Method for laser welding a plurality of assemblies

Abstract

The invention relates to a method for welding workpieces which form a plurality of assemblies (C11-C29) arranged in at least one row, in which the workpieces are clamped to one another, in sequence assembly by assembly, by means of two clamping frames (30, 32) which are moved in increments and operate alternatingly and are welded to one another by means of a steerable laser beam source (48), characterised in that the laser beam source (48) is moved synchronously with the clamping frame (30, 32) but continuously along the at least one row of assemblies.

Description

[0001] PROCESS FOR LASER WELDING A VARIETY OF COMPONENTS

[0002] The invention relates to a method for welding workpieces which form a plurality of assemblies arranged in at least one row, in which the workpieces are clamped together assembly by assembly in sequence by means of at least two stepwise moving, alternately operating clamping frames and are welded together by means of a steerable laser beam source.

[0003] In particular, the invention relates to a method for welding contact sheets to cylindrical battery cells in a battery module formed by a plurality of the cells.

[0004] A method of this type is known from CN 108 77 2638 A, in which the laser beam source is arranged stationary above the rows of battery cells. The use of two clamping frames operating in push-pull motion achieves high productivity, as one of the clamping frames can be moved to the next position while the other clamping frame holds the workpieces being welded. A disadvantage, however, is that for the battery cells located at the ends of the rows, the laser beam hits the cell at a relatively large angle of incidence, which impairs the efficiency of energy transfer and the quality of the weld seam.

[0005] An alternative method is known in practice in which each laser beam source is assigned a single clamping frame, which, together with the laser beam source, is moved step by step across the row of battery cells. The laser beam source can then be positioned so that the laser beam always hits the workpieces to be welded at a right angle. However, high productivity with this method can only be achieved through the use of several expensive laser beam sources. A further disadvantage is that the laser beam source must be accelerated and stopped in rapid succession during its cyclical movement along the row of battery cells, exposing the sensitive optics to high inertial forces.

[0006] The object of the invention is to provide a method that allows high productivity and the production of high-quality weld seams with a given number of laser beam sources. This object is achieved according to the invention in that the laser beam source is moved synchronously with the clamping frames but continuously along at least one row of assemblies.

[0007] Because the laser beam source moves with the clamping frame, an almost vertical incidence of the laser beam across the entire row of assemblies can be achieved, even with very long rows of assemblies. Because the laser beam source is continuously moving, it is subject to significantly lower mechanical stress. While there is a certain degree of relative movement between the laser beam source and the clamping frames, as the clamping frames advance intermittently, this relative movement can be compensated for using the laser beam source's steerable optics.

[0008] Advantageous embodiments of the method are specified in the subclaims.

[0009] The clamping frames can work on parallel rows of assemblies or in overlapping operation on the same row.

[0010] The necessary movements of the clamping frames can be controlled by multi-axis robots. When machining cylindrical assemblies such as battery cells, the clamping frames can also be rotated around an axis parallel to the cylinder axes, allowing adaptation to different orientations of the weld spots.

[0011] The movements of the clamping frames in the direction parallel to the axes of the cylindrical assemblies can be force-dependently controlled so that the workpieces are pressed against each other with an adjustable clamping force. This ensures sufficient contact pressure for each individual assembly while simultaneously preventing mechanical overloading of the workpieces. Optionally, a position measurement can be performed during the drive movement. This allows you to check whether the positions of the workpieces in the direction parallel to the cylinder axes are within specified tolerance limits. If this is not the case, an error signal can be output.At least one camera can be mounted on a carriage that continuously moves the laser beam source. This camera can be used to optically record the position of the workpieces. This ensures that the clamping frames can be positioned correctly and the welds can be carried out precisely, even when there are certain tolerances in the arrangement of the workpieces. If the carriage is moved back and forth to process several rows of assemblies one after the other, a camera can be mounted on each side of the carriage that is leading and trailing so that the workpieces can be optically recorded and the necessary digital image processing can take place in good time before each welding process. The trailing camera can then be used, for example, for quality control of the weld seams.

[0012] An extraction device for extracting welding gases can also be mounted on the carriage carrying the laser beam source. The extraction device is then also subject to minimal mechanical stress, as it is continuously moving. Similarly, a gassing device for welding in a protective gas atmosphere can also be installed on the carriage.

[0013] The invention also relates to a welding device which is designed to carry out the method described above.

[0014] In the following, an embodiment example is explained in more detail using the drawing.

[0015] They show:

[0016] Fig. 1 to 4 are schematic side views of a welding device according to the invention in different operating stages;

[0017] Figs. 5 and 6 are schematic end views of the device in different operating stages;

[0018] Fig. 7 shows two rows of battery cells and associated electrode sheets in plan view, together with parts of the welding device; Fig. 8 shows a section along the line VIII-VIII in Fig. 7; and

[0019] Fig. 9 to 11 views analogous to Fig. 7 for different operating stages of the device.

[0020] Fig. 1 shows a row of essentially cylindrical assemblies C11 to C19, which are arranged upright on a flat substrate 10. The substrate 10 can be a platform or a tray or, alternatively, a conveyor on which the assemblies are transported to and from the assembly in a direction perpendicular to the plane of the drawing in Fig. 1. In this example, the assemblies C11 to C19 are battery cells, which will be referred to below as cells C11 to C19. Of a second row of battery cells, which is located behind the row of cells C11 to C19, only one cell C21 can be seen in Fig. 1 at the left end of the row. In the reference symbols C11 ... C19, C21, . . ., C29, the first digit (1 or 2) identifies the row, and the second digit (1 to 9) identifies the position of the cell in the row.

[0021] Although not visible in Fig. 1, each battery cell has a circular electrode at the top in the middle, forming a positive terminal 12, and an annular electrode surrounding the positive terminal 12 at a distance, forming a negative terminal 14 and being electrically insulated from the positive terminal 12 (see Fig. 8).

[0022] Fig. 1 also shows a series of electrode sheets P1 to P7 ("workpieces" within the meaning of claim 1) resting on the two rows of battery cells and intended to be connected to the positive and negative poles 12, 14 of the battery cells by laser welding according to a specific scheme that will be explained in more detail later. For performing these welds, a welding device 16, shown in Fig. 1, is provided, which covers the substrate 10 and the rows of cells C11 - C29 in the manner of a gantry. The gantry has vertical end walls 18, 20 that protrude on either side of the substrate 10 and are connected to each other at the top by two cross members 22, 24. In Fig. 1, only the cross member 22 is visible. The second cross member 24 located behind it can be seen, for example, in the end view in Fig. 5.

[0023] As shown in Fig. 1, the welding device 16 also has two positioning systems, e.g., robots 26, 28, each of which serves to manipulate a clamping frame 30 or 32 in several axes. The robot 26 is movable along the crossbeam 22 in a direction x, in which the rows of battery cells extend, and is capable of holding the clamping frame 30 in a position in which it is located above the first row of cells C11 to C19. Correspondingly, the robot 28 is movable in the direction x along the crossbeam 24 and is capable of holding the clamping frame 32 in a position in which it is located above the same row of cells C11 to C19.

[0024] In the sectional view in Fig. 8, the clamping frame 32 is shown in a position above the cell C29. Each of the two clamping frames 30, 32 has an approximately cylindrical shape with a base 34 in which a central welding opening 36 and a peripheral welding opening 38 are recessed. As Fig. 1 shows, the clamping frame 30 is held on a rotary drive 40, which in turn is held on a z-axis drive 42 that enables movement of the clamping frame in a (vertical) direction z parallel to the axes of the cylindrical battery cells. The z-axis drive 42 is held on the underside of a y-axis drive 44, which in turn is movable in a direction x parallel to the rows of battery cells along the crosshead 22. As Fig. 5 shows, the clamping frame 32 is also held on the associated traverse 24 via a rotary drive 40, a z-axis drive 42 and a y-axis drive 44 and can be moved along it.The y-axis drives 44 allow the z-axis drives 42 and thus also the clamping frames 30, 32 to be moved in a y direction perpendicular to the rows of battery cells and perpendicular to the (vertical) z-axis. The z-axis drives 42 enable vertical movement of the clamping frames 30, 32 along the z-axis. The rotary drives 40 each have an overall L-shaped configuration with a vertical leg and a horizontal leg, at the free end of which the clamping frame 30 or 32 is located. The rotary drives 40 can, for example, be designed as belt drives that are housed in the horizontal legs. With the help of these rotary drives 40, the cylindrical clamping frames 30, 32 can each be rotated about their axis, which runs parallel to the z-axis.The robots 26, 28 thus allow the axes of the cylindrical clamping frames 30, 32 to be aligned with the axis of a battery cell and then to rotate the clamping frame so that the welding openings 36, 38 assume a desired orientation.

[0025] A carriage 46 is mounted on the crossbeam 24 and is continuously movable in the direction x along this crossbeam. A laser beam source 48 is mounted on an extension arm of the carriage 46 such that it is located above a gap between the two crossbeams 22, 24 (see Fig. 5). The laser beam source 48 is designed in a known manner to generate a high-energy laser beam 50, to focus this laser beam by means of a lens 52 onto a plane in which the positive and negative poles 12, 14 of the battery cells are located, and to direct this laser beam onto the positive or negative pole 12, 14 and the supporting surface resting thereon by means of an electronically controlled mirror system.

[0026] Part of one of the electrode sheets PI to P7, so that the respective electrode sheet and the battery terminal are mechanically and electrically connected to each other by a weld seam. Fig. 1 also shows two cameras 54, 56, which are arranged in the direction x in front of and behind the robots 26, 28 and allow the position of the electrode cells PI to P7 and the position of the battery cells to be optically recorded. Digital image processing can then generate control data for precise control of the robots 26, 28 and precise control of the mirror system of the laser beam source 48.

[0027] In the illustration in Fig. 5, the cameras 54, 56 have been omitted for clarity. Instead, Fig. 5 shows parts of an extraction system or a combined extraction and gassing system 58, which is also mounted on the carriage 46 and serves to apply a shielding gas to the respective welding location and / or to extract the welding gases generated during the welding process. The parts of the extraction and gassing system 58 are arranged in the x direction in front of and behind the laser beam source 48 so that they do not impede the propagation of the laser beam 50 to the respective welding point.

[0028] In Fig. 1, the welding device 16 is shown in a state in which the clamping frame 30 is lowered onto the electrode sheets P2 and P3 to clamp portions of these electrode sheets against the positive and negative terminals of cell C13, respectively. With the electrode sheets and the cell clamped in this manner, the laser beam 50 is directed through the welding openings 36 and 38 successively onto the positive and negative terminals of cell C13 to weld the battery terminals to the electrode sheets.

[0029] In a previous work step, the clamping frame 32 clamped parts of the electrode sheets P1 and P2 against cell C12, and the poles of this cell were welded to the electrode sheets. However, in the stage shown in Fig. 1, the clamping frame 32 was raised by means of the z-axis drive 42 and retracted by means of the y-axis drive 44 in the direction perpendicular to the plane of the drawing in Fig. 1, so that it can now be moved past the clamping frame 30 in the x-direction. In Fig. 2, the robot 28 has reached a position in which it is aligned in the z-direction with the next cell C14. The clamping frame 30 continues to hold the electrode sheets P2 and P3 clamped against cell C13, and the welding process continues with the aid of the laser beam 50. Meanwhile, the carriage 46 was continuously moved in the direction x, so that the camera 56 has now moved somewhat closer to the robot 26.The relative movement of the carriage 46 relative to the robot 26 is continuously compensated during the welding process by corresponding deflection of the laser beam 50.

[0030] In Fig. 3, the welding process at cell C13 is complete. Clamping frame 30 has been raised and retracted in the -y direction (toward the viewer). Meanwhile, clamping frame 32 has been aligned with the axis of cell C14 and lowered onto this cell, so that welding can now begin on this cell.

[0031] In Fig. 4, the welding process has begun at cell C14, and the clamping frame 30 has been moved in the x-direction to the position of cell CI5. Meanwhile, the carriage 46 has continued to move continuously in the x-direction, so that no collision occurs between the robot 28 and the camera 54.

[0032] In this way, the robots 26 and 28 are moved stepwise and alternately (in push-pull) in the x-direction along the rows of battery cells, while the carriage 46 with the laser beam source 48 is continuously tracked. When the last cell C19 in the first row is reached, the welding device 16 and the substrate 10 are moved relative to each other in the y-direction until the laser beam source and the robots are then located above the second row of battery cells C21 to C29. The robots 26, 28 and the carriage 46 then move in the x-direction to perform the welds on the cells C29 to C21 in the second row. Here, too, the robots 26, 28 move stepwise, while the carriage 46 is continuously moved. During this phase, the positions of the contact plates P1 to P7 and the battery cells are recorded by the camera 56, which moves ahead in this direction of movement.The trailing camera 54 can then be used to take an image of the completed welds to check the quality of the welds.

[0033] In a modified embodiment, the clamping frames 30, 32 can also be constructed in multiple parts. For example, two independently movable sub-frames can be provided for the two battery terminals.

[0034] While in the example shown here, each row of battery cells has only nine cells, in practice, the number of cells per row can be significantly larger. Likewise, a significantly larger number of rows of cells can be arranged on the substrate 10.

[0035] The state of the welding device 16 shown in Fig. 5 corresponds to the state in Fig. 1, where the clamping frame 30 is lowered onto the battery cell C13 (which, however, is obscured by the cell C11 in Fig. 5). The clamping frame 32 is retracted in the -y direction so that the horizontal arms of the rotary drives 40, which are directed toward one another, can move past each other in the x direction.

[0036] The state in Fig. 6 corresponds to the state in Fig. 4, where welding is performed on cell C14 while the contact sheets P3 and P4 are held by the clamping frame 32. The robot 26 has lifted the clamping frame 30 and retracted it in the y-direction so that the rotary drives 40 do not collide with each other during the movement in the x-direction.

[0037] Fig. 7 shows a possible contacting scheme for the electrode sheets and battery cells. In the (simplified) example described here, the positive poles of cells C11, C21, and C22 are connected to each other by the electrode sheet P1. For this purpose, the electrode sheet P1 has three spring-loaded contacts 60 offset in the z-direction, which are to be welded to the positive poles 12 of the cells. The negative poles 14 of these three cells are connected to the positive poles of cells C12, C23, and C13 by the contact sheet P2. The contact sheet P2 therefore has spring-loaded contacts 60 for the positive poles and contacts 62 offset in the z-direction for the negative poles 14.

[0038] Accordingly, contact plate P3 connects the negative terminals of this group of three cells to the positive terminals of the next group of three, formed by cells C24, C14, and C25. This pattern continues up to contact plate P6. The final contact plate P7 connects the negative terminals of the last group of three cells C18, C29, and C19.

[0039] The total of eighteen battery cells are thus interconnected into six groups of three cells, with the three cells in each group connected in parallel. This forms a battery module whose positive voltage tap is contact plate PI and whose negative voltage tap is contact plate P7.

[0040] Fig. 8 shows the angled shape of contacts 60 and 62 of contact plates P6 and P7, which contact the positive terminal 12 and the negative terminal 14 of cell C29. During welding of this cell, the clamping frame 32 is placed on this cell C29, so that its base 34 presses the contacts 60 and 62 against the battery terminals, while the welding openings 36 and 38 allow the laser beam to pass through to the welding points.

[0041] In Fig. 7, the clamping frames 30 and 32 and the associated rotary drives 40 are shown in the same positions as in Fig. 1. The clamping frame 30 clamps the cell C13 and the associated contact plates. In the previous step, the cell C12 and the associated contact plates were clamped with the clamping frame 32, which is now retracted in the Y direction. The position of the peripheral welding opening 38 of the clamping frame 32 corresponds to the position of the contact 62 of the contact plate P3 belonging to the cell C12.

[0042] In Fig. 9, the clamping frame 32 has moved one step in the x-direction past the clamping frame 30 so that it is now at the level of cell C14. With the help of the rotary drive 40, the clamping frame 32 has been rotated 180° about its axis so that the peripheral welding opening 38 now corresponds to the position of the contact 62 for the negative pole of cell C14 as soon as the axis of the clamping frame 32 is aligned with the axis of this cell. In Fig. 10, this alignment has taken place so that the welding opening 38 is now flush with the contact. At the same time, the clamping frame 30 has been retracted in the y-direction so that it can move past the clamping frame 32 in the next step into the position shown in Fig. 11. In the subsequent steps, the clamping frame 32 is rotated 180° in each step, while the clamping frame 30 can maintain its angular position with this contacting scheme.However, contacting schemes are also conceivable in which the angular positions of both clamping frames must be changed.

Claims

PATENT CLAIMS 1. Method for welding workpieces which form a plurality of assemblies (Cl 1-C29) arranged in at least one row, in which the workpieces are clamped together assembly by assembly in succession with the aid of at least two stepwise moved, alternately operating clamping frames (30, 32) and are welded together by means of a steerable laser beam source (48), characterized in that the laser beam source (48) is moved synchronously with the clamping frame (30, 32) but continuously along the at least one row of assemblies.

2. Method according to claim 1, in which the two clamping frames (30, 32) operate in overlapping use on the same row of assemblies (Cl 1 -Cl 9).

3. The method according to claim 1 or 2, wherein the two clamping frames (30, 32) are each moved independently of one another in at least two axes by means of a robot (26, 28).

4. The method according to one of the preceding claims, for cylindrical assemblies (C11 - C29) with weld points arranged non-rotationally symmetrically to the cylinder axis, wherein the clamping frames (30, 32) are adapted to different orientations of the weld points by being rotated by the respective robot (26, 28) about an axis (z) coaxial with the cylinder axis of the assembly.

5. Method according to claim 4, wherein the assemblies (C1 1-C29) are battery cells and the positions of the welding points are the positions of contacts (60, 62) of contact plates (P1 - P7) which are to be welded to the positive and negative poles (12, 14) of the battery cells.

6. Method according to one of the preceding claims, wherein the movements of the clamping frames (30, 32) in a direction (z) perpendicular to the at least one row of assemblies are controlled in a force-dependent manner such that the workpieces to be welded are clamped against one another with an adjustable contact force.

7. Method according to claim 6, in which the positions of the workpieces in the direction perpendicular to the row of assemblies are checked before welding is carried out by measuring the distance travelled by the clamping frame (30, 32) in this direction.

8. Method according to one of the preceding claims, in which the positions of the workpieces are recorded with a digital camera before each welding and the necessary movements of the clamping frames (30, 32) and the necessary deflections of the laser beam (50) of the laser beam source (48) are determined by digital image analysis.

9. Method according to claim 8, wherein after a number of welds the quality of the weld seams is checked by means of a digital camera (56) and by means of digital image analysis.

10. Method according to one of the preceding claims, in which a suction and / or gassing device (58) is moved together with the laser beam source (48) continuously in the direction (x) parallel to the at least one row of the assemblies (C1 1-C29).

11. Welding device with a laser beam source (48) and two clamping frames (32, 36) for clamping workpieces, and with drive devices for moving the laser beam source (48) and the clamping frames (30, 32), characterized in that that the drive devices are configured to carry out the method according to one of the preceding claims.

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