@inproceedings{22193, abstract = {{The process-related occurrence of varying cooling rates at different positions within the part cake is an important challenge regarding the part quality and reproducibility of the polymer laser sintering process. Temperature history dependent parameters are for example the part warpage, the crystallization behavior or powder ageing effects, which have to be considered for optimized process controls. Nevertheless, the inner temperature distribution and history during the cooling process is difficult to measure and less known yet. In this work, a Finite Element (FE) model is developed to understand and predict the temperature distribution and history within the part cake during the cooling process. Therefore, the thermal boundary conditions of a laser sintering system are analyzed and relevant parameters are identified. A basic FE model is set up in ABAQUS CAE software considering a part-free powder cake. Important thermal parameters of the bulk powder and the environment are adjusted and verified in relation to experimental in-process measured data. With this model it is possible to predict position-dependent cooling rates as a function of significant job parameters, for example the job height or the environmental conditions during the cooling phase. In combination with extended in-process temperature measurements and a consideration of built parts, this model will be an important tool for the development of optimized process controls.}}, author = {{Josupeit, Stefan and Ordia, L. and Schmid, Hans-Joachim}}, booktitle = {{International Conference on Additive Technologies}}, isbn = {{978-961-281-579-0}}, pages = {{222--227}}, title = {{{Development of a Basic Model to Simulate the Laser Sintering Cooling Process}}}, doi = {{https://www.researchgate.net/profile/Saeed_Khademzadeh2/publication/303022441_Geometrical_characterization_of_thin_walls_produced_by_micro_laser_sintering/links/5735cc7f08ae298602e08f1f/Geometrical-characterization-of-thin-walls-produced-by-micro-laser-sintering.pdf}}, volume = {{5}}, year = {{2014}}, } @inproceedings{22203, abstract = {{One barrier of laser sintering (LS) to become the main process for Direct Manufacturing (DM) is the surface quality of LS parts. Hence, the property which has to be improved is the rough surfaces of LS parts due to the layered structure. Another additional effect is the incomplete melting of powder particles on the surface due to the high process temperature. In this paper we demonstrate our approach of a theoretical model for the topography of LS part surfaces. We investigated the surface roughness as a function of surface orientation. Considering that the model involves further variables as layer thickness, particle density and particle size distribution to describe the topography precisely. Experimental results were used to optimize and check the results of the model.}}, author = {{Delfs, Patrick and Schmid, Hans-Joachim}}, booktitle = {{25th Annual International Solid Freeform Fabrication Symposium}}, pages = {{1250--1258}}, title = {{{Simulation of the Surface Topography on Laser Sintered Polymer Parts}}}, doi = {{http://utw10945.utweb.utexas.edu/sites/default/files/2014-098-Delfs.pdf}}, volume = {{25}}, year = {{2014}}, } @article{22186, abstract = {{The reproducibility and reliability of quality aspects are an important challenge of the polymer laser sintering process. However, existing quality concepts and standardization activities considering influencing factors along the whole process chain have not been validated experimentally yet. In this work, these factors are analyzed and kept constant to obtain a reliable material data set for different layer thicknesses and testing temperatures. In addition, material qualities regarding powder ageing effects are analyzed using different build heights and layer thicknesses: while an increase of the layer thickness reduces mechanical part strength and density, it also results in a less intense thermal ageing of unmolten powder due to shorter build times.}}, author = {{Rüsenberg, Stefan and Josupeit, Stefan and Schmid, Hans-Joachim}}, issn = {{1687-8140}}, journal = {{Advances in Mechanical Engineering}}, publisher = {{SAGE Publications}}, title = {{{A method to characterize the quality of a polymer laser sintering process }}}, doi = {{10.1155/2014/185374}}, volume = {{6}}, year = {{2014}}, } @article{26129, abstract = {{Because of the large surface area of colloids interface effects are dominant in contrast to volume effects. The study presents experimental results of the direct transfer of magnetite nanoparticles from an aqueous to a non-miscible organic phase. The starting point is a water-based colloid that is synthesized through a precipitation reaction. The transfer is based on the adsorption of surfactants onto the particle surface at the liquid–liquid interface. While penetrating the liquid–liquid interface, the particles are covered with surfactants and a partial de-agglomeration is initiated. The intention is to produce a stable organic colloid, which has important applications in industry. The optimized process parameters for the successful phase transfer process, the adsorption reactions at the liquid–liquid interface and the stabilization of primary particles in the organic phase are demonstrated.}}, author = {{Erler, Jacqueline and Machunsky, Stefanie and Grimm, Philipp and Schmid, Hans-Joachim and Peuker, Urs A.}}, issn = {{0032-5910}}, journal = {{Powder Technology}}, pages = {{265--269}}, title = {{{Liquid–liquid phase transfer of magnetite nanoparticles — Evaluation of surfactants}}}, doi = {{10.1016/j.powtec.2012.09.047}}, volume = {{247}}, year = {{2013}}, } @article{26130, abstract = {{Zur Erfüllung der Anforderungen der novellierten ersten Bundesimmissionsschutzverordnung (1. BImSchV: Verordnung über kleine und mittlere Feuerungsanlagen) wurde ein Schlauchfiltersystem für den Gebrauch in kleinen und mittleren Feuerungsanlagen entwickelt. Ein zur Filtration benötigtes Filterhilfsmittel wird vollautomatisch portioniert, dispergiert und dem Prozess zugeführt. Mit dieser Technik ist es möglich, den Feinstaubgehalt im Abgas auf unter 1 mg m^3 i.N. zu senken und damit die geforderten Grenzwerte weit zu unterschreiten. }}, author = {{Schiller, Sascha and Schmid, Hans-Joachim}}, issn = {{0009-286X}}, journal = {{Chemie Ingenieur Technik}}, pages = {{1324--1328}}, title = {{{Hocheffiziente Feinstaubabscheidung aus Kleinfeuerungsanlagen mit einem Schlauchfilter}}}, doi = {{10.1002/cite.201200114}}, year = {{2013}}, } @inproceedings{22175, abstract = {{In this work, the quality of laser sintered parts is investigated along a defined process chain for a nylon 12 material (PA 2200) on an EOSINT P395 laser sintering system. Important influencing factors are figured out. Rheological powder characterization methods are investigated as well as mechanical, physical and other chosen part properties. The concept allows reproducible part quality characteristics and is used to obtain (testing) temperature dependent material data. It can also be extended on further materials based on nylon 12: PA 2241 FR, which is convenient for the aircraft industry due to its flame-retardant properties, and PA 2221, which has economic advantages due to a lower material consumption.}}, author = {{Josupeit, Stefan and Rüsenberg, Stefan and Schmid, Hans-Joachim}}, booktitle = {{24th Annual International Solid Freeform Fabrication Symposium }}, pages = {{44--54}}, title = {{{A material-based quality concept for polymer laser sintering}}}, doi = {{http://utw10945.utweb.utexas.edu/Manuscripts/2013/2013-03-Josupeit.pdf}}, volume = {{24}}, year = {{2013}}, } @inproceedings{22192, abstract = {{Laser Sintering is a powder based additive manufacturing technology. The amount of used powder, which is not sintered, can be refreshed and used for further building jobs. Due to cost reduction, better mechanical properties and a simpler processing it is reasonable to combine virgin and used powder for part manufacturing. During the building time the powder is thermally loaded and its structure is changed. State of the art in laser sintering is a defined powder ratio. Since the powder ageing depends on the individual history of sintering, this procedure cannot ensure a defined powder quality. However, for a serial production it is necessary to characterize the raw material, as well as all other steps along the process chain, in order to ensure a high reproducibility and reliability. Rheological, physical and particle properties are considered to correlate powder and chosen material properties. Different powder qualities adjusted by the Melt Volume Rate (MVR) are tested using promising rheological properties like viscosity or molecular weight. Investigations about powder bed density, bulk properties as well as thermal characterization complement the experimental setup. These parameters are correlated with mechanical, electrical, thermal and physical material properties of laser sintered parts. The most important influencing factors along the process chain are kept constant. At the end a procedure is shown to obtain a defined powder quality. This procedure will be transferred to other materials and will be tested using other laser sintering machines of the same type as well as other types.}}, author = {{Rüsenberg, Stefan and Schmid, Hans-Joachim}}, booktitle = {{International Conference of the Polymer-Processing-Society (PPS)}}, title = {{{Advanced characterization method of Nylon 12 materials for application in laser sinter processing}}}, doi = {{10.1063/1.4873877}}, volume = {{29}}, year = {{2013}}, } @inproceedings{22197, author = {{Josupeit, Stefan and Rüsenberg, Stefan and Schmid, Hans-Joachim}}, booktitle = {{Merseburger Rapid Prototyping Forum}}, title = {{{Mechanische und rheologische Untersuchungen neuer Laser Sinter Materialien}}}, doi = {{https://www.rp-netzwerk.de/images/stories/pdf/rapid_7/Universitaet_Paderborn_DMRC_RP-Forum2013.pdf}}, volume = {{7}}, year = {{2013}}, } @inproceedings{22201, author = {{Rüsenberg, Stefan and Bagsik, A. and Büsching, J. and Schmid, Hans-Joachim}}, booktitle = {{RapidTech}}, title = {{{Additiv versus Konventionell: Benchmarking am Beispiel eines Designs aus der Luftfahrtindustrie}}}, year = {{2013}}, } @article{26132, abstract = {{Wood-Plastic-Composite (WPC) zeigen im Vergleich zu reinen Kunststoffen ein sehr unterschiedliches und überaus komplexes Material- und Fließverhalten. Letzteres ist für die Verarbeitung der Composite von entscheidender Bedeutung. Im Folgenden werden die Ergebnisse rheologischer Charakterisierungen sowie einiger Untersuchungen zum Füllverhalten im Spritzgießprozess dargestellt. Dabei werden auch auftretende Herausforderungen und mögliche Lösungsansätze diskutiert. }}, author = {{Kirchhoff, Nadine and Schröder, Cathrin and Stute, Daniel and Moritzer, Elmar and Schmid, Hans-Joachim}}, issn = {{0009-286X}}, journal = {{Chemie Ingenieur Technik}}, pages = {{1584--1589}}, title = {{{Wood-Plastic-Composites: Rheologische Charakterisierung und Füllverhalten im Spritzgießprozess}}}, doi = {{10.1002/cite.201100223}}, year = {{2012}}, } @article{26133, abstract = {{The sintering of vitreous nanoparticle doublets is investigated numerically by a volume of fluid method coupled to Hamaker summation and experimentally by a high-temperature sintering flow reactor as well as by doublet shape analysis in the transmission electron microscope. In particular, the characteristic differences between nanoparticulate and bulk sintering are studied. The sintering mechanism of vitreous nanoparticles is determined to be viscous flow with interparticle van der Waals interactions acting as additional driving force. The early stages of the nanoparticle sintering kinetics are inversely proportional to the square of the particle size, instead of an indirect proportionality to the first order of the particle size for the entire bulk process. The transition between nanoparticulate and bulk sintering is localised to primary particle diameters of approx. 200–300 nm.}}, author = {{Kirchhof, M.J. and Förster, H. and Schmid, Hans-Joachim and Peukert, W.}}, issn = {{0021-8502}}, journal = {{Journal of Aerosol Science}}, pages = {{26--39}}, title = {{{Sintering kinetics and mechanism of vitreous nanoparticles}}}, doi = {{10.1016/j.jaerosci.2011.10.006}}, volume = {{45}}, year = {{2012}}, } @inproceedings{22174, abstract = {{The quality of laser sintered parts, in this work, manufactured by polymer laser sintering by using an EOSINT P395 Laser Sintering system, depends on several steps along the process chain. The first step is the characterization of the powder quality, whereas the rheological and physical investigations of nylon 12 powder are shown. By changing some important influencing factors, for example the powder ratio, the powder ageing and the moisture content, the influence on mechanical and physical properties, density and porosity, are investigated. The composition of the used powder is known. The previous process (storage conditions, etc.) as well as the laser sintering process (regarding energy density, temperature, etc.) is kept constant for the duration of this work. Regarding the post process in this work the cooling down phase is investigated as well. With an automatically blasting system it is possible to keep the post process parameters blasting distance and blasting time, constant. All of the tests will be performed using dry and conditioned test specimens. This work is showing the dependence on mechanical, rheological and physical parameters by varying important influencing factors along the laser sintering process quality chain.}}, author = {{Rüsenberg, Stefan and Weiffen, R. and Knoop, F. and Schmid, Hans-Joachim}}, booktitle = {{23rd Annual International Solid Freeform Fabrication Symposium}}, pages = {{1024--1044}}, title = {{{Controlling the Quality of Laser Sintered Parts Along the Process Chain}}}, doi = {{http://utw10945.utweb.utexas.edu/Manuscripts/2012/2012-78-Ruesenberg.pdf}}, volume = {{23}}, year = {{2012}}, } @inproceedings{22204, abstract = {{Material properties of parts from additive manufacturing are influenced by a huge number of material, operational and job parameters. This work aims to identify the most important ones and to investigate mechanical properties as depending on those parameters. Test specimens were produced with standard PA12 powder on an EOSINT P390 and P395, respectively. The influence of the orientation and placement of parts in the building chamber were investigated systematically. The mechanical properties}}, author = {{Rüsenberg, Stefan and Schmid, Hans-Joachim}}, booktitle = {{The European Forum on Additive Manufacturing}}, title = {{{Mechanical Properties as a Result of multitude of Parameters}}}, doi = {{https://afpr.asso.fr/content/assises/2012/actes/papiers/s5_2.pdf}}, volume = {{17}}, year = {{2012}}, } @inproceedings{22188, abstract = {{The aim of this paper is the description and evaluation of physical properties like porosity and density and their influence on mechanical properties of laser sintered polyamide parts. For example, by reducing the porosity an increase of mechanical properties is possible. The correlation of laser parameters to these properties is investigated in detail. The energy density is an important parameter for the laser sintering process. By changing laser power, scan velocity and hatch distance an influence on manufactured components is given. A systematic variation of all three laser parameters is performed. A comparison of results obtained at constant energy densities obtained by varying these relevant parameters accordingly is shown as well.}}, author = {{Rüsenberg, Stefan and Schmidt, L. and Schmid, Hans-Joachim}}, booktitle = {{22th Annual International Solid Freeform Fabrication Symposium}}, pages = {{239--251}}, title = {{{Mechanical and Physical Properties - A Way to asses quality of Laser Sintered Parts}}}, doi = {{http://utw10945.utweb.utexas.edu/Manuscripts/2011/2011-19-Ruesenberg.pdf}}, volume = {{22}}, year = {{2011}}, } @book{22191, author = {{Rüsenberg, Stefan and Schmidt, L. and Hosse, H. and Schmid, Hans-Joachim}}, isbn = {{978-0-429-21774-6}}, pages = {{531--538}}, title = {{{Porosity as a key to increase material properties of laser sintered parts}}}, doi = {{10.1201/b11341}}, year = {{2011}}, } @article{26134, abstract = {{This work investigates the mechanisms which lead to the formation of silicon nanoparticles with narrow size distributions by means of population balance modeling. The model accounts for the full aerosol process, including chemical reaction, nucleation from supersaturated vapor, growth and agglomeration. The results are in good agreement with experimental data. The effects of the process parameters temperature, silane concentration and reactor total pressure are systematically investigated. The simulation allows an in-depth insight into the particle formation mechanism and reveals the key requirements which are necessary for the generation of narrow particle size distributions. In this mechanism, only a short nucleation burst occurs, while surface growth plays the dominant role in silane precursor consumption. A key role is attributed to condensation, because the numerical calculations can only reflect the experimental observations, if the condensation mechanism is included in the model.}}, author = {{Körmer, R. and Schmid, Hans-Joachim and Peukert, W.}}, issn = {{0021-8502}}, journal = {{Journal of Aerosol Science}}, number = {{11}}, pages = {{1008--1019}}, title = {{{Aerosol synthesis of silicon nanoparticles with narrow size distribution—Part 2: Theoretical analysis of the formation mechanism}}}, doi = {{10.1016/j.jaerosci.2010.08.002}}, volume = {{41}}, year = {{2010}}, } @article{26135, abstract = {{A study on the feasibility of aerosol processing of nearly monodisperse silicon nanoparticles via pyrolysis of monosilane in a hot wall reactor is presented. For optimal conditions silicon nanoparticles with a geometric standard deviation of 1.06 were synthesized at a production rate of 0.7 g/h. The size of the particles could be precisely controlled in the range of 20–40 nm, whilst maintaining a geometric standard deviation in the range of 1.06–1.08, by proper choice of the governing parameters temperature, residence time and precursor concentration. The results show that narrow particle size distributions can only be obtained in the temperature range between 900 and 1100 °C, as long as both the initial silane concentration (1 mbar silane partial pressure) and the reactor total pressure are low (25 mbar). This regime for the production of narrow particle size distributions has not been identified in prior work on the thermal decomposition of silane. Narrowly distributed particles can be obtained under conditions where nucleation and particle growth are separated and the agglomeration rates are negligible.}}, author = {{Körmer, R. and Jank, M.P.M. and Ryssel, H. and Schmid, Hans-Joachim and Peukert, W.}}, issn = {{0021-8502}}, journal = {{Journal of Aerosol Science}}, number = {{11}}, pages = {{998--1007}}, title = {{{Aerosol synthesis of silicon nanoparticles with narrow size distribution—Part 1: Experimental investigations}}}, doi = {{10.1016/j.jaerosci.2010.05.007}}, volume = {{41}}, year = {{2010}}, } @article{26136, abstract = {{To improve the understanding of the poor dispersability of fumed silica nanoparticle agglomerates, the stability of highly defined agglomerated model particles was investigated. The high temperature synthesis conditions for fumed silica were simulated by tempering. Along with electron-microscopical analysis of the sintering necks, the interparticle forces were investigated by energy resolved fragmentation analysis based on low pressure impaction. At temperatures above 1,000 °C the fragmentability of the agglomerates rapidly decreased while the energy necessary for fragmentation increased. The development of sintering necks was observed for temperatures exceeding 1,300 °C. Comparison of the experimental data with the fragmentation behaviour of a commercially produced fumed silica indicated solid state contacts (sintering necks) as being most numerous in the agglomerates resulting in limited fragmentability.}}, author = {{Seipenbusch, M. and Rothenbacher, S. and Kirchhoff, M. and Schmid, Hans-Joachim and Kasper, G. and Weber, A. P.}}, issn = {{1388-0764}}, journal = {{Journal of Nanoparticle Research}}, number = {{6}}, pages = {{2037--2044}}, title = {{{Interparticle forces in silica nanoparticle agglomerates}}}, doi = {{10.1007/s11051-009-9760-5}}, volume = {{12}}, year = {{2010}}, } @misc{58272, author = {{Woppowa, Jan and Schmid, Hans-Joachim}}, booktitle = {{rhs}}, number = {{2011}}, pages = {{139--140}}, title = {{{Gastfreundschaft. Ein Modell für den konfessionellen Religionsunterricht der Zukunft}}}, volume = {{54}}, year = {{2010}}, } @article{26137, abstract = {{In this paper, we consider a model for precipitation experiments based on the population balance equation. The study revealed a high sensitivity of the system with respect to the modeling of intrinsic parameters, motivating a comprehensive validation of the estimates. In the forward simulation the impact of the influencing parameters including surface energy, nucleus size and distribution is investigated. Subsequently we construct a simplified model of the precipitation process in such a way that it is orbitally flat in terms of control theory, which enables the inverse calculation of the parameters. The numerical results of the inverse simulation for the interfacial energy have been compared to a physical model. The possibility of solving the inverse problem provides a promising way of estimating hardly measurable quantities for more complex molecules.}}, author = {{Vassilev, Vassil and Gröschel, Michael and Schmid, Hans-Joachim and Peukert, Wolfgang and Leugering, Günter}}, issn = {{0009-2509}}, journal = {{Chemical Engineering Science}}, number = {{6}}, pages = {{2183--2189}}, title = {{{Interfacial energy estimation in a precipitation reaction using the flatness based control of the moment trajectories}}}, doi = {{10.1016/j.ces.2009.12.014}}, volume = {{65}}, year = {{2009}}, }