Laser cutting method and laser cutting equipment

Abstract

The invention relates to a method for laser cutting a workpiece (14) having a thickness (16) of less than 6 mm, wherein a first laser beam (18), a second laser beam (20) and a gas jet are directed onto an incident surface (24) of the workpiece (14), wherein the laser beams (18, 20) at least partially overlap one another on the workpiece (14), wherein the first laser beam (18) has a smaller focal diameter than the second laser beam (20), wherein the beam parameter product of the first laser beam (18) is at most 5 mm*mrad, wherein the power share of the second laser beam (20) in the total laser power is less than 20%, and a cutting seam with a cutting edge of removed material is formed on the incident surface (24) of the workpiece (14). The invention also relates to a laser cutting device (10) for laser cutting a plate-shaped workpiece (14) along a cutting line, the laser cutting device comprising: a laser light source device (28) for superimposing a first laser beam (18) and a second laser beam (20) in a cutting zone (26), wherein the first laser beam (18) has a smaller focal diameter (54) than the second laser beam (20), wherein the beam parameter product of the first laser beam (18) is at most 5 mm*mrad and the power share of the second laser beam (20) in the total laser power is less than 20%; a nozzle (27) for directing a gas jet toward the cutting zone (26); and a moving device (66) for moving the cutting zone (26) along the cutting line relative to the workpiece (14).

Description

Technical Field

[0001] The present invention relates to a method for laser cutting a workpiece having a thickness of less than 6 mm. The present invention also relates to a laser cutting device for laser cutting a plate-like workpiece, in particular a three-dimensionally shaped workpiece, along a three-dimensional cutting line. Background Art

[0002] As the focal point diameter becomes smaller, the feed rate (cutting speed) during laser cutting increases at the same laser power. However, this is subject to limitations: if the focal point is too small, the cut quality becomes unacceptable. Burrs, in particular, can form. This burr formation is caused by the fact that as the kerf becomes smaller, the cutting gas enters less and less, making it impossible to ensure the proper discharge of the melt.

[0003] For these reasons, efforts have been focused in recent years on influencing the beam properties and, in particular, increasing the focal diameter when cutting increasingly thick workpieces with solid-state lasers in order to produce wider cutting kerfs and improve melt drainage.

[0004] Thus, for example, WO 2011124671 A1, WO 2013000942 A1, WO 2014060091A1, US20180188544 A1 or WO 2018104575 A1 describe influencing the beam quality and thus the focusing capability of the solid-state laser beam by coupling the beam into different cores of a multi-core optical fiber in order to be able to cut different workpieces, in particular workpieces with different thicknesses.

[0005] Furthermore, DE 60206184 T2 or JP 2000005892 A proposes, during laser cutting, to split the laser beam into a plurality of partial beams using a transmissive or reflective optical element. These partial beams are focused in the workpiece with a plurality of focal points offset in the beam propagation direction. The goal is also to be able to cut workpieces that are as thick as possible. Summary of the Invention

[0006] The object of the present invention is to provide a laser cutting method for thin workpieces having a thickness of less than 6 mm, which combines a high cutting speed with good cutting quality. Furthermore, the object of the present invention is to provide a laser cutting device for the efficient and economical laser cutting of workpieces having a thickness of less than 6 mm with good cutting quality, which is particularly suitable for cutting three-dimensionally shaped sheet metal.

[0007] According to the invention, this object is achieved by the method and the laser cutting device according to the invention. The invention also provides advantageous variants or embodiments.

[0008] According to the present invention, a method for laser cutting a workpiece having a thickness of less than 6 mm is provided. Workpieces having this thickness are typically cut using 3D laser cutting equipment and are used, for example, in vehicle body construction. The workpiece is preferably cut along a three-dimensionally extending cutting line. Laser cutting is preferably achieved by laser melting cutting. In laser melting cutting, the material of the workpiece is melted to form a cutting seam and blown out of the cutting seam in liquid form. The workpiece can be a sheet material, in particular a three-dimensionally formed sheet material. The workpiece is preferably composed of a metallic and / or electrically conductive material. The method according to the present invention is preferably implemented using the laser cutting equipment according to the present invention described below.

[0009] In the laser cutting method according to the present invention, a first laser beam, a second laser beam and a gas jet are directed toward the incident surface of a workpiece. The two laser beams and the gas jet melt the material and remove it from the workpiece, thereby forming a cutting seam. The incident surface is the surface of the workpiece onto which the light beam and the jet impinge. After the cutting seam is formed, parts of the light beam and the jet typically exit the workpiece on opposite exit surfaces. The first laser beam and the second laser beam are typically formed by a single laser beam each. Alternatively, however, the first laser beam and / or in particular the second laser beam can each consist of a plurality of partial beams. The two laser beams can be generated by a common laser light source and separated from each other by a beam splitter. Alternatively, each of the two laser beams can be generated by a separate laser light source. The cutting gas in the gas jet directed toward the incident surface or blown into the cutting seam can be, for example, nitrogen or compressed air. In certain cases, the cutting gas can also be argon.

[0010] The laser beams at least partially overlap on the workpiece. In other words, the two laser beams simultaneously cover a common area on the workpiece surface, in the workpiece volume, or in the cutting kerf. Preferably, the first laser beam extends completely within the second laser beam in the area of the workpiece. In particular, the two laser beams can be superimposed to form a single overall laser beam.

[0011] The first laser beam has a smaller focal diameter than the second laser beam. According to the present invention, the beam parameter product of the first laser beam is at most 5 mm*mrad. The beam parameter product of the first laser beam is preferably at most 3 mm*mrad, and particularly preferably at most 2 mm*mrad. The high beam quality of the first laser beam enables particularly high cutting speeds. In other words, the low beam parameter product of the first laser beam, i.e., the high beam quality, can increase the productivity of the method according to the present invention. The beam parameter product is defined as the product of the half-angle of the laser beam in the far field and the radius of the laser beam at its narrowest point, i.e., half the focal diameter.

[0012] According to the present invention, the second laser beam contributes less than 20% of the total laser power. The total laser power is the sum of the laser powers of the first and second laser beams. In other words, the first laser beam contributes at least 80% of the total laser power. The second laser beam contributes greater than zero. Typically, the second laser beam contributes at least 2%, preferably at least 3%, of the total laser power. According to the present invention, for thin workpieces having a thickness of less than 6 mm, the high beam quality and small focal diameter of the actual cutting beam (the first laser beam) enable increased cutting speed (and thus increased productivity), while at the same time, when a certain portion of the total laser power is focused onto the workpiece with a larger diameter (i.e., by the second laser beam), a high-quality cut profile is achieved at the cut seam. The total laser power can be at least 1 kW, preferably at least 2 kW.

[0013] The coupling efficiency of the cutting gas from the gas jet into the cutting slot is improved by a second, lower-power laser beam surrounding the first laser beam (the actual cutting beam). According to the present invention, the method parameters are selected so that the cutting slot is geometrically shaped to create flow conditions favorable for the cutting gas. According to the present invention, a cutting slot is formed on the entrance surface of the workpiece, representing the cutting edge of the removed material. A cutting edge of the removed material should be understood in particular to mean a cutting edge with a removal, i.e., a rounded or chamfered cutting edge. The total intensity profile of the superimposed laser beams is designed so that the cutting slot is funnel-shaped at the entrance surface. The funnel forms an introduction radius or an introduction bevel on the cutting side of the cutting slot. The funnel allows the cutting gas to flow into the cutting slot with less resistance. Pressure losses due to impact and turbulence are significantly lower at the cutting edge of the removed material than at an angular, right-angled (sharp-angled) edge.

[0014] The cutting edge is preferably rounded. The radius of the cutting edge can be at least 20 μm, preferably at least 25 μm and / or at most 100 μm, preferably at most 60 μm, particularly preferably at most 35 μm. More particularly preferably, the radius is 30 μm. At these radius values, particularly favorable conditions for the inflow of cutting gas are achieved.

[0015] The method parameters are selected to achieve the highest possible cutting speed (productivity) while also achieving good cut quality. On the one hand, the power of the actual cutting beam (first laser beam), which has a small beam diameter and high beam quality, must be sufficiently high to achieve a high cutting speed. On the other hand, the power of the partial beam (second laser beam), which has a larger beam diameter, must be sufficiently high to create a region of removed material at the cut edge of the kerf. The power contribution of the outer, second laser beam is advantageously selected based on the thickness of the workpiece.

[0016] The thickness of the workpiece can be less than 5 mm and preferably greater than 3 mm. The thickness can in particular be 4 mm. The power contribution of the second laser beam to the total laser power is preferably less than 15%.

[0017] The thickness of the workpiece can be less than 3 mm and preferably greater than 1 mm. The thickness can in particular be 2 mm. The power share of the second laser beam in the total laser power is preferably less than 7%, in particular 5%.

[0018] The aforementioned values contribute to achieving a good match between enlarging the cutting slot entry (by removing material at the entry surface by the cutting edge) and the highest possible productivity, ie the cutting speed.

[0019] The focal point of the first laser beam can be located upstream of the focal point of the second laser beam in the direction of propagation of the laser beams. The focal point of the first laser beam can be located inside the workpiece, preferably in the half of the workpiece closer to the incident surface, or outside the workpiece. The focal point of the second laser beam is located deeper inside the workpiece or closer to the incident surface. The focal point of the (high-power) first laser beam is preferably located in the region of the workpiece surface. In particular, the distance between the focal point of the first laser beam and the incident surface can be less than 30% of the workpiece thickness, preferably less than 15%. The distance between the focal points of the two laser beams is preferably at most 2 mm, in particular at most 1 mm, and typically between 0.5 and 0.7 mm.

[0020] The distance between the focal point of the second laser beam and the incident surface of the workpiece can be at most twice the Rayleigh length of the second laser beam. The Rayleigh length is defined as the quotient of the product of the refractive index of the propagation medium, pi, and the square of the radius of the laser beam at the focal point, divided by the vacuum wavelength of the laser beam.

[0021] The focal diameter of the second laser beam can be at least twice, preferably at least three times, and / or at most five times, preferably at most four times, the focal diameter of the first laser beam. The focal diameter of the first laser beam can in particular be at least 50 μm, preferably at least 80 μm, and / or at most 300 μm, preferably at most 150 μm. This value range has proven suitable for various workpiece thicknesses up to 6 mm.

[0022] The propagation axes of the two laser beams can be tilted relative to each other or preferably parallel to each other. Advantageously, the propagation axes coincide.

[0023] The divergence angles of the first laser beam and the second laser beam in the far field can be identical or differ by at most ΔΘ=100 mrad. This allows a simple design of the optical system for guiding and focusing the laser beams, which contributes to the process reliability of the method.

[0024] The two laser beams can overlap eccentrically relative to one another. However, they are advantageously overlapped concentrically. This allows cutting in all directions without having to adjust the orientation of the two laser beams to the cutting direction, for example by rotating the optics in the cutting head.

[0025] The two laser beams can be emitted from a multi-core optical fiber having a first core for the first laser beam and a second core for the second laser beam. The multi-core optical fiber can include optical fibers extending parallel to one another. Preferably, the second core surrounds the first core. In other words, the first core is arranged radially inwardly of the second core. Thus, the second core is designed as a ring-shaped optical fiber. In particular, the first and second cores can be concentric with one another.

[0026] The first fiber core emitting the first laser beam may have a diameter of at most 100 μm, preferably at most 50 μm. The second fiber core emitting the second laser beam may have a diameter of at most 300 μm, preferably at most 200 μm.

[0027] The cutting gas jet can be ejected from a conical nozzle, a bypass nozzle, or a Laval nozzle with a circular or elliptical opening diameter. The gas pressure, in particular the dynamic gas pressure, after exiting the nozzle can be at least 16 bar, preferably at least 18 bar, and / or at most 24 bar, preferably at most 22 bar. With this gas pressure, the workpiece material can be reliably blown out of the cut slit, in particular without forming burrs on the exit surface.

[0028] Furthermore, the present invention relates to a laser cutting device for laser cutting, in particular three-dimensionally shaped, plate-like workpieces, along a cutting line, in particular three-dimensionally. The laser cutting device is preferably a laser melting cutting device for laser melting cutting. The laser cutting device is advantageously configured to carry out the aforementioned laser cutting method according to the present invention. The aforementioned specific features can be provided, in particular, in the laser cutting device according to the present invention. The laser cutting device can be configured to generate a first laser beam, a second laser beam, and / or a gas jet having the aforementioned parameters and to direct them toward the workpiece in the aforementioned manner.

[0029] The laser cutting apparatus includes a laser light source device for superimposing a first laser beam and a second laser beam in a cutting zone. The first laser beam has a smaller beam diameter and focal diameter than the second laser beam. The beam parameter product of the first laser beam is at most 5 mm*mrad, preferably at most 3 mm*mrad. The power contribution of the second laser beam to the total laser power is less than 20%. The laser light source device may include optical means for focusing the two laser beams in the cutting zone.

[0030] The laser cutting machine also has a nozzle for directing a gas jet toward the cutting zone. The gas jet provides cutting gas, such as nitrogen, compressed air, or argon, to remove the workpiece material from the cut seam created during laser cutting. The two laser beams are typically emitted through the nozzle.

[0031] The laser cutting device also has a moving device for moving the cutting area relative to the workpiece along the three-dimensional cutting line. The laser cutting device can have a workpiece holder, which is fixedly arranged on the laser cutting device, especially on the machine tool of the laser cutting device. The optical device of the laser light source device or the entire laser light source device and the nozzle can be particularly shifted or rotated translationally and / or rotationally relative to the machine tool. Alternatively, the workpiece holder can be movably arranged on the machine tool of the laser cutting device. The optical device or the laser light source device and the nozzle can then be fixedly arranged on the laser cutting device. It is also conceivable to set several degrees of freedom of relative movement by the movability of the workpiece holder, for example in one or more translation directions, and to set additional degrees of freedom by the movability of the optical device or the laser light source device and the nozzle, especially by the rotatability around one or more axes.

[0032] Further features and advantages of the present invention are apparent from the description and the accompanying drawings. According to the present invention, the aforementioned features and further features can each be used individually or in any suitable combination. The exemplary embodiments shown and described are not to be understood as a definitive enumeration, but rather have an exemplary character for outlining the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The invention is illustrated in the drawings and explained in greater detail with reference to exemplary embodiments, in which:

[0034] Figure 1a A schematic side view shows the laser cutting device according to the invention during the implementation of the laser cutting method according to the invention, wherein a first laser beam is superimposed on a second laser beam, which emerges from a common multi-core optical fiber and overlaps one another in the cutting zone on the workpiece;

[0035] Figure 1b Shown cut Figure 1a A schematic cross-sectional view of a multi-core optical fiber of a laser cutting device, wherein it can be seen that a first fiber core for a first laser beam is concentrically arranged inside a second fiber core for a second laser beam;

[0036] Figure 2 A schematic flow chart showing a laser beam method according to the present invention;

[0037] Figure 3a A schematic diagram showing beam paths of a first laser beam and a second laser beam in a laser cutting method according to the present invention;

[0038] Figure 3b A schematic diagram showing beam paths of a first laser beam and a second laser beam when emitted from a multi-core optical fiber having two concentric cores in a laser cutting method according to the present invention;

[0039] Figure 4a A schematic perspective illustration shows a workpiece during the machining of a cut seam within the framework of the laser cutting method according to the invention, wherein two laser beams and a gas jet emerging from a nozzle are directed toward an impact surface of the workpiece;

[0040] Figure 4b Show Figure 4a A schematic cross-sectional view of a workpiece in the region of a cutting slit having a rounded cutting edge at the entrance surface;

[0041] Figure 4c A schematic cross-sectional view shows an alternative embodiment of a cutting edge at the cutting seam in a variant of the laser cutting method according to the invention, the cutting edge having a chamfer between the cutting side and the entrance surface;

[0042] Figure 5 shows a schematic cross section of a workpiece having a cutting seam produced by a laser cutting method according to the prior art;

[0043] Figure 6a 6 b shows a schematic diagram of a further laser cutting device according to the invention during the implementation of the laser cutting method according to the invention, wherein a first laser beam is superimposed on a second laser beam, the first laser beam and the second laser beam being generated in separate laser light sources and focused at different depths in the workpiece;

[0044] Figure 7a A diagram showing a cutting speed experimentally determined during the laser cutting method according to the invention, which also results in a good cut edge quality, as a function of the focus position of the first laser beam relative to the incident surface for a power share of the second laser beam of 10% of the total laser power;

[0045] Figure 7b Shown with Figure 7a A similar diagram, however, for the case where the power contribution of the second laser beam to the total laser power is 5%. DETAILED DESCRIPTION

[0046] Figure 1a The laser cutting device 10 is schematically shown during the implementation of a laser cutting method, in this case a laser melting cutting method. In the laser cutting method, a cutting seam 12 is produced in a workpiece 14 (see the following supplementary reference). Figure 4a). The workpiece 14 is plate-shaped and has a thickness 16 of less than 6 mm. The thickness 16 is 2 mm in this example. The workpiece 14 can be bent three-dimensionally at least in places in a manner not specifically shown.

[0047] To produce the cutting seam 12 in the workpiece 14, a first laser beam 18, a second laser beam 20, and a gas jet 22 are directed toward an impact surface 24 of the workpiece 14. Here, too, the two laser beams 18, 20 and typically the gas jet 22 overlap in a cutting zone 26. During laser melting cutting, the material of the workpiece 14 is liquefied in the cutting zone 26 and expelled by the gas jet 22, forming the cutting seam 12.

[0048] exist Figure 2 The basic process of the laser cutting method is shown in the flowchart. In step 102, a first laser beam 18 is generated and directed toward the incident surface 24 of the workpiece 14. In step 104, a second laser beam 20 is generated and directed toward the incident surface 24 of the workpiece 14. In step 106, a gas jet 22 is generated and directed toward the incident surface 24 of the workpiece 14. The gas jet 22 and the two laser beams 18 and 20 can be emitted from a nozzle 27. The two laser beams 18, 20 and the gas jet 22 overlap in the cutting zone 26. In step 108, the cutting seam 12 is produced in the workpiece 14 by the two laser beams 18, 20 and the gas jet 22. Steps 102, 104, 106, and step 108, which results from the preceding steps, are generally performed simultaneously. The distance 70 between the nozzle 27 and the incident surface 24 of the workpiece 14 can be, for example, 2 mm, but this distance can also be larger or smaller. The dynamic gas pressure of the cutting gas ejected from the nozzle 27 may be, for example, 20 bar.

[0049] The two laser beams 18, 20 are generated by a laser light source device 28, see Figure 1a The laser light source device 28 includes a single laser light source 30, such as a solid-state laser. The laser light source 30 emits a single output laser beam 32. In a beam splitter 34, the output laser beam 32 is split into a first laser beam 18 and a second laser beam 20. These two laser beams 18, 20 are guided to an optical system 38 of a cutting head (not specifically shown) of the laser cutting device 10 using a multi-core optical fiber 36.

[0050] The multi-core optical fiber 36 has a first core 40 for the first laser beam 18 and a second core 42 for the second laser beam 20, see also Figure 1bThe second fiber core 42 is designed in this case in the form of a ring fiber, which circumferentially surrounds the first fiber core 40. The first fiber core 40 and the second fiber core 42 can be arranged concentrically with each other. The diameter 44 of the first fiber core 40 can be 40 μm. The diameter 46 of the second fiber core 42 can be 150 μm. An intermediate cladding (not shown) having a lower refractive index than the fiber cores 40, 42 can be arranged between the fiber cores 40, 42.

[0051] Figure 3a and Figure 3b The paths of the two laser beams 18 , 20 are shown schematically. Figure 3a The beam paths in the area of workpiece 14 are shown. The ordinate z corresponds to the propagation direction of the two laser beams 18 , 20 . The focal points of the two laser beams 18 , 20 are, by way of example, at z=0. In principle, the focal points of the two laser beams 18 , 20 can be offset relative to one another in the propagation direction. The abscissa x corresponds to the radius of the laser beams 18 , 20 at the respective positions along their propagation axis 48 . The two laser beams 18 , 20 extend concentrically with one another.

[0052] The beam diameter 50 of the first laser beam 18 is smaller than the beam diameter 52 of the second laser beam 20 in the region of the workpiece 14 to be cut. The focal diameter 54 of the first laser beam 18 is in particular smaller than the focal diameter 56 of the second laser beam 20. The focal diameter 56 of the second laser beam 20 can be 3.5 times larger than the focal diameter 54 of the first laser beam 18. The beam parameter product of the first laser beam 18 is less than 5 mm*mrad, for example, in this case 2 mm*mrad.

[0053] Figure 3b The two laser beams 18, 20 are shown as they proceed from the end of the multi-core optical fiber 36 and have divergence angles θ1, θ2. The divergence angle θ1 of the first laser beam 18 and the divergence angle θ2 of the second laser beam 20 approach each other asymptotically and are of equal size in the far field, as are the beam diameters 50, 52 of the two laser beams 18, 20.

[0054] The power share of the second laser beam 20 in the total laser power (the sum of the laser powers of the two laser beams 18, 20) is less than 20%. In the case of a thickness 16 of the workpiece 14 of 2 mm, the power share of the second laser beam 20 can be 5%, for example.

[0055] The aforementioned design of the laser cutting method enables the cutting edge 58 of the cutting seam 12 to be designed to remove material at the incident surface 24 , see Figure 4aIn other words, the laser cutting method according to the present invention achieves that the cutting flank 60 of the cutting slit 12 and the entrance surface 24 do not adjoin each other with a sharp edge, but rather that a region of removed material is formed in the region of the cutting edge 58. This improves the flow of the cutting gas of the gas jet 22 into the cutting slit 12. Consequently, the formation of burrs on the exit surface 62 of the workpiece 14 opposite the entrance surface 24 can be prevented.

[0056] In contrast, in the laser cutting method according to the prior art, the cutting edge 58' of the cutting seam 12' has a sharp edge at the incident surface 24' of the workpiece 14', see Figure 5 Consequently, less cutting gas enters the cutting seam 12 ′, and the cutting quality or the possible cutting speed is still lower compared to the laser cutting method according to the invention.

[0057] Figure 4b The cutting edge 58 shown in the laser cutting method according to the invention can be designed to be rounded. In order to achieve particularly favorable inflow conditions for the cutting gas of the gas jet 22, the radius 64 of the cutting edge 58 can be 30 μm.

[0058] Figure 4c The area of removed material at the cutting edge 58 shown can also be designed as a chamfer. The height or width of the chamfer can be at least 20 μm, preferably at least 25 μm and / or at most 100 μm, preferably at most 60 μm, more preferably at most 35 μm. The height and width of the chamfer can be, for example, 30 μm.

[0059] In order to move the cutting seam 12 along a particularly three-dimensional cutting line, the cutting zone 26 is moved relative to the workpiece 14. For this purpose, the laser cutting device 10 can have a moving device 66, see Figure 1a The displacement device 66 can have a workpiece carrier 68 that is displaceable relative to the stationary machine bed. The workpiece 14 is held on the workpiece carrier 68 .

[0060] Figure 6a and Figure 6b By way of example and schematically, another variant of the laser cutting device 10 is shown during the implementation of the laser cutting method. Here, the laser light source device 28 of the laser cutting device 10 has two separate laser light sources 30a and 30b for generating the first laser beam 18 and the second laser beam 20. The laser light sources 30a, 30b can be, for example, CO2 lasers, solid-state lasers, or diode lasers. The laser light source device 28 also has an optical device 38 for superimposing the two laser beams 18, 20 into a total laser beam, which optical device includes, for example, an aperture mirror 38a ( Figure 6a ) or wavelength selective beam splitter 38a'( Figure 6b) and focusing lens 38b. The laser beams 18, 20 can be superimposed concentrically on one another so that they propagate along a common propagation axis 48 toward the workpiece 14.

[0061] The focal point 72 of the first laser beam 18 can be offset along the propagation axis 48 relative to the focal point 74 of the second laser beam 20. The focal point 72 of the first laser beam 18 is located upstream of the focal point 74 of the second laser beam 20 in the propagation direction of the laser beams 18, 20. The distance 76 between the focal points 72, 74 along the propagation axis 48 can be, for example, 0.7 mm.

[0062] The second focus 74 and preferably the first focus 72 may also be located inside the workpiece 14, i.e., on the other side of the incident surface 24 in the propagation direction of the laser beams 18, 20. The distance 78 between the first focus 72 and the incident surface 24 may be, for example, one-quarter of the thickness 16 of the workpiece 14. The distance 80 between the second focus 74 and the incident surface 24 may be less than twice the Rayleigh length of the second laser beam 20, for example, 1.5 times.

[0063] Other parameters of the laser cutting apparatus 10 of FIG. 6 or the laser cutting method described herein may be the same as those in the aforementioned laser cutting method and Figure 1a Accordingly, the arrangement described here of the focal points 72, 74 of the two laser beams 18, 20 relative to one another and to the workpiece 14 can also be provided in the aforementioned laser cutting method and Figure 1a In the laser cutting device 10.

[0064] The moving unit 66 of the laser cutting device 10 of FIG6 can be designed to flip the optical device 38 or a part of the optical device 38 relative to the workpiece 14. In addition, the optical device 38 and the workpiece 14 can be moved in translation relative to each other. In this way, the cutting area 26 can be moved along a cutting line that extends in particular three-dimensionally to form a cutting seam. In particular, when the workpiece 14 has a three-dimensionally shaped incident surface 24, it can be set by flipping so that the laser beams 18, 20 and the gas jet 22 are incident on the workpiece 14 at least approximately vertically. Figure 1a In the laser cutting device 10 , the optical device 38 or a portion of the optical device 38 can also be flipped relative to the workpiece 14 .

[0065] Figure 7a and Figure 7b The cutting speed determined experimentally during the laser cutting method according to the invention and still achieving a good quality of the cut seam 12, in particular the cut flanks 60 and the cut edge 58, is shown in relation to the relative speed of the first laser beam to the nozzle 27 (see Figure 4a ) of the focal position of the exit opening (here labeled "ES"). Figure 7aIn the diagram of FIG, the power share of the second laser beam 20 in the total laser power is 10%; Figure 7b In the diagram of FIG. 1 , the power share of the second laser beam 20 in the total laser power is 5%.

[0066] Figure 7a and Figure 7b The diagram shows the cutting of a workpiece with a thickness 16 of 2 mm at a total laser power of 3 kW. The plotted points each represent the maximum possible cutting speed at which good cut quality is still achieved. In other words, good cut quality is achieved for the parameter pairs within the plotted lines. It can be seen that with a power contribution of 5% for the second laser beam 20, significantly higher cutting speeds can be achieved compared to a power contribution of 10%. The power contribution of the second laser beam 20 must not yet reach zero; instead, it must ensure that the inflow of cutting gas into the cut seam 12 is improved by forming a cutting edge 58 of removed material, thereby ensuring, in particular, that no burrs are formed on the exit surface 62 of the workpiece 14.

[0067] Furthermore, experiments have shown that workpieces with a cutting thickness 16 of less than 6 mm can be cut more than 30% faster, ie at a maximum of 24 m / min, with a small focus diameter 54 of 100 μm of the first laser beam 18 than with a focus diameter 54 of 150 μm.

[0068] Reference Signs List

[0069] Laser cutting equipment 10

[0070] Cutting seam 12

[0071] Workpiece 14

[0072] Thickness of workpiece 16

[0073] First laser beam 18

[0074] Second laser beam 20

[0075] Gas jet 22

[0076] Incident surface 24

[0077] Cutting Area 26

[0078] Nozzle 27

[0079] Laser light source device 28

[0080] Laser light source 30

[0081] Output laser beam 32

[0082] Beam splitter 34

[0083] Multi-core optical fiber 36

[0084] Optical devices 38

[0085] Aperture mirror 38a

[0086] Beam splitter 38a'

[0087] Focusing lens 38b

[0088] First fiber core 40

[0089] Second core 42

[0090] The diameter 44 of the first fiber core 40

[0091] The diameter 46 of the second core 42

[0092] Propagation axis 48

[0093] The beam diameter 50 of the first laser beam 18

[0094] The beam diameter 52 of the second laser beam 20

[0095] The focal point diameter 54 of the first laser beam 18

[0096] The focal diameter 56 of the second laser beam 20

[0097] Cutting edge 58

[0098] Cutting side 60

[0099] Exit surface 62

[0100] The radius 64 of the cutting edge 58

[0101] Mobile device 66

[0102] Workpiece rack 68

[0103] The distance 70 between the nozzle 27 and the incident surface 24

[0104] Focus 72 of first laser beam 18

[0105] The focus 74 of the second laser beam 20

[0106] The distance 76 between the focal points 72 and 74

[0107] The distance 78 between the first focal point 72 and the incident surface 24

[0108] The distance 80 between the second focus 74 and the incident surface 24 is

[0109] Divergence angles Θ1, Θ2

[0110] Step 102: Direct the first laser beam 18 toward the incident surface 24

[0111] Step 104: Direct the second laser beam 20 toward the incident surface 24

[0112] Step 106: Direct the gas jet 22 toward the incident surface 24

[0113] Step 108 : Producing a cutting seam 12 in the workpiece 14 .

Claims

1. A method for laser cutting a workpiece (14) having a thickness (16) of less than 6 mm, in, directing a first laser beam (18), a second laser beam (20) and a gas jet (22) toward an incident surface (24) of the workpiece (14), wherein the first laser beam and the second laser beam at least partially overlap each other on the workpiece (14), wherein the first laser beam (18) has a smaller focal diameter than the second laser beam (20), wherein the beam parameter product of the first laser beam (18) is at most 5 mm*mrad, wherein the power share of the second laser beam (20) in the total laser power is less than 20%, and A cutting slit (12) is formed, the cutting slit having a cutting edge (58) from which material is removed at the incident surface (24) of the workpiece (14), the radius (64) of the cutting edge (58) being at most 100 μm.

2. The method according to claim 1, characterized in that The beam parameter product of the first laser beam (18) is at most 3 mm*mrad.

3. The method according to claim 1 or 2, characterized in that The radius (64) of the cutting edge (58) is 20 μm to 100 μm.

4. The method according to claim 1 or 2, characterized in that The thickness (16) of the workpiece (14) is less than 5 mm and greater than 3 mm, and the power share of the second laser beam (20) in the total laser power is less than 15%.

5. The method according to claim 1 or 2, characterized in that The thickness (16) of the workpiece (14) is less than 3 mm and greater than 1 mm, and the power share of the second laser beam (20) in the total laser power is less than 7%.

6. The method according to claim 1 or 2, characterized in that The focus of the first laser beam (18) is located upstream of the focus of the second laser beam (20) in the propagation direction.

7. The method according to claim 1 or 2, characterized in that The spacing (76) between the focal points of the first laser beam and the second laser beam is no greater than 2 mm.

8. The method according to claim 1 or 2, characterized in that The distance (80) between the focus of the second laser beam (20) and the incident surface (24) of the workpiece (14) is at most twice the Rayleigh length of the second laser beam (20).

9. The method according to claim 1 or 2, characterized in that The focal diameter of the second laser beam (20) is at least twice the focal diameter of the first laser beam (18).

10. The method according to claim 1 or 2, characterized in that The far-field divergence angle of the first laser beam (18) and the far-field divergence angle of the second laser beam (20) differ by a maximum of 100 mrad or are the same.

11. The method according to claim 1 or 2, characterized in that The first laser beam and the second laser beam are superimposed concentrically on each other.

12. The method according to claim 1 or 2, characterized in that A first laser beam and a second laser beam are emitted from a multi-core optical fiber (36) having a first core (40) for the first laser beam (18) and a second core (42) for the second laser beam (20).

13. The method according to claim 12, characterized in that The first core (40) has a diameter (44) of at most 100 μm.

14. The method according to claim 1 or 2, characterized in that The gas pressure of the gas jet (22) is at least 16 bar.

15. The method according to claim 1 or 2, characterized in that The laser cutting is laser melting cutting; The workpiece is metal; The workpiece is electrically conductive.

16. The method according to claim 1, characterized in that The beam parameter product of the first laser beam (18) is at most 2 mm*mrad.

17. The method according to claim 1 or 2, characterized in that The radius (64) of the cutting edge (58) is 25 μm to 100 μm.

18. The method according to claim 1 or 2, characterized in that The radius (64) of the cutting edge (58) is at most 60 μm.

19. The method according to claim 1 or 2, characterized in that The radius (64) of the cutting edge (58) is at most 35 μm.

20. The method according to claim 1 or 2, characterized in that The thickness (16) of the workpiece (14) is less than 3 mm and greater than 1 mm, and the power share of the second laser beam (20) in the total laser power is less than 5%.

21. The method according to claim 1 or 2, characterized in that The spacing (76) between the focal points of the first laser beam and the second laser beam is at most 1 mm.

22. The method according to claim 1 or 2, characterized in that The focal diameter of the second laser beam (20) is at least three times the focal diameter of the first laser beam (18).

23. The method according to claim 1 or 2, characterized in that The focal diameter of the second laser beam (20) is at most five times the focal diameter of the first laser beam (18).

24. The method according to claim 1 or 2, characterized in that The focal diameter of the second laser beam (20) is at most four times the focal diameter of the first laser beam (18).

25. The method according to claim 12, wherein The second fiber core (42) concentrically surrounds the first fiber core (40).

26. The method according to claim 12, wherein The first core (40) has a diameter (44) of at most 50 μm.

27. The method according to claim 1 or 2, characterized in that The gas pressure of the gas jet (22) is at least 18 bar.

28. The method according to claim 1 or 2, characterized in that The gas pressure of the gas jet (22) is at most 24 bar.

29. The method according to claim 1 or 2, characterized in that The gas pressure of the gas jet (22) is at most 22 bar.

30. A laser cutting device (10) for laser cutting a plate-shaped workpiece (14) along a cutting line, the laser cutting device comprising: a laser light source device (28) for superimposing a first laser beam (18) and a second laser beam (20) in a cutting zone (26), wherein the first laser beam (18) has a smaller focal diameter than the second laser beam (20), wherein the beam parameter product of the first laser beam (18) is at most 5 mm*mrad, and wherein the power share of the second laser beam (20) in the total laser power is less than 20%; - a nozzle (27) for directing the gas jet (22) towards the cutting zone (26); - a movement device (66) for moving the cutting zone (26) relative to the workpiece (14) along the cutting line, The laser cutting device is configured to carry out the method according to any one of claims 1 to 29 .

31. The laser cutting device according to claim 30, characterized in that The cutting line is a three-dimensional cutting line; The workpiece is a three-dimensionally formed workpiece.

Images