The cut of mid-line should be the first cut, the second batch cut and the third micro-cut. They are separately designed to meet the requirements of their characteristics. They are divided into three pulse width segments and pulse generating circuits with different characteristics of current waveforms. Minimum pulse width of micro-finishing is 0.3 ugs. In order to ensure the minimum distortion of the pulse discharge current waveform which is finally fed into the discharge gap, the measures suitable for the transmission of high frequency power pulses are selected in the output of power pulses.

Servo control circuit of one-way EDM wire cutting machine tool is selected for middle wire cutting. The circuit adopts pulse width sampling method and pulse discharge sampling method. Even if the pulse width is 1.2 microseconds, the circuit can complete the feed of servo tracking control worktable according to the sampling and discharging conditions. Different servo tracking and tracking sensitivities are selected for the first, second and third micro-incisions. After choosing this servo control circuit and cutting it in the second time, the error of precision of the sample can be corrected to about 5 micron. After the third fine cutting, the accuracy of the specimens can be repaired to 3 microns. After the fourth precise cutting, the surface roughness of the specimens can reach Ra 0.7 um. In this way, the servo control circuit creates conditions for the micro-cutting of high precision and low surface roughness.