U.S. patent application number 14/785301 was filed with the patent office on 2016-03-24 for hot press forming device for coated steel and hot press forming method using same.
This patent application is currently assigned to POSCO. The applicant listed for this patent is POSCO. Invention is credited to Jong-Won Choi, Dong-Jin Kim, Hong-Gee Kim, Kyung-Seok Oh.
Application Number | 20160082496 14/785301 |
Document ID | / |
Family ID | 51731524 |
Filed Date | 2016-03-24 |
United States Patent
Application |
20160082496 |
Kind Code |
A1 |
Kim; Hong-Gee ; et
al. |
March 24, 2016 |
HOT PRESS FORMING DEVICE FOR COATED STEEL AND HOT PRESS FORMING
METHOD USING SAME
Abstract
The present invention relates to a hot press forming device for
coated steel and a hot press forming method using the same, which
can reduce the generation of fine cracks of a molding and can
obtain uniform material properties.
Inventors: |
Kim; Hong-Gee;
(Jeollanam-do, KR) ; Choi; Jong-Won;
(Jeollanam-do, KR) ; Oh; Kyung-Seok;
(Jeollanam-do, KR) ; Kim; Dong-Jin; (Jeollanam-do,
KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
POSCO |
Gyeongsangbuk-do |
|
KR |
|
|
Assignee: |
POSCO
Gyeongsangbuk-do
KR
|
Family ID: |
51731524 |
Appl. No.: |
14/785301 |
Filed: |
December 24, 2013 |
PCT Filed: |
December 24, 2013 |
PCT NO: |
PCT/KR13/12110 |
371 Date: |
October 16, 2015 |
Current U.S.
Class: |
72/352 |
Current CPC
Class: |
B21D 22/022 20130101;
B21D 22/208 20130101; B21D 22/06 20130101 |
International
Class: |
B21D 22/02 20060101
B21D022/02 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 19, 2013 |
KR |
10-2013-0043485 |
Claims
1. A hot press forming (HPF) device for forming coated steel, the
HPF device comprising an upper die and a lower die, wherein the
upper and lower dies constrain a portion of a blank, and the HPF
device further comprises a cam configured to form another portion
of the blank not constrained by the upper and lower dies in order
to form a shaped portion.
2. The HPF device of claim 1, wherein the cam is moved in a
direction different from directions in which the upper and lower
dies are moved.
3. The HPF device of claim 1, wherein the cam is disposed between
the upper and lower dies.
4. The HPF device of claim 1, wherein the cam is separate from a
portion of the upper die or the lower die.
5. An HPF method for forming coated steel, the HPF method
comprising: heating a blank; forming the heated blank using an HPF
device; and cooling the formed blank, wherein in the forming of the
heated blank, a portion of the heated blank is constrained by upper
and lower dies of the HPF device, and another portion of the heated
blank not constrained by the upper and lower dies is formed by a
cam in order to form a shaped portion.
6. The HPF method of claim 5, wherein in the forming of the heated
blank, the cam is moved in a direction different from directions in
which the upper and lower dies are moved.
7. The HPF method of claim 5, wherein the cam is disposed between
the upper and lower dies.
8. The HPF method of claim 5, wherein the cam is separate from a
portion of the upper die or the lower die.
9. The HPF method of claim 5, wherein in the heating of the blank,
the blank is entirely heated to a temperature equal to or higher
than an A3 temperature of the blank, or the blank is heated to a
temperature equal to or higher than the A3 temperature of the blank
in a predetermined region and to a temperature equal to or lower
than an A1 temperature of the blank in another region.
Description
BACKGROUND
[0001] 1. Technical Field
[0002] The present disclosure relates to a hot press forming (HPF)
device and an HPF method using the HPF device, and more
particularly, to an HPF device and method for forming coated
steel.
[0003] 2. Background Art
[0004] Recently, automobile manufactures have increased the use of
high-strength materials in order to manufacture eco-friendly,
fuel-saving, light automotive parts satisfying social needs.
However, high-strength materials are difficult to form into desired
shapes because of problems such as spring back and difficulty in
maintaining dimensions, and thus the use of high-strength materials
is limited.
[0005] These problems related with formability may be solved by
manufacturing high-strength parts in a way of forming high-strength
materials into desired shapes at high temperatures guaranteeing
good formability, and rapidly cooling the formed high-strength
materials in dies. This method is called "hot press forming (HPF)."
Parts having a degree of strength equal to or greater than 1500 MPa
may be manufactured by the HPF method.
[0006] In an HPF process of the related art, steel blanks are
heated to 900.degree. C. or higher and are then pressed. However,
when steel blanks are heated, scale may form on the surfaces of the
steel blanks due to oxidation. Therefore, after the HPF process,
additional processes such as a shot blasting process may be
performed to remove scale from formed products. In addition, the
corrosion resistance of products manufactured by the HPF method is
inferior to that of coated products.
[0007] To address these problems, U.S. Pat. No. 6,296,805 (Patent
Document 1) has proposed a method of forming an aluminous coating
layer on a steel sheet, the aluminous coating layer withstanding
severe environments of a heating furnace, suppressing the oxidation
of the steel sheet, and forming a corrosion resistant aluminum (Al)
passive film on the steel sheet.
[0008] However, although such Al-coated materials have a high
degree of resistance to high temperatures, the corrosion resistance
of the Al-coated materials is inferior to the corrosion resistance
of materials coated with zinc (Zn) by a sacrificial anode method,
and the manufacturing costs of the Al-coated materials are high.
Therefore, there has been increasing interest in methods of using
Zn-coated materials.
[0009] However, if Zn-coated materials are heated to a high
temperature and are then formed into parts, micro cracks having a
size of about 10 .mu.m to 30 .mu.m may be formed in walls of the
parts, thereby deteriorating the properties of the parts such as
bendability. Therefore, the application of Zn-coated materials is
limited.
DESCRIPTION
Technical Problem
[0010] Aspects of the present disclosure may provide a hot press
forming (HPF) device for performing an HPF process on coated steel,
particularly zinc (Zn)-coated steel while reducing the formation of
microcracks in a formed product and imparting uniform properties to
the formed product, and an HPF method using the HPF device.
Technical Solution
[0011] According to an aspect of the present disclosure, a hot
press forming (HPF) device for forming coated steel may include an
upper die and a lower die, wherein the upper and lower dies may
constrain a portion of a blank, and the HPF device may further
include a cam configured to form another portion of the blank not
constrained by the upper and lower dies in order to form a shaped
portion.
[0012] According to another aspect of the present disclosure, an
HPF method for forming coated steel may include: heating a blank;
forming the heated blank using an HPF device; and cooling the
formed blank, wherein in the forming of the heated blank, a portion
of the heated blank may be constrained by upper and lower dies of
the HPF device, and another portion of the heated blank not
constrained by the upper and lower dies may be formed by a cam in
order to form a shaped portion.
Advantageous Effects
[0013] According to the present disclosure, when coated steel such
as zinc (Zn)-coated steel is processed through a hot press forming
(HPF) process, the formation of micro cracks in formed products may
be reduced, and the formed products may have a high degree of
formability such as bendability. In addition, formed products
having high quality may be produced, and particularly, shaped
portions of the formed products may have uniform properties.
DESCRIPTION OF DRAWINGS
[0014] FIG. 1 is a schematic view illustrating a hot press forming
(HPF) device and method of the related art.
[0015] FIG. 2 is a view illustrating a shaped portion of a formed
product manufactured by an HPF method of the related art.
[0016] FIG. 3 is a schematic view illustrating plastic strain in
the formed product manufactured by the HPF method of the related
art.
[0017] FIG. 4 is a schematic view illustrating an exemplary HPF
device and method according to an exemplary embodiment of the
present disclosure.
[0018] FIG. 5 is a schematic view illustrating plastic strain in a
formed product manufactured according to the exemplary embodiment
of the present disclosure.
[0019] FIG. 6 is a schematic view illustrating an exemplary HPF
device and method according to another exemplary embodiment of the
present disclosure.
[0020] FIG. 7(a) is a schematic view illustrating plastic strain in
a formed product manufactured by a method of the related art, and
FIG. 7(b) is a schematic view illustrating plastic strain in a
formed product manufactured according to the other exemplary
embodiment of the present disclosure.
[0021] FIG. 8(a) is an image of a shaped portion of a formed
product manufactured by a method of the related art, and FIG. 8(b)
is an image of a shaped portion of the formed product manufactured
according to the other exemplary embodiment of the present
disclosure.
BEST MODE
[0022] The inventors have found that if coated steel, particularly
zinc (Zn)-coated steel, is subjected to a hot press forming (HPF)
process, formed parts (formed products) have micro cracks (very
small cracks or microcracks), and the properties of the formed
products are not uniform because of non-uniform cooling at shaped
portions of the formed products. Thus, the inventors have conducted
research to solve these problems.
[0023] Exemplary embodiments of the present disclosure will now be
described in detail with reference to the accompanying drawings.
However, the accompanying drawings are for illustrative purposes
only and are not intended to limit the scope of the present
invention.
[0024] FIG. 1 is a schematic view illustrating an HPF process of
the related art. As illustrated in FIG. 1, in an HPF process, a
heated blank is placed between an upper die and a lower die and is
then pressed using the upper and lower dies to produce a formed
product.
[0025] FIG. 2 illustrates a surface of a shaped portion of coated
steel after the coated steel is processed by an HPF method of the
related art as illustrated in FIG. 1. As illustrated in FIG. 2,
formed products made of coated steel through an HPF process of the
related art had micro cracks in shaped portions of the formed
products.
[0026] To analyze reasons for this, plastic strain in a formed
product illustrated in FIG. 2 was analyzed, and results of the
analysis are illustrated in FIG. 3. As illustrated in FIG. 3, the
formed product produced using an HPF device of the related art had
an excessive amount of plastic deformation at the shaped portion of
the formed product, and micro cracks were formed in the shaped
portion.
[0027] In detail, micro cracks were formed in a wall of the shaped
portion, especially at a lower end portion of the wall of the
shaped portion because of concentrated deformation on the lower end
portion. The design shape of the formed product may be modified to
reduce deformation. However, it may not be easy to modify the
design shape of the formed product because of limitations to the
change of design. Therefore, the inventors have invented a method
of using a cam for reducing deformation and micro cracks.
[0028] In addition, when a blank is pressed between upper and lower
dies, the thickness of the blank is reduced at a shaped portion of
the blank, and a narrow gap is formed between the blank and the
upper and lower dies. As a result, when the blank is cooled in the
dies after the blank is pressed, the blank is not uniformly cooled,
and thus properties of the shaped portion of the blank are
deteriorated.
[0029] Therefore, the inventors have invented an HPF device
configured to prevent the generation of micro cracks in formed
products and impart uniform properties to formed products, and an
HPF method using the HPF device.
[0030] First, the HPF device of the present disclosure will be
described in detail.
[0031] The HPF device of the present disclosure includes: an upper
die and a lower die configured to constrain a portion of a blank;
and a cam configured to deform a non-constrained portion of the
blank to form a shaped portion.
[0032] The cam forms a shaped portion while moving in a direction
different from directions in which the upper and lower dies
move.
[0033] FIG. 4 is a schematic view illustrating an exemplary HPF
device according to an exemplary embodiment of the present
disclosure. As shown in FIG. 4, the HPF device of the exemplary
embodiment of the present disclosure includes upper and lower dies,
and cams between the upper and lower dies. An HPF device of the
related art such as that illustrated in FIG. 1 includes no cam, and
when a blank is pressed using the HPF device of the related art,
upper and lower dies of the HPF device are used to constrain the
blank.
[0034] However, when a blank is pressed using the HPF device of the
exemplary embodiment of the present disclosure, the upper and lower
dies constrain a portion of the blank, and a non-constrained
portion of the blank is formed using the cams to form a shaped
portion. In the HPF device illustrated in FIG. 4, the cams move in
horizontal directions independent of the upper and lower dies
moving in vertical directions, in order to form a shaped
portion.
[0035] When the shaped portion is formed, the plastic deformation
of the shaped portion is distributed by the cams. That is, as
illustrated in FIG. 4, when a blank is pressed into a desired shape
using the HPF device of the exemplary embodiment of the present
disclosure, the upper and lower dies constrain and shape a portion
of the blank, and the cams move to shape another portion of the
blank not constrained by the upper and lower dies.
[0036] In the HPF device illustrated in FIG. 4, the cams are
provided in addition to the upper and lower dies.
[0037] FIG. 5 illustrates plastic strain in a formed product
manufactured using the HPF device illustrated in FIG. 4, the
plastic strain being measured by analysis on forming. When the
results shown in FIG. 5 are compared with the results shown in FIG.
3, the plastic deformation of a shaped portion of the formed
product produced using the HPF device of the exemplary embodiments
of the present disclosure is markedly reduced. Therefore, the
formation of micro cracks may be markedly reduced in products
manufactured using the HPF device of the exemplary embodiment of
the present disclosure.
[0038] Another exemplary HPF device is illustrated in FIG. 6
according to another exemplary embodiment of the present
disclosure. In the HPF device illustrated in FIG. 6, cams are
provided separate from upper and lower dies.
[0039] In the HPF device illustrated in FIG. 6, the upper and lower
dies constrain a blank to fix the blank, and forming of the blank
is performed substantially by the cams. That is, the upper and
lower dies fix the blank, and the cams form the blank while moving
at predetermined angles.
[0040] FIG. 7(b) illustrates plastic strain in a formed product
manufactured using the HPF device illustrated in FIG. 6, the
plastic strain being measured by analysis on forming. FIG. 7(a)
illustrates plastic strain in a formed product produced by a method
of the related art. Referring to FIGS. 7(a) and 7(b), the plastic
strain in the formed product (FIG. 7(b)) produced by the HPF device
of the other exemplary embodiment of the present disclosure is much
lower than the plastic strain in the formed product (FIG. 7(a))
produced by the related-art method.
[0041] In addition, FIG. 8(a) illustrates a surface of a shaped
portion of the formed product manufactured using the HPF device
illustrated in FIG. 6, and FIG. 8(b) illustrates a surface of a
shaped portion of a formed product manufactured using an HPF device
of the related art. Referring to FIG. 8(a), the formed product
manufactured using the HPF device of the other exemplary embodiment
of the present disclosure does not have a large micro crack
developed to base steel. However, referring to FIG. 8(a), a large
micro crack is formed in base steel of the formed product.
[0042] In addition, an exemplary embodiment of the present
disclosure provides an HPF method for forming coated steel.
Hereinafter, the HPF method will be described in detail.
[0043] According to the HPF method of the exemplary embodiment of
the present disclosure, a prepared blank is heated and formed in an
HPF device.
[0044] As illustrated in FIG. 4 and FIG. 6, upper and lower dies of
the HPF device are used to constrain a portion of the blank, and
cams of the HPF device are used to form a non-constrained portion
of the blank to form a shaped portion.
[0045] In the example illustrated in FIG. 4, the upper and lower
dies of the HPF device are used to constrain and form a portion of
the blank, and the cams of the HPF device are used to form a
non-constrained portion of the blank while moving to the
non-constrained portion of the blank to complete forming. Unlike
this, in the example illustrated in FIG. 6, although the upper die
constrains the lower die, the upper and lower dies are not involved
in forming, and the cams form a portion of the blank while being
moved.
[0046] According to an HPF method of the related art as shown in
FIG. 1, when a portion of a blank is formed, the portion of the
blank continuously undergoes plastic deformation due to friction.
Therefore, the portion has a large amount of plastic deformation
after the forming, and thus micro cracks may be formed in the
shaped portion. As a result, formed products having poor
bendability and formability may be manufactured. Moreover, a shaped
portion having undergone continuous deformation may have a more
reduced thickness than the other portion. In this case, when the
blank is cooled, since the shaped portion is not in uniform contact
with the dies, the shaped portion may not be uniformly cooled, and
thus may have non-uniform properties.
[0047] However, according to the HPF method of the exemplary
embodiment of the present disclosure, as illustrated in FIGS. 4 and
6, when a portion of the blank is formed, the portion does not
continuously undergo plastic deformation, thereby preventing the
formation of micro cracks in the portion and a decrease in the
thickness of the portion. In addition, since the cams push the
portion against the dies, the portion and the dies may be reliably
brought into contact with each other, and after the blank is
cooled, the portion may have uniform properties.
[0048] Meanwhile, the blank may be uniformly heated to have the
same temperature, or may be heated to a relatively high temperature
in some region and a relatively low temperature in the other region
in order to produce a multi-strength formed product.
[0049] In detail, the entire region of the blank may be heated to a
temperature equal to or higher than an A3 temperature of the blank,
or the blank may be heated to a temperature equal to or higher than
the A3 temperature in a predetermined region and to a temperature
equal to or lower than an A1 temperature of the blank in another
region.
[0050] In the former case, the entire region of a product formed by
the HPF method may have a high degree of strength, and in the
latter case, a multi-strength product may be formed by the HPF
method. The multi-strength product may have a relatively high
degree of strength in a region heated to a relatively high
temperature and a relatively low degree of strength in a region
heated to a relatively low temperature.
[0051] In the above, any heating method may be used. That is, any
method used in the related art to heat steel may be used. For
example, the blank may be heated in the atmosphere of a heating
furnace or using an induction heating device.
[0052] After the blank is completely formed, the blank is cooled.
For example, the blank may be indirectly cooled by cooling the dies
of the HPF device. However, cooling of the blank is not limited
thereto. In addition, cooling conditions generally used in an HPF
method of the related art may be used.
* * * * *