Abstract
In the electric discharge machining system, the determination of the gap between the anode and the cathode is a difficult point of this kind of machining approach. An accurate mathematical model of interelectrode gap is obtained, and the precise control of the gap is achieved on this basis. In this paper, based on the example of discharge machining of P-type single crystal Si, the theoretical analysis proved that the discharge channel can be equivalent to pure resistance, and the physical model of the interelectrode gap and voltage and current was established. The order and parameters of the EDM system model were determined by adopting the system identification theory. We designed the minimum variance self-correcting controller to accurately control the interelectrode gap in combination with the actual machining process. Experimental results show that the interelectrode gap model can correctly reflect the interelectrode gap in the actual machining process; the minimum variance self-correcting controller eliminates the short circuit phenomenon during processing and can stably track different desired gaps; the material removal rate and the surface roughness decrease with the increase of the interelectrode gap.
Highlights
Single crystal Si is the most widely used semiconductor material [1, 2], when adopting conventional machining methods; it has low efficiency and poor surface quality, but it is easy to collapse
Dauw and Wong et al [20,21,22] used the voltage threshold method to detect the electrode gap; this method is simple, it requires a large number of tests and the thresholds for stable and transitional arc discharges are difficult to determine, and the determined voltage threshold has no universality; for different processing conditions, the corresponding threshold voltage should be determined according to the specific situation
Bhattacharyya et al [24] adopted the Mathematical Problems in Engineering radio frequency signal (RFS) detection method to monitor the gap distance according to different discharge gap RFS characteristics corresponding to different gap discharge state
Summary
Single crystal Si is the most widely used semiconductor material [1, 2], when adopting conventional machining methods; it has low efficiency and poor surface quality, but it is easy to collapse. E discharge mechanism of EDM is rather complex and is often affected by many factors such as adhesion, cavitation, and short-circuit phenomena [15, 16], which brings considerable difficulties to detection and control. Since discharge conditions such as no-load, transitional arc, stable arc, and short circuit [3, 4, 17] seriously affect processing efficiency and surface quality, the EDM equipment is required to have a perfect interelectrode gap detection and control system. To solve the above problem, the EDM of P-type single crystal Si is used as an example to establish the EDM interelectrode gap equivalent resistance model; the order and parameters of the model are determined by system identification theory. e minimum variance self-correction controller is designed to accurately control the interelectrode gap and verified by actual machining
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