Note: Descriptions are shown in the official language in which they were submitted.
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My invention relates to a method of manufacturing
vehicle wheel rims from materials characterized by having a rela-
tively low ductility such as aluminum, or high strength, low alloy
(HSLA) steel. By my method wheel rims of aluminum or IISLA steel
may be manufactured using conventional mass production rim rolling
apparatus presently used in the manufacture of SAE 1010 steel rims.
Prior art roll forming techniques for forming wheel rims from
sheet material have proven unsuccessful when applied to aluminum
materials. Because of aluminum's lower ductility, sheet aluminum
when roll formed on conventional rim rolling equipment resists the
necessary stretching especially at the butt weld, to form an accep-
table wheel rim section.
In the manufacture of steel wheel rims a strip of
rolled sheet steel is coiled and butt welded to form a cylindri-
cal hoop or band. After deburring the butt weld, the cylindrical
band is first placed in a press wherein the lateral edges of the
band are flared radially outward. Flaring of the edges serves
to preform the rim flange area and provide a band cross-sectional
profile suitable for retention on roll forming equipment used
for subsequent forming operations. After flaring of the lateral
edges the band is subjected to a series of roll forming opera-
tions whereby the band is progressively formed into the final
desired cross-sectional p~ofile and circumference. During roll
forming and sizing operations the band circumference expectant-
ly increases. Thus the initial dimensions of the strip from
which the band is formed are selected to accommodate such mate-
rial elongation.
While the above described process has proven succes-
ful in the manufacture of SAE 1010 steel wheel rims it has not
heretofore been successful for the manufacture of wheel rims
from materials having a ductility significantly lower than that
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of SAE 1010 steel. Thus the prior art has been unsuccessful in
roll forming aluminum sheet material into acceptable wheel rims.
Because of aluminum's lower ductility bands of aluminum, having
the dimensions as heretofore used in forming steel rims of a
given wheel size, have not met the efficiency standards required
for mass production. Because of aluminum's resistance to stret-
ching ~low ductility) the band lateral edges may not be flared
to the same extent that a steel band is flared, without fractur-
ing the butt weld. Increasing the band circumference to reduce
the stress at the weld results in an oversize rim because of
band growth during the roll forming operations.
Because of the aforementioned problems aluminum wheels
heretofore have been produced by casting or forging techniques.
However, cast or forged aluminum wheels are costly to manufacture
and, because of the lower properties of cast aluminum or the
processing requirement of forged aluminum, the wheels have such
mass that no significant weight savings is realized. Therefore,
it is preferable to use mill rolled aluminum sheet to take full
advantage of the material's high strength, lower processing costs,
~0 and overall lower weight.
By~my new method, wheel rims may be roll formed from
any sheet material having a relatively low ductility, particular-
ly aluminum, using conventional rim rolling e~uipment.
According to one aspect of the invention, a method of
making a wheel rim comprises the steps of providing a cylindrical
band of material, deforming a portion of said band material bet-
ween the lateral edges thereof, radially inward forming a circum-
ferential well depression, strain hardening the material within
said circumferential well thereby increasing the strength of
said well material, reshaping the well bottom and effecting draw
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forming of the bead seat areas through coac-tion of the strain
hardened well material and the bead seat area material by forcing
said well radially outward while radially restricting the band
material on opposite sides of the well.
According to another aspect of the invention, there is
provided in a method of roll forming a vehicle wheel rim wherein
a cylindrical band of material is first operated upon to form a
circumferential well spaced between the lateral sides thereof
and subsequently operated upon to form the bead seat areas on
either side of the well, the improvement comprising, coining the
circumferential well to work harden the material such that the
well material is characterized by having greater strength and
lower ductility than the remaining band material.
According to a further aspect of the invention, there
is provided an intermediate article of manufacture comprising a
cylindrical band of metallic, low ductility, material having a
circumferential recessed portion spaced between the lateral sides
thereof, wherein the material of the recessed portion has a
greater strength and lower ductility than the remaining band
material, the greater strength and lower ductility being imported
to the recessed portion by coining the recessed material between
two matched roll diesO
In the manufacture of a wheel rim by roll forming dis-
closed herein,a strip of sheet material is preferably first formed
into a hoop, by coiling and buttwelding the ends thereof. The
hoop or band is then preferably placed in a press to flare the
lateral edges radially outward preforming the rim flanges and pro-
viding a band cross-section suitable for positioning on the roll
forming machine. Because of aluminum's low ductility it is
difficult to flare the band edges to the same extent as that in
forming a steel rim, without over-stressing the butt weld.
Therefore, it is desirable to form the initial band such that
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its circumference more closely approximates that of the finished
rim that is customary in the manufacture of steel rims.
The first roll forming operation comprises rolling the
drop center form well into the flared band. Because of the
generally larger band diameter the well must be rolled deeper
than customary for the smaller diameter steel band. Having rolled
the well into the band, the material in the well area is wor]c or
strain hardened by a coining or metal squeezing process whereby
the well material is rolled between a pair of opposing matched
roll dies such that the well material is compressed between the
roll dies filling the gap therebetween. Strengthening of
.
well area material through work hardening is most critical
to the success of the subsequent roll forming operations.
In the second roll forming operation, roll pressure is
applied radially inward on the tire seat areas and radially out-
ward on the work hardened well. The tire seat areas being weaker
than the deep work hardened well are caused to shrink while the
deep well circumference is increased.
During the preferred third rolling operation, the rim
section is completed to profile by curling the flanges, flatten-
ing the outboard hump and sizing the rim diametrically for -the
final sizing operations using an expanding press and a shrinking
operation known as a "True-Centric" for dimensional control.
In the drawings:
Figure 1 is a perspective view showing a strip of
sheet stock used to form a wheel rim in accordance with the
method of this invention.
Figure 2 is a perspective view showing the strip of
stock as shown in Figure 1 formed into a hoop.
Figure 3 is a perspective view showing the wheel rim
in its final configuration.
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Figures 4 through 7 are cross-sectional views showing
the steps in the forming operation.
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Figure 4 shows the initial forming step.
Figure 5 shows the configuration of the rim at the end
of the first roll forming operation.
Figure 6 shows the configuration of the rim at the
end of the second roll ~orming operation.
Figure 7 shows the configuration at the end of the
third roll forming operation.
Althou~h the following description of my invention re-
fers specifically to aluminum, it is to be understood that my
new method of roll forming a wheel rim may be equally applied
to any suitable material exhibiting low ductility, for example
high strength low alloy (~SLA) steels and other mild materials
such as SAE 1010 mild steel.
Referring now to the figures. Figure 1 illustrates an
elongated strip 11 of aluminum sheet material suitable for form-
ing into a wheel rim in accord with the principles of my inven-
tion. Because of the significantly lower ductility of aluminum
over steel, I have found it desirable to increase the strip
length and correspondingly decrease the strip width over that
~ommonly used for manufacturing a steel rim. For exmaple in
producing a typical lS inch by 6 inch wheel rim from aluminum
I have found it preferable to increase the strip length by appro-
ximately 5.8% over that suitable for steel and decrease the
strip width by approximately 4%.
Blank 11 is first rolled into the shape of a hoop 13,
shown in Figure 2, and the opposing ends flash butt welded form-
ing weld line 12. The thus formed ~and, shown in Figure 2, is
subsequently passed through multiple forming operations result-
ing in a finished wheel rim 24 illustrate~ in Figure 3. Figures
4 through 7 progressively illustrate the band cross-sectional
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profiles resulting fr~m each of four sequenced forming operations.
The profile of Figure 4 is preferably obtained by a press opera-
tion while the profiles of Figures 5 through 7 are obtained by
roll forming operations.
The first forming operation comprises preforming the
rim flange area by flaring the band lateral edges 25 and 26 radi-
ally outward as shown in Figure 4. Preferabl~ the edge ~laring
operation is per~ormed in a press wherein the band may also be
rounded out to a more true cylindrical configuration. For a 15
inch by 6 inch wheel rim, I have found it desirable to flare the
edge periphery radially outward approximately nine and one-half
(9-1/2) percent larger than the circumference of hoop 13. Be-
cause of the low ductility of the material, flaring the band
eges significantly further will overstress the butt weld result-
ing in weld fractures. Therefore, the amount of edge flaring is
limited by the butt weld strength properties. Thus the ductility
of the particular material being used largely determines the
inital band dimensions.
Once flared, the band is placed on a forming roll for
the fixst roll forming operation. This first roll forming opera-
tion is believed critical to the success of subsequent roll form-
ing operations and the ultimate success in roll forming of an
aluminum wheel rim.
In the first roll forming operation, a well portion,
indicated generally by reference numeral 27 in Figure 5, is form-
ed by progressively rolling the material within this region to
assume a diameter less than that of the band 13. Again by way
of example for a 15x6" aluminum wheel rim I have found it desir-
able to roll the well portion into ~he band to the extent that
the well inside diameter D5 is approximately 11.8% less than the
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original band diameter D4. Since the initial band circumference
is 9-1/2% greater than that used in manufacturing a steel rim of
comparable size (15x6") the depth of the well is approximately
35 percent deeper than that otherwise rolled into a steel band
during the first roll forming operation. Upon rolling the deep
well into the band the well area is further work hardened by
continued rolling of the well area between the forming pressure
rolls. This deeper, work hardened well is believed essential so
that shrinking the tire seats and safety bead areas may be ac-
complished in the second roll forming operation. Quantitativelythe exact amount of work hardening required is not presently
known, it must be qualitatively determined by experimentation
taking into consideration such parameters as material ductility~
weldability, and strain hardening properties plus initial band
circumference, thickness, and the width and depth of the well.
During roll forming of the well portion 27, the dia-
meter of the adjacent rim, bead seats indicated by reference
numeral 28 and 29, may be expected to increase. The amount of
such increase being related to the well 27 depth. In roll form-
ing an aluminum rim of the 15x6" size, this increase is approxi-
matel~y 3.2%.
The second roll forming operation results in a band
cross-sectional profile substantially as illustrated in Figure
6. During this rolling operation band-roll contact is made and
forces applied to effect flattening of the well portion into a
flattened configuration 33 and circumferentially shrink or draw
forming the bead seat and safety hump areas radially inward. Roll
pressure is applied radially outward upon the inside diameter of
the work hardened well 27 as indicated by force vector F as shown
in Figure 6. A resulting reaction pressure, indicated by force
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vectors R, is applied over the bead set and safety hump surface
areas. Deep well 27 is thusly forced radially outward ultimately
assuming the well profile shown in Figure 6. Since the well 27
material exhibits greater strength, because of prior work harden-
ing, reactive forces R radially urge bead seat areas 31 and 32
radially inward effecting circumferential shrinkage through mate-
rial compression. As the rolling operation progresses and the
bead seat areas shrink, an equilibrium of internal material stes-
ses develops to the extent that the deep well side walls 23 and
24 subsequently collapse to form side walls 30 and 34 and the
flattened bottom 33. Upon collapse of deep well walls 23 and 24
a general increase of material thickness is achieved in the well
radii areas indicated by reference numerals ~0 and 41. Further
material thickness increases are achieved in the bead seat and
safety hump areas 31 and 32 because of material compression.
The flanges 25 and 26 remain but are altered somewhat in configur-
ation as a comparison between Figures 5 and 6 will readily reveal.
During the second roll forming operation as performed
in the manufacture of a 15x6" aluminum rim the well 33 circumfer-
enca is increased approximately 2.6% over that of well 27 asformed in the first roll forming operation. However, the bead
seat areas 31 and 32 are reduced in circumference by approximate-
ly 1.58~ from that of areas 28 and 29.
The final roll forming operation results in the rim
profile as shown in Figure 4 wherein the flanges, which previously
existed at the edges of the rim, are rolled over into their
final flange configuration 34 and 35. Final sizing of the bead
seats 31 and 3~ and final formation of the safety humps 36 and
37 is also done during this roll forming operation. At the same
time, the well portion 33 is finished to correct form.
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At the completion of the rolling operation, the rim
is expanded slightly to an oversize outside diameter and the inside
diameter at the well, indicated by the reference numeral 38 in
Figure 7, is sized to be slightly smaller than the disk or cen-
ter of the wheel which will then be assembled to complete the
finished wheel.
It should be readily apparent that the described method
reduces stretching and thinning of the metal during the rim form-
ing operation as well as, by the expedient of work hardening,
confining metal movement during the rolling operations to the
areas desired. Thus, an improved rim with increased thickness
at the well and bead seat corners resultsusing relatively conven-
tional forming techniques and apparatus which is used for forming
conventional steel rims. This new method of rim forming performs
equally as well with (HSLA) high strength low alloy steels and
mild materials.
Once understanding the theory and method described
above for roll forming of an aluminum rim one skilled in the art
of steel wheel manufacture may apply the principles to ~oll form-
~0 ing aluminum rims of most any other size by qualitatively deter-
mining the initial band dimensions and initial well depth neces-
sary to successfully form such a wheel rim.
Although the above description teaches forming the
material band or hoop by coiling and w~lding the abutting free
widthwise ends it is equally suitable to form wheel rims em-
ploying the teachings of my invention using circumferentially
endless bands of material such as may be formed by extrusion
or spinning techniques.
While the above description constitutes the preferred
embodiment of my invention, it will be appreciated that the inven-
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tion is susceptible to modification, variation and change with-
out departing from the proper scope or fair meaning of the accom-
panying claims.
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