# Patent

## Title
Wire chopper module for EDM system

## Abstract

A wire chopper module for processing spent electrode emerging from an EDM system employs replaceable inserts that are also movable relative to the feed path of the electrode. Shifting the position of the inserts relative to the feed path of the electrode allows more than one portion of each cutting edge on the insert to be used. Each insert has more than one cutting edge and can be rotated and re-inserted to present a completely new cutting edge. Removable multi-edge inserts that are repositionable relative to the feed path of the spent electrode permit renewal of the cutting edges of the wire chopper module with increased frequency and reduced cost. The wire chopper module also incorporates a flywheel to increase the moment of inertia of the rotating cutting inserts as an aid in overcoming jams. Sharp cutting edges and increased rotational momentum improve the reliability of the inventive wire chopper module.

## Background
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention generally relates to the processing of used electrode discharged from an electrical discharge machining (EDM) system and more particularly to a wire chopper module for shearing used electrode wire into many small pieces which accumulate in a relatively dense pile.
2. Description of the Related Art
The process of electrical discharge machining (EDM) is well known. An electrical potential (voltage) is established between a continuously moving EDM electrode and an electrically conductive workpiece. The potential is raised to a level at which a discharge is created between the EDM electrode and the workpiece. The intense heat generated by the discharge will melt and/or vaporize a portion of both the workpiece and the electrode to thereby remove, in a very small increment, a piece of the workpiece. By generating a large number of such discharges, a large number of increments are removed from the workpiece whereby the workpiece can be cut very precisely to have a desired planar contour. A dielectric fluid is used to establish the necessary electrical conditions to initiate the discharge and to flush debris from the active machining area.
The EDM process erodes the wire electrode as well as the workpiece. Therefore, EDM systems continuously renew the wire electrode from a coil. Spent electrode wire has previously been allowed to accumulate in a reservoir below the EDM system. This approach proved unacceptable because the wire has a tendency for expansion in the reservoir. This necessitates frequent intervention by the operator because the wire forms entanglements, which rapidly fill the space available in the reservoir. It is known to crimp the electrode wire by making it pass between two toothed wheels or also to cut it into small pieces which possess the capability of accumulating in a relatively dense pile. A device for cutting the wire into pieces is described in U.S. Pat. No. 4,016,395.
A continuing problem with prior art wire-chopping devices is the rapid wear of the tool edges used to section the wire. EDM wire is typically comprised of tough metal alloys to give it the requisite tensile strength. Chopping this wire results in high wear to cutting surfaces. If cutting surfaces wear to the extent that the wire is no longer chopped cleanly, the wire-chopping device can jam resulting in a machine shutdown.
Reliable processing of spent EDM electrode is essential to reliable operation of EDM equipment, for example, at night or over a weekend. EDM systems frequently require a large capital investment, which motivates the owner to keep the machines in use as continuously as possible. Failure of the electrode disposal device results in expensive downtime. The premium placed on reliable electrode disposal has necessitated frequent service typically including replacement of portions or the entire wire-chopping device to renew the cutting surfaces.
One prior art wire-chopping device comprises a plurality of blades mounted to a rotating shaft. A stationary wire guide orifice is positioned to feed wire into the blades generally transversely to the axis of blade rotation. The wire is sheared transverse to its feed path as the blades pass the exit orifice of the wire guide. The blades and wire guide orifice are constructed of tungsten carbide or similar hardened material to increase their durability. The blades are permanently fixed to a shaft of the wire-chopping device by welding or other known process for fixing a hard cutting edge to a cutting tool. The prior art discloses a wire-chopping device in which the wire guide orifice has two possible locations, each of which guide the spent electrode into axially spaced portions of the cutting blades. When one portion of the cutting blade is dulled, the wire guide orifice is repositioned to feed wire toward a fresh cutting surface on the cutting blades. Once the cutting blades are dulled in both available locations, the prior art wire-chopping device must be removed and discarded or remanufactured by inserting a new shaft with new cutting blades.
The prior art wire-chopping devices of the rotating blade/stationary anvil type require frequent replacement to renew the permanently attached blade cutting surfaces. This results in high expense and the necessity to maintain an inventory of remanufactured and/or new wire-chopping devices. There is a need in the art for a wire-chopping device in which the cutting surfaces can be frequently and inexpensively renewed without necessitating replacement of the entire device.
SUMMARY OF THE INVENTION
Briefly stated, a preferred embodiment of the present invention comprises a wire chopper module in which both the stationary and rotating cutting tool edges used to shear spent EDM electrode are both repositionable and replaceable. Repositioning the cutting edges relative to the feed path of the spent electrode greatly extends the serviceable life of each cutting edge by permitting multiple uses of each edge. When all the available cutting edges are used, replacement of the cutting edges is easily accomplished in the field by replacement of an insert carrying the cutting edge. Thus, cutting edges can be renewed more frequently and with less expense, resulting in increased EDM system reliability.
One preferred embodiment of the wire chopper module in accordance with the present invention comprises a frame that supports a shaft for rotation in bearings. The shaft includes a plurality of longitudinal channels configured to receive and retain replaceable inserts. Each of the disclosed cutting inserts includes two cutting surfaces. The shaft includes an arrangement for fixing the cutting inserts in alternative positions along the length of the shaft. A different portion of the cutting edge on the insert is used to shear the wire in each position. In this manner the channel, shaft and replaceable, repositionable, two-edge cutting inserts allow each insert to present four fresh active cutting edges. The inserts are replaceable and repositionable without replacement or extensive disassembly of a wire chopper module in accordance with the present invention.
A removable anvil holder supports an anvil whose cutting edge cooperates with the rotating cutting inserts to shear spent electrode transversely to its feed direction. The anvil holder defines a generally conical wire guide orifice that extends from an entrance opening to a smaller exit opening. The exit opening directs the spent electrode over the active cutting edge of the anvil and into the rotating cutting edges of the cutting inserts. A preferred embodiment of the anvil holder includes a slot or opening which receives a removable anvil having a plurality of cutting edges. The slot or opening is configured to permit movement of the anvil relative to the exit opening so that more than one portion of each anvil cutting edge is available to shear the spent electrode.
In accordance with the present invention, one preferred embodiment of the anvil is configured as a square slab of carbide or hard material that is received in the anvil holder in any of eight positions to present eight new cutting edges before requiring replacement. The anvil is movable relative to the wire guide orifice exit opening so that each of the eight cutting edges on the anvil can be used at least twice. As a result, a wire chopper module in accordance with the present invention can utilize the same anvil to present sixteen new cutting edges, greatly reducing the cost of renewing the stationary cutting edge in the inventive wire chopper module.
A wire chopper module in accordance with the present invention also includes a flywheel mounted to the shaft to increase the moment of inertia of the rotating shaft and cutting inserts. This increased moment of inertia helps avoid jams that may occur when cutting surfaces become dull.
An object of the present invention is to provide a new and improved wire chopper module for an EDM system that permits renewal of both the rotating and stationary cutting edges without necessitating major disassembly or replacement of the wire chopper module.
Another object of the present invention is to provide a new and improved wire chopper module for an EDM system that reduces the cost and increases the reliability of EDM system operation.
A further object of the present invention is to reduce the cost and complexity associated with renewing the cutting edges of a wire chopper module for an EDM system.



BRIEF DESCRIPTION OF THE DRAWINGS
Other objects and advantages of the present invention will be apparent from the following detailed description, claims and drawings in which:
FIG. 1 is a perspective view of a wire chopper module in accordance with the present invention;
FIG. 2 is an exploded view of the wire chopper module of FIG. 1;
FIG. 3 is a side view of the wire chopper module of FIG. 1;
FIG. 4 is a sectional view through the wire chopper module of FIG. 3 taken along line 4—4 thereof;
FIG. 5 is a side view of a shaft for use in conjunction with the wire chopper module of FIGS. 1-4; and
FIG. 6 is a right end view of the shaft of FIG. 5.



DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
With reference to FIGS. 1-6, wherein like numbers refer to similar parts, one preferred embodiment of a wire chopper module in accordance with the present invention is illustrated in FIGS. 1-4. The wire chopper module 100 is inserted in the path of spent wire electrode exiting from an EDM system. The illustrated wire chopper module 100 comprises a frame assembled from a front end cap 22 and a rear end cap 20 that receive four body pins 30, 30a. Bearings 24 are received in each of the end caps 20, 22 to support the shaft 60 for rotation within the frame. In the illustrated embodiment, one of the body pins 30a defines an aid 32 for positioning an anvil holder 40.
The anvil holder 40 of the illustrated preferred embodiment 100 is mounted between two of the body pins 30, 30a. A lower semi-cylindrical cutout 45 on the anvil holder 40 is configured to fit over the body pin 30a at the positioning aid 32. The upper surface 47 of the anvil holder 40 is configured to slide under an adjacent body pin 30 and snap into place such that the anvil holder is compressively engaged between the two body pins. The anvil holder 40 is provided with a jack screw 44 in a threaded bore that serves to jack the upper portion of the anvil holder 40 away from its snapped engagement between the body pins 30, 30a. Driving the jack screw 44 brings it into contact with the body pin 30 and pivots the anvil holder 40 out of snapped engagement.
The anvil holder 40 defines a wire guide orifice 42 in the form of a conical opening. The wire guide orifice 42 extends from an entrance opening to a smaller exit opening 43. The anvil holder 40 also defines a slot or opening 49 for reception of an anvil 70. The anvil 70 is supported in the anvil holder 40 with one of the cutting edges on the anvil and a portion of an anvil surface defining a working portion of the exit opening 43 in the anvil holder 40. By working portion, it is meant that this portion of the exit opening 43 acts in cooperation with the rotating cutting edges to shear the spent electrode (not illustrated).
A preferred embodiment of the anvil 70 is a square slab which can be received in any one of eight positions into the slot 49 defined in the anvil holder 40. It will be apparent that each of these eight positions presents a fresh cutting edge 72 for shearing the EDM electrode as it passes through the wire guide orifice 42.
As best seen in FIG. 2, the anvil holder 40 is configured to compressively engage the anvil 70 when the anvil holder is snapped between the body pins 30, 30a. The slot 49 for receiving the anvil 70 allows lateral movement of the anvil relative to the exit orifice 43 when the anvil holder 40 is not fixed between the body pins 30, 30a. This lateral movement permits each of the eight cutting edges 72 of the anvil 70 to be used at least two times. Thus, each anvil 70 can be rotated and positioned to present at least sixteen fresh cutting edge portions before requiring replacement.
The shaft 60 in the illustrated embodiment defines four longitudinally extending channels 62 configured to receive and retain removable and repositionable cutting inserts 80. Each of the cutting inserts 80 is configured to have two cutting edges 82. When mounted to the shaft 60, one cutting edge 82 is positioned to radially project from the shaft 60 while the other cutting edge 82 is received in a channel 62. The complementary cross-sectional configurations (best seen in FIG. 4) of the channels 62 and the received cutting inserts 80 allow the cutting inserts to move longitudinally along the shaft 60. The shaft 60 also defines a plurality of radial grooves 66 intersecting the channels 62. A shaft portion 64 of reduced cross section permits insertion and removal of inserts 80 from the channels 62 without removal of the shaft 60 from the frame 20, 22, 30, 30a. 
With reference to FIGS. 5 and 6, the illustrated embodiment of the shaft 60 defines four longitudinal channels 62 equiangularly arranged around the circumference of the shaft. The shaft 60 also defines four radial grooves 66 intersecting the longitudinal channels 62. Channel portions between the grooves 66 interact with the sectional configuration of the inserts 80, as best seen in FIG. 4, to retain the inserts for rotation with the shaft 60. The radial grooves 66 allow each insert 80 to be retained to the shaft 60 in either of two longitudinal positions 61, 63. Rings 68 disposed in two axially spaced grooves 66 define the longitudinal positions 61, 63 for the inserts by blocking movement of the inserts 80 along the channels 62. Rings placed in grooves A and C (of FIG. 5) define a first position 61 for the inserts 80, while rings received in grooves B and D define a second longitudinal position 63. This arrangement permits each cutting edge 82 on the inserts 80 to be renewed by repositioning the insert 80 so that a fresh portion of the cutting edge 82 is presented adjacent the working portion of the wire guide orifice 42 defined by the anvil 70.
FIG. 4 illustrates the compressed engagement of the anvil holder 40 between two of the body pins 30, 30a. The jack screw 44 is arranged to push the anvil holder 40 away from one of the body pins 30 and release it from this snapped in, compressed engagement. FIG. 4 also illustrates a slit 41 in the anvil holder 40 adjacent the anvil receiving opening 49. This slit 41 gives some flexibility to the anvil holder 40 around the anvil 70. When released from between the body pins 30, 30a, the anvil holder 40 permits removal and/or repositioning of the retained anvil 70. When installed to the frame, the compressed relationship of the anvil holder 40 between the body pins 30, 30a securely retains the received anvil 70 in its selected position relative to the exit 43 of the wire guide orifice 42.
In the illustrated embodiment, elastic O-rings 68 are utilized to retain the received inserts 80 in a selected longitudinal position. It will be understood by those of skill in the art that this function might be served by snap rings, e-clips, O-rings formed of metal coil spring, or the like. Other configurations for retaining the movable inserts 80 in a selected longitudinal position are intended to be within the scope of the present invention.
From the above description, it will be understood that each anvil 70 can be repositioned to present sixteen fresh cutting edges and each insert 80 can be repositioned to present four fresh cutting edges. The anvil 70 and each insert 80 can be replaced without necessitating significant disassembly of the wire chopper module 100. By significantly reducing the cost and complexity of renewing the cutting edges of a wire chopper module, the present invention makes it practical to more frequently renew the cutting edges and thereby increase the reliability of EDM equipment incorporating the inventive wire chopper module.
The illustrated embodiment for a wire chopper module 100 in accordance with the present invention also includes a flywheel 50 fixed to the shaft 60. The flywheel 50 increases the rotational inertia of the moving parts of a wire-chopper in accordance with the present invention. This increased inertia allows the inventive wire chopper module 100 to avoid many of the jams that may have occurred in prior art wire-choppers as the cutting surfaces became dulled. A jam that is avoided prevents stoppage of the EDM system and increases productivity.
While a preferred embodiment of the foregoing invention has been set forth for purposes of illustration, the foregoing description should not be deemed a limitation of the invention herein. Accordingly, various modifications, adaptations and alternatives may occur to one skilled in the art without departing from the spirit and the scope of the present invention.

## Claims

1. A chopper module for shearing wire into numerous discrete sections, said chopper module comprising:
a frame; 
a shaft supported for rotation within the frame about an axis of rotation generally perpendicular to a feed path of the wire, said shaft having an outside surface, a channeled portion defining a plurality of longitudinal channels between longitudinally extending side walls, and an open portion axially interrupting said channeled portion, the side walls of each said channel defining a channel width transverse to said axis of rotation that is greater radially inwardly of said outside surface than at said outside surface; 
a cutting insert disposed in each of said channels for rotation with the shaft, said inserts having a cross sectional shape that is complementary to said channel width such that said inserts are radially retained by said side walls while being longitudinally slidably movable in said channels; and 
a wire guide mounted to the frame and having a cutting edge in fixed position relative to the rotating shaft, 
wherein each said cutting insert is removable by sliding the insert out of said channel into said open portion and insertable by sliding the insert from said open portion into said channel, said inserts being removable and insertable while the shaft is mounted for rotation within the frame, wire fed through said wire guide is sheared between the fixed cutting edge and a rotating cutting insert, relative movement between the fixed cutting edge and the cutting inserts being generally transverse to the feed path of the wire.

2. The chopper module of claim 1, comprising a flywheel fixed to said shaft for rotation therewith.

3. The chopper module of claim 1, wherein the plurality of longitudinal channels comprises four longitudinal channels.

4. The chopper module of claim 1, wherein each said cutting insert comprises a plurality of chopping edges, one of said chopping edges of said cutting insert radially spaced from and generally parallel to said shaft axis while the other of said chopping edges is part of the cutting insert received in one of said channels to retain the cutting insert to the shaft for rotation therewith.

5. The chopper module of claim 4, comprising means for fixing said inserts in a longitudinal position on said shaft selected from a plurality of available longitudinal positions, each of said available longitudinal positions permitting a different portion of each chopping edge to shear the wire.

6. The chopper module of claim 5, wherein the means for fixing said inserts in a selected longitudinal position comprises:
a plurality of axially spaced grooves around a circumference of said shaft transverse to and intersecting said channels; and 
a plurality of rings disposable in said grooves to impede longitudinal movement of said inserts relative to said shaft.

7. The chopper module of claim 6, wherein said plurality of rings comprise two elastic rings that are movable among said grooves and said elastic rings disposed in a complementary pair of said plurality of grooves define a selected longitudinal position for said inserts.

8. The chopper module of claim 6, said plurality of grooves comprises two complementary pairs of grooves that define two alternatively selectable longitudinal positions for said inserts.