Document Type] Specification
[Title of the Invention] PRODUCTION METHOD OF WHEEL RIM, AND
PRODUCTION METHOD OF VEHICLE WHEEL RIM
[Technical Field of the Invention]
[OOOl]
The present invention relates to a production method of a wheel rim and a
production method of a vehicle wheel rim.
Priority is claimed on Japanese Patent Application No. 2014-051431, filed on
March 14,2014, the content of which is incorporated herein by reference.
[Related Art]
[0002]
As an example of a wheel rim, a vehicle wheel rim is shown in FIG. 12. A
vehicle wheel 1 is constituted by a substantially cylindrical rim la, and a disc 1 b fixed
to the rim la. In the rim la, a rim shape including a drop 2, wells 3a and 3b, a ledge 4,
bead seats 5a and 5b, flanges 6a and 6b, and the like is formed.
[0003]
A production method of the rim la generally includes a step of correcting an
uncoiled steel strip to be flat using a roller, a step of obtaining a flat sheet by cutting the
corrected steel strip, a step of bending the obtained flat sheet into a cylindrical shape, a
step of obtaining a cylindrical rim material by butt-welding both end edges of the bent
flat sheet, a flaring step of increasing the diameters of both opening end edges of the rim
material, a plurality of rolling steps of forming the rim material into the rim shape, and
an expanding step of adjusting the rim diameter.
[0004]
The rim la of the vehicle wheel 1 is required to be lightweight and have
sufficient strength. The degree of stress generated in the rim la varies depending on
the region and use situations. For example, when a vehicle steadily travels, stress in
the drop 2 increases, aid when the vehicle collides with a curbstone, stress in the flange
6a or 6b increases. However, in the rim la, there is a region which does not receive
high stress and does not require high strength regardless of the travelling state of the
vehicle. Such a region may be reduced in thickness as long as a certain degree of
strength is ensured. As a result, it is possible to achieve a reduction in the weight of
the rim la. On the other hand, during collision with the curbstone, high stress is
exerted on the opening end edge (the flange 6a or 6b) of the rim la which particularly
faces the outside, and it is effective for increasing the thickness of such a region to be
strengthened.
[OOOS]
I-Iowever, the opening end edge of the rim la has a longer circumference than
those of the drop 2 and the like and is likely to be thinned in the rolling steps.
Therefore, for example, in Patent Document 1, in order to produce a rim, a sheet
material having different sheet thicknesses in a transverse direction is produced in
advance, and the sheet thickness of a region corresponding to the opening end edge of
, the rim (a region called an "edge portion" in Patent Document 1) is formed to be greater
than that of a region corresponding to the other region (a region called a "bottom
portion" in Patent Document 1).
[OOO6]
Patent Document 2 discloses an invention related to "a forming method of a
vehicle wheel, which is performed by nipping a disk-shaped forming material between
an end surface of a mandrel having a spinning forming die on its outer circumference
and a tailstock that opposes the end surface, the method including a spinning step of
pressing the forming material against the forming die using a spinning roller moved
along the forming die, and a thickening step of moving a thickening roller, which has a
circumferential wall portion that opposes the forming die and a side wall portion that
extends in a direction substantially perpendicular to a rotating shaft of the mandrel,
toward the inside in a radial direction of the mandrel, thereby deforming a
circumferential edge portion of the forming material so as to be thickened and forming
an outer edge flange portion of a wheel rim between an inner end surface that rises
toward the outside in the radial direction from an inner end portion of the forming die to
the inner end portion and a circumferential wall portion to a side wall portion of the
thickening roller".
[Citation List]
[Patent Document]
[OOO7]
[Patent Document 11 Japanese Unexamined Patent Application, First
Publication No. S59-109404
[Patent Document 21 Japanese Unexamined Patent ~ ~ ~ l i c a t iFoirnst,
Publication No. H6-182471
[Disclosure of the Invention]
[Problems to be Solved by the Invention]
[OOO8]
In the production method described in Patent Document 1, since the step of
producing the sheet material having different sheet thicknesses in the transverse
direction in advance is needed, there is a problem of an increase in production costs.
In addition, there is a need to change a groove shape of a roller according to a
cross-sectional shape of the rim, and it is difficult to easily change the cross-sectional
shape'in consideration of time and effort. Furthermore, in a case of using the sheet
material having different sheet thicknesses in the transverse direction, it is dificult to
perform control of bending of the sheet material to obtain a cylindrical rim material with
, good accuracy. arefore, obtaining a cylindrical rim material with high dimensional
accuracy requires a complex production step.
[0009]
On the other hand, as in the production method described in Patent Document 2,
in the method of thickening an opening end edge by moving the thickening roller in a
radial direction of a cylindrical rim material, successive processing in which the rim
material disposed on an outer circumferential.surface of the mandrel is repeatedly
locally deformed by the thickening roller is mainly performed. ~ u i itnhe~ th ickening
in this method, there is a need to use a spinning machine, resulting in low production
efficiency and an increase in production costs. Particularly in a case where the
spinning machine is provided in advance as in a production step of an aluminum wheel
or the like, it is relatively easy to employ this method. However, in a case of a rim
produced basically by a rolling step as in a production step of a steel wheel rim, an
increase in costs for the addition of the spinning machine is incurred.
[OOlO]
The present invention has been made taking the foregoing circumstances into
consideration, and an object thereof is to provide a production method of a wheel rim
and a production method of a vehicle wheel rim capable of thickening of an opening
end edge of a wheel rim with no reduction in production efficiency, and good
dimensional accuracy.
[Means for Solving the Problem]
[OOll]
In order to accomplish the object, the inventors conducted intensive research
on a method of producing a cylindrical rim material and thereafter thickening an
opening end edge of the rim material without buckling and completed the present
invention.
[0012]
That is, the gist of each of aspects of the present invention is as follows.
(1) According to an aspect of the present invention, a production method of a
wheel rim includes: a step of forming a cylindrical rim material into a rim shape; and a
step of increasing a sheet thickness of at least one opening end edge of the rim matcrial
at least one of before and after the step of forming of the cylindrical rim material, in
which, in the step of increasing of the sheet thickness, in a state in which the opening
end edge is inserted into an annular groove of a die provided with the annular groove
which is wider than the sheet thicltness of the opening end edge, a thickened portion is
formed by exerting a compressive load in an axial direction of the rim material on the
opening end edge.
[0013]
(2) In the production method of a wheel rim described in (I), the step of
increasing of the sheet thickness may include heating the opening end edge.
[0014]
(3) In the production method of a wheel rim described in (2), after the heating
of the opening end edge, the opening end edge may be inserted into the annular groove
to receive the compressive load.
[0015]
(4) In the production method of a wheel rim described in (2), the compressive
load may be exerted on the opening end edge while the opening end edge is heated in a
state of being inserted into the annular groove.
[0016]
(5) In the production method of a wheel rim described in any one of (2) to (4),
in a case where a width of a heated region of the opening end edge in the axial direction
before the compressive load is exerted is referred to as Wh and the width of the
thickened portion after the compressive load is exerted is referred to as W, Wh>W may
he satisfied.
[OO 171
(6) In the production method of a wheel rim described in any one of (2) to (5),
in a case where a depth of the annular groove in the axial direction is referred to as D
and the width of the heated region of the opening end edge before the co~npressivelo ad
is exerted is referred to as Wh, D>Wh may be satisfied.
[0018]
(7) In the production method of a wheel rim described in any one of (2) to (6),
a heating temperature ofthe opening end edge may be within a range of 450°C to
850°C.
[0019]
(8) 111 the production method ofa wheel rim described in any one of (1) to (7),
in the step of increasing of the sheet thickness, the compressive load may be exerted
while an inner circumferential surface of the opening end edge is supported by an inner
wall of the annular groove during the increasing of the sheet thickness and an outer
circ-unferential surface of the opening end edge is supported by an outer wall of the
annular groove which is wider than the inner wall.
[0020]
(9) A production method of a vehicle wheel of the present invention includes: a
step of fixing a disc into the wheel rim obtained in the production method of a wheel
rim described in any one of (1) to (8).
[0021]
(10) In the production method of a vehicle wheel described in (9), in the step of
increasing of the sheet thickness, the thickened portion may be formed i i at least the
opening end edge of both the opening end edges of the rim material, which faces the
outside when mounted in a vehicle.
[Effects of the Invention]
[0022]
According to the production method of a wheel rim described in (1) of the
present invention, the opening end edge of the wheel rim such as a vehicle wheel rim
can be thickened with no reduction in production efficiency, and good dimensional
accuracy. Therefore, even when the rim material is thinned due to a reduction in the
weight of the wheel rim, sufficient strength can be obtained by thickening the opening
end edge.
[0023]
In addition, in a case of the production method of a wheel rim described in (2)
to (7), since the opening end edge can be locally softened through heating, it becomes
possible to more stably perform the thickening without the occurrence buckling.
In addition, in a case of the production method of a wheel rim described in (S),
it becomes possible to perform the thickening while more reliably preventing the
occurrence of buckling of the opening end edge.
In addition, in a case of the production method oPa vehicle wheel rim
described in (9) and (lo), it becomes possible to obtain the same effects as those of the
production method of a wheel rim described in (1).
[Brief Description of the Drawings]
100241
FIG. 1 is a view showing a first embodiment of the present invention and is a
flowchart showing a production method of a vehicle wheel rim.
FIG. 2 is a view showing the embodiment and is a sectional view before a
thickening stcp.
FIG. 3 is a view showing the embodiment and is a sectional view during the
thickening step.
FIG. 4A is a view showing the embodiment and is a partial sectional view
corresponding to the section A of FIG. 3 before the thickening step.
FIG. 4B is a view showing an intermediate stage of the thickening step in the
,! embodiment and is a,partial sectional view corresponding to the section A of FIG. 3.
FIG. 4C is a view showing an intermediate stage of the thickening step in the
embodiment and is a partial sectional view corresponding to the section A of FIG. 3.
FIG. 41) is a view showi~lga n intermediate stage of the thickening step in the
embodiment and is a partial sectional view corresponding to the section A of FIG. 3.
FIG. 5 is a view showing the embodiment and is a partial sectional view
corresponding to the section A of FIG. 3.
FIG. 6 is a graph showing the relationship between a heating temperature of a
steel at a high temperature and after heating and cooling and yield stress which is a
member strength.
FIG. 7 is a view showing a modification example of the present invention and
is a partial sectional view corre, .s. ponding to FIG. 4B.
FIG. 8 is a view showing a sheet thickness distribution in a case where a 2.36
mm even thickness rim material is formed into a rim shape, in which the horizontal axis
represents a position in a rim width direction and the vertical axis represents a sheet
thickness.
FIG. 9 is a view showing a sheet thickness distribution after forming the rim
shape in a case where a rim material which has a thickness of 2.36 mm and has a
circumferential edge portion thickened to 2.60 mm is used, in which the horizontal axis
represents a position in a rim width direction and the vertical axis represents a sheet
thickness.
FIG. 10 is a view showing a sheet thickness distribution after forming the rim
shape in a case where a rim material which has a thickness of 2.36 mm and has a
circun~ferentiael dge portion thickened to 2.90 mm is used, in-which the horizontal axis
represents a position in a rim width direction and the vertical axis represents a sheet
thickness.
FIG. 11 is a view showing a sheet thickness distribution after forming the rim
shape in a case where a rim material which has a thickness of 2.00 mm and has a
circumferential edge portion thickened to 2.60 rnm is used, in which the horizontal axis
represents a position in a rim width direction and the vertical axis represents a sheet
thickness.
FIG. 12 is a view showing an example of a wheel structure and is a vehicle
wheel in a case of being viewed in a section including an axis.
[Embodiments of the Invention]
[0025]
As an example of a production method of a wheel rim according to the present
invention, each embodiment regarding a method of producing a vehicle wheel rim will
be described. However, the production method of the present invention can also be
applied to production of various types of wheel rims in addition to the vehicle wheel
I rim.
When a vehicle wheel rim is produced, first, there is a need to obtain a
cylindrical rim material from a flat sheet, and as the method, a general method may be
employed. For example, as shown in the flowchart of FIG. 1, the cylindrical rim
material may be obtained by a step S1 of uncoiling a steel strip that is wound in a coil
shape and correcting the steel strip using a roller, a step S2 of obtaining a flat sheet by
cutting the corrected steel strip into predetermined dimensions, a bending step S3 of
bending the obtained flat sheet into a cylindrical shape, a butt-welding step S4 of
butt-welding both end edges of the bent flat sheet, and a finishing step S5 of removing
burr of the weld.
Each embodiment of a method of producing a vehicle wheel rim from the rim
material obtained as described above will be subsequently described below.
to0261
First Embodiment]
In a production method of a vehicle wheel rim according to a fist embodiment
of the present invention, the cylindrical rim material is subjected to a thickening step S6
of thickening at least one of a pair of opening end edges (hereinafter, sometimes
referred to as "circumferential edge portions", which are a pair of annular portions
denoted by reference numeral 21 in FIG. 2) thereof, a flaring step S7 of increasing the
:;
I diameters of both the opening end edges of the rim material, a plurality of rolling steps
S8 of forming the rim material into a rim shape, and an expanding step S9 of adjusting
i the rim diameter. As a result, a rim is completed.
(
As an example of the rim shape, as in the rim la described with reference to
,I
FIG. 12, a shape including the drop 2, the wells 3a and 3b, the ledge 4, the bead seats 5a
and 5b, the flanges 6a and 6b, and the like may be employed.
[0027]
Specific contents of the flaring step S7 and the rolling steps S8 are not
particularly limited, and a general method may be employed. The flaring step S7 is a
step of increasing the diameters of the circumferential edge portions of the rim material
by pressing the circumferential edge portions of the cylindrical rim material using a
forming tool. In addition, in the rolling steps S8, the cylindrical rim material that is
flared is rolled while being nipped between a pair of rolls with predetermined concave
and convex portions formed therein, thereby being formed into the rim shape. The
rolling steps S8 include, for example, a drop forming step, a flange forming step, and a
finish forming step.
[0028]
The thickening step S6 includes: a heating step of forming, in the
circumferential edge portion 21 of a rim material 20, a heated region 22 which is heated
in advance to have reduced deformation resistance; and a pressing step of thickening the
heated region 22 by performing pressing, for example, using a die 10 (10a and lob)
shown in FIGS. 2 and 3 after the heating step.
The heating step is performed as a pre-treatment of the pressing step.
However, the pressing step which is the base ofthe thickening step S6 will he described
first, and thereafter the heating step will be subsequently described.
[0029]
As shown in FIG. 2, the die 10 is constituted by a pressing die 10a having an
annular groove 11 and a supporting die lob which supports the inner circumferential
surface ofthe rim material 20, the dies forming a pair.
The pressing die 10a is a disk-shaped die having a greater outer diameter than
that of the rim material 20, and includes an inner circular convex portion lOal which is
formed on the inside with respect to the annular groove 11 as the boundary, and an outer
circular convex portion 10a2 which is formed on the outside of the annular groove 1 I.
In other words, the annular groove 11 is defined by the outer circumferential surface of
the inner circular convex portion 10a1, the inner circumferential surface of the outer
circular convex portion 10a2, and a bottom surface formed on the inside of the outer
circumferential surface and the inner circumferential surface which face each other.
1003 01
The annular groove 11 is coaxial with the center of the pressing die 10a and has
the same groove width and groove depth at any position in the circumferential direction
thereof.
The outer circular convex portion 10a2 has a greater height from the bottom
surface of the annular groove 11 than that of the inner circular convex portion 10al. In
addition, in the outer circular convex portion 10a2, a chamfer having an arc shape in a
sectional view is formed to be smoothly connected to the inner circumferentiai surface
of the annular groove 11. Since the chamfer is fom~edt,h e rim material 20 can be
smoothly guided and inserted into the annular groove 11.
[003 11
The supporting die 10b includes a base portion lob1 having a disk shape, and a
columnar portion lob2 which is formed on the base portion lob1 to be integrated
, therewith on the same axis as that of the base portion 1Ob1. In order to support the
inner circumferential surface of the rim material 20 on the inside, the outer diameter of
the columnar portion lob2 is determined to be close to the inner diameter of the inner
circumferential surface of the rim material 20 and to ensure a clearance necessary for
fitting of the rim material 20 on the outside.
In addition, the height of the columnar portion lob2 is smaller than the axial
height of the rim material 20. This is because the thickening of the rim material 20 is
to be performed. Details will be described later.
[0032]
During the thickening step S6, in the pressing step after the heating step, fust,
as shown in FIGS. 2 and 3, in a state in which the rim material 20 is held by the
supporting die lob, the pressing die 10a is put thereon. At this time, the pressing die
10a is put so as to allow one circumferential edge portion 21 of the rim material 20 to be
accommodated in the annular groove 11.
More specifically, first, as shown in FIG. 2, the rim material 20 is externally
fitted to the columnar portion lob2 of the supporting die 10b on the same axis. As a
result, as shown in FIG. 3, the other circumferential edge portion 21 which is the lower
end of the rim material 20 abuts the upper surface of the base portion lob1 srich that the
rim material 20 is disposed to achieve a state in which an axial load on the rim material
20 is supported by the upper surface of the base portion lob1 and the circumferential
edge portion 21 extends upward from the upper surface of the columnar portion 10b2 by
predetermined dimensions.
[0033]
Subsequently, the pressing die 10a is lowered from the upper side of the rim
material 20 while allowing the circumferential edge portion 21 of the rim material 20
and the arn~ularg roove 11 to be coaxial with each other, and the circumferential edge
portion 21 is coaxially accommodated in the annular groove 11. In addition, when the
circumferential edge portion 21 of the rim material 20 reaches the bottom surface of the
annular groove 11, the state shown in FIG. 3 is achieved. In this state, the columnar
portion 10b2, the rim material 20, and the annular groove I1 are coaxial with each other.
Moreover, a predetermined gap g is provided between the lower surface of the inner
circular convex portion lOal of the pressing die 1 Oa and the upper surface of the
columnar portion lob2 of the supporting die lob. The gap g acts as a compression
margin.
The pressing die 10a is further lowered toward the rim material 20 from the
state of FIG. 3 in which the circumferential edge portion 21 of the rim material 20 is
accommodated in the annular groove 11 as described above, and a compressive load is
exerted in the axial direction (a direction indicated by the white arrow in FIG. 3) on the
circumferential edge portion 21 of the rim material 20 and particularly the heated region
22 in the circumferential edge portion 21 is thickened and deformed so as to fill the
annular groove 11. At a point of time when the gap g becomes zero, compression is
ended.
Thereafter, when the pressing die 10a is detached from the rim material 20 and
the rim material 20 is further detached from the supporting die lob, bnly the
circumferential edge portion 21 of the rim material 20 has a greater sheet thickness than
those of other portions, and the thickening step S6 is completed.
The flaring step S7, the rolling steps S8, and the expanding step S9 are
performed on the rim material 20 after the thickening step S6. By welding and fixing
(a step S10 in FIG. 1) the disc to the rim processed as described above, a vehicle wheel
rim is completed.
[0034]
In addition, the supporting die lob is a die having a main function of
preventing bending of the rim material 20. Therefore, there may be no gap between
the inner circumferential surface of the rim material 20 and the outer circumferential
surface of the columnar portion 1Ob2. However, when the gap is too narrow, it
becomes difficult to attach and detach the rim material 20. Therefore, a certain degree
of gap is preferably present. For example, the difference in dimensions between the
inner diameter of the rim material 20 and the outer diameter of the columnar portion
lob2 may be set to 1.0 mm to 3.0 mm. In this case, the gap is substantially the half of
the difference in dimensions and this becomes 0.5 rnrn to 1.5 mm.
[0035]
In addition, in this embodiment, the supporting die lob which supports the
inner circumferential surface of the rim material 20 with the outer circumferential
surface of the columnar portion lob2 is described. However; the embodiment is not
limited to this configuration. For example, a supporting die (not shown) which covers
the outer circumferential surface of the rim material 20 to cover the outer
circumferential surface, or a supporting die (not shown) which supports both the inner
circumferential surface and the outer circumferential surface of the rim material 20 may
also be employed.
The thickening S6 in this embodiment is performed on one ofthe pair of
circumferential edge portions 21 in the cylindrical rim material 20 and may also be
performed on both thereof. In addition, in a case where the thickening step S6 is
, performed only one of the pair of circumferential edge portions 21, the thickening step
S6 is preferably performed on the circumferential edge portion that faces the outside
when the vehicle wheel rim is mounted in a vehicle.
Furthermore, in this embodiment, the thickening step S6 is performed before
the rim shaping (before the rolling steps S8). However, the embodiment is not limited
thereto, and the rim shaping may be performed first and the thickening step S6 may be
performed thereafter. Otherwise, the thickening step S6 may be performed in two
stages and each stage may be performed before and after the rim shaping.
[0036]
The gist of the production method of the vehicle wheel rim according to this
embodiment described above is summarized as follows.
The production method of the vehicle wheel rim according to this embodiment
includes: a forming step (the rolling steps S8) of forming the cylindrical rim material 20
into the rim shape; and the thickening step S6 of increasing the sheet thickness of at
least one of the circumferential edge portions 21 of the rim material 20 at least one of
before and after the forming step. In addition, in the thickening step S6, in a state in
which the circumferential edge portion 21 which is provided with the heated region 22
in advance is inserted into the annular groove 11 of the pressing die 10a having the
annular groove 11 which has a width greater than the sheet thickness of the
circumferential edge portion 21, a compressive load in the axial direction of the rim
material 20 is exerted on the circumferential edge portion 21, thereby forming a
thickened portion.
[0037]
;. According to this embodiment described above, the thickening is performed by
compression using the die 10. Therefore, compared to thickening using a spinning
machine, the circumferential edge portion 21 of the rim material 20 can be thickened
within a shorter period of time. Therefore, the processing can be performed within
cycle times ofthe steps S1 to S5, and the steps S7 to S9 before and after the thickening
step S6, and thus production efficiency is not reduced. That is, in a case where a
plurality of rim materials 20 are processcd in each of the steps S1 to S9 shown in FIG 1
while being sequentially transported, the number of products produced per unit time,
that is, production efficiency is determined by the step (for example, the rolling steps
S8)that requires the longest operation time among the steps Sl to S9. In a case where
the thickening step S6 is considered from this viewpoint, the thickening step S6 can be
ended within a shorter period of time than that of the rolling steps S8. Therefore, the
production efficiency is not reduced.
... In addition, since an expensive apparatus such as a spinning machine is not
used but the relatively simple pressing device is used, a small increase in production
cost is required for the thickening.
[0038]
Although the pressing step which is the base of the thickening step S6 has been
described, in order to selectively thicken only the circumferential edge portion 21
during the pressing step of the rim material 20, the deformation resistance of the
circumferential edge portion 21 needs to be reduced in advance. A pre-treatment for
this is the heating step. Details thereof will be described in association with the
contents of the pressing step.
That is, in the production method of the vehicle wheel rim according to this
embodiment, when the thickening step S6 is performed, as shown in FIG. 4A, the heated
region 22 which is heated in advance to have reduced deformation resistance is formed
in the circumferential edge portion 21 of the rim material 20. Thereafter, as shown in
FIG. 4B, the circumferential edge portion 21 including the heated region 22 is
accommodated in the annular groove 1 I , and a compressive load is exerted in the axial
direction (the direction indicated by the white arrow) of the rim material 20 is in this
state. Therefore, as shown in FIGS. 4C and 4D, it becomes easier to selectively
thicken only the circumferential edge portion 21 of the rim material 20. A heated
width (Wh) of the heated region 22 in the circumferential edge portion 21 is preferably
equal to or greater than an estimated thickened length (W) of the thickened porlion
formed in the circumferential edge portion 21 of the rim material 20.
[0039]
In addition, the heated width (Wh) means the length of the heated region 22 in
the circumferential edge pdrtion 21, and the heated region 22 mean, for example, a'.
region at 450°C or higher. In addition, the heating temperature of the circumferential
edge portion 21 may be set to a temperature range in which the deformation resistance
(strength) of the rim material 20 is sufficiently decreased to enable thickening to be
easily performed and sufficient strength can be recovered after cooling. In addition, a
heating method is not particularly limited and well-known methods such as induction
I heating or radiation heating may be employed. Among various heating methods,
induction heating is particularly preferable from the viewpoint of good heating
efficiency and ease of installation in an apparatus.
[0040]
Details of a procedure in which the circumferential edge portion 21 (the heated
region 22) in the rim material 20 receives a compressive load in the annular groove 11
, and is thickened will be described with reference to FIG. 5.
In FIG. 5, the heated region 22 which is heated and reaches a temperature range,
which will be described later, in the circumferential edge portion 21 is a portion
indicated by the heated width Wh. In addition, in a state before a compressive load is
exerted, the heated region 22 is provided with a gap tl from the annular groove 11 on
the inner circumferential surface side of the circumferential edge portion 21 and a gap t2
from the annular groove 11 on the outer circumferential surface side of the
circumferential edge portion 21. In addition, in a case where the thickness of the
heated region 22 is referred to as t3, the sum of tl+t2+t3 becomes substantially the same
as the thickness of the circumferential edge portion 21 obtained after the thickening.
In practice, by estimating that the thickness t3 will slightly decrease due to thermal
contraction after cooling, the gaps tl and t2 are preferably set to slightly greater values.
[0041]
When the heated region 22 shown in FIG. 5 receives a compressive load
directed toward the lower side in the figure from the annular groove 11, the length
thereof gradually decreases. As compressive deformation proceeds, the thickness of
the heated region 22 at each position in the vertical direction is evenly thickened and
finally fills the annular groove 11. As a result, the heated region 22 is thickened into
an even thickness at any position in the axial direction of the annular groove 11.
In addition, as a thickening method, both the inner circumferential surface and
the outer circumferential surface of the circumferential edge portion 21 may be
subjected to the thickening so as to be evenly thickened, or only one of the inner
i
'I circumferential surface and the outer circumferential surface may be subjected to the
:I thickening so as to I he. thickened. 4 [0042] ' .
!
il
i! In addition, an appropriate range of the heating temperature of the heated
region 22 is preferably set to be equal to or higher than a temperature at which the yield
stress during heating of the rim material 20 becomes half (50%) of the yield stress
before the heating and to be equal to or lower than a temperature at which the yield
stress after the heating and cooling becomes 90% of the yield stress before the heating.
For example, the heating temperature of the heated region 22 when steel is postulated as
the material used for the rim is preferably within a range of 450°C to 850°C.
[0043]
FIG. 6 shows an example in which a high tensile strength steel sheet having a
yield stress of 800 ~ l m mis h~eat ed and the yield stress thereof is measured after the
heating and cooling. As shown in FIG. 6, at a heating temperature of 45OoC, the yield
a stress cannot be reduced to 400 ~ l m mor l~ess (half of the original yield stress or less)
and thus deformation resistance is insufficiently reduced. On the other hand, when the
heating temperature is 450°C or higher, the yield stress can be reduced to 400 ~ l m tonr ~
less through heating, and furthermore, the yield stress after cooling can be recovered to
a value close to the original yield stress. When the heating temperature is excessively
increased, the yield stress after cooling is insufficiently recovered and sufficient strength
for the vehicle wheel rim cann6t be ensured (for example, at 800°C, the yield stress
after the cooling is reduced to 450 ~ l m m ~ )T.h erefore, in consideration of the balance
between a reduction in the yield stress through heating and the recovery of the yield
stress after the cooling, the heating temperature is preferably set to 450°C to 850°C in a
case of high tensile strength steel although the heating temperature is dependent on the
material of the rim material 20. More specifically, in this temperature range, a range of
500°C to 750°C is more preferable.
100441
In addition, at the point of time when the thickening step S6 is almost
completed as shown in FIG. 4D, the thickened portion comes into contact with the wall
surface of the annular groove 11. However, as the cooling proceeds, the thickness of
the thickened portion that thermally expands slightly decreases, and the thickened
portion can be easily removed from the annular groove 11.
[0045]
The depth of the annular groove 11 (reference numeral D of FIG. 4A) is
preferably equal to or greater than the heated width Wh of the circumferential edge
portion 21 (see FIGS. 4A and 5). In a case where this is not satisfied, there may be
cases where the circumferential edge portion 21 buckles and tlus has an adverse effect
on the dimensioilal accuracy of an end product.
[0046]
In addition, in this embodiment, at least one of the circumferential edge
portions 21 of the cylindrical rim material 20 is thickened. However, particularly in a
case of use as the vehicle wheel rim, the circumferential edge portion which becomes at
least the outer circumferential edge portion is preferably thickened. The reason is that
the outer circumferential edge portion of the vehicle wheel rim requires high strength
during a collision with a curbstone. When the collision strength of this portion can he
incrcased, the other portions can be thinned, which contributes to a reduction in the
overall weight of a vehicle wheel. As a result, a vehicle provided with a plurality of
vehicle wheels can be reduced, and it becomes possible to exhibit effects regarding fuel
efficiency improvement and countermeasures for environmental pollution.
In addition, this embodiment can be applied to produce vehicle wheel rims
with various materials and is particularly appropriate for the production of a steel wheel
rim. Particularly, this embodiment is suitable for the production of a high tensile
strenglh steel wheel rim.
[0047]
As described above in detail, in the production method of the vehicle wheel rim
of this embodiment, the thickening step S6 includes the heating step of heating the
circumferential edge portion 21. That is, the circumferential edge portion 21 is heated
and is thereafter inserted into the annular groove 11 to receive a compressive load.
In addition, in the axial diection of the rim material 20, in a case where the
width of the heated region 22 of the circumferential edge portion 21 before the annular
groove is exerted is referred to as Wh and the width of the thickened portion after the
compressive load is exerted is referred to as W, Wh>W is satisfied.
Furthermore, in the axial diection of the rim material 20, in a case where the
depth of the annular groove 11 is referred to as D and the width of the heated region 22
of the circumferential edge portion 21 before the compressive load is exerted is referred
to as Wh, D>Wh is satisfied.
[0048]
Furthermore, the heating temperature of the circumferential edge portion 21 is
within a range of 450°C to 850°C.
Furthermore, in the thickening step S6, the thickened portion is formed in at
least the outer opening end edge, which faces the outside when mounted in a vehicle, in
both the circumferential edge portions 21 of the rim material 20.
[0049]
[Second Embodiment]
A production method of a vehicle wheel rim according to a second embodiment
of the present invention will be described below. This embodiment corresponds to a
modification example of the first embodiment, and differences from those of the first
embodiment will be mainly described. The other configurations are considered to be
the same as those of the first embodiment, and overlapping description thereof will be
omitted.
[0050]
In this embodiment, a temperature gradient in the vertical direction in FIG. 5
(the aiial direction of the rim material 20) is applied to the heating temperature of the
heated region 22.
That is, the heated region 22 is heated to have a temperature gradient such that
, an opening front end,edge which abuts the annular groove 11 receives a compressive
load first has the highest temperature and the temperature gradually decreases toward
the inside from the opening front end edge. However, the temperature in the heated
region 22 preferably satisfies the temperature range of 450°C to 850°C (more preferably
500°C to 750°C) described above at any point.
[OOS l]
By applying the temperature gradient, it becomes possible to apply a
deformation resistance distribution (strength distribution) in which the deformation
resistance (strength) gradually decreases toward the opening front end edge from the
innermost position farthest from the opening front end edge, to the circumferential edge
portion 21 in the heated region 22. Since the deformation resistance distribution
(strength distribution) is applied, thickening and deformation of the circumferential
edge portion 21 in the thickening step S6 is locally started at the opening front end edge
which has relatively low deformation resistance (strength) in the heated region 22, this
local deformation gradually propagates toward the inner position, and thickening of the
entirety of the heated region 22 is finally completed.
As described above, thickening and deformation of the heated region 22 during
the thickening are always performed only on the processing front end edge. Therefore,
it becomes possible to prevent buckling deformation of the circumferential edge portion
21 and reliably prevent the generation of wrinkles.
[0052]
In each of the embodiments, the production object is the vehicle wheel rim.
However, the production object of the present invention is not limited only to the
vehicle wheel rim. For example, the production object can also be applied to a
production method of a wheel rim for a truck or an agricultural machine.
In addition, in each of the embodiments, the material of the vehicle wheel rim
is high tensile strength steel. However, the material is not limited thereto, and the
vehicle wheel rim may also be produced by using a material made of an
aluminum-magnesium alloy.
[0053]
In addition, in each of the embodiments, in the thickening step S6, the
circumferential edge portion 21 is heated before being inserted into the annular groove
11, and thereafter the thickening is performed on the circumferential edge portion 21
through compression. However, the heating and the thickening through compression
may also be simultaneously performed.
That is, among the steps of FIGS. 4A to 4D described as the thickening step S6,
in the stage of FIG. 4A before the circumferential edge portion 21 is inserted into the
annular groove 11, heating of the circumferential edge portion 21 is not performed, and
in the state of FIG. 4B in which the circumferential edge portion 21 is inserted into the
annular groove 11, heating of the circumferential edge portion 21 is started. In
addition, while the heating of the circumferential edge portion 21 is continuonsly
performed as it is, the compression shown in FIGS. 4C and 4D is simultaneously
performed.
In addition, as the heating method in this case, in addition to heating through
induction heating, a method of heating the pressing die 10a itself and heating the
circumferential edge portion 21 with the opening end edge through heat transfer caused
by the contact between the pressing die 10a and the circumferential edge portion 2 1 may
also be employed.
[0054]
In addition, in each of the embodiments, the annular groove 11 is provided in
the pressing die 10a and is formed by the annular inner wall surface and the outer wall
surface having the same axis and the bottom wall surface which connects the inner wall
surface and the outer wall surface, and in a case where the height from the bottom wall
surface to the outer wall surface in the axial direction of the rim material 20 is referred
to as H1 and the height from the bottom wall surface to the inner wall surface is referred
to as H2, Hl=H2 is satisfied. However, the embodiments are not limited only to this
configuration, and for example, as shown in FIG. 7, the thickening may be performed
using a pressing die 10a which satisfies Hl>H2.
That is, in the thickening step S6, the compression may also be performed
- while supporting the inner circumferential surface of the circumferential edge portion
y.. 21 with the inner wall surface of the annular groove 11 during the thickening and
supporting the outer circumferential surface of the circumferential edge portion 21 with
the outer wall surface of the annular groove 11, which is wider than the inner wall.
In addition, in each of the embodiments, the deformation resistance is locally
reduced by performing the heating step. However, means other than heating may also
be employed as long as the deformation resistance can be reduced. However, among
various means, it can be said that heating is the best means from the viewpoint of ease
of application or the like.
Furthermore, the deformation resistance may also be locally reduced in
advance by performing annealing or the like on a portion which is to become the
circumferential edge portion 21 in a state a steel strip or in a state of a flat sheet cut
from the steel strip.
[Examples]
[0055]
In order to check the effects of the production method of the vehicle wheel rim
of the first embodiment, the following inspection is performed in Examples.
That is, first, a plurality of flat sheets (two types of thicknesses bf 2.36 mm and
2.00 mm with the same yield stress of 800 ~ / m mm~a)de of high tensile strength steel
were prepared, each of the flat sheet was bent into a cylindrical shape, and both end
edges thereof were butt-welded, thereby obtaining two types of cylindrical rim materials
(each in which the radius of the outer circumferential surface was 170 mm and the
width parallel to the axial direction of the cylinder was 202 mm).
Subsequently, the circumferential edge portion of each of the cylindrical rim
materials was thickened, flared, and formed into a rim shape though rolling steps.
[0056]
The thickening step S6 for thickening the circumferential edge portion was
performed after the circumferential edge portion was heated to 700°C in advance, using
the pressing die 10a and the supporting die lob shown in FIGS. 4A to 4D. Two types
of heated widths Wh of a case of 20 mm and a case of 28 mm were prepared. The
depth of the annular groove 11 of the pressing die 1 Oa was set to 30 mm.
In addition, for comparison, some of cylindrical rim materials in which the
circumferential edge portion was not thickened were prepared, and these rim materials
were flared and shaped into a rim shape through the rolling steps in the same manner.
[0057]
The results of various cases described above will be described below.
First, in Comparative Example in which the thickening was not performed
although the 2.36 mm even thickness rim material was used, as shown in FIG. 8, the
circumferential edge portion of the produced rim was thinned to 2.22 mm.
[0058]
On the other hand, as shown in FIG. 9, in Example in which the rim material
which had a thickness of 2.36 mm and had the circumferential edge portion thickened to
2.60 mm was used, the thicknesses of regions other than the rim circumferential edge
portion were the same as those of Comparative Example shown in FIG. 7 in a state after
the rim material was formed into the rim shape, but the thickness of the rim
circumferential edge portion could be increased to 2.43 mm.
[0059]
In addition, as shown in FIG. 10, in Example in which the rim material which
had a thickness of 2.36 mm and had the circumferential edge portion thickened to 2.90
mm was used, the thicknesses of regions other than the rim circumferential edge portion
were the same as those of Comparative Example shown in FIG. 7 in a state after the rim
material was formed into the rim shape, but the thickness ofthe rim circumferential
edge portion could be increased to 2.71 mm.
[0060]
Furthermore, as shown in FIG. 11, in Example in which the rim material which
had a thickness of 2.00 mm and had the circumferential edge portion thickened to 2.60
mm was used, while the thicknesses of regions other than the rim circumferential edge
portion were in a range of 1.91 mm to 2.06 mm, the thickness of the rim circumferential
edge portion could be increased to 2.46 mm.
[Industrial Applicability]
[0061]
According to the present invention, a portion corresponding to the opening end
edge (circumferential edge portion) of a wheel rim such as a vehicle wheel rim can be
thickened with no reduction in production efficiency, and good dimensional accuracy.
Therefore, even when the opening end edge (circumferential edge portion) of the rim
material is thinned due to a reduction in the weight of the wheel rim, sufficient strength
can be obtained by thickening the opening end edge. The present invention is
particularly effective in producing a vehicle wheel rim using high tensile strength steel.
[Brief Description of the Reference Symbols]
[0062]
1 : VEHICLE WHEEL RIM (WHEEL RIM)
la: RIM
lb: DISC
2: DROP
3a, 3b: WELL
4: LEDGE
5a, 5b: BEAD SEAT
6a, 6b: FLANGE
10: DIE
10a: PRESSING DIE
lob: SUPPORTING DIE
1 1 : ANNULAR GROOVE
20: RIM MATERIAL
21: CIRCUMFERENTIAL EDGE PORTION, OPENING END EDGE OF
RIM MATERIAL
22: HEATED REGION
[Document Type] CLAIMS
1. A production method of a wheel rim comprising:
a step of forming a cylindrical rim material into a rim shape; and
a step of inc~easinga sheet thickness of at least one opening end edge of the
rim material at least one of before and after the step of forming of the cylindrical rim
material,
wherein, in the step of increasing of the sheet thickness, in a state in which the
opening end edge is inserted into an annular groove of a die provided with the annular
groove which is wider than the sheet thickness of the opening end edge, a thickened
portion is formed by exerting a compressive load in an axial direction of the rim
material on the opening end edge.
2. The production method of a wheel rim according to claim 1,
wherein the step of increasing of the sheet thickness includes heating the
opening end edge.
3. The production method of a wheel rim according to claim 2,
wherein, after the heating of the opening end edge, the opening end edge is
inserted into the annular groove to receive the compressive load.
4. The production method of a wheel rim according to claim 2,
wherein the compressive load is exerted on the opening end edge while the
opening end edge is heated in a state of being inserted into the annular groove.
5. The production method of a wheel rim according to any one of claims 2 to 4,
wherein, in a case where a width of a heated region of the opening end edge in
the axial direction before the compressive load is exerted is referred to as Wh and a
width of the thickened portion after the compressive load is exerted is referred to as W,
Wh>W is satisfied.
6. The production method of a wheel rim according to any one of claims 2 to 5,
wherein, in a case where a depth of the annular groove in the axial direction is
referred to as D and the width of the heated region of the opening end edge before the
compressive load is exerted is referred to as Wh, D>Wh is satisfied.
!
i 7. The production metliod of a wheel rim according to aiiy one of claims 2 to 6,
I I wherein a heating ten~peratureo f the opening end edge is wi!bin a range of
8. The production method of a wheel rim according to any one of claims 1 to 7,
wherein, in the step of increasing of the sheet thicluiess, the cornpressi~relo ad
is exerted while an inner ci~cuderentiasl urrace of the opcniag end edge is suppoited
by an inner wall of the annular groove during tlie increasing of tlie sheet thiclc~iessa nd
, .
an outer sircurnferential surface of the opening end edge is supported by an outer wall
of tlie aru~ularg roove which is wider than the im~e~wall.
9. A production method of a vehicle wheel coniprisiiig:
a step of fixing a disc illto the wlieel ~ i mob tai~icdin the production method of
a wheel ~ i macc ording to any one of claims 1 to 8.
!
10. The production method of a vehicle wheel according to claim 9,
<
wherein, in the step of increasing oftbe sheet tlucla~esst,h e tluclcened portion
is forined in at least the o. .p. ening end edge of both the opening end edges of the rim
43 material, which faces the outside when ~noul~teind a vehicle.