Background of the Invention The light alloy rim for wheels must be suitably shaped to allow easy mounting of the tyre, to guarantee a perfect seal of the air inflation pressure of the"tubeless"type tyres (without an inner tube) that are commonly used today, and satisfy the technical requirements imposed by the existing norms and international bodies for product approval and certification.

As it is known, the rim of a wheel can be an integral part of the wheel itself (mono-block wheels) or one of the parts, which, when joined mechanically to others, forms the modular wheel (normally composed of two or three pieces).

In both cases, at present, rims are obtained, in the majority of cases, by means of casting technology. Other less common methods include, for example, forging and hot pressing.

Casting technology is divided, in turn, into two main methods: gravity casting and low-pressure casting. Today,

rims or mono-block wheels are produced by gravity casting using light alloys of various compositions. However, this method presents some disadvantages, including: - an elevated time needed for the solidification of the casting (around five minutes), - on average, a 10 Kg finished piece requires another 10 Kg of light alloy, such as feeders or branches of casting to guarantee the soundness of the melted casting, - the impossibility of using thermal treatment alloys, and -the great waste of energy required for melting the alloy.

The low pressure casting method allows the problems of gravity casting to be eliminated, or at least reduced: - the time needed for solidification of the casting is reduced to about four minutes, -stocks needed for successful casting are reduced to a value of about 25%, - it is possible to use thermally treatable light alloys.

However, this method also presents some disadvantages, such as the difficulty in maintaining and guaranteeing the soundness of the casting in areas near the entrance hole of the material melted in the die, and the great waste of energy required to melt the alloy.

Objects and summary of the invention

Object of the present invention is to propose a method for producing light alloy rims for wheels, which enables the above said problems resulting from the current production methods to be remedied, maintaining an elevated quality of the finished product.

Another object of the invention is to realise a light alloy rim for wheels from a suitable rolled product, exploiting its properties of ductility, deformability and weldability.

The proposed method basically provides that the rim is obtained from a rolled product using a series of cold plastic deformations carried out on said original rolled product. These plastic deformations comprise, at least, the punching of the rolled product, the drawing of the punched piece, the shearing of its excess parts, particularly of the bottom, the re-edging of its ends and the shaping of the lateral surface according to the desired profile.

The advantages offered by this method for realising the rim can be summarised as follows: - time needed for realising a piece equal to about one minute; - stock needed in quantities equal to about 5% of the weight of the finished piece ; - wide range of choice and possibility of using rolled sections on the market with normal characteristics or characteristics for thermal treatment;

- mechanical working performed cold to avoid wasting energy on melting the alloy, thus resulting in a practically inexistent environmental impact.

Brief description of the drawings An example of practical embodiment of the invention will be described below in further detail with reference to the accompanying drawings that are indicative and not limiting, wherein: - figures 1 and la show the punching phase of a rolled material and a disc resulting from this operation; -figures 2 and 2a show the drawing phase of the disc obtained from the punching and the resulting piece; -figures 3 and 3a show the shearing phase of the piece obtained from the drawing and the resulting piece; -figures 4 and 4a show the straightening on one of the edges of the piece obtained from the previous phase, and the relative resulting product ; - figures 5 and 5a show the re-edging of an edge, and calibration of the piece obtained during the previous phase ; and - figures 6 and 6a show the shaping of the piece obtained from the previous phase and the resulting rim.

The method according to the invention allows to obtain a light alloy rim for wheels, for example aluminium alloy, from a rolled product 11 of a suitable thickness and size.

The rolled product 11 is punched using a standard punch cutter 12 to obtain a disc 13 with a suitable diameter. The disc 14 is drawn with a press 14 that has a punch 15 to obtain a hollow cylindrical body 16, with a bottom 16', and an externally folded edge 16". After the drawing, the excess parts of the body 16, in other words the bottom 16', and the outermost part of the edge 16"are cut using a press 17 with a shearing die 18. At this point, the body 16 has an edge 19 facing inwards, from the part opposite the edge 16". Said edge 19 is thus straightened using a press 20 with a punch 21 and then re-edged using a suitable press 22 so that this too is facing outwards. At the same time, the body 16, which at this point presents a tubular structure, is calibrated.

Finally, the body 16, thus calibrated and edged, is shaped according to the requested profile, and in keeping with the existing norms using a specific machine and a shaped die 23.