JP2003230928A - Form rolling method and form rolling flat die - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To eliminate the rise-up of a chamfered part to tooth faces and burrs which occur at the chamfered part of the end face of a gear or the like, in form-rolling gears, splines or the like by a form-rolling flat die. <P>SOLUTION: In a form rolling method, a pair of flat dies 1, 2 are arranged in parallel in symmetrical positions, a form rolling material 7 is rotatably supported and held between the flat dies, and the flat dies are moved relative to each other to perform plastic working to the outer periphery of the form rolling material 7. The form rolling flat die is constituted of an outer periphery form rolling part 3 for performing elastic working to the outer periphery 8 of the form rolling material 7 and a chamfering part forming part 4 which is arranged separately from and adjacent to the outer periphery form rolling part and performs the plastic working to the chamfering part 12 of the edge of a form rolling material outer periphery. After the application of the form rolling to the outer periphery and the chamfering part with the form rolling flat dies, deformed parts 17 which are formed on mating surfaces 32, 42 between the outer periphery form rolling, and the chamfering part is further subjected to outer periphery form rolling by a broadening part 34 (finishing part 37c) provided on the outer periphery form rolling part. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flat die for rolling in which the outer periphery of a material to be rolled is plastically worked and at the same time, the chamfer of the plastically worked end is plastically worked, and particularly to the end chamfering of the tooth surfaces of gears and involute splines. A suitable flat die for rolling.

[0002]

2. Description of the Related Art A spline rolling portion used for a shaft part of a transmission of an automobile is completed by heat treatment after rolling by a flat die. Involute spline holes are broached on the mating parts such as gears that are connected to the shaft parts, and they are assembled by press fitting or sliding. In this assembling work, it is necessary to accurately match the phases of the spline shaft and the spline of the hole, which makes automatic assembly difficult. Therefore, it can be easily imagined that if the end surface of the shaft spline portion is chamfered, the assembly work can be performed by rough phase determination. However, adding a new process such as chamfering for the end chamfering increases the cost of parts and poses a problem.

Therefore, there is an example in which a spur gear and a helical gear of an automobile transmission are chamfered by a gear rolling method. For example, JP-A-2-80146
In the gazette, there is an example in which a chamfering process is performed by engaging a gear to which a gear part has been processed with a chamfering rotary tool, and a gear rolling molding die is separately provided to form a tooth surface bulge caused by the chamfering process. It is disclosed. However, in this case, since chamfering molding is performed and the tooth surface is bulged with another molding die, there is a problem that processing time is required. When this method is applied to the flat die method generally used in the spline rolling, there is a problem that the apparatus becomes complicated because two steps are required. On the other hand, Japanese Utility Model Application Laid-Open No. 60-24437 discloses that a protrusion is formed at a portion facing a chamfered portion of a workpiece, and a tooth surface of the workpiece is subjected to rolling and chamfering. The rolling method and the rack method are disclosed.

[0004]

However, in order to manufacture a die in which the tooth surface processing portion and the chamfered portion are integrated,
There was a problem that a very high processing cost was required. Therefore, in Japanese Patent Publication No. 5-38667, a gear rolling method is used, in which the tooth forming portion and the chamfer forming portion are separately manufactured and fixed so that they are in phase with each other. Further, in Japanese Unexamined Patent Publication No. 8-71899, the chamfering of the end face of the pin instead of the gear is performed by the same method. However, if the spline rolling die and the chamfering die are separately manufactured, and are integrally arranged and subjected to the rolling process, there is a problem that the spline portion and the chamfered portion are raised to the tooth surface and burr occurs. It was

In view of the above problems, an object of the present invention is to provide an outer peripheral rolling portion for plastically working the outer periphery of the rolled object, and an axial end portion of the outer peripheral portion of the rolled object provided adjacent to the outer peripheral rolling portion. In the flat die for rolling, which comprises the chamfered portion and the chamfered portion that is plastically worked, it is to eliminate the swelling and burrs that occur in the adjacent portion between the outer peripheral rolling portion and the chamfered portion. In particular, it is to eliminate the swelling and burrs on the tooth surface generated at the chamfered portion of the end surface of the gear or spline.

[0006]

SUMMARY OF THE INVENTION In the present invention, a pair of flat dies are arranged in parallel at symmetrical positions, and an object to be rolled is rotatably supported between the flat dies and sandwiched between the flat dies. In a rolling method in which a die is relatively moved to plastically work the outer circumference of the rolled object, the flat die for rolling is adjacent to the outer peripheral rolling section for plastically working the outer circumference of the rolled object, and the outer circumferential rolling section. And a chamfer forming portion that plastically processes the chamfered portion of the axial end portion of the outer peripheral portion of the rolling object,
After rolling the outer periphery and the chamfered portion with the flat die for rolling,
By providing a rolling processing method in which a deformed portion of the rolled object generated at the mating surface of the outer peripheral rolling portion and the chamfered portion is further outer peripheral rolled by a finishing portion provided in the outer peripheral rolling portion. The above problem was solved.

(Operation) That is, a pair of flat dies are arranged in parallel at symmetrical positions, and the object to be rolled is rotatably supported between the flat dies and is sandwiched between the flat dies, and the flat dies are relatively moved. By doing so, the outer peripheral rolling portion and the chamfer forming portion provided adjacent to the outer peripheral rolling portion simultaneously roll the outer peripheral portion of the workpiece and the chamfered portion at the end portion in the axial direction. However, at this time, in the mating surfaces of the outer peripheral rolling portion and the chamfer forming portion which are adjacent to each other, a manufacturing error of the outer peripheral rolling portion and the chamfer forming portion,
There is a slight discontinuity in the shape due to misalignment of the assembly, and due to the swelling force of the material during the rolling process, irregularities such as swelling of meat and burrs occur on the tooth surface. However, in the present invention, after the outer periphery and the chamfered portion are rolled by the flat die for rolling, the deformed portion of the rolling object is further outer peripherally rolled by the finishing portion provided in the outer peripheral rolling portion. A deformed portion such as a bulge or a flash generated on the adjoining portion of the outer peripheral rolling portion and the chamfer forming portion, that is, a raised portion or a flash, is crushed by the finishing portion of the outer peripheral rolling portion. As a result, a good rolled product without bulging of the chamfered portion at the end and burrs can be obtained.

As such a rolling method, it is possible to perform re-rolling by a rolling die for outer peripheral finishing, which is provided separately with a rolling object having a deformed portion in which the outer periphery and the chamfered portion are simultaneously rolled. In this method, it takes time and labor to increase the number of devices and change the setup. Therefore, by shifting in the axial direction so that the chamfered part of the rolled object does not interfere with the chamfer forming part, the rolled object is reversely rotated back to the finishing tooth part, and further rolled forward to rotate from the escape tooth part. The object to be rolled may be taken out.

The above-mentioned method requires two rounds of rolling and axial movement forward / reverse operation. On the other hand, like the conventional rolling process using a flat die, it is desired to roll the workpiece only by rotating it in one direction. Therefore, in the invention according to claim 2, a pair of flat dies are arranged in parallel at symmetrical positions, and the object to be rolled is rotatably supported between the flat dies and sandwiched between the flat dies. In a rolling flat die for relatively moving the outer circumference of the rolling object to be plastically worked, the rolling flat die is an outer circumferential rolling section for plastically working the outer circumference of the rolling object, and the outer circumferential rolling section. And a chamfer forming portion which is provided separately from the outer peripheral rolling portion and adjacent to the outer peripheral rolling portion and plastically processes the chamfered portion of the end portion in the axial direction of the outer peripheral portion of the rolling object, and the length of the outer peripheral rolling portion. Is longer than the end of the chamfer forming portion in the longitudinal direction, and the outer peripheral rolling part is adjacent to or away from the end of the chamfer forming portion and protrudes toward the chamfer forming portion at a portion longer than the end. The above-mentioned section is provided by providing the formed flat die for rolling. It was resolved.

(Operation) That is, a pair of flat dies are arranged in parallel at symmetrical positions, and the object to be rolled is rotatably supported between the flat dies and sandwiched between the flat dies, and the flat dies are relatively moved. By doing so, the outer peripheral rolling portion and the chamfer forming portion that is installed adjacent to the outer peripheral rolling portion and is separate from the outer peripheral rolling portion can roll the outer peripheral portion of the rolling object and the chamfered portion of the axial end portion. It is done at the same time. At this time, there is a slight discontinuity in the shape due to a manufacturing error between the outer peripheral rolling portion and the chamfer forming portion and a deviation in the assembly between the outer peripheral rolling portion and the chamfer forming portion which are adjacent to each other. Due to the swelling force of the material at that time, swelling of the meat and irregular portions such as burrs occur near the chamfered portion. In the invention of claim 2, the length of the outer peripheral rolling portion is made longer than the end of the chamfer forming portion in the longitudinal direction, and the outer peripheral rolling portion is formed so as to project toward the chamfer forming portion. After the above, the vicinity of the chamfered end chamfered portion of the rolling object is further rolled by the outer peripheral rolling portion. Therefore, a bulge, a burr, or the like generated in the adjacent portion between the outer peripheral rolling portion and the chamfer forming portion, that is, the joint portion is crushed by the wide outer peripheral rolling portion formed by the overhang. As a result, a good rolling product having no chamfer on the end face and having a chamfered portion is obtained by unidirectional rotation.

Incidentally, the reciprocating motion is not limited to the one-direction rotation. Further, the chamfer forming portion is not limited to one location on one side adjacent to the outer peripheral rolling portion, but may be disposed on several locations such as on both sides or in an intermediate position. It is important that the outer peripheral rolling portion rises up after the end of the chamfer forming portion and is raised, and burrs are further rolled by the outer peripheral rolling portion. Therefore, it goes without saying that the amount of overhang may be any width as long as it can be rolled up and the flash can be rolled. Also,
The projecting position is preferably provided adjacent to the end of the chamfer forming portion, but it may be provided with a gap or may be provided separately. Providing an overhanging position adjacent to the end of the chamfer forming portion facilitates positioning in the longitudinal direction and makes the mounting firm.

The above-described object to be rolled is effective for a chamfered end face, but is particularly suitable for chamfering the tooth face end face of a spline or a gear. Therefore, in the invention according to claim 3, the rolling flat die is provided adjacent to the outer peripheral rolling portion having a tooth groove for plastically processing the outer peripheral tooth portion of the workpiece and the outer peripheral rolling portion. It is preferable that the chamfered portion at the axial end portion of the outer peripheral tooth portion of the workpiece be a rolling flat die including a chamfer forming portion that is plastically worked.

In the case of gears, splines, etc., the outer peripheral rolling portion and the chamfer forming portion of the teeth which form the gears and splines have a slight shape due to manufacturing errors and misalignment. Discontinuities are likely to occur, and the swelling force of the material during the rolling process is likely to cause swelling, burrs, etc., especially on the tooth surface. According to the present invention, after chamfering, the outer peripheral rolling unit further rolls the gear and the spline,
It is possible to correct bulges and burrs on the tooth surface.

More specifically, a general rolling gear is composed of a biting tooth portion, a finishing tooth portion and a relief tooth portion. In accordance with this, in the invention of claim 4, the outer peripheral rolling portion is , Toothed teeth, finish teeth, relief teeth,
The chamfer forming portion is provided adjacent to the biting tooth portion to the first half of the finishing tooth portion. As a result, the configuration of the conventional flat die for rolling can be made almost the same, and the conventional rolling machine can be used as it is or with a small modification.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described with reference to the drawings when applied to machining a spline shaft. 1A and 1B show one side of a flat die for rolling showing an embodiment of the present invention, FIG. 1A is a plan view, FIG. 1B is a side view,
(C) is a cross-sectional view taken along the line AA of (b), FIG. 2 is a plan view of the chamfer forming portion, (b) is a side view, and (c) is a cross-sectional view taken along the line BB of (b). FIG. 3 is a perspective view showing a state in which spline rolling processing is being performed on an object to be rolled (hereinafter referred to as a work) with the pair of flat dies for rolling shown in FIG. 1. Further, FIG. 4 is a front view of a work before rolling used in the embodiment of the present invention, and FIG. 5 is a work immediately after simultaneous rolling of spline rolling and chamfering of the spline end showing the embodiment of the present invention. FIG. 6 is a front view of FIG.
FIG. 3 is a front view of the work after the modified portion of the spline (outer peripheral surface) rolling and the chamfering of the spline end (tooth surface) showing the embodiment of the present invention, and showing the vicinity of the -C line cross section of FIG. 1. . As shown in FIG. 1, rolling flat dies 1 and 2 of the present invention
Is a tooth groove 31 for spline machining in the direction perpendicular to the longitudinal direction.
The outer peripheral rolling portion 3 formed with the outer peripheral rolling portion is adjacent to one side of the outer peripheral rolling portion and is a spline machining tooth groove 31 which is separate from the outer peripheral rolling portion.
The side surface 32 and the chamfer forming portion 4 having the same side surface-shaped chamfering groove 41.

The outer peripheral rolling portion 3 has a notch portion 5, and the side surface 42 of the chamfer forming portion 4 and the terminal end 43 in the longitudinal direction are brought into contact with the notch portion, respectively. It is fixed to. Further, the outer peripheral rolling portion 3 extends in the longitudinal direction and is longer than the longitudinal end 43 of the chamfer forming portion 4, and the portion wider than the end projects toward the chamfer forming portion and has a wide portion having a widened tooth groove 33. 34 are provided. Further, the outer peripheral rolling portion 3 is formed from a machining start end 35 with a biting tooth portion 36 whose tooth height gradually increases, a finish tooth portion 37 whose tooth height is constant, and a relief tooth portion 38 whose tooth height gradually decreases. The mating surface 51 of the cutout portion 5 with which the terminal end 43 of the chamfer forming portion abuts is set to be the region of the finishing tooth portion 37. In addition, from the finish tooth start position 37a to the end 4
The dimension 37b up to 3 and the dimension 37c from the terminal end 43 to the finishing tooth end position 37d are at least 1 / of the workpiece.
The size is equivalent to two or more turns.

As described above, as shown in FIG. 2, the chamfer forming portion 4 has the tooth groove 31 for spline processing of the outer peripheral rolling portion.
The chamfered groove 41 is formed corresponding to the above, and the tooth profile of the side surface (the mating surface) 42 of the chamfer groove is set so as to substantially match the tooth profile of the side surface 32 of the mating surface of the outer peripheral rolling portion. Further, the chamfered groove 41 has an angle α (30
It is preferable that the tooth heights h from the die mounting surface 6 are the same.

As shown in FIG. 4, the material of the workpiece 7 to be processed has a cylindrical portion 8 to be machined on a part of the shafts 7a and 7b, and both end portions of the cylindrical portion are tapered surfaces 9 and 9, respectively.
It is set to 10. Reference numeral 51 is a centering tool for holding the workpiece in rotation, and 52 is a centering hole into which the tip of the centering tool is fitted. In the embodiment of the present invention, a spline is created in the cylindrical portion 8 of the work 7 shown in FIG. 4, and the tooth surface on the left taper portion 9 side is chamfered as viewed in FIG. The right taper portion 10 side merely forms a conventional tooth surface, and chamfering is not performed.
As shown in FIG. 3, the work 7 is rolled into a pair of rolling flat dies 1 shown in FIG. 1 and rolling flat dies 2 which are axially symmetrical with respect to the tooth groove direction axis shown in FIG. Place them in parallel. The configuration of the rolling flat die 2 is the same as that of the rolling flat die 1, and the same components as those of the rolling flat die 1 are designated by the same reference numerals and the description thereof will be omitted. The left end 8a of the cylindrical portion of the work 7 is a mating surface 32 (42) between the outer peripheral rolling portion 3 and the chamfer forming portion 4.
The work is rotatably supported from the side of the biting tooth 36 so as to be sandwiched between the flat dies 1 and 2, and the flat dies are relatively moved in synchronization with each other by a synchronizing device (not shown) to perform the rolling process. .

First, from the biting tooth portion 36 to the finishing tooth portion first half 37b, the spline portion 11 and the chamfered portion 12 are simultaneously rolled on the outer periphery of the work 7 as shown in FIG.
The left taper surface 9 is reduced in diameter and deformed. At this time, the tooth groove 31 of the outer peripheral rolling portion 3 and the chamfer forming portion 4 on the mating surface 32 are formed.
Since the tooth profile of the chamfered groove 41 is the same, the geometrical shapes of the spline portion 11 and the chamfered portion 12 of the work 7 are substantially continuous, and the chamfered groove 41 is rounded up at an angle α. The chamfered portion 12 of the surface is formed in a substantially V-shaped tapered surface with a rounded bottom so as to be axially narrowed from the tooth surface with the tooth tip 13 interposed therebetween. In addition, the outer peripheral rolling portion 3
Since the tooth height h of the chamfer forming portion 4 and the tooth groove 31 of the left chamfer forming portion 4 are the same, the left taper surface 9 is further formed on the upper surface 45 of the chamfer forming portion 4.
It is pressed by and is rolled into an extension 15 having the same height as the tooth bottom 14. The tip 16 of the extension 15 has a free shape, for example, a wavy shape, because there is nothing to limit the deformation. Further, the taper surface 9 remains at the taper end. Similarly, a part 9a of the tapered surface 9 is left in the vicinity of the left tip of the tooth 13a. This facilitates the flow of the material at the time of rolling, reduces the influence of processing error, reduces the occurrence of bulging of the mating surface and burrs, and facilitates rolling processing. The right side surface 10 of the work is splined along the taper surface without being chamfered.
Is formed.

However, in the rolling process of the spline portion 11 and the chamfered portion 12 up to the first half 37b of the finishing tooth portion,
As shown in FIG. 5, an abnormal portion 17 such as a slight bulge or a burr may be generated in the vicinity 13a of the mating face tooth surface as shown in FIG. 5 due to a manufacturing error between the outer peripheral rolling portion 3 and the chamfer forming portion 4 or a deviation in assembly. There is. Then, the rolling flat dies 1 and 2 are further moved, and as shown in FIG. 6, at the wide portion 34 (finishing tooth latter half 37c) which is widened after the terminal end 43 of the chamfer forming portion, the outer periphery, that is, the spline rolling. Continue processing.
As a result, the abnormal portion 17 such as the raised tooth surface or flash
Is crushed by the tooth gap 33 of the wide portion 34,
The flat dies 1 and 2 for rolling are moved, and the work 7 is taken out from the relief tooth portion 38. When the machining of the workpiece 7 machined by such a process is completed, a good spline shaft having a chamfered end surface and a raised tooth surface and no burrs as shown in FIG. 6 can be obtained.

The mating surface 18 between the tooth bottom 14 and the extension 15 of the work 7 may have a rise or a burr due to an error or the like. However, when the spline is actually assembled, the tooth bottom 14 does not interfere with each other. Since there is almost no such difference, it is sufficient to reduce the occurrence of abnormal portions by increasing the accuracy of adjusting the mating surfaces. If you dare to modify, wide part 3 of the outer peripheral rolling part
The tooth height of the finishing tooth part of 4 is slightly increased and the tooth bottom 1
4 may be rolled.

[0022]

As described above, according to the present invention,
An outer peripheral rolling part that plastically processes the outer periphery of the workpiece (work),
In a rolling process method using a pair of flat dies, which is provided adjacent to the outer peripheral rolling part and includes a chamfer forming part that plastically processes the chamfered part of the axial end of the outer peripheral part of the rolling object, the outer periphery and the chamfered part. After rolling, the deformed part of the rolling object generated at the mating surface of the outer peripheral rolling part and the chamfered part was further outer peripheral rolled by the finishing tooth part provided in the outer peripheral rolling part. Elimination of bulging and burrs caused by rolling. In addition, since the length of the outer peripheral rolling portion is made longer than the longitudinal end of the chamfer forming portion, and the lengthened portion of the outer peripheral rolling portion is widened by projecting toward the chamfer forming portion, there is no bulge or burr. A good rolled product was obtained by unidirectional rotation.

Further, since the outer peripheral rolling portion having a concavo-convex shape for forming a gear or a spline and the chamfer forming portion of the tooth portion are used, and after the chamfering, the gear or the spline is further rolled by the outer peripheral rolling portion. It became suitable for correcting swelling and burrs on the tooth surface. Further, the outer peripheral rolling portion is composed of a biting tooth portion, a finishing tooth portion and a relief tooth portion, and a chamfer forming portion is provided adjacently from the biting tooth portion to the first half of the finishing tooth portion. Since the structure is almost the same and the conventional rolling machine can be used as it is or with a small modification, the structure and processing are simple, and a low-cost chamfering die for mass production is provided. became. Also, it has become possible to provide a chamfered spline shaft that allows easy assembly of the spline.

[Brief description of drawings]

1A is a plan view, FIG. 1B is a side view, and FIG. 1C is a sectional view taken along the line AA of FIG. 1B, showing one of flat rolling dies for rolling according to an embodiment of the present invention. is there.

FIG. 2A is a plan view, FIG. 2B is a side view, and FIG. 2C is a side view of a chamfer forming portion of a flat die for rolling according to an embodiment of the present invention.
Is a cross section taken along line BB of (b).

FIG. 3 shows a method for processing a flat die for rolling according to an embodiment of the present invention, showing a state in which a pair of flat dies for rolling shown in FIG. It is a perspective view.

FIG. 4 is a front view of the work before rolling used in the embodiment of the present invention.

5 is a front view of the work immediately after the simultaneous rolling of the spline rolling and the chamfering of the spline end according to the embodiment of the present invention, and shows the vicinity of the cross section taken along the line AA of FIG. 1. FIG.

FIG. 6 is a spline (outer peripheral surface) showing an embodiment of the invention.
FIG. 2 is a front view of the work after the modified portion of the rolling and chamfering of the spline end (tooth surface end) has been corrected, and shows the vicinity of the -C line cross section of FIG. 1.

[Explanation of symbols]

Flat dies for rolling 3 Outer rolling part 4 Chamfer forming section 7 Rolled products 8 Rolled object outer circumference 12 Chamfer 17 Deformed part 31 Tooth groove 32, 42 mating surface 36 Biting teeth 37 Finishing teeth 37b Finishing tooth first half 38 Escape teeth 43 end

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yu Sumitani             1-1-1, Fujikoshihonmachi, Toyama City, Toyama Prefecture             Fuji Koshinai Co., Ltd.

Claims (4)

[Claims] 1. A pair of flat dies are arranged parallel to each other at symmetrical positions, and a rolling object is rotatably supported between the flat dies and is sandwiched between the flat dies, and the flat dies are relatively moved to rotate the flat dies. In the rolling processing method of plastically working the outer periphery of a workpiece, the rolling flat die is provided with an outer peripheral rolling portion that plastically processes the outer periphery of the rolled workpiece, and the outer periphery of the rolled workpiece that is provided adjacent to the outer peripheral rolling portion. Consisting of a chamfer forming portion that plastically processes the chamfered portion at the end in the axial direction of the part, and after rolling the outer periphery and the chamfered portion with the flat die for rolling, the outer peripheral rolling portion and the chamfered portion A rolling method, wherein the deformed portion of the rolled object produced on the mating surfaces is further rolled on the outer periphery by a finishing portion provided on the outer peripheral rolling portion. 2. A pair of flat dies are arranged parallel to each other at symmetrical positions, and the object to be rolled is rotatably supported between the flat dies and sandwiched between the flat dies, and the flat dies are relatively moved to rotate the flat dies. In a rolling flat die for plastically processing the outer periphery of a workpiece, the rolling flat die is a peripheral rolling portion that plastically processes the outer periphery of the workpiece, and the peripheral rolling portion is a separate body from the outer peripheral rolling portion. A chamfer forming portion which is provided adjacent to the forging portion and plastically processes the chamfered portion of the axial end portion of the outer peripheral portion of the rolling object, and the length of the outer peripheral rolling portion is equal to that of the chamfer forming portion. It is made longer than the end in the longitudinal direction, and the outer peripheral rolling portion is formed adjacent to or away from the end of the chamfer forming part and extends toward the chamfer forming part at a portion longer than the end. Flat die for rolling. 3. The rolling flat die has an outer peripheral rolling portion having a tooth groove for plastically processing the outer peripheral tooth portion of the rolled object, and an outer circumferential tooth portion of the rolled object provided adjacent to the outer peripheral rolling portion. The rolling flat die according to claim 2, which is a rolling flat die including a chamfer forming portion that plastically processes the chamfered portion at the end in the axial direction. 4. The outer peripheral rolling portion includes a chamfer tooth portion, a finishing tooth portion, and a relief tooth portion, and the chamfer forming portion is provided adjacent to the chamfer tooth portion to the first half of the finishing tooth portion. The flat die for rolling according to claim 2 or 3, wherein