Method for cutting workpiece with laser beam

Abstract

The invention relates to a method for cutting a planar workpiece with a laser beam, in which the focal position of the laser beam is oscillated during the relative movement of the workpiece and the laser beam, and in which the beam quality M2 of a laser source (110) is at most 12, M2 < = 12.

Description

Technical Field

[0001] This invention relates to a method for cutting planar workpieces using a laser beam. Background Technology

[0002] During the cutting process, the laser beam irradiates one side of the workpiece, which is referred to here as the top surface. Opposite to this side along the thickness direction z is the bottom surface of the workpiece, whose thickness in the thickness direction z is t. To perform the cutting, i.e., to cut or separate the workpiece, for example, along a line, the workpiece and the laser beam are moved relative to each other in the feed direction (versetzt) ​​(conversely, or rather, slid relative to each other). This feed direction is at an angle to the thickness direction z, specifically perpendicular to it. Summary of the Invention

[0003] The technical problem upon which this invention is based is to provide an advantageous method for cutting workpieces with a laser beam.

[0004] This is solved by the method of the present invention, in which a laser beam is guided onto the workpiece by an optical system having a beam-changing element. Here, the laser source is selected to achieve a beam quality M. 2 At most 8, meaning that, in short, the laser beam has a relatively narrow waist. This can have advantages, for example, allowing for higher feed rates (with a correspondingly narrower kerf). However, the narrowing of the laser beam, i.e., the relatively strong beam contraction, may also increase the risk of plasma formation, which can be detrimental to the cutting process (see below for details).

[0005] Therefore, the principle of this invention lies in: although a laser beam with significant beam contraction is provided, i.e., M 2 A laser source with a focal length of ≤12 is used, but during relative movement or relative feed, the focal position oscillates at least partially along the thickness direction z. Compared to a static laser beam, this widens the diameter, or beam contraction, in the equivalent value (Gleichwert) of the focal position, thus allowing for more stable and improved process control. In other words, the oscillation enables stable process control even with increased feed rates, i.e., it expands the process window. The beam quality is given by the following equation:

[0006]

[0007] Where w0 is the beam waist of the static laser beam, i.e., the half-beam diameter at the focal point. θ corresponds to the divergence angle, and λ corresponds to the wavelength of the laser beam. M 2 Other preferred upper limits can be, for example, 10, 8, 7, 6, 5, 4, 3 or 2, and possible lower limits can be, for example, 1.

[0008] Other preferred embodiments of the method and corresponding apparatus according to the invention are given in the claims and the entire disclosure. While different categories of claims are not always distinguished in detail, the disclosure always implicitly refers to both the method and the apparatus or its use.

[0009] According to a preferred embodiment, the focal position is oscillated such that the diameter at the resulting focal point is at least 5% larger than the diameter at the focal point of a static laser beam (the same laser beam without oscillation), and more particularly preferably at least 10% or at least 20% larger. Possible upper limits may be, for example, 300%, 200%, 150%, or 100%. Specifically, for an oscillating beam, the diameter is taken at an equivalent value (offset) of the oscillating focal position, which is obtained by averaging over time (Zeitverlauf) (see below). The desired increase in diameter can be achieved, for example, by adjusting the amplitude (greater amplitude → larger diameter) and / or by changing the caustics and / or adjusting the intensity distribution.

[0010] The energy density distribution in a workpiece can be influenced, for example, by the oscillation frequency. For this purpose, an overlap ratio O as defined below can be considered, for example. The inventors have found that when this overlap ratio is at least 50%, a constant energy density distribution along the feed direction can be assumed. The overlap ratio is given by the following formula:

[0011]

[0012] Where w0 is the waist of the static laser beam, i.e., the half-beam diameter at the focal point, v is the feed rate, and f is the oscillation frequency.

[0013] According to a preferred embodiment, the oscillation focal position is at an amplitude at most equal to the workpiece thickness. Another upper limit could be at most 0.5 times the workpiece thickness, and unrelatedly, a possible lower limit is at least 0.3 times the workpiece thickness. The workpiece thickness may vary along the feed direction, in which case the amplitude of the z-direction oscillation can preferably also be adjusted. If the workpiece thickness along the feed direction is constant, the amplitude can be varied, for example, compared to another workpiece with a different thickness.

[0014] According to a preferred embodiment, when cutting a thickness t, the focal position is oscillated with a first amplitude, while when cutting a comparatively larger thickness, the focal position is oscillated with a second amplitude, which is greater than the first amplitude. As discussed earlier, different thicknesses may occur at different locations on the same workpiece, and / or when workpieces have different thicknesses, the amplitude can be adjusted from one workpiece to another. For even smaller thicknesses, oscillation can be performed with a third amplitude, which is smaller than the first amplitude. Typically, these amplitudes, i.e., the second amplitude versus the first amplitude, and possibly the third amplitude versus the first amplitude, can differ in magnitude by at least 10%, 20%, or 30%, with possible upper limits such as up to 500%, 400%, 300%, or 200%.

[0015] According to a preferred embodiment, during cutting, relative movement is performed at a first feed rate v1 at a first time point or a first time interval. At this time, the focal position oscillates at a first frequency. At a second time point or a second time interval, relative movement is performed at a second feed rate v2, which is greater than the first feed rate v1. At this time, the focal position oscillates at a second frequency, which is greater than the first frequency. Here, the frequencies may differ by at least 10%, 20%, or 30% (possibly upper limits such as up to 500%, 400%, 300%, or 200%).

[0016] According to a preferred embodiment, the focal position is oscillated such that the equivalent value of the intensity distribution Iz of the laser beam measured along the thickness direction z around the focal position is broadened (over time, i.e., considered on a time-averaged basis), meaning that the intensity distribution along the thickness direction z is broader than in the static case (when the same laser beam is not oscillating). The intensity distribution in the static case can, in particular, be a Gaussian distribution, while the intensity distribution Iz along the oscillating laser beam is broadened in contrast. Therefore, for example, at z values ​​that take half the width of the Gaussian distribution, the intensity of the oscillating laser beam can be greater than in the static case.

[0017] In a preferred embodiment, the intensity distribution Iz of the oscillating laser beam is a top-hat-profil (considered over time, i.e., time-averaged). The intensity distribution Iz can also, for example, be annular, with a minimum value approximately at the center (a donut distribution); alternatively, it can also have a maximum value at the center of the annulus. In other words, in some embodiments, the intensity at the equivalent value at the focal point may be equal to or even less than the intensity at the equivalent z-value around the focal point. Figuratively speaking, using such an intensity distribution along the thickness direction z allows for a more uniform intensity input, or energy input, into the workpiece.

[0018] According to a preferred embodiment, the equivalent value of the focal position, i.e., the offset, is set so that it lies outside the upper half of the workpiece thickness t. This variation is independent of the M of the main claim. 2 Laser sources with a value of ≤8 may also be meaningful and should therefore be disclosed accordingly, with combination with them being preferred.

[0019] Typically, in laser beam cutting, such as in fusion cutting, the energy of the laser beam or absorbed laser radiation is used to melt or partially evaporate the material of the workpiece. One of the inventors' working hypotheses is that as the cutting speed increases, the angle of the cutting front increases, which, for example, increases the proportion of absorbed radiation (e.g., due to a greater overlap between the laser beam and the cutting front, or due to angle-dependent absorptivity). As a result, this could, for example, lead to an increase in temperature in the cutting front region, potentially increasing the proportion of evaporated material and, for example, causing uncontrolled plasma formation.

[0020] This consumes energy from the laser radiation, and plasma formation can lead to defocusing or beam deflection. Plasma formation typically interferes with the cutting process and can even cause kerf tearing, both of which are undesirable. Altered energy coupling can, for example, lower the cutting front temperature, and the effects of gas dynamics can interfere with melt ejection. Oscillation can prevent plasma formation or push back the boundaries of plasma formation, thereby enabling, for example, higher feed rates (e.g., which can increase throughput, making economic sense).

[0021] While plasma formation can be suppressed by shifting the equivalent value of the focal position, i.e., the offset, toward the top surface of the workpiece, the inventors observed an increase in burr formation on the bottom surface of the workpiece in this case. Overall, the principle of the invention, namely the combination of oscillation and offset position (outside the upper half of the thickness t), can increase the feed rate while achieving a clean cut.

[0022] A "planar" workpiece has an extension in the thickness direction z that is several times smaller than its extension in the plane direction at an angle or perpendicular to it. For example, it can be a metal sheet, plate, or metal billet, such as a housing component or body part. Typically, the material is a metal, which naturally includes alloys. The thickness t is observed at the position where the laser beam irradiates the top surface at the corresponding time point during processing, i.e., at the location of the cutting front. The thickness direction z is perpendicular to the top surface. Generally, the workpiece does not need to have a uniform thickness; the thickness can take different values ​​along the feed direction. However, it is preferable to have a uniform thickness, especially if the workpiece is a parallel planar plate.

[0023] For illustration, the thickness t can be, for example, at least 0.5 mm, and typically in the range of several millimeters. The possible upper limit for the thickness t can be in the range of centimeters, for example, up to 50 cm, 10 cm, 6 cm, or 4 cm. In principle, the risk of plasma formation increases with increasing material thickness and cutting speed (i.e., feed rate). This relative movement of the workpiece and the laser beam, viewed separately in a fixed coordinate system, can be achieved by moving the laser beam and / or the workpiece, i.e., moving the workpiece, for example, under the laser beam.

[0024] The focal position is the z-position of the laser beam at a given time point along the beam direction; in other words, it is the position of the beam waist at that moment. The equivalent value (offset) of the focal position is derived as an average value, i.e., averaged over time. For illustration, the focal position can oscillate between a minimum and a maximum value in the z-direction (the minimum is the minimum distance from the focal position to the focusing optics of the machining head, and the maximum is the maximum distance, both measured along the beam), with the equivalent value lying in between, for example, in the middle (but usually not). In other words, the offset can correspond to the static focal position, while the dynamic focal position, with its oscillations, oscillates around this equivalent value. Furthermore, the equivalent value of the focal position can be located where the focal point would be when z-oscillations are not occurring (i.e., z-oscillations are off).

[0025] During oscillation, the focal position may, for example, move into or through the upper half of the thickness t, but the average value (equivalent value) should lie outside of it. Typically, the equivalent value of the focal position can also, for example, lie above the top surface, i.e., outside the workpiece. Referring to the percentage notation discussed below (0% for the bottom surface / 100% for the top surface), the equivalent value of the focal position can therefore also lie at a value greater than 100%. In this case, plasma formation may be less important, but beam oscillation can, for example, reduce the risk of spontaneous combustion and cut-off tearing.

[0026] According to a preferred embodiment, the equivalent value of the focal position is less than 50% of the percentage designation relative to the thickness t. Here, by definition, the percentage designation is 0% at the bottom surface of the workpiece and increases from the bottom surface to the top surface along the workpiece thickness t, with 100% located at the top surface of the workpiece. Preferably, the equivalent value is at most 40%, i.e., offset downwards by at least 10% relative to the center of the thickness.

[0027] Typically, the equivalent value of the focal position can also be located below the workpiece, i.e., below the bottom surface (a negative percentage value relative to the percentage designation). In a preferred embodiment, unlike this, the equivalent value of the focal position is at least 0%, i.e., in or above the bottom surface (but outside the upper half). Particularly preferably, it is at least 10%. In conjunction with the previous paragraph, the equivalent value of the focal position can therefore be, for example, in the range of 0%-50% of the percentage designation, particularly 10%-40%.

[0028] According to a preferred embodiment, the focal position oscillates at a frequency of at least 500 Hz, preferably at least 750 Hz, in the thickness direction z. High-frequency oscillation allows for dynamic adjustment of the beam shape (particularly beam caustics) and intensity distribution, for example. Instead of this, or in conjunction with the aforementioned lower limit, a preferred upper limit may be, for example, 5 kHz, further and particularly preferably at most 4 kHz or at most 3 kHz. Generally, the reference to "frequency" does not necessarily mean oscillation at a single frequency; the frequency can also vary (preferably within the range of the aforementioned lower / upper limits). Furthermore, the term "frequency" does not necessarily mean a sinusoidal shape, although this may be preferred; it can also typically be, for example, a sawtooth shape, etc.

[0029] A preferred embodiment involves the amplitude of the focal position oscillating in the thickness direction z. Here, the amplitude is determined according to the static Rayleigh length. z R Given that the static Rayleigh length is the distance along the optical axis required for a static laser beam (without z-oscillation) to double in cross-sectional area from its beam waist, the distance is given by the Rayleigh length z. R The amplitude of the oscillation is at least 0.1 times the Rayleigh length z. R Further lower limits can be at least 0.25 times, 0.5 times, 0.75 times, or 1 times the Rayleigh length z. R Alternatively, or in combination with this, the upper limit can be, for example, up to 8, 6, 4, 3, or 2 times the Rayleigh length z. R .

[0030] According to a preferred embodiment, in a static state, i.e., in the case of a laser beam without oscillation, the diameter of the laser beam at the focal point, i.e., the beam waist, is at least 10 μm, more preferably at least 18 μm, 30 μm, or at least 50 μm and 100 μm. Preferred upper limits may be increasingly preferred, in the order mentioned, at most 350 μm, 250 μm, 200 μm, or 150 μm.

[0031] In a preferred embodiment, the laser beam oscillates only in the thickness direction z, i.e., there is no oscillation along or transverse to the feed direction (no beam wobbling). This can, for example, improve process control and simplify the technical implementation of oscillation.

[0032] The change of focal position can typically be achieved using a beam-changing element, which can in principle be transmissive. However, in a preferred embodiment, it is a deformable reflector, i.e., a reflector with a deformable reflective surface. For possible implementations, exemplary reference is made to a mirror design according to DE 102021 102 096B4, which can be operated in an oscillating manner by corresponding manipulation or adjustment (commercially available is Zwobbel from ROBUST AO GmbH). Thus, oscillation is applied, for example, by a corresponding oscillating deformation of the reflective surface. The laser beam can be focused by a focusing system, such as a focusing lens or focusing lens system. The beam-changing element, particularly the deformable reflector, can be arranged upstream or downstream of the focusing system relative to the beam propagation.

[0033] According to a preferred embodiment, the focal position is oscillated with an asymmetric signal waveform. In other words, the duty cycle of the signal waveform is not equal to 50%. Figuratively speaking, by deviating from the average duty cycle, the intensity distribution can be shifted more towards one side or the other side of the focal position equivalent value. Preferably, the duty cycle can be adjusted so that the energy density distribution is shifted towards the top surface of the workpiece; in other words, the energy density above the focal position equivalent value can therefore be higher than the energy density below the focal position equivalent value.

[0034] The present invention also relates to an apparatus for cutting planar workpieces with a laser beam, wherein the apparatus includes a laser source, a workpiece receiving portion for arranging the workpiece, and an optical system. According to a preferred variant, the M of the laser source... 2 The maximum is 8, see the opening disclosure, also regarding other upper and lower limits. The optical system here has a beam-changing element, by which the focal position of the laser beam can be changed or shaped along the propagation direction and thus relative to the component in the depth direction (see above).

[0035] The laser source can be, for example, a high-power laser, such as a fiber laser, disk laser, diode laser, or CO2 laser. The wavelength of the laser radiation can be, for example, in the ultraviolet to mid-infrared range. The optical system guides the laser beam emitted by the laser source during operation to the workpiece, that is, to the workpiece receiving section used to accommodate the workpiece.

[0036] A beam conversion element is configured to oscillate the focal position of a laser beam. According to a preferred embodiment, it is configured to maintain the equivalent value of the focal position outside the upper half of the workpiece. This configuration may, for example, mean that instructions are stored in the control unit (e.g., a machine controller) of the device or beam conversion element, causing the beam conversion element to oscillate the laser beam passing through it during operation, and in doing so, to maintain the offset outside the upper half of the workpiece. An apparatus of this kind, having a laser source, a workpiece housing, and an optical system, should also be disclosed, wherein a workpiece of thickness t is arranged in the workpiece housing.

[0037] Furthermore, the present invention relates to the use of an apparatus having a laser source, a workpiece receiving portion, and an optical system for cutting workpieces. Here, the focal point position is oscillated during the cutting process, and the equivalent value of the focal point position is preferably located outside the upper half of the workpiece thickness t; see above for further details.

[0038] Part of the content of this invention can also be summarized as follows:

[0039] 1. A method for cutting a planar workpiece (10) with a laser beam (20), wherein the laser beam (20) is emitted from a laser source (110) and guided onto the workpiece (10) through an optical system (120),

[0040] In order to cut, the workpiece (10) and the laser beam (20) are moved relative to each other in the feed direction (25).

[0041] Furthermore, the optical system (120) includes a beam conversion element (125) that, during relative movement, causes the focal position (21) of the laser beam (20) to oscillate at least partially in the thickness direction z of the workpiece (10) perpendicular to the feed direction.

[0042] Furthermore, the beam quality M of the laser source (110) 2 At most 12, M 2 ≤12.

[0043] 2. According to the method described above, the oscillation frequency f is set according to the feed rate v, such that the overlap rate...

[0044]

[0045] At least 50%.

[0046] 3. According to the method of aspect 1 or 2, wherein the workpiece (10) has a thickness t and oscillates at the focal position (21) with a first amplitude, the first amplitude being at most twice the thickness t of the workpiece.

[0047] 4. The method according to any of the foregoing aspects, wherein the workpiece (10) has a thickness t and oscillates at a focal position (21) with a first amplitude, wherein when cutting a thickness greater than the thickness t, the focal position (21) oscillates with a second amplitude greater than the first amplitude.

[0048] 5. The method according to any of the foregoing aspects, wherein when relative movement is made in the feed direction (25) at a first feed speed v1, the focal position (21) is oscillated at a first frequency, wherein when relative movement is made in the feed direction (25) at a second feed speed v2 greater than the first feed speed v1, the focal position (21) is oscillated at a second frequency greater than the first frequency.

[0049] 6. The method according to any of the foregoing aspects, wherein the focal position (21) of the laser beam (20) is oscillated at least partially in the thickness direction z such that at the equivalent value (22) of the focal position (21), the diameter d of the laser beam (20) is at least 5% larger than the diameter of the static laser beam (20) at the focal position.

[0050] 7. The method according to any of the foregoing aspects, wherein the focal position (21) of the laser beam (20) is oscillated at least partially in the thickness direction z such that the intensity distribution I of the laser beam (20) measured along the thickness direction z is... z The equivalent value (22) around the focal position (21) is wider than the intensity distribution of the static laser beam (20).

[0051] 8. According to the method of aspect 7, wherein the intensity distribution I of the laser beam (20) is measured along the thickness direction z. z The equivalent value (22) around the focal position (21) has a flat-top distribution or a ring-shaped distribution, such as a donut-like distribution.

[0052] 9. The method according to any of the foregoing aspects, wherein the laser beam (20) irradiates the top surface (10.1) of the workpiece (10), which is opposite the bottom surface (10.2) of the workpiece (10) in the thickness direction z, wherein the equivalent value (22) of the focal position (21) is located outside the upper half t1 of the thickness t, measured from the bottom surface (10.2) to the top surface (10.1) of the workpiece (10).

[0053] 10. According to the method of aspect 5, the equivalent value (22) of the focal position (21) is located above the workpiece (10).

[0054] 11. According to the method of aspect 5, the equivalent value (22) of the focal position (21) is less than 50% relative to the percentage marking of thickness t from 0% at the bottom surface (10.2) of the workpiece (10) to 100% at the top surface (10.1).

[0055] 12. According to the method of aspect 11, the equivalent value (22) of the focal position (21) is at most 40%.

[0056] 13. According to the method of aspect 11 or 12, wherein the equivalent value (22) of the focal position (21) is located below the workpiece (10), i.e., below 0%.

[0057] 14. According to the method of aspect 12 or 13, wherein the equivalent value (22) of the focal position (21) is at least 0%.

[0058] 15. According to the method of aspect 14, the equivalent value (22) of the focal position (21) is at least 10%.

[0059] 16. The method according to any of the foregoing aspects, wherein the frequency f of the oscillation is at least 500 Hz and / or at most 5 kHz.

[0060] 17. The method according to any of the foregoing aspects, wherein the amplitude of the oscillation is at least half and / or at most eight times the Rayleigh length of the static laser beam (20).

[0061] 18. The method according to any of the foregoing aspects, wherein the diameter of the static laser beam (20) at the focal point is at least 10 μm and / or at most 350 μm.

[0062] 19. The method according to any of the foregoing aspects, wherein the laser beam (20) oscillates only in the thickness direction z.

[0063] 20. The method according to any of the foregoing aspects, wherein the beam conversion element (125) has a deformable reflector (126) through which the laser beam (20) is guided onto the workpiece (10), wherein oscillation is applied to the laser beam (20) through the deformable reflector (126).

[0064] 21. The method according to any of the foregoing aspects, wherein the signal waveform used to oscillate the focal position (21) in the thickness direction z of the workpiece (10) is asymmetric, i.e., the duty cycle is not equal to 50%.

[0065] 22. An apparatus (100) for cutting a planar workpiece (10) with a laser beam (20), comprising: a laser source (110) for emitting the laser beam (20); a workpiece receiving portion for arranging the workpiece (10); and an optical system (120) for guiding the laser beam (20) onto the top surface (10.1) of the workpiece (10) arranged in the workpiece receiving portion; wherein the beam quality M of the laser source (110) is... 2 At most 12, M 2 ≤12, wherein the optical system (120) has a beam conversion element (125) which can change the focal position (21) of the laser beam (20), and wherein the beam conversion element (125) is configured to oscillate the focal position (21) of the laser beam (20) at least partially in the thickness direction z when the workpiece (10) and the laser beam (20) move relative to each other.

[0066] 23. An apparatus (100) for cutting a planar workpiece (10) with a laser beam (20) comprises: a laser source (110) for emitting the laser beam (20); a workpiece receiving portion for arranging the workpiece (10) having a thickness t; and an optical system (120) for guiding the laser beam (20) onto the top surface (10.1) of the workpiece (10) arranged in the workpiece receiving portion; wherein the optical system (120) has a beam conversion element (125) by means of which the focal position (21) of the laser beam (20) can be changed, and wherein the beam conversion element (125) is configured to oscillate the focal position (21) of the laser beam (20) at least partially in the thickness direction z when the workpiece (10) and the laser beam (20) move relative to each other, and in the process maintain an equivalent value (22) of the focal position (21) outside the upper half t1 of the thickness t.

[0067] 24. The use of the apparatus (100) according to aspect 22 or 23 for cutting workpiece (10), particularly by any one of aspects 1 to 21.

[0068] 25. The use of the device (100) according to aspect 22 or 23, wherein the amplitude of the oscillation is adjusted according to the thickness t of the workpiece, and / or the frequency f of the oscillation is adjusted according to the cutting speed. Attached Figure Description

[0069] The invention will now be described in detail based on embodiments, wherein various features may also be essential to the invention in other combinations, and as previously stated, all categories of the invention are implicitly involved.

[0070] Figure 1a , 1b This demonstrates how the cutting front of the laser beam becomes increasingly inclined as the feed rate increases;

[0071] Figure 2 A device for laser beam cutting is shown, and the oscillation of the focal position is demonstrated;

[0072] Figure 3a 、 3b The cutting front and the cutting profile without oscillation of the focal position are shown;

[0073] Figure 4a 、 4b The cutting front and the cutting profile with oscillation of the focal position are shown;

[0074] Figure 5 The laser beam diameter adjusted by oscillation is shown, as well as a comparison with the static case;

[0075] Figure 6 The different intensity distributions adjusted by oscillation are shown, as well as a comparison with the static case. Detailed implementation

[0076] Figure 1a In a schematic sectional view, a planar workpiece 10, here a plate, is shown, and the workpiece or the plate is cut with a laser beam 20. The laser beam irradiates the top surface 10. f of the workpiece 10, and the bottom surface 10.2 is opposite in the thickness direction z. By the relative movement of the workpiece 10 and the laser beam 20, a cut 30 is introduced into the workpiece 10 in the feed direction 25, which is Figure 1a from left to right in the figure. Due to the feed, i.e., the relative movement at a speed v1, the cutting front 31 is somewhat inclined.

[0077] Figure 1b The same initial situation with the workpiece 10 and the laser beam 20 is shown, but in this case the feed speed v2 is higher (v1 < v2). The cutting front 31 is again inclined and is inclined more strongly than Figure 1a in the figure. This may for example lead to plasma formation or hindered melt ejection, see the details in the introduction part of the specification.

[0078] Figure 2 A schematic section of a planar workpiece 10 is shown again, and first it is shown how the focal position 21 of the laser beam 20 oscillates in the thickness direction z. In Figure 2In the illustrated case, the focal position 21 is at a minimum value 21.2, and over time, it oscillates between this minimum value 21.2 and a maximum value 21.1. This oscillation (e.g., at a frequency of 2-3 kHz) helps prevent plasma formation even at high feed rates (compared to no oscillation at the same feed rate). The equivalent value 22 of the focal position 21 is located outside the upper half t1 of the thickness t, i.e., within the lower half t2. The offset can be particularly between 10% and 40% relative to the markings of 0% for the bottom surface 10.2 and 100% for the top surface 10.1.

[0079] Figure 2 Details of the device 100 are also shown. This device primarily includes a laser source 110, which emits a laser beam 20 during operation. The laser source 110 in this example has M... 2 ≤2. The laser beam 20 is guided onto the workpiece 10 by an optical system 120, which includes a beam conversion element 125, implemented here as a deformable reflector 126. Furthermore, a focusing system 127 is provided, which converges (focuses) the laser beam 20 onto the workpiece 10. Oscillations at the focal position 21 are applied to the laser beam 20 via the beam conversion element 125, or deformable mirror 126. The feed direction 25 is perpendicular to the drawing plane.

[0080] Figure 3a This again demonstrates the tilting of the cutting front 31 as it moves along the feed direction 25, without oscillation at the focal position. Figure 3b The outline of the resulting cut 30 is shown, i.e., looking at the cut 30 along the feed direction.

[0081] Figure 4a For comparison, it is shown how the cutting front 31 changes through oscillation, i.e., becomes steeper. Figure 3a and Figure 4a (The feed rate is the same in both cases). Furthermore, as can be seen at the lower end of the cutting front 31, melt discharge is also positively affected. The resulting profile is... Figure 4b As shown, the view is still along the feed direction towards cut 30. Its contouring is less pronounced, and burr formation can be prevented through the equivalent position achieved by the aforementioned oscillation.

[0082] Figure 5 The diameter d (x-axis) of the laser beam 20 along the thickness direction z (y-axis) is shown. Here, the dashed line represents the static comparison case, i.e., the laser beam 20 without oscillation. The laser source (not shown here) has M... 2≤8, therefore the laser beam 20 experiences relatively strong beam contraction at the focal point. The solid line shows the profile resulting from the oscillation at the focal position, with the diameter d, averaged over time, particularly at the equivalent value 22, being larger than the static case (and further affected by increasing or decreasing the amplitude and / or frequency). Furthermore, with the oscillation, the Rayleigh length z... R (Averaged over time) also increases, which can positively influence the geometry of the cut.

[0083] Figure 6 Intensity distribution I is shown z That is, the intensity varies with the thickness direction z, averaged over time. In a static comparison, represented by a dashed line, a Gaussian intensity distribution is obtained. By oscillating at the focal point, a flat-top distribution 61 can be obtained, and further increasing the amplitude produces a donut distribution 62.

Claims

1. A method of cutting a planar workpiece (10) with a laser beam (20), wherein, The laser beam (20) is emitted by a laser source (110) and guided onto the workpiece (10) by an optical system (120), wherein, for cutting, the workpiece (10) and the laser beam (20) are moved relative to each other in a feed direction (25), and wherein the optical system (120) has a beam transformation element (125) with which a focal point position (21) of the laser beam (20) is at least partially oscillated in a thickness direction z of the workpiece (10) perpendicular to the feed direction during the relative movement, And wherein the beam quality M of the laser source (110) is 2 at most 12, M 2 ≤ 12.

2. The method of claim 1, wherein, the frequency f of the oscillation is adjusted as a function of the feed speed v such that the overlap ratio is at least 50%.

3. The method of claim 1 or 2, wherein, The workpiece (10) has a thickness t, and the focal point position (21) is oscillated with a first amplitude which is at most equal to the workpiece thickness t.

4. The method according to any of the preceding claims, wherein, The workpiece (10) has a thickness t, and the focal point position (21) is oscillated with a first amplitude, wherein the focal point position (21) is oscillated with a second amplitude which is greater than the first amplitude when cutting a thickness which is greater compared to the thickness t.

5. The method according to any of the preceding claims, wherein, The focal point position (21) is oscillated with a first frequency when the relative movement is carried out in the feed direction (25) with a first feed speed vi, wherein the focal point position (21) is oscillated with a second frequency which is greater than the first frequency when the relative movement is carried out in the feed direction (25) with a second feed speed v2 which is greater than the first feed speed vi.

6. The method according to any one of the preceding claims, wherein, oscillating the focus position (21) of the laser beam (20) at least partially in the thickness direction z such that the intensity distribution I of the laser beam (20) measured along the thickness direction z z The equivalent value (22) around the focus position (21) is wider than the intensity distribution of the static laser beam (20).

7. The method according to any of the preceding claims, wherein, The laser beam (20) impinges on a top surface (10.1) of the workpiece (10) which is opposite a bottom surface (10.2) of the workpiece (10) in the thickness direction z, wherein an equivalent value (22) of the focal point position (21) lies outside the upper half ti of the thickness t with respect to the thickness t of the workpiece (10) measured from the bottom surface (10.2) to the top surface (10.1) of the workpiece (10).

8. The method of claim 7, wherein, The equivalent value (22) of the focal point position (21) is below 50% with respect to the percentage scale from 0% at the bottom surface (10.2) to 100% at the top surface (10.1) of the thickness t of the workpiece (10).

9. The method according to any of the preceding claims, wherein, The frequency f of the oscillation is at least 500 Hz and / or at most 5 kHz.

10. The method of any of the preceding claims, wherein, The amplitude of the oscillation is at least half and / or at most eight times the Rayleigh length of the laser beam (20) in the static state.

11. The method of any of the preceding claims, wherein, The laser beam (20) is oscillated only in the thickness direction z.

12. The method of any of the preceding claims, wherein, The beam transformation element (125) has a deformable reflector (126) through which the laser beam (20) is guided onto the workpiece (10), wherein the oscillation is imposed on the laser beam (20) by the deformable reflector (126).

13. The method of any of the preceding claims, wherein, The signal waveform for oscillating the focal point position (21) in the thickness direction z of the workpiece (10) is asymmetrical, i.e. the duty cycle ≠ 50%.

14. An apparatus (100) for cutting a planar workpiece (10) with a laser beam (20), having: a laser source (110) for emitting the laser beam (20); a workpiece receptacle for arranging the workpiece (10); an optical system (120) for directing the laser beam (20) onto a top surface (10.1) of the workpiece (10) arranged in the workpiece receptacle; wherein, a beam quality M2 of the laser source (110) of at most 12, M2≤ 12, wherein the optical system (120) has a beam transformation element (125) with which a focal point position (21) of the laser beam (20) can be changed, and wherein the beam transformation element (125) is configured to oscillate the focal point position (21) of the laser beam (20) at least partially in a thickness direction z when the workpiece (10) and the laser beam (20) are moved relative to each other.

15. Use of the device (100) according to claim 14, wherein The amplitude of the oscillation is adjusted in accordance with the thickness t of the workpiece, and / or the frequency f of the oscillation is adjusted in accordance with the cutting speed.

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