F12
Additive Manufacturing 3

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13:20
conference time (CEST, Berlin)
Evaluation of the Temperature History During Extrusion Based Additive Manufacturing
27/10/2021 13:20 conference time (CEST, Berlin)
Room: F
R. Hein (DLR - Deutsches Zentrum für Luft- und Raumfahrt, DEU)
R. Hein (DLR - Deutsches Zentrum für Luft- und Raumfahrt, DEU)
Additive manufacturing (AM) is considered as a key technology for the efficient production of individualized components. The technique enables the tool-less production of complex geometries and designs that could not be realized cost-effectively with conventional manufacturing methods. The focus of the presentation is on the Fused Filament Fabrication (FFF), where a thermoplastic filament is extruded trough a nozzle. The material is deposited layer by layer until the final part is build. Thereby, high temperature gradients occur within the part when the hot material is deposited on the lower layers. During the printing process the lower layers are reheated several times so that the material properties are influenced even after the deposition has been made. The thermal history has major effects on crucial material properties such as the degree of crystallization or viscosity. An insufficient viscosity can lead to a weak bonding and reduced strengths between adjacent layers. An inadequate degree of crystallization influences both the structural properties such as the stiffness or the degree of bonding but also the dimensional accuracy due to subsequent shrinkage effects. Additionally, the temperature gradients cause residual stresses which are partly relaxed to varying part deformations. The remaining stresses can lead to premature failures. To achieve a high and repeatable part quality as well as a low scatter in the final part dimension an in-depth process understanding is required considering the underlying material-process-part-interactions. In order to analyze these complex multiphysics processes, manufacturing process simulations are suitable method. A main requirement for the numerical analysis of AM processes is the calculation of the thermal history as accurately as possible. The objective of this work is, therefore, to evaluate the prediction accuracy of currently available AM process simulation tools. For this purpose, an AM process simulation of a cuboid is performed using the Abaqus AM plug-in. The cuboid made of PETG is printed with a Prusa i3 MK3. In order to monitor the temperature history during the printing process very thin thermocouples (0.25mm) are integrated in the center and distributed over the part thickness. The machine code (gcode) is transferred to Abaqus and the transient temperature fields are predicted in dependency on the thermal boundary conditions. The predicted temperatures are compared to the measurements and the prediction accuracy is evaluated.
Additive Manufacturing, Process simulation, Thermal history, Thermoplastic materials
13:40
conference time (CEST, Berlin)
Finite Element Analysis of Post-build and Inter-layer Rolling for Large-scale Components Deposited by Wire Arc Additive Manufacturing
27/10/2021 13:40 conference time (CEST, Berlin)
Room: F
Y. Sun, V. Gornyakov, J. Ding, S. Williams (Cranfield University, GBR)
Y. Sun, V. Gornyakov, J. Ding, S. Williams (Cranfield University, GBR)
In recent decade high demand was observed for economical small-batch fabrication of components for aerospace, defense, and oil and gas industries. Wire Arc Additive Manufacturing (WAAM) is a promising candidate technology for replacement or supplement of conventional fabrication processes that rely on billets and forgings. However, WAAM-built parts suffer from residual stress and distortion, which limit wider application of WAAM in the industry. High-pressure post-build and inter-layer rolling was found effective to mitigate residual stress and distortion, but the mitigation mechanism is complicated and needs to be understood. Finite element analysis method proves robust and accurate for simulation of thermo-mechanical effects that occur during WAAM and rolling processes. However, large-scale post-build and inter-layer rolling simulations are challenging due to enormous computational cost. In this study an efficient modelling technique was developed for simulation of large-scale manufacturing processes through determination of steady-state solution using a reduced-size model and then mapping the solution to the full-size component. This technique has been successfully implemented for investigation of residual stress and plastic strain evolution during post-build and inter-layer rolling of a WAAM deposited wall. The numerical predictions were verified against experimental results. The tensile plastic strain induced by the rolling caused relaxation of the tensile residual stress generated by the WAAM deposition. Cyclic formation of tensile residual stress occurred during the WAAM deposition, whereas inter-layer rolling counteracted the residual stress development. The slotted roller induced larger magnitude longitudinal plastic strain and more efficiently reduced tensile residual stress in the WAAM wall, as compared to the flat roller. The residual stress, plastic strain and distortion were also compared for the rolled WAAM component before and after clamps removal. It was found that the clamps removal caused minor redistribution of residual stress in the post-build and inter-layer rolled components, since the rolling already mitigated the WAAM residual stress in the clamped condition.
Wire Arc Additive Manufacturing, large scale components, residual stress, distortion, inter-layer rolling, post-build rolling, FE modelling
14:00
conference time (CEST, Berlin)
Printing Path Based Modeling of FFF Meso-structures for Finite Element Analysis
27/10/2021 14:00 conference time (CEST, Berlin)
Room: F
M. Springmann, S. Mirzaei, P. Middendorf (Universität Stuttgart IFB, DEU)
M. Springmann, S. Mirzaei, P. Middendorf (Universität Stuttgart IFB, DEU)
The Fused Filament Fabrication process (FFF) is a well-known and widely used additive manufacturing process to produce mainly prototypes and pilot series using thermoplastic materials. Continuous improvements in printer hardware and the development of suitable materials make its use in end-products conceivable. The additive manufacturing principle allows the production of geometrically complex components, e.g. topology-optimized components, which would be impossible using conventional manufacturing processes. Due to the layer-by-layer printing principle and manifold process parameters, FFF components usually exhibit a complex meso-structure and show strong anisotropy of the mechanical properties. The meso-structure is created by path-based extrusion of the filaments and thus determines the mechanical behavior of the structure. The relationships between meso-structure and mechanical behavior cannot be captured by common design methods. Due to the lack of structural mechanical analysis capabilities, the use of FFF components in end-use applications requires component-specific experimental validation. In this work, an approach for realistic modeling of the meso-structure of FFF components for a finite element analysis (FEA) is developed. The model is based on the actual printing path. Using a Python script, the relevant coordinates can be extracted from the machine code and movements without material extrusion can be removed. Based on the extracted coordinates, a wireframe model of the printing path is generated in a CAD environment. The geometry of the individual filaments as solids is created by sweeping an elliptical filament cross-section along the wireframe model. Subsequently, the generated meso-structure is partitioned and meshed using the FEM software ABAQUS. A study is performed with the aim of investigating the required number of elements, their size and the expected computational effort. The method is validated with tensile experiments. For this purpose, flat tensile specimens with 100% infill and a 0°/90° oriented infill are fabricated and tested. Using the printing path based modeling method, the tensile tests are modeled and simulated in ABAQUS.
Additive Manufacturing, Fused Filament Fabrication, Printing path based Mesostructural Modeling, Finite Element Analysis
14:20
conference time (CEST, Berlin)
Thermo-mechanical Modelling for Metal Additive Manufacturing
27/10/2021 14:20 conference time (CEST, Berlin)
Room: F
M. Mashhood, A. Zilian, B. Peters, (Universität Luxemburg, LUX); D. Baroli (Aachen Institute for Advanced Study in Computational Engineering Science (AICES), DEU); E. Wyart (Plastic Omnium Advanced Innovation and Research, BEL)
M. Mashhood, A. Zilian, B. Peters, (Universität Luxemburg, LUX); D. Baroli (Aachen Institute for Advanced Study in Computational Engineering Science (AICES), DEU); E. Wyart (Plastic Omnium Advanced Innovation and Research, BEL)
The additive manufacturing (AM) is suitable approach for the manufacturing of complex metal parts in future. The thermal strain and stress play vital role in characteristic of the manufactured metal part. After the laser creates melt pool in the metal powder bed, the thermal strain and residual stress come into play in solidified melt pool during cooling down and reheating of material. In the course of complete process, the material properties are also function of material temperature. So in this scientific contribution, modelling and solution of energy balance equation tracks down the evolution of the temperature profile in the part being manufacture. For the structural analysis, the elasto-plastic material is assumed. The thermal loads due to the thermal conduction are applied at the specimen under production, which results in elasto-plastic deformation. The Finite Element Analysis (FEA) platform FEniCS [1] is utilized for the simulation of models under consideration. This platform offers the range of element types and functionalities for FEA of evolving metal part during AM process. It predicts the part-scale temperature solution and the residual distortion displacements in the result of permanent deformation in solidified melt pool. In result, the thermomechanical analysis platform is settled and also its application is widened by activating the finite elements in domain for layer by layer addition of material. Which now has to be further developed for advanced elements activation strategy as well as exploring the possibilities of hybrid approaches in this respect[2]. REFERENCES [1] Alnaes, M. S. Blechta, J. Hake, J. Johansson, A. Kehlet, B. Logg, A. Richardson, C. Ring, J.Rognes, M. E. and Wells, G. N. The FEniCS Project Version 1.5. Archive of Numerical Soft-ware(2015), Vol. 3., 100:9–23. [2] Carraturo, M. and Kollmannsberger, S. and Reali, A. and Auricchio, F. and Rank, E. An immersed boundary approach for residual stress evaluation in SLM processes.
Selective Laser Melting, Metal Additive Manufacturing, Thermomechanical Coupling
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