Electric heating – Metal heating – Cutting or disintegrating
Patent
1982-08-26
1985-02-12
Paschall, M. H.
Electric heating
Metal heating
Cutting or disintegrating
219 69M, B23P 108
Patent
active
044993595
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a shape compensating method used in wire-cut electric discharge machining, and more particularly to a shape compensating method which can automatically correct a machining error based on the flexure of a wire electrode due to electric discharge.
A wire-cut electric discharge machine is such that a predetermined gap is maintained between a wire electrode and a workpiece, while a voltage is applied therebetween to cause a spark discharge across the gap, whereby the workpiece is cut by the discharge energy. Accordingly, when the workpiece is moved relative to the wire on the basis of machining command data, it can be machined into a desired shape. In the wire-cut electric discharge machine, however, when the wire electrode advances in a groove in the workpiece in a predetermined direction while cutting the workpiece, a pressure attributed to the electric discharge develops between the wire electrode and the workpiece, with the result that the wire electrode is pushed back in the direction opposite to the advancing direction. Therefore, the wire electrode lies behind the position of wire guides used therewith. That is, the wire electrode flexes. When performing the electric discharge machining of a straight line, the flexure is not a serious problem. In contrast, in a case where the advancing direction of the workpiece has been changed into the orthogonal direction on the basis of a machining command in order to machine a corner, the discharging part of the wire electrode is dragged inward on account of the flexure of the wire electrode due to the electric discharge, and unlike the commanded shape, the machining path of the groove deviates on the inner side considerably, so that the machined shape becomes blunt. Also when performing a machining operation to create a circular arc, a similar error develops. This necessitates a countermeasure in which the flexure value of the wire electrode is measured in advance, and when machining the corner, the workpiece is moved to a somewhat greater extent in correspondence with the flexure value. In the prior art, however, no appropriate control technique for compensating and controlling these errors has been established.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a shape compensating method in wire-cut electric discharge machining which can correct the path of a wire electrode by determining flexure value, thereby reducing machining errors. To accomplish this object, the extent of flexure the wire electrode of an electric discharge machine has at a certain feed speed and under a specified machining groove width and wire diameter, is calculated by an NC (numerical control) in advance, and the path of the wire electrode is corrected by the use of the resulting flexure values D.sub.T and D.sub.R in a tangential direction, respectively and radial direction (D.sub.R =0 for rectilinear motion). More specifically, the correlation equations between the original coordinate positions (x.sub.i, y.sub.i) of the wire electrode and the corrected coordinate positions (X.sub.i, Y.sub.i) thereof are obtained beforehand, and the corrected coordinate positions are successively calculated by the use of the known flexure values. Accordingly, letting (X.sub.i-1, Y.sub.i-1) denote a corrected position a short time ago (this position being known) and (X.sub.i, Y.sub.i) denote the next corrected position calculated, movement values .DELTA.X and .DELTA.Y are obtained as follows: pulse distributions are executed to rotate motors, whereby the flexure values in a straight machining operation and a circular arc machining operation are compensated.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an explanatory view of wire-cut electric discharge machining;
FIG. 2 is a view for elucidating the flexure of a wire electrode;
FIGS. 3 and 4 are explanatory views for elucidating machining errors caused by the flexure; FIGS. 5, 6, 7 and 8 are explanatory diagrams for calculating flexure values in a tangential direction and a radial direction;
FI
REFERENCES:
patent: 4081652 (1978-03-01), Janicke et al.
patent: 4314133 (1982-02-01), Pfau et al.
AGIE, "Force Effects in ED-Cutting", pp. 1-8, 5/31/76, vol. 118, #1.
Fanuc Ltd
Paschall M. H.
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