TY - JOUR A1 - Stichel, Thomas A1 - Geißler, Bastian A1 - Jander, Julius A1 - Laumer, Tobias A1 - Frick, Thomas A1 - Roth, Stephan T1 - Electrophotographic multi-material powder deposition for additive manufacturing JF - Journal of Laser Applications N2 - In this paper, the use of electrophotographic polymer powder transfer for the preparation of multi-material layers is discussed with respect to the application in powder bed-based additive manufacturing technologies as selective laser sintering (SLS). Therefore, the challenges of this task are considered verifying the critical process steps in order to develop a concept for an electrophotograhic laser sintering machine. On that basis, an experimental setup with a two-chamber design is realized which enables the investigation of the electrophotographic powder transfer at typical process conditions of SLS. Using this setup, transfer tests of polypropylene powder patterns were performed and qualitatively analyzed by photographic imaging. The results confirm the high potential of the application of electrophotography for multi-material powder deposition and show how a residual electrophotographic powder deposition can be achieved in general, which is independent from the already produced part height, in order to build up three-dimensional multi-material components. Y1 - 2018 U6 - https://doi.org/10.2351/1.5040619 VL - 30 IS - 3 PB - AIP Publishing ER - TY - CHAP A1 - Laumer, Tobias A1 - Stichel, Thomas A1 - Bock, Thomas A1 - Amend, Philipp A1 - Schmidt, Michael T1 - Characterization of temperature-dependent optical material properties of polymer powders T2 - AIP Conference Proceedings N2 - In former works, the optical material properties of different polymer powders used for Laser Beam Melting (LBM) at room temperature have been analyzed. With a measurement setup using two integration spheres, it was shown that the optical material properties of polymer powders differ significantly due to multiple reflections within the powder compared to solid bodies of the same material. Additionally, the absorption behavior of the single particles shows an important influence on the overall optical material properties, especially the reflectance of the powder bed. Now the setup is modified to allow measurements at higher temperatures. Because crystalline areas of semi-crystalline thermoplastics are mainly responsible for the absorption of the laser radiation, the influence of the temperature increase on the overall optical material properties is analyzed. As material, conventional polyamide 12 and polypropylene as new polymer powder material, is used. By comparing results at room temperature and at higher temperatures towards the melting point, the temperature-dependent optical material properties and their influence on the beam-matter interaction during the process are discussed. It is shown that the phase transition during melting leads to significant changes of the optical material properties of the analyzed powders. KW - laser beam melting KW - material qualification KW - Optical Material Properties KW - Polymers Y1 - 2014 U6 - https://doi.org/10.1063/1.4918508 IS - 1 PB - AIP Publishing ER - TY - JOUR A1 - Stichel, Thomas A1 - Frick, Thomas A1 - Laumer, Tobias A1 - Tenner, Felix A1 - Hausotte, Tino A1 - Merklein, Marion A1 - Schmidt, Michael T1 - A Round Robin study for selective laser sintering of polymers: Back tracing of the pore morphology to the process parameters JF - Journal of Materials Processing Technology N2 - The mechanical properties of polymer parts built by Selective Laser Sintering are strongly related to the internal microstructure which differs with the applied production parameters. The paper focuses on the back tracing of the pore morphology of laser sintered polyamide-12 samples to the process parameters. Therefore, a data base is used which is supplied by a Round Robin initiative and includes mechanical tensile tests and the microstructural analysis of the pore morphology of several different sample charges built with different machines. The pore morphologies (porosity, pore density, pore shape and pore arrangement) measured by X-ray computed tomography are compared and discussed regarding the employed parameters and the resulting mechanical properties. The investigations point out that pore density is a superior indicator than porosity for mechanical issues. This is especially valid along the build direction since pore morphology has shown to be strongly anisotropic. Moreover, the analysis revealed that pore density is strongly affected by the process temperature, which is proved to be essential for the fabrication of mechanical robust parts using Selective Laser Sintering. Y1 - 2018 U6 - https://doi.org/10.1016/j.jmatprotec.2017.10.013 VL - 252 IS - February SP - 537 EP - 545 PB - Elsevier ER - TY - JOUR A1 - Stichel, Thomas A1 - Frick, Thomas A1 - Laumer, Tobias A1 - Tenner, Felix A1 - Hausotte, Tino A1 - Merklein, Marion A1 - Schmidt, Michael T1 - A Round Robin study for Selective Laser Sintering of polyamide 12: Microstructural origin of the mechanical properties JF - Optics & Laser Technology N2 - The mechanical and microstructural investigation of polymer parts (polyamide 12) fabricated by Selective Laser Sintering as part of a Round Robin initiative is presented. The paper focuses on the microstructural analysis of the Round Robin samples and their evaluation regarding their effect on mechanical properties with respect to each other. Therefore optical microscopy on microtomed samples, X-ray computed tomography and Differential Scanning Calorimetry is used to determine the morphology of residual particle cores and of internal pores. Y1 - 2017 U6 - https://doi.org/10.1016/j.optlastec.2016.09.042 VL - 89 SP - 31 EP - 40 PB - Elsevier ER - TY - CHAP A1 - Laumer, Tobias A1 - Schmidt, Michael A1 - Stichel, Thomas T1 - Influence of temperature gradients on the part properties for the simultaneous laser beam melting of polymers T2 - Proceedings of Laser in Manfacturing Conference 2015, June 22 - June 25, 2015 Munich, Germany N2 - 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. KW - additive manufacturing KW - laser beam melting of polymers KW - multi-material parts Y1 - 2015 UR - https://www.wlt.de/lim/Proceedings/Stick/PDF/Contribution241_final.pdf ER - TY - JOUR A1 - Stichel, Thomas A1 - Laumer, Tobias A1 - Linnenweber, Tim A1 - Amend, Philipp A1 - Roth, Stephan T1 - Mass Flow Characterization of Selective Deposition of Polymer Powders with Vibrating Nozzles for Laser Beam Melting of Multi-material Components JF - Physics Procedia N2 - 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. KW - laser beam melting KW - multi-material deposition KW - polymer powder KW - vibration-controlled powder nozzle Y1 - 2016 U6 - https://doi.org/10.1016/j.phpro.2016.08.099 SN - 1875-3892 SN - 1875-3884 VL - 83 SP - 947 EP - 953 PB - Elsevier CY - Amsterdam [u.a.] ER - TY - CHAP A1 - Laumer, Tobias A1 - Appel, Peter A1 - Stichel, Thomas A1 - Amend, Philipp T1 - Untersuchungen zum Absorptionsverhalten von Pulverschüttungen für das Laserstrahlschmelzen von Kunststoffen Conference T2 - Rapid.Tech, 2013, Erfurt N2 - 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 Festkörpern 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 pulverförmigen Werkstoffen bei einer Wellenlänge von 10,6 µm eines CO2-Lasers und unterschiedlichen Schichtstärken 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 für den Schmelzprozess zu geringe Absorption des reinen Kunststoffes wie im Fall von Polyethylen-Pulver bei einer Wellenlänge von 10,6 µm gezielt erhöht werden, wodurch die Entwicklung neuer Pulverwerkstoffe erleichtert wird. KW - Additive Fertigung KW - Laserstrahlschmelzen von Kunststoffen KW - Werkstoffqualifizierung Y1 - 2013 UR - https://www.researchgate.net/publication/274250200_Untersuchungen_zum_Absorptionsverhalten_von_Pulverschuttungen_fur_das_Laserstrahlschmelzen_von_Kunststoffen ER - TY - CHAP A1 - Laumer, Tobias A1 - Koopmann, Jonas A1 - Stichel, Thomas A1 - Amend, Philipp T1 - Generation of multi-material parts with alternating material layers by Simultaneous Laser Beam Meltingof polymers T2 - International Conference on Additive Technologies, 15 - 17 Oct 2014, Wien N2 - 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. KW - additive manufacturing KW - Multi-Material Parts KW - Simultaneous Laser Beam Melting Y1 - 2014 UR - https://www.researchgate.net/publication/274250275_Generation_of_multi-material_parts_with_alternating_material_layers_by_Simultaneous_Laser_Beam_Meltingof_polymers ER - TY - CHAP A1 - Stichel, Thomas A1 - Amend, Philipp A1 - Laumer, Tobias A1 - Roth, Stephan T1 - Electrostatic Multi-Material Powder Deposition for Simultaneous Laser Beam Melting T2 - International Conference on Information, Communication and Automation Technologies (ICAT), 2014, Wien N2 - In this paper, the use of electrostatic polymer powder transfer methods for the preparation of multi-material layers is discussed with respect to the application in Simultaneous Laser Beam Melting (SLBM). Therefore, the basic principles of the single process steps as well as the challenges in combination with SLBM are considered verifying the critical process steps. On that base, process concepts are developed which might enable the fabrication of high quality multi-material parts in the future. Moreover, since the polymer powders typically used with Laser Beam Melting differ strongly from common toners for e. g. electrophotographic printing, an experimental setup was built to study the powder transfer with an electrically chargeable transfer plate using polyamide 12 powder. The results of this study show that transfer of powders usable for Laser Beam Melting can be achieved, but depends on the electric field strength which is a function of the gap between transfer and substrate plate and the intermediate electric potential. Y1 - 2014 UR - https://www.researchgate.net/publication/280154608_Electrostatic_Multi-Material_Powder_Deposition_for_Simultaneous_Laser_Beam_Melting ER - TY - JOUR A1 - Stichel, Thomas A1 - Amend, Philipp A1 - Laumer, Tobias A1 - Roth, Stephan T1 - Polymer Powder Deposition using Vibrating Capillary Nozzles for Additive Manufacturing JF - Information, Communication and Automation Technologies (ICAT), 2014, Wien N2 - Abstract — In this report, the dry delivery of polyamide 12 (PA 12) powder for the preparation of powder layers in laser beam melting (LBM) is investigated. Therefore, an experimental setup was built which consists of a glass nozzle assembled on a piezo-electric actuator. By applying a sinusoidal voltage signal to the actuator, the nozzle is set into vibration mode which enhances the powder delivery through the nozzle. By using this effect, powder mass flow is controlled and a valve-like start and stop function is realized. In order to identify suitable process parameters, a broad range of vibration modes were investigated using two nozzles made from glass with different orifice diameters. Therefore, the vibration frequency and the voltage signal of the actuator were varied and the resulting mass flow was detected by a balance. It was found that both the frequency and the voltage signal affect the mass flow and its stability but with different impact. Moreover, powder lines were deposited with different velocities in order to characterize the setup regarding applicability for highly selective powder deposition for LBM. KW - multi-material deposition KW - additive manufacturing KW - vibrating nozzle KW - dry powder delivery KW - polyamide 12 Y1 - 2014 ER -