TY - CHAP A1 - Rosenberger, Manuel A1 - Belle, Stefan A1 - Hellmann, Ralf T1 - Optical interrogation of bragg grating sensors using tunable fibre based bandpass filter T2 - Proceedings of the 20st international science conference, Mittweida KW - Bragg-Reflektor KW - Sensor Y1 - 2014 ER - TY - CHAP A1 - Belle, Stefan A1 - Rosenberger, Manuel A1 - Hellmann, Ralf T1 - Optical fibre sensing in the production process and storage of biofuels T2 - Proceeding XXV microCAD, International scientific conference, 2011, Section A KW - Biokraftstoff Y1 - 2014 SP - 21 EP - 26 ER - TY - CHAP A1 - Adelmann, Benedikt A1 - Neumeier, Benedikt A1 - Schleier, Max A1 - Wilmann, Eugen A1 - Hellmann, Ralf T1 - Optical cutting tear detection system for industrial fiber laser based cutting machines T2 - Lasers in Manufacturing Conference 2015 KW - Laserschneiden KW - Faserlaser Y1 - 2015 ER - TY - CHAP A1 - Kalmár, László A1 - Hellmann, Ralf A1 - Régert, Tamás A1 - Varga, Zoltan T1 - Numerical simulation of heat transfer procedure in high power LED modules T2 - Proceedings of the 12th technical and scientific meeting KW - Lumineszenzdiode KW - Wärmeübertragung KW - Simulation Y1 - 2011 SP - 18 EP - 20 ER - TY - CHAP A1 - Kalmár, László A1 - Hellmann, Ralf A1 - Régert, Tamás A1 - Varga, Zoltan T1 - Numerical investigation of unsteady heat transport procedure in high power LED module T2 - GEP KW - LED module KW - Lumineszenzdiode Y1 - 2012 VL - 2012 IS - 1 SP - 43 EP - 46 ER - TY - CHAP A1 - Kalmár, László A1 - Hellmann, Ralf A1 - Régert, Tamás A1 - Varga, Zoltan T1 - Numerical investigation of heat transport procedure in high power LED modules T2 - Proceedings of the XXVI International MicroCAD Conference, Miskolc (Hungary) KW - heat transport procedure KW - Lumineszenzdiode KW - Wärmeübertragung Y1 - 2012 SP - 43 EP - 46 ER - TY - CHAP A1 - Sommer, David A1 - Truetsch, Ben A1 - Esen, Cemal A1 - Hellmann, Ralf T1 - Microstructural Fracture Behaviour of PBF-LB/M Inconel 718 Components within different HIP Processes T2 - Lasers in Manufacturing, München, Juni 2025 N2 - We report on a study of different hot isostatic pressing (HIP) cycles, improving the mechanical properties of additively manufactured Inconel 718 components. For this, PBF-LB/M built components are post-processed by different HIP sequences, as gas pressure and processing time are varied, leading to differences in microstructure and material characteristics. Static and dynamic mechanical testing are performed, evaluating the changes in mechanical properties with particular focus on the ultimate tensile strength and endurance limit. Furthermore, metallographic analysis is employed to investigate the achieved density and microhardness. Microstructural analysis, showing the grain boundaries, is used to identify generated phases and precipitations of the material matrix. Moreover, the fracture behaviour is classified by grain deformation during mechanical testing. As the HIP leads to microstructural changes of Inconel 718 components, mechanical properties can be improved significantly, enhancing the ultimate tensile strength and simultaneously the endurance limit. KW - Isostatisches Heißpressen Y1 - 2025 ER - TY - CHAP A1 - Koller, Georg A1 - Hessler, Steffen A1 - Rosenberger, Manuel A1 - Belle, Stefan A1 - Hellmann, Ralf T1 - Micro-structured optical waveguide fabrication in PMMA using low frequency reactive ion etching T2 - Proceedings of the XXVI International MicroCAD Conference – Sensing Technologies, Miskolc (Hungary) KW - waveguide fabrication KW - Wellenleiter Y1 - 2012 ER - TY - CHAP A1 - Schwarz, Simon A1 - Rung, Stefan A1 - Esen, Cemal A1 - Hellmann, Ralf T1 - Manufacturing of optical elements by non-contact laser processing T2 - Seventh European Seminar on Precision Optics Manufacturing, Proceedings KW - Laserbearbeitung KW - Optisches Bauelement Y1 - 2020 IS - 11478 ER - TY - CHAP A1 - Risch, Anna A1 - Hühnlein, Kristof A1 - Knöll, Jürgen A1 - Hellmann, Ralf T1 - Laserscribing of transparent conductive oxides - a comparative study using nanosecond and picosecond pulsed solid state lasers T2 - Proceedings of the 20st International Scientific Conference, Mittweida, 2009 KW - Festkörperlaser Y1 - 2014 ER - TY - CHAP A1 - Rung, Stefan A1 - Bischoff, Christian A1 - Jäger, Erwin A1 - Umhofer, Udo A1 - Hellmann, Ralf T1 - Laser thin film ablation with multiple beams and tailored beam profiles T2 - Proceedings of SPIE 8967, Laser Applications in Microelectronic and Optoelectronic Manufacturing (LAMOM) XIX KW - Thin film KW - Ablation KW - Top-Hat KW - Parallel Processing KW - Beam-Splitter KW - Laserablation KW - Dünnschichttechnik Y1 - 2014 VL - 8967 ER - TY - CHAP A1 - Rung, Stefan A1 - Hellmann, Ralf T1 - Laser scribing of metallized transparent conductive oxide – A comparative study using top hat and Gaussian beam profiles T2 - Proceedings of the XXVI International MicroCAD Conference – Material Processing Technologies KW - laser scribing KW - Laserbearbeitung KW - Laserritzen Y1 - 2012 ER - TY - CHAP A1 - Jäger, Erwin A1 - Rädel, Ulrich A1 - Bischoff, Christian A1 - Umhofer, Udo A1 - Rung, Stefan A1 - Hellmann, Ralf T1 - Laser micromachining – parallel processing with multiple top hat beams T2 - 8th International Conference on Photonic Technologies LANE 2014 KW - Laserbearbeitung Y1 - 2014 ER - TY - CHAP A1 - Risch, Anna A1 - Hellmann, Ralf T1 - Laser induced modification of GZO thin film T2 - Proceeding XXV microCAD, International scientific conference, 2011, Section K: Material science/Material processing technologies KW - Laser KW - Dünne Schicht Y1 - 2014 SP - 69 EP - 74 ER - TY - CHAP A1 - Hasenstab, Stefan A1 - Adelmann, Benedikt A1 - Hellmann, Ralf T1 - Laser Cutting of Alumina and Aluminum Nitride with a 500 W Single Mode Fiber Laser T2 - XXVII. microCAD International Scientific Conference KW - Laserschneiden KW - Aluminiumoxide Y1 - 2013 ER - TY - CHAP A1 - Risch, Anna A1 - Hellmann, Ralf T1 - ITO thin film laser patterning by picosecond laser T2 - Proceeding XXV microCAD, International scientific conference, 2011, Section K: Material science/Material processing technologies KW - Laserbearbeitung Y1 - 2014 SP - 63 EP - 68 ER - TY - CHAP A1 - Belle, Stefan A1 - Scheurich, Steffen A1 - Hellmann, Ralf T1 - Interrogation water content in organic solvents by planar bragg grating sensors T2 - Proceedings SENSOR KW - Bragg-Reflektor KW - Sensor Y1 - 2014 SN - 978-3-9810993-6-2 IS - Vol. II, P3.2 SP - 324 EP - 329 ER - TY - CHAP A1 - Roth, Gian-Luca A1 - Esen, Cemal A1 - Hellmann, Ralf T1 - Internal micro structuring of transparent optical polymers by fs laser T2 - Laser-based Micro-and Nanoprocessing XIV 2020 N2 - Lab-on-chip systems are based on components to transport, mix, separate and analyse small volumes of different fluids. The consecutive integration of more complex functions into a single and compact chip demands on multilayer systems. As the classical production using a stacking and joining of single processed layers is elaborate and limited in terms of multilayer structures, an uprising trend to fabricate those devices is the internal, three dimensional processing of transparent substrates by using ultrashort laser pulses. In this study, we report on the generation of internal hollow architectures created by focused 514nm femtosecond laser pulses inside optical polymer bulk materials of different polymers. The three-dimensional channel layout is implemented by moving the sample using three-dimensional motorized stages, allowing arbitrary complex shaped internal channel architectures. Size and cross sectional shape of a single internal generated microchannel are determined by the intensity distribution of the focal voxel. In particular, we show a comprehensive parameter study to improve this laser process with respect to a higher processing speed and stability. KW - Femtosekundenlaser Y1 - 2020 U6 - https://doi.org/10.1117/12.2543487 VL - 11268 SP - 112681L PB - International Society for Optics and Photonics ER - TY - CHAP A1 - Sauer, Theresia A1 - Kefer, Stefan A1 - Ruppert, Wolfgang A1 - Hellmann, Ralf A1 - Kaloudis, Michael T1 - Integration of Bragg grating sensors in components made of carbon fiber reinforced polymers T2 - Tagungsband der 20. GMA/ITG-Fachtagung Sensoren und Messsysteme 2019, 25.06.2019 - 26.06.2019, Nürnberg, Deutschland N2 - This contribution discusses the integration of polymer planar Bragg grating sensors (PPBG) into carbon fiber reinforced polymer (CFRP) components. For the first time, it is shown that PPBGs based on cyclic olefin copolymers can be integrated into commercial-grade composites, thereby withstanding the demanding production processes. Pre-impregnated fibers are stacked and partially modified to form a sensor pocket. Afterwards, the CFRP specimen containing the optical sensor is cured in a heated mechanical press for 2 hours at a pressure of 7 bar and a temperature of 120 °C. A subsequent evalutaion of the sensor signal shows a Bragg wavelength shift of 1236 pm and a decline in signal amplitude of -2 dB. Three-point flexural tests of the cured sample reveal a linear behavior of the sensor signal towards external loads. The determined sensitivity in dependence of the CFRP specimen's maximum central deflection is -112 pm/mm, while correlation to the applied force results in a sensitivity of -5 pm/N. KW - Bragg grating sensors KW - carbon fiber reinforced polymers KW - cyclic olefin copolymers KW - structural health monitoring KW - Bragg-Reflektor Y1 - 2019 SN - 978-3-9819376-0-2 U6 - https://doi.org/10.5162/sensoren2019/P3.12 SP - 806 EP - 810 ER - TY - CHAP A1 - Sommer, David A1 - Peters, Maximilian A1 - Esen, Cemal A1 - Hellmann, Ralf T1 - Influence of in-situ high-speed milling within a hybrid additive manufacturing approach on the fatigue behaviour of Inconel 718 lattice structures T2 - Lasers in Manufacturing, München, Juni 2025 N2 - As lattice structures in various designs are used in additive manufacturing for lightweight components, the mechanical characterisation and fracture behaviour is of upmost importance for their industrial application. In this study, the fatigue behaviour of Inconel 718 lattice structures is evaluated, comparing sole PBF-LB/M to a hybrid additive manufacturing process combining PBF-LB/M with in-situ high-speed milling. At first, the static and dynamic mechanical load behaviour of different packing densities is analysed, determining the compressive strength and the endurance limit. Secondly, hybrid additive manufactured components are compared to PBF-LB/M built parts with respect to these mechanical properties, revealing improved compressive properties and modified regimes of fatigue. In addition, differences in fracture behaviour are qualified by fractographic and surface analysis. Overall, it can be summarized that the mechanical load characteristics, especially the fatigue behaviour, are improved for hybrid additively manufactured components with a superior surface quality of Ra < 1 µm. KW - Hochgeschwindigkeitsfräsen Y1 - 2025 ER -