Method for checking the quality of at least one electrode cap for at least one resistance spot welding process

Abstract

The invention relates to a method for checking the quality of at least one electrode cap (10) for at least one resistance spot welding process (S10). The invention includes the electrode cap cutter (20) comprising at least one force sensor (24) which, during the milling pass (S20), determines a force value (26) of a force applied between the milling tool (22) and the respective electrode cap (10). For each milling pass (S20) of the respective electrode cap (10), a measurement curve is determined that describes the force value determined by the force sensor (24) as a function of a specific time point during the milling pass (S20). The measurement curve is checked to see if it exhibits at least one predefinable characteristic feature.Depending on the number and / or nature of at least one characteristic feature that the respective measurement curve assigned to the electrode cap (10) exhibits, a milling quality specification is assigned to the electrode cap (10), which describes a quality of the respective electrode cap (10) after the milling process (S20).

Description

[0001] The invention relates to a method for checking the quality of at least one electrode cap for at least one resistance spot welding process. Furthermore, a system comprising an electrode cap cutter and at least one electrode cap is disclosed.

[0002] To join at least two electrically conductive workpieces, at least one resistance spot welding process, as known from the prior art, can be used. In the resistance spot welding process, for example, the at least two workpieces to be joined can be placed between two electrode caps, so that an electric current flows between the electrode caps and through the workpieces to be joined. This generates heat, which can lead to localized and / or area-based melting of the workpieces, causing them to bond together at the point and / or in the area as they cool. The point and / or area where the workpieces are joined is also referred to as the weld point and / or weld spot.Additionally, the resistance spot welding process can include applying a force to the workpieces via the electrodes, for example by pressing the workpieces against each other.

[0003] A resistance spot welding process creates a spatially limited joint between at least two workpieces. To clarify, a "resistance spot welding process" here refers to a single pass of creating or establishing a single joint. To join at least two workpieces over a larger area, multiple resistance spot welding processes can be performed.

[0004] During at least one resistance spot welding process, a deposit can form on at least one of the electrode caps. This deposit could be, for example, weld metal deposited by a weld spatter. Additionally or alternatively, when machining hot-formed steel, the deposit could consist of alloying elements from the steel. This deposit can, for example, improve the conductivity of the current to the workpiece. Without this deposit, the welding temperature and / or heat in the workpiece can increase, leading to a higher probability of weld spatter formation.Additionally or alternatively, when using the resistance spot welding process for galvanized steel, at least a ring-shaped deposit can form on the electrode. This deposit reduces the current flowing into the workpieces compared to when the electrode is not present, potentially leading to a weaker weld between them.

[0005] To remove at least one deposit, it is provided in particular that at least one of the electrode caps used for at least one resistance spot welding process is milled off using at least one electrode cap milling cutter. This can be carried out after a predefinable number of resistance spot welding processes, for example, after between 50 and 200, and in particular after between 100 and 150 resistance spot welding processes. Exactly one weld spot can be created in each resistance spot welding process. An example of the electrode cap milling cutter is given in utility model DE 201 06 635 U1, where the electrode cap milling cutter is referred to as a cap milling machine.

[0006] A cleaning device for cleaning a welding electrode for a welding tool and a method for cleaning the welding electrode is disclosed by way of example in DE 10 2022 202 659 A1.

[0007] DE 11 2021 005 634 T5 discloses a control device comprising an operating command generation unit for controlling at least one of a first drive source for applying pressure to an electrode, a second drive source for driving a polishing tool for polishing the electrode, and a third drive source for changing the position and / or orientation of the electrode and the polishing tool relative to the other(s), and changing an operating command for the first drive source or at least one of the third drive source and the second drive source, such that it is peak-shaped and valley-shaped during at least one operating cycle of the polishing tool.

[0008] JP 2008 - 207 189 A discloses a method for milling a welding electrode.

[0009] After milling off at least one electrode cap, it may be necessary to determine the quality of the milling before using at least one electrode cap for at least one further resistance spot welding process.

[0010] The object of the invention is to provide a method by which the quality of the milling of the electrode cap and / or the quality of the electrode cap after milling can be determined in a simple and / or effective manner.

[0011] The problem is solved by the subject matter of the independent patent claims. Advantageous embodiments of the invention are described by the dependent patent claims, the following description, and the figures.

[0012] The invention relates to a method for checking the quality or suitability of at least one electrode cap for at least one resistance spot welding process. The quality check is carried out, in particular, between at least two resistance spot welding processes, for example, to verify whether the quality of the electrode cap is sufficient for the at least one further resistance spot welding process. Between the at least two resistance spot welding processes, the electrode cap can be milled or cleaned by milling, wherein, during a milling pass, a milling tool of an electrode cap cutter removes at least a deposit from the electrode cap by milling off at least a portion of a surface of the respective electrode cap.This means, in particular, that a milling pass is performed for each electrode cap, which includes the removal of at least one layer, especially the top layer and / or a part of the surface, of the electrode cap. Such milling using an electrode cap milling cutter is known from the prior art.

[0013] According to the invention, a quality inspection is performed to verify the quality of the at least one electrode cap after milling. The quality of the electrode cap after milling, in particular, describes its suitability for achieving a predefined weld quality in a resistance spot welding process. The milling process is characterized, in particular, by the removal of a portion of the surface and / or an upper layer of the respective electrode cap using the electrode cap milling cutter. The weld quality can be specified, for example, by the diameter of a lens, i.e., the diameter of the area that liquefies during the resistance spot welding process, as is known, for example, from the prior art.Additionally or alternatively, the quality of the electrode cap describes in particular the probability of at least one weld spatter occurring during a resistance spot welding process after the milling pass, in which, for example, liquid weld metal splashes away from the welding point.

[0014] The quality control is based on the electrode cap milling cutter including at least one force sensor that detects the force exerted between the milling tool and the respective electrode cap during the milling process. This means, for example, that the force with which the milling tool presses against the electrode cap is determined during the milling process, while at least part of the surface and / or the upper layer of the respective electrode cap is removed. The force sensor could, for example, be a piezoelectric sensor known from the prior art, which offers the advantage of being small enough to be integrated into an electrode cap milling cutter and / or possessing a predefinable measurement accuracy.

[0015] For each milling pass of the respective electrode cap, a measurement curve is determined that describes the force value measured by the force sensor as a function of a specific point in time during the milling process. This means, in particular, that the force value recorded by the force sensor is continuously measured and / or at predefined intervals throughout the entire milling process. The force values ​​can be ordered in the sequence of their temporal measurement and / or generation, forming the measurement curve. Thus, a time series of force values ​​is determined. The measurement curve can be generated, in particular, by interpolating between the force values. The measurement curve specifically describes at which point in time during the milling process each force value was measured by the force sensor.The time can be specified, for example, relative to the start and / or beginning of the milling pass. The force values ​​can represent absolute values ​​or relative change values ​​with respect to the respective previous value, the latter embodiment being advantageously easier to implement technically.

[0016] The measurement curve is checked to see if it exhibits at least one predefined characteristic feature. This characteristic feature could be, for example, that the measurement curve deviates from a predefined shape, and / or that the measurement curve deviates from a predefined shape within a predefined range of the milling process, and / or that the measurement curve exceeds and / or falls below a predefined limit value at at least one point during the milling process.

[0017] Depending on the number and / or severity of at least one characteristic feature exhibited by the measurement curve associated with the electrode cap, a milling quality rating is assigned to the electrode cap. This rating describes the quality of the respective electrode cap after the milling process. The milling quality rating allows, in particular, the quality of the milling process itself to be specified based on the quality of the electrode cap after the milling process. Specifically, this means that for each characteristic feature identified in the respective measurement curve, the frequency and / or intensity (how often and / or how pronounced) of the characteristic feature is determined. For example, it can be determined how often the measurement curve deviates from a predefined trend and / or exceeds or falls below a predefined limit.Additionally or alternatively, it can be determined how much a deviation of the measurement curve deviates from a predefined curve shape and / or how far the measurement curve exceeds and / or falls below the predefined limit value. It can be stipulated that the milling quality rating is lower the more frequently and / or strongly the respective characteristic feature is represented in the measurement curve. Additionally or alternatively, the milling quality rating can be lower the more of the characteristic features are determined in the respective measurement curve. This means, in particular, that the milling quality rating is higher the closer the measurement curve is to a predefined curve shape. It can be stipulated that the quality of the respective electrode cap is higher the higher the milling quality rating.This means, in particular, that the quality of at least one resistance spot welding process after the milling process is higher the higher the quality of the respective electrode cap after the milling process.

[0018] The electrode cap will be used for at least one further resistance spot welding process if the milling quality exceeds a predefined quality threshold and / or lies within a predefined quality threshold range. The predefined quality threshold can be a limit value. The predefined quality threshold range can be a range between two limit values. If the milling quality of the respective electrode cap exceeds the predefined quality threshold and / or lies within the predefined quality threshold range, it can be stipulated that at least a predefined quality can be achieved in at least one resistance spot welding process after the milling pass.For example, in the case of an electrode cap with a milling quality specification that exceeds the predefined quality threshold and / or whose milling quality specification lies within the predefined quality threshold range, the lens diameter, i.e., the diameter of the area with liquid material in a resistance spot welding process, can have a predefined average value and / or lie within a predefined size interval and / or fluctuations in the lens diameter do not exceed a predefined fluctuation value. The lens diameter and / or the value of the fluctuations depend in particular on the workpieces and / or the application of the resistance spot welding process.

[0019] The invention offers the advantage that the data required to determine the milling quality are generated during the milling process itself. This eliminates the need for subsequent quality checks of the electrode cap, resulting in reduced milling time and less time spent on quality inspection. Specifically, no additional step after milling is required to check the quality of at least one electrode cap.

[0020] Further developments of the invention result in additional advantages.

[0021] Further development includes the requirement that at least one of the at least one predefinable characteristic feature is present in that the force value at a given time during the milling process exceeds a maximum force value assigned to that time. This means, in particular, that a maximum force value is assigned to different time points and / or to each time point on the measurement curve and / or within a predefinable range of the measurement curve. The maximum force value at one time point on the measurement curve can differ from the maximum force value at another time point on the measurement curve.

[0022] In particular, the maximum force value can be specified relative to a reference measurement curve. The reference measurement curve can be a curve as it would be recorded during an ideal milling pass. Additionally or alternatively, the reference measurement curve can be a curve that results from the average of several milling passes. This means, specifically, that at least one milling pass is performed for each of the different electrode caps, the measurement curve is determined for each pass, and the reference measurement curve is calculated as the average of these determined curves.Additionally or alternatively, the reference measurement curve can be determined by describing several milling passes for different electrode caps from multiple measurement curves. These passes must exhibit a milling quality rating that exceeds the predefined quality threshold and / or falls within the predefined quality threshold range. For example, at least 10, 50, or 100 measurement curves from different milling passes can be used to determine the reference measurement curve.

[0023] The maximum force value at a predefined time on the measurement curve is, in particular, higher than the value exhibited by the reference measurement curve at that predefined time. Specifically, it can be provided that the difference between the reference measurement curve and the maximum force value at a time described by the measurement curve is smaller the later that time is within a time interval described by the measurement curve.

[0024] In addition to the reference curve, a standard deviation of the curves used to determine the reference curve can be calculated using a method known from the prior art. The standard deviation indicates, in particular, how much the curves used to determine the reference curve deviate, on average, from the reference curve and / or from each other. Specifically, the standard deviation depends on the time point within the curve and / or within the reference curve. The maximum force value at a given time point in the curve can correspond to the value of the reference curve at that time point plus the standard deviation and / or a multiple of the standard deviation at that time point.

[0025] If the measurement curve exceeds the respective maximum force value at a given time, this can be considered a characteristic feature. It can be stipulated that at least one of the predefined characteristic features is present as soon as the measurement curve deviates from the reference measurement curve by more than the standard deviation assigned to that time and / or exceeds the maximum force value at that time.

[0026] If at least one of these characteristic features is present, specifically if the maximum force value is exceeded by the measurement curve and / or if the standard deviation relative to the reference measurement curve is exceeded by the measurement curve at at least one point in time during the milling process and / or at a point in time described by the measurement curve, the respective electrode cap to which the measurement curve is assigned may be assigned a lower milling quality rating. This means, in particular, that if at least one of these characteristic features is present in the measurement curve, the respective electrode cap will be assigned a lower milling quality rating than if, for example, the characteristic feature had not been determined in the measurement curve.

[0027] The advantage of this advanced training is that it provides an easily determinable criterion by which at least one characteristic feature can be identified. This allows, in particular, the milling quality specification to be easily determined and / or verified to ensure that the milling quality exceeds the predefined quality threshold and / or falls within the predefined quality threshold range. Specifically, this provides a fast and / or computationally efficient method for determining the quality of the respective electrode cap after milling.

[0028] Further training includes the determination of at least one characteristic feature and / or at least one machine malfunction feature, which is shown in the measurement curve of the milling process with a faulty electrode cap cutter, by a machine learning model, which is trained with different measurement curves that show different milling quality specifications, whereby each measurement curve intended for training the machine learning model is assigned the respective milling quality specification and / or information on whether the electrode cap cutter is faulty.

[0029] This means, in particular, that several measurement curves are provided, each describing a milling pass for an electrode cap.

[0030] Each of the various measurement curves can be assigned a corresponding milling quality rating, which describes the quality of the electrode cap whose milling process is represented by the respective measurement curve. Additionally or alternatively, the measurement curve can be assigned information on whether the electrode cap cutter is defective. A defective electrode cap cutter can be, for example, a dull and / or incorrectly adjusted milling tool. Additionally or alternatively, the electrode cap cutter can be defective and / or rated as defective if a predefined percentage, for example, at least 20%, at least 50%, and / or at least 70%, of the electrode caps that pass through the milling process with this electrode cap cutter exhibit a milling quality rating that falls below the predefined quality threshold and / or lies outside the predefined quality threshold range.

[0031] The various measurement curves, each associated with milling quality information and / or whether the electrode cap cutter is defective, can be fed into a machine learning model for training. Based on these measurement curves, which can form the training data for the machine learning model, at least one characteristic feature can be determined.At least one characteristic feature can be determined, for example, by comparing the various measurement curves and identifying which at least one property, at least one part, in particular at least 50% and / or at least 80% and / or at least 90%, of the measurement curves exhibits that fall below the specified quality threshold and / or that lie outside the specified quality threshold range and / or were determined for a defective electrode cap milling cutter, but which is not exhibited by the measurement curves and / or by at least 50% and / or at least 80% and / or at least 90% of the measurement curves that exceed the specified quality threshold and / or that lie within the specified quality threshold range and / or were not determined for a defective electrode cap milling cutter.It may be provided that the measurement curve of an electrode cap, whose milling quality specification falls below the quality threshold and / or whose milling quality specification lies outside the predefinable quality threshold range, is assigned an (insufficient) quality that falls below the quality threshold and / or lies outside the predefinable quality threshold range, so that in particular the measurement curve falls below the quality threshold and / or lies outside the predefinable quality threshold range.It may be provided that the measurement curve of an electrode cap, whose milling quality specification exceeds the quality threshold and / or whose milling quality specification lies within the predefinable quality threshold range, is assigned a quality that exceeds the quality threshold and / or lies within the predefinable quality threshold range, so that in particular the measurement curve exceeds the quality threshold and / or lies within the predefinable quality threshold range.

[0032] One advantage of this advanced training is that machine learning can be used to easily determine at least one characteristic feature. Specifically, it can be defined how reliably and / or securely the characteristic feature can distinguish a measurement curve that falls below the predefined quality threshold and / or lies outside the predefined quality threshold range and / or was generated using a faulty electrode cap cutter, from a measurement curve whose milling quality exceeds the predefined quality threshold and / or lies within the predefined quality threshold range and / or is not generated using a faulty electrode cap cutter.

[0033] Further training includes the conclusion that a faulty electrode cap milling cutter is present if, during several successive milling passes of different electrode caps with the same electrode cap milling cutter, the different electrode caps fall below a predefinable milling quality and / or if, during several successive milling passes of different electrode caps with the same electrode cap milling cutter, at least one of the characteristic features in the measurement curve of the different electrode caps is determined.

[0034] The defective electrode cap milling cutter is specifically one where the milling quality of the electrode caps after milling falls below the predefined quality threshold and / or lies outside the predefined quality threshold range, regardless of the condition of the electrode caps before milling (especially if the milling quality was already below the predefined quality threshold before milling). In particular, the reason for the milling quality falling below the predefined quality threshold and / or lying outside the predefined quality threshold range lies within the electrode cap milling cutter itself, if it is defective.For example, an incorrect setting of the electrode cap cutter and / or a dull milling tool and / or an incorrectly set milling tool and / or incorrect programming of the electrode cap cutter can lead to a faulty electrode cap cutter.

[0035] A defective electrode cap cutter can be identified by comparing multiple milling passes of different electrode caps, all performed with the same cutter. If, for all electrode caps and / or a predefined portion of the electrode caps (e.g., at least 80% and / or at least 90% of the electrode caps), all milled with the same cutter, a milling quality rating is determined that falls below a predefined milling quality rating and / or the predefined quality threshold and / or is outside the predefined quality threshold range and / or exhibits at least one characteristic feature, then the electrode cap cutter can be considered defective.

[0036] It may be possible to have the system issue a notification when a faulty electrode cap cutter is detected, indicating, for example, that the electrode cap cutter needs to be repaired and / or replaced. Additionally or alternatively, an automated correction of the electrode cap cutter can be performed, for example, by automatically adjusting its settings.

[0037] The advantage of this advanced training is that it allows for the simple identification of a faulty electrode cap milling cutter, thereby determining the cause of errors resulting from the milling quality falling below the specified quality threshold and / or falling outside the specified quality threshold range. In particular, correcting the faulty electrode cap milling cutter can prevent the need for rework of multiple electrode caps.

[0038] Further training includes repeating the milling process and / or performing targeted rework on any electrode cap whose milling quality falls below the specified quality threshold and / or falls outside the specified quality threshold range. Specifically, this means that if it is detected that the milling quality of an electrode cap falls below the specified quality threshold and / or falls outside the specified quality threshold range, the electrode cap will be re-milled using the same electrode cap cutter and / or a different electrode cap cutter will be used, and / or targeted rework will be performed on that electrode cap.

[0039] The repeated milling process includes, in particular, the re-milling of the electrode cap, for example by removing part of the surface of the respective electrode cap and / or removing a layer and / or an upper layer and / or part of the surface of the electrode cap.

[0040] The targeted post-processing of the electrode cap includes, in particular, determining, for example, using the measurement curve, where the electrode cap differs from an electrode cap whose milling quality exceeds the specified quality threshold and / or lies within the specified quality threshold range. This means, for example, that a 3D model of the electrode cap is created, for instance, based on the measurement curve, and this 3D model is compared with a model of a reference electrode cap whose milling quality exceeds the specified quality threshold and / or lies within the specified quality threshold range.The 3D model of the electrode cap can be derived from the measurement curve, for example, by assigning a profile height to each of the force values ​​recorded at different times during the milling process. These force values ​​correspond to different points and / or locations on the electrode cap's surface, and together they form a height profile of the electrode cap. Based on this height profile, the 3D model of the electrode cap can be created and compared to the model of the reference electrode cap. Any areas where the 3D model of the electrode cap differs from the model of the reference electrode cap, particularly by more than a predefined threshold, can be highlighted so that these areas can be corrected manually and / or automatically.In particular, each marked location can be assigned a value indicating how much material must and / or should be removed from that location so that, after targeted post-processing of the electrode cap, it has a milling quality specification that exceeds the predefinable quality threshold and / or lies within the predefinable quality threshold range.

[0041] Each subsequent milling pass and / or targeted reworking of the electrode cap results in a revised electrode cap. Following this revision, a quality inspection is performed. This inspection determines the milling quality of the revised electrode cap and / or whether it falls below or outside the specified quality threshold.

[0042] The advantage of this advanced training is that electrode caps whose milling quality falls below the specified quality threshold and / or whose milling quality falls outside the specified quality threshold range can be reworked. This prevents the use of such electrode caps for any further resistance spot welding processes, as, for example, a specified quality of resistance spot welding cannot be guaranteed with these caps. By reworking the electrode caps, for example, through a repeat milling pass and / or targeted rework, the milling quality can be easily improved, thus enabling their use in at least one resistance spot welding process.

[0043] Further training includes the sorting out of the electrode cap and / or the reworked electrode cap and its use in no further resistance spot welding process if the milling quality specification of the reworked electrode cap falls below the predefined quality threshold and / or if the milling quality specification of the reworked electrode cap lies outside the predefined quality threshold range. This means, in particular, that the milling quality specification of the electrode cap is determined, and it is ascertained whether this milling quality specification falls below the predefined quality threshold and / or lies outside the predefined quality threshold range.If the milling quality falls below the specified quality threshold and / or is outside the specified quality threshold range, the milling process can be repeated and / or targeted reworking of the electrode cap can be carried out, resulting in a revised electrode cap for which the milling quality can also be determined. If the milling quality of the revised electrode cap falls below the specified quality threshold and / or is outside the specified quality threshold range, the revised electrode cap can be rejected, meaning that no further resistance spot welding process will be performed with it.

[0044] This prevents, in particular, the quality of a weld point produced by a resistance spot welding process from falling below a predefined quality value due to an electrode cap whose milling quality falls below or outside the predefined quality threshold range. Specifically, for a previously repaired electrode cap, further rework could be disproportionately costly, as an unsuccessful attempt has already been made. This would necessitate more extensive reworking of the electrode cap to improve the milling quality. The further training offers the particular advantage of saving costs associated with unsuccessful rework of an already improved electrode cap.

[0045] Further training includes checking a predefined number of weld points from resistance welding processes that were last performed with the electrode cap prior to quality inspection. This check is carried out if the milling quality falls below the predefined quality threshold and / or is outside the predefined quality threshold range, and / or if the force value exceeds a predefined maximum force value at an initial point in the measurement curve. Specifically, this means determining whether an electrode cap has a milling quality that falls below the predefined quality threshold and / or is outside the predefined quality threshold range, and / or whether the force value exceeds a predefined maximum force value at an initial point in the measurement curve.The predefinable maximum force value is, in particular, the maximum force value already described elsewhere in the application. The initial period of the measurement curve can be characterized, in particular, by the fact that it begins with the start of the measurement curve and has a predefinable duration, which is, in particular, shorter than the duration of the entire measurement curve. For example, the predefinable duration can be the time required by the milling tool for at least one and / or at least two and / or at least ten revolutions around the electrode cap and / or the electrode cap itself.

[0046] If the milling quality specification indicates that the maximum force value is exceeded during the initial phase of the measurement curve, and / or that the quality threshold is not met, and / or that the value is outside the specified quality threshold range, it may be necessary to determine which resistance spot welding processes were performed using this electrode cap. This allows for the identification of which weld points, i.e., which joints between at least two workpieces, were created using resistance spot welding processes and / or this electrode cap. It may also be necessary to verify at least a specified number of weld points that were last performed with this electrode cap prior to its quality inspection.This means, in particular, that the timing of the weld points from resistance welding processes using the electrode cap is determined relative to the start of the quality inspection. A predefined number of weld points is then selected, and / or those weld points are selected that are closest in time to when the quality inspection of the electrode cap began. In total, a predefined number of weld points, for example, at least 50, at least 20, at least 10, or the number of weld points between the last quality inspection and the current quality inspection of the electrode cap, can be selected for subsequent inspection.

[0047] The inspection of the weld points from the resistance spot welding processes includes, in particular, determining the quality of the weld points, for example by determining the lens diameter and / or by using a quality check of a weld point from a resistance spot welding process known from the prior art.

[0048] The advantage of this advanced training is that it allows for the simple identification of weld points where the probability of falling below a predefined quality value exceeds a predefined threshold. This is particularly relevant because the most recently performed weld points are checked when it is determined that the milling quality of the electrode cap falls below the predefined quality threshold and / or is outside the predefined quality threshold range. This is because falling below the predefined quality threshold due to the milling quality specification and / or being outside the predefined quality threshold range due to the milling quality specification can indicate an electrode cap for which a resistance spot welding process with a predefined quality is not possible.

[0049] Further training includes the following: In addition to the milling quality specification, an electrical quality specification is determined by measuring the electrical resistance of the electrode cap. Specifically, this means that the milling quality specification for the electrode cap is determined through quality control. Furthermore, an electrical resistance measurement is performed, as is used, for example, in the prior art for verifying the quality of the electrode cap. This electrical resistance measurement involves bringing the two electrode caps together, for example, so that they touch, instead of clamping at least two workpieces between them. The two electrode caps make contact, in particular, at the points that, during a resistance spot welding process, each contact at least one of the materials.While the two electrode caps are in contact, at least one of which is the electrode cap for which the milling quality specification was determined during quality control and / or at least one of the electrode caps, in particular the other electrode cap, is a reference electrode cap, a current may be provided to flow between the two electrode caps, allowing an electrical resistance between and / or within the electrode caps to be determined. This electrical resistance measurement allows the electrical quality specification to be determined, which, like the milling quality specification, can describe the quality of the electrode cap after the milling process.

[0050] The electrode cap will only be used for at least one resistance spot welding process, and in particular for at least one upcoming and / or future resistance spot welding process, if both the milling quality specification and the electrical quality specification exceed the predefined quality threshold and / or are within the predefined quality threshold range. This offers the advantage of more precise verification and / or the advantage of being able to detect with greater certainty if the electrode cap would lead to a reduced weld quality in a future resistance spot welding process.

[0051] Further training includes performing a quality check after a predefined number of resistance spot welding processes. Specifically, this means that after manufacturing, an electrode cap undergoes a predefined number of resistance spot welding processes, for example, between 50 and 200 and / or between 100 and 150, each producing one weld spot. A quality check is then performed. If the milling quality determined during the electrode cap's quality check exceeds the predefined quality threshold and / or falls within the predefined quality threshold range, the electrode cap can be used for another predefined number of resistance spot welding processes.

[0052] During the milling process, the size and / or diameter of the electrode cap is determined from the measurement curve. If a predefined size threshold is not met, the electrode cap is rejected instead of undergoing further quality control. Specifically, this means that the quality control check uses the measurement curve generated during the milling process to determine the size and / or diameter of the electrode cap after milling. The size and / or diameter of the electrode cap changes with each milling pass and / or quality control check, as each milling pass and / or quality control check involves removing the coating of the electrode cap and / or milling away a portion of the electrode cap's surface, thus reducing the diameter and / or size of the electrode cap with each pass.

[0053] From the measurement curve of each milling pass, which describes the force value (which can be lower the smaller the size and / or diameter of the electrode cap), the diameter and / or size of the electrode cap after the milling pass can be determined. If the size and / or diameter of the electrode cap falls below the predefined size threshold, this may mean that after a further milling pass, the size and / or diameter of the electrode cap is so small that the electrode cap cannot be used for any further resistance spot welding process, and / or that if the electrode cap is used for a further resistance spot welding process, a predefined quality for the weld spot cannot be guaranteed, and / or not with a predefined probability.If the size and / or diameter of the electrode cap falls below the specified size threshold, it may be provided that the electrode cap is marked so that, instead of a further milling process, the electrode cap is automatically sorted out during the next quality check.

[0054] The further training offers the advantage that, prior to quality control, the electrode cap is inspected to determine whether it can be used for at least one more resistance spot welding process based on its wear, size, and / or diameter. This results in a more effective method for quality control of the electrode cap and / or for determining whether an electrode cap needs to be rejected.

[0055] For use cases or application situations that may arise during the procedure and are not explicitly described here, it may be provided that, according to the procedure, an error message and / or a request for user feedback is issued and / or a default setting and / or a predetermined initial state is set.

[0056] Furthermore, a system comprising an electrode cap cutter and at least one electrode cap is disclosed, which is configured to carry out the method according to the invention.

[0057] The invention also includes the control device for the electrode cap milling cutter. The control device can comprise a data processing device or a processor circuit configured to execute an embodiment of the method according to the invention. For this purpose, the processor circuit can comprise at least one microprocessor and / or at least one microcontroller and / or at least one FPGA (Field Programmable Gate Array) and / or at least one DSP (Digital Signal Processor). In particular, a CPU (Central Processing Unit), a GPU (Graphics Processing Unit), or an NPU (Neural Processing Unit) can be used as the microprocessor. Furthermore, the processor circuit can comprise program code configured to execute the embodiment of the method according to the invention when performed by the processor circuit.The program code can be stored in a data memory of the processor device. The processor device can be based, for example, on at least one circuit board and / or on at least one SoC (System on Chip).

[0058] The invention also includes further developments of the system according to the invention, which have features already described in connection with the further developments of the method according to the invention. For this reason, the corresponding further developments of the system according to the invention are not described again here.

[0059] As a further solution, the invention also includes a computer-readable storage medium comprising program code which, when executed by a computer or a computer network, causes it to execute an embodiment of the method according to the invention. The storage medium can be provided at least partially as a non-volatile data storage medium (e.g., as flash memory and / or as an SSD - solid state drive) and / or at least partially as a volatile data storage medium (e.g., as RAM - random access memory). The storage medium can be located within the computer or computer network. However, the storage medium can also be operated, for example, as an app store server and / or cloud server on the internet. The computer or computer network can provide a processor circuit with, for example, at least one microprocessor.The program code can be provided as binary code, assembly code, source code in a programming language (e.g., C), or a program script (e.g., Python). Alternatively, the computer-readable storage medium can be implemented as a signal containing computer-readable data, such as a time-varying voltage signal or a radio signal.

[0060] The invention also includes combinations of the features of the described embodiments. The invention therefore also includes realizations that each exhibit a combination of the features of several of the described embodiments, provided that the embodiments have not been described as mutually exclusive.

[0061] The following are exemplary embodiments of the invention described. This is illustrated by: Fig. 1 an exemplary schematic representation of the method according to the invention; and Fig. 2 an exemplary insertion of an electrode cap into an electrode cap cutter after at least one resistance spot welding process.

[0062] The exemplary embodiments described below are preferred embodiments of the invention. In these exemplary embodiments, the described components each represent individual features of the invention, which can be considered independently of one another and each further develops the invention independently. Therefore, the disclosure is intended to include combinations of features of the embodiments other than those shown. Furthermore, the described embodiments can also be supplemented by further features of the invention already described.

[0063] In the figures, identical reference symbols denote functionally equivalent elements.

[0064] Fig. Figure 1 shows exemplary steps of a procedure for checking the quality of at least one electrode cap 10, wherein not all of the steps shown need to be carried out to check the electrode cap 10 and / or only a part of the steps shown can be carried out.

[0065] The method for verifying the quality of at least one electrode cap 10 can be used for an electrode cap 10 that can be used for at least one resistance spot welding process S10. A resistance spot welding process S10 is, in particular, a process in which at least two workpieces 12 are joined together by melting a portion of the workpieces 12, especially in a localized area, pressing the workpieces 12 against each other by a force, and solidifying the molten area as the workpieces 12 cool. The molten area can be referred to as a lens 14, and the quality of the resistance spot welding process S10 can be determined via its lens diameter 16.A resistance spot welding process S10 can in particular create a weld point which can be characterized by the fact that at least two workpieces 12 are joined together, in particular within a predefinable delimited area.

[0066] To create the weld point at a predetermined location, a welding current can be supplied to the at least two workpieces 12 via electrode caps 10, between which at least two workpieces 12 are clamped and / or between which the at least two workpieces 12 are located, wherein the electrode cap 10 contacts and / or touches at least one of the workpieces 12, by which the material of the at least two workpieces 12 is melted at least in certain areas.

[0067] During a resistance spot welding process S10, at least one deposit 18 can form on the electrode cap 10, which negatively affects the quality of a subsequent resistance spot welding process and / or subsequent resistance spot welding processes S10. In particular, the at least one deposit 18 can lead to the at least two workpieces 12 not being as firmly joined after the resistance spot welding process S10 as they would be if the resistance spot welding process S10 were carried out with electrode caps 10 without the at least one deposit 18 and / or if an ideal resistance spot welding process S10 were carried out.

[0068] After at least one resistance spot welding process S10, it may be provided that at least one deposit 18 is removed. In order to remove the at least one deposit 18, it may be provided that the electrode cap 10 is milled using an electrode cap milling cutter 20, which in particular includes the fact that during a milling pass S20, for example, a surface and / or an upper layer and / or an outer layer of the electrode cap 10 is removed by means of a milling tool 22 of the electrode cap milling cutter 20.

[0069] It may be provided that during the removal of the layer and / or during the milling of the electrode cap 10 with the electrode cap cutter 20, i.e., in particular during the milling pass S20, a quality check of the electrode cap 10 is carried out, which describes the quality of the electrode cap 10 after the milling pass S20. This quality of the electrode cap 10 after the milling pass S20 can be described and / or specified via the milling quality specification. This quality check is in Fig. This is exemplified by step S21. The milling quality specification can be determined rule-based, for example, by defining at least one limit value, such as a maximum force value. Additionally or alternatively, the milling quality specification can be determined data-based, for example, by means of anomaly detection and / or machine learning (e.g., using a regression model), which can be trained using training data and / or categorized data.

[0070] To determine the milling quality specification, the electrode cap cutter 20 may be provided with at least one force sensor 24 which determines a force value 26 at various times during the milling process S20. The determination of the force value is in Fig. 1. This is summarized for example under step S11. The force value describes, in particular, the force 26 that is exerted between the electrode cap 10 and the milling tool 22 of the electrode cap cutter 20, which can be used to mill the electrode cap 10. This means, in particular, that the force value describes the force 26 with which the milling tool 22 presses against the electrode cap 10 during the milling pass S20 and / or vice versa. The force 26 is, in particular, perpendicular to the surface of the electrode cap 10 at the location of the milling tool 22.

[0071] During the milling process S20, the force value is recorded at various times, particularly continuously. This allows, especially in Fig.As exemplified by step S12, a measurement curve is created that indicates the respective force value at different times during the milling operation S20. This means that the measurement curve assigns a force value to each point in time during the milling operation S20. It may be possible to continuously record and / or determine the force values, and / or it may be possible to determine the force values ​​at predetermined times and / or within predetermined time periods during the milling operation S20, and to interpolate between the determined force values ​​to generate the measurement curve.

[0072] The determined measurement curve can be checked, for example in step S13, to determine whether it exhibits at least one characteristic feature. This characteristic feature is, in particular, a feature of the measurement curve of electrode cap 10 whose milling quality falls below a predefined quality threshold, but which is not present in a measurement curve of electrode cap 10 whose milling quality exceeds the predefined quality threshold. The characteristic feature could, for example, be an exceedance of a maximum force value by the measurement curve. For instance, a maximum force value could be assigned to each point in time in the measurement curve, and different points in time within the measurement curve could be assigned different maximum force values.If the measurement curve exceeds the maximum force value assigned to the respective time, the characteristic feature of exceeding the maximum force value can be assigned to the measurement curve.

[0073] Additionally or alternatively, characteristic features and / or at least one characteristic feature can be determined by providing training data to a machine learning model. The training data could, for example, consist of measurement curves, each of which is assigned the milling quality rating of electrode cap 10 after milling operation S20. This allows the machine learning model to determine, by comparing the training data, and in particular by comparing the different measurement curves, which features of the measurement curve are typical for a given milling quality rating range and / or can be assigned to a given milling quality rating.Additionally or alternatively, the training data may indicate whether the measurement curve was recorded with a faulty electrode cap cutter 20, so that the machine learning model can determine at least one characteristic feature by which a faulty electrode cap cutter 20 can be inferred from the measurement curve.

[0074] The characteristic features are, in particular, features of the measurement curve that exhibit measurement curves, especially a predefinable percentage of the measurement curves of the training data, for example, at least 50% or at least 80% and / or at least 90% of the measurement curves of the training data to which a milling quality indication is assigned that is lower than a predefinable quality threshold. In particular, none and / or a maximum of 10% and / or a maximum of 20% and / or a maximum of 50% of the measurement curves of the training data whose electrode cap 10 is assigned a milling quality indication after the milling pass S20 that exceeds the predefinable quality threshold exhibit the respective characteristic feature.

[0075] Depending on the number and / or severity of the characteristic features exhibited by a measurement curve, a conclusion can be drawn, for example in step S14, regarding the milling quality of the electrode cap 10 for which the measurement curve was determined during milling operation S20. It can be stipulated that the more characteristic features the measurement curve includes and / or the more pronounced a characteristic feature of the measurement curve is, the lower the milling quality rating assigned to the respective measurement curve and thus to the respective electrode cap 10 after milling operation S20.

[0076] In addition to the milling quality specification, an electrical quality specification can be determined, for example in step S15, using a prior art method for verifying the quality of an electrode cap 10. This method may include measuring the electrical resistance between two electrode caps 10, in particular between a reference electrode cap and the electrode cap 10 for which the electrical quality specification is to be given. The electrical quality specification can be determined, for example, by bringing the two electrode caps 10 together and passing a current through them while measuring the electrical resistance. It may be possible to use the electrode cap 10 for at least one further resistance spot welding process S10 if the milling quality specification exceeds a predefinable quality threshold.In particular, it may be intended that the electrode cap 10 is used for at least one resistance spot welding process S10 only if both the milling quality specification and the electrical quality specification exceed the predefinable quality threshold. The predefinable quality threshold may, in particular, be chosen such that an electrode cap 10 whose milling quality specification exceeds the predefinable quality threshold and / or an electrode cap 10 whose electrical quality specification exceeds the predefinable quality threshold produces a weld spot in at least one resistance spot welding process S10 that exhibits at least a predefinable quality.

[0077] The quality of a weld spot from a resistance spot welding process S10 can be specified, for example, by the lens diameter 16. The lens diameter 16 describes, in particular, the diameter of the area that was liquefied during the resistance spot welding process S10 and which, after cooling, can ensure the cohesion of the at least two workpieces 12 (lens 14).

[0078] If it is determined that the milling quality falls below the predefined quality threshold, it may be stipulated, for example in step S30, that another milling pass S20 is performed and / or targeted reworking of the electrode cap 10 is carried out. This means, in particular, that at least part of the surface of the electrode cap 10, for which a milling pass S20 has already been performed, is abraded and / or removed, especially with the aim of increasing the milling quality. The rework, which includes, in particular, repeating the milling pass S20 and / or the targeted reworking of the electrode cap 10, results in the reworked electrode cap 10, for which a new quality inspection is carried out. This means, in particular, that an electrical quality rating and / or a milling quality rating is determined for the reworked electrode cap 10.If the quality inspection of the repaired electrode cap 10 reveals a milling quality specification and / or an electrical quality specification that falls below the specified quality threshold, the electrode cap 10 may be rejected. This means, in particular, that the electrode cap 10 will not be used for any further resistance spot welding process S10.

[0079] An electrode cap 10 whose milling quality rating falls below the predefined quality threshold may have exhibited at least one deposit 18 before the milling operation, which could cause the quality of resistance spot welding processes S10 to fall below a predefined quality before the milling operation S20. Accordingly, it may be necessary to check the last weld spots produced before the milling operation from resistance spot welding processes S10, which were carried out with an electrode cap 10 whose milling quality rating after the milling operation S20 falls below the predefined quality threshold and / or whose measurement curve exceeds a predefined maximum force value in an initial period of the measurement curve. The check may include examining these weld spots for their quality, for example, by determining the lens diameter 16 of the weld spots.A check of recently performed weld points can be carried out if a predefined maximum force value is exceeded at the beginning of the measurement curve. This is primarily because a force value that is high at the beginning of the measurement curve, and thus exceeds the maximum force value, indicates at least one deposit 18 on the electrode cap 10, which can cause the predefined quality of recently performed weld points to fall below a certain level.

[0080] If the milling quality specifications of several different electrode caps 10, which have each undergone the milling cycle S20 consecutively with the same electrode cap cutter 20, fall below the predefinable quality threshold and / or exhibit at least one characteristic defect, this may indicate a defective electrode cap cutter 20. In particular, it may be provided that in this case a warning is issued indicating that a defective electrode cap cutter 20 may be present.

[0081] With each milling pass S20, a layer is removed from the electrode cap 10, thus reducing the size and / or diameter of the electrode cap 10 with each milling pass S20. If the diameter and / or size of the electrode cap 10 falls below a predefinable size threshold, it may be necessary that the size and / or diameter of the electrode cap 10 be too small after a further milling pass S20, so that a predefinable quality for at least one further resistance spot welding process S10 cannot be guaranteed. For this reason, it may be necessary to determine the size and / or diameter of the electrode cap 10 during a milling pass S20 using the measurement curve. This can be done by inferring the size and / or diameter from the force 26 applied between the milling tool 22 and the electrode cap 10.The smaller the diameter and / or size of the electrode cap 10, the lower the force 26 exerted between the electrode cap 10 and the milling tool 22. If the size and / or diameter of the electrode cap 10 falls below a predefinable size threshold, it may be provided that the electrode cap 10 is marked so that, after a predefinable number of resistance spot welding processes S10, after which a quality inspection should normally be carried out, the electrode cap 10 is sorted out instead of being used for any further resistance spot welding process S10.

[0082] Overall, the examples show how a method for quality control can be provided by evaluating the sensor data during the mechanical processing of the electrode caps.

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