Description
Title of Invention:
METHOD FOR PRODUCING CURVED PART, AND SKELETON
STRUCTURE MEMBER OF BODY SHELL OF AUTOMOBILE
Technical Field
[0001] The present invention relates to a method for producing a cullred part
having a hat-shaped cross section by press-fonning a metal niaterial sheet, and a
skeleton structure ~netilbero f a body shell of automobile.
Background Art
[0002] A press-formed part having a hat-shaped cross section and an external
shape being curved in its lengthwise direction is used as a skeleton structure
member of a body shell of automobile, such as a side member (a front side member
and a rear side member). This press-formed part is a critical part for ensuring
crash perfor~nanceo f an automobile, and is required higher strength for enhancing
collision safety and promoting weight a reduction of the body. Conventionally,
this press-formed part has been produced by applying a press-forming method
based on the draw-forming of a metal material sheet.
(00031 Figure 18A is a perspective view to show an example of a cullred part
having a hat-shaped cross section (hereafter, simply referred to as a "curved part")
10, Figure 18B is a top view of the curved part 10, Figure 18C is a side view of the
curved part 10, Figure 18D is a front view of the curved part 10 seen fro111 one end
thereof, and further Figure 18E is a perspective view to explain a convex curved
portion 1 1 a and a concave curved portion 1 1 b of the curved part 10. Further,
Figure 19A is a cross-sectional view to schematically show a drawing machine for
producing the curved part 10 by prior art, Figure 19B is a cross-sectional view to
show a stage in which a metal material sheet 201 is interposed and constrained
between a die 202 and a blank holder 203, and between the die 202 and a punch 204,
Figure 19C is a cross-sectional view to show a stage in which the punch 204 is
pushed inward fro111 the stage shown in Figure 19B, and Figure 19D is a crosssectional
view to show a stage in which the punch 204 is further pushed inward
frotn the stage sho~vnin Figure 19C to be fully pushed inward with respect to the
die 202. Further, Figure 20A is a perspective view to sho~vth e metal nlaterial
sheet 201, and Figure 20B is a perspective view to show a drawn panel 301 which is
produced by prior art sho~vnin Figures 19A to 19D.
[0004] For example, \vhen producing the cuived part 10 sho~~ilnn F igures 18A to
18E, first, as sho~vnin Figure 19A, the inetal inaterial sheet 20 1 sl10117n in Figure
20A is placed between the blank holder 203 and the die 202, and between the punch
204 and the die 202. Next, as sho~vnin Figure 19B, the periphery of the inetal
inaterial sheet 201 is interposed and pressurized by the die 202 and the blallk holder
203. Next, as shown in Figures 19C and 19D, the central portion of the metal
inaterial sheet 201 is caused to bulge by the punch 204, thereby draw-for~ningth e
metal material sheet 201 into a desired shape. Since, in this process of drawforming,
the periphery of the metal material sheet 201 is held by the die 202 and the
blank holder 203 as shown in Figure 19C, the inner portion of the lnetal material
sheet 201 is formed by the punch 204 while being subjected to tension. The metal
material sheet 201 is caused to flow into the die 202 wit11 its periphery being
constrained to some degree by the die 202 and the blank holder 203, thus being
formed into the dra~vipl anel 301 having the shape shown in Figure 20B. The
curved part 10 shown in Figures 18A to 18E is produced by cutting off an unwanted
part of the periphery of the drawn panel 301.
[0005] Figure 21 is a perspective view to show regions of the drawn panel 301
shown in Figure 20B, where cracks and wrinkles are likely to occur.
When producing the curved part 10 by a press-forming method based on
draw-forming, as shown in Figure 21, wrinkles attributable to a surplus of the
material are likely to occur in a top plate 301a of a concave curved portion 3 1 lb and
a flange 301b of a convex curved portion 3 1 la of the drawn panel 301 at a stage in
which the metal material sheet is formed into the drawn panel 301. In order to
suppress the occurrence of wrinkles, it is effective in general to prevent the metal
material sheet 201 fiom excessively flowing into the die 202 by enhancing the
constraint of the periphery of the lnetal lnaterial sheet 201 in the forming process by
means of increasing the pressurizing force of the blank holder 203 or adding a draw
bead on the blank holder 203.
[0006] Ho~~revewrh, en the metal nlaterial sheet 201 is prevented from flowing
into the die 202 by those means, the sheet thickness will be excessively decreased in
the top sheet 30 lc of the convex curved po~tion3 1 la, the flange 301d of the
concave curved portion 3 1 lb, and an end portion 301e in the length\vise direction of
the drawn panel 301 so that a crack ~vilol ccur in these areas 301c, 301d, and 301e
\vhen the ineta1 inaterial sheet 201 is a inaterial having lo~vex tensibility.
[0007] For that reason, to produce a curved part 10, n~hichis represented by, for
esanlple, a side nle~nberb, y a press-forming neth hod based on draw-forming
nlithout causing cracks and wrinkles, it becomes difficult to use a high-strength
material (for examnple, a high tensile strength steel sheet) having low extensibility as
the metal nlaterial sheet 201 so that a low strength material having high
extensibility has to be used. For this reason, the sheet thickness of the metal
material sheet 201 has to be increased to ensure the strength required for the curved
part 10, and thus the weight reduction of a skeleton structure member of a body
shell is impaired.
[0008] Further, when producing the curved part 10 by a press-fonning method
based on draw-forming, since an unwanted part which exists in the outer periphery
of the drawn panel 301 is to be cut off and discarded, the yield of the material will
also decrease.
[0009] It is noted that Patent Literatures 1 to 4 propose a technique to bendforming
a part having a cross section, which is simple and uniform in the
lengthw~ised irection, such as a hat-shaped cross section and a Z-shape cross section.
Ho~veverP, atent Literatures 1 to 4 do not disclose a method for producing a part
having a co~nplicateds hape such as that of the curved part 10.
Citation List
Patent Literature
[OO lo]
Patent Literature 1 : Japanese Patent Laid-Open No.2003- 103306
Patent Literature 2: Japanese Patent Laid-Open No.2004-154859
Patent Literature 3: Japanese Patent Laid-Open No.2006-015404
Patent Literature 4: Japanese Patent Laid-Open No.2008-307557
Sumlnary of Invention
Technical Problem
[0011] The present invention has been made in view of the above described
problenls of prior art, and has its obsect to provide: a method for producing, at a
high yield, a c u ~ ~peadrt having a hat-shaped cross section and an external shape
being curved in its length~vised irection, ~i~hicish s uitably used for a side lnetnber
(for exanlple, a front side lnen~bera nd a rear side member) which is a skeleton
structure nlenlber of a body shell of automobile by press-fonning without causing
wrinkles in a top plate of a concave curved portion and a flange of a convex curved
portion, and cracks in a top plate of a convex curved portion, a flange of a concave
curved poition, and further an end portion in the lengthwise direction; and a
skeleton structure tnelnber such as a side member which is produced by this method.
[0012] Further, it is an object of the present invention to produce the above
described skeleton structure member by using not only a low strength lnaterial
having high extensibility but also a high strength material having low extensibility
(for example, a high tensile strength steel sheet having a tensile strength of not less
than 440 MPa) as the metal lnaterial sheet.
Solution to Probletn
[0013] The present invention is described as follo~vs:
(1) A method for producing a curved part by cold or ~var~prnes s-forming a metal
material sheet by using a press-forming apparatus including a die and a pad, and a
punch and a blank holder which are disposed to be opposed to the die and the pad,
the curved body comprising a main body having: a hat-shaped cross section which
is made up of an elongated top plate, two vei-tical walls connecting to both side
edges of the top plate and extending in a direction substantially perpendicular to the
top plate, and two outwardly directed flanges which connect to the two vertical
~vallsre spectively, and an external shape in which each of the top plate, the two
vertical walls and the two ouhvardly directed flanges is curved in an arc shape in a
height direction of the vertical walls in a portion in the lengthwise direction of the
top plate,
wherein the curved part having the hat-shaped cross section is formed by
moving the blank holder and the die relatively with respect to the pad and the punch
to a side ~vl~etrhee punch and the blank holder are disposed 1vit11 the nietal ~naterial
sheet as a boundary ~vhilem aintaining a state in ~vliicha portion to be fornled into
the top plate in the nletal material sheet, \vhich is disposed behveen the die and the
blank holder, and between the pad and the punch, is pressed against the punch with
the pad so as to be pressurized and interposed, and portions to be formed into the
vertical ~vallsa nd the ouhvardly directed flanges in the nletal material sheet are
pressed against the die with the blank holder so as to be pressurized and interposed.
[0014] In the present invention, the term "cold" means an atmosphere of a roonl
tenlperature, and the term "\varinn nleans an at~nospllereo f a temperature higher
than "cold" and less than Ac3, preferably not Inore than Acl.
(2) The method for producing a curved part according to item (I), wherein the pad
is connected to a pad pressurizing apparatus having a fixed stroke, and the blank
holder is connected to a blank holder pressurizing apparatus, and wherein after
coinpletion of the forming of the curved part,
the die and the pad are separated from the blank holder and the punch to take
out the cutved part from the press-forming apparatus, after the blank holder is fixed
so as not to relatively move with respect to the punch and is arranged so as not to
press the curved part against the die, by using the pad pressurizing apparatus and the
blank holder pressurizing apparatus.
(3) The method for producing a curved part according to item (I), wherein the pad
is connected to a pad pressurizing apparatus, and the blank holder is connected to a
blank holder pressurizing apparatus having a fixed stroke, and wherein after
co~npletiono f the fornling of the curved part,
the die and the pad are separated from the blank holder and the punch to take
out the curved part from the press-forming apparatus, after the pad is fixed so as not
to relatively move with respect to the die and is arranged so as not to press the
curved part against the punch, by using the pad pressurizing apparatus and the blank
holder pressurizing apparatus.
(4) The method for producing a curved part according to any one of items (1) to (3),
wherein the die has an internal shape including shapes of outer surfaces of each of
the vertical walls and the flanges in the curved part, the pad has an exterior shape
including a shape of an outer surface of the top plate in the curved part, the punch
has an external shape including shapes of inner surfaces of each of the top plate and
the vertical \valls in the curved part, and the blank holder has an external shape
including shapes of inner surfaces of the flanges in the curved part.
(5) The method for producing a curved part according to any one of items (1) to (4),
wherein an interior angle formed by the top plate and the vertical wall in the cross
sectional shape is 90 to 92O.
(6) The il~ethodf or producing a cunled part according to any one of iteins (1) to (51,
wherein the clearance behveen a portion in the die ~vhichf orins the vertical \vall and
the portion in the punch ~vhichfo rlns the vertical \vall is 100 to 120% of the sheet
thickness of the metal nlaterial sheet at the time of coinpleting the formation of the
curved part.
(7) The method for producing a curved part according to any one of items (1) to (6),
wherein the nletal material sheet is a steel sheet having a sheet thickness of 0.8 to
3.2 inm and a tensile strength of 200 to 1600 MPa.
(8) The method for producing a curved part according to any one of items (1) to (7),
wherein a portion of the metal material sheet to be formed into the top plate is
pressurized by being pressed against the punch at a pressing pressure of not less
than 0.1 MPa by the pad, and a portion of the metal material sheet to be formed into
the vertical wall and the outwardly directed flange is pressurized by being pressed
against the die at a pressing pressure of not less than 0.1 MPa by the blank holder.
(9) The method for producing a curved part according to any one of items (1) to (8),
wherein the metal material sheet is a preworked metal sheet which is obtained by
pre~vorkingth e inetal material sheet.
(10) The method for producing a curved part according to any one of items (2) to
(9), wherein the cullred part taken out from the press-forming apparatus is subjected
to post~vorking.
(1 1) A skeleton structure member of a body shell of an automobile, coinprising a
main body having: a hat-shaped cross section ~vhichis made up of an elongated top
plate, t~vove rtical walls connecting to both side edges of the top plate and extending
in a direction substantially perpendicular to the top plate, and hvo outwardly
directed flanges which connect to the two vertical walls respectively; and an
external shape in which each of the top plate, the hvo vertical walls and the two
ouhvardly directed flanges is curved in an arc shape including a curved portion in a
height direction of the vertical walls in a portion in a lengthwise direction of the top
plate,
wherein the main body is a cold or warm press-fonned body, which uses a
steel sheet having a tensile strength of not less than 440 MPa and a sheet tliick~less
of I .O to 2.3 111111 as a material, and the reduction rate of the sheet thickness of a
cul-ved portion with respect to that of a re~nainingp ortion excepting the curved
portion is not more than 15%.
[0015] The skeleton structure tnenlber of a body shell relating to the present
invention is exemplified by a front side ine~ube\rv l~ichc onstitutes an engine
compartment, a rear side member which is joined to the lower surface of a rear floor
panel, and further, a floor center tunnel which is joined to the front floor panel, and
the like.
Advantageous Effects of Invention
[0016] According to the presetlt invention, since the metal material sheet is
formed by moving the blank holder and the die relatively with respect to the pad
and the punch to the side where the punch and the blank holder are disposed with
the metal ~nateriasl heet as a boundary while maintaining a state in which a portion
of the nletal material sheet to be formed into the top plate is interposed and
constrained by the pad and the punch, and portions of the metal material sheet to be
formed into the vertical ~vallsa nd the flanges are interposed and constrained by the
blank holder and the die, it is possible to prevent the occurrence of wrinkles in the
top plate and the flanges, and form the metal ~nateriasl heet through the plastic
defolrnlatiotl in \vhich shear deformation of the vertical walls is dominant. For this
reason, there is 110 need of applying large tension to the metal material sheet during
forming, and therefore it is possible to decrease the excess ~nateriawl hich is a part
to be discarded in the metal material sheet, thereby improving the yield and solving
the above described problem.
Brief Description of Drawings
[0017]
[Figure 11 Figure 1 is a perspective view to sho\v in a simplified and exploded
fashion a press-forming apparatus for carrying out the production method relating to
the present invention to produce a curved part.
[Figure 2A] Figure 2A is a sinlplified cross-sectional vie~vto show a state at the
start of processing by the press-fortning apparatus sho\vn in Figure 1.
[Figure 2B] Figure 2B is a simplified cross-sectional vie\v to sl10157 a state in ~vhich
a illeta1 material sheet is interposed and constrained behveen the die and the blank
holder, and behveen the pad and the punch in the press-forming apparatus shown in
Figure 1.
[Figure 2C] Figure 2C is a sinlplified cross-sectional view to sho~va state in which
the punch is pushed inward from the stage shown in Figure 2B.
[Figure 2D] Figure 2D is a sitnplified cross-sectional view to show a state in which
the punch is hrther pushed inward from the stage shown in Figure 2C so that the
punch is fully pushed inward with respect to the die.
[Figure 31 Figure 3 is a perspective view to show in a simplified and exploded
fashion another press-forming apparatus for carlying out the production method
relating to the present invention to produce a curved part.
[Figure 4A] Figure 4A is a sirnplified cross-sectional view to show a state at the
start of processing by the press-fonning apparatus shown in Figure 3.
[Figure 4B] Figure 4B is a simplified cross-sectional view to show a state in which
the metal material sheet is interposed and constrained behveen the die and the blank
holder, and between the pad and the punch of the press-forming apparatus shown in
Figure 3.
[Figure 4C] Figure 4C is a simplified cross-sectional view to show a state in which
the punch is pushed in~vardfr otn the stage shown in Figure 4B.
[Figure 4D] Figure 4D is a simplified cross-sectional view to show a state in which
the punch is further pushed inward from the stage sl~o\vnin Figure 4C and thereby
the punch is fully pushed inward with respect to the die.
[Figure 5A] Figure 5A is an explanatory diagram to show the principle of the
present invention.
[Figure SB] Figure 5B is an explanatory diagram to show shear wrinkles which may
occur when carrying out the present invention.
[Figure SC] Figure 5C is a side view to sho~vsh ear wrinkles ~vhichm ay occur when
carrying out the present invention.
[Figure 6A] Figure 6A is an explanatory diagram to show collditions to prevent the
occurrence of shear wrinkles, by sho~i~inang interior angle 8 fornled by the vertical
wall and the top plate, and the clearance between the die and the vertical wall
portion of the punch.
[Figure 6B] Figure 6B is an explanatory diagram to show collditions to prevent the
occurrellce of shear wrinkles, by showing an interior angle 8 for~lledb y the vertical
wall and the top plate, and a clearance at a vertical wall portion betwee11 the die and
the punch.
[Figure 7A] Figure 7A is an explanatory diagraln to show defects which may occur
~vhenth e curved part is taken out from the metal mold after the punch is fully
pushed inward the die thereby forming the metal material sheet into the curved part.
[Figure 7B] Figure 78 is an explanatory diagram to show a stage in which the
punch is retreated with respect to the die from the state shown in Figure 7A.
[Figure 7C] Figure 7C is an explanatory diagraln to show a stage in which the
punch has been fully retreated with respect to the die from the state shown in Figure
7B.
[Figure 8A] Figure 8A is an explanatory diagraln to show a method for solving
defects shown by Figures 7A to 7C.
[Figure 8B] Figure 8B is an explanatory diagram to show a stage in which the
punch is retreated with respect to the die from the state shown in Figure 8A.
[Figure 8C] Figure 8C is an explanatory diagram to show a stage in which the
punch has been fully retreated with respect to the die from the state shown in Figure
8B.
[Figure 9A] Figure 9A is an explanatory diagram to show another method for
solving the defects shown by Figures 7A to 7C.
[Figure 9B] Figure 9B is an explanatory diagram to show a stage in which the
punch is retreated with respect to the die from the state shown in Figure 9A.
[Figure 9C] Figure 9C is an explanatory diagram to show a stage in which the
punch has been hlly retreated with respect to the die from the state of Figure 9B.
[Figure 10A] Figure 10A is a perspective view to sho~van exanlple of a cu~vedpa rt
having a hat-shaped cross section which is produced by applying the present
invention.
[Figure IOB] Figure 10B is a plan vie137 seen from the above of the curved part
sho~vnin Figure 10A.
[Figure 10C] Figure 10C is a side view of the cul-ved part sho~vnin Figure 10A.
[Figure 10D] Figure 10D is a cross-sectional view of A-A in Figure 10C.
[Figure 1 11 Figure 11 is an explanatory diagram to show a clearance b in Table 1.
[Figure 12AJ Figure 12A is a perspective view to show another exanlple of the
curved part having a hat-shaped cross section, which is produced by applying the
present invention.
[Figure 12B] Figure 12B is a plan view seen from above of the curved part shown
in Figure 12A.
[Figure 12C] Figure 12C is a side view of the cu~vedp art shown in Figure 12A.
[Figure 12D] Figure 12D is a front view seen from one end of the curved part
sho~vnin Figure 12A.
[Figure 13A] Figure 13A is a perspective view to show another example of the
curved part having a hat-shaped cross section, which is produced by applying the
present invention.
[Figure 13B] Figure 13B is a plan view seen from above of the curved part shown
in Figure 13A.
[Figure 13C] Figure 13C is a side view of the curved past shown in Figure 13A.
[Figure 13D] Figure 13D is a front view seen fiom one end of the curved part
shown in Figure 13A.
[Figure 14A] Figure 14A is a perspective view to show a further example of the
curved part having a hat-shaped cross section, which is produced by applying the
present invention.
[Figure 14B] Figure 14B is a plan view seen from above of the curved part shown
in Figure 14A.
[Figure 14C] Figure 14C is a side view of the curved part shown in Figure 14A.
[Figure 14D] Figure 14D is a front view seen from one end of the curved part
shown in Figure 14A.
[Figure 15A] Figure 15A is a perspective view to show a further exalnple of the
curved part having a hat-shaped cross section, ~vhichis produced by applying the
present invention and in ~vhicho utnrardly directed flanges are extended fro111a part
of the entire length.
[Figure 15BJ Figure 15B is a plan view seen fro111 above of the curved part sho~vn
in Figure 15A.
[Figure 15C] Figure 15C is a side view of the curved part shown in Figure 15A.
[Figure 15DJ Figure 15D is a front vie~vs een fro111 one end of the curved part
sho~vnin Figure 15A.
[Figure 16AJ Figure 16A is a perspective view of a curved part, which is a further
example of the culved part having a hat-shaped cross section and produced by
applying the present invention, and in which a top plate is enlarged fiom one end to
the other end.
[Figure 16B] Figure 16B is a plan view seen from above of the curved part shown
in Figure 16A.
[Figure 16C] Figure 16C is a side view of the curved part shown in Figure 16A.
[Figure 16DJ Figure 16D is a front view seen from one end of the curved part
shown in Figure 16A.
[Figure 17A] Figure 17A is an explanatory diagram of the method of the present
invention for producing a curved part by using a preworked blank, showing a
perspective view of the metal material sheet to be used in this method.
[Figure 17B] Figure 17B is a perspective view to sho~va state in which the metal
material sheet shown in Figure 17A is preworked.
[Figure 17C] Figure 17C is a perspective view of a cullred part which is formed
from the preworked metal material sheet shown in Figure 17B.
[Figure 17D] Figure 17D is a perspective view to show the curved part sho~vnin
Figure 17C as being further trimmed.
[Figure 18A] Figure 18A is a perspective view to show an exanlple of a culved part
having a hat-shaped cross section.
[Figure 18B] Figure 18B is a top view of the curved part.
[Figure 18C] Figure 18C is a side view of the curved part.
[Figure 18D] Figure 18D is a front view of the curved part seen froin one end
thereof.
[Figure 18E] Figure 18E is a perspective view to explain a convex curved portion
and a concave cullred portion of the curved part.
[Figure 19A] Figure 19A is a cross-sectional vie\v to schematically show a dranring
machine for producing a curved part by prior art.
[Figure 19B] Figure 19B is a cross-sectional view to sho~va stage in which a nletal
~llaterials heet is interposed and constrained behveen a die and a blank holder and
behveen the die and a punch.
[Figure 19C1 Figure 19C is a cross-sectional view to sho\v a stage in which the
punch is further pushed inward from the stage slio\\rn in Figure 19B.
[Figure 19D] Figure 19D is a cross-sectional view to show a stage in which the
punch is further pushed inward from the stage shown in Figure 19C to be fully
pushed inward with respect to the die.
[Figure 20A1 Figure 20A is a perspective view to show a metal material sheet.
[Figure 20B] Figure 20B is a perspective view to show a drawn panel which is
produced by prior art sho~vnin Figures 19A to 19D.
[Figure 211 Figure 21 is a perspective view to show regions of the drawn panel
shown in Figure 20B, where cracks and wrinkles are likely to occur.
Reference Signs List
[OO 181
10 Curved part
11 Top plate
12a Vertical wall
12b Vertical wall
13a Flange
13b Flange
14a Ridgeline
14b Ridgeline
15a Concave line
15b Concave line
502 Die
503 Pad
504 Punch
505 Blank holder
506 Pad pressurizing apparatus
507 Blank holder pressurizing apparatus
Description of Embodin~ents
[0019] The present invention \vill be described ~vithre ference to the appended
dran~ings.
According to the present invention, a curved part 10 sho\vn in Figures 18A to
18E can be produced.
As sho\vn in Figures 18A to 18E, the curved part 10 has a hat-shaped crosssectional
shape which is made up of a top plate 11, vertical walls 12a and 12b which
respectively connect to both side edges of the top plate 11, and outwardly directed
flanges 13a and 13b which connect to the side edges of the vertical walls 12a and
12b opposite to the side edges connecting to the top plate and extend in the opposite
direction to that of the top plate 11.
[0020] Ridgelines 14a and 14b are formed behveen the top plate 11 and the
vertical walls 12a and 12b. Moreover concave lines 15a and 15b are forlned
behveen the vertical wall 12a, 12b and the outwardly directed flange 13a, 13b.
The ridgelines 14a and 14b and the concave lines 15a and 15b are disposed
substantially in parallel. The top plate 11 has a convex cuwed portion 1 la ~vhich
is curved in an arc shape toward the outside (the external side of the top plate 11) of
the hat-shaped cross-sectional shape, and a concave cullred poition 1 1 b which is
curved in an arc shape toward the inside (the internal side of the top plate 11) of the
hat-shaped cross-sectional shape.
[0021] The ridgeline 14a forlned by the top plate 11 and the vertical wall 12a is
curved in an arc shape in regions 16a and 17a corresponding to the convex cunred
portion 1 la and the concave curved portion 1 lb, and also the ridgeline 14b formed
by the top plate 11 and the vertical wall 12b is cullred in an arc shape in regions 16b
and 17b corresponding to the convex curved portion 11 a and the concave curved
portion llb. That is, the curved part 10 takes on an S-shape in the side view as
shown in Figure 18C, and in other ~vordst,h e vertical walls 12a and 12b are formed
of S-shaped flat plates.
[0022] Here, the tern1 "arc shape" is not limited to a part of a conlplete circular arc,
arid niay be, for exalnl~lea, part of an ellipse, hyperbola, sine curve, and other
curves.
Thus, the curved part 10 has a main body 10a. The main body 10a has a
hat-shaped cross sectional shape which is made up of: the elol~gatedto p plate 11,
the hvo vertical ~valls1 2a and 12b which connect to both side edges of the top plate
I I and extend in a direction substantially perpendicular to the top plate 11, and t\vo
ouhvardly directed flanges 13a and 13b ~vhichc onnect to the hvo vertical ~valls1 2a
and 12b, respectively. Further, the main body 10a has an external shape in which
each of the top plate 11, the hvo vertical walls 12a and 12b, and the two outwardly
directed flanges 13a and 13b is cullred in an arc shape in a height direction of the
vertical wall 12a, 12b in a poitioti in the lengthwise direction of the top plate 11.
LO0231 Figure 1 is a perspective view to show in a simplified and exploded
fashion a press-forming apparatus 501 for carlying out the production method
relating to the present invention to produce a curved past 10. As sho~vnin Figure
1, the press-forming apparatus 501 has a die 502, a pad 503, a punch 504, and a
blank holder 505.
[0024] The die 502 has an internal shape which includes the respective external
shapes of the vertical wall 12a, 12b and the flange 13a, 13b of the curved part 10.
The pad 503 has an external shape including the external shape of the top plate 11
of the curved part 10. The punch 504 is disposed in opposition to the die 502 and
the pad 503, and has an external shape including respective internal shapes of the
top plate 11 and the vertical wall 12a, 12b of the curved part 10. Further, the blank
holder 505 has an external shape which includes the internal shape of the flange 13a,
13b of the curved part 10.
[0025] Figure 2A is a simplified cross-sectional view to show a state at the start of
processing by the press-forming apparatus 501. Figure 2B is a simplified crosssectional
view to show a state in which a metal material sheet 601 is interposed and
constrained behveen the die 502 and the holder 505, and behveen the pad 503 and
the punch 504 in the press-fonning apparatus 501. Figure 2C is a sitnplified crosssectional
view to show a state in which the punch 504 is pushed inward from the
stage shown in Figure 2B. Figure 2D is a simplified cross-sectional view to show
a state it1 ~vl~icthhe punch 504 is further pushed inward from the stage s h o ~ ~in n
Figure 2C so that the punch 504 is fully pushed inward with respect to the die 502.
[0026] As sho~vnin Figures 2A to 2D, the pad 503 is connected to and suppo~ted
by a pad pressurizing apparatus 506 including a gas cushion, a hydraulic apparatus,
a spring or an electric drive apparatus, and is able to pressurize a metal material
sheet 601 to press it against the top portion of the punch 504.
[0027] Moreover, the blank holder 505 is cotu~ectedto and supported by a blank
holder pressurizing apparatus 507 including a gas cushion, a hydraulic apparatus, a
spring or electric drive apparatus, and is able to pressurize the 111etal material sheet
601 to press it against the die 502.
[0028] First, as shown in Figure 2A, the metal material sheet 601 is placed
behveen the die 502 and the blank holder 505, and behveen the pad 503 and the
punch 504.
Next, as shown in Figure 2B, the portion of the metal material sheet 601
which is to be formed into the top plate 11 is pressed against the punch 504 by
means of the pad 503, thereby being pressurized and interposed behween the both.
Moreover, the portions of the metal material sheet 601 which are to be for~ned
respectively into the vertical ~valls1 2a and 12b and the ouhvardly directed flanges
13a and 13b are pressed against the die 502 by means of the blank holder 505,
thereby being pressurized and interposed between the both.
[0029] As a result of that the portion of the metal material sheet 601 which is to
be formed into the top plate 10 is pressed against the punch 504 by means of the
pad 503 which is pressurized by the pad pressurizing apparatus 506, and is thereby
pressurized and interposed behveen the both, the metal material sheet 601 is held in
a state in which out-of-plane defortllatio~ils inhibited. Moreover, as a result of
that the portions of the metal material sheet 601 which are to be formed respectively
into the vertical walls and the outwardly directed flanges are pressed against the die
502 by means of the blank holder 505 which is pressurized by the blank holder
pressurizing apparatus 507, and is pressurized and interposed bet~veenth e both, the
metal material sheet 601 is held in a state in which out-of-plane defor~natioits~
inhibited.
[0030] By nloving the blank holder 505 and the die 502 in this state to a side,
where the punch 504 and the blank holder 505 are disposed with the ~netaml aterial
sheet 601 as a boundary, relatively with respect to the pad 503 and the punch 504,
the metal nlaterial sheet 60 1 is for~ned.
[0031] As sho~vnin Figure 2C, as the punch 504 and the blank holder 505 1110\7e,
the metal nlaterial sheet 601 interposed bet~veenth e punch 504 and the blank holder
505 flo~vsto inside the die 502, and thereby the vertical walls 12a and 12b are
for~ned.
[0032] Then, as sho~vnin Figure 2D, the forn~ingis completed at a stage in \vhich
the punch 504 and the blank holder 505 have moved a predeternlined distance to
ensure the necessarj~h eight of the vertical ~valls1 2a and 12b.
Here, in the exanlple shown in Figures 2A to 2D, the die 502 is pushed
inward in a state in which the punch 504 is fixed, and the pad 503 presses the metal
material sheet 601 to the punch 504 thereby being ilntnobile during the process of
forming. However, the present invention will not be limited to this embodiment.
[0033] Figure 3 is a perspective view to show in a simplified and exploded
fashion another press-forming apparatus 501- 1 for carrying out the production
method relating to the present invention to produce a curved part 10. Moreover,
Figure 4A is a simplified cross-sectional view to show a state at the start of
processing by the press-fonning apparatus 501-1 shown in Figure 3; Figure 4B is a
sitnplified cross-sectional view to show a state in which the metal material sheet
60 1 is interposed and constrained behveen a die 602 and a holder 605, and between
a pad 603 and a punch 604 of the press-fonning apparatus 501-1 shown in Figure 3;
Figure 4C is a sinlplified cross-sectional view to show a state in which the punch
604 is pushed inward fiom the stage shown in Figure 4B; and Figure 4D is a
simplified cross-sectional view to show a state in which the punch 604 is further
pushed inward from the stage shown in Figure 4C and thereby the punch 604 is
fully pushed inward with respect to the die 602.
[0034] In contrast to the example shown in Figure I and Figures 2A to 2D, it is
also possible to move the blank holder 605 and the die 602 relatively with respect to
the pad 603 and the punch 604 to the side where the punch 604 and the blank holder
605 are disposed with the metal material sheet 601 as a boundary by pushing the
punch 604 inward thereby nloving the pad 603 together with the puncll604 in a
state in which the die 602 is fixed, and the blank holder 605 presses the metal
material sheet 601 to the die 602 thereby being iln~nobilea s shorvn in Figure 3 and
Figures 4A to 4D. That is, the example SIIOTV~I ill Figure 3 and Figures 4A to 4D is
the same as one sho~vnin Figure 1 and Figures 2A to 2D with regard to the relative
movement of the n~etaml old, and can form the metal material sheet 601 into the
curved part 10 in1 the sallle manner.
[0035] Since the portion of the lnetal ~llaterials heet 601 \vhic11 is to be forllled
into the top plate 1 1 is pressurized and interposed by the pad 503 and the punch 504
~vhileth e vertical ~valls1 2a and 12b are forll~edo, ut-of-plane defor~natiollw ill not
occur in the llletal lnaterial sheet 60 1 if the pressurizing force is sufficient, and it is
possible to co~llpletelyp revent the occurrence of ~vrinkles. Moreover, the portions
of the lnetal lnaterial sheet 601 which are to be fornled into the flanges 13a and 13b
are also pressurized and interposed by the blank holder 505 and the die 502, out-ofplane
deforlnation will not occur in the metal material sheet 601 if the pressurizing
force is sufficient, and it is possible to coinpletely prevent the occurrence of
wrinkles.
[0036] When the above mentioned pressurizing force is insufficient, the out-ofplane
deformation of the metal lnaterial sheet 601 cannot be prevented, and
wrinkles will occur. When the metal material sheet 601 is a steel sheet having a
sheet thickness: not less than 0.8 lnln and not more than 3.2 mm, and a tensile
strength: not less than 200 MPa and not Inore than 1600 MPa, which is corm~lonly
used as a skeleton structure inember of a body shell of automobile, such as a side
member (a front side Inember and a rear side member) etc., the above mentioned
pressurizing force is desirably not less than 0.1 MPa.
[0037] Figure 5A is an explanatory diagram to show the principle of the present
invention, Figure 5B is a perspective view to sho~vsh ear wrinkles which rnay occur
when carrying out the present invention, and Figure 5C is a side view to show shear
wrinkles which may occur when carrying out the present invention.
[0038] In the present invention, portions of the lnetal nlaterial sheet 601 which are
to be formed into the vertical ~valls 12a and 12b are, a portion which is to be formed
into the top plate 11 is pressurized and interposed by the pad 503 and the punch 504.
Moreover, portions which are to be formed into the flanges 13a and 13b are also
pressurized and interposed by the blank holder 505 and the die 502. Further, any
of the portion to be formed into the top plate 11, the portions to be formed into the
vertical walls 12a and 12b, and the portions to be for~nedin to the outwardly
directed flanges 13a and 13b is formed so as to be cunled in an arc shape in a height
direction of the vertical ~vall1 2a, 12b. As a result of this, the portions to be
forrned into the ve~ticawl alls 12a and 12b are subjected to shear deformation as
sho~vnin Figure 5A. Therefore, according to the present invention, the metal
nlaterial sheet 601 can be formed into the curved part 10 through the plastic
defonnation in ~vhichs hear defornlation of the portions to be fornled into the
vertical \valls 12a and 12b is dominant. Since shear defor~nationis defor~nation
\vllich exhibits very small anlount of area change, and therefore very s~nall
thich~essc hange between before and after the deformation, decrease in the sheet
thickness of the vertical ~valls 12a and 12b of the curved part 10 is suppressed.
[0039] Further, although the portions to be formed into the top plate 11 and the
ouhvardly directed flanges 13a and 13b are bent out of plane, since they are not
subjected to large tensile deformation and colnpressive deformation, decrease in the
sheet thickness is also suppressed for the portions of the top plate 11 and the
outwardly directed flanges 13a and 13b, resulting in suppression of decrease in the
sheet thickness as the entire curved part 10.
[0040] Moreover, since the portions of the metal material sheet 601 to be formed
into the vertical walls 12a and 12b are subjected to shear deformation, they will
undergo colnpressive deformation in a lnini~nu~prni ncipal strain direction of shear
deformation ~vhileth e vertical walls 12a and 12b are formed. Therefore, if the
clearance of the vertical wall portions of the die 502 and the punch 504 is excessive,
shear wrinkles 18 occur as shown in Figures 5B and 5C. To suppress the
occurrence of such shear ~vrinkles 18, it is effective to set the clearance between the
die 502 and the punch 504, vvl~ichis the clearance at the portions for forming the
vertical walls 12a and 12b, to be small and close to the thickness of the metal
material sheet 601, while the vertical walls 12a and 12b are fonned.
(004 11 Figure 6A is an explanatory diagram to show conditions to prevent the
occurrence of shear wrinkles 18, by showing an interior angle 0 forrned by the
vertical wall 12a, 12b and the top plate 11, and a clearance b at a portion where the
vertical wall 12a, 12b is fornled, which is a clearance between the die 502 and the
punch 504. Figure 6B is an explanatory diagram to show conditions to prevent the
occurrence of shear wrinkles, by showing an interior angle 0 formed by the vertical
wall 12a, 12b and the top plate 11, and a clearance b at a portion ~vhereth e vertical
nrall 12a, 12b is formed, ~vhichis a clearance between the die 502 and the punch
504.
[0042] As shown in Figures 6A and 6B, the interior angle 8 fortned by the vertical
\vall 12a, 12b and the top plate 11 needs to be not less than 90" such that the interior
angle 8 does not form a negative angle of the tnetal ~nolda t the time of forming.
However, if the interior angle 8 is excessively larger than 90°, the clearance at an
early stage of fornling becon~esla rge. For this reason, it is advantageous that the
interior angle 8 is not less than 90" and not nlore than an angle ~vhichis as close as
possible to 90°. For example, taking a case as an example in \vhich a steel sheet
having a sheet thickness: not less than 0.8 nnn and not more than 3.2 mm, and a
tensile strength: not less than 200 MPa and not tnore than 1600 MPa, which is
commonly used as a skeleton structure member of a body shell of automobile, such
as a side member (a front side member and a rear side member) etc. is used as the
metal tnaterial sheet 601 to for111 a culved part 10 of which the height of the vertical
wall 12a, 12b is not more than 200 mtn, when the interior angle 8 is more than 92",
wrinkles may occur on the vertical walls 12a and 12b as shown in Figure 6B, and
therefore it is desirable that the interior angle 8 formed by the top plate 11 and the
vertical wall 12a, 12b is not less than 90" and not tnore than 92", and that a
clearance b at the portion for forming the vertical wall 12a, 12b, ~vhichis a
clearance between the die 502 and the punch 504 at the time when the forming of
vertical wall 12a, 12b is comnpleted, is not less than 100% and not more than 120%
of the sheet thickness of the tnetal nlaterial sheet 601.
[0043] Figure 7A is an explanatory diagratn to show defects which may occur
when the cullred part 10 is taken out from the metal mold after the punch 504 is
fully pushed inward the die 502, thereby forming the tnctal lnaterial sheet 601 into
the curved part 10; Figure 7B is an explanatory diagratn to show a stage in which
the punch 504 is retreated with respect to the die 502 fiom the state shown in Figure
7A; and further Figure 7C is an explanatory diagram to show a stage in which the
punch 504 has been filly retreated with respect to the die 502 from the state shown
in Figure 7B.
[0044] As shown in Figure 7A to 7C, if the die 502 is separated from the punch
504 to make a gap between the tnetal molds to take out the curved part 10 from the
tnetal tnolds after fortning the tnetal material sheet 601 into the curved part 10,
since the pad 503 and the blank holder 505 are respectively pressurized by the pad
pressurizing apparatus 506 and the blank holder pressurizing apparatus 507, the
curved part 10 is subjected to pressurizing forces in opposite directions fro111 the
pad 503 and the blank holder 505 respectively, and is thereby defortned and crushed
so that a curved part 10 of a predeter~llined shape will not be achieved.
[0045] Figure 8A is an ex plat la tor)^ diagram to sho~ira nlethod for solving defects
shown by Figures 7.4 to 7C; Figure 8B is an explanatory diagram to sho~va stage in
~vhictlh~e punch 504 is retreated with respect to the die 502 fro111 the state shown in
Figure 8A; and further Figure 8C is an explanatory diagram to show a stage in
which the punch 504 has been fully retreated with respect to the die 502 from the
state shown in Figure 8B.
[0046] If after the metal nlaterial sheet 601 is formed into the curved part 10, the
die 502 and the pad pressurizing apparatus 506 are separated from the blank holder
505 in a state in which the blank holder 505 is fixed so as not to move relative to the
punch 504 and the blank holder 505 does not press the curved part 10 which has
been formed against the die 502, as shown in Figures 8A to SC, although the pad
503 pressurizes the curved part 10 until the pad pressurizing apparatus 506 extends
to an stroke end, when the pad pressurizing apparatus 506 moves not less than a
fixed distance and the pad pressurizing apparatus 506 extends out to the stroke end,
the pad 503 thereafter departs from the punch 504, so that the die 502 and the pad
503 can be departed from the blank holder 505 and the punch 504 without the
curved part 901 being subjected to pressurization from the pad 503 and the blank
holder 505 at the same time, and thereby the culved part 10 can be taken out from
the inetal molds.
[0047] Figure 9A is an explanatory diagraln to show another method for solving
the defects shown by Figures 7A to 7C; Figure 9B is an explanatory diagram to
show a stage in which the punch is retreated with respect to the die from the state
shown in Figure 9A; and further Figure 9C is an explanatory diagram to show a
stage in which the punch has been fully retreated with respect to the die fkom the
state of Figure 9B.
[0048] If, after the metal material sheet 601 is formed into the curved part 10, the
pad 503 and the die 502 are separated from the blank holder 505 and the punch 504
in a state in which the pad 503 is fixed so as not to relatively tnove with respect to
the die 502, and is arranged so as not to press the curved part 10 against the punch
504, as shown in Figures 9A to 9C, the blank holder 505 ~vilpl ressurize the cullled
part 10 until the blank holder pressurizing apparatus 507 extends to the stroke end;
ho~~evwehre n the die 502 inoves not less than a predeter~niaedd istance, and the
blank holder pressurizing apparatus 507 extends out to the stroke end, tllereafter the
blank holder 505 departs fronl the die 502, and the cun~edp art 10 not being
sub-jected to pressurization from the pad 503 and the blank holder 505 at the sanle
tin~eso that the die 502 and the pad 503 can be separated froln the blank holder 505
and the punch 504, and thereby the curved part 10 can be taken out from the metal
molds.
[0049] Figure 10A is a perspective view to show an exatnple of a cullred part 100
which is produced by applying the present invention; Figure 10B is a plan view
seen fsom the above of the culved part 100; Figure 10C is a side view of tlle curved
part 100; and Figure 10D is a cross-sectional view of A-A in Figure C. Further,
Figure 11 is an explanatory diagram to show a clearance b in Table 1 described
below.
[0050] In Figures 10A to 10D, a reference sytnbol lOOa denotes a main body,
reference symbol 11 1 a top plate, reference synlbols 112a and 112b vertical walls,
and reference sj~~nbo1l1s3 a and 113b outwardly directed flanges. Table 1 sho~vs
various examples, in which curved part 100 shown in Figures IOA to 1OD is
produced, in summary.
In Table 1, an angle 8 is an interior angle 0 formed by the vertical wall 112a,
112b and the top plate 1 11 as sho\vn in Figure 10D, and a clearance b is a gap
between the pad 503 and the punch 504, behveen the die 502 and the punch 504, or
between the die 502 and the blank holder 505.
[Table 11

[0052] Any of Exanlples 1 to 19 ill Table 1 is an inventive example of the present
invel~tiona, nd "occurrence of wrinkles" in Table 1 indicates that wrinkles have
occurred at an allo\vable level, in wliich (1) Exanlples 1 to 5 are exanlples in which
the angle f3 of the vertical ~vall1 12a, 112b is varied; (2) Examples 6 to 9 are
examples in ~vhichth e sheet thickness t is varied with respect to the clearance of the
metal molds, Inore specifically, a constant clearance b, (3) Exanlples 10 to 13 are
examples in which the pressure (pad pressure) to be applied to the pad 503 is varied,
(4) Examples 14 to 16 are exan~plesin which the pressure to be applied to the blank
holder 505 is varied, and (5) Examples 17 to 19 are exanlples in which the tensile
strength of the nlaterial is varied. The occurrence of wrinkles in the curved part
100 produced in each Example was verified.
[0053] Figure 12A is a perspective view to show another example of a curved part
110 which is produced by applying the present invention; Figure 12B is a plan view
seen from above of the curved part 110; Figure 12C is a side view of the curved part
110; and further Figure 12D is a front view seen from one end of the curved part
shown in Figure 12A.
[0054] As shown in Figures 12A to 12D, the curved part 110 includes: a top plate
112; vertical walls 114 and 116 extended in parallel with each other along ridgelines
112a and 1 12b of the top plate 112; and out~vardlyd irected flanges 118a and 1 18b
which respectively connect to leading edges of the vertical walls 114 and 116; and
has a generally hat-shaped cross section.
[0055] Moreover, the top plate 112 forms a cu~vedsu rface which does not lie in
one plane and is curved in a substantially S-shape. The ouhvardly directed flanges
1 l8a and 118b are extended substantially in parallel with the top plate 112, and as
in the top plate 112, forms a curved surface which does not lie in one plane and is
cumed in a substantially S-shape. The vertical wails 114 and 116 form a curved
surface which does not lie in one plane and is curved in a substantially S-shape.
[0056] Figure 13A is a perspective view to show another example 120 of the
curved part, which is produced by applying tic present invention, Figure 13B is a
plan view seen from above of the curved part 120, Figure 13C is a side view of the
curved part 120, and further Figure 13D is a front view seen from one end of the
curved part 120.
[0057] As sl~oo\vnin Figures 13A to 13D, the curved part 120 includes: a top plate
122; vertical walls 124 and 126 extended in parallel ~vithe ach other along ridgelines
122a and 122b of the top plate 122; and ouhvardly directed flanges 128a and 128b
which respectively connect to leading edges of the vertical walls 124 and 126, and
has a shape curved to the upper side in a side view as sho\vn in Figure 13C, that is,
an ouhvardly bulged shape. The top plate 122 fornls a curved surface ~vhichd oes
not lie in one plane and is curved ouhvardly, and the out~vardlyd irected flanges
128a and 128b are extended substantially in parallel with the top plate 122. The
vertical walls 124 and 126 are made up of flat plates which are parallel with the
page face of Figure 13C.
[0058] Figure 14A is a perspective view to sho~va further example 130 of the
curved part, which is produced by applying the present invention, Figure 14B is a
plan view seen from above of the curved part 130, Figure 14C is a side view of the
curved part 130, and Figure 14D is a front view seen from one end of the curved
past 130.
[0059] As shown in Figures 14A to 14D, the curved part 130 has, in contrast to
the curved part 120 shown in Figures 13A to 13D, a shape which is curved to the
lower side in a side view, that is, an inwardly concave shape. The curved part 130
includes: a top plate 132; vertical walls 134 and 136 extended in parallel with each
other along ridgelines 132a and 132b of the top plate 132; and ouhvardly directed
flanges 138a and 138b \vl~icrle~s pectively connect to leading edges of the vertical
walls 134 and 136, and has a shape curved downwardly in a side view as shown in
Figure 14C, that is, an in~vardlyc oncave shape. The top plate 132 forms a culved
surface which does not lie in one plane and is culved inwardly. The ouhvardly
directed flanges 138a and 13% are extended substantially in parallel with the top
plate 132. The vertical walls 134 and 136 are made up of flat plates which are
parallel with the page face of Figure 14C.
[0060] Figure 15A is a perspective view to show a further exalilple of the curved
part 140, which is produced by applying the present invention and in which
outwardly directed flanges 148a and 148b are extended from a part of the entire
length of the cullred part, Figure 15B is a plan view seen from above of the curved
part 140, Figure 15C is a side view of the curved part 140, and further Figure 15D is
a front view seen from one end of the cul-ved part 140.
[0061] As sho~vnin Figures 15A to 15D, the curved part 140 includes: a top plate
142; vertical walls 144 and 146 extended in parallel ~vithe ach other along ridgelines
142a and 142b of the top plate 142; and ouhvardly directed flanges 148a and 148b
\vhich respectively connect to leading edges of the vertical ~valls1 44 aud 146, and
has a generally hat-shaped cross section. Moreover, the top plate 142 for~nsa
curved surface ~vhichd oes not lie in one plane and is cullred in a substantially Sshape.
The outwardly directed flanges 148a and 148b are extended substantially in
parallel with the top plate 142, and as in the top plate 142, form a curved surface
which does not lie in one plane and is curved in a substantially S-shape. The
vcrtical walls 144 and 146 also form a curved surface which does not lie in one
plane and is curved in a substantially S-shape.
[0062] The curved part 140 is different from the curved part 110 shown in Figures
12A to 12D in that the ouhvardly directed flanges 148a and 148b are not extended
over the entire length of the vertical walls 144 and 146. That is, the vertical walls
144, 146 include a portion which does not include the out~vardlyd irected flange
148a, 148b. In Figures 15A to 15D, the ouhvardly directed flange 148a, 148b has
a length shorter than the length of the vertical walls 144, 146, from one end of the
curved part 140 and along a loxver edge portion of the vertical ~valls1 44, 146.
Further, although the ouhvardly directed flanges 148a and 148b may be configured
to lave the same length, they may also have different lengths as shown in Figures
15B and 15D.
[0063] The curved part 140 is suitably used as a rear side member which is an
example of skeleton structure ~nenlbersc onstituting a body shell of automobile.
The curved part 140 includes a main body 140a.
The inail1 body 140a has a hat-shaped cross sectional shape which is made up
of: an elongated top plate 142,hvo vertical walls 144 and 146 which connect to
both side edges of the top plate 142 and extend in a direction substantially
perpendicular to the top plate 142, and two outwardly directed flanges 148a and
148b which connect to a pait of each of the two vertical walls 144 and 146,
respectively.
[0064] Moreover, the main body 140a exhibits an external shape includiug a
curved portion 149a in ~vhiche ach of the top plate 142, the two vertical ~valls1 44
aud 146, and the hvo ouhvardly directed flanges 148a and 148b is curved in an arc
shape in a height direction of the vertical walls 144, 146 in a portion in the
length~vised irection of the top plate 142.
[0064] The inain body 140a is a cold or nrarin press-forined body, ~i41ichu ses a
steel sheet having a tensile strength of not less than 440 MPa and a sheet thickness
of 1 .0 to 2.3 111111 as the material.
The reduction rate of the sheet thickness of the cuwed portion 149a with
respect to that of a remaining portion 149b except the cuived portion 149a is not
more than 15%.
[0065] To produce a curved member 140 by a press-forming method based on the
conventional draw-forming which has been described with reference to Figures 18
to 21, a low strength steel sheet having a tensile strength of not more than 400 MPa
has to be used as the material, and the reduction rate of the sheet thickness of the
curved portion 149A with respect to that of the re~nainingp ortion 149b excepting
the curved poi-tion 149a is about 20 to 35% which is very large. Although, for this
reason, reinforcement of the curved portion 149a such as adding a reinforcing
member has been needed, the curved inember 140 obtained by the present invention
has enough strength to obviate the need of reinforcing the curved portion 149a,
since it can use a steel sheet having a tensile strength of not less than 440 MPa and a
sheet thickness of 1.0 to 2.3 inln as the material, and the above described reduction
rate of the sheet thickness is significantly suppressed to be not Inore than 15%.
[0067] Figure 16A is a perspective view of a curved part 150, which is a further
example of the curved past produced by applying the present invention, and in
which a top plate 152 is enlarged from one end to the other end, Figure 16B is a
plan view seen from above of the curved part 150, Figure 16C is a side view of the
curved part 150, and Figure 16D is a front view seen fsom one end of the curved
part 150.
[0068] As shown in Figures 16A to 16D, the curved part 150 includes: a top plate
152; vertical walls 154 and 156 extended in parallel with each other along ridgelines
152a and 152b of the top plate 152; and outwardly directed flanges 158a aud 158b
which respectively connect to leading edges of the vertical \valls 154 and 156, and
exhibits a substantially S-shape in a side view. The top plate 152 for~nsa curved
surface nrhich does not lie in one plane and is curved in a substantially S-shape.
The ouhvardly directed flanges 158a and 158b are extended substantially in parallel
n~ithth e top plate 152, and as in the top plate 152, fortlls a cullred surface which
does not lie in one plane and is curved in a substantially S-shape. Each of the
vertical ~valls1 54 and 156 is curved in a substantially S-shape in a plane parallel
with the page face of Figure 21C. Although the ~vidtho f the top plate 12 is
constant in the lengthwise direction in the curved part 10 of Figures 18A to 18E,
that of the top plate 152 is enlarged fiom one end toward the other end of the culved
part 150, in the curved part 150 of Figures 16A to 16D.
[0069] Figure 17A is an explanatory diagram of the method of the present
invention for producing a curved part 70 by using a pre~vorkedb lank, showing a
perspective view of the nletal material sheet 72 to be used in this method, Figure
17B is a perspective view to show a state in which the metal material sheet 72 is
preworked, Figure 17C is a perspective view of a cullred part which is formed from
the preworked metal material sheet, and further Figure 17D is a perspective view to
show the curved part shown in Figure 17C as being further trimmed.
[0070] Further, in the present invention, the metal material sheet may be
preworked, and thereafter the preworked metal material sheet may be press-formed
by the above described method.
For example, the metal material sheet 72, which is cut out into a
predetermined shape as shown in Figure 17A, is preworked to form a plurality of
seat surfaces 74 as shown in Figure 17B, and thereafter the metal material sheet 72
having the plurality of seat surfaces 74 is press-formed into a press-formed body 76
by the above described method as shown in Figure 17C.
[0071] Since, in the above described process, the top plate poition is pressed
against the punch with the pad, it is preferable, to prevent the preworked seat
surfaces 74 from being defonned, to providc shapes corresponding to seat surfaces
74 on each of the pad and the punch so that the metal material sheet can be
pressurized and interposed without causing the seat surfaces 74 to be deformed.
Moreover, after press-folming, post working such as trimlning map be performned to
obtain a comnplete product 70 as sho~vmin Figure 17D.
1. A nlethod for producing a curved part by cold or warm press-forming a nletal
inaterial sheet by using a press-forming apparatus including a die and a pad, and a
punch and a blank holder which are disposed to be opposed to the die and the pad,
the curved part conlprising a main body having: a hat-shaped cross section ~vhichis
made up of an elongated top plate, hvo vertical ~vallsc onnecting to both side edges
of the top plate and extending in a direction substantially perpendicular to the top
plate, and h i 7 0 out\vardly directed flanges which connect to the two vertical \~~alls
respectively; and an external shape in which each of the top plate, the hvo vertical
walls and the two outwardly directed flanges is cullred in an arc shape in a height
direction of the vertical walls in a portion in a lengthwise direction of the top plate,
wherein the curved part is formed by moving the blank holder and the die
relatively with respect to the pad and the punch to a side where the punch and the
blank holder are disposed while maintaining a state in which a portion to be fonned
into the top plate in the metal material sheet, which is disposed behveen the die and
the blank holder, and behveen the pad and the punch, is pressed against the punch
with the pad so as to be pressurized and interposed, and portions to be formed into
the vertical walls and the outwardly directed flanges in the metal material sheet are
pressed against the die with the blank holder so as to be pressurized and interposed.
2. The method for producing a cullred part according to claim 1, wherein the
pad is connected to a pad pressurizi~lga pparatus having a fixed stroke, and the
blank holder is connected to a blank holder pressuriziilg apparatus, and wherein
after co~npletiono f the forming of the curved part,
the die and the pad are separated kom the blank holder and the punch to take
out the cullred part from the press-forming apparatus, after the blank holder is fixed
so as not to relatively move with respect to the punch and is arranged so as not to
press the curved part against the die, by using the pad pressurizing apparatus and the
blank holder pressurizing apparatus.
3. The nlethod for producing a curved part according to claitn I, ~vhereinth e
pad is connected to a pad pressurizing apparatus, and the blank holder is connected
to a blank holder pressurizing apparatus having a fixed stroke, and wherein after
co~npletiono f the forlning of the cunied part,
the die and the pad are separated fro111 the blank holder and the punch to take
out the curved part frotn the press-for~ninga pparatus, after the pad is fixed so as not
to relatively move \\pith respect to the die and is arranged so as not to press the
curved part against the punch, by using the pad pressurizing apparatus and the blank
holder pressurizing apparatus.
4. The method for producing a curved part according to any one of claims I to 3,
wherein
the die has an internal shape including shapes of outer surfaces of each of the
vertical walls and the flanges in the curved part, the pad has an exterior shape
includitlg a shape of an outer surface of the top plate in the curved part, the punch
has an external shape itlcluding shapes of inner surfaces of each of the top plate and
the vertical walls in the cullred part, and the blank holder has an external shape
including shapes of inner surfaces of the flanges in the curved part.
5. The method for producing a culved part according to any one of claims 1 to 4,
wherein an interior angle formed by the top plate and the vertical wall in the cross
sectional shape is 90 to 92'.
6. The method for producing a cu~~lepadr t according to any one of claims 1 to 5,
wherein a clearance between a portion in the die w~hichf orms the vertical wall and a
portion in the punch which forms the vertical wall is 100 to 120% of the sheet
thickness of the nletal material sheet at the time of completing the formation of the
curved part.
7. The lnethod for producing a curved part according to any one of claims 1 to 6,
wherein the metal material sheet is a steel sheet having a sheet thichiess of 0.8 to
3.2 tnm and a tensile strength of 200 to 1600 MPa.
8. The inetl~odfo r producing a curved pait according to any one of clainls 1 to 7,
~vhereina portion of the inetal inaterial sheet to be formed into the top plate is
pressurized by being pressed against the punch at a pressing pressure of not less
than 0.1 MPa by the pad, and a portion of the nletal inaterial sheet to be formed into
the vertical wall and the ouhvardly directed flange is pressurized by being pressed
against the die at a pressing pressure of not less than 0.1 MPa by the blank holder.
~~, .
9. The nlethod for producing a curved pai-t according to any one of claims 1 to 8,
wherein the metal material sheet is a preworked inetal sheet which is obtained by
preworking the metal material sheet.
10. The method for producing a curved part according to any one of claims 2 to 9,
wherein the cullred part taken out from the press-forming apparatus is subjected to
postworking.
11. A skeleton structure member of a body shell of an automobile, coinprising a
main body having: a hat-shaped cross section which is made up of an elongated top
plate, tvvo vertical walls connecting to both side edges of the top plate and extending
in a direction substantially perpendicular to the top plate, and two outwardly
directed flanges which connect to the two vertical walls respectively; and an
external shape including a curved portion in which each of the top plate, the two
vertical nlalls and the hvo ouh\lardiy directed flanges is curved in an arc shape in a
height direction of the vertical walls in a portion in a lengthwise direction of the lop
plate, wllerein
the main body is a cold or warm press-formed body, which uses a steel sheet
having a tensile strength of not less than 440 MPa and a sheet thiclness of 1 .O to 2.3
inln as a inaterial thereof, and a reduction rate of the sheet thickness of the curved
portion with respect to that of a remaining portion excepting the currred portion is
not Inore than 15%.