Workpiece edge rounding technology

Abstract

The invention relates to a method for cutting a metal workpiece (14) by means of a laser beam, said laser beam having a total laser power Ptotal. The laser beam has: a first laser sub-beam (18) having a first laser power P1; a second laser beam (20) adjoining the first laser beam (18) and having a second laser power P2; and a third laser sub-beam (22) adjoining the second laser sub-beam (20) and having a third laser power P3. And for P1, 0.33 * Ptotal < = P1 < = 0.85 * Ptotal. 0.06 * Ptotal < = P2 < = 0.48 * Ptotal is applied to P2. And for P3, P3 is more than or equal to 0.01 * Ptotal and less than or equal to 0.30 * Ptotal. The invention further relates to a laser cutting machine (10) and to a computer program product for the computer-aided implementation of the method, as well as to a workpiece (14) having special edge properties.

Description

Field of the Invention

[0001] The present invention relates to the field of laser (melting) cutting. In particular, the present invention relates to a method, an apparatus, and a computer program product for laser cutting a workpiece and simultaneously forming a chamfer at the upper end of the cut edge. In addition, the present invention also relates to a workpiece that can be manufactured by the above method. Background Art

[0002] The method for laser melting cutting belongs to the known prior art. When performing laser melting cutting, generally, a laser beam and a cutting gas beam are used as a processing beam and directed onto a workpiece to be cut, especially a metal workpiece. The processing beam moves relative to the workpiece along a predetermined cutting profile. Among them, the workpiece is melted by the laser beam along the cutting profile, and the melt is discharged downward by the cutting gas beam to form a cut.

[0003] In the prior art, there are also some known methods in which the laser beam has at least two intensity regions. Among them, the core region of the laser beam provides the energy for forming the cut, while the edge region surrounding the core region of the laser beam generates a chamfer or a fillet at the upper end of the cut. Thereby, the coupling of the cutting gas into the cut can be improved (see DE 10 2020 205 948 A1). On the other hand, by generating a chamfer (see, for example, DE 10 2019 125 103A1), the transition between the cut edge and the workpiece surface can be improved tactually.

[0004] In these known methods, due to the material removal when generating a chamfer at the upper end of the cut edge, irregular melt attachments, that is, so-called "drawing", usually form on the cut edge below the chamfer because the material of the chamfer can no longer be completely discharged from the cut.

[0005] Therefore, the object of the present invention is to further improve the quality of the cut edge. Summary of the Invention

[0006] The object on which the present invention is based is achieved by the subject matter of the independent claims. Other feasible design solutions of the present invention are given in the dependent claims, the description, and the drawings. The features, advantages, and possible design solutions described in the description for the subject matter of any independent claim should be regarded as corresponding features, advantages, and possible design solutions of the corresponding subject matter of other independent claims and any combination of the multiple subject matters of the independent claims (if necessary, in combination with one or more dependent claims) at least similarly.

[0007] A first aspect of the present invention provides a method for cutting a metal workpiece with a laser beam. In the method, a total laser power of P is provided totala laser beam. The laser beam has: a first laser sub-beam having a first laser power P1; a second laser sub-beam having a second laser power P2 adjacent to the first laser sub-beam; and a third laser sub-beam having a third laser power P3 adjacent to the second laser sub-beam. Here, for P1, it applies that: 0.33*P total ≤P1≤0.85*P total For P2, it applies that: 0.06*P total ≤P2≤0.48*P total For P3, it applies that: 0.01*P total ≤P3≤0.30*P total .

[0008] The laser beam is usually aligned with a process gas beam or a cutting gas beam along a predetermined contour to the workpiece. Here, the workpiece is melted and discharged downward from the formed cut by the process gas beam.

[0009] The total laser power P total is obtained by adding the laser powers P1, P2, and P3 of the laser sub-beams.

[0010] For P1, the following is preferably applicable: 0.45*P total ≤P1≤0.85*P total , more preferably 0.48*P total ≤P1≤0.63*P total . For P2, the following is preferably applicable: 0.09*P total ≤P2≤0.23*P total . For P3, the following is preferably applicable: 0.18*P total ≤P3≤0.30*P total .

[0011] The first laser sub-beam provides the energy for generating the cut, while the second and third laser sub-beams cause chamfering at the upper end of the cut respectively. The higher the power of the first laser sub-beam P1, the greater the cutting speed can be selected. The cutting speed is the feed speed of the processing beam composed of the laser beam and the process gas beam / cutting gas beam relative to the workpiece surface. For example, if the first laser power P1 is reduced by 20%, the cutting speed may need to be reduced by an amount between 10% and 20% to ensure good cutting results, especially to ensure a high quality of the cut edge.

[0012] According to a preferred embodiment, a laser beam can be provided by means of a multi-core optical fiber of a laser cutting system. The multi-core optical fiber includes a first core for providing a first laser sub-beam, wherein the first core has a circular cross-section with an outer diameter preferably of 100 μm. In addition, the multi-core optical fiber includes a second core for providing the second laser sub-beam, wherein the second core has an annular cross-section with an outer diameter preferably of 400 μm, and wherein the second core is arranged concentrically around the first core. The multi-core optical fiber further includes a third core for providing the third laser sub-beam, wherein the third core has an annular cross-section with an outer diameter preferably of 700 μm, and wherein the third core is arranged concentrically around the second core.

[0013] These cores can be spaced apart from each other by means of an intermediate cladding layer. The intermediate cladding layer can have a thickness of at least 5 μm and / or at most 20 μm, preferably at most 10 μm.

[0014] Other cores can also be provided to provide other sub-beams. In this way, the intensity distribution on the workpiece can be adjusted more precisely. In principle, it can be preset that the laser power in the first laser sub-beam is greater than the laser power of each of the other laser sub-beams.

[0015] The beam profile of the laser beam in the beam focus (i.e., in the focal plane of the laser beam) essentially corresponds to the cross-section of the core of the optical fiber multiplied by an imaging ratio that can be pre-given by the focusing optics.

[0016] The laser sub-beams can be provided by splitting a common original laser beam. The original laser beam can be provided by a single laser beam source or a combination of multiple laser beam sources. For example, an original laser beam in free beam form can be split into two sub-beams by means of appropriate optical elements (such as wedge-shaped optical elements or birefringent elements). Then, one of the sub-beams can be split again by means of appropriate optical elements. In this way, the original laser beam can be split into three laser sub-beams, which are focused onto the end of the optical fiber for coupling into the corresponding cores of the multi-core or multi-core optical fiber.

[0017] According to an alternative variant, the laser sub-beams can also be provided by individually guided (multiple) original laser beams. These original laser beams can be guided to the multi-core optical fiber by means of optical fibers respectively from a single laser beam source or a combination consisting of multiple laser beam sources (in particular, consisting of multiple laser modules of a fiber laser), and coupled into the corresponding cores respectively, in particular by means of fusion splicing.

[0018] The workpiece to be machined can preferably be a plate-shaped or tubular workpiece. The workpiece preferably can have a thickness or wall thickness of at least 5 mm, more preferably at least 10 mm. In addition, the workpiece can preferably be made of structural steel.

[0019] According to a second aspect of the invention, there is provided a laser cutting machine for cutting workpieces. The laser cutting machine includes at least one laser beam source, a process gas supply device, and a multi-core optical fiber. The multi-core optical fiber has a central first core and at least two cores annularly surrounding the first core for providing a central first laser sub-beam, a second laser sub-beam annularly surrounding the first laser sub-beam, and a third laser sub-beam annularly surrounding the second laser sub-beam. In addition, the laser cutting machine includes a focusing device for focusing the laser sub-beams in the direction towards the workpiece to be machined, and a cutting nozzle configured to direct the process gas or cutting gas together with the laser sub-beams onto the workpiece. The laser cutting machine also includes a control device configured to control the above-described laser cutting machine to perform the method according to any of the above-described variant embodiments.

[0020] In particular, nitrogen or other inert gases can be used as the process gas. Oxygen or compressed air for performing a flame cutting process can also be used as the process gas.

[0021] The laser beam source can include a plurality of laser modules, in particular fiber laser modules. In principle, the laser beam source can include one or more solid-state lasers (such as fiber lasers and / or disk lasers) and / or diode lasers.

[0022] The structure of the multi-core optical fiber has been described above in connection with the method according to the invention. Please refer to the description there.

[0023] In addition, the laser cutting machine may further include a beam splitting device configured to split the original laser beam provided by the laser beam source into first, second, and third laser sub-beams and couple these laser sub-beams into corresponding cores of the multi-core optical fiber. Accordingly, the laser beam source may be configured to provide a single original laser beam. For example, the beam splitting device may have two optical elements arranged successively in the beam propagation direction, such as wedge-shaped or birefringent optical elements, which are configured to first split the original laser beam into a first laser sub-beam and another laser sub-beam, and the other laser sub-beam is then split by the second optical element into second and third laser sub-beams. In this case, the power distribution between the laser beams can be controlled by changing the pose of the optical elements relative to the incident laser beam, in particular by pivoting or rotating. Alternatively, the laser beam source may be configured to provide a plurality of original laser beams, which are respectively coupled to the corresponding cores of the multi-core optical fiber through optical fibers, in particular by welding using fusion splicing. According to this configuration, the laser power of the laser sub-beams can be adjusted by providing corresponding laser power at the laser beam source.

[0024] According to a third aspect of the present invention, there is also provided a computer program product comprising program information for being read by a control unit of a laser cutting machine so as to execute the method according to any of the above-mentioned solutions by means of the laser cutting machine.

[0025] According to a fourth aspect of the present invention, there is also provided a plate-shaped or tubular metal workpiece having at least one workpiece edge. The workpiece has a rounding at least in a transition portion between the workpiece edge and a workpiece surface along at least one section of the workpiece edge. The rounding has a radius between 0.1 mm and 2 mm, and preferably the rounding radius is between 0.2 mm and 1.25 mm. In addition, the workpiece has a first roughness in a first edge upper region immediately below the rounding along the workpiece edge. In a second edge middle region immediately below the edge upper region along the workpiece edge, the workpiece has a second roughness smaller than the first roughness. In a third edge lower region immediately below the edge middle region along the workpiece edge, the workpiece has a third roughness greater than the second roughness.

[0026] The first, second, and third edge regions preferably extend parallel to the workpiece surface or parallel to the rounding. The edge upper region immediately below the rounding is characterized by the attachment of melt, i.e., so-called drawing, which substantially determines the first roughness.

[0027] The average width of the upper edge region can be at most twice as large as the fillet radius, preferably at most 1.5 times as large, and more preferably at most exactly the same as the fillet radius. By minimizing the upper edge region below the fillet, the quality of the workpiece edge can be improved. Description of the Drawings

[0028] The following description of the preferred embodiments is used to elaborate the present invention in detail in conjunction with the drawings.

[0029] The drawings show:

[0030] Figure 1a A schematic diagram of a laser cutting machine according to the present invention;

[0031] Figure 1b A schematic cross-sectional view of a multi-core optical fiber of a laser cutting machine according to the present invention;

[0032] Figure 2 A schematic flow diagram of a laser cutting method according to the present invention;

[0033] Figure 3 A perspective view of a workpiece during the introduction of a cut during a laser cutting method according to the present invention, wherein the laser sub-beam and the process gas beam emitted from the cutting nozzle are aligned with the workpiece surface;

[0034] Figure 4a A perspective view of a workpiece according to the present invention; and

[0035] Figure 4b A schematic diagram of the cut edge of a workpiece according to the present invention. Detailed Description of the Preferred Embodiments

[0036] Figure 1a The laser cutting machine 10 during the execution of the laser cutting method is shown here. Here, the laser cutting machine 10 is a laser melting cutting machine. In the laser cutting method, a cut 12 (see Figure 3 , which will be further referred to below) is introduced into the workpiece 14. The workpiece 14 is configured as a plate and has a thickness 16 of, for example, 10 mm.

[0037] To produce the cut 12 in the workpiece 14, a laser beam including the first laser sub-beam 18, the second laser sub-beam 20, and the third laser sub-beam 22 is directed onto the workpiece surface 24 of the workpiece 14 together with a process gas beam ( Figure 1a not shown in the figure). Here, the laser sub-beams 18, 20, 22 and the process gas beam overlap with each other in the cutting zone 26. During the laser melting cutting, the material of the workpiece 14 is liquefied in the cutting zone 26 and discharged by the process gas beam to form the cut 12.

[0038] The basic practice of the laser cutting method is as follows Figure 2 shown in the flowchart of FIG. In step 102, the first laser sub-beam 18 is generated and directed onto the workpiece surface 24 of the workpiece 14. In step 104, the second laser sub-beam 20 is generated and directed onto the workpiece surface 24. In step 106, the third laser sub-beam 22 is generated and directed onto the workpiece surface 24. Steps 102, 104, and 106 are carried out substantially simultaneously and constitute a common step 108, in which the laser sub-beams 18, 20, 22 are directed onto the workpiece surface 24 along a pre-given cutting profile together with the process gas beam. Here, the process gas beam and the three laser sub-beams 18, 20, 22 can be emitted from the nozzle 27 together. For example, the distance 70 between the nozzle 27 and the workpiece surface 24 of the workpiece 14 can be 2 mm (see Figure 3 ), but this distance can also be larger or smaller. For example, the dynamic gas pressure of the cutting gas discharged from the nozzle 27 can be 20 bar. The arrow 50 (see Figure 1a and 4b ) indicates the feed direction of the laser cutting head 27 relative to the workpiece surface 24. In other words, the feed direction corresponds to the cutting direction.

[0039] The laser sub-beams 18, 20, 22 can be provided by one or more original laser beams 32 generated in one or more laser beam sources 30. Each laser beam source can be a solid-state laser (especially a fiber laser or a disk laser) or a diode laser. For example, the original laser beam 32 can be divided into the first laser sub-beam 18, the second laser sub-beam 20, and the third laser sub-beam 22 by one or more beam splitters. Alternatively, the laser sub-beams 18, 20, 22 can also be provided by a plurality of separate and independent laser beam sources. The laser sub-beams 18, 20, 22 are coupled into the multi-core optical fiber 36 and guided to the optical device 38 of the cutting head (not shown) of the laser cutting machine 10 through the multi-core optical fiber 36.

[0040] The multi-core optical fiber 36 has a first core 40 for the first laser sub-beam 18, a second core 42 for the second laser sub-beam 20, and a third core 44 for the third laser sub-beam 22 (see Figure 1b)。The second core 42 and the third core 44 are each configured as an annular optical fiber here. The cores 40, 42, 44 can be arranged in a concentric manner with respect to each other. The diameter of the first core 40 can be 100 μm. The outer diameter of the second core 42 can be 400 μm. The outer diameter of the third core 44 can be 700 μm. The cores 40, 42, 44 can be spaced apart from each other by an intermediate cladding having a refractive index lower than that of the cores. For example, such a cladding can have a thickness of at least 5 μm each. The inner diameters of the second core 42 and the third core 44 can also be determined from the thicknesses of the respective claddings.

[0041] In order to produce a chamfered cut edge at the transition to the workpiece surface 24, a laser beam having a total power P total is provided. For this purpose, for the laser power P1 of the first laser sub-beam: 0.33*P total ≤P1≤0.85*P total applies. For the laser power P2 of the second laser sub-beam: 0.06*P total ≤P2≤0.48*P total applies, and for the laser power P3 of the third laser sub-beam: 0.01*P total ≤P3≤0.30*P total applies. By distributing the power within the given ranges, a particularly high-quality cut edge can be produced, especially in combination with the given diameters of the cores 40, 42, 44. For example, the following combinations have proven to be particularly suitable power distribution patterns: P1 = 0.62*P total , P2 = 0.18*P total , P3 = 0.20*P total ; P1 = 0.63*P total , P2 = 0.1*P total , P3 = 0.27*P total ; P1 = 0.49*P total , P2 = 0.21*P total , P3 = 0.30*P total . Therefore, the following ranges can be specified for a particularly preferred power distribution scheme: 0.49*P total ≤P1≤0.63*P total , 0.1*P total ≤P2≤0.21*P total , 0.2*P total ≤P3≤0.3*P total .

[0042] For example, when cutting a workpiece 14 in the shape of a structural steel plate with a thickness of 10 mm according to the present invention, a rounding can be generated at the upper end of the cut edge simultaneously. For example, the rounding can have a rounding radius of 1 mm. A solid-state laser (such as a disk laser or a fiber laser) with a laser power of 12 kW can be used for cutting. In order to split the original laser beam 32, two motor-pivotable wedge beam splitters (wedge-shaped transparent optical elements) can be successively arranged in the optical path of the original laser beam 32. By controlling the movement of the wedge beam splitters in the optical path, the power allocated to the first, second, and third laser sub-beams can be controlled. For example, 62% of the original laser beam 32 with a laser power of 7.44 kW can be coupled into the first core 40 of the multi-core optical fiber 36 to form the first laser sub-beam 18. 18.4% of the original laser beam 32 with a laser power of 2.208 kW can be coupled into the second core 42 to form the second laser sub-beam 20, and 19.6% of the original laser beam 32 with a laser power of 2.352 kW can be coupled into the third core 44 to form the third laser sub-beam 22. The feed rate is preferably set corresponding to the power and diameter of the first laser sub-beam. Therefore, it is also preferable to select the highest possible first laser power P1 of the first laser sub-beam 18 within a given range to improve the efficiency of the cutting method.

[0043] In Figure 4a and Figure 4b FIG. schematically shows the plate-shaped workpiece 14 with a cut edge 15 according to the present invention. The workpiece 14 is preferably made of structural steel. The workpiece 14 has a rounding 17 at the transition between the cut edge 15 and the workpiece surface 24. The rounding radius of the rounding 17 can be between 0.1 mm and 2 mm, for example, 0.5 mm. In Figure 4bIn [the figure], the workpiece 14 is schematically shown from a side view perspective observing the cut edge 15. The cut 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 cut edge 15 has a melt attachment, which is unavoidable in the case of remelting caused by the second laser sub-beam 20 and the third laser sub-beam 22. By the power distribution of the laser beam according to the present invention, the upper edge region 152 can be kept particularly narrow. The subsequent middle edge region 154 is characterized by a particularly low roughness. According to the present invention, the special power distribution is conducive to maximizing the middle edge region 154, so that the edge quality of the workpiece 14 can be improved. In the lower edge region 156, due to the formation of streaks 157 during the laser melting cutting process, the roughness is slightly increased compared with the middle edge region. Based on the present invention, a workpiece 14 with a particularly smooth edge surface compared with the prior art can be provided, and this workpiece can be manufactured particularly effectively in one working step. Starting from the rounding 17 with a low roughness value, the roughness value increases only over a narrow width in the upper edge region 152, and then decreases again in the middle edge region 14 and slightly increases in the lower edge region. In order to determine the width of the upper edge region 152, an average value can be obtained from the lengths of the respective melt filaments 153. The upper edge region 152 can preferably be at most 1.5 times as large as the rounding radius, and more preferably at most exactly the same size as it.

Claims

1. A method for cutting a metal workpiece (14) by means of a laser beam, wherein, Providing a laser beam having a total laser power P total ; Wherein, the laser beam has: a first laser sub-beam (18) having a first laser power P1; a second laser sub-beam (20) adjacent to the first laser sub-beam (18) and having a second laser power P2; and a third laser sub-beam (22) adjacent to the second laser sub-beam (20) and having a third laser power P3; Among them, for P1, the following applies: 0.33 * P total ≤ P1 ≤ 0.85 * P total ; Among them, for P2, the following applies: 0.06 * P total ≤ P2 ≤ 0.48 * P total ; and Among them, for P3, the following applies: 0.01 * P total ≤ P3 ≤ 0.30 * P total .

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

3. The method according to claim 1 or 2, wherein, The laser sub-beams (18, 20, 22) are provided by splitting a common original laser beam (32).

4. The method according to claim 1 or 2, wherein, The laser sub-beams (18, 20, 22) are provided by original laser beams that are guided separately and independently from each other.

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

6. A 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 optical fiber (36) having a central first core (40) and at least two cores (42, 44) annularly surrounding the first core (40), for providing a central first laser sub-beam (18), a second laser sub-beam (20) annularly surrounding the first laser sub-beam (18), and a third laser sub-beam (22) annularly surrounding the second laser sub-beam (20); A focusing device for focusing the laser sub-beams (18, 20, 22) in the direction towards the workpiece (14); A cutting nozzle (27) configured to direct the process gas together with the laser sub-beams (18, 20, 22) onto the workpiece (14); and A control device configured to control the laser cutting machine (10) to perform the method according to any one of claims 1 to 5.

7. The laser cutting machine (10) according to claim 6, further comprising: A beam splitting device configured to split the original laser beam (32) provided by the laser beam source (30) into the first, second, and third laser sub-beams (18, 20, 22), and couple the laser sub-beams (18, 20, 22) into the corresponding cores (40, 42, 44) of the multi-core optical fiber (36).

8. A computer program product comprising program information for being read by the control unit of a laser cutting machine (10) in order to perform the method according to any one of claims 1 to 5 by means of the laser cutting machine (10).

9. A plate-shaped or tubular metal workpiece (14) having at least one workpiece edge (15), wherein, The workpiece (14) has a rounding (17) at least in a section of the workpiece edge (15) at the transition between the workpiece edge (15) and the 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 smaller than the first roughness in a second intermediate edge region (154) of the workpiece edge (15) immediately below the upper edge region (152), and wherein the workpiece (15) has a third roughness greater than the second roughness in a third lower edge region (156) of the workpiece edge (15) immediately below the intermediate edge region (154).

10. The workpiece (14) according to claim 9, wherein, The upper edge region (152) has an average width that is at most 2 times as large, preferably at most 1.5 times as large, and more preferably exactly as large as the rounding radius.

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