TY - CHAP A1 - Käsbauer, Johannes A1 - Schmailzl, Anton A1 - Hierl, Stefan T1 - Simulationsgestützte Prozessentwicklung beim Laser Durchstrahlschweißen von Thermoplasten ohne absorbierende Füllstoffe T2 - 36. CADFEM ANSYS Simulation Conference, 10.-12. Oktober 2018, Leipzig Y1 - 2018 SP - 1 EP - 9 ER - TY - CHAP A1 - Maiwald, Frederik ED - Mottok, Jürgen ED - Reichenberger, Marcus ED - Bogner, Werner T1 - Simulation of Pyrometer Based Temperature Measurement Systems using Non-Sequential Raytracing T2 - Applied Research Conference 2018, ARC 2018, 10 July 2018, Deggendorf Y1 - 2018 SP - 168 EP - 171 PB - pro Business GmbH CY - Berlin ER - TY - CHAP A1 - Meisner, Dennis A1 - Forstner, Lukas A1 - Kaftiranis, Nikitas A1 - Hierl, Stefan T1 - Investigation of process improvements through laser preheating in extrusion-based additive manufacturing process T2 - Lasers in Manufacturing Conference (LIM 2023), 26. Juni bis 29. Juni 2023, München N2 - 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. KW - fused layer modeling KW - laser preheating KW - anisotropy KW - interlayer bonding KW - mesostructure Y1 - 2023 UR - https://www.wlt.de/sites/default/files/2023-09/Contribution_140.pdf PB - Wissenschaftliche Gesellschaft Lasertechnik und Photonik e.V. (WLT) ER - TY - JOUR A1 - Maiwald, Frederik A1 - Roider, Clemens A1 - Schmidt, Michael A1 - Hierl, Stefan T1 - Optical Coherence Tomography for 3D Weld Seam Localization in Absorber-Free Laser Transmission Welding JF - Applied Sciences N2 - 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. KW - image processing KW - laser transmission welding KW - optical coherence tomography KW - process monitoring KW - transparent polymers Y1 - 2022 U6 - https://doi.org/10.3390/app12052718 N1 - Corresponding author: Frederik Maiwald VL - 12 IS - 5 SP - 1 EP - 11 PB - MPDI CY - Basel ER - TY - JOUR A1 - Maiwald, Frederik A1 - Kroth, Lea A1 - Geiger, René A1 - Schmitt, Bernhard A1 - Hierl, Stefan A1 - Schmidt, Michael T1 - Laser welding of polymer foils with spatially adapted intensity distributions JF - Joining Plastics N2 - 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. KW - Laserschweissen KW - Kunststofffolie Y1 - 2025 U6 - https://doi.org/10.53192/JP20250146 SN - 1864-3450 IS - 1 SP - 46 EP - 52 PB - DVS Media CY - Düsseldorf ER - TY - GEN A1 - Maiwald, Frederik A1 - Dzafic, Adelisa A1 - Hierl, Stefan T1 - Messung der Schmelzefließgeschwindigkeit beim Laser-Durchstrahlschweißen von Kunststoffen T2 - Laser in der Elektronikproduktion & Feinwerktechnik - LEF 2021, Erlangen, 22.04.2021 KW - Laserdurchstrahlschweissen KW - Kunststoff KW - Schmelzen KW - Fließgeschwindigkeit Y1 - 2021 ER - TY - JOUR A1 - Dzafic, Adelisa A1 - Maiwald, Frederik A1 - Hierl, Stefan T1 - Messung der Schmelzefließgeschwindigkeit beim Laser-Durchstrahlschweißen von Kunststoffen JF - Werkstoffe in der Fertigung KW - Laserdurchstrahlschweissen KW - Kunststoff KW - Schmelzen KW - Fließgeschwindigkeit Y1 - 2021 SN - 0939-2629 VL - 57 IS - 3 SP - 31 EP - 33 PB - HW-Verl. CY - Mering ER - TY - JOUR A1 - Hofmann, A. A1 - Hierl, Stefan T1 - Kontrolliertes Laserdurchstrahlschweißen JF - Kunststoffe N2 - Obwohl das Laserdurchstrahlschweißen sehr reproduzierbar arbeitet, können Fehler aus den Vorprozessen Compoundieren, Spritzgießen etc. das Schweißergebnis negativ beeinflussen. Dem Anwender steht inzwischen eine breite Palette an Prozessüberwachungsmethoden zur Verfügung, um eine gleich bleibende Produktqualität zu erzielen. Y1 - 2005 UR - https://res.cloudinary.com/sternwald-systems/raw/upload/v1/hugoprd/ARTIKEL_ATTACH/0023FE89_2E241FF70B1C/cf76c9103f760b78d6a3d1b7ecab28f0903541fb/KU_2005_06_Qualitaetssicherung-Kontrolliertes-Laserdurchstrahlschweissen.pdf VL - 95 IS - 6 SP - 36 EP - 38 PB - Hanser ER - TY - JOUR A1 - Maiwald, Frederik A1 - Hierl, Stefan T1 - Absorber-free laser transmission welding of transparent polymers JF - Laser Systems Europe KW - Medical KW - Fibre lasers KW - Welding KW - Plastics Y1 - 2021 UR - https://www.lasersystemseurope.com/analysis-opinion/absorber-free-laser-transmission-welding-transparent-polymers VL - 50 IS - Spring 2021 PB - Europa Science CY - Cambridge ER - TY - GEN A1 - Maiwald, Frederik A1 - Schulze, Julian A1 - Schmidt, Michael A1 - Hierl, Stefan T1 - In-situ optical coherence tomography for spatio-temporal analysis of melt pool crystallization in absorber-free laser transmission welding of polymers T2 - The 9th International Congress on Laser Advanced Materials Processing (LAMP2025), Ise-city, Mie-prefecture, Japan, June 10 to June 13, 2025 Y1 - 2025 PB - Japan Laser Processing Society ER - TY - JOUR A1 - Reindl, Thomas A1 - Meisner, Dennis A1 - Hierl, Stefan T1 - Benchmarking of plastic-based Additive Manufacturing Processes JF - RTejournal - Forum für Rapid Technologie N2 - 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. KW - Additive Manufacturing KW - benchmark artifact KW - dimensional accuracy KW - Fused Layer Modeling KW - mechanical properties KW - Multi Jet Fusion KW - process benchmark KW - Selective Laser Sintering KW - surface quality Y1 - 2023 U6 - https://doi.org/https://doi.org/10.58134/fh-aachen-rte_2023_002 PB - Fachhochschule Aachen ER - TY - CHAP A1 - Maiwald, Frederik A1 - Kroth, Lea A1 - Laskin, Alexander A1 - Hierl, Stefan A1 - Schmidt, Michael T1 - Enlarging the process window in absorber-free laser transmission welding of polymer foils using tailored laser intensity distribution T2 - Procedia CIRP N2 - 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. Y1 - 2024 U6 - https://doi.org/10.1016/j.procir.2024.08.159 N1 - accepted by publisher VL - 124 SP - 489 EP - 493 PB - Elsevier ER - TY - PAT A1 - Maiwald, Frederik A1 - Hierl, Stefan T1 - Laser welding device for clamping and welding components and method for clamping and welding components Y1 - 2023 UR - https://data.epo.org/publication-server/rest/v1.0/publication-dates/20230830/patents/EP4234213NWA1/document.pdf ER - TY - THES A1 - Schmailzl, Anton ED - Franke, Jörg ED - Hanenkamp, Nico ED - Hausotte, Tino ED - Merklein, Marion ED - Müller, Sebastian ED - Schmidt, Michael ED - Wartzack, Sandro T1 - Festigkeits- und zeitoptimierte Prozessführung beim quasi-simultanen Laser-Durchstrahlschweißen N2 - 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 für die Messaufgabe kalibriert. Es wird gezeigt, dass die detektierte Wärmestrahlung dem Kern der Schweißnaht zuzuordnen ist. Die Kerntemperatur in der quasi-stationären Prozessphase steht in direkter Korrelation mit der Schweißnahtfestigkeit. Mit steigender Kerntemperatur bzw. Molekülbeweglichkeit erhöht sich die Wahrscheinlichkeit der Bildung von Molekül-Verschlaufungen in der Fügeebene. 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 für eine festigkeits- und zeitoptimierten Prozessführung des quasi-simultanen Laser-Durchstrahlschweißens nutzbar. N2 - The demand on thermoplastic components for lightweight constructions is continuously rising in the automotive as well as in the aerospace industry. The quasi-simultaneous laser transmission welding is an established joining technique in industry, but so far, it is usually not used for high strength applications as well as for safety-relevant components. This is caused by the lack of process understanding in case of producing high strength joints. Especially the temperature in the joining zone is a crucial process characteristic. Up to now, it was not measured in the needed precision. The quasi-simultaneous laser transmission welding of polyamide 6, especially the correlation between process characteristics and the joint strength is analyzed in this work. Therefore, a 3D-scanner with integrated pyrometer was realized and calibrated for the measurement task. It is shown, that the detected heat radiation is mainly coming from the core of the weld seam. The core temperature in the quasi-stationary process state is in direct correlation with the joint strength. The core temperature represents the mobility of the macromolecules in the polymer. An increased mobility leads to a better diffusion, relaxation or retardation of the macromolecules across the joining interface. A process window is defined on basis of the core temperature. The process setting which leads to a high joint strength as well as to the shortest irradiation time is found on the upper corner of the process window. The temperature can be measured with the needed precision by using the herein shown 3D-scanner with integrated pyrometer as well as by using the developed numerical process model. In conclusion, these tools for process diagnostics and the results of this work are useful for the production of welds with high joint strength and short welding times. KW - Laserschweißen KW - Kunststoffe KW - Prozessüberwachung KW - Laserscanner KW - Ingenieurwissenschaften KW - Maschinenbau KW - Produktionstechnik Y1 - 2022 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:29-opus4-207070 PB - FAU University Press CY - Erlangen ER -