Note: Descriptions are shown in the official language in which they were submitted.
CA 02238267 1998-OS-21
WO 97/19771 PCTlIB96/01489
METHOD FOR FABRICATING A ONE-PIECE
METAL VEIiICLE WFIEEL
BACKGROUND OF THE INVENTION
' 1. FIELD OF THE INVENTION
The present invention relates to an improved
' method for fabricating a vehicle wheel constructed
as a one-piece part from sheet metal and to a one-
piece metal vehicle wheel constructed by the
improved method.
2. STATE OF THE PRIOR ART
Vehicle wheels to be mounted on a vehicle and
for supporting a tire thereon are usually made of
metal. The fabrication of such metal wheels
typically involves multiple components and
multiple shaping and connecting operations. For
example, a typical process presently employed to
manufacture a metal wheel involves at least the
following steps: Rolling an elongated rectangular
piece of metal to form a rim; welding the ends of
the rolled rectangular piece of metal to form a
continuous cylindrical rim; cleaning the welded
area; sizing the substantially cylindrical rim to
its finished dimensions; separately fabricating an
inside hub member and connecting, as by welding,
the inside hub member to the interior of the rim.
A vehicle wheel fabricated from a single
piece of metal requires less material to construct
and is substantially simpler to fabricate as there
are fewer parts to construct and there are no
connecting steps involved, thus resulting in cost
savings. In addition, one-piece construction
eliminates stress concentrations, which can be
associated with connections between non-integral
components.
Vehicle wheels fabricated from a single piece
of metal are known in the art_ For example, U.S.
CA 02238267 1998-OS-21
WO 97119771 PCT/IB96/01489
Patent No. 2,075,294 discloses a method of forming
both the hub and rim of a vehicle wheel from a
single forged or cast metal blank. The process
involves a number of successive steps, such as
forging, rolling, and forming steps, for producing
a one-piece vehicle wheel.
U.S. Patent No. 3,129,496 also discloses a
manufacturing method for producing a wheel,
including the rim and the hub portion thereof,
from a single cylindrical blank. The cylindrical
blank is constructed from an elongated rectangular
piece which is rolled into a substantially
cylindrical form, and the ends thereof are then
welded together. The cylindrical blank is then
formed into a wheel by a series of sequential
steps, which include a roll extrusion step and a
series of horizontal and vertical linear stroke
die forming steps. Because this process involves
at least one welding operation, however, the full
advantages of a true one-piece construction are
not realized.
Finally, British Patent 406,186 discloses a
metal wheel formed from a single piece of sheet
metal by a series of linear stamping operations,
and Japanese Patent Application No. 60-13327
discloses a metal wheel formed from a single piece
of sheet metal by a series of stamping and rolling
operations.
While methods for fabricating one-piece metal
vehicle wheels are known, there nevertheless
remains the constant need and challenge to improve
the strength, reliability, and cost effectiveness
of a one-piece metal vehicle wheel while at the
same time reducing the weight thereof and
simplifying the fabrication thereof.
2
CA 02238267 1998-OS-21
WO 97/19771 PCT/IB96/01489
SUMMARY OF THE INVENTION
It is an object of the present invention to
provide an improved method for fabricating a one-
piece metal vehicle wheel which meets the
aforementioned needs and challenges. Specifically
provided is a method of forming a metal, one-piece
vehicle wheel for supporting a tire thereon, the
wheel having an axial centerline, a rim for
mounting radially inward edges of the tire, and a
hub for supporting the wheel on a vehicle, the
method comprising: providing a sheet metal blank;
shaping the blank in a first axial direction to
construct a dish-shaped wall and to construct an
outside wall and a first side wall of the rim for
supporting the radially inward edge of the tire to
be mounted, the outside wall including an axial
portion generally parallel to the axial centerline
and a first contour portion extending from the
axial portion of the outside wall to the first
side wall; shaping a central portion of the dish-
shaped wall in a second axial direction to
construct the hub in a generally domed shape and
to fold an annular, radially outward portion of
the dish-shaped wall inside the outside wall to
construct an inside wall in surrounding relation
to the hub; piercing a valve hole in the first
contour portion, the valve hole being constructed
and arranged to receive a tire valve stem; shaping
the inside wall radially outwardly.toward the
axial portion of the outside wall, flattening the
hub, and trimming an outer peripheral portion of
the first side wall; shaping the inside wall so
that an extent of the inside wall is parallel to
' and in contact with the axial portion of the
outside wall to construct a double walled axial
' portion and shaping an outer peripheral edge of
the first side wall to construct a first side wall
3
CA 02238267 1998-OS-21
WO 97/i9771 PCT/IB96/01489
stiffening flange; shaping a portion of the double
walled axial portion radially outwardly to
construct a second contour portion of the rim;
shaping a portion of the hub in the first axial
direction to construct a first offset constructed ,
an arranged to stiffen the hub and shaping a
plurality of hub-stiffening embosses in the hub, ,
the plurality of hub-stiffening embosses being
circumferentially spaced and radially arranged in
surrounding relation to the centerline of the
wheel; shaping the first offset in the second
axial direction to construct a second offset
constructed and arranged to further stiffen the
hub, shaping a portion of the second contour to
construct a second side wall for supporting the
radially inward edge of the tire to be mounted,
and reshaping the first offset and the plurality
of hub-stiffening embosses to ensure that the
first offset and the plurality of hub-stiffening
embosses are sized correctly; piercing a center
hole and a plurality of wheel mounting holes
surrounding the center hole in the hub; and
shaping a plurality of rim-stiffening embosses in
the rim and shaping the center hole and each of
the plurality of wheel mounting holes to construct
a center hole flange for the center hole and a
wheel mounting hole flange for each of the
plurality of wheel mounting holes.
These and other objects of the present
invention will become more apparent during the
course of the following detailed description and
appended claims. The invention may best be
understood with reference to the accompanying
drawings wherein an illustrative embodiment is '
shown.
4
CA 02238267 1998-OS-21
WO 97/19771 PCT/IB96/01489
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an isometric view of a one piece
metal vehicle wheel constructed in accordance with
the improved method of the present invention;
FIG. 2 is a plan view of the one piece metal
vehicle wheel shown in FIG. 1;
FIG. 2A is a half sectional view of the one
piece vehicle wheel of FIG.. 2 taken along the line
A-A;
FIG. 2B is a half sectional view of the one
piece vehicle wheel of FIG. 2 along the direction
indicated by line B-B;
FIG. 2C is a half sectional view of the one
piece vehicle wheel of FIG. 2 along the direction
indicated by line C-C;
FIG. 3 is a half sectional view of a
partially fabricated vehicle wheel illustrating
the first step of the method of the present
invention;
FIG. 4 is a half sectional view of a
partially fabricated vehicle wheel illustrating
the second step of the method of the present
invention;
FIG. 5 is a half sectional view of a
partially fabricated vehicle wheel illustrating
the third step of the method of the present
invention;
FIG. 6 is a half sectional view of a
partially fabricated vehicle wheel illustrating
the fourth step of the method of the present
invention;
FIG. 7 is a half sectional view of a
partially fabricated vehicle wheel illustrating
the fifth step of the method of the present
invention;
FIG. 8 is a half sectional view of a
partially fabricated vehicle wheel illustrating
5
CA 02238267 1998-OS-21
WO 97/19771 PCT/IB96/01489
the sixth step of the method of the present
invention;
FIG. 9 is a half sectional view of a
partially fabricated vehicle wheel illustrating
the seventh step of the method of the present
invention;
FIG. 10 is a half sectional view of a
partially fabricated vehicle wheel illustrating
the eighth step of the method of the present
invention; and
FIG. 11 i.s a half sectional view of a
completed vehicle wheel illustrating the ninth
step of the method of the present invention.
DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED
EXEMPLARY EMBODIMENT
A one piece metal vehicle wheel constructed
by the improved method of the present invention is
designated by reference no. 2 in FIGS. 1 and 2.
The wheel 2 comprises a substantially circular rim
56 extending around the periphery of the wheel.
The rim 56 includes an axial portion 14, centered
axially on the rim and being substantially
parallel. to a centerline of the wheel 2. As shown
in FIG. 2C, the rim 56 further includes a first
contour portion 16 protruding at an angle radially
away from the axial portion 14 and an annular
first sidewall 18 extending generally axially from
the centerline of the wheel 2 for engaging one
radially inward edge of a tire (not shown) to be
mounted on the wheel. The rim 56 further includes
a second contour portion 34 protruding at an angle
radially away from the axial portion 14 and a
second side wall 44 for engaging the other ,
radially inward edge of a tire to be mounted on
the wheel.
The rim 56 also includes a plurality of
circumferentially spaced, radially arranged rim
6
CA 02238267 1998-OS-21
WO 97/19771 , PCT/fB96/01489
stiffening embosses 54. Each of the rim
stiffening embosses 54 is axially centered within
the rim 56 and serves to rigidify the rim 5&.
The wheel 2 further includes a hub portion 22
located radially inwardly from the rim 56. The
hub 22 has formed therein a generally circular
first offset portion 36 that is bent or otherwise
shaped out of the plane of the hub 22 so as to
provide radial stiffness for the hub. The hub 22
further includes a generally circular second
offset 42 located radially inwardly of the first
offset 36. The second offset 42 is formed in a
plane different from that of the hub 22 and the
first offset 36 and provides additional radial
stiffness for the hub 22.
The hub 22 also has formed therein a
plurality of inner hub stiffening embosses 38
circumferentially spaced and radially arranged
about the centerline of the wheel 2. Also
provided are a plurality of outer hub stiffening
embosses 40 circumferentially spaced and radially
arranged about the centerline of the wheel 2. As
shown in FIGS. 1-2C, the outer hub stiffening
embosses 40 are disposed radially outwardly from
25. the inner hub stiffening embosses 38. The inner
hub stiffening embosses 38 and the outer hub
stiffening embosses 40 provide additional radial,
axial, and torsional stiffness for the rim 22.
Formed within the second offset 42 are a
plurality of circumferentially spaced sockets 39,
which are radially arranged about the centerline
of the wheel 2. Formed within each socket 39 is a
wheel mounting hole 52 for fixing the wheel to the
- axle of a vehicle, as by a bolt (not shown) .
Around the periphery of each wheel mounting hole
46 is a wheel mounting hole flange 52. The wheel
mounting hole flange 52 serves to stiffen the
7
CA 02238267 1998-OS-21
WO 97!19771 PC'flIB96/01489
wheel mounting hole 46 and further serves as a
bolt centering surface which engages a mating
frusto-conical surface beneath the head of a
mounting bolt (not shown).
A center aperture 48 is formed at the radial
center of the hub 22. The center aperture 48
includes an aperture stiffening flange 50 for
stiffening the center aperture 48.
The present method for fabricating a one-
piece metal vehicle wheel preferably comprises a
nine station transfer die in which are performed a
series of metal shaping operations, such as
drawing, forming, and punching operations. The
nine preferred stations in their preferred
35 sequence are shown in FIGS. 3-I1, each of which
show a cross-section of a vehicle wheel in various
stages of the fabrication process. Because the
vehicle wheel is symmetrical about an axial
centerline thereof, only a half sectional view is
shown.
Throughout this detailed description,
reference is made to the tools and dies that
perform the various shaping, i.e., forming and
drawing, operations. Because the tooling used in
each of the shaping operations are conventional
devices which. are well known in the metal
stamping/forming arts, the tools and dies
themselves are not shown in the figures.
Furthermore, by not showing the conventional
tooling involved in the shaping operations, it is
possible to show, by use of phantom lines, before-
and-after views of the partially fabricated wheel
in the particular station.
As shown in FIG. 3, a preferably circular and
substantially flat metal blank, shown in phantom
and indicated by reference number 10, is placed
between the dies of the first station. A lower
8
CA 02238267 1998-OS-21
WO 97/19771 PCT/IB96/01489
die member, or punch, is disposed below the blank
I0. An annular upper tool, moving in a linear
vertical stroke fashion, draws the blank 10 over
the punch in the axial direction A to form a
circular, dish-shaped wall 12 and an outside wall
which includes a generally cylindrical axial
portion 14, which is generally parallel to the
axial centerline of the wheel, an annular contour
portion 16 protruding at an angle radially away
from the axial portion 14, and an annular first
side wall 18, extending generally perpendicularly
to the axial centerline of the wheel for engaging
one radially inward edge of a tire (not shown) to
be mounted on the wheel. The first side wall 18
will form a portion of a rim for supporting the
radially inward edges of a tire (not shown) to be
mounted on the wheel.
Throughout this detailed description, the
terms "upper" and "lower" are not intended to be
limiting. They are used merely to describe a
position relative to the vehicle wheel oriented as
shown in the figures.
The radius of the blank 10, the radial
distance between the centerline and the axial
portion 14, and the radial width of the first side
wall 18, as well as various other pertinent
dimensions, will vary according to the desired
dimensions of the finished wheel. The depth d of
this first deep draw shown in FIG. 3 is preferably
approximately 1 5/8 times the desired finished rim
width.
The lower die member, or punch, has a cross-
sectional shape which corresponds to the shape of
the dish-shaped wall 12 and the axial portion 14.
The upper die member has a cross-sectional shape
which corresponds to the contour portion 16 and
the first side wall 18.
9
CA 02238267 1998-OS-21
WO 97/19771 PCT/IB96/01489
As shown in FIG. 4, in the second station of
the method of the present invention, a central
portion of the dish-shaped wall 12 is drawn in the
axial direction A to construct the generally dome-
s shaped hub 22 of the wheel. An annular outer
peripheral portion of the dish-shaped wall 12 is
folded inside the axial portion 14, and an axial
end portion 15 of the axial portion 14 is folded
over itself to construct the inside wall 20 in
annularly surrounding relation to the hub 22.
An upper punch member and a lower die member
are provided. The dish-shaped wall 12 is drawn
over the upper punch member by generating a
relative vertical linear stroke motion between the
lower die member and the upper punch member with
the blank therebetween.
A punch, included as part of an upper die
member, which may correspond to the upper punch
member, is driven through the contour portion 16
at a specified circumferential position into a
punch receiving die of the lower die member in a
known manner, such as by the wedge action of
interengaging annular surfaces, to remove a
circular portion 26 from the contour portion 16 to
fashion the valve hole 24. Following the hole
punching operation, the punch is retracted into
the upper die member, such as by a spring, to
permit the upper die member to disengage from the
lower die member.
The valve hole punching step has been
described in conjunction with the second station
of the method of the present invention as
illustrated in FIG. 4. Due to the configuration
of the forming and/or drawing punches and dies
associated with each of the respective stations of
the method of the present invention, there is
sufficient room to perform the valve hole punching
CA 02238267 1998-OS-21
WO 97/19771 PCTJIB96/01489
step in only a limited number of stations.
Station 2 is the preferred station for performing
the valve hole punching step. It will be_
understood, however, that the valve hole punching
step may be performed in conjunction with other
stations of the method, to be described below.
As shown in FIG. 5, the third station of the
method of the present invention includes the step
of flattening the hub 22 from the position shown
in phantom to the position shown in cross-section
so that it is substantially perpendicular to the
centerline of the wheel. The hub is flattened by
a stamping operation involving a linear vertical
stroke motion between an upper punch member and a
lower die member. Furthermore, in the third
station illustrated in FIG. 5, an outer peripheral
portion 28 of the first side wall 18 is trimmed to
ensure a clean, substantially circular edge for
the aide wall 18. The trimming operating is
preferably performed by a circular lower punch
having an outside diameter corresponding to the
desired outside diameter of the finished side wall
and an annular upper cutting tool outwardly
disposed from the lower punch member and movable
with respect to the lower punch in coaxial
fashion. In order to provide for the relative
coaxial motion between the lower punch and the
upper annular cutting tool, an annular clearance
between the lower punch and the upper annular tool
must be provided. It is presently preferred that
the clearance be approximately 10~ of the material
thickness of the blank.
As shown in FIG. 6, in the fourth station of
the method of the present invention, the inside
wall 20 is drawn outwardly from the position shown
in phantom to a position substantially parallel to
and in contact with the axial portion 14 of the
11
CA 02238267 1998-OS-21
WO 97!19771 PCT/IS96/01489
outside wall so as to construct a double walled
axial portion 32. The double walled axial portion
32 includes an inner radial wall 31 and an outer
radial wall 33.
Inside wall 20 is drawn radially outwardly by
a cam action, horizontal stroke forming operation.
The forming operation is performed by a
conventional segmented expanding device. An upper
die member, having a plurality of radially
l0 arranged sliding mandrel segments arranged about a
central wedge member, is placed inside the inside
wall 20 by a vertical linear stroke motion. A
second upper die member, moving in vertical linear
stroke fashion, forces the central wedge member
downwardly causing the mandrel segments to move
radially outwardly.
Also, in the station illustrated in FIG. 6,
the outward peripheral edge of the first side wall
18 is wiped over to construct side wall stiffening
flange 30. The wiping operation is performed by a
lower punch having an outside diameter less than
the overall diameter to the outward peripheral
edge of the first side wall 18 and an upper
annular die member relatively moveable in a
coaxial fashion with respect to the lower punch
member in a vertical linear stroke to wipe or fold
the outer peripheral edge of the side wall 18 over
the outer peripheral edge of the lower punch
member.
As shown in FIG. 7, in the fifth station of
the method of the present invention, the double
walled axial portion 32, shown in phantom, is bent
radially outwardly to form the second contour 34
protruding at an angle radially away from the
axial portion 14. Second contour 34 is preferably
formed by an inner die member disposed within the
inside wall 20 of the wheel and having a plurality
12
CA 02238267 1998-OS-21
WO 97/19771 PCT/IB96l01489
of radially arranged outwardly slidable inner
mandrel segments arranged about a central wedge
and an outer die member disposed annularly about
the periphery of the wheel and having a plurality
of radially arranged inwardly slidable outer
mandrel segments. As discussed above with respect
to FIG. 6, the inner mandrel segments are moved
radially outwardly by the action of a wedge member
moving vertically. The outer mandrel segments are
moved radially inwardly by the action of a cam or
wedge ring moving vertically.
As shown in FIG. 8, in the sixth station of
the method of the present invention, a.circular
central portion of the hub 22 is drawn in the
axial direction A to construct a first offset 36
of the hub 22. Offset 36 is preferably formed by
means of an upper die member and a lower punch
member having' a size corresponding to the size of
the first offset 36, as shown in FIG. 8.
Also in station six, a plurality of inner hub
stiffening embosses 38 and outer hub stiffening
embosses 40 are stamped into the hub 22. The hub-
stiffening embosses are circumferentially spaced
and radially arranged in surrounding relation to
the centerline of the wheel, the inner hub-
stiffening embosses 38 being radially closer to
the centerline and the outer hub-stiffening
embosses 40 being further radially remote from the
centerline.
The inner hub-stiffening embosses 38 are
preferably formed by an upper punch member and a
lower die member, the upper punch member moving
with respect to the lower die member in vertical
linear stroke fashion. The upper punch member has
a plurality of radially arranged circumferentially
spaced inner mandrel portions which are received
by associated radially arranged circumferentially
13
CA 02238267 1998-OS-21
WO 97/19771 PCT/IB96/01489
spaced inner mandrel receiving portions of the
lower die member. When the upper die member
engages the wheel, each inner mandrel portion of
the upper die member shapes a portion of the hub
by forcing a portion of the hub into a
corresponding mandrel receiving portion of the
lower die member.
The outer hub stiffening embosses 40 are
preferably formed by a lower punch member and an
upper die member, the lower punch member moving
with respect to the upper die member in vertical
linear stroke fashion. The lower die member has a
plurality of radially arranged circumferentially
spaced outer mandrel portions that are received by
associated radially arranged circumferentially
spaced mandrel receiving portions of the upper
punch member. When the lower die member engages
the wheel, each outer mandrel portion of the lower
die member shapes a portion of the hub by forcing
a portion of the hub into a corresponding mandrel
receiving portion of the upper die member.
The number of inner hub stiffening embosses
38 and outer hub stiffening embosses 40 each
preferably corresponds to the number of wheel
mounting holes, to be discussed below.
Because station six involves no other tool
members disposed about the outside periphery of
the partially fabricated wheel, a hole-punching
die member disposed around about the periphery of
the wheel could be used in this station.
Therefore, the valve hole 24 punching step,
discussed above in conjunction with station two of
the preferred embodiment (see FIG. 4), could
alternatively be performed at station six. ~
As shown in FIG. 9, at the seventh station of
the method of the present invention, a central
portion of the first offset 36 of the hub 22 is
14
CA 02238267 1998-OS-21
WO 97/19??1 PCTJIB96/01489
drawn in the axial direction B to construct a
second offset 42 of the hub 22. The second offset
42 is preferable drawn by an appropriate upper
punch member having a radius corresponding to the
desired radius of the second offset 42, and an
appropriate lower die member.
Also at the seventh station, a plurality of
circumferentially spaced sockets 39 are formed in
the area of the second offset 42. The sockets 39
are radially arranged in surrounding relation to
the centerline of the wheel.
Also at station seven. the outer r~Pr; mhPra'1
portion of the second contour 34 is bent radially
outwardly to a position substantially
perpendicular to the centerline of the wheel to
construct the second side wall 44 for engaging the
other radially inward edge of a tire to be mounted
on the wheel, thus substantially completing the
fabrication of a tire engaging rim 56 around the
periphery of the wheel. The second side wall 44
includes inner rim wall 43, outer rim wall 45, and
a curved segment 41 integrally connecting the
inner rim wall 43 and the outer rim wall 45.
The second side wall 44 is preferably formed
by an appropriate upper die member and an outer
die ring disposed about the periphery of the wheel
and having a plurality of radially arranged
inwardly sliding outer mandrel segments, which are
moved radially inwardly by the action of a cam or
wedge ring moving vertically.
Finally, at the seventh station of the method
of the present invention, a reshaping, or
restriking, operating is preferably performed on
- the first offset 36, the inner hub stiffening
embosses 38, and the outer hub stiffening embosses
. 40 to ensure that each of these features is sized
correctly.
CA 02238267 1998-OS-21
WO 97/I9771 PC'T/IB96/01489
As shown in FIG. 10, at the eighth station of
the method of the present invention, a circular
disk portion 58 is removed, as by a punch
operation, from the center of the hub 22 to
fashion a center aperture 48. In addition, a _
plurality of circular disk portions 60 of the hub
22 are removed, as by punch operations, from the ,
hub 22 to fashion a plurality of wheel mounting
holes 46 disposed within the sockets 39 in a
surrounding relationship to the center aperture
48. The center aperture 48 and the plurality of
wheel mounting holes 46 are preferably fashioned
by a conventional upper punch member and a lower
die member, the upper punch member being moved in
a vertical linear stroke manner into the lower die
member to remove the material to fashion the
center aperture 48 and the plurality of wheel
mounting holes 46. The number of wheel mounting
holes 46 preferably corresponds to the number of
inner hub stiffening embosses 38 and the number of
outer hub stiffening embosses 40, and vice versa.
The actual number of wheel mounting holes
typically varies from 4 to 6 holes.
Because station eight involves no tool
members disposed about the outside periphery of
the partially fabricated wheel, a hole-punching
die member disposed about the periphery of the
wheel could be used in this station. Therefore,
the valve hole 24 punching step, discussed above
in conjunction with station two of the preferred
embodiment (see FIG. 4), could alternatively be
performed at station 8.
As shown in FIG. 11, in a ninth station of
the method of the present invention, a peripheral '
edge of the center aperture 48 is extruded in the
axial direction A to construct an aperture
stiffening flange 50 around the periphery of the
1&
CA 02238267 1998-OS-21
WO 97/19771 PCT/IB96/01489
center aperture 48. Also, a peripheral portion of
each of the plurality of wheel mounting holes 46
is extruded in the axial direction A to construct
a hole stiffening flange 52 around the periphery
of each of the wheel mounting holes 46. The hole
stiffening flange 52 also serves to center a wheel
mounting bolt (not show), which may have a frusto-
conical surface for engaging the flange 52, when
the bolt is inserted through the hole.
ZO Finally, a plurality of rim stiffening
embosses 54 are formed in the rim 56 by deforming
portions of the rim 56 radially inwardly. The rim
stiffening embosses 54 are substantially axially
centered on the rim 56 and are circumferentially
spaced about the periphery of the rim 56. The rim
stiffening embosses 54 are preferably formed by an
outer die member disposed around the outer
periphery of the wheel and having a plurality of
circumferentially spaced radially arranged
inwardly slidable mandrel segments, which are
moved radially inwardly by the action of a cam or
wedge ring moving vertically.
A wheel fabricated by the method of the
present invention preferably is constructed of a
high strength material, such as 1010 steel or 1080
steel, and preferably has a material thickness
ranging from 0.120" to 0.140".
The method of the present invention has been
described in terms of the preferred sequence of
fabrication stations and the preferred steps to be
performed at each station. The sequence of
stations, and the steps performed at each station
may, to some extent, deviate from the preferred
embodiment described herein. Due to spatial and
other limitations, however, there are certain
steps which may be performed only at specific
stations. An example of such a step is the valve
17
CA 02238267 1998-OS-21
WO 97/19771 PCT/IB96/01489
hole punching step, described above, which may
feasibly be performed only at stations two, six,
or eight. It is also preferred that certain
combinations of steps not be performed at the same
station. For example, lateral forming steps, such
as those performed at stations four, five seven,
and nine should not be performed at a station
where cutting or punching steps are performed,
such as at stations two, three, and eight. This
is because lateral forming operations can cause
the partially fabricated wheel to shift laterally,
which can result in misalignment of punches and
dies and misplacement of cuts or punched holes.
It is preferable that cutting and punching
operations be combined with vertical drawing
steps.
It will be realized that the foregoing
preferred specific embodiment of the method of the
present invention has been shown and described for
the purpose of illustrating the functional and
structural principles of this invention and is
subject to change without departure from such
principles. Therefore, this invention includes
all modifications encompassed within the spirit
and scope of the following claims.
18
