Method and apparatus for producing a stepped hollow article

A method and apparatus for producing a stepped hollow component such as, for example, a gear blank. A solid slug, provided with a disc portion and a projecting portion, is placed in a rigid cylindrical recess formed between a counterpunch and a hollow mold. An annular upper surface of the disc portion and a side surface of the projecting portion are precompressed by an outer punch so as to restrain an outer periphery of the solid slug. A closed-base hole is formed in a center of the solid slug by a plastic deformation caused by an inner punch. The plastic deformation by the inner punch causes material of the solid slug to flow biaxially in the radial and axial direction of the solid slug.

BACKGROUND OF THE INVENTION 
The present invention relates to a cold forming method and apparatus for 
producing a stepped hollow component such as, for example, a gear blank. 
In, for example, "Impact Machining", page 57, FIG. 3.19, Verson Co., 
Corona-Sha, a method is proposed which employs six press steps between the 
cutting of a metal bar and a final coining operation. More particularly, 
between the cutting and final coining operation at least two annealing 
steps and three lubrication treatments are required. Moreover, in the 
proposed method it is necessary to provide a relatively large capacity 
press in order to bear the heavy processing load which occurs particularly 
during rearward and forward extrusion steps; however, a disadvantage of 
the requirement for a large capacity press resides in the fact that a 
service life of the molds is significantly reduced by virtue of the high 
pressure applied to them during the press operation. Furthermore, an 
excessive number of steps in the proposed method tends to reduce a 
dimensional accuracy of the produced stepped hollow component. 
The aim underlying the present invention essentially resides in providing a 
method and apparatus for producing stepped hollow components, which method 
and apparatus reduce the processing load while also reducing the number of 
process steps to which the hollow components must be exposed thereby 
increasing the overall dimensional accuracy of the produced component. 
In accordance with advantageous features of the present invention, a 
stepped hollow article or component is attained by placing a solid slug 
provided with a disc portion and projecting portion in a rigid cylindrical 
recess, restraining an outer periphery of the disc portion and a side 
surface of the projectiong portion, and forming a closed-base hole in a 
center of the solid slug by a plastic deformation. 
Advantageously, in accordance with further features of the present 
invention, for the purposes of restraining the outer periphery of the disc 
portion and side surface of the projecting portion, an annular lower 
surface and the side surface of the disc portion are restrained and an 
annular upper surface of the disc portion is precompressed so as to 
simultaneously restrain the side surface of the projecting portion. 
In order to form the closed-base hole in the center of the solid slug, in 
accordance with the present invention, a press member is driven into the 
center of the projecting portion. Additionally, the press member may be 
driven to the point so as to punch out the base forming the closed hole in 
the center of the solid slug. 
The rigid cylindrical recess may, in accordance with the present invention, 
be formed between a hollow mold and a counter punch, with the hollow mold 
accommodating the disc portion and the counter punch being adapted to fit 
into a lower part of a central bore of the hollow mold. Advantageously, 
the precompressing of the annular upper surface of the disc portion is 
accomplished by an outer punch fitting into the central bore in the hollow 
mold so as to simultaneously restrain the side surface of the projecting 
portion. An inner punch, fitting into a central bore of the outer punch is 
independently driven into the center of the projecting portion, with the 
plastic deformation being caused by the inner punch whereby the material 
of the solid slug flows biaxially in the radial and axial directions of 
the solid slug. 
In accordance with advantageous features of the apparatus of the present 
invention, a first means is provided for mounting a solid slug provided 
with the disc portion and the projecting portion, with a second means 
being provided for accommodating the disc portion and the first means 
which is adapted to fit into the lower part of the central bore of the 
second means so that a recess is formed therebetween. Third means are 
adjustably fitted into the upper part of the central bore of the second 
means for precompressing an annular upper surface of the disc portion so 
as to restrain an outer periphery of the disc portion and the side surface 
of the projecting portion of the solid slug. A fourth means is fitted into 
a central bore of the third means and is driven independently for forming 
a closed base hole in a center of the projecting portion by plastic 
deformation which causes the material of the solid slug to flow biaxially 
in the radial and axial directions of the solid slug. 
Advantageously, in accordance with further features of the present 
invention, the third means is arranged to be moved upwardly so as to 
absorb excessive forces caused in an axial direction of the boss portion 
by the plastic flow of material when the fourth means is operated. 
An object of the present invention resides in providing a method and 
apparatus which enables the production of stepped hollow components with a 
high dimensional accuracy by using a minimum of processing steps in a low 
load by cold forming. 
Another object of the present invention resides in providing a method and 
apparatus which relies upon a biaxial plastic flow, namely, in radial and 
axial directions, so as to enable a reduction in the working pressure and 
ensure a high precision process and article. 
Another object of the present invention resides in providing a method and 
apparauts for producing a stepped hollow component which avoids, by simple 
means, shortcomings and disadvantages encountered in the prior art. 
Yet another object of the present invention resides in providing a method 
and apparatus for producing stepped hollow components which may be readily 
carried out without the use of large capacity presses. 
Yet another object of the present invention resides in providing a method 
and apparatus for producing a stepped hollow component which may be formed 
by a single press operation. 
A still further object of the present invention resides in providing a 
method and apparatus for producing a stepped hollow component by cold 
forming which enables a marked improvement in the overall production 
efficiency. 
These and other objects, features, and advantages of the present invention 
will become more apparent from the following description when taken in 
connection with the accompanying drawings which show, for the purposes of 
illustration only, several embodiments in accordance with the present 
invention.

DETAILED DESCRIPTION 
Referring now to the drawings wherein like reference numerals are used 
throughout the various views and, more particularly, to FIGS. 1-4, 
according to these figures, a cylindrical metallic member 1 is cut from a 
round metallic bar so as to have a predetermined volume or weight, with 
upper and lower end surfaces 1a, 1b of the cylindrical metallic member 1 
being displosed in parallel with each other. A solid slug 2 is formed from 
the cylindrical metallic member 1. For this purpose, the solid slug 2 is 
mounted in a hollow mold 11 in the manner shown most clearly in the left 
hand portion of FIG. 5 and is formed in the manner shown in the right hand 
portion of FIG. 5. The slug 2 is further processed in the manner shown in 
FIG. 6 so as to form a slug 3 with a central closed hole 3e. The slug 3 is 
formed into a stepped hollow component 4 by punching out of the base of 
the slug 3 by a press (not shown). 
As shown in FIG. 3, the slug 3 includes a disc-like flange portion 3a, 
having a lower surface portion 3d and an upper surface 3g, and a boss 
portion 3b in the form of an annular projection, with the boss portion 3b 
including an upper end surface 3c. A closed hole 3e is formed in a center 
of the boss portion 3b. 
As shown most clearly in FIG. 5, a cold forming apparatus for producing the 
stepped hollow component 4 includes a hard plate 13 fixed into a central 
bore formed in a pedestal 14 mounted on a rigid base 30, and a counter 
punch 12 mounted within the hard plate 13. A hollow mold 11 is placed on 
top of the hard plate 13 and is secured to the pedestal 14 by fastening 
member 15 which are, for example, threadably secured to the pedestal 14. 
The solid slug 2 is positioned in a recess formed by the hollow mold 11 
and an upper surface of the counter punch 12 fitting in the central bore. 
A movable pressurizing portion 10 is disposed above the hollow mold 11 and 
pressure in an oil passage 22, provided in a cylinder block 20, is 
increased by a pressure control member (not shown) to lower a piston block 
21 so that a lower end of the outer punch 16, attached to the lower end of 
the piston block 21, contacts the annular upper surface 2e of the solid 
slug 2 and the side surface 2f of the projecting portion thereby 
restraining the solid slug 2. Subsequently, as a pressure receiving member 
19 of a cylindrical member positioned within the central bore of the 
cylinder block 20 through a holder 18 is depressed or lowered, a lower end 
of the inner punch 17 comes into contact with the solid slug 2 so that it 
pushes the boss portion 3b backward while forming the flange portion 3a. 
More particularly, a plastic flow takes place not unit axially but 
biaxially in both the radial and axial direction. 
As shown in FIG. 6, while the hydraulically-operated outer punch 16 imparts 
a force .delta..sub.0 to the annular upper surface 2e of the solid slug 2, 
the material of this region flows in a direction of the arrows as a result 
of the lowering of the inner punch because the lower surface 2c is 
prevented from moving by the counter punch 12. Consequently, the outer 
configuration of the flange portion 3a of the slug 2 is changed from a 
barrel shape to a cylindrical shape, while the boss portion 2b is 
elongated in an upward direction so that the slug assumes the shape shown 
most clearly in FIG. 3. The pressure applied to the annular upper surface 
2e through the outer punch 16 is adjustable and the outer punch 16 is 
arranged so as to be moved upwardly so as to absorb the excessive force 
caused in the axial direction of the boss portion 3b by the plastic flow 
of the material when the inner punch 17 is lowered so that the region 
between the upper surface 3g of the flange portion 3a and the side surface 
3f of the boss portion 3b is free from the generation of cracks. 
Thereafter, a force applied to the pressure receiving surface 19 is relaxed 
so as to allow the cylinder block 20 to move upwardly and separate the 
outer punch 16 and the inner punch 17 from the slug 3, with the slug 3 
being removed as the counter punch 12 is raised by a push rod 32 provided 
in a central bore in the rigid base 30. The slug 3 can be removed from the 
hollow mold 11 without much difficulty if an application of oil and a 
punch-treatment are performed before the solid slug 2 is placed in the 
hollow mold 11. 
As shown in FIG. 4, in the stepped hollow component 4, a punched-out 
portion 4b in the lower part of the hole 4a is a region from which a waste 
part 5 has been removed and it has a smooth surface although an annular 
line remains. The punching out of the hole bottom can be accomplished 
easily by a simple press (not shown). Annealing is thereafter conducted to 
remove residual stresses and obtain the stepped hollow component 4 which 
is suitable for use as, for example, a gear blank in which teeth are cut 
in the flange portion. 
In accordance with the method of the present invention for producing a 
stepped hollow component 4, a slug with a flange portion 3a and a boss 
portion 3b can easily be obtained by the process which comprises the steps 
of placing a solid slug 2 provided with a disk portion and a projecting 
portion in the form of a cylindrical bar into a rigid cylindrical recess, 
restraining the annular upper surface of the disc portion and side surface 
of the projection portion by an annular edge of an outer punch 16, and 
driving an inner punch 17 into the center of the projecting portion. From 
this slug 3, a stepped hollow component 4 can easily be obtained simply by 
punching out the base of the hole into which the inner punch 17 was 
driven. 
One advantage of the method of the present invention over conventional 
methods resides in the fact that the flange portions 3a and boss portion 
3b of the stepped hollow component 4 with a closed central hole can be 
formed simultaneously in one action by a cold forming apparatus of the 
type illustrated in FIGS. 5 and 6 so that the production efficiency can be 
markedly improved. Moreover, in conventional methods which employ a 
plurality of steps, i.e., a plurality of annealings and a plurality of 
bonderizing treatments, in accordance with the method of the present 
invention, the annealing and bonderizing treatment need only be carried 
out once. 
Furthermore, since the hollow component 4 can, in accordance with the 
method and apparatus of the present invention, be formed by a single press 
operation, the number of molds is reduced and the pressure force can be 
adjusted to a minimum required level. More particularly, since plastic 
flow takes place not uniaxially but biaxially in the radial and axial 
direction, the working pressure is reduced so as to ensure a high 
precision process. 
FIGS. 7 and 8 provide another example of a stepped hollow component which 
may be produced in accordance with the method and apparatus of the present 
invention. More particularly, as shown in FIGS. 7 and 8, boss portions 6b, 
6c are formed on upper and lower sides of a flange portion 6a so that the 
slug 6 of FIGS. 7 and 8 differ from that of FIG. 3 in that a boss portion 
6c is also formed on a lower surface of the flange 6a. A closed hole 6d is 
formed, in the manner described hereinabove, by an inner punch 17 disposed 
above the slug 6. An upper surface of the counterpunch 12 described 
hereinabove is provided with a recess (not shown) for receiving or 
accommodating the boss portion 6c. The slug 6 is formed by the same 
process as that which produces the slug 3 of FIG. 3, that is, using the 
cold forming apparatus of FIG. 5. 
As shown in FIG. 8, by punching out a base of the closed hole 6d, it is 
possible to produce a stepped hollow component 7 from a relatively simple 
slug 6, with the stepped hollow component 7 being provided with a hole 7a, 
a punched portion 7e, and a punched out waste portion 8. 
By virtue of the method and apparatus for producing the stepped hollow 
component 7, it is possible to provide a stepped hollow component 7 having 
boss portions on both sides thereof, with the hollow component 7 being 
produced with a high efficiency and with good structural accuracy by using 
a counter punch of the same type that is used in the first described 
embodiment, with such counter punch being provided, on an upper surface 
thereof, with a recess for receiving or accommodating the lower boss 
portion 6c. 
While we have shown and described several embodiments in accordance with 
the present invention, it is understood that the same is not limited 
thereto, but is susceptible of numerous changes and modifications as known 
to one having ordinary skill in the art and we therefore do not wish to be 
limited to the details shown and described herein, but intend to cover all 
such modifications as are encompassed by the scope of the appended claims.