Abstract:
The finishing part ( 4 ) of this helical broach ( 1 ) is formed by a first shell ( 20 ) and a second shell ( 30 ) which are divided in the axial direction, and is obtained by forming a first finishing blade ( 50 ), which comprises a prescribed gear tooth helix angle (α) end a first blade groove helix angle (β 1 ), on the aforementioned first shell ( 20 ) and forming a second finishing blade ( 60 ), which comprises the aforementioned prescribed gear tooth helix angle (α) and a second blade groove helix angle (β 2 ) which differs from the aforementioned first blade groove helix angle (β 1 ) on the aforementioned second shell ( 30 ).

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a helical broach. 
       BACKGROUND ART 
       [0002]    As a working method of cutting an internal gear which is a typo of gear, there is broaching in which a broach is used as a cutting tool in which blades are arranged in a saw shape (for example, PTL 1). This is internal work performed on a workpiece by installing, in a broaching machine as a working machine dedicated to broaching, a broach and the workplace as a piece to be cut, and pulling the broach with respect to the workpiece or pulling the workplace with respect to the fixed broach. 
         [0003]    A broach is a bar-shaped bladed material in which a large number of cutting blades are arranged to be formed in a saw shape, and the cutting blades of the broach are arranged in dimensional order such that the height and the blade width of the blades gradually increase from one end side (the leading end of the cutting direction) toward the other end side (the trailing end of the cutting direction). One of the features of the broach is that various working processes can be combined, in a single cutting tool. For example, in a case where a broach having a roughing section for roughing of the workplace and a finishing section for finishing of the workpiece is used, in the broaching machine, roughing and finishing are completed only by pulling the broach with respect to the workpiece once such that the workpiece can be forced to an internal gear. 
         [0004]    Since broaching is performed by only pulling the workpiece or the broach once, working speed from roughing to finishing of the workpiece is faster than that of other internal work. In addition, the finished dimensions of the workpiece by broaching become substantially the same as those of the final blades (finishing blades at the rearmost end of the cutting direction) of the broach used for working, and thus cutting work can be performed with high accuracy and the repetition accuracy of the cutting work is high. 
         [0005]    As a type of broach, there is a helical broach. This is for cutting a workplace to a helical internal gear in which the tooth lead of the internal gear is inclined with respect to the axis of the gear. The helical broach and the workplace are installed on a broaching machine and the helical broach is pulled with respect to the workplace while being rotated, thereby forming the workplace to the helical internal gear. 
         [0006]    An example of an existing helical broach is illustrated in  FIG. 4 , and a method of finishing a workplace in the existing helical broach is illustrated in  FIG. 5 . 
         [0007]    As illustrated in  FIG. 4 , a helical broach  101  includes a roughing section  103  and a finishing section  104 , and roughing blades (not illustrated) in the roughing section  103  and finishing blades  150  ( FIG. 5 ) in the finishing section  104  are arranged to be inclined with respect to the axial direction of the helical broach  101 . 
         [0008]    In the roughing blades (not illustrated) in the roughing section  103  and the finishing blades  150  in the finishing section  104 , a gear tooth helix angle α is set along the tooth lead direction of the helical internal gear to be formed. In order to enhance the working accuracy and the like, in the finishing blades  150  in the finishing section  104 , a blade groove helix angle β may further be set. 
         [0009]    In addition, the blade groove helix angle β is set to a direction that is not perpendicular to the direction of the gear tooth helix angle α in order to enhance the working accuracy and the like. Therefore, as illustrated in  FIG. 5 , one end portion  151  (upper left portion in  FIG. 5 ) in the finishing blade  150  has an acute angle, and the other end portion  152  (lower left portion in  FIG. 5 ) has an obtuse angle. 
         [0010]    In addition, in order to enhance the working accuracy and the like, in the finishing section  104  of che helical broach  101 , a single finishing blade  150  is set to abut and cut only one of tooth surfaces including a left tooth surface  170  in a work-piece W (one tooth surface along the tooth lead of the workpiece W) and a right tooth surface  180  (the other tooth surface along che cooth lead of the workpiece W). That is, the finishing blades  150  in the finishing section  104  of the helical broach  101  are formed to be divided into left tooth surface finishing blades  150   a  which cut only the left tooth surfaces  170  in the workplace W and right tooth surface finishing blades  150   b  which cut only the right tooth surfaces  180  in the workpiece W. 
         [0011]    Therefore, the left tooth surface finishing blade  150   a  performs cutting by allowing an acute angle portion  151  to abut the left tooth surface  170  in the workpiece W, and the right tooth surface finishing blade  150   b  performs cutting by allowing an obtuse angle portion  152  to abut the right tooth surface  180  in the workpiece W. 
       CITATION LIST 
     Patent Literature 
       [0012]    [PTL 1] Japanese Patent Application Publication No. 2009-220261 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0013]    However, in a case where the tooth surface (the right tooth surface  180  in  FIG. 5 ) of the workpiece W is cut by the obtuse angle portion  152 , the surface roughness of the cut surface is increased compared to a case where the tooth surface (the left tooth surface  170  in  FIG. 5 ) of the workpiece W is cut by the acute angle portion  151 . Therefore, a cutting amount d 2  (the amount of the tooth surface of the workpiece W being cut by each blade) with which the obtuse angle portion  152  performs cutting has to be set to be smaller than a cutting amount d 1  with which the acute angle  151  perforins cutting. Accordingly, in order to cut equal amounts of the left tooth surface  170  and the right tooth surface  180  of the workpiece W, the number of blades of the obtuse angle portion  152  needs to be greater than the number of blades of the acute angle portion  151 . This results in an increase in the axial length of the finishing section  104 , that is, a shell  120 , and thus causes an increase in the size of the tool and the working machine and an increase in the manufacturing cost. 
         [0014]    The present invention has been made by taking the foregoing problems into consideration, and an object thereof is to reduce the axial length of a finishing section by allowing no difference in the cutting accuracy between a right tooth surface and a left tooth surface of a workpiece which is a piece to be cut, during broaching by a helical broach. 
       Solution to Problem 
       [0015]    A helical broach according to a first invention to solve the problems is a helical broach including: a cylindrical shell in which finishing blades having a predetermined gear tooth helix angle are formed on an outer peripheral side, in which the shell includes a first shell and a second shell which are divided in an axial direction, a first finishing blade having the gear tooth helix angle and a first blade groove helix angle is formed in the first shell, and a second finishing blade having the gear tooth helix angle and a second blade groove helix angle which is different from the first blade groove helix angle is formed in the second shell. 
         [0016]    A helical broach according to a second invention to solve the problems is the helical broach according to the first invention, in which the first finishing blade cuts one tooth surface along a tooth lead in a piece to be cut, and the second finishing blade cuts the other tooth surface along the tooth lead in the piece to be cut. 
         [0017]    A helical broach according to a third invention to solve the problems is the helical broach according to the first or second invention, in which both of a rake angle of the first finishing blade and a rake angle of the second finishing blade are an acute angle. 
       Advantageous Effects of Invention 
       [0018]    According to the helical broach according to the first invention, since the shell has the structure divided into the first shell and the second shell, the finishing blades having different gear tooth helix angles can be formed in the single helical broach. For example, the first finishing blade in the first shell has an appropriate shape to cut one surface in the piece to be cut, and the second finishing blade in the second shell has an appropriate shape to cut the other surface in the piece to be cut stxch that the finishing blades that match the surfaces of the piece to be cut can be formed. 
         [0019]    According to the helical broach according to the second invention, since the first finishing blade in the first shell cuts one surface in the piece to be cut and the second finishing blade in the second shell cuts the other surface in the piece to foe cut, the finishing blades that toatch the surfaces of the piece to be cut can be formed. For example, the finishing blades having an appropriate acute angle for the cutting perform cutting while abutting a right tooth surface and a left tooth surface of the piece to be cut, and thus the working accuracy and the surface roughness of the cut surface of the piece to be cut can be enhanced. 
         [0020]    According to the helical broach according to the third invention, since the right tooth surface and the left tooth surface of the piece to be cut are cut by the finishing blades having an appropriate acute angle for the cutting, the working accuracy and the surface roughness of the cut surface of the piece to be cut can be enhanced. In addition, the tooth surfaces of the piece to be cut are not cut by finishing blades having an obtuse angle which is not appropriate for the cutting. Accordingly, there is no need to reduce cutting amounts unlike the related art and the cutting amounts of the finishing blades can be set to be sufficiently large. Therefore, the axial lengths of the shell in which the first shell and the second shell are assembled, and the finishing section can be reduced, and thus the tool and the working machine can also be reduced in size, thereby reducing the manufacturing cost. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0021]      FIG. 1  is a side view illustrating a helical broach according to Embodiment 1. 
           [0022]      FIG. 2  is a side view and a longitudinal sectional view illustrating shells of the helical broach of Embodiment 1. 
           [0023]      FIG. 3  is an explanatory view illustrating finishing by the helical broach according to Embodiment 1. 
           [0024]      FIG. 4  is a side view illustrating an example of an existing helical broach. 
           [0025]      FIG. 5  is an explanatory view illustrating an example of finishing by the existing helical broach. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0026]    Hereinafter, an embodiment of a helical broach according to the present invention will be described in detail with reference to the accompanying drawings. As a matter of course, the present invention is not limited to the following embodiment, and it is natural that various modifications can be made without departing from the spirit of the present invention. 
       Embodiment 1 
       [0027]    First, the structure of the helical broach according to Embodiment 1 of the present invention will be described with reference to  FIGS. 1 to 3 . 
         [0028]    A helical broach  1  according to this embodiment is a cutting tool for forming a substantially cylindrical workpiece W which is a piece to be cut, to a helical internal gear having a gear tooth helix angle α. As illustrated in  FIG. 1 , the helical broach  1  includes a shank section  2  to be installed in a broaching machine (not illustrated), a roughing section  3  for roughing of the workpiece W, and a finishing section  4  for finishing of the rough-worked workpiece W and is formed by assembling a first shell  20  and a second shell  30  included in the finishing section  4  to a broach body  10  having the shank section  2  and the roughing section  3 . 
         [0029]    The roughing section  3  is formed integrally with the broach body  10  such that roughing blades having a gear tooth helix angle α protrude toward the outer peripheral side of the helical broach  1  in a radial direction. In addition, in order to form teeth having predetermined dimensions in the workplace W, the roughing blades are arranged such that the height of the blades gradually increases from the leading end of the cutting direction toward the trailing end of the cutting direction. 
         [0030]    Each of the first shell  20  and the second shell  30  in the finishing section  4  forms a substantially cylindrical shape. As illustrated in  FIG. 2 , the first shell  20  and the second shell  30  are arranged in an axial direction of the helical broach  1 , are engaged with a shell engagement portion  11  of the broach body in, and are assembled such that the first shell  20  abuts a shell abutsing surface  12  of the broach body  10  and the second shell  30  is pressed toward the leading end (the left side in  FIG. 2 ) of the cutting direction by a fastener  40  together with the first shell  20 . In addition, the fastener  40  is fixed to the broach body  10  by a bolt (not illustrated) or the like. 
         [0031]    In order to relatively align the phases in a peripheral direction (around the axis of the helical broach  1 ) of the broach body  10  and the first and second shells  20  and  30  in the helical broach  1 , a positioning protrusion  13  is provided in the shell abutting surface  12 , a positioning groove  21  is provided in one end (the left end in  FIG. 2 ) of the first shell  20 , a positioning protrusion  22  is provided in the other end (the right end in  FIG. 2 ) of the first shell  20 , and a positioning groove  31  is provided in one end (the left end in  FIG. 2 ) of the second shell  30 . 
         [0032]    The first shell  20  and the second shell  30  are assembled to the broach body  10  in a state in which positioning protrusion  13  of the shell abutting surface  12  and the positioning groove  21  of the first shell  20  are fitted to each other and the positioning protrusion  22  of the first shell  20  and the positioning groove  31  of the second shell  30  are fitted to each other, that is, in a state in which the phases are relatively aligned with each other. 
         [0033]    In this embodiment, since the finishing section  4  has a structure divided into the first shell  20  and the second shell  30 , the first shell  20  and the second shell  30  included in the finishing section  4  may be formed with different finishing blades  50  and  60  ( FIG. 3 ). 
         [0034]    As illustrated in  FIG. 3 , in this embodiment, in the finishing blades  50  of the first shell  20 , a cutting amount d 1  is set to cut only the left tooth surface  70  (one tooth surface along the tooth lead of the workpiece W) in the workpiece W, and a blade groove helix angle β 1  is set with respect to a direction perpendicular to the axis of the first shell  20  so as to allow a rake angle θ 1  with which the left tooth surface  70  in the workpiece W is cut to be an acute angle. In the finishing blades  60  of the second shell  30 , a cutting amount d 2  is set to cut only a right tooth surface  80  (the other tooth surface along the tooth lead of the workpiece W) in the workpiece W, and a blade groove helix angle β 2  is set with respect to a direction perpendicular to the axis of the second shell  30  so as to allow a rake angle θ 2  with which the right tooth surface  80  in the workpiece W is cut, to be an acute angle. 
         [0035]    That is, in this embodiment, the first shell  20  is a shell for the left tooth surface, in which the finishing blades  50  that cut only the left tooth surface  70  in the workpiece W at the rake angle θ 1  which is an acute angle are provided, and the second shell  30  is a shell for the tight tooth surface, in which the finishing blades  60  that cut only the right tooth surface  80  in the workpiece W at the rake angle θ 2  which is an acute angle are provided. 
         [0036]    In order to form each of the left tooth surface  70  and the right tooth surface  80  in the workpiece W to predetermined dimensions, the finishing blades  50  in the first shell  20  and the finishing blades  60  in the second shell  30  are formed to be arranged such that the width of the blades gradually increases from the leading end of the cutting direction toward the trailing end of the cutting direction. 
         [0037]    In general, in the working blades of a cutting tool, a cutting portion having an acute angle has a higher cutting ability than that of those having an obtuse angle and enables cutting with good surface roughness for cut surfaces. 
         [0038]    Therefore, in this embodiment, the blade groove helix angle β 1  is set to allow the rake angle θ 1  with which the finishing blades  50  in the first shell  20  cut the left tooth surface  70  in the workplace W to be an acute angle, and the blade groove helix angle β 2  is set to allow the rake angle θ 2  with which the finishing blades  60  in the second shell  30  cut the right tooth surface  80  in the workplace W to be an acute angle. 
         [0039]    The finishing blades  50  in the first shell  20  abut the left tooth surface  70  in the workpiece W with the cutting amount d 1  and have guide surfaces  51  that abut the right tooth surface  80  in the workplace W. Since the guide surfaces  51  are provided in the finishing blades  50 , the finishing blades  50  are prevented from wobbling toward the right tooth surface  80  in the workpiece W due to the cutting reaction force when cutting the left tooth surface  70  in the workpiece w and thus can accurately cut the left tooth surface  70  in the workpiece W only with the cutting amount d 1 . 
         [0040]    The finishing blades  60  in the second shell  30  abut the right tooth surface  80  in the workpiece W with the cutting amount d 2  and have guide surfaces  61  that abut the left tooth surface  70  in the workpiece W. Since the guide surfaces  61  are provided in the finishing blades  60 , the finishing blades  60  are prevented from wobbling toward the left tooth surface  70  in the workpiece W due to the cutting reaction force when cutting the right tooth surface  80  in the workpiece W and thus can accurately cut the right tooth surface  80  in the workpiece W only with the cutting amount d 2 . 
         [0041]    In addition, the finishing blades  50  and  60  are subjected to work such as chamfering (not illustrated) so as not to allow the guide surfaces  51  and  61  to cut the right tooth surface  80  and the left tooth surface  70  in the workpiece W. 
         [0042]    Next, finishing by the helical broach according to Embodiment 1 of the present invention will be described with reference to  FIGS. 1 to 3 . 
         [0043]    The helical, broach  1  according to Embodiment 1 of the present invention and the workpiece W are installed in the broaching machine (not illustrated), and when the helical broach  1  is moved in the axial direction while being pulled with respect to the workpiece W, the workpiece W can be formed to a helical internal gear as described below. 
         [0044]    First, the roughing blades (not illustrated) in the roughing section  3  of the helical broach  1  come into contact with the inner peripheral surface of the substantially cylindrical workpiece W. By the roughing blades arranged such that the height of the blades gradually increases from the leading end of the cutting direction toward the trailing end of the cutting direction, teeth having predetermined dimensions are formed in the workpiece W. 
         [0045]    Subsequently, the finishing blades  50  in the first shell  20  positioned at the leading end of the cutting direction in the finishing section  4  of the helical broach  1  come into contact with the left tooth surface  70  and the right tooth surface  80  in the workpiece W subjected to roughing. The finishing blades  50  abut the left tooth surface  70  in the workpiece W with the cutting amount d 1 , and the guide surfaces  51  of the finishing blades  50  abut the right tooth surface  80  in the workpiece W. 
         [0046]    Since the guide surfaces  51  of the finishing blades  50  abut the right tooth surface  80  in the workpiece W, the finishing blades  50  are prevented from wobbling toward the right tooth surface  80  in the workpiece W due to the cutting reaction force when cutting the left tooth surface  70  in the workpiece W and thus can accurately cut the left tooth surface  70  in the workpiece W only with the cutting amount d 1 . By the finishing blades  50  that are arranged such that the width of the blades gradually increases from the leading and of the cutting direction toward the trailing end of the cutting direction, the left tooth surface  70  in the workpiece W are cut to predetermined finished dimensions. 
         [0047]    Subsequently, the finishing blades  60  in the second shell  30  positioned at the trailing end of the cutting direction in the finishing section  4  of the helical broach  1  come into contact with the left tooth surface  70  subjected to finishing and the right tooth surface  80  subjected to roughing in the workpiece W. The finishing blades  60  abut the right tooth surface  80  in the workpiece W with the cutting amount d 2 , and the guide surfaces  61  of she finishing blades  60  abut she left tooth surface  70  in the workpiece W. 
         [0048]    Since the guide surfaces  61  of the finishing blades  60  abut the left tooth surface  70  in the workpiece W, the finishing blades  60  are prevented from wobbling toward the left tooth surface  70  in the workpiece W due to the cutting reaction force when cutting the right tooth surface  80  in the workpiece W and thus can accurately cut the right tooth surface  80  in the workpiece W only with the cutting amount d 2 . By the finishing blades  60  that are arranged such that the width of the blades gradually increases from the leading end of the cutting direction toward the trailing end of the cutting direction, the right tooth surface  80  in the workpiece W are cut to predetermined finished dimensions. 
         [0049]    As described above, by broaching using the helical broach  1  according to Embodiment 1 of the present invention, the left tooth surface  70  and the right tooth surface  80  in the workpiece W are accurately cut to predetermined finished dimensions, thereby forming a helical internal gear having high accuracy. 
         [0050]    Since the finishing blades  50  having the blade groove helix angle β 1  with respect to the gear tooth helix angle α are formed in the first shell  20 , the rake angle θ 1  of the finishing blades  50  is an acute angle. Accordingly, the cutting ability of the finishing blades  50  in the first shell  20  is high, and the surface roughness of the surface cut by the finishing blades  50  is enhanced. Therefore, the cutting amount d 1  of the left tooth surface  70  in the workpiece W by the finishing blades  50  in the first shells  20  can be set to be sufficiently large. 
         [0051]    Since the finishing blades  60  having the blade groove helix angle β 2  with respect to the gear tooth helix angle α are formed in the second shell  30 , the rake angle θ 2  of the finishing blades  60  is an acute angle. Accordingly, the cutting ability of the finishing blades  60  in the second shell  30  is high, and the surface roughness of the surface cut by the finishing blades  60  is enhanced. Therefore, the cutting amount d 2  of the right tooth surface  80  in the workpiece W by the finishing blades  60  in the second shells  30  can be set to be sufficiently large as in the first shell  20 . 
         [0052]    In the related art, as illustrated in  FIG. 5 , one tooth surface (the left sooth surface  170  in  FIG. 5 ) of the left tooth surface  170  and the right tooth surface  180  in the workpiece W is cut by the acute angle portion  151  (a portion having an acute rake angle) of the finishing blade  150  in the shell  120 , and the other tooth surface (the right tooth surface  180  in  FIG. 5 ) is cut by the obtuse angle portion  152  (a portion having an obtuse rake angle) of the finishing blade  150  in the shell  120 . Therefore, the surface roughness of the surface cut by the obtuse angle portion  152  is coarse, and thus the cutting amount d cannot be set to be sufficiently large. Accordingly, the number of blades of the obtuse angle portion  152  is set to be larger than the number of blades of the acute angle portion  151 . That is, the number of blades of the obtuse angle portion  152  is larger than the number of blades of the acute angle portion  151 , and thus the finishing section  104 , that is, the shell  120  is elongated in the axial direction. 
         [0053]    In the helical broach  1  according to this embodiment, as illustrated, in  FIG. 3 , the left tooth surface  70  and the right tooth surface  80  in the workpiece W are cut by the finishing blades  50  in which the rake angle θ 1  is an acute angle in the first shell  20  and by the finishing blades  60  in which the rake angle θ 2  is an acute angle in the second shell  30 . Therefore, the surface roughness of the surface cut by the finishing blades  50  and  60  is good and the cutting amounts d 1  and d 2  can be set to be sufficiently large. Accordingly, the axial length of the finishing section  4 , that is, the first shell  20  and the second shell  30  can be smaller than the axial length of the existing shell  120 . 
       REFERENCE SIGNS LIST 
       [0054]      1  Helical Broach 
         [0055]      2  Shank Section 
         [0056]      3  Roughing Section 
         [0057]      4  Finishing Section 
         [0058]      10  Broach Body 
         [0059]      11  Shell Engagement Portion of Broach Body 
         [0060]      12  Shell Abutting Surface of Broach Body 
         [0061]      13  Positioning Protrusion of Broach Body 
         [0062]      20  First Shell 
         [0063]      21  Positioning Groove of First Shell 
         [0064]      22  Positioning Protrusion of First Shell 
         [0065]      30  Second Shell 
         [0066]      31  Positioning Groove of Second Shell 
         [0067]      40  Fastener 
         [0068]      50  Finishing Blade in First Shell 
         [0069]      51  Guide Surface 
         [0070]      60  Finishing Blade in Second Shell 
         [0071]      61  Guide Surface 
         [0072]      70  Left Tooth Surface in Workpiece 
         [0073]      30  Right Tooth Surface in Workpiece