PROCESS MONITORING METHOD FOR MONITORING THE JOINING OF AT LEAST TWO WORKPIECES BY MEANS OF A SELF-PIERCING RIVETING DEVICE HAVING JOINING TONGS, AND DEVICE HAVING A CONTROL UNIT DESIGNED TO CARRY OUT SUCH A METHOD

Abstract

A process monitoring method for monitoring the joining of at least two workpieces by means of a self-piercing riveting device having a joining gun including a) a total sheet metal thickness, a rivet length and a bending constant of the joining gun are detected for a plurality of joining operations for each operation before joining; b) a punch path for a certain force, an end force, a path end value for the end force, a setting path of the rivet, and a rivet head end position are detected for the plurality of joining operations; c) a force/path window for the joining operations is determined; and d) a determined force/path window of one additional joining operation is compared to the force/path window of the joining operations determined in step c), and the additional joining operation is monitored so that any joining-related defects are identified.

Claims

1. A process monitoring method for monitoring the joining of at least two workpieces by means of a self-piercing riveting device having joining tongs, wherein the at least two workpieces are arranged between a punch and a counter-holder, and wherein a rivet arranged between the punch and a workpiece facing the punch is pressed by means of the punch into the at least two workpieces when a force F in the direction towards the counter-holder is applied to the punch, wherein a) a total thickness, a rivet length, and a bending constant of the joining tongs are recorded for a plurality of joining operations before joining, b) a punch displacement at a specific force, an end force, a displacement end value at the end force, a setting displacement of the rivet, and a rivet head end position are recorded for the plurality of joining operations during and/or after joining, c) in dependence on the parameters recorded in step a) and step b), an absolute force/displacement window and/or a relative force/displacement end window of the plurality of joining operations is/are determined, and d) a determined absolute force/displacement window and/or a relative force/displacement end window of at least one further joining operation is/are compared with the absolute force/displacement window and/or the relative force/displacement end window determined in step c) of the plurality of joining operations, wherein the at least one further joining operation is monitored so that a fault in joining is identified.

2. The method as claimed in claim 1, wherein relevant quality-determining regions of the joining operation are determined, wherein the process monitoring is reduced to the relevant quality-determining regions.

3. The method as claimed in claim 2, wherein the relevant quality-determining regions are determined time-dependently and/or displacement-dependently.

4. The method as claimed in claim 1, wherein, in step d), a fault in joining is identified above a specific threshold value of a difference between the determined absolute force/displacement window and the relative force/displacement end window of the further joining operation and the determined absolute force/displacement window and/or the relative force/displacement end window of the plurality of joining operations.

5. The method as claimed in claim 4, wherein the threshold value is determined by comparison with at least one standard component and/or by learning on the basis of a plurality of joining operations.

6. The method as claimed in claim 1, wherein the parameters in step a) and in step b) are determined in at least one specific time and/or displacement range during pressing in of the punch.

7. The method as claimed in claim 1, wherein a gradient is not used for identifying a fault in joining.

8. The method as claimed in claim 1, wherein the recorded parameters in step a) and b) for determining the absolute force/displacement window and/or the relative force/displacement end window are weighted differently.

9. The method as claimed in claim 1, wherein at least one of a force/displacement profile and/or a force/time profile of the joining operation, is used for the process monitoring.

10. A device having a control unit designed to carry out a method as claimed in claim 1, wherein the device further has a self-piercing riveting device having joining tongs, a punch and a counter-holder, wherein a force F in the direction towards the counter-holder can be applied to the punch so that a rivet can be pressed into at least two workpieces arranged between the punch and the counter-holder, wherein the device has sensors for recording the parameters, and at least one evaluation unit for determining an absolute force/displacement window and a relative force/displacement end window of a plurality of joining operations and comparing it with a determined absolute force/displacement window and/or a relative force/displacement end window of at least one further joining operation.

11. The method as claimed in claim 1, wherein the parameters in step a) and in step b) determined in at least one time and/or displacement range in which, based on experience, a fault is to be expected.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0032] The present invention will be explained in greater detail hereinbelow with reference to the drawing. The single FIGURE shows, in a flow diagram, a schematic representation of an exemplary embodiment of a process monitoring method for monitoring the joining of at least two workpieces by means of a self-piercing riveting device having joining tongs.

DETAILED DESCRIPTION OF THE INVENTION

[0033] The FIGURE shows, in a flow diagram, a schematic representation of an exemplary embodiment of a process monitoring method for monitoring the joining of at least two workpieces by means of a self-piercing riveting device having joining tongs. In the process monitoring method for monitoring the joining of at least two workpieces by means of a self-piercing riveting device having joining tongs, the at least two workpieces are arranged between a punch and a counter-holder, wherein a rivet arranged between the punch and a workpiece facing the punch is pressed by means of the punch into the at least two workpieces in that a force F in the direction towards the counter-holder is applied to the punch. In step a), a total thickness, a rivet length, and a bending constant of the joining tongs are recorded for a plurality of joining operations before joining. In step b), a punch displacement at a specific force, an end force, a displacement end value at the end force, a setting displacement of the rivet, and a rivet head end position are recorded for the plurality of joining operations during and/or after joining. In step c), in dependence on the parameters recorded in step a) and step b), an absolute force/displacement window and/or a relative force/displacement end window of the plurality of joining operations is/are determined. In step d), a determined absolute force/displacement window and/or a relative force/displacement end window of at least one further joining operation is/are compared with the absolute force/displacement window and/or the relative force/displacement end window determined in step c) of the plurality of joining operations, wherein the at least one further joining operation is monitored so that a fault in joining is identified.

[0034] Improved quality control is thereby ensured. The number of components incorrectly identified as faulty is reduced. Advantageously, costs are reduced and more rapid production is made possible.

[0035] In an embodiment of the present invention, relevant quality-determining regions of the joining operation are determined, wherein the process monitoring is reduced to the relevant quality-determining regions.

[0036] In a further embodiment of the present invention, the relevant quality-determining regions are determined time-dependently and/or displacement-dependently.

[0037] In a further embodiment of the present invention, in step d) a fault in joining is identified above a specific threshold value of a difference between the determined absolute force/displacement window and the relative force/displacement end window of the further joining operation and the determined absolute force/displacement window and/or the relative force/displacement end window of the plurality of joining operations.

[0038] In a further embodiment of the present invention, the threshold value is determined by comparison with at least one standard component and/or by learning on the basis of a plurality of joining operations.

[0039] In a further embodiment of the present invention, the parameters in step a) and in step b) are determined in at least one specific time and/or displacement range during pressing in of the punch, preferably in at least one time and/or displacement range in which, based on experience, a fault is to be expected.

[0040] In a further embodiment of the present invention, a gradient is not used for the process monitoring, in particular for identifying a fault in joining.

[0041] In a further embodiment of the present invention, the recorded parameters in step a) and b) for determining the absolute force/displacement window and/or the relative force/displacement end window are weighted differently.

[0042] In a further embodiment of the present invention, at least one further parameter, in particular, a force/displacement profile and/or a force/time profile of the joining operation, is used for the process monitoring.

[0043] The method is carried out, in particular, in a device having a control unit which is designed to carry out the method. The device has a self-piercing riveting device having joining tongs, a punch and a counter-holder, wherein a force F in the direction towards the counter-holder can be applied to the punch so that a rivet can be pressed into at least two workpieces arranged between the punch and the counter-holder, wherein the device has sensors for recording the parameters, and at least one evaluation unit for determining an absolute force/displacement window and a relative force/displacement end window of a plurality of joining operations and comparing it with a determined absolute force/displacement window and/or a relative force/displacement end window of at least one further joining operation.