METHOD AND APPARATUS FOR MANUFACTURING A RIM BED BY MEANS OF COLD FORMING

Abstract

A method for manufacturing a substantially rotationally symmetric rim bed having a wall thickness varying along the longitudinal axis by means of cold forming, wherein the side walls of a substantially cylindrical metal bed having a substantially constant wall thickness are flared radially outwards in a pressing operation, and wherein the wall thickness of the flared side walls is varied along the longitudinal axis by means of flow-spinning, with axial stretching and profiling of the sides. The invention further relates to an apparatus for manufacturing a rim bed by means of cold forming.

Description

The invention relates to a method for manufacturing a substantially rotationally symmetric rim bed having a wall thickness varying along the longitudinal axis by means of cold forming.

Such a method is known from WO 2004/035243 and is used for manufacturing a so-called weight-optimized rim bed for a rim for a tire.

In such a weight-optimized rim bed, which is, for instance, used in a rim for a passenger car, truck or trailer, the thickness of the rim bed varies along the longitudinal axis. Then, at different locations along the longitudinal axis, the thickness of the rim bed can be chosen such that this is just sufficient for absorbing the local loads. Thus, the rim bed may, for instance, be chosen so as to be relatively thick near the center of its axial length, in order to weld the rim bed there with the disk of the rim. In the adjacent areas, the thickness of the rim bed can then, for instance, be chosen so as to be considerably smaller, whereas the thickness closer to the sides of the rim is usually chosen so as to be larger.

In the known method, the cylindrical steel bed is pre-pressed from the outsides inwards to the center by means of flow-spinning. Here, the more outer parts of the bed are brought to a nominal thickness and any excess material is brought to the center of the length of the longitudinal axis and the bed is pre-profiled. Then, in a second flow-spinning operation, in two movements, the bed is stretched from the center axially outwards towards the sides at locations where the thickness of the rim bed needs to be reduced.

Compared to a manufacturing process in which the flow-spinning takes place after rolling the profile, as described in DE 2647464, too great a deformation of the bed material can be prevented, so that dressing of the sides of the rim bed can be prevented.

Over the process described in WO 02/053307, in which, during flow-spinning, the bed is processed on a cylindrical mandrel, the process described in WO 2004/035243 has the advantage that already some pre-profiling occurs.

However, a drawback of the method according to WO 2004/035243 is that it still is relatively expensive and time-consuming.

Therefore, the invention contemplates a method of the type stated in the opening paragraph, with which, wile maintaining the advantages, these drawbacks can be prevented. To this end, the invention provides a method for manufacturing a substantially rotationally symmetric rim bed having a wall thickness varying along the longitudinal axis by means of cold forming, wherein the side walls of a substantially cylindrical metal bed having a substantially constant wall thickness are flared radially outwards in a pressing operation, and wherein the wall thickness of the flared side walls is varied along the longitudinal axis by means of flow-spinning, with axial stretching and profiling of the sides.

By using a cylindrical metal bed with sides flared radially outwards, the bed can be pre-profiled, or even finally profiled, in one flow-spinning step without dressing of the sides being necessary.

Preferably, here, the material of the bed can move freely in feeding direction. In particular, here, during flow-spinning, the flared side walls of the bed can be pressed from a free position onto a mandrel. In forward flow-spinning in this manner, the material still to be deformed runs clear of the mandrel and does not run against a stop in feeding direction, which yields a favorable interplay of forces. In particular, a removing operation can be omitted in forming the cylindrical bed into a brim bed.

In an advantageous manner, during flow-spinning, in a first flow-spinning step, the bed is pressed down on a mandrel near the center area of the length of the longitudinal axis. As a result, the bed can be positioned well, so that, during further flow-spinning, a high size and form accuracy can be achieved.

In an advantageous manner, during flow-spinning, in a second processing step, the bed is axially stretched, radially thinned and profiled from the center area of the longitudinal axis in two opposite, outwardly directed movements with radial pressing down on a mandrel.

Here, the flow-spinning is carried out in axially outwardly directed basic movements from the center area of the longitudinal axis of the bed towards the respective sides, while the still loose material to be profiled is pressed down on the mandrel.

If necessary, the pre-profiled, flow-spun bed can also be rolled to a rim bed by means of roll forming.

Preferably, radial expansion of the bed only takes place after flow-spinning or after the profiling step following flow-spinning.

The invention further relates to an apparatus for manufacturing a substantially rotationally symmetric rim bed having a wall thickness varying along the longitudinal axis by means of cold forming, wherein a substantially cylindrical metal bed having a substantially constant wall thickness is provided with sides flared radially outwards in a pressing operation, and wherein the wall thickness of the flared sides is varied along the longitudinal axis by means of flow-spinning, with axial stretching and profiling of the sides. The apparatus is preferably provided with a flow-spinning station for profiling and axially stretching the flared bed with radial pressing down, and with a pressing station for radially outward flaring of the sides of a cylindrical bed, while the flow -spinning station connects downstream to the pressing station.

The invention will be explained in more detail with reference to the exemplary embodiment shown in a drawing.

In the drawing:

FIG. 1 shows a flow diagram of a production line for a rim bed according to the invention;

FIG. 2A shows a schematic longitudinal cross-section of the flared cylindrical bed having a thickness substantially constant along the longitudinal axis;

FIG. 2B shows a schematic longitudinal cross-section of a bed which is pre-profiled by means of flow-spinning on the basis of FIG. 2A, where it is clearly visible that the thickness of the bed varies along the longitudinal axis 1;

FIG. 3 shows a schematic longitudinal cross-section of a pressing station for radially outward flaring of the side walls of a cylindrical bed;

FIGS. 4A and 4B show two schematic longitudinal cross-sections of a flow-spinning station during fixing and stretching/profiling the bed with flared sides, respectively;

FIG. 5A shows a schematic side elevational view of three successive roll formers;

FIG. 5B shows a schematic longitudinal cross-section of a roll former in which a pre-profiled bed is profiled; and

FIG. 6 shows a schematic side elevational view of a radial expander.

It is noted that the Figures are only schematic representations of a preferred embodiment of the invention which are given exclusively by way of non-limiting exemplary embodiments. In the Figures, same or corresponding parts are designated by the same reference numerals.

FIG. 1 schematically shows a flow diagram for a production line P for a rim. In a preparation part 1 of the line, metal strips are cut to length in a first step 1.1 and formed into a cylindrical bed in a second group of steps 1.2. Here, the strip is successively coiled (1.2.1) and its front ends are welded to each other (1.2.2), after which the weld is dressed (1.2.3).

In a second part 2 of the line, the cylindrical rim bed having a constant wall thickness formed in part 1 is formed into a profiled rim bed in a profiling line (2.1) and then tested for leakage and provided with a valve hole (2.2). The profiling takes place by means of cold forming of the material, i.e. the material is not melted and no removing takes place. In a first processing station 2.1.1, the side walls of the bed are flared radially outwards to the basic form shown in FIG. 3 in an axially inwardly directed pressing operation with the aid of mandrels. Then, as will be elucidated hereinafter, in a second processing station 2.1.2, the wall thickness of the flared bed is varied along the longitudinal axis by means of flow-spinning with simultaneous pre-profiling of the bed.

Then, in a third processing station 2.1.3, the pre-profiled bed is profiled to a rim bed by means of roll formers, after which the profiled bed is radially expanded to the desired size in a fourth processing station 2.1.4.

After a check for leaks and provision of the valve hole, the rim bed is ready to be assembled with the disk to a rim in an assembly part 3 of the production line. Depending on the type of rim, the disk is connected with the rim bed at a predetermined location along the longitudinal axis.

In FIG. 2A, a longitudinal cross-section of the flared cylindrical bed 10 having a constant diameter along the longitudinal axis is shown.

In FIG. 2B, the pre-profiled bed 20 is shown, while it is clearly visible that the thickness t of the bed varies over the length of the longitudinal axis 1.

In FIG. 4A, the flow-spinning station 2.1.2 is schematically shown.

The flow-spinning station is provided with two rotatably arranged mandrels 11A, 11B which are each axially slidable along the longitudinal axis 1 of the flared bed 10. In the Figure, the mandrels 11 are each placed from a side 12A, 12B of the flared bed 10 to the center area M of the length of the longitudinal axis 1 of the bed. During the sliding in of the mandrels 11A, 11B, the bed is clamped at its sides 12A, 12B with the aid of slidable stop collars 14.

The flow-spinning station further comprises one or more rollers 13 which can move radially with respect to the longitudinal axis of the bed 10 and which are further translatable with respect to the longitudinal axis of the bed 10. The rollers 13 are further rotatably arranged with respect to the flared bed 10. Here, the rollers 13 and/or the flared bed 10 can rotate with respect to the fixed world during production.

FIG. 4A shows how, in a first processing step, the flared bed 10 is pressed down on the mandrels 11A, 11B near the center area M of the length l of the longitudinal axis of the bed 10 in a first flow-spinning step. The thickness t of the center area M remains substantially equal.

Then, as shown in FIG. 4B, with the aid of the rollers 13A, 13B, the material of the bed 10 is moved outwards along longitudinal axis 1 in two successive, opposite movements with radial pressing down, so that, with axial stretching of the bed 10, the thickness t of the bed 10 is locally reduced.

At the same time, the material of the flared side of the bed 10 is pressed down from the free position on the mandrel 11 by the rollers 13A, 13B, so that the side wall of the bed 10 is pre-profiled to the pre-profiled bed 20 shown in FIG. 2B. It is noted that, in the schematic view, the thickness t only varies little over the longitudinal axis 1. It will be clear that, in practice, the thickness variation may be greater or smaller than shown herein. Also, more or fewer areas having different thicknesses can be formed than shown herein.

During the processing process, the bed material flows outwards with respect to the center of the longitudinal axis towards the side. If desired, during the second processing step, the sides of the bed 12A, 12B can be supported by means of the slidable stop collars 14. FIG. 4B, however, shows that the slidable stop collars do not support the sides 12A, 12B.

After processing, the stop collars 14 are again brought into contact with the sides 12A, 12B, after which the mandrels 11A, 11B are axially withdrawn. With axial withdrawal of the stop collars 14, the pre-profiled bed 20 can then be removed.

So, in the second processing step shown in FIG. 4B, from the center, two successive, sideward flow-spinning operations are carried out. It is of course possible to carry out flow-spinning operations from the center to both sides simultaneously.

It is noted that the invention is not limited to the embodiments shown herein and that many variations are possible within the scope of the invention as set forth in the following claims.

Claims

1. A method for manufacturing a substantially rotationally symmetric rim bed having a wall thickness varying along the longitudinal axis by means of cold forming, wherein the side walls of a substantially cylindrical metal bed having a substantially constant wall thickness are flared radially outwards in a pressing operation, and wherein the wall thickness of the flared side walls is varied along the longitudinal axis by means of flow-spinning, with axial stretching and profiling of the sides.

2. A method according to claim 1, wherein, during flow-spinning, the flared side walls of the bed are pressed down from a free position on a mandrel.

3. A method according to claim 1, wherein, during flow-spinning, in a first flow-spinning step, the bed is pressed down on a mandrel near the center of the length of the longitudinal axis.

4. A method according to claim 3, wherein, during flow-spinning, in a second processing step, the bed is axially stretched, radially thinned and profiled from the center area of the longitudinal axis in two opposite, outwardly directed movements with radial pressing down on a mandrel.

5. A method according to, claim 1 wherein the pre-profiled, flow-spun bed is rolled to a rim bed by means of roll forming.

6. A method according to claim 1, wherein the bed is only radially expanded after flow-spinning and optionally roll forming.

7. An apparatus for manufacturing a substantially rotationally symmetric rim bed having a wall thickness varying along the longitudinal axis by means of cold forming, wherein a substantially cylindrical metal bed having a substantially constant wall thickness is provided with sides flared radially outwards in a pressing operation, and wherein the wall thickness of the flared sides is varied along the longitudinal axis by means of flow-spinning, with axial stretching and profiling of the sides.

8. An apparatus according to claim 7, wherein, during flow-spinning, the flared side walls of the bed are pressed down from a free position on a mandrel.

9. An apparatus according to claim 8, wherein a pressing station is provided for radially outward flaring of the sides of a cylindrical bed.

10. An apparatus according to claim 8, wherein a flow-spinning station is provided for profiling and axially stretching the flared bed.

11. An apparatus according to claim 10, wherein the flow-spinning station connects downstream to the pressing station.

12. An apparatus according to claim 10, wherein the flow-spinning station is located upstream of a rolling station for rolling the pre-profiled, flow-spun bed to a rim bed.