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- Lange, Jonathan, et al.
(author)
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Novel lithographic printing techniques enabling sustainable and high quality multi material manufacturing process for future space outposts
- 2021
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In: IAC 2021 Congress Proceedings, 72nd International Astronautical Congress (IAC), Dubai, United Arab Emirates. - : International Astronautical Federation (IAF).
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Conference paper (peer-reviewed)abstract
- Several challenges remain before the full potential of on-orbit manufacturing can be realized. There may be some limitations to the types of items that can be manufactured in space. Such limitations could be caused by a variety of factors, including the materials required for a particular structure, the size of the object to be manufactured, the time required to execute the architecture, the configuration of the object being manufactured, and the raw material needed to support the manufacturing process. The complementary challenge to the relevant fabrication processes is the possibility to achieve the required precision demanded by geometrically complex structures and the ability to be versatile in processing a broad material spectrum. In this context, novel lithographic 3D printing techniques will be an asset to pave the way towards overcoming these challenges. Currently, the European Space Agency (ESA) is investigating the implementation of such technology in the context of a lunar base. In particular, two different applications are being studied: • Lithography-Based Ceramic Manufacturing (LCM), where the ceramic powder is distributed in a photocurable monomer formulation in presence of a photoinitiator. Ceramic materials are extensively used in a vast number of technological processes as well as in space applications. They are usually considered as the material of choice for applications where other materials such as plastic and metal fail to deliver the required performance. The LCM process will also allow processing lunar regolith simulant adding value to the current material portfolio of this technique, as well as to the range of processes potentially applicable on the lunar or Martian surface. • Lithography-based Metal Manufacturing (LMM) for processing metallic powders. In contrast to the currently predominantly used powder bed fusion (direct metal laser melting) techniques, this process uses a paste/suspension as feedstock and hence, does not rely on the use of highly spherical gas atomized powders. This will enable the utilization of recycled powders from scrap metals that are available at Moon bases or of metallic alloys reduced from lunar regolith, thus providing higher flexibility in accepting raw material with poor quality and purity. The paper addresses the results from both activities in terms of printed parts quality (roughness, density, resolution and accuracy) as well as the implementation requirements for the whole process chain, including suitable pre- and post-processing steps, with the aim to achieve a zero-waste flow in a lunar environment.
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- Riede, M., et al.
(author)
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Material characterization of AISI 316L flexure pivot bearings fabricated by additive manufacturing
- 2019
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In: Materials. - : MDPI. - 1996-1944 .- 1996-1944. ; 12:15
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Journal article (peer-reviewed)abstract
- Recently, additive manufacturing (AM) by laser metal deposition (LMD) has become a key technology for fabricating highly complex parts without any support structures. Compared to the well-known powder bed fusion process, LMD enhances manufacturing possibilities to overcome AM-specific challenges such as process inherent porosity, minor build rates, and limited part size. Moreover, the advantages aforementioned combined with conventional machining enable novel manufacturing approaches in various fields of applications. Within this contribution, the additive manufacturing of filigree flexure pivots using 316L-Si by means of LMD with powder is presented. Frictionless flexure pivot bearings are used in space mechanisms that require high reliability, accuracy, and technical cleanliness. As a contribution to part qualification, the manufacturing process, powder material, and fabricated specimens were investigated in a comprehensive manner. Due to its major impact on the process, the chemical powder composition was characterized in detail by energy dispersive X-ray spectroscopy (EDX) and inductively coupled plasma optical emission spectrometry (ICP-OES). Moreover, a profound characterization of the powder morphology and flowability was carried out using scanning electron microscopy (SEM) and novel rheological investigation techniques. Furthermore, quantitative image analysis, mechanical testing, laser scanning microscopy, and 3D shape measurement of manufactured specimens were conducted. As a result, the gained knowledge was applied for the AM-specific redesign of the flexure pivot. Finally, a qualified flexure pivot has been manufactured in a hybrid manner to subsequently ensure its long-term durability in a lifetime test bench.
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- Moritz, J., et al.
(author)
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Functional integration approaches via laser powder bed processing
- 2019
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In: Journal of laser applications. - : Laser Institute of America. - 1042-346X .- 1938-1387. ; 31:2
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Journal article (peer-reviewed)abstract
- Additive manufacturing design rules are different from those of conventional fabrication techniques. These allow geometries that would not be possible to achieve otherwise. One example of application is the integration of functional parts as part of the manufacturing process. Conceivable applications range from mechanical functions like integration of moving parts or thermodynamic functions, for example, cooling channels or incorporation of electric circuits for electrical functionalization [J. Glasschroeder, E. Prager, and M. F. Zaeh, Rapid Prototyping J. 21, 207–215 (2015)]. Nevertheless, the potential of functional integration using powder-bed processes is far from being exhausted. The present approach addresses the generation of inner cavities and internal structures of titanium-based parts or components by the use of selective laser melting. This paper focusses on the investigation of voids and cavities regarding their capabilities to add new functions to the material. To this end, comprehensive characterization is performed using destructive as well as nondestructive testing methods. These include 3D scanning, computed tomography, and surface roughness measurements as well as microscopic analysis. Voids and cavities were filled with different thermoplastic materials, followed by the qualitative assessment of the mold filling and resulting material properties. Finally, applications are derived and evaluated with respect to the field of lightweight design or damping structures.
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- Shen, Ruidan, et al.
(author)
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Insights into the importance of WPD-loop sequence for activity and structure in protein tyrosine phosphatases
- 2022
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In: Chemical Science. - : Royal Society of Chemistry. - 2041-6520 .- 2041-6539. ; 13:45, s. 13524-13540
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Journal article (peer-reviewed)abstract
- Protein tyrosine phosphatases (PTPs) possess a conserved mobile catalytic loop, the WPD-loop, which brings an aspartic acid into the active site where it acts as an acid/base catalyst. Prior experimental and computational studies, focused on the human enzyme PTP1B and the PTP from Yersinia pestis, YopH, suggested that loop conformational dynamics are important in regulating both catalysis and evolvability. We have generated a chimeric protein in which the WPD-loop of YopH is transposed into PTP1B, and eight chimeras that systematically restored the loop sequence back to native PTP1B. Of these, four chimeras were soluble and were subjected to detailed biochemical and structural characterization, and a computational analysis of their WPD-loop dynamics. The chimeras maintain backbone structural integrity, with somewhat slower rates than either wild-type parent, and show differences in the pH dependency of catalysis, and changes in the effect of Mg2+. The chimeric proteins' WPD-loops differ significantly in their relative stability and rigidity. The time required for interconversion, coupled with electrostatic effects revealed by simulations, likely accounts for the activity differences between chimeras, and relative to the native enzymes. Our results further the understanding of connections between enzyme activity and the dynamics of catalytically important groups, particularly the effects of non-catalytic residues on key conformational equilibria.
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