Fraunhofer-Institut für Produktionsanlagen und Konstruktionstechnik IPK

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Manufacturing 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.

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Droplet removal from PVD-coated micro-milling tools with the immersed tumbling process

2017 , Uhlmann, E. , Kuche, Y. , Oberschmidt, D. , Polte, J.

The physical vapour deposition (PVD) process is widely used for the coating of cutting tools. The increased hardness and temperature stability permitted a higher cutting speed and longer tool life in comparison to uncoated tools. Within the PVD-process droplets of the target can be deposited on the coated surface. The consequence is an inhomogeneous surface of the cutting tools with an increased surface roughness. In this study, the immersed tumbling process is used for the droplet removal of micro-milling tools. The results show the functionality of the process for the droplet removal depending of the lapping media and process parameters in connection with the amount and size of the droplets.

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Geometric 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.

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Verfahren zur automatisierten Reinigung

2014 , Uhlmann, E. , Oberschmidt, D. , Kuche, Y.

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Cutting 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 [1], 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.

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Wear behaviour of diamond coated micro-milling tools during micro machining

2017 , Uhlmann, E. , Kuche, Y. , Oberschmidt, D. , Polte, J.

Graphite electrodes are used in the die sinking process for manufacturing of micro structured tools in the die and mould fabrication. They are machined using the micro-milling process. During the cutting process graphite grains have strong abrasive effects on the cutting edges and lead to high tool wear. Consequences are short path length lc and geometrical errors. One approach to reduce tool wear is the tool coating with diamond. The diamond coating changes the cutting edge micro geometry which has influences on the process behaviour. In this paper, the wear behaviour of micro-milling tools with diameter D = 0.5 mm and different micro geometries is analysed and discussed. The results show better wear behaviour for prepared and coated tools.

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Effects of different cutting edge preparation methods on micro milling performance

2016 , Uhlmann, E. , Oberschmidt, D. , Kuche, Y. , Löwenstein, A. , Winker, I.

In micro milling, which is mostly used in mold and die making, process reliability and predictability of tool failure are important. Particularly in precision and micro machining, tool breakage is hardly detectable and the requirements on accuracy are very high. Immersed tumbling is an appropriate process for the defined cutting edge preparation of micro milling tools. Its effects like increasing tool wear performance and tool life has been evaluated. In this paper, different cutting edge preparation processes showed that in cutting tests different effects occur regarding tool wear, process forces and surface quality. Immersed tumbling leads to the lowest active force Fa, but magnet finishing leads still do a slightly better surface quality.

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Mikrofräswerkzeuge 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.

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Influence of cutting edge preparation on the performance of micro milling tools

2016 , Uhlmann, E. , Oberschmidt, D. , Löwenstein, A. , Kuche, Y.

A main reason for premature tool failure in micro milling is the irregular wear behavior of the cutting tools. An approach to improve the tool wear behavior is a defined cutting edge preparation using immersed tumbling. A particular challenge is the cutting edge preparation of micro milling tools with small diameters D ⤠0.5 mm. High loads within the preparation process can lead to outbreaks of the cutting edge and tool breakage. Furthermore, the influence of changed cutting edge geometry regarding the process behavior has to be more examined for these tool diameters. In this paper, micro milling tools with a diameter D = 0.2 mm will be prepared and the influence on the cutting process will be presented and discussed. The experiments will show a better wear behavior for the prepared tools and an improved surface roughness on the machined workpiece.

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Automatisierte Qualitätskontrolle

2015 , Uhlmann, E. , Oberschmidt, D. , Löwenstein, A. , Kuche, Y. , Wiemann, S.

Inhalt eines Forschungsprojektes der Firma OTEC Präzisionsfinish GmbH und des Fraunhofer-Instituts für Produktionsanlagen und Konstruktionstechnik IPK ist die Entwicklung eines Maschinenprototypen zur Feinbearbeitung mit automatisierter Qualitätskontrolle durch integrierte optische Messtechnik und Messsoftware. Im Rahmen des durch das Zentrale Innovationsprogramm Mittelstand (ZIM) vom Bundesministerium für Wirtschaft und Energie (BMWi) geförderten Projektes wurde dazu eine kompakte, für die Automatisierung und Integration von Messtechnik ausgelegte Maschine entwickelt. Mithilfe dieser Maschine können Werkstücke, wie etwa Nockenwellen oder Zerspanwerkzeuge, mit dem Verfahren Tauchgleitläppen bearbeitet und definierte Kantenradien erzeugt sowie in einem automatisierten Prozess gemessen werden. This paper presents a machine prototype for the finishing of edges and surfaces of work pieces. The prototype has an integrated optical measurement device, which can be used for the control of the process results and possibly automated remachining. The machine is used for the preparation of milling tools. Process parameters and their effects are analyzed and an approach for the automated setting of the process parameters is shown.

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