorithm can accurately capture the key characteristics of the keyhole, including its diameter and centroid. In addition, it can also successfully reproduce the experimentally observed phenomena of keyhole tailing. The overall shape of the keyhole appears smooth, without exhibiting obvious instability features. Furthermore, the time-averaged keyhole shape is compared under different magnetic flux densities when an external oscillating magnetic field is applied. The results indicate that the application of external magnetic fields does not fundamentally alter the overall keyhole shape. With increasing magnetic flux density, the trailing tail becomes progressively less pronounced and a noticeable increase in the curvature of the rear wall is observed. The standard deviation of the keyhole diameter can serve as an effective index for evaluating the keyhole instability. Keyhole stability in LBW of aluminium alloys is improved under the assistance of electromagnetic fields, and this stabilization is positively correlated with increasing magnetic flux density. T2 - 14th International Seminar Numerical Analysis of Weldability CY - Seggau, Austria DA - 21.09.2025 KW - Laser beam welding KW - Keyhole reconstruction KW - Electromagnetic weld pool support KW - Porosity defects KW - Keyhole stability PY - 2025 AN - OPUS4-64257 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Bachmann, Marcel T1 - Elucidation of the Laser Beam Energy Attenuation by the Vapor Plume Formation during High Power Laser Beam Welding N2 - In high-power laser beam welding, a common phenomenon is the formation of a keyhole caused by the rapid evaporation of the material. Under atmospheric pressure, this evaporation generates a vapor plume that interacts with the laser beam, leading to energy attenuation and scattering of the laser radiation along its path. These interactions affect the stability of the process and the overall weld quality. This study investigates the influence of the vapor plume on the weld pool and keyhole dynamics during high-power laser beam welding of AlMg3 aluminum alloy through experimental and numerical approaches. The primary goal is to identify key vapor plume characteristics, particularly its length fluctuations, and to improve the accuracy of the numerical models. To achieve this, an algorithm was developed for the automated measurement of the vapor plume length using high-speed imaging and advanced data processing techniques. The measured plume length is then used to estimate the additional vapor heating and laser energy attenuation using the Beer–Lambert law. A refined numerical CFD model, incorporating 3D transient heat transfer, fluid flow, and ray tracing, was developed to evaluate the vapor plume’s impact. Results show that already the time-averaged plume length effectively captures its transient influence and aligns well with experimental weld seam geometries. Additionally, energy scattering and absorption caused by the vapor plume led to a wider weld pool at the top surface. The study also shows an increased percentage of keyhole collapses due to the reduced laser power absorption at the keyhole bottom, further highlighting the importance of accurately modeling vapor plume effects. T2 - International Congress of Applications of Lasers & Electro-Optics 2025 CY - Orlando, FL, USA DA - 12.10.2025 KW - Laser beam welding KW - Vapor plume formation KW - Weld pool KW - Keyhole dynamics KW - Numerical modeling PY - 2025 AN - OPUS4-64816 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Meng, Xiangmeng T1 - Prediction of weld pool and keyhole geometries in high-power laser beam welding through a physics-informed generative approach N2 - The weld pool and keyhole geometries are critical characteristics in evaluating the stability of the high-power laser beam welding (LBW) process and determining the resultant weld quality. However, obtaining these data through experimental or numerical methods remains challenging due to the difficulties in experimental measurements and the high computational demands of numerical modelling. This paper presents a physics-informed generative approach for predicting weld pool and keyhole geometries in the LBW process. With the help of a well experimentally validated numerical model considering the underlying physics in the LBW, the geometries of the weld pool and keyhole under various welding conditions are calculated, serving as the dataset of the generative model. A Conditional Variational Autoencoder (CVAE) model is employed to generate realistic 2D weld pool and keyhole geometries from the welding parameters. We utilize a β-VAE model with the Evidence Lower Bound (ELBO) loss function and include Kullback-Leibler divergence annealing to better optimize model performance and stability during training. The generated results show a good agreement with the ground truth from the numerical simulation. The proposed approach exhibits the potential of physics-informed generative models for a rapid and accurate prediction of the weld pool geometries across a diverse range of process parameters, offering a computationally efficient alternative to full numerical simulations for process optimization and control in laser beam welding processes. T2 - The 45th annual International Congress on Applications of Lasers & Electro-Optics CY - Orlando, FL, USA DA - 12.10.2025 KW - Laser beam welding KW - Generative artificial intelligence KW - Machine Learning KW - Numerical Simulation KW - Weld pool KW - Keyhole dynamics PY - 2025 AN - OPUS4-64812 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Gumenyuk, Andrey T1 - Strain distribution vs strain evolution during solidification cracking CTW test for laser beam welding of 1 mm austenitic stainless steels N2 - Laser welding is a widely established manufacturing process across many industrial sectors. However, solidification cracking and the weldability of materials have remained contentious issues for many years, particularly concerning the causes of hot crack formation. The local distribution of total strain was measured in close proximity to the solidification zone during laser welding of AISI 304 and AISI 310S stainless steels, using the Controlled Tensile Weldability (CTW) test. In this setup, 1 mm thick weld coupons were subjected to a defined external tensile load during welding. Mechanical loading parameters were varied by adjusting the strain rate and ultimate strain level to identify the critical conditions that lead to solidification crack formation along the weld seam centerline. Using Digital Image Correlation (DIC) and the optical flow method [1], we estimated the local strain distribution at the surface near the molten pool and tracked its evolution across several characteristic zones—before, during, and after the application of mechanical loading. The results revealed that solidification crack formation coincides with regions of high plastic deformation within a critical temperature range. Furthermore, we identified a clear relationship between strain rate and both crack initiation probability and maximum local strain. Importantly, neither strain rate nor maximum strain alone is sufficient to predict cracking; instead, their combined effect must be considered to accurately assess hot cracking susceptibility. T2 - AJP 2025 CY - Coimbra, Portugal DA - 16.10.2025 KW - Laser beam welding KW - Solidification cracking KW - Optical measurement PY - 2025 AN - OPUS4-64431 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -