Browsing by Author "Liewald, Mathias"

Now showing 1 - 12 of 12

Open Access
Abschlussbericht zum Projekt "Ressourcenschonende Mischschweißverbindungen für Hochleistungs-Leichtbauverbunde"
(Stuttgart : Institut für Materialprüfung, Werkstoffkunde und Festigkeitslehre (IMWF) der Universität Stuttgart, 2018) Panzer, Florian; Werz, Martin; Nguyen, Phuc Lanh; Schneider, Matthias; Weihe, Stefan; Liewald, Mathias
Im Rahmen des Projektes wurde das Rührreibschweißen als ressourceneffizientes und umweltfreundliches Fertigungsverfahren zur Herstellung von beanspruchungs- und gewichtsoptimierten Automobilbauteilen erforscht. Dabei galt es, Aluminium und Stahl in verschiedenen Dicken durch Rührreibschweißen zu fügen und durch anschließendes Umformen zum End- bzw. Zwischenprodukt umzuformen. Die auf die Festigkeiten der Werkstoffe angepassten Blechdicken führen zu einer optimalen Ausnutzung der Werkstoffe, da an jeder Stelle der Werkstoff verwendet werden kann, der die lokalen Anforderungen am besten erfüllt. Durch den Einsatz dieser sogenannten Tailor Welded Blanks sinkt der Werkstoffverbrauch insgesamt und es können auf Leichtbau optimierte Bauteile hergestellt werden. Im Rahmen des Projektes wurden verschiedene Aluminium- und Stahlgüten in unterschiedlichen Dicken durch Rührreibschweißen gefügt und die Festigkeits- sowie Umformeigenschaften ermittelt. Da die Einhaltung von engen Toleranzen mit hohen Kosten in der Fertigung einhergeht, wurden die für den Prozess notwendigen Toleranzen untersucht, Lösungen zum Umgang mit diesen Toleranzen erarbeitet und Anforderungen an Anlagen zur Produktion von Tailor Welded Blanks identifiziert. Zudem wurde das Umformen von Blechen mit unterschiedlichen Materialen und Blechdicken untersucht. Darüber hinaus wurde eine Reihe weiterer Themen wie das Verschweißen von Gusswerkstoffen und Wärmebehandlungsstrategien beleuchtet. Abschließend wurden Demonstratorbauteile in Form von Tailor Welded Blanks in Aluminium-Stahl- Mischbauweise durch Rührreibschweißen und anschließendes Umformen gefertigt.
Open Access
Dry metal forming using volatile lubricants injected into the forming tool through flow-optimized, laser-drilled microholes
(2020) Henn, Manuel; Reichardt, Gerd; Weber, Rudolf; Graf, Thomas; Liewald, Mathias
A novel tribologic system was developed in which volatile lubricants (carbon dioxide-CO2 or nitrogen-N2) were used as a substitute for mineral oil-based lubricants in deep drawing processes. This process allows an intermediate medium to be introduced into the tool contact surfaces under high pressure by flow-optimized, laser-drilled microholes. This eliminates the need for subsequent cost-intensive cleaning processes as volatile lubricants evaporate while expanding to ambient pressure without leaving any residue. This article gives an overview of the current findings to enable and characterize the novel tribologic system. The areas of microhole laser drilling by ultrashort pulsed laser radiation, characterization of the novel tribologic system and realization of the system using a prototype tool will be described.
Open Access
Efficient net shape forming of high-strength sheet metal parts by Transversal Compression Drawing
(2023) Briesenick, David; Liewald, Mathias
In this contribution, a new forming method is presented for high-strength steel sheet metal materials called Transversal Compression Drawing (TCD). For TCD, the blankholder of the conventional deep drawing process is replaced by sliders introducing a vertical force along the blank edge. Compared to conventional deep drawing, compressive stresses are thereby superimposed in the flange area of the sheet metal material, reducing the springback of formed components and the forces required during the process. Proof of this is provided here on the basis of numerical investigations in which conventional deep drawing and TCD are compared using the example of an “S-Rail” component made from DP980. Results of these investigations reveal that with TCD a maximum reduction in springback by more than 5 mm is achieved, leading to an improvement in the component´s overall shape accuracy of more than 55%. Furthermore, frictional work is decreased by − 6.92 kJ/kg, resulting in an overall reduction of maximum forming forces by 67.4%. Besides, TCD enables a trim-free net shape forming of the final part contour in a single operation and an increased material utilization of 4.5% from coil to part. Not least, no sheet thinning occurs with TCD, whereas a maximum thinning of 12% is observed with the conventional deep drawing process.
Open Access
Einsatz von ML beim Scheren im offenen Schnitt : Bestimmung von mechanischen Blechkennwerten durch Maschinelles Lernen im offenen Beschnitt
(2023) Görz, Marcel; Schenek, Adrian; Liewald, Mathias; Riedmüller, Kim Rouven
Open Access
Friction and wear behavior of deep drawing tools using volatile lubricants injected through laser-drilled micro-holes
(2021) Reichardt, Gerd; Henn, Manuel; Reichle, Paul; Umlauf, Georg; Riedmüller, Kim; Weber, Rudolf; Barz, Jakob; Liewald, Mathias; Graf, Thomas; Tovar, Günter E. M.
In deep drawing processes, the use of lubricants is mandatory in order to prevent wear on tools and surface damage to the formed sheet metal components. Here, frequently used lubricants are synthetic and mineral oils, emulsions, and waxes. However, these conventional lubricants have to be applied to the sheet material prior to the forming operation and removed afterwards by cleaning processes. Additionally, the lubricants often contain substances that are harmful to the environment and to human health. To counteract these economic and ecological disadvantages, research is currently being conducted on a novel tribological system. For this, volatile media such as liquid carbon dioxide and gaseous nitrogen are being used, and are introduced directly into the friction zones between the tool and the sheet metal material during deep drawing under high pressure through special laser-drilled micro-holes. This paper covers the latest investigations and findings regarding the design of flow-optimized micro-holes, the laser drilling process, the friction characterization on tool radii, and the tool wear to be expected when using the lubrication medium CO2.
Open Access
Kontrolle und Identifizierung von Pressteilen im freien Fall : Digitalisierung beim Kaltfließpressen durch Freifallinspektion und -kontrolle
(2023) Deliktas, Tahsin; Liewald, Mathias; Clauß, Philipp; Schmid-Schirling, Tobias; Kuntz, Iris; Feurer, Matthias; Dimitropoulos, Georgios; Wientapper, Folker; Räuchle, Friedrich
Open Access
Perspectives on data-driven models and its potentials in metal forming and blanking technologies
(2022) Liewald, Mathias; Bergs, Thomas; Groche, Peter; Behrens, Bernd-Arno; Briesenick, David; Müller, Martina; Niemietz, Philipp; Kubik, Christian; Müller, Felix
Today, design and operation of manufacturing processes heavily rely on the use of models, some analytical, empirical or numerical i.e. finite element simulations. Models do reflect reality as best as their design and structure may appear, but in many cases, they are based on simplifying assumptions and abstractions. Reality in production, i.e. reflected by measures such as forces, deflections, travels, vibrations etc. during the process execution, is tremendously characterised by noise and fluctuations revealing a stochastic nature. In metal forming such kind of impact on produced product today in detail is neither explainable nor supported by the aforementioned models. In industrial manufacturing the game to deal with process data changed completely and engineers learned to value the high significance of information included in such digital signals. It should be acknowledged that process data gained from real process environments in many cases contain plenty of technological information, which may lead to increase efficiency of production, to reduce downtime or to avoid scrap. For this reason, authors started to focus on process data gained from numerous metal forming technologies and sheet metal blanking in order to use them for process design objectives. The supporting idea was found in a potential combination of conventional process design strategies with new models purely based on digital signals captured by sensors, actuators and production equipment in general. To utilise established models combined with process data, the following obstacles have to be addressed: (1) acquired process data is biased by sensor artifacts and often lacks data quality requirements; (2) mathematical models such as neural networks heavily rely on high quantities of training data with good quality and sufficient context, but such quantities often are not available or impossible to gain; (3) data-driven black-box models often lack interpretability of containing results, further opposing difficulties to assess their plausibility and extract new knowledge. In this paper, an insight on usage of available data science methods like feature-engineering and clustering on metal forming and blanking process data is presented. Therefore, the paper is complemented with recent approaches of data-driven models and methods for capturing, revealing and explaining previously invisible process interactions. In addition, authors follow with descriptions about recent findings and current challenges of four practical use cases taken from different domains in metal forming and blanking. Finally, authors present and discuss a structure for data-driven process modelling as an approach to extent existing data-driven models and derive process knowledge from process data objecting a robust metal forming system design. The paper also aims to figure out future demands in research in this challenging field of increasing robustness for such kind of manufacturing processes.
Open Access
Residual stresses in deep-drawn cups made of duplex stainless steel X2CrNiN23-4 : influence of the drawing depth
(2021) Simon, Nicola; Erdle, Hannes; Walzer, Stefan; Gibmeier, Jens; Böhlke, Thomas; Liewald, Mathias
Residual stress development in deep drawing processes is investigated based on cylindrical cups made of duplex stainless steel sheet. Using a two-scale approach combining finite element modelling with a mean field homogenization scheme the macro residual stresses as well as the phase-specific micro residual stresses regarding the phases ferrite and austenite are calculated for steel X2CrNiN23-4 for various drawing depths. The simulation approach allows for the numerical efficient prediction of the macro and phase-specific micro residual stress in every integration point of the entire component. The simulation results are validated by means of X‑ray diffraction residual stress analysis applied to a deep-drawn cup manufactured using corresponding process parameters. The results clearly indicate that the fast simulation approach is well suited for the numerical prediction of residual stresses induced by deep drawing for the two-phase duplex steel; the numerical results are in good agreement with the experimental data. Regarding the investigated process, a significant influence of the drawing depth, in particular on the evolution of the residual stress distribution in drawing direction, is observed. Considering the appropriate phase-specific strain hardening, the two-scale approach is also well suited for the prediction of phase specific residual stresses on the component level.
Open Access
Study on mixing behaviour of aluminium-ceramic powder having high SiC volume fractions up to 50 vol.%
(2023) Speth, Marco; Riedmueller, Kim Rouven; Liewald, Mathias
Aluminium matrix composites (AMC) do combine a high lightweight potential with a wide range of specific mechanical or thermal properties, depending on their material composition or the content of reinforcement particles, respectively. Currently, the three main production technologies for manufacturing such AMC are powder metallurgy, semi-solid processes and casting. Here, the AMC´s reinforcement proportion that can be processed depends on the chosen manufacturing strategy and is therefore often limited to a maximum value of 30 vol. %, due to agglomeration and porosity problems. In this context, the main objective is to understand the fundamental mixing behaviour of powder mixtures for AMC green body production having reinforcement contents of up to 50 vol.% SiCp. For this purpose, powder mixtures of monomodal AlSi7Mg0.6 and different SiCp fractions were prepared with different mixing times and speeds to investigate the influence of these mixing parameters on the homogeneity of the particle distribution. Afterwards, the influence of powder size on the mixing process was investigated. The results showed that a slower mixing speed resulted in faster homogenisation as well as a larger particle size can be faster mixed. Furthermore, a regression model was developed using mixing time, speed and particle loading, to determine sufficient mixing parameters.
Open Access
The “third body” approach to joining of metals by simple shear under pressure
(2024) Beygelzimer, Yan; Grötzinger, Karl C.; Liewald, Mathias; Estrin, Yuri; Kulagin, Roman
A continuum mechanics approach to cold welding (CW) of metals under shear is considered. The main idea is to treat a weld joint as an extra material-a “third body” in its own right. Its properties stem from plastic co‐deformation of the two contacting alloys. The mechanical characteristics of the weld joint, i.e., its strength and plasticity in the complex stress state, are determined by the deformation history of the “third body.” The proposed approach enables a unified description of the CW process itself, as well as the subsequent variation of shape of the composite material with the weld joint.
Open Access
Volatile lubricants injected through laser drilled micro holes enable efficiently hydrocarbon-free lubrication for deep drawing processes
(2023) Reichle, Paul; Reichardt, Gerd; Henn, Manuel; Umlauf, Georg; Barz, Jakob; Riedmüller, Kim Rouven; Liewald, Mathias; Tovar, Günter E. M.
In order to reduce the use of classic lubricants such as synthetic or mineral oils, emulsions or waxes in the deep drawing process, a new tribological system based on volatile lubricants was investigated. In this system, a volatile medium is injected under high pressure through laser drilled micro holes directly into the contact zone between the tool and the sheet metal and serves as a temporary lubricant. In order to investigate this tribological system under realistic conditions, strip drawing experiments with different volatile lubricants (air, nitrogen, carbon dioxide and argon) were performed on galvanized sheets. Therefore, a new generation of strip drawing tools was designed and numerically calculated for low elastic deformations to ensure a uniform contact pressure distribution over the entire friction contact area. To obtain a homogeneous distribution of the volatile lubricants, a number of micro holes with a depth of several millimeters were drilled into the hardened strip drawing jaws using ultrashort pulsed laser radiation. Taking into account the capabilities of this laser drilling technique in terms of size and shape of the micro holes, computational fluid dynamics simulations were performed to predict the flow behavior of the lubricant within the micro hole as well as the contact zone and were compared with observable effects in outflow tests. The chemical composition of the acting tribological layers was characterized by means of X-ray photoelectron spectroscopy and their changes during the deep drawing process were correlated with the lubricants used as well as the measured wear and friction values.
Open Access
Zyklische Scherprüfung metallischer Folien : Nutzen von Daten in der Umformtechnik - Potenziale der Digitalisierung
(2023) Karadogan, Celalettin; Beck, Maxim; Cyron, Patrick; Riedmüller, Kim Rouven; Liewald, Mathias