@article{LaunhardtWoerzLodereretal., author = {Launhardt, M. and W{\"o}rz, A. and Loderer, A. and Laumer, Tobias and Drummer, Dietmar and Hausotte, Tino and Schmidt, M.}, 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{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 polymers: Back tracing of the pore morphology to the process parameters}, series = {Journal of Materials Processing Technology}, volume = {252}, journal = {Journal of Materials Processing Technology}, number = {February}, publisher = {Elsevier}, doi = {10.1016/j.jmatprotec.2017.10.013}, pages = {537 -- 545}, abstract = {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.}, language = {en} } @article{HeinlLaumerBayeretal., author = {Heinl, M. and Laumer, Tobias and Bayer, F. and Hausotte, Tino}, title = {Temperature-dependent optical material properties of polymer powders regarding in-situ measurement techniques in additive manufacturing}, series = {Polymer Testing}, volume = {71}, journal = {Polymer Testing}, number = {October}, publisher = {Elsevier}, doi = {10.1016/j.polymertesting.2018.09.016}, pages = {378 -- 383}, abstract = {Due to the growing number of applications for Additive Manufacturing (AM), an increasing need for enhanced quality control methods exists. Here optical measurement techniques are often used for in-situ monitoring in AM. There is a great potential to standardize and improve applications of optical measurement devices in accordance to the increasing requirements of measuring tasks. Beside the optical material qualifications, especially process-oriented changes in optical effects are of great relevance for in-situ evaluations. The optical modifications may be attributed to aggregate specific phase transitions coming along with variable emitted wavelengths. A measuring setup with two integrations spheres and a heated process chamber have been developed to analyze the optical interactions of laser radiation and visual illumination with the powder. The process oriented analysis for selective laser sintering lead to improved operating conditions in the field of in-situ measurements in combination with an accurate evaluation of the absorption ratio of the examined powder.}, language = {en} } @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} }