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 - 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 - 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 -