JOINING STRUCTURE
The present invention relates to a joining structure.
Priority is claimed on Japanese Patent Application No. 2014-175620, filed
August 29, 2014, and Japanese Patent Application No. 2015-020332, filed February 04,
2015, the contents of which are incorporated herein by reference.
[Background Art]
[0002]
Automobile vehicle bodies having monocoque structure are assembled by
joining a plurality of formed panels in a state where respective edge parts are
overlapped on each other. Resistance spot welding, laser welding, or the like is used
for the welding between the formed panels. In the automobile vehicle bodies,
structural members, such as a side sill (locker), a side member, and various pillars, are
joined to a portion to which a high load is applied and a portion on which a heavy load,
such as an engine, is mounted. Accordingly, rigidity and strength required for the
automobile vehicle bodies are guaranteed.
[0003]
In recent years, it is required that the joining strength between the respective
structural members and various rigidities (torsional rigidity and bending rigidity)
thereof are further enhanced. Meanwhile, in order to reduce the amount of emission
of greenhouse gases by virtue of improvement in fuel efficiency, further weight
reduction of the respective structural members is also required.
- 1 -
[0004]
For example, a joining structure between a side sill that is a structural member
of an automobile vehicle body, and another structural member is disclosed in the
following Patent Document I. Inward flanges that are bent toward the inside of the
side sill is provided at an end part of the side sill in a longitudinal direction. The side
sill is joined to the other structural member (for example, a lower A pillar) via the
above inward flanges.
[0005]
The following Patent Document 2 discloses a vehicle side part structure
including a side sill outer panel having a side sill outer part, a side sill stiffener that
extends in a forward-backward direction of a vehicle body inside the side sill outer part
and is joined to the side sill outer part, a rear wheel housing member having a front
wall that faces a rear end of the side sill stiffener, and a coupling member having a rear
wall that is connected to a rear end part of the side sill stiffener and stops up a rear end
opening of the side sill stiffener, the front wall of the rear wheel housing member and a
rear wall of the coupling member being joined together. According to this vehicle
side part structure, rigidity on a side sill rear end side can be improved.
[0006]
Moreover, the following Patent Document 3 discloses a frontside member
having a frontside member main body and a kick-up part located below the frontside
member main body at a rear part thereof. This frontside member is configured by
butting a pair ofleft and right inner member and onter member against each other to
perform spot welding of these members. The inner member and the outer member
have upward-downward intermediate parts that are formed in a recessed shape so as to
- 2 -
be in contact with each other. By butting the upward-downward intermediate parts
against each other to perform spot welding of these intem1ediate pmis, the fronts ide
member is provided with a coupling part.
[0007]
FIG. 22 is a view illustrating an example of the structure of a general
automobile vehicle body 200. As illustrated in FIG. 22, the automobile vehicle body
200 includes a side sill (locker) 202, an A pillar (front pillar) 203, a B pillar (center
pillar) 204, a roof rail 205, and the like as structural members.
[0008]
With higher performance of automobiles, further enhancing the rigidity
(torsional rigidity and bending rigidity) of the automobile vehicle body 200 to further
improve comport, such as operation stability and silence, is required.
[0009]
FIG. 23 is a perspective view illustrating an example of the side sill202. In
addition, in order to make the drawing easily understood, even in FIG. 23, a side sill
inner panel 206 and a side sill outer panel 207 are illustrated in a transparent state by
two-dot chain lines.
[0010]
As illustrated in FIG. 23, the side sill202 has a closed section consisting of
the side sill inner panel 206, the side sill outer panel 207, a first reinforcement 208, and
a second reinforcement 209.
[0011]
The side sill inner panel 206 has two flanges 206a m1d 206b at both end parts
thereof in a width direction, respectively, a11d has a hat -shaped cross-sectional shape
- 3 -
having these two flanges 206a and 206b as clements.
The side sill outer panel 207 has two flanges 207a and 207b at both end parts
thereof in a width direction, respectively, and has a hat-shaped cross-sectional shape
having these two flanges 207a and 207b as elements.
[0012]
The first reinforcement 208 is disposed between the two flanges 206a and
206b and the two flanges 207a and 207b, and is joined to the side sill inner panel 206
and the side sill outer panel207 by welding nuggets 210 (mass of melted metal)
formed by the resistance spot welding, in a state where the first reinforcement is
overlapped on the side sill inner panel 206 and the side sill outer panel 207 in a threelayer
overlapped manner.
The second reinforcement 209, similar to the first reinforcement 208, is also
disposed between the two flanges 206a and 206b and the two flanges 207a and 207b,
and is joined to the side sill inner panel 206 and the side sill outer panel 207 by the
welding nuggets 210 formed by the resistance spot welding, in a state where the
second reinforcement is overlapped on the side sill inner panel 206 and the side sill
outer panel 207 in a three-layer overlapped manner. Moreover, the first
reinforcement 208 and the second reinforcement 209 are struck (made to abut) against
each other or disposed apart from each other, in the longitudinal direction of each of
the side sill inner panel 206 and the side sill outer panel 207.
In addition, usually, since the welding nuggets 210 are formed at a sheetthickness-
direction central part, the welding nuggets 210 cannot be viewed from the
outside. However, for convenience of description, the welding nuggets 210 are
illustrated in FIG. 23 so that the positions of the welding nuggets can be recognized.
- 4 -
[0013]
In this way, most of the structural members used for the structural bodies are
assembled by welding. For this reason, in order to enhance the rigidity of the
automobile vehicle body, it is effective to use linear continuous welding, such as laser
welding, electric arc welding, or plasma welding. On the other hand, since the
resistance spot welding that is most frequently used because of low costs as a method
for welding the structural members of the automobile vehicle body is not continuous
welding but dot-like discontinuous welding, this resistance spot welding is more
disadvantageous in respect of the rigidity of the structural members than the
continuous welding. For this reason, even if the resistance spot welding is used,
techniques that can improve the rigidity of the automobile vehicle body have been
developed.
[0014]
For example, various kinds of structural members assembled by the resistance
spot welding are disclosed in the following Patent Documents 4 to 6.
[Citation List]
[Patent Literature]
[0015]
Patent Document 1: Japanese Unexamined Patent Application, First
Publication No. 2012-144185
Patent Document 2: Japanese Patent No. 5411245
Patent Document 3: Japanese Patent No. 3820867
Patent Document 4: Japanese Patent No. 5082249
- 5 -
Patent Document 5: Japanese Patent No. 5599553
Patent Document 6: Japanese Patent No. 5261984
[Summary oflnvention]
[Technical Problem]
[0016]
In the joining structure of the automobile vehicle body disclosed in Patent
Document I, the side sill is joined to the other structural member via the inward
flanges in a state where a gap is present between inward flanges adjacent to each other.
That is, since the side sill and the other structural member are joined together in a state
where the adjacent inward flanges are apart from each other, the rigidity of the side sill
decreases. As a result, a function required as the side sill declines.
Additionally, in order to suppress the decrease in the rigidity of the side sill, a
method for joining side sill and the other structural member by joining overlapped
parts ofthe inward flanges and their vicinities in state where the adjacent inward
flanges are overlapped on each other is also considered. However, in this method, an
increase in weight is caused due to overlapping of portions of the adjacent inward
flanges on each other. As a result, it becomes difficult to realize significant weight
reduction that is extremely strongly required for current automobile vehicle bodies for
reduction of global warming gases.
[0017]
In the structure disclosed in Patent Document 2, it is necessary to use a new
component such as the coupling member. That is, in this structure, an increase in
weight is caused due to addition of the coupling member. As a result, it becomes
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difficult to realize weight reduction that is strongly required for the automobile vehicle
bodies as described above.
[0018]
In the structure disclosed in Patent Document 3, butting spot welding is
performed on a surface that originally has a low joining strength and becomes
perpendicular to a collision direction (vehicle longitudinal direction). Therefore,
breaking easily occurs in a spot welding part at the time of a collision, and desired
collision properties cannot be obtained. Additionally, if only edges of different
members are subjected to the butting spot welding, these members are apt to be
fractured.
[0019]
A side si11202 having a structure having a closed section consisting of the
structural members illustrated in FIG. 23; that is, the side sill inner panel 206, the side
sill outer panel 207, the first reinforcement 208, and the second reinforcement 209 and
having a structure in which the first reinforcement 208 and the second reinforcement
209 arc butted against or disposed apart from the side sill inner panel 206 and the side
sill outer panel 207 in a longitudinal direction of each thereof is not disposed or
suggest in Patent Documents 4 to 6.
(0020]
For this reason, the side sill 202 having a structure that can enhance rigidity as
much as possible even by the resistance spot welding cannot be provided even if it is
based on the inventions disclosed in Patent Documents 4 to 6.
[0021]
As described above, the structural members ofthe automobile vehicle body
- 7 -
such as the side sill 202 need to be low in cost, light in weight, and high in rigidity.
Although it is possible to enhance the rigidity of the structural members by expanding
the welding range of the two flanges 206a and 206b and the two flanges 207a and 207b
in the side sill 202 (for example, increasing the number of times of spot welding (the
number of welding nuggets)), an increase in welding cost resulting from expanding the
welding range cannot be denied.
[0022]
Additionally, if the two flanges 206a and 206b and the two flanges 207a and
207b are overlapped on each other and joined together in the longitudinal direction of
each of the side sill inner panel206 and the side sill outer panel207, the rigidity of the
structural members can be enhanced. However, not only material costs increase
correspondingly but also the weight of the structural members increases.
[0023]
For this reason, it is necessary to develop structural members having a
structure that can improve rigidity per one spot welding without expanding the welding
range of the two flanges 206a and 206b and the two flanges 207a and 207b.
[0024]
In this way, in recent years, it is necessary to realize three requirements such
as cost reduction, weight reduction, and higher rigidity for the structural bodies in a
well-balanced manner. For example, if the welding range ofthe flanges is expanded
by increasing the number of times of spot welding, the rigidity of the automobile
vehicle body is improved but welding costs rise inevitably with the expansion of the
welding range. Additionally, if the flanges are enlarged, the rigidity of the
automobile vehicle body is improved but material costs increase and the weight of the
- 8 -
automobile vehicle body also increases, with an increase in size of the tlanges. As a
result, it becomes difficult to realize weight reduction of the automobile vehicle body.
In the above description, the automobile vehicle body has been mentioned as
an example as a structural body in which cost reduction, weight reduction, and higher
rigidity are required. However, cost reduction, weight reduction, and higher rigidity
are often required for, for example, other structural bodies, such as vehicle bodies of
railroad vehicles and fuselages of aircrafts, without being limited to the automobile
vehicle body.
Therefore, in recent years, it is very important to develop techniques capable
of realizing cost reduction, the weight reduction, and higher rigidity required for
structural bodies including the automobile vehicle body in a well-balanced manner.
[0025]
The invention has been made in view of the above circumstances, and an
object thereof is to provide a joining structure capable of realizing three requirements
such as cost reduction, weight reduction, and higher rigidity for structual bodies in a
well-balanced manner.
[Solution to Problem]
[0026]
The invention adopts the following means in order to solve the above
problems to achieve the relevant object.
(l)Ajoining structure related to an aspect of the invention includes a first
metal sheet and a pair of second metal sheets. Each of the pair of second metal sheets
is overlapped on the first metal sheet in a state where an end surface of one of the
- 9 -
second metal sheets and an end surface of the other second metal sheet face each other,
and the end smfaces that face each other are integrally joined to the first metal sheet by
means of a single mass of melted metaL
[0027]
(2) In the joining structure described in the above (I), the pair of second metal
sheets may be present on the same plane.
[0028]
(3) In the joining structure described in the above (I) or (2), a distance
between the end surfaces that face each other may be equal to or more than 0 mm and
less than I mm.
[0029)
( 4) In the joining structure described in the above (I) or (2), the following
Conditional Expression (a) may be satisfied when a sheet thickness of the pair of
second metal sheets is defined as t (mm) and the distance between the end surfaces that
face each other is defined as G (mm).
0 mm2 :<: G x t < 1 mm2 (a)
[0030)
(5) In the joining structure described in the above (1) or (2), the distance
between the end surfaces that face each other may be less than 40% of the sheet
thickness ofthe second metal sheets.
[0031)
(6) In the joining structure described in any one of the above (1) to (5), an
extension length of the end surfaces that face each other may be equal to or more than
3 mm and less than 50 mrn.
- 10 -
[0032]
(7) In the joining structure described in any one of the above (I) to (6), the
pair of second metal sheets may be a pair of inward flanges provided in a materialaxis-
direction end part of a metal-formed sheet having a constant sectional shape in the
material axis direction.
[0033]
(8) In the joining structure described in the above (7), the sectional shape of
the metal-formed sheet may be an angular shape, a channel shape, or a quadrangular
shape.
[0034]
(9) In the joining structure described in the above (7) or (8), the metal-formed
sheet may be a side sill of an automobile vehicle body, and the first metal sheet may be
a portion of a lower A pillar of the automobile vehicle body.
[0035]
(I 0) The joining structure described in any one of the above (1) to (6) may
further include a third metal sheet. The pair of second metal sheets may be
sandwiched between the first metal sheet and the third metal sheet, and the end
surfaces that face each other may be integrally joined to the first metal sheet and the
third metal sheet by means of the mass of melted metal.
[0036]
(11) In the joining structnre described in the above (10), the first metal sheet
may be a flange provided in a first metal-formed sheet having a hat-like sectional
shape in the material axis direction, and the third metal sheet may be a flange provided
in a second metal-formed sheet having a hat-like sectional shape in the material axis
- 11 -
direction.
[0037]
(12) In the joining structure described in the above (11), the first metal-formed
sheet may be a side sill outer panel of an automobile vehicle body, the second metalformed
sheet may be a side sill inner panel of the automobile vehicle body, and each of
the pair of second metal sheets may be a reinforcement or a center pillar inner panel of
the automobile vehicle body.
[Advantageous Effects of Invention]
[0038]
According to the above aspect of the invention, a joining structure capable of
realizing three requirements such as cost reduction, weight reduction, and higher
rigidity for the structural bodies in a well-balanced manner can be provided.
[Brief Description of Drawings]
[0039]
FIG. 1 is a perspective view schematically illustrating a joining structure 1
(the joining structure between a side sill2 and a lower A pillar 3) related to a first
embodiment of the invention.
FIG. 2 is a view when the joining structure I illustrated in FIG. 1 is seen from
the lower A pillar 3 side.
FIG. 3 is anA-A arrow sectional view (a sheet -thickness-direction sectional
view of a welding spot) of the joining structure I illustrated in FIG. 2.
FIG. 4 is an enlarged view of a place where a welding nugget 17 is formed in
- 12 -
the joining structure I illustrated in FIG. 2.
FIG. 5 is an explanatory view illustrating an analytic model of the joining
structure 1.
FIG. 6 is a side view illustrating a longitudinal end part of a side sill in the
analytic model in an extracted manner.
FIG. 7 A is an explanatory view of an analytic model (Related-Art Shape 1) of
a related-art example.
FIG. 78 is an explanatory view of the analytic model (Related-Art Shape 1) of
the related-art example.
FIG. 7C is an explanatory view of the analytic model (Related-Art Shape 1) of
the related-art example.
FIG. 70 is an explanatory view of the analytic model (Related-Art Shape 1) of
the related-art example.
FIG. 8A is an explanatory view of an analytic model (Related-Art Shape 2) of
the related-art example.
FIG. 88 is an explanatory view of the analytic model (Related-Art Shape 2) of
the related-art example.
FIG. 8C is an explanatory view of the analytic model (Related-Art Shape 2) of
the related-art example.
FIG. 80 is an explanatory view of the analytic model (Related-Art Shape 2) of
the related-art example.
FIG. 9Ais an explanatory view of an analytic model (developed shape) of an
example of the invention.
FIG. 98 is an explanatory view of an analytic model (developed shape) of the
- 13 -
example of the invention.
FIG. 9C is an explanatory view of an analytic model (developed shape) of the
example of the invention.
FIG. 90 is an explanatory view of an analytic model (developed shape) of the
example of the invention.
FIG. 10 is a graph illustrating torsional rigidity in the case of 8-spot welding
and 12-spot welding regarding the analytic modes of Related-Art Shapes 1 and 2 and
the developed shapes.
FIG. II is a graph illustrating torsional rigidity/the number of welded parts in
the case of the 8-spot welding and the 12-spot welding regarding the analytic modes of
Related-Art Shapes 1 and 2 and the developed shapes.
FIG. 12 is a graph illustrating torsional rigidity/( weight of planes of inward
flanges) in the case of the 8-spot welding and the 12-spot welding regarding the
analytic modes of Related-Art Shapes 1 and 2 and the developed shapes.
FIG. 13 is an explanatory view illustrating strain distribution when the
analytic modes of Related-Art Shapes I and 2 and the developed shapes are rotated by
one degree.
FIG. 14 illustrates results obtained by analyzing a relationship between a gap
(inter-end-surface distance) between inward flanges adjacent to each other, and the
torsional rigidity regarding the developed shape illustrated in FIG. 9C.
FIG. 15 is a perspective view schematically illustrating a joining structure 111
(a joining structure among a side sill inner panel106, a side sill outer panel107, a first
reinforcement 108, and a second reinforcement 109) related to a second embodiment
of the invention.
- 14 -
FIG. 16 is a Barrow view of FIG. 15.
FIG. 17 is a C-C arrow sectional view (a sheet -thickness-direction sectional
view of a welding spot) of a welding spot illustrated in FIG. 16.
FIG. 18 is an explanatory view illustrating the sectional shape of side sills.
FIG. 19 is an explanatory view illustrating respective arrangements of the first
reinforcement and the second reinforcement and the positions of welding nuggets in
side sills of the related-art examples and a side sill of the example of the invention.
FIG. 20 is a graph illustrating analysis results in an example.
FIG. 21 is a graph illustrating analysis results in the example.
FIG. 22 is an explanatory view illustrating an example of a body shell of an
automobile vehicle body.
FIG. 23 is a perspective view illustrating an example of the side sill.
[Description of Embodiments]
[0040]
Hereinafter, embodiments of the invention will be described referring the
drawings. In addition, an automobile vehicle body will be exemplified and described
as a structural body in which cost reduction, weight reduction, and higher rigidity are
required.
[0041]
(First Embodiment)
A first embodiment of the invention will first be described. As already
described, the automobile vehicle body includes a side sill and a lower A pillar as
structural members. In the following first embodiment, a form in which a joining
- 15 -
structure of the invention is applied to a joining structure between the side sill and the
lower A pillar will be described.
FIG. l is a perspective view schematically illustrating a joining stmcture l
(the joining stmcture between a side sill2 and a lower A pillar 3) related to the first
embodiment of the invention. FIG. 2 is a view when the joining structure l illustrated
in FIG. l is seen from the lower A pillar 3 side.
[0042]
In addition, although the joining structure l between the side sill 2 and the
lower A pillar 3 will be described in the first embodiment, the invention is not limited
only to this form. Respective shapes of the side sill 2 and the lower A pillar 3 are
simplified and illustrated in FIGS. 1 and 2. Additionally, in FIGS. 1 and 2, in order to
make the drawings easily understood, the lower A pillar 3 is illustrated in a perspective
state, using two-dot chain line.
[0043]
(Side Sill2)
The side sill2 is a metal-formed sheet having a constant sectional shape (a
quadrangular shape in the present embodiment) in a material axis direction (an arrow
direction illustrated in FIG. 1 ). More specifically, the side sill 2 is an elongated
hollow tubular press-formed body made of high tensile strength steel sheet of which
the tensile strength is nommlly in a class of 590 MPa (preferably in a class of 780 MPa
and still more desirably in a class of 980 MPa). The press forming may be cold press
or may be hot press.
[0044]
The side si112 includes at least a first surface 4, a first ridgeline 5, and a
- 16 -
second surface 6.
The first surface 4 extends in the material axis direction. The first ridgeline
5 is connected to the first surface 4 and extends in the material axis direction.
Moreover, the second surface 6 is connected to the first ridgeline 5 and extends in the
material axis direction.
[0045]
The side sill 2 has a substantially quadrangular cross-sectional shape. For
that reason, the side sill2 further includes a second ridgeline 7 connected to the second
surface 6, a third surface 8 connected to the second ridgeline 7, a third ridgeline 9
connected to the third surface 8, a fourth surface 10 connected to the third ridgeline 9,
and a fourth ridgeline 11 connected to the fourth surface 10 and the first surface 4.
[0046]
The side sill 2 may have not the quadrangular cross-sectional shape but, for
example, a substantially angular cross-sectional shape. In this case, the side sill 2 has
only the first surface 4, the first ridgeline 5, and the second surface 6. Additionally,
the side sill 2 may have a channel-like sectional shape. In this case, the side sill 2 has
only the first surface 4, the second surface 6, the third surface 8, the first ridgeline 5,
and the second ridgeline 7.
[0047]
A first inward flange 13, a second inward flange 14, a third inward flange 15,
and a fourth inward flange 16 are provided at a material-axis-direction end part 12 of
the side sill 2 so as to be present on the same plane.
[0048]
The first inward flange 13 is fonned to be connected to the first surface 4.
- 17 -
The second inward flange 14 is connected to the second surface 6, and is
formed with a gap between the second inward flange 14 and the first inward flange 13
without overlapping the first inward flange 13.
As illustrated in FIG 2, a first end surface 13a of the first inward flange 13
and a second end surface 14b of the second inward flange 14 face each other on the
same plane. A pair ofthe first inward flange 13 and the second inward flange 14
corresponds to a pair of second metal sheets in the invention.
[0049]
The third inward flange 15 is connected to the third surface 8, and is formed
with a gap between the third inward flange 15 and the second inward flange 14 without
overlapping the second inward flange 14.
As illustrated in FIG. 2, a first end surface 14a of the second inward flange 14
and a second end surface 15b ofthe third inward flange 15 face each other on the same
plane. A pair ofthe second inward flange 14 and the third inward flange 15 also
corresponds to the pair of second metal sheets in the invention.
[0050]
The fourth inward flange 16 is connected to the fourth surface 10, and is
formed with a gap between the fourth inward flange 16 and the third inward flange 15
without overlapping the third inward flange 15.
As illustrated in FIG 2, a first end surface 15a of the third inward flange 15
and a second end surface 16b ofthe fourth inward flange 16 face each other on the
same plane. A pair of the third inward flange 15 and the fourth inward flange 16 also
corresponds to the pair of second metal sheets in the invention.
[0051]
- 18 -
Additionally, the fourth inward flange 16 is formed with a gap between the
fourth inward flange 16 and the first inward flange 13 without overlapping the first
inward flange 13.
As illustrated in FIG 2, a first end surface 16a of the tourlh inward flange 16
and a second end surface 13b of the first inward flange 13 face each other on the same
plane. A pair of the fourth inward flange 16 and the first inward flange 13 also
corresponds to the pair of second metal sheets in the invention.
[0052]
(Lower A Pillar 3)
The lower A pillar 3 is a press-formed product of high tensile strength steel
sheet, similar to the side sill 2. The side sill 2 is joined to a flat part (hereinafter, fhis
is referred to as a flat part) 31 of the lower A pillar 3. The flat part 31 that is a portion
ofthe lower A pillar 3 corresponds to a first metal sheet in the invention. The side sill
2 is joined to the flat part 31 of the lower A pillar 3 via the first inward flange 13, the
second inward flange 14, the third inward flange 15, and the fourth inward flange 16,
for example, by resistance spot welding.
[0053]
(Joining between Side Sill2 and Lower A Pillar 3)
As illustrated in FIG 2, each of the first inward flange 13 and the second
inward flange 14 is overlapped on the flat part 31 of the lower A pillar 3 and is joined
thereto by fhe resistance spot welding, in a state where the first end surface 13a of the
first inward flange 13 and the second end surface 14b of the second inward flange 14
face each other.
FIG 3 is an A-A arrow sectional view (a sheet -thickness-direction sectional
- 19 -
view of a welding spot) ofthe joining structure I illustrated in FIG. 2. As illustrated
in FIG. 3, the first end surface 13a of the first inward 1lange 13 and the second end
surface 14b of the second inward flange 14 (the end surfaces that face each other) are
integrally joined to the flat part 31 of the lower A pillar 3 by means of a single mass of
melted metal (hereinafter referred to as a welding nugget) 17 formed so as to spread in
an elliptical shape from the joining surface (sheet -thickness-direction central part) by
the resistance spot welding.
In addition, the mass of melted metal is a part that is obtained when metal
melted due to high-temperature heat caused by a welding process gets cold and
solidifies, and that exhibits firm joining between metal members. Generally, the mass
of melted metal formed by the resistance spot welding is referred to as the welding
nugget (or simply a nugget).
[0054]
As illustrated in FIG. 2, each ofthe second inward flange 14 and the third
inward flange 15 is overlapped on the flat part 31 of the lower A pillar 3 and is joined
thereto by the resistance spot welding, in a state where the first end surface 14a of the
second inward flange 14 and the second end surface 15b of the third inward flange 15
face each other.
The first end surface 14a of the second inward flange 14 and the second end
surface 15b of the third inward flange 15 (the end surfaces that face each other) are
integrally joined to the flat part 31 of the lower A pillar 3 by means of a single welding
nugget 18 formed so as to spread in an elliptical shape from the joining surface (sheet -
thickness-direction central part) by the resistance spot welding. In addition, since the
sectional shape of the welding nugget 18 is the same as that of the sectional shape of
- 20 -
the welding nugget 17 illustrated in FIG 3, illustration of the sectional shape of the
welding nugget 18 is omitted.
[0055]
As illustrated in FIG 2, each ofthe third inward flange 15 and the fourth
inward flange 16 is overlapped on the flat part 31 of the lower A pillar 3 and is joined
thereto by the resistance spot welding, in a state where the first end surface 15a of the
third inward flange 15 and the second end surface 16b ofthe fourth inward flange 16
face each other.
The first end surface I 5a ofthe third inward flange I 5 and the second end
surface 16b ofthe fourth inward flange 16 (the end surfaces that face each other) are
integrally joined to the flat part 31 of the lower A pillar 3 by means of a single welding
nugget 19 formed so as to spread in an elliptical shape from the joining surface (sheet -
thickness-direction central part) by the resistance spot welding. In addition, since the
sectional shape ofthe welding nugget 19 is the same as that of the sectional shape of
the welding nugget 17 illustrated in FIG 3, illustration of the sectional shape of the
welding nugget 19 is omitted.
[0056]
As illustrated in FIG 2, each of the fourth inward flange 16 and the first
inward flange 13 is overlapped on the flat part 31 of the lower A pillar 3 and is joined
thereto by the resistance spot welding, in a state where the first end surface 16a of the
fourth inward flange 16 and the second end surface 13b of the first inward flange 13
face each other.
The first end surface 16a of the fourth inward flange 16 and the second end
surface 13b ofthe first inward flange 13 (the end surfaces that face each other) are
- 21 -
integrally joined to the flat part 31 of the lower A pillar 3 by means of a single welding
nugget 20 formed so as to spread in an elliptical shape from the joining surface (sheetthickness-
direction central part) by the resistance spot welding. In addition, since the
sectional shape of the welding nugget 20 is the same as that of the sectional shape of
the welding nugget 17 illustrated in FIG. 3, illustration of the sectional shape of the
welding nugget 20 is omitted.
[0057]
The joining strength between the side sill 2 and the lower A pillar 3 is
dependent on the size (nugget diameter) of each of the welding nuggets 17, 18, 19, and
20. Therefore, it is necessary to appropriately control the nugget diameter of each of
the welding nuggets 17, 18, 19, and 20 by performing the resistance spot welding
under welding conditions (the pressing force of an electrode, a current value,
energization time, and the like) according to a required joining strength.
For example, it is preferable to set the welding conditions such that the nugget
diameter becomes equal to or more than 2.5-,/t. Here, tis the sheet thickness (that is,
the sheet thickness of the side sill2) of each of the inward flanges 13 to 16, and the
unit thereof is mm. It is more preferable to set the welding conditions such that the
nugget diameter becomes equal to or more than 3. o-,Jt, and it is stillmore preferable to
set the welding conditions such that the nugget diameter becomes equal to or more
than 4.0-,/t.
[0058]
It is desirable that all of the first inward flange 13, the second inward flange
14, the third inward flange 15, and the fourth inward flange 16 are present substantially
on the same plane in order to guarantee weldability, especially resistance spot
- 22 -
weldability or laser weldability. In other words, it is preferable that the inward
flanges 13 to 16 come in close contact (surface contact) with the flat part 31 of the
lower A pillar 3 without overlapping each other.
[0059]
FIG 4 is an enlarged view of a place where the welding nugget 17 is formed
in the joining structure I illustrated in FIG 2. As illustrated in FIG 4, it is preferable
that a distance G between the first end surface !3a of the first inward flange 13 and the
second end surface !4b of the second inward flange 14 (the distance between the end
surfaces that face each other: hereinafter referred to as an inter-end-surface distance) is
equal to or more than 0 m111 and less than I mm. This distance is for guaranteeing all
of weight reduction, and weldability with the lower A pillar 3, especially resistance
spot weldability or laser weldability.
Although this distance will be described in detail, the welding nugget 17
cannot be stably formed in a case where the inter-end-surface distance G is equal to or
more than 1 111111. Thus, the torsion rigidity of the joining structure I decreases.
From a viewpoint of improvement in the torsion rigidity, the inter-end-surface distance
G is more preferably equal to or more than 0 mm and less than 0.3 mm and still more
preferably equal to or more than 0 mm and less than 0.1 mm. Particularly, when the
side sill2 is defonned, it is recommended that the inter-end-surface distance G is less
than 0.1 mm such that the first end surface 13a ofthe first inward flange 13 and the
second end surface 14b of the second inward flange 14 come into contact with each
other.
[0060]
Additionally, in a case where the sheet thickness t (unit is mm) of the inward
- 23 -
t1anges 13 and 14 is large, melted metal is scattered at the time of the resistance spot
welding. Therefore, the inter-end-surface distance G may be standardized by the
sheet thickness t. A conditional expression in a case where the inter-end-surface
distance G is standardized by the sheet thickness t is as follows.
Preferable conditional expression: 0 1111112 :S G x t < 1 m1112 (a)
More preferable conditional expression: 0 111m2 :S G x t < 0.3 mm2 (b)
Still more conditional expression: ·o mm2 :S G x t < 0.1 mm2 (c)
[0061]
Additionally, in a case where a preferable range ofthe inter-end-surface
distance G is defined by the percentage of the sheet thickness t, it is preferable that the
inter-end-surface distance G is equal to or more than 0 mm and less than 40% of the
sheet thickness t. Since the welding nugget 17 cannot be stably formed in a case
where the inter-end-surface distance G is equal to or more than 40% of the sheet
thickness t, the torsion rigidity of the joining structure I decreases. From a the
viewpoint of improvement in the torsion rigidity, it is more preferable the inter-endsurface
distance G is equal to or more than 0 mm and less than I 0% of the sheet
thickness t.
[0062]
The reason why the inter-end-surface distance G is specified is because, if the
inter-end-surface distance G is too long, weld metal melted from between end surfaces
at the time of the resistance spot welding may leak out and a desired welding strength
may not be obtained.
[0063]
As illustrated in FIG. 4, it is preferable that the extension length D of the first
- 24 -
end surface 13a of the tlrst inward t1ange 13 and the second end surface 14b of the
second inward t1ange 14 (the extension length ofthe end surfaces that face each other
is referred to as end surface length) is equal to or more than 3 mm and less than 50 mm.
In a case where the end surface length Dis less than 3 mm, it becomes difficult to
perform the resistance spot welding. Even if welding can be performed by laser
welding or the like instead of the resistance spot welding, rigidity as a member cannot
be guaranteed in a case where end surface length D is less than 3 111111. In a case
where end surface length Dis equal to or more than 50 mm, the weight of the side sill
2 increases. As a result, an increase in the weight of the automobile vehicle body is
caused. If the balance between higher rigidity and weight reduction is taken into
consideration, it is more preferable that the end surface length D is equal to or more
than 3 mm and less than 20 mm.
[0064]
It is preferable that The conditions of the inter-end-surface distance G and the
conditions of the end surface length Dare applied not only to the pair ofthe first
inward t1ange 13 and the second inward t1ange 14 but also to the pair of the second
inward t1ange 14 and the third inward t1ange 15, the pair of the third inward t1ange 15
and the fourth inward t1ange 16, and the pair of the fourth inward t1ange 16 and the
first inward flange 13.
[0065]
Although a form in which the inward t1anges 13 to 16 of the side sill 2 and the
t1at part 31 of the lower A pillar 3 are joined together by the four welding nuggets 17 to
20 is illustrated in FIGS. 1 and 2, the inward t1anges 13 to 16 and the t1at part 31 may
be joined together even in places other than the places where the welding nuggets 17 to
- 25 -
20 are present. Accordingly, it is possible to further enhance the joining strength
between the side sill 2 and the lower A pillar 3. However, since welding costs rises
with an increase in the welding spots, the total of welding spots may be appropriately
determined taking into consideration required joining strength and manufacturing costs.
[0066]
In addition, although the side sil12 is manufactured by press-forming a blank,
which is a stock, using well-known techniques, the side sill2 may be manufactured by
performing blank press working after the inward flanges 13 to 16 are formed at edge
parts of the blank in its longitudinal direction. Otherwise, the inward flanges 13 to 16
may be formed after a main body portion of the side sill2 is formed by the blank press
working.
[0067]
Although a case where the masses of melted metal (welding nuggets) formed
by the resistance spot welding are used for the joining between the structural members
has been illustrated in the above description, for example, masses of melted metal
formed by discontinuous welding, such as electric arc welding, laser welding, and laser
electric arc welding, in addition to the resistance spot welding, may be used for the
joining between the structural members. As the shapes of the masses of melted metal
formed by these kinds of discontinuous welding, a C shape, an 0 shape, an elliptical
shape, a linear shape, a curved shape, a waveform shape, a spiral shape, and the like
are exemplified.
[0068]
According to the joining structure 1 related to the first embodiment as
described above, it is possible to achieve higher rigidity ofthe automobile vehicle body
- 26 -
(particularly, a joining portion between the side sill 2 and the lower A pillar 3) while
minimizing the amount of expansion of the flanges without increasing the number of
times of resistance spot welding (the number of welding nuggets). That is, according
to the joining structure 1, it is possible to realize three requirements such as cost
reduction, weight reduction, and higher rigidity for the structural bodies in a wellbalanced
manner.
Hereinafter, the grounds on which the above effects are obtained by the
joining structure 1 will be described referring to the following example.
[Example]
[0069]
An analytic model of the joining structure I illustrated in FIG. I was made,
numerical analysis was performed, and the performance of the joining structure I was
evaluated. FIG. 5 is an explanatory view illustrating the analytic model 21, and FIG.
6 is a side view illustrating a longitudinal end part of a side sill 22 in the analytic
model 21 in an extracted manner.
[0070]
In the analytic model21, similar to the joining structure 1, four inward flanges
are provided at each of both ends 21 a and 21 b of the side sill 22 (of which the entire
length thereof is 500 mm and the curvature radius of a first ridgeline is 5 mm) in the
longitudinal direction. The four inward flanges formed at each of both the ends 21 a
or 21 b are joined to each of end sheets 23 and 24 serving as rigid bodies that are flat
parts of the lower A pillar, with a joining strength equivalent to the joining strength of
the resistance spot welding. In addition, the flat parts 23 and 24 of the side sill22 and
-27-
the lower A pillar are made of high tensile strength steel sheets with a sheet thickness
of 1.4 mm and a tensile strength of 590 MPa.
[0071]
Then, in the analysis of the analytic model21, the torsional rigidity was
evaluated by rotating the end sheet 24 by one degree around a central axis of the side
sill 22, in a state the end sheet 23 is completely contained.
[0072]
FIGS. 7 A to 70 are explanatory views of an analytic model (Related-Art
Shape 1) of a related-art example. FIG. 7 A is a perspective view illustrating the side
sill22 in the analytic model of the related-art example. FIG. 78 is an A arrow view in
FIG. 7 A. FIGS. 7C and 70 are explanatory views illustrating resistance spot welding
positions of the analytic model of the related-art example. FIG. 7C illustrates a case
of 8-spot welding, and FIG. 70 illustrates a case of 12-spot welding. In addition, the
length of one side of the resistance spot welding that forms a square shape is 4.7 mm.
This is also the same in Related-Art Shape 2 and developed shapes to be described
below.
[0073]
As illustrated in FIG. 7 A, in the analytic model (Related-Art Shape 1 ), four
inward flanges are spaced apart without overlapping each other. The width wh of
each of the four inward flanges is 14 mm. A gap (inter-end-surface distance) between
the inward flanges adjacent to each other is 7 mm at a shortest distance within a plane
where the four inward flanges are present. Square marks in FIGS. 7C and 70
schematically represent welding nuggets formed by the resistance spot welding.
[0074]
- 28 -
FIGS. SA to SD arc explanatory views of an analytic model (Related-Art
Shape 2) of a related-art example. FIG. SA is a perspective view illustrating a side sill
25 in the analytic model of the related-art example. FIG. 8B is an A arrow view in
FIG. SA FIGS. 8C and 8D are explanations illustrating resistance spot welding
positions of the analytic model of the related-art example. FIG. SC illustrates a ease
of S-spot welding, and FIG. SD illustrates a case of 12-spot welding. Square marks in
FIGS. SC and 8D schematically represent welding nuggets formed by the resistance
spot welding.
[0075]
As illustrated in FIG. SA, in the analytic model (related-art shape 2), a step is
formed in one of two inward flanges adjacent to each other, and the two inward flanges
are joined (welded) to the step part in which these inward flanges are overlapped on
each other. The width of each of the four inward flanges is 14mm.
[0076]
FIGS. 9A to 9D are explanatory views of an analytic model (developed shape)
of an example of the invention. FIG. 9A is a perspective view illustrating a side sill in
the analytic model of the related-art example. FIG. 9B is an A arrow view in FIG. 9A.
FIGS. 9C and 9D are explanatory views illustrating resistance spot welding positions
of the analytic model of the related-art example. FIG. 9C illustrates a case of 8-spot
welding, and FIG. 9D illustrates a case of 12-spot welding. Square marks in FIGS.
9C and 9D schematically represent welding nuggets formed by the resistance spot
welding.
[0077]
As illustrated in FIG. 9A., in the analytic model (developed shape), one end
- 29 -
surface and the other end surface of two inward tlanges adjacent to each other face
each other on the same plane and come in close contact with each other. That is, the
inter-end-surface distance is 0 mm. The one end surface and the other end surface are
integrally joined to an end sheet (equivalent to the flat part of the lower A pillar) (not
illustrate) by a single welding nugget
[0078]
FIG I 0 is a graph illustrating the torsional rigidity in the case of 8-spot
welding and 12-spot welding regarding the analytic modes of Related-Art Shapes 1
and 2 and the developed shapes. FIG 11 is a graph illustrating the torsional
rigidity/the number of welded parts (the number of welding nuggets) in the case of 8-
spot welding and 12-spot welding regarding the analytic modes of Related-Art Shapes
1 and 2 and the developed shapes. FIG 12 is a graph illustrating torsional
rigidity/( weight ofplanes of the inward flanges) in the case of the 8-spot welding and
the 12-spot welding regarding the analytic modes of Related-Art Shapes I and 2 and
the developed shapes.
[0079]
As illustrated in FIGS. 10 and 11, it can be seen that, if shapes in which the
numbers of welded parts are the same number are compared with each other, the
torsional rigidity and the torsional rigidity per one welded part in the developed shapes
are the highest Additionally, as illustrated in FIG 10, it can be seen that the 8-spot
welding of a developed shape has a higher rigidity than the 12-spot welding of
Related-Art Shape 1. Moreover, since the developed shapes have no overlapping of
the inward flanges compared to the Related-Art Shape 2, it can be seen that the
developed shapes are lightweight
- 30 -
[0080]
FIG 13 is a graph illustrating strain distribution when the analytic modes of
Related-Art Shapes 1 and 2 and the developed shapes are rotated by one degree.
Figures in FIG. 13 represent values of shear stresses at sheet thickness centers analyzed
pointed by lines.
[0081]
The superiority of the developed shapes over Related-Art Shapes I and 2 will
be described, referring to FIG 13.
(Superiority of Developed Shapes over Related-Art Shape I)
Even if the developed shapes have simply the same number of welding points
(the same number of welding nuggets) as Related-Art Shape 1, the number of
constraint points in one flange of the 8-spot welding is two as illustrated in FIG 78 in
Related-Art Shape 1. In contrast, in the developed shapes, the number of constraint
points in the one flange of the 8-spot welding become three as illustrated in FIG. 78.
As a result, since the number of points that constrains the flange increases, developed
shapes have higher rigidity than Related-art Shape I.
(Superiority of Developed Shapes Compared with Related-Art Shape 2)
It is necessary to provide a stepped part equivalent to the sheet thickness at an
end part of each of the inward flanges of Related-Art Shape 2 so as to be overlapped
on its adjacent inward flange, and this stepped part becomes a stress concentration part.
In contrast, in the developed shapes, all of adjacent inward flanges can be made
completely flat. For this reason, comer portions of the inward flanges in Related-Art
shape 2 are constrained at points of the welded parts. In contrast, in the developed
shapes, edges (end surfaces) of the inward flanges come in contact with each other in
- 31 -
addition to the constraint allhe points; therefore, the corner portions can be constrained
by lines. For this reason, due to these two influences, in the developed shapes, as
illustrated in the graph ofF! G. 13, the shear stress of the inward flanges becomes
unilorm without being concentrated more than Related-Art Shape 2. Accordingly, the
shear stress becomes unitorm, and rigidity is improved.
[0082]
FIG. 14 illustrates results obtained by analyzing a relationship between the
gap (inter-end-surface distance) between inward flanges adjacent to each other, and the
torsional rigidity regarding the developed shape illustrated in FIG. 9C. As illustrated
in FIG. 14, ifthe inter-end-surface distance becomes equal to or more than I mm, the
torsional rigidity decreases greatly. Thus, it can be seen that it is preferable that the
inter-end-surface distance is equal to or more than 0 mm and less than I mm.
Additionally, it can be seen from FIG. 14 that the inter-end-surface distance is more
preferably equal to or more than 0 mm and less than 0.3 mm, and most preferably
equal to or more than 0 mm and less than 0.1 mm. Particularly, it can be sent that the
torsional rigidity can be markedly improved by set the inter-end-surface distance to 0
mm, that is, bringing the end surfaces that face each other into close contact with each
other.
[0083]
According to the example ofthe invention Uoining structure I), it was proved
from the above analysis results that the three requirements such as the cost reduction,
weight reduction, and higher rigidity for the structural bodies can be realized in a wellbalanced
manner.
Additionally, according to the example of the invention (joining structure I),
- 32 -
it is not necessary to overlap the flanges on each other unlike Related-Art Shape 2.
Thus, compared to Related-Art Shape 2, the number of processes for welding operation
between the side sill and the lower A pillar can be reduced.
[0084]
(Second Embodiment)
Next, a second embodiment of the invention will first be described. As
described with reference to FIG. 23, the automobile vehicle body includes a side sill
inner panel, a side sill outer panel, a first reinforcement, and a second reinforcement as
the structural members. In the second embodiment, a form in which the joining
structure of the invention is applied to a joining structure between these structural
members will be described. Additionally, at least one of the above first reinforcement
and the second reinforcement may be a center pillar inner panel.
FIG. 15 is a perspective view schematically illustrating a joining structure Ill
(a joining structure among a side sill inner panel 106, a side sill outer panel 107, a first
reinforcement 108, and a second reinforcement 1 09) related to the second embodiment
of the invention. FIG. 16 is a 8 arrow view of FIG. 15. In addition, in order to make
the drawings easily understood, even in FIGS. 15 and 16, the side sill inner panel 106
and the side sill outer panel 1 07 are illustrated in a transparent state by two-dot chain
lines. Additionally, although a case where the joining structure 111 itself is a side sill
becomes an example in the subsequent description, the invention is not limited to the
side sill and is applied to a roof rail, an A pillar, or the like.
[0085]
As illustrated in FIG. 15, the joining structure (that is, the side sill) Ill has a
closed section consisting of the side sill inner panel 106, the side sill outer panel 107,
- 33 -
the first reinforcement I 08, and the second reinforcement I 09.
[0086]
The side sill inner panel106 is a metal-formed sheet having a constant
sectional shape in the material axis direction, more specifically, a press-formed sheet
consisting of high tensile strength steel sheet. The side sill inner panel106 has two
flanges 1 06a and 1 06b, respectively, at both end parts thereof in the width direction.
The side sill inner panel I 06 has a hat-shaped cross-sectional shape having the
two flanges l 06a and 1 06b as elements.
The side sill outer panell07 is a metal-formed sheet having a constant
sectional shape in the material axis direction, more specifically, a press-formed sheet
consisting of high tensile strength steel sheet. The side sill outer panel107 has two
flanges 107a and l07b, respectively, at both end parts thereof in the width direction.
The side sill outer panel 107 has a hat-shaped cross-sectional shape having the two
flanges 1 07 a and 1 07b as elements.
[0087]
The first reinforcement 108 is a flat sheet consisting of high tensile strength
steel sheet. The first reinforcement I 08 is disposed between the two flanges I 06a and
106b and the two flanges 107a and 107b, and is joined to the side sill inner panel106
and the side sill outer panel 107 by the welding nuggets 112 formed by the resistance
spot welding, in a state where the first reinforcement is overlapped on the side sill
inner panel l 06 and the side sill outer panel l 07 in a three-layer overlapped manner.
In addition, a state where the welding nuggets 112 are visualized is illustrated in FIG
15.
[0088]
- 34 -
Similar to the first reinforcement I 08, the second reinforcement I 09 is a tlat
sheet consisting of high tensile strength steel sheet. The second reinforcement I 09 is
disposed between the two flanges l06a and 106b and the two flanges I 07a and l07b,
and is joined to the side sill inner panel l 06 and the side sill outer panel l 07 by the
welding nuggets 112 formed by the resistance spot welding, in a state where the first
reinforcement is overlapped on the side sill inner panel 106 and the side sill outer panel
I 07 in a three-layer overlapped manner.
[0089]
The first reinforcement I 08 and the second reinforcement I 09 are butted
against each other or disposed at a predetermined distance from each other, in the
longitudinal direction of each of the side sill inner panel 106 and the side sill outer
panell07.
[0090]
As illustrated in FIGS. 15 and 16, the first reinforcement 108 and the second
reinforcement I 09 are sandwiched between the side sill inner panel 106 and the side
sill outer panel 107, in a state where an end surface 1 08a of the first reinforcement 108
and an end surface l09a of the second reinforcement 109 face each other on the same
plane.
[0091]
FIG. 17 is a C-C arrow sectional view (a sheet-thickness-direction sectional
view of a welding spot) of a welding spot illustrated in FIG. 16. As illustrated in
FIGS. 16 and 17, the end surface 1 08a of the first reinforcement 108 and the end
surface 109a ofthe second reinforcement 109 (the end surfaces that face each other)
are integrally joined to a flange 1 06a of the side sill inner panel 106 and a flange 107 a
- 35 -
of the side sill outer panel 107 by a single welding nugget 113a formed so as to spread
in an elliptical shape from the joining surface (sheet-thickness-direction central part)
by the resistance spot welding.
[0092]
In this way, in the second embodiment, if attention is paid to the welding spot
(welding nugget ll3a) illustrated in FIG. 16, the first reinforcement I 08 and the second
reinforcement 109 correspond to the pair of second metal sheets in the invention, and
the flange 106a of the side sill inner panel 106 corresponds to the first metal sheet in
the invention, and the flange I 07a of the side sill outer panel 107 in the invention
corresponds to a third metal sheet.
[0093]
As illustrated in FIG. 15, the end surface I 08a of the first reinforcement 108
and the end surface 1 09a of the second reinforcement 1 09 (the end surfaces that face
each other) are integrally joined to a flange 106b of the side sill inner panel I 06 and a
flange I 07b of the side sill outer panel107 by a single welding nugget 113b formed so
as to spread in an elliptical shape from the joining surface (sheet-thickness-direction
central part) by the resistance spot welding. In addition, since the sectional shape of
the welding nugget ll3b in the thickness direction is the same as that of the sectional
shape of the welding nugget 113a illustrated in FIG. 17, illustration of the sectional
shape ofthe welding nugget 113b is omitted.
[0094]
In this way, in the second embodiment, if attention is paid to the welding
nugget 113b, the first reinforcement 108 and the second reinforcement 109 correspond
to the pair of second metal sheets in the invention, and the flange I 06b of the side sill
- 36 -
inner panel I 06 corresponds to the first metal sheet in the invention, and the flange
I 07b of the side sill outer panel I 07 in the invention corresponds to a third metal sheet.
[0095]
The joining strength among the side sill inner panel 106, the side sill outer
panel I 07, the first reinforcement 108, and the second reinforcement 109 is dependent
on the size (nugget diameter) of each of the welding nuggets 112, 113a, and 113b.
Therefore, it is necessary to appropriately control the nugget diameter of each of the
welding nuggets 112, 113a, and 113b by performing the resistance spot welding under
welding conditions (the pressing force of an electrode, a current value, energization
time, and the like) according to a required joining strength. For example, it is
preferable to set the welding conditions such that the nugget diameter becomes equal
to or more than 2.5-Yt. Here, t is the sheet thickness of each of the reinforcements 108
to 109, and the unit thereof is mm. It is more preferable to set the welding conditions
such that the nugget diameter becomes equal to or more than 3.0-Yt, and it is still more
preferable to set the welding conditions such that the nugget diameter becomes equal
to or more than 4.0-Yt.
[0096]
It is desirable that both of the first reinforcement 108 and the second
reinforcement 109 are present substantially on the same plane in order to guarantee
weldability, especially resistance spot weldability or laser weldability. In other words,
it is preferable that the first reinforcement 108 and the second reinforcement 109 come
in close contact (surface contact) with the flanges 1 06a and I 06b of the side sill inner
panel106 and the flanges 107a and 107b of the side sill outer panel107 without
overlapping each other.
- 37 -
[0097]
Similar to the tlrst embodiment, even in the second embodiment, it is
preferable that the distance (inter-end-surface distance) G between the end surface
108a of the first reinforcement 108 and the end surface 109a of the second
reinforcement 109 is equal to or more than 0 mm and less than 1mm (refer to FIGS.
15 and 16). Additionally, similar to the first embodiment, even in the second
embodiment, from a viewpoint of improvement in the torsion rigidity, the inter-endsurface
distance G is more preferably equal to or more than 0 mm and less than 0.3
mm and still more preferably equal to or more than 0 mm and less than 0.1 mm.
[0098]
Additionally, similar to the first embodiment, even in the second embodiment,
in a case where the sheet thickness t (unit is mm) of the first reinforcement I 08 and the
second reinforcement 109 is large, melted metal is scattered at the time of the
resistance spot welding. Therefore, the inter-end-surface distance G may be
standardized by the sheet thickness t. A conditional expression in a case where the
inter-end-surface distance G is standardized by the sheet thickness tis the same as
Conditional Expressions (a) to (c) described in the first embodiment.
[0099]
Additionally, similar to the first embodiment, even in the second embodiment,
in a case where a preferable range of the inter-end-surface distance G is defined by the
percentage of the sheet thickness t, it is preferable that the inter-end-surface distance G
is equal to or more than 0 mm and less than 40% of the sheet thickness t. Since the
welding nuggets 113a and 113b cannot be stably formed in a case where the inter-endsurface
distance G is equal to or more than 40% of the sheet thickness t, the torsion
- 38 -
rigidity of the joining structure Ill decreases. From a the viewpoint of improvement
in the torsion rigidity, it is more preferable the inter-end-surface distance G is equal to
or more than 0 mm and less than I 0% of the sheet thickness t.
[0100]
The reason why the inter-end-surface distance G is specified is because, if the
inter-end-surface distance G is too long, weld metal melted from between end surfaces
at the time of the resistance spot welding may leak out and a desired welding strength
may not be obtained.
[0101]
Similar to the first embodiment, even in the second embodiment, it is
preferable that the extension length (end surface length) D of the end surface 108a of
the first reinforcement I 08 and the end surface I 09a of the second reinforcement I 09 is
equal to or more than 3 mm and less than 50 mm (refer to FIG. 16). Here, as
illustrated in FIG. 16, the end surface length Din the second embodiment is the length
of a portion overlapping the flanges I 06a and 107a, in the entire length of the end
surfaces 1 08a and I 09a that face each other. Meanwhile, the end surface length D in
a welding spot opposite to the welding spot illustrated in FIG. 16, that is, a formation
spot of the welding nugget 113b, is the length of a portion overlapping the flanges
!06b and 107b, in the entire length of the end surfaces 108a and 109a that face each
other.
[0102]
In a case where the end surface length D is less than 3 mm, it becomes
difficult to perform the resistance spot welding. Even if welding can be performed by
laser welding or the like instead of the resistance spot welding, rigidity as a member
- 39 -
cannot be guaranteed in a case where end surface length D is less than 3 mm. In a
case where end surface length D is equal to or more than 50 mm, the weight of the
member increases. As a result, an increase in the weight of the automobile vehicle
body is caused. If the balance between higher rigidity and weight reduction is taken
into consideration, it is more preferable that the end surface length D is equal to or
more than 3 mm and less than 20 mm.
[0103]
Although a case where the masses of melted metal (welding nuggets) formed
by the resistance spot welding are used for the joining between the structural members
has been illustrated in the above description, for example, masses of melted metal
formed by discontinuous welding, such as electric arc welding, laser welding, and laser
electric arc welding, in addition to the resistance spot welding, may be used for the
joining between the structural members. As the shapes ofthe masses of melted metal
formed by these kinds of discontinuous welding, a C shape, an 0 shape, an elliptical
shape, a linear shape, a curved shape, a waveform shape, a spiral shape, and the like
are exemplified.
[0104]
For this reason, in the joining structure Ill, even by using the dot-like
discontinuous welding such as the resistance spot welding, a high torsional rigidity
around the axial center is obtained at low costs while suppressing an increase in weight
[0105]
In the above description, since the joining structure Ill is the side sill, a case
where the first reinforcement 108 and the second reinforcement 109 are sandwiched
between the side sill inner panel 106 and the side sill outer panel107 is exemplified.
- 40 -
However, the invention is not limited to this case, and can also be applied to a form in
which a pair of reinforcements (the pair of second metal sheets) are sandwiched
between an upper panel (the first metal sheet) and a lower panel (the third metal sheet).
[0106]
According to the joining structure 111 related to the second embodiment as
described above, it is possible to achieve higher rigidity of the automobile vehicle body
(particularly, improvement in the torsional rigidity of the side sill itself) while
minimizing the area of the reinforcements overlapped on the panels without increasing
the number of times of resistance spot welding (the number of welding nuggets).
That is, according to the joining structure Ill, it is possible to realize three
requirements such as cost reduction, weight reduction, and higher rigidity for the
structural bodies in a well-balanced manner.
Hereinafter, the grounds on which the above effects are obtained by the
joining structure Ill will be described referring to the following example.
[Example]
[0107]
Regarding the joining structure (side sill) lll illustrated in FIG. 15 and the
side sills 2-1 to 2-3 of the related-art example having the structure as illustrated in FIG.
23, the torsional rigidity when torsion ofO.l deg from a central angle was given to the
side sills by applying torsion around the axial center to the other end part in a state
where one end part is constrained was obtained by numerical analysis.
[0108]
FIG. 18 is an explanatory view illustrating a cross-sectional shape of the side
- 41 -
sill Ill and the side sills 2-1 to 2-3. In addition, the sheet thickness center position of
each of the side sill inner pane1106, the side sill outerpanel107, the 1hst
reinforcement 108, and the second reinforcement 109 is illustrated in FIG. 18.
[0109]
In this analysis, both of respective lengths Ll and 12 of the first
reinforcement 108 and the second reinforcement 109 and 12 were set to 239.975 mm,
and the inter-end-surface distance G was 0.05 mm. Additionally, respective strengths
and sheet thicknesses of the side sill inner panel 106, the side sill outer panel 107, the
first reinforcement 108, and the second reinforcement 109 were as follows.
-Side sill inner panel106: 980 MPa, 1.0 mm
-Side sill outer panel107: 980 MPa, 1.0 mm
-First reinforcement 108: 980 MPa, 1.0 mm
-Second reinforcement 109: 980 MPa, 1.0 mm
[011 0]
(a) to (d) of FIG. 19 are explanatory views illustrating respective arrangements
of the first reinforcement 108 and the second reinforcement 109 and the positions of
the welding nuggets 110, 112, ll3a, and ll3b in side sills 2-1 to 2-3 of the related-art
examples and the side sill 111 of the example of the invention.
[0 Ill]
Analysis results are illustrated in graphs of FIGS. 20 and 21. FIG. 20 is a
graph illustrating the torsional rigidity when torsion ofO.l deg of from the central
angle is given to the side sills 2-1, 2-2, and Ill. FIG. 21 is a graph illustrating the
torsional rigidity when torsion ofO.l deg from the central angle per one welding
nugget is given to the side sills 2-3 and 111.
- 42 -
l 0 ll2]
It can be seen from the graphs of FIGS. 20 and 21 that, according to the
invention, compared to the related att, even by performing welding using the dot-like
discontinuous welding such as the resistance spot welding, a high torsional rigidity
around the axial center is obtained at low costs while suppressing an increase in weight.
[0 113]
Although the first and second embodiments of the invention have been
described above, the invention is not limited to this, and the invention can be modified
in various forms without departing from the scope of the invention.
[0114]
Although a case where the joining structure of the invention is applied to the
joining structure between the side sill2 and the lower A pillar 3 has been exemplified
in the above first embodiment, for example, the joining structure (the joining structure
described in the first embodiment) of the invention can also be applied to a joining
structure between a side sill 202 and a Lower C pillar 220 that are illustrated in FIG. 22,
or a joining structure between the side sill 202 and a cross member 230.
[0115]
A case where the joining structure of the invention is applied to the joining
structure of the side sill inner panel 106, the side sill outer panel 107, the first
reinforcement I 08, and the second reinforcement 109 has been exemplified in the
above second embodiment. However, for example, in a case where a structure in
which a pair of reinforcements are sandwiched between two panels is needed to be
adopted in a B pillar 204 or a roof rail 205 illustrated in FIG. 22, the joining structure
Goining structure described in the second embodiment) of the invention can also be
- 43 -
applied to that structure.
l 0 116]
In the above first and second embodiments, the automobile vehicle body has
been mentioned as an example as the structural body in which cost reduction, weight
reduction, and higher rigidity are required. However, the joining stmcture of the
invention can also be applied to, for example, other structural bodies, such as vehicle
bodies of railroad vehicles and fuselages of aircrafts, without being limited to the
automobile vehicle body.
[Reference Signs List]
[0117]
I: JOINING STRUCTURE
2: SIDE SILL (METAL-FORMED SHEET)
3: LOWERAPILLAR
13: FIRST INWARD FLANGE (SECOND METAL SHEET)
14: SECOND INWARD FLANGE (SECOND METAL SHEET)
15: THIRD INWARD FLANGE (SECOND METAL SHEET)
16: FOURTH INWARD FLANGE (SECOND METAL SHEET)
31: FLAT PART OF LOWER A PILLAR (FIRST METAL SHEET)
17 to 20: WELDING NUGGET (MASS OF MELTED METAL)
111: JOINING STRUCTURE
106: SIDE SILL INNER PANEL (FIRST METAL-FORMED SHEET)
107: SIDE SILL OUTER PANEL (SECOND METAL-FORMED SHEET)
106A, 106B: FLANGE (FIRST METAL SHEET)
- 44 -
I 07 A, 107B: FLANGE (THIRD METAL SHEET)
108: FIRST REINFORCEMENT (SECOND METAL SHEET)
109: SECOND REINFORCEMENT (SECOND METAL SHEET)
113A, 113B WELDING NUGGET (MASS OF MElTED METAL)

Claims
I. A joining structure comprising:
a first metal sheet; and
a pair of second metal sheets,
wherein each of the pair of second metal sheets is overlapped on the first
metal sheet in a state where an end surface of one of the second metal sheets and an
end surface of the other second metal sheet face each other, and
wherein the end surfaces that face each other are integrally joined to the first
metal sheet by means of a single mass of melted metal.
2. The joining structure according to claim I,
wherein the pair of second metal sheets is present on the same plane.
3. The joining structure according to claim I or 2,
wherein a distance between the end surfaces that face each other is equal to or
more than 0 mm and less than I mm.
4. The joining structure according to claim 1 or 2,
wherein the following Conditional Expression (a) is satisfied when a sheet
thickness of the pair of second metal sheets is defined as t (mm) and the distance
between the end surfaces that face each other is defined as G (mm).
Omm2 <::Gxt< 1 mm2 (a)
5. The joining structure according to claim 1 or 2,
- 46 -
wherein the distance between the end surfaces that face each other is less than
40% of the sheet thickness of the second metal sheets.
6. The joining structure according to any one of claims 1 to 5,
wherein an extension length of the end surfaces that face each other is equal to
or more than 3 mm and less than 50 mm.
7. The joining structure according to any one of claims I to 6,
wherein the pair of second metal sheets is a pair of inward flanges provided in
a material-axis-direction end part of a metal-formed sheet having a constant sectional
shape in the material axis direction.
8. The joining structure according to claim 7,
wherein the sectional shape of the metal-formed sheet is an angular shape, a
channel shape, or a quadrangular shape.
9. The joining structure according to claim 7 or 8,
wherein the metal-formed sheet is a side sill of an automobile vehicle body,
and the first metal sheet is a portion of a lower A pillar of the automobile vehicle body.
10. The joining structure according to any one of claims 1 to 6, further comprising:
a third metal sheet,
wherein, in a state where the pair of second metal sheets is sandwiched
between the first metal sheet and the third metal sheet, the end surfaces that face each
- 47 -
other are integrally joined to the first metal sheet and the third metal sheet by means of
the mass of melted metal.
11. The joining structure according to claim 10,
wherein the first metal sheet is a flange provided in a first metal-formed sheet
having a hat-like sectional shape in the material axis direction, and
wherein the third metal sheet is a flange provided in a second metal-formed
sheet having a hat-like sectional shape in the material axis direction.
12. The joining structure according to claim 11,
wherein the first metal-formed sheet is a side sill outer panel of an automobile
vehicle body,
wherein the second metal-formed sheet is a side sill inner panel ofthe
automobile vehicle body, and
wherein each of the pair of second metal sheets is a reinforcement or a center
pillar inner panel of the automobile vehicle body.