Abstract:
The present invention provides a method of producing a member with a face-geared surface including the steps of: 
     (a) an initial process preparing a work piece and a hob, the work piece having an area to be geared, the hob having a blade, the hob being brought into an axial movement when rotated through an angle of 360 degrees about its longitudinal axis, the initial process bringing the work piece to oppose the hob with a distance; 
     (b) a geared surface forming process forming a geared surface on a part of the area by rotating the hob about its longitudinal axis in one direction through an angle of less than 360 degrees after an establishment of a mutual engagement between the hob and the work piece which results from moving at least one of the hob and the work piece in a radial direction of the hob; 
     (c) a retracting process retracting the at least one of the hob and the work piece in the radial direction of the hob to establish a separation of the hob from the work piece before the hob completes its 360 degree rotation about its longitudinal axis, the retracting process retracting the hob in its longitudinal direction through a distance which is equal to an axial movement amount of the hob resulting from rotating the hob; and 
     (d) a repeating process repeating the geared surface forming process and the retracting process to produce a full face-geared surface on the area of the work piece

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is based on and claims priority under 35 U.S.C. §119 to Japanese Patent Application 2006-077024 filed on Mar. 20, 2006, the entire content of which is incorporated herein by reference. 
       FIELD OF THE INVENTION 
       [0002]    The present invention relates to a method for manufacturing a member having a face-geared surface, for example a face gear, an electrode for a process or the like. 
       BACKGROUND 
       [0003]      FIG. 11A  and  FIG. 11B  each illustrates a spiral bevel gear meshing with a pinion.  FIG. 12A  and  FIG. 12B  each illustrates a face gear meshing with a pinion. The spiral bevel gear rolling contacts with the pinion on every portion on a pitch line thereof. The face gear, rolling contacts with the pinion only at a point at which a segment of a line equivalent to the pitch line of the spiral bevel gear is crossed. In recent years, attention has been paid to the face gear, since, in comparison with the spiral bevel gear, it is advantageous in terms of cost efficiency. 
         [0004]    Methods for gear cutting of such a face gear include a plunge cut method and a tangential feed method (“Machines and Tools”, July issue, 1998, pages 16 to 20). According to the plunge cut method, in a state in which a cutter faces a work piece, the cutter is disposed in a direction in which a shaft axis of the cutter and that of the work piece cross each other; while the cutter and the work piece are rotated at the same time, the cutter is fed toward the work piece; and then, gear cutting is performed on the work piece. According to the tangential feed method, in a state in which a cutter does not face a work piece at an initial position, the cutter is disposed in a direction in which a shaft axis of the cutter and that of the work piece cross each other; while the cutter and the work piece are rotated at the same time, the cutter is fed while being reciprocally moved along a radial direction of the work piece; and then, gear cutting is performed on the work piece. 
         [0005]    According to the methods described above, although a face gear is formed, the level of efficiency in forming a face-geared surface are not always sufficient. In the related industrial field, a demand exists for developing a method for forming a face-geared surface efficiently. 
         [0006]    A need thus exists to provide a manufacturing method by which a face-geared surface is formed efficiently. 
       SUMMARY OF THE INVENTION 
       [0007]    According to an aspect of the present invention, a method of producing a member having a face-geared surface includes steps of: (a) an initial operation preparing a work piece and a hob, the work piece having a partial area on which a face-geared surface is formed, the hob having a cutting blade, the hob being brought into an axial movement when rotated by an angle of 360 degrees about its longitudinal axis, the initial operation bringing the work piece to face the hob with a distance; (b) a face-geared surface forming operation forming the face-geared surface on the partial area of the work piece by rotating the hob about its longitudinal axis in one direction by an angle of less than 360 degrees after establishing of a mutual engagement between the hob and the work piece, which results from moving at least one of the hob and the work piece in a radial direction of the hob; and (c) a retracting operation retracting the at least one of the hob and the work piece in the radial direction of the hob to establish a separation of the hob from the work piece before the hob completes its 360 degree rotation about its longitudinal axis, the retracting operation retracting the hob in its longitudinal direction through a distance which is equal to an axial movement amount of the hob resulting from rotating the hob; wherein the face-geared surface forming operation and the retracting operation are repeated in order to form a full face-geared surface on the partial area of the work piece. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    The foregoing and additional features and characteristics of the present invention will become more apparent from the following detailed description considered with reference to the accompanying drawings, wherein: 
           [0009]      FIG. 1  illustrates a front view indicating states of a work piece and a hob immediately before a process is applied to the work piece by the hob; 
           [0010]      FIG. 2  illustrates a front view indicating states of the work piece and the hob immediately before a process is applied to the work piece by the hob; 
           [0011]      FIG. 3  illustrates a front view indicating states of the work piece and the hob, which are not offset; 
           [0012]      FIG. 4A  illustrates a diagram indicating a state at which the work piece is processed by a rotation of the hob; 
           [0013]      FIG. 4B  illustrates a diagram indicating a state at which the work piece is processed by the rotation of the hob; 
           [0014]      FIG. 4C  illustrates a diagram indicating a state at which the work piece is processed by the rotation of the hob; 
           [0015]      FIG. 4D  illustrates a diagram indicating a state at which the work piece is processed by the rotation of the hob; 
           [0016]      FIG. 4E  illustrates a diagram indicating a state at which the work piece is processed by the rotation of the hob; 
           [0017]      FIG. 4F  illustrates a diagram indicating a state at which the work piece is processed by the rotation of the hob; 
           [0018]      FIG. 5  illustrates a front view of the hob; 
           [0019]      FIG. 6A  illustrates a diagram indicating a process of producing a faced-gear, according to the second embodiment; 
           [0020]      FIG. 6B  illustrates a diagram indicating a process of producing a faced-gear, according to the second embodiment; 
           [0021]      FIG. 6C  illustrates a diagram indicating a process of producing a faced-gear, according to the second embodiment; 
           [0022]      FIG. 6D  illustrates a diagram indicating a process of producing a faced-gear, according to the second embodiment; 
           [0023]      FIG. 6E  illustrates a diagram indicating a process of producing a faced-gear, according to the second embodiment; 
           [0024]      FIG. 7  illustrates a diagram indicating a process of producing a faced-gear, according to the third embodiment; 
           [0025]      FIG. 8  illustrates a diagram indicating a process of producing a faced-gear, according to the fourth embodiment; 
           [0026]      FIG. 9  illustrates a diagram indicating a process of producing a faced-gear, according to the fifth embodiment; 
           [0027]      FIG. 10A  illustrates a diagram indicating a process of producing a faced-gear, according to the sixth embodiment; 
           [0028]      FIG. 10B  illustrates a diagram indicating a process of producing a faced-gear, according to the sixth embodiment; 
           [0029]      FIG. 10C  illustrates a diagram indicating a process of producing a faced-gear, according to the sixth embodiment; 
           [0030]      FIG. 10D  illustrates a diagram indicating a process of producing a faced-gear, according to the sixth embodiment; 
           [0031]      FIG. 10E  illustrates a diagram indicating a process of producing a faced-gear, according to the sixth embodiment; 
           [0032]      FIG. 11A  illustrates a cross section indicating a spiral bevel gear meshing with a pinion related to a prior art; 
           [0033]      FIG. 11B  illustrates a perspective view indicating the spiral bevel gear meshing with the pinion related to the prior art; 
           [0034]      FIG. 12A  illustrates a cross section indicating a face gear meshing with a pinion related to a prior art; and 
           [0035]      FIG. 12B  illustrates a perspective view indicating the face gear meshing with the pinion related to the prior art. 
       
    
    
     DETAILED DESCRIPTION 
       [0036]    According to the method of the present invention, a hob having a cutting blade and a work piece are prepared, and then, an initial operation is made so as to establish a state in which the hob and the work piece are positioned away from each other and face each other. In the initial operation, it is preferable that the work piece, and its shaft axis, and the hob, and its shaft axis, are positioned so as to form 90 degrees. It is preferable that the cutting blade of the hob is formed in a worm shape (in a helical screw shape). However, it should be noted that the hob has a vertical groove that crosses the cutting blade. 
         [0037]    After the initial operation, an operation of forming a face-geared surface is performed. In the face-geared surface forming operation, while the hob is rotated in one direction around its shaft axis, at least one of the hob and the work piece is advanced in a radial direction of the hob so that the hob and the work piece are pressed against each other. In this manner, during a period of one rotation around the shaft axis of the hob, a face-geared surface forming operation is completed in such a way that, within a degree of rotation of the hob of less than one rotation, a face-geared surface is formed on the work piece. In the face-geared surface forming operation, it is preferable that the work piece is in a non-rotating state. 
         [0038]    A retracting operation is performed after the face-geared surface forming operation. During the retracting operation, in the course of one rotation around the shaft axis of the hob, within the remaining degree of rotation of the hob, at least one of the hob or the work piece is retracted in the radial direction of the hob so that the hob and the work piece are positioned away from each other. In addition, in order to compensate for the movement in an axial direction of the hob that had occurred by the rotation of the hob during the face-geared surface forming operation, the hob is moved, for example outwardly, along a direction of the shaft axis of the hob. Further, in the retracting operation, it is preferable to feed the work piece so as to moved around the shaft axis of the work piece within a predetermined degree. In this manner, an area for the next gear-cut operation can be constantly faces the hob. 
         [0039]    The face-geared surface forming operation and the retracting operation, described above, are repeatedly performed, and eventually, a face-geared surface is formed on the work piece. The face-geared surface may preferably be a helical gear. 
         [0040]    Members having a face-geared surface include a gear member having a face-geared surface (a face gear per se) or an electrode having a face-geared surface. 
         [0041]    Electrical discharge machining, or electrochemical machining, is performed by use of an electrode formed in the aforementioned manner, whereby the face-geared surface of the electrode can be transfered on a die member. In this manner, a molding die is formed which has a face-geared surface formed by transfered the electrode face-geared surface thereon. Examples of the molding die are a resin molding for molding a resin molding article, a power pressurization molding for a molding powder before a process of sintering; and a molding for forging so as to mold a cast product. 
       First Embodiment 
       [0042]    Hereinafter, a first embodiment of the present invention will be described with reference to  FIG. 1  to  FIG. 5 . The present embodiment is provided as an example of forming a face gear  5  by means of the hob  41 . In order to implement a forming method of continuous gear cutting of the face gear  5 , it is preferable to take into consideration the following factors. 
         [0043]    (1) It is preferable to obtain a relative movement, which is adequate for gear cutting and machining for a work piece  2 , between a cutting blade  42  of the hob  41  and the work piece  2 . 
         [0044]    (2) Among the cutting blades  42  of the hobs  41 , it is preferable to ensure that the cutting blades  42  used as many as possible. 
         [0045]    (3) It is preferable to utilize or shorten an idling time of the hob  41 , in other words, to utilize or shorten a non-cutting time of the hob  41 . 
         [0046]    In order to achieve these factors, according to the present embodiment, a regular hob  41  is employed. In addition, a forming method of continuous gear cutting is provided for controlling advancing of a hob shaft head  4  (the direction indicated by arrow L 1  in an inward direction of the work piece radial direction); retracting of the hob shaft head  4  (the direction indicated by arrow L 2  in an outward direction of the work piece radial direction);the rotation of the hob shaft head  4  around a hob shaft axis  40  (longitudinal axis); advancing of a work piece shaft head  3  (the direction indicated by arrow F 1 ), retracting of the work piece shaft head  3  (the direction indicated by arrow F 2 ); and rotation of the work piece  2  around a work piece shaft axis  30  (longitudinal axis). Thus the face gear  5  is formed efficiently without rotating the hob  41  in a reverse direction of a gear cutting direction, while the hob  41  is being rotated around the hob shaft axis  40  in the gear cutting direction. 
         [0047]      FIG. 1  and  FIG. 2  schematically illustrate an apparatus for conducting the method of the present invention. The apparatus is a face gear cutting machine of simultaneous four-shaft control, or a hobbing machine having similar functions. This apparatus is equipped with the work piece shaft head  3  for rotating the work piece  2  around the work piece shaft axis  30 ; and the hob shaft head  4  for rotating the hob  41  around the hob shaft axis  40 . The hob  41  used in an aspect of  FIG. 1  is a right torsion hob. 
         [0048]    In other words, the work piece shaft head  3  has a function of rotating the work piece  2  around the work piece shaft axis  30  and a function of advancing and retracting the work piece  2  in a direction along the work piece shaft axis  30  (the direction indicated by the arrow F 1  or the arrow F 2 ). The hob shaft head  4  has a function of rotating the hob  41  around the hob shaft axis  40  and a function of advancing and retracting the hob  41  in a direction along the hob shaft axis  40  (the direction indicated by the arrow L 1  and the arrow L 2 ). As shown in  FIG. 1  and  FIG. 2 , the hob shaft axis  40  exists on a horizontal face. The work piece shaft axis  30  and the hob shaft axis  40  both exist on a horizontal face, and they cross each other at a predetermined angle θ (θ=90 degrees). 
         [0049]    A material that is capable of cutting (for example, an iron-based metal, a copper-based metal, a carbon material such as graphite, or a resin material) is used as a base material for the work piece  2 . The work piece  2  has a ring-shaped gear cutting area  20  that completes one circumference of the work piece shaft axis  30 . The work piece  2  is gear cut, and then, serves as the face gear  5 . A distance from an internal end to an external end in a tooth-widthwise direction of a gear cutting area  20  of the work piece  2 , serving as the face gear  5 , is defined as M (refer to  FIG. 1 ). Therefore, the distance M is equivalent to a distance from an internal end  23  to an external end  24  in a tooth-widthwise direction of the gear cutting area  20  of the face gear  5  that is formed at the work piece  2 . 
         [0050]    The hob  41  serves as a gear-cutting tool, and is formed in a cylindrical shape. As shown in  FIG. 5 , the hob  41  forms a warm-shaped cutting blade  42  (in a helical screw shape) on the outer periphery of the cylinder. The cutting blade  42  is wound around the hob shaft axis  40 . A vertical groove  43  is formed along an axially lengthwise direction of the hob  41 . A helix angle of the cutting blade  42  of the hob  41  is equal to that of a gear part of a pinion that serves as a counterpart gear meshing with that of the face gear  5  manufactured according to the method of the present embodiment. 
         [0051]    Such the hob  41  is a generally used hob. When the hob  41  makes one rotation of the hob shaft axis, the hob  41  advances by one pitch. The direction indicated by the arrow D represents a radial direction of the hob  41 . 
         [0052]    In this context, a full length MA of the hob  41  (refer to  FIG. 1 ) includes the dimensional distance M from an internal end  23  to an external end  24  of a tooth width of the face gear  5 . In addition, because the cutting blade  42  of the hob  41  is made to perform a screw movement, the full length MA further includes a distance that is substantially equivalent to one lead of the hob  41 . Further, when an offset exists between the hob shaft axis  40  and the work piece shaft axis  30 , the entire length MA of the hob  41  is defined taking into account the offset OA between the hob shaft axis  40  and the work piece shaft axis  30  (refer to  FIG. 2 ). When no offset exists between the hob shaft axis  40  and the work piece shaft axis  30 , with regard to the entire length MA of the hob  41 , there is no need to consider any amount of offset OA between the hob shaft axis  40  and the work piece shaft axis  30 . 
         [0053]    According to the embodiment, on the basis of specifications relevant to the tooth portion of the face gear  5  that serves as a manufacturing target, as shown in  FIG. 2 , the offset amount OA is formed between the hob shaft axis  40  and the work piece shaft axis  30 .  FIG. 3  schematically illustrates a state in which the offset amount OA between the hob shaft axis  40  and the work piece shaft axis  30  is 0. 
         [0054]      FIG. 1  and  FIG. 2  illustrate an exemplary initial operation. In the initial operation, as illustrated in  FIG. 1  and  FIG. 2 , the work piece  2  is coaxially mounted on the work piece shaft head  3  and the hob  41  is coaxially mount on the hob shaft head  4 . At this point, as illustrated in  FIG. 1 , an outer periphery of the hob  41  faces a gear cutting area  20  of the work piece  2  in a state in which they are positioned apart from each other by an initial gap W. Therefore, the hob  41  can make contact immediately with the gear-cutting area  20  of the work piece  2 . From this point, an improvement in production efficiency can be achieved. The initial gap W may varies depending on sizes such as that of the face gear. The initial gap W has been exemplified as between 1 and 5 millimeters, but need not be thus restricted. 
         [0055]    In the initial operation, as illustrated in  FIG. 1  and  FIG. 2 , as viewed in the direction indicated by the arrow X 1  that serves as a direction parallel to that of the work piece shaft axis  30 , the hob  41  transversely crosses a ring-shaped gear cutting area  20  of the work piece  2 . In other words, as viewed in the direction indicated by the arrow X 1 , the ring-shaped gear cutting area  20  of the work piece  2  and the hob  41  overlap with one another and the ring-shaped gear cutting area  20  of the work piece  2  faces the cutting blade  42  of the hob  41  each other. 
         [0056]    In this context, in the initial operation, as illustrated in  FIG. 2 , a distal end  41   a  in a lengthwise direction of the hob  41  is positioned in a radial direction that is more inward than an inner periphery  20   i  of the ring-shaped gear cutting area  20  of the work piece  2 . In addition, a proximal end  41   c  in a lengthwise direction of the hob  41  is positioned in a radial direction that is more outward than an outer periphery  20 p of the ring-shaped gear cutting area  20  of the work piece  2 . In such circumstances, the cutting blades  42  of the hobs  41  can be used as many as possible. Further, in gear cutting operation, the extent of movement of the hob  41  along the axially lengthwise direction can be reduced (the direction indicated by the arrow L 1  or L 2 ). Therefore, there is no need to move reciprocally the hob  41  from the outer periphery  20 p to the inner periphery  20 i of the ring-shaped gear cutting area  20  of the work piece  2 . 
         [0057]      FIG. 4A  through  FIG. 4F  illustrate respective stage of one rotation of the hob  41  around the hob shaft axis  40  thereof. In the initial operation described above, as illustrated in  FIG. 4A , the hob  41  is first set at a preliminary position at which the distal end  42 a of the cutting blade  42  of the hob  41  comes into contact with a surface of the gear cutting area  20  of the work piece  2 , and thus the initial gap W mentioned above becomes 0. In such circumstances, it is preferable that a center cutting blade  42  in an axially lengthwise direction of the hob  41  is employed as a reference. 
         [0058]    Moreover, the hob  41  is rotated around the hob shaft axis  40  in a direction that is the reverse (the direction indicated by arrow R 2 ) of the rotational direction (the direction indicated by arrow R 1 ), only by an angle of θ 2  (90 degrees). Further, as illustrated in  FIG. 4B , the hob  41  is positioned away from the work piece shaft axis  30  so as to substantially parallel thereto, separated by an initial gap W relative to a surface of the gear cutting area  20  of the work piece  2 . Therefore, the initial gap W in a direction that is parallel to the work piece shaft axis  30  is equivalent to a gap between the hob  41  and a surface of the gear cutting area  20  of the work piece  2 . A position B illustrated in  FIG. 4  is equivalent to a position at which a rotational angle a of the hob  41  is 0 degrees, and thus, this position is defined as a reference position. In other words, position B that is illustrated in  FIG. 4  is equivalent to a reference position at which the rotational angle a of the hob  41  is 0 degrees (start position of gear cutting). 
         [0059]    A position C illustrated in  FIG. 4  is equivalent to a position at which the rotational angle a of the hob  41  is 30 degrees. A position D illustrated in  FIG. 4  is equivalent to a position at which the rotational angle a of the hob  41  is 150 degrees. A position E illustrated in  FIG. 4  is equivalent to a position at which the rotational angle a of the hob  41  is 180 degrees. A position F illustrated in  FIG. 4  is equivalent to a position at which the rotation angle a of the hob  41  is 360 degrees. 
         [0060]    In  FIG. 4 , an interval  1  is equivalent to a range extending between the positions B and C, and the rotational angle a of the hob  41  is within a range of from 0 degrees to about 30 degrees. Similarly, an interval  2  is equivalent to a range extending between the positions C and D, and the rotational angle α of the hob  41  is within a range of from about 30 degrees to about 150 degrees; an interval  3  is equivalent to a range extending between the positions D and E, and the rotational angle a of the hob  41  is within a range of from about 150 degrees to about 180 degrees; and an interval  4  is equivalent to a range extending between the positions E and F, and the rotational angle a of the hob  41  is within a range of from about 180 degrees to about 360 degrees. 
         [0061]    With regard to interval  1 , as mentioned above, because this interval is equivalent to a range extending between the positions B and C, while the hob  41  is being rotated around the hob shaft axis  40  in a normal gear cutting direction (the unidirectional direction indicated by arrow R 1 ), the work piece  2  is advanced by means of the work piece shaft head  3  in the direction indicated by the arrow F 1  along the radial direction of the hob  41  (the direction indicated by arrow D). As a result, as illustrated in  FIG. 4C , the hob  41  and the work piece  2  are pressed against each other, and then, the hob  41  cuts into a surface of the gear cutting area of the work piece  2 . A depth of cut relative to the work piece  2  is referred to as KA (refer to  FIG. 4C ). 
         [0062]    In such circumstances, the hob  41  is retracted along the hob shaft axis  40  in the direction indicated by arrow L 2 . In this manner, the hob  41  is retracted while it is being rotated around the hob shaft axis  40 , and thus, the cutting blade  42  of the hob  41  performs a screw motion. At this time, as illustrated in  FIG. 4C  and  FIG. 4D , during a period of one rotation around the hob shaft axis  40  of the hob  41 , by virtue of a screw motion of the hob  41  that is equivalent to substantially a half rotation, or a rotation that is close thereto, a face-geared surface  50  is formed at the part of the gear cutting area  20  of the work piece  2 . 
         [0063]    A further description will now be provided. With regard to the interval  2  mentioned above, gear cutting is performed by means of the hob  41  relative to the gear cutting area  20  of the work piece  2 . In other words, as mentioned above, in a state in which the work piece  2  is retained in a non-rotation state (an immobile state), while the hob  41  is rotated around the hob shaft axis  40  in a gear cutting direction (an unidirectional direction indicated by arrow R 1 ), the hob  41  is retracted along the hob shaft axis  40  of the hob  41  in the direction indicated by arrow L 2 . In this manner, the cutting blade  42  of the hob  41  performs a screw motion. This can be said to be a motion that is equivalent to screw cutting by means of a screw tap. Therefore, as the hob  41 , a hob free of outer periphery relief or a hob with a lesser degree of outer periphery relief, can be used, thus contributing to a reduction in costs. 
         [0064]    During the course of one rotation around the hob shaft axis  40  of the hob  41 , by means of substantially a half rotation, or an approximate half rotation, a face-geared surface  50  is formed at a part of the gear cutting area  20  of the work piece  2 . In the face-geared surface forming operation described above, by virtue of the substantially half rotation of the hob  41 , the hob  41  moves along the hob shaft axis  40  in the direction indicated by arrow L 2 . This is an axial movement of the hob  41 . With reference to  FIG. 4D , a rotational angle at which the hob  41  cuts into the work piece  21  is defined as θW. According to  FIG. 4D , θW remains within a half rotation during a period of one rotation of the hob  41 , that is, within 180 degrees. 
         [0065]    As for interval  3 , since this interval is equivalent to the range of positions between D and E, during the course of one rotation around the hob shaft axis  40  of the hob  41 , the rotational angle θW of the hob  41  is between about 150 degrees and about 180 degrees, the work piece  2  is retracted from the work piece shaft head  3  along the radial direction of the hob  41  (the direction indicated by arrow D), in other words, in a direction indicated by arrow F 2 , and thus the hob  41  and the work piece  2  are positioned away from each other. At this time also, the hob  41  rotates in the gear cutting direction (the direction indicated by arrow R 1 ). 
         [0066]    As for interval  4 , because this interval is equivalent to the range of positions between E and F, during the course of the last half rotation of the hob  41  around the hob shaft axis  40  thereof (180 degrees to 360 degrees), in order to recompense for the axial movement of the hob  41  mentioned above (movement of the hob  41  along the direction indicated by the arrow L 2 ), movement that had occurred due to the first rotation of the hob  41  (zero degree to 180 degrees)in the face-geared surface forming operation described above, 
         [0067]    the hob  41  is advanced along the hob shaft axis  40  in the direction indicated by arrow L 1 . In this manner, in the axially lengthwise direction of the hob  41 , a positional relationship between the hob  41  and the work piece  2  is restored to their initial position. 
         [0068]    Further, in the interval  4 , in order to prepare for the next machining step, the work piece  2  is rotated by a slight amount around the work piece shaft axis  30  to a minimal degree in a work piece feed direction (the direction indicated by arrow EA). A feed is thereby provided to the work piece  2 . In addition, a ratio of the number of teeth between the hob  41  and the work piece  2 , and a degree of rotation (feeding) appropriate to the extent of feed of the work piece  2  are provided to the hob  41 . Alternatively, the feed of the hob  41  may be replaced with the axial movement along the hob shaft axis  40  of the hob  41 . In this manner, the initial position of the hob  41  can always be fixed, and similar machining can be performed even if a hob having a cutting blade within entire periphery thereof is not used. 
         [0069]    According to the present invention, the operations illustrated in  FIG. 4B  to  FIG. 4F , and described above, are repeatedly performed sequentially. In other words, during a period when one rotation of the hob  41  around the hob shaft axis  40  is taking place, there are sequentially performed: a cutting motion of the hob  41 ; a screw motion of the hob  41  for gear cutting; a spacing motion between the hob  41  and the work piece  2  caused by retraction of the work piece  2 ; and a motion of correcting the axial position of the cutting blade  42  of the hob  41  so as to prepare for the next machining. 
         [0070]    In the present embodiment, the gear cutting process of the work piece  2  is finished by completing one rotation of the work piece  2  around the work piece shaft axis  30  of the work piece  2 , that is, when the gear cutting area  20  of the work piece  2  is rotated by 360 degrees around the work piece shaft axis  30 , the gear cutting process is finished. The work piece  2  is thereby manufactured as the face gear  5  having a helical face-geared surface  50 . 
         [0071]    According to the present embodiment as mentioned above, at an initial position, the hob  41  faces the work piece  2  with a distance. Therefore, since the hob  41  can rapidly be put into contact with the work piece  2 , the entire processing time can be advantageously shortened, and, a face gear  5  can according be efficiently manufactured. For this face gear  5 , a worm (screw-shaped gear) is used as a pinion (a counterpart gear meshing with the face gear  5 ). 
         [0072]    Therefore, according to the present embodiment, a gear combination of the face gear  5  and the worm can be formed. A combination of the face gear  5  and the work piece is highly efficient in comparison with that of a worm gear and a worm wheel, and a highly-efficient, inexpensive reduction gear can be advantageously provided. 
         [0073]    Further, according to the present embodiment, in the face-geared surface forming operation, the face-geared surface  50  is formed by the less than one rotation of the hob  41  around the hob shaft axis  40 . Then, during the remaining rotation of the hob  41 , the work piece  2  is retracted so that the hob  41  and the work piece  2  are positioned away from each other. The idling time of the hob  41  is thereby shortened, and thus, the entire processing time can be shortened. 
         [0074]    In the present embodiment, in the face-geared surface forming operation and the retracting operation mentioned above, the hob  41  may be continuously rotated around the hob shaft axis  40  only in the gear cutting direction (the direction indicated by arrow R 1 ). In other words, in the face-geared surface forming operation and the retracting operation mentioned above, the hob  41  does not need to be rotated toward the direction (the direction indicated by arrow  2 ) that is opposite to the gear cutting direction (the direction indicated by arrow R 1 ). Therefore, this process can be the forming method of continuous gear cutting of the face gear  5 . 
         [0075]    In the present embodiment, machining for cutting out a tooth is performed at the interval  2 . At the interval  2 , the work piece  2  is still in a non-rotational state, and only the hob  41  performs a screw motion along the thread direction of the hob  41 . This motion is equivalent to screw cutting by means of a screw tap. Therefore, in a similar way to the case of the screw tap, for the hob  41  used in the gear cutting of the face gear  5 , a hob can be used that is free of an outer periphery relief, or a hob with lesser degree of outer periphery relief. This fact is advantageous in facilitating hob manufacturing. A hob having an outer periphery relief may of course be used. 
         [0076]    In the present embodiment, in the operation mentioned above, the work piece  2  is advanced by means of the work piece shaft head  3  in a forward direction (the direction indicated by arrow F 1 ), or is retracted in a backward direction (the direction indicated by arrow F 2 ). However, in areas illustrated in  FIG. 4B  to  FIG. 4E , the work piece  2  does not basically rotate around the work piece shaft axis  30 . However, as shown in  FIG. 4F , after gear cutting has been completed, the work piece  2  is rotated for the purpose of feeding by an amount of feeding in the feed direction (the direction indicated by arrow EA). In this manner, from among the gear cutting areas  20  of the work piece  2 , a new portion becomes so as to face the hob  41 . 
         [0077]    According to the present embodiment, at the interval  2 , while the hob  41  is being rotated around the hob shaft axis  40  in the gear cutting direction (the unidirectional direction indicated by arrow R 1 ), the hob  41  is retracted along the hob shaft axis  40  in the direction indicated by arrow L 2 . However, the invention is not limited thereto, and at the interval  2 , while the hob  41  is being rotated around the hob shaft axis  40  in the gear cutting direction (the unidirectional direction indicated by arrow R 1 ), instead of moving the hob  41  in such a way that the hob  41  is retracted relatively along the hob shaft axis  40  in the direction indicated by arrow L 2 , the work piece  2  may be moved toward the hob  41 . 
         [0078]    In the present embodiment described above, during the interval  3 , the work piece  2  is retracted along the radial direction of the hob  41  (direction indicated by the arrow D), in other words, in the direction indicated by arrow F 2  by means of the work piece shaft head  3 , and the hob  41  and the work piece  2  are thus positioned away from each other. However, the invention is not limited thereto, and instead of moving the hob  41 , the work piece  2  may be moved so as to relatively retract the work piece  2  by means of the work piece shaft head  3  in the direction indicated by arrow F 2 . 
         [0079]    In the present embodiment, since the precision of the tooth portion of the face gear  5  can be guaranteed, lapping and polishing by means of an actual gear is not necessary. Further, while a right screw hob has been used in the present embodiment, a left screw hob may also be used. In such a case, the axial direction movement of the hob at each interval needs to be inverted from that of the present embodiment. 
         [0080]    In the present embodiment, on the basis of the discussions relating to a face gear  5  that serves as a manufacturing target, as illustrated in  FIG. 2 , an offset amount OA is defined between the hob shaft axis  40  and the work piece shaft axis  30 . However, the invention is not limited thereto, and as illustrated in  FIG. 3 , an offset amount OA between the hob shaft axis  40  and the work piece shaft axis  30  may be set to 0. 
         [0081]    According to the present embodiment, on the face-geared surface  50 , a cross section of a tooth portion may be, or may not be, taken along an involute curve. 
         [0082]    While in the face gear  5 , manufactured in the embodiment described above, a worm (screw-shaped gear) is used as a pinion (counterpart gear meshing with the face gear  5 ), the invention is not limited thereto. A helical gear may serve as a counterpart gear. 
       Second Embodiment 
       [0083]      FIG. 6  illustrates a second embodiment of the present invention. The second embodiment is provided as an example in which the face gear is applied to a molding die  70  (member) for resin-molding the face gear. The present embodiment basically has the same configuration and the same advantageous effect as that in the first embodiment. Therefore,  FIG. 1  to  FIG. 5  can each be applied mutatis mutandis. However, according to the present embodiment, the work piece  2  is made of an electrode forming material such as graphite or a copper alloy. 
         [0084]    In the present embodiment, by means of an operation similar to that in the first embodiment, a face gear  5 C is manufactured for which the aforementioned electrode forming material is used as a base material. Further, as shown in  FIG. 6A  and  FIG. 6B , a face gear  5 C is employed as an electrode  6  for electrical discharge machining. Specifically, the electrode  6  for electrical discharge machining and a die member  8  are immersed in a metal working fluid  102  that has electrical insulation properties, and that is contained in a metal working fluid tank  100 . In this state, the electrode  6  and the die member  8  are made to approach one another, and are made to face each other. Then, an electric discharge is generated between the electrode  6  and the die member  8 , and, a helical face-geared surface  50 C that is formed on the electrode  6  is then transfered on the die member  8 . In this manner, as shown in  FIG. 6C , the mold die  70  is formed having a cavity  73  with a transfered face-geared surface  72  obtained by copying the face-geared surface  50 C thereon. 
         [0085]    The mold die  70  mentioned above is employed as a mold die for resin ejection molding. In other words, as illustrated in  FIG. 6D , the mold die  70  and a counterpart die  75  are die-clamped. Then, a resin material  300  that has fluidity is ejection-molded in a cavity  73  of the mold die  70 , and then, the resin material  300  is solidified. By die-opening the counterpart die  75  and the mold die  70 , a face gear  5 D that serves as a resin molded component can be obtained, the face gear  5 D which has a face-geared surface  50 D onto which a transfered face-geared surface  72  of the mold die  70  has been retransfered. For this face gear  5 D, a worm is used as a pinion (a counterpart gear meshing with the face gear  5 ). 
       Third Embodiment 
       [0086]      FIG. 7  illustrates a third embodiment. In the present embodiment, the mold die  70  is used as a mold die for sintering molding, the mold die having the cavity  73  with a transfered face-geared surface  72  that is made by copying the helical face-geared surface  50 C as mentioned above. In this case, the cavity  73  of the mold die  70  is filled with a metal powder material  310 . The metal powder material  310  is pressurized by means of a counterpart die  75 C and the mold die  70 . In this manner, a pressurized powdered member  5 E having a face-geared surface  50 E, onto which a transfered face-geared surface  72  of the mold die  70  has been retransfered, is produced. A face gear  5 E 1  that serves as a sintered article that has the face-geared surface  50 E 1  can be obtained by heating and retaining the pressurized powdered member  5 E under a sintering temperature environment. For this face gear  5 E 1 , a worm is used as a pinion (a counterpart gear meshing with the face gear  5 ). 
       Fourth Embodiment 
       [0087]      FIG. 8  illustrates a fourth embodiment of the invention. In the present embodiment, the aforementioned mold die  70  having the cavity  73  with the transfered face-geared surface  72  on which the helical face-geared surface  50 C has been transfered is employed as a mold die for forging molding. In this case, by employing the counter die  75 , a lump of metal  320  is pressurized and plastically deformed by means of the cavity  73  of the mold die  70 , and thus, a cast product is formed. In this manner, a face gear  5 F that serves as a cast product is molded, a face gear that has a face-geared surface  50 F onto which a transfered face-geared surface  72  of the mold die  70  has been retransfered. 
       Fifth Embodiment 
       [0088]      FIG. 9  illustrates a fifth embodiment. In the present embodiment, the mold die  70  is employed as a mold die for forging molding, the mold die having the cavity  73  with a transfered face-geared surface  72  onto which the aforementioned face-geared surface  50 C has been transfered. In a state in which the counterpart die  75  and the mold  70  are die-clamped, a molten metal  330  is poured and coagulated by means of the cavity  73  of the mold die  70 , and, thus, a forged product is formed. In this manner, a face gear  5 K that serves as a forged product is molded, a face gear that has a face-geared surface  50 K onto which the transfered face-geared surface  72  of the mold die  70  has been retransfered. 
       Sixth Embodiment 
       [0089]      FIG. 10  illustrates a sixth embodiment  6 . The present embodiment basically attains a common construction and a common advantageous effect. Therefore,  FIG. 1  to  FIG. 5  each can be applied mutatis mutandis. However, it should be noted that, according to the present embodiment, the work piece  2  is formed of an electrode forming material for electrochemical machining. 
         [0090]    In the present embodiment, a face gear  5 T made of an electrode forming material for electrochemical machining is formed by means of an operation similar to that of the first embodiment. This face gear  5 T is employed as an electrode  6 T for electrochemical machining. In other words, as illustrated in  FIG. 10A  and  FIG. 10B , the electrochemical machining electrode  6 T and the die member  8 T are immersed in an electrolyte solution  102 T contained in a tank  100 T. With the electrochemical machining electrode  6 T being a cathode (negative pole) and with the die member  8 T being an anode (positive pole), the electrode  6 T and the die member  8 T are set at an electrochemical machining device while they are opposite to each other. In this state, while power is being supplied between the cathode (negative pole) and the anode (positive pole), the electrode  6 T is fed to the die member  8 T. Then, the electrolyte solution is ejected from an electrolyte solution ejection pore  600 , which has been formed on the electrode  6 T, into a gap between the electrode  6 T and the die member  8 T. A surface part of the die member  8 T that serves as an anode is chemically eluted thereby. As a result, a face-geared surface  59 T that is formed on the electrode  6 T is transfered to the surface part of the die member  8 T. In such a manner, as illustrated in  FIG. 10C , a mold die  70  is formed which has a cavity  73 T with a transfered face-geared surface  72 T onto which a face-geared surface  50 T of the electrode  6 T has been transfered. 
         [0091]    The mold die  70  described above is employed as a mold die for resin ejection molding. In other words, the mold die  70  and the counterpart die  75  are die-clamped. Then, a resin material  350  that has fluidity is ejection-molded within a cavity  73 T of the mold die  70 , and, the resin material  350  is then solidified. By die-opening the mold die  70 , a face gear  5 T that serves as a resin molded component can be obtained, a face gear that has a face-geared surface  50 T onto which a transfered face-geared surface  72 T of the mold die  70  has been transfered. 
         [0092]    The present invention is not limited to the embodiments that are described above, and that are illustrated in the accompanying drawings, and can also be carried out by appropriate modification without departing from the spirit of the invention. 
       INDUSTRIAL APPLICABILITY 
       [0093]    According to the present invention, a face gear, an electric discharging electrode, or an electrolysis electrode, for example, can be exemplified as members that can be utilized according to a method for manufacturing the member having a face-geared surface. 
         [0094]    According to the present embodiment as mentioned above, at an initial position, the hob faces the work piece with a distance. Therefore, since the hob can rapidly be put into contact with the work piece, the entire processing time can be advantageously shortened, and, a face gear can according be efficiently manufactured. 
         [0095]    Further, according to the present embodiment, in the face-geared surface forming operation, the face-geared surface is formed by the less than one rotation (360 degrees) of the hob around the longitudinal axis thereof. Then, during the remaining rotation of the hob, the work piece is retracted so that the hob and the work piece are positioned away from each other. The idling time of the hob is thereby shortened, and thus, the entire processing time can be shortened. 
         [0096]    According to the present embodiment, the mold die with the cavity having the transfered face-geared surface is produced, and by means of such mold die, the face gear can be mass-produced. 
         [0097]    According to the present embodiment, the transfered face-geared surface of the mold die is further transfered to the molding material existing within the mold die. Thus, the face gear having the face-geared surface can be mass produced. 
         [0098]    The principles, preferred embodiment and mode of operation of the present invention have been described in the foregoing specification. However, the invention which is intended to be protected is not to be construed as limited to the particular embodiments disclosed. Further, the embodiments described herein are to be regarded as illustrative rather than restrictive. Variations and changes may be made by others, and equivalents employed, without departing from the sprit of the present invention. Accordingly, it is expressly intended that all such variations, changes and equivalents which fall within the spirit and scope of the present invention as defined in the claims, be embraced thereby.