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TECHNICAL BRIEFS

Automatic Stripping of Dielectric-Encased Wire Tool Electrode Used in Electrical Discharge Machining

[+] Author and Article Information
Seiji Kumagai1

Department of Machine Intelligence and Systems Engineering, Akita Prefectural University, Tsuchiya-aza-ebinokuchi 84-4, Yurihonjo 015-0055, Akita Prefecture, Japan

Naoki Sato, Koichi Takeda

Department of Machine Intelligence and Systems Engineering, Akita Prefectural University, Tsuchiya-aza-ebinokuchi 84-4, Yurihonjo 015-0055, Akita Prefecture, Japan

1

Corresponding author. E-mail: kumagai@akita-pu.ac.jp

J. Manuf. Sci. Eng 129(5), 973-978 (Feb 02, 2007) (6 pages) doi:10.1115/1.2738541 History: Received June 21, 2006; Revised February 02, 2007

A new electrical discharge machining (EDM) system using a wire encased in a dielectric jacket is proposed as an alternative to conventional hole-fabrication EDM systems. The jacket suppresses secondary discharges occurring between the sidewalls of the wire and the fabricated hole, which allows fabrication of holes with higher aspect ratios compared to those formed by a conventional EDM system using naked pipe electrodes. In this new system, the tip of the wire electrode is stripped by displacing the jacket, which produces continuous sparks for workpiece erosion and keeps the bore and shape of the fabricated holes constant. In the present study, we developed a control system to maintain the exposed length of the tip without the need for visual observation and without the assumption that wear is constant over time. The exposed length of the tip of the wire electrode is related to the feed speed (toward the workpiece) of the electrode system. The jacket was displaced when the feed speed of the electrode system exceeded a threshold value, which resulted in slowing of the electrode system feed. The feed speed was kept within the specified range by determining a threshold value, which led to maintenance of a constant exposed length of the tip. This control system was validated in actual drilling tests. Optimizing the threshold feed speed contributed to a higher machining speed.

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Copyright © 2007 by American Society of Mechanical Engineers
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Figures

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Figure 1

Machining example of the new EDM system for fabrication of a deep, narrow hole with an aspect ratio >300. The workpiece is an AISI1045 rod with a diameter of 22mm.

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Figure 2

Diagram of the concept of the EDM system using a dielectric-encased wire electrode

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Figure 3

Several drilling aspects at different exposed lengths of the wire (Lt)

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Figure 4

Bottom of a hole allowing deposition of insulating rust, leading to suspension of drilling

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Figure 5

Typical cross section of a hole fabricated in 20mm thick AISI1050 carbon steel: (a) inlet, (b) depth of 0.8mm, and (c) depth of 1.6mm

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Figure 6

Machining speed and wire wear rate under visual control of the tip and under automatic control in terms of the feed speed of the electrode system. Tap water (conductivity 80μS∕cm) is used as the working fluid and the capacitance is not connected to the gap in parallel. The diameter of the fabricated hole is 0.75–0.80mm.

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Figure 9

Typical feed behavior and feed speed of the electrode system in the present EDM system employing saline as the electrolytic working fluid (conductivity 250μS∕cm) and capacitance of 7.8μF at different values of Vth (0.030mm∕s, 0.060mm∕s, and 0.100mm∕s). Other conditions are as described in the caption to Fig. 8.

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Figure 10

Cumulative counts of spark current pulses during drilling tests employing saline as the electrolytic working fluid (conductivity 250μS∕cm) and capacitance of 7.8μF at different values of Vth

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Figure 8

Machining speed and wire wear rate under automatic control in terms of the feed speed of the electrode system. The working fluid is saline (conductivity 250μS∕cm). Capacitance of 7.8μF is connected to the gap in parallel. The diameter of the fabricated hole is 0.85–0.95mm.

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Figure 7

Typical feed behavior and feed speed of the electrode system at Vth=0.015mm∕s and 0.030mm∕s. Other conditions are as presented in the caption to Fig. 6.

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