Now showing 1 - 10 of 174
  • Publication
    Wolframschmelzcarbidbasierte MMC-Schichten für den industriellen Einsatz im Formenbau
    ( 2022)
    Langebeck, Anika
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    Jahnke, Christian
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    Wünderlich, Tim
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    Bohlen, Annika
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    Zur Steigerung der abrasiven Verschleißbeständigkeit können Oberflächen lokal mit Hartpartikeln verstärkt werden. Diese sogenannten Metal-Matrix-Composit(MMC)-Schichten können mittels Laserstrahldispergieren gefertigt und durch Mikrofräsen nachbearbeitet werden. Im hier vorgestellten Forschungsvorhaben wurde als Grundwerkstoff verwendete Aluminiumbronze (CuAl10Ni5Fe4) mit Wolframschmelzcarbid verstärkt. Der Hartpartikelgehalt kann dabei durch eine Steigerung des Pulvermassenstroms bis zur Packungsdichte des unverarbeiteten Pulvers erhöht werden. Über eine temperaturbasierte Leistungsregelung kann eine gleichbleibend homogene MMC-Schicht mit konstanter Dicke und Tiefe dispergiert werden. Durch das Mikrofräsen mit optimierten Parametern können qualitativ hochwertige MMC-Oberflächen für den industriellen Einsatz in Spritzgusswerkzeugen hergestellt werden. Dabei wurde vor allem der Zahnvorschub fz als kritischer Prozessparameter identifiziert.
  • Publication
    Numerical investigation into cleanability of support structures produced by powder bed fusion technology
    ( 2022)
    Campana, Giampaolo
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    Mele, Mattia
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    Raffaelli, Luca
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    Bergmann, André
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    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.
  • Publication
    Optimizing the sharpening process of hybrid-bonded diamond grinding wheels by means of a process model
    ( 2022) ;
    Muthulingam, Arunan
    The grinding wheel topography influences the cutting performance and thus the economic efficiency of a grinding process. In contrary to conventional grinding wheels, super abrasive grinding wheels should undergo an additional sharpening process after the initial profiling process to obtain a suitable microstructure of the grinding wheel. Due to the lack of scientific knowledge, the sharpening process is mostly performed manually in industrial practice. A CNC-controlled sharpening process can not only improve the reproducibility of grinding processes but also decrease the secondary processing time and thereby increase the economic efficiency significantly. To optimize the sharpening process, experimental investigations were carried out to identify the significant sharpening parameters influencing the grinding wheel topography. The sharpening block width lSb, the grain size of the sharpening block dkSb and the area-related material removal in sharpening VâSb were identi fied as the most significant parameters. Additional experiments were performed to further quantify the influence of the significant sharpening parameters. Based on that, a process model was developed to predict the required sharpening parameters for certain target topographies. By using the process model, constant work results and improved process reliability can be obtained.
  • Publication
    In situ microstructure analysis of Inconel 625 during laser powder bed fusion
    ( 2022)
    Schmeiser, Felix
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    Krohmer, Erwin
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    Wagner, Christian
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    Schell, Norbert
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    Reimers, Walter
    Laser powder bed fusion is an additive manufacturing process that employs highly focused laser radiation for selective melting of a metal powder bed. This process entails a complex heat flow and thermal management that results in characteristic, often highly textured microstructures, which lead to mechanical anisotropy. In this study, high-energy X-ray diffraction experiments were carried out to illuminate the formation and evolution of microstructural features during LPBF. The nickel-base alloy Inconel 625 was used for in situ experiments using a custom LPBF system designed for these investigations. The diffraction patterns yielded results regarding texture, lattice defects, recrystallization, and chemical segregation. A combination of high laser power and scanning speed results in a strong preferred crystallographic orientation, while low laser power and scanning speed showed no clear texture. The observation of a constant gauge volume revealed solid-state texture changes without remelting. They were related to in situ recrystallization processes caused by the repeated laser scanning. After recrystallization, the formation and growth of segregations were deduced from an increasing diffraction peak asymmetry and confirmed by ex situ scanning transmission electron microscopy.
  • Publication
    Simulating flow behaviour of wet particles within the immersed tumbling process
    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, Florianópolis, 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.
  • Publication
    Concept for an actuated variable tool electrode for use in sinking EDM
    ( 2021) ; ;
    Thißen, Kai
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    Schulte Westhoff, Bela
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    Masoud, Abd Elkarim
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    Maas, Jürgen
    Typically, a large number of individual tool electrodes has to be used in sinking electrical discharge machining (sinking EDM) to successfully machine a single workpiece. Due to non-uniform wear and insufficient flushing of the working gap electrode geometries have a significant effect on the process efficiency. This paper discusses the use of an actuated variable tool electrode for sinking EDM to reduce the number of required tool electrodes and to increase the overall process efficiency. A miniaturised linear actuator was developed to individually move electrode segments to form the target shape for the tool electrode. The coordinated actuation of bundled electrode segments introduces new methods for the active flushing within the working gap, which cannot be implemented in conventional sinking EDM. Intelligent sinking strategies can further improve process efficiency by creating and sinking sub-geometries into the workpiece offering improved flushing conditions compa red to the original geometry.
  • Publication
    Particle contact conditions for cutting edge preparation of micro-milling tools by the immersed tumbling process
    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, Florianópolis, 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. Especially 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.
  • Publication
    Reduction of erosion duration for electrical discharge drilling using a nature analogue algorithm with nested strategy types
    The required high economic efficiency, combined with the corresponding high quality demands, in the aerospace industry as well as in mould and tool making, motivate the necessity of finding suitable parameter combinations for the process of electrical discharge machining (EDM), e.g. when introducing new materials. To counteract this, various methods are being investigated in research for the optimisation of EDM. One new method is the stochastic optimisation procedure evolution strategy (ES). Due to its metaheuristic approach, this optimisation method is excellently suited for very complex processes in which the interrelationship of the individual influencing variables is not known. This publication presents the results of the investigation of the suitability of the ES optimisation method using the example of electrical discharge drilling. For this purpose, two nested ES-types were investigated. The electrode materials used were brass for the tool and stainless steel X5C rNi18-1 for the workpiece. As a result, the erosion duration could be reduced by 30 %. This investigation forms the basis for the use of nested ES types in electrical discharge drilling.
  • Publication
    Evaluation of carbon fiber reinforced polymer – CFRP – machining by applying industrial robots
    ( 2021)
    Grisol De Melo, Ever
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    Santos Silva, Jéssica Christina dos
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    Klein, Tiago Borsoi
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    Oliveira Gomes, Jefferson de
    Carbon 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.
  • Publication
    Modeling of Contact Forces for Brushing Tools
    ( 2021) ;
    Hoyer, Anton
    Brushing with bonded abrasives is a flexible finishing process used for the deburring and the rounding of workpiece edges as well as for the reduction of the surface roughness. Although industrially widespread, insufficient knowledge about the contact behavior of the abrasive filaments mainly causes applications to be based on experiential values. Therefore, this article aims to increase the applicability of physical process models by introducing a new prediction method, correlating the contact forces of single abrasive filaments, obtained by means of a multi-body simulation, with the experimentally determined process forces of full brushing tools during the surface finishing of ZrO2. It was concluded that aggressive process parameters may not necessarily lead to maximum productivity due to increased tool wear, whereas less aggressive process parameters might yield equally high contact forces and thus higher productivity.