Ostendorf, Andreas
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Ostendorf, Andreas
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Ostendorf, Andreas
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Item-typ:Veröffentlichung, UV-laserbasierte Oberflächenfluorierung von Polymeren(2015-10-01); ; ; The method of direct fluorination of polymeric components utilizing fluorine gas is an established tool for the adjustment of the free surface energy of these structures. With this tool, the contact angle of various liquids on these surfaces can be modified. If it is intended to fluorinate the surface only locally, the method of direct fluorination is not suitable. In this work, a novel process was investigated, which allows a local fluorination of a polymeric surface in a single process step. The polymer is exposed to a precursor gas, which contains bonded fluorine. The fluorine can be dissociated via UV photons. The generated fluorine radicals mainly react with the polymer surface close to their point of origin. Depending on the UV intensity distribution, the shape of the locally fluorinated area on the surface can be determined. With the investigated process, hydrophilic and hydrophobic areas can be generated on polymer surfaces, which i. e. can be used in the field of liquid sample handling of very small volumes.DissertationBand:0058581 232 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Dynamisches Prozessverhalten bei der laserinduzierten thermochemischen Mikrostrukturierung von Metallen(2018-12-05); ; ; This work deals with the process behavior of laser-induced thermochemical material removal of self-passivation metallic materials in order to enable a stable and process reliable micro structuring. The main focus hereby is on the identification of the causes and their influencing factors for the origin of discontinuities in process quality. The results show that laser-induced gas bubble formation, both by boiling of the electrolyte and by reaction-induced release of hydrogen, is a major contributor of the disruption of material removal. With the achieved knowledge and the model-based description of the removal process, suitable machining parameters for a high-quality and disturbance-free processing can be identified.DissertationBand:0067627 200 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Laser-induced thermochemical polishing of metals(2022-01-21); ; ; This work investigates material removal by laser-induced thermochemical machining (LCM) as a method for selectively polishing passive metals in applications where conventional finishing technologies induce unacceptable mechanical or thermal stresses. The main objectives are to identify reliable process conditions, to understand the effects of various process parameters on polishing and the corresponding mechanisms of action and to develop a model to predict surface roughness. A multipass LCM method is developed, which allows controlled polishing of different materials by adjusting laser power, spot diameter, scan passes, line spacing and scan velocity. The results show that polishing characteristics are determined by the laser-induced average thermal load and exposure time. Polishing can be understood as a geometric levelling process and can be predicted by a model based on local differences of the thermal gradient. The stable lower limit of roughness of the finished surface is mainly defined at the microstructural level by inhomogeneous etching between the face and boundaries of the grains. These findings present opportunities for flexible and selective adjustment of LCM process parameters to achieve the desired roughness level for surfaces of micro- and macroscopic dimensions.DissertationBand:0075414 354