@incollection{SchmailzlHuentelmannLooseetal., author = {Schmailzl, Anton and H{\"u}ntelmann, Sven and Loose, Tobias and K{\"a}sbauer, Johannes and Maiwald, Frederik and Hierl, Stefan}, title = {Potentials of the ALE-Method for Modeling Plastics Welding Processes, in Particular for the Quasi-Simultaneous Laser Transmission Welding}, series = {Mathematical Modelling of Weld Phenomena 12}, booktitle = {Mathematical Modelling of Weld Phenomena 12}, editor = {Sommitsch, Christof and Enzinger, Norbert and Mayr, Peter}, publisher = {Verlag der Technischen Universit{\"a}t Graz}, address = {Graz}, doi = {10.3217/978-3-85125-615-4-51}, pages = {965 -- 975}, abstract = {The Arbitrary-Lagrangian-Eulerian-Method (ALE-Method) offers the possibility to model the quasi-simultaneous laser transmission welding of plastics, in which a squeeze-flow of molten plastic occurs. It is of great interest to get a deeper understanding of the fluid-structure-interactions in the welding zone, since the occurring squeeze-flow transports heated material out of the joining zone, causinga temperature decrease inside.In addition, the numerical modelling offers the possibility to investigate the flow conditions in the joining zone. The aim of this article is to show the potentials of the ALE-Method to simulatethe quasi-simultaneous laser transmission welding with the commercially available software LS-DYNA. The central challenge is to realize a bi-directionalthermo-mechanically coupled simulation,which considers the comparatively high thermal expansion and calculates the interactions of solid and melted plastic correctly. Finally, the potentials of the ALE element formulations for the mathematical description of welding processesare shown, especially for those with a squeeze-flow.}, language = {en} } @inproceedings{SchmailzlHierlSchmidt, author = {Schmailzl, Anton and Hierl, Stefan and Schmidt, Michael}, title = {Gap-Bridging during Quasi-Simultaneous Laser Transmission Welding}, series = {Physics Procedia}, volume = {83}, booktitle = {Physics Procedia}, editor = {Schmidt, Michael}, publisher = {Elsevier}, address = {Amsterdam [u.a.]}, issn = {1875-3892}, doi = {10.1016/j.phpro.2016.08.113}, pages = {1073 -- 1082}, abstract = {Tightness is often the main requirement for quasi-simultaneous laser transmission welds. However, remaining gaps cannot be detected by the used set-path monitoring. By using a pyrometer in combination with a 3D-scanner, weld seam interruptions can be localized precisely while welding, due to temperature deviations along the weld contour. To analyze the temperature signal in correlation to the progress of gap-bridging, T-joint samples with predefined gaps are welded. The set-path is measured synchronously. Additionally, the temperature distribution and the influence of the thermal expansion of the polymers are studied by a thermo-mechanical FEM-process simulation. On top of that, the melt blow-out of the welded samples is analyzed using μCT-measurements. The experiments have shown that closing of a gap can be identified reliably by the temperature signal and that the squeezed melt flow into the gap and the thermal expansion in the gap zone accelerates gap-bridging. Furthermore the inserted heat can be adapted in the fault zone, in order to avoid thermal damage.}, language = {en} } @inproceedings{SchmailzlQuandtSchmidtetal., author = {Schmailzl, Anton and Quandt, Benjamin and Schmidt, Michael and Hierl, Stefan}, title = {In-Situ Process Monitoring during Laser Transmission Welding of PA6-GF30}, series = {Procedia CIRP}, volume = {74}, booktitle = {Procedia CIRP}, doi = {10.1016/j.procir.2018.08.131}, pages = {524 -- 527}, abstract = {Quasi-simultaneous laser transmission welding is preferably used for packaging sensors and electronics. In order to protect the components from moisture, a hermetic encapsulation is needed. However, local weld seam interruptions cannot be identified with the commonly used set-path monitoring. By using a pyrometer, coaxially integrated into a 3D-scanner, gaps between the joining partners can be allocated on basis of the measured temperature. However, the scattering of the heat radiation, especially caused by the fiber reinforcement of the plastics, leads to a reduction of the accessible heat radiation, which makes the identification of gaps considerably more difficult. The herein used experimental setup is characterized by a small detection spot and only by a slight weakening of the heat radiation inside the scanner. Hence, for welding PA6-GF30, the detection of small sized gaps is possible, even if a glass fiber content of 30 percent (wt.) and a weld seam width with approximately 1 mm are given.}, language = {en} } @article{SchmailzlHierlSiebenetal., author = {Schmailzl, Anton and Hierl, Stefan and Sieben, Manuel and Brunnecker, Frank}, title = {Optimierung der Spanndruckverteilung beim Laserdurchstrahlschweißen komplexer Bauteile mittels FE-Berechnung}, series = {JOINING PLASTICS}, volume = {7}, journal = {JOINING PLASTICS}, number = {1}, pages = {30 -- 34}, language = {de} } @article{MaiwaldEnglmaierHierl, author = {Maiwald, Frederik and Englmaier, Stephan and Hierl, Stefan}, title = {Online pyrometry for weld seam localization in absorber-free laser transmission welding of transparent polymers}, series = {Journal of Laser Micro/Nanoengineering}, volume = {Vol. 16}, journal = {Journal of Laser Micro/Nanoengineering}, number = {1}, publisher = {Japan Laser Processing Society}, issn = {1880-0688}, doi = {10.2961/jlmn.2021.01.2002}, pages = {8 -- 13}, abstract = {Production of optical and medical devices makes high demands on cleanliness, precision, visual appearance and reliability. Advantages of laser transmission welding - contactless input of energy, high precision, no adhesives and no particle formation - can be fully exploited for this use. For absorber-free welding, lasers emitting in the polymers' intrinsic absorption spectrum between 1.6 μm and 2 μm are used. Focusing the laser beam with high NA provides large intensity gradients inside the specimen and enables selective fusing of the joining zone without affecting the surface. Since a molten upper surface leads to visible and palpable irregularities and causes warpage, the verticalexpansion of the weld seam is crucial. To meet the high quality and reliability required in the medical and optical industry, online monitoring of the seam is necessary. The aim of this work is the localization and evaluation of the weld seam using pyrometry. First, the emitted thermal radiation is computed, enabling signal analysis regarding origin and spectrum. Thus, assessment of measurement spectrum and forecast of the signal in dependence on seam shape and position is possible. Finally, welding tests with Topas 8007-04 are performed at 200 mm/s feed rate and monitored with 100 kHz. The comparison of tracked data with thin-cuts demonstrates that weld seam localization by pyrometry is possible, enabling online assessment of the process.}, subject = {Laserdurchstrahlschweissen}, language = {en} } @inproceedings{KaesbauerSchmailzlPrehmetal., author = {K{\"a}sbauer, Johannes and Schmailzl, Anton and Prehm, Jens and Loose, Tobias and Hierl, Stefan}, title = {Simulation of Quasi-Simultaneous Laser Transmission Welding of Plastics}, series = {Procedia CIRP}, volume = {94}, booktitle = {Procedia CIRP}, publisher = {Elsevier}, doi = {10.1016/j.procir.2020.09.136}, pages = {737 -- 741}, abstract = {Thermo-mechanical simulation offers great opportunities to optimize welding processes of plastics. For realistic simulation, the temperature dependent mechanical properties need to be implemented from ambient temperature to temperatures above the flow temperature. Standard test methods are insufficient for characterization in the entire temperature range because close to the flow temperature the material is too soft for tensile tests and too stiff for rheometry. Therefore, an optimization strategy is developed, that determines unknown material parameters by testing in welding simulations. The unknown parameters are iteratively adjusted to minimize the mismatch between computed and measured set-paths. Thus, important process characteristics are calculated realistically, enabling the computer aided assessment of the weld quality.}, subject = {Kunststoffschweißen}, language = {en} } @inproceedings{MaiwaldEnglmaierHierl, author = {Maiwald, Frederik and Englmaier, Stephan and Hierl, Stefan}, title = {Absorber-free Laser Transmission Welding of Transparent Polymers using Fixed Focus Optics and 3D Laser Scanner}, series = {Procedia CIRP}, volume = {94}, booktitle = {Procedia CIRP}, publisher = {Elsevier}, doi = {10.1016/j.procir.2020.09.117}, pages = {686 -- 690}, abstract = {Laser transmission welding is a well-known joining technology for thermoplastics, providing reliable and hermetical sealing without adhesives or particle formation. The main advantages of laser-based energy input - high precision, no additional adhesive and no particle emission - are essential for medical and optical applications. To obtain sufficient absorption in visually transparent polymers, thulium fibre lasers emitting in the polymers' intrinsic absorption spectrum are used. Optics with high numerical aperture provide large intensity gradients inside the specimen, enabling selective fusing in the joining zone. Although the basic feasibility has already been demonstrated, the welding process lacks stability and productivity. Aim of this work is the determination of optimized settings for a fast and reliable welding process. Thus, the interplay of process parameters as well as their impact on the seam are analysed by thermal simulations. Calculated settings are verified by welding tests with COC, PA6 and PETG, using a fixed-focus optics and a 3D laser scanner with up to 200 mm/s feed rate.}, language = {en} } @article{SchmailzlKaesbauerMartanetal., author = {Schmailzl, Anton and K{\"a}sbauer, Johannes and Martan, Jiř{\´i} and Honnerov{\´a}, Petra and Sch{\"a}fer, Felix and Fichtl, Maximilian and Lehrer, Tobias and Pruš{\´a}kov{\´a}, L. and Tesař, Jiř{\´i} and Sk{\´a}la, J. and Honner, Milan and Hierl, Stefan}, title = {Measurement of Core Temperature through Semi-Transparent Polyamide 6 using Scanner-Integrated Pyrometer in Laser Welding}, series = {International Journal of Heat and Mass Transfer}, volume = {146}, journal = {International Journal of Heat and Mass Transfer}, number = {January}, publisher = {Elsevier}, doi = {10.1016/j.ijheatmasstransfer.2019.118814}, abstract = {Predicting the core temperature during welding is an ambitious aim in many research works. In this work, a 3D-scanner with integrated pyrometer is characterized and used to measure the temperature during quasi-simultaneous laser transmission welding of polyamide 6. However, due to welding in an overlap configuration, the heat radiation emitted from the joining zone of a laser transmission weld has to pass through the upper polymer, which is itself a semi-transparent emitter. Therefore, the spectral filtering of the heat radiation in the upper polymer is taken into account by calibrating the pyrometer for the measurement task. Thermal process simulations are performed to compare the temperature field with the measured temperature signal. The absorption coefficients of the polymers are measured, in order to get precise results from the computation. The temperature signals during welding are in good agreement with the computed mean temperature inside the detection spot, located in the joining area. This is also true for varying laser power, laser beam diameter and the carbon black content in the lower polymer. Both, the computed mean temperature and the temperature signal are representing the core temperature. In order to evaluate the spatial sensitivity of the measurement system, the emitted heat radiation from both polymers is calculated on basis of the computed temperature field. Hereby it is found, that more than 90 percent of the detected heat radiation comes from the joining area, which is a crucial information for contact-free temperature measurement tasks on semi-transparent polymers.}, language = {en} } @article{KaesbauerSchmailzlWeberetal., author = {K{\"a}sbauer, Johannes and Schmailzl, Anton and Weber, Ulrich and Hierl, Stefan and Jaus, Tobias and Schwalme, Michael}, title = {Simulationsgest{\"u}tzte Evaluierung von Strahloszillationsmustern beim quasi-simultanen Laser-Durchstrahlschweißen}, series = {JOINING PLASTICS - F{\"u}gen von Kunststoffen}, volume = {13}, journal = {JOINING PLASTICS - F{\"u}gen von Kunststoffen}, number = {2}, publisher = {DVS-Verl., Verl. f{\"u}r Schweißen und Verwandte Verfahren}, address = {D{\"u}sseldorf}, pages = {102 -- 109}, language = {de} } @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} } @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} }