Optimization of the cutting process when laser cutting a workpiece

Abstract

Method for cutting a workpiece (1) using a laser beam (10), comprising: Splitting the laser beam (10) by a beam shaping element (400) into a primary beam (10a) and at least one secondary beam (10b); and Directing the primary beam (10a) and the secondary beam (10b) along a cutting path to form a cutting edge (3), wherein the secondary beam (10b) follows the primary beam (10a), wherein the primary beam (10a) and the secondary beam (10b) are unpolarized, wherein the beam shaping element (400) comprises at least one light-refracting wedge plate (400'), wherein the application of the primary beam (10a) and the secondary beam (10b) comprises: forming a primary spot and at least one secondary spot on the workpiece, wherein at least one splitting parameter for splitting the laser beam (10) is set depending on at least one process parameter, and wherein the at least one splitting parameter comprises: a number of secondary beams (10b), a focus position of the primary beam (10a) and / or the secondary beam (10b), a focus diameter of the primary beam (10a) and / or the secondary beam (10b), a power of the primary beam (10a) and / or the secondary beam (10b), a power distribution between the primary beam (10a) and the at least one secondary beam (10b), and a distance between the primary beam (10a) and the at least one secondary beam (10b).

Description

Technical area

[0001] The present invention relates to a method for cutting a workpiece by means of a laser beam, as well as a laser processing device which is configured to carry out the method. background

[0002] In a laser processing device for cutting a workpiece by means of a laser beam, the laser beam emerging from a laser beam source or an end of a laser guide fiber is guided onto a workpiece to be processed by means of beam guiding and focusing optics in order to form a cutting joint at a laser spot on the workpiece by melting and / or evaporating material.

[0003] US 2002 / 0088784 A1 and US 6,664,504 B2 describe a system for cutting or welding with a laser beam, in which a main laser beam is divided into a central beam and a peripheral beam of annular or cylindrical shape, the central beam being focused on a focusing point and the peripheral beam being focused on an annular focusing zone which is separate from the focusing point.

[0004] DE 11 2014 006 673 T5 and WO 2016 / 029396 A1 describe an optical lens with multiple focal points on the optical axis, which is used in laser processing.

[0005] DE 10 2008 053 ​​397 A1 describes a method for fusion cutting of workpieces with laser radiation, in which the angle of inclination of the cutting front is changed by adjusting the radial extension of the laser beam in the beam propagation direction of a laser beam and / or a movement of the focal point of the laser beam superimposed on the feed movement.

[0006] DE 10 2019 108 681 A1 describes a device and method for generating a multiple spot in laser material processing by repeatedly reflecting a portion of the laser beam. In an example with a double spot, shifting mirrors changes the power distribution between two partial beams. Tilting a mirror creates a small angle between the two partial beams, causing them to strike at different positions on the workpiece.

[0007] DE 10 2018 205 545 A1 describes a laser processing head for processing a workpiece using a laser beam, in particular for laser cutting, comprising a birefringent beam splitter element for splitting the laser beam into two partial beams. The birefringent beam splitter element has a beam exit surface that is not aligned parallel to the beam entrance surface. A focusing optics focuses the partial beams.

[0008] DE 10 2007 024 701 A1 describes a method for removing material from a workpiece over a predetermined removal depth using a laser beam consisting of one or more partial beams, each having a defined beam axis, wherein the axis of the laser beam or the respective axes of the partial beams is / are guided together along a removal line at a predetermined traversing speed. In one example, several laser beams are used to adjust the angle of incidence of the removal front, or a laser beam is split into several beam parts using beam-splitting optics. The individual laser beams or partial beams are set to different focus depths and the individual laser beams or partial beams are set to a smaller beam radius, a larger Rayleigh length, and a higher power with increasing focus depth.In one example, the angles of incidence are adjusted by additionally adjusting the position of the beam axis of the individual laser beams or partial beams monotonically offset against the ablation direction with increasing focus depth.

[0009] DE 10 2007 059 987 A1 describes a method for keyhole-free fusion cutting of a workpiece. The workpiece is melted by a laser beam along a kerf to be created, and the resulting melt is expelled from the kerf by a high-pressure gas jet. At least one laser beam follows the laser beam in the cutting direction and influences the melt. In examples, the foci of the laser beams are offset from each other in the beam direction, the power is distributed between the leading laser beam and the trailing laser beam in a ratio of approximately 60:40, or the two laser beams are two partial beams of the same laser beam.

[0010] US 2010 / 0044353 A1 describes a laser cutting process using multiple laser beams generated by a beam splitter or a diffractive optical element. A first laser beam generates a melt and forms a keyhole. At least one second laser beam is directed onto selected surface regions of the melt.

[0011] DE 19961918 A1 describes a method for laser material processing with at least two laser beam foci, wherein a deflection of the laser light is generated by the combination of two cylindrical lenses.

[0012] DE 10261422 A1 describes a laser welding and soldering process in which a laser beam is split into at least two separately focusable partial laser beams by means of a variable optical arrangement with a lens system.

[0013] DE 102019219462 A1 describes a method for cutting a glass element. Beam shaping is performed using a diffractive optical element that can be pivoted into the beam path of the processing laser.

[0014] WO 2011 / 154461 A2 describes a method for laser cutting in which two partial beams offset from one another in the feed direction are generated by means of a beam splitter in the form of a wedge plate partially projecting into the laser beam.

[0015] JP H11-347762 A and JP 2000 210785 A describe a laser welding process in which a laser beam is split by means of a wedge prism that can be moved into the beam path.

[0016] EP 2953184 A1 describes a plane-parallel plate as an optical element for beam splitting, which is inserted at an angle into the beam path of a laser beam. Summary of the invention

[0017] During laser cutting, the surface roughness at the cutting surface increases with increasing cutting speed until the cut is reached. The reason for this is a decrease in the local cutting front angle or a locally reduced angle of incidence of the laser radiation, which leads to a local maximum of the absorbed irradiance. As the cutting speed increases, the absorbed irradiance on the cutting front can become uneven, which in turn can lead to the following disadvantages: An increase in the absorbed irradiance can cause the material to begin to evaporate. This causes an increased volume of material to be melted locally. The volume flow of the molten material is then largely expelled above the evaporation position via the cutting surfaces. A large proportion solidifies on the cutting surface, causing the surface roughness to increase.The achievable surface roughness can therefore be determined by the ratio between melted and extruded material. If no more material is extruded from the underside of the workpiece, the cut will break.

[0018] It is an object of the present invention to provide a method and a laser processing device for cutting a workpiece using a laser beam to enable the precise and clean formation of a cutting kerf in a cost-effective manner, even at higher cutting speeds and / or with a lower surface roughness of the cutting surface. It is desirable to optimize the laser cutting process with respect to the cutting speed and / or the surface roughness of the cutting surface, especially for material thicknesses ≥ 1 mm or even ≥ 10 mm.

[0019] The problem is solved by the features of the independent claim. Features of preferred embodiments are specified in the subclaims.

[0020] According to one aspect, a method for cutting a workpiece using a laser beam comprises: splitting the laser beam by a beam-shaping element into a primary beam and at least one secondary beam; and irradiating the primary beam and the secondary beam along a cutting path to form a kerf, wherein the secondary beam follows the primary beam, wherein at least one splitting parameter for splitting the laser beam is set as a function of at least one process parameter, and wherein the at least one splitting parameter comprises: a number of secondary beams, a focus position of the primary beam and / or the secondary beam, a focus diameter of the primary beam and / or the secondary beam, a power of the primary beam and / or the secondary beam, a power distribution between the primary beam and the at least one secondary beam, and a distance between the primary beam and the at least one secondary beam.The distance between the primary beam and at least one secondary beam is defined by the (lateral) distance between the foci or focus positions of the primary beam and the secondary beam and can also be referred to as the spot distance (i.e., the distance between the so-called primary spot and the so-called secondary spot). The distance is therefore independent of the working distance or distance to the workpiece surface.

[0021] The irradiation of the primary beam and the secondary beam comprises: forming a primary spot or main laser spot and at least one secondary spot or auxiliary laser spot on the workpiece.

[0022] The invention is based on the basic idea of ​​generating a double or multiple laser spot of the laser beam along a cutting path for cutting a workpiece by splitting the laser beam. By adjusting at least one splitting parameter depending on a process parameter, the energy input into the processing zone (particularly at the positions of the respective laser spots) can be controlled. A secondary spot is thus positioned in the process interaction zone, following the primary spot in the cutting direction. By irradiating the secondary beam, which follows the primary beam, a local maximum of the absorbed irradiance on the cutting front or reaching the evaporation temperature can be specifically avoided.The secondary beam, positioned downstream of the primary beam in the cutting direction, can prevent a decrease in the local cutting front angle and the associated uneven increase in absorbed irradiance. Taking into account the causal relationships in the process zone described above, it is thus possible to specifically adjust the distribution parameters and thereby increase the maximum cutting speed and / or reduce the surface roughness of the cut surface.

[0023] The splitting parameters are parameters for splitting the laser beam into the primary beam and the at least one secondary beam. In a processing area, laser light from the laser beam is absorbed, forming the kerf. The primary beam or main laser beam forms a primary laser spot or primary laser spot or primary spot or main laser spot, and the at least one secondary beam or auxiliary laser beam forms at least one secondary laser spot or secondary laser spot or secondary spot or auxiliary laser spot. Due to the beam splitting, the energy input into the workpiece is distributed between the primary laser spot and the at least one secondary laser spot, with the secondary beam following the primary beam along the cutting path and at least one of the splitting parameters being adjusted depending on at least one process parameter.This enables better control or execution and quality of the cutting process, especially at high cutting speeds, and / or enables a higher cutting speed.

[0024] The cutting speed is a relative speed between the primary beam along the cutting path and the workpiece. For example, the laser beam can be moved across the workpiece, e.g., by moving the laser processing device that irradiates the laser beam or by a scanner unit in the laser processing device, and / or the workpiece can be moved at a feed rate.

[0025] The setting of at least one of the division parameters as a function of at least one process parameter can be carried out in particular during cutting.

[0026] The primary beam and the secondary beam are unpolarized. Preferably, the beam-shaping element is a non-birefringent optical element, meaning that no birefringence occurs when the laser beam is split by the beam-shaping element.

[0027] The secondary beam follows the primary beam, i.e., at least one secondary beam is guided behind the primary beam, following in the cutting direction. During cutting, the secondary beam thus strikes a respective processing area after the primary beam. Both the primary beam and the secondary beam are irradiated along the cutting path. During cutting, the secondary beam can thus strike a processing area already processed by the primary beam and / or enlarge the processing area. By splitting the laser beam and adjusting at least one of the splitting parameters, the geometry of the cutting front along the cutting path and / or transversely to it can be influenced or controlled.

[0028] The at least one secondary beam can, for example, be guided along the same path as the primary beam, i.e., it can sweep over the same workpiece surface. However, one of the at least one secondary beam can also be guided transversely offset to the path on which the primary beam is guided; in this case, both the secondary beam and the primary beam are guided along the cutting path. The path on which the primary beam is guided is also referred to as the primary path and preferably corresponds to the cutting path. The secondary beam is guided in the wake of the primary beam, preferably on the primary path of the primary beam, i.e., on the same path as the primary beam.

[0029] The primary beam and the at least one secondary beam are preferably irradiated into the same processing area, i.e., into the interaction area of ​​the laser beam with the workpiece. This means that they are irradiated simultaneously into the same processing area. The interaction area can also be referred to as the process interaction zone. The interaction area can comprise a melt pool or a melt film with partial evaporation.

[0030] In embodiments, several secondary beams can be irradiated one after the other along the cutting path. Preferably, both the primary beam and the several secondary beams are guided one after the other along the same path, e.g., along the cutting path.

[0031] Preferably, the primary beam and the secondary beam are offset or spaced apart from one another. Therefore, the primary beam and the secondary beam preferably do not overlap on the workpiece surface, and / or the foci of the primary beam and the secondary beam preferably do not overlap. Preferably, the primary beam and the secondary beam are not coaxial. Preferably, the primary beam and the secondary beam each have a point-shaped or circular beam cross-section. They are therefore preferably not annular. For example, the primary beam and the respective secondary beam can each form a point-shaped or circular laser spot on the workpiece.

[0032] The primary beam and at least one secondary beam are hereinafter also referred to as partial beams.

[0033] The cutting process can be, for example, a laser fusion cutting process or a laser flame cutting process. Cutting with inert process gas (laser fusion cutting), such as nitrogen and / or argon, which, for example, exits the cutting head coaxially with the processing laser and acts on the processing zone, particularly benefits from this process. In laser flame cutting, slag adhesion in the wake of the kerf can be prevented by adjusting at least one separation parameter, thus ensuring a successful laser cut.

[0034] Preferably, at least one of the splitting parameters is adjusted as a function of at least one process parameter. The process parameters can include at least one of the following process parameters: the cutting speed, in particular the current cutting speed, the material thickness of the workpiece (in particular at the position of the kerf to be formed), the material type (e.g. metal or plastic) or the material (e.g. copper, steel, aluminum) of the workpiece, a nozzle type, a nozzle geometry, a nozzle opening diameter, a beam parameter product of the non-split laser beam, a divergence angle of the non-split laser beam, a fiber diameter of an optical fiber ora fiber optic cable (for coupling the laser beam into the laser processing head), a laser power of the non-split laser beam, a pulse-on time of the non-split laser beam, a pulse-off time of the non-split laser beam, a pulse peak power of the non-split laser beam, a process gas type (inert or reactive), a process gas pressure, a process gas (e.g. argon, oxygen, compressed air, nitrogen), a focus position of the non-split laser beam (in particular the focus position in the direction orthogonal to the surface of the workpiece at the processing position or in the propagation direction of the laser beam), the imaging ratio of an optical system of a laser processing device radiating the primary beam and the secondary beam, the focus diameter of the non-split laser beam, the distance to the workpiece (in particular the distance of the laser processing device or the laser processing head orof the nozzle to the workpiece surface), the cutting front angle or the local angle of incidence (of the primary beam and / or a secondary beam) at the cutting front, the cutting depth, the maximum cutting depth above which irregular grooves are formed on the cutting surface (i.e. the cutting depth above which grooves on the cutting surface begin to become irregular). The imaging ratio can in particular be the imaging ratio of a laser processing head for irradiating the primary beam and the at least one secondary beam along the cutting path, in particular the imaging ratio of an optical system of the laser processing head. The imaging ratio can, for example, be the ratio of the focus diameter to the fiber core diameter in the case of a laser beam supplied via an optical fiber.

[0035] The irradiation of the primary beam and the secondary beam along a cutting path can, for example, comprise adjusting the beam-shaping element, wherein a position of the secondary beam is adjusted relative to the primary beam. Adjusting the beam-shaping element can, for example, comprise rotating the beam-shaping element about an optical axis of the incident laser beam and / or adjusting an insertion length by which the beam-shaping element is inserted into the laser beam. In this way, the secondary beam can follow the primary beam at an adjustable distance and / or in an adjustable direction.

[0036] In embodiments, the primary beam and the secondary beam are irradiated by a laser processing head, wherein the laser processing head comprises: the beam-shaping element for splitting the laser beam into the primary beam and the at least one secondary beam. The laser processing head can in particular further comprise: collimating optics for collimating the laser beam and focusing optics for focusing the laser beam. The collimated laser beam can be an (approximately) collinear beam bundle, or a beam bundle / laser beam with reduced divergence compared to the supplied laser beam. The focusing optics can comprise transmitting and / or reflecting optical elements, such as lenses, lens packages, mirrors, mirror packages, an F-theta lens, or the like. The beam-shaping element is preferably separate from the focusing optics. The focusing optics are preferably arranged downstream of the beam-shaping element in the beam path.The beam-shaping element can be arranged downstream of the collimating optics. Thus, the beam-shaping element can be arranged in the collimated laser beam. In particular, the beam-shaping element can be arranged between the collimating optics and the focusing optics. Alternatively, the collimating optics can be arranged downstream of the beam-shaping element. Thus, the beam-shaping element can be arranged in the divergent (supplied) laser beam.

[0037] A focus of the primary beam and a focus of the secondary beam can, for example, be in or below or above the formed primary spot or secondary spot, or on or below or above a surface of the workpiece.

[0038] Preferably, the primary beam and the at least one secondary beam pass through the same (common) collimation optics and / or focusing optics.

[0039] The beam-shaping element can be a movable, switchable, or deactivatable beam-shaping element. For example, the splitting of the laser beam into the primary beam and the at least one secondary beam can be switched on and off by the beam-shaping element, and / or the beam-shaping element can be moved out of the beam path of the laser beam and into the beam path of the laser beam.

[0040] In embodiments, the beam-shaping element comprises or is a refractive optical element, in particular a non-polarizing refractive optical element. Preferably, the beam-shaping element is optically isotropic.

[0041] Refraction, also known as refraction or diffraction, occurs when light passes through an interface or surface where the refractive index changes abruptly. Refraction occurs particularly when light hits the interface or surface of the refractive plate at an angle other than 90°.

[0042] Preferably, the beam-shaping element is configured to deflect the secondary beam passing through the beam-shaping element. For example, the beam-shaping element may have an optical surface arranged obliquely to a beam plane of the incident laser beam, such as an optical surface of a wedge plate. The beam plane is a plane to which the incident laser beam is orthogonal (i.e., normal).

[0043] The beam-shaping element can comprise at least one refractive plate. It comprises a refractive wedge plate. Preferably, the respective refractive plate is optically isotropic.

[0044] In embodiments, the at least one splitting parameter is adjusted by moving the beam-shaping element.

[0045] A refractive optical element as a beam-shaping element can greatly simplify the adjustment of a splitting parameter and enable a simple design. Unlike, for example, when using mirrors, a refractive optical element can enable direct adjustment of a splitting parameter, for example, by moving (rotating, tilting, pivoting, or shifting) the refractive optical element (or a respective light-refracting plate).

[0046] For example, a distance between the primary beam and the at least one secondary beam can be adjusted by rotating the beam-shaping element or by adjusting an arrangement angle of the beam-shaping element. Thus, a spot spacing can be easily adjusted. For example, the beam-shaping element can be rotated about an axis parallel to the beam plane. The arrangement angle can be an angle of an optical surface of the beam-shaping element with respect to the beam plane.

[0047] For example, adjusting a power distribution between the primary beam and the at least one secondary beam may comprise moving the beam-shaping element (e.g., a refractive plate) or at least one refractive plate of the beam-shaping element in a direction transverse to the optical axis of the incident laser beam. For example, adjusting a power distribution between the primary beam and the at least one secondary beam may comprise adjusting an overlap of the beam-shaping element (or at least one refractive plate of the beam-shaping element) with a cross-section of the laser beam.

[0048] For example, adjusting a number of the secondary beams may comprise moving the beam-shaping element (e.g., a refractive plate) or at least one refractive plate of the beam-shaping element in a direction transverse to the optical axis of the incident laser beam.

[0049] A refractive optical element can also be referred to as a light-refracting optical element or refractive optical element. The beam-shaping element can, for example, comprise or be at least one wedge plate, an axicon array, at least one lens package, and / or a plate arranged at an angle to the propagation direction of the laser beam. The plate can, for example, have parallel optical surfaces. An optical surface is a surface through which the at least one partial beam enters the light-refracting plate or exits the light-refracting plate. The optical surfaces are mutually opposite surfaces of the plate. The plate can thus also be a plate in which the first surface, through which the partial beam enters the plate, is parallel to the second surface, through which the partial beam exits the plate.By splitting the laser beam using a refractive optical element, the laser beam can be split using the smallest possible number of optical elements. In particular, power loss of the beam-shaping element can be minimized.

[0050] For example, the beam-shaping element can have at least one refractive plate, wherein each refractive plate is assigned a partial beam of the laser beam, which passes at least through this partial beam. A plurality of refractive plates can, for example, be arranged staggered one behind the other along the propagation direction of the laser beam, wherein preferably a first partial beam (e.g. the primary beam) does not pass through any of the refractive plates, a second partial beam (e.g. a first secondary beam) only passes through a first refractive plate, and a respective further partial beam (e.g. a further secondary beam) additionally passes through a further one of the refractive plates. A plurality of refractive plates can, for example, be arranged next to one another offset in a direction transverse to the propagation direction of the laser beam, wherein a respective partial beam (e.g.a secondary beam) passes through one (or only one) respective refractive plate. For example, a first partial beam (e.g., the primary beam) does not pass through any of the refractive plates.

[0051] In embodiments, the beam-shaping element comprises or is at least one refractive plate arranged in a partial cross-section of the laser beam, wherein a partial beam, in particular the primary beam, does not pass through the at least one refractive plate. Preferably, the at least one secondary beam passes through the at least one refractive plate along a propagation direction. Preferably, the refractive plate is configured to leave unpolarized laser light passing through the refractive plate unpolarized in the propagation direction. It may, for example, be non-polarizing.

[0052] The refractive plate can also be referred to as a refractive plate or a refracting plate. The refractive plate can be a wedge plate or have parallel optical surfaces. The refractive plate is a refractive optical element. Preferably, the refractive plate is optically isotropic.

[0053] The step of splitting the laser beam by a beam-shaping element into a primary beam and at least one secondary beam can, for example, be a step of splitting the laser beam by at least one light-refracting plate into a primary beam and at least one secondary beam, wherein the at least one light-refracting plate is arranged in a partial cross-section of the laser beam, wherein the primary beam does not pass through the at least one light-refracting plate, and wherein the at least one secondary beam passes through the at least one light-refracting plate along a respective propagation direction, wherein the light-refracting plate is configured to leave unpolarized laser light passing through the light-refracting plate in the propagation direction unpolarized.

[0054] The propagation direction of the respective partial beam (e.g. secondary beam) in the plate can also be referred to as the direction in which the partial beam passes through the plate.

[0055] The refractive plate allows the laser beam to be split to create a double or multiple laser spot without changing the polarization properties of the laser beam. Only a portion of the laser beam passes through a refractive plate and is thereby deflected relative to the other portion of the laser beam. This makes it possible to obtain advantageous polarization properties of the laser beam (at least for one partial beam), in particular for both the primary beam and the at least one secondary beam.

[0056] The refractive plate is designed to keep unpolarized laser light unpolarized, in particular when it passes through the refractive plate in the direction of propagation. It is thus designed to retain the polarization properties of unpolarized laser light, in particular when this light passes through the refractive plate in the direction of propagation. In other words, the refractive plate is designed to retain the degree of polarization of unpolarized laser light. If a randomly polarized or unpolarized laser beam is used, the laser beam's polarization is not changed when it passes through the refractive plate and, in particular, is not polarized. This can make it possible to generate a desired intensity ratio of primary beam to secondary beam without an unacceptably high absorption occurring in the beam path of the laser beam due to beam splitting by polarization.In contrast to beam splitting by a birefringent element, no polarization of the generated primary and secondary beams takes place, and a desired intensity ratio can be created by appropriate arrangement of the refractive plate.

[0057] For example, at least one of the splitting parameters, which is set as a function of at least one process parameter, can be set by adjusting the at least one light-refracting plate.

[0058] A partial beam, e.g., the primary beam, does not pass through the refractive plate. This means that the partial beam in question passes right past the refractive plate.

[0059] In embodiments, at least one of the laser beam, the primary beam, and the at least one secondary beam is unpolarized. Unpolarized light can also be referred to as randomly polarized light with alternating random polarization.

[0060] In embodiments, the beam-shaping element comprises at least one refractive wedge plate. The wedge plate can be the described refractive plate.

[0061] For example, the thickness of the wedge plate can increase or decrease in a direction from an edge region of the laser beam's cross-section to an optical axis of the incident laser beam, depending on the wedge angle of the wedge plate. For example, the wedge plate can extend transversely to this direction on both sides, in particular, extend at least across the laser beam's cross-section on both sides, or extend beyond the laser beam's cross-section on both sides.

[0062] Preferably, the wedge angle of the wedge plate is in the range of 0.001 rad to 0.1 rad, more preferably in the range of 0.001 rad to 0.01 rad or even of 0.0015 rad to 0.00567 rad.

[0063] In embodiments, the beam-shaping element comprises at least one light-refracting plate having an inclination angle to the beam plane of the incident laser beam on at least one optical surface, wherein the inclination angle is set within a range of -0.9 rad to 0.9 rad, preferably within a range of -0.27 rad to 0.27 rad.

[0064] Preferably, this optical surface is a surface through which the partial beam in question exits the refractive plate.

[0065] Preferably, this optical surface extends in a direction from an edge region of the laser beam to an optical axis of the incident laser beam, corresponding to the angle of inclination obliquely to the beam plane. For example, the wedge plate can extend transversely to this direction on both sides, in particular extend at least across the beam cross-section of the laser beam on both sides, or extend beyond the beam cross-section of the laser beam on both sides.

[0066] The refractive plate may be a wedge plate. If the refractive plate has parallel optical surfaces, the inclination angle is preferably not equal to 0.000 rad, i.e., not equal to 0 mrad.

[0067] Preferably, a distance d between a laser spot of the at least one secondary beam and a laser spot of the primary beam along the cutting direction is set within a range of 0.1 mm to 2 mm, preferably within a range of 0.225 mm to 0.85 mm.

[0068] Preferably, the power component of the primary beam, based on the total power of the primary beam and the at least one secondary beam, is set within a range of 0.1 to 0.9, preferably within a range of 0.2 to 0.8. The power component can, in particular, be different from 0.5. The primary beam preferably has the highest power of the partial beams. A power component of the primary beam less than 0.5 can also provide advantages in laser melting and / or laser flame cutting.

[0069] For example, the workpiece is a metallic workpiece, in particular made of a steel alloy, aluminum alloy, copper alloy, and / or brass alloy. The workpiece can in particular be made of a structural steel alloy, stainless steel alloy, aluminum alloy, copper alloy, and / or brass alloy. The workpiece can also be made of aluminum, copper, or brass.

[0070] The workpiece preferably has a material thickness of ≥ 1 mm, in particular a material thickness of ≥ 10 mm. The material thickness is defined as the dimension of the workpiece in the beam propagation direction, i.e., in the direction of the cutting depth.

[0071] The laser beam preferably has wavelengths in the infrared range, for example, between 780 nm and 1400 nm, in particular between 1000 nm and 1100 nm. This has the advantage of allowing the use of a cost-effective IR laser source. However, the laser beam can also have a wavelength in the visible green or blue range, in particular in the range between 400 nm and 450 nm or between 510 nm and 550 nm.

[0072] According to a further aspect, a laser processing device for cutting a workpiece by means of a laser beam comprises: a laser processing head for irradiating a primary beam and at least one secondary beam along a cutting path to form a cutting kerf, wherein the laser processing head has a beam-shaping element for splitting the laser beam into the primary beam and the at least one secondary beam; and a control unit configured to carry out a method according to one of the preceding claims.

[0073] The control unit can be configured in particular to carry out the described method for cutting a workpiece by means of the laser beam.

[0074] The laser processing head comprises, for example, a housing and a beam path for the laser beam arranged therein, with the beam-shaping element arranged in the beam path. As described above, the laser processing head can comprise the beam-shaping element, collimating optics, and focusing optics, and / or a fiber socket for an optical fiber for supplying the laser beam. The laser processing head can comprise a movement device for the described movement and / or rotation of the beam-shaping element or the optical element or the light-refracting plate. Brief description of the drawings

[0075] Embodiments of the invention are described in detail below with reference to figures. Fig. 1 schematically shows a laser processing apparatus according to an embodiment of the present invention; Fig. 2 schematically shows a process interaction zone during cutting according to a comparative example; Fig. 3 shows X-ray and microscope images of a fusion cutting process; Fig. 4 schematically shows a process interaction zone during cutting according to an embodiment of the present invention; Fig. Figure 5 schematically shows the splitting of the laser beam by a device according to an embodiment of the present invention; and Fig. 6 schematically shows the splitting of the laser beam by a beam shaping element in the form of a wedge plate according to an embodiment of the present invention. Detailed description of the embodiments

[0076] In the following, unless otherwise stated, the same reference symbols are used for identical and equivalent elements.

[0077] Fig. Figure 1 schematically shows a structure of a laser processing device for cutting a workpiece using a laser beam according to an embodiment of the present invention. The invention is explained below using the example of a laser processing device for laser fusion cutting of a workpiece, but is not limited thereto. The laser processing device can also be a laser processing device for laser flame cutting.

[0078] The laser processing device comprises a laser processing head 100 for irradiating a laser beam 10 onto a workpiece 1. For example, the laser beam 10 generated by a laser source 200 can be coupled into the laser processing head 100 via an optical fiber 210, optionally via a fiber socket 220. The laser beam 10 is split into two partial beams 10a, 10b by a beam shaping element 400, as shown by way of example in Fig. 5 and Fig. 6. Of the partial beams 10a, 10b, a first partial beam 10a is a primary beam, and the further partial beam (or the further partial beams) 10b is a secondary beam that follows the primary beam 10a along the cutting path. In Fig. 1 the cutting path runs from left to right.

[0079] The beam-shaping element 400 comprises at least one optical element that transmits the laser beam 10 (processing beam), such as a refractive optical element, at least one refractive plate, or at least one refractive wedge plate. An optical system of the laser processing head 100 further comprises, in addition to the beam-shaping element 400, collimating optics 110 and focusing optics 120. Preferably, the beam-shaping element 400 is arranged in the collimated laser beam 10, i.e., between the collimating optics 110 and the focusing optics 120, so that the splitting into the two partial beams 10a, 10b occurs based on the approximately collimated laser beam 10. In other words, the beam-shaping element 400 can be arranged downstream of the collimating optics 110 in the laser beam propagation direction. The two partial beams 10a, 10b can then be focused by the common focusing optics 120 for laser cutting.Alternatively, a separate focusing optics 120 can be provided for each partial beam 10a, 10b in order to adjust the focus positions of the two partial beams 10, 10b independently of each other.

[0080] The beam shaping element 400 can also be arranged upstream of the collimation optics 110 in the laser beam propagation direction, as shown in dashed lines, so that the division into the two partial beams 10a, 10b takes place based on the divergent laser beam 10.

[0081] Although a division of the laser beam 10 into exactly two partial beams 10a, 10b is described here, the disclosure is not limited thereto. The laser beam 10 can be divided into two or more partial beams.

[0082] During laser cutting, the laser beam 10 is moved relative to the workpiece 1 at the cutting speed s. The laser beam 10, or processing beam, is guided and focused onto the workpiece 1 by the optical system (processing optics) 110, 120, 400. Each of the partial beams 10a, 10b forms a laser spot on the workpiece 1. The processing optics and their individual elements, in particular the beam-shaping element 400, are controlled by a higher-level control unit 300, for example, via a respective associated movement device. The control unit 300 is particularly configured to carry out a method according to embodiments of the present invention.

[0083] A method according to embodiments of the present invention for cutting a workpiece using a laser beam comprises the steps of: splitting the laser beam by a beam-shaping element into a primary beam and at least one secondary beam; and irradiating the primary beam and the secondary beam along a cutting path to form a kerf, wherein the secondary beam follows the primary beam. For splitting the laser beam, at least one splitting parameter is set as a function of at least one process parameter in order to specifically control an energy input into the process interaction zone. Thus, at least one splitting parameter for splitting the laser beam 10 is set as a function of at least one process parameter.The at least one splitting parameter comprises: a number of secondary beams 10b, a focus position of the primary beam 10a and / or the secondary beam 10b, a focus diameter of the primary beam 10a and / or the secondary beam 10b, a power of the primary beam 10a and / or the secondary beam 10b, a power distribution between the primary beam 10a and the at least one secondary beam 10b and a distance between the primary beam 10a and the at least one secondary beam 10b. The process parameters can comprise at least one of the following process parameters: the cutting speed, in particular the instantaneous cutting speed, the material thickness of the workpiece (in particular at the position of the kerf to be formed), the material type (e.g. metal or plastic) or the material (e.g. copper, steel, aluminum) of the workpiece, a process gas type (inert or reactive), a process gas pressure, a process gas (e.g.Argon, oxygen, compressed air, nitrogen), a focus position of the unsplit laser beam (in particular the focus position in the direction orthogonal to the surface of the workpiece at the processing position or in the propagation direction of the laser beam), the imaging ratio of an optical system of a laser processing device irradiating the primary beam and the secondary beam, the focus diameter of the unsplit laser beam, the distance to the workpiece (in particular the distance of the laser processing device or the laser processing head or the nozzle to the workpiece surface), the cutting front angle or the local angle of incidence (of the primary beam and / or a secondary beam) at the cutting front, the cutting depth, the maximum cutting depth from which irregular grooves are formed on the cutting surface (i.e. the cutting depth from which grooves on the cutting surface begin to become irregular).

[0084] The beam-shaping element 400 can be switchable. This means, for example, that the beam-shaping element 400 can be moved out of the beam path of the laser beam 10. Thus, if necessary, conventional laser cutting is also possible without the splitting of the laser beam 10 by the beam-shaping element 400.

[0085] According to one embodiment, the beam-shaping element 400 is rotatable about the laser beam axis (the optical axis A of the laser beam or the beam path). Thus, with a varying cutting direction, i.e., a varying direction of the cutting path, the secondary beam 10b can be guided along the cutting path by rotating the beam-shaping element 400. In particular, the beam-shaping element 400 can be controlled, for example, depending on the feed direction of the workpiece 1.

[0086] Fig. Figure 2 schematically shows a comparative example of a process interaction zone during laser fusion cutting with a single laser beam 10' with power P, which forms a single laser spot on the workpiece 1. In the example shown, the cutting front 2 has an irregular profile with different local cutting front angles. The local cutting front angle is the angle between the cutting front and the orthogonal to the beam propagation direction of the laser beam 10'. The angle between the local surface normal n→ (Vector n) of the cutting front 2 and the beam propagation direction of the incident laser beam 10' is called the local angle of incidence θ. Thus, the local cutting front angle corresponds to the local angle of incidence θ.

[0087] Fig. 2 shows irregular scores 4 in the left-hand area of ​​the formed kerf 3. The cutting limit (cut break) is defined as the cutting speed s above which the workpiece 1 is no longer separated. At cutting speeds s just below the cutting limit or with unfavorably selected process parameters, poor surface quality of the cut surfaces occurs, among other things. This poor quality is characterized, among other things, by uneven scoring, which causes high surface roughness. Irregular scores are characterized by a strong local change in their course along the cutting depth (in the direction of beam propagation). The cutting depth at which the scores 4 begin to become uneven corresponds to the cutting depth at which the local angle of incidence θ decreases unacceptably. In such a case, local evaporation 6 of the workpiece material occurs at this position.

[0088] In Fig. Figure 3 shows schematic X-ray images (top row) and microscope images (bottom row) of a fusion cutting process of stainless steel as a function of the cutting speed s. The cutting speed s is specified in each case. At a cutting speed s of 1 m / min, the scoring pattern is regular. At a cutting speed s > 1 m / min, the scoring pattern is irregular. With increasing cutting speed s, a locally increasing bulge (recognizable by the bright area) is visible in the X-ray image at the cutting front or at the cutting surfaces (arrow). At this position, the local angle of incidence θ is smaller. At this position, the evaporation temperature of the material is reached. At this position, the melt is increasingly driven across the cutting surfaces against the cutting direction and / or orthogonal to the laser beam axis or beam propagation direction.At this position, the scoring pattern in the microscope image becomes irregular (arrow). A cut break occurred at the highest cutting speed of 2.8 m / min.

[0089] Fig. 4 schematically shows a process interaction zone during cutting according to an embodiment of the present invention, wherein a primary laser spot is formed by the primary beam 10a with power P1 and a secondary laser spot is formed by the secondary beam 10b with power P2. By means of the beam-shaping element 400, for example a wedge plate, in the processing optics, a secondary laser spot or secondary laser spot of the secondary beam 10b is positioned in the process interaction zone following the main laser spot of the primary beam 10a in the cutting direction. The secondary laser spot of the secondary beam 10b prevents incipient evaporation by preventing the local angle of incidence θ from being self-regulated and reduced due to a locally lacking absorbed energy. The local angle of incidence θ is thus kept closer to 90°.

[0090] Fig. 5 and Fig. 6 schematically show the splitting of the laser beam according to embodiments of the invention. Fig. 5 shows a beam-shaping element 400 in the form of a wedge plate 400', which is arranged in a portion of the beam intersection of the laser beam 10. The wedge plate 400' has a wedge angle α. As shown, the thickness of the wedge plate 400' increases in a direction from an edge region of the beam intersection of the laser beam 10 to an optical axis A of the laser beam 10 incident on the wedge plate 400', corresponding to the wedge angle α. In the transverse direction thereto, for example, transversely to the local cutting path direction, the wedge plate 400' extends on both sides across the beam cross-section of the laser beam 10. The wedge plate 400' in the processing optics positions a secondary laser spot or auxiliary laser spot (power P2) in the process interaction zone, in addition to the primary laser spot or main laser spot (power P1) in the cutting direction. The wedge plate 400' in the collimated beam splits it so that the primary laser spot 10p and the secondary laser spot 10s are formed.The laser spots 10p, 10s can be located, as shown, in the plane E of the beam focus of the primary beam 10a and the beam focus of the primary beam 10b. However, they can also be located above or below the plane E of the beam focuses. By adjusting a (lateral) position v of the wedge plate 400' in the direction R, the power ratio P1 / P can be adjusted. ges or P2 / P ges of P1 or P2 as the splitting parameter, where: P ges = P1 + P2, where P ges is the total power of the laser beam 10 irradiated onto the workpiece 1.

[0091] According to the orientation of the wedge plate 400' with increasing thickness from the edge region of the beam cross-section to the optical axis A, a beam waist 12 is formed in the formed double beam of the partial beams 10a, 10b.

[0092] To generate a plurality of secondary beams 10b and / or to adjust the number of secondary beams as a splitting parameter, at least one further wedge plate 400" may be provided, for example, which covers a different partial cross-section of the laser beam 10 than the first wedge plate 400'. This can be adjustable or adjustable in a similar manner to the wedge plate 400'.

[0093] Further adjustment options for the wedge plate 400' (or 400") are in Fig. 6 illustrates. Fig. 6 shows a variant of the embodiment according to Fig. 5. The rear optical surface of the wedge plate 400' in the beam propagation direction has an inclination angle β to the beam plane S of the incident laser beam 10. Accordingly, the first optical surface of the wedge plate 400' in the beam propagation direction has an inclination angle α + β to the beam plane S of the incident laser beam.

[0094] By varying the wedge angle α, the distance d between the laser spots 10p, 10s is set as the splitting parameter. By setting a position h (height position, parallel to the beam propagation direction), the distance between the beam waist 12 and the double foci 10p, 10s in the propagation direction of the laser beam is set as the splitting parameter. By setting the inclination angle β, which can also be referred to as the installation angle, the distance d between the laser spots 10p, 10s and the distance between the beam waist 12 and the double foci 10p, 10s in the propagation direction are set as the splitting parameter. The wedge angle α and the inclination angle β determine whether the double focus is above or below the beam waist 12. In the case of α - β <0, the beam waist 12 lies below the double focus, in the case of α - β >0, the beam waist 12 lies above the double focus. In the same way as in Fig.5, by adjusting the position or distance v, the power ratio P1 / P ges of the primary beam (with power P1) and the power component P2 / P ges of the secondary beam (with power P2) can be set as a splitting parameter, where again: P ges = P1 + P2.

[0095] Experiments have demonstrated the impact of the double foci compared to a cutting process using a standard laser beam, i.e., a single-spot laser beam. When cutting 10 mm and 20 mm stainless steel beams with 6 kW laser power (total power), the maximum cutting speed could be increased by 19% and 23%, respectively, by appropriately selecting the splitting parameters, in particular, by appropriately selecting the spot spacing and the power distribution between the primary beam 10a and the secondary beam 10b.

[0096] The maximum cutting speed, the surface roughness of the cutting surface, and the dross formation depend on a variety of parameters, including the locally absorbed irradiance on the cutting front. For a targeted or controlled energy input of the processing laser into the processing zone, according to the present invention, in a method for cutting a workpiece using a laser beam, the laser beam is split by a beam-shaping element into a primary beam and at least one secondary beam. The primary beam and the secondary beam are irradiated along a cutting path to form a kerf, with the secondary beam following the primary beam.By adjusting at least one of the splitting parameters depending on at least one process parameter, the laser cutting process can be optimized with respect to a maximum cutting speed and / or a minimum surface roughness of the cutting surface, particularly for material thicknesses or cutting depths greater than 1 mm or, in particular, greater than or equal to 10 mm. This enables a precise and clean formation of the cutting kerf even at higher cutting speeds, while the beam-shaping element can be precisely adjusted and provided cost-effectively.

Claims

[1] Method for cutting a workpiece (1) by means of a laser beam (10), comprising: Splitting the laser beam (10) by a beam shaping element (400) into a primary beam (10a) and at least one secondary beam (10b); and irradiating the primary beam (10a) and the secondary beam (10b) along a cutting path to form a cutting groove (3), wherein the secondary beam (10b) follows the primary beam (10a), wherein the primary beam (10a) and the secondary beam (10b) are unpolarized, wherein the beam-shaping element (400) comprises at least one light-refracting wedge plate (400'), wherein the irradiation of the primary beam (10a) and the secondary beam (10b) comprises: forming a primary spot and at least one secondary spot on the workpiece, wherein at least one splitting parameter for splitting the laser beam (10) is set as a function of at least one process parameter, and wherein the at least one splitting parameter comprises: a number of secondary beams (10b), a focus position of the primary beam (10a) and / or the secondary beam (10b), a focus diameter of the primary beam (10a) and / or the secondary beam (10b), a power of the primary beam (10a) and / or the secondary beam (10b), a power distribution between the primary beam (10a) and the at least one secondary beam (10b), and a distance between the primary beam (10a) and the at least one secondary beam (10b). [2] Method according to claim 1, wherein at least one of the splitting parameters is adjusted depending on at least one of the following process parameters: a cutting speed (s), a distance to the workpiece (1), a nozzle type, a nozzle geometry, a nozzle opening diameter, a beam parameter product of the unsplit laser beam (10), a divergence angle of the unsplit laser beam (10), a fiber diameter of the optical fiber cable, a laser power of the unsplit laser beam (10), a pulse-on time of the unsplit laser beam (10), a pulse-off time of the unsplit laser beam (10), a pulse peak power of the unsplit laser beam (10), a material thickness of the workpiece (1), a material type or a material of the workpiece (1), an imaging ratio of an optical system (110, 120) of a laser processing device radiating the primary beam (10a) and the secondary beam (10b),a focus position of the unsplit laser beam (10), a focus diameter of the unsplit laser beam (10), a local angle of incidence (θ) at the cutting front (2), a process gas, a process gas type, a process gas pressure, a cutting depth, and a maximum cutting depth from which irregular grooves (4) are formed on the cutting surface. [3] Method according to one of the preceding claims, wherein the beam shaping element (400) is a refractive optical element and / or a non-polarizing refractive optical element. [4] Method according to one of the preceding claims, wherein the setting of the at least one splitting parameter is carried out by moving the beam-shaping element (400). [5] Method according to one of the preceding claims, wherein the division of the laser beam (10) into the primary beam (10a) and the at least one secondary beam (10b) can be switched on and off by the beam shaping element (400). [6] Method according to one of the preceding claims, wherein the beam shaping element (400) can be moved out of the beam path of the laser beam (10) and into the beam path of the laser beam (10). [7] Method according to one of the preceding claims, wherein the light-refracting wedge plate (400') is arranged in a partial cross-section of the laser beam (10), wherein the primary beam (10a) does not pass through the at least one light-refracting wedge plate (400'), wherein the at least one secondary beam (10b) passes through the at least one light-refracting wedge plate (400') along a propagation direction. [8] Method according to one of the preceding claims, wherein the wedge angle (α) of the wedge plate (400') is in the range from 0.001 rad to 0.1 rad, preferably in the range from 0.001 rad to 0.01 rad or from 0.0015 rad to 0.00567 rad. [9] Method according to one of the preceding claims, wherein the light-refracting wedge plate (400') has an inclination angle (β) to the beam plane (S) of the incident laser beam (10) on at least one optical surface, wherein the inclination angle (β) is set within a range of -0.9 rad to 0.9 rad, preferably within a range of -0.27 rad to 0.27 rad. [10] Method according to one of the preceding claims, wherein a distance (d) between a laser spot (10s) of the at least one secondary beam (10b) and a laser spot (10p) of the primary beam (10a) along the cutting direction is set within a range of 0.05 mm to 4 mm, preferably within a range of 0.225 mm to 0.85 mm. [11] Method according to one of the preceding claims, wherein a power component (P1 / P ges ) of the primary beam (10a) relative to the total power (P ges ) of the primary beam (10a) and the at least one secondary beam (10b) is set within a range of 0.1 to 0.9, preferably within a range of 0.2 to 0.

8. [12] Method according to one of the preceding claims, wherein the workpiece (1) is a metallic workpiece (1), in particular made of a steel alloy, aluminum alloy, copper alloy and / or brass alloy. [13] Method according to one of the preceding claims, wherein the method is a laser fusion cutting method and / or a laser flame cutting method. [14] Laser processing device for cutting a workpiece (1) by means of a laser beam (10), comprising: a laser processing head (100) for irradiating a primary beam (10a) and at least one secondary beam (10b) along a cutting path to form a cutting groove (3), wherein the laser processing head (100) has a beam-shaping element (400) for splitting the laser beam (10) into the primary beam (10a) and the at least one secondary beam (10b), wherein the beam-shaping element (400) comprises at least one light-refracting wedge plate (400'); and a control unit (300) configured to carry out a method according to any one of the preceding claims.

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