Fraunhofer-Institut für Produktionsanlagen und Konstruktionstechnik IPK

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Validation of different tungsten carbide-cobalt grades as tool electrode material for sinking EDM

2022 , Uhlmann, Eckart , Bolz, Robert , Polte, Mitchel , Börnstein, Julian

In sinking electrical discharge machining (EDM), tool electrode wear is crucial for an economical production. The tool electrode wear affects the process efficiency and determines the number of required tool electrodes for a specific machining process. Therefore, the relative tool wear, describing the relation of removed material volume between tool and workpiece electrode, needs to be minimised. The tool wear characteristics in sinking EDM depend strongly on EDM processing parameters and the applied electrode materials. Especially in micro-EDM, a significant increase of relative tool wear is representative. Because of its thermophysical properties tungsten carbide-cobalt (WC-Co) is a suitable material for the application as sinking EDM tool electrode. The economical production of WC-Co form electrodes for EDM sinking is enabled by recent advancements in precision milling of hard materials. Due to non-existent research on which composition of WC-Co is most advantageous for the application as sinking EDM tool electrode material, previous investigations have been intensified to describe correlations between material properties, EDM processing parameters and EDM processing results concerning material removal rate and relative tool wear. Therefore, various WC-Co grades with differing grain size and cobalt content were analysed in sinking EDM experimental studies. It was observed that the factor grain size showed an ambiguous effect concerning the process results. An increasing cobalt content led to a reduction of relative tool wear, which can be explained by the microstructure of the cobalt binder phase with its higher electrical conductivity. The WC-Co grades with beneficial EDM processing results have been further investigated in EDM parameter studies with differing tool electrode geometries. The experimental results concerning relative tool wear, with a minimum of 3 % for macro- and 5 % for micro-sized geometries, proved the suitability of specific WC-Co compositions as tool electrode material for sinking EDM.

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Fundamental research of applying tungsten carbide-cobalt as tool electrode material for sinking EDM

2020 , Uhlmann, Eckart , Polte, Mitchel , Bolz, Robert , Börnstein, Julian

The manufacturing process milling is limited in machining specific geometries like inner contours with sharp edges, high aspect ratios or defined radii. Sinking EDM (S-EDM) is an appropriate process to machine complex features if the negative geometry is machinable. The tool electrode wear is a critical factor, because it affects machining accuracy and process efficiency. The tool electrode wear depends on S-EDM processing parameters, the geometry and material of the tool electrode. The material tungsten carbide-cobalt owns suitable thermophysical properties for the application as tool electrode material in EDM. Most applications of tungsten carbide-cobalt in EDM are limited to EDM drilling processes, where tungsten carbide tube electrodes are widely used. The advancements in milling of hard materials enable an economic manufacturing of tungsten carbide-cobalt form electrodes for sinking EDM applications. However, it is not investigated which composition of the material tungsten carbide-cobalt is the most appropriate for the application as tool electrode material in S-EDM. Additionally, there are no suitable EDM process parameters in order to benefit from the material characteristics of the respective tungsten carbide-cobalt. Focus of this work is the analysis of different tungsten carbide grades regarding the average grain size and the cobalt content in order to identify correlations between the material characteristics and the EDM process results. Therefore, eight different tungsten carbide grades with four different grain sizes and five different cobalt contents were applied in S-EDM experimental analysis. The experimental studies showed a general suitability of tungsten carbide-cobalt tool electrodes for EDM-processing, where the material removal rate is comparable to commonly used tool electrode materials. Nevertheless, the relative tool wear shows inferior results. It could be observed that higher cobalt content and coarser grain size of the applied tungsten carbide tool electrodes are advantageous for S-EDM.

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Dry-ED milling of micro-scale contours with high-speed rotating tungsten tube electrodes

2020 , Uhlmann, Eckart , Perfilov, I. , Yabroudi, Sami , Mevert, Ricardo , Polte, Mitchel

This paper presents machining results for dry-ED milling of micro-scale contours by use of a new machine tool, including a relaxation generator, designed for dry-EDM. To implement the dry-ED milling process tungsten tube electrodes were used. The gas is injected through the tubular tool electrode under high pressure. Additionally, a high-speed EDM spindle was used to overcome process instabilities and increase the material removal rate due to better flushing conditions. Further, fluid simulations of the flushing conditions are presented in this paper. It is found that the use of gaseous dielectrics enables much better machining results in terms of shape accuracy and tool wear. The simulations provide new insights in the flushing conditions when using gaseous dielectrics. The calculated fluid flow pattern shows a great agreement with the observed depositions of reattached molten material on the tool and workpiece surface. The results presented as well as the hardware introduced enable the industrial application of dry-EDM for the first time.

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