EP3481565B1 - Stretch bending machine and method for deforming a workpiece - Google Patents

Description

The invention relates to a stretch bending machine for deforming workpieces, and a method for deforming the workpiece using the stretch bending machine.

From the prior art, variously constructed stretch bending machines are known in which the workpiece to be machined is clamped between two hydraulically driven clamping receptacles and a tensile force is exerted on the workpiece in the tensile direction by means of a hydraulic cylinder. A pressure force is exerted on the workpiece transversely to the pulling direction by means of a pressure stamp of a pressure device, the pressure stamp also being driven by means of a hydraulic cylinder.

From the EP 2 910 318 A1 , of the US 2013/008221 A1 and the U.S. 2,459,132 A Generic stretch bending machines are known.

The stretch bending machines known from the prior art have the disadvantage that the application of the tensile force to the workpiece and also the deformation of the workpiece by these known stretch bending machines have only insufficient accuracy.

The object of the present invention was to overcome the disadvantages of the prior art and to provide a stretch bending machine and a method for deforming workpieces by means of which the workpiece can be deformed with high precision.

This object is achieved by a device and a method according to the claims.

• einen Maschinenrahmen;
• eine erste Spannaufnahme mit einem ersten Spannkopf zum Spannen einer ersten Seite des Werkstücks, wobei die erste Spannaufnahme am Maschinenrahmen angeordnet ist;
• eine zweite Spannaufnahme mit einem zweiten Spannkopf zum Spannen einer zweiten Seite des Werkstücks, wobei die zweite Spannaufnahme distanziert zur ersten Spannaufnahme am Maschinenrahmen angeordnet ist und wobei die beiden Spannköpfe zum Aufbringen einer Zugkraft in Zugrichtung auf das Werkstück ausgebildet sind;
• eine Druckvorrichtung mit einem Druckstempel zum Verformen des Werkstückes, wobei die Druckvorrichtung zwischen erster Spannaufnahme und zweiter Spannaufnahme am Maschinenrahmen angeordnet ist, wobei der Druckstempel zum Aufbringen einer Druckkraft in einer quer zur Zugrichtung liegenden Druckrichtung ausgebildet ist.

According to the invention, a stretch bending machine is designed for deforming workpieces. The stretch bending machine includes:

• a machine frame;
• a first clamping fixture with a first clamping head for clamping a first side of the workpiece, the first clamping fixture being arranged on the machine frame;
• a second clamping receptacle with a second clamping head for clamping a second side of the workpiece, wherein the second clamping holder is arranged at a distance from the first clamping holder on the machine frame and wherein the two clamping heads are designed to apply a tensile force in the tensile direction to the workpiece;
• a pressure device with a pressure stamp for deforming the workpiece, the pressure device being arranged between the first clamping fixture and the second clamping fixture on the machine frame, the pressure stamp being designed to apply a pressure force in a pressure direction transverse to the pulling direction.

The two clamping receptacles are designed to be flexible with regard to the application of the pulling direction.

The advantage of the design of the stretch bending machine according to the invention is that the clamping receptacles can be flexibly adapted to the respective degree of deformation of the workpiece to be deformed.

Furthermore, the two clamping receptacles each include an electric motor, in particular a servomotor, for adjusting the clamping head and are thus designed to apply a tensile force to the workpiece. The clamping heads are positioned with a high degree of accuracy thanks to the electric motor drive of the chuck.

In addition, a high tensile force can be applied to the workpiece by the electric motor drive by means of the clamping heads, this being easily adjustable and controllable. In addition, such a drive can be integrated into the stretch bending machine simply, inexpensively and in a space-saving manner. Furthermore, it is not necessary for a hydraulic unit to be provided for the electric motor drive, so that the operation of the stretch bending machine can be simplified and also carried out in an environmentally friendly manner. Furthermore, it can be useful if the electric motor of the clamping fixture, in particular with the interposition of a reduction gear, is coupled to an adjusting thread, in particular a ball screw drive, the electric motor being held on a motor holder and the clamping head being mounted on the motor holder by means of a linear guide so that it can be adjusted relative to the motor holder is, wherein the ball screw is designed to initiate a linear adjustment and an adjustment force in the clamping head. The advantage here is that a spindle drive, in particular a ball screw drive, is designed to transmit high forces and has as little play as possible. The clamping head can be mounted on the motor mount so as to be displaceable in the horizontal direction by means of the linear guide.

Furthermore, it can be provided that the plunger is arranged adjustably on the machine frame by means of an electric motor, in particular a servo motor, the electric motor being held on a motor mount which is coupled to the machine frame and the plunger mounted on the machine frame in an adjustable manner by means of a linear guide relative to the motor mount is, wherein an adjusting thread, in particular a ball screw, is designed for introducing a linear adjustment and an adjusting force in the plunger and is coupled to the electric motor of the printing device, in particular with the interposition of a reduction gear. The advantage here is that a spindle drive, in particular a ball screw drive, is designed to transmit high forces and has as little play as possible.

In addition, it can be provided that the clamping receptacle has a base unit which is coupled to the machine frame and has a swivel unit which is pivotably mounted in the base unit with respect to a swivel axis, the electric motor together with the motor holder and also the clamping head being included in the swivel unit and are jointly pivotable relative to the base unit of the clamping receptacle. The advantage here is that with such a design of the clamping fixture it can be achieved that the clamping head can be freely pivoted with the workpiece during the deformation of the workpiece and thus the tensile force on the workpiece can be flexibly adapted to the current deformation angle and constantly along the workpiece clamps a neutral fiber of the workpiece takes place.

An embodiment is also advantageous according to which it can be provided that the swivel unit of the clamping fixture is coupled to an actuator, in particular a hydraulic cylinder or a pneumatic cylinder, by means of which the swivel unit can be actively rotated relative to the base unit. The advantage here is that the swivel unit can be actively rotated by this measure and can thus be returned to its starting position or receiving position after the end of the bending process.

According to a further development, it is possible that the clamping head is designed to accommodate workpieces which are designed as a hollow profile, an inner clamping unit being designed which is used for frictional clamping of an inside of the workpieces and an outer clamping unit being designed which is designed for frictional clamping an outside of the workpieces is used. The advantage here is that a hollow profile can be clamped by the inner clamping unit and by the outer clamping unit in such a way that it is not deformed or compressed in an undesirable manner.

Furthermore, it can be useful if the inner clamping unit has a first clamping finger and a second clamping finger, which are provided with their outwardly directed contact surface for contact with an inside of the workpiece and that a wedge element is arranged between the two clamping fingers, whereby by axial displacement of the wedge element, the distance between the two contact surfaces of the clamping fingers can be adjusted by means of an adjusting means. The advantage here is that an inner clamping unit designed in this way has a simple structure and can apply the highest possible clamping force to the workpiece while utilizing the limited space.

In addition, it can be provided that the outer clamping unit has a first clamping finger and a second clamping finger, which are provided with their inwardly directed contact surface for contact with an outside of the workpiece and that a wedge element is arranged outside each of the two clamping fingers, whereby axial Displacement of the wedge elements, by means of an adjusting means, the distance between the two contact surfaces of the clamping fingers can be adjusted. The advantage here is that an outer clamping unit designed in this way has a simple structure and can apply the highest possible clamping force to the workpiece while utilizing the limited space.

Furthermore, it can be provided that a spring element is arranged between the two clamping fingers of the outer clamping unit, by means of which a restoring force is exerted on both clamping fingers. The advantage here is that the two clamping fingers of the outer clamping unit are pressed apart by the spring element and can thus easily be returned to their starting position.

According to a particular embodiment, it is possible that both the first clamping head and the second clamping head have a compression spring, by means of which the workpiece can be arranged centrally between the two clamping heads before the clamping heads are closed. The advantage here is that this measure means that the workpiece is not exactly to be picked up must be placed centrally in the stretch bending machine, but that when the two clamping heads move towards each other, the workpiece can first come to rest on one of the two clamping heads and then the workpiece is centered by the same pressure distribution in the compression springs of the two clamping heads by further infeed movement of the two clamping heads.

According to an advantageous development it can be provided that a first support pad is formed on the machine frame, on which the undeformed workpiece can be placed, the first support pad being displaceable in the vertical direction and that a second support pad is formed on the machine frame on which the deformed workpiece can be placed is, wherein the second support pad is displaceable in the vertical direction. It can thereby be achieved that the workpiece to be machined can be inserted into the support and does not have to be held by the machine operator for the clamping process.

In particular, it can be advantageous if the plunger has an upper plunger part and a lower plunger part, the two plunger parts forming an insert groove with a groove base and two mutually aligned groove walls, which are each formed on a pressure stamp part, and wherein the workpiece can be received in the insert groove and wherein the distance between the two plunger parts can be adjusted relative to one another by means of an adjusting means, so that the two groove walls can be moved towards one another. The advantage here is that the formed profile can be squeezed by means of the two pressure ram parts that can be moved relative to one another after the forming process has ended, so that any bulges can be pressed out of the profile.

Furthermore, it can be provided that the two clamping receptacles have a rough adjustment by means of which the distance between the clamping receptacles can be roughly adjusted to the workpiece length. The advantage here is that this measure enables the stretch bending machine to be used for workpieces of different lengths.

In addition, it can be provided that the clamping head of the clamping receptacle is adjustable between 50mm and 1,000mm, in particular between 100mm and 500mm, preferably between 150mm and 250mm, relative to the motor mount. The advantage here is that the clamping head can be adjusted in a sufficiently large area and can be built as small as possible.

An embodiment is also advantageous, according to which it can be provided that the pressure stamp of the printing device is adjustable between 50mm and 2000mm, in particular between 100mm and 1000mm, preferably between 200mm and 300mm relative to the motor mount. The advantage here is that the pressure ram can be adjusted in a sufficiently large area and can be built as small as possible.

• Einlegen eines Werkstückes in die Streckbiegemaschine;
• Aufeinanderzubewegen der beiden Spannköpfe, bis das Werkstück an der ersten Seite im ersten Spannkopf und an der zweiten Seite im zweiten Spannkopf gespannt werden kann;
• Spannen des Werkstückes in den beiden Spannköpfen;
• Aufbringen einer Zugkraft in Zugrichtung auf das Werkstück mittels den beiden Spannköpfen;
• Verfahren des Druckstempels der Druckvorrichtung quer zur Zugrichtung und dadurch Verformen des Werkstückes;
• Während dem Verfahren des Druckstempels gleichzeitiges Verfahren der beiden Spannköpfe, sodass die Verformung des Werkstückes ausgeglichen wird;
• Öffnen der Spannköpfe nach dem Beenden des Verformvorganges;
• Voneinanderwegbewegen der beiden Spannköpfe und dadurch freigeben des Werkstückes;
• Herausnehmen des Werkstückes aus der Streckbiegemaschine, wobei die beiden Spannaufnahmen jeweils einen Elektromotor, insbesondere einen Servomotor, zum Verstellen des Spannkopfes und somit zum Aufbringen einer Zugkraft auf das Werkstück umfassen.

According to the invention, a method for deforming a workpiece is provided using a stretch bending machine described above. The procedure comprises the following procedural steps:

• Inserting a workpiece into the stretch bending machine;
• Moving the two clamping heads towards one another until the workpiece can be clamped on the first side in the first clamping head and on the second side in the second clamping head;
• Clamping the workpiece in the two clamping heads;
• Applying a tensile force in the tensile direction to the workpiece by means of the two clamping heads;
• Moving the plunger of the printing device transversely to the direction of pull and thereby deforming the workpiece;
• While the pressure ram is moving, the two clamping heads move simultaneously so that the deformation of the workpiece is compensated for;
• Opening of the clamping heads after the end of the deformation process;
• Moving the two clamping heads away from each other and thereby releasing the workpiece;
• Removing the workpiece from the stretch bending machine, the two clamping receptacles each comprising an electric motor, in particular a servomotor, for adjusting the clamping head and thus for applying a tensile force to the workpiece.

The advantage of the method according to the invention is that the workpiece can be manufactured with a high degree of accuracy and the deformation parameters can also be precisely adhered to during the deformation process of the workpiece.

Furthermore, it can be useful if the tensile force applied to the workpiece by means of the two clamping heads is selected such that the workpiece is between 5% and 100%, in particular between 20% and 95%, preferably between 70% and 80% of the yield point of the workpiece is stressed. The advantage here is that a tensile force in the specified range of the yield point of the workpiece means that the workpiece can be easily deformed and the internal stresses in the workpiece can be kept as low as possible after the deformation process.

In addition, it can be provided that the necessary tensile force is calculated by storing the workpiece geometry and the strength properties of the workpiece. The advantage here is that by means of this measure, the necessary tensile force can be determined mathematically and can thus have an exact value.

As an alternative to this, it is conceivable that a tension is applied to the workpiece and not the level of the tensile force is specified as a parameter, but that the workpiece is stretched to a certain% value of its initial length. As a result, the yield point of the workpiece can be set independently of the cross-sectional area of the workpiece.

Furthermore, it can be provided that the tensile force actually applied to the workpiece is determined by measuring the motor current and thus determining the torque of the electric motors of the clamping fixture. The advantage here is that this measure enables the actually applied tensile force to be determined simply and with sufficient accuracy.

Alternatively, external measuring sensors can be provided to determine the tensile force actually applied to the workpiece.

According to a particular embodiment, it is possible for the two clamping heads to be moved synchronously during the deformation process, with the center of the workpiece being held in the center of the plunger by means of active path control. The advantage here is that the center of the workpiece is held in the center of the plunger during the deformation process and thus a uniform deformation of the workpiece can be achieved.

According to an advantageous development, it can be provided that during the deformation process the swivel unit of the clamping receptacle can be freely swiveled relative to the base unit of the clamping receptacle and is swiveled by the workpiece. The advantage here is that through this measure the clamping head exerts a pure tensile force on the workpiece and no bending moment is introduced into it.

In particular, it can be advantageous if, after the deformation process has ended and the two clamping heads have moved away from each other, the swivel unit of the clamping receptacle is pivoted back into a receiving position by means of the actuator of the clamping receptacle. The advantage here is that this measure returns the stretch bending machine to its starting position and is therefore ready to accept a new workpiece.

Furthermore, it can be provided that the first support pad is moved vertically upwards in order to insert the workpiece into the stretch bending machine and the first support pad is moved downwards after the workpiece is clamped in the clamping heads. The advantage here is that this measure allows the workpiece to be easily inserted into the stretch bending machine.

In addition, it can be provided that after the end of the deformation process and before the clamping heads are opened, the second support pad is displaced upwards in the vertical direction and is used to hold the workpiece. The advantage here is that when the clamping heads are opened, the workpiece can be placed directly in the stretch bending machine.

An embodiment is also advantageous, according to which it can be provided that the upper pressure stamp part and the lower pressure stamp part are moved towards one another after the end of the deformation process in order to be able to impress any bulges in the workpiece. In this way, any bulges in the workpiece resulting from the deformation process can be smoothed.

Alternatively, it can be provided that the upper plunger part and the lower plunger part are in a clamping position that is moved towards one another during the deformation process are held and after the end of the deformation process are spaced from each other to release the workpiece. The advantage of this embodiment variant is that the workpiece is already held in shape or position several times during the deformation process and that after the deformation process has been carried out, the workpiece can be removed from the plunger easily and with little effort.

All linear guides described in this document are designed in the illustrated embodiments in the form of recirculating ball bearings. However, it is also conceivable that the linear guides are designed, for example, in the form of form-fitting sliding guides, for example dovetail guides.

All of the spindle drives described in this document are in the form of ball screws in the illustrated embodiments. However, it is also conceivable that the spindle drives are designed, for example, as normal adjusting threads, such as trapezoidal threads.

The electric motors described in this document are preferably designed in the form of servomotors. However, all other types of electric motors which have a corresponding control can also be used.

The in the individual adjustment units of the clamping fixtures and pressure device i.e.

Forces occurring in electric motors due to the deformation of the workpiece can be detected, for example, by monitoring the motor current and thus the motor torque of the individual electric motors. As an alternative to this, it is also possible that force sensors or torque sensors, for example, directly detect the forces that occur.

The electric motors can have internal position sensors which can be used to calculate the position of the components to be driven using the angle of rotation of the electric motor. Alternatively, it is also possible that the position of the components to be driven is recorded directly by means of displacement sensors.

It can also be provided that the electric motors are coupled to a gear.

Furthermore, it can be provided that the clamping heads are designed to be rotatable with respect to a horizontally lying axis. In this way, it can be achieved that in addition to the bending caused by the pressure stamp, a torsion can also be generated in the workpiece. In particular, it can be provided that the clamping heads can be driven by means of a rotary drive and the rotation can be actively set.

Furthermore, it can be useful if the pressure stamp has a variable width. This can be achieved, for example, in that the pressure stamp is designed to be divided with respect to its width and that the two side halves of the pressure stamp can be displaced relative to one another. As a result, the bending position on the workpiece can be varied or different design variants of the workpiece can be produced.

In addition, it can be provided that the inner clamping unit is designed to seal the hollow profile and that a medium can be introduced into the hollow profile by means of the stretch bending machine in order to be able to apply overpressure in the hollow profile, for example. The medium can for example be a gas or a liquid, such as hydraulic oil. This measure makes it possible to avoid any indentations occurring in the workpiece during the deformation process. In addition, the medium can be preheated or cooled so that a certain temperature can be applied to the workpiece.

Furthermore, it can be provided that heat or cold can be applied locally to the workpiece by means of a heating or cooling device arranged on the stretch bending machine. This can be achieved, for example, by means of a gas burner which is aimed at the workpiece in the area of the bending point of the workpiece. Furthermore, it is also conceivable that such a heating or cooling device is formed in the pressure stamp. The heating or cooling device can for example also be designed in the form of a coil for induction heating. The structure in the workpiece can be influenced locally by the heating or cooling device. This can be necessary in particular in the area of the forming point.

Furthermore, it can be provided that a detection means, in particular an optical detection means, such as a camera or a laser for position and position detection of the Workpiece is provided. This position detection enables the workpiece to be picked up in the correct position in the clamping heads of the stretch bending machine. In addition, the current deformation of the workpiece can be checked by the detection means during the deformation process.

Furthermore, it can be provided that a core is inserted into the cavity of a workpiece, in particular designed as a hollow profile, before the start of the deformation process. The advantage here is that the workpiece is supported from the inside when the core is used, which is inserted into the cavity. Thus, deformations of the wall thickness of the workpiece are prevented.

For a better understanding of the invention, it is explained in more detail with reference to the following figures.

Fig. 1

eine perspektivische Ansicht eines ersten Ausführungsbeispiels einer Streckbiegemaschine;

Fig. 2

eine weitere perspektivische Ansicht des ersten Ausführungsbeispiels einer Streckbiegemaschine;

Fig. 3

eine perspektivische Ansicht eines Ausführungsbeispiels eines Druckstempels der Streckbiegemaschine;

Fig. 4

eine perspektivische Ansicht eines Ausführungsbeispiels einer Spannaufnahme der Streckbiegemaschine;

Fig. 5

eine weitere perspektivische Ansicht des Ausführungsbeispiels der Spannaufnahme der Streckbiegemaschine;

Fig. 6

eine perspektivische Ansicht eines Ausführungsbeispiels einer Schwenkeinheit der Spannaufnahme der Streckbiegemaschine;

Fig. 7

eine Schnittdarstellung des Spannkopfes gemäß der Schnittlinie VII-VII in Fig. 6;

Fig. 8

eine schematische Darstellung eines ersten Ausführungsbeispiels eines Kerns zum Stützen des Werkstückes;

Fig. 9

eine schematische Darstellung eines zweiten Ausführungsbeispiels eines Kerns zum Stützen des Werkstückes.

They each show in a greatly simplified, schematic representation:

Fig. 1

a perspective view of a first embodiment of a stretch bending machine;

Fig. 2

a further perspective view of the first embodiment of a stretch bending machine;

Fig. 3

a perspective view of an embodiment of a pressure ram of the stretch bending machine;

Fig. 4

a perspective view of an embodiment of a clamping receptacle of the stretch bending machine;

Fig. 5

a further perspective view of the embodiment of the clamping receptacle of the stretch bending machine;

Fig. 6

a perspective view of an embodiment of a swivel unit of the clamping receptacle of the stretch bending machine;

Fig. 7

a sectional view of the clamping head according to the section line VII-VII in Fig. 6 ;

Fig. 8

a schematic representation of a first embodiment of a core for supporting the workpiece;

Fig. 9

a schematic representation of a second embodiment of a core for supporting the workpiece.

By way of introduction, it should be noted that in the differently described embodiments, the same parts are provided with the same reference numerals or the same component names, whereby the disclosures contained in the entire description can be transferred accordingly to the same parts with the same reference numerals or the same component names. The location details chosen in the description, such as above, below, to the side, etc., referring to the figure immediately described and shown, and if there is a change in position, these position details are to be transferred to the new position accordingly.

The Figures 1 and 2 each show a perspective view from different angles of an exemplary embodiment of a stretch bending machine 1 for deforming workpieces 2, the same reference symbols or component names being used for the same parts. The following description is based on an overview of the Figures 1 and 2 created.

The stretch bending machine 1 comprises a machine frame 3 on which a first clamping fixture 4 with a first clamping head 5 and a second clamping fixture 6 with a second clamping head 7 are arranged. The first clamping head 5 is used to pick up and clamping a first side 8 of the workpiece 2 and the second clamping head 7 is used to pick up and clamp a second side 9 of the workpiece 2. The clamping receptacles 4, 6 are arranged at a distance 10 from one another, the distance 10 corresponds approximately to a length of the workpiece 2.

Preferably, workpieces 2 are deformed on the stretch bending machine 1 according to the invention, which have an elongate extension and are designed, for example, in the form of rods, flat iron, tubes, hollow profiles and the like. In the present embodiment, the workpiece 2 is designed in the form of a hollow profile, which is therefore a Has inner side 11 and an outer side 12, which define a wall thickness of the hollow profile.

The first clamping head 5 and the second clamping head 7 serve not only to clamp and hold the workpiece 2, but can also be displaced in a pulling direction 13, whereby a tensile stress can be applied to the workpiece 2. The direction of pull 13 lies parallel to the longitudinal direction of the workpiece 2.

The first clamping head 5 and the second clamping head 7 can be accommodated in the clamping receptacles 4, 6 such that differently designed clamping heads 5, 7 can be accommodated in the clamping receptacles 4, 6 for differently designed workpieces 2.

Furthermore, a printing device 14 with a pressure stamp 15 is provided, which is also arranged on the machine frame 3.

In an alternative embodiment it can also be provided that the first clamping receptacle 4, the second clamping receptacle 6 and the pressure device 14 are mounted directly on a hall floor and thus the machine frame 3 can be dispensed with and replaced by the hall floor or another receptacle.

The direction of pull 13 lies parallel to the longitudinal direction of the workpiece 2.

The pressure ram 15 can be displaced in a pressure direction 16 lying transversely to the pulling direction 13. It can preferably be provided that the individual components, in particular the first clamping fixture, the second clamping fixture 6 and the pressure device 14 are arranged on the stretch bending machine 1 in such a way that both the pulling direction 13 and the pushing direction 16 lie in a horizontal plane and at right angles are arranged on top of one another.

By adjusting the plunger 15 in the direction of pressure 16 and pressing it onto the workpiece 2, it can be deformed in the stretch bending machine 1 with simultaneous tensile loading.

For the sake of clarity, the Figures 1 and 2 the workpiece 2 is shown both in the undeformed starting position, in which it is just aligned, and in its curved shape after the end of the bending process.

To adapt the first clamping receptacle 4 or the second clamping receptacle 6 to workpieces 2 of different lengths, provision can be made for a coarse adjustment 17 to be formed between the clamping receptacles 4, 6 and the machine frame 3. In the simplest case, the coarse adjustment 17 can be designed in the form of a row of holes which is arranged in the machine frame 3 and corresponds to corresponding counter-holes in the clamping receptacle 4, 6. Depending on which holes are selected for inserting the fastening means between the clamping receptacle 4, 6 and the machine frame 3, the distance 10 between the clamping receptacles 4, 6 can be varied. It is preferably provided that the clamping receptacles 4, 6 are arranged at the same distance from the center 18 of the pressure die 15. It can thereby be achieved that the center 19 of the workpiece 2, or the longitudinal center of the workpiece 2, can also be brought into congruence with the center 18 of the pressure stamp 15.

The plunger 15 of the printing device 14 is preferably coupled to a linear guide 20, by means of which it is arranged on the machine frame 3 so that it can be displaced in the printing direction 16. In particular, it can be provided that the linear guide 20 is designed in the form of a recirculating ball bearing guide, wherein a guide rail 21 can be provided which is attached to the machine frame 3 and which interacts with a guide carriage 22. In particular, it can be provided that two of the guide rails 21 are formed which are arranged at a distance from one another on the machine frame 3 and that a plunger receptacle 23 is formed, on which two guide carriages 22 are attached per guide rail 21. A total of four guide carriages 22 can therefore be attached to the plunger receptacle 23.

The plunger 15 can be arranged on the plunger receptacle 23 so that it can be coupled, so that different plungers 15 can be used for differently designed workpieces 2.

It can further be provided that the plunger receptacle 23 is coupled to an adjusting means 24, whereby the plunger 15 can be displaced between a retracted rest position and an advanced reshaping position. If the plunger 15 is in the retracted rest position, a straight and undeformed workpiece 2 can be inserted between the first clamping receptacle 4 and the second clamping receptacle 6.

How particularly good in Fig. 1 As can be seen, it can be provided that the adjustment means 24 of the pressure device 14 is implemented in the form of a ball screw drive 30. In particular, it can be provided that a recirculating ball nut 31 is connected to the plunger receptacle 23 and that a recirculating ball spindle 32 is mounted in a motor mount 33 of the pressure device 14. The motor mount 33 of the printing device 14 is fixedly coupled to the machine frame 3. Furthermore, an electric motor 34 is provided for driving the recirculating ball screw 32, which can be optionally coupled to a reduction gear 35. The electric motor 34 is preferably also fastened or arranged on the motor mount 33. Thus, by activating or rotating the electric motor 34, the plunger 15 can be shifted horizontally in the printing direction 16.

Furthermore, it can be provided that a first support pad 25 is formed on the machine frame 3, in which the workpiece 2 to be machined can be inserted and held. It is preferably provided that the first support pad 25 can be displaced in the vertical direction 27 by means of an adjustment means 26. As a result, after the workpiece 2 has been received in the clamping receptacles 4, 6, the first support pad 25 can be moved downward and thus disengaged in order to enable the workpiece to be freely deformed. As a result, the workpiece 2 is released for the forming process.

Analogously to this, a second support pad 28 can be provided, which serves to hold the workpiece 2 in the deformed state. The second support pad 28 can also be adjusted by means of an adjustment means 29 in the vertical direction 27 between a retracted position and a raised support position.

Both the first support pad 25 and the second support pad 28 can have a plurality of individual support elements which are arranged at a distance from one another.

Fig. 3 shows a perspective view of the plunger 15 with the plunger receptacle 23, again with the same reference numerals or component designations for the same parts as in the preceding Figures 1 and 2 be used. To avoid unnecessary repetition, please refer to the detailed description in the preceding section Figures 1 and 2 pointed out or referred to.

In the Fig. 3 the guide carriages 22, which are arranged on the plunger receptacle 23, are clearly visible.

How out Fig. 3 also visible, it can be provided that the pressure stamp 15 comprises an upper pressure stamp part 36 and a lower pressure stamp part 37. The plunger parts 36, 37 can form an insert groove 38 in which the workpiece 2 can be received.

Such an insert groove 38 can, for example, also be formed in the case of a one-piece pressure stamp 15.

The insert groove 38 has a groove base 39 which is delimited by a groove wall 40 of the upper pressure ram 36 and by a groove wall 41 of the lower pressure ram 37. In particular, it can be provided that the upper pressure ram 36 and the lower pressure ram 37 are displaceable relative to one another, so that a distance 42 between the two pressure ram parts 36, 37 to one another can be adjusted in a predefined adjustment range. The distance 42 is preferably specified as the normal distance between the groove wall 40 of the upper pressure ram 36 and the groove wall 41 of the lower pressure ram 37. In other words, by adjusting the two plunger parts 36, 37, the distance between the two groove walls 40, 41 and thus the groove width can be varied. In particular, it can be provided that an adjusting means 43 is formed which is used to adjust the two pressure stamp parts 36, 37 with respect to one another. The actuating means 43 can be designed, for example, in the form of a hydraulic cylinder, a pneumatic cylinder or some other unit, such as an electric motor with a spindle drive or an electric motor with an eccentric shaft.

In the present exemplary embodiment it is provided that two adjusting means 43 are provided, which are arranged at a distance from one another and are used to adjust the pressure stamp parts 36, 37. The implementation of two adjusting means 43 has the advantage that, on the one hand, the possible compressive force that can be applied can be increased and, on the other hand, the compressive force can be introduced symmetrically into the groove walls 40, 41.

To adjust the two plunger parts 36, 37 to each other, it can be provided that either the upper plunger part 36 or the lower plunger part 37 are rigidly coupled to the plunger receptacle 23 and the respective other plunger part 36, 37 is movable relative to the rigidly coupled plunger part.

In a further embodiment variant it can also be provided that the pressure stamp parts 36, 37 are coupled to one another via a mechanism, the two pressure stamp parts being moved synchronously towards one another or moved away from one another. As a result, it can be achieved that the two groove walls 40, 41 are fed equally towards the workpiece 2.

The groove walls 40, 41 can serve during the deformation process to avoid bulges in the workpiece or provision can be made for any bulges that have arisen in the workpiece to be expressed by moving the groove walls 40, 41 towards one another.

How out Fig. 3 Furthermore, it can be seen that the pressure stamp 36 can be divided into a left and a right pressure stamp part, so that a width 86 of the pressure stamp 36 can be variably adjusted.

Furthermore, it can be provided that a detection means 87 is designed to detect the workpiece before and / or during and / or after the forming process.

Furthermore, it can be provided that heat or cold can be applied locally to the workpiece 2 by means of a heating or cooling device 88 arranged on the stretch bending machine 1.

In the Figures 4 and 5 the first clamping receptacle 4 is shown in two perspective views from two different directions, again with the same reference numerals or component designations for the same parts as in the preceding Figures 1 and 2 be used. To avoid unnecessary repetition, please refer to the detailed description in the preceding section Figures 1 and 2 pointed out or referred to.

The individual components of the first clamping receptacle 4 are based on a synopsis of Figures 1 , 2 , 4th and 5 described. How particularly good in Fig. 1 As can be seen, the first clamping receptacle 4 and the second clamping receptacle 6 are constructed identically in terms of their operating principle, the second clamping receptacle 6 being only a mirrored version of the first clamping receptacle 4. For the sake of brevity, the Fig. 4 and 5 only the first clamping fixture 4 is described. It is clear to the person skilled in the art how the individual components of the first clamping receptacle 4 are to be folded over onto the second clamping receptacle 6 in a mirrored manner.

As from the Fig. 4 and 5 As can be seen, it can be provided that the clamping receptacle 4, 6 has a base unit 44, which is preferably rigidly coupled to the machine frame 3 via fastening means. The base unit 44 can be made in one piece, for example in the form of a welded component with several components welded together. The individual components of the base unit 44 can of course also be connected to one another by means of fastening means.

In a further embodiment variant, it can also be provided that the base unit 44 is designed in one piece in the form of a cast part.

A pivot unit 45 can be accommodated in the base unit 44, which pivot unit can be pivoted relative to the base unit 44 with respect to a pivot axis 46. The pivot axis 46 is preferably oriented vertically. In particular, it can be provided that the pivot unit 45 of the clamping receptacle 4, 6 is received or mounted on an upper side 47 of the base unit 44 and on an underside 48 of the base unit 44.

In a first embodiment, it can be provided that a pivot bearing 49 is formed on the top side 47 or on the bottom side 48 of the base unit 44.

In an alternative embodiment, it can be provided that bolts are arranged both on the upper side 47 and on the lower side 48 of the base unit 44 and the pivot bearing 49 is formed on the pivot unit 45.

The pivot bearing 49 for the pivotable mounting of the pivot unit 45 relative to the base unit 44 can be implemented by means of ball bearings or, for example, by means of slide bearings.

Furthermore, it can be provided that the swivel unit 45 is coupled to an actuator 50, by means of which the swivel unit 45 can be actively swiveled relative to the base unit 44. The actuator 50 can
is coupled to the swivel unit 45 by means of a lever 51 and can thus serve to initiate a rotary movement in the swivel unit 45.

The actuator 50 is formed by an electric motor which is used directly or indirectly to initiate the rotary movement in the swivel unit 45.

As from the Figures 4 and 5 As can clearly be seen, it can be provided that the base of the swivel unit 45 is formed by a motor mount 52. All of the components built into the swivel unit 45 can be attached to the motor mount 52. The motor mount 52 is pivotably arranged on the base unit 44 of the clamping receptacle 4, 6.

Like the base unit 44, the motor mount 52 can likewise be designed in one piece or in one piece in various embodiments.

How particularly good in Fig. 5 As can be seen, a linear guide 53 can be formed by means of which the clamping head 5, 7 is accommodated in the motor mount 52 in a linearly displaceable manner. Analogous to the linear guide 20 of the printing device 14, two guide rails 54 can be arranged on the motor mount 52, with which two guide carriages 55 each cooperate, which are arranged on the clamping head 5, 7.

Furthermore, an adjustment means 56 is provided, by means of which the clamping head 5, 7 can be actively linearly displaced relative to the motor mount 52. The adjusting means 56 can, for example, a Include spindle drive. In particular, it can be provided that a ball screw 57 is formed which is used to adjust the clamping head 5, 7. The ball screw drive 57 can comprise a recirculating ball nut 58 which is rigidly connected to the clamping head 5, 7. Furthermore, a recirculating ball screw 59 can be provided which cooperates with the recirculating ball nut 58.

The ball screw 59 can be mounted in a spindle bearing 60 which is rigidly coupled to the motor mount 52. Furthermore, it can be provided that an electric motor 61, 62 is used to drive the recirculating ball screw 59. The electric motor 61, 62 can be coupled to the ball screw 59 via a reduction gear 63.

Fig. 6 FIG. 11 shows a perspective view of a variant of the swivel unit 45 without showing the base unit 44. For the sake of clarity, FIG Fig. 6 The adjusting means 56, in particular the electric motor 61, 62 and the ball screw drive 57 for adjusting the clamping head 5, 7 are also not shown.

How out Fig. 6 As can be seen, it can be provided that an upper axle journal 64 and a lower axle journal 65 are accommodated on the motor mount 52 and interact with the pivot bearing 49 arranged in the base unit 44. The upper axle journal 64 can preferably be designed in such a way that it serves to receive the lever 51 to which the actuator 50 is coupled. The two axle journals 64, 65 can preferably be coupled to the motor mount 52 by means of fastening means.

In Fig. 6 it can also be seen that the clamping head 5, 7 can have an inner clamping unit 66 which is used to clamp the inside 11 of the workpiece 2. Furthermore, the clamping head 5, 7 can have an outer clamping unit 67 which is used to clamp the outer side 12 of the workpiece 2.

Furthermore, a compression spring 68 can be provided, which in Fig. 6 is shown symbolically and is arranged in the clamping head 5, 7, the compression spring 68 acting in the pulling direction 13 and serving to center the workpiece 2.

Fig. 7 shows a sectional view of the clamping head 5, 7 according to the section line VII-VII in Fig. 6 . How out Fig. 7 As can be seen, the inner clamping unit 66 has a first clamping finger 69 and a second clamping finger 70. The first clamping finger 69 has a contact surface 71 which is directed outwards. The second clamping finger 70 has a contact surface 72 which is also directed outwards. The contact surfaces 71, 72 of the clamping fingers 69, 70 are used for a non-positive connection or for non-positive reception with the inside 11 of the workpiece 2. Between the two clamping fingers 69, 70 a wedge element 73 is arranged, which moves in the adjustment direction 74 with respect to the clamping fingers 69, 70 is adjustable.

In particular, a distance 75 between the contact surfaces 71, 72 of the two clamping fingers 69, 70 of the inner clamping unit 66 can be adjusted by means of an adjusting means 76. In the present exemplary embodiment, it can be provided that the adjustment means 76 is designed to move the wedge element 73 in the adjustment direction 74. The adjustment means 76 can be designed, for example, in the form of a hydraulic cylinder or a pneumatic cylinder. By shifting the wedge element 73 or by means of the wedge surfaces formed between the wedge element 73 and the clamping fingers 69, 70, the two clamping fingers 69, 70 can be pressed apart and the distance 75 between the contact surfaces 71, 72 of the clamping fingers 69, 70 can be adjusted. The distance 75 can be increased by pulling the wedge element 73 in a direction facing away from the workpiece 2. The distance 75 can be reduced in that the wedge element 73 is pushed out. The spring stiffness of the clamping fingers 69, 70 is used in this case to move the clamping fingers 69, 70 towards one another when the wedge element 73 is pushed out.

The outer clamping unit 67 can also have a first clamping finger 77 and a second clamping finger 78. The two clamping fingers 77, 78 have contact surfaces 79, 78 which are aligned with one another and are used to clamp the outside 12 of the workpiece 2.

In the case of the outer clamping unit 67, too, a distance between the two contact surfaces 79, 80 can be adjusted by means of an adjusting means 82. Analogously to the inner clamping unit 66, it can be provided that outside the two clamping fingers 77, 78 of the outer clamping unit 67 a wedge element 83 or, in this case, two wedge elements 83 are arranged, which can adjust the distance 81 of the contact surfaces 79, 80 of the outer clamping unit 67 by displacement in the adjustment direction 77 via corresponding wedge surfaces. For this purpose, the wedge elements 83 of the outer clamping unit 67 are coupled to the adjusting means 82 of the outer clamping unit 67.

Furthermore, a spring element 84 can be provided which presses the two clamping fingers 77, 78 of the outer clamping unit 67 apart and thus holds them in their open position or serves to reset the two clamping fingers 77, 78 during opening.

The wedge surfaces between the wedge elements 83 and the clamping fingers 77, 78 can be designed in such a way that when the wedge elements 83 are pushed forward in the direction of workpiece 2, the clamping fingers 77, 78 of the outer clamping unit 67 are moved towards one another and thus the workpiece 2 can be clamped . When the wedge elements 83 are withdrawn, the clamping fingers 77, 78 can move apart again due to the force exerted by the spring element 84.

Furthermore, a stop 85, which serves as a depth stop for the workpiece 2, can be formed on the inner clamping unit 66 or on the outer clamping unit 67.

Both the contact surfaces 71, 72 of the inner clamping unit 66 and the contact surfaces 79, 80 of the outer clamping unit 67 can have micro-toothing or something else to increase the friction and thus to increase the clamping force.

It can also be provided that lubrication grooves are formed on the individual sliding surfaces of the wedge elements 73, 83, which serve to supply the sliding surfaces with lubricant in order to minimize wear. Correspondingly, several grease nipples can be provided in the inner clamping unit 66 and in the outer clamping unit 67.

Based on a synopsis of the Figs. 1 to 7 the sequence for reshaping the workpiece 2 by means of the stretch bending machine 1 is explained in the following part of the description.

In a first process step, the workpiece 2, which is straight and undeformed, is placed in the stretch bending machine 1. Here it can be provided that the first support pad 25 is shifted upwards and thus serves to receive the workpiece 2.

The clamping heads 5, 7 can then be moved symmetrically towards one another in the pulling direction 13 in order to be able to introduce the workpiece 2 into the clamping head 5, 7. The compression spring 68 arranged in the clamping heads 5, 7 can ensure that a workpiece 2 that is not 100% centrally inserted is centered when the clamping heads 5, 7 move towards one another, and the center 19 of the workpiece 2 is thus aligned with the center 18 of the plunger 15 .

The inner clamping unit 66 and the outer clamping unit 67 of the two clamping heads 5, 7 can then be closed in order to clamp the workpiece 2 in the clamping heads 5, 7.

After the workpiece 2 has been clamped in the two clamping heads 5, 7, the first support pad 25 can be moved downwards and thus disengaged in order to enable the workpiece 2 to be freely deformed by the plunger 15.

Subsequently or in parallel with the previous step, the two clamping heads 5, 7 can be moved symmetrically away from one another in the pulling direction 13, and a pulling force can thereby be applied to the workpiece 2.

Subsequently, the plunger 15 can be moved towards the workpiece 2 in the pressure direction 16 and deform it. During this deformation process, the total length of the workpiece 2 is shortened due to the deformation. It is therefore necessary for the clamping heads 5, 7 to yield in the direction of the center 18 of the plunger 15 in order to be able to maintain a certain tensile force.

In particular, it can be provided that the clamping heads 5, 7 are displaced in such a way that the center 19 of the workpiece 2 remains in the center 18 of the plunger 15 during the bending process.

In addition, during this process, the clamping heads 5, 7 are freely pivotable in the respective clamping receptacle 4, 6 in order not to apply any bending moment to the workpiece 2, but rather around the workpiece 2 on its first side 8 or on its second side 9 with a clean To claim tensile force.

During the forming process, the workpiece 2 can be received in the insert groove 38 of the plunger 15. It can be provided here that the groove walls 40 and 41 serve to stabilize the workpiece 2 or prevent bulges on the workpiece 2.

As already described, it is possible that the groove walls 40, 41 are kept at a predetermined distance 42 from one another during the entire forming process or that the distance 42 between the two groove walls 40, 41 and thus the workpiece is reduced only after the forming process has ended 2 is pressed into shape.

The two groove walls 40, 41 are then removed from one another, and thus the distance 42 is increased, as a result of which the workpiece 2 is released.

Parallel to this or afterwards, the clamping units 66, 67 of the clamping heads 5, 7 can be opened and the workpiece 2 can thereby be released.

The second support pad 28, which serves to hold the finished, formed workpiece, can then be moved upwards.

The clamping heads 5, 7 can then be displaced away from the workpiece 2 so that they disengage from the workpiece 2.

The workpiece 2 thus rests on the second support pad 28 and can be removed from the stretch bending machine 1.

In preparation for receiving a new workpiece 2, the second support pad 28 can then be shifted downwards and the first support pad 25 for receiving the new workpiece 2 can be shifted upwards. At the same time, the pressure stamp 15 are moved to its starting position. At the same time, the clamping heads 5, 7 can be moved back into their starting position by means of the actuator 50.

Fig. 8 shows a schematic representation of a first exemplary embodiment of a core 89. The core 89 has several core segments 90 which are coupled to one another by means of a connection 91. The segmentation of the core 89 makes it flexible in its longitudinal extension and can adapt to the curvature of the workpiece 2. The connection 91 of the individual core segments 90 can be implemented, for example, by means of a leaf spring. As an alternative to this, it can also be provided that the individual core segments 90 are coupled to one another by cables.

In particular, it is provided that the core 89 is inserted into the workpiece 2 designed as a hollow profile before the bending process. During the bending process, the core 89 then serves to ensure that the cross-section of the workpiece 2 is retained to some extent and that it does not buckle or buckle. After the end of the bending process, the core 89 can be pulled out of the workpiece 2 again.

Fig. 9 FIG. 11 shows another embodiment of a core 89. As from FIG Fig. 9 As can be seen, it can be provided that the core 89 is used, for example, for bending open profiles, such as a C-profile. It can be provided here that the core 89 has corresponding recesses into which the leg or legs of the workpiece 2 are inserted. During the bending process, the legs of the workpiece 2 are guided and can therefore be protected against buckling.

For the sake of clarity, it should finally be pointed out that for a better understanding of the structure, some elements have been shown not to scale and / or enlarged and / or reduced.

List of reference symbols

1 Stretch bending machine 30th Ball screw pressure device 2 workpiece 3 Machine frame 31 Ball screw nut pressure device 4th first clamping fixture 5 first clamping head 32 Ball screw pressure device 6 second clamping fixture 7th second clamping head 33 Motor mount printing device 8th first side workpiece 34 Electric motor printing device 9 second side workpiece 35 Reduction gear pressure device 10 Distance between clamping fixtures 36 upper stamp part 11 Inside workpiece 37 lower pressure stamp part 12 Outside workpiece 38 Insert groove 13 Direction of pull 39 Groove base 14th Printing device 40 Groove wall upper plunger part 15th Stamp 41 Groove wall lower pressure stamp part 16 Print direction 42 Distance between the ram parts 17th Coarse adjustment 43 Adjusting means pressure stamp parts 18th Center stamp 44 Basic unit clamping fixture 19th Center workpiece 45 Swivel unit clamping fixture 20th Linear guide printing device 46 Swivel axis clamping fixture 21st Guide rail 47 Top of the base unit 22nd Guide carriage 48 Base unit underside 23 Stamp holder 49 Swivel bearing clamping fixture 24 Adjusting means pressure device 50 Actuator clamping fixture 25th first support pad 51 lever 26th Adjusting means first support pad 52 Motor bracket clamping fixture 27 vertical direction 53 Linear guide clamping fixture 28 second support pad 54 Guide rail 29 Adjusting means second support pad 55 Guide carriage 56 Adjusting means 78 second clamping finger outer clamping unit 57 Ball screw drive chuck 79 Contact surface of first clamping finger 58 Recirculating ball nut clamping holder 80 Contact surface of the second clamping finger 81 Distance between contact surfaces and outer clamping fingers 59 Ball screw clamping fixture 82 Adjusting means outer clamping unit 60 Spindle bearing 61 Electric motor first clamping fixture 83 Wedge element outer clamping unit 62 Electric motor second clamping fixture 84 Spring element 85 attack 63 Reduction gear chuck 86 Width stamp 87 Detection means 64 Upper stub axle 88 Heating or cooling device 65 Lower stub axle 89 core 66 inner clamping unit 90 Core segment 67 outer clamping unit 91 connection 68 Compression spring clamping head 69 first clamping finger inner clamping unit 70 second clamping finger inner clamping unit 71 Contact surface of first clamping finger 72 Contact surface of the second clamping finger 73 Wedge element inner clamping unit 74 Adjustment direction 75 Distance between contact surfaces, inner clamping fingers 76 Adjusting means inner clamping unit 77 first clamping finger outer clamping unit

Claims (27)

1. A stretch bending machine (1) for deforming workpieces (2), said stretch bending machine (1) comprising:

   a machine frame (3);

   a first clamping holder (4) having a first clamping head (5) for clamping a first side (8) of the workpiece (2), wherein the first clamping holder (4) is arranged on the machine frame (3);

   a second clamping holder (6) having a second clamping head (7) for clamping a second side (9) of the workpiece (2), wherein the second clamping holder (6) is arranged on the machine frame (3) at a distance (10) from the first clamping holder (4) and wherein the two clamping heads (5, 7) are designed to apply a pulling force onto the workpiece (2) in a pulling direction (13);

   a pressing device (14) having a pressing die (15) for deforming the workpiece (2),

   wherein the pressing device (14) is arranged on the machine frame (3) between the first clamping holder (4) and the second clamping holder (6), wherein the pressing die (15) is designed to apply a pressing force in a pressing direction (16) lying transversely with respect to the pulling direction (13), wherein the two clamping holders (4, 6) are designed to be flexible with respect to the application of the pulling direction (13),

   characterized in that the two clamping holders (4, 6) each comprise an electric motor (61, 62), in particular a servomotor, for adjusting the clamping head (5, 7) and thus for applying a pulling force onto the workpiece (2).
2. The stretch bending machine according to claim 1, characterized in that the electric motor (61, 62) of the clamping holder (4, 6) is coupled to an adjusting thread, in particular a ball screw drive (57), in particular with interposition of a reduction gear (63), wherein the electric motor (61, 62) is held on a motor mount (52) and the clamping head (5, 7) is mounted on the motor mount (52) so as to be adjustable relative thereto by means of a linear guide (53), wherein the ball screw drive (57) is designed to introduce a linear adjustment and an adjusting force into the clamping head (5, 7).
3. The stretch bending machine according to one of claims 1 to 2, characterized in that the pressing die (15) is arranged on the machine frame (3) so as to be adjustable by means of an electric motor (34), in particular a servomotor, wherein the electric motor (34) is held on a motor mount (33) which is coupled to the machine frame (3) and the pressing die (15) is mounted on the machine frame (3) so as to be adjustable relative to the motor mount (52) by means of a linear guide (20), wherein an adjusting thread, in particular a ball screw drive (30) is designed to introduce a linear adjustment and an adjusting force into the pressing die (15) and is coupled to the electric motor (34) of the pressing device (14), in particular with interposition of a reduction gear (35).
4. The stretch bending machine according to one of the preceding claims, characterized in that the clamping holder (4, 6) comprises a base unit (44), which is coupled to the machine frame (3), and a pivoting unit (45), which is mounted in the base unit (44) so as to be pivotable with respect to a pivot axis (46), wherein the electric motor (61, 62) along with the motor mount (52) as well as the clamping head (5, 7) are comprised in the pivoting unit (45) and are pivotable together with respect to the base unit (44) of the clamping holder (4, 6).
5. The stretch bending machine according to claim 4, characterized in that the pivoting unit (45) of the clamping holder (4, 6) is coupled to an actuator (50), in particular a hydraulic cylinder or a pneumatic cylinder, by means of which the pivoting unit (45) can be actively rotated towards the base unit (44).
6. The stretch bending machine according to one of the preceding claims, characterized in that the clamping head (5, 7) is designed for holding workpieces (2) embodied as hollow profiles, wherein an inner clamping unit (66) is formed, which serves for clamping an inner side (11) of the workpieces (2) in a force-fitted manner and wherein an outer clamping unit (67) is formed, which serves for clamping an outer side (12) of the workpieces (2) in a force-fitted manner.
7. The stretch bending machine according to claim 6, characterized in that the inner clamping unit (66) has a first clamping finger (69) and a second clamping finger (70) which are provided for contacting an inner side (11) of the workpiece (2) with their contact surface (71, 72) facing outwards and that a wedge element (73) is arranged between the two clamping fingers (69, 70), wherein by displacement of the wedge element (73) by means of an adjusting means (76), the distance (75) between the two contact surfaces (71, 72) of the clamping fingers (69, 70) can be adjusted.
8. The stretch bending machine according to claim 6 or 7, characterized in that the outer clamping unit (67) has a first clamping finger (77) and a second clamping finger (78) which are provided for contacting an outer side (12) of the workpiece (2) with their contact surface (79, 80) facing inwards and that a wedge element (83) is in each case arranged outside of the two clamping fingers (77, 78), wherein by axial displacement of the wedge elements (83) by means of an adjusting means (82), the distance (81) between the two contact surfaces (79, 80) of the clamping fingers (77) can be adjusted.
9. The stretch bending machine according to claim 8, characterized in that a spring element (84), by means of which a restoring force is exerted onto both clamping fingers (77, 78), is arranged between the two clamping fingers (77, 78).
10. The stretch bending machine according to one of the preceding claims, characterized in that both the first clamping head (5) and the second clamping head (7) comprise a compression spring (68) by means of which the workpiece (2) can be centrally arranged between the two clamping heads (5, 7) prior to closing of the clamping heads (5, 7).
11. The stretch bending machine according to one of the preceding claims, characterized in that a first support table (25) onto which the undeformed workpiece (2) can be placed is formed on the machine frame (3), wherein the first support table (25) can be displaced in vertical direction (27) and that a second support table (28) onto which the deformed workpiece (2) can be placed is formed on the machine frame (3), wherein the second support table (28) can be displaced in vertical direction (27).
12. The stretch bending machine according to one of the preceding claims, characterized in that the pressing die (15) comprises an upper pressing die part (36) and a lower pressing die part (37), wherein the two pressing die parts (36, 37) form an insertion groove (38) with a groove base (39) and two groove walls (40, 41) facing one another, which are each formed on a pressing die part (36, 37), and wherein the workpiece (2) can be held in the insertion groove (38) and wherein the two pressing die parts (36, 37) can be adjusted in their distance (42) relative to one another by means of an adjusting means (43), such that the two groove walls (40, 41) can be moved towards one another.
13. The stretch bending machine according to one of the preceding claims, characterized in that the two clamping holders (4, 6) comprise a coarse adjustment system (17) by means of which the distance (10) of the clamping holders (4, 6) with respect to one another can be coarsely set to the length of the workpiece (2).
14. The stretch bending machine according to one of the preceding claims, characterized in that the clamping head (5, 7) of the clamping holder (4, 6) can be adjusted between 50 mm and 1,000 mm, in particular between 100 mm and 500 mm, preferably between 150 mm and 250 mm, relative to the motor mount (52).
15. The stretch bending machine according to one of the preceding claims, characterized in that the pressing die (15) of the pressing device (14) can be adjusted between 50 mm and 2,000 mm, in particular between 100 mm and 1,000 mm, preferably between 200 mm and 300 mm, relative to the motor mount (52).
16. A method for deforming a workpiece (2) using a stretch bending machine (1) according to one of the preceding claims, wherein the method comprises the following method steps:

    - inserting a workpiece (2) into the stretch bending machine (1);

    - moving the two clamping heads (5, 7) towards one another until the workpiece (2) can be clamped in the first clamping head (5) on the first side (8) and in the second clamping head (7) on the second side (9);

    - clamping the workpiece (2) in the two clamping heads (5, 7);

    - applying a pulling force onto the workpiece (2) in the pulling direction (13) by means of the two clamping heads (5, 7);

    - displacing the pressing die (15) of the pressing device (14) transversely to the pulling direction (13) and thereby deforming the workpiece (2);

    - during the displacement of the pressing die (15), simultaneous displacement of the two clamping heads (5, 7) such that the deformation of the workpiece (2) is compensated;

    - opening the clamping heads (5, 7) after termination of the deformation operation;

    - moving the two clamping heads (5, 7) away from one another and thereby releasing the workpiece (2);

    - removing the workpiece (2) from the stretch bending machine (1),
    characterized in that the two clamping holders (4, 6) each comprise an electric motor (61, 62), in particular a servomotor, for adjusting the clamping head (5, 7) and thus for applying a pulling force onto the workpiece (2).
17. The method according to claim 16, characterized in that the pulling force applied onto the workpiece (2) by means of the two clamping heads (5, 7) is selected such that the workpiece (2) is loaded by between 5% and 100%, in particular between 20% and 95%, preferably between 70% and 80% of the yield point of the workpiece (2).
18. The method according to claim 16 or 17, characterized in that the required pulling force is calculated by depositing the workpiece geometry (2) and the strength characteristics of the workpiece (2).
19. The method according to one of claims 16 to 18, characterized in that the pulling force actually applied onto the workpiece (2) is determined by measuring the motor current and thus determining the torque of the electric motors (61, 62) of the clamping holder (4, 6).
20. The method according to one of claims 16 to 19, characterized in that the displacement of the two clamping heads (5, 7) is carried out synchronously during the deformation operation, wherein the center (19) of the workpiece (2) is kept in the center (18) of the pressing die (15) by means of active track control.
21. The method according to one of claims 16 to 20, characterized in that during the deformation operation, the pivoting unit (45) of the clamping holder (4, 6) is freely pivotable relative to the base unit (44) of the clamping holder (4, 6) and is pivoted by the workpiece (2).
22. The method according to one of claims 16 to 21, characterized in that after termination of the deformation operation and moving the two clamping heads (5, 7) away from one another, the pivoting unit (45) of the clamping holder (4, 6) is pivoted back into a receiving position by means of the actuator (50) of the clamping holder (4, 6).
23. The method according to one of claims 16 to 22, characterized in that for inserting the workpiece (2) into the stretch bending machine (1), the first support table (25) is displaced upwards in vertical direction (27) and after clamping the workpiece (2) in the clamping heads (5, 7), the first support table (25) is displaced downwards.
24. The method according to one of claims 16 to 23, characterized in that after termination of the deformation operation and prior to opening the clamping heads (5, 7), the second support table (28) is displaced upwards in vertical direction (27) and serves for holding the workpiece (2).
25. The method according to one of claims 16 to 24, characterized in that the upper pressing die part (36) and the lower pressing die part (37) are moved towards one another after termination of the deformation operation so as to be able to press in potential protuberances in the workpiece (2).
26. The method according to one of claims 16 to 25, characterized in that the upper pressing die part (36) and the lower pressing die part (37) are held in a clamping position moved towards one another during the deformation operation and are distanced from one another so as to release the workpiece (2) after termination of the deformation operation.
27. The method according to one of claims 16 to 26, characterized in that prior to the beginning of the deformation operation, a core (89) is inserted into the cavity of a workpiece (2) which is in particular formed as a hollow profile.

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