@article{26109, abstract = {{Temperature effects in the polymer laser sintering process are an important aspect regarding the process reproducibility and part quality. Depending on the job layout and position within the part cake, individual temperature histories occur during the process. Temperature history dependent effects are for example part warpage, the crystallization rate and powder ageing effects. This work focuses on temperatures and heat flow within laser sintered part cakes. Therefore, a thermal Finite Element (FE) model of a part cake is developed based on experimental in-process temperature measurements. Thermal boundary conditions and properties of the used bulk polymer powder are analyzed and relevant parameters are identified. The model is validated and optimized considering different job heights and ambient conditions during the cooling phase. It is finally possible to predict position-dependent temperature histories as a function of significant job parameters. The model allows a transfer of the results for varied boundary conditions during cooling. In combination with an implementation of built parts, this model will be an important tool for the development of optimized process controls and cooling strategies.}}, author = {{Josupeit, Stefan and Ordia, Lavish and Schmid, Hans-Joachim}}, issn = {{2214-8604}}, journal = {{Additive Manufacturing}}, pages = {{189--196}}, title = {{{Modelling of temperatures and heat flow within laser sintered part cakes}}}, doi = {{10.1016/j.addma.2016.06.002}}, year = {{2016}}, } @article{26111, abstract = {{The shape and fracture of the free surface frequently limits the measuring range and impedes the use of optical velocimetric techniques in parallel plate and cone plate setups. To prevent this, various kinds of edge guards are often employed. In the present study, we elucidate how an edge guard distorts the steady velocity profile in a parallel plate setup. To this end, we analyzed the velocity field of a strongly shear-thinning fluid, a Newtonian fluid and a set of suspensions via particle image velocimetry in a parallel plate device. Several guard ring sizes were studied. The distortion is described by a simple three parameter model. These parameters are mostly constant for different fluids and suspensions with particle volume fractions below 45%. With increasing radius, the guard ring.s influence approaches a limiting value that we attribute to the influence of the fluid surrounding the gap. Our results indicate a limiting ratio of the difference between plate radius and guard to gap size that should always be exceeded. In the presence of a guard ring, even Newtonian fluids do not exhibit a constant shear rate for most radial distances within the gap. This distortion of the velocity field challenges the simple superposition approach of unguarded device and guard influence that is prevalent in the literature.}}, author = {{Schmid, Hans-Joachim and Pieper, S.}}, journal = {{Applied Rheology}}, title = {{{Guard ring induced distortion of the steady velocity profile in a parallel plate rheometer}}}, doi = {{10.3933/APPLRHEOL-26-64533}}, year = {{2016}}, } @article{26118, abstract = {{Suspensions are subject to confinement induced structuring, i.e. layering, at the confining surfaces. While most of the previous work focused on layering in Couette cells, the present study aimed to characterize the resulting layers at the plates of a parallel plate rheometer with regard to their relative particle concentration. The particle concentration profile over the radial distance was characterized for various mean concentrations and gap heights. To this end, we mapped the distribution of fluorescently dyed tracer particles in density and refractive index matched suspensions. The results indicate that layering at the surfaces stabilizes as the ratio between gap height and particle diameter increases. For lower gap heights, i.e. as the suspension approaches a two dimensional state, the layer concentration was non-uniform over the plates. In general, results were quantitatively different for the upper and lower plate and the concentration profiles were noticeably asymmetric. We conclude that this is probably the result of the rheometer loading or the start-up process. The stable layers as well as the inhomogeneous particle distribution in general offer an explanation for the lack of transferability of viscosimetric results between different setups.}}, author = {{Pieper, Sven and Schmid, Hans-Joachim}}, issn = {{0377-0257}}, journal = {{Journal of Non-Newtonian Fluid Mechanics}}, pages = {{1--7}}, title = {{{Layer-formation of non-colloidal suspensions in a parallel plate rheometer under steady shear}}}, doi = {{10.1016/j.jnnfm.2016.04.004}}, year = {{2016}}, } @book{27443, author = {{Gausemeier, Jürgen and Schmidt, Michael and Anderl, Reiner and Schmid, Hans-Joachim and Leyens, Christoph and Seliger, Günther and Karg, Michael and Kage, Martin}}, publisher = {{acatech - Deutsche Akademie der Technikwissenschaften}}, title = {{{Additive Fertigung}}}, year = {{2016}}, } @inproceedings{22180, abstract = {{The implementation of lattice structures into additive manufactured parts is an important method to decrease part weight maintaining a high specific payload. However, the manufacturability of lattice structures and mechanical properties for polymer laser sintering are quite unknown yet. To examine the manufacturability, sandwich structures with different cell types, cell sizes and lattice bar widths were designed, manufactured and evaluated. A decisive criterion is for example a sufficient powder removal. In a second step, manufacturable structures were analyzed using four-point-bending tests. Experimental data is compared to the density of the lattice structures and allows for a direct comparison of different cell types with varied geometrical attributes. The results of this work are guidelines for the design and dimensioning of laser sintered lattice structures.}}, author = {{Josupeit, Stefan and Delfs, Patrick and Menge, Dennis and Schmid, Hans-Joachim}}, booktitle = {{27th Annual International Solid Freeform Fabrication Symposium }}, pages = {{2077--2086}}, title = {{{Manufacturability and Mechanical Characterization of Laser Sintered Lattice Structures}}}, doi = {{http://utw10945.utweb.utexas.edu/sites/default/files/2016/166-Josupeit.pdf}}, volume = {{27}}, year = {{2016}}, } @article{22185, abstract = {{The layered structure of Additive Manufacturing processes results in a stair- stepping effect of the surface topographies. In general, the impact of this effect strongly depends on the build angle of a surface, whereas the overall surface roughness is additionally caused by the resolution of the specific AM process. The aim of this work is the prediction of the surface quality in dependence of the building orientation of a part. These results can finally be used to optimize the orientation to get a desired surface quality. As not all parts of the component surface are equally important, a preselection of areas can be used to improve the overall surface quality of relevant areas. The model uses the digital AMF format of a part. Each triangle is assigned with a roughness value and by testing different orientations the best one can be found. This approach needs a database for the surface qualities. This must be done separately for each Additive Manufacturing process and is shown exemplarily with a surface topography simulation for the laser sintering process.}}, author = {{Delfs, Patrick and Tows, Marcel and Schmid, Hans-Joachim}}, isbn = {{2214-8604}}, journal = {{Additive Manufacturing}}, number = {{12, Part B}}, pages = {{214--320}}, publisher = {{Elsevier}}, title = {{{Optimized build orientation of additive manufactured parts for improved surface quality and build time}}}, doi = {{10.1016/j.addma.2016.06.003}}, volume = {{2}}, year = {{2016}}, } @inproceedings{22190, author = {{Delfs, Patrick and Schmid, Hans-Joachim}}, booktitle = {{Fraunhofer Direct Digital Manufacturing Conference}}, isbn = {{978-3-8396-1001-5}}, pages = {{411--414}}, title = {{{Extended Analysis of the Surface Topography of Laser Sintered Polymer Parts }}}, doi = {{https://www.bookshop.fraunhofer.de/buch/fraunhofer-direct-digital-manufacturing-conference-ddmc-2016/245111#}}, volume = {{3}}, year = {{2016}}, } @inproceedings{22194, author = {{Josupeit, Stefan and Schmid, Hans-Joachim}}, booktitle = {{International Congress on Particle Technology (PARTEC) }}, title = {{{Thermal properties of polyamide 12 powder for application in laser sintering}}}, year = {{2016}}, } @inproceedings{22200, abstract = {{In the polymer laser sinter process, part quality depends on many influencing factors along the process chain. For application of the technology in series production and an integration of laser sintered parts into a technical environment, the dimensional accuracy of parts has to be taken into account. Therefore, occuring deviatons and their scattering have to be reduced and homogenized based on process parameters and build job layout. In this work, the dimensional accuracy of laser sintered parts is analyzed for varied parameter values. Influences of different process and geometrical build job parameters on dimensional deviatons are figured out. The experimental results allow an evaluation of more and less important influences. Finally, measures are deduced to reduce and homogenize dimensional deviations.}}, author = {{Josupeit, Stefan and Delfs, Patrick and Lieneke, Tobias and Adam, Guido and Gessler, Monika and Pfisterer, H. and Schmid, Hans-Joachim}}, booktitle = {{Rapid Tech - International Trade Show & Conference for Additive Manufacturing }}, isbn = {{978-3-446-45060-8}}, pages = {{107--120}}, title = {{{Dimensional accuracy of polymer laser sintered parts: Influences and measures}}}, doi = {{10.3139/9783446450608.009}}, year = {{2016}}, } @inproceedings{22404, abstract = {{Additive Manufacturing (AM), also known as 3D printing, is a relatively new technology which enables the toolless production of components and entire assemblies directly from a CAD file. Today, the technology is still not widely used in industrial production. It is mainly limited to special applications, although it shows great potential. In this paper, first approaches are shown to apply AM to the production of rotors for permanent magnet synchronous machines (PMSM). The possibilities of a lightweight design with a low moment of inertia as well as the influence on the magnetic anisotropy for an improved sensorless control of PMSM are pointed out. The results clearly demonstrate the great potential of additive manufacturing in electrical engineering applications.}}, author = {{Lammers, Stefan and Adam, Guido and Schmid, Hans-Joachim and Mrozek, Rafael and Oberacker, Rainer and Hoffmann, Michael and Quattrone, Francesco and Ponick, Bernd}}, booktitle = {{EDPC 2016}}, isbn = {{978-1-5090-2908-2}}, title = {{{Additive Manufacturing of a Lightweight Rotor for a Permanent Magnet Synchronous Machine}}}, doi = {{10.1109/EDPC.2016.7851312}}, year = {{2016}}, } @inproceedings{22408, author = {{Josupeit, Stefan and Delfs, Patrick and Lieneke, Tobias and Schmid, Hans-Joachim}}, booktitle = {{27th Annual International Solid Freeform Fabrication Symposium }}, title = {{{Influences on the dimensional Accuracy of Laser Sintered Parts along the Process Chain}}}, year = {{2016}}, } @book{26113, abstract = {{In the polymer laser sinter process, part quality depends on many influencing factors along the process chain. For application of the technology in series production and an integration of laser sintered parts into a technical environment, the dimensional accuracy of parts has to be taken into account. Therefore, occurring deviations of the process have to be known to define tolerances for part design. Dimensional deviations and their scattering have to be reduced and homogenized based on process parameters and build job layout. In this work, the dimensional accuracy of laser sintered parts is analyzed for varied parameter values. Influences of different process and geometrical build job parameters on dimensional deviations are figured out. The experimental results allow an evaluation of more and less important influences. Finally, measures are deduced to reduce and homogenize dimensional deviations.}}, editor = {{Kniffka, Wieland and Eichmann, Michael and Witt, Gerd and Josupeit, S. and Delfs, P. and Lieneke, Tobias and Adam, G. and Schmid, Hans-Joachim}}, isbn = {{978-3-446-45017-2}}, title = {{{Geometrische Genauigkeit von Lasersinter-Bauteilen: Einflüsse und Maßnahmen / Dimensional accuracy of polymer laser sintered parts: Influences and measures}}}, doi = {{10.3139/9783446450608.009}}, year = {{2016}}, } @article{21947, abstract = {{Wall slip is a long-known phenomenon in the field of rheology. Nevertheless, the origin and the evolution are not completely clear yet. Regarding suspensions, the effect becomes even more complicated, because different mechanisms like pure slip or slip due to particle migration have to be taken into account. Furthermore, suspensions themselves show many flow anomalies and the isolation of slip is complicated. In order to develop working physical models, further insight is necessary. In this work, we measured experimentally the wall slip velocities of different highly filled suspensions in a rectangular slit die directly with respect to the particle concentration and the particle size. The slip velocities were obtained using a particle image velocimetry (PIV) system. The suspensions consisting of a castor oil–cinnamon oil blend and PMMA particles were matched in terms of refractive indexes to appear transparent. Hereby, possible optical path lengths larger than 15 mm were achieved. The slip velocities were found to be in a quadratic relation to the wall shear stress. Furthermore, the overall flow rate as well as the particle concentration has a direct influence on the slip. Concerning the shear stress, there seem to be two regions of slip with different physical characteristics. Furthermore, we estimated the slip layer thickness directly from the velocity profiles and propose a new interpretation. The PIV technique is used to investigate the viscosity and implicit the concentration profile in the slit die. It is shown that the particle migration process is quite fast.}}, author = {{Jesinghausen, Steffen and Weiffen, Rene and Schmid, Hans-Joachim}}, issn = {{0723-4864}}, journal = {{Experiments in Fluids}}, keywords = {{Rheology, Wall Slip, Slip, apparent slip, suspension}}, title = {{{Direct measurement of wall slip and slip layer thickness of non-Brownian hard-sphere suspensions in rectangular channel flows}}}, doi = {{10.1007/s00348-016-2241-6}}, year = {{2016}}, } @article{25140, author = {{Pieper, Sven and Schmid, Hans-Joachim}}, issn = {{0377-0257}}, journal = {{Journal of Non-Newtonian Fluid Mechanics}}, pages = {{1--7}}, title = {{{Layer-formation of non-colloidal suspensions in a parallel plate rheometer under steady shear}}}, doi = {{10.1016/j.jnnfm.2016.04.004}}, year = {{2016}}, } @article{26108, abstract = {{The highly efficient filtration of ultrafine dust emitted by biomass combustion processes with a baghouse filter has been successfully tested in the last years. To protect the filter material from the very small and sticky fine dust particles and to guarantee very high total collection efficiencies (> 99 %) in a long-term stable process, the use of a precoat is necessary. Tests done in a laboratory and a real-application plant show that the reuse of precoat materials can lead to significant savings. Considering the influences of different combustion processes, the associated precoat efficiencies could be calculated. With these characteristic ratios, it is possible to evaluate different process settings. Hence, the amount and the cost of the needed precoat could be reduced significantly.}}, author = {{Schiller, Sascha and Hellmich, Christoph and Schmid, Hans-Joachim}}, issn = {{0930-7516}}, journal = {{Chemical Engineering & Technology}}, pages = {{491--498}}, title = {{{Evaluation of the Efficiency of Filtration Processes Using Precoat Materials}}}, doi = {{10.1002/ceat.201500385}}, year = {{2015}}, } @inbook{26119, abstract = {{The emphasis of the study presented is on a new process of particle extraction to transfer magnetite nanoparticles from an aqueous into an immiscible organic phase directly through the liquid-liquid interface. For the production of high-quality organosols, stabilized colloidal and functionalized particles are required in a liquid organic phase. The mechanism of phase transfer is initiated by adsorption and chemical binding of surfactants (fatty acids) at the particle surface. The resulting physico-chemical dispersion of the hydrophobically modified particles leads to the formation of the stabilized organic colloid, or organosol. The aim here is to demonstrate the entire chain of the transfer process in a continuous miniplant, which comprises particle synthesis, conditioning, and transfer, and which uses a drop column for extraction and as a transfer device. Based on the investigation of the governing principles and the material parameters, the results obtained for the transfer kinetics in the individual contact devices (centrifuge, single-drop column, and drop column for different operations) are used for the dimensioning of the entire process chain.}}, author = {{Erler, Jacqueline V. and Machunsky, Stefanie and Franke, Steffen and Grimm, Philipp and Schmid, Hans-Joachim and Peuker, Urs A.}}, booktitle = {{Colloid Process Engineering}}, title = {{{Process Development of a Liquid-Liquid Phase Transfer of Colloidal Particles for Production of High-Quality Organosols}}}, doi = {{10.1007/978-3-319-15129-8_16}}, year = {{2015}}, } @article{26121, abstract = {{The conditioning of the aerosol particle population into a bipolar charge equilibrium is an essential prerequisite to calculate the particle number size distribution using mobility particle size spectrometers. This is commonly realized by diffusion charging of bipolar air ions generated by e.g. a 85Kr source. Because of strict legal regulations on radioactive sources in several countries, soft-X-ray (SXR) appears as a suitable alternative. However, multiple measurements showed a systematical and significant difference between the particle charge distribution delivered by a radioactive source and an SXR charger, respectively. In this investigation, a calibrated particle charge distribution, suitable for the SXR chargers, was calculated based on the Fuchs model. An approximation analogous to the commonly used Wiedensohler approximation formula (Wiedensohler, 1988) was computed. The use of the new SXR approximation of the bipolar charge equilibrium for the inversion of an electrical mobility distribution to a particle number size distribution improves the comparability of these results, compared to measurements involving a 85Kr charger or to bipolar chargers using radioactive material in general. A systematic error in case of using the SXR charger could be eliminated and hence the root mean square deviation could be reduced from 13% using the common parameters for both charger types to 7% using the new SXR approximation for the SXR bipolar charger.}}, author = {{Tigges, L. and Wiedensohler, A. and Weinhold, K. and Gandhi, J. and Schmid, Hans-Joachim}}, issn = {{0021-8502}}, journal = {{Journal of Aerosol Science}}, pages = {{77--86}}, title = {{{Bipolar charge distribution of a soft X-ray diffusion charger}}}, doi = {{10.1016/j.jaerosci.2015.07.002}}, year = {{2015}}, } @article{26122, abstract = {{An essential part of mobility particle size spectroscopy is the prediction of the aerosol charge distribution in a highly concentrated bipolar ion environment. This charge distribution can be readily calculated, but is depending on several environmental conditions. These influences are investigated theoretically. The first part of this work deals with a sensitivity analysis using the Fuchs model (Fuchs, 1963) to determine the variation of the resulting charge distributions depending on the input parameters. It is demonstrated, that the main influencing variable is the difference between the positive and negative ion mobility. A sensitivity analysis reveals that a reasonable variation of the ion mobilities may lead to variations of the particle density distribution up to±20%. The second part investigates the evolution of the charge distribution along the tubing downstream of the bipolar charger exit starting with equal ion concentrations for positive and negative ions. Due to wall losses depending on ion mobility a non-equilibrium charge distribution is developing along the plumbing. The evolution of the particle charge distribution is determined using a coupled population balance model. Even though the non-equilibrium character is clearly shown, it turns out that this effect is negligible at conditions typical for particle size measurements.}}, author = {{Tigges, L. and Jain, A. and Schmid, Hans-Joachim}}, issn = {{0021-8502}}, journal = {{Journal of Aerosol Science}}, pages = {{119--134}}, title = {{{On the bipolar charge distribution used for mobility particle sizing: Theoretical considerations}}}, doi = {{10.1016/j.jaerosci.2015.05.010}}, year = {{2015}}, } @article{26123, abstract = {{The precipitation of sticky and ultrafine particles has become increasingly important. Biomass burners are one important example for ultrafine dust emission sources with ever growing importance. Therefore, a baghouse filter has been developed, which combines excellent separation efficiency (> 99%, clean air dust loading of < 1 mg/m3) with convenience in operation. However, in order to prevent clogging of the filter cloth by sticky and ultrafine particles, it is necessary to use a precoat layer (e.g. hydrated limestone powder). If this technology is applied to larger scale processes, e.g. biomass burning for industrial drying processes, the reuse of the precoat material can generate significant savings. Therefore, extended tests on recycling of used precoat material have been performed. Particularly, the influence of precoat injection parameters and various mixing strategies of used and virgin powder for refreshing the precoat material have been investigated. Different mixtures have been characterised by their ability to disintegrate, flowability and filtration behaviour. It is clearly demonstrated that upon redispersing the used precoat fine dust mainly adheres to the coarse precoat with only a limited number of dust agglomerates being produced in addition. For each kind of precoat a minimum amount is determined in order to ensure a long-term stable process. This way a saving potential of between 40–67% has been found. An economic and ecologic process has been developed to precipitate ultrafine dust in a baghouse filter system using precoat materials.}}, author = {{Schiller, Sascha and Schmid, Hans-Joachim}}, issn = {{0032-5910}}, journal = {{Powder Technology}}, pages = {{96--105}}, title = {{{Highly efficient filtration of ultrafine dust in baghouse filters using precoat materials}}}, doi = {{10.1016/j.powtec.2015.03.048}}, year = {{2015}}, } @article{26124, abstract = {{Capillary forces between particles often dominate other adhesion forces. However, the calculation of the shape of capillary bridges and the resulting force is complex, so often assumptions and approximations are used. These assumptions are not useful for nanoscale particles. Therefore, a simulation method was established to calculate numerically the shape of the meniscus and derive the corresponding capillary bridge force. The main focus are nanoscaled particles with liquid bridges formed by condensing air humidity. The dependence of the capillary force on various parameters such as particle sizes, contact angle and humidity was investigated and it is demonstrated that often-used assumptions cannot be used for nanoscaled particles without remarkable mistake.}}, author = {{Dörmann, Michael and Schmid, Hans-Joachim}}, issn = {{1877-7058}}, journal = {{Procedia Engineering}}, pages = {{14--23}}, title = {{{Simulation of Capillary Bridges between Particles}}}, doi = {{10.1016/j.proeng.2015.01.102}}, year = {{2015}}, }