@inproceedings{LaumerSchmidtStichel, author = {Laumer, Tobias and Schmidt, Michael and Stichel, Thomas}, title = {Correlation Analysis of Different Building Parameters on the Part Properties of Parts Built by Simultaneous Laser Beam Melting of Polymers}, series = {Fraunhofer Direct Digital Manufacturing Conference DDMC 2016 : Conference Proceedings, March 2016, Berlin}, booktitle = {Fraunhofer Direct Digital Manufacturing Conference DDMC 2016 : Conference Proceedings, March 2016, Berlin}, publisher = {Fraunhofer Verlag}, abstract = {Simultaneous Laser Beam Melting of polymers (SLBM) allows the generation of multi-material components,consisting of different thermoplastic polymers, within one additive building process. Besides the common advantagesof conventional Laser Beam Melting (LBM), multi-material components built by SLBM can fulfill different productrequirements like different chemical resistances or haptic material properties within a single part. To achieve suchparts, different powder materials are deposited next to each other and preheated a few degrees below their meltingtemperatures by infrared emitters and laser radiation (λ = 10.60 μm), before in the last step the preheated powdersare molten simultaneously by an additional laser source (λ = 1.94 μm). In this paper, different polymer powders likepolypropylene (PP) and polyamide 12 (PA12) are used for the generation of multi-material specimens. By varyingdifferent building parameters according to a specified design of experiments, their influence on the part properties isanalyzed. Important building parameters are the intensity and the irradiation time of the laser beam used for meltingthe preheated powders. Besides using tensile tests to determine the tensile strength and the elongation at break, theaverage part height in dependence of the energy input is analyzed. The overall aim is to specify the correlationbetween different building parameters regarding the energy deposition on the resulting part properties.}, language = {en} } @inproceedings{LaumerStichelBocketal., author = {Laumer, Tobias and Stichel, Thomas and Bock, Thomas and Amend, Philipp and Schmidt, Michael}, title = {Characterization of temperature-dependent optical material properties of polymer powders}, series = {AIP Conference Proceedings}, booktitle = {AIP Conference Proceedings}, number = {1}, publisher = {AIP Publishing}, doi = {10.1063/1.4918508}, abstract = {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.}, language = {en} } @article{LaumerStichelRathsetal., author = {Laumer, Tobias and Stichel, Thomas and Raths, Max and Schmidt, Michael}, title = {Analysis of the Influence of Different Flowability on Part Characteristics Regarding the Simultaneous Laser Beam Melting of Polymers}, series = {Physics Procedia}, volume = {83}, journal = {Physics Procedia}, publisher = {Elsevier}, issn = {1875-3892}, doi = {10.1016/j.phpro.2016.08.098}, pages = {937 -- 946}, abstract = {Powder based Additive Manufacturing technologies offer huge potential for building parts with almost no geometrical restrictions, but both the process controlling as well as the part properties are strongly dependent on different material characteristics of the material, like the flowability. In this work, different weight percentages of nano-scaled silica dioxide particles (Aerosil®) are admixed to pure polyethylene and polypropylene powder and the resulting flowability is determined. Besides using the Hausner ratio as standardized value, the degree of coverage is introduced as a new characteristic to quantify the powder flowability. The degrees of coverage are compared to the Hausner ratios to allow a discussion and evaluation about the different characteristic values. Additionally, tensile bars consisting of polypropylene are generated to determine the porosity by cross sections and the mechanical part properties by tensile testing. As mechanical part properties, the tensile strength and elongation at break are determined and the effects of different powder flowability on these properties are analyzed.}, 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} } @inproceedings{SchmailzlGeisslerMaiwaldetal., author = {Schmailzl, Anton and Geißler, Bastian and Maiwald, Frederik and Laumer, Tobias and Schmidt, Michael and Hierl, Stefan}, title = {Transformation of Weld Seam Geometry in Laser Transmission Welding by Using an Additional Integrated Thulium Fiber Laser}, series = {Lasers in Manufacturing - LIM 2017, Conference Proceedings}, booktitle = {Lasers in Manufacturing - LIM 2017, Conference Proceedings}, editor = {Esen, Cermal}, address = {M{\"u}nchen}, pages = {1 -- 10}, language = {en} } @article{LaumerKargSchmidt, author = {Laumer, Tobias and Karg, Michael Cornelius Hermann and Schmidt, Michael}, title = {Laser Beam Melting of Multi-Material Components}, series = {Physics Procedia}, volume = {39}, journal = {Physics Procedia}, publisher = {Elsevier}, issn = {1875-3892}, doi = {10.1016/j.phpro.2012.10.068}, pages = {518 -- 525}, abstract = {First results regarding the realisation of multi-material components manufactured by Laser Beam Melting of polymers and metals are published. For realising composite structures from polymer powders by additive manufacturing, at first relevant material properties regarding compatibility have to be analysed. The paper shows the main requirements for compatibility between different materials and offers first results in form of a compatibility matrix of possible combinations for composite structures.For achieving gradient properties of additively manufactured metal parts by using composite materials the composition of alloying components in the powder and adapted process strategies are varied. As an alternative to atomizing pre-alloyed materials, mixtures of different powders are investigated.}, language = {en} } @article{OsmanlicWudyLaumeretal., author = {Osmanlic, Fuad and Wudy, Katrin and Laumer, Tobias and Schmidt, Michael and Drummer, Dietmar and K{\"o}rner, Carolin}, title = {Modeling of Laser Beam Absorption in a Polymer Powder Bed}, series = {Polymers}, volume = {10}, journal = {Polymers}, number = {7}, publisher = {MDPI}, doi = {10.3390/polym10070784}, pages = {1 -- 11}, abstract = {In order to understand the absorption characteristic, a ray trace model is developed by taking into account the reflection, absorption and refraction. The ray paths are resolved on a sub-powder grid. For validation, the simulation results are compared to analytic solutions of the irradiation of the laser beam onto a plain surface. In addition, the absorptance, reflectance and transmittance of PA12 powder layers measured by an integration sphere setup are compared with the numerical results of our model. It is shown that the effective penetration depth can be lower than the penetration depth in bulk material for polymer powders and, therefore, can increase the energy density at the powder bed surface. The implications for modeling of the selective laser sintering (SLS) process and the processability of fine powder distributions and high powder bed densities are discussed.}, language = {en} } @article{GeisslerLaumerWuebbekeetal., author = {Geißler, Bastian and Laumer, Tobias and W{\"u}bbeke, Andrea and Lakemeyer, Patrick and Frick, Thomas and Sch{\"o}ppner, Volker and Schmidt, Michael}, title = {Analysis of the interaction between the temperature field and the weld seam morphology in laser transmission welding by using two different discrete laser wavelengths}, series = {Journal of Laser Applications}, volume = {30}, journal = {Journal of Laser Applications}, number = {3}, publisher = {AIP Publishing}, issn = {1938-1387}, doi = {10.2351/1.5040617}, abstract = {Laser transmission welding is a non-contact and efficient process technology for joining thermoplastic polymers. In the conventional process, laser sources in the wavelength range of 1 μm are usually used. Therefore, most of the laser radiation is transmitted through the upper joining partner and absorbed only in the lower joining partner. As a result, the possibilities to influence the temperature field especially in the upper joining partner are limited. To overcome these limitations, an additional thulium fiber-laser with a wavelength of 1.94 μm is used in this study and coaxially aligned with a diode laser. The use of an additional thulium fiber-laser leads to a significant absorption in the upper joining partner. Through this approach, it is shown that the temperature field and the weld seam geometry can be influenced by using these two different discrete laser wavelengths. Depending on the intensity distribution of both lasers, an increase of the size of the heat affected zone in the upper joining partner can be observed. In order to develop a better process understanding, a thermal finite element model is built up and verified by comparing the calculated size of the heat affected zone for different process parameters with the experimental data. The model is able to represent the influence of both laser sources on the temperature field and is used to calculate characteristics of the temperature field, such as maximum temperatures or cooling rates. The characteristics are then used to explain the weld seam morphology, such as occurrence and size of spherulitic structures in the weld seam.}, language = {en} } @article{KuehnMehlLaumeretal., author = {Kuehn, Cornelius and Mehl, Oliver and Laumer, Tobias and Witt, Gerd}, title = {Comparison between the optical properties of injection molded and additive manufactured components}, series = {Procedia CIRP}, volume = {74}, journal = {Procedia CIRP}, publisher = {Elsevier}, doi = {10.1016/j.procir.2018.08.106}, pages = {259 -- 263}, abstract = {Fused Layer Manufacturing (FLM) is an additive technology based on polymer material extrusion. Due to variations in temperature during the manufacturing process and the resulting stress between the stacked layers, the final parts show anisotropic mechanical properties. One possible approach for their reduction is the immediate local preheating of the surface via laser radiation. At first, our research examines the influence of laser parameters as wavelength, power, velocity and area of impact for the preheating of the surface. In addition, an overview of possible parameter combinations is given based on the selection of raw materials, its colors, thicknesses and the manufacturing process. Initially, the absorption level of the materials regarding the emitted wavelength is detected using a spectrophotometer. Subsequently, preheating tests are conducted with different laser types while the temperature is determined by a thermal camera. The selected laser type is planned to get mounted on a prototype-machine for further in-situ preheating experiments on FLM parts during the manufacturing process.}, language = {en} } @article{GeisslerLaumerWuebbekeetal., author = {Geißler, Bastian and Laumer, Tobias and W{\"u}bbeke, Andrea and Frick, Thomas and Sch{\"o}ppner, Volker and Schmidt, Michael}, title = {Analysis of the Weld Seam Morphology of Polypropylene in Laser Transmission Welding}, series = {Journal of Manufacturing Science and Engineering}, volume = {140}, journal = {Journal of Manufacturing Science and Engineering}, number = {11}, publisher = {ASME}, doi = {10.1115/1.4040876}, pages = {7}, abstract = {Laser transmission welding is a well-known joining technology for welding thermoplastics. Although the process is already used industrially, fundamental process-structure-property relationships are not fully understood and are therefore the subject of current research. One aspect of these mentioned process-structure-property relationships is the interaction between the temperature field during the welding process, the weld seam morphology of semi-crystalline thermoplastics, and the weld seam strength. In this study, the influence of the line energy on the weld seam morphology of polypropylenes is analyzed. For this purpose, the size of spherulites in the weld seam is investigated, as well as different occurring phases of polypropylene (a- and b-phase). It is shown that both the spherulite size of the a-phase and the amount of b-phase increase with increasing line energy. For the explanation and discussion of the results, a temperature-dependent thermal simulation model is used to derive characteristic attributes of the temperature field (maximum temperatures, cooling rates, temperature gradients).}, 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} } @phdthesis{Laumer, author = {Laumer, Tobias}, title = {Erzeugung von thermoplastischen Werkstoffverbunden mittels simultanem, intensit{\"a}tsselektivem Laserstrahlschmelzen}, publisher = {Meisenbach}, address = {Bamberg}, isbn = {978-3-87525-428-0}, abstract = {Mittels des entwickelten additiven Fertigungsprozesses des simultanen, intensit{\"a}tsselektiven Laserstrahlschmelzens lassen sich Werkstoffverbunde bestehend aus unterschiedlichen Polymerwerkstoffen mit hohen Bauteilfestigkeiten realisieren. Die zuk{\"u}nftig realisierbaren Werkstoffverbunde k{\"o}nnen dabei durch eine {\"o}rtlich variable Ausnutzung der unterschiedlichen Werkstoffeigenschaften die hinsichtlich lokal definierter Belastungsprofile gestellten Anforderungen an komplexe Multi-Material-Bauteile erf{\"u}llen. Dadurch lassen sich neue Anwendungsfelder f{\"u}r die additive Fertigung von Werkstoffverbunden erschließen.}, language = {de} } @inproceedings{SchmidtFanselowWirthetal., author = {Schmidt, Jochen and Fanselow, Stephanie and Wirth, Karl-Ernst and Peukert, Wolfgang and Hiller, Saskia and Laumer, Tobias and Schmidt, Michael}, title = {Herstellung von Polyolefinstrahlschmelzmaterialien mittels Schmelzeemulgieren zum Einsatz in der additiven Fertigung}, series = {Neue Entwicklungen in der Additiven Fertigung}, booktitle = {Neue Entwicklungen in der Additiven Fertigung}, editor = {Witt, Gerd and Wegner, Andreas and Sehrt, Jan}, publisher = {Springer}, address = {Berlin, Heidelberg}, isbn = {978-3-662-48472-2}, doi = {10.1007/978-3-662-48473-9_2}, pages = {13 -- 23}, abstract = {Im Rahmen dieses Beitrags wird das Schmelzeemulgieren als Verfahren zur Herstel-lung von Polymermikropartikeln vorgestellt. In diesem Prozess wird zun{\"a}chst ein Polymergranulat in einer kontinuierlichen Phase in Gegenwart geeigneter Additive in einem R{\"u}hrbeh{\"a}lter aufgeschmolzen, die Rohemulsion in einer Rotor-Stator-Einheit feinemulgiert und anschließend zu einer Suspension abgek{\"u}hlt. Der Einfluss von Prozessparametern und Systemzusam-mensetzung auf das Emulgierergebnis wird diskutiert und die Anwendbarkeit des Verfahrens f{\"u}r polymere Mikropartikeln anhand von Polypropylen (PP) und Polyethylen (PE-HD) dargestellt. Die erhaltenen Suspensionen werden zur {\"U}berf{\"u}hrung in Pulverform spr{\"u}hgetrocknet und die Fließeigenschaften des Pulvers analysiert. Durch trockenes Beschichten mit pyrogener Kiesels{\"a}ure kann die Fließf{\"a}higkeit der erhaltenen Partikeln weiter verbessert werden. Das Verfahren bietet somit einen neuen Zugang zur Herstellung neuer Ausgangsmaterialien f{\"u}r die Additive Fertigung.}, language = {de} } @inproceedings{AmendMrotzekLaumeretal., author = {Amend, Philipp and Mrotzek, Tino and Laumer, Tobias and Wolf, Michel and Roth, Stephan and Gude, Maik and Schmidt, Michael}, title = {Experimental Investigations on Laser-based Hot-melt Bonding and Injection Molding for Laser-structured Metal Plastic Hybrids}, series = {Laser in Manufacturing (LIM 2017), Munich, Germany}, booktitle = {Laser in Manufacturing (LIM 2017), Munich, Germany}, isbn = {978-3-87525-428-0}, abstract = {The use of thermoplastics in lightweight construction is continuing to grow. This implies the need for suitable joining techniques to combine thermoplastics with other materials, such as metals, to gain tailored multi-material parts. In this paper latest results of experimental investigations on laser-based hot-melt bonding and injection molding for laser-structured metal plastic hybrids are presented. As materials stainless steel and short-fiber reinforced polyamide are used. The stainless steel surface is structured with a nanosecond pulse laser before joining to improve the mechanical adhesion between the dissimilar materials. Thereby, different structure depths in the range between 16.6 ± 1.2 µm and 66.5 ± 2.5 µm as well as different hatch distances between 70 and 300 µm are realized. The laser-based joining process is carried out irradiating the metallic surface multiple times. Positioned below the metal in T-joint configuration, the thermoplastic melts as a result of heat transfer and acts as hot-melt cohesive. Besides, hybrid joints are manufactured using injection molding. For experiments, the mold temperature as well as the melt temperature are varied. Regardless of the joining process, the hybrid joints are mechanically characterized by tensile tests. The results demonstrate that for both joining processes strong laser-structured metal plastic hybrids can be realized.}, language = {en} } @inproceedings{Laumer, author = {Laumer, Tobias}, title = {The influence of micro-sized structures on the compound strength of multi-material components built by Simultaneous Laser Beam Melting of Polymers}, series = {Proceedings of LPM2016 - the 17th International Symposium on Laser Precision Microfabrication, 2016, Xian, China}, booktitle = {Proceedings of LPM2016 - the 17th International Symposium on Laser Precision Microfabrication, 2016, Xian, China}, abstract = {Simultaneous laser beam melting (SLBM) allows the direct realization of multi-material components consisting of different polymer materials by a single Additive Manufacturing (AM) process. To achieve a high compound strength between different materials by adhesive bonding, a common boundary zone based on diffusion of the macromolecules is necessary and thus, both materials needs to be compatible regarding their specific adhesion compatibility. However, by SLBM also incompatible polymers can be processed to multi-material parts. If two incompatible polymers are processed, a positive locking between the different materials is necessary to achieve a connection between the materials. The positive locking results of a random mixture process of the different powder materials during the powder deposition process by a two chamber recoater system, which leads to the forming of undercuts of one material in the other during the melting and recrystallization. In this paper, thermoplastic elastomer (TPE) and polypropylene (PP) powders, which are incompatible, are processed to multi-material specimens. By qualifying basic material properties, their influence on the process and especially on the forming of undercuts in the boundary zone is analyzed. To also allow the analysis of the influence of both material and process parameters on the resulting part properties, tensile test specimens are built and their tensile strength is determined. Additionally, cross sections of the boundary zone are prepared and analyzed by microscope images.}, language = {en} }