Patent Document

TECHNICAL FIELD 
     This technology includes methods, systems, and devices for using an electrode on a computer numerical control (CNC) machine tool. 
     BACKGROUND 
     Electrical discharge machining (EDM) is a particular type of CNC machine tool process. An EDM process shapes a workpiece by striking the workpiece with sparks emitted from an EDM electrode. The manner in which the sparks act upon the workpiece is determined by factors including the shape and position of the electrode. A complex workpiece feature, such as a turbine airfoil, may require a correspondingly complex shape for the electrode. If the electrode becomes worn through multiple EDM cycles, it can be restored to its original shape in a process known as redressing. 
     SUMMARY 
     An apparatus is configured for use with an electrode and a CNC machine tool. The apparatus includes a holder configured to hold the electrode in a position projecting outward from the holder, and a pull stud configured to mount the holder on the CNC machine tool. The apparatus further includes a driving mechanism that is operative to provide a motive force, and a coupling configured to couple the holder with the driving mechanism when the holder is not mounted on the CNC machine tool. The holder is configured to transmit the motive force from the coupling to the electrode in the holder to move the electrode outward of the holder. 
     A method includes the steps of placing an electrode holder in a position defining a path of movement for an electrode to be moved outward of the holder, and moving an electrode outward of the holder along the path of movement. The electrode is preferably moved outward of the holder under a force applied automatically, such a pneumatic pressure force, without a manually applied force. Outward movement of the electrode is stopped by a structure that is spaced a predetermined distance from the holder. This places the electrode in an extended position projecting the predetermined distance outward from the holder. 
     In a preferred implementation, the electrode holder is mounted on a milling machine in a position defining a path of movement for an electrode to be moved outward of the holder. The electrode is moved outward of the holder along the path of movement while the holder remains on the milling machine. Outward movement of the electrode is stopped by a structure that is located in the path of movement at a position spaced a predetermined distance from the holder. This places the electrode in an extended position projecting the predetermined distance outward from the holder on the milling machine. The method further includes the step of redressing the electrode while the electrode remains in the extended position projecting the predetermined distance outward from the holder on the milling machine. 
     A more extensive method includes the steps of (a) moving the electrode in the holder to a position projecting a predetermined distance outward from the holder, and (b) mounting the holder on a CNC machine tool with the electrode in the position projecting the predetermined distance outward from the holder. Further steps include (c) performing multiple machining jobs with the electrode while the holder remains mounted on the CNC machine tool with the electrode in the holder, and (d) while maintaining the electrode in the holder, removing the holder from the CNC machine tool at the conclusion of the multiple machining jobs, redressing the electrode, and repeating steps (b) and (c) with the redressed electrode. Step (d) is preferably repeated without removing the electrode from the holder. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side view of an electrode holder with an electrode projecting outward from the holder. 
         FIG. 2  is a rear perspective view of the parts shown in  FIG. 1 . 
         FIG. 3  is an exploded rear perspective view of the electrode holder, with fasteners omitted for clarity of illustration. 
         FIG. 4  is a side sectional view of the electrode holder. 
         FIG. 5  is a front view of the electrode holder. 
         FIG. 5A  is a partially sectional view of the holder as shown in  FIG. 5 . 
         FIGS. 6-9  are views similar to  FIG. 4 , showing different steps taken in a method of using the electrode holder. 
         FIG. 10  is a view of the electrode holder in position on a CNC machine tool. 
         FIG. 11  also is a view similar to  FIG. 4 , and shows another step taken in the method of using the electrode holder. 
         FIG. 12  is a schematic view of a system for using the electrode holder. 
         FIG. 13  is a schematic view of parts of the system of  FIG. 12 . 
     
    
    
     DETAILED DESCRIPTION 
     The apparatus shown in the drawings has parts that are examples of the elements recited in the apparatus claims, and can be operated in steps that are examples of the elements recited in the method claims. The following description thus includes examples of how a person of ordinary skill in the art can make and use the claimed invention. It is intended to meet the requirements of enablement and best mode without imposing limitations that are not recited in the claims. 
     A holder  10  for an electrode  12  is shown in  FIG. 1 . The holder  10  is configured for mounting on a CNC machine tool. In this particular embodiment, the electrode  12  is an EDM electrode, and the holder  10  is configured for mounting on an EDM machine for movement along and about a first axis  15 . The electrode  12  is an elongated part that projects longitudinally outward from the holder  10  along a second axis  17  at an acute angle to the first axis  15 . An outer end portion  18  of the electrode  12  is thus arranged for engagement with a workpiece in an EDM process for shaping the workpiece. 
     The configuration of the outer end portion  18  of the electrode  12 , as well as the location and orientation of the electrode  12  relative to the axes  15  and  17 , is predetermined with reference to the size and shape specified for the structural feature of the workpiece to be formed in the EDM process. In this particular embodiment, the structural feature to be formed by the electrode  12  is a turbine airfoil. As multiple features are formed by repeated engagement of the electrode  12  with the workpiece, the resulting wear causes the shape of the outer end portion  18  to change. Wear at the outer end portion  18  also reduces the length of the electrode  12 . It is therefore necessary to redress the outer end portion  18  of the electrode  12 , and also to reposition the electrode  12  axially, after multiple cycles of use. 
     The parts of the holder  10  shown in  FIGS. 1-3  include a main body  30 , a cover  32 , and a back plate  34 . As best shown in  FIGS. 4 and 5 , these parts of the holder  10  together define an elongated chamber  37  with an open front end  39  for receiving the electrode  12 . Specifically, a major length portion of the electrode  12  has planar side surfaces  42  ( FIG. 3 ) that provide a rectangular cross sectional shape. The main body  30  and the cover  32  have corresponding planar surfaces  44  and  46 . Those surfaces  44  and  46  provide the chamber  37  with a rectangular cross sectional shape that is sized for the major length portion of the electrode  12  to fit closely within the chamber  37 . The back plate  34  defines the rear end of the chamber  37 , and has an elastomeric pad  50  on its inner side. 
     A pneumatic port  61  is centered on the first axis  15  at the rear of the main body  30 . Passages  63  in the main body  30  communicate the port  61  with the chamber  37 . A pull stud  64  ( FIG. 6 ) extends through a central opening  65  in a mounting plate  68  at the rear of the main body  30 . The pull stud  64  and mounting plate  68  are configured to couple and decouple the holder  10  with a chucking apparatus on an EDM machine in a known manner. An EDM fluid passage  69  extending through the pull stud  64  communicates with the port  61 . This enables the pull stud  64  to serve as a pneumatic coupling for communicating the holder  10  with a source of pneumatic pressure when the holder  10  is decoupled from an EDM machine. 
     A pair of locking pins  70 , one of which is shown in  FIG. 5A , are arranged in the pneumatic passages  63  beside a pair of air inlet slots  71  at the chamber  37 . Each locking pin  70  has an inclined, flat wedge surface  72  that projects transversely inward of the chamber  37  through the corresponding slot  71 . When the passages  63  are pressurized pneumatically, the locking pins  70  are moved lengthwise against springs  74 . This shifts the wedge surfaces  72  outward of the chamber  37  to provide clearance for insertion of the electrode  12  into the chamber  37 . When the pressure is relieved, the springs  74  push the locking pins  70  back toward their original positions. This presses the wedge surfaces  72  against the electrode  12  to secure it in the chamber  37 . 
     Other parts of the holder  10  include a spring  80  and a link  82 . The spring  80  extends alongside the cover  32  in a direction parallel to the second axis  17 . A front end  84  of the spring  80  is anchored to the cover  32 . A rear end  86  of the spring  80  is connected to the link  82 , which is movable lengthwise relative to the cover  32 . The link  82  extends through a guide  88  on the cover  32 , and is fastened to the back plate  34  at the rear of the cover  32 . When the spring  80  is in the original, unstressed condition shown in the drawings, it holds the back plate  34  against the cover  32  to close the rear end of the chamber  37 . 
     The electrode  12  is installed in the holder  10  in a series of steps, as shown in  FIGS. 6-9 . First, the holder  10  is mounted on a chucking apparatus  100  on a milling machine. The chucking apparatus  100  is adapted to communicate the pneumatic coupling/pull stud  64  with a source  104  of pneumatic pressure. As shown schematically, the pneumatic connection includes a standard pneumatic hose swivel  105  for rotation with the chucking apparatus  100 , and a valve  106  between the swivel  105  and the source  104 . When the valve  106  is open, pneumatic pressure is supplied from the source  104  to the chamber  37  through the valve  106 , the swivel  105 , the pneumatic coupling/stud  64 , and the passages  63  in the main body  30  of the holder  10 . The electrode  12  can then be inserted into the chamber  37  past the locking pins  70 . 
     As shown in  FIG. 7 , a probe  108  on a multi axis spindle  110  is moved against the outer end  112  of the electrode  12  to move the electrode  12  more fully inward of the chamber  37 . The probe  108  may push the inner end  114  of the electrode  12  against the elastomeric pad  50  on the back plate  34 . The spring  80  can extend to allow the back plate  34  to move rearward from the cover  32  under the force applied by the electrode  12 , and can then contract to return the back plate  34  to the cover  32 . This protects the electrode  12  by damping the impact of the inner end  114  against the pad  50  and the back plate  34 . 
     In the step shown in  FIG. 8 , the spindle  110  carries the probe  108  to a position that is spaced from the holder  10  a predetermined distance D along the axis  17 . As the probe  108  is being moved away from the holder  10 , a pneumatic thrust acts on the inner end  114  of the electrode  12  to push the electrode against the probe  108 , and thus moves the electrode  12  along the axis  17  with the probe  108 . When the probe  108  is stopped at its spaced position, it stops the advancing electrode  12  in a position projecting the predetermined distance D outward from the holder  10 . 
     When the electrode  12  has been advanced to the position of  FIG. 8 , the pneumatic pressure in the chamber  37  is relieved, and the probe  108  is withdrawn as shown in  FIG. 9 . The holder  10  is then transferred from the chucking apparatus  100  on the milling machine to a chucking apparatus  118  ( FIG. 10 ) on an EDM machine for multiple machining cycles on the EDM machine. 
     At the conclusion of a predetermined number of EDM cycles, or when inspection of the electrode  12  indicates wear for which redressing is needed, the holder  10  is removed from the EDM machine, but the worn electrode  12  is not removed from the holder  10 . The holder  10  and worn electrode  12  are transferred together from the EDM machine back to the milling machine for redressing of the worn electrode  12  in the holder  10 . 
     With the holder  10  again mounted on the chucking apparatus  100  on the milling machine, the probe  108  is again deployed to move the worn electrode  12  inward of the chamber  37 . This is accomplished in the manner described above with reference to  FIG. 7 , but the reduced length of the worn electrode  12  may prevent the inner end  118  from impacting the pad  50  on the back plate  34 . The probe  108  is next moved away from the holder  10  along the axis  17 , and the chamber  37  is again pressurized to move the redressed electrode  12  back outward with the probe  108  until the probe  108  is stopped at the location where the worn electrode  12  projects outward the distance D, as described above with reference to  FIG. 8 . 
     In the next step, as shown in  FIG. 11 , a milling cutter  120  on the spindle  110  is deployed to restore the outer end portion  18  of the worn electrode  12  to its original configuration. The chucking apparatus  100  on the milling machine can rotate the holder  10  about the first axis  15  as needed for the cutter  120  to access the electrode  12  from all sides in the cutting step. When reshaping of the outer end portion  18  is complete, the holder  10  with the redressed electrode  12  is ready to be transferred back to the EDM machine for another series of machining cycles with the redressed electrode  12 . 
     In the initial step described above with reference to  FIG. 6 , the electrode  12  is preferably inserted into the chamber  37  manually, and the holder  10  is preferably mounted on the milling machine automatically. The steps of transferring the holder  10  between the milling machine and the EDM machine, with the electrode  12  remaining in place in the holder  10 , also are preferably performed automatically. 
     For example, a system  140  for transferring the holder  10  is shown schematically in the top view of  FIG. 12 . This system  140  includes a robot  142  mounted on a horizontal track  143 . The robot  142  has an arm  144  with a fork  148 . The arm  144  is pivotal about a vertical axis  149 , and is telescopic radially relative to the axis  149  to move the fork  148  into and out of operative association with work stations that are spaced apart along the track  143 . The number of components and work stations in such a system may vary, but the illustrated embodiment includes a milling machine  150 , multiple CNC machine tools  154 , and a carousel  158 . 
     The milling machine  150  includes the chucking apparatus  100  described above. The milling machine  150  also includes the multi-axis spindle  110  for the probe  108  and the cutter  120 . Each CNC machine tool  154  in this particular embodiment is an EDM machine with a chucking apparatus  118  as described above. The carousel  158  has a supply of holders  10 , each of which is EDM-ready with a pneumatic coupling/stud  64  and a new or redressed EDM electrode  12  projecting the predetermined distance D outward from the holder  10 . The new electrodes  12  could be placed in their holders  10  on the milling machine  150  as described above, or on a similar machine that is not necessarily adapted for milling. The fork  148  on the robot arm  144  is configured to move into and out of engagement with a pneumatic coupling/stud  64  to lift, carry, and release a holder  10  in a known manner. 
     A controller  160 , as shown schematically in  FIG. 13 , is operatively associated with the robot  142 , the milling machine  150 , the EDM machines  154  and the carousel  158 . The controller  160  may comprise any suitable programmable logic controller or other control device, or combination of such control devices among the various machines, and has hardware and/or software configured to operate the robot  142 , the milling machine  150 , the EDM machines  154  and the carousel  158  as described and claimed. The controller  160  is also configured to operate the valve  106  between the milling machine  150  and the source  104  of pneumatic pressure as described and claimed. 
     In an example of operation of the system  140 , the robot  142  loads each EDM machine  154  with an EDM-ready holder  10  from the supply on the carousel  158 . When any one of the electrodes  12  at the EDM machines  154  requires redressing after multiple machining cycles, the robot  142  transfers the holder  10  with the worn electrode  12  back to the carousel  158 , and replaces it with another EDM-ready holder  10  taken from the supply on carousel  158 . 
     While the machining operations are being performed at the EDM machines  154 , the robot  142  can replenish the supply of EDM-ready holders  10  at the carousel  158  without interrupting the EDM operation. This is accomplished by transferring holders  10  with worn electrodes  12  back and forth from the carousel  158  to the milling machine  150  for redressing while EDM machining operations continue at the EDM machines  154  with other holders  10  having either new or redressed electrodes  12 . 
     This written description sets for the best mode of the invention, and describes the invention so as to enable a person of ordinary skill in the art to make and use the invention, by presenting examples of the elements recited in the claims. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those of ordinary skill in the art. Such other examples are intended to be within the scope of the claims if they do not differ from the literal language of the claims, or if they have insubstantial differences from the literal language of the claims.

Technology Category: b