Laser device and method for machining at least one workpiece by means of at least two laser beams

Abstract

The invention relates to a laser device (10) having the features of claim 1 for machining, in particular laser-welding, at least one workpiece (12) by means of at least two laser beams (14) and to a method having the features of the additional independent claim for machining, in particular laser-welding, at least one workpiece (12) by means of at least two laser beams (14).

Description

[0001] Title: Laser device and method for processing at least one workpiece by means of at least two laser beams

[0002] Description

[0003] The invention relates to a laser device for processing at least one workpiece having the features of claim 1 and to a method for processing at least one workpiece having the features of the independent claim.

[0004] When laser welding at least two components, CW (continuous wave) lasers with a constant power over the duration of the laser welding are usually used for deep welding. In particular when deep welding metallic materials with a low viscosity, instabilities can arise in the welding area, especially in the so-called keyhole. This can result in spatter, pores and / or an irregular weld depth, for example. To reduce such instabilities, several laser beams can be superimposed. However, this cannot eliminate all instabilities, especially with metallic materials with low viscosity.

[0005] It is therefore an object of the present invention to provide a laser device and a method for processing, in particular laser welding, at least one workpiece, wherein the above disadvantages are eliminated.

[0006] The above object is achieved by a laser device for processing at least one workpiece using at least two laser beams, having the features of claim 1. The processing may involve laser welding.

[0007] The laser device is designed to generate at least two, in particular at least four, laser beams, each with a different output power, to focus them on the workpiece, and to vary the output power of the laser beams with a variation frequency of at least 50 kHz (kilohertz) and a variation amplitude of at least 10% of the output power. The variation amplitude can be either positive or negative. In other words, the output power can be periodically increased (with a positive variation amplitude) and / or reduced (with a negative variation amplitude).

[0008] In this way, an (additional) stabilization of the keyhole can be achieved, particularly in workpieces with a lower viscosity, whereby the spatter and pores decrease and the most continuous welding depth possible can be achieved. The instabilities of the keyhole can be avoided or at least reduced in particular by increasing and reducing the steam rate and the steam pressure quickly enough so that a collapse of the keyhole can be avoided. In other words, the keyhole can be stabilized by a targeted influencing of the steam pressure (or the steam rate), which can lead to fewer spatter, pores and a constant welding depth. In particular, a stabilization of a wall of the keyhole can be achieved.

[0009] The laser device may include a beam-shaping element for generating a multi-focus beam. The beam-shaping element may include one or more optical wedges.

[0010] According to a further development of the laser device, all laser beams can be designed identically.

[0011] This makes it possible to simplify the generation of laser beams and to implement them using simple means.

[0012] According to a development of the laser device, at least one laser beam, in particular at least two laser beams, can each have a higher power than the remaining laser beams. For example, it is conceivable that with two laser beams, a first laser beam can be arranged in a feed direction upstream of a second laser beam, wherein the power of the first laser beam can be higher than the power of the second laser beam. Accordingly, with four laser beams, for example, two first laser beams can be arranged in the feed direction upstream of two second laser beams, wherein the two first laser beams can have a higher power than the two second laser beams. With four laser beams, the laser beams can be focused or arranged in a quadrangular, in particular rectangular, preferably square, pattern on the workpiece.

[0013] This allows the weld area, especially the keyhole, to be further stabilized. This can further reduce instability (within the keyhole) and lead to fewer spatters and pores, as well as a consistent weld penetration.

[0014] According to a further development of the laser device, the laser device for generating the laser beams can comprise a CW laser. The laser device can be configured such that the laser beams are each modulated with a modulation frequency and a modulation amplitude. The modulation frequency can correspond to the variation frequency, and the modulation amplitude can correspond to the variation amplitude. The CW laser can have an average power of at least 0.2 kW (kilowatts), preferably at least 4 kW.

[0015] This allows the laser beams to be generated using simple means.

[0016] It is also conceivable for the laser device for generating the laser beams to comprise a pulsed laser. In this case, a pulse repetition rate of the pulsed laser can correspond to the variation frequency. The pulsed laser can have an average power of at least 0.2 kW, preferably at least 4 kW, and / or a pulse energy of at least 10 mJ (millioule), preferably at least 50 mJ. It is conceivable for the core region of the laser spot to be generated by means of a pulsed laser (in particular an ns (nanosecond) pulsed laser) and the ring region of the laser spot to be generated by means of a CW laser, or vice versa.

[0017] The pulsed laser and / or the CW laser can each have a beam parameter product of a maximum of 8 mm*mrad (millimeters*milliradians). The pulsed laser and / or the CW laser can each be designed as a (multi-mode) NIR (Near Infrared) laser. It is also conceivable that the pulsed laser and / or the CW laser can each be designed as a laser in the visible range (VIS laser) with a wavelength in a blue or green wavelength range. The pulsed laser and / or the CW laser can each be designed as a solid-state laser.

[0018] The laser device may include a control device. The control device may be configured to program and / or control the (high-frequency) modulation or pulsation with a variation frequency of at least 50 kHz.

[0019] According to a development of the laser device, the laser device can be set up in such a way that the laser beams each generate a laser spot on the workpiece. The laser spot can have a core region and a ring region. The core region can be circular. The ring region can be ring-shaped. The core region can be arranged within the ring region. An average laser power density in the core region can be higher than an average laser power density in the ring region. The average laser power density in the ring region can in particular be a maximum of 5% of the laser power. To generate the core or ring region,

[0020] Ring areas, the laser device can comprise an optical element for beam splitting, in particular a wedge switch.

[0021] This allows for further stabilization of the weld area, especially the keyhole. This can further reduce instability (within the keyhole), resulting in fewer spatters and pores, and a consistent weld penetration.

[0022] According to a further development of the laser device, the laser device for generating the laser beams and / or the laser spots can comprise a fiber (2 in 1 fiber) with a core region and a ring region. The core region of the fiber can have an outer diameter of at most 30 pm (micrometers), in particular of at most 20 pm, preferably of at most 10 pm (e.g. for fundamental mode or single mode). Alternatively, the core region of the fiber can have a larger outer diameter, in particular of at least 50 pm or 100 pm (e.g. for multi-mode). The ring region can have an outer diameter of 200 pm or 400 pm. The core region can be arranged within the ring region. The ratio between the outer diameter of the core region and the outer diameter of the ring region can be in the range from 1:2 to 1:9, in particular 1:3, 1:4 or 1:6. The core region can have a cladding.The cladding can be arranged between the core region and the ring region. The cladding can have a maximum thickness of 10 pm.

[0023] This allows for further stabilization of the weld area, especially the keyhole. This can further reduce instability (within the keyhole), reduce spatter and pores, and ensure consistent weld penetration.

[0024] According to a further development of the laser device, the laser device can be configured such that a rise time and / or fall time of the variation amplitude is a maximum of 10 pm.

[0025] In this case, the rise time refers to the time required to increase the laser power to a maximum value (e.g., the positive variation amplitude). Similarly, the fall time refers to the time required to reduce the laser power to a minimum value (e.g., the negative variation amplitude).

[0026] This allows the weld area, especially the keyhole, to be further stabilized. This can further reduce instability (within the keyhole) and lead to fewer spatters and pores, as well as a consistent weld penetration.

[0027] According to a further development of the laser device, the laser device can comprise a pivoting optic for moving the laser beams over the workpiece. The pivoting optic can be designed as a welding optic. The pivoting optic can have an image ratio in a range from 1:1 to 5:1.

[0028] This allows for simple means of advancing the laser beams along the workpiece. According to a further development of the laser device, the laser device can comprise at least one nozzle for supplying a shielding gas (cutting or welding gas) to the workpiece. The nozzle can have a Laval internal geometry.

[0029] This allows the protective gas to be supplied using simple means, thus further optimising the machining of the workpiece.

[0030] The above object is further achieved by a method for machining at least one workpiece using at least two laser beams with the features of the independent claim. The machining may involve laser welding. The method comprises the following steps:

[0031] Providing the workpiece. The workpiece can be made of metal, in particular aluminum and / or copper. In the molten state (at melting temperature), the workpiece can have a viscosity of maximum 5 mPa*s (millipascals*second). The workpiece can have a thickness of maximum 4 mm (millimeters).

[0032] Generating and focusing at least two, in particular at least four, laser beams, each with an output power, onto the workpiece.

[0033] Varying, in particular pulsing or modulating, the laser beams with a variation frequency of at least 50 kHz and a variation amplitude of at least 10% of the

[0034] Output power . A rise time and / or

[0035] Decay time of the variation amplitude less than 10 ps

[0036] (microseconds). The variation amplitude can be either positive or negative. In other words, the output power can be periodically increased (with a positive variation amplitude) and / or reduced (with a negative variation amplitude).

[0037] In this way, an (additional) stabilization of the keyhole can be achieved, particularly in workpieces with a lower viscosity, whereby the spatter and pores decrease and the most continuous welding depth possible can be achieved. The instabilities of the keyhole can be avoided or at least reduced in particular by increasing and reducing the steam rate and the steam pressure quickly enough so that a collapse of the keyhole can be avoided. In other words, the keyhole can be stabilized by a targeted influencing of the steam pressure (or the steam rate), which can lead to fewer spatter, pores and a constant welding depth. In particular, a stabilization of a wall of the keyhole can be achieved.

[0038] The method may comprise the step of:

[0039] Supplying a protective gas (cutting or welding gas) to the workpiece, particularly in the area where the workpiece is being processed. This can be achieved using a nozzle, particularly one with a Laval internal geometry.

[0040] According to a further development of the method, the method may comprise the step:

[0041] Moving the laser beams and / or the workpiece in order to generate a feed of the laser beams focused on the workpiece in a feed direction. The laser beams can be moved over the workpiece by means of pivoting optics. The movement of the laser beams and / or the workpiece can be a relative movement between the laser beams and the workpiece. In other words, either the laser beams or the workpiece or both can be moved. At least one first laser beam is arranged in front of at least one second laser beam in the feed direction. The first laser beam has a higher power than the second laser beam. It is also conceivable for at least two first laser beams to be arranged in front of at least two second laser beams in the feed direction, the first laser beams having a higher power than the second laser beams.

[0042] In this way, a continuous machining of the workpiece, for example a weld seam, can be produced using simple means, whereby the keyhole, in particular at least one wall of the keyhole, can be further stabilized.

[0043] According to a further development of the method, a laser device as described above can be used to carry out the method.

[0044] With regard to the advantages that can be achieved, reference is made to the relevant explanations regarding the laser device. The measures described in connection with the laser device and / or those explained below can be used to further refine the method.

[0045] Further features, details and advantages of the invention emerge from the wording of the claims and from the following description of an embodiment with reference to the

[0046] Drawings showing:

[0047] Fig. 1 is a schematic representation of a laser device for processing at least one workpiece;

[0048] Fig. 2 is a schematic diagram of a power curve of a CW laser of the laser device according to Figure 1.

[0049] Figure 1 schematically shows a laser device 10 for processing at least one workpiece 12 using at least two laser beams 14. In this case, the processing involves laser welding.

[0050] The laser device 10 is configured to generate at least two, in particular at least four, laser beams 14, each having an output power 16 (cf. Figure 2), and to focus them onto the workpiece 12. The laser device 10 is further configured to vary the output power 16 of the laser beams 14 with a variation frequency of at least 50 kHz and a variation amplitude 18 of at least 10% of the output power 16.

[0051] The laser device 10 can also be configured such that a rise time and / or a fall time of the variation amplitude 18 is a maximum of 10 ps.

[0052] The laser beams 14 are each identical in the present case. It is also conceivable for at least one laser beam 14, in particular at least two laser beams 14, to each have a higher power than the remaining laser beams 14. The laser device 10 can comprise a CW laser for generating the laser beams 14. The laser device 10 can be set up such that the laser beams 14 are modulated with a modulation frequency and a modulation amplitude. The modulation frequency can correspond to the variation frequency and the modulation amplitude to the variation amplitude 18. The CW laser can have an average power of at least 1 kW, in particular of at least 4 kW.

[0053] The laser device 10 comprises a pivoting optics system 20 for moving the laser beams 14 over the workpiece 12. The pivoting optics system 20 can have an imaging ratio in a range from 1:1 to 5:1. The pivoting optics system 10 is designed as a welding optics system.

[0054] The laser device 10 can comprise at least one nozzle for supplying a protective gas to the workpiece 12. This can be a nozzle with a Laval internal geometry.

[0055] The laser device 10 can be configured such that the laser beams 14 each generate a laser spot on the workpiece 12. The laser spot can have a core region, which is in particular circular. The laser spot can have a ring region, which is in particular annular. The core region of the laser spot can be arranged in the ring region of the laser spot. An average laser power density in the core region of the laser spot can be higher than an average laser power density in the ring region of the laser spot. To generate the laser beams 14 and / or the laser spots, the laser device 10 can comprise at least one fiber. The fiber can comprise a core region and a ring region. The core region can be arranged within the ring region. The core region can have an outer diameter of 50 pm or 100 pm. The ring region can have an outer diameter of 200 pm or 400 pm.

[0056] Figure 2 shows a schematic diagram of a power curve of the CW laser of the laser device 10 according to Figure 1 .

[0057] In the diagram shown, the power 22 of the CW laser of the laser device 10 is plotted in watts over time 24 in seconds. In other words, the x-axis represents time 24 in seconds, and the y-axis represents power 22 in watts.

[0058] The power 22 of the CW laser is modulated in this case with the modulation frequency and the modulation amplitude. In other words, the output power 16 of the CW laser is periodically varied by at least 10% (modulation amplitude). The output power 16 of the CW laser is thus changed by the modulation amplitude or the variation amplitude 18 at regular intervals of a maximum of 20 ps (since the modulation frequency or variation frequency is at least 50 kHz). In the example shown, the output power 16 is reduced by the variation amplitude 18 at intervals of a maximum of 20 ps and increased again to the value of the output power 16. In this case, the variation amplitude is greater than 10% and less than 100% of the output power 16. The rise time is the time required to increase the power 22 of the CW laser from a minimum value to a maximum value (in this case the value of the output power 16).Accordingly, the fall time is the time required to reduce the power 22 of the CW laser from the maximum value to the minimum value. This is merely a schematic diagram, so the rise time and fall time are shown as vertical edges (= zero seconds) and are therefore not to scale. The rise time and fall time can each be less than 10 ps.

[0059] In the following, a method for processing, in particular laser welding, at least one workpiece 12 is described with reference to Figures 1 and 2. The method comprises the following steps:

[0060] Providing the workpiece 12. The workpiece 12 can be made of metal, in particular aluminum and / or copper. The workpiece 12 can have a viscosity of a maximum of 5 mPa*s in the molten state.

[0061] Generating and focusing at least two, in particular at least four, laser beams 14, each with an output power 16, onto the workpiece 12.

[0062] Varying, in particular pulsing or modulating, the laser beams 14 with a variation frequency of at least 50 kHz and a variation amplitude 18 of at least 10% of the output power 16. A rise time and / or a fall time of the variation amplitude 18 can be less than 10 ps.

[0063] The method may comprise the step of:

[0064] Moving the laser beams 14 and / or the workpiece 12 in order to generate a feed of the laser beams 14 focused on the workpiece 12 in a feed direction. At least one first laser beam 14 is arranged in front of at least one second laser beam 14 in the feed direction. The first laser beam 14 can have a higher power than the second laser beam 14. If there are at least four laser beams 14, at least two first laser beams 14 can be arranged in front of at least two second laser beams 14 in the feed direction. The first laser beams 14 can each have a higher power than the second laser beams 14.

[0065] To carry out the method, a laser device 10 according to the above embodiments, in particular the laser device 10 shown in Figure 1, can be used.

Claims

Patent claims 1. Laser device (10) for processing, in particular laser welding, at least one workpiece (12) by means of at least two laser beams (14), wherein the laser device (10) is configured to generate at least two, in particular at least four, laser beams (14), each with an output power (16), to focus them on the workpiece (12) and to vary the output power (16) of the laser beams (14) with a variation frequency of at least 50 kHz and a variation amplitude (18) of at least 10% of the output power (16).

2. Laser device (10) according to claim 1, characterized in that all laser beams (14) are each identically designed.

3. Laser device (10) according to claim 1, characterized in that at least one laser beam (14), in particular at least two laser beams (14), each have a higher power than the remaining laser beams (14).

4. Laser device (10) according to one of the preceding claims, characterized in that the laser device (10) for generating the at least two laser beams (14), in particular all laser beams (14), comprises at least one CW laser, wherein the laser device (10) is set up in such a way that the at least two laser beams (14), in particular all laser beams (14), each with a modulation frequency and a modulation amplitude, wherein the modulation frequency corresponds to the variation frequency and the modulation amplitude corresponds to the variation amplitude (18), in particular wherein the CW laser has an average power of at least 0.2 kW, preferably at least 4 kW.

5. Laser device (10) according to one of the preceding claims, characterized in that the laser device (10) is set up such that the laser beams (14) each generate a laser spot on the workpiece (12), wherein the laser spot has a, in particular circular, core region and a, in particular annular, ring region, wherein an average laser power density in the core region is higher than an average laser power density in the ring region.

6. Laser device (10) according to the preceding claim, characterized in that the laser device (10) for generating the laser beams (14) and / or the laser spots comprises at least one fiber with a core region and a ring region.

7. Laser device (10) according to one of the preceding claims, characterized in that the laser device (10) is arranged such that a rise and / or fall time of the variation amplitude (18) is a maximum of 10 ps.

8. Laser device (10) according to one of the preceding claims, characterized in that the laser device (10) has a pivoting optics (20) for moving the laser beams (14) over the workpiece (12), in particular wherein the pivoting optics (20) have an imaging ratio in a range of 1:1 to 5:

1.

9. Laser device (10) according to one of the preceding claims, characterized in that the laser device (10) comprises at least one nozzle for supplying a protective gas to the workpiece (12), in particular wherein the nozzle has a Laval internal geometry.

10. Method for processing, in particular laser welding, at least one workpiece (12) by means of at least two laser beams (14), comprising the steps: Providing the workpiece (12), in particular wherein the workpiece (12) is made of metal, preferably aluminum and / or copper, and has a viscosity of at most 5 mPa*s in the molten state; Generating and focusing at least two, in particular at least four, laser beams (14), each with an output power (16), onto the workpiece (12); Varying, in particular pulsing or modulating, the laser beams (14) with a variation frequency of at least 50 kHz and a variation amplitude (18) of at least 10% of the output power (16), in particular wherein the rise and / or fall time of the variation amplitude (18) is a maximum of 10 ps.

11. The method according to claim 10, characterized in that the method comprises the step: Moving the laser beams (14) and / or the Workpiece (12) in order to generate a feed of the laser beams (14) focused on the workpiece (12) in a feed direction, wherein at least one first laser beam (14) is arranged in the feed direction in front of at least one second laser beam (14), wherein the first laser beam (14) has a higher power than the second laser beam (14), in particular wherein at least two first laser beams (14) are arranged in the feed direction in front of at least two second laser beams (14), wherein the first Laser beams (14) have a higher power than the second laser beams (14).

12. Method according to claim 10 or 11, characterized in that a laser device (10) according to one of claims 1 to 9 is used to carry out the method.

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