Method for analyzing welded joints during laser welding of workpieces

Abstract

The invention relates to a method for analyzing a weld connection during laser welding of workpieces (30a, 30b), the method comprising: detecting (S1) a first measurement signal (P1, P2) for process radiation generated during the laser welding; detecting (S2) a second measurement signal (P3) for radiation reflected by the workpieces (30a, 30b); determining (S3) whether a gap (S) is present between the workpieces based on the first measurement signal (P1, P2); and, if it is determined that a gap (S) is present, determining (S4) whether a weld connection is present based on the second measurement signal (P3).

Description

Technical Field

[0001] The invention relates to a method for analyzing a welded joint during laser welding of workpieces, in particular during the laser welding process. Background Art

[0002] In a laser processing system for processing workpieces using a laser beam, a laser beam emitted from one end of a laser source or laser-conducting fiber is focused or bundled onto the workpiece to be processed using beam guidance and focusing optics. This processing can include, for example, laser welding. The laser processing system can include laser processing equipment, such as a laser processing head, particularly a laser welding head. When laser welding workpieces, it is particularly important to continuously monitor the welding process to ensure processing quality. This includes detecting processing errors.

[0003] The machining process is typically monitored by detecting and analyzing various parameters of the process radiation, also referred to as process beam, process light, or process radiation. This includes, for example, plasma radiation generated by the machining process from the workpiece surface, process radiation in the infrared range (e.g., temperature radiation), or process radiation in the visible range. An evaluation is then performed, in which the corresponding measurement signals are checked to see whether certain conditions are met. If one or more measurement signals meet predefined conditions during machining, an error signal is output. Accordingly, the machined workpiece can be labeled as "good" or "qualified" (i.e., suitable for reprocessing or sale) or as "bad" or "substandard" (i.e., scrap). Continuous monitoring of the laser machining process typically occurs in real time during the process, and is therefore also referred to as online process monitoring or in-line process monitoring.

[0004] Application DE 10 2019 122 047 describes a sensor module for monitoring a laser welding process, which has a plurality of detectors or sensors that detect different parameters of the process radiation and output them as measurement signals.

[0005] In the field of electric vehicles, batteries play a central role. The individual battery cells (also called storage battery cells) are connected to each other, that is, they are connected. A composite structure composed of multiple battery cells is called a "battery module". This connection is usually achieved by laser welding. Here, the dischargers (ableiter) of the battery cells are typically connected to each other in overlapping seams by laser welding. The weld seam has, for example, a so-called "I-shaped seam" geometry. The materials are usually aluminum and copper. Typical connections or material combinations are copper-copper, aluminum-aluminum and copper-aluminum. Therefore, when connecting battery cells to form a battery module, it is important for successful module construction that there is an electrical connection between the connected workpieces, that is, current can flow between the connected workpieces or through the weld seam. Only in this case is the contact connection successful.

[0006] During laser welding, in particular in overlapping seams with I-shaped seams, typical error patterns can occur. This includes gaps between the workpieces. This error can be tolerated when there is a weld connection, i.e., when the gap is bridged by the molten material of the workpieces, i.e., when, despite the presence of a gap, there is still an electrical connection between the workpieces to be welded. This is also referred to as a "weld with a gap bridge" or a "gap with an (electrical) connection." Another typical error pattern is called a "false friend" (English: false friend, German: falscher Freund)." Here, there is a gap between the connected workpieces, wherein the gap is not bridged and therefore there is no (electrical) connection between the workpieces. This is also referred to as a "weld without a gap bridge" or a "gap without an (electrical) connection." In other words, the gap between the workpieces should be as non-existent as possible or as small as possible.

[0007] When viewed from above, especially during inspection after laser welding has been performed, it is not possible to distinguish purely visually whether there is a weld that conforms to regulations, i.e., a weld without a gap (also referred to as a "good weld" or a "zero-gap weld"), or whether there is a weld with a gap but a gap bridge, i.e., a welded connection with a gap, or a weld with a gap but no gap bridge. Currently, it is not possible to detect false objects during the welding process. Summary of the Invention

[0008] The object of the present invention is to analyze or evaluate welded connections between workpieces in laser welding in a simple and rapid manner.

[0009] The object of the present invention is to enable a simple and rapid differentiation during laser welding between welds without a gap and welds with a gap.

[0010] In particular, the object of the present invention is to identify, in the case of a weld with a gap between the workpieces, whether a gap with a gap bridge, i.e., an electrical contact between the workpieces, or a gap without a connection, i.e., without an electrical contact between the workpieces, is present.

[0011] Another object of the present invention is to enable an analysis or differentiation to be carried out in real time, in particular during the laser welding process of the welded connection.

[0012] This object is achieved by the present invention. The present invention also provides advantageous embodiments and developments.

[0013] The present invention is based on the idea of ​​detecting and suitably evaluating measurement signals based on process radiation and backreflected laser radiation generated during laser welding of welded connections, in particular during the laser welding process, in order to thereby analyze or differentiate welds or welded connections. The measurement signals can be detected by a sensor, in particular a photodiode.

[0014] According to one aspect of the present invention, a method for analyzing or evaluating welded joints during laser welding of workpieces is provided, wherein the method comprises the following steps: detecting a first measurement signal for process radiation generated during laser welding; detecting a second measurement signal for radiation reflected by the workpieces; determining whether a gap exists between the connected workpieces based on the first measurement signal; and, if the presence of a gap is determined, determining whether a welded joint exists based on the second measurement signal. The reflected radiation may include at least one of the following: reflected laser radiation of a (processing) laser beam, reflected LED radiation or LED light, and reflected pilot laser radiation. The method may further include irradiating the LED radiation or illuminating with the aid of the LED light, in particular irradiating a current processing position or an area surrounding a current point of incidence of the (processing) laser beam. The method may further include irradiating the pilot laser beam, in particular into the current processing position or an area surrounding a current point of incidence of the (processing) laser beam. The reflected radiation or pilot laser beam or LED light can have any wavelength, in particular a wavelength in the infrared range or in the green or blue visible range. In particular, the LED light source or pilot laser beam source can have a wavelength of approximately 630 nm or approximately 530 nm, for example. Preferably, at least a portion of the beam path of the LED light or pilot laser beam incident on the processing region extends coaxially with the beam path of the processing laser beam.

[0015] Therefore, the method according to the present invention can be used to identify whether a gap exists between connected workpieces. In addition, the method according to the present invention can be used to identify whether a welded connection exists. The welded connection can represent an electrical and / or mechanical (i.e., physical) welded connection, i.e., an electrical connection or a mechanical connection exists between the workpieces. A welded connection exists when there is no gap between the connected workpieces (so-called zero gap), or when there is a gap but the gap is bridged (a gap with a gap bridge). When the gap is not bridged, there is no welded connection. Therefore, for example, when connecting battery cells to form a battery module, the method for analyzing welded electrical connections can be used in particular to identify whether an electrical connection is missing between the connected workpieces. Therefore, according to the present invention, it is possible to distinguish between good welds or welds without gaps and welds with gaps, and it is possible to distinguish between welds with gaps and welds without gap bridges.

[0016] Furthermore, welds can be classified as: (i) welds that meet specifications, i.e., welds without gaps (also referred to as "good welds" or "zero-gap welds"), (ii) welds with gaps and gap bridges, so that there is (electrical or mechanical) contact between the connected workpieces, and (iii) welds with gaps but no gap bridges, so that there is no (electrical or mechanical) contact between the connected workpieces. This classification is preferably also performed during laser welding, i.e., during the laser welding process used to produce the weld.

[0017] Preferably, when the presence of a welded connection is determined, the workpieces connected by laser welding are evaluated or marked as "good" or "qualified", and when the absence of a welded connection is determined, they are evaluated or marked as "poor" or "inferior". Based on this, the laser welding can also be regulated or controlled. For example, processing parameters such as the provided laser power, the distance between the laser processing device and the workpiece, the focal position and / or the focus position of the laser beam used for laser processing can be adjusted or regulated, especially in real time. The method can also include: outputting an error to the workpiece when the absence of a welded connection is determined, and / or outputting a warning to the workpiece when the presence of a gap is determined, especially a gap with a gap width greater than a predetermined value.

[0018] In one embodiment, the presence of a weld connection or a gap bridge can be determined based on the second measurement signal only if the presence of a gap has been determined in advance.

[0019] At least one step of the method according to the present invention can be performed during laser welding of the weld, in particular in real time. Therefore, the method according to the present invention can be referred to as an "in-line method." Preferably, the first and / or second measurement signals are detected during laser welding. Similarly, the presence of a gap and / or the presence of a welded connection or gap bridging can be determined during laser welding. Preferably, the entire method according to the present invention is performed during laser welding.

[0020] The method according to the invention can be used, in particular during laser welding, to weld the overlapping seams Or used in parallel seams (Parallels to β).

[0021] The first measurement signal and / or the second measurement signal can be based on a measurement of radiation intensity. In particular, the first measurement signal can be based on a measurement of the radiation intensity of process radiation, and / or the second measurement signal can be based on a measurement of the radiation intensity of reflected radiation, for example, reflected laser radiation. The process radiation generated during laser welding can include temperature radiation in the infrared wavelength range and / or plasma radiation in the visible wavelength range.

[0022] The first measurement signal can be detected in a first wavelength range that is higher than the wavelength of the laser beam used for laser welding and / or higher than the wavelength of the reflected radiation. Alternatively or additionally, the first measurement signal can be detected in a second wavelength range that is lower than the wavelength of the laser beam used for laser welding and / or lower than the wavelength of the reflected radiation. The first wavelength range can correspond to the infrared wavelength range of light. In other words, the first measurement signal in the first wavelength range can correspond to temperature radiation. The second wavelength range can correspond to the visible range of light. In other words, the first measurement signal in the second wavelength range can correspond to plasma radiation. The first measurement signal in the first wavelength range can be detected by at least one first photodiode having spectral sensitivity in the first wavelength range. The first measurement signal in the second wavelength range can be detected by at least one second photodiode having spectral sensitivity in the second wavelength range. In other words, the first measurement signal is preferably detected separately in the first wavelength range and in the second wavelength range, or respectively by at least one photodiode.

[0023] The second measurement signal or reflected radiation, in particular reflected laser radiation, or the laser beam for laser welding or the incident pilot laser beam or incident LED light, can be in the infrared, blue, or green wavelength range or spectral range. In other words, an infrared laser beam source can be used as the beam source for the (processing) laser beam or the pilot laser beam. Alternatively, the laser beam source for the laser welding laser beam or the pilot laser beam can emit in the green or blue spectral range or wavelength range.

[0024] That is, the first measurement signal can be detected based on the detection of the radiation intensity of process radiation in a first wavelength range, in particular in the infrared range, in order to detect temperature radiation, and / or the first measurement signal can be detected based on the detection of the radiation intensity of process radiation in a second wavelength range, in particular in the visible range, in order to detect plasma radiation. Accordingly, the first measurement signal detected in the first wavelength range can be referred to as a "temperature signal." Accordingly, the first measurement signal detected in the second wavelength range can be referred to as a "plasma signal."

[0025] The process radiation generated during laser welding can be detected as a first measurement signal by at least one (first and / or second) photodiode, and / or the reflected radiation can be detected as a second measurement signal by at least one (third) photodiode. The third photodiode can have a spectral sensitivity in the wavelength range of the laser light used for laser welding. In other words, the first and second measurement signals are preferably detected separately, or respectively by at least one photodiode. The photodiodes preferably have different spectral sensitivities.

[0026] Determining whether a gap exists between the workpieces can include determining a gap width based on the first measurement signal. In this case, the presence of a gap is determined when the gap width is greater than a predetermined gap width limit value. The gap width limit value can be between 50 μm and 200 μm, in particular between 100 μm and 175 μm, or can be 50 μm, 100 μm, or 150 μm.

[0027] The gap width can be defined, for example, as the shortest distance between the connected workpieces adjacent to the weld or weld seam but outside the weld or weld seam. For example, the gap width can be defined as the shortest distance between oppositely arranged workpiece surfaces, for example in the case of overlapping or parallel joints.

[0028] Determining whether a gap exists between the workpieces may include determining whether the first measurement signal is lower than a reference value or a reference curve. If the first measurement signal is detected for the first wavelength range and the second wavelength range, respectively, it may be determined whether the first measurement signal for the first wavelength range is lower than the first reference value or the first reference curve, and whether the first measurement signal for the second wavelength range is lower than the second reference value or the second reference curve. The reference curve may be a lower envelope curve. In this case, when the measurement signal is lower than the reference value or the reference curve, it may be determined that a gap exists between the workpieces. Determining whether a gap exists between the workpieces may also include determining whether the first measurement signal drops below the reference value or the reference curve. In this case, when the measurement signal drops below the reference value or the reference curve, it may be determined that a gap exists between the workpieces.

[0029] Determining whether a gap exists between the workpieces can include calculating a first integral of the first measurement signal. In this case, the presence of a gap between the workpieces can be determined when the first integral falls below a predetermined first integral limit. The first integral can be calculated over at least one range of the first measurement signal.

[0030] Alternatively or additionally, determining whether a gap exists between the workpieces can include determining a first average value of the first measurement signal. In this case, the presence of a gap between the workpieces can be determined if the first average value falls below a predetermined first average value limit value. A first average value curve can be determined over at least one range of the first measurement signal.

[0031] Alternatively or additionally, determining whether a gap exists between the workpieces can include determining a first outlier frequency of the first measurement signal. In this case, the presence of a gap between the workpieces can be determined when the outlier frequency of the first measurement signal exceeds a predetermined first outlier limit value. The first outlier frequency can be determined within at least one range of the first measurement signal.

[0032] If the first measurement signal is detected for the first wavelength range and the second wavelength range, respectively, determining whether a gap exists between the workpieces can include calculating a first integral of the first measurement signal (i.e., the temperature signal) detected in the first wavelength range and calculating a second integral of the first measurement signal (i.e., the plasma signal) detected in the second wavelength range, wherein the presence of a gap between the workpieces is determined when the first integral is below a predetermined first integral limit value and / or when the second integral is below a predetermined second average value limit value.

[0033] If the first measurement signal is detected for the first wavelength range and the second wavelength range, respectively, determining whether a gap exists between the workpieces can include calculating a first average value of the first measurement signal (i.e., the temperature signal) detected in the first wavelength range and calculating a second average value of the first measurement signal (i.e., the plasma signal) detected in the second wavelength range, wherein the presence of a gap between the workpieces is determined when the first average value is below a predetermined first average value limit value and / or when the second average value is below a predetermined second average value limit value.

[0034] If the first measurement signal is detected for a first wavelength range and a second wavelength range, respectively, determining whether a gap exists between the workpieces can include determining a first outlier frequency of the first measurement signal (i.e., the temperature signal) detected in the first wavelength range and calculating a second outlier frequency of the first measurement signal (i.e., the plasma signal) detected in the second wavelength range. In this case, the presence of a gap between the workpieces can be determined when the first outlier frequency is above a predetermined first outlier limit value and / or when the second outlier frequency is above a predetermined second outlier limit value.

[0035] The outlier frequency can be defined as the frequency or number of values ​​of the first measurement signal that lie outside a predefined envelope curve for the first measurement signal. The outlier frequency can be specified as a percentage with respect to an observed and / or predefined time interval or measurement interval or with respect to an observed and / or predefined range of the first measurement signal. Alternatively, the outlier frequency can be specified as an absolute value. If the first measurement signal is detected in a first wavelength range and a second wavelength range, the first outlier frequency and the second outlier frequency can be determined separately, i.e. the first outlier frequency is determined based on the frequency or number of values ​​of the first measurement signal of the first wavelength range that lie outside a predefined first envelope curve for the first measurement signal, and the second outlier frequency is determined based on the frequency or number of values ​​of the first measurement signal of the second wavelength range that lie outside a predefined second envelope curve for the first measurement signal.

[0036] The determination of whether a welded connection or a gap bridge is present can be based on the noise of the second measurement signal. The noise can be determined, for example, as a deviation from the mean value of the second measurement signal within a predetermined time interval or measurement interval or within a observed and / or predetermined range of the second measurement signal, and an amplification factor can optionally be provided. The noise can also be referred to as the "noise signal" or "noise component" of the second measurement signal.

[0037] The absence of a welded connection or a gap bridge can be determined if the outlier frequency of the noise of the second measurement signal is above a predefined first noise limit and / or if the integral of the noise of the second measurement signal is above a predefined second noise limit.

[0038] The outlier frequency of the noise of the second measurement signal can be defined as the frequency or number of noise values ​​that lie outside a predetermined envelope curve and / or a predetermined tolerance range for the noise. The outlier frequency can be specified as a percentage relative to an observed and / or predetermined time interval or measurement interval or relative to the range of the second measurement signal. Alternatively, the outlier frequency can be specified as an absolute value.

[0039] At least one of the workpieces can include or consist of aluminum and / or copper and / or nickel. In particular, one of the workpieces can consist of aluminum, while the other of the workpieces can include copper, wherein the latter can optionally be coated with nickel (layer thickness, for example, 8 μm). This coating can be applied electrolytically.

[0040] At least one of the workpieces has a thickness of 0.10 mm to 0.50 mm, preferably a thickness of 0.15 mm to 0.35 mm, particularly preferably a thickness of 0.20 mm to 0.30 mm.

[0041] The workpiece may be or may include a plate or a discharger. One of the workpieces may include a battery, a battery module, and / or a battery cell, and / or another of the workpieces may include a discharger. A welded electrical connection between the discharger and the battery cell may be analyzed as a weld.

[0042] According to another aspect of the present disclosure, a method for laser welding a first workpiece and a second workpiece is proposed, the method comprising the following steps: arranging the workpieces so that a first surface of the first workpiece and a first surface of the second workpiece are superimposed on each other or connected to each other; laser welding the workpieces by irradiating a laser beam onto the second surface of the first workpiece to construct a weld connection between the workpieces, wherein the second surface of the first workpiece is opposite to the first surface of the first workpiece, and / or laser welding is performed by irradiating a laser beam onto the second surface of the second workpiece to construct a weld connection between the workpieces, wherein the second surface of the second workpiece is opposite to the first surface of the second workpiece; and performing the aforementioned method for analyzing the weld connection.

[0043] The first and second surfaces of the first workpiece and / or the first and second surfaces of the second workpiece may be configured parallel to one another. The first and / or second workpiece may be configured as a plate or a discharger, or may include a plate or a discharger. The first and second surfaces of the workpieces may be referred to as major surfaces of the workpieces.

[0044] The first surfaces of the workpieces may be in contact in at least one region. In another region, a gap may exist between the workpieces.

[0045] The workpieces can be arranged with the goal that gaps between the workpieces are non-existent or as small as possible. The workpieces can be arranged in overlapping joints or parallel joints.

[0046] The method according to the present invention can be performed by a laser processing system comprising a laser processing device, in particular a laser welding head, for processing a workpiece using a laser beam, and a sensor module. The laser processing device may include a beam splitter for coupling process radiation out of the beam path of the laser beam. The laser processing device may include an optical output for coupling out the process radiation, and the sensor module may include an optical input for coupling in the process radiation emitted from the laser processing device. The sensor module includes at least one detector for detecting the process radiation and for detecting reflected radiation, in this example, reflected laser radiation of the (processing) laser beam. In one embodiment, the laser processing system may include an LED illumination unit for injecting LED light. In this case, the reflected radiation detected by the sensor module includes reflected LED radiation or reflected LED light. In another embodiment, the laser processing system may include a pilot laser unit for injecting a pilot laser beam. In this case, the reflected radiation detected by the sensor module includes reflected pilot laser radiation or reflected LED light. The pilot laser unit may include a pilot laser beam source. The laser processing system may include a pilot laser beam source, for example, for generating a pilot laser beam having a wavelength of approximately 630 nm or approximately 530 nm. Alternatively or additionally, the laser processing system may include an LED source for generating LED light. The LED light may be coupled into the beam path of the processing laser beam or into the laser processing device, for example, via a beam splitter. A sensor module may be coupled to the laser processing device. At least one detector may be configured to detect at least one beam parameter of the process radiation, in particular, its intensity within a specific wavelength range. The at least one detector may also be configured to output a measurement signal based on this detection. The detector may include a photodiode and / or a photodiode array and / or a camera, for example, a CMOS-based or CCD-based camera. The sensor module may include multiple detectors, each configured to detect the process radiation at different wavelengths or within different wavelength ranges. The laser processing system may also include a control unit. The control unit may be configured to receive an analog measurement signal from the at least one detector. The control unit can be configured to execute a method according to one of the embodiments listed in the present disclosure for analyzing a weld connection. The control unit can also be configured to regulate or control a laser processing system, in particular a laser processing device, in the manner described above based on the results of the analysis.

[0047] The corresponding detectors may be sensitive only at specific wavelengths or only within specific wavelength ranges. For example, a first detector may be sensitive in the visible range of light, a second detector may be sensitive in the infrared range, and / or a third detector may be sensitive in the wavelength range of the laser emission of the laser processing system. That is, the detectors may be configured so that they are sensitive in different wavelength ranges. According to one embodiment, the sensor module includes a first detector having a photodiode sensitive in the visible spectrum of light to detect plasma process emission or plasma radiation, a second detector having a photodiode sensitive in the infrared wavelength range to detect temperature process emission or temperature radiation, and a third detector having a photodiode sensitive in the laser emission wavelength range to detect back reflections from the laser of the laser processing system. Thus, the method according to the invention can be performed with the aid of a laser processing system. In particular, the described sensor module can detect a first measurement signal, in particular a temperature signal and / or a plasma signal, and a second measurement signal.

[0048] According to the present disclosure, a method is proposed for detecting gaps, in particular by means of a sensor such as a photodiode, and in particular for distinguishing gaps having a connection or a feedthrough from gaps having no connection or feedthrough. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] The present invention will be described in detail below with reference to the accompanying drawings.

[0050] Figure 1 A schematic diagram of a laser processing system for processing a workpiece by means of a laser beam, the laser processing system being used to carry out a method for analyzing a weld connection according to an embodiment of the present disclosure;

[0051] Figure 2 Show Figure 1 Detailed schematic diagram of the sensor module of the laser processing system shown in;

[0052] Figure 3 A flow chart showing a method for analyzing a weld connection during laser welding according to an embodiment of the present disclosure;

[0053] Figures 4A-4D shows a welded connection that has been analyzed using a method for analyzing welded connections during laser welding of workpieces according to an embodiment of the present disclosure;

[0054] Figures 5A-5Dshows, by way of example, a time profile of a measurement signal detected by a method according to an embodiment for analyzing a weld connection during laser welding of workpieces; and

[0055] Figure 6 The determination of the gap width by a method for analyzing a weld joint during laser welding of workpieces according to one embodiment of the present disclosure is shown by way of example. DETAILED DESCRIPTION

[0056] Unless otherwise indicated, the same reference numerals are used below for identical and identically functioning elements.

[0057] Figure 1 A schematic diagram of a laser processing system for processing a workpiece by means of a (processing) laser beam according to embodiments of the present disclosure is schematically shown. Figure 2 Show Figure 1 Detailed schematic diagram of the sensor module of the laser processing system is shown.

[0058] The laser processing system 1 includes a laser processing device 10 , a sensor module 20 , and a control unit 40 .

[0059] The laser processing device 10 can be configured, for example, as a laser processing head, in particular a laser welding head, which is configured to focus or bundle a (processing) laser beam (not shown) emitted from a laser source or one end of a laser-conducting fiber onto a workpiece 30a, 30b to be processed using beam guidance and focusing optics (not shown) in order to thereby perform processing or a processing process. This processing can, in particular, include laser welding. During processing, process radiation 11 is generated, which enters the laser processing device 10 and is coupled out of the beam path of the laser beam by a beam splitter 12. This process radiation is directed into a sensor module 20 and is incident there on at least one detector D1, D2, D3.

[0060] For processing, the workpieces 30a, 30b can be arranged such that they overlap one another. In particular, the workpieces 30a, 30b can be arranged in parallel joints or overlapping joints.

[0061] like Figure 1 As shown, for example, the lower surface of workpiece 30a is opposite the upper surface of workpiece 30b, and the laser beam impinges on the upper surface of workpiece 30a. The upper and lower surfaces of workpieces 30a, 30b may also be referred to as main faces or main surfaces of workpieces 30a, 30b.

[0062] As shown in the figure, the laser beam preferably impinges on the upper surface or upper main surface of the workpiece 30a substantially perpendicularly to the main surface of the workpiece 30a, 30b. Therefore, the laser beam does not impinge on the edge or edge of the workpiece 30a, 30b, or the laser beam does not impinge parallel to the main surface of the workpiece 30a, 30b.

[0063] Thus, the generated process radiation 11 is emitted from the upper surface or upper main surface of the workpiece 30a. Thus, the process radiation 11 is preferably detected from the upper surface of the workpiece 30a. Likewise, the reflected radiation is preferably detected from the upper surface of the workpiece 30a. In one embodiment, not shown, the laser processing system may include an LED lighting unit for emitting LED light into a processing region on the workpiece. In this case, the reflected radiation detected by the sensor module includes reflected LED radiation or reflected LED light. In another embodiment, not shown, the laser processing system may include a pilot laser unit for emitting a pilot laser beam into a processing region on the workpiece. In this case, the reflected radiation detected by the sensor module includes reflected pilot laser radiation or reflected LED light. The pilot laser unit may include a pilot laser beam source.

[0064] In particular, for laser welding workpieces 30a and 30b, the workpieces 30a and 30b should be arranged in an overlapping or parallel joint so that there is no gap between the thus arranged workpieces 30a and 30b, or the gap is minimized. As shown in the figure, an (undesirable) gap exists between the workpieces 30a and 30b, that is, between the upper surface of workpiece 30b and the lower surface of workpiece 30a. When viewing the workpieces 30a and 30b from above, particularly when viewing the upper surface of workpiece 30a or the lower surface of workpiece 30b, it is not possible to detect whether there is a gap between the workpieces 30a and 30b.

[0065] like Figure 2As shown, the sensor module 20 preferably includes a plurality of detectors or sensors D1, D2, and D3, which are configured to detect different parameters of the process radiation 11, such as intensity, and output measurement signals based thereon. Each of the detectors D1, D2, and D3 can include a photodiode, a photodiode array, or a pixel array. Preferably, the detectors include photodiodes or sensors for the visible spectral range, photodiodes or sensors for the infrared spectral range, and photodiodes or sensors for the wavelength range of the laser beam, the incident pilot laser beam, or the incident LED light. Furthermore, the sensor module 20 can include a plurality of beam splitters 221 and 222 to split the process radiation 11 and direct it toward the respective detectors D1, D2, and D3. The beam splitters 221 and 222 can be configured as partially transparent mirrors and, depending on the embodiment, can be wavelength-selective.

[0066] The control unit 40 is connected to the sensor module 20 and receives the measurement signals from the detectors D1, D2, and D3. The control unit 40 can be configured to record the measurement signals from the detectors D1, D2, and D3. The control unit 40 can be configured to determine and / or analyze the processing results of the laser processing, and in particular, to analyze the welded connection. The control unit 40 can also be configured to control the laser processing device 10 based on the analysis results.

[0067] The laser processing system 1 may be configured to perform a laser processing process, in particular laser welding, and to perform a method according to embodiments of the present disclosure for analyzing welded connections during laser welding of workpieces.

[0068] Figure 3 A flow chart of a method for analyzing weld connections during laser welding of workpieces according to an embodiment of the present disclosure is shown.

[0069] The method starts with detecting a first measurement signal for process radiation generated during laser welding (step S1). The method also includes detecting a second measurement signal for radiation reflected by the workpiece (step S2). According to an embodiment, the detection of the first measurement signal and the detection of the second measurement signal can be performed simultaneously. Subsequently, it is determined whether there is a gap between the workpieces based on the first measurement signal (step S3). If it is determined that there is a gap, it is determined based on the second measurement signal whether there is or is a weld connection or a gap bridge between the two workpieces (step S4). In other words, it is determined whether there is an electrical connection or a mechanical connection between the workpieces.

[0070] The method can thus be used to identify whether a gap exists between connected workpieces. The method can also be used to identify whether a gap bridge, i.e., a welded connection, in particular an electrical and mechanical welded connection, exists. In particular, the method can be used to analyze welded electrical connections, for example, to identify whether an electrical connection is missing between connected workpieces. Thus, it is possible to distinguish whether a weld that meets the requirements, i.e., a weld without a gap (also referred to as a "good weld" or a "weld with zero gap") exists, whether a weld with a gap and a gap bridge exists, thereby providing an electrical connection between the connected workpieces, or whether a weld with a gap but no gap bridge exists, thereby providing no electrical connection between the connected workpieces.

[0071] The first measurement signal is preferably detected in two different wavelength ranges. For example, the first measurement signal can be detected when the radiation intensity of process radiation in a first wavelength range, which is higher than the wavelength of the reflected radiation or higher than the wavelength of the laser beam used for laser welding, in particular in the infrared range, is detected, and when the radiation intensity of process radiation in a second wavelength range, which is lower than the wavelength of the reflected radiation or lower than the wavelength of the laser beam, in particular in the visible range, is detected. The first measurement signal detected in the first wavelength range can correspond to temperature radiation and can be referred to as a "temperature signal." The first measurement signal detected in the second wavelength range can correspond to plasma radiation and can be referred to as a "plasma signal." However, it is also possible to detect or analyze only the first measurement signal in only one of these wavelength ranges. As described above, the reflected radiation can include an incident pilot laser beam of a (processing) laser beam used for the welding process, or reflected laser radiation, or reflected laser radiation of incident LED light.

[0072] exist Figure 1 and Figure 2 In an exemplary embodiment, the plasma signal can be detected by a detector D1 that is sensitive in a wavelength range below the wavelength of the reflected radiation or the laser beam, in particular in the visible wavelength range of light, in order to detect the intensity of the plasma process radiation. The temperature signal can be detected by a detector D2 that is sensitive in a wavelength range above the wavelength of the reflected radiation or the laser beam, in particular in the infrared wavelength range of light, in order to detect the intensity of the process radiation in the infrared spectral range or the temperature spectral range, i.e., the intensity of the temperature radiation. The second measurement signal can be detected by a detector D3 that is sensitive in a wavelength range of the reflected radiation or the laser beam, in order to detect backreflections of the laser of the laser processing system.

[0073] According to embodiments, determining whether a gap exists between the workpieces (step S3) may include calculating a first integral of the plasma signal and a second integral of the temperature signal. In this case, the presence of a gap between the workpieces may be determined when the first integral is below a predetermined first integral limit and / or when the second integral is below a predetermined second integral limit.

[0074] According to embodiments, determining whether a welded connection or a gap bridge is present (step S4) can be performed based on the noise of the second measurement signal. In this case, the absence of a welded connection or a gap bridge can be determined when the frequency of outliers in the noise of the second measurement signal exceeds a predetermined first noise limit and / or when the integral of the noise of the second measurement signal exceeds a predetermined second noise limit. The noise can be defined as a deviation from an average value of the second measurement signal, preferably within a predetermined time interval or measurement signal, and can be amplified, in particular, by a predetermined factor. The average value can be predetermined or determined based on the second measurement signal.

[0075] According to an embodiment, at least one of steps S1 to S4 may be performed during laser welding of the weld connection.

[0076] Preferably, one of the workpieces comprises a battery, a battery module and / or a battery cell, and the other of the workpieces comprises a discharger. In this case, the method according to an embodiment of the present disclosure can be used to analyze the welded electrical connection between the discharger and the battery, battery module or battery cell. In particular, one of the workpieces can be made of aluminum, and the other of the workpieces can be made of copper and coated with nickel. The coating can be applied by electroplating. At least one of the workpieces can have a thickness of 0.10 mm to 0.50 mm, preferably a thickness of 0.15 mm to 0.35 mm, and particularly preferably a thickness of 0.20 mm to 0.30 mm.

[0077] In one embodiment, the dischargers of two or more batteries are welded or interconnected. The dischargers can be made of copper (Cu) or aluminum (Al). In particular, the discharger of a first battery can be made of aluminum or copper, and the discharger of a second battery can be made of aluminum or copper, thereby forming a welded connection between aluminum and aluminum (Al-Al), copper and copper (Cu-Cu), or aluminum and copper (Al-Cu).

[0078] The laser welding may include airtight welding of a cell housing of a battery cell, welding of a membrane of a cell cover of a battery cell, welding of a connection terminal in a cell cover of a battery cell, and welding of a burst plate of a cell cover of a battery cell.

[0079] The method according to embodiments of the present disclosure can be used, in particular, for analyzing welded connections in overlapping or parallel seams during laser welding of workpieces, and in particular in I-shaped welds.

[0080] Figures 4A-4D A welded connection that has been analyzed using a method for analyzing welded connections during laser welding of workpieces according to embodiments of the present disclosure is shown.

[0081] Figures 4A-4D In each case, the upper row ("camera") shows a top view of an I-shaped weld seam produced in an overlap joint during laser welding, and in each case a cross-sectional view of the corresponding weld seam is shown in the middle row. In each case, a schematic view of the cross-sectional view is shown in the lower row. When looking down at the respective workpiece 30a, 30b or the respective weld seam, it is not possible to distinguish whether there is a weld without a gap, a weld with a gap and a gap bridge, or a weld with a gap but no gap bridge. As shown in FIG. Figure 1 As described, the upper surface of the workpiece 30a is viewed from above.

[0082] Figure 4A The first column ("Gap: 0 μm") shows a weld seam that meets specifications, also referred to as a "good weld," which has been identified using a method for analyzing welded joints during laser welding of workpieces according to embodiments of the present disclosure. The welded workpieces 30a, 30b (shown here as sheet metal) have no gap between them, and current can flow through the weld seam. The resulting welded joint is labeled "good weld" or "0 gap."

[0083] Figures 4B-4D Typical error patterns are shown, which have been identified using a method according to embodiments of the present disclosure for analyzing welded connections during laser welding of workpieces.

[0084] Figure 4B The second column ("Gap: 100 μm") shows the gap S between the two welded workpieces 30a, 30b. This gap S can be tolerated because it is bridged ( Figure 4B (See the gap bridge "B" in the figure). Therefore, despite the presence of gap S, there is still an electrical connection between the welded workpieces, that is, a weld connection. This is also referred to as a "weld with a gap bridge" or a "gap with an (electrical) connection or (electrical) connection."

[0085] Figure 4C and Figure 4BThe third and fourth columns ("Gap: 150 μm" and "Gap: 200 μm") show further typical error patterns, also referred to as "error objects." Here, a gap S exists between welded workpieces 30a, 30b, which is not bridged, resulting in no electrical connection between the workpieces. This is also referred to as a "weld without gap bridging" or a "gap without (electrical) connection or (electrical) connection." In other words, no weld connection exists.

[0086] exist Figures 5A to 5D , the time profile of a measurement signal detected by a method according to an embodiment for analyzing a weld connection during laser welding of workpieces is shown by way of example.

[0087] exist Figures 5A to 5D In the embodiment shown, a first measurement signal has been recorded in the first wavelength range and the second wavelength range, the first measurement signal comprising the plasma signal P1 and the temperature signal P2. The second measurement signal for the reflected laser light is referred to as the back reflection signal P3. Figures 5A-5D An exemplary profile of the measurement signals P1 , P2 and P3 for a laser welding process is shown. Furthermore, the curve of the noise of the measurement signal P3 is shown as “P3 noise”.

[0088] A method according to an embodiment of the present disclosure includes detecting a plasma signal P1 and a temperature signal P2. The presence of a gap between the workpieces is determined when, for example, the plasma signal P1 and / or the temperature signal P2 decreases, i.e., lies above, falls below, or drops below the corresponding lower envelope curve. This can be determined, for example, by calculating a first integral of the plasma signal P1 and a second integral of the temperature signal P2. A gap is present when the first integral is below a predetermined first integral limit and / or when the second integral is below a predetermined second integral limit. If a gap is present, the presence of a welded joint or a gap bridge is determined based on the backreflection signal P3. A welded joint or a gap bridge is not present when the frequency of outliers in the backreflection signal P3's noise exceeds a predetermined first noise limit and / or when the integral of the backreflection signal P3's noise exceeds a predetermined second noise limit. Otherwise, a gap with a gap bridge, i.e., a welded joint, is present.

[0089] On the one hand, this method can distinguish between good welds, i.e., welds without a gap between the workpieces, and welds with a gap. On the other hand, this method can distinguish between welds with a gap but a gap bridge and welds with a gap but no gap bridge.

[0090] exist Figure 5AIn the case of laser welding, the integral of the plasma signal P1 and the integral of the temperature signal P2 are above the corresponding limit values. The weld produced during the laser welding process is called a "good weld". There is a weld connection with zero gap between the workpieces connected in this way. In particular, there is an electrical connection or electrical connection between the connected workpieces. This corresponds to Figure 4A Solder connections shown.

[0091] exist Figures 5B-5D In the example, plasma signal P1 and temperature signal P2 decrease relative to respective predetermined reference values ​​or envelope curves. In other words, the integral of plasma signal P1 and the integral of temperature signal P2 fall below respective limit values. The weld produced in the corresponding laser welding process is designated as a weld with a gap.

[0092] According to one embodiment, it is sufficient if either the integral of the plasma signal P1 or the integral of the temperature signal P2 is below a corresponding limit value. According to another embodiment, the presence of a gap can only be determined if both the integral of the plasma signal P1 and the integral of the temperature signal P2 are below a corresponding limit value.

[0093] exist Figure 5B There is a gap with a gap width of 100 μm between the workpieces. Figure 5C There is a gap with a gap width of 150 μm between the workpieces. Figure 5D In the embodiment, a gap having a gap width of 200 μm exists between the workpieces. Figures 5B-5D The weld shown corresponds to Figures 4B-4D The weld shown. The gap width can be determined based on the integral value of the plasma signal P1 and / or the integral value of the temperature signal P2. When the integral value is in a first range, a gap width having a first value or a first value range can be assigned to the corresponding weld. Correspondingly, a gap width having a second value or a second value range can be assigned to an integral value in a second range, and so on. Figure 6 exemplarily described for the plasma signal P1.

[0094] for Figures 5B-5D Now, it is determined whether a weld connection still exists between the workpieces and, accordingly, whether an electrical contact or connection exists. For this purpose, the noise of the backreflected signal P3, ie, the P3 noise, is analyzed.

[0095] exist Figure 5B In the example, the outlier frequency of the noise of the back reflection signal P3 is below a predetermined first noise limit value. Therefore, it is determined that, despite the presence of the gap, a welded connection or a gap bridge exists between the workpieces.

[0096] exist Figure 5C and 5D In the example, the outlier frequency of the noise of the backreflected signal P3 is higher than a predetermined first noise limit value. It is therefore determined that no weld connection or gap bridge exists between the workpieces and therefore no electrical contact exists.

[0097] The present invention is based on the recognition that during laser welding, a good weld can be distinguished from a weld with a gap in an overlap joint by a decrease in the intensity of the plasma signal and the temperature signal during the laser welding process. Furthermore, the present invention is based on the recognition that a weld with a gap and a gap bridge can be distinguished from a weld with a gap but no gap bridge by a significant increase in the noise of the backreflected signal of the radiation reflected by the workpiece. Therefore, the combination of the plasma and temperature signals with the backreflected signal provides a clear, unique, and unambiguous statement about the presence or absence of a weld connection, in particular an electrical connection, between the workpieces. The presence of a gap can be considered a necessary condition for the gap not to be bridged, while excessive noise can be considered a sufficient condition. Thus, the presence of an erroneous object can be clearly and uniquely identified.

Claims

1. A method for analyzing a weld connection during laser welding of workpieces (30a, 30b), the method comprising: - detecting a first measurement signal (P1, P2) for the process radiation generated during the laser welding; - detecting a second measurement signal (P3) for radiation reflected by said workpiece (30a, 30b); - determining whether a gap (S) exists between the workpieces (30a, 30b) based on the first measurement signal (P1, P2); and - when it is determined that a gap (S) is present, determining whether a weld connection is present based on the second measurement signal (P3).

2. The method according to claim 1, wherein The reflected radiation includes at least one of the following: reflected laser radiation of a processing laser beam for laser welding, reflected radiation of LED light incident into the processing region, and reflected laser radiation of a pilot laser beam incident into the processing region.

3. The method according to claim 1 or 2, wherein: The first measurement signal (P1, P2) and / or the second measurement signal (P3) is based on the detection of radiation intensity.

4. The method according to claim 1 or 2, wherein: The first measurement signal (P1, P2) is detected in a first wavelength range which is higher than the wavelength of the processing laser beam used for the laser welding and / or higher than the wavelength of the reflected radiation, and / or The first measurement signal (P1, P2) is detected in a second wavelength range which is below the wavelength of the processing laser beam used for the laser welding and / or below the wavelength of the reflected radiation.

5. The method according to claim 1 or 2, wherein: The process radiation detected as the first measurement signal ( P1 , P2 ) is temperature radiation in the infrared spectral range and / or plasma radiation in the visible spectral range.

6. The method according to claim 1 or 2, wherein: The reflected radiation detected as the second measurement signal (P3) lies in the infrared spectral range or in the green or blue visible spectral range.

7. The method according to claim 1 or 2, wherein: Determining whether a gap (S) exists between the workpieces (30a, 30b) comprises determining a gap width based on the first measurement signals (P1, P2), and In this case, when the gap width is greater than a predetermined gap width limit value, it is determined that a gap (S) exists.

8. The method according to claim 1 or 2, wherein: Determining whether a gap (S) exists between the workpieces (30a, 30b) comprises determining whether the first measurement signal (P1, P2) is lower than a reference value or a reference curve, or falls below a reference value or a reference curve, When the first measurement signal (P1, P2) is lower than the reference value or the reference curve, or drops below the reference value or the reference curve, it is determined that there is a gap (S) between the workpieces (30a, 30b).

9. The method according to claim 1 or 2, wherein: Determining whether a gap (S) exists between the workpieces (30a, 30b) comprises first integrating the first measurement signals (P1, P2) and / or first averaging the first measurement signals (P1, P2). The presence of a gap (S) between the workpieces (30a, 30b) is determined when the first integral falls below a predefined first integral limit value and / or when the first average value falls below a predefined first average value limit value.

10. The method according to claim 1 or 2, wherein: The first measurement signal (P1, P2) is detected in a first wavelength range, the first wavelength range being higher than the wavelength of the reflected radiation or higher than the wavelength of the processing laser beam used for the laser welding, and in a second wavelength range being lower than the wavelength of the reflected radiation or lower than the wavelength of the processing laser beam used for the laser welding; determining whether a gap (S) is present between the workpieces (30a, 30b) comprises a first integral of the first measurement signal (P1) detected in the first wavelength range and a second integral of the first measurement signal (P2) detected in the second wavelength range, and The presence of a gap (S) between the workpieces (30a, 30b) is determined when the first integral falls below a predetermined first integration limit value and / or when the second integral falls below a predetermined second integration limit value.

11. The method according to claim 1 or 2, wherein: The presence of a weld connection is determined based on the noise of the second measurement signal (P3).

12. The method according to claim 11, wherein - when the frequency of outliers of the noise of the second measurement signal (P3) is higher than a predetermined first noise limit value, and / or The absence of a welded connection is determined when the integral of the noise of the second measurement signal (P3) is above a predefined second noise limit value.

13. The method according to claim 1 or 2, wherein: At least one of the workpieces (30a, 30b) comprises aluminum and / or copper and / or nickel or consists of aluminum and / or copper and / or nickel.

14. The method according to claim 1 or 2, wherein: At least one of the workpieces has a thickness of 0.10 mm to 0.50 mm.

15. The method according to claim 1 or 2, wherein: At least one of the workpieces has a thickness of 0.15 mm to 0.35 mm.

16. The method according to claim 1 or 2, wherein: At least one of the workpieces has a thickness of 0.20 mm to 0.30 mm.

17. The method according to claim 1 or 2, wherein: The workpiece (30a, 30b) comprises a discharger of a first cell and a discharger of a second cell, wherein a welded electrical connection between the dischargers of the cells is considered a welded connection.

18. The method according to claim 1 or 2, wherein: During laser welding, the workpieces are arranged in overlapping or parallel joints.

19. A method for laser welding workpieces, the workpieces comprising a first workpiece (30a) and a second workpiece (30b), the method comprising the steps of: - arranging the workpieces (30a, 30b) such that the first surface of the first workpiece (30a) and the first surface of the second workpiece (30b) are stacked one above the other; - laser welding the workpieces (30a, 30b) by irradiating a machining laser beam onto a second surface of the first workpiece (30a) to form a welded connection between the workpieces (30a, 30b), wherein the second surface of the first workpiece (30a) is opposite to the first surface of the first workpiece (30a), and / or laser welding by irradiating a machining laser beam onto a second surface of the second workpiece (30b) to form a welded connection between the workpieces (30a, 30b), wherein the second surface of the second workpiece (30b) is opposite to the first surface of the second workpiece (30b); - performing the method according to claim 1 for analyzing welded connections during laser welding of workpieces.

20. The method according to claim 19, wherein The workpieces are arranged in overlapping joints or parallel joints.

21. The method according to claim 19 or 20, wherein The first surfaces of the workpieces (30a, 30b) touch in at least one region, and / or a gap is present in another region between the first surfaces of the workpieces (30a, 30b).

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