| Summary: | 碩士 === 華梵大學 === 機電工程學系博碩專班 === 100 === This paper presents a novel pulse generator for cutting of polycrystalline diamond (PCD) by micro wire-EDM. Three pulse control methods (AC power supply pulse control method, fixed pulse width modulation pulse control method and improved AC power supply pulse control method) have been proposed to achieve high frequency and low energy discharge pulses. The improved AC power supply pulse control method enables the pulse generator to provide a period of 10 μs off duty cycle followed by a period of duty cycle for reionization of the dielectric in the spark. Compared to the other two methods, the improved AC method can provide smaller peak current and discharge duration and thereby achieving smaller slit width, thermal damaged layer and better surface finish. A series of experiments were carried out to investigate the effect of open voltage on machining performance. An increase of open voltage increases peak current, thus producing greater discharge energy and therefore, contributing to improvements in machining feedrate, but leading to a larger slit width and thermal damaged layer, worse surface finish and surface quality. Finally, the developed pulse generator using anti-electrolysis circuitry and digital signal processor based pulse control circuit has been successfully integrated into a prototype micro wire-EDM machine developed by a local machine tool builder. Experimental results not only demonstrate that the developed pulse generator can achieve a feedrate of 1.5 mm/min, a surface finish of 0.7 μm Ra and a damaged layer of 25 μm on PCD surface, which fills all requirements for the fabrication of PCD wheels, they also have verified the applicability of this new technique in micro wire-EDM.
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