In-situ measurement methods and laser welding processes

Abstract

The invention relates to an in-situ measuring method for quality assurance, in particular in laser welding, in which a welding depth in a height direction (z) is continuously determined in a horizontal plane (xy) along a predeterminable seam path (210), wherein in the measuring method with an OCT scanner at at least three measuring points (300, 301, 302, 303) a height measurement value (420) of a surface of an upper joining partner (120) is determined, the at least three height measurement values ​​(420) are compared with one another and a position error (130) of the upper joining partner (120) is determined from the comparison. The invention further relates to a laser welding method in which a weld seam (200) running in a horizontal plane (xy) along a predeterminable seam path (210) is produced between two joining partners (110, 120) arranged one above the other in the height direction (z), wherein an in-situ measuring method according to the invention is carried out during welding.

Description

[0001] The invention relates to an in-situ measuring method according to the preamble of claim 1 and a laser welding method according to the preamble of claim 4.

[0002] Laser welding is playing an increasingly important role in industry today, particularly in the development and production of lithium-ion cells and lithium-ion batteries. The laser technology used often places increased demands on the components to be joined in terms of position tolerance, surface quality, contamination, or the permissible gap between the joining partners. This gap frequently results from an inclination of the upper joining partner to the lower joining partner, meaning that plane parallelism between the two partners is not achieved. Laser welding processes are generally very gap-sensitive; there is often talk of a required technical zero gap for such joining processes, or of various defect patterns such as the "false friend," i.e. a seemingly flawless weld seam with a perfect appearance, but with no or only inadequate connection.Even with sophisticated clamping technology, it is not always possible to produce the required technical zero gap in a process-safe manner in reality.

[0003] Various measuring instruments are used today to evaluate weld seam quality. One of the most promising quality assurance systems is optical coherence tomography (OCT), which is used to measure the weld penetration in real time during the welding process, i.e., in situ. For this purpose, a laser welding device can be combined with an OCT scanner, which scans the forming weld seam and thus provides information about the weld penetration.

[0004] US 11 835 468 B2 discloses an apparatus and method for testing air voids in a lead film of a battery to perform a simple and accurate overall inspection of a gap between a lead film and the terminal lug boundary using OCT. An object to be tested, in which the lead film is attached to a terminal lug, is conveyed by a conveyor device, the conveyed object is gripped and loaded into an inspection position, the object is aligned such that an OCT focus is formed on an interface between the terminal lug and the lead film of the object, an inspection image of the gap between the terminal lug and the lead film is obtained by scanning the interface between the terminal lug and the lead film using an OCT scanner above the inspection position, and the obtained inspection image of the gap is analyzed, thereby determining the connection quality of the lead film.

[0005] There is a need for measurement methods that enable reliable detection of position errors of the joining partners, especially during laser welding.

[0006] The object is achieved according to the invention by an in-situ measuring method according to the characterizing part of claim 1 and a laser welding method according to the characterizing part of claim 4.

[0007] Advantageous embodiments of the invention are the subject of the subclaims.

[0008] To achieve the object, the invention proposes an in-situ measuring method for quality assurance, in particular in laser welding, in which a welding depth is continuously determined in a height direction in a horizontal plane along a predeterminable seam path, wherein an OCT scanner is used to determine a height measurement value of a surface of an upper joining partner at at least three measuring points, the at least three height measurement values ​​are compared with one another, and a position error of the upper joining partner is determined from the comparison.

[0009] If an OCT scanner is already used in a welding process to determine the penetration depth, it can also advantageously be used to determine the height measurements of the surface of the upper joining partner according to the invention. Otherwise, the welding device can also be combined with an OCT scanner specifically for determining the height measurements of the surface of the upper joining partner according to the invention.

[0010] For example, battery cells are interconnected by electrically connecting their cell terminals using cell connectors, which are designed, for example, as sheet metal strips. To create a secure connection between a cell terminal and a cell connector, a weld seam is created between them using laser welding. In such a case, for example, the cell terminal is the lower joining partner and the cell connector is the upper joining partner. The welding laser beam is directed onto the upward-facing surface of the upper joining partner, and the energy input melts the materials of the upper joining partner, i.e. the cell connector, and the lower joining partner, i.e. the cell connector, i.e. the cell terminal, and welds them together as the resulting melt cools.

[0011] For quality assurance purposes, the depth of the keyhole forming at the point of impact of the welding laser is continuously measured during welding using an OCT scanner in order to be able to make a statement about the achieved welding depth and thus determine whether the weld seam has achieved a sufficient connection between the cell connector and the cell terminal.

[0012] According to the invention, the same OCT scanner is now used simultaneously to determine a height measurement value at at least three measuring points on the upward-facing surface of the upper joining partner. The positions of these three measuring points are advantageously located on or along the seam path, which is scanned by the OCT scanner anyway, and in any case outside, for example, next to, the weld seam, to avoid distorting the measured values.

[0013] Advantageously, the proposed in-situ measurement method can provide for a first measuring point to be determined in front of the seam or at the beginning of the seam, and for a first height measurement to be determined at the first measuring point. It can also be advantageous for a second measuring point to be determined in the seam and a third measuring point to be determined at the end of the seam or behind the seam, at positions as far apart as possible and as far away from the first measuring point, and for a second height measurement to be determined at the second measuring point and a third height measurement to be determined at the third measuring point.

[0014] The proposed in-situ measurement method can be particularly advantageously integrated into a laser welding process in which a weld seam running in a horizontal plane along a predeterminable seam path is created between two joining partners arranged one above the other in the height direction. In this case, it can advantageously be provided that an inlet section is inserted before the seam path, on which a first measuring point is determined. In other words, a pure scanning section is inserted before the start of welding, in which a first height measurement is carried out. It can also advantageously be provided that an outlet section is inserted after the seam path, on which a third measuring point is determined. In other words, after the completion of welding, a pure scanning section is inserted in which a third height measurement is carried out.The second measurement can be taken during the weld, i.e., within the weld line, with the measurement point there preferably positioned at the greatest possible distance from the first and third measurement points. The larger the triangle formed by the three measurement points in the xy plane, the more accurately the inclination of the upper joining partner can be determined.

[0015] The invention provides a measurement strategy for detecting angular misalignment between the joining partners during laser welding and primarily addresses the resulting gap issues in the manufacturing process. The invention offers the possibility of making the laser welding process, or rather the quality system used, more robust. A possible misalignment of the upper joining partner can be detected in real time during the actual welding operation using the quality system used. This then directly indicates a point-like or surface-wide gap. This method then makes it possible to make a statement about an existing gap despite a positive OCT result (quality system used). This makes the quality system more robust overall and minimizes the risk of overlooking potential welding defects (false friend) as much as possible.This process also makes it possible to detect welding defects at an early stage so that they can be reworked if necessary, especially in areas that do not have a gap.

[0016] The inventive solution to the problem lies in the fact that the OCT quality system used is not only used for welding depth measurement. The goal is to integrate at least three measurement contours, measuring lines, or measuring points into the path geometry or scan path scanned by the optics of the OCT scanner by skillfully adapting the geometry of the planned weld seam path in order to record a height profile in the z-direction at these points. The measuring points should advantageously be located as far apart as possible within the pressure piece used, for example, as the vertices of an isosceles or equilateral triangle, in order to create a kind of tripod, whereby a plane spanned by the at least three height measurements can be determined.

[0017] This plane shows a z-profile of an upper surface of the upper joining partner and thus, if applicable, an angular deviation of the upper joining partner relative to the lower joining partner, thus enabling a check for plane parallelism of the joining partners. With the first measuring point, a reference position can be generated with respect to the lower joining partner, which advantageously lies in a previously programmed range in which this is also expected. A possible deviation of the z-values, i.e. the height measurements, in the second and third, and possibly in further measuring points, reveals an inclination of this plane and thus of the upper joining partner. With this plane created by the measurement, it can then be determined with respect to the lower joining partner whether the upper joining partner has an angular offset from the lower joining partner, which would consequently indicate a gap between the joining partners.This allows the quality of the OCT measurement result to be improved with minor adjustments during the welding process and to protect it against gaps or angular misalignment.

[0018] OCT scanners, which are already used in laser welding to measure the penetration depth, also offer the potential to measure the surface of a component in the z-direction. With this function and at least three defining measuring sections or measuring points, which are integrated into the actual laser welding contour, i.e., the planned seam path, and / or in front of and behind it in an additional scanning section without laser power, the system can create a height profile of the component to be welded at these points. This results in perhaps the most important advantage: the verification of the plane parallelism of the upper joining partner, for example, a cell connector, to the lower joining partner, for example, a cell to be welded.

[0019] Without the method according to the invention, a deviation in the measurement result of a height measurement at any measuring point along the seam would simply be interpreted as a weld penetration depth. With the method according to the invention, however, a misalignment or a gap between the joining partners can be detected. This invention thus improves the control properties of the OCT system. In addition, the plane generated by three or more measuring sections or measuring points can be used to define the possible rework area, which will definitely be gap-free. The proposed measurement strategy thus offers the possibility of even better testing of quality characteristics with existing equipment, without additional equipment costs, and only minimal adjustments to the welding geometry or the traversing geometry of the optics are required.

[0020] Embodiments of the invention are explained in more detail below with reference to drawings.

[0021] Showing: Fig. 1 schematically shows a faultless joining of two joining partners, Fig. 2 schematically shows a faulty joining of two joining partners, Fig. 3 schematically shows a seam path, a welding result and a longitudinal section through a weld seam, and Fig. 4 schematically shows the sequence of a method according to the invention according to an embodiment.

[0022] Corresponding parts are provided with the same reference numerals in all figures.

[0023] In Fig. Figure 1 schematically shows two views of a flawless joining of two joining partners 110, 120. A cell connector 520 is the upper joining partner 110 and lies horizontally and thus without a position error 130 on the horizontal upper side of a cell pole 510 of a cell 500, which is the lower joining partner 120.

[0024] In contrast, in the Fig. 2 schematically shows two views of the cell connector 520, i.e., the upper joining partner 120, rotated relative to the horizontal surface of the cell pole 510, i.e., the lower joining partner 110, resulting in a positional error 130 in the form of a gap 131. The object of the invention is to automatically detect such positional errors 130.

[0025] Fig. Figure 3 schematically shows a planned seam path 210 in a horizontal xy plane, which is preceded by a first scanning path 220, namely an inlet path 221, and followed by a second scanning path 220, namely an outlet path 222. With this planned seam path 210, the weld 200 was performed, by which an upper joining partner 120, namely a cell connector 520, was welded to a lower joining partner 110, namely a cell pole 510 of a cell 500. Also in Fig. 3 shows a longitudinal section through an xz-plane of the weld 200 that has been made, which connects the upper joining partner 120, i.e. the cell connector 520, with the lower joining partner 110, i.e. the cell pole 510, from which the achieved welding depths can be seen.

[0026] As in Fig. As shown in Figure 4, three measuring points 300 were defined in the xy plane in a method according to the invention. The defined measuring points 300 include a first measuring point 301, a second measuring point 302, and a third measuring point 303.

[0027] The first measuring point 301 is arranged in the first scanning section 220, which serves as an inlet section 221 for a welding device (not shown here) with an OCT scanner (also not shown), in which no welding is yet taking place.

[0028] The second measuring point 302 is arranged in the seam path 210 in which the actual welding takes place.

[0029] The third measuring point 303 is arranged in the second scanning section 220, which serves as the exit section 222 for the welding device and the OCT scanner, in which no more welding takes place.

[0030] The measuring points 300 are defined such that they span an equilateral measuring triangle 310, so that the measuring points 300 have the greatest possible distance relative to each other in the xy plane.

[0031] This is also in Fig. The diagram included in Figure 4 shows the results of the height measurement performed by the OCT scanner in the z-direction. The horizontal axis of the diagram shows the measurement position 410 of the OCT scanner in the xy plane, i.e., along the inlet section 221, the seam path 210, and the outlet section 222, with the height measurement values ​​420 determined along said section being represented by the vertical axis of the diagram.

[0032] The first measuring point 301 is located at the beginning of the inlet section 221. This is followed by measured values ​​along the seam path 210, which indicate the achieved welding depth. The second measuring point 302 is located at the transition from the seam path 210 to the outlet section 222, and the third measuring point 303 is located at the end of the outlet section 222. As can be seen in the diagram, the height measured values ​​420 at the second measuring point 302 and the third measuring point 303 deviate from the reference value of the first measuring point 301, which indicates a position error 130 of the upper joining partner 120, the size of which can be calculated from the height measured values ​​420. List of reference symbols 110 lower joining partner 120 upper joining partner 130 position errors 131 gap 200 weld seam 210 Seam pattern 220 scan path 221 Inlet section 222 run-off section 300 measuring points 301 first measuring point 302 second measuring point 303 third measuring point 310 measuring triangle 410 Measuring position in xy plane 420 Height measurement in z-direction 500 cells 510 cell pole 520 cell connectors x, y horizontal directions z Vertical direction QUOTES CONTAINED IN THE DESCRIPTION

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

[0000] US 11 835 468 B2

[0004]

Claims

In-situ measuring method for quality assurance, in particular in laser welding, in which a welding depth in a height direction (z) is continuously determined in a horizontal plane (xy) along a predeterminable seam path (210), characterized in that an OCT scanner is used to determine a height measurement value (420) of a surface of an upper joining partner (120) at at least three measuring points (300, 301, 302, 303), the at least three height measurement values ​​(420) are compared with one another and a position error (130) of the upper joining partner (120) is determined from the comparison. In-situ measuring method according to claim 1, characterized in that a first measuring point (301) is determined in front of the seam path (210) or at the beginning of the seam path (210) and a first height measurement value (420) is determined at the first measuring point (301). In-situ measuring method according to claim 1 or 2, characterized in that a second measuring point (302) in the seam path (210) and a third measuring point (303) at the end of the seam path (210) or behind the seam path (210) are determined at positions as far apart as possible and as far away from the first measuring point (301), and a second height measurement value (420) is determined at the second measuring point (302) and a third height measurement value (420) is determined at the third measuring point (303). Laser welding method in which a weld seam (200) running in a horizontal plane (xy) along a predeterminable seam path (210) is produced between two joining partners (110, 120) arranged one above the other in the height direction (z), characterized in that an in-situ measuring method according to one of claims 1 to 3 is carried out during welding. Laser welding method according to claim 4, characterized in that an inlet section (221) is inserted before the seam path (210), on which a first measuring point (301) is determined. Laser welding method according to claim 4 or 5, characterized in that a run-out section (222) is inserted after the seam path (210), on which a third measuring point (303) is determined.

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