Technical Field
[0001]
The present invention relates to a helical broach.

Background Art
[0002]
10 As a working method of cutting an internal gear
which is a type 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
15 broaching machine as a working machine dedicated to
broaching, a broach and the workpiece as a piece to be cut,
and pulling the broach with respect to the workpiece or
pulling the workpiece with respect to the fixed broach.
[0003]
20 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
25 side (the leading end of the cutting direction) toward the
3
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 workpiece and a finishin5 g
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 formed to an internal
10 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
15 internal work. In addition, the finished dimensions of
the workpiece by broaching become substantially the same
as those of the final blades of the broach used for
working, and thus cutting work can be performed with high
accuracy and the repetition accuracy of the cutting work
20 is high.
[0005]
As a type of broach, there is a helical broach. This
is for cutting a workpiece to a helical internal gear in
which the tooth lead of the internal gear is inclined with
25 respect to the axis of the gear. The helical broach and
4
the workpiece are installed on a broaching machine and the
helical broach is pulled with respect to the workpiece
while being rotated, thereby forming the workpiece to the
helical internal gear.
[00065 ]
An example of an existing helical broach is
illustrated in Fig. 4, and finishing of a workpiece by the
existing helical broach is illustrated in Fig. 5.
As illustrated in Fig. 4, a helical broach 101
10 includes a roughing section 103 and a finishing section
104, and roughing blades (not illustrated) in the roughing
section 103 and finishing blades 130 (Fig. 5) in the
finishing section 104 are arranged to be inclined with
respect to the axial direction of the helical broach 101.
15 [0007]
In the roughing blades (not illustrated) in the
roughing section 103 and the finishing blades 130 in the
finishing section 104, a tooth gear helix angle a is set
along the tooth lead direction of the helical internal
20 gear to be formed. In order to enhance the working
accuracy and the like, in the finishing blades 130 in the
finishing section 104, a blade groove helix angle b may
further be set.
[0008]
25 In addition, the blade groove helix angle b is set to
5
a direction that is not perpendicular to the direction of
the tooth gear helix angle a in order to enhance the
working accuracy and the like. Therefore, as illustrated
in Fig. 5, one end portion 131 in the finishing blade 130
has an acute angle, and the other end portion 132 has a5 n
obtuse angle.
[0009]
In addition, in order to enhance the working
accuracy and the like, in the finishing section 104 of the
10 helical broach 101, a single finishing blade 130 is set to
abut and cut only one of tooth surfaces including a left
tooth surface 150 in a workpiece W (one tooth surface
along the tooth lead of the workpiece W) and a right tooth
surface 160 (the other tooth surface along the tooth lead
15 of the workpiece W). That is, the finishing blades 130 in
the finishing section 104 of the helical broach 101 are
set to be divided into left tooth surface finishing blades
130a which cut only the left tooth surfaces 150 in the
workpiece W and right tooth surface finishing blades 130b
20 which cut only the right tooth surfaces 160 in the
workpiece W.
[0010]
The finishing section 104 needs a necessary number
of left tooth surface finishing blades 130a and right
25 tooth surface finishing blades 130b for forming the
6
workpiece W to a helical internal gear having
predetermined dimensions, and the left tooth surface
finishing blades 130a and the right tooth surface
finishing blades 130b are arranged along the tooth gear
helix angle a. Therefore, a shell 120 is elongated in th5 e
axial direction.
Citation List
Patent Literature
[0011]
10 [PTL 1] Japanese Patent Application Publication No.
2005-144639
Summary of Invention
Technical Problem
[0012]
15 In a case where at least a portion of the finishing
blades 130 in the shell 120 cannot cut the workpiece W to
predetermined dimensions due to damage, wear, and the like,
the shell 120 has to be replaced regardless of the state
of the other portions of the finishing blades 130 in the
20 shell 120. The shell 120 is long and precise and is thus
an expensive cutting tool, and the replacement of the
shell 120 in the broach requires high cost.
[0013]
As a matter of course, the finishing blades 130 may
25 also be re-ground to achieve a state in which the shell
7
120 is usable. However, when the re-grinding is repeated,
the blade width of the finishing blades 130 decreases, and
thus the shell 120 for broaching does not return to a
usable state.
[00145 ]
In the invention described in PTL 1, a helical
broach is provided with finishing blades capable of
cutting both tooth surfaces of the workpiece W. Therefore,
compared to the shell 120 in the existing helical broach
10 101 illustrated in Fig. 4, the axial length of the shell
according to the invention described in PTL 1 is halved,
and thus the manufacturing cost and replacement cost of
the shell can be suppressed in half. However, the shell
according to the invention described in PTL 1 is a
15 sufficiently long cutting tool, and the manufacture and
replacement thereof requires high cost.
[0015]
The present invention has been made taking the
foregoing problems into consideration, and an object
20 thereof is to significantly suppress the cost of
replacement of a shell in a helical broach due to damage,
wear, and the like of finishing blades.
Solution to Problem
[0016]
25 A helical broach according to a first invention to
8
solve the problems is a helical broach including: a
cylindrical shell in which finishing blades having a
predetermined tooth gear helix angle are formed on an
outer peripheral side, in which the shell includes a
plurality of wafer shells and has a structure divided i5 n
an axial direction, the wafer shells have finishing blades
corresponding to tooth grooves in a piece to be cut, and
in the finishing blades in the plurality of wafer shells,
a blade width gradually increases with each of the wafer
10 shells from a leading end of a cutting direction toward a
trailing end of the cutting direction.
[0017]
A helical broach according to a second invention to
solve the problems is the helical broach according to the
15 first invention, in which, in a case where the finishing
blade provided in the wafer shell positioned at a rearmost
end of the cutting direction is in a state of being unable
to cut the piece to be cut to predetermined dimensions, a
new wafer shell is inserted into the rearmost end of the
20 cutting direction, and the wafer shell positioned at a
foremost end of the cutting direction is removed and
installation positions of the wafer shells assembled and
arranged in the axial direction are moved toward the
leading end of the cutting direction, thereby forming a
25 new shell.
9
[0018]
A helical broach according to a third invention to
solve the problems is the helical broach according to the
first invention, in which the finishing blades in the
wafer shells cut both tooth surfaces along a tooth lead i5 n
the piece to be cut.
[0019]
A helical broach according to a fourth invention to
solve the problems is the helical broach according to the
10 third invention, in which all of rake angles at which the
finishing blades in the wafer shells abut both of the
tooth surfaces along the tooth lead in the piece to be cut
are acute angles.
Advantageous Effects of Invention
15 [0020]
According to the helical broach according to the
first invention, since the shell has the structure divided
in the axial direction, in a case where a portion of the
finishing blades in the divided wafer shells cannot cut
20 the piece to be cut to predetermined dimensions due to
damage, wear, and the like, only the wafer shells having
the portion of the finishing blades may be replaced.
Therefore, the replacement cost of the shell can be
significantly suppressed. In addition, since each of the
25 wafer shells has, as the finishing blade, each blade
10
corresponding to the tooth groove in the piece to be cut,
when the finishing blades are formed in the wafer shells,
there is no concern of interference of a grinding wheel or
the like for forming the finishing blades with the
adjacent blades, and the finishing blades can be formed i5 n
various shapes by setting the relief angle (second relief)
of the blade to be large or the like.
[0021]
According to the helical broach according to the
10 second invention, since the installation position of each
of the wafer shells is moved toward the leading end of the
cutting direction, the finishing blades which are reduced
in size due to re-grinding or the like are not immediately
discarded but are re-used. Therefore, the use period of
15 each of the wafer shells can be significantly increased
and thus the running cost of the shell can be
significantly suppressed.
[0022]
According to the helical broach according to the
20 third invention, since the finishing blades in the wafer
shells cut both of the tooth surfaces along the tooth lead
in the piece to be cut, the number of finishing blades can
be reduced. Therefore, the axial length of the shell can
be reduced, and thus a reduction in the size of the
25 helical broach can be achieved.
11
[0023]
According to the helical broach according to the
fourth invention, since all of the rake angles at which
the finishing blades in the wafer shells cut both of the
tooth surfaces along the tooth lead in the piece to be cu5 t
are appropriate acute angles for cutting, the work
accuracy and the surface precision of the cut surfaces of
the piece to be cut can be enhanced. In addition, the
cutting amounts of the finishing blades can be set to
10 sufficiently large amounts, and thus the number of
finishing blades can be reduced. Therefore, the axial
length of the shell can be reduced, and thus a reduction
in the size of the helical broach can be achieved.
Brief Description of Drawings
15 [0024]
Fig. 1 is a side view illustrating a helical broach
according to Embodiment 1.
Fig. 2 is a side view and a longitudinal sectional
view illustrating wafer shells of the helical broach of
20 Embodiment 1.
Fig. 3 is an explanatory view illustrating finishing
by the helical broach according to Embodiment 1.
Fig. 4 is a side view illustrating an example of an
existing helical broach.
25 Fig. 5 is an explanatory view illustrating an
12
example of finishing by the existing helical broach.
Description of Embodiments
[0025]
Hereinafter, an embodiment of a helical broach
according to the present invention will be described i5 n
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
10 spirit of the present invention.
Embodiment 1
[0026]
First, the structure of the helical broach according
to Embodiment 1 of the present invention will be described
15 with reference to Figs. 1 to 3.
[0027]
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
20 internal gear having a tooth gear helix angle a. 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
25 of the rough-worked workpiece W and is formed by
13
assembling a plurality of (in this embodiment, N) wafer
shells 20W(1), 20W(2), …, 20W(N) as a shell constituting the
finishing section 4, to a broach body 10 having the shank
section 2 and the roughing section 3.
[00285 ]
In the roughing section 3, roughing blades (not
illustrated) having a tooth gear helix angle a are formed
integrally with the broach body 10 to protrude toward the
outer peripheral side of the helical broach 1 in the
10 radial direction and form a plurality of blade groups
corresponding to each of the tooth grooves in the
workpiece W. In addition, in order to form teeth having
predetermined dimensions in the workpiece W, the roughing
blades in the blade groups are arranged along the tooth
15 gear helix angle a such that the height of the blades
gradually increases from the leading end of the cutting
direction (the left side in Fig. 1) toward the trailing
end of the cutting direction (the right side in Fig. 1).
[0029]
20 In the finishing section 4, the plurality of wafer
shells 20W(1) to 20W(N) which are substantially cylindrical
are arranged in the axial direction of the helical broach
1 and are assembled to the broach body 10. In the wafer
shells 20W(1) to 20W(N), as illustrated in Fig. 2, finishing
25 blades 30W(1) to 30W(N) having a tooth gear helix angle a are
14
formed to protrude toward the outer peripheral side of the
wafer shells 20W(1) to 20W(N) in the radial direction, and
since the wafer shells 20W(1) to 20W(N) are sequentially
arranged along the axial direction of the helical broach 1,
the finishing blades 30W(1) to 30W(N) form a plurality o5 f
blade groups which follow the tooth gear helix angle a to
correspond to each of the tooth grooves in the workpiece W.
[0030]
In order to form teeth having predetermined
10 dimensions in the workpiece W, the finishing blades 30W(1)
to 30W(N) in the blade groups are arranged such that the
width of the blades gradually increases with each of the
wafer shells 20W(1) to 20W(N) from the leading end of the
cutting direction (the left side in Fig. 2) toward the
15 trailing end of the cutting direction (the right side in
Fig. 2).
[0031]
That is, in the first wafer shell 20W(1) from the
leading end of the cutting direction, the first smallest
20 blades are respectively provided in the blade groups, and
in the second wafer shell 20W(2) from the leading end of
the cutting direction, the second smallest blades are
respectively provided in the blade groups. In the same
manner, in the third to N-th wafer shells 20W(3) to 20W(N)
25 from the leading end of the cutting direction, the third
15
to N-th smallest blades are respectively provided in the
blade groups.
[0032]
As a matter of course, the number of each of
finishing blades 30W(1) to 30W(N) respectively provided i5 n
the wafer shells 20W(1) to 20W(N) is not limited to one in
each of the blade groups as in this embodiment and a
plurality of blades may also be provided in each of the
blades. Considering the degree of freedom of the shapes
10 of the respective finishing blades 30W(1) to 30W(N) provided
in the wafer shells 20W(1) to 20W(N), which will be described
later, it is preferable that the number of blades in each
of the blade groups is one.
[0033]
15 As illustrated in Figs. 1 and 2, the wafer shells
20W(1) to 20W(N) are arranged in the axial direction of the
helical broach 1, are engaged with a shell engagement
portion 11 of the broach body 10, and are assembled such
that the first wafer shell 20W(1) from the leading end of
20 the cutting direction abuts a shell abutting surface 12 of
the broach body 10, and the N-th wafer shell 20W(N) from
the leading end of the cutting direction is pressed toward
the leading end of the cutting direction by a fastener 40
together with the first to (N-1)-th wafer shells 20W(1) to
25 20W(N-1) from the leading end of the cutting direction (the
16
left side in Figs. 1 and 2) positioned closer to the
leading end of the cutting direction than the N-th wafer
shell 20W(N). In addition, the fastener 40 is fixed to the
broach body 10 by a bolt (not illustrated) or the like.
[00345 ]
In order to relatively align the phases in the
peripheral direction (around the axis of the helical
broach 1) in the broach body 10 and the wafer shells 20W(1)
to 20W(N), a positioning protrusion 13 is provided in the
10 shell abutting surface 12, positioning grooves 21W(1) to
21W(N) are respectively provided in one end (the left end
in Fig. 2) of the wafer shells 20W(1) to 20W(N), positioning
protrusions 22W(1) to 22W(N) are provided in the other end
(the right end in Fig. 2) of the wafer shells 20W(1) to
15 20W(N), and a positioning groove 41 is provided in one end
(the left end in Fig. 2) of the fastener 40.
[0035]
The positioning protrusion 13 of the shell abutting
surface 12 and the positioning groove 21W(1) of the first
20 wafer shell 20W(1) from the leading end of the cutting
direction are fitted to each other, and the positioning
protrusion 22W(1) of the first wafer shell 20W(1) from the
leading end of the cutting direction and the positioning
groove 21W(2) of the second wafer shell 20W(2) from the
25 leading end of the cutting direction are fitted to each
17
other. In the same manner, in the second to N-th wafer
shells 20W(2) to 20W(N) from the leading end of the cutting
direction, the positioning protrusions 21W(2) to 21W(N) are
respectively fitted to the corresponding positioning
grooves 22W(2) to 22W(N) in the wafer shells 20W(2) to 20W(5 N)
such that the wafer shells 20W(1) to 20W(N) are assembled to
the broach body 10 in a state in which the positioning
protrusion 22W(N) of the wafer shell 20W(N) positioned at the
N-th position (at the rearmost end in the cutting
10 direction) from the leading end of the cutting direction
is fitted to the positioning groove 41 of the fastener 40,
that is, in a state in which the phases are relatively
aligned with each other.
[0036]
15 The positioning grooves 21W(1) to 21W(N) and the
positioning protrusions 22W(1) to 22W(N) in the wafer shells
20W(1) to 20W(N), are provided at predetermined positions
with respect to the finishing blades 30W(1) to 30W(N) in the
wafer shells 20W(1) to 20W(N). That is, the installation
20 positions of the positioning grooves 21W(1) to 21W(N) and the
positioning protrusions 22W(1) to 22W(N) with respect to the
finishing blades 30W(1) to 30W(N) are the same in any of the
wafer shells 20W(1) to 20W(N).
[0037]
25 Therefore, when the wafer shells 20W(1) to 20W(N) are
18
assembled to the broach body 10 in dimensional order such
that the blade width gradually increases, as illustrated
in Fig. 2, the finishing blades 30W(1) to 30W(N) are
positioned to be arranged to follow the tooth gear helix
angle a, and the positioning grooves 21W(1) to 21W(N) and th5 e
positioning protrusions 22W(1) to 22W(N) are positioned to
also be arranged to follow the tooth gear helix angle a in
the wafer shells 20W(1) to 20W(N).
[0038]
10 The finishing blades 30W(1) to 30W(N) are individually
worked by a working machine (not illustrated) and a
grinding wheel (not illustrated) to be formed in the wafer
shells 20W(1) to 20W(N). The finishing blades 30W(1) to 30W(N)
are provided such that the blade width gradually increases
15 with each of the wafer shells 20W(1) to 20W(N). Therefore,
in each of the wafer shells 20W(1) to 20W(N), the blades are
not adjacent to each other along the tooth gear helix
angle a. Accordingly, when the finishing blades 30W(1) to
30W(N) are formed in the wafer shells 20W(1) to 20W(N), there
20 is no concern of the grinding wheel interfering with the
adjacent blades, and the finishing blades 30W(1) to 30W(N)
can be formed in various shapes by setting the relief
angle (second relief) of the blade to be large or the like.
[0039]
25 That is, compared to the finishing blades 130 (Figs.
19
4 and 5) in the integration type shell 120 of the existing
helical broach 101, in the wafer shells 20W(1) to 20W(N)
which are division type shells of the helical broach 1
according to this embodiment, the degree of freedom of the
shapes of the finishing blades 30W(1) to 30W(N) formed by th5 e
grinding wheel or the like is high.
[0040]
In this embodiment, the finishing blades 30W(1) to
30W(N) in the wafer shells 20W(1) to 20W(N) are set to cut
10 both tooth surfaces 50 and 60 including the left tooth
surface 50 (one tooth surface along the tooth lead of the
workpiece W) and the right tooth surface 60 (the other
tooth surface along the tooth lead of the workpiece W) in
each workpiece W and cut each of both tooth surfaces 50
15 and 60 in the workpiece W with the same cutting amount
dW(1) to dW(N).
[0041]
In addition, in this embodiment, the finishing
blades 30W(1) to 30W(N) in the wafer shells 20W(1) to 20W(N)
20 are set to cut both of the left tooth surface 50 and the
right tooth surface 60 in the workpiece W with rake angles
qW(1) to qW(N) and are set so as to allow the rake angles
qW(1) to qW(N) to be appropriate acute angles for the cutting.
[0042]
25 In general, in the working blades of a cutting tool,
20
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.
Therefore, in this embodiment, the finishing blade5 s
30W(1) to 30W(N) in the wafer shells 20W(1) to 20W(N) are set
so as to allow the rake angles qW(1) to qW(N) with which both
of the tooth surfaces 50 and 60 in the workpiece W are cut
to be an acute angle.
10 [0043]
That is, in this embodiment, the wafer shells 20W(1)
to 20W(N) are wafer shells for both tooth surfaces in which
the finishing blades 30W(1) to 30W(N) that cut both of the
left tooth surface 50 and the right tooth surface 60 in
15 the workpiece W with the acute rake angles qW(1) to qW(N) are
provided.
[0044]
As a matter of course, the helical broach according
to the present invention is not limited to the finishing
20 blades for both tooth surfaces as in this embodiment and
may also be applied to finishing blades that cut one tooth
surface at a time. In addition, the cutting amounts dW(1)
to dW(N) and the rake angles qW(1) to qW(N) with which the
left tooth surface 50 and the right tooth surface 60 in
25 the workpiece W are cut may have numerical values that
21
vary between the left tooth surface 50 and the right tooth
surface 60.
[0045]
Subsequently, the finishing of the helical broach
according to Embodiment 1 of the present invention will b5 e
described with reference to Figs. 1 to 3.
[0046]
The helical broach 1 according to Embodiment 1 of
the present invention and the workpiece W are installed in
10 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 the helical internal gear as
described below.
15 [0047]
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
20 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.
25 [0048]
22
Next, as illustrated in Fig. 3, the finishing blade
30W(1) in the first wafer shell 20W(1) positioned at the
first position from the leading end of the cutting
direction in the finishing section 4 of the helical broach
1 comes into contact with the left tooth surface 50 an5 d
the right tooth surface 60 in the workpiece W subjected to
roughing. The finishing blade 30W(1) abuts both of the
tooth surfaces 50 and 60 in the workpiece W with the
cutting amount dW(1). Therefore, both of the tooth surfaces
10 50 and 60 in the workpiece W subjected to roughing are cut
with the cutting amount dW(1).
[0049]
Subsequently, the finishing blade 30W(2) in the second
wafer shell 20W(2) positioned at the second position from
15 the leading end of the cutting direction in the finishing
section 4 of the helical broach 1 comes into contact with
the left tooth surface 50 and the right tooth surface 60
cut by the finishing blade 30W(1) in the first wafer shell
20W(1). The finishing blade 30W(2) abuts both of the tooth
20 surfaces 50 and 60 in the workpiece W with the cutting
amount dW(2). Therefore, both of the tooth surfaces 50 and
60 in the workpiece W are further cut with the cutting
amount dW(2).
[0050]
25 In the same manner, the finishing blades 30W(3) to
23
30W(N) in the third to N-th wafer shells 20W(3) to 20W(N)
positioned at the third to N-th positions from the leading
end of the cutting direction in the finishing section 4 of
the helical broach 1 sequentially come into contact with
the left tooth surface 50 and the right tooth surface 65 0
in the workpiece W. The finishing blades 30W(3) to 30W(N)
sequentially abut both of the tooth surfaces 50 and 60 in
the workpiece W with the cutting amounts dW(3) to dW(N).
Therefore, both of the tooth surfaces 50 and 60 in the
10 workpiece W are further cut sequentially with the cutting
amounts dW(3) to dW(N).
[0051]
That is, by the finishing blades 30W(1) to 30W(N) that
are arranged such that the blade width gradually increases
15 from the leading end of the cutting direction toward the
trailing end of the cutting direction, the left tooth
surface 50 and the right tooth surface 60 in the workpiece
W are cut sequentially with the cutting amounts dW(1) to
dW(N) to predetermined finished dimensions.
20 [0052]
As described above, by broaching using the helical
broach 1 according to Embodiment 1 of the present
invention, the left tooth surface 50 and the right tooth
surface 60 in the workpiece W are accurately cut to
25 predetermined finished dimensions, thereby forming a
24
helical internal gear having high accuracy.
[0053]
Next, a case where the finishing blades 30W(1) to
30W(N) of the finishing section 4 in the helical broach
according to Embodiment 1 of the present invention are i5 n
a state of being unable to cut the workpiece W to
predetermined dimensions due to wear and the like will be
described with reference to Figs. 1 to 3.
[0054]
10 The finishing blades 30W(1) to 30W(N) in the finishing
section 4 wear due to the repeated broaching operations
using the helical broach 1 according to Embodiment 1 of
the present invention described above. During cutting by
the worn finishing blades 30W(1) to 30W(N), the left tooth
15 surface 50 and the right tooth surface 60 in the workpiece
W cannot be cut with the predetermined cutting amounts
dW(1) to dW(N). That is, the workpiece W cannot be formed to
a helical internal gear having predetermined dimensions.
[0055]
20 First, each of the wafer shells 20W(1) to 20W(N) are
removed from the broach body 10, and the finishing blades
30W(1) to 30W(N) in the wafer shells 20W(1) to 20W(N) are reground
to predetermined dimensions so as to be able to
form the workpiece W to a helical internal gear having
25 predetermined dimensions.
25
[0056]
When wear and re-grinding of the finishing blades
30W(1) to 30W(N) in the wafer shells 20W(1) to 20W(N) are
repeated, the ground surfaces of the finishing blades
30W(1) to 30W(N) in the finishing section 4 reach the secon5 d
relief and thus the blade width of the finishing blades
30W(1) to 30W(N) becomes too small. That is, even when the
finishing blades 30W(1) to 30W(N) are re-ground, the
finishing blades 30W(1) to 30W(N) cannot have predetermined
10 dimensions and cannot cut the left tooth surface 50 and
the right tooth surface 60 in the workpiece W with the
predetermined cutting amounts dW(1) to dW(N). Particularly,
the finishing blade 30W(N) positioned at the rearmost end
of the cutting direction determines the final dimensions
15 of the workpiece W and is thus important. When the
finishing blade 30W(N) is reduced in size, the workpiece W
cannot be formed to a helical internal gear having
predetermined dimensions.
[0057]
20 In this embodiment, in a case where the finishing
blade 30W(N) positioned at the rearmost end of the cutting
direction is reduced in size, a new wafer shell 20W(N+1)
having a finishing blade 30W(N+1) having predetermined
dimensions is inserted into the (N+1)-th position from the
25 leading end of the cutting direction which is closer to
26
the trailing end of the cutting direction than the wafer
shell 20W(N) positioned at the N-th position from the
leading end of the cutting direction, that is, into the
rearmost end of the cutting direction. Accordingly, the
workpiece W is finally cut by the new finishing blad5 e
30W(N+1) positioned at the rearmost end of the cutting
direction, and thus the workpiece W can be formed to a
helical internal gear having predetermined dimensions.
[0058]
10 In addition, since the new wafer shell 20W(N+1) is
inserted into the rearmost end of the cutting direction,
the number of wafer shells 20W(1) to 20W(N+1) is increased
and thus the finishing section 4 is elongated in the axial
direction. Here, the wafer shell 20W(1) positioned at the
15 foremost end of the cutting direction is removed.
[0059]
The finishing blade 30W(1) in the wafer shell 20W(1)
positioned at the foremost end of the cutting direction is
also reduced in size due to the wear and the repeated re20
grinding operations and is thus in a state of being unable
to sufficiently cut both of the tooth surfaces 50 and 60
in the workpiece W subjected to roughing. Therefore, it
may be considered that the finishing blade 30W(1) needs to
be discarded.
25 [0060]
27
In addition, initially, since the finishing blade
30W(2) in the second wafer shell 20W(2) positioned at the
second position from the leading end of the cutting
direction is also reduced in size due to the wear and the
repeated re-grinding operations, by the re-grindin5 g
operations, the finishing blade 30W(2) is further re-ground
to the dimensions corresponding to the finishing blade
30W(1) in the first wafer shell 20W(1) initially positioned
at the first position from the leading end of the cutting
10 direction. The second wafer shell 20W(2) positioned at the
second position is moved toward the leading end of the
cutting direction to serve as the first wafer shell 20W(1)
positioned at the first position.
[0061]
15 In the same manner, the finishing blades 30W(3) to
30W(N) in the third to N-th wafer shells 20W(3) to 20W(N)
initially positioned at the third to N-th positions are
re-ground to the dimensions corresponding to the finishing
blades 30W(2) to 30W(N-1) in the second to (N-1)-th wafer
20 shells 20W(2) to 20W(N-1) initially positioned at the second
to (N-1)-th positions from the leading end of the cutting
direction, and the third to N-th wafer shells 20W(3) to
20W(N) initially positioned at the third to N-th positions
are moved toward the leading end of the cutting direction
25 to serve as the second to (N-1)-th wafer shells 20W(2) to
28
20W(N-1) positioned at the second to (N-1)-th positions.
[0062]
In this embodiment, the positioning grooves 21W(1) to
21W(N) and the positioning protrusions 22W(1) to 22W(N) in the
wafer shells 20W(1) to 20W(N) are provided at predetermine5 d
positions with respect to the finishing blades 30W(1) to
30W(N) in the wafer shells 20W(1) to 20W(N). Therefore, in a
case where the installation positions of the second to Nth
wafer shells 20W(2) to 20W(N) are moved toward the leading
10 end of the cutting direction as described above, the
second to N-th wafer shells 20W(2) to 20W(N) are assembled
while being slightly changed in phases along the tooth
gear helix angle a.
[0063]
15 That is, the positions of the finishing blades 30W(2)
to 30W(N) in the helical broach 1, that is, the positions
of the finishing blades 30W(2) to 30W(N) in the finishing
section 4 with respect to the roughing blades (not
illustrated) in the roughing section 3 are not changed.
20 Therefore, there is no influence on the cutting of the
workpiece W during broaching.
[0064]
As described above, by inserting the new wafer shell
20W(N+1) into the rearmost end of the cutting direction and
25 removing the wafer shell 20W(1) positioned at the foremost
29
end of the cutting direction, a new shell can be formed.
[0065]
In the helical broach 1 according to this embodiment,
as illustrated in Fig. 3, the left tooth surface 50 and
the right tooth surface 60 of the workpiece W can be cu5 t
with the rake angles qW(1) to qW(N) of the finishing blades
30W(1) to 30W(N) in the wafer shells 20W(1) to 20W(N), and thus
the surface roughness of the cut surfaces cut by the
finishing blades 30W(1) to 30W(N) is good and the cutting
10 amounts dW(1) to dW(N) can be set to sufficiently large
amounts.
[0066]
Therefore, the number of finishing blades in the
finishing section 4 along the tooth gear helix angle a can
15 be reduced, that is, the number of wafer shells 20W(1) to
20W(N) can be reduced. Accordingly, the axial length of the
wafer shells 20W(1) to 20W(N) as the shell can be reduced to
be smaller than the axial length of the existing shell 120.
[0067]
20 In addition, it is preferable that the cutting
conditions such as the cutting amounts dW(1) to dW(N) and the
rake angles qW(1) to qW(N) of the finishing blades 30W(1) to
30W(N) in the wafer shells 20W(1) to 20W(N) are equally set.
By equally setting the cutting conditions of the finishing
25 blades 30W(1) to 30W(N), the wear times and wear amounts of
30
the finishing blades 30W(1) to 30W(N) are equal to each other.
Therefore, the replacement times of the wafer shells 20W(1)
to 20W(N) can be substantially adjusted.
[0068]
Accordingly, not all the wafer shells 20W(1) to 20W(5 N)
corresponding to the shell are not discarded, and the
wafer shells 20W(1) to 20W(N) positioned at the rearmost end
of the cutting direction are sequentially replaced at the
leading end of the cutting direction as the finishing
10 blades 30W(1) to 30W(N) wear. Therefore, the wafer shells
20W(1) to 20W(N) as the shell can be used for a longer period
than the typical shell.
Reference Signs List
[0069]
15 1 HELICAL BROACH
2 SHANK SECTION
3 ROUGHING SECTION
4 FINISHING SECTION
10 BROACH BODY
20 11 SHELL ENGAGEMENT PORTION OF BROACH BODY
12 SHELL ABUTTING SURFACE OF BROACH BODY
13 POSITIONING PROTRUSION OF BROACH BODY
20 WAFER SHELL
21 POSITIONING GROOVE OF WAFER SHELL
25 22 POSITIONING PROTRUSION OF WAFER SHELL
31
30 FINISHING BLADE
40 FASTENER
41 POSITIONING GROOVE OF FASTENER
50 LEFT TOOTH SURFACE IN WORKPIECE
60 RIGHT TOOTH SURFACE IN WORKPIEC5 E

I/We Claim:
[Claim 1]
A helical broach comprising:
a cylindrical shell in which finishing blades havin5 g
a predetermined tooth gear helix angle are formed on an
outer peripheral side,
wherein the shell includes a plurality of wafer
shells and has a structure divided in an axial direction,
10 the wafer shells have finishing blades corresponding
to tooth grooves in a piece to be cut, and
in the finishing blades in the plurality of wafer
shells, a blade width gradually increases with each of the
wafer shells from a leading end of a cutting direction
15 toward a trailing end of the cutting direction.
[Claim 2]
The helical broach according to claim 1,
wherein, in a case where the finishing blade
20 provided in the wafer shell positioned at a rearmost end
of the cutting direction is in a state of being unable to
cut the piece to be cut to predetermined dimensions, a new
wafer shell is inserted into the rearmost end of the
cutting direction, and the wafer shell positioned at a
25 foremost end of the cutting direction is removed and
33
installation positions of the wafer shells assembled and
arranged in the axial direction are moved toward the
leading end of the cutting direction, thereby forming a
new shell.
5
[Claim 3]
The helical broach according to claim 1,
wherein the finishing blades in the wafer shells cut
both tooth surfaces along a tooth lead in the piece to be
10 cut.
[Claim 4]
The helical broach according to claim 3,
wherein all of rake angles at which the finishing
15 blades in the wafer shells abut both of the tooth surfaces
along the tooth lead in the piece to be cut are acute
angles.