METHOD AND MECHANICAL ARRANGEMENT FOR PRODUCING A WALL PROFILE ON A PLASTICALLY DEFORMABLE HOLLOW BODY WALL

Description

CROSS REFERENCE TO RELATED APPLICATIONS

Applicant claims priority under 35 U.S.C. § 119 of European Application No. 24198629.8 filed Sep. 5, 2024, the disclosure of which is incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a method for producing a wall profile on an inside of a plastically deformable hollow body wall of a hollow body, wherein the hollow body wall delimits a cavity of the hollow body, which cavity is open on at least one side thus forming a cavity opening, and wherein the hollow body wall is formed

• • by arranging a forming mandrel having a forming mandrel profile in the interior of the cavity of the hollow body in such a way that the forming mandrel extends with the forming mandrel profile along the hollow body wall and
  • by arranging a forming die provided with a die opening on the outside of the hollow body and moving it with a forming movement along the hollow body wall passing through the die opening relative to the hollow body wall and relative to the forming mandrel, wherein the wall profile is produced on the inside of the hollow body wall in that material of the hollow body wall is plasticized due to the forming movement of the forming die, and the forming mandrel profile is reproduced on the inside of the hollow body wall as the wall profile.

The invention also relates to a mechanical arrangement for carrying out the aforementioned method.

2. Description of the Related Art

For example, in the production of hollow shafts for automotive engineering, shaft blanks must be provided with a wall profile, in particular with internal toothing, on the inside of their wall. The inner profile produced on the wall of the shaft blank is intended, on the finished hollow shaft, to interact with an outer profile of a counterpart inserted into the interior of the hollow shaft and thereby to create a positive-fit connection between the hollow shaft and the counterpart that is effective around the shaft axis.

EP 4 155 001 A1 discloses, inter alia for such applications, a generic method and a generic mechanical arrangement.

In the case of the prior art, a forming mandrel, which is provided on its outside with a forming mandrel toothing and has a uniform cross-section over the entire mandrel length, is arranged inside a shaft blank to be formed. A forming die with a die opening is placed on the shaft blank and moved with a forming movement along the shaft blank passing through the die opening and relative to the forming mandrel arranged inside the shaft blank. Due to the forming movement of the forming die, the wall of the shaft blank is formed in that plasticized material of the wall of the shaft blank enters into intertooth spaces of the forming mandrel toothing, and thereby forms a tooth profile on the inside of the wall of the shaft blank.

SUMMARY OF THE INVENTION

The object of the present invention is to provide for the case in which, after completion of the forming of the hollow body wall, the cross-section of the cavity delimited by the formed hollow body wall narrows over a partial length of the hollow body wall and thereby makes it more difficult to insert a counterpart to be received by the formed hollow body into the cavity of the formed hollow body. Such a cross-sectional narrowing of the cavity of the formed hollow body can be the result of a material-induced non-uniform elastic recovery of the hollow body wall over the length of the formed hollow body, which occurs automatically when the forming mandrel is removed from the interior of the hollow body after completion of the forming process. Another conceivable cause for a cross-sectional narrowing of the type mentioned is, for example, the subsequent attachment of an additional component to the outside of the finished formed hollow body wall, if the additional component encloses the hollow body wall annularly in its circumferential direction and is prestressed in the circumferential direction for fixing to the hollow body wall.

According to the invention, the aforementioned object is achieved by a method and a mechanical arrangement as described below.

In the case of the invention, a stepped forming mandrel is used, which has a mandrel portion with an enlarged cross-section and a mandrel portion with a reduced cross-section. A forming mandrel profile portion is provided on each of the mandrel portions. The forming mandrel profiles of the two mandrel portions preferably have an identical basic geometry, wherein the forming mandrel profile of the mandrel portion with an enlarged cross-section is scaled outwards in the transverse direction of the hollow body wall, i.e., towards the hollow body wall, compared to the forming mandrel profile of the mandrel portion with a reduced cross-section. The transition between the forming mandrel profile of the mandrel portion with an enlarged cross-section and the forming mandrel profile of the mandrel portion with a reduced cross-section can be stepped or continuous.

In order to form the hollow body wall which is to be provided with a wall profile on the inside, the forming mandrel is arranged inside the cavity of the hollow body in such a way that the mandrel portion with an enlarged cross-section comes to lie with its forming mandrel profile portion at the level of a first longitudinal portion of the hollow body wall. The mandrel portion with a reduced cross-section is arranged in the hollow body interior with its forming mandrel profile portion at the level of a second longitudinal portion of the hollow body wall following the first longitudinal portion of the hollow body wall along the hollow body wall. The longitudinal portion of the hollow body wall associated with the cross-sectionally enlarged mandrel portion can be located at one end of the hollow body, but can also be spaced from the hollow body ends.

During its forming movement, the forming die is moved by the forming drive along the hollow body wall relative to the mandrel portion of the forming mandrel with an enlarged cross-section and relative to the mandrel portion with a reduced cross-section. A die drive is preferably provided as the forming drive.

The hollow body wall is at least inhibited against movement in the direction of the forming movement of the forming die. For this purpose, a stop can be provided for the end, situated in the direction of the forming movement, of the hollow body to be formed. Alternatively or additionally, it is possible, among other things, to effectively fix the hollow body to be formed, during the forming movement of the forming die using a clamping device, in the direction of the forming movement of the forming die.

Due to the forming movement of the forming die and the associated plasticization of material of the hollow body wall, the forming mandrel profile portion of the cross-sectionally enlarged mandrel portion is reproduced, on the inside of the first longitudinal portion of the hollow body wall, as a first wall profile portion of the wall profile. On the inside of the second longitudinal portion of the hollow body wall, the forming mandrel profile portion of the reduced-cross-section mandrel portion creates a second wall profile portion of the wall profile.

The forming movement of the forming die can be carried out in one pass along the mandrel portion with an enlarged cross-section and along the mandrel portion with a reduced cross-section. However, it is also possible to divide the forming movement of the forming die into separate partial movements. In this case, the forming die can, for example, move, with a first partial movement of the forming movement, only along one of the two mandrel portions while reproducing its mandrel profile portion on the inside of a longitudinal portion of the hollow body wall assigned thereto, before the forming die—if necessary, after a previous repositioning of the forming mandrel along the hollow body wall to be formed—is moved, with a second partial movement of the forming movement, along the other of the two mandrel portions and then reproduces the mandrel profile portion of the other mandrel portion on the inside of a longitudinal portion of the hollow body wall assigned thereto.

As long as the forming mandrel is still inside the cavity of the formed hollow body, the hollow body provided with the wall profile has, in the region formed by the mandrel portion with an enlarged cross-section, a cavity cross-section which is delimited by the hollow body wall and which has an oversize compared to the cavity cross-section in the region of the hollow body formed by the mandrel portion with a reduced cross-section.

The oversize of the mandrel portion with an enlarged cross-section compared to the mandrel portion with a reduced cross-section is determined by calculation, simulation, and/or empirically and, for example, depending upon the specific application, in particular depending upon the material properties of the hollow body wall to be formed.

The oversize of the mandrel portion with an enlarged cross-section compared to the mandrel portion with a reduced cross-section can be selected in such a way that an elastic recovery of the hollow body wall, which occurs to a greater extent in the first longitudinal portion of the hollow body wall after the forming mandrel has been removed from the formed hollow body, is compensated for to an extent, due to which, after the forming mandrel has been removed from the formed hollow body, a uniform cavity cross-section that is matched to the cross-section of the counterpart to be received is permanently produced along the first and second longitudinal portions of the hollow body wall.

Alternatively, it is possible to dimension the oversize of the mandrel portion with the enlarged cross-section compared to the mandrel portion with the reduced cross-section in such a way that, after removal of the forming mandrel, in the first longitudinal portion of the hollow body wall an oversize of the cavity cross-section initially remains, compared to the cavity cross-section of the longitudinal portion(s) of the hollow body wall adjacent to the first longitudinal portion. This option for dimensioning the oversize of the mandrel portion with an enlarged cross-section compared to the mandrel portion with a reduced cross-section is preferably used in cases in which, after the forming process, an additional component is applied to the outside of the hollow body wall, which additional component surrounds the hollow body wall annularly in its circumferential direction and is prestressed in the circumferential direction for fixing to the hollow body wall, and thereby narrows the cavity cross-section existing before the application of the additional component. Under the effect of the additional component, the cavity cross-section at the first longitudinal portion of the formed hollow body wall adapts to the cavity cross-section in the region of the longitudinal portion(s) of the formed hollow body wall adjacent to the first longitudinal portion.

Particular embodiments of the method and of the mechanical arrangement are described below.

In a further development of the invention, the forming mandrel is arranged in the interior of the cavity of the hollow body in such a way that the forming mandrel extends with the mandrel portion with an enlarged cross-section at the level of a first longitudinal portion, provided with the cavity opening, of the hollow body wall. This measure according to the invention is particularly advantageous in view of the fact that an elastic recovery of the hollow body wall in the region of the cavity opening that is increased compared to the remaining length of the hollow body wall often occurs after the forming mandrel has been removed from the formed hollow body.

In a preferred embodiment of the method according to the invention, a mandrel movement of the forming mandrel directed counter to the forming movement of the forming die is superimposed on the forming movement of the forming die, wherein the forming mandrel is connected to the hollow body wall with a positive fit and/or with a non-positive fit during the mandrel movement. This is particularly recommended in cases in which the hollow body to be formed is at least inhibited, on the side of the forming die located in the direction of movement, against movement in the direction of movement of the forming die. Due to the forming movement of the forming die, the forming mandrel takes plasticized material of the hollow body wall with it in its direction of movement and thus prevents the hollow body wall from being undesirably compressed due to the forming movement of the forming die in the region that is located in front of the forming die in the direction of the forming movement.

In a further development of the mechanical arrangement according to the invention, a corresponding mandrel drive is provided for moving the forming mandrel. The mandrel movement preferably ends with the forming movement of the forming die. The distance traveled by the forming mandrel during the mandrel movement is in particular dimensioned in such a way that it corresponds to the increase in length of the hollow body wall caused by the forming process or slightly exceeds the increase in length of the hollow body wall.

Variants of the method according to the invention that are particularly relevant in practice are described below.

According to one embodiment, a wall toothing is created as the wall profile on the inside of the hollow body wall, with teeth and intertooth spaces running along the hollow body wall. The counterpart to be inserted into the formed hollow body is provided with a corresponding counter-toothing.

In a further development of the method, a further feature provides, in addition to the production of an internal toothing, the production of an external toothing on the hollow body to be formed. The external toothing of the formed hollow body wall can, for example, be used to attach and permanently position an additional component of the type mentioned above on the outside of the hollow body wall.

According to another embodiment, the hollow body to be formed is tubular in design. The hollow body wall designed as a tube wall is provided with an inner profile with an internal toothing and with an external toothing as described above.

As a result of the method, during the forming according to the invention, the dimension of the hollow body wall increases along the axis of movement of the forming movement of the forming die.

If the first longitudinal portion and the second longitudinal portion of the hollow body wall to be formed have a uniform thickness, the first longitudinal portion of the hollow body wall elongates proportionally more than the second longitudinal portion of the hollow body wall during the forming process, since the forming mandrel interacting with the forming die has a larger cross-section at the first longitudinal portion of the hollow body wall than at the second longitudinal portion of the hollow body wall.

In order to limit the method-induced increase in length of the hollow body wall during the forming process, a further embodiment provides, as a preparatory measure prior to the interaction of the forming die and the forming mandrel, a reduction in the thickness of the hollow body wall in the first longitudinal portion of the hollow body wall particularly affected by the method-induced elongation, compared to the thickness of the hollow body wall in the second longitudinal portion of the hollow body wall.

In a further development of the mechanical arrangement according to the invention, in order to reduce the thickness of the first longitudinal portion of the hollow body wall, a device, preferably designed as a rotary swaging device, is provided for partially reducing the thickness of the hollow body wall.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and features of the invention will become apparent from the following detailed description considered in connection with the accompanying drawings. It is to be understood, however, that the drawings are designed as an illustration only and not as a definition of the limits of the invention.

In the drawings,

FIG. 1 shows a shaft blank for the production of a profiled hollow shaft for a motor vehicle;

FIG. 2 shows a forming mandrel of a forming device for forming the shaft blank according to FIG. 1;

FIG. 3 shows a representation illustrating a forming process carried out using a mechanical arrangement for the production of a profiled hollow shaft from the shaft blank according to FIG. 1;

FIG. 4 shows a sectional view of the profiled hollow shaft manufactured from the shaft blank according to FIG. 1 in a sectional plane running along the line IV-IV in FIG. 3;

FIG. 5 shows representations illustrating a further forming process carried out using the mechanical arrangement according to FIG. 3 for the production of a profiled hollow shaft from the shaft blank according to FIG. 1; and

FIG. 6 shows representations illustrating a forming process carried out using the mechanical arrangement according to FIG. 3 for the production of a profiled hollow shaft from another shaft blank.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 shows a hollow body in the form of a tubular shaft blank 1 with a tubular wall 2 as the hollow body wall. The tube wall 2, which is circular in cross-section, is made of alloyed steel and is plastically deformable. It delimits a cavity 3 which is open on both sides and has a cavity opening 4 at one longitudinal end.

A profiled hollow shaft 100 for a motor vehicle is manufactured from the shaft blank 1 in the manner described below (FIG. 3).

To produce the profiled hollow shaft 100, a partial length l of the shaft blank 1 is formed by a mechanical arrangement 5 shown schematically in FIG. 3 and in the process is provided on the inside of the tube wall 2 with a wall toothing forming an internal toothing and with a wall toothing forming an external toothing.

The mechanical arrangement 5 has, as a forming device, a forming machine 6 with a forming tool 7, which in turn comprises a forming mandrel 8 and a forming die 9.

The forming mandrel 8 shown in isolation in FIG. 2 is provided with a forming mandrel profile in the form of a forming mandrel toothing 10. The forming mandrel toothing 10 comprises, as a first forming mandrel profile portion, a first forming mandrel toothing portion 11 on a mandrel portion 12 of the forming mandrel 8 with an enlarged cross-section and, as a second forming mandrel profile portion, a second forming mandrel toothing portion 13 on a mandrel portion 14 of the forming mandrel 8 with a reduced cross-section.

The forming toothings of the first forming mandrel toothing portion 11 and of the second forming mandrel toothing portion 13 have an identical basic geometry. However, the forming toothing of the first forming mandrel toothing portion 11 is scaled outwards in the radial direction of the forming mandrel 8 compared to the forming toothing of the second forming mandrel toothing portion 13. A continuous transition 15 is formed between the two mandrel toothing portions 11, 13.

The forming die 9 comprises a die opening 16 with a calibration section 17. At the calibration section 17 of the die opening 16, the forming die 9 is provided with a forming die toothing 18.

In addition to the forming mandrel 8 and the forming die 9, the forming machine 6 comprises a motorized mandrel drive 19, which in the example shown is hydraulic, and, as a forming drive, a motorized die drive 20, which in the example shown is also hydraulic.

To produce the wall toothings on the partial length l of the tube wall 2, the forming die 9 is moved by the die drive 20 to the right end of the shaft blank 1 in FIG. 1. The forming mandrel 8 is then advanced by means of the mandrel drive 19 through the die opening 16 of the forming die 9 into the cavity 3 of the tube wall 2 until the forming mandrel 8 projects with its leading end beyond the left-side boundary of the partial length l of the tube wall 2 in FIG. 1 and extends with the cross-sectionally widened mandrel section 12 at the level of the cavity opening 4 and along a first longitudinal section l₁ of the tube wall 2 provided with the cavity opening 4. The mandrel portion 14 with a reduced cross-section of the forming mandrel 8 comes to lie on the partial length l of the tube wall 2 at the level of a second longitudinal section l₂ of the tube wall 2 following the first longitudinal section of the tube wall 2 along the tube wall 2. The resulting positions of the forming mandrel 8 and the forming die 9 are indicated by dashed lines in FIG. 1.

In the circumferential direction of the tube wall 2, the forming mandrel 8 and the forming die 9 are aligned relative to one another in such a way that, on the tube wall 2, teeth of the forming die toothing 18 are situated opposite intertooth spaces of the forming mandrel toothing 10, and intertooth spaces of the forming die toothing 18 are situated opposite teeth of the forming mandrel toothing 10.

Following from the resulting conditions, the forming die 9 is moved by the die drive 20 with a movement in the direction of an arrow 21 along the tube wall 2 passing through the die opening 16 relative to the tube wall 2 and relative to the forming mandrel 8.

For the duration of the forming movement of the die 9, the shaft blank 1 is prevented from moving in the direction 21 of the forming movement of the forming die 9 by a clamping device 22 of the forming machine 6, which is shown highly schematically in FIG. 3.

The forming movement of the forming die 9 in the direction of the arrow 21 begins when the die opening 16 runs onto the tube wall 2. Already slightly earlier than this, a mandrel movement of the forming mandrel 8 in the direction of an arrow 23 begins, which movement is effected by the mandrel drive 19 and is directed opposite to the forming movement of the forming die 9.

With the start of the forming movement of the forming die 9, the tube wall 2 is pressed by the forming die 9 against the forming mandrel 8, thereby creating a non-positive, i.e. force-fit, connection between the tube wall 2 and the forming mandrel 8.

Due to the forming movement of the forming die 9, material of the tube wall 2 is plasticized. As a result, the forming die toothing 18 is reproduced on the outside of the tube wall 2, and the forming mandrel toothing 10 is reproduced on the inside of the tube wall 2. This creates a wall profile in the form of an external toothing 24 on the outside of the tube wall 2 and a wall profile in the form of an internal toothing 25 on the inside of the tube wall 2 (FIG. 4).

Due to the existing non-positive connection, the forming mandrel 8, during its mandrel movement opposite to the forming movement of the forming die 9, exerts tensile stress on the tube wall 2 in the direction of arrow 23. This prevents compression of the tube wall 2, fixed by the clamping device 22, on the side of the forming die 9 located in the direction 21 of the forming movement.

FIG. 3 shows the conditions at the end of the forming process.

Due to the method, the tube wall 2 has increased in length during its forming by the forming tool 7. The first longitudinal portion l₁ and the second longitudinal portion l₂ and thus also the partial length l of the tube wall 2 of the profiled hollow shaft 100 present after the forming are consequently each larger than the first longitudinal portion l₁, the second longitudinal portion l₂, and the partial length l of the tube wall 2 of the shaft blank 1.

If the forming mandrel 8 and the forming die 9 are removed from the profiled hollow shaft 100 after completion of the forming process, the formed tube wall 2 of the profiled hollow shaft 100 elastically recovers to a certain extent in the radial direction. This elastic recovery is more pronounced in the first longitudinal portion l₁ located near the hollow body opening 4 than in the region of the second longitudinal portion l₂ of the tube wall 2. Nevertheless, after removing the forming mandrel 8 and the forming die 9 from the profiled hollow shaft 100, due to the cross-sectional oversize—empirically measured in the present case—of the cross-sectionally enlarged mandrel portion 12 used for forming the first longitudinal portion l₁ of the tube wall 2, compared to the cross-sectionally reduced mandrel portion 14 used for the forming of the second longitudinal portion l₂ of the tube wall 2, there remains an oversize of the cavity cross-section of the first longitudinal portion l₁ compared to the cavity cross-section of the second longitudinal portion l₂ of the tube wall 2 of the profiled hollow shaft 100.

This machining result is desirable because, after the completion of the profiled hollow shaft 100 in the region of the first longitudinal portion l₁, an additional component is attached to the profiled hollow shaft 100, which component encloses the tube wall 2 of the profiled hollow shaft 100 in the circumferential direction and which is prestressed in the circumferential direction and thereby narrows the cross-section of the cavity 3 of the profiled hollow shaft 100 present in the region of the cavity opening 4 after completion of the forming process. In the example shown, an additional component is provided which is a rotary encoder (not shown) of a device for detecting the rotational position of the profiled hollow shaft 100 on the motor vehicle equipped with the profiled hollow shaft 100.

The oversize of the cavity cross-section of the first longitudinal portion l₁, initially present after completion of the forming process, compared to the second longitudinal portion l₂ of the tube wall 2 of the profiled hollow shaft 100, is dimensioned, due to a corresponding dimensioning of the cross-sectional oversize of the cross-sectionally enlarged mandrel portion 12 of the forming mandrel 8 compared to the cross-sectionally reduced mandrel portion 14 of the forming mandrel 8, in such a way that it is compensated for by the fixing of the additional component on the outside of the profiled hollow shaft 100, and consequently, after the fixing of the additional component on the first longitudinal portion l₁ and the second longitudinal portion l₂ of the tube wall 2 of the profiled hollow shaft 100, there results an at least approximately uniform cavity cross-section which is matched to the cross-section of the externally toothed counterpart to be received by the profiled hollow shaft 100.

As a further functional unit of the mechanical arrangement 5, a device designed as a rotary swaging device 26 for the partial thickness reduction of the tube wall 2 is shown in FIG. 3.

If necessary, in preparation for a forming process of the type described above, the rotary swaging device 26 can be used to reduce the thickness of the tube wall 2 of the shaft blank 1 in the first longitudinal portion l₁ compared to the thickness of the tube wall 2 in the second longitudinal portion l₂. As a result of the reduction in thickness, the increase in length of the first longitudinal portion l₁ of the tube wall 2 during the forming process is desirably reduced compared to the conditions in the case of uniform wall thickness.

The forming processes illustrated in FIGS. 5 and 6 are also carried out by the mechanical arrangement 5 shown in FIG. 3, and, in FIGS. 5 and 6, the shaft blank formed in each case is also fixed against movement in its longitudinal direction during the entire forming process by the clamping device 22. However, the method sequence and the position of the cross-sectionally enlarged longitudinal portion of the tube wall 2 on the profiled hollow shaft 100 differ from the method sequence and the method result of FIG. 3.

As in the case of the forming process according to FIG. 3, at the beginning of the forming process according to FIG. 5, the forming die 9 is also moved to the right end of the shaft blank 1 by the die drive 20, and the forming mandrel 8 is advanced by the mandrel drive 19 through the die opening 16 of the forming die 9 into the cavity 3 of the tube wall 2. The forming mandrel 8 pushed into the cavity 3 of the tube wall 2 also projects with its leading end beyond the left-side boundary in FIG. 1 of the partial length l of the tube wall 2 of the shaft blank 1, but the forming mandrel 8 is arranged in the interior of the cavity 3 of the tube wall 2 only with the mandrel portion 14 having a reduced cross-section. The cross-sectionally enlarged mandrel portion 12 initially remains outside the cavity 3.

Starting from this, the forming die 9 performs a first forming movement to the left in FIG. 5, while at the same time the forming mandrel 8 is moved in the opposite direction to the right in FIG. 5. At the end of this first method step, the conditions of the partial illustration (1) of FIG. 5 result. Using the forming die 9, the entire partial length l of the tube wall 2 of the shaft blank 1 was formed over the mandrel portion 14 of the forming mandrel 8 with a reduced cross-section and in the process was provided with an internal toothing.

Due to the method, the tube wall 2 has elongated. With its right-side end in the partial illustration (1) of FIG. 5, the formed tube wall 2 extends up to close to the transition 15 between the mandrel portion 14 with a reduced cross-section arranged inside the cavity 3 of the tube wall 2 and the mandrel portion 12 with an enlarged cross-section of the forming mandrel 8, which is still arranged outside the cavity 3.

With the forming die 9 remaining in the position of partial illustration (1), the forming mandrel 8 is now moved to the left in FIG. 5 such that the forming mandrel 8 with the mandrel portion 12 with the enlarged cross-section enters into the cavity 3 of the tube wall 2 and consequently widens the cavity 3 of the tube wall 2 at an end portion of the tube wall 2 on the right in FIG. 5, increasing the outer diameter of the tube wall 2 (partial illustration (2) of FIG. 5).

After completion of the mandrel movement, the forming die 9 sitting on the tube wall 2 is moved from its previous position in FIG. 5 to the right along the tube wall 2 and along the mandrel portion 14 with a reduced cross-section and, with a second forming movement, along a part of the mandrel portion 12 with an enlarged cross-section of the forming mandrel 8. During its forming movement over the relevant partial length of the cross-sectionally enlarged mandrel portion 12, the forming die 9 reduces, in the region of the cross-sectionally enlarged mandrel portion 12 that it passes through, the outer diameter of the tube wall 2, which was previously enlarged by the cross-sectionally enlarged mandrel portion 12, to the original outer diameter. At the same time, the widening of the cavity 3 inside the tube wall 2 caused by the mandrel portion 12 with an enlarged cross-section is maintained. The thickness of the tube wall 2 is consequently reduced over that partial length of the tube wall 2 which is arranged at the level of the partial length of the cross-sectionally enlarged mandrel portion 12 passed through by the forming die 9.

At the end of its second forming movement, the forming die 9 is arranged on the end portion of the tube wall 2 previously widened by the forming mandrel 8, at a distance from the cavity opening 4 (partial illustration (3) of FIG. 5).

The forming mandrel 8 does not change its position during the last-executed die movement. A mandrel movement counter to the movement of the forming die 9 can be dispensed with, since the tube wall 2, which is still fixed by the clamping device 22, is subjected to tensile stress by the forming die 9 moving to the right in FIG. 5, and therefore there is no need to fear any significant compression of the tube wall 2 on the side of the forming die 9 located in the direction of movement of the forming die 9.

After the forming die 9 has reached the position shown in the partial illustration (3) of FIG. 5, with the forming die 9 remaining in its position, the forming mandrel 8 is moved out of the cavity 3 of the tube wall 2 to the right in FIG. 5 with the cross-sectionally enlarged mandrel portion 12. As a result, the forming mandrel 8 with the cross-sectionally reduced mandrel portion 14 comes to lie inside the cavity 3 of the tube wall 2 at the level of the end portion of the tube wall 2 which was not previously passed by the forming die 9 (partial illustration (4) of FIG. 5).

Finally, the forming die 9 is moved to the right from its position according to the partial illustrations (3) and (4) of FIG. 5. In doing so, the forming die 9 eliminates, over the partial length of the end portion of the tube wall 2 that it passes through, the enlargement of the outer diameter of the tube wall 2 caused by the mandrel portion 12 with an enlarged cross-section in the method step according to partial illustration (2) of FIG. 5. Since the forming die 9 moves along the mandrel portion 14 with a reduced cross-section, the reduction in the outer diameter does not result in a thinning of the tube wall 2, but does result in a reduction of the cavity cross-section enlarged in the method step according to the partial illustration (2) of FIG. 5.

The result of the forming process according to FIG. 5 is the profiled hollow shaft 100 shown in partial illustration (6) of FIG. 5.

Over the entire partial length l, the profiled hollow shaft 100 has a uniform outer diameter and an external toothing running without offset along the tube wall 2. In two longitudinal portions l₂ of the partial length l, the cavity 3 of the formed tube wall 2 has a uniform cross-section, and the tube wall 2 has the same thickness. In a longitudinal portion l₁ lying between the longitudinal portions l₂ and spaced apart from the cavity opening 4, the cross-section of the cavity 3 of the formed tube wall 2 is enlarged compared to the cavity cross-section in the two longitudinal portions l₂. The thickness of the tube wall 2 in the longitudinal portion l₁ is smaller than the thickness of the tube wall 2 in the two longitudinal portions l₂.

The geometry of the shaft blank formed according to FIG. 6 differs from the geometry of the shaft blank machined according to FIGS. 3 and 5. In particular, the geometry of the shaft blank formed according to FIG. 6 allows the forming mandrel 8 to be inserted into the shaft blank from the left side in FIG. 6 far enough that the forming mandrel 8 comes to lie with the mandrel portion 12 with the enlarged cross-section and with the mandrel portion 14 with the reduced cross-section at the level of the partial length l of the shaft blank to be formed.

As in the case of the forming processes according to FIGS. 3 and 5, at the beginning of the forming process according to FIG. 6, the forming die 9 is moved by the die drive 20 to the right end of the shaft blank to be formed. The forming mandrel 8 is advanced into the cavity 3 of the tube wall 2 from the opposite side by the mandrel drive 19 in FIG. 6.

The forming mandrel 8 introduced into the cavity 3 of the tube wall 2 extends with the cross-sectionally enlarged mandrel portion 12 along a first longitudinal portion l₁ of the tube wall 2 arranged at a distance from the longitudinal ends of the shaft blank. The mandrel portion 14 with a reduced cross-section of the forming mandrel 8 comes to lie on the partial length l of the tube wall 2 at the level of a second longitudinal section l₂ of the tube wall 2 following the first longitudinal section l₁ of the tube wall 2 along the tube wall 2.

Based upon the resulting conditions, the forming die 9 is moved to the left in FIG. 6 by the die drive 20, with a forming movement. The forming movement of the forming die 9 is superimposed by a movement of the forming mandrel 8 directed to the right in FIG. 6, using the mandrel drive 19.

In addition to the non-positive connection produced by the forming die 9, there is also a positive connection between the forming mandrel 8 and the tube wall 2 at the transition 15 between the mandrel portion 12 with an enlarged cross-section and the mandrel portion 14 with a reduced cross-section.

After completion of the forming of the tube wall 2, the forming die 9 is moved to the right, starting from the conditions shown in partial illustration (1) of FIG. 6. The forming mandrel 8 is removed from the cavity 3 of the now-profiled hollow shaft 100 with a movement directed to the left in FIG. 6.

The partial length l of the tube wall 2 of the profiled hollow shaft 100 shown in partial illustration (2) of FIG. 6 has a longitudinal portion l₁ and a longitudinal portion l₂ with a uniform outer diameter and an external toothing running without offset in the longitudinal direction of the tube wall 2. The cross-section of the cavity 3 inside the internally toothed tube wall 2 is enlarged in the longitudinal portion l₁ compared to the cavity cross-section in the longitudinal portion l₂. In the longitudinal portion l₁, the tube wall 2 is thinner than in the longitudinal portion l₂.

Also prior to the forming processes illustrated in FIGS. 5 and 6, the thickness of the tube wall 2 to be formed can be reduced, using the rotary swaging device 26 of the machine arrangement 5, in that region which is assigned to the cross-sectionally enlarged mandrel portion 12 of the forming mandrel 8 in the subsequent forming process.

Although only a few embodiments of the present invention have been shown and described, it is to be understood that many changes and modifications may be made thereunto without departing from the spirit and scope of the invention.