DE102018105893B4 - Method and device for quality evaluation in resistance welding and computer program product, control device and use - Google Patents

Abstract

Quality evaluation method for characterizing resistance-welded welded components (1) in conductive capacitor discharge (KE) welding systems by evaluating at least one welding parameter (P1, Pn) from the group: welding current, welding voltage, welding force, resistance, melting path, welding time; a recorded course of the welding parameter to be evaluated being provided as a curve (PK) of the respective welding parameter; characterized by evaluating the curve (PK) by reading out at least one parameter (K1, Kn) of the respective curve as a function of time and optionally also as a function of at least one other the welding parameters, with at least the amount of the welding current and a change in slope and/or gradient of the welding current curve and the time of the respective welding current and the change in slope being evaluated as parameters (K1, Kn);comparing the parameter (K1, Kn) with at least one target value ( VI, Vn) for the parameter, with at least the slope and/or a gradient of the respective curve (PK) being evaluated as the parameter (K1, Kn), with the target value (VI, Vn) being based on a section of the course of the respectively evaluated curve (PK) of the welding parameter (P1, Pn) to be evaluated is/is defined; andevaluating the quality of the welded component (1) based on the comparison of the parameters (K1, Kn), in particular with regard to the amount of a deviation of the parameter from the target value.

Description

TECHNICAL AREA

The present invention relates to a method and a device for characterizing resistance-welded welded components, in particular in conductive capacitor discharge welding systems, by evaluating at least one welding parameter. Furthermore, the invention also relates to the use of automation technology for this purpose. In particular, the invention relates to a method and a device according to the preamble of the respective independent claim.

BACKGROUND OF THE INVENTION

Resistance welding, in particular capacitor discharge welding (KE welding) is a process that can be used to produce any type of semi-finished product, assembly component or precision component, in particular components that have to withstand high loads, e.g. gear components. When KE welding (resistance pressure welding) is carried out with a contact force, two components are pressed together with a predefined force (e.g. 5 to 300kN, in particular 20 to 100kN), in particular on a contact surface with a predefined cross-section (in particular ring hump), and then in a very short Time interval (e.g. 10ms) to conduct a large amount of energy (up to 160kJ, e.g. 30kJ) over the contact surface and thereby achieve local melting (in particular of a ring hump) and material-locking connection. The charging of a capacitor and the application of the welding force are independent of each other and can optionally also take place simultaneously. In particular, the components are continuously pressed against one another and, depending on the melting of the material on the contact surface or depending on the welding force, also moved towards one another (in particular 0.1 to 2 mm, e.g. 0.5 to 1 mm). The whole process usually takes only a few milliseconds, e.g. 10ms.

KE welding can be characterized as a resistance welding process, in particular a projection welding process, e.g. by the following features: short welding times in the range from 3 to 15ms; Welding currents of up to 1,000kA; comparatively low secondary voltage in a range of less than 40V; high charging voltages of the capacitors up to 4,000V.

In many cases, the components must have a high level of manufacturing accuracy even before they are welded. For example, the flatness of the contact surface should be less than 0.05mm. Since the welded components are often installed as machine elements or components with a safety-relevant function, it is necessary to work more or less error-free, especially fully automated with short cycle times and large quantities, e.g. with welded parts for the automotive industry (e.g. fastenings for driver's seats). For example, the melting path should be predefinable in a tolerance range of less than 0.05mm. Reliable quality control on the welding systems is therefore of great importance, on the one hand for the manufacturers of the welding systems and on the other hand for the operators of these welding systems. In particular, quality control must be able to be carried out individually for each welded component. With many types of components, collecting only random samples is very risky, with unforeseeable consequences in terms of product liability law. The welding quality of many components must therefore be documented in many areas, in particular in accordance with the DIN EN ISO 9001 standard.

The efforts of manufacturers and operators to enable quality control that is as comprehensive as possible can be summarized under the term "quality monitoring". For the operators of the welding systems, it is of great advantage if the "quality monitoring" can be carried out as comprehensively as possible during production. In addition to continuous quality control, random samples can be taken, e.g. as part of tensile, compression or extrusion tests or by checking the torsional strength. The quality control can be carried out both statically and dynamically. Other examples of analyzes are micrographs, metallography in general, and ultrasonic examinations. However, the random quality control requires a comparatively long time and cannot easily be carried out simultaneously with the manufacturing process. Not least for cost reasons, this type of quality control is limited to a small proportion of the welded components produced.

Up to now, quality control has usually been carried out by evaluating individual peaks or maxima or minima in curves of welding parameters, in particular in the case of comparatively inexpensive components in mass production, or by referring to an envelope curve or to a pair of envelope curves enveloping the respective measurement curve, by means of which Tolerance range is defined around a target curve, especially with comparatively expensive components. If the measurement curve runs out of the tolerance range, the corresponding welded component must be marked as scrap (NOK) or must be reworked. In many cases, however, post-processing is not possible, so the parts have to be disposed of or recycled. the quality Quality control can be carried out, for example, with regard to the path (lowering path = setting path + sinking path) or force (pre-force, welding force) parameter.

Other important welding parameters, especially for KE welding, can be mentioned: current rise time, peak current, welding time, current flow time, effective value of the welding current (integral of the current strength over the welding time). The following process variables can be mentioned: welding energy, charging voltage, area under the welding current curve (current-time integral), electrode pre-force, welding force, force drop (reduction in welding force due to inertia of the electrodes). With regard to further special features of KE welding, reference is also made to the data sheet DVS 2911 "Capacitor discharge welding" of the DSV German Association for Welding and Related Processes e.V.

A typical course of resistance welding can be described as follows: After the parts to be joined or welded components have been inserted, the electrodes are closed and a preliminary force is first built up, then a parts check takes place, after which a welding force is built up and, optionally, a lead time is observed. The discharge is then initiated. The current intensity runs through a sinusoidal or sinusoidal curve with a flattening edge, and the welding force experiences a drop in force due to a relative movement of the parts to be joined. Experience has shown that the welding process is complete once the current has dropped to half the maximum. After the ZERO current has been reached, the electrodes are opened again and the welded welding component is removed or ejected or discharged.

Up to now it has been customary to monitor the maximum value of the current intensity or its point in time and optionally also to take it into account when controlling the welding system.

The publication EP 0 373 422 A1 describes an envelope criterion for quality analysis, independent of the type of welding parameter. Also the patent DE 31 21 497 C2 describes the quality analysis by referring to a tolerance band.

the EP 1 249 298 B1 describes a method for quality control in conventional frequency-dependent resistance spot welding of metal sheets and wires, in which the welding current at the welding point is evaluated by recording the first and second derivative of the alternating current over time, with the quality analysis being performed by correlating the second or third derivative of the current according to the Time is done with a quality quantity, especially taking into account the frequency. Optionally, the frequency response of the optionally first to third derivation is examined by a neural network.

The following publications describe further aspects in connection with quality analysis and/or quality-optimizing measures: DE 10 2014 109 216 A1 , U.S. 3,509,311 A , U.S.A. 4,493,965 , U.S. 2017/0 291 249 A1 , U.S. 4,694,135 A , DE 10 2013 217 583 A1 , US 2013/0 248 505 A1 , DE 10 2015 114 957 A1 , U.S. 2017/0 316 556 A1 .

It has now been shown that both the evaluation based on peaks and the evaluation using envelope curves can only roughly characterize the respective welded component. A more detailed evaluation and a more reliable, more precise characterization is desirable.

SUMMARY OF THE INVENTION

The task is to provide a method and a device for quality monitoring on welding systems or for controlling resistance welding systems or for quality control of resistance-welded components, with which the quality can be measured as precisely as possible or with regard to a large number of criteria or in a particularly flexible manner for different types of welds can be evaluated, especially in capacitor discharge welding (KE welding). Another object is to design the method and the device in such a way that the welded components can be analyzed in a flexible or individual manner with regard to at least one welding parameter. Last but not least, it is a task to characterize welded components as promptly as possible during resistance welding or to control a resistance welding system depending on the recorded and evaluated parameters, in particular in such a way that component-specific tracing is made possible.

At least one of these objects is achieved by a method according to claim 1 and by a device according to the subordinate device claim. Advantageous developments of the invention are explained in the respective dependent claims. The features of the exemplary embodiments described below can be combined with one another unless this is explicitly denied.

• Auswerten der Kurve durch Auslesen wenigstens einer Kenngröße der jeweiligen Kurve, insbesondere der Steigung und/oder eines Gradienten, als Funktion der Zeit (zeitlicher Verlauf) und wahlweise auch als Funktion wenigstens eines weiteren der Schweißparameter; Vergleichen der Kenngröße, insbesondere Vergleichen der Steigung und/oder eines Gradienten, mit wenigstens einem (insbesondere für das jeweilige Schweißbauteil spezifisch vorgebbaren) Sollwert für die Kenngröße, insbesondere mit einem Mindest- und/oder Mittel- und/oder Maximalwert, insbesondere mit Zeitbezug, wobei der Sollwert basierend auf einem zeitlich vorgelagerten Abschnitt des Verlaufs des auszuwertenden Schweißparameters der jeweils ausgewerteten Kurve definiert ist/wird; und Auswerten der Qualität des Schweißbauteils basierend auf dem Vergleich der Kenngrößen bzw. basierend auf dem Vergleich der Schweißparameter, insbesondere in Hinblick auf den Betrag einer Abweichung der Kenngröße vom Sollwert. Die Definition des Sollwertes aus der Kurve selbst ermöglicht insbesondere auch eine individuelle Bezugnahme auf die jeweilige Schweißung. Dabei kann insbesondere auch ein einzelner Gleichstromimpuls oder eine Mehrzahl aufeinanderfolgender Gleichstromimpulse ausgewertet werden.

A quality evaluation method is provided for characterizing resistance-welded welded components, in particular in con ductive KE welding systems, by evaluating at least one welding parameter from the group: welding current, welding voltage, welding force (in particular corresponding to a contact pressure of the electrodes against one another), resistance, melting path (corresponding to a relative displacement of the parts to be joined to one another), welding time; a recorded profile of the welding parameter to be evaluated being provided as a curve (measured simultaneously with welding or already stored) of the respective welding parameter. According to the invention, it is proposed to also carry out the following steps:

• evaluating the curve by reading out at least one parameter of the respective curve, in particular the slope and/or a gradient, as a function of time (time progression) and optionally also as a function of at least one other of the welding parameters; Comparing the characteristic, in particular comparing the slope and/or a gradient, with at least one target value (which can be specified specifically for the respective welded component) for the characteristic, in particular with a minimum and/or mean and/or maximum value, in particular with a time reference, wherein the target value is/is defined based on a preceding section of the course of the welding parameter to be evaluated of the respectively evaluated curve; and evaluating the quality of the welded component based on the comparison of the parameters or based on the comparison of the welding parameters, in particular with regard to the amount of a deviation of the parameter from the target value. The definition of the target value from the curve itself also enables, in particular, an individual reference to the respective weld. In this case, in particular, a single direct current pulse or a plurality of consecutive direct current pulses can also be evaluated.

In particular, this method can work without envelopes. The evaluation can take place automatically by referring to a section of the course of the respectively evaluated curve that precedes in time, in particular by referring to setpoint values stored in a table. The evaluation based on the discussion of curves with regard to individual welding parameters can, in particular, provide greater accuracy than an analysis solely in relation to maximum tolerance limits (envelope curve criterion).

According to the invention, quality control for welded components is made easier, and the analysis becomes comparatively exact and reliable. In contrast to the envelope curve tolerance criterion, in which only the exceeding of certain tolerance ranges is evaluated, the curve discussion according to the invention can be used to carry out a more in-depth analysis, in particular with regard to only very small deviations that may still be within the tolerance range, i.e. also to investigate the causes of certain irregularities. One or more evaluation criteria can be defined in a much more targeted or application-specific manner than with the envelope tolerance criterion.

In this case, the evaluation of the curve can correspond to a curve discussion with regard to a plurality of characteristic numbers of a respective curve. The curve or the profile of the welding parameter can be recorded using standard measuring methods and also stored in a data memory and read out for evaluation, optionally simultaneously or in real time, or after the welding. Welding parameters can be detected in a known manner, in particular with known sensors, e.g. also by means of a displacement sensor (detection of the melting path) and/or a Rogowski coil (detection of the welding current).

The characterization can be understood as an evaluation of properties of the welded components, in particular indirectly via the welding current. The melting path and/or a weld seam width, for example, can also be evaluated. For example, the welding seam width or the connection/material connection surface between the parts to be joined can be inferred from the melting path. It has also been shown that a correlation between the course of the current and the occurrence of welding spatter can be evaluated. The characterization can include an identification of the welded component, in particular in a table, which enables a subsequent optional correlation of the parameters or curves with the respective welded component, in particular when tracing manufacturing steps, e.g. in the event of material failure. The characterization can also provide the (data) basis for a control loop for controlling the welding process, or at least for identifying defective welded components (rejects).

A respective target value can also be defined as a function of the type of welding or the type of parts to be joined.

So far, especially in CD welding, only the minimum and maximum values (in particular the current curve) and a time reference have usually been evaluated. Up to now, dents or other local up and down movements of the curve could not be recognized at all, or at least not in a satisfactory manner. in the In contrast to this, the accuracy of the method according to the invention also enables reject parts (so-called “not OK” NOK parts) to be automatically ejected during production/manufacturing.

It is worth mentioning that it is not easy to control or regulate KE welding (process or system). Rather, capacitors are charged with a large amount of energy, which is then discharged over a very short period of 0.1 to 1000ms, e.g. 1 to 100ms, in particular 2 to 50ms. Figuratively speaking, sluice gates are opened and the flow that then flows cannot be easily influenced. At least up to now, system-based control was unthinkable. The present invention can therefore already provide a major advantage in that defective parts (so-called n.i.O. parts) can be better recognized by the new detection method and optionally also ejected, especially directly after the welding process in automated processes with high quantities.

Since the target value is/is defined based on the detected profile of the welding parameter to be evaluated, reference can be made individually to a respective welding process. In particular, it is not necessary to work with envelopes. As a result, the process can be individually adapted to various welded components and peculiarities of welding processes in a comparatively flexible and variable manner. In particular, kinks or dents can be detected particularly easily, in particular with a relative reference to the curvature or gradient change that is usual in the corresponding curve profile in the corresponding time segment.

In this case, the setpoint is/is defined based on a preceding section of the profile of the respectively evaluated curve, and optionally also based on the corresponding section of a standard curve already defined for the respective welding process. In particular, the setpoint can also be specified based on a gradient determined from the course of the curve. The respective gradient (be it a difference in measured values, be it a squared gradient, or an absolute value) can supply the target value either alone or in combination with other curve characteristics.

A welded component is a component made from at least two parts to be joined by material bonding.

The welding current is to be understood in particular as the current conducted through the welded components (joining parts) during welding. The welding voltage is to be understood in particular as the voltage applied to the welded components during the welding. The welding force is to be understood in particular as the mechanical force of the electrodes exerted on the welded components during the welding. Resistance is to be understood in particular as the electrical resistance that occurs via the welded components during welding. A melting path (relative displacement) is to be understood in particular as a change in path of one joining part relative to the other joining part during welding, e.g. when a weld projection melts at least approximately according to the height of the weld projection.

In addition to the evaluation according to the invention, the course of the curve of welding parameters can also be characterized as follows, here with reference to a current curve: current rise time until the peak current is reached (maximum); amount of peak current (maximum); Welding time as the time between reaching a trigger threshold (especially ≤5% of the full scale value) and the drop to 50% of the peak current; Current flow time as the time between reaching the trigger threshold (≤5% of the full scale value) and the drop to 5% of the peak current (in particular for determining the hold time to avoid opening the electrodes under current flow); Effective value of the welding current (integral of the current over the welding time).

The development of the respective parameter is to be understood as a course, in particular in each case as a function of a predefinable further parameter, in particular as a function of time. The recorded or stored measurement curve is to be understood as a curve, in a representation selected in each case, in particular as a function of at least one further parameter. Depending on the selected scale or reference parameters, the curve can change. However, the course or development of the parameter remains unaffected.

A setpoint is to be understood in particular as an instantaneous or time-related, curve-related tolerance value. According to the invention, the target value can be read from the time profile, i.e. by referring to a section of the measurement curve that precedes the time, for example in the time interval of 0.01 to 0.5 ms before the evaluation or comparison time, and optionally also by reference to a subsequent section if the Evaluation should be carried out retrospectively. The reference can be made directly to a previously measured section and choice can also be carried out on a standard curve. A (more recent) target value can also be defined by referring to earlier (older) measured values of the same measurement curve, so that an individual expected value can be determined from a particular curve, optionally with additional reference to one or more standard curves. An individual tolerance range can also be assigned to the desired value, corresponding to a desired range. The target value is not taken from a standardized curve, but is determined from the previous course of the curve to be evaluated.

A gradient is to be understood as meaning a relative change in a predefinable section of the respective curve in relation to the temporally preceding section, in particular determined by difference formation. Here, the term “gradient” can also include the corresponding gradient in squared form and/or the corresponding squared gradient with a root (corresponding to a magnitude value), unless this is excluded by explicit reference. Working with a gradient instead of or in addition to working with an incline can make it easier, for example, to define threshold values and thereby make the evaluation even more variable and/or more precise.

Until now, the evaluation of distinctive (static) values was carried out in particular by reference to tolerance envelopes. In this case, reference can be made to minima and maxima, and a time reference of these peaks can be evaluated. Based on envelope curves, only a certain tolerance value/range is often used, but this can be too wide (too imprecise) or too narrow (too sensitive). It has been shown that a discontinuous or non-monotonic curve (dent, turning points, fluctuation, discontinuity, etc.) with regard to the respective parameter cannot be registered or evaluated in a satisfactory manner. It has been shown that quality assurance can become more resilient if a curve discussion is undertaken with regard to individual parameters of a time course, in particular independent of frequency when evaluating pulse-like direct current discharges.

In contrast to an evaluation using tolerance envelope curves, the curve discussion according to the invention with regard to at least one parameter makes it possible to detect and evaluate discontinuous or non-monotonic curve profiles. Various other quality or tolerance criteria can be defined, e.g. the slope of the curve or the change in slope (derivation). In particular, welded components can be characterized in which a curve with a dent or a point of inflection or a peak appears during welding. These curve shape tolerance criteria can also be combined with one or more envelope curve tolerance criteria.

Capacitor pulse welding is also to be understood as KE welding, that is to say welding by means of energy emitted by at least one capacitor in at least one pulse.

According to one embodiment, the target value is/is defined based on the detected profile or gradient in a time interval of 0.1 to 1000 ms (milliseconds) before the comparison time. This enables an individual reference to the respective curve section. In this case, the time interval can also be predetermined by a sampling rate.

According to one embodiment, the curve is evaluated independently of a defined sampling rate, or at a predefined sampling rate, with the target value based on the previous sample or the corresponding parameter or based on a group of up to ten of the previous samples or based on a group of up to 10% of all samples is/is defined. Typical sampling rates are e.g. in the range from 10kHz to 20kHz

According to one embodiment, the curve is evaluated at a sampling rate of up to 150 kHz, in particular in the range from 1 kHz to at least 10 kHz or in the range from 2 kHz to at least 4 kHz, with the target value being based on the previous sampling value or the corresponding parameter or based on a group of up to ten of the previous samples or based on a group of up to 10% of all samples. This reference to previous samples can, in a comparatively accurate and individual way, reveal unusual variations which can indicate a faulty weld.

At least the slope (1st derivative) and/or a gradient of the respective curve is evaluated as a parameter, in particular a (optionally fictitious) zero crossing and/or a minimum or maximum or saddle point or an inflection point, in particular with a time reference (or reference to time interval). This enables, for example, the evaluation of a kink, a discontinuity, or an abnormal change in slope. In this case, the desired value can correspond, for example, to a gradient in a definable time interval of several microseconds or milliseconds, in particular as a function of the sampling rate, for example corresponding to a multiple of the time between two samplings gen. With a sampling rate of 100,000Hz, there is only a comparatively small time window, even with several samplings. The period of time can also be significantly longer, or, for example, be or begin 0.5 to 1ms before the point in time to be evaluated.

According to one embodiment, at least the derivation of the slope and/or a gradient of the respective curve is evaluated as a parameter (2nd derivation), in particular a zero crossing and/or a minimum or maximum or saddle point or a turning point of the slope and/or the gradient, in particular with a time reference (or reference to a time interval). In this way, the curvature of the curve in particular can be analyzed so that even small dents (synonym: local turning points, fluctuations, discontinuities, etc.) can be detected. Depending on the type of welding process or the type of parts to be joined, the quality can be evaluated individually from the course of the slope or the course of the first derivation of the slope.

According to one embodiment, the evaluation takes place with regard to monotony and/or continuity of the curve, in particular with regard to a deviation from a predefinable monotony of the current curve. In particular, this also enables the evaluation specifically in the rising or falling area of the curve.

According to one embodiment, the evaluation takes place with regard to an inflection point of the second derivative of the current curve behind a maximum on a falling flank of the current curve, in particular with a time reference (or reference to a time interval). In particular, this also enables a correlation with the welding time.

According to one embodiment, the quality is evaluated at least also based on the welding parameter welding current and the corresponding index or parameter of the time profile of the welding current. This provides options with regard to various aspects of the evaluation, especially with good reproducibility.

Experience has shown that the falling edge of the current curve has a monotonously falling negative slope, and experience has shown that it becomes steadily flatter. It has been shown that a discontinuity or a deviation from a certain monotony or an increase or decrease in the slope of the current curve can be evaluated with good resilience and reliability as an indication of reduced welding quality, especially in a range up to half the welding current being reached [ i _h ] or [1/2i _p ], or half the welding time [t _h ]. It has been shown that a variation up to the moment when half the welding current or half the welding time is reached can be more meaningful than a variation afterwards, and that the corresponding evaluation in the corresponding time window can be used in an efficient manner when optimizing the method.

According to one embodiment, the course over time of the at least one parameter of the curve is also compared with a standard curve of the corresponding parameter, with the parameter deviating from the target value at a plurality of comparison points of the curve at a plurality of measurement times. This can additionally secure the evaluation or make it more reliable. The respective standard curve can, for example, be defined from several example measurements or standard welds for a respective component or for a respective system or a respective tool concept. A single standard weld can be used for this, or a number of e.g. ten welds, all of which have led to good welded parts (okay (OK) parts).

According to one embodiment, an inflection point of the respective parameter or its profile, in particular an inflection point of the slope and/or a gradient, is evaluated. This allows specific reference to specific phases or times of the welding process and can simplify root cause analysis.

According to one embodiment, a zero crossing or a minimum or maximum or saddle point of the parameter or its profile, in particular the slope and/or a gradient, is evaluated. This also simplifies the comparison with expected values and facilitates the chronological classification of characteristic events with regard to the entire welding process. The zero crossing can also be a fictitious zero crossing with regard to a predefined value, e.g. a predefined positive current value.

According to one embodiment, a point of intersection of the respective curve with another curve is evaluated. This expands the analysis, especially in the case of multiple discharges. The further curve can, for example, be recorded in the case of multiple discharges from the same capacitor or from several capacitors, which enables an analysis of e.g. starting processes, especially in the case of current curves.

According to one embodiment, a discontinuity or a discontinuous course of the respective parameter is evaluated. The respective discontinuity can in particular be related to time be assigned to one of several possible causes. This makes it easier to investigate the causes and optimize the welding system.

According to one embodiment, at least two or three turning points of the respective curve are evaluated, in particular in a current profile, in particular in a time interval of 0.01 to 100 ms. This also enables the characteristics of the same curve to be correlated in relation to one another, particularly with respect to time, and can facilitate the attribution of abnormalities. Evaluating three inflection points, particularly within a predefined time window, can identify a bulge-like dip (hill, wave).

According to one specific embodiment, a section of the curve is evaluated after an inflection point or after a maximum with respect to a falling edge of the curve, in particular with or using or based on the gradient parameter. This also enables an analysis of the setting behavior and melting, i.e. a phase in which the parts are joined and bonded to one another. A phase or a time window until the welding current drops to half has proven to be particularly meaningful. A flank is to be understood in particular as a section of the curve delimited by at least one minimum, maximum, saddle point or point of inflection.

At least the magnitude of the welding current and a change in slope and/or gradient of the welding current curve and the point in time of the respective welding current and the change in slope are evaluated as parameters (time-related parameters). The evaluation of current measured values in particular enables a comparatively simple assignment and error analysis.

According to one embodiment, the comparison is made at least at a predefined point in time during the course of the respective weld, in particular when a rate of change exceeds a minimum threshold value, in particular in relation to time. Referring to the rate of change (in particular individual rates of change over time) also allows for the ignoring of supposed errors and can focus the analysis on the actual abnormalities.

According to one embodiment, the comparison takes place at a predefined time interval relative to an inflection point or maximum of the curve, in particular with respect to a maximum of a current curve. This facilitates the assignment of detected abnormalities and can define additional selection criteria or error criteria.

According to one embodiment, at least two of the welding parameters of the group are evaluated and optionally compared with one another, in particular three or four of the welding parameters from the group. This also enables more reliable cause research, for example an evaluation of measured current values in relation to measured resistance and/or voltage values. At least both the welding current and the melting path are preferably evaluated.

According to one embodiment, the method is carried out for welded components made from lightweight materials. This provides the aforementioned advantages in a particularly noticeable way. In particular, a very reliable, reproducible way of evaluation can take place. It has been shown that when welding lightweight materials (for example aluminum) compared to the welding of steel, at least one variation that is characteristic of lightweight materials occurs, in particular in the melting behavior, in particular in the course of the current. The evaluation according to the invention can be carried out with a particularly high resilience with regard to lightweight welded parts (e.g. aluminum-steel material combination, or aluminum-aluminium), in particular with regard to comparatively pronounced dents (synonymous: turning points, fluctuations, discontinuities) in the current profile.

According to one embodiment, the method is carried out repeatedly in multi-stage welding (in particular in sequential multiple discharge) based on at least two curves, in particular based on at least two curves recorded independently of one another (in particular during tempering or stress-relief annealing of the welded component) or based on a pair of curves which a subsequent curve departs from a falling edge of a preceding curve (sequential multiple discharging, in particular by means of a plurality of capacitors or capacitor banks). This also enables a reliable, reproducible analysis of multiple discharges.

In addition to evaluating the course over time, the evaluation can also be carried out with regard to individual points or peaks (minimum or maximum) of the curve and/or with regard to at least one envelope curve (laid around the curve or along one side or both sides of the curve). This expands the scope of the evaluation and can also facilitate cross-checking (verifying analysis results).

According to one embodiment, a sinusoidal DC pulse provided by at least one capacitor is evaluated as the welding current, in particular over a period of 0.1 to 1000 ms (for the discharging or welding time), in particular less than 10 ms. The evaluation can take place with regard to individual time intervals (in particular <1 ms) of the curve.

According to one embodiment, the evaluation and/or comparison is frequency-independent, in particular exclusively based on the characteristic variable slope of the current curve (1st derivative of the current curve) and/or gradient of the current curve. The frequency-independent evaluation provides a straightforward way of analysis and can reduce the complexity of the evaluation. According to the invention, a frequency reference is not necessarily required. For the type of evaluation, it is irrelevant in which time frame (e.g. between 5 and 20ms) and at which frequency the respective pulse discharges take place.

According to one embodiment, the method also includes the step of characterizing the respective welded component based on the comparison of the parameter. Last but not least, this enables the labeling and classification of correctly manufactured parts and NOK parts. The characterization can include storing the corresponding data, optionally correlated with the corresponding welded component, in a data memory of a resistance welding system or in a control device. The characterization can include activation of an output unit depending on the comparison and the evaluated quality, for identifying weld components of poor quality.

At least one of the aforementioned objects is also achieved, as mentioned, by a method for performing and monitoring the quality of a resistance weld, in particular a capacitor discharge weld, using a quality evaluation method on a resistance welding device as described above, the method being carried out during conductive resistance pressure welding, in particular with a welding force in range from 0.1 to 1,000kN (kiloNewton); and/or wherein the method is carried out as projection or press-fit welding, analyzing a curve of the corresponding welding force parameter, in particular at a welding current in the range of 1 to 10,000kA; and/or wherein the method is carried out by means of pulsed direct current discharge. This results in the advantages mentioned above.

The method can be performed in multi-stage resistance pressure welding (press-fit welding) by applying a welding force ranging from 0.1 to 1,000kN or greater and analyzing a curve of the corresponding welding force parameter. The method can be carried out in resistance fusion welding, in particular with a welding current in the range from 1 to 10,000 kA, in particular 10 to 200 kA

According to one specific embodiment, at least one welding parameter is adjusted during the welding, in particular in response to an evaluation of the amount of the deviation of the parameter from/from a target value (amount greater than the specifiable maximum tolerance). The adaptation can take place, for example, with regard to a welding force, for example after detecting two to three faulty parts. Optionally, the welding energy can also be adjusted, in particular with regard to an adjustment of the welding current (e.g. in response to a process-related or system-related reduction in the welding current, e.g. based on a target specification of 50kA, in particular based on a trend from the last three or more welds). This enables continuous system or process optimization and, if necessary, also the avoidance of a large number of errors in the batch currently being manufactured (e.g. 100 pieces of welded components). Not only is regulation possible after the process, but also during the welding process. For example, it was found that welding spatter can be avoided by suddenly increasing the welding force.

According to one embodiment, the method also includes: Controlling an output unit and/or an ejection unit of the resistance welding device depending on the comparison and the evaluated quality, for characterizing or partially or fully automatically ejecting poor-quality welding components, in particular during welding (identification and/or ejection of so-called NOK parts, optionally in real time). This also reduces the risk of n.i.o. parts entering circulation. The ejection can also be carried out partially automatically or manually, based on a machine marking of n.i.O. parts.

At least one of the aforementioned objects is also achieved, as mentioned, by a method for producing a resistance-welded welded component, in particular by capacitor discharge welding using a resistance welding system, with a previously quality evaluation method described further above or a method for execution and quality monitoring previously described further above is carried out. This results in the advantages mentioned above.

At least one of the aforementioned tasks is also achieved, as mentioned, by a computer program product designed to characterize resistance-welded welded components in KE welding systems by evaluating at least one welding parameter from the group: welding current, welding voltage, welding force, resistance, melting path, welding time; wherein a recorded time profile of the welding parameter to be evaluated is provided as a curve of the respective welding parameter, and by comparing at least one parameter of the respective curve with at least one setpoint value for the parameter defined based on a preceding section of the profile of the welding parameter to be evaluated, and by evaluating the quality based on the comparison, and by correlating the respective welded component with a first index for sufficiently high quality or with a second index for insufficient quality, in particular individually specific in relation to the respective parameter, in particular set up to carry out a quality evaluation method previously described above . This results in the advantages mentioned above.

At least one of the aforementioned objects is also achieved by a data carrier with such a computer program product stored thereon or a database described here stored thereon, or by a computer or a computer system or a virtual machine or at least one hardware element therewith.

At least one of the aforementioned objects is also achieved, as mentioned, by a computer program product set up for controlling or regulating a resistance welding system for carrying out a method for carrying out and quality monitoring of a resistance welding method, described above, or a method for producing a resistance-welded welded component, described above. This results in the advantages mentioned above.

As mentioned, at least one of the aforementioned tasks is also achieved by using a database with setpoint values stored therein for the respective parameter when executing a method previously described further above. This results in the advantages mentioned above. The analysis based on the target values already stored in a/the database is carried out in addition to the evaluation of the preceding section of the course of the respectively evaluated curve.

As mentioned, at least one of the aforementioned objects is also achieved by using a quality evaluation method previously described above during resistance welding, in particular during the welding individually for a respective welded component. This results in the advantages mentioned above.

As mentioned, at least one of the aforementioned objects is also achieved by a welding parameter evaluation device set up for characterizing resistance-welded welded components, in particular simultaneously during resistance welding in capacitor discharge (KE) welding systems, set up for evaluating at least one welding parameter from the group: welding current, welding voltage, welding force, resistance, fusion path, welding time; with an output unit for displaying or outputting the welding parameters or curves of the welding parameters, the welding parameter evaluation device being set up to provide a curve of the respective welding parameter, the welding parameter evaluation device being set up to evaluate the respective curve by reading out at least one parameter of the respective curve, and being set up to Comparison of the parameter with at least one setpoint value for the parameter that is defined based on a preceding section of the profile of the welding parameter to be evaluated, and is set up to evaluate the quality based on the comparison. This results in the advantages mentioned above.

The welding parameter evaluation device can have corresponding measuring devices, in particular current, voltage, force and/or displacement sensors. According to one variant, the measuring devices are provided in a control unit which controls/regulates the resistance welding system.

According to one exemplary embodiment, the welding parameter evaluation device is set up to correlate the respective welding parameter and the corresponding welded component. This also enables grouping into error categories, or classification in terms of the severity/relevance of abnormalities. At the same time, the system or process can be monitored, for example based on the welding current, because the current conducted through the welded component can be assigned directly to the system. The analysis according to the invention can therefore can be used directly for system or process optimization.

At least one of the aforementioned objects is also achieved by a control device set up to control or regulate a resistance welding device when welding welded components, comprising at least one previously described welding parameter evaluation device and set up to record the respective welding parameter. This provides the aforementioned advantages. For this purpose, the control device can have a data memory for storing at least one of the welding parameters and the corresponding measuring devices.

At least one of the aforementioned objects is also achieved by a resistance welding device with a previously described welding parameter evaluation device and/or with a previously described control device, in particular in the form of a KE welding system. In particular, the welding system is set up to set at least one parameter in one of the following ranges: welding force from 5 to 300kN, welding time from 0.1ms to 1,000ms, amount of welding energy of up to 160kJ, melting path from 0.1 to 2mm. This provides the aforementioned advantages.

character list

• 1, 2, 3 jeweils in schematischer Darstellung eine Kurve des Verlaufes des Schweißparameters Schweißstrom und eines diesbezüglichen Gradienten-Parameters, als Datengrundlage für ein Verfahren gemäß einer Ausführungsform;
• 4A, 4B, 4C, 4D jeweils in schematischer Darstellung eine Kurve des Verlaufes des Schweißparameters Abschmelzweg (relative Verlagerung) und eines diesbezüglichen Gradienten-Parameters, als Datengrundlage für ein Verfahren gemäß einer Ausführungsform;
• 5 in schematischer Darstellung eine Vorrichtung gemäß einem Ausführungsbeispiel;
• 6A, 6B jeweils in schematischer Darstellung charakteristische Kurven des Verlaufes des Schweißparameters Schweißstrom jeweils entsprechend einer Mehrfachentladung;
• 7 in schematischer Darstellung eine charakteristische Kurve des Verlaufes des Schweißparameters Schweißstrom in Relation zu einer Normkurve und zu Hüllkurven, als Datengrundlage für ein Verfahren gemäß einer Ausführungsform, unter Einbezug eines Hüllkurvenkriteriums;
• 8 in schematischer Darstellung eine Vorrichtung gemäß einem weiteren Ausführungsbeispiel; und
• 9 in schematischer Darstellung einzelne Schritte eines Verfahrens gemäß einer Ausführungsform.

The invention is described in more detail in the following drawing figures, reference being made to the other drawing figures for reference symbols which are not explicitly described in a respective drawing figure. Show it:

• 1 , 2 , 3 in each case a schematic representation of a curve of the profile of the welding parameter welding current and a related gradient parameter, as a data basis for a method according to one embodiment;
• 4A , 4B , 4C , 4D in each case a schematic representation of a curve of the course of the welding parameter melting path (relative displacement) and a related gradient parameter, as a data basis for a method according to one embodiment;
• 5 a schematic representation of a device according to an embodiment;
• 6A , 6B each in a schematic representation of characteristic curves of the course of the welding parameter welding current, each corresponding to a multiple discharge;
• 7 a schematic representation of a characteristic curve of the course of the welding parameter welding current in relation to a standard curve and to envelope curves, as a data basis for a method according to an embodiment, including an envelope criterion;
• 8th a schematic representation of a device according to a further embodiment; and
• 9 a schematic representation of individual steps of a method according to one embodiment.

DETAILED DESCRIPTION OF THE FIGURES

The method according to the invention is described below by way of example with reference to a typical current curve P1. The explanations can be applied analogously to another of the welding parameters mentioned here, in particular to the welding voltage P2, the welding force P3, the resistance P4 and/or the melting path P5, or also to another welding parameter Pn.

In the 1A , 1B , 1C , 1D shows a comparison of (absolute) measured current values P1 of a current parameter curve PK (rising edge PK1, falling edge PK2) with target values, or a reference of time-related current measured values to profiles, gradients or rises in specific time intervals. All curves are presented in terms of samples (sequence numbers) plotted on the abscissa (e.g. 1 to 150 samples).

In the 1A The curve PK shown shows the course of the current, with individual sampling values (sequential numbers on the abscissa) being plotted as a function of the current (in kiloamperes [kA]; ordinate, for example 1 to 15kA). An advantage of working with a gradient parameter can be seen in the comparatively simple way of defining threshold values and exclusion criteria. For example, the course of the gradient ( 1D ) shows that the rate of change of the measured values becomes weaker and weaker from a certain point in time. By defining a maximum target value for the rate of change, for example, dips (synonymous: turning points, fluctuations, discontinuities) in the decay behavior can be recognized comparatively easily, specifically individually, without reference to standard envelope curves. This provides high variability when using the evaluation method.

the inside 1A shown course (sinusoidal decay behavior of the falling flank PK2) can be viewed as an exemplary course of a healthy, high-quality KE weld (OK parts). The following parameters should be emphasized: K1 according to the first derivation (here: gradient of the current curve); K2 according to the second derivative; K5 corresponding to a maximum; K8 corresponding to a (fictitious or real) zero crossing; Kn is listed as an optional additional parameter.

In the 2A , 2 B , 2C , 2D a comparable illustration is made with reference to a defect. All curves are shown in terms of sample values (sequence numbers) plotted on the abscissa. 2A shows samples or sequential numbers plotted on the abscissa and the current in kiloamperes [kA] plotted on the ordinate. The following parameters should be emphasized: K4 corresponding to a minimum; K7 corresponding to a saddle point; K9 corresponding to a discontinuity.

the inside 2A The curve shown (e.g. 1 to 30kA) can be viewed as an example of a faulty KE weld (NOK parts) (two peaks; downward dent, characterized by several turning points and optionally also by discontinuities; collapse of the current value in the area of the maximum with subsequent increase).

In the 3A , 3B , 3C , 3D a comparable illustration is made with reference to a correctly manufactured welded component. All curves are shown in terms of samples (sequence numbers, for example for 200 samples) plotted on the abscissa. 3A shows sample values or sequence numbers plotted on the abscissa and the current in kiloamperes [kA] plotted on the ordinate (e.g. 1 to 25kA). The curve shown can be viewed as an example curve for OK parts. In comparison to 1A the course of the current is more elongated (over time). Both the rising and the falling edge are less steep.

In 3A different times are shown for relative reference. Starting from a predefined absolute point in time t1, a predefined point in time t2 with a relative time reference can be defined (t1 corresponds, for example, to the absolute maximum, and t2 corresponds, for example, to one millisecond after the absolute maximum). Target values VI, V2, Vn can now be defined in particular in a first time interval ΔT1 and/or in a second time interval ΔT2, in each case with reference to at least one of the points in time t1, t2. The following parameter is to be emphasized: K6 corresponding to a turning point. This parameter can also specify one of the points in time for reference to the setpoint definition.

In the 4A , 4B , 4C , 4D a comparable illustration is made with reference to a correctly manufactured welded component (OK part) by analyzing the melting path. All curves are shown in terms of sample values (sequence numbers) plotted on the abscissa. 4A relates to a path measurement value, in particular directly to the melting path (sampled values or sequence numbers, plotted on the abscissa, and melting path in millimeters [mm], plotted on the ordinate). With this type of evaluation, for example, two criteria or parameters can be defined, in particular a threshold value and the sign of the gradient; a negative rate of change can be evaluated alone or in combination with other parameters as a not ok part. The curve shown can be seen as an example of the curve of a KE weld of a standard welded component or a lightweight component. The vibrations that can be read out in the course of the melting path can be caused by natural vibrations of the plant. Depending on whether a frequency corresponding to the natural frequency of the system is set during welding, or how close a vibration is to the natural frequency of the system during welding, vibration occurs to a greater or lesser extent. With many types of welds, there are no vibrations at all and therefore no fluctuations in the course of the melting curve. The question of whether a welded part is OK can be analyzed independently of these vibrations, or taking the vibrations into account, in particular with additional reference to a vibration standard curve, which can be determined for a specific system based on empirical values, for example.

In 4A a discontinuity K9 can be seen in the course of the local relative displacement (melting path), a kind of oscillation. The discontinuity K9 characterizes, for example, a brief standstill or deceleration, possibly due to a jerk or an obstacle to be overcome in the material of the component, and/or due to the system technology due to the elasticity of the system when repositioning. Assuming that the contact pressure has remained constant, a material defect in at least one of the parts to be joined can be inferred, for example. Optionally, a comparison can be made with a vibration standard curve of the system, optionally taking the natural frequency into account. The following parameter is to be emphasized: K3 corresponding to a relative position (particularly relative time reference) of the parameter curve PK to the curve PK' of another of the parameters, here as an example to the current curve.

In the case of the measurements discussed above, the evaluation can be carried out with regard to both a rising and a falling edge of the curve.

In the 5 shows a welding parameter evaluation device 10 integrated into a resistance welding device 40, in particular a KE resistance welding system. The resistance welding device 40 comprises a processing station 40.1, at least one welding cylinder 41 (welding electrode, pressure stamp), at least one ejection unit 43 and at least one capacitor 45 or a capacitor battery.

A welded component 1 consists of a first joining part 1a and a second joining part 1b, or the welded component 1 is to be produced by material bonding of these joining parts. For this purpose, the welded component 1 is clamped at contact surfaces 1.1 between the welding cylinders 41, subjected to a welding force and held in position. The welding process can be initiated by charging the capacitor 45 and initiating the discharge (e.g. thyristor firing). The welding force is already applied and can optionally be exerted continuously on the parts to be joined by spring force and/or an actuator, with the effect that the welding cylinder 41 is displaced as soon as the material is melted.

The process can be monitored and selectively regulated by means of a control device 30 . The control device 30 can interact with the individual components, in particular control the ejection unit 43, which is indicated by the dotted line.

Some measuring devices or sensors are also integrated into the resistance welding device 40, which are each connected to the control device 30, and their arrangement in 5 is only to be understood as an example. The following are particularly worth mentioning: first measuring device 31, in particular a force sensor; second measuring device 33, in particular a current sensor (eg Rogowski coil or Rogowski belt); third measuring device 35, in particular a voltage sensor; fourth measuring device 37, in particular a resistance sensor; fifth measuring device 39, in particular displacement sensor. A computer program product 20 and an output unit 11, in particular with a display (display unit), can be mentioned as further components.

In the 6A a multiple discharge is illustrated, in which the subsequent discharge already begins at the falling edge of the preceding discharge, for example corresponding to welding on a conductive stop or press-in welding. The rising edge of the subsequent weld descends from the falling edge of the previous weld. This type of multiple discharge is carried out in particular using a plurality of batteries or using a capacitor bank. Such a sequential discharging can also be accomplished, for example, by means of a plurality of capacitors (capacitor battery). A combined evaluation can also be carried out. Conceivable measuring points in time also correspond in particular to the respective maxima and the point in time at which the subsequent curve PK′ departs from the first curve PK.

In the 6B a multiple discharge is illustrated, in which the subsequent discharge is completely decoupled and takes place after the preceding discharge, for example corresponding to a annealing of the joining zone. The joining or welding force is, for example, 3 to 300kN (although the welding force can vary), the welding time is, for example, 0.1 to 1,000ms, and the welding energy is, for example, 10kJ or 50kJ or up to 160kJ, particularly in relation to the first time upstream curve. This type of multiple discharge can also be carried out using only a single capacitor, which is recharged.

In the 7 an envelope criterion or a tolerance criterion is illustrated. Two envelope curves HK enclose a curve PK of at least one recorded parameter to be evaluated, and a standard curve NK is provided as a reference curve. A tolerance range Δ is defined by the distance between the two enveloping envelope curves and optionally also by a distance between the detected curve PK and the standard curve NK. It can be seen that various abnormalities and discontinuities or turning points in the course of the measurement curve PK can only be evaluated if a very narrow tolerance range is defined. However, if there is a dent (K4, K5; synonymous: turning points with a fluctuation in the form of a wave or a bulge or a local peak in the lateral direction), e.g. in an area close to the standard curve NK (still in the tolerance range, within the the tolerance zone delimited by the envelope curves HK), this cannot be recognized or evaluated at all, or at least not in a simple manner. In contrast to this tolerance-related evaluation based on standardized tolerances, the evaluation can be carried out according to the invention by reference to setpoint values VI, V2, Vn determined from the curve. The target values are each determined from the previous course (which is the dashed line is indicated), in particular a few milliseconds or even microseconds.

In the 8th is an arrangement comparable to that in 5 described.

In the 9 process steps and control points are illustrated as examples. The individual steps are explained below in chronological order. First, in an initiating step S0, welding parameters, in particular direct current parameters, are provided or regulated. In this regard, welding parameters such as force, current, voltage can be controlled by a system in a first control point R1. In a first step S1, a profile of at least one parameter P1 is recorded and made available; Pn. The first step can include a selection S1.1 of a time interval in the course, in particular with a relative time reference to at least one parameter K1; Kn. In a second control point R2, a time positioning can take place relative to the selected parameters (time adjustment). In a second step S2, a curve PK, PK′ characterizing the course of the parameters is evaluated, including a setpoint definition S2.1. In a third control point R3, there is an optional check of setpoint definitions or a plausibility check, in particular an adjustment of an adequate time interval for defining the setpoint. In a third step S3, a comparison takes place, in particular comprising the comparison S3.1 of individual measured values with setpoint values defined specifically for the curve or additionally also the comparison S3.2 based on one or more tolerance and envelope criteria ( 7 ). In a fourth control point R4, quality criteria are optionally selected or adapted. In a fourth step S4, the quality is evaluated, in particular including a characterization S4.1 as a high-quality part (in particular using the first code number Kz1) or a defective part (in particular using the second code number Kz2). In a fifth control point R5, reject parts are optionally discharged. In a fifth step S5, an output unit 11 and/or an ejection unit 43 is activated, wherein step S5 can include marking S5.1 of the welded component and/or assigning the identifier to the welded component (attributing a first code Kz1 or a second Kz2). . Optionally, the system 40 can also be stopped. Step S5 can include an ejection S5.2 or a separate ejection of NOK parts.

Reference List

1

welded component

1a

first joining part

1b

second joining part

1.1

contact surface

10

Welding parameter evaluation device

11

Output unit, in particular with a display (display unit)

20

computer program product

30

control device

31

first measuring device, in particular a force sensor

33

second measuring device, in particular a current sensor

35

third measuring device, in particular a voltage sensor

37

fourth measuring device, in particular a resistance sensor

39

fifth measuring device, in particular displacement sensor

40

Resistance welding device, in particular KE resistance welding system

40.1

processing station

41

Pressure stamp or welding cylinder

43

ejector unit

45

Capacitor or capacitor battery

K1

first parameter, especially slope (first derivative)

K2

second parameter, in particular second derivative

K3

Third parameter, in particular relative position (in particular relative time reference) of the curve to the curve or to a parameter of another of the parameters

K4

fourth parameter, in particular minimum

K5

fifth parameter, in particular maximum

K6

sixth parameter, in particular turning point

K7

seventh parameter, in particular the saddle point

K8

Eighth parameter, in particular (fictitious or real) zero crossing

K9

ninth parameter, in particular discontinuity

Kn

further parameter

Kz1, Kz2

first and second number

P1

first welding parameter, in particular welding current

p2

second welding parameter, in particular welding voltage

P3

third welding parameter, in particular welding force

P4

fourth welding parameter, especially resistance

P5

Fifth welding parameter, in particular melting path (relative displacement or contact pressure path)

pm

other welding parameters

HK

envelope

NK

standard curve

PC

Curve or course of a respective welding parameter

PC'

another curve

PK1

rising edge

PC2

falling edge

PKS

curve intersection

R1

First control point (system), especially for controlling welding parameters such as force, current, voltage

R2

second control point (evaluation), in particular temporal positioning relative to parameters

R3

Third control point (evaluation), in particular checking of setpoint definitions or plausibility, in particular adjustment of a time interval for defining the setpoint

R4

Fourth control point (evaluation), in particular selection or adjustment of quality criteria

R5

Fifth rule point (appendix), in particular ejection of rejects

S0

Provision or regulation of welding parameters, in particular direct current parameters

S1

first step, in particular recording and providing a history of a parameter

S1.1

Selection of a time interval in the course, in particular with a relative time reference to a parameter

S2

second step, in particular evaluating a curve characterizing the course of the parameters

S2.1

setpoint definition

S3

third step, especially comparing

53.1

Comparison of individual measured values with curve-specific target values

S3.2

Compare based on tolerance and envelope criteria

S4

fourth step, in particular evaluating the quality

S4.1

Characterize as a high-quality ok part or as a not ok part

S5

Controlling an output unit and/or an ejection unit

S5.1

Marking of the welded component and/or assignment of the marking to the welded component

S5.2

Ejection or separate ejection of n.i.O. parts

t1

predefined absolute point in time

t2

predefined point in time with a relative time reference

Δ

tolerance range

ΔT1

first time interval

ΔT2

second time interval

V1

first setpoint

v2

second setpoint

vs

another target value

Claims (18)

Quality evaluation method for characterizing resistance-welded welded components (1) in conductive capacitor discharge (KE) welding systems by evaluating at least one welding parameter (P1, Pn) from the group: welding current, welding voltage, welding force, resistance, melting path, welding time; a recorded course of the welding parameter to be evaluated being provided as a curve (PK) of the respective welding parameter; characterized by evaluating the curve (PK) by reading out at least one parameter (K1, Kn) of the respective curve as a function of time and optionally also as a function of at least one other of the welding parameters, with at least the amount of the welding current and a change in slope and/or gradient of the welding current curve and the time of the respective welding current and the change in slope being evaluated as parameters (K1, Kn); Comparing the parameter (K1, Kn) with at least one target value (VI, Vn) for the parameter, with at least the slope and/or a gradient of the respective curve (PK) being evaluated as the parameter (K1, Kn), with the target value ( VI, Vn) is/is defined based on a preceding section of the profile of the respectively evaluated curve (PK) of the welding parameter (P1, Pn) to be evaluated; and evaluating the quality of the welded component (1) based on the comparison of the parameters (K1, Kn), in particular with regard to the amount of a deviation of the parameter from the target value. Quality evaluation method according to the preceding method claim, wherein the target value (VI, Vn) is/is defined based on the detected curve or gradient in a time interval of 0.1 to 1000 ms before the comparison time; and/or the curve is evaluated independently of a sampling rate; or wherein the curve is evaluated at a predefined sampling rate, wherein the target value (V1, Vn) is defined based on the previous sample or based on a group of up to ten of the previous samples or based on a group of up to 10% of all samples it will. Quality evaluation method according to one of the preceding method claims, wherein at least one zero crossing and/or a minimum or maximum or saddle point or a point of inflection of the slope and/or the gradient of the respective curve (PK) is evaluated as a parameter (K1, Kn), in particular with reference to time; and/or wherein at least the derivation of the slope and/or the gradient of the respective curve (PK) is evaluated as a parameter (K1, Kn), in particular a zero crossing and/or a minimum or maximum or saddle point or a turning point of the slope and/or of the gradient, especially with reference to time. Quality evaluation method according to one of the preceding method claims, wherein the evaluation takes place with regard to monotony and/or continuity of the curve (PK), in particular with regard to a deviation from a predefinable monotony of the current curve; and/or wherein the evaluation with regard to an inflection point of the second derivative of the current curve takes place behind a maximum on a falling edge (PK2) of the current curve, in particular with reference to time. Quality evaluation method according to one of the preceding method claims, in which a sinusoidal direct current pulse provided by at least one capacitor (45) is evaluated as the welding current, in particular over a period of 0.1 to 1000 ms. Quality evaluation method according to one of the preceding method claims, wherein the evaluation and/or comparison takes place independently of frequency, in particular exclusively based on the characteristic variable slope of the current curve and/or gradient of the current curve. Quality evaluation method according to one of the preceding method claims, in which the course over time of the at least one parameter (K1, Kn) of the curve (PK) is compared with a standard curve (NK) of the corresponding parameter, with a deviation of the parameter from the setpoint at a plurality of Comparison points of the curve takes place at a plurality of measurement times. Quality evaluation method according to one of the preceding method claims, wherein a turning point of the respective parameter (K1, Kn), in particular a turning point of the slope and/or a gradient, is evaluated; and/or wherein a zero crossing or a minimum or maximum or saddle point of the parameter (K1, Kn), in particular the slope and/or the gradient, is evaluated; and/or wherein an intersection (PKS) of the respective curve (PK) with a further curve (PK') is evaluated; and/or wherein a discontinuity or a discontinuous course of the respective parameter (K1, Kn) is evaluated; and/or wherein at least two or three turning points of the respective curve (PK) are evaluated, in particular in a current profile, in particular in a time interval of 0.01 to 100 ms. Quality evaluation method according to one of the preceding method claims, in which a section of the curve is evaluated after a turning point or after a maximum with respect to a falling edge (PK2) of the curve, in particular with the slope parameter. Quality evaluation method according to one of the preceding method claims, wherein the comparison is made at least at a predefined point in time during the course of the respective weld, in particular when a rate of change exceeds a minimum threshold value, in particular in relation to time; or where the comparison in a predefined time interval relative to an inflection point or maximum of the curve, in particular with respect to a maximum of a current curve. Quality evaluation method according to one of the preceding method claims, wherein the method is carried out repeatedly in the case of multi-stage welding, in particular in the case of sequential multiple unloading, based on at least two curves (PK, PK'), in particular based on at least two curves recorded independently of one another, in particular during starting or Stress-relief annealing of the welded component, or based on a pair of curves in which a subsequent curve departs from a falling edge (PK2) of a preceding curve, in particular in the case of sequential multiple discharging, in particular by means of a plurality of capacitors. Method for carrying out and monitoring the quality of a resistance weld, in particular a KE weld, using a quality evaluation method according to one of the preceding method claims on a resistance welding device (40), the method being carried out during conductive resistance pressure welding, in particular with a welding force in the range from 0.1 to 1,000 kN; and/or wherein the method is carried out as projection or press-fit welding, analyzing a curve of the corresponding welding force parameter, in particular at a welding current in the range of 1 to 10,000kA; and/or wherein the method is carried out by means of pulsed direct current discharge. Method according to the preceding method claim, further comprising: activating an output unit (11) and/or an ejection unit (43) of the resistance welding device (40) depending on the comparison and the evaluated quality, for characterizing or for the semi-automatic or fully automatic ejection of welding components (1st ), especially during welding. Computer program product (20) set up for characterizing resistance-welded welded components (1) in KE welding systems by evaluating at least one welding parameter (P1, Pn) from the group: welding current, welding voltage, welding force, resistance, melting path, welding time; wherein a recorded time profile of the welding parameter (P1, Pn) to be evaluated is provided as a curve (PK) of the respective welding parameter (P1, Pn), wherein at least the amount of the welding current and a change in slope and/or gradient of the Welding current curve and the time of the respective welding current and the change in slope are evaluated; and by comparing at least one parameter (K1, Kn) of the respective curve (PK) with at least one setpoint value (V) for the parameter (K1, Kn) defined based on a temporally preceding section of the detected profile of the welding parameter (P1, Pn) to be evaluated , wherein at least the slope and/or a gradient of the respective curve (PK) is evaluated as a parameter (K1, Kn), and by evaluating the quality based on the comparison, and by correlating the respective welded component (1) with a first key figure ( Kzl) for sufficiently high quality or with a second index (Kz2) for insufficient quality, in particular individually specific in relation to the respective parameter, in particular set up to carry out a quality evaluation method according to one of the preceding method claims. Use of a quality evaluation method according to one of the methods claims 1 until 11 during resistance welding, in particular during welding individually for a respective welded component (1). Welding parameter evaluation device (10) set up for characterizing resistance-welded welded components (1), in particular simultaneously during resistance welding, in capacitor discharge (KE) welding systems, set up for evaluating at least one welding parameter (P1, Pn) from the group: welding current, welding voltage, welding force, resistance , melting path, welding time; with an output unit (11) for displaying or outputting the welding parameters or curves (PK) of the welding parameters (P1, Pn), the welding parameter evaluation device being set up to provide a curve (PK) of the respective welding parameter (P1, Pn); characterized in that the welding parameter evaluation device (10) is set up to evaluate the respective curve (PK) by reading out at least one parameter (K1, Kn) of the respective curve (PK), with at least the magnitude of the welding current and a change in slope and/or change in gradient of the welding current curve and the point in time of the respective welding current and the change in slope are evaluated, and it is set up to compare the parameter (K1, Kn) with at least one based on a preceding section of the detected profile of the welding parameter (P1, Pn) defined setpoint (V1, Vn) for the parameter (K1, Kn), with at least the slope and/or a gradient of the respective curve (PK) being used as the parameter (K1, Kn). is evaluated and is arranged to evaluate the quality based on the comparison. Control device (30) set up for controlling or regulating a resistance welding device (40) when welding welded components (1), comprising at least one welding parameter evaluation device (10) according to the preceding claim, and set up for detecting the respective welding parameter (P1, Pn). Resistance welding device (40) with a welding parameter evaluation device (10) and/or with a control device (30) according to one of the Claims 16 or 17 , especially in the design as a KE welding system.

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