Abstract
In single discharge machining of a 0.1mm tungsten electrode with 30 to 50A discharge current and several hundreds of microseconds duration, a needle of 20 to 40μm in diameter has been made instantaneously. To understand this phenomenon, a stroboscopic imaging system with a Q-switched Nd : YAG laser is used to observe the dynamical change of the electrode during and after the discharge pulse. In the oil, the electrode shape could not be observed. The gap during discharge can not be observed due to dark, round image of a bubble formed by the discharge. The laser beam is thought to be reflected and/or refracted at the bubble's surface. Some approaches has been tried so as to without generating a bubble. An effective method is putting a thin layer of oil film on the workpiece. As a result of observation of the gap region, the formation of a needle-shaped electrode with a single discharge occurs in the interval from 100 to 350μs after the discharge stops.
