CN115703173A - Method and laser processing device for cutting a workpiece by means of a laser beam - Google Patents

Abstract

The invention relates to a method for cutting a workpiece by means of a laser beam, comprising: dividing the laser beam into a primary beam and at least one secondary beam by a beam shaping element; and injecting the primary beam and the secondary beam along a cutting path so as to construct a kerf, wherein the secondary beam follows the primary beam, wherein at least one of the following dividing parameters is adjusted according to at least one process parameter, the dividing parameters comprising: a number of the secondary beams, a focal position of the primary beam and/or of the secondary beam, a focal diameter of the primary beam and/or of the secondary beam, a power distribution between the primary beam and the at least one secondary beam and a separation between the primary beam and the at least one secondary beam; and to a laser machining device having a control unit for carrying out the method.

Description

Method and laser processing device for cutting a workpiece by means of a laser beam

technical field

The invention relates to a method for cutting a workpiece by means of a laser beam and to a laser processing device designed to carry out the method.

Background technique

In laser processing systems for cutting workpieces by means of a laser beam, the laser beam emerging from the laser beam source or from one end of the laser-conducting fiber is directed onto the workpiece to be processed by means of beam-guiding optics and focusing optics in order to The kerf is formed in the laser spot on the workpiece by melting and/or evaporating material.

US 2002/0088784 A1 and US 6,664,504 B2 describe a system for cutting or welding with a laser beam, wherein the main laser beam is divided into a central beam and an annular or cylindrical peripheral beam, wherein The central beam is focused on a focal point, and the peripheral beams are focused on an annular focal zone, which is separated from the focal point.

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

DE 10 2008 053 397 A1 describes a method for the fusion cutting of workpieces by means of laser radiation, wherein by adapting the radial extension of the laser beam in the beam propagation direction of the laser beam and/or by laser The movement of the focus of the beam superimposed on the feed movement changes the inclination angle of the cutting front.

DE 10 2019 108 681 A1 describes a device and a method for generating multiple light spots during laser material processing by multiple mirror reflections of parts of a laser beam. In the case of a double spot, movement of the mirror causes a change in the power division between the two sub-beams. The tilting of the mirror produces a small angle between the two beamlets, so that the beamlets impinge on the workpiece at different positions.

DE 10 2018 205 545 A1 describes a laser processing head for processing workpieces by means of a laser beam, in particular for laser cutting, which laser processing head comprises a birefringent beam-splitting element for dividing the laser beam into Divided into two sub-beams. The birefringent beam-splitting element has a beam exit surface aligned non-parallel to the beam entry surface. Focusing optics focus the sub-beams.

Contents of the invention

During laser cutting, the surface roughness increases with increasing cutting speed on the cutting surface until the cutting interruption is reached. The reason for this is a reduction in the local cutting front angle or a locally reduced angle of incidence of the following laser radiation which leads to a local maximum in the absorbed radiation intensity. Thus, as the cutting speed increases, the absorbed radiation intensity over the cutting front may become non-uniform, which in turn may lead to the disadvantage that material may start to evaporate due to the increased absorbed radiation intensity. As a result, more material volumes are melted locally. The volume flow of molten material is then largely discharged through the cutting surface above the evaporation point. Most of it solidifies here on the cut surface, so that the surface roughness increases. The achievable surface roughness can thus be indicated by the ratio between melted material and discharged material. Cutting is interrupted if material is no longer expelled from the underside of the workpiece.

The object of the present invention is to provide a method and a laser processing device for cutting workpieces by means of a laser beam, so that even at high cutting speeds and/or with low surface roughness of the cutting surface In this case, a precise and clean formation of the kerf is also achieved in a cost-effective manner. It is desirable to optimize the laser cutting process with regard to the cutting speed and/or the surface roughness of the cut surface, especially in the case of material strengths > 1 mm, or even > 10 mm.

This object is solved by a method and a device according to the invention for cutting a workpiece by means of a laser beam. Features of a preferred embodiment are given in a development.

According to one aspect, the method for cutting a workpiece by means of a laser beam comprises: dividing the laser beam into a primary beam and at least one secondary beam by means of a beam shaping element; and directing the primary beam and the secondary beam along The cutting path is injected in order to form the kerf, wherein the secondary beam follows the primary beam, wherein at least one division parameter is adjusted as a function of at least one process parameter for dividing the laser beam, and wherein at least one division Parameters include: number of secondary beams, focal position of primary beams and/or secondary beams, focal diameter of primary beams and/or secondary beams, primary beams and/or secondary beams The power of the beams, the power distribution between the primary beam and the at least one secondary beam, and the distance between the primary beam and the at least one secondary beam. The distance between the primary beam and the at least one secondary beam is defined by the (transverse) distance of the focal points or focal positions of the primary beam and of the secondary beam and can also be referred to as the spot distance (the so-called primary beam The distance between the spot and the so-called secondary spot). Therefore, the distance does not depend on the working distance or distance from the workpiece surface.

The injection of the primary beam and the secondary beam can include forming a primary or primary laser spot and at least one secondary or secondary laser spot on the workpiece.

The invention is based on the basic idea of generating a double or multiple laser spot of the laser beam by dividing it along the cutting path for cutting the workpiece and controlling it into the processing zone by adjusting at least one parameter of the division according to the process parameters (especially at the position of the corresponding laser spot) energy input. The secondary light spot is thus positioned in the process interaction region in such a way that it follows the primary light spot in the cutting direction. Through the injection of the secondary beam following the primary beam, local maxima of the absorbed radiation intensity at the cutting front or reaching the evaporation temperature can be avoided in a targeted manner. Because the secondary beam positioned in such a way that it follows the primary spot in the cutting direction makes it possible to avoid a reduction in the local cutting front angle and an associated inhomogeneous increase in the absorbed radiation intensity. Taking into account the above-mentioned interaction in the process area, it is thus possible to adjust the division parameters in a targeted manner and thereby increase the maximum cutting speed and/or reduce the surface roughness of the cutting surface.

或初级激光光斑

或初级光斑或主激光光斑，至少一个次级射束或次要激光射束形成至少一个次级激光斑点或次级激光光斑或次级光斑或次要激光光斑。通过射束划分，到工件中的能量输入分布到初级激光光斑和至少一个次级激光光斑上，其中，次级射束沿着切割路径跟随初级射束，并且根据至少一个工艺参数调整划分参数中的至少一个划分参数。这尤其在高切割速度的情况下实现切割过程的更好的控制或者实施和质量，和/或实现更高的切割速度。The division parameter is a parameter for dividing the laser beam into a primary beam and at least one secondary beam. Absorption of the laser light of the laser beam takes place in the processing region, whereby the incision is formed. The main beam or main laser beam forms the primary laser spot

or primary laser spot

Either the primary or main laser spot, at least one secondary or secondary laser beam forms at least one secondary or secondary laser spot or secondary or secondary laser spot. By beam splitting, the energy input into the workpiece is distributed over the primary laser spot and at least one secondary laser spot, wherein the secondary beam follows the primary beam along the cutting path and the splitting parameters are adjusted as a function of at least one process parameter At least one partition parameter for . This enables better control or implementation and quality of the cutting process, especially at high cutting speeds, and/or enables higher cutting speeds.

The cutting speed is the relative speed between the primary beam and the workpiece along the cutting path. For example, the laser beam can be moved on the workpiece, for example by moving the laser processing device into which the laser beam is injected or by a scanning unit in the laser processing device, and/or the workpiece can be moved at a feed rate.

The adjustment of at least one of the dividing parameters as a function of the at least one process parameter can take place in particular during cutting.

Preferably, the primary radiation and/or the secondary radiation are unpolarized. Preferably, the beam shaping element is a non-birefringent optical element, ie no birefringence occurs when the laser beam is split by the beam shaping element.

The secondary beam follows the primary beam, ie at least one secondary beam is guided behind the primary beam in a following manner in the cutting direction. During cutting, therefore, the secondary beam enters the corresponding processing region after the primary beam. Both the primary jet and the secondary jet are injected along the cutting path. During cutting, the secondary beam can thus impinge on the processing area already processed by the primary beam and/or the processing area can be enlarged. By dividing the laser beam and adjusting at least one of the dividing parameters, the geometry of the cutting front along the cutting path and/or transversely to the cutting path can be influenced or controlled.

The at least one secondary beam can, for example, be guided on the same path as the primary beam, ie scan the same workpiece surface as the primary beam. However, one of the at least one secondary beam can also be guided laterally offset relative to the path on which the primary beam is guided; here, not only the secondary beam but also the primary beam The beams are all directed along the cutting path. The path along which the primary beam is guided is also referred to as the primary beam 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, ie on the same path as the primary beam.

The primary beam and the at least one secondary beam preferably radiate into the same processing region, ie into an interaction region of the laser beam with the workpiece. This means that the primary beam and the at least one secondary beam are radiated simultaneously into the same processing region. This interaction region may also be referred to as a process interaction region. The interaction region can comprise a molten pool or can comprise a molten film with sometimes evaporation.

In an embodiment, a plurality of secondary beams may be injected sequentially along the cutting path. Preferably, not only the primary beam but also a plurality of secondary beams are guided successively on the same path, for example a cutting path.

Preferably, the primary beam and the secondary beam are offset from one another or spaced apart from one another. Therefore, preferably, the primary beam and the secondary beam do not overlap on the workpiece surface, and/or the focal points of the primary beam and of 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 punctiform or circular beam cross section. Therefore, the primary jet and the secondary jet are preferably not annular. For example, the primary beam and the corresponding secondary beam can each form a punctiform or circular laser spot on the workpiece.

The primary beam and the at least one secondary beam are also referred to below as partial beams.

The cutting method can be, for example, a method for laser fusion cutting or a method for laser ablation cutting. Cutting with the aid of an inert process gas (laser fusion cutting), for example nitrogen and/or argon, which escapes from the cutting head coaxially with the processing laser, for example, benefits from this method in particular And have an impact on the processing area. During laser ablation cutting, the adhesion of slag in the wake of the kerf can be prevented and successful laser cutting can be ensured by adjusting at least one dividing parameter.

Preferably, at least one of the division parameters is adjusted according to at least one process parameter. The process parameters may include at least one of the following process parameters: cutting speed, especially instantaneous cutting speed, material strength or thickness of the workpiece (especially at the position of the kerf to be formed), material of the workpiece Type (e.g. metal or plastic) or material (e.g. copper, steel, aluminium), nozzle type, nozzle geometry, nozzle opening diameter, beam parameter product of the undivided laser beam, undivided laser beam Divergence angle, fiber diameter of the optical fiber or fiber optic cable (for coupling the laser beam into the laser processing head), laser power of the undivided laser beam, pulse of the undivided laser beam On time, pulse off time of the undivided laser beam, pulse peak power of the undivided laser beam, type of process gas (inert or reactive), process gas pressure, process gas (e.g. argon, oxygen, compressed air, nitrogen), the focus position of the undivided laser beam (especially in the direction perpendicular to the surface of the workpiece at the processing position or the focus position in the propagation direction of the laser beam), so that the primary beam The imaging ratio of the optical system of the laser processing equipment where the laser beam and the secondary beam enter, the focal diameter of the undivided laser beam, and the distance from the workpiece (especially the distance between the laser processing equipment or the laser processing head or nozzle and the surface of the workpiece pitch), the cutting front angle or (of the primary beam and/or of the secondary beam) the local angle of incidence on the cutting front, the cutting depth, the following maximum cutting depth, from which the maximum cutting depth is formed on the cutting surface Regular grooves (ie the depth of cut from which the grooves on the cut surface become irregular). The imaging scale can be, in particular, an imaging scale of a laser processing head for radiating the primary beam and the at least one secondary beam along the cutting path, in particular an imaging scale of an optical system of the laser processing head. For example in the case of a laser beam supplied via an optical fiber, the imaging ratio can be the ratio of the focal spot diameter to the fiber core diameter.

The injection of the primary beam and of the secondary beam along the cutting path can include, for example, an adjustment of the beam shaping element, wherein the position of the secondary beam relative to the primary beam is adjusted. The adjustment of the beam shaping element can include, for example, a rotation of the beam shaping element about the optical axis of the incident laser beam and/or an adjustment of the introduction length of the beam shaping element 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.

In one embodiment, the primary beam and the secondary beam are fed through the laser processing head, wherein the laser processing head comprises a beam shaping element for splitting the laser beam into a primary beam and at least one secondary beam . In particular, the laser processing head can further comprise collimation optics for collimating the laser beam and focusing optics for focusing the laser beam. The collimated laser beam can be a (nearly) collinear beam bundle or a beam bundle/laser beam with a reduced divergence compared to the supplied laser beam. Focusing optics may include transmissive and/or reflective optical elements such as lenses, lens groups, mirrors, mirror groups, F-Theta lenses, or the like. The beam shaping element is preferably separate from the focusing optics. Preferably, the focusing optics are arranged downstream of the beam shaping element in the beam path. The beam shaping element can be arranged behind the collimation 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, collimation optics may be behind the beam shaping element. Thus, the beam shaping element can be arranged in the diverging (supplied) laser beam.

The focal point of the primary beam and the focal point of the secondary beam can be located, for example, in or below or above the formed primary or secondary spot, or can be located on or below or above the surface of the workpiece.

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

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

In an embodiment, 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.

Light refraction (also known as refraction or diffraction) occurs when light penetrates an interface or surface where the index of refraction changes abruptly. In particular, light refraction occurs when light is incident on the cross-section or surface of the light-refractive plate at an angle not equal to 90°.

Preferably, the beam shaping element is provided for deflecting the secondary beam passing through the beam shaping element. For example, the beam shaping element can have an optical surface which is arranged obliquely to the beam plane of the incident laser beam, for example an optical surface of a wedge plate. The plane to which the incident laser beam is perpendicular (ie normal) is referred to as the beam plane.

The beam shaping element may comprise at least one light-refracting plate, for example a wedge plate. Preferably, the corresponding light-refracting plates are optically isotropic.

In an embodiment, the adjustment of the at least one division parameter is effected by movement of the beam-shaping element.

Refractive optical elements as beam shaping elements can greatly simplify the adjustment of the division parameters and allow a simple construction. Thus, unlike for example the case of using mirrors, the refractive optic enables a direct adjustment of the division parameters by, for example, moving the refractive optic (or the corresponding light-refracting plate) (rotation, tilting, pivoting, shift).

For example, the adjustment of the distance between the primary beam and the at least one secondary beam can be effected by rotating the beam shaping element or by adjusting the angle of arrangement of the beam shaping element. Therefore, the spot pitch can be easily adjusted. For example, the beam shaping element may rotate about an axis parallel to the plane of the beam. The arrangement angle can be the angle of the optical surface of the beam-shaping element with respect to the beam plane.

For example, the adjustment of the power distribution between the primary beam and the at least one secondary beam may comprise a beam shaping element (for example a light-refracting plate) or at least one light-refracting plate of the beam shaping element transverse to the incident laser radiation. movement in the direction of the beam's optical axis. For example, the adjustment of the power distribution between the primary beam and the at least one secondary beam may comprise an adjustment of the overlap of the beam shaping element (or at least one light-refracting plate of the beam shaping element) with the cross-section of the laser beam Adjustment.

For example, the adjustment of the number of secondary beams may comprise a movement of the beam shaping element (eg a light-refracting plate) or at least one light-refracting plate of the beam-shaping element in a direction transverse to the optical axis of the incident laser beam .

Refractive optics may also be referred to as photorefractive optics or refraction optics. The beam shaping element can comprise or can be, for example, at least one wedge plate, an axicon array, at least one lens array and/or a plate arranged obliquely with respect to the direction of propagation of the laser beam. The plate can, for example, have parallel optical surfaces. An optical surface is one through which at least one partial beam enters the light-refracting plate or emerges from the light-refracting plate. The optical faces are the opposite faces of the plate. Thus, the plate can also be a plate in which the first surface is parallel to the second surface, through which the sub-beams enter the plate, through which the sub-beams pass from the shot from the board. By dividing the laser beam by refractive optical elements, it is possible to achieve division of the laser beam with as few optical elements as possible. In particular, the power loss of the beam shaping element can be minimized.

For example, the beam shaping element can have at least one beam-refracting plate, each beam-refracting plate being assigned at least one sub-beam of the laser beam which passes through the beam-refracting plate. A plurality of light-refracting plates can be arranged, for example, in stages (gestaffelt) one after the other along the direction of propagation of the laser beam, wherein, preferably, the first sub-beams (eg primary beams) do not pass through any of the light-refracting plates Refractive plate through which the second sub-beams (eg first secondary beams) only pass through the first light-refracting plate and corresponding further sub-beams (eg further secondary beams) additionally pass through the light-refracting plate respectively An additional light-refracting plate in the plate. A plurality of light-refracting plates can, for example, be arranged side by side offset in a direction transverse to the direction of propagation of the laser beam, wherein a corresponding sub-beam (for example a secondary beam) passes through one (or only one) corresponding beam Refractive plate. For example, the first sub-beams (eg primary beams) do not pass through any of the light-refracting plates.

In an embodiment, the beam shaping element comprises or is at least one light-refracting plate, which is arranged in a partial cross-section of the laser beam, wherein the sub-beams, in particular the primary beam, do not pass through all said at least one light refraction plate. Preferably, the at least one secondary beam passes through the at least one light-refracting plate along the direction of propagation. Preferably, the light-refracting plate is provided to keep the unpolarized laser light passing through the light-refracting plate unpolarized in the direction of propagation. The light-refracting plate can be non-polarizing, for example.

The light refraction plate may also be referred to as a refraction plate or a refractive plate. The light-refracting plate may be a wedge-shaped plate or may have parallel optical faces. The light-refracting plate is a refractive optical element. Preferably, the corresponding light-refracting plates are optically isotropic.

The step of dividing the laser beam into a primary beam and at least one secondary beam by means of a beam shaping element, for example, may be the division of the laser beam into a primary beam and at least one secondary beam by means of at least one light-refracting plate step, wherein 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 at least one secondary beam propagates along the corresponding The direction passes through the at least one light-refracting plate, wherein the light-refracting plate is arranged to keep unpolarized laser light passing through the light-refracting plate in the direction of propagation unpolarized.

The direction of propagation of the corresponding beamlets (eg secondary beams) in the plate can also be referred to as the through direction in which the beamlets pass through the plate.

The light-refracting plate makes it possible to divide the laser beam in order to generate a double or multiple laser spot of the laser beam without changing the polarization properties of the laser beam, in that only part of the laser beam passes through the light-refracting plate and thus deflected relative to another part of the laser beam. This makes it possible (at least for one sub-beam) to obtain advantageous polarization properties of the laser beam, in particular not only for the primary beam but also for at least one secondary beam.

The light-refracting plate is provided to keep the unpolarized laser light unpolarized, especially if it passes through the light-refracting plate in the direction of propagation. Thus, the light-refracting plate is arranged to obtain polarization properties of unpolarized laser light, especially when the unpolarized laser light passes through the light-refracting plate in the direction of propagation. That is, the light refraction plate is provided for obtaining the degree of polarization of unpolarized laser light. Thus, when randomly polarized laser beams or unpolarized laser beams are used, the laser beams do not change in their polarization and in particular are not polarized when passing through the light-refracting plate. This can make it possible to produce the desired intensity ratio of the primary beam and the secondary beam without impermissibly high absorption in the beam path of the laser beam due to the beam splitting by means of polarization. In contrast to the beam splitting by means of birefringent elements, no polarization of the resulting primary and secondary beams takes place, and the desired intensity ratio can be produced by a suitable arrangement of the light-refracting plates.

For example, among the division parameters, at least one division parameter adjusted according to at least one process parameter can be adjusted by adjusting at least one light refraction plate.

Partial beams, for example primary beams, do not pass through the light-refracting plate. This means that the relevant beamlets pass by the light-refracting plate.

In an embodiment, at least one of the laser beam, the primary beam and the at least one secondary beam is unpolarized. Unpolarized light may also be referred to as randomly polarized light with alternating random polarizations.

In an embodiment, the beam shaping element comprises at least one light-refracting wedge. The wedge-shaped plate may be a light-refracting plate as described.

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

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

In an embodiment, the beam shaping element comprises at least one light-refractive plate having an inclination angle on at least one optical face with respect to the beam plane of the incident laser beam, wherein at -0.9 rad The inclination angle is adjusted in the range of -0.9 rad, preferably -0.27 rad to 0.27 rad.

Preferably, the optical surface is such that the relevant beamlets emerge from the light-refracting plate through this surface.

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

The light refraction plate may be a wedge plate. In the case where the light refraction plate has parallel optical surfaces, preferably, the inclination angle is not equal to 0.000rad, ie not equal to 0mrad.

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

Preferably, the power share of the primary beam relative to the total power of the primary beam and the at least one secondary beam is set in a range of 0.1 to 0.9, preferably in a range of 0.2 to 0.8. In particular, this power share may not be equal to 0.5. Preferably, the primary beam has the maximum power of the partial beams. A power fraction of the primary beam of less than 0.5 can also bring advantages during laser fusion cutting and/or laser ablation cutting.

For example, the workpiece is a metal workpiece, in particular made of a steel alloy, an aluminum alloy, a copper alloy and/or a brass alloy. The workpiece can in particular be made of structural steel alloys, stainless steel alloys, aluminum alloys, copper alloys and/or brass alloys. The workpiece can also be made of aluminium, copper or brass.

The workpiece preferably has a material strength of ≧1 mm, in particular a material strength of ≧10 mm. Material strength is to be understood as the extent of the workpiece in the direction of beam propagation, ie in the direction of the cutting depth.

Preferably, the laser beam has a wavelength in the infrared range, for example between 780 nm and 1400 nm, in particular between 1000 nm and 1100 nm. This has the advantage that cost-effective IR laser sources can be used. 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.

According to another aspect, a laser processing device for cutting workpieces with a laser beam comprises a laser processing head for injecting a primary beam and at least one secondary beam along a cutting path in order to form the cut slit, wherein the laser processing head has a beam shaping element for dividing the laser beam into a primary beam and at least one secondary beam; and a control unit configured to execute according to The method described in any one of the above-mentioned embodiments.

In particular, the control unit can be configured to carry out the described method for cutting a workpiece by means of a laser beam.

The laser machining head has, for example, a housing and a beam path for the laser beam arranged in the housing, wherein the beam shaping element is arranged in the beam path. As mentioned above, the laser processing head can comprise beam shaping elements, collimating optics and focusing optics and/or a fiber sleeve for an optical fiber 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 of the optical element or of the light deflection plate.

Description of drawings

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

Fig. 1 schematically shows a laser processing device according to an embodiment of the present invention;

Figure 2 schematically shows the process interaction zone during cutting according to a comparative example;

Fig. 3 shows the X-ray photo and micrograph of fusion cutting process;

Figure 4 schematically shows the process interaction zone during cutting according to one embodiment of the invention;

FIG. 5 schematically shows the division of the laser beam according to one embodiment of the invention;

FIG. 6 schematically shows the division of a laser beam by a beam shaping element in the form of a wedge plate according to one embodiment of the invention.

Detailed ways

In the following, unless otherwise stated, the same reference numerals are used for identical and identically acting elements.

FIG. 1 schematically shows the design of a laser processing device for cutting workpieces by means of a laser beam according to one embodiment of the invention. In the following, the present invention will be described by taking a laser processing device for performing laser fusion cutting on a workpiece as an example, but the present invention is not limited thereto. The laser processing equipment may also be laser processing equipment for laser ablation cutting.

The laser processing system includes a laser processing head 100 for injecting a laser beam 10 onto a workpiece 1 . For example, laser beam 10 generated by laser source 200 can be coupled into laser processing head 100 via optical fiber 210 , optionally via fiber sleeve 220 . Laser beam 10 is divided by beam shaping element 400 into two sub-beams 10a, 10b, as shown, for example, in FIGS. 5 and 6 . A first of the sub-beams 10a, 10b 10a is the primary beam and the other sub-beam (or further sub-beam) 10b is the secondary beam which follows the primary beam along the cutting path Beam 10a. In Figure 1, the cutting path runs from left to right.

The beam shaping element 400 comprises at least one optical element which transmits the laser beam 10 (processing beam), for example a refractive optical element, at least one light-refracting plate or at least one light-refracting wedge. The optical system of the laser processing head 100 includes, in addition to the beam shaping element 400 , a collimation optic 110 and a focusing optic 120 . Preferably, the beam shaping element 400 is arranged in the collimated laser beam 10 , ie between the collimating optics 110 and the focusing optics 120 , so that based on the approximately collimated laser beam 10 a division into Two sub-beams 10a, 10b. In other words, the beam shaping element 400 can be arranged behind the collimation optics 110 in the propagation direction of the laser beam. The two sub-beams 10 a , 10 b can then be focused by a common focusing optics 120 for laser cutting. Alternatively, a separate focusing optics 120 may be provided for each sub-beam 10a, 10b in order to adjust the focus position of the two sub-beams 10a, 10b independently of one another.

The beam shaping element 400 can also be arranged in front of the collimation optics 110 in the direction of propagation of the laser beam, as indicated by the dashed lines, so that a split into two sub-beams 10 a , 10 b is achieved based on the diverging laser beam 10 .

Even though in the present case the division of the laser beam 10 into exactly two sub-beams 10 a , 10 b is described, the disclosure is not restricted thereto. The laser beam 10 can be divided into two or more sub-beams.

During laser cutting, the laser beam 10 is moved relative to the workpiece 1 at a cutting speed s. The laser beam 10 or the processing beam is guided and focused onto the workpiece 1 by means of an optical system (processing optics) 110 , 120 , 400 . In this case, each of the sub-beams 10 a , 10 b forms a laser spot on the workpiece 1 . The processing optics and its individual elements, in particular the beam shaping element 400 , are controlled by a superordinate control unit 300 , for example by correspondingly assigned motion devices. In particular, the control unit 300 is designed to carry out the method according to an embodiment of the invention.

The method according to an embodiment of the invention for cutting a workpiece by means of a laser beam comprises the steps of: dividing the laser beam into a primary beam and at least one secondary beam by means of a beam shaping element; The primary beam and the secondary beam are injected along a cutting path in order 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 control the energy input into the process interaction region in a targeted manner. That is, at least one division parameter for dividing the laser beam 10 is adjusted as a function of at least one process parameter. The at least one division parameter comprises: number of secondary beams 10b, focal position of primary beam 10a and/or secondary beam 10b, focal diameter of primary beam 10a and/or secondary beam 10b, primary beam 10a The power of beam 10a and/or of secondary beam 10b, the power distribution between primary beam 10a and at least one secondary beam 10b and the distance between primary beam 10a and at least one secondary beam 10b. The process parameters may comprise at least one of the following process parameters: cutting speed, especially instantaneous cutting speed; material strength or thickness of the workpiece (especially at the position of the kerf to be constructed); material of the workpiece Type (e.g. metal or plastic) or material (e.g. copper, steel, aluminum); process gas type (inert or reactive); process gas pressure; process gas (e.g. argon, oxygen, compressed air, nitrogen); not classified The focus position of the laser beam (especially in the direction perpendicular to the surface of the workpiece at the processing position or in the direction of propagation of the laser beam); The imaging ratio of the optical system of the laser processing equipment; the focal diameter of the undivided laser beam; the distance from the workpiece (especially the distance between the laser processing equipment or the laser processing head or the nozzle and the surface of the workpiece); the cutting front angle or (primary beam and/or secondary beam) local angle of incidence on the cutting front; depth of cut; the following maximum depth of cut from which irregular grooves are formed on the cutting face (i.e. the following depth of cut , the grooves on the cut surface become irregular from this depth of cut).

The beam shaping element 400 may be switchable. That is to say, for example, that beam shaping element 400 can be moved out of the beam path of laser beam 10 . Thus, conventional laser cutting can also be carried out by means of the beam shaping element 400 without dividing the laser beam 10 , if desired.

According to one embodiment, the beam shaping element 400 is rotatable about the laser beam axis (optical axis A of the laser beam or of the beam path). Thus, in the case of a changing cutting direction, ie a changing direction of the cutting path, secondary beam 10 b can follow primary beam 10 a along the cutting path by rotating beam shaping element 400 . In particular, for example, the beam shaping element 400 can be controlled as a function of the feed direction of the workpiece 1 .

(矢量n)与入射的激光射束10‘的射束传播方向之间的角被称为局部入射角θ。因此，局部切割前沿角相应于局部入射角θ。FIG. 2 schematically shows a comparative example of the process interaction range during laser fusion cutting with a single laser beam 10 ′ having a power P, which forms a single laser spot on a workpiece 1 . In the example shown, the cutting front 2 has an irregular course with different local cutting front angles. The angle between the cutting front and the line perpendicular to the beam propagation direction of the laser beam 10 ′ is referred to as the local cutting front angle. Local face normal of cutting front 2

The angle between (vector n) and the beam propagation direction of the incident laser beam 10 ′ is referred to as the local angle of incidence θ. Thus, the local cutting front angle corresponds to the local angle of incidence θ.

FIG. 2 shows, in the region on the left, irregular grooves 4 on the formed incisions 3 . The cutting speed s is defined as the separation limit (cutting interruption) at which no further separation of the workpiece 1 takes place. In the case of a cutting speed s slightly below this separation limit or in the case of unfavorably selected process parameters, a poor surface quality of the cut surface also occurs. This poor quality is mainly characterized by irregular groove formations which ensure a high surface roughness. Irregular grooves are characterized by strong local variations in their course along the cutting depth (in the direction of beam propagation). The cutting depth at which the groove 4 becomes irregular corresponds to the cutting depth at which the local angle of incidence θ decreases in an impermissible manner. In this case, local evaporation 6 of workpiece material occurs at this location.

FIG. 3 schematically shows radiographs (upper row) and micrographs (lower row) of a fusion cutting process of stainless steel as a function of the cutting speed s. The cutting speed s is specified separately. In the case of a cutting speed s of 1 m/min, the groove image is regularly structured. In the case of cutting speed s>1m/min, the groove image is irregular. As the cutting speed s increases, locally larger protrusions (visible by bright areas) can be seen in the X-ray images on the cutting front or on the cutting surface (arrows). At this position, the local angle of incidence θ is smaller. At this point the evaporation temperature of the material is reached. In this position, the melt is increasingly driven onto the cutting surface counter to the cutting direction and/or perpendicular to the laser beam axis or beam propagation direction. At this location, the trench image in the micrograph is irregular (arrow). Cutting interruptions occurred at the highest cutting speed of 2.8 m/min.

FIG. 4 schematically shows the process interaction region during cutting according to one embodiment of the invention, wherein the primary laser spot is formed by the primary beam 10 a with power P ₁ and the secondary laser spot is formed by the primary beam 10 a with power P ₂ The secondary beam 10b is formed. By means of a beam shaping element 400 in the processing optics, such as a wedge plate, the secondary laser spot of the secondary beam 10b or the secondary laser spot of the secondary laser spot is positioned to the process mutual in such a way that it follows the main laser spot of the primary beam 10a in the cutting direction. in the area of action. The secondary laser spot of the secondary beam 10 b prevents the onset of evaporation by avoiding a self-regulating reduction of the local angle of incidence θ due to locally missing absorbed energy. Therefore, the local angle of incidence θ is kept close to 90°.

5 and 6 schematically show the division of the laser beam according to an embodiment of the invention. FIG. 5 shows a beam shaping element 400 in the form of a wedge plate 400 ′ which is arranged in a part of the beam cross section of the laser beam 10 . The wedge plate 400' has a wedge angle α. As shown, corresponding to the wedge angle α, the thickness of the wedge plate 400 ′ is in the direction from the edge region of the beam cross section of the laser beam 10 to the optical axis A of the laser beam 10 incident on the wedge plate 400 ′ increase. In a transverse direction relative thereto, for example transversely to the partial cutting path direction, the wedge plate 400 ′ extends on both sides over the beam cross section of the laser beam 10 . With the wedge-shaped plate 400' in the processing optics, the secondary laser spot or the secondary laser spot (power P ₂ ) is positioned to the process mutual in such a way that it follows the primary laser spot or the main laser spot (power P ₁ ) in the cutting direction. in the area of action. A wedge plate 400' in the collimated beam divides the collimated beam forming a primary laser spot 10p and a secondary laser spot 10s. The laser spots 10 p , 10 s can lie, as shown, in a plane E of the beam focus of the primary beam 10 a and the beam focus of the primary beam 10 b. However, the laser spot can also lie above or below the plane E of the beam focus. By adjusting the (transverse) position v of the wedge plate 400' in the direction R, it is possible to adjust the power share P ₁ /P _ges or P ₂ /P _ges of P ₁ or P ₂ as division parameter, where applicable: P _ges =P ₁ +P ₂ , where P _ges is the total power of the laser beam 10 incident on the workpiece 1 .

Corresponding to the orientation of the wedge plate 400 ′, which has an increasing thickness from the edge region of the beam cross section to the optical axis A, the beam waist 12 is formed in the resulting double beam of the partial beams 10 a , 10 b.

In order to generate a plurality of secondary beams 10 b and/or to adjust the number of secondary beams as division parameter, for example at least one further wedge plate 400 ″ can be provided, which is connected to the first wedge plate 400 ′. Different partial cross-sections of the laser beam 10 are covered. The further wedge plate, like wedge plate 400 ′, can be adjusted or adjusted in a corresponding manner.

Further adjustment possibilities of the wedge plate 400' (or 400") are illustrated in FIG. 6. FIG. 6 shows a variant of the embodiment according to FIG. The surface here has an inclination angle β to the beam plane S of the incident laser beam 10. Correspondingly, the first optical surface in the direction of beam propagation of the wedge plate 400' has an angle of inclination β to the incident laser beam 10. The inclination angle α+β of the beam plane S.

The spacing d of the laser spots 10p, 10s as a division parameter is adjusted by changing the wedge angle. By adjusting the position h (height position, parallel to the direction of beam propagation), the distance between the beam waist 12 and the bifocals 10 p , 10 s in the direction of propagation of the laser beam is adjusted as a division parameter. By adjusting the inclination angle β, which can also be referred to as the installation angle, the distance d of the laser spots 10 p , 10 s and the distance between the beam waist 12 and the bifocal 10 p , 10 s in the direction of propagation are adjusted as division parameters. The wedge angle α and the tilt angle β determine whether the bifocal is located above or below the beam waist 12 . In the case of α−β<0, the beam waist 12 is located below the bifocal, and in the case of α−β>0, the beam waist 12 is located above the bifocal. In the same way as in FIG. 5 , the power share P ₁ /P _ges of the primary beam (with power P ₁ ) and the secondary beam (with power P ₂ ) can be adjusted as division parameters by adjusting the position or distance v The power share P ₂ /P _ges , where again it applies: P _ges =P ₁ +P ₂ .

The influence of the double focus compared to the cutting method with a standard laser beam, ie with a single spot, can be demonstrated in experiments. In the case of cutting 10 mm or 20 mm of stainless steel with a laser power (total power) of 6 kW, by suitable selection of the division parameters, in particular by suitable selection of the spot spacing and the power distribution between the primary beam 10a and the secondary beam 10b , the maximum cutting speed can be increased by 19% or 23%.

The maximum cutting speed, the surface roughness of the cut face and the burr formation depend on many parameters, mainly on the local, absorbed radiation intensity at the cutting front. Therefore, for a targeted or controlled energy input of the processing laser into the processing region, according to the invention, in a method for cutting workpieces with the aid of the laser beam, the laser beam is divided by the beam shaping element into A primary jet and at least one secondary jet are injected along a cutting path in order to form a kerf, wherein the secondary jet follows the primary jet. By adjusting at least one of the division parameters according to at least one process parameter, the laser cutting process can be optimized with respect to the maximum cutting speed and/or the surface roughness of the cut surface, especially for materials greater than 1 mm or especially greater than or equal to 10 mm strength or depth of cut. As a result, precise and clean formation of the kerf can be achieved even at higher cutting speeds, wherein the beam-shaping element can be precisely adjusted and can be produced cost-effectively.

Claims (15)

1. A method for cutting a workpiece (1) by means of a laser beam (10), the method comprising: The laser beam (10) is divided by a beam shaping element (400) into a primary beam (10a) and at least one secondary beam (10b); and The primary beam (10a) and the secondary beam (10b) are injected along a cutting path to form a kerf (3), wherein the secondary beam (10b) follows the primary beam bundle (10a), wherein at least one division parameter for dividing the laser beam (10) is adjusted according to at least one process parameter, wherein the at least one division parameter comprises: the number of the secondary beams (10b), the primary The focus position of the beam (10a) and/or the secondary beam (10b), the focal diameter of the primary beam (10a) and/or the secondary beam (10b), the primary the power of the beam (10a) and/or of the secondary beam (10b), the power distribution between the primary beam (10a) and the at least one secondary beam (10b), and the The distance between the primary jet (10a) and the at least one secondary jet (10b). 2. The method according to claim 1 , wherein at least one of the division parameters is adjusted according to at least one of the following process parameters: cutting speed (s), relative to the workpiece (1) Distance, nozzle type, nozzle geometry, nozzle opening diameter, beam parameter product of the undivided laser beam (10), divergence angle of said undivided laser beam (10), fibers of the optical cable diameter, laser power of the undivided laser beam (10), pulse on time of the undivided laser beam (10), pulse off time of the undivided laser beam (10) time, the pulse peak power of the undivided laser beam (10), the material intensity of the workpiece (1), the material type or material of the workpiece (1), making the primary beam (10a) and the imaging ratio of the optical system (110, 120) of the laser processing equipment where the secondary beam (10b) enters, the focus position of the undivided laser beam (10), the undivided Focus diameter of laser beam (10), local angle of incidence (θ) on said cutting front (2), process gas, process gas type, process gas pressure, depth of cut, and maximum depth of cut as follows: from said Irregular grooves (4) are formed on the cutting surface from the maximum cutting depth. 3. The method according to any 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. The method according to any one of the preceding claims, wherein the adjustment of the at least one division parameter is effected by movement of the beam shaping element (400). 5. The method as claimed in claim 1, wherein the splitting of the laser beam (10) into the primary beams (10a) by means of the beam shaping element (400) can be switched on and off ) and said division of said at least one secondary beam (10b). 6. The method according to any one of the preceding claims, wherein the beam shaping element (400) is movable out of the beam path of the laser beam (10) and into the In the beam path of the laser beam (10). 7. The method according to any one of the preceding claims, wherein the beam shaping element (400) comprises at least one light-refracting plate (400') arranged at the laser beam In a partial cross-section of the beam (10), wherein said primary beam (10a) does not pass through said at least one light-refracting plate (400'), Wherein, the at least one secondary beam (10b) passes through the at least one light-refracting plate (400') along the propagation direction. 8. The method according to any one of the preceding claims, wherein the beam shaping element (400) comprises at least one light-refracting wedge (400'). 9. The method according to claim 8, wherein the wedge angle (α) of the wedge plate (400') is in the range of 0.001 rad to 0.1 rad, preferably 0.001 rad to 0.01 rad or 0.0015 rad to 0.00567 rad in the range. 10. The method according to any one of the preceding claims, wherein the beam shaping element (400) comprises at least one light-refracting plate having a relative incidence on at least one optical surface The inclination angle (β) of the beam plane (S) of the laser beam (10), wherein the inclination angle is adjusted in the range of -0.9rad to 0.9rad, preferably in the range of -0.27rad to 0.27rad (β). 11. The method according to any one of the preceding claims, wherein the laser light of the at least one secondary beam (10b) is adjusted in the range of 0.05 mm to 4 mm, preferably in the range of 0.225 mm to 0.85 mm The distance (d) along the cutting direction between the spot (10s) and the laser spot (10p) of the primary beam (10a). 12. The method according to any one of the preceding claims, wherein the adjustment of the primary beam (10a) relative to the primary beam ( 10a) and the power fraction (P ₁ /P _{ges ) of the total power (P ges )} of the at least one secondary beam ( 10b ). 13. The method according to any one of the preceding claims, wherein the workpiece (1) is a metal workpiece (1), in particular made of a steel alloy, an aluminum alloy, a copper alloy and/or a brass alloy. 14. The method according to any one of the preceding claims, wherein the method is a method for laser fusion cutting and/or a method for laser ablation cutting. 15. A laser processing device for cutting a workpiece (1) by means of a laser beam (10), said laser processing device comprising: a laser processing head for injecting a primary beam (10a) and at least one secondary beam (10b) along a cutting path in order to form a kerf (3), wherein the laser processing head having a beam shaping element (400) for splitting the laser beam (10) into the primary beam (10a) and the at least one secondary beam (10b); and A control unit (300) configured to carry out the method according to any one of the preceding claims.

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