@inproceedings{51218, abstract = {{Polymer composites represent the industry standard in injection molding for the production of plastic components with increased requirements in terms of heat resistance and stiffness. In the field of laser sintering (LS), these materials are less common so far. In order to extend the available material variety for the LS process, new ceramic-filled Polyamide 613 powders are investigated within the scope of this work. Here, the resulting properties from two different powder production methods are compared. One filled powder is produced by dry blending and the other powder with the same filler and filling ratio is produced by encapsulating the filler particles inside the polymer particles within the dissolution-precipitation process. It was found that encapsulating the filler particles can provide certain benefits for the processability, for example an improved powder flowability or better filler dispersion. However, encapsulating the filler also alters the thermal properties of the precipitated powder. }}, author = {{Kletetzka, Ivo and Neitzel, Fabian and Schmid, Hans-Joachim}}, booktitle = {{Proceedings of the 34th Annual International Solid Freeform Fabrication Symposium}}, editor = {{Beaman, Joseph}}, keywords = {{Additive Manufacturing, Laser Sintering, Filled Materials, Composites, Polyamide 613}}, location = {{Austin}}, title = {{{Assessing the Impact of the Powder Production Method on Ceramic-filled Polyamide Composites made by Laser Sintering}}}, doi = {{https://doi.org/10.26153/tsw/50931}}, year = {{2023}}, } @inproceedings{46862, abstract = {{The high flammability of components manufactured by laser sintering (LS) using standard polyamide 12 (PA12) powder still severely restricts their use in industries such as electronics, aviation, and transportation. A key factor for the further establishment of LS is the expansion of the material portfolio with, for example, refreshable and halogen-free flame-retardant (FR) powder materials. Accordingly, various halogen-free FRs are investigated in this work and evaluated with respect to their use in LS. First, their decomposition behavior and mode of action are examined. Subsequently, the additives are dry blended with PA12 to investigate properties relevant for LS, such as particle morphology, thermal behavior and melt viscosity. Afterwards, test specimens for UL94 vertical flame-retardancy tests are produced by processing the dry blends on an EOS P3 LS system. Finally, the process stability of the process-aged powder blends is investigated by again examining the thermal behavior and melt viscosity.}}, author = {{Neitzel, Fabian and Kletetzka, Ivo and Schmid, Hans-Joachim}}, booktitle = {{Proceedings of the 34th Annual International Solid Freeform Fabrication Symposium}}, editor = {{Beaman, Joseph}}, keywords = {{Additive Manufacturing, Laser Sintering, Flame Retardant, Polyamide 12}}, location = {{Austin}}, title = {{{Halogen-Free Flame Retardant Powder Materials for Laser Sintering: Evaluation and Process Stability Analysis}}}, doi = {{https://doi.org/10.26153/tsw/50926}}, year = {{2023}}, } @article{43046, abstract = {{In the laser sintering technology, the semi-crystalline polymer material is exposed to elevated temperatures during processing, which leads to serious material ageing for most materials. This has already been investigated intensively by various authors. However, the ageing of the material at ambient temperatures during shelf life has not been the focus so far. The need to analyse the shelf life can be derived from an ecological and economic point of view. This work is focusing on the shelf life of PA2200 (PA12). To reduce the potential influences of powder production fluctuations, two different powder batches stored for 5.5 years and 6.5 years are investigated and compared to a reference powder produced 0.5 years before these investigations. Multiple powder analyses and part characterisations have been performed. A significant yellowing and molecular chain length reduction can be derived from the measurement results. Whereas the influence on mechanical part performance was minor, the parts built with the stored powders are more yellowish. As it is most likely that this is due to the consumption of polyamide stabilisers, it can be assumed that these parts will be subject to significantly faster ageing. Therefore, it is still not recommended to use the stored powders for critical parts or light intense and humid environments.}}, author = {{Klippstein, Sven Helge and Kletetzka, Ivo and Sural, Ilknur and Schmid, Hans-Joachim}}, journal = {{The International Journal of Advanced Manufacturing Technology }}, keywords = {{Selective laser sintering, Shelf life, Polyamide 12, powder, PA2200, material ageing}}, publisher = {{Springer}}, title = {{{Influence of a prolonged shelf time on PA12 laser sintering powder and resulting part properties}}}, doi = {{https://doi.org/10.1007/s00170-023-11243-1}}, year = {{2023}}, } @inproceedings{23760, abstract = {{The laser sintering process has been a well-established AM process for many years. Disadvantages of LS are the low material variety and the thermal damage of the unprocessed material. The low temperature laser sintering attacks at this point and processes powder material at a build chamber temperature lower than the recrystallization temperature. This drastic reduction in temperature results in significantly less thermal damage to the material. This work deals with the low temperature laser sintering of Polyamide 12 (PA12) on a commercial, unmodified laser sintering system to compare it to standard laser sintered PA12 and to create the basis for low temperature laser sintering of high temperature materials on such a system. First results by changing the exposure parameters and by fixing parts on a building platform show a processing of PA12 on an EOS P396 at a build chamber temperature less than 100 °C instead of standard approx. 175 °C.}}, author = {{Menge, Dennis and Schmid, Hans-Joachim}}, keywords = {{Low Temp LS, Low Temperature Laser Sintering, Polyamid 12}}, location = {{Austin, TX}}, title = {{{Low Temperature Laser Sintering on a Standard System: First Attempts and Results with PA12}}}, year = {{2021}}, } @phdthesis{24753, abstract = {{Polymer Laser Sintering (LS) is one of the most used Additive Manufacturing (AM) technologies for the tool-less production of polymer parts. The raw material is a polymer powder which is melted layerwise by the use of laser energy. Especially for the production of single parts, small series, individualized and complex structures, the technology is yet established in few branches. However, inhomogeneous and hardly controllable thermal effects during manufacturing limit the build reproducibility. The present work focuses on temperatures within so-called part cakes, their time dependency and their influence on process quality. Therefore, a temperature measurement system is implemented into a commercial laser sintering machine. Based on the experimental data a model to simulate heat transfer within part cakes is set up. Individual thermal histories during processing are successfully correlated with position dependent powder ageing effects. Another focus is on the analysis of a recycling optimized material. First results of correlations between thermal histories and part properties are shown in order to provide an outlook to further research. The data and knowledge gained through this work can be used to understand thermal effects in greater depth and to increase the process quality via optimizations.}}, author = {{Josupeit, Stefan}}, isbn = {{978-3-8440-6720-0}}, keywords = {{Additive Manufacturing, Polymer Laser Sintering, Polymer Science}}, pages = {{178}}, publisher = {{Shaker Verlag GmbH}}, title = {{{On the Influence of Thermal Histories within Part Cakes on the Polymer Laser Sintering Process}}}, volume = {{11}}, year = {{2019}}, }