SLM-Topo: Development of a process specific topology optimization method for additive manufacturing of lightweight structures examplified by the SLM process
Lightweight Construction, Textile Technology
Mechanical Properties of Metallic Materials and their Microstructural Origins
Final Report Abstract
In this DFG project, a topology optimization method for the synthesis of stiffness-optimized designs was developed, which takes into account the inhomogeneously distributed elastic material parameters (Young's modulus, shear modulus, transverse contraction number) due to the process of selective laser melting (SLM) on the basis of geometric characteristics (nearsurface areas and overhangs) and complies with a global strength restriction. The developed optimization method is characterized by the fact that in each iteration of the topology optimization an interruption takes place first. Then, based on the design resulting from the interruption, the three porous areas including the corresponding material properties are determined from the SLM and transferred to the next iteration as input parameters for the calculation. This procedure is repeated until a convergence criterion is reached. This creates an opportunity to integrate the boundary conditions of the SLM in a sensitivity-based topology optimization. The claim is that the targeted, iterative manipulation of the topology optimization can achieve an improved product design in terms of stiffness compared to a standardized topology optimization. The results of the optimization method show that with a restriction-free optimization, the iterative interruption and adaptation of the material properties produces a design that has an enlarged surface area and prefers thin structures compared to a standard topology optimization. This generates an increased weight-specific stiffness compared to a standard topology optimization. The additional introduction of a maximum stress restriction leads to the conclusion that the iterative consideration of the porous areas redistributes the available material in such a way that the maximum permissible stresses can be better maintained and at the same time a lower overall stress level is achieved. To investigate the formation of process-related porosity, test specimens with different process parameters were first produced using the SLM process. By means of archimedean and metallographic investigations, a clear influence of the process parameters on the formation of porosity could be demonstrated. Based on this, ultra-sound spectroscopic analyses showed that the material stiffness decreases with increasing porosity. Furthermore, a slight elastic anisotropy was shown, especially with unsuitable process parameters, which could be attributed to the morphology of the pores using micro-computed tomography (µCT) examinations. Finally, optimized SLM process parameters could be derived from the results, with which the following investigations were carried out. As a characteristic value for the maximum stress criterion used in the context of topology optimization, the yield strength of the test specimens built up using SLM was first determined using tensile tests. The investigation of geometric characteristics was carried out using reference test specimens. µCT investigations showed the formation of three characteristic areas with regard to porosity: contour, hatching and interface areas. The size and shape of the characteristic areas are strongly dependent on the build-up angle. Using numerical characterization methods, the local stiffness in the characteristic areas was finally determined and entered into the database for transfer to the optimization algorithm.
Publications
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SLM-Topo – A topology optimization method for additive manufacturing of lightweight design structures using the selective laser melting process. In NAFEMS Nordic Seminar (S. 62–63). Helsinki, Finnland.
Albers, A., Holoch, J., Dietrich, S. & Spadinger, M.
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Einfluss unterschiedlicher Modellierung von Randschicht und innerem Volumen auf eine 2D Topologieoptimierung. In NAFEMS DACH Konferenz (S. 106–109). Online Konferenz.
Holoch, J., Träger, L. & Albers, A.
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SLM- Topo – Prozessspezifische Topologieoptimierungsmethode für im Selektiven Laserschmelzen gefertigte Leichtbaustrukturen. Industrie 4.0 Management, S. 45–49.
Holoch, J., Czink, S., Spadinger, M., Dietrich, S., Schulze, V. & Albers, A.
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Investigation on the Influence of Different Modeling of Multiple Surface Layers on a 3D Topology Optimization. In NAFEMS World Congress (S. 1–14). Online Konferenz.
Holoch, J., Lenhardt, S., Renz, R. & Albers, A.
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Additive Fertigung von Aluminiumstrukturen im SLM-Prozess: Berücksichtigung der Prozesscharakteristiken in einer Topologieoptimierung zur Unterstützung der Designfindung. NAFEMS Online-Magazin, 61(1), 65–73.
Holoch, J., Lenhardt, S. & Albers, A.
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Design of Selective Laser Melting (SLM) Structures: Consideration of Different Material Properties in Multiple Surface Layers Resulting from the Manufacturing in a Topology Optimization. Algorithms, 15(3), 99.
Holoch, Jan; Lenhardt, Sven; Revfi, Sven & Albers, Albert
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Einfluss verschiedener Bauteilabmes sungen auf eine Topologieoptimierungsmethode zur iterativen Berücksichtigung elas tischer Materialeigenschaften aus dem SLM. In NAFEMS DACH Konferenz (S. 495– 500). Bamberg.
Holoch, J., Lenhardt, S. & Albers, A.
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SLM-Topo: Topology optimisation designed for laser based additive manufacturing
Czink, S. & Holoch, J.
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Ultrasonic evaluation of elastic properties in laser powder bed fusion manufactured AlSi10Mg components. NDT & E International, 132, 102729.
Czink, Steffen; Dietrich, Stefan & Schulze, Volker
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Influence of Different Building Directions on a Topology Optimization Method for the Iterative Consideration of Varying Elastic Material Properties from Powder Bed Fusion. In NAFEMS World Congress (S. 1–4). Tampa, USA.
Holoch, J. & Albers, A.
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Process-Specific Topology Optimization Method Based on Laser-Based Additive Manufacturing of AlSi10Mg Components: Material Characterization and Evaluation. Processes, 11(3), 648.
Czink, Steffen; Holoch, Jan; Renz, Robert; Schulze, Volker; Albers, Albert & Dietrich, Stefan
