Joining Device With Clamping Device And Joining Method

Abstract

A joining method for joining at least two workpieces with a joining device and a joining device for joining workpieces are disclosed. The joining device comprises a joining head having a retaining device for a joining element and by means of which the joining element can be guided along or arranged on a joining axis, a punch with which a setting movement of the joining element can be executed, the punch being movable along the joining axis by a first drive unit, and a clamping device with which one or more workpieces can be compressed in a joining direction, wherein the clamping device is movable through a second drive unit different from the first drive unit.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a bypass continuation of International Application No. PCT / EP2024 / 074870, filed on September 5, 2024, which claims the benefit and priority of European Application No. 23196228.3, filed on September 8, 2023. The entire disclosure of each of the above applications is incorporated herein by reference.FIELD

[0002] The present disclosure relates to a joining device, in particular, a joining device adapted to join a workpiece arrangement (for instance at least two sheets or workpieces arranged one above the other) with a joining element and without a preformed (for example, predrilled or pre-punched) hole or holes in the component prior to the joining, the joining device comprising a clamping device. The present disclosure also relates to a process for joining a workpiece arrangement. BACKGROUND

[0003] Joining methods and joining devices of the above-mentioned kind are widely known, especially in the field of punch riveting or direct screwing, and are used for example in automotive engineering.

[0004] It is known to use, during a mechanical joining process, a joining device with a punch, with which a setting movement can be executed, and a clamping device. The clamping device performs different functions such as pressing together the members of a workpiece arrangement to avoid any gap between the workpieces, avoiding or influencing a possible displacement of adhesive between the workpieces, and reducing the workpiece deformation during the joining process.

[0005] Document DE 102005031917 A1 discloses a method for joining in which, in a first step, a main piston and a clamping device are pressed against the workpieces with a comparatively low force, so that the workpieces are held immovably in contact with one another and with a die.

[0006] Document CH689299 discloses a joining device comprising a clamping device with a probe for checking the position of a rivet or a workpiece.

[0007] Document DE102017106449 for instance discloses a joining device with a hydraulic system and comprising a punch with which a linear, nonrotating setting movement can be executed, a clamping device with which one or more components can be compressed in a joining direction, and with a drive unit that operates in at least two steps with which the punch and the clamping device can be moved by one motor and several gearboxes.

[0008] DE102012019809A1 discloses a method for punch riveting two sheets arranged one above the other on a base of a punch riveting device, between which an adhesive is introduced. The joining device to perform the method comprises a C-frame with a die, a punch and a clamping device. An electric motor is arranged to drive the punch and the clamping device.

[0009] JP2007203307 discloses a joining device comprising a punch and a retaining device with a clamp shaft adapted to apply a clamping force on materials to be joined. A servomotor controls the motion of the punch. As a moving means for moving the clamp shaft, an air cylinder or a hydraulic cylinder can be used in addition to the servo motor.

[0010] DE102016007332A1 and DE10319411 disclose a setting tool with a receiver (or retaining device) adapted to apply a clamping force to workpieces to be joined.

[0011] DE19905527A1 discloses a joining device with a punch and a clamping device. To join the workpieces, a piston-cylinder unit of the clamping device is first actuated until a mouthpiece rests on the upper side of the workpieces and presses them against a die with controllable force. During the adjustment movement, a slide takes the entire joining tool downwards, so that a piston-cylinder unit of the joining tool only has to carry out the remaining feed movement and the joining movement.

[0012] The mechanical joining processes known normally use a spring-loaded, hydraulic or pneumatic clamping device. The clamping force profile of the clamping device is either estimated considering the spring characteristics or is a constant with hydraulic and pneumatic systems. The entire force applied to the workpiece arrangement by the joining device is formed by the addition of the clamping force and the force generated by the punch. For a joining device allowing a one-sided joining process, the entire force acts on the robot supporting the joining device and / or the workpiece arrangement, which leads to a need to provide a robust equipment which is cumbersome, expensive and requires large space. For double-sided joining, the entire force leads to the bending of the frames used. For example, for self-piercing riveting (as an illustrative example only), the entire force leads to the bending of the C-frames used. Such bending causes lateral and angular offsets and has an impact on the joint quality. Larger robots or equipment to avoid these drawbacks are costly, require space and provide a lower agility. SUMMARY

[0013] An object of the present disclosure is therefore to provide a joining device which is flexible, compact and a joining method by means of which the joining process can be better controlled and hence performed more effectively.

[0014] Accordingly, the present disclosure provides a joining device and a joining method for joining workpieces. More particularly, the joining device comprises a joining head having:

[0015] a retaining device for a joining element and by means of which the joining element can be guided along or arranged on a joining axis;

[0016] a punch with which a setting movement of the joining element can be executed, the punch being movable along the joining axis by a first drive unit; and

[0017] a clamping device with which one or more workpieces can be compressed in a joining direction,

[0018] wherein the clamping device is movable through a second drive unit different from the first drive unit.

[0019] The addition of a second drive unit to control the clamping device allows the clamping device to be controlled independently or depending on the punch. The second drive unit can be controlled independently from the first drive unit. The clamping device can be controlled and / or monitored on force and / or displacement, and in addition with possible time-delay. The clamping device can apply, during the setting steps of the joining element with the punch, different clamping forces to or displacement with regard to the workpieces. The clamping device can be eventually rigidly attached to the second drive unit (without stiffness-reducing measures such as springs or dampers), and thus a precise displacement or force can be applied, without corrective measures. The addition of another drive unit in a joining device has always been regarded as a problem since it increases the weight of the device and complicates the control command. However, in the present case, when a dedicated drive unit is connected to the clamping device, it reduces the space requirements, the price and the weight of the holding parts supporting the joining device. Indeed, thanks to this second drive unit connected to the clamping device, the holding parts of the joining device (robot arms, …) can be downsized without decreasing the performance of the joining device. Besides, the joining time can be reduced due to a better flexibility for the motion of the punch and the clamping device during the setting steps. Finally, such a joining device, with an independently controlled clamping device, can be used to join several different materials and workpieces, and notably brittle cast materials.

[0020] In an embodiment, the second drive unit is a servo-electric drive with a spindle. The servo-electric drive is lightweight, and easy to control. No need of hydraulic or pneumatic connection. In an embodiment, the first drive unit is a servo-electric drive with a spindle. Alternatively, the first and / or second drive unit could also be a hydraulic and / or pneumatic and / or electric drive unit. A linear or a rotational drive unit may also be considered

[0021] In an embodiment, the second drive unit moves the clamping device along a clamping axis, the clamping axis being parallel to but not confluent with the joining axis. In other words, the clamping axis extends parallel to the joining axis at a non-zero distance. This improves the flexibility for the motion of the clamping device with regard to the retaining device of the punch. The clamping force is still applied at or in the vicinity of the joining point.

[0022] In an embodiment, the second drive unit is oriented at an angle with regard to the first drive unit, the angle being between 0 and 90 degrees. The compacity or space requirement of the joining device can thus be improved.

[0023] In an embodiment, a thermal device is arranged on the clamping device and moves together with the clamping device. In an embodiment, the thermal device can be a plasma torch, a laser heating system, an induction heating system, an electric arc or similar. Thus, the joining device may be used to perform a thermally assisted joining process such as a plasma joining or a joining process with plasma cleaning. The presence of an independently-controlled clamping device is advantageous with such a thermal device. Indeed, the exact force applied to the workpiece can be controlled and thus, the thermal transmission between the workpiece due to the thermal device can easily be controlled or adjusted. More particularly, the clamping device allows the clamping of the workpieces during the use of the thermal device and before the retaining device (also called receiver) contacts the workpiece. Thus, the thermal device does not damage the front end of the retaining device (or receiver), but the thermal treatment is still realized in a controlled manner with the right clamping force being applied to the workpieces, even if the retaining device does not yet contact the upper workpiece.

[0024] In an embodiment, the clamping device comprises a surface detection unit adapted to detect a surface of the workpiece. The clamping device thus performs several functions. The surface detection can be done with or without contact. For instance, a laser distance measurement can be realized, an inductive or capacitive sensor can also be used. A mechanical contact measurement can equally be implemented. The surface detection of the workpiece may help to determine the best joining parameters (displacements, ...) during the setting step or eventually detect possible mistakes (absence of a workpiece).

[0025] In an embodiment, the joining device includes a sensor unit adapted to measure a temperature. Notably, the sensor unit is adapted to measure, with or without contact, a temperature of the workpiece.

[0026] In an embodiment, the clamping device comprises a hollow cylindrical clamp adapted to be arranged around the punch and the retaining device. Thus, the clamping device does not interfere with the punch or the retaining device but acts on the workpiece area to be joined directly. In an alternative embodiment, the clamping device comprises a clamp having a C-shaped cross-section or a U-shaped cross-section. For instance, the clamping device or clamp is in two parts with a first part having a C or U-shape in cross-section and a second part being cylindrical and hollow. The first part being adapted to face the workpiece arrangement. The second part being adapted to be connected to the rest of the joining device.

[0027] In an embodiment, the clamp has an external diameter between 10 and 30 millimeters. This allows a precise clamping area portion without interfering with the punch or the retaining device. Alternatively, the clamping device may, in cross-section, have a C-shape, have a U-shape, have a ring-shape with apertures or slots arranged at different angles, or be parallelepipedal or be composed of two or more parallelepipeds. In other embodiments, clamping pins or rods may be used. For instance, one, two, three or more clamping pins may be used. The shape of the clamp may be variable along its length. For instance, the three or more pins may be connected to a ring.

[0028] In an embodiment, the joining device comprises a load measurement system. For example, the load measurement system is a load cell. The load measurement system may be integrated within the joining device, or more particularly the clamping device (internal system), or may be external. The load cell measures the clamping force and thus an exact control and command of the clamping force profile can be done. In another embodiment, the clamping force measurement could be realized via the motor current or by installing a central load cell for both joining and the clamping axis. The punch may also comprise its own load measurement system.

[0029] The present disclosure is also directed to a joining method for joining at least two workpieces with a joining device, the joining method comprising the following steps of:

[0030] providing a workpiece arrangement comprising an upper workpiece surface and a lower workpiece surface;

[0031] providing a joining device as above-described, the joining device being arranged at a non-zero distance above the workpiece arrangement;

[0032] moving the clamping device along the clamping axis until the clamping device contacts the upper workpiece surface;

[0033] applying a first predetermined clamping force;

[0034] applying a second predetermined clamping force; and

[0035] setting a joining element within the workpiece arrangement by moving the punch along the setting device to move the joining element into the workpiece arrangement.

[0036] Such a method allows a better control of the joining process. For instance, the clamping device can apply a high first predetermined clamping force to the workpiece to close any gap which might be present between the workpiece or, during a thermally assisted joining process, to optimize the heat transfer between the first and the second workpiece. Due to the design of two axes (clamping axis and joining axis), the clamping force may thus be decreased, and may even thus be cancelled, by the setting force on a need basis and replaced by the setting force. Depending on the process parameters, materials to be joined and joining element, the setting of the clamping force and setting force may be freely implemented.

[0037] In an embodiment, the clamping device comprises a sensor unit providing force, displacement and time data. In an embodiment, clamping force profile and clamping device displacement profile and / or clamping force profile and joining element displacement profile and / or clamping force and time profile are recorded. All data or values in relation to force or displacement can thus be evaluated. Such data can be used by a controller to determine the best joining parameter. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The teachings of the present disclosure and their advantages will be better understood from the reading of the following description, given by way of example only and with reference to the accompanying drawings, of which:

[0039] FIG. 1 shows a perspective view of a joining device according to the present disclosure with a clamping dive, a punch and a retaining device;

[0040] FIG. 2A and FIG. 2B show a perspective view of a cylindrical clamp included in the clamping device of a joining device according to the present disclosure;

[0041] FIG. 3 shows sectional view of the front end of a joining device according to the present disclosure;

[0042] FIG. 4A to FIG. 4G show different possible steps of a joining process according to the present disclosure with, for each step, the corresponding clamping force profile; and

[0043] FIG. 5A to FIG. 5G show different possible embodiments in cross section of a clamping device of a joining device according to the present disclosure. DETAILED DESCRIPTION

[0044] The embodiments of the disclosure will be best understood by reference to the drawings, wherein the same reference signs designate identical or similar elements. It will be readily understood that the components of the disclosed embodiments, as generally described and illustrated in the figures herein, could be arranged and designed in a wide variety of different configurations. Thus, the following detailed description of the embodiments of the systems and methods of the disclosure is not intended to limit the scope of the disclosure, as claimed, but is merely representative of possible embodiments of the disclosure.

[0045] FIG. 1 shows a perspective view of a joining device 10. The joining device 10 is adapted to carry out a method for joining a workpiece arrangement W comprising at least a first and a second workpiece W1, W2 (or sheet) arranged one above the other, together with a joining element 20. The joining device 10 comprises a joining head 12, which can be moved freely in the space by means of a robot (not represented). Eventually, as an alternative, the joining device 10 can be fixed to a structure and the workpieces to be joined moved toward the joining device 10 when needed. The joining head 12 can be, for instance, mounted on one arm of the robot. The joining device 10 or joining head 12 comprises retaining device 14, a punch 16 and a first drive unit 18. The retaining device 14, punch 16 and first drive unit 18 are arranged longitudinally extending along a joining axis X.

[0046] The retaining device 14 is adapted to retain the joining element 20. The joining element 20 may, for example, be a pin, a screw, a rivet, etc. More particularly, the joining element 20 may be similar or substantially similar to the joining element described in EP22165638.2 from the applicant. The retaining device 14 guides or arranges the joining element 20 along the joining axis X. The punch 16 is adapted to drive or actuate the joining element 20 toward the workpiece arrangement W in order to carry out the joining. The retaining device 14 and the punch 16 may be both arranged coaxially to the joining axis X. The punch 16 may be adapted to penetrate the retaining device 14 in order to drive the joining element 20 toward and into the workpiece arrangement W. The punch 16 allows a setting movement of the joining element 20. Notably, the punch 16 allows a linear setting movement. The punch 16 is movable along the joining axis X by the first drive unit 18. In one embodiment, the first drive unit 18 is an operating module comprising a motor, notably a servo motor or a servo drive, adapted to move to a specific position, speed or torque based on an input signal from a controller. The first drive unit 18 controls movement of the punch 16 along the joining axis X. In other embodiments, the first drive unit 18 could also be a hydraulic and / or pneumatic and / or electric drive unit. A linear or a rotational drive unit may also be considered.

[0047] The joining device 10 further comprises a clamping device 22 adapted to compress or press the workpiece arrangement W in the joining direction. The clamping device 22 is movable and controlled by a second drive unit 24. The second drive unit 24 is different from the first drive unit 18. For instance, the second drive unit 24 may be less powerful than the first drive unit 18. In other embodiments, depending on the joining process, the second drive unit 24 and the first drive unit 18 may be similar drive units with similar power. In one embodiment, the second drive unit 24 comprises a servo-electric drive and thus the clamping device 22 is controlled by its own servo-electric drive. In a possible alternative embodiment, the second drive unit 24 could also be a hydraulic and / or pneumatic and / or electric drive unit. A linear or a rotational drive unit may also be considered. The second drive unit 24 moves and controls the clamping device 22 along a clamping axis Y. In a first embodiment, the clamping axis Y may be parallel to the joining axis X, but separated from the joining axis X by a non-zero distance. In a second embodiment, the clamping axis Y may be coaxial with the joining axis X (in such case, for example, the first and second drive units 18, 24 may be arranged one above the other or concentric with each other with for instance a hollow motor). The first drive unit 18 may be arranged at an angle with regard to the second drive unit 24. The angle may be between 0 and 90 degrees. In an embodiment, the clamping device 22 may be driven by its own robot. In such case, for instance, a command can be sent from a controller to the robot controlling the clamping device 22. The robot executes the command and carries out the clamping process independently from the rest of the joining device 10 and setting equipment. Then, the setting process with the first drive unit 18 and the punch 16 can be started (for instance, a signal may be sent by the robot to start the setting process or an integrated system may automatically send a command to start the setting process of the joining element 20). The setting and clamping steps may also occur simultaneously.

[0048] A controller can control the first and second drive units 18, 24 independently and / or dependently of each other depending on the requirements of the joining process.

[0049] The clamping device 22 may comprise a clamp 26. Different shapes of clamps are possible, as depicted in FIG. 5A to FIG. 5G. For instance, as depicted in FIG. 5C (but also in FIG. 2A and FIG. 2B), the clamp 26 may have a portion forming a U-shape in sectional view. The clamp 26 has an outside diameter between 10 and 30 millimeters (mm). The clamp 26 defines a hole or recess and the joining element 20 is adapted to be moved within the recess for its setting. More particularly, the punch 16 and at least a portion of the retaining device 14 can be guided inside the recess. As depicted in FIG. 2A and FIG. 2B, the clamping device or clamp 26 is in two parts with a first part having a C or U-shape in cross-section and a second part, directly connected to the first part, being cylindrical and hollow. The clamp may also be a hollow cylindrical clamp 26’, as visible in FIG. 5A. In another embodiment, the clamp 26’’ may have a C-shape in a cross-sectional view, as shown in FIG. 5B. The clamp 26’’’ may also be curved in cross-section view, as visible in FIG. 5D or be composed by two curved parts defining a recess as visible in the clamp 26(4) of FIG. 5E. In another embodiment, a straight pin can also be implemented as a clamp 26(5) as depicted in FIG. 5F or two straight posts 26(6) as visible in FIG. 5G defining an area in which the joining element 20 can be moved to be set by the punch 16.

[0050] The clamp 26, 26’, 26’’, 26’’’, 26(4) , 26(5) , 26(6) extends longitudinally between the first end 28 and the second end 30 along the joining axis X. A chamfer may be arranged at the first end 28. The first end 28 comprises a contact surface 32 adapted to contact the workpiece arrangement W. The clamp 26, 26’, 26’’, 26’’’, 26(4), 26(5), 26(6) may comprise on its lateral side a window 34. On the second end 30, an attachment portion 38 for the attachment of the hollow cylindrical clamp 26 to the rest of the clamping device 22 is arranged.

[0051] In all the embodiments of FIG. 5A to FIG. 5G, the attachment portion 38 extends from the clamp 26, 26’, 26’’, 26’’’, 26(4), 26(5), 26(6) to the rest of the clamping device 22. As better seen in FIG. 3, the attachment portion 38 may at least partially extend parallel to the joining axis X at a non-zero distance from the outer surface of the clamp 26, in order to avoid any interference with the punch 16 or the retaining device 14.

[0052] The clamping device 22 may comprise a surface detection unit 40 adapted to detect an upper surface of the workpiece arrangement W. The surface detection unit 40 may comprise a laser adapted to measure without contact the distance from the workpiece, or a capacitive sensor or an inductive sensor or any other contactless proximity sensor. Alternatively, the surface detection unit 40 may comprise a device for a mechanical or touch measurement for tactile surface recognition. The surface detection may be realized with or without additional component.

[0053] The clamping device 22 may comprise a load measurement system or an integrated load cell 54 adapted to directly measure the clamping force F applied by the clamping device 22 to the workpiece arrangement W. The load measurement system 54 will measure the clamping force and send it to a controller to monitor and / or control the correct implementation of the setting steps (better described below).

[0054] The clamping device 22 comprises a recess or a portion adapted to receive or connect a thermal device 56 directly to the clamping device 22. In other words, the thermal device 56 is arranged on the clamping device 22. The thermal device 56 is for instance a plasma torch. The plasma torch will thermally assist the joining process. Patent publication EP3515632A1 from the applicant explains for instance how the plasma torch may assist the joining process. In other embodiments, the thermal device 56 may be a laser heating system, and induction heating system, an electric arc or similar equipment.

[0055] FIG. 4A to FIG. 4G shows the different possible step of a joining method according to the present disclosure. A clamping force (F) vs. time (t) curve is associated with each schematic representation of the various process steps.

[0056] In a first step, visible in FIG. 4A, the joining device 10 is arranged (for instance by the robot mentioned above) above the workpiece arrangement W. The joining device 10 does not contact the workpiece arrangement W. The workpiece arrangement W comprises at least two workpieces (or sheets) W1, W2 arranged one above the other. In other embodiments, more than two workpieces may be used. The workpieces may be made in high strength material or brittle cast material or extrusion material. Optionally, an adhesive is provided between the two workpieces.

[0057] In a second step, the clamping device 22 is moved toward the workpiece arrangement W until it contacts the upper surface of the workpiece arrangement W (see FIG. 4B). The upper surface may be recognized by the surface detection unit 40 described above, which can be realized via a function integrated in the already existing parts or which can be an additional component. For instance, a resistance force signal may be sent to a controller to determine the contact with the upper surface of the workpiece. If the joining process is thermally assisted by a plasma torch for instance, the plasma torch 56 may heat the workpiece arrangement W, as schematically visible in FIG. 4B.

[0058] A gap (not represented) between the workpieces may be detected by the clamping device 22 by the analysis of the force / time or force / displacement profile of the clamping device 22, notably though the load measurement system or load cell 54. In the case where a gap is detected, the clamping device 22 is controlled by a controller to close the gap by applying for instance a greater clamping force (see for instance FIG. 4C). In an alternative embodiment, such gap may also be already closed by the initial predetermined clamping force. Any adhesive retained into the gap is thus displaced to the side.

[0059] A first predetermined clamping force F1 is then applied to the workpiece arrangement W (see FIG. 4D). In FIG. 4D, the clamping force vs. time curve shows a rather important first predetermined clamping force F1. In case of a thermally assisted joining process, a great clamping force may be advantageous for allowing heat transmission between the first workpiece W1 and the at least second workpiece W2. In another alternative, the clamping force may remain very limited in order to avoid or limit heat transmission between two workpieces.

[0060] In FIG. 4E, the clamping force F is reduced to prevent the heat transfer to the lower workpiece. An excess of heat in the first or upper workpiece W1 compared to the second or lower workpiece W2 takes place. By varying the clamping force in the setting process, the heat flow between the workpieces W1, W2 can be specifically controlled. For example, when the clamping force is reduced, the entire force (comprising the clamping and the setting force) is reduced. When the clamping force is reduced, during a thermally assisted joining process, the upper workpiece W1 can be heated and the heat transmission of the upper workpiece W1 to the lower workpiece W2 is reduced, such that for instance in case of an upper workpiece W1 in high strength steel, the strength of the material or the flow stress is locally reduced which allows to reduce as well the setting force.

[0061] In FIG. 4F, the clamping force F reaches a second predetermined clamping force F2 corresponding to the setting step. As soon as the clamping force reaches the second predetermined value, the joining element 20 can be set by the punch 16 within the workpiece arrangement W. The joining element 20 may also be set before. The joining element 20 is pressed through the at least two workpieces W1, W2 with a determined setting force. The effort applied during the setting step to the joining equipment corresponds to the addition of the setting force and the clamping force. The clamping force during the setting step may be controlled at a lower or higher level depending on the setting parameters. It is to be noted that the setting force may also be reduced by the thermal device 56, as described in more details in EP3515632A1.

[0062] In a last step, the clamping device 22 is moved back to an exit position (see FIG. 4G). By recording the force / displacement or force / time profile, conclusions can be drawn about a possible spring back of the workpieces W1, W2 after setting.

[0063] joining device 10

[0064] workpiece arrangement W

[0065] a first and a second workpiece W1, W2

[0066] joining head 12

[0067] retaining device 14

[0068] punch 16

[0069] first drive unit 18

[0070] joining axis X

[0071] joining element 20

[0072] clamping device 22

[0073] second drive unit 24

[0074] clamping axis Y

[0075] clamp 26, 26’, 26’’, 26’’’, 26(4), 26(5), 26(6)

[0076] first end 28

[0077] second end 30

[0078] contact surface 32

[0079] window 34

[0080] attachment portion 38

[0081] surface detection unit 40

[0082] load measurement system or load cell 54

[0083] clamping force F

[0084] thermal device 56

[0085] first predetermined clamping force F1

[0086] second predetermined clamping force F2

Claims

1. A joining device for joining workpieces, the joining device comprising a joining head having: a retaining device for a joining element, wherein the joining element can be guided along or arranged on a joining axis via the retaining device; a punch with which a setting movement of the joining element can be executed, the punch being movable along the joining axis by a first drive unit ; and a clamping device with which one or more of the workpieces can be compressed in a joining direction, wherein the clamping device is movable through a second drive unit.

2. The joining device according to claim 1, wherein the second drive unit is a servo-electric drive with a spindle.

3. The joining device according to claim 1, wherein the second drive unit moves the clamping device along a clamping axis, the clamping axis being parallel to but not confluent with the joining axis.

4. The joining device according to claim 1, wherein the second drive unit is oriented with regard to the first drive unit at an angle between 0 and 90 degrees.

5. The joining device according to claim 1, wherein a thermal device is arranged on the clamping device and moves together with the clamping device.

6. The joining device according to claim 5, wherein the thermal device is a plasma torch.

7. The joining device according to claim 1, wherein the clamping device comprises a surface detection unit adapted to detect a surface of the workpieces.

8. The joining device according to claim 1, wherein the first drive unit is a servo-electric drive with a spindle.

9. The joining device according to claim 1, wherein the clamping device comprises a clamp with a U-shaped cross-section perpendicular to the joining axis adapted to be arranged around the punch and the retaining device.

10. The joining device according to claim 9, wherein the clamp has an external diameter between 10 and 30 millimeters.

11. The joining device according to claim 1, wherein the clamping device comprises an integrated load measurement system.

12. A joining method for joining at least two workpieces with a joining device, the joining device including a clamping device, a punch, a retaining device, and a setting device, the joining method comprising: providing a workpiece arrangement comprising an upper workpiece and a lower workpiece; providing the joining device, the joining device being arranged at a non-zero distance above the workpiece arrangement, the joining device being loaded with a joining element; moving the clamping device along a clamping axis until the clamping device contacts a surface of the upper workpiece; applying a first predetermined clamping force; and setting the joining element within the workpiece arrangement by moving the punch and / or the retaining device along the setting device to move the joining element into the workpiece arrangement.

13. The joining method according to claim 12, wherein the clamping device comprises a sensor unit providing force, displacement and time data.

14. The joining method according to claim 12, further comprising recording a clamping force profile and a clamping device displacement profile and / or the clamping force profile and a joining element displacement profile and / or a clamping force and time profile.

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