Fraunhofer-Institut für Produktionsanlagen und Konstruktionstechnik IPK

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  • Publication
    Simulating flow behaviour of wet particles within the immersed tumbling process
    ( 2021)
    Uhlmann, Eckart
    ;
    Polte, Julian
    ;
    Kuche, Yves
    ;
    Landua, Fabian
    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
    Particle contact conditions for cutting edge preparation of micro-milling tools by the immersed tumbling process
    ( 2021)
    Uhlmann, Eckart
    ;
    Polte, Julian
    ;
    Kuche, Yves
    ;
    Landua, Fabian
    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
    DEM-simulation of particle behaviour during cutting edge preparation of micro-milling tools by immersed tumbling
    ( 2020)
    Uhlmann, Eckart
    ;
    Polte, Mitchel
    ;
    Polte, Julian
    ;
    Kuche, Yves
    The micro-milling process is widely used in industry for the manufacturing of complex geometries for a wide range of materials. To increase the tool life and cutting length the cutting edge preparation could be successfully established. Within preliminary investigations the immersed tumbling process was identified as the most promising process for cutting edge preparation of micro-milling tools. The process enables a reproducible cutting edge preparation with constant cutting edge radii as well as low chipping of the cutting edges. 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. Therefore, the process simulation using discrete element methods (DEM) offers the possibility of an improved understanding of the process behaviour. In this investigation simulation studies about the cutting edge preparation of micr o-milling tools using the immersed tumbling process will be presented. The DEM with the software ROCKY DEM from the company ESSS, Florianópolis, Brasil, was used and a process model was derived. The investigations show that the software can be successfully used for the visualisation of the immersed tumbling process and the flow mechanisms can be examined more closely.
  • Publication
    Development of monolithic ceramic milling tools for machining graphite
    ( 2020)
    Uhlmann, Eckart
    ;
    Polte, Mitchel
    ;
    Polte, Julian
    ;
    Kuche, Yves
    ;
    Hocke, Toni
    Due to the 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 are in focus to overcome these challenges. Besides copper, graphite is the most important electrode material for electrical discharge machining (EDM). The machining of graphite leads to high tool wear due to a strong abrasive effect. Short tool life has a considerable influence on the economic efficiency of manufacturing processes. Currently, for the machining of graphite cost intensive diamond coated carbide tools are applied. In order to reduce machining costs, innovative cutting materials and dedicated manufacturing processes have to be applied. First results show a great potential of ceramics as tool material for machining graphite. The aim of this investigation is the characterisation and identification of novel ceramic cutting materials and the evaluation of an innovative tool micro-geometry especially designed for machining graphite. Therefore, the cutting material properties such as hardness, fracture toughness and wear resistance of four ceramic materials were investigated. Various hardness tests and particle blasting tests were carried out. Based on this investigations to manufacture the ceramic milling tools, a specific and innovative tool micro-geometry with defined angles was used. Thereby, a suitable cutting ceramic was identified, which represents a promising approach for an optimised machining of graphite.
  • Publication
    Development of a machining strategy for diamond slide burnishing burnishing tools made of polycrystalline diamond (PCD)
    ( 2020)
    Uhlmann, Eckart
    ;
    Polte, Mitchel
    ;
    Polte, Julian
    ;
    Kuche, Yves
    ;
    Wendorf, S.
    ;
    Siebel, D.
    High demands on product quality force companies to reduce production costs. Due to the growing international competition, optical surfaces for tool and mould making need to be produced economically. These surfaces are commonly produced using ultra-precision cutting. However, the efficiency is limited due to low feed velocities vf, small depth of cut ap and associated long process times tPr. An innovative manufacturing process represents diamond burnishing, which can be carried out directly after the high-precision milling process. For this purpose, super-hard materials made of single crystalline diamond (SCD) are currently used as tool materials. Since the material costs are high and the availability is limited, SCD needs to be substituted. An innovative substitution material is polycrystalline diamond (PCD). Within this paper, a machining strategy for the high-precision production of PCD spheres for diamond slide burnishing tools is presented. The processes grinding, p olishing and electrical discharge machining (EDM) were applied. Therefore, the manufacturing costs, the surface roughness, the shape accuracy as well as the concentricity accuracy were analysed. Based on these investigations, an efficient and economical machining strategy for the production of high-precision spherical geometries made of PCD can be provided. First results showed that the prefered machining strategy uses a cross-process chain consisting of grinding and polishing. Thereby, the advantages of both processes with the fast manufacturing of the macro-geometry by the grinding process as well as the high surface qualities, which can be achieved by the polishing process, are combined.
  • Publication
    Increased efficiency and accuracy in ultra-precision machining through adapted CAM software
    ( 2020)
    Uhlmann, Eckart
    ;
    Polte, Julian
    ;
    Hein, Christoph
    ;
    Kuche, Yves
    ;
    Dörr, Martin
    CAM software is widely used through the last 40 years for a broad field of applications. The networkability of machine tools and the digitally integrated production as an existing trend for the next years and exponentially increasing computing power enable direct data transfer between CAD/CAM software and machine tool. Increments ar < 5 nm are common in ultra-precision CNC codes and are not supported by most traditional CAM software. Therefore, ultra-precision machining often remains a manufacturing process with high manual effort in the machine setting and the generation of CNC codes. In order to increase the degree of automation in ultra-precision machining, machine manufacturers are developing their own, customised CAM software. The studies presented in this paper investigate the influence of different process preparation on relevant parameters during ultra-precision face turning of an n surface with monocrystalline diamond tools. Machine-specific CAM software is com pared with manual CNC code creation from a point cloud. The influence on the workpiece characteristics dimensional accuracy GF and average roughness depth Ra is investigated. The influence of the chosen strategy for the generation of the CNC code on the machining time tm is examined to compare the economics of the strategies. In order to keep the comparison significant, the cutting parameters cutting depth ap and feed f are kept constant in all strategies. Decreasing machining time tm increases efficiency in comparison to manual CNC code creation.
  • Publication
    Wear behaviour of HIPIMS coated micro-milling tools with cutting edge preparation for machining steel moulds
    ( 2018)
    Uhlmann, Eckart
    ;
    Kuche, Yves
    ;
    Polte, Julian
    ;
    Polte, Mitchel
    Micro-milling is an appropriate process for the industrial production of precision parts in the mould and die industry. Decisive for a long tool life is the wear resistance, which can be improved by cutting edge preparation technologies and tool coatings. Especially the improvement of the coating technology with the high power impulse magnetron sputtering (HIPIMS) provides improved tool wear behaviour and longer path length lc. Further studies compare two different HIPIMS-coatings of micro-milling tools for machining the mould steel X13NiMnCuAl4-2-1-1. Furthermore, the tool wear could be reduced due to cutting edge preparation using immersed tumbling process. In consequence of the increased cutting edge radii rβ the measured active forces Fa increased slightly. Best results were achieved for micro-milling tools with cutting edge preparation and AlTiN coating.