DE102011077754A1 - Device useful for welding first metal element with second metal element by resistance welding, comprises welding electrode arrangement, electric welding current supply and arrangement for monitoring welding process - Google Patents

Abstract

Device for welding at least one first metal element (40) with at least one second metal element (42) by resistance welding, comprises: a welding electrode arrangement with at least two welding electrodes, which define a welding gap (24) and are movable between a receiving position and a welding position relative to each other; an electric welding current supply (68) for introducing a welding current between the spaced welding electrodes in the welding position on the metal elements; and an arrangement for monitoring the welding process on the basis of detected thermal radiation. Device for welding at least one first metal element (40) with at least one second metal element (42) by resistance welding, comprises: a welding electrode arrangement with at least two welding electrodes, which define a welding gap (24) and are movable between a receiving position and a welding position relative to each other and with which a contact pressure is generated between the first and the second metal element in the welding position by common terminals of metal elements between the welding electrodes; an electric welding current supply (68) for introducing a welding current between the spaced welding electrodes in the welding position on the metal elements; and an arrangement for monitoring the welding process on the basis of detected thermal radiation, comprising at least one heat radiation detector (50), which receives heat radiation from the region of the welding gap when welding electrodes are arranged in the welding position, and an evaluation device which is designed to receive at least one output signal of the heat radiation detector, which is dependent on the receiving heat radiation and to evaluate with respect to at least one monitoring criterion. An independent claim is also included for monitoring the welding process based on the detected heat radiation during the welding of at least one first metal element with at least one second metal element by resistance welding.

Description

According to one aspect, the invention relates to a device for welding at least one first metal element with at least one second metal element by resistance welding, comprising: a welding electrode arrangement having at least two welding electrodes which define a welding gap and are movable relative to one another between a receiving position and a welding position and with which the welding position, a contact pressure between the first and the second metal element can be generated by clamping the metal elements together between the welding electrodes, and an electric welding power supply for introducing a welding current between the welding electrodes arranged in the welding position via the metal elements.

It is known to monitor the welding process based on the welding current, the welding voltage, the electrode pressure and the Nachsetzwegs in resistance welding devices. These quantities can only provide information about the course of the welding process in a rather indirect manner and thus do not clearly show the achieved quality of the welding process.

By contrast, it is an object of the invention to more directly monitor resistance welding processes, in particular with regard to the quality of the welded joint that has been produced. To solve this problem, it is proposed for the device mentioned that it has an arrangement for monitoring the welding process on the basis of detected heat radiation, comprising: at least one heat radiation detector, which receives heat radiation from the region of the welding gap when welding electrodes are arranged in the welding position, and an evaluation device adapted to receive at least one of the receiving heat radiation dependent output of the heat radiation detector and to evaluate with respect to at least one monitoring criterion.

In another aspect, the invention further provides a method for monitoring the welding process on the basis of detected thermal radiation when welding at least one first metal element to at least one second metal element by resistance welding by means of a welding electrode arrangement having at least two welding electrodes defining a welding gap and between a receiving position and a welding position are movable relative to each other and with which in the welding position, a contact pressure between the first and the second metal element by common clamping of the metal elements between the welding electrodes can be generated, and an electric welding power supply for initiating a welding current between the arranged in the welding position Welding electrodes on the metal elements, in which by means of at least one heat radiation detector angeo in the welding position During a welding operation, welding electrodes receive heat radiation from the region of the welding gap as a result of welding current flowing over the metal elements, and at least one of the receiving heat radiation-dependent output signal of the heat radiation detector is evaluated with respect to at least one monitoring criterion.

In resistance welding, so much heat is generated by the current flow through the two materials to be connected at the pad via the contact resistance that the materials combine. This occurs in the transition between the solid state to the liquid state of the materials. Depending on the material properties, the introduced electrical power causes temperatures that can be measured as heat radiation. The heat radiation is typically in a wavelength range of about 3 microns to 800 nm, ie in the infrared to red-yellow visible electromagnetic spectrum. This corresponds to a temperature range of black body radiation of about 600 ° C to 2000 ° C.

The detection of thermal radiation can be done for example with one or more photoelements whose sensitivity z. B. is between 3 microns to 0.8 microns. Expediently, such a photoelement or such photoelements may be located in an electrode holder or in a welding arm of the welding device according to the invention, since in the region of the welding electrode due to the electrode geometry and a cooling that is frequently realized significantly lower temperatures usually occur and thus heat radiation only with a significantly longer wavelength is radiated as from the heated by the introduced electric power materials to connect. The thermal radiation thus detected depends on the course of the welding process and can, for. B. be used in terms of intensity, shape and spectrum for the control of the welded joint.

It is especially, but not exclusively, thought that the device according to the invention is designed to weld at least one contact metal blank to a connection surface of a metallic carrier part made of sheet metal or flat material by resistance welding. For this purpose, the device may comprise components known per se, for example as follows: a A support assembly for supporting the support member in a position in which a contact part loading space of the mounting surface of the support member is within the welding gap; a contact metal blank feeder for feeding contact metal blanks to a contact metal blank transfer position associated with the contact part loading place; drive means for moving the welding electrodes between the picking position and the welding position and for generating a contact pressure between the carrier part and a respective contact metal blank positioned at the contact part mounting location of the carrier part by clamping the carrier part and the contact metal blank together between the welding electrodes in the welding position; and a control means for controlling the contact metal blank feed, the drive means and the welding power supply.

Thus, according to the invention, a device for welding at least one contact metal blank to a connection surface of a metal carrier part made of sheet metal or flat material by resistance welding is also specifically provided, which comprises: a welding electrode arrangement having at least two welding electrodes defining a welding gap and changing the gap width of the welding gap between a receiving position and a welding position are movable relative to each other; a support assembly for supporting the support member in a position in which a contact-part insertion space of the attachment surface of the support member is within the welding gap; a contact metal blank feeder for feeding contact metal blanks to a contact metal blank transfer position associated with the contact part loading place; a drive means for moving the welding electrodes between the picking position and the welding position and for generating a contact pressure between the carrier part and a respective contact metal blank positioned at the contact part mounting position of the carrier part by clamping the carrier part and the contact metal blank together between the welding electrodes in the welding position; an electric welding power supply for introducing a welding current between the welding electrodes arranged in the welding position via the contact metal blank and the support member, for welding the contact metal blank to the support member at the contact part mounting position thereof; and a control means for controlling the contact metal blank feed, the drive means and the welding power supply.

Such devices are known, for example DE 24 54 804 03 . DE 24 62 790 C2 . DE 26 15 364 C2 . DE 197 55 166 A1 . DE 103 47 074 A1 . DE 103 47 075 A1 and DE 10 2009 045 252 A1 ,

According to the invention, the device for welding at least one contact metal blank to a bumping surface of a metal carrier part made of sheet metal or flat material by resistance welding is characterized in that an arrangement for monitoring the welding process based on detected heat radiation is provided, which comprises: at least one heat radiation detector, which in in the Welding position arranged welding electrodes receives heat radiation from the region of the welding gap; and an evaluation device, which is designed to receive at least one of the receiving heat radiation-dependent output signal of the heat radiation detector and to evaluate with respect to at least one monitoring criterion.

With regard to the supply of contact metal blanks, it should be noted that the contact part transfer position can advantageously correspond to the contact part insertion position in the welding gap.

In order to be able to detect heat radiation from the region of the welding gap which reflects the course of the welding process better, at least one of the welding electrodes can be provided with an observation passage through which heat radiation can exit from the region of the welding gap when the welding electrodes are arranged in the welding position and via which the heat radiation detector Thermal radiation receives. In this context, it is primarily, but not exclusively, conceived that the observation passage is designed as an observation channel extending from a contact side of the welding electrode defining the welding gap to a rear side of the welding electrode.

With regard to the device for welding at least one contact metal blank to the application surface of a metallic carrier part, it is proposed to be particularly expedient that a welding electrode engaging in the welding position on a rear side of the carrier part opposite the attachment surface of the carrier part is designed with the observation passage. Also in this context is thought specifically to the realization of the observation passage as an observation channel. In this case, the opening in the welding electrode can be kept quite small (for example less than 15% of the electrode surface acting on the rear side of the carrier part). Through this opening or the observation passage, the measurement of the heat radiation intensity can be done well because the surrounding Due to its lower temperature, the electrode material behaves approximately like a black body and is determinable relative to the temperature of the weld.

In general, it is proposed that, in the case of welding electrodes arranged in the welding position, thermal radiation can emerge from the region of the welding gap from the surface area of the rear side of the carrier part which corresponds to the contact part mounting location of the mounting surface. If the observation passage is formed by the observation channel already mentioned, this can expediently extend substantially orthogonal to the surface region of the rear side of the carrier part which is opposite to the contact part-determining location of the attachment surface.

In principle, there are many possibilities for ensuring that the heat radiation emerging from the region of the welding gap, in particular through the observation passage, is supplied to the at least one heat radiation detector without or with as little loss as possible. There are also basically many possibilities where the heat radiation detector is positioned with respect to the welding gap or the welding electrodes. In general, in this context, it is contemplated that the thermal radiation detector receives the thermal radiation from the region of the welding gap or from a surface region of one of the metal elements or the carrier part via an optical arrangement, which preferably comprises at least one of the following components: a radiation conductor arrangement , at least one lens element, and at least one spectral filter.

Suitably, the heat radiation detector, possibly together with at least one associated optical component, may be arranged in a recess of a welding electrode holder holding the welding electrode with the observation passage.

Another possibility is that the heat radiation detector is arranged separately from a welding electrode holder holding the welding electrode with the observation passage. In this context, it can be provided that an input end of a radiation conductor arrangement which supplies the heat radiation to the heat radiation detector and, preferably, at least one associated optical component is arranged in a recess of the welding electrode holder.

A spectrally selective detection of the heat radiation can be useful to monitor the welding process well. For this purpose, the heat radiation detector may be assigned a spectral filter arrangement which is designed to selectively transmit at least one wavelength range to the heat radiation detector from the thermal radiation emanating from the region of the welding gap or from one / the surface region of one of the metal elements or the carrier part.

It can also be useful to record the thermal radiation simultaneously with respect to different spectral components. For this purpose, it is proposed that the heat radiation detector has a plurality of heat radiation detector elements or that a plurality of heat radiation detectors are provided, with which different spectral components of the heat radiation emanating from the region of the welding gap or from one / the surface region of one of the metal elements or the carrier part can be detected simultaneously. In this connection, it can be provided that the plurality of heat radiation detector elements or the plurality of heat radiation detectors have different spectral sensitivity bandwidths and / or at least one of the heat radiation detector elements or heat radiation detectors is assigned at least one spectral filter having a specific spectral transmission bandwidth.

Concerning the evaluation by the evaluation device, it is proposed that the evaluation device is designed to detect at least one first welding signature characterizing the welding process or its time profile based on the at least one output signal of the at least one heat radiation detector during a welding operation and at least one of these Evaluate monitoring criterion.

The term "signature" is intended here to address only one or more features of the heat radiation detected by the heat radiation detector with respect to a welding operation (or other inference to variables permitting the course of the welding process, see below). It may be a summary feature, such as an average intensity of the detected heat radiation over the course of the welding process or an integrated intensity of the intensity detected over a time interval, as well as the intensity curve itself (such as the amount of all over a period of observation Intensity values) and / or can be around these characteristic quantities, such as maximum intensity, exceeding or not exceeding an intensity threshold, shape of the intensity curve, etc. If this is intensity, this term also includes the intensity representing measured values such as the output voltage of a photoelement.

It is specifically contemplated that the first welding signature comprises at least one signature value, the summation, if appropriate as time average or as integral value or as rms value, the intensity of the heat radiation received by the heat radiation detector during a welding process or the intensity of at least one spectral component of this heat radiation represents, and / or that the first welding signature comprises at least one signature value profile representing the time course of the intensity of the received during a welding operation of the heat radiation detector heat radiation or the time course of the intensity of at least a spectral portion of this heat radiation.

In addition, other inferences on the course of the welding process or the quality of the welding permitting quantities can be used to monitor the welding process. For example, it is thought that the evaluation device is designed to detect at least one second welding signature characterizing the welding process or its time profile based on at least one output signal of the welding power supply and / or by means of at least one sensor detecting at least one electrical variable of the welding current evaluate at least one monitoring criterion. In this case, the evaluation device can be embodied specifically and particularly advantageously for evaluating the first welding signature in relation to the second welding signature in accordance with a monitoring criterion. For example, it is possible to judge the first welding signature as a function of the second welding signature in terms of whether the welding process has proceeded correctly and the required quality has been achieved.

The second welding signature may comprise at least one signature value which is summarily, if appropriate as time average or as integral value or as rms value, at least one electrical variable of i) the current intensity of the welding current, ii) a voltage drop across the metal elements or contact metal blank and Represent carrier voltage and iii) represents an introduced in this electric power or energy. Alternatively or in addition, the second welding signature may comprise at least one signature value profile which represents the time profile of at least one electrical quantity of i) the current intensity of the welding current, ii) a voltage representing a voltage drop across the metal elements or the contact metal blank and the carrier part, and iii) one in represents this introduced electrical power or energy.

Furthermore, the evaluation device can be advantageously designed to detect the contact pressure or a temporal contact pressure profile during the welding process by means of at least one force sensor or / and by at least one displacement sensor at least one of the welding electrodes, in particular a time course of the Nachsetzens and / or Nachsetzweg at least one of the welding electrodes to detect during the welding process as a third welding signature and to evaluate these with respect to at least one monitoring criterion. In this context, it is thought that the evaluation device is designed to evaluate the first welding signature with respect to the third welding signature in accordance with a monitoring criterion. Thus, for example, the first welding signature as a function of the third welding signature can be judged as to whether the welding process has proceeded correctly and the desired welding quality has been achieved. Suitably, the evaluation device may be designed to evaluate the first welding signature with respect to the second welding signature and with respect to the third welding signature in accordance with a monitoring criterion. Thus, for example, the first welding signature can be judged as a function of the second welding signature and as a function of the third welding signature as to whether the welding process has proceeded correctly and the quality of the welding to be achieved has been achieved.

A particularly reliable monitoring of the welding process can be based on reference data obtained in a corresponding welding or several corresponding welding operations, with which a reference good part was generated, which in a review, possibly a mechanically destructive check, for good and the quality requirements were met. Such reference data may relate to one of the aforementioned weld signatures, in particular at least the first weld signature, preferably the first and second weld signatures or the first and third weld signatures, most preferably the first, second and third weld signatures. In this context, it is proposed that the evaluation device is designed to compare at least one welding signature, in particular at least the first welding signature, with at least one reference welding signature.

Thus, for example, the evaluation of a measurement signal of a photoelement or of a plurality of photoelements with respect to its temporal course can be compared with a corresponding time profile of the photoelement measurement signal recorded in the generation of the reference good part to decide whether or not the welding now carried out also meets the quality requirements.

Instead of a direct comparison with at least one reference welding signature, it is preferred that the evaluation device is designed to check at least one welding signature, in particular at least the first welding signature, to determine whether it fulfills at least one predetermined reference condition. The predefined reference condition is preferably a condition which was derived from at least one welding signature which was obtained when generating a reference good part or during the generation of a bad part, and indicates that the welding process on which the weld signature to be checked has been successfully completed failed.

A first reference condition may provide a minimum threshold and / or a maximum threshold for at least one weld signature value. A second reference condition may provide a minimum threshold or / and a maximum threshold for a temporal integral over weld signature values. A third reference condition may provide an allowable value corrector for temporally successive weld signature values.

It is not necessary that always all basically provided evaluations are carried out by the evaluation device. For example, it could be that if a certain monitoring criterion is not met, the required quality of the weld is certainly not reached, so that no further evaluations are useful. Correspondingly, it could be that the fulfillment of another monitoring criterion reliably indicates the fulfillment of the quality requirements, so that further evaluations are likewise unnecessary. It is therefore generally proposed that the evaluation device is designed to evaluate the output signal of the heat radiation detector and / or at least one signature value of the first welding signature with respect to a first monitoring criterion, and at least one further evaluation according to at least one further monitoring criterion based on the output signal of the heat radiation detector and / or based on at least one of the first, second, and third weld signatures only if the first monitoring criterion is met (alternatively: not met, depending on the wording of the monitoring criterion, see the following note).

It should be noted that each monitoring criterion corresponds to a complementary monitoring criterion, such that, if the monitoring criterion is fulfilled, the complementary monitoring criterion is not satisfied, and if, if the monitoring criterion is not met, the complementary monitoring criterion is satisfied. Each questionable question can therefore be formulated both positively and negatively.

The device according to the invention or its evaluation device is preferably designed for carrying out the method according to the invention as stated above and described below with regard to preferred developments.

The method provided by the invention for monitoring the welding process on the basis of detected thermal radiation during welding of at least one first metal element with at least one second metal element by resistance welding can be developed in a similar manner as the device according to the invention. Thus, the heat radiation from the region of the welding gap can be received through an observation passage, preferably an observation channel, of at least one of the welding electrodes. The heat radiation from the area of the welding gap can be spectrally filtered. The output signal of the heat radiation detector can be detected time-resolved.

Furthermore, in the method, one or more welding signatures can be detected. Thus, on the basis of the at least one output signal of the at least one heat radiation detector during a welding operation, at least one first welding signature characterizing the welding process or its temporal course can be detected. Furthermore, on the basis of at least one output signal of the welding power supply and / or by means of at least one sensor detecting at least one electrical variable of the welding current, at least one second welding signature characterizing the welding process or its time characteristic can be detected. Further, by means of at least one force sensor, the contact pressure or a temporal contact pressure curve during the welding process and / or by means of at least one displacement sensor, a readjustment of the welding electrodes, in particular a time course of the Nachsetzens and / or a Nachsetzweg the welding electrodes are detected during the welding process as a third welding signature.

At least one welding signature with respect to at least one monitoring criterion can be evaluated. It is preferred that, according to at least one monitoring criterion, a plurality of welding signatures are evaluated with respect to one another.

According to a monitoring criterion, the evaluation may include the comparison of at least one welding signature with reference, data, for example at least one reference welding signature or data derived from at least one reference welding signature (such as minimum value to be achieved, permissible value range). In this regard, it is primarily thought of the first welding signature, but also to the second and the third welding signature.

The reference welding signature may be a welding signature detected during a welding operation, which has resulted in a predetermined requirement of welding the metal elements. In this regard, it is primarily thought of the first welding signature, but also to the second and the third welding signature. However, the reference data may also be comparison data obtained from successful test welding operations and applicable with a monitoring criterion to a currently recorded weld signature to assess weld quality.

Preferably, at least one welding signature, in particular at least the first welding signature, is checked to see whether it fulfills at least one predetermined reference condition. In particular, it is contemplated that the weld signature is checked for whether at least one weld signature value exceeds a minimum threshold and / or does not exceed a maximum threshold. It is also expedient, if the welding signature is checked for whether a temporal integral over welding signature values exceeds a minimum threshold or / and does not exceed a maximum threshold. Furthermore, the welding signature can be checked for whether temporally successive welding signature values are within a permissible value range.

As already mentioned, the method according to the invention will as a rule relate to determining the quality of the welding on the basis of the mentioned evaluation. Suitably, the welding and the monitoring and evaluation by means of a device according to the invention as proposed above and explained in terms of preferred developments can be performed.

The invention will be explained in more detail below with reference to an exemplary embodiment shown in the figures.

1 shows a sectional view along the line AA in 2 an embodiment of a welding device according to the invention.

2 shows the welding device of 1 in a top view.

3 shows the tail of the 1 in a back view.

4 shows the area of two welding electrodes of the welding device of 1 to 3 in an enlarged sectional view.

5 1 schematically shows a carrier part with a contact metal blank arranged thereon in the welding gap of an embodiment of the welding device according to the invention (FIG. 5a ), with an enlarged view of the welding gap between the welding electrodes ( 5b ).

6 schematically shows components of an embodiment of a welding device according to the invention and their electrical interconnection.

7 shows exemplary waveforms of a photoelement output voltage and a welding current during a welding process.

8th serves with the subfigures 8a and 8b to explain two purely exemplary monitoring criteria related to the photoelement output voltage.

In 1 is a side sectional view of an embodiment of a device according to the invention for welding at least a first metal element with at least one second metal element by resistance welding, namely a device for welding at least one contact metal blank to a mounting surface of a metallic support member made of sheet metal or flat material by resistance welding, shown, so an example of an inventive welding device 10 , This welding machine 10 comprises as frame elements a stationary welding arm 12 and a movable, in particular a to the plane of the 1 orthogonal pivot axis relative to the stationary pivot arm 12 swiveling welding arm 14 , The welding arms 12 and 14 have at their front longitudinal ends 12a and 12b welding electrodes 16 and 18 on. These welding electrodes 16 . 18 are by means of a respective electrode holder 20 respectively. 22 with the relevant welding arm 12 respectively. 14 connected. The welding electrodes 16 . 18 define a welding gap between them 24 ,

The welding machine 10 serves to weld contact metal blanks on a flat support. For this purpose, a respective contact metal blank 40 in the welding gap 24 fed and on the carrier 42 positioned, and then it will be the Contact metal blank and the vehicle 42 clamped between the electrodes to produce a contact pressure and a welding current across the electrodes through the contact metal blank 40 and the carrier 42 passed to the contact metal blank 40 on the carrier 42 to weld and thus a contact 40 ' to provide on the carrier. The respective contact metal blank to be supplied is preferably separated from a wire or strip, for which purpose a corresponding wire roll may be provided, from which a wire serving for the production of contact metal blanks is fed to the welding device. The welding machine 10 may further comprise means for controlling the wire and for feeding the wire or strip. Furthermore, the welding device 10 a transport device which transports the wire by a desired length towards the welding electrodes and then holds the wire during the welding operation. Furthermore, a supply device for feeding a respective carrier part or for advancing the carrier part (in particular if a contact metal blank is to be welded to a plurality of placement stations for forming a respective contact part) may be provided.

In the carrier part 42 it may be a carrier tape or section of a carrier tape, so that the of the lower welding arm 12 by means of the electrode holder 16 held welding electrode 16 also be designated as a band electrode.

The welding device is driven by a motor drive, which ensures a synchrony of the various handling, transport and other movements including the relative movement of the two welding electrodes between a receiving position and a welding position.

A more detailed explanation of the mechanics and control of such a welding device is unnecessary, since corresponding welding devices are well known. Reference is made to the following patent literature: DE 24 54 804 03 . DE 24 62 790 C2 . DE 26 15 364 C2 . DE 103 47 074 A1 . DE 103 47 075 A1 . DE 197 55 166 A1 and DE 10 2009 045 252 A1 , The invention can in principle be realized on the basis of any of these prior art devices as well as other such devices known in the art. The disclosure of said patent literature publications is incorporated by reference into the disclosure of the present application.

According to the invention, a process monitoring, in particular quality monitoring, of the resistance welding processes for welding a respective contact metal blank to the carrier part is provided for the formation of a respective contact.

Quality monitoring or process monitoring of resistance welding operations is known per se and conventionally for example by means of sensors for measuring current, force, displacement and voltage in order to monitor the welding current, the welding voltage, the electrode pressure and the Nachsetzweg.

According to the invention, a monitoring of the respective welding process on the basis of detected heat radiation from the welding gap, which is a measure of the temperature occurring during welding due to the introduced at the contact resistance between the materials to be connected electrical power. Reference is made to the well-known relationship between the output of an optical pyrometer or pyrometric detector and the temperature of a non-contact object measured according to the Stefan Boltzmann law and the well-known principles of infrared thermometry.

It has been found that an absolute temperature determination is generally not necessary, so that regularly a relative temperature measurement is sufficient. Ideally, not only a summary temperature value (or the temperature-representing measured value) is taken as the basis of the evaluation, but the temperature value course (measured value profile), which is recorded with a suitable sensor element (photoelement) or several such elements. In addition, it is also possible to fall back on the quantities which have already been conventionally used in welding quality monitoring during monitoring or evaluation.

In the 1 and 4 is a corresponding, with a photoelement 51 executed sensor with 50 designated. The sensor 50 can be designed with an integrated optics to supply incidental heat radiation as completely as possible to the photoelement.

In the embodiment, the sensor detects 50 that of one on the welding electrode 16 lying on the underside of the support element at a contact part placement place opposite thermal radiation emanating over an observation channel 52 the sensor 50 fed. The observation channel 52 extends from the welding gap defining upper side of the stationary electrode 16 and in the electrode holder 20 received lower end surface of the electrode 16 to the sensor 50 is in a contact with the inserted electrode 16 subsequent area of a receiving recess of the electrode holder 20 arranged, in immediate neighborhood to the lower exit end of the observation channel 52 ,

The through the observation channel 52 formed opening in the welding gap bounding and the support part 42 each contacting surface of the welding electrode 16 should be small (for example, less than 15%) compared to the contact dimensions of the material to be welded, here the support part held. The measurement of the radiation intensity can be done well through this opening or through the observation channel, because the surrounding electrode material due to the temperature compared to the temperature significantly lower temperature behaves approximately as a black body and with this lower temperature in a determinable relation to the temperature of the weld stands. Often, the welding electrodes are cooled so that the electrode material is substantially colder than the weld.

If the welding is carried out correctly, the highest temperature occurs at the welding point, ie at the point of contact between the materials to be welded. This contact point is not directly accessible for a temperature measurement. However, it has surprisingly been found that the lower temperature compared to the temperature at the bottom of the support member for monitoring the welding well and obviously reflects the temperature profile at the actual weld well, although the heat of the lower welding electrode 16 Overlying underside must first be supplied by the heat conduction occurring in the material and will also be distributed in the material of the support member to some extent and also discharged from the electrode to the full extent.

Is the opening in the electrode 16 due to the observation channel is not too large, resulting from the opening uneven current flow and the resulting non-uniform contact force leading to no relevant in practice impairment of the contact surface and thus realized welding process. On the back of the carrier part 42 As a rule, a possibly resulting impression of the observation channel opening can easily be accepted.

It should be noted that a sensor detecting the thermal radiation alternatively also the sensor with the upper movable electrode 18 in contact top of the contact metal blank 40 could be assigned, for which the upper electrode 18 could be executed with a corresponding observation channel and the corresponding sensor, for example, in the receiving space of the upper electrode holder 22 could be arranged. In contrast, however, is realized in the illustrated embodiment assignment of the sensor 50 to the lower stationary electrode 16 in contact with the underside of the carrier part is preferred.

6 schematically illustrates an electrical interconnection of various sensors and other components of an embodiment of a welding device according to the invention. It may be the welder of the 1 to 4 act, which is assumed below. Shown are the upper, movable electrode 18 and the lower, stationary electrode 16 with the observation channel 52 and a photoelement 51 of the sensor 50 , The upper electrode is by means of a through a function block 60 represented drive means between a receiving position and a welding position along a welding movement line relative to the stationary welding electrode 16 adjustable. The movement is through the double arrow 62 represents. The movement of the welding electrode 18 and especially also the Nachsetzen during the welding and then the total resulting from the welding Nachsetzweg is by a displacement sensor 64 detectable, and by means of the welding electrode 18 applied to the elements to be welded, the contact pressure between the elements determining contact force can with a force sensor 66 be recorded. The functional coupling of these sensors 64 . 66 is also symbolized by double arrows.

A per se known components such as a transformer, etc. having welding power supply is through a functional block 68 represents at the two electrodes 16 and 18 via suitable connection lines 70 and 72 are connected. The resulting welding current can be measured by means of an ammeter 74 be detected, and between the welding electrodes 16 and 18 occurring welding voltage by means of a voltage measuring device 76 , From the measured data for the current and the voltage, the electrical power introduced into the contact resistance between the materials to be welded can also be determined.

A control unit 80 controls via a control line 82 the drive device 60 and via a control line 84 the welding power supply 68 at. The addressed sensors transmit measured signals representing the detected variables via measuring signal lines 86 . 88 . 90 and 92 to the control unit 80 out. Also the detector 50 with his photoelement 51 is via connection lines 94 and 96 at the control unit 80 connected. For the sake of simplicity, it is assumed that the control unit 80 all for the detection of thermal radiation by means of the photoelement 51 contains necessary electronics. But it can also easily the sensor 50 be implemented with integrated electronics and then over a signal line to the controller 80 be connected.

The control unit 80 is set up, in particular programmed, to carry out an evaluation of the variables detected via the various sensors or measuring devices or of the resulting measuring signals in order to assess a welding process carried out in each case, in particular in the sense of quality or process monitoring. The control unit 80 In this respect, an evaluation device which receives output signals of the addressed sensors and measuring devices and evaluates them with regard to a monitoring criterion or with respect to a plurality of monitoring criteria.

To the control unit 80 can be connected to other electronics, such as through the function block 98 represents. So could the function block 98 represent an interface device with which the controller 80 is programmable and with the values detected by the sensors and by the control unit 80 on the basis of which prepared evaluation results can be displayed, printed out or stored on a screen.

Preferably, all of the addressed sensors and in any case at least the heat radiation detector 50 designed to record the course of the welding process by means of the respective measured variable time-resolved.

7 shows an example of detecting the heat radiation from the observation channel 52 the stationary electrode 16 by means of the photoelement 51 having heat radiation detector 50 for a successful welding process, with which a contact metal blank 40 on the carrier part or carrier tape 42 according to the quality requirements to form a contact 40 ' was welded on. It may in particular be measurement results in relation to a welding operation, with which a so-called reference good part was generated, which was found in a review, possibly a mechanically destructive test, for good.

In the lower diagram is the course of the means of welding power supply 68 and the electrodes 16 and 18 represented by the welding current conducted to be welded elements. An increase in the temperature is only apparent after a relatively long-lasting current flow at time t ₁ . Shortly after time t ₁ , the output voltage of the transformer, possibly output in the form of voltage pulses, became the welding power supply 68 set to zero, so that the current waveform between the times t ₂ and t ₄ shows the resulting from the inductance of the transformer after switching off current drop. The maximum of the output voltage signal of the photoelement occurs at a time t ₃ between the times t ₂ and t ₄ .

In addition to the with the ammeter 74 measured current signal is in the case of providing the voltmeter 76 In addition, a corresponding voltage signal of the voltage applied between electrodes available. Are the sensors 64 and 66 provided, so are also additionally the course of the contact pressure (possibly substantially constant, depending on the design of the drive means) and the Nachsetzens and the total then Nachsetzweg available for the evaluation available. In addition, the course of the electrical power can be determined from the current measured values and the voltage measured values. Through integration over time further values of interest or relevant for further evaluation can be determined. Thus, the integral of the photoelement intensity measurement over time is a meaningful measure of the resulting overall effect of the welding current or applied electrical power during a welding operation. Integration of the electrical power over time results in the introduced energy converted into heat.

It is also a wavelength-selective detection of the heat radiation into consideration, which can be done suitably by a corresponding passage bandwidth having spectral filter. Preferably, the thermal radiation is detected simultaneously in a plurality of different bandwidths, for which purpose a plurality of photoelements can be provided, to each of which a separate spectral filter having a specific bandwidth can be assigned. However, it has also been found that on the basis of a broadband thermal radiation detection with a single photoelement as in the case of the examples of the figures leads to good results.

Preferably by the control unit 80 The evaluation carried out can be based on a number of pre-programmed monitoring criteria, of which several criteria which have been found to be particularly expedient are treated as examples below.

A first criterion related to the photoelement output signal is the criterion that the photoelement output signal must exceed a threshold "min". If the voltage threshold "min" is not exceeded, it is an improper welding process, with which no welding between the elements to be welded has been achieved or at least the quality requirements with respect to this welding have not been met. It is based on the threshold "min" in. Represented by a horizontal line 7 directed.

A second monitoring criterion, also related to the photoelement output voltage, is in FIG 8a) illustrated. The temporal integration over the photoelement output voltage between the intersections of the voltage curve with the threshold line "min" corresponding to the hatched area in 8a) must give a value that is within a target range. A suitable criterion in this context is that the resulting integral value exceeds a lower threshold. Another suitable criterion in this context is that the resulting integral value does not exceed an upper threshold. Particularly suitable appears the criterion that the resulting integral value is in a limited by a lower threshold and an upper threshold range.

It should be noted that additionally or alternatively, corresponding criteria with respect to the overall course of the photoelement output voltage approximately between the times t ₁ and t ₅ of 7 can be defined.

Another particularly useful monitoring criterion is in 8b) illustrated. This monitoring criterion also sensitively addresses welding-impairing events that are not necessarily identifiable with the criteria that have been discussed so far. In 8b) For example, with respect to the photoelement output voltage, a target process window or setpoint value corridor is represented by two dashed lines. According to this criterion, no measured value for the photoelement output voltage may be outside the measuring voltage range bounded by the two dashed lines. This criterion can be used, for example, to identify events such as splashing away hot material during welding, which could result in a brief drop in temperature, but which can not necessarily be identified with the previously discussed criteria.

Other criteria may apply to the others, from the sensors or gauges 64 . 66 . 74 and 76 provided measured values as well as values derived from these measured values. Furthermore, it is possible to evaluate various of these measured values or derived values with respect to each other in order to evaluate the quality of the welding process.

Candidate criteria may conveniently be defined based on comparative or reference measurements on successful welding operations that have resulted in a reference good part or parts lying in a quality bandwidth. For example, the threshold "min", the thresholds for the temporal integral of the output voltage curve of the photoelement ( 8a) ) and the limit curves defining the target process window ( 8b) ) be determined on the basis of such comparison or reference measurements. Changes to the elements to be welded in terms of material and geometry or even a changeover of the welding device for welding completely different elements will usually result in a re-determination of the incoming thresholds, parameters, etc. in the applicable criteria. Such parameters and thresholds may be stored in a memory of the controller 80 be stored or programmed by means of an interface device in the control unit.

On the basis of the quality inspection of the welding process can be done by means of appropriate handling and conveyors Ausselektion the not quality requirements of sufficient parts, ie "bad parts" to weed out of the quality requirements "good parts" as a committee. If necessary, this sorting out can take place only after separation of the carrier part or carrier belt and separation of corresponding individual parts.

• – Auswertung des Messsignals des Wärmestrahlungsdetektors bzw. mehrerer Wärmestrahlungsdetektoren bzw. mehrerer Detektorelemente eines Wärmestrahlungsdetektors hinsichtlich des zeitlichen Verlaufs, insbesondere Überschreiten einer Mindestschwelle und Lage in einem Soll-Prozessfenster, die aus Vergleichsmessungen in Bezug auf ein Referenz-Gutteil bzw. mehrere Referenz-Gutteile bestimmt wurden;
• – Auswertung des Wärmestrahlungsdetektor-Messsignals bzw. solcher Wärmestrahlungsdetektor-Messsignale, die sich aufgrund einer spektralen Filterung der Wärmestrahltung ergeben;
• – Auswertung der Signalintensität für zwei oder mehr Wärmestrahlungsdetektorelemente (Photoelemente) mit unterschiedlicher spektraler Empfindlichkeit, ggf. unter Verrechnung der Intensitäten in der Art eines Weißabgleichs einer CCD-Digitalkamera mit drei Photoelementen;
• – Auswertung des Messsignals des Wärmestrahlungsdetektorelements (Photoelements) bzw. mehrerer Wärmestrahlungsdetektorelemente (Photoelemente) in Beziehung zur eingebrachten elektrischen Leistung der Schweißsteuerung in Form des Schweißstromes, der mit der am Kontaktwiderstand zwischen den zu verschweißenden Materialien die zur Erwärmung führende eingebrachte elektrische Leistung bestimmt;
• – Auswertung des Messsignals des Wärmestrahlungsdetektorelements (Photoelements) bzw. mehrerer Wärmestrahlungsdetektorelemente (Photoelemente) in Beziehung zur eingebrachten Leistung der Schweißstromversorgung in Form der aus der Spannung an den Elektroden und dem Schweißstrom ermittelten elektrischen Leistung;
• – Auswertung des Messsignals des Wärmestrahlungsdetektorelements (Photoelements) bzw. mehrerer Wärmestrahlungsdetektorelemente (Photoelemente) in Beziehung zu der an den Schweißelektroden anliegenden Spannung;
• – Auswertung der resultierenden Wirkung aufgrund des Schweißstroms anhand des Integrals über die die Intensität der erfassten Wärmestrahlung repräsentierenden Wärmestrahlungsdetektorspannung (Photoelementspannung) über die Zeit;
• – Auswertung des Messsignals des Wärmestrahlungsdetektorelements (Photoelements) bzw. mehrerer Wärmestrahlungsdetektorelemente (Photoelemente) in Beziehung zum Verlauf des Nachsetzens der Schweißung während des Schweißvorgangs oder/und in Beziehung zum aus der Schweißung insgesamt resultierenden Nachsetzweg;
• – Auswertung durch Setzen eines Minimalwerts für die Wärmestrahlungsintensität bzw. Photoelementspannung und weitere Auswertung nur dann, wenn dieser Minimalwert von der Messwertkurve überschritten wird.

Overall, welding monitoring and quality monitoring can be done in a variety of ways, including the following functions:

• - Evaluation of the measurement signal of the heat radiation detector or a plurality of heat radiation detectors or a plurality of detector elements of a heat radiation detector with respect to the time course, in particular exceeding a minimum threshold and position in a target process window, which determines from comparative measurements with respect to a reference Goodteil or more reference good parts were;
• - Evaluation of the heat radiation detector measurement signal or such heat radiation detector measurement signals resulting from a spectral filtering of the heat radiation;
• - Evaluation of the signal intensity for two or more heat radiation detector elements (photoelements) with different spectral sensitivity, possibly taking into account the intensities in the manner of a white balance of a CCD digital camera with three photoelements;
• - Evaluation of the measurement signal of the heat radiation detector element (photoelements) or more heat radiation detector elements (photoelements) in relation to the introduced electrical power of the welding control in the form of the welding current, which determines with the contact resistance between the materials to be welded introduced the leading to heating introduced electrical power;
• - Evaluating the measurement signal of the heat radiation detecting element (photoelements) or more heat radiation detecting elements (photo elements) in relation to the introduced power of the welding power supply in the form of the determined from the voltage across the electrodes and the welding current electrical power;
• - Evaluation of the measurement signal of the heat radiation detecting element (photoelements) or more heat radiation detecting elements (photo elements) in relation to the voltage applied to the welding electrodes voltage;
• - Evaluation of the resulting effect due to the welding current based on the integral on the heat radiation detection voltage representing the intensity of the detected heat radiation (photoelement voltage) over time;
• Evaluation of the measurement signal of the heat radiation detector element (photoelements) or of a plurality of heat radiation detector elements (photoelements) in relation to the course of the resetting of the weld during the welding process or / and in relation to the total path resulting from the welding;
• - Evaluation by setting a minimum value for the heat radiation intensity or photoelement voltage and further evaluation only if this minimum value is exceeded by the measured value curve.

In the course of these evaluations, various mathematical operations such as integration, differential formation, addition and multiplication and combination of these operations can be applied. Expediently, fuzzy methods (so-called fuzzy logic) can also be used for the evaluation. Such evaluations make possible, directly or indirectly, statements about the formation of a welded zone of two materials and their quality. The course of the welding and the welding process parameters and thus also the criteria that can be used for monitoring and checking may depend on the material properties and the material geometry to be welded. To name as examples are different material thicknesses, lengths and widths, different heat capacities due to different material compositions, different geometries of the contact between the materials to be welded (for example, flat contact or only punctual contact due to welding warts). With only partial contact of the welding materials to one another, deformations of the material or of the materials can occur to a particular extent.

Due to the monitoring of the welding process on the basis of the heat radiation according to the invention, deviating or defective contacting of the materials by the welding electrodes can be detected, which in extreme cases, for example due to electrode wear, can lead to too high a contact resistance between an electrode and the material to be welded. up to the displacement of the heat zone to the contact point between the material and the welding electrode.

A device for welding at least two metal elements 40 . 42 Resistance welding by means of a welding electrode arrangement is distinguished by an arrangement for monitoring the welding process on the basis of detected thermal radiation. It is at least a heat radiation detector 50 . 51 provided, which in arranged in a welding position welding electrodes 16 . 18 Heat radiation from the area of a welding gap 24 receives. An evaluation device 80 receives at least one of the received heat radiation dependent output signal of the heat radiation detector 50 . 51 and evaluates this with respect to at least one monitoring criterion. A method for monitoring the welding process on the basis of detected heat radiation when welding at least two metal elements by resistance welding provides that by means of at least one heat radiation detector 50 . 51 when welding electrodes arranged in a welding position receive heat radiation from the region of the welding gap during a welding operation as a consequence of welding current flowing over the metal elements and at least one output signal of the heat radiation detector dependent on the received heat radiation 50 . 51 is evaluated with respect to at least one monitoring criterion.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 245480403 [0009, 0053]
• DE 2462790 C2 [0009, 0053]
• DE 2615364 C2 [0009, 0053]
• DE 19755166 A1 [0009, 0053]
• DE 10347074 A1 [0009, 0053]
• DE 10347075 A1 [0009, 0053]
• DE 102009045252 A1 [0009, 0053]

Claims (25)

Device for welding at least one first metal element ( 40 ) with at least one second metal element ( 42 by resistance welding, comprising: a welding electrode arrangement having at least two welding electrodes ( 16 . 18 ), which has a welding gap ( 24 ) and are movable relative to each other between a receiving position and a welding position and with which in the welding position, a contact pressure between the first ( 40 ) and the second ( 42 ) Metal element by joint clamping of the metal elements between the welding electrodes ( 16 . 18 ) is producible; - an electrical welding power supply ( 68 ) for introducing a welding current between the welding electrodes arranged in the welding position ( 16 . 18 ) over the metal elements ( 40 . 42 ); characterized by an arrangement for monitoring the welding process on the basis of detected thermal radiation, comprising: - at least one thermal radiation detector ( 50 . 51 ), which at welding electrodes arranged in the welding position ( 16 . 18 ) Receives heat radiation from the region of the welding gap; An evaluation device ( 80 ), which is designed for at least one of the receiving heat radiation dependent output signal of the heat radiation detector ( 50 . 51 ) and to evaluate with respect to at least one monitoring criterion. Device according to claim 1, designed for welding at least one contact metal blank ( 40 ) on a mounting surface of a metallic support part ( 42 sheet metal or sheet material by resistance welding, comprising: - a support assembly for supporting the support member in a position in which a contact part mounting space of the mounting surface of the support member ( 42 ) within the welding gap ( 24 ) lies; A contact metal blank feed for feeding contact metal blanks ( 40 ) to a contact metal blank transfer position associated with the contact part loading space; A drive device ( 60 ) for moving the welding electrodes ( 16 . 18 ) between the receiving position and the welding position and for generating a contact pressure between the carrier part ( 42 ) and a respective contact metal blank positioned at the contact part mounting location of the carrier part ( 40 ) by mutual clamping of the carrier part ( 42 ) and the contact metal blank ( 40 ) between the welding electrodes ( 16 . 18 ) in the welding position; A control device ( 80 ) for controlling the contact metal blank feed, the drive device ( 60 ) and the welding power supply ( 68 ). Device according to claim 1 or 2, characterized by at least one observation passage ( 52 ) in at least one ( 16 ) of the welding electrodes ( 16 . 18 ), by the welding electrodes arranged in the welding position heat radiation from the region of the welding gap ( 24 ) and via which the heat radiation detector ( 50 . 51 ) receives the heat radiation, wherein the observation passage is preferably as from a the welding gap ( 24 ) defining the contact side of the welding electrode ( 16 ) to a back side of the welding electrode ( 16 ) extending observation channel ( 52 ) is executed. Device according to claim 3 and according to claim 2, characterized in that in the welding position at a to the mounting surface of the support member ( 42 ) opposite the back of the support member attacking welding electrode ( 16 ) with the observation passage ( 52 ) is executed. Device according to claim 4, characterized in that the observation passage ( 52 ) is designed such that when arranged in the welding position welding electrodes ( 16 . 18 ) Heat radiation from a surface area corresponding to the contact part mounting space of the mounting surface, the opposite surface area of the rear side of the support part ( 42 ) through the observation passage ( 52 ) from the area of the welding gap ( 24 ) can escape. Device according to claim 5, characterized in that the observation channel forming the observation passage ( 52 ) substantially orthogonal to the surface area of the rear side of the support part opposite the contact part mounting space of the attachment surface ( 42 ). Device according to one of claims 1 to 6, in any case with reference back to claim 3, characterized in that the thermal radiation detector ( 50 . 51 ) and preferably at least one associated optical component in a recess of a welding electrode ( 16 ) with the observation passage holding welding electrode holder ( 20 ) is arranged. Device according to one of claims 1 to 6, characterized in that the heat radiation detector is arranged separately from a holding the welding electrode with the observation passage welding electrode holder. Device according to claim 8, characterized in that an input end of one or more of the heat radiation to the heat radiation detector supplying radiation conductor arrangement and preferably at least one associated optical component is arranged in a recess of the welding electrode holder. Device according to one of claims 1 to 9, characterized in that the evaluation device ( 80 ) is designed for, based on the at least one output signal of the at least one heat radiation detector ( 50 . 51 ) during a welding operation to detect at least one of the welding process or its time characteristic characterizing first welding signature and to evaluate these with respect to at least one monitoring criterion. Device according to one of claims 1 to 10, characterized in that the evaluation device ( 80 ) is designed for this, based on at least one output signal of the welding power supply and / or by means of at least one at least one electrical variable of the welding current detecting sensor ( 74 . 76 ) to detect at least one of the welding process or its time characteristic characterizing second welding signature and to evaluate them with respect to at least one monitoring criterion. Device according to one of claims 1 to 11, characterized in that the evaluation device is designed for this, by means of at least one force sensor ( 66 ) to detect the contact pressure or a temporal contact pressure profile during the welding process and / or by means of at least one displacement sensor ( 64 ) an updating of at least one ( 18 ) of the welding electrodes ( 16 . 18 ), in particular a time course of the Nachsetzens and / or a Nachsetzweg at least one ( 18 ) of the welding electrodes ( 16 . 18 ), during the welding process to detect as a third welding signature and to evaluate them with respect to at least one monitoring criterion. Device according to one of claims 1 to 12, characterized in that the device ( 10 ) or their evaluation device ( 80 ) for carrying out the method of at least one of the following claims. Method for monitoring the welding process on the basis of detected thermal radiation during welding of at least one first metal element ( 40 ) with at least one second metal element ( 42 by resistance welding by means of a welding electrode arrangement with at least two welding electrodes ( 16 . 18 ), which has a welding gap ( 24 ) and are movable relative to each other between a receiving position and a welding position and with which in the welding position, a contact pressure between the first ( 40 ) and the second ( 42 ) Metal element by joint clamping of the metal elements between the welding electrodes ( 16 . 18 ), and - an electrical welding power supply ( 68 ) for introducing a welding current between the welding electrodes arranged in the welding position ( 16 . 18 ) over the metal elements ( 40 . 42 ), in which by means of at least one heat radiation detector ( 50 . 51 ) in the welding position arranged welding electrodes ( 16 . 18 ) during a welding operation in succession over the metal elements ( 40 . 42 ) flowing welding heat radiation from the region of the welding gap ( 24 ) and at least one of the receiving heat radiation dependent output signal of the heat radiation detector ( 50 . 51 ) is evaluated with respect to at least one monitoring criterion. A method according to claim 14, characterized in that the heat radiation from the region of the welding gap ( 24 ) through an observation passage ( 52 ), preferably an observation channel ( 52 ), at least one of the welding electrodes is received, or / and that the heat radiation from the region of the welding gap ( 24 ) is spectrally filtered, or / and that the output signal of the heat radiation detector ( 50 . 51 ) is recorded time-resolved. Method according to claim 14 or 15, characterized in that on the basis of the at least one output signal of the at least one heat radiation detector ( 50 . 51 during a welding operation, at least one first welding signature characterizing the welding process or its time characteristic is detected, or / and that based on at least one output signal of the welding power supply and / or by means of at least one sensor (at least one electrical variable of the welding current). 74 . 76 ) at least one of the welding process or its time characteristic characterizing second welding signature is detected, and / or that by means of at least one force sensor ( 66 ) the contact pressure or a temporal contact pressure profile during the welding process and / or by means of at least one displacement sensor, a readjustment of at least one ( 18 ) of the welding electrodes ( 16 . 18 ), in particular a time course of the Nachsetzens and / or a Nachsetzweg at least one ( 18 ) of the welding electrodes ( 16 . 18 ) is detected during the welding process as a third welding signature. Method according to claim 16, that at least one welding signature is evaluated with respect to at least one monitoring criterion or / and that according to at least one monitoring criterion, a plurality of welding signatures are evaluated with respect to each other. A method according to claim 16 or 17, characterized in that according to a monitoring criterion, the evaluation comprises the comparison of at least one welding signature, in particular the first welding signature, with reference data, such as at least one reference welding signature or at least one reference welding signature derived data. A method according to claim 18, characterized in that the reference welding signature is a welding signature recorded during a welding operation, in particular a first welding signature, which corresponds to a predetermined requirement of welding the metal elements ( 40 . 42 ) has led. A method according to claim 18 or 19, characterized in that at least one welding signature, in particular at least the first welding signature, is checked for whether it meets at least one predetermined reference condition. A method according to claim 20, characterized in that the welding signature is checked for whether at least one welding signature value exceeds a minimum threshold (min) or / and does not exceed a maximum threshold. A method according to claim 20 or 21, characterized in that the welding signature is checked for whether a temporal integral over welding signature values exceeds a minimum threshold and / or does not exceed a maximum threshold. Device according to one of claims 20 to 22, characterized in that the welding signature is checked for whether temporally successive welding signature values are within a permissible value range. Method according to one of claims 16 to 23, characterized in that based on the evaluation of a quality of the weld is determined. Method according to one of claims 14 to 24, characterized in that the welding and the monitoring and evaluation by means ( 10 ) is carried out according to one of claims 1 to 13.

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