Improvement of Wire Electrical Discharge Machining Characteristics in Machining Boron-doped Polycrystalline Diamond Using a Novel Iso-pulse Generator
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This study aims to present a novel iso-pulse generator for improving machining characteristics of boron-doped polycrystalline composite diamond (BD-PCD) by wire electrical discharge machining (wire-EDM). The transistor-controlled pulse generator composed of a high-power source circuit, a low-power source circuit, a snubber circuit and a complex programmable logic device based pulse control circuit was devised to provide a high open voltage during the ignition period and a low peak current with a fixed discharge duration for sparking as well as identify gap states as normal sparks and abnormal sparks based on the duration of ignition delay time. Pulse on-time and pulse interval of each spark are regulated in real-time to achieve the stability of machining operation while preventing wire electrode from breaking according to the identified gap state. Compared to a conventional iso-frequency pulse generator, the developed iso-pulse generator can provide smaller variation of peak current and discharge duration and thus, the latter can enable the wire-EDM process to produce smaller surface damages and better surface quality than the former. Experimental results not only verify the iso-pulse generator can achieve a fine surface finish as low as Ra 0.247 μm on machined surface of BD-PCD through one rough and one finish machining operation, they also demonstrate that the developed system can enable a table-top wire-EDM machine to successfully sharpen the cutting edge of BD-PCD end milling tools.
KeywordsWire-EDM Boron-doped polycrystalline composite diamond Pulse generator Surface finish
List of Symbols
- M1, M2, M3
Metal-oxide semiconductor field-effect transistor (MOSFET)
- P1, P2, P3
Pulse control signal of MOSFET
Threshold pulse signal
Ignition delay time
Pulse duration of high-power source
A threshold period of 1 μs
Spark generating signal
This research was supported by the Ministry of Science and Technology, Taiwan under Grant No. :MOST 104-2221-E-167 -035 -MY2.
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