U.S. patent application number 11/686705 was filed with the patent office on 2007-09-06 for method and apparatus for plastic working of hollow rack bar and hollow rack bar.
This patent application is currently assigned to Minako Matsuoka. Invention is credited to Seiji Shiokawa.
Application Number | 20070204668 11/686705 |
Document ID | / |
Family ID | 37969713 |
Filed Date | 2007-09-06 |
United States Patent
Application |
20070204668 |
Kind Code |
A1 |
Shiokawa; Seiji |
September 6, 2007 |
METHOD AND APPARATUS FOR PLASTIC WORKING OF HOLLOW RACK BAR AND
HOLLOW RACK BAR
Abstract
A preparatory working device by which a work piece to be fed to
a rack bar forging device is obtained. The device is provided with
a die sets for obtaining a diameter reduction at a location of a
blank pipe, which becomes a toothed part of a rack bar, while the
wall thickness being substantially unchanged or slightly increased.
The device is further provided with a die set for reducing a wall
thickness at a location of the blank pipe, which becomes a
connection part of the rack bar. The wall thickness reduction is
one half of the initial thickness, which causes the length of the
work piece to be elongated. Then a rack bar forging by a die set is
done.
Inventors: |
Shiokawa; Seiji;
(Mishima-shi, JP) |
Correspondence
Address: |
DITTHAVONG MORI & STEINER, P.C.
918 Prince St.
Alexandria
VA
22314
US
|
Assignee: |
Matsuoka; Minako
Mishima-shi
JP
Shiokawa; Hirohisa
Tokyo-to
JP
Shiokawa; Akimasa
Tokyo-to
JP
|
Family ID: |
37969713 |
Appl. No.: |
11/686705 |
Filed: |
March 15, 2007 |
Current U.S.
Class: |
72/370.15 |
Current CPC
Class: |
B21K 1/768 20130101;
B21K 1/767 20130101 |
Class at
Publication: |
72/370.15 |
International
Class: |
B21C 37/30 20060101
B21C037/30 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 3, 2006 |
JP |
2006-093190 |
Claims
1. Method for producing a rack bar comprising the steps of:
providing a work piece of pipe shape; subjecting the pipe shaped
work piece to plastic workings for adjusting wall thickness of the
work piece to desired values at the respective positions along the
length of the work piece corresponding to functions as required,
and; forging linearly spaced toothed portions on the work piece
after subjected to said wall thickness adjustment, thereby
obtaining a rack bar.
2. Method according to claim 1, wherein the adjustment of the wall
thickness values is done by a single integrated step.
3. Method according to claim 1, wherein the adjustment of the wall
thickness values is done by a plurality of divided steps.
4. Method for producing a rack bar comprising the steps of:
providing a work piece of pipe shape; subjecting the pipe shaped
work piece to plastic workings for reducing the wall thickness of
the work piece except at a location where the rack is to be formed,
while freeing the corresponding plastic extension of the work piece
along the length of the work piece, and; forging linearly spaced
toothed portions on the portion of the work piece of unchanged wall
thickness or slightly increased wall thickness after subjected to
said local wall thickness adjustment, thereby obtaining a rack
bar.
5. Method according to claim 4, wherein the adjustment of the wall
thickness values is done by a single integrated step.
6. Method according to claim 4, wherein the adjustment of the wall
thickness values is done by a plurality of divided steps.
7. In an apparatus for producing a rack bar from a pipe shaped work
piece, wherein the work piece is held by a die set having linearly
spaced toothed portions, and a mandrel is inserted to the work
piece so that toothed portion corresponding to the toothed portions
on the die set are forged to the pipe shaped work piece, the
improvement comprising a device for effecting an adjustment of the
wall thickness of the work piece to desired values at the
respective positions along the length of the work piece
corresponding to functions as required, prior to the execution of
the forging of the rack bar.
8. An apparatus according to claim 7, wherein said device
comprising: a die set including an elongated mandrel and a
plurality of dies, and; a driving means for moving the work piece
to the first die set for effecting the desired adjusting wall
thickness of the work piece.
9. A hollow rack bar used as a steering part of a vehicle, which is
forged from a pipe shaped blank, including a first portion of a
wall thickness, which substantially the same as or slightly
increased from the wall thickness of the blank pipe and a second
portion of a wall thickness, which is highly reduced from the wall
thickness of the blank pipe and which is elongated for a length
corresponding to the reduction of the wall thickness, the rack
portion being formed on the first portion of the blank pipe.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of Invention
[0002] The present invention relates to a production of rack bar in
a steering mechanism of a vehicle from a pipe shaped blank by
plastic working, and, more particularly, to its improvement, by
which an increased reduction in the weight of the product is
obtained in comparison with the prior art.
[0003] 2. Description of Related Art
[0004] A rack bar is a main part of a steering system of a vehicle
and has conventionally been produced by machining from a solid bar
of a rounded cross-sectional shape by using originally a hobbing
machine and recently a broaching machine. However, such a machining
from a solid bar of rounded cross-sectional shape makes the product
to be heavy. Therefore, a solution has been proposed, wherein the
machined product is subjected to a subsequent boring by using a gun
drill to obtain a hollow structure, thereby reducing the weight.
However, this solution makes the production cost to be increased on
one hand and, on the other hand, makes the resource consumption
efficiency to be reduced.
[0005] Thus, the applicants of this application et al have proposed
an improvement, wherein a plastic working (forging) of a pipe
shaped blank is done for obtaining a rack bar of a reduced weight
while keeping a reduced resource consumption as well as an
increased vehicle performance. In this rack forging technology, a
pipe shaped blank is held by a die set having toothed portions at a
side facing the blank and a mandrel is inserted into the hollow
space of the blank, so that toothed portions corresponding to those
of the die set are copied to the blank. See specifications of
Japanese Patent No. 3547378, Japanese Patent No. 3607204 and
Japanese Patent No. 3607205 and Japanese Un-Examined Patent
Publication (Kokai) No. 2006-026703.
[0006] In the prior art disclosed in above patents, pipe shaped
blanks just supplied by manufacturers of predetermined fixed wall
thickness of a value of about 4 mm are used. This predetermined
wall thickness of the blank pipe is decided by the tooth height
desired for the particular rack bar. In order to obtain an
increased tooth height of a rack bare, a blank pipe of in increased
wall thickness is needed at locations where the toothed portions
are created. In the prior art, a blank pipe of a uniform value of
wall thickness was used, resulting in an excessive wall thickness
at the locations other than the toothed portions. Thus, the prior
art is defective in an increased product weight and reduced
material consumption efficiency. Thus, a long felt need has been
existed as far as a reduced production cost, increased material
consumption efficiency and increased performance are concerned.
SUMMARY OF THE INVENTION
[0007] The present invention aims to overcome the above
difficulties in the prior art and, in particular, to provide a
technology, by which an effective use of the material along the
entire length of the blank is realized, a desired performance as a
rack bar is obtained and increased degrees of a weight reduction, a
cost performance, a resource saving and a vehicle performance is
realized.
[0008] According to the present invention, a method for forging a
of a rack bar of radially outwardly copied type is provided,
wherein a pipe shaped work piece is held by a die set, the material
of the work piece is plastically flown to the die set located
diametrically outward from the work piece in a manner that a
toothed shape of the die set is copied to the work piece. The
present invention features that an adjustment of the cross
sectional area of the work piece is preliminary done by a local
increase or decrease of wall thickness of the work piece prior to
the execution of the rack forging process of radial expanded copied
type. Namely, upon the execution of the preliminary adjustment of
the cross-sectional area, a work piece is subjected to plastic
workings for desirably increasing or decreasing the wall thickness
at the respective axial positions of the work piece along the
length thereof. As a result, desired values of cross-sectional area
corresponding to desired functions at the respective portions of
the work piece along its length are obtained.
[0009] The above mentioned adjustment of the wall thickness of work
piece at the respective portions along its length is carried out by
so-called swaging or ironing process under a single stage or a
plurality of divided stages.
[0010] An adjustment of the cross-sectional area according to the
present invention is carried out by an apparatus, which is
constructed by a combined die set having an elongated mandrel and a
plurality of dies and a vertical or horizontal hydraulic cylinder
mechanism, which is cooperated with the die set in a manner that a
desired local increase or decrease of the wall thickness of the
blank pipe is obtained at respective positions of the blank pipe
along its length. In place of the hydraulic cylinder mechanism, any
suitable reciprocating mechanism, such as a ball screw type, where
a rotating movement is converted to a linear movement, may be
employed.
[0011] In a power steering mechanism of an electric operated type,
a rack bar of VGR (variable gear ratio) type is usually used. In
this type of mechanism, it is needed that values of the pitch as
well as the inclination angle of toothed portions are varied along
the length. Such a construction of the VGR rack bar makes it
difficult that it is machined from a solid work piece. Therefore, a
forging from a pipe shaped blank is usually employed. Furthermore,
unlike the hydraulic operated type, the electric operated type
requires an increased bending strength of toothed portion, i.e., an
increased size of tooth part as well as an increased thickness.
[0012] The present invention can achieve this goal, while obtaining
the maximum reduction of the weight of a rack bar. Namely,
according to the present invention, a forging of toothed portions
is done by a radially outwardly directed plastic flow of metal of a
pipe shaped blank while preventing fibrous metals from being
broken. Under such principle of rack formation, an adjustment of
the cross sectional area of the blank pipe is essential and has
been done by a grinding. In contrast, according to the present
invention, a plastic working is done for obtaining a desired
increase or decrease in the wall thickness at locations along the
length of the work piece, so as to obtain desired values of
cross-sectional area, corresponding to the desired functions
required at the respective locations. In more detail, at the
location where a toothed form is to be formed, a wall thickness
corresponding to the wall thickness of the blank pipe is basically
maintained, so that a desired toothed shape is obtained under the
plastic flow, although a wall thickness increase by a diameter
reduction can be taken when it is necessary.
[0013] In comparison, at locations other than the location for the
formation of the toothed portions, a desired strength is obtained,
even when the wall thickness is smaller than the wall thickness of
the blank pipe. Therefore, according to the present invention, a
wall thickness reduction is done so long as a desired strength
within a permissible range is obtained. A wall thickness reduction
may be done by ironing, which causes the work piece to be axially
elongated. Namely, in the present invention, the length of the
product must be decided while an axial elongation as generated by
the reduction of the wall thickness of the blank pipe is taken into
the consideration. In other words, in the present invention, a
blank pipe of a reduced axial length for a value corresponding the
axial elongation can be used, resulting in a corresponding
reduction of the weight of product. Namely, in the prior art as in
'378, '204, '205 or '703 patent, the weight of a product is almost
equal to that of the blank pipe and is about 1,236 kg when the
blank of wall thickness of 4 mm and of a diameter of 25 mm has a
length of 615 mm. In contrast, in the present invention, the value
of wall thickness at toothed portions is maintained to that of the
blank pipe, i.e., 4 mm and the wall thickness of the portion other
than the toothed portion is reduced to 2 mm by an ironing process,
while keeping the desired strength of the product. Thus, according
to the present invention, it is possible to use a blank pipe of a
reduced length for a value corresponding to the lengthwise
elongation as generated by the ironing. The inventor has found that
a desired performance is obtained even when the length of a blank
pipe is reduced so that the weight of a blank pipe, i.e., the
weight of a product is reduced to 920 g, although the weight
reduction depends on a length of toothed portions having a value of
a wall thickness, corresponding to that of the blank pipe. In this
example, a weight reduction of the present invention is 25.6% over
the prior art as in '378, '204, '205 or '703 patent and is, even,
better than 60% over the prior art where a solid blank rather than
the pipe shaped blank is used. Irrespective of such an additional
process like a swaging or ironing for obtaining a cross sectional
area control, a substantial reduction of the cost is obtained.
Assuming that a material cost is 170 yen/kg, a resultant reduction
of the material cost would be (1.236-0.920).times.170=53.7 yen per
one product. In addition, the redemption cost of the die set would
be, at the most, 10 yen per one product. It will thus be understood
that a material cost reduction of about 48 yen per one product is
possible. Furthermore, as a result of a reduction of a weight of a
product, i.e., a rack bar, a resultant reduction in the weight of a
vehicle is obtained, which assists in an improvement of a drive
ability of the vehicle, on one hand, and, on the other hand, in a
reduction in a fuel consumption efficiency. The reduction in the
fuel consumption efficiency per one car would be minimal but is
significant in view of a huge automobile market, which might be
amount to 70,000,000 cars in worldwide.
[0014] Furthermore, as a result of the ironing after the swaging, a
highly improved surface roughness is obtained not only at the inner
surface but also at the outer surface, which allows a dimension to
be controlled within a tolerance of microns, thereby allowing a
increased product quality and precision to be easily obtained.
BRIEF EXPLANATION OF ATTACHED DRAWINGS
[0015] FIGS. 1a to 1e are schematic views of a series of stages for
producing a rack bar according to the present invention.
[0016] FIG. 2 is a schematic view of a process for forging a rack
bar from a pipe shaped blank by using a shuttle type rack bar
forging system.
[0017] FIGS. 3a to 3c are schematic views of a series of stages for
carrying out a diameter reduction of a blank pipe.
[0018] FIGS. 4a to 4g are schematic views of a series of stages for
carrying out a wall thickness reduction of a blank after subjected
to the diameter reduction process.
[0019] FIGS. 5a to 5d are schematic views of a series of stages for
obtaining, from an initial blank, under one shot principle, a
worked blank suitably for a supply to a subsequent rack bar forging
process.
BEST MODE FOR PRACTICING THE INVENTION
[0020] FIGS. 1a to 1e illustrates a series of steps or stages for
forming a rack bar according to the present invention. In FIG. 1a,
a reference numeral 10 denotes a blank pipe (intermediate part) or
a work piece supplied from a maker after subjected to a phosphate
coating process. In FIG. 1a, the wall thickness of a blank is
designated by to and its length by L.sub.0, respectively. In this
particular embodiment, the wall thickness t.sub.0 has a value of 4
mm, the material at a portion (tooth profile forming portion) of
the blank pipe of this value of wall thickness is subjected to
radially outwardly directed plastic flow, resulting in a formation
of toothed portions of desired values of height and strength.
[0021] At a second step as shown in FIG. 1b, a first stage diameter
reduction is done only at the tooth profile forming portion.
Namely, at the location 10' of the blank pipe of a predetermined
length from its left-hand end is subjected to a diameter reduction,
so that the wall thickness t.sub.1 is obtained, which is equal to
or slightly increased over the wall thickness to of the blank pipe.
Such a diameter reduction is done by a swaging process as will be
explained later. The length of the reduced diameter part 10'
corresponds to that of a toothed part 11 (FIG. 1e) of a rack bar.
The remaining portion, which was not subjected to the diameter
reduction, is designated by 10''.
[0022] At a third step as shown in FIG. 1c, a wall thickness
reduction is done at a part of a rack bar, which becomes a
connection part (axially extended part from the toothed part). As
illustrated above, a wall thickness t.sub.0 of 4 mm of a blank pipe
is suitable for the toothed part to obtain desired values of tooth
height and strength needed for a rack bar product after the
completion of a forging process. However, such a value of wall
thickness of 4 mm is excessive for the connection part in view of
its designated function, since the connection part is less stressed
when compared with the toothed part. Thus, a portion of a blank
pipe, which becomes a connection part of a rack bar as a forged
product, is subjected to a plastic working so that a wall thickness
reduction is done from t.sub.0 of a blank pipe to t.sub.2, which
is, for example, about 1/2 of t.sub.0, i.e.,
t.sub.2.apprxeq.0.5.times.t.sub.0 (=2 mm). For obtaining such a
wall thickness reduction, an ironing process may be employed, which
accompanies with an elongation of the blank pipe from a length of
L.sub.0 to L.sub.1. In short, in a blank pipe, as an axial
extension of a reduced diameter portion 10-1 of a wall thickness of
t.sub.1 corresponding to the portion 10' in FIG. 1b, a wall
thickness reduced portion 10-2 of a wall thickness of t.sub.2 is
formed as shown in FIG. 1c. The length L.sub.1 corresponds to a
length of a rack bar as a final product. In the prior art, a blank
pipe of a length corresponding to that of a product is needed.
Contrary to this, the length L.sub.1 corresponding to that a
product is obtained by a wall thickness reduction accompanied with
the corresponding axial elongation. Thus, an initial blank pipe of
a reduced length can be employed for a value corresponding to an
axial elongation as obtained during a wall thickness reduction
process. In short, in comparison with the prior art, a blank pipe
length can be reduced from a value of L.sub.1 to a value of
L.sub.0. Thus, a corresponding material consumption as well as
weight reduction are obtained, thereby obtaining a material cost
reduction as well as a running cost reduction.
[0023] In the third step shown in FIG. 1c, a relatively short
length portion 10-3 is left, which has a value of thickness to
corresponding to that of the initial blank pipe. This value of wall
thickness at the portion 10-3 is suitable for machining screw
threads for an engagement with a part of a steering mechanism.
Preferably, prior to such a machining, a process for a diameter
reduction is done so that a desired reduced value of inner diameter
is obtained, which is suitable for the machining.
[0024] Also in the third step in FIG. 1c, the reduced diameter
portion 10-1 is obtained by additionally reduce the diameter of the
portion 10' obtained at the second step in FIG. 2b.
[0025] At a fourth step shown in FIG. 1d, in the blank pipe as
obtained at the third step, a flattening is done at a location of
the blank pipe where toothed portions are to be formed. Namely, the
reduced diameter portion 10-1 of the blank is, at its upper surface
10-1A, flattened, resulting in a semi-circular cross-sectional
shape of the blank at the portion 10-1.
[0026] A fifth step is shown in FIG. 1e, where a forging of toothed
portions is done at the flattened portion 10-1A of the blank pipe.
Namely, the blank pipe is held by a die set and mandrels are
inserted to the blank pipe alternately between left-handed and
right-handed directions. As a result, a rack bar forging is done in
a manner that toothed portions on the die set are copied to the
blank pipe, so that toothed portions 11 are formed as shown in FIG.
1e. The rack bar fording may be done by a system as describe in any
of '378, '204, '205 and '703 patents. Namely, any of elongated type
mandrel as in '378, '204 or '205 patent or a shuttle type mandrel
as in '703 patent may be desirably used. In the embodiment, the
latter shuttle type mandrel as shown in FIG. 2 is used. Namely,
FIG. 2 shows a combined type die set for a rack bar forging, which
includes a bottom die 12 and a top die 14, between which the blank
pipe 10 is held. As explained in detail in '703 patent, short sized
mandrels (shuttles) 16a and 16b are arranged on the left-handed and
the right-handed sides of the die set. Outwardly from the shuttles
16a and 16b, pusher rods 17a and 17b are respectively arranged in a
manner that the pusher rods 17a and 17 engage, at respective ends,
with recesses 15a and 15b at the ends of the shuttles 16a and 16b.
The reduced diameter portion 10-1 of the blank pipe is arranged
between the upper and lower dies 12 and 14. Under a closed
condition between the dies, the upper wall 10-1A of the reduced
diameter portion 10-1 of the blank pipe is pressed by toothed
portion 14A of the upper die 14 and is substantially flattened,
thereby completing the flattening process as explained with
reference to FIG. 1d and allowing the rack forging process to be
instantly commenced. Namely, a reciprocating movement of the
shuttle shaped mandrels 16a and 16b by the pusher rods 17a and 17b
is obtained in a manner that the mandrels 16a and 16b are
alternately inserted to the blank pipe 10 held between the dies 12
and 14. As a result, the metal of the blank pipe at the diametric
reduced portion 10-1 is plastically flown radially outwardly toward
the toothed portions 14A of the upper die 14, so that a forging of
toothed portions on the flattened surface 10-1A of the diametric
reduced portion 10-1 of the blank pipe is done in a manner that the
toothed shape 11 of the die is copied to the blank pipe 10.
[0027] After the completion of the forging of the rack bar,
conventional processes for finishing to a product are done, which
includes a correction of a curving, additional swaging at both
ends, a working of grooves, a working of width-across-flat portion,
an inner diameter tapping, a quench-and-temper process, an outer
diameter machining, a test of meshed condition and anti-corrosive
treatment, et al. The thus obtained final product is wrapped and
shipped. Any more detailed explanation of these processes are
omitted, since they are not directly related with the essence of
the present invention.
[0028] Now, a diameter reduction process as schematically
illustrated in FIG. 1b and a wall thickness reducing process at a
connection portion as schematically illustrated in FIG. 1c, as
preliminary steps for a cross-sectional area adjustment process
prior to a rack bar forging process will be explained in more
detail. First, the diameter reduction process in FIG. 1b will be
explained in more detail with reference to FIGS. 3a to 3c. A die
set for practicing this step includes a die holder 20, a die set
constructed by a guide 22, a drawing die 23 and a squeezing die 24,
which are, in series, inserted to the holder 20, and a mandrel 26
of a three stepped shape. The mandrel 26 is connected to a
hydraulic cylinder mechanism (not shown). The mandrel 26 is formed
with a front portion 26-1 of reduced diameter and having a length
corresponding to that of the toothed portion 11 (FIG. 1e) of a rack
bar as a final product. Furthermore, the mandrel 26 is, at its rear
end, formed with a rear portion 26-2 of an increased diameter.
[0029] A diameter reduction process as practiced by the device
shown in FIGS. 3a to 3c will be explained. Namely, at the first
stage as shown in FIG. 3a, a blank pipe 10 after the completion of
a phosphate coating process is mounted to the mandrel 8. As
explained in FIG. 1a, the blank pipe 10 has a length of L.sub.0 and
a wall thickness of t.sub.0, which is uniform along the entire
length. The mandrel 26 is moved forward as shown by an arrow a in
FIG. 3a, which causes the blank pipe 10 to be pushed as shown by
arrows a' in FIG. 3b due to the fact that the diameter expanded
portion 26-2 of the mandrel 26 contacts, at its end surface
(shoulder), with the blank 10. As a result, the blank 10 is, first,
inserted into the die holder 20 and then into the guide 22 under a
guide action of a tapered portion 22A at the inlet end of the guide
22. During the movement in the guide 22, the blank 10 is
substantially not subjected to any plastic deformation, thereby
keeping the outer diameter of the blank pipe to be unchanged. In
other words, a small clearance exists between the inner diameter of
the blank pipe 10 and the front portion 26-1 of the mandrel 26.
[0030] A further forward movement of the blank 10 causes the latter
to be introduced into the drawing die 23 via its tapered inlet
portion 23A, so that the blank 10 is subjected to a diameter
reduction in a manner that a clearance with respect to the front
portion 26-1 of the mandrel 26 is diminished. In FIG. 3b, a portion
of the blank 10 thus subjected to diameter reduction is designated
by a reference numeral 10' and a portion of the blank 10 of the
original diameter not subjected to diameter reduction is designated
by a reference numeral 10''. The reduced diameter portion 10' has a
length, which corresponds to that of a toothed portion of a rack as
the final product. In short, a worked blank (intermediate product),
which corresponds to the work piece shown in FIG. 1b, is thus
obtained.
[0031] In this embodiment, the mandrel 26 is finally and
additionally moved in the forward direction as shown in FIG. 3c, so
that the reduced diameter portion 10' is, at its tip end, squeezed
by a die 24 and the squeezed portion of the work piece is
designated by a reference numeral 10'''. Although such a squeezed
portion 10''' is not shown in the corresponding FIG. 1b, it is used
for an engagement with a mandrel during a subsequent wall thickness
reduction process and is cut and removed after the completion of
the use.
[0032] FIGS. 4a to 4g illustrates the detail of a wall thickness
reduction process and a diameter reduction process at the
connecting portion of the rack bar as explained schematically in
FIG. 1c. A plastic working device for a wall thickness reduction is
provided, which includes a long stroke hydraulic cylinder device
(not shown), a mandrel 30 connected to the hydraulic cylinder
device so that the mandrel 30 is axially reciprocated, a die 32
cooperating with the mandrel 30 for a diameter reduction, and a
striker 34 for a diameter expansion at an axial end and which is
shown in FIG. 4a at its position radially outwardly retracted as
illustrated by arrows b'. The mandrel 30 forms a stepped member
constructed by an inlet or front part 30-1, an intermediate part
30-2 of an increased diameter connected to the part 30-1 and a rear
part 30-3 of a reduced diameter to that of the inlet part 30-1 for
a connection with a hydraulic mechanism (not shown). The inlet part
30-1 and the increased diameter part 30-2 have values of length,
which correspond, respectively, to those of a toothed part and a
connection part (shaft) of a rack bar as a final product.
[0033] FIG. 4a illustrates a condition of the plastic working
device, whereat a blank pipe 10 after subjected to the preliminary
diameter reduction process by the device in FIG. 3 is held by the
mandrel 30. As shown in FIG. 4a, the mandrel 30 has an outer
profile, which corresponds to an inner profile of the blank at an
area from the portion 10' to 10''. The inlet part 30-1 of the
mandrel 30 is, at its leading end, contacted with the squeezed part
10''' as obtained at the process as shown in FIG. 3c. Then, a
hydraulic pressure is introduced into the hydraulic cylinder
mechanism, causing its piston rod (not shown) to be extended, so
that the mandrel 30 in connection with the piston is moved
forwardly as shown by an arrow a. Due to the fact that the leading
end of the inlet part 30-1 of the mandrel is in contact with the
squeezed part 10''' of the mandrel 10, the blank 10 is entrained by
the movement of the mandrel 30 toward the die 32 as shown by the
arrow a. As a result, the blank 10 is introduced into the die 32
from the squeezed part 10'''. The portion 10' of the blank after
the squeezed part 10''' in the direction of its movement as shown
by the arrow a has a value of an outer diameter, which is slightly
larger than that of the inner diameter of the die 32. However, the
difference in these values substantially corresponds to a clearance
of the portion 10' with respect to the inlet part 30-1. Therefore,
the portion 10' is subjected to a slight diameter reduction and the
work piece is not substantially subjected to any wall thickness
reduction or is subjected only to a very slight wall thickness
reduction. Namely, it is shown in FIG. 4b that no wall thickness
change occurs in the portions 10''' and 10' even after the passage
of the die 32.
[0034] During the further forward movement of the mandrel 30, its
diameter expanded portion 30-2 is faced with the wall thickness
reduction die 32 via the portion 10'' of values of the wall
thickness and the outer diameter, which are substantially unchanged
with respect to those of the initial blank pipe. The portion 10''
has a value of an outer diameter, which is properly larger than
that of an inner diameter of the die 32 for a wall thickness of the
work piece. The difference of these values is, for example, about
one half of the wall thickness of the work piece. As a result, the
portion 10'' (FIG. 4a) of the blank is subjected to an ironing
operation by the die 32 during the forward movement of the blank as
shown by the arrow a, so that a wall thickness reduction as well as
an axial elongation are occurred in the portion 10'' of the blank.
This thin walled portion obtained from the portion 10'' on the
increased diameter portion 30-2 in FIG. 4a, which is passed through
the die 32A and is subjected to a wall thickness reduction, is
illustrated by 10-2 in FIG. 4b. In accordance with the progress of
this ironing process, the length portion 10'' of the work piece
located rearward from the die 32 and of the same wall thickness as
that of the initial blank pipe is gradually reduced, while moved
toward the connection portion 30-3 on the increased diameter
portion 30-2 of the mandrel 30. Finally, a relatively short length
of the portion 10'' of the same wall thickness as that of the
initial blank pipe is left on the connection portion 30-3 of the
mandrel under a condition that the portion 10'' is passed through
the die 32 as shown in FIG. 4b. At the extremity position in the
forward stroke of the mandrel as shown by the arrow a as shown in
FIG. 4b, the work piece is completely passed through the die 32 and
the rearward end surface of the blank 10 exceeds slightly from the
front end surface of the striker 34, which is under in its
retracted position.
[0035] At the next step as shown in FIG. 4c, the striker 34 is,
from the radially retracted position, moved radially inwardly as
shown by arrows b toward a position, whereat the front end of the
striker 34 is contacted with the connection part 30-3 of the
mandrel.
[0036] Then, a switching of the introduction of the hydraulic
cylinder mechanism is done in a manner that the mandrel 30 is
retracted in the right-handed direction as shown by an arrow c. Due
to the fact that the rear end portion 10'' of the blank 10 is
contacted with a shoulder portion 30-4 of the mandrel located
between the diameter expanded part 30-2 and the inner diameter
setting part 30-3, the blank 30 is entrained by the movement of the
mandrel 30 until the part 10'' is made contacted with the striker
34. However, when the rearward movement of the mandrel 30 in the
direction as shown by the arrow c is done until the portion 10'' is
made contact with the striker 34, the entrained movement of the
blank 10 is ceased due to the fact that the blank is engaged with
the striker 34, on one hand and, on the other hand, the rearward
movement of the mandrel 30 in the direction as shown by the arrow c
is continued. During such a rearward movement of the mandrel 30 in
the direction as shown by the arrow c, the large diameter part 30-2
is engaged with the part 10'' of the work piece, so that the latter
is radially outwardly displaced. Thus, at the rear end of the work
piece, a part 10-3 is formed as shown in FIG. 4d, which part has a
value of wall thickness nearly equal to that of an initial blank
pipe and which is radially outwardly expanded with respect to the
wall thickness reduced part 10-2. At the later stage, the part 10-3
may be subjected to a diameter reduction process, so as to obtain
an increased wall thickness, which is suitable for a subsequent
tapping operation. In FIG. 4d, a fully retracted position of the
mandrel 30 is illustrated.
[0037] At the following stage, the work piece in FIG. 4d after
subjected to the wall thickness reduction and the axial elongation
is subjected to the processes as shown in FIGS. 4e to 4g for
obtaining a diameter reduction (second stage diameter reduction) of
the work piece at location, which corresponds to a toothed part of
a rack bar as a product. Thus, a device for diameter reduction is
provided, which comprises a mandrel 36 and a die 37. The mandrel 36
is formed with a front part 36-1 of reduced diameter, a taper part
36-2 and a base part 36-3, which is in connection with a hydraulic
cylinder (not shown). At the first step in FIG. 4e, to the mandrel
36, the work piece as obtained at the step in FIG. 4d is
inserted.
[0038] An introduction of a hydraulic pressure to the hydraulic
cylinder causes the mandrel 36 to be moved forward, so that the
work piece on the mandrel 36 is introduced into the die 37. As a
result of the introduction of the mandrel into the die 37, the
portions 10''' and 10' of the work are subjected to a diameter
reduction for a value corresponding to a difference between the
inner diameter of die 37 and the outer diameter of the work.
[0039] FIG. 4f illustrates the most forwardly moved position of the
mandrel 36 with respect to the die 37, whereat the shoulder portion
36-2 of the mandrel 36 is faced with the die at its inlet end. The
part 10' (FIG. 4e) of the work is, at its entire length, subjected
to a diameter reduction while keeping the wall thickness being
unchanged, thereby obtaining a reduced diameter portion 10-1 as
shown in FIG. 4f having a tip end as illustrated by 10-1'. From
this extreme position, the mandrel 36 is retracted in the rearward
or reverse direction as shown by an arrow c in FIG. 4g. The part
10-1 of a reduced diameter as also illustrated in FIG. 1c is thus
obtained. Then, the tip end portion 10-1' needed only for the
engagement with the mandrel 36 during the execution of the diameter
reduction is now unnecessary and thus cut off. The part 10-1 of a
reduced diameter as also illustrated in FIG. 1c is thus obtained.
The worked blank pipe as illustrated in FIG. 1c is thus obtained.
The worked blank in FIG. 1c is then subjected to the processes of a
rack forging as already explained with reference to FIGS. 1d and
1e.
[0040] FIGS. 5a to 5d illustrate a second embodiment of the present
invention, wherein preliminary plastic working processes for
obtaining a work piece, i.e., a diameter reduction at a location
becoming a toothed part of a rack bar and a wall thickness
reduction as a location becoming a connection part (shaft part) of
the rack bar as illustrated in FIGS. 1b and 1c, respectively are
done under one shot principle from a blank pipe after subjected to
the phosphate coating process followed only by a squeezing at its
tip end. In this embodiment, a plastic working device is provided,
which is constructed by a die set 38 and a mandrel 39. The die set
is constructed by an outer cylindrical body (die holder) 40 and an
end-to-end connected structure of a series of members, which
includes a first guide cylinder 42, a squeeze die 44, a second
guide cylinder 46 and a diameter reduction die 48. The outer
cylindrical body 40 is, at its front end, formed with an inward
projected portion 40-1, with which the diameter reducing die 48
located at the front end of the end-to-end connected combined die
structure is engaged, while a retainer member 49 is screwed to the
rear end of the outer cylindrical body 40 in manner that the member
49 is engaged with the first guide cylinder 42 located at the rear
end of the end-to-end connected structure, so that the structure is
fixed to the outer cylindrical body 40. The first guide cylinder 42
has a front end 42A outwardly tapered for a smooth introduction of
the blank by the mandrel 39, which is followed by a remained part
of a uniformed inner diameter. The squeeze die 44 is formed with an
inner stepped part 44A, which is cooperated with the mandrel for
obtaining a wall thickness reduction of blank. The squeeze die 44
is connected, via the second guide cylinder 46 of an uniform inner
diameter, to diameter reducing die 48, which has a tapered par 48A,
which functions purely for diameter reduction of the tip end of the
blank while keeping its wall thickness. In short, the combined die
structure is cooperated with the mandrel 50 for carrying out the
designated working.
[0041] The mandrel 39 is formed with a rear large diameter part 50,
a middle diameter part 52 and a front small diameter part 52-2. The
mandrel 39 is connected with a hydraulic cylinder mechanism (not
shown) for obtaining a reciprocated movement of the mandrel 39. The
middle diameter part 52 is formed with a tapered part 52-1, from
which the small diameter part 52-2 is axially forwardly projected.
Finally, the plastic working device is further provided with a
blank knockout pin 54 for removing a product after completion of
the designated processes.
[0042] An operation of the second embodiment of the present
invention will now be explained. As illustrated with reference to
FIG. 1a, the work piece 10 is an original blank pipe supplied from
a maker, to which a phosphate coating process has been completed.
In addition, the work piece has been subjected a squeezing process
only at its leading end, while the remaining part is left at a
straight shape with a uniform wall thickness. The work piece (blank
pipe) 10 is introduced into the plastic working device by means of
the mandrel 39 moving in the left-handed direction as shown by an
arrow a in FIG. 5a. Namely, the mandrel receives the work piece 10
without substantial clearance at the middle diameter part 52 and
engages with the squeezed tip end 10a of the work piece at the
front small diameter part 52-2. As a result, the work piece 10 is
entrained by the forward movement of the mandrel 39 as shown by the
arrow a. However, any substantial working is not obtained, i.e.,
the diameter as well as the wall thickness of the work piece are
unchanged, until a condition is obtained, where the front end of
the work piece 10 is made contact with the stepped part 44A of the
squeezing die 44 as shown in FIG. 5a.
[0043] An introduction of the hydraulic pressure into the hydraulic
cylinder device for operating the mandrel is continued from the
condition as shown in FIG. 5a, so that the mandrel is moved
forwardly to a condition as shown in FIG. 5b, where the tapered
part 52-1 of the mandrel 39 is faced with the tapered part 44A of
the squeezing die 44. The mandrel 39 is further forwardly moved
from the condition as shown in FIG. 5b, which causes the blank 10
to be also forwardly moved, while the contact of the blank with the
squeezed part 10a. During the forward movement, the blank 10 is
passed through the die 44, so that the blank 10 is subjected to a
diameter reduction process. After the completion of the diameter
reduction process, the portion 10'''' of reduced diameter of the is
made substantial contact with the front small diameter part 52-2 of
the mandrel. However, the value of wall thickness of the portion
10'''' is slightly increased or substantially unchanged with
respect to the value of wall thickness of the initial blank.
However, the portion 10''''' of the blank, which is located on the
middle diameter part 52 of the mandrel and which is engaged with
the squeezing die 44, is subjected to a wall thickness reduction.
The remaining portion 10-3 of the blank located rearward from the
die 44 is not subjected to diameter reduction, i.e., the outer
diameter is maintained. However, this portion 10-3 of the unchanged
outer diameter of the blank is pushed back on the middle diameter
part 52 of the mandrel 39 in the rearward direction in accordance
with the progress of the wall thickness reduction by the squeezing
die 44. In short, a rearward push-back type wall thickness
reduction is done.
[0044] When the mandrel 39 is further moved in the forward
direction from the condition as shown in FIGS. 5b to 5c, a
cooperation of the middle diameter portion 52 of the mandrel with
the taper portion 44A of the die 44 is obtained, which causes the
blank pipe to be subjected to a wall thickness reduction, so that
the wall thickness reduced portion 10''''' is created, while the
portion 10-3 of the unchanged wall thickness is pushed back in the
rearward direction as shown by arrows b. As a result, an elongation
of the axial length of the work, which corresponds to the degree of
the wall thickness reduction, is obtained. The further forward
movement finally causes the blank to be engaged with the die 48 and
to be subjected to a diameter reduction, so that a reduced diameter
portion 10-1 of a substantially unchanged wall thickness is
projected out of the die 48 as shown in FIG. 5d. As a result, a
worked blank member of substantially the same as that explained
with reference to FIG. 1c, is created, which is constructed by a
diameter reduced part 10-1 of a value of wall thickness unchanged
with respect to that of the initial blank pipe (a part becoming a
toothed part of a rack bar as a final product), a wall thickness
reduced part 10-2 of a value of the thickness reduced, for example,
to one half of that of the blank pipe (a part becoming a connection
part of the rack bar as a final product) and an end part 10-3
having a cross sectional area allowing an additional tapping
working (a part for forming a screw portion for connection with an
adjacent part).
[0045] In short, this second embodiment is advantageous in that a
worked blank for forging a rack bar is obtained under one shot
process from a straight blank pipe while preparatory works are
eliminated except for a squeezing process at the tip end, resulting
in a high efficiency of the process.
[0046] In the embodiments as explained, the hydraulic cylinder
device for operating a mandrel is illustrated as horizontal type.
However, a hydraulic cylinder device of vertical type may also be
used. In addition, in place of such a hydraulic cylinder device, a
mechanism such as an elongated ball screw operated by a servomotor
of a variable velocity may also be used.
* * * * *