EP2380675B1 - Method for meandering plastic reforming of bent goods with over-bending - Google Patents

Description

• a) ungebogenes, gerades Biegegut wird mittels einer ersten äußeren Biegeeinheit, einer mittleren Biegeeinheit und einer zweiten äußeren Biegeeinheit ergriffen, insbesondere wobei die mittlere Biegeeinheit zentral zwischen den äußeren Biegeeinheiten angreift;
• b) die äußeren Biegeeinheiten werden relativ aufeinander zu bewegt und die mittlere Biegeeinheit wird relativ von der Verbindungslinie der äußeren Biegeeinheiten weg bewegt.

The invention relates to a method for meandering, plastic deformation of bent material, in particular tubes, with the following steps:

• a) unbent, straight Biegegut is taken by means of a first outer bending unit, a middle bending unit and a second outer bending unit, in particular wherein the central bending unit acts centrally between the outer bending units;
• b) the outer bending units are moved relative to each other and the middle bending unit is relatively moved away from the connecting line of the outer bending units.

Such a method is from the DE 101 10 217 A1 known.

Meander-shaped deformed structures, in particular meander-shaped deformed pipes, are required, for example, for the production of solar modules for hot water preparation or for other heat exchanger applications.

In the production of such meander-shaped structures, a material to be bent is typically unwound from a coil-like stock ("coil"), directed to a straight strand and fed to a bending station. There is also the possibility that previously caught and directed bending material is fed to the bending station. The straight material to be bent is then gripped with (at least) three bending units (also called bending heads). Two outer bending units are relatively moved towards each other when the bending material is gripped, and a third bending unit is simultaneously moved relatively away from the connecting line of the two outer bending units. This will pull a loop. By repeating this process on successive sections of the Biegeguts arises the meandering structure.

The Biegegut, which is typically made of steel, copper or other metallic material, is not only plastically, but also elastically deformed when moving the bending heads. After releasing the Biegeguts of the bending units springs back a part of the deformation of the Biegeguts imposed by the bending units back. Therefore, in the manufacture of a structure, the bending heads are moved a little further than the desired structure corresponds (so-called "overbending"), so that the desired structure results after the springback of the elastic deformation.

In meandering structures, parallel meander arms are desired in most cases, ie, in a meander loop to be pulled, the material to be bent should be plastically deformed by an angle of 180 °, ie 90 ° Meandering, to be bent. The meander arms have to be bent over a bendable material (in particular the material and the shape of the Biegeguts) dependent angle, usually by about 5 °, corresponding to a total bending angle of 95 ° per Mäanderarm.

If the meandering arm length is quite large compared to the distance of the meandering arms, however, the outer bending units encounter each other when the loop is pulled, even at a slight overbending angle. This limits the plastically deflectable bending angle per meandering arm, with long meandering arms below the 90 ° required for parallel meandering arms.

In order to be able to produce parallel meander arms in long meandering arms, it is known that the bent material in the area of the loop end can be slightly pushed in with the bending finger after bending, so that a noticeable dent results in the bending material. On the one hand, however, the production process becomes more complex, and on the other hand, the kink deteriorates the strength of the meandering structure and the flow behavior of circulating water flowing in the meandering structure, for example when the meandering structure is used in a heat exchanger.

The DE 101 10 217 A1 describes a tube bending machine comprising three longitudinally movable bending devices, with which meander-shaped structures can be made, wherein a central bending device is moved perpendicular to the longitudinal direction. The bending devices are preceded by a stationary roller straightening section through which the material to be bent is fed to the bending devices. To implement the bending devices, they can be moved away from the bending material laterally.

Object of the invention

The invention has for its object to allow for the production of meandering structures larger plastic bending angle in the context of looping.

Brief description of the invention

This object is achieved by a method of the type mentioned above, which is characterized in that c) the outer bending units are guided relative to each other slightly offset past each other, wherein the mutual offset of the outer bending units is so small that in the bending material with respect to the offset direction only an elastic, but not a plastic deformation takes place,
and wherein the entire bending process takes place substantially in only one bending level, which is spanned by the three bending units, and this orientation is left only by the offset in the elastic deformation region of the material to be bent.

According to the present invention, the loop drawing is performed during the deformation of Biegegut so that, in particular for the purpose of overbending, the two outer bending heads not only towards each other, but continue past each other and beyond a certain distance away from each other. For this purpose, the bending heads are slightly offset from each other. The offset usually occurs in the course of the relative process of the outer bending heads towards each other. In particular, in a first period of time, first of all, a relative movement of the outer bending heads can take place directly toward one another, which is then superimposed on an offset movement in a later period of the bending process. The offset may also occur during an interruption of the approach movement of the two outer flexures. But it is also possible to realize the offset in that the outer bending units already at the beginning of the bending process does not move directly to each other, but the relative Approach movement of the outer bending heads from the beginning has a certain deviation from the original course direction of the still unbent, straight Biegeguts.

In the context of the invention, the gripped bending material is crossed in the area between the outer bending units and the middle bending unit, and a significantly greater overbending is possible than without offset if the outer bending units would block each other. The greater overbending makes it possible in particular to produce a parallel meander course, even if the ratio of meander length to meander spacing is relatively large.

Since the offset remains in the elastic range, no post-deformation needs to be applied to eliminate unwanted bends in the direction of the sequence of meander loops. In particular, directly planar meander structures can easily be bent using the method according to the invention.

Tubular Biegegut, which can be used in the invention, typically has a circular cross section; but there are also other cross sections, such as oval or square cross sections possible.

Preferred variants of the invention

In a preferred variant of the method it is provided that the relative movement of the outer bending units takes place in a first direction in step b), that the relative offset of the outer bending units takes place in step c) in a second direction which is at least approximately perpendicular to a bending plane, which is spanned by the three bending units, and that in step c), the outer bending units are guided past each other at least approximately parallel to the first direction. This variant has proven itself in practice; It is particularly easy to implement and with little space. Note that the offset motion in the second direction is typically superimposed on a portion of the relative travel of the outer flexure heads in the first direction. The location of a bending unit here means the location of the access of the bending unit to the material to be bent.

Also preferred is a method variant in which one of the outer bending units is held stationary during steps b) and c). By keeping an external bending unit stationary during the bending process (in steps b) and c), the process flow and the structure of the associated bending machine are simplified. It should be noted that the fixed bending unit can be switched over for the purpose of removing and threading in the bent item or a change in the bending angle, for example by offset transversely to the first direction.

In an advantageous variant of the method, it is provided that in step b) the outer bending units are moved horizontally relative to one another, and the middle bending unit is moved vertically and horizontally. The horizontal movements of the outer bending unit and the middle bending unit are typically in parallel directions. In this case, the method or an associated bending machine requires only a relatively small footprint (footprint).

Particularly preferred is a variant of the method, in which the outer bending units are guided past each other so far that parallel elastic meandering sections are formed after elastic recovery of the overbending of the bending material. Especially with relatively long meandering arms, such meandering structures can be produced particularly easily with the method according to the invention.

• eine erste äußere Biegeeinheit, eine zweite äußere Biegeeinheit und eine mittlere Biegeeinheit,
• sowie Mittel, um die Biegeeinheiten von einer ersten Arbeitsposition, in welcher sie das ungebogene, gerade verlaufende Biegegut ergreifen können, in eine zweite Arbeitsposition, in welcher sie das Biegegut maximal verformen können, zu überführen,

wobei die Mittel dazu ausgebildet sind, für das Überführen der Biegeeinheiten von der ersten Arbeitsposition in die zweite Arbeitsposition die äußeren Biegeeinheiten relativ aufeinander zu zu verfahren und die mittlere Biegeeinheit relativ von der Verbindungslinie der äußeren Biegeeinheiten weg zu verfahren, dadurch gekennzeichnet, dass die Mittel dazu ausgebildet sind, in einem zweiten Teil des Überführens der Biegeeinheiten von der ersten Arbeitsposition in die zweite Arbeitsposition die beiden äußeren Biegeeinheiten geringfügig gegeneinander versetzt aneinander vorbei zu führen, wobei der gegenseitige Versatz der äußeren Biegeeinheiten so gering ist, dass im Biegegut bezüglich der Versatzrichtung lediglich eine elastische, nicht aber eine plastische Verformung erfolgt, und wobei die Mittel weiterhin so ausgebildet sind, dass der gesamte Biegevorgang im Wesentlichen in nur einer Biegegutebene erfolgt, die durch die drei Biegeeinheiten aufgespannt wird, und diese Ausrichtung lediglich durch den Versatz im elastischen Verformungsbereich des Biegeguts verlassen wird. Dadurch sind größere Überbiegewinkel möglich als bei herkömmlichen Biegemaschinen, so dass insbesondere bei langen Mäanderarmen große plastische Biegewinkel, insbesondere von 90° pro Mäanderarm, gefertigt werden können. Bevorzugt sind die Mittel dazu ausgebildet, erst im zweiten Teil des Überführens die beiden äußeren Biegeeinheiten gegeneinander zu versetzen; es ist aber auch möglich, die Mittel so auszubilden, dass bereits von Beginn des Biegeprozesses an die relative Bewegung der äußeren Biegeeinheiten geringfügig aneinander vorbei zielt.In the context of the present invention also includes a bending machine for the meandering plastic deformation of Biegegut, in particular of pipes comprising

• a first outer bending unit, a second outer bending unit and a middle bending unit,
• and means for transferring the bending units from a first working position in which they can grasp the unbent, straight running bending material to a second working position in which they can maximally deform the bending material,

wherein the means are arranged to relatively move the outer bending units relative to each other for transferring the bending units from the first working position to the second working position and to relatively move the mean bending unit away from the connecting line of the outer bending units, characterized in that the means therefor are formed, in a second part of the transfer of the bending units from the first working position to the second working position, the two outer bending units slightly offset from each other to lead past each other, wherein the mutual offset of the outer bending units is so small that in the bending material with respect to the displacement direction only one elastic, but not a plastic deformation takes place, and wherein the means are further formed so that the entire bending process is carried out substantially in only one bending plane, which is spanned by the three bending units, and this Ausri Just leave by the offset in the elastic deformation range of the Biegeguts. As a result, larger overbending angles are possible than in conventional bending machines, so that large plastic bending angles, in particular of 90 ° per meandering arm, can be produced, in particular with long meandering arms. Preferably, the means are adapted to offset the two outer bending units against each other only in the second part of the transfer; but it is also possible to form the means so that even from the beginning of the bending process to the relative movement of the outer bending units slightly over each other.

Particularly preferred is an embodiment of the bending machine according to the invention, which is characterized in that a straight running guide is provided, on which the first outer bending unit is movable, wherein one of the outer bending units with a transverse carriage transverse to the guide direction between a first, aligned position and a second offset position is movable, in particular wherein the second outer bending unit along the guide is not movable, and that in the first, aligned position of the cross slide, the first outer bending unit is straight (directly) to the second outer bending unit to be moved, and in the second offset position, the first outer bending unit on the second outer bending unit is moved past. This embodiment saves space and has proven itself in practice. Preferably, the first outer bending unit with the cross slide is movable, and the second outer bending unit is stationary (not movable on the guide) formed. Preferred is a development of this embodiment, in which the position of the cross slide in the transverse direction with a drive, in particular a pneumatic cylinder, is adjustable. In the simplest case, the drive only serves to switch between the first, aligned position and the second, offset position. In this development, the location at which the offset is applied, can be adjusted by the program, whereby this development can be easily adapted to different shapes of meander loops (especially different meander lengths and meander distances). In particular, a sufficient distance to a separation unit (or other clamping unit) before applying the offset can be set to avoid plastic deformation in the region between the separation unit and the first outer bending unit. Pneumatic cylinders for the method of cross slide are particularly cost.

In an alternative development it is provided that the first outer bending unit with the cross slide is movable, and that along the guide positive guide means are arranged with which the cross slide is aligned in the process along the guide in the transverse direction, in particular wherein the cross slide roll on lateral bands or can slide off. In this case, a collision of the outer bending units is excluded in the context of incorrect operation. A positive guide (such as a slide guide) also simplifies the control of the bending machine.

Another advantageous embodiment of the bending machine according to the invention is characterized in that a guide is provided, on which the first outer bending unit is movable, that the second outer bending unit is not formed along the guide movable, that the guide in a first straight portion extends in that the first outer bending unit in the first section is straight on the second outer one Bending unit is movable, that the guide in a second straight section parallel to the first section, but with an offset to the second outer bending unit, wherein the offset is sufficient that the first outer bending unit on the second section of the guide can pass the second outer bending unit , especially just can happen, and that between the two straight sections, the guide has a curved intermediate section. In this embodiment, a collision of the outer bending units is also excluded by incorrect operations, since the guide leads the first outer bending unit always past the second outer bending unit. In the transition between the straight sections, the guide is curved here. A cross slide is not necessary in this embodiment.

In a preferred embodiment of this embodiment, it is provided that the guide extends in a horizontal plane, and the central bending unit is movable in a vertical plane. This structure requires only a small footprint (footprint).

Particularly preferred is also an embodiment in which the bending machine is adapted to guide the central bending unit by at least 800 mm, preferably at least 2500 mm from the connection line of the outer bending units, and the outer bending units by at least 200 mm, preferably at least 500 mm to lead past each other. Meandering structures with long, parallel meandering arms can be fabricated with these dimensions for stretch path and overbending path.

In a preferred embodiment, the bending machine is designed for carrying out a method according to the invention described above. Finally, in the context of the present invention, the use of a bending machine according to the invention, described above for meandering, plastic deformation of Biegegut, in particular of tubes, in particular wherein a method described above, inventive method is used.

Further advantages of the invention will become apparent from the description and the drawings. Likewise, according to the invention, the above-mentioned features and those which are still further developed can each be used individually for themselves or for a plurality of combinations of any kind. The embodiments shown and described are not to be understood as exhaustive enumeration, but rather have exemplary character for the description of the invention.

Detailed description of the invention and drawing

Fig. 1a bis 1e

den Ablauf des erfindungsgemäßen Biegeverfahrens in verschiedenen Stadien an einer erfindungsgemäßen Biegemaschine, mit gerader Führung, in schematischer Seitenansicht;

Fig. 2a

das Stadium gemäß Fig. 1 a in einer schematischen Aufsicht;

Fig. 2b

das Stadium gemäß Fig. 1d in einer schematischen Aufsicht;

Fig. 3

eine schematische Aufsicht auf eine weitere Ausführungsform einer erfindungsgemäßen Biegemaschine, mit gekrümmter Führung.

The invention is illustrated in the drawing and will be explained in more detail with reference to embodiments. Show it:

Fig. 1a to 1e

the sequence of the bending process according to the invention in various stages on a bending machine according to the invention, with a straight guide, in a schematic side view;

Fig. 2a

according to the stage Fig. 1 a in a schematic plan view;

Fig. 2b

according to the stage Fig. 1d in a schematic plan;

Fig. 3

a schematic plan view of another embodiment of a bending machine according to the invention, with curved guide.

The FIGS. 1a to 1e and Fig. 2a and 2b illustrate by way of example the sequence of the method according to the invention on an exemplary bending machine 1 according to the invention.

The bending machine 1, see. FIGS. 1a and 2a , Has a machine bed 2, on which a straight guide 3 is formed. On the guide 3, a first outer bending unit (bending head) 4 can be moved by means of a base carriage 15 in the guide direction (here x-direction, x, y and z form an orthogonal system). A middle bending unit (bending head) 5 (in Fig. 2a is thereof for simplicity only the bending core 5a shown) is in a vertical plane (here xz plane) with linear slide 7a, 7b movable. Furthermore, a stationary (not movable along the guide direction) second outer bending unit (bending head) 6 is fixed to the machine bed 2. On the guide 3, a notching unit 8 and separation unit 9 are further movable (the movements of the notching unit 8 and the separation unit 9 during the bending process are not shown below for simplicity).

The bending machine 1 deforms Biegegut 10 to a meander-shaped structure 11, wherein the loops 12 of the meandering structure 11 are pulled sequentially.

In a starting position ( Fig. 1a . Fig. 2a ), the Biegegut 10 is aligned and is gripped by the three bending units 4, 5, 6; In this case, bending cores 4a, 5a, 6a (bending tools) and bending fingers (for example, bending rollers or sliders) are applied from two sides to the Biegegut 10. The bending units 4, 5, 6 (ie the places where the Bending units 4, 5, 6 each attack on Biegegut 10) are arranged in a line (first working position, AP1).

Then the drawing of the next loop is started, cf. Fig. 1b , In this case, the middle bending unit 5 is pulled upwards (away from the connecting line of the outer bending units 4 , 6) with the bending material 10 grasped (note that the proportions in the figures are exaggerated, the bending material 10 is not appreciably stretched in the axial direction), and the two outer bending units 4, 6 move relative to each other (so-called first direction, here x-direction). For the latter relative movement, however, only the first outer bending unit 4 moves on the guide 3 to the right. In order to remain in the x direction in the middle between the outer bending units 4, 6, the mean bending unit 5 simultaneously moves slightly to the right. The travel paths of the bending units 4, 5 are typically precalculated for the desired structure 11 and synchronized via an electronic control, not shown.

It should be noted that when moving the first outer bending unit 4 Biegegut 10 is retraced in the bending machine 1 from the left.

In the further process of the bending units 4, 5, cf. Fig. 1c , the two outer bending units 4, 6 continue to approach until finally the meandering arms (meandering portions) 13a, 13b of the loop 13 to be pulled are aligned parallel to one another. If the deformation process were stopped here, the meander arms 13a, 13b would spring back elastically and spread apart again (similar to FIG Fig. 1b shown). Therefore, according to the invention, the deformation process is continued.

To continue the deformation process, cf. Fig. 1d and Fig. 2b , a transverse slide 14 is used, which is mounted on the base carriage 15 in a direction transverse to the guide direction (so-called offset direction or second direction, here γ-direction), with a pneumatic cylinder 16 is movable. On the cross slide 14, the first outer bending unit 4 is arranged.

In the first part of the bending process, the cross slide was in a first, aligned position GP, cf. Fig. 2a with which the bending core 4a could be moved directly onto the bending core 6a. The cross slide 14 is then moved away from the second outer bending unit 6 in a second, offset position VP before reaching the second outer bending unit 6, so that the first outer bending unit 4 (and in particular its bending core 4a), the second outer bending unit 6 (and in particular their bending core 6a) can pass in the x-direction (first direction) in further process. Due to the insignificance of the offset, the Biegegut 10 is only elastic, but not plastically deformed. Then the staggered, first outer bending unit 4, together with the bending material 10 held, is moved past the second outer bending unit 6. In this case, in the projection onto the vertical plane (here xz-plane, approximately corresponding to the bending plane), the bending material 10 or the meandering arms 13a, 13b, cf. Fig. 2b , The middle bending unit 5 (in Fig. 2b only indicated by the associated bending core 5a) must be tracked further (in the x direction corresponding to half the way of the first outer bending unit 4, and slightly in the z direction).

The FIG. 2b shows the second working position AP2, in which the bending material 10 is maximally deformed (plastic and elastic). In the area between, for example, the separation unit 9 and the first outer bending unit 4 (or its bending core 4a) and furthermore between the first outer bending unit 4 (or its bending core 4a) and the middle bending unit (or its bending core 5a), the bending material 10 runs due to the offset of the first outer bending unit 4 not quite parallel to the xz plane. By contrast, the material to be bent between the middle bending unit 5 (or its bending core 5a) and the second outer bending unit (or its bending core 6a) runs parallel to the xz plane. Note that the basic structures of the outer bending units 4, 6 are respectively disposed on opposite sides with respect to the bending material 10 (or the bending plane), so that mutual obstructions are substantially limited to the bending cores (bending tools) 4a, 6a.

The bending machine 1 presented here is designed, in particular by a sufficiently long guide 3, to provide an overbending path ÜW of at least 500 mm. The intermediate bending unit 5 further has an extension path SW away from the connecting line of the first and second outer bending units 4, 6 of at least 2500 mm in the illustrated bending machine 1.

Then the bending units 4, 5 are moved back again. In the position of Fig. 1e the elastic deformation of the loop 13 is just spring-back (both in the x-direction and in the γ-direction), so that the bending units 4, 5, 6 can be released from the material 10 to be bent. The permanent plastic deformation results in a parallel alignment of the meander arms 13a, 13b. The finished loop 13 (or the entire previous meander structure can be offset by a meander distance to the right with a handling unit, not shown).

It should be noted that the bending units 4, 5, 6 in the invention may have special mechanisms for threading in and out of the Biegeguts 10, in particular (along a vertical vertical bending plane here divisible bending cores, or in the γ-direction adjustable bending cores, approximately with three positions for two different bending grooves on the bending core (one for start and end pieces of a meander structure 11, and one for normal loops 12) and for a retracted position for threading and unthreading. The travel paths of the bending units 4, 5 for overbending are freely programmable and can be easily changed (corrected) in particular in a batch change (ie to another shape of the meander structure).

It should be noted that within the scope of the invention more than three bending units can also be used, for example two separate middle bending units, if a particularly large spacing of the meandering arms is desired.

The FIG. 3 illustrates a schematic plan view of another construction of a bending machine 1 according to the invention.

In this bending machine 1, a first outer bending unit 4 is movable on a guide 20, which has a first, straight portion 20a, a curved intermediate portion 20b and a second straight portion 20c.

While the first outer bending unit 4 moves on the first portion 20a, it (or its bending core 4a) is guided directly to a stationary second outer bending unit 6 (or its bending core 6a) to or from this. While the first outer bending unit 4 in an initial position (first working position, in Fig. 3 shown) is on this portion 20a, the Biegegut 10 can be taken in a straight alignment with all the bending units 4, 5, 6, see. also the middle bending unit 5.

In the intermediate portion 20b, the first outer bending unit 4 is slightly offset from the second outer bending unit 6 in the γ direction, so that the first outer bending unit 4 (or its bending core 4a) in the second straight portion 20c at the second outer bending unit 6 (or their Biegekern 6a) can be passed over, see. the dashed lines, passed by first outer bending unit 4 '.

In summary, the present invention proposes for the production of meander-shaped structures in the context of a bending process to establish an overbend, in which the ends of the Biegegutabschnittes to be deformed (typically defined by the clamping of two outer bending units) are slightly offset relative to each other and past each other. As a result, a very strong overbend is possible, which allows a parallel alignment of the meander arms in the context of plastic deformation even with large aspect ratios in meander loops. The displacement is typically carried out in a second part of the bending process, while in the first part of the bending process typically the ends of the Biegegutabschnitts to be deformed are moved directly towards each other. The entire bending process typically takes place essentially in only one plane (bending material plane); only by the offset to the mutual passing of the ends of the Biegegutabschnittes this orientation is left slightly (in the elastic deformation region).

Claims (14)

1. Method for meandering plastic deformation of bending material (10), in particular pipes, having the following steps:

   a) unbent, straight bending material (10) is gripped by means of a first external bending unit (4), a central bending unit (5) and a second external bending unit (6), in particular with the central bending unit (5) engaging centrally between the external bending units (4, 6);

   b) the external bending units (4, 6) are moved towards each other in relative terms and the central bending unit (5) is moved away from the connection line of the external bending units (4, 6) in relative terms;
   characterised in that

   c) the external bending units (4, 6) are guided past each other in a manner slightly offset relative to each other, the mutual offset of the external bending units (4, 6) being so small that only a resilient but not a plastic deformation is carried out in the bending material (10) with respect to the offset direction (y),

   and the entire bending operation being carried out substantially in only one bending material plane which is defined by means of the three bending units (4, 5, 6), and this orientation being left only by the offset in the resilient deformation region of the bending material (10).
2. Method according to claim 1,
   characterised in that
   the relative movement of the external bending units (4, 6) is carried out in step b) in a first direction (x),
   in that the relative offset of the external bending units (4, 6) is carried out in step c) in a second direction (y), which is at least substantially perpendicular relative to a bending material plane which is defined by the three bending units (4, 5, 6),
   and in that in step c) the external bending units (4, 6) are guided past each other at least substantially parallel with the first direction (x).
3. Method according to either of the preceding claims, characterised in that one of the external bending units (6) is retained in a fixed manner during the steps b) and c).
4. Method according to any one of the preceding claims, characterised in that, in step b), the external bending units (4, 6) are moved horizontally relative to each other, and the central bending unit (5) is moved vertically and horizontally.
5. Method according to any one of the preceding claims, characterised in that the external bending units (4, 6) are guided past each other precisely to such an extent that, after resilient return of the overbending of the bending material (10), parallel meandering portions (13a, 13b) are formed.
6. Bending machine (1) for the meandering plastic deformation of bending material (10), in particular pipes,
   comprising:

   - a first external bending unit (4), a second external bending unit (6) and a central bending unit (5),

   - and means for moving the bending units (4, 5, 6) from a first operating position (AP1), in which they can grip the unbent straight bending material (10), into a second operating position (AP2) in which they can deform the bending material (10) to the maximum extent,

   the means being configured to move the external bending units (4, 6) towards each other in relative terms in order to move the bending units (4, 5, 6) from the first operating position (AP1) into the second operating position (AP2), and to move the central bending unit (5) away from the connection line of the external bending units (4, 6) in relative terms, characterised in that
   the means are constructed, in a second portion of the movement of the bending units (4, 5, 6) from the first operating position (AP1) into the second operating position (AP2), to guide the two external bending units (4, 6) past each other in a manner slightly offset relative to each other, the mutual offset of the external bending units (4, 6) being so small that only a resilient but not a plastic deformation takes place in the bending material (10) with respect to the offset direction (y),
   and in that the means are further constructed in such a manner that the entire bending operation is carried out substantially in only one bending material plane which is defined by the three bending units (4, 5, 6), and this orientation is left only by the offset in the resilient deformation region of the bending material (10).
7. Bending machine (1) according to claim 6, characterised in that
   there is provided a straight guide (3), on which the first external bending unit (4) can be displaced,
   one of the external bending units (4) being able to be displaced with a transverse sliding member (14) transversely relative to the guiding direction (x) between a first aligned position (GP) and a second offset position (VP),
   in particular with the second external bending unit (6) being constructed so as not to be able to be displaced along the guide (3),
   and in that, in the first aligned position (GP) of the transverse sliding member (14), the first external bending unit (4) can be displaced in a straight manner towards the second external bending unit (6), and, in the second offset position (VP), the first external bending unit (4) can be displaced past the second external bending unit (6).
8. Bending machine (1) according to claim 7, characterised in that the position of the transverse sliding member (14) can be adjusted in the transverse direction (y) by means of a drive, in particular a pneumatic cylinder (16).
9. Bending machine (1) according to claim 7, characterised in that the first external bending unit (4) can be displaced with the transverse sliding member (14) and in that there are arranged along the guide (3) force-guiding means, by means of which the transverse sliding member (14) is orientated during displacement along the guide (3) in a transverse direction (y),
   in particular with the transverse sliding member (14) being able to roll or slide on lateral strips.
10. Bending machine (1) according to claim 6, characterised in that there is provided a guide (20) on which the first external bending unit (4) can be displaced,
    in that the second external bending unit (6) is constructed so as not to be able to be displaced along the guide (20),
    in that the guide (20) extends in a first straight portion (20a) in such a manner that the first external bending unit (4) in the first portion (20a) is displaceable in a straight manner towards the second external bending unit (6),
    in that the guide (20) in a second straight portion (20c) extends parallel with the first portion (20a) but offset with respect to the second external bending unit (6), the offset being sufficient for the first external bending unit (4) to be able to pass, in particular to just be able to pass, the second external bending unit (6) on the second portion (20c) of the guide (20),
    and in that, between the two straight portions (20a, 20c), the guide (20) has a curved intermediate portion (20b).
11. Bending machine (1) according to claim 10, characterised in that the guide (20) extends in a horizontal plane, and the central bending unit (5) can be displaced in a vertical plane.
12. Bending machine (1) according to any one of claims 6 to 11, characterised in that the bending machine (1) is constructed to guide the central bending unit (5) by at least 800 mm, preferably at least 2500 mm away from the connection line of the external bending units (4, 6), and to guide the external bending units (4, 6) past each other by at least 200 mm, preferably at least 500 mm.
13. Bending machine (1) according to any one of claims 6 to 12, constructed to carry out a method according to any one of claims 1 to 6.
14. Use of a bending machine (1) according to any one of claims 6 to 13 for the meandering plastic deformation of bending material (10), in particular of pipes,
    in particular with a method according to any one of claims 1 to 6 being used.

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