@article{StichelFrickLaumeretal., author = {Stichel, Thomas and Frick, Thomas and Laumer, Tobias and Tenner, Felix and Hausotte, Tino and Merklein, Marion and Schmidt, Michael}, title = {A Round Robin study for Selective Laser Sintering of polyamide 12: Microstructural origin of the mechanical properties}, series = {Optics \& Laser Technology}, volume = {89}, journal = {Optics \& Laser Technology}, publisher = {Elsevier}, doi = {10.1016/j.optlastec.2016.09.042}, pages = {31 -- 40}, abstract = {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.}, language = {en} } @article{LaunhardtWoerzLodereretal., author = {Launhardt, M. and W{\"o}rz, A. and Loderer, A. and Laumer, Tobias and Drummer, Dietmar and Hausotte, Tino and Schmidt, Michael}, title = {Detecting surface roughness on SLS parts with various measuring techniques}, series = {Polymer Testing}, volume = {53}, journal = {Polymer Testing}, publisher = {Elsevier}, address = {Amsterdam}, isbn = {0142-9418}, issn = {1873-2348}, doi = {10.1016/j.polymertesting.2016.05.022}, pages = {217 -- 226}, abstract = {Selective Laser Sintering (SLS) is an additive manufacturing technique whereby a laser melts polymer powder layer by layer to generate three-dimensional parts. It enables the fabrication of parts with high degrees of complexity, nearly no geometrical restrictions, and without the necessity of a tool or a mold. Due to the orientation in the building space, the processing parameters, and the powder properties, the resulting parts possess an increased surface roughness. In comparison to other manufacturing techniques, e.g. injection molding, the surface roughness of SLS parts results from partially melted powder particles on the surface layer. The actual surface roughness must thus be characterized with respect to the part's eventual application. At the moment, there is no knowledge regarding which measuring technique is most suitable for detecting and quantifying SLS parts' surface roughness. The scope of this paper is to compare tactile profile measurement methods, as established in industry, to optical measurement techniques such as Focus Variation, Fringe Projection Technique (FPT), and Confocal Laser Scanning Microscope (CLSM). The advantages and disadvantages of each method are presented and, additionally, the effect of tactile measurement on a part's surface is investigated.}, language = {en} } @article{HupfeldLaumerSticheletal., author = {Hupfeld, T. and Laumer, Tobias and Stichel, T. and Schuffenhauer, T. and Heberle, J. and Schmidt, Michael and Barcikowski, S. and G{\"o}kce, B.}, title = {A new approach to coat PA12 powders with laser-generated nanoparticles for selective laser sintering}, series = {Procedia CIRP}, volume = {74}, journal = {Procedia CIRP}, publisher = {Elsevier}, doi = {10.1016/j.procir.2018.08.103}, pages = {244 -- 248}, abstract = {The modification of selective laser sintering (SLS) powder materials by nanoadditives offers the possibility to adapt the powder properties to the laser sintering process or the resulting part properties. To avoid agglomeration of the nanofiller, a new approach in which surfactant-free laser-generated colloidal nanoparticles are adsorbed onto the polymer surface directly in an aqueous solution is demonstrated. Based on this novel approach, polyamide 12 (PA12) powders are decorated with metal and oxide nanoparticles and processed via SLS. Electron microscopy and confocal laser scanning imaging are utilized to analyze the dispersion of the filler.}, language = {en} } @article{LaumerStichelNagulinetal., author = {Laumer, Tobias and Stichel, T. and Nagulin, K. and Schmidt, Michael}, title = {Optical analysis of polymer powder materials for Selective Laser Sintering}, series = {Polymer Testing}, volume = {56}, journal = {Polymer Testing}, publisher = {Elsevier Science}, address = {Amsterdam [u.a.]}, issn = {1873-2348}, doi = {10.1016/j.polymertesting.2016.10.010}, pages = {207 -- 213}, abstract = {This study increases the basic understanding of optical material properties of polymer powders used in selective laser sintering (SLS). Therefore, different polymer powder materials were analyzed regarding their optical material properties with an integration spheres measurement setup. By the measurements a direct connection between the absorption behavior of the solid material and the overall optical material characteristics of the same material in powdery form could be shown. The results were used to develop an advanced explanation model for the optical material properties of powders. At present, existing explanation models only consider the occurring of multiple reflections in the gaps between the particles to explain the overall optical material properties of powder materials. Thus, by also considering the absorption behavior of the single particles, the basic understanding of the beam-matter interaction and their effect on the optical material properties of powder materials can be expanded.}, language = {en} } @article{StichelRathsLaumeretal., author = {Stichel, T. and Raths, Max and Laumer, Tobias and Roth, Stephan}, title = {Multi-Material Deposition of Polymer Powders with Vibrating Nozzles for a New Approach of Laser Sintering}, series = {Journal of Laser Micro/Nanoengineering (JLMN)}, volume = {13}, journal = {Journal of Laser Micro/Nanoengineering (JLMN)}, number = {2}, publisher = {JLPS-Japan Laser Processing Society}, doi = {10.2961/jlmn.2018.02.0002}, pages = {55 -- 62}, abstract = {Conventional Selective Laser Sintering of polymers is restricted to the processing of single materials. The fabrication of components consisting of different material regions is a challenge which cannot be realized by standard coating devices basing on blades or rollers. Thus, advanced coating and deposition techniques are needed which enable the precise and reliable control over very small powder quantities in order to prepare arbitrary powder patterns with high accuracy and repeatability. In this report, the delivery of polymer powder by vibrating nozzles inside laser sintering machines is investigated. Therefore, a steel nozzle attached to a piezo actuator is integrated into a machine, whereas the nozzle itself features internal channels which allow the precise control over the powder temperature using heat transfer oil. The setup is used to study the influence of different system configurations on the powder deposition characteristics as resolution and layer surface roughness. The results show that temperature influences the mass flow depending on the material used and that a precise deposition of powder pattern with microscale resolution is possible with optimized parameters. Finally, the multimaterial powder pattern is fused by a new illumination strategy of laser sintering which is called Simultaneous Intensity-Selective Laser Sintering in order to demonstrate the potential of this new approach.}, language = {en} } @inproceedings{LaumerStichelSachsetal., author = {Laumer, Tobias and Stichel, T. and Sachs, Marius and Amend, Philipp and Schmidt, Michael}, title = {Qualification and modification of new polymer powders for laser beam melting using Ulbricht spheres}, series = {High value manufacturing : Advanced research in virtual and rapid prototyping ; Proceedings of the 6th International Conference on Advanced Research and Rapid Prototyping, Leiraia, Portugal, 1-5 October, 2013}, booktitle = {High value manufacturing : Advanced research in virtual and rapid prototyping ; Proceedings of the 6th International Conference on Advanced Research and Rapid Prototyping, Leiraia, Portugal, 1-5 October, 2013}, editor = {B{\´a}rtolo, Paulo}, publisher = {CRC Press}, address = {Boca Raton}, isbn = {978-1-138-00137-4}, pages = {255 -- 260}, abstract = {The restricted amount of available materials for Laser Beam Melting (LBM) of polymers is one of the main limitations for expanding the technology. Current qualification methods deal with problems like inadequate powder flowability or high part porosities among others but do not offer a detailed analysis of the important beam-matter-interaction between powder particles and electro-magnetic laser radiation. In this paper, polyethylene powder is qualified for the LBM process and specifically analyzed regarding the optical material properties of the powder for a wavelength of 10.6 μm. By admixing graphite as absorption intensifier the change of the optical material properties and the thereby connected processing parameters are analyzed. Furthermore an explanation approach is given to explain the relation between different transmittances of different powder particles and the optical material properties of the polymer powders.}, language = {en} } @article{KuettnerFischerLaumer, author = {Kuettner, Andreas and Fischer, Samuel and Laumer, Tobias}, title = {Mechanical and structural characterization of heat-staked parts realized by selective laser sintering of polyamide 12}, series = {The International Journal of Advanced Manufacturing Technology}, journal = {The International Journal of Advanced Manufacturing Technology}, publisher = {Springer}, doi = {10.1007/s00170-025-17319-4}, pages = {20}, abstract = {Heat staking is a joining process in which thermoplastic pins are formed by heat and pressure in a form-fitting and insoluble way. This study evaluates the mechanical performance and microstructure of selective laser sintered (SLS) polyamide 12 (PA 12) components before and after heat staking, compared with conventionally turned reference specimens. The components were characterized using tensile tests, micrographs, microscopy, and micro-CT measurements. For the tests, the forces and temperatures during heat staking were varied to determine the best process parameters. Tensile tests revealed that SLS joints achieved strengths of up to 33.6 MPa, approaching the 39.9 MPa of the turned references. Microstructural analysis showed a marked reduction in porosity due to heat staking. Porosity decreased from 3.9\% to 1.56\% at a staking force of 300 N and from 4.29\% to 0.81\% at 1000 N, highlighting the beneficial effect of increased force. These results demonstrate that heat staking parameters significantly influence local densification and mechanical performance, and that, under suitable conditions, SLS components can achieve joint strengths comparable to conventionally manufactured parts. The study shows that the heat staking process parameters have a significant influence on the local microstructure and thus on the mechanical performance and provides a basis for optimizing SLS components for new heat staking applications.}, language = {en} }