Method for laser welding a workpiece with quick change between welding zones with different welding materials

Abstract

A method for laser welding a workpiece (17), wherein: a laser beam (8) is directed to the workpiece (17) by means of an optical scanning unit (13); using the laser beam (8) and in any order, a first part (21) is welded to a base element (20) at least in a first welding zone (31) and a second part (22) is welded to the base element (20) in a second welding zone (32);and the first part (21) and the second part (22) are made of different materials, at least in the region of the first and second welding zones (21, 22), the method is characterized in that the laser energy of the laser beam (8) can be variably divided at least between a central component (KA) corresponding to a central beam (9) of the laser beam, and an annular component corresponding to an annular beam (10) surrounding the central beam (9), and in that the division of the laser energy into the central component (KA) and the annular component is selected differently when welding the first welding zone (21) and when welding the second welding zone (22). The invention allows for faster production of workpieces, in which parts made of different materials are welded to a base element.

Description

[0001] The invention relates to a method for laser welding a workpiece, wherein a laser beam is directed at the workpiece by means of a scanner optic, wherein a first component is welded to a base component in an arbitrary sequence at least in a first welding zone and a second component is welded to the base component in a second welding zone, and wherein the first component and the second component consist of different materials at least in the area of ​​the first and second welding zones.

[0002] Laser welding is a powerful process for joining workpiece components into a single workpiece. It is primarily used when high welding speed, a narrow weld seam, or minimal thermal distortion of the workpiece is required.

[0003] In many cases, laser welding is used to weld several components to a base component. For example, in electric battery cells, the cathode is often made of aluminum (Al) or an aluminum alloy, and the anode of copper (Cu) or a copper alloy, and these two components are to be welded to a common base component of the cell.

[0004] Typically, for laser welding, the workpiece to be welded (or its components to be welded together) is positioned in front of a scanner optic. The scanner optic generally comprises an input for laser radiation, to which a fiber optic cable is usually connected, various optical elements (usually a collimating lens or collimating lens system and a focusing lens or focusing lens system), and an adjustable deflection device (usually a mirror adjustable with piezoelectric elements) that allows the orientation of the laser beam exiting the scanner optic relative to the workpiece to be changed. This is particularly useful for guiding the laser beam along a desired weld path (weld seam) or for successively directing the laser beam to different welding zones where the various components are welded to the base component.

[0005] For laser welding components made of different materials, varying spot sizes of the welding laser beam are often advantageous, particularly to minimize spatter and porosity. To achieve this, the distance between the scanner optics or the laser processing head and the workpiece can be adjusted in the beam propagation direction. For example, in a first relative position of the scanner optics to the workpiece, if the workpiece surface facing the laser beam is located in the focal plane of the laser beam, the spot size of the laser beam on the workpiece surface is at its smallest. By moving the workpiece surface out of the focal plane to a second relative position, the spot size of the laser beam on the workpiece surface can be increased.

[0006] However, the scanning optics process relative to the workpiece is complex and relatively time-consuming. Therefore, if components of different materials are to be welded sequentially onto a common base component, the manufacturing process becomes comparatively slow using the method described above; when manufacturing such workpieces in series, the delay caused by adjusting the scanner optics occurs with each individual workpiece.

[0007] From DE 10 2010 003 750 A1, it is known to modify the beam profile characteristics of a laser beam using a multiclad fiber comprising at least one core fiber and one ring fiber. An output laser beam is fed partly (core component) into a core fiber and partly (ring component) into a ring fiber; these components can be changed, for example, by the position of an optical wedge in the output laser beam upstream of the fiber end of the multiclad fiber. The multiclad fiber can thus provide a modified laser beam with a core beam and a ring beam with adjustable components.

[0008] CN 207 353 371 U, which forms the basis for the preamble of claim 1, discloses a connection structure for batteries, in particular for electric vehicles. The connection structure comprises, by way of example, two connecting plates which can be joined to a cover plate by means of laser welding.

[0009] A cover plate for a lithium-ion battery is known from CN 102 637 835 A. At least one terminal can be connected to the cover plate by laser welding.

[0010] In DE 10 2019 218398 A1 a method for joining busbars is disclosed, wherein the busbars are joined together by laser welding. Object of the invention

[0011] The object of the invention is to present a method for laser welding a workpiece, which can accelerate the production of workpieces in which components made of different materials are welded onto a base component. Description of the invention

[0012] This problem is solved according to the invention by a method of the type mentioned at the outset, which is characterized in that a laser energy of the laser beam can be variably divided at least between a core portion, corresponding to a core beam of the laser beam, and a ring portion, corresponding to a ring beam surrounding the core beam, and that the division of the laser energy onto the core portion and the ring portion is selected differently when welding the first weld zone and when welding the second weld zone.

[0013] The invention provides for the ability to select different distributions of laser energy between a core portion and a ring portion during laser welding of at least two components made of different materials onto a common base component. By changing the distribution of laser power between the core portion and the ring portion, it is possible to modify or adjust the effective spot size of the welding laser beam on the workpiece surface facing the laser beam. This allows the spot size to be adapted to the conditions in the different welding zones or on the different components, and in particular to their different materials. Simultaneously, the intensity profile of the (entire) laser beam is also modified or adjusted during processing. Both of these factors can be used to improve the quality of the laser welding in the different welding zones or components.to optimize the different components, and in particular to minimize splashes and pores.

[0014] These changes or adjustments do not require changing the position of the scanner optics, which would be complex and time-consuming. Therefore, according to the invention, the position of the scanner optics relative to the workpiece is preferably kept constant during welding of the first and second weld zones, and especially during transitions between weld zones. Alternatively, to change the (effective) spot size when changing weld zones, a combination of a (relative) movement of the workpiece and scanner optics, as well as switching the distribution of the laser energy between the core and ring portions, can be used. In this case, a significant reduction in the (relative) travel distance can be achieved, which leads to a corresponding reduction in the non-productive time for changing weld zones and can therefore significantly accelerate the welding process overall.Changing the distribution of laser power is quick and easy, for example by slightly adjusting an optical wedge, and in particular does not cause any noticeable downtime.

[0015] The effective spot size of a laser beam or beam component (e.g., of an entire laser beam comprising the core and ring components, or of a core beam alone, or of a ring beam alone) can be determined according to the 86% criterion. According to the 86% criterion, the spot size of a laser beam is defined by the diameter of a circular area (coaxial with the laser beam) within which 86% of the laser beam's power is concentrated.

[0016] By changing the effective spot size via the distribution of laser energy between the core and ring portions, it is possible to easily and quickly adjust the weld width (width of the weld seam perpendicular to the feed direction), which is important in many applications, particularly to suit the different materials of the various components. For example, a comparatively wide weld seam can be selected for aluminum-based cathodes and a comparatively narrow weld seam for copper-based anodes, especially to account for the different melt properties (viscosities and wetting properties) of the materials involved. The inventive method, or rather the adjustment of the spot size, can be used in particular to achieve a uniform weld penetration depth in the different welding zones or for the different components. Likewise, welding defects, especially spatter and porosity, can be minimized.

[0017] To increase the weld width / spot size, the annular portion is increased relative to the core portion. To decrease the weld width / spot size, the annular portion is decreased relative to the core portion. In this way, the effective spot size can be adjusted essentially within a range between the spot size of the annular portion (alone) and the spot size of the core portion (alone). Note that changing the distribution of the laser energy between the core and annular portions does not change the spot size of the core or the spot size of the annular portion. In a particularly simple embodiment of the inventive method, the spot size of the core beam and the spot size of the annular beam remain constant when switching between the first and second welding zones.

[0018] The workpiece to be manufactured is welded together from the base component and (at least) two sub-components. Typically, the laser beam power remains constant throughout the welding process (both across and within the different welding zones). The first and second welding zones are spaced apart at least perpendicular to the beam propagation direction. Typically, the two welding zones are equidistant from the scanner optics on the workpiece (in the beam propagation direction), and any angular offset from the optical axis of the scanner optics is either negligibly small (e.g., less than 5°) or at least approximately the same for both welding zones (e.g., with a difference of less than 5°).

[0019] The ring beam typically has a constant intensity along its circumference (usually generated by splitting an output laser beam into a core fiber and a ring fiber, and multiple reflections of the laser light within the ring fiber); however, it is also possible to use a ring beam with several consecutive local maxima along its circumference (for example, generated with a diffractive optical element (DOE) or a refractive optical element (ROE)). The scanner optics are usually chosen as 2D scanner optics, with a fixed focus position in the beam propagation direction in front of the scanner optics.Typically, the laser beam is provided via an optical fiber cable with a core fiber and a ring fiber. The core fiber diameter (CFD) is usually in the range of 10 µm–50 µm (for single mode) or 50 µm–400 µm, particularly 50 µm–200 µm (for multi-mode), and the outer ring fiber diameter (ARFD) is usually in the range of 20 µm–500 µm, particularly 40–200 µm (for single mode), or 40 µm–2000 µm, particularly 80 µm–800 µm (for multi-mode). The CFD:ARFD ratio is usually 1:2 to 1:10, preferably 1:4. One (front) fiber end of the optical fiber cable is connected to the scanner optics (processing head). One (rear) fiber end of the optical fiber cable is connected to a laser source (laser module), and in some variants, to multiple laser sources (laser modules). A laser source for the invention can be configured for continuous wave (CW) or pulsed operation. Within the scope of the invention, single-mode or multi-mode operation can be selected.

[0020] In the context of the invention, a fiber laser is preferably used as the laser source; alternatively, a disk laser can also be used as the laser source, for example. Preferred variants of the invention

[0021] A particularly preferred variant of the inventive method is one in which the position of the scanner optics relative to the workpiece remains constant during the welding of the first and second welding zones. The workpiece and scanner optics are therefore not moved relative to each other, even when changing the welding zone on the workpiece. This allows for a significant acceleration in the processing of the workpiece, and especially in the processing of a large number of consecutively processed workpieces in a series, since the scanner optics do not move relative to the workpiece and therefore incur no idle time. Spot size adjustment can be performed quickly and easily simply by switching the distribution of the laser energy between the core and ring components.Furthermore, a particularly simple design of the welding apparatus can be used if desired, since a correspondingly fast, automated movement between the workpiece and the scanner optics is generally not required.

[0022] A preferred variant of the inventive method provides that, on average during the welding of the first weld zone and the welding of the second weld zone, the core components of the laser energy differ by at least 20%, preferably at least 30%. This allows for a particularly significant change in the effective spot size (or effective total diameter) of the laser beam. By switching the distribution of the laser energy between the weld zones, the weld width is also switched, corresponding to the "effective total diameter" of the laser beam (approximately determined according to the 86% criterion, measured on the workpiece surface facing the laser). Typically, the effective total diameter of the laser beam also changes by at least 20%, preferably at least 30%, from the first weld zone to the second weld zone, relative to the larger diameter.

[0023] A preferred variant is one which provides that, on average over time and / or during a main phase of welding the first weld zone, the following applies to the core fraction KA1: 0% ≤ KA1 ≤ 60%, preferably 20% ≤ KA1 ≤ 50%, and that on average over time and / or during a main phase of welding the second weld zone, the following applies to the core fraction KA2: 40% ≤ KA2 ≤ 100%, preferably 50% ≤ KA2 ≤ 70%. In this variant, KA1 also generally applies. <KA2, bevorzugt KA1≤KA2-20%, besonders bevorzugt KA1≤KA2-30%. Eine solche Aufteilung der Laserenergie hat sich in der Praxis bewährt, insbesondere für ein Schweißen einer Al-basierten ersten Komponente an der ersten Schweißzone und einer Cu-basierten zweiten Komponente an der zweiten Schweißzone.

[0024] A particularly preferred variant is one in which the first component consists of aluminum or an aluminum alloy, at least in the area of ​​the first weld zone, and the second component consists of copper or a copper alloy, at least in the area of ​​the second weld zone. The first component (al / al alloy, typically with at least 50 wt% Al) can be designated as a cathode and the second component (copper / copper alloy, typically with at least 50 wt% Cu) as an anode of a battery or battery cell. The base component can be made of, for example, aluminum or steel. Terminals (local coatings) can be provided on the base component in the area of ​​the components to be welded on, in particular made of aluminum, aluminum alloys, copper, or copper alloys, with a terminal made of the same material preferably being selected for each component (less frequently, an aluminum / al alloy component can be welded onto a copper / copper alloy terminal).The aluminum alloy can be selected as a 1000 series alloy. The copper alloy can be selected as either CU-EPT or CU-OF. This approach has proven successful in practice when manufacturing aluminum-based and copper-based components. For both types of components, spatter-free and pore-free welds could be produced by switching the energy distribution, without moving the scanner optics relative to the workpiece.

[0025] A variant that provides for is particularly preferred. that the workpiece is part of an electric battery, in particular a cover for a prismatic cell of the electric battery, and that the first component forms a cathode and the second component an anode for the electric battery, in particular wherein the first component and the second component are each designed as a fork-like soft connector for the prismatic cell. The method according to the invention efficiently ensures the high quality of the welds and / or the high reliability of the manufactured battery parts required for electric batteries.

[0026] A preferred variant involves increasing the core portion of the laser energy during an initial phase of welding the first weld zone and / or the second weld zone, and / or decreasing it during a final phase. Such power ramps can, in particular, reduce spatter at the beginning and porosity at the end of the respective process (welding a given weld zone). Typically, the laser energy distribution remains constant during a main phase (between the initial and final phases) of welding a given weld zone. The power ramps in the initial and final phases of welding a given weld zone are typically applied over a period of 5–500 ms, preferably 10–50 ms.In an initial phase, the core component can, for example, begin at a value that is reduced by (at least) 20%, or even by (at least) 40%, compared to the target value (in the main phase). In a final phase, the core component can, for example, end at a value that is reduced by (at least) 20%, or even by (at least) 40%, compared to the target value (in the main phase). The power ramps are typically set up linearly over time.

[0027] A preferred variant involves splitting an output laser beam into the core beam and the ring beam using a variable splitting device to generate the laser beam. This is particularly easy to set up; in particular, only one laser module (one laser source) is required for the output laser beam.

[0028] A preferred further development of this variant provides that, with the variable splitting device, the output laser beam is fed into a core fiber and a ring fiber surrounding the core fiber in corresponding proportions, according to the desired distribution of the laser energy. In particular, the variable splitting device includes a movable optical wedge. The core beam and the ring beam can be easily generated via the core fiber and the ring fiber, especially with a relatively uniform intensity distribution over the respective beam cross-section, both radially and azimuthally. The movable optical wedge is particularly easy to set up.

[0029] In another development, the variable splitting device guides the output laser beam past and through a diffractive optical element (DOE) or refractive optical element (ROE) according to the desired laser energy distribution, particularly in that the DOE or ROE is movable. The portion of the beam directed by the DOE or ROE is deflected (optionally into several local maxima), and this deflected portion forms the ring beam. The undeflected portion of the beam passing by the DOE or ROE constitutes the core beam. This setup is simple and space-saving to implement; a multiclad fiber is not required.

[0030] An alternative, advantageous variant provides that the core beam is generated by a first laser module and the ring beam by a second laser module, wherein the power of the first laser module and the power of the second laser module are variably adjustable, in particular wherein the first laser module feeds a first pre-laser beam into a core fiber, and the second laser module feeds a second pre-laser beam into a ring fiber surrounding the core fiber. In this variant, the laser power in the core beam and the laser power in the ring beam can be adjusted independently of each other in a particularly simple manner. Using the core fiber and the ring fiber, the core beam and the ring beam can be provided with a comparatively uniform intensity distribution, both azimuthally and radially.

[0031] In a preferred embodiment, the following applies to the diameters KSD' of the core beam and ARSD' of the ring beam, measured on a workpiece surface facing the laser beam: 1 / 10 ≤ KSD ′ / ARSD ′ ≤ 1 / 2 , preferably 1 / 3 ≤ KSD' / ARSD' ≤ 1 / 5, particularly preferably KSD' / ARSD'=1 / 4. These ranges for the core beam diameter KSD' and the (outer) ring beam diameter ARSD' have proven effective in practice and are usually sufficient for adapting to the conditions of different components (e.g., Al-based and Cu-based).

[0032] A particularly preferred variant is one in which the diameters KSD' of the core beam and ARSD' of the ring beam, measured at a workpiece surface facing the laser beam, remain constant during the welding of the first and second weld zones. This is particularly easy to set up, especially with a 2D scanner optic (and weld zones equidistant from the scanner optic in the beam propagation direction).

[0033] In an alternative configuration, the scanner optics are designed as 3D scanner optics, and during the welding of the first and second weld zones, the diameters KSD' of the core beam and ARSD' of the ring beam, measured at a workpiece surface facing the laser beam, are changed by adjusting the focus position in the direction of laser beam propagation using the 3D scanner optics. This increases the area within which the effective spot size of the entire laser beam can be adjusted (especially for weld zones equidistant from the scanner optics in the direction of beam propagation). Typically, the focus position is changed only when switching between weld zones.

[0034] A variant that provides for, remains particularly preferred. that, for the laser beam during welding of the first weld zone and / or the second weld zone in a focal plane, the core beam has a core beam diameter KSD within which 86% of the laser power of the core beam is present, the ring beam has an outer ring beam diameter ARSD within which 86% of the laser power of the ring beam is present, and the ring beam has an inner ring beam diameter IRSD on which the same circumferentially averaged radiance of the ring beam is present as on the outer ring beam diameter ARSD, such that 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 results, and that ILB≤0.3*KSD and ILB<10µm*AV, with AV being the imaging ratio of the scanner optics, in particular where the laser beam is provided at a fiber end of an optical fiber cable.and the optical fiber is formed with at least one core fiber with a core fiber diameter KFD, a ring fiber surrounding the core fiber in a ring shape with an outer ring fiber diameter ARFD, and a cladding layer located between the core fiber and the ring fiber and surrounding the core fiber with a cladding layer thickness MSD, with MSD≤0.3*KFD and MSD<10µm.

[0035] This process results in particularly stable vapor capillaries and, consequently, very few welding defects such as spatter, pores, or cracks. In particular, MSD ≤ 0.2 * KFD and / or ILB ≤ 0.2 * KSD, preferably MSD ≤ 0.15 * KFD and / or ILB ≤ 0.15 * KSD, and especially preferably MSD ≤ 0.1 * KFD and / or ILB ≤ 0.1 * KSD. Furthermore, MSD ≤ 9 µm and / or ILB ≤ 9 µm * AV, preferably MSD ≤ 7 µm and / or ILB ≤ 7 µm * AV, and especially preferably MSD ≤ 6 µm and / or ILB ≤ 6 µm * AV, can also apply.

[0036] A preferred method variant is in which the welding of the first weld zone and the welding of the second weld zone are carried out in such a way that For a weld penetration depth ET, 100 µm ≤ ET ≤ 5 mm applies, and / or for an aspect ratio T:B of a depth T to a width B of a generated weld seam, T:B ≥ 0.5:1 applies, and / or for a beam parameter product SPP of the laser beam, in single-mode 0.38 mm*mrad ≤ SSP ≤ 16 mm*mrad applies, preferably with SSP ≤ 0.6 mm*mrad, or in multi-mode SSP ≤ 100 mm*mrad applies, preferably with SSP ≤ 32 mm*mrad, and / or for a total diameter GD' of the laser beam on the workpiece surface facing the laser beam, in single-mode 10 µm ≤ GD' ≤ 300 µm applies, preferably with 30 µm ≤ GD' ≤ 70 µm applies, or in multi-mode 50µm≤GD'≤1200µm applies, and / or the laser beam is generated with at least one IR laser with a mean wavelength MWL of 800nm≤MWL≤1200nm, preferably 1030nm≤MWL≤1070nm, or at least one VIS laser, in particular with a mean wavelength MWL of 400nm≤MWL≤450nm or 500nm≤MWL≤530nm, and / or the scanner optics have an imaging ratio AV of 1:1 ≤ AV ≤ 5:1, preferably 1.5:1 ≤ AV ≤ 2:1.These parameters have proven effective in practice. The (effective) total diameter GD' ("spot size") can be determined using the 86% criterion for the (entire) laser beam.

[0037] Further advantages of the invention will become apparent from the description and the drawing. Likewise, the features mentioned above and those described in more detail below can each be used individually or in any combination according to the invention. The embodiments shown and described are not to be understood as an exhaustive list, but rather serve as examples for illustrating the invention. Detailed description of the invention and drawing

[0038] Fig. 1a shows a schematic longitudinal section along an optical fiber cable of an exemplary, variable splitting device for dividing the laser energy of a laser beam, according to the invention; Fig. 1b shows a fiber end of the optical fiber cable made of Fig. 1ain top view; Fig. 2 shows a schematic longitudinal section of an exemplary scanner optic for the invention; Fig. 3 illustrates in a schematic side view the processing of an exemplary workpiece within the framework of the method according to the invention; Fig. 3b shows a schematic top view of the workpiece of Fig. 3b Fig. 4a shows a diagram of the laser intensity of a laser beam as a function of its position perpendicular to the beam propagation direction in the focal plane during laser welding of a first component in a first welding zone of a workpiece in an exemplary embodiment of the method according to the invention; Fig. 4b shows a schematic diagram of the laser intensity of the laser beam as a function of its position perpendicular to the beam propagation direction in the focal plane during laser welding of a second component in a second welding zone of the workpiece in the embodiment of Fig. 4a; Fig. 5 shows a schematic diagram of the time course of the core portion during welding of the first and second welding zones in an exemplary embodiment of the invention; Fig. 6 shows a schematic perspective view of a cover of a prismatic cell of an electric battery, which has been welded using the method according to the invention.

[0039] The Figures 1a to 3b Illustrate various parts of an exemplary setup for laser welding of workpieces, with which the inventive method can be carried out.

[0040] As in Fig. 1a It is evident that an output laser beam is used. 1 using a focusing lens 34 into a rear fiber end 2 a multiclad fiber 3 (which here is configured as a double-clad fiber) is fed in. An optical wedge protrudes into the beam path of the output laser beam 1. 4one, in the situation shown, radially from the outside to approximately the middle of the output laser beam 1.

[0041] A first part 1a of the output laser beam 1, which is guided past the optical wedge 4 (in Fig. 1a The lower part of the output laser beam 1) is focused by the focusing lens 34 at the rear end of the fiber 2 into a core fiber. 5 fed into the multiclad fiber 3. A second part 1b of the output laser beam 1, which is deflected by the optical wedge 4 (in Fig. 1a the upper part of the output laser beam 1) is focused by the focusing lens 4 at the rear end of the fiber 2 into a ring fiber 6 fed into the multiclad fiber 3.

[0042] At a front fiber end 7 The Multiclad Fiber 3 now represents a reshaped laser beam. 8 available. The laser beam 8 comprises a core beam. 9, which emerges from the core fiber 5, and forms a ring beam 10,which emerges from the ring fiber 6. Core beam 9 and ring beam 10 emerge from the fiber end 7 in a fundamentally divergent direction. The total laser energy of the laser beam 8 (which essentially corresponds to the laser energy of the output laser beam 1) is divided between the core beam 9 (core component, originating from the first part 1a) and the ring beam 10 (ring component, originating from the second part 1b) according to the division caused by the optical wedge 4.

[0043] To change the distribution of the laser energy between the core component and the ring component, the optical wedge 4 can be positioned perpendicular to a beam propagation direction. SA of the output laser beam 1 along a direction of travel VR The procedure is as follows. For example, if the optical wedge 4 is started from the situation of Fig. 1aWhen the optical wedge 4 is pulled upwards (further out of the output laser beam 1), the core fraction is increased and the ring fraction is decreased; conversely, when the optical wedge 4 is moved downwards (further into the output laser beam 1), the core fraction is decreased and the ring fraction is increased. The optical wedge 4 in the output laser beam 1 in front of the rear fiber end 2 of the multiclad fiber 3 thus forms a variable splitting device. 26 out of.

[0044] Note that in other designs, the generation of the core beam and the ring beam, and the division of laser energy between the core beam and the ring beam, can also be achieved in other ways, for example by means of several independent laser modules or by means of a DOE or ROE that can be moved to a different distance into the output laser beam (not shown in detail).

[0045] Fig. 1b shows, in top view, the front fiber end 7 of the multiclad fiber 3 of Fig. 1a The core fiber 5 is circular in cross-section and has a core fiber diameter KFD The outer diameter of the ring fiber 6, which in the example shown is 75 µm, is also circular in cross-section and has an outer ring fiber diameter of 75 µm. ARFD and an inner ring fiber diameter IRFD on, which in the example shown are formed with ARFD=300µm and IRFD=90mm. A cladding layer arranged between the core fiber 5 and the ring fiber 6. 11 has a mantle layer thickness MSD 7.5 µm from here. Around the outer ring fiber 6 is another cladding layer. 12 arranged. The ratio of MSD to KFD is therefore approximately MSD = 0.15 * KFD. In another example, KFD could be chosen to be 75 µm and ARFD to be 400 µm.

[0046] Note that the geometry of the cross-section of the core fiber 5 and the ring fiber 6 essentially corresponds to the beam cross-section of the laser beam 8 with core beam 9 and ring beam 10 at the front fiber end 7, or (according to imaging by the scanner optics) in a focal plane of the laser beam 8, in the latter case stretched or compressed according to the imaging ratio AV of the image. In particular, core beam 9 and ring beam 10 are also circular in cross-section according to the fiber geometry (see also Fig. 1a (to this).

[0047] As in Fig. 2 As shown, the multiclad fiber 3 is connected to a scanner optic. 13 connected. In the illustrated design, the laser beam 8 exiting at the front fiber end 7 (which already includes the core beam and the ring beam) is collimated by a collimating lens. 14 collimated. The collimated (parallelized) laser beam 8a encounters a scanner mirror 15,which can be tilted about two axes, in the coordinate system of Fig. 2 around the x-axis and around the y-axis (which runs perpendicular to the plane of the drawing; x, y, z form a Cartesian coordinate system). A reflected, collimated laser beam 8b is then focused by a focusing lens 16 in the direction of a workpiece to be welded 17 into a focal plane FE Too focused. In the illustrated example, there is a surface facing the laser beam 8. 18 of workpiece 17 in the focal plane FE.

[0048] By swiveling the scanner mirror 15, the laser beam 8 or its laser spot can be adjusted. 19 on the surface 18 of the workpiece 17, in particular to trace (i.e. to produce) desired weld seams on the workpiece 17 or to switch between different welding zones on the workpiece, in each of which a weld seam is to be produced.

[0049] In the example shown, the surface 18 of the workpiece 17 (at least where laser processing is to take place on the workpiece 17) is approximately perpendicular to the mean beam propagation direction SA of the laser beam 8; the mean beam propagation direction SA here essentially corresponds to the optical axis of the focusing lens 16, and lies in the z-direction.

[0050] During the processing of the workpiece 17 with the laser beam 8, including during the change between welding zones, the relative position of the scanner optics 13 and the workpiece 17 remain fixed in the variant presented here, in particular with regard to their distance in the z-direction. Fig. 2(which runs along the beam propagation direction SA). The scanner optics 13 are not moved (however, the scanner mirror 15 is pivoted within the scanner optics 13). In an alternative embodiment, a relative movement between the workpiece 17 and the scanner optics 13 can also be provided during the processing of the workpiece 17, wherein the relative travel distance for setting an effective spot size during welding zone changes can be shortened by switching the distribution of the laser energy according to the invention (not shown in detail).

[0051] In the illustrated design, the distance (in the z-direction) of the focal plane FE to the scanner optics 13 is fixed; the scanner optics 13 is thus designed as a 2D scanner optic. In an alternative design, the position of the focal plane FE relative to the scanner optics 13 can also be variable, for example by moving the focusing lens 16 in the z-direction within the scanner optics 13 (not shown in detail).

[0052] In Fig. 3a The machining of workpiece 17 according to the invention will be explained in more detail. Workpiece 17 comprises a basic component. 20, on which a first component 21 and a second component 22 to be welded on. In the illustrated example, the basic component 20 is a lid. 20a for a prismatic cell of an electric battery, where the lid 20a is made of an aluminum alloy. The first component 21 is a cathode. 21a for the cell, wherein the first component 21 is a fork-shaped soft connector 21b is trained (see also Fig. 6 The first component 21a is also made of an aluminum alloy. The second component 22 is an anode. 22a for the cell, with the second component 22 again acting as a fork-like soft connector 22b is trained (see also Fig. 6); the second component 22 is made of a copper alloy.

[0053] During the processing of the workpiece 17, the processing laser beam 8 emanating from the scanner optics 13 is directed (in any order) successively onto a first welding zone. 31 and a second welding zone 32 directed to weld the first component 21 in the first welding zone 31 and the second component 22 in the second welding zone 32 to the base component 20. In the illustrated variant, the two components 21, 22 are located in front of the base component 20 (with respect to the mean beam propagation direction SA); this is also generally preferred.

[0054] As in Fig. 3b As can be seen, in the variant shown, ring-shaped closed welds are produced, according to a respective path. 23of the laser spot 19 of the laser beam 8 on the surface 18 of the workpiece 17, where this surface 18 lies on the components 21, 22. Alternatively, for example, a hatching pattern could also be welded (not shown in detail).

[0055] Since the two components 21 and 22 are made of different materials, the welding effect of a laser beam is fundamentally different on each component. This can manifest itself, for example, in different formations of weld defects (spatter, pores, cracks, etc.). The different materials can particularly affect the respective weld penetration depth. ET have; the weld penetration depth ET is the depth to which the material of the workpiece 17 is melted by the laser beam 8, cf. the exemplary melting fronts indicated here. 24, 25 in Fig. 3a. In principle, it is desirable to optimize the welding effect for each component 21, 22 or each material involved, and, for example, to minimize welding defects or to achieve an approximately same weld penetration depth ET for all components 21, 22 in many applications.

[0056] Within the scope of the invention, for this purpose, when the welding zone 31, 32 on the workpiece 17 is changed, the energy distribution in the laser beam 8 is switched between the core portion (core beam) and the ring portion (ring beam); however, in the illustrated variant, the position of the workpiece 17 relative to the scanner optics 13 remains the same.

[0057] Possible different distributions of laser energy between the two welding zones 31, 32 or components 21, 22, as can be carried out according to the invention, are shown by reference to the Figures 4a and 4bTo illustrate this, both figures show a diagram of the local laser intensity as a function of position along an axis x that is perpendicular to the beam propagation direction and passes through a central axis of the laser beam ("intensity profile"). Note that the laser beam is essentially rotationally symmetric about this central axis.

[0058] The intensity profiles are shown in the focal plane. Note that the focal plane preferably coincides with the workpiece surface facing the laser beam; in this case, the intensity profile shown for the focal plane corresponds simultaneously to the intensity profile on the workpiece surface (and the unprimed quantities shown for the focal plane correspond simultaneously to the primed quantities of the workpiece surface, e.g., KSD = KSD', etc.).

[0059] The intensity is given in arbitrary units. The intensity profiles can be structured similarly to those in the Figures 1a to 3b explained.

[0060] The Fig. 4a This shows an intensity profile as it is applied in the first welding zone when welding the first component. For this purpose, a first core component KA1 of 20% and a first ring component RA1 of 80% were chosen as the energy distribution. Thus, a core beam 9 and a ring beam 10 are superimposed in the intensity profile.

[0061] The core beam 9 causes a central, local intensity maximum, with a maximum intensity of approximately 1.5 au. One core beam diameter KSDThe diameter of the core beam, determined according to the 86% criterion (so that 86% of the laser power of the core beam 9 lies within the diameter KSD), is approximately 75 µm. The ring beam 10 has a plateau region on either side of the core beam maximum, with a maximum intensity of approximately 1.0 au. An outer ring beam diameter ARSD The diameter of the ring beam 10, determined according to the 86% criterion (such that 86% of the laser power of the ring beam 10 lies within the diameter ARSD), is approximately 400 µm. At the location of ARSD, on the outside of the ring beam, the intensity of the ring beam 10 has already decreased somewhat compared to the maximum intensity of the plateau region. If one searches for the corresponding (same) intensity on the inside of the ring beam 10, this results in an inner ring beam diameter. IRSD which here is approximately 160 µm. In the example shown, the intensity gap width is ILBThe gap between ring beam 10 and core beam 9 is approximately 43 µm, calculated from (160 µm - 75 µm) / 2, corresponding to (IRSD - KSD) / 2. Note that in other embodiments, significantly smaller intensity gap widths (ILB) can be selected, in particular such that ILB ≤ 0.3 * KSD.

[0062] A total beam diameter GD The spot diameter of the entire laser beam, i.e., the superposition of core beam 9 and ring beam 10, determined according to the 86% criterion (so that 86% of the laser power of the entire laser beam lies within GD), is approximately 340 µm. This comparatively large spot diameter is used here to weld the aluminum alloy of a cathode as a first component.

[0063] Then, using the same total laser power, a copper alloy anode is to be welded as a second component to the same workpiece. For this, the laser energy distribution is switched, e.g., by moving the optical wedge as shown in Fig. 1ashown. The Fig. 4b The intensity profile is shown as it is now applied in the second welding zone when welding the second component. For this, a second core component KA2 of 60% and a second ring component RA2 of 40% are selected as the new energy distribution. The intensity profile therefore again shows a superimposed core beam 9 and a ring beam 10. During the switchover, 40% of the laser power was shifted from the ring component to the core component.

[0064] The core beam 9 produces a significantly higher, central, local intensity maximum, with a maximum intensity of approximately 4.5 au. The core beam diameter KSD of core beam 9, determined according to the 86% criterion, remains unchanged at approximately 75 µm. The ring beam 10 again has a plateau region on either side of the core beam maximum, but with a significantly lower maximum intensity of approximately 0.5 au. The outer ring beam diameter ARSD of ring beam 10, determined according to the 86% criterion, remains unchanged at approximately 400 µm. At the location of ARSD, the intensity of ring beam 10 has already decreased somewhat compared to the maximum intensity of the plateau region. If the corresponding intensity is sought on the inner side of ring beam 10, the inner ring beam diameter IRSD is obtained, which also remains unchanged at approximately 160 µm.

[0065] The total beam diameter GD of the entire laser beam, i.e., the superposition of core beam 9 and ring beam 10, determined according to the 86% criterion, is only approximately 220 µm here. This is because more intensity is now concentrated on small radii, particularly in the area of ​​core beam 9, and less laser intensity is concentrated on larger radii. The relatively small spot size is well suited for welding the copper alloy of the second component.

[0066] Note that the total power of the laser beam did not change during the switchover.

[0067] The Fig. 5 illustrates a typical temporal profile of the energy distribution of a laser beam to the core portion KA and the ring portion RA during the welding of the first weld zone 31 and the second weld zone 32, as also shown in the example of Fig. 4a and Fig. 4b can be applied. The graph on the right represents time t, and the graph on the top represents the kernel fraction KA in %; note that KA+RA=100%.

[0068] In the first welding zone 31, an initial phase AP The core fraction KA increases linearly from 0% to 20% over time t. In a main phase HP The core KA share remains constant at 20%. In a final phase EP The core component KA is linearly reduced from 20% to 0% over time. The power ramps in the initial phase AP and the final phase EP reduce weld defects, particularly spatter formation during penetration and porosity formation during the initial penetration of the first component. Note that the initial phase AP and the final phase EP are usually much shorter than the main phase HP (typically with AP ≤ 0.1*HP and EP ≤ 0.1*EP). Therefore, the welding of the first weld zone 31 is primarily characterized by the main phase HP, and the core component KA in the main phase HA is considered the first core component. KA1Here, KA1 is denoted as 20%. If the initial phase AP and the final phase EP should have a larger share, KA1 can alternatively be determined as the time average of the core share KA over AP, HP and EP overall (not shown in detail).

[0069] In the second weld zone 32, the core content KA is increased linearly from 20% to 60% over time t during an initial phase AP. During the main phase HP, the core content KA remains constant at 60%. In the final phase EP, the core content EP is decreased linearly from 60% to 20% over time. These power ramps in the initial phase AP and the final phase EP reduce weld defects, particularly spatter formation during penetration and porosity formation during the second component's removal. Note that the initial phase AP and the final phase EP are usually much shorter than the main phase HP (typically AP ≤ 0.1 * HP and EP ≤ 0.1 * EP). Therefore, the welding of the second weld zone 32 is primarily characterized by the main phase HP, and the core content KA in the main phase HA is considered a second core content. KA2Here, KA2 is denoted as 60%. If the initial phase AP and the final phase EP should have a larger share, KA2 can alternatively be determined as the time average of the core share KA over AP, HP and EP overall (not shown in detail).

[0070] In the example shown, KA1 and KA2 differ by 40%. Note that, within the scope of the invention, a difference of at least 20% is preferred, and furthermore, a difference of at least 30% is particularly preferred. Note that in the diagrams of Fig. 4a, 4b Previously, the intensity distributions from the main phases HP were shown.

[0071] The Fig. 6Figure 1 shows a workpiece 17 that was welded using the inventive method. The workpiece 17 comprises, as a basic component 20, a cover 20a of a prismatic cell of an electric battery. A cathode 21a, designed as a fork-shaped soft connector 21b made of an aluminum alloy, and an anode 22a, also designed as a fork-shaped soft connector 22b made of a copper alloy, were welded to the cover 20a using the inventive method. A cover is also shown on the cover 20a. 33 appropriate. Reference symbol list

[0072] 1 Output laser beam 1 First part (output laser beam) 1 Second part (output laser beam) 2 Rear fiber end 3 Multiclad fiber 4 Optical wedge 5 Core fiber 6 Ring fiber 7 Front fiber end 8 Laser beam 8 A-collimated laser beam 8 Reflected laser beam 9 Core beam 10 Ring beam 11 Cladding layer 12 Further cladding layer 13 Scanner optics 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 component 20a Cover 21 First component 21a Cathode 21b Soft connector 22 Second component 22a Anode 22b Soft connector 23 Path of the laser beam 24 Melt front 25 Melt front 26 Variable splitting device 31 First weld zone 32 Second weld zone 33 Cover 34 Focusing lens AP Initial phase ARFD Outer ring fiber diameter ARSD Outer ring beam diameter (focus plane) EP Final phase E Penetration depth FEF Focus plane GD Overall diameter (focus plane) HP Main phase I Intensity ILB Intensity gap width IRFD Inner ring fiber diameter IRSD Inner ring beam diameter (focus plane) KAK Core fraction KA1 First core fraction (core fraction in first weld zone) KA2 Second core fraction (core fraction in second weld zone) KFD Core fiber diameter KSD Core beam diameter (focus plane) MSD Sheath thickness SA Beam propagation direction t Time VR Traverse direction x Direction y Direction z Direction

Claims

1. A method for laser welding a workpiece (17), wherein a laser beam (8) is directed onto the workpiece (17) by means of scanner optics (13), wherein, using the laser beam (8) and in any order, a first component (21) is welded to a base part (20) at least in a first welding zone (31) and a second component (22) is welded to the base part (20) in a second welding zone (32), and wherein the first component (21) and the second component (22) consist of different materials, at least in the region of the first and the second welding zone (21, 22), characterized in that a laser energy of the laser beam (8) can be variably split up at least between a core portion (KA) corresponding to a core beam (9) of the laser beam and an annular portion corresponding to an annular beam (10) surrounding the core beam (9), and in that the splitting-up of the laser energy into the core portion (KA) and the annular portion is selected differently during the welding of the first welding zone (31) and during the welding of the second welding zone (32).

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

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

4. The method according to any one of the preceding claims, characterized in that the following applies for the core portion KA1, as a time average and / or in a main phase during the welding of the first welding zone (31): 0%≤KA1≤60%, preferably 20%≤KA1≤50%, and in that the following applies for the core portion KA2, as a time average and / or in a main phase during the welding of the second welding zone (32): 40%≤KA2≤100%, preferably 50%≤KA2≤70%.

5. The method according to any one of the preceding claims, characterized in that the first component (21) consists of Al or an Al alloy, at least in the region of the first welding zone (31), and the second component (32) consists of Cu or a Cu alloy, at least in the region of the second welding zone.

6. The method according to any one of the preceding claims, characterized in that, the workpiece (17) is a part of an electric battery, in particular a cover (20a) for a prismatic cell of the electric battery, and in that the first component (21) forms a cathode (21a) and the second component (22) forms an anode (22a) for the electric battery, in particular wherein the first component (21) and the second component (22) are each designed as fork-like soft connectors (21b, 22b) for the prismatic cell.

7. The method according to any one of the preceding claims, characterized in that, during the welding of the first welding zone (31) and / or during the welding of 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 reduced during an end phase (EP).

8. The method according to any one of claims 1 to 7, characterized in that in order to generate the laser beam (8) a starting laser beam (1) is split up into the core beam (9) and the annular beam (10) using a variable splitting device (26).

9. The method according to claim 8, characterized in that, using the variable splitting device (26) the starting laser beam (1) is fed in in correspondence to the desired splitting up of the laser energy, with corresponding portions, into a core fiber (5) and into an annular fiber (6) surrounding the core fiber (5), in particular wherein the variable splitting device (26) comprises a displaceable optical wedge (4).

10. The method according to claim 8, characterized in that, using the variable splitting device (26), the starting laser beam (1) is guided, in correspondence to the desired splitting up of the laser energy, with corresponding portions, past the DOE or ROE and through the DOE or ROE, in particular wherein the DOE or ROE is displaceable.

11. The method according to any one of claims 1 to 7, characterized in that to generate the laser beam (8) the core beam (9) is generated using a first laser module and the annular beam (10) is generated using a second laser module, wherein the power of the first laser module and the power of the second laser module are variably adjustable, in particular wherein the first laser module feeds in a first pre-laser beam into a core fiber (5) and the second laser module feeds in a second pre-laser beam into an annular fiber (6) surrounding the core fiber (5).

12. The method according to any one of the preceding claims, characterized in that the following applies for the diameters KSD' of the core beam (9) and ARSD' of the annular beam (10), measured at a 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.

13. The method according to any one of claims 1 to 12, characterized in that the diameters KSD' of the core beam (9) and ARSD' of the annular beam (10), measured on a workpiece surface (18) facing the laser beam, remain constant during the welding of the first welding zone (31) and the second welding zone (32).

14. The method according to any one of claims 1 to 12, characterized in that the scanner optics (13) are designed as 3D scanner optics and that the diameters KSD' of the core beam (9) and ARSD' of the annular beam (10), measured on a workpiece surface (18) facing the laser beam (8), are changed during the welding of the first welding zone (31) and the second welding zone (32) by means of the 3D scanner optics by changing the focal length in the direction of propagation (SA) of the laser beam (8).

15. The method according to any one of the preceding claims, characterized in that for the laser beam (8), during welding of the first welding zone (31) and / or the second welding zone (32) in a focal plane (FE), - the core beam (9) has a core beam diameter KSD within which 86% of the laser power of the core beam (9) exists, - the annular beam (10) has an outer annular beam diameter ARSD within which 86% of the laser power of the annular beam (10) exists, and - the annular beam (10) has an inner annular beam diameter IRSD at which a beam density of the annular beam (10), averaged over the circumference, is the same as that existing at the outer annular beam diameter ARSD such that an intensity gap results between the inner annular beam diameter IRSD and the core beam diameter KSD, with an intensity gap width ILB=(IRSD-KSD) / 2, and that ILB≤0.3*KSD and ILB<10µm*AV, where AV is the imaging ratio of the scanner optics (13), in particular wherein the laser beam (8) is provided at a fiber end (7) of a fiber optic cable (3), and the fiber optic cable (3) is designed at least with a core fiber (5) with a core fiber diameter KFD, an annular fiber (6) surrounding the core fiber (5) annularly, with an outer annular fiber diameter ARFD and a sheath layer (11) lying between the core fiber (5) and the annular fiber (6) and surrounding the core fiber (5), with a sheath layer thickness MSD, where MSD≤0.3*KFD and MSD<10µm.

16. The method according to any one of the preceding claims, characterized in that the welding of the first welding zone (31) and the welding of the second welding zone (32) takes place such that - for a welding penetration depth ET, the following applies: 100µm ≤ ET ≤ 5mm, and / or - for an aspect ratio T:B of a depth T relative to a width B of a generated weld seam, the following applies: T:B ≥ 0.5:1, and / or - for a beam parameter product SPP of the laser beam (8) in single mode, 0.38mm*mrad≤SSP≤16mm*mrad applies, preferably at SSP≤0.6mm*mrad, or in multi mode, SSP≤100mm*mrad applies, preferably at SSP≤32mm*mrad, and / or - for a total diameter GD' of the laser beam (8) on the workpiece surface (18) facing the laser beam (8) in single mode, 10µm≤GD'≤300µm applies, preferably at 30µm≤GD'≤70µm, or in multi mode 50µm≤GD'≤1200µm applies, and / or - the laser beam (8) with at least one IR laser, is generated with an average wavelength MWL at 800nm≤MWL≤1200nm, preferably 1030nm≤MWL≤1070nm, or with at least one VIS laser, in particular with an average wavelength MWL at 400nm≤MWL≤450nm or 500nm≤MWL≤530nm, and / or - the scanner optics (13) have an imaging ratio AV at 1:1 ≤ AV ≤ 5:1, preferably 1.5:1 ≤ AV ≤ 2:1.

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