Helical broach

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 () end a first blade groove helix angle (.sub.1), on the aforementioned first shell (20) and forming a second finishing blade (60), which comprises the aforementioned prescribed gear tooth helix angle () and a second blade groove helix angle (.sub.2) which differs from the aforementioned first blade groove helix angle (.sub.1), on the aforementioned second shell (30).

Claims

1. A helical broach comprising: a cylindrical shell in which finishing blades having a predetermined gear tooth helix angle are formed on an outer peripheral side, wherein the shell includes a first shell and a second shell which are divided in an axial direction, in the first shell, a first finishing blade having the gear tooth helix angle and a first blade groove helix angle is formed, and in the second shell, 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; wherein the diameters of the first and second finishing blades in said first and second shells are substantially constant in the axial direction.

2. The helical broach according to claim 1, wherein 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.

3. The helical broach according to claim 1, wherein both of a tool angle of the first finishing blade and a tool angle of the second finishing blade are an acute angle.

4. The helical broach according to claim 2, wherein both of a tool angle of the first finishing blade and a tool angle of the second finishing blade are an acute angle.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a side view illustrating a helical broach according to Embodiment 1.

(2) FIG. 2 is a side view and a longitudinal sectional view illustrating shells of the helical broach of Embodiment 1.

(3) FIG. 3 is an explanatory view illustrating finishing by the helical broach according to Embodiment 1.

(4) FIG. 4 is a side view illustrating an example of an existing helical broach.

(5) FIG. 5 is an explanatory view illustrating an example of finishing by the existing helical broach.

DESCRIPTION OF EMBODIMENTS

(6) 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

(7) 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.

(8) 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 . 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.

(9) The roughing section 3 is formed integrally with the broach body 10 such that roughing blades having a gear tooth helix angle 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.

(10) 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 abutting 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.

(11) 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.

(12) 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.

(13) 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).

(14) As illustrated in FIG. 3, in this embodiment, in the finishing blades 50 of the first shell 20, a cutting amount d.sub.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 .sub.1 is set with respect to a direction perpendicular to the axis of the first shell 20 so as to allow a tool angle .sub.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.sub.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 .sub.2 is set with respect to a direction perpendicular to the axis of the second shell 30 so as to allow a tool angle .sub.2 with which the right tooth surface 80 in the workpiece W is cut, to be an acute angle.

(15) 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 tool angle .sub.1 which is an acute angle are provided, and the second shell 30 is a shell for the right tooth surface, in which the finishing blades 60 that cut only the right tooth surface 80 in the workpiece W at the tool angle .sub.2 which is an acute angle are provided.

(16) 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.

(17) 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.

(18) Therefore, in this embodiment, the blade groove helix angle .sub.1 is set to allow the tool angle .sub.1 with which the finishing blades 50 in the first shell 20 cut the left tooth surface 70 in the workpiece W to be an acute angle, and the blade groove helix angle .sub.2 is set to allow the tool angle .sub.2 with which the finishing blades 60 in the second shell 30 cut the right tooth surface 80 in the workpiece W to be an acute angle.

(19) The finishing blades 50 in the first shell 20 abut the left tooth surface 70 in the workpiece W with the cutting amount d.sub.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.sub.1.

(20) The finishing blades 60 in the second shell 30 abut the right tooth surface 80 in the workpiece W with the cutting amount d.sub.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.sub.2.

(21) 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.

(22) Next, finishing by the helical broach according to Embodiment 1 of the present invention will be described with reference to FIGS. 1 to 3.

(23) 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.

(24) 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.

(25) 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.sub.1, and the guide surfaces 51 of the finishing blades 50 abut the right tooth surface 80 in the workpiece W.

(26) 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.sub.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.

(27) 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.sub.2, and the guide surfaces 61 of she finishing blades 60 abut she left tooth surface 70 in the workpiece W.

(28) 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.sub.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.

(29) 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.

(30) Since the finishing blades 50 having the blade groove helix angle .sub.1 with respect to the gear tooth helix angle are formed in the first shell 20, the tool angle .sub.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.sub.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.

(31) Since the finishing blades 60 having the blade groove helix angle .sub.2 with respect to the gear tooth helix angle are formed in the second shell 30, the tool angle .sub.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.sub.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.

(32) In the related art, as illustrated in FIG. 5, one tooth surface (the left tooth 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 tool 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 tool 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.

(33) 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 tool angle .sub.1 is an acute angle in the first shell 20 and by the finishing blades 60 in which the tool angle .sub.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.sub.1 and d.sub.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

(34) 1 HELICAL BROACH 2 SHANK SECTION 3 ROUGHING SECTION 4 FINISHING SECTION 10 BROACH BODY 11 SHELL ENGAGEMENT PORTION OF BROACH BODY 12 SHELL ABUTTING SURFACE OF BROACH BODY 13 POSITIONING PROTRUSION OF BROACH BODY 20 FIRST SHELL 21 POSITIONING GROOVE OF FIRST SHELL 22 POSITIONING PROTRUSION OF FIRST SHELL 30 SECOND SHELL 31 POSITIONING GROOVE OF SECOND SHELL 40 FASTENER 50 FINISHING BLADE IN FIRST SHELL 51 GUIDE SURFACE 60 FINISHING BLADE IN SECOND SHELL 61 GUIDE SURFACE 70 LEFT TOOTH SURFACE IN WORKPIECE 80 RIGHT TOOTH SURFACE IN WORKPIECE