EDM drilling of ultra-high aspect ratio micro holes with insulated tools

This work presents an innovative method for the Electrical Discharge Drilling of ultra-high aspect ratio (AR > 30) micro holes. It makes use of tools insulated on the sidewall by means of a coating. The concept is to promote the process stability of micro EDM deep drilling by preventing secondary sparks. The performance of standard and customized tools is compared and reviewed against the main criteria of shape quality, tool wear and machining time. Process capabilities are also defined for a given coating. Micro holes within 0.2 mm in diameter and aspect ratio (AR) up to about 120 could be obtained within 1 h. A micro punching die is also realized by combining this strategy with micro wire EDM.