TY - CHAP A1 - Schmailzl, Anton A1 - Geißler, Bastian A1 - Maiwald, Frederik A1 - Laumer, Tobias A1 - Schmidt, Michael A1 - Hierl, Stefan ED - Esen, Cermal T1 - Transformation of Weld Seam Geometry in Laser Transmission Welding by Using an Additional Integrated Thulium Fiber Laser T2 - Lasers in Manufacturing - LIM 2017, Conference Proceedings Y1 - 2017 N1 - CD-ROM SP - 1 EP - 10 CY - München 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 - 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 - 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 - CHAP A1 - Maiwald, Frederik A1 - Fries, Fabian A1 - Schulze, Julian A1 - Honnerová, Petra A1 - Hierl, Stefan A1 - Schmidt, Michael T1 - Optical coherence tomography for in situ weld seam monitoring in absorber-free laser transmission welding T2 - Laser Applications in Microelectronic and Optoelectronic Manufacturing (LAMOM) XXX, 25-31 January 2025, San Francisco, California, United States N2 - Optical and medical devices are frequently made of polymers and place high demands on precision, cleanliness, and reliability of the manufacturing processes used. Absorber-free laser transmission welding is well-suited for joining these devices: the energy input is contactless, no adhesives, additives, or absorbers are required, and the fiber lasers used enable precise weld seams. As the weld seam geometry is decisive for the joint strength and thus crucial for the quality of the product, the welding process is monitored in-situ using Optical Coherence Tomography (OCT). Subsequently, the weld seam geometry is identified automatically using the AI model "Segment Anything" (SAM), which performs semantic segmentation of the OCT data without requiring any training from the user. Welding tests using polyamide six indicate that the seam size is measured with an accuracy of a few hundredths of a millimeter, showing excellent agreement with microscopic images of microtome sections. Y1 - 2025 U6 - https://doi.org/10.1117/12.3040607 PB - SPIE ER -