THE DEPENDENCE OF INTERSPACE DISCHARGE TRANSITIVITY UPON THE GAP DEBRIS IN PRECISION ELECTRODISCHARGE MACHINING

The present study confirms the indispensable stabilizing role of gap d ebris in precision electrodischarge machining (EDM). It is well known that failure to evacuate surfeited debris in a spark gap results in ar cing that damages the tool electrode as well as the work. A machining process in pure kerosene is very unstable due to arcing. The latter ca use for arcing is frequently observed, but is poorly understood. It is a well-known fact that the presence of minute particles in insulating liquids drastically lowers breakdown strength. A. stable process with out arcing depends on discharge transitivity rather than on the ease o f breakdown. As a result, an easy breakdown process with the help of t he foreign particles does not show the entire stabilizing contribution of debris. Our experimental and analytical investigations on general precision EDM reveal that discharge transitivity in gap space relies o n the presence of a sedimentary debris layer on the work's surface. Ac tually, the inherent transitivity due to surface irregularity will dis appear because of the very low surface roughness (R-a < 3 mu m). Spark movement should be attributed to effects from the mechanical impact o f discharge pulses, the distribution of breakdown strength, and the di stribution of electrical field. We can derive a process model regardin g the tendency of spark movement to expound the functions of debris co ntent and gap size. Pertinent new understanding will eventually give a n explanation of the complicated role of gap debris. A process model w ill lead to a more relevant conception of gap size and its control tha n most currently accepted understanding. (C) 1997 Elsevier Science S.A .