@inproceedings{23074, author = {{Koke, Isabel and Dibblee, Katharina and Hankeln, Frederik and Seidel, Stefan and Trächtler, Ansgar and Schmid, Hans-Joachim}}, booktitle = {{ 44. Jahrestagung der Deutschen Gesellschaft für Hochschuldidaktik - Hochschuldidaktik im Dialog, Paderborn}}, title = {{{Tutorenprogramm und Vertiefungsberatung stellen Weichen in entscheidenden Phasen des Student Life-Cycles in Maschinenbaustudiengängen}}}, year = {{2015}}, } @article{26125, abstract = {{We investigated an explanation for the length dependence of apparent wall slip in capillary and slit die experiments that had been implied in earlier studies. Firstly, we used a very long slit die fitted with six equidistant pressure transducers and an adjustable outlet. It was found that, all other parameters being equal, the impact of pressure on the flow behavior of suspensions was not different from the impact on the unfilled matrix fluid. Particle-related properties, such as apparent wall slip, were therefore not influenced by pressure as assumed by other authors. Secondly, we determined wall slip velocities by both the Mooney method and numerical simulation, based on an implementation of Phillips constitutive equation for particle migration. This led to a similar length dependence of wall slip as had been reported in an earlier work. We concluded that this was due to the transient nature of particle migration and its interrelationship with apparent wall slip, rather than an influence of pressure.}}, author = {{Pieper, Sven and Kirchhoff, Nadine and Schmid, Hans-Joachim}}, issn = {{0035-4511}}, journal = {{Rheologica Acta}}, pages = {{69--75}}, title = {{{Absence of pressure sensitivity of apparent wall slip in pressure-driven flow of non-colloidal suspensions}}}, doi = {{10.1007/s00397-014-0815-x}}, year = {{2014}}, } @article{26126, abstract = {{Ultrafine dust separation from different sources like industry, traffic, or private households has become increasingly important in the last decade. A compact baghouse filter system has been developed which is suitable for pellet heaters. For filtration, a precoat material is required to prevent clogging of the filter media by the ultrafine dust particles. In order to ensure the best performance of this filter system, different combinations of filter media and precoat materials, e.g., grade efficiencies and the cake area load for the various filter media, were investigated in a special test rig. With this highly efficient technology, extremely high separation efficiencies of > 99 % and ultrafine dust concentrations of > 1 mg cm−3 could be reached in a long-term stable process.}}, author = {{Schiller, Sascha and Schmid, Hans-Joachim}}, issn = {{0930-7516}}, journal = {{Chemical Engineering & Technology}}, pages = {{1009--1020}}, title = {{{Ultrafine Dust Filtration Using Precoat Materials Considering the Influence of Filter Media}}}, doi = {{10.1002/ceat.201300856}}, year = {{2014}}, } @article{26127, abstract = {{Capillary forces are very important as they exceed in general other adhesion forces. But at the same time the exact calculation of these forces is very complex, so often assumptions and approximations are used. Previous research was done with regard to micrometer sized particles, but the behavior of nanoscale particles is different. Hence, the results for micrometer sized particles cannot be directly transferred when considering nanoscale particles. Therefore, a simulation method was developed to calculate numerically the shape of a rotationally symmetrical capillary bridge between two spherical particles or a particle and a plate. The capillary bridge in the gap between the particles is formed due to capillary condensation and is in thermodynamic equilibrium with the gas phase. Hence the Kelvin equation and the Young–Laplace equation can be used to calculate the profile of the capillary bridge, depending on the relative humidity of the surrounding air. The bridge profile consists of several elements that are determined consecutively and interpolated linearly. After the shape is determined, the volume and force, divided into capillary pressure force and surface tension force, can be calculated. The validation of this numerical model will be shown by comparison with several different analytical calculations for micrometer-sized particles. Furthermore, it is demonstrated that two often used approximations, (1) the toroidal approximation and (2) the use of an effective radius, cannot be used for nanoscale particles without remarkable mistake. It will be discussed how the capillary force and its components depend on different parameters, like particle size, relative humidity, contact angle, and distance, respectively. The rupture of a capillary bridge due to particle separation will also be presented.}}, author = {{Dörmann, Michael and Schmid, Hans-Joachim}}, issn = {{0743-7463}}, journal = {{Langmuir}}, pages = {{1055--1062}}, title = {{{Simulation of Capillary Bridges between Nanoscale Particles}}}, doi = {{10.1021/la404409k}}, year = {{2014}}, } @inproceedings{22176, 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 Herale, A.A. and Li, Z. 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}}, } @inproceedings{22177, abstract = {{An uneven temperature distribution and varying cooling rates at different positions within the part cake are two of the most important challenges regarding the part quality and reproducibility of the polymer laser sintering process. In the presented work, a temperature measurement system is implemented within an EOSINT P395 laser sintering system. It allows the determination of a three dimensional temperature distribution and history during the full build and cooling process. The influence of important job parameters, for example the packing density, job height and layer thickness, can be figured out. In combination with a finite element simulation of the cooling process, the temperature measurement will be the basis for optimized process controls.}}, author = {{Josupeit, Stefan and Schmid, Hans-Joachim}}, booktitle = {{25th Annual International Solid Freeform Fabrication Symposium}}, pages = {{49--58}}, title = {{{Three-dimensional in-process temperature measurement of laser sintered part cakes}}}, doi = {{http://utw10945.utweb.utexas.edu/sites/default/files/2014-006-Josupeit.pdf}}, volume = {{25}}, year = {{2014}}, } @inproceedings{22184, abstract = {{Polymer laser sintering is one of the most important additive manufacturing technologies for the tool-less production of three-dimensional prototypes and end-use parts. In this process, parts are manufactured layerwise out of a polymer powder by laser exposure. After the building process, these parts are located within a loose bulk powder cake. Due to long process times and high process temperatures, this powder ages thermally, which reduces the recyclability of the material. As a result, mixtures of used and virgin powder ("refreshed" powder) with a mixture ratio of approximately 50% are commonly used in the industry. The goal of this work is to determine the exact influence of different powder ages on resulting part quality characteristics, especially the mechanical behavior and the surface quality. Therefore, refreshed powder with different qualities adjusted by the melt volume rate (MVR) was processed along a defined process quality chain. To analyze the part qualities, mechanical tensile and profilometer tests were performed. The focus is on an application-oriented test set-up to ensure the usability of the results in the industry. The material used is polyamide 12 (PA 2200) processed on an EOSINT P395 laser sintering system from EOS GmbH, Krailling, Germany.}}, author = {{Josupeit, Stefan and Rüsenberg, Stefan and Rupp, N. and Gessler, Monika and Schmid, Hans-Joachim}}, booktitle = {{72nd Annual Technical Conference of the Society of Plastics Engineers (ANTEC 2014)}}, isbn = {{978-1-634-39708-7}}, number = {{3}}, pages = {{2383--2385}}, title = {{{Thermal ageing of polyamide 12 used for polymer laser sintering - influence on part quality characteristics}}}, doi = {{https://www.researchgate.net/publication/283135483_Thermal_ageing_of_polyamide_12_used_for_polymer_laser_sintering_-_Influence_on_part_quality_characteristics}}, volume = {{72}}, year = {{2014}}, } @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}}, }