TY - JOUR A1 - Yalçınyüz, Aybike A1 - Raute, Julius A1 - Gonzalez-Gutierrez, Joamin A1 - Pei, Eujin A1 - Biegler, Max A1 - Rethmeier, Michael T1 - Electron Beam Bonding: A novel method for joining additively manufactured carbon fiber thermoplastic composites with aluminum to produce multi-material joints for lightweight applications N2 - In recent years, new solutions have been explored to reduce the weight of components for the automotive, railway, and aerospace industries. For this reason, Carbon Fiber Composites (CFCs) have increasingly replaced metals in products that need to be lightweight. However, due to their poor thermal conductivity, CFCs have limited use in applications requiring efficient heat dissipation. In such applications, conventionally manufactured metal alloys are typically utilized. To address these limitations, a novel approach using a combination of additively manufactured aluminum and CFCs is proposed to exploit the distinct advantages of both materials. These innovative hybrid structures aim to combine good structural and thermal management properties with reduced weight compared to conventionally produced metal products. In this study, additively manufactured aluminum alloy (AlSi10Mg) and short carbon fiber Polyamide 6 composite (sCF-PA6) are utilized to produce metal–polymer pairs using electron beam energy to bond the two materials. Direct irradiation of short CFCs with electron beam leads to polymer degradation. Thus, a novel method “Electron Beam Bonding” for joining CFCs with aluminum alloy in various joint configurations using electron beam technology is demonstrated. This innovative approach presents a promising solution for creating metal–polymer multi-materials for lightweight applications. KW - Electron beam bonding KW - Multi-material KW - Lightweight KW - Additive manufactured materials KW - Short carbon fiber composites KW - AlSi10Mg KW - Joining PY - 2025 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-641705 DO - https://doi.org/10.1007/s40964-025-01206-1 SN - 2363-9512 SP - 1 EP - 7 PB - Springer International Publishing CY - Cham AN - OPUS4-64170 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Artinov, Antoni A1 - Bachmann, Marcel A1 - Meng, Xiangmeng A1 - Karkhin, V. A1 - Rethmeier, Michael 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] KW - Hot cracking KW - Bulge effect KW - Numerical modelling KW - Laser beam welding KW - Deep penetration PY - 2020 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-512783 DO - https://doi.org/10.1016/j.procir.2020.09.002 SN - 2212-8271 VL - 94 SP - 5 EP - 10 PB - Elsevier B.V. CY - Amsterdam [u.a.] AN - OPUS4-51278 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Srinivasan, Krishnanand A1 - Gumenyuk, Andrey A1 - Rethmeier, Michael T1 - Laser Metal Deposition of Rene 80—Microstructure and Solidification Behavior Modelling N2 - New developments in nickel-based superalloys and production methods, such as the use of additive manufacturing (AM), can result in innovative designs for turbines. It is crucial to understand how the material behaves during the AM process to advance the industrial use of these techniques. An analytical model based on reaction–diffusion formalism is developed to better explain the solidification behavior of the material during laser metal deposition (LMD). The well-known Scheil–Gulliver theory has some drawbacks, such as the assumption of equilibrium at the solid–liquid interface, which is addressed by this method. The solidified fractions under the Scheil model and the pure equilibrium model are calculated using CALPHAD simulations. A differential scanning calorimeter is used to measure the heat flow during the solid–liquid phase transformation, the result of which is further converted to solidified fractions. The analytical model is compared with all the other models for validation. KW - Laser metal deposition KW - Solidification behavior KW - Additive manufacturing KW - Analytical model KW - Nickel‐based superalloy PY - 2024 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-612095 DO - https://doi.org/10.3390/mi15101234 SN - 2072-666X VL - 15 IS - 10 SP - 1 EP - 14 PB - MDPI AN - OPUS4-61209 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Bakir, Nasim A1 - Gumenyuk, Andrey A1 - Rethmeier, Michael T1 - Determination of critical local straining conditions for solidification cracking at laser beam welding by experimental and numerical methods N2 - AbstractThe 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 crack‐sensitive 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 susceptibility 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. The use of numerical simulations serves a dual purpose by validating the accuracy of measurement methods and examining experimentally determined values for their actual influence on the formation of solidification cracks. A three‐dimensional finite element (FE) model implemented with ANSYS is used to simulate strains and stresses during welding. The credibility of the model was first established by validation using experimental temperature measurements. Subsequently, structural simulations were carried out under external load. The results of the simulations showed commendable agreement with the strain measurements performed using the developed technique. KW - Laser beam welding KW - Solidification cracking KW - FEM simulation PY - 2024 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-612044 DO - https://doi.org/10.1002/pamm.202400020 SN - 1617-7061 VL - 24 IS - 2 SP - 1 EP - 16 PB - Wiley AN - OPUS4-61204 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Gumenyuk, Andrey A1 - Üstündağ, Ömer A1 - Pelz, Till A1 - Bakir, Nasim A1 - Gerhards, Benjamin A1 - Schleser, Markus A1 - Rethmeier, Michael T1 - Single pass laser vacuum welding of thick steel plates using electromagnetic support N2 - The increasing demand for renewable energy produced by offshore wind turbines goes along with an increased demand in the production of offshore wind turbine foundations, so called “monopiles”, which are made by joining thick metal sheets. The industrial standard of multi-layer submerged arc welding (SAW) for joining of thick metal sheets is the current bottleneck in the production of monopiles. A possible increase in productivity by the implementation of high-power laser welding in a newly developed mobile vacuum chamber (MoVac) and an electromagnetic root support is the subject of this study. Single run butt welds are performed in flat position on S355 mild steel of thicknesses up to 80 mm using a disc laser system with 1030 nm wavelength and a maximum output of 60 kW. The laser optic is fixed on the MoVac-System which is held and manipulated by an articulated robot. KW - Laser beam welding KW - Laser welding with mobile vacuum PY - 2024 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-612068 DO - https://doi.org/10.1016/j.procir.2024.08.145 VL - 124 SP - 418 EP - 423 PB - Elsevier BV AN - OPUS4-61206 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Gumenyuk, Andrey A1 - Bakir, Nasim A1 - Rethmeier, Michael 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. KW - Laser beam welding KW - Two-colour thermography KW - Solidification cracking PY - 2024 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-612070 DO - https://doi.org/10.1016/j.procir.2024.08.155 VL - 124 SP - 468 EP - 471 PB - Elsevier BV AN - OPUS4-61207 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Yang, Keke A1 - El-Sari, Bassel A1 - Olfert, Viktoria A1 - Wang, Zhuoqun A1 - Biegler, Max A1 - Rethmeier, Michael A1 - Meschut, Gerson T1 - Expulsion prevention in resistance spot welding of dissimilar joints with ultra-high strength steel: An analysis of the mechanism and effect of preheating current N2 - The widespread adoption of ultra-high strength steels, due to their high bulk resistivity, intensifies expulsion issues in resistance spot welding (RSW), deteriorating both the spot weld and surface quality. This study presents a novel approach to prevent expulsion by employing a preheating current. Through characteristic analysis of joint formation under critical welding current, the importance of plastic material encapsulation around the weld nugget (plastic shell) at high temperatures in preventing expulsion is highlighted. To evaluate the effect of preheating on the plastic shell and understand its mechanism in expulsion prevention, a two-dimensional welding simulation model for dissimilar ultra-high strength steel joints was established. The results showed that optimal preheating enhances the thickness of the plastic shell, improving its ability to encapsulate the weld nugget during the primary welding phase, thereby diminishing expulsion risks. Experimental validation confirmed that by employing the optimal preheating current, the maximum nugget diameter was enhanced to 9.42 mm, marking an increase of 13.4 % and extending the weldable current range by 27.5 %. Under quasi-static cross-tensile loading, joints with preheating demonstrated a 7.9 % enhancement in maximum load-bearing capacity compared to joints without preheating, showing a reproducible and complete pull-out failure mode within the heat-affected zone. This study offers a prevention method based on underlying mechanisms, providing a new perspective for future research on welding parameter optimization with the aim of expulsion prevention. KW - Resistance spot welding KW - Finite element modelling KW - Preheating KW - Weldable current range KW - Ultra-high strength steel PY - 2024 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-621719 DO - https://doi.org/10.1016/j.jmapro.2024.06.034 VL - 124 SP - 489 EP - 502 PB - Elsevier Ltd. AN - OPUS4-62171 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Uhlmann, Eckart A1 - Polte, Julian A1 - Fasselt, Janek Maria A1 - Müller, Vinzenz A1 - Klötzer-Freese, Christian A1 - Kleba-Ehrhardt, Rafael A1 - Biegler, Max A1 - Rethmeier, Michael T1 - A Comparative Evaluation of Powder Characteristics of Recycled Material from Bronze Grinding Chips for Additive Manufacturing N2 - In the manufacturing process of ship propellers, large quantities of grinding chips are generated. These grinding chips result from the finishing of the blade surfaces after the primary casting process of the propeller. The aim of this study was to investigate and compare different preparation processes used to produce chip powders with sufficient powder quality for the additive manufacturing process of directed energy deposition. The preparation of the samples was performed through different sieving, milling and re-melting processes. For the characterization of the prepared samples, powder analysis according to relevant industry standards was carried out. It was found that the re-melting processes result in superior powder quality for additive manufacturing in terms of particle size, morphology, and flowability. For some characteristics, the powder exhibits even better properties than those of commercial powders. Furthermore, the powder properties of the milled samples demonstrate a promising potential for u KW - Grinding chips KW - Comminution KW - Aluminium bronze KW - Additive manufacturing KW - Recycling KW - Sustainability PY - 2024 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-621696 DO - https://doi.org/10.3390/ma17143396 VL - 17 IS - 14 SP - 1 EP - 15 PB - MDPI AG AN - OPUS4-62169 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Raute, Julius A1 - Beret, Alexander A1 - Biegler, Max A1 - Rethmeier, Michael T1 - Life cycle assessment in additive manufacturing of copper alloys—comparison between laser and electron beam N2 - Additive manufacturing is becoming increasingly important for industrial production. In this context, directed energy deposition processes are in demand to achieve high deposition rates. In addition to the well-known laser-based processes, the electron beam has also reached industrial market maturity. The wire electron beam additive manufacturing offers advantages in the processing of copper materials, for example. In the literature, the higher energy efficiency and the resulting improvement in the carbon footprint of the electron beam are highlighted. However, there is a lack of practical studies with measurement data to quantify the potential of the technology. In this work, a comparative life cycle assessment between wire electron beam additive manufacturing (DED-EB) and laser powder additive manufacturing (DED-LB) is carried out. This involves determining the resources for manufacturing, producing a test component using both processes, and measuring the entire energy consumption. The environmental impact is then estimated using the factors global warming potential (GWP100), photochemical ozone creation potential (POCP), acidification potential (AP), and eutrophication potential (EP). It can be seen that wire electron beam additive manufacturing is characterized by a significantly lower energy requirement. In addition, the use of wire ensures greater resource efficiency, which leads to overall better life cycle assessment results. KW - Life cycle assessment (LCA) KW - Additive manufacturing KW - Directed energy deposition KW - Wire electron beam additive manufacturing KW - Copper alloys PY - 2024 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-621705 DO - https://doi.org/10.1007/s40194-024-01856-9 SP - 3169 EP - 3176 PB - Springer Science and Business Media LLC AN - OPUS4-62170 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Marquardt, R. A1 - Biegler, M. A1 - Rethmeier, Michael T1 - Functionally graded material for improved wear resistance manufactured by directed energy deposition N2 - Protecting components against wear and corrosion is a common way to improve their lifetime. This can be achieved by coating them with a hardfacing material. Common coatings consist of materials such as tungsten carbide or cobalt-chromium alloys, also known as Stellite. Hardfacing materials can be deposited by welding methods like plasma welding or laser cladding. The discrete change of the base material to the hardfacing layer can lead to cracks and chipping. Studies showed a reduced risk of cracking when a functionally graded material is used to create a smooth transition between the base and the hardfacing. Gradings from austenitic steel to cobalt-chromium alloys are already known in the literature. However, there is no knowledge about austenitic- ferritic duplex steels as base material. Therefore, this study aims to demonstrate the feasibility of a functionally graded material from duplex steel to cobalt-chromium alloy with a new approach. By using powder-based directed energy deposition, a graded material with smooth material transition is manufactured additively. Cracking and porosity are examined through metallography. Microhardness measurements as well as the analysis of the chemical composition by energy dispersive X-ray spectroscopy and X-ray fluorescence are used to validate the build-up strategy. KW - Additive manufacturing KW - Functionally graded material KW - Functionally graded additive manufacturing KW - Directed energy deposition KW - Laser metal deposition PY - 2024 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-621683 DO - https://doi.org/10.1007/s40964-024-00879-4 SP - 1 EP - 6 PB - Springer Science and Business Media LLC AN - OPUS4-62168 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Yang, Fan A1 - Meng, Xiangmeng A1 - Putra, Stephen Nugraha A1 - Bachmann, Marcel A1 - Rethmeier, Michael T1 - Assessment of keyhole stability in laser beam welding with external magnetic field using numerical simulation N2 - The challenge of understanding the physical mechanisms behind porosity reduction by a magnetic field during laser beam welding (LBW) is partly due to the difficulty in quantitatively evaluating keyhole stability. The commonly used index, such as keyhole depth, is typically one-dimensional, which is insufficient to capture the dynamic and three-dimensional fluctuations of the keyhole. In this paper, by utilizing a 3D multiphysical model of LBW with magnetic field, a novel keyhole geometry reconstruction algorithm has been developed to describe the keyhole profile and its fluctuation in a statistical manner to evaluate keyhole stability quantitatively. An equivalent diameter is proposed in this algorithm to reduce the irregularity of the keyhole geometry. The calculation results indicate that the time-averaged keyhole shape over 300 ms in the LBWof steel is conical, regardless of the application of an external magnetic field, which provides a more representative shape. Meanwhile, it is observed from the statistical aspect that the keyhole diameter becomes smaller, except the top part, under the influence of the magnetic field. The standard deviation of the equivalent diameter can be used as a physical variable to assess the keyhole stability quantitatively. The application of an external magnetic field can produce a noticeable reduction of the standard deviation of the equivalent diameter, namely, stabilizing the keyhole during LBW of steel. However, the different contribution from the keyhole stability affected by a magnetic field in suppressing porosity is different with materials. T2 - International Congress of Applications of Lasers & Electro-Optics 2024 CY - Los Angeles, CA, USA DA - 04.11.2024 KW - Deep penetration laser beam welding KW - Numerical simulation KW - Keyhole shape KW - Keyhole stability KW - Magnetic field PY - 2024 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-614984 DO - https://doi.org/10.2351/7.0001528 VL - 36 IS - 4 SP - 1 EP - 7 PB - AIP Publishing CY - Melville, NY AN - OPUS4-61498 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 - Rethmeier, Michael T1 - 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 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-616070 DO - https://doi.org/10.2351/7.0001537 SN - 1042-346X VL - 36 IS - 3 SP - 1 EP - 6 PB - AIP Publishing AN - OPUS4-61607 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Putra, Stephen Nugraha A1 - Meng, Xiangmeng A1 - Yang, Fan A1 - Bachmann, Marcel A1 - Rethmeier, Michael 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 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-616146 DO - https://doi.org/10.1016/j.procir.2024.08.179 VL - 124 SP - 585 EP - 589 PB - Elsevier B.V. CY - Amsterdam AN - OPUS4-61614 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR 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 - CIRP Conference on Photonic Technologies [LANE 2024] CY - Fürth, Germany DA - 15.09.2024 KW - Laser beam welding KW - Aluminum alloy KW - Process Porosity KW - Porosity suppression KW - Magnetohydrodynamic technology PY - 2024 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-616053 DO - https://doi.org/10.1016/j.procir.2024.08.175 VL - 124 SP - 565 EP - 569 PB - Elsevier B.V. AN - OPUS4-61605 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Meng, Xiangmeng A1 - Bachmann, Marcel A1 - Yang, Fan A1 - Rethmeier, Michael T1 - Toward prediction and insight of porosity formation in laser welding: A physics-informed deep learning framework N2 - The laser welding process is an important manufacturing technology for metallic materials. However, its application is often hindered by the occurrence of porosity defects. By far, an accurate prediction of the porosity defects and an insight into its formation mechanism are still challenging due to the highly nonlinear physics involved. In this paper, we propose a physics-informed deep learning (PIDL) framework by utilizing mechanistic modeling and experimental data to predict the porosity level during laser beam welding of aluminum alloys. With a proper selection of the physical variables (features) concerning the solidification, liquid metal flow, keyhole stability, and weld pool geometry, the PIDL model shows great superiority in predicting the porosity ratio, with a reduction of mean square error by 41 %, in comparison with the conventional DL model trained with welding parameters. Furthermore, the selected variables are fused into dimensionless features with explicit physical meanings to improve the interpretability and extendibility of the PIDL model. Based on a well-trained PIDL model, the hierarchical importance of the physical variables/procedures on the porosity formation is for the first time revealed with the help of the Shapley Additive Explanations analysis. The keyhole ratio is identified as the most influential factor in the porosity formation, followed by the downward flow-driven drag force, which offers a valuable guideline for process optimization and porosity minimization. KW - Laser beam welding KW - Physics-informed deep learning KW - Porosity prediction KW - Feature fusion KW - Hierarchical importance PY - 2025 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-624708 DO - https://doi.org/10.1016/j.actamat.2025.120740 VL - 286 SP - 1 EP - 13 PB - Elsevier B.V. AN - OPUS4-62470 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Seitz, Georg A1 - Bantle, Patrick A1 - Biegler, Max A1 - Elsner, Beatrix A. M. A1 - Rethmeier, Michael T1 - An Inherent Strain Method Using Progressive Element Activation for Fast Distortion Calculation in Directed Energy Deposition N2 - The finite element analysis (FEA) simulation of directed energy deposition (DED) processes offers many potential cost savings during the build job optimization process, through, e.g., distortion predictions. However, the biggest challenge is the long calculation time, frequently exceeding the actual build time. One way of simplifying the simulation with the aim of reducing the calculation times is the inherent strain method. While this method is already used commercially in the simulation of powder bed-based processes and conventional welding technologies, its use in DED is still the subject of research. In this work, an inverse determination of an inherent strain is carried out on a 20-layer-high, single-track-wide wall, common theories are reviewed, and an approach based on thermal strain is introduced. As a result, the calculation time could be reduced by 83% and the accuracy remained at 92%. KW - Inherent strain method KW - Simulation KW - Finite element analysis KW - Directed energy deposition KW - Additive manufacturing PY - 2024 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-622595 DO - https://doi.org/10.3390/met14121338 SN - 2075-4701 VL - 14 IS - 12 SP - 1 EP - 12 PB - MDPI AN - OPUS4-62259 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Schmolke, Tobias A1 - Brunner-Schwer, Christian A1 - Biegler, Max A1 - Rethmeier, Michael A1 - Meschut, Gerson T1 - On welding of high-strength steels using laser beam welding and resistance spot weld bonding with emphasis on seam leak tightness N2 - The design of most electric vehicles provides for the positioning of the heavy energy storage units in the underbody of the cars. In addition to crash safety, the battery housing has to meet high requirements for gas tightness. In order to test the use of high-strength steels for this sub-assembly, this paper examines welded joints utilizing resistance spot weld bonding and laser remote welding, with special regard to the gas tightness of the welds. For this purpose, the pressure difference test and helium sniffer leak detection are presented and applied. The combination of both leak test methods has proven ideal in experimental investigations. For laser remote welding, gas-tight seams can be achieved with an inter-sheet gap of 0.1 mm, even if occasionally leaking samples cannot be prevented. Resistance spot welding suits gas-tight joining with both one- and two-component adhesives. Against the background of leak tightness, process fluctuations that lead to weld spatter and defects in the adhesive layer must be prevented with high priority. KW - Resistance spot weld bonding KW - Laser welding KW - Seam leak tightness KW - High-strength steel KW - Leak testing KW - Helium sniffer leak detection PY - 2023 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-624250 DO - https://doi.org/10.3390/jmmp7030116 SN - 2504-4494 VL - 7 IS - 3 SP - 1 EP - 14 PB - MDPI CY - Basel AN - OPUS4-62425 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Yang, Keke A1 - Sowada, Matthias A1 - Olfert, Viktoria A1 - Seitz, Georg A1 - Schreiber, Vincent A1 - Heitmann, Marcel A1 - Hein, David A1 - Biegler, Max A1 - Jüttner, Sven A1 - Rethmeier, Michael A1 - Meschut, Gerson T1 - Influence of liquid metal embrittlement on the failure behavior of dissimilar spot welds with advanced high-strength steel: A component study N2 - This study investigates the effects of liquid metal embrittlement (LME) cracks on the mechanical performance of resistance spot-welded joints in zinc-coated advanced high-strength steel (AHSS) at the component level. To this end, a novel component-level test specimen featuring a hat and L-shaped profile was developed to identify critical failure points under three-point bending loads. Load-bearing capacity tests were subsequently conducted under both quasi-static and impact loading conditions, specifically targeting LME cracks with an average depth reaching 63.6% of the sheet thickness. By monitoring the surface strain of spot welds affected by LME cracks, the study visualizes stress concentration effects at the crack tips and traces the propagation of these cracks into the base material, which ultimately leads to material tearing and joint failure. The findings reveal that the effect of LME cracks in reducing load-bearing capacity is more pronounced under impact loading than under quasi-static loading, highlighting a previously underexplored aspect of LME behavior under impact loading. Specifically, the peak load decreased by 3.9% and 10.8%, while energy absorption declined by 52.2% and 78.3% under quasistatic and impact loading, respectively. KW - Liquid metal embrittlement KW - Resistance spot welding KW - Impact loading KW - Crack propagation KW - Advanced high-strength steel PY - 2024 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-621727 DO - https://doi.org/10.1016/j.jmrt.2024.11.166 VL - 33 SP - 8321 EP - 8328 PB - Elsevier B.V. AN - OPUS4-62172 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Lemke, Josefine A1 - Höfemann, Matthias A1 - Biegler, Max A1 - Rethmeier, Michael T1 - Process strategies for optimizing the cooling behaviour of laser-welded Tailor Welded Blanks made of advanced high strength steels (AHSS) N2 - AHSS with 1000 MPa tensile strength show promising properties for the use in Tailor Welded Blanks (TWBs) to locally strengthen car body parts. Challenges in laser beam welding of the sheets are hardness-drops and -peaks in the heat-affected zone (HAZ) and weld, which cause risks during cold-forming. This happens due to rapid cooling caused by laser welding. A numerical approach aiming for slower cooling rates in the weld region is presented in this article. Laser welded sheets served as reference for setting up a process simulation. Models for pre-heating and a coaxial setup with power split were set up. A correlation between cooling-rate and hardness in the joining zone was established and applied to the modelled strategy. Splitting the power led to a slightly narrower weld seam and experimental pre-heating of the sheets to 600 °C could lower total seam hardening. It achieved a homogenization of the fusion zone. KW - AHSS KW - Laser welding KW - Tailor Welded Blanks KW - Hardness KW - FEM KW - HAZ PY - 2024 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-622324 DO - https://doi.org/10.1016/j.procir.2024.08.176 VL - 124 SP - 570 EP - 573 PB - Elsevier B.V. AN - OPUS4-62232 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Akyel, Fatma A1 - Üstündag, Ömer A1 - Bakir, Nasim A1 - Brunner-Schwer, Christian A1 - Gumenyuk, Andrey A1 - Rethmeier, Michael T1 - Influence of heat input on cooling rates and mechanical properties of laser hybrid welded thick structural steels N2 - Laser hybrid welding presents several challenges when used to weld thick steels. A typical weld is divided into the arcdominated and laser-dominated zone. These zones lead to variations in the mechanical properties of the weld. The laserdominated zone is of particular importance regarding mechanical properties, notably Charpy impact toughness, due to the high cooling rates and the absence of filler wire. The low heat input of the laser can lead to martensitic microstructure causing hardening and deterioration of impact toughness. The high heat input of the arc can lead to grain coarsening and even loss of impact toughness. This study examines the influence of heat input on the cooling rates, microstructure and mechanical properties of single-pass laser hybrid welded steels of S355J2 and EH36 with thicknesses up to 30 mm. The experiments were performed with a 20-kW fibre laser and a contactless electromagnetic weld backing in the butt-joint configuration in 1G welding position. The cooling time was measured in three different locations near the fusion lines corresponding to different heights of the seam using a special configuration with pyrometers, collimators and optical fibres. The test specimens for the Charpy impact testing and tensile testing were extracted in three different depths. The experiments indicated that a heat input of 1.6 kJ/mm–2 kJ/mm, 2 kJ/mm–2.4 kJ/mm and 3.7 kJ/mm were recommended when single-pass laser hybrid welding of 20-, 25-, and 30-mm-thick structural steels regarding the minimum requirements of the mechanical properties, respectively. KW - Laser hybrid welding KW - Heat input KW - Mechanical properties KW - Charpy impact toughness KW - Cooling rate PY - 2025 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-625282 DO - https://doi.org/10.1007/s40194-025-01924-8 SN - 1878-6669 SP - 1 EP - 15 PB - Springer CY - United Kingdom AN - OPUS4-62528 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -