Fraunhofer-Institut für Produktionsanlagen und Konstruktionstechnik IPK
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PublicationNumerical investigation into cleanability of support structures produced by powder bed fusion technology( 2022)
;Campana, G. ;Uhlmann, E. ;Mele, M. ;Raffaelli, L. ;Bergmann, A. ;Kochan, J.Polte, J.Purpose: Support structures used in laser powder bed fusion are often difficult to clean from unsintered powder at the end of the process. This issue can be significantly reduced through a proper design of these auxiliary structures. This paper aims to investigate preliminary the airflow within differently oriented support structures and to provide design guidelines to enhance their cleanability, especially the depowdering of them. Design/methodology/approach: This study investigates the cleanability of support structures in powder bed fusion technology. Digital models of cleaning operations were designed through computer-aided engineering systems. Simulations of the airflow running into the powder entrapped within the thin walls of auxiliary supports were implemented by computational fluid dynamics. This approach was applied to a set of randomly generated geometrical configurations to determine the air turbulence intensity depending on their design. Findings: The resul ts, which are based on the assumption that a relationship exists between turbulence and powder removal effectiveness, demonstrated that the maximum cleanability is obtainable through specific relative rotations between consecutive support structures. Furthermore, it was possible to highlight the considerable influence of the auxiliary structures next to the fluid inlet. These relevant findings establish optimal design rules for the cleanability of parts manufactured by powder bed fusion processes. Originality/value: This study presents a preliminary investigation into the cleanability of support structures in laser powder bed fusion, which has not been addressed by previous literature. The results allow for a better understanding of the fluid dynamics during cleaning operations. New guidelines to enhance the cleanability of support structures are provided based on the results of simulations.
PublicationModeling of the wet immersed tumbling process with the Discrete Element Method (DEM)( 2021)
;Uhlmann, E. ;Fürstenau, J.-P. ;Kuche, Y. ;Yabroudi, S. ;Polte, J.Polte, M.Immersed tumbling is an industrially established process for finishing of components made of metal, ceramic or plastic. In this process, the components are completely surrounded by a wet, abrasive medium, which allows burrs to be removed and surfaces to be polished. In order to gain specific insights into the influence and flow properties of the abrasive media used in this process, numerical approaches using the Discrete Element Method (DEM) with the Rocky DEM software are presented within these investigations. A complete process simulation could be realised by means of a digital machine tool. The immersed tumbling process with cone-shaped polymer abrasive media is implemented by use of a liquid bridge model. The results were validated by experiments with an industrially used immersed tumbling machine tool and for the first time allow sound statements about the contact conditions and interactions of the abrasive media with the workpiece.
PublicationHolistic Concept towards a Reference Architecture Model for Predictive Maintenance( 2021)
;Uhlmann, E. ;Polte, J.Koutrakis, N.-S.In the era of digital transformation of factories, one of the most challenging applications of the Industrial Internet of Things (IIoT) is predictive maintenance. This paper presents a holistic concept for predictive maintenance together with a reference architecture that includes data acquisition on the sensor level, edge computing and digital twin applications. For that purpose, condition-based maintenance, lifecycle monitoring and digital assistance systems are integrated to develop application-specific digital twins based on the proposed architecture, integrating heterogenous data sources in order to enhance the accuracy of the machine learning models. The concept is illustrated through an experimental use case.
PublicationEvaluation of carbon fiber reinforced polymer - CFRP - machining by applying industrial robots( 2021)
;Grisol De Melo, E. ;Santos Silva, J.C. Dos ;Klein, T.B. ;Polte, J. ;Uhlmann, E.Oliveira Gomes, J. DeCarbon fiber reinforced polymer (CFRP) is widely used in high-tech industries because of its interesting characteristics and properties. This material presents good strength and stiffness, relatively low density, high damping ability, good dimensional stability, and good corrosion resistance. However, the machinability of composite materials is complex because of the matrix/fiber interface, being a challenging machining material. The CFRP milling process is still necessary to meet dimensional tolerances, the manufacture of difficult-to-mold features like pockets or complexes advance surfaces, finish the edges of laminated composites, or drill holes for the assembly of the components. Besides, the demand for low-cost, reconfigurable manufacturing systems of the industry demonstrates that the application of industrial robots (IRs) in the CFRP milling process becomes an alternative for providing automation and flexibility. Therefore, the objective of this work is to evaluate the performance of the low payload IR KUKA KR60 HA in a milling experiment of CFRP, which indicates its potential application as an alternative to milling process. Furthermore, the influence of the cutting tool geometry as well as the cutting parameters in the machining behavior with IRs is evaluated.
PublicationTitanium Ti-6Al-4V alloy milling by applying industrial robots( 2021)
;Grisol de Melo, E. ;Mohnke, C. ;Polte, J. ;Oliveira Gomes, J. deUhlmann, E.Robotic machining is an alternative to manufacturing processes that combines the technologies of a high-performance machine tool with the flexibility of a 6-axis jointed arm robot. With their large working area, industrial robots are of particular interest for processing large-volume components and large structures, like aircraft components. An influencing variable, which is particularly relevant for milling processes with industrial robots are the cutting force F and the resulting dimensional deviation D. Milling tests of titanium alloys were carried out with an industrial robot and the results compared with a conventional machine tool. Due to the low thermal conductivity and high chemical reactivity of the Ti-6Al-4V alloy, heat is generated and increases the temperature in the contact region of the cutting tool/work piece. That has an impact on the cutting tool wear and increases the cutting force F, and consequently, the dimensional deviation D and the machined surface quality. The aim of the investigations is to find a suitable parameter selection and machining strategy for machining titanium alloys with minimal deviation D and an appropriate surface finish.
PublicationAgiles Modellieren von Servicetätigkeiten( 2021)
;Uhlmann, E. ;Bösing, M. ;Polte, J. ;Kirsch, L. ;Altmann, I.Emmerling, R.Kontextsensitive Assistenzsysteme bieten ein großes Potenzial zur Optimierung von Arbeitsabläufen. Durch die Einbindung Digitaler Zwillinge können unmittelbar Kontextinformationen zur Verfügung gestellt werden, wobei die Modellierung der Arbeitsabläufe derzeit wenig standardisiert ist. Die in diesem Beitrag vorgestellte Lösung zeigt eine interaktive Software-Applikation für kontextsensitive Assistenzsysteme in Kombination mit Prozesspatterns für die Modellierung von Servicefällen.
PublicationInfluence of the fatty acid profile on the lubricating film formation in micro-milling process on 7050-T7451 aluminum alloy( 2020)
;Chanes de Souza, M. ;Wiesner, H.M. ;Kuche, Y. ;Polte, J. ;Oliveira Gomes, J. deUhlmann, E.This work studies the technical performance of vegetable-based metalworking fluids as a more environment-friendly alternative for micro-milling on 7050-T7451 aluminum alloy. Micro-milling investigations were performed using two vegetable-based oils, two emulsions prepared with the same vegetable-based oil and a commercial emulsion for comparison. It was noted that the vegetable-based oils with high oleic fatty acid profile provide better lubrication films than mid-oleic fatty acid profiles. However, the wear of the cutting tools is slightly more pronounced when the high oleic oil was used. When these oils were used for the preparation of vegetable-based emulsions, the high oleic emulsion presents better lubricating potential and provides high surface quality than the mid-oleic emulsion. However, the wear of the cutting tool was similar. The vegetable-based metalworking fluids showed similar performance than the commercial reference. Therefore, the oil with high oleic fatty acid profiles presents good technical performance and can be used in vegetable-based metalworking fluids formulations.
PublicationReduktion thermisch bedingter Verlagerungen durch Integration von Peltierelementen in eine Hochfrequenzmotorspindel( 2020)
;Uhlmann, E. ;Salein, S. ;Iden, N. ;Polte, J. ;Temme, P. ;Hartung, D.Perschewski, S.During machining of parts, a significant proportion of geometrical errors is caused by thermally induced shifts of the positional correlation between tool and workpiece. This is due to electrical and mechanical power losses, which induce significant heat flow rates into the adjacent machine tool components. The drives and bearings of motorised spindles represent such significant heat sources. Due to their position close to the cutting point, motorised spindles have a considerable influence on the achievable working accuracy of machine tools. In order to reduce the thermal displacements of motorised spindles, the Institute for Machine Tools and Factory Management (IWF) and the Alfred Jäger GmbH develop a thermoelectric temperature control system for motorised spindles. The solution approach is based on prismatic as well as tubular Peltier modules, which allow a direct temperature control of the precisionrelated components. Especially, in case of changing induced heat flow rates, the system offers the Potenzial to maintain a thermal steady state by controlled cooling or heating and thus, a reduction of thermally induced displacements. On basis of experimentally determined data of a scaled-down test bench, the functionality of the thermoelectric temperature control system as well as the positive effects on the thermal system behaviour could be demonstrated. In addition, the current state of development of the thermoelectrically tempered motorized spindle is presented and the Potenzial to reduce thermally induced displacements is pointed out.
PublicationApplication of additive manufactured tungsten carbide-cobalt electrodes with interior flushing channels in S-EDM( 2020)
;Uhlmann, E. ;Polte, J. ;Bolz, R. ;Yabroudi, S. ;Streckenbach, J.Bergmann, A.Application fields of electrical discharge machining (EDM) are limited due to given process conditions. Manufacturing of parts with high aspect ratios and the application of multi-axis machining are limited due to process instabilities caused by removed particles. A promising approach to improve EDM process conditions, especially in sinking EDM (S-EDM), is the utilization of flushing channels in the tool electrode. However, with increasing complexity of the tool electrode geometry and the local integration of these flushing channels, conventional tool electrode manufacturing by cutting is limited. In contrast to that, the machining process selective laser melting (SLM) does not have such limitations. The appropriate integration of flushing channels, even for complex electrode geometries, improves process conditions during EDM in a variety of applications. This leads to a higher material removal rate and reduced tool wear compared to machining without flushing. Additionally, the number of required tool electrodes can be reduced, as SLM enables an efficient integration and miniaturization of all features in a single electrode. Because of its wear resistance and stability, tungsten carbide is an ideal tool electrode material, which is commonly applied in drilling EDM. After identifying suitable process parameters for roughing EDM with additively manufactured tungsten carbide cobalt tool electrodes, different forms of flushing channels were analysed in order to establish a fast process with minimum tool electrode wear. The results concerning material removal rate and the relative tool wear could be improved by applying internal flushing, though the tool wear stayed at a worse level compared to conventional tool electrode materials.
PublicationUrsachenanalyse zur Verfügbarkeitssteigerung von Werkzeugmaschinen( 2020)
;Uhlmann, E. ;Dumitrescu, R. ;Polte, J. ;Meyer, M.Simsek, D.The reliability of machine tools is a critical factor for the success of manufacturing companies. By analyzing data in product planning, machine manufacturers can eliminate causes of failure and systematically improve machines. However, comprehensive data analysis poses great challenges for many companies. The methodology presented in this paper addres-ses this problem and supports companies in the goal-driven data analysis.