Technique for rounding workpiece edges

Abstract

The invention relates to a method for cutting a metal workpiece (14) using a laser beam, said laser beam being provided with a total laser output power Ptotal. The laser beam has a first laser partial beam 18) which has a first laser output power P1, a second laser partial beam (20) which adjoins the first laser partial beam (18) and has a second laser output power P2, and a third laser partial beam (22) which adjoins the second laser partial beam (20) and has a third laser output power P3. For P1, the following applies: 0.33*Ptotal ≤ P1 ≤ 0.85*Ptotal. For P2, the following applies: 0.06*Ptotal ≤ P2 ≤ 0.48*Ptotal. For P3, the following applies: 0.01*Ptotal ≤ P3 ≤ 0.30*Ptotal. The invention additionally relates to a laser cutting machine (10), to a computer program for the computer-aided implementation of the method, and to a workpiece (14) with special edge properties.

Description

[0001] Technique for rounding a workpiece edge

[0002] Field of the invention

[0003] The present invention relates to the field of laser (fusion) cutting. In particular, the invention relates to a method, a device, and a computer program product for laser cutting a workpiece while simultaneously forming a rounded portion at the upper end of the cutting edge. Furthermore, the invention relates to a workpiece that can be produced using the method.

[0004] State of the art

[0005] Methods for laser fusion cutting are known from the prior art. In laser fusion cutting, a laser beam, together with a cutting gas jet, is typically directed as the processing beam onto a workpiece to be cut, particularly a metallic one. The processing beam is moved relative to the workpiece along a predefined cutting contour, with the workpiece being melted by the laser beam along the cutting contour, and the melt is expelled downward by the cutting gas jet, forming a cutting gap.

[0006] Furthermore, methods are known from the prior art in which the laser beam has at least two intensity ranges, with a core region of the laser beam providing the energy to generate the cutting gap, and an edge region of the laser beam surrounding the core region creating a rounded portion or a chamfer at the upper end of the cutting gap. This can improve the coupling of the cutting gas into the cutting gap (see [Fig.]).

[0007] DE 10 2020 205 948 Al). On the other hand, by creating a rounded edge (cf. e.g. DE 10 2019 125 103 Al), the haptic quality of the transition between the cutting edge and the workpiece surface can be enhanced.

[0008] Due to the material removal when creating a fillet at the upper end of the cutting edge, irregular melt adhesions, so-called "threads", usually form on the cutting edge below the fillet in the known processes, since the material of the fillet can no longer be completely expelled from the cutting gap.

[0009] An object of the present invention is therefore to further increase the quality of the cutting edge.

[0010] The invention

[0011] The problem underlying the invention is solved by the subject matter of the independent claims. Further possible embodiments of the invention are specified in the subclaims, the description, and the drawings. Features, advantages, and possible embodiments presented in the description for one of the subject matter of the independent claims are to be regarded at least analogously as features, advantages, and possible embodiments of the respective subject matter of the other independent claims, as well as any possible combination of the subject matter of the independent claims, optionally in conjunction with one or more of the subclaims.

[0012] According to a first aspect of the invention, a method for cutting a metallic workpiece using a laser beam is provided. In the method, the laser beam is provided with a total laser power Ptotai. The laser beam has a first laser sub-beam with a first laser power Pi, a second laser sub-beam adjacent to the first laser sub-beam with a second laser power P2, and a third laser sub-beam adjacent to the second laser sub-beam with a third laser power P3. The following applies for Pi: ​​0.33*Ptotai < Pi < 0.85*Ptotai. For P2: 0.06*Ptotai < P2 < 0.48*Ptotai. For P3: 0.01*Ptotai < P3 < 0.30*Ptotai.

[0013] The laser beam is usually directed at the workpiece along a predefined contour, along with a process gas jet or a cutting gas jet. The workpiece is melted and then blown downwards out of the resulting cutting gap by the process gas jet. The total laser power Ptotai is calculated by adding the laser powers Pi, P2, and P3 of the partial laser beams.

[0014] Preferably, the following applies to Pi: 0.45* Ptotai < Pi < 0.85* Ptotai, more preferably 0.48* Ptotai < Pi < 0.63* Ptotai. Preferably, the following applies to P2: 0.09* Ptotai < P2 < 0.23* Ptotai. Preferably, the following applies to P3: 0.18* Ptotal < P3 < 0.30* Ptotal.

[0015] The first laser beam provides the energy to generate the cutting gap, while the second and third laser beams each round the edges at the upper end of the cutting gap. The higher the power of the first laser beam, Pi, the higher the cutting speed can be selected—that is, the feed rate of the processing beam (comprising the laser beam and the process gas jet / cutting gas jet) relative to the workpiece surface. For example, if the first laser power, Pi, is reduced by 20%, a reduction in the cutting speed of between 10% and 20% may be necessary to ensure a good cutting result, especially high-quality cutting edges.

[0016] According to a preferred variant, the laser beam can be provided by means of a multi-core fiber of a laser cutting system. The multi-core fiber comprises a first fiber core for providing the first partial laser beam, wherein the first fiber core has a circular cross-section, preferably with an outer diameter of 100 pm. The multi-core fiber further comprises a second fiber core for providing the second partial laser beam, wherein the second fiber core has an annular cross-section, preferably with an outer diameter of 400 pm, and wherein the second fiber core is arranged concentrically around the first fiber core. The multi-core fiber further comprises a third fiber core for providing the third partial laser beam, wherein the third fiber core has an annular cross-section, preferably with an outer diameter of 700 pm, and wherein the third fiber core is arranged concentrically around the second fiber core.The fiber cores can be spaced apart from each other by an intermediate cladding. The intermediate cladding can have a thickness of at least 5 μm and / or at most 20 μm, preferably at most 10 μm.

[0017] Additional fiber cores can also be provided to provide additional partial beams. This allows the intensity distribution on the workpiece to be adjusted even more precisely. In principle, the laser power in the first partial laser beam can be greater than the laser power in each of the subsequent partial laser beams.

[0018] The beam profile of the laser beam in the beam focus (i.e. in a focal plane of the laser beam) essentially corresponds to the cross-section of the fiber cores of the optical fiber multiplied by an imaging ratio that can be specified by a focus optics.

[0019] The partial laser beams can be generated by splitting a common raw laser beam. The raw laser beam can be generated by a single laser source or a combination of multiple laser sources. For example, the raw laser beam in the free beam can be split into two partial beams using appropriate optical elements (e.g., wedge-shaped optical elements or birefringent elements). One of the partial beams can then be split again using appropriate optical elements. In this way, the raw laser beam can be split into three partial laser beams, which are focused onto the fiber end for coupling into the corresponding fiber core of the multicore or multi-core fiber.

[0020] According to an alternative variant, the partial laser beams can also be provided from separately guided raw laser beams. The raw laser beams can each be guided from a single laser beam source or a combination of multiple laser beam sources (in particular, multiple laser modules of a fiber laser) to the multi-core fiber via optical fibers and coupled into the corresponding fiber core, in particular by splicing. The workpiece to be machined can preferably be a plate-shaped or tubular workpiece. The workpiece can preferably have a workpiece thickness or a wall thickness of at least 5 mm, more preferably of at least 10 mm. Furthermore, the workpiece can preferably be made of structural steel.

[0021] According to a second aspect of the invention, a laser cutting machine for cutting a workpiece is provided. The laser cutting machine comprises at least one laser beam source, a process gas supply, and a multi-core fiber. The multi-core fiber has a central, first fiber core and at least two additional fiber cores annularly surrounding the first fiber core for providing a central, first laser beam, a second laser beam annularly surrounding the first laser beam, and a third laser beam annularly surrounding the second laser beam. Furthermore, the laser cutting machine comprises a focusing device configured to focus the laser beams toward a workpiece to be machined, and a cutting nozzle configured to direct the process gas or cutting gas, together with the laser beams, onto the workpiece.The laser cutting machine also comprises a control device which is designed to control the laser cutting machine to carry out the method according to one of the variants described above.

[0022] Nitrogen or another inert gas can be used as the process gas. Oxygen, for example, can be used for flame cutting, or compressed air can also be used as the process gas.

[0023] The laser beam source can comprise multiple laser modules, in particular fiber laser modules. The laser beam source can generally comprise one or more solid-state lasers (e.g., fiber lasers and / or disk lasers) and / or diode lasers. The structure of the multi-core fiber has already been described above in connection with the method according to the invention. Reference is made to the description therein.

[0024] The laser cutting machine can further comprise a beam splitting device designed to split a raw laser beam provided by the laser beam source into the first, second, and third partial laser beams and to couple the partial laser beams into the respective fiber cores of the multi-core fiber. The laser beam source can accordingly be designed to provide a single raw laser beam. The beam splitting device can, for example, have two optical elements, e.g., wedge-shaped or birefringent elements, arranged one behind the other in the beam propagation direction, which are designed to first split the raw laser beam into the first partial beam and a further partial beam, which is in turn split by the second optical element into the second and third partial beams.In this case, the power distribution between the laser beams can be controlled by changing the position, in particular by pivoting or rotating, of the optical elements relative to the respective incident laser beam. Alternatively, the laser beam source can be configured to provide multiple raw laser beams, each of which is coupled to a corresponding fiber core of the multi-core fiber by means of optical fibers, in particular by splicing. According to this configuration, the laser powers of the partial laser beams can be adjusted by providing a corresponding laser power at the laser beam source.

[0025] According to a third aspect of the invention, a computer program product is provided which contains program information for reading out by the control unit of a laser cutting machine in order to carry out a method according to one of the variants described above by means of the laser cutting machine.

[0026] According to a fourth aspect of the invention, a plate-shaped or tubular metallic workpiece with at least one workpiece edge is provided. The workpiece has a fillet along at least a portion of the workpiece edge at the transition between the workpiece edge and a workpiece surface. The fillet has a fillet radius between 0.1 mm and 2 mm, preferably between 0.2 mm and 1.25 mm. Furthermore, the workpiece has a first roughness in a first, upper edge region of the workpiece edge, immediately below the fillet. In a second, middle edge region of the workpiece edge, immediately below the upper edge region, the workpiece has a second roughness that is less than the first roughness. In a third, lower edge region, immediately below the middle edge region, the workpiece has a third roughness that is greater than the second roughness.

[0027] Preferably, the first, second, and third edge regions extend parallel to the workpiece surface or to the fillet. The upper edge region, immediately below the fillet, is characterized by melt adhesions, so-called threads, which essentially determine the first roughness.

[0028] The upper edge area can have an average width that is at most 2 times, preferably at most 1.5 times, and even more preferably at most the same size as the radius of the fillet. The quality of the workpiece edge is increased by minimizing the upper edge area below the fillet.

[0029] Examples of implementation

[0030] The following description of preferred embodiments, in conjunction with the drawings, serves to explain the invention in more detail.

[0031] They show:

[0032] Fig. 1a shows a schematic representation of a laser cutting machine according to the invention; Fig. 1b shows a schematic representation of the cross-section of a multi-core fiber of a laser cutting machine according to the invention;

[0033] Fig. 2 A schematic flow diagram of a laser cutting method according to the invention;

[0034] Fig. 3 A workpiece during the introduction of a cutting gap in the context of a laser cutting method according to the invention, wherein the partial laser beams and a process gas jet emerging from the cutting nozzle are directed onto a surface of the workpiece, in a schematic perspective view;

[0035] Fig. 4a Schematically a workpiece according to the invention in a perspective view; and

[0036] Fig. 4b Schematic view of a cutting edge of a workpiece according to the invention.

[0037] Figure 1a shows a laser cutting machine 10 during a laser cutting process. The laser cutting machine 10 is a laser melting cutting machine. During the laser cutting process, a cutting gap 12 (see Figure 3, to which reference is made below) is introduced into a workpiece 14. The workpiece 14 is plate-shaped and has a thickness 16 of, for example, 10 mm.

[0038] In order to create the cutting gap 12 in the workpiece 14, a laser beam comprising a first laser beam 18, a second laser beam 20, and a third laser beam 22, together with a process gas jet (not shown in Figure 1a), is directed onto a workpiece surface 24 of the workpiece 14. The laser beams 18, 20, 22 and the process gas jet overlap one another in a cutting zone 26. During laser fusion cutting, the material of the workpiece 14 is liquefied in the cutting zone 26 and expelled by the process gas jet, forming the cutting gap 12. The basic procedure for the laser cutting method is shown in the flow chart in Figure 2. In a step 102, the first laser beam 18 is generated and directed onto the workpiece surface 24 of the workpiece 14. In a step 104, the second laser beam 20 is generated and directed onto the workpiece surface 24.In a cut 106, the third laser beam 22 is generated and directed onto the workpiece surface 24. Steps 102, 104, 106 are generally performed simultaneously and result in a common step 108, in which the laser beams 18, 20, 22, together with the process gas jet, are directed onto the workpiece surface 24 along a predeterminable cutting contour. The process gas jet and the three laser beams 18, 20, 22 can exit together from a nozzle 27. A distance 70 between the nozzle 27 and the workpiece surface 24 of the workpiece 14 can be, for example, 2 mm (see Figure 3), but the distance can also be greater or smaller. A dynamic gas pressure of the cutting gas exiting the nozzle 27 can be, for example, 20 bar. The arrow 50 (compare Figures 1a and 4b) indicates a feed direction in which the laser cutting head 27 is moved relative to the workpiece surface 24.In other words, the feed direction corresponds to a cutting direction.

[0039] The partial laser beams 18, 20, 22 can be provided from one or more raw laser beams 32 generated in one or more laser beam sources 30. Each laser beam source can be a solid-state laser (in particular a fiber laser or a disk laser) or a diode laser. The raw laser beam 32 can be split, for example, by one or more beam splitters into the first partial laser beam 18, the second partial laser beam 20, and the third partial laser beam 22. Alternatively, the partial laser beams 18, 20, 22 can also be provided by separate laser beam sources. The partial laser beams 18, 20, 22 are coupled into a multi-core fiber 36 and guided by the multi-core fiber 36 to an optics system 38 of a cutting head (not shown in detail) of the laser cutting machine 10.

[0040] The multi-core fiber 36 has a first fiber core 40 for the first laser beam 18, a second fiber core 42 for the second laser beam 20, and a third fiber core 44 for the third laser beam 22 (see also Figure 1b). The second fiber core 42 and the third fiber core 44 are each formed as a ring fiber. The fiber cores 40, 42, 44 can be arranged concentrically to one another. A diameter of the first fiber core 40 can be 100 μm. An outer diameter of the second fiber core 42 can be 400 μm. An outer diameter of the third fiber core 44 can be 700 μm. The fiber cores 40, 42, 44 can each be spaced from one another by an intermediate cladding with a lower refractive index than the fiber cores. Such a cladding can each have a thickness of, for example, at least 5 μm.The thickness of the respective cladding also determines the inner diameter of the second fiber core 42 and the third fiber core 44.

[0041] To create a cutting edge with a rounded transition to the workpiece surface 24, the laser beam is provided with a total power Ptotai. The laser power Pi of the first partial laser beam is: 0.33* Ptotai < Pi < 0.85* Ptotai. The laser power P2 of the second partial laser beam is: 0.06* Ptotai < P2 < 0.48* Ptotai, and the laser power P3 of the third partial laser beam is: 0.01* Ptotai < P3 < 0.30* Ptotai. With a power distribution within the specified ranges, particularly in combination with the given diameters of the fiber cores 40, 42, 44, particularly high-quality cutting edges have been achieved. The following combinations have proven to be particularly suitable power distributions: Pi = 0.62*Ptotai, P2 = 0.18*Ptotai, P3 = 0.20*Ptotai; Pi = 0.63*Ptotai, P2 = 0.1*Ptotal, P3 = 0.27*Ptotai; Pl = 0.49*Ptotal, P2 = 0.21*Ptotal, P3 = 0.30*Ptotal.A particularly preferred power distribution can therefore be specified with the following ranges: 0.49* Ptotai < Pi < 0.63*Ptotai, 0.1*Ptotai < P2 < 0.21*Ptotal, 0.2* Ptotal < P3 < 0.3* Ptotal.

[0042] For example, when cutting a 10 mm thick, plate-shaped workpiece 14 made of structural steel according to the present invention, a rounding can be created simultaneously at the upper end of the cutting edge. The rounding can, for example, have a rounding radius of 1 mm. A solid-state laser (e.g., a disk laser or a fiber laser) with a laser power of 12 kW can be used for cutting. To split the raw laser beam 32, two motor-driven pivoting wedge switches (wedge-shaped transparent optical elements) can be provided one behind the other in the beam path of the raw laser beam 32. By controlled displacement of the wedge switches in the beam path, the power distribution between the first, second, and third laser sub-beams can be controlled. For example, 62% of the raw laser beam 32 with 7.44 kW laser power can be coupled into the first fiber core 40 of the multi-core fiber 36 to form the first laser sub-beam 18.18.4% of the raw laser beam 32 with a laser power of 2.208 kW can be coupled into the second fiber core 42 to form the second partial laser beam 20, and 19.6% of the raw laser beam 32 with a laser power of 2.352 kW can be coupled into the third fiber core 44 to form the third partial laser beam 22. The feed rate is preferably adjusted according to the power and diameter of the first partial laser beam. Therefore, it may also be preferable to select the first laser power Pi of the first partial laser beam 18 as high as possible within the specified range in order to increase the efficiency of the cutting process.

[0043] Figures 4a and 4b Figure 4b schematically illustrates a plate-shaped workpiece 14 according to the invention with a cutting edge 15. The workpiece 14 is preferably made of structural steel. At the transition between the cutting edge 15 and the workpiece surface 24, the workpiece 14 has a rounding 17. The rounding 17 can have a rounding radius of between 0.1 mm and 2 mm, for example 0.5 mm. Figure 4b schematically illustrates the workpiece 14 in a side view looking at the cutting edge 15. The cutting edge 15 can be divided into three regions below the rounding 17: a first, upper edge region 152, a second, middle edge region 154, and a third, lower edge region 156. In the upper edge region, the cutting edge 15 has melt adhesions that are unavoidable during remelting by the second and third partial laser beams 20, 22.Due to the inventive power distribution of the laser beam, the upper edge region 152 can be kept particularly narrow. The adjoining central edge region 154 is characterized by particularly low roughness. According to the present invention, the central edge region 154 can be advantageously maximized through the special power distribution, thus improving the edge quality of the workpiece 14. In the lower edge region 156, the roughness increases slightly again compared to the central edge region due to the formation of grooves 157 during the laser fusion cutting process. Due to the present invention, a workpiece 14 can be provided with a particularly smooth edge surface compared to the prior art, which can be manufactured particularly efficiently in a single work step.Starting from the fillet 17, which has a low roughness value, the roughness value in the upper edge region 152 increases only over a short width and then decreases again in the middle edge region 14 before increasing slightly again in the lower edge region. To determine the width of the upper edge region 152, an average value can be calculated from the length of the individual melt threads 153. The upper edge region 152 can preferably be at most 1.5 times as large, more preferably at most as large as the fillet radius.

Claims

Patent claims 1. A method for cutting a metallic workpiece (14) by means of a laser beam, wherein the laser beam is provided with a total laser power Ptotai; wherein the laser beam has a first partial laser beam (18) with a first laser power Pi, a second partial laser beam (20) adjacent to the first partial laser beam (18) with a second laser power P2, and a third partial laser beam (22) adjacent to the second partial laser beam (20) with a third laser power P3; wherein the following applies to Pi: 0.33*Ptotai < Pi < 0.85*Ptotai; wherein the following applies to P2: 0.06*Ptotai < P2 < 0.48*Ptotai; and wherein the following applies to P3: 0.01*Ptotai < P3 < 0.30*Ptotai.

2. The method according to claim 1, wherein the laser beam is provided by means of a multi-core fiber (36) of a laser cutting machine, and wherein the multi-core fiber (36) comprises: a first fiber core (40) for providing the first laser partial beam (18), wherein the first fiber core (40) has a circular cross-section, preferably with an outer diameter of 100 pm; a second fiber core (42) for providing the second laser partial beam (20), wherein the second fiber core (42) has an annular cross-section, preferably with an outer diameter of 400 pm, and wherein the second fiber core (42) is arranged concentrically around the first fiber core (40); and a third fiber core (44) for providing the third laser partial beam (22), wherein the third fiber core (44) has an annular cross-section, preferably with an outer diameter of 700 pm, and wherein the third fiber core (44) is arranged concentrically around the second fiber core (42).

3. Method according to claim 1 or 2, wherein partial laser beams (18, 20, 22) are provided by splitting a common raw laser beam (32).

4. Method according to claim 1 or 2, wherein the partial laser beams (18, 20, 22) are provided from separately guided raw laser beams.

5. Method according to one of the preceding claims, wherein the workpiece (14) is a plate-shaped or tubular workpiece, preferably with a workpiece thickness (16) or a wall thickness of at least 5 mm, more preferably of at least 10 mm; and / or wherein the workpiece (14) is made of structural steel.

6. Laser cutting machine (10) for cutting a workpiece (14), the laser cutting machine comprising: A laser beam source (30); A process gas supply; A multi-core fiber (36) with a central, first fiber core (40) and at least two fiber cores (42, 44) surrounding the first fiber core (40) in a ring shape for providing a first, central laser partial beam (18), a second laser partial beam (20) surrounding the first laser partial beam (18) in a ring shape and a third laser partial beam (22) surrounding the second laser partial beam (20) in a ring shape; A focusing device for focusing the partial laser beams (18, 20, 22) in the direction of the workpiece (14); A cutting nozzle (27) designed to direct the process gas together with the partial laser beams (18, 20, 22) onto the workpiece (14); and A control device which is designed to control the laser cutting machine (10) for carrying out the method according to one of claims 1 to 5.

7. Laser cutting machine (10) according to claim 6, further comprising: A beam splitting device designed to split a raw laser beam (32) provided by the laser beam source (30) into the first, second and third partial laser beams (18, 20, 22) and to couple the partial laser beams (18, 20, 22) into the respective fiber cores (40, 42, 44) of the multi-core fiber (36).

8. Computer program product containing program information for reading out by the control unit of a laser cutting machine (10) in order to carry out a method according to one of claims 1 to 5 by means of the laser cutting machine (10).

9. A plate-shaped or tubular, metallic workpiece (14) with at least one workpiece edge (15), wherein the workpiece (14) has a rounding (17) along at least a portion of the workpiece edge (15) at the transition between the workpiece edge (15) and a workpiece surface (24) of the workpiece (14), wherein the rounding (17) has a rounding radius between 0.1 mm and 2 mm, preferably between 0.2 mm and 1.25 mm, and wherein the workpiece (14) has a first roughness in a first, upper edge region (152) of the workpiece edge (15), immediately below the rounding (17), wherein the workpiece (14) has a second roughness in a second, central edge region (154) of the workpiece edge (15), immediately below the upper edge region (152), which is less than the first roughness, and wherein the workpiece (15) has a third, lower edge region (156),immediately below the central edge region (154) has a third roughness which is greater than the second roughness., 10. Workpiece (14) according to claim 9, wherein the upper edge region (152) has an average width which is at most 2 times as large, preferably at most 1.5 times as large, even more preferably at most the same size as the fillet radius.

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