GB2308996A - Alloy vehicle road wheels and methods of manufacturing them. - Google Patents

Abstract

A method of manufacturing an alloy road wheel comprises the steps of providing a wheel blank by squeeze casting, the casting process itself shaping the profile of the wheel to some extent and carrying out a metal working or machining operation on the cast rim of the blank to either partially or completely form the desired finished rim profile.

Description

ALLOY VEHICLE ROAD WHEELS AND METHODS OF MANUFACTURING THEM This invention relates to alloy vehicle road wheels and to methods of manufacturing them.

There are in common use in the alloy wheel manufacturing industry two major methods of casting alloy wheels, the first by means of so-called gravity die casting and the second by means of so-called low pressure die casting.

It is also known to employ a method known as squeeze casting in which the cast metal is subjected to relatively high pressure, typically in the region of about one thousand Kg per square centimetre compared with gravity and low pressure casting which is carried out at a pressure of around 1Kg per square centimetre. There has also been proposed a method of manufacturing an alloy wheel which involves taking as the starting material a circular blank cut or stamped from a pre-manufactured rolled sheet alloy, pressing it into an approximation to the central wheel disc profile, splitting the rim area to bifurcate it and then rolling or spinning the resulting bifurcated periphery into the required rim profile. Such a method is disclosed in UK patent application no, 2, 132, 515.

In a variant of such a method the starting material is a cast billet which is then subjected to orbital rolling to form the billet into a rotationally symmetrical disc following which the rim edges are split and the two resulting bifurcations are then shaped by spin forging to form the desired rim profile. Such a method is disclosed in EP-A-O 509 610.

It is also possible to manufacture an alloy wheel by starting with sheet alloy which is then pressed.

In manufacturing a wheel there are three basic considerations, namely freedom of design (styling), simplicity of manufacture and providing the finished wheel with the required strength.

Within and between the known approaches there can be subtle and sophisticated variations depending upon whether the emphasis is on simplifying the manufacture or increasing the wheel strength with consequent weight saving.

The present invention is concerned with providing a method of manufacturing alloy wheels (typically of aluminium) which will strike a balance between the above discussed criteria to enable a relatively strong and light alloy wheel to be to produced whilst at the same time keeping the manufacturing method relatively simple and thus less expensive than manufacturing methods which would employ a greater number of stages.

According to the present invention a method of manufacturing an alloy road wheel comprises the steps of: (a) providing a wheel blank by squeeze casting, the casting process itself shaping the profile of the wheel to some extent; and (b) carrying out a metal working and/or machining operation on the cast rim of the blank to either partially or completely form the desired finished rim profile.

Such a process results in castings which have substantially the desired finished or net shape and with strength properties similar to forgings.

The term "squeeze casting" is intended to relate to a casting method in which the cast metal whilst still in a plastic state is subjected to relatively high pressure (typically about a thousand Kg per square centimetre) sufficient to result in substantially zero porosity castings.

According to one aspect of the present invention the rim edge of the blank is unshaped in the casting process and is subsequently subject to a bifurcation operation, the resulting bifurcated portions of the rim then being worked into the desired rim profile, such working being typically by spinning or rolling.

According to a second aspect of the present invention the rim edge is cast in a relatively narrow bifurcated form, the resulting bifurcations then being worked into the desired rim profile, such working being typically by spinning or rolling.

According to a third aspect of the present invention the rim edge is cast in a wide bifurcated form with bifurcations which are subsequently in line with one another and substantially normal to the main central disc of the wheel blank, the bifurcations then being worked into the desired rim profile, such working being typically by spinning or rolling.

How the invention may be carried out will now be described by way of example only and with reference to the accompanying drawings in which: Figure 1 is a perspective view of a squeeze cast wheel disc at the first stage in a manufacturing process according to the present invention; Figure 2 illustrates the next stage in the manufacturing process of figure 1; Figure 3 illustrates the third stage in the manufacturing process of figure 1; Figure 4 is a fragmentary sectional view of half the disc blank shown in figure 1; Figure 5 is a view similar to figure 4 and equivalent to figure 2 in terms of the manufacturing stage; Figure 6 is a view similar to figures 4 and 5 and equivalent to figure 3 in terms of the manufacturing stage; Figure 7 is a view similar to figures 4 to 6 showing the final stage of manufacture;; Figure 8 is the equivalent to figure 4 but showing a second embodiment of the invention; Figure 9 is equivalent to figure 4 but showing a third embodiment of the invention; Figure 10 is a fragmentary perspective view of a finished alloy wheel manufactured according to the present invention.

Prior Art A known process for manufacturing alloy road wheels involves firstly pressing out a blank, splitting the rim of the blank and then spinning or rolling the split rim, as described earlier in this specification.

More particularly this process can involve the following steps.

The first step is to press a circular blank out of a high quality pre-manufactured wrought alloy metal sheet, the latter being bought-in by the wheel manufacturer and being relatively expensive and placing limitations on the freedom of design (styling).

There then follows a series of pressing operations designed to shape the circular blank into the desired configuration and cross-section and to form the central hole in the disc together with bolt holes. There could typically be four pressing stages.

After the central portion of the disc has thus been shaped into the desired cross-section the rim of the disc is then split to cause it to be bifurcated, the splitting operation taking place in conditions in which the blank is preheated.

There then follows an initial rolling operation, again under elevated temperature, followed by a final cold rolling stage.

It will thus be seen that this known method of manufacture involves firstly the wheel manufacturer purchasing relatively expensive pre-manufactured sheet or wrought alloy, and then carrying out a relatively large number (in this example seven) shaping operations on the initially flat blank. The process is therefore relatively expensive.

The Invention In the method of manufacture according to the present invention the pre-manufactured high quality relatively expensive alloy sheet material is not used but instead is replaced by the wheel manufacturer producing a squeeze cast alloy blank. By utilising squeeze casting an alloy blank can be produced which has virtually no porosity.

Referring to figures 1 and 4 the aforesaid blank is illustrated at 1 from which figures it will be seen that it has been cast so that the central portion of the blank is substantially of the final finished profile for the central disc 2 of the wheel. The blank has a central aperture 3.

In the second stage of the manufacturing process, illustrated in figures 2 and 5, the periphery of the circular blank 1 is split to form bifurcations 4 and 5 of unequal thickness in order to provide sufficient metal for working into the two parts of the rim.

More specifically, the circular blank could typically be 9mm thick with the bifurcation 4 being 4mm thick and the bifurcation 5 being Smm thick. These dimensions are approximate. However, depending on the size of the wheel these dimensions could be more or less.

The third stage of the manufacturing process is illustrated in figures 3 and 6 in which the bifurcations 4 and 5 are worked into the shapes illustrated typically by a rolling or spinning operation which is itself known.

The second and third stages just described, are carried out in conditions of elevated temperature, typically in the range of 200-400C.

The final stage of the process is illustrated in figure 7 in which the partially shaped and formed bifurcations 4 and 5 of figure 6 have now been further worked and shaped to produce the final desired profile for the rim of the alloy wheel.

The method, or methods, by which the bifurcation step shown in figures 2 and 5 may be effected will be described later.

It will be appreciated from the above described manufacturing process that the number of steps that it contains is significantly less than the prior art process described earlier.

This has been achieved primarily by taking as the starting point a squeeze casting which can be shaped at that initial stage to approximate to the finished desired contour, at least far as the central portion of the wheel is concerned. The use of a squeeze casting process ensures that the alloy has sufficient strength.

If the whole rim where to be cast in subtantially its final form it would be necessary to employ an alloy incorporating elements which could promote fluidity, e.g. silicon. However, such alloys are relatively brittle. By the use of the present invention it is possible to employ a wrought alloy which, although not as easy to cast, will provide greater strength and roll forming properties.

Although figure 8 looks substantially the same as figure 5, figure 8 in fact represents the initial cross-section of the cast blank. In particular, this initial casting is shaped to already provide the bifurcations 4 and 5.

By casting the initial blank with this cross-section the second stage already described above with reference to figures 2 and 5 is eliminated so that the process then continues with the stage shown in figures 3 and 6 as the second stage of the process instead of being the third stage of the process.

The final stage of this modified process would be again as illustrated in figure 7.

If it was desired to reduce even further the amount of working to which the blank would be subjected in order to produce the final rim profile then the initial cast blank can take the form shown in figure 9.

In this third embodiment of the invention the bifurcations 4 and 5 are pre-cast so that they are substantially in line with one another and approximately normal to the general plane of the pre-cast disc.

With this arrangement the bifurcations 4 and 5 require less working than with the previously described two embodiments of the invention.

Again the final stage in the process would be as shown in figure 7, the intermediate stage being shown in figure 6.

With regard to figure 9 it is known to cast a wheel blank in this kind of configuration but such castings are low pressure castings which would not have the strength and relatively light weight of a wheel produced by the method of the present invention.

The rim splitting operation refereed to earlier could be carried out in a number of ways. For example, the splitting could be achieved by the use of a splitting tool in the form of a wheel and in which the edge to be split is heated in order to facilitate the splitting.

Depending on the alloy being used a heat treatment can be carried out either during or after the machining operations to improve the mechanical properties of the wheel. Eventually this heat treatment is followed by the machining of some critical dimensions of the wheel.

Claims (6)

1. A method of manufacturing an alloy road wheel comprises the steps of: (a) providing a wheel blank by squeeze casting, the casting process itself shaping the profile of the wheel to some extent; and (b) carrying out a metal working or machining operation on the cast rim of the blank to either partially or completely form the desired finished rim profile

2. A method as claimed in claim 1 in which the rim edge of the blank is unshaped in the casting process and is subsequently subject to a bifurcation operation, the resulting bifurcated portions of the rim then being worked into the desired rim profile, such working being typically by spinning or rolling.

3. A method as claimed in claim 1 in which the rim edge is cast in a relatively narrow bifurcated form, the resulting bifurcations then being worked into the desired rim profile, such working being typically by spinning or rolling.

4. A method as claimed in claim 1 in which the rim edge is cast in a wide bifurcated form with bifurcations which are substantially in line with one another and substantially normal to the main central disc of the wheel blank, the bifurcations then being worked into the desired rim profile, such working being typically by spinning or rolling.

5. A method of manufacturing an alloy road wheel substantially as herein before described with reference to and as shown in Figures 1 to 7 or Figure 8 or Figure 9 of the accompanying drawings.

6. An alloy road wheel manufacture by the method as claimed in any previous claim.