Fraunhofer-Institut für Produktionsanlagen und Konstruktionstechnik IPK
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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.
PublicationDevelopment of a machining strategy for diamond slide burnishing burnishing tools made of polycrystalline diamond (PCD)( 2020)
;Uhlmann, E. ;Polte, M. ;Polte, J. ;Kuche, Y. ;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.
PublicationDevelopment of monolithic ceramic milling tools for machining graphite( 2020)
;Uhlmann, E. ;Polte, M. ;Polte, J. ;Kuche, Y.Hocke, T.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.
PublicationDEM-simulation of particle behaviour during cutting edge preparation of micro-milling tools by immersed tumbling( 2020)
;Uhlmann, E. ;Polte, M. ;Polte, J.Kuche, Y.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, FlorianÃ³polis, 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.
PublicationCutting force prediction in micro-milling considering the cutting edge micro-geometry( 2019)
;Uhlmann, E. ;Polte, J. ;Wiesner, H.M. ;Kuche, Y.Polte, M.The micro-milling process is used for a wide range of materials and enables the manufacturing of complex geometries with micro-features. One important factor for the tool life is the cutting force Fc, which depends on the applied technology, process parameters and cutting edge micro-geometry. High cutting forces Fc can lead to tool breakage in the transition between the shank and the cutting part of cemented carbide end mills. The prediction of cutting forces Fc in micro-milling processes through cutting force models could potentially decrease the hazard of tool breakage. By including the cutting edge radius rv into the prediction model, additional correction factors can be avoided. Therefore, further knowledge about the applicability of those models for the micro-milling process with chip thickness h < 0.01 mm is needed. In this investigation, the cutting force model of KOTSCHENREUTHER , which takes the cutting edge radius rv into account is used for the cutting force prediction in micro-milling. In order to validate this model, an innovative lead free copper alloy CuZn21Si3P is machined. Cemented carbide micro-milling tools with tool diameter D = 1 mm were used. The manufacturing of different cutting edge radii rv was realised with the immersed tumbling process. During milling experiments with a five-axis high precision machine tool the cutting forces Fc were measured. Cutting forces in a range of 6 N < Fc < 26 N were detected. The results show good correlations between the predicted and experimental determined cutting forces Fc. Furthermore, the measured cutting edge radii rv show a high influence on the deviation of the measured and predicted cutting forces Fc.
PublicationManufacturing of graphite electrodes with high geometrical requirements( 2019)
;Uhlmann, E. ;Kuche, Y. ;Polte, J.Polte, M.Graphite is widely used for the die-sinking electrical discharge machining (EDM) process, especially for the roughing process. For the manufacturing of graphite electrodes the milling process is mainly used. The process enables fast processing times tP and high geometrical flexibility. In consequence of the cutting behaviour of graphite micro-components with geometrical features can be manufactured. In this contribution the manufacturing of micro-pins and bridges with aspect ratios of A = 1:50 were machined with diamond coated milling tools. By variation of the depth of cut ap and the width of cut ae it can be shown that the influence of the depth of cut ap is quite bigger than the influence of the width of cut ae. This results in consequence of the higher stability of the geometrical features by improved force distribution.
PublicationMikrofräswerkzeuge mit Schneiden aus cBN( 2018)
;Uhlmann, E. ;Polte, J. ;Polte, M. ;Kuche, Y.Wiesner, H.Die Mikrozerspanung ist eine Kerntechnologie bei der Fertigung von Mikrospritzgussformen. Die hohen Ansprüche an die geometrische Genauigkeit und Oberflächenrauheit erfordern den Einsatz hochfester Werkstoffe. Jedoch unterliegen aktuelle Fräswerkzeuge bei der Mikrozerspanung einem hohen Verschleiß. Einen Lösungsansatz bietet der erfolgreich in der Makrozerspanung eingesetzte Schneidstoff kubisch-kristallinesBornitrid(cBN). Ziel der Untersuchungen war es daher, detaillierte Informationen zur Bearbeitung von gehärtetem Stahl mit cBN-Mikrofräswerkzeugen bereitstellen zu können.
PublicationGeometric deviations in the production of micro-milling tools and their influence on the cutting process( 2016)
;Uhlmann, E. ;Oberschmidt, D. ;Kuche, Y.Polte, M.For micro-milling tools with decreasing diameter D < 0.5 mm the requirements for the manufacturing rise up and the risk of geometrical deviations of the cutting edges increase. In this investigation industrial produced micro-milling tools with a diameter of D = 0.2 mm made of cemented carbide were analysed. Micro-milling tools with variable macro geometry were selected and used for the machining of mould steel. The influence of the geometrical deviations on the wear behaviour and the surface roughness of the machined steel were examined. It is shown that the variable tool geometry lead to wear of the minor cutting edges S'. Furthermore, an influence on the surface roughness of the machined workpiece is determined.