Process for joining two joining partners by laser welding

Abstract

The invention relates to a method for joining two joining partners (3, 5) by laser welding, wherein an upper joining partner (5) is positioned above a lower joining partner (3) with a gap (10) between the joining partners (3, 5), wherein a first weld seam (7) is produced on the upper joining partner (5) by a laser beam (L) in that the material of the upper joining partner (5) is melted locally so that the resulting melt sinks and bridges the gap (10), wherein by lateral offset of the laser beam (L) next to the first weld seam (7) by means of the laser beam (L) a second weld seam (8) is produced in such a way that a welding depth is created in the material of the lower joining partner (3), wherein by lateral offset of the laser beam (L) next to the first weld seam (7) on a side opposite the second weld seam (8) a third weld seam (9) is generated in such a waythat a penetration depth is created in the material of the lower joining partner (3), whereby the second weld seam (8) and the third weld seam (9) are executed so as to overlap the first weld seam (7). The second and third weld seams (8, 9) are executed so that their molten pools overlap each other.

Description

[0001] The invention relates to a method for joining two joining partners by laser welding according to the preamble of claim 1, an assembly according to claim 5 and an electrically powered vehicle according to claim 6.

[0002] Laser welding is becoming increasingly important in industry, 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 finish, contamination, or the permissible gap between the joining partners.

[0003] DE 10 2022 000 181 A1 describes the electrical contacting of components using a welded joint whose primary path has two ends. At each end of the primary path, a final contour of the welded joint is arranged, which has a curved profile.

[0004] DE 10 2022 115 661 B3 describes a method for joining a metallic top sheet to a metallic carrier by laser welding. A welding step, in which the material of the carrier and the adjacent top sheet are melted together in a welding area, is preceded by a pretreatment step for pretreating the welding area, which includes forming the welding area into a bead curved toward the carrier. The method is characterized in that the bead is formed by scanning the welding area with a beam of a pulsed forming laser.

[0005] The invention is based on the object of providing a novel method for joining two joining partners by laser welding, a novel assembly and a novel electrically powered vehicle.

[0006] The object is achieved according to the invention by a method for joining two joining partners by laser welding with the features of claim 1, an assembly with the features of claim 5 and an electrically driven vehicle with the features of claim 6.

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

[0008] A method for joining two joining partners by laser welding is proposed, wherein an upper joining partner is positioned above a lower joining partner with a gap between the joining partners, wherein a first weld seam is produced on the upper joining partner by a laser beam in that the material of the upper joining partner is melted locally so that the resulting melt sinks and bridges the gap, wherein by lateral offset of the laser beam next to the first weld seam a second weld seam is produced by means of the laser beam in such a way that a welding depth is created in the material of the lower joining partner, wherein by lateral offset of the laser beam next to the first weld seam on a side opposite the second weld seam a third weld seam is produced in such a way that a welding depth is created in the material of the lower joining partner.According to the invention, the second weld and the third weld are formed overlapping the first weld. The second and third welds are formed such that their molten pools overlap each other.

[0009] In one embodiment, welding parameters for creating the first weld seam are selected such that no penetration occurs in the material of the lower joining partner. The first weld seam merely bridges the gap.

[0010] In one embodiment, the second and / or the third weld seam are / is performed such that their molten pool(s) overlap(s) with the molten pool of the first weld seam by at least 40%, for example by 40%, 50% or 60%.

[0011] In one embodiment, the weld seams are curved or straight. For example, according to one aspect, the weld seams can be realized by means of a single weld seam.

[0012] According to one aspect of the present invention, an assembly is proposed comprising at least two joining partners which are joined to one another by laser welding using the method described above.

[0013] In one embodiment, the assembly is configured as an electric battery with multiple battery cells. One of the joining partners is configured as an electrical contact of a battery cell, and the other joining partner is configured as a cell connector for contacting the electrical contact with an electrical contact of another battery cell.

[0014] The battery can be designed or used as a drive battery of an electrically powered vehicle.

[0015] The electrically powered vehicle can, for example, be designed as a passenger car, commercial vehicle or bus.

[0016] The seam contour and the manufacturing concept according to the present invention primarily address gap issues in the manufacturing process. The solution according to the invention offers the possibility of making the laser welding process of two joining partners more robust. For example, two aluminum components are joined together by laser welding. The method thus offers the possibility of making a laser welding process more robust in order to reduce the frequency of joining errors. The concept also offers the possibility of potentially mitigating component tolerances, since a previously defined gap can be bridged by welding.

[0017] Laser welding processes are generally very gap-sensitive; a technical zero gap is often required for such joints. Unfortunately, this is not always possible in reality, even with sophisticated clamping technology, which is why methods and methods must be found to reliably weld such gaps within a certain range. The solution according to the invention enables the user to make their laser welding process more robust for this issue. This has the advantage that corresponding gaps between the components can be technically permitted to mitigate tolerances or to make the laser welding process fundamentally more robust to minimize potential defective production (scrap).

[0018] Embodiments of the invention are explained in more detail below with reference to drawings.

[0019] Showing: Fig. 1 a schematic detailed view of a battery cell with two electrical contacts, each of which has a cell connector resting on it without a gap, Fig. 2 a schematic detailed view of a battery cell with two electrical contacts, wherein a cell connector with a gap is positioned above one of the contacts, Fig. 3 a schematic view of a welding contour, Fig. 4 a schematic view of two joining partners with a first weld seam, Fig. 5 a schematic view of the two joining partners with a second weld seam, Fig. 6 a schematic view of the two joining partners with a third weld seam, and Fig. 7 a schematic view of the two joining partners with the second and third weld seam.

[0020] Corresponding parts are provided with the same reference numerals in all figures.

[0021] Fig. 1 is a schematic detailed view of a battery cell 1 with two electrical contacts 2, 3, on each of which a cell connector 4, 5 rests without a gap.

[0022] Fig. Figure 2 is a schematic detailed view of a battery cell 1 with two electrical contacts 2, 3. A cell connector 4 rests on one contact 2 without a gap. A cell connector 5 with a gap 10 of, for example, 0.2 mm is positioned above the other contact 3.

[0023] Fig. 3 is a schematic view of a welding contour 6 with which a laser beam L is used during laser welding to connect two joining partners 3, 5, for example the Fig. 2 shown electrical contact 3 and the cell connector 5.

[0024] Fig. 4 is a schematic view of the two joining partners 3, 5 with a first weld seam 7, which is created by traversing a first section 6.1 of the welding contour 6.

[0025] The first weld seam 7 serves as a sacrificial weld to close the gap 10 between the joining partners 3, 5. The material of the upper joining partner 5 is locally melted from above by means of the laser beam L. The resulting melt sinks and bridges the gap 10. This does not necessarily result in a weld penetration in the material of the lower joining partner 3. In particular, welding parameters can be selected such that no weld penetration is created in the material of the lower joining partner 3.

[0026] Fig. 5 is a schematic view of the two joining partners 3, 5 with a second weld seam 8, which is created by traversing a second section 6.2 of the welding contour 6.

[0027] A second weld seam 8 is drawn at a distance next to the first weld seam 7 using the laser beam L. In particular, welding parameters can be selected such that a penetration depth is created in the material of the underlying joining partner 3. The second weld seam 8 therefore connects both joining partners 3, 5.

[0028] A notch effect may occur after the first weld 7.

[0029] Fig. 6 is a schematic view of the two joining partners 3, 5 with a third weld seam 9, which is created by traversing a third section 6.3 of the welding contour 6.

[0030] In this case, a third weld 9 is drawn at a distance next to the first weld 7 on a side opposite the second weld 8 using the laser beam L. In particular, welding parameters can be selected such that a welding depth is created in the material of the joining partner 3 located below. The third weld 9 therefore connects both joining partners 3, 5 and closes the possible notch. Fig. The gap shown in Figure 6 between the second weld seam 8 and the third weld seam 9 is ideally not present, since the molten pool of the third weld seam 9 should overlap with the molten pool of the second weld seam 8 as much as possible.

[0031] Weld seams 7, 8, 9 can be curved as shown, for example, with a radius in a range of approximately 6 mm to 8 mm, for example, 7 mm. However, comparable results can also be achieved with straight weld seams 7, 8, 9. The distance between weld seams 7, 8, 9 depends on the laser program used, in particular the relationship between welding speed and power. For example, the distance between weld seams 7, 8, 9 can be approximately 0.9 mm at a power of 1900 W and a speed of 333 mm / s.

[0032] Fig. Figure 7 is a schematic view of the two joining partners 3, 5 with the second and third weld seams 8, 9.

[0033] The weld seams 8, 9 have sunk slightly on an upper side of the upper joining partner 5.

[0034] The subsidence of the weld seams 8, 9 depends on the existing gap 10 between the components 3, 5. It has been shown that the weld seams 8, 9 can subside between 0.05 mm and 0.3 mm depending on the seam configuration and gap 10. For example, with a gap 10 of 0.2 mm, a subsidence of 0.15 to 0.25 mm can be expected.

[0035] According to the present invention, the welding contour 6 is designed such that the three adjacent weld seams 7, 8, 9 overlap one another. The middle, first weld seam 7 should be welded first in order to lower the melt in the event of a possible gap 10 between the two joining partners 3, 5. This initially leads to a deliberate joining defect. According to the present invention, however, the first weld seam 7 serves to close the gap 10 between the joining partners 3, 5. In the second step, the second weld seam 8 can now be drawn. The molten pool of the second weld seam 8 should overlap at least 40% with the first weld seam 7 in order to be able to utilize the melt deposited by the first weld seam 7. This means that the gap 10 can be eliminated by the first weld seam 7 or at least its effect can be significantly minimized, which can lead to a more robust welding process.It has been shown that gap bridging capacity can be increased by up to 20% to 40%. In the third step, the third weld 9 will be repeated on the side of the first weld 7 opposite the second weld 8 in order to form a weld flank on both sides, increase the joining cross-section, and counteract potential notch effects.

[0036] At the end of the first weld seam 7, the laser beam L can be redirected in an arc to create the second weld seam 8. At the end of the second weld seam 8, the laser beam L can be redirected in an arc to create the third weld seam 9.

[0037] The features and advantages described herein with respect to a method for joining two joining partners by laser welding also relate to an assembly described herein and an electrically powered vehicle described herein, and vice versa. List of reference symbols 1 battery cell 2 Contact 3 Contact, joining partner 4 cell connectors 5 cell connectors, joining partners 6 Welding contour Sections 6.1 to 6.3 7 Weld seam 8 Weld seam 9 Weld seam 10 gap L laser beam

Claims

[1] Method for joining two joining partners (3, 5) by laser welding, wherein an upper joining partner (5) is positioned above a lower joining partner (3) with a gap (10) between the joining partners (3, 5), wherein a first weld seam (7) is produced on the upper joining partner (5) by a laser beam (L) in that the material of the upper joining partner (5) is melted locally so that the resulting melt sinks and bridges the gap (10), wherein by lateral offset of the laser beam (L) next to the first weld seam (7) by means of the laser beam (L) a second weld seam (8) is produced in such a way that a welding depth is created in the material of the lower joining partner (3), wherein by lateral offset of the laser beam (L) next to the first weld seam (7) on a side opposite the second weld seam (8) a third weld seam (9) is produced in such a way that a welding depth is created in the material of the lower joining partner (3),wherein the second weld seam (8) and the third weld seam (9) are made overlapping with the first weld seam (7), , characterized by that the second and third weld seams (8, 9) are made so that their molten pools overlap each other. [2] Method according to claim 1, characterized by that welding parameters for creating the first weld seam (7) are selected in such a way that no welding depth is created in the material of the lower joining partner (3). [3] Method according to one of the preceding claims, characterized by that the second and / or the third weld seam (8, 9) are / will be carried out in such a way that their melt pool(s) overlap(s) with the melt pool of the first weld seam (7) by at least 40%. [4] Method according to one of the preceding claims, characterized by that the weld seams (7, 8, 9) are curved or straight. [5] Method according to one of the preceding claims, wherein an assembly is formed in which one of the joining partners (3) is designed as an electrical contact (3) of at least one battery cell (1), and in that the other joining partner (5) is designed as a cell connector (5) for contacting the electrical contact (3) with an electrical contact (2, 3) of another battery cell (1). [6] Electrically powered vehicle comprising an assembly designed as a drive battery manufactured by the method according to claim 5.

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