Fraunhofer-Institut für Produktionsanlagen und Konstruktionstechnik IPK

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DEM simulation of centrifugal disc finishing

2022 , Uhlmann, Eckart , Polte, Julian , Kuche, Yves , Landua, Fabian

The finishing of small components with complex geometries is a major industrial challenge. One process that is suitable for targeted post-processing is centrifugal disc finishing with wet and dry media. In this process, the workpieces float as bulk material together with the abrasive particles in a container and are completely surrounded by the abrasive medium. As shown in previous studies, the Discrete Element Method (DEM) is suitable for investigations of grinding processes with specified workpiece motions. To simulate unpredictable workpiece motion, a new approach is being tested in which the workpieces themselves are treated as particles. Within this research paper, results for the post-processing of centrifugal disc finishing with the software ROCKY DEM are presented. The investigation results show good correlation between the numerical determined pressures and the analysis results of the rounded workpiece edges on test components made of mould-steel X13NiMnCuAl4-2-1-1.

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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.

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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.

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Influence of cutting edge micro-geometry in micro-milling of copper alloys with reduced lead content

2018 , Uhlmann, Eckart , Kuche, Yves , Polte, Julian , Polte, Mitchel

Especially copper-zinc alloys (CuZn) with good machining properties are used for electrical components and fittings. By using copper alloys with lead content of 1 % < Pb < 3 % an improved chip breakage can be achieved. Legal regulations require the reduction of lead and demand further knowledge about the effect of the material properties in interaction with the used micro-milling tools. In this contribution the cutting conditions of copper as well as four copper alloys were examined. The results show considerable differences in the resultant surface roughness and burr formation. Furthermore, the influence of two different tool geometries and variied cutting edge micro-geometries were investigated while machining CuZn21Si3P. Thereby, tools with increased cutting edge radii rv showed increased active forces Fa, burr height h0 and decreased surface roughness.

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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.

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Influence of the fatty acid profile on the lubricating film formation in micro-milling process on 7050-T7451 aluminum alloy

2020 , Chanes de Souza, Milena , Wiesner, Hagen Maximilian , Kuche, Yves , Polte, Julian , De Oliveira Gomes Júnior, Jefferson , Uhlmann, Eckart

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.

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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.

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Modeling of the wet immersed tumbling process with the Discrete Element Method (DEM)

2021 , Uhlmann, Eckart , Fürstenau, J.-P. , Kuche, Yves , Yabroudi, Sami , Polte, Julian , Polte, Mitchel

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.

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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.

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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.

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