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(11) | EP 0 089 520 A2 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Process for manufacturing metal rims for vehicle wheels and products so obtained |
| (57) Shaped metal rims for vehicle wheels, particularly tire rims of aluminium alloy for
wheels of motor vehicles, obtained by hydroforming of a tubular section either extruded
or of another type, said section being significantly smaller in diameter than said
rims. |
[0001] This invention relates to a simplified process for manufacturing metal rims for vehicle wheels, in particular tire rims of aluminium alloy for wheels of motor vehicles, preferably weldless.
Background of the invention
[0002] As is known, the aluminium alloy tire rims for motor vehicle wheels are presently manufactured starting from a flat plate which is caused to assume the tire rim shape by means of the following operations :
- cutting from a plate the material cut down size neces- saty for the tire rim to be obtained;
- roller leveling said cut down size to assume the shape of an open flat (i.e. non-shaped) cylinder;
- welding the edges of the cylinder so obtained to obtain a not yet shaped tire rim;
- rolling said tire rim to impart the desired shape to it;
- final trimming.
[0004] The process schematically described hereinabove is operatively complex due to the number of single operations involved and - chiefly - leads to the obtainment of tire rims with weld, such weld representing, as is known,a solution of continuity of the metal structures in general and of the tire rim in the particular case in question.
Summary of the invention
[0005] Thus, it is an object of the present invention to provide a simplified process suited to manufacture metal tire rims, preferably weldless, for vehicle wheels, particularly weldless tire rims of aluminium alloy for motor vehicle wheels.
[0006] The abovesaid object and still other ones which will be apparent to those skilled in the art from the following description, is achieved, according to the present invention, by a hydroforming process which consists in imparting the desired shape to the wall of a metal pipe cut down size, preferably of the extruded type, by applicating to the inside of said pipe - previously inserted into a female die-matrix having inner walls profiled according to the shape to be imparted to the desired tire rim - a hydraulic pressure, by means of a press of conventional type, thus obtaining a rough profiled tire rim ready for the final finish (trimming by turning and the like).
[0007] More particularly, the process and the relevant device are described in detail hereinafter, according to a preferred but non-exclusive embodiment thereof, making reference to the annexed (only) table of drawing.
Brief description of the drawings
[0008]
- Figure 1 shows - in median longitudinal section - a pipe cut down size ready for the hydroforming operation;
- figure 2 shows - in median longitudinal section and schematically - the die-matrix and the pipe already shaped as a rough tire rim;
- figure 3 shows - in median longitudinal section - the finished tire rim.
Detailed description of the invention
[0009] Referring to such figures, the above process consists of the following steps:
a) cutting, from a metal pipe either extruded or of another type, a cut down size 1 having a length proportioned to the shaped surface of the tire rim to be obtained (plus the proper allowance) and hydroforming thereof in die-matrix 2 by means of the hydraulic pressure of a fluid 4 which causes the pipe wall to expand against the wall of said die-matrix and thereby causes said pipe to assume the same shape of the die-matrix. The outside diameter of said cut down size may be significantly smaller than the minimum inside diameter of die-matrix 2, because during the subsequent hydroforming operation the pipe undergoes a radial expansion and a longitudinal creep (with relevant shortening): that permits to render the strain-hardening of the pipe material little important, since it is evident that the stretching ensuing from the radial expansion is substantially compensated by the longitudinal creep. Therefore the material retains, after forming, its ultimate elongation characteristics substantially unchanged or in any case poorly modified, such characteristics proving to be superior to those of the same material deformed by rolling.
[0010] It is clearly understood that, although a sensible increase in the diameter of the pipe (in the shaped form) is obtained, the pipe thickness undergoes substantially no reductions or insignificant reductions, thus having the technical-economical advantage of utilizing, as a starting semifinished product, a pipe with a diameter significantly reduced as compared with the one of the finished tire rim;
b) trimming-finish of the edges of rough tire rim 3 (obtained in the above-illustrated step, and removed from the die-matrix) by mechanical working, for example by turning, till assuming the height sizes of finished tire rim 5, ready for the successive assembly to the disc-wheel, accomplished e.g. by means of welding.
[0011] Particularly suited materials to be employed for the manufacturing of tire rims according to the process of the present invention are the aluminium alloys of the Al-Mg type of the known Series AA 5000, the Al-Mg-Si alloys of the known Series AA 6000, and the Al-Zn-Mg or Al-Zn-Mg-Cu alloys of the known Series AA 7000.
[0012] It is apparent, however, that the process is applicable to many other metal materials, suitable for manufacturing rims for vehicle wheels, and it is applicable in any case to tubular sections types different from the extruded type (e.g. drawn tubular sections or pipes obtained from plate by welding).
[0013] The process forming the object of the present invention is particularly utilized for tire rims of wheels for motor vehicles; it is employable with technical-economical advantages also for manufacturing rims and tire rims for the most different types of vehicles, also in connection with the fact that the process itself can be practiced to obtain, instead of one rough rim only for each individual hydroforming operation, a plurality of rims (or tire rims), in this case starting from a pipe having a length proportioned to the desired number of rough rims to be obtained for every single forming operation, and utilizing, for said operation, a "multiple" die-matrix, i.e. having a plurality of "impressions", namely as are required to obtain the desired number of rims.
[0014] Cut-trimming operations,to be carried out after the above-described multiple hydroforming, permit to obtain the finished rims.
[0015] The advantages offered by the present invention can be therefore summarized as follows :
- process simplification : in fact, the process substantially consists in a single hydroforming operation, to be carried out also with a multiple die;
- obtainment of tire rims starting from an extruded pipe or from another type of pipe having a significantly smaller diameter than said tire rims (and therefore of common manufacture).