Abstract:
A wire guide for an electric discharge machine is designed with three elongated, cylindrical ceramic rods which close around the electrode wire to maintain its center orientation. The ceramic rods are removably held in pivotal clamps for replacement when they become worn. The clamps are inter-linked to move toward and away from one another, with an infinite range of adjustment; and once the rods are positioned to clamp the wire electrode, the jaws are locked in position during the operation of the electric discharge machine.

Description:
BACKGROUND 
     Electric discharge machines (EDM) are commonly used for making precise cuts, holes and otherwise shaping electrically conductive materials, such as steel, copper and the like. EDM machines employ a thin, consumable hollow wire, typically made of copper, using the spark discharge of the wire (internally cooled with water flow through it) to effect the EDM machining of various parts. In order to guide the wire, it is necessary to provide a device to center it and to hold the wire as it revolves and is moved downwardly through the EDM apparatus. 
     When EDM apparatus is used to bore holes or other shapes through a work piece, the hollow wire electrode is fed through the guide onto the work piece, where electro-erosion between the wire and the work piece forms a bore or hole through the work piece. This hole is a precise image of the wire electrode. In this type of machine, the wire electrode continuously is consumed during the cutting process; so that it continuously must be replenished by feeding it through the centering guide. 
     When an EDM apparatus is used to cut through a work piece in a precise pattern, a hollow wire electrode is unwound from a supply spool and is wound back around a return spool, with the spools both rotating to provide a precise constant rate of movement of the wire between them. Again, a centering wire guide is utilized between the two spools to accurately locate the moving wire electrode with respect to the workpiece. This causes the EDM discharge, which occurs between the wire and the work piece, to be accurately located with respect to the work piece which is moved under the control of a computer operated system to effect the desired cut through the work piece. In this type of system, the wire electrode is only partially consumed; but it still must be continually replenished as the exterior surface of the electrode is depleted through the discharge operation. 
     It has been common to use an orifice or circular collar wire guide of fixed diameter to guide the moving wire electrode in an EDM apparatus. Typically, the orifice or collar is manufactured to be slightly larger than the external diameter of the wire electrode. The United State patents to Iwasaki U.S. Pat. No. 5,086,202 and Fricke U.S. Pat. No. 5,214,260 both disclose fixed diameter wire guide in the form of circular collars. Apart from the absolute precision with which the orifices or circular openings in such fixed diameter wire guides must be manufactured, the guides also must be replaced when they become even slightly worn. In addition, if an EDM apparatus is changed over from the use of a machining wire of one diameter to a wire of another diameter, it is necessary to replace the wire guide in order to accommodate the different diameter wire electrode. Each time a new diameter is required, or replacement of an existing orifice because of wear is required, it is necessary to shut down the EDM apparatus while the changeover or replacement takes place. Such “down time” is non-productive, and results in increased overall cost of EDM machining, which is not desirable. 
     The United States patent to Shin U.S. Pat. No. 5,958,260 is directed to a three point guide for centering the wire electrode of an EDM machine. This patent, however, discloses a system which requires fixed rod diameters selected for each different wire diameter to be used by the guide. As a consequence, the changeover requirements which are mentioned above, with respect to the Iwasaki and Fricke patents, also apply to the Shih patent apparatus requiring precision rod diameters and necessary down time for effecting replacement and changeover of the guide wire rods themselves. 
     Attempts to provide a more universal centering of the wire electrode of an EDM machine have included three point supports, or multi-point supports which are spring biased to hold the guides against the wire electrodes. The Unitde States patent to Nakayama U.S. Pat. No. 4,686,344 employs three balls or three rings which are biased by springs or fluid cylinders to engage the wire electrode, and thereby center it between the balls or rings during the feeding of the wire in the EDM machining operation. The use of spring force, however, as disclosed in the Nakayama patent, is not entirely reliable for accurate centering because the springs themselves may exhibit different amounts of force, which would then allow the wire electrode to deviate from its desired path. 
     Another spring operated centering device is disclosed in the Unitde States patent to Walser U.S. Pat. No. 4,791,264. This patent uses a wire guide with a pair of L-shaped legs, which are biased by means of a centering spring around the electrode wire, to provide the desired tension and centering of the wire. Once again, this is a spring biasing mechanism, subject to the inherent disadvantages of such mechanisms, which reduces its reliability for precision machining operations. 
     Two other United State patents Truty U.S. Pat. No. 5,585,013 and Aso U.S. Pat. No. 4,833,291, and are directed to wire guides providing a three point support. The device of Truty uses three or more spherical-balls which are biased against the wire by means of gravity as the balls rest on the walls of a generally tapered bore. There is little disclosure in the patent as to how the device disclosed in Truty actually works, although it appears that a spring bias is used to press the balls downwardly against the tapered surface, and therefore, toward the center against the wire electrode of the EDM apparatus. 
     In the device of the Aso patent, a three point support also is provided. A triangular groove is provided in one guide; and a flat surface is provided in another, to press against the wire, providing a three point support as the wire moves through the guide. The device of Aso relies upon spring tension to press the guide members toward one another against the sire passing through the guide. 
     Accordingly, it is desirable to provide an accurate, easily adjustable EDM machine wire guide which overcomes the disadvantages of the prior art mentioned above, which is easy to use, easy to adjust, and easy to maintain while providing precision accuracy in the apparatus in which is it used. 
     SUMMARY OF THE INVENTION 
     In accordance with a preferred embodiment of the invention, a support guide for a wire electrode in an electric discharge machine includes a main housing. This housing has spaced apart upper and lower portions, in the form of parallel plates with aligned openings through them, through which the wire electrode passes. Three alignment jaws each are pivotally mounted to the housing in the space between the upper and lower plates for rotation toward and away from one another, and from a central axis passing through the jaws and the openings in the upper and lower plates. A linking mechanism is pivotally attached to the jaws to move them simultaneously toward and away from the central axis by substantially identical amounts. 
     In a more specific embodiment of the invention, the alignment jaws include clamps each of which hold an elongated cylindrical ceramic rod, with the ceramic rods contacting the wire electrode during operation of the centering device. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a top, left, front perspective view of a preferred embodiment of the invention; 
     FIG. 2 is a top, right, perspective view of the embodiment shown in FIG. 1; 
     FIG. 3 is a bottom, right, perspective view of the embodiment shown in FIGS. 1 and 2; 
     FIG. 4 is an exploded view of the embodiment shown in FIGS. 1,  2  and  3 ; 
     FIG. 5 is a side view of the embodiment shown in FIGS. 1 to  3  in a first position of operation; 
     FIG. 6 is a sectional taken along the line  6 — 6  of FIG. 5; 
     FIG. 7 is a side view of the embodiment of FIGS. 1 to  3  in a second state of operation; 
     FIG. 8 is a sectional view taken along the line  8 — 8  of FIG. 7; 
     FIG. 9 is a top view of the embodiment of FIGS. 1 through 3 showing the positioning of the mechanism for centering a wire electrode; 
     FIG. 10 is a top view of the embodiment shown in FIG. 9 in a different position of operation; 
     FIG. 11 is an enlarged view of the portion circled as  11  in FIG. 10 to illustrate details of that portion; 
     FIG. 12 is perspective view of a ceramic rod used in the embodiment of the invention illustrated in FIGS. 9,  10  and  11 ; 
     FIG. 13 is an enlarged view similar to that of FIG. 11 showing an alternative embodiment; 
     FIG. 14 is a perspective view of a ceramic rod of the type used in the alternative embodiment of FIG. 13; 
     FIG. 15 is a side view of a ceramic rod of the type shown in FIG. 12; 
     FIG. 16 is an end view of the rod shown in FIG. 15; 
     FIG. 17 is a side view of the ceramic rod shown in FIG. 14; 
     FIG. 18 is an end view of the rod shown in FIG. 17; 
     FIG. 19 is a detail of one of the clamping jaws of a preferred embodiment of the invention; 
     FIG. 20 is a cross-sectional view taken along the line  20 — 20  of FIG. 19; 
     FIG. 21 is an enlarged view of a portion of the embodiment circled in FIG. 19; 
     FIG. 22 is a top view of another one of the clamping jaws of the preferred embodiment of the invention; 
     FIG. 23 is a cross—sectional view taken along the line  23 — 23  of FIG. 22; 
     FIG. 24 is a top view of a third clamping jaw used in a preferred embodiment of the invention; 
     FIG. 25 is a cross-sectional view taken along the line  25 — 25  of FIG. 24; 
     FIG. 26 is a top view of a linking lever of the preferred embodiment of the invention; 
     FIG. 27 is a side view of the lever shown in FIG. 26; 
     FIG. 28 is a top view of another linking lever used in the preferred embodiment of the invention; 
     FIG. 29 is a cross-sectional view taken along the line  29 — 29  of FIG. 28; 
     FIG. 30 is a top view of the housing used in the preferred embodiment shown in FIGS. 1 through 4; 
     FIG. 31 is a cross-sectional view taken along the line  31 — 31  of FIG. 30; 
     FIG. 32 is an end view of the housing shown in FIG. 30; and 
     FIG. 33 is an enlarged view of an alternative jaw used in conjunction with the ceramic rod shown in FIGS. 14,  17  and  18 . 
    
    
     DETAILED DESCRIPTION 
     Reference now should be made to drawings, in which the same reference numbers are used throughout the different figures to designate the same or similar components. FIGS. 1,  2  and  3  each are perspective views from the top left front, top left right, and bottom right of a preferred embodiment of the invention. These figures depict a support guide for a hollow wire electrode (or similar element) as used in an electric discharge machine, or the like. No details of the wire feeding mechanism, wire take up mechanism (if any), or of other parts of the EDM machine are shown, since all of these parts are standard; and the wire guide which is described and shown in the various figures may be used with any standard EDM machine. FIG. 4 is an exploded view of the apparatus shown in FIGS. 1,  2  and  3 ; and reference to all of the figures may be made for an understanding of how the various parts fit together and are assembled. 
     The wire guide support includes a basic block  45 , which may be attached to the frame of the EDM machine with which the preferred embodiment of the invention is to be used. This attachment is by means of fasteners  78  which pass upwardly through the block  45 , through adjustment slots  80 , and upward through a spring steel plate  44  having similar slots aligned with the slots  80 . The plate  44  is attached to the top of the block  45  by means of threaded fasteners  82 , as most clearly illustrated in FIGS. 1 and 4. 
     As can be seen from an examination of all of FIGS. 1,  2  and  3 , the plate  44  extends to the right (as viewed in FIGS.  1  and  4 ). An adjustable mounting block  43  is located intermediate the block  45  and a housing  40  for the wire guide assembly. The block  43  is attached to the block  45  through a central fastener  74  to allow a limited amount of relative rotation about the fastener  74 . A set screw  76  then is used to secure the block  43  in the rotated position once the adjustment in the rotational direction of the block  43  with respect to the block  45  has been effected. Further adjustment in a side-to-side manner of the block  43 , relative to the housing  40 , is effected by a pair of adjusting rods  70 , the location of which is shown most clearly in FIGS. 4,  6  and  8 . The adjusting rods  70  interface between the front (right-hand end as viewed in FIG. 4) face of the block  43  and the rear (left-hand as viewed in FIG. 4) of the wire guide assembly housing  40 . Once the adjustment has been effected, a pair of set screws  72  engage the rods  70  to secure the relative left to right tilt of the housing  40 , with respect to the block  43  for the desired adjustment. 
     FIGS. 30 and 32 illustrate in greater detail the manner in which this is done. The adjusting rods  70  enter into recesses  151  in the housing  40  and the set screws  72  are threaded through appropriate passages  152  and  154  to engage the rods  70 . The respective location of the rods  70  in the passageways in the block  43  and in the passageways  151  (FIG. 31) of the housing  40  for the wire guide assembly is illustrated most clearly in FIGS. 6 and 8. 
     As is most apparent from FIGS. 4,  5 ,  7 ,  30 ,  31  and  32 , the support guide assembly is placed in the housing  40 . The right-hand end of the housing  40  (as viewed in FIGS. 1,  4 ,  5 ,  7 , and  31 ) is hollowed out to form a U-shaped cross section, with an upper plate spaced from a lower plate in parallel planes. A generally circular cut-out  42  is formed through both of these plates; and the central axis of this generally circular cut-out is perpendicular to the planes of the upper and lower plates formed in the open end of the housing  40 . 
     Three sets of aligned holes  68  are equally angularly spaced around the circular opening  42 , through both the upper and lower plates of the block  40 , as illustrated most clearly in FIGS. 4,  11  and  30 . These holes  68  support pivot shafts  64 , which extend through both plates and, through the opening between them, to pivotally secure each of three different alignment jaws  50 ,  52  and  54 . One pivot shaft  64  passes through the pivot opening  106  in the jaw  50  (FIG.  19 ). The pivot shaft  64  for the jaw  52  passes through the opening  132  (FIG.  24 ); and the pivot shaft  64  for the generally Y-shaped jaw  54  passes through the opening  110  (FIG.  22 ). Thus, each of the three jaws,  50 ,  52  and  54  are free to achieve rotational pivotal movement about the corresponding pivot shafts  64  passing through them. 
     The remainder of the positioning mechanism for the jaws  50 ,  52  and  54  is provided by a pair of elongated links  48  and  56 , shown in the exploded view of FIG.  4  and shown in detail in FIGS. 26 through 29. The link  48  has a thumb engagement projection at its midpoint extending beyond the edge of the main housing  40 , as illustrated in various ones of the figures, such as  2 ,  3 ,  6 ,  8 ,  9  and  10 . This link  48  has a pair of pivot pin receiving apertures  140  and  142  in it, which align, respectively, with the apertures  108  in the alignment jaw  50  (FIG. 19) and the aperture  112  in the alignment jaw  54  (FIG.  22 ). Pivot pins  66  interconnect these apertures. Similarly, the pivot linkage  56  is pivotally engaged by pivot pins  66  through its aperture  144  to the aperture  114  of the jaw  54  (FIG. 22) and through its aperture  146  (FIG. 29) to the aperture  130  (FIG. 24) of the alignment jaw  52 . The interrelationships of all of these various linkages and the relative movement which is effected through them is shown most clearly in FIGS. 4,  6  and  8 . 
     The final element of structure for holding the alignment jaws in place once an adjustment has been made, is effected through a thumbscrew  46  passing through a slot  150  in the top of the wire guide assembly housing  40 , as shown most clearly in FIGS. 4,  30  and  31 . This thumbscrew  46  threads into a central threaded aperture  148  in a raised hub  156  on the pivot  56  to hold everything tightly against further rotation once the thumbscrew  46  is engaged to pull the top surface of the hub  156  into engagement with the bottom surface of the upper plate of the cavity in which these elements are placed. When this is done, no further rotation of any of the parts takes place. When the thumbscrew  46  is released to allow pivotal movement of all of the various parts, as described above, the jaws  50 ,  52  and  54  are allowed limited relative pivotal movement toward and away from the central axis through the circular opening of the wire guide assembly housing, as described above. 
     The actual contact members for engaging the wire electrode of an electric discharge machine comprise short segments of solid cylindrical ceramic rods  62 , shown most clearly in FIGS. 12,  15  and  16 . The ceramic rods typically have a length of one-half inch to ⅞ inches, or greater. The rods  62  may extend all of the way to the part undergoing machining, if desired. These rods  62  are greater in length than the clamping ends of the adjustment jaws  50 ,  52  and  56 , as is readily apparent from an examination of FIGS. 1,  5  and  7 . The rods  62  typically carry a hardness of 88 to 90 Rockwell, or Coors AD 998. The other elements of the structure which has been described above typically are made of stainless steel. The ceramic rods  62  are non-conductive; so that they may be in contact with the wire electrode of the EDM machine during its operation. The typical external diameter of the rod  62  is 0.093 inches for use with wire electrodes having a range of external diameters of 0.006 inches to 2.50 inches. These dimensions are typical for a general range of applications; but, obviously, the various dimensions of the different parts can be adjusted in accordance with any particular specific situation requiring different dimensions. 
     The ceramic guide rods  62  are held in place by means of C-shaped clamp members on the ends of each of the alignment jaws  50 ,  52  and  54 . FIG. 19 shows the clamp  100  on the jaws  50 . This clamp has an internal diameter slightly greater than the external diameter of the rod  62 . The clamp  100  extends slightly past a diameter of the rod  62  to hold the rod  62  in place when a set screw  60  is tightened to squeeze the jaw  100  about the external surface of all or a portion of the rod  62  by a squeezing action of the slot  102  shown in the lever  50 . This is shown most clearly in FIGS. 19,  20  and  21  for the jaw  50 . Similar clamping or holding of the rods  62  in the levers  52  and  54  is effected by means of the jaws  116  in the lever  54  and  126  in the lever  52 , via movement of the slots  118  for the lever  54  and  128  for the lever  52  through tightening or releasing of an adjustment screw  60  in each of these jaws. These features are illustrated in FIGS. 22 and 23 for the jaw  54 , and in FIGS. 24 and 25 for the jaw  52 . 
     As is readily apparent from an examination of FIGS. 19 through 25, rapid and effective changing of a worn ceramic guide rod  62  and replacement with a new guide rod  62 , may be implemented without dismantling the support wire guide assembly. This is apparent from an examination of FIGS.  5 , 6 , 9  and  10 , for example, which illustrate the openness and accessibility of the set screws  60  for effecting such a change. 
     Adjustment of the alignment jaws  50 , 52 , 54  to place the three ceramic rods  62  into contact with a wire electrode passing vertically through them, along. the central axis of the circular opening  42 , is effected by moving the thumb lever extension on the lever  48  back and forth from left to right, as viewed in FIGS. 4,  6 ,  8 ,  9  and  10 . FIGS. 5 and 6 illustrate the adjustment of the device to place the rods  62  in contact with one another, thereby forming the smallest aperture through which a wire electrode may pass. This is effected by pushing the extension on the lever  48  toward the left, as viewed in FIGS. 4 and 6. This causes all of the alignment jaws  50 ,  52  and  54  to rotate about their pivots  64  in a counterclockwise direction, causing the jaws to come together as viewed in FIG.  6 . 
     When the thumb extension on the lever arm  48  is pushed or pulled to the right, as viewed in FIGS. 4,  6 ,  8  and  9 , the jaws  50 ,  52  and  54  are caused to pivot clockwise about the pivot pins  64  to open the jaws,.as shown in FIG.  8 . FIG. 9 shows the jaws at a position which is intermediate that of FIGS. 6 and 8. In FIG.  9 , the jaws  50 , 52  and  54  are in contact with a wire electrode  90 , shown in dotted lines in FIG.  9 . 
     It should be noted that the adjustability of the jaws  50 ,  52 ,  54  from the smallest opening shown in FIG. 6 to the largest one shown in FIG. 8 is infinite. To effect centering on a wire electrode or on a solid gauge pin for establishing an initial adjustment, the wire or pin is placed in the opening between all of the rods with the device in its wide open position, such as shown in FIG.  8 . The thumb extension on the lever  48  then is moved to the left, as viewed in FIGS. 4 and 6, until the wire or gauge pin is engaged as shown in FIG.  9 . The pressure to which this adjustment is made is selected to be tight enough to prevent the gauge pin or actual wire electrode from falling out. Once the adjustment has been made, the thumbscrew  46  is tightened as described previously. The adjustment then is held and maintained throughout operation of the device, until such time as a readjustment or a different sized wire electrode is to be used. The open end of the housing  42  permits a wire or gauge pin to be moved through the open end, past the alignment jaws  50  and  52  in the opening, which is most apparent from an examination of FIG.  8 . Typically, however, the gauge pin or the actual EDM wire is passed vertically downwardly through the device in the opening, prior to engagement of the rods  62  with the EDM wire. It should be noted that the longitudinal axes through the rods  62  are all parallel with one another and parallel with the vertical central axis passing through the circular openings  42  in the upper and lower plates of the housing  40 . 
     For EDM wires having very small external diameters, a different configuration of a ceramic rod is used. This configuration is shown in FIGS. 14,  17  and  18 . In all other respects, the apparatus works in the same manner as described above in conjunction with the use of the ceramic guide rods  62 . The rods  62 A of FIGS. 14,  17  and  18 , however. have an elongated flat surface  92  diametrically opposite an elongated point formed by two other flats  94  and  96 , as shown most clearly in FIG.  18 . The clamps on the ends of the jaws are then modified, in the manner surface  101  adjacent the slot  102  to be engaged by the flat surface  92  extending the length of the rod  62 A. When the rods  62 A are clamped in position in all three of the clamping jaws  50 ,  52  and  54 , the relative points between the surfaces  94  and  96  allow for much smaller diameter wire electrodes to be engaged by the device. The modifications which are shown for doing this are illustrated in FIGS. 10 and 13, with the enlarged view of FIG. 13 showing the manner in which the elongated ridge between the surfaces  94  and  96  interacts with similar ridges on the other rods  62 A in the various jaws  50 ,  52  and  54  to allow very small diameter wire to be held and guided by the wire guide support assembly. The manner of operation of the assembly, however, is identical, whether cylindrical rods  62  are used or the modified shapes of the rods  62 A are employed. 
     The foregoing description of the preferred embodiment of the invention is to be considered as illustrative and not as limiting. Various changes and modifications will occur to those skilled in the art for performing substantially the same function, in substantially the same way, to achieve substantially the same result, without departing from the true scope of the invention as defined in the appended claims.