TY - JOUR A1 - Sommer, David A1 - Götzendorfer, Babette A1 - Esen, Cemal A1 - Hellmann, Ralf T1 - Design Rules for Hybrid Additive Manufacturing Combining Selective Laser Melting and Micromilling JF - Design and Post Processing for Metal Additive Manufacturing N2 - We report on a comprehensive study to evaluate fundamental properties of a hybrid manufacturing approach, combining selective laser melting and high speed milling, and to characterize typical geometrical features and conclude on a catalogue of design rules. As for any additive manufacturing approach, the understanding of the machine properties and the process behaviour as well as such a selection guide is of upmost importance to foster the implementation of new machining concepts and support design engineers. Geometrical accuracy between digitally designed and physically realized parts made of maraging steel and dimensional limits are analyzed by stripe line projection. In particular, we identify design rules for numerous basic geometric elements like walls, cylinders, angles, inclinations, overhangs, notches, inner and outer radii of spheres, chamfers in build direction, and holes of different shape, respectively, as being manufactured by the hybrid approach and compare them to sole selective laser melting. While the cutting tool defines the manufacturability of, e.g., edges and corners, the milling itself improves the surface roughness to Ra < 2 µm. Thus, the given advantages of this hybrid process, e.g., space-resolved and custom-designed roughness and the superior geometrical accuracy are evaluated. Finally, we exemplify the potential of this particular promising hybrid approach by demonstrating an injection mold with a conformal cooling for a charge socket for an electro mobile KW - hybrid additive manufacturing; high-speed milling; selective laser melting; construction rules KW - Selektives Laserschmelzen KW - Hochgeschwindigkeitsfräsen Y1 - 2021 UR - https://www.mdpi.com/1996-1944/14/19/5753 U6 - https://doi.org/https://doi.org/10.3390/ma14195753 VL - 14 IS - 19 SP - 1 EP - 23 ER - TY - JOUR A1 - Sommer, David A1 - Pape, Dominik A1 - Esen, Cemal A1 - Hellmann, Ralf T1 - Tool Wear and Milling Characteristics for Hybrid Additive Manufacturing Combining Laser Powder Bed Fusion and In Situ High-Speed Milling JF - Ultra-Precision Manufacturing Technology for Difficult-to-Machine Materials N2 - We report on milling and tool wear characteristics of hybrid additive manufacturing comprising laser powder bed fusion and in situ high-speed milling, a particular process in which the cutter mills inside the powder bed without any cooling lubricant being applicable. Flank wear is found to be the dominant wear characteristic with its temporal evolution over utilization period revealing the typical s-shaped dependence. The flank wear land width is measured by microscopy and correlated to the achievable surface roughness of milled 3D-printed parts, showing that for flank wear levels up to 100 μm a superior surface roughness below 3 μm is accessible for hybrid additive manufacturing. Further, based on this correlation recommended tool, life scenarios can be deduced. In addition, by optimizing the finishing tool start position and the number of afore-built layers, the milling process is improved with respect to the maximum millable angle for undercut surfaces of 3D-printed parts to 30° for the roughing process and to 40° for the entire machining process including finishing KW - hybrid additive manufacturing; high-speed milling; laser powder bed fusion; tool wear KW - Hochgeschwindigkeitsfräsen KW - Werkzeugverschleiß Y1 - 2022 UR - https://www.mdpi.com/1996-1944/15/3/1236 U6 - https://doi.org/https://doi.org/10.3390/ma15031236 VL - 15 IS - 3 SP - 1 EP - 13 ER - TY - CHAP A1 - Franz, Daniel A1 - Roth, Gian-Luca A1 - Rung, Stefan A1 - Esen, Cemal A1 - Hellmann, Ralf T1 - Superimposed beam deflection using acousto-optical deflectors in combination with a galvanometer scanner T2 - Lasers in Manufacturing - LiM 2021 KW - Galvanometer Y1 - 2021 ER - TY - CHAP A1 - Schwarz, Simon A1 - Rung, Stefan A1 - Esen, Cemal A1 - Hellmann, Ralf T1 - Current results on laser-based production of complex optics in glass T2 - 10. Wetzlarer Herbsttagung "Moderne Optikfertigung", 29. - 30. September 2020, Wetzlar KW - Laserbearbeitung KW - Fertigungstechnik Y1 - 2020 ER - TY - CHAP A1 - Schwarz, Simon A1 - Rung, Stefan A1 - Esen, Cemal A1 - Hellmann, Ralf T1 - UKP-Prozess mit anschließendem CO2-Laserpolieren zur Fertigung komplexer Optiken T2 - 10. Workshop Laserbearbeitung von Glaswerkstoffen KW - Linse KW - Array KW - Laserbearbeitung KW - Ultrakurzzeitlaser KW - Kohlendioxidlaser Y1 - 2020 ER - TY - JOUR A1 - Schleier, Max A1 - Adelmann, Benedikt A1 - Esen, Cemal A1 - Glatzel, Uwe A1 - Hellmann, Ralf T1 - Development and evaluation of an image processing algorithm for monitoring fiber laser fusion cutting by a high-speed camera JF - Journal of Laser Applications KW - Laser cutting KW - Image processing KW - Optical imaging KW - Image sensors KW - Laser applications KW - Faserlaser KW - Laserschneiden KW - Bildverarbeitung Y1 - 2021 UR - https://doi.org/10.2351/7.0000391 U6 - https://doi.org/10.2351/7.0000391 VL - 2021 IS - 33 SP - 032004 EP - 032004 ER - TY - JOUR A1 - Zettl, Julian A1 - Rung, Stefan A1 - Esen, Cemal A1 - Hellmann, Ralf T1 - Tangential Laser Turning of Fused Silica Using Ultra-short Laser Pulses JF - Journal of Laser Micro/Nanoengineering N2 - Laser turning with ultra-short laser pulses provides the possibility of manufacturing rotationally symmetric geometries, even of hard to machine materials as fused silica, down to a micrometer scale. In this laser micro machining approach, the laser beam is oriented perpendicularly to the rotational axis and tangentially to the material, whereas the target geometry is realized by moving the constantly rotating specimen according to the specified geometry under the focused laser spot. Due to the fric-tion-less laser ablation it is possible to realize a turning process in fused silica without the use of a contacting tool and therefore without causing mechanical tensions in the work piece. The processing head focuses the laser to a calculated spot size of 18 μm in diameter and the applied processing gas pressure assists in removing the ablated material. In this study, femto-second laser turning of fused silica with a diameter of 3.7 mm is investigated. The influence of the applied pulse energy is stated and the use of a trepanning optic during the turning process is characterized. Furthermore, compre-hensive parameter studies in order to optimize roughness and to find the maximum achievable abla-tion rate are shown. Limited by the mechanical speed of the rotational axis, the highest feasible abla-tion rate is 19.5 mm³/min. A roughness of Ra 0.65 μm are demonstrated. KW - Ultra-short Laser Pulses KW - Laser Turning KW - Fused Silica KW - Ablation Rate KW - Process Efficiency KW - Laserbearbeitung KW - Mikrobearbeitung KW - Quarzglas KW - Ultrakurzer Lichtimpuls Y1 - 2021 U6 - https://doi.org/10.2961/jlmn.2021.01.2008 VL - 16 IS - 1 SP - 42 EP - 46 ER - TY - JOUR A1 - Zettl, Julian A1 - Klar, Maximilian A1 - Rung, Stefan A1 - Esen, Cemal A1 - Hellmann, Ralf T1 - Laser turning with ultrashort laser pulses JF - Journal of Manufacturing Processes N2 - We report on a comprehensive micromachining study of rotationally symmetric parts using femtosecond laser. A laser turning process with tangential impingement of the laser radiation complemented by a trepanning optics is implemented as to accomplish a true laser lathe micromachining approach. With the objective of optimized ablation rate and reduced surface roughness, the influence of pulse energy, feed rate, trepanning diameter and angular beam incidence, respectively, is investigated for processing stellite rods. We find the smallest feasible feature sizes of 8.5 μm in diameter and smoothest surfaces with an arithmetic average of the roughness profile as low as 0.18 μm. The surface roughness, however, appears to be limited by the occurrence of laser induced periodic surface structures provoked by the femtosecond laser radiation. Furthermore, the variation of the fluence in accordance to the incidence on a curved surface is discussed and the heat input into the material is examined through a longitudinal cross section. KW - Ultrashort laser pulses KW - Turning KW - Ablation rate KW - Tangential processing KW - Trepanning optic KW - Ultrakurzer Lichtimpuls KW - Laserbearbeitung KW - Mikrobearbeitung KW - Femtosekundenlaser Y1 - 2021 U6 - https://doi.org/10.1016/j.jmapro.2021.06.025 VL - 2021 IS - 68 SP - 1562 EP - 1568 ER - TY - JOUR A1 - Schwarz, Simon A1 - Rung, Stefan A1 - Esen, Cemal A1 - Hellmann, Ralf T1 - Enhanced ablation efficiency using GHz bursts in micromachining fused silica JF - Optics Letters KW - Fräsen KW - Mikrobearbeitung KW - Quarzglas KW - Femtosekundenlaser Y1 - 2021 VL - 46 IS - 2 SP - 282 EP - 285 ER - TY - JOUR A1 - Schwarz, Simon A1 - Götzendorfer, Babette A1 - Rung, Stefan A1 - Esen, Cemal A1 - Hellmann, Ralf T1 - Compact Beam Homogenizer Module with Laser-Fabricated Lens-Arrays JF - applied sciences KW - Femtosekundenlaser KW - Linse KW - Array Y1 - 2021 VL - 2021 IS - 11 SP - 1018 EP - 1018 ER - TY - JOUR A1 - Schwarz, Simon A1 - Rung, Stefan A1 - Esen, Cemal A1 - Hellmann, Ralf T1 - Ultrashort pulsed laser backside ablation of fused silica JF - Optics Express KW - Femtosekundenlaser KW - Quarzglas KW - Mikrobearbeitung Y1 - 2021 VL - 29 IS - 15 SP - 23477 EP - 23486 ER - TY - JOUR A1 - Rung, Stefan A1 - Bokan, Kevin A1 - Kleinwort, Frederick A1 - Schwarz, Simon A1 - Simon, Peter A1 - Klein-Wiele, Jan-Hendrik A1 - Esen, Cemal A1 - Hellmann, Ralf T1 - Possibilities of Dry and Lubricated Friction Modification Enabled by Different Ultrashort Laser-Based Surface Structuring Methods JF - Lubricants N2 - In this contribution we report on the possibilities of dry and lubricated friction modification introduced by different laser surface texturing methods. We compare the potential of Laser-Induced Periodic Surface Structures and Laser Beam Interference Ablation on 100Cr6 steel in a linear reciprocating ball-on-disc configuration using 100Cr6 steel and tungsten carbide balls with load forces between 50mN and 1000 mN. For dry friction, we find a possibility to reduce the coefficient of friction and we observe a pronounced direction dependency for surfaces fabricated by Laser Beam Interference Ablation. Furthermore, Laser-Induced Periodic Surface Structures result in a load-dependent friction reduction for lubricated linear reciprocating movements. This work helps to identify the modification behaviour of laser generated micro structures with feature sizes of approximately 1μm and reveals new possibilities for surface engineering KW - laser-induced periodic surface structures KW - laser beam interference ablation KW - dry friction KW - lubricated friction KW - laser surface texturing KW - Laser KW - Oberflächenstruktur Y1 - 2019 U6 - https://doi.org/10.3390/lubricants7050043 VL - 7 IS - 43 SP - 1 EP - 13 ER - TY - JOUR A1 - Rung, Stefan A1 - Bokan, Kevin A1 - Rutsch, Kevin A1 - Schwarz, Simon A1 - Esen, Cemal A1 - Hellmann, Ralf T1 - Laser Induced Periodic Surface Structures on 100Cr6 Steel for Modification of Friction Demonstrated with Stribeck Test JF - Journal of Laser Micro/Nanoengineering N2 - In this contribution, we report on surface functionalization by introducing laser induced periodic surface structures on 100Cr6 bearing steel to modify complex tribological properties. The advanced approach of this study is the measurement of the coefficient of friction by performing a ball-on-disk Stribeck test on laser structured surfaces with polytetrafluoroethylene balls in a lubricant environment. The Stribeck test reveals the modified friction behavior using translation speeds up to 106 mm/min and load forces between 100 mN and 5000 mN. Our results show increased stiction and coefficient of friction for laser structured surfaces in the regime of boundary lubrication which is attributed to the laser induced surface asperities. Decreased coefficient of friction is observed in the regime of mixed and hydrodynamic lubrication, i.e. for velocities higher than 1000 mm/min, for surfaces covered by laser induced periodic surface structures with low spatial frequency. KW - Laser KW - Oberflächenstruktur Y1 - 2018 U6 - https://doi.org/10.2961/jlmn.2018.03.0004 VL - 13 IS - 3 SP - 160 EP - 165 ER - TY - JOUR A1 - Schwarz, Simon A1 - Rung, Stefan A1 - Esen, Cemal A1 - Hellmann, Ralf T1 - Fabrication of a high-quality axicon by femtosecond laser ablation and CO2 laser polishing for quasi-Bessel beam generation JF - Optics Express KW - Femtosekundenlaser Y1 - 2018 VL - 26 IS - 18 SP - 23287 EP - 23294 ER - TY - JOUR A1 - Schwarz, Simon A1 - Rung, Stefan A1 - Esen, Cemal A1 - Hellmann, Ralf T1 - Influence of pulse duration on high-precision manufacturing of 3D geometries JF - Journal of Laser Micro/Nanoengineering KW - Dreidimensionale Geometrie Y1 - 2018 VL - 13 IS - 3 SP - 292 EP - 295 ER - TY - JOUR A1 - Schwarz, Simon A1 - Rung, Stefan A1 - Esen, Cemal A1 - Hellmann, Ralf T1 - Homogeneous low spatial frequency LIPSS on dielectric materials generated by beam-shaped femtosecond pulsed laser irradiation JF - Journal of Laser Micro/Nanoengineering KW - Femtosekundenlaser Y1 - 2018 VL - 13 IS - 2 SP - 90 EP - 94 ER - TY - JOUR A1 - Schwarz, Simon A1 - Rung, Stefan A1 - Esen, Cemal A1 - Hellmann, Ralf T1 - Rapid fabrication of precise glass axicon arrays by an all laser-based manufacturing technology JF - Journal of Laser Applications KW - Femtosekundenlaser Y1 - 2020 VL - 32 IS - 1 SP - 012001 EP - 012001 ER - TY - JOUR A1 - Schwarz, Simon A1 - Rung, Stefan A1 - Esen, Cemal A1 - Hellmann, Ralf T1 - Surface Plasmon Polariton Triggered Generation of 1D-Low Spatial Frequency LIPSS on Fused Silica JF - Applied Sciences KW - Femtosekundenlaser KW - Quarzglas Y1 - 2018 VL - 8 IS - 9 SP - 1624 EP - 1624 ER - TY - JOUR A1 - Roth, Gian-Luca A1 - Esen, Cemal A1 - Hellmann, Ralf T1 - Control of femtosecond laser generated microfluidic channels inside poly (methyl methacrylate) JF - Journal of Laser Applications N2 - In this study, the authors report on femtosecond laser direct generation of microchannels inside poly(methyl methacrylate) with variable dimensions ranging from a channel height of 20 to 350 μm and an aspect ratio down to 1.2. Focused ultrashort laser pulses are used to trigger a material modification in the focal area which can be selectively opened by a subsequent annealing process. A 3D microchannel architecture can easily be realized by moving the specimen using motorized stages, allowing freely chosen complex shaped channel layouts. While the laser wavelength is identified as one of the main parameters determining process effectiveness, another core of this study is the variation of channel dimensions by the numerical aperture of the applied objective to focus the laser. The authors find that both size and shape of the modified region and the resulting microchannel can be controlled by altering the numerical aperture. KW - Femtosekundenlaser KW - Polymethylmethacrylate Y1 - 2018 VL - 30 IS - 3 SP - 032016-1 EP - 032016-6 ER - TY - JOUR A1 - Roth, Gian-Luca A1 - Esen, Cemal A1 - Hellmann, Ralf T1 - Circular microchannels inside bulk polymethylmethacrylate generated by femtosecond laser using slit beam shaping JF - Journal of Laser Applications N2 - The authors report on the laser generation of three-dimensional microchannel architectures with fundamentally unlimited channel length by focused 514 nm femtosecond laser pulses inside polymethylmethacrylate bulk material. The three-dimensional channel layout is implemented by moving the specimen using three-dimensional motorized stages, allowing freely chosen complex shaped channel architectures. Based on nonlinear absorption of high intensities around the focal volume, a material modification, including a refractive-index shift is triggered. After laser exposure, the channel is created by a gaseous degradation of exposed areas during an annealing process. Cross section and aspect ratio of thus generated microchannels are strongly influenced by the numerical aperture of the applied objective. To obtain a circular cross-sectional shape, high focusing objectives are necessary. In this report, the authors improve the existing setup by using an elliptical input beam, transforming the intensity distribution of the focal area in the propagation direction to a circular shape even for low and medium numerical aperture focusing objectives and therefore avoiding a small working distance as a limiting factor for processing depth. The elliptical input beam is obtained by insertion of a slit mask in front of the focusing objective. The ellipticity of the incident beam defines the aspect ratio of the generated microchannels. Furthermore, the size of internal microchannels is adjustable by varying laser and annealing process parameters. KW - Femtosekundenlaser Y1 - 2019 VL - 31 IS - 2 SP - 022603-1 EP - 022603-5 ER -