Corona discharge with a discharge current of a few hundred microamperes can blow out a small candle flame within about 1 cm of a discharge point. A pinwheel, with radial metal spokes and pointed tips bent to point along the circumference of a circle, can be made to rotate if energized by a corona discharge; the rotation is due to differential electric attraction between the metal spokes and the space charge shield region that surrounds the tips. Corona discharge A corona discharge is an electrical discharge brought on by the ionization of a fluid such as air surrounding a conductor that is
Electrical discharge machining using the CNC drawing plotter and optical line follower techniques was produced in 1974. Dulebohn later used the same plotter CNC program to directly control the EDM machine, and the first CNC EDM machine was produced in 1976. Commercial wire EDM capability and use has advanced substantially during recent decades. Feed rates have increased and surface finish can be finely controlled. Electrical discharge machining is a machining method primarily used for hard metals or those that would be very difficult to machine with traditional techniques. EDM typically works with materials that are electrically conductive, although methods have also been proposed