Method for determining a vapor capillary depth

Abstract

A method for determining a vapor capillary depth (Zdepth) in relation to a surface of a conductor end arrangement (26), comprising at least two conductor ends, in particular a pair of conductor ends, comprises the following method steps: a. Determining a surface value (Zpre, Zin, Zpost) describing the position of the surface in the area of ​​the conductor end arrangement (26) before or after a welding process, b. Performing the welding process with a laser beam (14) by directing the laser beam (14) towards the end face of at least one conductor end (22, 24) of a conductor and by introducing energy into the at least one conductor end (22, 24), c. Performing a depth measurement of a vapor capillary at the current position of the laser beam (14) and determining a depth value (Zcapill), d. Determining a vapor capillary depth (Zdepth) from the surface value (Zpre, Zin, Zpost) and the depth value (Zcapill), in particular by calculating the difference.

Description

[0001] The invention relates to a method for determining a vapor capillary depth in relation to a surface of a conductor end arrangement.

[0002] For the construction of stators in electric motors, it is known to provide a stator cage made of an insulating material, into which electrical conductors, in particular so-called hairpins made of an electrically conductive material, preferably copper, are inserted. The hairpins can, for example, be clamp-shaped or linear and, after being inserted into the stator cage, lie parallel to each other and essentially in the axial direction of the stator or the electric motor within the stator cage. A multitude of such hairpins are inserted around the circumference of the stator cage, which initially have no mechanical or electrical connection to each other during assembly or manufacturing.After being inserted into the stator cage and after any necessary forming and / or shortening, and any necessary pretreatment, such as paint removal, the free ends of the hairpins are preferably joined together in pairs, for example by welding, to form a complete stator winding. This joining process creates both a mechanical and an electrically conductive connection between the free ends of the respective hairpin pairs, so that the hairpins, which were initially separate after insertion, are now connected. By joining the hairpins, a continuous stator winding, mechanically and electrically connected, can be formed.

[0003] A corresponding welding process for joining hairpins is known, for example, from EP 4 104 963 A1.

[0004] Quality assurance in the welding of e-mobility components is of paramount importance due to the risk of vehicle fires resulting from short circuits at poor-quality welds. Measuring a vapor capillary alone is insufficient to characterize the quality of the welding process.

[0005] The object of the present invention is therefore to provide a method that allows for the reliable detection and evaluation of a welding process by which at least two conductor ends are joined.

[0006] According to a first aspect of the invention, the problem is solved by a method for determining a vapor capillary depth in relation to a surface of a conductor end arrangement, comprising at least two conductor ends, in particular a pair of conductor ends, with the following method steps: a. Determining a surface value describing the position of the surface in the area of ​​the conductor end arrangement before or after a welding process, b. Performing the welding process with a laser beam, in particular by directing the laser beam towards at least one conductor end of a conductor and by introducing energy into the at least one conductor end, c. Performing a depth measurement of a vapor capillary at the current position of the laser beam and determining a depth value, d. Determining a vapor capillary depth from the surface value and the depth value, in particular by calculating the difference.

[0007] During laser welding, a deep, narrow, vapor-filled hole forms, known as a vapor capillary or keyhole. The vapor capillary is surrounded by molten metal. As the laser beam moves across the joint, the vapor capillary moves with it through the workpiece. The depth of the vapor capillary is of particular interest because it directly affects the quality of the weld.

[0008] The term "surface value" can be understood, within the meaning of the present invention, as a measurand used to describe the position of the surface in the area of ​​the conductor end assembly. The surface value can be determined before or after the welding process and used as a reference value for determining the vapor capillary depth. The surface measurement can be performed on one or more, in particular two, conductor ends. When measuring more than one conductor end, the minimum, maximum, or average of the measured values ​​can be used as the surface value.

[0009] The technical advantages of this method lie particularly in the precise determination of the welding depth. By determining the vapor capillary depth, the quality of the welding process can be monitored and improved. This is especially relevant in applications where precise control of the welding parameters is essential for product integrity and performance. Furthermore, the precise determination of the vapor capillary depth enables optimized laser energy control, thereby increasing the efficiency of the welding process.

[0010] Furthermore, monitoring of the vapor capillary depth using predefined limits may be provided. It is also conceivable that a quality assessment may be generated.

[0011] Surface measurement can be performed before or after the welding process to determine the surface value.

[0012] The term "surface measurement" can be understood, within the meaning of the present invention, as a method for determining the physical position of the surface of one or more conductor ends. This measurement provides precise data on the topographical characteristics of the weld joint or the conductor ends and serves as a basis for further calculations, such as the vapor capillary depth.

[0013] Surface measurement enables the accurate determination of the surface value, which is essential for the precise calculation of the vapor capillary depth.

[0014] It may be possible to perform the surface measurement inline before switching on the laser beam.

[0015] The term "inline" can be understood, within the meaning of the present invention, to mean that the measurement is carried out as part of a continuous manufacturing or processing line without interrupting the process flow. This means that the surface measurement takes place immediately before the welding process and in close spatial and temporal proximity to the corresponding welding process, in particular before a vapor capillary has formed.

[0016] The technical advantages of inline surface measurement are significant, particularly with regard to efficiency and process control. Since the measurement is performed directly before the welding process, the acquired values ​​can be used immediately to adjust the welding procedure. This allows for rapid adaptation of the laser beam to the given surface conditions and optimization of the welding result. Furthermore, inline measurement contributes to increased production efficiency because no separate measurement processes are required and the information is immediately available.

[0017] It may be provided that the surface measurement is carried out using a liquid or solidified weld bead, especially immediately after switching off the laser beam.

[0018] In laser welding, the conductor ends first melt. This creates a molten pool, resulting in a weld bead. This weld bead can be liquid if the solidification phase is not yet complete, or already solid if the cooling process has already hardened the material joint. Due to the surface tension of the molten metal, the surface of the weld bead is generally curved in both the liquid and solidified states. The surface area can be defined as the minimum, maximum, or average value of the surface area.

[0019] The technical advantages of using a liquid or solidified weld bead for surface measurement lie particularly in the accuracy of the measurement with regard to the actual welding results. Measurement using the weld bead provides detailed insights into the outcome of the welding process and allows for the immediate evaluation of key quality characteristics of the weld. For example, the surface texture of the weld bead can provide information about the uniformity of the energy input as well as potential defects or irregularities in the welding process. Performing this measurement immediately after the laser beam is switched off helps to capture the condition of the weld at a critical point in time, before the materials have been affected by further production steps. This enables timely quality control and, if necessary, process correction.

[0020] Surface and / or depth measurements can be performed using optical coherence tomography. Optical coherence tomography (OCT) is based on the fundamental principle of light wave interference and enables the detection of height differences along a measurement beam axis in the micrometer range.

[0021] For the purposes of the present invention, the term "depth measurement" can be understood as a measurement designed to determine the spatial extent of the vapor capillary, particularly in a principal direction of extension of the conductor ends, for example along the z-axis. Optical coherence tomography makes it possible to perform such measurements with high precision and resolution.

[0022] The technical advantages of optical coherence tomography (OCT) for depth measurement lie in its ability to enable fast and accurate real-time determination of vapor capillary depth. This is particularly relevant for complex welding processes where monitoring the weld depth is crucial for joint quality. Furthermore, OCT measurement is advantageous because it does not affect the weld seam. This leads to improved quality assurance during the welding process and can contribute to enhancing the safety of e-mobility applications.

[0023] According to an advantageous variant of the method, the surface measurement is carried out by performing a first line scan over the conductor end arrangement, in particular one or two conductor ends, or the weld bead using a measuring beam.

[0024] “Line scan” means that a measuring beam is guided along a defined path or line across the conductor end arrangement or the weld bead, continuously recording measurement data.

[0025] It is particularly preferred if the surface measurement is performed by conducting a second line scan with the measuring beam in a direction perpendicular to the first line scan. This means that the surface data is acquired in two different directions intersecting at right angles, thus enabling a two-dimensional characterization of the surface. An extreme value, in particular a maximum or minimum of the surface value, can therefore be determined, especially for a curved surface. Averaging is also possible using this method.

[0026] First, a maximum of the measurement can be determined with the first line scan, and then the second line scan can be performed through the location of the maximum.

[0027] In particular, the maximum size of a sweat bead can be found in this way with a small number of scans.

[0028] It may be provided that the surface value is determined as a minimum, a maximum, or an average value of the surface measurement.

[0029] The technical advantages of determining the surface finish using these characteristic values ​​lie in the differentiated evaluation of the conductor ends' surface condition before or after the welding process. The minimum value indicates potential depressions or indentations, while the maximum reveals protrusions or peaks. The mean value can be used as an indicator of the surface's position. These various measurements can be used to adapt the welding process to the specific surface conditions, thereby achieving high consistency and quality in the welds. The selection of the specific characteristic values ​​depends on the requirements of the welding process and the desired weld properties, and can contribute to targeted process control and quality improvement.

[0030] Surface measurement can provide further information, such as the roundness of the weld bead. This information can then be used for quality assessment.

[0031] It may be necessary to perform the depth measurement at the end of the welding process, particularly immediately before switching off the laser beam. A specific depth value or an averaged depth value can be used to determine the vapor capillary depth.

[0032] The term "at the end of the welding process" can be understood, within the meaning of the present invention, as the point in time at which the welding process is almost complete and shortly before the laser beam is interrupted. This is a critical phase in which the final assessment of the weld depth can be carried out before the heat and energy input into the material ceases.

[0033] This allows for a direct assessment of the weld depth produced by the welding process. Such a measurement point is particularly relevant for determining the final weld depth, which is crucial for the quality of the weld joint.

[0034] According to one method variant, it can be provided that the determination of surface and depth values ​​is carried out according to the following method steps: a. Before switching on the laser beam, a first surface value is determined for the first conductor end, and then after switching on the laser beam, a first depth value is determined for the first conductor end. b. Subsequently, before switching on the laser beam, a second surface value is determined for the second conductor end, and then after switching on the laser beam, a second depth value is determined for the second conductor end. c. Subsequently, a third surface value is determined as the average of the first and second surface values, and a third depth value is determined as the average of the first and second depth values.

[0035] The technical advantages of this method lie in the sequential and systematic acquisition of surface and depth values, which makes it possible to obtain a detailed and comprehensive picture of both the initial surface and the resulting weld depth. By comparing the measured surface values ​​before welding with the depth values ​​after welding, the quality of the welding process can be assessed. This can be used for precise control of the laser-guided welding process and for optimizing the welding parameters. Furthermore, calculating average values ​​makes it possible to smooth out fluctuations in the measured values ​​and thus obtain a robust measurement result that representatively reflects the quality of the weld.

[0036] According to a further aspect of the invention, it can be provided that a laser welding system is provided with a laser welding device, a measuring device and a control system, wherein the control system is connected to the laser welding device and the measuring device via data technology and is configured to carry out the method according to the invention.

[0037] The laser welding device performs the actual welding process with the laser beam, while the measuring device is used to record relevant measurement data before, during and / or after the welding process.

[0038] The control system acts as the core component of the laser welding system, coordinating, controlling, and monitoring the functions of the laser welding unit and the measuring device. The control system can be configured to process all available data and, based on this, optimally adjust the laser welding process.

[0039] The use of optical coherence tomography by the measuring device in conjunction with intelligent control enables precise monitoring and adjustment of the welding process for quality assurance.

[0040] According to a further aspect of the invention, a computer program product can be provided which contains machine-readable control instructions. When these control instructions are loaded into a controller of a laser welding system according to the invention, they cause the laser welding system to carry out the process according to the invention.

[0041] Further features and advantages of the invention will become apparent from the following detailed description of exemplary embodiments of the invention with reference to the figures in the drawing, which show essential details of the invention, as well as from the claims. The features shown therein are not necessarily to scale and are depicted in such a way that the inventive features are clearly visible. The various features can be implemented individually or in any combination in variants of the invention.

[0042] The schematic drawing shows exemplary embodiments of the invention in various stages of use, which are explained in more detail in the following description.

[0043] They show: Fig. 1. A highly schematic representation of a laser welding system; Fig. 2 schematically the performance of a line scan across the end faces of two conductor ends; Fig. 3. The representation of two surface values ​​as a result of the line scan. Fig. 4. Measuring the surface area of ​​a weld bead using two line scans; Fig. 5 the result of the measurement of a first line scan parallel to an x-direction; Fig. 6 the result of the measurement according to a second line scan parallel to a y-direction; Fig. 7. Determining a vapor capillary depth after measuring the surface of a conductor end arrangement; Fig. 8. Determining a vapor capillary depth by measuring the surface of the conductor end assembly inline. Fig. 9. Determining the vapor capillary depth, whereby the surface of the conductor end arrangement is measured after the laser welding process has been carried out.

[0044] The Fig. Figure 1 shows a laser welding system 10 comprising a laser welding device 12. The laser welding device 12 allows a laser beam 14 to be directed onto the conductor ends 22, 24 of a conductor end assembly 26 in order to melt and weld the conductor ends 22, 24. The laser beam 14 can be directed onto the end faces 21, 23 of the conductor ends 22, 24. In the exemplary embodiment, only two conductor ends 22, 24 are shown. However, a conductor end assembly 26 can also have more than two conductor ends 22, 24. A pair of conductor ends with two conductor ends 22, 24 is, however, the most common application.

[0045] The laser welding process can be controlled by a controller 20. For this purpose, the controller 20 is connected to the laser welding device 12 via a signal connection.

[0046] Furthermore, the laser welding system 10 includes a measuring device 16 that can emit a measuring beam 18, in particular directed at the conductor end assembly 26. The measuring device 16 can be a coherence tomograph, in particular for performing an OCT coherence measurement procedure. The measuring device 16 can have an OCT scanner through which the measuring beam 18 can be guided over the conductor end assembly 26. The measuring device 16 is also connected to the control unit 20 via a signal connection.

[0047] To analyze the quality of a welding process, it is desirable to determine the vapor capillary depth in relation to a surface of the conductor end assembly 26. It is therefore necessary to determine a surface value that describes the location of the surface of the conductor end assembly 26. The surface of the conductor end assembly 26 can, for example, be formed by surfaces 21 and 23.

[0048] In Fig. Figure 2 shows that a line scan 30 can be performed across the conductor ends 22, 24 using the measuring beam 18. In the illustrated embodiment, the line scan 30 runs in the y-direction. The line scan 30 is performed before the conductor ends 22, 24 are melted by the laser beam 14. In particular, the line scan 30 can be performed at a large time interval after the laser beam 14 is switched on. A surface value such as a maximum Zmax,pre or a minimum Zmin,pre can be determined, as shown in the Fig. 3 is shown.

[0049] Instead of determining a surface value before the laser welding process, it is also possible to determine a surface value after the laser welding process has been carried out, in particular using a still liquid or just solidified weld bead 26a, as is done in the Fig. Figure 4 shows that a first line scan 32 is performed parallel to the x-direction. Subsequently, based on the measurement result 32a (see Figure 4), the following steps are taken: Fig. 5) A maximum Zmax,x of the height measurement is determined by the line scan, 32. The location Xzmax where the maximum Zmax,x occurs is determined. Subsequently, a second line scan 34, perpendicular to the first line scan 32, can be performed, with the second line scan 34 being carried out at the location Xzmax, i.e., passing through the maximum of the first line scan 32. The corresponding measurement result 34a can be, as described in the Fig. As shown in section 6, the results are evaluated in order to determine a maximum Zmax,post as a surface value.

[0050] The Fig. Figure 7 shows the determination of a vapor capillary depth Zdepth. In the example shown, the Fig. 7. A surface value Zpre corresponding to the Fig. 3 determined, whereby the minimum Zmin,pre was chosen for determining the vapor capillary depth Zdepth in this case. Zpre was therefore determined before the laser welding process was carried out. At a time interval, the laser beam 14 was switched on at time ton, so that the conductor ends 22, 24 melted and a vapor capillary was formed. The depth Zcapill of the vapor capillary was determined using the measuring beam 18. Zcapill can be determined, in particular, as the height value when the laser beam 14 is switched off at time toff. In the illustrated embodiment, the vapor capillary depth Zdepth is determined as the difference between Zcapill and Zpre, whereby the minimum Zmin,pre was used as the surface value in this case. In principle, however, it would also be conceivable to use the value Zmax,pre of the Fig. 3 or to use an average of the recorded values ​​Zpre.

[0051] In the exemplary embodiment of the Fig. 8. The surface value is determined inline. This means that the line scan 30 is performed immediately before the laser beam 14 is switched on at time ton. The corresponding surface value in this case is Zin. The laser beam 14 is switched on from ton to toff. At time toff, or in its immediate vicinity, a depth value Zcapill of the vapor capillary is determined. The vapor capillary depth Zdepth is determined by calculating the difference.

[0052] The Fig. Figure 9 shows an embodiment in which the surface value is determined after the laser welding process. First, the laser beam 14 is switched on at time ton. At time toff or in its immediate vicinity, the depth value Zcapill is determined using coherence tomography. Subsequently, the weld bead 26a is used, as described in the Fig.As shown in Figures 4-6, the surface area Zpost, specifically the maximum value Zmax,post, is determined. The vapor capillary depth Zdepth is determined as the difference between Zcapill and Zpost. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] EP 4 104 963 A1

[0003]

Claims

[1] Method for determining a vapor capillary depth (Zdepth) in relation to a surface of a conductor end arrangement (26), comprising at least two conductor ends, in particular a pair of conductor ends, comprising the method steps: a. Determining a surface value (Zpre, Zin, Zpost) describing the position of the surface in the area of ​​the conductor end arrangement (26) before or after a welding process, b. Performing the welding process with a laser beam (14), in particular by directing the laser beam (14) towards at least one conductor end (22, 24) of a conductor and by introducing energy into the at least one conductor end (22, 24), c. Performing a depth measurement of a vapor capillary at the current position of the laser beam (14) and determining a depth value (Zcapill), d. Determining a vapor capillary depth (Zdepth) from the surface value (Zpre, Zin, Zpost) and the depth value (Zcapill), in particular by calculating the difference. [2] Method according to claim 1, characterized by , that to determine the surface value (Zpre, Zin, Zpost) a surface measurement is carried out before or after the welding process. [3] Method according to any one of the preceding claims, characterized by , that the surface measurement is carried out inline before the laser beam (14) is switched on (tone). [4] Method according to any one of the preceding claims, characterized by that the surface measurement is carried out using a liquid or solidified weld bead (26a), in particular immediately after switching off (toff) the laser beam (14). [5] Method according to any one of the preceding claims, characterized by that the surface measurement is carried out using optical coherence tomography. [6] Method according to any one of the preceding claims, characterized by that the depth measurement is performed using optical coherence tomography. [7] Method according to any one of the preceding claims, characterized by , that the surface measurement is carried out by performing a first line scan (30, 32) with a measuring beam (18) over the conductor end arrangement (26), in particular one or two conductor ends (22, 24), or the weld bead (26a). [8] Method according to claim 7, characterized by , that the surface measurement is carried out by performing a second line scan (34) with the measuring beam (18) in a direction perpendicular to the first line scan (32). [9] Method according to claim 8, characterized by , that first a maximum (Zmax,x) of the measurement is determined with the first line scan (32) and the second line scan (34) is passed through the location (Xzmax) of the maximum (Zmax,x). [10] Method according to any one of the preceding claims, characterized by, that the surface value (Zpre, Zin, Zpost) is determined as a minimum (Zmin,pre), a maximum (Zmax,pre, Zmax,post) or a mean value of the surface measurement. [11] Method according to any one of the preceding claims, characterized by that the depth measurement is carried out at the end of the welding process. [12] Method according to any one of the preceding claims, characterized by , that a. before switching on the laser beam (14) a first surface value (Zpre) for the first conductor end (22) is determined and then after switching on (ton) the laser beam (14) a first depth value (Zcapill) for the first conductor end (22) is determined, b. subsequently, before switching on the laser beam (14), a second surface value (Zpre) for the second conductor end (24) is determined, and then after switching on (ton) the laser beam (14), a second depth value (Zcapill) for the second conductor end (22) is determined, c. subsequently determining a third surface value as the average of the first and second surface values ​​(Zpre) and determining a third depth value (Zcapill) as the average of the first and second depth values ​​(Zcapill). [13] Laser welding system (10) comprising a laser welding device (12), a measuring device (16) and a control system (20) which is connected to the laser welding device (12) and the measuring device (16) via data technology and which is configured to carry out the method according to one of the preceding claims. [14] Computer program product containing machine-readable control instructions which, when loaded into a controller (20) of a laser welding system (10) according to claim 14, cause the laser welding system (10) to perform the method according to any one of claims 1 to 13.

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