Abstract:
A pivotal two-piece EDM electrode holder having a stationary base; a rotating head pivotally positioned over the stationary base; two end caps on the stationary base; and a pocket positioned in the center of the rotating head for receiving an electrode. Adjustment apparatus secure the rotating head in the desired position to the stationary base during the EDM process.

Description:
The present invention relates to an electrode holder suitable for use in making gates, sub-gates or other angled burns. In particular, this invention relates to a two-piece, pivotal gate electrode holder applied in electrical discharge machining (EDM) so as to eliminate time spent on producing temporary holders and allow installation of gates on any size mold. 
     BACKGROUND OF THE INVENTION 
     Plastic parts, whether they be plastic spoons or dashboard components, are molded in plastic injection molds. Many times the mold produced to manufacture these parts have features in the cavity or the runner system that require EDM burning to be done on angles (for example sub-gates). A sub-gate is a feature that allows the plastic injected into the mold to get into the cavity region. Gates have typically been installed in molds either by 1) making a temporary holder out of inexpensive material incorporating the angle at which the gate is to be installed and then burning the gate into the mold or 2) tipping the mold at an angle to allow the burning process to be done in a purely “Z” direction. The disadvantages of the above processes are that the temporary holder is usually discarded thereby wasting time and money in producing this temporary holder for one use and that tipping the mold is not practical when working with larger molds. The injected plastic gets into the mold cavity region by means of a gate. 
     These disadvantages are overcome by the two-piece holder joined by a common pivot point held in place by a holding means of the present invention. A variety of electrode holders for use in EDM have been disclosed in the relevant art but none of the references uncovered disclose or suggest the invention at hand. 
     U.S. Pat. No. 2,978,616, issued Apr. 4, 1961 to Pfau, discloses an electrode holder for use with an electroerosion machine, comprising a magnetic chuck having two circular discs of ferromagnetic material having flat end faces contacting each other, one of the discs being movable in the unmagnetized state and adapted to support the electrode, the other disc being stationary and having a first projection overlapping the movable disc and a second projection limiting the movement of the movable disc along the overlapping projection and defining the assembled position of the discs; and a means for creating a magnetic field holding the two discs in assembled position. 
     U.S. Pat. No. 3,614,370, issued Oct. 19, 1971 to Italo, discloses an electrode holder adapted to be used with an electric discharge machine which has an electrically conductive electrode, comprising a main housing that is generally annular to define a central opening having a central axis along which the electrode is fed during use; a base element rotatably supported by the main housing; an adjusting ring supported by the base element to be movable relative thereto; and electrically nonconductive guide rollers disposed symmetrically about the central axis to engage the electrode. 
     U.S. Pat. No. 4,319,115, issued Mar. 9, 1982 to Bonga, discloses an electrode tool holder for an EDM apparatus which can support either an electrode tool of large size or an electrode tool of small size, comprising an EDM apparatus with a ram consisting of two separate, linear moveably slide members, wherein one of the slide members carries a holder for an electrode tool of small dimension and wherein a second slide member is arranged to be coupled to the first slide member for supporting an electrode tool of large dimension. 
     U.S. Pat. No. 4,713,515, issued Dec. 15, 1987 to Choi, discloses an electrode holder for electric discharge processing machines that clamps the electrode in two perpendicular directions by clamp members, wherein each of the two clamp members slidably rests on a base seat which has side portions that extend at right angles to each other. The electrode holder disclosed in the &#39;515 reference does not allow for the electrode to be placed in a plurality of positions while the rotating head of the electrode holder of the present invention allows the electrode to be placed a variety of different positions. 
     U.S. Pat. No. 4,853,512, issued Aug. 1, 1989 to Scheider, discloses a spark erosion machining apparatus with an electrode changing mechanism having an electrode storage means and electrode support members, wherein the electrode storage means comprises linkage means pivotally connecting the electrode support members to at least one side wall of the tub of the machining apparatus and wherein the electrode support members are pivotal from a retracted rest position near said side wall of the tub into an operating position in which they protrude from the side wall of the tub towards the interior of the tub into an operating region. While the electrode support members of the &#39;512 patent are pivotal, the support member are pivotal only from the rest to the operating positions. In contrast, the rotating head of the present invention allows the electrode holder to be pivoted to a variety of operating positions. 
     U.S. Pat. No. 5,324,907 issued Jun. 28, 1994 to Wallace, discloses an EDM apparatus having a support base with adjustable slides mounted thereon; a cam arm mounted at one end on a piston rod that is used to cause vertical movement of the cam arm; a bore in the opposing end of the cam arm that rotatably receives a sleeve; and an electrode holder pivotally mounted in the sleeve such that one end of the electrode holder extends beyond the end of the sleeve, the electrode holder being movable between a first normal working position and a second non-working position that corresponds to movement of the cam arm. As in the &#39;512 reference, the &#39;907 reference only allows for pivoting the electrode holder between working and non-working positions, whereas the present invention provides for pivoting the electrode holder into a variety of working positions. 
     U.S. Pat. No. 5,791,803 issued Aug. 11, 1998 to Nordquist, discloses a compressive holding device serving as an electrode support having two coupling pieces and forcible elements for reversibly, axially, and compressively engaging the two coupling pieces in mutual engagement, where one of the coupling pieces has a plurality of aligning elements and the other coupling piece has a plurality of cooperating elements, and the aligning elements and/or cooperating elements are subjected to a force in the circumferential direction. 
     SUMMARY OF INVENTION 
     The object of the present invention is to provide a gate electrode holder that is reusable and compatible with a variety of mold sizes. A preferred embodiment of this invention is directed to a sub gate holder electrode holder for use in electric discharge machining (EDM). 
     This object is accomplished by the preferred embodiment of the present invention which provides for a sub gate electrode holder used in EDM comprising a stationary base having a first end and a second end; a rotating head having a first end and a second end, wherein the first end of the rotating head is pivotally positioned over the second end of the stationary base; two end caps affixable the second end of the stationary base; and a pocket positioned in the center of the second end of the rotating head for receiving an electrode. 
     The second end of the stationary base contains a spreader screw hole and a split. When a spreader screw is inserted and tightened into the spreader screw hole, the split allows the cylindrical end to flex, thereby securing the rotating head in the desired position to the cylindrical end of the stationary base. When the EDM process is complete, the spreader screw is removed, thereby releasing the stationary base from the rotating head and allowing the rotating head to be rotated into a new position for reuse. 
     The present invention also discloses an alternative preferred embodiment functioning exactly as the preferred embodiment but having a slightly different form in that the end caps are secured to the rotating head instead of the stationary base, and the rotating head has a slot as opposed to a pocket for receiving the electrode and has a plurality of screws (preferably five) for securing the electrode in place. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an exploded view of the preferred embodiment of the electrode holder of the present invention in the orientation. 
     FIG. 2 illustrates the assembled electrode holder of the present invention in EDM orientation. 
     FIG. 3 is an exploded view of an alternative embodiment of the electrode holder of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As shown in FIG. 1, the electrode holder  10  of the present invention is comprised of a stationary base  20  having a first end  21  and a second end  22  and a rotating head  30  having a first end  31  and second end  32 . 
     First end  21  of stationary base  20  is preferably cubical in form and affixed to the ram of an EDM machine (not shown). Second end  22  of stationary base  20  is cylindrical in form having a first flat end  22   a  and a second flat end  22   b.  First end  31  of rotating head  30  is concave in form to allow positioning over second cylindrical end  22  of stationary base  20 . Second end  32  of rotating head  30  is cubical in form and has a pocket  33  located in its center for holding the electrode  34 . Pocket screws  35   a  and  35   b  are positioned within second end  32  of rotating head  30  and extend into pocket  33  to secure the electrode  34  in place. FIG.  1 . The electrode  34  is preferably composed of either carbon or copper. 
     The second end  22  of stationary base  20  contains a tapered spreader screw hole  23  for receiving spreader screw  40 , a center screw hole  24  for receiving end cap screws  41   a  and  41   b,  a dowel hole  25  for receiving dowel  42 , and a split  26  as shown in FIGS. 1 and 2. Center screw hole  24  is positioned in the center of second end  22  of stationary base  20  and extends from first flat end  22   a  to second flat end  22   b.  Spreader screw hole  23  runs parallel to center screw hole  24  from first flat end  22   a  to second flat end  22   b  through the portion of second end  22  of stationary base  20  adjacent to rotating head  30 . Dowel hole  25  runs parallel to center screw hole  24  from first flat end  22   a  to second flat end  22   b  through the portion of second end  22  of stationary base  20  adjacent to first end  21  of stationary base  20 . Split  26 , which extends from first flat end  22   a  to second flat end  22   b,  begins at dowel hole  25  and runs completely through the center of second end  22  of stationary base  20  in the direction of the rotating head  30 . 
     When spreader screw  40  is inserted in spreader screw hole  23 , the spreader screw taper seats out on the taper in the spreader screw hole  23  and forces apart the second end  22  of stationary base  20  at split  26 . This flexing of second end  22  of stationary base  20  applies pressure to the first end  31  of rotating head  30  thereby securing rotating head  30  in place. The rotating head  30  should be pivoted into its desired position before tightening spreader screw  40 . 
     As shown in FIG. 2, dowel  42  is inserted into dowel hole  25  for aligning end caps  50   a  and  50   b  to each flat end  22   a  and  22   b  of stationary base  20  in order to trap rotating head  30  onto stationary base  20 . Each end cap  50   a  and  50   b  has an end cap dowel hole  51   a  and  51   b  respectively through which dowel  42  slides. Each end cap  50   a  and  50   b  is secured to flat ends  22   a  and  22   b  of stationary base  20  by inserting end cap screws  41   a  and  41   b  through end cap center screw holes  52   a  and  52   b  respectively into center screw hole  24 . End caps  50   a  and  50   b  also provide end cap spreader screw holes  53   a  and  53   b  to allow for the insertion of spreader screw  40  into the spreader screw hole  23  of second end  22  of stationary base  20  after moving rotating head  30  into the desired position. 
     In order to adjust the electrode holder, the user must take hold of both the rotating head  30  and the stationary base  20  and adjust the holder to the angle of choice. Rotating head  30  can be rotated along the circumference of the second cylindrical end  22  of stationary base  20  in order to achieve the necessary position for any particular EDM process. When rotating head  30  is in the desired position, the user must tighten spreader screw  40  approximately ¾ turn. When spreader screw  40  is tightened to the point of resistance, rotating head  40  will remain in its set position. When the EDM process is complete, the pocket screws  35   a  and  35   b  are loosened or removed to allow removal of electrode  34  from the pocket  33  thereby freeing the pocket to receive another electrode. To readjust sub gate electrode holder  10 , spreader screw  40  is backed out approximately ¾ turn so that the head moves freely to another position. To disassemble electrode holder  10 , spreader screw  40  is backed out and center screw  41   b  (the center screw opposite the side of the spreader screw  40 ) is removed to allow removal of end cap  50   b  and the disengagement of stationary base  20  and rotating head  30 . 
     In an alternative preferred embodiment of the present invention shown in FIG. 3, the electrode holder  10  functions in the manner described above but is larger to accommodate larger electrode blanks. Furthermore, the end caps  50   a  and  50   b  are secured to the first end  31  of rotating head  30  instead of being secured to the second end  22  of stationary base  20 . In other embodiments, the rotating head has a slot  36  as opposed to pocket  33  for receiving electrode  34  and has a plurality of screws  37  (preferably five) extending through second end  32  of rotating head  30  and into slot  36  to secure electrode  34  in place. 
     It is intended that all modifications obvious to persons skilled in the art are encompassed within the scope of this invention as defined by the claims below.