@article{GradNadammalSchultheissetal., author = {Grad, Marius and Nadammal, Naresh and Schultheiss, Ulrich and Lulla, Philipp and Noster, Ulf}, title = {An Integrative Experimental Approach to Design Optimization and Removal Strategies of Supporting Structures Used during L-PBF of SS316L Aortic Stents}, series = {Applied Sciences}, volume = {11}, journal = {Applied Sciences}, number = {19}, publisher = {MPDL}, doi = {10.3390/app11199176}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:898-opus4-25612}, pages = {1 -- 22}, abstract = {One of the fundamental challenges in L-PBF of filigree geometries, such as aortic stents used in biomedical applications, is the requirement for a robust yet easily removable support structure that allows each component to be successfully fabricated without distortion. To solve this challenge, an integrative experimental approach was attempted in the present study by identifying an optimal support structure design and an optimized support removal strategy for this design. The specimens were manufactured using four different support structure designs based on the geometry exposed to the laser beam during the L-PBF. Support removal procedures included sand blasting (SB), glass bead blasting (GB), and electrochemical polishing (ECP). The two best-performing designs (line and cross) were chosen due to shorter lead times and lower material consumption. As an additional factor that indicates a stable design, the breaking load requirement to remove the support structures was determined. A modified line support with a 145° included angle was shown to be the best support structure design in terms of breaking load, material consumption, and manufacturing time. All three procedures were used to ensure residue-free support removal for this modified line support design, with ECP proving to be the most effective.}, language = {en} } @inproceedings{MaiwaldTroegerHierl, author = {Maiwald, Frederik and Tr{\"o}ger, Johannes and Hierl, Stefan}, title = {Automated weld seam evaluation and 2D simulation parameter calibration for absorber-free laser transmission welding}, series = {Lasers in Manufacturing Conference (LIM 2023), 26. Juni bis 29. Juni 2023, M{\"u}nchen}, booktitle = {Lasers in Manufacturing Conference (LIM 2023), 26. Juni bis 29. Juni 2023, M{\"u}nchen}, publisher = {Wissenschaftliche Gesellschaft Lasertechnik und Photonik e.V. (WLT)}, pages = {10}, abstract = {Absorber-free laser transmission welding enables clean and precise joining of plastics without additives or adhesives. It is therefore well suited to produce optical and medical devices, which place high demands on cleanliness and accuracy. However, the weld usually has an undesirably large vertical expansion, causing bulges and distortion. To improve this, the intensity distribution of the laser beam as well as the processing strategy must be adapted. Due to the complexity, this is aided by process simulation. However, simulation parameter calibration and verification are usually done considering the seam width and height, which is of limited significance. To overcome this, we propose a new method for image processing of microtome sections, determining the spatially resolved geometry of the weld. Thus, the deviation between experiment and simulation can be calculated pixel by pixel. This spatially resolved value is predestined for the calibration of the simulation parameters: For a parameter field with 18 different settings, the total deviation between experiment and simulation is less than 11 \% after calibration.}, language = {en} } @article{GradNadammalTytkoetal., author = {Grad, Marius and Nadammal, Naresh and Tytko, Darius and Noster, Ulf}, title = {On the nanoindentation behavior of a TiC layer formed through thermo-reactive diffusion during hot pressing of Ti and cast iron}, series = {Materials Letters: X}, volume = {15}, journal = {Materials Letters: X}, number = {September}, publisher = {Elsevier}, address = {Amsterdam, Niederlande}, issn = {2590-1508}, doi = {10.1016/j.mlblux.2022.100161}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:898-opus4-50066}, pages = {1 -- 4}, abstract = {Hot pressing of pure Ti and cast iron under vacuum formed a ~15 μm wide TiC-layer through the thermoreactive diffusion process. Nanoindentation testing of the TiC-layer revealed average hardness and elastic modulus values of ~35 GPa and ~400 GPa, respectively. High-resolution indentation mapping indicated hardness change across the boundary with peak values observed within the TiC-layer. Solid state high temperature diffusion holds significant potential for developing uniform hard coatings on pure Ti/Ti-alloys.}, language = {en} } @article{ZacherlWopperSchwanzeretal., author = {Zacherl, Florian and Wopper, Christoph and Schwanzer, Peter and Rabl, Hans-Peter}, title = {Potential of the Synthetic Fuel Oxymethylene Ether (OME) for the Usage in a Single-Cylinder Non-Road Diesel Engine: Thermodynamics and Emissions}, series = {Energies}, volume = {15}, journal = {Energies}, number = {21}, publisher = {MDPI}, doi = {10.3390/en15217932}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:898-opus4-55350}, pages = {1 -- 26}, abstract = {Non-road sectors, such as agriculture and construction machinery, require high energy densities and flexibility in use, which is why diesel engines are mainly used. The use of climate-neutral fuels, produced from renewable energies, such as Oxymethylene Ether (OME) as a diesel substitute, can significantly reduce CO2 and pollutant emissions in these sectors. In addition to CO2 neutrality, OME also offers improved combustion characteristics compared to diesel fuel, eliminating the soot-NOx trade-off and thus enabling new opportunities in engine design and calibration. In this paper, the combustion of pure OME on a close-to-production, single-cylinder non-road diesel engine with a pump-line-nozzle injection system is analyzed. A variation of the center of combustion at constant power output was performed for diesel and OME at different operating points. Two injectors were investigated with OME. A study on ignition delay and a detailed thermodynamic analysis was carried out. In addition, the exhaust emissions CO, NOx, VOC, as well as particulate-matter, -number and -size distributions were measured. With OME, a significantly shorter ignition delay as well as a shortened combustion duration could be observed, despite a longer injection duration. In addition, the maximum injection pressure increases. VOC and CO emissions are reduced. Particulate matter was reduced by more than 99\% and particle number (>10 nm) was reduced by multiple orders of magnitude. The median of the particle size distribution shifts from 60 to 85 nm (diesel) into a diameter range of sub 23 nm (OME). A significant reduction of NOx emissions with OME enables new degrees of freedom in engine calibration and an efficiency advantage without hardware adaption.}, language = {en} } @inproceedings{GerschSchulzKral, author = {Gersch, Sebastian and Schulz, Carsten and Kral, Christopher}, title = {Verifizierung der Prozessstabilit{\"a}t einer konstruierten WAAM-Anlage zum Induzieren von Eigenspannungen in generativ gefertigten Strukturen}, series = {9. Mitteldeutsches Forum - 3D-Druck in der Anwendung: 29. Juni 2022, Jena}, booktitle = {9. Mitteldeutsches Forum - 3D-Druck in der Anwendung: 29. Juni 2022, Jena}, doi = {10.35096/othr/pub-5600}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:898-opus4-56006}, abstract = {Heutzutage werden Strukturen h{\"a}ufig aufwendig konstruiert und nachtr{\"a}glich mithilfe von numerischen Verfahren optimiert. Dennoch kommt es zu erheblichen Sch{\"a}den infolge von Erm{\"u}dungsbr{\"u}chen bei wechselnd beanspruchten Bauteilen. Ein Großteil dieser Sch{\"a}den hat den Ursprung in den im Inneren herrschenden Spannungszust{\"a}nden, den sogenannten Eigenspannungen. Diese Eigenspannungen heben sich innerhalb des Bauteils auf und f{\"u}hren zu keiner Formabweichung des Bauteils, weswegen diese Spannungen in Form und Lage nur schwer detektierbar sind und sich h{\"a}ufig negativ auf die Betriebsfestigkeit von Strukturen auswirken. Mithilfe neuartiger numerischer Methoden k{\"o}nnen thermomechanische Simulationen angefertigt und Verformungen, sowie Spannungszust{\"a}nde abgeleitet werden. Durch diese Optionen ergeben sich neue Anwendungen, die das Potenzial von Fertigungsverfahren in Hinblick auf die Ausnutzung spezieller Eigenschaften neu er{\"o}ffnen. Durch die geschickte Anwendung und Vernetzung der Simulation mit der Fertigung k{\"o}nnen Eigenspannungen gezielt in Lage und Richtung schon w{\"a}hrend der Produktion des Bauteils eingebracht werden. Im theoretischen Vergleich zu konventionell gefertigten Bauteilen entstehen Strukturen, die hinsichtlich ihrer Bauteillebensdauer optimiert sind.}, language = {de} } @inproceedings{HerrmannSchaefferLehmannetal., author = {Herrmann, David and Schaeffer, Leon and Lehmann, Lukas and B{\"o}hm, Valter and Rieffel, John}, title = {Basic Investigations on a Compliant 2D Tensegrity Grid for the Use in Soft Robotic Applications}, series = {2024 6th International Conference on Reconfigurable Mechanisms and Robots (ReMAR), 23-26 June 2024, Chicago, IL, USA}, booktitle = {2024 6th International Conference on Reconfigurable Mechanisms and Robots (ReMAR), 23-26 June 2024, Chicago, IL, USA}, publisher = {IEEE}, isbn = {979-8-3503-9596-9}, doi = {10.1109/ReMAR61031.2024.10619926}, pages = {652 -- 657}, abstract = {The use of compliant tensegrity grids in soft robotic applications is a promising research topic. By using these grids, systems with large shape and stiffness change ability can be realized. In this paper, different tensegrity grid variants, consisting of rigid members indirectly connected via compliant tensioned members, are presented. A selected grid variant is analyzed in more detail for shape adaptation. Therefore the use of the grid as end effector in form-fit grippers is selected as a specific application case. Covariance Matrix Adaptation Evolution Strategies are used to optimize actuators for two given shape function variants and an evaluation is carried out.}, language = {en} } @inproceedings{LaumerSchmidtStichel, author = {Laumer, Tobias and Schmidt, Michael and Stichel, Thomas}, title = {Influence of temperature gradients on the part properties for the simultaneous laser beam melting of polymers}, series = {Proceedings of Laser in Manfacturing Conference 2015, June 22 - June 25, 2015 Munich, Germany}, booktitle = {Proceedings of Laser in Manfacturing Conference 2015, June 22 - June 25, 2015 Munich, Germany}, organization = {German Scientific Laser Society (WLT e.V.)}, abstract = {By Laser Beam Melting of polymers (LBM), parts with almost any geometry can be built directly out of CAD files without the need for additional tools. Thus, prototypes or parts in small series production can be generated within short times. Up to now, no multi-material parts have been built by LBM, which is a major limitation of the technology. To realize multi-material parts, new mechanisms for depositing different polymer powders as well as a new irradiation strategy are needed, by which polymers with different melting temperatures can be warmed to their specific preheating temperatures and be molten simultaneously. This is achieved by simultaneous laser beam melting (SLBM). In the process, two different materials are deposited next to each other and preheated a few degrees below their melting temperatures by infrared emitters and laser radiation (λ = 10.60 µm), before in the last step the two preheated powders are molten simultaneously by an additional laser (λ = 1.94 µm). So far, multi-material tensile bars have been realized and analyzed regarding their boundary zone between both materials. The experiments showed that the temperature gradients in the boundary zone and along the building direction seem to be of great importance for the process stability and the resulting part properties. Therefore, a detailed analysis of the occurring temperature gradients during the process is needed to identify adequate process adjustments regarding the temperature controlling. To analyze the temperature gradients, thermocouples positioned inside the powder bed are used. By varying the temperature of the building platform, the influence of different temperature gradients on the resulting part properties is shown.}, language = {en} } @article{StichelLaumerLinnenweberetal., author = {Stichel, Thomas and Laumer, Tobias and Linnenweber, Tim and Amend, Philipp and Roth, Stephan}, title = {Mass Flow Characterization of Selective Deposition of Polymer Powders with Vibrating Nozzles for Laser Beam Melting of Multi-material Components}, series = {Physics Procedia}, volume = {83}, journal = {Physics Procedia}, publisher = {Elsevier}, address = {Amsterdam [u.a.]}, issn = {1875-3892}, doi = {10.1016/j.phpro.2016.08.099}, pages = {947 -- 953}, abstract = {The generation of multi-material components by laser beam melting (LBM) is a challenge which requires the invention of new coating devices for preparation of arbitrary powder patterns. One solution is the usage of vibration-controlled nozzles for selective deposition of polymer powders. Powder flow can be initiated by vibration enabling a start-stop function without using any mechanical shutter. In this report, the delivery of polymer powder by vibrating nozzles is investigated with respect to their application in LBM machines. Therefore, a steel nozzle attached to a piezo actor and a weighing cell is used in order to measure the stability and time-dependence of the powder mass flow upon vibration excitation with the usage of different kind of powder formulations. The results show that precompression of the powder inside the nozzle by vibration excitation is essential to realize a reliable start-stop function with reproducible discharge cyles and to prevent a initial flush of powder flow. Moreover, the use of different powder materials showed that mass flow is even possible with powders which are not optimized regarding flowability, but is readily enhanced with a factor of 2 to 3 by admixing Aerosil® fumed silica.}, language = {en} } @inproceedings{LaumerAppelSticheletal., author = {Laumer, Tobias and Appel, Peter and Stichel, Thomas and Amend, Philipp}, title = {Untersuchungen zum Absorptionsverhalten von Pulversch{\"u}ttungen f{\"u}r das Laserstrahlschmelzen von Kunststoffen Conference}, series = {Rapid.Tech, 2013, Erfurt}, booktitle = {Rapid.Tech, 2013, Erfurt}, abstract = {Die Energieeinbringung in Form von elektromagnetischer Strahlung in das Pulverbett beim selektiven Laserstrahlschmelzprozess von Kunststoffen wird maßgeblich durch das Absorptionsverhalten der Pulverwerkstoffe bestimmt. Aufgrund von Vielfachreflexionen an den einzelnen Pulverpartikeln in den Poren weisen Pulverwerkstoffe im Vergleich zu makroskopischen Festk{\"o}rpern andere Absorptionseigenschaften auf. Im vorliegenden Beitrag wird daher ein geeigneter Messaufbau zur Bestimmung der optischen Materialeigenschaften von verschiedenen Pulverwerkstoffen vorgestellt. Mittels eines Ulbricht-Kugel-Messaufbaus wird der Reflexions-, der Transmissions- und der Absorptionsgrad von pulverf{\"o}rmigen Werkstoffen bei einer Wellenl{\"a}nge von 10,6 µm eines CO2-Lasers und unterschiedlichen Schichtst{\"a}rken ermittelt. Neben den Werkstoffen Polyamid 12 und Polyethylen im reinen Zustand werden Mischungen mit Additiven, wie beispielsweise Graphit, analysiert und verglichen. Durch die Beimischungen kann eine f{\"u}r den Schmelzprozess zu geringe Absorption des reinen Kunststoffes wie im Fall von Polyethylen-Pulver bei einer Wellenl{\"a}nge von 10,6 µm gezielt erh{\"o}ht werden, wodurch die Entwicklung neuer Pulverwerkstoffe erleichtert wird.}, language = {de} } @inproceedings{LaumerKoopmannSticheletal., author = {Laumer, Tobias and Koopmann, Jonas and Stichel, Thomas and Amend, Philipp}, title = {Generation of multi-material parts with alternating material layers by Simultaneous Laser Beam Meltingof polymers}, series = {International Conference on Additive Technologies, 15 - 17 Oct 2014, Wien}, booktitle = {International Conference on Additive Technologies, 15 - 17 Oct 2014, Wien}, abstract = {By using Additive Manufacturing technologies, like Laser Beam Melting (LBM) of polymers, parts can be realized within single days and necessary modifications can be quickly adapted. With increasing complexity, products are often made out of different polymer materials and the need for multi-material parts is an increasing industry requirement, which cannot be fulfilled by the single material parts realizable by LBM. Therefore, Simultaneous Laser Beam Melting (SLBM) as a new Additive Manufacturing technology offers the possibility to build parts consisting of different polymer materials. The realizable parts combine different material properties, like differing stiffness or chemical resistances, within a single part. Up to now, different materials are deposited next to each other on the building platform, thus the boundary surface between the different polymers is orientated perpendicular to the building direction. For this paper, the polymer powders are alternated in building direction. Thus, the boundary surface is orientated horizontally and is larger, both influencing the boundary surface and resulting part properties, which are analyzed by a high-resolution thermal imaging system and by cross sections.}, language = {en} }