Technique for producing rounded edges

Abstract

The invention relates to a method for machining a metal workpiece (W) by means of a machining beam (20) which comprises a first laser beam (22) and a second laser beam (24) arranged at least partly next to the first laser beam (22) and which also comprises a process gas jet. The method has the following steps: cutting the workpiece (W) by guiding the machining beam (20) along a cutting contour using a first machining parameter set; and post-processing at least one workpiece (W) cut edge produced during the cutting process by guiding the machining beam (20) along a post-processing contour, which corresponds to the cutting contour or runs parallel to the cutting contour, using a second machining parameter set. The invention additionally relates to a device for implementing the method and to a metal workpiece which can be produced using the method.

Description

[0001] Technique for creating an edge rounding

[0002] Field of the invention

[0003] The present invention relates to the field of laser processing of metallic workpieces, particularly plate or tubular workpieces. In particular, the invention relates to a technique for post-processing workpiece edges using a laser beam.

[0004] State of the art

[0005] Methods for post-processing cut edges of metallic workpieces are known from the prior art, in which a laser beam is used to irradiate the contour of a workpiece part that has been at least partially cut out of a workpiece with the laser beam, thereby changing the edge quality. WO 2020 / 173970 A1, for example, describes a method in which, in a first processing step, a cutting gap is created in a workpiece by means of laser cutting, and in a second processing step, the cutting gap is at least partially traversed again using different processing parameters of the laser cutting system in order to modify the cut edge. DE 10 2019 125 103 A1 describes a method in which, using a processing laser beam that has different energy intensity ranges, rough processing (in particularCutting with the creation of cutting edges) and fine machining (in particular rounding and / or chamfering of the created cutting edges) is carried out.

[0006] The present invention is based on the object of improving the state of the art. In particular, the possibilities for creating fillets at the transition between the workpiece surface and the cutting edge of a metal workpiece cut by laser beam cutting are to be improved. The invention

[0007] To achieve the object underlying the invention, a method for processing a metallic workpiece using a processing beam is provided. The processing beam comprises a first laser beam and a second laser beam arranged at least partially next to the first laser beam. For example, the first laser beam and the second laser beam can also (partially) overlap. In a plane of the workpiece surface, the images of the first laser beam and the second laser beam are adjacent to one another, preferably without overlap or spaced apart by a small separating gap. The processing beam further comprises a process gas beam. In particular, nitrogen, a gas mixture comprising nitrogen, or another inert gas or gas mixture can be used as the process gas.Preferably, the process gas jet can be generated by means of a processing nozzle of a processing head and directed, together with at least one of the laser beams, onto the workpiece to be processed. The workpiece can, in particular, be a plate- or tubular workpiece, preferably made of a steel material.

[0008] The method comprises, in a first step, cutting the workpiece by guiding the machining beam along a cutting contour and using a first set of machining parameters.

[0009] In a second step, which in particular immediately follows the first processing step, the method comprises post-processing at least one cutting edge of the workpiece generated during cutting by guiding the processing beam along a post-processing contour which corresponds to the cutting contour or which runs parallel to the cutting contour, and using a second set of processing parameters.

[0010] The first processing parameter set and the second processing parameter set may differ from each other, for example, at least with regard to the laser power used, the gas pressure used, and / or the feed rate used.

[0011] The proposed method allows workpieces to be first machined by cutting in a single operation, and the resulting cut edges can then be precisely rounded. Compared to the state of the art, the proposed method enables larger fillet radii (0.5 mm and more) with very good fillet quality. In particular, fillets with a smooth surface transition between the workpiece surface and the cutting flank surface (i.e., no material overhang) can be created, preferably with a uniform fillet radius (i.e., no flattened fillets).

[0012] According to a preferred variant, the first laser beam can have a higher intensity than the second laser beam. Intensity refers to the power of the respective laser beam per area. For example, the intensity ratios in a common focal plane of the laser beams can be decisive. Intensity can be understood, in particular, as an intensity averaged over the area of ​​the respective laser beam in its focal plane. The area of ​​the laser beam in its focal plane can be determined, for example, using the 80% method or the second-moment method.

[0013] The second laser beam can preferably be directed onto the workpiece coaxially to the first laser beam, wherein the second laser beam preferably has a closed beam profile, in particular an annular beam profile, so that the second laser beam encloses the first laser beam.

[0014] In particular, the first and second laser beams can be sub-beams of a common laser beam. The total power of the laser beam can preferably be distributed among the sub-beams in any desired ratio. A technique for variably splitting a laser beam into several sub-beams is described, for example, in WO 2011 / 124671 A1 by the applicant. It is understood that more than two laser beams can also be included in the processing beam, with two adjacent laser (sub-beams) preferably having different intensities.

[0015] In the method according to the invention, the first set of processing parameters can comprise the simultaneous use of the first laser beam and the second laser beam. In other words, it can be provided that the first laser beam and the second laser beam are switched on or active when cutting the workpiece. According to an alternative variant, it is also conceivable that only the first laser beam is active during cutting.

[0016] The second processing parameter set can, in particular, comprise the use of the first laser beam without the second laser beam. This means that the second laser beam can be switched off or inactive during post-processing of the cutting edge. Alternatively or additionally, however, the second laser beam can also be activated during post-processing.

[0017] The post-processing contour, which is followed by the processing beam during post-processing, can have an offset from the cutting contour in the direction of the cutting edge to be post-processed, which can be between 0.1 mm and 1 mm. This offset in the direction of the cutting edge to be post-processed allows the energy required to modify the cutting edge to be applied more precisely to the required workpiece area. This can increase the efficiency of the process.

[0018] According to a preferred variant of the method, a rounding with a first radius or a chamfer with a chamfer height can be created at the upper end of the cut edge to be reworked during cutting by irradiating the workpiece with the second laser beam, wherein the rounding or the chamfer is enlarged during rework to a rounding with a second radius, wherein the second radius is larger than the first radius or the chamfer height. During cutting, a chamfer with rounded ends can also be created - i.e., a hybrid between a rounding and a chamfer. Creating the rounding and / or the chamfer during cutting preferably includes material removal. In other words, it can be provided that the edge is not merely melted by the second laser beam, but that workpiece material is also removed through the cutting gap by means of the process gas jet.By removing material in the first process step, material removal during post-processing and to create the larger fillet is no longer necessary, or only minimally. Material removal generally prevents any material protrusion of the fillet from the workpiece surface and the cutting flank.

[0019] The first fillet radius, or the height of the chamfer, can be between 0.1 mm and 0.7 mm, for example. The second radius of the fillet, which is enlarged in the post-processing step, can be between 0.2 mm and 1.5 mm, for example.

[0020] The second set of processing parameters can specify a process gas pressure that is lower than the process gas pressure according to the first set of parameters. For example, the pressure in the chamber of a processing nozzle used for machining during post-processing can be a maximum of 0.3 bar, preferably a maximum of 0.1 bar, overpressure compared to ambient pressure. The low gas pressure used contributes to reducing turbulence during post-processing and to creating a particularly smooth surface along the fillet. In this way, a particularly uniform and smooth fillet can be created. An excessively strong gas jet could deform the fillet. Furthermore, the low pressure during post-processing can keep gas consumption to a minimum.

[0021] Advantageously, it can be provided that the distance between the end face of a nozzle, via which the processing jet is directed onto the workpiece, and the workpiece surface is smaller according to the first processing parameter set than according to the second processing parameter set. In other words, the distance between the nozzle and the workpiece is greater during post-processing than during cutting the workpiece.

[0022] Preferably, in the method according to the invention, in a first step, a workpiece part can be cut out of the workpiece along the cutting contour, using the first set of machining parameters, except for at least one remaining material web, which connects the workpiece part to a remaining workpiece or an adjacent workpiece part of the workpiece. Furthermore, the cutting edge of the workpiece part can be reworked in a second step using the second set of machining parameters. The created cutting edge can thus be reworked with modified parameters using the same machining head. In a subsequent, third step, the at least one material web can be severed.

[0023] The cutting can also be performed, for example, with the machining beam, for example, using the first set of machining parameters. Alternatively, the at least one material web can also be removed mechanically, in particular by pushing, knocking, or shaking the workpiece part out of a surrounding residual workpiece or residual skeleton of the workpiece, or by bending or shaking off several workpiece parts held together by material webs. The material web can extend across the full thickness of the workpiece as a so-called "microjoint" or have a reduced height (so-called "nanojoint"). The use of nanojoints has the advantage that the cut edge can be reworked along the entire circumference of the workpiece part during post-processing.Furthermore, the material web can be formed as a so-called "microweld," i.e., as a weld point, preferably at the upper end of the cutting gap, which holds together the parts of the workpiece separated by the cutting gap (workpiece parts and / or residual workpiece or residual grid parts). To achieve the object underlying the invention, a device for machining a metallic workpiece by means of a machining beam is further provided. The machining beam comprises a first laser beam and a second laser beam arranged at least partially adjacent to the first laser beam, as well as a process gas beam.

[0024] The device comprises a workpiece support for supporting the workpiece during a machining process. Furthermore, the device comprises at least one laser beam source for providing the laser radiation for the first and second laser beams. The laser beam source can preferably be a solid-state laser, e.g., a fiber laser with one or more fiber laser modules, a disk laser, or a diode laser. The device further comprises a process gas supply for providing the process gas, as well as a machining head with focusing optics, wherein the machining head is configured to direct the machining beam onto the workpiece surface.The device comprises a multiclad fiber with a core region and at least one ring region surrounding the core region, wherein the multiclad fiber is configured to guide or transport the first laser beam within the core region and the second laser beam within the ring region from the laser beam source to the processing head. The device also comprises a control device configured to control the device to carry out a method according to one of the variants described above.

[0025] The device may in particular be a laser cutting system, for example a flatbed laser cutting system or a tube laser cutting system.

[0026] A device according to the invention can preferably comprise a beam splitting device arranged between the laser beam source and the multi-clad fiber, and configured to split a laser input beam provided by the laser beam source into the first laser beam and the second laser beam. The beam splitting device couples the first laser beam into the core region of the multi-clad fiber and the second laser beam into the ring region of the multi-clad fiber. As already mentioned above, more than two laser beams can be included in the processing beam. Accordingly, the multi-clad fiber can also comprise a plurality of ring regions, preferably arranged concentrically to one another, each of which is configured to guide a corresponding laser (partial) beam.The beam splitting device can, for example, comprise a so-called wedge switch, which is arranged in the beam path of the laser input beam and, by lateral displacement relative to the laser input beam, controllably couples portions of the laser input beam into the core region and / or the ring region of the multi-clad fiber. A principle for beam splitting using a wedge switch is described, for example, in WO 2011 / 124671 A1, or in the applicant's German patent application with the official file number 10 2022 110 078.2.

[0027] According to a further aspect of the present invention, a metallic workpiece is provided. The workpiece comprises a base body having a top side and a bottom side opposite the top side. The base body further comprises an edge that extends laterally, along an outer contour or an inner contour of the base body. The base body has a rounded portion along at least part of the outer contour and / or the inner contour at the transition between the top side and the edge, which rounded portion extends over a height of at least 0.2 mm, preferably of at least 0.5 mm, wherein the base body has a lower surface roughness along the rounded portion than along the rest of the edge.

[0028] An edge surface of the base body, which may in particular correspond to a cutting flank, preferably extends substantially perpendicular to the surface of the base body.

[0029] A workpiece according to the invention can preferably have a rounding with a height of 0.2 mm to 1.5 mm. The height of the rounding corresponds to the rounding radius. The rounding can further be characterized in that it has no material elevations that protrude upwards on the workpiece surface or laterally beyond the edge surface. In other words, the rounding can have a continuous transition on the workpiece surface and on the edge surface. This can improve the haptics at the upper end of the workpiece edge. When the workpiece is coated with a coating agent, e.g. with a varnish, the uniformity of the coating on the workpiece edge can be improved by the smooth transition of the rounding. Furthermore, the smooth rounding reduces the risk of injury when handling the workpiece or workpiece part.

[0030] The surface roughness along the fillet may preferably be no more than Rz 30.

[0031] The workpiece can be manufactured particularly efficiently using a process according to one of the variants described above. The workpiece can therefore be at least partially cut out of a workpiece, e.g., a plate-shaped workpiece, in a single operation and reworked in the area of ​​the resulting cut edges to form the advantageous edge roundings.

[0032] Examples of implementation

[0033] The following description of preferred embodiments, in conjunction with the drawings, serves to explain the invention in more detail.

[0034] They show:

[0035] Figs. 1a-b are views illustrating a machining method according to the invention according to a variant;

[0036] Fig. 2 A further illustration to illustrate a machining method according to the invention; Fig. 3 Schematically a front view of the cutting edge of a workpiece or a workpiece part according to the present invention; and

[0037] Figs. 4-5 representations of workpiece parts according to the invention.

[0038] A processing method according to the invention is described below by way of example with reference to Figures 1a and 1b. An arrangement for laser processing a metallic workpiece W is shown schematically. A processing beam 20, which comprises a first laser beam 22 and a second laser beam 24, as well as a process gas jet (not shown in the figures), is directed onto the surface of the workpiece W by means of a processing nozzle (likewise not shown). According to the example shown, the first laser beam 22 and the second laser beam 24 are partial beams of a common laser beam which is provided by means of a multi-clad fiber, here a 2-in-1 fiber 10, wherein the first partial beam 22 is provided via a core region 12 and the second partial beam 24 is provided via an annular region of the 2-in-1 fiber 10.The laser beams 22 and 24 are focused toward the workpiece W by means of a focusing optics, schematically represented here by a focusing lens 30, and are directed, together with the process gas, onto the workpiece surface via the processing nozzle. To process the workpiece W, the processing beam is moved relative to the workpiece surface using predefined processing parameters.

[0039] The workpiece W is cut in a first method step using a first set of parameters, wherein a workpiece part Wi is locally separated from a remaining workpiece W2 by a cutting gap. During cutting, a rounding 42a or chamfer 42b (cf. Fig. 2, step a)) is simultaneously created at the upper ends of the cutting flanks by the action of the second laser beam 24, which has a lower intensity than the first laser beam 22. During the creation of the rounding 42a or chamfer 42b, material is removed under the action of the process gas, which is directed at the workpiece W at high pressure. It may be preferred for the rounding 42a to have a chamfer-like, flattened shape. In a second method step, the created cutting edge is again traversed with the processing beam 20 using a second set of parameters (cf. Figs. 1b and 2b).The fillet 42a or chamfer 42b produced during cutting is enlarged so that a final fillet 44 of high quality is created.

[0040] For example, the method can be used to machine a plate-shaped workpiece W made of CrNi steel, which has a thickness of 2 mm, on a 2D laser flatbed machine with 12 kW laser power according to the invention. First, the first method step of cutting can be implemented using the first set of processing parameters. A beam switch in the laser input beam can couple the laser power simultaneously into both the core region 12 and the ring region 14 of the 2-in-1 fiber. The core beam (first laser beam 22) creates the separating cut, the ring beam (second laser beam 24) ensures melting and thus at least partially rounds the workpiece surface or upper cutting edge 42a, with material also being removed in the region of the rounding 42a. For cutting, for example, the first partial beam 22 with a laser power of approximately 8 kW is coupled into the core region 12 with a diameter of 100 pm.The second partial beam 24 with a laser power of approximately 4 kW is coupled into the ring area 14 with an outer diameter of 400 pm. The imaging ratio is 2.1. The focus diameter (of the second laser beam 24) is 840 pm. The feed rate is 40 m / min. The focus position is in the area of ​​the workpiece surface or just below the surface, e.g. approximately 0.5 mm below the workpiece surface. Nitrogen is used as the cutting gas. The cutting gas pressure is 23 bar (overpressure compared to ambient pressure) with a nozzle distance of 4 mm from the workpiece surface. The processing nozzle (or cutting nozzle) has a diameter of 2.3 mm. The rounding 42a created during cutting has a height of approximately 0.2 mm. The second process step of post-processing is then implemented using the second set of processing parameters.Between cutting and post-processing, the laser beam can preferably be switched off and the cutting head moved back to the starting point of the cut. For post-processing or rounding the cutting edge, the cutting head can be offset by 0.2 mm relative to the cutting contour in the direction of the cutting edge to be post-processed (good part contour), and the cutting edge can be traced again with modified processing parameters according to the second processing parameter set. The distance between the nozzle and the workpiece W can be 5 mm, with a focus diameter of the first laser (partial) beam 22 of 210 pm and a laser power of 370 W. The laser power for post-processing can therefore preferably be significantly lower than for cutting. The second laser (partial) beam 24 can be switched off for post-processing according to the described exemplary variant.The process gas pressure is, for example, 0.2 bar, and the focal plane of the first laser beam 22 can be approximately 2 mm above the nozzle end face, i.e., within the nozzle body. The feed rate can be 2.2 m / min. The feed rate according to the second set of processing parameters can therefore be significantly lower than the feed rate according to the first set of processing parameters. This can increase the quality of the rounding. The rounding created with the processing parameters described above can have a rounding radius of approximately 0.5 mm.

[0041] Figure 2 shows a variant of the method according to the invention in which a chamfer 42b is created during cutting (cf. step a)). When creating the chamfer 42b, the material removal is maximized compared to a rounding 42a (cf. Fig. 1a) at the same height. The size or radius or height of the final rounding 44 depends significantly on the material removal at the rounding point during cutting. During post-processing in the second method step (cf. step b) in Fig. 2), preferably no further material removal takes place. The process gas pressure can therefore be selected to be significantly lower than during cutting, whereby the shape and surface quality of the rounding can be improved. Figure 2 also illustrates the displacement of the processing beam 20 for post-processing relative to the cutting contour in the direction of the cutting edge to be post-processed.To improve process gas coverage, especially during the post-processing step, a nozzle with the largest possible diameter can be used for the entire machining process. For example, using a nozzle with an orifice diameter of 10 mm can reduce the cutting gas pressure compared to the above example. Furthermore, when rounding the cutting edge in the post-processing step, the shielding gas coverage of the machining area can be improved, thus counteracting the formation of tarnish on the workpiece surface.

[0042] Figure 3 shows a front view of a workpiece edge of a workpiece or workpiece part Wi according to the invention. The workpiece part Wi was not completely cut out in the first process step and was connected to the surrounding remaining workpiece or an adjacent workpiece part via a material web—here in the form of a nanojoint 50. Due to the reduced height of the nanojoint 50, the rounding 44 could be created along the entire workpiece circumference in the second process step before the nanojoint 50 was severed to separate the workpiece part Wi. The surface of the workpiece part Wi along the rounding 44 has a roughness of at most Rz30.

[0043] Figures 4 and 5 each show workpiece parts Wi according to the present invention, the representation according to Figure 5 approximately corresponding to the schematic representation according to Figure 3. In Figures 4 and 5, the shiny surface can be seen along the generated roundings 44, which extend (cf. Figure 4) along the inner contour and the outer contour of the workpiece part Wi.

Claims

Patent claims 1. Method for processing a metallic workpiece (W) using a processing beam (20) comprising a first laser beam (22) and a second laser beam (24) arranged at least partially next to the first laser beam (22), as well as a process gas jet, the method comprising the steps: Cutting the workpiece (W) by guiding the machining beam (20) along a cutting contour and using a first machining parameter set; and Post-processing at least one cutting edge of the workpiece (W) produced during cutting by guiding the machining beam (20) along a post-processing contour that corresponds to the cutting contour or that runs parallel to the cutting contour, and using a second machining parameter set.

2. The method of claim 1, wherein the first laser beam (22) has a higher intensity than the second laser beam (24).

3. Method according to claim 1 or 2, wherein the second laser beam (24) is directed coaxially to the first laser beam (22) towards the workpiece (W); and wherein the second laser beam (24) preferably has a closed beam profile, in particular an annular beam profile, such that the second laser beam (24) surrounds the first laser beam (22).

4. Method according to one of the preceding claims, wherein the first processing parameter set comprises the simultaneous use of the first laser beam (22) and the second laser beam (24).

5. Method according to any one of the preceding claims, wherein the second processing parameter set includes the use of the first laser beam (22) without the second laser beam (24).

6. Method according to one of the preceding claims, wherein the post-processing contour has an offset to the cutting contour in the direction of the cutting edge to be post-processed, which is between 0.1 mm and 1 mm.

7. Method according to one of the preceding claims, wherein during cutting, a rounding (42a) with a first radius or a chamfer (42b) with a chamfer height is produced at the upper end of the cutting edge to be reworked by irradiating the workpiece (W) with the second laser beam (24); and wherein the rounding (42a) or the chamfer (42b) is enlarged during rework to a rounding (44) with a second radius, wherein the second radius is larger than the first radius or than the chamfer height.

8. Method according to one of the preceding claims, wherein the second processing parameter set specifies a process gas pressure which is lower than a process gas pressure according to the first processing parameter set.

9. Method according to one of the preceding claims, wherein the processing jet (20) is directed onto the workpiece (W) via a nozzle of a processing head; and wherein a distance between the nozzle end face and the workpiece surface is less according to the first processing parameter set than according to the second processing parameter set.

10. Method according to one of the preceding claims, wherein in a first step a workpiece part (Wi) is removed from the workpiece (W) along the cutting contour except for at least one remaining The material web (50) is cut out using the first machining parameter set, which connects the workpiece part (Wi) to a remaining workpiece (W2) or an adjacent workpiece part of the workpiece (W); wherein in a second step the cut edge of the workpiece part (Wi) is reworked using the second machining parameter set; and wherein in a third step the at least one material web (50) is cut through.

11. Device for processing a metallic workpiece (W) by means of a processing beam (20) comprising a first laser beam (22) and a second laser beam (24) arranged at least partially next to the first laser beam (22), as well as a process gas jet, the device comprising: A workpiece support for storing the workpiece (W) during a machining process; At least one laser beam source to provide the laser radiation for the first and the second laser beam (22, 24); A process gas supply for providing the process gas; A machining head with a focusing optic (30), wherein the machining head is designed to direct the machining beam onto the workpiece surface; A multi-clad fiber (10) with a core region (12) and at least one ring region (14) surrounding the core region (12), wherein the multi-clad fiber (10) is configured to transport the first laser beam (22) within the core region (12) and the second laser beam (24) within the ring region (14) from the laser beam source to the processing head; and A control device designed to control the apparatus for carrying out the method according to any one of claims 1 to 10.

12. Device according to claim 11, further comprising: A beam splitting device arranged between the laser beam source and the multiclad fiber (10), and configured to provide a to split the laser input beam provided by the laser beam source into the first laser beam (22) and the second laser beam (24), wherein the first laser beam (22) can be coupled into the core region (12) of the multi-clad fiber (10) and the second laser beam (24) can be coupled into the ring region (14) of the multi-clad fiber (10) by means of the beam splitting device.

13. Metallic workpiece (W) comprising: a base body with a top surface and a bottom surface opposite the top surface; wherein the base body comprises an edge extending laterally along an outer contour or an inner contour of the base body; wherein the base body has a rounding (44) along at least a part of the outer contour and / or the inner contour at the transition between the top surface and the edge, extending over a height of at least 0.2 mm, preferably at least 0.5 mm; and wherein the base body has a lower surface roughness along the rounding (44) than along the remainder of the edge.

14. Workpiece according to claim 13, wherein the workpiece edge can be produced by a method according to any one of claims 1 to 10.

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