Device and method for processing at least one workpiece by means of at least one laser beam

Abstract

The invention relates to a laser device (10) for processing, in particular laser welding, at least one workpiece (12) by means of at least one laser beam (14) with features of claim 1 and to a method for processing, in particular laser welding, at least one workpiece (12) by means of at least one laser beam (14) with features of the independent claim.

Description

The invention relates to a laser device for machining at least one workpiece having features of claim 1 and to a method for machining at least one workpiece having features of the subordinate claim.When laser welding at least two components, continuous wave (CW) lasers with a constant power are usually used for the depth welding over the duration of the laser welding. In particular, when deep welding metallic materials having a low viscosity, instabilities can arise in the welding region, in particular in the so-called keyhole. For example, it is possible to use a switch. Spatter, pores and / or an irregular welding depth are produced. In order to reduce such instabilities, a plurality of laser beams can be superimposed. As a result, in particular in the case of metallic materials with low viscosity, however, not all instabilities can be eliminated.It is therefore the object of the present invention to provide a laser device and a method for machining, in particular laser welding, at least one workpiece, wherein the above disadvantages are eliminated.The above object is achieved by a laser device for machining at least one workpiece by means of at least one laser beam having the features of claim 1. The machining may be laser welding.The laser device is configured to generate the laser beam with an output power, focus the laser beam on the workpiece, and vary the output power of the laser beam 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 both positive and negative. In other words, the output power may be increased periodically (at positive variation amplitude) or reduced (at negative variation amplitude). The laser device is configured such that a rise time and / or a fall time of the variation amplitude is at most 10 μs (microseconds).In the present case, rise time means the time required to increase the laser power to a maximum value (for example the positive variation amplitude). Accordingly, a falling time means the time required to reduce the laser power (output power) to a minimum value (for example, the negative variation amplitude).This makes it possible to achieve (additional) stabilization of the keyhole, in particular in workpieces having a lower viscosity, as a result of which the sprays and pores can be removed and a welding depth which is as continuous as possible can be achieved. The instabilities of the keyhole can be avoided or at least reduced in particular by the steam rate and the steam pressure being increased and reduced rapidly enough so that a collapsing of the keyhole can be avoided. In other words, the keyhole can be stabilized by specifically influencing the vapor pressure (or the vapor rate), which can lead to fewer spatters, pores and a constant welding depth.According to a further development of the laser device, the laser device can comprise a CW laser for generating the laser beam. In this case, the laser device can be configured such that the laser beam is modulated with a modulation frequency and a modulation amplitude. In this case, the modulation frequency can correspond to the variation frequency and the modulation amplitude can correspond to the variation amplitude. The CW laser may have an average power of at least 0.2 kW, preferably at least 4 kW.As a result, the laser beam can be generated with simple means.It is likewise conceivable that the laser device for generating the laser beam can comprise a pulsed laser. In this case, a pulse repetition rate of the pulsed laser can correspond to the variation frequency. The pulsed laser may have an average power of at least 0.2 kW (kilowatts), preferably at least 4 kW, and / or a pulse energy of at least 10 mJ (millijoules), preferably at least 50 mJ.It is conceivable that the core region of the laser spot is generated by means of a pulsed laser (in particular an ns(nanosecond) pulsed laser) and the ring region of the laser spot is generated by means of a CW laser or vice versa.The pulsed laser and / or the CW laser can each have a beam parameter product of at most 8 mm* mrad (millimeter* mrad). The pulsed laser and / or the CW laser can each be configured as a (multimode) NIR laser (near infrared). It is likewise conceivable that the pulsed laser and / or the CW laser can each be configured 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.The laser device may comprise a control device. The control device can be configured for programming and / or controlling the (high-frequency) modulation or pulsation with the variation frequency of at least 50 kHz.The laser device may have a nozzle for supplying a protective gas (cutting or welding gas) to the workpiece. This can have a Laval inner geometry.According to a development of the laser device, the laser device can be configured such that the laser beam generates a laser spot on the workpiece. The laser spot may have a core region and a ring region. The core region can be circular. The annular region can be of annular configuration. The core portion may be disposed within the ring portion. 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 be, in particular, at most 5% of the laser power.This allows the welding region, in particular the keyhole, to be further stabilized. This can lead to a further reduction of instability (within the keyhole) and to fewer spatters and pores, as well as a constant welding depth.According to a further development of the laser device, the laser device for generating the laser beam and / or the laser spot 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 μm (micrometers), in particular of at most 20 μm, preferably of at most 10 μm (for example in the case of basic mode or single mode). Alternatively, the core region of the fiber can have a larger outer diameter, in particular of at least 50 μm or 100 μm (for example in the case of multimode). Alternatively or additionally, the ring region can have an outer diameter of 200 μm or 400 μm. The core portion may be disposed within the ring portion. 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 (cladding). The cladding may be disposed between the core portion and the ring portion. The cladding may have a thickness of at most 10 μm.This allows the welding region, in particular the keyhole, to be further stabilized. This can lead to a further reduction of instability (within the keyhole) and to fewer spatters and pores, as well as a constant welding depth.According to a development of the laser device, the laser device can be configured such that at least two laser beams are generated and focused on the workpiece. In particular, at least four laser beams can be generated and focused onto the workpiece. In particular, all laser beams can each be identical. Accordingly, all laser spots generated by the respective laser beams on the workpiece can also be configured identically in each case. To generate a plurality of laser beams, the laser device can comprise an optical element for beam splitting, in particular a wedge splitter.This allows the welding region, in particular the keyhole, to be further stabilized. This can lead to a further reduction of instability (within the keyhole) and to fewer spatters and pores, as well as a constant welding depth.According to a further development of the laser device, the laser device can comprise a scanner optics for moving the laser beam over the workpiece. The scanner optics may have an imaging ratio in a range of 1:1 to 5:1, preferably 1.9:1 or 3.4:1.As a result, the laser beam can be optimally focused on the workpiece and / or moved over the workpiece with simple means.According to a further development of the laser device, the laser device can comprise an optical sensor for detecting the position of the laser beam and / or of the workpiece. The optical sensor can be designed as a camera-based sensor or as a camera. It is likewise conceivable that the optical sensor can be designed as an interferometer-based sensor system. The laser beam and the optical sensor may be calibrated to each other.This allows position control of the laser beam and / or of the workpiece to be implemented using simple means. As a result, the machining, in particular the laser welding, of the workpiece can be implemented as accurately as possible.The above object is further achieved by a method for machining at least one workpiece having the features of the subordinate claim. The machining may be laser welding. The method comprises the steps of:providing the workpiece. The workpiece can be formed from metal, in particular aluminum and / or copper. The workpiece can have a viscosity of at most 5 mPa*s (millipascal*s) in the molten state (at melting temperature). The workpiece can have a thickness of at most 4 mm.generating and focusing at least one laser beam having an output power on the workpiece.varying, in particular pulsing or modulating, the laser beam with a variation frequency of at least 50 kHz, a variation amplitude of at least 10% of the output power and a rise time and / or fall time of the variation amplitude of at most 10 μs (microseconds). The variation amplitude may be both positive and negative. In other words, the output power may be increased periodically (at positive variation amplitude) and / or reduced (at negative variation amplitude).This makes it possible to achieve (additional) stabilization of the keyhole, in particular in workpieces having a lower viscosity, as a result of which the sprays and pores can be removed and a welding depth which is as continuous as possible can be achieved. The instabilities of the keyhole can be avoided or at least reduced in particular by the steam rate and the steam pressure being increased and reduced rapidly enough so that a collapsing of the keyhole can be avoided. In other words, the keyhole can be stabilized by specifically influencing the vapor pressure (or the vapor rate), which can lead to fewer spatters, pores and a constant welding depth.The method may comprise the step of:supplying a protective gas (cutting gas or welding gas) to the workpiece, in particular into the region of machining the workpiece. This can be implemented by means of a nozzle, in particular with a Laval inner geometry.According to a development of the method, the method can comprise the step:moving the laser beam and / or the workpiece to produce a feed of the laser beam produced on the workpiece. In this case, the laser beam can be moved over the workpiece by means of a scanner optics. The movement of the laser beam and / or of the workpiece can be a relative movement between the laser beam and the workpiece. In other words, either the laser beam or the workpiece, or both, may be moved.In this way, a continuous machining of the workpiece, for example a weld seam, can be produced with simple means.According to a development of the method, the method can comprise the step:determining a position of the laser beam and / or of the workpiece. This can be implemented by means of an optical sensor.Possible readjustment of a machining position of the laser beam and / or of the workpiece.As a result, position control and, in the event of a deviation, corresponding readjustment of the laser beam and / or of the workpiece can be implemented using simple means.According to a development of the method, a laser device according to the above explanations can be used to carry out the method.With regard to the advantages which can be achieved thereby, reference is made to the relevant explanations relating to the laser device. For a further embodiment of the method, the measures described in connection with the laser device and / or the measures explained below can be used.Further features, details and advantages of the invention are evident from the wording of the claims and from the following description of an exemplary embodiment on the basis of the drawings. The following are shown: FIG. 1 shows a schematic illustration of a laser device for machining at least one workpiece; FIG. 2 shows a schematic diagram of a power profile of a CW laser of the laser device according to FIG. 1.In the following description and in the figures, corresponding components and elements bear the same reference numerals.FIG. 1 schematically illustrates a laser device 10 for machining at least one workpiece 12 by means of at least one laser beam 14. In the present case, the machining is laser welding.The laser device 10 is configured to generate the laser beam 14 with an output power 16 (cf. FIG. 2 ) and to focus it on the workpiece 12. The laser device 10 is further configured to vary the output power 16 of the laser beam 14 with a variation frequency of at least 50 kHz and a variation amplitude 18 of at least 10% of the output power 16. The laser device 10 is configured such that a rise time 20 and / or a fall time 22 of the variation amplitude 18 is a maximum of 10 μs.The laser device 10 can comprise a CW laser for generating the laser beam 14. The laser device 10 can be configured such that the laser beam 14 is modulated with a modulation frequency and a modulation amplitude. In this case, the modulation frequency can correspond to the variation frequency and the modulation amplitude can correspond to the variation amplitude 18. The CW laser may have an average power of at least 1 kW, in particular of at least 4 kW.The laser device 10 comprises a scanner optics 24 for moving the laser beam 14 over the workpiece 12.The laser device 10 in the present case additionally comprises an optical sensor 26 for detecting the position of the laser beam 14 and / or of the workpiece 12.The laser device 10 can be configured such that the laser beam 14 generates a laser spot on the workpiece 12, wherein the laser spot can have an, in particular circular, core region. The laser spot can have an, in particular ring-shaped, ring region. In this case, 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 beam 14 and / or the laser spot, the laser device 10 can comprise a fiber. The fiber may include a core portion and a ring portion. The core portion may be disposed within the ring portion. The core region may have an outer diameter of 50 μm or 100 μm. The ring region may have an outer diameter of 200 μm or 400 μm.The laser device 10 can be configured such that at least two, in particular at least four, laser beams 14 are generated and focused on the workpiece 12. In this case, all laser beams 14 (or the laser spots generated by the respective laser beams 14) can each be configured identically.FIG. 2 shows a schematic diagram of a power profile of the CW laser of the laser device 10 according to FIG. 1.In the diagram shown, a power 28 of the CW laser of the laser device 10 is plotted in watts over time 30 in seconds. In other words, the time 30 is shown in seconds on the x-axis and the power 28 is shown in watts on the y-axis.The power 28 of the CW laser is modulated in the present 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). Thus, the output power 16 of the CW laser is changed by the modulation amplitude or the variation amplitude 18 at regular intervals of at most 20 μs (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 at most 20 μs and increased again to the value of the output power 16. In the present case, the variation amplitude is greater than 10% and less than 100% of the output power 16.The rise time 20 is the time required to increase the CW laser power 28 from a minimum value to a maximum value (presently the output power value 16). Accordingly, the decay time 22 is the time required to reduce the power 28 of the CW laser from the maximum value to the minimum value. The rise time 20 and the fall time 22 are in the present case in each case at most 10 μs.A method for machining, in particular laser welding, at least one workpiece 12 is described below with reference to FIGS. 1 and 2. The method comprises the steps of:Providing the workpiece 12. The workpiece 12 can have a viscosity of at most 5 mPa*s in the molten state.generating and focusing at least one laser beam 14 having an output power 16 onto the workpiece 12.varying, in particular pulsing or modulating, the laser beam 14 with a variation frequency of at least 50 kHz, a variation amplitude 18 of at least 10% of the output power 16 and a rise time 20 and / or a fall time 22 of the variation amplitude 18 of at most 10 μs.The method may comprise the step of:moving the laser beam 14 and / or the workpiece 12 to produce a feed of the laser beam 14 focused on the workpiece 12.The method may further comprise the step of:Ascertaining the position of the laser beam 14 and / or of the workpiece 12 This can be implemented by means of an optical sensor 26.To carry out the method, a laser device 10 according to the above explanations, in particular the laser device 10 shown in FIG. 1, can be used.

Claims

Laser device (10) for machining, in particular laser welding, at least one workpiece (12) by means of at least one laser beam (14), wherein the laser device (10) is configured to generate the laser beam (14) with an output power (16), focus it onto the workpiece (12) and vary the output power (16) of the laser beam (14) with a variation frequency of at least 50 kHz and a variation amplitude (18) of at least 10% of the output power (16), wherein the laser device (10) is configured such that a rise time (20) and / or a fall time (22) of the variation amplitude (18) is a maximum of 10 μs.The laser device (10) according to claim 1, characterized in that the laser device (10) for generating the laser beam (14) comprises a CW laser, wherein the laser device (10) is configured such that the laser beam (14) is modulated 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.Laser device (10) according to Claim 1 or 2, characterized in that the laser device (10) is configured in such a way that the laser beam (14) generates a laser spot on the workpiece (12), wherein the laser spot has an, in particular circular, core region and an, 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.Laser device (10) according to the preceding claim, characterized in that the laser device (10) for generating the laser beam (14) and / or the laser spot comprises a fiber having a core region and a ring region.Laser device (10) according to one of the preceding claims, characterized in that the laser device (10) is configured such that at least two, in particular at least four, laser beams (14) are generated and focused on the workpiece (12), in particular wherein all laser beams (14) are each identically configured.Laser device (10) according to one of the preceding claims, characterized in that the laser device (10) comprises a scanner optical unit (24) for moving the laser beam (14) over the workpiece (12), in particular wherein the scanner optical unit (24) has an imaging ratio in a range from 1:1 to 5:1, preferably of 1.9:1 or 3.4:1.Laser device (10) according to one of the preceding claims, characterized in that the laser device (10) comprises an optical sensor (26) for detecting the position of the laser beam (14) and / or of the workpiece (12).Method for machining, in particular laser welding, at least one workpiece (12), comprising the steps: - providing the workpiece (12), in particular wherein the workpiece (12) is formed from 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 one laser beam (14) with an output power (16) onto the workpiece (12); - varying, in particular pulsing or modulating, the laser beam (14) with a variation frequency of at least 50 kHz, a variation amplitude (18) of at least 10% of the output power (16) and a rise time (20) and / or a fall time (22) of the variation amplitude (18) of at most 10 μs.Method according to claim 8, characterized in that the method comprises the step of: - moving the laser beam (14) and / or the workpiece (12) in order to generate a feed of the laser beam (14) focused on the workpiece (12).Method according to Claim 8 or 9, characterized in that the method comprises the step of: - determining a position of the laser beam (14) and / or of the workpiece (12), in particular by means of an optical sensor (26), and - optionally readjustment of a machining position of the laser beam (14) and / or of the workpiece (12).Method according to one of Claims 8 to 10, characterized in that a laser device (10) according to one of Claims 1 to 7 is used to carry out the method.

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