Abstract:
A method of making a rim of sheet metal for a vehicle wheel, in which:
       a rectangular geometric shape is cut out of a blank of sheet metal;   the blank is bent to obtain a cylindrical hoop;   the two free edges of the hoop are welded together;   at least one cylindrical flow spinning operation is performed to obtain a profile of given thickness of the hoop, zones of constant thickness being adjacent to zones of variable thickness;   a cut is made perpendicular to the axis of the hoop out of at least one lateral edge of the hoop;   the hoop is profiled to obtain the rim; and   the size of the said rim is set.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This is a continuation of international application No. PCT/EP 01/12601, filed Oct. 31, 2001, published in French as international publication No. WO 02/38303 on May 16, 2002 and claiming priority to French application No. 00/14675 filed Nov. 13, 2000, the entire contents of each of which are incorporated by reference. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention relates to vehicle wheels and in particular to an improved method of making a wheel rim. 
   2. The Related Art 
   U.S. Pat. No. 5,579,578 discloses a method of making a wheel rim for a vehicle, which has the following operations:
         cutting a rectangular geometric shape out of a blank of sheet metal;   bending the blank to obtain a cylindrical hoop;   welding the two free edges of the hoop together;   setting the size of the hoop to a given diameter;   performing a cylindrical flow spinning operation on the hoop to obtain a profile of the hoop having two axial ends and a thinner intermediate zone;   profiling the hoop by a series of rolling operations to obtain the rim; and   setting the size of the said rim.       

   This patent states that performing the flow spinning operations before the roll profiling provides for a wheel rim with good manufacturing tolerances. 
   However, the flow spinning operations on the hoop of a wheel rim are liable to result in hoops that have an axial width that varies over its circumference. Additionally, in some instances, perpendicularity faults are observed between the plane defined by the edge of the hoop and that defined by the axis of the hoop. These variations and faults may cause instability during the succeeding operations of rolling the hoop, and they may also make it more difficult to attach the balance weights for the wheels in places. 
   SUMMARY OF THE INVENTION 
   An object of the present invention is to provide a method of manufacturing a wheel rim that can avoid the aforementioned problems. 
   A further object of the invention is to provide an improved method of making a wheel rim which is capable of reducing, to a substantial extent, the manufacturing variations of the wheel rims. 
   Still, a further object is to provide a method of making a wheel rim which allows lighter-weight wheels to be obtained. 
   A method of making a rim of sheet metal for a vehicle wheel according to an embodiment of the invention comprises the following steps:
         a rectangular geometric shape is cut out of a blank of sheet metal;   the blank is bent to obtain a cylindrical hoop;   the two free edges of the hoop are welded together;   at least one cylindrical flow spinning operation is performed to obtain a profile of given thickness of the hoop, zones of constant thickness being adjacent to zones of variable thickness;   a cut is made perpendicular to the axis of the hoop out of at least one lateral edge of the hoop;   the hoop is profiled to obtain the rim; and   the size of the said rim is set.       

   The operation of cutting perpendicular to the axis of the hoop out of at least one lateral edge of the hoop after the cylindrical flow spinning operation has the advantage of eliminating entirely or partly the excess thickness of the two ends of the finished rim, which reduces the final weight of the rim. It should be noted that the reduction in thickness during a flow spinning operation cannot be applied to the two lateral edges of the hoop. This thickness is thus necessarily identical to the thickness of the metal starting blank. This operation also ensures that the edge of the hoop is properly planar and that this plane is at a right angle to the axis of this same hoop. 
   The cutting-out operation may be performed from the inner side of the rim, which is the side of the rim that is intended to face towards the inside of the vehicle. This has the advantage of reducing the thickness of the inside hook of the rim, this hook being less exposed to impact than the outside hook. 
   The cutting-out operation may also be applied to the two lateral edges of the hoop. The advantage is then to maximize the reduction in weight of the rim and to obtain excellent planarity of the lateral edges of the hoop and outstanding regularity in the axial width of the hoop. 
   It is possible to cut out at the edge of the hoop only a part of the zone not subject to flow spinning. In this case, all the advantages linked with the geometric quality of the hoop obtained are obtained, but the reduction in weight is limited. 
   It is also possible to cut out at the edge of the hoop at least a part of the zone subject to flow spinning. The final rim will then have a particularly substantial advantage as regards its weight. 
   In one embodiment of the invention, the plane of cutting out of an edge of the hoop is defined with reference to a characteristic point on the profile of the hoop after the flow spinning operation. This characteristic point may in particular be a point of transition between a zone of constant thickness and a zone of variable thickness. 
   It is thus possible to adjust the position of the transition zones between flow spun zones and the edge of the hoop. This improves the ability to observe tolerances of the dimensions of the final rim. 
   Additional objects and advantages of the invention will be set forth in part in the more detailed description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. 
   It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed. 
   The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate various embodiments of the invention and, together with the description, serve to explain the principles of the invention. 

   
     DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a section of a conventional rim, with assembly below the mounting groove. 
       FIG. 2  shows the different steps of a method of making a wheel according to one embodiment of the invention. 
       FIGS. 3 ,  4  and  5  illustrate diagrammatically different steps in the method of making a rim according to the invention. 
       FIG. 6  shows diagrammatically a first type of fault encountered after the flow spinning operations. 
       FIG. 7  shows diagrammatically a second type of fault encountered after the flow spinning operations. 
       FIG. 8  shows diagrammatically a third type of fault encountered after the flow spinning operations. 
       FIGS. 9(   a ) and  9 ( b ) show diagrammatically a detail of a first hoop corresponding to the rim hook after the flow spinning operations, and the part of the rim resulting therefrom after profiling. 
       FIGS. 10(   a ) and  10 ( b ) illustrate diagrammatically a detail of a second hoop corresponding to the rim hook after the flow spinning operations, and the part of the rim resulting therefrom after profiling. 
       FIGS. 11(   a ) and  11 ( b ) illustrate diagrammatically a detail of a third hoop corresponding to the rim hook after the flow spinning operations, and the part of the rim resulting therefrom after profiling. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Reference will now be made in detail to the present invention. 
     FIG. 1  shows a partial section of a conventional wheel of sheet steel. This wheel  1  comprises a rim  2  and a disc  3 . This figure illustrates the median plane of the wheel, plane P. This plane is disposed equidistant from the two hooks of the rim. The axially inside and outside positions are defined with reference to the median plane P. 
   The rim has an outer hook  4 , an outer seat  5 , a hump  6 , a mounting groove  7 , an inner seat  9  and an inner hook  10 . The disc  3  comprises a hub support face  11 , a transition zone  12  and an assembly edge  13 . Assembly is performed by fitting it below the mounting groove  7 . Also visible in this figure is the axis of rotation A of the wheel. 
   A method of making wheel rims according to an embodiment of the invention is illustrated in  FIG. 2 . Initially, a sheet metal blank, made of, for example, steel, aluminum, or alloys, is bent to give it a generally cylindrical hoop shape  14  with two free edges. Then the hoop  14  is welded, such as by a flash welding, resistance welding, or other procedure. This hoop  14  has a constant thickness ( FIG. 3 ). 
   The hoop  14  is then preferably expanded to size. For example, the hoop may be expanded to size with the aid of a sizing tool shown diagrammatically in  FIG. 4 . The expansion is obtained by displacing a cam  15  that moves apart the sectors  16  around which the hoop  14  is installed. 
   In  FIG. 5 , the flat profile desired for the rims is obtained by cylindrical flow spinning. In one embodiment, the flow spinning procedure used is reverse flow spinning. The hoop  14  is mounted on a mandrel  17  and comes to bear against a wall of the system  18  for immobilizing the hoop  14 . The mandrel  17  is then rotated, and at least two rolls  19  roll over the radially outer surface of the hoop  14  in the zones where the thickness is to be reduced. Relative to the mandrel  17 , the rolls  19  are displaced axially in the direction of the axis X, applying a radial and tangential force such that the flow of the material is in the direction Y. This flow of material is in the opposite direction to that of displacement of the rolls  19 .  FIG. 5  illustrates diagrammatically the hoop  20  obtained, with a variable profile. 
   This procedure of reverse flow spinning does not allow the thickness of the entire hoop to be reduced. In fact, each side of the hoop has to have a zone left which does not undergo flow spinning. On the side on which the rolls act, this would run the risk of destabilizing the hoop and damaging the rolls. On the side with the device for fixing the hoop and acting as a stop, a zone of axial width L min  has to be left so that this device can clamp the edge of the hoop and rotate it during the flow spinning operation. 
     FIG. 6  illustrates a first fault that the hoop  20  is susceptible of suffering after the flow spinning operations. This fault is in the form of local variations in the axial width of the hoop  20 . These variations are observed in particular on the side on which the rolls act. The edge  24  is not perfectly cylindrical, having local variations in its axial position. These variations automatically have an effect on the profile of the rim. It is thus possible to have variations in the profile of the edge of the hooks, which may make it difficult to position or fix the balance weights in places. 
   Performing a cutting operation out of the two edges of the hoop after the flow spinning operations ensures a constant width in the hoop at all points on it. 
     FIG. 7  illustrates a second fault that may be observed, namely a fault in the perpendicularity between the plane defined by the edge  24  of the hoop  20  and that defined by the axis of the hoop  20 . The angle α between these two planes may reach 1 to 2 degrees. 
   Performing a cutting operation out of an edge of the hoop after the flow spinning operations ensures the plane defined by this edge of the hoop is at a right angle to the axis of this hoop. 
     FIG. 8  illustrates a third fault. In this figure, a part profile of two hoops  25  and  26  is visible. These two profiles are substantially identical, except for the length of the zones not subject to flow spinning, on the side abutting against the mandrel, which is shown in the left-hand side of the figure. These zones,  27  for the hoop  25 , and  28  for the hoop  26 , differ by a length d. This deviation is due to a variation between the two hoops in the thickness of the starting blank. The thickness of the starting blank of the hoop  26  is greater than that of the hoop  25 . Despite this variation in the initial thickness, the profile of the two hoops is substantially identical after flow spinning, because the relative displacement of the rolls is linked to the axial thickening of the zones subject to flow spinning. On the other hand, for the same axial width of the hoops, the zone which is effectively subject to flow spinning is axially smaller for a thicker hoop. For a wheel rim for a passenger car having a diameter of 15 inches (381 mm), a variation in thickness of 0.05 mm may bring about a variation in the axial width of 5 mm in the zone not subject to flow spinning on the abutting side. 
   This problem is obviated by taking as a reference a characteristic point R on the profile of the hoop after the flow spinning operations, in order to define the position of the planes D 1  and D 2  for cutting out the edges of the hoop. This point R is advantageously taken adjacent to a zone of variable thickness and a zone of fixed thickness, as illustrated in  FIG. 8 . To increase precision, a system of checking the profile can be used to determine the position of the cutting-out plane or two cutting-out planes, as appropriate. It should be noted that the edge of the hoop on the side on which the rolls act should not be used as a reference point R since this is the edge most sensitive to the variations and undulations, as mentioned above. 
     FIG. 9(   a ) illustrates diagrammatically the profile of one of the ends of the hoop  20  after the flow spinning operation. This profile comprises an outer zone  21  not subject to flow spinning, of axial width L min  and thickness e corresponding to the thickness of the starting blank, a transition zone  22  in which the thickness lessens progressively and a zone  23  of reduced thickness e 1 . 
     FIG. 9(   b ) shows the profile of the outer edge of the rim obtained after the operations of roll profiling. The first zone  21  of  FIG. 9(   a ) corresponds to the edge  31  of the rim hook  4 . The zone of reduced thickness  23  of  FIG. 9(   a ) corresponds to the seat  5  of the rim and to the start  29  of the hook. The transition zone  22  of  FIG. 9(   a ) corresponds to the intermediate zone  30 . 
   The hook  4  of the rim thus has three adjacent zones: the zone  29  of reduced thickness identical to that of the seat  5 , the transition zone  30 , whereof the thickness increases progressively, and the zone  31  of thickness e identical to that of the starting blank. 
   The hook  4  in  FIG. 9(   b ) thus shows an excess thickness which may or may not be necessary, depending on the type of wheel concerned. 
     FIGS. 10(   a ) and  10 ( b ) and  FIGS. 11(   a ) and  11 ( b ) show two shapes of hooks obtained from two different cutting-out operations. In the case of  FIG. 10 , the plane of cutting out D is located axially at a spacing L from the point where the zone  21  not subject to flow spinning, of thickness e, and the transition zone  22 , of a thickness variable between e and e 1 , meet. The result is that, after the cutting-out operation, the hook  4  has a zone  32  of reduced thickness e. The rim is therefore lighter in weight. 
   In  FIG. 11 , the plane of cutting out is located in the zone  23 , which has been subject to flow spinning in order to reduce its thickness from e to e 1 . The hook obtained after the profiling operations therefore has an identical thickness over its entire length. This therefore gives the maximum reduction in weight. 
   It should be noted that in order to make the embodiments shown in  FIGS. 9 to 11  clearer, their scale in the direction perpendicular to the axis of the hoop has been made approximately five times that of the scale in the direction of the axis of the hoop. 
   Various methods of cutting out of the edge of the hoop, such as by turning or roll cutting, are known to those skilled in the art. After the operations of roll profiling the hoop, the rims thus obtained are set to the correct size, then fitted onto appropriate discs. 
     FIG. 2  includes a step of machining the zone for fitting on the rim which is also well known to one skilled in the art. This step is optional. The objective of this step is to optimize the cylindrical geometric shape of the fitting zone in the case of sensitive assembly. 
   The present invention can be variously modified without departing from the spirit and scope of the invention. 
   Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents. 
   The disclosures of each reference cited above is herein incorporated by reference.