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Labus Zlatanovic, Danka; Bergmann, Jean Pierre; Balos, Sebastian; Gräzel, Michael; Pejic, Dragan; Sovilj, Platon; Goel, Saurav;
Influence of rotational speed on the electrical and mechanical properties of the friction stir spot welded aluminium alloy sheets. - In: Welding in the world, ISSN 1878-6669, Bd. 66 (2022), 6, S. 1179-1190

An efficient and productive joining technique to weld aluminium has become a priority challenge for promoting the use of aluminium in the electrical industry. One of the challenges is to obtain welds with superior mechanical properties with the consistent quality of weld surface as well as low electrical resistance. In this paper, the influence of rotational speed during the friction stir spot welding of AA 5754-H111 was studied to analyse the mechanical and electrical properties of the welds. The results from two rotational speeds (1000 rpm and 4500 rpm) are presented and compared to the base material. It was observed that the samples welded at 1000 rpm showed a higher average shear failure load (˜ 1.1 kN) compared to the samples welded at 4500 rpm (˜ 0.94 kN). The microhardness of the samples welded at 1000 rpm was higher than that of the base material, while the microhardness of samples welded at 4500 rpm was lower. It was also found that the friction welded sheets, regardless of the rotational speed used, showed increased electrical resistance compared to the base material, albeit this increase for the samples welded at 1000 rpm was about 42%, compared to samples welded at 4500 rpm where this increase was just 14%.
Mir, Amir; Luo, Xichun; Llavori, Iñigo; Roy, Anish; Labus Zlatanovic, Danka; Joshi, Shrikrishna N.; Goel, Saurav;
Challenges and issues in continuum modelling of tribology, wear, cutting and other processes involving high-strain rate plastic deformation of metals. - In: Journal of the mechanical behavior of biomedical materials, ISSN 1878-0180, Bd. 130 (2022), 105185, S. 1-24

Contribution of finite element method (FEM) as a modelling and simulation technique to represent complex tribological processes has improved our understanding about various biomaterials. This paper presents a review of the advances in the domain of finite element (FE) modelling for simulating tribology, wear, cutting and other processes involving high-strain rate plastic deformation of metals used in bio tribology and machining. Although the study is largely focused on material removal cases in metals, the modelling strategies can be applied to a wide range of other materials. This study discusses the development of friction models, meshing and remeshing strategies, and constitutive material models. The mesh-based and meshless formulations employed for bio tribological simulations with their advantages and limitations are also discussed. The output solution variables including scratch forces, local temperature, residual stresses are analyzed as a function of input variables.
Paffhausen, Michael;
Rührreibschweißen mit einem Industrieroboter unter Berücksichtigung der Einsatzkriterien für die automobile Großserienfertigung. - Ilmenau : Universitätsverlag Ilmenau, 2022. - 1 Online-Ressource (225 Seiten). - (Fertigungstechnik - aus den Grundlagen für die Anwendung ; Band 13)
Technische Universität Ilmenau, Dissertation 2021

Das Fügeverfahren "Rührreibschweißen" ermöglicht die Herstellung reproduzierbar hochwertiger Schweißverbindungen. Aufgrund der sehr hohen Prozesskräfte werden in der Produktion vorzugsweise Sonder- und Werkzeugmaschinen eingesetzt. In der automobilen Großserienfertigung wird jedoch der Einsatz von Standard-Industrierobotern für das Rührreibschweißen als kostengünstigere und flexiblere Alternative favorisiert. Im Rahmen der Arbeit werden die Leistungskenngrößen des Industrieroboters zunächst ohne Bearbeitungskräfte analysiert. In diesem Zusammenhang werden die Pose- und Bahn-Wiederholgenauigkeit des Industrieroboters an unterschiedlichen Referenzbahnen in der Ebene quantifiziert. Hier ist festzustellen, dass der Roboter den Genauigkeitsanforderungen des Schweißverfahrens genügt. Bei der Analyse der Wechselwirkungen zwischen Prozess und Roboterstruktur wird jedoch deutlich, dass die Arbeitsgenauigkeit des Industrieroboters durch die resultierenden Prozesskräfte beim Rührreib-schweißen signifikant beeinflusst wird; ohne ein "Nachteachen" oder eine Offline-Korrektur der programmierten Soll-Bahn werden die mechanischen Eigenschaften der Fügeverbindung durch die mangelnde Arbeitsgenauigkeit des Industrieroboters negativ beeinflusst. Bei der Analyse kann nachgewiesen werden, dass die Abdrängung des Werkzeugs nicht nur von den resultierenden Prozesskräften abhängt, sondern auch signifikant durch die Richtung des Vektors der Bahngeschwindigkeit beim Bahnschweißen beeinflusst wird. Bei der Analyse der statischen und dynamischen Systemeigenschaften des Roboters wird gezeigt, dass die nichtlinearen Steifigkeiten der Roboterstruktur maßgeblich von den Gelenkstellungen und der Belastungsrichtung abhängen. Aus den Erkenntnissen der Systemanalyse wird eine modellbasierte Offline-Bahnkorrektur, die Nachgiebigkeiten und Wechselwirkungen zwischen Prozess und Roboter berücksichtigt, entwickelt.
Schwarz, Elisabeth Birgit; Bleier, Fabian; Günter, Friedhelm; Mikut, Ralf; Bergmann, Jean Pierre;
Improving process monitoring of ultrasonic metal welding using classical machine learning methods and process-informed time series evaluation. - In: Journal of manufacturing processes, Bd. 77 (2022), S. 54-62

Ultrasonic metal welding (USMW) is an industrially applied joining technology that is highly complex since the weld quality is influenced by numerous factors. The relationships between these factors and the quality remain partly unavailable resulting in a need for improvement in process monitoring and quality management. This work focuses on exploring the relationships between tensile shear strength (TSS) of Cu-sheet welds and process curves from welding machine and additional vibration sensors at sonotrode and anvil. Discovered relationships would enable an improved process monitoring, when valid for a broad parameter range. To ensure the latter, examinations are carried out on a central composite design of experiments (DoE) data set. For the whole data set as well as for single data points, the process curves are examined in detail comprising visualizations and discussions of revealed trends. These trends are related to process physics to clarify their relevance for the TSS. Based on physical process knowledge, more than 700 features are extracted from the curves. The extraction approach is not limited to the present setup and enables a quantitative evaluation of the relation between TSS and process curves. Most important features are derived from the generator power and the anvil vibration. Finally, linear regression as well as multi-layer perceptron regression are used to predict the TSS based on the most relevant features. Comparing the obtained regression results with the reference model, that is the polynomial regression model from standard DoE evaluation, a prediction improvement of nearly 50% is achieved. These results suggest the employed signals as a suited basis for an improved USMW process monitoring.
Seibold, Marc; Schricker, Klaus; Bergmann, Jean Pierre;
Systematic adjustment of the joining time in pulsed laser beam welding of aluminum-copper joints by means of a closed-loop control. - In: Journal of advanced joining processes, ISSN 2666-3309, Bd. 5 (2022), 100104, S. 1-6

Electric mobility has become increasingly important in recent years. For this purpose, the use of copper is essential due to its electrical properties. In order to save weight and costs, copper is replaced by aluminum in many electrical conductors.In this paper, the required joining time for pulsed laser beam welding of aluminum-copper joints is investigated to minimize the mixing of both materials. By using an external controller and photodiodes, it was possible to develop a real-time pulse control laser welding process based on process emissions. The spectral emission was used to detect when the lower joining partner is reached during the deep welding process. The control enables the adjustment of different joining times, on the one hand by a signal drop of the spectral emission, on the other hand by a specific time. The laser pulse was terminated between 500 - 800 [my]s after reaching this event. This led to differences in process conditions, resulting in significant changes in mechanical properties. In this way, a decisive influence was exerted on the resulting joining zone. The interaction duration and the work piece transition are of primary interest. By comparing the results with high-speed recordings in the half-section set-up, the resulting mechanisms can be identified. It could be shown that the breakup time have an high impact for the shear tensile force and the welding depth. A Change in the breakup time of 40 [my]s could lead to high changes in the tensile shear force.
Gester, Andreas; Wagner, Guntram; Pöthig, Pascal; Bergmann, Jean Pierre; Fritzsche, Marco;
Analysis of the oscillation behavior during ultrasonic welding of EN AW-1070 wire strands and EN CW004A terminals. - In: Welding in the world, ISSN 1878-6669, Bd. 66 (2022), 3, S. 567-576

For fulfilling the demand of durable yet lightweight electrical connections in transportation industries, ultrasonic metal welding (USMW) sees widespread use in these branches. As the ultrasound oscillations utilized in the welding procedure occur at a range of only a few micrometers at frequencies of 20-100 kHz for an overall duration of only 50-1500 ms, it is not possible to observe the compaction behavior with the bare eye. This paper focusses on investigating the oscillation behavior of the horn, the anvil, and the joining partners during the welding procedure by utilizing an array of synchronized laser vibrometers and performing welds with incrementing time stages. The oscillation data is correlated with temperature measurements in the welding zone as well as tensile testing results. Inter alia the formation of sidebands at the fundamental frequency as well as 2nd- and 3rd-order harmonics has been observed for the anvil, terminal, and wire front face when exceeding optimal weld time which would lead to maximum joint strength. Following the assumption of other research groups, the cause of these sidebands could be a change in relative motion of these components. As the terminal is slipping with increasing weld time, it could be assumed that the reason for the sidebands is low-frequency movement of the anvil, modulated onto the fundamental frequency, additionally indicating successful bonding of the stranded wire and the terminal. Furthermore, this slipping of the terminal on the anvil could lead to increased wear of the anvil knurls.
Reimche, Maxim; Geißhirt, M.; Berghof, Steffen; Bergmann, Jean Pierre;
Innovative methodology to determine process costs for manufacturing within production networks. - In: Production at the leading edge of technology, (2022), S. 656-665

Companies that manufacture their own products and also provide after-market service are common and usually involve in-house manufacturing and assembly. The limited capacity of in-house resources and the requirement to meet delivery deadlines forces companies to deviate from the cost-optimal production strategy and to produce quantities according to demand instead of optimal lot sizes. A selective increase in the capacity of heavily utilized resources, e.g. by additional capacity of platforms or participation in peer-to-peer networks, enables companies to make savings on setup costs by producing selected articles in optimal load sizes. Such savings can be used to price third-party capacity. This paper presents a new method for pricing the procurement of capacity in a peer-to-peer network and demonstrates it on an industrial example.

Kraus, Matthias; Winkler, Paul; Hammer, Stefan; Reimann, Jan; Hildebrand, Jörg; Bergmann, Jean Pierre;
Geometric imperfections of additive manufactured members. - In: Engineering structures, ISSN 0141-0296, Bd. 252 (2022), 113596

Challenges in civil engineering and construction industries increase, and simultaneously it is necessary to provide a sustainable utilization of resources. Optimising material applications and manufacturing processes is therefore essential for modern constructions. Highly optimised structural components are already in use in lightweight constructions as well as in aircraft and vehicle industries. In the course of digitisation, new possibilities have evolved in recent years for producing individual and optimized solutions with regard to the consumption of materials, especially in construction industries. Methods of generative or additive manufacturing are employed to develop various prototypes of structural components. In this context, Wire-Arc-Additive-Manufacturing (WAAM) is a promising method for steel structures. However, it remains to be investigated to what extent dimensional accuracy, surface finish, weld quality and repeated thermal influences from the build-up process affect the structural behaviour of corresponding members. This paper deals with the geometric imperfections of corresponding additively manufactured profiles and exemplifies their influence on the bearing capacity.
Girkes, Florian; Berghof, Steffen; Bergmann, Jean Pierre;
Case-based reasoning for cost and capacity demand planning of new products in the early phase of product development :
Case-Based Reasoning zur Kosten- und Kapazitätsbedarfsplanung von neuen Produkten : in der frühen Phase der Produktentwicklung. - In: Zeitschrift für wirtschaftlichen Fabrikbetrieb, ISSN 2511-0896, Bd. 116 (2021), 9, S. 569-572

Zur Verkürzung der Zeitspanne zwischen der Entwicklung bis zur Auslieferung von neuen Produkten wird am Fachgebiet Fertigungstechnik der TU Ilmenau eine Methode entwickelt, mit der bereits in der Entwicklungsphase Kapazitäten für die Produktion reserviert und die Kostenkalkulation angegangen werden können, damit Unternehmen ihre Liefertermine einhalten und Kosten senken können. Grundlage dieser Methode bilden Typenvertreter, die durch Ähnlichkeiten zu bereits umgesetzten Produkten durch Verfahren des maschinellen Lernens abgeleitet und verbessert werden.
Pöthig, Pascal; Gester, Andreas; Roder, Kristina; Wagner, Guntram; Bergmann, Jean Pierre;
Erarbeitung von Bewertungsstrategien für das Ultraschallschweißen von Aluminium-Litzen und Kupfer-Kontaktteilen. - In: Werkstoffe in der Fertigung, ISSN 0939-2629, (2021), 5, S. 34-35

Der vorgestellte Beitrag beschäftigt sich mit der Untersuchung von geeigneten Bewertungskriterien beim Ultraschallschweißen von Aluminium-Litzen und Kupfer-Kontaktteilen. Der Fokus lag hierbei auf dem Erzeugen verschiedener Kompaktierungszustände durch die Variation der Schweißkraft sowie dessen Auswirkungen auf die Trennkraft und den elektrischen Widerstand. Es konnte gezeigt werden, dass sehr gute Anbindungseigenschaften erzielt werden können, jedoch eine zu geringe bzw. zu starke Kompaktierung nicht geeignet ist. Eine zu geringe Kompaktierung äußert sich in einer unzureichenden Anbindung des Kabels an den Ableiter, während eine zu starke Kompaktierung zum Abtrennen von einzelnen Litzen sowie zu Rissen und dem Bilden von Trennebenen führt. Beides resultiert in verringerten mechanischen und elektrischen Eigenschaften. Somit lassen sich die besten Verbindungeigenschaften für die betrachtete Materialkombination in einem Zwischenbereich (FS = 1170 N - 1340 N) erzielen, was mit den vorgestellten Bewertungskriterien ermittelt werden kann.