JPH06190491A - Manufacture of hollow shaftlike forging - Google Patents

Abstract

PURPOSE:To provide a manufacturing method for hollow shaftlike forging, in which even in the case of forming a bottom surface in a punch-forming hole near the step part of a shaft part with stepping, reverse-tapered under fill part can be avoided. CONSTITUTION:In this forging it is shown that the inner diameter of an inner peripheral wall surface 52b in the punchforming hole 52 is do, the outer diameter of an outer peripheral wall surface 50d in the large diameter shaft part of the shaft part 50 with stepping is Do, the outer diameter of an outer peripheral wall surface 50c in the small diameter shaft part is D2, the distance of an inclining surface 52d in the axial direction is alpha, and the distance of an inclining surface 52c in the right angle direction to the axis is beta. The outer peripheral wall surface 50d is drawn and extended together with the punch-forming hole 52. In the case of being about 42% of the drawing degree, (alpha/beta) is made to be about 2-3 and in the case of being about 28% of the drawing degree, (alpha/alpha) is made to be about 5 and in the case of being about 15% of the drawing degree, (alpha/beta) is made to be about 15.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a hollow shaft forged product. This forged product is, for example, a drive system component of a vehicle,
Specifically, it can be applied to side gear shafts, differential drive pinions and the like.

[0002]

2. Description of the Related Art As a hollow shaft-shaped forged product, a forged product used for a side gear shaft of a drive system of a vehicle is provided. The prior art will be described by taking this forged product as an example. This forged product has a stepped shaft portion and a flange portion extending in the centrifugal direction at one end of the stepped shaft portion. In this forged product, in order to contribute to weight reduction, a bottomed central shaft hole is formed in a portion where a twisting force is hard to act during rotation, that is, along the axis thereof. The central shaft hole is formed by cutting with a drill blade or by forging by pressing a forging punch die.

By the way, when a small-diameter central shaft hole is formed by cutting with a drill blade, the axial length of the shaft hole is limited in order to avoid breakage of the drill blade. Further, because of the use of the drill blade, the boundary area between the bottom surface of the shaft hole and the inner peripheral wall surface of the shaft hole is inevitably sharp, which induces stress concentration and is disadvantageous in securing strength. Further, when the small diameter central shaft hole is forged by the forging punch die, similarly, there is a limit in the axial length of the shaft hole in order to avoid breakage of the forging punch die.

[0004]

Therefore, the applicant of the present invention is
We have developed a method to form a narrowed hole with a long axial length by narrowing a stepped shaft with a bottomed central shaft hole and extending it in the axial direction. However, in the method, when the hole bottom surface is located near the step, which is the boundary area between the large-diameter shaft portion and the small-diameter shaft portion, a reverse taper cutout is formed at the peripheral edge of the hole bottom surface. Occurs.

FIG. 14 showing a schematic form of this is shown.
A description will be added with reference to (A) and (B). That is, in FIG.
As shown in FIG. 14A, a stepped shaft portion 901 having a central shaft hole 900 having an inner diameter α1 and a hole bottom surface 904 is used, and an outer peripheral wall surface 901a having an outer diameter α2 is narrowed and extended in the axial direction.
A narrowed hole 900 ′ having a long axial length shown in FIG.
In this case, the inner diameter of the throttle hole 900 ′ is reduced by Δd due to the reduced diameter. That is, the inner peripheral wall surface 901b defining the central shaft hole 900 before the restriction is formed by the restriction in the centripetal direction, that is, in FIG.
Since it moves in the direction of arrow X1 shown in FIG.
In 0 ′, a reverse taper-shaped cutout portion 905 is formed at the peripheral edge portion of the hole bottom surface 904 ′. Inverted taper cutout 9
No. 05 causes stress concentration, and is not preferable in securing the strength of the drive component.

Particularly, when the hole bottom surface 904 is arranged near the step portion 910, that is, when the diameter of the central shaft hole 900 is α1, α1 is above the step portion 910 and below the step portion 910. In the case where the hole bottom surface 904 is arranged in the region L8 defined by α1 respectively, the reverse taper-shaped cutout portion 905 becomes remarkable. The present invention has been made in view of the above circumstances, and an object thereof is to provide a stepped shaft portion in which a hole bottom surface is formed in the vicinity of a step portion which is a boundary region between a large diameter shaft portion and a small diameter shaft portion. An object of the present invention is to provide a method for manufacturing a hollow shaft-shaped forged product, which is targeted for forged products, can avoid a reverse taper-shaped flesh portion that tends to occur in a drawing process, and is advantageous in securing strength.

[0007]

A method for manufacturing a hollow shaft-shaped forged product according to the present invention comprises a large-diameter shaft portion having a large outer diameter and a small-diameter shaft continuously connected to the large-diameter shaft portion via a step portion. Obtaining a forged product having a stepped shaft portion provided with a stepped portion and a bottomed central shaft hole formed in the stepped shaft portion and opening at the shaft end surface of the large diameter shaft portion; and the center of the forged product The shaft hole is unrestrained, the outer peripheral surface of the large-diameter shaft part of the stepped shaft part is narrowed together with the central shaft hole, and the central shaft hole is made into a substantially straight throttle hole. It is a method of manufacturing a forged product, and the center shaft hole of the forged product before drawing is the center shaft hole in one direction and the other direction of the axial direction of the stepped shaft part with reference to the step part. Is located in a region defined by a distance that is approximately equal to the diameter of the hole, and the inner diameter of the peripheral edge of the hole bottom surface of the central shaft hole becomes smaller toward the hole bottom surface. Comprising a slope, in a section through the axis of the forged product, and the distance of the inclined surface in the axial direction alpha,
When the distance of the inclined surface in the direction perpendicular to the axis is β, (α
/ Β) is a value of 1 to 15 and is characterized in that the value of (α / β) is made smaller as the drawing workability is increased in the drawing process.

In the method of the present invention, the drawing workability in the drawing process is generally 15 to 45%. The degree of drawing is [{(D8) ^2- (D9) ² } / (D8) ² ] x.
Means 100. Here, D8 means the outer diameter before drawing, and D9 means the outer diameter after drawing.

[0009]

[Function] Since the value of (α / β) is reduced as the degree of drawing is increased, even if the drawing process is performed, the peripheral portion of the hole bottom surface of the substantially straight drawing hole is The inner diameter is maintained so that the inner diameter becomes smaller as it goes to.

[0010]

EXAMPLE An example in which the method of the present invention is applied to the manufacture of a side gear shaft as a driving component will be described for each step with reference to FIGS. In the sectional view of the forged product, hatching is omitted to avoid complication. (Rough ground forging step) In this example, first, a round bar material 1 (material: medium carbon steel S45C) having shaft end faces 1a, 1b and outer peripheral wall surface 1c shown by chain lines in FIG. In the hot state (about 1100 to 1250 ° C.), 1 is strongly pressed and crushed in the axial direction to obtain a disc material 2 shown by a solid line in FIG. The disc material 2 has shaft end surfaces 2a and 2b and an outer peripheral wall surface 2c. Next, the disc material 2 shown by a chain line in FIG. 1 (B) is hot-forged in a hot state to obtain a forged land product 3 shown by a solid line in FIG. 1 (B). The rough forged product 3 has an outer peripheral wall surface 30a,
30b, a conical surface 30c, and a shaft end surface 30d, and a wasteland shaft portion 30 defined by the outer peripheral wall surface 32a and a conical surface 32b.

(Finishing forging process) Next, the forged product 3 is subjected to finish forging in a hot state, and the forged product 4 shown by a solid line in FIG.
To get The forged product 4 includes a stepped shaft portion 40, a rough bottomed hole 42 formed at one end of the stepped shaft portion 40, and a centrifugally extending flange portion 46 having an outer burr portion 44. The stepped shaft portion 40 includes outer peripheral wall surfaces 40a and 40b, a conical surface 40c.
And the shaft end faces 40d and 40e. The rough bottomed hole 42 is defined by a conical inner peripheral wall surface 42a and a hole bottom surface 42b. The flange portion 46 is defined by an outer peripheral wall surface 46a and an inner peripheral wall surface 46b. The outer burr portion 44 of the forged product 4 is removed by a deburring die (not shown) in a hot state.

(Hot Extrusion Process) Next, a hot extrusion process is carried out by using the forged product 4 from which the outer burr 44 is removed to obtain a forged product 5 shown by a solid line in FIG. As shown in FIG. 2, the forged product 5 includes a stepped shaft portion 50, a bottomed punch forming hole 52 opened at one end of the stepped shaft portion 50, and a centrifugal direction from one end of the stepped shaft portion 50. And an extended flange portion 54. The stepped shaft portion 50 includes shaft end surfaces 50a and 50b and an outer peripheral wall surface 50.
c, 50d and the conical surface 50e. Here, the outer peripheral wall surface 50d constitutes a large-diameter shaft portion, and the outer peripheral wall surface 50d
c constitutes a small diameter shaft portion, and the conical surface 50e constitutes a step portion.

The punch forming hole 52 has a conical inner peripheral wall surface 5.
2a, straight inner peripheral wall surface 52b, inclined surface 52c, and hole bottom surface 5
2d. The bottom surface 52d of the hole is arranged at substantially the same height as the conical surface 50e forming the step. The flange 54 has substantially the same shape and size as the flange 46 after the outer burr 44 is removed.
In carrying out such a hot extrusion step, a hot extrusion die 100 shown in FIG. 8 is used. The hot extrusion die 100 is
A lower die 104 having a cavity 103 held in a holding portion 102 of the lower bolster 101, a shaft-shaped KO die 105 inserted in a lower portion of the cavity 103, an extrusion plate 106 for pushing up the KO die 105, and an upper bolster 110. Holding part 1
11 and a forging punch die 112 held by 11.
The outer peripheral surface of the pressing die portion 112a of the forging punch die 112 has a conical shape whose outer diameter decreases toward the tip surface 111c.

Here, the left half (A) of FIG. 8 shows the state where the forging punch die 112 has moved to the bottom dead center, and the right half (B) of FIG. 8 shows the forging punch die 112 after forging the top dead center. Shows the state of transition to. And hot state (950 to 1100 ℃
With the stepped shaft portion 40 of the forged product 4 set in the cavity 103 of the lower die 104, the upper bolster 110 descends, and the push-in die portion 112a at the tip of the forging punch die 112 descends to form a rough shape. Push it into the bottom hole 42. Thereby, the meat around the rough bottomed hole 42, that is, the meat forming the stepped shaft portion 40 is extruded in the direction opposite to the transfer direction of the forging punch die 112, that is, in the arrow A1 direction shown in FIG. Thus, the rough bottomed hole 42 is used as a punch forming hole 52 (central shaft hole in the present invention). The hole shape of the punch forming hole 52 substantially corresponds to the shape of the pressing die portion 112a of the forging punch die 112.

This step is a backward extrusion method in which the meat is extruded in the direction opposite to the moving direction of the forging punch die 112. Here, in this step, the backward extrusion is adopted instead of the forward extrusion, because the deformability of the material is large and the step is performed in a hot state advantageous to deep hole formation, so that problems such as necking can be avoided. This is because. As a result of such backward extrusion,
The forged product 5 shown by the solid line in FIG. 2 is obtained.

(Cold drawing step of the first stage) Next, referring to FIG.
The first stage cold drawing process is performed using the forged product 5 indicated by the solid line, and the outer peripheral wall surface 50d of the stepped shaft portion 50 of the forged product 5 is
The outer diameter of the region D1 is narrowed to obtain a forged product 6 shown by a solid line in FIG. As can be seen from the area D1 in FIG.
Of the total length D3 of the outer peripheral wall surface 50d, the flange portion 54 thereof
The root region D2 on the side is not narrowed. Further, the region D4 of the outer peripheral wall surface 50c on the tip side of the shaft is not narrowed.

In the cold drawing process, the cylindrical wall portion forming the region D1 of the stepped shaft portion 50 of the forged product 5 is extended along with the punch forming hole 52 in the axial front direction, that is, in the arrow A2 direction. As shown in FIG. 3, the forged product 6 after the cold drawing process
Is a stepped shaft portion 60, a bottomed primary throttle hole 62 that opens at one end of the stepped shaft portion 60, and a flange portion 64 that extends from one end of the stepped shaft portion 60 in the centrifugal direction. With. The stepped shaft portion 60 includes shaft end surfaces 60a and 60b, an outer peripheral wall surface 60c,
It is defined by 60d and 60e and conical surfaces 60f and 60h.

As shown in FIG. 3, the primary throttle 62 has a conical inner peripheral wall surface 62a, a straight inner peripheral wall surface 62b, a conical inner peripheral wall surface 62c, an inner peripheral wall surface 62d and a hole bottom surface 62e. And the rounded surface 62f. As can be understood from FIG. 3, the rounded surface 62f suppresses the reverse taper of the peripheral edge portion of the hole bottom surface 62e, and the inner diameter gradually decreases from the lower end of the inner peripheral wall surface 62d toward the outer peripheral edge of the hole bottom surface 62e. It is tapered. The flange portion 64 has substantially the same shape and size as the flange portion 46 from which the outer burr portion 44 is removed.

In the above-mentioned first stage cold drawing step,
The diaphragm device 200 for the first stage shown in FIG. 9 is used. The expansion device 200 includes a mold 20 held on the lower bolster 201 side.
2a to 202f, the KO pin 203, and the upper bolster 21
Punch die 211 held on the 0 side and interlocking rod 212
It has and. The molds 202f and 202e form a mold hole 206.

The left half (A) of FIG. 9 is the punch die 2
11 shows a state where the die moves to the bottom dead center, and the right half (B) of FIG. 9 shows a state where the punch die 211 has moved to the top dead center after forging. One locking portion 212a of the interlocking rod 212 is the tubular portion 20 mounted on the push-out plate 207 on the lower bolster 201 side.
8 and the other locking portion 2 of the interlocking rod 212.
12b is locked to the holding portion 214 on the upper bolster 210 side. Further, as shown in the right half (B) of FIG. 9, the punch mold 211 includes a pressing protrusion 211c defined by a flat surface 211a and a conical surface 211b, and a shoulder portion 211d formed by a ring-shaped flat surface. Is equipped with.

In the cold drawing process of the first stage, the upper bolster 210 is inserted into the punch die 2 with the lower part of the stepped shaft portion 50 of the forged product 5 inserted into the die hole 206 of the drawing device 200.
It descends with 11. Accordingly, the flat surface 211a of the punch die 211 and the shaft end surface 50b of the stepped shaft portion 50 of the forged product 5 are joined together.
Press hard on. As a result, the stepped shaft portion 50 of the forged product 5 is forcibly pushed into the die hole 206, and as described above,
The area D1 of the outer peripheral wall surface 50d of 0 is narrowed together with the punch forming hole 52.

In the cold drawing process of the first stage, the flat surface 211a of the punch die 211 presses the shaft end surface 50b, but the punch die 211 is not inserted into the punch forming hole 52, so the punch forming hole 52 is formed. Remains hollow and unrestrained. The right half of FIG. 9 (B)
As can be understood from the above, when the punch die 211 rises to the top dead center, the upper bolster 210 rises and the upper bolster 21
The holding part 214 on the 0 side is the locking part 212 of the interlocking rod 212.
Since b is lifted, the locking portion 212 of the interlocking rod 212
a lifts the tubular portion 208 and the pushing plate 207,
KO pin 203 is lifted by 7 and KO pin 20
The shaft end face 60a of the stepped shaft portion 60 of the forged product 6 is pushed up by the upper end face of the forged product 6, and the mold release is performed.

(Cold drawing step of the second stage) Next, referring to FIG.
Using the forged product 6 indicated by the solid line, the second stage cold drawing process is performed, and the outer peripheral wall surface 60d of the stepped shaft portion 60 of the forged product 6 is
The outer diameter of the area D1 'of the forged product 7 shown by the solid line in FIG.
To get As a result of the cold drawing process of the second stage, the tubular meat portion forming the region D1 ′ of the stepped shaft portion 60 of the forged product 6 is
It is extended in the axial direction, that is, in the arrow A2 direction together with the next throttle hole 62.

Even in the cold drawing process of the second stage, the root region D2 on the flange portion 64 side is not drawn. Similarly, the region D4 shown in FIG. 3 of the outer peripheral wall surface 60e on the shaft tip side is not narrowed. As shown in FIG. 5, the forged product 7 that has undergone the second stage cold drawing step has a stepped shaft portion 70 and a bottomed substantially straight shape that opens at one end of the stepped shaft portion 70. It has a secondary throttle hole 72 and a flange portion 74 extending from one end of the stepped shaft portion 70 in the centrifugal direction. The stepped shaft portion 70 is defined by shaft end surfaces 70a, 70b, outer peripheral wall surfaces 70c, 70d, 70e and conical surfaces 70f, 70h. Secondary aperture 7
2 is defined by a conical inner peripheral wall surface 72a, an inner peripheral wall surface 72c, a hole bottom surface 72e, and a rounded surface 72f.

As can be seen from FIG. 5, the rounded surface 72f
Is for suppressing a reverse taper-shaped cut-out portion on the peripheral edge of the hole bottom surface 72e, and from the lower end of the inner peripheral wall surface 72c to the hole bottom surface 72e.
The inner diameter gradually decreases toward the outer periphery of the. As a result of the cold drawing of the second stage described above, the second
The diameter of the secondary throttle hole 72 is probably smaller than the diameter of the primary throttle hole 62. The flange portion 74 of the forged product 7 has substantially the same shape and dimensions as the flange portion 46.

In performing the cold drawing process of the second stage, a drawing device (not shown) having basically the same structure as the above-mentioned drawing device for the first stage is used. However, this drawing device is provided with a die hole having a diameter smaller than the outer diameter of the outer peripheral wall surface 60d of the stepped shaft portion 60 of the forged product 6. Also in the cold drawing process of the second stage, as in the cold drawing process of the first stage, the punch die descends and strongly presses the shaft end surface 60b of the stepped shaft portion 60 of the forged product 6.

In the cold drawing process of the second stage, as in the cold drawing process of the first stage, the punch die presses the shaft end face 60b, but the punch die has the primary drawing hole 6b.
Since it is not inserted in No. 2, the primary throttle hole 62 is hollow, that is, in an unrestrained state. As described above, both the first stage drawing process and the second stage drawing process for sequentially narrowing the inner diameter of the punch forming hole 52 are performed in the cold state, so the flange of the forged product 4 obtained in the finish forging process The shape of the portion 46 does not substantially deform even in the first stage drawing process and the second stage drawing process.

(Deformation of Punch Forming Hole 52) Now, with reference to FIGS. 4A and 4B, the process of deforming the hole shape of the punch forming hole 52 in the first stage cold drawing step will be further described. Add. FIG. 4A is an enlarged view of the main part of the form shown by the solid line in FIG. 2, and FIG. 4B is an enlarged view of the main part of the form shown by the solid line in FIG. As shown in FIG. 4A, in the forged product 5 that has undergone the hot extrusion process, the inner diameter of the inner peripheral wall surface 52b of the punch forming hole 52 is indicated by do (about 21 mm), and the outer peripheral wall surface of the stepped shaft portion 50. The outer diameter of 50d is indicated by Do (about 47 mm), the outer diameter of the outer peripheral wall surface 50c is indicated by D ₂ (about 38 mm), the distance of the inclined surface 52c in the axial direction is α (about 10 mm), and in the direction perpendicular to the axis. The distance of the inclined surface 52c is indicated by β (about 2 mm).

As can be understood from FIG. 4 (A), the inner peripheral wall surface 52b of the stepped shaft portion 50 of the forged product 5 moves in the direction of arrow X2 and contracts by the above-described first stage cold drawing process. The diameter of the inner peripheral wall surface 62d is the inner peripheral wall surface 62d shown in FIG. As a result, in the primary throttle hole 62 shown in FIG. 4B, the rounded surface 62f which is the peripheral edge of the hole bottom surface 62e.
Is maintained in a forward tapered shape whose inner diameter decreases toward the hole bottom surface 62e. That is, the reverse taper-shaped recessed portion where stress concentration is induced is not formed.

By the way, FIG. 10 schematically shows the configuration of FIG. In FIG. 10, the inclined surface 5
2c is schematically illustrated as an inclined straight line. In FIG. 10, the distance of the inclined surface 52c in the axial direction is indicated by α, and the distance of the inclined surface 52c in the direction perpendicular to the axis is indicated by β. Further, the upper end of the inclined surface 52c is indicated by point A, the lower end of the inclined surface 52c is indicated by point Q, the small diameter end of the conical surface 50e forming the step is indicated by point P, and from point A to point P. The distance in the axial direction of is indicated by yo. Note that FIG. 10 is merely a schematic diagram, and the points A, Q, and P are actually defined by the circular arcs.

Here, the region of the characteristic line K1 in FIG. 11 is a ratio (α / β) indicating the degree of inclination of the inclined surface 52c when the inclined surface 52c is deformed straight by a diaphragm.
Shows the relationship between the drawing degree and the drawing degree. A large value of (α / β) means that the inclined surface 52c has a steep slope, and (α / β)
The small β) means that the inclined surface 52c has a gentle slope. In the region of the characteristic line K1, for example, (α / β) is about 2 to 5 when the drawing degree is about 42%, and (α / β) is 3 when the drawing degree is about 28%.
If the drawing workability is about 15% (α
/ Β is about 10 to 15. That is, the characteristic line K1 is
This means that the value of (α / β) is decreased and the inclined surface 52c is gently inclined as the drawing degree increases.

If the first stage drawing process is carried out under the condition that the region of the characteristic line K1 in FIG. 11 is satisfied, the inclined surface 52c becomes straight even after the drawing, and the direction of inclination does not become an inverse taper. . In the method of this embodiment, the characteristic line K1
In the state where (α / β) has a gentler gradient than the condition that satisfies the area
c is reliably maintained in the forward taper shape and does not become a reverse taper-shaped cutout portion where stress concentration is induced.

Generally, the punch forming hole 5 before drawing is performed.
The diameter ratio (Do / do) of 2 is 1.2 to 4.0, and the point A
Is located 5 to 20 mm above the point P.
Further, the region of the characteristic line K3 in FIG. 12 shows the relationship between the above-mentioned distance yo in the axial direction and the drawing workability when the forward tapered inclined surface 52c is deformed straight by drawing. In order to straighten the forward tapered inclined surface 52c by drawing, as shown by the characteristic line K3, as the drawing workability increases, the distance y is in the range of 5 to 20 mm.
It is preferable to increase o, that is, to set the position A of the upper end of the inclined surface 52c to the upper side.

In the method of this embodiment, the cold drawing step of the first stage is performed under the condition that the regions of the characteristic lines K1 and K3 are satisfied, or the condition in which the margin is taken into consideration. In the narrowed hole 62, the rounded surface 62f, which is the peripheral portion of the hole bottom surface 62e, is maintained in a forward tapered shape, and is not in a reverse tapered shape. In the method of this embodiment,
The second stage cold drawing process is performed under the condition that the regions of the characteristic lines K1 and K3 are satisfied, or under the condition that the margin is taken into consideration. Therefore, in the secondary drawing hole 72, the hole bottom surface 72e thereof is formed. The rounded surface 72f, which is the peripheral edge portion, is maintained in a forward taper shape and is not in a reverse taper shape in which stress concentration is induced.

Further, in this embodiment, since the secondary constricted hole 72 is formed without using the processing by the drill blade, there is no cutting of the forging flow (streamline), which is advantageous in securing the strength. The forged product 7 manufactured as described above undergoes quenching and tempering treatment, blasting treatment, and coating treatment, and is then spline processed and bolt hole processed to form a side gear shaft. (Product) FIGS. 6 and 7 show the side gear shaft 8. That is, basically, the spline 80 is formed on the outer peripheral wall surface 70e of the stepped shaft portion 70 of the forged product 7 that has undergone the second stage cold drawing process.
And a bolt hole 82 is formed in the flange portion 74 of the forged product 7. As shown in FIG. 7, a bearing 90 is fitted on the outer peripheral wall surface 70 c of the stepped shaft portion 70.

As can be understood from FIG. 7, the spline 80 is provided in the area F2 while avoiding the area F1 in which the aperture 72 is formed. (Other Examples) In the above-described embodiment, hot forging is performed to obtain the forged product 5, but the present invention is not limited to this, and warm forging may be performed in an intermediate temperature range between hot and cold. .

FIGS. 13A to 13D schematically show another example. This example is applied to a forged product of a differential drive pinion as a drive component. In this example, the rough forged product 400 (material: Cr-Mo case hardening steel) shown in FIG. 13 (A) is used. This forged land 40
Reference numeral 0 is a round bar-shaped material, which has a rough shaft portion 410 having a bottomed rough hole and a rough umbrella portion 44 as a flange portion.
It has 0 and. The rough stepped shaft portion 400 is the outer peripheral wall surface 400.
a, 400b, conical surface 400c and shaft end surfaces 400d, 4
00e. The wasteland umbrella portion 440 is the outer peripheral wall surface 4
40a and the end face 440c.

Next, a forging punch die is pushed into the rough ground forged product 400 to obtain a forged product 500 shown in FIG. 13 (B). The forged product 500 includes a stepped shaft portion 510, a bottomed punch forming hole 520 opened at one end of the stepped shaft portion 510, and the stepped shaft portion 5.
10 and an umbrella portion 540 extending from one end. The stepped shaft portion 510 includes a shaft end surface 510a and an outer peripheral wall surface 510b,
It is defined by 510c and the conical surface 510d. The punch forming hole 520 is defined by an inner peripheral wall surface 520a, a hole bottom surface 520e, and an inclined surface 520f. The umbrella portion 540 has substantially the same shape and size as the umbrella portion 440 after the burr is removed.

Next, a first stage cold drawing process is carried out using the forged product 500, and the outer peripheral wall surface 510b (large diameter shaft part in the present invention) of the stepped shaft portion 510 of the forged product 500 is removed. The outer diameter of the region K1 is reduced and the forged product 60 shown in FIG.
Get 0. In the drawing step, the cylindrical wall portion forming the region K1 of the stepped shaft portion 510 is extended along with the punch forming hole 520 in the axial front direction, that is, in the arrow A2 direction.
At this time, in the stepped shaft portion 510, the root region K2 on the umbrella portion 540 side and the region K3 of the outer peripheral wall surface 510c on the shaft tip side are not narrowed.

As shown in FIG. 13C, this forged product 60
Reference numeral 0 denotes a stepped shaft portion 610, a bottomed primary throttle hole 620 that opens at one end of the stepped shaft portion 610, and an umbrella portion 640 that extends from one end of the stepped shaft portion 610 in the centrifugal direction. With and. The stepped shaft portion 610 includes a shaft end surface 610 a and an outer peripheral wall surface 610.
b, 610c, 610d and the conical surfaces 610e, 610f. The primary throttle hole 620 is a stepped hole and is defined by the inner peripheral wall surfaces 620a and 620b, the hole bottom surface 620e, and the rounded surface 620f. The umbrella portion 640 has substantially the same shape and size as the umbrella portion 440.

Next, the forged product 600 is subjected to the second stage cold drawing process to form the stepped shaft portion 610 of the forged product 600.
The outer diameter of the region K5 of the outer peripheral wall surface 610c is narrowed to a narrowed region K6 to obtain a forged product 700 shown in FIG. 13 (D). At this time, the cylindrical wall portion forming the region K5 of the outer peripheral wall surface 610c is extended in the axial forward direction, that is, in the arrow A2 direction together with the primary throttle hole 620.

Forged product 7 that has undergone the second stage cold drawing process
00 is a stepped shaft portion 710, as shown in FIG.
A bottomed secondary throttle hole 7 opened at one end of the stepped shaft portion 710.
20 and an umbrella portion 740 extending in the centrifugal direction from one end of the stepped shaft portion 710. The stepped shaft portion 710 includes a shaft end surface 710a and outer peripheral wall surfaces 710b, 710c, 710d, 7a.
10e and the conical surfaces 710f, 710h, 710i. The secondary throttle hole 720 is a stepped hole, and includes inner peripheral wall surfaces 720a, 720b, 720c and a conical inner peripheral wall surface 72.
0e, 720f, hole bottom surface 720h, and rounded surface 720i. As a result of the above-mentioned aperture, the secondary aperture 7
The hole diameter of 20 is squeezed so that it is smaller than the hole diameter of the primary throttle hole 620. The umbrella portion 740 is the umbrella portion 4
The shape and size are substantially the same as those of 40.

Here, the vicinity of the hole bottom surface 520e of the punch forming hole 520 shown in FIG. 13 (B) has basically the same shape as that shown in FIG. 4 (A). See also FIG.
The vicinity of the bottom surface 620e of the aperture 620 shown in FIG.
It has a form basically similar to the form shown in (B).
Therefore, after the cold drawing in the first step and the second step, in the same manner as described above, in the secondary throttle hole 720, the rounded surface 720i does not become the reverse tapered recessed portion, and the hole bottom surface 72 is formed.
The inner diameter becomes smaller toward 0h.

Forged product 700 manufactured as described above
Is subjected to normalizing treatment, blasting treatment, and after cutting the entire outer peripheral surface, gears are formed on the outer peripheral wall surface 740a of the umbrella portion 740 by gear cutting, and splines are formed on the outer peripheral surface 710d of the shaft portion 710 by gear cutting. Formed to become a differential drive pinion. The above examples are applied to the side gear shaft and the differential drive pinion, but the present invention is not limited to this, and can be applied to other hollow shaft forged products with flanges.

[0045]

According to the method of the present invention, even if the hole bottom surface of the central shaft hole is arranged near the stepped portion, a reverse taper-shaped cutout portion which causes stress concentration is generated. Can be avoided.

[Brief description of drawings]

1A to 1C are cross-sectional views showing steps from a round bar to a finish forged product to obtain a finish forged product.

FIG. 2 is a cross-sectional view showing a forged product in which a punch forming hole is formed by performing a hot backward extrusion process.

FIG. 3 is a cross-sectional view showing a forged product in which a first-stage cold drawing process has been performed and primary drawing holes have been formed.

4A and 4B are enlarged cross-sectional views of a main part for explaining a deformation process of a punch forming hole.

FIG. 5 is a cross-sectional view showing a forged product which has been subjected to a second stage cold drawing process to form secondary drawn holes.

FIG. 6 is a plan view of a side gear shaft.

FIG. 7 is a sectional view of the side gear shaft, taken along line NN in FIG.

FIG. 8 is a cross-sectional view showing an apparatus for performing a hot backward extrusion step.

FIG. 9 is a cross-sectional view showing an apparatus for performing a cold front extrusion step.

FIG. 10 is an enlarged cross-sectional view of a main part for explaining the configuration of a punch forming hole before performing a drawing step.

FIG. 11 is a graph showing the relationship between (α / β) and the drawing workability.

FIG. 12 is a graph showing the relationship between the axial distance yo and the drawing workability.

13A to 13D are cross-sectional views showing a forged product in each step according to another example.

FIG. 14 (A) is a cross-sectional view in the vicinity of the central axial hole before the drawing according to the prior art, and FIG. 14 (B) is a cross-sectional view in the vicinity of the drawing hole after the drawing according to the prior art.

[Explanation of symbols]

In the figure, 4 is a forged product, 5 is a forged product, 50 is a stepped shaft portion, 5
2 is a punch forming hole (central shaft hole), 52d is a hole bottom surface, 6 is a forged product, 62 is a primary drawing hole, 62e is a hole bottom surface, 72 is a secondary drawing hole, and 72e is a hole bottom surface.

Claims (1)

[Claims] 1. A stepped shaft portion having a large-diameter shaft portion having a large outer diameter and a small-diameter shaft portion connected to the large-diameter shaft portion via a step portion, and the stepped shaft portion. A step of obtaining a forged product having a bottomed central shaft hole that is formed and opens at the shaft end face of the large-diameter shaft part; and forcing the central shaft hole of the forged product into an unrestrained state, A method for manufacturing a hollow shaft-shaped forged product by sequentially performing a drawing step of drawing an outer peripheral surface of a large-diameter shaft part together with the central shaft hole, and making the central shaft hole a substantially straight drawing hole, The center shaft hole of the forged product before drawing has its bottom surface approximately equal to the diameter of the center shaft hole in one direction and the other direction of the axial direction of the stepped shaft part with reference to the step part. The forged product is provided with an inclined surface which is arranged in a region defined by the distance and whose inner diameter at the peripheral edge of the hole bottom surface of the central shaft hole becomes smaller toward the hole bottom surface. (Α / β) is a value of 1 to 15, where α is the distance between the inclined surfaces in the axial direction and β is the distance between the inclined surfaces in the direction perpendicular to the axis in the cross section. A method of manufacturing a hollow shaft-shaped forged product, characterized in that the value of (α / β) is reduced as the degree of drawing is increased.