TY - JOUR A1 - Meng, Xiangmeng A1 - Artinov, Antoni A1 - Bachmann, Marcel A1 - Üstündag, Ömer A1 - Gumenyuk, Andrey A1 - Rethmeier, Michael T1 - The detrimental molten pool narrowing phenomenon in wire feed laser beam welding and its suppression by magnetohydrodynamic technique N2 - Element transport in the wire feed laser beam welding (WFLBW) is directly determined by the molten pool shape and thermo-fluid flow therein. In this paper, an untypical molten pool profile, i.e., elongated at its top and bottom but narrowed at the middle, is found experimentally by real-time metal/glass observa- tion and numerically by multi-physical modeling. Ex-situ X-ray fluorescence element mapping is used to characterize the element dilution status in the fusion zone. For the first time, the detrimental influence of the molten pool narrowing on the element transport is identified and discussed, combining the exper- imental and numerical results. A magnetohydrodynamic technique is utilized to suppress the narrowing, aiming at a more homogenous element distribution. It is found that due to the interaction of the two dominant circulations from the top and bottom regions of the molten pool, a low-temperature region is formed. It leads to an untypical growth of the mushy zone, narrowing the molten pool in the middle re- gion. Its detrimental effect on material mixing is non-negligible considering the direct blocking effect on the downward flow and the premature solidification at the middle region. The Lorentz force from a trans- verse oscillating magnetic field can change the flow pattern into a single-circulation type. The downward transfer channel is widened, and its premature solidification is prevented because the low-temperature- gradient region is mitigated. This paper provides a supplementary reason regarding the common issue of insufficient material mixing during LBW, and a promising technique to optimize the process. KW - Thermo-fluid flow KW - Element transport KW - Laser beam welding KW - Magnetohydrodynamics KW - Multi-physical modeling PY - 2022 U6 - https://doi.org/10.1016/j.ijheatmasstransfer.2022.122913 VL - 193 SP - 122913 PB - Elsevier B.V. AN - OPUS4-55006 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Meng, Xiangmeng A1 - Putra, Stephen Nugraha A1 - Bachmann, Marcel A1 - Artinov, Antoni A1 - Rethmeier, Michael T1 - 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 raytracing 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 noncontinuous 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. KW - Laser beam welding KW - Laser energy distribution KW - Weld pool dynamics KW - Ray teacing PY - 2022 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:b43-562429 SN - 1042-346X VL - 34 IS - 4 SP - 042023-1 EP - 042023-8 PB - Laser Institute of America CY - Orlando, Fla. AN - OPUS4-56242 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 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:b43-545067 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 - 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 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:b43-543322 SP - 1 EP - 9 PB - Wiley AN - OPUS4-54332 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Artinov, Antoni A1 - Bachmann, Marcel A1 - Rethmeier, Michael A1 - Karkhin, V. A1 - Khomich, P. T1 - Modeling of hydrodynamic and thermal processes at laser welding with through penetration N2 - A mathematical model for physical processes in fusion welding has been developed. It is based on the equivalent heat source concept and consists of two parts: thermo-hydrodynamics of the weld pool and heat conduction in the weldment outside the pool. In thermo-hydrodynamic problem, temperature – dependent material properties, keyhole shape, thermo-capillary and natural convection, phase transformations and other physical phenomena are taken into consideration. Solution of the thermo-hydrodynamic problem by the finite element method is demonstrated with keyhole laser beam welding of a 15 mm thick steel plate. Thermo-capillary convection is primarily responsible for the intricate convex-concave melt pool shape and pool enlargement near the plate surfaces. The calculated and experimental molten pool dimensions are in close agreement. KW - Laser welding KW - Weld pool modeling KW - Heat conduction KW - Greens function method PY - 2021 U6 - https://doi.org/10.1080/09507116.2021.1989209 SP - 1 EP - 12 PB - Taylor & Francis Group AN - OPUS4-54022 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 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:b43-539149 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 - 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 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:b43-532170 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 - JOUR A1 - Meng, Xiangmeng A1 - Bachmann, Marcel A1 - Artinov, Antoni A1 - Rethmier, Michael T1 - A study of the magnetohydrodynamic effect on keyhole dynamics and defect mitigation in laser beam welding N2 - In this paper, the highly transient keyhole dynamics, e.g., laser absorption, keyhole geometry, and fluctuation, etc., under a magnetic field are investigated using an experimental approach and multi-physical modeling. The model provides accurate predictions to the variation of penetration depth and weld pool profiles caused by the MHD effect, which is validated by the measurements of optical micrographs and in-situ metal/glass observation. The micro-X-ray computed tomography shows a remarkable reduction of keyhole-induced porosity with the magnetic field. The correlation between the porosity mitigation and the weld pool dynamics influenced by the magnetic field is built comprehensively. It is found that the magnetic field gives a direct impact on the laser energy absorption at the keyhole front wall by changing the protrusion movement. The porosity mitigation comes from multiple physical aspects, including keyhole stabilization, widening of the bubble floating channel, and the electromagnetic expulsive force. Their contributions vary according to the bubble size. The findings provide a deeper insight into the relationship between electromagnetic parameters, keyhole dynamics, and suppression of keyhole-relevant defects. KW - Laser beam welding (LBW) KW - Keyhole dynamics KW - Porosity KW - Magnetohydrodynamics (MHD) KW - X-ray computed tomography KW - Multi-physical modeling PY - 2022 U6 - https://doi.org/10.1016/j.jmatprotec.2022.117636 SN - 0924-0136 VL - 307 SP - 117636 PB - Elsevier B.V. AN - OPUS4-55378 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 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:b43-557759 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 - Artinov, Antoni A1 - Bachmann, Marcel A1 - Rethmeier, Michael T1 - Equivalent heat source approach in a 3D transient heat transfer simulation of full-penetration high power laser beam welding of thick metal plates N2 - A three-dimensional multi-physics numerical model was developed for the calculation of an appropriate equivalent volumetric heat source and the prediction of the transient thermal cycle during and after fusion welding. Thus the modelling process was separated into two studies. First, the stationary process simulation of full-penetration keyhole laser beam welding of a 15 mm low-alloyed steel thick plate in flat position at a welding speed of 2 m/min and a laser power of 18 kW was performed. A fixed keyhole with a right circular cone shape was used to consider the energy absorbed by the workpiece and to calibrate the model. In the calculation of the weld pool geometry and the local temperature field, the effects of phase transition, thermo-capillary convection, natural convection and temperature-dependent material properties up to evaporation temperature were taken into account. The obtained local temperature field was then used in a subsequent study as an equivalent heat source for the computation of the transient thermal field during the laser welding process and the cooling stage of the part. The system of partial differential equations, describing the stationary heat transfer and the fluid dynamics, were strongly coupled and solved with the commercial finite element software COMSOL Multiphysics 5.0. The energy input in the transient heat transfer simulation was realised by prescription of the nodes temperature. The prescribed nodes reproduced the calculated local temperature field defining the equivalent volumetric heat source. Their translational motion through the part was modelled by a moving mesh approach. An additional remeshing condition and helper lines were used to avoid highly distorted elements. The positions of the elements of the polygonal mesh were calculated with the Laplace’s smoothing approach. Good correlation between the numerically calculated and the experimentally observed weld bead shapes and transient temperature distributions was found. KW - Laser beam welding KW - Process simulation KW - Equivalent heat source KW - Transient heat transfer KW - Deformed geometry PY - 2018 UR - https://authors.elsevier.com/a/1WbSq44xZwola U6 - https://doi.org/10.1016/j.ijheatmasstransfer.2018.02.058 SN - 0017-9310 SN - 1879-2189 VL - 122 SP - 1003 EP - 1013 PB - Elsevier Ltd. CY - Amsterdam [u.a.] AN - OPUS4-44272 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -