METHOD AND APPARATUS FOR JOINING A JOINING ELEMENT ONTO A WORKPIECE

Abstract

A method for joining a joining element onto a workpiece, in particular for stud welding or stud gluing. The method steps including providing the joining element the workpiece; detecting a characteristic variable of the workpiece or of the joining element; evaluating the characteristic variable and classifying it into one a first or a second variable class; performing the joining process, if the characteristic variable is classified into the first variable class; or performing a cleaning process on the workpiece or on the joining element and then performing the joining process after the cleaning process, if the characteristic variable is classified into the second variable class.

Claims

1. A method for joining a joining element onto a workpiece, in particular for stud welding or stud gluing, wherein the method comprises the steps: providing the joining element and the workpiece; detecting a characteristic variable of one of the workpiece or the joining element; evaluating the characteristic variable and classifying the characteristic variable into one of a first variable class or a second variable class; and performing a joining process, if the characteristic variable was classified into the first variable class; or performing a cleaning process on one of the workpiece or on the joining element and then performing a joining process after the cleaning process, if the characteristic variable was classified into the second variable class.

2. A method according to claim 1, wherein the cleaning process is performed using a cleaning medium.

3. A method according to claim 2, wherein the cleaning medium comprises a gas.

4. A method according to claim 2, wherein the cleaning medium comprises an ice jet.

5. A method according to claim 1, wherein the detecting step comprises one of the following detection processes: a contact resistance measurement, a measurement of the electrical conductivity, and a fluorescence measurement.

6. A method according to claim 1, wherein the joining process is performed with one of standard joining parameters or with joining parameters which have been modified in relation to the standard joining parameters, and wherein the joining process performed after the cleaning process is performed using the standard joining parameters.

7. A method according to claim 6, wherein: in the evaluating step, if the characteristic variable is classified into the first variable class, then the characteristic variable in the first variable class is further sub-classified as being within a first value range or a second value range, and in performing the joining process step, the joining process is performed using standard joining parameters, if the characteristic variable lies within the first value range, or the joining process is performed using modified joining parameters, if the characteristic variable lies within the second value range.

8. A method according to claim 1, wherein the cleaning process is performed for a time period of a length from 0.1 seconds to 5 seconds.

9. A method according to claim 1, wherein after the cleaning process the characteristic variable is detected again, and subsequently an evaluation of the characteristic variable is performed again, before the joining process is performed.

10. A method according to claim 1, wherein, after the joining process step, the method further includes a step of performing a supplementary cleaning process.

11. A method according to claim 6, wherein the step of performing the joining process, the joining parameters include whether the joining process includes a preceding arc cleaning process.

12. A joining apparatus for joining a joining element onto a workpiece, the joining apparatus comprising: a joining head including a holding device for holding the joining element and moving the joining element along a joining axis in relation to the workpiece; a detection device for detecting a characteristic variable of the workpiece or of the joining element; an evaluation device for evaluating the characteristic variable; a cleaning device for performing a cleaning process on the workpiece or on the joining element; and wherein the joining apparatus performs a method comprising the steps of: providing the joining element and the workpiece; detecting with the detection device the characteristic variable of one of the workpiece or the joining element; evaluating with the evaluation device the characteristic variable and classifying the characteristic variable into one of a first variable class or a second variable class; and performing with the joining head a joining process, if the characteristic variable was classified into the first variable class, or performing with the cleaning device a cleaning process on one of the workpiece or on the joining element, and then performing with the joining head a joining process after the cleaning process, if the characteristic variable was classified into the second variable class.

13. A joining apparatus according to claim 12, wherein the cleaning device is fixed to the joining head, and the cleaning device is oriented at an angle () ranging between 10 and 45 in relation to the joining axis.

14. A joining apparatus according to claim 12, wherein the detection device is fixed to the joining head.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Illustrative embodiments of the invention are represented in the drawing and are explained in greater detail in the following description, wherein:

[0062] FIG. 1 shows a schematic representation of an embodiment of a joining apparatus according to the invention.

[0063] FIG. 2 shows a time lapse diagram of an exemplary joining method according to the invention.

[0064] FIG. 3 shows a flow chart of an exemplary method according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0065] In FIG. 1 a joining apparatus is represented in schematic form and is denoted in general terms by 10.

[0066] The joining apparatus 10 comprises a joining head 12 or a joining gun, wherein the joining head 12 is preferably fixed to an arm 14 of a robot 16 and is hence movable in three dimensions in space.

[0067] The joining apparatus serves to join joining elements 18 onto workpieces 20. The joining elements can, in particular, be studs. The workpieces 20 can, in particular, be metal plates. The joining apparatus 10 is preferably used in the field of body making of motor vehicles.

[0068] The material of the workpiece 20 and of the joining element 18 is respectively preferably aluminium or an aluminium alloy.

[0069] For the performance of a joining process, the joining element 18 is held in a holding device 24 of the joining head 12 and oriented in a joining axis 22, which is preferably perpendicular to a surface of the workpiece 20.

[0070] The holding device 24 is preferably connected to a power source 26 and is configured to pass a joining current i into the joining element 18. The workpiece 20 is connected, for instance, to an earth (or a ground source), as is indicated in FIG. 1.

[0071] In FIG. 1 is further indicated that the joining apparatus 10 can have a feeding device 28, by means of which joining elements (indicated by a T in FIG. 1) can be driven by automated means to the holding device 24.

[0072] In order to obtain consistent joining results, the joining apparatus 10 comprises a detection device 32, which is configured to detect at least one characteristic variable of the workpiece 20, such as, for instance, a surface quality, a surface character, etc. Quality surface and surface character mean any property of the structure, not only a surface contamination. Material structures like grain size, surface quality or roughness may be taken into consideration. The detection device 32 can be provided separate from the joining head 12, but can also be fixed to the joining head 12, as indicated in FIG. 1. In this case, it is preferred if the detection device 32 is oriented along a detection axis 34 which assumes an angle in relation to the joining axis 22. This angle can range, for instance, from 10 to 45.

[0073] The joining apparatus 10 further comprises a cleaning device 36. The cleaning device 36 is designed to apply a cleaning medium R to the surface of the workpiece 20. The cleaning device 36 can be configured separate from the joining head 12. For instance, the cleaning device 36 is, however, fixed to the joining head 12, as is indicated schematically in FIG. 1. In this case, it is preferred if the cleaning device 36 is oriented along a cleaning axis 38 which is oriented at an angle in relation to the joining axis 22. The value of the angle can, for instance, likewise range from 10 to 45.

[0074] The joining apparatus 10 further comprises an evaluation device 40, which is designed to evaluate a characteristic variable, detected by the detection device 32, of the workpiece 20. The evaluation device 40 can be arranged separate from the joining head 12, yet can also be integrated in the latter or in the power source 26.

[0075] In FIG. 2 is represented in schematic form a time lapse diagram 44, which shows a detection process E, a cleaning process R, an arc cleaning process C and a joining process F.

[0076] In the implementation of the method according to the invention, firstly, in a time period TE, at least one characteristic variable of the workpiece is detected, as is indicated at E in FIG. 2.

[0077] After this, the at least one characteristic variable is evaluated, which is not represented in FIG. 2. If the at least one characteristic variable is classified into a first variable class, directly following this a joining process F can be performed, optionally with the intervening performance of an arc cleaning process C.

[0078] For the representation of a joining process F, FIG. 2 shows the height h of the joining element 18 in relation to the surface of the workpiece 20 during the performance of the joining process, as well as the quantity of a current i which is passed into the holding device and hence into the joining element 18.

[0079] The joining process F begins after the joining element 18 has been lowered onto the surface of the workpiece 20 (h=0). After this, the current i is switched on and a pilot arc is drawn (i=iP). The joining element 18 is subsequently raised from the workpiece 20. Following this, the current i can be increased from iP to a welding current iS in order to fuse the reciprocal joining surfaces. After this, the workpiece is lowered again, to be precise preferably to below the surface of the workpiece 20, so that a short circuit is formed and the current i is lowered to 0. With this, the joining process F is concluded.

[0080] An optionally previously performed arc cleaning process C includes producing, at least once, an arc having an inverse polarity, by means of which ionized component parts on the surface of the workpiece 20 make their way in the direction towards the joining element 18.

[0081] After the detection process E and the subsequent evaluation, it is established whether the at least one characteristic variable falls into a first or a second variable class. In the event of classification in a first variable class, a subsequent cleaning process R, which is represented in FIG. 2, can be omitted, as mentioned, and it is possible to proceed directly to the joining process F, which takes place at a time TF, where necessary with a preceding arc cleaning at a space in time TC.

[0082] Insofar as the at least one characteristic variable falls into the second variable class, the cleaning process R is performed, to be precise using a cleaning device 36 and a cleaning medium, namely for a time period TR which preferably ranges from 0.1 seconds to 5 seconds, yet is preferably less than 3 seconds, in particular less than 2 seconds.

[0083] Following this, the joining process F is then performed, where necessary with preceding arc cleaning process C.

[0084] In FIG. 3 is represented an exemplary embodiment of a method according to the invention in the form of a block diagram 50.

[0085] The method 50 includes after a start, in a detection step 52, the detection of at least one characteristic variable of the workpiece 20.

[0086] In a subsequent evaluation step 54, the at least one characteristic variable is evaluated and classified either into a first or into a second variable class. Insofar as a classification is made into the first variable class, it is further evaluated whether the at least one characteristic variable falls into a first value range or into a second value range within the first variable class.

[0087] If the at least one characteristic variable of the workpiece 20 falls into the first value range of the first variable class, in an interrogation step 56 it is decided that a subsequent joining process F is performable with standard joining parameters, and this joining process is subsequently performed, as is shown at 58. The method is subsequently ended.

[0088] Insofar as the at least one characteristic variable does not fall into the first value range, in a subsequent interrogation step 60 it is enquired whether the at least one characteristic variable falls into the second value range within the first variable class. If this is the case, in a step 62 an adaptation is made of the joining parameters, so that the subsequent joining process 64 is performed with modified joining parameters. The adaptation of the joining parameters is here made preferably as a function of the at least one characteristic variable.

[0089] Insofar as it is established in the step 60 that the at least one characteristic variable falls into the second variable class, following this, in a step 66, a cleaning process is firstly performed.

[0090] After this, a joining process 68 takes place, to be precise preferably with standard joining parameters.

[0091] After the joining processes 58, 64, 68, the method is normally respectively ended. Where necessary, a subsequent, supplementary cleaning process 70 can also be performed, however, in which, for instance, traces of smoke residue due to the welding operation are removed. This supplementary cleaning process can be realized, for instance, using the same cleaning medium as the cleaning process 66.

[0092] In FIG. 3, it is further indicated that, after the performance of the cleaning process 66, a loopback is optionally performed, such that a detection of the at least one characteristic variable takes place at 52 and, after this, the following steps are likewise performed, depending on the evaluation of the at least one characteristic variable.

[0093] In a further embodiment, it is possible to first classify the workpiece (or classify several areas of the workpiece), then to perform a cleaning (if needed) and when the entire workpiece, or at least a portion of the workpiece is cleaned, perform one or several joining steps. Thus, several joining processes may be performed after evaluation of the characteristic variable and classification said characteristic variable into the first variable class.

[0094] Several cleaning processes may also be performed after evaluation of the characteristic variable and classification said characteristic variable into the second variable class. Following the cleaning processes, several joining processes are performed.

[0095] According to the present invention, the evaluation and the assessment includes grouping values to a resulting variable which then allows choosing the correct set of joining parameters.

[0096] Although exemplary embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes may be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.