TY - GEN A1 - Imran, Muhammad A1 - Afzal, Muhammad Junaid A1 - Buhl, Johannes A1 - Bambach, Markus A1 - Dunlap, Anthony A1 - Schwedt, Alexander A1 - Aretz, Anke A1 - Wang, Shuhan A1 - Lohmar, Johannes A1 - Hirt, Gerhard T1 - Evaluation of process-induced damage based on dynamic recrystallization during hot caliber rolling T2 - Production Engineering Y1 - 2020 U6 - https://doi.org/10.1007/s11740-019-00932-0 SN - 1863-7353 SN - 0944-6524 VL - 14 IS - 1 SP - 5 EP - 16 ER - TY - BOOK A1 - Bähr, Martin A1 - Buhl, Johannes A1 - Radow, Georg A1 - Schmidt, Johannes A1 - Bambach, Markus A1 - Breuß, Michael A1 - Fügenschuh, Armin T1 - Stable honeycomb structures and temperature based trajectory optimization for wire-arc additive manufacturing Y1 - 2019 U6 - https://doi.org/10.26127/btuopen-5079 CY - Cottbus ER - TY - RPRT A1 - Beisegel, Jesse A1 - Buhl, Johannes A1 - Izar, Rameez A1 - Schmidt, Johannes A1 - Bambach, Markus A1 - Fügenschuh, Armin ED - Fügenschuh, Armin T1 - Mixed-integer programming for additive manufacturing Y1 - 2021 U6 - https://doi.org/10.26127/BTUOpen-5731 CY - Cottbus ER - TY - BOOK A1 - Schmidt, Johannes A1 - Buhl, Johannes A1 - Fügenschuh, Armin T1 - A finite element approach for trajectory optimization in Wire-Arc Additive Manufacturing Y1 - 2021 U6 - https://doi.org/10.26127/BTUOpen-5575 CY - Cottbus ER - TY - GEN A1 - Bähr, Martin A1 - Buhl, Johannes A1 - Radow, Georg A1 - Schmidt, Johannes A1 - Bambach, Markus A1 - Breuß, Michael A1 - Fügenschuh, Armin T1 - Stable honeycomb structures and temperature based trajectory optimization for wire-arc additive manufacturing T2 - Optimization and Engineering N2 - We consider two mathematical problems that are connected and occur in the layer-wise production process of a workpiece using wire-arc additive manufacturing. As the first task, we consider the automatic construction of a honeycomb structure, given the boundary of a shape of interest. In doing this, we employ Lloyd’s algorithm in two different realizations. For computing the incorporated Voronoi tesselation we consider the use of a Delaunay triangulation or alternatively, the eikonal equation. We compare and modify these approaches with the aim of combining their respective advantages. Then in the second task, to find an optimal tool path guaranteeing minimal production time and high quality of the workpiece, a mixed-integer linear programming problem is derived. The model takes thermal conduction and radiation during the process into account and aims to minimize temperature gradients inside the material. Its solvability for standard mixed-integer solvers is demonstrated on several test-instances. The results are compared with manufactured workpieces. KW - Mixed-integer linear programming KW - Geometric optimization KW - Eikonal equation KW - Heat transmission KW - Additive manufacturing KW - Centroidal Voronoi tesselation Y1 - 2021 U6 - https://doi.org/10.1007/s11081-020-09552-5 SN - 1573-2924 VL - 22 IS - 2 SP - 913 EP - 974 ER - TY - GEN A1 - Bambach, Markus A1 - Fügenschuh, Armin A1 - Buhl, Johannes A1 - Jensch, Felix A1 - Schmidt, Johannes ED - Bambach, Markus T1 - Mathematical Modeling and Optimization for Powder-Based Additive Manufacturing T2 - Procedia Manufacturing; Part of Special issue: 23rd International Conference on Material Forming Y1 - 2020 U6 - https://doi.org/10.1016/j.promfg.2020.04.158 SN - 2351-9789 VL - 47 SP - 1159 EP - 1163 ER - TY - CHAP A1 - Beisegel, Jesse A1 - Buhl, Johannes A1 - Israr, Rameez A1 - Schmidt, Johannes A1 - Bambach, Martin A1 - Fügenschuh, Armin ED - Cristiani, Emiliano ED - Falcone, Maurizio ED - Tozza, Silvia T1 - Mixed-Integer Programming Models for Two Metal Additive Manufacturing Methods T2 - Mathematical Methods for Objects Reconstruction Y1 - 2023 SN - 978-981-9907-75-5 SN - 978-981-9907-76-2 SP - 121 EP - 155 PB - Springer CY - Heidelberg ER - TY - GEN A1 - Israr, Rameez A1 - Buhl, Johannes A1 - Bambach, Markus T1 - A study on power-controlled wire-arc additive manufacturing using a data-driven surrogate model T2 - The International Journal of Advanced Manufacturing Technology N2 - Wire-arc additive manufacturing (WAAM) provides an alternative for the production of various metal products needed in medium to large batch sizes due to its high deposition rates. However, the cyclic heat input in WAAM may cause local overheating. To avoid adverse effects on the performance of the part, interlayer dwelling and active cooling are used, but these measures increase the process time. Alternatively, the temperature during the WAAM process could be controlled by optimizing the welding power. The present work aims at introducing and implementing a novel temperature management approach by adjusting the weld-bead cross-section along with the welding power to reduce the heat accumulation in the WAAM process. The temperature evolution during welding of weld beads of different cross-sections is investigated and a database of the relation between optimal welding power for beads of various sizes and different pre-heating temperatures was established. The numerical results are validated experimentally with a block-shaped geometry. The results show that by the proposed method, the test shape made was welded with lower energy consumption and process time as compared to conventional constant-power WAAM. The proposed approach efficiently manages the thermal input and reduces the need for pausing the process. Hence, the defects related to heat accumulation might be reduced, and the process efficiency increased. Y1 - 2021 U6 - https://doi.org/10.1007/s00170-021-07358-y SN - 1433-3015 SN - 0268-3768 VL - 177 IS - 7-8 SP - 2133 EP - 2147 ER - TY - GEN A1 - Gerold, Stefanie A1 - Buhl, Johannes A1 - Geiger, Sonja M. T1 - How to Enhance Time Wealth? Insights from Changes in Time Use and Working Conditions During the COVID-19 Lockdown in Germany T2 - Social Indicators Research N2 - This paper investigates the changes in time use, working conditions and subjective time wealth during the COVID-19 pandemic in Germany. Our analysis draws on panel data collected before and during the first lockdown among 786 employees. It employs a recently developed scale on time wealth which has been suggested as a comprehensive measure to capture the subjective experience of time. We provide separate analyses according to gender and essential occupation. First-difference regressions are applied to examine how changes in time use and changes in working conditions during the lockdown affected subjective time wealth. Our results show a general growth in time wealth during the lockdown which is, among other factors, driven by a decline in work hours and an increase in sleep duration. We also find positive effects on time wealth from decreased time pressure at work, more autonomy in organising one’s working day, and an improved reconciliation of work and private life. This study contributes to existing research by identifying key aspects how to improve time wealth among employees. Y1 - 2023 U6 - https://doi.org/10.1007/s11205-023-03252-0 SN - 1573-0921 VL - 171 SP - 349 EP - 371 ER - TY - GEN A1 - Nguyen, Lam A1 - Buhl, Johannes A1 - Bambach, Markus ED - Bambach, Markus T1 - Multi-bead Overlapping Models for Tool Path Generation in Wire-Arc Additive Manufacturing Processes T2 - Procedia Manufacturing; Part of Special issue: 23rd International Conference on Material Forming Y1 - 2020 U6 - https://doi.org/10.1016/j.promfg.2020.04.129 SN - 2351-9789 VL - 47 SP - 1123 EP - 1128 ER - TY - GEN A1 - Hajavifard, Ramin A1 - Maqbool, Fawad A1 - Schmiedt-Kalenborn, Anke A1 - Buhl, Johannes A1 - Bambach, Markus T1 - Integrated Forming and Surface Engineering of Disc Springs by Inducing Residual Stresses by Incremental Sheet Forming T2 - Materials Y1 - 2019 U6 - https://doi.org/10.3390/ma12101646 SN - 1996-1944 VL - 12 IS - 10 ER - TY - GEN A1 - Emdadi, Aliakbar A1 - Bolz, Sebastian A1 - Buhl, Johannes A1 - Weiß, Sabine A1 - Bambach, Markus T1 - Laser Powder Bed Fusion Additive Manufacturing of Fe3Al-1.5Ta Iron Aluminide with Strengthening Laves Phase T2 - Metals Y1 - 2022 U6 - https://doi.org/10.3390/met12060997 SN - 2075-4701 VL - 12 IS - 6 ER - TY - CHAP A1 - Israr, Rameez A1 - Buhl, Johannes ED - Khan, Wasim Ahmed T1 - An Introduction to Additive Manufacturing (AM) of Metals and Its Trends in Wire-Arc Additive Manufacturing (WAAM) Simulations T2 - Machine Tools : An Industry 4.0 Perspective Y1 - 2023 U6 - https://doi.org/10.1201/9781003220985 PB - CRC Press CY - Boca Raton ER - TY - GEN A1 - Ertugrul, Gökhan A1 - Hälsig, Andre A1 - Hensel, Jonas A1 - Buhl, Johannes A1 - Härtel, Sebastian T1 - Efficient Multi-Material and High Deposition Coating including Additive Manufacturing by Tandem Plasma Transferred Arc Welding for Functionally Graded Structures T2 - Metals KW - additive manufacturing powder KW - 3D Plasma Metal Deposition (3DPMD) KW - austenitic stainless steel KW - super-duplex stainless steel KW - multi-material KW - functionally graded KW - high deposition rate KW - arc KW - powder Y1 - 2022 U6 - https://doi.org/10.3390/met12081336 SN - 2075-4701 VL - 12 IS - 8 SP - 1 EP - 17 ER - TY - GEN A1 - Buhl, Johannes A1 - Härtel, Sebastian A1 - Besong, Lemopi Isidore ED - Mocellin, Katia T1 - Temperature Control of the Two-Point Incremental Forming Process to Achieve Homogeneous Martensite Content Based on Finite Element Simulations T2 - Proceedings of the 14th International Conference on the Technology of Plasticity - Current Trends in the Technology of Plasticity, ICTP 2023 - Volume 1 N2 - Deformation-induced martensite has been observed in the incremental sheet forming of metastable austenitic stainless steels (MASS). The presence of martensite improves the characteristics of the springs. Martensite transformation usually occurs at low temperatures (<70 ℃). Depending on the tool speed, incremental forming of disk springs requires between 3 to 5 min. The forming time needs to be short to increase the process output in industrial settings. However, accelerating the process leads to high temperatures above the martensite transformation temperature that suppress martensite formation, necessitating temperature control during forming. It is suggested to enhance the martensite content of the blank by cooling during the forming operation. In this contribution, two-point incremental sheet forming is conducted to determine the influence of process temperature on the phase content of MASS disk springs. A temperature-dependent phase change material model that includes the strain rate effect is implemented in finite element (FE) simulations to predict the martensite content. FE simulations are performed to investigate the convection coefficients and cooling time leading to process temperatures below 70 ℃. The framework can be used to control and speed up the incremental forming of disk springs while maintaining a high martensite content. Y1 - 2023 SN - 978-3-031-41022-2 SN - 978-3-031-41023-9 U6 - https://doi.org/10.1007/978-3-031-41023-9_74 SN - 2195-4356 SP - 739 EP - 747 PB - Springer CY - Cham ER - TY - GEN A1 - Breuß, Michael A1 - Buhl, Johannes A1 - Mansouri Yarahmadi, Ashkan A1 - Bambach, Markus A1 - Peter, Pascal T1 - A Simple Approach to Stiffness Enhancement of a Printable Shape by Hamilton-Jacobi Skeletonization T2 - Procedia Manufacturing N2 - The 3D-Printing technology is ready to produce parts with specific properties like individual stiffness. Based on a predefined outer shape, the inner structure of a printed part defines mainly the mechanical features. By Hamilton-Jacobi skeletonization, a stiffness enhancement of a printable shape can be achieved in a way, that a novel AM-corner includes linear axis function. Originating in the field of shape analysis in computer vision and graphics, the so-called medial axis transform (MAT) is designed for the computation of a structure that resembles the bone structure of biological shapes. The input for MAT computation is typically a shape’s boundary. The arising topological skeletons have proven to provide a useful concept for many applications; however, their computation is generally intricate and also known to rely on many parameters, diminishing the accessibility of skeletonization methods. In this work, the classical Hamilton-Jacobi skeletonization approach is adopted to compute a stability enhancing shape structure. As the basic method has not been designed for the context of additive manufacturing, a set of suitable modifications are introduced to design an algorithm that suits our intended purpose. Unlike the traditional skeletonization schemes, the resulting method appears to be robust and in practice almost completely automated as we can identify useful generic parameter settings. By a finite element method (FEM) study, the elastic stress properties of the AM-corner with linear axis function is validated and printed with in metal (1.4404) with the 3D Selected Laser Melting (SLM) system AconityMIDI. The AM-knot with skeletonization guides approximately 20 times better than a standard knot. While the first obtained results are shown as 2.5 dimensional shapes, it is emphasized that the proposed algorithm offers many possibilities for extensions to three dimensions and variations in context of additive manufacturing. KW - Skeletonization KW - Hamilton-Jacobi skeletonization KW - stiffness enhancement KW - 3D printing KW - additive manufacturing Y1 - 2020 U6 - https://doi.org/10.1016/j.promfg.2020.04.147 SN - 2351-9789 N1 - 23rd International Conference on Material Forming (ESAFORM 2020) VL - Vol. 47 SP - 1190 EP - 1196 ER - TY - GEN A1 - Israr, Rameez A1 - Buhl, Johannes A1 - Härtel, Sebastian A1 - Bambach, Markus T1 - Reinforcement of Tooling Using Residual Stresses Generated by Cladding by Arc Welding T2 - Metals N2 - Cladding is typically used to protect components from wear and corrosion while also improving the aesthetic value and reliability of the substrate. The cladding process induces significant residual stresses due to the temperature difference between the substrate and the clad layer. However, these residual stresses could be effectively utilized by modifying processes and geometrical parameters. This paper introduces a novel methodology for using the weld-cladding process as a cost-effective alternative to various existing reinforcement techniques. The numerical analyses are performed to maximize the reinforcement of a cylindrical tool. The investigation of how the weld cladding develops compressive stresses on the specimen in response to a change in the weld beads and the welding sequence is presented. For the benchmark shape, experimental verification of the numerical model is performed. The influence of the distance between the weld beads and the effect of the tool diameter is numerically investigated. Furthermore, the variation in compressive stresses due to temperature fluctuations during the extrusion process has been evaluated. The results showed that adequate compressive stresses are generated on the welded parts through the cladding process after cooling. More compressive stresses are induced in the tool as the cross-section of the weld bead is increased. Furthermore, keeping a gap between the adjacent beads improves tool reinforcement. Hence, the targeted reinforcement of the substrate can be achieved by optimizing the welding sequence and process parameters. KW - Additive Manufacturing (AM) KW - Wire Arc Additive Manufacturing (WAAM) KW - weld cladding KW - residual stresses KW - reinforcement KW - hole drilling method KW - LS-Dyna KW - numerical simulation Y1 - 2022 U6 - https://doi.org/10.3390/met12060984 SN - 2075-4701 VL - 12 IS - 6 ER - TY - GEN A1 - Afzal, Muhammad Junaid A1 - Maqbool, Fawad A1 - Hajavifard, Ramin A1 - Buhl, Johannes A1 - Walther, Frank A1 - Bambach, Markus ED - Bambach, Markus T1 - Modeling the Residual Stresses Induced in the Metastable Austenitic Stainless Steel Disc Springs manufactured by Incremental Sheet Forming by a Combined Hardening Model with Phase Transformation T2 - Procedia Manufacturing : Part of Special issue: 23rd International Conference on Material Forming Y1 - 2020 U6 - https://doi.org/10.1016/j.promfg.2020.04.300 SN - 2351-9789 VL - 47 SP - 1410 EP - 1415 ER - TY - GEN A1 - Jensch, Felix A1 - Buhl, Johannes A1 - Laue, Robert A1 - Härtel, Sebastian T1 - Application of the plane-strain-compression-test to determine the local mechanical properties of LPBF-manufactured 316l components T2 - Material Forming: The 26th International ESAFORM Conference on Material Forming, Kraków, Poland, April 19-21, 2023 KW - LPBF-Process, Local Properties, Plane-Strain-Compression-Test Y1 - 2023 U6 - https://doi.org/10.21741/9781644902479-17 VL - 28 SP - 149 EP - 149 ER - TY - GEN A1 - Sydow, Benjamin A1 - Jhanji, Avantika A1 - Hälsig, André A1 - Buhl, Johannes A1 - Härtel, Sebastian T1 - The Benefit of the Process Combination of Wire Arc Additive Manufacturing (WAAM) and Forming—A Numerical and Experimental Study T2 - Metals KW - WAAM KW - forming KW - process combination KW - simulation KW - recrystallization KW - hardness KW - heat treatment cycle KW - fine grained mild steel KW - microstructure evolution Y1 - 2022 U6 - https://doi.org/10.3390/met12060988 SN - 2075-4701 VL - 12 IS - 6 ER -