Research on micro-EDM with an auxiliary electrode to suppress stray-current corrosion on C17200 beryllium copper alloy in deionized water
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Beryllium copper alloys known as high-reliability engineered materials are widely used in many engineering fields. Micro-electrical discharge machining (micro-EDM) provides a safely and effectively machining process to machine beryllium copper alloys regardless of their toxicity and mechanical strength. During micro-EDM, the higher material removal rate and the lower electrode wear rate are observed when deionized water is used as a dielectric fluid. However, there are many stray-current corrosion pits on the end surface of holes which directly affect the performance and life span of parts. In this study, the method of auxiliary electrode was used to suppress the effects of stray-current corrosion on the end surfaces of holes on C17200 beryllium copper alloy. The end surfaces of holes were protected by sacrificing the auxiliary electrode. The feasibility of micro-EDM with an auxiliary electrode was verified by an experiment of a hole machined with half coved by the auxiliary electrode and the others without. The effects of the thickness of the auxiliary electrode on end surface quality and machining time were studied. The effects of the auxiliary electrode to suppress stray-current corrosion on C17200 beryllium copper alloy were proved under diffident pulse currents and pulse widths. Machining time and electrode wear were investigated. The results show that the electrode wear is scarcely affected by the auxiliary electrode. However, the machining time is slightly increased when the pulse current is lower than 0.55 A, and the pulse width is shorter than 20 μs. Beyond that level, the effect of the auxiliary electrode on machining time is not obvious. The end surface quality decreases when the pulse width is longer than 20 μs. In addition, the results also show that, when the thickness of the auxiliary electrode is 60 μm, a value of 0.34 A pulse current and 20 μs pulse width could be considered as ideal parameters for C17200 beryllium copper alloy machined by micro-EDM with an auxiliary electrode in deionized water. Furthermore, it is confirmed that the auxiliary electrode can be easily fixed on different radii of curvature surface and effectively protect the end surface of micro-holes from stray-current corrosion.
KeywordsMicro-EDM Auxiliary electrode Stray-current corrosion Hole Beryllium copper Deionized water
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