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Kästner, Christian; Neugebauer, Matthias; Schricker, Klaus; Bergmann, Jean Pierre
Increasing productivity of pulsed laser cladding of hot crack susceptible nickel-base superalloys by decoupling heat components. - In: Welding and cutting, ISSN 1612-3433, Bd. 20 (2021), 3, S. 236-242

Wire-assisted pulsed laser beam welding is one option for processing high-strength γ'-precipitation hardening nickel-base superalloys. It facilitates crack-reduced repair of similar material pairings through material-adapted pulse shapes. The limited average power output of pulsed laser beam sources confines the deposition rate and thus the productivity of the welding process. The decoupling of heat sources, i. e. the application of the hot-wire technology and base material preheating, may increase the deposition rate since the energy for melting base and filler material is not solely provided by the laser beam source.



Köhler, Tobias; Kleinhenz, Ludwig; Schäfer, Philipp Matthias; Bergmann, Jean Pierre; Peters, Diana
Development of a methodology for the digital representation of manufacturing technology capabilities. - In: Conference on Production Systems and Logistics, (2021), S. 478-488

The demand for efficient and digital systems for supporting the decision making during the design of a product is a key issue in manufacturing companies. Decisions made during the development and design of a product have a strong impact on the costs and delivery times of a product. Hence, a digital system which supports the engineer during and after the development process with information about the manufacturability of the product can reduce the production costs and times. In order to be able to evaluate the manufacturing capabilities at manufacturing process and machine level, there is a need to represent them in a digital way. Digital knowledge bases like taxonomies and ontologies provide the possibility for a representation of manufacturing resources. The state of the art shows different approaches for the use of ontologies in the domain of subtractive manufacturing processes as well as additive manufacturing (AM) processes. The goal of this work is the semantical representation of manufacturing technology capabilities with focus on AMmachines and processes. In this paper we introduce taxonomies of Manufacturing Features and Manufacturing Restrictions which were developed in accordance with current standards. To enrich the taxonomies with information, it was enhanced by relations between different manufacturing related entities in a knowledge graph. If manufacturing processes and machines can be digitally mapped, described and linked to the geometric information of a product together with information on the current performance of the company/network, bottlenecks and delivery delays during the manufacturing of parts can be avoided.



https://doi.org/10.15488/11259
Hasieber, Michael; Grätzel, Michael; Bergmann, Jean Pierre
Characterization and analysis of effective wear mechanisms on FSW tools. - In: Friction stir welding and processing XI, (2021), S. 21-34

This study systematically analyzes effective wear mechanisms at the shoulder and probe, separately for plunging and welding. The investigations were carried out with a robotic welding setup in which AA-6060 T66 sheets with a thickness of 8 mm were joined by weld seam lengths of up to 80 m. To compare and differentiate the wear mechanisms between plunging and welding, repeated plunging cycles were initially investigated without tool movement. Subsequent experiments consider welding as well, whereby adhesion, abrasion, surface fatigue, and tribochemical reactions which were characterized for various weld seam lengths. During welding of the AA-6060 T66 sheets, the tool material 1.2344 (X40CrMoV5-1) exhibited abrasive wear that occurred due to self-damaging of the FSW tool. The wear analysis showed that no significant wear occurred during the plunging stage.



Hammer, Stefan; Rasche, Stefan; Hildebrand, Jörg; Bergmann, Jean Pierre; Spiegler, Jennifer; Kuhlmann, Ulrike; Mückenheim, Uwe; Keitel, Steffen
Load-bearing capacity of butt welded joints of high-strength steels in steel construction :
Tragfähigkeit von Stumpfnahtverbindungen höherfester Stähle im Stahlbau. - In: Schweissen und Schneiden, ISSN 0036-7184, Bd. 73 (2021), 10, S. 710-717

Höherfeste Stähle erlauben hohe Beanspruchungen, insbesondere im Zugbereich, in Konstruktionen aufzunehmen und führen zur Reduzierung tragender Querschnitte, zur Verringerung des Materialverbrauchs und der Herstellungskosten. Da die Bemessungsregeln für Verbindungen ausschließlich auf Konzepten beruhen, die für normalfeste Stähle bis fy,k = 360 N/mm^2 entwickelt wurden, können die Vorteile höherfester Stähle nicht voll ausgenutzt werden. Das hier vorgestellte Forschungsvorhaben hat durchgeschweißte Stumpfnähte von höherfesten Stählen untersucht. Es wurden Empfehlungen für eine effiziente Schweißnahtvorbereitung beim Metallschutzgasschweißen (MSG) der Stumpfnähte höherfester Stähle sowie für eine Optimierung des Energieeintrags entwickelt. Die Reduzierung des Energieeintrags wirkt einer Gefügeausbildung entgegen, die die statische Tragfähigkeit vermindert. Kleine und mittlere Unternehmen (KMU) können von neuen Regeln zur Nahtbemessung profitieren, die den Einfluss des Schweißprozesses und des Schweißzusatzwerkstoffs auf die Tragfähigkeit der Stumpfnähte erfassen und die Regeln nach EN 1993-1-8 vorteilhaft ergänzen können.



Sarcev, Branislava Petronijevic; Labus Zlatanovic, Danka; Hadnadjev, Miroslav; Pilic, Branka; Sarcev, Ivan; Markovic, Dubravka; Balos, Sebastian
Mechanical and rheological properties of flowable resin composites modified with low addition of hydrophilic and hydrophobic TiO2 nanoparticles. - In: Materiale plastice, ISSN 2537-5741, Bd. 58 (2021), 2, S. 80-90

The aim of this work was to find the influence of the addition of low amount of hydrophilic and hydrophobic TiO2 nanoparticles on compressive strength, microhardness and rheological properties of flowable dental composite material. Specimens were prepared by adding 0.05; 0.2 and 1 wt. % of hydrophilic and hydrophobic 20 nm TiO2 nanoparticles. These specimens were compared to non-modified control specimens in compressive strength and microhardness. Furthermore, their rheological properties were determined. The optimal nanoparticle loading was 0.2 % hydrophobic TiO2, resulting in significantly higher compressive strength and microhardness than those of the control specimen group. Mechanical properties of flowable composites reinforced with hydrophilic and hydrophobic TiO2 at higher loadings are lower than those of control specimens, which is the result of nanoparticle agglomeration. TiO2 nanoparticles addition resulted in the decrease in viscosity in all specimens except for the specimewn with 1% hydrophilic TiO2 nanoparticles. In accordance to the obtained results, hydrophobic nanoparticle addition results in a more resistant and durable material, combined with an increased flowability compared to a non-modified composite.



https://doi.org/10.37358/MP.21.2.5480
Tchouaha Tankoua, Aristide; Köhler, Tobias; Bergmann, Jean Pierre; Grätzel, Michael; Betz, Philip; Lindenau, Dirk
Tool downscaling effects on the friction stir spot welding process and properties of current-carrying welded aluminum-copper joints for E-Mobility applications. - In: Metals, ISSN 2075-4701, Bd. 11 (2021), 12, 1949, S. 1-20

According to the technical breakthrough towards E-Mobility, current-carrying dissimilar joints between aluminum and copper are gaining an increasing relevance for the automotive industry and thus, coming into focus of many research activities. The joining of dissimilar material in general is well known to be a challenging task. Furthermore, the current-carrying joining components in E-Drive consist of pure aluminum and copper materials with relatively thin sheet thickness, which are thermally and mechanically very sensitive, as well as highly heat and electrically conductive. This results in additional challenges for the joining process. Due to their properties, friction stir welding and especially fiction stir spot welding (FSSW) using pinless tools - i.e., as hybrid friction diffusion bonding process (HFDB) is more and more attractive for new application fields and particularly promising for aluminum-copper joining tasks in E-Mobility. However, the feasibility is restricted because of the relatively high process forces required during friction stir welding. Thus, to fulfill the high process and quality requirements in this above-mentioned application field, further research and process development towards process force reduction are necessary. This work deals with the application of the tool downscaling strategy as a mean of process force reduction in FSSW of thin aluminum and copper sheets for current-carrying applications in E-Mobility, where the components are very sensitive to high mechanical loads. The tool downscaling approach enables constant weld quality in similar process time of about 0.5 s despite reduced process forces and torques. By reducing the tool diameter from 10 mm to 6 mm, the process force could be reduced by 36% and the torque by over 50%. Furthermore, a similar heat propagation behavior in the component is observable. These results provide a good basis for the joining of E-Drive components with thermal and mechanical sensitive sheet materials using the pinless FSSW process.



https://doi.org/10.3390/met11121949
Regensburg, Anna;
Hybrid Friction Eutectic Bonding (HFEB) - stoffschlüssiges Fügen von Aluminium und Kupfer unter Nutzung der eutektischen Reaktion. - Ilmenau : Universitätsverlag Ilmenau, 2021. - 1 Online-Ressource (X, 177 Seiten). - (Fertigungstechnik - aus den Grundlagen für die Anwendung ; Band 12)
Technische Universität Ilmenau, Dissertation 2021

Ansätze des werkstofflichen Leichtbaus mit dem Ziel der Gewichts- und Ressourcenoptimierung in elektrischen Verbindungen haben das Fügen von Aluminium-Kupfer-Mischverbindungen zu einem stark verfolgten Forschungsschwerpunkt der letzten Jahre gemacht. Im Rahmen von Elektromobilität sowie allgemeiner Erhöhung von Komfort- und Sicherheitsstandards ergeben sich hierfür hohe Herausforderungen an die einzusetzenden Fügetechnologien. Der Zielzustand für elektrische Verbindungen besteht in großflächigen, duktilen Verbindungen mit geringem Kontaktwiderstand. Je nach Verfahren werden diese Ziele jedoch durch die Bildung spröder, intermetallischer Phasen oder erhöhte Grenzflächen- und Bauteilverformung nur zum Teil erreicht. In der vorliegenden Arbeit wurde gezielt die Bildung einer eutektischen Schmelze zwischen Aluminium und Kupfer genutzt, um den Lösungsraum zwischen Press- und Schmelzschweißverfahren zu nutzen. Während der Initialkontakt der Grenzflächen durch Fügedruck während des Rührreibpunktschweißens beschleunigt wird, findet die Vergrößerung und Benetzung der Fügefläche durch die Bildung einer eutektischen Schmelze statt. Diese bildet sich zwischen den Grundwerkstoffen, ohne dass diese in die flüssige Phase übergehen. In Abhängigkeit der Prozessführung kann der Pressschweißprozess hier erneut genutzt werden, um die Schmelze aus der Fügezone zu verdrängen. Somit kann das Erstarrungsverhalten gezielt beeinflusst werden, während sich weitere Vorteile durch den Abtransport von Einschlüssen und Verunreinigungen ergeben. Durch eine angepasste Prozessführung können vollflächige Anbindungen in kurzer Prozesszeit von weniger als 0,5 s erzielt werden. Die Bildung weiterer Sprödphasen außerhalb des eutektischen Systems wird durch die Limitierung der Spitzentemperatur und des Energieeintrags verhindert. Zusätzlich kann die Schmelzebildung als Reduzierung des Materialwiderstands während des kraftgeregelten Prozesses detektiert und diese für weitere Prozessansätze genutzt werden. Weitere Optimierungsansätze zeigen sich beim Übertrag auf weitere Pressschweißverfahren und Bauteilgeometrien.



https://doi.org/10.22032/dbt.50162
Schulz, Alexander; Bartsch, Heike; Gutzeit, Nam; Matthes, Sebastian; Glaser, Marcus; Ruh, Andreas; Müller, Jens; Schaaf, Peter; Bergmann, Jean Pierre; Wiese, Steffen
Characterization of reactive multilayer systems deposited on LTCC featuring different surface morphologies. - In: MikroSystemTechnik, (2021), S. 506-510

Baloochi, Mostafa; Shekhawat, Deepshikha; Riegler, Sascha Sebastian; Matthes, Sebastian; Glaser, Marcus; Schaaf, Peter; Bergmann, Jean Pierre; Gallino, Isabella; Pezoldt, Jörg
Influence of initial temperature and convective heat loss on the self-propagating reaction in Al/Ni multilayer foils. - In: Materials, ISSN 1996-1944, Bd. 14 (2021), 24, 7815, insges. 15 S.

A two-dimensional numerical model for self-propagating reactions in Al/Ni multilayer foils was developed. It was used to study thermal properties, convective heat loss, and the effect of initial temperature on the self-propagating reaction in Al/Ni multilayer foils. For model adjustments by experimental results, these Al/Ni multilayer foils were fabricated by the magnetron sputtering technique with a 1:1 atomic ratio. Heat of reaction of the fabricated foils was determined employing Differential Scanning Calorimetry (DSC). Self-propagating reaction was initiated by an electrical spark on the surface of the foils. The movement of the reaction front was recorded with a high-speed camera. Activation energy is fitted with these velocity data from the high-speed camera to adjust the numerical model. Calculated reaction front temperature of the self-propagating reaction was compared with the temperature obtained by time-resolved pyrometer measurements. X-ray diffraction results confirmed that all reactants reacted and formed a B2 NiAl phase. Finally, it is predicted that (1) increasing thermal conductivity of the final product increases the reaction front velocity; (2) effect of heat convection losses on reaction characteristics is insignificant, e.g., the foils can maintain their characteristics in water; and (3) with increasing initial temperature of the foils, the reaction front velocity and the reaction temperature increased.



https://doi.org/10.3390/ma14247815
Schricker, Klaus; Baumann, Andreas; Bergmann, Jean Pierre
Local shielding gas supply in remote laser beam welding. - In: Journal of manufacturing and materials processing, ISSN 2504-4494, Bd. 5 (2021), 4, 139, insges. 19 S.

The use of shielding gases in laser beam welding is of particular interest for materials interacting with ambient oxygen, e.g., copper, titanium or high-alloy steels. These materials are often processed by remote laser beam welding where short welds (e.g., up to 40 mm seam length) are commonly used. Such setups prevent gas nozzles from being carried along on the optics due to the scanner application and a small area needs to be served locally with inert gas. The article provides systematic investigations into the interaction of laser beam processes and parameters of inert gas supply based on a modular flat jet nozzle. Based on the characterization of the developed nozzle by means of high-speed Schlieren imaging and constant temperature anemometry, investigations with heat conduction welding and deep penetration welding were performed. Bead-on-plate welds were carried out on stainless steel AISI 304 for this purpose using a disc laser and a remote welding system. Argon was used as shielding gas. The interaction between Reynolds number, geometrical parameters and welding/flow direction was considered. The findings were proved by transferring the results to a complex weld seam geometry (C-shape).



https://doi.org/10.3390/jmmp5040139