Electric heating – Metal heating – Cutting or disintegrating
Patent
1990-12-10
1992-12-15
Evans, Geoffrey S.
Electric heating
Metal heating
Cutting or disintegrating
219 6918, B23H 102
Patent
active
051719576
DESCRIPTION:
BRIEF SUMMARY
CROSS REFERENCE TO RELATED APPLICATIONS
This application is a National Phase application of PCT/CH90/00142 filed Jun. 6, 1990 and based up on EP 89 110458.0 filed Jun. 9, 1989 under the International Convention.
FIELD OF THE INVENTION
The present invention relates to generator for electric discharge machining of metallic workpieces by means of an electrode of liquid or metallic material, whereby electrode and workpiece are separated from one another for a working gap, which generator contains a principal circuit for the generation and transmission of impulses to electrode and workpiece.
BACKGROUND OF THE INVENTION
In EDM (electric discharge machining) technology, various pulse generators are used depending on the task at hand. For EDM cutting, deionized water is primary used as dielectric because of its good properties, in particular in view of the good material removal properties as to the workpiece. For the attainment of maximum material removal, the pulse generator must have certain properties.
Known pulse generators exhibit, when deionized water is used as the dielectric in the working gap, the disadvantage that the potential maximum material removal per unit of discharge energy cannot be attained because the duration of the pulse cannot be made substantially shorter than 1 microsecond, and the decay curve of the current pulse cannot be made sufficiently steep. This is due to the fact that the electrical output elements used in the principal circuit of the pulse generator for current limitation and current control cannot follow the requisite short pulse duration and steep decay curve.
A pulse generator for wire EDM which can furnish short pulses of one microsecond and high currents of several hundred amperes is described in German patent No. 2,735,403. A further shortening of the pulses and a further increase in the steepness of the decay curve is not possible resistances because of the stray inductivity of the output. Furthermore, this pulse generator exhibits, because of the output resistance, an economically unacceptable loss of efficiency.
To avoid these disadvantages, a pulse generator is described in the European Pat. No. 160,989 which has a good efficiency, because it exhibits inductivity in the principal circuit in place of the output resistance. For this reason, neither the desired short pulse duration nor the steep decay curve can be improved with this generator to the extent that the pulse duration lies at 0.1 microsecond and the decay curve of the current pulses lies at over 1000 amperes per microsecond. This derives from the fact that the working current must flow via at least five switching elements.
OBJECTS OF THE INVENTION
It is the object of the invention to avoid the disadvantages of the known pulse generators, particularly for EDM cutting and, furthermore, to assure that a pulse duration down to 100 nanoseconds and an incline of the delay curve to several 1000 amperes per microsecond can be achieved, thereby increasing the material removal per unit of discharge energy, increased.
It is a further object of the invention to provide a pulse generator whereby the fast interruption of the current, eliminates deleterious effects of short circuit pulses and arcing on the surfaces of the workpiece and electrode.
As is known, the spark erosive discharges follow statistical laws. The working pulses, idling impulses, short circuit pulses the degenerate pulses (e.g. arcs) are distributed statistically. Their sequence is uncorrelated. It is known that the short circuit and degenerate pulses cause deterioration of the surface of the workpiece and are greatest cause of wear of the electrode. For a wire electrode, this means that a high wire velocity must be used with the danger of wire breakage.
SUMMARY OF THE INVENTION
These objects are attained by a pulse generator subscribing to the following conditions:
the principal circuit does not contain passive output elements, but only at least two fast electronic switches and diodes in at least equal number;
a sensing element which is alloca
REFERENCES:
patent: 4267423 (1981-05-01), Bell, Jr. et al.
patent: 4361745 (1982-11-01), Rupert et al.
patent: 4614854 (1986-09-01), Obara et al.
patent: 4678885 (1987-07-01), Dresti et al.
patent: 4800248 (1989-01-01), Futamura et al.
High Speed Pulse Discrimination for Real-Time EDM Analysis-D. Dauw et al, Belgium, no publication date.
Dubno Herbert
Evans Geoffrey S.
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