DESCRIPTION
TITLE OF INVENTION: METHOD FOR PRODUCING PRESS-FORMED
PRODUCT AND AUTOMOBILE LOWER ARM
TECHNICAL FIELD
[0001]
The present invention relates to a method for producing a press-formed
product (example: an automobile lower arm) from a blank metal plate by pressworking.
Further, the present invention relates to an automobile lower arm
(hereinafter, simply referred to as "a lower arm") produced by the production
method.
BACKGROUND ART
[0002]
In an automobile, vehicle wheels are mounted to a vehicle body via a
suspension system (a suspension). One of members that constitute the suspension
system is a lower arm. One end part of the lower arm is attached to the vehicle
body via a frame (more specifically, a suspension member) of the suspension system.
A vehicle wheel (more specifically, a wheel) is attached to the other end part of the
lower arm. From the viewpoint of reduction in weight, it is desirable to adopt a
press-formed product to the lower arm.
[0003]
FIG. 1 and FIG. 2 are perspective views schematically showing shape
examples of the press-formed products that are usable as lower arms. Among these
Figures, FIG. 1 shows a press-formed product of a first example, and FIG. 2 shows a
press-formed product of a second example. Press-formed products 10 shown in FIG.
1 and FIG. 2 each includes a main body part 11 and a protruded part 12. The main
body part 11 extends in an L-shape or a bow-shape along a lengthwise direction in
plan view. Of both ends ofthe main body part 11, one end part (hereinafter, also
referred to as "a first end part") 11a is an end part that is attached to an automobile
vehicle body. Hereinafter, the first end part 11 a will also be referred to as "the
2-
vehicle body attaching end part". The other end part (hereinafter, also referred to as
"a second end part") 11 b is an end part that is attached to an automobile vehicle
wheel. Hereinafter, the second end part 11 b will also be referred to as "the vehicle
wheel attaching end part". In each of FIG 1 and FIG 2, a side to be connected to
the vehicle wheel will be designated by reference sign ''W", whereas a side to be
connected to a vehicle body will be designated by reference sign "B".
[0004]
The protrqded part 12 protrudes outward of bending from a bent part of
the main body part 11. FIG. 1 and FIG. 2 each show an embodiment in which the
protruded part 12 is provided substantially in a middle in the lengthwise direction of
the main body part 11. As well as the first end part 11 a of the main body part 11,
the protruded part 12 is a part that is attached to an automobile vehicle body.
[0005]
Sectional shapes ofthe main body part 11 and the protruded part 12 are
both groove-shaped. That is, the main body p~rt 11 and the protruded part 12 each
include top plate parts 13a and 13b, and vertical wall parts 14a, 14b and 14c. The
vertical wall parts 14a to 14c each extend from opposite sides ofthe top plate parts
13a and 13b. On a surface ofthe top plate part 13a ofthe main body part 11, a
groove part 15 along the lengthwise direction ofthe main body part 11 is provided.
[0006]
In a case ofthe press-formed product 10 ofthe first example shown in FIG.
1, the groove part 15 is provided in a domain on the first end part (the vehicle body
attaching end part) 11a side from a root ofthe protruded part 12 in the surface of the
top plate part 13a. That is, the groove part 15 is provided to a vicinity ofthe first
end part 11 a from a vicinity of the root of the protruded part 12. The groove part 15
becomes deeper toward the first end part 11 a. Consequently, a bottom surface of
the groove part 15 is an inclined surface. Note that the depth of the groove part is
made constant without inclining the b,ottom surface of the groove part in some cases.
[0007]
In the case ofthe press-formed product 10 of the second example shown
in FIG 2, the groove part 15 is provided in a domain from the first end part (the
vehicle body attaching end part) 11a to the second end part (the vehicle wheel
attaching end part) 11 b so as to pass through the root of the protruded part I2, in the
surface of the top plate part J3a of the main body part I1.
[0008]
Among the vertical wall parts 14a to I4c, the vertical wall part I4a that
extends from the first end part (the vehicle body attaching end part) 11a of the main
body part 1I to the protruded part 12 has a bay-shaped corner part I6 that connects
the main body part 1I and the protruded part 12. Hereinafter, the vertical wall part
I4a will also be referred to as "the first vertical wall part". A ridge part 17 is
formed by the first vertical wall part I4a and the top plate parts I3a, 13b (refer to the
thick line portions in FIG. 1 and FIG. 2). In the ridge part I7, a portion overlaid on
the corner part I6 is in a circular-arc shape. In the ridge part I7, an angle that is
formed by a portion which is on the main body part 1I side from the corner part I6
and a portion which is on the protruded part I2 side from the corner part I6 is an
acute angle.
[0009]
Hereinafter, the vertical wall part I4b that extends from the first end part
(the vehicle body attaching end part) II a of the main body part II to the second end
part (the vehicle wheel attaching end part) 1I b of the main body part 1I will also be
referred to as "the second vertical wall part". The vertical wall part 14c that extends
from the second end part (the vehicle wheel attaching end part) II b of the main
body part II to the protruded part I2 will also be referred to as "the third vertical
wall part".
[0010]
The press-formed products I 0 in the shapes as above are formed by
applying press-working to blank metal plates. In accordance with necessity,
restriking is applied to a region that cannot be formed by press-working, such as a
very small R part, and thereby shape finish or shape fixation are performed. Further,
for the purpose of finishing to a final shape, trimming, boring, welding and the like
are applied in accordance with necessity.
[00 II]
When the lower arm as a press-formed product is produced, the type of
forming that is applied to a blank metal plate is mainly stretch flanging. The prior
4
arts concerning stretch flanging include the following.
[00 12]
Japanese Patent Application Publication No. 2011-230189 (Patent
Literature 1) discloses a technique of performing press-working in a warm condition
by heating a steel plate. In the technique ofPatent Literature 1, a high-strength
steel plate of a precipitation strengthening type is used as the steel plate, and
performs press-working of the steel plate which is heated to a predetermined
temperature T at an average forming speed of 200 mm/s or more. At this time, the
heating temperature T of the steel plate and a softening temperature TL of the steel
plate satisfy a relation ofTL- 100 ~ T ~ TL. Patent Literature I indicates that
thereby, even when a high-strength steel plate which is difficult to subject to pressworking
is used as a starting material, a press-formed product can be produced
without reducing production efficiency.
[0013]
Japanese Patent Application Publicatipn No. 2009-160655 (Patent
Literature 2) discloses a technique for producing a press-formed product with a
flange (a vertical wall part). In the technique of Patent Literature 2, as the blank
metal plate, a blank is used, which is composed of a blank part for a substrate
corresponding to a flat-shaped substrate, and a blankpart for a concave-shaped
flange that is bending-formed into a concave-shaped outer circumferential edge of
the blank part for a substrate. The concave-shaped blank part is constituted of a
blank part for a convex-shaped flange where stretch flanging deformation occurs,
and a blank part for an adjacent flange that is adjacent to the blank part for a convexshaped
flange. An outer circumferential edge of the blank part for a convex-shaped
flange is formed in a predetermined range. Patent Literature 2 indicates that thereby,
tensile stress concentration that occurs to the convex-shaped flange part of the pressformed
product can be dispersed to both end portions, and a stretch flange crack can
be suppressed.
[0014]
Japanese Patent Application Publication No. 06-87039 (Patent Literature
3) discloses a technique of burring that forms a cylindrical part at a circumferential
edge of a hole. In the technique of Patent Literature 3, drawing is performed by
5
~-- .·
setting a draw radius to be large in a first step. In a subsequent second step,
restriking is applied to the draw part formed in the first step, and an entire bottom
part of the draw part is further pierced at a last stage of the work. Thereby, a
vertical wall part of a remaining draw part by piercing of the bottom part directly
becomes a cylindrical burring part, and stretch flanging is not needed. Patent
Literature 3 indicates that consequently, even if the draw radius is set to be large,
and a drawing height is enlarged to a work limit, a problem in forming such as a
crack does not occur.
CITATION LIST
PATENT LITERATURES
[OOI5]
Patent Literature I: Japanese Patent Application Publication No. 20 II-230 189
Patent Literature 2: Japanese Patent Application Publication No. 2009-I60655
Patent Literature 3: Japanese Patent Applicatio~ Publication No. 06-87039
SUMMARY OF INVENTION
TECHNICAL PROBLEM
[0016]
Conventionally, the lower arm of a press-formed product is produced by
sequentially going through a first step and a second step as follows. In the first step,
draw-forming is applied to a blank metal plate by press-working. In the second step,
bending is applied to the metal plate which is draw-formed in the first step, by pressworking.
[0017]
FIG. 3A to FIG. 3C, and FIG. 4A to FIG. 4C each relates to a press-formed
product usable as a lower arm, and each is a perspective view for explaining an
example of a production process step of a conventional method. Among these
Figures, FIG. 3A to FIG. 3C show a case of producing the press-formed product I 0
ofthe first example shown in FIG. 1, and FIG. 4A to FIG. 4C show a case of
producing the press-formed product 10 of the second example shown in FIG. 2.
Further, FIG. 3A and FIG. 4A show shapes of respective blank metal plates. FIG.
6
i ..•.
r:f
38 and FIG 48 show shapes of the metal plates after the respective first steps. FIG
3C and FIG 4C show shapes of the press-formed products obtained by going
through the respective second steps. In order to obtain the press-formed products
10 in the shapes shown in FIG 3C and FIG. 4C, trimming is sometimes performed in
an upstream step or a downstream step of the second step.
[0018]
FIG. 5 and FIG 7 are perspective views schematically showing shape
examples of a press die that is used in the first step of the conventional method.
FIG 6 and FIG 8 are perspective views schematically showing shape examples of a
press die that is used in the second step of the conventional method. Among these
Figures, FIG 5 and FIG. 6 each show the case of producing the press-formed product
ofthe first example shown in FIG. 1, and FIG. 7 and FIG. 8 each show the case of
producing the press-formed product of the second example shown in FIG. 2.
[0019]
When the press-formed product 10 ofthe first example shown in FIG. 1 is
produced, a die 41a is used as an upper die 40a in the first step, as shown in FIG. 5.
As a lower die 50 a, a punch 51 a and a blank holder 52a that are paired with the
upper die 40a are used. The same applies to the case of producing the press-formed
product 10 ofthe second example shown in FIG. 2, as shown in FIG 7. FIG. 5 and
FIG. 7 each show a shape of a front end part (a surface that abuts on the metal plate)
with respect to the die 41 a, and a shape of a front end part (a surface that abuts on
the metal plate) with respect to the blank holder 52a, in order to make the
configuration easily understandable.
[0020]
In the case of producing the press-formed product 1 0 of the first example
shown in FIG 1, a die 41 band a pad 42b are used as an upper die 40b in the second
step, as shown in FIG 6. As a lower die SOb, a punch 51 b which is paired with the
upper die 40b is used. As shown in FIG 8, the same applies to the case of
producing the press-formed product 1 0 of the second example shown in FIG 2. FIG.
6 and FIG. 8 each show a shape of a front end part (a surface that abuts on the metal
plate) with respect to the die 41 b, and shows a shape of a front end part (a surface
that abuts on the metal plate) with respect to the pad 42b, in order to make the
configuration easily understandable.
[0021]
As shown in FIG. 3A, FIG. 38 and FIG. 5, in the case of producing the
press-formed product 10 ofthe first example shown in FIG. 1, press-working is
applied to a blank metal plate 21 by using the die 41 a, the punch 51 a and the blank
holder 52a in the first step by the conventional method, whereby a surface shape of a
top plate part is formed throughout an entire range. Thereby, a groove part 15 is
entirely formed. At the same time, the vertical wall part (the first vertical wall part)
14a is formed, which extends to the protruded part from the first end part (the
vehicle body attaching end part) of the main body part, among the vertical wall parts.
At this time, working ofthe blank metal plate 21 advances in a state in which an
outer side ofthe first vertical wall part 14a is held by the blank holder 52a and the
die 41 a. A forming mode in the first step is draw-forming. The same applies to
the case ofproducing the press-formed product 10 ofthe second example shown in
FIG. 2, as shown in FIG. 4A, FIG. 48 and FIG. 7.
[0022]
As shown in FIG. 38, FIG. 3C and FIG. 6, in the case of producing the
press-formed product 1 0 of the first example shown in FIG. 1, in the second step by
the conventional method, press-working is applied to the metal plate 22 after the
first step by using the die 41 b, the pad 42b and the punch 51 b. Thereby, the
remaining vertical wall parts, that is, the second vertical wall part 14b and the third
vertical wall part 14c are formed. At this time, in order to prevent a positional
deviation of the metal plate 22, the working of the metal plate 22 advances in a state
where a domain of the top plate part in the metal plate 22 is held by the pad 42b and
the punch 51 b. A forming mode in the second step is bending. The same applies
to the case of producing the press-formed product 10 of the second example shown
in FIG. 2, as shown in FIG. 48, FIG. 4C and FIG. 8.
[0023]
When a press-formed product is produced by the conventional method as
above, rupture may occur in the first step or the second step. In the first step or the
second step, the rupture occurs to a part 22c (hereinafter, also referred to as "a
stretch flanging deformation part") that undergoes stretch flanging deformation.
.,
,;
The stretch flanging deformation part 22c corresponds to a corner part 16 that
connects the main body part and the protruded part in the first vertical wall part 14a,
and an outer side domain 22h of the corner part 16 (refer to shaded portions in FIG.
3B and FIG. 4B).
[0024]
In the first step according to the conventional method, inflow of the
material from the top plate part to the stretch flanging deformation part 22c is
promoted by using the blank holder 52a, and stretch flanging deformation is reduced.
However, even though countermeasure like this is applied, rupture may occur to the
stretch flanging deformation part 22c.
[0025]
In this respect, in the technique of Patent Literature 1 described above, in
order to enhance stretch flanging performance, a high-strength steel plate of a
precipitation strengthening type is used as a steel plate, and press-working is
performed in a warm condition. However, in this technique, the step of heating the
steel plate is required, and therefore, productivity is reduced as compared with pressworking
in a cold condition.
[0026]
In the technique of Patent Literature 2, by optimizing the shape of the
blank metal plate, stress concentration that occurs to the region which undergoes
stretch flanging deformation is dispersed, and a stretch flange crack is suppressed.
However, there is a limitation on dispersion of stress concentration by optimization
of the shape of the starting material, and suppression of rupture in the stretch
flanging deformation part is insufficient.
[0027]
In the technique of Patent Literature 3 described above, burring is used.
A draw part which is formed by the burring is in an axisymmetric cylindrical shape.
Meanwhile, a stretch flanging deformation part of the lower arm is not in an
axisymmetric shape. Consequently, even if inflow of the material is promoted by
drawing, a crack may occur to the stretch flanging deformation part.
[0028]
The present invention is made in the light of the above described
circumstances, and an objective of the present invention is to provide a method for
producing a press-formed product that reduces stretch flanging deformation in a
stretch flanging deformation part, and can restrain rupture in the stretch flanging
deformation part, at a time of producing the press-formed product in a shape
conforming to an automobile lower arm. Further, an objective of the present
invention is to provide an automobile lower arm with high strength in which rupture
is suppressed in the stretch flanging deformation part.
SOLUTION TO PROBLEM
[0029]
A method for producing a press-formed product according to one
embodiment of the present invention is a method for producing a press-formed
product from a blank metal plate.
The press-formed product includes a main body part that bends along a
lengthwise direction in plan view and has a first end part and a second end part
respectively on both ends of the main body part, and a protruded part that protrudes
outward of bending from a bent part of the main body part.
The main body part and the protruded part each include top plate parts and
vertical wall parts each extending from opposite side's ofthe top plate parts.
A groove part along the lengthwise direction of the main body part is
provided on a surface of the top plate part of the main body part.
Among the vertical wall parts, the vertical wall part extending from the
first end part of the main body part to the protruded part has a comer part connecting
the main body part and the protruded part.
In a ridge part formed by the top plate part and the vertical wall part
extending from the first end part of the main body part to the protruded part, an
angle that is formed by a part which is on the main body part side from the comer
part and a part which is on the protruded part side from the comer part is an acute
angle.
The method for producing the press-formed product includes a first step;
and a second step.
In the first step, by applying press-working to the blank metal plate, a
\0
surface shape on the second end part side from the bent part of the main body part is
formed, in a surface shape of the top plate part, and further the vertical wall part
extending from the first end part side of the main body part to the protruded part is
formed.
In the second step, a surface shape on the first end part side from the bent
part of the main body part is formed, in the surface shape of the top plate part, by
applying press-working to the blank metal plate after the first step.
[0030]
In the above described production method, the following configuration can
be adopted.
The groove part of the press-formed product is provided in a domain from
the first end part to the second end part so as to pass through a root of the protruded
part, in the surface ofthe top plate part of the main body part.
formed.
formed.
[0031]
In the first step, a part on the second end part side of the groove part is
In the second step, a part on the first end part side of the groove part is
In the case ofthe production method, in the first step, when a circle having
a radius of 35% of a length of the main body part is drawn centered at a point that is
located nearest to the second end part side in the corner part, a part or a whole of a
portion on the second end part side of the groove part is preferably located in the
circle.
[0032]
Further, in the above described production method, the following
configuration can be adopted.
The groove part of the press-formed product is provided in a domain on
the first end part side from a root of the protruded part, in the surface of the top plate
part of the main body part,
[0033]
The groove part is not formed in the first step.
The groove part is formed in the second step.
\ In any one ofthe production methods described above, the following
configuration can .be adopted.
The press-formed product is an automobile lower arm,
The first end part and the protruded part of the main body part are attached
to a vehicle body of an automobile.
The second end part of the main body part is attached to a vehicle wheel
ofthe automobile.
[0034]
An automobile lower arm according to one embodiment of the present
invention is formed from a blank metal plate by press-working.
The lower arm includes a main body part that bends along a lengthwise
direction in plan view and has a vehicle body attaching end part and a vehicle wheel
attaching end part respectively on both ends of the main body part, and a vehicle
body attaching protruded part that protrudes outward of bending from a bent part of
the main body part.
The main body part and the protruded part each include top plate parts and
vertical wall parts each extending from opposite sides of the top plate parts.
A groove part along the lengthwise direction of the main body part is
provided on a surface ofthe top plate part of the main body part.
Among the vertical wall parts, the vertical wall part extending from the
vehicle body attaching end part of the main body part to the protruded part has a
corner part connecting the main body part and the protruded part.
In a ridge part formed by the vertical wall part extending from the vehicle
body attaching end part of the main body part to the protruded part, and the top plate
part, an angle that is formed by a part which is on the main body part side from the.
corner part and a part which is on the protruded part side from the corner part is an
acute angle.
A tensile strength TS [MPa] is 440 MPa or more.
A maximum height Hmax [mm] ofthe corner part of the vertical wall part
satisfies Formula (1) as follows:
Hmax > -0.0103 X TS + 26.051 (1)
l2
fl-
ADVANTAGEOUS EFFECTS OF INVENTION
[0035]
The method for producing a press-formed product of the present invention
can reduce stretch flanging deformation in a stretch flanging deformation part, and
restrain rupture in the stretch flanging deformation part, by going through the first
step and the second step at the time of producing the press-formed product in the
shape conforming to an automobile lower arm. Further, the automobile lower arm
of the present invention has high strength, with rupture suppressed in the stretch
flanging deformation part.
BRIEF DESCRIPTION OF ORA WINGS
[0036]
[FIG. I] FIG. I is a persP,ective view schematically showing a press-formed product
of a first example.
[FIG. 2] FIG. 2 is a perspective view schematic~lly showing a press-formed product
of a second example.
[FIG. 3A] FIG. 3A relates to a press-formed product of a first example, is a
perspective view for explaining an example of a production process step of a
conventional method, and shows a shape of a blank rhetal plate.
[FIG. 3B] FIG. 3B relates to the press-formed product of the first example, is a
perspective view for explaining an example of the production process step of the
conventional method, and shows a shape of the metal plate after a first step.
[FIG. 3C] FIG. 3C relates to the press-formed product of the first example, is a
perspective view for explaining an example ofthe production process step of the
conventional method, and shows a shape of a press-formed product that is obtained
by going through a second step.
[FIG. 4A] FIG. 4A relates to a press-formed product of a second example, is a
perspective view for explaining an example of a production process step of a
conventional method, and shows a shape of a blank metal plate.
[FIG. 4B] FIG. 4B relates to the press-formed product of the second example, is a
perspective view for explaining an example of the production process step of the
conventional method, and shows a shape of the metal plate after a first step.
l3
[FIG. 4C] FIG. 4C relates to the press-formed product of the second example, is a
perspective view for explaining an example ofthe production process step of the
conventional method, and shows a shape of a press-formed product obtained by
going through a second step.
[FIG. 5] FIG. 5 relates to the press-formed product of the first example, and is a
perspective view schematically showing a shape example of a press die that is used
in the first step ofthe conventional method.
[FIG. 6] FIG. 6 relates to the press-formed product of the first example, and is a
perspective view schematically showing a shape example of a press die that is used
in the second step of the conventional method.
[FIG. 7] FIG. 7relates to the press-formed product of the second example, and is a
perspective view schematically showing a shape example of a press die that is used
in the first step ofthe conventional method.
[FIG. 8] FIG. 8 relates to the press-formed product of the second example, and is a
perspective view schematically showing a shape example of a press die that is used
in the second step of the conventional method.
[FIG. 9A] FIG. 9A is a perspective view for explaining an example of a production
process step of a first embodiment, and shows a shape of a blank metal plate.
[FIG. 9B] FIG. 9B is a perspective view for explaining an example of the production
process step of the first embodiment, and shows a shape of the metal plate after a
first step.
[FIG. 9C] FIG. 9C is a perspective view for explaining an example of the production
process step of the first embodiment, and shows a shape of a press-formed product
obtained by going through a second step.
[FIG. 1 0] FIG. 1 0 is a perspective view schematically showing a shape example of a
press die that is used in the first step of the first embodiment.
[FIG. llA] FIG. IIA is a perspective view for explaining an example of a production
process step of a second embodiment, and shows a shape of a blank metal plate.
[FIG. liB] FIG. liB is a perspective view for explaining an example of the
production process step of the second embodiment, and shows a shape of the metal
plate after the first step.
[FIG. 11 C] FIG. 11 C is a perspective view for explaining an example of the
14
production process step of the second embodiment, and shows a shape of a pressformed
product obtained by going through a second step.
[FIG. 12] FIG. 12 is a perspective view schematically showing a shape example of a
press die that is used in the first step of the second embodiment.
[FIG. 13A] FIG. 13A is a plane view showing a flow state of a material of a stretch
flanging deformation part in the first step, and shows a case by the conventional
method.
[FIG. 138] FIG. 138 is a plan view showing a flow state of a material of a stretch
flanging deformation part in the first step, and shows a case by a comparative
method.
[FIG. 13C] FIG. 13C is a plan view showing a flow state of a material of a stretch
flanging deformation part in the first step, and shows a case according to the second
embodiment.
[FIG. 14] FIG. 14 is a diagram showing a relation between a tensile strength of a
blank metal plate and a limit forming height by press-working.
DESCRIPTION OF EMBODIMENTS
[0037]
In order to achieve the above described objectives, the present inventor
has conducted various analyses and tests, and kept earnest studies. As a result, the
present inventor has obtained the following finding. When a press-formed product
in a shape conforming to a lower arm, that is, a press-formed product including a
main body part and a protruded part and provided with a groove part on a surface of
a top plate part is produced by press-working, if a shape of a press die is optimized
in a first step, inflow of a material to a stretch flanging deformation part is further
promoted. Thereby, stretch flanging deformation in the stretch flanging
deformation part is reduced, and rupture in the stretch flanging deformation part is
suppressed. As a result, it becomes possible to produce a press-formed product (a
lower arm) in which rupture is suppressed in the stretch flanging deformation part.
[0038]
More specifically, irrespective of an installation range of the groove part,
in the first step, a surface shape on a second end part side from a bent part of the
\5
-Ymain
body part in a surface shape of the top plate part is formed without forming a
surface shape on a first end part side from the bent part of the main body part, and a
vertical wall part that extends from the first end part side of the main body part to
the protruded part can be further formed. Subsequently, in a second step, the
surface shape on the first end part side from the bent part of the main body part, in
the surface shape of the top plate part can be formed. When the press-formed
product is a lower arm, the first end part is a vehicle body attaching end part, and the
second end part is a vehicle wheel attaching end part.
[0039]
For example, in a case of producing a press-formed product in which a
groove part is provided in only a domain on the first end part side from the bent part
of the main body part, the groove part is not formed in the first step, but the groove
part is formed in the second step. Further, in a case of producing a press-formed
product in which a groove part is provided in a domain from the first end part to the
second end part, a part on the second end part s~de of the groove part is formed in
the first step, and a remaining part (the part on the first end part side) ofthe groove
part is formed in the second step.
[0040]
Hereinafter, embodiments of the present invention will be described with
reference to Figures. Here, a case where the press-formed product is a lower arm
will be illustrated.
[0041]
[First embodiment]
FIG. 9A to FIG. 9C relate to a press-formed product usable as a lower arm,
and are perspective views explaining an example of a production process step
according to a production method of a first embodiment. Among these Figures, FIG.
9A shows a shape of a blank metal plate. FIG. 9B shows a shape of the metal plate
after a first step. FIG. 9C shows a shape of the press-formed product obtained by
going through a second step. The production method of the first embodiment is
applied to a case of producing a press-formed product 10 of a first example shown in
FIG. 1. A groove part 15 of the press-formed product 10 is provided in only a
domain on a first end part (a vehicle body attaching end part) 11a side from a root of
lb
;-Wa
protruded part 12, in a surface of a top plate part 13a of a main body part 11, as
shown in FIG I and FIG 9C. In order to obtain the press-formed product I 0 in a
shape shown in Fl G 9C, trimming is sometimes performed in an upstream process
or a downstream process of a second step.
[0042]
FIG. 1 0 is a perspective view schematically showing a shape example of a
press die that is used in the first step in the production method of the first
embodiment. As shown in FIG 1 0, in the first step, a die 41 c is used as an upper
die 40c. As a lower die 50c, a punch 51 c and a blank holder 52c that are paired
with the upper die 40c are used. In order to make a configuration easily
understandable, FIG 10 shows a shape of a front end part (a surface that abuts on the
metal plate) with respect to the die 41 c, and shows a shape of a front end part (a
surface that abuts on the metal plate), with respect to the blank holder 52c.
[0043]
In the second step, a press die shown in FIG. 6 described above is used as
in the second step ofthe conventional method. That is, as shown in FIG. 6
described above, a die 41 b and a pad 42b are used as an upper die 40b. As a lower
die 50b, a punch 51 b which is paired with the upper die 40b is used.
[0044]
As shown in FIG. 9A, FIG. 9B and FIG. 10, in the first step, by applying
press-working to a blank metal plate 21 by using the die 41 c, the punch 51 c and the
blank holder 52c, a surface shape on the second end part side from the bent part of
the main body part is formed, in the surface shape of the top plate part. In the
press-formed product 10 which is a target in the first embodiment, the groove part
15 is not present on the surface of the top plate part 13a on the second end part 11 b
side (refer to FIG 1). Consequently, the groove part 15 is not formed, as shown in
FIG 9B. At the same time, a vertical wall part (a first vertical wall part) 14a that
extends to the protruded part from the first end part (the vehicle body attaching end
part) of the main body part in the vertical wall parts is formed. At this time,
working ofthe blank metal plate 21 advances in a state where the outer side ofthe
first vertical wall part 14a is held by the blank holder 52c and the die 41c. A
forming mode in the first step is draw-forming.
;J-1-
[0045]
As shown in FIG. 6, FIG. 9B and FIG. 9C, in the second step, a surface
shape on the first end part side from the bent part of the main body part is formed, in
the surface shape of the top plate part, by applying press-working to a metal plate 22
after the first step, by using the die 41 b, the pad 42b and the punch 51 b similarly to
the second step of the conventional method. Thereby, as shown in FIG. 9C, the
groove part 15 is formed. At the same time, the remaining vertical wall parts, that
is, a second vertical wall part 14b and a third vertical wall part 14c are formed. At
this time, in order to prevent a positional deviation of the metal plate 22, the
working of the metal plate 22 advances in a state where a domain of the top plate
part in the metal plate 22 is held by the pad 42b and the punch 51 b. A forming
mode in the second step is bending.
[0046]
Here, in the conventional method, in the first step, the vertical wall part
l4a is formed with the groove part 15, as described above. At this time, the
material in the domain on the second end part (the vehicle wheel attaching end part)
side from a root of the protruded part in the top plate part of the main body part is
brought into both the groove part 15 and the stretch flanging deformation part 22c
(refer to the broken line arrows in FIG. 3B described 'above). By the bringing of the
material to the groove part 15, the bringing of the material to the stretch flanging
deformation part 22c is reduced.
[0047]
In contrast with this, in the first embodiment, in the first step, the first
vertical wall part 14a is formed without forming the groove part 15. At this time, a
material in a domain on the second end part (the vehicle wheel attaching end part)
side from the root of the (lrotruded part in the top plate part of the main body part is
brought into only the stretch flanging deformation part 22c (refer to the broken line
arrow in FIG. 9B). Since there is no bringing of the material into the groove part 15,
bringing of the material to the stretch flanging deformation part 22c is further
promoted. As a result, the stretch flanging deformation in the stretch flanging
deformation part 22c is reduced, and rupture in the stretch flanging deformation part
is suppressed. Accordingly, it becomes possible to produce a press-formed product
~-
(the lower arm) in which rupture is suppressed in the stretch flanging deformation
part.
[0048]
As described above, suppression of rupture in the stretch flanging
deformation part by the production method of the first embodiment is by the
bringing of the material in the first step. A mechanism of the suppression of rupture
similarly applies to the second step.
[0049]
According to the production method of the first embodiment, stretch
flanging deformation in the stretch flanging deformation part is reduced as described
above. Consequently, even in the case of using a high-tensile strength steel plate as
the blank metal plate, rupture in the stretch flanging deformation part can be
suppressed. Further, it becomes possible to more increase a forming height of a
vertical wall part, in particular, a forming height of a corner part of the first vertical
wall part to be the stretch flanging deformation part, and a degree of freedom of
design of the press-formed product (the lower arm) is enhanced.
[0050]
In the case of using a high-tensile strength steel plate as the blank metal
plate, if the tensile strength becomes more than 440 MPa, occurrence of rupture in
the stretch flanging deformation part becomes remarkable. In this respect,
according to the production method of the first embodiment, rupture in the stretch
flanging deformation part can be suppressed even in the case of using the hightensile
strength steel plate with a tensile strength of 440 MPa or more.
Consequently, the production method of the first embodiment is especially useful in
the case of using a high-tensile strength steel plate with a tensile strength of 440
MPa or more. Thereby, a press-formed product (a lower arm) with a high strength
and a high rigidity in which rupture is suppressed in the stretch flanging deformation
part is obtained.
[0051]
The production method of the first embodiment described above can be
changed as follows.
[0052]
Forming of the vertical wall part (the second vertical wall part) 14b
extending from the first end part (the vehicle body attaching end part) of the main
body part to the second end part (the vehicle wheel attaching end part) of the main
body part may be performed in either of the first step and the second step. Further,
if a downstream step of applying press-working by using another press die is
provided subsequently to the second step, forming ofthe second vertical wall part
14b can be performed in the downstream step. From the viewpoint of further
promoting inflow of the material to the stretch flanging deformation part 22c in the
first step, forming of the second vertical wall part 14b is preferably performed in the
second step or the downstream step of the second step.
[0053]
Forming of the vertical wall part (the third vertical wall part) 14c
extending to the protruded part from the second end part (the vehicle wheel
attaching end part) of the main body part may be performed in either of the first step
and the second step. Further, a downstream st('(p of applying press-working by
using another press die is provided subsequently to the second step, forming of the
third vertical wall part 14c can be performed in the downstream step. From the
viewpoint of further promoting inflow ofthe material to the stretch flanging
deformation part 22c in the first step, forming of the third vertical wall part 14c is
preferably performed in the second step or the downstream step of the second step.
[0054]
In the second step, the pad can be omitted, as the ·upper die which is paired
with the punch. Press-working in this case is performed by the die and the punch.
However, in this case, in order to form the groove part 15, a convex part
corresponding to the groove part 15 needs to be provided in the die. Further, in
order to prevent the position ofthe metal plate from deviating at the time of pressworking,
a guide pin is preferably installed.
[0055]
In fact, if the pad 42b is used in the second step, forming of the groove
part 15 precedes forming of the second vertical wall part 14b and the third vertical
wall part 14c. Thereby, inflow ofthe material toward the groove part 15 from a
region that is formed into the second vertical wall part 14b is promoted. As a result,
zo
~-
outflow of the material from the stretch flanging deformation part 22c is more
reduced, so that stretch flanging deformation in the stretch flanging deformation part
22c is more reduced, and rupture in the stretch flanging deformation part 22c is
more suppressed. Consequently, use of the pad is preferable in the second step.
[0056]
The first step and the second step may be continued, or in accordance with
necessity, another step (example: a piercing step, a trimming step or the like) may be
added to between the first step and the second step.
[0057]
Trimming is not indispensable. This is because if the outline shape of the
blank metal plate is set properly, the shape of the press-formed product which is
obtained by going through the first step and the second step can be formed into the
product shape.
[0058]
[Second embodiment]
FIG. 11A to FIG. 11C relate to a press-formed product usable as a lower
arm, and are perspective views each explaining an example of a production process
step according to a production method of a second embodiment. Among these
Figures, FIG. 11 A shows a shape of a blank metal plate. FIG. 11 B shows a shape of
a metal plate after a first step. FIG. 11 C shows a shape of the press-formed product
obtained by going through a second step. FIG. 12 is a perspective view
schematically showing a shape example of a press die that is used in the first step in
the production method of the second embodiment. The production method of the
second embodiment is applied to a case of producing the press-formed product 10 of
the second example shown in FIG. 2. As shown in FIG. 2 and FIG. 11 C, the groove
part 15 of the press-formed product 1 0 is provided in a wide-ranging domain from
the first end part (the vehicle body attaching end part) 11a to the second end part
(the vehicle wheel attaching end part) 11 b so as to pass through the root of the
protruded part 12, in a surface of the top plate part 13a of the main body part 11.
[0059]
The second embodiment is based on the configuration of the
aforementioned first embodiment. Hereinafter, explanation overlapping with the
2-;.X'-
first embodiment will be properly omitted.
[0060]
As shown in FIG. llA, FIG. liB and FIG. 12, in a first step, a surface
shape on a second end part side from a bent part of a main body part is formed, in a
surface shape of a top plate part, by applying press-working to the blank metal plate
21 by using the die 41 c, the punch 51 c and the blank holder 52c. Thereby, as
shown in FIG. liB, a part (hereinafter, also referred to as "a second-end-part-side
groove part") 22a on the second end part (the vehicle wheel attaching end part) 11 b
side of the groove part 15 is formed. At the same time, the vertical wall part (the
first vertical wall part) 14a extending to a protruded part from a first end part (a
vehicle body attaching end part) ofthe main body part, in the vertical wall parts, is
formed.
[0061]
In a second step, the press die shown in FIG. 8 described above is used as
in the second step ofthe conventional method. , As shown in FIG. 8, FIG. liB and
FIG. 11 C, in the second step, a surface shape on a first end part side from the bent
part of the main body part is formed, in the surface shape of the top plate part, by
applying press-working to the metal plate 22 after the first step, by using the die 41 b,
the pad 42b and the punch 51 b. Thereby, as shown in FIG. 11 C, a remaining part
(hereinafter, also referred to as "a first-end-part-side groove part") of the groove part
15 is formed. At the same time, remaining vertical wall parts, that is, the second
vertical wall part 14b and the third vertical wall part 14c are formed.
[0062]
Here, a mechanism of rupture in the stretch flanging deformation part 22c
being suppressed by the production method of the second embodiment will be
described.
[0063]
FIG. 13A to FIG. 13C are plan views each showing a flow state of a
material of a stretch flanging deformation part in the first step. Among these
Figures, FIG. 13A shows a case according to the conventional method. FIG. 13B
shows a case according to a comparative method. FIG. 13C shows a case according
to the second embodiment. These Figures each show a shape of the stretch flanging
deformation part 22c and a periphery thereof in the metal plate 22 after the first step.
Shapes of the blank metal plates are shown by the two-dot chain lines.
[0064]
As shown in FIG. 13A, in the conventional method, the entire groove part
15 from the first end part to the second end part is formed in the first step.
Consequently, an outer edge 22f (refer to the thick line portion in FIG. 13A) of a part
that is formed into the third vertical wall part in the second step moves to the groove
part 15 side and the stretch flanging deformation part 22c side. That is, in the first
step of the conventional method, the material flows to the arrow to which shading is
applied in FIG. 13A, and the material flows into the stretch flanging deformation
part 22c.
[0065]
Meanwhile, the outer edge 22g (refer to the thick line portion in FIG. 13A)
of the first vertical wall part moves to the groove part 15 side. Consequently, in the
first step of the conventional method, the material flows to the direction shown by
the arrow to which cross-hatching is applied in FIG. 13A, and the material flows out
from the stretch flanging deformation part 22c. By outflow of the material from the
stretch flanging deformation part 22c, deformation in the stretch flange deformation
part 22c increases, where rupture occurs.
[0066]
The comparative method is a method for reference which does not form
the groove part 15 in the first step, as shown in FIG. 13B. In the comparative
method, shearing deformation advances in a domain enclosed by the broken line in
FIG. 138, at the time of the material flowing into the stretch flanging deformation
part 22c. Since deformation resistance of the shearing deformation is large, inflow
of the material to the stretch flanging deformation part 22c is inhibited. As a result,
the outer edge 22f (refer to the thick line portion in FIG. 138) of a part which is to
be formed into the third vertical wall part in the second step moves to the stretch
flanging deformation part 22c side, but a moving amount of the outer edge 22f
decreases as compared with the conventional method. That is, inflow of the
material to the stretch flanging deformation part 22c is reduced.
[0067]
23
Meanwhile, the outer edge 22g (refer to the thick line portion in FIG. 13B)
of the first vertical wall part moves inward. However, since a groove part is not
formed in the first step of the comparative method, a moving amount of the outer
edge 22g decreases as compared with the conventional method. Consequently,
according to the comparative method, outflow of the material from the stretch
flanging deformation part 22c is reduced as compared with the conventional method.
[0068]
As above, in the comparative method, inflow of the material to the stretch
flanging deformation part 22c in the direction shown by the arrow to which shading
is applied in FIG. 13 B is reduced as compared with the conventional method.
Further, outflow of the material from the stretch flanging deformation part 22c in the
direction shown by the arrow to which cross-hatching is applied in FIG. 13B is
reduced. As a result, deformation in the stretch flanging deformation part 22c
increases more, and occurrence of rupture in this part becomes remarkable.
[0069]
In contrast with this, in the second embodiment, only the second-end-partside
groove part 22a of the groove part is formed in the first step, as shown in FIG.
13C. In this case, the material flows into the second-end-part-side groove part 22a
and the stretch flanging deformation part 22c. The material flows into the secondend-
part-side groove part 22a, whereby occurrence of sharing deformation as in the
comparative method is prevented, and inflow of the material to the stretch flanging
deformation part 22c is promoted. Consequently, the outer edge 22f (refer to the
thick line portion in FIG. 13C) of the part which is to be formed into the third
vertical wall part in the second step moves to the groove part 15 side and the stretch
flanging deformation part 22c side as in the conventional method. That is, in the
first step of the second embodiment, inflow of the material to the stretch flanging
deformation part 22c is kept to the same extent as in the conventional example.
[0070]
Meanwhile, the outer edge 22g (refer to the thick line portion in FIG. 13C)
ofthe first vertical wall part moves inward. However, since only the second-endpart-
side groove part 22a is formed in the first step of the second embodiment, the
moving amount of the outer edge 22g decreases as compared with the conventional
'2-4
h.: ;
'
-.2<-
method. Consequently, according to the second embodiment, outflow of the
material from the stretch flanging deformation part 22c is reduced as compared with
the conventional method.
[0071]
As above, in the second embodiment, inflow of the material to the stretch
flanging deformation part 22c in the direction shown by the arrow to which shading
is applied in FIG 13C is kept at the same extent as compared with the conventional
method. Further, outflow of the material from the stretch flanging deformation part
22c in the direction shown by the arrow to which cross-hatching is applied in FIG
13C is reduced. As a result, stretch flanging deformation in the stretch flanging
deformation part 22c is reduced, and occurrence of rupture in this part is suppressed.
[0072]
In the case of the second embodiment, when a circle C is drawn centered
at a point 22d that is located nearest to the second end part (the vehicle wheel
attaching end part) side of the corner part of the, first vertical wall part which is the
stretch flanging deformation part in the first step, as shown in FIG 13C, a part or a
whole of the second-end-part-side groove part 22a is preferably located inside the
circle C. Here, a radius [mm] of the circle Cis 35% of a length [mm] of the main
body part 11. The length of the main body part 11 is a distance [ mm] in a straight
line from the first end part (the vehicle body attaching end part) 11a to the second
end part (the vehicle wheel attaching end part) 11 bas shown in the FIG 2 described
above. In measurement of the length of the main body part 11, as respective
positions of the first end part 11 a and the second end part 11 b, center points PI and
P2 in a width direction in the top plate part 13a of the main body part 11 are
respectively adopted.
[0073]
If a part or a whole of the second-end-part-side groove part 22a is located
inside the circle C, inflow of the material to the stretch flanging deformation part
22c attributable to forming the second-end-part-side groove part 22a is promoted
more effectively in the first step. As a result, stretch flanging deformation in the
stretch flanging deformation part 22c is more reduced, and occurrence of rupture in
this part is more suppressed. From the viewpoint of increasing the effect more, the
radius of the circle Cis preferably 30% of the length of the main body part 11.
[0074]
Further, when a part or a whole of the second-end-part-side groove part
22a formed in the first step is located inside the circle C, an end part 22e of the
second-end-part-side groove part 22a may be disposed on either of the first end part
side and the second end part side, with the center point 22d of the circle C as a
reference. However, if the end part 22e of the second-end-part-side groove part 22a
is disposed at the first end part {the vehicle body attaching end part) side, there
arises the fear of increasing outflow of the material from the stretch flanging
deformation part 22c in the direction shown by the arrow to which cross-hatching is
applied in FIG 13C. Consequently, the end part 22e of the second-end-part-side
groove part 22a is preferably disposed on the second end part (the vehicle wheel
attaching end part) side from the center point 22d of the circle C.
[0075]
As described above, suppression of n.~pture in the stretch flanging
deformation part according to the production method of the second embodiment is
by flow of the material in the first step. The mechanism of rupture suppression
similarly applies to the second step.
[0076]
[Press-formed product]
According to the production methods of the present embodiments
described above, press-formed products in which rupture is suppressed in the stretch
flanging deformation parts can be obtained even when a high-tensile strength steel
plate with a tensile strength of 440 MPa-class is used as a blank metal plate.
Consequently, the press-formed products of the present embodiments have a high
strength, and rupture is suppressed in the stretch flanging deformation parts. A use
purpose of the press-formed products is not limited as long as the press-formed
products are in the shapes conforming to lower arms.
[0077]
Further, according to the production methods of the present embodiments,
stretch flanging deformation can be reduced in the stretch flanging deformation parts.
Consequently, formed heights ofthe vertical wall parts of the press-formed products,
26
-x:-
in particular, formed heights of the corner parts of the first vertical wall parts which
are to be the stretch flanging deformation parts can be made higher.
[0078]
Here, a result of investigating a limit height capable of being formed by
press-working will be shown, with respect to the height of the corner part of the first
vertical wall part in a press-formed product. The limit forming height of the corner
part was investigated for each of variou·s steel plates with different tensile strengths
in both the production method of the present embodiment and the conventional
method. In the investigation, the actual values of the actual working tests
conducted by the inventor and the result of FEM analysis were used.
[0079]
FIG. 14 is a diagram showing a relation between a tensile strength of the
blank metal plate and a limit forming height by press-working. FIG. 14
representatively shows a result of a case of using a steel plate of 590 MPa-class and
a steel plate of980 MPa-class. As shown in FlO. 14, a limit forming height H
[mm] of the corner part reduces proportionally to a tensile strength TS [MPa] of the
steel plate in both of the cases of the production method of the present embodiment
and the conventional method. Especially in the case of the conventional method, a
limit forming height Hiim [mm] ofthe corner part is expressed by Formula{A) as
follows.
Him = -0.0103 X TS + 26.051 (A)
[0080]
Meanwhile, in the case of the production method of the present
embodiment, the limit forming height Him [mm] ofthe corner part is expressed by
Formula (B) as follows.
Him= -0.0103 X TS + 29.051 (B)
[0081]
From the relations of Formula (A) and Formula (B) described above, the
limit forming height according to the production method of the present embodiment
increases by approximately 3 mm as compared with the conventional method. That
is, according to the production method of the present embodiment, the forming
height of the corner part can be made higher than the limit forming height of the
Yconventional
method expressed by Formula (A) described above.
[0082]
Accordingly, in the press-formed product of the present embodiment, a
maximum height Hmax [ mm] of the corner part of the first vertical wall part which is
to be the stretch flanging deformation part can be made to satisfy Formula (1) as
follows on the basis of Formula (A) described above. As a matter of course, the
press-formed product of the present embodiment can be made the product having a
tensile strength of 440 MPa or more.
Hmax > -0.0103 X TS + 26.051 (1)
EXAMPLES
[0083]
In order to confirm the effect of the present invention, tests on example 1
and example 2 below were carried out by FEM analyses. In the FEM analyses of
both of example 1 and example 2, press-formed products usable as lower arms were
produced by applying press-working to blank metal plates, and degrees of stretch
flanging deformation were evaluated by plate thickness decrease rates of the stretch
flanging deformation parts at this time.
[0084]
[Example 1]
In the test of example 1, a press-formed product in the shape of the first
example shown in FIG. 1 described above was produced in order to confirm the
effect ofthe first embodiment. The groove part of the press-formed product is
provided in only the domain on the first end part side, in the surface of the top plate
part of the main body part. At this time, a high-tensile strength steel plate with a
plate thickness of 2.6 mm, and a tensile strength of 960 MPa-class was used as the
blank metal plate.
[0085]
In Inventive Example I of the present invention, the press dies shown in
FIG. I 0 and FIG. 6 described above were used, and press-working was applied to the
blank metal plate by the first step shown in FIG. 9A and FIG. 9B described above,
and the second step shown in FIG. 9B and FIG. 9C described above.
;)t8'-
[0086]
Meanwhile, in the conventional example 1, the press dies shown in FIG. 5
and FIG. 6 described above were used, and press-working was applied to the blank
metal plate by the first step shown in FIG. 3A and FIG. 3B described above, and the
second step shown in FIG. 3B and FIG. 3C described above. The other conditions
were set as the same as in the Inventive Example 1 of the present invention.
[0087]
In both of the Inventive Example I of the present invention and the
conventional example 1, for the respective first steps and second steps, the plate
thicknesses of the stretch flange parts were measured before and after the steps, and
plate thickness reduction rates of the stretch flanging deformation parts were
obtained. The plate thickness reduction rates here were set as the plate thickness
reduction rates in the positions where the plate thicknesses were reduced most in
domains of the stretch flanging deformation parts, that is, the maximum plate
thickness reduction rates.
[0088]
In the conventional example 1, a whole ofthe groove part was formed in
the first step. As a result, the plate thickness reduction rates of the stretch flanging
deformation part in the first step and the second step 'were respectively II.6% and
33.5%.
[0089]
In contrast with this, in the Inventive Example 1 ofthe present invention, a
whole of the groove part was formed in the second step, without forming the groove
part in the first step. The plate thickness reduction rates of the stretch flanging
deformation part in the first step and the second step were respectively 8.0% and
26.3%. That is, in the Inventive Example I ofthe present invention, readily
producing of the stretch flanging deformation part ~as enhanced as compared with
the conventional example I.
[0090]
From the above, it has become clear that according to the first
embodiment, the stretch flanging deformation in the stretch flanging deformation
part can be reduced, and rupture in the stretch flanging deformation part can be
suppressed.
[0091]
[Example 2]
~-
In the test of example 2, the press-formed product in the shape of the
second example shown in FIG. 2 described above was produced in order to confirm
the effect of the second embodiment. The groove part of the press-formed product
was provided in a wide-ranging domain from the first end part (the vehicle body
attaching end part) to the second end part (the vehicle wheel attaching end part), of
the surface of the top plate part of the main body part. At this time, a high-tensile
strength steel plate with a plate thickness of2.6 mm and a tensile strength of980
MPa-class was used as the blank metal plate. A distance in a straight line from the
first end part to the second end part of the main body part, that is, the length of the
main body part was 400 mm.
[0092]
In Inventive Example 2 of the present invention, press-working was
applied to the blank metal plate by the first step shown in FIG. llA and FIG. liB
described above, and the second step shown in FIG. 11 B and FIG. 11 C described
above, by using the press dies shown in FIG. 12 and FIG. 8 described above.
Trimming was applied to the resultant press-formed product. The point 22d located
nearest to the second end part side in the corner part of the first vertical wall part
which is to be the stretch flanging deformation part was set as a reference, and the
end part 22e of the second-end-part-side groove part 22a which is formed in the first
step was disposed on the second end part side from the reference point 22d. The
shortest distanced (refer to FIG. 13C described above) between the second-end-partside
groove part 22a and the reference point 22d was set as 40 mm. Consequently,
when a circle having a radius of35% ofthe length (400 mm) of the main body part,
that is, a circle having a radius of 140 mm was drawn centered at the reference point
22d, a part of the second-end-part-side groove part 22a was in a state located in the
circle.
[0093]
Meanwhile, in the conventional example 2, press-working was applied to
the blank metal plate by the first step shown in FIG. 4A and FIG. 4B described above,
3o
and the second step shown in FIG. 4B and FIG. 4C described above, by using the
press dies shown in FIG. 7 and FIG. 8 described above. Further, in Comparative
Example 2 for reference, a whole of the groove part was formed in the second step
without forming the groove part in the first step. The other conditions were set as
the same as in the Inventive Example 2 ofthe present invention.
[0094]
In each of the Inventive Example 2 of the present invention, the
conventional example 2 and Comparative Example 2, for the respective first step,
second step and trimming step, the plate thickness of the flange part was measured
before and after the steps, and the plate thickness reduction rates of the stretch
flanging deformation part were obtained. The plate thickness reduction rate in this
case was the plate thickness reduction rate in the position where the plate thickness
was most reduced in the domain of the stretch flanging deformation part, that is, the
maximum plate thickness reduction rate. The test result is shown in Table 1 as
follows.
[0095]
[Table 1]
Category
Conventional
example 2
Comparative
Example 2
Inventive
Example 2 of
present
invention
[0096]
Formed part of
groove part in
first step
Whole
None
Second-end-partside
groove part
TABLE 1
Plate thickness reduction rate of stretch
flanging deformation part(%)
First step Second step Trimming step
17.9 33.3 24.9
28.6 38.5 29.7
14.7 26.5 14.7
From Table 1, the following is shown. In the conventional example 2, the
whole of the groove part was formed in the first step. As a result, the plate
thickness reduction rates of the stretch flanging deformation part in the first step, the
1 '
:)?"-
second step and the trimming step were respectively 17.9%, 33.3% and 24.9%. In
contrast with this, in the Comparative Example 2, the plate thickness reduction rates
of the stretch flanging deformation part in the first step, the second step and the
trimming step were all worsened.
[0097]
In the Inventive Example 2 of the present invention, the second-end-partside
groove part of the groove part was formed in the first step, and the remaining
first-end-part-side groove part was formed in the second step. As a result, the plate
thickness reduction rates of the stretch flanging deformation part in the first step, the
second step and the trimming step were respectively 14.7%, 26.5% and 14.7%.
That is, in the Inventive Example 2 ofthe present invention, formability of the
stretch flanging deformation part was enhanced as compared with the conventional
example 2.
[0098]
From the above, it has become clear that according to the second
embodiment, the stretch flanging deformation in the stretch flanging deformation
part can be reduced, and rupture in the stretch flanging deformation part can be
suppressed.
[0099]
Further, it is needless to say that the present invention is not limited to the
above described embodiments, and various changes can be made within the range
without departing from the spirit of the present invention.
INDUSTRIAL APPLICABILITY
[0100]
The production method of a press-formed product of the present invention
is useful in production of a press-formed product in the shape conforming to an
automobile lower arm. In particular, the production method of the present
invention is useful for production of a lower arm with a high strength and a high
rigidity.
REFERENCE SIGNS LIST
[0101]
part,
10: Press formed product (lower arm), 11: Main body part,
11a: First end part of main body part (vehicle body attaching end part),
11 b: Second end part of main body part (vehicle wheel attaching end part)
12: Protruded part,
13a: Top plate part of main body part, 13b: Top plate part of protruded
14a: Vertical wall part (first vertical wall part) extending from first end
part (vehicle body attaching end part) of main body part to protruded part,
14b: Vertical wall part (second vertical wall part) extending from first end
part (vehicle body attaching end part) of main body part to second end part (vehicle
wheel attaching end part) of main body part,
14c: Vertical wall part (third vertical wall part) extending from second end
part (vehicle wheel attaching end part) of main body part to protruded part,
15: Groove part, 16: Corner part,
17: Ridge formed by first vertical wall part and top plate part,
21: Blank metal plate, 22: Metal plate after first step,
22a: Part (second-end-part-side groove part) on second end part (vehicle
wheel attaching end part) side of groove part, 22c: Stretch flanging deformation
part,
22d: Point located nearest to second end part (vehicle wheel attaching end
part) side in corner part
22e: End part of second-end-part-side groove part,
22f: Outer edge of part formed into third vertical wall part,
22g: Outer edge of first vertical wall part, 22h: Outer side domain of
corner part,
40a to 40c: Upper die, 41 a to 41 c: Die, 42b: Pad,
50a to 50c: Lower die, 51 a to 51 c: Punch,
52a, 52c: Blank holder, B: Vehicle body side, W: Vehicle wheel side

We claim:
1. A method for producing a press-formed product from a blank metal plate,
wherein the press-formed product includes a main body part that bends
along a lengthwise direction in plan view and has a first end part and a second end
part respectively on both ends of the main body part, and a protruded part that
protrudes outward ·of bending from a bent part of the main body part,
the main body part and the protruded part each comprise top plate parts
and vertical wall parts each extending from opposite sides of the top plate parts,
a groove part along the lengthwise direction of the main body part is
provided on a surface of the top plate part of the main body part,
among the vertical wall parts, the vertical wall part extending from the
first end part of the main body part to the protruded part has a corner part connecting
the main body part and the protruded part, and
in a ridge part formed by the top plate part and the vertical wall part
extending from the first end part of the main body part to the protruded part, an
angle that is formed by a part which is on the main body side from the corner part
and a part which is on the protruded part side from the corner part is an acute angle,
'
the method for producing the. press-formed product comprising: a first
step; and a second step,
wherein in the first step, by applying press-working to the blank metal
plate, a surface shape on the second end part side from the bent part of the main
body part is formed, in a surface shape of the top plate part, and further the vertical
wall part extending from the first end part side of the main body part to the
protruded part is formed, and
in the second step, a surface shape on the first end part side from the bent
part of the main body part is formed, in the surface shape of the top plate part, by
applying press-working to the blank metal plate after the first step.
2. The method for producing a press-formed product according to claim 1,
wherein the groove part of the press-formed product is provided in a
domain from the first end part to the second end part so as to pass through a root of
34
the protruded part, in the surface of the top plate part of the main body part,
in the first step, a part on the second end part side of the groove part is
formed, and
in the second step, a part on the first end part side of the groove part is
formed.
3. The method for producing a press-formed product according to claim 2,
wherein in the first step, when a circle having a radius of 35% of a length
of the main body part is drawn centered at a point that is located nearest to the
second end part side in the corner part, a part or a whole of a portion on the second
end part side of the groove part is located in the circle.
4. The method for producing a press-formed product according to claim 1,
wherein the groove part of the press-formed product is provided in a
domain on the first end part side from a root of~he protruded part, in the surface of
the top plate part of the main body part,
the groove part is not formed in the first step, and
the groove part is formed in the second step.
5. The method for producing a press-formed product according to any one of
claims 1 to 4,
wherein the press-formed product is an automobile lower arm,
the first end part and the protruded part of the main body part are attached
to a vehicle body of an automobile, and
the second end part of the main body part is attached to a vehicle wheel of
the automobile.
6. An automobile lower arm formed from a blank metal plate by pressworking,
the lower arm, comprising: a main body part that bends along a lengthwise
direction in plan view and has a vehicle body attaching end part and a vehicle wheel
attaching end part respectively on both ends of.the main body part; and a vehicle
3S
body attaching protruded part that protrudes outward of bending from a bentpart of
the main body part,
wherein the main body part and the protruded part each comprise top plate
parts, and vertical wall parts each extending from opposite sides ofthe top plate
parts,
a groove part along the lengthwise direction of the main body part is
provided on a surface of the top plate part of the main body part,
among the vertical wall parts, the vertical wall part extending from the
vehicle body attaching end part of the main body part to the protruded part has a
corner part connecting the main body part and the protruded part, and
in a ridge part formed by the top plate part and the vertical wall part
extending from the vehicle body attaching end part of the main body part to the
protruded part, an angle that is formed by a part which is on the main body part side
from the corner part and a part which is on the protruded part side from the corner
part is an acute angle,
a tensile strength TS [MPa] of the automobile lower arm is 440 MPa or
more, and
a maximum height Hmax [ mm] of the corner part of the vertical wall part
satisfies Formula (l) as follows:
Hmax > -0.0103 X TS + 26.051 (1)