GB2171350A

GB2171350A - Production of tubes by cold working

Info

Publication number: GB2171350A
Application number: GB08604103A
Authority: GB
Inventors: Dietfried Tresser; Paul Moeser; Herbert Frielingsdorf; Helmut Riemscheid
Original assignee: Laeis GmbH; Uni Cardan AG
Current assignee: GKN Automotive GmbH; Laeis GmbH
Priority date: 1985-02-22
Filing date: 1986-02-19
Publication date: 1986-08-28
Also published as: JPS61245914A; GB8604103D0; IT1186402B; DE3506220A1; FR2577827A1; GB2171350B; IT8523107A0

Abstract

Tubular blanks having a predetermined wall thickness are subjected to cold working including a stretching operation to produce an elongate region of reduced thickness adjacent one end of the tube or intermediate of the ends of the tube. One end or each end of the resultant tube will have a wall thickness which is substantially the same as that of the tubular blank. The tube produced may be an articulated shaft serving for torque transmission in motor vehicles. After reducing one end of the blank in a die (4, Figure 1), an intermediate stretching reduction operation is performed in a die 9. <IMAGE>

Description

SPECIFICATION Production of tubes by cold working The invention relates to a process for the production of tubes with relatively thick-walled ends by cold working of a tubular blank.

Tubes of the aforementioned type are used, for example, as articulated shafts for the driving gear of motor vehicles. German Patent Specification DE PS 30 09 277, for instance, proposes an articulated shaft in which the middle zone of the tube has at least two stages of which the wall thicknesses are such that all cross-sections of the tube have the same mechanical strength.

A process of the kind mentioned at the beginning is described in French Patent Specification 25 34 159. In this prior process a hollow component of constant external diameter is produced by cold drawing in one direction. The starting point is a reduced and thickened end which later has to be processed mechanically or turned over towards the inside by one or more pressing operations. This method does not enable reductions, let alone widenings, to be carried out at both ends. If this is done at all a special machine has to be used for the purpose.

From German Patent Specification DE-PS 30 21 481 a special drawing process is known which can only be adopted economically for manufacture on special drawing machines. It is true that this known process enables the tube walls to be thickened both towards the inside and towards the outside at any desired points, but the correct position in respect of the required workpiece here again depends on the accuracy with which the material is cut to the necessary lengths, calling for special measuring methods. The ends can be neither widened nor reduced by this process.

For the production of tubes with thickened ends German Patent Specification DE-PS 28 12 803 makes known a process in which the ends undergo a hot upsetting and reducing operation. The hot conversion not only causes scale to form but also results in an unsatisfactory structure. A process of such a kind, moreover, ihvolves excessive operating costs.

The purpose of the invention is to propose a process by which hollow boes especially articulated shafts serving for torque transmission in motor vehicles and light-weight construction, can be cold worked economically and to accurate dimensions, with wall parts thickened at the tube ends subjected to particular stress, and an over-all consolidation of the starting material can be obtained by means of cold deformation. The process is capable of being carried out on standard tube-end conversion machines, so that no special or individ ually designed machines have to be used.

According to this invention there is provided a process for the production of tubes from tubular blanks having a predetermined wall thickness by cold working, the cold working including a stretching operation to produce an elongate region of reduced wall thickness adjacent one end of the tube or intermediate of the ends of the tube wherein one end or each end of the resultant tube has a wall thickness which is substantially the same as that of the tubular blank.

The process according to the invention thus applies the principle of selecting the initial part as the site of the relatively thick-walled cross-section, producing the thinner zones or other cross-sections by stretching and reduction operations, i.e. without wastage of material and without the need for refinishing. In this process, with relatively thick-walls at both ends, a residual piece having the initial wall thickness is left unaffected by the stretch reduction operation, while in the case of tubes with a relatively thick-wall at one end only the entire residual piece of the tube is stretched. This makes it possible not only to reduce the diameter of the tube end or ends but also, if necessary, to widen them to an external diameter greater than that of the relatively thin-walled part of the tube.The process according to the invention thus enables tubes with relatively thick-walled end parts to be produced at considerably reduced cost, owing to the saving of material alone, also enabling a noticeable increase in strength to be obtained in the stretched zone and where the ends are cold worked, by the use of tube cold working machines of the conventional kind.

It is thus possible with the invention to produce workpieces of widely varying shapes to accurate dimensions from a simple workpiece taking the form of a hollow body and that with blanks of appropriate accuracy it is possible to dispense with all refinishing operations. Usually in practice all that has to be done is to free the end surfaces of surplus material caused by varying workpiece dimensions.

By way of example a preferred form of process embodying the invention will be explained in greater detail by reference to a sequence plan of sectional views illustrated in the accompanying drawings. The sequence is as follows: Figure 1 Reduction of a first end of a tube, Figure 2 Profiling of the first end of the tube, Figure 3 A first stretching operation for the production of a thin-walled middle part of the tube, Figure 4 A second stretching operation for the further reduction of the thin-walled middle part of the tube, Figure 5 An arrangement following the completion of the first end of the tube, Figure 6 The reduction of a second end of the tube, Figure 7 An alternative widening of the second end of the tube, Figure 8 A further reduction of the second end of the tube, Figure 9 A process of calibrating the tube, Figure 10 A process of profiling the second end of the tube, and Figures 11 and 12 A process of widening the previously reduced end of the tube.

The drawings show a device for the cold working of a tubular blank to a tube 1 only shown schematically. In each case above a median line 2 of the device the components of the device and the blank or the tube itselfare shown in the initial position or prior to the cold working, while below the median line 2 in each case the device is shown in the position which it occupies after the cold working operation, so that the tube likewise is illustrated in its state following the said operation.

In Figure 1 a tube 1 being formed from a tubular blank is affixed in a clamp jaw unit 3 of a collet not shown in detail. A cold working tool 4 can be adjusted from the position above the median line 2 to the position underneath the said median line 2 by movement in the direction of the arrow. Within the cold working tool 4 a calibrating mandrel 5 is inserted, this being subjected to the action of a spring 6. On the side facing away from the calibrating mandrel 5 a stretching mandrel 7 can be introduced from the other side of the tube 1. The stretching mandrel 7 is already fixed in the blank but has not yet reached its final position.When the cold working tool 4 is moved up, e.g. by means of an operating cylinder not shown in the drawing, onto that end of the tube which is to be seen on the right hand side of the drawing, a cold working operation takes place, the external geometry of the end of the tube corresponding to that of the cold working tool and the internal geometry of the blank corresponding to that of the calibrating mandrel 5, where the cylindrical zone of the cold working is concerned. After this end reduction the tube 1 is still secured in the clamp jaw unit 3, and by means of a profiling tool 8(Figure 2) and a displacement in the direction shown by the arrow that end of the tube reduced in Figure 1 can undergo a profiling operation, e.g. be provided with a taper or serration which can eventually be utilized for the transmission of a torque.Needless to say, the reduced end of the tube can also be provided with an internal system of teeth by means of an appropriately shaped tool.

In Figure 3 the stretching mandrel 7 is moved towards an inner shoulder belonging to the tube 1 and situated at the transition to the reduced end.

The arrangement consisting of the tube 1 and the stretching mandrel 7 is finally moved towards the clamp jaw unit 3 as a fixed stop, after which said clamp jaws are closed. A stretching tool 9 is moved along the tube 1, stretching the material to a certain distance in the process, so that a thinner wall is created in the middle or adjacent part of the tube, the initial wall being maintained in the end zone of the tube.

In order to ensure that the tube 1 will still adhere to the stretching mandrel 7 on the return movement of the stretching tool 9 a steady-rest 11 is provided.

Figure 4 shows a further stretching process. In this case the stretching is effected by means of the second stretching tool 12 in a similar manner to the operation illustrated in Figure 3 and may be regarded as valid for all further conceivable stretching operations.

Figure 5 shows the extraction of the stretching mandrel 7. For this purpose the clamp jaws of the clamp jaw unit 3 are slightly open so that the stretching mandrel 7 can be drawn back unhindered, in which process said clamp jaws, however, act as a stripping device for the tube 1. In order to ensure that the tube 1 will remain in the line of operation a prismatic mounting attachment 13 is prQ- vided, which is moved from below into the line of operation before the stretching mandrel 7 is extracted.

Figures 6 - 10 show an additional cold working of the second end of the tube and also illustrates further processes. For the cold working of the second end of the tube it is advisable, as shown in Figure 6, for the semi-finished tube 1 to be fed to the machine once more after being turned through an angle of 180 , as a large number of additional stages in the process can follow. With a clamping mandrel 14 the tube 1 is finally moved by its externally thickened end into the operating position. By means of a reducing tool 15 and an inserted calibrating mandrel 16 the end diameter is reduced to accurate dimensions, in accordance with the diameter of the stretched-reduced middle part of the tube.

As an alternative to the reduction shown in Figure 6 for the second end of the tube this end can be widened as shown in Figure 7 by means of a widening mandrel 17 and an external tool 19 caused to move in advance via springs 18.

Figure 8 shows how by means of a further cold working tool 21 the second end of the tube can be further reduced. With the use of the cold working tool 4 and the calibrated mandrel 5 in accordance with Figure 1 the reduction operation can be effected to exactly the same dimensions as in the case of the first end of the tube.

In place of or additionally to the reduction shown in Figure 8 it is possible, for example, for a calibration to be carried out in accordance with Figure 9, in which case the tube 1 may be calibrated by means of a calibrating tool 22 at least over the entire length of the stretched diameter of the tube 1.

In Figure 10 the second end of the tube is profiled by the aid of profiling tool 8 used for the first end.

Finally, Figures 11 - 12 show how a tube 1 produced by the steps in the process which are shown in Figures 1 - 3 has been stretched, except for the reduced end, on the right hand side, over the entire remaining part of the tube. For this purpose the stretching tool 9 has been moved over the left end of the tube 1.

As may be seen from Figure 12, the stretching mandrel 7 has been drawn back to some extent, the slightly open clamping jaws of the unit 3 acting as a stripping device. The stretch-reduced part of the tube 1 is then clamped onto the mandrel and the right-hand thickened end of the tube widened by means of an internal and external tool 23 simultaneously and by a calibrating operation.

Claims

1. A process for the production of tubes from tubular blanks having a predetermined wall thickness by cold working, the cold working including a stretching operation to produce an elongate region of reduced wall thickness adjacent one end of the tube or intermediate of the ends of the tube wherein one end or each end of the resultant tube has a wall thickness which is substantially the same as that of the tubular blank.

2. A process according to claim 1, wherein initially one end of the tubular blank becomes reduced in its internal and external diameters without substantially altering the wall thickness of the said end of the tube after which the part of the blank adjacent to the said end of the tube becomes reduced in its external diameter by a single-stage or multi-stage stretching operation.

3. A process according to claim 2, wherein the said one end of the tubular blank which becomes reduced in its internal and external diameters is subsequently widened after the stretching operation to an external diameter greater than that of the part of the blank adjacent to the said end of the tube which has become reduced in its external diameter by the said stretching operation.

4. A process according to claim 2 or claim 3, wherein the other end of the tubular blank becomes reduced in its external diameter to the external diameter of the said part of the blank which has been reduced by the said stretching operation, without substantially altering the wall thickness of the said other end.

5. A process according to claim 2 or claim 3, wherein the other end of the tubular blank becomes widened in its external diameter to an external diameter greater than the external diameter of the said part of the blank which has been reduced by the said stretching operation.

6. A process according to claim 2 or claim 3, wherein the other end of the tubular blank becomes reduced in its external diameter and its internal diameter.

7. A process according to any one of claims 2 to 6, wherein the tube is turned through 180 before subjecting the other end of the tube to a cold working operation.

8. A process according to any preceding claim, wherein the tube is calibrated at least over the length of the said part of the tubular blank which has been reduced by the said stretching operation.

9. A process according to any preceding claim, wherein at least one of the ends of the tube is profiled to form a taper or serration.

10. A process for the production of tubes from tubular blanks substantially as herein described with reference to any one of the accompanying drawings.