TY - JOUR A1 - Spranger, Felix A1 - Schirdewahn, S. A1 - Kromm, Arne A1 - Merklein, M. A1 - Hilgenberg, Kai T1 - On the influence of TiB2, TiC, and TiN hard particles on the microstructure of localized laser dispersed AISI D2 tool steel surfaces N2 - The control of friction and wear is a major concern in many industrial applications. A promising method for tailored surface modification is the so-called laser implantation technique. This method combines surface texturing and material optimization in one processing step by a localized dispersing of hard ceramic particles using pulsed laser radiation. Wear resistant, protruding micrometric features (implants) with defined geometry can be created in a deterministic pattern where needed on highly stressed surfaces, i.e., on forming or cutting tools. However, in order to maintain the implants over the tool’s lifetime, a suitable selection of hard ceramic particles is a prerequisite. They must provide a defect-free metal matrix composite with a high share of homogeneously distributed particles and, especially, high implant hardness. In this study, TiN, TiC, and TiB2 hard particles were compared as implant materials for the first time. By a systematic variation of pulse power and pulse duration, their dispersing behavior and influence on the material properties of AISI D2 tool steel were investigated. Although all powder materials had grain sizes smaller than 10 μm, it was possible to disperse them by pulsed laser radiation and to obtain defect-free protruding implants. The highest share of dispersed particles (∼64%) was observed for TiB2. By scanning electron microscopy and energy dispersive x-ray spectroscopy, it was also shown that a significant share of the preplaced particles was dissolved by the laser beam and precipitated as nanometer sized particles within the matrix during solidification. These in situ formed particles have a decisive influence on the material properties. While the TiN and TiC implants have shown maximum hardness values of 750 and 850 HV1, the TiB2 implants have shown the highest hardness values with more than 1600 HV1. By x-ray diffraction, it was possible to ascribe the lower hardness values of TiC and TiN implants to high amounts of retained austenite in the metal matrix. By implanting TiB2, the formation of retained austenite was successfully suppressed due to the in situ formation of TiC particles, which was proven by electron backscatter diffraction. In conclusion, all the implant materials are basically suitable for laser implantation on AISI D2 tool steel. However, TiB2 has shown the most promising results. T2 - ICALEO 2019 CY - Orlando, FL, USA DA - 07.10.2019 KW - Laser implantation KW - Surface texturing KW - AISI D2 KW - TiB2 KW - TiN KW - TiC KW - Retained Austenite KW - Localized laser dispersing PY - 2020 DO - https://doi.org/10.2351/7.0000059 VL - 32 IS - 2 SP - 022028 EP - 022028-9 PB - AIP Publishing AN - OPUS4-50712 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - El-Batahgy, A. A1 - Saiyah, A. A1 - Khafagi, S. A1 - Gumenyuk, Andrey A1 - Gook, S. A1 - Rethmeier, Michael T1 - Shielded metal arc welding of 9%Ni steel using matching ferritic filler metal N2 - Motivated by the tensile strength loss of 9%Ni steel arc welded joints made using Ni-based austenitic filler metals, the feasibility of maintaining the tensile strength using matching ferritic filler metal has been demonstrated. In comparison with shielded metal arc welded joint made using Ni-based austenitic electrode ENiCrMo-6, higher tensile strength comparable to that of the base metal was obtained using matching ferritic electrode. Besides, sufficient impact toughness energies with much lower mismatch were obtained for weld metal and heat-affected zone. Welded joint with a lower mechanical mismatching is of considerable importance for achieving acceptable combination of tensile strength and impact toughness.Abetter combination of These mechanical properties is ensured by applying a post weld heat treatment. KW - Mechanical mismatching KW - Mechanical properties KW - Microstructure KW - Austenitic welding electrode KW - Matching ferritic welding electrode PY - 2020 DO - https://doi.org/10.1080/13621718.2020.1846936 SN - 1362-1718 SP - 1 EP - 7 PB - Taylor & Francis AN - OPUS4-51835 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Heßmann, Jennifer A1 - Bachmann, Marcel A1 - Hilgenberg, Kai T1 - Numerical and experimental investigation of controlled weld pool displacement by electromagnetic forces for joining dissimilar materials N2 - In order to reduce CO2 emissions, an increasing interest in lightweight construction exists in the automotive industry, especially the multi-material-design approach. The main construction materials here are steels and aluminium alloys. Due to their different physical material properties and limited mutual solubility, these two materials cannot be joined thermally without difficulty. This paper presents a new joining approach for dissimilar materials. It uses electromagnetic displacement of a laser-generated melt pool to produce overlap joints between 1 mm steel (1.0330) and 2 mm aluminium alloy (EN AW 5754). Contactless induced Lorentz forces are generated by an alternating current (AC) magnet system. The controlled displacement of the aluminium alloy melt into the hole of the overlying steel sheet is investigated through numerical and experimental studies. The numerical results are compared with cross sections and thermocouple measurements. For the first time, it is possible to achieve a reproducible controlled melt pool displacement on thin sheets to produce overlap joints between dissimilar materials. KW - Displacement KW - Laser beam welding KW - Dissimilar materials KW - Joining technology KW - Electromagnetic field KW - Lorentz force KW - Numerical investigation PY - 2020 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-516640 DO - https://doi.org/10.3390/met10111447 VL - 10 IS - 11 SP - 1447 EP - 1462 PB - MDPI CY - Basel, Schweiz AN - OPUS4-51664 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Ivanov, S. A1 - Artinov, Antoni A1 - Zemlyakov, E. A1 - Karpov, I. A1 - Rylov, S. A1 - Em, V. T1 - Spatiotemporal Evolution of Stress Field during Direct Laser Deposition of Multilayer Thin Wall of Ti-6Al-4V N2 - The present work seeks to extend the level of understanding of the stress field evolution during direct laser deposition (DLD) of a 3.2 mm thick multilayer wall of Ti-6Al-4V alloy by theoretical and experimental studies. The process conditions were close to the conditions used to produce large-sized structures by the DLD method, resulting in specimens having the same thermal history. A simulation procedure based on the implicit finite element method was developed for the theoretical study of the stress field evolution. The accuracy of the simulation was significantly improved by using experimentally obtained temperature-dependent mechanical properties of the DLD-processed Ti-6Al4V alloy. The residual stress field in the buildup was experimentally measured by neutron diffraction. The stress-free lattice parameter, which is decisive for the measured stresses, was determined using both a plane stress approach and a force-momentum balance. The influence of the inhomogeneity of the residual stress field on the accuracy of the experimental measurement and the validation of the simulation procedure are analyzed and discussed. Based on the numerical results it was found that the non-uniformity of the through-thickness stress distribution reaches a maximum in the central cross-section, while at the buildup ends the stresses are distributed almost uniformly. The components of the principal stresses are tensile at the buildup ends near the substrate. Furthermore, the calculated equivalent plastic strain reaches 5.9% near the buildup end, where the deposited layers are completed, while the plastic strain is practically equal to the experimentally measured ductility of the DLD-processed alloy, which is 6.2%. The experimentally measured residual stresses obtained by the force-momentum balance and the plane stress approach differ slightly from each other. KW - Direct laser deposition KW - Finite element simulation KW - Neutron diffraction KW - Residual stresses KW - Ti-6Al-4V KW - Mechanical properties PY - 2022 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-542444 DO - https://doi.org/10.3390/ma15010263 VL - 15 IS - 263 SP - 1 EP - 20 PB - MDPI AN - OPUS4-54244 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 DO - 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 - Meng, Xiangmeng A1 - Putra, Stephen Nugraha A1 - Bachmann, Marcel A1 - Rethmier, Michael T1 - Influence of the spatial laser energy absorption on the molten pool dynamics in high-power laser beam welding N2 - The spatial laser energy absorption inside the keyhole is decisive for the dynamic molten pool behaviors and the resultant weld properties in high-power laser beam welding (LBW). In this paper, a numerical simulation of the LBW process, considering the 3D transient heat transfer, fluid flow, and keyhole dynamics, is implemented, in which the free surface is tracked by the volume-of-fluid algorithm. The underlying laser-material interactions, i.e., the multiple reflections and Fresnel absorption, are considered by an advanced ray-tracing method based on a localized level-set strategy and a temperature-dependent absorption coefficient. The laser energy absorption is analyzed from a time-averaged point of view for a better statistical representation. It is found for the first time that a significant drop in the time-averaged laser energy absorption occurs at the focus position of the laser beam and that the rest of the keyhole region has relatively homogeneous absorbed energy. This unique absorption pattern may lead to a certain keyhole instability and have a strong correlation with the detrimental bulging and narrowing phenomena in the molten pool. The influence of different focus positions of the laser beam on the keyhole dynamics and molten pool profile is also analyzed. The obtained numerical results are compared with experimental measurements to ensure the validity of the proposed model. KW - Laser beam welding KW - Laser energy absorption KW - Molten pool KW - Keyhole dynamics KW - Numerical modeling PY - 2023 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-587531 DO - https://doi.org/10.2351/7.0001078 SN - 1042-346X VL - 35 IS - 4 SP - 1 EP - 8 PB - AIP Publishing AN - OPUS4-58753 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Yang, Chunliang A1 - Yan, Fan A1 - Meng, Xiangmeng A1 - Putra, Stephen Nugraha A1 - Bachmann, Marcel A1 - Rethmeier, Michael T1 - Phase-field simulation of the dendrite growth in aluminum alloy AA5754 during alternating current electromagnetic stirring laser beam welding N2 - Electromagnetic stirring is known to promote material flow, reduce porosity, uniform elements distribution, and refine grain in laser beam welding (LBW), which enhances the applicability of LBW in various industries. In this study, a phase-field model of dendrite growth in AA5754 Al alloy electromagnetic stirring laser beam welding was established. The model considered the thermal electromagnetic Lorentz force resulting from the interaction between the electric field generated by the Seebeck effect and the magnetic field, as well as the temperature gradient and solidification rate of the solidification interface obtained from the computational fluid dynamics electromagnetic stirring LBW model. The variation rules of dendrite growth with different magnetic parameters and effects are analyzed. Comprehensively, the magnetic field promotes the solidification rate, thus promoting interfacial instability and a large magnetic flux density leads to a faster interface instability. The solidification rate as well as the temperature gradient affect the growth rate, and the accelerated growth caused by the so lidification rate with a high frequency and a large magnetic flux density effectively inhibits the slow growth caused by the temperature gradient. The thermal electromagnetic Lorentz force is the main factor for the branch increment at low frequencies, while both thermal electromagnetic Lorentz force and temperature gradient in crease the number of branches at high frequencies. The calculated average branch numbers considering various factors in the stable stage under different magnetic parameters were consistent with the results of the scanning electron microscope tests. KW - Laser beam welding KW - Electromagnetic KW - Aluminum alloys KW - Phase field method KW - Dendrite growth PY - 2024 DO - https://doi.org/10.1016/j.ijheatmasstransfer.2023.124754 SN - 0017-9310 VL - 218 SP - 1 EP - 16 PB - Elsevier Ltd. AN - OPUS4-58489 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Zhang, X. A1 - Shi, L. A1 - Wu, C. A1 - Yang, Chunliang A1 - Gao, S. T1 - Multi-phase modelling of heat and mass transfer during Ti/Al dissimilar friction stir welding process N2 - Friction stir welding (FSW) has the capacity to join the Al/Ti dissimilar structures with superior mechanical properties. The microstructures and mechanical characteristics of Al/Ti dissimilar FSW joints are determined by the heat and mass transfer during the welding process. However, a quantitative study of the Al/Ti dissimilar FSW process is lacking. Therefore, using the computational fluid dynamics (CFD) and volume of fluid (VOF) approach, a multi-phase model was constructed for quantitatively analyzing the heat and mass transfer behaviour in dissimilar FSW of TC4 titanium alloy and AA2024-T4 aluminium alloy. The mixed material was treated as a functionally graded material (FGM) to compute the thermophysical characteristics at the weld nugget zone (WNZ). Due to the vast disparity in the thermophysical characteristics of aluminum and titanium alloy, the temperature field in Al/Ti dissimilar FSW was severely asymmetric. The temperature of titanium alloy on the advancing side (AS) was higher than that of aluminium alloy on the retreating side (RS) at the same distance from the tool centre line near the tool shoulder, but it was lower than that of aluminium alloy on the RS without the influence of the shoulder. Due to the high flow stress of titanium alloy, plastic material flow mostly occurred on the RS of aluminium alloy in the Al/Ti dissimilar FSW, with its percentage exceeding 80%. This model was validated by experiment results. KW - Dissimilar friction stir welding KW - Al/Ti dissimilar joints KW - Temperature distribution KW - Heat generation KW - Plastic material flow PY - 2023 DO - https://doi.org/10.1016/j.jmapro.2023.03.037 SN - 2212-4616 VL - 94 SP - 240 EP - 254 PB - Elsevier Ltd. AN - OPUS4-57265 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Diller, Johannes A1 - Siebert, Ludwig A1 - Winkler, Michael A1 - Siebert, Dorina A1 - Blankenhagen, Jakob A1 - Wenzler, David A1 - Radlbeck, Christina A1 - Mensinger, Martin T1 - An integrated approach for detecting and classifying pores and surface topology for fatigue assessment 316L manufactured by powder bed fusion of metals using a laser beam using μ$$ \mu $$CT and machine learning algorithms N2 - AbstractThis research aims to detect and analyze critical internal and surface defects in metal components manufactured by powder bed fusion of metals using a laser beam (PBF‐LB/M). The aim is to assess their impact on the fatigue behavior. Therefore, a combination of methods, including image processing of micro‐computed tomography (CT) scans, fatigue testing, and machine learning, was applied. A workflow was established to contribute to the nondestructive assessment of component quality and mechanical properties. Additionally, this study illustrates the application of machine learning to address a classification problem, specifically the categorization of pores into gas pores and lack of fusion pores. Although it was shown that internal defects exhibited a reduced impact on fatigue behavior compared with surface defects, it was noted that surface defects exert a higher influence on fatigue behavior. A machine learning algorithm was developed to predict the fatigue life using surface defect features as input parameters. KW - Fatigue KW - Machine learning KW - Micro-computed tomography KW - Powder bed fusion of metals using a laser beam KW - Quality assurance PY - 2024 DO - https://doi.org/10.1111/ffe.14375 SN - 8756-758X SP - 1 EP - 16 PB - John Wiley & Sons Ltd. AN - OPUS4-60593 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Marko, A. A1 - Bähring, S. A1 - Raute, J. A1 - Biegler, M. A1 - Rethmeier, Michael T1 - Transferability of ANN-generated parameter sets from welding tracks to 3D-geometries in Directed Energy Deposition N2 - Directed energy deposition (DED) has been in industrial use as a coating process for many years. Modern applications include the repair of existing components and additive manufacturing. The main advantages of DED are high deposition rates and low energy input. However, the process is influenced by a variety of parameters affecting the component quality. Artificial neural networks (ANNs) offer the possibility of mapping complex processes such as DED. They can serve as a tool for predicting optimal process parameters and quality characteristics. Previous research only refers to weld beads: a transferability to additively manufactured three-dimensional components has not been investigated. In the context of this work, an ANN is generated based on 86 weld beads. Quality categories (poor, medium, and good) are chosen as target variables to combine several quality features. The applicability of this categorization compared to conventional characteristics is discussed in detail. The ANN predicts the quality category of weld beads with an average accuracy of 81.5%. Two randomly generated parameter sets predicted as “good” by the network are then used to build tracks, coatings,walls, and cubes. It is shown that ANN trained with weld beads are suitable for complex parameter predictions in a limited way. KW - Welding parameter KW - Quality assurance KW - DED KW - Artificial neural network KW - Additive manufacturing PY - 2022 DO - https://doi.org/10.1515/mt-2022-0054 SN - 0025-5300 VL - 64 IS - 11 SP - 1586 EP - 1596 PB - De Gruyter AN - OPUS4-56278 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Shi, L. A1 - Chen, J. A1 - Yang, Chunliang A1 - Chen, G. A1 - Wu, C. T1 - Thermal-fluid-structure coupling analysis of void defect in friction stir welding N2 - Understanding the void defect formation mechanism and simultaneous predicting the tool service life in friction stir welding are critical for optimizing the welding parameters. However, the void defect formation mechanism in friction stir welding is not yet elucidated. In this study, a novel integrated thermal-fluid-structure coupling model of the friction stir welding process was proposed for simultaneous prediction of the weld formation and tool service life. A new non-uniform distribution model of the tool-workpiece contact pressure was proposed to describe the interaction between the tool and the workpiece. The void defect formation mechanism was quantitatively studied using the proposed integrated thermal-fluid-structure coupling model. The results show that the plastic material flows in the horizontal direction and can completely fill the cavity behind the tool for the welding condition of forming a sound weld. While the tool-workpiece contact interfacial frictional shear stress in the rear of the tool is decreased significantly which leads to a severe decrease in the plastic material flow velocity. Therefore, after bypassing the tool from the retreating side, the plastic material at the bottom of the weld stagnates, and void defect forms in the middle and lower part of the weld at the advancing side. The difference between the maximum and the minimum tool-workpiece contact pressure could serve as a numerical criterion to predict void defects. A sound joint is formed when the difference is lower than the critical value of 15 MPa, while a void defect is formed in the weld if it is higher than this critical value. The maximum equivalent stress acting on the tool is located at the pin root with severe stress concentration at a high welding speed. The front of the tool is subjected to tensile stress while its rear is subjected to compressive stress, therefore the tool is apt to fracture at its root under an inappropriate welding condition. The average normal stress of the tool varies periodically with its period consistent with the rotation period of the tool. The service life of the tool is decreased with the increase in welding speed and the decrease in rotation speed. The model is validated by experimental results. KW - Friction stir welding KW - Thermal-fluid-structure coupling model KW - Tool-workpiece interaction KW - Void defect formation mechanism KW - Tool service life PY - 2023 DO - https://doi.org/10.1016/j.ijmecsci.2022.107969 SN - 0020-7403 VL - 241 SP - 1 EP - 17 PB - Elsevier Ltd. AN - OPUS4-56929 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kempf, A. A1 - Hilgenberg, Kai T1 - Influence of sub-cell structure on the mechanical properties of AlSi10Mg manufactured by laser powder bed fusion N2 - AlSi10Mg is one of the most applied alloys for laser powder bed fusion (LPBF) technology, due to its great possibilities for implementing new lightweight concepts such as in automotive industries. For the component design it is necessary to know about the mechanical properties and the mechanical behaviour. The many published strength properties of LPBF processed AlSi10Mg show significant differences up to approximately 225 MPa in ultimate tensile strength (UTS) and 195 MPa in yield strength (YS). To understand these varying properties, a ring trial was carried out manufacturing specimens on 6 LPBF machines with different parameters and build-up strategies. They were studied in the as-built (AB) condition and after heat treatment at 300 °C for 30 min, respectively. For examining the mechanical properties, tensile tests and hardness measurements were carried out. The microstructure was characterized by optical light microscopy (OM), field emission scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD) and electron backscatter diffraction (EBSD). The identified differences in strength properties were discussed based on the 4 strengthening mechanism known for metallic materials and at the background of material defects. It was found that the size of the typical sub-cell structure of LPBF AlSi10Mg affected substantially the mechanical properties in the AB condition, in which with decreasing sub-cell size strength increased. If heat treatment was applied, the strength properties decreased and did not differ anymore. Since annealing led to coarsened sub-cells, whereas the grains itself did not change in size, the influence of sub-cell structure on strength was further confirmed. In addition, acicular precipitates in the AB condition were observed at specimens from one LPBF machine showing the lowest tensile elongation. KW - Laser powder bed fusion KW - AlSi10Mg KW - Mechanical properties KW - Microstructure PY - 2020 DO - https://doi.org/10.1016/j.msea.2020.138976 VL - 776 SP - Paper 138976, 12 PB - Elsevier B.V. AN - OPUS4-50316 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 process porosity suppression by magnetohydrodynamic technology during the laser beam welding of aluminum alloy N2 - Magnetohydrodynamic (MHD) technology is acknowledged as a promising method for mitigating the porosity defects in laser-welded joints of aluminum alloys. A transient 3D multi-physical numerical model of laser beam welding (LBW), coupled with the MHD and oscillating metal vapor plume model, is developed to study the suppression mechanisms of process porosity by an external magnetic field. The experimental results demonstrate that the porosity ratio is reduced by 93.5 % as the oscillating magnetic field is applied. This significant reduction confirms the effectiveness of the MHD technology in suppressing porosity defects. A downward time-averaged Lorentz force is induced in the weld pool, which affects the fluid flow pattern and the weld pool profile. The change of the flowing pattern in the weld pool by the magnetic field does not always have a positive effect on the porosity suppression. In addition, an analytical model shows that the bubble escape window is expanded by 62 % under the effect of the oscillating magnetic field. The additional upward velocity provided by the electromagnetic expulsive force on the bubbles and the change of weld pool profile are considered favorable factors in eliminating the porosity defects. The numerical and analytical model developed for analyzing the bubble escape window have been validated by experimental results. KW - Laser beam welding KW - Aluminum alloy KW - Process porosity defects KW - Magnetohydrodynamic technology KW - Bubble escape KW - Numerical simulation PY - 2025 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-637642 DO - https://doi.org/10.1016/j.ijheatmasstransfer.2025.127525 SN - 0017-9310 VL - 253 SP - 1 EP - 13 PB - Elsevier Ltd. AN - OPUS4-63764 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Artinov, Antoni A1 - Karkhin, V. A1 - Bachmann, Marcel A1 - Rethmeier, Michael T1 - Mathematical modeling of the geometrical differences between the weld end crater and the steady-state weld pool N2 - The geometrical characteristics of the weld end crater are commonly used as a means of validating numerical results in welding simulations. In this paper, an analytical model is developed for calculating the cooling stage of the welding process after the moving energy source is turned off. Solutions for various combinations of heat sources and heated bodies are found. It is shown that after turning off the Energy source, additional melting of the base material in the longitudinal direction may occur due to the overheated liquid metal. The developed technique is applied to complete-penetration keyhole laser beam welding of 2 mm thick austenitic stainless-steel plate 316L at a Welding speed of 20 mm/s and a laser power of 2.3 kW. The results show a theoretical increase in the weld end crater length of up to 19% compared to the length of the steady-state weld pool. It is found that at the moment of switch off, the weld end crater center, where solidification of the liquid metal ends, is shifted from the heat source axis toward the weld pool tail. The solidification rate and the direction of crystallization of the molten material during the welding process and those in the weld end crater differ significantly. A good agreement between the computational results and the welding experiments is achieved. KW - Weld end crater KW - Steady-state weld pool KW - Mathematical modeling KW - Solidification KW - Laser beam welding PY - 2020 DO - https://doi.org/10.2351/7.0000068 VL - 32 IS - 2 SP - 022024-1 EP - 022024-6 PB - AIP Publishing AN - OPUS4-50767 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Yang, Keke A1 - Wang, Zhuoqun A1 - Haak, Viktor A1 - Olfert, Viktoria A1 - El-Sari, Bassel A1 - Hein, David A1 - Biegler, Max A1 - Rethmeier, Michael A1 - Meschut, Gerson T1 - A novel welding schedule for expanding the expulsion-free process window in resistance spot welding of dissimilar joints with ultra-high strength steel N2 - This study introduces a novel approach to expanding the maximum expulsion-free process window in resistance spot welding (RSW) of dissimilar joints between ultra-high strength steel (UHSS) and mild steel. Quantitative analysis revealed that expulsion is driven by the interaction between nugget growth rate and plastic shell thickness. Based on this finding, the welding schedule was optimized by applying a preheating current to form an initial plastic shell, followed by a ramp-up current profile during the main welding phase. Welding simulations indicated that the ramp-up current slowed nugget growth, improved plastic shell formation, and prevented nugget breakthrough, thereby reducing the risk of expulsion. Experimental validation showed a 19 % increase in maximum expulsion-free heat input, with the nugget diameter increasing by 7.6 % to 8.94 mm compared to the reference welding schedule. Furthermore, even when expulsion occurred beyond the process window, this optimization delayed its occurrence, minimizing its impact on spot weld quality. Finally, the optimized welding schedule also exhibited significant robustness. Despite a 2 mm initial gap disturbance, the maximum expulsionfree heat input increased by 57 %, while the nugget diameter grew by 30 % to 8.92 mm. These results confirm that the proposed approach effectively extends the process window by preventing expulsion and enhances process stability. KW - Expulsion KW - Resistance spot welding KW - Finite element modelling KW - Preheating KW - Ultra-high-strength steel PY - 2025 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-626877 DO - https://doi.org/10.1016/j.jmapro.2025.02.009 SN - 2212-4616 VL - 137 SP - 306 EP - 309 PB - Elsevier BV AN - OPUS4-62687 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Artinov, Antoni A1 - Meng, Xiangmeng A1 - Bachmann, Marcel A1 - Rethmeier, Michael T1 - Study on the transition behavior of the bulging effect during deep penetration laser beam welding N2 - The present work is devoted to the study of the transition behavior of the recently confirmed widening of the weld pool, known as the bulging effect, during high-power deep penetration laser beam welding of thick unalloyed steel sheets. A three-dimensional transient multi-physics numerical model is developed, allowing for the prediction of the bulge formation and the study of its temporal behavior. The model is generalized to account automatically for the transition from partial to complete penetration. Several experimental measurements and observations, such as drilling period, weld pool length, temperature, efficiency, and metallographic cross-sections are used to verify the model and assure the plausibility of the numerical results. The analysis of the calculated temperature and velocity distributions, as well as the evolution of the keyhole geometry, shows that the formation of a bulging region strongly depends on the penetration depth of the weld. Based on the numerical results, the bulge is found to occur transiently, having its transition from a slight bulge to a fully developed bulging between penetration depths of 6 mm and 9 mm, respectively. KW - Laser beam welding KW - Deep penetration KW - Bulge formation KW - Numerical modeling PY - 2022 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-545067 DO - https://doi.org/10.1016/j.ijheatmasstransfer.2021.122171 VL - 184 SP - 122171 PB - Elsevier Ltd. AN - OPUS4-54506 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Bachmann, Marcel A1 - Meng, Xiangmeng A1 - Artinov, Antoni A1 - Rethmeier, Michael T1 - Elucidation of the Bulging Effect by an Improved Ray-Tracing Algorithm in Deep Penetration Wire Feed Laser Beam Welding and its Influence on the Mixing Behavior N2 - Herein, an improved ray-tracing routine using a virtual mesh refinement approach is adopted in a 3D transientmultiphysics computational fluid Dynamics model for deep penetration wire feed laser beam welding. In a previous study, it was shown that the improved localization of the reflection points of the subrays within the keyhole leads to a more realistic development of the keyhole Depth being validated with experimental results. Another effect investigated in Detail herein is a drastic change in the flow behavior in the weld pool, which promotes the occurrence of a necking area in the solidification line and subsequent bulging under specific circumstances. This has a detrimental effect on the filler material element transport in the weld pool, leading to an inhomogeneous dilution of the added material. The numerical observations are backed up by experimentally obtained data, allowing to provide a clear physics-based explanation of the reduced mixing behavior of the filler wire in the melt pool. KW - Bulging effects KW - Numerical welding simulations KW - Ray-tracing methods KW - Wire feed laser beam welding PY - 2022 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-543322 DO - https://doi.org/10.1002/adem.202101299 SP - 1 EP - 9 PB - Wiley AN - OPUS4-54332 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Marko, A. A1 - Bähring, S. A1 - Raute, J. A1 - Biegler, M. A1 - Rethmeier, Michael T1 - Quality Prediction in Directed Energy Deposition Using Artificial Neural Networks Based on Process Signals N2 - The Directed Energy Deposition process is used in a wide range of applications including the repair, coating or modification of existing structures and the additive manufacturing of individual parts. As the process is frequently applied in the aerospace industry, the requirements for quality assurance are extremely high. Therefore, more and more sensor systems are being implemented for process monitoring. To evaluate the generated data, suitable methods must be developed. A solution, in this context, was the application of artificial neural networks (ANNs). This article demonstrates how measurement data can be used as input data for ANNs. The measurement data were generated using a pyrometer, an emission spectrometer, a camera (Charge-Coupled Device) and a laser scanner. First, a concept for the extraction of relevant features from dynamic measurement data series was presented. The developed method was then applied to generate a data set for the quality prediction of various geometries, including weld beads, coatings and cubes. The results were compared to ANNs trained with process parameters such as laser power, scan speed and powder mass flow. It was shown that the use of measurement data provides additional value. Neural networks trained with measurement data achieve significantly higher prediction accuracy, especially for more complex geometries. KW - DED KW - Artificial neural network KW - Process monitoring KW - Quality assurance KW - Data preparation PY - 2022 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-547039 DO - https://doi.org/10.3390/app12083955 VL - 12 IS - 8 SP - 1 EP - 13 PB - MDPI AN - OPUS4-54703 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Straße, Anne A1 - Gumenyuk, Andrey A1 - Rethmeier, Michael T1 - Study on Duplex Stainless Steel Powder Compositions for the Coating of thick Plates of Laser Beam Welding N2 - Duplex stainless steels combine the positive properties of its two phases, austenite and ferrite. Due to its good corrosion resistance, high tensile strength, and good ductility, it has multiple applications. But laser beam welding of duplex steels changes the balanced phase distribution in favor of ferrite. This results in a higher vulnerability to corrosion and a lower ductility. Herein, different powder combinations consisting of duplex and nickel for coating layers by laser metal deposition (LMD) are investigated. Afterward, laser tracks are welded, and the temperature cycles are measured. The ferrite content of the tracks is analyzed by feritscope, metallographic analysis, and electron backscatter diffraction. The goal is the development of a powder mixture allowing for a duplex microstructure in a two-step process, where first the edges of the weld partners are coated with the powder mixture by LMD and second those edges are laser beam welded. The powder mixture identified by the pretests is tested in the two-step process and analyzed by metallographic analysis, energy-dispersive X-ray spectroscopy, and Vickers hardness tests. The resulting weld seams show a balanced duplex microstructure with a homogenous nickel distribution and a hardness of the weld seam similar to the base material. KW - Duplex AISI 2205 KW - Laser metal deposition KW - Laser beam welding KW - Nickel KW - Stainless steels PY - 2022 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-547024 DO - https://doi.org/10.1002/adem.202101327 SN - 1438-1656 SP - 1 EP - 11 PB - Wiley-VCH CY - Weinheim AN - OPUS4-54702 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Geisen, O. A1 - Müller, V. A1 - Graf, B. A1 - Rethmeier, Michael T1 - Integrated weld preparation designs for the joining of L‑PBF and conventional components via TIG welding N2 - size limitations and high production costs of L-PBF make it competitive for smaller, highly complex components, while the less complex elements of an assembly are manufactured conventionally. This leads to scenarios that use L-PBF only where it’s beneficial, and it require an integration and joining to form the final product. For example, L-PBF combustion swirlers are welded onto cast parts to produce combustion systems for stationary gas turbines. Today, the welding process requires complex welding fixtures and tack welds to ensure the correct alignment and positioning of the parts for repeatable weld results. In this paper, L-PBF and milled weld preparations are presented as a way to simplify the Tungsten inert gas (TIG) welding of rotationally symmetrical geometries using integrated features for alignment and fixation. Pipe specimens with the proposed designs are manufactured in Inconel 625 using L-PBF and milling. The pipe assembly is tested and TIG welding is performed for validation. 3D scans of the pipes before and after welding are evaluated, and the weld quality is examined via metallography and computed tomography (CT) scans. All welds produced in this study passed the highest evaluation group B according to DIN 5817. Thanks to good component alignment, safe handling, and a stable welding process, the developed designs eliminate the need for part-specific fixtures, simplify the process chain, and increase the process reliability. The results are applicable to a wide range of components with similar requirements. KW - L-PBF KW - AM feature integration KW - TIG welding KW - Integrated alignment features KW - Pipe weld preparation KW - Dissimilar joints KW - Inconel 625 PY - 2022 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-547042 DO - https://doi.org/10.1007/s40964-021-00221-2 SN - 2363-9512 SP - 1 EP - 11 PB - Springer AN - OPUS4-54704 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -