METHOD FOR MANUFACTURED A LIGHT ALLOY HYBRID WHEEL, COMPRISING A FRONT FLANGE AND A RIM

Abstract

The light-alloy hybrid wheel manufacture method implementing the following separate operation phases: - creating a flange (2), having an inner profile (2a) capable of making up a tire bead seat; - creating a rim having, on one side, an outer profile (1a) capable of forming a tire bead seat and, on the other side, a circular flank (1b) intended to be assembled with part (2b) of the flange (2); and - assembling the flange (2) with the rim (1), at the seat (2a) of said flange (2) and at the circular flank (1b) of the rim (1). Said method is characterized in that assembly of the rim (1) with the flange (2) is carried out by welding the circular flank (1b) of the rim and the flange (2) using a single friction stir weld (5) using a slug in a position enabling access on both sides of the weld.

Description

METHOD FOR MANUFACTURED A LIGHT ALLOY HYBRID WHEEL, COMPRISING A FRONT FLANGE AND A RIM The invention relates to the technical sector of wheels, in particular for vehicles, motor vehicles, and also to the sector of foundry and forging for the manufacture of light alloy parts, for example based on aluminium or magnesium, intended in particular for the automotive industry. We know, for example, of the production of wheels with a one-piece rim and flange obtained by molding, but requiring complex and costly technical means and resulting in very substantial thickness dimensions, thus leading to a weight of the resulting wheel that is too high compared to current requirements. In terms of prior art according to figure 1, relating to the two aspects mentioned above, it is already known to produce hybrid wheels (R) in two parts comprising a rim part (1) and a front flange (2) or wheel flange, these two parts being joined together by different means of connection. One effective method was proposed, for example, in patent EP 0 854 792, which describes a two-part hybrid wheel produced using a specific process. The connection between the rim and the flange is ensured by a welded joint obtained through a cyclic friction welding operation. This technology, which is being used by one of the Applicant's subsidiaries, satisfactorily meets market requirements. However, the implementation of this process presents some drawbacks in relation to new market demands, such as achieving a 20 to 30% reduction in product weight while maintaining a competitive price. Furthermore, in this patent EP 0 854 792, the wheel's forged rim is based on a centrifugally cast tube, which is then shaped by rolling or friction welding to obtain the final rim configuration. These operations are lengthy and costly. Furthermore, the Applicant uses a technology combining a casting phase and a forging phase for aluminum alloy parts, known under the brand name "COBAP ESS". This technology is defined in patent EP 1 19 365 and consists of creating a casting preform by pouring a light alloy such as aluminum alloy, then transferring the resulting preform into a forging die with dimensions significantly smaller than the preform, and then performing a forging operation to obtain the desired properties of the final part. A deburring operation is then performed on the periphery of the final part obtained after forging. The applicant already uses this technology to produce wheels, as defined in patent FR 2 981 605, of which it is also the holder. In this patent, the wheel flange is manufactured using COBAPRESS technology, which allows for weight reduction. The flange undergoes a forging step between two dies during this process. This forging step is costly, particularly for small production runs where the manufacture of these forging dies has a significant impact on the cost. It should be noted that wheel rims must be fitted with profiles acting as seats (3) for supporting and retaining the tire beads (4). To achieve weight reduction in this area, a recess was created by forming a cavity (6) between the two welds (5) intended to connect the rim portion (1) to the flange portion (2) (Figure 5). Other solutions have been proposed according to the prior art.Thus, from the point of view of the weight reduction of the flange, different solutions for hollowing out the seat of the tire bead have been described. For example, in patent EP 1230099, the holder presents a solution where one of the tire bead seats extends inward from the inner surface of the wheel rim wall in a self-supporting manner, while the outer profile of the wheel rim is not constrained by the inner profile of the tire bead. This shape, which runs around the entire circumference of the part, allows for weight reduction, but drilling and valve positioning are difficult in this configuration. US patent 5271663 describes another embodiment, but using a different manufacturing technology. Recesses are machined into the less stressed areas of the tire bead seat. These recesses allow for weight reduction as well as wheel balancing. However, machining these recesses is a lengthy and expensive operation. Thus, according to the prior art mentioned above, existing solutions for making recesses in the tire bead seat result in significant chip removal and are therefore long and costly. US patent 65361 describes further examples of a two-part hybrid wheel. The rim is made by rolling a strip of metal and then butt-welding the two ends of this strip. The front flange is made by casting or forging, incorporating cutouts for the tire bead. The rim and front flange are then joined by welding, for example, electron beam, arc, friction, or inertia welding. This second weld is performed on the outside of the wheel and then machined. The Applicant's approach was therefore, based on the aforementioned technologies, to consider a design solution for a two-part hybrid wheel made of lightweight alloy, improved compared to known solutions and meeting market needs. The applicant was therefore required to design and develop a new process based on a specific selection of operational phases. Thus, and according to a first feature of the invention, the manufacturing process for a hybrid light alloy wheel, particularly one based on aluminum or magnesium, comprising a front flange and a rim, involves the following different operational phases, according to which: - the flange is made with an internal profile suitable for forming a tire bead seat; - the rim is made with, on one side, an external profile suitable for forming a seat for a tire bead, and on the other side, a circular sidewall for assembly with a part of the flange; - the flange is assembled with the rim, at the level of the seat of said flange and the circular side of the rim. The process is characterized by the fact that the rim and flange are joined by welding the circular sidewall of the rim and the flange together using a single friction stir weld with a pin, positioned to allow access from both sides of the weld. Friction stir welding with a pin is known as Friction Stir Welding (FSW). The weld is performed by mixing the material in a paste-like state, i.e., in the solid phase. This technique makes it possible to weld alloys (particularly aluminum) that are not weldable or are difficult to weld using conventional techniques involving melting the material. Furthermore, solid-phase welding avoids the formation of bubbles that can occur during a liquid-solid transition.The material undergoes a smaller temperature increase, resulting in a heat-affected zone (HAZ) with improved mechanical properties compared to conventional techniques. This enhances the weld's resistance to static stress and fatigue. Advantageously, recesses are made at the level of the flange seat, said recesses not covering the circumference of the wheel, and having a "U" profile oriented towards the circular assembly area of ​​the rim. The flange can be made by casting, by forging, or by a double operation of casting and forging. According to a first embodiment, the double casting and forging operation includes a casting operation of a foundry preform, a transfer of said preform into a forging die, a forging operation of said preform in order to obtain the flange, and a deburring to obtain said flange. According to a second embodiment, the double casting and forging operation includes a casting operation of a foundry preform, a storage of said preform, a transfer of said preform into a furnace to heat it, a transfer of said preform into a forging die, a forging operation of said preform to obtain the flange, and a deburring to obtain said flange. Preferably, when the flange is produced by a double casting and forging operation, the recesses are made in the tire bead seat on the flange during the casting operation. Advantageously, the rim can be produced by following successive operations: a circular sidewall fabrication operation; a single-step expansion operation of this circular sidewall to the dimensions of the final rim; then a cold or hot flow-forming operation of the circular sidewall until the rim is obtained in its final shape and profile, with a shoulder only on the side that will not be welded to the flange. In practice, during the manufacturing operation, the circular flank can be obtained by any technique suitable for the intended application. According to a preferred embodiment, the circular side is produced by hot or cold extrusion of a light alloy billet. Alternatively, the circular side is produced by casting in a foundry. According to another alternative, the circular flank is made by powder sintering. Other techniques can be implemented to manufacture the circular side, without departing from the scope of the invention. Preferably, the expansion and flow forming operations are carried out cold. Also preferably: - Friction stir welding is preceded by a machining operation of the areas to be joined; - Friction stir welding is followed by a machining operation on both sides (internal and external) of the weld intended to remove the burr and any defects at the bottom of the weld. The process according to the invention offers many advantages, which will become apparent upon reading this description. Expansion and flow turning operations can be simplified in particular compared to patents F 2 981 605 and EP1230099B1 due to the use of a single weld instead of two. As with patents FR 2 981 605 and EP1230099B1, the wheel perfectly meets the manufacturers' specifications in terms of fatigue and impact resistance while having a significant weight saving compared to wheels obtained in traditional casting. Compared to the previously mentioned patents, this invention simplifies the expansion process, which is completed in a single step instead of two, and simplifies the flow-turning process because the final rim profile has a much less complex geometry due to the single weld. It should also be noted that a single weld allows for a greater variety of flange designs. These features, and others, will become clear from the rest of the description. To define the object of the invention illustrated, without limitation, in the figures of the drawings, - Figure 1 represents, according to the prior art, the production of a hybrid wheel in two parts with a rim part and a flange part. - Figure 2 shows the mounting of the tire on the rim with the positioning of the tire beads on their seat. - Figure 3 schematically represents, according to the prior art, the successive operations PI, P2, P3 of obtaining the rim profile. - Figure 4 schematically represents, according to the invention, the successive operations P1 (obtaining a circular sidewall), P2 (one-step expansion of said circular sidewall), P3 (flow forming operation of the circular sidewall to obtain the rim profile). - Figure 5 represents a cross-sectional view illustrating the profile of the rim according to the prior art, showing a cavity formed on the rim. - Figure 6 represents a cross-sectional view illustrating the rim profile according to the invention with the realization of a single weld and the formation of recesses in one of the tire bead seats. - Figure 7 shows a front view of the hybrid wheel with an illustration of the cutouts. In order to make the object of the invention more concrete, it is now described in a non-limiting manner illustrated by the figures in the drawings. As previously mentioned, the rim profile (1) is simplified by the use of a single weld (5) for joining it to the flange (2). The rim (1) has a circular profile (1a) that serves as a seat for the tire, but only on the inner side of the wheel. The other profile (2a), which also serves as a seat for the tire, is formed by the flange (2). Some characteristics and advantages of the process of the invention are highlighted below. Figures 3 and 4 show the steps for obtaining the rim (1), respectively according to the prior art and according to the invention. In the context of the invention, the rim (1) is produced by means of an operation (PI) of manufacturing a blank in the form of a circular sidewall (lb); then an operation (P2) of expanding in a single step this circular sidewall (lb) to the dimensions of the final rim (1); and finally an operation (P3) of cold or hot flow forming of the circular sidewall (lb) until the rim (1) is obtained in its final shape and profile, comprising the remaining part of the circular sidewall (lb) on the side which will be welded to the flange (2) and a shoulder (la) only on the side which will not be welded to the flange (2). According to a preferred embodiment of the manufacturing operation (PI), a light alloy billet is produced and then transformed into a circular blank (lb) by hot or cold extrusion. Compared to other known techniques, this allows for obtaining a blank (lb) with very high elongation. The expansion operation (P2) of the blank (lb) can thus be carried out cold, i.e., at ambient temperature, which avoids its reheating before expansion. Furthermore, this high elongation allows for a cold flow forming operation (P3) to be performed after the cold expansion operation (P2). The rim material (1) undergoes significant work hardening during the cold flow forming operation (P3). Before welding to the flange (2), the rim (1) is therefore subjected to a heat treatment (e.g., T6: solution heat treatment, quenching, tempering), during which the energy stored during work hardening is released.This allows for fine grain recrystallization in the rim material (1). Its microstructure is therefore very fine and the mechanical characteristics of the rim (1) are improved compared to a hot forming technique. In step P3 of Figure 3, the rim profile (1) required to obtain the cavity (6) shown in Figure 5 is represented when the connection between the flange and the rim is made using two welds. The simplified rim profile (1) can be seen in step P3 of Figure 4. This profile is indeed much simpler than the one illustrated in French patent FR 2 981 605 shown in step P3 of Figure 3. This simplification is made possible by the use of a single weld (5) on the wheel constituting the invention. The external profile (la) of the rim (1) now requires only one shoulder forming a tire bead seat, instead of two. This results in a reduction in cycle time and a simplification of the flow forming machine, thereby lowering costs. The other profile (2a), acting as a seat for the tire, is made by the flange (2). Having a single weld (5), as illustrated in Figure 6, also greatly simplifies the welding operation compared to a double weld. This is because the weld is made in a single direction perpendicular to the rim, unlike a double-weld wheel where the welds are made in two different directions. It is no longer necessary to rotate the welding spindle, and the assembly is simplified, thus reducing costs while also improving cycle time and reducing wear on the welding pin. The welding operation (5) is performed at the junction of part (2b) of the flange (2) and the circular sidewall (lb) of the rim (1). Furthermore, having a single weld (5) allows access to both sides of the weld. This makes it possible to machine both sides of the weld. This machining, commonly performed on sheets intended for the aerospace industry, allows for the removal of any weld burrs as well as any defects in the weld root, often present in friction stir welding. These defects correspond to poor mixing of the alloy, which creates unwelded lips in the weld root. Burrs or unwelded lips are defects that create crack initiation points during fatigue stress on the wheel. Their elimination is therefore a significant advantage in terms of process reliability. Access to both sides of the weld also allows for a frequency penetrant test on the weld, ensuring the stability of the welding process and guaranteeing the absence of defects.For a wheel with two welds, access to both sides of the weld is not guaranteed. Therefore, it is necessary to section a wheel to perform this frequency inspection. Since this inspection is destructive, it results in the loss of part of the production and thus an increase in costs for wheels with a closed cavity (6). Essentially and importantly for the invention, the valve area is also greatly simplified. Indeed, for a wheel with two welds, drilling the valve creates an opening in the cavity (6). Most manufacturers do not want open cavities in wheels because this opening can allow water, gravel, or other objects to accumulate. A weld surrounding the valve hole was therefore necessary to close the cavity (6) and prevent water retention. This weld thus represented an additional step to the process described in patents FR 2981605 and EP 1230099, resulting in an additional cost. Furthermore, according to the invention, manufacturing the wheel in two parts before welding it allows for the creation of more complex shapes that would be impossible to demold in a one-piece wheel. This technology makes it possible to create recesses (7) in the flange (2), for example, in the form of cavities, as can be seen in Figure 7. These recesses are created either by casting, forging, or during the casting stage of the "COBAPRESS" process. They are located at one of the tire bead seats (3) in the flange (2) and do not cover the circumference of the wheel. In fact, some areas (8) are solid to increase the rigidity and strength of the wheel. These solid areas (8) also greatly facilitate tire mounting. Indeed, without these solid areas, the tire bead can become lodged in the cavities (7) during mounting.This tire bead can be difficult to reposition on its seat during mounting, and the solid areas create a slope that greatly facilitates this operation. One area is also left without a recess to allow for drilling and positioning the valve with a simple geometry (9), as shown in Figure 7. The recesses (7), as depicted in Figures 6 and 7, have a U-shaped profile oriented towards the weld (5). Creating recesses is not a new technique. In practice, producing these recesses during a forging or casting step is economical because it eliminates the need for machining. This results in savings in cycle time and cost. The material usage, i.e., the amount of material used relative to the usable material, is also reduced.In practice, and according to the invention, it is remarkable for the combination of different operational phases of the process, which provides, in practical terms, a great many of the aforementioned advantages compared to the prior art. This optimization therefore required substantial research and development investments and did not stem from prior art knowledge.

Claims

DEMANDS 1- Method for manufacturing a hybrid light alloy wheel, in particular based on aluminium or magnesium, comprising a front flange (2) and a rim (1), the method implementing the following different operating phases: - the flange (2) is made with an internal profile (2a) suitable for forming a tire bead seat; - the rim (1) is made with, on one side, an external profile (la) suitable for forming a seat for a tire bead, and on the other side, a circular sidewall (lb) for assembly with a part (2b) of the flange (2); - the flange (2) is assembled with the rim (1), at the level of the seat (2a) of said flange (2) and the circular side (lb) of the rim (1); characterized in that the assembly between the rim (1) and the flange (2) is achieved by welding the circular side (lb) of the rim (1) and the flange (2) using a single friction stir weld (5) with a pin, in a position allowing access from both sides of the weld. 2- Method according to claim 1, characterized in that recesses (7) are made at the level of the seat (2a) of the flange (2), said recesses (7) not covering the circumference of the wheel, and having a “U” profile oriented towards the circular side (lb) of the rim (1). 3- A method according to any one of claims 1 and 2, characterized in that the flange (2) is made by casting.

4. A method according to any one of claims 1 and 2, characterized in that the flange (2) is produced by forging.

5. A method according to any one of claims 1 and 2, characterized in that the flange (2) is produced by a double casting and forging operation. 6- Method according to claim 5, characterized in that the double casting and forging operation comprises a casting operation of a foundry preform, a transfer of said preform into a forging die, a forging operation of said preform in order to obtain the flange (2), and a deburring to obtain said flange (2). 7- Method according to claim 5, characterized in that the double casting and forging operation comprises a casting operation of a foundry preform, a storage of said preform, a transfer of said preform into a furnace allowing it to be heated, a transfer of said preform into a forging die, a forging operation of said preform in order to obtain the flange (2), and a deburring to obtain said flange (2).

8. A method according to claim 2, characterized in that when the flange (2) is produced by a double casting and forging operation, the recesses (7) are formed in the tire bead seat (2a) on the flange (2) during the casting operation.

9. A method according to any one of the preceding claims, characterized in that the rim (1) is produced by means of the following successive operations: - an operation (PI) for manufacturing a circular blank (lb); - a single-step expansion operation (P2) of this circular side (lb) to the dimensions of the final rim; - a cold or hot flow forming operation (P2) of the circular side (lb) to obtain the rim (1) in its final shape and profile, having a shoulder only on the side that will not be welded to the flange (2). 10- Method according to claim 9, characterized in that in the manufacturing operation (PI), the circular flank (lb) is produced by hot or cold extrusion of a light alloy billet. 1 1- Method according to claim 9, characterized in that in the manufacturing operation (PI), the circular flank (lb) is produced by casting in a foundry. 12- Method according to claim 9, characterized in that in the manufacturing operation (PI), the circular flank (lb) is produced by powder sintering. 13- A process according to any one of claims 9 to 12, characterized in that the expansion operation (P2) and the flow-turning operation (P3) are carried out cold. 14- A method according to any one of the preceding claims, characterized in that friction stir welding is preceded by a machining operation of the areas to be joined. 15- A method according to any one of the preceding claims, characterized in that friction stir welding is followed by a machining operation on both sides of the weld intended to remove the burr and any defects at the bottom of the weld.