Method for producing a weld seam, and laser welding machine

Abstract

The invention relates to a method for producing a weld seam, which extends along a closed trajectory (54), by means of a laser welding machine (10) for connecting a first workpiece (12) and a second workpiece (14) together in a fluid-tight manner, comprising: providing the first workpiece (12) and the second workpiece (14), wherein at least one of the two workpieces (12, 14) is formed from a die-cast aluminium material or from a wrought aluminium alloy; directing a first laser beam (22) of the laser welding machine (10) and a second laser beam (24) of the laser welding machine (10) simultaneously onto the two workpieces (12, 14) such that two separate molten baths (58) are formed, in particular are formed simultaneously; and successively traversing at least one section (62) of the trajectory (54) with the first laser beam (22) and the second laser beam (24) such that the section (62) is traversed a first time by the first laser beam (22) and a second time by the second laser beam (24).

Description

[0001] Title: Method for producing a weld seam and

[0002] laser welding machine

[0003] Description

[0004] The invention relates to a method for producing a weld seam and a laser welding machine.

[0005] In electromobility, assemblies are typically used that must be sealed against various fluids. Typical fluids include coolants or protective gases that create a suitable atmosphere for sensitive components. For such fluids to perform their intended function, the assembly must be fluid-tight. This required fluid tightness is often achieved by joining two components of the assembly with a fluid-tight weld.

[0006] In electromobility, components based on aluminum alloys are of great importance, particularly due to their low specific weight. To create a fluid-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 fluid-tight joint. However, bonding is also relatively complex and often requires lengthy curing processes, and the bonded joint can be sensitive to high temperatures.

[0007] 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.

[0008] Laser welding of fluid-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. As a result, weld sink marks, edge notches, or holes can occur. These problems, combined with cracks and pores in the weld, can cause leaks, rendering the welded components unsuitable for applications requiring fluid tightness. Furthermore, the strong turbulence in the weld pool often results in excessive weld spatter, which contaminates the surrounding area and leads to material loss at the weld.

[0009] DE 10 2021 206 486 A1 describes a method in which an output laser beam is generated using a multi-fiber, preferably a 2-in-1 fiber, such that several laser spots on the surface of a component each have a core portion and a ring portion. The average power density is higher in the core portion than in the ring portion. The method is particularly suitable for welding aluminum-containing components, since the output laser beam is divided into several partial beams and, accordingly, several laser spots on the component surface.

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

[0011] It is therefore an object of the invention to provide a method for the rapid and cost-effective production of a particularly reliable fluid-tight weld. It is a further object of the invention to provide a laser welding machine for producing such a fluid-tight weld.

[0012] The invention solves this problem by providing a method with the features of claim 1 and a laser welding machine with the features of claim 13. Advantageous further developments and / or embodiments of the invention are described in the dependent claims.

[0013] A method according to the invention is designed for producing a weld seam extending along a closed trajectory, in particular a fluid-tight weld seam, using a laser welding machine for the fluid-tight joining of a first workpiece and a second workpiece.The method comprises: providing the first workpiece and the second workpiece, wherein at least one of the two workpieces is made of an aluminum die-casting material or an aluminum wrought alloy; simultaneously directing a first laser beam of the laser welding machine and a second laser beam of the laser welding machine onto the two workpieces, so that, in particular simultaneously, two separate melt pools are formed; and successively traversing at least one section of the trajectory with the first laser beam and the second laser beam, so that the section is traversed once with the first laser beam and once with the second laser beam.

[0014] Advantageously, by simultaneously forming two separate melt pools, the production time of the weld seam can be reduced, thereby achieving higher productivity.

[0015] By passing the weld section twice, it is advantageous to ensure that any pores formed during the first pass close during the second pass, thereby reducing or completely preventing cracking. In particular, the cracks and / or pores formed during the first pass can be degassed by the second pass. Degassing can occur via a vapor capillary that forms during the second pass. This reduces the occurrence of weld defects and results in a particularly fluid-tight weld.

[0016] For example, at least one of the two workpieces may contain hydrogen pores. During the first pass, a section of the weld may melt, causing the hydrogen pores located in the heat-affected zone of the first laser beam's melt pool to expand uncontrollably and potentially explode. This can result in such melt pool dynamics that material ejection and / or pores occur. Once the weld area has solidified after the first pass, the pores can no longer close. The second pass can remelt the weld area already melted during the first pass. Since the hydrogen pores have already expanded and potentially exploded during the first pass, the melt pool dynamics during the second pass are lower compared to the first.During the second pass, any pores created during the first pass can close. In other words, the first pass can be performed to achieve a predetermined weld penetration depth, thus determining the weld strength. The second pass can repair any defects from the first pass, resulting in a media-tight, and especially gas-tight, weld.

[0017] During the sequential process, the two melt pools cannot merge into a single melt pool.

[0018] The welding depth can be, for example, 2 mm (millimeters) or 1.8 mm.

[0019] A trajectory can also be described as a path, track, or route. A closed trajectory is one that has neither a starting point nor an endpoint.

[0020] Fluid-tightness means that a fluid located between the first and second workpieces cannot unintentionally pass through the weld seam. Therefore, this process can be particularly suitable for manufacturing cooling structures.

[0021] The fluid can be a liquid, for example water, or a gas, for example air. Preferably, the fluid-tight weld can be a gas-tight weld. The fluid-tight joining of the two workpieces can be achieved by means of the weld.

[0022] After the two workpieces have been positioned, the process can involve arranging them relative to each other to form either a lap joint or a butt joint. If the two workpieces are arranged in a lap joint, the weld can be created using a deep penetration welding process. During the deep penetration welding process, one workpiece can be welded into the other. If the two workpieces are arranged in a butt joint, the weld can be created by melting adjacent areas of the two workpieces. This allows molten material from the first workpiece and molten material from the second workpiece to mix together.

[0023] The first workpiece and the second workpiece can each be made of die-cast aluminum or wrought aluminum alloy. Alternatively, one of the two workpieces can be made of die-cast aluminum and the other of wrought aluminum alloy. For example, one of the two workpieces can be a die-cast aluminum housing and the other a wrought aluminum alloy lid for the housing.

[0024] The first workpiece can be made of an aluminum material of class 3000, 5000 or 6000 and the second workpiece can be made of an aluminum material of class 3000, 5000 or 6000.

[0025] The first workpiece and / or the second workpiece can each have a thickness of at least 1 mm.

[0026] The weld penetration depth can be less than or equal to 10 mm, in particular 4 mm. Preferably, the weld depth can be less than 10 mm, in particular 4 mm.

[0027] Each of the two laser beams can be directed at the workpieces in such a way that at the point where the laser beam hits one of the two workpieces, it is thermally heated, thus forming the melt pool.

[0028] The first laser beam during the first scan of the section and the second laser beam during the second scan of the section can have the same beam parameters.

[0029] The path along which the first laser beam moves during the first scan of the section, and the path along which the second laser beam moves during the second scan of the section, can be identical or have a lateral offset from each other. The lateral offset can have a maximum value of 0.5 mm.

[0030] The process can include: generating the first laser beam and the second laser beam. The first laser beam and / or the second laser beam can each be a multimode laser beam.

[0031] The first and second laser beams can be generated using the same laser source or different laser sources. The first and / or second laser beams can each be generated using a fiber laser or a disk laser. The first and / or second laser beams can each have a wavelength in the range of 800 nm to 1200 nm, particularly 1030 nm to 1070 nm. Preferably, the laser beam can have a wavelength of 1030 nm, 1064 nm, or 1070 nm. Alternatively, the laser beam can have a wavelength in the range of 400 nm to 450 nm or 500 nm to 550 nm. Preferably, the laser beam can have a wavelength of 515 nm.

[0032] The distance between the melt pool for the first run and the melt pool for the second run can be greater than the length of the melt pool for the first run.

[0033] Another aspect of the process can be that the first workpiece is connected to the second workpiece in a gas-tight manner by means of the weld seam.

[0034] Another aspect of the process is that it enables robust and / or reliable sealing welding of aluminum die-cast components. In particular, this can increase process reliability.

[0035] In a further development of the procedure, the process includes: successively traversing at least one further section of the trajectory with the first laser beam and with the second laser beam, so that the further section is traversed once with the second laser beam and once with the first laser beam.

[0036] Advantageously, this further reduces the welding time. In particular, the sequential scanning of the first section and the subsequent scanning of the next section can be performed simultaneously. The first scanning of the section with the first laser beam and the first scanning of the next section with the second laser beam can be performed simultaneously. Subsequently, the second scanning of the section with the second laser beam and the second scanning of the next section with the first laser beam can be performed simultaneously.

[0037] The term "first pass" can refer to the first pass of the section with the first laser beam and / or the first pass of the subsequent section with the second laser beam. The term "second pass" can refer to the second pass of the section with the second laser beam and / or the second pass of the subsequent section with the first laser beam. In a further development of the method, the trajectory section connects directly to the subsequent section. Advantageously, this allows the second laser beam to complete the first pass of the subsequent section and simultaneously begin the second pass. This eliminates the need for a start and end ramp for the second laser beam, resulting in a higher weld quality.

[0038] In particular, the end of one section of the trajectory can be directly connected to the beginning of the next section of the trajectory and / or the end of the next section of the trajectory can be directly connected to the beginning of the next section of the trajectory.

[0039] In a further development of the method, the distance between the melt pool of the first laser beam and the melt pool of the second laser beam is at least 1 cm (centimeter), in particular 2 cm. Advantageously, this ensures that two separate melt pools are formed.

[0040] In a further development of the method, the distance between the melt pool of the first laser beam and the melt pool of the second laser beam is at most 10 cm, in particular 8 cm. This allows for particularly long trajectories, for example trajectories over 1 m (meter) long.

[0041] In a further development of the method, the melt pool of the second laser beam, when traversing the first section of the trajectory, has a depth that is at most 10% shallower than that of the first laser beam when traversing the same section. Additionally or alternatively, the melt pool of the first laser beam, when traversing the next section of the trajectory, has a depth that is at most 10% shallower than that of the second laser beam when traversing the next section. Advantageously, this ensures that only material that was already melted during the first pass can be melted during the second pass.

[0042] In particular, the melt pool of the second laser beam, when traversing a section of the trajectory, can be at most 10% narrower than the melt pool of the first laser beam when traversing that section. Additionally or alternatively, the melt pool of the first laser beam, when traversing the further section of the trajectory, can be at most 10% narrower than the melt pool of the second laser beam when traversing that further section. In a further development of the method, the second traversal is performed with lower power, in particular lower laser power, and / or a lower feed rate than the first traversal. Advantageously, this results in the melt pool being smaller during the second traversal than during the first.

[0043] In other words, the power of the second laser beam during the second scan of the section may be lower than the power of the first laser beam during the first scan of the section and / or the power of the first laser beam during the second scan of the further section may be lower than the power of the second laser beam during the first scan of the further section.

[0044] The feed rate of the second laser beam during the second scan of the section may be lower than the feed rate of the first laser beam during the first scan of the section and / or the feed rate of the first laser beam during the second scan of the further section may be lower than the feed rate of the second laser beam during the first scan of the further section.

[0045] The feed rate during the first run can be at least 10 m / min (meters per minute).

[0046] The feed rate can be the speed at which a laser beam is moved relative to the two workpieces.

[0047] In a further development of the process, the length of a segment of the trajectory is equal to 50% of the total trajectory length. Additionally or alternatively, the length of another segment of the trajectory is equal to 50% of the total trajectory length. Advantageously, this allows the weld to be produced using precisely two laser beams, which simultaneously begin and end the first and second passes. This results in a minimal weld production time when using exactly two laser beams.

[0048] In a further development of the process, a large number of laser beams, for example 3, 4, 5, or 6, are directed simultaneously at the two workpieces, so that a number of melt pools corresponding to the number of laser beams directed at the two workpieces are formed. The melt pools are distributed at equal distances from each other along the trajectory. Advantageously, this further minimizes the welding time.

[0049] In a further development of the process, the first laser beam and / or the second laser beam are each configured as a beam bundle composed of a plurality, in particular 2, 3, or 4, of partial beams. Advantageously, this allows for the stabilization of a vapor capillary that forms upon irradiation with the first laser beam and / or the second laser beam. It also allows for the targeted widening of the weld seam, thereby achieving improved gas tightness.

[0050] Each partial beam can create a laser spot on either of the two workpieces upon impact. The partial beams of each beam bundle can be arranged transversely offset from each other.

[0051] The diameters of the partial beams of the first laser beam and / or the second laser beam can be the same. Alternatively, the diameters of the partial beams of the first laser beam and / or the second laser beam can differ. In particular, the largest diameter of the partial beams of the first laser beam and / or the second laser beam can be at most ten times larger than the smallest diameter of the partial beams of the first laser beam and / or the second laser beam.

[0052] In a further development of the process, the first laser beam and / or the second laser beam form at least one laser spot with a core component and an annular component on the surface of one of the two workpieces. Advantageously, this allows for a particularly high weld quality. If the first laser beam and / or the second laser beam is each formed as a beam bundle consisting of a plurality of partial beams, each partial beam can form at least one laser spot with a core component and an annular component on the surface of one of the two workpieces.

[0053] The core component can have a beam parameter product with a value in the range of 0.38 mm*mrad (millimeters*milliradians) to 16 mm*mrad, in particular less than or equal to 0.6 mm*mrad or less than or equal to 8 mm*mrad. If the core component is single-mode similar, the beam parameter product can have a value less than or equal to 0.6 mm*mrad. If the core component is multi-mode similar, the beam parameter product can have a value less than or equal to 8 mm*mrad. The diameter of the core component on either of the two workpieces can have a value in the range of 10 pm (micrometers) to 300 pm, in particular 30 pm to 70 pm or 50 pm to 120 pm. If the core component is single-mode similar, the diameter of the core component on either of the two workpieces can have a value in the range of 30 pm to 70 pm.If the core portion is multi-mode similar, the diameter of the core portion on one of the two workpieces can have a value in the range of 50 pm to 1200 pm.

[0054] In a further development of the process, a process light is recorded by a monitoring device during the second pass to detect defects. Advantageously, this allows for repair of the defect. For example, the position of the defect can be traced a third time using a laser beam, particularly the first or second laser beam. This allows the third pass to be performed without additional handling of the component, further reducing the weld production time. Alternatively, the third pass can be performed after a leak test.

[0055] A laser welding machine according to the invention is designed for producing a weld seam extending along a closed trajectory for the fluid-tight joining of a first workpiece and a second workpiece. The laser welding machine comprises a laser beam source device for simultaneously generating a first laser beam and a second laser beam, a beam guidance device for simultaneously directing the first laser beam and the second laser beam onto the two workpieces, and a control device.The control device is designed to control the beam guidance device in such a way that by simultaneously directing the first laser beam and the second laser beam onto the two workpieces, two separate melt pools are formed, and that at least one section of the trajectory is traversed successively with the first laser beam and the second laser beam, so that the section is traversed once with the first laser beam and once with the second laser beam.

[0056] The laser welding machine is specifically designed and configured to perform a previously described process. The aforementioned description of the process can also apply to laser welding machines with identical or functionally equivalent features. The laser beam source device can have a single laser beam source for generating both the first and second laser beams. Alternatively, the laser beam source device can have a first laser beam source for generating the first laser beam and a second laser beam source for generating the second laser beam. In other words, the first and second laser beams can be generated with the same laser beam source or with different laser beam sources.

[0057] The first laser beam and / or the second laser beam can each be generated using a fiber laser or a disk laser.

[0058] It is also conceivable that the laser beam source device is designed as a single laser beam source and the beam guidance device includes a diffractive optical element that splits the laser beam from the single laser beam source into a first and a second laser beam. The distance between the diffractive optical element and the two workpieces can be chosen such that the first and second laser beams form two separate melt pools. The sequential processing of the first and / or second section can be achieved by rotating the diffractive optical element. Advantageously, this can lead to a further reduction in manufacturing time, a compact arrangement, and / or direction independence.

[0059] The beam guidance device can be configured to guide the first and second laser beams from the laser beam source to the two workpieces. The beam guidance device can be configured to deflect the first and second laser beams such that the two laser beams traverse the first and / or second sections of the trajectory sequentially.

[0060] The beam guidance device can include multiple mirrors for deflecting the laser beam. At least one mirror of the beam guidance device can be a movable mirror, for example, a mirror movable by a galvanometer drive.

[0061] The beam guidance system can include a scanner optic, a flying optic, or a processing head over which the two laser beams are guided. The scanner optic and / or the flying optic can have an imaging ratio in the range of 1:1 to 5:1, particularly in the range of 1.5:1 to 2:1. This allows for optimal energy input into the two workpieces.

[0062] The beam guidance device can comprise at least one first optical fiber with a core and a cladding, and one second optical fiber with a core and a cladding. The first optical fiber can be configured to adjust the core and ring components of the first laser beam. The second optical fiber can be configured to adjust the core and ring components of the second laser beam. Details regarding the adjustment of the core and ring components using an optical fiber can be found in WO 2011 / 124671 A1. In particular, the description of the adjustment of the core and ring components using an optical fiber in WO 2011 / 124671 A1 is hereby incorporated by reference into this description. Specifically, the power of the core component of one of the two laser beams, relative to the total power of the laser beam, can be adjusted in a range between 0% and 100%.

[0063] The two optical fibers can each be configured as an active fiber and act as a laser beam source. In this case, the optical fiber of the beam guidance device and the laser beam source device can be configured as a single component. Alternatively, the two optical fibers can each be configured as a passive fiber.

[0064] The core of each optical fiber can be surrounded by a cladding. The core can have a diameter in the range of 10 pm to 50 pm if the core portion is single-mode similar, or a diameter in the range of 50 pm to 400 pm, particularly 50 pm to 200 pm, if the core portion is multi-mode similar.

[0065] The cladding of each optical fiber can have a diameter in the range of 40 pm to 2000 pm, in particular 80 pm to 800 pm.

[0066] The core-to-ring diameter ratio of any optical fiber can range from 1:2 to 1:10. In particular, the core-to-ring diameter ratio of any optical fiber can be 1:4.

[0067] The beam guidance device can comprise at least a first optic and a second optic. The first optic can be configured to split the first laser beam into a plurality, in particular 2, 3, 4 or 5, of partial beams. The second optic can be configured to split the second laser beam into a plurality, in particular 2, 3, 4 or 5, of partial beams.

[0068] The first optic and / or the second optic can each include an optical element for splitting the laser beam into partial beams. This optical element can be, for example, a multifocal lens, an optical wedge plate, a diffractive optical element, or a refractive optical element.

[0069] The control unit may include an electrical computing unit, in particular a computer and / or a microcontroller.

[0070] The control device can be configured to control the beam guidance device for directing the two laser beams onto the two workpieces and for successively traversing the section and the next section of the trajectory with the two laser beams.

[0071] Further advantages and advantageous embodiments of the invention can be seen from the figures, their description, and the claims. All features disclosed in the figures, their description, and the claims can be essential to the invention, both individually and in any combination. The figures show:

[0072] Fig. 1 shows a schematic representation of a laser welding machine during the production of a weld seam for the fluid-tight joining of a first workpiece and a second workpiece together,

[0073] Fig. 2 shows a schematic top view of the two workpieces from Fig. 1 before the weld is made.

[0074] Fig. 3 shows a schematic top view of the two workpieces from Fig. 1 during the welding process, and

[0075] Fig. 4 shows a schematic top view of the two workpieces during the production of the weld seam according to a further embodiment.

[0076] Fig. 1 shows a laser welding machine 10 during the production of a weld. The weld joins a first workpiece 12 and a second workpiece 14 together in a fluid-tight manner. The two workpieces 12, 14 are arranged relative to each other, forming an overlap joint. The production of the weld is a deep penetration welding process.

[0077] The two workpieces, 12 and 14, are each made of die-cast aluminum. The first workpiece, 12, has a thickness of 2 mm, and the second workpiece, 14, has a thickness of 5 mm. The weld seam has a depth of 4 mm.

[0078] By welding the two workpieces 12, 14 together, a cooling element is produced through which a cooling fluid, for example in the form of a gas or a liquid, can flow. To prevent the cooling fluid from unintentionally escaping the cooling element, the weld seam must be fluid-tight.

[0079] The laser welding machine 10 has a laser beam source device 16. The laser beam source device 16 has a first laser beam source 18 and a second laser beam source 20. The first laser beam source 18 is designed to generate a first laser beam 22 and the second laser beam source 20 is designed to generate a second laser beam 24.

[0080] Cross-sections 26 of the first laser beam 22 and the second laser beam 24 after leaving the two laser beam sources 18, 20 are shown above the laser welding machine 10. The first laser beam and the second laser beam each have a wavelength of 1064 nm.

[0081] The laser welding machine 10 has a beam guidance device 28. The beam guidance device 28 is designed to guide the first laser beam 22 from the first laser beam source 18 and the second laser beam 24 from the second laser beam source 20 to the two workpieces 12, 14.

[0082] The beam guidance device 28 has a first optical fiber 32 and a second optical fiber 34. The first laser beam 22 passes through the first optical fiber 32 and the second laser beam 24 passes through the second optical fiber 34.

[0083] The two optical fibers 32, 34 each have a core and a cladding. The laser beams 22, 24 are each partially coupled into the core and partially into the cladding. After exiting the optical fibers 32, 34, the two laser beams 22, 24 each have a core portion 36 and a ring portion 38 in their cross-section. A power ratio between the core portion 36 and the ring portion 38 is adjustable.

[0084] Cross-sections 40 of the first laser beam 22 and the second laser beam 24 after leaving the two optical fibers 32, 34 are shown above the laser welding machine 10.

[0085] The beam guidance device 28 has a first diffractive optical element 42 and a second diffractive optical element 44. The first diffractive optical element 42 is configured to split the first laser beam 22 into four equal partial beams. The second diffractive optical element 44 is configured to split the second laser beam 24 into four equal partial beams. Thus, the two laser beams 22, 24 are each configured as a beam bundle. The partial beams of each laser beam 22, 24 are arranged transversely offset from one another. In the illustrated embodiment of Fig. 1, the partial beams are arranged in a square configuration within a cross-section of the laser beams 22, 24.

[0086] Cross-sections 46 of the first laser beam 22 and the second laser beam 24 after passing the diffractive optical elements 42, 44 are shown above the laser welding machine 10.

[0087] The two diffractive optical elements 42, 44 are each rotatably mounted. This allows the arrangement of the partial beams of the first laser beam 22 and the second laser beam 24 to be rotated by rotating the respective diffractive optical element 42, 44. By rotating the arrangement of the partial beams, it can be aligned, in particular with the course of a trajectory.

[0088] The beam guidance device 28 has a plurality of mirrors 48 for deflecting the laser beams 22, 24. In Fig. 1, for the sake of clarity, only a first mirror 48 for directing the first laser beam 22 onto the two workpieces 12, 14 and a second mirror 50 for directing the second laser beam 24 onto the two workpieces 12, 14 are shown.

[0089] The two mirrors 48, 50 are each designed as movable mirrors. Each mirror 48, 50 has a drive mechanism for powering its movement. During the welding process, the two laser beams 22, 24 are directed onto the two workpieces 12, 14 by means of the two mirrors 48, 50. The two laser beams 22, 24 strike the first workpiece 12 simultaneously. The point of impact of the first laser beam 22 on the first workpiece 12 and the point of impact of the second laser beam 24 on the first workpiece 12 are distinct. The two laser beams 22, 24 thermally heat the two workpieces 12, 14 locally, forming a weld pool on each.

[0090] The laser welding machine 10 has a control device 52 in the form of a computer, which is designed to control the beam guidance device 28 in such a way that by simultaneously directing the first laser beam 22 and the second laser beam 24 onto the two workpieces 12, 14, two separate melt pools are formed.

[0091] Fig. 2 shows a top view of the two workpieces 12, 14, looking towards the first workpiece 12 before the weld is made. The second workpiece 14 is positioned below the first workpiece 12.

[0092] Figure 2 shows a dashed line representing a trajectory 54 along which the weld to be produced is to extend. Trajectory 54 is a closed trajectory without a starting point or an end point. Figure 2 also shows two further trajectories 56 along which additional welds are to extend. These further trajectories 56 are not closed trajectories.

[0093] Fig. 3 shows the two workpieces from Fig. 2 during the welding process. The two laser beams 22, 24 strike the two workpieces 12, 14, and two separate molten pools 58 are formed.

[0094] The distance between the melt pool 58 of the first laser beam 22 and the melt pool 58 of the second laser beam 24 is in the range of 1 cm to 10 cm. In other words, the already solidified material of the two workpieces 12, 14 between the two melt pools 58 has a length in the range of 1 cm to 10 cm.

[0095] The control unit 52 controls the beam guidance unit 28 for the production of the weld seam such that the two laser beams 22, 24 trace the trajectory 54 in the direction of movement 60. The two laser beams 22, 24 trace the trajectory 54 sequentially. The trajectory 54 has a section 62 and a further section 64. Section 62 connects directly to the further section 64. The lengths of section 62 and the further section 64 differ from each other.

[0096] The trajectory 54 is traversed with the two laser beams 22, 24 in such a way that section 62 is traversed once with the first laser beam 22 and once with the second laser beam 24, and that the further section 64 is traversed once with the second laser beam 24 and once with the first laser beam 22.

[0097] The first scanning of the further section 64 with the second laser beam 24 and the first scanning of section 62 with the first laser beam 22 occur at least partially simultaneously. After the first scanning of the further section 64, the second scanning of section 62 with the second laser beam 24 takes place. The second scanning of section 62 with the second laser beam 24 occurs simultaneously while the first laser beam 22 scans section 62 for the first time. After the first scanning of section 62, the second scanning of the further section 64 with the first laser beam 22 takes place. Thus, the first and second scanning occur at least partially, and in particular predominantly, simultaneously.

[0098] The second laser beam 24 has a lower laser power during the second scan of section 62 than the first laser beam 22 during the first scan of section 62, and the first laser beam 22 has a lower laser power during the second scan of the further section 64 than the second laser beam 24 during the first scan of the further section 64. Advantageously, this results in the melt pools 58 being smaller during the second scan than during the first scan, so that only material that was melted during the first scan is melted during the second scan.

[0099] The weld pool 58 of the second laser beam 24 has a depth and width that are at most 10% less when traversing section 62 than the weld pool 58 of the first laser beam 22 when traversing section 62. The weld pool 58 of the first laser beam 22 has a depth and width that are at most 10% less when traversing the further section 64 than the weld pool 58 of the second laser beam 24 when traversing the further section 64. Figure 4 shows a further embodiment of producing the weld seam according to Figure 3, in which the same reference numerals are used for identical and functionally equivalent elements. In this respect, reference can be made to the above descriptions of the embodiment in Figure 3, so that essentially only the existing differences are discussed.

[0100] The length of section 62 is equal to 50% of the length of trajectory 54, and the length of the further section 64 is equal to 50% of the length of trajectory 54. This places the melt pool 58 of the first laser beam 22 and the melt pool 58 of the second laser beam 24 opposite each other. During the welding process, the melt pool 58 of the first laser beam 22 and the melt pool 58 of the second laser beam 24 can be connected by an imaginary straight line. This imaginary line passes through the centroid of an area enclosed and / or bounded by the closed trajectory 54.

[0101] The first scan of section 62 with the first laser beam 22 and the first scan of the next section 64 with the second laser beam 24 are performed simultaneously. The second scan of the next section 64 with the first laser beam 22 and the second scan of section 62 with the second laser beam 24 are performed simultaneously.

[0102] Fig. 1 shows that the laser welding machine 10 has a monitoring device 66 for detecting the process glow during the second traverse of the trajectory 54. Based on the detected process glow, the control unit 52 can detect whether a defect occurs during the second traverse. The control unit 52 is configured to determine the position of the defect based on the detected process glow. The control unit 52 is configured to trace the position of the defect a third time with the first or the second laser beam 22, 24.

[0103] In a further embodiment not shown, the laser welding machine 10 can be configured to generate more than two laser beams simultaneously and direct them towards the two workpieces, so that a number of melt pools corresponding to the number of laser beams directed towards the two workpieces is formed.

Claims

Patent claims 1. Method for producing a weld seam extending along a closed trajectory (54) using a laser welding machine (10) for fluid-tight joining of a first workpiece (12) and a second workpiece (14) together, comprising: Providing the first workpiece (12) and the second workpiece (14), wherein at least one of the two workpieces (12, 14) is made of an aluminum die-casting material or of an aluminum wrought alloy, directing a first laser beam (22) of the laser welding machine (10) and a second laser beam (24) of the laser welding machine (10) simultaneously onto the two workpieces (12, 14), so that, in particular simultaneously, two separate melt pools (58) are formed, and successively traversing at least one section (62) of the trajectory (54) with the first laser beam (22) and the second laser beam (24), so that the section (62) is traversed once with the first laser beam (22) and once with the second laser beam (24).

2. Method according to claim 1, wherein the method comprises: successively traversing at least one further section (64) of the trajectory (54) with the first laser beam (22) and with the second laser beam (24), such that the further section (64) is traversed a first time with the second laser beam (24) and a second time with the first laser beam (22).

3. Method according to claim 2, wherein the section (62) of the trajectory (54) is directly connected to the further section (64) of the trajectory (54).

4. Method according to one of the preceding claims, wherein the distance between the melting bath (58) of the first laser beam (22) and the melting bath (58) of the second laser beam (24) is at least 1 cm, in particular 2 cm.

5. Method according to any of the preceding claims, wherein the distance between the melting bath (58) of the first laser beam (22) and the melting bath (58) of the second laser beam (24) is at most 10 cm, in particular 8 cm.

6. Method according to one of the preceding claims, wherein the melt pool (58) of the second laser beam (24) has a depth that is at most 10% less than the melt pool (58) of the first laser beam (22) when traversing the section (62) of the trajectory (54), and / or wherein the melt pool (58) of the first laser beam (22) has a depth that is at most 10% less than the melt pool (58) of the second laser beam (24) when traversing the further section (64) of the trajectory (54).

7. Method according to one of the preceding claims, wherein the second run is performed with lower power and / or lower feed rate than the first run.

8. Method according to one of the preceding claims, wherein a length of section (62) of the trajectory (54) is equal to 50% of a length of the trajectory (54), and / or wherein a length of further section (64) of the trajectory (54) is equal to 50% of the length of the trajectory (54).

9. Method according to one of the preceding claims, wherein a plurality of laser beams (22, 24) are directed simultaneously onto the two workpieces (12, 14), such that a number of melt pools (58) corresponding to the number of laser beams (22, 24) directed onto the two workpieces (12, 14) are formed, wherein the melt pools (58) are distributed at equal distances from each other along the trajectory (54).

10. Method according to one of the preceding claims, wherein the first laser beam (22) and / or the second laser beam (24) is each configured as a beam bundle formed from a plurality of partial beams.

11. Method according to one of the preceding claims, wherein the first laser beam (22) and / or the second laser beam (24) forms at least one laser spot with a core portion (36) and a ring portion (38) on a surface of the two workpieces (12, 14).

12. Method according to one of the preceding claims, wherein during the second run a process glow is recorded by a monitoring device (66) for the purpose of detecting defects.

13. Laser welding machine (10) for producing a weld seam extending along a closed trajectory (54) for fluid-tight joining of a first workpiece (12) and a second workpiece (14) together, comprising: a laser beam source device (16) for simultaneously generating a first laser beam (22) and a second laser beam (24), a beam guidance device (28) for simultaneously directing the first laser beam (22) and the second laser beam (24) onto the two workpieces (12, 14), and a control device (52) configured to control the beam guidance device (28) such that the simultaneous directing of the first laser beam (22) and the second laser beam (24) onto the two workpieces (12, 14) results in the welding of the first workpiece (12, 14) simultaneously.14) two separate melt pools (58) are formed and that at least one section (62) of the trajectory (54) is traversed successively with the first laser beam (22) and the second laser beam (24), so that the section (62) is traversed once with the first laser beam (22) and once with the second laser beam (24).

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