TY - CONF A1 - Artinov, Antoni A1 - Kising, Pascal A1 - Bachmann, Marcel A1 - Meng, Xiangmeng A1 - Rethmeier, Michael 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 crosssections. 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 - 2023 SN - 978-3-85125-968-1 SN - 978-3-85125-969-8 SN - 2410-0544 VL - 13 SP - 161 EP - 188 PB - Verlag der Technischen Universität Graz AN - OPUS4-58803 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Artinov, Antoni A1 - Meng, Xiangmeng A1 - Bachmann, Marcel A1 - Rethmeier, Michael T1 - Study on the transition behavior of the bulging effect during deep penetration laser beam welding N2 - The present work is devoted to the study of the transition behavior of the recently confirmed widening of the weld pool, known as the bulging effect, during high-power deep penetration laser beam welding of thick unalloyed steel sheets. A three-dimensional transient multi-physics numerical model is developed, allowing for the prediction of the bulge formation and the study of its temporal behavior. The model is generalized to account automatically for the transition from partial to complete penetration. Several experimental measurements and observations, such as drilling period, weld pool length, temperature, efficiency, and metallographic cross-sections are used to verify the model and assure the plausibility of the numerical results. The analysis of the calculated temperature and velocity distributions, as well as the evolution of the keyhole geometry, shows that the formation of a bulging region strongly depends on the penetration depth of the weld. Based on the numerical results, the bulge is found to occur transiently, having its transition from a slight bulge to a fully developed bulging between penetration depths of 6 mm and 9 mm, respectively. KW - Laser beam welding KW - Deep penetration KW - Bulge formation KW - Numerical modeling PY - 2022 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-545067 DO - https://doi.org/10.1016/j.ijheatmasstransfer.2021.122171 VL - 184 SP - 122171 PB - Elsevier Ltd. AN - OPUS4-54506 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Artinov, Antoni A1 - Meng, Xiangmeng A1 - Bachmann, Marcel A1 - Rethmeier, Michael T1 - Numerical analysis of the partial penetration high power laser beam welding of thick sheets at high process speeds N2 - The present work is devoted to the numerical analysis of the high-power laser beam welding of thick sheets at different welding speeds. A three-dimensional transient multi-physics numerical model is developed, allowing for the prediction of the keyhole geometry and the final penetration depth. Two ray tracing algorithms are implemented and compared, namely a standard ray tracing approach and an approach using a virtual mesh refinement for a more accurate calculation of the reflection points. Both algorithms are found to provide sufficient accuracy for the prediction of the keyhole depth during laser beam welding with process speeds of up to 1.5 m/min. However, with the standard algorithm, the penetration depth is underestimated by the model for a process speed of 2.5 m/min due to a trapping effect of the laser energy in the top region. In contrast, the virtually refined ray tracing approach results in high accuracy results for process speeds of both 1.5 m/min and 2.5 m/min. A detailed study on the trapping effect is provided, accompanied by a benchmark including a predefined keyhole geometry with typical characteristics for the high-power laser beam welding of thick plates at high process speed, such as deep keyhole, inclined front keyhole wall, and a hump. KW - High-power laser beam welding KW - High process speeds KW - Deep penetration KW - Numerical modeling KW - Ray tracing PY - 2021 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-532170 DO - https://doi.org/10.3390/met11081319 SN - 2075-4701 VL - 11 IS - 8 SP - 1 EP - 16 PB - MDPI CY - Basel AN - OPUS4-53217 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Artinov, Antoni A1 - Meng, Xiangmeng A1 - Bachmann, Marcel A1 - Rethmeier, Michael 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 crosssections. 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 - 13th International Seminar "Numerical Analysis of Weldability" CY - Seggau, Austria DA - 04.09.2022 KW - Laser beam welding KW - Deep penetration KW - Bulge formation KW - Numerical modeling PY - 2023 SN - 978-3-85125-968-1 SN - 978-3-85125-969-8 SN - 2410-0544 VL - 13 SP - 101 EP - 126 PB - Verlag der Technischen Universität Graz AN - OPUS4-58802 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Artinov, Antoni A1 - Meng, Xiangmeng A1 - Bakir, Nasim A1 - Üstündag, Ömer A1 - Bachmann, Marcel A1 - Gumenyuk, Andrey 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 an infrared camera 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 more frequently during partial penetration above 6 mm and complete penetration above 8 mm penetration depth, respectively. 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 - 18th Nordic Laser Materials Processing Conference (18th NOLAMP) KW - High-power laser beam welding KW - Bulge effect KW - Solidification cracking KW - Multi-physical modelling KW - Metal mixing PY - 2021 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-539149 DO - https://doi.org/10.1088/1757-899X/1135/1/012003 VL - 1135 IS - 012003 SP - 1 EP - 11 PB - IOP Publishing AN - OPUS4-53914 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 - 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 - 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 - 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 - 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 - JOUR 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. KW - Laser beam welding KW - Laser energy distribution KW - Ray tracing KW - Numerical modeling PY - 2023 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-584748 DO - https://doi.org/10.2351/7.0001079 VL - 35 IS - 4 SP - 1 EP - 9 PB - Laser Institute of America AN - OPUS4-58474 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 the 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 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 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, USA DA - 16.10.2023 KW - Laser beam welding KW - Laser energy distribution KW - Ray tracing KW - Numerical modeling PY - 2023 SP - 1 EP - 10 AN - OPUS4-58475 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Bachmann, Marcel A1 - Artinov, Antoni A1 - Meng, Xiangmeng A1 - Rethmeier, Michael T1 - Numerical study of the bulging effect in deep penetration laser beam welding N2 - This article is devoted to the study of the bulging effect in deep penetration laser beam welding. The numerical results of the investigations are based upon experimental results from previous studies to reveal the relationship between the bulging effect and the hot cracking formation, as well as the mixing of alloying elements in the weld pool. The widening of the molten pool in its center area can be observed in full penetration as well as in partial penetration welds on 8 mm and 12 mm thick structural steel plates, respectively. The weld pool shape is extracted from the simulations to evaluate the extent of the necking of the solidification line as well as the bulging phenomena and its influence on the hot cracking phenomena. Relying on an earlier numerical study utilizing a fixed keyhole, simulation models considering a dynamic keyhole are developed thereto. Additionally, the mixing behavior of alloying elements during partial penetration is investigated. The link between the bulge and the studied phenomena is found to be significant. T2 - Lasers in Manufacturing Conference 2021 CY - Online meeting DA - 21.06.2021 KW - Deep penetration laser beam welding KW - Welding simulation KW - Solidification cracking KW - Bulging effect PY - 2021 SP - 1 EP - 8 AN - OPUS4-52848 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. Firstly, the local variation of the solidification sequence of the weld pool causes an increase in the hot-cracking susceptibility due to a locally delayed solidification. Secondly, 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 non-homogeneous 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 which 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 - Numerical process simulation PY - 2022 SP - 1 AN - OPUS4-56532 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Bachmann, Marcel A1 - Meng, Xiangmeng A1 - Artinov, Antoni A1 - Rethmeier, Michael T1 - Elucidation of the Bulging Effect by an Improved Ray-Tracing Algorithm in Deep Penetration Wire Feed Laser Beam Welding and its Influence on the Mixing Behavior N2 - Herein, an improved ray-tracing routine using a virtual mesh refinement approach is adopted in a 3D transientmultiphysics computational fluid Dynamics model for deep penetration wire feed laser beam welding. In a previous study, it was shown that the improved localization of the reflection points of the subrays within the keyhole leads to a more realistic development of the keyhole Depth being validated with experimental results. Another effect investigated in Detail herein is a drastic change in the flow behavior in the weld pool, which promotes the occurrence of a necking area in the solidification line and subsequent bulging under specific circumstances. This has a detrimental effect on the filler material element transport in the weld pool, leading to an inhomogeneous dilution of the added material. The numerical observations are backed up by experimentally obtained data, allowing to provide a clear physics-based explanation of the reduced mixing behavior of the filler wire in the melt pool. KW - Bulging effects KW - Numerical welding simulations KW - Ray-tracing methods KW - Wire feed laser beam welding PY - 2022 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-543322 DO - https://doi.org/10.1002/adem.202101299 SP - 1 EP - 9 PB - Wiley AN - OPUS4-54332 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR 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 hot-cracking 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 non-homogeneous 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. KW - Weld pool shape KW - Laser beam welding KW - Solidification KW - Porosity KW - Numerical process simulation PY - 2022 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-557759 DO - https://doi.org/10.2351/7.0000733 SN - 1042-346X VL - 34 IS - 4 SP - 1 EP - 7 PB - Laser Institute of America CY - Orlando, Fla. AN - OPUS4-55775 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Bachmann, Marcel A1 - Meng, Xiangmeng A1 - Artinov, Antoni A1 - Rethmeier, Michael T1 - Investigating defects caused by narrow pool shapes in deep penetration welding N2 - Laser beam welding is a widely used joining technique in many industrial applications. This is mainly due to its many unique advantages, especially compared to conventional arc welding processes. These advantages include, among others, highly concentrated energy deposition, low total heat input and a capacity to penetrate deep into the material while causing only small welding distortions. However, at the same time, the small dimension of the laser spot, high solidification rates, and small dimensions of the weld pool itself can provoke issues regarding the assembly tolerances of the workpiece, the hot-cracking phenomena, as well as keyhole-induced bubbles escaping from the melt. Weld pool shapes in laser beam welding are elongated at the external, free surfaces under the action of the main driving forces in the melt – such as recoil pressure and surface tension forces – while being shorter in the internal areas of the weld pool. This leads to a regular solidification sequence from the internal zones toward the free surfaces, e.g. from the bottom to the top in partial penetration welding. However, in recent studies reported in the literature and seen in the experimental and numerical investigations of BAM Bundesanstalt für Materialforschung und -prüfung in Berlin, it was found that an internal narrowing phenomenon can occur that is often accompanied by a distinct bulging of the weld bead in deeper zones. As the internal behaviour of the melt during the process is hardly optically accessible, several numerical models and experimental techniques were established to visualise the mechanisms of the formation of the bulging and the narrowing phenomenon and to reveal the consequences on the solidification sequence, pore formation, and filler metal dilution. KW - Weld pool shape KW - Laser beam welding KW - Solidification PY - 2022 SN - 1759-0752 IS - 57 SP - 28 EP - 29 PB - Europa Science CY - Cambridge, UK AN - OPUS4-56995 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -