Abstract:
On a machine for bending rod-shaped or tubular workpieces, which includes a bending head having a bending mandrel mounted on a rotational axis and rotatable by means of a rotary drive, and having a clamping device for pressing the workpiece to be bent against a forming groove on the bending mandrel and also a feeding device for the workpiece to be processed, whereby the clamping device is positionable relative to the bending mandrel and can is also pivotable concentrically to the rotational axis of the bending mandrel, the clamping device is attached to two mutually independent rotary drives, one of which performs its pivoting movement about the rotational axis of the bending mandrel, and via the other of which it can be moved with respect to the bending mandrel by using an interposed conversion transmission that converts a rotary motion to a linear motion, whereby the bending head includes three concentrically nested rotary shafts for transmitting the drive of the three rotary drives to the bending mandrel, to the conversion transmission and to the clamping device, each of which is connected to one of the rotary drives.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to a machine for bending rod-shaped or tubular workpieces, whereby the bending apparatus includes a bending head having a bending mandrel mounted on a rotational axis and rotatable by means of a rotary drive, and having a clamping device for pressing the workpiece to be bent against a forming groove on the bending mandrel, whereby the bending head also has a feeding device for the workpiece to be processed, and the clamping device is positionable relative to the bending mandrel and is also pivotable concentrically to the rotational axis of the bending mandrel.  
       BACKGROUND OF THE INVENTION  
       [0002]     Such bending apparatus are used in modern bending machines for rod-like workpieces and for prefabricated conduits primarily having larger cross sections.  
         [0003]     In such cases the bending apparatus constitutes a plurality of units whose interaction makes good bending results possible, especially in the case of tubular workpieces with thin walls.  
         [0004]     A bending apparatus should ideally be able to satisfy a majority of particular requirements in that it should be able to perform the following functions: right-hand and left-hand bending, draw bending and curling, coiling, producing a bend directly after a different bend without an intervening straight segment, producing bends with different radii, bending pipes of different diameters, preventing wrinkling, three-dimensional bending, and enabling simple retooling.  
         [0005]     Bending devices are known with bending heads that must be e.g. pivoted to convert from left to right coiling (see EP 1 226 887 B1, EP 1 291 094 B1 and EP 1 350 578 A1), or which are constructed symmetrically (WO 03/053 606 A1). Likewise, the possibility of exchanging a bending head for such a conversion is also known.  
         [0006]     Also prior art is the use of multi-stage dies for producing different bending radii and for processing workpieces of different diameters, as well as the use of forming jaws for producing sequential bends without an intervening straight segment (see EP 1 350 578 A1 and WO 03/053 606 A1). The use of a slide rail to support and track the material is also known (see EP 1 291 094, EP 0 963 800 B1 und U.S. Pat. No. 6,651,475).  
         [0007]     WO 2004/000479 A1 describes a bending apparatus of the type named at the beginning that can be used both for left-hand and for right-hand bending, without the bending mandrel having to be changed. It is essentially circular in design and has two circular forming grooves arranged on it that are axially offset from one another, one of which is used for left-hand bending and the other for right-hand bending. However, positioned on each of the forming grooves, at the place where the free end of the bent pipe again emerges tangentially from the ring groove when bending pipe, is a corresponding forming piece that itself has a straight-line forming segment that branches off tangentially from the corresponding forming groove, so that an end piece of the pipe to be bent that diverges in a straight line tangentially from the bend lies in this section of the forming groove. For bending, the pipe delivered by a feed device is placed and pressed against the corresponding forming groove section of the forming piece that diverges tangentially from the forming groove in question, by means of a clamping device that can be moved relative to the bending mandrel, after which, when the pipe is clamped in place, the clamping device is pivoted together with the bending mandrel concentrically to the rotational axis of the latter, until behind the straight-line section of the forming groove, in the adjacent ring groove, the pipe is bent accordingly during the rotation. The clamping device is then separated from the bending mandrel, and the bent area of the bent pipe is removed from the forming groove of the bending mandrel and its straight-running end area is removed from the forming groove section of the forming piece.  
         [0008]     If the same pipe is then to receive e.g. another bend in the other direction, which is to be e.g. directly adjacent to the first bend, the piece of pipe that has already been bent is moved to the other side of the bending mandrel, to the elevation of the other forming groove on the bending mandrel. At the same time, the clamping device is pivoted about the rotational axis of the bending mandrel relative to the latter so that it is positioned on the other side of the mandrel, and the pipe is again present between it and the bending mandrel. The pipe is then re-clamped between the clamping device and the bending mandrel (there again in a forming piece mounted correspondingly on the other forming groove, having a segment of forming groove that runs in a straight line, emerging tangentially from the forming groove of the bending mandrel), and the new bend in the pipe is then produced by rotating both the clamping device and the bending mandrel about the rotational axis of the bending mandrel, this time in the opposite direction.  
         [0009]     Since there are two forming grooves on the bending mandrel, axially offset to one another, for left-hand and right-hand bending, each of which has an associated fitting with the straight-line segment of forming groove, and since (because of the difference in bending direction) the two fittings protrude linearly from the bending mandrel in opposite directions, albeit by different amounts, accordingly the clamping device, since in each of its pivoted positions for the two bending directions it must cooperate with one of the forming grooves and the associated forming segment at different heights, must also have forming grooves positioned corresponding to the difference in level to press the pipe against the bending mandrel and its forming segments. This requires geometrically that the corresponding forming grooves, as well as the fittings on the bending mandrel, must also be adjacent to one another, which results in a complicated structure and a relatively great width of the clamping device, but which is not favorable in view of the desired compact construction of such bending devices. The same is also true of the wrinkle smoother utilized there in the form of relatively long guide strips immediately upstream of the clamping device in the feeding direction of the pipe, with a corresponding forming groove for placing the wire. Here too, because of the difference in height of the forming grooves on the bending mandrel with respect to left-hand and right-hand bending, two different smoothing strips must be used that point in opposite directions, where each embodies a forming groove, and that must also be moved by corresponding travel distances next to the sliding mandrel. This too takes up more space than desired. The publication says nothing about how the movement of the clamping device relative to the bending mandrel is realized, but it can be seen from the illustrative figures in the publication that a shifting occurs along a guide strip that is mounted on the underside of the clamping device and is overlapped and positively gripped by the latter, for which it is quite obvious that a linear drive must be used, although this is not described in further detail there.  
         [0010]     Starting from this basis, the object of the invention is now to improve such a bending device such that the clamping device gets by with an especially small space requirement and a separate linear positioning motor is not needed for the linear movement of the clamping device.  
       SUMMARY OF THE INVENTION  
       [0011]     This is accomplished according to the present invention in a bending apparatus of the type named at the beginning in that the clamping device is attached to two mutually independent rotary drives, one of which performs its pivoting movement about the rotational axis of the bending mandrel, and via the other of which it can be moved with respect to the bending mandrel using an interposed conversion transmission that converts a rotary motion to a linear motion, whereby the bending mandrel includes three concentrically nested rotary shafts for transmitting the force from the three rotary shafts to the bending mandrel, to the conversion transmission and to the clamping device, each of which is connected to one of the rotary drives.  
         [0012]     Preferably the innermost rotary shaft carries the bending mandrel, which is mounted at the very top of the bending head, while—again preferably—the middle rotary shaft drives the conversion transmission, which is mounted on the bending head below the bending mandrel, to produce the linear motion for the clamping device, whereby the outermost rotary shaft is preferably connected rotationally fixed to a supporting plate that is positioned below the conversion transmission, on which plate the clamping device is mounted such that it can be moved in one direction toward the bending mandrel.  
         [0013]     With the bending device according to the present invention, having the linear adjusting motion of the clamping device also derived from a rotary drive (using an interposed conversion transmission) creates the option of transmitting force from the three rotary drives to the desired parts via three concentrically nested rotary shafts, and thereby achieving an especially compact overall design for the bending head, whereby it is not difficult to realize the integration of such a conversion transmission into the overall construction of the three concentric shafts within the framework of the bending head. The necessity of using a separate linear drive that must be mounted separately on the outside is avoided. The motors for the three rotary drives are activated for example using a program control unit, whereby the rotary motion can be converted especially quickly and precisely via the conversion transmission to the linear motion of the clamping device relative to the mandrel. At the same time, it is possible to set a desired pressing force with which the clamping device presses the pipe against the forming groove in the bending mandrel without any problem.  
         [0014]     The conversion transmission can be of any suitable constructional design. Especially preferred however is for the conversion transmission to include a disk cam containing a groove that runs eccentrically to its axis of rotation, which is engaged by a formed piece that conforms to the cross section of the groove and is attached to the clamping device, which can be shifted in the groove, and whose distance from the axis of rotation of the disk cam can be changed by turning the disk cam. That makes it possible, in conjunction with a type of linkage guide, to quickly bring about a corresponding linear adjustment motion of the clamping device through the rotary movement of the disk cam, whereby the drive is not only very compact, but the adjustment motions can also be carried out especially quickly.  
         [0015]     At the same time, the clamping device preferably has a holding device which is affixed to the disk cam so that they rotate together, as well as a tensioning block that is borne so that it can slide in a linear guide that is mounted on the holding device, and to which the formed piece that engages the groove in the disk cam is attached. This results in a very effective and yet simple design for the conversion transmission.  
         [0016]     At the same time, the tensioning block is advantageously provided with an interchangeable attached clamping jaw, in which there is a forming groove that corresponds to the position of the forming groove in the bending head and that matches the shape of the workpiece that is to be clamped. As a result, when the workpiece to be bent is changed, the shape of the forming groove can easily be adapted to its changed shape dimensions by merely changing the clamping jaw.  
         [0017]     Especially preferred here is for the tensioning block to be attached to a holding element that carries the formed piece via it and engage the linear guide, where, again preferably, this holding element in turn sits on a carrier piece to which it is attached in such a way that it can be shifted in a direction perpendicular to the alignment of the linear guide, and on which the formed piece is mounted so that it has a sliding engagement with the linear guide. Especially preferred is for the holding element to be attached to a drive device on the carrier piece, for moving it with respect to the latter.  
         [0018]     This achieves all-in-all a very compact overall construction for the clamping device, which is also accompanied by a very small space requirement.  
         [0019]     Especially recommended with a bending apparatus according to the present invention is for there to also be a wrinkle smoother immediately upstream of the clamping device, when viewed in the feed direction of the workpiece, by which wrinkling of the workpiece to be bent can be prevented in the area of the workpiece directly upstream of the bend. That prevents the material to be bent, e.g. tubing, from wrinkling or tearing during the bending process. Any suitable design can be used for the wrinkle smoother, but it is especially preferable for it to have slip jaws that can be placed in contact with the workpiece that is to be bent.  
         [0020]     For controlling the three different rotary drives and possible additional drive devices (e.g. for positioning the holding element on the carrier piece), it is advantageous to provide a program control device.  
         [0021]     Another preferable design of the bending device according to the present invention also consists in providing an additional drive device by which the bending head can be moved in two directions that are perpendicular to one another and both of which are perpendicular in turn to the feed direction of the workpiece to be bent, which results in the possibility of lowering the bending head below the pipe, which is held by a clamping head and protrudes from it (possibly already with a bend in the area of one of its ends) underneath it over to its other side, and then raising it again, in order to thereby bend the workpiece in the other bending direction, whereby in this case the clamping device merely has to be rotated by 180°, and the bending mandrel with the forming groove on its opposite side must be brought into the correct orientation to the side of the pipe which then faces it. With the exception of the lowering and lateral shifting movement and the raising of the bending head, everything else can be achieved with rotary motions of the bending mandrel or of the clamping device (about the same rotational axis as the bending mandrel), whereby the linear motion of the clamping device against the bending mandrel can then again be produced via the third rotary drive, as before (whereby it is only necessary to also rotate the conversion transmission to a position that is rotated by 180°).  
         [0022]     Another advantageous embodiment of the bending apparatus according to the present invention also consists in there being, on the side of the workpiece where the clamping device is arranged, instead of a wrinkle smoother, a fixed guide roller that is placed upstream of the clamping device and that can be mounted such that it can also press against the corresponding side of the workpiece with a certain pressure, if desired.  
         [0023]     Yet another preferred embodiment of the present invention also consists in having both the bending mandrel and the clamping jaw of the tensioning block designed in the form of a roller with a guide groove to be placed in contact with the facing side of the workpiece to be bent, which again results in a simplified design of the bending device according to the present invention, with an especially compact construction. If the wrinkle smoother, again preferably, then has at least two pressure rollers (instead of the sliders) arranged in sequence in the feed direction of the workpiece to be bent, a bending apparatus according to the present invention is then produced with which it is also possible to produce the desired bend in the coiling process. Depending on the position of the roller of the tensioning block relative to the bending mandrel, the bending radius produced in the workpiece can be changed continuously by the clamping device, which makes it possible to produce elliptical, oval or spiral-shaped bends.  
         [0024]     Any suitable shape of bending mandrel can be used in the bending apparatus according to the present invention, such as e.g. in the shape of a circular roller with a corresponding circumferential forming groove. But it is especially preferred for the bending mandrel to be designed such that when viewed parallel to its pivoting axis it has a shape that is not rotationally symmetrical, but is symmetrical to a central axis that is perpendicular to the axis of rotation and passes through it, whereby the forming groove on the bending mandrel, for contacting one side of the workpiece to be bent, viewed relative to this longitudinal central axis, is also positioned symmetrically on both sides of the bending mandrel. One such embodiment results in an especially preferably usable bending mandrel that does not have to be rotated by some 180°, even when changing the bending direction, but rather only by a small angle. On the whole, the bending device according to the present invention is of very compact and space-saving design; it can be used readily for both right-hand and left-hand bending, while still always preserving the advantage that the rotary shafts for the bending mandrel, conversion transmission and clamping device can bring about the corresponding motions of these individual devices through pure rotary motions, and about a common central axis as well (because of the concentrically positioned transmission shafts). This permits especially rapid and precise control of the individual motions, independent of one another.  
         [0025]     The bending device according to the present invention is constructed very compactly and permits great freedom of bending, namely both small intervals between successive bends and small intervals from the bends to the ends of the prefabricated pipe workpieces, making it possible to ensure gentle material handling. At the same time, the possibility also exists of constructing the utilized bending dies in multiple stages, so as to be able to form both different bending radii and pipe material of different diameters with a single die. The many degrees of freedom of the apparatus realized in the invention enable optimal adjustability to the particular circumstances, such as e.g. the pipe diameter, wall thickness, material, and bending radius. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0026]     The principle of the invention will be explained in greater detail below by example on the basis of the drawing. The figures show the following:  
         [0027]      FIG. 1 : an oblique perspective view of a bending device according to the present invention;  
         [0028]      FIG. 2 : a sectional representation (partially in principle) according to a position of the cutting plane perpendicular to the direction of feed of the workpiece to be processed, and through the common rotational axis of the three concentrically nested rotary shafts;  
         [0029]      FIG. 3 : an exploded perspective view of the upper section of the bending head on a bending apparatus according to the present invention;  
         [0030]      FIG. 4 : the parts shown in  FIG. 3  in the assembled state (in partial section);  
         [0031]      FIG. 5 : a top view (in principle) of a bending head according to the present invention, with a pipe inserted;  
         [0032]      FIG. 6 : the depiction from  FIG. 5 , but with the clamping device and wrinkle smoother in contact position;  
         [0033]      FIG. 7 : the top view according to  FIG. 6 , but after the pipe has been bent by 90°;  
         [0034]      FIG. 8 : a top view showing the principle of a bending head as in  FIGS. 5 through 7 , but here in the starting position for bending in the direction opposite that in the depictions in  FIGS. 5 through 7  (with the pipe workpiece lying on top and the bending head moved down);  
         [0035]      FIG. 9 : the depiction from  FIG. 8 , with the slip jaw of the wrinkle smoother moved to the other side and its guide jaws rotated;  
         [0036]      FIG. 10 : the depiction from  FIG. 9 , but with the slip jaw of the wrinkle smoother repositioned to the final lateral position on the opposite side and its guide jaws rotated by nearly 180°;  
         [0037]      FIG. 11 : a top view of the bending head of  FIGS. 8 through 10  with the clamping device moved into position, the bending mandrel aligned, and the wrinkle smoother moved in;  
         [0038]      FIG. 12 : an oblique perspective view of a bending device according to the present invention in the position shown in a top view in  FIG. 11 ;  
         [0039]      FIG. 13 : an oblique perspective view to portray the principle of another embodiment of a bending head on a bending apparatus according to the present invention, and  
         [0040]      FIG. 14 : a top view of yet another embodiment of a bending head on a bending apparatus according to the present invention that is suitable for producing the bending of the pipe workpiece by coiling. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0041]     In the following description of the figures, the portrayals in  FIGS. 1 through 12  refer to a first, especially advantageous embodiment of a bending device, while  FIG. 13  portrays (in oblique perspective view) a different embodiment of a bending head on such a bending apparatus, and  FIG. 14  is a top view showing the principle of yet another embodiment of a bending head. In all of the figures, including when they relate to modified embodiments, the same reference symbols are used for the same parts.  
         [0042]     We will first examine  FIGS. 1 through 12 , which portray a first embodiment of a bending apparatus.  
         [0043]      FIG. 1  shows a perspective view (obliquely from in front and above) of a bending device  1  shortly before a right-hand bend is executed, while  FIG. 12  shows the same oblique perspective portrayal of the same bending apparatus  1 , but in the starting state before a left-hand bending procedure.  
         [0044]     As can be seen from  FIG. 1 , bending device  1  includes essentially three important devices, namely a bending head  2  (with a clamping device  3 ), also a slide rail  4  (as a feed device) and a wrinkle smoother  5 . These three devices are used to produce bends in prefabricated conduits or pipes  6 , in order to achieve good reshaping results without wrinkling or cracking on the pipe  6 .  
         [0045]     Bending apparatus  1  can travel in its entirety on a horizontal motion path a and a vertical motion path b by means of a suitable corresponding drive (which is however not depicted in the figures).  
         [0046]     Bending head  2  comprises first of all a carrier body  2 A, on top of which a bending mandrel  7  that can rotate about a central axis M is mounted. Lying against the side of the bending mandrel  7  is a tubular workpiece  6  (with a relatively thin wall) in a forming groove  8  that is formed on the bending mandrel and runs around three sides thereof, the shape of the groove being matched to the shape of the pipe  6 . Pipe  6  is fed in direction c by a transport device (not portrayed in the figures), from which it emerges through a clamping jaw (also not portrayed in the figures), but by means of which it can be held in a particular fixed position at any time. It is also possible by means of the feed device and the clamping jaw to rotate the pipe  6  around its longitudinal axis in direction d, and in fact in both directions of rotation.  
         [0047]     As can be seen from the cross section in  FIG. 2  (showing a sectional view along a cutting plane that lies perpendicular to the longitudinal direction of the fed pipe  6  and runs through the rotational axis M of the bending mandrel  7 ), the carrier body  2 A, shown in principle in  FIG. 2  with only a single continuous line, includes an arrangement of three concentrically nested rotary shafts  9 ′,  10 ′ and  11 ′ that are in the form of hollow shafts rotating inside one another. The three different hatchings in  FIG. 2  portray the individual power transmission paths from the three rotary drives  9 ,  10 ,  11  via the associated rotary shafts  9 ′,  10 ′,  11 ′ to the parts to be rotated, whereby each hatching identifies the parts that belong to one drive train.  
         [0048]     Here each of the rotary shafts  9 ′,  10 ′ and  11 ′ is driven by means of its own rotary drive  9 ,  10  and  11 , whereby rotary drive  9  sits directly beneath the rotary shaft  9  for the bending mandrel  2 , which [rotary shaft] is located centrally in the middle, the bending mandrel in turn being attached to the upper end of rotary shaft  9 ′ with an intermediate tool holder  7 ′ which is also only portrayed in principle. Rotary drive  9  directly drives rotary shaft  9 ′, tool holder  7 ′, and bending mandrel  7 , which sits on the latter.  
         [0049]     The middle shaft  10 ′ of the concentric rotary shaft arrangement is driven at its lower end via a belt drive  13  by a rotary drive  10 , and itself drives a disk cam  25  via a rotary flange  10 ″ attached to it; the disk cam will be examined more closely below.  
         [0050]     The outer rotary shaft  11 ′ of the concentric rotary shaft arrangement is driven via a belt drive  14  by a rotary drive  11 . Attached to its upper end is a rotatable supporting plate  15  to which a holding device  16  is attached and in which a linear guide  17  is formed, which—this will be examined later—allows the guidance of a linear motion in the direction of the position of bending mandrel  7  (or away from it) for a part that slides in the linear guide  17 .  
         [0051]     Assigned to the side of bending mandrel  7  is a tensioning block  18  (see  FIGS. 1 and 2  and in particular the enlarged depictions in  FIGS. 3 and 4 ), which has an interchangeable clamping jaw  19  on its side facing bending mandrel  7 , in which (as can be seen especially well from  FIG. 3 ) a forming groove  28  of a size corresponding to the shape of the pipe  6  is formed, facing the pipe  6  that is to be bent.  
         [0052]     Tensioning block  18 , with clamping jaw  19 , is attached to a holding element  20 , e.g. with screws that are not shown.  
         [0053]     Holding element  20  in turn sits on a carrier piece  21  in the manner that can be seen clearly from the exploded view in  FIG. 3 : on the underside of the holding element  20  is a T-shaped forming groove  22 , open toward the bottom, that runs transverse to the direction of movement of the clamping jaw  18  and into which a tenon  21 ′ mounted on top of the carrier piece  21  and having a corresponding T-shaped cross section can be inserted with positive fit. That makes it possible to slide holding piece  20  laterally on the carrier piece, transverse to the direction of motion of tensioning block  18 , in order to be able to set a very specific position of tensioning block  18  relative to rotating mandrel  7 .  
         [0054]     Mounted on the underside of carrier piece  21  is a formed piece in the form of a rotatable roller  23  that protrudes there and engages a corresponding shaped groove  27  (see  FIGS. 1 through 4 ). This roller  25  sits on a holding bolt  26  anchored in carrier piece  21  and can rotate freely.  
         [0055]     In addition, carrier piece  21  is shaped such that it is guided on both of its sides by the linear or longitudinal guide  17  located there in holding device  16  and can be shifted in the longitudinal direction of the latter, as shown in particular by  FIG. 2  and by  FIG. 4 , which shows a partially sectional view at that location.  
         [0056]     When disk cam  25  is rotated by rotary drive  10  via belt drive  13  and rotary shaft  10 ′, this means that the shaped groove  27  that is formed eccentrically on the disk cam  25  correspondingly shifts the roller  23  that engages it relative to the rotational axis M through the change in its rotational position, which leads via linear guide  17  to a corresponding shifting movement of holding element  20  and of tensioning block  18  mounted on the latter with its clamping jaw  19  in the direction of the rotary mandrel  7  or away from it.  
         [0057]     Holding device  16  with the linear guides  17  mounted on it, cooperating with carrier piece  21 , the rotatable roller  23  attached to the latter by means of holding bolt  26 , and cam disk  25  with the eccentrically running groove  27  formed in it, cooperate to form a conversion transmission  24 , turning the rotary motion of rotary shaft  10 ′, whose purpose is to shift the clamping device  3 , into a linear shifting motion of holding piece  21  (and thereby of the holding element  20  mounted on it and of the tensioning block  18  with clamping jaw  19 ). The fact that holding device  16  is attached to supporting plate  15  ensures that linear guides  17  in holding device  16  do not also turn when cam plate  25  rotates, if supporting plate  15  is not set in rotary motion itself. In this way, transmission of the rotary motion of cam plate  5  into a linear motion of carrier piece  21 , and thus of clamping device  3  for clamping the pipe segment  6  or releasing it, is ensured. At the same time, it is possible to ensure that clamping device  3  presses pipe segment  6  against bending mandrel  7  with a desired or prescribed clamping force. In this condition, the bending procedure can then be undertaken, while keeping the tubular workpiece  6  clamped in place, to perform the bending procedure by rotating the cam plate  25  and the supporting plate  15  together.  
         [0058]     As can be seen especially well from  FIGS. 3 and 4 , on top of holding device  16  sits a fork-shaped cover plate  29  that has a front section that is essentially round with a circular interior opening for placing it on the upper end of rotary flange  10 ″, and emerging from this section two lateral arms  30  of the fork which extend in the longitudinal direction of holding device  16 , each of which lies on top of a different side part  33  of holding device  16  and is attached to it by means of screws via holes  31  bored in these fork arms, for which there are matching holes  32  on the top of the side parts  33 . The lateral fork arms  30  of cover plate  29  are somewhat wider than the respective top of a side part  33  lying below them, and with the free gap  30 ′ between them form an additional longitudinal guide for a stepped upper shaped area  21 ″ of carrier piece  21 , so that the latter, when it moves longitudinally in the direction of bending mandrel  7  or back from it, is guided both by this gap  30 ′ between the fork arms  30  and by the longitudinal strips of linear guide  17  that are mounted below it in the holding device  16 . At its end that is turned away from rotary mandrel  7 , holding device  16  has a connecting plate  34  that projects upward somewhat over the side parts  33 , which closes off the internal space  35  that exists between the side arms  33  and the supporting plate  15 , away from the direction of bending mandrel  7 . At the same time, this connecting plate  34  also serves as an end stop for carrier piece  21 , defining a maximum extended position.  
         [0059]     As can also be seen from  FIG. 3 , on the underside of each side part  33  there is a cutout  36  that enables the cam disk  25  with the groove  27  formed on it to be passed through it between the particular side part  33  and the outer circumference of the rotary flange  10 ″ when the cam disk  25  is rotated, as can be seen in detail from  FIGS. 3 and 4 , whose portrayal is explicitly referenced in this respect.  
         [0060]      FIGS. 5 through 7  now show in principle in a top view of the bending head from  FIGS. 1 through 4 , various sequences for producing a 90° bend in a prefabricated pipe  6  having thin walls.  
         [0061]      FIG. 6  first shows the insertion position of bending device  1 , in which bending mandrel  7  is placed with its forming groove  8  against the facing side of the fed-in pipe  6 , while clamping head  3  is removed from bending mandrel  7  and pipe  6 . From the wrinkle smoother  4 , on the side where bending mandrel  7  is located, two guide jaws  38  that also have grooves  41  formed on them ( FIG. 12 ) are likewise placed against the workpiece  6  in alignment with the forming groove  8  of bending mandrel  7 , whereby each guide jaw  38  is attached by means of a screw  39  to an associated holder  40 , as can be seen from  FIG. 1 .  
         [0062]     On the opposite side of pipe  6 , assigned to clamping jaw  38 , there is a slip jaw  37  of wrinkle smoother  4 , which, like clamping device  3 , is withdrawn from the wire  6  in the insertion position, as shown in  FIG. 5 .  
         [0063]     As  FIG. 1  shows, slide rail  4  is mounted on bending head  2  and contains two spindle drives  60 ,  61 , via which a plate  62  with slip jaw  37  can be positioned in a plane. Slide rail  4  is always positioned on the side of tensioning block  18  with respect to the axis of pipe  6 . A slip jaw  37  is in contact with pipe  6 . Depending on the application, slide rail  4  has different functions to perform during the bending procedure. It runs e.g. with pipe  8 , draws it back, or pushes it forward, for example to prevent the formation of cracks in the raw material. In the exemplary embodiment shown in  FIG. 1 , slide rail  4  is also used to position the holding element  20  with tensioning block  18  and clamping jaws  19 , as well as to rotate the holder  40  with the guide jaws  38  of wrinkle smoother  5 .  
         [0064]     The holder  40  of wrinkle smoother  5 , with the guide jaws  38  attached to it, is attached to the slide rail  4  by means of pairs of linear guides  63 . The linear guide pairs  63  are connected to one another via bridge  64 . Wrinkle smoother  5  can be moved or repositioned by suitable means (not shown in detail) in the direction of the arrow F ( FIG. 1 ), and can at the same time be rotated relative to the bending mandrel  7  (by means that are also not shown in detail). That makes it possible to ensure optimal adjustment of the wrinkle smoother  5  for both left-hand and right-hand bending.  
         [0065]     In the insertion position shown in  FIG. 5 , if pipe  6  is placed against the facing forming grooves  8  and  41  ( FIG. 12 ) of the rotary mandrel  7  and of the two guide jaws  38  of the wrinkle smoother  5 , the clamping device  3  is then brought into contact with the side of pipe  6  that is opposite the rotary mandrel  7  by rotating the cam disk  25  in the direction of arrow y 2  and is rigidly clamped with a desired clamping force. This situation is shown in  FIG. 6 .  
         [0066]     Then follows, as shown in  FIG. 7 , a rotation of bending mandrel  7  at the same time, in the same direction and at the same speed (in rotational direction w), and of supporting plate  15  (together with holding device  16 ) and of disk cam  25  in rotational direction y 2  (as indicated in  FIG. 7 ) by 90°, whereby (by suitable means that are not shown) the slip jaw  37  of wrinkle smoother  5  is moved linearly further along with the pipe  6 , in conformity with the feed velocity of the latter and in contact with it, in direction f shown in  FIG. 7 .  
         [0067]     Through cooperation between bending mandrel  7  and clamping device  3 , pipe  6  is bent by 90° in forming groove  8  in a circular end section  46  (see  FIG. 11 ) of bending mandrel  7  (in the area of the latter around its rotational axis M), and then reaches an end position, as shown in  FIG. 7 . A right-hand bend is shown in  FIG. 7 .  
         [0068]      FIGS. 8 through 11  now show, also in a top view like  FIGS. 5 through 7 , a bend in the opposite direction to that in  FIGS. 5 through 7 , namely a left-hand bend.  
         [0069]     To this end, the bent pipe  6  is first held by a clamping jaw (not shown in  FIG. 1 ) in the position that can be seen from  FIG. 7 . Next, by rotating the disk cam  25 , the clamping jaw  19  is moved away from bending mandrel  7 ; slip jaw  37  of wrinkle smoother  5  is also moved linearly away from wire  6 . Next pipe segment  6  is advanced sufficiently far, and at the same time rotated upward by 90° (in rotational direction d) so that the pipe end (already bent earlier) points vertically upward, as can be seen in the perspective representation in  FIG. 12  (but already in the clamped state there).  
         [0070]     When pipe  6  is released, bending head  2  is withdrawn vertically downward (in direction b), so that bending head  2  with bending mandrel  7  lies entirely beneath the pipe  6  that protrudes from the clamping jaw, after which, as  FIG. 8  shows, bending mandrel  7  is rotated away from the former bending direction in rotational direction w (as indicated in  FIG. 8 ). The parts of the underlying bending head  2  covered by pipe  6  are sketched in only with dashed lines in  FIGS. 8 through 10 .  
         [0071]     At the same time, the guide jaws  38  of wrinkle smoother  5  are also rotated in the direction shown by the arrow in  FIG. 8 , the slip jaw  37  having been retracted from the end position shown in  FIG. 7  by a corresponding motion of slide rail  4  in the direction f shown in  FIG. 8 . The intermediate position thus attained is shown in  FIG. 8 .  
         [0072]      FIG. 9  shows an additional operational step in which, with bending head  2  still positioned beneath the pipe segment  6 , the clamping device  3  from  FIG. 5  is now brought to a position 180° opposed, by rotating the supporting plate  15  (with the holding device  16  and the clamping device  3  mounted on it) and the disk cam  25  by 90° (in rotational direction y 1 ) jointly, with equal speed and in the same direction.  
         [0073]     In addition, the guide jaws  38  of wrinkle smoother  5  are rotated further counter-clockwise (in  FIG. 9 ), and likewise slip jaw  37  is also moved in the direction of arrow f′ to the other side of pipe  6 . This intermediate position can be seen from  FIG. 9 .  
         [0074]      FIG. 10  shows the position that is reached when slip jaw  37  together with clamping device  3  is brought to a position that corresponds to the position in  FIG. 5 , but where all the elements are on the side of pipe  6  opposite the position in  FIG. 5 .  
         [0075]     Finally,  FIG. 1I  shows the starting positions of pipe  6 , clamping device  3 , bending mandrel  7  and wrinkle smoother  5  relative to each other for a left-hand bend, corresponding in principle to the starting position for the bending procedure that corresponds to the position in  FIG. 6  for right-hand bending. Here slip jaw  37  has been moved from the intermediate position shown in  FIG. 10  somewhat further away from pipe  6 , so that there is once again on the whole an open insertion position for pipe  6 . Next bending head  2  is again moved upward (in direction b (from  FIG. 1 )), and together with bending mandrel  7  and slip jaw  37  of wrinkle smoother  5  is then placed in contact with the one side (in  FIG. 11  the right side) of pipe segment  6 , bending mandrel  7  already having been rotated with its forming groove  8  that faces pipe  6  aligned with the longitudinal axis of pipe  6 . Next, by rotating the disk cam  25  accordingly, the tensioning block  18  of clamping device  3  is placed with clamping jaw  19  against the other side of pipe  6 , and accordingly slip jaw  37  is also brought into contact with pipe  6  with its forming groove  41  likewise on this side. Thus the starting position (clamped position) of pipe  6  shown in  FIG. 11  is attained, from which a corresponding left-hand bend can be produced by simultaneously rotating bending mandrel  7 , clamping device  3  and disk cam  25  by 90° (counter-clockwise in  FIG. 11 ).  
         [0076]     The starting position attained in  FIG. 11  before the bending process (to the left) is shown once more in  FIG. 12  in a perspective view of the bending device from above.  
         [0077]     With regard to the shape of bending mandrel  7 , as it is employed in the embodiment according to  FIGS. 1 through 11 , reference is made once more to the portrayal in  FIG. 11 :  
         [0078]     In the top view, bending mandrel  7  is not rotationally symmetrical, but it is mirror-symmetrical about a central plane X-X (“axis of symmetry”) that runs through its axis of rotation (corresponding to the axis of rotation M of the three nested rotary shafts  9 ′,  10 ′ and  11 ′). The forming groove  8  formed on bending mandrel  7  runs along the two longitudinal sides of the bending mandrel  7  shown in  FIG. 11  and in the zone  46  in which its ends are joined to one another via a circular path, so that the forming groove  8  runs continuously over a total of three sides of bending mandrel  7 , with its own shape symmetrical to the central plane X-X. This means that the utilized bending mandrel  7  is able to work with only a single shaping groove  8 , and that it is not necessary to utilize different forming grooves, let alone at different axial heights of bending mandrel  7 .  
         [0079]      FIGS. 13 and 14  once again show oblique perspective views of the principle of two other versions of a bending head  2 :  
         [0080]     The embodiment according to  FIG. 13  achieves an especially compact construction, but this configuration is only recommended if there is no danger of cracking or wrinkling in the pipe to be bent, so that the slide rail  4  and the wrinkle smoother  5  are unnecessary.  
         [0081]     In the embodiment according to  FIG. 13 , the slip jaw  37  of wrinkle smoother  5  is replaced by a guide roller  42  that is mounted so that it can rotate freely and guides the pipe that is to be bent before it enters the forming groove  8  of bending mandrel  7 .  
         [0082]     In the embodiment shown here, bending mandrel  7  comprises in principle a bending roller, which however does not have a complete circular circumference, but in which part of the circumference of the circle is cut away, as shown by  FIG. 13 , to which reference is made.  
         [0083]     In this embodiment the clamping device  3  includes a clamping jaw  43  that is held by a holding device  44  portrayed in  FIG. 13  only in principle (shown in  FIG. 13  in the form of a pin), that is formed in a radially running slot guiding device  45  (in the form of an elongated hole) in supporting plate  15 . This holding device  44  is guided beneath support plate  15 , e.g. in an eccentric guide groove (not visible) that passes around the central axis M of rotating head  2  for moving the clamping jaw  43  relative to the pipe  6 . This eccentric forming groove (not shown in detail in  FIG. 13 ) can be attached on the top of a plate or the like that is rotatable about the central axis M but is located beneath the supporting plate  15  and which for its part is rotatable via the middle rotary shaft  10 ′ of the three nested rotary shafts  9 ′,  10 ′,  11 ′ for producing a shifting movement of the clamping jaw  43 . A more detailed description of the special mechanism for this is not necessary, however, since the person skilled in the art is familiar with the design of such a rotary guide for shifting the movement of holding device  44 . In other respects it functions by the same principle as the forming groove/roller arrangement according to  FIG. 1 .  
         [0084]     The additional embodiment of a bending head  2  portrayed in  FIG. 14  differs from the other embodiments described earlier in particular in that here, instead of the slip jaw  37 , two guide rollers  47 ,  48  are provided for lateral contact against the pipe  6  that is to be bent and are positioned upstream of the tensioning block  3  (viewed in the transport direction c of the pipe  6 ).  
         [0085]     On clamping head  3 , clamping jaw  19  is also no longer provided with a guide groove, as in the embodiments in the previous figures, but with a bending roller  49  with which the desired shaping of pipe  6  can be carried out.  
         [0086]     In this embodiment the bending mandrel is designed as a bending roller  50  with a circumferential forming groove to be placed in contact with the pipe segment  6 .  
         [0087]     The movement of the clamping device  3 , the rotation of the bending mandrel  50 , and the positioning and tracking of the wrinkle smoother  5  are accomplished in the same way as with the embodiments according to  FIGS. 1 through 13 , through corresponding program control of the three utilized rotary drives  9 ,  10  and  11 , which act on three concentrically nested rotary shafts  9 ′,  10 ′ and  11 ′ on the parts to be moved, as already shown in principle in the sectional depiction in  FIG. 2 .  
         [0088]     The present invention may be embodied in other specific forms without departing from the central attributes thereof, therefore, the illustrated embodiments should be considered in all respects as illustrative and not restrictive, reference being made to the appended claims rather than the foregoing description to indicate the scope of the invention.