JP2018080826A - Ring gear, gear device and mold for manufacturing ring gear - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide ring gears with improved concentricity, and a gear reduction device.SOLUTION: The ring gear includes a one-piece annular body made from powder metallurgy material, and a first ring gear part and a second ring gear part formed on a surface of the annular body. The first ring gear part and the second ring gear part are arranged along an axial direction of the annular body. The ring gear has a density less than 92% of its theoretical density and a mass of 6.0 to 8.0 grams per cubic millimeter. The present invention further provides a mold for manufacturing the ring gear. The ring gear of the present invention includes two ring gears integrally formed at once, and the two ring gears have improved concentricity.SELECTED DRAWING: Figure 2

Description

The present invention relates to the field of gears, and more particularly to a ring gear and a gear device using the ring gear.

[0003] In the conventional two-stage gear reduction device, the ring gear of the first planetary gear train and the ring gear of the second planetary gear train are usually formed separately. Generally, each ring gear has a connection portion that is machined after forming the ring gear, and the connection portions of the two ring gears are connected together by fasteners such as screw bolts or pins. A ring gear made in this way requires secondary machining and subsequent machine connections and is therefore expensive. Furthermore, eccentricity is likely to occur between the two ring gears due to the manufacturing or assembly process.

[0004] An object of the present invention is to improve the concentricity of a ring gear.

[0005] In one aspect of the present invention, a ring gear is provided. The ring gear includes a first ring gear portion including a first annular body, and a plurality of first teeth formed on a surface of the first annular body, a second annular body, and a second annular body. A second ring gear portion including a plurality of second teeth formed on the surface of the main body. The first ring gear portion and the second ring gear portion are integrally formed from powder metal. The ring gear has a density of less than 92% of its theoretical density and a mass of 6.0 to 8.0 grams per cubic millimeter

[0006] The ring gear preferably has a mass of 6.2 to 7.2 grams per cubic millimeter.

[0007] Preferably, the first tooth is a twisted tooth and the second tooth is a straight tooth.

[0008] Preferably, the first tooth is a straight tooth and the second tooth is a twisted tooth.

[0009] Preferably, the first tooth and the second tooth are both twisted teeth and have opposite helical directions.

[0010] Preferably, the first tooth and the second tooth are both twisted teeth and have the same helical direction.

[0011] It is preferable that the first teeth and the second teeth have unequal pitches.

[0012] Alternatively, the pitch of the first and second teeth can be the same.

[0013] It is preferable that the first teeth and the second teeth have the same number of teeth.

[0014] Alternatively, the number of teeth of the first tooth and the second tooth may be equal.

[0015] Preferably, the first tooth and the second tooth are not equal in tooth height.

[0016] Alternatively, the tooth height of the first tooth and the second tooth may be equal.

[0017] The ring gear is preferably formed integrally in one cavity so that there is no connection mark between the first annular body and the second annular body.

[0018] The ring gear preferably has a smooth outer peripheral surface, that is, no connection line.

[0019] It is preferable that pores are formed in the powder metallurgy powder of the ring gear, and the maximum size of the long sides of the pores is less than 0.2 mm.

[0020] The first annular body forms a plurality of attachment portions, each attachment portion has a through hole, the attachment portion at least partially overlaps the first teeth in the axial direction of the ring gear, and / or The second annular body forms a plurality of attachment portions, and through holes are defined in each attachment portion, and the attachment portions preferably overlap at least partially with the second teeth in the axial direction of the ring gear.

[0021] The gear ring provided by the first aspect of the present invention can be used in a gear device such as a planetary gear reduction device. The planetary gear device includes a first planetary gear train and a second planetary gear train. The first planetary gear train is driven around the first sun gear by rotation of the first sun gear, the first planetary gear set surrounding the first sun gear, and the first planetary gear set. Including the first carrier. Each planetary gear of the first planetary gear set meshes with both the first sun gear and the first ring gear portion on the inner peripheral surface of the ring gear. The second planetary gear train is driven around the second sun gear by rotation of the second sun gear, the second planetary gear set surrounding the second sun gear, and the second planetary gear set. A second carrier. Each planetary gear of the second planetary gear set meshes with both the second sun gear and the second ring gear portion on the inner peripheral surface of the ring gear.

[0022] The gear device further includes a flange attached to an end of the ring gear, and the flange includes a flange main body that abuts on the end of the ring gear, and a connection portion that extends from the flange main body and is inserted into the ring gear. It is preferable to comprise.

[0023] One of the first annular body and the second annular body forms a plurality of recessed mounting portions, and the connection portion forms a plurality of engaging portions projecting from the outer peripheral surface thereof, and the projecting engagement. The mating portions are preferably housed in recessed mounting portions, respectively.

[0024] Preferably, the connecting portion has a round circumferential surface configured to contact the tips of the teeth of the ring gear.

[0025] In another aspect, the present invention provides a mold for manufacturing the ring gear described above. The mold includes an intermediate mold including a forming cavity, a first hollow upper punch body, an upper punch including a second upper punch body housed in the first upper punch body, and a first hollow. A lower punch body, and a lower punch including a second lower punch body housed in the first lower punch body, the outer diameter of the first lower punch body and the first upper side The outer diameter of the punch body matches the inner diameter of the molding cavity of the intermediate mold, the outer diameter of the second lower punch body is equal to the outer diameter of the second upper punch body, and the second lower punch body Each of the second upper punch bodies has external meshing teeth.

[0026] A torsion tooth having a tooth shape corresponding to the tooth profile of the first tooth of the ring gear is formed on the outer surface of the second upper punch body, and the second surface is formed on the inner surface of the first upper punch body. Preferably, a twisted tooth that meshes with the twisted tooth of the upper punch body is formed.

[0027] The composite ring gear of the present invention is integrally formed in a single cavity into a single part.
The assembly of the first ring gear part and the second ring gear part is omitted, thereby avoiding secondary machining, reducing costs, and the first ring gear part and the second ring gear part. Concentricity improves.

It is a figure which shows the ring gear by the 1st Embodiment of this invention. It is sectional drawing of the ring gear of FIG. It is sectional drawing of the ring gear by the 2nd Embodiment of this invention. It is sectional drawing of the ring gear by the 3rd Embodiment of this invention. It is sectional drawing of the ring gear by the 4th Embodiment of this invention. It is a figure which shows the 5th Embodiment of this invention, and the part for connecting a flange is each integrally formed by the 1st ring gear part and 2nd ring gear part of a ring gear. FIG. 7 is a cross-sectional view of the ring gear of FIG. 6, and a portion for connecting a flange to the first ring gear portion and the second ring gear portion of the ring gear is formed integrally. It is sectional drawing of the 1st ring gear part of FIG. 6, and the 2nd ring gear part of a ring gear, A flange is each connected to both ring parts. It is a figure which shows the flange to which the 1st ring gear part and 2nd ring gear part of FIG. 8 are connected. It is sectional drawing of the metal mold | die for forming the ring gear of FIG. It is sectional drawing of the gear reduction device which uses the ring gear of this invention.

Hereinafter, embodiments of the present invention will be further described with reference to the accompanying drawings.

[0040] Referring to FIGS. 1 and 2, the present invention provides a ring gear 100 made from powder metallurgy material. Narrow and long pores are formed between the powder metallurgy particles of the ring gear 100, and the maximum size of the long sides of the narrow and long pores is less than 0.2 mm. In this embodiment, the ring gear 100 is a composite ring gear that includes a first ring gear portion 10 and a second ring gear portion 20. The first ring gear portion 10 includes a first annular body and a plurality of first teeth 11 formed on the inner surface of the first annular body. The second ring gear portion 20 includes a second annular body and a plurality of second teeth 21 formed on the inner surface of the second annular body. The first ring gear portion 10 and the second ring gear portion 20 are integrally formed. That is, the first and second annular bodies, and the first teeth 11 and the second teeth 21 have an integral structure and are integrally formed into a single part. The first annular body of the first ring gear portion 10 and the second annular body of the second ring gear portion 20 are formed in cooperation with the annular body of the ring gear 100. In this embodiment, the two-stage teeth 11 and 21 of the ring gear are formed on the inner peripheral surface of the annular body. In this embodiment, the assembly of the first ring gear part 10 and the second ring gear part 20 is no longer required, so that the first ring gear 10 and the second ring gear part 20 are Secondary machining can be avoided, the axial length of the ring gear 100 can be reduced and costs can be reduced, while eccentricity due to errors during the manufacture or assembly of parts can be avoided, Therefore, the eccentricity of the first ring gear portion 10 and the second ring gear portion 20 can be improved.

[0041] The ring gear 100 has a density of less than 92% of its theoretical density and a mass of 6.0 grams per cubic millimeter or a twist angle of 8.0 grams, from 6.2 to 7.2 grams. It is preferable.

A first tooth 11 is integrally formed on the inner peripheral surface of the first ring gear portion 10. Second teeth 21 are integrally formed on the inner peripheral surface of the second ring gear portion 20. The axially inner end of the first tooth 11 is connected to the inner end of the second tooth 21, and the axially outer end of the first tooth 11 is flush with the end face of the annular body of the ring gear, The outer end of the second tooth 21 in the axial direction is preferably flush with the end face of the ring gear opposite to the annular body. In an alternative embodiment, the inner end of the first tooth 11 and the inner end of the second tooth 21 can be separated, but instead are separated by a radial distance, i.e. the inner side of the first tooth 11. A partition region without teeth is formed between the end and the inner end of the second tooth 21, and the partition region has a smooth inner surface.

[0043] In this embodiment, the first teeth 11 and the second teeth 21 have the same number of teeth, different tooth thicknesses, and different tooth heights. It should be understood that the first tooth 11 and the second tooth 21 may not have the same number of teeth and may have the same tooth thickness and height, and can be configured according to needs. The cross-sectional view of each first tooth 11 and / or each second tooth 21 is involute and can instead be triangular, rectangular or trapezoidal.

[0044] In this embodiment, the first tooth 11 has a twisted tooth with a twist angle of 10 ° to 30 °, preferably 19 °, 20 ° or 21 °. The second teeth 21 are straight teeth, and the axial length of the first teeth 11 is shorter than the axial length of the second teeth 21.

[0045] It should be understood that the first tooth 11 and the second tooth 21 can be configured in other ways.

[0046] Referring to FIG. 3, in this embodiment, the first tooth 11 is a straight tooth and the second tooth 21 has a twist angle of 0 ° to 10 °, preferably 19 °, 20 ° or 21 ° twisted teeth. The axial length of the first tooth 11 is shorter than the axial length of the second tooth 21.

[0047] Referring to FIG. 4, in this embodiment, both the first tooth 11 and the second tooth 21 are twisted teeth having the same twist angle but opposite spiral directions, The axial length of the teeth 11 is shorter than the axial length of the second teeth 21. It should be understood that the axial length of the first tooth 11 can be longer than the axial length of the second tooth 21.

[0048] Referring to FIG. 5, in this embodiment, both the first tooth 11 and the second tooth 21 are twisted teeth and have the same helical direction but different twist angles. The twist angle of the first tooth 11 is larger than the twist angle of the second tooth 21, and the axial length of the first tooth 11 is shorter than the axial length of the second tooth 21. The twist angle of the first tooth 11 may be smaller than the twist angle of the second tooth 21, and the axial length of the first tooth 11 is larger than the axial length of the second tooth 21. I want you to understand that.

[0049] It is understood that both the first tooth 11 and the second tooth 21 can be disposed on the outer peripheral surface of the annular body, or one can be disposed on the outer peripheral surface of the annular body and the other can be disposed on the inner peripheral surface. I want.

[0050] It should be understood that the first tooth 11 and the second tooth 21 may or may not have the same number and height of teeth. The slots between the first teeth 11 of the first ring gear portion 10 can be aligned and communicated with the slots between the second teeth 21 of the second ring gear portion 21. Alternatively, the slots may not be aligned with or in communication with each other.

[0051] The ring gear 100 has a density of less than 92% of its theoretical density and a mass of 6.0 to 8.0 grams per cubic millimeter so that it is easy to integrally form the ring gear. Preferably there is. The first ring gear portion 10 having the first teeth 11 and the second ring gear portion 20 having the second teeth 21 are once formed as a single piece, which is the first ring gear 10. And the second ring gear portion 20 is not formed separately. Accordingly, the production efficiency is increased, and the concentricity between the first ring gear portion 10 and the second ring gear portion 20 is improved. The density of the ring gear 100 may be uniform or non-uniform.

[0052] Referring to FIGS. 6 and 7, in another embodiment of the present invention, the first ring gear portion 10 and the second ring gear portion 20 further include a mounting portion 12 for connecting to a flange. And 22 are integrally formed. In particular, a plurality of first recessed mounting portions 12 are integrally formed on the inner peripheral surface of the first ring gear portion 10. The first recessed mounting portion 12 preferably extends to the axial end face of the first ring gear portion 10. The first recessed mounting portion 12 has a mounting surface 14. The radial depth of the recessed mounting portion 12 is greater than or equal to the radial height of the first tooth 11. A first through hole 13 is defined in each first recessed mounting portion 12, and the first through hole 13 can penetrate the side wall of the first ring gear portion 10 in the radial direction. Similarly, the second recessed mounting portion 22 and the second through hole 23 are formed in the other end of the ring gear 100, that is, the second ring gear portion 20. The second recessed mounting portion 22 has a mounting surface 24. The radial depth of the recessed mounting portion 22 is greater than or equal to the radial height of the second tooth 21. In order to facilitate the assembly of the flange, the cross-section of each of the first recessed mounting portion 12 and the second recessed mounting portion 22 is trapezoidal, and the outer end of the ring gear in the axial direction is more than the inner end. Is also preferably large. The mounting surfaces 14 and 24 are preferably bent. In this embodiment, the number of the first recessed mounting portions 12 and the number of the second recessed mounting portions 22 are both 4, and the four first recessed mounting portions 12 and the four second recessed portions. The mounting portions 22 are arranged uniformly along the circumferential direction of the ring gear 10.

[0053] When the connection with the flange is described with reference to FIGS. 8 and 9, the flange for connecting to the first ring gear portion 10 is referred to as the first flange 30 and the second ring gear. The flange for connecting to the part 20 is called the second gear 40.

The first flange 30 includes a first flange body 31 and a first connection portion 32 formed at one end of the first flange body 31. The first connection portion 32 can be inserted inside the first ring gear portion 10 of the ring gear 100. The first connecting portion 32 preferably has an annular circumferential surface, the annular circumferential surface is in contact with the tip of the first tooth 11 of the first ring gear portion 10, and the flange 30 is the first. It is preferably configured to ensure that it is coaxial with the ring gear portion 10. The first flange 30 has an axial first center hole 311 to allow the drive shaft or driven shaft to pass therethrough. The first attachment portion 32 has a plurality of first protruding blocks 33 formed on the outer peripheral surface thereof. Each first protruding block 33 is housed in one corresponding first recessed mounting portion 12 of the first ring gear portion 10, with the outer surface of the block 33 facing the mounting surface 14 of the mounting portion 12. Yes. Each first protruding block 33 has a blind hole 34 aligned with the first through hole 13 of one corresponding first recessed mounting portion 12, and the pin passes through the blind hole 34 and the first through hole 34. Allows the ring gear portion 10 and the first flange 30 to be connected together.

[0055] After integrally forming the first teeth 11 on the mounting surface 14, the first through hole 13 can be drilled or punched, resulting in the first through hole. A burr is formed around 13. In this regard, each first protruding block 33 provides a recessed area adjacent to the blind hole 34 to prevent interference between the burr and the first protruding block 33. In this embodiment, the recessed area is a vertical groove 331 located on both sides of the blind hole 34. In connecting the first flange 30 to the first ring gear portion 10, the burr caused by the first through hole 13 of the first ring gear portion 10 can be accommodated in the vertical groove 331, and the pin Does not interfere with fasteners such as pins when embedded in holes 13 and 34.

[0056] The second flange 40 is configured in a manner similar to the first flange 30, and includes a second flange body 41, and a second attachment portion 42 formed at one end of the second flange body 41. including. The second flange 41 has an axial second center hole 411 to allow the driven shaft to pass therethrough. The second mounting portion 42 is preferably annular, with a plurality of second protruding blocks 43 formed on the outer peripheral surface thereof. Each second projecting block 43 is formed with a recessed region like a vertical groove 431 on both side surfaces of the second through hole 44. In connecting the second flange 40 to the second ring gear portion 20, each second protruding block 43 has an outer surface facing the mounting surface 24 of the mounting portion 22, and the second ring gear portion 20. The burr due to the second through hole 23 of the second ring gear portion 20 can be received in the vertical groove 431 and the pin can be received in the hole 23 and When embedded in 44, interference with fasteners such as pins is avoided. The second connecting portion 42 has a round circumferential surface, the circumferential surface contacts the tip of the second tooth 21 of the second ring gear portion 20, and the flange 40 is connected to the second ring gear portion 20. It is preferably configured to ensure that it is coaxial.

FIG. 10 illustrates a mold 200 for forming the ring gear 100 of the present invention. The mold 200 includes an intermediate mold 50, an upper punch, and a lower punch. The intermediate mold 50 includes a cavity 501. The lower punch includes a first lower hollow punch body 51 and a second lower punch body 52 accommodated in the first lower punch body 51. The upper punch includes a first upper hollow punch body 53 and a second upper punch body 54 accommodated in the first upper punch body 53. The outer diameter of the first lower punch body 51 and the outer diameter of the first upper punch body 53 coincide with the inner diameter of the cavity 501 of the intermediate mold 50. The outer diameter of the second lower punch body 52 is equal to the outer diameter of the second upper punch body 54. External teeth are formed on each of the second lower punch body 52 and the second upper punch body 54. The ring gear 100 is formed by filling the cavity 501 of the intermediate mold 50 and compressing metal powder. The formation temperature can be normal / ambient temperature or slightly higher than normal / ambient temperature (less than 200 degrees Celsius).

[0058] During the compression process, the second upper mold body 54 extends to a preset position within the cavity 501 of the intermediate mold 50 to push the second lower punch body 52 outward a predetermined distance. it can. During the powder metallurgy and compression process, the first upper punch body 53 can be inserted through the cavity 501 to compress the filled powder. After the compression process, the upper and lower punches are continuously released, thereby completing the shaping of the ring gear 100.

A twisted tooth having a tooth shape corresponding to the tooth shape of the first tooth 11 can be formed on the outer surface of the second upper punch body 54. Twist teeth that mesh with the twist teeth of the second upper punch body 54 can also be formed on the inner surface of the first upper punch body 53.

[0060] Straight teeth or twisted teeth can be formed on the inner surface of the first lower punch body 51, and the tooth profile of the second teeth 21 is formed on the outer surface of the second lower punch body 52. It is possible to form straight teeth or twisted teeth corresponding to the tooth shape.

[0061] In the ring gear 100 of the present invention, one cavity is formed by using a powder metal and a compression process, and the manufacturing process is simple and reliable. Further, there is no connection mark between the first annular body of the first ring gear portion 10 and the second annular body of the second ring gear portion 20, and the annular body of the ring gear 10 has a boundary line on the upper surface. Has a smooth outer peripheral surface that is not formed.

[0062] The ring gear can be formed by compression in a single step at a relatively low temperature (less than 200 degrees Celsius). In this case, the maximum size of the long sides of the pores between the powder metallurgy particles of the sintered ring gear 100 is less than 0.2 mm, and the density of the ring gear 100 is less than 92% of its theoretical density.

FIG. 11 illustrates a gear device that uses the ring gear 300 of the present invention. The gear device 300 is preferably a planetary gear reduction device, which includes a ring gear 100, a first planetary gear train 210, and a second planetary gear train 220. The first planetary gear train 210 and the second planetary gear train 220 are disposed in the ring gear 100. The ring gear 100 includes a first ring gear portion 10 and a second ring gear portion 20. The first ring gear portion 10 has first teeth 11 on its inner peripheral surface, and the second ring gear portion 20 has second teeth 21 on its inner peripheral surface.

[0064] The first planetary gear train 210 includes a first sun gear 211, a first planetary gear set 212, and a first rotating carrier 213. The outer peripheral surface of the first sun gear 211 includes the first external teeth 11. Each planetary gear of the first planetary gear set 212 meshes with both the first external teeth and the first teeth. Thus, if the first sun gear 211 rotates, each planetary gear of the first planetary gear set 212 rotates about both its own axis and the first sun gear 211, and the first rotating carrier 213 is driven.

[0065] The second planetary gear train 220 includes a second sun gear 221, a second planetary gear set 222, and a second rotating carrier 223. The second sun gear 221 is fixed to the first rotating carrier 213 and can be rotated together with the first rotating carrier 213. The outer peripheral surface of the second sun gear 221 includes second external teeth. Each planetary gear of the second planetary gear set 222 meshes with both the second external teeth and the second teeth 21. As the second sun gear 221 rotates, each planetary gear of the second planetary gear set 222 rotates about both its own axis and the second sun gear 221, resulting in a second rotating carrier 223. Drive. By using the ring gear 100 of the present invention, the gear reduction device 300 has a reduced axial size, improved concentricity, and a smaller structure. The gear reduction device 300 is driven by a motor and then drives the power lift gate of the vehicle.

[0066] Although the present invention has been described with reference to one or more embodiments, the above description of the embodiments is used only to enable those skilled in the art to make or use the present invention. It should be understood that various modifications can be made by those skilled in the art without departing from the spirit or scope of the invention. The embodiments illustrated herein should not be construed as limiting the invention, the scope of which is determined by reference to the following claims.

10 first ring gear part 11 first tooth 20 second ring gear part 21 second tooth 100 ring gear

Claims (15)

Ring gear,
A first ring gear portion including a first annular body and a plurality of first teeth formed on a surface of the first annular body;
A second ring gear portion including a second annular body and a plurality of second teeth formed on a surface of the second annular body;
The first ring gear portion and the second ring gear portion are integrally formed from powder metal, the ring gear having a density of less than 92% of its theoretical density and a mass of 6. 5 per cubic millimeter. Ring gear characterized in that it is 0 to 8.0 grams.   The ring gear of claim 1, wherein the ring gear has a mass of 6.2 to 7.2 grams per cubic millimeter.   The ring gear according to claim 1, wherein the first tooth is a twisted tooth, and the second tooth is a straight tooth.   The ring gear according to claim 1, wherein the first teeth and the second teeth are both twisted teeth, and the spiral directions of the first teeth and the second teeth are the same.   The ring gear according to claim 1, wherein the first teeth and the second teeth are both twisted teeth, and the spiral directions of the first teeth and the second teeth are opposite to each other.   The ring gear according to claim 1, wherein the first tooth has a twist angle of 10 to 30 degrees.   The ring gear according to any one of claims 1 to 6, wherein the ring gear is integrally formed in one cavity so that there is no connection mark between the first annular body and the second annular body. Ring gear as described in.   The narrow and long pore is formed between the powder metallurgy particles of the ring gear, and the maximum size of the long side of the narrow and long pore is less than 0.2 mm, according to any one of claims 1 to 7. Ring gear. The first annular body forms a plurality of attachment portions, each attachment portion has a through-hole, the attachment portion at least partially overlaps the first teeth in the axial direction of the ring gear; and And / or the second annular body forms a plurality of attachment portions, each of the attachment portions has a through hole, and the attachment portion at least partially overlaps the second teeth in the axial direction of the ring gear. The ring gear according to any one of claims 1 to 8. A gear device,
A first sun gear, a first planetary gear set surrounding the first sun gear, and a first carrier driven around the first sun gear by rotation of the first planetary gear set; A first planetary gear train including:
A second sun gear, a second planetary gear set surrounding the second sun gear, and a second carrier driven around the second sun gear by rotation of the second planetary gear set A second planetary gear train including
2. The ring gear according to claim 1, wherein the first planetary gear train and the second planetary gear train are disposed in the ring gear, and each planetary gear of the first planetary gear set includes: The ring gear meshes with both the first sun gear and the first tooth, and each planetary gear of the second planetary gear set includes the second sun gear and the second tooth of the ring gear. A gear device comprising: a ring gear meshing with both.   The flange further includes a flange attached to an end of the ring gear, the flange being in contact with the end of the ring gear, and a connection portion extending from the flange body and inserted into the ring gear. The gear device according to claim 10, comprising:   One of the first annular body and the second annular body forms a plurality of recessed mounting portions, and the connection portion forms a plurality of engaging portions projecting from the outer peripheral surface thereof, and projects The gear device according to claim 11, wherein engaging portions are respectively accommodated in the recessed mounting portions.   The gear device according to claim 11 or 12, wherein the connection portion has a round circumferential surface configured to contact a tip of the tooth of the ring gear. A mold for producing the ring gear according to claim 1,
An intermediate mold including a molding cavity;
An upper punch including a first hollow upper punch body and a second upper punch body housed in the first upper punch body;
A lower punch including a first hollow lower punch body and a second lower punch body housed in the first lower punch body, wherein the first lower punch body The outer diameter and the outer diameter of the first upper punch body coincide with the inner diameter of the molding cavity of the intermediate mold, and the outer diameter of the second lower punch body is equal to that of the second upper punch body. A mold having an outer diameter equal to the outer diameter, and external meshing teeth formed on each of the second lower punch body and the second upper punch body.   A torsion tooth having a tooth shape corresponding to a tooth shape of the first tooth of the ring gear is formed on the outer surface of the second upper punch body, and the second surface is formed on the inner surface of the first upper punch body. The mold according to claim 14, wherein a twisted tooth is formed that meshes with the twisted tooth of the upper punch body.