Abstract
The electric discharge machining (EDM) interelectrode gap directly determines the discharge state, which affects the machining efficiency, workpiece surface quality, and the tool wear rate. The measurement of the real-time varying interelectrode gap during machining is extremely difficult, and so obtaining an accurate mathematical model of the dynamic interelectrode gap will make EDM gap control possible. Based on p-type single-crystal silicon EDM, a flat-plate capacitance model is introduced to analyze the time-domain characteristics of the inter-electrode voltage in the breakdown delay phase. Further, we theoretically established a physical model of the interelectrode spacing d and the charging time constant τ of the plate capacitor. The least-squares fitting of the experimental data was used to determine the model coefficients, and in combination with the actual machining process, a minimum-variance self-tuning controller was designed to control the interelectrode gap in real time. The experimental verification results show that the established physical model can correctly predict the interelectrode gap in the actual machining process. The minimum-variance self-tuning controller improves machining stability, and eliminates the occurrence of the short-circuit state.
Highlights
IntroductionSingle-crystal Si is a difficult-to-machine material with high brittleness and high hardness [1,2]
Single-crystal Si is a difficult-to-machine material with high brittleness and high hardness [1,2].Electric discharge machining (EDM) [3,4,5] technology for high-efficiency, the high-quality processing of single-crystal Si has become a research topic of great interest [6,7,8,9]
According to different gaps between the electrode and the workpiece, the electric discharge machining (EDM) discharge state can be divided into five types: The no-load state, normal spark discharge state, transitional arc state, stable arc state, and short-circuit state [4,11]
Summary
Single-crystal Si is a difficult-to-machine material with high brittleness and high hardness [1,2]. According to different gaps between the electrode and the workpiece, the EDM discharge state can be divided into five types: The no-load state, normal spark discharge state, transitional arc state, stable arc state, and short-circuit state [4,11]. The discharge mechanism of EDM is very complex and is often affected by many factors, such as adhesion, cavitation, and short-circuit phenomena [12,13], that make it difficult to detect and control the gap between electrodes. The literature [19,20] has established an EDM stochastic model using the spark frequency as the feedback signal of the discharge gap to adjust the servo feed rate, which can reduce the change of the control process and improve the machining efficiency. We theoretically established the physical model of the interelectrode gap d and the flat-plate capacitor charging time constant τ, and designed a minimum-variance self-tuning controller to control the interelectrode gap
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