Method for manufacturing discs for wheels, particularly for commercial vehicles

Abstract

 The method comprises the operations of:
- providing a strip of sheet metal (1) substantially shaped like an elongated parallelogram with an essentially uniform thickness;
- bending such a strip of sheet metal (1) and welding together the end portions (1a, 1b) so as to make a substantially cylindrical ring; and
- subjecting the ring (2) to press-moulding and shaping operations through plastic deformation so as to give it a desired shape.
The strip of sheet metal (1) is bent so that its end portions (1a, 1b) are level and such end limbs (1a, 1b) are brought together and butt welded substantially on a same plane, so as to obtain a ring (2) which has a chordal flattened wall portion (1a, 1b).
Before undergoing the aforementioned prcss-moulding and shaping operations, the ring (2) is subjected to a preliminary rounding operation through radial expansion.

Description

[0001] The present invention refers to wheels for motor vehicles of the type comprising a rim to which a disc is welded, and concerns in particular a method for making the disc for such a wheel.

[0002] More specifically the invention concerns a method for manufacturing a disc for a wheel comprising the operations of:

• providing a strip of sheet metal substantially shaped like an elongated parallelogram, with an essentially uniform thickness;
• bending such a strip of sheet metal and welding the end limbs together so as to form a substantially cylindrical ring; and
• subjecting said ring to pressing and shaping operations through plastic deformation, so as to give it a desired shape.

[0003] Such a type of method is described for example in the European patent application no. EP-1867408-A.

[0004] The method described in such a document provides that the starting strip of sheet metal is bent on its entire extension, and its end portions, correspondingly arched, are brought together and butt welded. The butt welding of such end portions is indeed problematic: the end surfaces of said portions which are brought together form an angle, even though small, bringing them closer together on the inner side of the ring than on the outer side; the welding requires special tools, and it is difficult to keep the welding arch stable and uniform. The further machining of the weld bead, for the removal of excess metal, is more complicated. Overall, the welding operation is not very "sturdy", and is quite affected by the variations in the process parameters. The mechanical characteristics of the welds can have an excessive variability.

[0005] One purpose of the present invention is therefore that of putting forward a method of the type specified above, suitable for allowing the drawbacks previously outlined to be overcome.

[0006] These and other purposes are obtained according to the invention with a method of the type defined above, characterized in that:

• the aforementioned strip of sheet metal is bent so that its end portions are level;
• said end portions are brought together and butt welded to one another substantially on a same plane, so as to obtain a ring which has a chordal flattened wall portion; and in that
• before undergoing the aforementioned pressing and shaping operations, said ring is subjected to a preliminary rounding operation through radial expansion.

[0007] According to a further characteristic, in said rounding operation, the expansion of the ring is preferably of a greater magnitude in a first axial portion thereof, so that its remaining axial portion takes a substantially cone-shaped configuration. Thanks to such a characteristic the risks of instability of the ring are reduced when it is subjected to plastic deformation loads having a large component in the axial direction.

[0008] Further characteristics and advantages of the invention shall become clear in the following detailed description, given simply as an example and not for limiting purposes with reference to the attached drawings, in which:

figure 1 is a plan view of a sheet of sheet metal used for making a wheel disc according to the invention;

figure 2 is a perspective view of a ring obtained by bending and welding the end portions, left on the same plane, of the sheet of sheet metal of figure 1;

figure 3 is a partial side view of the ring shown in figure 2;

figure 4 is a perspective view of a ring obtained starting from that in figure 2, through an operation of rounding by radial expansion carried out on an axial portion of such a ring;

figure 5 is a perspective view of an annular shell element obtainable starting from the ring of figure 4 through a pressing operation;

figures 6 and 7 are perspective views, partially sectioned, which show the tools for two successive pressing operations;

figure 8 is a perspective view of an annular shell element obtained through operations of flow forming: and

figure 9 is a perspective view of a wheel disc obtained starting from the shell element of figure 8, through final shearing operations of openings or windows.

[0009] With reference to the drawings, in the method according to the invention the making of a disc of a wheel for a motor vehicle begins with the provision of a strip of sheet metal, indicated with 1 in figure 1, having a general shape like an elongated parallelogram, preferably with a rectangular shape, and having an essentially uniform thickness.

[0010] In the case of a wheel for a truck or other commercial/industrial vehicles, such a thickness can be, for example, about 8-16 mm.

[0011] The strip of sheet metal 1 is then shaped: it is mainly bent, leaving however, that its end portions or limbs, indicated with 1a and 1b in figures 1 and 2, remain level. The end faces of the limbs 1a and 1b of the strip 1 are brought together, and then welded, on substantially a same plane, so as to make a substantially cylindrical ring 2, which has a chordal flattened wall portion, formed by the two limbs 1a and 1b brought together and welded.

[0012] With reference to figure 3, the central axis of the ring 2 is indicated O, and the flattened limbs 1a and 1b are advantageously subtended by an angle α having extension between 5° and 15°, and preferably equal to about 10°.

[0013] The bringing together, and then the butt welding, of the end limbs 1a and 1b is extremely easy, and does not require special tools. In fact, bringing together said limbs on substantially a same plane improves the matching of the end surfaces or faces of said limbs, making it uniform. The subsequent excess metal removal processes at the welding are also easier, as are the subsequent finishing operations of the welded area.

[0014] The mechanical characteristics of the welds thus made have a narrower variation range, with a substantial improvement of the general quality.

[0015] After the welding and the following accessory processes, but before the subsequent pressing and shaping operations, the ring 2 of figure 2 is subjected to a preliminary rounding operation through radial expansion with per se known tools.

[0016] Preferably, although not necessarily, in such a rounding operation the expansion is of greater magnitude in a first axial portion of the ring 2, so that the remaining axial portion of such a ring takes a substantially cone-shaped configuration. Figure 4 shows the ring 2 after such an operation: the lower portion 2a subjected to radial expansion is substantially cylindrical, whereas the remaining axial portion 2b is essentially shaped like a truncated cone. The height h_a of the expanded portion 2a is preferably greater than that of the remaining portion 2b. Advantageously, the height h_a can be equal to about three times the height h_b.

[0017] The extent to which the portion 2b is shaped like a cone, expressed as the difference in radius Δr between its ends (figure 4), can take values of about 1-5 mm.

[0018] After the aforementioned preliminary rounding operation, the ring 2 is advantageously subjected to a material removal process, in particular turning, to bring the axial height or length to a predetermined nominal value, and to make its circular end edges level and parallel with each other. Such an operation is extremely important, as it allows possible imperfections of alignment and welding of the two end limbs 1a and 1b of the initial strip 1 to be eliminated, avoiding that in the following operations of plastic deformation of the ring, it suffers anomalous stress and reducing the effects of wear due to press-moulding tools.

[0019] In the aforementioned material removal process advantageously the corners of the edges of the ring 2 which must drag against the moulds or shapes in the following operations are belevelled or rounded.

[0020] The ring 2 is then subjected to press-moulding operations.

[0021] In a first moulding operation the edge with the greatest diameter of the ring 2 is axially brought into abutment against a stop surface, so that the material of the ring is made to flow radially towards the centre, at its edge with smaller diameter.

[0022] Figure 5 of the attached drawings shows an annular shell element 3 obtained through such a first moulding operation, made for example with (per se known) tools schematically and partially illustrated in figure 6. Such tools comprise an upper mould 10 and a lower matching mould 11, where the latter has an annular abutment or stop surface 11a for the edge of the ring with greater diameter.

[0023] By comparing figures 4 and 5 it can be quickly gathered how through the first moulding operation, the annular shell 3 has a smaller diameter that is smaller than the corresponding diameter of the starting ring 2, and a larger diameter that is substantially larger than the corresponding diameter of the starting ring. Moreover, the axial height or length of the annular shell 3 is shorter than the height of the starting ring 2.

[0024] The first moulding operation is advantageously followed by a second one, in which the material of the ring is made to flow radially towards the centre, at its edge with the smaller diameter, whereas the material at its edge with greater diameter is made to flow radially outwards and longitudinally. This can be made, for example, with the tools schematically and partially illustrated in figure 7, in which the upper mould 13, in addition to what has already been described, has, at the bottom, a central cylindrical ridge 13a, functioning as a "centrer" intended to define the diameter of the smallest opening 4a of the annular shell obtained through said second moulding operation (as seen in particular in figure 8).

[0025] The semi-finished element 4 can then be subjected to forming operation with a lathe to reach the intended distribution of thickness, and of shearing, for making in such a semi-finished element a plurality of openings or windows, intended for example to allow fixing elements of the disc-wheel to pass to the corresponding wheel hub, as ventilation openings, or simply for aesthetic purposes as shown, for example, in figure 9.

[0026] Advantageously, the starting strip of sheet metal 1 (figure 1) is made in steel, in particular steel with low alloying element content, for example steel having a manganese content substantially between 0.15% and 0.80% of the total weight, and having a stretching percentage greater than 25%.

[0027] Of course, the principle of the invention remaining the same, the embodiments and the details can be widely varied with respect to what has been described and illustrated purely as an example and not for limiting purposes, without for this reason departing from the scope of the invention as defined in the attached claims.

Claims

1. Method for manufacturing a disc (4) for a wheel of a motor vehicle, comprising the operations of:

- providing a strip of sheet metal (1) substantially shaped like an elongated parallelogram with an essentially uniform thickness;

- bending said strip of sheet metal (1) and welding together the end portions (1a, 1b) thereof so as to form a substantially cylindrical ring; and

- subjecting said ring (2) to pressing and shaping operations through plastic deformation so as to give it a desired shape;

the method being characterized in that:

- the strip of sheet metal (1) is bent so that its end portions (1a, 1b) are level;

- said end portions (1a, 1b) are brought together and butt welded substantially on a same plane, so as to obtain a ring (2) which has a chordal flattened wall portion (1a, 1b); and in that

- before undergoing the aforementioned pressing and shaping operations, said ring (2) is subjected to a preliminary rounding operation through radial expansion.

2. Method according to claim 1, wherein, in said rounding operation, the expansion is of a greater magnitude in a first axial portion (2a) of the ring (2), so that the remaining axial portion (2b) of the ring (2) takes a substantially cone-shaped configuration.

3. Method according to claim 1 or 2, wherein said ring (2) is subjected to an operation of material removal, in particular a turning operation, to bring its height or axial length to a predetermined nominal value, and to make its end edges level and parallel to each other.

4. Method according to claim 3, wherein said operation of material removal, in particular turning, is carried out after the aforementioned preliminary rounding operation.

5. Method according to claim 3 or 4, wherein, in said operation of material removal, the corners of the edges of the ring (2) which must drag against the moulds or shapes in the following operations are bevelled or rounded.

6. Method according to any one of the previous claims, wherein the aforementioned level end portions (1a, 1b) have an extension such that in cross-section they are each subtended by an angle (α) between 5° and 15°, and preferably of around 10°, said angle (α) having vertex on the axis (0) of the ring (2).

7. Method according to any one of the previous claims, wherein the aforementioned remaining axial portion (2b) of the ring (2) which has a substantially cone-shaped configuration, extends over about 25% of the axial height or length of the ring (2).

8. Method according to any one of the previous claims, wherein said pressing operations comprise a first moulding operation in which the edge with the greatest diameter of the ring (2) is axially brought into abutment against a stop surface (11a), so that the material of the ring (2) is then made to flow radially towards the centre, at the edge with smaller diameter of the said ring (2).

9. Method according to any one of the previous claims, wherein said pressing operations comprise a second moulding operation, in which the edge with smaller diameter of the ring (3) is radially brought into abutment against a centring element (13a), so that the material of the ring (3) is then made to flow radially outwards and longitudinally towards the edge with greater diameter of said ring (3).

10. Method according to one of the previous claims, wherein said pressing operations comprise a moulding operation in which the material of the ring (3) is made to flow radially towards the centre, at the edge with smaller diameter, whereas the material at the edge with greatest diameter is made to flow radially outwards and longitudinally.

11. Method according to any one of the previous claims, wherein said strip of sheet metal (1) is made from steel, in particular steel with low alloying elements content.

12. Method according to claim 11, wherein the strip of sheet metal (1) is made from steel having a manganese content of substantially between 0.15% and 0.80% of the total weight.

Drawing