Electric heating – Metal heating – Cutting or disintegrating
Patent
1997-07-28
1998-12-22
Evans, Geoffrey S.
Electric heating
Metal heating
Cutting or disintegrating
B23H 710
Patent
active
058522697
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a wire cut electrical discharge machining method and device for machining of a workpiece by electrical discharges using a wire-shaped tool electrode. In particular, the present invention relates to a method and device for measuring a contact position by causing a wire electrode to contact a workpiece and for detecting the resulting electrical contact.
BACKGROUND OF THE INVENTION
A wire cut electrical discharge machining device is known which forms a desired profile in a workpiece in a manner analogous to a band saw, but which operates by generating electrical discharges between a wire-shaped tool electrode which travels between a pair of wire guides and the workpiece to be machined. This wire cut electrical discharge machining device is appropriate for precision forming of a desired profile in the workpiece to be machined.
Before electrical discharge machining, the workpiece and the wire electrode are mounted in the machine. Generally, the workpiece is affixed to a work stand placed on an XY table in such a way that its top surface can be oriented parallel to the XY plane. The wire electrode is oriented to travel in a direction perpendicular to the XY plane by means of a pair of wire guides. The position of the workpiece reference surface with respect to the wire electrode is then determined. In many cases, this reference surface is assigned to be a polished side of the workpiece which is parallel to the wire electrode axis. In general, the wire electrode is brought into contact with the workpiece reference surface while a voltage is applied between the workpiece and the wire electrode, which is oriented perpendicular to the XY plane, and the contact position is measured by detection of their electrical contact. The applied voltage may be an AC or a DC voltage of from several volts to several 10 s of volts.
A conventional device for measuring the position of the contact point in a wire cut electrical discharge machining device will now be explained, with reference to FIG. 14.
A workpiece W is affixed to the top surface of work stand 4, which is provided on XY table 2, and is capable of moving in the mutually orthogonal X and Y directions. A wire supply device 8 is provided which provides wire electrode 6 from a bobbin 9 along a specified transport path to an appropriate recovery bucket 16. The wire supply device 8 includes a pair of rollers 10 and 12, which are provided in the vicinity of the recovery bucket 16, and which pull the wire electrode 6. In addition, the wire supply device 8 includes multiple pulleys and a tensioning device which impart a specified tension to the wire electrode 6. In the illustrated wire cut electrical discharge machining device, after the wire electrode 6 is unwound from the bobbin 9 it passes through a guide pulley 14 and is fed to a tension applying device 22 which includes a pulley 16', a powder brake 18, and a pinch roller 20. In addition, the wire electrode passes through a guide pulley 21, a pair of wire guides 24 and 26 respectively arrayed above and below a workpiece W, a guide pulley 23, and a pair of rollers 10 and 12, and is fed to the recovery bucket 16.
A feeder 28, which provides a current for the wire electrode 6, is placed in contact with the wire electrode 6 between the guide pulley 21 and an upper wire guide 24. The feeder 28 is connected to the voltage supply section 30 which applies a voltage to the "gap" formed between the wire electrode 6 and the workpiece W, and to the contact detection section 32, which detects contact between the wire electrode 6 and the workpiece W. The voltage supply section 30 and contact detection section 32 are respectively connected to the upper portion of an electrically conductive work stand 4. The contact detection section 32 detection signal is supplied to an NC device 33, which includes a microcomputer. That NC device 33 controls the entire wire cut electrical discharge machining system. Application of a voltage from the voltage supply section 30 to the gap is also c
REFERENCES:
patent: 5003147 (1991-03-01), Kawanabe et al.
patent: 5170026 (1992-12-01), Suga et al.
patent: 5254826 (1993-10-01), Kimura et al.
patent: 5744775 (1998-04-01), Yasuda et al.
Kaneko Yuji
Toyonaga Tatsuo
Evans Geoffrey S.
Sodick Co. Ltd.
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