Device and method for generating laser radiation with different power and brilliance

Abstract

Device (1) for generating either a first output laser radiation (13) with lower power and higher brilliance or a second output laser radiation (14) with higher power and lower brilliance for laser material processing of workpieces of different thicknesses, comprising a first diode laser unit (2) for generating a first input laser radiation (3) with higher brilliance by dense wavelength coupling of several diode laser beams (10) of the first diode laser unit (2), a second diode laser unit (4) for generating a second input laser beam (5) with lower brilliance by geometric superposition of several diode laser beams (11) of the second diode laser unit (4), an optical fiber in the form of a double or multiple core fiber (6) with at least one first and second fiber core (7, 8) or in the form of a graded index fiber (16), and at least one optical element (9) for coupling the first input laser radiation (3) into the first fiber core (7) and the second input laser radiation (5) into the second fiber core (8) of the double or multiple core fiber (6) or for coupling the first input laser radiation (3) into a first region and the second input laser radiation (5) into a second region of the graded index fiber (16), such that the first input laser radiation (3) is coupled out as a first output laser radiation (13) for laser material processing of thin workpieces and the first and second input laser radiation (3, 5) together as a second output laser radiation (14) for laser material processing of thick workpieces from a fiber end (6b) of the optical fiber (6).

Description

[0001] The invention relates to a device and a method for generating either a first output laser radiation with lower power and higher brilliance or a second output laser radiation with higher power and lower brilliance.

[0002] Workpieces made of structural steel (e.g., S235) with large workpiece thicknesses (> 5 mm) are generally cut by laser flame cutting, i.e., with the addition of oxygen. Efficient flame cutting in such structural steel sheets requires high laser power and poor beam quality (beam parameter product > 16 mm*mrad). Workpieces, especially those made of stainless steel or aluminum, with thin workpiece thicknesses (< 5 mm), on the other hand, are cut by laser fusion cutting, i.e., with nitrogen or argon as the cutting gas, which is forced through the kerf at pressures between 2 and 20 bar.

[0003] The current development of densely wavelength-coupled, DWM (Dense Wavelength Multiplexing) diode lasers for laser cutting aims at a high laser output power with the best possible beam quality (beam parameter product < 4 mm*mrad), which is very well suited for laser fusion cutting (of stainless steel sheets), but less optimal for flame cutting in structural steel sheets.

[0004] DWM diode lasers are known, for example, from US 6 192 062 B1, US 6 208 679 B1, US 6 327 292 B1, US 9 306 369 B2, US 9 391 713 B2, US 2016 / 0 336 714 A1, WO 2016 / 062 758 A1 and DE 10 2011 003 142 A1.

[0005] US 2013 / 0 215 914 A1 discloses a setup in which a fiber laser with good beam quality and a solid-state laser with poor beam quality are used for processing. The first input laser radiation generated by the fiber laser is coupled only into the fiber core, while the second input laser radiation generated by the solid-state laser is coupled into the fiber core and the fiber cladding of a transport fiber. Both are coupled out together as a single output laser beam.

[0006] Furthermore, EP 1 848 074 A1 discloses a laser source in which the pump radiation is controlled such that it either lies at an absorption maximum of an active medium and the output laser radiation is mainly provided by the active medium and has a good beam quality, or lies outside the absorption of the active medium and the output laser radiation is mainly provided by the pump source and has a poor beam quality.

[0007] Finally, US 8 008 600 B2 discloses a laser processing machine with a fiber laser, wherein both the input laser radiation generated by the fiber laser and the pump laser radiation not absorbed in the fiber laser are coupled into a transport fiber and coupled out together as an output laser beam for processing.

[0008] EP 2 624 031 A1 discloses a method and arrangement for generating a laser beam with different beam profile characteristics to better meet material processing requirements. By using multi-clad fibers, especially double-clad fibers, the laser beam can be coupled into different core regions of the fiber as needed. This allows the beam profile to be flexibly adapted, for example, for applications that require either high beam quality with a sharp focus (such as laser cutting) or a uniform intensity distribution (such as laser welding).

[0009] Furthermore, DE 10 2012 219 074 A1 discloses a laser cutting machine and a method for cutting workpieces of varying thicknesses. This machine can automatically adjust the laser beam depending on the workpiece thickness, without the need for complex retooling or the use of multiple machines. Thin workpieces are processed with a narrow focus beam for precise cutting, while thick workpieces receive a wider focus beam to optimize the cut and remove slag. The laser beam characteristics are adjusted directly during processing.

[0010] In contrast, it is the object of the present invention to provide a device and a method for generating either a first output laser radiation with lower power and higher brilliance or a second output laser radiation with higher power and lower brilliance.

[0011] This object is achieved according to the invention by a device for selectively generating either a first output laser radiation with lower power and higher brilliance or a second output laser radiation with higher power and lower brilliance for laser material processing of workpieces of different thicknesses, comprising a first diode laser unit for generating a first input laser radiation with higher brilliance by dense wavelength coupling of several diode laser beams of the first diode laser unit, a second diode laser unit for generating a second input laser radiation with lower brilliance by geometrically superimposing several diode laser beams of the second diode laser unit, an optical fiber in the form of a double-core or multi-core fiber with at least a first and second fiber core or in the form of a gradient index fiber,and at least one optical element for coupling the first input laser radiation into the first fiber core and the second input laser radiation into the second fiber core of the double- or multi-core fiber, or for coupling the first input laser radiation into a first region and the second input laser radiation into a second region of the gradient-index fiber, so that the first input laser radiation is coupled out of one fiber end of the optical fiber as a first output laser radiation for the laser material processing of thin workpieces, and the first and second input laser radiation are coupled out together as a second output laser radiation for the laser material processing of thick workpieces.

[0012] The diode laser units can each comprise multiple diode laser modules. A diode laser module can have one or more single emitters, or one or more diode bars with multiple emitters. The single emitters or diode bars are arranged in a one- or two-dimensional array, with the array consisting of a vertical and / or horizontal stack of single emitters or diode bars.

[0013] According to the invention, the first diode laser unit is a densely wavelength-coupled DWM diode laser, and the second diode laser unit is a diode laser with low beam quality. By coupling the second input laser radiation generated by the second diode laser unit into the second fiber core, a higher laser power is available for the flame cut. The higher laser output power enables a higher feed rate, and thicker sheet thicknesses can be cut. The reduced beam quality (approx. 16 mm*mrad) leads to better cut edge quality during flame cutting. When cutting thinner workpieces, the required laser power is lower. The second diode laser unit can therefore be switched off, allowing the machine to be operated energy-efficiently.

[0014] According to the invention, the following basic idea is pursued: The laser power of the non-wavelength-coupled (non-DWM) input laser beam is added to the laser power of the densely wavelength-coupled DWM beam with reduced beam quality, resulting in an overall higher output power and a lower beam quality of the output laser beam and having a beneficial effect on both the cutting speed and the cut edge quality, especially when flame cutting workpieces with large thicknesses.

[0015] In the case of a double- or multi-core fiber, the first fiber core is particularly preferably formed as an inner fiber core and the second fiber core as an outer fiber core that surrounds the inner fiber core in a ring. Thus, the first input laser radiation is coupled into the inner fiber core and the second input laser radiation into the outer fiber core.

[0016] The at least one optical element, e.g. a common lens or a lens for each of the two input laser radiations, can further be designed to couple the first and second input laser radiation into the optical fiber at a different coupling angle and / or with different divergence.

[0017] As tests have shown, for thin and thick sheet metal processing, the first input laser radiation should have a beam parameter product of no more than 4 mm*mrad and the second input laser radiation should have a beam parameter product of at least 16 mm*mrad.

[0018] Preferably, a focusing device is arranged in the beam path of the first and second output laser beams, which focuses the first and second output laser beams into a focal plane. As tests have shown, for thin and thick sheet metal processing, the focal diameter of the first output beam in the focal plane should be between 30 µm and 500 µm, and the focal diameter of the second output beam in the focal plane should be between 700 µm and 900 µm.

[0019] The wavelength range of the second input laser radiation is preferably outside the wavelength range of the first input laser radiation, for example the first input laser radiation is in a wavelength range of 900 nm to 950 nm and the second input laser radiation is in a wavelength range of 960 nm and 965 nm.

[0020] Advantageously, a coupling optics system is arranged in the beam path of the first and second input laser radiations between the first diode laser unit and the second diode laser unit on the one hand, and the optical fiber on the other hand, which superimposes the first input laser radiation and the second input laser radiation. The coupling optics system can, for example, be a wavelength-selective mirror (multilayer mirror) that is transparent to the first input laser radiation and reflective to the second input laser radiation, or vice versa. For this purpose, the two diode laser units must emit in two different wavelength ranges. Alternatively, the two input laser radiations can also be coupled via polarization.In this case, the coupling optics is designed as a polarization beam splitter, which is reflective for the polarization direction of the first input laser radiation and transmissive for the polarization direction of the second input laser radiation, or vice versa.

[0021] In a further aspect, the invention also relates to a method for generating either a first output laser radiation with lower power and higher brilliance or a second output laser radiation with higher power and lower brilliance for the laser material processing of workpieces of different thicknesses, comprising the steps: Generating a first input laser radiation with higher brilliance by dense wavelength coupling of several diode laser beams, Generating a second input laser radiation with lower brilliance by geometrically superimposing several diode laser beams, and coupling the first input laser radiation into a first fiber core and the second input laser radiation into a second fiber core of an optical fiber designed as a double- or multi-core fiber, or coupling the first input laser radiation into a first region and the second input laser radiation into a second region of an optical fiber designed as a gradient index fiber, Generating the first output laser radiation by coupling out the coupled first input laser radiation from a fiber end of the optical fiber for laser material processing of thin workpieces, and Generating the second output laser radiation by jointly coupling out the coupled first and second input laser radiation from the fiber end of the optical fiber for laser material processing of thick workpieces.

[0022] Preferably, thin workpieces with a sheet thickness of less than 5 mm are cut with the first output laser radiation and thick workpieces, in particular structural steel sheets, with a sheet thickness of greater than 5 mm are cut with the second output laser radiation.

[0023] In a preferred method variant, the first and second output laser beams are focused into a focal plane, wherein the focal diameter of the first output beam lies between 30 µm and 500 µm and the focal diameter of the second output beam lies between 700 µm and 900 µm in the focal plane. In an alternative method variant, the first and second output laser beams are focused such that the position of their focal points lies in two different focal planes in the beam propagation direction.

[0024] Further advantages and advantageous embodiments of the subject matter of the invention will become apparent from the description, the claims, and the drawings. Likewise, the above-mentioned and further listed features can be used individually or in combination. The embodiments shown and described are not to be understood as an exhaustive list, but rather as examples for describing the invention.

[0025] They show: Fig. 1 schematically shows a device according to the invention for generating different laser radiation for laser material processing; Fig. 2a, Fig. 2b the input end face of a double core fiber ( Fig. 2a) and a gradient index fiber ( Fig. 2b).

[0026] The Fig. The device 1 shown in Figure 1 serves to generate different laser radiation for laser material processing, for example to process sheets of different thicknesses.

[0027] The device 1 comprises a first diode laser unit 2 for generating a first input laser radiation 3 with higher brilliance, a second diode laser unit 4 for generating a second input laser radiation 5 with lower brilliance, an optical fiber in the form of a double-core fiber 6 with an inner fiber core 7 and with an outer fiber core 8 surrounding the inner fiber core 7 in a ring shape ( Fig. 2a), as well as a first lens 9 for coupling the first input laser radiation 3 into the inner fiber core 7 and the second input laser radiation 5 into the outer fiber core 8 at a fiber end 6a of the double-core fiber 6. The input laser radiation 3, 5 can also be coupled into the double-core fiber 6 in another way, for example with the aid of further optical fibers into which the input laser radiation 3 and 5 of the diode laser units 2 and 4 are each coupled and which are spliced ​​to the double-core fiber 6 at the inner and outer fiber cores 7, 8 and can thus be regarded as an optical element for coupling. The second input laser radiation can also be coupled at a location other than the fiber end 6a of the double-core fiber.

[0028] As in Fig. As indicated in Figure 2a, in the example shown here, at the input-side fiber end 6a, the first input laser radiation 3 is coupled only into the inner fiber core 7 and the second input laser radiation 5 is coupled only into the outer fiber core 8. The two lenses 9 can be configured to couple the first and second input laser radiation 3, 5 into the double-core fiber 6 at different coupling angles and / or with different divergences.

[0029] The two diode laser units 2, 4 can each comprise a plurality of diode laser modules, which in turn have one or more single emitters, or one or more diode bars with multiple emitters. The individual emitters form a laser source; the single emitters or diode bars can be arranged in a one- and / or two-dimensional array. The array consists of a vertical or horizontal stack of single emitters or diode bars. The first diode laser unit 2 generates the first input laser radiation 3 with the higher brilliance through dense wavelength coupling of a plurality of diode laser beams 10 of the first diode laser unit 2, and the second diode laser unit 4 generates the second input laser radiation 5 with the lower brilliance through geometric superposition of a plurality of diode laser beams 11 of the second diode laser unit 4.For example, the first input laser radiation 3 can have a beam parameter product of at most 4 mm*mrad, and the second input laser radiation 5 can have a beam parameter product of at least 16 mm*mrad. Preferably, the wavelength range of the second input laser radiation 5 lies outside the wavelength range of the first input laser radiation 3, for example, the first input laser radiation 3 lies in a wavelength range from 900 nm to 950 nm, and the second input laser radiation 5 lies in a wavelength range from 960 nm to 965 nm.

[0030] In the beam path of the first and second input laser radiations 3, 5, a coupling optic 12 is arranged between the first and second diode laser units 2, 4 on the one hand and the dual-core fiber 6 on the other, which superimposes the first and second input laser radiations 3, 5. In the illustrated embodiment, the coupling optic 12 is designed as a wavelength-selective mirror that is reflective for the first input laser radiation 3 and transmissive for the second input laser radiation 5. Alternatively, the coupling optic 12 can also be designed as a polarization beam splitter that is reflective for the polarization direction of the first input laser radiation 3 and transmissive for the polarization direction of the second input laser radiation 5.

[0031] From the other fiber end 6b, either the coupled first input laser radiation 3 is coupled out as a first output laser radiation 13 or the first and second input laser radiation 3, 5 are coupled out together as a second output laser radiation 14, so that the first output laser radiation 13 has a higher beam quality and a lower power and the second output laser radiation 14 has a lower beam quality and a higher power.

[0032] A focusing device 15 (e.g. a focusing lens) is arranged in the beam path of the first and second output laser radiation 13, 14, which focuses the first and second output laser radiation 13, 14 into a focal plane 16. The focal diameter of the first output radiation 13 in the focal plane can be, for example, between 30 µm and 500 µm, and the focal diameter of the second output radiation in the focal plane can be, for example, between 700 µm and 900 µm. A sheet to be processed is arranged in the focal plane 16, wherein thin sheets with a sheet thickness of less than 5 mm can be cut with the first output radiation 13 and thick sheets, in particular structural steel sheets, with a sheet thickness of greater than 5 mm can be cut with the second output laser radiation 14.Instead of being focused in the same focal plane, the first and second output laser beams 13, 14 can also be focused such that the position of their focal points in the beam propagation direction lies in two different focal planes.

[0033] As in Fig. As shown in Figure 2b, a gradient index fiber 16 can alternatively be used as the optical fiber, wherein the first and second input laser radiation 3, 5 are coupled into different regions of the input-side fiber end 6a of the gradient index fiber 16.

[0034] Unlike in Fig.1, where each of the two diode laser units 2, 4, which radiate at 90° to each other, is followed by its own lens 9, the two diode laser units 2, 4 can also be arranged so that they radiate in the same direction. In this case, a common lens can be used for the first and second input laser radiation 3, 5. This common lens can be configured to couple the first and second input laser radiation 3, 5 into the optical fiber 6, 16 at different coupling angles and / or with different divergences.

Claims

[1] Device (1) for generating either a first output laser radiation (13) with lower power and higher brilliance or a second output laser radiation (14) with higher power and lower brilliance for the laser material processing of workpieces of different thicknesses, comprising a first diode laser unit (2) for generating a first input laser radiation (3) with higher brilliance by dense wavelength coupling of several diode laser beams (10) of the first diode laser unit (2), a second diode laser unit (4) for generating a second input laser radiation (5) with lower brilliance by geometrically superimposing several diode laser beams (11) of the second diode laser unit (4), an optical fiber in the form of a double-core or multi-core fiber (6) with at least a first and second fiber core (7, 8) or in the form of a gradient index fiber (16), and at least one optical element (9) for coupling the first input laser radiation (3) into the first fiber core (7) and the second input laser radiation (5) into the second fiber core (8) of the double-core or multiple-core fiber (6) or for coupling the first input laser radiation (3) into a first region and the second input laser radiation (5) into a second region of the gradient index fiber (16), so that the first input laser radiation (3) is coupled out as a first output laser radiation (13) for the laser material processing of thin workpieces and the first and second input laser radiation (3, 5) are coupled out together as a second output laser radiation (14) for the laser material processing of thick workpieces from a fiber end (6b) of the optical fiber (6). [2] Device according to claim 1, characterized bythat the first fiber core (7) is designed as an inner fiber core and the second fiber core (8) is designed as an outer fiber core which surrounds the inner fiber core in a ring shape. [3] Device according to claim 1 or 2, characterized by that the at least one optical element (9) is designed to couple the first and second input laser radiation (3, 5) into the optical fiber (6) at a different coupling angle and / or with different divergence. [4] Device according to one of the preceding claims, characterized by that the first input laser radiation (3) has a beam parameter product of at most 4 mm*mrad and the second input laser radiation (5) has a beam parameter product of at least 16 mm*mrad. [5] Device according to one of the preceding claims, characterized byin that a focusing device (15) is arranged in the beam path of the first and second output laser radiation (13, 14), which focuses the first and second output laser radiation (13, 14) into a focal plane (16), wherein in the focal plane (16) the focus diameter (D1) of the first output radiation (13) is between 30 µm and 500 µm and the focus diameter (D2) of the second output radiation (14) is between 700 µm and 900 µm. [6] Device according to one of the preceding claims, characterized by that the wavelength range of the second input laser radiation (5) lies outside the wavelength range of the first input laser radiation (3). [7] Device according to claim 6, characterized by that the first input laser radiation (3) is in a wavelength range from 900 nm to 950 nm and the second input laser radiation (5) is in a wavelength range from 960 nm to 965 nm. [8] Device according to one of the preceding claims, characterized bythat in the beam path of the first and second input laser radiations (3, 5) between the first diode laser unit (2) and the second diode laser unit (4) on the one hand and the optical fiber (6) on the other hand, a coupling optic (12) is arranged, which overlays the first and second input laser radiation (3, 5). [9] Device according to claim 8, characterized by that the coupling optics (12) is designed as a wavelength-selective mirror which is transparent to the first input laser radiation (3) and reflective to the second input laser radiation (5), or vice versa. [10] Device according to claim 8, characterized by that the coupling optics (12) is designed as a polarization beam splitter which is reflective for the polarization direction of the first input laser radiation (3) and transmissive for the polarization direction of the second input laser radiation (5), or vice versa. [11] Method for generating either a first output laser radiation (13) with lower power and higher brilliance or a second output laser radiation (14) with higher power and lower brilliance for the laser material processing of workpieces of different thicknesses, comprising the steps: Generating a first input laser radiation (3) with higher brilliance by dense wavelength coupling of several diode laser beams (10), Generating a second input laser radiation (5) with lower brilliance by geometrically superimposing several diode laser beams (11), Coupling the first input laser radiation (3) into a first fiber core (7) and the second input laser radiation (5) into a second fiber core (8) of an optical fiber (6) designed as a double- or multi-core fiber, or coupling the first input laser radiation (3) into a first region and the second input laser radiation (5) into a second region of an optical fiber (16) designed as a gradient index fiber, generating the first output laser radiation (13) by coupling out the coupled-in first input laser radiation (3) from a fiber end (6b) of the optical fiber (6; 16) for the laser material processing of thin workpieces, and Generating the second output laser radiation (14) by jointly coupling out the coupled first and second input laser radiation (3, 5) from the fiber end (6b) of the optical fiber (6; 16) for the laser material processing of thick workpieces. [12] Method according to claim 11, characterized bythat thin workpieces with a thickness of less than 5 mm are cut with the first output laser radiation (13) and thick workpieces with a thickness of greater than 5 mm are cut with the second output laser radiation (14). [13] Method according to claim 11 or 12, characterized by that the first and second output laser radiation (13, 14) are focused into a focal plane, wherein in the focal plane the focus diameter (D1) of the first output radiation (13) is between 30 µm and 500 µm and the focus diameter (D2) of the second output radiation (14) is between 700 µm and 900 µm. [14] Method according to claim 11 or 12, characterized by that the first and second output laser radiation (13, 14) are focused such that the position of their focal points in the beam propagation direction lies in two different focal planes.

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