EP1399321A1

EP1399321A1 - Method of producing a light alloy wheel rim and an improved light alloy wheel rim for a motor vehicle

Info

Publication number: EP1399321A1
Application number: EP02767536A
Authority: EP
Inventors: Philippe Meyer
Original assignee: Montupet SA
Current assignee: Montupet SA
Priority date: 2001-06-29
Filing date: 2002-07-01
Publication date: 2004-03-24
Also published as: US20050034305A1; FR2826609A1; WO2003002359A1; FR2826609B1

Abstract

The invention relates to a wheel rim made from a light alloy, such as an aluminium-based alloy, comprising a front face (10) and a tyre tread (20) which are welded together. The inventive method of producing the wheel rim (J) comprises the following steps: moulding of the front face (10) with a light alloy; provision of a weldable alloy strip with structural hardening; curving of said strip to produce a generally cylindrical shape; welding of the ends in relation to the curved strip with fusion of the strip material; forming of the strip by necking and/or spinning in order to form the tyre tread (20); and welding of the front face and the tyre tread to one another.

Description

The present invention relates to a method for producing light alloy rims, in particular aluminum alloy, in particular for motor vehicles. More particularly, the invention ^" provides a method of producing a rim which has improved properties both in terms of lightness and mechanical strength, as well as a new rim having these improved properties.

State of the art

Most light alloy rims are now made in one piece by molding, most often using a mold filling technique from below at low pressure, or more rarely from above at gravity.

These two filling techniques have the drawback of forcing the solidification of the alloy fprmant the rim to be controlled throughout the latter and over significant distances. Thus, typically, during filling at low pressure, solidification must be controlled from the inner rim hook to the center of the rim, in the middle of the front face (located in the lower part of the mold) at which filling is carried out with liquid metal at low pressure and where solidification ends.

Such solidification control is relatively problematic for small diameter rims (typically up to 15 inches); on the other hand, it becomes much more delicate for rims with a larger diameter, due to the corresponding increase in the mass of metal. Such an increase in fact leads to a slowing down of the molding rates and a greater difficulty in avoiding molding defects of the shrinkage type.

In addition, the rim styles ^" which are developing strongly these days are rims of the so-called" full face "type according to Anglo-Saxon terminology, that is to say whose front panel does not have the usual shrinkage relative to the outer rim hook, but on the contrary approaches or even tangents this rim hook, which creates a large mass under the support of the tire.

Figure la of the drawings shows in axial half-section the shape of such a "full face" rim Ja, the aforementioned large mass Ma. By comparison, Figure lb shows in opposite axial half-section the shape of a more conventional rim Jb.

The existence of this mass Ma difficult to solidify --rapidement is detrimental not only to the _whole, production process, because the rates are slowed, but also relief - always sought because it is the one of the essential advantages of light alloy rims - because the mold structure used does not avoid these large masses under the support of the tire. It will also be emphasized that the molding of a single-piece rim has the drawback of requiring relatively complex molds composed, as shown in FIG. 2, of a sole S, of an upper core NS and of clevis C1 and C2, the sole defining a rising channel Ch for the supply of liquid metal under low pressure. Finally, it should be noted that the use of a single material, essential when making a one-piece rim, poses problems in terms of impact resistance and behavior in the ^" dent test ^" , in particular at the hooks of rim, and it is then necessary to significantly increase the thickness of the material at these rim hooks.

It has also been proposed for many years to produce rims in two parts. The general idea consists in molding the front face (external face) of the rim by a conventional light alloy molding process, in particular at low pressure, and in producing the tread in a wrought alloy.

However, the techniques used today are ill-suited to this type of product. Thus the tread is produced for example by butt welding (“butt welding” according to English terminology) before being laminated, in an approach similar to that of steel rims. After this part has been produced, the previously machined front face is then attached to this tread.

This known technology has multiple drawbacks. First, the Applicant has been able to demonstrate that butt welding was not easily achievable for alloys with structural hardening (such as Al-Si-Mg alloys of series 6000, subject to hardening by precipitation during '' a heat treatment of solution-quenching-tempering), but could only be in practice for alloys without structural hardening (such than 5000 series alloys). However, these latter alloys have the disadvantage of having a low resistance potential, which does not exceed that of the casting alloys usually used such as 1 ^" alloy known under the designation AS7G (aluminum alloy at 7% by weight of silicon and 0.3% by weight of magnesium).

In addition, the investments necessary for this technology are very heavy, not only for butt welding but also for subsequent shaping by rolling on rollers.

Variants of this technology exist, and relate to different types of attachment between the front face and the tread, but these variants do not solve the main problems mentioned above, and in particular the problem of the mechanical resistance of the alloy used for the tread.

Another still known technology consists in working - from a circular blank which is gradually pushed back on a mandrel to produce a one-piece tread. The bottom of the blank, useless after forming the tread, is then cut and lost. It is understood that this makes the process extremely expensive and economically unsuitable for the mass-produced automobile market.

Summary of the invention

The present invention aims to propose a method for producing a light alloy rim which overcomes or at least alleviates the above-mentioned problems and which makes it possible to obtain a light rim at minimum cost, while retaining adequate mechanical properties. . In this regard, it was surprisingly found that by using a light alloy with structural hardening for the tread, and by shaping this tread by bending, it was possible to use a technique of fusion welding of the parts (opposite ends) while obtaining final mechanical characteristics "in particular in terms of resistance of the welded region, which were entirely satisfactory. Thus the present invention proposes according to a first aspect a method of manufacturing a light alloy rim, such as an aluminum-based alloy, for a motor vehicle, the rim comprising a front face and a tread welded to each other, characterized in that it comprises the steps following:

- molding of the front face with a light alloy,

- providing a structurally hardened alloy strip ^"-soudable,

- bending this strip to give it a generally cylindrical shape,

- welding of the ends opposite the curved strip with fusion of the strip material,

- shaping of the strip by shrinking and / or pushing back, to form the tread, and - welding of the front face and the tread with one another.

Preferred, but not limiting, aspects of this process are:

- The step of shaping the strip is preceded by a step of expanding the strip, after welding of its ends to one another. the shaping step is preceded by an at least partial dissolution and quenching operation.

- the weldable structural hardening alloy is an aluminum alloy of the standard 6000 series.

the step of welding the ends opposite the tread is carried out ^" by a welding technique chosen from the group comprising welding by electron beam, welding by electron beam under vacuum, MIG (metal / inert gas) welding, MIG Tandem welding, Laser welding and combined M.I .G. / Laser welding.

the molding operation of the front face comprises the production of at least one weight reduction recess, coming from molding. at least one recess is on an inner side of the front face.

- At least one recess is located in the vicinity of a connection zone between the front face and the tread.

- At least one recess opens in a demolding direction of the front face.

According to a second aspect, the present invention provides a light alloy rim, such as an aluminum-based alloy, for a motor vehicle, the rim comprising a front face in light alloy and a tread also in light alloy. welded to each other, characterized in that the tread is produced by bending and shaping a piece of alloy with weldable structural hardening, with its ends opposite the welded curved strip to each other with fusion of the material of the strip. Preferred but non-limiting aspects of this rim are the following:

- the weldable structural hardening alloy is an aluminum alloy of the standard 6000 series. ^" - its front face comprises at least one weight reduction recess, coming from molding. at least one recess is located inner side of the front panel.

- At least one recess opens in a demolding direction of the front face.

- the rim has two rim hooks, one of which is formed at the front face and the other of which is formed at the tread.

Brief description of the drawings

Other aspects, aims and advantages of the present invention will appear better on reading the following detailed description of a preferred embodiment thereof, given by way of example and made with reference to the accompanying drawings. _ In the drawings, in addition to Figures 1 and 2 already presented above: Figure 3a is a half front view of a rim according to an exemplary embodiment of the invention, Figure 3b is a half view in section axial of the rim of FIG. 3a, Figure 4 is a perspective view of a tread of the rim of Figures 3a and 3b, after two first steps of bending and welding, and Figure 5 illustrates by three cross sections respectively the shape of the strip bearing before subsequent forming, and the appearance of the tread after two subsequent shaping operations.

Detailed description of a preferred embodiment

We will now describe a method for producing a light alloy rim consisting of a front face, preferably having all the lightening that is authorized by the sole molding of this front face, and in particular weight reduction under the supports for the tire. . This front face is welded with a tread band produced according to a range making it possible to use a wrought alloy with any structural hardening provided that it is weldable.

Figures 3a and 3b of the drawings illustrate a rim J produced according to the invention in two parts, namely a front face 10 and a tread 20. a Figure 3 of the drawings illustrates the type of lightening which is carried out roughly molding on the rear of the front face of the rim, avoiding, with respect to the one-piece section of FIG. la, to mold the metal in zones 11 and 12 which open, in a direction parallel to the axis xx, towards the inside of the rim. FIG. 3b also shows the front rim hook CJ1, formed at the level of the front face 10 to proximity of the recesses 11, 12, and the rear rim hook CJ2, formed at the level of the tread 20. It is important to note here that the type of geometry shown in FIG. 3b is likely to be obtained at using very simple molds, consisting for example of two elements, namely a sole (that is to say the lower part of the mold ^" , producing the front face of the rim with its chosen style) and an upper core (producing the rear face of the rim, and comprising projecting parts which will define the lightening zones 11 and 12).

Since the front face 10 and the tread 20 are produced separately, unlike the low pressure one-piece or other molding process mentioned in the introduction, it is possible here to very violently cool the periphery of the front face, and to obtain from this has an increased fineness of microstructure and properties ^" 'at the rim core which it is not possible to obtain by molding a complete monobloc rim, the advantage being all the more appreciable as the diameter of the rim is great.

As an indication, we present in Table I below the compared properties of a 15 inch monobloc rim molded at low pressure in accordance with the prior art and of a front face alone, having the same style and also molded in low pressure. In both cases, the metal temperature in the oven was 710 ° C, the alloy used was an AS7G alloy modified with 120 ppm of strontium, refined with titanium diboride TiB ₂ and the filling speed was 7mbars / second . After demolding and deburring, a so-called T6 treatment was applied to the two parts, comprising the following steps:

- dissolving for 5 hours at 535 ° C, - soaking in water at 50 ° C,

- returned for 3 hours 30 minutes at 160 ° C.

The properties obtained, measured according to the NF standardized tensile tests on tensile specimens taken from the arms of the rim, are indicated in Table I below.

Table I

Test tube Rm (MPa) RpO, 2 (MPa) A (%)

(1) 278 220 5.5

(2) ^{W "} - 285 192 13.0

(1): Front face of molded monobloc rim (2): Front face molded only

The better properties obtained for the molded front face alone are explained by a lesser presence of _. micro-shrinkage, resulting from more efficient cooling of the periphery of the front face. This therefore results in an improved microstructure which is also favorable to the fatigue resistance of the rim.

As far as the tread is concerned, the range used is as follows: from a blank sheet made of light alloy, cut to the desired thickness (typically of the order of 3 to 4.5 mm for 15 to 17 inch rims, a strip is produced by bending the sheet to give it a cylindrical shape and welding it end to end by a welding technique illustrated in FIG. 4. This technique is preferably a electron beam welding, vacuum or not, or an MIG (inert metal 7 gas) welding technique and its different variants, MIG Tandem welding, Laser welding or combined M.I .G. / Laser. Thus, according to this welding technique, the use of the conventional technique known as "butt welding" mentioned in the introduction, which it turns out cannot be applied effectively to an alloy with structural hardening, is avoided, and the you can work with a wide variety of weldable hardening alloys.

The tread is then subjected to a series of shaping operations essentially by shrinking according to the following sequence of steps: - prior widening by expansion of the tread; this operation can be carried out on any type of known expander, for example with segments or else with internal shapes pressed against each other; it has the advantage, in addition to facilitating the subsequent shaping of the tread, to test the quality of its butt weld before any subsequent operation; in this regard, poor weld quality will be revealed at this stage by cracks in line with the welded area; - obtaining the final geometry by a series of shrinking steps as illustrated by way of example in Figure 5, starting from a straight shape in a direction aa; these operations are carried out on a steel mandrel of suitable geometry and on conventional shrinking forming machines (or alternatively by embossing). In order to benefit from an optimum deformation capacity specific to structural hardening alloys, the tread is worked in the above shaping steps, preferably cold in the so-called "T4" state ( solution followed by quenching) or in a thermal state corresponding to a partial dissolution, so as to preserve a potential for subsequent structural hardening.

Once these operations have been carried out, the tread is welded to the front face. Preferably, for reasons of weight, a butt welding technique as shown in FIG. 3b is used, the weld bead being indicated at 30. Other techniques ^" can also be used. In addition, for ensure good mutual positioning of the front face and the tread, a small centering heel can be provided.

To weld the front face with the tread, conventional welding techniques can be used such as electron beam welding, M.I.G. (metal / inert gas) and its different variants, welding M.I.G. Tandem, laser welding or combined welding M.I .G. /Laser.

Advantageously, this welding operation is preceded by a light machining of the tread at the level of the welding zone, which makes it possible to obtain a clean and dimensionally well calibrated surface. In the same spirit, a slight machining on the other side of the tread ensures a good surface appearance and excellent dimensional precision. Those skilled in the art will easily know how to choose the settings for the welding operation so as to minimize the deformation of the rim, so as ^" not to have to remanufacture the rim after this operation.

The rim is then ready for the usual final operations of surface treatment, application of paint and baking, then inspection.

In this regard, obtaining the final mechanical characteristics preferably results from an income achieved simply by the curing operation of the paint applied to the entire rim (after welding the front face with the tread and after surface treatment), typically for 20 minutes at a temperature of the order of 160 ° to 185 ° C.

It is - of course possible as a variant to produce an income separately from this cooking, and / or to produce this income on the tread alone, before welding on the front face. In the latter case, the front face undergoes its own heat treatment, if necessary, such as dissolution and quenching.

It will be noted here that it is preferable to avoid dissolving and quenching after the operation of welding the tread on the front face, this in order to avoid relatively large deformations caused by quenching, which would require a new annealing of the entire rim, and therefore of the tread. By way of example, we will find in Table II below the compared properties of a hollow tread rim belonging to a one-piece molded rim as described in the introductory part of this application, with a diameter 15 inch, made of AS7G molding alloy, and a tread belonging to ^"" a rim of the same diameter made according to the invention. The tread of the rim according to the invention was produced with the following succession of steps:

- cutting of an original sheet of alloy 6081 (designation according to the American "Aluminum Association"), 4 mm thick,

- bending into a cylinder, - welding of the cylinder by tandem MIG process, subsequent shaping according to the steps illustrated in Figure 5, to obtain a tread ^' with a thickness of approximately 3 mm in the rim recess (at near the weld 30) and with a thickness of 4 to 4.5 mm in the area of the hook CJ2,

- returned to 185 ° C, practiced on the sole tread before welding on the front face.

Table II

Test tube Rm (MPa) RpO, 2 (MPa) A (%)

(1) 269 203 4.5

(2) 260 210 16.0

(1): Tread recessed rim on a monobloc rim (2): hollow tread rim on rim two parts according to the invention

It follows from Tables I and II above that a rim produced in two parts in accordance with the present invention is capable of satisfying substantially as well as a monobloc rim to current "specifications.

If we now compare these two 15-inch rims in terms of weight, we can see a significant weight gain; concretely, the monobloc wheel of the prior art will weigh approximately 7.9 kg, while the two-part rim according to the invention will weigh approximately 6.5 kg, ie a weight gain of nearly 20% which is considerable.

Of course, the present invention is in no way limited to the embodiment described and illustrated, and those skilled in the art will be able to make numerous variants or modifications to it.

Claims

1. A method of manufacturing a light alloy rim (J), such as an aluminum-based alloy, for a motor vehicle, the rim comprising a front face (10) and a tread (20) welded together. to one another, characterized in that it ^" comprises the following stages:

- molding of the front face (10) with a light alloy,

- supply of a weldable structural hardening alloy strip,

- bending of this strip to give it a generally cylindrical shape, - welding of the ends opposite the curved strip with melting of the material of the strip,

- shaping of the strip by shrinking and / or pushing back, ^"' to form the tread (20), and

- welding of the front face and the tread with each other.

2. Method according to claim 1, characterized in that the step of shaping the strip is preceded by a step of expanding the strip, after welding of its ends to one another.

3. Method according to one of claims 1 and 2, characterized in that the shaping step is preceded by an at least partial dissolution and quenching operation.

4. Method according to one of claims 1 to 3, characterized in that the weldable structural hardening alloy is an aluminum alloy of the standard series 6000.

5. Method according to one of claims 1 to 4, characterized in that the step of welding the ends facing the tread is carried out by a welding technique chosen from the group comprising welding by electron beam, vacuum electron beam welding, MIG welding (metal / inert gas), welding M.I.G. Tandem, Laser welding and M.I.G. /Laser.

6. Method according to one of claims 1 to 5, characterized in that the operation of molding the front face ( ^' 10J "comprises the production of at least one recess for' weight reduction (11, 12), come from molding.

7. Method according to claim 6, characterized in that at least one recess (11, 12) is located on an inner side of the front face (10).

8. Method according to one of claims 6 and 7, characterized in that at least one recess (11, 12) is located in the vicinity of a connection zone between the front face (10) and the tread ( 20).

9. Method according to one of claims 6 to 8, characterized in that at least one recess (11, 12) opens in a demolding direction of the front face.

10. Rim (J) made of light alloy, such as an aluminum-based alloy, for a motor vehicle, the rim comprising a front face (10) made of light alloy and a tread (20) also made of light alloy welded to each other, characterized in that the tread (20) is produced by bending and shaping a piece of alloy with structural hardening weldable, with its ends facing the curved strip welded to each other with fusion of the strip material.

11. Rim according to claim 10, characterized in that the weldable structural hardening alloy is an aluminum alloy of the standard series 6000.

12. Rim according to claim 11, characterized in that the front face (10) comprises at least one recess (11, 12) for weight reduction, coming from molding.

13. Rim according to claim 12, characterized in that at least one recess (11, 12) is located on an inner side of the front face.

14. Rim according to one of claims 12 and 13, characterized in that at least one recess (11, 12) is located in the vicinity of a connection zone between the front face and the tread.

15. Rim according to one of claims 12 to 14, characterized in that at least one recess (11, 12) opens in a demolding direction of the front face.

16. A rim according to one of Claims 10 to 15, characterized in that it has ^of them hooks rim (CJ1, CJ2), one (CJ1) is formed at the front face (10) and the other (CJ2) of which is formed at the level of the tread (20).