JP6520637B2 - Forging method - Google Patents

Description

The present invention relates to a forging method, and more particularly to a forging method of rotary forging using a partial die.

  There is known a method called so-called rotary forging in which a forged material is intermittently pressed and forged by an upper die and a lower die while rotating a disk-like forged object relative to the upper die or the lower die. There is. In such a forging method by rotary forging, a method for forging an object having a large outer diameter with a smaller load is required.

  For example, Patent Document 1 discloses an apparatus for manufacturing a disk-like forging that performs forging by pressing the forging by reciprocating linear motion of an upper anvil having a plurality of pressing surfaces. According to this technology, the area required for pressing by the upper anvil can be small, and it is possible to forge a forging having a relatively large outer diameter even with a small-capacity manufacturing apparatus. In this method, a square bar-like upper gold plating having a length capable of pressing an area from the end of the forging through the central axis to the end opposite to the end as an upper lining for pressing the forging. You are using

  Further, as a partial mold, a part of a split type in which the region in the vicinity of the central axis of the forged object is not pressurized, and the region from the region between the central axis of the forged object and the outer peripheral edge to the region from the outer peripheral edge is pressed The type is known. According to this partial mold of the split type, it is possible to forge a forging having a large outer diameter efficiently with less load.

JP, 2009-12059, A

  In the upper anvil lining described in Patent Document 1, it is possible to reduce the load given to the forging to some extent as compared with the case of using the entire surface type. However, in the case of forging a forged object having a larger outer diameter, the method described in Patent Document 1 does not necessarily have a sufficient effect of reducing the load applied to the forged object.

  In addition, when the above-described split-type partial die is used, the end of the partial die is likely to bite into the object at the time of pressing. For this reason, there is a problem that it is difficult to separate the forging and the partial die after pressing with the partial die, and it is not possible to smoothly shift to the subsequent rotation process of the forging.

  An object of the present invention is to efficiently forge an object to be forged with a small load using a plurality of partial dies, and to perform forging treatment smoothly.

A preferred embodiment of the forging method according to the present invention is a forging method in which an object to be forged is disposed between an upper mold and a lower mold and the forged object is forged, and the forging of the upper mold or the lower mold. at least one of said a plurality of partial type which is disposed enclosing circumferentially the center axis of the forging, the region between the central axis and the outer peripheral portion, a circular ring-shaped around the said central axis The forged object in which the groove portion is formed is disposed between the upper mold and the lower mold with the groove portion facing the partial mold, and at least one of the upper mold and the lower mold is The part mold is rotated while being rotated about the central axis of the forging to bring a portion of the partial mold into contact with a partial area of the groove and leaving an area where the partial mold is not in contact in the groove. Moving the forged object side without contacting the region surrounded by the groove portion of the forged object Characterized in that pressurizing the 該被 forging.

As a preferred embodiment of the forging according to the present invention, in the area between the central axis and the outer peripheral portion, characterized in that the ring-shaped groove around the central shaft is formed .

  According to the present invention, a plurality of partial dies can be used to efficiently forge a forged object with a small load, and the forging process can be smoothly performed.

FIG. 7 is a plan view for explaining the forging method according to the first embodiment. It is the sectional view on the AA line of FIG. It is sectional drawing which shows the structure of the to-be-forged object 1 arrange | positioned between the upper type | mold 11 of the forge type | mold shown in FIG. 1, and the lower type | mold 21. As shown in FIG. It is sectional drawing which shows the state at the time of the pressurization of the to-be-forged object 1 by the upper mold | type 11 and the lower mold | type 21 shown in FIG. FIG. 7 is a cross-sectional view showing the configuration of a forged product 1P obtained by the forging method according to Example 1. FIG. 10 is a cross-sectional view showing the configuration of a forged object 51 used in the forging method according to Example 2. FIG. 8 is a view for explaining a forging method according to a second embodiment. It is sectional drawing which shows the state at the time of the pressurization of the forged object 51 by the upper mold | type 31 and lower mold | type 41 which are shown in FIG. FIG. 18 is a cross-sectional view showing the configuration of a forged product 51P obtained by the forging method according to Example 2. FIG. 14 is a view for explaining a forging method according to a third embodiment. It is sectional drawing which shows the state at the time of the pressurization of the forged object 101 by the upper mold | type 111 and lower mold | type 121 which are shown in FIG. FIG. 18 is a view showing a modification of the forging method according to the third embodiment.

The forging method according to the first embodiment of the present invention will be described below.
FIG. 1 is a plan view for explaining a forging method according to a first embodiment, and FIG. 2 is a cross-sectional view taken along the line AA of FIG.

  As shown in FIG. 1, a forging die 100 that performs rotational forging includes a lower die 21 which is an overall die having a circular planar shape, and an upper die 11 disposed to face the lower die 21.

  As shown in FIG. 2, in the lower mold 21, a cored bar 22 which is a truncated cone-shaped convex portion is formed in a region including the central axis 21 </ b> L. In the upper mold 11, a plurality of divided type partial molds 12 (four partial molds in the drawing) are arranged in the circumferential direction so as to surround the central axis 21L of the lower mold 21.

  First, the forging 1 is disposed between the upper mold 11 and the lower mold 21. FIG. 2 shows the state of the upper mold 11, the lower mold 21 and the forging 1 at this time. In FIG. 3, the structure of the to-be-forged object 1 arrange | positioned between the upper mold | type 11 and the lower mold | type 21 is shown with sectional drawing.

  As shown in FIG. 3, the entire forging 1 has a substantially cylindrical shape, and has main surfaces on both sides thereof. An annular groove 2 centered on the central axis 1L of the forging 1 is formed in a region between the central axis 1L and the outer peripheral portion 4 on one main surface 1a of the forging 1 . The inner peripheral surface of the groove portion 2 has a curved shape.

  Further, a central hole 3 is formed in the central region of the other main surface 1b of the object 1 to be forged. The central hole 3 is formed as a truncated cone-shaped recess (a blind hole), and the center thereof is formed to coincide with the central axis 1 L which is the central axis of the groove 2. In the example shown in FIG. 3, although the central hole 3 is formed as a recess in the object to be forged 1, the central hole 3 may be formed as a through hole.

  As shown in FIG. 2, the center hole 3 of the object 1 is fitted to the cored bar 22 of the lower die 21. Thereby, the object 1 is fixed on the lower mold 21 in a state of being centered with respect to the upper mold 11 and in a state where the groove 2 faces the partial mold 12 of the upper mold 11. As a result, the plurality of partial dies 12 constituting the upper die 11 are arranged in the circumferential direction so as to surround the central axis 1L of the object 1 (see FIG. 1).

  In the example shown in FIG. 2, the lower mold 21 is provided with the cored bar 22, but the lower mold 21 may not necessarily have the cored bar 22. However, in order to prevent the center of the forging 1 from shifting from the centers of the upper mold 11 and the lower mold 21 in the forging process to be described later, a method using a cored bar 22 as the lower mold 21 is used. Is good.

  Further, FIG. 2 shows an example in which the cored bar 22 is formed as a convex portion in which a part of the lower mold 21 is raised, but as the cored bar 22, for example, a member separate from the lower mold 21 May be attached to the lower die 21 as appropriate.

  Next, the upper die 11 is moved in the direction of the forging 1 to press the forging 1 to forge. The state of the upper mold 11, the lower mold 21 and the forging 1 at this time is shown in FIG.

  As shown in FIGS. 2 and 4, each partial die 12 of the upper die 11 has a curved surface at its end 12e installed on the side of the central axis 21L of the lower die 21 (the central axis 1L of the object 1 to be forged). ing. The curved surface shape of the end 12 e is formed so as to protrude toward the central axis 21 L as it goes from the pressing surface 12 a side for pressing the workpiece 1 to the surface 12 b side on the opposite side.

  At the time of pressing of the forging 1, a part of each partial die 12 formed in this way is brought into contact with a partial region in the groove 2 and the outer peripheral part 4 of the forging 1 to Is moved in the direction of the forging 1. At this time, the position of the end 12 e of each partial die 12 is appropriately adjusted so that each partial die 12 does not contact the region 5 surrounded by the groove 2 in the main surface 1 a of the forging 1, The partial die 12 which is the upper die 11 is moved to the forged object 1 side.

  Further, in the groove portion 2, a portion of the partial mold 12 is in contact with the region 2a on the outer peripheral side, and a noncontact region 2b in which the partial die 12 is not in contact is left on the inner peripheral side of the groove portion 2. , The partial die 12 is moved to the forged object 1 side.

  In the example shown in FIG. 2, the inner peripheral surface of the groove portion 2 is formed in a curved surface shape whose radius of curvature is smaller than that of the outer peripheral side. Therefore, by moving each partial die 12 vertically from the position shown in FIG. 2 in the direction of the object 1 (vertical direction in FIG. 2), the contact region 2a of the partial die 12 and the non-contact region 2a are not The forging 1 can be pressurized in a state in which the contact area 2b and the contact area 2b coexist (see FIG. 4).

  With the movement of the upper die 11 to the forged object 1 side, the region on the outer peripheral side of the groove portion 2 of the forged object 1 is pressed by the upper die 11, and the thickness of the pressed portion is reduced. The outer diameter of the object 1 as a whole is enlarged.

Next, the upper die 11 is moved in the direction in which it is separated from the object 1.
As described above, each partial mold 12 which is the upper mold 11 is in contact with the area 2 a on the outer peripheral side of the groove 2 in a state where the non-contact area 2 b is left on the inner peripheral side of the groove 2. 1 is pressurized. Thereby, the force of the radial direction which acts on the forging object 1 from each partial type | mold 12 is reduced, and it is prevented that each partial type | mold 12 bites into the forged object 1. FIG. Therefore, the upper mold 11 can be easily separated from the forging 1.

  After separating the upper mold 11 from the forging 1, the upper mold 11 is rotated about a central axis 1 L of the forging 1 by a predetermined angle. Next, the upper die 11 after rotation is moved again to the forging 1 side in the same manner as described above, and the forging 1 is pressed.

  After repeating the series of operations described above a plurality of times, the upper die 11 is separated from the obtained forging 1P, and the forging 1P is taken out from the lower die 21. The configuration of the forging 1P obtained by the forging method according to the first embodiment is shown in FIG.

  According to the forging method of the first embodiment, the forging 1P shown in FIG. 5 can be obtained by forging with a small load. Further, biting of each partial die 12 into the forging 1 at the time of pressurization is prevented, and forging processing can be performed smoothly.

  In Example 1, although the example which formed the inner skin of slot 2 in curved surface shape was shown, the slot 2 may form the inner skin in the shape of a rectangle, for example. This shape is the same as in the second embodiment.

  Next, a forging method according to a second embodiment will be described with reference to FIGS.

  Example 2 is an example which uses a partial type | mold for both an upper type | mold and a lower type | mold, and presses the to-be-forged object 51 which has a groove part in both main surfaces by this upper type | mold and a lower type | mold from both surfaces. FIG. 6 is a cross-sectional view showing the structure of the forging object 51. As shown in FIG.

  The to-be-forged object 51 has the main surfaces on the both surfaces, the groove part 52 is formed in the one main surface 51a, and the groove part 53 is formed in the other main surface 51b. The grooves 52 and 53 are respectively formed in an annular shape around the central axis 51L of the forging object 51 in a region between the central axis 51L of the forging object 51 and the outer peripheral portion 54.

  FIG. 7 is a view for explaining the forging method according to the second embodiment. As shown in FIG. 7, in the forging die 200 for rotational forging, the upper die 31 is constituted by a plurality of partial dies 32 of a plurality of split dies, and the lower die 41 is constituted by a plurality of partial dies 42 for a plurality of split dies There is. Partial mold 32 and partial mold 42 are circumferentially arranged so as to surround common central axis 200L.

  The partial mold 32 and the partial mold 42 have the same shape as the partial mold 12 of the first embodiment. That is, the curved surface shapes of the end 32e of the partial mold 32 and the end 42e of the partial mold 42 are respectively directed from the pressing surfaces 32a and 42a for pressing the object 51 to the opposite surfaces 32b and 42b. As a result, it is formed to protrude toward the central axis 200L side.

  First, the object to be forged 51 is disposed between the upper die 31 and the lower die 41. The object to be forged 51 is disposed between the upper mold 31 and the lower mold 41 with the groove 52 facing the partial mold 32 of the upper mold 31 and the groove 53 facing the partial mold 42 of the lower mold 41. . The forging object 51 is disposed between the upper die 31 and the lower die 41 such that the central axis 51 L of the object to be forged 51 coincides with the central axes 200 L of the partial dies 32 and 42. As a result, the plurality of partial dies 32 and the plurality of partial dies 42 are arranged in the circumferential direction so as to surround the central axis 51 L of the object to be forged 51.

  Next, the upper die 31 and the lower die 41 are moved in the direction of the forging object 51 to press the forging object 51 for forging. The state of the upper mold 31, the lower mold 41 and the forging object 51 at this time is shown in FIG.

  The positional relationship between the partial mold 32 of the upper mold 31 and the partial mold 42 of the lower mold 41 and the forging 51 at the time of pressurization is the same as the positional relation between the upper mold 11 and the forging 1 in the first embodiment. is there. That is, when the forging 51 is pressurized, a part of the partial mold 32 is brought into contact with a partial region in the groove 52 and the outer peripheral part 54 of the forging 51, and a part of the partial die 42 is a groove The entire partial molds 32 and 42 are respectively moved in the direction of the forged object 51 by contacting a partial region in the portion 53 and the outer peripheral portion 54 of the forged object 51. At this time, the end portions 32e and 42e of the surface of the object to be forged 51 do not contact the partial molds 32 and 42 respectively with the region 55 surrounded by the groove 52 and the region 56 surrounded by the groove 53. After adjusting the position appropriately, the partial dies 32 and 42 are moved to the forged object 51 side.

  In the groove 52, a part of the partial mold 32 is in contact with the region 52a on the outer peripheral side, and a noncontact region 52b in which the partial die 32 is not in contact is left on the inner peripheral side of the groove 52. , The partial die 32 is moved to the forged object 51 side. Similarly, in the groove portion 53, a part of the partial mold 42 is in contact with the region 53a on the outer peripheral side, and a noncontact region 53b which does not contact the partial die 42 remains on the inner peripheral side of the groove 53. , The partial die 42 is moved to the forged object 51 side.

  Also in the second embodiment, the inner peripheral surfaces of the grooves 52 and 53 have a curved shape, and the inner peripheral side is formed to have a smaller radius of curvature than the outer peripheral side. Therefore, by moving the partial molds 32 and 42 vertically from the position shown in FIG. 7 in the direction (vertical direction in FIG. 7) of the object to be forged 51, the partial molds 32 in the grooves 52 and 53, respectively. The forging object 51 can be pressurized in a state where the 42 contact areas 52a and 53a and the non-contact areas 52b and 53b coexist.

  With the movement of the upper die 31 and the lower die 41 to the forged object 51 side, the region on the outer peripheral side of the grooves 52 and 53 of the forged object 51 is pressurized by the upper die 31 and the lower die 41 The thickness at the portion is reduced, and the outer diameter of the entire forging object 51 is increased.

  Next, the upper die 31 and the lower die 41 are moved in the direction in which they are separated from the forging object 51. Also in the second embodiment, the partial mold 32 and the partial mold 42 press the object to be forged 51 with the non-contact areas 52b and 53b remaining in the grooves 52 and 53, respectively. For this reason, the radial force acting on the forging object 51 from the partial mold 32 and the partial mold 42 is reduced, and the partial mold 32 and the partial molds 42 are prevented from biting into the forging object 51. ing. Therefore, the upper mold 31 and the lower mold 41 can be easily separated from the object to be forged 51.

  After separating the upper die 31 and the lower die 41 from the forging object 51, the upper die 31 and the lower die 41 are rotated about a central axis 51L of the forging object 51, that is, the central axis 200L by a predetermined angle. Next, the upper die 31 and the lower die 41 after rotation are moved again to the forging object 51 in the same manner as described above, and the forging object 51 is pressed.

  After repeating the series of operations described above a plurality of times, the upper die 31 and the lower die 41 are separated from the obtained forging 51P, and the obtained forging 51P is taken out from the upper die 31 and the lower die 41. . The configuration of the forging 51P obtained by the forging method according to the second embodiment is shown in FIG.

  According to the forging method of the second embodiment, the forging object 51 is pressed with a smaller load than that of the first embodiment because the forging object 51 is pressurized from both sides by the partial mold 32 and the partial mold 42. be able to. Further, biting of the partial mold 32 and the partial mold 42 into the forging object 51 at the time of pressing is prevented, and forging processing can be performed smoothly.

  In the example shown in FIGS. 7 and 8, the groove 52 and the groove 53 are formed to have substantially the same diameter, but the groove 52 and the groove 53 are formed according to the shape of the final product to be aimed. May be formed with different diameters. However, from the viewpoint of ease of forging, the groove 52 and the groove 53 should preferably be formed to have the same diameter.

Next, a forging method according to the third embodiment will be described with reference to FIGS. 10 and 11.
Example 3 describes the first forging step performed in the former stage of Example 1. That is, Example 3 uses the upper mold 111 described later as the first upper mold, and the lower mold 121 described later as the first lower mold, and uses the forging 1 described in Example 1 as an intermediate. It is a first forging process to obtain as a forging.

  In addition, the forging process of Example 1 turns into a forging process performed in the back | latter stage of Example 3. FIG. That is, Example 1 used the upper mold 11 as the second upper mold, used the lower mold 21 as the second lower mold, and forged the intermediate forging obtained in Example 3 as a forging. As a second forging step.

  The forging die 300 used in the third embodiment has a lower die 121 which is an overall die having a circular planar shape, and an upper die 111 which is an overall die that is disposed to face the lower die 121. Similar to the lower mold 121, the upper mold 111 also has a circular planar shape.

  The lower mold 121 has a projecting portion 122 formed in an annular shape. In addition, the upper mold 111 has a convex portion 112 formed in the central region. The upper mold 111 and the lower mold 121 are disposed such that the center of the convex portion 112 coincides with the central axis 122 L of the annular protruding portion 122.

  As shown in FIG. 10, first, a forged object 101 (hereinafter, the forged object 101 is referred to as a billet 101) is disposed on the lower die 121. The billet 101 is disposed in the area surrounded by the annular ridge 122. Thereby, the billet 101 is installed on the lower mold 121 in a state of being centered with respect to the convex portion 112 of the upper mold 111.

  That is, the annular protruding portion 122 can be used for shape transfer to the billet 101 described later and can be used as centering for the upper mold 111 having the convex portion 112.

  From the viewpoint of centering the billet 101 with respect to the convex portion 112 of the upper mold 111, the inner circumferential diameter r1 of the annular ridge portion 122 is smaller in difference from the diameter r2 of the outermost circumferential portion of the billet 101 Good. On the other hand, from the viewpoint of ease of installation when the billet 101 is installed on the lower die 121, the inner peripheral diameter r1 of the annular ridge 122 is different from the diameter r2 of the outermost periphery of the billet 101 Is better. For this reason, the inner circumferential diameter r1 of the protruding portion 122 and the diameter r2 of the outermost circumferential portion of the billet 101 may be appropriately determined in consideration of the above points.

  As the billet 101, for example, a cylindrical body having a diameter r2 of the outermost periphery thereof smaller by about 1 mm to 50 mm with respect to the inner peripheral diameter r1 of the annular ridge 122 is installed on the lower mold 121.

  Next, the upper mold 111 is moved in the direction of the billet 101, and the billet 101 is pressed by the upper mold 111 to forge. A cross-sectional view of the upper mold 111, the lower mold 121, and the billet 101 at this time is shown in FIG.

  As the upper mold 111 moves to the billet 101 side, the whole of the billet 101 is pressed by the upper mold 111, the overall height decreases, and the outer diameter of the entire billet 101 increases.

  At this time, the shape of the ridge 122 is transferred to the billet 101 by the lower mold 121, and the groove 2 (see FIGS. 2 and 3) is formed in the billet 101. The shape is transferred, and the central hole 3 is formed in the billet 101. Thus, a forged product 101P having the shape of the forging 1 is obtained.

  Further, the billet 101 is installed on the lower die 121 in a state of being centered with respect to the convex portion 112 of the upper die 111 by the annular ridge portion 122. Therefore, the groove 2 is formed in the billet 101 substantially concentrically with the central hole 3. That is, the groove 2 is formed such that its central axis substantially coincides with the center of the central hole 3.

  Although FIG. 10 shows an example in the case of forming the center hole 3 in the billet 101, for example, when forging the obtained forged object 101P as the forged object 1, the cored bar 22 (see FIG. 2). When using the lower mold 21 having no), in FIGS. 10 and 11, a flat mold may be used as the upper mold 111.

  When the forging 101P forged by the method described in the third embodiment is forged as the forging 1 by the method of the first embodiment, is it possible to replace the top and bottom of the forging 101P obtained in the third embodiment? Or, the upper and lower molds 11 and 21 shown in FIGS. 2 and 4 may be interchanged.

  In the third embodiment, the method of forming the groove portion 2 and the central hole 3 in the billet 101 by forging is described, but the groove portion 2 and the central hole 3 are formed by removal processing such as machining, for example. You may do so.

  The third embodiment shows an example in which the groove portion 2 is formed by pressing the protruding portion 122 against the billet 101 while forging the billet 101 using the lower die 121 in which the protruding portion 122 is formed. However, as shown in FIG. 12, for example, the groove 2 is formed by using the forging die 400 having the second upper die 213 in which the ring-like member 212 is attached to the flat plate member 211. It may be made to press against 101.

DESCRIPTION OF SYMBOLS 1, 51 ... Forging thing, 1a, 1b, 51a, 51b ... Main surface of forging thing 1L, 51L ... Central axis of forging thing 1P, 51P, 101P ... Forging thing 2, 52, 53 ... Groove part 2a: a region on the outer peripheral side in the groove portion 2 2b: a region on the inner peripheral side in the groove portion 52 a: a region on the outer peripheral side of the groove portion 52 52b: a region on the inner peripheral side of the groove portion 52; Area on the outer peripheral side, 53b: area on the inner peripheral side of groove 53, 3: central hole, 4, 54: outer peripheral part of forged object 5, 55, 56: area surrounded by groove 2, 11, 31, 111 upper mold 12, 12, 42 partial mold 12a 32a 42a partial pressure surface 12b 32b 42b surface opposite to partial pressure surface 12e 32e 42e partial Ends of dies, 21, 41, 121 ... lower dies, 21 L ... central axis of lower dies 21, 22 ... core metal, 10 200, 300, 400 ... forging type, 200 L ... central axis of forging type 200, 101 ... billet, 112 ... convex portion of upper mold 111, 122 ... projecting portion, 122 L ... central axis of projecting portion 122, 211 ... Plate material 212 Ring-shaped member 213 Upper mold r1 Inner circumferential diameter of the ridge portion 122 r2 Diameter of the outermost circumference of the billet 101

Claims (5)

A forging method for placing a forging between an upper die and a lower die and forging the forging,
At least one of the upper mold and the lower mold is a plurality of partial molds disposed circumferentially around a central axis of the object to be forged,
In the area between the central axis and the outer peripheral portion, the object to be forged product annular-shaped groove is formed around the central axis, the lower and the upper mold of the groove to face said subtyping Place between the mold and
Rotating at least one of the upper mold and the lower mold about a central axis of the forging;
The partial mold is surrounded by the groove of the forging while the partial mold is partially in contact with the partial area of the groove and the area in which the partial mold is not in contact remains in the groove. A forging method characterized in that the forged product is pressed by moving it to the forged product side without contacting the forged area.   The forging method according to claim 1, wherein the object to be forged in which the inner peripheral surface of the groove has a curved surface shape is disposed between the upper mold and the lower mold. The lower mold is an overall mold in which a convex portion is formed in a region including the central axis of the lower mold,
The upper mold is a plurality of partial molds disposed circumferentially around a central axis of the lower mold,
The forged object in which a recess is formed in a region including the central axis of the groove on the main surface opposite to the forming surface of the groove is fitted to the protrusion of the lower mold with the recess, and the upper The forging method according to claim 1, wherein the forging method is disposed between a mold and the lower mold. Both the upper and lower molds are partial molds,
The forging method according to claim 1, wherein the groove portion is formed on both main surfaces of the forging material, and the forging material is disposed between the upper die and the lower die. A forging method for placing a forging between an upper die and a lower die and forging the forging,
As the upper mold, prepare a first upper mold which is an overall mold having a convex portion in a central region,
As the lower mold, prepare a first lower mold which is an overall mold having annular ridges,
A first object to be forged is disposed between the first upper mold and the first lower mold disposed with the center of the convex portion and the central axis of the ridge portion being aligned. pressurizing the first object to be forging by the upper mold and the first lower mold 1, the first forging step of producing the intermediate forging forming an annular-shaped groove by the ridge,
As the upper die and the lower die, there are provided a second upper die and a second lower die, at least one of which is a plurality of partial dies disposed circumferentially around the central axis of the intermediate forging. And
The intermediate forging is disposed between the second upper die and the second lower die, with the groove facing the partial die,
Rotating at least one of the second upper mold or the second lower mold about a central axis of the intermediate forging;
The partial mold is surrounded by the groove of the intermediate forging while the partial mold is in contact with a partial area of the groove and the area in which the partial mold is not in contact remains in the groove. And a second forging step of pressing the intermediate forging by moving it to the side of the intermediate forging without contacting the area.

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