TY - CONF A1 - Pavlov, V.A. A1 - Zavialov, S.V. A1 - Bakir, Nasim A1 - Gumenyuk, Andrey A1 - Rethmeier, Michael T1 - Development of a measuring technology of strain field in welds N2 - In the article considered the problem of hot cracks occurrence during laser welding process. The main reason of their appearance is strain. The optical method for measuring full field strain locally near the solidification front during laser welding process is proposed. The proposed method of optical measurement allows to determine the real values of the critical strain for various materials characterizing the occurrence of hot cracks in laser welding process. T2 - 20th international conference "Digital signal processing and applications DSPA-2018" CY - Moskau, Russia DA - 28.03.2018 KW - Solidification cracking KW - Critical strain KW - Strain rate KW - Optical measurement KW - Laser welding KW - In situ strain PY - 2018 SN - 978-5-905278-33-4 SP - 749 EP - 754 AN - OPUS4-44910 LA - rus AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Biegler, M. A1 - Wang, J. A1 - Graf, B. A1 - Rethmeier, Michael T1 - Automated tool-path generation for rapid manufacturing and numerical simulation of additive manufacturing LMD geometries N2 - In additive manufacturing (AM) Laser Metal Deposition (LMD), parts are built by welding layers of powder feedstock onto a substrate. Applications for steel powders include forging tools and structural components for various industries. For large parts, the choice of tool-paths influences the build-rate, the part performance and the distortions in a highly geometry-dependent manner. With weld-path lengths in the range of hundreds of meters, a reliable, automated tool path generation is essential for the usability of LMD processes. In this contribution, automated tool-path generation approaches are shown and their results are discussed for arbitrary geometries. The investigated path strategies are the classical approaches: “Zig-zag-” and “contour-parallel-strategies”. After generation, the tool-paths are automatically formatted into g-code for experimental build-up and ASCII for a numerical simulation model. Finally, the tool paths are discussed in regards to volume-fill, microstructure and porosity for the experimental samples. This work presents a part of the IGF project 18737N “Welding distortion simulation” (FOSTA P1140) T2 - 4th European Steel Technology and Application Days CY - Dusseldorf, Germany DA - 24.06.2019 KW - Additive manufacturing KW - Directed Energy Deposition KW - Path planning KW - DED KW - Mechanical properties KW - Porosity PY - 2019 SP - 1 AN - OPUS4-50045 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Petrat, T. A1 - Brunner-Schwer, C. A1 - Graf, B. A1 - Rethmeier, Michael T1 - Microstructure of Inconel 718 parts with constant mass energy input manufactured with direct energy deposition N2 - The laser-based direct energy deposition (DED) as a technology for additive manufacturing allows the production of near net shape components. Industrial applications require a stable process to ensure reproducible quality. Instabilities in the manufacturing process can lead to faulty components which do not meet the required properties. The DED process is adjusted by various parameters such as laser power, velocity, powder mass flow and spot diameter, which interact with each other. A frequently used comparative parameter in welding is the energy per unit length and is calculated from the laser power and the velocity in laser welding. The powder per unit length comparative parameter in the DED process has also be taken into account, because this filler material absorbs energy in addition to the base material. This paper deals with the influence of mass energy as a comparative parameter for determining the properties of additively manufactured parts. The same energy per unit length of 60 J/mm as well as the same powder per unit length of 7.2 mg/mm can be adjusted with different parameter sets. The energy per unit length and the powder per unit length determine the mass energy. The laser power is varied within the experiments between 400 W and 900 W. Energy per unit length and powder per unit length are kept constant by adjusting velocity and powder mass flow. Using the example of Inconel 718, experiments are carried out with the determined parameter sets. In a first step, individual tracks are produced and analyzed by means of micro section. The geometry of the tracks shows differences in height and width. In addition, the increasing laser power leads to a higher dilution of the base material. To determine the suitability of the parameters for additive manufacturing use, the individual tracks are used to build up parts with a square base area of 20x20 mm². An investigation by Archimedean principle shows a higher porosity with lower laser power. By further analysis of the micro sections, it can be seen that at low laser power, connection errors occur between the tracks. The results show that laser power, velocity and powder mass flow have to be considered in particular, because a constant mass energy can lead to different geometric as well as microscopic properties. KW - Direct energy deposition KW - Porosity KW - Inconel 718 KW - Additive manufacturing KW - Laser metal deposition PY - 2019 SN - 2351-9789 SP - 1 EP - 12 PB - Elsevier B.V. AN - OPUS4-50007 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Fritzsche, André A1 - Hilgenberg, Kai A1 - Rethmeier, Michael T1 - Influence of welding parameters on electromagnetic supported degassing of die-casted and wrought aluminum N2 - The paper describes a systematic investigation of the EM influenced laser beam welding of the aluminum die casting alloy AlSi12(Fe) in comparison to a reference material, a wrought aluminum alloy AlMg3. By using of a face centred CCD test plan, the influencing variables laser power, welding velocity and magnetic flux density are varied with regard to their influence on the remaining porosity. The global pore fraction of the weld seams was analyzed by X-ray images with ImageJ. This enabled a qualitatively very good regression model to be derived for the respective material, which identifies the dominant influencing variables. The results prove, statistically verified, for the investigated parameter range, that - the magnetic flux density is the main cause for the porosity reduction, - the porosity rises with increasing laser power the porosity in the weld seams rises, - the influence of the welding velocity is negligible, - the pore quantity in wrought alloy is more strongly minimized by the magnetic flux density than in die casting, - the porosity decreases due to the EM influence by approx. 70 % compared to the unaffected welds. This effect is emphasized by the contour line charts, which illustrate the relationship between laser power and magnetic flux density. With the exception of the quadratic influence of B at the wrought alloy, the statistical correlation shows a linear development of the respective influence variables for both aluminum alloys. In order to investigate these deviations, further simulations with a focus on weld pool geometry and weld pool flow are to be performed. In addition, the welding results can be classified in accordance with DIN EN ISO 13919-2 in the highest evaluation group B for AlMg3 and in evaluation group C for AlSi12(Fe) by applying a magnetic flux density of 350 mT. The analysis of the CT images at constant laser power and welding velocity allows a direct comparison both between the two alloys and also as a function of the magnetic flux density with regard to the number and size of pores. An increase in the magnetic flux density leads to a significant decrease in the number and volume of pores, which can be seen more clearly in wrought alloy than in die casting. Very acceptable results can be achieved for both materials and different welding parameters. This successfully demonstrates the desired process robustness and functionality of the EM system for practical applications. For subsequent investigations of overlap joints, the lowest possible laser power and a high magnetic flux density are recommended. T2 - 38th International Congress on Applications of Lasers & Electro-Optics CY - Orlando, FL, USA DA - 07.10.2019 KW - AISI D2 KW - Laser implantation KW - Surface texturing KW - TiB2 PY - 2019 SN - 978-1-940168-1-42 SP - Paper Macro 1202 AN - OPUS4-50009 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Rethmeier, Michael A1 - Gook, S. A1 - Üstündag, Ömer A1 - Gumenyuk, Andrey T1 - Vermeidung von Schweißimperfektionen im Überlappbereich bei laserstrahlhybrid-geschweißten Rundnähten N2 - Schwerpunkte: Strategie zur Vermeidung von Schweißimperfektionen im Überlappbereich beilaserhybridgeschweißten Rundnähten für 9.5 mm dicke Rohre. Anpassung der Laserleistung in Kombination mit der Defokussierung des Laserstrahls sowie einer Endkraterfüllung am Ende der Schweißnaht führte zu einer besseren Nahtausbildung. Herausrampung der Energie des Schweißprozesses, sodass ein Übergang von Durchschweißung zu einer Einschweißung mit gewünschter kelchförmiger Nahtgeometrie stattfand. Einstellung eines Wärmestaus durch Defokussierung und Verschiebung des Laserstrahls führt zu einem gut ausgebildeten Überlappbereich ohne Poren, Risse. Schweißungen an Rohrabschnitten mit einer max. Wandstärke von 15 mm, bei gegebenenfalls weiteren Parameteranpassungen. T2 - DVS Congress 2019 CY - Rostock, Germany DA - 16.09.2019 KW - Rundnähte KW - Laserhybridschweißen KW - Endkrater PY - 2019 AN - OPUS4-49895 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Rethmeier, Michael A1 - Gumenyuk, Andrey A1 - Artinov, Antoni A1 - Meng, Xiangmeng A1 - Bakir, Nasim A1 - Üstündag, Ömer A1 - Bachmann, Marcel T1 - The bulging effect and its relevance in high power laser beam welding N2 - The present work deals with the recently confirmed widening of the weld pool interface, known as a bulging effect, and its relevance in high power laser beam welding. A combined experimental and numerical approach is utilized to study the influence of the bulge on the hot cracking formation and the transport of alloying elements in the molten pool. A technique using a quartz glass, a direct-diode laser illumination, a high speed camera, and two thermal imaging cameras is applied to visualize the weld pool geometry in the longitudinal section. The study examines the relevance of the bulging effect on both, partial and complete penetration, as well as for different sheet thicknesses ranging from 8 mm to 25 mm. The numerical analysis shows that the formation of a bulge region is highly dependent on the penetration depth and occurs above 10 mm penetration depth. The location of the bulge correlates strongly with the cracking location. The obtained experimental and numerical results reveal that the bulging effect increases the hot cracking susceptibility and limits the transfer of alloying elements from the top of the weld pool to the weld root T2 - The 18th Nordic Laser Materials Processing Conference CY - Lulea, Sweden DA - 18.01.2022 KW - Laser beam welding KW - Melt pool dinamics PY - 2022 AN - OPUS4-54333 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - El-Sari, B. A1 - Biegler, M. A1 - Rethmeier, Michael T1 - Verbesserung der Vorhersagegüte von künstlichen neuronalen Netzen zum Widerstandspunktschweißen durch Auswertung des dynamischen Widerstands N2 - Das Widerstandspunktschweißen ist ein etabliertes Fügeverfahren in der Automobilindustrie. Es wird vor allem bei der Herstellung sicherheitsrelevanter Bauteile, zum Beispiel der Karosserie, eingesetzt. Daher ist eine kontinuierliche Prozessüberwachung unerlässlich, um die hohen Qualitätsanforderungen zu erfüllen. Künstliche neuronale Netzalgorithmen können zur Auswertung der Prozessparameter und -signale eingesetzt werden, um die individuelle Schweißpunktqualität zu gewährleisten. Die Vorhersagegenauigkeit solcher Algorithmen hängt von dem zur Verfügung gestellten Trainingsdatensatz ab. In diesem Beitrag wird untersucht, inwieweit die Vorhersagegüte eines künstlichen neuronalen Netzes durch Auswertung einer Prozessgröße, dem dynamischen Widerstand, verbessert werden kann. KW - Künstliche Intelligenz KW - Qualität KW - Neuronales Netz KW - Widerstandspunktschweißen PY - 2021 SP - 785 EP - 789 AN - OPUS4-53976 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Raute, J. A1 - Biegler, M. A1 - Rethmeier, Michael T1 - Elektronenstrahl schweißt additiv gefertigte Nickel-Superlegierungen N2 - Die Additive Fertigung ist ideal zur Herstellung und Reparatur komplexer Bauteile aus hochfesten Werkstoffen. Doch es fehlen Fügeverfahren, die Heißrisse vermeiden. Die Lösung heißt Elektronenstrahl. KW - Additive Fertigung PY - 2021 SP - 1 EP - 6 AN - OPUS4-53979 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Artinov, Antoni A1 - Bachmann, Marcel A1 - Rethmeier, Michael A1 - Karkhin, V. A1 - Khomich, P. T1 - Modeling of hydrodynamic and thermal processes at laser welding with through penetration N2 - A mathematical model for physical processes in fusion welding has been developed. It is based on the equivalent heat source concept and consists of two parts: thermo-hydrodynamics of the weld pool and heat conduction in the weldment outside the pool. In thermo-hydrodynamic problem, temperature – dependent material properties, keyhole shape, thermo-capillary and natural convection, phase transformations and other physical phenomena are taken into consideration. Solution of the thermo-hydrodynamic problem by the finite element method is demonstrated with keyhole laser beam welding of a 15 mm thick steel plate. Thermo-capillary convection is primarily responsible for the intricate convex-concave melt pool shape and pool enlargement near the plate surfaces. The calculated and experimental molten pool dimensions are in close agreement. KW - Laser welding KW - Weld pool modeling KW - Heat conduction KW - Greens function method PY - 2021 DO - https://doi.org/10.1080/09507116.2021.1989209 SP - 1 EP - 12 PB - Taylor & Francis Group AN - OPUS4-54022 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Biegler, M. A1 - El-Sari, B. A1 - Rethmeier, Michael A1 - Finus, F. T1 - Schweißen unter Zug – LME-Eingangsprüfung für die Autoindustrie N2 - Der Trend zum Leichtbau und die Transformation zur E-Mobilität in der Automobilindustrie befeuern die Entwicklung neuer hochfester Stähle für den Karosseriebau. Derartige Werkstoffe sind beim Widerstandspunktschweißen besonders rissanfällig (LME). Das Schweißen unter Zug stellt eine effektive Methode um die LME-Anfälligkeit unterschiedlicher Werkstoffe qualitativ zu bestimmen. KW - Automobilindustrie KW - Widerstandspunktschweißen KW - Liquid Metal Embrittlement KW - Zinkbeschichtung KW - Hochfester Stahl PY - 2021 IS - 6 SP - 54 EP - 55 AN - OPUS4-54057 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -