Electric heating – Metal heating – Cutting or disintegrating
Patent
1984-05-22
1986-09-30
Albritton, Clarence L.
Electric heating
Metal heating
Cutting or disintegrating
219 69P, 219 69S, B23H 102
Patent
active
046148540
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to an electric discharge machining control circuit in a wire cut electric discharge machine for performing electric discharge machining using a wire electrode. The electric discharge machining control circuit has a specific circuit for controlling a second cut after a first cut.
In a wire cut electric discharge machine, a predetermined voltage is applied to a gap formed between a wire electrode and a workpiece so as to cause a discharge between the wire electrode and the workpiece, thereby cutting the workpiece by a small amount each time via the discharge energy. Conventionally, after the first cut has been performed, the second cut is performed to correct the shape of the workpiece, smooth any rough surface, and remove any irregularities caused by machining during the first cut. In order to smooth a roughened surface, a low discharge energy is preferably used. When a low discharge energy is used, the shape of the workpiece can be easily corrected. However, when a thick workpiece is machined with low discharge energy, a machined wall surface of the workpiece is curved, thereby resulting in a loss of linearity. For example, when a workpiece having a thickness of 60 mm is subjected to the second cut, an internal portion is removed by 20 to 30 .mu.m from the edge of the machined wall surface, thereby often resulting in a loss of linearity of the cut surface.
When the discharge energy is increased, the linearity of the cut surface can be improved. However, the wire vibrates due to a discharge pressure and moves away from from the machined wall surface. As a result, sufficient shape corection cannot be performed.
For this reason, extensive studies and experiments have been made on the second cut process. It was found that the above drawback could be eliminated by decreasing an average machining voltage during the second cut operation.
SUMMARY OF THE INVENTION
It is a first object of the present invention to provide an electric discharge machining control circuit for a wire cut electric discharge machine, wherein an average applied voltage during machining is decreased so as to easily perform shape correction, smooth roughened surfaces, and removal of any irregularities, thereby allowing a second cut to be performed with highly precise linearity.
It is a second object of the present invention to provide an electric discharge machining control circuit for a wire cut electric discharge machine which can stabilize dscharge machining during the second cut.
In order to achieve the above objects of the present invention, there is provided an electric discharge machining control circuit having a pulse oscillation control circuit for generating a pulse, stream an electric discharge machining circuit which charges a capacitor through a switching element which is turned on/off in response to the pulses from said pulse oscillation control circuit, and discharges a charge current between a wire electrode and a workpiece; and a short-circuit detector for detecting machining voltage between said wire electrode and for the workpiece and comparing the machining voltage with a reference voltage to detect a short circuit between the wire electrode and the workpiece, so that a numerical control device causes said pulse oscillator control circuit to stop generating the pulse stream when said short-circuit detector produces a short-circuit detection signal, wherein the electric discharge machining control circuit further comprises a reference voltage switching circuit for decreasing the reference voltage applied to the short-circuit detector when a second cut instruction signal is generated, thereby decreasing the average machining voltage used to perform a second of the workpiece.
According to the present invention there is also provided an interval signal blocking circuit for generating a second cut instruction signal and to block an interval signal generated from an interval signal oscillator, thus stopping generation of the pulse stream at predetermined intervals whe
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Izumiya Shunzo
Obara Haruki
Albritton Clarence L.
Evans Geoffrey S.
Fanuc Ltd
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