EP3131690B1

EP3131690B1 - Method for producing wheel disc forms on flow-forming machines

Info

Publication number: EP3131690B1
Application number: EP15728148.6A
Authority: EP
Inventors: Matthias Gruetgen; Carlos Eduardo LOPES; Marcelo Yumoto GRAZIANI
Original assignee: Maxion Wheels Holding GmbH
Current assignee: Maxion Wheels Holding GmbH
Priority date: 2014-04-15
Filing date: 2015-04-15
Publication date: 2022-08-17
Anticipated expiration: 2035-04-15
Also published as: CN106457340B; BR112016017583A2; EP3131690A1; CN106457340A; DE102014105400A1; WO2015159231A1

Description

The invention relates to a method for producing wheel disc forms, which have an attachment flange, a disc transition surface and a disc margin, for vehicle wheels from preferably metallic preforms on a flow-forming machine which has a spinning mandrel which is rotatable about an axis of rotation, and at least one spinning roller, which is adjustable radially relative to the axis of rotation, for the flow forming of the preform against the spinning mandrel and production of a flow-formed transition surface on the wheel disc form, according to the preamble of claim 1.
It is known from DE 21 56 551 for a preform, such as for example a ring-shaped planar blank, to be formed on a flow-forming machine by flow-forming or metal spinning to create a wheel disc form. In subsequent punching and cutting steps, the central hole, the bolt holes and ventilation holes are then punched out in order, in a rapid manufacturing cycle, to produce a wheel disc with attachment flange, transition surface and disc margin, which wheel disc is connected to a separately produced wheel rim part preferably by way of welded connections between disc margin and wheel rim inner side in order to produce a vehicle wheel for utility vehicles or passenger motor vehicles.
The entire flow-forming process in a flow-forming machine is performed in one chucking operation and normally by means of multiple spinning rollers which are controlled independently of one another in terms of motion and which perform shape-changing work in succession. The applicant, for example, uses a flow-forming machine with three spinning rollers by means of which the preform is, from the outside, pressed and flow-formed against the forming contour of a spinning mandrel which is rotatable about a horizontal axis of rotation. In the chucking region of the preform between a face side of the spinning mandrel and a holding-down means, the wheel disc form has the initial thickness of the preform, whereas the transition surface and the disc margin are flow-formed and are correspondingly provided with a wall thickness which is reduced in relation to the initial thickness of the preform and which decreases toward the disc margin in a manner dependent on the distance from the chucking region. The wheel disc forms produced by the applicant in accordance with this method are, after the punching of the ventilation holes and punching or drilling of the bolt holes on the attachment flange, subjected to material removal by turning with cutting action by a few 1/10 mm both at the inside and at the outside, and also, the disc margin is subjected to material removal by turning to this extent on the outer side, in order to achieve optimized planar abutment of the vehicle wheel against a vehicle hub, and also in order to improve the contraction of the wheel disc, with the disc margin uniformly rounded on the outer side by the material removal by turning, in the separately manufactured wheel rim part. The applicant also performs reworking of the disc margin and of the central hole on the wheel disc form.
During the flow-forming or metal spinning, rotationally symmetrical wheel disc forms are produced which have uniform surfaces on the inner side and on the outer side and an improved matrix structure in particular in the flow-formed transition surface, via which all of the forces and loads must be transmitted between wheel rim and vehicle hub while a vehicle is in motion. A further advantage of the flow forming or metal spinning process lies in the material saving in relation to wheel discs produced for example by deep drawing.
To reduce the material outlay for the production of wheel discs, EP 1 473 097 B1 proposes for example that the preform be produced from a rectangular metal strip, which is pre-rolled by cold rolling to form a partial circular ring, is subsequently deformed into a conical band by roll bending and, after the welding of the ends of said band, is provided with the attachment flange on a flow-forming machine.
Other developments, such as for example DE 196 15 675 A1 or DE 198 60 732 A1 , relate to the flow-forming of the wheel rim part, which is subsequently connected for example to a disc part produced in a casting process.
EP 2 556 895 A1 discloses a separation disc for centrifugal separators and a method for manufacturing such separation discs. The separation discs are intended to be arranged in a stack of similar separation discs, for which purpose they receive by the manufacturing process, a pattern of small size, spacing members, to provide equidistant interspaces of separation discs in the stack. In order to produce the spacing members, a mandrel against which the material of the separation disc preform is spinned during manufacture receives deformations, leading to corresponding spacing members on the separation disc.
US 2012/0177879 A1 refers to drums with a tooth profile. In order to avoid undesirable burrs and surface flares, which would need to be removed in additional machining steps, the drum is produced in a flow forming process against the mandrel, which mandrel comprises channels and protuberances to define a tooth profile in the flow formed part. Subsequent to the flow forming, windows can be formed either by a punching process or by a machining process.
A method for producing wheels by roll forming to obtain wheels as laid down in the preamble of claim 1 is known from EP 2 460 603 A1 . The known method aims to produce wheels having a uniform mass in the axial direction and in the circumferential direction, resulting in high dynamic balance precision.
It is an object of the invention to improve the manufacture of vehicle wheels with wheel discs produced by flow-forming, and in the process to make it possible to realize material savings during manufacture and possibly a reduction in weight of the finished vehicle wheel without the need for additional working steps which lengthen the manufacture of the wheel disc.
Said object is achieved with a method according to claim 1 . With regard to the method, the preform is flow-formed against a spinning mandrel which has multiple local elevations arranged so as to be distributed over the circumference in order to generate zones which are formed so as to be distributed over the circumference of the wheel disc form and which have material reductions in the flow-formed transition surface of the wheel disc form. The invention is consequently based on the basic concept of generating, during the flow forming or metal spinning process, not a uniformly rotationally symmetrical wheel disc form but a wheel disc form which is non-uniform in the circumferential direction, and on which, by means of the spinning mandrel, material reductions are created or generated in regions of the finished vehicle wheel which are removed in order to realize ventilation holes.
According to further aspects of the invention, zones with material reductions could also be generated in the disc margin, or, by depressions in the mandrel, zones with material accumulations could also be generated in the flow-formed transition surface or in the disc margin. In particular, with the combined creation of zones with material reduction and material accumulation, the material that is additionally displaced by pressing or rolling in the region of the material reductions can not only be used for generating the material accumulations, but can at the same time also contribute to a situation in which the preform is provided with smaller initial dimensions than a preform without zones with material reductions which is converted into a wheel disc form on the flow-forming machine.
Since, in the method according to the invention, zones with material accumulation or material reduction are generated so as to be distributed over the circumference, it is necessary for this to be allowed for in the subsequent method steps. In the method for producing the wheel disc from the wheel disc form, it is therefore particularly advantageous if, in a subsequent method step, ventilation holes are formed in the wheel disc form by way of a punching or cutting process, wherein said ventilation holes are preferably formed in the transition surface of the wheel disc form between zones with material reductions or alternatively between zones with material accumulations. It is particularly advantageous if, during the flow-forming against the spinning mandrel, material reductions are created in zones of the transition surface which, in a subsequent method step, are removed in a punching or cutting process for the production of ventilation holes. The particular advantage of this embodiment lies in the fact that, already during the flow-forming of the wheel disc form, material reductions are created in regions which will be removed at a later point in time in any case during the punching or cutting of the ventilation holes. In this case, the larger the ventilation holes will be on the finished vehicle wheel, the more material can be displaced out of said regions and into other regions situated further remote on the wheel disc in the flow-forming direction, that is to say generally into regions situated radially further to the outside.
Since, in the case of a vehicle wheel, the most uniform possible concentricity should be ensured, it may be advantageous for all or at least a multiplicity of the individual zones with material accumulation or with material reduction to be arranged so as to be distributed uniformly over the circumference.
On a finished vehicle wheel, the internal pressure in the vehicle tyre is generated and altered by way of a valve. Said valve, by way of its valve mass, generates an imbalance on the vehicle wheel. Since, in modern vehicle wheels, use is made of valves with integrated air pressure measurement sensor, this additional weight is generally compensated by way of balancing weights required for this purpose. In a further alternative method implementation, it is possible, during the flow forming against the spinning mandrel, for at least one asymmetrical material accumulation to be generated as a valve balancing weight for a valve imbalance, or at least one asymmetrical material reduction is generated for the purpose of compensating for a valve imbalance brought about by the valve weight. If use is made of a zone with material reduction for valve weight compensation purposes, the overall weight can be reduced yet further.
In the particularly preferred method implementation, during the flow forming, in the disc margin and/or in the transition surface in the region of the transition of the transition surface to the disc margin, zones with material accumulation and/or zones with material reduction are generated so as to alternate in the circumferential direction. For this purpose, it may suffice if, preferably in the disc margin, zones with material accumulation are created in each case so as to be offset with respect to one another in the circumferential direction, which zones with material accumulation are then each adjoined by a zone with the material thickness that the wheel disc has imparted to it in any case by the flow-forming process; it is then consequently not necessary, albeit possible, for an additional zone with material reduction to also be created in each case between zones with material accumulation in the disc margin. The zones with material accumulation in the disc margin, or in the region of the transition of the transition surface to the disc margin, reinforce the wheel disc form and thus also the wheel disc preferably in those regions which, during and/or after the punching or cutting of the ventilation holes, lie in an axial elongation of said ventilation holes. During the punching or cutting of the ventilation holes, it must merely be ensured that the ventilation holes are produced in the correct regions which are predefined or determined by the non-uniform wheel disc contour attained according to the invention, in particular the material accumulations and material reductions.
The method is used to procude a vehicle wheel, and a wheel disc part after the production of the ventilation holes. In the vehicle wheel, at least one zone with material reduction generated during the flow forming is formed on the inner side or the outer side of the transition surface between adjacent ventilation holes and/or between the ventilation holes at the disc margin and/or at the disc margin in an axial elongation of each ventilation hole. In this case, too, the basic concept is that, already during the flow-forming, a uniform material thickness is not generated all the way around in the circumferential direction, but instead, material is saved by way of zones with different material thicknesses, and/or regions that are subjected to structurally greater or different loading are strengthened by way of zones with material accumulations.
In a vehicle wheel, at least one zone with material reduction, preferably at least one rib-shaped or broad strip-shaped zone with material reduction, is formed on the transition surface between adjacent ventilation holes in the circumferential direction. This refinement utilizes the fact that the webs that remain between the ventilation holes do not require a large material thickness over their entire axial extent along the transition surface, and instead, it suffices there for only certain regions, in particular regions around the ventilation holes, to have an adequate material thickness. Outside said regions, it is thus possible for material to be saved, and for said material to then be used again for generating zones with material accumulation, primarily in the disc margin.
In a refinement, at least one zone with material accumulation, preferably at least one strip-shaped zone with material accumulation, is formed on the transition surface so as to be offset in the radial and axial direction toward the disc margin relative to the ventilation holes, and/or in that in each case at least one zone with material accumulation, preferably at least one strip-shaped zone with material accumulation, is formed at the disc margin in an axial and radial elongation of the ventilation holes. By means of the material accumulation in an axial and radial elongation of the ventilation holes on the transition surface, and/or preferably at the disc margin, the marginal region, which is in effect situated in the shadow of the ventilation holes, of the disc is reinforced in relation to regions situated between the ventilation holes in an elongation of the webs, whereby in particular, on the finished vehicle wheel, in which the disc connection to the wheel rim is realized by way of weld seams, an improved material distribution and at the same time lower loading of the weld seams are achieved.
In an alternative or additional refinement, at least one zone with material accumulation, preferably at least one web-like zone with material accumulation, may be formed at the transition between transition surface and disc margin, in each case between adjacent ventilation holes. The disc margin, which is normally perpendicular or approximately perpendicular to the attachment flange and which thus runs in substantially cylindrical fashion about the wheel axis, is additionally stiffened in relation to the transition surface by way of this measure, which improves the fatigue strength of vehicle wheels. In a preferred refinement, it is then the case that in each case exactly one web-like zone with material accumulation or in each case exactly two web-like zones with material accumulation is/are formed between adjacent ventilation holes, wherein preferably each web-like zone originates at a point offset in the circumferential direction adjacent to a ventilation hole and/or two web-like zones arranged to both sides of a ventilation hole lie with a 90° angular offset with respect to one another relative to the central point of said ventilation hole. The web-like zones consequently effect local additional stiffening between disc margin and transition surface.
In the particularly preferred refinement, the material accumulations and/or material reductions are formed on the inner side of the transition surface or of the wheel disc. A corresponding wheel disc form for a vehicle wheel of said type is consequently generated by virtue of the preform being rolled or flow-formed against the outer contour of a spinning mandrel, whereby it is then possible for the material accumulations or material reductions to be formed only on the subsequent inner side of the wheel disc or of the wheel disc form.
In general, the zones with material accumulations and/or material reductions are formed on the transition surface and/or at the disc margin so as to be distributed uniformly in the circumferential direction and/or so as to be distributed at equal angular intervals with respect to one another, so as not to generate any additional imbalance in the wheel disc or wheel disc form. In the context of the invention, it is however also possible for the valve weight to already be at least partially compensated during the manufacture of the disc form in that, on the transition surface or at the disc margin, there is formed at least one asymmetrical material accumulation as valve balancing mass or at least one asymmetrical material reduction for compensating for a valve weight.
Furthermore, it is preferably possible for material accumulations which extend in ring-shaped, circular, oval or strip-shaped form at least partially around the ventilation holes to be formed in order to reinforce the wheel disc in zones close to ventilation hole margins in relation to zones remote from ventilation holes. Here, it is self-evident that the ventilation holes do not have to be of circular form, but may also be of oval, V-shaped or a window-like form, thus resulting in corresponding profiles of the ventilation hole margins.
The zones with material accumulations or material reductions each have marginal edges running in the radial direction and delimiting edges running in the circumferential direction. It is particularly advantageous if in each case the two marginal edges of a zone run obliquely or in curved fashion with respect to the wheel axis and the spacing between the marginal edges increases toward the disc edge. Although the inner diameter of a wheel disc generally increases continuously from the attachment flange to the disc margin, if material accumulations or material reductions are generated, it must however additionally be ensured that the wheel discs can be pulled off the spinning mandrel, which is improved by way of marginal edges which run obliquely or in curved fashion.
In a yet further alternative or additional refinement, it is possible for multiple in particular stud-like material accumulations to be formed around each ventilation hole, wherein preferably, some or all of said material accumulations extend as far as the ventilation hole edge and/or said material accumulations lie with a 90° angular offset with respect to one another relative to the central point of said ventilation hole. During load tests of vehicle wheels, failures or weakening of the wheel discs have sometimes been found to occur in regions which, in relation to a plane which intersects a ventilation hole in axially parallel fashion and centrally, lie offset with respect to said plane by approximately 45°. The creation of two material accumulations which lie in each case with a 90° offset with respect to one another and correspondingly a 45° offset with respect to the central plane ensures local reinforcement of the wheel disc in the region of these otherwise critical ventilation hole margins.
For using the method, the forming contour of a spinning mandrel can be equipped with multiple local elevations and/or depressions arranged so as to be distributed over the circumference in order, during the flow-forming process, to generate multiple zones which are formed so as to be distributed over the circumference of the wheel disc form and which have material accumulations or material reductions. The depressions or elevations on the spinning mandrel then generate the material accumulations or material reductions in the transition surface, which is flow-formed against the spinning mandrel by means of the spinning rollers, of the wheel disc or of the wheel disc form.
A corresponding spinning mandrel normally has a face wall which interacts with a holding-down means on the machine, in the region of which face wall flow-forming cannot be performed, whereby, in a preferred refinement, said region is then used for generating the attachment flange on the wheel disc form, and a side wall as a forming contour for the forming of the transition surface and the disc margin. In a particularly preferred refinement of a corresponding spinning mandrel, the side wall is equipped with multiple elongate elevations arranged so as to be distributed uniformly over the circumference of the side wall, wherein preferably, a circular, oval or U-shaped elevation is formed between elongate elevations formed so as to be offset circumferentially relative to one another. The circular, oval or U-shaped elevation then serves for realizing material reductions in regions in which the ventilation holes will subsequently be generated, whereas the further elongate elevations exist in those regions in which, subsequently, the transition surface of the wheel disc connects the disc margin between the ventilation holes to the attachment flange in web-like fashion. Alternatively or in addition, the side wall, as a forming contour for the disc margin, may be formed with multiple ring segment-shaped depressions which are arranged so as to be distributed uniformly over the circumference of the side wall and which extend in the circumferential direction, wherein preferably, in each case one ring segment-shaped depression is arranged axially offset with respect to a circular, oval or U-shaped elevation formed on the side wall and/or is arranged axially offset and circumferentially offset with respect to the elongate elevations. The ring segment-shaped depressions consequently serve for realizing material accumulations in those regions of the disc margin which, on the wheel disc, lie in an axial elongation of a ventilation hole after the punching of the ventilation holes.
In a yet further alternative or additional refinement, the side wall may be equipped with multiple circular ring-shaped, ring-shaped, strip-shaped or partially ring segment-shaped and strip-shaped elevations which are distributed uniformly with respect to one another and over the circumference and which serve for the forming of zones with material reductions between punched or cut regions for ventilation holes.
The depressions or elevations have margins which run in the axial direction of the spinning mandrel, which margins preferably run obliquely and/or in curved fashion such that the spacing between the margins increases in the flow-forming direction.
In method implementation , it is particularly advantageous if the zones with material accumulation in the transition surface, or in the disc margin, at least partially have a greater material thickness than the material thickness in the regions surrounding said zones, and/or if the zones with material reduction in the transition surface, or in the disc margin, at least partially have a smaller material thickness than the material thickness in those regions of the transition surface which surround said zones. Consequently, where reference is made here to material accumulation or material reduction, this may be realized already by virtue of the wheel disc form, as viewed in the circumferential direction, being provided with a smaller material thickness in the region of the material reduction than in the adjacent regions, or being provided with a greater material thickness in the region of the material accumulation than in the adjacent regions. The change in material thickness should in this case be appreciable, that is to say should amount to at least 3% or 5% or 10%, or more, of the initial thickness of the preform, and/or should amount to more than 5%, preferably more than 10% or 15%, relative to adjacent zones.
Further advantages and refinements of the method according to the invention, will emerge from the following description of the exemplary embodiments shown in the figures. The exemplary embodiments serve in this case for illustration of the invention, without restricting the invention to the individual exemplary embodiments. In the drawing:

Figure 1: shows, on the basis of a schematically indicated flow-forming machine, the method sequence during the flow forming of a preform;
Figure 2: shows, in a perspective view, a schematically indicated exemplary embodiment of a spinning mandrel for use in the method according to the invention for producing a flow-formed wheel disc form according to the invention as per a first exemplary embodiment;
Figure 3: shows a wheel disc produced using the spinning mandrel from Figure 2, with ventilation holes and bore holes already having been produced, in a view of the disc inner side;
Figure 4: shows the wheel disc from Figure 3 in a side view;
Figure 4A: shows a section through a ventilation hole and the disc margin in an axial elongation of said ventilation hole in the case of the wheel disc as per Figure 3;
Figure 5: shows a sectional view along V-V in Figure 4;
Figure 6: shows a section through a ventilation hole before the punching-out of the ventilation hole with a punched slug still present and indicated by way of its punched margin;
Figure 7: shows a wheel disc according to a second design variant according to the invention in different section planes in each disc half;
Figure 8: shows a detail view of the section through the right-hand half of the wheel disc as per Figure 7;
Figure 9: shows a sectional view along IX-IX in Figure 7;
Figure 10: shows a sectional view through a wheel disc as per a third design variant according to the invention in different section planes in each disc half;
Figure 11: shows a sectional view along XI-XI in Figure 10;
Figure 12: shows a sectional view through a wheel disc as per a fourth design variant according to the invention in different section planes in each disc half;
Figure 13: shows a detail view of XIII in Figure 12;
Figure 14: shows a wheel disc as per a fifth design variant according to the invention in a plan view;
Figure 15: shows a sectional view along XV-XV in Figure 14;
Figure 16: shows a section through the right-hand disc half in Figure 15 in an enlarged view;
Figure 17: shows a central horizontal section through two adjacent ventilation holes in the case of the wheel disc from Figure 14;
Figure 18: shows a plan view of a vehicle wheel having a wheel disc as per a sixth design variant;
Figure 19: shows a sectional view along XIX-XIX in Figure 18;
Figure 20: shows a detail view of the detail XX in Figure 19;
Figure 21: shows a plan view of a vehicle wheel having a wheel disc as per a seventh design variant according to the invention;
Figure 22: shows the vehicle wheel from Figure 21 in longitudinal section;
Figure 23: shows a sectional view along XXIII-XXIII in Figure 22;
Figure 24: shows a longitudinal section through a wheel disc form as per an eighth design variant before the punching-out of ventilation holes;
Figure 25: shows the right-hand wheel disc margin from Figure 24 in an enlarged view; and
Figure 26: shows a horizontal section through the ventilation hole region in Figure 24.

In Figure 1, in schematically highly simplified form for the purposes of explaining the method sequence during the flow-forming of preforms to form wheel disc forms or wheel discs, the reference sign 1 denotes a flow-forming machine. Only those machine parts of the flow-forming machine 1 which are of particular importance for the flow-forming process are illustrated, specifically a main spindle 2 that can be driven for example by way of a gearing (not shown), a spinning mandrel 3 which is connected rotationally conjointly and in exchangeable fashion to the main spindle 2 and which has the negative contour of the wheel disc form 70 to be produced, a holding-down tool 4, and multiple spinning rollers 5. In the schematic view in Figure 1, two spinning rollers 5 are shown, which are controlled independently of one another in accordance with a predefined rolling programme and which, temporally in succession, cause a preform 6, which in the case of the method implementation illustrated is composed of a cylindrical sheet-metal blank 6 with a predefined uniform material thickness of for example 14 mm, to be pushed against the outer contour or forming contour of the spinning mandrel 3, which can be rotated at high rotational speed about the axis of rotation D by means of the main spindle 2, and flow-formed. The flow-forming machine 1 may preferably have three or four spinning rollers 5, wherein the spinning rollers may have different diameters and different contours than one another in order to achieve an optimum result of the flow-forming of a wheel disc or wheel disc form 70. The illustration in figure 1 serves merely for visualization, as the method according to the invention may in principle be performed on any flow-forming machine which is suitable for the manufacture of wheel disc forms or wheel discs by means of flow forming or metal spinning.
Figure 2 shows a spinning mandrel 3 for the production of a wheel disc form 70 or a wheel disc 10 as illustrated in Figures 3 to 6. Here, in the present description, the expression "wheel disc form" is used for the intermediate product which is present after the flow-forming process and which duly already substantially has the contour of the final wheel disc, but without subsequent cutting of the wheel margin and of the central hole having been performed, and before the punching, cutting and/or drilling processes for producing the ventilation holes and the bolt holes have been performed. Where reference is made in the present application to "wheel discs", it is at least the case that the punching or cutting processes for the ventilation holes have already been performed, and it is preferably also the case that the marginal edges of the central hole and of the disc margin have then been subjected to reworking (for example cutting, deburring) and the bolt holes for wheel bolts have also been drilled or cut. Furthermore, the surface of the wheel disc may be mechanically reworked, beaten flat and/or stamped in order that the wheel disc, as disc part, can be connected to a wheel rim part to form a vehicle wheel. Mechanical reworking may in particular be performed by way of cutting processes on the attachment flange (if appropriate on both sides) and at the disc margin (on the outer side) before the wheel disc is connected to the wheel rim part to form the vehicle wheel.
Reference will now initially be made to Figures 2 to 6. Figure 2 shows a spinning mandrel 3 according to the invention for the production of the wheel disc 10 according to the invention as per a first design alternative, as shown in Figure 3, on the flow-forming machine 1 shown for example in Figure 1. Here, the wheel disc 10 serves preferably for the production of a vehicle wheel for a utility vehicle, for which reason it has a relatively large central hole 11 around which there is formed an attachment flange 12 equipped with a total of ten bolt holes 21, said attachment flange being formed by the nondeformed surface part of the preform (blank 6 in Figure 1). The attachment flange 12 merges integrally into a conically widening disc transition surface 13 which ends in a substantially cylindrical or ring-shaped disc margin 14 with a central point that coincides with the wheel axis R. The attachment flange 12, the disc transition surface 13 and the disc margin 14 are formed by flow-forming of the preform against the spinning mandrel 3 shown in Figure 2, wherein substantially only the transition surface 13 and the disc margin 14 are deformed during the flow-forming, that is to say are flow-formed. For this purpose, the spinning mandrel 3 illustrated in Figure 2 correspondingly has a face wall 7 and a side wall 8 which has two different sections, wherein that section 8A of the side wall 8 which directly adjoins the face wall 7 running perpendicular to the axis of rotation of the spinning mandrel 3 serves for the generation of the disc transition surface on the wheel disc 10 or wheel disc form, and for this purpose, said section correspondingly widens conically in the flow-forming direction. The first section 8A is then adjoined by a second section 8B of the side wall 8, which during the flow-forming process serves for generating the disc margin (14 in the case of the wheel disc 10 or wheel disc form). At the start of the flow-forming process, the preform 6 which is in this case of ring-shaped form lies, as indicated in Figure 1, by way of an inner sub-section against the face wall 7 of the spinning mandrel 3 and is pressed against the face wall 7 by means of the holding-down tool (4 in Figure 1). As the holding-down means 4 must be adequately supported on the preform 6 in the region of the face wall 7 of the spinning mandrel 3, no deformation of the preform can be performed in this sub-region during the flow-forming by way of the spinning rollers 5.
By contrast to the spinning mandreles hitherto used in the prior art for the flow-forming process, the spinning mandrel 3 according to the invention has, in the section 8A of the side wall 8, multiple local elevations 41 distributed over the circumference, said elevations in this case being circular, wherein the spinning mandrel 3 in Figure 2 is equipped, in each case between two adjacent local circular elevations 41, with a further, strip-shaped elevation 42. As viewed in the circumferential direction, a circular elevation 41 and a strip-shaped elevation 42 alternate in each case on the section 8A of the side wall 8 of the spinning mandrel 3. As the preform is flow-formed against the spinning mandrel 3 during the flow-forming process, the elevations 41, 42 on the form or contour of the spinning mandrel 3 have the effect that, during the flow forming, on the wheel disc form or wheel disc 10 as per Figure 3, the disc transition surface 13 is provided with circular zones with material reductions, said zones being distributed uniformly over the circumference of said disc transition surface, specifically at all locations where the spinning mandrel 3 has a circular elevation 41; furthermore, during the flow-forming process, the transition surface 13 is provided, in each case between two such circular zones with material reduction, with in each case one strip-shaped zone 15 with material reduction, specifically where the strip-shaped elevations 42 are formed on the spinning mandrel 3; during the flow-forming against the outer contour of the spinning mandrel 3, the zones 15 with material reduction have an effect exclusively on the inner side 16 of the wheel disc 10, specifically by virtue of the fact that the thickness of the disc wall between the inner side 16 of the wheel disc 10 and the outer side 17 is smaller in the region of a zone 15 with material reduction than in the adjacent zones, and consequently, on the inner side 16, a surface contour is created which is rotationally asymmetrical. The extent of the thickness reduction is determined by the dimension of the height of the elevations 41 and 42 on the spinning mandrel 3. By contrast, the outer side 17 of the wheel disc has, as can be clearly seen in Figure 4, a rotationally symmetrical contour, because, during the flow forming, the spinning rollers (5 in Figure 1) bear against the outer side 17, and perform the deformation work, while the spinning mandrel with the preform rotates at high rotational speed. The zones with circular material reduction are duly no longer visible in the wheel disc 10 in Figure 3, because said zones have been cut away during the punching or cutting of the ventilation holes 18 and removed together with the cut-out punched slugs; however, Figure 5 shows the state of a wheel disc form 70 after the flow forming and before the removal of the punched slugs 71 in order to produce the ventilation hole 18 with an, in this case, circular ventilation hole margin 88 in the flow-formed transition surface 13. On the punched slug 71, the correspondingly circular zones 72 with material reduction generated on the wheel disc form 70 by means of the circular elevations 41 on the spinning mandrel 3 can be clearly seen.
The spinning mandrel 3 as per Figure 2 furthermore has, in the section 8B of the side wall 8, and consequently in the section which serves for generating the disc margin 14 on the wheel disc 10 during the flow-forming process, a local depression 46 in each case in a radial, axially parallel elongation of the region in which the circular elevations 41 are formed, wherein, on the section 8B, between two regions with local depression 46, there is formed in each case one region 47 which lies in an elongation of the strip-shaped elevation 42, said region being implemented either as a local elevation or else as a zone with a cylindrical surface (that is to say without elevation or depression). This specific shaping of the side wall 8B has the effect, during the flow forming of the preform against the spinning mandrel 3, that the disc margin 14, as can already be clearly seen in Figure 3, is provided, in each case in an elongation of a ventilation hole 18, that is to say in effect behind or in the shadow of a ventilation hole 18, with a disc margin section 19 as a zone with material accumulation; by contrast, in an axial elongation of the intermediate region 24 equipped with the strip-shaped zone 15 between two ventilation holes 18, there is formed a disc margin section 20 which is substantially the same material thickness as the sections of the wheel disc 10 in regions where the spinning mandrel 3 had neither elevations nor depressions. For illustration, it is also pointed out that, self-evidently, the ventilation holes 18 are punched only after the disc margin sections 19 of relatively large material thickness have already been formed during the flow-forming process, and that the disc margin sections 20 could also be provided with a slightly reduced material thickness in relation to other regions of the transition surface.
By virtue of the fact that zones 72 with material reductions have been created, by way of the circular elevations 41 on the spinning mandrel, in the region of the punched slugs 71 that will later be removed in order to produce the ventilation holes 18, and also by virtue of the fact that a strip-shaped zone 15 with material reduction is created in each case in intermediate regions 24 between two ventilation holes 18, it is correspondingly possible for more starting material to flow into the disc margin 14 during the flow-forming process, whereby the preform for the production of the wheel disc form 10 can, for an identical wheel disc width to be produced, be provided with a smaller outer diameter than a preform used for the flow-forming of a wheel disc of the same disc width but without material reduction. In addition to this material saving for the preform, it is simultaneously the case that the wheel disc 10 has a weight reduction imparted to it by the strip-shaped material reductions 15 between two ventilation holes 18, and at the same time has a structural reinforcement imparted to it by the strip-shaped or rib-shaped configuration, wherein the weight savings attained in the zones 15 by way of material reductions are greater than the increase in material owing to the zones 19 with material accumulation at the disc margin 14. Of particular advantage with regard to the fluctuating loads on a vehicle wheel while the vehicle is in motion are the material accumulations in the sections 19 at the disc margin 14 including the interposed sections 20 with at least smaller material thickness, and possibly even reduced material thickness, in relation to that in the sections 19. During continuous-load operation of a vehicle wheel, material cracks occur in particular in the disc margin 14 behind or in the axial elongation of the ventilation holes 18, and sometimes also in the intermediate regions between said ventilation holes 18, or fractures occur in the connecting weld seams between the disc margin and the wheel rim part. In the case of a vehicle wheel having a disc part according to the invention, that is to say a wheel disc 10, this effect is counteracted by way of the different material thicknesses in the disc margin 14 in the sections 19 in an axial elongation behind the ventilation holes 18 and in the sections 20 in elongation of the intermediate regions 24 between two ventilation holes 18.
The wheel disc 10 for a utility vehicle wheel has, in the exemplary embodiment shown in Figures 3 to 10, ten bolt holes 21 in the attachment flange 12, ten ventilation holes 18 and correspondingly also ten strip-shaped zones 15 with material reductions as stiffening ribs on the inner side 16 of the transition surface 13. Each strip-shaped zone 15 with material reduction in the wheel disc 10 has in each case two marginal edges 15A running in the radial direction, wherein each marginal edge 15A runs obliquely with respect to the wheel axis R, and furthermore, the distance A between the marginal edges 15A increases preferably in continuous fashion toward the disc margin 14. From the sectional view in Figure 4, it can be clearly seen that the material thickness D1 in the region of the attachment flange 12, which corresponds to the initial thickness of the preform at least before any material removal by turning of the base surfaces of the attachment flange 12, is considerably greater than the material thickness D2 in the disc transition surface 13, for example at the margin of a ventilation hole 18 (compare Figure 6). In this case, the material thickness D2 is at a minimum normally approximately 30-40% of the initial thickness D1, and lies rather in the range of approximately 40-50% of the initial thickness D1. In the region of the strip-shaped zone 15 with material reduction, which simultaneously serves to realize a stiffening rib, the material thickness D3 decreases considerably once again, as can be seen particularly clearly both in the sectional view in the upper half of Figure 4 and also in the sectional view in Figure 6. There, the material thickness D3 may locally amount to for example only 60% to 80% of the material thickness D2 in the surrounding flow-formed regions of the transition surface, and may possibly amount to only approximately 10% to 30% of the material thickness D1 in the attachment flange 12. In the regions surrounding the strip-shaped zone 15 with material reduction, and preferably also in the boundary region of the ventilation holes 18, the material thickness is D2. At this juncture, it is furthermore pointed out that the figures do not illustrate that, owing to the flow-forming used in the method, there is a process-induced slight continuous decrease in thickness in the flow-forming direction, that is to say from the attachment flange 12 toward the disc margin 14.
The sectional view in Figure 4A illustrates the material accumulation at the disc margin 14 in an (in this case central) radial elongation of the ventilation holes 18. The dotted line in the detail view in Figure 4A indicates the material thickness D2, that is to say the material thickness that the disc margin 14 is provided with during the flow-forming process in the region of the sections 20 which are duly flow-formed but which are not thickened by way of material accumulation. Since zones 20 with material accumulation are formed in the disc margin 14 by means of the depressions (46, Figure 2) on the spinning mandrel, the disc margin 14 is locally provided with a material thickness D4 which is greater than the material thicknesses D2 and D3. In this case, the (maximum) material thickening D4, which preferably amounts to 5 to 10% in relation to the adjoining regions with the material thickness D2, is smaller than the (maximum) material thinning D3, which preferably amounts to 10 to 30% relative to the adjoining regions with the material thickness D2. In the region of the punched slugs 71 or ventilation holes 18, it is in turn possible for the minimum material thickness D5 to be reduced yet further, as the entire slug is removed. In general, the following applies at any rate at the end of the metal spinning or flow-forming process: $D1 > D4 > D2 > D3 \geq D5$
The relative relationships may, at the end of the flow-forming process, be defined approximately as follows: $1.2 \geq D4 / D2 > 1$
$1 > D3 / D2 \geq 0.7$
With regard to the thickness dimensions, it is also pointed out that, in particular in order to avoid abrupt thickness transitions, transition zones are generated in each case, within which there is a continuous change in thickness from one thickness to the other thickness. This is also illustrated in Figures 5 and 6. The above-stated values therefore relate to guide values for the maximum thickening (material accumulation) and maximum thinning (material reduction). For the initial thickness D1 in the attachment flange 12 and the material thickness at the disc margin 14 in the case of the weldedtogether vehicle wheel, it must also be taken into consideration that the attachment flange 12 may be subjected to material removal by turning with cutting action on both sides, for example by 0.3 mm on each side, and the disc margin 14 may also, at least on the outer side, be subjected to material removal by turning with cutting action by for example 0.1 mm to 0.5 mm, or subjected to other reworking, such that then, on the finished vehicle wheel or disc part, the disc margin 14 has no changes in thickness or only minimal changes in thickness, which however existed with greater differences in the wheel disc form as an intermediate product of the manufacturing process.
In the case of the wheel disc 110 shown in Figures 7 to 9, components of identical function are denoted by reference signs increased by 100. As in the preceding exemplary embodiment, said wheel disc is a wheel disc 110 for a utility vehicle wheel with ten bolt holes 121 in the attachment flange 112 and ten ventilation holes 118 in the disc transition surface 113 that has been flow-formed against a spinning mandrel (not shown) during the flow-forming process, and it is preferably also the case, as in the preceding exemplary embodiment, that the disc margin 114 has, in each case in a radial elongation of a ventilation hole 118, sections 119 which have a greater material thickness than sections 120 at the disc margin which lie in an elongation of an intermediate section 124 between two ventilation holes 118, as illustrated in the right-hand half of Figure 7. The main difference between the wheel disc 110 as per Figure 7 and the preceding exemplary embodiment lies in the shapes of the zones 115 with material reductions in the intermediate section 124 between two ventilation holes 118. In the case of the wheel disc 110, the zone 115 with material reductions has three areas 131, 132, 133 which are delimited with respect to one another, wherein each of said areas has a material thickness D3 smaller than the initial thickness D1 of the preform, as remains present in the attachment flange 112 of the wheel disc 110. The material thickness D3 is also smaller than the thickness D4 in the region of the sections 119 at the disc margin 114, in the form of zones with material accumulation, and is also smaller than the thickness D2 in the region of those sections of the wheel disc transition surface 113 which surround the areas 131, 132, 133. In the exemplary embodiment shown, all three areas 131, 132, 133 have a slightly trapezoidal shape with marginal edges running obliquely with respect to the radial direction, said marginal edges being denoted by 136 in the case of area 131, 137 in the case of area 132, and 138 in the case of area 133, wherein the distance A between the respective marginal edges 136, 137, 138 increases in the direction of the disc margin 114 both within an area 131, 132, 133 and also from one area to another. That area 131 which is situated closest to the attachment flange 112 consequently has the smallest area width, and the area 133 situated closest to the disc margin 114 has the greatest width.
Perpendicular to the wheel axis R, the area has delimiting edges 141, 142, the area 132 has delimiting edges 143, 144, and the area 133 has delimiting edges 145, 146, the length of which increases, in each case from the smallest length of the delimiting edge 141 to the greatest length at the delimiting edge 146, correspondingly to the increase in width of the areas 131, 132, 133. In particular, it can be clearly seen from the sectional views in Figures 8 and 9 that each area 131, 132, 133 has a distinct zone with substantially constant reduced thickness D3, whereas, in particular in the region of the marginal edges 134-138 and the delimiting edges 141-146, the thickness changes continuously to the material thickness D2 in that region of the transition surface 113 which surrounds the ventilation holes 118 or the areas 131, 132, 133. Owing to the structure of the intermediate section 124 between two ventilation holes 118 being broken up by areas, with a zone 115 with material reduction being realized in or with each area 131, 132, 133, it is correspondingly the case that a greater amount of material is provided which can flow into the disc margin 114 during the flow-forming process. At the same time, the multiple areas 131-133 serve to realize a reduction in the overall weight of the wheel disc, and the intermediate webs 151 and 152 that remain between two adjacent areas 131, 132 serve to generate, between areas 132, 133, additional stiffening of the region between two ventilation holes 118 and of the disc transition surface 113 as a whole.
In the third variant of a wheel disc 210 illustrated in Figures 10 and 11, it is in turn the case that a total of ten bolt holes 121 and one central hole 211 are formed on the attachment flange 212, with ten ventilation holes 218 and ten zones 215 with material reductions being formed in each case between two ventilation holes 218 in the disc transition surface 213 that has been flow-formed during the flow-forming process. The upper delimiting edges 241 of each zone 215 with material reduction lie above the region of extent of the ventilation holes 218. At the same time, the delimiting edge 241 together with the marginal edges 235 of the zones 215 extend partially, as viewed in the radial direction, to a point in front of the ventilation holes 218. Each zone 215 consequently has a corner region 251 between the marginal edge 235 and that marginal edge 241 which is closer to the attachment flange, which corner region causes the intermediate section 224 between two ventilation holes 218 to be narrowed to the relatively small material thickness D3, which has the result not only that additional material is moved away out of the region between the ventilation holes 218 and the attachment flange 212 in the region of the transition surface 213, but at the same time that the rigidity of the disc transition surface 213 is reduced slightly also above the ventilation holes 218 (as seen in Figure 10), which improves the continuous loading capability of the disc transition surface 213, which is, owing to ventilation holes 218, in any case of non-uniform flexural stiffness. In the exemplary embodiment shown, the lateral delimiting edges 235 of the zones 215 run in straight form from the disc margin 214 to a point slightly above the centre of the ventilation holes 218, and above this, proceeding from the upper delimiting edge 241 of the zone 215, run in curved fashion, in this case partially even with the same radius of curvature as that of the ventilation holes 218 (which will be punched out at a later point in time). In the exemplary embodiment shown, the lower delimiting edge 242 lies substantially at the level of the lower tangent to each ventilation hole 218; the lower delimiting edge 242 could also lie lower and thus closer to the disc margin 214. In the case of the wheel disc 210, it is again not illustrated in detail that, during the flow-forming process, at the disc margin 214, in each case in a radial elongation of each ventilation hole 218, sections which are offset circumferentially are generated in the form of zones with material accumulation, and thus with a greater material thickness than in the region of those sections which lie at the disc margin 214 in each case in an elongation of the intermediate sections 224.
Figures 12 and 13 show a fourth exemplary embodiment of a wheel disc 310 with attachment flange 312, disc transition surface 313 that has been flow-formed during the flow-forming process, and disc margin 314. The ventilation holes 318 have already been formed in a punching or cutting process subsequent to the flow-forming step. In the exemplary embodiment shown, the disc transition surface 313 is provided, up to a point close to the lower margin of the individual ventilation holes 318, with a constant diameter all the way around, self-evidently interrupted by the ventilation holes 318 that are punched out in certain regions. As in the case of the preceding examples, considerable economic advantages are attained if a spinning mandrel for the production of the wheel disc 310 has elevations on the spinning mandrel in those regions which are to be cut out or punched out at a later point in time to form ventilation holes 318, which elevations correspondingly lead to zones with material reductions on the inner side of the wheel disc form for the wheel disc 310, because, since said regions can be punched out as ventilation holes 318, it is possible for the material saved by way of the material reduction to be used for generating sections with material accumulation, for example also at the disc margin 314 preferably in a radial elongation of the individual ventilation holes 318. In the exemplary embodiment shown, in the case of the wheel disc 310, two projecting webs 351 per ventilation hole 318, said webs forming zones with material accumulation, are formed on the disc inner side 316 so as to be distributed over the inner circumference, wherein each of said webs 315, as can be clearly seen in particular also from Figure 13, originates on the inner side 316 of the transition surface 313 in the region of the disc transition surface 313 and extends into the region of the disc margin 314. In this case, in each case two webs 351 as zones with material accumulation are provided per ventilation hole 318, and there are consequently twice as many webs 351 as ventilation holes 318. The two webs 351 assigned to a respective ventilation hole 318 have the same angular spacing to a radial plane which bisects a ventilation hole 318 and simultaneously extends through the wheel axis R. The angular spacing from one web 351 to the next but one web 351 is dependent on the number of ventilation holes 318, and is in each case equal among the webs, whereby overall, a symmetrical distribution of the pairs of webs 351 over the circumference is realized. In the region of the disc transition surface 313, the individual webs 351 originate at a point above a tangent to the lower delimiting margin of the individual ventilation holes 318, that is to say adjacent to a ventilation hole, whereby each web 351 effects flexural stiffening between disc margin 314, at one side, and transition surface 313 even in regions alongside the ventilation holes 318 as viewed in the circumferential direction. The surface contour 352 of each individual web 351 may run in planar fashion, as in the exemplary embodiment shown, though may also run in curved fashion or have some other profile, and is defined by the shape of a depression in the spinning mandrel, with which the individual webs 351 are then formed on the inner side 316 of the wheel disc 310 during the flow-forming process. Even if no zones with material reduction are formed on the disc inner side 316 in the case of the wheel disc 310, it would be possible for zones with material reductions, such as have been described with reference to the preceding exemplary embodiments or will also be described below, to be provided in addition to the webs. Furthermore, it would be possible for only a single web to be provided for each ventilation hole, which web is possibly of stronger design than the web illustrated here and is then arranged centrally between two ventilation holes.
The wheel disc 410 shown in Figures 14 to 17 has also been produced by flow-forming of a circular blank against a spinning mandrel on a flow-forming machine, but not by flow-forming of a plate-type blank against the outer contour of a spinning mandrel, and instead by flow-forming of a blank that has been pre-formed into a pot shape against the inner contour of a correspondingly hollow-domed spinning mandrel. Owing to this modified method implementation, the wheel disc 410 has a rotationally symmetrical inner side 416, whereas on the outer side 417 of the transition surface 413 of the wheel disc 410, a zone 415 with material reduction has been generated between every two ventilation holes 418. In the case of the wheel disc 410, too, the attachment flange 412 forms the holding-down surface for the preform, which is however subjected to pre-rolling or pre-drawing before the flow-forming process such that it can be inserted, for example in the form of a pot, into the cavity of a spinning mandrel. Subsequently, the transition surface 413 is rolled, and in the process flow-formed, by way of flow-forming action against the inner side 416, against the inner wall of the spinning mandrel, whereby the outer side 417 of the transition surface 413 and of the disc margin 414 is provided with the inner contour of the spinning mandrel; the spinning mandrel has, owing to the method implementation, the negative shape of the outer side 417 of the wheel disc 410. Ten ventilation holes 418 have been punched out in the transition surface 413 by punching after the flow-forming process, wherein each ventilation hole 418 is, during the punching process, positioned such that a zone 415 with material reduction is positioned symmetrically between in each case two adjacent ventilation holes 418.
It can be clearly seen in particular from the views in Figures 16 and 17 that the material thickness D3 in the region of the zones 415 with material reduction is considerably smaller than the thickness D2 in the other flow-formed regions of the disc transition surface 413. The zone 415 with material reduction forms in each case a lens-shaped recess on the outer side 417 of the transition surface 413, wherein all of the zones 415 or recesses extend substantially in a band along the circumference in which the ventilation holes 418 have also been punched out. As in the preceding exemplary embodiments, it is possible in this refinement, too, for the disc margin 414 to be provided with sections with zones with material accumulation in particular in a radial elongation of the ventilation holes 418, whereas the sections in a radial elongation of the lens-shaped zones 415 with material reduction are provided either with the other material thickness D2 or with a material thickness further reduced in relation thereto.
Figures 18 to 20 show a vehicle wheel 550 in which a wheel disc 510 produced by flow-forming in accordance with the method according to the invention is connected to a wheel rim part 560 of arbitrary type of construction by way of the disc margin 514 of the wheel disc 510. The wheel rim part 560 is in this case provided, in the flank of a safety hump 561, with a valve hole for receiving a valve 562, which gives rise to an imbalance of the vehicle wheel 550 as the latter rotates. In the case of the vehicle wheel 550, said imbalance is substantially compensated by virtue of the fact that, as can be seen particularly clearly from Figure 18, the wheel disc 510 is equipped with two zones 590 with material accumulation, wherein the additional mass created by the two material accumulation zones 590 on the inner side 516 of the transition surface 513 is coordinated with the overall weight of the valve 562 and the position thereof relative to the wheel axis. As is known per se, the wheel disc 510 and the wheel rim part 560 are connected to one another such that the valve hole for the valve 562, and thus also the valve 562, lie centrally in relation to one of the ventilation holes 518. In the case of a wheel disc 510 with ten ventilation holes 518, a ventilation hole 518 is in turn situated on the inner side of the wheel disc 510 situated opposite the valve 562. The two stud-like zones 590 with material accumulation as balancing weights for the valve 562 are thus formed integrally in the transition surface 513 to both sides of said ventilation hole 518 which is situated opposite the valve hole or valve 562, in this case exactly centrally between in each case two ventilation holes 518. The two zones 590 with material accumulation may in this case serve, in a subsequent punching step, as a marker for setting the position of the wheel disc 510 in relation to the punching tools in order that the ventilation holes 518 are in each case punched out with the correct angular spacing to the zones 590. In the exemplary embodiment shown, with the exception of the zones 590 with material accumulation as weight compensation for the valve 562, the wheel disc 510 has no further separately implemented zones with material accumulation or material reduction. As explained with regard to the preceding exemplary embodiments, however, it is preferably the case that the disc margin is formed, in sections, with zones with material accumulation in a radial elongation of the individual ventilation holes 518, wherein, in each case in a radial elongation of the intermediate section 524 between two ventilation holes, sections are formed on the disc margin 514 which either form zones with material reduction or which have the same material thickness as the "normal" regions of the transition surface 513. Furthermore, it is preferably the case, during the flow-forming of the wheel disc 510, that a zone with material reduction (not shown) is provided in each case in that region of the disc transition surface 513 in which the ventilation holes 518 will be punched out at a later point in time, in order that the material saved there can be displaced into the disc margin 514 and/or can be used as material for the zones with material accumulation. It would also be possible, in addition to the zones 590 which form the balancing mass for the valve 562, to form further, for example strip-shaped or rib-shaped zones with material reduction or material accumulation, as has been described by way of example with regard to the preceding exemplary embodiments.
In the case of the vehicle wheel 650 shown in Figures 21 to 23, an alternative design is implemented for the compensation of the weight of the valve 662. The vehicle wheel 650 has a wheel rim part 660 which is of substantially arbitrary form and which has a valve hole 663 for receiving a valve 662, and the wheel disc 610 produced by flow-forming is, by way of the disc margin 614 generated during the flow-forming process, connected rotationally conjointly to the wheel rim inner side of the wheel rim part 660 by means of weld seams (not illustrated in detail). In this case, too, in the assembled state of wheel rim part 660 and wheel disc 610, the valve 662 is positioned so as to lie centrally with respect to a ventilation hole 618 in the flow-formed transition surface 613 of the wheel disc 610. To both sides of said ventilation hole 618 which lies, in effect, in front of the valve 662, two relatively small, in this case recess-like zones 690 with material reduction are formed in the transition surface 613 on the inner side 616 of the wheel disc 610, which zones have been generated by means of corresponding elevations on the outer side of the side wall of the spinning mandrel during the flow-forming process. In this case, too, said zones 690 with material reduction may be used for setting or centring the position of the wheel disc form before all of the ventilation holes 618 are punched out, in order that, after the punching of the ventilation holes 618, the two zones 690 lie exactly centrally between two ventilation holes 618. The weight that is saved by way of the zones 690 is coordinated with the valve weight of the valve 662 and the distance thereof from the axis of rotation, in order to compensate for the imbalance of the vehicle wheel 650 caused by the valve 662. After the punching of the ventilation holes 618, the two zones 690 with depressions in the form of circular recesses as material reduction lie in the centre of the intermediate sections 624 between in each case two adjacent ventilation holes 618. In this case, too, as in the case of the preceding exemplary embodiment, it would be possible for material reductions to be formed in those regions which are subsequently punched out, and/or at the disc margin may preferably, as viewed in the circumferential direction, have alternating sections of different material thicknesses, wherein preferably, sections with material accumulations lie in a radial elongation of the ventilation holes 618, even though this is not illustrated in detail.
Figures 24 to 26 show an eighth exemplary embodiment, wherein these figures show a wheel disc form 770 as could be present at the end of the flow-forming step. The attachment flange 712, the transition surface 713 and the disc margin 714 have duly already been formed on the wheel disc form 770, but neither bolt holes nor ventilation holes have been punched out. The positions of the ventilation holes to be produced during the punching process (or for example laser-cutting process) is indicated, by way of the ventilation hole margin, in the figures by the line 788. In this case, too, the flow-forming of the preform is performed against a spinning mandrel which has at least depressions for forming in each case four stud-like zones 765 with material accumulation on the inner side 716 of the transition surface 713 during the flow-forming step, wherein, as can be seen very clearly from the figures, said individual zones 765 are positioned such that a sub-region of each zone 765 lies outside the ventilation hole margin 788 and another sub-region of each zone 765 lies within the respective ventilation hole that has yet to be punched out. In a subsequent punching step (or cutting step), it is then the case, during the production of the ventilation holes, that each of said individual zones 765 is split such that each zone 765 extends up to the margin of the ventilation hole. In each case four zones 765 around the ventilation holes (compare line 788) are positioned in relation to the central point or the radial plane E of each ventilation hole such that said zones have an angular spacing of 90° to one another and, in relation to the radial plane E through a ventilation hole, are each offset by 45° with respect to said radial plane. With these stud-like zones 765 with material accumulation which extend up to the margin of each ventilation hole, the marginal region of the ventilation holes is locally reinforced, specifically in a region in which, under continuous loading, the greatest fluctuating loads occur, which can be better absorbed and compensated by the material accumulation and slightly greater material thickness. Also, in the case of the refinement as per Figures 24 to 26, the additional material required for the zones 765 with material accumulation can be removed in particular from the central region of the slug 771 which is removed during the punching process, and in which, correspondingly, a zone 772 with material reduction is correspondingly formed, said zone in this case again being circular. Since said slug 771 is removed in any case during the punching process, it can be thinned to any desired extent as long as a minimum thickness is not required for the material flow during the metal spinning or flow forming of the disc form 770. Instead of four stud-like zones, it would also be possible for only two stud-like zones with material accumulation to be provided, which preferably lie at the ventilation hole margin closest to the disc margin.
Numerous modifications which are intended to fall within the scope of protection of the appended claims emerge to a person skilled in the art from the above description. It has already been discussed that the design variants illustrated in the individual figures may be combined with one another; in particular, in the case of a refinement with a balancing weight, it would also be possible for other zones with material accumulation or material reduction to be created during the flow-forming process. The spinning mandrel then correspondingly has elevations on the side wall, which elevations serve to generate material reductions in the transition surface or in the disc margin, or depressions, in order to correspondingly create zones with material accumulation in the transition surface or in the disc margin. In all of the refinements of the spinning mandrel and of the wheel discs produced therewith, the disc margin is preferably provided with the contour that has been explained in detail with regard to Figures 2 to 6. Individual zones may be provided with different material reductions, and also different shapes, wherein preferably, identical shapes are formed so as to be distributed over the circumference.

Claims

Method for producing wheel disc forms, which have an attachment flange, a disc transition surface and a disc margin, for vehicle wheels from preferably metallic preforms on a flow-forming machine (1) which has a spinning mandrel (3) being rotatable about an axis of rotation, and at least one spinning roller (5), which is adjustable radially relative to the axis of rotation, for the flow forming of the preform against the spinning mandrel and production of a flow-formed transition surface on the wheel disc form, wherein in a subsequent method step, ventilation holes (18) are formed in the wheel disc form by way of a punching or cutting process, characterized in that the preform (6) is flow-formed against a spinning mandrel (3) which has multiple local elevations being distributed over the circumference in order to generate zones which are distributed over the circumference of the wheel disc form and which have material reductions in the flow-formed transition surface, with the transition surface receiving transition zones having varying thickness comprising continuous change in thickness, and wherein in the subsequent method step, zones with material reductions created during the flow form step are removed for the production of the ventilation holes.
Method according to Claim 1 , characterized in that, during the flow forming against the spinning mandrel, zones (72; 772) with material reductions are created in the disc margin of the wheel disc form, and/or that in the subsequent method step, the ventilation holes (18) are formed in the wheel disc form between zones (15) with material accumulations or between the zones with material reductions.
Method according to one of Claims 1 or 2, characterized in that, during the flow forming against the spinning mandrel, at least one asymmetrical material accumulation (590) is generated as a valve balancing weight for a valve imbalance, or at least one asymmetrical material reduction (690) is generated for the purpose of compensating for a valve imbalance.
Method according to one of Claims 1 to 3, characterized in that, during the flow forming, in the disc margin (14) and/or in the transition surface in the region of the transition of the transition surface to the disc margin, zones (19) with material accumulation and/or zones with material reduction are generated which alternate in the circumferential direction.
Method according to one of Claims 1 to 4, characterized in that the zones (15; 115) with material reduction in the transition surface, or in the disc margin, at least partially have a smaller material thickness (D3; D5) than the material thickness (D2) in those regions of the transition surface, or of the disc margin, which surround said zones.