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 -