TECHNICAL FIELD
[0001]
The present invention relates to a panel-shaped formed product and a method
for producing a panel-shaped formed product. More specifically, the present
invention relates to a panel-shaped formed product suitable for an automobile door
inner panel, and a method for producing the same.
BACKGROUND ART
[0002]
A door of an automobile is produced by mainly combining a door inner panel
and a door outer panel. The door of an automobile is attached with a window glass,
a window driving device, an acoustic speaker, a handle, and the like. To
accommodate these, a space is required between the door inner panel and the door
outer panel. For that reason, for example, a vertical wall portion is provided on the
door inner panel. Also, when the door of the automobile is closed, the vehicle
interior needs to be sealed by the door. For that reason, for example, a step portion
is provided in the vertical wall portion of the door inner panel. As a result of the
step portion of the vertical wall portion facing a pillar of a vehicle body or the like,
the tightness of the vehicle interior is ensured.
[0003]
A door inner panel used for a side door of an automobile or the like is formed
by subjecting a metal sheet such as a steel sheet to press working. In general, since
the shape of the door inner panel is complicated, the metal sheet may be allowed to
significantly deform. In such a case, cracks, wrinkles or the like may occur in the
formed door inner panel. Therefore, a metal sheet with high workability is used for
the starting material of the door inner panel. Since the metal sheet with high
workability has low strength, the door inner panel has low strength as well.
1-
Accordingly, it is often the case that the door inner panel is attached with a
reinforcing member (for example, a beltline reinforcement, a door impact beam, or
the like).
[0004]
A structure of a door inner panel is disclosed in Japanese Patent Application
Publication No. 2007-296953 (Patent Literature 1), Japanese Patent Application
Publication No. 2008-94353 (Patent Literature 2), and Japanese Patent Application
Publication No. 2013-112133 (Patent Literature 3). A method for producing a door
inner panel is disclosed in Japanese Patent Application Publication No. 2013-189173
(Patent Literature 4), Japanese Patent Application Publication No. 2001-38426
(Patent Literature 5), Japanese Patent Application Publication No. 2011-147970
(Patent Literature 6), and Japanese Patent Application Publication No. 2011-50971
(Patent Literature 7).
[0005]
A door inner panel disclosed in Patent Literature 1 includes a beltline
reinforcement. The beltline reinforcement is joined along a vehicle body fore-andaft
direction in a beltline portion of the door inner panel. Patent Literature 1
describes that such configuration allows the beltline reinforcement to bear a collision
load in the vehicle body fore-and-aft direction, thereby effectively reducing the
bending moment acting on the beltline portion.
[0006]
In a door inner panel disclosed in Patent Literature 2, when a collision load is
applied from a side face of the vehicle body, the door inner panel and a beltline
reinforcement are brought into contact with each other, and a load absorbing portion
of the door inner panel is deformed. Patent Literature 2 describes that as a result of
such arrangement, the load absorbing portion absorbs part of the load applied in a
thickness direction of the door inner panel so that the rigidity of the door inner panel
is ensured.
[0007]
In a side door disclosed in Patent Literature 3, it is configured such that a rear
end portion and a fore end portion of a beltline reinforcement formed by hot
stamping have a lower strength and a lower rigidity than those of the main body
3
-/-
portion. As a result, when a collision load is applied from the front face of the
vehicle body, the rear end portion of the beltline reinforcement is plastically
deformed, thereby increasing the contact area with a center pillar. Patent Literature
3 describes that such deformation ofthe rear end portion of the beltline
reinforcement can absorb the energy of collision.
[0008]
In a method for producing a door inner panel disclosed in Patent Literature 4,
a first formed body having a vertical wall portion and a second formed body are
welded together, and the welded formed body is processed by hot pressing or rolling.
Patent Literature 4 describes that such arrangement makes it possible to provide a
longer-length structural component for a vehicle body, which has excellent load
bearing performance per unit weight thereof.
[0009]
In a method for producing a door inner panel disclosed in Patent Literature 5,
a wrinkle pressing force during press working of a high-strength steel sheet is
specified. A relationship between a curvature of wall warping generated during
forming and a wrinkle pressing force is obtained in advance. On the basis of this
relationship, a wrinkle pressing force is applied such that the curvature of wall
waring is reduced. Patent Literature 5 describes that such arrangement makes it
possible to form a trapezoidal member of high-strength steel sheet with high
dimensional accuracy.
[0010]
In a method for producing a door inner panel disclosed in Patent Literature 6,
a die and a holder of a hot press forming apparatus are operated together to presswork
a sheet to be processed. This makes it possible to prevent breakage of the
sheet to be processed and occurrence of wrinkles thereof during forming. Further,
Patent Literature 6 describes that such arrangement can ensure dimensional accuracy
of the formed product after forming.
[0011]
In a method for producing a door inner panel disclosed in Patent Literature 7,
in hot press forming, a spacing between a die and a holder is controlled during
/
processing of a formed product. Patent Literature 7 describes that such arrangement
makes it possible to suppress wrinkles of a formed product.
CITATION LIST
PATENT LITERATURE
[0012]
Patent Literature 1: Japanese Patent Application Publication No. 2007-296953
Patent Literature 2: Japanese Patent Application Publication No. 2008-94353
Patent Literature 3: Japanese Patent Application Publication No. 2013-112133
Patent Literature 4: Japanese Patent Application Publication No. 2013-189173
Patent Literature 5: Japanese Patent Application Publication No. 2001-38426
Patent Literature 6: Japanese Patent Application Publication No. 2011-14 7970
Patent Literature 7: Japanese Patent Application Publication No. 2011-50971
SUMMARY OF INVENTION
TECHNICAL PROBLEM
[0013]
However, in the door inner panels of Patent Literatures 1, 2, and 3, a separate
reinforcing member such as a beltline reinforcement is indispensable in order to
secure collision characteristics. For this reason, a door produced from the door
inner panels ofPatent Literatures 1, 2, and 3 has a low manufacturing efficiency and
a high cost. Moreover, the steel sheet used for forming the door inner panel is a
low-strength soft steel sheet. Therefore, cracks, wrinkles, or the like are less likely
occur in the formed door inner panel. However, when the door inner panel has
adjacent vertical wall portions, and the vertical wall portion has a step portion, it is
likely that cracks, wrinkles or the like occur.
[0014]
In the production methods of Patent Literatures 4 to 7, when each vertical
wall portion extending from a border of a top panel portion of the formed door inner
panel is adjacent to each other, cracks, wrinkles, and the like may occur.
[0015]
j-
An object of the present invention is to provide a high-strength panel-shaped
formed product which has fewer defects such as cracks and wrinkles even if it has a
shape of a high degree of forming difficulty. Further, another object of the present
invention is to provide a method for producing a high-strength panel-shaped formed
product which has fewer defects such as cracks and wrinkles even if it is formed into
a shape of a high degree of forming difficulty.
SOLUTION TO PROBLEM
[0016]
A panel-shaped formed product made of a metal sheet according to an
embodiment of the present invention includes a top panel portion, an opening portion,
and a vertical wall portion. The top panel portion is polygonal. The opening
portion is provided in the top panel portion. The vertical wall portion extends from
at least not less than two adjacent borders among borders of the top panel portion.
At least one pair of each vertical wall portion of pairs of adjacent vertical wall
portions among the vertical wall portions has a step portion.
[0017]
A method for producing a panel-shaped formed product according to an
embodiment of the present invention is applied to production of a panel-shaped
formed product having a top panel portion, a vertical wall portion, and a step portion.
The top panel portion is polygonal. The vertical wall portion extends from at least
not less than two adjacent borders among borders of the top panel portion. And, a
step portion is provided in at least one pair of each vertical wall portion of pairs of
adjacent vertical wall portions among the vertical wall portions.
[0018]
The production method includes a preparation step, a heating step, and a press
forming step. In the preparation step, a blank material made of a metal sheet is
prepared. In the heating step, the blank material is heated. In the press forming
step, the heated blank material is subjected to press working by hot stamping to form
the blank material into a panel-shaped formed product
[0019]
I
The press forming step uses a press working apparatus including a die, a first
punch, a second punch, and a blank holder. The die includes a form engraved
portion in which the shape of the panel-shaped formed product is shaped. The first
punch has a front end surface which faces the die and in which the shape of the top
panel portion is shaped. The second punch is adjacent to the outside of the first
punch and has a front end surface which faces the die and in which the shape of the
step portion is shaped. The blank holder is adjacent to at least a portion of the
outside of the second punch, and faces the die. The blank material is disposed
between the die, and the blank holder, the first punch, and the second punch. The
blank holder, the first punch, and the second punch move relative to the die, and the
first punch and the second punch are pushed in on the blank material to form a panelshaped
formed product.
ADVANTAGEOUS EFFECTS OF INVENTION
[0020]
A panel-shaped formed product according to the present invention has a high
strength and fewer defects such as cracks and wrinkles. A method for producing a
panel-shaped formed product according to the present invention enables production
of a panel-shaped formed product having a shape of a high degree of forming
difficulty while suppressing defects such as cracks and wrinkles.
BRIEF DESCRIPTION OF DRAWINGS
[0021]
[FIG. 1] FIG. 1 is a perspective view of a door inner panel according to a first
embodiment.
[FIG. 2] FIG. 2 is a perspective view of a door inner panel different from that of FIG.
1.
[FIG. 3] FIG. 3 is a schematic view of a vertical cross section of a side door for an
automobile.
[FIG. 4] FIG. 4 is a schematic view of a horizontal cross section of a side door for an
automobile and its vicinity.
[FIG. 5] FIG. 5 is a perspective view of a door inner panel according to a second
embodiment.
[FIG. 6] FIG. 6 is a perspective view of a door inner panel according to a third
embodiment.
[FIG. 7] FIG. 7 is a perspective view of a door inner panel according to a fourth
embodiment.
[FIG. 8] FIG. 8 is a schematic view of a hot stamping apparatus used for press
forming of the door inner panel of the present embodiment.
[FIG. 9A] FIG. 9A shows a stage of clamping a blank material with a blank holder in
a press forming step of the present embodiment.
[FIG. 9B] FIG. 9B shows a state in which pushing in by a second punch is completed
in the press forming step of the present embodiment.
[FIG. 9C] FIG. 9C shows a state in which pushing in by a first punch is completed in
the press forming step of the present embodiment.
[FIG. 10] FIG. 10 is a cross-sectional view showing a state during press working by a
general hot stamping apparatus.
[FIG. llA] FIG. llA shows a stage of clamping a blank material with a blank holder
in a press forming step different from that of FIGS. 9A to 9C.
[FIG. liB] FIG. liB shows a state in which pushing in by the second punch is
completed in a press forming step different from that of FIGS. 9A to 9C.
[FIG. 11 C] FIG. 11 C shows a state in which pushing in by the first punch is
completed in a press forming step different from that of FIGS. 9A to 9C.
[FIG. 12] FIG. 12 is a perspective view of a door inner panel of a fifth embodiment.
[FIG. 13A] FIG. 13A is a perspective view of a starting material of the door inner
panel shown in FIG. 12, showing a state before being punched an opening portion.
[FIG. 13B] FIG. 13B is a perspective view of a starting material of the door inner
panel shown in FIG. 12, showing a state after being punched an opening portion and
immediately before being subjected to hot stamping.
[FIG. 14] FIG. 14 is a perspective view of a door inner panel of a sixth embodiment.
[FIG. 15] FIG. 15 is a perspective view of the door inner panel of a seventh
embodiment.
I
[FIG. 16A] FIG. 16A is a perspective view of a starting material ofthe door inner
panel shown in FIG. 15, showing a state before being punched an opening portion.
[FIG. 16B] FIG. 16B is a perspective view of a starting material of the door inner
panel shown in FIG. 15, showing a state after being punched an opening portion and
immediately before being subjected to hot stamping.
[FIG. 17] FIG. 17 is a perspective view of a door inner panel of an eighth
embodiment.
[FIG. 18] FIG. 18 is a perspective view of a door inner panel of a ninth embodiment.
[FIG. 19A] FIG. 19A is a perspective view of the starting material of the door inner
panel shown in FIG. 18, showing a state before being punched an opening portion.
[FIG. 19B] FIG. 19B is a perspective view ofthe starting material ofthe door inner
panel shown in FIG. 18, showing a state after being punched an opening portion and
immediately before being subjected to hot stamping.
[FIG. 20] FIG. 20 is a perspective view of a door inner panel different from that of
FIG. 18.
[FIG. 21] FIG. 21 is a perspective view of the starting material of the door inner
panel shown in FIG. 20, showing a state after being punched an 'opening portion and
immediately before being subjected to hot stamping.
[FIG. 22] FIG. 22 is a perspective view of a door inner panel of a tenth embodiment.
[FIG. 23A] FIG. 23A is a perspective view of a starting material of the door inner
panel shown in FIG. 22, showing a state before being punched an opening portion.
[FIG. 23B] FIG. 23B is a perspective view of the starting material of the door inner
panel shown in FIG. 22, showing a state after being punched an opening portion and
immediately before being subjected to hot stamping.
[FIG. 24] FIG. 24 shows dimensions of a die used in the analysis of the present
example.
[FIG. 25A] FIG. 25A shows a sheet thickness reduction rate of a door inner panel of
Inventive Example 1.
[FIG. 25B] FIG. 25B shows curvature distribution of the door inner panel of
Inventive Example 1.
[FIG. 26A] FIG. 26A shows a sheet thickness reduction rate of a door inner panel of
Inventive Example 2.
[FIG. 26B] FIG. 26B shows curvature distribution of the door inner panel of
Inventive Example 2.
[FIG. 27 A] FIG. 27 A shows a sheet thickness reduction rate of a door inner panel of
Comparative Example.
[FIG. 27B] FIG. 27B shows curvature distributionofthe door inner panel of
Comparative Example.
DESCRIPTION OF EMBODIMENTS
[0022]
A panel-shaped formed product made of a metal sheet according to an
embodiment of the present invention includes a top panel portion, an opening portion,
and a vertical wall portion. The top panel portion is polygonal. The opening
portion is provided in the top panel portion. The vertical wall portion extends from
at least not less than two adjacent borders among borders of the top panel portion.
At least one pair of each vertical wall portion of pairs of adjacent vertical wall
portions among the vertical wall portions has a step portion.
[0023]
The panel-shaped formed product of the present embodiment includes vertical
wall portions which are adjacent to each other and have a step portion. As a result,
the panel-shaped formed product of the present embodiment can enhance the
tightness ofvehicle interior.
[0024]
Preferably, the panel-shaped formed product has a tensile strength of not less
than 1200 MPa.
[0025]
Applying such a panel-shaped formed product to a door inner panel for an
automobile will result in improvement of collision characteristic thereof.
[0026]
Preferably, the panel-shaped formed product is a door inner panel for an
automobile, which has no vertical wall portion on a border on the vehicle upper side
among borders of the top panel portion. Thus, the door inner panel can be
combined with the door outer panel to form a side door for an automobile. A side
to
-1-
window glass and others are accommodated between the door outer panel and the
door inner panel
[0027]
Preferably, the opening portion is provided so as to leave a peripheral edge
portion of the top panel portion. As a result, an edge portion on the vehicle upper
side including the border on the vehicle upper side out of the peripheral edge portion
of the top panel portion forms a beltline portion of the door inner panel.
[0028]
Preferably, an edge portion on the vehicle upper side including a border on
the vehicle upper side of the top panel portion is provided with at least one of a
recessed portion and a protruded portion along the edge portion on the vehicle upper
side. In this case, the upper edge on the vehicle upper side of the top panel portion
(beltline portion) is responsible for the role of a beltline reinforcement that reinforces
the top panel portion. In other words, the door inner panel and the beltline
reinforcement are integrated. As a result, it is possible to reduce the weight and the
production cost of the door inner panel.
[0029]
Preferably, the top panel portion of the panel-shaped formed product has a
boundary portion for dividing the opening portion into a plurality of portions. In
the boundary portion, at least one of a recessed portion and a protruded portion is
provided along the boundary portion. In this case, the boundary portion of the top
panel portion plays a role of a door impact beam that reinforces the top panel portion.
In other words, the door inner panel and the door impact beam are integrated. As a
result, it is possible to reduce the weight and the production cost of the door inner
panel.
[0030]
Preferably, the metal sheet is a steel sheet. In this case, the panel-shaped
formed product, which can be formed by hot stamping, has a high strength and fewer
defects such as cracks and wrinkles.
[0031]
In the case of a door inner panel, the sheet thickness of a region of a lowerside
vertical wall portion including a border on the lower side of the top panel
II
portion is larger than the sheet thickness of a region adjacent to that region. The
lower-side vertical wall portion having a large sheet thickness will improve collision
characteristic.
[0032]
In the case of the door inner panel described above, preferably, the sheet
thickness of a region of a front-side vertical wall portion including a border on the
front side of the top panel portion is larger than the sheet thickness of a region
adjacent to that region. The front-side vertical wall portion corresponds to an
attaching portion of a hinge to be connected to the pillar. The front-side vertical
wall portion having a large sheet thickness sufficiently ensures the strength of the
hinge attaching portion.
[0033]
In the case of the door inner panel described above, preferably, the sheet
thickness of a region of an edge portion on the vehicle upper side including a border
on the vehicle upper side of the top panel portion is larger than the sheet thickness of
a region adjacent to that region. The edge portion on the vehicle upper side
including the border on the vehicle upper side out of the peripheral edge portion of
the top panel portion forms a beltline portion of the door inner panel. The edge
portion on the vehicle upper side having a large sheet thickness improves collision
characteristics.
[0034]
In the case of the door inner panel described above, preferably, the top panel
portion has a boundary portion which divides the opening portion into a plurality of
portions, and the sheet thickness of a region of the boundary portion is larger than the
sheet thickness of a region adjacent to that region. The boundary portion having a
large sheet thickness improves collision characteristics.
[0035]
A reinforcing member such as a beltline reinforcement or a door impact beam
may be added to the door inner panel described above. When these reinforcing
members are added, the reinforcing members may be attached so as to be superposed
on the above-described recessed portion or convex portion, etc. or may be attached to
another area. In that case, even when a material having a lower cost than that of a
12-
I conventional reinforcing material, such as a thin sheet material and a low-strength
material is used, it is possible to satisfy various characteristics. Further, it is also
possible to simplify the shape of the reinforcing member to be attached additionally.
For that reason, even when the reinforcing member is added, it is possible to
suppress the production cost.
[0036]
A method for producing a panel-shaped formed product according to an
embodiment of the present invention is applied to production of a panel-shaped
formed product including a top panel portion, a vertical wall portion, and a step
portion. The top panel portion is polygonal. The vertical wall portion extends
from at least not less than two adjacent borders among borders of the top panel
portion. And a step portion is provided in at least one pair of each vertical wall
portion of pairs of adjacent vertical wall portions among the vertical wall portions.
[0037]
The production method includes a preparation step, a heating step, and a press
forming step. In the preparation step, a blank material made of a metal sheet is
prepared. In the heating step, the blank material is heated. In the press forming
step, the heated blank material is subjected to press working by hot stamping, thereby
forming the blank material into a panel-shaped formed product.
[0038]
In the press forming step, a press working apparatus including a die, a first
punch, a second punch, and a blank holder is used. The die has a die engraved
portion in which the shape of the panel-shaped formed product is shaped. The first
punch has a front end surface which faces the die and in which the shape of the top
panel portion is shaped. The second punch is adjacent to the outside of the first
punch and has a front end surface which faces the die and in which the shape of the
step portion is shaped. The blank holder is located adjacent to at least a portion of
the outside of the second punch and faces the die. The blank material is disposed
between the die, and the blank holder, the first punch, and the second punch. The
blank holder, the first punch, and the second punch move relative to the die, and the
first punch and the second punch are pushed in on the blank material to form a panelshaped
formed product.
13
-rf-
[0039]
The method for producing a panel-shaped formed product of the present
embodiment enables production of a panel-shaped formed product having a shape of
a high degree of forming difficulty, while suppressing defects such as cracks and
wrinkles. The shape of a high degree of forming difficulty includes, for example,
one in which adjacent vertical wall portions of the panel-shaped formed product have
a step portion.
[0040]
Preferably, the blank material has an opening portion at a position
corresponding to a top panel portion of the panel-shaped formed product.
[0041]
As a result of that, the top panel portion is formed through stretch flange
forming. Thus, it is possible to suppress cracks, wrinkles, etc. of the panel-shaped
formed product.
[0042]
Preferably, in the press forming step, pushing in on the blank material by the
second punch is completed prior to pushing in on the blank material by the first
punch.
[0043]
In this case, in the press forming step, the pushing in on the blank material by
the first punch may be started when the pushing in on the blank material by the
second punch is completed or after the pushing in is completed. Moreover, in the
press forming step, the pushing in on the blank material by the first punch may be
started before the pushing in on the blank material by the second punch is completed.
[0044]
As a result, the second punch together with the die holds down the blank
material prior to the first punch. As a result, it is possible to further suppress cracks,
wrinkles, etc. of the panel-shaped formed product. Holding down the blank
material means that the blank material is completely clamped by the punch and the
die so as not to be pushed in further. Further, completion of pushing in on the blank
material by each individual punch means that the blank material becomes held down.
[0045]
-IPreferably,
the tensile strength of the panel-shaped formed product after
forming is not less than 1200 MPa.
[0046]
Applying such a panel-shaped formed product to a door inner panel for an
automobile allows improvement in collision characteristics.
[0047]
Preferably, the die engraved portion of the die used in the press forming step
satisfies the following conditions: d2 2 40 mm, and dlld2 < 0.8, where d1 is a depth
from a reference surface facing the blank holder to a step surface facing the second
punch, and d2 is a depth from the reference surface to a die bottom surface facing the
first punch.
[0048]
In this case, applying the panel-shaped formed product to a door inner panel
for an automobile allows to obtain a sufficient amount of space for accommodating
the window glass and others. It is also possible to improve the tightness of vehicle
interior.
[0049]
The metal sheet described above is preferably a steel sheet. In this case, the
strength of the formed panel-shaped formed product is increased by quenching
through hot stamping. The steel sheet may be a tailored blank. This makes it
possible to enhance strength only in a necessary place, and also to reduce the sheet
thickness.
[0050]
Hereinafter, embodiments of the present invention will be described in detail
with reference to the drawings. The same or corresponding parts are denoted by the
same reference symbols, and description thereof will not be repeated. In the present
embodiments, a case of a door inner panel for a vehicle, in which a panel-shaped
formed product is made of steel sheet, will be described as an example.
[0051]
[First embodiment]
FIG. 1 is a perspective view of a door inner panel of a first embodiment.
Referring to FIG. 1, a door inner panel1 includes: a top panel portion 2; an opening
-~
portion 3; a vertical wall portion 4, a step portion 5, and a flange portion 6. The
planar shape of the top panel portion 2 is polygonal. The polygon may be, for
example, a quadrangle or a pentagon. A comer part of a polygon may have a round
shape. FIG. 1 shows an exemplary case in which the planar shape of the top panel
portion 2 is a pentagon. In the door inner panel 1, a border on the vehicle upper
side of the top panel portion 2 forms a beltline BL. In the present embodiment, a
case in which the sheet thickness of the steel sheet is constant will be described.
Therefore, the sheet thickness of the door inner panel 1 is also constant over the
entire area. In a strict sense, however, a slight increase or decrease of the sheet
thickness will be caused by press forming.
[0052]
The vertical wall portion 4 extends from at least not less than two adjacent
borders among borders of the top panel portion 2. FIG. 1 shows an exemplary case
in which the vertical wall portion 4 extends from four borders 2A, 2B, 2C, and 2D
excluding the border (beltline BL) on the vehicle upper side among five borders of
the pentagonal top panel portion 2. However, the number of borders ofthe top
panel portion 2 from which the vertical wall portion 4 extends is not limited to four.
The vertical wall portion 4 may extend from each of two or more adjacent borders of
the top panel portion 2. When the vertical wall portion 4 extends from each border
of the two or more adjacent borders of the top panel portion 2, each vertical wall
portion extending from each border will be adjacent to each other. FIG. 1 shows an
exemplary case in which the vertical wall portion 4 extends perpendicular to the top
panel portion 2. However, the vertical wall portion 4 may not be strictly
perpendicular to the top panel portion 2. The top panel portion 2 is protruded from
the flange portion 6 by the vertical wall portion 4, thereby forming a space for
accommodating a window glass and others.
[0053]
The step portion 5 extends outward from a vertical wall portion 4A connected
to the top panel portion 2. An outer edge of the step portion 5 is connected to a
vertical wall portion 4B connected to the flange portion 6. FIG. 1 shows an
exemplary case in which the surface of the step portion 5 is parallel with the top
panel portion 2. However, the surface of the step portion 5 may not be s~rictly
\b
-;6-
parallel with the top panel portion 2. FIG. 1 shows an exemplary case in which
three adjacent vertical wall portions 4 have a step portion 5. In other words, a case
in which there are two pairs of adjacent vertical wall portions 4, and the two pairs
each have the step portion 5. However, the number of pairs ofthe vertical wall
portions 4 having the step portion 5 is not limited to two. At least one pair among
pairs of adjacent vertical wall portions 4 may have a step portion 5. FIG. 1 shows
an exemplary case in which one step of step portion 5 is provided in the vertical wall
portion 4. However, the number of steps of the step portion 5 is not limited to one,
but may be plural.
[0054]
The top panel portion 2 includes an opening portion 3. When the door inner
panel 1 is made of a steel sheet, the top panel portion 2 is formed through stretch
flange deformation. Since the top panel portion 2 has the opening portion 3, it is
susceptible to stretch flange deformation. FIG. 1 shows an exemplary case in which
an opening portion 3 is provided at one location so as to leave a peripheral edge
portion of the top panel portion 2. However, the number oflocations of the opening
portion 3 is not limited to one. The top panel portion 2 may include a plurality of
opening portions 3. The shape of the opening portion 3 may be circular, elliptic,
polygonal, or the like, and is not particularly limited. In the door inner panel 1 for
an automobile, an acoustic speaker, a handle, and the like are attached in the opening
portion 3.
[0055]
FIG. 2 is a perspective view of a door inner panel having an opening portion 3
having a shape different from that in FIG. 1. Referring to FIG. 2, the opening
portion 3 extends over one border of a peripheral edge portion of a top panel portion
2. In other words, the opening portion 3 is provided such that a beltline BL is
interrupted. In this case, a reinforcing member such as a beltline reinforcement may
be attached to the beltline BL.
[0056]
FIG. 3 is a schematic view of a vertical cross section of a side door for an
automobile. Referring to FIG. 3, the side door is produced by combining a door
outer panel A and a door inner panel 1. A space SP is a space between the door
-/1-
outer panel A and the door inner panel 1. An acoustic speaker, a window glass, a
window drive device, and the like may be accommodated in the space SP. For that
reason, it is often the case that the space SP is formed by providing a vertical wall
portion 4 in the door inner panel 1.
[0057]
In the door inner panel 1, a border on a vehicle upper side of the top panel
portion 2 is a beltline BL. The beltline BL is located on an entrance/exit side of a
window (not shown). When the window is opened, the window glass is lowered
and accommodated in the space SP. Therefore, there is no vertical wall portion in
the beltline BL.
[0058]
FIG. 4 is a schematic view of a horizontal cross section of a side door for an
automobile and its vicinity. Referring to FIG. 4, the step portion 5 faces a pillar B
of the vehicle body. For that reason, the door inner panel 1 of the present
embodiment allows to improve the tightness of vehicle interior of an automobile
compared to a door inner panel having no step portion 5. A seal member may be
disposed between the step portion 5 and the pillar B. In this case, it is possible to
further improve the tightness of vehicle interior. The seal member is, for example,
a rubber.
[0059]
A hinge to be connected to a pillar (not shown) is attached to the vertical wall
portion 4 on the vehicle front side including a border 2A of the top panel portion 2 on
the vehicle front side.
[0060]
The symbol h1 shown in FIG. 4 indicates a height from the flange portion 6 to
the step portion 5. And h2 indicates a height from the flange portion 6 to the top
panel portion 2. The door inner panel 1 of the present embodiment preferably
satisfies conditions: h2;::: 40 mm, and h1/h2 < 0.8. This is because when h2 < 40
mm, the space SP that accommodates a window glass and others is too small. Also
that is because when h1/h2;::: 0.8, the tightness of vehicle interior deteriorates as a
result of a small distance between the top panel portion 2 and the step portion 5.
[0061]
[Second embodiment]
FIG. 5 is a perspective view of a door inner panel of a second embodiment.
A door inner panel 1 of a second embodiment shown in FIG. 5 is based on the door
inner panel1 of the first embodiment described above. The same applies to a third
and fourth embodiments to be described later, and overlapping explanation will be
appropriately omitted.
[0062]
Referring to FIG. 5, in the door inner panel 1 of the second embodiment, a
step portion 5 is provided in all of the four adjacent vertical wall portions 4 (three
pairs of vertical wall portions 4). In this case, the step portion 5 faces a center pillar,
a front pillar, a side sill, and the like of the vehicle body. Accordingly, it is possible
to further improve the tightness of vehicle interior.
[0063]
[Third embodiment]
FIG. 6 is a perspective view of a door inner panel of a third embodiment.
Referring to FIG. 6, a door inner panel1 of the third embodiment shows a case in
which a vertical wall portion 4 extends from four borders except the beltline BL out
of the five borders of the top panel portion 2 having a pentagon shape, and a step
portion 5 is provided in three vertical wall portions 4 of four adjacent vertical wall
portions 4.
[0064]
In the door inner panel1 of the third embodiment, there is provided in an edge
portion 21 on the vehicle upper side including a beltline BL ofthe top panel portion
2 (hereinafter referred to as a "beltline portion"), a recessed portion 7 along that
beltline portion 21. Forming the recessed portion 7 increases a cross-sectional
secondary moment of the beltline portion 21 of the top panel portion 2. In other
words, the recessed portion 7 increases the strength of the beltline portion 21. In
general, the beltline portion of a door inner panel is often reinforced by attaching a
reinforcing member such as a beltline reinforcement thereto. In this regard, in the
door inner panel 1 of the third embodiment, a beltline portion 21 having a recessed
portion 7 is provided integrally in the top panel portion 2. In other words, in the
third embodiment, the beltline reinforcement is integrated into the door inner panel.
-ITherefore,
the beltline portion 21 does not need to be reinforced by a separate
beltline reinforcement. As a result of that, it is possible to reduce the number of
components and assembly man-hours of a door, and further to reduce the weight of
the door.
[0065]
A protruded portion in place of the recessed portion 7 may be provided in the
beltline portion 21, or both of the recessed portion 7 and the protruded portion may
be provided. Forming the protruded portion will equally increase the crosssectional
secondary moment ofthe beltline portion 21 ofthe top panel portion 2.
[0066]
[Fourth embodiment]
FIG. 7 is a perspective view of a door inner panel of a fourth embodiment.
Referring to FIG. 7, in a door inner panel1 of the fourth embodiment, the opening
portion of the first embodiment shown in FIG. 1 is divided into multiple portions.
In other words, a plurality of opening portions are provided in the top panel portion 2.
FIG. 7 shows an exemplary case in which two opening portions 3A and 3B are
provided.
[0067]
In the door inner panel1 of the fourth embodiment, the top panel portion 2
includes a boundary portion 22 between the opening portions 3A and 3B. The
boundary portion 22 is provided with a recessed portion 8 along the boundary portion
22. Forming the recessed portion 8 increases the cross-sectional secondary moment
of the boundary portion 22 of the top panel portion 2. In other words, the recessed
portion 8 increases the strength of the boundary portion 22. Generally, in order to
enhance the strength of a side door, the top panel portion of the door inner panel is
often reinforced by attaching a reinforcing member such as a door impact beam
thereto. In this regard, in the door inner panel 1 of the fourth embodiment, a
boundary portion 22 having a recessed portion 8 is integrally provided in the top
panel portion 2. In other words, in the fourth embodiment, a door impact beam is
integrated with the door inner panel. Accordingly, the top panel portion 2 does not
need to be reinforced by a door impact beam or the like. As a result, it is possible to
-Preduce
the number of components and assembly man-hours of a door, and further to
reduce the weight of the door.
[0068]
A protruded portion in place of the recessed portion 8 may be provided in the
boundary portion 22, or both of the recessed portion 8 and the protruded portion may
be provided. Forming the protruded portion will equally increase the crosssectional
secondary moment of the boundary portion 22 of the top panel portion 2.
[0069]
Either one or both of the recessed portion 7 and the protruded portion shown
in FIG. 6 may be added to the beltline portion 21 of the door inner panel1 of the
fourth embodiment shown in FIG. 7.
[0070]
Here, a panel-shaped inner panel like a door inner panel, in which a step
portion is provided at vertical wall portions adjacent to each other, is very difficult to
be formed, and is likely to have defects such as cracks and wrinkles at the time of
press forming. For that reason, conventionally, a low-strength steel sheet having
high ductility is used as the starting material when forming a formed product having
a complicated shape. As a result of that, there has been a limit in the improvement
of collision characteristics of a panel-shaped formed product. In this regard, by
providing an opening portion in the top panel portion and applying hot stamping
thereto, defects such as cracks, wrinkles, and the like are suppressed even when the
formed product has a complicated shape having a vertical wall portion and a step
portion, making it possible to obtain a high-strength panel-shaped formed product
having a tensile strength of not less than 1200 MPa.
[0071]
The steel sheet to be used as the starting material of the panel-shaped formed
product of the present embodiment preferably contains, in mass%, carbon (C): not
less than 0.11 %. When the steel sheet contains not less than 0.11% of carbon, it is
possible to increase the strength of the panel-shaped formed product after hot
stamping.
[0072]
2--r-
By increasing the strength of the panel-shaped formed product as described
above, and applying it to a door inner panel of an automobile, the collision
characteristics of a door will be improved. The hardness of the panel-shaped
formed product is preferably not less than HV 380 in the Vickers hardness. A
hardness ofHV 380 corresponds to a tensile strength of 1200 MPa. The Vickers
hardness HV conforms to JIS Z 2244.
[0073]
A door inner panel having a high tensile strength is usually difficult to be
formed. Hereinafter, an example of a method for producing the door inner panel of
the above-described embodiments will be described. The following production
method shows an exemplary case in which the door inner panel to be produced is
made of a steel sheet and has a tensile strength ofnot less than 1200 MPa.
[0074]
[Production method]
A method for producing a door inner panel of the present embodiment
includes a preparation step, a heating step, and a press forming step by hot stamping.
In the preparation step, a blank material made of a steel sheet is prepared. In the
heating step, the blank material is heated. In the press forming step, the heated
blank material is subjected to press working, and at the same time, the formed door
inner panel is quenched. In the press forming step of the present embodiment, a hot
stamping apparatus is used as a press working apparatus.
[0075]
[Hot stamping apparatus 1 0]
FIG. 8 is cross sectional view to schematically show a hot stamping apparatus
for producing a door inner panel of the present embodiment. Referring to FIG. 8,
the hot stamping apparatus 10 includes a punch 11 and a blank holder 14 as an upper
die, and a die 15 as a lower die.
[0076]
The punch 11 includes a first punch 12 and a second punch ·13. The first
punch 12 includes a front end surface 12A. The front end surface 12A of the first
punch 12 is shaped with a shape of a top panel portion of the door inner panel. The
second punch 13 includes a front end surface 13A. The front end surface 13A of
the second punch 13 is shaped with the shape of the step portion of the door inner
panel. The punch 11 pushes in a blank material S on a die engraved portion 16 of
the die 15 to form a door inner panel.
[0077]
The blank holder 14 is disposed adjacent to at least a part of the outside of the
second punch 13. The blank holder 14 has a front end surface 14A. The front end
surface 14A ofthe blank holder 14 faces a reference surface 16C of the die 15. The
blank holder 14 clamps the blank material S between itself and the reference surface
16C of the die 15.
[0078]
The die 15 includes a die engraved portion 16. The die engraved portion 16
includes a die bottom surface 16A, a step surface 16B, and a reference surface 16C.
The die bottom surface 16A faces the front end surface 12A of the first punch 12.
The step surface 16B faces the front end surface 13A of the second punch 13.
[0079]
The first punch 12, the second punch 13, and the blank holder 14 are
supported by an upper die holder 17. A pressurizing member (not shown) is
provided between the second punch 13 and the blank holder 14, and the upper die
holder 17. The pressurizing member is a hydraulic cylinder, a gas cylinder, a spring,
a rubber, or the like. The die 15 is secured to a lower die holder 18. The upper die
holder 17 is attached to a slide (not shown). The lower die holder 18 is attached to
a bolster plate (not shown). Here, the hot stamping apparatus 10 is not limited to
the case shown in FIG. 8. For example, the first punch 12, the second punch 13,
and the blank holder 14 may be individually attached to a movable slide.
[0080]
The die bottom surface 16A and the front end surface 12A of the first punch
12 forms the top panel portion 2 of the door inner panel 1 shown in FIG. 1. The
step surface 16B and the front end surface 13A of the second punch 13 form the step
portion 5 ofthe door inner panel1 shown in FIG. 1. The reference surface 16C and
the front end surface 14A of the blank holder 14 form the flange portion 6 of the door
inner panel 1 shown in FIG. 1.
[0081]
-~
In the die 15, a depth d1 from the reference surface 16C to the step surface
16B, and a depth d2 from the reference surface 16C to the die bottom surface 16A
preferably satisfy conditions: d2 ~ 40 mm, and dlld2 < 0.8. The depth d1 and the
depth d2 respectively correspond to the height h1 and the height h2 shown in FIG. 4.
Therefore, when d2 < 40 mm, the space for accommodating a window glass and
others is too small. Moreover, when dlld2 ~ 0.8, since the distance between the top
panel portion 2 and the step portion 5 is small, the tightness of vehicle interior
deteriorates.
[0082]
The hot stamping apparatus 1 0 of the present embodiment shows a case in
which it includes a punch 11 and a blank holder 14 above the apparatus, and the die
15 below the apparatus. However, the arrangement will not be limited to the case
shown in FIG. 8. In other words, in the hot stamping apparatus 10, the arrangement
of the punch 11 and the blank holder 14, and the die 15 may be inverted upside down.
In short, any configuration may be adopted provided that the punch 11 and the blank
holder 14 are relatively movable with respect to the die 15. Hereinafter, the steps of
the production method of the present embodiment will be described.
[0083]
[Preparation step]
In the preparation step, a blank material made of a steel sheet is prepared.
The steel sheet of the door inner panel of the present embodiment preferably contains
carbon (c): not less than 0.11 %. When the steel sheet contains not less than 0.11%
of carbon, it is possible to increase the strength of the door inner panel after hot
stamping.
[0084]
[Heating step]
In the heating step, the blank material is heated by a heating apparatus (not
shown). When the blank material is a steel sheet, the heating temperature is
preferably not less than 700°C. The heating temperature is, for example, 900°C.
The heating temperature is appropriately set depending on a material type, a degree
of forming difficulty, or the like. In the hot stamping, since the blank material is
heated to be softened, it is possible to form a complicated shape. The complicated
-Ishape
includes, for example, a shape like a door inner panel I shown in FIG. I, in
which adjacent vertical wall portions 4 have a step portion 5.
[0085]
Preferably, the blank material is heated to not less than an AI transformation
point of the material. The blank material is more preferably heated to not less than
an A3 transformation point. In the hot stamping, concurrently with the blank
material being press formed, the formed door inner panel is quenched. When the
blank material is heated to not less than the AI point, the door inner panel after
quenching will have a martensitic structure, and thus a high strength.
[0086]
[Press forming step]
FIGS. 9A to 9C are cross sectional views schematically showing the press
forming step of the present embodiment. FIG. 9A shows a stage of clamping a
blank materialS with a blank holder I4. FIG. 9B shows a state when pushing in by
the second punch 13 is completed. FIG. 9C shows a state when pushing in by the
first punch I2 is completed.
[0087]
Referring to FIG. 9A, the heated blank materialS is placed in the hot
stamping apparatus I 0. After the blank material S is placed, the slide moves down.
This causes the blank materialS to be clamped between the front end surface I4A of
the blank holder I4 and the reference surface I6C of the die I5. However, the
spacing between the front end surface I4A of the blank holder I4 and the reference
surface I6C of the die I5 is preferably larger than the thickness of the blank material
S. In other words, ·a gap is provided between the blank material S and the front end
surface I4A of the blank holder I4. The size of the gap is, for example, 0.1 mm.
When the blank material S is brought into contact with the blank holder I4, a portion
of the blank materialS, which is brought into contact with the blank holder I4, is
cooled before the blank materialS is press formed. For that reason, the cooling rate
of the blank materialS varies at locations, and therefore the strength of the formed
product varies at locations. Therefore, it is preferable that a slight gap is provided
between the front end surface I4A of the blank holder I4 and the blank material S.
[0088]
·-~
-4-
Referring to FIG. 9B, as the slide further moves down, the blank materialS is
pointing formed by the punch 11 and the die 15. FIG. 9B shows a case in which
when pushing in on the blank material S by the second punch 13 is completed, the
front end surface 12A of the first punch 12 is located at the same height as the front
end surface 13A of the second punch 13. In other words, it shows a case in which
concurrently with completion of pushing in on the blank material S by the second
punch 13, pushing in on the blank materialS by the first punch 12 is started.
However, when pushing in on the blank materialS by the second punch 13 is
completed, the height of the front end surface 12A of the first punch 12 is not limited
to the same height as that of the front end surface 13A of the second punch 13. The
front end surface 12A of the first punch 12 at this moment may be located either at a
higher position or at a lower position than that of the front end surface 13A ofthe
second punch 13. In other words, after the pushing in on the blank materialS by
the second punch 13 is completed, the pushing in on the blank material S by the first
punch 12 may be started. Moreover, before the pushing in on the blank materialS
by the second punch 13 is completed, the pushing in on the blank material S by the
first punch 12 may be started. In either case, the pushing in by the first punch 12
will not be completed prior to the pushing in by the second punch 13. Note that
holding down of the blank material by the blank holder and the die only needs to be
performed by the time the forming by the second punch is completed.
[0089]
Referring to FIG. 9C, after the pushing in by the second punch 13 is
completed, the first punch 12 moves down and the blank materialS is pointing
formed. At this moment, a portion of the blank materialS, which has been pushed
in by the second punch 13, is restricted by the second punch 13. This allows
suppression of wrinkles which occur in the vicinity of the step portion of the door
inner panel. This point will be described in detail below.
[0090]
[Suppression of cracks and wrinkles]
FIG. 10 is a cross-sectional view showing a state during press working by a
common hot stamping apparatus. FIG. 10 shows an enlarged view of the vicinity of
a step surface of the die of the common hot stamping apparatus. Referring to FIG.
-/-
10, in a hot stamping apparatus 200, front end surfaces 21 OA and 21 OB of a punch
210 are integrally shaped with the punch 210. As a result ofthat the front end
surfaces 21 OA and 21 OB of the punch 210 simultaneously reach a die bottom surface
220A and a step surface 220B of a die 220. The distance over which the front end
surface 21 OA pushes in on the blank material S is longer than that of the front end
surface 210B. As a result ofthat, as shown in FIG. 10, when the punch 210 is
moved down, first, the front end surface 21 OA pushes in on the blank material S.
At this moment, a portion S1 of the blank materialS is not restricted by the front end
surface 210B ofthe punch 210 and the step surface 220B ofthe die 220. In other
words, the portion S1 of the blank materialS will not come into contact with the
front end surface 210B ofthe punch 210 and the step surface 220B of the die 220.
[0091]
In hot stamping, the blank material is cooled by the contact between the blank
material, and the punch, the die, and the like. Therefore, in the stage shown in FIG.
10 during press working, a portion S1 of the blank materialS is not cooled. The
portion S1 ofthe blank materialS is cooled when the punch 210 is further pushed in
from the position shown in FIG. 10. In short, when a door inner panel in which a
step portion is provided in a vertical wall portion is formed by a punch 210 in which
shapes of the top panel portion and the step portion of the door inner panel are
integrally shaped, a portion S1 of the blank materialS is cooled slower than the other
portions.
[0092]
If the cooling of the blank materialS is partially delayed, the strength and
ductility of the blank materialS may be partially different. In this case, cracks and
wrinkles are more likely to occur in the formed door inner panel. As shown in FIG.
1, when adjacent vertical wall portions 4 of the door inner panel1 have a step portion
5, particularly cracks and wrinkles become more likely to occur. When the strength
of the door inner panel after forming is high, cracks, wrinkles and the like become
further likely to occur.
[0093]
A method for producing a door inner panel of the present embodiment uses,
as shown in FIG. 8, a hot stamping apparatus 10 including a first punch 12 and a
second punch 13. As a result, the top panel portion 2 and the step portion 5 of the
door inner panel1 as shown in FIG. 1 are formed by separate punches. In addition,
pushing in by the second punch 13 is completed prior to pushing in by the first punch
12. Thereby, when one of the punches forms the top panel portion 2, the other
punch holds down the step portion 5 of the door inner panell. Therefore, when the
top panel portion 2 is formed, an unrestricted portion of the blank material is reduced,
thereby allowing to suppress cracks and wrinkles of the door inner panel.
[0094]
The blank material S may have an opening portion. In this case, the blank
material S has an opening portion at a position facing the die bottom surface 16A of
the die 15. As a result, as shown in FIG. 1, a door inner panel 1 having an opening
portion 3 in the top panel portion 2 is formed. In other words, the opening portion
of the blank materialS corresponds to the opening portion 3 of the door inner panell.
When the blank material S has an opening portion, the top panel portion 2 is formed
by stretch flange forming. Specifically, when the first punch 12 processes the blank
material S, an outer edge of the opening portion extends in a direction in which the
opening portion extends. Therefore, cracks are less likely to occur even when the
first punch 12 is pushed in. Further, in hot stamping, since the blank materialS is
heated, its ductility is improved, thus facilitating stretch flange forming.
[0095]
[Other production methods]
FIGS. 11A to 11 C are cross-sectional views to schematically show a press
forming step, which is different from that of FIGS. 9A to 9C. FIG. 11A shows a
stage of clamping a blank materialS with a blank holder 14. FIG. 11B shows a
state when pushing in by the second punch 13 is completed. FIG. 11C shows a
state when pushing in by the first punch 12 is completed
[0096]
Referring to FIG. 11B, in a press forming step which is different from that in
FIG. 9A to 9C, when pushing in on the blank materialS by the second punch 13 is
completed, the front end surface 12A of the first punch 12 is located below the front
end surface 13A of the second punch 13. In other words, before pushing in on the
blank material S by the second punch 13 is completed, the pushing in on the blank
-;/-
materialS by the first punch 12 is started. At this time, the pushing in on the blank
materialS by the first punch 12 has not been completed. In this case as well, the
second punch 13 holds down the blank material S before the pushing in by the first
punch 12 is completed. As a result, even if a door inner panel having a shape of a
high degree of forming difficulty is formed, it is possible to suppress cracks, wrinkles,
and the like. FIGS. 11A to 11 C show a case in which a blank material S has an
opening portion 31. Accordingly, the top panel portion of the door inner panel is
formed by stretch flange forming.
[0097]
In hot stamping, quenching is performed simultaneously with the forming of
the blank material. Specifically, the blank material is cooled by contact with a
punch, a die, and a holder. As a result, a high-strength door inner panel can be
formed. The high-strength door inner panel is, for example, a formed product
having a tensile strength of not less than 1200 MPa.
[0098]
In a production method of the present embodiment, the height position of the
front end surface 12A of the first punch 12 is not particularly limited before pushing
in by the second punch 13 is completed. In short, the first punch 12 may first push
in the blank material S, or the second punch 13 may first push in the blank material S.
It is only needed that the pushing in on the blank material S by the second punch 13
is completed prior to the pushing in on the blank materialS by the first punch 12.
As a result, it is possible to form a door inner panel having a shape of a high degree
of forming difficulty. Moreover, moving down of the blank holder only needs to be
performed by the time the pushing in by the second punch is completed.
[0099]
However, when a low-strength steel sheet having high ductility is used for the
steel sheet, the pushing in on the blank materialS by the first punch 12 may be
completed prior to the pushing in on the blank material S by the second punch 13.
In short, since the production method of the present embodiment uses a divided
punch, it is possible to press form the door inner panel into shapes of various degrees
of forming difficulty.
[0100]
/-
The production method of the present embodiment has described a case in
which a door inner panel is produced by a hot stamping apparatus including a first
and second punches. However, the number of punches is not limited to two. The
second punch may be divided into multiple punches. In short, a hot stamping
apparatus including three or more punches may be used. In this case, multiple step
portions are provided on the vertical wall portion of the door inner panel
[0101]
In the production method described above, the steel sheet may be a tailored
blank. Hereinafter, an example of the door inner panel which is produced from a
tailored blank will be described.
[0102]
[Fifth embodiment]
FIG. 12 is a perspective view of a door inner panel of a fifth embodiment.
FIG. 13A and FIG. 13B are perspective views each showing a starting material of the
door inner panel shown in FIG. 12. Of these figures, FIG. 13A shows a state being
punched an opening portion. FIG. 13B shows a state after being punched an
opening portion, and immediately before subjected to hot stamping.
[0103]
Compared with the door inner panels of the first to fourth embodiments
described above, the door inner panel of the fifth embodiment shown in FIG. 12 is
similar in that it is formed by hot stamping as described above, but is different in that
it uses a tailored blank as the starting material. The tailored blank is broadly
classified into a tailored welded blank (hereinafter referred to as "TWB") and a
tailored rolled blank (hereinafter also referred to as "TRB "). TWB is a blank in
which multiple kinds of steel sheets having different sheet thicknesses, tensile
strengths, etc. are integrated together by welding (for example, butt welding). On
the other hand, TRB is a blank in which the sheet thickness is varied by changing the
spacing of the rolling rolls in the production of the steel sheet. FIGS. 13A and 13B
show an exemplary case in which the tailored blank is TRB.
[0104]
Referring to FIG. 12, in the door inner panel1 of the fifth embodiment, a step
portion 5 is provided in all of four adjacent vertical wall portions 4 (three pairs of
vertical wall portions 4) as in the door inner panel 1 of the second embodiment
shown in FIG. 5. The opening portion 3 is provided at one place so as to leave a
peripheral edge portion of the top panel portion 2. In this door inner panel 1, the
sheet thickness of a region of an edge portion (beltline portion 21) on the vehicle
upper side including a border (beltline BL) on the vehicle upper side of the top panel
portion 2 is larger than that of a region adjacent to this region. In other words, the
sheet thickness of the door inner panel 1 is not constant, and the sheet thickness of
the beltline portion 21 is increased. As a result, the strength of the beltline portion
21 is increased so that the collision characteristic of the door inner panel is improved.
In addition, when there is a region other than the beltline portion 21, in which high
strength is not required, it is expected to reduce the weight of the door inner panel1
by decreasing the sheet thickness of that region.
[0105]
The door inner panel 1 of the fifth embodiment is produced by using a starting
material (TRB) shown in FIGS. 13A and 13B. Specifically, first, a TRB 30 having
a contour shape corresponding to the contour shape of the door inner panel 1 is
prepared as shown in FIG. 13A. In this TRB 30, the sheet thickness of a region
corresponding to the beltline portion 21 of the door inner panel 1 is larger than those
of other regions. Next, the TRB 30 is formed with an opening portion 31
corresponding to the opening portion 3 of the top panel portion 2 of the door inner
panel 1. This opening portion 31 is formed, for example, by punching. By
subjecting the TRB 30 having such opening portion 31 to the hot stamping as
described above, it is possible to form the door inner panel 1 as shown in FIG. 12.
[0106]
In the fifth embodiment, a TWB may be used, as the starting material, in place
ofthe TRB.
[0107]
[Sixth embodiment]
FIG. 14 is a perspective view of a door inner panel of a sixth embodiment.
The door inner panel1 of the sixth embodiment shown in FIG. 14 is a modification
of the door inner panel of the fifth embodiment shown in FIG. 12 modified according
to the third embodiment.
3l
~-:.
;
[0108]
Referring to FIG. 14, in the door inner panel 1 of the sixth embodiment, as
with the door inner panel 1 of the third embodiment shown in FIG. 6, a recessed
portion 7 is provided in the beltline portion 21 of the top panel portion 2 along the
beltline portion 21 as in the door inner panel 1 of the third embodiment shown in FIG.
6. Since the recessed portion 7 is provided in the beltline portion 21 having a large
sheet thickness, the strength of the beltline portion 21 is further increased. Thus,
the beltline portion 21 also plays a role of a beltline reinforcement. The beltline
portion 21 may be provided either with a protruded portion in place of the recessed
portion 7, or with both the recessed portion 7 and the protruded portion.
[0109]
The door inner panel 1 of the sixth embodiment is produced by using the
starting material shown in FIGS. 13A and 13B as in the fifth embodiment. The
recessed portion 7 is formed by hot stamping.
[0110]
[Seventh embodiment]
FIG. 15 is a perspective view of a door inner panel of a seventh embodiment.
FIGS. 16A and 16B are perspective views each showing the starting material of the
door inner panel shown in FIG. 15. Of these figures, FIG. 16A shows a state before
being punched an opening portion. FIG. 16B shows a state after being punched the
opening portion, and immediately before being subjected to hot stamping. The door
inner panel I of the seventh embodiment shown in FIG. 15 is a modification of the
door inner panel I of the fifth embodiment shown in FIG. 12 modified according to
the fourth embodiment.
[0 Ill]
Referring to FIG. 15, in the door inner panel 1 of the seventh embodiment, a
plurality of opening portions 3A and 3B are provided in the top panel portion 2 as in
the door inner panel I ofthe fourth embodiment. FIG. 15 shows an exemplary case
in which two opening portions 3A and 3B are provided. The top panel portion 2
has a boundary portion 22 between the opening portions 3A and 3B. The boundary
portion 22 extends in a fore-and-aft direction substantially parallel to the beltline
portion 21. In this door inner panel 1, the sheet thickness of a region of the beltline
portion 21 of the top panel portion 2 is larger than that of a region adjacent to this
region. Further, the sheet thickness of a region of the boundary portion 22 of the
top panel portion 2 is larger than that of a region adjacent to this region. In other
words, the sheet thickness of the door inner panel 1 is not constant, but the sheet
thicknesses of the beltline portion 21 and the boundary portion 22 are increased. As
a result, the strength ofthe beltline portion 21 and the boundary portion 22 is
increased, and the collision characteristic of the door inner panel is improved.
Moreover, when there is a region other than the boundary portion 22, in which high
strength is not required, it is expected to reduce the weight of the door inner panel 1
by reducing the sheet thickness of that region.
[0112]
The door inner panel 1 of the seventh embodiment is produced by using the
starting material shown in FIGS. 16A and 16B. Specifically, first, a TRB 30 having
a contour shape corresponding to the contour shape of the door inner panel 1 is
prepared as shown in FIG. 16A. In this TRB 30, the sheet thickness of regions
respectively corresponding to the beltline portion 21 and the boundary portion 22 of
the door inner panel 1 are larger than those of other regions. Next, the TRB 30 is
formed with opening portions 31A and 31B corresponding to the opening portions
3A and 3B of the top panel portion 2 of the door inner panel I. By applying the hot
stamping described above to the TRB 30 having such opening portions 31A and 31B,
it is possible to form the door inner panel 1 shown in FIG. 15.
[0113]
The door inner panel1 of the seventh embodiment may also be varied such
that the sheet thickness of either one of the beltline portion 21 and the boundary
portion 22 is increased.
[0114]
[Eighth embodiment]
FIG. 17 is a perspective view of a door inner panel of an eighth embodiment.
The door inner panel1 of the eighth embodiment shown in FIG. 17 is a modification
of the door inner panel1 of the seventh embodiment shown in FIG. 15 modified
according to the fourth embodiment.
[0115]
Referring to FIG. 17, in the door inner panel 1 of the eighth embodiment, a
recessed portion 8 is provided in the boundary portion 22 of the top panel portion 2,
as in the door inner panel 1 of the fourth embodiment, along the boundary portion 22.
Since the recessed portion 8 is provided in the boundary portion 22 having a large
sheet thickness, the strength of the boundary portion 21 is further increased. As a
result, the boundary portion 22 also plays a role of a door impact beam. The
boundary portion 22 may be provided with a protruded portion in place of the
recessed portion 8, or both of the recessed portion 8 and the protruded portion.
[0 116]
The door inner panel 1 of the eighth embodiment is produced by using the
starting material shown in FIGS. 16A and 16B as in the seventh embodiment. The
recessed portion 8 is formed by hot stamping.
[0117]
[Ninth embodiment]
FIG. 18 is a perspective view of a door inner panel of a ninth embodiment.
FIGS. 19A and 19B are each a perspective view showing the starting material ofthe
door inner panel shown in FIG. 18. Of these figures, FIG. 19A shows a state before
being punched an opening portion. FIG. 19B shows a state after being punched the
opening portion and immediately before being subjected to hot stamping.
[0 118]
Referring to FIG. 18, in the door inner panel1 of the ninth embodiment, the
sheet thickness of a region of a lower-side vertical wall portion 4 including a lowerside
border 2B of the top panel portion 2 is larger than that of a region adjacent to
that region. In other words, the sheet thickness of the door inner panell is not
constant, but the sheet thickness of the lower-side vertical wall portion 4 is increased.
As a result, strength of the lower-side vertical wall portion 4 is increased, and the
collision characteristic of the door inner panel is improved. In addition, when there
is a region other than the lower-side vertical wall portion 4, in which high strength is
not required, it is also expected to reduce the weight of the door inner panel1 by
reducing the sheet thickness of that region. FIG. 18 shows an exemplary case in
which the sheet thickness is increased in a lower-side step portion 5 and a lower-side
flange portion 6, in addition to the lower-side vertical wall portions 4A and 4B.
-r-
[0119]
The door inner panel 1 of a ninth embodiment is produced by using the
starting material shown in FIGS. 19A and 19B. Specifically, first, a TRB 30 having
a contour shape corresponding to the contour shape of the door inner panel 1 is
prepared. In this TRB 30, the sheet thickness of a region corresponding to a lowerside
vertical wall portion 4 of the door inner panel1 is larger than those of other
regions. Next, the TRB 30 is formed with an opening portion 31 corresponding to
the opening portion 3 of the top panel portion 2 of the door inner panel I. By
applying the hot stamping described above to the TRB 30 having such opening
portion 31, it is possible to form the door inner panel1 shown in FIG. 18.
[0120]
Note that the door inner panel 1 of the fifth to eighth embodiment may also be
varied such that the sheet thickness of lower-side vertical wall portion 4 is increased
according to the ninth embodiment.
[0121]
FIG. 20 is a perspective view of a door inner panel having an opening portion
3 having a shape different from that of FIG. 18. FIG. 21, which is a perspective
view showing the starting material of the door inner panel shown in FIG. 20, shows a
state after being punched the opening portion and immediately before being
subjected to hot stamping.
[0122]
In the door inner panel 1 shown in FIG. 20, an opening portion 3 extends over
one border of a peripheral edge portion of a top panel portion 2. In other words, the
opening portion 3 is provided so that a beltline BL is interrupted. In this case, as
shown in FIG. 21, an opening portion 31 corresponding to the opening portion 3 of
the top panel portion 2 of the door inner panel 1 is formed in the TRB 30 before the
punching processing shown in FIG. 19A. By applying the hot stamping described
above to the TRB 30 having such opening portion 31, it is possible to form the door
inner panel1 shown in FIG. 20.
[0123]
[Tenth embodiment]
-;5-
FIG. 22 is a perspective view of a door inner panel of a tenth embodiment.
FIGS. 23A and 23B are each a perspective view showing a starting material of the
door inner panel shown in FIG. 22. Of these figures, FIG. 23A shows a state before
being punched an opening portion. FIG. 23B shows a state after being punched the
opening portion and immediately before being subjected to hot stamping.
[0124]
Referring to FIG. 22, in a door inner panel 1 of a tenth embodiment, the sheet
thickness of a region of a front-side vertical wall portion 4 (vertical wall portion 4A)
including a front-side border 2A of the top panel portion 2 is larger than that of a
region adjacent to the region. In other words, the sheet thickness of the door inner
panel 1 is not constant, but the sheet thickness of the front-side vertical wall portion
4 is increased. As a result, the strength of the front-side vertical wall portion 4 to
which a hinge is attached is increased. In addition, when there is a region other
than the front-side vertical wall portion 4, in which high strength is not required, it is
expected to reduce the weight of the door inner panel1 by decreasing the sheet
thickness of that region. FIG. 22 shows an exemplary case in which in addition to
the front-side vertical wall portions 4A and 4B, the thicknesses of the front-side step
portion 5 and the front-side flange portion 6 are also increased.
[0125]
The door inner panel 1 of a tenth embodiment is produced using the starting
material shown in FIGS. 23A and 23B. Specifically, first, as shown in FIG. 23A, a
TRB 30 having a contour shape corresponding to the contour shape of the door inner
panel 1 is prepared. In this TRB 30, the sheet thickness of a region corresponding
to the front-side vertical wall portion 4 of the door inner panel1 is larger than those
of other regions. Next, the TRB 30 is formed with an opening portion 31
corresponding to the opening portion 3 of the top panel portion 2 of the door inner
panel 1. By applying the above described hot stamping to the TRB 30 having such
opening portion 31, it is possible to form the door inner panel1 shown in FIG. 22.
[0126]
Note that using a TWB as the starting material makes it possible to vary the
door inner panel 1 of the fifth to ninth embodiments according to the present
embodiment such that the sheet thickness of the front-side vertical wall portion 4 is
increased. This is because the TWB has a larger degree of freedom for combining
steel sheets.
[0127]
In the above description, a case in which the material of the door inner panel
is a steel sheet is described. However, the material of the door inner panel is not
limited to a steel sheet, but any metal sheet may be used. The metal sheet may be
made of, for example, aluminum, an aluminum alloy, a multi-layer steel sheet,
titanium, magnesium, or the like. Further, in the above description, a case in which
the panel-shaped formed product is a door inner panel is described. However, the
panel-shaped formed product is not limited to the door inner panel.

We claim:
1. A panel-shaped formed product made of a metal sheet, comprising:
a polygonal top panel portion,
an opening portion provided in the top panel portion, and
a vertical wall portion extending from at least not less than two adjacent
borders among borders of the top panel portion, wherein
at least one pair of each vertical wall portion of pairs of adjacent vertical wall
portions among the vertical wall portions has a step portion.
2. The panel-shaped formed product according to claim 1, wherein
the panel-shaped formed product has a tensile strength of not less than 1200
MPa.
3. The panel-shaped formed product according to claim 1 or 2, wherein
the panel-shaped formed product is a door inner panel for an automobile, and
does not have the vertical wall portion on a border on vehicle upper side among
borders of the top panel portion.
4. The panel-shaped formed product according to claim 3, wherein
the opening portion is provided such that a peripheral portion ofthe top panel
portion is left out.
5. The panel-shaped (ormed product according to claim 4, wherein
in an edge portion on vehicle upper side including a border on the vehicle
upper side of the top panel portion, at least one of a recessed portion and a protruded
portion is provided along the edge portion on vehicle upper side.
6. The panel-shaped formed product according to claim 4 or 5, wherein
the top panel portion has a boundary portion for dividing the opening portion
into a plurality of portions, and at least one ofthe recessed portion and the protruded
portion is provided along the boundary portion.
-y-
7. The panel-shaped formed product according to any one of claims 1 to 6,
wherein
the metal sheet is a steel sheet.
8. The panel-shaped formed product according to any one of claims 3 to 7,
wherein
a sheet thickness of a region of a lower-side vertical wall portion including a
border on a lower side of the top panel portion is larger than the sheet thickness of a
region adjacent to the afore-mentioned region.
9. The panel-shaped formed product according to any one of claims 3 to 8,
wherein
a sheet thickness of a region of a front-side vertical wall portion including a
border on a front side of the top panel portion is larger than the sheet thickness of a
region adjacent to that region.
10. The panel-shaped formed product according to any one of claims 4 to 9,
wherein
a sheet thickness of a region of an edge portion on the vehicle upper side
including a border on the vehicle upper side of the top panel portion is larger than the
sheet thickness of a region adjacent to the afore-mentioned region.
11. The panel-shaped formed product according to any one of claims 4 to 10,
wherein
the top panel portion has a boundary portion that divides the opening portion
into a plurality of portions, and the sheet thickness of a region of the boundary
portion is larger than the sheet thickness of a region adjacent to the afore-mentioned
regiOn.
12. A method for producing a panel-shaped formed product, wherein
the panel-shaped formed product includes a polygonal top panel portion, a
vertical wall portion extending from at least not less than two adjacent borders
among borders of the top panel portion, and a step portion provided in at least one
pair of each vertical wall portion of pairs of adjacent vertical wall portions among the
vertical wall portions,
the production method comprising:
a preparation step of preparing a blank material made of a metal sheet,
a heating step of heating the blank material, and
a press forming step of applying press working by hot stamping forming to
the heated blank material to form the blank material into the panel-shaped formed
product, wherein
the press forming step uses a press working apparatus that includes:
a die having a die engraved portion in which the shape of the panel-shaped
formed product is formed,
a first punch having a front end surface which faces the die and in which the
shape of the top panel portion is shaped,
a second punch which is adjacent to outside of the first punch and has a front
end surface in which the shape of the step portion is shaped, and
a blank holder existing adjacent to at least a part of the outside of the second
punch and facing the die, wherein
the blank material is disposed between the die, and the blank holder, the first
punch and the second punch, and the blank holder, the first punch, and the second
punch are relatively moved with respect to the die to push in the first punch and the
second punch on the blank material, thereby forming the same into the panel-shaped
formed product.
13. The method for producing a panel-shaped formed product according to claim
12, wherein
the blank material has an opening portion at a position corresponding to the
top panel portion.
14. The method for producing a panel-shaped formed product according to claim
12 or 13, wherein
-1-
in the press forming step, pushing in on the blank material by the second
punch is completed prior to pushing in on the blank material by the first punch.
15. The method for producing the panel-shaped formed product according to
claim 14, wherein
in the press forming step, when the pushing in on the blank material by the
second punch is completed or after the pushing in is completed, pushing in on the
blank material by the first punch is started.
16. The method for producing a panel-shaped formed product according to claim
14, wherein
in the press forming step, before pushing in on the blank material by the
second punch is completed, pushing in on the blank material by the first punch is
started.
17. The method for producing a panel-shaped formed product according to any
one of claims 12 to 16, wherein
a tensile strength of the panel-shaped formed product after forming is not less
than 1200 MPa.
18. The method for producing a panel-shaped formed product according to any
one of claims 12 to 17, wherein
the die engraved portion of the die used in the press forming step satisfies
conditions: d2;::: 40 mm, and dlld2 < 0.8, where d1 is a depth from a reference
surface facing the blank holder to a step surface facing the second punch, and d2 is a
depth from the reference surface to a die bottom surface facing the first punch.
19. The method for producing a panel-shaped formed product according to any
one of claims 12 to 18, wherein
the metal sheet is a steel sheet.
20. The method for producing a panel-shaped formed product according to claim
19, wherein
the steel sheet is a tailored blank.