METHOD FOR MACHINING A METAL WORKPIECE AND LASER DEVICE

Abstract

The invention relates to a method for machining a metallic workpiece (W), in which a machining beam (18) is directed onto the workpiece (W) and moved in a cutting direction (24) relative to the workpiece at varying feed rates, wherein the machining beam (18) comprises a first laser beam (20) having a first intensity for cutting the workpiece (W) and at least one second laser beam (22) having a second intensity which is lower than the first intensity, whereby a rounded cutting edge (30) is produced by means of the at least one second laser beam (22);and depending on a predetermined rounding radius of the cutting edge (30), a linear energy to be introduced into the workpiece (W) by means of the at least one second laser beam (22) is determined and the second intensity of the at least one second laser beam (22) is adjusted depending on the varying feed rate, whereby the linear energy introduced into the workpiece (W) by means of the second laser beam (22) is constant along the entire cutting contour (32);

Description

[0001] The invention relates to a method for machining a metallic workpiece and a laser device for machining a metallic workpiece.

[0002] DE 10 2019 125 103 A1 discloses a processing device for laser processing a workpiece, in particular for laser cutting. This processing device comprises a device for generating a processing laser beam for rough machining the workpiece, in particular for creating cuts with cutting edges in the workpiece. Furthermore, the processing device comprises a device for dividing the processing laser beam into at least two energy intensity ranges, wherein a first energy intensity range for rough machining the workpiece has a greater temporally integrated radiation energy than at least a second energy intensity range for at least partial fine machining of a cutting edge.

[0003] The object of the present invention is to provide a solution which enables a uniform rounding of a cutting edge cut by means of a laser device, regardless of the geometry of the cutting edge.

[0004] This object is achieved according to the invention 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.

[0005] The invention relates to a method for machining a metallic workpiece, which is particularly plate- or tubular in shape. The method provides that a machining beam is directed at the workpiece and moved in a cutting direction relative to the workpiece at a feed rate that varies depending on a cutting contour to be cut. The machining beam is provided by a laser device. Directing the machining beam at the workpiece means that the machining beam is provided by the laser device, is aligned with the workpiece, and impinges on the workpiece surface.Varying feed rate means that the laser beam is moved along a first region of the cutting contour at a first feed rate and along a second region of the cutting contour that differs from the first region at a second feed rate that differs from the first feed rate. This means that the processing beam is moved at different speeds along different regions of the cutting contour.

[0006] The processing beam comprises a first laser beam with a first intensity, which is intended for cutting the workpiece in a thickness direction. In other words, when processing the metallic workpiece, the workpiece is cut in its thickness direction by means of the first laser beam. The processing beam further comprises a second laser beam which impinges on a workpiece surface of the workpiece next to the first laser beam and has a second intensity that is lower than the first intensity of the first laser beam. The processing beam thus comprises the first laser beam and the second laser beam which is arranged at least partially next to the first laser beam. For example, the first laser beam and the second laser beam can at least partially overlap. A rounded cutting edge of the workpiece is produced by means of the second laser beam.The second laser beam can thus cause the workpiece material to flow, rounding any cutting edges created when the workpiece was cut with the first laser beam. This minimizes the need for post-processing of the workpiece. The processing beam thus enables the workpiece to be cut, creating rounded cutting edges. Subsequent rounding of cutting edges is thus eliminated.

[0007] The method further provides for determining a linear energy to be introduced into the workpiece by means of the at least one second laser beam as a function of a predetermined rounding radius to be achieved for the cutting edge. Furthermore, the intensity of the at least one second laser beam is adjusted during processing as a function of the varying feed rate, as a result of which the linear energy introduced into the workpiece for rounding by means of the second laser beam is constant along the entire cutting contour. The linear energy is a frequently chosen measure for the thermal load on a workpiece. The linear energy describes an energy input per unit length. The linear energy thus represents a measure of the energy supplied to the workpiece during the welding process.By ensuring that the energy input per unit length for rounding into the workpiece is constant along the entire cutting contour, it can be achieved that the cutting edge has the specified rounding radius to be achieved over its entire length - and thus along the entire cutting contour. If the intensity of the second laser beam remained constant, the energy input per unit length would increase if the feed rate were slowed down. By adjusting the second intensity of the second laser beam as a function of the feed rate, it can be ensured that the energy input per unit length can be kept constant along the entire cutting contour when the feed rate is increased by increasing the second intensity and when the feed rate is decreased by decreasing the second intensity of the second laser beam.

[0008] In a possible further development of the invention, it is provided that the first laser beam and the at least one second laser beam are guided alongside one another in a line running perpendicular to the cutting direction on the workpiece surface. In particular, the at least one second laser beam has an annular cross-section and circumferentially surrounds the first laser beam. In other words, the processing beam is moved in the cutting direction relative to the workpiece surface, whereby the laser beams are guided alongside one another across the workpiece surface. As a result, the laser beams are arranged alongside one another in a plane spanned by the workpiece surface, perpendicular to the cutting direction.In particular, the laser beams can be arranged next to one another perpendicular to the cutting direction and perpendicular to the thickness direction of the workpiece, which coincides with a beam direction in which the laser beams impinge on the workpiece. The second laser beam is thus arranged closer to a part of the workpiece that remains during cutting of the workpiece than the first laser beam, whereby cut edges created during cutting of the workpiece by means of the first laser beam can be rounded off by remelting and thus flowing of material. The cut edges are rounded off in particular immediately upon their creation by means of the second laser beam, whereby the risk of creating sharp cut edges can be kept particularly low. The first laser beam and the second laser beam can be arranged concentrically to one another.This means that an image of the first laser beam on the workpiece surface forms an inner region of the processing beam, and the image of the second laser beam circumferentially encloses the image of the first laser beam. For this purpose, the image of the first laser beam can be at least substantially circular or elliptical, while the image of the second laser beam is annular and thus surrounds the image of the first laser beam in a ring-like manner. In a plane of the workpiece surface, the images of the first laser beam and the second laser beam can be adjacent to one another without overlap or spaced apart by a small separation gap.

[0009] In a further possible embodiment of the invention, the feed rate when cutting along a corner or a curve of the cutting contour with a radius below a predetermined curve limit is selected to be lower than when cutting along a straight section or a curve of the cutting contour with a radius greater than or equal to the predetermined curve limit. For example, the first feed rate can be 40 meters per minute and the second feed rate can be three meters per minute.In other words, the machining beam is moved along the cutting contour in a first area, which includes a straight section or a curve of the cutting contour whose radius is greater than or equal to the specified curve limit, at the first feed rate, and in the second area, which includes a corner or a curve of the cutting contour with a radius below the specified curve limit, at a second feed rate that is lower than the first feed rate. The straighter the path along which the machining beam is moved, the faster the machining beam can be moved precisely. The odder the path along which the machining beam is to be moved, the lower the maximum feed rate at which the machining beam can be moved in order to still achieve a specified cut precision.In order to achieve the specified rounding radius of the cutting edge in both the even area and the odd area of ​​the cutting contour, the second intensity of the second laser beam is thus adjusted as a function of the feed rate, in particular as a function of the change in the feed rate, in order to ensure that, despite the different feed rates or the varying feed rate, the energy per unit length introduced into the workpiece along the cutting contour is at least substantially the same over the entire length of the cutting contour.

[0010] In a further possible embodiment of the invention, it is provided that the processing beam is provided by means of a laser device. This laser device comprises an optical waveguide, a laser beam generation unit and a beam splitting device. The laser device is in particular a solid-state laser (e.g. fiber laser or disk laser) or a diode laser. The optical waveguide can thus be a fiber (or optical fiber), in particular a multi-clad fiber such as a 2-in-1 fiber or a 3-in-1 fiber. The optical waveguide comprises a core region and at least one ring region. If the optical waveguide is designed as a 2-in-1 fiber, then the optical waveguide comprises the core region and a ring region surrounding the core region on the circumference.If the optical fiber is designed as a 3-in-1 fiber, the optical fiber comprises the core region and two ring regions: an inner ring region and an outer ring region. The inner ring region encloses the core region on the circumference, and the outer ring region encloses both the core region and the inner ring region on the circumference. In this case, the core region and the two ring regions are arranged concentrically to one another. The laser beam generation unit is configured to generate a laser input beam. In the method, the laser input beam is thus generated by means of the laser beam generation unit. By means of the beam splitting device, the laser input beam is split between the core region for generating the first laser beam and between the at least one ring region for generating the at least one second laser beam.The beam splitting device can be used to adjust which portion of the laser input beam is to be coupled into the core region and which portion of the laser input beam is to be coupled into the at least one ring region. Thus, the intensity of the respective laser beams can be adjusted using the beam splitting device. The provision of the laser device with the beam splitting device enables the intensities of the first laser beam and the second laser beam to be adjusted particularly precisely across an entire intensity range from 0 to 100 percent by splitting the laser input beam.

[0011] In this case, it is provided that the second intensity of the at least one second laser beam is adjusted by adjusting the ratio of the division of the laser input beam between the core region and the at least one annular region by means of the beam splitting device. The division of the laser input beam between the core region and the at least one annular region can thus be adjusted in order to adjust the intensity of the second laser beam. The second intensity of the second laser beam can be adjusted particularly easily and quickly by means of the beam splitting device. The beam splitting device can, for example, comprise at least one wedge switch which is configured to divide the laser input beam between the core region and the at least one annular region.

[0012] In a further possible embodiment of the invention, it is provided that, in order to adjust the second intensity of the at least one second laser beam, an intensity of the laser input beam provided by the laser beam generation unit, which is split into the first laser beam and the at least one second laser beam, is adjusted. In other words, the intensity of the laser input beam is modified by the laser beam generation unit, whereby the intensity of the portion of the laser input beam which is coupled into the ring region for generating the second laser beam by the beam splitting device is adjusted. By adjusting the intensity of the laser input beam, the intensity of the second laser beam can be modified particularly easily.In particular, adjusting the second intensity of the second laser beam by adjusting the intensity of the laser input beam allows the division of the laser input beam into the core region and the ring region of the optical fiber to remain unchanged by means of the beam splitting device. It is thus particularly easy to increase or decrease, in addition to the second intensity of the second laser beam, the first intensity of the first laser beam in direct proportion to the second intensity of the second laser beam. This ensures that not only is the energy per unit length introduced into the workpiece by means of the second laser beam constant along the entire cutting contour, but also that the energy per unit length introduced into the workpiece by means of the first laser beam constant along the entire cutting contour.

[0013] In an alternative possible embodiment of the invention, it is provided that the first laser beam is provided by means of a first laser beam generation unit and the at least one second laser beam is provided by means of a second laser beam generation unit separate from the first laser beam generation unit, whereby the second intensity of the at least one second laser beam can be adjusted independently of the first intensity of the first laser beam. In this case, it is possible for the first laser beam generation unit to couple the first laser input beam into the core region of the optical waveguide of the laser device and for the second laser beam generation unit to couple the second laser input beam into the ring region of the optical waveguide. It can be provided that the laser device has a separate laser beam generation unit for each region of the optical waveguide.If the optical fiber has two ring regions, the laser device can have three separate laser beam generation units. By providing separate laser beam generation units for the respective laser beams, the intensities of the individual laser beams of the processing beam can be individually controlled particularly easily.

[0014] In this context, it can be provided in particular that when cutting along a corner or a curve of the cutting contour with a radius below a predetermined curve limit value, the first laser beam is provided by the first laser beam generation unit with a pulsed first intensity and the second laser beam is provided by the second laser beam generation unit with an unpulsed second intensity. By pulsing the first laser beam when cutting corners or when cutting curves with small radii, the corner or the small radius of the cutting contour can be cut particularly precisely. By pulsing, beading on the cutting edge in the area of ​​the corner or in the area of ​​the small radius can be particularly effectively avoided.Because the second laser beam is also provided with unpulsed second intensity in the area of ​​the corner or curve with a small radius, reliable, uniform rounding of the cutting edge created during cutting can be ensured even in the area of ​​the corner or curve with a small radius.

[0015] In a further possible embodiment of the invention, it is provided that the second intensity of the second laser beam is adjusted directly proportional to a change in the feed rate. The energy per unit length results from the quotient of the second intensity of the second laser beam as the numerator and the feed rate as the denominator. In order to achieve a constant energy per unit length across the entire cutting contour, when the feed rate is reduced, the second intensity of the second laser beam must also be reduced, in particular directly proportional to the feed rate, in order to ensure that the ratio of second intensity to feed rate and consequently the energy per unit length remains the same. In this way, it can be achieved that the cutting edge has at least substantially the same rounding radius along the entire cutting contour.

[0016] In a further possible embodiment of the invention, the processing beam has a minimum laser power of at least 800 watts during processing. This means that the intensity of the processing beam is always at least 800 watts when processing the workpiece. As a result, reliable cutting and rounding of the cutting edge created during cutting can be ensured even at low feed rates.

[0017] The invention further relates to a laser device for machining a metallic workpiece by means of a machining beam, comprising a laser device configured to direct the machining beam onto the workpiece and to move it in a cutting direction relative to the workpiece at a feed rate that varies depending on a cutting contour to be cut. The machining beam comprises a first laser beam having a first intensity for cutting the workpiece in a thickness direction and at least one second laser beam impinging on a workpiece surface of the workpiece alongside the first laser beam, having a second intensity that is lower than the first intensity. As a result, a rounded cutting edge can be produced by means of the at least one second laser beam.

[0018] The laser device further comprises a control device configured to control the setting of the second intensity of the second laser beam in a method as already described in connection with the method according to the invention for machining the metallic workpiece. In other words, the control device is configured to determine, as a function of a predetermined rounding radius of the cutting edge to be achieved, a linear energy to be introduced into the workpiece by means of the at least one second laser beam. Furthermore, the control device is configured to trigger the second intensity of the at least one second laser beam to be adjusted during machining as a function of the varying feed rate, whereby the linear energy introduced into the workpiece for rounding by means of the second laser beam is constant along the entire cutting contour.The workpiece can be supported on a workpiece support during the machining process, for example. The laser device can be part of a laser cutting system, such as a flatbed laser cutting system or a tube laser cutting system.

[0019] The processing beam can be provided with at least three laser beams with mutually different intensities, which are arranged next to one another in a line running perpendicular to the cutting direction on the workpiece surface. To generate the processing beam with the at least three laser beams, the laser device comprising the optical waveguide designed as a 3-in-1 fiber can be used. Alternatively, the respective laser beams can be provided by separate laser devices, with a separate laser device being provided for each laser beam.By providing three laser beams with different intensities, the workpiece can be cut using the first laser beam, while the second and third laser beams, which can also have different intensities, can provide a rounded cutting edge of the workpiece. By providing the second and third laser beams with different intensities, a rounded contour of the cutting edge can be specified with particular precision.

[0020] If the optical fiber comprises the core region and two further ring regions, then when the laser input beam is coupled into both the core region and both ring regions, a first laser beam, a second laser beam and a third laser beam are created. The third laser beam is arranged next to the first and second laser beams and thus strikes the workpiece surface next to the first laser beam and the second laser beam when the processing beam is aligned with the workpiece. In particular, the third laser beam can enclose the second laser beam circumferentially and have a ring-shaped image on the workpiece surface. The processing beam can thus centrally comprise the first laser beam, the second laser beam, which surrounds the first laser beam in a ring, and the third laser beam, which surrounds the second laser beam in a ring.

[0021] Further features of the invention can be derived from the following description of the figures and from the drawings. The features and combinations of features mentioned above in the description, as well as the features and combinations of features shown below in the description of the figures and / or in the figures alone, can be used not only in the respective combinations specified, but also in other combinations or on their own, without departing from the scope of the invention.

[0022] The drawing shows: Fig. 1 a schematic side view of a laser device by means of which a metallic workpiece is processed; Fig. 2 a schematic sectional view of the metallic workpiece machined by means of a machining beam of the laser device; Fig. 3 a schematic plan view of a cutting contour along which the workpiece is to be cut.

[0023] Identical or functionally equivalent elements are provided with the same reference numerals in the figures.

[0024] In Fig. 1 shows individual components of a laser device. Fig. 1 shows an optical waveguide 10 and a focusing lens 12 of a focusing optics. The focusing lens 12 is configured to focus light beams provided by the optical waveguide 10. The laser device comprises a laser beam generation unit (not shown in the figures) which is configured to generate a laser input beam. Furthermore, the laser device comprises the Fig. 1, which in this case is designed as a multi-clad fiber, specifically as a 2-in-1 fiber. This 2-in-1 fiber comprises a core region 14 and an annular region 16 circumferentially surrounding the core region 14. As an alternative to the design of the multi-clad fiber as a 2-in-1 fiber, the multi-clad fiber can be designed as a so-called 3-in-1 fiber with a core region 14, an inner annular region, and an outer annular region, wherein the inner annular region circumferentially surrounds the core region 14 and the outer annular region circumferentially surrounds the inner annular region. The laser device further comprises a beam splitting device (not shown in the figures), by means of which the laser input beam provided by the laser beam generation unit can be split between the core region 14 and the annular region 16.In particular, the beam splitting device is configured to adjust the proportional splitting of the laser input beam between the core region 14 and the ring region 16.

[0025] For processing a metallic workpiece W, a processing beam 18 is provided by the laser device and directed onto the workpiece W. In this case, the processing beam 18 comprises a first laser beam 20 and a second laser beam 22. In this case, the first laser beam 20 and the second laser beam 22 are respective partial beams of a common laser beam provided by the multi-clad fiber. The first laser beam 20 is provided via the core region 14 and the second laser beam 22 via the ring region 16 of the 2-in-1 fiber. The laser beams 20, 22 are focused in the direction of the workpiece W by means of focusing optics, in this case the focusing lens 12. For processing the metallic workpiece W, the processing beam 18 is moved relative to the workpiece W in a cutting direction 24 extending into the image plane.The processing beam 18 is thus moved in the cutting direction 24 over a workpiece surface 26 of the workpiece W. The workpiece W is processed by means of the laser beams 20, 22 of the processing beam 18 impinging on the workpiece surface 26. The first laser beam 20 has a first intensity and the second laser beam 22 has a second intensity that is lower than the first intensity of the first laser beam 20. The first laser beam 20 is configured to cut the workpiece W in its thickness direction 28. The workpiece W can be cut through across its entire thickness in the thickness direction 28 by means of the first laser beam 20. The second laser beam 22 is configured to produce a rounded cutting edge 30.In other words, during machining of the workpiece W, the workpiece W is divided into a first workpiece part W1 and a second workpiece part W2 by means of the machining beam 18, wherein the second laser beam 22 ensures that respective cutting edges 30 of the first workpiece part W1 and the second workpiece part W2 are rounded after machining.

[0026] If a 3-in-1 fiber is used as the multi-clad fiber, the processing beam 18 can comprise three laser beams with mutually different intensities, which are arranged next to one another in a line running perpendicular to the cutting direction 24 on the workpiece surface 26.

[0027] In Fig. 2, the area in which the workpiece W is cut by means of the processing beam 18 is shown enlarged. It can be seen particularly clearly that the first laser beam 20 and the second laser beam 22 are arranged next to one another in a line running perpendicular to the cutting direction 24 on the unprocessed workpiece surface 26. In this case, the second laser beam 22 can have an annular image on the unprocessed workpiece surface 26, which image encloses an image of the first laser beam 20, which can in particular be circular, on the outer circumference. Alternatively, the second laser beam 22 can be arranged only next to the first laser beam 20 and not completely enclose the image of the first laser beam 20. In this case, the second laser beam 22 is arranged next to the first laser beam 20 towards the resulting cutting edge 30, whereby the cutting edge 30 is rounded.

[0028] In Fig. 3, the workpiece W is shown in a plan view, showing how the processing beam 18 is aligned with a cutting contour 32 to be cut. In order to separate the first workpiece part W1 and the second workpiece part W2 from each other, the processing beam 18 is guided along the cutting contour 32 in the cutting direction 24. The processing beam 18 is in Fig. 3 as a circular projection onto the workpiece surface 26 of the workpiece W. As in Fig.3, the cutting contour 32 in the present case has first regions 34 in which the cutting contour 32 runs at least substantially straight, and second regions 36 in which the cutting contour 32 has a corner or a curve with a radius below a predetermined curve limit value. For reasons of control of the laser device providing the processing beam 18, the result can be that the processing beam 18 is moved at a first feed rate in the first regions 34 and at a second feed rate that is lower than the first feed rate in the second regions 36. For example, the processing beam 18 is moved at a feed rate of 40 meters per minute in the first regions 34 and at a feed rate of three meters per minute in the second regions 36.In order to avoid that, due to the different feed rates in different areas of the cutting contour 32, different levels of energy per unit length are introduced into the workpiece by means of the second laser beam 22 and, as a result, the cutting edge 30 has different rounding radii along the entire cutting contour 32, it is provided that the second intensity of the at least one second laser beam 22 is adjusted during machining as a function of the varying feed rate.For this purpose, a linear energy to be introduced into the workpiece W by means of the at least one second laser beam 22 can be determined as a function of a predetermined rounding radius to be achieved of the cutting edge 30, and the second intensity of the at least one second laser beam 22 can be adjusted during machining as a function of the varying feed rate such that the linear energy introduced into the workpiece W for rounding by means of the second laser beam 22 is constant along the entire cutting contour 32. In particular, it is provided that the second intensity of the second laser beam 22 is adjusted directly proportional to a change in the feed rate. However, a limit can be specified that the at least one second laser beam 22 must have at least a minimum laser power of 800 watts during machining.

[0029] The second intensity of the at least one second laser beam 22 can be adjusted by using the beam splitting device to adjust the ratio of the splitting of the laser input beam between the core region 14 and the at least one ring region 16. Alternatively or additionally, to adjust the second intensity of the second laser beam 22, an intensity of the laser input beam provided by the laser beam generation unit, which is split into the first laser beam 20 and the second laser beam 22, can be adjusted. Alternatively, it is possible for the first laser beam 20 to be provided by a first laser beam generation unit and the second laser beam 22 to be provided by a second laser beam generation unit separate from the first laser beam generation unit.As a result, the second intensity of the second laser beam 22 can be adjusted independently of the first intensity of the first laser beam 20. In particular, when the laser beams 20, 22 are provided by means of different laser beam generation units, it is possible for the first laser beam 20 to be provided with a pulsed first intensity, at least in the respective second regions 36, while the second laser beam 22 is provided with a non-pulsed second intensity.

[0030] The invention described is based on the problem that when edge rounding with a 2-in-1 laser light cable, a 3-in-1 laser light cable, or an n-in-1 laser light cable, or with all 2D laser edge rounding processes that are carried out in direct cutting, the problem of excess power at corners and smaller radii of the cutting contour 32 exists, provided the second intensity of the second laser beam 22 is kept constant during processing. This can lead to the rounding radius at the corner or at a small radius of the cutting contour 32 becoming a chamfer instead of an edge rounding. To solve this problem, the energy per unit length for generating the rounding radius must be kept constant along the entire cutting contour 32. This means that the laser power for rounding must be reduced linearly with the feed rate when the cutting feed is reduced, but in particular must not be reduced to zero watts.

[0031] A first possibility for solving this problem is to reduce both the laser power for cutting and the laser power for edge rounding linearly with the feed rate by adjusting the laser power for both cutting and edge rounding. A second possibility for solving this problem is to reduce the laser power in the ring region 16 and thus in the fiber cladding, in particular by increasing the laser power in the core region 14 and thus a fiber core, by adjusting a wedge switch position of a wedge switch of the beam splitting device. This reduces the laser power in the fiber cladding of the fiber optic cable and instead introduces more laser power into the core region 14 of the fiber optic cable, in particular in such a way that the energy per unit length introduced into the workpiece by the second laser beam 22 is constant over the entire cutting contour 32.Both of the above options can be combined.

[0032] When edge rounding on 2D laser flatbed machines, with 2-in-1 fiber optic cables, 3-in-1 fiber optic cables, or n-in-1 fiber optic cables, or optics that include optical elements for beam splitting, such as the beam splitting device, the same laser input beam is used for cutting and edge rounding. The laser input beam with n-in-1 fiber optic cables is split between the fiber core and the fiber cladding or fiber claddings. With the different power components of the laser input beam in the fiber core and in the fiber cladding or fiber claddings, cutting and a resulting cut edge 30 can be performed simultaneously. Cutting is performed with the power in the fiber core, while the cut edge 30 is rounded using the laser power in the fiber cladding or fiber claddings.Especially when cutting thin sheet metal as workpiece W at high feed rates, the feed rate in these second regions 36 must be significantly reduced at contour corners and radii of the cutting contour 32 below the specified curve limit. If the laser power in the fiber cladding, which is used to round the cutting edge 30, remains constant, then the energy per unit length in the second regions 36 increases at the reduced feed rate, and a chamfer forms in the second regions 36 instead of a rounding at the cutting edge 30.

[0033] To solve this problem, the intensity of the laser input beam can be reduced linearly with the feed rate reduction. However, the laser power of the laser input beam should not be reduced to zero watts, as otherwise, edge rounding of the cutting edge 30 would no longer occur at the corners. A minimum laser power for a laser device with a 3-in-1 fiber optic cable is 800 watts for the laser input beam to ensure reliable rounding of the cutting edge 30. The energy per unit length for rounding must be kept constant along the entire cutting contour 32, which in this case is achieved by adjusting the laser power of the laser input beam and thus the laser power for both cutting and edge rounding.Another possibility for keeping the energy per unit length constant when rounding the cutting edge 30 is to reduce the laser power in the cladding and thus in the ring region 16 of the fiber optic cable by increasing the laser power in the core region 14 of the fiber optic cable. This can be achieved by adjusting a wedge switch of the beam splitting device of the laser device. This reduces the laser power of the laser input beam introduced into the fiber cladding by coupling more of the laser power of the laser input beam into the fiber core of the fiber optic cable. The wedge switch in the case of a 2-in-1 fiber optic cable, or both wedge switches in the case of a 3-in-1 fiber optic cable, are moved during cutting and thus during the processing of the workpiece W. The wedge switch positions are coupled in particular to the feed rate.If the feed rate is reduced, the at least one wedge switch is moved to a position where more laser power of the laser input beam is coupled into the fiber core. The more the feed rate is reduced, the more laser power of the laser input beam is coupled into the fiber core. The minimum remaining laser power in the fiber cladding should be at least 800 watts to ensure the reliable creation of a rounded cut edge 30. If the feed rate increases again, the at least one wedge switch can be moved such that more of the laser power of the laser input beam is coupled into the at least one ring region 16 and thus into the fiber cladding. Here, too, a constant energy per unit length along the entire cutting contour 32 is crucial.

[0034] Within the scope of the process, for example, a two-millimeter CrNi steel workpiece can be machined using a ten-kilowatt laser as the laser device. A standard cutting feed rate without edge rounding can be 50 meters per minute. If a rounding radius of 0.6 millimeters is to be applied to the cutting edge 30, then two kilowatts of the laser power of the laser input beam can be coupled into at least one fiber cladding, in particular the two fiber claddings when using the 3-in-1 fiber optic cable, and eight kilowatts of the laser power of the laser input beam can be coupled into the fiber core and thus used for cutting. Due to the 20 percent power reduction in the fiber core, the cutting feed rate must be reduced by 20 percent to 40 meters per minute compared to cutting without edge rounding.With a laser power of two kilowatts in at least one fiber cladding and eight kilowatts in the fiber core of the laser input beam, the cutting contour 32 can now be very well rounded over a straight section. At corners of the cutting contour 32, the feed rate of 40 meters per minute must be reduced due to the dynamics. As a result, with the laser power of at least one second laser beam 22 remaining constant, the energy per unit length for rounding at the corner of the cutting contour 32 would increase and the radius of 0.6 millimeters would become a chamfer. In order to ensure that the specified rounding radius of 0.6 millimeters can also be maintained at the corner of the cutting contour 32, the laser power of the second laser beam 22 must be reduced linearly with the feed rate. Using a linear characteristic curve, it can be ensured that the rounding radius is kept constant across the entire cutting contour 32.A reduction in the feed rate from 40 meters per minute to three meters per minute results in a reduction in the laser power of the laser input beam from ten kilowatts to 1.5 kilowatts.

[0035] The two laser beams 20, 22 could be provided by two different laser beam generation units. One of the laser beam generation units can couple the generated first laser input beam only into the fiber core, and the second laser beam generation unit can couple the generated second laser input beam only into the fiber cladding. By reducing the feed rate along the cutting contour 32, both laser beam generation units can be adjusted separately and differently. The laser beam generation unit, which couples the laser power for cutting into the fiber core, can be operated in a pulsed mode during corner travel to prevent beading at the cutting edge 30 in the corner.Meanwhile, the second laser beam generation unit, which is used for edge rounding, can be operated by simply reducing the laser power of the input laser beam, which is adjusted linearly to reduce the feed rate. This allows the cutting quality to be adjusted independently of the edge rounding.

[0036] Overall, the invention shows how edge rounding can be implemented on corners and small radii of a cutting contour 32. LIST OF REFERENCE SYMBOLS W workpiece W1 first workpiece part W2 second workpiece part 10 optical fibers 12 Focusing lens 14 Core area 16 ring area 18 Processing beam 20 first laser beam 22 second laser beam 24 Cutting direction 26 Workpiece surface 28 Thickness direction 30 cutting edge 32 Cutting contour 34 first area 36 second area QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2019 125 103 A1

[0002]

Claims

[1] Method for machining a metallic workpiece (W), in which - a processing beam (18) is directed onto the workpiece (W) and moved in a cutting direction (24) relative to the workpiece at a feed rate varying depending on a cutting contour (32) to be cut, wherein the processing beam (18) comprises a first laser beam (20) with a first intensity for cutting the workpiece (W) in a thickness direction (28) and at least one second laser beam (22) impinging on a workpiece surface (26) of the workpiece (W) in addition to the first laser beam (20) with a second intensity lower than the first intensity, whereby a rounded cutting edge (30) is produced by means of the at least one second laser beam (22); and - depending on a predetermined rounding radius of the cutting edge (30) to be achieved, a line energy to be introduced into the workpiece (W) by means of the at least one second laser beam (22) is determined and the second intensity of the at least one second laser beam (22) is adjusted during machining as a function of the varying feed rate, whereby the line energy introduced into the workpiece (W) for rounding by means of the second laser beam (22) is constant along the entire cutting contour (32). [2] Method according to claim 1, wherein the first laser beam (20) and the at least one second laser beam (22) are guided next to one another in a line running perpendicular to the cutting direction (24) on the workpiece surface (26), in particular the at least one second laser beam (22) has an annular cross-section and encloses the first laser beam (20) circumferentially. [3] Method according to claim 1 or 2, wherein the feed rate when cutting along a corner or a curve of the cutting contour (32) with a radius below a predetermined curve limit value is selected to be smaller than when cutting along a straight section or a curve of the cutting contour (32) with a radius greater than or equal to the predetermined curve limit value. [4] Method according to one of the preceding claims, wherein the processing beam (18) is provided by means of a laser device which - an optical waveguide (10) having a core region (14) and at least one ring region (16), - a laser beam generating unit by means of which a laser input beam is generated, and - comprises a beam splitting device by means of which the laser input beam is split between the core region (14) for generating the first laser beam (20) and the at least one ring region (16) for generating the at least one second laser beam (22), wherein the second intensity of the at least one second laser beam (22) is adjusted by adjusting the ratio of the splitting of the laser input beam between the core region (14) and the at least one ring region (16) by means of the beam splitting device. [5] Method according to one of the preceding claims, wherein for adjusting the second intensity of the at least one second laser beam (22) an intensity of a laser input beam provided by means of a laser beam generation unit, which is split into the first laser beam (20) and into the at least one second laser beam (22), is set. [6] Method according to one of claims 1 to 3, wherein the first laser beam (20) is provided by means of a first laser beam generating unit and the at least one second laser beam (22) is provided by means of a second laser beam generating unit separate from the first laser beam generating unit, whereby the second intensity of the at least one second laser beam (22) can be adjusted independently of the first intensity of the first laser beam (20). [7] Method according to claim 6, wherein when cutting along a corner or a curve of the cutting contour (32) with a radius below a predetermined curve limit value, the first laser beam (20) is provided by means of the first laser beam generating unit with a pulsed first intensity and the second laser beam (22) is provided by means of the second laser beam generating unit with an unpulsed second intensity. [8] Method according to one of the preceding claims, wherein the second intensity of the second laser beam (22) is adjusted directly proportional to a change in the feed rate. [9] Method according to one of the preceding claims, wherein the processing beam (18) has at least a minimum laser power of 800 watts during processing. [10] Laser device for machining a metallic workpiece (W), comprising a laser device which is configured to direct a machining beam (18) onto the workpiece (W) and to move it in a cutting direction (24) relative to the workpiece (W) at a feed rate varying depending on a cutting contour (32) to be cut, wherein the machining beam (18) comprises a first laser beam (20) with a first intensity for cutting the workpiece (W) in a thickness direction (28) and at least one second laser beam (22) impinging on a workpiece surface (26) of the workpiece (W) in addition to the first laser beam (20) with a second intensity which is lower than the first intensity, whereby a rounded cutting edge (30) is produced by means of the at least one second laser beam (22), wherein the laser device comprises a control device which is configured toto control the setting of the second intensity of the second laser beam (22) in a method according to one of the preceding claims.,

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