DESCRIPTION
TITLE OF INVENTION: AUTOMOBILE STRUCTURAL MEMBER AND
MANUFACTURING METHOD OF THE SAME
TECHNICAL FIELD
[OOOl] The present invention relates to an
automobile structural member constituting an
automobile vehicle body and a manufacturing method of
the same. Concretely, the present invention relates
to an automobile structural member having a closed
transverse section shape constituted by combining a
metal sheet such as a thin steel sheet and a molded
body of a metal sheet, for example, and a
manufacturing method of the same.
BACKGROUND ART
[00021 Among automobile structural members used as
skeletal frame members of an automobile vehicle body
(body shell) having a monocoque structure, cited as
the member on which a three-point bending load is
supposed to act at a time of collision accident are a
side sill, a bumper reinforcement, a center pillar,
and so on.
[0003] A high three-point bending load is required
of the above automobile structural member
(hereinafter, referred simply to as an "automobile
structural member) in order to secure a vehicle
interior space at the time of collision or in order
to transmit an impact load at the time of collision
to another automobile structural member efficiently
Further, the automobile structural member itself is
required to have an excellent impact absorption
performance to three-point bending. In the present
specification, the tree-point bending load and the
impact absorption performance to the three-point
bending which the automobile structural member has
are combinedly referred to as a bending-crushing
performance. Further, not only the bending-crushing
performance but also weight reduction and cross
section reduction for the purpose of fuel consumption
improvement of an automobile is strongly required of
the automobile structural member.
[0004] The automobile structural member is assembled,
in general, by spot welding a first composing member
made of a steel sheet molded into a hat shape in
cross section having an outward flange and a closing
plate being a second composing member made of a steel
sheet, using the outward flange as a welding margin.
In the present specification, the member with a hatshaped
cross section which has the outward flange is
referred to as a hat member. In other words, the hat
member has a hat-shaped transverse section shape made
by two outward flanges, two bent portions each
connected to 'the two outward flanges, two vertical
wall portions each connected to the two bent portions,
two edge line portions each connected to the two
vertical wall portions, and one groove bottom portion
to which the two edge line portions are connected.
[0005] Heretofore, various inventions have been
suggested for the purpose of suppressing increase of
a weight of a first composing member being a hat
member and for obtaining an excellent bendingcrushing
performance.
[0006] Patent Literature 1 discloses an automobile
structural member in which a reference range of ( R +
7) mm is set, with a radius of a bent portion being R,
on at least one surface of two surfaces forming the
bent portion from a center of the bent portion in a
transverse section of a first composing member being
a hat member molded by press bending of a steel sheet
containing C: 0.05 to 0.3% (in the present
specification, " % " related to a chemical composition
means 'mass%" as long as not mentioned otherwise) and
Mn: 0.5 to 3.0%, one or a plurality of quenchstrengthened
portion (s) is (are) formed along the
bent portion in the reference range by laser
irradiation or high-frequency heating, and an
occupancy ratio of 20% or more in relation to a total
reference range length of a total width of the
quench-strengthened portion in the reference range is
secured for all the surfaces constituting all the
bent portions of the first composing member. It is
disclosed that according to this automobile
structural member an impact crushing resistance can
be improved effectively by small formation of the
quench-strengthened portion while good press
moldability is secured.
[ 0 0 0 7 ] Patent Literature 2 discloses an automobile
structural member having a barrel unit which has a
closed transverse section shape formed by a first
composing member being a hat member and a second
composing member and in which the first composing
member and the second composing member are spotwelded
by an outward flange, the automobile
structural member being interposed by filling a resin
layer in a region sandwiched by a bent portion
neighboring the outward flange and the second
composing member. It is disclosed that according to
this automobile structural member light weight and
excellent bending-crushing performance are had.
[ 0 0 0 8 ] On the other hand, Patent Literature 3
discloses an automobile structural member made by
joining, by laser-welding, inward flanges of two
composing members with recessed cross sections to
each other, in a manner that bottom surface inner
walls thereof face each other. It is disclosed that
according to such an automobile structural member
changing of a bending load property can increase an
energy absorption amount.
CITATION LIST
PATENT LITERATURE
[ 0 0 0 9 ] Patent Literature 1: Japanese Laid-open
Patent Publication No. 11-152541
Patent Literature 2: Japanese Laid-open Patent
Publication No. 2011-168082
Patent Literature 3: Japanese Laid-open Patent
Publication No. 2003-54445
SUMMARY OF INVENTION
TECHNICAL PROBLEM
[0010] In order for the first composing member being
the hat member disclosed in Patent Literatures 1, 2
to have a high three-point bending load, it is
important to suppress deformation of the transverse
section shape of the hat member at a time of impact
load placement as far as possible and to transmit the
impact load efficiently from the second composing
member to a vertical wall portion of the first
composing member.
[0011] Here, when the impact load is transmitted
from the closing plate being the second composing
member to the hat member being the first composing
member, the impact load inputted from a closing plate
side is transmitted to the vertical wall portion via
the bent portion which inevitably exists between the
outward flange and the vertical wall portion of the
first composing member. Therefore, the vertical wall
portion is apt to be buckle-deformed early, so that
the impact load cannot be transmitted efficiently to
the vertical wall portion of the first composing
member. In other words, in order to improve a
bending-crushing performance of an automobile
structural member, it is effective to suppress
occurrence of buckling deformation of a vertical wall
portion at a time of impact load placement.
[0012] However, though the invention disclosed in
Patent Literature 1 suppresses deformation of the
transverse section shape of the hat member by quenchstrengthening
the bent portion of the hat member
being the first composing member, the suppression is
not enough to transmit the impact load efficiently to
the vertical wall portion. Further, in the invention
disclosed in Patent Literature 1, laser irradiation
or high-frequency induction heating to the bent
portion of the hat member is required to be carried
out after the hat member and the closing plate are
welded and assembled via the outward flange, and
increase in man-hour and cost necessary for
manufacturing is inevitable.
[0013] Further, since the invention disclosed in
Patent Literature 2 suppresses deformation of the
vertical wall portion by fil1ing.a resin in a region
(space) sandwiched by the bent portion neighboring
the outward flange of the hat member and the second
composing member, a bending-crushing performance can
be heightened in some measure. However, in addition
to spot-welding the first composing member and the
second composing member by using the outward flange
as the welding margin, filling of the resin in the
above-described region is required, and increase in
man-hour and cost necessary for manufacturing is
inevitable.
[0014] Further, in both inventions disclosed in
Patent Literatures 1, 2, in order to use spot-welding
for wedding of the first composing member and the
second composing member, it is necessary to provide
an outward flange of a width of normally about 20 to
30 mm as a welding margin in the first composing
member. Since contribution of the outward flange to
a bending-crushing performance is small, weight
reduction and cross section reduction by curtailment
of the width of the outward flange is desired, but
neither invention disclosed in Patent Literature 1, 2
can contrive weight reduction and cross section
reduction by curtailment of the width of the outward
flange.
[0015] On the other hand, the invention disclosed in
Patent Literature 3 can contrive weight reduction and
cross section reduction of the automobile structural
member by joining the inward flanges to each other,
compared with an outward flange. However, since the
inward flanges are joined by laser welding in which
welding is carried out by melting an interface, a
region sandwiched by the bent portions neighboring
the inward flanges still have spaces. Therefore,
when an impact load is transmitted to one composing
member from the other composing member, the impact
load inputted from the other composing member side is
transmitted to the vertical wall portion via the bent
portion between the inward flange and the vertical
wall portion of the one composing member. Therefore,
similarly to in the automobile structural member
constituted with the hat member disclosed in Patent
Literature 1, there is a problem that the vertical
wall portion is apt to be buckle-deformed early and
that the impact load cannot be transmitted
efficiently to the vertical wall portion of the one
composing member.
SOLUTION TO PROBLEM
[0016] Since spot-welding is capable of welding a
plurality of overlapped thin steel sheets in quite a
short welding time of about 0.1 to 0.5 seconds
efficiently and easily, conventionally spot-welding
has been widely used for welding of an automobile
structural member or an automobile vehicle body, in
particular. Thus, in assembling an automobile
structural member by welding a first composing member
and a second composing member, it has been a
technical common sense among those skilled in the art
to form an outward flange to be a welding margin in
the first composing member and to spot-weld to the
second composing member with the outward flange.
[0017] As a result that the present inventors have
conducted keen examination to solve the abovedescribed
problems, it is configured that an inward
flange instead of an outward flange is formed in a
first composing member, that the first composing
member and a second composing member are overlapped
via the inward flange, and that, in at least a part
of a region being a region between a bent portion
continued to the inward flange and the second
composing member, the region being an extension of a
vertical wall portion toward the second composing
member, a load transmission portion joining the bent
portion and the second composing member is formed.
The present inventors find that, therefore, man-hour
and cost necessary for manufacturing can be
suppressed to a degree similar to that in a
conventional automobile structural member and that a
bending-crushing performance of an automobile
structural member can be substantially improved from
a bending-crushing performance of the conventional
automobile structural member, and further conducted
keen examination,, to complete the present invention.
[0018] The present invention will be described as
below, when explained with reference to Fig. 18 to
Fig. 1D showing an example of a transverse section
shape of an automobile structural member according to
the present invention and Fig. 2 being a drawing
extractingly showing a periphery of a load
transmission" portion in the automobile structural
member according to the present invention.
[0019] (1) An automobile structural member 2 to 4 is
an automobile structural member 2 to 4 which has a
closed transverse section shape constituted with at
least a first composing member 12 made of a molded
body of a metal sheet and second composing member 13
to 15 made of a metal sheet or a molded body of a
metal sheet and joined to the first composing member
12, the first composing member 12 having a vertical
wall portion 12c, a bent portion 12b connected to the
vertical wall portion 12c and bent toward an inner
side of the closed transverse section shape, and an
inward flange 12a connected to the bent portion 12b,
and it is characterized in that the automobile
structural member includes: a load transmission
portion 20 which is formed in at least a part of a
region being a region between the bent portion 12b
and the second composing member 13 to 15 and being a
region of an extension of the vertical wall portion
12c toward the second composing member 13 to 15, and
which joins the bent portion 12b and the second
composing member 13 to 15.
[0020] (2) It is characterized in that when a width
of the load transmission portion 20 toward a plate
thickness direction of the vertical wall portion 12c
is indicated as WT and a plate thickness of the
vertical wall portion 12c is indicated as t, 0.3t 5
WT 1.0t is satisfied.
(3) It is characterized in that the load
transmission portion 20 is a part of a joining
portion 21 filling a part or all of a space 22 formed
between the bent portion 12b and the second composing
member 13 to 15, and that in the joining portion 21 a
joining width L being a range in contact with the
second composing member 13 to 15 is longer than a
width WT of the load transmission portion 20.
(4) It is characterized in that in the bent
portion 12b, hardness of at least a range which the
load transmission portion 20 is in contact with is
higher than hardness of a base material of the first
composing member 12.
(5) It is characterized in that the load
transmission portion 20 is formed intermittently
through a longitudinal direction of the automobile
structural member 2 to 4.
[0021] (6) A manufacturing method of an automobile
structural member 2 to 4 which has a closed
transverse section shape constituted with at least a
first composing member 12 made of a molded body of a
metal sheet and a second composing member 13 to 15
made of a metal sheet or a molded body of a metal
sheet and joined to the first composing member, the
first composing member 12 having a vertical wall
portion 12c, a bent portion 12b connected to the
vertical wall portion 12c and bent toward an inner
side of the closed transverse section shape, and an
inward flange 12a connected to the bent portion 12b,
it is characterized in that the manufacturing method
of the automobile structural member includes: forming
a load transmission portion 20 which joins the bent
portion 12b and the second composing member 13 to 15
by welding using a filler metal in at least a part of
a region being a region between the bent portion 12b
and the second composing member 13 to 15, the region
being an extension of the vertical wall portion 12c
toward the second composing member 13 to 15.
[0022] (7) It is characterized in that the load
transmission portion 20 is formed by a plurality of
welding operations by using the filler metal.
(8) It is characterized in that welding lengths
are each different in at least two operations of the
plurality of welding operations.
(9) It is characterized in that the load
transmission portion 20 is a part of a joining
portion 21 filling a part or all of a space formed
between the bent portion 12b and the second composing
member 13 to 15, that the load transmission portion
20 is formed by a plurality of welding operations by
using the filler metal, that in the first welding
operation, welding is carried out so that a width WT
of the load transmission portion 20 satisfies WT <
0.6t and a joining width L being a range in which the
joining portion 21 is in contact with the second
composing member 13 to 15 satisfies 0 < L, and that
in the second or later welding operation, welding is
carried out so that the width WT of the load
transmission portion 20 satisfies 0.6t 5 WT 5 1.0t.
(10) It is characterized in that the load
transmission portion 20 is formed intermittently
through a longitudinal direction of the automobile
structural member 2 to 4.
(11) It is characterized in that the load
transmission portion 20 is formed by arc welding or
laser-arc hybrid welding by using the filler metal.
[0023] In these present inventions, the first
composing member 12 has the transverse section shape
constituted by, for example, a groove bottom portion
12e which exists extended in a first direction
(direction orthogonal to a paper surface of Fig. 1B
to Fig. ID), two edge line portions 12d, 12d which
are connected to the groove bottom portion 12e in
both edge portions in a width direction orthogonal to
the first direction, two vertical wall portions 12c,
12c which are each connected to the two edge line
portions 12d, 12d, two bent portions 12b, 12b which
are each connected to the two vertical wall portions
12c, 12c and bent toward an inner side of the closed
transverse section shape, and two inward flanges 12a,
12a which are each connected to the two bent portions
12b, 12b.
[0024] In these present inventions, the second
composing member 13 may be a metal material of a flat
plate shape as a closing plate as shown in Fig. 1B.
Further, the second composing member 1.4, 15 may be a
molded body of a metal sheet, the molded boy having a
shape which has a transverse section shape similar to
that of the first composing member 12 as shown in Fig
1C and Fig. ID, for example. In this case, it
suffices that the inward flanges 12a, 12a formed in
the first composing member 12 and the inward flanges
16a, 16a formed in the second composing member 14, 15
are overlapped with each other.
[0025] In these present inventions, when a curvature
radius of the bent portion 12b is too large,
formation of the load transmission portion 20 by an
easy means such as arc welding or laser-arc hybrid
welding becomes not easy, and thus the curvature
radius of the bent portion 12b is desirable to be 8
mm or less. In contrast, when the curvature radius
is tried to be made too small, molding of the first
composing member 12 becomes difficult, and thus the
curvature radius is desirable to be 2 mm or more.
[0026] Further, the automobile structural member 2
to 4 according to the present invention is used as a
skeletal frame member of an automobile vehicle body
(body shell) having a monocoque structure.
Concretely, the automobile structural member 2 to 4
is used for a side sill, a bumper reinforcement, and
a center pillar.
ADVANTAGEOUS EFFECTS OF INVENTION
[0027] According to an automobile structural member
of the present invention, it is possible to improve a
bending crushing performance from a bending crushing
performance of a conventional automobile structural
member.
BRIEF DESCRIPTION OF DRAWINGS
[0028] [Fig. lA] Fig. 1A is a diagram showing an
example of a transverse section shape of a
conventional automobile structural member;
[Fig. lB] Fig. 1B is a diagram showing an example
of a transverse section shape of an automobile
structural member of a first embodiment;
[Fig. lC] Fig. 1C is a diagram showing an example
of a transverse section shape of an automobile ,
structural member of a second embodiment;
[Fig. ID] Fig. 1D is a diagram showing an example
of a transverse section shape of an automobile
structural member of a third embodiment;
[Fig. 21 Fig. 2 is a diagram showing a periphery
of a load transmission portion in the automobile
structural member of the present embodiment;
[Fig. 3A] Fig. 3A is a diagram showing a
transverse section shape of an automobile structural
member of a first comparative example;
[Fig. 3B] Fig. 3B is a diagram showing a
transverse section shape of an automobile structural
member of a second comparative example;
[Fig. 3C] Fig. 3C is a diagram showing a
transverse section shape of the automobile structural
member of a present invention example;
[Fig. 41 Fig. 4 is a graph showing a loaddisplacement
curve at a time that a plate thickness
is 2.0 mm and that a curvature radius of a bent
portion is 6 mm;
[Fig. 5A] Fig. 5A is a graph showing a maximum
bending load-curvature radius of bent portion at a
time that aplate thickness is 1.2 mm;
[Fig. 5B] Fig. 5B is a graph showing a maximum
bending load-curvature radius of bent portion at a
time that a plate thickness is 2.0 mm;
[Fig. 61 Fig. 6 is a diagram showing a transverse
shape of an inward flange periphery of an automobile
structural member;
[Fig. 7A] Fig. 7A is graph showing a maximum
bending load-height of first composing member at a
time that a plate thickness is 1.2 mm;
[Fig. 7B] Fig. 7B is a graph showing a maximum
bending load-height of first composing member at a
time that a plate thickness is 2.0 mm;
[Fig. 8A] Fig. 8A is a perspective view showing
an example of an automobile structural member welded
intermittently; and
[Fig. 881 Fig. 8B is a perspective view showing
an example of an automobile structural member in
which a welding length is changed in correspondence
with the number of welding operations.
DESCRIPTION OF EMBODIMENTS
[0029] Hereinafter, embodiments for implementing the
present invention will be described. Note that in
the description hereinafter, there is exemplified a
case where an automobile structural member according
to the present invention is a side sill. However,
the present invention is not limited to the side sill,
but is applicable to an automobile structural member
which has a closed transverse section shape
constituted with the aforementioned first composing
member and second composing member and to which a
three-point bending load is supposed to be placed at
a time of collision of an automobile, such as a
bumper reinforcement and a center pillar, for example.
[0030] Fig. 1A is a diagram showing an example of a
transverse section shape of a conventional automobile
structural member 1. Fig. 1B to Fig. 1D are diagrams
each showing an example of a transverse section shape
of an automobile structural member 2 to 4 according
to the present embodiment. Further, Fig. 2 is a
diagram showing a periphery of a load transmission
portion 20 in the automobile structural member 2
according to the present invention. Fig. 2 is the
diagram obtained by enlarging a part A in Fig. lB,
and similar explanation is also applicable to Fig. 1C
and Fig. 1D.
[0031] First, the conventional automobile structural
member 1 will be simply described with reference to
Fig. 1A.
The automobile structural member 1 has a first
composing member 10 and a second composing member 11.
[0032] The first composing member 10 has two outward
flanges 10a, 10a, two bent portions lob, lob each
connected to the two outward flanges 10a, lob, two
vertical wall portions 10c, 10c each connected to the
two bent portions lob, lob, two edge line portions
10d, 10d each connected to the two vertical wall
portions 10c, 10c, and one groove bottom portion 10e
to which the two edge line portions 10d, 10d are each
connected.
[0033] The first composing member 10 has a
transverse section shape of a hat shape constituted
with the two outward flanges 10a, 10a, the two bent
portions lob, lob, the two vertical wall portions 10c,
10c, the two edge line portions 10d, 10d, and the one
groove bottom portion 10e. As described above, the
first composing member 10 is a molded body (hat
member) with a hat-shaped cross section which has the
outward flange 10a.
[0034] On the other hand, the second composing
member 11 is a closing plate and is formed into a
flat plate shape.
The first composing member 10 and the second
composing member 11 are assembled by being spotwelded
by using the outward flanges 10a, 10a as
welding mar'gins.
[0035] Differently from the automobile structural
member 1 shown in Fig. lA, there is also a case where
the second composing member 11 is a molded body (hat
member) with a hat-shaped cross section which has an
outward flange similarly to the first composing
member 10. In this case, the first composing member
10 and the second composing member 11 are assembled
as a result that the respective outward flanges are
spot-welded by using each outward flange as the
welding margin in a state where the outward flanges
are overlapped on each other.
100361 The automobile structural member 1 is fixedly
supported at two places on both end sides of a
longitudinal direction (direction orthogonal to a
paper surface of Fig. 1A) and constitutes a side sill
composing an automobile vehicle body (body shell).
[0037] The automobile structural member 1 is a
member supposed to receive an impact load F between
two fixedly supporting position on both end sides of
the longitudinal direction (direction orthogonal to
the paper surface of Fig. lA), the impact load F
being placed from the second composing member 11
toward the first composing member 10.
[0038] When the impact load is placed from the
second composing member 11 toward the first composing
member 10, the impact load inputted from the second
composing member 11 is transmitted to the outward
flanges 10a, 10a, the bent portions lob, lob, the
vertical wall portions 10c, 10c of the first
composing member 10 in sequence. In other words,
since the inputted impact load is transmitted to the
vertical wall portions 10c, 10c inevitably via the
bent portions lob, lob, the vertical wall portions
10c, 10c are apt to be buckle-deformed early, and it
is difficult to transmit the impact load to the
vertical wall portions 10c, 10c efficiently.
COO391 Next, the automobile structural members 2 to
4 according to the present embodiment will be
described with reference to Fig. 18 to Fig. ID.
[0040] Since the automobile structural member 2 to 4
according to the present embodiment has at least a
first composing member 12, a second composing member
13, 14, 15, and a load transmission portion 20, the
above are described in sequence.
[0041] Here, the first composing member 12 and the
second composing member 13, 14, 15 are each molded
bodies constituted with a cold-rolled steel sheet, a
hot-rolled steel sheet, and further a plated steel
sheet, for example, and a kind, strength, a thickness,
or the like of the steel sheet is not limited. For
example, when the automobile structural member 2 to 4
is a side sill, in general, a 440 to 980 MPa class
high-tension steel sheet with a thickness of about
1.2 mm to 2.0 mm is used, but it is also possible to
use a 1180 to 1470 MPa class high-tension steel sheet
and to thin a'plate thickness to as far as about 1.0
mm. As will be described later, when a joining
portion 21 (load transmission portion) is formed by
arc welding or laser-arc hybrid welding, it is
desirable to use a steel sheet of 1.0 mm or more in
o r d e r t o r e d u c e d e f o r m a t i o n due t o t h e r m a l s t r a i n .
LO0421 [ F i r s t Composing Member]
The f i r s t composing member 12 is made by a molded
body of a p l a t e m a t e r i a l , and h a s a groove bottom
p o r t i o n 12e, two edge l i n e p o r t i o n s 12d, 12d, trio
v e r t i c a l w a l l p o r t i o n s 12c, 12c, two bent p o r t i o n s
12b, 12b, and t r i o i n w a r d f l a n g e s 12a, 1 2 a .
[0043] The groove bottom p o r t i o n 12e i s e x t e n d e d i n
a f i r s t d i r e c t i o n ( d i r e c t i o n o r t h o g o n a l t o a p a p e r
s u r f a c e of F i g . 1 B t o F i g . I D ) . The two edge l i n e
p o r t i o n s 12d, 12d a r e c o n n e c t e d t o t h e g r o o v e b o t t o m
p o r t i o n 12e i n both edge p o r t i o n s i n a width
d i r e c t i o n o r t h o g o n a l t o t h e f i r s t d i r e c t i o n . The two
v e r t i c a l w a l l p o r t i o n s 12c, 12c a r e each c o n n e c t e d t o
t h e two edge l i n e p o r t i o n s 12d, 12d. The two b e n t
p o r t i o n s 12b, 12b a r e each c o n n e c t e d t o t h e two
v e r t i c a l w a l l p o r t i o n s 12c, 12c and b e n t toward an
i n n e r s i d e of a c l o s e d t r a n s v e r s e s e c t i o n s h a p e .
F u r t h e r , t h e two inward f l a n g e s 12a, 12a a r e each
c o n n e c t e d t o t h e two bent p o r t i o n s 12b, 12b.
Note t h a t i n F i g . l B , a boundary between t h e
v e r t i c a l w a l l p o r t i o n s 12c, 12c and t h e b e n t p o r t i o n s
12b, 12b and a boundary between t h e bent p o r t i o n s 12b,
12b and t h e inward f l a n g e s 12a, 12a a r e i n d i c a t e d by
two-dot c h a i n l i n e s .
[0044] The f i r s t composing member 12 has t h e
t r a n s v e r s e s e c t i o n shape c o n s t i t u t e d with t h e groove
bottom p o r t i o n 12e, t h e two edge l i n e p o r t i o n s 12d,
12d, the two vertical wall portions 12c, 12c, the two
bent portions 12b, 12b, and the two inward flanges
12a, 12a.
[0045] As described above, the first composing
member 12 has the vertical wall portions 12c, 12c,
the bent portions 12b, 12b, and the inward flanges
12a, 12a connected to the bent portions 12b, 12b.
[0046] Here, if a curvature radius of the bent
portions 12b, 12b exceeds 8 mm, amounts of spaces
formed between the bent portions 12b, 12b and the
second composing member 13 become large. Thus, when
the load transmission portion 20 is formed by welding
in which a filler metal is used such as laterdescribed
arc welding and laser-arc hybrid welding,
not only a joining cost is increased but also an
amount of the filler metal is required to be
increased. Therefore, welding heating input becomes
large, leading to easy occurrence of deformation or
burn-through of the first composing member 12 and the
second composing member 13 to 15 due to thermal
strain. Further, when the load transmission portion
20 is formed by brazing or bonding, a joining cost is
increased. Thus, the curvature radius of the bent
portions 12b, 12b is desirable to be 8 mm or less,
and is more desirable to be 6 mm or less.
[0047] From such a viewpoint it is not necessary to
set a lower limit of the curvature radius of the bent
portions 12b, 12b, but it is difficult to mold bent
portions 12b, 12b with a curvature radius of less
than 2 mm in an industrial mass production line.
Therefore, the curvature radius of the bent portions
12b, 12b is desirable to be 2 mm or more.
Note that the curvature radius of the bent
portion means a curvature radius of a curved surface
on an outer side of curved surfaces of the bent
portion 12b, the curved surface on the outer side
having the larger curved radius.
[0048] The first composing member 12 may be molded
by any molding method, and the molding method is not
limited to a specific one. However, if a
manufacturing cost is increased by press molding in
order to form an inward flange 12a, molding can be
carried out by roll forming or by using a press brake.
[0049] [Second Composing Member]
The second composing member 13 to 15 is joined to
the first composing member 12 via the inward flanges
12a, 12a. Thereby, the automobile structural member
2 to 4 has the closed transverse section shape
constituted with the first composing member 12 and
the second composing member 13 to 15.
[0050] As shown in Fig. 1B, the second composing
member 13 according to a first embodiment is a plate
material such as a closing plate, for example. The
automobile structural member 2 of the first
embodiment, when a width of the first structural
member 12 is indicated as W1 and a width of the
second composing member 13 is indicated as W2, is
formed to satisfy W2 > W1.
[0051] On the other hand, as shown in Fig. 1C and
Fig. ID, the second composing member 14, 15 according
to second and third embodiment is a molded body
having a transverse section shape similar to that of
the first composing member 12, for example.
Concretely, the second composing member 14, 15 has a
groove bottom portion 16e extended to a first
direction (direction orthogonal to a paper surface of
Fig. 1C, Fig. ID), two edge line portions 16d, 16d
connected to the groove bottom portion 16e in both
edge portions in a width direction orthogonal to the
first direction, two vertical wall portions 16c, 16c
each connected to the two edge line portions 16d, 16d,
two bent portions 16b, 16b each connected to the two
vertical wall portions 16c, 16c and bent toward an
inner side of the closed transverse section shape,
and two inward flanges 16a, 16a each connected to the
two bent portions 16b, 16b.
Automobile structural member 3, 4 is configured
as a result that the inward flanges 12a, 12a formed
in the first composing member 12 and the inward
flanges 16a, 16a formed in the second composing
member 14, 15 are overlapped on each other.
[0052] A second composing member 14 of a second
embodiment has a transverse section shape the same as
that of a first composing member 12.
On the other hand, a second composing member 15
of a third embodiment has a transverse section shape
in which a groove bottom portion 16e and inward
flanges 16a, 16a are longer in a width direction than
that of a first composing member 12. Therefore, when
a width of the first composing member 12 is indicated
as W1 and a width of the second composing member 15
is indicated as W2, the second composing member 15 of
the third embodiment is formed to satisfy W2 > W1.
[0053] The second composing member 14, 15 having the
inward flanges 16a, 16a may be molded by any molding
method, and the molding method is not limited to a
specific one. However, if a manufacturing cost is
increased by press molding in order to form an inward
flange 16a, molding can be carried out by roll
forming or by using a press brake.
[0054] Note that the automobile structural member 2
to 4 may further have a composing member other than
the first composing member 12 and the second
composing member 13, 14, 15. For example, it is
possible to have a third composing member between the
first composing member 12 and the second composing
member, the third composing member functioning as a
reinforcement by being three-layer lap-welded with
the first composing member 12 and the second
composing member.
[0055] [Load Transmission Portion]
Here, as shown in Fig. 2, the load transmission
portion 20 which the automobile structural member 2
of the first embodiment has will be described, and
the same applies to the automobile structural members
3, 4 of the second and third embodiments.
As shown in Fig. 2, the load transmission portion
20 is formed in a part or all of a region being a
region between the bent portion 12b of the first
composing member 12 and the second composing member
13 and being a region of an extension of the vertical
wall portion 12c toward the second composing member
13.
LO0561 The load transmission portion 20 constitutes
a part of a joining portion 21 which joins the first
composing member 12 and the second composing member
13. Therefore, the load transmission portion 20
joins the bent portion 12b and the second composing
member 13 in the above-described region.
[0057] The joining portion 21 is formed by filling a
part or all of a space 22 which exists between the
bent portion 12b and the second composing member 13.
The space 22 is formed in an outer side of a closed
section constituted with the first composing member
12 and the second composing member 13. Therefore,
the joini'ng portion 21 can be formed easily by means
such as arc welding, laser-arc hybrid welding, and
further, brazing, and bonding, without increasing an
assembly process.
[00581 Further, in arc welding, laser-arc hybrid
welding, and further, brazing, strength of the
joining portion 21 including the load transmission
portion 20 can be adjusted by kinds of a welding wire
as the filler metal. For example, by using a highstrength
wire, it is also possible to make strength
of the joining portion 21 higher than steel sheet
strength of the first composing member 12 and steel
sheet strength of the second composing member 13.
[0059] In particular, when the joining portion 21 is
formed by arc welding or laser-arc hybrid welding, a
neighborhood of the bent portion 12b of the first
composing member 12 is quench-strengthened by heat
input at a time of welding. Therefore, the joining
portion 21 including the load transmission portion 20
is desirable to be formed by arc welding or laser-arc
hybrid welding by using a filler metal. In this case,
the joining portion 21 is mainly deposited metal
formed as a result that the filler metal is moved to
the space 22 between the bent portion 12b and the
second composing member 13.
[0060] Further, as shown in Fig. 2, when a joining
width being a range in which the joining portion 21
is formed in the second composing member 13 is
indicated as L (mm) and a width (hereinafter,
referred to as a load transmission portion width) of
the load transmission portion 20 to a plate thickness
direction of the vertical wall portion 12c is
indicated as WT (mm), the joining width L is
desirable to be longer than the load transmission
portion width WT.
In order to make the joining width L longer than
the load transmission portion width WT, it is
desirable that the width W2 of the second composing
member 13, 15 is formed longer than the width W1 of
the first composing member 12, as in the automobile
structural member 2 shown in Fig. 1B and the
automobile structural member 4 shown in Fig. ID. In
other words, it is desirable that both ends in the
width direction of the second composing member 13, 15
are positioned in outer sides than both ends in the
width direction of the first composing member 12.
As a result that the joining width L of the
joining portion 21 is made long as described above,
the joining portion 21 is formed to be broadened
toward the second composing member 13, so that an
impact load transmitted from the second composing
member 13, 15 to the first composing member 12 can be
transmitted effectively to the vertical wall portion
12c.
Further, as shown in Fig. 2, when a width
(hereinafter, bent portion width) of the bent portion
12b is indicated as Wb, it is possible to form the
joining portion 21 to be broadened toward the second
composing member 13 by making the joining width L
longer than the bent portion width Wb.
[0061] According to the automobile structural member
2 to 4, as described above, the joining portion 21
can be formed easily by a proper operation means such
as arc welding, laser-arc hybrid welding, brazing,
and bonding, without increasing the assembly process.
Therefore, formation of the joining portion 21 is
easy and the load transmission portion 20 can be
formed efficiently.
[0062] Further, according to the automobile
structural member 2 to 4, it is possible to transmit
the impact load transmitted from the second composing
member 13, 14, 15 to the first composing member 12 to
the vertical wall portion 12c effectively by the load
transmission portion 20 not by way of the bent
portion l2b. Therefore, the automobile structural
member 2 to 4 can improve a bending crushing
performance by a large margin from a bending-crushing
performance of the conventional automobile structural
member.
[0063] Further, since the joining portion 21 which
joins the first composing member 12 and the second
composing member 13, 14, 15 is formed, a joining
portion is not required to be formed at overlapped
portions of the inward flanges 12a, 12a and the
second composing member 13. Therefore, in a width of
the inward flanges 12a, 12a, it becomes unnecessary
to secure a spot welding margin of about 20 to 30 mm
as in a width of the outward flange of the first
composing member constituting the conventional
automobile structural member. In other words, it
suffices that the automobile structural member 2 to 4
has a width (for example, about 5 to 10 mm) enough to
secure butt welding accuracy of the first composing
member 12 and the second composing member 13, 14, 15,
and thus substantial weight reduction can be
contrived compared with the conventional automobile
structural member.
[0064] Further, the joining portion 21 can be formed
easily by the proper means such as arc welding,
laser-arc hybrid welding, and further, brazing, and
bonding, without increasing the assembly process.
Therefore, the automobile structural member 2 to 4
can suppress man-hour and cost necessary for
manufacturing to a degree similar to that in the
conventional automobile composing member.
[0065] Further, since the automobile structural
member 2 to 4 does not have an outward flange which
the conventional automobile structural member has, it
is possible to contrive cross section reduction in
relation to the conventional automobile structural
member.
[0066] Further, hardness of a range which at least
the load transmission portion 20 is in contact with
is desirable to be higher than hardness of a base
material of the first composing member. By forming
the joining portion 21 which includes the load
transmission portion 20 by welding, a neighborhood of
the bent portion 12b of the first composing member 12
is quench-strengthened by heat input at a time of
welding. As described above, as a result that the
bent portion 12b of the first composing member 12 and
its neighborhood are strengthened by heat input at
the time of welding, deformation of transverse
section shape of the automobile structural member 2
to 4 is suppressed to improve a maximum bending load.
In particular, the range in which the hardness of the
first composing member 12 becomes high due to heat
input at the time of welding is desirable to be as
broad as from the bent portion 12b through the
vertical wall portion 12c. In order to harden
broadly as far as to the vertical wall portion 2c, a
curvature radius of the bent portion 12b is made
small. Further, in view of a welding condition, it
is devised to heighten an arc welding voltage, to
defocus a laser focal point, or the like, in a range
where weldability is not impaired.
[0067] Further, the longer the load transmission
portion width WT of the load transmission portion 20
is, the larger the maximum bending load becomes.
When the joining portion 21 including the load
transmission portion 20 is formed by welding, the
longer load transmission portion width WT can be
realized by increasing an amount of a filler metal.
On the other hand, in order to increase the amount of
the filler metal, a welding current is required to be
heightened, and thus, there is a possibility that the
first composing member 12 or the second composing
member is burned through. Thus, when the joining
portion 21 including the load transmission portion 20
is to be formed, it is desirable that the same part
is welded by a plurality of operations. By welding
the same part by the plurality of operations, a
welding input heat amount to the first composing
member 12 and the second composing member 13 each
time can be reduced, so that the first composing
member 12 and the second composing member 13 can be
prevented from burn-through.
[0068] Further, when the joining portion 21
including the load transmission portion 20 is formed
by welding, thermal strain occurs in the automobile
structural member. When the thermal strain is large,
there is a possibility that a dimension error occurs
in relation to a desired dimension of the automobile
structural member. Thus, when the thermal strain
becomes large, it is desirable to weld intermittently
through an entire length of the automobile structural
member. As a result of welding intermittently
through the entire length of the automobile
structural member 2 to 4, influence of the thermal
strain can be decreased, enabling suppression of
occurrence of the dimension error.
[00691 (Example)
[Comparison of Maximum Bending Loads]
Next, performances between an automobile
structural member of a comparative example and an
automobile structural member of a present invention
example are compared.
Fig. 3A is a diagram showing a transverse section
shape of an automobile structural member 31 of a
first comparative example.
The automobile structural member 31 of the first
comparative example is fabricated by spot welding an
outward flange 10a of a hat member 10 being a first
composing member and a closing plate 11 being a
second composing member. Here, a curvature radius R
of a bent portion lob shown in Fig. 3A is 6 mm.
[0070] Spot welding is carried out with a spot pitch
being 30 mm for an entire length of 600 mm in a
longitudinal direction. With regard to a welding
condition, a pressurizing force is 3920 N, a power-on
time is changed in correspondence with a plate
thickness, being 0.27 seconds for a plate thickness
of 1.2 mm and 0.4 seconds for a plate thickness of
2.0 mrn described later, and a welding current is
adjusted to be able to obtain a nugget diameter of 5J
t for each plate thickness t (note that "t" is
included inJ).
[0071] Fig. 3B is a diagram showing a transverse
section shape of an automobile structural member 32
of a second comparative example.
The automobile structural member 32 of the second
comparative example is fabricated by laser welding a
bent portion 12b formed between an inward flange 12a
and a vertical wall portion 12c of a first composing
member 12, and a closing plate 13 being a second
composing member from an arrow B direction. 'R"
shown in Fig. 3B indicates a curvature radius of the
bent portions 12b, 12b. Further, a height H of the
first composing member 12 is 60 mm.
[0072] Laser welding simply melts and joins the bent
portions 12b, 12b and the closing plate 13.
Therefore, in the automobile structural member 32 of
the second comparative example, a load transmission
portion is not formed between the bent portions 12b,
12b and the closing plate 13.
In laser welding, continuous welding is carried
out through an entire length of 600 mm in a
longitudinal direction, a welding speed is constant
at 2m/min, an output is changed in correspondence
with a plate thickness, 2.5 kW for a plate thickness
of 1.2 mm and 4.0 kW for a plate thickness of 2.0 mm
described later. Further, just focus is applied to a
laser focal point.
[0073] Fig. 3C is a diagram showing a transverse
section shape of an automobile structural member 33
of the present invention example.
The automobile structural member 33 of the
present invention example is fabricated by arc
welding a bent portion 12b formed between an inward
flange 12a and a vertical wall portion 12c of a first
composing member 12, and a closing plate 13 being a
second composing member. "R" shown in Fig. 3C
indicates a curvature radius of the bent portions 12b,
12b. Further, a height H of the first composing
member 12 is 60 mm.
[0074] In arc welding, the bent portions 12b, 12b
and the closing plate 13 are joined by using a
welding wire as a filler metal. Therefore, in the
automobile structural member 33 of the present
invention example, load transmission portions 20 are
formed in spaces between the bent portions 12a, 12a
and the closing plate 13.
In arc welding, continuous welding is carried out
through an entire length of 600 mm in a longitudinal
direction, a welding speed is constant at 60 mm/min,
a welding current and a welding voltage are changed
between 110 A to 170 A, and 15 V to 20 V, in
correspondence with a plate thickness. Further, as
shield gas, Ar + 20% COz is used, and as the welding
wire, a welding wire of 60 kgf class of ij 1/2 mm is
used.
[0075] Here, automobile structural members 31, 32,
33 having transverse section shapes shown in Fig. 3A
to Fig. 3C respectively are fabricated by using 440
MPa class non-plating steel sheets with a plate
thickness of 1.2 mm and a plate thickness of 2.0 mm.
On this occasion, the automobile structural members
32, 33 of the second comparative example 2 and the
present invention example are fabricated by changing
the curvature radius R of the bent portions 12b, 12b
from 2 mm to 10 mm at an interval of 2 mm per plate
thickness of the steel sheet.
[0076] A bending performance of each of the
fabricated automobile structural members 31, 32, 33
is evaluated by static three-point bending test. As
a test condition, a supporting point interval is 500
mm, a supporting point curvature radius is 30 mm, an
impactor curvature radius is 150 mm, and a crushing
speed is 50 mm/min
Table 1 shows test results of maximum bending
loads.
Fig. 4 shows a graph of a load-displacement curve
at a time that an impactor is displaced in a
representative case where a plate thickness is 2.0 mm
and a curvature radius R of a bent portion is 6 mm.
Fig. 5A shows a graph of maximum bending loadcurvature
radius of bent portion at a time of a plate
thickness of 1. 2 mm, and Fig. 5B shows a graph of a
maximum bending load-curvature radius of bent portion
at a time of a plate thickness of 2.0 mm.
[0077] [Table 11
Plate
Thickness
t
~m)
1.2
Welding
Method
Spot
Welding
Curvature
Radius of
Bent
portioll
R(mm)
6
Load
T r a ~ ~ s u l i s s i o ~ l
Portion
Width
W T
-
Joining
MTidth
L
-
Maxillluln
Bending
Load
(kN)
15.0
Classification
F i r s t
Co~nparative
Esample
Second
Comparative
Example
Secoild
Comparative
Example
Second
Comparative
Esaillple
Second
Colilparative
Example
Second
Comparative
Exainple
Present
Invention
Exaiilple
Present
Invention
Exai~iple
Present
Invention
Example
Present
Illventioil
Example
-
Laser
Welding
Arc
gelding
Spot First
A1elding Coinpaxative
Example
Second
Comparative
Esample
Second
Comparative
Exaiilple
Second
Comparative
Example
Second
Comparative
Example
Second
Comparative
Esaiilple
Present
Invention
Laser
Nelding
Arc
Neldiilg Invention
Example
Present
Iilvelltioll
Exainple
[0078] As shown in Table 1, in the first comparative
8
10
example and the second comparative example, since in
neither case a load transmission portion is formed,
columns of the load transmission portion width WT and
the joining width L are vacant. On the other hand,
in the present invention example, since the load
0.3t
O.Ot
transmission portion 20 is formed, values obtained by
measuring the load transmission portion width WT and
the joining width L are listed. On this occasion,
the spaces between the bent portions 12b, 12b and the
closing plate 13 are increased as the curvature
O.5t
O.lt
radius R of the bent portion 12b becomes larger, and
the load transmission portion width WT and the
joining width L become small.
[0079] As shown in Fig. 4, when compared with a case
of the curvature radius R of 6 mm, the load is larger
39.3
35.2
in the present invention example than the first
Present
Invention
Example
-
comparative example and the second comparative
example at any displacement.
Further, as shown in Fig. 5A and Fig. 5B, when
compared with a case of the curvature radius R of 6
mm, the maximum bending load is larger in order of
the present invention example, the first comparative
example, and the second comparative example. As
described above, it can be verified that the bending
crushing performance can be substantially improved in
the present invention example. Note that the reason
why the maximum bending load is larger in the first
comparative example than in the second comparative
example is a difference between lengths of respective
flanges and lengths of the second composing members.
[0080] Further, when the second comparative example
and the present invention example are compared, the
maximum bending load of the present invention example
is larger than that of the second comparative example
in any curvature radius R of bent portion 12b.
Therefore, it can be verified that by forming the
load transmission portion 20 as in the present
invention example the maximum bending load is
improved more than in the second comparative example
in which a load transmission portion 20 is not formed
Further, when the second comparative example and
the present invention example are compared, in a case
where the curvature radius R of the bent portion 12b
is 2 mm or more to 8 mm or less and further in a case
where the curvature radius R is 2 mm or more to 6 mm
or less, the maximum bending load is substantially
larger in the present invention example than in the
second comparative example. Since respective shapes
of the first composing members 12 and the second
composing members 13 are the same in the present
invention example and the second comparative example,
a relative difference between the maximum bending
loads is considered to be attributed to a difference
between load transmission portion widths WT.
[0081] Therefore, from the test results of the plate
thickness of 1.2 mm of Table 1, when the load
transmission portion width WT satisfies 0.2t 5 WT 5
l.Ot, preferably 0.55t 5 WT 5 1.0t, it is possible
to make the maximum bending load in particular larger
than in the second comparative example.
Further, from the test results of the plate
thickness of 2.0 mm of Table 1, when the load
transmission portion width WT satisfies 0.3t I WT 5
1. Ot, preferably 0.6t 5 WT i 1. Ot, it is possible to
make the maximum bending load in particular larger
than in the second comparative example.
In other words, it is desirable to form the load
transmission portion 20 so that the load transmission
portion width WT satisfies a relation of 0.3t 5 WT 5
1.0t, preferably 0.6t 5 WT l.Ot, a common range
between the plate thickness of 1.2 mm and the plate
thickness of 2.0 mm being extracted.
[0082] [Hardness of Bent Portion]
Next, hardness of the automobile structural
member 33 of the present invention example after
welding is verified.
Fig. 6 is a diagram showing a transverse section
shape around the inward flange 12a of the automobile
structural member 33 of the present invention example.
The automobile structural member 33 of the present
invention example is fabricated by using a 440 MPa
class non-plated steel sheet with a thickness of 1.2
mm shown in Table 1, with a curvature radius R of the
bent portion 12b being 6 mm. A condition of the arc
welding is the same as the welding condition in the
arc welding in Table 1.
[0083] Here, Vickers hardness is measured by pushing
an indenter to the first composing member 12 at
positions P1 to P16 shown in Fig. 6, in a direction
orthogonal to a paper surface of Fig. 6. Note that
Vickers hardness of a base material of the first
composing member 12 before welding is about 140 Hv.
[0084] As a result, PI to P5 shown in Fig. 6 are
about 140 Hv, becoming gradually harder toward the
bent portion 12b, Pg to Plq are about 250 Hv, becoming
gradually lower toward the vertical wall portion 12c,
P15 is about 220 Hv, and P16 is about 170 Hv.
[0085] Therefore, it can be verified that in the
bent portion 12b of the automobile structural member
33 of the invention example, hardness of a range
which at least the load transmission portion 20 is in
contact with is higher than hardness of the base
material of the first composing member 35.
[008 61 [Chemical Component]
Further, by setting a carbon equivalent Ceq to be
0.15 or more, it is possible to harden the bent
portion 12b and a neighborhood of the bent portion
12b of the first composing member 12 by heat input at
the time of welding.
Here, the carbon equivalent Ceq is represented by
the following formula.
Ceq =
C + Si/24 + Mn/6 + Ni/40 + Cr/5 + Mo/4 + V / 4
In contrast, when the carbon equivalent Ceq is
set to be too high, there is an apprehension of
brittle fracture or hydrogen embrittlement, and thus
the carbon equivalent Ceq is desirable to be 0.6 or
less.
[0087] [Height and Plate thickness of First
Composing Member]
Next, influence which a height H and a plate
thickness t of the first composing member 12 give to
the maximum bending load is verified. Here, by using
440 MPa class non-plated steel sheets with a plate
thickness of 1.2 mm and a plate thickness of 2.0 mm,
the automobile structural member 32 of the second
comparative example shown in Fig. 3B and the
automobile structural member 33 of the present
invention example shown in Fig. 3C are fabricate
respectively. On this occasion, with the steel sheet
with the plate thickness of 1.2 mm, ones with the
heights H of the first composing members 12 of 30 mm
and 60 mm are fabricated, and with the steel sheet
with the plate thickness of 2.0 mm, ones with the
heights H of the first composing members 12 of 30 mm,
60 mm, and 90 mm are fabricated. Note that the
curvature radiuses R of the bent portions 12b are all
6.0 mm.
roo881 A bending performance of each of the
fabricated automobile structural members 32, 33 is
evaluated by a static three-point bending test. A
test condition is similar to the test condition of
Table 1.
Table 2 shows test results of maximum bending
tests.
Fig. 7A shows a graph of a maximum bending loadheight
in a case of the plate thickness of 1.2 mm,
and Fig. 7B shows a graph of a maxim bending loadheight
in a case of the plate thickness of 2.0 mm.
[0089] [Table 21
[0090] As shown in Table 2, in the second
Inventioli
Example
comparative example, since a load transmission
9 0
portion is not formed, columns of the load
transmission portion width WT and the joining width L
O.Gt
are vacant. On the other hand, in the present
invention example, since the load transmission
l.lt
portion 20 is formed, values obtained by measuring
the load transmission portion width WT and the
58.4
Present
Illvention
Example
joining width L are listed.
As shown in Fig. 7A and Fig. 7 8 , when compared in
a case of the height H of 30 mm of the first
composing member 12, the maximum bending load is
larger in the present invention example than in the
second comparative example.
Further, when compared in cases of heights H of
60 mm and 90 mm of the first composing member 12, the
maximum bending load is substantially larger in the
present invention example than in the second
comparative example. When the height H of the first
composing member 12 is high, such as 60 mm and 90 mm,
the shape allows easier buckling deformation of the
vertical wall portion 12c, compared with the case of
the low height H such as 30 mm. Therefore, it is
supposed that forming the load transmission portion
20 suppresses deformation of the vertical wall
portion 12c more. Therefore, in the first composing
member 12 whose vertical wall portion 12c is easy to
be buckle-deformed as in the present invention
example, by forming the load transmission portion 20,
it is possible to exhibit a higher effect of
deformation suppression of the transverse section
shape.
[0091] Here, with the plate thickness of the first
composing member 12 being indicated as 't" and the
height being indicated as "H", H/t can be used as an
index representing easiness to be buckle-deformed.
From the test result of the plate thickness of 1.2 mm,
it is desirable to form the load transmission portion
20 in the first composing member 12 in which H/t 2 50
is satisfied. From the result result of the plate
thickness of 1.2 mm, it is desirable to form the load
transmission portion 20 in the first composing member
12 in which H/t > 30 is satisfied. In other words, a
common range being extracted, it is desirable to form
the load transmission portion 20 in the first
composing member 12 in which a relation of H/t > 50
is satisfied.
In contrast, since too large H/t makes an
automobile structural member large, H/t is desirable
to be 90 or less.
[0092] [Number of Welding Operations]
Next, there is described a case where, when the
joining portion 21 including the load transmission
portion 20 is formed by welding, the same place is
welded by a plurality of operations in order to
prevent the first composing member 12 or the second
composing member from being burned through.
For example, in the first operation, welding is
carried out to an entire length of the automobile
structural member so that the load transmission
portion width WT satisfies 0 < WT < 0.3t (preferably
0 < WT < 0.6t) or so that the load transmission
portion width WT satisfies WT < 0.3t (preferably WT <
0.6'~) and the joining length L satisfies. 0 < L, and
in the second operation (or second or later
operation), welding is carried out through the entire
length so that the load transmission portion width WT
satisfies 0.3t 5 WT 2 1.0t (preferably, 0.6t 5 WT s
1.0t).
Further, for example, in the first operation,
welding is carried out through the entire length of
the automobile structural member so that the load
transmission portion width WT satisfies 0.3t 2 WT 5
1.0t (preferably, 0.6t 5 WT 5 l.Ot), and in the
second operation (or in second or later operation),
welding is carried out to regulate a shape through
the entire length so that the joining width L becomes
larger than the load transmission portion width WT.
As a result of welding the same place by the
plurality of operations as above, compared with a
case where the load transmission portion 20 and the
joining portion 21 are made to have a desired load
transmission portion width WT by one operation, it is
possible to reduce a welding heat input amount to the
first composing member 12 and the second composing
member per operation of welding, enabling prevention
of burn-through of the first composing member 12 or
the second composing member 13. In particular, when
the curvature radius R of the bent portion 12 is
larger than 8 mm, by welding by the plurality of
operations; it is possible to make the load
transmission portion width WT satisfy 0.6t 5 WT 5
1.0t easily, and further, it is also possible to
prevent burn-through.
[0093] [Length of Welding]
Next, there is verified a case where a length of
welding is formed intermittently in order to reduce
influence of thermal strain when the joining portion
21 including the load transmission portion 20 is
formed by welding.
Fig. 8A is a perspective view showing an example
of an automobile structural member 41 welded
intermittently. In the automobile structural member
41 shown in Fig. 8A, an entire length of of a first
composing member 12 is indicated as LA, a length of a
joining portion 21, that is, a length (hereinafter,
referred to as a welding length) of welding is
indicated as LB, and a welding pitch is indicated as
P. By intermittently welding as above, influence of
thermal strain can be reduced and occurrence of a
dimension error can be suppressed.
[0094] Here, automobile structural members in which
welding lengths LB and welding pitches P are varied
are fabricated, and maximum bending loads are
compared. Here, by using a 440 MPa class non-plating
steel sheet with a thickness of 2.0 mm and setting an
entire length of a first composing member 12 to be
600 mm, setting a height H to be 60 mm, and setting a
curvature radius R of a bent portion 12b to be 6 mm,
an automobile structural member 33 shown in Fig. 3C
is fabricated with the welding length LB and the
welding pitch P being varied. Note that a welding
condition is the same as the welding condition in arc
welding of Table 1 except the welding length LB and
the welding pitch P.
[0095] A bending performance of each of fabricated
automobile structural members 33 is evaluated by a
static three-point bending test. A test condition is
similar to the test condition of Table 1.
Table 3 shows test results of the maximum ending
tests.
[0096] [Table 31
[0097] The first invention example to the third
invention example shown in Table 3 each have the same
load transmission portion width WT and the same
joining width L. Further, in the first invention
example, since the welding length LB is the same as
an entire length of the first composing member 12, a
column for the welding pitch P is vacant.
As shown in Table 3, in the second invention
example and the third invention example in which arc
welding is carried out intermittently, maximum
bending loads are smaller compared with that in the
first invention example in which arc welding is
carried out for the entire length. On the other hand,
in the third invention example, though the welding
length LB and the- welding pitch P are shorter
compared with those in the second invention example,
the maximum bending load is large. Therefore, when a
joining portion 21 including a load transmission
portion 20 is to be formed intermittently by welding,
shortening a welding length LB and a welding pitch P
can reduce influence of thermal strain, so that
reduction of a maximum bending load can be suppressed.
[0098] Further, in at least two welding operations
among the plurality of welding operations, the
welding lengths can each be changed. Here, a case
where two welding operations are carried out will be
exemplified.
Fig. 8B is a perspective view showing an example
of an automobile structural member 42 in which the
welding length is changed in correspondence with the
number of welding operations. In the automobile
structural member 42 shown in Fig. 8B, the welding
length in the first welding operation is LA being an
entire length of the first composing member 12, the
welding length in the second welding operation is LB,
and the welding pitch is P.
[0099] Here, automobile composing members whose
welding lengths are changed in correspondence with
the number of welding operations are fabricated and
maximum bending loads are compared. Here, an
automobile structural member 33 shown in Fig. 3C is
fabricated by using a 440 MPa class non-plated steel
sheet with a plate thickness of 2.0 mm, with an
entire length of the first composing member 12 being
600 mm, a height H being 60 mm, a curvature radius R
of a bent portion 12b being 10 mm, while the welding
length of the first welding operation and the welding
length of the second welding operation are changed.
Note that welding conditions for both the first
welding operation and the second welding operation
are the same as the welding condition in arc welding
of Table 1 except the welding length LB and the
welding pitch P.
[0100] A bending performance of each of fabricated
automobile structural members 33 is evaluated by a
static three-point bending test. A test condition is
similar to the test condition of Table 1.
Table 4 shows test results of maximum bending
tests.
[0101] [Table 41
[0102] The fourth invention example and the fifth
invention example shown in Table 4, when positions to
which the second welding operations are applied are
compared, each have the same load transmission
portion width WT and the same joining width L.
Further, in the fourth invention example, since the
welding length LB is the same as the entire length of
the first composing member 12 in each of the first
operation and the second operation, columns for the
welding pitch P are vacant.
As shown in Table 4, in the fifth invention
example in which intermittent arc welding is carried
out in the second operation, a maximum bending load
is smaller by 5% than in the fourth invention example
in which arc welding is carried out for the entire
length in all the operations. Therefore, when the
plurality of welding operations are carried out,
intermittent welding in the second and later
operation can reduce burn-through and influence of
thermal strain, so that reduction of the maximum
Plate
Thickness
t
(111111)
2.0
Welding
Method
Arc
Welding
Welding
Length
LB of
First
Operation
L B ( ~ ~ )
GOO
,600
Welding
Pitch P of
First
operation
"("")
-
-
Welding
LLeBn gotfh
Second
Operation
L B ( ~ ~ I )
GOO
50
Welding
Pitch P of
Second
Operation
P(mm)
-
5 0
Maximum
Bendillg
Load
(kN)
47.5
45
Classification
Fourth
Invention
Esan~ple
Fifth
Inventioli
Example
bending load can be suppressed.
For example, in the first operation, welding is
carried out through the entire length so that the
load transmission portion width WT satisfies 0 < WT <
0.3t (preferably 0 < WT < 0. 6t) or so that the load
transmission portion width WT satisfies WT < 0.3t
(preferablyWT < 0.63t) and the joining width L
satisfies 0 < L, and in the second operation (or
second or later operation), welding is carried out to
a welding length shorter than the entire length so as
to satisfy 0.3t WT 1.0t (preferably 0.6t WT 5
l.Ot), whereby it is possible to suppress reduction
of the maximum bending load and to curtail an amount
of filler metal.
[0103] Hereinabove, though the present invention has
been described together with the aforementioned
embodiments, the present invention is not limited
only to those embodiments, and modification is
possible within the scope of the present invention.
INDUSTRIAL APPLICABILITY
[0104] The present invention can be used for a
member on which a three-point bending load is
supposed to act at a collision accident, among
automobile structural members used as skeletal frame
members of an automobile vehicle body.

CLAIMS
[Claim 1] An automobile structural member which has
a closed transverse section shape constituted with at
least a first composing member made of a molded body
of a metal sheet and a second composing member made
of a metal sheet or a molded body of a metal sheet
and joined to the first composing member, the first
composing member having a vertical wall portion, a
bent portion connected to the vertical wall portion
and bent toward an inner side of the closed
transverse section shape, and an inward flange
connected to the bent portion, the automobile
structural member comprising:
a load transmission portion which is formed in at
least a part of a region being a region between the
bent portion and the second composing member and
being a region of an extension of the vertical wall
portion toward the second composing member, and which
joins the bent portion and the second composing
member.
[Claim 2] The automobile structural member according
to claim 1,
wherein when a width of the load transmission
portion toward a plate thickness direction of the
vertical wall portion is indicated as WT and a plate
thickness of the vertical wall portion is indicated
as t
0.3t ( WT 5 1.0t
is satisfied.
[Claim 3] The automobile structural member according
to claim 1 or claim 2,
wherein the load transmission portion is a part
of a joining portion filling a part or all of a space
formed between the bent portion and the second
composing member, and
wherein in the joining portion a joining width
being a range in contact with the second composing
member is longer than a width of the load
transmission portion.
[Claim 4] The automobile structural member according
to any one of claim 1 to claim 3,
wherein in the bent portion, hardness of at least
a range which the load transmission portion is in
contact with is higher than hardness of a base
material of the first composing member.
[Claim 5]The automobile structural member according
to any one of claim 1 to claim 4,
wherein the load transmission portion is formed
intermittently through a longitudinal direction of
the automobile structural member.
[Claim 6] A manufacturing method of an automobile
structural member which has a closed transverse
section shape constituted with at least a first
composing member made of a molded body of a metal
sheet and a second composing member made of a metal
sheet or a molded body of a metal sheet and joined to
the first composing member, the first composing
member having a vertical wall portion, a bent portion
connected to the vertical wall portion and bent
toward an inner side of the closed transverse section
shape, and an inward flange connected to the bent
portion, the manufacturing method of the automobile
structural member comprising:
forming a load transmission portion in at least a
part of a region being a region between the bent
portion and the second composing member, the region
being an extension of the vertical wall portion
toward the second composing member, and which joins
the bent portion and the second composingmember by
welding using a filler metal.
[Claim 71 The manufacturing method of the automobile
structural member according to claim 6,
wherein the load transmission portion is formed
by a plurality of welding operations by using the
filler metal.
[Claim 81 The manufacturing method of the automobile
structural member according to claim 7,
wherein welding lengths are each different in at
least two operations of the plurality of welding
operations.
[Claim 93 The manufacturing method of the automobile
structural member according to any one of claim 6 to
claim 8,
wherein the load transmission portion is a part
of a joining portion filling a part or all of a space
formed between the bent portion and the second
composing member,
wherein the load transmission portion is formed
by a plurality of welding operations by using the
filler metal, and
wherein in the first welding operation, welding
is carried out so that a width WT of the load
transmission portion satisfies WT < 0.6t and a
joining width L being a range in which the joining
portion is in contact with the second composing
member satisfies 0 < L, and
wherein in the second or later welding operation,
welding is carried out so that the width WT of the
1
load transmission portion satisfies 0.6t 5 WT 1.0t.
[Claim 101 The manufacturing method of the
automobile structural member according to any one of
claim 6 to claim 9,
wherein the load transmission portion is formed
i
intermittently through a longitudinal direction of
the automobile structural member.
[Claim 111 The manufacturing method of the
automobile structural member according to any one of
claim 6 to claim 10,
wherein the load transmission portion is formed
by arc welding or laser-arc hybrid welding by using
the filler metal.