Method for laser welding workpieces with rapid alternation of weld zones with different welded materials

Abstract

A method of laser welding a workpiece (17), comprising: directing a laser beam (8) to the workpiece (17) by a scanner optics (13); and, in any order, welding at least a first component (21) to a base part (20) in a first welding zone (31) by the laser beam (8) and welding a second component (22) to the base part (20) in a second welding zone (32), the first component (21) and the second component (22) being welded to each other in at least the first welding zone and the second welding zone (32). in the region of the welding zones (31, 32) of different materials, characterized in that the laser energy of the laser beam (8) can be variably divided at least between a core portion (KA) corresponding to a core beam (9) of the laser beam and a ring portion corresponding to a ring beam (10) surrounding the core beam (9), and the division of the laser energy to the core portion (KA) and the ring portion is selected differently for the welding of the first welding zone (31) and for the welding of the second welding zone (32). By means of the invention, components made of different materials can be welded to a base part, accelerating the production of workpieces.

Description

[Technical field]

[0001] The present invention relates to a method for laser welding workpieces, A laser beam is directed to the workpiece by scanner optics; at least a first component is welded to the base piece at a first welding zone and a second component is welded to the base piece at a second welding zone by the laser beam in any order; The first component and the second component are made of different materials at least in the region of the first weld zone and the second weld zone. [Background technology]

[0002] Laser welding is a high performance method for joining workpiece components to a workpiece. Laser welding is primarily used when high welding speeds, narrow weld seams, or little thermal distortion of the workpiece are required.

[0003] Laser welding often requires welding multiple components to a base part, for example in a battery cell the cathode is often made of aluminum (Al) or an aluminum alloy and the anode is often made of copper (Cu) or a copper alloy, and these two components must be welded to a common base part of the cell.

[0004] For laser welding, the workpieces to be welded (or the workpiece parts that have to be welded together) are usually placed in front of the scanner optics, which usually includes a laser radiation inlet, to which a fiber optic cable is typically connected, various optical elements (usually collimating lenses or collimating lens systems as well as focusing lenses or focusing lens systems) and adjustable deflectors (usually piezo-adjustable mirrors) by means of which the orientation of the laser beam emerging from the scanner optics can be changed relative to the workpiece, in particular to guide the laser beam along a desired welding path (weld seam) or even to direct the laser beam successively to different welding zones where different components are welded to the base part.

[0005] For laser welding components of different materials, in particular to minimize spatter and porosity, it is often advantageous to have different spot sizes of the welding laser beam. For this purpose, the distance between the scanner optics or the laser processing head and the workpiece can be changed in the beam propagation direction. For example, if in a first relative position of the scanner optics with respect to the workpiece the workpiece surface facing the laser beam is in the focal plane of the laser beam, the spot size of the laser beam on the workpiece surface is minimal. By moving the workpiece surface from the focal plane relative to a second relative position, the spot size of the laser beam on the workpiece surface can be enlarged.

[0006] However, moving the scanner optics relative to the workpiece is complicated and requires a relatively large amount of time, so that when the workpiece has components of different materials welded to a common base part one after another, the above procedure makes the production of the workpiece relatively slow, and when such workpieces are produced in large quantities, delays caused by the adjustment of the scanner optics occur for each workpiece.

[0007] From (Patent Document 1) it is known to vary the beam profile characteristics of a laser beam using a multi-clad fiber comprising at least one core fiber and one ring fiber. An output laser beam is fed in part (core portion) into the core fiber and in another part (ring portion) into the ring fiber, and these parts can be varied, for example, by the position of an optical wedge in the output laser beam in front of the fiber end of the multi-clad fiber. Thus, a multi-clad fiber can be used to provide a modified laser beam comprising a core beam and a ring beam with adjustable portions. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] DE 102010003750 Summary of the Invention [Problem to be solved by the invention]

[0009] The object of the invention is to provide a method for laser welding workpieces, which allows accelerating the production of workpieces, in which components made of different materials are welded to a base part. [Means for solving the problem]

[0010] This problem is solved according to the invention by providing that the laser energy of the laser beam can be variably divided at least between a core portion of the laser beam, which corresponds to a core beam, and a ring portion, which corresponds to a ring beam surrounding the core beam; the division of the laser energy into the core portion and the ring portion is selected differently for welding the first welding zone and for welding the second welding zone; The problem is solved by a method of the kind mentioned in the introduction, which is characterized in that

[0011] Within the scope of the present invention, it is provided to select differently the division of the laser energy into the core part and the ring part when laser welding at least two components of different materials to a common base part. By changing the division of the laser power between the core part and the ring part, it is possible to change or adjust the effective spot size of the welding laser beam on the surface of the workpiece facing the laser beam, respectively. This allows the spot size to be adapted to the conditions of different welding zones or different components, in particular to different materials of these components. At the same time, the intensity profile of the laser beam (as a whole) is also changed or adjusted during processing. Both can be used to optimize the quality of the laser welds in different welding zones or different components, in particular to minimize spatter and porosity.

[0012] These changes or adjustments do not require complex and time-consuming changes in the position of the scanner optics. Therefore, within the scope of the present invention, it is preferred that the position of the scanner optics relative to the workpiece is kept constant during the welding of the first and second welding zones, especially when the welding zones are switched. Alternatively, in order to change the (effective) spot size when the welding zones are switched, a combination of a (relative) movement of the workpiece and the scanner optics and a switching of the division of the laser energy between the core part and the ring part can be applied, in which case a significant reduction in the (relative) movement path can be achieved and the associated time for switching the welding zones is accordingly reduced, and therefore the welding method as a whole can also be significantly accelerated. The change in the division of the laser power is possible quickly and with little effort, for example by slightly moving the optical wedge, and does not cause any particularly noticeable associated time.

[0013] The effective spot size of a laser beam or beam portion (e.g., the entire laser beam including the core portion and the ring portion, or the core beam alone, or the ring beam alone) can be determined according to the 86% criterion, where the spot size of a laser beam is defined by the diameter of a circular surface (coaxial with the laser beam) that contains 86% of the laser power of the laser beam.

[0014] By varying the division of the laser energy into the core and the ring parts and thus changing the effective spot size, the seam width (width of the weld seam transverse to the direction of travel), which is important for many applications, can be easily and quickly adjusted, in particular to different materials of different components. For example, a relatively wide seam can be selected for an Al-based cathode and a relatively narrow seam for a Cu-based anode, in particular to take into account the different melting properties (viscosity and wetting properties) of the materials involved. The method or the adaptation of the spot size according to the invention can be used in particular to achieve the same penetration depth in different weld zones or in different components. Welding defects, in particular spatter and porosity, can also be minimized.

[0015] To increase the seam width / spot size, the ring portion is increased compared to the core portion. To decrease the seam width / spot size, the ring portion is decreased compared to the core portion. In this way, the effective spot size can be adjusted substantially in the range between the spot size of the ring portion (alone) and the spot size of the core portion (alone). It should be noted that by changing the division of the laser energy into the core portion and the ring portion, the spot size of the core portion and the spot size of the ring portion, respectively, are not changed. Correspondingly, in a particularly simple variant of the method according to the invention, the spot size of the core beam and the spot size of the ring beam remain constant when the first and second welding zones are interchanged.

[0016] The workpiece to be manufactured is integrated by welding (at least) two components with a base part. Typically, during welding of the workpiece, the laser power of the laser beam remains constant in time as a whole (both across and within the different welding zones). The first and second welding zones are spaced apart from each other at least transversely to the beam propagation direction. Typically, the two welding zones in the workpiece are at the same distance from the scanner optics (in the beam propagation direction), and any angular offset with respect to the optical axis of the scanner optics is negligibly small (e.g. less than 5°) or at least approximately the same for both welding zones, respectively (e.g. difference of less than 5°).

[0017] The ring beam most often has an invariant intensity in the circumferential direction (most often generated by splitting the output laser beam into a core fiber and a ring fiber and multiple reflections of the laser light in the ring fiber), but it is also possible to use a ring beam with multiple circumferentially consecutive local maxima (e.g. generated using a DOE, diffractive optical element, or an ROE, refractive optical element). The scanner optics is most often selected as a 2D scanner optics with a fixed focal position in front of the scanner optics in the beam propagation direction. Typically, the laser beam is provided via a fiber optic cable having a core fiber and a ring fiber, the core fiber diameter KFD is usually selected in the range of 10 μm to 50 μm (for single mode) or 50 μm to 400 μm, in particular 50 μm to 200 μm (for multimode), and the (outer) ring fiber diameter ARFD is usually selected in the range of 20 μm to 500 μm, in particular 40 to 200 μm (for single mode) or 40 μm to 2000 μm, in particular 80 μm to 800 μm (for multimode). The ratio of KFD:ARFD is usually 1:2 to 1:10, preferably 1:4. One (front) fiber end of the fiber optic cable is connected to the scanner optics (processing head). The other (rear) fiber end of the fiber optic cable is connected to a laser source (laser module), and in some variants also to multiple laser sources (laser modules). The laser source of the present invention can be configured for CW or pulsed operation. Within the scope of the present invention, single-mode or multimode operation can be selected.

[0018] Within the scope of the present invention, a fiber laser is preferably used as the laser source, alternatively, for example a disk laser can also be used as the laser source.

[0019] Preferred Variants of the Invention A variant of the method according to the invention is particularly preferred, in which the position of the scanner optics remains the same relative to the workpiece when welding the first welding zone and when welding the second welding zone. That is, the workpiece and the scanner optics are not moved relative to each other when the welding zones at the workpiece are exchanged. This allows very high accelerations to be achieved when processing workpieces, in particular when processing a series of many workpieces that are processed one after the other, since no relative movement of the scanner optics relative to the workpiece takes place and thus no associated time occurs. A quick adaptation of the spot size can be achieved simply by switching the division of the laser energy between the core and the ring parts. Furthermore, a correspondingly quick automatic movement between the workpiece and the scanner optics is not essentially required, so that a particularly simple structure of the welding device can be used if necessary.

[0020] A variant of the method according to the invention is preferred, which provides that the core portion of the laser energy differs by at least 20%, preferably at least 30%, on average in time during the welding of the first welding zone and during the welding of the second welding zone. This allows a particularly large change in the effective spot size (or effective total diameter) of the laser beam to be achieved. By switching the distribution of the laser energy between the welding zones, the seam width is also switched depending on the "effective total diameter" of the laser beam (measured, for example, on the workpiece surface facing the laser and determined according to the 86% criterion). Typically, the effective total diameter of the laser beam from the first welding zone to the second welding zone changes likewise by at least 20%, preferably at least 30%, relative to the larger diameter.

[0021] Furthermore, on average in time during welding of the first welding zone and / or in the main phase, the core part KA1 0%≦KA1≦60%, preferably 20%≦KA1≦50% applies; On average in time during welding of the second welding zone and / or in the main phase, the core part KA2, 40% ≤ KA2 ≤ 100%, preferably 50% ≤ KA2 ≤ 70% is applied. A modified form that provides this is preferred. In this modified form, basically, further KA1 < KA2, preferably KA1 ≤ KA2 - 20%, particularly preferably KA1 ≤ KA2 - 30% is also applied. Such splitting of laser energy has been demonstrated to be effective in practice, especially when welding a first Al-based component in the first welding zone and a second Cu-based component in the second welding zone.

[0022] A modified form in which the first component is made of Al or an Al alloy at least in the region of the first welding zone and the second component is made of Cu or a Cu alloy at least in the second welding zone is particularly preferred. The first component (Al / Al alloy, usually at least 50 wt% Al) can be provided as the cathode of a battery or a battery cell, and the second component (Cu / Cu alloy, usually at least 50 wt% Cu) can be provided as the anode. The base part can be made of, for example, aluminum or steel. Terminals (local coatings) made of Al, Al alloy, Cu, or Cu alloy can be provided in the region of the base part where the components are welded, and preferably, terminals made of the same material as each component are selected (it is relatively rare for a component made of Al / Al alloy to be welded to a terminal made of Cu / Cu alloy). The Al alloy can be selected as a 1000 series alloy. The Cu alloy can be selected as CU-EPT or CU-OF. This procedure has been demonstrated to be effective in practice when manufacturing Al-based and Cu-based components. For both types of components, by switching the energy distribution without moving the scanner optical system relative to the workpiece, a weld seam with less spatter and porosity can be generated.

[0023] The workpiece is a member of a battery, particularly a lid for a prismatic cell of a battery, and The first component forms a cathode of the battery, and the second component forms an anode, and in particular, the first component and the second component are each formed as a fork-shaped soft connector of a prismatic cell; The method according to the invention can be used to efficiently ensure the high quality of the weld seams required for batteries or the high reliability of the battery components produced.

[0024] Furthermore, variants are preferred in which the core portion of the laser energy increases during the initial phase and / or decreases during the final phase when welding the first welding zone and / or when welding the second welding zone. Such power ramps can reduce spatter at the beginning of the respective process (of the welding of the respective welding zone) and porosity at the end. Usually, when welding the respective welding zone during the main phase (between the initial and final phase), the division of the laser energy remains constant. The power ramps in the initial and final phases of welding the respective welding zone are usually applied over a period of 5 to 500 ms, preferably 10 to 50 ms. In the initial phase, the core portion can start with a value that is reduced, for example, by (at least) 20%, or even by (at least) 40%, compared to the target value (of the main phase). In the final phase, the core portion can end with a value that is reduced, for example, by (at least) 20%, or even by (at least) 40%, compared to the target value (of the main phase). Usually, the power ramps are set to be linear with time.

[0025] To generate the laser beam, a variant is preferred in which the output laser beam is split into a core beam and a ring beam by means of a variable splitting device, which is particularly simple to set up and in particular requires only a laser module (laser source) for the output laser beam.

[0026] A preferred development of this variant provides that the output laser beam is fed to the core fiber and to the ring fiber surrounding the core fiber with corresponding portions according to the desired division of the laser energy by means of a variable splitting device, in particular the variable splitting device comprising a movable optical wedge. The core beam and the ring beam can be easily generated via the core fiber and the ring fiber with a particularly relatively uniform intensity distribution over the respective beam cross section both in the radial and azimuth directions. The movable optical wedge can be particularly easily set.

[0027] In another development, it is provided that, using a variable splitting device, the output laser beam passes by the DOE or ROE with corresponding portions according to the desired split of the laser energy, passing through the DOE or ROE, in particular the DOE or ROE being movable. Using a DOE (diffractive optical element) or ROE (refractive optical element), the beam portion incident on it is deflected (possibly into several local maxima), this deflected beam portion providing the ring beam. The undeflected beam portion passing by the DOE or ROE is the core portion. This structure can be realized simply and space-savingly, and no multi-clad fiber is required.

[0028] An alternative advantageous variant is that for generating the laser beam, the core beam is generated by a first laser module and the ring beam is generated by a second laser module, and the power of the first laser module and the power of the second laser module are variably adjustable; In particular, the first laser module provides a first pre-laser beam to the core fiber, and the second laser module provides a second pre-laser beam to the ring fiber surrounding the core fiber. In this variant, the laser power of the core beam and the laser power of the ring beam can be adjusted independently of each other in a particularly simple manner. The core beam and the ring beam can provide a relatively uniform intensity distribution both in the azimuth direction and in the radial direction through the core fiber and the ring fiber.

[0029] In a preferred variant, the diameter KSD' of the core beam and the diameter ARSD' of the ring beam, measured at the workpiece surface facing the laser beam, are 1 / 10≦KSD' / ARSD'≦1 / 2, Preferably, 1 / 3≦KSD′ / ARSD′≦1 / 5, Particularly preferably, it is provided that KSD' / ARSD'=1 / 4 applies. These ranges of the core beam diameter KSD' and the (outer) ring beam diameter ARSD' have proven to be effective in practice and are often sufficient to accommodate the requirements of various components (e.g. Al- and Cu-based).

[0030] Particularly preferred is a variant in which the diameter KSD' of the core beam and the diameter ARSD' of the ring beam, measured at the workpiece surface facing the laser beam, remain constant during the welding of the first and second welding zones, which can be set particularly simply by means of 2D scanner optics (and welding zones that are equidistant in the beam propagation direction from the scanner optics).

[0031] In an alternative variant, it is provided that the scanner optics is formed as a 3D scanner optics and that the core beam diameter KSD' and the ring beam diameter ARSD', measured at the workpiece surface facing the laser beam during welding of the first and second welding zones, are changed by changing the focal position in the direction of propagation of the laser beam using the 3D scanner optics. This allows to expand the range in which the effective spot size of the entire processing laser beam can be adjusted (especially for welding zones that are equidistant from the scanner optics in the direction of beam propagation). Usually, the focal position is changed only when the welding zones are replaced.

[0032] Furthermore, when the laser beam is in a focal plane during welding of the first welding zone and / or the second welding zone, - the core beam has a core beam diameter KSD, and 86% of the laser power of the core beam is within the core beam diameter; - the ring beam has an outer ring beam diameter ARSD, and 86% of the laser power of the ring beam is within the outer ring beam diameter; - the ring beam has an inner ring beam diameter IRSD, at which there is the same radiation density averaged around the circumference of the ring beam as there is at the outer ring beam diameter ARSD, resulting in an intensity gap between the inner ring beam diameter IRSD and the core beam diameter KSD with an intensity gap width ILB=(IRSD-KSD) / 2; ILB≦0.3*KSD and ILB<10μm*AV, where AV is the imaging ratio of the scanner optics; In particular, the laser beam is provided to a fiber end of a fiber optic cable, the fiber optic cable being formed at least by a core fiber having a core fiber diameter KFD, a ring fiber surrounding the core fiber in a ring shape and having an outer ring fiber diameter ARFD, and an outer jacket layer located between the core fiber and the ring fiber, surrounding the core fiber, and having an outer jacket layer thickness MSD, where MSD, MSD≦0.3*KFD and MSD<10 μm. Particularly preferred is a variant which provides. This procedure results in a particularly stable vapor capillary and correspondingly particularly few welding defects such as spatters, porosity or cracks. In particular, MSD≦0.2*KFD and / or even ILB≦0.2*KSD, preferably MSD≦0.15*KFD and / or even ILB≦0.15*KSD, particularly preferably MSD≦0.1*KFD and / or even ILB≦0.1*KSD may also be applied. Furthermore, in particular MSD≦9 μm and / or ILB≦9 μm*AV, preferably MSD≦7 μm and / or ILB≦7 μm*AV, particularly preferably MSD≦6 μm and / or ILB≦6 μm*AV may also be applied.

[0033] The welding of the first welding zone and the welding of the second welding zone are - the penetration depth ET is 100 μm ≤ ET ≤ 5 mm, and / or - the aspect ratio between the depth T and width B of the resulting weld seam is T:B ≥ 0.5:1; and / or the beam parameter product SPP of the laser beam in single mode is 0.38 mm*mrad≦SSP≦16 mm*mrad, preferably SSP≦0.6 mm*mrad, or in multimode is SSP≦100 mm*mrad, preferably SSP≦32 mm*mrad, and / or - in single mode, the total diameter GD' of the laser beam at the workpiece surface facing the laser beam is 10 μm≦GD'≦300 μm, preferably 30 μm≦GD'≦70 μm, or in multimode, 50 μm≦GD'≦1200 μm; and / or the laser beam is generated by means of at least one IR laser with a medium wavelength MWL of 800 nm≦MWL≦1200 nm, preferably 1030 nm≦MWL≦1070 nm, or at least one VIS laser with a medium wavelength MWL of 400 nm≦MWL≦450 mm or 500 nm≦MWL≦530 mm, and / or The scanner optics has an imaging ratio AV of 1:1≦AV≦5:1, preferably 1.5:1≦AV≦2:1. A variant of the method is preferred, in which the parameters are as follows: These parameters have been proven to be effective in practice: The (effective) total diameter GD' ("spot size") can be determined by the 86% criterion of the (total) laser beam.

[0034] Also included within the scope of the present invention is a prismatic cell for a battery, comprising a lid and two fork-shaped soft connectors, the first and second components of which are welded to the lid as a base part by using the method according to any one of the claims. The lid for the prismatic cell can be produced within the scope of the present invention in a simple, fast and high quality manner. The first and second components are usually formed by an Al-based cathode and a Cu-based anode.

[0035] Further advantages of the invention will become apparent from the following description and the drawings. Likewise, according to the invention, the features mentioned above and those described in further detail can be used individually or in any combination. The illustrated and described embodiments should not be understood as an exhaustive enumeration, but rather have an exemplary character for explaining the invention. [Brief description of the drawings]

[0036] [Figure 1a] 1 shows a schematic longitudinal cross-section along an optical fiber cable in the region of an exemplary variable splitting device for splitting the laser energy of a laser beam of the present invention. [Figure 1b] FIG. 1b shows a top view of the fiber end of the fiber optic cable of FIG. [Diagram 2] 1 shows a schematic cross-sectional view of an exemplary scanner optical system of the present invention; [Figure 3a] 1 shows a schematic side view of the processing of an exemplary workpiece within the scope of the method according to the invention; [Figure 3b] 3b shows a schematic top view of the workpiece of FIG. 3b. [Figure 4a] 1 shows a diagram of the laser intensity of a laser beam as a function of location transverse to the beam propagation direction in the focal plane during laser welding of a first component in a first welding zone of a workpiece according to an exemplary variant of the method according to the present invention. [Figure 4b] 4b shows a schematic diagram of the laser intensity of the laser beam as a function of the location transverse to the beam propagation direction in the focal plane during laser welding of a second component in a second welding zone of a workpiece according to the variant of FIG. 4a. [Diagram 5] 5 shows a schematic diagram of the time course of a core part during welding of the first and second welding zones according to an exemplary variant according to the invention; [Figure 6] 1 shows a schematic perspective view of a prismatic cell lid of a battery welded using the method according to the invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0037] 1a to 3b show different parts of an exemplary structure for laser welding workpieces, in which the method according to the invention can be carried out.

[0038] As can be seen in Fig. 1a, an output laser beam 1 is fed into a fiber end 2 behind a multi-clad fiber 3 (here formed as a double-clad fiber) by a focusing lens 34. An optical wedge 4 protrudes into the beam path of the output laser beam 1 from the outside in a radial direction in the situation shown to approximately the center of the output laser beam 1.

[0039] A first portion 1a of the output laser beam 1 (in FIG. 1a, the lower portion of the output laser beam 1) passing by the optical wedge 4 is fed from a focusing lens 34 at the rear fiber end 2 into a core fiber 5 of the multi-clad fiber 3. A second portion 1b of the output laser beam 1 (in FIG. 1a, the upper portion of the output laser beam 1) deflected by the optical wedge 4 is fed from a focusing lens 34 at the rear fiber end 2 into a ring fiber 6 of the multi-clad fiber 3.

[0040] The multi-clad fiber 3 then provides a modified laser beam 8 at the front fiber end 7. The laser beam 8 includes a core beam 9 emerging from the core fiber 5 and a ring beam 10 emerging from the ring fiber 6. The core beam 9 and the ring beam 10 essentially diverge and emerge from the fiber end 7. The total laser energy of the laser beam 8 (substantially corresponding to the laser energy of the output laser beam 1) is split into a core beam 9 (core portion originating from the first portion 1a) and a ring beam 10 (ring portion originating from the second portion 1b) according to the division caused by the optical wedge 4.

[0041] To vary the splitting of the laser energy into the core and ring portions, the optical wedge 4 can be moved transversely to the beam propagation direction SA of the output laser beam 1 along a moving direction VR. For example, if the optical wedge 4 is pulled upwards (further out of the output laser beam 1) from the situation in Fig. 1a, the core portion increases and the ring portion decreases. Conversely, if the optical wedge 4 is moved downwards (further into the output laser beam 1), the core portion decreases and the ring portion increases. Thus, the optical wedge 4 at the output laser beam 1 before the fiber end 2 after the multi-clad fiber 3 forms a variable splitting device 26.

[0042] It should be noted that in other formats, the generation of the core beam and ring beam can be accomplished in other ways, and the division of the laser energy into the core beam and ring beam can be accomplished in other ways, such as by multiple independent laser modules, or by a DOE or ROE (not described in detail) that can be moved various distances into the output laser beam.

[0043] FIG. 1b shows a top view of the front fiber end 7 of the multi-clad fiber 3 of FIG. 1a. The core fiber 5 has a circular cross section and a core fiber diameter KFD, which in the illustrated example is 75 μm. The ring fiber 6, which surrounds the core fiber 5 in a ring shape, also has a circular cross section and has an outer ring fiber diameter ARFD and an inner ring fiber diameter IRFD, which in the illustrated example are formed with ARFD=300 μm and IRFD=90 mm. The cladding layer 11, which is arranged between the core fiber 5 and the ring fiber 6, has a cladding layer thickness MSD of 7.5 μm here. A further cladding layer 12 is arranged around the outside of the ring fiber 6. That is to say, the ratio between MSD and KFD is here about MSD=0.15*KFD. In another example, for example, a KFD of 75 μm and an ARFD of 400 μm can also be selected.

[0044] It should be noted that the cross-sectional geometry of the core fiber 5 and the ring fiber 6 substantially corresponds to the beam cross-section of the laser beam 8, including the core beam 9 and the ring beam 10, at the former fiber end 7 or at the focal plane of the laser beam 8 (after imaging by the scanner optics), in the latter case stretched or compressed according to the imaging ratio AV of the imaging. Thus, in particular the core beam 9 and the ring beam 10 are also circular in cross-section, corresponding to the fiber geometry (see also FIG. 1 a in this regard).

[0045] As shown in Fig. 2, the multi-clad fiber 3 is connected to a scanner optics 13. In the illustrated form, the laser beam 8 (already including the core beam and the ring beam) emerging from the previous fiber end 7 is collimated by a collimating lens 14. The collimated (parallelized) laser beam 8a impinges on a scanner mirror 15, which is tiltable about two axes, the x-axis and the y-axis in the coordinate system of Fig. 2 (which run perpendicular to the drawing plane, x, y, z forming a Cartesian coordinate system). The reflected collimated laser beam 8b is then focused by a focusing lens 16 in a focal plane FE in the direction of the workpiece 17 to be welded. In the illustrated example, the surface 18 of the workpiece 17 facing the laser beam 8 is located in the focal plane FE.

[0046] By pivoting the scanner mirror 15, the laser beam 8 or its laser spot 19 can be moved on the surface 18 of the workpiece 17, in particular to trace (i.e. create) a desired weld seam on the workpiece 17, or to alternate between different welding zones of the workpiece where the weld seam is to be created, respectively.

[0047] In the illustrated example, the surface 18 of the workpiece 17 (at least where laser processing is performed on the workpiece 17) is located approximately perpendicular to the mean beam propagation direction SA of the laser beam 8, which here substantially corresponds to the optical axis of the focusing lens 16, here in the z direction.

[0048] During processing of the workpiece 17 by the laser beam 8, including during the changeover of the welding zone, the relative positions of the scanner optics 13 and the workpiece 17 in the variant presented here remain fixed, in particular with respect to their distance in the z-direction in FIG. 2 (extending along the beam propagation direction SA). The scanner optics 13 is not moved (although the scanner mirror 15 is pivoted within the scanner optics 13). In an alternative variant, a relative movement between the workpiece 17 and the scanner optics 13 can also be provided when processing the workpiece 17, and according to the invention, the division of the laser energy is switched (not described in detail) to shorten the relative movement path for adjusting the effective spot size when the welding zone is changed over.

[0049] In addition, in the illustrated version, the distance (z-direction) between the focal plane FE and the scanner optics 13 is fixed, i.e. the scanner optics 13 is formed as a 2D scanner optics.) In an alternative version, the position of the focal plane FE can also be changeable relative to the scanner optics 13, for example by moving a focusing lens 16 in the scanner optics 13 in the z-direction (not described in detail).

[0050] In Fig. 3a the processing of the workpiece 17 according to the invention is explained in detail. Here, the workpiece 17 comprises a base part 20, onto which a first component 21 and a second component 22 are welded. In the illustrated example, the base part 20 is a lid 20a for a prismatic cell of a battery, the lid 20a being made here from an Al alloy. The first component 21 is here the cathode 21a of the cell, the first component 21 being formed as a fork-shaped soft connector 21b (see also Fig. 6 for this) and the first component 21 being also made here from an Al alloy. The second component 22 is here the anode 22a of the cell, the second component 22 also being formed as a fork-shaped soft connector 22b (see also Fig. 6 for this) and the second component 22 being made here from a Cu alloy.

[0051] During processing of the workpiece 17, the processing laser beam 8 emerging from the scanner optics 13 is directed one after the other (in any order) to a first welding zone 31 and a second welding zone 32, in which the first component 21 is welded to the base part 20 and the second component 22 is welded to the base part 20 in the first welding zone 31 and in which the second welding zone 32. In the illustrated variant, the two components 21, 22 are then located in front of the base part 20 (with respect to the mean beam propagation direction SA), which is also generally preferred.

[0052] As can be seen in Fig. 3b, in the illustrated variant, a ring-shaped closed weld seam is then produced corresponding to the respective path 23 of the laser spot 19 of the laser beam 8 on the surface 18 of the workpiece 17, which surface 18 here lies on the components 21, 22. Alternatively, for example, linear (hatched) welding is also possible (not described in detail).

[0053] Since the two components 21, 22 are made of different materials, the welding action of the laser beam on both components 21, 22 is fundamentally different. This can result, for example, in different forms of welding defects (spatter, porosity, cracks, etc.). The different materials can in particular affect the respective penetration depth ET, which is the depth to which the material of the workpiece 17 is melted by the laser beam 8, see the melting fronts 24, 25 shown by way of example in FIG. 3a. Essentially, it is desirable to optimize the welding action for each component 21, 22 or material involved, and for example to minimize welding defects or, in many applications, to achieve approximately the same penetration depth ET for all components 21, 22.

[0054] For this purpose, within the scope of the present invention, when the welding zones 31, 32 of the workpiece 17 are interchanged, the energy distribution of the laser beam 8 is switched between a core portion (core beam) and a ring portion (ring beam), while in the illustrated variant the position of the workpiece 17 relative to the scanner optics 13 remains the same.

[0055] Possible different laser energy divisions to the two welding zones 31, 32 or components 21, 22, which can be performed according to the invention, are explained by way of example on the basis of Fig. 4a and Fig. 4b. Both figures respectively show a diagram of the local laser intensity as a function of location along an x-axis perpendicular to the beam propagation direction and passing through the central axis of the laser beam ("intensity profile"). It should be noted that the laser beam is substantially rotationally symmetrical about this central axis.

[0056] The intensity profiles are shown at the respective focal planes. It should be noted that the focal planes preferably coincide with the workpiece surface facing the laser beam, in which case the intensity profiles at the focal planes shown simultaneously correspond to the intensity profiles at the workpiece surface (and the size of the focal planes shown without the apostrophes simultaneously corresponds to the size of the workpiece surface with the apostrophes, e.g. KSD=KSD', etc.).

[0057] The intensities are each expressed in the arbitrary unit au. The intensity profile can be produced by a structure similar to that described in Figures 1a to 3b.

[0058] 4a shows the intensity profile applied in the first weld zone when welding the first component. For this, the energy division was selected as 20% for the first core part KA1 and 80% for the first ring part RA1. The core beam 9 and the ring beam 10 are therefore superimposed in the intensity profile.

[0059] The core beam 9 gives rise to a central local intensity maximum, with a maximum intensity of about 1.5 au. The core beam diameter KSD of the core beam, determined according to the 86% criterion (thus 86% of the laser power of the core beam 9 is located within the diameter KSD), is here about 75 μm. The ring beam 10 has plateau regions on each side of the core beam maximum, with a maximum intensity of about 1.0 au. The ring beam diameter ARSD outside the ring beam 10, determined according to the 86% criterion (thus 86% of the laser power of the ring beam 10 is located within the diameter ARSD), is here about 400 μm. At the location of the ARSD, i.e. outside the ring beam, the intensity of the ring beam 10 is already somewhat reduced compared to the maximum intensity of the plateau region. If we look for the corresponding (same) intensity inside the ring beam 10, we thereby obtain the inner ring beam diameter IRSD, which is here about 160 μm. In the illustrated example, the intensity gap width ILB between the ring beam 10 and the core beam 9 is calculated from (160 μm to 75 μm) / 2, which corresponds to (IRSD-KSD) / 2, and is here about 43 μm. It should be noted that in other embodiments a significantly smaller intensity gap width ILB can be chosen, thus in particular ILB≦0.3*KSD.

[0060] The total beam diameter GD of the entire laser beam, i.e. the overlap of the core beam 9 and the ring beam 10, determined according to the 86% criterion (so that 86% of the laser power of the entire laser beam is located within GD), is here about 340 μm. This relatively large spot diameter is used here for welding the Al alloy of the cathode as the first component.

[0061] Then, the Cu alloy of the anode as the second component is welded to the same workpiece with the same overall laser power. For this, the distribution of the laser energy is switched, for example by moving the optical wedge as shown in FIG. 1a. FIG. 4b shows the intensity profile applied to the second welding zone when welding the second component. For this, the new energy division is selected as 60% for the second core part KA2 and 40% for the second ring part RA2. This means that the core beam 9 and the ring beam 10 are superimposed again in the intensity profile. When switching, 40% of the laser power is now transferred from the ring part to the core part.

[0062] The core beam 9 gives rise to a significantly higher central local intensity maximum with a maximum intensity of about 4.5 au. The core beam diameter KSD of the core beam 9, determined according to the 86% criterion, remains unchanged at about 75 μm. The ring beam 10 again has one plateau region each on either side of the core beam maximum, but the maximum intensity is here significantly lower at about 0.5 au. The outer ring beam diameter ARSD of the ring beam 10, determined according to the 86% criterion, remains unchanged at about 400 μm. At the location of the ARSD, the intensity of the ring beam 10 is already somewhat reduced compared to the maximum intensity of the plateau region. If we look for the corresponding intensity inside the ring beam 10, we thereby obtain an inner ring beam diameter IRSD that remains unchanged at about 160 μm.

[0063] However, the total beam diameter GD of the entire laser beam, i.e. the overlap of the core beam 9 and the ring beam 10, determined according to the 86% criterion, is here only about 220 μm. This is due to the higher intensity at small radii and the lower laser intensity at larger radii, especially in the region of the core beam 9. The relatively small spot size is well suited for welding the Cu alloy of the second component.

[0064] It should be noted that when switching, the total power of the laser beam does not change.

[0065] Figure 5 shows a typical time course of the energy distribution of the laser beam to the core portion KA and the ring portion RA throughout the welds of the first weld zone 31 and the second weld zone 32, as also applicable in the examples of Figures 4a and 4b. It should be noted that on the right the time t is plotted and above the core portion KA in %, where KA+RA=100%.

[0066] In the first welding zone 31, in the initial phase AP, the core portion KA increases linearly with time t from 0% to 20%. In the main phase HP, the core portion KA remains constant at 20%. In the final phase EP, the core portion KA decreases linearly with time from 20% to 0%. The power ramp in the initial phase AP and in the final phase EP allows to reduce welding defects in the first component, in particular spatter formation during piercing and porosity formation during cutting out of the first component. It should be noted that the initial phase AP and the final phase EP are in most cases much shorter than the main phase HP (typically AP≦0.1*HP and EP≦0.1*EP). Thus, the weld of the first welding zone 31 is mainly characterized by the main phase HP, and the core portion KA in the main phase HA is called the first core portion KA1, where KA1=20%. If the initial phase AP and the final phase EP have a larger proportion, KA1 can alternatively be determined as the time average of the core portion KA across AP, HP, and EP (not described in detail).

[0067] In the second welding zone 32, in the initial phase AP, the core portion KA increases linearly with time t from 20% to 60%. In the main phase HP, the core portion KA remains constant at 60%. In the final phase EP, the core portion EP decreases linearly with time from 60% to 20%. The power ramp of the initial phase AP and final phase EP also allows to reduce welding defects, in particular spatter formation during piercing and porosity formation during cutting out of the second component. It should be noted that the initial phase AP and final phase EP are in most cases much shorter than the main phase HP (typically AP≦0.1*HP and EP≦0.1*EP). Thus, the weld of the second welding zone 32 is mainly characterized by the main phase HP, and the core portion KA of the main phase HA is called the second core portion KA2, where KA2=60%. If the initial phase AP and final phase EP have a larger proportion, KA2 can alternatively be determined as the time average of the core portion KA over AP, HP and EP (not described in detail).

[0068] In the illustrated example, KA1 and KA2 differ by 40%. It should be noted that within the scope of the present invention, a difference of at least 20% is preferred, and even a difference of at least 30% is particularly preferred. It should be noted that the intensity distribution of the main phase HP has already been shown in the diagrams of Figs. 4a and 4b.

[0069] 6 shows a workpiece 17 welded using the method according to the invention. The workpiece 17 comprises as base part 20 the lid 20a of a prismatic cell of a battery, onto which as first component 21 a cathode 21a formed as a fork-shaped soft connector 21b made of Al and as second component 22 an anode 22a also formed as a fork-shaped soft connector 22b made of a Cu alloy, welded using the method according to the invention. In addition to that, a cover 33 is now also attached to the lid 20a. [Explanation of symbols]

[0070] 1 Output laser beam 1a First section (output laser beam) 1b Second part (output laser beam) 2 Rear fiber end 3 Multi-clad fiber 4 Optical Wedge 5-core fiber 6 Ring Fiber 7 Front Fiber End 8 Laser Beam 8a Collimated laser beam 8b Reflected laser beam 9 Core Beam 10 Ring Beam 11 Outer layer 12 Another outer layer 13 Scanner Optical System 14 Collimating lens 15 Scanner Mirror 16 Focusing Lens 17 Workpiece 18 Surface (of the workpiece, facing the laser beam) 19 Laser Spot 20 Base Parts 20a lid 21 First Component 21a Cathode 21b Soft Connector 22 Second Component 22a Anode 22b Soft Connector 23 Laser beam path 24 Melting Front 25 Melting Front 26 Variable division device 31 First Welding Zone 32 Second Welding Zone 33 Cover 34 Focusing Lens AP Initial Phase ARFD Outer Ring Fiber Diameter ARSD Ring Beam Outer Diameter (Focal Plane) EP Final Phase ET Penetration Depth FE focal plane GD Total diameter (focal plane) HP Main Phase I strength ILB Strength Gap Width IRFD Inner Ring Fiber Diameter IRSD Inner Ring Beam Diameter (Focal Plane) KA core part KA1 First core part (first weld zone core part) KA2 First core part (core part of second welding zone) KFD Core Fiber Diameter KSD Core Beam Diameter (Focal Plane) MSD Coating Thickness SA beam propagation direction t time VR movement direction x direction y direction z direction

Claims

1. A method of laser welding a workpiece (17), comprising the steps of: A laser beam (8) is directed to the workpiece (17) by scanner optics (13); said laser beam (8) welds, in any order, at least a first component (21) to a base part (20) in a first welding zone (31) and a second component (22) to said base part (20) in a second welding zone (32); The method, wherein the first component (21) and the second component (22) are made of different materials at least in the region of the first and second weld zones (31, 32), the laser energy of the laser beam (8) can be variably divided at least between a core portion (KA) corresponding to a core beam (9) of the laser beam and a ring portion corresponding to a ring beam (10) surrounding the core beam (9); the division of the laser energy into the core portion (KA) and into the ring portion is selected differently for the welding of the first welding zone (31) and for the welding of the second welding zone (32); The method comprising:

2. 2. The method according to claim 1, characterized in that the position of the scanner optics (13) with respect to the workpiece (17) remains the same for welding the first welding zone (31) and for welding the second welding zone (32).

3. 3. The method according to claim 1 or 2, characterized in that, averaged over time during the welding of the first welding zone (31) and during the welding of the second welding zone (32), the core portion (KA) of the laser energy differs by at least 20%, preferably by at least 30%.

4. On average over time during welding of the first welding zone (31) and / or in the main phase, the core part KA1 is 0%≦KA1≦60%, preferably 20%≦KA1≦50% applies; On average over time during welding of the second welding zone (32) and / or in the main phase, the core part KA2 is 40%≦KA2≦100%, preferably 50%≦KA2≦70% is applied.

3. The method according to claim 1 or 2, characterized in that

5. 3. The method according to claim 1, characterized in that the first component (21) consists of Al or an Al alloy at least in the region of the first weld zone (31) and the second component (22) consists of Cu or a Cu alloy at least in the region of the second weld zone.

6. The workpiece (17) is a part of a battery, in particular a prismatic cell lid (20a) of the battery; The first component (21) forms the cathode (21a) of the battery, and the second component (22) forms the anode (22a), and in particular, the first component (21) and the second component (22) are each formed as a fork-shaped soft connector (21b, 22b) of the prismatic cell.

3. The method according to claim 1 or 2, characterized in that

7. 3. The method according to claim 1 or 2, characterized in that when welding the first welding zone (31) and / or when welding the second welding zone (32), the core portion (KA) of the laser energy is increased during an initial phase (AP) and / or the core portion (KA) of the laser energy is decreased during a final phase (EP).

8. 3. The method according to claim 1 or 2, characterized in that to generate the laser beam (8), an output laser beam (1) is split into the core beam (9) and the ring beam (10) using a variable splitting device (26).

9. 9. The method according to claim 8, characterized in that, by means of the variable splitting device (26), the output laser beam (1) is fed into a core fiber (5) and into a ring fiber (6) surrounding the core fiber (5) with corresponding portions according to a desired split of the laser energy, in particular, the variable splitting device (26) comprising a movable optical wedge (4).

10. 9. The method according to claim 8, characterized in that by means of the variable splitting device (26), the output laser beam (1) passes by and through a DOE or ROE with corresponding portions according to a desired split of the laser energy, in particular the DOE or ROE is movable.

11. 3. The method according to claim 1 or 2, characterized in that for generating the laser beam (8), the core beam (9) is generated by a first laser module and the ring beam (10) is generated by a second laser module, the power of the first laser module and the power of the second laser module are variably adjustable, in particular the first laser module supplies a first pre-laser beam to a core fiber (5) and the second laser module supplies a second pre-laser beam to a ring fiber (6) surrounding the core fiber (5).

12. a diameter KSD' of the core beam (9) and a diameter ARSD' of the ring beam (10) measured at the workpiece surface (18) facing the laser beam (8); 1 / 10≦KSD' / ARSD'≦1 / 2, Preferably, 1 / 3≦KSD′ / ARSD′≦1 / 5, Particularly preferably, KSD' / ARSD'=1 / 4 is applied.

3. The method according to claim 1 or 2.

13. 3. The method according to claim 1 or 2, characterized in that during welding of the first welding zone (31) and the second welding zone (32), the diameter KSD' of the core beam (9) and the diameter ARSD' of the ring beam (10), measured at the workpiece surface (18) facing the laser beam, remain constant.

14. 3. The method according to claim 1 or 2, characterized in that the scanner optics (13) is formed as a 3D scanner optics and, during welding of the first welding zone (31) and the second welding zone (32), the diameter KSD' of the core beam (9) and the diameter ARSD' of the ring beam (10), measured at a workpiece surface (18) facing the laser beam (8), are changed by changing a focal position in the propagation direction (SA) of the laser beam (8) using the 3D scanner optics.

15. When the laser beam (8) is in a focal plane (FE) during welding of the first welding zone (31) and / or the second welding zone (32), the core beam (9) has a core beam diameter KSD, and 86% of the laser power of the core beam (9) is within the core beam diameter; the ring beam (10) has an outer ring beam diameter ARSD, and 86% of the laser power of the ring beam (10) is within the outer ring beam diameter; the ring beam (10) has an inner ring beam diameter I RSD , at which there is the same radiation density averaged around the circumference of the ring beam (10) as there is at the outer ring beam diameter A RSD , resulting in an intensity gap between the inner ring beam diameter I RSD and the core beam diameter K SD of an intensity gap width I L B = ( I RSD - K SD ) / 2; ILB≦0.3*KSD and ILB<10 μm*AV, where AV is the imaging ratio of the scanner optics (13), In particular, the laser beam (8) is provided to a fiber end (7) of a fiber optic cable (3), the fiber optic cable (3) being formed at least by a core fiber (5) having a core fiber diameter KFD, a ring fiber (6) surrounding the core fiber (5) in a ring shape and having an outer ring fiber diameter ARFD, and an outer jacket layer (11) located between the core fiber (5) and the ring fiber (6), surrounding the core fiber (5), and having an outer jacket layer thickness MSD, where MSD, MSD≦0.3*KFD and MSD<10 μm; 3. The method according to claim 1 or 2, characterized in that

16. The welding of the first welding zone (31) and the welding of the second welding zone (32) The penetration depth ET is 100 μm≦ET≦5 mm, and / or and / or the aspect ratio T:B between the depth T and width B of the weld seam to be produced is T:B ≥ 0.5:1; and / or In single mode, the beam parameter product of the laser beam (8) is 0.38 mm*mrad≦SSP≦16 mm*mrad, preferably SSP≦0.6 mm*mrad, or in multimode, SSP≦100 mm*mrad, preferably SSP≦32 mm*mrad, and / or and / or the total diameter GD' of the laser beam (8) at the workpiece surface (18) facing the laser beam (8) is such that in single mode 10 μm≦GD′≦300 μm, preferably 30 μm≦GD′≦70 μm, or in multimode 50 μm≦GD′≦1200 μm; the laser beam (8) is generated by at least one IR laser with a medium wavelength MWL of 800 nm≦MWL≦1200 nm, preferably 1030 nm≦MWL≦1070 nm, or at least one VIS laser with a medium wavelength MWL of 400 nm≦MWL≦450 mm or 500 nm≦MWL≦530 mm, in particular; and / or The scanner optical system (13) has an imaging ratio AV of 1:1≦AV≦5:1, preferably 1.5:1≦AV≦2:

1.

3. The method according to claim 1 or 2.

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