Implementation of a handling system for using carbon fibres as tool electrodes in micro-ED drilling

Electrical discharge machining (EDM) processes represent an established process for the machining of complex geometries in hard to cut and electrically conductive materials. Nevertheless, micro-electrical discharge drilling still poses the challenge of machining holes with diameters dh ≤ 50 μm. The preparation of even smaller pin tool electrodes demands a great amount of non-productive time, which often involves the use of additional electrical discharge dressing processes for its manufacturing. A possible solution is the use of single carbon fibres with diameters 5 μm ≤ del ≤ 10 μm as tool electrodes. The use of these single fibres comprises a challenge due to their geometrical and mechanical properties, e.g. diameter and brittleness. To overcome this challenge, an existing handling system for carbon fibres was re-designed considering the obstacles that arose with the use of previous versions of such systems. This includes the replacement of the liquid rubber coating of the movable clamping jaw in order to use foam rubber to achieve a better distribution of the clamping force that establishes the electrical contact between the carbon fibre and a conducting copper plate. The geometry of the borosilicate glass micro-pipette was redesigned to ensure an accurate positioning of the carbon fibre due to its inner tip diameter 15 μm ≤ dt ≤ 35 μm and to enable the use of fibre electrodes with a length of 15 mm ≤ le ≤ 25 mm. This hinders the deflection of the fibre tip during the machining process and enables the precise guidance of the fibre. Furthermore, the developed handling system was implemented for performing single discharge experiments, in which parameters such as open circuit voltage, charge current and discharge capacity were varied in order to determine their influence on the material removal process.