Performance and Limitations of the Conventional Electrode Materials for Erosion of High Aspect Ratio Microcavities

Abstract

The low electrode wear strategy based on a carbonaceous layer formation on electrodes considerably increases resource efficiency in the conventional die-sinking EDM. However, the smallest electrode projection area Ap for using the strategy is limited to 0.1 mm2 and maximum pulse current 3A, possibly due to the pulse re-opening phenomenon. In this work, using a novel generator circuit, pulse re-openings have been restricted up to pulse durations 100 μs and a current of 1A. Hence, the performance of conventional electrode materials is evaluated in order to push the limits of the low wear strategy. However, when using graphite and copper infiltrated graphite microelectrodes, bending of the electrodes is observed, especially in the tip region. The simulation of temperature in the microelectrodes suggests abnormal carbonaceous build up process. This explanation is also concurrent to the observation of a process instability resulting in irreproducible electrode wear behaviour. For copper microelectrodes, another phenomenon is observed where overcuts are produced in the eroded cavities. These overcuts are produced by sparks with high discharge voltage. Sliding of the plasma channel from the electrode corners to the side surfaces is proposed to cause such discharges and overcuts. Thus, underlying mechanisms limiting the low wear strategy in micro-EDM are identified.