Method for monitoring attachment area when laser welding a copper-containing bent rod conductor

Abstract

A method for monitoring the attachment area (9) when laser welding copper-containing curved rod-shaped conductors (1a, 1b), in particular hairpins of electric motors, is characterized in that the two rod-shaped conductors (1a, 1b) are arranged in a partially overlapping manner and are welded to one another by a process laser beam (7), wherein a weld bead (8) is formed and causes the rod-shaped conductors (1a, 1b) to be connected to one another, it is characterized in that at least one measured variable that varies with the temperature of the weld bead (8) is measured as a function of time (t) over at least a portion (56) of the weld bead (8) during cooling of the weld bead (8) after the action of the process laser beam (7) has ended, wherein a parameter that depends on the heat capacity of the weld bead (8) is determined from the at least one measured variable, and wherein the attachment area (9) is determined qualitatively or quantitatively from the parameter. The invention provides a method for monitoring the attachment area when laser welding copper-containing curved rod-shaped conductors, which can be easily, quickly and non-destructively performed.

Description

Technical Field

[0001] This invention relates to a method for monitoring the adhesion area during laser welding of copper-containing bent rod-shaped conductors, particularly hairpins for electric motors.

[0002] In this configuration, two rod-shaped conductors are arranged in a partially overlapping manner and welded together by a processing laser beam.

[0003] In this process, solder beads are formed, which connect the rod-shaped conductors to each other. Background Technology

[0004] Copper-containing bent rod-shaped conductors (especially so-called hairpins) are installed in electrodynamic machines, such as electric motors or generators. The rod-shaped conductors are arranged according to a set electrical interconnection and welded together to form an electromagnet. In this case, the electrodynamic machine typically includes dozens, usually hundreds, of bent rod-shaped conductors, which must be welded together in pairs.

[0005] The key here is to provide a sufficient cross-sectional area through the weld so that current can flow from one rod conductor to another (“attachment area”). If the attachment area is too small, there is a risk of significant ohmic heating, efficiency loss, or even rendering the electric motor unusable during operation.

[0006] Rod-shaped conductors are typically welded using a laser beam (“laser welding”). For this, the laser beam is typically directed at the end faces of two overlapping rod-shaped conductors, which are usually pressed against each other. This allows heat to be introduced into the conductors, melting them and, after solidification, joining them together through refracted weld beads. Typically, the laser beam is directed at the rod-shaped conductors at a predetermined power for a predetermined time, thereby usually achieving a sufficiently large attachment area.

[0007] However, due to contamination or roughness on the surface of the rod conductor, the reflectivity of the rod conductor to the laser beam, and therefore the actual energy input, may vary. Similarly, incorrect positioning of the rod conductor (e.g., gaps or misalignment, or inaccurate laser beam positioning) can also lead to variations in the actual energy input. If the energy input is too low, too little material is melted, resulting in a weld bead that is too small and provides too little adhesion area. Excessive spatter formation during laser welding can also lead to weld beads that are too small and have insufficient adhesion area.

[0008] The size of the resulting attachment area can be determined by X-ray analysis. For this, the rod-shaped conductor must be brought to a suitable X-ray machine to produce a post-weld X-ray image, which is complex from an equipment standpoint. The metallographic cross-section of the weld bead is also known, but this is quite complex and detrimental to the weld. Summary of the Invention

[0009] The purpose of this invention is to provide a method for monitoring the attachment area during laser welding of copper-containing bent rod-shaped conductors, the method being easy, fast and non-destructive to perform.

[0010] According to the present invention, this objective is achieved by a method of the type described at the beginning of this document, characterized by:

[0011] At least one measured variable relating to the temperature of the solder bead is measured as a function of time at least on a portion of the solder bead during its cooling process after the laser beam has finished working.

[0012] The parameter that depends on the heat capacity of the solder ball is determined by measuring at least one variable.

[0013] Furthermore, the attachment area is determined qualitatively or quantitatively based on this parameter.

[0014] Within the scope of the method of this invention, the size or quality of the weld bead is indirectly determined by removing the heat introduced by the laser welding from the weld bead after the laser welding process is completed. Typically, the size of the adhesion area can be inferred from the size of the weld bead, thus allowing for monitoring of the adhesion area.

[0015] It should be noted that, according to the inventors' experience, determining the size of a solder bead directly, for example by analyzing an optical image of the bead, is usually not reliable enough due to the irregularity of the rod-shaped conductor, especially the inclined surface at the end of the rod-shaped conductor.

[0016] At the end of the processing laser beam's action, the solder bead is approximately at the evaporation temperature of the rod-shaped conductor material; correspondingly, heat approximately proportional to the mass of the solder bead is stored in the solder bead.

[0017] The stored heat is derived from the heat conduction path present under given welding conditions, which is predetermined by the size and material of the rod conductors, rather than depending on the size of the solder ball (in normal welding, i.e., the solder ball is in contact with the rod conductor across its entire cross-section). A good approximation is that the heat stored in the solder ball is extracted via two rod conductors in a one-dimensional manner. In this case, the heat flow through the rod conductors is restricted.

[0018] The more heat initially stored in the solder ball, the slower it cools. Cooling behavior is observed by measuring variables. Therefore, the initially stored heat, and thus the (absolute) heat capacity, can be inferred from the cooling behavior.

[0019] Measurement variables describing the properties of at least a portion of the solder ball that are directly or indirectly affected by temperature (e.g., through phase state) are measured as a function of time; this allows observation of the solder ball's cooling behavior and determination of parameters dependent on the solder ball's (absolute) heat capacity. These parameters, dependent on (absolute) heat capacity, indicate the solder ball's mass, as the solder ball's (absolute) heat capacity is proportional to its mass.

[0020] The quality of the solder ball determines its geometry, and thus the adhesion area provided by the solder ball or weld between the rod conductors, particularly for conducting current. The adhesion area can then be deduced from these parameters by calibrating for a given weld condition (specifically, the size and material of the rod conductors).

[0021] To calibrate the monitoring of the adhesion area, the measurement variables can be measured separately for some weld sections, thereby determining the parameters, and the actual adhesion area can also be routinely determined separately (e.g., by X-ray inspection or metallographic cross-section) (“calibration experiment”). The relationship between the parameters and the actual adhesion area is then derived from this calibration experiment (for a given weld condition). In subsequent welds (under the same weld conditions), this relationship can be used to qualitatively or quantitatively determine the adhesion area based on the parameters, without the need for routine determination of the actual adhesion area again.

[0022] A typical qualitative determination of the attachment area is limited to indicating whether the attachment area is large enough (weld "iO", compliant) or insufficiently large (weld "niO", non-compliant). A typical quantitative description is a direct surface description of the attachment area (e.g., "5.5mm"). 2 ”).

[0023] Preferred variants of the present invention

[0024] General Variation

[0025] A preferred variant of the method of the present invention provides:

[0026] Two rod-shaped conductors are arranged such that their end regions are parallel to each other and placed next to each other.

[0027] In particular, the end regions of the rod-shaped conductors are pressed together in a planar manner.

[0028] The end faces of the rod-shaped conductor are approximately at the same height relative to the longitudinal direction of the end region of the rod-shaped conductor.

[0029] Furthermore, the processing laser beam is aligned with the two rod-shaped conductors in such a way that solder beads are formed at the end faces of the rod-shaped conductors.

[0030] In particular, the end region of the rod-shaped conductor is generally vertically upward, and the processing laser beam falls approximately vertically onto the end face of that end side. When solder beads are formed on the end face of the rod-shaped conductor, heat dissipation from the solder beads is significant, and the method of the present invention is particularly precise. Typically, the processing laser beam is directly aimed at the end face of said end side and moves back and forth between the rod-shaped conductors, for example, in a circular trajectory. When the end region (legs) of the rod-shaped conductor is oriented vertically upward, the solder beads formed thereon (initially still liquid) are particularly stable.

[0031] A particularly preferred variation involves observing at least a portion of the weld bead in the visible and / or infrared spectral range to measure the variable. Observation in the visible or infrared spectral range is readily and cost-effectively achieved, for example, using a camera or photodiode. Many welding devices already have optical observation systems, such as those for the relative orientation of the laser beam and the workpiece, and these can also be used by the method of the present invention. It should be noted that the observation is preferably performed at a frequency of at least 100 Hz.

[0032] In this preferred development of the variant, the at least one measurement variable is measured on a portion of the solder bead, which is opposite to the portion of the rod-shaped conductor affected by the laser beam.

[0033] In particular, the at least one measured variable is measured on the portion of the solder bead located at its upper center. By measuring the variable on this portion, heat extraction can be observed with particular reliability; in particular, edge effects caused by the irregularity of the rod-shaped conductor are minimized. Solder solidification typically occurs at the upper center of the solder bead, so the solidification time can be determined particularly easily here.

[0034] Variations related to measurement variables

[0035] In an advantageous variation, the at least one measurement variable includes the intensity of thermionic emission of at least that portion of the solder ball. The intensity of thermionic emission can be measured and evaluated relatively easily.

[0036] A related favorable development rule is that the intensity of thermionic emission is measured only within a limited spectral range.

[0037] In particular, the finite spectral range is no greater than 800 nm to 1100 nm.

[0038] In particular, for the purpose of limiting the spectral range, bandpass filters and / or broadband filters are arranged in front of the sensor device used to measure the intensity of thermionic emission.

[0039] Furthermore, the wavelength range of the processing laser beam is particularly important as it falls outside a finite spectral range. For copper-containing rod-shaped conductors, the spectral range of 800 nm to 1100 nm is especially meaningful for determining temperature-dependent measurement variables. By blocking the wavelength of the processing laser beam, overloading the sensor device used can be avoided. When the wavelength of the processing laser beam is approximately 1030 nm, a bandpass filter can be used, for example, to limit the measurement spectrum to 800–1000 nm, or a broadband filter can be used to selectively block the wavelength range around 1030 nm. In particular, a measurement spectral range <1000 nm can also be selected.

[0040] A preferred variant specification,

[0041] During the cooling of the solder ball, the solder ball is illuminated using an observation beam, particularly an observation laser beam.

[0042] Furthermore, the at least one measurement variable includes the intensity of the observation beam reflected at the surface of the solder bead. As the solder bead cools, and particularly in the case of a phase transition (solidification), the reflectivity of the solder bead to the observation beam changes, which can be utilized by this variation. The bandwidth of the observation beam is typically narrow (e.g., a full-spectrum width of 40 nm or less, typically 20 nm or less), and preferably originates from an observation laser, particularly a diode laser, or an LED or LED ring. Due to the use of the observation beam, the attachment area can be monitored with particular accuracy. It should be noted that in practice, the thermionic emission of the solder bead is superimposed on the reflected observation beam, and these two effects (or related intensities) are measured together in principle, for example, as the average gray value of a portion of a camera image or as the gray value of a photodiode.

[0043] Preferably, the development of this variant is specified,

[0044] The intensity of the reflected observation beam is measured only within a limited spectral range around the average wavelength of the observation beam.

[0045] In particular, the finite spectral range is no greater than + / -20 nm or + / -10 nm around the average wavelength of the observed beam.

[0046] Furthermore, specifically for the purpose of limiting the spectral range, a bandpass filter is positioned in front of the sensor device used to measure the intensity of the reflected observation beam. By limiting the spectral range around the average wavelength of the observation beam, the (alternatively existing) thermionic emission is made to a lesser extent superimposed on or tampered with the measurement of the measured variable.

[0047] Another preferred development is one in which a polarization filter is positioned in front of a sensor device used to measure the intensity of the reflected observation beam.

[0048] In particular, a linear polarizer was selected as the polarization filter. This improves the contrast when observing the solder beads through the reflected observation beam.

[0049] The development of variations, including those for observing the intensity of the observation beam used for thermion emission and / or reflection, involves using a camera to observe the weld bead and determining the intensity of the observation beam for thermion emission and / or reflection at a portion of the weld bead by determining the average grayscale value of a portion of the image recorded by the camera. This process is relatively simple and has proven its value in practice; after all, suitable cameras are usually available in welding setups, for example, for positioning the laser beam on the workpiece.

[0050] In another development, which includes a variation involving the observation of the intensity of the observation beam for thermionization emission and / or reflection, a photodiode is used to observe the solder bead, and the intensity of the observation beam for thermionization emission and / or reflection at least a portion of the solder bead is determined as the grayscale value of the photodiode. Using a photodiode to determine the grayscale value is particularly cost-effective.

[0051] Furthermore, a preferred variation is to include the temperature at least on a portion of the solder ball as the measurement variable. Measuring the temperature at least on a portion of the solder ball itself directly describes the cooling behavior of the solder ball, thus allowing for particularly accurate and reliable monitoring of the attachment area. However, from an equipment perspective, temperature measurement is relatively complex.

[0052] A preferred development of this variant is that the temperature is measured using a quotient pyrometric method, where the intensity of the thermionic emission of at least that portion of the solder ball is measured at two different wavelengths. Measurements performed using the quotient pyrometric method are particularly reliable. For this purpose, photodiodes with narrow-bandpass filters, which are selective for these two different wavelengths, can be used. Alternatively, a thermal imaging camera can be used, or the measured spectrum can be matched with a gray radiator (e.g., copper).

[0053] Variations of parameters

[0054] A particularly preferred variation is that the parameter is the duration of time that passes between a first defined state and a second defined state during the solder ball's cooling process. This duration can be measured relatively easily. Typically, at least one of the defined states is identified by a time curve of that at least one measured variable. A typical defined state is the attainment of a specific temperature or the identification of a phase transition.

[0055] In a preferred development of this variant, the first defined state is the termination of the processing laser beam's action. The time when the processing laser beam's action ends ("disconnection") is typically known or predetermined by the controller of the welding process, and therefore does not need to be determined separately.

[0056] Another preferred development is that the second defined state is complete solidification of the solder ball. Typically, the phase transition from liquid to solid can be easily identified optically and is therefore well-suited as the second defined state. Here, both emission behavior and reflectivity change relatively significantly. Furthermore, (complete) solidification can also be identified optically by the complete cessation of movement on the solder ball.

[0057] In a favorable development, the first and / or second defined states are identified by measuring variables reaching a threshold. This process is particularly simple. In particular, complete solidification of the solder ball can be identified by the intensity of thermionic emission reaching (or breaking through) a threshold.

[0058] Another preferred development is that the first and / or second defined states are identified by means of the first and / or second time derivatives of the measured variable reaching a threshold, particularly after the measured variable has previously fluctuated only within a predetermined limit for a predetermined minimum duration, by means of the first and / or second time derivatives of the measured variable reaching the threshold. Information about the cooling curve, particularly about the phase transition, is generally easier to identify in the first or second derivatives of the measured variable than in the measured variable itself. In particular, the solidification of the solder ball causes an increase in the reflectivity of the observed beam, which can be easily identified as a positive gradient in the first derivative of the intensity of the reflected laser radiation.

[0059] A preferred variation is that the parameter is the temporal gradient of the measured variable, which is determined at a predetermined time or averaged over a predetermined time period. For example, the gradient can be determined directly after the processing laser beam has finished acting, or it can be determined by averaging over tens of milliseconds after the processing time period ends. In particular, the measured variable can be temperature or the intensity of thermionic emission. Specifically, the gradient with respect to temperature or the intensity of thermionic emission can be determined while the solder bead is still completely liquid.

[0060] Variations used to evaluate parameters

[0061] A preferred variation of the method of the present invention is specified as follows:

[0062] The parameter, or the attachment area quantitatively determined based on the parameter, is compared with the decision value.

[0063] If the decision value is not met, the bonding area of ​​the solder ball is identified as too small, in which case the relevant rod conductor will be removed or additional soldered.

[0064] If the decision value is reached, the attachment area is identified as large enough, and the continued use of the associated rod conductor is permitted. This process is particularly simple.

[0065] A favorable development of this variant stipulates that the proportion of the cross-section of the rod conductor not covered by the solder ball is determined by a camera, and if the proportion of the uncovered cross-section exceeds a limit value, even if this decision value is reached, the adhesion area of ​​the welded portion of the rod conductor is identified as too small. If the solder ball does not completely cover the cross-section of the rod conductor, the mutual adhesion area of ​​the rod conductors cannot be adequately characterized by the quality or size of the solder ball. Instead, it can be assumed that the cross-section limiting electrical conduction between the rod conductors lies in the contact area between the solder ball and the rod conductor. If it is too small, the welded portion is unusable, just as in the case where the solder ball is too small. This development further increases the reliability of identifying electrically unusable welded portions.

[0066] Another preferred variation involves sequentially welding multiple pairs of rod conductors, wherein one or more welding parameters are optimized and / or adjusted in a control loop as these pairs of conductors are welded, such that the parameter, or the attachment area quantitatively determined based on the parameter, is set to a predetermined target value for the welded pair of conductors. This approach allows for improved quality of the produced welds and minimizes the number of rejection and / or rework processes.

[0067] Laser welding equipment for the method of the present invention

[0068] The scope of this invention also includes an apparatus for laser welding of copper-containing bent rod-shaped conductors, particularly hairpins for electric motors.

[0069] The equipment has a holding device that allows two rod-shaped conductors to be arranged in an overlapping manner. Specifically, the holding device includes a stator carrier having multiple rod-shaped conductors to be welded.

[0070] Furthermore, the device has a laser processing head that provides a processing laser beam. This laser beam is used to weld the two rod-shaped conductors together, forming weld beads that connect the rod-shaped conductors to each other.

[0071] The device is characterized by,

[0072] The device also includes a sensor unit through which at least one measurable variable that changes with the temperature of the solder ball can be measured at least on a portion of the solder ball during its cooling process, after the laser beam has finished its operation.

[0073] Furthermore, the device also includes an electronic evaluation unit configured, and in particular programmed, to determine parameters dependent on the heat capacity of the solder ball based on at least one measured variable.

[0074] Furthermore, the electronic evaluation device is configured, and in particular programmed, to qualitatively or quantitatively determine the adhesion area established by the solder beads based on this parameter. The device of the present invention is particularly configured to perform the methods described above, or can be used to perform the methods described above. Using this device allows for easy, rapid, and non-destructive monitoring of the adhesion area online during laser welding of copper-containing bent rod-shaped conductors, particularly during the fabrication of the welded portion.

[0075] Other advantages of the invention will become apparent from the description and drawings. Similarly, according to the invention, the features mentioned above and those further described herein can be used individually or in any combination as a plurality of features. The illustrated and described embodiments should not be construed as exhaustive, but rather serve as illustrative features for summarizing the invention. Attached Figure Description

[0076] Figure 1a A schematic side view of two bent rod-shaped conductors arranged in a partially overlapping manner is shown. Within the scope of the invention, these two bent rod-shaped conductors should be welded to each other.

[0077] Figure 1b It shows Figure 1a A schematic oblique view of the adjacent end regions of two rod-shaped conductors; this view is a view of the end faces.

[0078] Figure 2 A schematic side view of the end regions of two rod-shaped conductors welded and interconnected by solder beads according to the present invention is shown, with the attachment area marked.

[0079] Figure 3 A graph is shown representing the adhesion area determined by X-rays and the measured solidification time for six exemplary weld measurement samples;

[0080] Figure 4 A schematic diagram of a first embodiment of an apparatus for laser welding according to the present invention is shown, wherein the intensity of thermionic emission on a portion of a weld bead is measured by a camera;

[0081] Figure 5a A schematic side view of the end regions of two rod-shaped conductors welded and interconnected by solder beads according to the present invention is shown. Figure 4 The image recorded by the device's camera and the corresponding area of ​​this image corresponding to the upper central part of the solder ball are marked out, and this area is selected to determine thermionic emission;

[0082] Figure 5bA schematic side view of the end regions of two rod-shaped conductors welded and interconnected by solder beads according to the present invention is shown. An image recorded by a camera arranged alternatively and a portion of this image corresponding to the portion of the solder bead located on one side of the solder bead are marked. This portion is selected for determining thermionic emission.

[0083] Figure 6 A schematic diagram of the present invention is shown, which represents the average gray value as a function of time (upper part) corresponding to the intensity of thermionic emission observed on a portion of the solder ball during the solder ball cooling process, as well as the first derivative of the gray value with respect to time (middle part) and the second derivative of the gray value with respect to time (lower part).

[0084] Figure 7 A schematic diagram of a second embodiment of an apparatus for laser welding according to the present invention is shown, in which the intensity of the laser beam reflected at the weld bead is measured and observed by a camera.

[0085] Figure 8 A schematic diagram of the present invention is shown, illustrating the process of cooling solder balls by... Figure 7 The device observes the superposition of the thermionic emission intensity and the reflected observation laser beam intensity on a portion of the solder ball, corresponding to the average gray value as a function of time (upper part), and the first derivative of the gray value with respect to time (middle part) and the second derivative of the gray value with respect to time (lower part).

[0086] Figure 9 A schematic diagram of a third embodiment of an apparatus for laser welding according to the present invention is shown, wherein the temperature of the weld bead is measured by a quotient high-temperature measurement method;

[0087] Figure 10 A schematic diagram of the present invention is shown, illustrating the process of solder ball cooling. Figure 9 The temperature as a function of time (upper part) observed on a portion of the solder ball in the device, as well as the first derivative of temperature with respect to time (middle part) and the second derivative of temperature with respect to time (lower part).

[0088] Figure 11a A schematic plan view of the solder beads at the ends of the end regions of the two rod-shaped conductors of the present invention is shown, the cross-section of the end regions of the rod-shaped conductors being completely covered by the solder beads;

[0089] Figure 11b A schematic plan view of the solder beads at the ends of the end regions of the two rod-shaped conductors of the present invention is shown, the cross-section of the end regions of the rod-shaped conductors being only partially covered by the solder beads. Detailed Implementation

[0090] In the schematic side view, Figure 1aTwo bent copper rod-shaped conductors 1a and 1b are shown. These rod-shaped conductors are in the form of so-called hairpins and are used to manufacture electro-powered machines (such as electric motors). Each rod-shaped conductor 1a and 1b is generally U-shaped and includes two legs (sides) 2a and 3a and 2b and 3b and a middle section 4a and 4b connecting these legs.

[0091] The rod-shaped conductors 1a and 1b should be electrically connected to each other, and for this purpose, they should be welded to each other at their end regions 5a and 5b. For this purpose, the legs 3a of the first rod-shaped conductor 1a and the legs 2b of the second rod-shaped conductor 1b are arranged in an overlapping manner and are also arranged close to each other.

[0092] from Figure 1b A schematic oblique view of the mid-end regions 5a and 5b shows that the end faces 6a and 6b of the two rod-shaped conductors 1a and 1b are arranged at approximately the same height, and the long sides 11a and 11b of the end regions 5a and 5b of the legs 3a and 2b are planarly adjacent and flush with each other, with the legs 3a and 2b pressed against each other in a manner not shown in more detail. The legs 3a and 2b are parallel to each other and vertically oriented, such that the two end faces 6a and 6b are oriented upwards.

[0093] To weld the two end regions 5a, 5b, a processing laser beam 7 is used, which sweeps across the end faces 6a, 6b in a repeating circular trajectory 12. Here, the processing laser beam 7 is incident approximately perpendicularly onto the end faces 6a, 6b; it should be noted that the angle of incidence of the processing laser beam 7 typically varies slightly when manufacturing various rod-shaped conductor pairs to avoid interference with what is usually arranged on the stator carrier (not shown in more detail here; but see, for example...). Figure 4 The rod-shaped conductors 1a and 1b in the laser beam 7 shift too frequently. Here, the laser beam 7 typically does not deviate more than 40° from the vertical incidence.

[0094] By the action of the processing laser beam 7, the materials of the rod-shaped conductors 1a and 1b melt near their end faces 6a and 6b, forming so-called solder beads. It should be noted that, typically for multiple pairs of rod-shaped conductors to be welded, a predetermined laser power is used for a predetermined time period, and within the scope of this invention, the adhesion area of ​​these rod-shaped conductors should be monitored.

[0095] Figure 2 The end regions 5a and 5b of the laser-welded rod conductors 1a and 1b are shown. The rod conductors 1a and 1b are electrically connected to each other via solder beads 8. Here, the solder beads 8 are typically fully positioned on both rod conductors 1a and 1b, that is, covering their complete cross-sectional areas Qa and Qb respectively (for more details on this, please see below). Figure 11a ).

[0096] The quality of the conductive connection between the two rod-shaped conductors 1a and 1b is primarily determined by the so-called attachment area 9. It is the cross-sectional area provided by the solder ball 8 that can be used to conduct current from the first rod-shaped conductor 1a to the second rod-shaped conductor 1b, and it roughly corresponds to the cross-section of the solder ball 8 in the contact plane of the mutually abutting long sides 11a and 11b of the legs 3a and 2b of the rod-shaped conductors 1a and 1b.

[0097] Generally, the larger the attachment area 9, the larger the solder ball 8. Since the end regions 5a and 5b of the rod conductors 1a and 1b are often irregular (e.g., irregular or obliquely shortened before the soldering process begins), the size of the solder ball 8 (whether its height H or its volume) is difficult to determine. In particular, according to the inventors' experience, it is almost impossible to reliably determine the size of the solder ball 8 by direct image evaluation.

[0098] Therefore, the present invention provides a method for indirectly determining the size of the solder bead 8 by tracking the cooling profile of the solder bead 8 after the processing laser beam has been deactivated. When the processing laser beam has been deactivated, the entire solder bead 8 is typically approximately at the melting temperature T of the material of the rod-shaped conductors 1a and 1b. S (It should be noted that the processing laser beam causes some evaporation of the material in the rod conductors 1a and 1b.) The subsequent heat dissipation of the solder bead 8 is effectively achieved solely through the two rod conductors 1a and 1b, and is therefore limited by the thermal conductivity of the rod conductor material and their available cross-sectional areas Qa and Qb (“one-dimensional heat dissipation”). The larger the solder bead 8, the more heat energy must be dissipated through the rod conductors 1a and 1b. Under these limited heat dissipation conditions, this results in the temperature of the larger solder bead 8 decreasing more slowly over time than that of the smaller solder bead 8.

[0099] Therefore, this invention specifies that a measurement variable depending on the temperature of solder ball 8 (or a portion of solder ball 8) is measured as a function of time, and a parameter depending on the (absolute) heat capacity of the solder ball is determined based on this measurement variable. The (absolute) heat capacity of solder ball 8 is proportional to its mass, and therefore also proportional to its volume or size. Accordingly, the attachment area can then be qualitatively or quantitatively inferred from this parameter.

[0100] In particular, temperature-related variables can be measured relatively easily using optical means. Specifically, the intensity of thermionic emission from the solder ball can be measured, for example, using a camera or photodiode; similarly, the temperature of at least a portion of the solder ball can also be used as a measurement variable. A parameter that depends on the heat capacity of the solder ball 8 and is particularly easy to determine is the duration between the discontinuation of the processing laser beam and the (complete) solidification of the solder ball (“solidification time”); similarly, the temperature gradient can also be used as a parameter.

[0101] In different experimental measurements of samples (wherein the present invention uses and Figure 1b and Figure 2 The diagram shows the machining laser beam used to weld the end region of the rod-shaped conductor model, corresponding to the geometry shown. Figure 3 The solidification time determined by optical observation (see circular markers) and the actual attachment area determined by conventional X-ray analysis (see square markers) are shown separately. It is clear that the attachment area is strongly correlated with the solidification area. Accordingly, the attachment area can be inferred from the solidification time and can be determined qualitatively and quantitatively.

[0102] from Figure 3 The graph clearly shows that after a solidification time of approximately 140 ms, a thickness of approximately 8 mm was obtained. 2 The attachment area. For example, in this situation, within the range of monitoring the attachment area of ​​the welded part of the rod-shaped conductor, at least 8mm should be ensured. 2 The attachment area can be deduced from a solidification time of less than 140 ms ("decision value") to be less than 8 mm. 2 The insufficient adhesion area, and for a solidification time greater than 140 ms, an 8 mm thickness can be deduced. 2 Or a larger, sufficient attachment area. This would be a typical qualitative determination of the attachment area. Welds with attachment areas identified as too small are typically sent for supplementary welding.

[0103] If needed, a simple linear functional relationship between, for example, setting time and attachment area can also be obtained from this graph. A good approximation, applicable here to setting time EZ and attachment area AF, is:

[0104] AF(EZ) = 0.0419 mm 2 / ms*EZ+2.426mm 2

[0105] Through this functional relationship, it is also easy to derive a quantitative statement about the adhesion area from the solidification time parameter.

[0106] like Figure 3 As shown, determining the attachment area qualitatively or quantitatively based on parameters requires calibration measurements for the corresponding welding conditions (especially the size, arrangement, and material of the rod conductor).

[0107] If necessary, the welding parameters (such as laser power or the duration of the processing laser beam) can be optimized or adjusted based on the quantitative determination of the attachment area.

[0108] In the diagram, Figure 4 The structure of a first apparatus 40 for laser welding according to the present invention is shown, by which the method of the present invention can be performed.

[0109] The device 40 includes a processing laser 41 through which a processing laser beam with a wavelength of 1030 nm (not shown in detail, but see [reference needed]) is emitted. Figure 1b The end regions 5a and 5b of a pair of rod conductors 1a and 1b can be directed through a semi-transparent mirror 42 and through a scanning mirror 43 of a programmable focusing optical unit 43a. The rod conductors 1a and 1b are arranged in a holding device 50, which is implemented here as a stator carrier 51 for an electric motor; the holding device 50 typically holds more than thirty pairs of rod conductors simultaneously.

[0110] After the laser beam is deactivated, the resulting solder beads (not shown in detail, but refer to relevant information) are... Figure 2 Thermionic emission 44 is displayed. Thermionic emission 44 is imaged onto sensor device 46, which is camera 47 in this case, via scanning mirror 43, translucent mirror 42, mirror 45, and collimating lens 57; alternatively, photodiode can also be used as sensor device 46 (not shown in detail, but referenced). Figure 9 An optical filter 48 is positioned in front of the camera 47, and here a bandpass filter 49 is used, which allows only the spectral range of 800 nm to 1000 nm to pass through. The camera 47 is connected to the electronic evaluation device 52. According to the beam path depicted here, the camera 47 is pointed from above at the end regions 5a, 5b of the rod conductors 1a, 1b, or the solder beads there.

[0111] The programmable focusing optics unit 43a, along with mirrors 42 and 45 and a camera 47, are combined to form a laser processing head 53; however, it should be noted that the camera can also be arranged independently of the laser processing head, particularly for pointing at the solder beads from the side.

[0112] Here, as Figure 5a As schematically shown, an image 54 of the solder bead 8 is captured from above using camera 47. An average grayscale value (average brightness) is determined as a measurement variable from a portion 55 of image 54; this grayscale value corresponds to the intensity of thermionic emission from the solder bead 8 in a portion 56 corresponding to the portion 55 of the solder bead 8, where this portion 56 is located at the center of the upper part of the solder bead 8. Therefore, this portion 56 is opposite to the aforementioned partial surface (end-side end face) on which the processing laser beam is incident before (in this respect, refer to...) Figure 1b ).

[0113] Alternatively, the camera can be pointed sideways at solder bead 8, such as... Figure 5b The depicted portion 55 of the corresponding image 54 is then typically selected away from the edge of the solder bead 8, roughly in the middle 55 of the solder bead.

[0114] Figure 6The upper part shows a schematic diagram of a typical curve of the average gray value G as a function of time t during solder ball cooling. This is achieved using... Figure 4 The grayscale value G corresponds to the thermionic emission intensity of the solder bead. The average grayscale value is measured from the moment the processing laser is shut down until after the phase transition of the solder bead from the liquid phase to the solid phase.

[0115] The evaporation temperature T of the material corresponding to the rod-shaped conductor was measured directly when the processing laser beam was off. V grayscale value G(T) V After the processing laser is deactivated (marked "laser off"), the grayscale value G decreases in time intervals I, II, and III according to the temperature drop of the still completely liquid solder bead, and then remains at a nearly constant value G(T) in interval IV during the recrystallization (solidification) stage of the solder bead as it develops from the bottom to the top. S This value corresponds to the melting temperature T of the rod-shaped conductor material. S In interval IV, the grayscale value G is determined on the portion of the solder bead that remains liquid. In intervals V, VI, and VII, where the final, still liquid upper portion of the solder bead is observed to solidify, the grayscale value decreases significantly due to the marked reduction in thermionic emission via the liquid-solid phase transition. In interval VI, the solidification front migrates through the evaluated portion of the camera image, where G exhibits its steepest and approximately linear curve. Then, in the subsequent interval VIII, the grayscale value G continues to decrease, but the decrease is significantly slower corresponding to the gradual further reduction in temperature of the fully solidified solder bead.

[0116] By using the intersection point SP1 of the curve of grayscale value G(t) and the first threshold SW1, which preferably corresponds to the grayscale value of the (expected) value range of interval VI, the actual solidification time EZ (corresponding to the duration from the beginning of interval I to the end of interval VII) can be determined in a simple manner with a good approximation, for example, by using an electronic evaluation unit (it should be noted that the flat curves in regions VII and VIII will lead to a significantly larger error in the determination of the intersection point there). It should also be noted that intervals V, VI, and VII are typically shorter than intervals I, II, III, and IV. If necessary, the known (expected) time offset ZV between the intersection point SP1 and the end of solidification can be added to the determined time of intersection point SP1 to better approximate the actual solidification time EZ.

[0117] Another way to determine the solidification time EZ is to use the first time derivative G' of the grayscale value G, as shown in the reference. Figure 6The intermediate graph; this derivative can be calculated numerically. The decrease in thermionic emission during solidification of the solder ball in intervals V, VI, and VII can be better identified in the first derivative G' than in the curve of G; solidification in interval V can be well identified by G' becoming negative. However, since a similar (negative) value of G' also appears at the onset of cooling, for example in interval I, the solidification time EZ is approximately determined by the intersection point SP2 of the G' curve and the line just below the second threshold SW2, with respect to which the curve of G previously only varied within predetermined limits G1 and G2 at the minimum duration MD. This latter criterion is satisfied only at the intersection point SP2 in interval IV (where G' is approximately "0") and before the start of interval V (e.g., not satisfied in intervals I, II, and VII), thus the result is that the second intersection point SP2 is uniquely determined. It should also be noted that intervals V, VI, and VII are shorter than intervals I, II, III, and IV; if necessary, the known (expected) time offset between the intersection SP2 and the end of solidification can be added to the time of intersection SP1 again to determine the solidification time EZ more accurately (see above).

[0118] The solidification time EZ can also be determined more accurately based on the second time derivative G” of the gray value G, see [reference]. Figure 6 The figure below illustrates this; the second-order time derivative can also be calculated digitally, for example, in an electronic evaluation unit. In this case, complete solidification is determined very precisely by the intersection point SP3 of the curve G” and the line of the third threshold SW3, which is chosen to be significantly larger than “0”, such that the threshold SW3 is first reached in interval VII (instead, for example, in interval III). If necessary, this can also be guaranteed here by the previously elapsed shortest duration, within which the gray value G changes only within predetermined limits, and the known (expected) time offset between the determined intersection point SP3 and the actual end of solidification can be added again to determine EZ more accurately (not shown in detail, but see above).

[0119] The average gradient G' of the gray value G over a predetermined time period, preferably between two times t1 and t2 selected within interval II. M (Relative to time) is also well-suited as a parameter dependent on absolute heat capacity (except for the solidification time EZ). In this interval II, the absolute value of G' is relatively large and approximately constant, and therefore can be well determined.

[0120] It should be noted that the curves G, G', and G” are depicted in an idealized manner here. In practice, the curves depicted here usually vary over time; however, good curve smoothing can be achieved by using a sufficiently large integration surface (a portion of the image observed by the camera).

[0121] In the diagram, Figure 7 The structure of a second apparatus 40 for laser welding according to the present invention is shown, by which the method of the invention can be performed. Only related to... Figure 4 The obvious difference between the equipment.

[0122] exist Figure 7 In device 40, during the cooling of solder beads on rod conductors 1a and 1b, the solder beads are illuminated by an observation beam 71 from an observation light source 70 (in this case, an observation laser) through a semi-transparent mirror 45a. The observation beam is an observation laser beam with an average wavelength of 810 nm. The observation light source 70 does not introduce significant energy into the rod conductors 1a and 1b, but the observation laser beam 71 is reflected at the solder beads according to their temperature. The intensity of the observation beam 71 reflected at the solder beads, along with the thermionization emission 44 of the solder beads, is recorded in camera 47.

[0123] A narrowband bandpass filter 73, which serves as optical filter 48 (allowing only wavelengths in the range of 800 nm to 820 nm to pass through), is positioned in front of camera 47 to minimize the proportion of thermionic emission 44 in the measured intensity or measured grayscale value at camera 47.

[0124] Optionally, a polarization filter 74 may be provided in front of the camera 47, which can be used to improve the contrast in the image recorded by the camera 47.

[0125] Figure 8 The upper part shows a schematic graph of a typical curve of the average gray value G as a function of time t during solder ball cooling. It is shown using... Figure 7 The grayscale value G corresponds to the superposition of the intensity of the thermionic emission of the solder bead and the intensity of the reflected laser beam observed. Only explanations related to... Figure 6 The obvious difference.

[0126] In the first three intervals (I, II, and III), thermionic emission dominates the intensity measured at the camera; therefore, this largely corresponds to... Figure 6 The curve in the figure shows that the grayscale value G decreases as the temperature decreases, based on the thermionic emission of the liquid solder bead. The grayscale value G remains constant again in interval IV.

[0127] However, starting from interval IV, the dominant factor in grayscale values ​​is the intensity of the observed laser beam reflected from the solder bead. With the liquid-solid phase transition that begins in interval V, the reflectivity of the solder bead increases significantly (or its absorptivity decreases significantly), and the grayscale value G increases accordingly. In interval VIII, after the solder bead has completely solidified, the intensity of the reflected laser remains approximately constant.

[0128] This is best determined by the time first derivative G' of the grayscale value G, referencing... Figure 8 The intermediate chart in the diagram. When the curve of G' intersects the line of threshold SW4 (which is chosen to be slightly above 0) for the first time, the intersection point SP4 corresponds well to the solidification time EZ; if necessary, the known (expected) time offset ZV between the time of intersection point SP4 and the end of solidification (at the end of interval VII) can be added to the determined time of intersection point SP4 to determine EZ more accurately.

[0129] Alternatively, a threshold SW5 (at intersection SP5) for reaching the grayscale value G or a threshold SW6 (at intersection SP6) for reaching the second derivative G” of the grayscale value G (see the figure below) may also be provided to determine the solidification time EZ, but they should be guaranteed by the preceding minimum duration MD (drawn at G in the exemplary upper top chart, and guaranteeing intersection SP5), during which the grayscale value G only varies within predetermined limits G1, G2.

[0130] In the diagram, Figure 9 The structure of a third apparatus 40 for laser welding according to the present invention is shown, by which the method of the present invention can be performed. Again, only the analogy is explained. Figure 4 The obvious difference between the equipment.

[0131] The device 40 is configured for the high-temperature quotient determination method and accordingly includes two sensor devices 46 (constructed here as two photodiodes 90, 91), which are illuminated by the thermionization emission 44 of the solder beads at the rod-shaped conductors 1a, 1b. The two photodiodes 90, 91 are connected to the electronic evaluation device 52.

[0132] An optical filter 48, configured as a narrowband bandpass filter 93, is positioned in front of the photodiode 90. This optical filter allows only light of a first average wavelength λ1 to pass through, typically within a small surrounding wavelength range of + / -30 nm or less, preferably + / -20 nm. Similarly, an optical filter 48, configured as a narrowband bandpass filter 94, is positioned in front of the photodiode 91. This optical filter allows only light of a second average wavelength λ2 to pass through, typically within a small surrounding wavelength range of + / -30 nm or less, preferably + / -20 nm. For example, λ1 is 1550 nm and λ2 is 1620 nm. The temperature of the solder bead (or its observed portion) can be determined as a measurement variable based on the intensity ratio at the two wavelengths λ1 and λ2.

[0133] Figure 10 The upper part shows a schematic graph of a typical curve of temperature T as a function of time t during solder ball cooling, which is presented using... Figure 9 The temperature was observed using the equipment; here, the temperature was observed in the upper central part of the solder ball. The temperature T curve is compared with... Figure 6The grayscale curves of the thermionic emission explained in the text are largely similar, especially showing a significant temperature drop at the beginning of intervals I, II, and III, and a constant value corresponding to the melting temperature T over a relatively long period in interval IV. S The temperature T is such that, in this respect, the evaluation of temperature T can be performed in a manner similar to the grayscale value evaluation (qv) of thermionic emission, which is why it does not need to be repeated here. However, it should be noted that during the solidification of the last part of the solder ball (in the observed partial area), the (average) temperature remains almost constant and varies only slightly. This last part of the solder ball remains liquid for the longest period of time in intervals V, VI, and VII, which is the upper part of the solder ball observed here; only after the solder ball has completely solidified at the end of interval VII does the temperature slowly decrease again, with a roughly constant gradient T'. Preferably, in this case, it is just below the melting temperature T. S A threshold SW7 (e.g., at the beginning of the expected interval VIII) is applied to temperature T so that the time through intersection SP7 is used to determine the solidification time EZ as a parameter with a good approximation. Similarly, the average temperature gradient T' between times t1 and t2 in interval II can also be determined well. M As a parameter.

[0134] During the laser welding process of the end regions 5a and 5b of the rod-shaped conductors 1a and 1b, the cross sections Qa and Qb of the rod-shaped conductors 1a and 1b (perpendicular to the direction of legs 3a and 2b) are usually completely covered by the weld beads 8, such as Figure 11a The top view is shown schematically.

[0135] However, very occasionally, due to spatter formation, solder ball 8 may not completely cover the cross-section of one or both of the rod conductors 1a and 1b, such as... Figure 11b As depicted. In the example shown, approximately 1 / 3 of the cross-section Qa of the rod conductor 1a is the uncovered proportion QaU, and approximately 2 / 3 of the cross-section Qa is the proportion QaB covered by solder beads 8. For the rod conductor 1b, approximately 1 / 50 of the cross-section Qb is the uncovered proportion QbU, and approximately 49 / 50 of the cross-section Qb is the proportion QbB covered by solder beads 8, which has almost no effect. In general, approximately 1 / 6 of the entire cross-section Q = Qa + Qb of the rod conductors 1a and 1b is uncovered, which is equivalent to approximately 1 / 6 of the entire cross-section Q being uncovered proportion QU.

[0136] Within the scope of this invention, it can be categorized that if the uncovered proportion QU of Q exceeds the limit value GW, the attachment area can be classified as insufficient, regardless of the observation of the measured variable and the parameters determined therefrom. Preferably, the limit value GW is determined to be 0.10 or less relative to the entire cross-section Q, preferably 0.05 or less. As a result, poor electrical connections between the rod conductors 1a and 1b can be identified and eliminated, if necessary, by supplementary soldering.

[0137] It is also dangerous if the proportion QB of the entire cross-section Q of the rod conductors 1a and 1b covered by the solder ball is too small, because it leads to poor heat dissipation of the solder ball 8. The slowing of cooling of the solder ball 8 is assumed to be due to its large size, and correspondingly, a sufficiently large attachment area is assumed when observing temperature-related measurements and parameters determined according to the present invention, even though the attachment area is actually too small. This problem can be solved by additionally determining the uncovered proportion QU, which can be easily achieved through optical evaluation of a top view of the solder ball. It should be noted that QU + QB = 1.

[0138] List of reference numerals

[0139] 1a, 1b Rod-shaped conductors

[0140] 2a, 2b (left) leg

[0141] 3a, 3b (right) leg

[0142] 4a, 4b Central Section

[0143] 5a, 5b end regions

[0144] 6a and 6b end faces

[0145] 7. Processing laser beams

[0146] 8 solder balls

[0147] 9. Attached Area

[0148] Long sides of 11a and 11b

[0149] 12 Circular Trajectory

[0150] 40 devices

[0151] 41. Processing Lasers

[0152] 42 Semi-transparent mirror

[0153] 43 Scanning mirror

[0154] 43a Programmable Focusing Optical Unit

[0155] 44 Thermionic emission

[0156] 45 Reflector

[0157] 45a Semi-transparent mirror

[0158] 46 Sensor Devices

[0159] 47 cameras

[0160] 48 Optical Filters

[0161] 49 Bandpass Filter

[0162] 50 Holding device

[0163] 51 Stator Carrier

[0164] 52 Electronic evaluation device

[0165] 53 Laser processing head

[0166] 54 images

[0167] 55. Partial area of ​​the image

[0168] 56. Solder ball portion

[0169] 57 Collimating Lens

[0170] 70. Observe the light source

[0171] 71 Observe the beam of light

[0172] 73 Bandpass Filter

[0173] 74 Polarization Filter

[0174] 90 photodiode

[0175] 91 Photodiode

[0176] 93 Bandpass Filter

[0177] 94 Bandpass Filter

[0178] EZ solidification time

[0179] G grayscale value

[0180] G' First derivative of gray value with respect to time

[0181] G' M Average gradient of gray values

[0182] G” is the second derivative of the gray value with respect to time.

[0183] Limits of G1 and G2 (measured variables)

[0184] GW (for uncovered) limit

[0185] H. Height of solder ball

[0186] Minimum Duration of MD

[0187] Q. Cross-sections of the two rod-shaped conductors.

[0188] Qa is the cross-section of rod-shaped conductor 1a.

[0189] The cross-section of rod-shaped conductor 1b.

[0190] QaB Coverage ratio of the cross section of rod-shaped conductor 1a

[0191] The coverage ratio of the cross section of the rod-shaped conductor 1b in QbB.

[0192] QaU Uncovered percentage of the cross-section of rod-shaped conductor 1a

[0193] The percentage of the cross-section of the QbU rod conductor 1b that is not covered.

[0194] QU The percentage of uncovered cross-sections of two rod-shaped conductors.

[0195] SP1-SP7 intersection

[0196] SW1-SW7 thresholds

[0197] t time

[0198] t1, t2 time

[0199] T temperature

[0200] T', the first derivative of temperature with respect to time

[0201] T' M Average temperature gradient

[0202] T” is the second derivative of temperature with respect to time.

[0203] T S melting temperature

[0204] T V Evaporation temperature

[0205] ZV Time Offset.

Claims

1. A method for monitoring the adhesion area (9) during laser welding of copper-containing bent rod-shaped conductors (1a, 1b), wherein, Two rod-shaped conductors (1a, 1b) are arranged in a partially overlapping manner and welded together by means of a processing laser beam (7). Solder beads (8) are formed to connect the rod-shaped conductors (1a, 1b) to each other. Its characteristics are, At least one measured variable relating to the temperature of the solder bead (8) is measured as a function of time t at least on a portion (56) of the solder bead (8) during the cooling period after the action of the processing laser beam (7) has ended. The parameters that depend on the heat capacity of the solder ball (8) are determined from the at least one measured variable. The attachment area (9) is determined qualitatively or quantitatively by the parameters that depend on the heat capacity of the solder ball (8).

2. The method for monitoring the attachment area (9) during laser welding of copper-containing bent rod-shaped conductors (1a, 1b) as described in claim 1, characterized in that, Two rod-shaped conductors (1a, 1b) are arranged such that their end regions (5a, 5b) are parallel to each other and adjacent to each other. The end faces (6a, 6b) on the end sides of the rod-shaped conductors (1a, 1b) are at the same height with respect to the longitudinal extension direction of the end regions (5a, 5b) of the rod-shaped conductors (1a, 1b). The processing laser beam (7) is directed onto two rod-shaped conductors (1a, 1b) such that the solder bead (8) is formed at the end faces (6a, 6b) on the end sides of the rod-shaped conductors (1a, 1b).

3. The method for monitoring the attachment area (9) during laser welding of copper-containing bent rod-shaped conductors (1a, 1b) as described in claim 1 or 2, characterized in that, At least a portion (56) of the solder bead (8) is observed in the visible spectral range and / or the infrared spectral range to measure the at least one measurement variable.

4. The method for monitoring the attachment area (9) during laser welding of copper-containing bent rod-shaped conductors (1a, 1b) as described in claim 3, characterized in that, The at least one measurement variable is measured on a portion of the solder bead that faces the portion of the rod-shaped conductor (1a, 1b) that is acted upon by the laser beam (7).

5. The method for monitoring the attachment area (9) during laser welding of copper-containing bent rod-shaped conductors (1a, 1b) as described in claim 3, characterized in that, The at least one measurement variable includes the intensity of the thermionic emission (44) of at least a portion (56) of the solder ball (8).

6. The method for monitoring the attachment area (9) during laser welding of copper-containing bent rod-shaped conductors (1a, 1b) as described in claim 5, characterized in that, The intensity of the thermionic emission (44) was measured only within a limited spectral range.

7. The method for monitoring the adhesion area (9) during laser welding of copper-containing bent rod-shaped conductors (1a, 1b) as described in claim 1, characterized in that, During the cooling of the solder ball (8), the solder ball (8) is illuminated with an observation beam (71). The at least one measurement variable includes the intensity of the observation beam (71) reflected at the surface of the solder ball (8).

8. The method for monitoring the attachment area (9) during laser welding of copper-containing bent rod-shaped conductors (1a, 1b) as described in claim 7, characterized in that, The intensity of the reflected observation beam (71) is measured only within a limited spectral range around the average wavelength of the observation beam (71).

9. The method for monitoring the attachment area (9) during laser welding of copper-containing bent rod-shaped conductors (1a, 1b) as described in claim 7 or 8, characterized in that, A polarization filter (74) is positioned in front of a sensor device (46) that measures the intensity of the reflected observation beam (71).

10. The method for monitoring the attachment area (9) during laser welding of copper-containing bent rod-shaped conductors (1a, 1b) as described in claim 5, characterized in that, The solder ball (8) is observed with a camera (47), and the intensity of the thermal ion emission (44) and / or reflected observation beam (71) at a portion (56) of the solder ball (8) is determined by the camera (47) in a portion (55) of the image (54) recorded by the camera (47) by determining the average gray value G of the camera (47) in that portion (55) of the image (54) recorded by the camera (47).

11. The method for monitoring the attachment area (9) during laser welding of copper-containing bent rod-shaped conductors (1a, 1b) as described in claim 5, characterized in that, The solder bead (8) is observed using a photodiode (90, 91), and the intensity of the thermionic emission (44) and / or reflected observation beam (71) at least a portion (56) of the solder bead (8) is determined as the gray value G of the photodiode (90, 91).

12. The method for monitoring the attachment area (9) during laser welding of copper-containing bent rod-shaped conductors (1a, 1b) as described in claim 3 or 4, characterized in that, The at least one measured variable includes the temperature T at least on a portion of the solder ball (8).

13. The method for monitoring the attachment area (9) during laser welding of copper-containing bent rod-shaped conductors (1a, 1b) as described in claim 12, characterized in that, The temperature T is measured by means of the quotient high temperature determination method, wherein the intensity of the thermionic emission (44) of at least the portion (56) of the solder ball (8) is measured at two different wavelengths.

14. The method for monitoring the attachment area (9) during laser welding of copper-containing bent rod-shaped conductors (1a, 1b) as described in claim 1, characterized in that, The parameter that depends on the heat capacity of the solder ball (8) is the duration that passes between the first defined state and the second defined state during the cooling of the solder ball (8).

15. The method for monitoring the attachment area (9) during laser welding of copper-containing bent rod-shaped conductors (1a, 1b) as described in claim 14, characterized in that, The first defined state is the end of the action of the processing laser beam (7).

16. The method for monitoring the attachment area (9) during laser welding of copper-containing bent rod-shaped conductors (1a, 1b) as described in claim 14 or 15, characterized in that, The second defined state is the complete solidification of the solder ball (8).

17. The method for monitoring the attachment area (9) during laser welding of copper-containing bent rod-shaped conductors (1a, 1b) as described in claim 14 or 15, characterized in that, The first defined state and / or the second defined state are identified by the at least one measured variable reaching a threshold.

18. The method for monitoring the attachment area (9) during laser welding of copper-containing bent rod-shaped conductors (1a, 1b) as described in claim 14 or 15, characterized in that, The first defined state and / or the second defined state are identified in the following ways: The first-order time derivative and / or second-order time derivative of at least one measured variable reaches a threshold.

19. The method for monitoring the attachment area (9) during laser welding of copper-containing bent rod-shaped conductors (1a, 1b) as described in claim 1 or 2, characterized in that, The parameter that depends on the heat capacity of the solder ball (8) is the time gradient of the at least one measured variable, which is determined at a predetermined time or averaged over a predetermined time period.

20. The method for monitoring the attachment area (9) during laser welding of copper-containing bent rod-shaped conductors (1a, 1b) as described in claim 1 or 2, characterized in that, The attachment area (9) determined quantitatively by the parameter depending on the heat capacity of the solder ball (8) is compared with the decision value. If the decision value is not reached, the attachment area (9) of the welded part is identified as too small. If the decision value is reached, the attachment area (9) is identified as large enough to allow the continued use of the associated rod conductor (1a, 1b).

21. The method for monitoring the attachment area (9) during laser welding of copper-containing bent rod-shaped conductors (1a, 1b) as described in claim 20, characterized in that, by means of... The camera (47) determines the proportion QU of the cross section Q of the rod conductor (1a, 1b) that is not covered by the solder ball (8), and if the proportion QU of the uncovered cross section Q exceeds the limit value GW, the attachment area (9) of the solder part of the rod conductor (1a, 1b) is identified as too small even if the decision value is reached.

22. The method for monitoring the attachment area (9) during laser welding of copper-containing bent rod-shaped conductors (1a, 1b) as described in claim 1 or 2, characterized in that, Multiple pairs of rod conductors (1a, 1b) are successively welded, wherein one or more welding parameters are optimized and / or adjusted in the control loop during the welding of these pairs of rod conductors (1a, 1b) such that the attachment area (9) of the pair of rod conductors (1a, 1b) for welding, which is determined by the parameter depending on the heat capacity of the solder ball (8) or by the parameter depending on the heat capacity of the solder ball (8), is set to a predetermined target value.

23. The method for monitoring the attachment area (9) during laser welding of copper-containing bent rod-shaped conductors (1a, 1b) as described in claim 1 or 2, characterized in that, The bent rod-shaped conductors (1a, 1b) are the hairpins of the electric motor.

24. The method for monitoring the attachment area (9) during laser welding of copper-containing bent rod-shaped conductors (1a, 1b) as described in claim 2, characterized in that, The end regions (5a, 5b) of the rod-shaped conductors (1a, 1b) are pressed together in a planar manner.

25. The method for monitoring the attachment area (9) during laser welding of copper-containing bent rod-shaped conductors (1a, 1b) as described in claim 2, characterized in that, The end regions (5a, 5b) of the rod-shaped conductors (1a, 1b) point vertically upwards, and the processing laser beam (7) falls vertically onto the end faces (6a, 6b) of the end sides.

26. The method for monitoring the attachment area (9) during laser welding of copper-containing bent rod-shaped conductors (1a, 1b) as described in claim 4, characterized in that, The at least one measurement variable is measured on the portion of the solder bead (8) located at the upper center of the solder bead (8).

27. The method for monitoring the attachment area (9) during laser welding of copper-containing bent rod-shaped conductors (1a, 1b) as described in claim 6, characterized in that, The finite spectral range is no greater than 800 nm to 1100 nm.

28. The method for monitoring the attachment area (9) during laser welding of copper-containing bent rod-shaped conductors (1a, 1b) as described in claim 6, characterized in that, To limit the finite spectral range, a bandpass filter (49) and / or a broadband filter are arranged in front of the sensor device (46) used to measure the intensity of thermionic emission (44).

29. The method for monitoring the attachment area (9) during laser welding of copper-containing bent rod-shaped conductors (1a, 1b) as described in claim 6, characterized in that, The wavelength range of the processing laser beam (7) is outside the finite spectral range.

30. The method for monitoring the attachment area (9) during laser welding of copper-containing bent rod-shaped conductors (1a, 1b) as described in claim 7, characterized in that, The observation beam (71) is an observation laser beam.

31. The method for monitoring the attachment area (9) during laser welding of copper-containing bent rod-shaped conductors (1a, 1b) as described in claim 8, characterized in that, The finite spectral range is no greater than + / -20 nm or + / -10 nm around the average wavelength of the observed beam (71).

32. The method for monitoring the attachment area (9) during laser welding of copper-containing bent rod-shaped conductors (1a, 1b) as described in claim 8, characterized in that, In order to limit the finite spectral range, a bandpass filter (73) is arranged in front of the sensor device (46) that measures the intensity of the reflected observation beam (71).

33. The method for monitoring the attachment area (9) during laser welding of copper-containing bent rod-shaped conductors (1a, 1b) as described in claim 9, characterized in that, The polarization filter (74) is selected as a linear polarizer.

34. The method for monitoring the attachment area (9) during laser welding of copper-containing bent rod-shaped conductors (1a, 1b) as described in claim 18, characterized in that, After the at least one measured variable has previously fluctuated only within a predetermined limit for a predetermined minimum duration, the first-order time derivative and / or second-order time derivative of the at least one measured variable reaches a threshold.

35. The method for monitoring the attachment area (9) during laser welding of copper-containing bent rod-shaped conductors (1a, 1b) as described in claim 20, characterized in that, If the attachment area (9) of the welded part is identified as too small, the relevant rod conductors (1a, 1b) are discarded or additional welding is performed.

36. An apparatus (40) for laser welding copper-containing bent rod-shaped conductors (1a, 1b), comprising: The holding device (50) allows two rod-shaped conductors (1a, 1b) to be arranged in an overlapping manner; A laser processing head (53) provides a processing laser beam (7) for welding the two rod-shaped conductors (1a, 1b) together to form a weld bead (8), which connects the rod-shaped conductors (1a, 1b) to each other. The laser beam (7) is characterized in that... The device (40) also includes a sensor device (46) by which at least one measurement variable of the temperature change of the solder bead (8) can be measured at least on a portion (56) of the solder bead (8) during the cooling period after the action of the processing laser beam (7) ends. The device (40) also has an electronic evaluation device (52) configured to determine parameters dependent on the heat capacity of the solder ball (8) from the at least one measured variable. The electronic evaluation device (52) is also configured to qualitatively or quantitatively determine the attachment area (9) established by the solder ball (8) by the parameter depending on the heat capacity of the solder ball (8).

37. The apparatus (40) for laser welding copper-containing bent rod-shaped conductors (1a, 1b) as described in claim 36, characterized in that, The bent rod-shaped conductors (1a, 1b) are the hairpins of the electric motor.

38. The apparatus (40) for laser welding copper-containing bent rod-shaped conductors (1a, 1b) as described in claim 36, characterized in that, The holding device (50) includes a stator carrier (51) which includes a plurality of rod-shaped conductors (1a, 1b) to be welded.

39. The apparatus (40) for laser welding copper-containing bent rod-shaped conductors (1a, 1b) as described in claim 36, characterized in that, The electronic evaluation device (52) is programmed to determine parameters dependent on the heat capacity of the solder ball (8) by the measured at least one measurement variable.

40. The apparatus (40) for laser welding copper-containing bent rod-shaped conductors (1a, 1b) as described in claim 36, characterized in that, The electronic evaluation device (52) is programmed to qualitatively or quantitatively determine the attachment area (9) established by the solder ball (8) by the parameters depending on the heat capacity of the solder ball (8).

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