TY - GEN A1 - Lehrer, Tobias A1 - Kaps, Arne A1 - Daiminger, Tobias A1 - Lepenies, Ingolf A1 - Duddeck, Fabian A1 - Wagner, Marcus T1 - Analysis of Global Sensitivities for One-Step and Multi-step Deep-Drawing Simulations T2 - 16th German LS-DYNA Forum : October 11-13, 2022, Bamberg, Germany and online : Book of Abstracts N2 - In practical use cases, simulation engineers are confronted with uncertainties in the simulation parameters. Normally, trust in a model is built from experience, practical assumptions, and parameter studies. This approach, though, is based on the assumption that few parameter combinations are sufficient to represent the whole design space. This lacks an appraisable mathematical basis. To get insights into which parameters most strongly affect the results, a global sensitivity analysis can be conducted [2, 3]. The results are utilized to rank the most influential parameters and to filter less relevant ones. This gives feedback which improved set of input data will lead to more certainty in the simulation results. To enable this in the framework of multi-fidelity analysis and optimization, we compare here global sensitivities and uncertainties of the implicit One-Step approach (low-fidelity) with those of the explicit multi-step deep drawing approach (high-fidelity). Y1 - 2022 UR - https://www.dynamore.de/de/fortbildung/konferenzen/vergangene/16-ls-dyna-forum-2022/2022-proceedings.pdf SN - 978-3-9816215-8-7 SP - 117 EP - 118 PB - DYNAmore GmbH CY - Stuttgart ER - TY - CHAP A1 - Wagner, Marcus A1 - Lehrer, Tobias A1 - Franke, Markus A1 - Al-Abadi, Ali A1 - Gamil, Ahmed T1 - A Tank Resonance Model for Power Transformers T2 - ARWtr 2022 proceedings, 2022 7th Advanced Research Workshop on Transformers (ARWtr): October (23)24-26, 2022, Baiona, Spain N2 - During the factory acceptance test, the sound levels are measured. If the measured sound levels exceed pre-specified values, modifications on the transformer’s active part and/or tank need to be conducted. Tank resonance, if occurs, at twice main power frequency and its higher harmonics is one of the main reasons of amplifying the generated sound levels. Therefore, it is preferable to know already in the design stage about the occurrence of the tank resonance and propose reliable tank solutions. The current study presents a newly developed model for calculating the mode shapes and its corresponding eigenfrequencies of the tank. Y1 - 2022 U6 - https://doi.org/10.23919/ARWtr54586.2022.9959917 SP - 7 EP - 12 PB - IEEE ER - TY - JOUR A1 - Schmailzl, Anton A1 - Käsbauer, Johannes A1 - Martan, Jiří A1 - Honnerová, Petra A1 - Schäfer, Felix A1 - Fichtl, Maximilian A1 - Lehrer, Tobias A1 - Prušáková, L. A1 - Tesař, Jiří A1 - Skála, J. A1 - Honner, Milan A1 - Hierl, Stefan T1 - Measurement of Core Temperature through Semi-Transparent Polyamide 6 using Scanner-Integrated Pyrometer in Laser Welding JF - International Journal of Heat and Mass Transfer N2 - Predicting the core temperature during welding is an ambitious aim in many research works. In this work, a 3D-scanner with integrated pyrometer is characterized and used to measure the temperature during quasi-simultaneous laser transmission welding of polyamide 6. However, due to welding in an overlap configuration, the heat radiation emitted from the joining zone of a laser transmission weld has to pass through the upper polymer, which is itself a semi-transparent emitter. Therefore, the spectral filtering of the heat radiation in the upper polymer is taken into account by calibrating the pyrometer for the measurement task. Thermal process simulations are performed to compare the temperature field with the measured temperature signal. The absorption coefficients of the polymers are measured, in order to get precise results from the computation. The temperature signals during welding are in good agreement with the computed mean temperature inside the detection spot, located in the joining area. This is also true for varying laser power, laser beam diameter and the carbon black content in the lower polymer. Both, the computed mean temperature and the temperature signal are representing the core temperature. In order to evaluate the spatial sensitivity of the measurement system, the emitted heat radiation from both polymers is calculated on basis of the computed temperature field. Hereby it is found, that more than 90 percent of the detected heat radiation comes from the joining area, which is a crucial information for contact-free temperature measurement tasks on semi-transparent polymers. KW - Semi-transparent polymer KW - Pyrometer KW - Laser transmission welding KW - Temperature KW - measurement Y1 - 2020 U6 - https://doi.org/10.1016/j.ijheatmasstransfer.2019.118814 VL - 146 IS - January PB - Elsevier ER - TY - GEN A1 - Lehrer, Tobias A1 - Stocker, Philipp A1 - Duddeck, Fabian A1 - Wagner, Marcus T1 - Comparison of Low- vs. High-Dimensional Machine Learning Approaches for Sheet Metal Drawability Assessment T2 - Third International Conference on Computational Science and AI in Industry (CSAI 2023), Trondheim, Norway, 28-30 August 2023 N2 - Developing new deep-drawn sheet metal parts is a challenging task due to conflicting demands for low costs, durability, and crash properties. Ensuring manufacturability throughout geometrical changes adds to the complexity, leading engineers to rely on experience-driven iterative design changes that compromise requirements and lack reproducibility. Finite Element (FE) simulation models are employed to ensure manufacturability, albeit at the expense of high computational costs and delays in part development. To improve efficiency, a Machine learning (ML)-centered approach was proposed to ensure manufacturability. However, the limited availability of data raises uncertainty about whether a low- or high-dimensional ML approach is most suitable for drawability assessment. This work compares the accuracy of a low-dimensional, feature-based Linear Support Vector surrogate and an adapted high-dimensional PointNet model under different dataset sizes. The dataset is composed of parametrically generated, U-shaped structural sheet metal parts. We use a one-step simulation scheme and evaluate results with a Forming Limit Diagram (FLD) to label drawability. Results show the point of transition to be at about 500 training samples, from which onwards Deep learning is advantageous. Moreover, the generalizability of these models is tested on a second dataset with topologically similar components. This is to assess the potential for a geometrically more comprehensive evaluation. We discuss several influences on model performances and outline future potentials. Y1 - 2023 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:898-opus4-64772 PB - International Centre for Numerical Methods in Engineering ER - TY - JOUR A1 - Lehrer, Tobias A1 - Kaps, Arne A1 - Lepenies, Ingolf A1 - Duddeck, Fabian A1 - Wagner, Marcus T1 - Classification and regression models for drawability assessment in deep drawing JF - International Journal of Material Forming Y1 - 2023 IS - Noch nicht erschienen PB - Springer ER - TY - JOUR A1 - Lehrer, Tobias A1 - Kaps, Arne A1 - Lepenies, Ingolf A1 - Duddeck, Fabian A1 - Wagner, Marcus T1 - 2S-ML: A simulation-based classification and regression approach for drawability assessment in deep drawing JF - International Journal of Material Forming N2 - New structural sheet metal parts are developed in an iterative, time-consuming manner. To improve the reproducibility and speed up the iterative drawability assessment, we propose a novel low-dimensional multi-fidelity inspired machine learning architecture. The approach utilizes the results of low-fidelity and high-fidelity finite element deep drawing simulation schemes. It hereby relies not only on parameters, but also on additional features to improve the generalization ability and applicability of the drawability assessment compared to classical approaches. Using the machine learning approach on a generated data set for a wide range of different cross-die drawing configurations, a classifier is trained to distinguish between drawable and non-drawable setups. Furthermore, two regression models, one for drawable and one for non-drawable designs are developed that rank designs by drawability. At instantaneous evaluation time, classification scores of high accuracy as well as regression scores of high quality for both regressors are achieved. The presented models can substitute low-fidelity finite element models due to their low evaluation times while at the same time, their predictive quality is close to high-fidelity models. This approach may enable fast and efficient assessments of designs in early development phases at the accuracy of a later design phase in the future. KW - One-step KW - Deep drawing KW - Drawability KW - Meta-modeling KW - Machine learning Y1 - 2023 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:898-opus4-64664 N1 - Corresponding author: Tobias Lehrer VL - 16 SP - 1 EP - 17 PB - Springer ER - TY - JOUR A1 - Kaps, Arne A1 - Lehrer, Tobias A1 - Lepenies, Ingolf A1 - Wagner, Marcus A1 - Duddeck, Fabian T1 - Multi-fidelity optimization of metal sheets concerning manufacturability in deep-drawing processes JF - Structural and Multidisciplinary Optimization N2 - Multi-fidelity optimization, which complements an expensive high-fidelity function with cheaper low-fidelity functions, has been successfully applied in many fields of structural optimization. In the present work, an exemplary cross-die deep-drawing optimization problem is investigated to compare different objective functions and to assess the performance of a multi-fidelity efficient global optimization technique. To that end, hierarchical kriging is combined with an infill criterion called variable-fidelity expected improvement. Findings depend significantly on the choice of objective function, highlighting the importance of careful consideration when defining an objective function. We show that one function based on the share of bad elements in a forming limit diagram is not well suited to optimize the example problem. In contrast, two other definitions of objective functions, the average sheet thickness reduction and an averaged limit violation in the forming limit diagram, confirm the potential of a multi-fidelity approach. They significantly reduce computational cost at comparable result quality or even improve result quality compared to a single-fidelity optimization. KW - Multi-fidelity optimization KW - Efficient global optimization KW - Sheet metal forming KW - Deep drawing Y1 - 2023 U6 - https://doi.org/10.1007/s00158-023-03631-8 VL - 66 PB - Springer Nature ER - TY - JOUR A1 - Lehrer, Tobias A1 - Kaps, Arne A1 - Lepenies, Ingolf A1 - Raponi, Elena A1 - Wagner, Marcus A1 - Duddeck, Fabian T1 - Complementing Drawability Assessment of Deep-Drawn Components with Surrogate-Based Global Sensitivity Analysis JF - ASCE-ASME Journal of Risk and Uncertainty in Engineering Systems, Part B: Mechanical Engineering N2 - In the early-stage development of sheet metal parts, key design properties of new structures must be specified. As these decisions are made under significant uncertainty regarding drawing configuration changes, they sometimes result in the development of new parts that, at a later design stage, will not be drawable. As a result, there is a need to increase the certainty of experience-driven drawing configuration decisions. Complementing this process with a global sensitivity analysis can provide insight into the impact of various changes in drawing configurations on drawability, unveiling cost-effective strategies to ensure the drawability of new parts. However, when quantitative global sensitivity approaches, such as Sobol's method, are utilized, the computational requirements for obtaining Sobol indices can become prohibitive even for small application problems. To circumvent computational limitations, we evaluate the applicability of different surrogate models engaged in computing global design variable sensitivities for the drawability assessment of a deep-drawn component. Here, we show in an exemplary application problem, that both a standard kriging model and an ensemble model can provide commendable results at a fraction of the computational cost. Moreover, we compare our surrogate models to existing approaches in the field. Furthermore, we show that the error introduced by the surrogate models is of the same order of magnitude as that from the choice of drawability measure. In consequence, our surrogate models can improve the cost-effective development of a component in the early design phase. KW - sheet metal forming KW - deep drawing KW - global sensitivity analysis KW - variance-based sensitivity analysis KW - metamodeling Y1 - 2024 U6 - https://doi.org/10.1115/1.4065143 SN - 2332-9025 SP - 1 EP - 10 PB - ASME ER -