METHOD OF PRODUCING A RIVETED JOINT

Abstract

A joining method for setting a rivet in a workpiece comprises the steps of: providing a setting tool including a frame, a punch, a die, a clamping device, a drive unit, and a control device; providing a predetermined maximal rivet setting speed to the control device; providing the rivet and the workpiece; feeding the rivet into the setting tool; and setting the rivet in the workpiece, the setting step further comprising: moving the punch at a first punch speed; slowing the punch to a second punch speed before the rivet contacts the workpiece; and driving the rivet into the workpiece by moving the punch and monitoring the punch to ensure the punch does not exceed the predetermined maximal rivet setting speed.

Claims

1. A joining method for setting a rivet in a workpiece comprising the steps of: providing a setting tool comprising a frame, a punch that is displaceable on the frame along a joining axis (X), a die that is mounted on the frame, a clamping device with which one or more components can be compressed in a joining direction, and the punch being guided in the clamping device by a drive unit and a control device; providing a predetermined maximal rivet setting speed, providing the rivet, feeding the rivet into the setting tool, and setting the rivet in the workpiece, the setting step further comprising: in a first stage, moving the punch at a first punch speed (S1); in a second stage, slowing the punch until the punch reaches a second punch speed (S2), wherein the second punch speed is reached at the latest when the rivet first contacts the workpiece, the second punch speed is less than the first punch speed; and in a third stage, moving the punch and monitoring the punch to ensure the punch does not exceed the predetermined maximal rivet setting speed.

2. The joining method according to claim 1, further comprising a step of defining a predetermined maximal rivet length, and the rivet defines a length less than the predetermined maximal rivet length, and the second punch speed is reached when the punch arrives at a position equal to the predetermined maximal rivet length from the workpiece.

3. The joining method according to claim 1, wherein the first punch speed (S1) is within a range of 150-1000 mm/s.

4. The joining method according to claim 1, wherein the second punch speed (S2) and/or the maximal predetermined rivet setting speed is within a range of 10-300 mm/s.

5. The joining method according to claim 1, wherein the predetermined maximal rivet setting speed is below 100 mm/s.

6. The joining method according to claim 1, wherein the drive unit slows the punch such that the second rivet speed (S2) is no more than the predetermined maximal rivet setting speed when the rivet first contacts the workpiece.

7. The joining method according to claim 2, wherein the drive unit slows the punch such that the second rivet speed (S2) is no more than the predetermined maximal rivet setting speed when the punch arrives at a position equal to the predetermined maximal rivet length from the workpiece.

8. The joining method according to claim 1, wherein a deformation of the frame during the setting step is detected by a monitoring unit and a course of movement during the setting step is corrected as a function of the deformation.

9. The joining method according to claim 1, wherein a first relative movement between the frame and the clamping device is measured by a first sensor and/or a second relative movement between the frame and the punch is measured by a second sensor.

10. The joining method according to claim 9, wherein the first sensor and/or the second sensor is a linear path recorder.

11. The joining method according to claim 1, wherein the workpiece includes a first workpiece and a second workpiece, and the first workpiece is a high strength steel workpiece.

12. The joining method according to claim 11, wherein the workpiece further includes a third workpiece, and first workpiece and the second workpiece are two upper layers and are high strength steel workpieces.

13. The joining method according to claim 1, wherein the predetermined maximal rivet setting speed is adjustable.

14. A joining method for setting a rivet in a workpiece comprising the steps of: providing a setting tool comprising a frame, a punch that is displaceable on the frame along a joining axis (X), a die that is mounted on the frame, a clamping device with which the workpiece can be compressed in a joining direction, and the punch being guided in the clamping device by a drive unit and a control device; providing a predetermined maximal rivet setting speed to the device; providing the rivet and the workpiece; feeding the rivet into the setting tool; and setting the rivet in the workpiece, the setting step comprising: moving the punch at a first punch speed (S1); slowing the punch from the first punch speed until the punch is moving at a second punch speed (S2) less than the first punch speed, and the second punch speed is reached no later than when the rivet first contacts the workpiece, and while the rivet penetrates into the workpiece, moving the punch at a third punch speed, monitoring the third punch speed, and maintaining the third punch speed at no more than the predetermined maximal rivet setting speed.

15. The joining method according to claim 14, further comprising a step of defining a predetermined maximal rivet length not less than a length of the rivet, and the second punch speed is reached when the punch arrives at a position equal to the predetermined maximal rivet length from the workpiece.

16. The joining method according to claim 14, wherein the first punch speed (S1) is within a range of 150-1000 mm/s.

17. The joining method according to claim 14, wherein the second punch speed (S2) and/or the maximal predetermined rivet setting speed is within a range of 10-300 mm/s.

18. The joining method according to claim 14, wherein the predetermined maximal rivet setting speed is below 100 mm/s.

19. The joining method according to claim 14, wherein the step of setting the rivet, the drive unit slows the punch such that the second rivet speed (S2) is no more than the predetermined maximal rivet setting speed when the rivet first contacts the workpiece.

20. The joining method according to claim 15, wherein the step of setting the rivet, the drive unit slows the punch such that the second punch speed (S2) is no more than the predetermined maximal rivet setting speed when the punch arrives at a position equal to the predetermined maximal rivet length from the workpiece.

21. The joining method according to claim 14, wherein the setting step further comprises: detecting a deformation of the frame by a monitoring unit and adjusting a course of movement as a function of the deformation detected.

22. The joining method according to claim 21, wherein a first relative movement between the frame and the clamping device is measured by a first sensor and/or a second relative movement between the frame and the punch is measured by a second sensor.

23. The joining method according to claim 22, wherein the first sensor and/or the second sensor is a linear path recorder.

24. The joining method according to claim 14, wherein the workpiece includes a first workpiece and a second workpiece, and the first workpiece comprises a high strength steel.

25. The joining method according to claim 24, wherein the workpiece further includes a third workpiece, and the second workpiece comprises a high strength steel.

26. The joining method according to claim 14, wherein the predetermined maximal rivet setting speed is adjustable in the control device.

27. The joining method according to claim 21, wherein the step of adjusting a course of movement further comprises: calculating a rectification tool force in the control device with the input of the monitoring unit; and/or adjusting a position of the punch and/or the third punch speed to achieve a predetermined target position for the rivet in the workpiece.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Various other aspects and further examples are also described in the following detailed description and in the attached claims with reference to the accompanying drawings, in which:

[0027] FIG. 1 schematically shows a setting tool comprising a frame, a punch that is displaceable on the frame along a joining axis, a die that is mounted on the frame, and a clamping device with which one or more components can be compressed in a joining direction, the punch being guided in the clamping device by a drive unit;

[0028] FIG. 2A shows a schematic diagram of the commanded and actual punch speed profile during the joining method;

[0029] FIG. 2B shows the schematic diagram of FIG. 2A with the commanded punch speed profile and the tool rectification force profile measured and used to command a precise setting;

[0030] FIG. 3A shows a schematic diagram of the punch speed in function of the relative punch position;

[0031] FIG. 3B shows the schematic diagram of FIG. 3A with the punch speed in function of the relative punch position and the tool rectification force profile measured and used to command a precise setting.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0032] 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. The steps of a method do not necessarily need to be executed in any specific order, or even sequentially, nor need the steps be executed only once, unless otherwise specified.

[0033] In some cases, well-known features, structures, or operations are not shown or described in detail. Furthermore, the described features, structures, or operations may be combined in any suitable manner in one or more embodiments. It will also be readily understood that the components of the embodiments, as generally described and illustrated in the figures herein, could be arranged and designed in a wide variety of different configurations.

[0034] FIG. 1 schematically shows a joining arrangement 10 for carrying out the joining method. The joining arrangement 10 comprises a setting tool 12. The setting tool 12 comprises a joining head which either can be mounted in a stationary fashion or can be moved by means of a robot 14. A feeder arrangement with a feeder hose 16 can be provided. The feeder hose 16 feeds singulated rivets 18 to the joining head, for example by means of air blast. Alternatively, a feeder arrangement can also have a magazine on the joining head, which is used to transfer singulated rivets automatically into a holder.

[0035] The joining head further comprises a counterforce structure or frame 20. Typically, such frame 20 is a C-shaped frame composed of a solid material. A punch 22 displaceable on the frame 20 along a joining axis X is also provided. The punch 22 can be controlled by a drive unit 24 and a control device 26. The drive unit 24 may comprise an actuator to actuate the punch 22.

[0036] The joining head further comprises a die 28 that is mounted on the frame 20, and a clamping device 30. The die 28 is mounted at one end of the frame 20, wherein the clamping device 30 is mounted at the other end of the frame 20. The punch 22 is guided in the clamping device 30 by the drive unit 24. The clamping device 30 is adapted to be biased in the joining direction or in the direction of the die 28.

[0037] The joining arrangement 10 serves to connect a first workpiece 32 and a second workpiece 34 which, for example, can be designed as metal sheets, by a rivet 18. The setting tool 12 can also be used to join together more than two workpieces 32, 34. For instance, three workpieces are joined, and the two upper layers are high strength steel workpieces. The rivet 18 can be for example a self-piercing rivet 18 or punch rivet which can be a hollow or a semi-hollow punch rivet. The workpieces 32, 34 are for instance made of high strength steel. The control device 26 can be programmed such that a predetermined maximal rivet length can be entered. This predetermined maximal rivet length can be adjusted by an operator and corresponds to the maximal length of a rivet used for the joining method. The length of the rivet is the axial length and correspond to the length between the head of the rivet and the foot of the rivet. The predetermined maximal rivet length is given by an operator and can depend on the joining operations to be executed. For example, for joining operations in the automotive industry, a predetermined maximal rivet length of 8 mm can be used. The self-piercing rivet 18 can for instance be mechanically coated or galvanic coated for instance. The rivet 18 can be a self-piercing rivet as described in EP2631022A1 and EP3424611 for instance are directed to an improved die. US2020261966A1.

[0038] To set the rivet 18 in the workpieces 32, 34, the workpieces 32, 34 are placed on the die 28. The punch 22 is then moved by means of the drive unit 24 in the direction toward the die 28. In this case, the clamping device 30 first contacts a surface of the uppermost workpiece 32 and presses the workpieces 32, 34 together in the joining direction.

[0039] The punch 22 is driven in a first stage R1 at a first punch speed S1. The first punch speed S1 is for instance between 150 and 1000 mm/s. The first punch speed S1 can be constant or not. More particularly the first punch speed S1 can be raised to a particular maximal value, for instance 300 mm/s. The first punch speed S1 is commanded by the control device 26. The punch 22 is driven at the first punch speed S1 by the drive unit 24 and then the punch speed decreases until the punch reaches a position which corresponds to the given maximal rivet length. The punch speed slowly decreases from the first punch speed S1 to a second punch speed S2 such that as soon as the punch reaches the position corresponding to the predetermined maximal rivet length, it reaches the second punch speed S2. The punch speed reduction corresponds to a second stage R2. The second punch speed S2 is for instance a constant speed or sensibly constant speed. The second punch speed S2 is lower than the first punch speed S1.

[0040] During the motion of the punch 22 toward the die 28, the punch 22 contacts the head of the rivet and therefore drive the rivet into the workpiece arrangement to realize the connection. This stage corresponds to a third stage R3, during which the punch 22 drives the rivet 18 into the workpiece at the second punch speed and the rivet speed is monitored to ensure it does not exceed a predetermined maximal rivet setting speed. The predetermined maximal rivet setting speed is a data which is defined by the operator before the joining method in the control device. The predetermined maximal rivet setting speed and the second punch speed are correlated. The predetermined maximal rivet setting speed can be adjusted by an operator depending on the joining operation, the workpiece material, the rivet material, the rivet geometry, the die geometry, . . . . For instance, with a mechanically coated rivet, the predetermined maximal rivet setting speed is within a range of 10-300 mm/s. The predetermined maximal rivet setting speed can be below 100 mm/s, or even below 50 mm/s in a particular embodiment.

[0041] The predetermined maximal rivet length allows to ensure that the speed is decreased before or when the rivet contacts first the workpiece and therefore to determine when the punch speed needs to be decreased such that the lower punch speed to avoid the cracks on the rivet has a minimum impact on the cycle time.

[0042] In order to correctly monitor the rivet speed during the setting step, the setting tool comprises a monitoring unit 36 adapted to detect the deformation of the frame 20 during the setting process and a course of movement during the setting step can be corrected by the control device as a function of the deformation. Thus, the actual displacement of the punch 22 and/or the rivet 18 can be determined, and the actual rivet speed correctly monitored. A first sensor 38 measures the relative movement between clamping device 30 and frame 20. This sensor is preferably a linear path recorder consisting of a kind of ruler which makes the same movement as the clamping device and a counter which is fixed to the frame and counts markings on the ruler going past it. A second sensor 40 measures the relative movement between frame and punch.

[0043] The first sensor 38 and the second sensor 40 are connected to the monitoring unit 36, which can thereby detect the bending of the frame during action of force by the punch 22 and the clamping device 30 on the workpiece 32, 34. With the knowledge of the bending of the frame 20 detected in this way the movement of the punch can be adjusted in such a way that a constant penetration depth of the rivets is always ensured. More particularly, the position of the rivet with regard to the workpiece can always be measured. This allows to determine the exact punch position, but also the exact rivet speed and to monitor correctly that the rivet speed does not exceed the predetermined maximal rivet setting speed. The course of movement can thus be corrected by the control device during the riveting or setting or joining process as a function of the bending.

[0044] FIG. 2A shows in more details the speed profile of the punch 22 during the setting step. In FIG. 2A the X-axis represents the time and the Y-axis represents the punch speed. FIG. 2A shows two curves. The plain line curve corresponds to the speed command. It is the pre-programmed punch speed. The dotted line corresponds to the actual punch speed. As visible in FIG. 2A, the two curve profiles are very similar, notably due to the sensors and monitoring unit explained above. In an initial stage (not described in detail above), the punch speed is constantly increased until it reaches a plateau. The plateau corresponds to a maximal punch speed used to approach the rivet. The maximal punch speed is for instance the first punch speed S1. The punch speed is then decreased up to the second punch speed S2. The second punch speed S2 corresponds to the second plateau. The inflexion point between the second plateau S1 and the curve portion corresponding to the decreasing speed corresponds to the predetermined maximal rivet length. Indeed, as mentioned below the predetermined maximal rivet length determines the instant when the second punch speed S2 is reached. Once the rivet is set in the workpiece, the punch 22 is then driven away from the workpiece and returns to its initial position as quickly as possible, as visible in the last portion (right-handed portion) of the curve shown in FIG. 2A. A new rivet can be fed and a new setting step can then be undertaken on the same workpieces at a different area or on different workpieces.

[0045] FIG. 2B shows the pre-programmed punch speed as visible in FIG. 2A in plain line and the dotted line show the rectification tool force during the setting step. The rectification tool force is calculated by the monitoring unit and the control device via the measurement of the first and second sensors. The rectification tool force allows to correct in real time the position of the punch and the rivet and their speed such that the actual and target curve are sensibly similar, as visible in FIG. 2A.

[0046] FIG. 3A and FIG. 3B show the punch speed in function of the relative punch position. In FIG. 2A the X-axis represents the relative punch position, and the Y-axis represents the speed. Unlike FIG. 2A and FIG. 2, the curves in FIG. 3A and FIG. 3B only depicts the first stage R1, second stage R2 and third stage R3 of the setting step. The curves do not represent the return of the punch to its initial position after the setting of the rivet.

[0047] In FIG. 3A, the plain line curve represents the commanded relative punch position, and the dotted line curve represents the actual relative punch position. As visible, due to the sensors 38, 40 and the monitoring unit 36, the command and actual curved are sensibly similar. In the first stage R1, represented in the right-hand side of FIG. 3A, the first plateau shows the first punch speed S1, which then slowly decreases in the second stage to reach the second punch speed, lower than the first punch speed. The second punch speed S2 forms the second plateau and corresponds to the third stage. As seen in FIG. 3A, the punch speed reduction from the first punch speed S1 to the second punch speed S2 can be sensibly constant. FIG. 3B shows the commanded relative punch position in plain line, as visible in FIG. 3A and the dotted line show the rectification tool force at the different position of the punch. The rectification tool force allows to correct in real time the position of the punch and the rivet and their speed such that the actual and target curve are sensibly similar, as visible in FIG. 3A.

[0048] Joining arrangement 10, setting tool 12, robot 14, feeder hose 16, rivet 18, frame 20, punch 22, joining axis X, drive unit 24, control device 26, die 28, clamping device 30, first workpiece 32, second workpiece 34, first punch speed S1, second punch speed S2 first stage R1, second stage R2, third stage R3, monitoring unit 36, first sensor 38, and second sensor 40.