EP1995001A1 - Method and device for producing pipe connections - Google Patents

Abstract

The method involves fixing a pipe section in a matrix (9), opening out a pipe end (6) of the pipe section using a form bolt under the formation or removal of a profile of the pipe section. The form bolt has a layer (20) with a polygonal cross-section and another layer (21) with a round cross-section. An expanding device (23) is attached on the pipe end. The open-out pipe end is stretched in an axial direction during an expansion process. An independent claim is also included for a device for executing a method for producing pipe connections.

Description

The invention relates to a method and an apparatus for producing pipe connections, fittings and the like, in particular threaded connection.

Fittings are mass-produced goods that can be produced in extremely high quantities with maximum efficiency. However, compromises on quality must not be made. This places high demands on mechanical engineering, mold making and process engineering. As a "threaded connector" fittings are referred to in practice, having a threaded end and a set up for press-fitting end.

From the DE 100 31 989 A1 For example, a method of making stainless steel fittings is known. This method utilizes a die in which a pipe section is to be inserted as a blank and a compression mandrel which is pressed into the pipe end to widen the pipe end. The pipe wall is stretched in the circumferential direction. In addition, with a shoulder formed on the mandrel axial pressure is exerted on the front end of the pipe section, so that the pipe wall is compressed in the axial direction. This Process is used to produce an annular bead running all around the pipe wall into which an O-ring can be inserted as a seal.

Another method for producing press fitting, preferably made of copper, is known from DE 43 36 261 A1 known. This document discloses a multi-step process in which a pipe section is inserted as a blank in a split die. The blank thus held is compressed by means of a mandrel in the axial direction and possibly slightly widened. At the tube wall of the pipe end, an annular bead around running material forms. In a further step, the bead or bead is rolled from the inside with a roller running on an orbital track in order to form a smooth flawless seat for an O-ring.

The main focus of the previously known methods was the production of fittings with a seat for an O-ring. The fittings had the same connection technology at both ends, ie. each an O-ring seat and a pressing area for connecting a pipe. But the tube wall is so thin that no common thread can be applied if a threaded connector is to be produced.

From the DE 10 2005 014 940 A1 is a fitting with threaded connection and press connection is known, which is produced in a forming process. The thicker wall thickness for the threaded connection is produced by upsetting. The thread must then be created on the axially compressed material.

The object of the present invention is to provide a robust and highly efficient production process for the production of fittings, which at their two mutually opposite ends use a different connection technology.

Another object of the invention is to produce fittings having a section of non-round cross-section.

• Bei dem erfindungsgemäßen Verfahren wird das als Rohling dienende Rohrstück in eine Form oder Matrize eingesetzt und darin fixiert. Danach werden in beliebiger geeigneter Reihenfolge ein Abschnitt des Rohrstücks mittels eines Formdorns aufgeweitet, wobei eine vorhandene Profilierung des Rohrstücks beseitigt oder eine nicht vorhandene Profilierung des Rohrstücks erzeugt werden kann und es wird (vorher oder danach) eine Ziehvorrichtung auf das Rohrende aufgesetzt. Mit der Ziehvorrichtung wird an dem Rohrende ein Ziehvorgang ausgeführt, in dessen Verlauf das Rohrende in Axialrichtung gedehnt wird. Dadurch wird eine Reduktion der Wandstärke erreicht. Es entsteht ein Zwischenformling mit zwei Enden, die unterschiedliche Wandstärken aufweisen.

This object is achieved by the method according to claim 1 and with the device according to claim 14:

• In the method according to the invention, the tube piece serving as a blank is inserted into a mold or die and fixed therein. Thereafter, in any suitable order, a section of the pipe section is widened by means of a forming mandrel, whereby an existing profiling of the pipe section can be eliminated or a non-existent profiling of the pipe section can be produced and a drawing device is placed on the pipe end (before or after it). With the pulling device, a drawing operation is carried out at the pipe end, in the course of which the pipe end is stretched in the axial direction. As a result, a reduction of the wall thickness is achieved. The result is an intermediate molding with two ends, which have different wall thicknesses.

In this way, pipe sections can be formed into a product having a first end with thicker wall thickness, a second end with thinner wall thickness and between a profiled, eg octagonal or hexagonal section. At the two pipe ends different connection techniques can be realized. For example, the thick-walled pipe end may be provided with an external thread, an internal thread or other connecting means which requires a thicker wall. The thinner-walled tube end may be provided with another connection means, such as an annular bead into which an O-ring is to be inserted, the tube end then how to handle a pressfitting. It can also serve as a solder connection. Other joining techniques, which tend to favor thin-walled pipe ends, can also be used.

Preferably, the expansion of the pipe end takes place in two sub-steps. For this purpose, two different mandrels are used. The first mandrel is used in a first expansion step to expand the pipe end to a small diameter. In this case, a profiling can be generated in an intermediate portion of the pipe section. The profiling can for example be a hexagonal, octagonal or other profiling. This can be generated to final dimensions. However, the pipe end adjoining the profiled area is preferably widened to a desired extent. If the pipe piece serving as a blank already had an initial profile, this can be eliminated during the expansion. The cross section of the pipe end is then round regardless of an existing initial profile in any case.

The production (or preservation) of the profiling in the intermediate section and the widening of the pipe end are preferably carried out in a die which surrounds the profiled region of the pipe end on the outside. This part of the die is preferably formed in two or more parts, the parts being movable e.g. are mounted radially adjustable.

Another method step is a drawing operation to be performed at the pipe end. To carry out the same, a pulling device is attached to the pipe end. To the pulling device preferably include a pipe end outside the comprehensive draw ring and a mandrel. As a mandrel, for example, the Aufweitdorn the Aufweitschritts serve. If the widening step runs in two stages, this can be done for the second Expander used forming mandrel can be used as part of the pulling device.

During the drawing process, the wall thickness of the pipe end is reduced. It can be reduced to the appropriate level, for example, to form a compression nozzle. Other processing steps may follow, such as facing the end face of the pipe end, attaching one or more annular beads to accommodate O-rings or other elements, etc.

The continuation of the process now takes place at a second pipe end, which should preferably retain a thicker wall thickness. The pipe end can be widened with a further mandrel, for which purpose it is accommodated in the die, which conforms to the outside of the pipe end. If a tapered thread is to be attached to the pipe end, the pipe end can be radially compressed to obtain a conical basic shape. In this case, the pipe end, if necessary, be supported by one or more movable moldings from the inside.

If the blank initially had a polygonal cross-section, the polygonal shape can be removed during the widening step in order to give the pipe end a circular cross-section.

At the formation of the desired shape of the pipe end may be followed by another processing step such as facing, in which the end face of the pipe end is rotated smoothly. In further processing steps can be cut, rolled or otherwise applied to the outer surface of the pipe end an external thread.

If the pipe end has been widened conically, a conical internal thread can also be attached.

If the pipe end is cylindrical, an internal and / or external thread can be attached. In addition, grooves or flanges may be attached to seals or other sealants.

Further modifications are possible. Further advantageous details of the invention will become apparent from the drawing, the description or claims. The description and the drawing are limited to essential aspects of the invention and other circumstances. The drawing complements the description in the usual way.

• Figur 1 ein Rohrstück als Rohling, aus dem ein Fitting herzustellen ist, in längs geschnittener Ansicht,
• Figur 2 den Rohling nach Figur 1 in Draufsicht,
• Figur 3 eine Matrize mit zugehörigem Aufweitdorn nach Durchführung eines ersten Aufweitschritts in längs geschnittener Darstellung,
• Figur 4 die Matrize und eine Ziehvorrichtung sowie einen zweiten Aufweitdorn nach Durchführung des zweiten Aufweitschritts in längs geschnittener Darstellung,
• Figur 5 die Vorrichtung nach Figur 4 beim Durchführen eines Ziehvorgangs,
• Figur 6 eine Matrize und den Zwischenformling sowie einen Formdorn zur Aufweitung des zweiten Rohrendes,
• Figur 7 eine Matrize und Schieber zum Überführen des Rohrendes in eine Konusform in längs geschnittener Darstellung,
• Figur 8 eine zu der Vorrichtung nach Figur 7 alternative Ausführungsform in längs geschnittener Darstellung,
• Figur 9 den weitgehend fertig bearbeiteten Fitting in teilweise geschnittener Seitenansicht,
• Figur 10 den Fitting nach Figur 9 in Draufsicht,
• Figur 11 ein achteckiges Rechteckrohr in längs geschnittener Darstellung als Rohling für eine alternative Ausführungsform des erfindungsgemäßen Verfahrens,
• Figur 12 den Rohling nach Figur 11 in Draufsicht,
• Figur 13 eine Matrize, einen Aufweitdorn und den Rohling nach dem ersten Aufweitschritt in längs geschnittener Darstellung,
• Figur 14 die Matrize, einen zweiten Aufweitdorn und eine Ziehvorrichtung nebst Rohling nach Durchführung eines zweiten Aufweitschritts,
• Figur 15 die Matrize, den Rohling und die Ziehvorrichtung nach Durchführung des Ziehvorgangs in längs geschnittener Darstellung,
• Figur 16 eine Matrize und einen Aufweitdorn zur Aufweitung des zweiten Rohrendes nach Durchführung des Aufweitschritts in längs geschnittener Darstellung,
• Figur 17 eine Matrize und Schieberelemente zum konischen Verjüngen des Rohlings in längs geschnittener Prinzipdarstellung,
• Figur 18 eine alternative Ausführungsform der Vorrichtung zur Durchführung des Verfahrensschritts gemäß Figur 17 in längs geschnittener Darstellung,
• Figur 19 den weitgehend fertig gestellten Fitting in teilweise geschnittener Seitenansicht und
• Figur 20 den Fitting nach Figur 19 in Draufsicht.

In the drawings, embodiments of the invention are illustrated. Show it:

• FIG. 1 a piece of pipe as a blank, from which a fitting is to be made, in a longitudinal sectional view,
• FIG. 2 the blank after FIG. 1 in plan view,
• FIG. 3 a die with associated mandrel after performing a first Aufweitschritts in longitudinal section,
• FIG. 4 the die and a pulling device and a second mandrel after performing the second Aufweitschritts in longitudinal section,
• FIG. 5 the device after FIG. 4 when performing a drag,
• FIG. 6 a die and the intermediate molding and a forming mandrel for widening the second pipe end,
• FIG. 7 a die and slide for transferring the pipe end into a cone shape in longitudinal section,
• FIG. 8 one to the device after FIG. 7 alternative embodiment in longitudinal section,
• FIG. 9 the largely finished fitting in a partially sectioned side view,
• FIG. 10 the fitting after FIG. 9 in plan view,
• FIG. 11 an octagonal rectangular tube in longitudinal section as a blank for an alternative embodiment of the method according to the invention,
• FIG. 12 the blank after FIG. 11 in plan view,
• FIG. 13 a die, a mandrel and the blank after the first expansion step in longitudinal section,
• FIG. 14 the die, a second mandrel and a drawing device together with blank after performing a second Aufweitschritts,
• FIG. 15 the die, the blank and the drawing device after performing the drawing process in longitudinal section,
• FIG. 16 a die and an expanding mandrel for widening the second pipe end after performing the Aufweitschritts in longitudinal sectional view,
• FIG. 17 a die and slide elements for conically tapering the blank in a longitudinally sectioned schematic diagram,
• FIG. 18 an alternative embodiment of the apparatus for performing the method step according to FIG. 17 in longitudinal section,
• FIG. 19 the largely finished fitting in a partially sectioned side view and
• FIG. 20 the fitting after FIG. 19 in plan view.

In FIG. 1 a pipe section 1 is illustrated, from which the in FIG. 9 illustrated fitting 2 is to be produced. As FIG. 2 illustrated the pipe section 1 originally has a circular cross-section. The fitting 2, however, has two differently shaped ends 3, 4 and an interposed polygonal intermediate section 5. This one can, like FIG. 10 shows, have an octagonal cross section or a deviating cross section. The ends 3, 4 have emerged from the pipe ends 6, 7 of the pipe section 1. Between the pipe ends 6, 7 is a section 8, which is formed into the polygonal intermediate section 5. The section 8 and the pipe ends 6, 7 preferably have a matching diameter and cross-section.

For the implementation of the forming process, for example, a device is used which in the FIGS. 3, 4, 5 . 6 and alternatively contains 7 or 8 illustrated components. A first forming step is in FIG. 3 carried out. For this purpose, a die 9 is provided which has a central bore for receiving the pipe end 7 and also the end face 10 of the pipe end 7 is supported. To the die 7 may also include a core 11 which sits in the bore of the die and the pipe end 7 is supported from the inside.

Above the die further to the die associated with mold parts 12, 13 are provided, which define a polygonal cross section. This polygonal cross-section preferably corresponds to the desired outer shape of the intermediate section 5. The molded parts 12, 13 are preferably radially adjustable. There may be provided two, three or more correspondingly cooperating moldings, which are connected to not further illustrated adjusting devices.

For expanding the pipe end 6 and for shaping the portion 8 is an expanding mandrel 14, which is divided into several sections. A first section 15 has a cross section corresponding to the internal cross section of the parts 12, 13, but it has a reduced by the wall thickness of the intermediate portion 5 size. In the present example, section 15 is octagonal. The section 15 is followed by another preferably slightly conical section 16, which serves to expand the pipe end 6. On the outside, the pipe end 6 is surrounded by an annular die part 17, which has a cylindrical opening for this purpose. Between the sections 15 and 16, a transition section 18 is arranged, which forms a rounded transition between the sections 15, 16.

To carry out a second method step, the device is after FIG. 4 intended. To her belong a matrix 9, with the matrix 9 after FIG. 3 may be identical (but not necessarily). In turn, a core 11 is disposed therein to secure the pipe end 7 and prevent it from collapsing inwardly. To carry out the second expansion step, an expanding mandrel 19 is provided which in turn has a polygonal section 20 and a nearly cylindrical section 21 (of larger diameter). Between the two sections 20, 21, a relatively steep shoulder 22 is provided to bring the fitting to be produced in the corresponding area to final shape.

Instead of the female part 17, a draw ring 23 is now positioned over the pipe end 6. The draw ring 23 has an opening 24 which is substantially cylindrical or slightly conical. Its lower edge is formed by an annular surface 25 whose diameter is slightly larger than the diameter of the section 21 of the mandrel 19. The existing after expansion wall thickness of the pipe end. 6 However, is greater than the difference in diameter between the portion 21 and the annular surface 25. Accordingly, between the annular surface 25 and the remaining opening 24 is an in FIG. 4 indicated stage 22a present.

FIG. 6 illustrates a further die 26 for the continuation of the manufacturing process at the second tube end 7. The die 26 is constructed in several parts. A lower annular part 27 has a cylindrical opening with diameter of the first pipe end 6. In the interior of the pipe end 6, a core 28 may be placed, which supports the pipe end 6 inwardly and prevents it from collapsing under the influence of axial pressure.

The intermediate portion 5 may be encompassed by a plurality of adjustably mounted die parts 29, 30, the inner shape of which is adapted to the intermediate portion 5, to lie smoothly against this. Further die parts 31, 32 can surround a transition region 33 of the fitting 2 in order to support it. An upper die part 34 supports the pipe end 7 to the outside and has for this purpose a cylindrical passage opening of corresponding diameter.

The device after FIG. 6 is associated with an expanding mandrel 35 having a lower portion 36. This is adapted to the inner shape of the polygonal intermediate portion 5. A substantially cylindrical or slightly conical section 37, which serves to widen the pipe end 7, adjoins this via a rounded shoulder.

To further carry out the shaping process according to the invention, the device as shown FIG. 7 be designed to be visible. Again, the pipe end 6 is surrounded by a part 27 of a die 26, which also has die parts 29 to 32. These parts can be the same as in FIG. 6 be. It is also possible for the piece of pipe from the die 26 to FIG. 6 in a same or similar trained mold 26 after FIG. 7 to convict. However, the upper die part 34 is missing, so that the pipe end 7 protrudes freely out of the die 26. It can now elements 38, 39 of a pusher 40 act on the outside of the pipe end 7 in order to apply this with a radially inwardly directed force. The elements 38, 39 may be connected to a drive means connected in the radial direction movable slides, fingers or the like, which attach in particular to the upper edge of the pipe end 7. In addition, it is possible to combine the elements 38, 39 into a ring having a conical passage opening 41. By pressing the ring on the pipe end 7 this is converted into a corresponding cone.

Like the variant after FIG. 8 shows it is also possible and useful in many cases, when pressing the ring 38, 39, the pipe end 7 from the inside with a mandrel 42 support. This can consist of several movably mounted elements that can be adjusted in the radial direction. As a result, the diameter of the mandrel 42 can be changed in order first to expand it in the interior of the pipe end 7 and then to convert the pipe end 7 with the ring 38, 39 into a conical shape. Thereafter, the mandrel 42 can be reduced in diameter again and extended out of the pipe end 7.

• Zur Herstellung des Fittings 2 wird das Rohrstück 1 in die Matrize 9 nach Figur 3 eingesetzt. Mit dem Aufweitdorn 14 wird dann das Rohrende 6 aufgeweitet und der Zwischenabschnitt 5 in die Polygonalform überführt. Dies geschieht, indem der Dorn 14 in Richtung des Pfeils F in das Rohrende

6 und den Abschnitt 8 eingefahren und wieder heraus bewegt wird.The device described so far operates as follows:

• To produce the fitting 2, the pipe section 1 in the die 9 after FIG. 3 used. With the expanding mandrel 14, the pipe end 6 is then expanded and the intermediate section 5 is converted into the polygonal shape. This is done by the mandrel 14 in the direction of arrow F in the pipe end

6 and the section 8 retracted and moved out again.

After performing this first Aufweitschritts the mold parts 12, 13 and the female part 17 are removed. It is then moved the drawing ring 23 via the pipe end 6. The diameter thereof is slightly smaller than the diameter of the annular surface 25, so that the drawing ring 23 fits over the pipe end 6. Then, in a second widening step, the expanding mandrel 19 is retracted into the pipe end 6, which is thereby further widened. Its outer diameter is now larger than the inner diameter of the annular surface 25. This state is in FIG. 4 illustrated.

In a next step, in FIG. 5 is illustrated, there is a drag operation. In this it is assumed that the pipe end 7 is clamped between the core 11 and the annular lower part of the die 9 or otherwise secured against axial tension. While the expanding mandrel 19 is still seated in the pipe end 6 and the intermediate section 5, the drawing ring 23 in the axial direction ( FIG. 5 up) moves. With the annular surface 25, the wall thickness of the pipe end 6 is now reduced. The pipe end 6 expands in the axial direction. FIG. 5 illustrates the end of this drawing process.

At this stage, an intermediate molding is created, which has two pipe ends 6, 7 with different wall thicknesses. For individual applications, the intermediate molding may already be sufficiently processed. Mostly, however, further processing steps are required. For example, it may be necessary to smooth the upper edge, ie the end face of the pipe end 6, for example by facing. This process is not further illustrated.

FIG. 6 illustrates further processing steps that can be performed on the pipe end 7. For example, it may be important to further expand this. For this purpose, the female part 34 is pushed onto the pipe end 7 and made an expansion by means of the expanding mandrel 35. The female part 34 may be formed in one or more parts. Multi-part die parts can also be moved radially.

If, for example, a cone thread to be applied to the pipe end 7, the pipe end 7, as FIG. 7 illustrated, first converted into a cone shape. For this purpose, for example, a female part, which consists of a closed ring or individual parts 38, 39 is used. FIG. 7 illustrates the parts 38, 39 combined into a ring which is pressed in the direction of the arrow F on the pipe end 7. Its passage opening 41 characterizes the cone shape on the pipe end. 7

Alternatively, the tube end 7 can be supported in this process by the mandrel 42 from the inside, as FIG. 8 illustrated. It is also possible to make a conical widening of the pipe end 7.

After performing this step, the front end of the pipe end 7 can, if necessary, be turned flat or otherwise smoothed. In addition, other shapes can be attached to the fitting 2, for example by providing the pipe end 7 with a conical external thread. The fitting 2 is then completed.

• Die Matrize 9 weist eine polygonale Öffnung auf, die an die Polygonalform des Rohrendes 7 angepasst ist. Ebenso weist der Kern 11 einen Polygonalquerschnitt auf. Der Matrizenteil 17 hat hingegen eine vorzugsweise zylindrische Bohrung zur Aufnahme des aufzuweitenden Rohrendes 6. An seiner Unterseite kann er mit einem Bund 43 versehen sein, der die Formteile 12, 13 radial nach außen abstützt. Die entsprechenden Anlageflächen der Formteile 12, 13 und der Bund 43 können zu einer Längsmittelachse der Matrize 9 und des Rohrstücks 1 schräg angeordnet sein, so dass eine axiale Zustellbewegung des Matrizenteils 17 die Formteile 12, 13 radial nach innen gegen den profilierten Zwischenabschnitt 5 spannt.

The FIGS. 13 to 18 illustrate an alternative embodiment of the apparatus for performing the method on a pipe section 1 with polygonal cross-section, as the FIGS. 11 and 12 illustrate. For the device according to the FIGS. 13 to 18 and the fitting 2 after the FIGS. 19 and 20 apply the statements of the previous Description based on the already introduced reference numerals accordingly. In addition, the following applies:

• The die 9 has a polygonal opening which is adapted to the polygonal shape of the pipe end 7. Likewise, the core 11 has a polygonal cross section. The female part 17, however, has a preferably cylindrical bore for receiving the pipe end 6 to be expanded. On its underside, it can be provided with a collar 43, which supports the molded parts 12, 13 radially outward. The corresponding abutment surfaces of the mold parts 12, 13 and the collar 43 may be arranged obliquely to a longitudinal center axis of the die 9 and the pipe section 1, so that an axial feed movement of the female part 17, the mold parts 12, 13 biases against the profiled intermediate section 5 radially inwardly.

If the expanding mandrel 14 retracted into the pipe end 6, he expands this, with his section 16 eliminates the profiling. However, it remains in the area of the intermediate section 5.

Below is how FIG. 14 shows, pushed onto the expanded pipe end 6 of the pull ring 23. Then, the tube end 6 is widened so far by means of the second expanding mandrel 19 that its outer diameter exceeds the inner diameter of the annular surface 25. It closes, like FIG. 15 indicates the drawing step as already related to FIG. 5 has been described. The die 9 and the core 11 can be used to carry out the steps according to the FIGS. 13 to 15 be the same, ie the steps can all run in one station. The same applies with regard to FIGS. 3 to 5 ,

The further deformation of the pipe end 7 takes place according to the FIGS. 16 to 18 similar to that described above Wise. However, there is a difference in the deformation of the pipe end 7, which initially has a polygonal shape after performing the drawing step. The Aufweitdorn 35 eliminates the polygonal shape when it is retracted into the pipe end 7. Its cylindrical or slightly conical section 37 presses the tube wall smoothly against the corresponding cylindrical or slightly conical wall of the female part 34. Then, the pipe end 7, like the FIGS. 17 and 18 either with internal support by the mandrel 42 (FIG. FIG. 18 ) or without the same are converted into a cone shape, for which purpose the pressing device 40 is used. The obtained fitting 2 after FIGS. 19 and 20 corresponds to the fitting 2 after FIGS. 9 and 10 ,

Apparatuses and methods have been illustrated for making fittings 2 having different ends 3, 4 at which different joining measures can be accomplished. For example, the fitting 2 is a threaded connector, one end of which 4 may be formed as a press fitting and the other end 3 as a threaded end. Between the two ends 3, 4, an intermediate portion 5 is arranged with preferably polygonal cross-section. The preparation takes place starting from a pipe section 1 in a few process-safe process steps.

LIST OF REFERENCE NUMBERS

1

pipe section

2

fitting

3, 4

end up

5

intermediate section

6, 7

pipe end

8th

section

9

die

10

front

11

core

12, 13

moldings

14

mandrel

15, 16

section

17

female member

18

Transition section

19

mandrel

20, 21

section

22

Shoulder, 22a

23

drawing ring

24

opening

25

ring surface

26

die

27

part

28

core

29-32

female parts

33

Transition area

34

female member

35

mandrel

36, 37

section

38, 39

elements

40

pusher

41

Through opening

42

mandrel

43

Federation

F

arrow

Claims (22)

Method for producing pipe connections, in particular threaded connectors, with the following steps: Inserting a pipe section (1) into a die (9), Expanding a first pipe end (6) of the pipe section (1) by means of a forming mandrel (14) while forming or eliminating a profiling of the pipe section (1), Placing a pulling device (23) on the pipe end (6), Performing a pulling operation on the flared pipe end (6). A method according to claim 1, characterized in that the expansion of the pipe end (6) is carried out in two sub-steps. A method according to claim 2, characterized in that the pipe section is expanded in a first expansion step with a forming mandrel (14) to a predetermined extent, which is smaller than a nominal dimension. A method according to claim 2, characterized in that the pipe end (6) is widened in a second expansion step to a specified size. A method according to claim 1, characterized in that the pipe end (6) within the pulling device (23) is widened before performing the drawing operation. A method according to claim 4, characterized in that the second expansion step is performed within the pulling device (23). A method according to claim 1, characterized in that the first pipe end (6) is stretched during the drawing process in the axial direction, wherein its wall thickness is reduced. A method according to claim 1, characterized in that a second portion of the pipe section (1) which forms a second pipe end (7) is widened. A method according to claim 1, characterized in that a second portion of the pipe section (1) forming a second pipe end (7) is converted into a conical shape. A method according to claim 1, characterized in that a second portion of the pipe section (1) which forms a second pipe end (7) is provided with a thread. A method according to claim 1, characterized in that the forming mandrel (14, 19) has a section (15, 20) with a polygonal cross section and a section (16, 21) with a round cross section and that the tubular piece (1) at an intermediate portion (5 ), which is to maintain or maintain a polygonal cross-section, is supported in a mold section (12, 13) having the nominal dimension of the polygonal intermediate section (5). A method according to claim 1, characterized in that the pipe section (1) before carrying out the method has a circular cross-section. A method according to claim 1, characterized in that the pipe section (1) before carrying out the method has a polygonal cross-section. Device, in particular for carrying out the method according to claim 1,
with a first die part (9) which has an opening adapted to receive a pipe section (1) and adapted to the diameter of the pipe section (1),
with a second die part (12, 13) having a polygonal inner shape through which the pipe piece (1) extends,
with at least one expanding mandrel (14, 19) connected to a drive means for being axially moved into and out of a first pipe end (6) of the pipe section (1), and
with a pulling device (23) for axially stretching the tube end (6) widened by the expanding mandrel (14, 19). Apparatus according to claim 14, characterized in that the opening of the first Matrietzenteils (9) has a circular cross-section. Apparatus according to claim 14, characterized in that the opening of the first mold part (9) has a polygonal cross-section. Apparatus according to claim 14, characterized in that the second mold part (12, 13) in at least two radially adjustable mounted parts is divided. Apparatus according to claim 14, characterized in that at least two successive expanding mandrels (14, 19) are provided with different sizes. Apparatus according to claim 18, characterized in that the second expanding mandrel (19) of the pulling device (23) is associated. Apparatus according to claim 14, characterized in that the drawing device includes a drawing ring (23) which is positioned around the outer periphery of the portion to be expanded of the pipe end (6), while the mandrel is retracted into the pipe end (6). Apparatus according to claim 14, characterized in that the apparatus includes a die (26, 34) and an expanding mandrel (35) for a second portion of the pipe section (1) forming a second pipe end (7). Apparatus according to claim 14, characterized in that to the device comprises a pressing means (40) for transferring the axially non-stretched portion of the pipe end (7) in a cone shape.

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