GB2055065A - Method and apparatus for formation of rotary or curved work piece profile - Google Patents

Abstract

A flow forming apparatus and process applicable widely to the production of rotary or curved work piece profiles, is used, in a preferred application to produce a one piece wheel from a preformed billet or disc, with optional spinning or flow turning to produce a complex wheel rim profile. <IMAGE>

Description

SPECIFICATION Method and apparatus for formation of rotary or curved work piece profile This invention relates the flow forming of rotary or curved work pieces and is particularly, but not exclusively concerned with the formation of wheels, especially motor vehicle wheels, although it is generally applicable to the formation of a wide variety of work pieces with a curved surface configuration, not only circular but a variety of rounded configurations such as say eliptical or other conic section profiles.

Motor vehicle road wheels are commonly formed from pressed steel stamped from sheet or plate material, formed into the required configuration and welded together in a laborious fabrication process. Thus metal discs are stamped from sheet material along with metal strips which are then folded into a circular form and welded into an annulus of desired cross section and then welded to the pressed disc, which typically incorporates ventilation apertures, styling apertures and holes for the wheel hub and wheel bolts or studs.With the pressed steel method of fabrication it is difficult to achieve a good dynamic balance and this is aggravated by problems experienced in producing pneumatic tyre covers to fit the wheels with appropriate dynamic balance and the compounded dynamic balance problem must be resolved by a laborious matching process of wheels and tyres, with possible eventual compensation by added rim weights.

As an alternative to the pressed steel wheel, cast and in particular die cast metal wheels have been employed of metal alloys, in particular aluminium alloys, to achieve a high strength and low weight wheel, but such wheels are typically expensive to produce and the alloy material may be sufficiently soft to be vulnerable to superficial marking and corrosion.

According to the invention there is provided a method of forming a rotary work piece comprising the steps of flow forming a work piece preform by effecting a relative rotation between the preform and a rotary pressure tool to achieve a desired work piece configuration.

According to another aspect of the invention there is provided apparatus for performing the method comprising a roll forging press with means for supporting a rotary work piece, means for effecting relative rotation between the rotary work piece and a rotary forging tool and means for applying pressure between the work piece and tool to effect flow forming by a rotary forging process.

Thus the invention provides a unitary, or integral rotary work piece, in particular a wheel, flow formed by a rotary process which of its essence produces and maintains a natural dynamic balance for the rotary work piece or wheel.

In a preferred method and apparatus according to the invention, the preformed billet, for example in the form of a flat or flanged disc, possibly with a central aperture, is subjected to an initial material improvement stage, of material densifying and grain orientation, followed by a flow forming process preferably comprising roll forging by effecting relative rotation between the rotary work piece or preformed billet and a rotary roll forging die tool with the application of pressure to achieve an intermediate work piece or wheel configuration, followed by spin turning of the intermediate work piece or wheel form to the final rotary work piece or wheel configuration.

During the spin turning stage the outer perihery and tyre supporting rim of the wheel is formed from the extended peripheral rim or rim flange of the intermediate work piece of wheel preform.

More than one rotary roll forging die may be employed and indeed the rotary work piece may be held between two opposed rotary tools to achieve simultaneous and symmetrical formation of opposed work piece surfaces.

The term flow forming or flow rolling used herein is a generalised expression intended to cover the interaction of a rotating tool and work piece and in particular a rotating die tool and rotary work piece, and a particular form of such flow forming is a process which may be described as roll forging which has hitherto been used for only very limited specialised purposes but which may advantageously be adapted according to the present invention and used in conjunction with a spin forming process as described.

The invention may be applied to a preformed billet or wheel blank, either in the form of a thickened annulus whose outer periphery is engaged by a rotary tool and split or bifurcated into opposed peripheral limbs forming the opposed edges of the eventual wheel rim or flange; or alternatively the preform may be a flanged disc which can simply be laterally deformed into the required final rim configuration.

Forged billets of a cast preform may be used for the work piece blank.

Alternatively a thick walled tube may be employed for the work piece preform or blank.

The material improvement stage prior to flow forming may comprise selectively the steps of material densifying, blanking, casting, squeezing, forging, rolling or conventional impact/squeeze forging to reorientate the material grain flow and improve the physical properties. Any combination of these processes may be used to produce the initial thickened annulus or multiple flanged preform discussed above.

Flow forming may be essentially regarded as a means for rim formation of a rotary wheel blank, by extending the hub or web outwards into a desired configuration but without distorting the wheel as a whole.

After the flow forming and, if employed, the spin turning, a final pressing or stamping process may be employed to say, form .he wheel disc or web into the desired configuration and pattern, incorporating the necessary bolt or stud holes and ventilation apertures together with the necessary stiffening profile and bolt head or nut receiving recesses.

It should be appreciated that the dimensions of the work piece or wheel preform are arranged so that the initial volume of material can be flow formed or in particular roll forged to the equivalent metal volume with appropriate dimensions in the desired configuration.

The present invention enables steel, including high grade steel or metal alloy material to be pressed very thin at the centre and thus achieve in the case of high quality steel material, a wheel structure as strong and almost as light as aluminium. The flow forming process orientates the material grain in the preferred direction for improved strength and this may further be improved by the initial material improving referred to previously, and prior to the flow forming step.

Typically a 4" X 4" or a 6" X 19" billet may be worked upon by the present invention to produce an average sized road wheel of, say, 1 2" to 24" diameter and several inches in width.

The flow formed wheel can be finished as desired, for example by spraying with metal flake to achieve a metal finish, but the actual styling or trim finish pattern can be incorporated as part of the flow forming or roll forging operation, avoiding the need to fabricate a separate wheel trim.

The flow forming or roll forging tools need not be as expensive as the conventional impact forging tools because the work input to achieve the change in work piece configuration is not so energy demanding.

The present invention may be used to make a wheel incorporating its own hub and bearing casing or indeed the integral drive shaft, which may even be hollow by extending the flow forming or roll forging according to the intention.

Thus embodiments of the invention may enable a wheel to be achieved with a single tool from a flat disc or pancake with flanges or rims produced by roll forging, spinning, or flow turning. It is envisaged that spinning can be used to take the material thickness down to say as little as 3+mum with improved grain structure as previously indicated, as compared with punched out forms with the conventional pressed steel wheels. The latter requires expensive jigs and laborious fabrication process with a multiplicity of steps and it is envisaged that the process according to the present invention may be fully automated to produce say a production figure of three to four hundred wheels per hour from a machine according to the present invention.

Further developments of the present invention would enable a brake disc to be formed integrally with the wheel and the bearing housing previously discussed.

The weight reduction achievable in wheels formed by the present invention could enable a reduction in vehicle unsprung weight of say 601bs. giving advantages in economy of operation and suspension, handling and braking performance.

Of importance also is that the present invention entails minimal waste of material, particularly as compared with the conventional pressed disc wheel fabrication process. Thus by careful calculation of the initial volume of material flow forming, or in particular roll forging, may simply move that volume into the desired configuration. Any waste can be removed at the wheel periphery, for example by trimming with conventional cutting tools.

Nevertheless the waste is minimal compared with the typical 40% waste with conventional pressed steel fabrication.

The invention may be employed to produce wheels for any purpose and not simply motor vehicle wheels, although this is an important application.

There now follows a description of particular embodiments of the invention, by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows the work piece billet or blank for initial forming; Figure 2 shows a preform work piece disc for subsequent flow forming; Figure 3 shows a cross section of the annular disc shown in Fig. 2, revealing the thickened peripheral cross section; Figure 4 shows a flanged preform for subsequent flow forming; Figure 5 shows an off-set disc with a marginally thickened annular periphery relatively off-set to the central hub; Figure 6a and 6b shows successive stages in a split flow forming apparatus and process according to the invention; Figure 7 shows one form of split formed wheel cross section produced by the apparatus shown in Figs. 6a and 6b; ; Figure 8 shows another form of split formed wheel cross section to that shown in Fig. 7; Figures 9a, 9b, 9c and 9d show alternative - wheel rim cross section configurations which may be produced from an initial preform; Figures iota, lOb and 1 Oc show a further alternative wheel rim sections for formation from an initial preform; Figure ii shows in split section form the progressive formation of a wheel and rim from a preform with a flange of prescribed dimensions:: Figures 12a and 12b show respectively part cut-away and complete perspective views of a one piece or integral wheel form produced according to the invention; Figures 13a and 13b show successive stage in the production of a complex wheel rim form from a forged hub preform; Figure 14 shows a possible wheel hub bearing and mounting arrangement for the wheel shown in Fig. 1 3b; Figures 15a and 1 sub show progressive stages in the formation of a complex wheel form from a forged preform; Figures 16a and 16b show respectively sectional and elevational detailed views of the wheel profile and aperture pattern and configuration of the wheel shown in Fig. 1 sub.

Referring to the drawings, flow forming according to the invention may be performed on a variety of initial forms of work piece, such as are variously depicted in Figs. 1, 2, 3, 4 and 5 and of varying degrees of complexity in configuration and cross section.

Generally, the more complex the work piece preform, the closer the preform is to the final work piece shape consequently the less subsequent forming has to be performed. However, there is a practical limit to the amount of preforming which can be achieved with conventional processes without required, say, complex fabrication steps, separate machining operations, and large amounts of deformation energy.

In general, not only the preform shape but the constituent formation may be varied considerably from, say, a rolled or forged cast rectangular metal billet through to a forged or cast disc, thick walled tube, a pressed or stamped blank from strip or plate material, through a pressure die cast or spray cast from atomised metal particles.

The preform, whether in the form of a billet or a flattened disc or pancake, is further manipulated towards the required shape by conventional manufacturing techniques, such as impact or squeeze forging and this is followed by flow forming according to the present invention by a particular method which will vary according to the final work piece form.

Since the present invention may be particularly advantageously applied to wheels, the present embodiments are discussed in that context, although it should be appreciated that the invention is of much wider scope and is applicable to the formation or rotary or curved work pieces generally.

The preferred flow forming technique according to the invention, is a roll forging process by which a rotary tool, and in particular a rotary die, is applied to a rotary work piece, and in particular relative rotation is effected between the rotary work piece and rotary tool die under pressure to effect a continuous rotary applied lateral deformation upon the work piece. By this means it will be appreciated that the preformed discs such as shown in Figs. 2, 3 and 5 may be deflected at or adjacent the periphery to form a flange or rim; further deflection under the action of one or advantageously two opposed rotary die tools may be used to reduce and locally deform the rim or flange cross section progressively into the desired shape as shown in Figs. 7, 8, 9, 10, 11, 13 and 15.

In order to produce a laterally deformed flange of this character which is symmetrical abount the plane of the disc preform, a modified particular flow forming process, termed for convenience split forming, may be employed, in the generaly manner shown in Figs.

6a and 6b. Referring to to the latter, a work piece preform such as shown in Figs. 2, 3 and 5, and with a thickened annular periphery 1 3 and relatively thin co-planar hub 20 or offset hub 11 is mounted between opposed rotary dies 1 8a and 1 8b of a roll forging machine to impart the initial desired configuration to the disc.

The opposed dies 1 8a and 1 8b may have a central or axial complimentary nose and recess portion to form a central wheel hub and possibly also the hub aperture.

The periphery of the preform disc 1 2 clamped between the opposing rotary dies 1 8a and 1 8b is shaped by engaging the thickened annular rim or periphery 1 3 with an edged profile rotary die tool 1 5 mounted on a shaft 1 7 for rotation about an axis generally parallel to the rotational axes of the complimentary dies 1 8a and 1 8b and the intermediate clamped work piece disc preform 12. The tool 1 5 is moveable transversely with respect to the work piece and as indicated by opposed arrows and similarly the work piece itself can be moved axially relative to the tool 15.

The tool 1 5 has an edge profile generally complementary to the combined edge profile of 1 9 of the axially clamped together opposed die halves 1 8a and 1 8b. Thus as the tool 1 5 is moved towards the tools 18, to engage the outer edge of the thickened annular periphery of the work piece disc preform 1 2 so the periphery is split or bifurcated by the central up-standing annular rib or edge 1 6 of the tool 1 5 and as the tool is moved progressively inwards so this bifurcation is increased to the extent of eventually deforming the split thickened annular rim 1 3 into two portions which flow around the tool 1 5 and eventually over the combined tool surface 1 9 of the opposed die halves 1 8a and 1 8b. Thus in the final forming stage, the tool 1 5 is brought very close to the opposed tools 1 8a and 1 8b and the distinct splayed rim profile 21 of the then formed wheel still clamped between the opposed die halves 1 8a and 1 8b is defined closely between the outer periphery of the tool 1 5 and the combined tool surface 1 9. Thus the inner and outer profiles of the wheel rim 21 may be carefully formed. Variants in the precise rim configuration and the relationship of the rim to the web or hub of the wheel are shown in Figs. 7 and 8.

As an alternative to split forming or at least as a means of reducing the extent of forming required a preform such as shown in Fig. 4 may be employed, incorporating a distinct annular flange symmetrically disposed about the preform disc. Thus the extreme bifurcation described with reference to Figs. 6a and 6b is not required and simply the further and final lateral deformation of the existing preform flanges 14 such as may be achieved by a single or multiple rotary die tool.

Careful consideration is given to the choice of a preform configuration and fabrication method in order to optimise the use of the subsequent flow forming process for the final fabrication of the wheel. This is illustrated in Figs. 9a, 9b, 9c and 9d, referring to which a flow formed wheel rim profile as shown in Fig. 9c can be produced directly by flow forming from a forged preform of edged profile as shown in Fig. 9b rather than the more complex preform as shown in Fig. 9a which would have required initially more complexed forming operation. Further flow forming, in particular flow turning or metal spinning may be used to bring the intermediate profile shown in Fig. 9c into the final profile shown in Fig. 9d. Thus the complex profile of Fig. 9d has essentially been formed by integral flow forming process from a very crudely shaped blank shown in Fig. 9b.

A similar point is illustrated in Figs. 1 Oa, 1 Qb and 1 Oc in which a forged preform shown in Fig. 10c is produced in a rolling mill and the annular rim then pressed to the form shown in Fig. 1 Ob to enable flow forming, and in particular flow turning of the final complex rim profile as shown in Fig. 1 Oc.

Fig. 11 shows the advantageous combination of forming techniques with a pressing technique for the wheel disc or web; the initial rim dimensions of the forged preform being critically controlled to allow the desired volume of material to be flow formed, in particular by spinning or flow turning into the final complex form shown on the right hand side of the drawing.

The complexity of wheel configurations possible according to the invention as shown in Figs. 1 2a and 1 2b from which it is clear that the entire hub web and rim assembly of the wheel is integrally formed.

The further complexities of wheel fabrication are illustrated in Figs. 13, in particular Fig. 1 3a shows a forged hub preform which is subsequently flow formed into the complex finished wheel shape shown in Fig. 1 3b, whilst retaining the required hub configuration which may be advantageously used in the wheel hub bearing arrangement shown in Fig.

14, without the need for a separately forged wheel hub to which the wheel disc would normally be bolted. Thus referring to Fig. 14, roller or taper bearings 34 are mounted directly between a bearing mount 32 and a wheel hub 30 integrally formed with the wheel; a further sophistication being that a drive shaft 33 with hexagonal or splined end is drivingly interfitted with the internal profile of the integral wheel hub 30 achieving a simpler a more economical wheel bearing and drive assembly than that of conventional methods.

Further elaborations upon the wheel configuration are illustrated in Figs. 1 spa and 1 sub with complex pressing of the central wheel disc pattern according to the styling and structural requirements, details of which are shown in Figs. 16a and 16b.

In order to facilitate the subsequent flow forming according to the present invention, the manipulation of the initial preform may advantageously include a working of the material itself to improve its physical characteristics. For example the material may be densified in a forging, rolling or even a preliminary flow forming process to re-orientate the grain flow which in any event is advantageously maintained in the flow forming according to the present invention leading to improved structural characteristics.

Claims (21)

1. A method of forming a rotary work piece comprising the steps of flow forming. a work piece preform by effecting a relative rotation between the preform and a rotary pressure tool to achieve desired work piece size and configuration.

2. A method as claimed in Claim 1 in which flow forming is performed to achieve a desired intermediate work piece configuration and is followed by spinning to form a further or final work piece configuration.

3. A method as claimed in either of the preceding Claims including a stamping process to achieve a desired work piece pattern of material cut-outs or apertures.

4. A method as claimed in any of the preceding Claims including a metal finishing step

5. A method as claimed in Claim 4 in which the metal finishing step comprises metal spraying.

6. A method as claimed in any of the preceding Claims in which flow forming is achieved by a roll forging process by applying a rotating die tool to a rotating work piece to flow the work piece material outwards under pressure.

7. A method as claimed in Claim 6 performed upon a preformed work piece.

8. A method as claimed in Claim 6 performed upon preformed billet or blank.

9. A method as claimed in any of the preceding Claims including a material densify ing and grain forming step prior to flow forming.

10. A method as claimed in any of the preceding Claims including a spin rolling step in which a rotating die tool is applied to a rotating work piece under pressure to bifurcate or split the work piece edge configuration.

11. A method as claimed in any of the preceding Claims including material deformation of the work piece by the applied tool.

1 2. A method as claimed in any of the preceding Claims performed upon a cast preform.

1 3. A method as claimed in Claim 1 2 in which the cast preform is formed by pressure or spray casting.

14. A method as claimed in any of the preceding Claims performed upon any metal or metal composite work piece.

1 5. A method as claimed in Claim 14 in which the metal composite work piece is formed by powder metallurgy.

1 6. Apparatus for performing the method according to any of the preceding Claims.

1 7. Apparatus as claimed in Claim 1 6 comprising a roll forging press with means for supporting a rotary work piece, means for effecting relative rotation between the rotary work piece and a rotary forging tool and means for applying pressure between the work piece and tool to effect flow forming by a rotary forging process.

1 8. Apparatus as claimed in Claim 1 7 incorporating hydrostatic bearings for supporting the rotary work piece and/or the rotary roll forging die tool.

19. Apparatus as claimed in Claim 18 including spin forming means for applying a rotary metal spinning tool to the rotary work piece to further manipulate the configuration thereof.

20. A method of flow forming a rotary work piece substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

21. Apparatus for flow forming a rotary work piece substantially as hereinbefore described with reference to and as shown in the accompanying drawings.