[Technical Field]
[0001]
The present invention relates to a burring processing method, a method for
manufacturing a burring processed product, a burring processing mold, a burring
processing device, and a burring processed product. Priority is claimed on Japanese
Patent Application No. 2020-118459, filed July 9, 2020, the content of which is
incorporated herein by reference.
[Background Art]
[0002]
There is a technique of forming a substantially cylindrical burring processed
portion by performing burring processing on a prepared hole provided in a metal
component or a metal plate that is a workpiece. In this burring processing, a
circumferential portion of the prepared hole is extruded and a part thereof is formed into
a cylindrical shape to form the burring processed portion. In the burring processed
portion, a cylindrical flange (an upright portion) is connected to a part of the metal
component or the metal plate at a circumferential portion thereof via a curved portion.
Fatigue characteristics and dimensional accuracy are required for the burring processed
portion. For example, Patent Document 1 discloses a technique in which a compressive
stress is applied to an end portion of a burring processed portion by coining to relax a
tensile residual stress, and a compressive stress is locally concentrated on an inner
1
surface of a bend of a curved portion constituting a root of the burring processed portion
to inhibit wrinkles or cracks that occur on the inner surface. Also, as a burring
processing technique, there is an ironing burring processing method as described in
Patent Document 2.
[Citation List]
[Patent Document]
[0003]
[Patent Document 1]
Japanese Unexamined Patent Application, First Publication No. 2018-051609
[Patent Document 2]
Japanese Unexamined Patent Application, First Publication No. S58-44917
[Summary of Invention]
[Problems to be Solved by Invention]
[0004]
Incidentally, a burring processed portion is also used for undercarriage
components of a vehicle. In particular, undercarriage components of a vehicle such as a
lower arm and a trailing arm are required to have fatigue characteristics, but with some
burring processing methods, a tensile residual stress is likely to occur inside a curved
portion of a burring processed portion. When a fatigue load is applied to a component
in which a tensile residual stress occurs inside a curved portion of a burring processed
portion, the burring processed portion may be deformed. In addition, depending on a
burring processing method, minute cracks (in-bend cracks) may occur inside the curved
portion, and it may be necessary to change a shape such as increasing the radius of
curvature of the curved portion.
[0005]
2
The present invention has been made in view of the above problems, and an
object of the present invention is to provide a burring processing method, a method for
manufacturing a burring processed product, a burring processing mold, a burring
processing device, and a burring processed product in which generation of cracks in a
curved portion of a burring processed portion can be inhibited.
[Means for Solving the Problem]
[0006]
( 1) A burring processing method according to one aspect of the present invention
is a method for increasing a diameter of a prepared hole provided in a metal component
and bending a part of the metal component to form a burring processed portion including
an upright portion and a curved portion, in which, in a cross-section that passes through
an axis of the burring processed portion and is parallel to the axis of the burring
processed portion, a cross-sectional shape of the curved portion on an inner surface of the
curved portion consists of a curve, and a length of the curved portion in a direction
perpendicular to the axis of the burring processed portion is at least 1.2 times a height of
the curved portion in a direction parallel to the axis of the burring processed portion.
(2) A burring processing method according to one aspect of the present invention
is a method for forming a burring processed portion in a metal component provided with
a prepared hole using a mold including a die having a die hole, a holder, and a punch, in
which the metal component is sandwiched between the die and the holder, the punch is
inserted into the die hole along an axis of the die hole to increase a diameter of the
prepared hole and to bend a part of the metal component, thereby forming a burring
processed portion including an upright portion and a curved portion, and in a crosssection
that passes through the axis of the die hole and is parallel to the axis of the die
hole, a cross-sectional shape of a die shoulder consists of a curve, and a length of the die
3
shoulder in a direction perpendicular to the axis of the die hole is at least 1.2 times a
height of the die shoulder in a direction parallel to the axis of the die hole.
(3) In the burring processing method according to the above (1) or (2), when a
plate thickness around the prepared hole of the metal component is defined as t, and a
height of the curved portion in the direction parallel to the axis of the burring processed
portion is defined as h, the following Expression 1 may be satisfied.
h/t<0.6 .. · Expression 1
( 4) In the burring processing method according to any one of the above (1) to
(3), when the plate thickness around the prepared hole of the metal component is defined
as t, and a plate thickness of an opening side end portion of the upright portion is defined
as tb, the following Expression 2 may be satisfied.
tblt<0.9 .. · Expression 2
(5) In the burring processing method according to any one of the above (1) to
( 4 ), a value obtained by differentiating an expression representing the curve twice may be
larger than 0.
[0007]
( 6) A method for manufacturing a burring processed product according to one
aspect of the present invention includes a burring processed portion forming process of
increasing a diameter of a prepared hole provided in a metal component and bending a
part of the metal component to form a burring processed portion including an upright
portion and a curved portion, in which, in a cross-section that passes through an axis of
the burring processed portion and is parallel to the axis of the burring processed portion,
a cross-sectional shape of the curved portion on an inner surface of the curved portion
consists of a curve, and a length of the curved portion in a direction perpendicular to the
axis of the burring processed portion is at least 1.2 times a height of the curved portion in
4
a direction parallel to the axis of the burring processed portion.
(7) A method for manufacturing a burring processed product according to one
aspect of the present invention includes a burring processed portion forming process of
forming a burring processed portion in a metal component provided with a prepared hole
using a mold including a die having a die hole, a holder, and a punch, in which, in the
burring processed portion forming process, the metal component is sandwiched between
the die and the holder, the punch is inserted into the die hole along an axis of the die hole
to increase a diameter of the prepared hole and to bend a part of the metal component,
thereby forming a burring processed portion including an upright portion and a curved
portion, and in a cross-section that passes through the axis of the die hole and is parallel
to the axis of the die hole, a cross-sectional shape of a die shoulder consists of a curve,
and a length of the die shoulder in a direction perpendicular to the axis of the die hole is
at least 1.2 times a height of the die shoulder in a direction parallel to the axis of the die
hole.
(8) In the method for manufacturing a burring processed product according to
the above (6) or (7), a prepared hole forming process of forming the prepared hole in the
metal component may be further provided before the burring processed portion forming
process.
(9) In the method for manufacturing a burring processed product according to
any one of the above (6) to (8), when a plate thickness around the prepared hole of the
metal component is defined as t, and a height of the curved portion in the direction
parallel to the axis of the burring processed portion is defined as h, the following
Expression 1 may be satisfied.
h/t<0.6 .. · Expression 1
(1 0) In the method for manufacturing a burring processed product according to
5
any one of the above (6) to (9), when a plate thickness around the prepared hole of the
metal component is defined as t, and a plate thickness of an opening side end portion of
the upright portion is defined as tb, the following Expression 2 may be satisfied.
tb/t<0.9 .. · Expression 2
( 11) In the method for manufacturing a burring processed product according to
any one of the above (6) to (10), a value obtained by differentiating an expression
representing the curve twice may be larger than 0.
[0008]
(12) A burring processing mold according to one aspect of the present invention
is a mold that includes a die having a die hole, a holder holding a workpiece together
with the die, and a punch movable relative to the die and the holder, in which, in a crosssection
that passes through an axis of the die hole and is parallel to the axis of the die
hole, a cross-sectional shape of a die shoulder consists of a curve, and a length of the die
shoulder in a direction perpendicular to the axis of the die hole is at least 1.2 times a
height of the die shoulder in a direction parallel to the axis of the die hole.
(13) In the burring processing mold according to the above (12), the punch
includes a cylindrical portion having a diameter smaller than a diameter of the die hole
and the punch is configured to be inserted into the die hole along the axis of the die hole,
and when a clearance between the die hole and the cylindrical portion is defined as cl and
a height of the die shoulder in a direction parallel to the axis of the die hole in the crosssectional
shape is defined as hct, the following Expression 3 may be satisfied.
cl<1.5hct .. · Expression 3
(14) In the burring processing mold according to the above (12) or (13), a value
obtained by differentiating an expression representing the curve twice may be larger than
0.
6
[0009]
(15) A burring processing device according to one aspect of the present
invention includes the burring processing mold according to any one of the above (12) to
(14 ), in which, the device includes a drive mechanism configured to move the die, the
holder, and the punch relative to each other.
[0010]
( 16) A burring processed product according to one aspect of the present
invention includes a burring processed portion including an upright portion and a curved
portion, in which, in a cross-section that passes through an axis of the burring processed
portion and is parallel to the axis of the burring processed portion, a cross-sectional shape
of the curved portion on an inner surface of the curved portion consists of a curve, and a
length of the curved portion in a direction perpendicular to the axis of the burring
processed portion is at least 1.2 times a height of the curved portion in a direction parallel
to the axis of the burring processed portion.
(17) In the burring processed product according to the above (16), when a plate
thickness around the curved portion is defined as ts, and a height of the curved portion in
the direction parallel to the axis of the burring processed portion is defined as h, the
following Expression 4 may be satisfied.
h/ts<0.6 ···Expression 4
(18) In the burring processed product according to the above (16) or (17), when
a plate thickness around the curved portion is defined as ts, and a plate thickness of an
opening side end portion of the upright portion is defined as tb, the following Expression
5 may be satisfied.
tb/ts<0.9 · · · Expression 5
(19) The burring processed product according to any one of the above (16) to
7
(18) may be any of a lower arm, a trailing arm, and upper arm, which are used in a
vehicle.
(20) The burring processed product according to any one of the above (16) to
(18) may be a lower arm used in a vehicle, which further includes a cylindrical portion
and a cylindrical flange portion, in which, in a plane that is perpendicular to the axis of
the burring processed portion and passes through a center C in a length direction of the
cylindrical portion on an axis of the cylindrical portion, when an intersection between the
axis of the burring processed portion and the plane is defined as an intersection A, an
intersection between an axis of the cylindrical flange portion and the plane is defined as
an intersection B, and the smaller angle between a line segment AB connecting the
intersection A to the intersection B and a line segment AC connecting the intersection A
to the center Cis defined as 8, and in the range of 28 from the line segment AB to a side
on which the center C is located, and in the range of 28 from the line segment AB to a
side opposite to the side on which the center C is located, with the intersection A set as a
center, in the cross-section that passes through the axis of the burring processed portion
and is parallel to the axis of the burring processed portion, the cross-sectional shape of
the curved portion on the inner surface consists of a curve, and the length of the curved
portion in the direction perpendicular to the axis of the burring processed portion is at
least 1.2 times the height of the curved portion in the direction parallel to the axis of the
burring processed portion.
(21) In the burring processed product according to any one of the above (16) to
(20), a value obtained by differentiating an expression representing the curve twice may
be larger than 0.
[Effects of Invention]
[0011]
8
According to the present invention, it is possible to provide a burring processing
method, a method for manufacturing a burring processed product, a burring processing
mold, a burring processing device, and a burring processed product in which generation
of cracks in a burring processed portion can be inhibited.
[Brief Description of Drawings]
[0012]
Fig. 1 is a schematic cross-sectional view of a burring processed portion for
showing a state of compression strain and in-bend cracks in a curved portion of the
burring processed portion.
Fig. 2 is a schematic cross-sectional view of the burring processed portion for
describing a state in which a workpiece rises in a forming process of burring processing.
Figs. 3(A) to 3(C) are schematic plan views for describing the forming process
of burring processing.
Figs. 4(A) to 4(C) are schematic cross-sectional views for describing the
forming process of burring processing in Figs. 3(A) to 3(C), respectively.
Fig. 5 is a schematic cross-sectional view of a burring processed product for
describing a burring processed product according to a first embodiment.
Fig. 6 is a schematic cross-sectional view of a burring processed product for
describing xy coordinates for defining a cross-sectional shape of a curved portion on an
inner surface thereof.
Fig. 7 is a schematic cross-sectional view of the burring processed product for
describing coordinates for defining the curved portion and is a diagram showing an
example in which a part of the cross-sectional shape of the curved portion is a part of an
ellipse.
Fig. 8 is a schematic cross-sectional view of the burring processed product for
9
describing coordinates for defining the curved portion and is a diagram showing an
example in which a part of the cross-sectional shape of the curved portion is a part of a
parabola.
Fig. 9 is a schematic cross-sectional view of the burring processed product for
describing coordinates for defining the curved portion and is a diagram showing an
example in which a part of the cross-sectional shape of the curved portion is a part of a
s1ne curve.
Fig. 10 is a schematic cross-sectional view of a mold for describing a mold
according to a third embodiment.
Fig. 11 is a schematic cross-sectional view for describing a burring processing
method according to a third embodiment and is a diagram showing a state in which a
workpiece is sandwiched between a die and a holder.
Fig. 12 is a schematic cross-sectional view for describing the burring processing
method according to the third embodiment and is a diagram showing a state in which the
workpiece is deformed to the die side by a punch.
Fig. 13 is a schematic cross-sectional view for describing the burring processing
method according to the third embodiment and is a diagram showing a state in which the
punch has moved to a predetermined position and burring processing has been
completed.

[CLAIMS]
1. A burring processing method comprising increasing a diameter of a prepared hole
provided in a metal component and bending a part of the metal component to form a
burring processed portion including an upright portion and a curved portion,
wherein, in a cross-section that passes through an axis of the burring processed
portion and is parallel to the axis of the burring processed portion, a cross-sectional shape
of the curved portion on an inner surface of the curved portion consists of a curve, and a
length of the curved portion in a direction perpendicular to the axis of the burring
processed portion is at least 1.2 times a height of the curved portion in a direction parallel
to the axis of the burring processed portion.
2. A burring processing method comprising forming a burring processed portion in a
metal component provided with a prepared hole using a mold including a die having a die
hole, a holder, and a punch,
wherein the metal component is sandwiched between the die and the holder,
the punch is inserted into the die hole along an axis of the die hole to increase a
diameter of the prepared hole and to bend a part of the metal component, thereby forming
a burring processed portion including an upright portion and a curved portion, and
in a cross-section that passes through the axis of the die hole and is parallel to
the axis of the die hole, a cross-sectional shape of a die shoulder consists of a curve, and
a length of the die shoulder in a direction perpendicular to the axis of the die hole is at
least 1.2 times a height of the die shoulder in a direction parallel to the axis of the die
hole.
51
3. The burring processing method according to claim 1 or 2, wherein, when a plate
thickness around the prepared hole of the metal component is defined as t, and a height of
the curved portion in the direction parallel to the axis of the burring processed portion is
defined as h, the following Expression 1 is satisfied.
h/t<0.6 .. · Expression 1
4. The burring processing method according to any one of claims 1 to 3, wherein, when
a plate thickness around the prepared hole of the metal component is defined as t, and a
plate thickness of an opening side end portion of the upright portion is defined as tb, the
following Expression 2 is satisfied.
tblt<0.9 .. · Expression 2
5. The burring processing method according to any one of claims 1 to 4, wherein a
value obtained by differentiating the expression representing the curve twice is larger
than 0.
6. A method for manufacturing a burring processed product comprising a burring
processed portion forming process of increasing a diameter of a prepared hole provided
in a metal component and bending a part of the metal component to form a burring
processed portion including an upright portion and a curved portion,
wherein, in a cross-section that passes through an axis of the burring processed
portion and is parallel to the axis of the burring processed portion, a cross-sectional shape
of the curved portion on an inner surface of the curved portion consists of a curve, and a
length of the curved portion in a direction perpendicular to the axis of the burring
processed portion is at least 1.2 times a height of the curved portion in a direction parallel
52
to the axis of the burring processed portion.
7. A method for manufacturing a burring processed product comprising a burring
processed portion forming process of forming a burring processed portion in a metal
component provided with a prepared hole using a mold including a die having a die hole,
a holder, and a punch,
wherein, in the burring processed portion forming process, the metal component
is sandwiched between the die and the holder, the punch is inserted into the die hole
along an axis of the die hole to increase a diameter of the prepared hole and to bend a
part of the metal component, thereby forming a burring processed portion including an
upright portion and a curved portion, and
in a cross-section that passes through the axis of the die hole and is parallel to
the axis of the die hole, a cross-sectional shape of a die shoulder consists of a curve, and
a length of the die shoulder in a direction perpendicular to the axis of the die hole is at
least 1.2 times a height of the die shoulder in a direction parallel to the axis of the die
hole.
8. The method for manufacturing a burring processed product according to claim 6 or
7, further comprising a prepared hole forming process of forming the prepared hole in the
metal component before the burring processed portion forming process.
9. The method for manufacturing a burring processed product according to any one of
claims 6 to 8, wherein, when a plate thickness around the prepared hole of the metal
component is defined as t, and a height of the curved portion in the direction parallel to
the axis of the burring processed portion is defined as h, the following Expression 1 is
53
satisfied.
h/t<0.6 .. · Expression 1
10. The method for manufacturing a burring processed product according to any one of
claims 6 to 9, wherein, when a plate thickness around the prepared hole of the metal
component is defined as t, and a plate thickness of an opening side end portion of the
upright portion is defined as tb, the following Expression 2 is satisfied.
tblt<0.9 .. · Expression 2
11. The method for manufacturing a burring processed product according to any one of
claims 6 to 10, wherein a value obtained by differentiating an expression representing the
curve twice is larger than 0.
12. A burring processing mold comprising a die having a die hole, a holder holding a
workpiece together with the die, and a punch movable relative to the die and the holder,
wherein, in a cross-section that passes through an axis of the die hole and is
parallel to the axis of the die hole, a cross-sectional shape of a die shoulder consists of a
curve, and a length of the die shoulder in a direction perpendicular to the axis of the die
hole is at least 1.2 times a height of the die shoulder in a direction parallel to the axis of
the die hole.
13. The burring processing mold according to claim 12,
wherein the punch includes a cylindrical portion having a diameter smaller than
a diameter of the die hole, and the punch is configured to be inserted into the die hole
along the axis of the die hole, and
54
when a clearance between the die hole and the cylindrical portion is defined as
cl and a height of the die shoulder in a direction parallel to the axis of the die hole in the
cross-sectional shape is defined as hct, the following Expression 3 is satisfied.
cl<1.5hct .. · Expression 3
14. The burring processing mold according to claim 12 or 13, wherein a value obtained
by differentiating an expression representing the curve twice is larger than 0.
15. A burring processing device comprising the burring processing mold according to
any one of claims 12 to 14, and a drive mechanism configured to move the die, the
holder, and the punch relative to each other.
16. A burring processed product comprising a burring processed portion including an
upright portion and a curved portion,
wherein, in a cross-section that passes through an axis of the burring processed
portion and is parallel to the axis of the burring processed portion, a cross-sectional shape
of the curved portion on an inner surface of the curved portion consists of a curve, and a
length of the curved portion in a direction perpendicular to the axis of the burring
processed portion is at least 1.2 times a height of the curved portion in a direction parallel
to the axis of the burring processed portion.
17. The burring processed product according to claim 16, wherein, when a plate
thickness around the curved portion is defined as ts, and a height of the curved portion in
the direction parallel to the axis of the burring processed portion is defined as h, the
following Expression 4 is satisfied.
55
h/ts<0.6 ···Expression 4
18. The burring processed product according to claim 16 or 17, wherein, when a plate
thickness around the curved portion is defined as ts, and a plate thickness of an opening
side end portion of the upright portion is defined as tb, the following Expression 5 is
satisfied.
tb/ts<0.9 · · · Expression 5
19. The burring processed product according to any one of claims 16 to 18, wherein the
burring processed product is any of a lower arm, a trailing arm, and upper arm, which are
used in a vehicle.
20. The burring processed product according to any one of claims 16 to 18,
wherein the burring processed product is a lower arm used in a vehicle, which
further includes a cylindrical portion and a cylindrical flange portion,
in a plane that is perpendicular to the axis of the burring processed portion and
passes through a center C in a length direction of the cylindrical portion on an axis of the
cylindrical portion,
when an intersection between the axis of the burring processed portion and the
plane is defined as an intersection A, an intersection between an axis of the cylindrical
flange portion and the plane is defined as an intersection B, and the smaller angle
between a line segment AB connecting the intersection A to the intersection B and a line
segment AC connecting the intersection A to the center Cis defined as 8, and
in the range of 28 from the line segment AB to a side on which the center C is
located, and in the range of 28 from the line segment AB to a side opposite to the side on
56
which the center C is located, with the intersection A set as a center,
in the cross-section that passes through the axis of the burring processed portion
and is parallel to the axis of the burring processed portion, the cross-sectional shape of
the curved portion on the inner surface consists of a curve, and the length of the curved
portion in the direction perpendicular to the axis of the burring processed portion is at
least 1.2 times the height of the curved portion in the direction parallel to the axis of the
burring processed portion.
21. The burring processed product according to any one of claims 16 to 20, wherein a
value obtained by differentiating an expression representing the curve twice is larger than
0.