DESCRIPTION
TECHNICAL FIELD
[0001]
The present invention relates to a method for producin5 g
a hollow engine valve including a valve body in which a hollow
hole extending through a valve umbrella portion and a hollow
stem portion connected to the valve umbrella portion is formed.
BACKGROUND ART
10 [0002]
Among engine valves, various engine valves in which
insides thereof are formed to be hollow are recently provided
along with the increase in output and performance of an engine.
This design reduces the weight of a hollow engine valve as
15 compared to that of a solid engine valve and enables a
highly-accurate valve opening and closing operation to be
performed. A conventional method for producing such a hollow
engine valve is disclosed in, for example, Patent Document 1.
PRIOR ART DOCUMENT
20 PATENT DOCUMENT
[0003]
Patent Document 1: Japanese Patent No. 4390291
SUMMARY OF THE INVENTION
PROBLEMS TO BE SOLVED BY THE INVENTION
25 [0004]
In the conventional method for producing a hollow engine
valve, a valve body, a hollow stem member, and a stem end sealing
member are separately produced and then these members are joined
together to obtain the hollow engine valve which is a finished
30 product. Furthermore, out of these members, the valve body is
3
produced in the following method. A solid round bar which is
a raw material is shaped into a semi-finished product by
performing forging twice and then the semi-finished product is
subjected to a necking process (drawing process) to be shaped
into the valve body5 .
[0005]
However, as described above, in the conventional forging
step, the forging needs to be performed twice on the solid round
bar. Specifically, the solid round bar is shaped into a
10 glass-shaped intermediate product in the first forging and then
the intermediate product is shaped into the semi-finished
product in the second forging.
[0006]
Furthermore, in the second forging, a lower end portion
15 of the intermediate product is forged to be expanded outward
and is thereby shaped into a valve umbrella portion of the
semi-finished product. To perform such forging, shaping needs
to be performed with a core inserted in a hollow hole of the
glass-shaped intermediate product. In a case where the shaping
20 is performed with the core being inserted as described above,
the core needs to be inserted in the hollow hole of the
intermediate product shaped in the first forging, in the process
of expanding the lower portion of the intermediate product
outward. The outer diameter of the core is thus inevitably
25 smaller than the inner diameter of the hollow hole in the
intermediate product. Since the outer diameter of the core is
smaller than the inner diameter of the hollow hole in the
intermediate product, a step may be formed in the hollow hole.
[0007]
30 Such a step tends to be formed particularly when the
4
semi-finished product of the valve body is shaped by hot forging.
Moreover, the step not only causes drawing failure in the
necking process which is the subsequent step, but also becomes
a strength reduced portion which receives concentration of
stress in usage of the hollow engine valve5 .
[0008]
Moreover, a setting range of the inner diameter of the
hollow stem portion (hollow hole) of the valve body to be shaped
in the necking process is determined to some extent by the inner
10 diameter of the hollow stem portion (hollow hole) of the
semi-finished product at the start of the necking process.
Furthermore, since the thickness of the hollow stem portion in
the semi-finished product monotonically increases in the
necking process, a setting range of the thickness of the hollow
15 stem portion in the valve body which is the finished product
is determined to some extent by the thickness of the hollow stem
portion of the semi-finished product at the start of the necking
process. Accordingly, the conventional production method has
difficulty in producing a valve body (hollow engine valve) of
20 desired dimensions.
[0009]
The present invention has been made to solve the problems
described above, and an object thereof is to provide a method
for producing a hollow engine valve which can simplify
25 production steps and improve processing accuracy.
MEANS FOR SOLVING THE PROBLEMS
[0010]
A method for producing a hollow engine valve according
to a first aspect of the present invention for solving the
30 problems described above is a method for producing a hollow
5
engine valve including a valve body in which a hollow hole
extending through a valve umbrella portion and a hollow stem
portion connected to the valve umbrella portion is formed,
characterized in that the method comprises:
shaping a solid round bar which is a raw material of th5 e
valve body into a valve body semi-finished product in which a
semi-finished product hollow hole is formed, by performing hot
forging once, the semi-finished product hollow hole
corresponding to the hollow hole and extending through a
10 semi-finished product valve umbrella portion corresponding to
the valve umbrella portion and a semi-finished product hollow
stem portion corresponding to the hollow stem portion;
subjecting the valve body semi-finished product to a
rotary swaging process in which an outer peripheral surface of
15 the semi-finished product hollow stem portion is pressed while
the valve body semi-finished product is rotated, and thereby
reducing a diameter of the semi-finished product hollow stem
portion and increasing a stem length of the semi-finished
product hollow stem portion;
20 subjecting the valve body semi-finished product
subjected to the rotary swaging process to a necking process
in which the semi-finished product hollow stem portion and a
semi-finished product neck portion being a connection portion
between the semi-finished product valve umbrella portion and
25 the semi-finished product hollow stem portion are drawn
stepwise, and thereby reducing the diameter of the
semi-finished product hollow stem portion and increasing the
stem length of the semi-finished product hollow stem portion
to shape the valve body semi-finished product into the valve
30 body; and
6
joining a stem end sealing member to an end portion of
the hollow stem portion in the valve body to seal the hollow
hole.
[0011]
The method for producing a hollow engine valve accordin5 g
to a second aspect of the present invention for solving the
problems described above is characterized in that a
semi-finished product enlarged-diameter hole portion having an
inner diameter larger than an inner diameter of the
10 semi-finished product hollow hole is processed at a lower end
of the semi-finished product hollow hole in the semi-finished
product valve umbrella portion.
[0012]
The method for producing a hollow engine valve according
15 to a third aspect of the present invention for solving the
problems described above is characterized in that the
semi-finished product neck portion is processed to have a
predetermined thickness before the necking process.
[0013]
20 The method for producing a hollow engine valve according
to a fourth aspect of the present invention for solving the
problems described above is characterized in that the stem end
sealing member is joined to the end portion of the hollow stem
portion after metallic sodium as a coolant is put into the hollow
25 hole.
EFFECT OF THE INVENTION
[0014]
In the method for producing the hollow engine valve
according to the present invention, the solid round bar which
30 is the raw material of the valve body is shaped into the valve
7
body semi-finished product by performing hot forging once, and
the valve body semi-finished product is subjected to the rotary
swaging process and the necking process to be shaped into the
valve body which is the finished product. This can simplify
production steps and improve processing accuracy5 .
BRIEF DESCRIPTION OF THE DRAWINGS
[0015]
[Fig. 1] Fig. 1 is a vertical cross-sectional view of a
hollow engine valve produced in a method for producing a hollow
10 engine valve in one embodiment of the present invention.
[Fig. 2] Parts (a) to (f) are views showing, in sequence,
processes for shaping a solid round bar into a valve body.
[Fig. 3] Fig. 3 is a schematic configuration view of a press
die for hot forging and parts (a) to (d) are views showing, in
15 sequence, operations for shaping the solid round bar into a
semi-finished product.
[Fig. 4] Fig. 4 is view showing a cutting process performed
on a hollow hole of the semi-finished product.
[Fig. 5] Fig. 5 is a schematic configuration view of a rotary
20 swaging machine, part (a) is a plan view of the rotary swaging
machine, and part (b) is a side view of the rotary swaging
machine.
[Fig. 6] Fig. 6 is a view showing a cutting process performed
on a neck portion of the semi-finished product.
25 [Fig. 7] Fig. 7 is a schematic configuration view of a
necking machine and is a view showing operations of shaping the
semi-finished product into the valve body.
MODE FOR CARRYING OUT THE INVENTION
[0016]
30 A method for producing a hollow engine valve of the present
8
invention is described below in detail by using the drawings.
EMBODIMENT
[0017]
As shown in Fig. 1, a hollow engine valve 1 produced by
the production method of the present invention is used as a5 n
intake valve or an exhaust valve of an engine in a vehicle or
the like, and includes a hollow-shaft-shaped valve body 10 and
a shaft-shaped stem end sealing member 20. The valve body 10
and the stem end sealing member 20 are joined to each other at
10 stem ends thereof.
[0018]
Moreover, as shown in Fig. 1 and part (f) of Fig. 2, the
valve body 10 has an umbrella-shaped valve umbrella portion 10a
and a hollow-shaft-shaped hollow stem portion 10b. A hollow hole
15 10c is formed in the valve body 10 along outer shapes of the
valve umbrella portion 10a and the hollow stem portion 10b,
extending through the valve umbrella portion 10a and the hollow
stem portion 10b. A hollow hole 10c can be filled with metallic
sodium N as a coolant.
20 [0019]
Furthermore, an enlarged-diameter hole portion 10d is
formed at a lower end of the hollow hole 10c in the valve umbrella
portion 10a and the inner diameter d2 of the enlarged-diameter
hole portion 10d at a largest portion is larger than the inner
25 diameter of the hollow hole 10c. A neck portion 10e is formed
between the valve umbrella portion 10a and the hollow stem
portion 10b.
[0020]
For example, heat resistant steels such as SUH 1, SUH 3,
30 SUH 11, SUH 35, and SUH 38 can be employed as materials of the
9
valve body 10 and the stem end sealing member 20.
[0021]
Next, the method for producing the hollow engine valve
1 is described in detail by using Figs. 1 to 7.
[00225 ]
As shown in parts (a) to (f) of Fig. 2, a solid round bar
11 which is a raw material of the valve body 10 is subjected
to hot forging to be shaped into a semi-finished product 12;
then, the semi-finished product 12 is sequentially subjected
10 to a cutting process on a hollow hole 12c in a valve umbrella
portion 12a, a rotary swaging process (cold forging process)
on a hollow stem portion 12b, a cutting process (turning
process) on a neck portion 13e, and a necking process (drawing
process) on a hollow stem portion 13b and the neck portion 13e,
15 and the shape of the semi-finished product 12 is thereby changed
to the shape of a semi-finished product 13; thereafter, the
semi-finished product 13 is finally shaped to the valve body
10. It is preferable from the view point of processing accuracy
that the aforementioned necking process is, in principle, cold
20 forging in which the semi-finished product 13 is maintained at
normal temperature. However, depending on the processability
of the raw material, the necking process may be forging
performed in a state where the semi-finished product 13 is
heated.
25 [0023]
First, as shown in parts (a) and (b) of Fig. 2 and parts
(a) to (d) of Fig. 3, the solid round bar 11 formed in a
predetermined shape in advance is shaped into the semi-finished
product 12 by using a press die 40 for hot forging.
30 [0024]
10
As shown in part (a) of Fig. 3, the press die 40 includes
a columnar upper die (punch) 41 and a cylindrical lower die 42.
Out of these dies, the lower die 42 includes a die block 51,
a floating die 52, and a cylinder block 53. The floating die
52 and the cylinder block 53 are provided respectively abov5 e
and below the die block 51.
[0025]
A cylindrical housing portion 51a is formed in a center
portion of the die block 51 to penetrate the die block 51 in
10 an up-down direction. Furthermore, a core 54 is disposed in the
housing portion 51a to penetrate the housing portion 51a in the
up-down direction. In this case, the core 54 is supported
between the housing portion 51a and a top surface of the cylinder
block 53 in such a way that movement of the core 54 in an axial
15 direction (up-down direction) thereof is restricted.
[0026]
Moreover, a cylindrical knock-out pin 55 is disposed in
the housing portion 51a and the core 54 is inserted in a hollow
hole 55a of the knock-out pin 55. A flange portion 55b is formed
20 at a lower end of the knock-out pin 55 and is supported to be
slidable in the up-down direction in the housing portion 51a.
[0027]
Furthermore, multiple springs 56 are provided between an
inner peripheral surface of the housing portion 51a and an outer
25 peripheral surface of the knock-out pin 55. These springs 56
are interposed between a bottom surface of the floating die 52
and the flange portion 55b of the knock-out pin 55 in a compressed
state.
[0028]
30 A cavity 52a is formed in a center portion of the floating
11
die 52 to penetrate the floating die 52 in the up-down direction.
An upper end of the core 54 is disposed in a center portion of
the cavity 52a and an upper end of the knock-out pin 55 disposed
outside the core 54 in a radial direction is capable of advancing
into the cavity 52a from below the cavity 52a5 .
[0029]
Moreover, multiple pin slide holes 52b are provided in
an outer peripheral portion of the floating die 52 along a
circumferential direction thereof. These pin slide holes 52b
10 are formed to penetrate the floating die 52 in the up-down
direction. Furthermore, slide pins 57 are slidably supported
in the pin slide holes 52b and lower ends of the slide pins 57
are fixed to an upper portion of the die block 51.
[0030]
15 Meanwhile, a cylinder portion 53a is formed in a center
portion of the cylinder block 53 and a piston member 58 is
supported in the cylinder portion 53a to be slidable in the
up-down direction. An upper end of the piston member 58
penetrates an upper portion of the cylinder block 53 and a lower
20 portion of the die block 51 and can press a bottom surface of
the flange portion 55 in the housing portion 51a.
[0031]
In the case of shaping the solid round bar 11 into the
semi-finished product 12 by using the press die 40, as shown
25 in part (a) of Fig. 3, the lower die 42 is first lowered to a
lower-limit position and then the solid round bar 11 heated to
a predetermined temperature is placed on an upper end surface
of the core 54 disposed in the cavity 52a.
[0032]
30 Note that the solid round bar 11 is heated in advance to
12
a temperature of, for example, 950°C to 1200°C before the hot
forging. Moreover, when the solid round bar 11 heated to a
temperature within the aforementioned temperature range is
placed on the upper end surface of the core 54, an upper half
or more of the solid round bar 11 protrudes upward from an insid5 e
of the cavity 52a.
[0033]
Furthermore, since the piston member 58 is positioned at
a lower-limit position in the cylinder portion 53a at the start
10 of the aforementioned hot forging (at the start of moving of
the press die 40), the knock-out pin 55 is also disposed at a
lower-limit position in the housing portion 51a. Hence, a top
surface of the die block 51 and the bottom surface of the floating
die 52 are in tight contact with each other.
15 [0034]
Next, as shown in part (b) of Fig. 3, the lower die 42
is lifted from the lower-limit position until it comes into
contact with the upper die 41. The solid round bar 11 is thereby
pressed downward into the cavity 52a by the upper die 41 to cover
20 the upper end of the core 54. Specifically, the solid round bar
11 is made to fill a space surrounded by the upper die 41, the
cavity 52a, and the core 54, and is thus shaped into the
semi-finished product 12.
[0035]
25 Thereafter, as shown in part (c) of Fig. 3, the lower die
42 is lowered to the lower-limit position and then the piston
member 58 is moved upward. The flange portion 55b of the
knock-out pin 55 is thereby pressed upward by the piston member
58. Accordingly, the floating die 52 is lifted by biasing force
30 of the springs 56 and is spaced way from the die block 51. At
13
this time, when a lifting amount of the floating die 52 reaches
a predetermined lifting amount, the pin slide holes 52b and the
slide pins 57 come into contact with one another and the lifting
of the floating die 52 is restricted.
[00365 ]
Next, as shown in part (d) of Fig. 3, when the piston member
58 is moved further upward, only the knock-out pin 55 is lifted
against the biasing force of the springs 56. The semi-finished
product 12 fitted into the cavity 52a of the floating die 52
10 is thereby pushed upward by the knock-out pin 55. Specifically,
the semi-finished product 12 shaped in the cavity 52a is
separated from the core 54 and is pushed out from the cavity
52a by the pressing of the knock-out pin 55 from below.
[0037]
15 Performing the hot forging of the solid round bar 11 with
the press die 40 as described above allows the solid round bar
11 to be shaped into the semi-finished product 12 by performing
forging once. In this case, as shown in part (b) of Fig. 2, the
hollow hole 12c in the shaped semi-finished product 12 is formed
20 to have an inner diameter of d1.
[0038]
Moreover, shaping the solid round bar 11 into the
semi-finished product 12 by performing forging once can prevent
the aforementioned generation of the step formed in the case
25 where the solid round bar is shaped into the semi-finished
product by performing forging twice. This can not only simplify
the forging step but also improve the strength of the valve body
10 (hollow engine valve 1).
[0039]
30 Furthermore, since the lower die 42 of the press die 40
14
employs a floating structure in which the floating die 52 is
made to float by the springs 56, a press speed (moving speed
of the lower die 42) can be adjusted by adjusting the biasing
force of the springs 56. Due to this, when the solid round bar
11 is shaped into the semi-finished product 12, there ar5 e
exerted effects similar to those obtained in a case of using
a die for shaping which is performed with back pressure being
generated. Accordingly, the solid round bar 11 can be made to
dividedly flow to the valve umbrella portion 12a side and the
10 hollow stem portion 12b side in the semi-finished product 12.
As a result, the semi-finished product 12 shaped by the press
die 40 employing the floating structure can be greatly improved
in shapability, compared to a semi-finished product shaped by
a press mold having no floating structure.
15 [0040]
Next, as shown in parts (b) and (c) of Fig. 2 and Fig.
4, the hollow hole 12c of the semi-finished product 12 obtained
by the hot forging is subjected to the cutting process by using
a cutting tool 60.
20 [0041]
Specifically, as shown in Fig. 4, the cutting tool 60 is
first prepared. The cutting tool 60 includes a shaft-shaped tool
main body 61 and multiple cutting edges 62 provided at a front
end of the tool main body 61. Moreover, the cutting edges 62
25 are supported to be capable of advancing outward in a radial
direction of the tool main body 61.
[0042]
Next, the front end side of the cutting tool 60 is inserted
into the hollow hole 12c of the semi-finished product 12 and
30 the cutting tool 60 is then moved in a tool rotating axis
15
direction while being rotated. At the same time, the cutting
edges 62 are gradually moved outward in a tool radial direction.
A lower end of the hollow hole 12c is thereby cut by the cutting
edges 62 and an enlarged-diameter hole portion 12d is formed
in the lower end5 .
[0043]
At this time, as shown in part (c) of Fig. 2 and Fig. 4,
the enlarged-diameter hole portion 12d is formed such that the
inner diameter thereof gradually becomes larger toward a bottom
10 surface. The inner diameter d2 of the enlarged-diameter hole
portion 12d at a largest portion is larger than the inner
diameter d1 of the hollow hole 12c.
[0044]
In summary, as shown in part (b) of Fig. 2, the valve
15 umbrella portion 12a, the hollow stem portion 12b, the hollow
hole 12c which extends through the valve umbrella portion 12a
and the hollow stem portion 12b, and a neck portion 12e which
is a connection portion between the valve umbrella portion 12a
and the hollow stem portion 12b are formed in the semi-finished
20 product 12 subjected to the hot forging. Furthermore, as shown
in part (c) of Fig. 2, the enlarged-diameter hole portion 12d
is formed at the lower end of the hollow hole 12c in the valve
umbrella portion 12a in the semi-finished product 12 subjected
to the cutting process.
25 [0045]
The valve umbrella portion (semi-finished product valve
umbrella portion) 12a, the hollow stem portion (semi-finished
product hollow stem portion) 12b, the hollow hole
(semi-finished product hollow hole) 12c, the enlarged-diameter
30 hole portion (semi-finished product enlarged-diameter hole
16
portion) 12d, and the neck portion (semi-finished product neck
portion) 12e in the semi-finished product 12 correspond
respectively to the valve umbrella portion 10a, the hollow stem
portion 10b, the hollow hole 10c, the enlarged-diameter hole
portion 10d, and the neck portion 10e in the valve body 10 whic5 h
is a finished product.
[0046]
Next, as shown in parts (c) and (d) of Fig. 2 and parts
(a) and (b) of Fig. 5, the semi-finished product 12 obtained
10 by the cutting process is shaped into the semi-finished product
13 by using a rotary swaging machine 70 for cold forging.
[0047]
As shown in parts (a) and (b) of Fig. 5, the rotary swaging
machine 70 includes a rotating table 71, a core 72, and dies
15 73a, 73b.
[0048]
The rotating table 71 is supported to be rotatable about
its center axis and the semi-finished product 12 can be mounted
on a top surface of the rotating table 71. Moreover, the core
20 72 is disposed coaxially with the rotating table 71, above the
rotating table 71, and is supported to be rotatable about its
center axis and to be movable in a direction of its center axis.
Note that the outer diameter of the core 72 is smaller than the
inner diameter d1 of the hollow hole 12c in the semi-finished
25 product 12.
[0049]
Furthermore, the dies 73a, 73b are arranged opposite to
one another with the center axis of the rotating table 71 and
the core 72 being at the center. In each of pairs of the dies
30 73a, 73b disposed opposite to one another, the dies are
17
supported to come close and move away from each other in a radial
direction of the rotating table 71 and the core 72
(semi-finished product 12). Front end surfaces of the dies 73a,
73b are formed as surfaces curved along an outer peripheral
surface of the hollow stem portion 13b in the semi-finishe5 d
product 13 subjected to the rotary swaging process.
[0050]
When the semi-finished product 12 is to be shaped into
the semi-finished product 13 by using the rotary swaging machine
10 70, as shown in parts (a) and (b) of Fig. 5, the semi-finished
product 12 is first mounted on the rotating table 71 and then
the core 72 is inserted into the hollow hole 12c of the
semi-finished product 12. Next, the rotating table 71 and the
core 72 are rotated in the same direction and the core 72 and
15 the semi-finished product 12 are synchronously rotated. Then,
the dies 73a, 73b are pressed against an outer peripheral
surface of the hollow stem portion 12b in the rotated
semi-finished product 12.
[0051]
20 The semi-finished product 12 is thereby deformed in such
a way that the outer diameter of the hollow stem portion 12b
is reduced and the stem length of the hollow stem portion 12b
is increased, and is shaped into the semi-finished product 13.
At this time, as shown in part (d) of Fig. 2, the inner diameter,
25 at a largest portion, of an enlarged-diameter hole portion 13d
in the semi-finished product 13 is kept to be d2.
[0052]
In other words, the hollow stem portion 12b of the
semi-finished product 12 can be shaped into the hollow stem
30 portion 13b of the semi-finished product 13 in advance before
18
the necking process with a necking machine 90 to be described
later, by performing the rotary swaging process with the rotary
swaging machine 70 before the necking process. Accordingly, the
hollow stem portion 13b can be easily controlled to have
arbitrary dimensions. Moreover, setting the outer diameter o5 f
the core 72 and the curvatures of the front end surfaces of the
dies 73a, 73b to arbitrary dimensions not only can make the
thickness of the hollow stem portion 13b in the semi-finished
product 13 uniform but also allows the thickness of the hollow
10 stem portion 13b to be easily controlled such that the thickness
is made larger or smaller than the thickness of the hollow stem
portion 12b in the semi-finished product 12. Note that,
depending on the dimensions of the semi-finished product 13,
a rotary swaging process using no core 72 may be performed.
15 [0053]
Next, as shown in parts (d) and (e) of Fig. 2, and Fig.
6, the neck portion 13e of the semi-finished product 13 obtained
by the rotary swaging process is subjected to the cutting
process by using a tool 80.
20 [0054]
Specifically, as shown in Fig. 6, an outer peripheral
surface of the neck portion 13e in the semi-finished product
13 attached to a lathe turning machine (not illustrated) is cut
with the tool 80 mounted on the lathe turning machine while the
25 semi-finished product 13 is rotated about its axis. The outer
peripheral surface of the neck portion 13e is thereby shaped
in a round shape in which the thickness of the neck portion 13e
is a predetermined thickness.
[0055]
30 Cutting the outer peripheral surface of the neck portion
19
13e in the semi-finished product 13 and forming the neck portion
13e to have the predetermined thickness as described above can
prevent an inner peripheral surface of the neck portion 13e from
bulging inward in the necking process with the necking machine
90 to be described later5 .
[0056]
In summary, as shown in part (d) of Fig. 2, a valve umbrella
portion 13a, the hollow stem portion 13b, a hollow hole 13c which
extends through the valve umbrella portion 13a and the hollow
10 stem portion 13b, the enlarged-diameter hole portion 13d which
is provided at an lower end of the hollow hole 13c in the valve
umbrella portion 13a, and the neck portion 13e which is a
connection portion between the valve umbrella portion 13a and
the hollow stem portion 13b are formed in the semi-finished
15 product 13 subjected to rotary swaging process. Furthermore,
as shown in part (e) of Fig. 2, the thickness of the neck portion
13e is adjusted in the semi-finished product 13 subjected to
the cutting process.
[0057]
20 The valve umbrella portion (semi-finished product valve
umbrella portion) 13a, the hollow stem portion (semi-finished
product hollow stem portion) 13b, the hollow hole
(semi-finished product hollow hole) 13c, the enlarged-diameter
hole portion (semi-finished product enlarged-diameter hole
25 portion) 13d, and the neck portion (semi-finished product neck
portion) 13e in the semi-finished product 13 correspond
respectively to the valve umbrella portion 10a, the hollow stem
portion 10b, the hollow hole 10c, the enlarged-diameter hole
portion 10d, and the neck portion 10e in the valve body 10 which
30 is the finished product.
20
[0058]
Next, as shown in parts (e) and (f) of Fig. 2, and Fig.
7, the semi-finished product 13 obtained by the cutting process
is shaped into the valve body 10 by using the necking machine
90 for cold forging or warm forging5 .
[0059]
As shown in Fig. 7, the necking machine 90 draws the hollow
stem portion 13b and the neck portion 13e of the semi-finished
product 13 stepwise, and eventually shapes the semi-finished
10 product 13 into the valve body 10. A bed 91 is provided in a
lower portion of the necking machine 90 and a movable mount 92
is supported above the bed 91 to be capable of being lifted and
lowered.
[0060]
15 Moreover, tubular n dies D1, D2, ..., D(m-1), Dm, ...,
D(n-1), and Dn are provided on a bottom surface of the movable
mount 92 along a conveyance direction of the semi-finished
product 13. Here, index m refers to m-th in the order and index
n refers to n-th (last) in the order. Moreover, m