@article{HartmannKnoppShandyetal., author = {Hartmann, J{\"u}rgen and Knopp, Kevin and Shandy, Amir and Winterstein, Achim and Arduini, Mariacarla and Hemberger, Frank and Vidi, Stephan and Manara, Jochen and M{\"u}ller, Michael}, title = {Thermophysikalische Charakterisierung von W{\"a}rmed{\"a}mmschichten}, series = {tm - Technisches Messen}, volume = {88}, journal = {tm - Technisches Messen}, number = {12}, publisher = {Oldenbourg Wissenschaftsverlag}, doi = {10.1515/teme-2021-0074}, abstract = {Die Effizienzsteigerung moderner Gasturbinen erfordert die stetige Anhebung der Betriebstemperatur. Die derzeitigen Brenngastemperaturen liegen mit {\"u}ber 1400 °C signifikant {\"u}ber der kritischen Temperatur der verwendeten Turbinenst{\"a}hle. Zur Gew{\"a}hrleistung der Betriebssicherheit werden die Turbinenschaufeln neben Aktivk{\"u}hlung durch Beschichtung mit thermischen Schutzschichten, sogenannten thermal barrier coatings (TBC), gesch{\"u}tzt. Da es sich bei den TBC um Keramikschichten handelt, ist f{\"u}r die Erh{\"o}hung der Haftfestigkeit das Aufbringen eines Haftvermittlers (Verbindungsschicht) notwendig. Da die Eigenschaften d{\"u}nner Schichten stark von den Eigenschaften des Bulkmaterials abweichen k{\"o}nnen und zudem von der Herstellungsmethode beeinflusst werden, ist eine Untersuchung der thermischen und infrarot-optischen Eigenschaften der tats{\"a}chlichen Schichtstrukturen unumg{\"a}nglich, insbesondere im Hochtemperaturbereich. Hierf{\"u}r wurden Proben des reinen Tr{\"a}gerstahls, des Tr{\"a}gerstahls mit Haftvermittlerschicht und des kompletten Schichtsystems aus Tr{\"a}gerstahl, Haftvermittlerschicht und W{\"a}rmed{\"a}mmschicht verschiedener Dicken hergestellt und mittels Laser-Flash-Methode untersucht. Die Auswertung erfolgte dabei analytisch, ausgehend von der Tr{\"a}gerstahl-Einschichtprobe, {\"u}ber die Zweischicht- und Dreischichtsysteme. Vervollst{\"a}ndigt wurden diese Untersuchungen durch infrarot-optische Charakterisierungen, mit denen sich die W{\"a}rmeausbreitung durch die Schichtsysteme beschreiben l{\"a}sst. Zusammen mit den Laser-Flash Messungen erlaubt dies eine sp{\"a}tere Quantifizierung der einzelnen, bei Keramiken auftretenden, W{\"a}rmetransportmechanismen.}, language = {de} } @article{OchsWehnertHartmannetal., author = {Ochs, Dennis and Wehnert, Kira-Kristin and Hartmann, J{\"u}rgen and Schiffler, Andreas and Schmitt, Jan}, title = {Sustainable Aspects of a Metal Printing Process Chain with Laser Powder Bed Fusion (LPBF)}, series = {Procedia CIRP}, volume = {98}, journal = {Procedia CIRP}, publisher = {Elsevir}, pages = {613 -- 618}, abstract = {Production companies are getting more and more aware of the relevancy of energy costs and the environmental impact of their manufactured products. Hence, the knowledge about the energy intensity of new process technologies as metal printing becomes increasingly crucial. Therefore, data about the energy intensity of entire process chains allow a detailed assessment of the life cycle costs and environmental impact of metal printed parts. As metal printing with Laser Powder Bed Fusion (LPBF) is applied from rapid prototyping to serial manufacturing processes more and more, sustainability data are useful to support a valid scale-up scenario and energetic improvements of the 3D-printing machinery as well as peripheral aggregates used in the process chain. The contribution aims to increase the transparency of the LPBF process chain in terms of its energy consumption. Therefore a generalized model to assess sustainability aspects of metal printed parts is derived. For this purpose, the LPBF process chain with the essential pre-, main- and post-processes is evaluated regarding its energy intensity. Here, the sub-processes, for example wet and dry cleaning of the printer, sieving of the metal powder or sand-blasting of the part are analyzed as well as the main printing process. Based on the derived experimental data from an installed, industry-like process chain, a model is created, which tends to generalize the experimental findings to evaluate other metal printed parts and process chain variants in terms of their energy intensity.}, language = {en} } @article{JuergenArduiniManaraetal., author = {J{\"u}rgen, Hartmann and Arduini, Mariacarla and Manara, Jochen and Stark, Thomas and Ebert, Hans-Peter}, title = {Development and Evaluation of an Improved Apparatus for Measuring the Emissivity at High Temperatures}, series = {Sensors}, volume = {21}, journal = {Sensors}, number = {18}, issn = {1424-8220}, doi = {10.3390/s21186252}, abstract = {An improved apparatus for measuring the spectral directional emissivity in the wavelength range between 1 µm and 20 µm at temperatures up to 2400 K is presented in this paper. As a heating unit an inductor is used to warm up the specimen, as well as the blackbody reference to the specified temperatures. The heating unit is placed in a double-walled vacuum vessel. A defined temperature, as well as a homogenous temperature distribution of the whole surrounding is ensured by a heat transfer fluid flowing through the gap of the double-walled vessel. Additionally, the surrounding is coated with a high-emitting paint and serves as blackbody-like surrounding to ensure defined boundary conditions. For measuring the spectral directional emissivity at different emission angles, a movable mirror is installed in front of the specimen, which can be adjusted by a rotatable arrangement guiding the emitted radiation into the attached FTIR-spectrometer. The setup of the emissivity measurement apparatus (EMMA) and the measurement procedure are introduced, and the derived measurement results are presented. For evaluating the apparatus, measurements were performed on different materials. The determined emissivities agree well with values published in literature within the derived relative uncertainties below 4\% for most wavelengths.}, language = {en} } @article{WehnertOchsSchmittetal., author = {Wehnert, Kira-Kristin and Ochs, Dennis and Schmitt, Jan and Hartmann, J{\"u}rgen and Schiffler, Andreas}, title = {Reducing Lifecycle Costs due to Profile Scanning of the Powder Bed in Metal Printing}, series = {Procedia CIRP 98}, volume = {98}, journal = {Procedia CIRP 98}, publisher = {Elsevir}, pages = {684 -- 689}, abstract = {First time right is one major goal in powder based 3D metal printing. Reaching this goal is driven by reducing life cycle costs for quality measures, to minimize scrap rate and to increase productivity under optimal resource efficiency. Therefore, monitoring the state of the powder bed for each printed layer is state of the art in selective laser melting. In the most modern approaches the quality monitoring is done by computer vision systems working with an interference on trained neural networks with images taken after exposure and after recoating. There are two drawbacks of this monitoring method: First, the sensor signals - the image of the powder bed - give no direct height information. Second, the application of this method needs to be trained and labeled with reference images for several cases. The novel approach presented in this paper uses a laser line scanner attached to the recoating machine. With this new concept, a direct threshold measure can be applied during the recoating process to detect deviations in height level without prior knowledge. The evaluation can be done online during recoating and feedback to the controller to monitor each individual layer. Hence, in case of deviations the location in the printing plane is an inherent measurement and will be used to decide which severity of error is reported. The signal is used to control the process, either by starting the recoating process again or stopping the printing process. With this approach, the sources of error for each layer can be evaluated with deep information to evaluate the cause of the error. This allows a reduction of failure in the future, which saves material costs, reduces running time of the machine life cycle phase in serial production and results in less rework for manufactured parts. Also a shorter throughput time per print job results, which means that the employee can spent more time to other print jobs and making efficient use of the employee's work force. In summary, this novel approach will not only reduce material costs but also operating costs and thus optimize the entire life cycle cost structure. The paper presents a first feasibility and application of the described approach for test workpieces in comparison to conventional monitoring systems on an EOS M290 machine.}, language = {en} }