U.S. patent application number 16/437275 was filed with the patent office on 2019-11-28 for crash box and method for producing the same.
The applicant listed for this patent is NIPPON STEEL CORPORATION. Invention is credited to Yasuhiro Ito, Yoshiaki Nakazawa, Ryuichi NISHIMURA, Kenichiro Otsuka.
Application Number | 20190359157 16/437275 |
Document ID | / |
Family ID | 52812895 |
Filed Date | 2019-11-28 |
![](/patent/app/20190359157/US20190359157A1-20191128-D00000.png)
![](/patent/app/20190359157/US20190359157A1-20191128-D00001.png)
![](/patent/app/20190359157/US20190359157A1-20191128-D00002.png)
![](/patent/app/20190359157/US20190359157A1-20191128-D00003.png)
![](/patent/app/20190359157/US20190359157A1-20191128-D00004.png)
![](/patent/app/20190359157/US20190359157A1-20191128-D00005.png)
![](/patent/app/20190359157/US20190359157A1-20191128-D00006.png)
![](/patent/app/20190359157/US20190359157A1-20191128-D00007.png)
![](/patent/app/20190359157/US20190359157A1-20191128-D00008.png)
United States Patent
Application |
20190359157 |
Kind Code |
A1 |
NISHIMURA; Ryuichi ; et
al. |
November 28, 2019 |
CRASH BOX AND METHOD FOR PRODUCING THE SAME
Abstract
A crash box has excellent axial crushing performance and in
which, even if the sheet thickness of a tubular body constituting
the crash box is smaller than 1.4 mm, good welding can be performed
with the tubular body butted against a set plate. The crash box (1)
having a metallic longer-length tubular body and a method for
producing the crash box are provided. The tubular body has a basic
cross-sectional shape that is a flat polygon surrounded by a
plurality of ridges (2-1 to 2-4) extending in a longitudinal
direction and a plurality of side wall portions (4), includes one
or more groove portions (3-1 and 3-2) on side wall portions (4) on
long sides substantially parallel to the major axis direction of
the cross section that extend in longitudinal direction, and
includes outward flanges (5-1 to 5-4) in an end portion in the
longitudinal direction.
Inventors: |
NISHIMURA; Ryuichi; (Tokyo,
JP) ; Otsuka; Kenichiro; (Tokyo, JP) ; Ito;
Yasuhiro; (Tokyo, JP) ; Nakazawa; Yoshiaki;
(Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NIPPON STEEL CORPORATION |
Tokyo |
|
JP |
|
|
Family ID: |
52812895 |
Appl. No.: |
16/437275 |
Filed: |
June 11, 2019 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
15025414 |
Mar 28, 2016 |
10363892 |
|
|
PCT/JP2014/075191 |
Sep 24, 2014 |
|
|
|
16437275 |
|
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B60R 19/34 20130101;
B23K 9/0026 20130101; B23K 31/02 20130101; F16F 7/12 20130101; B62D
21/15 20130101; B23K 26/21 20151001; B23K 9/235 20130101; B23K
26/0093 20130101 |
International
Class: |
B60R 19/34 20060101
B60R019/34; B23K 31/02 20060101 B23K031/02; B23K 26/00 20060101
B23K026/00; B23K 9/235 20060101 B23K009/235; B62D 21/15 20060101
B62D021/15; B23K 26/21 20060101 B23K026/21; F16F 7/12 20060101
F16F007/12; B23K 9/00 20060101 B23K009/00 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 9, 2013 |
JP |
2013-212070 |
Claims
1-17. (canceled)
18. A method of producing crash box comprising a longer-length
metallic tubular body and a set plate including locking sections,
the locking sections are individually formed as a part of the set
plate, the tubular body having a basic cross-sectional shape that
is a polygon surrounded by a plurality of ridges extending in a
first direction and a plurality of side wall portions, the tubular
body including one or more groove portions in side wall portions on
long sides that are substantially parallel to a major axis
direction of the cross section, the groove portions extending in
the first direction, and the tubular body including a curved
portion molded integrally with the tubular body and outward flanges
continuing to the curved portion at an end portion of the tubular
body in the first direction, the set plate being welded to an end
of the tubular body having the outward flanges, and the locking
sections section being integral with the set plate and projecting
upwardly from a surface of a portion of the set plate positioned
within the tubular body, wherein the locking sections section of
the set plate are is butted against the curved portion of the
tubular body, wherein the method comprising following First Step,
Second Step, and Third Step; First Step: a step of, using a
pressing device including: a punch that includes a groove portion
that extends in a second direction and a side wall provided in an
end portion in the second direction; a die that is disposed facing
the punch; and a pad that includes a protrusion extending in the
second direction, to depress a developed blank of the tubular body
into the groove portion of the punch by a protrusion of the pad and
bend the developed blank using the die and the punch, so as to
produce two press molded bodies with an open cross-section, the
press molded bodies each having a basic cross-sectional shape that
is a polygon surrounded by a plurality of ridges extending in the
second direction and a plurality of side wall portions, the press
molded bodies each including one or more groove portions in side
wall portions on long sides substantially parallel a major axis
direction of the cross section, the groove portions extending in
the second direction, and the press molded bodies each including
outward flanges in an end portion in the second direction, the
outward flanges being continuous in a part of region along a
cross-section circumferential direction; and Second Step: a step of
overlapping and welding the two press molded bodies produced
through the first step, at plane portions that are each formed at
both ends in a cross-section circumferential direction of each of
the two press molded bodies, so as to produce the tubular body.
Third Step: a step of overlapping the tubular body obtained through
the second step and the set plate with the outward flanges
interposed therebetween, and attaching the tubular body to the set
plate by spot welding, fillet arc welding, or laser welding.
19. The method for producing a crash box according to claim 18,
wherein the polygon is a flat polygon.
20. The method for producing a crash box according to claim 18,
wherein the outward flanges are provided in all the ridges
excluding at least regions of the end portion corresponding to a
groove portion.
21. The method for producing a crash box according to claim 18,
wherein the outward flanges are molded integrally with the tubular
body.
22. The method for producing a crash box according to claim 18,
wherein the tubular body is a press molded body of the metal
sheet.
23. The method for producing a crash box according to claim 18,
wherein the metal sheet has a sheet thickness of 1.2 mm or
smaller.
24. The method for producing a crash box according to claim 18,
wherein the metal sheet has a sheet thickness of 1.0 mm or
smaller.
25. The method for producing a crash box according to claim 18,
wherein the metal sheet is a steel sheet having a tensile strength
of 440 MPa or higher.
26. The method for producing a crash box according to claim 18,
wherein the metal sheet is a steel sheet having a tensile strength
of 590 MPa or higher.
27. The method for producing a crash box according to claim 18,
wherein the polygon is a substantial quadrilateral.
28. The method for producing a crash box according to claim 18,
wherein the pad includes restraining portions that restrain
portions in the developed blank to be molded into ridges in a
vicinity of outward flanges, the portions in the developed blank to
be molded into the ridge in the vicinity of the outward flanges are
retained by the restraining portions.
29. The method for producing a crash box according to claim 28,
wherein the set plate includes a locking section that is provided
projecting from a surface of the plate and is butted against an
inner surface of an end portion in a longitudinal direction of the
tubular body.
Description
TECHNICAL FIELD
[0001] The present invention relates to a crash box that is to be
attached to an automobile body, and to a method for producing the
crash box. In particular, the present invention relates to, a crash
box that is to be attached to, for example, the front portion or
the rear portion of an automobile body and includes a tubular body
that buckles and is plastically deformed into a bellows when loaded
with impact load in the axis direction of the tubular body, so as
to absorb impact energy, the tubular body being a molded body made
of a metal sheet and to a method for producing the crash box.
BACKGROUND ART
[0002] An impact energy absorbing member that buckles by an impact
load in a collision to absorb collision energy is attached to a
vehicle. As one such impact energy absorbing member, a crash box is
known. A crash box includes a tubular body that is disposed in the
front and rear of a vehicle, being oriented in a front-back
direction. The crash box includes a set plate (an attachment plate)
that is welded to this tubular body at one end portion in the
longitudinal direction of the tubular body by butt arc welding or
the like.
[0003] A crash box is required to repeatedly and stably buckle in
its axis direction when loaded with a collision load in the axis
direction of the tubular body of the crash box. The present
applicants have disclosed in, for example, Patent Document 1, a
patented invention relating to a crash box that includes a tubular
body with groove portions. The groove portions are each provided in
such a manner as to project inward from a long side of a polygon
that forms the cross section of the crash box, and to extend in the
axis direction of the crash box. This crash box is ensured to, by
an impact load loaded in the axis direction, repeatedly buckle and
to be plastically deformed into a bellows so as to absorb impact
energy.
[0004] In recent years, in order to reduce the weight of a vehicle,
there has been considered the reduction in the sheet thickness of a
tubular body constituting a crash box. However, if the sheet
thickness of the tubular body of the crash box disclosed in Patent
Document 1 is reduced to about 1.2 to 1.4 mm or smaller, the end
portion of the tubular body is burned through by heat input in butt
arc welding with a set plate, raising the risk of declining the
strength of a weld zone.
[0005] The present applicant has proposed, in Patent Document 2, a
crash box that has one end portion in the axis direction of a
metallic tubular body, the one end portion being folded back 180
degrees to be formed into a folded portion.
LIST OF PRIOR ART DOCUMENTS
Patent Document
[0006] Patent Document 1: JP3912422B
[0007] Patent Document 2: JP2008-261493A
DISCLOSURE OF THE INVENTION
Problems to be Solved by the Invention
[0008] The above problem can be solved with the crash box disclosed
in Patent Document 2 to some extent. However, the crash box has a
problem in that the existence of the folded portion makes the
plastic deformation into a bellows hard to occur, which reduces
impact energy absorbing performance, and in that molding the folded
portion is difficult if the tubular body is formed of a
high-strength steel sheet.
[0009] An objective of the present invention is to provide a
lightweight crash box and a method for producing the crash box, the
crash box including a tubular body that can be well welded, with
the tubular body butted against a set plate, even if the sheet
thickness of the tubular body constituting the crash box is smaller
than 1.4 mm.
Means for Solving the Problems
[0010] The present invention will be described as follows.
(1) A crash box comprising a longer-length metallic tubular
body,
[0011] the tubular body having a basic cross-sectional shape that
is a polygon surrounded by a plurality of ridges extending in one
direction and a plurality of side wall portions, the tubular body
including one or more groove portions in side wall portions on long
sides that are substantially parallel to the major axis direction
of the cross section, the groove portions extending in the one
direction, and the tubular body including outward flanges in an end
portion in the one direction.
[0012] In other words, in the crash box that includes a
longer-length tubular body made of a steel sheet, the tubular body
having a basic cross-sectional shape that is a polygon surrounded
by a plurality of ridges extending in one direction and a plurality
of side wall portions, the tubular body including one or more
groove portions in side wall portions on long sides substantially
parallel to the major axis direction of the cross section, the
groove portions extending in the one direction, characterized in
that the tubular body includes outward flanges in an end portion in
the one direction.
[0013] In the present invention, if the polygon is a rhombus, the
long side in the present invention refers to each side of the
rhombus.
(2) The crash box according to the section 1, wherein the polygon
is a flat polygon. (3) The crash box according to the section 1 or
the section 2, wherein the outward flanges are provided in all the
ridges excluding at least regions of the end portion corresponding
to a groove portion. (4) The crash box according to any one of the
section 1 to the section 3, wherein the outward flanges are molded
integrally with the tubular body. (5) The crash box according to
any one of the section 1 to the section 4, wherein the tubular body
is a press molded body of the metal sheet. (6) The crash box
according to any one of the section 1 to the section 5, wherein the
metal sheet has a sheet thickness of 1.2 mm or smaller. (7) The
crash box according to any one of the section 1 to the section 5,
wherein the metal sheet has a sheet thickness of 1.0 mm or smaller.
(8) The crash box according to any one of the section 1 to the
section 7, wherein the metal sheet is a steel sheet having a
tensile strength of 440 MPa or higher. (9) The crash box according
to any one of the section 1 to the section 7, wherein the metal
sheet is a steel sheet having a tensile strength of 590 MPa or
higher. (10) The crash box according to any one of the section 1 to
the section 9, wherein the polygon is a substantial quadrilateral.
(11) The crash box according to any one of the section 1 to the
section 10, further comprising a set plate that is welded with the
outward flanges interposed therebetween. (12) The crash box
according to the section 11, wherein the set plate includes a
locking section that is provided projecting from a surface of the
plate and is butted against an inner surface of an end portion in a
longitudinal direction of the tubular body. (13) The crash box
according to claim 12, wherein the locking section includes a
curved portion (rise-up curvature portion) that is butted against a
curved portion formed in an end portion in one direction of the
tubular body so as to support the curved portion. (14) A method for
producing the crash box according to any one of the section 1 to
the section 10, the method comprising following First Step and
Second Step;
[0014] First Step: a step of, using a pressing device including: a
punch that includes a groove portion that extends in one direction
and a side wall provided in an end portion in the one direction; a
die that is disposed facing the punch; and a pad that includes a
protrusion extending in the one direction, to depress a developed
blank of the tubular body into the groove portion of the punch by a
protrusion of the pad and bend the developed blank using the die
and the punch, so as to produce two press molded bodies with an
open cross-section, the press molded bodies each having a basic
cross-sectional shape that is a polygon surrounded by a plurality
of ridges extending in the one direction and a plurality of side
wall portions, the press molded bodies each including one or more
groove portions in side wall portions on long sides substantially
parallel a major axis direction of the cross section, the groove
portions extending in the one direction, and the press molded
bodies each including outward flanges in an end portion in the one
direction, the outward flanges being continuous in a part of region
along a cross-section circumferential direction; and
[0015] Second Step: a step of overlapping and welding the two press
molded bodies produced through the first step, at plane portions
that are each formed at both ends in a cross-section
circumferential direction of each of the two press molded bodies,
so as to produce the tubular body.
(15) The method for producing a crash box according to the section
14, wherein the pad includes restraining portions that restrain
portions in the developed blank to be molded into ridges in a
vicinity of outward flanges, the portions in the developed blank to
be molded into the ridge in the vicinity of the outward flanges are
retained by the restraining portions. (16) A method of producing
the crash box according to any one of the section 11 to the section
13, the method comprising following First Step, Second Step, and
Third Step;
[0016] First Step: a step of, using a pressing device including: a
punch that includes a groove portion that extends in one direction
and a side wall provided in an end portion in the one direction; a
die that is disposed facing the punch; and a pad that includes a
protrusion extending in the one direction, to depress a developed
blank of the tubular body into the groove portion of the punch by a
protrusion of the pad and bend the developed blank using the dies
and the punch, so as to produce two press molded bodies with an
open cross-section, the press molded bodies each having a basic
cross-sectional shape that is a polygon surrounded by a plurality
of ridges extending in the one direction and a plurality of side
wall portions, the press molded bodies each including one or more
groove portions in side wall portions on long sides substantially
parallel a major axis direction of the cross section, the groove
portions extending in the one direction, and the press molded
bodies each including outward flanges in an end portion in the one
direction, the outward flanges being continuous in a part of region
along a cross-section circumferential direction; and
[0017] Second Step: a step of overlapping and welding the two press
molded bodies produced through the first step, at plane portions
that are each formed at both ends in a cross-section
circumferential direction of each of the two press molded bodies,
so as to produce the tubular body.
[0018] Third Step: a step of overlapping the tubular body obtained
through the second step and the set plate with the outward flanges
interposed therebetween, and attaching the tubular body to the set
plate by spot welding, fillet arc welding, or laser welding.
(17) The method for producing a crash box according to claim 16,
wherein the set plate includes a locking section that is provided
projecting from a surface of the plate and is butted against an
inner surface of an end portion in a longitudinal direction of the
tubular body.
Advantageous Effects of the Invention
[0019] According to the present invention, it is possible to
perform spot welding, fillet arc welding, or laser welding with
outward flanges formed on a tubular body and a set plate made to
overlap with each other. For this reason, even if the sheet
thickness of the tubular body is less than 1.4 to 1.2 mm, the
occurrence of poor welding such as burn-through, which is a problem
with the prior art, is prevented, increasing strength in a weld
zone. This allows for providing a lightweight crash box that
includes a tubular body having a sheet thickness of less than 1.4
to 1.2 mm.
[0020] In addition, in a crash box including curved portions
(rise-up curvature portions) and outward flanges in an end portion
in a longitudinal direction, in the case where the sheet thickness
of a tubular body is, in particular, smaller than 1.2 mm, an impact
load causes the end portion in the longitudinal direction of the
tubular body to collapse inside the cross section, generating
deformation that hinders stable repetitive buckling. This
phenomenon occurs conspicuously in particular when the impact load
acts in a direction oblique to the axis direction of the tubular
body.
[0021] The present invention uses a set plate including locking
sections that are provided projecting from a surface of the plate
and are butted against the inner surface of the tubular body to
retain an end portion in the longitudinal direction of the tubular
body. Accordingly, it is possible to suppress the above collapse,
increasing the impact energy absorbing performance of a crash box
that includes a tubular body having a small sheet thickness.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1 is an illustrative diagram illustrating a tubular
body that constitutes a crash box of the present embodiment, where
FIG. 1A is a perspective view illustrating the entirety thereof,
FIG. 1B is a front view, FIG. 1C is a side view, and FIG. 1D to F
are illustrative diagrams illustrating examples of the positions of
outward flanges.
[0023] FIG. 2 is an illustrative diagram schematically illustrating
the state where the tubular body and a set plate of the crash box
are attached to each other.
[0024] FIGS. 3A-C are illustrative diagrams schematically
illustrating locking sections provided in the set plate, with FIG.
3A showing a plan view of the set plate, FIG. 3B showing a cross
sectional view taken along the line I-1, and FIG. 3C showing a
diagram of the set plate and tubular body combined.
[0025] FIG. 4 is a schematic diagram illustrating an example of the
configuration of a pressing device for producing a press molded
body.
[0026] FIG. 5 is a schematic diagram illustrating the other example
of the configuration of the pressing device for producing the
tubular body of the embodiment.
[0027] FIG. 6 is an illustrative diagram schematically illustrating
a method for producing a crash box according to the present
invention, where FIG. 6A illustrates First Step, FIG. 6B
illustrates Second Step, and FIG. 6C illustrates Third Step.
[0028] FIGS. 7A and 7B are illustrative diagrams schematically
illustrating the shapes of developed blanks in examples.
[0029] FIGS. 8A and 8B are illustrative diagrams schematically
illustrating the shapes press molded bodies in the examples.
MODE FOR CARRYING OUT THE INVENTION
[0030] The present invention will be described with reference to
the accompanying drawings.
1. Crash box 0
[0031] FIG. 1 is an illustrative diagram illustrating a tubular
body 1 that constitutes a crash box 0 according to the present
invention, where FIG. 1A is a perspective view illustrating the
entirety thereof, FIG. 18B is a front view of the tubular body 1,
FIG. 1C is a side view of the tubular body 1, and FIGS. 1D to F are
cross sectional views of modifications 1-1 to 1-3 of the tubular
body 1.
[0032] The crash box 0 includes a metallic tubular body 1. The
tubular body 1 buckles into a bellows upon receiving an impact load
that is applied in the axis direction of the tubular body 1, so as
to absorb collision energy.
[0033] As illustrated in FIGS. 1A and 1B, the tubular body 1 has a
basic cross section that is a flat substantial quadrilateral. The
tubular body 1 includes one or more groove portions 3-1 and 3-2
each of which extends in the longitudinal direction of the tubular
body 1. The groove portions 3-1 and 3-2 are provided in positions
excluding ridges 2-1 to 2-4 that constitute the basic cross
section. The groove portions 3-1 and 3-2 are provided in side wall
portions 4 on long-side face sides that are parallel to the major
axis direction of the cross section. The groove portions 3-1 and
3-2 are groove portions each projecting toward the inside of the
cross section.
[0034] In this description, the tubular body 1 is used that has a
cross sectional shape being a substantial quadrilateral. However,
the present invention is not limited to this cross-sectional shape.
The tubular body 1 in the present invention may have a cross
sectional shape of, for example, a flat substantial polygon such as
a hexagon and an octagon. Preferably, the basic cross section is a
flat substantial quadrilateral, and one or more groove portions 3-1
and 3-2 are formed in two side wall portions 4 and 4 on long-side
face sides.
[0035] As illustrated in FIGS. 1A and 1B, the tubular body 1 is
formed by a first press molded body 10-1 and a second press molded
body 10-2 in combination, which will be described later. Each of
the first press molded body 10-1 and the second press molded body
10-2 is a press molded bodies made of a metal sheet.
[0036] In an end portion of the tubular body 1 in its longitudinal
direction, outward flanges 5-1 to 5-4 are provided in the region of
the side wall portion 4 excluding the groove portions 3-1 and 3-2.
The outward flanges 5-1 to 5-4 are molded integrally with the
tubular body 1.
[0037] The outward flanges 5-1 to 5-4 includes flat portions along
the circumferential direction of the cross-section, the flat
portions each having a width of 2 mm or more. A width B1 of the
outward flanges 5-1 to 5-4 along the ridges 2-1 to 2-4 is 2 mm or
more. A width B2 of the outward flanges 5-1 to 5-4 along the region
other than the ridges 2-1 to 2-4 is 10 mm or more. Now, the width
of the flange means a length in a direction perpendicular to the
cross-section circumferential direction of the outward flange
region (the length of only the flat portion, not including a curved
portion).
[0038] This description will be made about the case where spot
welding with the set plate is not performed on the outward flanges
5-1 to 5-4 along the ridges 2-1 to 2-4, but on outward flanges 5-1
to 5-4 along the region other than the ridges 2-1 to 2-4. The
present invention is not limited to this case. As illustrated in
FIG. 1D, the outward flanges 5-1 to 5-4 may be provided at least in
the range along the ridges 2-1 to 2-4, and as illustrated in FIG.
1E, it is preferable that, in addition to the ridges 2-1 to 2-4,
outward flanges 5-5 and 5-6 are provided on short-side side wall
portions 6-1 and 6-2, such that all portions other than the groove
portions are provided with the outward flanges. As illustrated in
FIG. 1F, it is more preferable that an outward flange 5-7 is
provided on the entire circumference of the cross-section.
[0039] The width of the outward flanges 5-1 to 5-4 is 2 mm or more
in portions where laser welding or fillet arc welding is to be
performed, and 10 mm or more in portions where spot welding will be
performed.
[0040] The cross-sectional shape of the groove portions 3-1 and 3-2
each have substantial trapezoid or triangular shape, the groove
depth of which is 10 to 35 mm. If the width of the bottom of the
groove portions 3-1 and 3-2 is insufficient, or if the depth of the
groove bottoms 3-1 and 3-2 is insufficient, the buckling
deformation of the tubular body 1 becomes unstable, and it is thus
difficult to obtain sufficiently the advantageous effect of
improving an impact energy absorbing performance that is brought by
the provision of the groove portions 3-1 and 3-2.
[0041] The length of the tubular body 1 in its axis direction is 80
to 300 mm, from the practical viewpoint.
[0042] The sheet thickness of the tubular body 1 is assumed to be
smaller than 1.4 mm, but is not limited to this configuration, and
can be 1.4 mm or larger. Note that the sheet thickness is
preferably smaller than 1.4 mm, more preferably 1.2 mm or smaller,
and most preferably 1.0 mm or smaller. The lower limit value of the
sheet thickness of the tubular body 1 is preferably 0.5 mm or
higher, from the viewpoint of ensuring a desired energy absorption.
This allows achieving the reduction of the crash box 0 in
weight.
[0043] The material of the tubular body 1 is assumed to be made of
a metal, and preferably made of a steel sheet, more preferably made
of a high-tensile steel sheet having a tensile strength of 440 MPa
or higher, and still more preferably made of a high-tensile steel
sheet having a tensile strength of 590 MPa or higher.
[0044] FIG. 2 is an illustrative diagram illustrating the state
where the tubular body 1 and a set plate 7, which constitute the
crash box 0, are attached to each other.
[0045] As illustrated in FIG. 2, the crash box 0 includes the
tubular body 1, which is described above, and the set plate 7. The
set plate 7 is attached to the tubular body 1 with the outward
flanges 5-1 to 5-4 provided in one end portion of the tubular body
1 interposed therebetween, by welding. One such welding is laser
welding, fillet arc welding, spot welding, or the like.
[0046] FIG. 3 is an illustrative diagram schematically illustrating
locking sections 8-1 to 8-4 that are provided in the set plate 7,
where FIG. 3A is a plan view of the set plate 7, FIG. 3B is a cross
sectional view of the set plate 7 taken along the line I-I, and
FIG. 3C is an illustrative diagram schematically illustrating the
state where the tubular body 1 are the set plate 7 are combined
with each other.
[0047] As illustrated in FIG. 3, the set plate 7 includes the
locking sections 8-1 to 8-4. The locking sections 8-1 to 8-4 are
provided projecting from a surface of the plate 7. The locking
sections 8-1 to 8-4 are butted against the inner surface of the
tubular body 1 to retain one end portion in the longitudinal
direction of the tubular body 1. That is, the locking sections 8-1
to 8-4 support the portions, along the ridges 2-1 to 2-4, of the
curved portions (rise-up curvature portions) of the outward flanges
5-1 to 5-4 in one end portion in the longitudinal direction of the
tubular body 1, from the inside of the main body 1. The locking
sections 8-1 to 8-4 preferably retain all the portions of the
curved portions (rise-up curvature portions) of the outward flanges
5-1 to 5-4 excluding the groove bottom portion, from the inside of
the tubular body 1.
[0048] As seen above, the locking sections 8-1 to 8-4 preferably
have curved portions 8a that are configured to be butted against
the curved portions (rise-up curvature portions) of the outward
flanges 5-1 to 5-4 so as to support the curved portions.
[0049] Note that it is preferable that the set plate 7 is formed
integrally. In this case, instead of forming the four locking
sections 8-1 to 8-4 individually, but for example, the locking
sections 8-1 and 8-4 may be integrally and consecutively formed
while the locking sections 8-2 and 8-3 may be integrally and
consecutively formed. In addition, locking sections 8-5 and 8-6 may
be further provided together with the locking sections 8-1 and,
8-4. The locking sections 8-5 and 8-6 retain portions corresponding
to the groove portions 3-1 and 3-2 from the inside of the tubular
body 1.
[0050] The locking sections 8-1 to 8-4 may exist in the curved
portions (rise-up curvature portions) of the flanges of the tubular
body 1, for example, in the portions corresponding to RI to 10 mm.
The locking sections 8-1 to 8-4 each preferably have a height that
is about one to ten times the sheet thickness of a metal sheet
forming the flange. The set plate 7 is manufactured by pressing,
for example, a steel sheet having a tensile strength of 270 to 980
MPa-class.
[0051] The crash box 0 according to the present invention is
configured as described above.
2. Method for Manufacturing Crash Box 0
[0052] FIG. 6 is an illustrative diagram schematically illustrating
a method for producing the crash box 0 according to the present
invention, where FIG. 6A illustrates a first step, FIG. 6B
illustrates a second step, and FIG. 6C illustrates a third
step.
[0053] The tubular body 1 that constitutes the crash box 0
through:
First Step: producing two press molded bodies 10 each having an
open cross-section from developed blanks, which will be described
later (FIG. 6A); and Second Step: producing the tubular body 1 from
the two press molded bodies 10 and 10 (FIG. 6B).
[0054] Furthermore, as illustrated in FIG. 6C, the crash box 0
including the tubular body 1 and the set plate 7 is produced
through a third step of attaching the set plate 7, by spot welding
or the like, to the tubular body 1 that is produced through the
second step. Note that the two press molded bodies 10 and 10 both
have an open cross-sectional shape that is obtained by dividing the
tubular body 1 into substantially two equal portions by a plane
including the central axis of the tubular body 1.
[First Step]
[0055] FIG. 4 is a schematic diagram illustrating an example of the
configuration of a pressing device 11 for producing the press
molded body 10.
[0056] In the first step, the pressing device 11 is used as
illustrated in FIG. 4. The pressing device 11 includes a punch 12,
a die 13, and a pad 14. The punch 12 includes a groove portion 12a
that extends in one direction (the longitudinal direction), and a
side wall 12b that is provided in an end portion in the
longitudinal direction. The die 13 is disposed facing the punch 12.
The pad 14 includes a protrusion 14a that extends in the
longitudinal direction and is disposed facing the punch 12.
[0057] By press molding the developed blanks 15 using the pressing
device 11, two press molded bodies 10, namely, a first press molded
body 10-1 and a second press molded body 10-2 are produced. The two
press molded bodies 10 have groove portions 3-1 and 3-2 that run in
one direction and includes outward flanges 5-1 to 5-4 that are
formed in one end portion of a longitudinal direction.
[0058] In the press molding in the first step, the developed blank
15 is depressed into the groove portion 12a of the punch 12 by the
protrusion 14a provided in the pad 14, and the developed blank 15
is bent by the die 13 and the punch 12. This yields a metal sheet
provided with a groove portion 3-1 that runs in the longitudinal
direction and outward flanges 5-1 and 5-2 that are formed in an end
portion in the longitudinal direction, in at least regions along a
circumferential direction in the cross-section excluding the groove
portion 3-1. Hereafter, the pad 14 will be also referred to as a
normal pad.
[0059] Note that the developed blank 15 refers to a blank having an
external shape obtained by developing the press molded body 10 to a
flat shape.
[0060] The above description of the first step is made about a
method of press molding using the pressing device 11, but the first
step is not limited to this molding method.
[0061] As the other molding method, for example, a pressing device
16 illustrated in FIG. 5 can be used.
[0062] FIG. 5 is a schematic diagram illustrating a configuration
example of the pressing device 16 that is the other pressing device
for producing the press molded body 10.
[0063] The pressing device 16 includes a punch 12 and a die 13 and
further includes a pad 17 (hereafter, also referred to as a ridge
pad). The punch 12 includes a groove portion 12a that extends in
one direction, and a side wall 12b that is provided in an end
portion in the longitudinal direction. The die 13 is disposed
facing the punch 12. The pad 17 includes a protrusion 17a that is
disposed facing the punch 12 and runs in one direction, and
restraining portions 17b that restrain the vicinity of portions in
the developed blank 15 that are to be molded into ridges 2-1 and
2-2 in the vicinity of the outward flanges 5-1 and 5-2.
[0064] In press molding, the restraining portions 17b restrain the
portions in the developed blank 15 that are to be molded into the
ridges 2-1 and 2-2 in the vicinity of the outward flanges 5-1 and
5-2. In addition, the protrusion 17a of the ridge pad 17 depresses
the developed blank 15 to the groove portion 12a of the punch 12.
Furthermore, the die 13 and the punch 12 bend the developed blank
15. This suppresses poor molding that occurs in the outward flanges
5-1 and 5-2 along the ridges 2-1 and 2-2 in press molding.
[0065] This produces the press molded body 10, the open
cross-section of which has the groove portion 3-1 extending in the
longitudinal direction and the outward flanges 5-1 and 5-2, in an
end portion in the longitudinal direction, the outward flanges 5-1
and 5-2 being continuous in the entire or a part of the region
along the cross-section circumferential direction.
[0066] If portions or the like right under the ridge pad 17
corresponding to the ridges 2-1 and 2-2 are not completely molded
in the molding process using the ridge pad 17, the portions may be
molded by following press working that includes bending (restrike),
which is performed in typical press molding.
[Second Step]
[0067] In the second step, the first press molded body 10-1 and the
second press molded body 10-2 are made to overlap each other at
plane portions that are formed at both ends of their cross-section
circumferential direction, and the overlapping portions are
attached to each other by appropriate welding means such as laser
welding and spot welding, so as to produce the tubular body 1.
[Third Step]
[0068] In the third step, the tubular body 1 obtained in the second
step is welded to the set plate 7 with the outward flanges 5-1 to
5-4 interposed therebetween, by welding means such as laser
welding, spot welding, and fillet arc welding. As the set plate 7,
it is preferable to use a set plate provided with the locking
sections 8-1 to 8-4.
[0069] In the above description, the employed form is a form that
includes the continuous outward flanges 5-1 to 5-4 in the region
excluding the groove portion, but is not limited to this form, and
may be a form in which the outward flanges 5-1 to 5-4 formed in the
above region have notches in portions of the flanges other than
those corresponding to the ridges 2-1 to 2-4 excluding the groove
portions.
[0070] The width or shape of the outward flanges 5-1 to 5-4 can be
modified as appropriate by adjusting the shape of the developed
blank 15.
EXAMPLE
[0071] Deformation behavior in the press molding of developed
blanks into the press molded bodies 10-1 and 10-2 (the first and
the second press molded bodies) using the pressing device 11
including the normal pad 14 illustrated in FIG. 4 or the pressing
device 16 including the ridge pad 17 illustrated in FIG. 5, was
analyzed by Finite Element Method) (Analysis 1).
[0072] FIG. 7 is an illustrative diagram schematically illustrating
shapes of developed blanks 15-1 and 15-2 in the example.
[0073] As the developed blanks, as illustrated in FIGS. 7A and 7B,
the blanks 15-1 and 15-2 of two types were used that were adjusted
such that the outward flanges 5-1 to 5-4 to be formed in an end
portion of the tubular body 1 were formed in the entire region in
the cross-section circumferential direction excluding parts of
region along the groove portions 3-1 and 3-2. The developed blank
15-1 was formed such that the width of the outward flanges 5-1 to
5-4 was substantially uniform and 15 mm. The developed blank 15-2
was formed such that the width of the outward flanges 5-1 to 5-4
along the ridges 2-1 to 2-4 was 2 mm and the width of the other
portions was 15 mm.
[0074] FIG. 8 is an illustrative diagram schematically illustrating
the shapes of a press molded body 10-pattern A and a press molded
body 10-pattern B in the examples, where FIG. 8A illustrates the
case of using the developed blank 15-1, and FIG. 8B illustrates the
case of using the developed blank 15-2.
[0075] Next, molded bodies were made to overlap each other at plane
portions, the molded bodies being each of two first press molded
bodies 10-pattern A and two second press molded body 10-pattern B
to which flanges are added in groove bottom portions, the plane
portions each being formed at both ends in a cross-section
circumferential direction of each of the molded bodies, and the
overlapping portions are subjected to spot welding to produce a
tubular body 1 that includes outward flanges 5-1 to 5-4.
[0076] Next, a crash box 0 was assembled, which includes the
tubular body 1 and a set plate 7 that is subjected to spot welding
with the outward flanges 5-1 to 5-4 provided in an end portion of
the tubular body 1 interposed therebetween, and buckling behavior
at the time of applying impact load to one end of the tubular body
1 constituting the crash box 0 was analyzed by Finite Element
Method (Analysis 2).
[0077] Note that there were two loading directions of the impact
load, a direction parallel to the longitudinal direction of the
tubular body 1 and a direction that inclines 5 degrees with respect
to the longitudinal direction.
[0078] The tubular body 1 had a length of 120 mm and a
cross-sectional dimension of 64 mm.times.93 mm.
[0079] The material of the blanks 15-1 and 15-2 were JSC440W (The
Japan Iron and Steel Federation Standard (JFS Standard)), which is
a 440 MPa-class cold-rolled steel sheet, and JSC590R (JFS
Standard), which is a 590 MPa-class cold-rolled steel sheet, and
there were two levels of sheet thickness, 1.0 mm and 1.2 mm.
[0080] In addition, the influence of the presence/absence of the
locking sections 8-1 to 8-4 in the set plate 7 was also examined.
The locking sections 8-1 to 8-4 each have shapes corresponding to
the shape of a curved portion (rise-up curvature portion), having
an inner R of 2 to 4 mm, and the height of the locking sections 8-1
to 8-4 is about 3 to 7 mm, which is somewhat higher than the value
of the inner R.
[0081] As a conventional example, a similar analysis was conducted
on a crash box produced by performing butt arc welding on a known
tubular body that was butted against a set plate, the known tubular
body having the cross-sectional shape of the tubular body 1
described above and not including outward flanges 5-1 to 5-4. The
material of the blank was JSC440W, and there were two levels of
sheet thickness, 1.0 mm and 1.2 mm.
[0082] Table 1 shows the results of Analysis 1. As illustrated in
Table 1, both the developed blanks 15-1 and 15-2 can yield a press
molded body that includes groove portions 3-1 and 3-2 that extends
in their longitudinal direction, and outward flanges 5-1 and 5-2 or
outward flanges 5-3 and 5-4 in an end portion of the longitudinal
direction, but with the developed blank 15-1, as compared with the
developed blank 15-2, there is a large increase in sheet thickness
at the roots of the outward flanges 5-1 and 5-2 or the outward
flanges 5-3 and 5-4 along ridges 2-1 and 2-2 or ridges 2-3 and 2-4,
in press molding, and there is a large decrease in sheet thickness
at the edges of the outward flanges 5-1 and 5-2 or the outward
flanges 5-3 and 5-4 along the ridges 2-1 and 2-2 or the ridges 2-3
and 2-4.
[0083] Alternatively, in the case of using the ridge pad 17, an
increase in sheet thickness at the roots and a decrease in sheet
thickness at the edges are small, which is good as compared with
the case of using the normal pad 14. Therefore, from the viewpoint
of avoiding the occurrence wrinkles with the increase in sheet
thickness and the occurrence of flange cracks with the decrease in
sheet thickness, it is desirable to perform press molding using the
ridge pad 17. In addition, it is desirable, as the developed blank
15-2, to make the width of the outward flanges 5-1 and 5-2 or the
outward flanges 5-3 and 5-4 along the vicinity of the ridges 2-1
and 2-2 or the ridges 2-3 and 2-4 smaller than the width of the
outward flanges 5-1 and 5-2 or the outward flanges 5-3 and 5-4 in
the other region.
TABLE-US-00001 TABLE 1 Sheet thickness fluctuations in the vicinity
of ridges Sheet Developed Decreasing rate in Increase rate in
Number Material thickness blank Pad sheet thickness *1 sheet
thickness *2 1 JSC590R 1.0 mm A Normal pad 22% 35% 2 JSC590R 1.0 mm
B Normal pad 15% 3% 3 JSC590R 1.0 mm A Ridge pad 17% 19% *1: Outer
end portions of outward flang *2: Root portions of outward
flanges
[0084] Table 2 shows principal conditions of Analysis 2, and Table
3 and Table 4 show the analysis results and weldabilities in
comparison.
TABLE-US-00002 TABLE 2 Material and Presence/absence sheet Shape
and width of of projecting in set Example thickness outward flanges
plate Collision face of impactor Inventive JSC 590R FIG. 8(a)
Present Perpendicular to longitudinal example 1 1.0 mm About 15 mm
over entire direction of tubular body perimeter Inventive JSC 590R
FIG. 8(b) Present Perpendicular to longitudinal example 2 1.0 mm 2
mm in ridges, 15 mm in direction of tubular body other portions
Inventive JSC 590R FIG. 8(b) Absent Perpendicular to longitudinal
example 3 1.0 mm 2 mm in ridges, 15 mm in direction of tubular body
other portions Inventive JSC 440W FIG. 8(b) Present Perpendicular
to longitudinal example 4 1.0 mm 2 mm in ridges, 15 mm in direction
of tubular body other portions Inventive JSC 440W FIG. 8(b) Present
Inclined 5 degrees, with example 5 1.0 mm 2 mm in ridges, 15 mm in
respect to plane other portions perpendicular to longitudinal
direction of tubular body, about an axis of rotation that is an
axis perpendicular to top surface Conventional JSC 440W Absent
Absent Perpendicular to longitudinal example 1 1.0 mm direction of
tubular body Inventive JSC 590R FIG. 8(a) Present Perpendicular to
longitudinal example 6 1.2 mm About 15 mm over entire direction of
tubular body perimeter Inventive JSC 590R FIG. 8(b) Present
Perpendicular to longitudinal example 7 1.2 mm 2 mm in ridges, 15
mm in direction of tubular body other portions Inventive JSC 590R
FIG. 8(b) Absent Perpendicular to longitudinal example 8 1.2 mm 2
mm in ridges, 15 mm in direction of tubular body other portions
Inventive JSC 440W FIG. 8(b) Present Perpendicular to longitudinal
example 9 1.2 mm 2 mm in ridges, 15 mm in direction of tubular body
other portions Inventive JSC 440W FIG. 8(b) Present Inclined 5
degrees, with example 10 1.2 mm 2 mm in ridges, 15 mm in respect to
plane other portions perpendicular to longitudinal direction of
tubular body, about an axis of rotation that is an axis
perpendicular to top surface Conventional JSC 440W Absent Absent
Perpendicular to longitudinal example 2 1.2 mm direction of tubular
body
TABLE-US-00003 TABLE 3 Buckling Absorbed Absorbed Examples
Weldability behavior energy *1 energy *2 Inventive example 1 Good
Very stable 98% 118% Inventive example 2 Good Very stable 94% 112%
Inventive example 3 Good Somewhat 85% 102% unstable Inventive
example 4 Good Very stable 73% 88% Inventive example 5 Good Stable
66% 80% Conventional Poor -- -- -- example 1 *1: Ratio of absorbed
energy at a stroke of 90 mm, it is 100% with a conventional example
2 (to be described) *2: Ratio of absorbed energy of per unit weight
at a stroke of 90 mm, it is 100% with the conventional example 2
(to be described)
TABLE-US-00004 TABLE 4 Absorbed Absorbed Examples Weldability
Buckling behavior energy *1 energy *2 Inventive Good Very stable
127% 127% example 6 Inventive Good Very stable 128% 128% example 7
Inventive Good Somewhat 127% 127% example 8 unstable Inventive Good
Very stable 104% 104% example 9 Inventive Good Stable 92% 92%
example 10 Conventional Somewhat Very stable 100% 100% example 2
poor*3 *1: Ratio of absorbed energy at a stroke of 90 mm, it is
100% with the conventional example 2 *2: Ratio of absorbed energy
of per unit weight at a stroke of 90 mm, it is 100% with the
conventional example 2 *3: "Somewhat poor" means that "it can
produce a good product, but it is inferior to Inventive Examples in
the stability of welding in mass production"
[0085] As shown in Tables 2 and 3, the conventional Example 1 has a
sheet thickness of 1.0 mm, which causes burn-through to easily
occur in butt arc welding, making it difficult to produce the crash
box.
[0086] In contrast to this, with the inventive examples 1 to 5, it
is possible to perform spot welding on the tubular body 1 to the
set plate 7 with the outward flanges 5-1 and 5-2 or the outward
flanges 5-3 and 5-4 interposed therebetween, which is available for
an impact energy absorbing structure for an automobile body. In
particular, it was found about the inventive examples 1, 2, and 4,
in which the locking sections 8-1 to 8-4 provided in the set plate
7 support the ridges 2-1 to 2-4 of the tubular body 1 from the
inside thereof, that the sheet thickness thereof is 1.0 mm, but a
collapse of root R portions toward the inside of the cross section
in an end portion in the longitudinal direction is suppressed,
resulting in a very stable buckling behavior, as with the
conventional example 2 the sheet thickness of which is 1.2 mm.
[0087] In addition, as illustrated by the inventive example 5, it
was found that the crash box exhibits stable buckling behavior even
when a face to collide (impactor) inclines with respect to a face
perpendicular to the longitudinal direction axis of the tubular
body 1. Note that, in the inventive example 3, a phenomenon was
recognized that the root R portions of the outward flanges 5-1 and
5-2 or the outward flanges 5-3 and 5-4 slightly collapses toward
the inside of the cross section, in the initial stage of impactor
stroke.
[0088] According to the present invention, it is possible to
attach, by spot welding or the like, the tubular body 1 to the set
plate 7 with the outward flanges 5-1 and 5-2 or the outward flanges
5-3 and 5-4 interposed therebetween, enabling the prevention of
poor welding such as burn-through in conventional butt arc welding
even for a tubular body 1 having a small sheet thickness, and thus
it is possible to produce a lightweight crash box having an
excellent impact energy absorbing performance.
[0089] In addition, it is understood by comparing between the
inventive examples 9 and 10 with the conventional example 2 in
Tables 2 and 4 that, according to the present invention, it is
possible to ensure a good weldability while keeping substantially
the same energy absorption and stable buckling behavior as those of
the conventional example.
REFERENCE SIGNS LIST
[0090] 0 Crash box [0091] 1 Tubular body [0092] 2-1 to 2-4 Ridge
[0093] 3-1, 3-2 Groove portion [0094] 5-1 to 5-4 Outward flange
* * * * *