Patent Publication Number: US-2009236318-A1

Title: Wire Electric Discharge Machining Apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a National Stage application of International Application No. PCT/JP2007/000282, with an international filing date of Mar. 22, 2007. 
    
    
     FIELD 
     The present invention relates to a wire electric discharge machining apparatus for machining a workpiece using a wire electrode that is running between a pair of wire guides. In particular, the present invention relates to a wire electric discharge machining apparatus provided with an automatic wire threader (“AWT”) for threading a wire electrode through guide holes of the pair of wire guides using a fluid jet. 
     ART 
     A wire guide assembly provided with a passage in which the wire electrode runs vertically, and a power feed contact, a wire guide and a flushing nozzle integrally combined along this passage, is known. Wire guide assemblies are attached to respective tips of upper and lower arms fixed to a head or a column. The power feed contact is a contact for supplying electrical current to a running wire electrode. The diameter of wire electrode is typically 0.20 mm or 0.25 mm. The wire guide typically has a guide hole that is 0.01 mm or 0.02 mm larger than the wire electrode. The flushing nozzle is attached to the wire guide assembly facing the workpiece. During machining, high pressure machining fluid is jetted to a machining gap coaxial with the wire electrode. In the case where an opening of the flushing nozzle is positioned close to the surface of the workpiece, the wire guide assembly is subjected to a strong reaction force due to the high pressure machining fluid. The wire guide assembly is therefore securely fixed to the arm. 
     Generally, an automatic wire threader for passing the wire electrode through the upper and lower wire guides is provided in a wire electric discharge machining apparatus. Automatic wire threaders in recent years have passed a wire electrode using a fluid jet. Japanese Examined Patent Application Publication No. 7-29246 discloses a pipe jet type automatic wire threader with a guide pipe that can pass through the wire guide assembly. The wire electrode is placed in the guide pipe and a fluid jet is supplied into the guide pipe. The external diameter of the guide pipe is normally about 2 mm. In the case where a pipe jet type automatic wire threader is used, it is typically necessary to form a passage through which the guide pipe can pass in the wire guide assembly. Therefore, the wire guide assembly includes an actuator for moving the wire guide and the power feed contact. Japanese registered utility model No. 2521251 discloses a wire guide capable of being split into a pair of guide pieces in order to allow a guide pipe to pass through (“split guide”). Each guide piece is manufactured from a hard material. If the pair of guide pieces are joined together, a substantially rectangular wire guide is formed, and a guide hole is formed in the joined section. 
     Unsplittable circular dice guides are said to exhibit higher positioning accuracy than current split guides when the wire electrode is inclined. A fluid jet and guide pipe for an AWT cannot pass through the guide hole of a dice guide. Japanese Laid-open patent application publication No. 5-406647 discloses a jet type automatic wire threader with an AWT jet nozzle provided between a dice guide and a flushing nozzle. The AWT jet nozzle forms a fluid jet for guiding the wire electrode into a start hole in the workpiece, and also into a guide hole of the lower wire guide. 
     SUMMARY 
     In one aspect of the present invention, the subject technology provides a wire electric discharge machining apparatus capable of simply exchanging a split guide with an unsplittable dice guide. In another aspect of the present invention, the subject technology provides a wire electric discharge machining apparatus that can selectively use a pipe jet type or jet type automatic wire threader depending on machining, without changing a wire guide assembly. 
     In one aspect of the invention, a wire electric discharge machining apparatus for machining a workpiece using a wire electrode that is running vertically between upper and lower wire guides is provided. The apparatus includes an upper wire guide assembly including a housing and an actuator, the housing being configured to selectively store a split guide formed from a pair of guide pieces, or an unsplittable dice guide, as an upper wire guide, and the actuator being configured to move at least one of the pair of guide pieces. The apparatus further includes a guide pipe configured to move vertically through the upper wire guide assembly and configured to form a fluid jet, and means for supplying the fluid jet to the guide pipe. 
     The housing may store the dice guide fitted into an adapter ( 70 ) having at least partially the same external shape as the split guide. 
     Also, when the housing stores the dice guide, the upper wire guide assembly may further include an AWT jet nozzle configured to form a fluid jet for automatic wire threading. The upper wire guide assembly may further include a jacket ( 90 ) having an inlet configured to introduce fluid to be supplied to the AWT jet nozzle. 
     Also, the upper wire guide assembly may further include a power feed contact, a power feed contact block configured to hold the power feed contact, and a pin fixed to the power feed contact block. The actuator may be connected to the power feed contact block, and the pin may be fitted into at least one ( 42 ) of the pair of guide pieces. 
     Further, when the housing stores the dice guide, the upper wire guide assembly may have an adapter that the dice guide fits into, and the adapter may further include an elongated hole configured to permit movement of the pin. 
     According to one aspect of the present invention, it is possible to selectively use a split guide or a dice guide depending on the machining. It is also possible to selectively use a pipe jet type or jet type automatic wire threader, by partial replacement of a wire guide assembly. 
     Additional features and advantages of the invention will be set forth in the description below, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross sectional drawing showing an example of a wire guide assembly including a split guide. 
         FIG. 2  is an exploded view partially showing the wire guide assembly of  FIG. 1 . 
         FIG. 3  is a cross sectional drawing showing an example of a wire guide assembly including a dice guide. 
         FIG. 4  is an exploded view partially showing the wire guide assembly of  FIG. 3 . 
         FIG. 5  is another cross sectional view partially showing the wire guide assembly of  FIG. 3 . 
         FIG. 6  is a front elevation showing an example of an automatic wire threader. 
     
    
    
     DETAILED DESCRIPTION 
     A wire guide assembly including a split guide will be described with reference to  FIGS. 1 and 2 . The upper wire guide assembly  1  may mainly be constructed from a housing  10 , a wire insertion block  20  and a power feed contact block  30 . A passage  2  in which the wire electrode (not shown) runs vertically may be provided on the upper wire guide assembly  1 . A power feed contact  3 , split guide  4  and flushing nozzle  50  may be arranged along the passage  2 . 
     The wire insertion block  20  may be integrally fixed to an upper side of the housing  10 . The wire insertion block  20  may have a conical hole  21  and a guide  22 . A guide hole  23  of the guide  22  may have a larger diameter than the external diameter of a guide pipe  86  for guiding the wire electrode. The conical hole  21  and the guide hole  23  may constitute part of the passage  2 . 
     The power feed contact block  30  may be provided inside the housing  10  below the wire insertion block  20 . The power feed contact  3  may be housed inside the power feed contact block  30  moveably in a direction orthogonal to the wire electrode. The power feed contact block  30  may have a holding member  31  for holding the power feed contact  3 . A pin  32  may be fixed to a lower part of a the power feed contact block  30 . A pin  32  may extend downwards through an elongated hole  12  formed in a lower part of the housing  10 . An actuator  7  formed from an air cylinder may be integrally attached to the housing  10 . The actuator  7  may be connected to the power feed contact block  30 , and the power feed contact block  30  can be slid horizontally by the actuator  7 . As a result of sliding of the power feed contact block  30 , the power feed contact  3  may advance or retreat with respect to the wire electrode. 
     The split guide  4  may be formed from a pair of guide pieces  42 ,  44 . If the guide pieces  42 ,  44  are joined, a guide hole  46  for the wire electrode may be formed. The guide hole  46  may have a diameter that is 0.01 or 0.02 mm larger than the wire electrode. The split guide  4  may be housed in a recess which is formed by the projecting section  11  of the housing  10 , and may be slidably held by a circular plate-shaped guide holder  48 . A nozzle cap  52  may be attached with screws to a lower part of the housing  10 , so as to cover the guide holder  48 . The nozzle cap  52  may be equipped with a flushing nozzle  50 . A tip end of the pin  32  is fitted into a through hole  43  of the guide piece  42 . In this way, the guide piece  42  may be configured to be slid horizontally by the actuator  7  in order to open and close the split guide  4 . 
     A pipe jet type automatic wire threading method will now be described. First, the power feed contact block  30  may be moved to the left in the drawing by the actuator  7 . In this way, the power feed contact  3  and the guide piece  42  may be retracted, and a passage that is sufficiently large to allow the guide pipe  86  to pass through may be formed inside the wire guide assembly  1 . The guide pipe  86  may be lowered downwards as far as possible through the wire guide assembly  1 . Together with supply of a fluid jet into the guide pipe  86 , the wire electrode may be fed downwards into the guide pipe  86 . Once the wire electrode passes through the lower wire guide (not shown) and reaches a take-up roller (not shown), automatic wire threading may be completed. 
     A wire guide assembly including an unsplittable dice guide will be described with reference to  FIGS. 3 to 5 . Similar elements are labeled with similar reference numerals as used in  FIG. 1 , and detailed description thereof will be omitted. The dice guide  6  may integrally hold a guide member  62  having a guide hole  66  for the wire electrode. The guide hole  66  may have a diameter that is 0.01 or 0.02 mm larger than the wire electrode. The dice guide  6  may be fitted into the adapter  70 . 
     In order to replace the wire guide, first of all the nozzle cap  52  and the guide holder  48  may be removed from the wire guide assembly  1  of  FIG. 1 . Next, the split guide  4  may be removed. The adapter  70  holding the dice guide  6  may be attached to a position where the split guide  4  is situated. The adapter  70  may partially have a rectangular external shape that is substantially the same as the split guide  4 , and so may be smoothly housed in the recess which is formed by the projecting section  11 . The adapter  70  may have an elongated hole  71  into which the pin  32  is inserted. The elongated hole  71  into which the pin  32  is inserted. The elongated hole  71  permits movement of the pin  32 . 
     An AWT jet nozzle  75  may be mounted at an inner side of a jacket  90 , and the jacket  90  may be detachably attached to the housing  10 . The AWT jet nozzle  75  may be positioned below the dice guide  6  so as to cover the guide member  62 . A gap between the dice guide  6  and the AWT jet nozzle  75  may form a flow path  76  for fluid for the AWT jet. A nozzle base  53  equipped with a flushing nozzle  50  may be attached to the jacket  90 . An opening  77  of the AWT jet nozzle  75  may be positioned between the guide member  62  and the flushing nozzle  50 . 
     The jacket  90  may have a fluid inlet  91 , and a fluid supply path  92  communicating with the fluid inlet  91 . The fluid inlet  91  may be connected to a fluid supply device by an appropriate flexible hose (not shown). As shown clearly in  FIG. 5 , the jacket  90  may further have a supply path  93  through which machining fluid is fed to the flushing nozzle  50 . A plurality of counterbores  72  may be formed in a lower part of the adapter  70 . The counterbores  72  may communicate with the fluid supply path  92  and the flow path  76 . 
     A jet type automatic wire threading method will now be described. First, the power feed contact block  30  may be moved to the left in the drawing by the actuator  7 . In this way, the power feed contact  3  may be retracted, and a tip end of the guide pipe  86  may be lowered to just above the guide member  62 . Together with supply of a fluid for an AWT jet into the guide pipe  86 , the wire electrode may be fed downwards into the guide pipe  86 . A tip of the wire electrode having passed through the dice guide  6  may be constrained by a fluid jet formed by the AWT jet nozzle  75 . Fluid for the AWT jet may pass through the fluid inlet  91 , fluid supply passage  92 , counterbores  72  and the flow path  76 , and may be jetted from the opening  77  of the AWT jet nozzle  75 . The wire electrode may be fed further downwards while being constrained by the fluid jet. Once the wire electrode passes through the lower wire guide and reaches the take-up roller, automatic wire threading may be completed. 
     One example of a device for implementing the pipe jet type and jet type automatic threading methods will be described with reference to  FIG. 6 . The automatic wire threader  8  may include a feed roller  81 , cutting roller  82 , jet supply port  83 , damper  84 , collection box  85  and guide pipe  86 . An unneeded part of the wire electrode may be cut off by supplying electrical current to the roller  82 . The cut off wire piece may be grasped with the damper  84  and supplied to the collection box  85 . The guide pipe  86  may be provided below the feed roller  81  for feeding the wire electrode downwards. Fluid for the AWT jet may be introduced from a jet supply port  83  and supplied into the guide pipe  86 . The jet supply port  83  may be connected to a fluid supply device by an appropriate flexible hose (not shown). 
     The embodiments have been chosen in order to explain the principles of the invention and its practical applications, and many modifications are possible in light of the above teaching. It is intended that the scope of the invention be defined by the claims appended hereto.