A method for manufacturing wheel discs, particularly for commercial vehicles

Abstract

 The method comprises the operations of:
- providing a strip (1) of sheet metal;
- curving this sheet-metal strip (1) and welding together its end portions (1a, 1b) so as to form a cylindrical ring (2) with a predefined diameter (d);
- subjecting the ring (2) to a first pressing operation so as to produce, by means of plastic deformation, a first annular shell part (3) shaped substantially in the manner of a truncated cone or annular sphere segment, having at its ends a smaller opening (3a) and a larger opening (3b), respectively, which are separated from each other by a predefined distance or height (h);
- subjecting this first shell part (3) to at least one second pressing operation so as to produce, by means of plastic deformation, a second annular shell part (4), which is again substantially in the form of a truncated conc, having a flattened, central, annular part (4c) and having a smaller height (h₂) and a larger opening (4b) bigger than those of the said first shell part (3); and
- subjecting said second annular shell part (4) to a final shaping operation so as to provide it with the desired form of the wheel disc (5).

Description

[0001] The present invention relates to motor vehicle wheels of the type comprising a rim to which a disc is welded and relates in particular to a method for manufacturing the disc for such a wheel.

[0002] At present wheel discs for commercial vehicles are mainly produced by means of pressing and/or flow-forming processes, from a square or round piece of flat sheet metal.

[0003] One object of the present invention is to propose a method for manufacturing wheel discs, which allows a drastic reduction in the machining waste and the production of discs with optimum mechanical properties.

[0004] These and other objects are achieved according to the invention with a method comprising the operations of:

• providing a strip of sheet metal substantially in the form of an elongated parallelogram with an essentially uniform thickness;
• curving this sheet-metal strip and welding together its end portions so as to form a cylindrical ring with a predefined diameter;
• subjecting said ring to a first pressing operation so as to produce, by means of plastic deformation, a first annular shell part shaped substantially in the manner of a truncated cone or annular sphere segment, having at its ends a smaller opening and larger opening, respectively, which are separated from each other by a predefined distance or height;
• subjecting said first shell part to at least one second pressing operation so as to produce, by means of plastic deformation, a second annular shell part, which is again substantially in the form of a truncated cone, having a flattened central annular part and having a smaller height and a larger opening bigger than those of the first shell part; and
• subjecting said second annular shell part to a final shaping operation so as to impart to it the desired form of the wheel disc.

[0005] The final shaping operation may a cold flow-forming operation or a shape-pressing operation.

[0006] Further characteristic features and advantages of the invention will appear from the detailed description which follows, provided purely by way of a non-limiting example, with reference to the accompanying drawings in which:

Figure 1 is a perspective view of a metal sheet used for manufacturing a wheel disc according to the invention;

Figure 2 is a perspective view of a cylindrical ring formed so as to be curved and by welding of the end portions of the metal sheet according to Figure 1;

Figures 3 and 4 are perspective views of annular shell parts which can be obtained by means of two successive pressing operations from the cylindrical ring according to Figure 2;

Figures 3a and 4a are partly sectioned perspective views which show the equipment for two successive pressing operations;

Figure 5 is a perspective view of an annular shell part obtained by means of a flow-forming operation from the shell part according to Figure 4;

Figure 6 is a perspective view of the annular shell part according to Figure 5 after a shearing operation (optional) for precise definition of its smaller opening; and

Figure 7 is a perspective view of the wheel disc obtained from the shell part according to Figure 6, by means of operations for final shearing of openings or windows.

[0007] With reference now to the drawings, with the method according to the invention, the manufacture of a wheel disc for a motor vehicle starts with the provision of a sheet-metal strip, denoted by 1 in Figure 1, generally formed in the manner of an elongated parallelogram which is preferably rectangular shaped and has an essentially uniform thickness.

[0008] In the case of a wheel for a lorry or other commercial/industrial vehicles, this thickness may be for example about 8-16 mm.

[0009] The sheet-metal strip 1 is then curved and its end portions 1a and 1b are welded together so as to form a cylindrical ring, denoted by 2 in Figure 2. In this figure, welding of the end sides or portions of the original strip 1 is indicated by 2a.

[0010] Conveniently said welding of the portions 1a and 1b of the sheet-metal strip 1 is formed end-to-end and without the addition of weld material.

[0011] After it has been completed, the weld is cleaned and rounded off and the entire ring 2 is also rounded by means of expansion.

[0012] The cylindrical ring 2 has a diameter d and a length or height h with respective predetermined values.

[0013] The cylindrical ring 2 then undergoes a first pressing operation so as to produce by means of plastic deformation a first annular shell part, denoted by 3 in Figure 3, shaped substantially in the manner of a truncated cone or annular sphere segment. This shell part 3 has at its ends a smaller opening 3a with a diameter d_m1 and a larger opening 3b with a diameter d_M1. The diameters d_m1 and d_M1 are respectively smaller than and greater than the diameter d of the cylindrical ring 2.

[0014] The shell part 3 according to Figure 3 has a height or distance between its openings 3a and 3b with a value h₁ less than the height h of the cylindrical ring 2 of Figure 2.

[0015] The pressing operation by means of which the cylindrical ring is converted into the shell part 3 is performed by means of a special die comprising two half-dies, one of which has a stop which limits expansion of one end of the cylindrical ring 2, forcing the other end of this cylindrical ring to be deformed in a centripetal manner, causing flow of the metallic material towards the axis, such that the smaller opening 3a of the shell part 3 is considerably smaller than the corresponding original opening of the cylindrical ring 2.

[0016] The annular shell part 3 then undergoes a further pressing operation so as to produce by means of plastic deformation a second annular shell part, denoted by 4 in Figure 4.

[0017] The annular shell part 4 is again shaped substantially in the manner of a truncated cone, but conveniently has a flattened central annular portion 4c and has a height h₂ which is significantly smaller than the height h₁ of the shell part 3 from which it is obtained. The shell part 4 has a larger opening 4b, the diameter d_M2 of which is significantly greater than the corresponding diameter d_M1 of the annular shell part 3.

[0018] The smaller opening 4a of the shell part 4 has a diameter d_m2 which is preferably smaller than the corresponding diameter d_m1 of the shell part 3, but could also be substantially the same as this diameter.

[0019] In order to produce the shell part 4, which is almost flattened in the manner of a disc, use is made of a die formed with two half-dies joined together, but without stop surfaces which limit the flow of the material away from or towards the axis (see Figure 3a).

[0020] The shell part 4 may optionally undergo a further pressing operation in order to obtain a semi-finished part having a central annular band which is nearly perfectly planar about the smaller opening. During this optional third pressing step it is possible to vary the degree of drawing of the semi-finished part, and the diameters of the smaller opening and the larger opening may remain unvaried or be slightly modified with respect to those of the original annular shell part.

[0021] The dies used during the first and in particular the second pressing operation (and if necessary also those used during the third optional pressing step) may be suitably curved so as to induce in the parts extra large deformations able to compensate for the resilient return movement thereof.

[0022] Then the shell part 4 undergoes a final shaping operation which may be a cold flow-forming operation or a shape pressing operation (Figure 4a) so as to give it the final desired form. The semi-finished part 5 according to Figure 5 is thus obtained, with a smaller opening 5a, a larger opening 5b and a substantially flat, central, annular band 5c.

[0023] The semi-finished part 5 may then undergo shearing operations, for example for the precise dimensional definition of its smaller opening 5a, as shown in Figure 6, and/or so as to form in this semi-finished article a plurality of further openings or windows intended, for example, to allow the insertion of parts for fixing the wheel disc to the corresponding wheel hub or to act as ventilation openings, or which are simply formed for aesthetic reasons, as is shown for example in Figure 7.

[0024] The precise dimensional definition of the smaller opening 5a of the semi-finished article 5 may, as an alternative to shearing or trimming, be performed by means of (lathe) machining with chip removal.

[0025] Obviously, without modifying the principle of the invention, the embodiments and the constructional details may be widely varied with respect to that which has been described and illustrated purely by way of a non-limiting example, without thereby departing from the scope of the invention as defined by the accompanying claims.

Claims

1. Method for manufacturing a disc (5) for a wheel of a motor vehicle, comprising the operations of:

- providing a strip (1) of sheet metal substantially in the form of an elongated parallelogram with an essentially uniform thickness;

- curving this sheet-metal strip (1) and welding together its end portions (1a, 1b) so as to form a cylindrical ring (2) with a predefined diameter (d);

- subjecting said ring (2) to a first pressing operation so as to produce, by means of plastic deformation, a first annular shell part (3) shaped substantially in the manner of a truncated cone or annular sphere segment, having at its ends a smaller opening (3a) and a larger opening (3b), respectively, which are separated from each other by a predefined distance or height (h);

- subjecting said first shell part (3) to at least one second pressing operation so as to produce, by means of plastic deformation, a second annular shell part (4), which is again substantially in the form of a truncated cone, having a flattened central annular part (4c) and having a smaller height (h₂) and a larger opening (4b) bigger than those of said first shell part (3); and

- subjecting said second annular shell part (4) to a final shaping operation so as to impart to it the desired form of the wheel disc (5).

2. Method according to Claim 1, in which the final shaping operation is a cold flow-forming operation.

3. Method according to Claim 1, in which the final shaping operation is a shape pressing operation.

4. Method according to one of the preceding claims, in which the smaller opening (3a) and the larger opening (3b) of said first annular shell part (3) have respective diameters (d_m1; d_M1) which are respectively smaller than and greater than the diameter (d) of the abovementioned cylindrical ring (2).

5. Method according to one of the preceding claims, in which the smaller opening (4a) of the abovementioned annular shell part (4) has a diameter (d_m2) which is smaller than or substantially the same as the corresponding diameter (d_m1) of the smaller opening (3a) of the abovementioned first annular shell part (3).

6. Method according to one of the preceding claims, in which said second annular shell part (4) undergoes a further pressing operation, so as to produce a semi-finished part having an essentially flat, central, annular portion.

7. Method according to any one of the preceding claims, in which said second annular shell part (4) or said semi-finished part (5) undergoes at least one shearing operation for precise dimensional definition of its smaller opening and/or for the formation of a plurality of openings or windows.

Drawing