Method and apparatus for laser cutting with a laser beam guided in a multicore optical fiber and related computer program product

Abstract

In a method for laser processing of a workpiece (2) by means of at least one laser beam (3), particularly for laser cutting, the at least one laser beam is guided in a multi-core optical fiber (5) in a direction toward the workpiece (2), the multi-core optical fiber having a plurality of, particularly at least three, fiber cores (6) arranged in parallel along a straight line (A), the number of fiber cores (6) into which the at least one laser beam (3) is coupled and / or the distribution of the laser power of the at least one laser beam (3) to the fiber cores (6) is determined according to the workpiece characteristics or processing parameters according to the invention.

Description

Technical Field

[0001] The present invention relates to a method and apparatus for laser processing, particularly laser cutting, of a workpiece by means of at least one laser beam, and related computer program products, wherein the laser beam is guided in a multi-core optical fiber in a direction toward the workpiece, the multi-core optical fiber having a plurality of, particularly at least three, optical fiber cores arranged in parallel along a straight line. Background Technology

[0002] Such methods and such devices are known, for example, from US 2018 / 0217408 A1.

[0003] One possibility for improving process efficiency and edge quality in laser cutting is to shape the intensity profile of the focused beam, for example, in the form of a line oriented along the feed direction or multiple sub-beams staggered from each other on the focal plane.

[0004] As known from US 2018 / 0217408 A1 and WO 2014 / 060091 A1, during cutting or welding, a transmission fiber with two linearly staggered fiber cores of different diameters is used between the laser and the processing head of the laser machine. The (sub)beams emitted from each fiber core are imaged on the workpiece at multiple focal points (multi-spots) by optical elements in the processing head.

[0005] Multi-core optical fibers with ring-shaped cores of different diameters are known from DE 10 2015 010 892 A1 and US 2018 / 0185960 A1. US 2018 / 0185960 A1 proposes superimposing beams emanating from different fiber cores and imaging them together in a "single spot" on the workpiece, or rotating the beams using a Dove prism and thus matching the beam profile to the processing direction.

[0006] As is known from WO 2016 / 025701 A1, a “Mickey Maus” beam profile is generated using parallel optical fibers with different core diameters.

[0007] DE 203 08 097 U1 and US 10,401,562 B2 illustrate apparatus for laser material processing, which has an optical fiber having multiple fiber cores arranged one-dimensionally as lines or two-dimensionally as fields in a transmission fiber. During material processing, a laser beam can be dynamically, i.e., time-varyingly, coupled to the individual fiber cores, resulting in a scanning motion of the coupled beam.

[0008] It is known from JP 2003290965 A that a laser beam can be transmitted to a processing head using an optical fiber bundle. The individual optical fibers are arranged in parallel and have fiber ends staggered in the z-direction. Therefore, multiple horizontally and vertically staggered beam focal points can be generated in the workpiece. Summary of the Invention

[0009] In contrast, the objective of this invention is to improve the method of the type described at the outset so that the beam profile of the laser beam can be matched particularly well to the laser cutting of metal workpieces, and to provide an apparatus suitable for performing the method.

[0010] In the case of the method mentioned at the outset, this task is accomplished according to the invention in the following manner: the number of fiber cores to which the at least one laser beam is coupled and / or the distribution of the laser power of the at least one laser beam to the fiber cores are set according to workpiece characteristics (e.g., thickness, material, surface condition, etc.) or processing parameters (e.g., feed rate, laser power, cutting profile, laser wavelength, process gas, etc.). Preferably, the at least one laser beam is coupled to multiple fiber cores to generate multiple output laser beams emanating from the multi-core fiber, the beam axes of which extend in a plane and are arranged in a straight line on the workpiece, and during laser processing, the straight line of these output laser beams rotates in the directions in which the laser beams move on the workpiece.

[0011] The distribution of at least one laser beam to different fiber cores can be accomplished, for example, by wedges arranged successively in the beam path of the input laser beam, as described in WO 2011 / 124671A1 ( Figure 3 As shown in [reference needed]. Alternatively, different modules of a fiber laser can be spliced ​​together using a single transmission fiber (“feed fiber”) to form the fiber core of a multi-core fiber, as illustrated in, for example, WO 2014 / 118516A1. According to the invention, a single laser beam can be coupled into the fiber core after corresponding beam splitting, or multiple, particularly different, laser beams can be coupled into the fiber core.

[0012] For example, the number of fiber cores to which laser radiation is coupled can be varied according to the workpiece thickness. As recognized by the invention, in order to improve the productivity and cutting quality of the cutting process, the length of the line formed by the individual (sub)laser beams must be variable to match the workpiece thickness. Here, the aim is to achieve maximum absorption of the laser beam across the entire inclined cutting front. The distribution of laser power in the fiber cores can also be varied according to the workpiece thickness. With increasing workpiece thickness, the laser power of the at least one laser beam is preferably coupled to an increasing number of fiber cores, and increasingly to the outermost fiber cores along the line.

[0013] In a preferred variant of the method, all fiber cores have the same diameter and are arranged with the smallest possible spacing between them (e.g., 10 μm). Each fiber core produces a separate focal point (spot) in the image region using conventional imaging optics (collimating and focusing lenses or zoom telescopes) in the processing head. By coupling laser radiation with a variable power distribution to each fiber core, a matched intensity distribution composed of combinations of single spots can be set in the image region, for example, in the form of a line approximated by single spots. Through flexible coupling, the resulting intensity profile is matched to the workpiece thickness: when coupled individually to the central core (e.g., with a diameter of 100 μm), a single focal point is obtained on the workpiece. This is advantageous for cutting thin workpieces with a maximum thickness of 6 mm. If the laser radiation is distributed across multiple fiber cores, a linear, non-rotationally symmetric beam profile is produced, which must be simultaneously rotated in the cutting unit corresponding to the feed direction, for example, by a combination of Dove prisms or cylindrical lenses. Within a medium workpiece thickness range of 8-12 mm, by coupling laser radiation into three fiber cores, each with a diameter of 100 μm, and subsequently imaging the output laser beams 2:1 onto the workpiece, a line length of approximately 650 μm is obtained in the focusing region of the sub-beams emanating from the fiber cores. For workpiece thicknesses greater than 12 mm, it is advantageous to distribute the laser beams to five fiber cores to further increase the line length. Here, the laser power is preferably distributed to these fiber cores such that, for workpiece thicknesses d starting from 8 mm, the laser power coupled to the middle fiber core is less than the laser power coupled to one or more outer fiber cores. Experiments using three collinearly arranged focal points with a power distribution of 40:20:40 have shown a significant increase in feed rate (orders of magnitude +60%) when cutting stainless steel. A power distribution of 50:30:20 is also advantageous because less further heat input is required behind and below in the cutting gap, as the melt itself already transfers heat downwards.

[0014] In another preferred variation of the method, at least some, and in particular all, of these fiber cores have different diameters. As the diameter of the fiber core decreases along this straight line in one direction, the multi-core fiber can be rotated simultaneously during laser cutting, causing the core diameter to decrease or increase in the opposite direction to the cutting direction. Particularly preferably, laser radiation is coupled to the different fiber cores with the same power.

[0015] For example, if the diameter of the fiber core decreases in the opposite direction to the cutting direction, such as 150 / 100 / 75 / 50 μm, the system can be designed such that when all sub-beams are focused on the upper side of the workpiece, the diameters of all sub-beams are approximately the same at the irradiation point on the inclined cutting front. Thus, the cutting gap wall extends vertically and does not have curvature caused by beam caustics. Furthermore, when cutting thicker workpieces, a larger cutting gap width is desirable to allow for better gas coupling into the cutting gap, better melt discharge, and better removal of the cut portion from the remaining workpiece. Therefore, in the case of thinner workpieces, laser power is coupled only to the smallest or two smallest fiber cores, while in the case of thicker workpieces, laser power is also coupled to fiber cores with larger diameters.

[0016] A variant in which the fiber core diameter increases in the opposite direction to the cutting direction can also have a beneficial effect on the cutting quality. For example, if the fiber core diameter increases in the opposite direction to the cutting direction, such as 100 / 150 / 200 / 250 μm, the cutting gap is gradually widened in this way. Each sub-beam completely cuts through the workpiece, and only a small amount of melt is generated therein, which flows downward in a laminar manner. The cut edge thus formed has only low edge roughness; however, in this variant of the method, the maximum possible cutting speed is lower.

[0017] Preferably, laser beams with different beam divergences are coupled into fiber cores of different diameters, for example, using lenses with different coupling focal lengths. This minimizes beam quality degradation when coupling to a larger fiber core. For example, if coupled to a 50 μm core at 100 mrad, it should be coupled to a 75 μm core at 67 mrad. Thus, the product of the beam parameters in both cores is the same. For even larger fiber cores, some degree of beam quality degradation must be accepted; otherwise, the required coupling divergence would be too small. However, this has only a negligible effect on cutting quality because the larger spot size at the workpiece surface is absorbed, and divergence does not play a major role here.

[0018] Preferably, different modes of varying beam quality from the at least one laser beam are coupled into different fiber cores, particularly into fiber cores with different diameters. For example, if the beam quality of the laser beam to be coupled actually requires a minimum fiber diameter of 100 μm, then the lower-order modes (i.e., those with significantly better beam quality) contained in the laser beam are coupled into fiber cores with a diameter <100 μm. The remaining power from the higher-order modes is deflected into fibers with a diameter of at least 100 μm. Different modes can also be coupled into fiber cores of the same diameter, thereby resulting in corresponding output laser beams with different beam qualities.

[0019] The present invention also relates to an apparatus for laser processing, particularly laser cutting, of a workpiece by means of at least one laser beam, the apparatus comprising: a multi-core optical fiber having a plurality, particularly at least three, fiber cores arranged in parallel along a straight line for guiding the at least one laser beam in a direction toward the workpiece; a coupling device for coupling the at least one laser beam to one or more of the fiber cores and / or variably distributing the laser power of the at least one laser beam to the fiber cores; and a machine control device programmed to implement the methods of the variants described above.

[0020] The multiple fiber cores can have the same diameter or different diameters, which in particular decrease in one direction along a straight line.

[0021] In a preferred embodiment, the fiber ends on the emitting side of the plurality of fiber cores can be staggered relative to each other in the longitudinal direction of the fiber, such that the focal points of the sub-beams emanating from these fiber cores are horizontally and vertically staggered relative to each other at the workpiece. Due to the staggered fiber ends, the individual laser beams are not focused into the same plane. The smaller the distance between the fiber ends and the collimating lens in the processing head, the deeper the corresponding focal point. Thus, the focal point position can be staggered corresponding to the cutting front edge tilt, so that the maximum intensity of the sub-beams acts directly on the workpiece at the position of the cutting front edge, thereby increasing the cutting speed.

[0022] Advantageously, a reclassifying optics device can be arranged in front of a multi-core fiber. This reclassifying optics "reclassifies" different modes of varying beam quality from at least one laser beam into different fiber cores, particularly into fiber cores with different diameters. Lower-order modes (i.e., those with significantly better beam quality) contained in the laser beam are selectively coupled into smaller-diameter fiber cores. This can be achieved, for example, by using a partitioned lens with concentrically arranged regions that have different inclinations relative to the beam axis of the laser beam. As the laser beam passes through the partitioned lens, the sub-regions of the input laser beam are deflected differently onto different cores of the fiber.

[0023] Preferably, the laser processing equipment has a processing head that is particularly movable relative to the workpiece, and at least the fiber end on the emitting side of the fiber core is fastened to the processing head.

[0024] Finally, the present invention also relates to a computer program product having code units that, when run on the machine control device of a laser processing machine, match all steps for performing the method according to the present invention.

[0025] Other advantages and advantageous designs of the subject matter of this invention can be derived from the specification, drawings, and claims. The features detailed above and below can also be applied individually or in any combination. The illustrated and described embodiments should not be construed as an exhaustive enumeration, but rather as exemplary features for the purpose of describing the invention. Attached Figure Description

[0026] In the attached diagram:

[0027] Figure 1 A laser processing machine according to the present invention, having a multi-core optical fiber, is schematically shown;

[0028] Figure 2 The geometric relationship between the cutting front edge, workpiece thickness, and linear length of the laser beam generated by the linear laser beam is shown.

[0029] Figure 3 This shows the relationship between the absorptivity of solid-state laser radiation in steel and the cutting front angle;

[0030] Figures 4a to 4e This illustrates a multi-core optical fiber with five fiber cores. Figure 4a These fiber cores each have the same diameter, and the power distribution of the fiber cores varies with different workpiece thicknesses. Figures 4b to 4e );

[0031] Figures 5a to 5c The cross-section of a multi-core optical fiber with four fiber cores is shown. Figure 5a These fiber cores each have a gradually decreasing core diameter, and the orientation of multi-core fibers with core diameters decreasing in the opposite direction to the cutting direction is as follows: Figure 5b ), and the inclined cutting front of the output laser beam with four fiber cores ( Figure 5c );

[0032] Figure 6a , Figure 6b The cross-section of a multi-core optical fiber with four fiber cores is shown. Figure 6a These fiber cores each have a gradually increasing core diameter, and the orientation of a multi-core fiber with a core diameter increasing in the opposite direction to the cutting direction is shown. Figure 6b );

[0033] Figures 7a to 7c The cross-section of a multi-core optical fiber with five fiber cores is shown. Figure 7a The fiber ends on the output side are staggered from each other in the longitudinal direction of the fiber. Figure 7b ), and the inclined cutting front of the output laser beam with five fiber cores ( Figure 7c );

[0034] Figure 8a , Figure 8b This illustrates a multi-core optical fiber with four fiber cores, the core diameter decreasing in the opposite direction to the cutting direction, and the fiber ends on the output side arranged staggered from each other in the longitudinal direction of the fiber. Figure 8a ), and the inclined cutting front of the output laser beam with four fiber cores ( Figure 8b );as well as

[0035] Figure 9 This invention illustrates a reclassification optics device for reclassifying the patterns of laser beams directed at the fiber cores of a multi-core optical fiber. Detailed Implementation

[0036] exist Figure 1 The device 1 shown is used for laser cutting of workpiece 2 by means of at least one laser beam 3, the device comprising:

[0037] -Laser beam generator 4 used to generate laser beam 3;

[0038] - Multi-core optical fiber 5, which has a plurality of fiber cores 6 arranged in parallel along a straight line A, which are used to guide the at least one laser beam 3 in the direction toward the workpiece 2.

[0039] -Coupled optics 7, which couples the laser beam 3 to one or more of the fiber cores 6 to generate one or more output laser beams 8 emanating from the multi-core fiber, the beam axis of which extends in a plane and is arranged on a straight line 13 on the workpiece surface, and the laser power of the laser beam 3 can be variably distributed to the fiber cores 6.

[0040] - A processing head 9, with a multi-core optical fiber 5 fastened thereto, and optical elements (e.g., collimating lens 11a and focusing lens 11b) arranged within the processing head for imaging the output laser beam 8 onto the workpiece 2, wherein the workpiece 2 and the processing head 9 can move relative to each other to cause the output laser beam 8 to move on the workpiece 2 along the feed direction or cutting direction v, and

[0041] - Machine control device 10, which controls laser beam generator 4 and coupling optics 7.

[0042] The multi-core optical fiber 5 can be formed from a single optical fiber having multiple fiber cores 6 and a common cladding, or alternatively constructed from multiple single optical fibers, each having a fiber core with its own cladding.

[0043] The distribution of the laser beam 3 to different fiber cores 3 can be achieved, for example, by wedges arranged sequentially in the beam path of the laser beam 3, as described in WO 2011 / 124671 A1. Figure 3As shown in [reference needed]. Alternatively, different modules of the fiber laser can be spliced ​​together from individual transmission fibers (“feed fibers”) to form the fiber core of a multi-core fiber 5, as illustrated in, for example, WO 2014 / 118516 A1. Each output laser beam 8 produces a separate focal point (single spot) 12 in the image region through imaging optics (collimating lens and focusing lens or zoom telescope) 11a, 11b located in the processing head 8.

[0044] According to the present invention, it has been recognized that, in order to improve the productivity and cutting quality of the cutting process, the length L of the line 13 formed by the individual output laser beams 8 must be variable in order to match the workpiece thickness d. Here, the objective is to achieve maximum absorption of the laser beam across the entire cutting front. Figure 2 As shown, in the case of a cutting front 14 inclined at a cutting front angle α, the applicable relationship between the thickness d of the workpiece 2 to be cut and the required length L of the laser line 13 is: L = d / tan(α). Figure 3 As shown, for cutting steel using a solid-state laser, the maximum absorptivity A = 45% is obtained for a cutting front angle α = 79°. For this cutting front angle α of 79°, the required length L of the laser line 13 is: L = d / tan(79°) = 0.2d. That is, when the workpiece 2 is 10mm thick, the length L should be 2mm, which is too long in practice. Conversely, if α = 85° is chosen, the absorptivity A is reduced by only 5 percentage points to A = 40%. When L = 0.09d, the required line length for this cutting front angle is significantly shorter, i.e., 900μm for a 10mm thick workpiece.

[0045] Figure 4a The multi-core fiber 5 shown has five fiber cores 6, each with the same diameter (e.g., 100 μm), linearly arranged in line A. These fiber cores are arranged with the smallest possible spacing (e.g., 10 μm) between them. By coupling one or more laser beams 3 with variable power distribution to each fiber core 6, a matched intensity distribution composed of single beams 12 can be set in the image region, for example, in the form of a line 13 approximated by single beams 12. Through flexible coupling, the resulting intensity profile matches the workpiece thickness d. When coupled only to the central fiber core 6, a single beam 12 is obtained on the workpiece 2. Figure 4bThis is advantageous for cutting thinner workpieces 2 with a maximum thickness d of 6 mm. If the laser beam 3 is distributed onto multiple fiber cores 6, a line 13 with three single spots 12 is produced, i.e., a linear, non-rotationally symmetric beam profile, which must be rotated simultaneously in the machining head 9, for example by a combination of Dove prisms (e.g., shown in US 2018 / 0185960 A1) or cylindrical lenses, corresponding to the feed direction v. In the medium workpiece thickness range of 8-12 mm, a line length in the range of 640 μm is obtained by coupling the input laser beam into the three fiber cores 6 and subsequently imaging the output laser beam 8 onto the workpiece 2 at a 2:1 ratio in the focal plane of the output laser beam 8. Figure 4c , Figure 4d Considering the divergence of each output laser beam 8 and the resulting widening of the last output laser beam 8 along the feed direction up to the bottom of the plate, an effective line length L within a range of 900 μm is obtained. When the workpiece thickness d is greater than 12 mm, it is advantageous to distribute the laser beam 3 to five fiber cores (…). Figure 4e For example, a power distribution of 30:15:10:15:30 is used to further increase the line length L. Here, the laser power is preferably distributed to the fiber cores 6 such that, for workpiece thicknesses d starting from 8 mm, the laser power coupled to the middle fiber core 6 is less than the laser power coupled to one or more outer fiber cores 6. Therefore, as the workpiece thickness d increases, the laser power is distributed to an increasing number of fiber cores 6, and increasingly coupled to the outer fiber cores 6 along line A. Three single beams 12 with a power distribution of 40:20:40 are used. Figure 4c Experiments have shown a significant increase in feed rate (orders of magnitude +60%) when cutting stainless steel. The power distribution is 50:30:20. Figure 4d It is also advantageous because less heat input is required further back in the cutting direction v and further down in the beam direction within the cutting gap, since the melt itself has already transferred heat downwards.

[0046] Figure 5a The multi-core optical fiber 5 shown has four fiber cores 6 linearly arranged in line A, the core diameters of which (e.g., 150 / 100 / 75 / 50 μm) decrease in one direction along line A. Here, laser radiation can be coupled to each of the four fiber cores 6 with the same power, for example. Figure 5b In this configuration, the multi-core fiber 5 is oriented as follows, such that the core diameter or single light spot 12 decreases in the opposite direction to the cutting direction v. For example... Figure 5cAs shown, the system can be designed such that when all output laser beams 8 are focused onto the upper side of the workpiece, the diameters of all output laser beams 8 are nearly identical at the irradiation point on the inclined cutting front 14. Thus, the cutting gap wall extends vertically and does not have curvature caused by beam caustics. Furthermore, when cutting a workpiece 2 with a large workpiece thickness d, a larger cutting gap width is desirable to allow for better coupling of gas into the cutting gap, better molten metal discharge, and better removal of the cut portion from the remaining workpiece. Therefore, when the workpiece thickness d is small, the laser power is advantageously coupled only to the smallest or the two smallest fiber cores 6, while when the workpiece thickness is large, the laser power can also be coupled to fiber cores 6 with larger diameters.

[0047] Preferably, the beams are coupled into the individual fiber cores 6 with different beam divergences, for example, through lenses with different coupling focal lengths. This minimizes beam quality degradation when coupling into larger fiber cores 6. For example, if 100 mrad is used to couple into a 50 μm fiber core, then 67 mrad should be used to couple into a 75 μm fiber core. Thus, the product of the beam parameters in the two fiber cores is the same. For larger fiber cores, some degree of beam quality degradation must be accepted; otherwise, the required divergence would be too small. However, this has only a negligible effect on the cutting quality because the larger single beam spot 12 at the workpiece surface is absorbed, and divergence does not play a major role here.

[0048] Figure 6a The multi-core optical fiber 5 shown has four fiber cores 6 linearly arranged in line A, the core diameters of which (e.g., 100 / 150 / 200 / 250 μm) decrease in one direction along line A. Figure 6b In this method, the multi-core fiber 5 is oriented such that the core diameter or single spot 12 increases in the opposite direction to the cutting direction v. In this way, the cutting gap gradually widens in the cutting direction v, which has a favorable effect on the cutting quality. Each output laser beam 8 completely cuts through the workpiece 2, and each produces only a small amount of melt, which flows downwards in a laminar manner. The resulting cut edge has only low edge roughness; however, in this variation of the method, the maximum possible cutting speed is relatively low.

[0049] like Figures 7a to 7cAs shown, the fiber ends 15 on the output side of the fiber core 6 can be arranged offset from each other in the longitudinal direction of the fiber, such that the foci 12 of the output laser beams 8 emerging from the fiber core 6 are horizontally offset from each other in the cutting direction v in the workpiece 2 and vertically offset from each other in the radiation direction. Due to the offset of the fiber ends 15, the individual output laser beams 8 are not focused into the same plane. The smaller the distance between the fiber end 15 and the collimating lens in the processing head 9, the deeper the corresponding focus 12. Thus, the foci 12 can be offset in depth corresponding to the inclination of the cutting front, such that the maximum intensity of the output laser beams 8 acts directly on the workpiece 2 at the location of the inclined cutting front 12 respectively and the cutting speed v can be increased. In the case of the same diameter of the fiber core 6, the output laser beam 8 at the rear in the cutting direction v does not completely pass through the cutting gap generated by the previous output laser beam 8, so that a relatively large amount of power has been absorbed at the upper side of the workpiece. This effect is avoided when the rear output laser beam 8 has an increasingly smaller beam diameter. Therefore, it is advantageous that the diameter of the fiber core 6 decreases in the opposite direction to the cutting direction v( Figure 8a , Figure 8b ). As described above, it is preferred to change the coupling divergence of the output laser beam 8 such that the beam parameter product in all fiber cores 6 is the same and thus the beam quality remains unchanged.

[0050] The beam quality of the laser beam 3 can be "reclassified" when the laser beam 3 is distributed to different fiber cores 6, i.e., the low-order (i.e., having significantly better beam quality) modes contained in the laser beam 3 are specifically coupled into the fiber core 6, which generate points further back in the feed direction, to improve their depth influence in the cutting gap. This can be achieved, for example, by Figure 9 a reclassification optical device 16 designed as a partition lens in, which has concentrically arranged regions that have different inclinations relative to the beam axis of the laser beam 3. When passing through the partition lens 16, sub-regions of the laser beam 3 are deflected differently onto different fiber cores 6. For example, if the beam quality SPP0 of the laser beam 3 used actually requires a minimum fiber diameter of 100 μm at a fixed coupling divergence, the low-order (i.e., having a smaller diameter and significantly better beam quality SPP < SPP0) modes contained in the laser beam 3 are coupled into the fiber core 6 with a diameter < 100 μm without significantly increasing the coupling divergence. The remaining power portion of the higher-order modes is deflected onto the fiber core 6 with a diameter of at least 100 μm. Since spots are generated further forward in the feed direction and these spots are absorbed further above the cutting front, the increase in beam divergence plays a minor role at these spots.

[0051] Because the power portion with better beam quality and lower divergence can be coupled into the fiber core 6 located further back in the feed direction, a "finer" output laser beam 8 with lower divergence is also obtained after the multi-core fiber 5. The aim here is that all the output laser beams 8 are focused onto the upper side of the workpiece using the same imaging optics 11a, 11b in the processing head 9, while still ensuring that, on the one hand, the beam diameter does not exceed a defined size (e.g., 400 μm) on the inclined cutting front 14, and on the other hand, that the individual beam located further back in the feed direction has not been (partially) absorbed at the upper side of the plate. This can also be achieved at deeper locations in the workpiece 2, i.e., for larger workpiece thicknesses d, due to the finer output laser beams 8 with lower divergence. With these variations of the method, the formation of burrs on the cut edge is significantly reduced while keeping the cutting speed v constant (i.e., keeping the productivity constant).

[0052] Instead of determining the laser beam 3 based on the workpiece thickness d as described above, the number of fiber cores 6 coupled to the laser beam 3 and / or the distribution of the laser power of the laser beam 3 to the fiber cores 6 can be determined based on other workpiece characteristics such as material, surface condition, or processing parameters such as feed rate, laser power, cutting profile, laser wavelength, process gas, etc.

[0053] Instead of distributing a single laser beam to each fiber core 6 by means of a beam splitter as described above, it is also possible to couple multiple different laser beams 3, each with a different laser power, into each fiber core 6.

Claims

1. A method for laser cutting a workpiece (2) by means of at least one laser beam (3), the at least one laser beam being guided in a multi-core optical fiber (5) in a direction toward the workpiece (2), the multi-core optical fiber having a plurality of fiber cores (6) arranged in parallel along a straight line (A). Its features are, The at least one laser beam (3) is coupled to multiple fiber cores in the fiber core (6) to generate multiple output laser beams (8) emanating from the multi-core fiber (5). The beam axes of the multiple output laser beams extend in a plane and are arranged in a straight line along the cutting direction (v) on the workpiece (2). During the laser cutting, the straight line of the output laser beams (8) is rotated to the direction in which the laser beam (3) moves on the workpiece (2). The number of optical fiber cores (6) coupled to the at least one laser beam (3) and / or the distribution of the laser power of the at least one laser beam (3) to the optical fiber cores (6) are determined according to the characteristics of the workpiece. As the workpiece thickness (d) increases, the laser power of the at least one laser beam (3) is distributed to an increasing number of fiber cores (6), and / or as the workpiece thickness (d) increases, the laser power of the at least one laser beam (3) is coupled to an increasing number of fiber cores (6) along the outer edge of the line (A).

2. The method according to claim 1, characterized in that, The multi-core optical fiber has at least three optical fiber cores (6) arranged side by side in parallel along a straight line (A).

3. The method according to claim 1 or 2, characterized in that, Multiple laser beams (3) are coupled into the fiber core (6).

4. The method according to claim 3, characterized in that, The multiple laser beams are different laser beams.

5. The method according to claim 1 or 2, characterized in that, All fiber cores (6) have the same diameter.

6. The method according to claim 1 or 2, characterized in that, At least some of the optical fiber cores (6) have different diameters.

7. The method according to claim 6, characterized in that, All fiber cores (6) have different diameters.

8. The method according to claim 6, characterized in that, The diameter of the optical fiber core (6) decreases in one direction along the straight line (A).

9. The method according to claim 1 or 2, characterized in that, Laser beams (3) with different beam divergence are coupled into fiber cores (6) with different diameters.

10. The method according to claim 1 or 2, characterized in that, Different modes of different beam qualities of the at least one laser beam (3) are coupled into different fiber cores (6).

11. An apparatus (1) for laser cutting a workpiece (2) by means of at least one laser beam (3), the apparatus comprising: A multi-core optical fiber (5) having a plurality of fiber cores (6) arranged in parallel along a straight line (A) for guiding at least one laser beam (3) in a direction toward the workpiece (2). A coupling optics (7) that couples the at least one laser beam (3) to one or more fiber cores in the fiber core (6) and / or variably distributes the laser power of the at least one laser beam (3) to the fiber core (6); and A machine control device (10) is programmed to implement the method according to any one of the preceding claims.

12. The device according to claim 11, characterized in that, The multi-core optical fiber has at least three fiber cores (6) arranged in parallel along a straight line (A).

13. The device according to claim 11 or 12, characterized in that, The plurality of optical fiber cores (6) have the same diameter.

14. The device according to claim 11 or 12, characterized in that, The plurality of optical fiber cores (6) have different diameters.

15. The device according to claim 14, characterized in that, The different diameters decrease in one direction along the straight line (A).

16. The device according to claim 11 or 12, characterized in that, The fiber ends (15) on the emitting side of the plurality of fiber cores (6) are arranged staggered from each other in the longitudinal direction of the fiber.

17. The device according to claim 11 or 12, characterized in that, A reclassification optics (16) is arranged in front of the multi-core optical fiber, which couples different modes of different beam qualities of the at least one laser beam (3) into different fiber cores (6).

18. The device according to claim 11 or 12, characterized in that, At least the fiber end of the fiber core (6) on the emitting side is fastened to the processing head.

19. The device according to claim 18, characterized in that, At least the fiber end of the fiber core (6) on the emitting side is fastened to a processing head (9) that is capable of moving relative to the workpiece (2).

20. A computer program product having code units configured to perform all steps of the method according to any one of claims 1 to 10 when the program is run on a machine control device (10) of a laser processing machine.

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