§
AA507
1 -
DESCRIPTION
Title of Invention: METHOD FOR BENDING SHEET METAL AND
PRODUCT OF SHEET METAL
5
Technical Field
[0001] The present invention relates to a method for
bending a sheet metal, capable of easily bending the
sheet metal without generating a problem such as a
10 crinkle, crack or springback, and relates to a product
manufactured by the bending method.
Background Art
[0002] In the prior art, by bending sheet metal,
15 constituted from iron, aluminum or alloy thereof, in a
predetermined shape, various products have been
manufactured for use in a vehicle such as a motorcar,
components, building materials, or furniture. As the
bending method, for example, a roll forming method for
20 continuously deforming an object, or press working by
means of a press brake, may be possible.
[0003] As a method for bending a sheet metal, PLT 1
discloses a continuous manufacturing method, wherein a
bent portion of a sheet material is locally heated and
25 softened while the sheet material is moved, and then the
sheet material is transmitted through rolls or a forming
device.
Citation List
Patent Literature
30 [0004] PLT 1: Japanese Patent Publication (A) No. S63-
188426
Summary of Invention
Problem to be Solved by the Invention
35 [0005] However, in the technique of PLT 1, it is
necessary to process the entirety of one coil when the
coil is manufactured, since a coil-shaped plate is
1^ - 2 -
continuously processed. Therefore, the technique is not
adequate for low-volume production. Further, there is a
problem regarding a space in the technique, since a
device such a laser must be arranged on a production
5 line.
[0006] On the other hand, in recent years, as a
product for use in a motorcar, a high-strength sheet
metal (for example, a high-strength steel plate having
tensile strength of 980 MPa or more) is used in order to
10 reduce the weight of the vehicle. However, the
workability of the steel plate is usually deteriorated as
the strength of the steel plate is increased, i.e., a
crinkle or crack is easily generated in a deformed
portion and a springback is easily generated in the
15 product. Therefore, a method for bending a sheet metal
without generating a crinkle or crack in a deformed
portion is desired, even when the sheet metal has a
tensile strength of 980 MPa or more.
[0007] Further, a product constituted from the high-
20 strength sheet metal is subjected to compressing or
bending force during use. Concretely, a front-side
member of a motorcar is subjected to compressing load in
the axial direction (or the front-back direction of the
body) in a head-on collision, a side sill of a motorcar
25 is subjected to bending load when lateral collision, and
a bumper is subjected to bending load in a head-on
collision, for example. Therefore, it is necessary that
a crack not be generated in the deformed portion of the
product not only in the bending process but also when the
30 product is subjected to such load.
[0008] The present invention was made in order to
solve the above problems in the prior art, and to provide
a method for bending a sheet metal, capable of easily
bending the sheet metal without generating a problem such
35 as a crinkle, crack or springback of the deformed
portion, and a product manufactured by the bending
method.
1^ 3 -
Means for Solving the Problem
[0009] According to the present invention, a method
for bending a sheet metal is provided, the method
5 comprising: a hardness adjusting process for changing
hardness of at least a part of the sheet metal so as to
form a blank including a high-hardness region and a lowhardness
region having hardness lower than hardness of
the high-hardness region; and a bending process for
10 bending the low-hardness region of the blank so as to
form a product.
[0010] The hardness adjusting process may comprise
forming an objective region to be processed in at least a
part of the sheet metal, wherein one side of the sheet
15 metal is formed as the low-hardness region and the other
side of the sheet metal is formed as the high-hardness
region.
Effects of Invention
20 [0011] In the method for bending a sheet metal of the
present invention, bending process can be properly
carried out without generating a crinkle or crack in a
deformed portion of a product or springback in the
product, by bending the low-hardness region of a blank.
25 Therefore, according to the method for bending a sheet
metal of the invention, a product having a predetermined
shape can be easily manufactured. Further, in the method
for bending a sheet metal of the invention, even when a
high-strength sheet metal having tensile strength of 980
30 MPa or more, for example, a portion deformed in the
bending process becomes the low-hardness region in the
hardness adjusting process. Therefore, the deformed
portion can be bent without generating a crack therein.
Accordingly, the method of the invention is suitable for
35 manufacturing components of a motorcar (for example, a
front side member, a side sill and a bumper), building
materials, or furniture by using a high-strength sheet
metal.
[0012] The method for bending a sheet metal of the
present invention includes the hardness adjusting process
for changing hardness of the sheet metal so as to form a
5 blank having a high-hardness region and a low-hardness
region having hardness lower than hardness of the highhardness
region. Therefore, a sheet metal having
different hardness required for a product may be used,
whereby a usable sheet metal may have a wide range of
10 hardness in comparison to when only a part of the sheet
metal is softened.
[0013] In the method for bending a sheet metal of the
present invention, since a previously prepared blank is
bent and deformed in the hardness adjusting process, it
15 is not necessary to continuously carry out the hardness
adjusting process and the bending process. Therefore,
the present invention is advantageous to low-volume
production, and is also advantageous in terms of a space,
since it is not necessary to arrange a device such as a
20 laser on a line.
[0014] Further, in the product of the present
invention, the hardness of the deformed portion deformed
in the bending process is lower than a portion which is
not deformed, whereby a crack is not generated in the
25 deformed portion when bending load applied to the product
is gradually increased. However, in a product having the
same hardness throughout as a non-deformed portion, a
crack may be generated in the deformed portion when
bending load is gradually increased, whereby a stress is
30 rapidly decreased when the bending load exceeds a maximum
load in many cases. On the other hand, in the invention,
a crack is not generated in the deformed portion, a
stress is gradually decreased when the bending load
exceeds a maximum load. Accordingly, in the product of
35 the invention, a total amount of absorbed energy of the
bending load is larger than the product having the same
hardness throughout as the non-deformed portion, whereby
^0t
- 5 -
the energy of the bending load is effectively absorbed in
the invention.
Brief Description of Drawings
5 [0015] FIG. 1 is a schematic perspective view of a
sheet metal according to a first embodiment of the
present invention.
FIG. 2 is an end view of an example of a product
manufactured from the sheet metal of FIG. 1 by a bending
10 method of the first embodiment of the invention.
FIG. 3 is a schematic view of an example of a mold
device used in hardness adjusting process of the bending
method of the first embodiment for manufacturing the
sheet metal of FIG. 1.
15 FIG. 4 is a schematic view of an example of a watercooling
device used in hardness adjusting process of the
bending method of the first embodiment for manufacturing
the sheet metal of FIG. 1.
FIG. 5A is an end view of another example of a
20 product manufactured by the bending method of the first
embodiment of the invention.
FIG. 5B is a schematic side view of a blank for
manufacturing the product of FIG. 5A.
FIG. 6 is a schematic view of another example of a
25 mold device used in hardness adjusting process of the
bending method of the first embodiment of the invention.
FIG. 7 is a schematic cross-sectional view of a
blank manufactured by the mold device of FIG. 6.
FIG. 8A is a schematic process chart for explaining
30 an example of bending process.
FIG. 83 is a schematic process chart for explaining
an example of bending process.
FIG. 8C is a schematic process chart for explaining
an example of bending process.
35 FIG. 8D is a schematic process chart for explaining
an example of bending process.
FIG. 9 is a schematic end view of a product
- 6 -
manufactured from the blank of FIG. 7 by the processes of
FIGs. 8A to 8D.
FIG. lOA is a schematic end view of a test piece for
carrying out a bending test.
5 FIG. lOB is a schematic view for explaining a method
of a bending test.
FIG. 11 is a schematic perspective view of a sheet
metal according to a second embodiment of the present
invention.
10 FIG. 12 is an end view of an example of a product
manufactured from the sheet metal of FIG. 11 by a bending
method of the second embodiment of the invention.
FIG. 13 is a schematic view of an example of a mold
device used in hardness adjusting process of the bending
15 method of the second embodiment for manufacturing the
sheet metal of FIG. 11.
FIG. 14 is a schematic view of an example of a
water-cooling device used in hardness adjusting process
of the bending method of the second embodiment for
20 manufacturing the sheet metal of FIG. 11.
FIG. 15 is a schematic view of an example of a
blasting machine used in hardness adjusting process of
the bending method of the second embodiment for
manufacturing the sheet metal of FIG. 11.
25 FIG. 16A is an end view of another example of a
product manufactured by the bending method of the second
embodiment of the invention.
FIG. 16B is a schematic side view of a blank for
manufacturing the product of FIG. 16A.
30 FIG. 17A is a side view of an example of a sheet
metal wherein an entirety thereof corresponds to an
objective region to be processed.
FIG. 17B is a schematic view for explaining hardness
adjusting process of the bending method according to the
35 second embodiment of the invention, wherein the sheet
metal of FIG. 17A is manufactured by using a mold device.
FIG. 17C is a schematic view for explaining hardness
- 7 -
adjusting process of the bending method according to the
second embodiment of the invention, wherein the sheet
metal of FIG. 17A is manufactured by using a watercooling
device.
5 FIG. 17D is a schematic view for explaining hardness
adjusting process of the bending method according to the
second embodiment of the invention, wherein the sheet
metal of FIG. 17A is manufactured by using a laser
device.
10 FIG. 18A is a schematic view of another example of a
mold device used in hardness adjusting process of the
bending method of the second embodiment of the invention.
FIG. 18B is a schematic cross-sectional view of a
blank manufactured by the mold device of FIG. 18A.
15 FIG. 19A is a schematic process chart for explaining
an example of bending process.
FIG. 19B is a schematic process chart for explaining
an example of bending process.
FIG. 19C is a schematic process chart for explaining
20 an example of bending process.
FIG. 19D is a schematic process chart for explaining
an example of bending process.
FIG. 20 is a schematic end view of a product
manufactured from the blank of FIG. 7 by the processes of
25 FIGs. 19A to 19D.
FIG. 21A is a schematic end view of a test piece for
carrying out a bending test.
FIG. 21B is a schematic view for explaining a method
of a bending test.
30 FIG. 22A is a view for explaining stress applied to
a deformed portion which is deformed by forming process
of a sheet metal, showing a schematic cross-section of
the deformed portion wherein hardness of an inside region
the deformed portion is lower than hardness of an outside
35 region of the deformed portion.
FIG. 22B is a view for explaining stress applied to
a deformed portion which is deformed by forming process
t
of a sheet metal, showing a schematic cross-section of
the deformed portion wherein hardness of the deformed
portion is constant in the thickness direction thereof.
FIG. 23A is a view for explaining stress applied to
5 a deformed portion which is deformed by forming process
of a sheet metal, showing a schematic cross-section of
the deformed portion of sheet metal A of FIG. 22A wherein
hardness of the deformed portion is uniform in the
thickness direction thereof.
10 FIG. 23B is a view for explaining a shape of a
deformed portion which is deformed by forming process of
a sheet metal, showing a schematic cross-section of the
deformed portion of sheet metal B of FIG. 22B.
15 Embodiments for Carrying out the Invention
[0016] Below, a first embodiment of the present
invention will be explained while referring to the
attached drawings.
A blank 10, as exemplified in FIG. 1, includes one
20 or more (two in the example of FIG. 1) low-hardness
regions 12 and a plurality of (three in the example of
FIG. 1) high-hardness regions 14, the regions being
formed by hardness adjusting process as described below
from a sheet metal of iron, iron alloy, aluminum or
25 aluminum alloy. Although blank 10 is a rectangular sheet
material in FIG. 1, the shape and dimension of blank 10
may be variously determined depending on intended use,
etc., of a product 20. Further, although low-hardness
regions 12 of blank 10 extend parallel to a longitudinal
30 direction, low-hardness regions 12 may extend nonparallel
depending on the shape and intended use of
product 20. Blank 10 may be a continuous web withdrawn
from a coil-shaped supply, for example, when a roll
forming method is used.
35 [0017] Blank 10 is bent along low-hardness regions 12,
by roll forming or press working using a press brake, and
formed as channel-shaped product 20 having a C-shaped or
4 - 9 -
cup-shaped cross-section, as shown in FIG. 2. In FIG. 2,
product 20 is a channel-shaped member having a generally
C-shaped cross-section, including a bottom wall 22, and
opposed side walls 24 vertically extending from both side
5 edges of bottom wall 22. Product 20 has two deformed
portions or edge portions 26, which are formed from lowhardness
regions 12 and extend in the longitudinal
direction. Each deformed portion or edge portion 26 has
a bend radius "R."
10 [0018] A width "B" of low-hardness region 12 may be
determined depending on bend radius R of deformed portion
26 of product 20. For example, as shown in FIG. 2, when
deformed portion 26 of product 20 has a band-shape which
is deformed so as to have constant bend radius R, it is
15 preferable that width B of low-hardness region 12 be
0. STIR to 1. STIR, as shown in FIGs. 1 and 2. By virtue of
low-hardness region 12 having width B within this range,
product 20 may have sufficient strength and workability
of black 10 is effectively improved in bending process.
20 [0019] In order that blank 10 has improved workability
while having sufficient strength, it is preferable that
the hardness of low-hardness region 12 be within a range
from 30% to 70% of the hardness of high-hardness region
14. When the hardness of low-hardness region 12 is too
25 low, the strength of product 20 is insufficient even when
the hardness of high-hardness region 14 is increased. On
the other hand, when the hardness of low-hardness region
12 is too high, the workability in the bending process is
insufficient when the hardness of high-hardness region 14
30 is high.
[0020] In the preferred embodiment of the invention,
in the hardness adjusting process, blank 10 is formed by
(1) changing the hardness of the entirety of the sheet
metal; or (2) changing the hardness of a part region of
35 the sheet metal so as to form one or more low-hardness
regions 12 in the sheet metal.
[0021] A method for forming blank 10 by changing the
- 10 -
hardness of the entirety of the sheet metal, for example,
includes a heating process for heating the entirety of
the sheet metal by means of a heating furnace (not shown)
or another heating device; and a hardening process for
5 quenching only a region to be high-hardness region 14 of
the heated sheet metal. The hardening process may be
carried out, for example, by cooling only the region to
be high-hardness region 14 by using a mold.
[0022] FIG. 3 shows a mold device 30 as an example of
10 the cooling device for carrying out the hardening process
of the invention. Mold device 30 includes a bed 32 fixed
to a floor of a factory, etc.; a lower mold 34 fixed to
an upper surface of bed 32; and an upper mold 36
configured to be moved in the vertical direction closer
15 to or away from lower mold 34 by means of a ram or a
suitable drive unit 38. Sheet metal 11 is positioned
between lower mold 34 and upper mold 36. On opposed
operating surfaces 34a and 36a of lower and upper molds
34 and 36, groove portions 34b and 36b are formed,
20 respectively, at positions corresponding to low-hardness
regions 12 of sheet metal 11 after the hardening process.
[0023] First, sheet metal 11 is transferred from the
heating furnace or heating device to mold device 30,
after being heated in the heating process, and is
25 positioned between lower and upper molds 34 and 36.
Then, upper mold 36 is moved toward lower mold 34 by
means of drive unit 38 so that operating surfaces 34a and
36a of lower and upper molds 34 and 36 come into contact
with sheet metal 11. In sheet metal 11, only a portion,
30 which contacts operating surfaces 34a and 36a of lower
and upper molds 34 and 36, is rapidly cooled and
hardened. In this regard, a portion of sheet metal 11,
which faces groove portions 34b and 36b of lower and
upper molds 34 and 36, is not rapidly cooled by lower and
35 upper molds 34 and 36. As such, the portion of sheet
metal 11, which faces groove portions 34b and 36b of
lower and upper molds 34 and 36, is gradually cooled and
%
- 11 -
becomes low-hardness region 12. On the other hand, the
portion, which contacts operating surfaces 34a and 36a of
lower and upper molds 34 and 36, is rapidly cooled and
becomes high-hardness region 14, whereby blank 10 is
5 formed.
[0024] Alternatively, the hardening process may be a
process for selectively water-cooling only a region to be
high-hardness region 14 of the sheet metal, for example,
as shown in FIG. 4. FIG. 4 shows a water-cooling device
10 40 as an example of the cooling device for carrying out
the hardening process of the invention. Water cooling
device 40 includes a plurality of first (or lower)
nozzles 42 which are arranged so as to face one side of
sheet metal (or a lower surface of sheet metal 11 in FIG.
15 4); a plurality of second (or upper) nozzles 44 which are
arranged so as to face the opposed side of sheet metal
(or an upper surface of sheet metal 11 in FIG. 4),
wherein cooling water CW can be supplied to the sides of
sheet metal 11. Lower nozzles 42 and upper nozzles 44
20 are positioned so as to face a portion of sheet metal 11
which becomes be high-hardness region 14 after the
hardening process. In order to prevent a portion of
sheet metal 11, which becomes low-hardness region 12
after the hardening process, from being wetted with
25 cooling water CW, water cooling device 40 may have lower
and upper masking members 46 and 48, which are positioned
to cover the portion of sheet metal 11 which becomes lowhardness
region 12 after the hardening process. Lower
and upper masking members 4 6 and 4 8 may have a drive unit
30 such as a hydraulic cylinder (not shown) for moving the
masking members closer to or away from sheet metal 11.
Further, lower and upper masking members 46 and 48 may
function as a clamper for correctly positioning and
holding sheet metal 11 relative to lower and upper
35 nozzles 42 and 44. Alternatively, water cooling device
40 may have another clamper for correctly positioning and
holding sheet metal 11 relative to lower and upper
- 12 -
nozzles 42 and 44.
[0025] First, sheet metal 11 is transferred from the
heating furnace or heating device to water cooling device
40, after being heated in the heating process, and is
5 positioned between lower and upper nozzles 42 and 44. In
this regard, lower and upper masking members 4 6 and 48
may be used as the clamper for correctly positioning and
holding sheet metal 11 relative to lower and upper
nozzles 42 and 44. Alternatively, as described above,
10 another clamper (not shown) may be used for correctly
positioning and holding sheet metal 11 relative to lower
and upper nozzles 42 and 44. Then, cooling water CW is
supplied from lower and upper nozzles 42 and 44 to a
portion of sheet metal 11, which becomes high-hardness
15 region 14 after the hardening process, so that this
portion is rapidly cooled and hardened. In this regard,
by using lower and upper masking members 4 6 and 48, a
portion of sheet metal 11, which becomes low-hardness
region 12 after the hardening process, is prevented from
20 being wetted by cooling water CW and from being rapidly
cooled. As such, the portion of sheet metal 11, which
faces lower and upper masking members 46 and 48, is
gradually cooled and becomes low-hardness region 12, and
the other portion is rapidly cooled and becomes high-
25 hardness region 14, whereby blank 10 is formed.
[0026] A method for forming blank 10 by changing the
hardness of a part region of the sheet metal, for
example, includes a welding process for positioning
another sheet metal, having hardness different from the
30 hardness of the sheet metal, in a region to be highhardness
region 14 or low-hardness region 12, and welding
the sheet metals to each other. By virtue of this
method, blank 10 is obtained, wherein one region of highhardness
region 14 and low-hardness region 12 is formed
35 by the same material as the sheet metal, and the other
region is a tailored blank formed by another sheet metal
having the different hardness.
- 13 -
[0027] The hardness adjusting process may include a
process for heating a region to be low-hardness region 12
by using a laser, for example. By virtue of this, blank
10 is obtained, wherein the hardness of low-hardness
5 region 12 of the blank is lower than the sheet metal.
[0028] Next, by bending or deforming low-hardness 12
of blank 10, product 20 as shown in FIG. 2 is formed
(bending process). For example, the bending process may
be carried out by press working using a press brake. For
10 example, the press brake includes a lower mold (or a die)
having a V-shaped groove corresponding to an outer shape
of deformed portion 26 of product 20 of FIG. 2; and an
upper mold (or a punch) having a front shape
corresponding to the groove of the lower mold. The press
15 brake is configured to position low-hardness region 12 of
blank 10 between the lower and upper molds, move the
upper mold toward the lower mold, and press low-hardness
region 12 of blank 10 against the lower mold so as to
deform blank 10. By using the press brake, column-shaped
20 product 20 having a C-shaped cross-section as shown in
FIG. 2 can be easily manufactured from blank 10.
[0029] A method for deforming low-hardness region 12
of blank 10 so as to form product 20 is not limited to
the press working using the press brake, and various
25 methods may be selected depending on the shape of product
20 and the material of blank 10, etc. For example, lowhardness
region 12 of blank 10 may be deformed by a roll
forming method.
[0030] Deformed portion 26 of product 20 is obtained
30 by bending low-hardness region 12. In this regard, the
strength of deformed portion 26 is increased due to workhardening
by the bending process. For example, when the
hardness of low-hardness region 12 of used blank 10 is
within a range from 30% to 70% of the hardness of high-
35 hardness region 14 of blank 10, the hardness of deformed
portion 26 of product 20 may be within a range from 40%
to 80% of the hardness of high-hardness region 14 (i.e..
- 14 -
a portion other than deformed portion 26).
[0031] This embodiment includes the hardness adjusting
process for changing the hardness of sheet metal 11 so as
to form blank 10 including high-hardness region 14 and
5 low-hardness region 12; and the bending process for
bending low-hardness region 12 of blank 10 so as to form
product 20. Since low-hardness region 12 is deformed in
the bending process, a crinkle or crack is prevented from
being generated in deformed portion 26 (or low-hardness
10 region 12) of product 20, and a springback is prevent
from being generated in product 20.
[0032] It is preferable that a high-strength steel
sheet having tensile strength of 980 MPa (corresponding
to Vickers hardness of Hv 310) or more be used as the
15 sheet metal. This is because such a steel sheet is
economic and the predetermined high- and low-hardness
regions can be easily and industrially formed.
[0033] The reason why the tensile strength is 980 MPa
or more is because a low-strength steel sheet having
20 tensile strength less than 980 MPa may be processed
without using the present invention, and thus the present
invention has few advantages. In fact, an upper limit of
the tensile strength corresponds to a maximum strength of
a steel sheet capable of being industrially produced, and
25 thus the upper limit is not specified in particular. For
example, the present invention can be applied to a steel
sheet having tensile strength of 1700 MPa.
[0034] In the above embodiment, product 20 as shown in
FIG. 2 is the channel-shaped member having the generally
30 C-shaped cross-section, including bottom wall 22, and
opposed side walls 24 vertically extending from both side
edges of bottom wall 22. However, the product of
invention is not limited to the shape in FIG. 2, and may
have any shape as long as the shape is formed by the
35 bending method of the invention. In particular, the
number and shape of deformed portion 26 of product 20 are
not limited to the example in FIG. 2. For example, the
^
- 15 -
product may have a shape of a product 50 as shown in FIG.
5A.
[0035] Product 50 as shown in FIG. 5A includes a pair
of rectangular column portions 52 connected to a bottom
5 wall or connecting portion 54, wherein a groove portion
50a extending in the longitudinal direction is formed
between column portions 52. Similarly to blank 10 as
shown in FIG. 1, a blank 10' for forming product 50
includes one or more (eight in the example of FIG. 5B)
10 low-hardness regions 12' and a plurality of (nine in the
example of FIG. 5B) high-hardness regions 14', the
regions being formed by hardness adjusting process as
described above from a sheet metal of iron, iron alloy,
aluminum or aluminum alloy. Although blank 10' of FIG.
15 5B is a rectangular sheet material similarly to blank 10
in FIG. 1, the shape and dimension of blank 10' may be
variously determined depending on intended use, etc., of
a product 50.
[0036] Similarly to product 20 of FIG. 1, product 50
20 of FIG. 5A may be manufactured by changing the hardness
of the sheet metal so as to form blank 10' including
high-hardness region 14' and low-hardness region 12' (the
hardness adjusting process); and by bending low-hardness
region 12' of blank 10' (the bending process). In
25 addition, as shown in FIG. 5A, eight deformed portions
56, each having a predetermined bend radius, are formed
in product 50. Low-hardness region 12' of blank 10' has
the shape of eight bands extending in the longitudinal
direction of blank 10' (or the direction perpendicular to
30 a paper of FIG. 5B) so that a region to be deformed
portions 56 of product 50 are included in low-hardness
region 12'.
[0037] (Example)
Hereinafter, examples of the present invention will
35 be explained with reference to FIGs. 6 to lOB.
By the method as described above, a product 60 as
shown in FIG. 9 was formed. In FIG. 9, a unit of length
1^ - 16 -
of numerical numbers is millimeters (mm). Product 60 of
FIG. 9 is a channel-shaped member, including a bottom
wall 62; opposed side walls 64 vertically extending from
both side edges of bottom wall 62; and a pair of flange
5 portions 66 extending inwardly from side walls 64
parallel to bottom wall 62, wherein an opening 60a is
formed between flange portions 66. As shown in FIG. 9,
product 60 has four deformed portions 68a to 68d, and a
bend radius "R2" of each deformed portion is 2 mm.
10 [0038] In order to manufacture product 60 as shown in
FIG. 9, rectangular sheet metals SMI and SM2 each having
a width of 220 mm, a length of 1200 mm, and a thickness
of 1.2 mm, were prepared. Sheet metals SMI and SM2 are
high-strength steel plates having compositions as
15 indicated in Table 1. Then, after sheet metals SMI and
SM2 were heated by means of a heating furnace to 900
degrees C (the heating process), a portion to be a highhardness
region 84 of a blank 80 (FIG. 7) was quenched by
using a mold device 70 having a lower mold 72 and an
20 upper mold 74 (schematically shown in FIG. 6) (the
hardening process), whereby blank 80 was formed. A unit
of length numerical numbers in FIGs. 6 and 7 is
millimeters (mm). As shown in FIG. 7, width B of a lowhardness
region 82 of blank 80 is 7 mm, and thus the
25 width of each of grooves 76 and 78 of lower and upper
molds 72 and 74 of mold device 70 is also 7 mm.
- 17
Table 1
SMI
SM2
C
0.16
0.22
Si
0.25
0.22
Mn
0.73
1.29
P
0.020
0.020
S
0.003
0.003
Cr
1.05
0.21
Al
0.025
0.040
B
0.002
0.002
Ti
0.020
0.024
Ac3(°C)
857
827
9 - 18 -
[0039] In relation to example 1 (sheet metal SMI) and
example 2 (sheet metal SM2) obtained as described above,
an average hardness of high-hardness region 84 (Hvh) and
an average hardness of low-hardness region 82 (Hvl) of
blank 80 were measured, and a ratio of the hardness of
the low-hardness region relative to the hardness of the
high-hardness region (Hvl/HvhxlOO%) was calculated. The
result is indicated in Table 2.
19 -
[0040]
Table 2
Inv.
Inv.
Comp.
Camp.
ex.
ex.
ex.
ex.
1
2
1
2
Sheet metal
SMI
SM2
SMI
SM2
Average hardness (Hv)
High-hardness region
412
501
411
503
Low-hardness region
276
336
-
-
Hardness ratio
(%)
67
67
-
-
- 20 -
[0041] Sheet metals SMI and SM2 similar to examples 1
and 2 were prepared, and heated by means of a heating
furnace to 900 degrees C (the heating process). After
that, by using a mold (not shown), the entirety of the
5 sheet metals were cooled under the same cooling condition
as high-hardness region 84 of blank 80 in examples 1 and
2 (the hardening process). As a result, blanks of
comparative examples 1 and 2 (sheet metals SMI and SM2)
were obtained, wherein the entirety of the blanks were
10 constituted by the high-hardness region without including
the low-hardness region. Table 2 indicates average
hardness (Hvh) of comparative examples 1 and 2.
[0042] The tensile strength of the blanks of (sheet
metals SMI and SM2) of comparative examples 1 and 2 in
15 Table 2 were 1360 MPa and 1690 MPa, respectively. From
this, it can be estimated that the tensile strength of
the high-hardness regions of the blanks (sheet metals SMI
and SM2) of examples 1 and 2 of the invention, having the
same chemical compositions and the same average hardness
20 as comparative examples 1 and 2, were generally equal to
1360 MPa and 1690 MPa, respectively.
[0043] As indicated in Table 2, blank 80 of examples 1
and 2 of the invention includes high-hardness region 84
having the same average hardness (Hvh) as the blank of
25 comparative examples 1 and 2, and low-hardness region 82
having average hardness (Hvl) lower than high-hardness
region 84.
[0044] As indicated in Table 2, the hardness ratio
(Hvl/Hvhxl00%) was 67% in both of examples 1 and 2.
30 Further, as a measurement result, the tensile strength of
the blank of comparative example 1 was 1200 MPa or more,
and the tensile strength of the blank of comparative
example 2 was 1500 MPa or more.
[0045] After that, as shown in FIGs. 8A to 8D, by
35 bending each low-hardness region 82 of the blanks of
examples 1 and 2 by means of a press brake, four deformed
portions 68a, 68b, 68c and 68d (FIG. 9) were sequentially
^
- 21 -
formed in channel-shaped product 60, whereby products PI
and P3 were obtained (the bending process).
[0046] In FIGs. 8A to 8D, press brake 90 includes a
lower mold (or a die) 92 having a V-shaped groove 92a
5 corresponding to an outer shape of each deformed portion
68a, 68b, 68c and 68d of product 60; and an upper mold
(or a punch) 94 having a front shape corresponding to
groove 92a of lower mold 92. One low-hardness region was
selected from four low-hardness regions 82 of blank 80,
10 and the selected region was positioned between lower mold
92 and upper mold 94. Then, upper mold 94 was downwardly
moved toward lower mold 92 so as to press and bend lowhardness
region 82 by lower and upper molds 92 and 94.
Such operations were sequentially carried out in relation
15 to other low-hardness regions 82.
[0047] By a bending process wherein low-hardness
regions 82 of blank 80 of examples 1 and 2 were bent by
means of a 21-stage roll forming machine, deformed
portions 68a, 68b, 68c and 68d (FIG. 9) of channel-shaped
20 product 60 were sequentially formed, whereby products P2
and P4 were obtained (the bending process).
[0048] By a bending process wherein the blanks of
comparative examples 1 and 2 were bent by means of a
press brake similarly to the process for products PI and
25 P3, channel-shaped products P5 and P7 were manufactured.
Further, by using the 21-stage roll forming machine as
described above, products P6 and P8 were manufactured
from the blanks of comparative examples 1 and 2.
[0049] In relation to products PI to P8 obtained as
30 such, a bending test was carried out, and a result
thereof is indicated in Table 3.
^^
22 -
Table 3
Formed
product
No.
PI
P2
P3
P4
P5
P6
P7
P8
Blank
Inv. ex. 1
Inv. ex. 2
Comp.ex.1
Comp. ex. 2
Sheet
metal
SMI
SM2
SMI
SM2
Result of forming
Forming
method
Press
brake
Roll
forming
Press
brake
Roll
forming
Press
brake
Roll
forming
Press
brake
Roll
forming
Corner
crack
No crack
No crack
No crack
No crack
No crack
No crack
No crack
Crack
Result of bending test
Peak
load
P (kN)
31.5
31.7
37.9
38.2
32.2
32.3
39.0
-
Corner
crack
No crack
No crack
No crack
No crack
Crack
Crack
Crack
-
Absorption
energy
E (J)
1205
1218
1480
1485
806
817
859
-
^
- 23 -
[0050] A test piece 100 as shown in FIG. lOA is
constituted by a hollow member including product 60 and a
steel plate 102 jointed to an opening 60a of product 60
by arc welding. The bending test was carried out by
5 using products PI to P8 as product 60. As steel plate
102, a sheet metal of the same material as the sheet
metal for manufacturing products PI to P7, and having a
width of 60 mm, a length of 1200 mm, and a thickness of
1.2 mm, was prepared. The above heating process and
10 hardening process were carried out in relation to the
sheet metal so that the sheet metal had the hardness
equivalent to high-hardness region 84.
[0051] Next, tubular test piece 100 obtained as such
was positioned so that steel plate 102 was directed
15 downward, as shown in FIG. lOB, and was positioned so as
to form a beam of test piece 100 having a span of 1000 mm
between two fulcrum points 53, 53, each fulcrum point
providing with a front end having a hemispherical shape
of a radius of 12.5 mm. Then, a three-point bending test
20 was carried out by positioning a jig 54 having a
hemispherical shape of a radius of 150 mm at the center
of the beam, and peak load (or maximum load) of the
bending load and absorption energy to a bending
deflection of 50 mm were determined.
25 [0052] In addition, in relation to products PI to P8,
the existence of a crack (or a corner crack) in deformed
portions 68a, 68b, 68c and 68d were visually checked in
the bending process and the bending test. The result was
indicated in Table 3.
30 [0053] As indicated in Table 3, in products PI to P4
using blank 80 of examples 1 and 2, the corner crack did
not occur in the bending process and the bending test.
The peak load of products PI to P3 was slightly
lower than respective products P5 to P7 manufactured by
35 using the sheet metal having the same compositions in the
same method. On the other hand, the absorption energy of
products PI to P3 was significantly higher than
w - 24 -
respective products P5 to P7.
[0054] In products P5 to P7 using the blank of
comparative examples 1 and 2, although the corner crack
did not occur in the bending process, the corner crack
5 occurred in the bending test.
Further, in product P8 using the blank of
comparative example 2 having the tensile strength of 1500
MPa or more, the corner crack occurred in the bending
process, and the bending test could not be carried out.
10 [0055] In addition, in order to manufacture product 60
as shown in FIG. 9, a sheet metal having a rectangular
shape in a planar view, a width of 220 mm, a length of
1200 mm, and a thickness of 1.2 mm, was prepared. The
sheet metal had a yield point (YP) of 742 MPa, tensile
15 strength (TS) of MPa, and an elongation (EL) of 2.7%.
[0056] Next, by heating a region of the sheet metal to
be low-hardness region 82 by means of a laser, the
hardness of the sheet metal was changed so as to blank 80
of example 3 having high-hardness region 84 and low-
20 hardness region 82 having the hardness lower than highhardness
region 84, as shown in FIG. 7 (the hardness
adjusting process).
[0057] The laser welding was carried out by using a 5
kw YAG laser. Since a region having a width of about 2
25 mm is heated at a welding speed of 15 m/min by using the
5 kw YAG laser, low-hardness region 82 of 7 mm to 8 mm
was formed by irradiating a laser in four rows at a 2 mm
pitch.
[0058] Average hardness (Hv) of the blank of example 3
30 obtained as such was measured, similarly to the average
hardness of blank 80 of example 1, and a result thereof
is indicated Table 4.
IK
- 25
[0059]
Table 4
Inv.
Comp.
ex.
ex.
3
3
Average hardness (Hv)
High-hardness region
295
297
Low-hardness region
145
-
Hardness ratio
(%)
49
-
^
- 26 -
[0060] By using the blank of example 3, a channelshaped
member or product P9 having the same shape as
product 60 of FIG. 9 was manufactured, by means of a
press brake, in the process similar to the process for
5 manufacturing product PI.
[0061] By using the blank of example 3, a channelshaped
member or product PIO having the same shape as
product 60 of FIG. 9 was manufactured, by means of a
press brake, in the process similar to the process for
10 manufacturing product P2.
[0062] Further, the sheet metal same as the sheet
metal used to form the blank of example 3 is referred to
as a blank of comparative example 3, and average hardness
(Hv) of the blank of comparative example 3 was measured,
15 similarly to the average hardness of the blank of example
3, and a result thereof is indicated Table 4.
[0063] By using the blank of comparative example 3, a
channel-shaped member or product Pll having the same
shape as product 60 of FIG. 9 was manufactured, by means
20 of a press brake, in the process similar to the process
for manufacturing product PI.
[0064] By using the blank of comparative example 3, a
channel-shaped member or product P12 having the same
shape as product 60 of FIG. 9 was manufactured, by means
25 of a press brake, in the process similar to the process
for manufacturing product P2.
[0065] In relation to products P9 to P12 obtained as
such, a bending test was carried out, and a result
thereof is indicated in Table 5. In addition, in
30 relation to products P9 to P12, the existence of a crack
(or a corner crack) in the deformed portions were
visually checked in the bending process and the bending
test similarly to product Pi. The result was indicated
in Table 3.
27
[0066]
Table 5
Formed
product
No.
P9
PIO
Pll
P12
Blank
Inv. ex. 3
Comp. ex. 3
Result of forming
Forming
method
Press
brake
Roll
forming
Press
brake
Roll
forming
Corner
crack
No crack
No crack
No crack
Crack
Result of bending test
Peak
load
P (kN)
19.1
19.3
19.9
-
Corner
crack
No crack
No crack
Crack
-
Absorption
energy
E (J)
755
762
401
-
- 28 -
[0067] As indicated in Table 5, in products P9 and PIO
using the blank of example 3, the corner crack did not
occur in the bending process and the bending test. The
peak load of product P9 was slightly lower than product
5 Pll manufactured by using the sheet metal having the same
compositions in the same method. On the other hand, the
absorption energy of product P9 was significantly higher
than product Pll.
[0068] On the other hand, the absorption energy of
10 product PIO was 700 J or more, which was significantly
higher than product Pll manufactured by using the sheet
metal having the same compositions.
[0069] In product Pll manufactured from the blank of
comparative example 3 by means of the press brake,
15 although the corner crack did not occur in the bending
process, the corner crack occurred in the bending test.
Further, in product P12 manufactured from the blank of
comparative example 3 in the roll forming, the corner
crack occurred in the bending process, and the bending
20 test could not be carried out.
[0070] Below, a second embodiment of the present
invention will be explained while referring to the
attached drawings.
A blank 110 exemplified in FIG. 11, to which the
25 bending method for a sheet metal of the invention is
applied, includes one or more (two in the example of FIG.
11) low-hardness regions 112 and a plurality of (three in
the example of FIG. 1) high-hardness regions 114, the
regions being formed by hardness adjusting process as
30 described below from a sheet metal of iron, iron alloy,
aluminum or aluminum alloy. Although blank 10 is a
rectangular sheet material in FIG. 1, the shape and
dimension of blank 10 may be variously determined
depending on intended use, etc., of a product 20.
35 Further, although low-hardness regions 12 of blank 10
extend parallel to a longitudinal direction, low-hardness
regions 12 may be extend non-parallel depending on the
- 29 -
shape and intended use of product 20. Blank 10 may be a
continuous web withdrawn from a coil-shaped supply, for
example, when a roll forming method is used. Unlike lowhardness
region 12 of blank 10 of the first embodiment,
5 each low-hardness region 112 extends from one side of
blank 110 to a generally center in the thickness
direction thereof, and does not reach the opposed side of
the blank. As such, an objective region 116 to be
processed having low-hardness region 112 and high-
10 hardness region 114 is formed in a part of the sheet
metal, wherein front and rear sides of objective region
116 have the different hardness. In addition, in the
embodiment of FIG. 11, high-hardness region 114 includes
three regions on one side including low-hardness region
15 112, while including one region on the other side.
[0071] The dimension of low-hardness region 112 of
objective region 116 in the thickness direction of the
sheet metal may be determined depending on the hardness
and/or the thickness of the sheet metal, the shape and/or
20 the production method of product 120, etc. In this
regard, it is preferable that the dimension of lowhardness
region 112 in the thickness direction be within
a range from 35% to 65% of the thickness of the sheet
metal, in order to obtain a remarkable effect due to
25 forming objective region 116 having the different
hardness in the front and rear sides. In addition,
although low-hardness regions 112 of blank 110 extend
parallel to the longitudinal direction in the embodiment
of FIG. 11, low-hardness regions 112 may extend non-
30 parallel depending on the shape and intended use of
product 120, etc.
[0072] Although blank 110 is a rectangular sheet
material in FIG. 11, the shape and dimension of blank 110
may be variously determined depending on intended use,
35 etc., of a product 120. Further, blank 110 may be a
continuous web withdrawn from a coil-shaped supply, for
example, when a roll forming method is used.
#
- 30 -
[0073] In this embodiment, the hardness of highhardness
region 114 on the rear side of objective region
116 is the same as the hardness of a region other than
objective region 116. However, the hardness of high-
5 hardness region 114 on the rear side of objective region
116 may be different from the hardness of the region
other than objective region 116, as long as the hardness
of high-hardness region 114 on the rear side of objective
region 116 is higher than low-hardness region 112.
10 Further, the hardness of the region other than objective
region 116 may be the same as the hardness of the front
side or the rear side of objective region 116, otherwise,
may be different from both the front side and the rear
side.
15 [0074] Similarly to the first embodiment. Blank 110 is
bent along objective region 116, by a roll forming
machine or press working using a press brake, and formed
as channel-shaped product 120 having a C-shaped or cupshaped
cross-section, as shown in FIG. 12. In FIG. 12,
20 product 120 is a channel-shaped member having a generally
C-shaped cross-section, including a bottom wall 122, and
opposed side walls 124 vertically extending from both
side edges of bottom wall 122. Product 120 has two
deformed portions or edge portions 126, which are formed
25 from objective regions 116 and extend in the longitudinal
direction. Each deformed portion or edge portion 126 has
a bend radius "R." In addition, in product 120, edge
portions 126 of blank 110 are bent in the same direction
with respect to one side of blank 110 (the upward
30 direction in FIGs. 11 and 12), so that all of an inside
region of deformed portion 126 of product 120 in FIG. 12
forms a surface of objective region 116 of FIG. 11.
[0075] A width "B" of low-hardness region 112 may be
determined depending on bend radius R of deformed portion
35 126 of product 120. For example, as shown in FIG. 12,
when deformed portion 126 of product 120 has a band-shape
which is deformed so as to have constant bend radius R,
- 31 -
it is preferable that width B of low-hardness region 112
be 0. STIR to 1.57tR, as shown in FIGs. 11 and 12. By virtue
of low-hardness region 112 having width B within this
range, product 120 may have sufficient strength and
5 workability of black 110 is effectively improved in
bending process.
[0076] In order that blank 110 has improved
workability while having sufficient strength, it is
preferable that the hardness of low-hardness region 112
10 be within a range from 30% to 80% of the hardness of
high-hardness region 114. When the hardness of lowhardness
region 112 is too low, the strength of product
120 is insufficient even when the hardness of highhardness
region 114 is increased. On the other hand,
15 when the hardness of low-hardness region 112 is too high,
the workability in the bending process is insufficient
when the hardness of high-hardness region 114 is high.
[0077] In the preferred embodiment of the invention,
in the hardness adjusting process, blank 110 is formed by
20 (1) changing the hardness of the entirety of the sheet
metal so as to form objective region 116 to be processed;
or (2) changing the hardness of a part region of the
sheet metal in the thickness direction so as to form one
or more low-hardness regions 112 in the sheet metal.
25 [0078] A method for forming blank 110 by changing the
hardness of the entirety of the sheet metal, for example,
includes a heating process for heating the entirety of
the sheet metal by means of a heating furnace (not shown)
or another heating device; and a hardening process for
30 quenching only a region to be high-hardness region 114 of
the heated sheet metal. The hardening process may be
carried out, for example, by cooling only the region to
be high-hardness region 114 by using a mold.
[0079] FIG. 13 shows a mold device 130 as an example
35 of the cooling device for carrying out the hardening
process of the second embodiment. Mold device 130
includes a bed 132 fixed to a floor of a factory, etc.; a
- 32 -
lower mold 134 fixed to an upper surface of bed 132; and
an upper mold 136 configured to be moved in the vertical
direction closer to or away from lower mold 134 by means
of a ram or a suitable drive unit 138. Sheet metal 111
5 is positioned between lower mold 134 and upper mold 136.
Lower and upper molds 134 and 136 have operating surfaces
134a and 136a opposed to each other, respectively. On
operating surface 134a of lower mold 134, a groove
portion 134b is formed, at a position corresponding to
10 low-hardness region 112 of sheet metal 111 after the
hardening process.
[0080] First, sheet metal 111 is transferred from the
heating furnace or heating device to mold device 130,
after being heated in the heating process, and is
15 positioned between lower and upper molds 134 and 136.
Then, upper mold 136 is moved toward lower mold 134 by
means of drive unit 138 so that operating surfaces 134a
and 136a of lower and upper molds 134 and 136 come into
contact with sheet metal 111. In sheet metal 111, only a
20 portion, which contacts operating surfaces 134a and 136a
of lower and upper molds 134 and 136, is rapidly cooled
and hardened. In this regard, a portion of sheet metal
111, which faces groove portion 134b of lower moldl 134,
is not rapidly cooled by lower mold 134. As such, the
25 portion of sheet metal 111, which faces groove portion
134b lower mold 134, is gradually cooled and becomes lowhardness
region 112. On the other hand, the portion,
which contacts operating surfaces 134a and 136a of lower
and upper molds 134 and 136, is rapidly cooled and
30 becomes high-hardness region 114, whereby blank 110 is
formed.
[0081] Alternatively, the hardening process may be a
process for selectively water-cooling only a region to be
high-hardness region 114 of the sheet metal, for example,
35 as shown in FIG. 14. FIG. 14 shows a water-cooling
device 140 as an example of the cooling device for
carrying out the hardening process of the invention.
#
- 33
Water cooling device 140 includes a plurality of first
(or lower) nozzles 142 which are arranged so as to face
one side of sheet metal (or a lower surface of sheet
metal 111 in FIG. 14); a plurality of second (or upper)
5 nozzles 144 which are arranged so as to face the opposed
side of sheet metal (or an upper surface of sheet metal
111 in FIG. 14), wherein cooling water CW can be supplied
to the sides of sheet metal 111. Lower nozzles 142 and
upper nozzles 144 are positioned so as to face a portion
10 of sheet metal 111 which becomes be high-hardness region
114 after the hardening process. In particular, in this
embodiment, upper nozzles 144 are positioned so as to
supply cooling water CW to the front side of sheet metal
111. In order to prevent a portion of sheet metal 111,
15 which becomes low-hardness region 112 after the hardening
process, from being wetted with cooling water CW, water
cooling device 140 may have a lower masking member 146,
which is positioned to cover the portion of sheet metal
111 which becomes low-hardness region 112 after the
20 hardening process. Lower masking member 14 6 may have a
drive unit such as a hydraulic cylinder (not shown) for
moving the masking member closer to or away from sheet
metal 111. Further, lower masking member 14 6 may
function as a retainer for correctly positioning and
25 holding sheet metal 111 relative to lower and upper
nozzles 142 and 144. Alternatively, water cooling device
140 may have another clamper for correctly positioning
and holding sheet metal 111 relative to lower and upper
nozzles 142 and 144.
30 [0082] First, sheet metal 111 is transferred from the
heating furnace or heating device to water cooling device
140, after being heated in the heating process, and is
positioned between lower and upper nozzles 142 and 144.
In this regard, lower masking member 146 may be used as
35 the retainer for correctly positioning and holding sheet
metal 111 relative to lower and upper nozzles 142 and
144. Alternatively, as described above, another clamper
#
34
(not shown) may be used for correctly positioning and
holding sheet metal 111 relative to lower and upper
nozzles 142 and 144. Then, cooling water CW is supplied
from lower and upper nozzles 142 and 144 to a portion of
5 sheet metal 111, which becomes high-hardness region 114
after the hardening process, so that this portion is
rapidly cooled and hardened. In this regard, by using
lower and upper masking members 146 and 148, a portion of
sheet metal 111, which becomes low-hardness region 112
10 after the hardening process, is prevented from being
wetted by cooling water CW and from being rapidly cooled.
As such, the portion of sheet metal 111, which faces
lower masking member 146, is gradually cooled and becomes
low-hardness region 112, and the other portion is rapidly
15 cooled and becomes high-hardness region 114, whereby
blank 110 is formed.
[0083] The hardness adjusting process in this
embodiment may include a shot peening process wherein
shots collide with at least the side of objective region
20 116 opposed to low-hardness region 112 of sheet metal
111. FIG. 15 shows a blasting machine 150 for carrying
out the shot peening. Blasting machine 150 includes a
plurality of first (or lower) nozzles 152 which are
arranged so as to face one side of sheet metal (or a
25 lower surface of sheet metal 111 in FIG. 15); a plurality
of second (or upper) nozzles 154 which are arranged so as
to face the opposed side of sheet metal (or an upper
surface of sheet metal 111 in FIG. 15), wherein shots
(particles of steel, glass, ceramic or plastic) can be
30 projected onto the sides of sheet metal 111. Preferably,
blasting machine 150 may have a masking member 154, which
is positioned to cover the portion of sheet metal 111
which becomes low-hardness region 112 after the shot
peening process, whereby shots can be selectively
35 projected onto only a region to be high-hardness region
114 (other than the region to be low-hardness region 112)
in sheet metal 111. By virtue of this, the side having
- 35 -
)
higher hardness (or high-hardness region 114) of
objective region 116, to which the shots are projected,
is formed, as shown in FIG. 15, and blank 110 can be
obtained wherein the hardness of high-hardness region 114
5 of objective region 116 is the same as the sheet metal.
[0084] In this regard, by projecting cast-iron shots
of 170 to 280 mesh (F-S170~280/JIS G5903) onto sheet
metal 111 by means of an impeller-type blasting machine,
the sheet metal can be sufficiently plastically deformed,
10 whereby a desired hardness of the sheet metal may be
obtained. In order to generate sufficient work-hardening
in the depth direction of sheet metal 111 without
generating a crack on the surface of sheet metal 111, it
is desirable to use spherical cast-iron shots having
15 Vickers hardness (Hv) of 650 or more. When cast-iron
shots of less than 170 mesh are used, a fine crack,
having the length of several micrometers to several tens
of micrometers on the surface of the sheet metal, may be
formed, due to the small curvature of the shot. On the
20 other hand, when cast-iron shots of more than 280 mesh
are used, the sheet metal cannot be sufficiently
plastically deformed due to the large curvature of the
shot. Therefore, it is preferable that the cast-iron
shots of 170 to 280 mesh be used and projected by means
25 of a mechanical impeller-type blasting machine capable of
applying kinetic energy to the shots.
[0085] The hardness adjusting process may include a
process for heating a region to be low-hardness region
112 by using a laser, from the side of sheet metal 111 on
30 which low-hardness region 112 exists. In this case, the
region heated by the laser becomes low-hardness region
112, and the other region becomes high-hardness region
114.
[0086] The hardness adjusting process may include a
35 process for carbonizing or nitriding a part of sheet
metal 111 so as to form high-hardness region 114.
[0087] Next, by bending blank 110 so that low-hardness
- 36 -
is positioned inside objective region 116 to be
processed, product 120 as shown in FIG. 12 is formed
(bending process). For example, the bending process may
be carried out by press working using a press brake. For
5 example, the press brake includes a lower mold (or a die)
having a V-shaped groove corresponding to an outer shape
of deformed portion 126 of product 120 of FIG. 12; and an
upper mold (or a punch) having a front shape
corresponding to the groove of the lower mold. The press
10 brake is configured to position low-hardness region 112
of blank 110 between the lower and upper molds, move the
upper mold toward the lower mold, and press low-hardness
region 112 of blank 110 against the lower mold so as to
deform blank 110. By using the press brake, column-
15 shaped product 120 having a C-shaped cross-section as
shown in FIG. 12 can be easily manufactured from blank
110.
[0088] A method for deforming low-hardness region 112
of blank 110 so as to form product 120 is not limited to
20 the press working using the press brake, and various
methods may be selected depending on the shape of product
120 and the material of blank 110, etc. For example,
low-hardness region 112 of blank 110 may be deformed by
means of a roll forming machine.
25 [0089] Deformed portion 126 of product 120 includes
low-hardness region 112. In this regard, the strength of
low-hardness region 112 is increased due to workhardening
by the bending process. For example, when the
hardness of low-hardness region 112 of used blank 110 is
30 within a range from 30% to 70% of the hardness of highhardness
region 114 of blank 110, the hardness of lowhardness
region 112 in deformed portion 126 of product
120 may be within a range from 40% to 85% of the hardness
of high-hardness region 114 other than deformed portion
35 126.
[0090] This embodiment includes the hardness adjusting
process for changing the hardness of sheet metal 111 in
- 37 - i
the thickness direction thereof so as to form blank 110
partially including objective region 116 to be processed
having the different hardness in the front and rear sides
thereof; and the bending process for bending blank 110 so
5 as to form product 120 wherein the side having lower
hardness (or low-hardness region 112) is inside objective
region 116. Since objective region 116 including lowhardness
region 112 is deformed in the bending process, a
crinkle or crack is prevented from being generated in
10 deformed portion 126 (or low-hardness region 112) of
product 120, and a springback is prevent from being
generated in product 120. Further, product 120 has high
strength, since a crack is unlikely to be generated in
deformed portion 126 when load is applied to product 120.
15 [0091] It is preferable that a high-strength steel
sheet having tensile strength of 980 MPa (corresponding
to Vickers hardness of Hv 310) or more be used as the
sheet metal. This is because such a steel sheet is
economic and the predetermined high- and low-hardness
20 regions can be easily and industrially formed.
[0092] The reason why the tensile strength is 980 MPa
or more is because a low-strength steel sheet having
tensile strength less than 980 MPa may be processed
without using the present invention, and thus the present
25 invention has few advantages. In fact, an upper limit of
the tensile strength corresponds to a maximum strength of
a steel sheet capable of being industrially produced, and
thus the upper limit is not specified in particular. For
example, the present invention can be applied to a steel
30 sheet having tensile strength of 1700 MPa.
[0093] In the above embodiment, product 120 as shown
in FIG. 12 is the channel-shaped member having the
generally C-shaped cross-section, including bottom wall
122, and opposed side walls 124 vertically extending from
35 both side edges of bottom wall 122. However, the product
of invention is not limited to such a shape of FIG. 12,
and may have any shape as long as the shape is formed by
- 38 -
I
the bending method of the invention. In particular, the
number and shape of deformed portion 126 of product 120
are not limited to the example of FIG. 12. For example,
the product may have a shape of a product 160 as shown in
5 FIG. 16A.
[0094] Product 160 as shown in FIG. 16A includes a
pair of rectangular column portions 162 connected to a
bottom wall or connecting portion 164, wherein a groove
portion 160a extending in the longitudinal direction is
10 formed between column portions 162. Similarly to blank
110 as shown in FIG. 11, a blank 110' for forming product
160 includes one or more (eight in the example of FIG.
16B) low-hardness regions 112' and a high-hardness
regions 114' corresponding to a region other than low-
15 hardness regions 112', the regions being formed by
hardness adjusting process as described above from a
sheet metal of iron, iron alloy, aluminum or aluminum
alloy. Although blank 110' of FIG. 16B is a rectangular
sheet material similarly to blank 110 in FIG. 11, the
20 shape and dimension of blank 110' may be variously
determined depending on intended use, etc., of a product
160. In addition, in blank 110' of FIG. 16B, lowhardness
regions 112' are formed on the both sides (upper
and lower sides in FIG. 16B) of blank 110'.
25 [0095] Similarly to product 120 of FIG. 11, product
160 of FIG. 16A may be manufactured by changing the
hardness of the sheet metal so as to form blank 110'
including high-hardness region 114' and low-hardness
region 112' (the hardness adjusting process); and by
30 bending an objective region to be processed 116'
including low-hardness region 112' and high-hardness
region 114' of blank 110' (the bending process). In
addition, as shown in FIG. 16A, eight deformed portions
166, each having a predetermined bend radius, are formed
35 in product 160. Low-hardness region 112' of blank 110'
has the shape of eight bands extending in the
longitudinal direction of blank 110' (or the direction
^
- 39 -
perpendicular to a paper of FIG. 16B) so that a region to
be deformed portions 166 of product 160 are included in
low-hardness region 112'.
[0096] In FIGs. 11 and 16A, blanks 110 and 110'
5 include objective regions 116 and 116' having the
different hardness in the front and rear sides thereof,
respectively, the objective regions being formed by
changing the hardness of sheet metals 111 and 111' in the
thickness direction thereof so that low-hardness regions
10 112 and 112' are formed in a part of the sheet metals,
respectively. However, the present invention is not
limited to as such. For example, as shown in FIG. 17A,
an objective region 116" to be processed may be formed
over the entirety of a blank 110".
15 [0097] In order to form blank 110" having objective
region 116" extending over the entirety of the blank, the
hardening process may be a process for cooling the
entirety of one side of the sheet metal by using a mold.
Concretely, as exemplified in FIG. 17B, for example, a
20 mold device 170 including an upper mold 172 may be
prepared, wherein upper mold 172 has a planar shape
corresponding to a planar shape of sheet metal 111".
After heating sheet metal 111" by means of a heating
furnace, etc., upper mold 172 of mold device 170 contacts
25 the entirety of one side of the sheet metal to be highhardness
region 114" so as to cool the region, whereby
the side contacting upper mold 172 becomes high-hardness
region 114" and the opposed side becomes low-hardness
region 112".
30 [0098] Alternatively, as exemplified in FIG. 170, the
hardening process may be a process for water-cooling the
entirety of one side (or an upper surface in FIG. 17C) of
sheet metal 111".
As shown in FIG. 17D, a process, for heating the
35 entirety of one side of sheet metal 111" to be lowhardness
region 112" by using a laser, may be carried
out. By using the method of FIG. 17D, blank 111",
^
- 40 -
including low-hardness region 112" having lower hardness
than sheet metal 111" and high-hardness region 114"
having the same hardness as sheet metal 111", is
obtained.
5 [0099] The other methods for forming objective region
116" extending over the entirety of blank 111" may
include: a shot peening process for projecting shots onto
one side of sheet metal 111"; a process for carbonizing
or nitriding one side of sheet metal 111"; and a process
10 for overlapping and rolling a high-hardness sheet metal
and a low-hardness sheet metal so as to form a multilayer
sheet (not shown).
[0100] (Example)
Hereinafter, examples of the present invention will
15 be explained with reference to FIGs. 18A to 21B.
By the method as described above, a product 180 as
shown in FIG. 20 was formed. In FIG. 20, a unit of
length of numerical numbers is millimeters (mm). Product
180 of FIG. 20 is a channel-shaped member, including a
20 bottom wall 182; opposed side walls 184 vertically
extending from both side edges of bottom wall 182; and a
pair of flange portions 186 extending inwardly from side
walls 184 parallel to bottom wall 182, wherein an opening
180a is formed between flange portions 186. As shown in
25 FIG. 20, product 180 has four deformed portions 188a to
188d, and a bend radius "R3" of each deformed portion is
2 mm.
[0101] In order to manufacture product 180 as shown in
FIG. 20, rectangular sheet metal SM2 having a width of
30 220 mm, a length of 1200 mm, and a thickness of 1.2 mm,
were prepared (see Table 1). Then, after sheet metal SM2
was heated by means of a heating furnace to 900 degrees C
(the heating process), a portion to be a high-hardness
region 194 of a blank 190 (FIG. 18B) was quenched by
35 using a mold device 200 having a lower mold 202 and an
upper mold 204 (schematically shown in FIG. 18A) (the
hardening process), whereby blank 190 was formed. By
- 41 -
means of mold device 200, in sheet metal SM2, a portion
facing groove portion 206 is gradually cooled (not cooled
by upper mold 204) and becomes low-hardness region 192,
and the other portion is rapidly cooled by means of lower
5 and upper molds 202 and 204 and becomes high-hardness
region 194.
[0102] When a contact time between the sheet metal and
molds 202, 204 is too short, the sheet metal is not
hardened. On the other hand, when the contact time is
10 too long, the non-contact region facing groove portion
206 of upper mold 204 is also hardened. Therefore, in
example 4, the contact time between the sheet metal and
molds 202, 204 was determined to 5 seconds, in view of
the thickness of the sheet metal, the planar shape of the
15 region to be low-hardness region 192, and the dimension
of low-hardness region 192 in the thickness direction of
the sheet metal, etc.
[0103] A unit of length numerical numbers in FIGs. 18A
and 18B is millimeters (mm). As shown in FIG. 18B, width
20 B of a low-hardness region 192 of blank 190 is 7 mm, and
thus the width of each of grooves 206 of upper mold 204
of mold device 200 is also 7 mm.
[0104] In relation to example 4 obtained as described
above, an average hardness of high-hardness region 194
25 (Hvh) and an average hardness of low-hardness region 192
(Hvl) of blank 190 were measured, and a ratio of the
hardness of the low-hardness region relative to the
hardness of the high-hardness region (Hvl/HvhxlOO%) was
calculated. The result is indicated in Table 6.
- 42 -
Table 6
Inv.
Inv.
Comp.
ex.
ex.
ex.
4
5
4
Average hardness (Hv)
High-hardness region
503
501
504
Low-hardness region
339
336
-
Hardness ratio
(%)
67
67
-
c - 43 -
[0105] Sheet metal SM2 similar to example 4 was
prepared, and heated by means of a heating furnace to 900
degrees C (the heating process). After that, by using a
mold (not shown) similar to lower mold 202 of mold device
5 200 of FIG. 18A, one side of the sheet metal was cooled
under the same cooling condition as high-hardness region
194 of blank 190 in example 4 (the hardening process).
As a result, a blank of example 5 was obtained, wherein
the entirety of one side of the blank was high-
10 lowhardness region and the entirety of the other side of
the blank was low-hardness region, and the entirety of
the blank was constituted by the objective region to be
processed. In example 5, the contact time between the
sheet metal and the mold was 8 seconds. Table 6
15 indicates average hardness of the high-hardness region
(Hvh) and average hardness of the low-hardness region
(Hvl) of the blank of example 5.
[0106] Also, sheet metal Siyi2 similar to example 4 was
prepared, and heated by means of a heating furnace to 900
20 degrees C (the heating process). After that, by using a
mold, the entirety of the sheet metal was cooled under
the same cooling condition as high-hardness region 194 of
blank 190 in example 4 (the hardening process). As a
result, a blank of comparative example 4 was obtained,
25 wherein the entirety of the blank was constituted by the
high-hardness region without including the low-hardness
region. Table 6 indicates average hardness (Hvh) of
comparative example 4.
[0107] The tensile strength of the blank of
30 comparative example 4 in Table 6 was 1690 MPa. From
this, it can be estimated that the tensile strength of
the high-hardness regions of the blanks (sheet metal SM2)
of examples 4 and 5 of the invention, having the same
chemical compositions and the same average hardness as
35 comparative example 4, were generally equal to 1690 MPa.
[0108] As indicated in Table 6, the hardness ratio
(Hvl/HvhxlOO%) was 67% in both of examples 4 and 5.
f - 44 -
Further, the tensile strength of the blank of comparative
example 4 was 1200 MPa or more.
[0109] After that, as shown in FIGs. 19A to 19D, by
bending each objective region 196 to be processed of
5 blank 190 of example 4 by means of a press brake so that
low-hardness region 192 is inside the objective region,
four deformed portions 188a, 188b, 188c and 188d (FIG.
20) were sequentially formed in channel-shaped product
180, whereby a product PPl was obtained (the bending
10 process) .
[0110] In FIGs. 19A to 19D, press brake 210 includes a
lower mold (or a die) 212 having a V-shaped groove 212a
corresponding to an outer shape of each deformed portion
188a, 188b, 188c and 188d of product 180; and an upper
15 mold (or a punch) 214 having a front shape corresponding
to groove 212a of lower mold 212. One objective region
to be processed was selected from four objective regions
196 of blank 190, and the selected region was positioned
between lower mold 212 and upper mold 214. Then, upper
20 mold 214 was downwardly moved toward lower mold 212 so as
to press and bend objective region 196 by lower and upper
molds 212 and 214. Such operations were sequentially
carried out in relation to other objective regions 196.
[0111] By a bending process wherein objective regions
25 196 of blank 190 of example 4 was bent by means of a 21-
stage roll forming machine so that low-hardness region
192 is inside the objective region, deformed portions
188a, 188b, 188c and 188d (FIG. 20) of channel-shaped
product 180 were sequentially formed, whereby a product
30 PP2 was obtained (the bending process).
[0112] By a bending process wherein the blank of
example 5 was bent by means of a press brake similarly to
the process for product PPl, a channel-shaped product PP3
as shown in FIG. 20 was manufactured.
35 [0113] By a bending process wherein the blank of
example 5 was bent by means of a 21-stage roll forming
machine similarly to the process for product PP2, a
f - 45 -
channel-shaped product PP4 as shown in FIG. 20 was
manufactured.
[0114] By a bending process wherein the blank of
comparative example 4 was bent by means of a press brake
5 similarly to the process for product PPl, a channelshaped
product PP5 as shown in FIG. 20 was manufactured.
[0115] Further, by a bending process wherein the
comparative example 4 was bent by means of a 21-stage
roll forming machine similarly to the process for product
10 PP2, a channel-shaped product PP6 as shown in FIG. 20 was
manufactured.
[0116] In relation to products PPl to PP6 obtained as
such, a bending test was carried out, and a result
thereof is indicated in Table 7.
- 46 -
Table 7
Formed
product
No.
PPl
PP2
PP3
PP4
PP5
PP6
Blank
Inv. ex. 4
Inv. ex. 5
Comp.ex.4
Result of forming
Forming
method
Press
brake
Roll
forming
Press
brake
Roll
forming
Press
brake
Roll
forming
Corner
crack
No crack
No crack
No crack
No crack
No crack
Crack
Result of bending test
Peak
load
P (kN)
38.6
39.1
35.4
35.7
39.0
-
Corner
crack
No crack
No crack
No crack
No crack
Crack
-
Absorption
energy
E (J)
1511
1515
1265
1277
859
-
f 47
[0117] A test piece 220 as shown in FIG. 21A is
constituted by a hollow member including product 180 and
a steel plate 222 jointed to an opening 180a of product
180 by arc welding. The bending test was carried out by
5 using products PPl to PP6 as product 180. As steel plate
222, a sheet metal of the same material as the sheet
metal for manufacturing products PPl to PP6, and having a
width of 60 mm, a length of 1200 mm, and a thickness of
1.2 mm, was prepared. The above heating process and
10 hardening process were carried out in relation to the
sheet metal so that the sheet metal had the hardness
equivalent to high-hardness region 194.
[0118] Next, tubular test piece 220 obtained as such
was positioned so that steel plate 222 was directed
15 downward, as shown in FIG. 21B, and was positioned so as
to form a beam of test piece 220 having a span of 1000 mm
between two fulcrum points 230, 230, each fulcrum point
providing with a front end having a hemispherical shape
of a radius of 12.5 mm. Then, a three-point bending test
20 was carried out by positioning a jig 232 having a
hemispherical shape of a radius of 150 mm at the center
of the beam, and peak load (or maximum load) of the
bending load and absorption energy to a bending
deflection of 50 mm were determined.
25 [0119] In addition, in relation to products PPl to
PP6, the existence of a crack (or a corner crack) in
deformed portions 188a, 188b, 188c and 188d were visually
checked in the bending process and the bending test. The
result was indicated in Table 7.
30 [0120] As indicated in Table 7, in products PPl to PP4
using the blanks of example 4 and 5, the corner crack did
not occur in the bending process and the bending test.
The peak load of product PPl was slightly lower than
product PP5 manufactured by using the sheet metal having
35 the same compositions in the same method. On the other
hand, the absorption energy of product PPl was
significantly higher than product PP5.
I?
- 48 -
[0121] The absorption energy of products PP2 to PP4
was 1200 J or more, which was significantly higher than
product PP5 manufactured by using the sheet metal having
the same compositions.
5 [0122] In product PP5 manufactured by bending the
blank of comparative example 4 by means of the press
brake, although the corner crack did not occur in the
bending process, the corner crack occurred in the bending
test.
10 Further, in product PP6 manufactured by bending the
blank of comparative example 4 by means of the roll
forming machine, the corner crack occurred in the bending
process, and the bending test could not be carried out.
[0123] Hereinafter, with reference to FIGs. 22A to
15 23B, a stress applied to a deformed portion by the
bending process and the shape of the bended deformed
portion will be explained, in relation to a sheet metal
"A" wherein the hardness of a region inside the deformed
portion is lower than the hardness of a region outside
20 the deformed portion; and a sheet metal "B" wherein the
hardness of the deformed portion is constant in the
thickness direction thereof. As shown in FIG. 22A, in
sheet metal A wherein the hardness of region 273 inside
the deformed portion is lower than the hardness of region
25 274 outside the deformed portion, when the stress is
applied to sheet metal A so as to deform the sheet metal,
a compressive stress is applied to region 273 inside the
deformed portion and a tensile stress is applied to
region 274 outside the deformed portion. In sheet metal
30 A, since the hardness of region 273 inside the deformed
portion is different from the hardness of region 274
outside the deformed portion, the magnitudes of the
stress when the plastic deformation is initiated are also
different in regions 273 and 274.
35 [0124] Concretely, since the hardness region 273
inside the deformed portion of sheet metal A is lower
than the hardness of region 274, region 273 is easily
- 49 -
plastically deformed by relatively low stress.
Therefore, in sheet metal A, region 273 inside the
deformed portion is plastically deformed by the stress
for deforming sheet metal A, in advance of region 274
5 outside the deformed portion. After that, region 274
outside the deformed portion is plastically deformed as
well as region 273, and finally, the deformed portion
having a predetermined shape as shown in FIG. 23B is
obtained.
10 [0125] In the deformed portion of sheet metal A
deformed as such, as shown in FIG. 22A, a compressive
strain 271a of inside region 273 is larger than a tensile
strain 271b of outside region 274. Therefore, in the
deformed portion of sheet metal A, as shown in FIG. 22A,
15 a neutral axis 7a, at which the compressive stress of
inside region 273 and the tensile stress of outside
region 274 balance, is positioned outside an intermediate
position of sheet metal A in the thickness direction
thereof.
20 [0126] Also, as shown in FIG. 22B, in sheet metal B
wherein the hardness of the deformed portion is constant
in the thickness direction thereof, when the stress is
applied to sheet metal B so as to deform the sheet metal,
a compressive stress is applied to a region inside the
25 deformed portion and a tensile stress is applied to a
region outside the deformed portion. However, unlike
sheet metal A, since the hardness of the region inside
the deformed portion is the same as the hardness of the
region outside the deformed portion in sheet metal B, the
30 magnitudes of the stress when the plastic deformation is
initiated are the same in the regions.
[0127] Therefore, in sheet metal B, by the stress for
deforming sheet metal B, the region inside the deformed
portion is plastically deformed simultaneously with the
35 region outside the deformed portion, and finally, the
deformed portion having a predetermined shape as shown in
FIG. 23B is obtained. In the deformed portion of sheet
i^R
- 50 -
metal B deformed as such, as shown in FIG. 22B, a
compressive strain 272a of the inside region is equal to
a tensile strain 272b of the outside region. Therefore,
in the deformed portion of sheet metal B, as shown in
5 FIG. 22B, a neutral axis 27b, at which the compressive
stress of the inside region and the tensile stress of the
outside region balance, is positioned at an intermediate
position of sheet metal B in the thickness direction
thereof.
10 [0126] As explained above, in sheet metals A and B, in
relation to the stress generated by the bending process,
the ratio of compressive strain 271a and tensile strain
271b is different from the ratio of compressive strain
272a and tensile strain 272b. Further, in the deformed
15 portion of sheet metal A, unlike sheet metal B, in
relation to the stress generated by the bending process,
compressive strain 271a of inside region 273 is larger
than tensile strain 271b of outside region 274. In this
regard, since inside region 273 of the deformed portion
20 is a region having low hardness in sheet metal A, a
crinkle and a crack are unlikely to be generated by the
bending process, and the inside region is deformed so as
to inwardly bulge at the deformed portion, as shown in
FIG. 23A.
25 [0129] In addition, in the deformed portion of sheet
metal A, unlike sheet metal B, in relation to the stress
generated by the bending process, tensile strain 271b of
outside region 274 is smaller than compressive strain
271a of inside region 273, whereby the load applied to
30 outside region 274 due to the bending process is reduced.
By virtue of this, although outside region 274 of the
deformed portion is a region having high hardness in
sheet metal A where a crinkle and a crack are likely to
be generated, disadvantages due to the bending process
35 can be avoided. Therefore, the disadvantages due to the
bending process are unlikely to be generated in sheet
metal A, and sheet metal A can be easily bent.
^
- 51 -
[013CJ] Further, as shown in FIG. 23A, the deformed
portion of sheet metal A is deformed so as to inwardly
budge, due to the difference between compressive strain
271a and tensile strain 271b generated by the stress for
5 the deformation. By virtue of this, for example, when
sheet metals A and B have the same thickness and the
sheet metals are deformed by the bending process so as to
have the same outside shape, a maximum thickness dl of
the deformed portion of sheet metal A is larger than a
10 maximum thickness d2 of the deformed portion of sheet
metal B.
[013t' ] Accordingly, a product obtained by the bending
process of sheet metal A is reinforced by the relatively
large maximum thickness dl of the deformed portion. By
15 virtue of this, the product obtained by the bending
process of sheet metal A has high strength, nevertheless
the hardness of inside region 273 of the deformed portion
is lower than outside region 274. Further, in the
product obtained by the bending process of sheet metal A,
20 a strain, which is generated by the load during use,
becomes smaller in outside region 274 having the hardness
higher than inside region 273, similarly to in the
bending process, whereby the load applied to outside
region 274 (where a crack is likely to be generated)
25 during use can be reduced. Therefore, in comparison to a
product obtained by the bending process of sheet metal B,
the entire of which has the same hardness as outside
region 274 of the deformed portion, a crack is unlikely
to be generated in the product obtained by the bending
30 process of sheet metal A due to the load during use.
Reference Signs List
[0131] 10 blank
12 low-hardness region
35 14 high-hardness region
20 product
22 bottom wall
4b 52
24 side wall
26 deformed portion
30 mold device
32 bed
5 34 lower mold
36 upper mold
38 drive unit
40 cooling device
42 lower nozzle
10 44 upper nozzle
4 6 lower masking member
4 8 upper masking member
50 product
52 rectangular column portion
15 54 bottom wall or connecting portion
60 product
60a opening
62 bottom wall
64 side wall
20 66 pair of flange portions
68 deformed portion
7 0 mold device
72 lower mold
7 4 upper mold
25 76 groove
7 8 groove
80 blank
82 low-hardness region
84 high-hardness region
30 90 press brake
92 lower mold
92a V-shaped groove
94 upper mold

^
- 53 -
CLAIMS
Claim 1
A method for bending a sheet metal, the method
comprising:
5 a hardness adjusting process for changing
hardness of at least a part of the sheet metal so as to
form a blank including a high-hardness region and a lowhardness
region having hardness lower than hardness of
the high-hardness region; and
10 a bending process for bending the low-hardness
region of the blank so as to form a product.
Claim 2
The method for bending a sheet metal according claim
15 1, wherein the hardness adjusting process includes a
heating process for heating an entirety of the sheet
metal and a hardening process for quenching only a region
to be the high-hardness region.
20 Claim 3
The method for bending a sheet metal according to
claim 2, wherein the hardening process is a process for
cooling only the region to be the high-hardness region by
using a mold.
25
Claim 4
The method for bending a sheet metal according to
claim 2, wherein the hardening process is a process for
water-cooling only the region to be the high-hardness
30 region.
Claim 5
The method for bending a sheet metal according to
claim 1, wherein the hardness adjusting process comprises
35 a welding process for positioning another sheet metal,
having hardness different from the hardness of the sheet
metal, in a region to be the high-hardness region or the
^
- 54 -
low-hardness region, and welding the sheet metals to each
other.
Claim 6
The method for bending a sheet metal according to
claim 1, wherein the hardness adjusting process is a
process for heating a region to be the low-hardness
region of the sheet metal, by using a laser.
10 Claim 7
The method for bending a sheet metal according to
any one of claims 1 to 6, wherein the hardness of the
low-hardness region is within a range from 30% to 70% of
the hardness of the high-hardness region.
15
Claim 8
The method for bending a sheet metal according to
any one of claims 1 to 7, wherein the low-hardness region
of the blank is deformed by using a press brake in the
20 bending process.
Claim 9
The method for bending a sheet metal according to
any one of claims 1 to 7, wherein the low-hardness region
25 of the blank is deformed by roll forming in the bending
process.
Claim 10
A product manufactured by the method for bending a
30 sheet metal according to any one of claims 1 to 9.
Claim 11
A method for manufacturing a blank as a product by
carrying out bending process, the method comprising:
35 a process for changing hardness of at least a
part of a sheet metal so as to form a blank having a
high-hardness region and a low-hardness region having
^
- 55 -
hardness lower than hardness of the high-hardness region,
wherein the low-hardness region is formed in a
region of the blank including a region which is deformed
by the bending process.
Claim 12
The method for bending a sheet metal according to
any one of claims 1 to 9, wherein the sheet metal is a
high-strength steel sheet having tensile strength of 980
10 MPa or more.
Claim 13
The product according to claim 10, wherein the sheet
metal is a high-strength steel sheet having tensile
15 strength of 980 MPa or more.
Claim 14
The method for manufacturing a blank according to
claim 11, wherein the sheet metal is a high-strength
20 steel sheet having tensile strength of 980 MPa or more.
Claim 15
The product according to claim 13, wherein Vickers
hardness of a region other than the deformed portion
25 which is deformed by the bending process is 310 or more,
and the hardness of the deformed portion is within a
range from 40% to 80% of the hardness of the region other
than the deformed portion.
30 Claim 16
The method for bending a sheet metal according to
claim 1, wherein the harness adjusting process comprises
forming an objective region to be processed in at least a
part of the sheet metal, wherein one side of the sheet
35 metal is formed as the low-hardness region and the other
side of the sheet metal is formed as the high-hardness
region.
^
10
35
- 56 -
Claim 17
The method for bending a sheet metal according to
claim 16, wherein the harness adjusting process comprises
a heating process for heating at least the objective
region over a thickness direction of the sheet metal, and
a hardening process for cooling a surface which
corresponds to the side of the objective region having
higher hardness.
Claim 18
The method for bending a sheet metal according to
claim 17, wherein the hardening process is a process for
cooling the surface which corresponds to the side of the
15 objective region having higher hardness.
Claim 19
The method for bending a sheet metal according to
claim 17, wherein the hardening process is a process for
20 water-cooling the surface which corresponds to the side
of the objective region having higher hardness.
Claim 20
The method for bending a sheet metal according to
25 claim 16, wherein the harness adjusting process is a
shot-peening process applied to one side of the sheet
metal to be at least the objective region.
Claim 21
30 The method for bending a sheet metal according to
any one of claims 16 to 20, wherein the hardness of the
side of the objective region having lower hardness is
within a range from 30% to 80% of the hardness of the
side of the objective region having higher hardness.
Claim 22
The method for bending a sheet metal according to
^
- 57 -
any one of claims 16 to 21, wherein the blank is deformed
by roll forming in the bending process.
Claim 23
5 The method for bending a sheet metal according to
any one of claims 16 to 22, wherein the sheet metal is a
high-strength steel sheet having tensile strength of 980
MPa or more.
10 Claim 24
A product manufactured by the method for bending a
sheet metal according to any one of claims 16 to 23.
Claim 25
15 A blank according to claim 24, wherein the sheet
metal is a high-strength steel sheet having tensile
strength of 980 MPa or more.
Claim 26
20 A method for manufacturing a blank by carrying out
bending process, the method comprising:
a process for changing hardness of a sheet
metal in a thickness direction thereof so as to form a
blank having an objective region to be processed, the
25 objective region being formed in at least a part of the
sheet metal so that the objective region includes front
and back sides having different hardness,
wherein the side of the objective region having
lower hardness is formed in an inside region of a
30 deformed portion which is deformed by the bending
process.
Claim 27
The method for manufacturing a blank according to
35 claim 26, wherein the sheet metal is a high-strength
steel sheet having tensile strength of 980 MPa or more.
- 58
Claim 28
The method for manufacturing a blank according to
claim 26, wherein Vickers hardness of a region other than
the deformed portion which is deformed by .the bending
process is 310 or more, and the hardness of inside of the
deformed portion is within a range from 40% to 85% of the
hardness of the region other than the deformed portion.