DE102011051057A1 - Method for manufacturing tube for exhaust systems of motor vehicles, involves generating regions of higher thickness and other regions of lower thickness in longitudinal direction of strip material - Google Patents

Abstract

The method involves generating a region (7) of higher thickness and another region (8) of lower thickness in longitudinal direction of the strip material. The strip material or blanks made of strip material are formed into a slotted tube. A closed tube is bent in one of the regions of the tube with higher thickness. An independent claim is also included for a tube for exhaust systems of motor vehicles.

Description

The invention relates to a pipe for exhaust systems of motor vehicles. Exhaust pipes for motor vehicles are used for targeted removal of exiting the engine exhaust. This exhaust pipes connect components of the exhaust system, such as catalytic converters, particulate filter, center and rear muffler, and finally lead the exhaust into the environment.

From the DE 101 58 358 A1 a pipe for exhaust systems of motor vehicles is known from several along the pipe longitudinal axis arranged portions whose dimensions are adapted to the operation of the vehicle acting on them, different loads. The mating sections on the mufflers and suspension sections are made of a sheet of thicker wall thickness than the sections therebetween. The entire pipe with the individual sections is made of a "tailored blanks" type board, that is, the board formed from individual flat, welded-together sheet metal blanks is formed into a tube and longitudinally welded. The thickness jumps are on the outside, so that the sections in the tube interior merge without any jump, so that flow losses are prevented.

From the DE 42 28 188 A1 is a vibration, bending and strain-absorbing front pipe of an internal combustion engine for permanently connecting an exhaust manifold with a catalyst bulb known. The pre-pipe is made in one piece by hydroforming, has a curved course with flowing transitions and an oval cross-section. The wall thickness of the front pipe is constant everywhere.

From the EP 1 479 458 A2 For example, a method of making tubes and profiles with variable wall length is known. The method comprises the steps of flexibly rolling endless strip material having variable longitudinal thickness of the strip material, reduced final thickness relative to the starting thickness, forming the strip material into an endless tube or profile, and cutting individual lengths of tube or profile from the endless tube or profile.

The present invention has for its object to provide a method for producing a pipe for exhaust systems of motor vehicles, which is simple and inexpensive, wherein the tube to be produced by the method have a low weight and at the same time reliable the loads of the pipe during manufacture and operation withstand.

The solution consists in a method for producing a pipe for exhaust systems of motor vehicles with the steps:
Flexible rolling of strip material, wherein in the longitudinal direction of the strip material a variable thickness is produced with at least first regions of greater thickness and second regions of smaller thickness,
Forming the strip material or blanks made from the strip material into a slotted tube,
Longitudinal welding of the slotted tube, whereby a tube closed in cross-section is produced,
Bending the closed tube in at least one of the first portions of the tube with a greater thickness, wherein by bending a curved pipe section is generated.

With this method, the production of a weight-optimized tube for exhaust systems of motor vehicles is achieved in an advantageous manner, which is simple and inexpensive. The wall thicknesses of the exhaust pipes are designed by the use of flexibly rolled strip so that only those pipe sections are made with a relatively high strip thickness, which are subjected to a high load during the manufacturing process or during operation in the vehicle. Low loaded areas can be made with a relatively small tape thickness. Overall, the components can be produced with the method according to the invention thus with little effort with significantly low material usage, which can be saved with identical function raw material and thus weight and cost. Fluctuations in commodity prices therefore have less impact on the price of the individual product.

It is understood that, depending on the requirements, the tube may also have one or more further regions, each of different thickness, in addition to the first regions of first thickness and second regions of second thickness. It is further provided that in the flexible rolling between the first regions of greater thickness and the second regions of smaller wall thickness each transition sections are formed, which in particular have a continuously varying over the length thickness between the adjacent regions of greater or smaller thickness.

According to a preferred embodiment, it is provided that, during flexible rolling, the length and the thickness of the at least one first region are designed as a function of the radius of curvature and the length of curvature of the curved pipe section to be produced during bending. During bending, pipe sections that are very hard to bend, that is to say with a small radius of curvature, can be designed in advance with flexible rolling with a particularly large wall thickness, while Pipe sections with small curvature may also have a smaller wall thickness. In any case, according to a favorable embodiment, it is also provided that the pipe sections with a small curvature have a greater material thickness than the wall thickness of a straight section of the pipe with the smallest material thickness.

Is particularly favorable for a good manufacturability and high stability, if the length of the flexible rolling produced at least a first portion of an average length of the pipe section produced during bending corresponds at least approximately. By "at least approximately" is meant that the curved portion is at least largely located in the region of greater wall thickness, preferably even completely disposed within the region of greater wall thickness. In this way it is ensured that the pipe reliably withstands the increased loads occurring during bending. Preferably, a plurality of curved pipe sections are produced by bending, between each of which are straight pipe sections, wherein the bending to produce the curved pipe sections takes place in each case in the first regions of the tube with a larger wall thickness. The length of the at least one first region having a greater thickness is preferably matched to the curved pipe section to be produced such that the transition sections adjoining the first region of greater thickness after bending at least partially or largely, preferably even completely within the straight following the curved pipe section Pipe section lie. This applies in a favorable manner for all transition sections that are adjacent to curved sections of the finished tube.

According to a preferred embodiment, it is provided that the bending takes place at least in one of the first regions of the tube with a greater first thickness. In this way, it is ensured that the bending areas which are subjected to greater stress in the production process are reliably produced in the desired form. The thicker first regions of the flexibly rolled strip material or of the finished tube preferably have a thickness of more than 0.9 mm, preferably more than 1.0 mm, in particular more than 1.1 mm. The thinner second regions of the flexibly rolled strip material or the finished tube preferably have a thickness of less than 1.0 mm, in particular less than 0.9 mm, or possibly even less than 0.8 mm. Between the thicker first regions and the thinner second regions there are transition regions, in which the wall thickness preferably varies continuously over the length. The length of the transition regions is relatively short compared to the length of the first and second regions, respectively.

After the flexible rolling, the strip material may be subjected to a heat treatment, preferably a recrystallization annealing. In recrystallization annealing, the material is heated to a temperature just above the recrystallization temperature. Particularly favorable for a continuous and thus rapid production, if the heat treatment is carried out in a continuous process, for example by means of inductive heating or inductive annealing. In this case, the strip material passes through an induction heater, are generated with the eddy currents, which heat the strip material. Another possibility for continuous heat treatment is the continuous annealing, in which the strip material is passed through an oven. Alternatively, a bell annealing can be carried out in which one or more coils are annealed in a closed oven.

By the heat treatment solidification of the material resulting from flexible rolling is reduced or dissolved. The rolled strip material again obtains a higher ductility and ductility, so that it can be processed more easily in the following process steps, wherein, in addition, the material properties of the end product to be produced are positively influenced. It is understood that the heat treatment for the inventive method is only optional, that is, the strip material can in principle be further processed without heat treatment by forming a tube.

According to a favorable embodiment, in addition to or alternatively to the heat treatment after the flexible rolling, even after the longitudinal welding and before the bending of the tube, a heat treatment of the tube take place. In this case, at least one or more subsections, if appropriate also the entire tube is heat treated, in particular recrystallization annealed. It is understood that this heat treatment can be carried out depending on the material properties to be set on the entire pipe or even selectively only in some areas. It is also conceivable that the tube without intermediate heat treatment after longitudinal seam welding of the processing by bending is supplied. With respect to the heat treatment before bending the pipe, what has been said above for the heat treatment before the pipe molding equally applies, so that the above description is referred to.

With regard to the process sequence, at least two options are conceivable. After a first possibility, the production of the tube is carried out continuously. This means that the process steps flexible rolling, if necessary recrystallization annealing, molding into a tube and Longitudinal seam welding, continuous on the endless material. Only after the forming and longitudinal welding of the endless tube is a cutting to individual pieces of pipe done. This procedure has the advantage of a high process speed and high efficiency associated therewith.

After a second possibility, the production of the tube is discontinuous. This means that the endless strip material is cut to size after the flexible rolls to individual boards. Subsequently, the individual boards are formed into a tube profile and longitudinally welded, during which optionally one or more heat treatments can be interposed.

The solution to the above object also exists in a pipe for exhaust systems of motor vehicles, manufactured according to one or more of the above-mentioned method sequences. It is provided that the tube has a variable wall thickness over the length and further straight portions and bent portions, wherein the thickness of the tube of at least a part number of the straight portions is smaller than in the bent portions.

Preferred embodiments will be explained below with reference to the drawing figures. Hereby shows:

1 an inventive method for producing a pipe for an exhaust system of a motor vehicle in a first embodiment;

2 an inventive method for producing a pipe for an exhaust system of a motor vehicle in a second embodiment;

3 an inventive method for producing a pipe for an exhaust system of a motor vehicle in a third embodiment;

4 an inventive method for producing a pipe for an exhaust system of a motor vehicle in a fourth embodiment;

5 in a perspective view a portion of the strip material after the flexible rolling according to the first method step A1, B1, C1 and D1 of the in 1 - 4 shown methods;

6 in the semi-longitudinal section a portion of the finished tube after longitudinal welding according to the process step A3, B3, C4 and D4 in the 1 - 4 shown methods;

7 a pipe according to the invention for an exhaust system of a motor vehicle, produced according to one of the in the 1 to 4 shown method, according to a possible embodiment before bending in side view; and

8th the pipe according to 7 after bending in perspective view. 1 shows a method according to the invention for producing a pipe for an exhaust system of a motor vehicle from a strip material 2 after a first process procedure A. In process step A1, the strip material 2 Being in the starting state on a coil 3 is wound in a rolling tool 11 machined rolling, by means of flexible rolling. This is the band material 2 , which has a largely constant sheet thickness over the length before the flexible rolling, by means of rollers 4 . 5 rolled in such a way that it receives a variable sheet thickness along the rolling direction. During rolling, the process is monitored and controlled using a sheet thickness measurement 6 determined data as input to control the rollers 4 . 5 be used. After the flexible rolling according to method step A1, the strip material has 2 each extending transversely to the rolling direction areas 7 . 8th . 9 . 10 with different thickness. A section of the flexibly rolled strip material is shown in detail in FIG 5 will be discussed in more detail below. The band material 2 becomes coil again after flexible rolling 3 wound up so that it can be fed to the next process step. It can also be further processed directly without intermediate winding, which is not shown separately here.

After a favorable procedure is provided that the thicker first areas 7 of the flexible rolled strip material have a thickness of more than 1.0 mm, in particular more than 1.1 mm and less than 1.4 mm. The thinner second areas 8th The flexible rolled strip material preferably has a thickness of less than 1.0 mm, in particular less than 0.9 mm and more than 0.6 mm. Between the thicker first areas 7 and the thinner second areas 8th There are transitional areas 9 . 10 in which the wall thickness preferably varies continuously over the length. The length of the transition areas 9 . 10 is shorter compared with the length of the first and second regions, respectively.

In the subsequent method step A2, the flexibly rolled strip material 2 ₁ to an endless tube 2 ₂ reshaped. The endless tube 2 ₂ is open in cross-section and may also be referred to as a slot tube due to the slot extending longitudinally between the free edges. As shown, the strip material becomes 2 ₁ after the high speed flexible rolls with a first winding speed on a coil 3 wound up and for forming the strip material for endless tube 2 ₂ with a second lower winding speed, which is optimized for forming the endless tube, unwound from this coil. However, it is also possible in principle to have method step A2 connected to method step A1 without intermediate winding to the coil. In this case, the rolling speed can be adapted to the best possible forming speed for forming to the endless tube, so that the process steps A1 and A2 can run synchronously.

The forming to the tube takes place in a corresponding plant 20 for round bending in the longitudinal direction of the strip material with a corresponding roller arrangement with shaping rollers. Such a system comprises a multiplicity of shaping rollers arranged one behind the other in the direction of production and having a regularly changing roller shape and / or axial position. The round bending system can be designed for example in the form of a Rollprofilieranlage.

In round bending, a contour of the pipe adapted to the requirement is generated. In particular, it is possible here that sections with a round cross-section, but also with an oval or elliptical cross-section, by means of the system 20 be generated. In this case, the oval or elliptical cross sections can be provided, for example, at the points which are subjected to a bending operation in a subsequent method step for producing a curved tube.

After the round bending of the strip material to form a slot tube according to method step A2, the endless slot tube in the following method step A3 becomes the tube closed in cross-section 2 ₃ longitudinally welded, preferably in blunt shock. The welding is preferably carried out with a high-energy beam, for example by means of laser welding or electron beam welding, although tungsten inert gas welding (TIG) can also be used. The welding system 30 is in 1 shown schematically.

Before welding, an edge preparation of the slot pipe can optionally be carried out in order to produce a uniform gap dimension. The edge processing of the lateral edges of the slot tube can be done for example by milling or planing.

After longitudinal welding becomes the endless tube 2 ₃ then in process step A4 in a cutting system 40 to individual pipe sections 2 ₄ cut to length. A cut pipe 2 ₄ is exemplary in detail 7 represented, which will be described in more detail below.

In the subsequent method step A5, the pipe sections 2 ₄ subjected to a bending process in a bending machine to the final shape of the exhaust pipe 2 ₅ for the exhaust system produce. The bending takes place in a bending plant, which is not shown here. Bending the longitudinally welded pipe 2 will be in the first areas 7 performed with greater thickness. In this way, it is ensured that the bending areas which are subjected to greater stress in the production process are reliably produced in the desired form. The bending causes curved pipe sections 13 . 15 . 17 . 19 . 22 generated between two curved pipe sections each have a straight pipe section 12 . 14 . 16 . 18 . 21 . 23 are arranged. The finished pipe to an exhaust pipe 2 ₅ is in 8th shown as a detail, which will be discussed in more detail below.

It is envisaged that the lengths of the first areas 7 with greater thickness in each case so on the length of the curved pipe sections to be produced 13 . 15 . 17 . 19 . 22 are tuned that the curved pipe sections produced after bending are at least largely within the respective first region of greater thickness. In this way it is ensured that the tube reliably withstands the increased loads occurring during bending and that sufficient material is available for stretching on the external radii, so that the finished tube is also in the curved areas 13 . 15 . 17 . 19 . 22 has sufficient stability. Furthermore, it can be seen that the first areas 7 greater thickness subsequent transition sections 9 . 10 after bending at least for the most part in the area of the straight pipe sections 12 . 14 . 16 . 18 . 21 . 23 lie. It is understood that even in straight areas of the tube, which are subject to increased loads in later operation, an increased sheet thickness can be provided.

2 shows a method according to the invention for producing a pipe for an exhaust system of a motor vehicle according to a second process control B. This largely corresponds to the method according to 1 , so that reference is made to the above description in terms of similarities. The same or modified components are provided with the same reference numerals, as in 1 , In the following, essentially the differences of the present method will be discussed.

The process steps B1 (rolling finishing), B2 (forming to the slit pipe) and B3 (longitudinal seam welding) are identical to the corresponding process steps A1, A2 and A3 of the in 1 shown method. Unlike the method after 1 finds in the present case the longitudinal seam welding according to process step B3 in the subsequent process step B4, a heat treatment of the longitudinally welded pipe instead.

For this purpose, the tube passes through 2 in a continuous process, a heat treatment plant 50 , in the 2 is shown schematically. In the heat treatment plants 50 becomes the longitudinally welded pipe 2 Annealed ₃ , preferably recrystallization annealed. The heat treatment, for example, by means of a so-called Kontiglühanlage, in which the pipe 23 passed through an oven, or by means of inductive heating.

It is possible to subject individual sections of the tube or the entire tube to a heat treatment. It is particularly favorable with regard to efficient process management if the areas which are subsequently subjected to a bending operation are annealed. Hereby, any existing solidification of the material in these areas is reduced or dissolved. The pipe material obtains a higher ductility and ductility, so that it can be processed more easily in the later B6 bending process. In addition, the material properties of the final product to be produced are positively influenced by the heat treatment.

After process step B4 of the heat treatment, the tube 2 ₄ further processed. Here, the process steps B5 (cutting of the pipe) and B6 (bending of the pipe) of the present embodiment correspond to the process steps A4 and A5 1 , to the description of which reference is made.

In 3 an inventive method for producing a pipe for an exhaust system of a motor vehicle according to a third process control C is shown. This largely corresponds to method B according to 2 , so that reference is made to the above description in terms of similarities. The same or modified components are provided with the same reference numerals, as in 2 , In the following, essentially the differences of the present method will be discussed.

The method step C1 (flexible rolling) is identical to the corresponding method step B1 of FIG 2 shown method. Unlike the method after 2 In the present case, after the flexible rolling according to method step C1 in the subsequent method step C2, a heat treatment of the flexibly rolled strip material takes place 2 ₁ instead. This is the band material 2 _{1 is} preferably subjected to recrystallization annealing in which the material is heated to a temperature just above the recrystallization temperature. The heat treatment can, as shown, be carried out by means of bell annealing, in which one or more coils 3 in a closed oven 60 be annealed. Alternatively, it is also possible to carry out the heat treatment in a continuous process, for example by means of inductive heating or by means of continuous annealing.

As a result of the heat treatment, solidifications of the material resulting from flexible rolling are advantageously reduced. The rolled strip material again receives a higher ductility and ductility, so that it can be processed further during the subsequent forming into a tube.

After the heat treatment according to method step C2, the tube 2 ₂ fed to its further processing. Incidentally, the process steps C3 (forming into the slit pipe), C4 (longitudinal seam welding), C5 (heat treatment), C6 (cutting the pipe), and C7 (bending the pipe) of the present embodiment correspond to the process steps B2 to B6 of the process according to FIG 2 , to the description of which reference is made.

4 shows a method according to the invention for producing a pipe for an exhaust system of a motor vehicle according to a fourth process management D. This largely corresponds to the method according to 1 , so that reference is made to the above description in terms of similarities. The same or modified components are provided with the same reference numerals, as in 1 , In the following, essentially the differences of the present method will be discussed. With the present method, the individual tubes are produced discontinuously, in contrast to the methods according to the 1 to 3 in which a continuous production takes place.

The method step D1 (rolling finishing) is identical to the corresponding method step A1 of FIG 1 shown method. Unlike the method after 1 In the present case, after the flexible rolling according to method step D1, in the following method step D2, first a smoothing of the flexibly rolled strip material takes place. The smoothing of the strip material takes place in a band straightening device 70 , In this context, it should be noted that even after method step A1 of in 1 shown method, or even in the 2 and 3 shown method, also a smoothing of the flexible rolled strip material can be made.

After smoothing, the strip material is cut to individual boards according to method step D3. The cutting is done in a separator 80 , In 4 is behind the separator in the production sequence 80 schematically a circuit board 2 ₃ recognizable, which is then fed to a further processing. A section of the board 2 ₃ is also in detail in 5 represented, which will be described in more detail below.

The from the band material 2 ₁ individually cut-to-size boards 2 ₃ then become pipes 2 ₄ reshaped. The forming is preferably by means of a thermoforming tool 90 accomplished. This is the board 2 ₃ inserted into the thermoforming tool and by means of punch, counter punch and die to a tube 2 _{4 formed} with längsverlaufendem slot between the edges.

After forming the blank into a tube according to method step D3, the slotted tube 2 ₄ longitudinally welded in the subsequent process step D4. This is done by means of a welding tool 30 which is in 4 is shown schematically. As a welding process, for example, laser welding and tungsten inert gas welding (TIG) in question.

Finally, the longitudinally welded pipe 2 ₅ subjected in step D5 a bending process, the process step A5 from 1 corresponds to whose description in this respect reference is made.

It goes without saying that modifications, in particular supplementary intermediate steps or subsequent method steps, can also be made in the present process control. For example, in the process according to 4 after the longitudinal seam welding, a heat treatment of the tubes take place, as described above in connection with the method step B4 according to FIG 2 or C5 according to 3 is described. By means of a heat treatment of at least partial sections of the pipe before the bending process, a favorable microstructure is created, so that even high degrees of deformation can be achieved during bending without weakening or damaging the material. It is also conceivable that the strip material is subjected to a heat treatment after the flexible rolling, as in connection with the method step C2 according to FIG 3 described.

In 5 a section of the strip material present after the flexible rolling, respectively the smoothed board is shown. Here are the first areas 7 with a larger sheet thickness and second areas 8th to recognize with a smaller sheet thickness. Here are the thicker first areas 8th preferably a thickness of more than 1.1 mm, while the thinner second regions preferably have a thickness of less than 0.9 mm. Between the thicker first areas 7 and the thinner second areas 8th There are transitional areas 9 . 10 in which the wall thickness preferably decreases continuously over the length in the direction of production ( 9 ) or increases ( 10 ). The length of the transition areas 9 . 10 is in comparison with the length of the first and second areas 7 . 8th relatively shorter.

6 shows a section of the tube in the semi-longitudinal section in a perspective view after the forming of the tube according to method step A2, B2, C3 and D4. Here are the areas 7 . 8th . 9 and 10 on the formed tube 2 to recognize.

In 7 a pipe according to the invention for an exhaust system of a motor vehicle is shown, which according to one of the in connection with the 1 to 4 after longitudinal welding and cutting, that is in (still) a straight state. It can be seen that the pipe 2 thicker first areas 7 ₁ - 7 ₇ , thinner second areas 8th ₁ - 8th ₆ , as well as transition sections 9 ₁ - 9 ₆ and 10 ₁ - 10 ₆ , which are shown hatched.

8th shows the pipe according to 7 after the subsequent bending process according to the in the 1 to 4 described process steps A5, B6, C7, respectively D6.

The tube has a curved course, which is adapted to the individual space conditions of the motor vehicle. It can be seen that the pipe 2 , starting from the first end 24 , first a straight section 12 having the thickness ranges 7 ₁ , 9 ₁ , 8th ₁ , to which a curved section 13 connects, largely in the thickness range 7 ₂ lies. The curved section 13 goes into a straight section 14 over, the broadest in the thickness range 8th ₂ is located and at the end of a curved section again 15 followed. Each in the transitions between the thickness range 8th ₂ lesser thickness to the two curved sections 13 . 15 are the transition areas 9 ₂ , 10 ₂ with variable material thickness. At the curved section 15 closes again a straight section 16 and an angled section 17 that is completely within a first range 7 _{4 is} greater material thickness. In this angled section 17 For example, a suspension for the exhaust pipe 2 be provided. Following the angled section 17 follow again a straight section 18 which is essentially in the second thickness range 8th _{4 is of} low wall thickness, a curved section 19 which is essentially in the first thickness range 7 ₅ with greater wall thickness is arranged, a straight section 21 in the thickness range 8th ₅ , a curvature 22 and, at the second end 25 , again a straight section 23 , The end of the straight section 23 has a first thickness range 7 ₇ with greater material thickness, so that here an increased stability for connection to a connection component, such as a catalyst or a silencer is given.

It is understood that in 7 , respectively 8th , Thickness profile of the tube shown is only exemplary and of course other thicknesses over the length are conceivable.

The advantage of the method described above is that it makes it possible to produce weight-optimized tubes for exhaust systems of motor vehicles. The wall thicknesses of the exhaust pipes are carried out by the use of flexibly rolled strip, especially in the curved sections with increased material thickness, so that reliably withstand the loads occurring during the manufacturing process and in the installed state during operation in the vehicle. Less stressed areas, in particular straight sections of the pipe, can be made with a relatively small material thickness, so that the exhaust pipes can be made overall with little effort with significantly lower material usage.

LIST OF REFERENCE NUMBERS

2

Semi-finished product, tube

3

coil

4

roller

5

roller

6

Strip thickness control

7

first area

8th

second area

9

Transition area

10

Transition area

11

rolling tool

12, 14, 16, 18, 21, 23

straight section

13, 15, 17, 19, 22

curved section

24

first end

25

second end

20

Bending conditioning

30

Longitudinal welding system

40

Ablängwerkzeug

50

Heat treatment plant

60

Heat treatment plant

70

Strip straightening tool

80

separating tool

90

forming tool

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 10158358 A1 [0002]
• DE 4228188 A1 [0003]
• EP 1479458 A2 [0004]

Claims (15)

Method for producing a pipe ( 2 ) for exhaust gas systems of motor vehicles, comprising the steps of: flexible rolling of strip material, wherein in the longitudinal direction of the strip material a variable thickness having at least first regions ( 7 ) of greater thickness and second areas ( 8th ), forming the strip material or blanks made of the strip material into a slotted tube, longitudinally welding the slotted tube to produce a tube closed in cross-section, bending the closed tube in at least one of the first regions (Fig. 7 ) of the tube of greater thickness, wherein by bending a curved pipe section ( 13 . 15 . 17 . 19 . 22 ) is produced. Method according to claim 1, characterized in that, during flexible rolling, the length and the thickness of the at least one first region ( 7 ) as a function of the radius of curvature and the length of curvature of the curved pipe section to be produced during bending ( 13 . 15 . 17 . 19 . 22 ) is designed. Method according to claim 1 or 2, characterized in that the length of the at least one first region generated during flexible rolling ( 7 ) an average length of the curved pipe section produced during bending ( 13 . 15 . 17 . 19 . 22 ) at least approximately. Method according to one of claims 1 to 3, characterized in that a plurality of curved pipe sections ( 13 . 15 . 17 . 19 . 22 ) are produced by bending, at their ends or between which respectively straight pipe sections ( 12 . 14 . 16 . 18 . 21 . 23 ), wherein the bending to produce the curved pipe sections ( 13 . 15 . 17 . 19 . 22 ) in the first areas ( 7 ) of the pipe ( 2 ) takes place with a larger wall thickness. Method according to one of claims 1 to 4, characterized in that during flexible rolling between the first regions ( 7 ) of greater thickness and the second regions ( 8th ) smaller wall thickness each transitional sections ( 9 . 10 ) are formed, which in particular have a continuously changing thickness over the length. Method according to one of claims 1 to 5, characterized in that the length of the at least one first region ( 7 ) with a greater thickness on the length of the curved pipe section ( 13 . 15 . 17 . 19 . 22 ) is tuned to the first area ( 7 ) of greater thickness subsequent transition sections ( 9 . 10 ) after bending at least as far as possible within the curved pipe section ( 13 . 15 . 17 . 19 . 22 ) subsequent straight pipe section ( 12 . 14 . 16 . 18 . 21 . 23 ) lie. Method according to one of claims 1 to 6, characterized in that after the flexible rolling of the strip material and before forming the tube ( 2 ) is provided as a further step, a heat treatment, wherein a recrystallization of the material takes place. Method according to one of claims 1 to 7, characterized in that after longitudinal welding and before bending of the tube ( 2 ) as a further step, a heat treatment at least of subsections of the tube ( 2 ) is provided, wherein a recrystallization of the material takes place. A method according to claim 8, characterized in that the heat treatment at least in the areas ( 7 ), which following a bending operation to produce the curved sections ( 13 . 15 . 17 . 19 . 22 ). A method according to claim 8 or 9, characterized in that the heat treatment in the continuous process, in particular by inductive annealing or by continuous annealing, takes place. Method according to one of claims 1 to 10, characterized in that the production of the tube ( 2 ) takes place discontinuously, that is, after the flexible rolling, a cutting of the strip material to individual boards takes place, wherein the boards are then subsequently converted to the tube profile. Method according to one of claims 1 to 10, characterized in that the production of the tube ( 2 ) takes place continuously, that is, after the forming and longitudinal welding of the endless tube, a cutting of the endless tube to individual tubes takes place. Method according to one of claims 1 to 12, characterized in that the first areas ( 7 ) have a thickness of more than 0.9 mm, in particular more than 1.0 mm, and that the second regions ( 8th ) have a thickness of less than 0.9 mm, in particular less than 0.8 mm. Method according to one of claims 1 to 13, characterized in that a steel material, in particular stainless steel is used as a material for the production of the tube. Pipe ( 2 ) for exhaust systems of motor vehicles, manufactured according to one of claims 1 to 14, wherein the tube has a variable wall thickness over the length, the tube being straight first sections ( 12 . 14 . 16 . 18 . 21 . 23 ) and curved second sections ( 13 . 15 . 17 . 19 . 22 ), wherein the thickness of the tube ( 2 ) at least a part number of the straight first sections ( 12 . 14 . 16 . 18 . 21 . 23 ) is smaller than in the curved second sections ( 13 . 15 . 17 . 19 . 22 ).

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