@phdthesis{24751, abstract = {{Das Thema der vorliegenden Dissertation ist die "Prozessqualifizierung zur verlässlichen Herstellung von Produkten im Polymer Lasersinterverfahren". Über eine definierte Qualitätsprozesskette werden sämtliche, auf die Produktqualität relevanten Einflussparameter, bestimmt und berücksichtigt. Unterschiedliche Methoden zur Materialcharakterisierung des pulverförmigen Ausgangsmaterials werden analysiert und bewertet. Rheologische sowie chemische Eigenschaften, aber auch die Partikelgrößenverteilung oder die Schüttdichte werden hinsichtlich Relevanz, Einfluss und Anwenderfreundlichkeit untersucht. Das Ziel ist eine sinnvolle Bestimmung des Ausgangszustandes des Pulvers anhand definierter, relevanter Materialeigenschaften, um reproduzierbare technische Bauteileigenschaften zu gewährleisten. Dazu werden mechanische, dynamisch-mechanische, physikalische, elektrische, thermische sowie chemische Untersuchungen durchgeführt und hinsichtlich wichtiger Einflussparameter evaluiert. Die Bestimmung erfolgt über entwickelte Referenzjobs, in denen die hauptsächlichen Einflussfaktoren auf das Polymer-Lasersinterverfahren entlang der Qualitätsprozesskette berücksichtigt werden. Die charakterisierten Daten dienen zur Auslegung eines fiktiven Produktes aus der Luftfahrtindustrie. Mit Hilfe dieser Methoden lassen sich Materialkennwerte für diverse Simulationstools eindeutig bestimmen um eine realitätsnahe Berechnung zu gewährleisten. }}, author = {{Rüsenberg, Stefan}}, keywords = {{Additive Fertigung, Polymere, Lasersintern, Methode, Qualität, Konstruktion, Eigenschaften, Material, Charakterisierung, Qualifizierung}}, pages = {{242}}, publisher = {{Shaker Verlag GmbH}}, title = {{{Prozessqualifizierung zur verlässlichen Herstellung von Produkten im Polymer Lasersinterverfahren}}}, volume = {{Band, 2}}, year = {{2015}}, } @inproceedings{22178, author = {{Delfs, Patrick and Li, Z. and Schmid, Hans-Joachim}}, booktitle = {{26th Annual International Solid Freeform Fabrication Symposium}}, pages = {{514--526}}, title = {{{Mass finishing of laser sintered parts}}}, doi = {{http://utw10945.utweb.utexas.edu/sites/default/files/2015/2015-41-Delfs.pdf}}, volume = {{26}}, year = {{2015}}, } @inproceedings{22179, abstract = {{The temperature distribution and history within laser sintered part cakes is an important aspect regarding the process quality and reproducibility of the polymer laser sintering process. Especially the temperature history during the build and cooling phase is decisive for powder ageing effects and the development of part quality characteristics. In this work, a measurement system for three-dimensional in-process temperature measurements is set up and the influence of different parameters on the inner part cake temperature distribution and history is analyzed. Important factors are not only geometrical build job parameters like the part packing density and build height, but also process parameters like the layer thickness and bulk powder density. Individual in-process temperature profiles at different positions within a part cake are finally correlated with powder ageing effects. The results of this work help to understand the temperature history dependency of powder and part properties and can therefore be used to develop optimized process controls.}}, author = {{Josupeit, Stefan and Schmid, Hans-Joachim}}, booktitle = {{26th Annual International Solid Freeform Fabrication Symposium}}, pages = {{190--199}}, title = {{{Temperature History within Laser Sintered Part Cakes and its Influence on Process Quality}}}, doi = {{http://utw10945.utweb.utexas.edu/sites/default/files/2015/2015-15-Josupeit.pdf}}, volume = {{26}}, year = {{2015}}, } @inproceedings{22187, abstract = {{Due to long process times at high temperatures, unmolten polyamide 12 material ages during the manufacturing process. Hence, it needs to be refreshed with new material for further build cycles. In application, refresh rates of about 50 % are commonly used. In this work, the recycling optimized material PA 2221 from EOS is analyzed along a series of 13 build and refresh cycles using a reduced refresh rate of 32 %. Before and after every build, the powder is analyzed regarding melt properties determined by MVR and DSC measurements. Thereby, in-process ageing effects are investigated and the steady-state conditions are determined accordingly. In addition, powder properties are directly linked to resulting mechanical and geometrical part properties. Key findings are a robust DSC measurement method for polyamide 12 powder, constant “circulated” material properties after three build/refresh cycles and robust tensile properties along the whole tested powder life cycle. As a result, process conditions of PA 2221 using reduced refresh rates can be derived from this work.}}, author = {{Josupeit, Stefan and Lohn, Johannes and Hermann, E. and Gessler, Monika and Tenbrink, S. and Schmid, Hans-Joachim}}, booktitle = {{26th Annual International Solid Freeform Fabrication Symposium}}, pages = {{540--549}}, title = {{{Material Properties of Laser Sintered Polyamide 12 as Function of Build Cycles Using Low Refresh Rates}}}, doi = {{http://utw10945.utweb.utexas.edu/sites/default/files/2015/2015-43-Josupeit.pdf}}, volume = {{26}}, year = {{2015}}, } @inproceedings{22189, abstract = {{The layered structure of Additive Manufacturing processes results in a stairstepping 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 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 every area of a part can be optimized, a predetermination of areas can be used to improve the surface quality of important areas. The model uses the digital STL format of a part as this is necessary for all AM machines to build it. 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 exemplary with a surface topography simulation for the laser sintering process.}}, author = {{Delfs, Patrick and Toews, Marcel and Schmid, Hans-Joachim}}, booktitle = {{26th Annual International Solid Freeform Fabrication Symposium}}, pages = {{1334--1344}}, title = {{{Surface roughness optimized alignment of parts for additive manufacturing processes}}}, doi = {{http://utw10945.utweb.utexas.edu/sites/default/files/2015/2015-107-Delfs.pdf}}, volume = {{26}}, year = {{2015}}, } @inproceedings{22199, abstract = {{Powder ageing effects due to thermal load usually lead to a limited recyclability of unmolten polyamide 12 powders in the laser sintering process. In this work, the recycling optimized material PA 2221 is analyzed regarding its ageing behavior along a series of more than ten build/refresh cycles using a refresh ratio of about 30%. Thereby, the melt viscosity is measured before and after every cycle and the “steady-state” condition is determined accordingly. In addition, the material properties of parts manufactured with PA 2221 are discussed dependent on different process parameters and compared to parts made of standard PA 2200 material with a refresh rate of about 50%. These parameters include the mechanical properties as well as for example the impact strength and geometrical properties as function of layer thickness and testing temperature. As a result, the optimal process conditions and achievable material properties for PA 2221 can be derived from this work.}}, author = {{Josupeit, Stefan and Tutzschky, S. and Gessler, M. and Schmid, Hans-Joachim}}, booktitle = {{Proceedings of the Rapid Tech 2015}}, isbn = {{978-3-662-48473-9}}, pages = {{63--78}}, publisher = {{Springer Vieweg}}, title = {{{Powder ageing and material properties of laser sintered polyamide 12 using low refresh rates}}}, doi = {{10.1007/978-3-662-48473-9_5}}, year = {{2015}}, } @inproceedings{22395, author = {{Lieneke, Tobias and Adam, Guido and Leuders, Stefan and Knoop, Frederick and Josupeit, Stefan and Delfs, Patrick and Funke, Nils and Zimmer, Detmar}}, booktitle = {{Proceedings of the Rapid Tech 2015}}, title = {{{Entwicklung einer Methode zur systematischen Erarbeitung von Maßtoleranzen für additive Fertigungsverfahren}}}, year = {{2015}}, } @inproceedings{22396, abstract = {{Additive manufacturing offers many technical and economical benefits. In order to profit from these benefits, it is necessary to consider the manufacturing limits and restrictions. This applies in particular to the geometrical accuracy. Therefore, the achievable geometrical accuracy needs to be investigated, which enables the determination of realistic tolerances. Thus, two different aims are considered. The first aim is the determination of dimensional tolerances that can be stated if additive manufacturing is used under normal workshop conditions. Within the second aim, relevant process parameters and manufacturing influences will be optimized in order to reduce dimensional deviations. To achieve both aims a method was developed first. This method identifies relevant influential factors on the geometrical accuracy for the processes Fused Deposition Modeling (FDM), Laser Sintering (LS) and Laser Melting (LM). Factors were selected that are expected to affect the geometrical accuracy mainly. The first investigations deal with measuring linear dimensions on a designed test specimen and the derivation of achievable dimensional tolerances. This paper will present both, the developed method and the first results of the experimental investigations.}}, author = {{Lieneke, Tobias and Adam, Guido and Leuders, Stefan and Knoop, Frederick and Josupeit, Stefan and Delfs, Patrick and Funke, Nils and Zimmer, Detmar}}, booktitle = {{26th Annual International Solid Freeform Fabrication Symposium}}, pages = {{371--384}}, title = {{{Systematical determination of tolerances for additive manufacturing by measuring linear dimensions}}}, doi = {{https://www.researchgate.net/publication/316827402_Systematical_Determination_of_Tolerances_for_Additive_Manufacturing_by_Measuring_Linear_Dimensions}}, volume = {{26}}, year = {{2015}}, } @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}}, } @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}}, } @phdthesis{42132, author = {{Gerkens, Stefan}}, isbn = {{978-3-8440-2421-0}}, pages = {{168}}, title = {{{In-situ Strukturcharakterisierung von CNT in polymerbasierten Nanokompositen Methodenentwicklung und Anwendung}}}, volume = {{1}}, year = {{2013}}, } @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}}, }