U.S. patent application number 12/125789 was filed with the patent office on 2008-11-27 for hot forming and in-situ cooling of metallic articles.
This patent application is currently assigned to HWASHIN CO., LTD.. Invention is credited to GI DONG LEE.
Application Number | 20080289393 12/125789 |
Document ID | / |
Family ID | 40071141 |
Filed Date | 2008-11-27 |
United States Patent
Application |
20080289393 |
Kind Code |
A1 |
LEE; GI DONG |
November 27, 2008 |
HOT FORMING AND IN-SITU COOLING OF METALLIC ARTICLES
Abstract
Disclosed herein is a hot forming method and apparatus that can
improve strength of a product via die operation. The hot forming
apparatus includes a lower die on which a workpiece is placed, an
upper die coupled to the lower die to press the workpiece, a holder
disposed between the upper and lower dies to form an inner space of
the workpiece, and a cooling unit to cool the workpiece. The hot
forming method includes coupling an upper die, a lower die and a
holder with a workpiece placed on the lower die, followed by
pressing the workpiece to perform a hot forming operation,
determining whether or not a preset time has elapsed after pressing
the workpiece, and cooling the workpiece by supplying a cooling
fluid around the workpiece, if the preset time has elapsed.
Inventors: |
LEE; GI DONG;
(YEONGCHEON-SI, KR) |
Correspondence
Address: |
KNOBBE MARTENS OLSON & BEAR LLP
2040 MAIN STREET, FOURTEENTH FLOOR
IRVINE
CA
92614
US
|
Assignee: |
HWASHIN CO., LTD.
YEONGCHEON-SI
KR
|
Family ID: |
40071141 |
Appl. No.: |
12/125789 |
Filed: |
May 22, 2008 |
Current U.S.
Class: |
72/342.2 ;
148/647; 72/342.1; 72/352; 72/358; 72/374 |
Current CPC
Class: |
B21D 22/025 20130101;
C21D 1/673 20130101; B21D 37/16 20130101; C21D 7/13 20130101; C21D
9/085 20130101 |
Class at
Publication: |
72/342.2 ;
72/374; 72/358; 72/352; 72/342.1; 148/647 |
International
Class: |
B21D 22/06 20060101
B21D022/06; C21D 8/00 20060101 C21D008/00; B21D 37/16 20060101
B21D037/16 |
Foreign Application Data
Date |
Code |
Application Number |
May 23, 2007 |
KR |
10-2007-0050418 |
Claims
1. A hot forming apparatus comprising: a lower die; an upper die
movable relative to the lower die, wherein the lower and upper dies
are configured to press a workpiece placed between the lower and
upper dies; a holder configured to hold the workpiece while placed
between the lower and upper dies; and a cooler configured to cool
the pressed workpiece while placed between the lower and upper
dies.
2. The apparatus according to claim 1, wherein the cooler is
configured to cool at least one of the lower die, the upper die,
and the holder.
3. The apparatus of claim 1, wherein the cooler is configured to
quench the workpiece so as to transform at least part of the
workpiece from austenite to martensite.
4. The apparatus according to claim 1, wherein the cooler
comprises: a cooling path provided in at least one of the lower
die, the upper die and the holder so as to flow a cooling fluid
therethrough; and a pump configured to pump the cooling fluid to
the cooling path.
5. The apparatus according to claim 4, wherein the cooling path
comprises a die path defined in the lower or upper die, and a
holder path defined in the holder.
6. The apparatus according to claim 5, wherein the holder path
comprises a suction path and an exhaust path surrounding the
suction path.
7. The apparatus according to claim 1, further comprising a guide
member provided between the lower and upper dies and configured to
guide movement of the upper die relative to the lower die.
8. The apparatus according to claim 1, wherein a space is defined
between the holder, the lower die and the upper die.
9. The apparatus according to claim 8, wherein the cooler comprises
a direct cooling path having an outlet configured to discharge
cooling fluid toward the space.
10. The apparatus according to claim 9, wherein the direct cooling
path is formed in at least one of the lower die, the upper die and
the holder.
11. The apparatus of claim 1, wherein the holder comprises an
insert configured to be inserted in the interior space of the
workpiece.
12. The apparatus of claim 1, wherein the holder comprises a
cam.
13. A hot forming method comprising: providing an apparatus
comprising an upper die, a lower die and a holder; holding a
workpiece with the holder between the upper die and the lower die;
moving the upper die relative to the lower die and pressing the
workpiece so as to perform a hot forming operation; maintaining
pressing of the workpiece for a predetermined time; and cooling
in-situ the pressed workpiece with a cooling fluid.
14. The method according to claim 13, wherein cooling comprises
quenching the workpiece to transform at least part of the workpiece
from austenite to martensite.
15. The method according to claim 13, wherein cooling comprises
circulating a cooling fluid through a cooling path formed in at
least one of the upper die, the lower die and the holder.
16. The method of claim 13, wherein the holder comprises an insert
which is inserted in the interior space of the workpiece.
17. The method according to claim 13, wherein cooling comprises
contacting the workpiece with a cooling fluid.
18. The method according to claim 13, further comprising
determining that the pressed workpiece reached a predetermined
temperature.
Description
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS
[0001] This application claims priority to and the benefit of
Korean Patent Application No. 10-2007-0050418, filed May 23, 2007,
the disclosure of which is incorporated herein by reference in its
entirety.
BACKGROUND
[0002] 1. Field
[0003] The present disclosure relates to hot forming of metallic
articles, and more particularly, to hot forming and cooling in-situ
of metallic articles.
[0004] 2. Description of the Related Technology
[0005] Although various kinds of products can be produced by hot
forming methods and apparatus, a torsion beam of a rear torsion
beam axle suspension for a vehicle will be described herein as one
example of the products produced thereby.
[0006] The torsion beam axle suspension is generally constituted by
the torsion beam and trailing arms attached to opposite ends of the
torsion beam, and serves to maintain a posture of the vehicle with
torsion of the torsion beam with respect to a centrifugal force
applied to a vehicle body upon cornering of the vehicle. Therefore,
the torsion beam is required to have a high torsion and bending
rigidity.
[0007] Initially, the torsion beam was formed by bending an iron
plate to have a U-shaped or V-shaped cross-section, and provided
therein with a torsion bar for reinforcement thereof, with the
opposite ends of the torsion beam welded to the trailing arms via a
separate reinforcing plate to ensure the high torsion and bending
rigidity.
[0008] With such a configuration, although the torsion beam can
satisfactorily meet the requirement of the high torsion and bending
rigidity by the reinforced strength, it has problems in that the
increased number of components, such as the torsion bar and the
reinforcing plate, and the increased number of assembling and
welding processes result in a significant reduction in
productivity, a very high frequency of defective products caused by
difficulty in tolerance management in welding, and reduction in
fuel efficiency of the vehicle by an increase in weight of the
final product.
[0009] The foregoing discussion is to provide general background
information, and does not constitute an admission of prior art.
SUMMARY
[0010] One aspect of the invention provides a hot forming apparatus
comprising: a lower die; an upper die movable relative to the lower
die, wherein the lower and upper dies are configured to press a
workpiece placed between the lower and upper dies; a holder
configured to hold the workpiece while placed between the lower and
upper dies; and a cooler configured to cool the pressed workpiece
while placed between the lower and upper dies.
[0011] In the foregoing apparatus, the cooler may be configured to
cool at least one of the lower die, the upper die, and the holder.
The cooler may be configured to quench the workpiece so as to
transform at least part of the workpiece from austenite to
martensite. The cooler may comprise a cooling path provided in at
least one of the lower die, the upper die and the holder so as to
flow a cooling fluid therethrough and a pump configured to pump the
cooling fluid to the cooling path. The cooling path may comprise a
die path defined in the lower or upper die, and a holder path
defined in the holder. The holder path may comprise a suction path
and an exhaust path surrounding the suction path.
[0012] Further in the foregoing apparatus, the apparatus may
further comprise a guide member provided between the lower and
upper dies and configured to guide movement of the upper die
relative to the lower die. A space may be defined between the
holder, the lower die and the upper die. The cooler may be a direct
cooling path having an outlet configured to discharge cooling fluid
toward the space. The direct cooling path may be formed in at least
one of the lower die, the upper die and the holder. The holder may
comprise an insert configured to be inserted in the interior space
of the workpiece. The holder may comprise a cam.
[0013] Another aspect of the invention provides a hot forming
method comprising: providing an apparatus comprising an upper die,
a lower die and a holder; holding a workpiece with the holder
between the upper die and the lower die; moving the upper die
relative to the lower die and pressing the workpiece so as to
perform a hot forming operation; maintaining pressing of the
workpiece for a predetermined time; and cooling in-situ the pressed
workpiece with a cooling fluid.
[0014] In the foregoing method, cooling may comprise quenching the
workpiece to transform at least part of the workpiece from
austenite to martensite. Cooling may comprise circulating a cooling
fluid through a cooling path formed in at least one of the upper
die, the lower die and the holder. The holder may comprise an
insert which is inserted in the interior space of the workpiece.
Cooling may comprise contacting the workpiece with a cooling fluid.
The method may further comprise determining that the pressed
workpiece reached a predetermined temperature.
[0015] An aspect of the present invention is to provide a hot
forming method and apparatus that can produce a product having a
bilateral symmetry.
[0016] It is another aspect of the present invention to provide the
hot forming method and apparatus that can improve the strength of
the product produced by die operation.
[0017] It is yet another aspect of the present invention to provide
the hot forming method and apparatus that can reduce occurrence of
defective products caused by shape deformation in die
operation.
[0018] In accordance with one aspect of the present invention, a
hot forming apparatus comprises: a lower die on which a workpiece
is placed; an upper die coupled to the lower die to press the
workpiece; a holder disposed between the upper and lower dies to
form an inner space of the workpiece; and a cooling unit to cool
the workpiece.
[0019] Preferably, the cooling unit is provided to at least one of
the lower die, the upper die, and the holder. Preferably, the
cooling unit is formed in the lower die, the upper die or the
holder.
[0020] The cooling unit may comprise a cooling path through which a
cooling fluid is supplied to transform structure of the workpiece
from austenite to martensite; a pump to supply the cooling fluid
into the cooling path; and a cooling pipe connecting the cooling
path to the pump. Preferably, the cooling path comprises a die path
defined inside the lower and upper dies; and a holder path defined
inside the holder. Preferably, the holder path comprises a suction
path and an exhaust path surrounding the suction path with an inner
wall of the exhaust path separated a predetermined distance from an
outer wall of the suction path.
[0021] Preferably, the apparatus further comprises a guide member
provided between the lower and upper dies.
[0022] Preferably, a space section is defined between the holder,
the lower die and the upper die.
[0023] Preferably, the apparatus further comprises a direct cooling
path to supply the cooling fluid to the space section.
[0024] Preferably, the direct cooling path is formed in at least
one of the lower die, the upper die and the holder.
[0025] In accordance with another aspect of the present invention,
a hot forming method comprises: coupling an upper die, a lower die
and a holder with a workpiece placed on the lower die, followed by
pressing the workpiece to perform a hot forming operation;
determining whether or not a preset time has elapsed after pressing
the workpiece; and cooling the workpiece by supplying a cooling
fluid around the workpiece, if the preset time has elapsed.
[0026] The cooling step may comprise quenching the workpiece to
have a predetermined temperature or less within a predetermined
time to transform structure of the workpiece from austenite to
martensite.
[0027] The cooling step may comprise circulating the cooling fluid
into at least one of the upper die, the lower die and the holder.
Preferably, the cooling step comprises circulating the cooling
fluid into the lower die, the upper die or the holder. In other
words, the present invention can be realized in various
modifications, for example, cooling the workpiece by circulating
the cooling fluid into at least one of the upper die, the lower die
and the holder, and alternatively, cooling the workpiece by
sequentially circulating the cooling fluid.
[0028] Preferably, the cooling step comprises supplying the cooling
fluid into a path defined between the holder, the upper die and the
lower die to make the cooling fluid contact the workpiece.
[0029] The method may further comprise: determining whether or not
the workpiece has a predetermined temperature or less after the
cooling step; and separating the upper die, the lower die and the
holder to eject the workpiece, if the workpiece has the
predetermined temperature or less.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] The above and other aspect, features and advantages of the
present invention will become apparent from the following
description of exemplary embodiments given in conjunction with the
accompanying drawings, in which:
[0031] FIG. 1 is a perspective view of a hot forming apparatus
according to one embodiment of the present invention;
[0032] FIG. 2 is a front sectional view illustrating a cooling path
of the hot forming apparatus according to one embodiment of the
present invention;
[0033] FIG. 3 is a side sectional view illustrating a cooling path
of a hot forming apparatus according to one embodiment of the
present invention;
[0034] FIG. 4 is a side sectional view illustrating a holder path
of the hot forming apparatus according to one embodiment of the
present invention;
[0035] FIG. 5 is a flow chart of a hot forming method according to
one embodiment of the present invention; and
[0036] FIG. 6 is a perspective view of a torsion beam produced by
the hot forming apparatus and method according to one embodiment of
the present invention;
[0037] FIG. 7 is a cross-sectional view taken along line A-A of
FIG. 6;
[0038] FIG. 8 is a cross-sectional view taken along line B-B of
FIG. 6; and
[0039] FIG. 9 is a cross-sectional view taken along line C-C of
FIG. 6.
DETAILED DESCRIPTION OF EMBODIMENTS
[0040] Embodiments of the present invention will be described in
detail with reference to the accompanying drawings. For descriptive
convenience, embodiments will be described based on a method of hot
forming a rear torsion beam axle suspension for a vehicle. The
drawings may be exaggerated in thickness of lines or size of
components for the purpose of descriptive convenience and clarity.
Furthermore, terms used herein should be defined in consideration
of functions of components of embodiments of the present invention
and thus can be changed according to the custom or intention of
users or operators. Therefore, definition of such terms should be
determined according to overall disclosures set forth herein.
Herein, the words "a," "an," and "the" are used interchangeably
with "at least one" to mean one or more of the elements being
described.
[0041] A torsion beam is formed by pressing a cylindrical pipe to
have a two-folded U-shaped or V-shaped cross-section at a central
region of the torsion beam for ensuring the torsion rigidity and to
have a -shaped cross-section at either side thereof for ensuring
the bending rigidity and a wide welding area with respect to the
trailing arm. With this configuration of the torsion beam, since
the torsion beam axle suspension permits reduction in the number of
components and processes such as assembling and welding while
ensuring sufficient torsion and bending rigidity, it is believed
that it can improve the productivity and the fuel efficiency of the
vehicle by weight reduction while reducing the frequency of
defective products, as compared with the typical torsion beam.
[0042] In forming the torsion beam to have such different
cross-sectional shapes at the different portions, since an increase
in the number of processes leads to a decrease in productivity and
an increase in manufacturing costs resulting in low price
competitiveness, it is desirable to obtain the torsion beam with a
minimal number of processes.
[0043] As a method and apparatus for producing products having the
U-shaped or V-shaped cross-section by pressing the cylindrical
pipe, it is known in the art to employ two sets of dies that
include lower dies having different shapes, or a single set of dies
that includes a single upper die and several lower dies moving to
one another.
[0044] The method using the two sets of dies comprises a primary
preform process and a secondary precision process, which are
performed with the pipe firmly secured by a mandrel at an initial
stage. The method using the single set of dies is performed by a
lathe-shaped upper die and the lower dies, which are divided into a
single middle-set of lower dies and two side-sets of lower dies,
which move to one another along a guide plane defined between the
lower dies and the upper die or between the lower dies. With these
methods and apparatus, it is believed that the product having the
overall U-shaped or V-shaped cross-section can be satisfactorily
produced. Additionally, when applied to the product having
different cross-sectional shapes at different portions as in the
torsion beam of the rear torsion beam axle suspension, these
methods and apparatus are believed to produce the product with a
minimal number of processes.
[0045] However, when forming the product, such as the torsion beam
of the torsion beam axle suspension, which has the different
cross-sectional shapes formed at the different portions and
continuously connected to one another, the method and apparatus as
described above may have a problem in that either end or a
deformable portion of the product is prone to be deformed or
damaged in die operation, since it is difficult to increase the
strength of the either end or the deformable portion over a
predetermined value.
[0046] FIG. 1 is a perspective view of a hot forming apparatus
according to one embodiment of the present invention, and FIG. 2 is
a front sectional view illustrating a cooling path of the hot
forming apparatus according to one embodiment of the present
invention.
[0047] Referring to FIGS. 1 and 2, the hot forming apparatus
according to one embodiment comprises a base 10, a lower die 30
disposed on the base 10 such that a workpiece can be placed on the
lower die 30, an upper die 20 movably disposed on the base 10 and
coupled to the lower die 30 for hot forming of the workpiece,
holders or side cores 40 movably disposed on the base 10 and
interposed between the upper die 20 and the lower die 30 to form a
hollow of the workpiece, and a cooling unit 50 provided to the
lower die 30, the upper die 20 and the holders 40 to cool the
workpiece after hot forming. In one embodiment, the holder has an
insert. In another embodiment, the holder has a cam.
[0048] The base 10 comprises a lower base 12 disposed on the floor
and having the lower die 30 mounted on the lower base 12, and an
upper base 14 located above the lower base 12 to be moved by a base
cylinder 16 in a perpendicular direction and having the upper die
20 mounted on the upper base 14.
[0049] When the upper base 14 and the upper die 20 are lowered by
driving the base cylinder 16 with a workpiece placed on the lower
die 30, the upper die 20 is coupled to the lower die 30, enabling a
press operation to be performed by the dies.
[0050] The upper and lower dies 20 and 30 are heated to a
predetermined temperature or more for hot forming of the workpiece.
A heating device (not shown) to heat the dies is well known to
those skilled in the art, and detailed description thereof will be
omitted hereinafter. Further, since the base cylinder 16 is a
hydraulic cylinder well also known in the art, detailed description
of the base cylinder and an operation thereof will be omitted
hereinafter.
[0051] A guide member 32 is provided between the lower die 30 and
the upper die 20 to assist in precise coupling between the upper
and lower dies 20 and 30.
[0052] Further, the guide member 32 serves to ensure the workpiece
is correctly placed at the center of the lower die 30, so that a
completed product can have a precise bilateral symmetry.
[0053] The guide member 32 is constituted by a guide piece that has
a certain size and is placed on an edge of a depression of the
lower die 30 where the workpiece will be seated. The guide piece
constituting the guide member 32 is coupled to an upper surface of
the lower die 30 by means of typical fastening members such as
bolts, rivets, etc.
[0054] The holders 40 are respectively provided to a pair of
cylinders 42 disposed horizontally on an upper surface of the lower
base 12.
[0055] When an arm of each cylinder 42 is protruded from the
cylinder 42, the holder 40 provided to an end of the arm is
interposed between the upper and lower dies 20 and 30, and when the
arm is inserted into the cylinder 42, the holder 40 is moved
outside a space defined between the upper and lower dies 20 and
30.
[0056] In the apparatus with such a configuration as described
above, when the cylinders 42 are driven with a pipe-shaped
workpiece seated on the lower die 30, the holders 40 are inserted
into opposite ends of the workpiece, respectively.
[0057] Then, when the base cylinder 16 is driven, the upper die 20
is lowered and coupled to the lower die 30, followed by hot forming
of the workpiece to produce a desired product, that is, a torsion
beam 70.
[0058] As described above, since the die machine including the
upper die 20, lower die 30, and holder 40 for manufacturing a
pipe-shaped beam is well known in the art, an exploded perspective
view of the upper die 20, lower die 30, and holders 40 is omitted
herein.
[0059] The cooling unit 50 is formed inside at least one of the
upper die 20, the lower die 30 and the holders 40. The cooling unit
50 comprises a cooling path 52 through which a cooling fluid is
supplied, a pump (not shown) to supply the cooling fluid into the
cooling path, 52, a cooling pipe 54 connecting the cooling path 52
to the pump, and a fluid tank (not shown) filled with the cooling
fluid and connected to the cooling pipe 54. The cooling path 52 is
disposed to transform the structure of the torsion beam 70 from
austenite formed by the hot forming operation to martensite with
the cooling fluid flowing through the cooling path 52. Preferably,
the cooling path 52 is disposed in the lower die 30, the upper die
20 or the holders 40 to allow quenching of the torsion beam. More
preferably, a plurality of cooling paths 52 are provided into the
lower die 30, the upper die 20 or the holders 40.
[0060] The cooling path 52 comprises a die path 52a defined inside
each of the upper and lower dies 20 and 30, and a holder path 52b
defined inside each of the holders 40.
[0061] The cooling pipe 54 comprises die pipes 54a extending from
the tank to the upper and lower dies 20 and 30, and holder pipes
54b extending from the tank to the holders 40.
[0062] The cooling pipe 54 is provided at a portion extending from
the tank with a valve 56, from which the cooling pipe 54 is divided
into the die pipes 54a and the holder pipes 54b.
[0063] With this configuration, when the pump is driven after the
hot forming, the cooling fluid is supplied along the cooling path
54 defined inside the lower die 30, the upper die 20 and the
holders 40, quenching the torsion beam 70 located between the lower
die 30, the upper die 20 and the holders 40 to have a predetermined
temperature or less.
[0064] The holder path 52b comprises a suction path 52c extending
from one end, that is, a suction port, of the holder 40 and an
exhaust path 52d surrounding the suction path 52c with an inner
wall of the exhaust path 52d separated a predetermined distance
from an outer wall of the suction path 52c.
[0065] Therefore, after being induced into the suction port of the
holder 40, the cooling fluid flows to the other end of the holder
40 along the suction path 52c, is discharged from the suction path
52c, flows along a space defined between the outer wall of the
suction path 52c and the inner wall of the exhaust path 52d, and is
finally discharged outside the holder 40.
[0066] The holder 40 has a square cross-sectional outer end, which
corresponds to the cylinder 42, and is gradually decreased in
cross-sectional area toward an inner center thereof.
[0067] The holder 40 has a V-shaped depression of which
cross-sectional area is decreased toward the inner center, so that
the torsion beam 70 can be formed to have a desired shape.
[0068] FIG. 3 is a side sectional view illustrating a cooling path
of a hot forming apparatus according to another embodiment of the
present invention, and FIG. 4 is a side sectional view illustrating
a holder path of the hot forming apparatus according to one
embodiment.
[0069] Referring to FIGS. 3 and 4, the hot forming apparatus
according to this embodiment is similar to the above embodiment in
that this embodiment also comprises a lower die 130, an upper die
120, holders 140, and a cooling unit 150. However, the cooling unit
150 of the hot forming apparatus according to this embodiment can
be differentiated from the cooling unit of the above embodiment in
view of various features.
[0070] The cooling unit 150 comprises a space section 100 defined
between each holder 140, the lower die 130 and the upper die
120.
[0071] According to this embodiment, the hot forming apparatus
further comprises a direct cooling path 110 to supply a cooling
fluid into the space section 100.
[0072] Therefore, the cooling fluid supplied along the direct
cooling fluid 110 to cool a torsion beam 70 facilitates cooling of
the torsion beam 70 by a direct contact with the torsion beam 70
after flowing into the space section 100.
[0073] Such a configuration and operation can facilitate
transformation of the microstructure of the torsion beam 70 from
austenite to martensite, allowing more effective reinforcement of
the torsion beam 70.
[0074] The direct cooling path 110 may be formed in at least one of
the lower die 130, the upper die 120 and the holder 140. In this
embodiment, the direct cooling path 110 is shown as being formed in
the holder 140.
[0075] However, the direct cooling path 110 may be formed in the
upper die 120 or the lower die 130. Alternatively, the direct
cooling path 11 may be formed by coupling grooves in each of the
components.
[0076] In the case where the direct cooling path 110 is formed in
the holder 140, preferably, the direct cooling path 110 extend from
an upper surface of the holder 140 into the holder 140 and is bent
to extend to the space section 100 between holder paths 152b such
that the direct cooling path 110 is communicated with the space
section 100.
[0077] Next, a hot forming method with the apparatus having the
configuration according to one embodiment of the present invention
will be described.
[0078] FIG. 5 is a flow chart of the hot forming method according
to one embodiment of the present invention, FIG. 6 is a perspective
view of a torsion beam produced by the hot forming apparatus and
method according to this embodiment, FIG. 7 is a cross-sectional
view taken along line A-A of FIG. 6, FIG. 8 is a cross-sectional
view taken along line B-B of FIG. 6, and FIG. 9 is a
cross-sectional view taken along line C-C of FIG. 6.
[0079] Referring to FIG. 5 to 9, the hot forming method of this
embodiment comprises coupling the upper die 20, the lower die 30
and the holders 40, with a workpiece placed on the lower die 30,
followed by pressing the workpiece to produce a torsion beam 70 by
a hot forming operation (hereinafter, pressing operation S10),
determining whether or not a preset time has elapsed after the
pressing operation S10 (hereinafter, hot forming completion
determining operation S20), cooling the torsion beam 70 by
supplying a cooling fluid around the torsion beam 70 (hereinafter,
cooling operation S30) if it is determined in the hot forming
completion determining operation S20 that the preset time has
elapsed, determining whether or not the torsion beam 70 has a
predetermined temperature or less after the cooling operation S30
(hereinafter, temperature determining operation S40), and
separating the upper die 20, the lower die 30 and the holders 40 to
eject the torsion beam 70 (hereinafter, separating operation S50)
if it is determined in the temperature determining operation S40
that the torsion beam 70 has the predetermined temperature or
less.
[0080] Hereinafter, the hot forming method of this embodiment will
be described in detail.
[0081] First, when the cylinders 42 are driven with a pipe-shaped
workpiece of metal seated on the lower die 30, the holders 40 are
inserted into the opposite ends of the workpiece.
[0082] As the base cylinder 16 is driven, the upper die 20 is
coupled to the lower die 30, followed by performing the pressing
operation S10 to produce the torsion beam 70.
[0083] At this time, the upper die 20, lower die 30 and holders 40
are heated at 600.about.900.degree. C. for the hot forming
operation.
[0084] The hot forming completion determining operation S20 is a
process to measure time for which hot forming is performed, and can
be performed by means of a typical time measuring device such as a
timer.
[0085] If it is determined in the hot forming completion
determining operation S20 that the preset time has elapsed, the
pump is driven to allow a cooling fluid to be supplied into the
lower die 30, the upper die 20 and the holders 40 along the cooling
pipes 54 and the cooling path 52, so that the cooling operation S30
can be performed for quenching the torsion beam 70.
[0086] Additionally, after being induced into the holders 40
through the holder pipes 54b, the cooling fluid flows to an inner
end of each of the holders 40 along the suction path 52c, is
discharged from the suction path 52c, flows along a space defined
between the suction path 52c and the exhaust path 52d, and is
finally discharged outside the holder 40.
[0087] In this manner, the torsion beam 70 is subjected to
quenching to have a temperature of 100.about.350.degree. C. within
about 1 second.
[0088] By such a cooling operation S30, the temperature of the
torsion beam 70 is lowered below a predetermined temperature or
less within a preset time to transform the structure of the torsion
beam 70 from austenite to martensite, thereby improving the
strength of the torsion beam 70.
[0089] At this time, the cooling fluid cools the torsion beam 70
while circulating through the lower die 30, upper die 20 and
holders 40.
[0090] Alternatively, the cooling operation S30 can be performed by
circulating the cooling fluid only into the lower and upper dies 30
and 20 or only into the lower die 30.
[0091] Additionally, the cooling operation S30 may further comprise
direct supplying the cooling fluid to the torsion beam 70 to
accelerate the cooling rate to further facilitate transformation of
the workpiece to the martensite structure.
[0092] For this purpose, the hot forming method may be performed
using the hot forming apparatus according to the embodiment as
shown in FIGS. 3 and 4.
[0093] In this method, when the cooling step S30 is started, a
cooling fluid is simultaneously supplied to the cooling path 152
and to the space section 100 along the direct cooling path 110.
[0094] Therefore, as the upper die 120, lower die 130 and holders
140 are cooled, the torsion beam 70 in contact with the upper die
120, lower die 130 and holders 140 is rapidly cooled. Here, the
cooling fluid supplied into the space section 100 is brought into
contact with the torsion beam 70 and accelerates cooling of the
torsion beam 70, so that a more effective cooling operation can be
obtained.
[0095] The temperature determining operation S40 is a process to
measure time for which the cooling fluid is supplied, and can be
performed using the typical time measuring device as in the hot
forming completion determining operation S20. If it is determined
in the temperature determining operation S40 that a preset time has
elapsed, manufacture of the torsion beam 70 is completed by
completing the cooling operation S30.
[0096] Then, the separating operation S50 is performed in such a
fashion that the base cylinder 16 and the cylinders 42 are driven
in the counterclockwise direction to separate the upper die 20 and
the lower die 30 while the holders 40 are separated from the
opposite ends of the torsion beam 70.
[0097] With such a configuration and operation of the apparatus as
described above, the torsion beam 70 is formed to have a
square-shaped cross-section at either end 74, a V-shaped
cross-section at a middle region 72 with upper and lower surfaces
brought into close contact with each other, and a combination of
the square-shaped cross-section and a V-shaped groove at a
connection region 76 between the middle region 72 and either end 74
in which the V-shaped groove of the connection region 76 is formed
on an upper center thereof.
[0098] As apparent from the above description, the hot forming
apparatus of one embodiment is provided with a guide member to
ensure a workpiece is seated on the center of a lower die and to
prevent the workpiece from being deviated from the center when the
upper die is coupled to the lower die, thereby providing a torsion
beam with a bilateral symmetry.
[0099] Further, for the hot forming apparatus and method of one
embodiment, a cooling unit is located in the hot forming apparatus
for quenching the hot formed torsion beam to facilitate
transformation of the torsion beam from austenite structure, which
is stable at high temperatures, into martensite structure, which is
stable at low temperatures and enhances the strength of the
workpiece, thereby effectively preventing deformation and damage of
the torsion beam.
[0100] Moreover, according to one embodiment of the present
invention, hot forming and quenching are performed in a single
process, and, the hot formed product is subjected to quenching with
an elapse of a preset time after the hot forming, thereby
simplifying the process and reducing a frequency of defective
products in die operation.
[0101] Although embodiments of the present invention has been
described with reference to the accompanying drawings, these
embodiments are provided for the illustrative purpose, and it will
be apparent to those skilled in the art that various modifications
and equivalent embodiments can be made from these embodiments
disclosed herein.
[0102] Furthermore, although embodiment so the present invention
has been described based on the torsion beam of the rear torsion
beam axle suspension for the vehicle as one example, embodiments of
the present invention can be applied to torsion beams of other
applications without being limited to the vehicle. Therefore, the
scope of the present invention should be limited only by the
accompanying claims as follows.
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