Electric heating – Metal heating – Cutting or disintegrating
Reexamination Certificate
1999-11-30
2001-11-20
Evans, Geoffrey S. (Department: 1725)
Electric heating
Metal heating
Cutting or disintegrating
Reexamination Certificate
active
06320151
ABSTRACT:
FIELD OF THE INVENTION
The invention concerns a method and apparatus for the most precise possible electrical discharge machining (EDM) of a workpiece by means of a wire electrode.
The purpose of the invention is to improve known electrical discharge machining methods with short pulses and low current intensities, so that very precise machining is made possible, in addition to high surface quality.
BACKGROUND OF THE INVENTION
Cavity-sinking or wire electric discharge machining is now already state-of-the-art with excellent surface quality of R
a
less than 0.1 &mgr;m and a material effect on the surface with a depth of less than 1 &mgr;m. Such machining requires generators that produce monopolar or bipolar pulses in the megahertz range with current intensities of a few amperes, in which the electrostatic forces F
E
and the erosion forces F
P
(plasma forces) during machining are of the same order of magnitude.
It is known that during electrical discharge machining the electrical resistance of the spark gap can be determined by means of a measurement current source during additionally generated periodic pauses between pulse groups and the servo drive, rinsing device and generator controlled with it (CH 650 433). This method has the task of determining the degree of contamination and discharge concentrations from the electrical resistance during cavity-sinking, and controlling the process with these values so that higher removal performance is achieved during unsupervised operation.
OBJECTS OF THE INVENTION
The task of the invention is to improve electrical discharge machining, and especially fine electrical discharge machining, so that the highest possible shape trueness can be achieved on the workpiece. During final cutting with wire electrodes, shape tolerances, corner errors and vertical profiles of better than 1 &mgr;m are to be achieved. During full cutting with fine wires in the range from 100 &mgr;m to 10 &mgr;m diameter, a significantly better shape tolerance is to be achieved, despite higher removal performance.
The advantages of the invention consist especially of the fact that each excursion of the wire electrode from the rest position is determined as accurately as possible and can be controlled. The erosion process thus becomes controllable in the micrometer range.
Another advantage is that the process values, i.e., the entirety of all adjustment parameters for a specific operation, can be determined in a much shorter time, since numerous interdependencies no longer need be considered.
Moreover, the additional investment in comparison with the benefit is limited, and it is even possible to retrofit already existing installations according to this concept.
Other advantages of the embodiment of the invention follow from the subsequent description of preferred practical examples.
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Angelella Stefano
D'Amario Rino
AGIE SA
Evans Geoffrey S.
Marshall Gerstein & Borun
LandOfFree
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