EP3924114B1 - Method and apparatus for axially shaping a tube - Google Patents

Description

The invention relates to a method according to the preamble of patent claim 1 and a device according to the preamble of patent claim 10 for axially forming a pipe with the aid of a mandrel guided in the pipe and an annular die guided on the outside of the pipe.

State of the art

Axial forming of pipes has been established in the metal industry for decades. Indentations, widening and special contours such as serrations, squares, etc. are among the standard applications. Axial forming means resource efficiency, uninterrupted fiber flow, work hardening of the pipe material and good surface quality of the formed areas. The main area of application for axial forming of pipes is the production of components for the automotive industry and general mechanical engineering. With the help of axial forming, lightweight components in particular can be easily manufactured; this is why axial forming is also used in current topics such as electromobility or the reduction of CO2 emissions. The forming is carried out with the help of a mandrel guided in the pipe and an annular die guided on the outside of the pipe, the inner diameter of which is usually smaller than the original outer diameter of the pipe. The Energy for the forming work is provided by both hydraulic and electromechanical systems.

A sub-case of general tube forming is the so-called axial stretching or ironing of the tube; see for example the textbook " Manufacturing technology by Fritz Schulze, Springer Vieweg Verlag, 10th edition, page 445, chapter 5.4.3 . During axial ironing, the annular gap between the die and the mandrel is typically set to a distance that is smaller than the original wall thickness of the pipe to be formed. The die and mandrel tool pair is then guided in the axial direction along the pipe to be formed, thereby reducing the wall thickness of the pipe accordingly.

The publication US 6 779 375 31 discloses a method for producing undercuts on the inside of a pipe by changing the relative position of a die and a mandrel to each other while they are moved along the pipe.

The printed publications EN 30 16 135 A1 , DE 30 21 481 A1 , EN 35 06 220 A1 and US 6 779 375 B1 each disclose at least partially the method steps according to the preamble of patent claim 1.

The publication US 2 535 339 A represents the closest state of the art.

Patent claims 1 and 10 have been delimited from this US document. An example of a tube forming process can also be found disclosed, for example, in the international patent application WO 2006/053590 A1 . A method is described there for producing hollow shafts with end sections of greater wall thickness and with at least one intermediate section of reduced wall thickness from a tube with an originally constant wall thickness. The production takes place, by first inserting a mandrel with a diameter graduated over its length into the pipe to be formed and then moving a ring die from the side with the tapered diameter of the mandrel lengthwise over the pipe with the inner mandrel. Firstly, the outer diameter of the original pipe is reduced and at the same time the displaced material of the pipe is pressed into the annular gap between the ring die and the stepped mandrel. Due to the gradation of the mandrel, stepped undercuts are created inside the pipe. The inner contour of the pipe created in this way corresponds complementarily to the profile of the stepped mandrel. In this way, undercuts are created inside the pipe above the stepped areas of the mandrel, which typically have a greater wall thickness than the original pipe. If the annular gap between the die and the section of the mandrel with the largest outer diameter is smaller than the original wall thickness of the mandrel, the pipe is stretched in this area, whereby the original wall thickness is reduced to a smaller wall thickness.

Disadvantageous in the WO 2006 / 053590 A1 known procedure is that the formation of undercuts inside the pipe is only possible with individual discrete wall thicknesses, as far as this is determined by the gradations in the outer diameter of the mandrel. In addition, the formation of a plurality of undercuts on the outside in the longitudinal direction of the pipe is not possible.

Pipes with undercuts on their inside and outside are also known from a company called "Schmittergroup"; see the following link on the Internet: https://www.schmittergroup.de/de/produkte/details/rohre-mit-variabler-wanddicke.html .

Based on this prior art, the invention is based on the object of developing a known method and a known device for forming a pipe in such a way that the formation of undercuts both inside and outside the pipe with a wall thickness that can be variably adjusted within limits becomes possible.

This object is achieved by the method claimed in claim 1. When the die with the leading mandrel reaches an end position, the following steps are carried out:
Reversing the direction of movement of the die and the mandrel from the pushing direction to an opposite pulling direction; first setting step: moving the die and the mandrel relative to each other to a first predetermined annular gap setting; and first forming step: moving the die and the mandrel in the pulling direction over a first section of the free pipe section while maintaining the first predetermined annular gap setting for forming the pipe.

The first and any subsequent adjustment steps allow the die and the mandrel to be moved relative to each other and thus the variable adjustment of the annular gap between the die and the mandrel to any desired size - preferably limited to the original outer diameter. Due to the presence of conical transition sections in both the annular die and the mandrel, undercuts in the forming area of the pipe, particularly within the original pipe wall thickness, are possible due to the variable adjustment of the annular gap. Depending on whether the conical transition sections taper or widen towards the free end of the pipe, the undercuts are possible on the inside and/or outside of the pipe. The formation of undercuts inside the pipe and on the outside of the pipe can be achieved in one operation. can be implemented on one and the same pipe at different longitudinal sections. As a sub-case of this, a thick-thin pipe with a constant inner bore can also be implemented, in which only local undercuts are formed on the outside. Alternatively, thick-thin pipes can also be designed with a constant outer diameter, but with undercuts inside the pipe and, if required, with different wall thicknesses.

The said undercuts are formed by moving a tool pairing of die and mandrel, which is preset with regard to the annular gap, over a section of the free pipe section. According to the invention, the die and mandrel are moved in the pulling direction to form the undercuts, i.e. when the tool pairing moves towards a forming device in which the die and mandrel are movably mounted and controlled. The pulling direction also means in particular a direction in which the pipe to be formed is subjected to a pulling load. In contrast to moving the die and mandrel in a pushing direction which is opposite to the pulling direction, in the pulling direction there is no risk of the pipe being deformed in an undesirable way when the tool pairing is moved, in particular being compressed or bent.

The claimed method advantageously enables the production of very different geometries on the pipes with regard to diameter tolerances and material thicknesses through program-controlled forming processes, without the geometries of the tools, i.e. the die and the mandrel, having to change during the forming process. The method according to the invention enables the use of simple (pre-)pipes that do not have to be pre-formed in separate process steps, and thus better value creation potential in component production. The use of forward and backward movements of the die-mandrel tool pair for forming of the pipe means resource efficiency. The method according to the invention enables a targeted reduction in the wall thickness of the pipes in limited local pipe sections in accordance with a previously made design. The local reduction in the wall thickness of a pipe can be desired, for example, to introduce a predetermined breaking point. A further advantage is the possibility of using inexpensive pre-pipes in accordance with the German Industrial Standard DIN EN 10305-3 instead of the previously required pipes of a more expensive quality in accordance with the DIN EN 10305-2 standard.

Definitions:

The term "free pipe section" means: non-clamped pipe section.

The terms "thrust" or "thrust direction" mean a direction away from a forming device from which the die and mandrel are moved and towards a clamping device. In particular, the thrust direction means a direction in which the tube to be formed is subjected to compression.

The term "tension direction" means a direction opposite to the shear direction. In the tension direction, the pipe to be formed is always subjected to tensile stress. There is no risk of the pipe being compressed or bent. However, when forming in the tension direction, there is a risk of the pipe being formed breaking or cracking if the tensile stress becomes too great.

The term "synchronous" in this description means the movement of the die and mandrel at the same speed in the same axial direction. Synchronous movement always takes place with a fixed annular gap. A change in the size of the annular gap always requires a relative movement of Die and mandrel move at different speeds, which excludes a synchronous movement of die and mandrel.

The term "vertical" refers to the y-direction of the coordinate system, as in Figure 1 shown.

The terms "left-hand stop" and "right-hand stop" refer to the representation in the figures. Accordingly, "left-hand stop" means the stop that limits the travel path of the mandrel in the pushing direction S. Analogously, "right-hand stop" means the stop that limits the travel path of the mandrel in the pulling direction Z.

The term "negative annular gap" refers to the annular gap which is formed by the conical transition sections of the die which taper towards the free end of the tube or the mandrel rod or the forming device in the figures. and mandrel. Irrespective of this, the conical transition flanks of the die and the mandrel can be designed to be convergent, parallel or diverging relative to one another. The conical transition sections can overlap or face each other at least to a certain extent in the vertical direction. In the figures, the mandrel is then offset to the left in relation to the die. In other words, the negative annular gap - seen in the pulling direction - is on the back of the die. Machining the pipe with a negative annular gap leads to the formation of an undercut on the outside of the pipe.

The term "minimal annular gap" means an annular gap with a minimum vertical distance between the die and the mandrel. It is formed in particular between the narrowest point of the annular die and an opposite, usually cylindrical (transition) section of the mandrel. As a rule, the die-mandrel tool pairing is selected before the start of the pipe forming process so that the minimum annular gap corresponds to a later desired minimum wall thickness of the pipe to be formed. The minimum wall thickness is usually selected to be less than or equal to the original wall thickness of the pipe. It can be achieved later by axially stretching the pipe.

The term "positive annular gap" means an annular gap which is spanned by the conical transition sections of the die and mandrel which widen in the figures towards the free end of the pipe or the mandrel rod or the forming device. Irrespective of this, the conical transition flanks of the die and the mandrel can be designed to be convergent, parallel or diverging relative to one another. The conical transition sections can be at least partially opposite one another in the vertical direction. In the figures, the mandrel is then offset to the right in relation to the center of the die. In other words, the positive annular gap - seen in the pulling direction - on the front side of the die. Machining the tube with a positive annular gap leads to the formation of an undercut on the inside of the tube.

According to the invention, after the first forming step, the sequence of steps, adjustment step and subsequent forming step, is repeated as often as desired, with the annular gap then being readjusted in each subsequent adjustment step.

This repeatability of the steps enables multiple undercuts to be formed inside and outside the pipe, distributed along the length of the free pipe section to be machined.

The provision of a cylindrical section in the longitudinal direction of the mandrel enables the setting of the minimum annular gap between the die and the mandrel when the said cylindrical section with the maximum external diameter of the mandrel is opposite the narrowest point of the annular die. When the die and the mandrel are moved in this relative position in the longitudinal direction of the pipe, the pipe is stretched axially if the set minimum annular distance between the die and the mandrel is smaller than the wall thickness of the pipe in the direction of tension.

Alternatively, the annular gap between mandrel and die can be set negatively or positively to form an undercut inside or on the outside of the tube.

Depending on the current situation and the previous forming of the pipe, the relative movement of the die and mandrel can take place in different ways during the adjustment steps. For example, in the first adjustment step, in which the direction of movement of the die and mandrel is reversed, it makes sense to stop the die briefly and then only move the mandrel relative to the die in order to set the desired annular gap. In other situations, it may be useful for the die to be continuously moved in the pulling direction and for the setting of the annular gap to be changed by moving the mandrel relative to the moving die. In other situations, it may be useful for the die to be temporarily moved a little way against the pulling direction, ie in the pushing direction, while the mandrel is stationary, in order to adjust the annular gap in the desired way.

Both to form the undercuts on the inside and outside of the pipe and to carry out the axial stretching of the pipe mentioned above, the die and the mandrel typically move synchronously with each other while maintaining a previously made setting of the annular gap. The synchronous movement of the die and the mandrel takes place until a desired length section of the pipe to be formed, in which the respective undercuts or stretching is to take place, has been traveled. It is particularly advantageous if the method according to the invention is used to alternately carry out the formation of undercuts and the stretching of the pipe in the longitudinal direction of the pipe on the pipe section to be formed.

The above-mentioned object of the invention is further achieved by a device for carrying out the inventive method according to patent claim 10.

The advantages of this device correspond to the advantages mentioned above with reference to the claimed method.

The control device required to carry out the method according to the invention for individually controlling the die and the mandrel is designed as an electronic control in particular for individually adjusting the annular gap for realizing the undercuts and the ironing. For adjusting However, the control device can also be designed in the form of a mechanical forced coupling to ensure the minimum annular gap, as is required in particular for axial stretching of the pipe. The design of a mechanical forced coupling is particularly simple and robust compared to an electronic control. Finally, it is advantageous if the mandrel is profiled - particularly in the longitudinal direction. With the help of a profiled design of the mandrel, e.g. if the mandrel has a gear-shaped cross-section, longitudinal grooves can be drawn or formed on the inside of the wall of the pipe with this mandrel.

Figur 1

die erfindungsgemäße Vorrichtung zur Durchführung des erfindungsgemäßen Verfahrens in einer Ausgangsstellung;

Figur 2

den Dorn und die Matrize in einer Anfangsposition zum Reduzieren des Außendurchmessers des Rohres;

Figur 3

die Matrize und den Dorn in einer Endstellung nach Reduzierung des Außendurchmessers des Rohres;

Figur 4

den Beginn eines ersten Abstreckens des Rohres beginnend ab einer Endposition;

Figur 5

das Ende des Abstreckens des Rohres über einem ersten Teilabschnitt des freien Endes des Rohres;

Figur 6

die Einstellung eines negativen Ringspaltes zu Beginn der Ausbildung einer Hinterschneidung an der Außenseite des Rohres;

Figur 7

die Beendigung der Ausbildung der Hinterschneidung an der Außenseite und den Beginn eines zweiten Abstreckvorganges;

Figur 8

das Ende des zweiten Abstreckvorganges;

Figur 9

die Änderung der Ringspalteinstellung am Ende des zweiten Abstreckens;

Figur 10

die Einstellung des Ringspaltes mit positiver Steigerung zum Einleiten der Ausbildung einer Hinterschneidung im Inneren des Rohres;

Figur 11

das Ende der Ausbildung der Hinterschneidung im Inneren des Rohres,

Figur 12

eine erneute Änderung der Einstellung des Ringspaltes zur Einleitung eines dritten axialen Abstreckvorganges;

Figur 13

das Ende der gesamten Rohrumforrmung mit von dem Rohr abgezogener Matrize und weitgehend herausgezogenem Dorn;

Figur 14

das umgeformte Rohr nach Durchführung der zuvor beschriebenen Umformschritte;

Figur 15

die Ausbildung von Längsrillen an der Innenseite des Rohres durch Verwendung eines Dorns mit zahnradförmigem Querschnitt;

Figur 16

die erfindungsgemäße Umformeinrichtung mit der Ausbildung einer Zwangskopplung bzw. Zwangsführung für die Matrize zu Beginn einer Reduzierung des Außendurchmessers;

Figur 17

die in eine Endposition in Schubrichtung verfahrene Umformeinrichtung mit linksseitigem Anschlag an einer Einspanneinrichtung; und

Figur 18

die Umformeinrichtung nach einer Umkehr ihrer Bewegungsrichtung in Zugrichtung mit nunmehr linksseitigem Anschlag der Matrize zeigt.

The description includes 18 figures, of which

Figure 1

the device according to the invention for carrying out the method according to the invention in a starting position;

Figure 2

the mandrel and die in an initial position for reducing the outside diameter of the pipe;

Figure 3

the die and the mandrel in a final position after reducing the outside diameter of the pipe;

Figure 4

the beginning of a first stretching of the pipe starting from an end position;

Figure 5

the end of the stretching of the tube over a first portion of the free end of the tube;

Figure 6

the setting of a negative annular gap at the beginning of the formation of an undercut on the outside of the pipe;

Figure 7

the completion of the formation of the undercut on the outside and the beginning of a second ironing process;

Figure 8

the end of the second ironing process;

Figure 9

the change of the annular gap setting at the end of the second ironing;

Figure 10

the setting of the annular gap with positive increase to initiate the formation of an undercut inside the pipe;

Figure 11

the end of the formation of the undercut inside the pipe,

Figure 12

a further change in the setting of the annular gap to initiate a third axial ironing process;

Figure 13

the end of the entire pipe forming process with the die removed from the pipe and the mandrel largely pulled out;

Figure 14

the formed tube after the previously described forming steps have been carried out;

Figure 15

the formation of longitudinal grooves on the inside of the pipe by using a mandrel with a gear-shaped cross-section;

Figure 16

the forming device according to the invention with the formation of a forced coupling or forced guidance for the die at the beginning of a reduction of the outer diameter;

Figure 17

the forming device moved to an end position in the direction of thrust with a left-hand stop on a clamping device; and

Figure 18

the forming device after a reversal of its direction of movement in the pulling direction with the die now stopped on the left side.

The invention is described in detail below with reference to the figures mentioned in the form of exemplary embodiments. In all figures, the same technical elements are designated by the same reference numerals.

Figure 1 shows the device according to the invention. It comprises a clamping device 140 for clamping a pipe 200 to be formed in such a way that a free section 210, ie a non-clamped section of the pipe 200 remains for forming. At the free end of the pipe 200, a forming device 150 can be seen in which an annular die 120 and a mandrel 110 arranged coaxially thereto are slidably mounted. In the embodiment shown here, the die 120 comprises two conical transition sections on the inside, of which a first transition section 120-1 tapers towards the free end of the pipe 200 and a second transition section 120-II widens towards the free end of the pipe 200. The mandrel 110 has on its outside a first conical transition section 110-I, which tapers towards the free end of the tube 200 and the forming device 150, and a transition section 110-II, which widens towards the free end of the tube 200 and the forming device 150. In between, a cylindrical transition section 110-III with a constant maximum outside diameter is formed. The pairing of annular die 120 and mandrel 110 is selected so that the minimum distance between the die at its narrowest point and the cylindrical section 110-III of the mandrel 110 with maximum outer diameter is less than or equal to the original wall thickness of the tube 200.

To carry out the method according to the invention, it is not absolutely necessary for the die 120 and the mandrel 110 to each have two conical transition sections. To create undercuts 220, 240 on the outside of the pipe 200, only the conical transition sections on the die 120 and the mandrel 110 are required, which taper towards the free pipe end 215. To create undercuts 220, 240 only inside the pipe 200, only the transition sections on the die 120 and the mandrel 110 are required, which widen towards the free pipe end 215 and towards the forming device 150. If only stretching of the pipe 200 is desired, only the presence of the cylindrical section 110-III on the 110 mandrel with maximum outside diameter without conical transition sections is required. Depending on the desired deformation of the tube 200, the die 120 and the mandrel 110 with the necessary transition sections and minimum annular gap must be selected.

The forming device 150 is assigned a control device 152 for moving the die 120 and the mandrel 110 independently of one another along the free section 110 of the tube 200 in a pushing direction S and a pulling direction Z. When the die 120 moves in the pushing direction, the tube 200 is subjected to pressure and there is a risk of the tube 200 bending and being compressed. When the tool pairing die 120 and mandrel 110 is moved in the pulling direction, there is a risk of the tube 200 tearing, particularly if the annular gap is set too narrow.

Figure 1 shows the starting position of mandrel 110 and die 120 for carrying out the method according to the invention. The mandrel 110 and the die 120 are arranged at the free end of the tube 200 and are aligned coaxially therewith. The mandrel 110 has already been inserted a little way into the free end of the clamped pipe 200.

Figure 2 shows the beginning of a desired reduction in the outside diameter of the pipe 200 by pushing the annular die 120 in the pushing direction S towards the clamping device 140. Because the smallest clear inside diameter D _M of the die 120 is smaller than the outside diameter D _R of the pipe 200, the desired reduction in the outside diameter occurs when the die 120 is moved in the pushing direction. The wall of the pipe 200 slides along the transition section 120-I of the die 120. The mandrel 110 runs ahead of the die 120 in the pushing direction S; it is not involved in the forming process itself in that its surface does not contribute to the forming, i.e. specifically to the reduction of the outside diameter. In this forming process, it serves at most to guide and support the pipe 200 against bending.

In contrast to the subsequent forming step, in which the die 120 and the mandrel 110 are moved in the pulling direction, the annular gap between the die 120 and the mandrel 110 is not important when reducing the outer diameter by moving the die 120 in the pushing direction; its size is irrelevant, in particular the mandrel 110 can advance so far in front of the die 120 that a conical transition section of the mandrel 110 facing the die 120 has no influence on the wall of the tube 200 when it is reduced by moving the die 120.

According to Figure 3 the reduction of the outer diameter D _R of the pipe 200 takes place over a substantial part of the free section 210, here specifically until the die 120 strikes the clamping device 140. Of course, the end of the reduced pipe section defined thereby is merely an example; In fact, the reduction of the tube 200 can also end before reaching the clamping device 140.

In Figure 3 It can be clearly seen that the material displaced when the outer diameter is reduced leads to an increase in the wall thickness of the tube 200 in the area of the reduced outer diameter.

In order to reverse this increase in wall thickness at least in a first section T1 of the free end of the tube 200, Figure 4 the die 120 and the mandrel 110 are moved to their minimum ring distance d _min in a first adjustment step. For this purpose, the direction of movement of the mandrel 110 is reversed from the pushing direction S to the opposite pulling direction Z and the mandrel 110 is moved towards the die 120. To set the minimum ring gap d _min , as mentioned, the mandrel 110 is moved relative to the die 120 in such a way that the cylindrical section 110-III of the mandrel is opposite the position of the ring die with the smallest ring diameter.

This adjustment of the minimum annular gap by changing the position of the die 120 and the mandrel 110 relative to each other can be done electronically or, as shown in the Figures 16 to 18 shown, with the aid of a mechanical forced coupling of die 120 and mandrel 110 within the forming device 150. Within the forming device 150, a carriage 153 is provided for axially moving the die 120 in the pushing and pulling direction. A mandrel rod 113 is arranged coaxially to the carriage 153 for axially moving the mandrel 110 in the pushing and pulling direction. With electronic control, the carriage 153 with the die 120 and the mandrel rod 113 with the mandrel 110 are moved independently of one another in the axial direction - electronically controlled.

In the case of forced coupling, the die 120 is mounted in or on the carriage 153 with an axial play x in the axial direction. Its movement is limited by two stops 150-I and 150-II in the axial direction. Figure 16 shown starting position at the beginning of a movement in the thrust direction to reduce the outside diameter, the die 120 strikes the right-hand stop 150-I within a travel carriage 153. From this starting situation, the travel carriage 153 is moved together with the die 120 and synchronously with the mandrel 110 in the thrust direction S towards the clamping device 140. Figure 17 shows the stop of the travel carriage 153 on the clamping device 140. During the said movement in the direction of thrust S, the die 120 always hits the right-hand stop 150-I. In the design of the forming device with the said forced coupling, the travel carriage 153 of the forming device 150 is mechanically coupled to the mandrel 110 or to the mandrel rod 113. This means that the mandrel 110 and the mandrel rod 113 follow a movement of the carriage 153 in the axial direction.

When the Figure 17 shown stop position of the slide 153 on the clamping device 140, the die 120 remains, as mentioned, at its right-hand stop position 150-I. At the same time, due to the forced coupling with the travel slide 153 - as during the entire previous pushing movement - the mandrel 110 is offset to the left or leads the die 120. In order to change the setting of the annular gap to the minimum annular gap d _min in this situation, the direction of movement of the slide 153 - and thus also the direction of movement of the mandrel 110 - is reversed from the pushing direction S to the pulling direction Z and the travel slide 153 initially moves together with the mandrel 110 a short distance in the axial direction according to the axial play x. Until then, the position of the die 120 remains unchanged, but the mandrel 110 is moved in the pulling direction towards the die 120. This changes the annular gap between die 120 and Dorn 110. The clearance x is dimensioned according to the invention so that Figure 18 exactly the cylindrical section 110-III of the mandrel 110 is moved below the smallest clear diameter of the die 120. In this way, according to Figure 18 the minimum annular gap d _min is preset for the subsequent forming step of axial ironing.

The minimum ring distance d _min can be less than or equal to the original wall thickness of the pipe 200. In any case, it is Figure 4 smaller than the wall thickness of the pipe 200 increased by the reduction of the outer diameter. Figure 4 shows the beginning of a subsequent first forming step in which the direction of movement of the die 120 is also reversed from the pushing direction S to the pulling direction Z. As part of this first forming step, the die 120 and the mandrel 110 are then moved in the pulling direction Z while maintaining the preset minimum ring distance d _min . The said axial stretching of the pipe takes place in order to reduce the increased wall thickness to the size of the ring gap d _min . The die 120 and the mandrel 110 preferably move synchronously. However, the synchronous movement is not absolutely necessary during the axial stretching; The only requirement would be that when the die 120 and the mandrel 110 are moved relative to each other, the area of the smallest inner diameter of the die 120 moves in the area of the cylindrical section of the mandrel 110, so that the minimum annular gap d _min remains constant during the axial ironing.

Figure 5 shows the end of the axial stretching over the first section T1 of the free pipe section.

At this point, according to Fig.6 After the first forming step, a second adjustment step is carried out, in which the annular gap between the die 120 and the mandrel is readjusted. In concrete terms, the annular gap is set negatively here, ie the adjustment is made in such a way that the annular gap is 110-I of the mandrel 110 and 120-I of the die 120 are clamped, which taper or run towards the free end 215 of the pipe 200. Viewed in the vertical direction, these transition sections are located opposite each other in some areas. The newly adjusted annular gap is located on the back of the die 120, viewed in the pulling direction Z. The change in the position of the die 120 and mandrel 110 relative to each other takes place in the area of a pipe section T _E2 following the first partial section T1.

The tool pairing die 120 and mandrel 110 is then moved further in the pulling direction Z with this new negative annular gap setting and an undercut 220 is created in the second forming section T2 on the outside of the previously reduced-thickness tube.

Figure 7 shows the end of the second forming section T2.

At the end of the desired length T2, the die 120 and the mandrel 110 are set to the minimum ring distance d _min , i.e. moved relative to each other. This is done via a further adjustment section T _E3 ; see Fig.7 .

According to Figure 8 The die 120 and mandrel 110 are then moved over a further section T3 of the free pipe section 210 while maintaining the minimum annular gap d _min . In this third section T3, the pipe 200 is stretched axially again to reduce the wall thickness to the minimum annular gap d _min .

According to the Figures 9 and 10 The ring gap setting is then changed again; this time to a positive ring gap. With this positive ring gap, the ring gap is spanned by the conical transition sections 120-II and 110-II of the die 120 and the mandrel 120, which lead to the free pipe end 215. With this positive annular gap setting, these conical transition sections with expansion towards the pipe end are generally at least partially opposite each other in the vertical direction. The positive annular gap is formed on the front side of the die 120 in the pulling direction. According to Figure 9 the positive annular gap setting is achieved by the die 120 temporarily reversing its direction of movement in the pushing direction at the end of the third section T3 and in this way changing its relative position to the stationary mandrel 110 in such a way that the said positive annular gap is established. However, this type of change in the setting of the annular gap is only an example; of course the relative position at the end of T3 could also be achieved by further moving the mandrel 110 in the pulling direction relative to the stationary die 120, for example, albeit with the expenditure of force. Of course, a movement of both the die 120 and the mandrel 110 relative to one another would also be conceivable.

A movement of the die 120 and the mandrel 110 while maintaining the now set positive annular gap leads to the formation of an undercut 240 on the inside of the tube 200, as shown in Figure 11 shown. The formation of the undercut 220, 240 extends over a section T4 of any desired length. At the end of the fourth section T4, the annular gap can be changed again, for example to the minimum ring distance d _min . After a further adjustment section TE5, a fifth section T5 is then obtained, again with an axially stretched tube; see the Figures 12 and 13 .

Figure 14 shows the finished tube 200 after all previously described individual steps have been carried out.

It is important to note that the sequence of steps explained here and the Figure 14 The final result shown in relation to the processing steps carried out only is exemplary. Thus, after the one-time reduction of the outside diameter of the pipe 200, any sequence of axial stretching, formation of undercuts 220, 240 on the outside of the pipe 200 and the formation of undercuts on the inside of the pipe 200 are possible. In particular, the sequence of sections with axial stretching and the formation of undercuts 220, 240 proposed here is not absolutely necessary. Rather, formed undercuts 220, 240 on the outside can also be immediately followed by formed undercuts 220, 240 on the inside of the pipe 200 in the pulling direction; and vice versa. The sections over which a deformation of the pipe 200 takes place can in principle be of any length; they are only limited by the length of the free section 210 of the tube 200. Thus, an axial ironing, the formation of an undercut 220, 240 on the outside or the formation of an undercut 220, 240 on the inside of the tube 200 can also take place continuously over the entire free section 210.

The wall thickness of the tube 200 in the area of an undercut 220, 240 depends on the actually set positive or negative ring distance, i.e. the actual distance between the conical transition sections. Due to the electronic adjustment of the die 120 and the mandrel 110 relative to each other, this distance and thus the wall thickness in the area of an undercut 220, 240 can be set very precisely to any desired dimension.

Figure 15 shows, as an example, the formed tube 200 when using a profiled mandrel 110, specifically when using a mandrel 110 with a gear-shaped cross-section. In this way, for example, an internal toothing 260 of the tube 200 can be realized over a large length in the case of very thin-walled tubes 200. The production of external toothing is also possible when using appropriate profiled ring dies. The forces required, especially tensile forces, to create such toothing are significantly lower than using dies 120 and mandrels 110 without corresponding toothing

List of reference symbols

110

mandrel

110-I

axially extending conical transition section of the mandrel, which tapers towards the free tube end;

110-II

axially extending conical transition section of the mandrel, which is widened towards the free tube end;

113

Mandrel bar

120

die

120-I

axially extending conical transition section of the die, which is tapered towards the free pipe end

120-II

axially extending conical transition section of the die, which is widened towards the free pipe end

130

Annular gap

140

Clamping device

150

Forming device

150-I

right-hand stop for die

150-II

left-hand stop for die

152

Control device

153

Traversing carriage

200

Pipe

210

free section of the pipe

215

free end of the pipe

220

Undercuts on the outside of the pipe

240

Undercuts on the inside of the pipe

260

Internal toothing of the pipe

S

Thrust direction

Z

Pull direction

E

End position

T1, T2, T3

Sections of the free pipe section with deformations

TE1, TE2, TE3

Transition sections of the free pipe section for changing the annular gap setting

DR

original outside diameter of the pipe

DM

Minimum inner diameter of the annular die

dmin

minimal annular gap

Claims (11)

1. A method for axially shaping a tube (200) with the aid of a mandrel (110), which is guided in the tube (200), and an annular die (120), which is guided on the outside of the tube (200) and the inside diameter of which is smaller than the original outside diameter of the tube (200);

   wherein the annular die (120) has on its inner side at least one conical, axially extending transitional section (120-I, 120-II), wherein the mandrel (110) has on its outer side at least one conical, axially extending transitional section (110-I, 110-II), and wherein the die and the mandrel form in their opposed position an annular gap (130) for passing through and shaping the wall of the tube (200);

   wherein the method comprises the following steps:

   - clamping the tube (200) with an original wall thickness in a clamping device (140) such that at least one free section (210) of the tube (200) remains in order to shape the tube (200);

   a) inserting the mandrel (110) into the tube (200) ;

   b) reducing the outside diameter of the tube (200) by moving the annular die (120) toward the clamping device (140) in a pushing direction (S) over the free section (210) of the tube (200), wherein the mandrel (110) leads the die (120) in the pushing direction; and

   wherein the following steps are carried out when an end position (E) is reached:

   c) reversing the direction of movement of the die (120) and the mandrel (110) from the pushing direction (S) into an opposite pulling direction (Z);

   d') first setting step: moving the die (120) and the mandrel (110) relative to one another to a first predetermined annular gap setting; and

   e') first shaping step: moving the die (120) and the mandrel (110) in the pulling direction (Z) over a first portion (T1) of the free tube section (210) while maintaining the first predetermined annular gap setting in order to shape the tube (200);

   characterized in

   that the step sequence setting step and subsequent shaping step is repeated at least one more time, wherein the die (120) and the mandrel (110) are set to a new annular gap setting, which differs from the respectively preceding annular gap setting, in each additional setting step; and in

   that the die (120) and the mandrel (110) are in at least one of the setting steps moved relative to one another to a negative annular gap setting, in which the conical transitional sections (110-I, 120-I)of the die (120) and the mandrel (110), which are tapered toward the free end (215) of the tube (200), form the annular gap on the rear side of the die viewed in the pulling direction (Z) of the die and the mandrel.
2. The method according to claim 1,
   characterized in

   that the mandrel (110) also has a cylindrical section (110-III) on its outer side in addition to the at least one conical transitional section (110-I, 110-II); and in

   that the die (120) and the mandrel (110) are in at least one of the setting steps set relative to one another to a minimal vertical annular clearance between the narrowest point of the annular die and the opposite cylindrical section (110-III) of the mandrel (110) .
3. The method according to claim 2,
   characterized in
   that axial wall ironing of the tube (200) to a wall thickness corresponding to the minimal vertical annular clearance takes place in the pulling direction (Z) in the subsequent shaping step.
4. The method according to claim 1,
   characterized in
   that the die (120) and the mandrel (110) are in at least one of the setting steps moved relative to one another to a positive annular gap setting, in which the conical transitional sections (110-II, 120-II)of the die (120) and the mandrel (110), which widen toward the free end of the tube (200), form the annular gap on the front side of the die viewed in the pulling direction (Z) of the die and the mandrel.
5. The method according to one of the preceding claims,
   characterized in
   that the die (120) is stopped and the mandrel (110) is moved relative to the die (120) in at least one of the setting steps.
6. The method according to one of claims 1 to 4,
   characterized in
   that the relative movement between the die (120) and the mandrel (110) in at least one of the setting steps takes place:

   - by moving the mandrel (110) while the die (120) continuously moves along in the pulling direction (Z) .
7. The method according to one of the preceding claims,
   characterized in
   that the die (120) and the mandrel (110) are moved synchronously in at least one of the shaping steps.
8. The method according to one of claims 1 to 7,
   characterized in

   that the minimal annular gap according to claim 2 is set in one of the setting steps; in

   that wall ironing of the tube (200) according to claim 3 takes place in the subsequent shaping step; and in that a negative annular gap setting takes place in the subsequent additional setting step such that an undercut (220) is formed on the outer side of the tube (200) in the subsequent additional shaping step; or in that a positive annular gap setting takes place in the subsequent additional setting step such that an undercut (240) is formed on the inner side of the tube (200) in the subsequent additional shaping step.
9. The method according to claim 8,
   characterized in

   that a setting step once again takes place after the formation of the undercut (220, 240) in order to set the minimal annular gap; and in

   that wall ironing of the tube (200) takes place in a subsequent additional shaping step.
10. An apparatus for axially shaping a tube (200), comprising:

    a clamping device (140) for clamping the tube (200) such that a free section (320) remains;

    a shaping device (150) that is aligned axially to the clamping device (140) and has an axially movable annular die (120) and a mandrel (110) that is coaxially guided within the annular die (120), wherein the die (120) and the mandrel respectively have a conical, axially extending transitional section (110-I, 110-II, 120-I, 120-II), and wherein the die (120) and the mandrel (110) form in their opposed position an annular gap for passing through and shaping the wall of the tube (200); and

    a control device (152) that is assigned to the shaping device (150) and serves for moving the die (120) and the mandrel (110) independently of one another along the free section of the tube (200) in order to shape the tube (200) in a pushing direction (S) and a pulling direction (Z);

    characterized in

    that the control device (152) furthermore is designed for carrying out the method according to one of the preceding claims; and in

    that the control (152) is realized in the form of a mechanical positive coupling between the die (120) and the mandrel (110) for setting the die (120) and the mandrel (110) to a minimal annular clearance to one another, wherein the shaping device (150) comprises:

    a carriage (153) for the die (120) and a mandrel bar (113) with the mandrel (110) rigidly fastened on the mandrel bar (113),

    wherein the carriage (153) is mechanically coupled to the mandrel bar (113) in order to move synchronously;

    wherein the die (120) is mounted in the carriage (153) in an axially movable manner with a free play x;

    wherein the free play x represents the travel of the mandrel (110) coupled to the carriage (153) between a left stop (150-I), which limits the travel of the mandrel in the pushing direction (S), and a right stop (150-II), which limits the travel of the mandrel in the pulling direction (Z), relative to the die (120); and

    wherein the cylindrical section (110-III) of the mandrel (110) lies opposite of the narrowest point of the die (120) in the right stop position such that the minimal annular gap (d_min) is formed between the mandrel (110) and the die (120).
11. The apparatus according to claim 10,
    characterized in
    that the mandrel (110) is profiled with a gearwheel-shaped cross section in the longitudinal direction.

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