JP2018001256A - Molding mold device of gear with crowning and molding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a molding mold device of a gear with crowning which can surely and stably mold crowning at a gear tooth, is reduced in the generation of a molding malfunction product, and favorable in a yield.SOLUTION: A molding mold device of a gear with crowning comprises: a workpiece pressing face 19; a first column part 10 having a first small-diameter part 11; a second column part 20 which is arranged so as to be coaxial with and opposite to the first column part 10, and has a second small-diameter part 21 at its tip; and a tooth form die 3 having a gear tooth forming part 30 at an internal peripheral face. A gear tooth 92 is formed at a workpiece external peripheral face 90 by pressure-inserting a cylindrical workpiece W into the tooth form die at the workpiece pressing face, and making both-tip faces 13, 23 of the first column part and the second column part approximate each other or abut on each other in the workpiece. The molding mold device also comprises a first metal mold set S which is constituted so that an annular protrusion 93 is formed on a workpiece internal peripheral face 91 by the small-diameter part and the second-diameter part, and a second metal mold set which is constituted so that crowning is formed at the gear tooth by making a part or the whole of a volume of the annular protrusion circulate into a workpiece peripheral wall part by using a diameter expansion punch.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a molding device for a crowned gear and a molding method.

  As a conventional molding apparatus and method for crowned gears, a core bar (mandrel) having an outer peripheral groove at the tip and a cylindrical punch provided on the core bar in an outer fitting shape are provided. And a lower die having a finished tooth profile die for forming gear teeth with crowning, and with the core metal inserted into the cylindrical workpiece, the workpiece is pressed with a cylindrical punch to finish the tooth profile die When the core is pulled out from the workpiece, one or all of the workpieces filled in the outer circumferential groove are formed. An apparatus and a method for forming a crowning on a gear tooth by forcibly flowing a portion into a peripheral wall portion of a workpiece is known (see, for example, Patent Document 1).

JP 2014-217876 A

  However, the above-described apparatus and method have a problem that the crowning formed on the gear teeth is small because the volume of the work filled in the outer circumferential concave groove of the core metal is very small, and the crowning can be stably formed. There was a problem of difficulty. Further, when the outer circumferential concave groove is deepened to increase the volume of the workpiece filled in the groove, there are problems that it becomes difficult to pull out the core metal and that durability is lowered.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a molding device and a molding method for a gear with a crowning that can form a crowning on a gear tooth reliably and stably, has few molding defects, and has a high yield.

  In order to achieve the above object, a gear molding apparatus for a crowned gear according to the present invention includes a workpiece pressing surface, a first cylindrical portion that protrudes from the workpiece pressing surface to one axial center and has a first small-diameter portion at the tip. A workpiece having a second cylindrical portion provided coaxially and in a face-to-face relationship with the first cylindrical portion and having a second small diameter portion at a tip thereof, and a tooth profile die having a gear tooth forming portion on an inner peripheral surface, At the same time, a cylindrical workpiece is press-fitted into the tooth profile die, and both tip surfaces of the first columnar portion and the second columnar portion are brought close to or in contact with each other to form gear teeth on the outer peripheral surface of the workpiece. A first mold set configured to form an annular ridge on the inner peripheral surface of the workpiece with the first small diameter portion and the second small diameter portion; and further, the inner diameter dimension of the annular ridge portion Equipped with a diameter expansion punch having a large outer diameter portion. , All or a portion of the volume of the annular convex portion by flowing the workpiece peripheral wall portion, it is to include a second mold set which is configured to form a crowning on the gear teeth.

  The crowned gear molding method according to the present invention includes a first cylindrical portion that protrudes from the workpiece pressing surface to one axial center and has a first small-diameter portion at the tip, and a second cylindrical portion that has the second small-diameter portion at the tip. Are arranged coaxially and face-to-face, and a cylindrical workpiece is press-fitted into the tooth profile die at the workpiece pressing surface, and both end surfaces of the first columnar portion and the second columnar portion are brought close to each other in the workpiece. A first step of forming a gear tooth on the outer peripheral surface of the work and forming an annular ridge on the inner peripheral surface of the work with the first small diameter portion and the second small diameter portion; Inserting a diameter-expansion punch having an outer diameter part larger than the inner diameter dimension of the ridge part into the center hole part of the work, and flowing part or all of the volume of the annular ridge part into the work peripheral wall part, A second step configured to form a crowning on the gear tooth; It is a method of.

  According to the present invention, it is possible to form a crowning having a reliable and appropriate shape and size on the gear teeth, to reduce molding defects, and to improve the yield. The durability of each member of the mold can be improved, and mass production can be performed easily and stably.

It is front sectional drawing which shows one Embodiment of this invention, Comprising: It is front sectional drawing of the shaping | molding preparation state of a 1st metal mold | die set. It is front sectional drawing which shows immediately after shaping | molding of a gear tooth and a cyclic | annular convex part. It is front sectional drawing of the shaping preparation state of a 2nd metal mold | die set. It is front sectional drawing which shows the punch insertion state for diameter expansion. It is a front half-cut sectional view of the mold preparation state showing another example of the second mold set. It is a front half section sectional view showing other examples of the 2nd metallic mold set, and showing a punch for diameter expansion. It is front sectional drawing which shows the other example of a 1st cylindrical part and a 2nd cylindrical part. It is front sectional drawing which shows another example of a 1st cylindrical part and a 2nd cylindrical part. It is front sectional drawing which shows the further another example of a 1st cylindrical part and a 2nd cylindrical part. It is front sectional drawing which shows the other example of the punch for diameter expansion. It is front sectional drawing which shows another example of the punch for diameter expansion. It is front sectional drawing which shows the other example of the punch for diameter expansion.

Hereinafter, the present invention will be described in detail based on illustrated embodiments.
As shown in FIG. 1 and FIG. 2, the molding tool device for a gear with crowning according to the present invention is a male having a workpiece pressing surface 19 and a columnar portion 10 protruding from the workpiece pressing surface 19 to one axial center Ya. A mold Sa is provided.
Furthermore, a tooth profile die (having a receiving hole 40 for receiving a cylindrical workpiece W and a gear tooth forming portion 30 for communicating with the receiving hole 40 for forging a helical gear on the inner peripheral surface ( A female die Sb including a first tooth profile die) 3 and a second cylindrical portion 20 disposed in a face-to-face and coaxial manner with the first cylindrical portion 10 is provided.

  A first mold set S having a male mold Sa and a female mold Sb is installed in a pressing force generating means such as a press machine (not shown), and the male mold Sa and the female mold Sb are connected to the first reference shaft. It is possible to move closer to and away from each other in the direction of the center L1. The first cylindrical portion 10, the accommodation hole 40, the tooth profile die 3, and the second cylindrical portion 20 are disposed coaxially with the first reference axis L1. Further, the first reference axis L1 and the workpiece axis Lw are arranged coaxially. In the illustrated example, the male mold Sa is used as the first upper mold and is provided on the pressing movement board (upper board) side of a press machine (not shown), and the female mold Sb is used as the first lower mold, The first reference axis L1 is arranged in a vertical shape on the lower board side.

The first cylindrical portion 10 protrudes from the workpiece pressing surface 19 that is orthogonal to the axial center with a predetermined protruding dimension.
The male mold Sa has the first columnar portion 10 as a shaft member, and the tip surface of a cylindrical member into which the shaft member is inserted so as to be differentially movable (movable) is used as a work pressing surface 19. In addition, you may provide the 1st cylindrical part 10 and the workpiece | work press surface 19 in one component (integral).
In the molding preparation state of FIG. 1, the second cylindrical portion 20 is disposed in an insertion shape in the center hole portion of the tooth profile die 3 from the one axis Ya side toward the other axis Yb.

The first cylindrical portion 10 and the second cylindrical portion 20 include straight first and second shaft portions 12 and 22 having predetermined first and second outer diameter dimensions d12 and d22, and first and second shafts. The first and second small-diameter portions 11 and 21 are formed at the tip with smaller dimensions than the portions 12 and 22, and the first and second tip surfaces 13 and 23 are orthogonal to the axial center.
The first shaft portion 12 and the second shaft portion 22, the first small diameter portion 11 and the second small diameter portion 21, the first tip surface 13 and the second tip surface 23 are formed in the same shape (same size).

The first small-diameter portion 11 and the second small-diameter portion 21 are tip portions having smaller diameter dimensions than the first and second shaft portions 12 and 22, and in FIGS. First and second taper portions 11e and 21e which are inclined from the tip ends of the shaft portions 12 and 22 in a reduced diameter shape, and a first projecting straight from the tips of the first and second taper portions 11e and 21e. A tapered stepped shape having second small diameter short cylindrical portions 11f and 21f.
Alternatively, as shown in FIG. 7, first and second curved concave portions (corner radius portions) 11 g and 21 g that are recessed radially inward from the tips of the first and second shaft portions 12 and 22, and the first and second It is good also as a corner stepped shape which has the 1st, 2nd small diameter short cylinder part 11f and 21f which protruded in the straight form from the front-end | tip of 2 curved concave parts 11g and 21g.
Alternatively, as shown in FIG. 8, the first small-diameter portion 11 and the second small-diameter portion 21 may be a curved concave shape (corner round shape) formed by the first and second curved concave portions 11g, 21g.
Alternatively, as shown in FIG. 9, the first small-diameter portion 11 and the second small-diameter portion 21 may be a tapered type formed with first and second tapered portions 11e and 21e.

In the tooth profile die 3, the gear tooth forming portion 30 formed on the inner peripheral surface can forge-mold the gear teeth 92 of the helical gear, and the forged gear teeth 92 are arranged in the direction of the tooth trace (tooth longitudinal direction). The tooth thickness is substantially uniform and the crowning is not formed.
In other words, the gear tooth forming part 30 of the tooth profile die 3 has a forming tooth that does not form a crowning (a forming tooth that does not correspond to the crowning). There is almost no change in the tooth thickness, and the tooth thickness is substantially uniform.

The accommodation hole 40 is a columnar space formed by the central hole of the cylindrical work guide 4 fixed in contact with the other end surface (upper end surface) 36 of the axial center of the tooth die 3.
The work guide 4 (accommodating hole portion 40) and the tooth profile die 3 (gear tooth forming portion 30) may be provided integrally.

Next, a method for using the first mold set S and a first step will be described.
As described above, the male mold Sa and the female mold Sb are provided, and the cylindrical workpiece W is accommodated in the accommodation hole 40 of the female mold Sb. The male mold Sa is lowered (the male mold Sa and the female mold Sb are relatively close to each other in the axial direction), and the first cylindrical portion 10 is inserted into the center hole 94 of the workpiece W (press-fit). However, the workpiece pressing surface 19 presses the other end surface (the axial center other Yb side end surface) 96 of the workpiece W and press-fits it into the tooth profile die 3.

Further, the workpiece W is pressed into the space J between the tooth profile die 3 and the second cylindrical portion 20 while the workpiece W is press-fitted into the tooth profile die 3 (the workpiece W is press-fitted into the second cylindrical portion 20 in an external fitting shape). ) In the center hole portion 94, both end surfaces (first and second end surfaces) 13 and 23 of the first cylindrical portion 10 and the second cylindrical portion 20 are brought into contact with each other, and the gear teeth 92 are attached to the work outer peripheral surface 90. The annular ridge 93 is formed on the work inner peripheral surface 91 by the first small diameter portion 11 and the second small diameter portion 21 while being molded. In addition, straight hole portions having a reference inner diameter dimension d94 between the first shaft portion 12 and the second shaft portion 22 are formed at both ends of the center hole portion 94.
In FIG. 2, the forming of the annular ridge 93 is completed by bringing the two end surfaces 13 and 23 into contact with each other, but the first end surface 13 and the second end surface 23 are set to a predetermined size. The forming of the annular ridge 93 may be finished in a separated state (just approach). In addition, when both front end surfaces 13 and 23 are contact | abutted, the shape of the cyclic | annular protruding item | line part 93 and internal diameter dimension d93 (refer FIG. 3) can be formed with high precision by a predetermined dimension.

  Thereafter, the male mold Sa is raised, the workpiece W is taken out from the female mold Sb, and the first process using the first mold set S is completed. That is, the first step has gear teeth 92 on the work outer peripheral surface 90 on one end side of the work and a non-gear portion 97 on the work outer peripheral surface 90 on the other end side of the work, and an annular ridge 93 is formed in the intermediate portion. An intermediate forged product W ′ having the center hole portion 94 is created. Further, the gear teeth 92 formed in the first step are helical gear teeth that are not formed with crowning and have a substantially uniform tooth thickness in the tooth longitudinal direction (tooth direction).

Next, a mold set for forming (giving) crowning on the gear teeth 92 of the workpiece W will be described.
As shown in FIG. 3 to FIG. 6, there is provided a pressing die Ta that has a cylindrical diameter-expanding punch 7 and is disposed on the other side of the axis Yb.
Further, a receiving die Tb provided with a short cylindrical positioning portion 61 inserted into the center hole portion 94 from one axial Ya side and a workpiece receiving surface 62 that supports the workpiece other end surface (processing reference surface) 96. It has.

A second mold set T having a pressing mold Ta and a receiving mold Tb is installed in a pressing force generating means such as a press machine (not shown), and the pressing mold Ta and the receiving mold Tb are connected to the second reference shaft. It is possible to move closer to and away from each other in the direction of the center L2. The diameter-expansion punch 7 and the positioning portion 61 are disposed coaxially with the second reference axis L2, and the positioning portion 61 is inserted into the center hole 94 of the workpiece W, so that the second reference axis L2 and the workpiece are aligned. The shaft center Lw is arranged coaxially. In the example shown in the figure, the pressing die Ta is provided as the second upper die on the pressing and moving plate (upper plate) side of the press, and the receiving die Tb is provided as the second lower die on the fixed platen (lower plate) side. And the second reference axis L2 is arranged vertically.
Further, the workpiece W is held (supported) in the receiving mold Tb with the top and bottom (upside down) reversed as compared with the first step of FIGS. 1 and 2. That is, the workpiece other end surface 96 is directed toward the one axial side Ya, the positioning portion 61 is inserted into the end portion of the workpiece other end surface 96 side (non-gear portion 97 side) in the center hole portion 94, The punch 7 for expanding the diameter is inserted from the end portion on the side (the gear tooth 92 side).

The diameter-expansion punch 7 includes a straight shaft-shaped outer diameter part 70 having an outer diameter dimension d70 for diameter expansion larger than the inner diameter dimension d93 of the annular ridge 93 of the workpiece W, and the distal end side of the outer diameter part 70. And a punch small-diameter portion 71 provided on the surface.
The outer diameter dimension d70 for expanding the diameter is set to be equal to or slightly smaller than the reference inner diameter dimension d94 of the center hole 94 of the workpiece W. The axial length of the outer diameter portion 70 is preferably longer than the axial length of the annular ridge 93.

The punch small-diameter portion 71 is a tip portion having a diameter smaller than that of the outer diameter portion 70, and in FIG. 3 to FIG. The taper stepped shape includes 71e and a punch small-diameter short cylindrical portion 71f protruding straight from the tip of the guide portion 71e.
Alternatively, as shown in FIG. 10, the punch small-diameter portion 71 may be only a tapered guide portion 71e that is inclined from the tip of the outer diameter portion 70 in a reduced-diameter shape.
Alternatively, as shown in FIG. 11, the punch small-diameter portion 71 includes a round-cornered (square-shaped) guide portion 71e that is curved and convex from the tip of the outer-diameter portion 70, and a straight from the tip of the guide portion 71e. It is good also as a square stepped shape which has the punch small diameter short cylinder part 71f projected in the shape.
Alternatively, as shown in FIG. 12, the punch small-diameter portion 71 may be only a round-corner (square-shaped) guide portion 71e.

The second mold set T shown in FIGS. 3 and 4 is provided with a cylindrical workpiece holding die 8 having an inner peripheral surface 80 for holding the non-gear portion 97 of the workpiece W on the receiving mold Tb. It is a thing.
The workpiece holding die 8 is provided so as to form a gap (gap) having a predetermined dimension in the radial direction between the workpiece teeth W and the gear teeth 92 of the workpiece W. It is provided so as not to contact (not regulate) the teeth 92.
In the second mold set T shown in FIGS. 5 and 6, the work holding die 8 is omitted (not used).

  The receiving die Tb may be provided with a finished tooth profile die (second tooth profile die) having a gear tooth finish molded portion (crowning gear tooth molded portion) as the work holding die 8. The finish tooth profile die has a gear tooth finish molding portion capable of forging a helical gear with crowning. Since the workpiece W on which the gear teeth 92 are formed is pressed radially outward on the gear tooth finish molding portion, the tooth thickness in the middle (center) portion of the gear tooth direction in the gear teeth 92 is greater than the tooth thickness at both ends. Forming (molding) thickening crowning. That is, the gear tooth finish molding portion has finish molding teeth corresponding to crowning (molded teeth in which the tooth thickness at the intermediate portion in the tooth line direction is thinner than both ends).

Next, the usage method and second step of the second mold set T will be described.
As described above, the pressing die Ta and the receiving die Tb are provided, and the work other end surface 96 is brought into contact with and supported by the work receiving surface 62 as shown in FIGS.
When the finish tooth profile die is provided, the gear teeth 92 of the workpiece W are engaged (screwed) and held in the gear tooth finish forming portion.

As shown in FIGS. 4 and 6, all or a part of the volume of the annular ridge 93 is forced to flow into the work peripheral wall 95 with the diameter-expanding punch 7, thereby forming a crowning on the gear tooth 92. Thus, a forged gear (forged product) having gear teeth 92 with crowning is created.
The diameter-expanding punch 7 is lowered and inserted into the center hole 94 of the workpiece W. Here, when the diameter-enlarging punch 7 is inserted into the center hole portion 94, the guide portion 71e and the outer-diameter portion 70 of the diameter-enlarging punch 7 are used to transfer all or part of the volume of the annular ridge 93 to the work peripheral wall. Forged gears with crowned gear teeth 92 are formed by forcibly flowing into the portion 95 and expanding (applying) crowning to the gear teeth 92 by expanding the intermediate portion of the gear teeth 92 To do. That is, it is possible to form (apply) crowning to the gear teeth 92 without using a finish tooth profile die having a gear tooth finish molded portion (crowning gear tooth molded portion).
When the finish tooth profile die is provided, the gear teeth 92 are plastically deformed along the gear tooth finish forming portion to form (apply) crowning.

Further, since the diameter expanding punch 7 has the guide portion 71e, it does not receive excessive resistance when it comes into contact with the annular ridge 93, and the volume of the annular ridge 93 is reduced to the peripheral wall of the workpiece W. Smoothly flow into section 95.
In the first step, the first small-diameter portion 11 is formed into a shape having a tapered portion with a reduced diameter as shown in FIGS. 1, 2 and 9, or a curved concave portion (corner as shown in FIGS. 7 and 8). By forming the shape having a rounded portion, the upper surface (surface at one end of the workpiece) 93a of the annular ridge 93 is inclined downward toward the radial inner side or hangs downward toward the radial inner side. Such a circular arc shape (R shape) can reduce the impact and frictional resistance, and can smoothly increase the diameter.

  In the present invention, the design can be changed, and the first mold set S and the second mold set T are set so that the first and second reference axis L1 and L2 are horizontal or inclined. It may be provided. The male mold Sa and the pressing mold Ta may be provided on the fixed board (lower board) side, and the female mold Sb and the receiving mold Tb may be provided on the pressing movement board (upper board) side. The shape of the first small-diameter portion 11 and the second small-diameter portion 21 is free, and the longitudinal cross-sectional shape of the annular ridge portion 93 to be formed is a trapezoidal mountain shape as shown in FIGS. 2 and 3, and as shown in FIG. A flat round mountain shape, a round mountain shape as shown in FIG. 8, a triangular mountain shape as shown in FIG. 3 to 6, the receiving mold Tb may be configured to hold the workpiece W in a state in which the workpiece other end surface 96 is directed to the other axial center Yb side (diameter enlargement punch 7 side). The finished tooth profile die is preferably divided structure, although not shown.

  As described above, the crown molding gear molding die apparatus according to the present invention includes the workpiece pressing surface 19 and the first cylindrical portion that protrudes from the workpiece pressing surface 19 to the one axial center Ya and has the first small diameter portion 11 at the tip. 10, a second cylindrical portion 20 having a second small-diameter portion 21 at the tip thereof coaxially and face-to-face with the first cylindrical portion 10, and a tooth profile die 3 having a gear tooth forming portion 30 on the inner peripheral surface, The cylindrical workpiece W is press-fitted into the tooth-shaped die 3 by the workpiece pressing surface 19, and both the end surfaces 13, 23 of the first columnar portion 10 and the second columnar portion 20 are brought close to or in contact with each other in the workpiece W. The first mold set S is configured such that the gear teeth 92 are formed on the work outer peripheral surface 90 and the annular ridge 93 is formed on the work inner peripheral surface 91 by the first small diameter portion 11 and the second small diameter portion 21. And a diameter-enlarging punch 7 having an outer diameter part 70 larger than the inner diameter dimension d93 of the annular ridge 93. 7, the second mold set T configured to flow a part or all of the volume of the annular ridge 93 into the work peripheral wall 95 to form the crowning on the gear teeth 92 is provided. A crowning having a reliable and appropriate shape and size can be formed on the gear teeth 92. The number of molding defects can be reduced and the yield can be improved. The durability of each member of the mold can be improved, and mass production can be performed easily and stably. The projecting dimension in the radial direction of the annular ridge 93 can be 100 μm or more, the volume of the annular ridge 93 is increased, and a large volume (meat) is allowed to flow to the work peripheral wall 95 to prevent crowning shortage. .

  In addition, the crowned gear molding method of the present invention includes a first cylindrical portion 10 that protrudes from the workpiece pressing surface 19 toward the axial center Ya and has a first small diameter portion 11 at the tip, and a second small diameter portion 21 at the tip. The second cylindrical portion 20 is provided coaxially and in a face-to-face manner, and a cylindrical workpiece W is press-fitted into the tooth-shaped die 3 by the workpiece pressing surface 19 and the first cylindrical portion 10 and the second column are formed in the workpiece W. Both end surfaces 13 and 23 of the portion 20 are brought close to or in contact with each other to form gear teeth 92 on the work outer peripheral surface 90 and the first small diameter portion 11 and the second small diameter portion 21 form an annular ridge on the work inner peripheral surface 91. Including a first step of forming the portion 93, and further inserting a diameter increasing punch 7 having an outer diameter portion 70 larger than the inner diameter d93 of the annular ridge 93 into the center hole portion 94 of the workpiece W, A part or all of the volume of the annular ridge 93 is caused to flow into the work peripheral wall 95 to form a crowning on the gear teeth 92. Since the second step is provided, a crowning having a reliable and appropriate shape and size can be formed on the gear teeth 92. The number of molding defects can be reduced and the yield can be improved. The durability of each member of the mold can be improved, and mass production can be performed easily and stably. The projecting dimension in the radial direction of the annular ridge 93 can be 100 μm or more, the volume of the annular ridge 93 is increased, and a large volume (meat) is allowed to flow to the work peripheral wall 95 to prevent crowning shortage. .

3 Tooth profile die 7 Diameter expansion punch
10 First cylindrical part
11 1st small diameter part
13 Tip surface
19 Work pressing surface
20 Second cylindrical part
21 2nd small diameter part
23 Tip surface
30 Gear tooth forming part
70 Outer diameter
90 Workpiece outer surface
91 Work surface
92 Gear teeth
93 Annular ridge
94 Center hole
95 Workpiece peripheral wall d93 Inside diameter S 1st mold set T 2nd mold set Ya One shaft center W Workpiece

Claims (2)

A workpiece pressing surface (19), a first cylindrical portion (10) projecting from the workpiece pressing surface (19) to one of the axial centers (Ya) and having a first small diameter portion (11) at the tip, and the first cylinder Tooth profile die having a second cylindrical portion (20) having a second small diameter portion (21) at the tip and a gear tooth forming portion (30) on the inner peripheral surface provided coaxially and face-to-face with the portion (10) 3), and press-fit a cylindrical workpiece (W) into the tooth profile die (3) at the workpiece pressing surface (19), and the first columnar portion (10) and the above in the workpiece (W) Both end surfaces (13) and (23) of the second cylindrical portion (20) are brought close to or in contact with each other to form gear teeth (92) on the work outer peripheral surface (90) and the first small diameter portion (11) and the above A first mold set (S) configured to form an annular ridge (93) on the work inner peripheral surface (91) with the second small diameter portion (21);
Furthermore, it comprises a diameter-expansion punch (7) having an outer diameter part (70) larger than the inner diameter dimension (d93) of the annular ridge part (93). A second mold set (T) configured to flow a part or all of the volume of the ridge (93) into the work peripheral wall (95) to form a crowning on the gear teeth (92). A molding die apparatus for a gear with a crowning, comprising: A first cylindrical portion (10) having a first small diameter portion (11) at the tip and a second small diameter portion (21) at the tip, which protrudes from the workpiece pressing surface (19) to one of the axial centers (Ya). A cylindrical part (20) is provided coaxially and face-to-face, and a cylindrical work (W) is press-fitted into the tooth-shaped die (3) by the work pressing surface (19) and the work (W) The first cylindrical portion (10) and the tip surfaces (13) and (23) of the second cylindrical portion (20) are brought close to or in contact with each other to form gear teeth (92) on the work outer peripheral surface (90) and A first step of forming an annular ridge (93) on the work inner peripheral surface (91) with the first small diameter portion (11) and the second small diameter portion (21);
Further, an expansion punch (7) having an outer diameter portion (70) larger than the inner diameter dimension (d93) of the annular ridge portion (93) is inserted into the center hole portion (94) of the workpiece (W). And a second step in which a part or all of the volume of the annular ridge (93) is caused to flow into the work peripheral wall (95) to form a crowning on the gear teeth (92). A method of forming a gear with a crowning characterized by the above.

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