Electric heating – Metal heating – Cutting or disintegrating
Reexamination Certificate
1999-11-23
2001-07-31
Evans, Geoffrey S. (Department: 1725)
Electric heating
Metal heating
Cutting or disintegrating
Reexamination Certificate
active
06268580
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to the field of electric discharge machining (EDM), and provides a device for holding a graphite electrode used in an EDM device.
Electric discharge machining (EDM) is a process used for machining steel. An electric arc, extending from a graphite electrode to the steel surface being machined, erodes away the steel by locally liquefying and cooling the steel, in the presence of a dielectric fluid. The key component in this process is the graphite electrode, which must be reliably supported and accurately positioned to provide a precisely machined product. Since the shape of the electrode determines the shape of the cavity formed during the EDM process, it is especially important to position the electrode accurately.
Various methods of holding the graphite electrode have been used in the prior art. It has been known, for example, to provide a holding device which grasps the electrode with a setscrew. Other methods use glue to attach the graphite to an electrode holder. Examples of holders for electrodes used in EDM are shown in U.S. Pat. Nos. 4,713,515 and 4,717,803, the disclosures of which are hereby incorporated by reference.
The electrode holding devices of the prior art generally have the disadvantage that they cannot be easily used with electrodes of widely varying sizes. Since graphite electrodes are relatively expensive, it is common to retain the unconsumed remnants of such electrodes after an EDM job is completed, for later use on another job. But using such remnants is often problematic because of their irregular size. To use a partially-consumed electrode efficiently, it is necessary to position the electrode properly relative to the workpiece.
The present invention provides a device which can conveniently and accurately hold electrodes of various sizes. The invention includes means for automatically maintaining the electrode on a desired center line, regardless of the size or shape of the electrode.
SUMMARY OF THE INVENTION
In one embodiment, the invention includes a pair of jaws mounted on a support. The support is attached to a shank which is intended to be held by an EDM device. One of the jaws is fixed to the support, and the other jaw is movable relative to the first jaw. A screw, which engages a threaded hole in the movable jaw, controls the position of the movable jaw relative to the fixed jaw. An EDM electrode can be inserted between the jaws, and rotation of the screw causes the distance between the jaws to change. The jaws can thereby be clamped around the electrode. Because of the adjustability of the jaws, the device can accommodate electrodes having a variety of thicknesses, limited only by the length of the screw and the size of the support.
In another, and more preferred embodiment, the holder includes a pair of jaws having grooves which mate with a tongue formed on a support. A threaded member, having two distinct threaded sections, is threadedly engaged in holes formed in the jaws. The threads of the two sections have mutually opposite orientations. The threaded member includes a region of reduced diameter, disposed between the threaded sections. The region is defined in part by two opposing walls. A positioning setscrew, held within a threaded hole in the support, is advanced such that the positioning setscrew enters the region of reduced diameter. The positioning setscrew has a non-threaded head whose width substantially fills the space between the walls. Thus, the threaded member is prevented from moving longitudinally when the threaded member is rotated.
Because the threaded member is prevented from moving longitudinally, when the threaded member is rotated, the rotation causes the jaws to move apart or together. Due to the position of the threaded member, the jaws maintain their relative positions relative to the center of the support. Thus, when an electrode is inserted between the jaws, the jaws can be tightened such that they maintain the electrode on center, virtually independently of the size or thickness of the electrode.
In another preferred embodiment, the non-threaded head of the positioning setscrew is eccentric relative to the longitudinal axis of the positioning setscrew. This arrangement allows one to compensate for small positioning errors caused by uncertainty about the exact position at which threaded engagement begins.
The support is rotatably mounted on a shank. The support preferably includes a plurality of tightening setscrews which, when tightened, prevent relative rotation between the support and the shank.
The invention therefore has the primary object of providing a holder for a graphite electrode used in electric discharge machining (EDM).
The invention has the further object of providing an electrode holder which can be used with a variety of electrodes, having many different sizes.
The invention has the further object of providing an electrode holder which automatically maintains the centering of the electrode regardless of the thickness of the electrode.
The invention has the further object of providing an electrode holder which permits the electrode to be easily attached and removed.
The invention has the further object of providing an adjustable holder for an EDM electrode.
The invention has the further object of providing an electrode holder which permits rotation of the workpiece.
The invention has the further object of providing an electrode holder in which an electrode can be precisely positioned.
The invention has the further object of reducing the cost of electric discharge machining, by providing an electrode holder which reduces waste of graphite electrodes.
The invention has the further object of increasing the efficiency of electric discharge machining.
The reader skilled in the art will recognize other objects and advantages of the invention, from a reading of the following brief description of the drawings, the detailed description of the invention, and the appended claims.
REFERENCES:
patent: 2847883 (1958-08-01), Bagby
patent: 3236516 (1966-02-01), Young
patent: 4713515 (1987-12-01), Choi
patent: 4717803 (1988-01-01), Alexandersson
patent: 4958818 (1990-09-01), Buchter
patent: 5219376 (1993-06-01), Vinohradsky
patent: 5248867 (1993-09-01), Ohba et al.
patent: 8-66831 (1996-03-01), None
Eilberg William H.
Evans Geoffrey S.
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