GB2062503A - Improvements in and relating to making wheel rims - Google Patents

Abstract

An improved method of making vehicle wheel rims 24 particularly suitable for use with materials having relatively low ductility, such as aluminium, is disclosed. A circumferential drop centre well 27 is formed about the periphery of the band 13 and work hardened so that the well material exhibits higher strength and lower ductility than the remaining band material. The bottom of the well 33 is reshaped and shrinking of the bead seat areas effected through coaction of the work hardened material of the well and the material of the bead seat area by forcing the well radially outwards while radially restricting the bead material on both sides of the well. <IMAGE>

Description

SPECIFICATION Improvements in and relating to wheel rims The invention relates to a method of manufacturing vehicle wheel rims from materials having a relatively low ductility such as aluminium, or high strength, low alloy (HSLA) steel. By this method, wheel rims of aluminium or HSLA steel may be manufactured using conventional mass production rim rolling apparatus currently used in the manufacture of SAE 1010 steel rims. Previously proposed roll forming techniques for forming wheel rims from sheet material have proven unsuccessful when applied to aluminium materials. Because of aluminium's lower ductility, sheet aluminium when roll formed on conventional rim rolling equipment resists the stretching necessary to form an acceptable wheel rim section.

In one conventional technique for the manufacture of steel wheel rims a strip of rolled sheet steel is coiled and butt welded to form a cylindrical hoop or band. After the butt weld has been deburred, 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 the roll forming equipment used for subsequent forming operations. After the flaring of the lateral edges the band is subjected to a series of roll forming operations in which the band is progressively formed into the final desired crosssectional profile and circumference. During roll forming and sizing operations the band circumference may be expected to increase.The initial dimensions of the strip from which the band is formed should be selected to accommodate this material elongation.

While the above described process has proven successful 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 of SAE 1010 steel. Thus the previously known method has been unsuccessful in roll forming aluminium sheet material into acceptable wheel rims. Because of aluminium's lower ductility, bands of aluminium having the dimensions customarily used in the past for forming steel rims of a given wheel size have not met the standards of efficiency required for mass production.

Because of aluminium's resistance to stretching (low ductility) the lateral edges of the band cannot be flared to the same extent as a steel band is flared without fracturing 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 aluminium wheels have in the past been produced by casting or forging techniques. However, cast or forged aluminium wheels are costly to manufacture and, because of the poorer properties of cast aluminium or the processing requirement of forged aluminium, the wheels have such a mass that no significant weight savings are obtained over conventional steel wheels. Therefore, it is preferable to use mill rolled aluminium sheet to take full advantage of the material's high strength, lower processing costs, and overall lower weight.

In the manufacture of a wheel rim by roll forming, a strip of sheet material is first formed into a hoop, by coiling and butt welding the ends thereof. The hoop or band is then placed in a press to flare the lateral edges radially outward preforming the rim flanges and providing a band cross-section suitable for positioning on the roll forming machine. Because of aluminium's low ductility it is difficult to flare the band edges to the same extent as in forming a steel rim, without overstressing the butt weld. Therefore, it is necessary to form the initial band such that its circumference more closely approximates that of the finished rim than is customary in the manufacture of steel rims.

It is an object of the invention to provide a method by which wheel rims may be roll formed from sheet material having a relatively low ductility, especially aluminium, using conventional rim rolling equipment.

The invention provides a method of making a wheel rim comprising the steps of: deforming a portion of a cylindrical band of material between the lateral edges the band radially inward forming an annular well depression and strain hardening the material of the well of the deformation, the further strain hardening the material of the well, reshaping the bottom of the well and effecting shrinking of the bead seat areas through coaction of the strain hardened material of the bead seat area by forcing the well radially outwards while radially restricting the band material on both sides of the well.

The first roll forming operation comprises rolling the drop centre form well into the flared band. Because of the generally larger band diameter the well must be rolled deeper than is customary with the smaller diameter steel band.

The well having been rolled into the band, the material in the well area is work or strain hardened by coining the well between matched roll dies.

Strengthening of the 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 tyre seat areas and radially outward on the work hardened well. The tyre seat areas being weaker than the deep work hardened well are caused to shrink while the deep well circumference is increased.

During the third rolling operation, the rim section is completed to profile by curling the flanges, flattening 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.

A method according to the invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a perspective view showing a strip of sheet stock that may be used to form a wheel rim by the method; 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; and Figures 4 to 7 are axial cross-sectional views of the wheel at various stages during the forming operation; 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 forming operation; and Figure 7 shows the configuration at the end of the third roll forming operation.

Although the following description of the invention refers specifically to aluminium, it is to be understood that the method may be equally applied to any suitable material exhibiting low ductility, for example high strength low alloy (HSLA) steels and other mild materials such as SAE 1010 mild steel.

Referring now to the drawings. Figure 1 shows an elongate strip 11 of aluminium sheet material suitable for forming into a wheel rim. Because aluminium is of significantly lower ductility then steel, it is desirable to increase the strip length and correspondingly decrease the strip width over that commonly used for manufacturing a steel rim. For example in producing a typical 15 inch by 6 inch (375 x 150 mm) wheel rim from aluminium it is preferable to increase the strip length by approximately 5.8% over that suitable for steel and decrease the strip width by approximately 4%.

The bank 1 1 is first rolled into the shape of a hoop 13, shown in Figure 2, and the opposing ends flash butt welded forming a weld line 12. The band thus formed is subsequently passed through multiple forming operations resulting in a finished wheel rim 24 illustrated in Figure 3. Figures 4 to 7 illustrate the band cross-sectional profiles resulting from each of four successive forming operations. The profile of Figure 4 is preferably obtained by a press operation while the profiles of Figures 5 to 7 are obtained by roll forming operations.

The first forming operation comprises preforming the rim flange area by flaring the lateral edge portions 25 and 26 of the band radially outward as shown in Figure 4. Preferably the edge flaring operation is performed in a press wherein the band may also be rounded to a more true cylindrical configuration. For a 15 inch by 6 inch wheel rim, it has been found desirable to flare the edge portions radially outward to give a circumference at the edge approximately nine and one-half (9T) percent larger than the circumference of the hoop 13. Because of the low ductility of the material, flaring the band edges significantly further will overstress the butt weld and may result 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 initial band dimensions.

Once flared, the band is placed on a forming roll for the first roll forming operation. This first roll forming operation is believed to be critical to the success in roll forming of an aluminium wheel rim.

In the first roll forming operation, a well portion, indicated generally by reference numeral 27 in Figure 5, is formed 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 15" x 6" aluminium wheel rim it has been found to be desirable to roll the well portion into the band to the extent that the inside diameter D5 at the well is approximately 1 1 .8to less than the original diameter D4 of the band 13.

Since the initial circumference of the band 1 3 is 9elf% greater than that used in manufacturing a steel rim of comparable size (15" x 6"), the well is approximately 35 percent deeper than that rolled into a steel band during this 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 to be essential so that the shrinking of the tyre seats and safety bead areas may be accomplished in the second roll forming operation.Quantitatively the exact amount of work hardening required is not at present 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 the roll forming of the well portion 27, the diameter of the adjacent rim bead seats 28 and 29 may be expected to increase. The amount of this increase is related to the depth of the well 27. In roll forming an aluminium rim of the 15 x 6".size, this increase is approximately 3.2%.

The second roll forming operation results in a band cross-sectional profile substantially as illustrated in Figure 6. During.this rolling operation contact is made between the band and the rolls and forces are applied to effect flattening of the well portion into a flattened configuration 33 and circumferentially shrink 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 vectors R, is applied over the bead seat and safety hump surface areas.

The deep well 27 is thus forced radially outwards, ultimately assuming the well profile shown in Figure 6. Since the material of the well 27 exhibits greater strength, because of its previous work hardening, the reaction forces R radially urge bead seat areas 31 and 32 radially inward effecting circumferential shrinkage through material compression. As the rolling operation progresses and the bead seat areas shrink, an equilibrium of internal material stresses develops to the extent that side walls 23 and 24 of the deep well 27 subsequently collapse to form side wells 30 and 34 and the flattened bottom 33. Upon collapse of the deep well walls 23 and 24 a general increase of material thickness is achieved in the sharply curved areas of the well indicated by reference numerals 40 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 configuration as a comparison between Figures 5 and 6 will readily reveal.

During the second roll forming operation as performed in the manufacture of a 1 5" x 6" aluminium rim the well 33 circumference is increased to approximately 2.6% over that of well 27 as formed in the first roll forming operation.

However, the bead seat areas 31 and 32 are reduced in circumference by approximately 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 39 and 35. Final sizing of the bead seats 31 and 32 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 the correct form.

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 centre 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 forming 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 results using relatively conventional 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 aluminium rim one skilled in the art of steel wheel manufacture may apply the principles to roll forming aluminium rims of other sizes by qualitatively determining the initial band dimensions and initial well depth necessary to successfully form such a wheel rim.

Although the material band or hoop is described above as being formed by coiling a strip and welding the abutting free ends it is equally possible to form wheel rims using circumferentially endless bands of material such as may be formed by extrusion or spinning techniques.

Claims (13)

1. A method of making a wheel rim comprising the steps of: deforming a portion of a cylindrical band of material between the lateral edges of the band radially inward forming an annular well depression and strain hardening the material of the well by the deformation, further strain hardening the material of the well, reshaping the bottom of the well and effecting shrinking of the bead seat areas through coaction of the strain hardened material of the well and the material of the bead seat area by forcing the well radially outwards while radially restricting the band material on both sides of the well.

2. A method as claimed in claim 1, wherein the cylindrical band of material is formed by bringing together and butt welding two opposite edges of a rectangular blank.

3. A method as claimed in claim 2, wherein the blank is of stock material.

4. A method as claimed in any of claims 1 to 3, wherein the edges of the cylindrical band are flared outwards before the well is formed.

5. A method as claimed in any one of claims 1 to 4, wherein the band is shaped between roll dies.

6. A method as claimed in claim 5, wherein the well is formed by rolling the band between roll dies.

7. A method as claimed in claim 6, wherein the said further strain-hardening of the material forming the well is carried out by continued rolling between the roll dies.

8. A method as claimed in any one of claims 1 to 7, wherein the said further strain-hardening of the material forming the well is carried out by squeezing the material between a pair of matched dies.

9. A method as claimed in any one of claims 1 to 8, wherein the reshaping of the well bottom effects draw forming of the bead seat areas through coaction of the work hardened well material and the bead seat area material.

10. A method as claimed in any of claims 1 to 9, wherein the further work hardening increases the strength and lowers the ductility of the circumferential well material, and the work hardening is of sufficient magnitude to promote subsequent forming operations.

11. A method of making a wheel rim, substantially as hereinbefore described with reference to the accompanying drawings.

12. A wheel rim made by a method as claimed in any of claims 1 toll.

13. A wheel comprising a rim as claimed in claim 12.