Laser welding process

Abstract

The invention relates to a laser welding process for joining a first joining partner (100) with a second joining partner (200), which are arranged in particular in a parallel or overlap joint, in which a laser beam (400) is directed onto a usable welding surface (110) of the first joining partner (100), thereby forming a weld pool (300) which extends in a thickness direction through the first joining partner (100) and into the second joining partner (200), wherein a laser energy of the laser beam (400) can be variably divided between a core beam (410) of the laser beam (400) and an annular beam (420) of the laser beam (400) that surrounds the core beam (410), wherein in a first step laser energy of the core beam (410) and the annular beam (420) is introduced together into the entire usable welding surface (110),and in a second step, laser energy only from the core beam (410) is introduced into a boundary region (120) that limits the usable welding area (110).

Description

[0001] The invention relates to a laser welding process according to the preamble of claim 1.

[0002] The BrightLine Weld laser technology from TRUMPF Laser- und Systemtechnik GmbH is frequently used to produce a laser weld seam with minimal spatter. For this purpose, the laser beam is divided into a core fiber and a ring fiber.

[0003] From DE 10 2010 003 750 A1, it is known to modify the beam profile characteristics of a laser beam using a multiclad fiber comprising at least one core fiber and one ring fiber. An output laser beam is fed partly (core component) into a core fiber and partly (ring component) into a ring fiber; these components can be changed, for example, by the position of an optical wedge in the output laser beam upstream of the fiber end of the multiclad fiber. The multiclad fiber can thus provide a modified laser beam with a core beam and a ring beam with adjustable components.

[0004] In DE 10 2021 126 754 A1, a method for laser welding a workpiece is disclosed, wherein a laser beam is directed onto the workpiece by means of a scanner optic, wherein a first component is welded to a base component in an arbitrary sequence at least in a first welding zone and a second component is welded to the base component in a second welding zone, and wherein the first component and the second component consist of different materials at least in the area of ​​the first and second welding zones, and wherein a laser energy of the laser beam can be variably divided at least between a core portion, corresponding to a core beam of the laser beam, and a ring portion, corresponding to a ring beam surrounding the core beam, and the division of the laser energy between the core portion and the ring portion is selected differently when welding the first welding zone and when welding the second welding zone.

[0005] As a rule, the ring fiber has significantly less power than the core fiber. This results in the weld bead to ing-on area ratio—that is, the ratio of the weld bead area required to the effective weld area between the joining partners—being significantly greater than 1. This means that more area is needed for the weld bead to achieve the required ing-on area between the joining partners. In other words, the ing-on area between the joining partners is significantly smaller than the weld bead area required to create it.

[0006] The invention is based on the objective of providing a laser welding process that makes it possible to improve the imaging ratio between the weld bead and the bonding surface, in order to produce the largest possible bonding surface between the joining partners, especially in confined spaces and a consequently limited usable welding area.

[0007] The problem is solved according to the invention by a laser welding process with the features of the characterizing part of claim 1.

[0008] Advantageous embodiments of the invention are the subject of the dependent claims.

[0009] In a laser welding process for joining a first joining partner with a second joining partner, which are in particular arranged in a parallel joint or lap joint, in which a laser beam is directed onto a usable welding surface of a first joining partner, thereby forming a weld pool that extends in a thickness direction through the first joining partner and into the second joining partner, wherein a laser energy of the laser beam can be variably divided between a core beam of the laser beam and a ring beam surrounding the core beam, it is proposed according to the invention that in a first step laser energy of the core beam and the ring beam is introduced together into the entire usable welding surface, and in a second step laser energy only of the core beam is introduced into an edge region limiting the usable welding surface.

[0010] The invention solves the underlying problem by combining different welding technologies, and in particular by a deep penetration welding process in which the welding takes place in two steps. A parameter variation occurs between the two steps.

[0011] In a first step, laser energy from the core beam and the ring beam is simultaneously introduced into the entire usable welding area, forming a molten pool that extends in a thickness direction through the first joining partner and into the second. The molten pool tapers in a V-shape, resulting in a smaller fusion area (i.e., the molten area in the joining plane where the two joining partners are in contact) than the molten area on the outside of the first joining partner (i.e., on the side where the laser energy is introduced by the laser beam). In other words, the resulting ratio of the weld bead to the weld area is greater than 1.

[0012] In a second step, all the laser energy is directed solely into the core beam, which then focuses the energy into a peripheral area that defines the usable welding surface. Due to the intense focusing of the laser energy in this second step, the initially sloping edges of the weld pool are melted almost perpendicularly, thus increasing the fusion area while the area occupied by the weld bead remains unchanged. As a result, the overall ratio of weld bead to weld area is nearly balanced. This second step generates only a small additional heat input, as it utilizes the existing temperature of the main weld and can be performed with a significantly reduced laser power compared to the first step.

[0013] The invention enables a significant improvement in the weld bead ratio, thereby considerably increasing the weld area between the joining partners. This is particularly advantageous for small welding areas, such as on the terminals of individual lithium-ion cells, especially cylindrical cells, as the available area can be utilized much more effectively. The main advantage of the invention lies in the optimal utilization of the usable welding area, i.e., the area available for the weld, and the bonding area between the joining partners, especially on small surfaces, is better utilized. This is particularly beneficial for welding the terminals of lithium-ion cells, where the usable welding area is significantly limited. Therefore, the weld bead to effective weld area ratio can be significantly improved to achieve the largest possible bonding area.

[0014] In one embodiment of the invention, it can be provided that, in the first step, the usable welding area is scanned by the laser beam. For example, the usable welding area can be scanned by the laser beam in a spiral pattern or line by line. It can further be provided that, in the first step, the usable welding area is scanned by the laser beam at a speed of 300 mm / s to 500 mm / s, preferably 400 mm / s. It can also be provided that, in the first step, the laser energy is delivered at a power of 3200 W to 4000 W, preferably 3600 W, wherein 50% to 70%, preferably 60%, of the laser energy is directed into the core beam and the remainder of the laser energy is directed into the annular beam.

[0015] In one embodiment of the invention, it can be provided that in the second step the edge region of the usable welding area is scanned by the laser beam. For example, the usable welding area can be scanned by the laser beam at a speed of 300 mm / s to 500 mm / s, preferably 400 mm / s. Furthermore, it can be provided that in the second step the laser energy is delivered at a power of 1200 W to 1600 W, preferably 1400 W, wherein 100% of the laser energy is introduced into the core beam.

[0016] An embodiment of the invention will be explained in more detail below with reference to the drawings.

[0017] This shows: Fig. 1. A schematic top view of the joining partners to be welded, Fig. 2 a schematic side view of the joining partners to be welded, Fig. 3 a schematic top view of the first step of the welding process, Fig. 4 a schematic side view of the first step of the welding process, Fig. 5 a schematic top view of the second step of the welding process, and Fig. 6 A schematic side view of the second step of the welding process.

[0018] Fig. 1 shows a top view and Fig. Figure 2 shows the corresponding side view of a pairing of a first joining partner 100 with a second joining partner 200, which are assembled in a parallel butt joint. Specifically, in the exemplary embodiment, this is a contacting system (first joining partner 100) and a cell terminal (second joining partner 200) of a battery, in which the battery cells are electrically contacted by welding to the contacting system. Fig. Figure 1 shows the usable welding area 110, which in the exemplary embodiment is approximately 28 mm. 2 is and is bounded by a boundary area of ​​120.

[0019] Fig. 3 shows a top view and Fig. Figure 4 shows the corresponding side view of the pairing of the first joining partner 100 with the second joining partner 200 in a first step of the embodiment of the laser welding process according to the invention.

[0020] In a first step, a laser beam 400 is generated, comprising a core beam 410 and a ring beam 420 surrounding the core beam 410. In the exemplary embodiment, the laser beam 400 is operated with a laser power of 3600 watts, of which approximately 60% is directed into the core beam 410 and 40% into the ring beam 420. The laser beam 400 is directed into the center of the usable welding area 110 and then guided in a spiral 430 from the center to the edge region 120 of the usable welding area 110. The usable welding area 110 is scanned at a speed of 400 mm / s, so that a melt pool 300 is created that extends through the first joining partner 100 and into the second joining partner 200. The melt pool 300 has, as can be seen particularly in the side view of the Fig. 4 can be seen, sloping flanks 310, whereby the area of ​​the melt pool 300 in the joining plane 320 is only about 18 mm 2is and is therefore significantly smaller than on the top side of the first joining partner 100, where the laser beam 400 hits the first joining partner 100 and the weld bead has an area of ​​approximately 28 mm 2 occupies.

[0021] Fig. 5 shows a top view and Fig. Figure 6 shows the corresponding side view of the pairing of the first joining partner 100 with the second joining partner 200 in a second step of the embodiment of the laser welding process according to the invention.

[0022] In the second step of the embodiment, the laser beam 400 is operated with a laser power of 1400 W, whereby 100% of the laser energy is directed into the core beam 410 of the laser beam 400. The edge region 120 of the usable welding area 110 is then scanned at a speed of 333 mm / s in the form of a ring 440. This melts the sloped flanks 310 of the weld pool 300, which were still inclined after the first step, until they are approximately perpendicular. This results in the weld pool area 300 being approximately 25 mm² in the joining plane 320. 2 is therefore almost as large as on the top side of the first joining partner 100, where the laser beam 400 hits the first joining partner 100 and the weld bead has an area of ​​approximately 28 mm 2 occupies. Reference symbol list 100 first joining partner 110 usable welding area 120 edge area 200 second joining partner 300 Melt bath 310 flank 320 joining plane 400 laser beam 410 core beam 420 ring beam 430 spiral 440 Ring 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] DE 10 2010 003 750 A1

[0003] DE 10 2021 126 754 A1

[0004]

Claims

Laser welding method for joining a first joining partner (100) with a second joining partner (200), which are in particular arranged in a parallel or overlap joint, in which a laser beam (400) is directed onto a usable welding surface (110) of the first joining partner (100), thereby forming a weld pool (300) which extends in a thickness direction through the first joining partner (100) and into the second joining partner (200), wherein a laser energy of the laser beam (400) is variably divisible between a core beam (410) of the laser beam (400) and an annular beam (420) of the laser beam (400) which surrounds the core beam (410), characterized in that in a first step laser energy of the core beam (410) and the annular beam (420) is introduced together into the entire usable welding surface (110),and in a second step, laser energy only from the core beam (410) is introduced into a boundary region (120) that limits the usable welding area (110). Laser welding method according to claim 1, characterized in that in the first step the usable welding area (110) is scanned by the laser beam (400). Laser welding method according to claim 2, characterized in that in the first step the usable welding area (110) is scanned by the laser beam (400) in a spiral pattern (430) or line by line. Laser welding method according to claim 2 or 3, characterized in that in the first step the usable welding area (110) is scanned by the laser beam (400) at a speed of 300 mm / s to 500 mm / s, preferably 400 mm / s. Laser welding method according to one of claims 1 to 4, characterized in that in the first step the laser energy is delivered with a power of 3200 W to 4000 W, preferably 3600 W, wherein 50% to 70%, preferably 60% of the laser energy is introduced into the core beam (410) and the remainder of the laser energy is introduced into the ring beam (420). Laser welding method according to one of claims 1 to 4, characterized in that in the second step the edge region (120) of the usable welding area (110) is scanned by the core beam (410) of the laser beam (400). Laser welding method according to claim 6, characterized in that in the second step the usable welding area (110) is scanned by the core beam (410) of the laser beam (400) at a speed of 250 mm / s to 450 mm / s, preferably 333 mm / s. Laser welding method according to one of claims 1 to 7, characterized in that in the second step the laser energy is delivered with a power of 1200 W to 1600 W, preferably 1400 W, wherein 100% of the laser energy is introduced into the core beam (410) of the laser beam (400).

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