Universität Stuttgart
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Item 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, MathiasResidual 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.Item Open Access Biomimetics design of sandwich-structured composites(2023) Kunzmann, Carsten; Aliakbarpour, Hamaseh; Ramezani, MaziarIn the context of energy efficiency and resource scarcity, lightweight construction has gained significant importance. Composite materials, particularly sandwich structures, have emerged as a key area within this field, finding numerous applications in various industries. The exceptional strength-to-weight ratio and the stiffness-to-weight ratio of sandwich structures allow the reduction in mass in components and structures without compromising strength. Among the widely used core designs, the honeycomb pattern, inspired by bee nests, has been extensively employed in the aviation and aerospace industry due to its lightweight and high resistance. The hexagonal cells of the honeycomb structure provide a dense arrangement, enhancing stiffness while reducing weight. However, nature offers a multitude of other structures that have evolved over time and hold great potential for lightweight construction. This paper focuses on the development, modeling, simulation, and testing of lightweight sandwich composites inspired by biological models, following the principles of biomimetics. Initially, natural and resilient design templates are researched and abstracted to create finished core structures. Numerical analysis is then employed to evaluate the structural and mechanical performance of these structures. The most promising designs are subsequently fabricated using 3D printing technology and subjected to three-point bending tests. Carbon-fiber-reinforced nylon filament was used for printing the face sheets, while polylactic acid (PLA+) was used as the core material. A honeycomb-core composite is also simulated and tested for comparative purposes, as it represents an established design in the market. Key properties such as stiffness, load-bearing capacity, and flexibility are assessed to determine the potential of the new core geometries. Several designs demonstrated improved characteristics compared to the honeycomb design, with the developed structures exhibiting a 38% increase in stiffness and an 18% enhancement in maximum load-bearing capacity.Item Open Access Cold forging of gear components by a modified Samanta process : conference proceedings(2020) Weiß, A.; Deliktas, T.; Liewald, M.; Missal, N.Cold forging of toothed components by extrusion is associated with high punching forces and tool loads, which requires the use of expensive and high-strength tool steels. High process forces result into a substantial tool deflection, which significantly reduces the precision of the toothed components. Thus, the development of alternative processes in order to reduce acting process forces in cold forging is of high interest. A potential process enhancement approach is to use a preform operation where the resulting preform can be formed partwise either in the same or in a subsequent die. Preforms allow to systematically control the material flow in subsequent forming operations. For this reason, the Institute for Metal Forming Technology in Stuttgart has developed a new cold extrusion process for manufacturing toothed components based on the conventional Samanta process. The newly developed die design of the Guided Material Flow-Samanta (GMF-Samanta) process enables efficient cold forging of gears. By means of numerical simulations and forging experiments it was successfully demonstrated that the new Guided Material Flow-Samanta process results into a significant reduction of punch force and normal pressure while simultaneously improving the die filling.Item 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, MathiasA 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.Item 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, FelixToday, 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.Item Open Access Efficient net shape forming of high-strength sheet metal parts by Transversal Compression Drawing(2023) Briesenick, David; Liewald, MathiasIn 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.Item 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.Item 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, MathiasItem 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, RomanA 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.Item 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