DE102004030545B3 - Method and device for hydroforming a hollow profile - Google Patents

Abstract

The invention relates to a method for hydroforming a hollow profile and comprises the following method steps: inserting the hollow profile (1) into a cavity (3) formed in a hollow mold (2); at least partially expanding an expansion body (4) into an inner space (5) of the hollow profile (1), such that the expansion body (4) essentially adapts itself to an inner contour (18) of the hollow profile (1); Forming the hollow profile (1) by expansion of the expansion body (4); and at least partially retracting the expansion body (4) from the interior (5) of the hollow profile (1) by contracting the expansion body (4) and a device suitable for carrying out this method. The invention is characterized by the fact that complex workpieces can be easily, cleanly, safely and accurately transformed in a swift manner.

Description

The The invention relates to a method and a device for hydroforming a hollow profile.

The hydroforming (see, for example EP 0 906 800 B1 ) is known as a relatively recent forming process which expands hollow, thin-walled components by means of a hydraulic internal pressure in a die form, superimposing a linear, axial tool movement. The process was mainly developed due to the progressive trend towards lightweight construction and usually starts with a tubular, deflected semi-finished product. To insert a blank and to remove the deformed workpieces, the tools must always be divided. Usually, the manufacturing process proceeds in the following steps: first, the tubular blank is placed in the opened tool and flooded with the hydraulic fluid; then the tool is closed and the end faces of the workpiece are sealed; finally follows the actual forming process, in which the workpiece from the inside is subjected to high pressure, whereby it deforms to the outside. After the first free expansion, it gradually attaches itself to the inner contour of the tool. Usually, due to the increased circumference and thus the increased surface material axially pushed over a tool movement.

adversely in known Hochdruckumformverfahren is, first, that used hydraulic fluid with the workpiece which is why, on the one hand, the workpiece then has to be cleaned, on the other hand from the workpiece contaminated hydraulic fluid must be disposed of. Especially against the background of an efficient Litigation is a removal of the pressure medium from an interior of the workpiece disadvantageous since this is associated with considerable expenditure of time. Another Disadvantage of these known hydroforming is that at Penetration of the workpiece, especially with a crack in a wall, hydraulic pressure medium from an interior of the workpiece gets into a gap between the workpiece and the tool and so the forming process is disturbed due to the pressure equalization. For many Applications, however, it is irrelevant whether the workpiece a Penetration experiences or not and one is interested in penetration even further To be able to transform.

Furthermore Such forming processes have a security problem since especially with complex preformed workpieces not always guaranteed can be that the interior of the workpiece free of air bubbles from a used hydraulic pressure medium is filled. In case of leaks the tool, in particular a jerky opening of the tool goes a not insignificant danger from the compressed air.

DE 195 33 828 C2 describes a device and a method for hydroforming, in which an elastic hollow body is pushed into a stamp in the interior of the blank.

DE 197 24 036 A1 describes a process for hydroforming in which an expansion body, which has inside a substantially rigid lance, is introduced into the blank. Again, mechanical actuation means are required to introduce the expansion body into the interior of the blank.

DE 699 06 537 T2 discloses an expansion molding method and apparatus wherein an elastomeric article is placed inside a blank to be machined and then deformed.

It is therefore an object of the invention, a method and a device to specify the hydroforming of a hollow profile, which hollow profiles to complex structures simple, clean, safe, environmentally friendly and can be reshaped with a high process speed.

These Task is solved through the respective objects the main claims. Further advantageous embodiments, each applied individually or can be combined with each other, are the subject of the respective dependent claims.

The inventive method for hydroforming a hollow profile comprises the following process steps: the hollow profile is in a cavity formed in a hollow shape brought in; an expansion body becomes at least partially in an interior of the hollow profile in such a way extended, that the expansion body essentially by itself an inner contour of the hollow profile adapts; the hollow profile is through Expansion of the expansion body transformed; and the expansion body is at least partially withdrawn from the interior of the hollow profile, by the expansion body is contracted.

The mold is advantageously made of a Formed plurality of moldings to allow removal of the workpiece, in particular the deformed hollow profile. The cavity of the mold is advantageously open only at one point for supplying a pressure medium and otherwise completely encloses the hollow profile. In addition, the hollow mold advantageously has a separate ventilation channel in order to discharge air displaced by the expansion body or, if appropriate, to discharge liquid present in the cavity. The introduction of the hollow profile can be done by simply inserting. It is also possible to preform the workpiece during insertion, in particular to squeeze or press.

Of the expansion body will be at least partially during its extension inserted into the interior of the hollow profile. This is advantageously effected by a special structure of the expansion body, when exposed to the expansion body with a pressure medium automatically causes expansion of the expansion body in the interior. For example, if it is an elongated hollow profile, stretches the expansion body predominantly in length during his Expansion into the interior. As a result, complicated means of movement to drive back and forth of the expansion body in and out of the interior simplified or even unnecessary, which also simplifies complicated high-pressure seals can be. The structure is advantageously by a drape of a Skin of the expansion body, in particular according to an accordion or bellows principle, educated. The structure serves to give the expansion body its own advantageously adapted to the interior of the hollow profile anisotropic To give expansion behavior. The expansion body expands such that it adapts itself to the interior of the hollow profile without getting on an inner surface or to adjust the inner contour of the hollow profile. This becomes the an excessive stress of the expansion body avoided in its expansion, on the other hand also allows a faster process, there the expansion body automatically inserts itself and not with the help of complicated movement means in the interior inserted the hollow profile must become. The expansion body is advantageously both expanded by means of the pressure generator and contracted: the pressure generator thus has two a double function. Due to the inherent adaptability function of the expansion body is a frictional contact of the expansion body with the inner contour of the Hollow profile reduced, whereby the expansion body is more protected against wear. Furthermore becomes an excessive expansion avoided and reduces the risk of cracking of the expansion body.

The Hollow profile is advantageously by a shock of the flowing pressure medium transformed abruptly. The push will for example, by the kinetic energy or the pressure surge of the incoming pressure medium causes. The hollow section can be multi-shell, open, semi-open, as Half or quarter shell designed with or without breakthroughs.

To the deformation of the expansion body is at least partially withdrawn from the interior, by acting, for example, with the help of an internal one Vacuum is contracted. The contraction of the expansion body becomes advantageously again accomplished with the above-mentioned structure, by sucking the pressure medium in the interior of the expansion body from the expansion body which causes the expansion body according to its structure folds up and / or rolls up. With the help of this procedure a simple, clean and safe process management is made possible. A formation of compressed air bubbles in the interior of the hollow profile is avoided, since the expansion body without more difficulty completely i.e. free of air bubbles filled with a pressure medium can be.

Of the expansion body is advantageously made of an elastomer, in particular of a Rubber, advantageously tissue-free, made. The structure of the expansion body For example, by the shape of a concertina or a Be given bellows. Also are screwed forms, such as a twisted accordion, in the sense of a stocking on the left drawn i. inverted in relation to the interior or in cross section meandering structures possible, to include a simple at least partial insertion or withdrawal to allow from the interior of the hollow profile.

advantageously, becomes the expansion body extended by exposure to an incompressible pressure medium. Therefor can for example oils or viscous media, such as. Fats, to be used. Because the print medium is not in contact passes with the hollow profile, is a cleaning of the deformed hollow profile not required by the print medium. In addition, the print medium be reused and must not be disposed of after use.

Advantageously, at least one further hollow profile is inserted or inserted into the cavity of the hollow mold and / or into the interior of the hollow profile. The method makes it possible to deform several hollow profiles at the same time or in succession and thus to produce multilayer structures. For this purpose, several hollow profiles in one another or next to each other, ie completely or only partially overlapping, are arranged and connected to each other by forming. In addition, chemical-technical compounds can be achieved.

With the method can easily complex structures using different Materials on brisk Be made way. For example, two or more hollow sections simultaneously reshaped with expansion of the expansion body. Is possible also, that is a hollow profile after forming the other hollow profile to transform by a further expansion of the expansion body. At the last Process variant, a workpiece is built up layer by layer.

In In a special embodiment, elements made of metal, plastic, Sintered materials or ceramics, in particular half-shell parts, pipe flanges, Tube branches connected by forming with the hollow profile. This allows targeted complex workpieces using different materials at different points of the Hollow profiles are interconnected. Special interesting appear connections between metals and ceramics or metals and plastics through which the beneficial properties of Ceramics or plastics, in particular their electrical as thermal insulation properties, with advantageous properties of metals, in particular their mechanical properties, with each other can be combined. hereby can for the made in each case specially adapted workpieces become.

advantageously, the hollow profile is heated before forming. A heating of the Hollow sections before forming allows to reshape hollow sections with large wall thicknesses, whereby on the one hand a tearing the wall can be prevented, on the other hand particularly robust workpieces can be produced. Possibly becomes the expansion body through a chilled Pressure medium continues to overheat protected.

Conveniently, is the hollow profile before insertion into the cavity of the mold preformed as e.g. pre-bent or with a structure (e.g., knobs) Mistake. This is particularly advantageous when the hollow profile strongly deformed and a single-stage hydroforming process would not be enough to achieve such strong deformations.

It is advantageous if the hollow section without compression and / or wrinkle-free is transformed. On the one hand, this means a cost saving due to low Material expenditure for the deformed hollow profile. On the other hand, so the adverse properties of wrinkles for avoided the further use of the workpiece. For example for some Application of the hydrodynamic flow characteristics of a molded Pipe when used as a fluid line (e.g., an exhaust line) should be used; Wrinkles form a flow resistance, at which undesirable Can accumulate deposits.

Conveniently, becomes the expansion body first prefilled with a pressure medium and subsequently becomes the expansion body with one or more pressure surges on inflated its full size and doing the workpiece deformed. In such a two-stage expansion process can the for the high pressure required pressure generators smaller and space-saving be configured by pre-filling with the help of a pump is accomplished, which the pressure medium from a simple tanks with a valve in the expansion body pumps.

advantageously, is sucked after forming the incompressible pressure medium from the expansion body. By sucking the expansion body contracts and at least partially withdrawn from the interior of the hollow profile. This will turn a particularly fast process control allows. Furthermore can Movement means for introducing the expansion body be made simpler in the interior of the hollow profile.

Around a treatment of hot To allow hollow sections which is particularly advantageous for strong wall thicknesses of the hollow profile is, it is beneficial to the outer surface of the expansion body with a heat protection layer, in particular a wax or Teflon layer, to coat. This heat protection layer causes the expansion body for the short Moment of his contact with the hollow profile during the forming process is not damaged. Although it is due to the at least partial retraction of the expansion body from the Interior of the hollow section the time of a contact between the expansion body and the hollow profile comparatively short, but helps such Heat protection layer in addition doing that, the flexible expansion body from a harmful Preserve heat.

Farther it is appropriate, the Mold on its inner surface with a sliding layer, in particular a wax, oil, grease or Teflon coating. The sliding layer serves to slide the material of the hollow profile along the inner surface of the To facilitate mold. This causes a tearing of a wall of the hollow profile counteracted.

The Hollow mold advantageously has two or more moldings, which are mechanically closed with each other. In contrast to Solutions, where the moldings of the mold with the help of hydraulic Cylinders are held together, there is an advantage of the mechanical Lock in that it works very simply, cheaply and safely.

advantageously, becomes the expansion body for one Plurality of expansion processes and / or for one Used a plurality of hollow profiles.

In a particular embodiment, in particular for solving the expansion body by a counter-pressure and / or for coating the hollow profile from inside, outside of the expansion body fed a second pressure medium into the interior via a pressure line. hereby the process is made flexible in that way it too be switched to a conventional Innendruckumformverfahren can. This is advantageous, on the one hand at a deadlock of the expansion body on the workpiece the expansion body solve by applying a back pressure, on the other hand, the second Pressure medium also with additives can be provided by the hollow section of the inside in particular Way mechanically-chemically coated. In such a Coating variant becomes comparatively little coating agent, which serves as a further pressure medium, because much of the Interior of the hollow profile is filled by the volume of the expansion body. The second pressure medium can also be used as a coolant for the expansion body Use of preheated hollow sections can be used. As coatings are in particular acid-resistant coatings such as. Resins (such as epoxy resin), ceramics or sintered materials especially useful.

It is also advantageous if the pressure line for feeding the second pressure medium is sealed by means of the expansion body. hereby are other valves for sealing the pressure line during operation of the expansion body Not required with only one print medium.

For special complex geometries of the workpiece to be machined, especially in complex Undercuts or turn edges, it may be useful that at least one further expansion body is at least partially in the interior of the hollow profile in such a way that he itself essentially the inner contour of the hollow profile adapts. By using multiple expansion body workpieces with separate cavities be made by forming. For the expert is understood by itself, that the use of multiple expansion bodies as well with expansion bodies is appropriate, not the suitability of a self-adaptation to the inner contour of the Hollow profiles possess.

The inventive device for forming a hollow profile comprises a hollow mold, a Cavity forms, in which a hollow profile is inserted, an expansion body, the in an interior of the hollow profile is insertable, and a pressure generator, which is in fluid communication with the expansion body, being the expansion body has a structure through which the expansion body in essentially by itself during its expansion at least partially in the interior of the hollow profile extend into and during essentially by itself, at least in part, of its contraction can withdraw from the interior of the hollow profile out.

With Help this device can a variety of arbitrarily shaped workpieces simultaneously and in faster Sequence be reshaped. With the help of the structure becomes a movement of the expansion body in particular a lengthwise extension along an oblong Hollow profile causes. The structure causes the expansion body itself defined spatial directions in a defined way stronger than in other spatial directions expands. It serves to cause the expansion body to automatically enter the interior of the hollow profile and after completion of the forming process automatically pulls out again. This is a support of the expansion body against an inner contour of the hollow profile substantially not required whereby on the one hand reduces the mechanical stress of the expansion body second, because of the automatic retraction behavior, a faster one Litigation allows becomes.

advantageously, is a pressure generator for generating an overpressure, in particular between 80 and 16000 bar, preferably between 150 and 1500 bar, especially preferably between 300 and 500 bar, depending on the form used and Used material used. Advantageously, with the pressure generator Also a negative pressure generated by the pressure medium from the expansion body withdrawn can be. With the pressure generator is advantageously an overpressure and a negative pressure can be generated.

The Hollow form has expediently at least two moldings that are mechanically closed together. Through a mechanical closure is a simple way ensures secure connection of the moldings used the mold.

In a particular embodiment of the inventions The device furthermore comprises a device for preforming the hollow profile. This is useful, in particular in the case of severe deformations or deformations of the hollow profile, in order to avoid multistage hydroforming processes.

to Deformation thick-walled hollow sections, the device advantageously comprises a heater for heating the hollow profile before its transformation. Due to the high temperatures of the hollow profile, a material flow during the forming process, which facilitates processing thicker wall thicknesses constant working pressure of the pressure medium allows.

The Device has a pressure generator in a special embodiment with a pressure transducer for incompressible fluids, in particular oil or fat, on. With the help of the pressure transducer can easily very high pressures in particular between 80 and 16000 bar, preferably between 150 and 1500 bar, more preferably between 300 and 500 bar, depending on used form and material used are generated.

In a particular embodiment of the device according to the invention is the expansion body its outer surface with designed a heat protection layer. Especially when editing hot Hollow profiles protects the heat protection layer the flexible expansion body, for example an elastomer is formed. To improve the material flow the mold is coated on its inner surface with a sliding layer. The Slip layer advantageously includes wax, oil, grease and / or Teflon additives.

advantageously, The device further comprises a check valve in the fluid-conducting connection. This will ensure that the soon after the forming process going backstroke not the pressure pipes for destroyed the pressure medium.

In In a particular embodiment, the device has a further Pressure line for acting on the interior outside of the expansion body, in particular to release of the expansion body by a counter-pressure and / or for coating the hollow profile from inside, up. With a counterpressure, a jammed with the workpiece expansion body be removed. The second print medium can also be used to the workpiece mechanically and / or chemically coating from the inside; with help the high pressure can produce a particularly durable coating become. With the second pressure line can with the described Device also conventional hydroforming be performed.

Advantageous is also, the expansion body with a sealing function for equip the pressure line. As a result, valves are unnecessary, the for the second pressure line would be required: the expansion body seals in its expansion the mouth from the second pressure line.

Independent of the special design of the expansion body with the structure can it basically be appropriate to provide at least one further expansion body in the interior of the hollow profile insertable is. This allows even workpieces be edited, the complicated undercuts or separate inside rooms exhibit.

Further Advantages are explained with reference to the following drawing. These should not limit the invention, but illustrate some ideas of the invention by way of example.

It demonstrate:

1 a device according to the invention in cross section;

2a an expansion body in cross-section in a relaxed state;

2 B after the expansion body 2a in an extended state;

3 an arrangement of the device according to the invention on a forming table;

4 a detailed view of a hollow profile in a mold with an expansion body;

5 a detailed view of another device according to the invention for hydroforming; and

6 the device according to the invention 5 in which the mold was separated from a pressure generator.

1 shows the device according to the invention in cross section with a hollow profile 1 which is in a cavity 3 a mold 2 is introduced, and in the interior 5 an expansion body 4 extends. The expansion body 4 is using a fluid-conducting connection 11 and a pressure generator 10 filled with a pressure medium, especially oil, so that it is in the interior 5 of the hollow profile 1 essentially extends by itself. He essentially carries out his stretching motion himself and does not need one through an inner contour 18 of the hollow profile 1 up brought counterforce or back pressure. The expansion body 4 fills the interior with complete pre-filling 5 of the hollow profile 1 out. Subsequently, the hollow profile 1 by pressing the pressure generator 10 , which is designed here as a pressure transducer, to an inner surface 8th the mold 2 pressed. With the help of a piston 15 of the pressure generator 10 Both an overpressure of about 350 bar can be built and a negative pressure generated, with the help of the expansion body 4 essentially by itself from the interior 5 then formed hollow profile 1 withdraws. A connection head 16 of the pressure generator 10 is form-fitting with the mold 2 for producing a fluid-conducting connection 11 connected. By appropriate shaping of the mold 2 can arbitrarily shaped hollow sections or other sub-profiles such as half-shell profiles, which may be straight or curved, are transformed. By introducing several hollow profiles 1 in the mold 2 Multi-layer structures can be produced. This is particularly important for workpieces that are to be made of various materials such as metal and ceramic or plastic. With the help of pressure pipes 17 becomes the expansion body 4 prefilled. A check valve 14 prevents kickback during or shortly after the forming process due to the kinetic energy of the piston 15 or the pressure medium in the pressure lines 17 feeds back. This will damage the pressure lines 17 prevented.

2a shows an expansion body 4 in cross-section in a relaxed state. By applying the interior of the expansion body 4 with a negative pressure, this continues to contract. The outer surface 7 of the expansion body 4 is coated with a heat-resistant layer to hollow profiles 1 which are heated to high temperatures to improve material flowability. This allows processing of hollow profiles 1 with comparatively large wall thicknesses. Through a structure 12 of the expansion body 4 becomes an expansion of the expansion body 4 in its longitudinal direction, so that at least partially inserting or retracting the expansion body 4 in or out of the interior 5 of the hollow profile 1 is made possible by the expansion body is exposed to a corresponding positive or negative pressure. A re-assembly of the device with a new unprocessed workpiece is thus facilitated.

2 B shows the expansion body 4 to 2a in a pre-filled condition. The structure 12 is due to the expansion of the expansion body 4 essentially disappeared. By specifying a pressure surge with the pressure generator 10 becomes the hollow profile 1 to the inner surface 8th the mold 2 pressed on and reshaped accordingly.

3 shows an arrangement of the device according to the invention on a workbench. The mechanical closure of the mold 2 , which consists of several molded parts 9 . 9 ' is set together, allows a space and cost-saving design of the forming device.

4 shows a section of the device according to the invention 1 , being a hollow profile 1 and an additional element 6 in the cavity 3 from two moldings 9 . 9 ' composite mold 2 is introduced. By applying the expansion body 4 with a pressure, the expansion body expands 4 in the interior 5 of the hollow profile 1 off and pushes the hollow profile 1 and the element 6 at a correspondingly high pressure of about 350 bar against the inner surface 8th the mold 2 , The mold 2 will with the help of in 1 shown connection head 6 sealed. In this way it is possible to use a hollow profile 1 with a plurality of elements, such as half-shell parts, pipe flanges, connections, pipe branches, etc. to connect. It is possible to build multi-layered, multi-layered and complex structures by using a plurality of hollow profiles arranged one inside the other or side by side. In particular, it is possible to connect a wide variety of materials, such as metals and ceramics or metals and plastics together.

5 shows a detailed view of a device according to the invention for hydroforming with an expansion body 4 , which is meander-shaped in cross-section. By actuating the piston 15 of the pressure generator 10 becomes the expansion body 4 via the fluid-conducting connection 11 subjected to oil as a pressure medium, whereby it due to the meandering structure 12 a stretching movement in the interior 5 of the hollow profile 1 performs. The structure serves to the expansion body 4 to impart an own anisotropic expansion behavior. The expansion body 4 expanding in such a way that it moves itself out of the interior 5 of the hollow profile 1 adapts. The adaptation of the expansion body 4 to the interior 5 of the hollow profile 1 is thus advantageously substantially without support of the expansion body 4 on an inner contour 18 the hollow profile 1 , As a result, on the one hand, excessive stress on the expansion body 4 avoided during its expansion, as well as allowing faster process control because of the expansion body 4 automatically inserts itself and not with the help of complicated movement means (not shown) in the interior 5 of the hollow profile 1 must be inserted. Via a ventilation line 20 can that of the expansion body 4 in the cavity 3 the mold 2 compressed air escapes. Via an additional pressure line 19 may be a second printing medium, in particular with additives that one Coating of the hollow profile 1 serve from inside, in the interior 5 outside the expansion body 4 be supplied. Via a ventilation line 20 can air out of the cavity 3 and / or the interior 5 escape. The expansion body 4 is equipped in such a way that it expands the additional pressure line 19 seals. Another sealing effect is achieved by the expanding during the forming hollow profile.

6 shows the device according to the invention 5 in which the mold 2 from the pressure generator 10 was separated. It can also be seen that any shaped, in particular angled, hollow profiles 1 can be transformed.

The invention relates to a method for hydroforming a hollow profile and comprises the following method steps: insertion of the hollow profile 1 in one in a mold 2 trained cavity 3 ; at least partial expansion of an expansion body 4 in an interior 5 of the hollow profile 1 in such a way that the expansion body 4 essentially by itself an inner contour 18 of the hollow profile 1 adapt; Forming the hollow profile 1 by expansion of the expansion body 4 ; and at least partially retracting the expansion body 4 from the interior 5 of the hollow profile 1 by removing the expansion body 4 is pulled together, as well as a device suitable for carrying out this method. The invention is characterized by the fact that complex workpieces can be easily, cleanly, safely, accurately transformed in a swift manner. The expansion body 4 contracts at a corresponding negative pressure in the pressure medium, which with the pressure generator 10 can be generated again from the interior 5 back.

1

hollow profile

2

mold

3

cavity

4

expansion body

5

inner space

6

element

7

outer surface of the expansion body 4

8th

Inner surface of the mold 2

9 9 '

moldings

10

pressure generator

11

fluid-conducting connection

12

structure

13

Device for preforming the hollow sections 1 . 1'

14

check valve

15

piston

16

connecting head

17

pressure line

18

inner contour

19

additional pressure line

20

vent line

Claims (27)

Method for hydroforming a hollow profile ( 1 ) comprising the following method steps - introducing the hollow profile ( 1 ) in a mold ( 2 ) formed cavity ( 3 ); At least partial expansion of an expansion body ( 4 ) in an interior ( 5 ) of the hollow profile ( 1 ) in such a way that the expansion body ( 4 ) substantially by itself an inner contour ( 18 ) of the hollow profile ( 1 ), wherein the expansion body is inserted substantially by itself in the interior of the hollow profile; - Forming the hollow profile ( 1 ) by expansion of the expansion body ( 4 ); At least partial retraction of the expansion body ( 4 ) from the interior ( 5 ) of the hollow profile ( 1 ), by the expansion body ( 4 ) is contracted. Process according to claim 1, wherein the expansion body ( 4 ) is expanded by exposure to an incompressible pressure medium, in particular an oil or a fat. Method according to one of the preceding claims, wherein in the cavity ( 3 ) of the mold ( 2 ) and / or in the interior ( 5 ) of the hollow profile ( 1 ) at least one further hollow profile is used. Method according to claim 3, wherein both hollow profiles ( 1 ) are formed simultaneously. Method according to claim 3, wherein said one hollow profile ( 1' ) after forming the other hollow profile ( 1 ) by a further expansion of the expansion body ( 4 ) is transformed. Method according to one of the preceding claims, wherein elements ( 6 ) made of metal, plastic, sintered materials or ceramics, in particular half-shell parts, pipe flanges, pipe branch, by forming with the hollow profile ( 1 ) get connected. Method according to one of the preceding claims, wherein the hollow profile ( 1 ) is heated before forming. Method according to one of the preceding claims, wherein the hollow profile ( 1 ) before insertion into the cavity ( 3 ) of the mold ( 2 ) is preformed. Method according to one of the preceding claims, wherein the hollow profile ( 1 ) is formed wrinkle-free. Method according to one of the preceding claims, wherein the expansion body ( 4 ) is first prefilled with the pressure medium and then inflated with a pressure surge to its full size. The method of claim 9 or 10, wherein after forming the incompressible pressure medium from the expansion body ( 4 ) is sucked off. Method according to one of the preceding claims, wherein the expansion body ( 4 ) on its outer surface ( 7 ) with a heat protection layer and / or the mold ( 2 ) on its inner surface ( 8th ) is coated with a sliding layer, in particular a wax or Teflon layer. Method according to one of the preceding claims, wherein the hollow mold ( 2 ) at least two moldings ( 9 . 9 ' ), which are mechanically closed together. Method according to one of the preceding claims, wherein the expansion body ( 4 ) for a plurality of expansion processes and / or for a plurality of hollow profiles ( 1 ) is used. Method according to one of the preceding claims, wherein, in particular for releasing the expansion body ( 4 ) by a counter-pressure and / or for coating the hollow profile ( 1 ) from inside, outside the expansion body ( 4 ) a second pressure medium in the interior ( 5 ) via a pressure line ( 19 ) is supplied. Method according to claim 15, wherein the pressure line ( 19 ) with the help of the expansion body ( 4 ) is sealed. Method according to one of the preceding claims, wherein at least one further expansion body at least partially in the interior ( 5 ) of the hollow profile ( 1 ) in such a way that it essentially extends itself from the inner contour ( 18 ) of the hollow profile ( 1 ) adapts. Device for forming a hollow profile comprising a hollow mold ( 2 ), which has a cavity ( 3 ) into which a hollow profile ( 1 ) is insertable, an expansion body ( 4 ) in an interior ( 5 ) of the hollow profile ( 1 ) is insertable, and a pressure generator ( 10 ), which in fluid-conducting connection (11) with the expansion body ( 4 ), wherein the expansion body ( 4 ) a structure ( 12 ), through which the expansion body ( 4 ) essentially by itself during its expansion at least partially into the interior ( 5 ) of the hollow profile ( 1 ) and during its contraction essentially by itself at least partially from the interior ( 5 ) of the hollow profile ( 1 ) can pull out, so that the expansion body is inserted substantially by itself the inner space of the hollow profile Apparatus according to claim 18, wherein with the pressure generator ( 12 ) an overpressure, in particular between 80 and 16000 bar, preferably between 150 and 1500 bar, more preferably between 300 and 500 bar, and a negative pressure can be generated. Device according to one of the preceding claims 18 or 19, wherein the hollow mold ( 2 ) at least two moldings ( 9 . 9 ' ), which are mechanically closed together. Device according to one of the preceding claims 18 to 20, further comprising means for preforming the hollow profile ( 1 ). Device according to one of the preceding claims 18 to 21, further comprising a heater ( 14 ) for heating the hollow profile ( 1 ) before its transformation. Device according to one of the preceding claims 18 to 22, wherein the pressure generator ( 10 ) comprises a pressure transducer for incompressible fluids, in particular an oil or a grease. Device according to one of the preceding claims 18 to 23, wherein the expansion body ( 4 ) on its outer surface ( 7 ) with a heat protection layer and / or the mold ( 2 ) on its inner surface ( 8th ) is coated with a sliding layer. Device according to one of the preceding claims 18 to 24, characterized by a check valve ( 14 ) in the fluid-conducting connection (11). Device according to one of the preceding claims 18 to 25, characterized by a further pressure line ( 19 ) for charging the interior ( 5 ) outside the expansion body ( 4 ) in particular for releasing the expansion body ( 4 ) by a counter-pressure and / or for coating the hollow profile ( 1 ) from inside. Apparatus according to claim 26, characterized by a sealing function of the expansion body for the pressure line ( 19 ). Device according to one of the preceding claims 18 to 27, characterized by at least one further expansion body, which in the interior space ( 5 ) of the hollow profile ( 1 ) is insertable.