@inproceedings{KaesbauerSchmailzlHierl, author = {K{\"a}sbauer, Johannes and Schmailzl, Anton and Hierl, Stefan}, title = {Simulationsgest{\"u}tzte Prozessentwicklung beim Laser Durchstrahlschweißen von Thermoplasten ohne absorbierende F{\"u}llstoffe}, series = {36. CADFEM ANSYS Simulation Conference, 10.-12. Oktober 2018, Leipzig}, booktitle = {36. CADFEM ANSYS Simulation Conference, 10.-12. Oktober 2018, Leipzig}, pages = {1 -- 9}, language = {de} } @inproceedings{Maiwald, author = {Maiwald, Frederik}, title = {Simulation of Pyrometer Based Temperature Measurement Systems using Non-Sequential Raytracing}, series = {Applied Research Conference 2018, ARC 2018, 10 July 2018, Deggendorf}, booktitle = {Applied Research Conference 2018, ARC 2018, 10 July 2018, Deggendorf}, editor = {Mottok, J{\"u}rgen and Reichenberger, Marcus and Bogner, Werner}, publisher = {pro Business GmbH}, address = {Berlin}, pages = {168 -- 171}, language = {en} } @inproceedings{MeisnerForstnerKaftiranisetal., author = {Meisner, Dennis and Forstner, Lukas and Kaftiranis, Nikitas and Hierl, Stefan}, title = {Investigation of process improvements through laser preheating in extrusion-based additive manufacturing process}, series = {Lasers in Manufacturing Conference (LIM 2023), 26. Juni bis 29. Juni 2023, M{\"u}nchen}, booktitle = {Lasers in Manufacturing Conference (LIM 2023), 26. Juni bis 29. Juni 2023, M{\"u}nchen}, publisher = {Wissenschaftliche Gesellschaft Lasertechnik und Photonik e.V. (WLT)}, pages = {10}, abstract = {Fused layer modeling (FLM) is widely used and is gaining more acceptance in the industry mainly due to its material variety and low costs. However, the usage is limited by a process-related anisotropy of the produced parts. The strength and ductility of the printed parts are significantly lower in the build-up direction than perpendicular to it. This is caused by insufficient interlayer bonding resulting from a reduced surface temperature in the process zone. To overcome this problem, a diode laser is integrated into the conventional FLM process to increase the surface temperature between the already printed surface and the newly applied substrate directly at the deposition zone. The investigations carried out show a significant improvement in the mesostructure, as well as a clear reduction in the anisotropy of the printed test specimens.}, language = {en} } @article{MaiwaldRoiderSchmidtetal., author = {Maiwald, Frederik and Roider, Clemens and Schmidt, Michael and Hierl, Stefan}, title = {Optical Coherence Tomography for 3D Weld Seam Localization in Absorber-Free Laser Transmission Welding}, series = {Applied Sciences}, volume = {12}, journal = {Applied Sciences}, number = {5}, publisher = {MPDI}, address = {Basel}, doi = {10.3390/app12052718}, pages = {1 -- 11}, abstract = {Quality and reliability are of the utmost importance for manufacturing in the optical and medical industries. Absorber-free laser transmission welding enables the precise joining of identical polymers without additives or adhesives and is well-suited to meet the demands of the aforementioned industries. To attain sufficient absorption of laser energy without absorbent additives, thulium fiber lasers, which emit in the polymers' intrinsic absorption spectrum, are used. Focusing the laser beam with a high numerical aperture provides significant intensity gradients inside the workpiece and enables selective fusing of the internal joining zone without affecting the surface of the device. Because seam size and position are crucial, the high-quality requirements demand internal weld seam monitoring. In this work, we propose a novel method to determine weld seam location and size using optical coherence tomography. Changes in optical material properties because of melting and re-solidification during welding allow for weld seam differentiation from the injection-molded base material. Automatic processing of the optical coherence tomography data enables the identification and measurement of the weld seam geometry. The results from our technique are consistent with microscopic images of microtome sections and demonstrate that weld seam localization in polyamide 6 is possible with an accuracy better than a tenth of a millimeter.}, language = {en} } @article{MaiwaldKrothGeigeretal., author = {Maiwald, Frederik and Kroth, Lea and Geiger, Ren{\´e} and Schmitt, Bernhard and Hierl, Stefan and Schmidt, Michael}, title = {Laser welding of polymer foils with spatially adapted intensity distributions}, series = {Joining Plastics}, journal = {Joining Plastics}, number = {1}, publisher = {DVS Media}, address = {D{\"u}sseldorf}, issn = {1864-3450}, doi = {10.53192/JP20250146}, pages = {46 -- 52}, abstract = {Absorber-free laser transmission welding is characterized by its contactless energy input and geometricflexibility and enables the precise and clean joining of polymer films without absorbing additives or adhesives. It is therefore well suited for applications with high demands regarding process reliability and cleanliness such as packaging, fluid containersor as sealing film in medicaland food industry. A homogeneous weld seam temperature is necessary for a large processwindow. In this work, the naturally Gaussian-shaped intensity distributionof the laser beam is there foreconverted into a donut-shaped and a flat-top-shaped distribution. When using the donut-shape, the processwindow for welding polypropylene or polyethylene films is increased by up to a factor of 3. At the same time, the weld seam strength almost corresponds to the strength of the base material.}, subject = {Laserschweissen}, language = {en} } @misc{MaiwaldDzaficHierl, author = {Maiwald, Frederik and Dzafic, Adelisa and Hierl, Stefan}, title = {Messung der Schmelzefließgeschwindigkeit beim Laser-Durchstrahlschweißen von Kunststoffen}, series = {Laser in der Elektronikproduktion \& Feinwerktechnik - LEF 2021, Erlangen, 22.04.2021}, journal = {Laser in der Elektronikproduktion \& Feinwerktechnik - LEF 2021, Erlangen, 22.04.2021}, subject = {Laserdurchstrahlschweissen}, language = {de} } @article{DzaficMaiwaldHierl, author = {Dzafic, Adelisa and Maiwald, Frederik and Hierl, Stefan}, title = {Messung der Schmelzefließgeschwindigkeit beim Laser-Durchstrahlschweißen von Kunststoffen}, series = {Werkstoffe in der Fertigung}, volume = {57}, journal = {Werkstoffe in der Fertigung}, number = {3}, publisher = {HW-Verl.}, address = {Mering}, issn = {0939-2629}, pages = {31 -- 33}, subject = {Laserdurchstrahlschweissen}, language = {de} } @article{HofmannHierl, author = {Hofmann, A. and Hierl, Stefan}, title = {Kontrolliertes Laserdurchstrahlschweißen}, series = {Kunststoffe}, volume = {95}, journal = {Kunststoffe}, number = {6}, publisher = {Hanser}, pages = {36 -- 38}, abstract = {Obwohl das Laserdurchstrahlschweißen sehr reproduzierbar arbeitet, k{\"o}nnen Fehler aus den Vorprozessen Compoundieren, Spritzgießen etc. das Schweißergebnis negativ beeinflussen. Dem Anwender steht inzwischen eine breite Palette an Prozess{\"u}berwachungsmethoden zur Verf{\"u}gung, um eine gleich bleibende Produktqualit{\"a}t zu erzielen.}, language = {de} } @article{MaiwaldHierl, author = {Maiwald, Frederik and Hierl, Stefan}, title = {Absorber-free laser transmission welding of transparent polymers}, series = {Laser Systems Europe}, volume = {50}, journal = {Laser Systems Europe}, number = {Spring 2021}, publisher = {Europa Science}, address = {Cambridge}, language = {en} } @misc{MaiwaldSchulzeSchmidtetal., author = {Maiwald, Frederik and Schulze, Julian and Schmidt, Michael and Hierl, Stefan}, title = {In-situ optical coherence tomography for spatio-temporal analysis of melt pool crystallization in absorber-free laser transmission welding of polymers}, series = {The 9th International Congress on Laser Advanced Materials Processing (LAMP2025), Ise-city, Mie-prefecture, Japan, June 10 to June 13, 2025}, journal = {The 9th International Congress on Laser Advanced Materials Processing (LAMP2025), Ise-city, Mie-prefecture, Japan, June 10 to June 13, 2025}, publisher = {Japan Laser Processing Society}, language = {en} } @article{ReindlMeisnerHierl, author = {Reindl, Thomas and Meisner, Dennis and Hierl, Stefan}, title = {Benchmarking of plastic-based Additive Manufacturing Processes}, series = {RTejournal - Forum f{\"u}r Rapid Technologie}, journal = {RTejournal - Forum f{\"u}r Rapid Technologie}, publisher = {Fachhochschule Aachen}, doi = {https://doi.org/10.58134/fh-aachen-rte_2023_002}, abstract = {Additive Manufacturing (AM) is a future-oriented manufacturing technology that is experiencing an enormous boom in the times of Industry 4.0. As a result, various AM technologies and printer models from different manufacturers are entering the market over a short time span. With the advancing establishment of this manufacturing technology for series applications, the expectations and requirements of the fabricated components are also increasing. However, a major challenge is the application-specific selection of the most suitable AM process due to a lack of comparable data. Furthermore, there needs to be more know-how regarding the geometrical and mechanical characteristics of AM parts. This paper addresses this problem by comparing the three most common plasticbased AM processes in the areas of surface quality, dimensional accuracy, and mechanical properties. Roughness measurements, evaluation of a benchmark artifact, tensile tests, and load increase tests are carried out. Based on the results, the individual possibilities and limitations of the compared AM processes can be detected.}, language = {en} } @inproceedings{MaiwaldKrothLaskinetal., author = {Maiwald, Frederik and Kroth, Lea and Laskin, Alexander and Hierl, Stefan and Schmidt, Michael}, title = {Enlarging the process window in absorber-free laser transmission welding of polymer foils using tailored laser intensity distribution}, series = {Procedia CIRP}, volume = {124}, booktitle = {Procedia CIRP}, publisher = {Elsevier}, doi = {10.1016/j.procir.2024.08.159}, pages = {489 -- 493}, abstract = {Absorber-free laser transmission welding enables precise and clean joining of polymer foils without absorbent additives or adhesives. It is well suited for applications in medical technology and food industry, which impose high demands on process reliability. To achieve a large process window and thus a reliable process, a homogeneous weld seam temperature is desirable. For this purpose, the intensity distribution of the laser beam is adapted locally by refractive beam shaping optics. Using a donut-shaped intensity distribution, the weld seam temperature is homogenized. Thus, the process window for welding polypropylene or polyethylene foils is enlarged up to a factor of 4 compared to a conventional, Gaussian-shaped distribution. This enables the reliable welding of even 85 µm thin foils, which could only be welded to a limited extent with a conventional laser intensity distribution.}, language = {en} } @misc{MaiwaldHierl, author = {Maiwald, Frederik and Hierl, Stefan}, title = {Laser welding device for clamping and welding components and method for clamping and welding components}, organization = {Ostbayerische Technische Hochschule Regensburg}, language = {en} } @phdthesis{Schmailzl, author = {Schmailzl, Anton}, title = {Festigkeits- und zeitoptimierte Prozessf{\"u}hrung beim quasi-simultanen Laser-Durchstrahlschweißen}, editor = {Franke, J{\"o}rg and Hanenkamp, Nico and Hausotte, Tino and Merklein, Marion and M{\"u}ller, Sebastian and Schmidt, Michael and Wartzack, Sandro}, publisher = {FAU University Press}, address = {Erlangen}, doi = {10.25593/978-3-96147-584-1}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:29-opus4-207070}, pages = {xiii, 157}, abstract = {Mit Blick auf Leichtbauanwendungen ist der Bedarf an thermoplastischen Strukturbauteilen sowohl in der Automobil- als auch in der Luftfahrtindustrie in den letzten Jahren deutlich angestiegen. Das quasi-simultane Laser-Durchstrahlschweißen ist ein etabliertes Kunststoffschweißverfahren, welches jedoch zur Herstellung von tragenden und sicherheitsrelevanten Bauteilen bislang kaum in Betracht gezogen wird. In der vorliegenden Arbeit wird die Korrelation zwischen dem Prozessablauf und der Schweißnahtfestigkeit beim quasi-simultanen Laser-Durchstrahlschweißen von Polyamid 6 (Ultramid B3s) erstmalig untersucht. Zur Prozessanalyse wird ein 3D-Scanner mit integriertem Pyrometer realisiert und f{\"u}r die Messaufgabe kalibriert. Es wird gezeigt, dass die detektierte W{\"a}rmestrahlung dem Kern der Schweißnaht zuzuordnen ist. Die Kerntemperatur in der quasi-station{\"a}ren Prozessphase steht in direkter Korrelation mit der Schweißnahtfestigkeit. Mit steigender Kerntemperatur bzw. Molek{\"u}lbeweglichkeit erh{\"o}ht sich die Wahrscheinlichkeit der Bildung von Molek{\"u}l-Verschlaufungen in der F{\"u}geebene. Zur Ermittlung der Kerntemperatur ist sowohl die in dieser Arbeit entwickelte Temperaturmesstechnik als auch die realisierte numerische Prozesssimulation nutzbar. Die Erkenntnisse in dieser Arbeit sind f{\"u}r eine festigkeits- und zeitoptimierten Prozessf{\"u}hrung des quasi-simultanen Laser-Durchstrahlschweißens nutzbar.}, language = {de} }