Electric heating – Metal heating – Cutting or disintegrating
Patent
1996-03-26
1998-05-26
Evans, Geoffrey S.
Electric heating
Metal heating
Cutting or disintegrating
B23H 100, B23H 706
Patent
active
057569541
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a method of machining a corner portion of a workpiece by a wire electric discharge machine.
BACKGROUND ART
A wire electric discharge machining is performed by applying a pulse voltage between a wire electrode with a predetermined tension and a workpiece so that a discharge is generated in a gap between the wire electrode and the workpiece, and in the machining a pressure such as discharge pressure is produced between the wire electrode and the workpiece to cause a warp of the wire electrode. The warp of the wire is not so serious a problem in machining a straight portion. However, in machining a corner portion the warp of the wire electrode lowers a machining accuracy.
There are known methods for preventing the machining accuracy of the corner portion from lowering, which are exemplified by the disclosure in Japanese Patent Publications (Kokoku) Nos. 56-20133 and 56-16007. According to the methods, the machining feed is interrupted or a machining condition such as the feed speed is changed at a position of changing the feed direction to reduce the warp of the wire electrode and thereby improve the machining accuracy of the corner portion. In the above methods, however, as control such as interrupting the machining feed is executed at the time when a machining point reaches the feed direction changing position. This means that the machining is performed without correcting the warp of the wire electrode until the machining point reaches the feed direction changing position, thereby causing a problem of lowering the machining accuracy in a section until the machining point arrives at the feed direction changing position.
Japanese Patent Publication (Kokoku) No. 63-25891 discloses a method of actually measuring a warp of the wire electrode by means of a sensor to correct a machining path. According to this method, the warp of wire electrode is corrected to some degree; however, perfect correction is not possible because the wire warp rates in the vicinities of upper and lower wire guides differ from that in the intermediate position between the upper and lower wire guides. Moreover, there arises a problem such that a sensor for measuring the warp of wire electrode must be arranged in a discharge machining section.
DISCLOSURE OF THE INVENTION
An object of the present invention is to provide a wire electric discharge machining method which is capable of improving a machining accuracy in a corner portion.
The wire electric discharge machining method of the present invention comprises the steps of: reducing a machining feed speed from a first machining feed speed to a second machining speed in a section from a point preceding a machining starting point of the corner portion by a first predetermined distance to the machining starting point of the corner portion; increasing an off-state time of the pulse voltage from a first off-state time to a second off-state time in a section from a point preceding the machining starting point of said corner portion by a second predetermined distance to the machining starting point of the corner portion; maintaining the machining feed speed at the second machining feed speed and the off-state time of the pulse voltage at the second off-state time during the corner portion machining; and restoring the machining feed speed to the first machining feed speed and the off-state time of the pulse voltage to the first off-state time after completing the corner portion machining.
Moreover, the flow rate of the machining fluid is reduced by a predetermined rate during the corner portion machining so as to prevent the warp of the wire electrode. In addition, the off-state time of pulse voltage during the corner portion machining is determined in dependence upon a thickness of the workpiece, and the machining feed speed in the corner portion is automatically determined in accordance with a curvature of the corner portion and the off-state time in the corner portion.
The reduction of machining feed speed is started from a point preceding
REFERENCES:
patent: 4081652 (1978-03-01), Janicke et al.
patent: 4292491 (1981-09-01), Tanaka et al.
patent: 4581513 (1986-04-01), Obara et al.
patent: 5410117 (1995-04-01), Reynier et al.
patent: 5504294 (1996-04-01), Izumiya et al.
Ito Masaya
Kamiguchi Masao
Ogata Toshiyuki
Evans Geoffrey S.
Fanuc Ltd.
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