@inproceedings{MaiwaldTroegerHierl, author = {Maiwald, Frederik and Tr{\"o}ger, Johannes and Hierl, Stefan}, title = {Automated weld seam evaluation and 2D simulation parameter calibration for absorber-free laser transmission welding}, 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 = {Absorber-free laser transmission welding enables clean and precise joining of plastics without additives or adhesives. It is therefore well suited to produce optical and medical devices, which place high demands on cleanliness and accuracy. However, the weld usually has an undesirably large vertical expansion, causing bulges and distortion. To improve this, the intensity distribution of the laser beam as well as the processing strategy must be adapted. Due to the complexity, this is aided by process simulation. However, simulation parameter calibration and verification are usually done considering the seam width and height, which is of limited significance. To overcome this, we propose a new method for image processing of microtome sections, determining the spatially resolved geometry of the weld. Thus, the deviation between experiment and simulation can be calculated pixel by pixel. This spatially resolved value is predestined for the calibration of the simulation parameters: For a parameter field with 18 different settings, the total deviation between experiment and simulation is less than 11 \% after calibration.}, language = {en} } @misc{MaiwaldSchmailzlHierl, author = {Maiwald, Frederik and Schmailzl, Anton and Hierl, Stefan}, title = {Thermo-mechanical computation of weld seam geometry in laser transmission welding}, series = {Applied Research Conference - ARC 2017, 7 July 2017, M{\"u}nchen}, journal = {Applied Research Conference - ARC 2017, 7 July 2017, M{\"u}nchen}, editor = {Klippel, Clemens and Mottok, J{\"u}rgen and Reichenberger, Marcus}, publisher = {pro Business GmbH}, address = {Berlin}, language = {en} } @misc{MeisnerKaftiranisMaiwaldetal., author = {Meisner, Dennis and Kaftiranis, Nikitas and Maiwald, Frederik and Rapp, Petra and Hierl, Stefan}, title = {Enhancing Layer Adhesion in Material Extrusion AM with Adaptive Laser Preheating Integrated in Printhead}, series = {LiM Conference 2025, Lasers in Manufacturing, June 23 - 26, 2025, Munich, Germany}, journal = {LiM Conference 2025, Lasers in Manufacturing, June 23 - 26, 2025, Munich, Germany}, publisher = {Wissenschaftliche Gesellschaft Lasertechnik und Photonik e.V.}, abstract = {Material extrusion is a widely used AM process and is gaining more acceptance in industry applications due to its material variety, flexibility, and low cost. However, its usage is limited by a process-related anisotropy caused by insufficient interlayer bonding due to reduced temperature in the process zone. To enhance layer adhesion, an adaptive laser preheating system is integrated in a conventional printhead around the extrusion nozzle. The setup with eight fiber coupled diode laser allows preheating in feed direction and investigation of various intensity profiles. The article describes the experimental setup and significant improvements achieved. Laser preheating with different intensity distributions (spot, sickle or ring shaped) show an incasement of up to 85 \% of the mechanical properties in the build-up direction. However, due to the additional energy input by the laser, controlled cooling of the workpiece becomes a crucial factor and is investigated as well.}, language = {en} } @inproceedings{SchmailzlGeisslerMaiwaldetal., author = {Schmailzl, Anton and Geißler, Bastian and Maiwald, Frederik and Laumer, Tobias and Schmidt, Michael and Hierl, Stefan}, title = {Transformation of Weld Seam Geometry in Laser Transmission Welding by Using an Additional Integrated Thulium Fiber Laser}, series = {Lasers in Manufacturing - LIM 2017, Conference Proceedings}, booktitle = {Lasers in Manufacturing - LIM 2017, Conference Proceedings}, editor = {Esen, Cermal}, address = {M{\"u}nchen}, pages = {1 -- 10}, language = {en} } @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} } @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{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 = {21st International Symposium on Laser Precision Microfabrication: Dresden, 26.06.2020}, booktitle = {21st International Symposium on Laser Precision Microfabrication: Dresden, 26.06.2020}, publisher = {Japan Laser Processing Society}, abstract = {Optical and medical devices made of transparent polymers are gaining popularity because of its cost advantages. The manufacturing technology must be able to meet the high demands of these applications. Advantages of laser transmission welding - contactless input of energy, precision, no adhesives and no particle formation - can be exploited here. For absorber-free welding, lasers emitting in the polymers' intrinsic absorption spectrum are used. Focusing the laser beam with high NA enables selective fusing of the joining zone. Since a molten upper surface leads to visible and palpable irregularities, the lateral expansion of the weld seam is monitored in this work. Welding tests with 1 mm thick plates of COC are performed and monitored by pyrometry. Distances between seam and surface measured in thin cuts and are compared with the pyrometer signal. This shows that the localization of the weld seam is possible and proper and faulty parts can be distinguished by pyrometry.}, subject = {Laserdurchstrahlschweissen}, language = {en} } @article{MaiwaldHierl, author = {Maiwald, Frederik and Hierl, Stefan}, title = {Pyrometerbasierte Prozess{\"u}berwachung beim Laserkunststoffschweißen}, series = {Photonik}, journal = {Photonik}, number = {52}, publisher = {AT-Fachverl.}, address = {Fellbach}, pages = {22 -- 25}, subject = {Laserschweissen}, language = {de} } @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} } @misc{MaiwaldHierl, author = {Maiwald, Frederik and Hierl, Stefan}, title = {Absorberfreies Laser-Durchstrahlschweißen transparenter Kunststoffe}, series = {InnovationForum Medizintechnik, Tuttlingen, 24.10.2019}, journal = {InnovationForum Medizintechnik, Tuttlingen, 24.10.2019}, language = {de} }