Fraunhofer-Institut für Produktionsanlagen und Konstruktionstechnik IPK
Now showing 1 - 10 of 44
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.
PublicationSimulating flow behaviour of wet particles within the immersed tumbling process( 2021)
;Uhlmann, E. ;Polte, J. ;Kuche, Y.Landua, F.For many production chains, it is mandatory to involve special finishing of the manufactured parts for the chipping of the edges as well as the polishing of surfaces. One commonly used method is the immersed tumbling process, where any workpiece is dragged through a particle filled container. In many cases, the immersed tumbling process operates in environments with added liquids, leading to changes in particle-tool interaction and general flow behaviour of the used particles. Whilst the discrete element method for simulating particles is mainly limited to dry particles, the used software ROCKY DEM from ESSS, FlorianÃ³polis, Brasil, comes with a built-in liquid-bridge model to simulate water-covered particles and granulate and furthermore an extension for system couplings with Ansys Fluent of the company ANSYS, INC., Canonsburg, Pennsylvania. The latter can be used to create from both software one three-phase-model with higher amounts of actually simulated water. In thi s study, small amounts of water were added to differently shaped particles using the build-in liquid-bridge model, to analyse and compare the particles flow characteristics in both, wet and dry environments. To gather significant information leading towards precise comparisons, the particles trajectories, velocities and resulting forces against the workpieces can be specifically observed and analysed, whilst this kind of process knowledge could previously never been taken into account without simulation.
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.
PublicationCutting edge preparation of monolithic ceramic milling tools( 2021)
;Uhlmann, E. ;Polte, M. ;Polte, J.Hocke, T.Due to international competition, continuous increases in productivity, product quality and reduction of production costs are required. Especially, the development of milling tools made of innovative cutting materials and application-specific tool geometries for the machining of brittle materials are in focus to overcome these challenges. One approach to improve the performance and the tool behaviour concerning milling of graphite is the use of monolithic ceramic milling tools. Unfortunately, the high brittleness of the ceramic leads to breakouts on the cutting edge during the grinding process. This results in an increased maximum chipping of the cutting edge, which has a significant influence on the milling process. To improve the breakout behaviour, a cutting edge preparation with the immersed tumbling process was applied. To enable a process reliable cutting edge preparation, a suitable lapping medium, the influence of the processing time as well as the depth of imme rsion were investigated. Besides the maximum chipping of the cutting edge, the rounded cutting edge radius was also analysed. The results show that a process reliable cutting edge preparation of monolithic ceramic milling tools with a maximum chipping of the cutting edge RS,max â¤ 3 Âµm and a rounded cutting edge radius of rÎ² â¤ 7 Âµm could be realised. In future investigations, the experimental applicability of monolithic ceramic milling tools will be proved.
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.
PublicationAdditive manufacturing of precision cemented carbide parts( 2021)
;Polte, J. ;Polte, M. ;Lahoda, C. ;Hocke, T.Uhlmann, E.Cemented carbide parts are commonly used as wear resistance components in a broad range of industry, e.g. for forming, mould making and matrices. At state of the art the machining of precision cemented carbide components by milling is strongly limited due to excessive tool wear and long machining times. Promising approaches for precision machining of cemented carbide components are dedicated cutting tool coatings, new cutting materials like binderless polycrystalline diamond and ultrasonic-assisted machining. Nevertheless, for all these approaches the components need to be machined of monolithic materials. The new approach addresses an innovative manufacturing process chain composed of near net shape Additive Manufacturing followed by a precision finishing process. Within this investigations for the manufacturing of precision cemented carbide parts, cemented carbide with a cobalt content of 17 % and a grain size in a range of 23 Âµm â¤ gs â¤ 40 Âµm were used. As Addit ive Manufacturing technology laser powder bed fusion was used. Diamond slide burnishing and immersed tumbling were investigated as finishing technologies. Based on the investigations, a dedicated process chain for the manufacturing of precision cemented carbide parts could be realised. The findings show that the developed process chain composed of near net shape Additive Manufacturing and the finishing process diamond slide burnishing enables the manufacturing of precision cemented carbide parts with a geometrical accuracy of ag â¤ 10 Âµm. Due to the finishing process the initial surface roughness after Additive Manufacturing could reduce by Ra = 89 %.
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.
PublicationParticle contact conditions for cutting edge preparation of micro-milling tools by the immersed tumbling process( 2021)
;Uhlmann, E. ;Polte, J. ;Kuche, Y.Landua, F.For increasing tool life and cutting length of micro-milling tools the cutting edge preparation was successfully established. Using the immersed tumbling process, a reproducible cutting edge preparation with constant cutting edge radii as well as low chipping of the cutting edges can be realised. For a profound understanding of the preparation process and the process mechanisms further knowledge about the particle interactions with cutting tools as well as the particle flow mechanisms needs to be obtained. In this investigation the preparation process of micro-milling tools was analysed and the contact-mechanisms as well as the resulting pressures were investigated by simulation studies. Using the discrete element method (DEM) with the software ROCKY DEM from the company ESSS, FlorianÃ³polis, Brasil, the immersed tumbling process could be modelled and particle contacts, particle traces as well as particle interactions with the micro-milling tool can be visualized. Espec ially the particle-tool interactions were more accurately investigated by analysing the stresses and particles shear work as well as correlations between these parameters to prove the comparability between the process simulation and the real preparation process.