The advantages of electrical discharge machining (EDM) over traditional machining have earned its wide applications in industrial world. However

the low machining stability caused by the inherent characteristics of EDM

high discharge frequency

small discharge gap

and strong disturbances

has hindered its further development

especially in deep

blind hole making because of difficulty in removing debris out of the gap in deep holes

causing the occurrences of arcing pulses and damaging work-piece surface. In order to improve process stability of machining deep and blind holes and solve the issue of machining such kind of high-melting-point

difficult-to-cut materials as titanium-zirconium-molybdenum alloy (TZM)

this paper has developed an adaptive double variable control system. In this control system electrode-discharge-cycle and gapservo-voltage were taken as control variables adaptively tuned

by two-step-ahead control strategy

with respect to variations of arcing ratios and discharging ratios respectively. One confirmation test demonstrated that this control system had improved machined depth of a hole more than 3.7 times from that by conventional EDM in machining Cr12MoV material. The other test confirmed that this control system helped to machine a blind hole

with a copper electrode of diameter 16mm

in the hard-tocut TZM of nearly 2640℃ melting point up to a depth of 93mm at an almost steady machining rate. The conventional EDM could hardly machine this kind of material. All these facts revealed that the developed adaptive double variable control system had endowed EDM with much stronger power to extend its applications in the newly developed materials.