METHOD FOR REMOVED MULTIPLE GRADING OF A WELD CONTAINMENT WITH MULTIPLE LASER SPOTS

Description

[0001] The invention relates to a method for welding together at least two aluminium-containing components according to the preamble of claim 1.

[0002] The aforementioned procedure became known from DE 10 2016 124 924 A1.

[0003] In electromobility, numerous applications require the assembly of components that are sealed against various media. Typical media requiring sealing include coolants and protective gases to create a suitable environment for sensitive components.

[0004] In electromobility, components based on aluminum alloys are of great importance, particularly due to their low specific weight. To create a leak-tight joint between aluminum components, soldering is currently the predominant method. Soldering requires the application of solder to create the joint. It is relatively complex and difficult; moreover, soldered joints can be susceptible to corrosion. Another option is to bond aluminum components together to create a leak-tight joint. However, bonding is also relatively complex and often requires lengthy curing processes, and the bonded joint can be sensitive to high temperatures.

[0005] Welding is a joining process used to permanently bond two workpieces together. Laser welding is typically used when high welding speeds, narrow and slender weld seams, and minimal thermal distortion are required. In laser welding, energy is supplied via a laser beam. To achieve high welding speeds, laser welding is preferably performed in the deep penetration welding regime, which creates a vapor capillary (keyhole) within the component material.

[0006] Laser welding of media-tight welds on aluminum components is challenging. Aluminum workpieces tend to exhibit strong turbulence in the weld pool during laser welding. This turbulence leads to uneven solidification of the weld. Consequently, weld sink marks, edge notches, or holes can occur. These problems, combined with cracks and pores in the weld, can result in leaks, rendering the welded components unsuitable for applications requiring media tightness. Furthermore, the strong turbulence in the weld pool often leads to excessive weld spatter, which contaminates the surrounding area and causes material loss at the weld.

[0007] From DE 10 2010 003 750 A1 it is known to modify the beam profile characteristics of a laser beam using a multi-clad fiber. This allows a laser beam with a core component and a ring component to be generated.

[0008] A laser welding device is known from DE 10 2016 124 924 A1, which is used for welding a sealing plate onto a housing body of a

[0009] A battery can be inserted, with the housing and sealing plate made of aluminum. A collimated laser beam is guided over a forming device that includes a diffractive optical element (DOE) with an aperture. The DOE can split an incident laser beam into several partial beams, for example, four partial beams arranged according to the corners of a square. Depending on the overlap of the collimated laser beam with the DOE or its aperture, a portion of the collimated laser beam is split into the partial beams by the DOE, or remains undistorted as it passes through the aperture.

[0010] In practice, it has therefore been shown that welded aluminum-containing components often have defects and are not media-tight. Object of the invention

[0011] The object of the invention is therefore to create a method for the rapid and cost-effective production of a particularly reliable media-tight welded joint. Description of the invention

[0012] This problem is solved according to the invention by a method according to claim 1. . The dependent patent claims reflect preferred further developments.

[0013] The problem is thus solved by a method mentioned at the outset, characterized in that the output laser beam is generated by means of a multi-fiber, in particular a 2-in-1 fiber, so that the several laser spots on the surface of the components each have a core component and a ring component, wherein after a first tracing of the weld contour the weld contour is at least partially traced a second time.

[0014] The second pass serves as a strategic safeguard for process reliability by remelting a previously welded contour. Experience has shown that remelting a welded contour is counterproductive, as the second pass typically introduces more defects into the weld contour than it eliminates. Surprisingly, however, it has been shown that the multiple laser spots according to the invention lead to a homogenization of the weld contour during the second pass. Any pores and holes from the first pass are eliminated, process reliability is increased, and a media-tight weld can be achieved at high process speeds (welding speeds) and short cycle times.The first pass thus serves to achieve the necessary weld penetration depth and therefore the necessary strength, whereas the additional second pass serves to repair possible, material-related unavoidable defects and to create a media-tight, especially gas-tight, weld contour.

[0015] The invention proposes splitting an initial laser beam into several partial beams and correspondingly several laser spots on the workpiece surface for welding aluminum-containing components. At least some of the laser spots (usually all laser spots or all but one) are arranged in a ring formation on the workpiece surface. Furthermore, beam shaping of the initial laser beam is provided using a multi-fiber, preferably a 2-in-1 fiber, which divides the laser power in the initial laser beam and in the partial beams, and thus in the individual laser spots, into a core portion with higher power density and a ring portion with lower power density (referred to as "2-in-1 technology" in the case of the 2-in-1 fiber). The multi-fiber comprises a central core fiber and one or more ring fibers that surround the core fiber in a ring-like configuration.The core fiber produces the core portion, and the ring portion produces the ring portion from one or more ring fibers (in the case of multiple ring fibers, the ring portion comprises several individual ring portions, which together then form the ring portion). According to the invention, the combination of these measures makes it possible to achieve high-quality laser welding of aluminum-containing components, and in particular to obtain a low-porosity and media-tight weld seam.

[0016] When using a single laser spot, the 2-in-1 technique does reduce spatter formation on aluminum components compared to the single-spot technique with a conventional (undistorted) laser beam. However, the remaining instabilities in the aluminum components still mean that the resulting weld is generally not media-tight. Due to the specific properties of aluminum in the component material, strong turbulence still occurs in the weld pool during welding. The keyhole may be too small compared to the generated weld pool when using a single beam. This results in numerous pores, which then make the weld permeable to the media.

[0017] Surprisingly, however, particularly stable keyholes could be obtained when using a multi-fiber or 2-in-1 technique with multiple laser spots in a ring arrangement during laser welding of aluminum components. Larger keyholes (compared to single keyholes with single laser spots) can be achieved within the scope of the invention; these are more stable and do not collapse. Instead, the molten metal can be displaced more reliably through the larger keyholes. Homogeneous solidification of the weld seam can be achieved.

[0018] The laser spot centers of the respective (successive / adjacent) laser spots in the ring formation can be conceptually connected to one another as a polygon, within which an inner surface (polygonal area) is enclosed. Within the area of ​​this polygonal area, the deep penetration welding according to the invention can essentially take place in the aluminum-containing components.

[0019] The laser welding process according to the invention generates a particularly large melt volume, especially leading upstream of a given vapor capillary (keyhole); in particular, the outer portions of the ring components (with respect to ring formation) can increase the melt volume. The laser spots can form a common melt. The leading, particularly large melt volume can reduce the dynamics of the melt and thus turbulence.

[0020] Within the scope of the invention, particularly large keyholes can be created, and the keyhole geometry changes (compared to a single-spot keyhole), and the absorption behavior of the laser radiation changes accordingly. In particular, a common keyhole can be formed by all laser spots or partial beams together. The molten metal can then flow around the respective vapor capillary as the welding process progresses. Overall, particularly high keyhole stability can be achieved. High welding speeds with good weld quality are possible, and in particular, media-tight welds of the aluminum-containing welds can be easily produced, especially in butt joints. It is particularly preferred that a cover is inserted into a component and butt-welded.

[0021] By arranging at least three laser spots in a ring formation, the directional dependence of the welding process can be reduced. With four or more laser spots in the ring formation (assuming a symmetrical arrangement of the laser spots), the welding process is already largely direction-independent. Furthermore, the ring formation can very effectively stabilize a common keyhole in the aluminum components. The entirety of the laser spots on the workpiece surface is referred to here as the weld pattern.

[0022] The partial beams are typically generated by guiding the initial laser beam between a collimating optic and a focusing optic over one or more optical elements that project into at least a portion of the beam cross-section of the initial laser beam. Typical optical elements for this purpose are wedge plates; however, other diffractive and refractive optical elements can also be used. In a preferred embodiment, two bifocal inserts arranged at a 90° angle to each other are employed. It is also possible to use a faceted plate as the optical element, which has ring-shaped facets (outer facets) corresponding to the desired number of laser spots in the ring formation. These facets are angled (beveled) at an angle β relative to a ground plane perpendicular to the beam propagation direction, typically with 0 < β ≤ 0.50°, often β ≤ 0.25°.The outer facets are typically rotated relative to each other by 360° / N, where N is the number of laser spots in the ring formation, around a central axis (the optical axis of the facet plate, corresponding to the beam propagation direction). If a central laser spot is also desired, an additional facet (central facet) can be provided, lying parallel to the base plane, with the outer facets adjoining the central facet radially inwards. The central facet is typically designed as a regular polygon. If a central laser spot is not desired, the outer facets can simply meet at a common central point radially inwards. A facet plate can generate virtually any number of laser spots, depending on the facet plate's configuration.

[0023] The laser spots are typically of the same size. Each laser spot in the ring formation typically has the same laser power. The laser spots in the ring formation are typically equidistant (with respect to their centers) from a common center (center of gravity) of all the laser spots.

[0024] The method is preferably characterized in that the average power density in the core portion is higher than the average power density in the ring portion.

[0025] The power proportions of the core and ring sections in a given laser spot can be adjusted by the proportion of the output laser beam directed into the core fiber and the one or more ring fibers of the multi-fiber assembly. The average power density in the core section is usually at least twice, and often at least four times, higher than in the ring section. The (outer) boundaries of the core and ring sections can be defined as the location where the local power density is less than half the average power density in the core or ring section, or, in the case of multiple ring fibers, at the outermost individual ring section. With approximately uniform power density within the core and ring sections, or, in the case of multiple ring fibers, at the outermost individual ring section, this corresponds to a FWHM criterion. The diameters, or their ratios, of the core fiber and the (outermost) ring fiber at the depicted fiber end determine the diameters, respectively.The ratios of the core and ring components in each laser spot are determined by the magnification ratio and thus the absolute size of the laser spots. This magnification can be selected or adjusted using the collimating and focusing optics.

[0026] The laser spots continuously trace the weld contour along its path (without wobbling), typically at a constant feed rate (welding speed). This creates the (media-tight) weld seam. Note that the local feed direction (welding direction) can change as the weld contour is traced, and consequently, so can the orientation of the weld pattern relative to the local feed direction. Due to the largely direction-independent nature of the weld pattern according to the invention, such changes in the local feed direction are largely uncritical when welding components according to the invention.

[0027] The weld contour can be formed as a butt joint, fillet weld, or lap weld. Laser welding can be performed as a butt weld or a through weld. Preferably, the aluminum-containing components are welded as a butt weld, either as a lap or lap joint, and particularly preferably as a butt weld. Note that the term "components welded together within the scope of the present invention" is to be understood locally with respect to the laser welding process; accordingly, the components to be welded can be separate before laser welding or already connected to each other independently of the joint to be welded.

[0028] Preferably, the weld contour is completely covered on the second pass. This achieves a completely media-tight weld contour in a simple manner and simplifies the process.

[0029] The components preferably contain at least 90% aluminum by weight.

[0030] A component can be made of die-cast aluminum or a wrought aluminum alloy. Preferably, one component consists of die-cast aluminum or a wrought aluminum alloy. More preferably, one component consists of die-cast aluminum and the other component of a wrought aluminum alloy. Such component combinations cannot be welded together in a media-tight manner in a productive way without the method according to the invention.

[0031] An Al 1XXX, 3XXX, 5XXX, 6XXX alloy is preferably used as the wrought aluminum alloy.

[0032] The second pass should melt less material than the first pass. According to the invention, the second pass is therefore performed with lower power and / or a higher feed rate than the first pass. The second pass is preferably performed with 2% to 20%, in particular with 5% to 15%, and most preferably with 8% to 12% less power per laser spot than the first pass. The second pass is preferably performed with a feed rate 2% to 20%, in particular with 5% to 15%, and most preferably with 8% to 12% higher than the first pass.

[0033] A lateral offset during the second pass is preferably less than 20mm compared to the first pass, particularly less than 10mm, and most preferably less than 5mm.

[0034] Furthermore, the remaining parameters are preferably chosen to be the same for the second pass as for the first. This results in the weld contour created in the first pass being completely or almost completely melted and homogenized.

[0035] The weld penetration depth is preferably less than 10 mm. Preferably, the weld penetration depth is less than 4 mm, particularly between 1 mm and 3 mm.

[0036] The weld contour, traced twice, can be captured by an optical sensor, allowing for the detection of defects. Any defects can then be identified and rectified. By inspecting the weld contour, time-consuming handling, particularly the unclamping, inspection, and re-clamping of the components, can be avoided.

[0037] The optical sensor can be in the form of a camera or a photodiode.

[0038] The image can be captured immediately after the second pass of the weld contour. By capturing the image immediately after the second pass, the process glow during the second pass can be detected and evaluated.

[0039] The beam path of the optical sensor can run coaxially to the beam path of the output laser beam, making the method particularly easy to implement in terms of design.

[0040] After the second pass, the weld contour can be traced at least partially a third time. A third pass can create a particularly media-tight, preferably gas-tight, weld joint.

[0041] The third pass is preferably only carried out if at least one defect was detected after the second pass.

[0042] To simplify the process, the weld contour is preferably completely traced on the third pass.

[0043] The weld penetration depth for the third pass is preferably selected to be substantially the same as for the second pass. In a preferred embodiment of the invention, the third pass is therefore performed with the same parameters as the second pass, within ±10%, particularly within ±5%, and most preferably within ±2%. The third pass can also be performed with higher power than the second pass, but then preferably with a correspondingly higher feed rate.

[0044] In a particularly preferred embodiment of the inventive method, the first pass is carried out with selected parameters, the second pass with lower power but the same feed rate (resulting in a lower penetration depth in the second pass than in the first pass), and the third pass with higher feed rate and higher power than the second pass (resulting in a substantially the same penetration depth as in the second pass).

[0045] The weld contour, scanned three times, can be recorded by an optical sensor, and defects can be detected. The optical sensor is preferably the same one used to record the weld contour twice. Typically, no defects are detected after the third scan, allowing the welded components to be certified as good parts through optical inspection.

[0046] The image is preferably captured during the third pass of the weld contour. Particularly preferably, the image is captured during the third pass in the same manner as during the second pass. This significantly reduces programming effort and process complexity.

[0047] A preferred variant of the inventive method for welding aluminium-containing components provides that the at least two components are butt-welded together, and that laser welding is carried out. as welding, wherein the welding depth corresponds to one lid thickness or at least 75% of one lid thickness,

[0048] Alternatively, as an overlap: Welding can be performed either as a partial weld, where the partial weld is made to at least 10% of the thickness of the lowest component of the lap joint, or as a through weld through all components of the lap joint. Welding in the lap joint has proven particularly effective in practice for producing media-tight welds, especially when performed as a partial weld. By leaving some solid material of the lowest component exposed, a reliable seal can be achieved through partial welding.

[0049] A particularly preferred variant involves the formation of a common vapor capillary from all laser spots within the components, surrounded by a common melt pool. This common vapor capillary is a continuous space within the components to be welded, containing metal vapor and surrounded by molten metal; the vapor capillaries of the individual laser spots (if used in isolation) merge to form this continuous space. The common vapor capillary (common keyhole) can be established through a suitable process, in particular by ensuring that the laser spots in the ring formation are not too far apart. The common keyhole is significantly larger than a keyhole that could be generated with a single laser beam (single spot). This larger keyhole, with its different geometric shape, influences the absorption behavior of the incident laser radiation.Several intensity peaks, corresponding to the multiple laser spots of the ring formation, are arranged in a ring-like pattern around the common keyhole; an additional intensity peak from another laser spot in the center of the ring formation may also be present. A keyhole is particularly stable at the location of a local intensity peak; the multiple intensity peaks at the common keyhole achieve overall stabilization of the large, shared keyhole. In contrast, with a single-spot keyhole, only the area of ​​a single intensity peak can be stabilized. The common vapor capillary (in the case of an overlap joint) preferably extends deep enough that even at an interface between the overlapping components to be welded, the cross-section of the common vapor capillary forms a continuous surface.Furthermore, the common vapor capillary (generally) preferably extends to such a depth that, at half the maximum depth of all segments of the common vapor capillary, the cross-section of the common vapor capillary forms a continuous surface. The cross-section is assumed to be perpendicular to the direction of jet propagation.

[0050] A preferred variant is one in which the multiple laser spots form an arrangement with rotational symmetry, with a count corresponding to the number of laser spots in the ring formation. This rotational symmetry results in a high degree of direction independence for the laser welding process; that is, the relative orientation of all the laser spots to the current feed direction plays no or only a very minor role in the welding process.

[0051] In one variant, all laser spots are arranged to form a ring. This is particularly easy to set up, for example, with two bifocal inserts in the case of four laser spots in the ring. Specifically, no laser spot is located in the center of the ring. In the case of only a few laser spots in the ring (for example, 3-5 laser spots), a well-stabilized, common keyhole can usually be created in this way.

[0052] In an alternative variant, the center of one laser spot is positioned in the middle of the ring formation. In other words, the laser spots of the ring formation are supplemented by another laser spot located in the center of the ring formation. This allows for additional stabilization of a common keyhole, particularly in the case of many laser spots in the ring formation (for example, four or more, preferably six or more). With many laser spots in the ring formation, a larger radius for the centers of the laser spots is usually chosen compared to a common center of the laser spots to reduce overlaps of the ring portions of the laser spots. The central laser spot can then stabilize the central region of the common keyhole and prevent local rebound in the keyhole in the central region.

[0053] In one variant, the ring formation is provided for by exactly three laser spots, in particular where the welding contour runs in such a way that during laser welding, at least predominantly with respect to the local feed direction One laser spot precedes the ring formation, and two laser spots follow the ring formation with the same position relative to the local feed direction.

[0054] Using three laser spots in a ring formation significantly reduces the directional dependence compared to two (or more) laser spots in a linear formation. The preferred, predominantly oriented welding pattern with one leading and two trailing laser spots, aligned with the local welding / feed direction, has proven effective in practice.

[0055] A particularly preferred variant is one in which the ring formation consists of exactly four laser spots. This allows for a very high degree of directional independence in a simple manner. The four laser spots of the ring formation are preferably arranged in a square.

[0056] In a further development of this variant, the welding contour runs in such a way that during laser welding, at least predominantly with respect to the local feed direction, a laser spot precedes the ring formation, two laser spots of the ring formation are arranged in the middle with the same position with respect to the local feed direction, and a laser spot follows the ring formation.

[0057] With this predominantly used orientation of the welding pattern (also called "trapezoidal" arrangement), a comparatively wide weld seam with four laser spots in the ring formation can be set up, and a particularly large and stable weld pool can be obtained.

[0058] A preferred alternative development is one in which the welding contour runs in such a way that, during laser welding, at least predominantly with respect to the local feed direction, Two laser spots precede the ring formation with the same position relative to the local feed direction, and two laser spots follow the ring formation with the same position relative to the local feed direction.

[0059] With this predominantly used orientation of the weld pattern (also called the "square" arrangement), a comparatively narrow weld seam can be created using four laser spots in a ring formation, thereby achieving particularly deep melting at high welding speeds and a stable weld pool. The predominant local welding direction / feed direction can correspond to one of the principal coordinate axes of the laser welding device used. Note that the orientation of the weld pattern changes when cornering, e.g., from the square arrangement to the trapezoidal arrangement and back to the square arrangement when negotiating a 90° turn.

[0060] In another variant, the ring formation is formed by exactly five laser spots, in particular where the welding contour runs in such a way that during laser welding, at least predominantly with respect to the local feed direction one laser spot precedes the ring formation, two laser spots of the ring formation are arranged in the middle with the same position with respect to the local feed direction, and two laser spots of the ring formation follow the ring formation with the same position with respect to the local feed direction.

[0061] This variant achieves even better direction independence. With one leading, two central, and two trailing laser spots, positioned in the predominantly used orientation of the welding pattern relative to the feed direction, a particularly stable weld pool is achieved.

[0062] In another embodiment, the ring formation is created by exactly six laser spots. An additional laser spot can be provided in the center of the ring formation. This allows for even greater directional independence. Note that a number of 3 to 6 laser spots in the ring formation is preferred within the scope of the invention; a larger number generally only results in minor improvements with regard to directional independence or melt pool stability.

[0063] A particularly preferred variant is one in which the ring components of adjacent laser spots within the ring formation are arranged in contact with each other. This allows for a very stable, common keyhole to be achieved during laser welding of the aluminum-containing components. The ring components of adjacent laser spots within the ring formation are considered to be in contact with each other if the distance between their laser spot centers corresponds to the sum of their respective half-diameters of their ring components, with a tolerance of ±10% of this sum.

[0064] In an alternative variant, the ring portions of adjacent laser spots within the ring formation are arranged in an overlapping manner, particularly where the core portions of laser spots within the ring formation do not overlap with the ring portions of adjacent laser spots within the ring formation. By overlapping the ring portions of the laser spots, especially without overlapping ring and core portions, local protrusions and recesses of a common keyhole with respect to depth into the components to be welded can often be reduced.

[0065] A further development of this variant is preferred, in which a maximum of two ring segments of laser spots from the ring formation overlap at any given location. This has proven effective for creating a particularly stable melt pool in aluminum-containing components.

[0066] A further development is also preferred in which the laser spots of the ring formation encompass a common center around which the ring components of the

[0067] The laser spots of the ring formation touch each other, in particular where exactly four laser spots are arranged in the ring formation. In this variant, which is typically set up without a laser spot in the center of the ring formation, a smooth and large keyhole with only minor local protrusions and recesses into the depth of the components to be welded can be created.

[0068] Another advantageous variant involves overlapping the ring components of all laser spots in the ring formation in a central region, particularly when exactly three laser spots are arranged in the ring formation. Especially in the case of only a few laser spots, such as three laser spots in the ring formation and without another laser spot located in the center of the ring formation, the overlap of the ring components of the laser spots in the ring arrangement can generate an auxiliary intensity peak in the central region. This peak can stabilize a common keyhole in addition to the intensity peaks of the core components of the laser spots.

[0069] In a preferred embodiment, the following parameters apply: for a diameter DK of the core portion and a diameter DR of the ring portion: 2 ≤ DR / DK ≤ 10, preferably 2.5 ≤ DR / DK ≤ 6, particularly preferably 3.5 ≤ DR / DK ≤ 5; and for a power fraction LK of the core portion in relation to the total power in a respective laser spot: 10% ≤ LK ≤ 90%, preferably 30% ≤ LK ≤ 70%, particularly preferably 40% ≤ LK ≤ 60%. These parameter ranges have proven effective in practice for aluminum-containing components to achieve stable keyholes and media-tight welds.

[0070] A variant that provides that is still preferred the components have a component thickness BD of 0.5 mm ≤ BD ≤ 5.0 mm, and / or the components are made of aluminum alloys of the 3000, 5000 or 6000 series, and / or the core portions of the laser spots have a diameter DK of 11 µm ≤ DK ≤ 200 µm, preferably 50 µm ≤ DK ≤ 150 µm, and the ring portions of the laser spots have a diameter DR of 50 µm ≤ DR ≤ 700 µm, preferably 200 µm ≤ DR ≤ 550 µm, and / or an average laser power P of the output laser beam is applied with P ≥ 2 kW, preferably P ≥ 4 kW, and / or a welding speed SG is applied with SG ≥ 5 m / min, preferably SG≥10m / min.

[0071] These parameters have also proven effective in practice for laser welding of aluminum-containing components. In particular, a particularly high welding speed SG can be set up within the scope of the invention.

[0072] Further advantages of the invention will become apparent from the description and the drawing. Detailed description of the invention and drawing

[0073] Fig. 1a shows a schematic side view of an exemplary welding optic with which the method according to the invention can be carried out. Fig. 1b shows the exemplary welding optic made of Fig. 1a rotated by 90°. Fig. 1c shows a schematic cross-sectional representation of an exemplary 2-in-1 fiber for the invention, as used as a laser light cable in Fig. 1a can be used and with which an output laser beam for the inventive method can be provided. Fig. 2 shows the welding pattern of a variant of the inventive method with four laser spots, as provided by the exemplary welding optics made of Fig. 1a can be produced. Fig. 3 shows a schematic longitudinal section of two components during welding with the weld pattern of Fig. 2 , to explain the method according to the invention. Fig. 4 shows a schematic cross-section of the vapor capillary of Fig. 3in the planes AA, BB, and CC. Fig. 5a shows the weld pattern of a variant of the method according to the invention, in which the ring portions of four laser spots are arranged partially overlapping and touching at a center point. Fig. 5b shows a weld pattern of a variant of the method according to the invention, in which the ring portions of three laser spots are arranged partially overlapping. Fig. 5c shows a weld pattern of a variant of the method according to the invention, in which the ring portions of five laser spots are arranged partially overlapping. Fig. 6a shows a schematic top view of an exemplary faceted plate as it can be used in a welding optic for generating multiple partial beams for the method according to the invention. Fig. 6b shows a schematic cross-section of the exemplary faceted plate made of Fig. 6aFig. 6c shows a welding pattern of a variant of the inventive method with six laser spots in a ring formation and a central laser spot, as shown by the exemplary faceted plate made of Fig. 6a Fig. 7 shows an experimental image of a longitudinal section of two aluminum-containing components after a first scan according to the inventive method. Fig. 8 shows a schematic side view of an exemplary welding optic with an optical sensor for recording a weld contour. Fig. 9 shows components welded in a butt joint. Fig. 10 shows a transverse section of two aluminum-containing components after carrying out the inventive method.

[0074] Fig. 1a shows an exemplary welding optic in a schematic side view 1, with which the inventive method can be carried out in a preferred variant. Fig. 1b The welding optics show 1 from Fig. 1a rotated by 90°.

[0075] The welding optics 1 includes a laser light cable. 2, which is a multi-fiber, here a 2-in-1 fiber. 2a, is designed to be a collimating lens 3, two bifocal inserts 4a, 4b, which are designed here as glass wedges, and a focusing lens 5. The bifocal inserts 4a, 4b are arranged one behind the other and rotated 90° relative to each other.

[0076] An output laser beam is transmitted via the laser light cable 2. 6 The output laser beam 6 is provided, exiting at one end of the laser light cable 2. The fiber end lies in the focus of the collimation lens 3, and the output laser beam 6 is collimated by the collimation lens 3, thus becoming a collimated laser beam. 7The collimated laser beam 7 is guided to the bifocal inserts 4a and 4b. The bifocal inserts 4a and 4b each occupy approximately half of the cross-section of the collimated laser beam 7. This allows the collimated laser beam 7 to be split into four partial beams in the exemplary welding optic 1 shown here. 8 The partial beams 8 are split. The partial beams are focused by the focusing lens 5 onto a surface of a component to be welded (not shown), thereby creating a welding pattern on the surface of the component consisting of four equally sized laser spots.

[0077] The average laser power P of the output laser beam 6 can be, for example, P ≥ 2 kW, preferably P ≥ 4 kW.

[0078] Fig. 1c Figure 1 shows an exemplary cross-section of the 2-in-1 fiber 2a, with which the output laser beam for the method according to the invention can be provided.

[0079] The 2-in-1 fiber 2a has a core fiber 9 with a core fiber diameter KFD and a ring fiber 10 with a ring fiber diameter RFD Typically, the core fiber diameter KFD can be selected to be, for example, 11 µm ≤ KFD ≤ 200 µm, preferably 30 µm ≤ KFD ≤ 150 µm, and the ring fiber diameter RFD can be, for example, 30 µm ≤ RFD ≤ 700 µm, preferably 100 µm ≤ RFD ≤ 550 µm. The imaging ratio of the welding optics (see...) Fig. 1a ), which includes the 2-in-1 fiber, is selected as 1:1 in the embodiment; in other embodiments, for example, an imaging ratio > 1:1 can also be selected.

[0080] The 2-in-1 fiber can be used to generate a laser beam that has a core component and a ring component (see, for example, [reference]). Fig. 2 regarding the laser spots) and serves as the output laser beam in welding optics (see Fig. 1aFor this purpose, an original laser beam (not shown in detail) is fed partly into the core fiber 9 and partly into the ring fiber 10, for example via an optical wedge (not shown in detail) that is partially inserted into the original laser beam.

[0081] In Fig. 2 is a schematic representation of a welding pattern 11 shown on the surface of a component to be welded, as evidenced by the exemplary welding optics from Fig. 1a can be generated.

[0082] Welding pattern 11 here comprises four equally sized laser spots. 12. The four laser spots 12 each have a core component 13 and a ring fraction 14 This is because the output laser beam is generated by the 2-in-1 fiber and therefore already has a core component and a ring component.

[0083] Each laser spot 14 has a laser spot center. 15.The core portion 13 has a diameter DK of 100 µm and the ring portion 14 has a diameter DR of 400 µm. The ratio DR / DK is therefore 4.

[0084] For a power fraction LK of the core portion 13 of a single laser spot 12, LK = 50% can be selected. In the variant shown here, the ring portion 14 has an area approximately 15 times larger than the core portion 13. The average power density in the core portion 13 is therefore about 15 times greater than the average power density in the ring portion 14.

[0085] The 12 laser spots are arranged in a ring formation. 16The laser spot centers 15 define the vertices of a polygon (here a square) that encloses an interior surface. The distance between two laser spot centers 15 of adjacent laser spots 12 in the ring formation 16 (e.g., the laser spot centers 15 of laser spots 12' and 12") is 400 µm. In the variant shown here, the ring portions 14 of the adjacent laser spots 12 in the ring formation 16 touch exactly. The distance between the laser spot centers 15 of the adjacent laser spots 12 in the ring formation 16 corresponds to the sum of half the diameters DR of the ring portions 14 of the participating laser spots 12.

[0086] The welding pattern 11 exhibits fourfold rotational symmetry, since the ring formation 16 is formed by four laser spots 12, which are rotated by 90° around a common center (center of gravity). 17can be transformed into one another. The laser spot centers 15 of the laser spots 12 of the ring formation 16 lie here on a circular line (shown as a dashed line) around the common center 17.

[0087] Regarding a local feed direction 18 The welding pattern 11 is arranged such that two laser spots 12a run ahead and two laser spots 12b chasing after them.

[0088] Fig. 3 shows a schematic longitudinal section of two components 19 during welding with a weld pattern as in Fig. 2 The figure is shown to illustrate a preferred embodiment of the method according to the invention. The joining situation of the two components 19 is a lap joint. Alternatively, and not shown here, the joining situation of the two components 19 can also be a butt joint.

[0089] Components 19 are made of an aluminum alloy. One upper component 19aThis indicates a component thickness BD or thickness D ob of approximately 2 mm. A bottom component 19b This indicates a component thickness BD or thickness. D unt of approximately 3 mm. Welding is performed here by inset welding. The longitudinal cut is defined centrally by two laser spots positioned 18 adjacent to each other with respect to the feed direction.

[0090] The longitudinal section of Fig. 3 The partial beams 8 contained are directed from the welding optics (not shown) onto the surface 20 the upper component 19a. The partial beams 8 penetrate from the surface 20 into the components 19 and vaporize the aluminum material in their immediate vicinity. A common vapor capillary is formed by the action of all partial beams 8 or all laser spots. 21(also called common keyhole or common metal vapor capillary), which extends down to the lowest component 19b. The common vapor capillary 21 forms a continuous volume within the components 19. In the regions near the core portions of the partial beams 8, the common vapor capillary 21 exhibits deeper segments. 21a (Protrusions) are present. In an area between the partial jets 8, the common vapor capillary 21 has a less deep-reaching section. 21b on ("return"). A maximum depth T max the common vapor capillary 21 at a lowest point 23 The difference here is approximately 4 mm.

[0091] By combining the 2-in-1 technique with multiple laser spots generated by the partial beams 8, the common vapor capillary 21 is particularly stable.

[0092] In the vicinity of the common vapor capillary 21, the aluminum material is melted, creating a molten pool.24 formed from liquid aluminum material. Since the partial jets 8 are welded relative to the components 19 in the feed direction 18 along a weld contour. 20a When moved, in the illustration shown to the left, the melt pool 24 is sagging to the right in cross-section. At a left edge 24a and at a lower edge 24b In the melting bath 24, aluminum material is melted, while at a right edge 24c The aluminum material in the melt bath solidified again.

[0093] The welding into the lowest component 19b is carried out to a weld penetration depth ET unt, which in the case shown is approximately 85% of the component thickness D unt. In this way, a good and media-tight weld can be achieved. In a variant not shown, it is also possible for the laser welding to be carried out as a through-welding through all components 19 of the lap joint.

[0094] Aluminum alloys from the 3000 series, 5000 series, or 6000 series can be selected for components 19. A welding speed SG of ≥5 m / min, preferably SG ≥10 m / min, can be selected.

[0095] In Fig. 4 are schematic cross-sections of the vapor capillary 21 of Fig. 3 shown in levels AA, BB and CC.

[0096] The dashed line shows an outline. 21a the vapor capillary 21 in plane AA of Fig. 3 , which lies at the interface between the upper and lower components, i.e. at a depth of approximately 2 mm. The vapor capillary 21 forms a continuous surface here.

[0097] The dashed line shows an outline 21b the vapor capillary 21 in plane BB of Fig. 3, which corresponds to a depth equal to half the maximum depth T max of the common vapor capillary, here at a depth of approximately 2.5 mm. Vapor capillary 21 forms a slightly smaller, but still continuous, area here.

[0098] A continuous line is used to create an outline. 21c of the vapor capillary 21 at a depth of approximately 3.8 mm of the vapor capillary 21 in the plane CC of Fig. 3 As shown, at this depth, the vapor capillary forms four separate (non-contiguous) sections in cross-section, each approximately circular. The CC plane therefore only intersects the vapor capillary in the region of the local projections.

[0099] In Fig. 5a Figure 11 is a schematic representation of a welding pattern 11 in cross-section with four laser spots 12 in ring formation, for a further variant of the invention.

[0100] The laser spots 12 are all the same size. The core portion 13 has a diameter DK of 100 µm and the ring portion 14 has a diameter DR of 400 µm. The ratio DR / DK is therefore 4.

[0101] The distance between two (diagonally) opposing laser spot centers of the laser spots 12 is 400 µm. In the variant shown here, the ring portions 14 of the opposing laser spots 12 touch precisely at their common center 17. The adjacent laser spots 12 are arranged overlapping each other. The core portions 13 do not overlap. The weld pattern 11 exhibits fourfold rotational symmetry, since the ring formation is created by four laser spots 12, which can be transformed into one another by rotating them 90° around their common center 17.

[0102] With respect to the indicated local feed direction 18, the welding pattern 11 is arranged such that the two laser spots 12a advance and the two laser spots 12b follow. The two laser spots 12a are located at identical positions with respect to the local feed direction 18. Likewise, the two laser spots 12b are located at identical positions with respect to the local feed direction 18.

[0103] In Fig. 5b is a schematic representation of a welding pattern 11 shown in cross-section with three laser spots 12 in ring formation, in a further variant of the invention.

[0104] The laser spots 12 are all the same size. The core portion 13 has a diameter DK of 300 µm and the ring portion 14 has a diameter DR of 800 µm. The ratio DR / DK is therefore 2.67.

[0105] The adjacent laser spots 12 are arranged overlapping with respect to the ring portions 14 and in a central area26 All three laser spots 12 overlap in the ring portions 14. The core portions 13 do not overlap.

[0106] With respect to the local feed direction 18 shown, the welding pattern 11 is arranged such that one laser spot 12a precedes it and two laser spots 12b follow it. The two laser spots 12b are located at identical positions with respect to the local feed direction 18. The laser spots 12b are spaced slightly closer to each other than the preceding laser spot 12a is to each of the following laser spots 12b (in each case with respect to the laser spot centers).

[0107] In Fig. 5c is a schematic representation of a welding pattern 11 shown in cross-section with five laser spots 12 in ring formation, in a further variant of the invention.

[0108] The laser spots 12 are all the same size. The core portion 13 has a diameter DK of 100 µm and the ring portion 14 has a diameter DR of 400 µm. The ratio DR / DK is therefore 4.

[0109] The distance between two adjacent laser spot centers 15 of the laser spots 12 in the ring formation is approximately 350 µm. In the variant shown here, the adjacent laser spots 12 in the ring formation are arranged overlapping with the ring portions 14. The weld pattern 11 exhibits fivefold rotational symmetry, since the ring formation is formed by five laser spots 12, which can be transformed into one another by rotating them 72° around the common center 17.

[0110] With regard to the local feed direction 18 shown, the welding pattern 11 is arranged such that one laser spot 12a leads, two laser spots 12b follow, and two laser spots 12cThe two trailing laser spots 12a and 12b are positioned centrally between them. The two trailing laser spots 12b are located at identical positions with respect to the local feed direction 18. Likewise, the two central laser spots 12c are located at identical positions with respect to the local feed direction 18.

[0111] Fig. 6a shows a schematic top view of an exemplary faceted plate 27, as it can be used in a welding optic to generate multiple partial beams for the method according to the invention.

[0112] The faceted plate 27, in the form shown here, includes a regularly hexagonal central facet. 28 (“Central facet”). The facet plate 27 comprises six outer facets arranged around it. 29 ("Outer facets"). The collimated laser beam 7 is directed onto the facet plate 27.

[0113] Fig. 6bshows a schematic cross-section of the exemplary faceted plate 27 made of Fig. 6a .

[0114] The outer facets 29 are wedge-shaped. A facet angle β here is approximately 0.15°, measured with respect to a ground plane 25 that is perpendicular to the direction of incidence of the collimated laser beam 7. The collimated laser beam 7 is directed onto the facet plate 27. In the region of the central facet 28, the collimated laser beam 7 is not deflected. In the regions of the six outer facets 29, the collimated laser beam 7 is deflected (refracted). This results in one undeflected partial beam 8 and six deflected partial beams 8.

[0115] Fig. 6c Figure 11 shows a welding pattern of a variant of the inventive method with six laser spots 12 in a ring formation and a central laser spot 12, as formed by the exemplary faceted plate 27 made of Fig. 6acan be generated. The central laser spot 12 is also referred to here as 12‴.

[0116] The laser spots 12 are all the same size. The core portion 13 has a diameter DK of 100 µm and the ring portion 14 has a diameter DR of 400 µm. The ratio DR / DK is therefore 4.

[0117] The distance between two adjacent laser spot centers 15 of the laser spots 12 in the ring formation is approximately 350 µm. In the variant shown here, the adjacent laser spots 12 in the ring formation are arranged overlapping with the ring portions 14. The central laser spot 12‴ overlaps all other laser spots 12 with respect to the ring portions 14. The core portions 13 do not overlap. The weld pattern 11 exhibits sixfold rotational symmetry, since the ring formation is formed by six laser spots 12, which can be transformed into one another by rotating them 60° around the common center 17; the central laser spot 12‴ remains unaffected by the rotation, as its laser spot center coincides with the common center 17.

[0118] With regard to the local feed direction 18, the welding pattern 11 is arranged such that the two laser spots 12a lead, the two laser spots 12b follow, and the three laser spots 12c are arranged centrally between the laser spots 12a, 12b.

[0119] Fig. 7 The image shows an experimental view of two aluminum-containing components that were welded together in an overlap joint using a variant of the inventive method. A cross-section was prepared and photographed under a light microscope.

[0120] The upper component has a thickness of approximately 1 mm, and the lower component has a thickness of approximately 2 mm. Welding was performed by penetrating approximately 40% into the lower component; the welding direction was perpendicular to the plane of the drawing. A virtually pore-free, media-tight weld was achieved.

[0121] In the present example, the welding pattern of Fig. 2(see above) was applied, with four laser spots in a square, touching arrangement. A (total) average laser power P = 3 kW and a welding speed SG = 5 m / min were selected. The power fraction in the core was 70%, the core diameter DK was 100 µm, and the ring diameter DR was 400 µm for each laser spot. The aluminum-containing components were made of the aluminum alloy AW-5083.

[0122] Fig. 8 Figure 1 shows a device 30 with a welding optic 1 for welding components 19 or for generating a weld contour 20a. According to the invention, the weld contour 20a is traversed multiple times, in particular completely multiple times. After or – preferably – during the traversal, an optical sensor 31 can determine whether a further traversal is necessary. The optical sensor 31 is preferably arranged coaxially to the beam path of partial beams 8.

[0123] Fig. 9The figure shows welded components, with a weld contour 20a created in a butt joint. A lid-shaped component was used before welding. 19c into the other vessel-shaped component 19d inserted.

[0124] Fig. 10 shows a cross-section of two welded components, where a double pass is evident from the weld contour 20a. Reference symbol list

[0125] 1 Welding optics 2 Laser light cable 2a 2-in-1 fiber 3 Collimation lens 4a, 4b Bifocal inserts 5 Focusing lens 6 Output laser beam 7 Collimated laser beam 8 Partial beam 9 Core fiber 10 Ring fiber 11 Welding pattern 12 Laser spot 12' Laser spot adjacent to laser spot 12" 12" Laser spot adjacent to laser spot 12' 12' Central laser spot 12a Leading laser spot 12b Trailing laser spot 12c Central laser spot 13 Core portion 14 Ring portion 15 Laser spot center 16 Ring formation 17 Common center 18 Feed direction 19 Component 19a Upper component 19b Darkest component 19c Lid-shaped component 19d Vessel-shaped component 20 Surface 20a Weld contour 21 Vapor capillary 21a Projection 21b Recess 23 Lowest point 24 Melt bath 24a Left edge 24b Lower edge 24c Right edge 25 Base plane 26 Central area 27 Facet plate 28 Central facet 29 Outer facets 30 Device 31 Optical sensor β Facet angle BD Component thickness DK Diameter of core portion D upper Component thickness DR Diameter of ring portion D lower Component thicknessbottom component ET unt Welding depth into the bottom component KFD core fiber diameter RFD ring fiber diameter T max maximum depth of the vapor capillary

Claims

1. A method for welding at least two aluminium-containing components (19), wherein each of the components (19) has a content of at least 75 wt% aluminium, wherein the welding takes place as laser welding in the deep penetration welding regime, wherein an output laser beam (6) is subdivided into a plurality of partial beams (8) that are directed onto the components (19) such that a plurality of laser spots (12) are produced on the surface (20) of the components (19), wherein the plurality of laser spots (12) on the surface (20) of the components (19) traverse a welding contour (20a), and wherein laser spot centres (15) of at least three laser spots (12) of the plurality of laser spots (12) are arranged in a ring formation (16), characterized in that the output laser beam (6) is produced by means of a multi-fibre, preferably a 2-in-1 fibre (2a), such that each of the plurality of laser spots (12) on the surface (20) of the components (19) has a core portion (13) and a ring portion (14), wherein after a first traversing of the welding contour (20a), the welding contour (20a) is traversed at least partially a second time, wherein the second traversing takes place at a lower power and / or higher advancement speed than the first traversing.

2. The method according to claim 1, characterized in that one component (19) has die cast aluminium or a wrought aluminium alloy.

3. The method according to one of the preceding claims, characterized in that, the weld penetration depth (ETunt) is less than 10mm.

4. The method according to one of the preceding claims, characterized in that, the doubly traversed welding contour (20a) is recorded by an optical sensor (31), and defects are detected.

5. The method according to claim 4, characterized in that the creation of the recording takes place during the second traversing of the welding contour (20a).

6. The method according to one of the preceding claims, characterized in that, after the second traversing of the welding contour (20a), the welding contour (20a) is traversed a third time, at least partially.

7. The method according to claim 6, characterized in that the triply traversed welding contour (20a) is recorded by an optical sensor (31), and defects are detected.

8. The method according to claim 7, characterized in that the creation of the recording takes place during the third traversing of the welding contour (20a).