The Phenomenon of Polarity in EDM Drilling Process Using Water Based Dielectrics

The polarity effect in EDM drilling was investigated using a water based dielectric. EDM drilling machines are hardly designed to change the polarity, although it is known from the EDM sinking process that the polarity is linked to the discharge time. It was found out that there is a current during the delay time and the open circuits when processing with negative tool electrode polarity. A separate experimental setup showed a water electrolysis. The electrolysis effect occurs simultaneously to the electrical discharge process when the tool electrode has a negative polarity. It could be shown that the tool electrode is fully covered with gas bubbles when the electrical voltage is applied. This phenomenon leads to a modified energy distribution in the narrow gap. The plasma channel growth rate at the tool electrode is much higher, leading to reduced thermal stress. Therefore a lower wear and a higher feed rate could be observed when using a negative tool electrode.