TY - CHAP A1 - Quandt, Benjamin ED - Mottok, Jürgen ED - Reichenberger, Marcus ED - Bogner, Werner T1 - Effect of the Detection Spot Size on pyrometric Temperature Signal at quasi-simultaneous Laser Transmission Welding T2 - Applied Research Conference 2018, ARC 2018, 10 July 2018, Deggendorf Y1 - 2018 SP - 261 EP - 264 PB - pro Business GmbH CY - Berlin ER - TY - CHAP A1 - Schäfer, Felix ED - Mottok, Jürgen ED - Reichenberger, Marcus ED - Bogner, Werner T1 - Temperature Measurement with Scanner-Integrated Pyrometer during Laser Transmission Welding with Clearweld Absorber T2 - Applied Research Conference 2018, ARC 2018, 10 July 2018, Deggendorf Y1 - 2018 SP - 258 EP - 260 PB - pro Business GmbH CY - Berlin 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 - 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 -