Electric heating – Metal heating – Cutting or disintegrating
Patent
1980-11-22
1983-07-05
Paschall, M. H.
Electric heating
Metal heating
Cutting or disintegrating
219 69G, 219 69C, B23P 108
Patent
active
043920411
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
BACKGROUND OF THE INVENTION
This invention relates to electric discharge machining apparatuses with a wire-shaped electrode for machining a workpiece by the use of electric discharge, and more particularly to a control device for use in the electric discharge machining apparatus, which is capable of optionally controlling machining electrical conditions according to variations in thickness of the workpiece and to the quality thereof.
In an electric discharge machining apparatus of this type, a metal wire about 0.05 to 0.3 mm in diameter is employed as its one electrode. Electrical discharge is caused between the electrode and a workpiece to be machined to melt the corresponding portion of the workpiece. The electrode is displaced relative to the workpiece in the X-Y plane to thereby electrically cut or cut a way the workpiece in a desired configuration. In this case, in general, the electrical discharge is carried out with a constant speed feed of 1 pulse/.mu.m; that is, the discharge is effected at a constant voltage in the machining gap without controlling the discharge energy.
This constant speed feed method can satisfactorily machine a workpiece if the workpiece is constant in thickness. However, in machining a workpiece which is variable in thickness, initially it is necessary to set the machining feed speed to a value for the maximum thickness (that is, the maximum machining area) of the workpiece, so that no short-circuiting occurs and the wire-shaped electrode may not be broken. Accordingly, in the constant speed feed method, the machining feed speed is relatively low. Thus, even in machining a portion of the workpiece which is smaller in thickness than the other portions, the machining feed speed is still maintained low. Therefore, the constant speed feed method is considerably low in machining efficiency. On the other hand, it is well known in the art that even if a workpiece is constant in thickness, in order to shape a workpiece to a configuration having an angular corner it is preferable to increase the machining feed speed or to decrease the discharge energy. Because the workpiece is machined sharply, i.e., the resultant corner is not round. Thus, the constant speed feed method in which the discharge energy is maintained unchanged still involves problems to be solved.
An electrical discharge machining apparatus has been proposed in the art in order to eliminate the above-described difficulties accompanying the constant speed machining method. In the conventional apparatus, a voltage across a machining gap, i.e., a machining voltage, is detected and a machining feed speed is controlled so that the voltage thus detected is constant. The arrangement and operation of the conventional apparatus will be described with reference to FIG. 1.
A machining electric source (3) supplies a machining current to a wire electrode (1) and a workpiece (2) to be machined. The average value Eg of the machining voltage and a reference voltage Eo are applied to an error voltage amplifier (4), which determines a machining feed speed F proportional to an error voltage which is the difference value between the machining voltage Eg and the reference voltage Eo. The machining feed speed F thus determined is distributed as an X-axis component Fx and a Y-axis component Fy by a speed distributor (5), which are adapted to drive an X-axis motor (6) and a Y-axis motor (7), respectively. In this connection, the following relation is established between the machining feed speed F provided by the amplifier (4) and the outputs Fx and Fy of the speed distributor (5):
In the above-described arrangement, when the gap between the wire-shaped electrode (1) and the workpiece (2) becomes smaller and accordingly the machining voltage Eg becomes lower than the reference voltage Eo, the machining feed speed F is reduced and the gap is widened so that the machining voltage Eg approaches the reference voltage Eo. In contrast, when the machining voltage Eg becomes higher than the reference voltage Eo, the machining feed speed F
REFERENCES:
patent: 4052583 (1977-10-01), Inoue
patent: 4057703 (1977-11-01), Pfau
patent: 4078163 (1978-03-01), Bell, Jr. et al.
Tanaka Yutaka
Yatomi Takeshi
Mitsubishi Denki & Kabushiki Kaisha
Paschall M. H.
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