Refine
Document Type
- Doctoral thesis (2)
- Working paper (2)
- Scientific article (1)
- Book (1)
Has Fulltext
- yes (6)
Is part of the Bibliography
- no (6)
Keywords
- Additive Fertigung (6) (remove)
Institute
Additive technologies are now widely used for the production of complex precise parts and have high potential for the production of forming dies. In this work, hot-forming dies optimized for additive manufacturing were developed and produced with wire arc direct energy deposition (WA-DED) and laser powder bed fusion (L-PBF) technologies. The concept of lightweight hot-forming dies with a 2D-lattice structure was developed, which reduced the weight of each die by 56%, from 14.2 kg to 6.1 kg, in production using L-PBF. Maraging/precipitation-hardened steel 17-4PH was used as an alternative to traditional hot-working steels with slightly lower mechanical properties and a much higher processability in the additive manufacturing process. The workability of the manufactured dies was confirmed by forging tests on an industrial screw press.
Recent advances in additive manufacturing offer promising opportunities for the fabrication of structures on existing micro-(opto-acoustic )electro-mechanical systems, i.e., chips. This is of particular significance in research and development due to the adaptability and adaptation speed of additive manufacturing. These advantages provide the ability to individualize the fabrication of structures and to enable the rapid prototyping approach. The combination of additive manufacturing on chip already enables current research, especially in photonic and microfluidic fields. Despite this, additive manufacturing on chip has never been applied to acoustic sensors or micro-positioning chips. Such devices could benefit from the mentioned advantages, especially for the fabrication of beam shaping waveguides, packaging, grating and end effector structures. Additive manufacturing by two-photon polymerization lithography gathers interest in industry and research due to its capabilities for the fabrication of structures with minimum feature sizes beyond the diffraction limit. The objective of this work is the investigation of additive manufacturing on chip by two-photon polymerization lithography at the example of an acoustic sensor and a micro-positioning chip. One of the greatest challenges is posed by the optical, thermodynamic, adhesion and alignment effects, which are introduced to the fabrication process by these complex substrates. Optical and thermodynamic models were established, and simulations were performed, culminating in a compensation method to address these effects, which was verified by parameter studies. The substrate alignment was investigated via optical technique, resulting in the development, manufacturing and verification of a novel alignment upgrade to the fabrication system employed in this work. The influence of process materials posed another challenge, as they led to chip performance alterations and restrictions. Chips treated with these materials were characterized, e.g., using high frequency optical microphones. Owing to the high precision of the alignment upgrade and the compensation method developed in this work, additive manufacturing on chip using two-photon polymerization lithography on the investigated devices was reported for the first time and presented for expedient examples, e.g., waveguides, end effectors and gratings. The residue contamination was determined as the main origin of the exhibited performance issues. Development strategies were recommended for further research, to enable additive manufacturing on chip insensitive to residual materials. In this work, the requirements for additive manufacturing on chip were illustrated and the fundamental arrangement to enable the rapid prototyping approach as well as design individualization were demonstrated. The compensation methods developed in this work facilitate upcoming research on desirable chip types that form the basis for optical and microfluidic applications.
Additive Manufacturing of metals has become relevant for industrial applications. The near net-shape production of components produced by Laser Powder Bed Fusion (PBF-LB/M) enables new possibilities in component design combined with a reduction of the amount of needed material. Omitting the extra material, that was part of conventionally produced components due to machining constraints, results in components which in consequence lack the inherent additional safety margins provided by the higher material consumption of conventionally produced components. Therefore, to use PBF-LB/M metals in safety critical applications an in-depth understanding of porosity and internal stresses in parts made by PBF-LB/M is needed. Only non-destructive testing methods—such as computed tomography and residual stress analysis using neutrons—enable the assessment of porosity and stresses in the whole part. In this thesis I tackled creep and tensile static deformed specimens to fill research gaps in this field in terms of analysing PBF-LB/M stainless steel AISI 316L: from structural properties to in-situ behaviour. The initial void population of AISI 316L is studied using X-ray and synchrotron micro computed tomography. Specimens produced with different process parameters were analysed to quantify the influence of process parameters on the initial void population. The possibility to close voids using the laser illumination of subsequent layers is discussed by a quantitative study of the ability of the laser to melt different multiples of the applied layer thickness. The formation of internal stress is inherent to components produced by the PBFLB/ M process. These stresses remain in the components after production as residual stresses. In this thesis a study is presented which aims to unravel the mechanisms that define the spatial distribution of the residual stresses, and their magnitude. In the end, the population of internal voids during mechanical testing is studied by X-ray micro computed tomography. The evolution of damage accumulation in creep specimens is studied at different stages of the creep test. Results are compared to a creep tested conventionally made specimen and to a PBF-LB/M specimen from a tensile test. An interconnection between the PBF-LB/M microstructure and the pattern of damage is revealed.
Effiziente Fertigungssysteme sind wichtiger denn je, um die steigenden Klimaauflagen und die damit verbundenen Anforderungen an die Ressourceneffizienz erfüllen zu können. Klassische Fertigungsverfahren haben dabei den Nachteil, dass diese entweder mit einem hohen Ressourcenverbrauch verbunden sind oder Produktvarianten nicht wirtschaftlich herstellen können. Zwar können additive Fertigungsverfahren wie Selective Laser Melting (SLM), Wire Arc Additive Manufacturing (WAAM) oder Laserpulverauftragschweißen (LPA) durch ihre hohe Flexibilität dieses Problem teilweise beheben, aber bei großvolumigen Bauteilen oder größeren Stückzahlen sind diese Verfahren mit langen Prozesszeiten verbunden und weisen damit eine geringe Produktivität auf.
Dahingegen können hybride Fertigungsverfahren bestehend aus einer Kombination aus einem werkzeuggebundenen Prozess (z. B. Schmieden) und einem werkzeuglosen Verfahren (z. B. Auftragschweißen) eine effiziente Lösung darstellen. Die Herausforderungen sind dabei, die Wechselwirkungen der Fertigungsverfahren zu untersuchen und die Teilprozesse aufeinander abzustimmen. Ziel war es, die negativen Auswirkungen einer Wärmeeinbringung und deren Effekte auf die Mikrostruktur sowie die daraus resultierende Härte und Festigkeit aufzuzeigen. Des Weiteren wurde die Prozessreihenfolge untersucht, mit der eine optimale Festigkeit erreicht werden kann.
Anhand von Beispielen wurden anschließend Richtlinien und Strategien für das Hybridverfahren abgeleitet. So konnte gezeigt werden, dass durch das Hybridverfahren der Werkstoffeinsatz mit bis zu 53,2 % gegenüber der reinen Zerspanung gesenkt werden kann. Die Prozesszeit liegt mit 4,4 bzw. 2,4 h deutlich unter der eines rein additiven Prozesses, was auf eine konkurrenzfähige Wirtschaftlichkeit hindeutet.
In wire-arc additive manufacturing (WAAM), the desired workpiece is built layerwise by a moving heat source depositing droplets of molten wire on a substrate plate. To reduce material accumulations, the trajectory of the weld source should be continuous, but transit moves without welding, called deadheading, are possible. The enormous heat of the weld source causes large temperature gradients, leading to a strain distribution in the welded material which can lead even to cracks. In summary, it can be concluded that the temperature gradient reduce the quality of the workpiece. We consider the problem of finding a trajectory of the weld source with minimal temperature deviation from a given target temperature for one layer of a workpiece with welding segments broader than the width of the weld pool. The temperature distribution is modeled using the finite element method. We formulate this problem as a mixed-integer linear programming model and demonstrate its solvability by a standard mixed-integer solver.
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.