DE102022101323A1 - Laser cutting process with adjustment of the focus position - Google Patents

Abstract

The invention relates to a cutting method (78) for laser beam flame cutting of metal, in particular plate-shaped, workpieces (14) with a laser cutting machine (12), with a focus (70) of a laser beam (22) being arranged above a nozzle orifice (38) of a cutting nozzle (34) and a focal position (68) of the focus (70) of the laser cutting machine (12) along a laser beam axis (50) of the laser beam (22) in a predetermined ratio to an orifice diameter the nozzle orifice (38) is set.

Description

Background of the Invention

The invention relates to a cutting method for laser beam flame cutting of metallic, in particular plate-shaped, workpieces with a laser cutting machine.

In laser beam cutting processes, in particular in oxygen flame cutting, so-called fringing fields of the laser beam lead to asymmetrical heating of the workpiece to be cut in the vicinity of an intended cutting area, which impairs the cutting quality.

Fringe fields are of particular importance in laser beam cutting processes with a focal position of the laser beam above the workpiece to be cut, with the focal position being within the cutting nozzle. Such process parameters are particularly well suited for cutting workpieces with a considerable thickness, for example ten millimeters or more, and with high laser powers, for example ten kilowatts or more, but lead to a considerable widening of the laser beam and consequently to large edge fields.

Therefore, in these processes, the nozzle opening is used as an optical aperture for the radial delimitation of the laser beam, whereby the laser radiation of the edge fields of the laser beam is held back by the cutting nozzle. However, as a result of the laser radiation absorbed by the cutting nozzle, material can be removed from the cutting nozzle, as a result of which the nozzle opening is widened. As a result, the laser radiation of the edge fields can radiate through the nozzle opening unhindered and leads to the impairment of the cut quality described above.

Another disadvantage is that with a pressure-controlled supply of cutting gas, the volume of the cutting gas at the cutting gap increases due to the nozzle opening being widened by the laser beam. This can lead to an increasing impairment of the cutting quality due to increased melting/oxidation of the melt from the cutting gap.

From the prior art, for example WO 2020 / 162 823 A2 or WO 2002/434 53 A1 , it is known to cut the inner contour of a nozzle opening before the actual machining process using a plasma or laser beam to improve the flow of the cutting gas through the nozzle opening and to align the laser beam coaxially with the nozzle opening.

From the DE 10 2008 058 422 A1 it is known in principle to control the focal position of the laser beam or the distance between the processing head and the workpiece by means of camera monitoring of a laser processing operation.

From the DE 10 2018 129 407 A1 it is known to monitor the diameter or center point of an outlet opening of a cutting nozzle using an optical coherence tomograph in order to make a correct nozzle selection as part of a machine nozzle exchange and to align the laser beam relative, eg decentrally, to the outlet opening.

From the WO 2012/107 331 A1 a device for monitoring and controlling a laser cutting process is known, in which case a laser beam can be adjusted by evaluating an image recorded from the workpiece surface.

From the WO 2013/186 317 A1 it is known, when laser processing a liquid, viscous or powdery material whose surface level varies over time, to readjust the focus position of the laser beam using an image of the apparent inner nozzle diameter so that the focus is always exactly on the surface of the material to be processed.

object of the invention

It is an object of the invention to propose a laser cutting method in which a high cutting quality can be ensured even with a geometric change in the nozzle opening.

Description of the invention

This object is achieved according to the invention by a cutting method of the type mentioned at the beginning with the characterizing features of claim 1.

In other words, the object is achieved according to the invention by a cutting method for laser beam flame cutting of metal, in particular plate-shaped, workpieces with a laser cutting machine, which is characterized in that a focus of a laser beam is arranged above a nozzle opening of a cutting nozzle and that a focus position of the focus of the Laser cutting machine along a laser beam axis of the laser beam in one predetermined ratio to an orifice diameter of the nozzle orifice is set.

The focus position is to be understood as the distance along the laser beam axis between the nozzle orifice and the position of the focus or focus point on the laser beam axis. The orifice diameter is to be understood as the diameter of the geometrically narrowest cross-section of the nozzle orifice in a plane perpendicular to the laser beam axis. The size of the nozzle orifice is described by the orifice diameter. The position of the orifice diameter can change as a result of an, in particular conical, widening of the nozzle orifice along the laser beam axis.

Here and in the following, the relationship between the focus position and the orifice diameter is described. This is of particular advantage with regard to their direct interaction. For the sake of completeness, it should be mentioned that other indications of the position of the focus are also possible. For example, the distance between the focus and the orifice diameter can be specified in terms of the distance between the orifice diameter and a focusing lens and the focal point distance from the focusing lens, or in terms of the distance to the workpiece.

In particular, the distance of the focus from the orifice diameter on the laser beam axis is set such that the laser beam is partially limited by the nozzle orifice, taking into account a laser beam widening. In other words, the ratio between the orifice diameter and the focus position is selected in such a way that the nozzle orifice acts as an optical diaphragm.

The nozzle orifice can delimit the laser beam radially to the laser beam axis of the laser beam. The degree of laser radiation retained by the nozzle orifice is preferably adjustable. A lower degree of limited laser radiation is advantageous with regard to a stability of the orifice diameter, since this is expanded less, in particular not, by the laser beam. A high level of laser confinement is beneficial in terms of sharper delineation of the laser beam, further enhancing cut quality.

The relationship between the orifice diameter and the focal position is predetermined. The inventors have recognized that a good cut quality can be obtained by selecting a suitable ratio, regardless of the actual orifice diameter. In particular, a cutting nozzle that has melted during laser cutting can continue to be used if the focus position is set in accordance with the currently available orifice diameter. A further improvement in the cutting quality can even be achieved as a result, since the laser beam enlarges the nozzle opening concentrically to its laser beam axis.

The mouth diameter is preferably at least 0.8 millimeters, particularly preferably at least 1 millimeter. More preferably, the mouth diameter is at most 3 millimeters, particularly preferably at most 2 millimeters. Fringe fields can hereby be prevented particularly well from being irradiated onto the workpiece.

The focus position is preferably at least six millimeters, particularly preferably at least seven millimeters. More preferably, the focus position is at most 30 millimeters, particularly preferably at most 25 millimeters. This can prevent excessive beam expansion of the laser beam. In particular with the aforesaid orifice diameters, this can lead to less radiation being absorbed by the cutting nozzle.

The ratio of the focus position to the mouth diameter is preferably at least 3, more preferably at least 5. More preferably, the ratio of the focus position to the mouth diameter is at most 16, more preferably at most 12. The ratios given represent a particularly favorable combination of the focus position and the mouth diameter Material removal at the cutting nozzle as well as the penetration of peripheral fields onto the workpiece can be prevented in a particularly reliable manner.

The relationship between the focus position and the orifice diameter is preferably predetermined in the form of an equation, a characteristic diagram and/or a data table. As a result, the focus position can be set particularly quickly and reliably to the muzzle diameter.

In the case of a mathematical equation, the relationship between muzzle diameter and focal position can be given by the equation: focal position (F _L ) is equal to a slope factor (m) multiplied by the muzzle diameter (D _M ) and subtracted by a constant (K). In formula notation: F _L = m*D _M -K. The opening diameter and/or the focus position are preferably specified in millimeters with an accuracy of tenths of a millimeter, in particular hundredths of a millimeter.

The slope factor (m) can have a minimum value of 9 and a maximum value of 14. The gradient factor (m) particularly preferably has the value 11. The constant (K) can be at least 1 millimeter and at most 10 millimeters. The constant (K) is particularly preferably 3 millimeters. The values given are particularly favorable with regard to good cutting quality and good stability of the muzzle diameter.

The predetermined ratio can include a focal position range within which the focal position is selected. In particular, the focal position can deviate from a mean value by half the focal position bandwidth to higher values and/or to lower values. As a result, the method can be adapted particularly easily to a predetermined cutting quality. The focal position bandwidth can be at most two millimeters, preferably at most one millimeter, particularly preferably at most half a millimeter.

According to the invention, the focus can be adjusted to the nozzle opening by changing the focus position in such a way that an outer partial area of the laser beam is limited or blocked by the nozzle opening. In the case of a widened nozzle orifice, the laser beam can therefore be adapted to the widened nozzle orifice by adjusting the focus position, so that marginal rays are limited or blocked by the nozzle orifice.

The cutting process is suitable for laser beam flame cutting of metal workpieces. Flat or plate-like workpieces can preferably be processed using the cutting method described.

According to the invention, the laser beam axis is to be understood as the central axis of the laser beam. The axial propagation direction of the laser beam is essentially along the laser beam axis in the direction of the workpiece to be machined.

In a preferred embodiment of the cutting method, it is provided that a respective ratio between the focus position and the diameter of the mouth is stored in a machine control of the laser cutting machine for different values of the mouth diameter. In the case of a previously described equation, a characteristic diagram and/or a table, it can be provided that these are stored in a data memory of the machine control. This allows easy and quick access to a corresponding predetermined ratio by the machine and/or craftsmen.

Also preferred is an embodiment of the cutting method in which the mouth diameter is measured and the focus position is set as a function of the measured mouth diameter. By measuring the orifice diameter, the focal position can be set particularly precisely using the predetermined ratio between the orifice diameter and the focal position, particularly if the orifice diameter deviates from a nominal value.

A preferred development of the cutting method provides that the opening diameter is measured manually by applying a measuring device. This can be done, for example, by applying a caliper gauge or a mandrel gauge and/or by computer-assisted measurement by a specialist. In this way, the mouth diameter can also be determined when the laser cutting machine is not in operation.

According to a development of the cutting method, it can be provided that--as an alternative or in addition to manually applying a measuring device--an image of the nozzle opening is evaluated to measure the diameter of the opening. An image of the orifice diameter can be created, for example, by contrast zones in the visible and/or invisible light spectrum, with the nozzle orifice having a contrast zone that differs from the cutting nozzle and is delimited from one another at the orifice diameter. A camera image of the nozzle orifice is preferably used to evaluate the orifice diameter. In this way, the mouth diameter can be measured efficiently. The camera can also be used to control the cutting process. The measurement with a camera image can also facilitate a visual check of the measured finish diameter.

More preferably, the image shows an inside of the nozzle orifice. In other words, the image is created by light directed onto the nozzle orifice in the laser beam propagation direction and reflected from the inside of the cutting nozzle. As a result, the imaging can be carried out particularly precisely.

The evaluation of the image, in particular the camera image, can be carried out by the specialist by measuring the contrast zones. The evaluation preferably takes place with the aid of a computer using image recognition software. The image recognition software may include a neural network. More preferably, the image is evaluated, in particular automatically, in the laser cutting machine. As a result, the method can be carried out more quickly.

The opening diameter is preferably measured during operation of the laser cutting machine.

In a preferred embodiment of the cutting method, it is provided that the nozzle diameter is measured cyclically. In other words, it can be provided that the nozzle diameter is changed at regular time intervals, for example every second, every minute and/or every hour, and/or at regular times, for example when the laser cutting machine is switched on and/or shut down, after the cutting nozzle has been changed and/or before a cutting process. As a result, the method can be integrated particularly well into existing manufacturing processes.

An embodiment of the cutting process in which the nozzle diameter—alternatively or additionally—is continuously measured is preferred. Continuous measurement is to be understood as meaning a permanent or sustained and permanently repeated measurement of the mouth diameter, so that only slight or no perceptible delays occur in the process flow. As a result, a particularly rapid reaction to a changing nozzle geometry can take place.

In a preferred development of the cutting method, the focus position is set cyclically. In other words, it can be provided that the focus position is changed at regular time intervals, for example every second, every minute and/or every hour, and/or at regular times, for example when the laser cutting machine is switched on and/or shut down, after the cutting nozzle has been changed and/or before a cutting process. The focus position is particularly preferably set immediately after the measurement of the mouth diameter with only a small or no perceptible time delay in the course of the process. In this case, the focus position can be adjusted within one second, for example. A particularly high cutting quality can be ensured in this way.

An embodiment of the cutting method is preferred in which the focus position is set automatically by the machine control. In other words, no human intervention is required to set the focus position after the specification or determination of the orifice diameter. The mouth diameter can, for example, be transmitted to the laser cutting machine via an interface, in particular a man-machine interface. As a result, the effort involved in adjusting the focus position can be reduced.

More preferably, the laser cutting machine or the machine control automatically adjusts the focus position as a function of the measured mouth diameter. For this purpose, the mouth diameter measured can be transmitted to the machine control by external measuring devices and/or manually by a specialist. The machine control preferably participates in the measurement of the mouth diameter. A separate transmission of the mouth diameter is then not necessary.

Also preferred is an embodiment of the cutting method in which the focus position is set immediately before and/or during a cutting process of the laser beam flame cutting, in particular by the machine control. The adjustment can take place with an active laser beam and/or an inactive laser beam. Preferably, the focus position is initially set with the laser beam inactive and then checked with the laser beam active. In the case of shorter cutting processes, the focus position can preferably be set at the beginning of the cutting process. With increasing duration of the cutting process, the focus position should preferably be readjusted at least once during the cutting process. As a result, the cutting quality can be kept particularly even and high.

In a preferred embodiment of the cutting method, it is provided that the nozzle mouth is widened by the laser beam of the laser cutting machine, in particular immediately before the mouth diameter is measured. In other words, the laser beam is directed onto the nozzle orifice by controlled or defined deflection of the focus position in such a way that the nozzle orifice is enlarged by material removal. The focus position is preferably increased in this case. An uneven formation of the nozzle orifice as a result of the laser beam effect can be corrected in this way, or the nozzle orifice can be delimited more sharply, as a result of which the orifice diameter can be measured more precisely.

A development of the cutting method is preferred in which the opening diameter is widened by a maximum of one millimeter, in particular by a maximum of half a millimeter. This can prevent excessive wear of the cutting nozzle by adjusting the focus position.

Also preferred is an embodiment of the cutting method in which a cutting gas pressure is adjusted as a function of the orifice diameter. In this way, the volume flow, which is increased as a result of the enlarged nozzle opening, can be compensated for. The cutting gas pressure is preferably set in a predetermined gas pressure ratio to the, in particular measured, orifice diameter and/or the focus position. This enables the focus position and the cutting gas pressure to be set particularly effectively as a function of the muzzle diameter.

In a preferred development of the cutting method, the cutting gas pressure is reduced as the diameter of the mouth increases. As a result, a volume flow or mass flow of the cutting gas can be kept at a desired value.

Further features and advantages of the invention result from the description, the claims and the drawing. According to the invention, the features mentioned above and those detailed below can each be used individually or collectively in any suitable combination. The embodiments shown and described are not to be understood as an exhaustive list, but rather have an exemplary character for the description of the invention.

character list

• 1 shows a laser cutting machine for laser beam flame cutting with a cutting head and a machine control in a schematic, perspective view.
• 2 shows a schematic representation of the measurement setup of the laser cutting machine 1 for measuring an orifice diameter of the nozzle orifice.
• 3 shows a schematic view of a laser beam beam path through the cutting head of the laser cutting machine in a cutting method according to the invention.
• 4 shows a schematic view of the laser beam beam path through the cutting head with the nozzle mouth widened.
• 5 shows a schematic view of the laser beam beam path through the cutting head after adjustment of the focus position.
• 6 shows a schematic sequence of the method according to the invention.

1 shows an arrangement 10 with a laser cutting machine 12 and a metal workpiece 14 arranged on the laser cutting machine 12 for laser beam flame cutting. The laser cutting machine 12 preferably has a CO ₂ laser, a solid-state laser or a diode laser as the laser beam generator 16, a movable cutting head 18 and a workpiece support 20 on which the metallic workpiece 14 is arranged. A laser beam 22 is generated in the laser beam generator 16 and is directed by means of a fiber optic cable (not shown) or deflection mirrors 24 (see 2 ) is guided from the laser beam generator 16 to the cutting head 18. The laser beam 22 is arranged in the cutting head 18 by means of focusing optics 26 (see 2 until 5 ) directed to the metallic workpiece 14. The laser cutting machine 12 is also supplied with cutting gas 28—preferably with oxygen. The cutting gas 28 is supplied to the cutting head 18--preferably under pressure control--from which it emerges together with the laser beam 22. The laser cutting machine 12 also includes a machine control 30 which is programmed to move the cutting head 18 relative to the metallic workpiece 14 in accordance with a cutting contour 32 . The machine control 30 is also programmed to focus the focusing optics 26 (see 2 until 5 ) relative to a cutting nozzle 34 (see 2 until 5 ) to proceed.

2 shows a schematic measuring setup 36 for optically measuring a nozzle orifice 38 of the cutting nozzle 34. The measuring setup 36 has a measuring device 40 which is arranged on the cutting head 18 of the laser cutting machine 12. The cutting head 18 has the cutting nozzle 34, the focusing optics 26 for focusing a laser beam 22 of the laser cutting machine 12, and a deflection mirror 24. The deflection mirror 24 can be part of a deflection system that has, in particular, a plurality of deflection mirrors 24 . In the present case, the deflection mirror 24 is designed to be partially transparent and therefore forms an entry-side component of the measuring device 40 for nozzle measurement.

The laser beam 22 - shown here by dashed lines - is generated by the laser beam generator 16 (see 1 ) coming by means of the deflection mirror 24 onto the focusing optics 26 - a converging lens of the focusing optics 26 is shown here by way of example - directed.

The deflection mirror 24 reflects the incident laser beam 22 (with a wavelength of 10 µm, for example) and transmits radiation 44 relevant for the nozzle measurement, coming from the cutting nozzle 34, in particular reflected from an inner surface 42 of the cutting nozzle 34, in a wavelength range that is Example between about 550 nm and 2000 nm. As an alternative to the partially transparent deflection mirror 24, a scraper mirror or a perforated mirror can also be used be used to supply reflected radiation 44 to the measuring device 40 . However, the use of a scraper mirror typically results in blocking out part of the reflected radiation 44 as well as limiting the laser beam diameter. The use of a perforated mirror generally leads to diffraction effects of the reflected radiation 44 and to a strong influence on the (CO ₂ -) laser radiation.

A further deflection mirror 46 is arranged behind the partially transparent deflection mirror 24 in the measuring device 40 and deflects the reflected radiation 44 onto a geometrically high-resolution camera 48 as an image acquisition unit. The camera 48 can be a high-speed camera, which is aligned coaxially to a laser beam axis 50 or to the extension 50a of the laser beam axis 50 by the additional deflection mirror 46 and is therefore independent of the direction. In principle, there is also the possibility of recording an image with the camera 48 using the incident light method, i.e. in the VIS wavelength range, possibly also in the NIR wavelength range, provided that an additional lighting source is provided that radiates in the NIR range, and alternatively the recording of the Process intrinsic luminosity in the UV and NIR/IR wavelength ranges.

In the present example, an in 2 imaging, focusing optical system 52, represented as a lens, is provided, which focuses the radiation 44 reflected for the nozzle measurement onto the camera 48. An aspheric design of the imaging optical system 52—here a lens—for focusing can prevent or at least reduce spherical aberrations during imaging.

At the in 2 In the example shown, a filter 54 in front of the camera 48 is advantageous if further radiation or wavelength components are to be excluded from the detection with the camera 48 . The filter 54 can be embodied, for example, as a narrow-band bandpass filter with a small half-width in order to avoid or reduce chromatic aberrations. The position of the camera 48 and the imaging optical element 52 present in the present example and/or the filter 54 along the extension 50a of the laser beam axis 50 can be adjusted and, if necessary, changed using a positioning system 56 known to those skilled in the art and, for the sake of simplicity, represented by a double arrow.

In the present example, the camera 48 is operated using the incident light method, ie an additional illumination source 58 is provided above the workpiece 14, which couples illumination radiation 62 into the beam path via a further partially transparent mirror 60 coaxially to the laser beam axis 50a. Laser diodes, e.g. with a wavelength of 658 nm, or diode lasers, e.g. with a wavelength of 808 nm, can be provided as an additional illumination source 58, which as in 2 shown coaxially, but can also be arranged off-axis to the laser beam axis 50. The additional lighting source 58 can be arranged, for example, outside (in particular above) the cutting head 18 . Alternatively, the illumination source 58 can be located within the cutting head 34 .

The reflected radiation 44 produces within the camera 48 a the inner surface 42 and the nozzle orifice 38 of the cutting nozzle 34. The is transmitted, for example, to an evaluation unit 66 which, for example, can be integrated into the machine controller 30 or connected to it.

The evaluation unit 66 measures an, in particular average, orifice diameter of the nozzle orifice 38 on the basis of of the nozzle orifice 38. The measured orifice diameter is then preferably used to determine a focal position 68 that is in a defined relationship to the measured orifice diameter (see 3 ). This focal position 68 can be determined in the evaluation unit 66 or in the machine controller 30 . The measured opening diameter is particularly preferably an input variable for an equation for calculating the focal position 68. The focal position 68 is then preferably set by the machine control 30, in particular automatically.

3 12 schematically shows a beam path through the focusing optics 26 and the cutting nozzle 34 of the cutting head 18 2 up to the metallic workpiece 14. Starting from the deflection mirror 24 (see 2 ) the illumination radiation 62 is directed onto the inner surface 42 of the cutting nozzle 34 coaxially to the laser beam axis 50 by means of the focusing optics 26 . A radiation 44 reflected by the inner surface 42 is directed in an opposite direction by means of the further deflection mirror 46 (see 2 ) on the camera 48 (see 2 ) directed.

In 3 the beam path of the laser beam 22 is also shown, which, starting from the deflection mirror 24, is directed onto the metallic workpiece 14 by means of the focusing optics 26. For this purpose, the focusing optics 26 bundle the laser beam 22 in a focus point or focus 70 of the laser beam 22. The laser beam 22 has a focus 70, which is in the focus position 68 above the nozzle orifice 38 is arranged. As shown, the focus 70 of the laser beam 22 is a position of the narrowest beam cross section of the laser beam 22. Starting from the focus 70, the beam cross section of the laser beam 22 widens in the radial direction as the beam propagates. A theoretical area of overlap 72 between the laser beam 22 and the cutting nozzle 34 is therefore formed in the vicinity of the nozzle opening 38 of the cutting nozzle 34 . In the overlapping area 72, the cutting nozzle 34 acts as an optical diaphragm and limits the laser beam 22 to a cutting beam 74 that has the opening diameter of the nozzle opening 38. In other words, the laser beam 22 touches the cutting nozzle 34. This allows a low-energy edge area of the laser beam 22 to be blocked by the cutting nozzle 34 be, whereby heating of the metallic workpiece 14 in the edge region of a cutting gap 76 is avoided. As a result, the cutting quality of the laser beam 22 on the metallic workpiece 14 is improved.

According to the embodiment shown, the opening diameter of the nozzle opening 38 is monitored by means of the camera 48 and the evaluation unit 66 .

4 12 schematically shows the beam path through the focusing optics 26 and the cutting nozzle 34 of the cutting head 18 3 . As a result of the action of the laser beam 22, the cutting nozzle 34 is in the overlapping area 72 (see 3 ) of laser beam 22 and cutting nozzle 34 completely removed. The cutting nozzle 34 or the nozzle opening 38 no longer acts as an optical aperture and the laser beam 22 radiates through the nozzle opening 38 unhindered. As a result, the metallic workpiece 14 heats up under the action of the laser radiation in the edge region of the laser beam 22, as a result of which the cutting quality in the cutting gap 76 is reduced.

Furthermore, as a result of an enlarged nozzle orifice 38, the gas volume of the outflowing cutting gas 28, which is regulated to a constant pressure, also increases (see 1 ). An increased volume of cutting gas at the cutting gap 76 leads to an increased melt volume, as a result of which the cutting quality can be additionally reduced. Gas consumption can also increase.

The changed opening diameter of the nozzle opening 38 is recorded using the camera 48 (see 2 ) and the evaluation unit 66 (see 2 ) measured. A changed focus position 68 is then determined and set.

Furthermore, it can be provided that the focal position 68 determined by the measured mouth diameter is measured with a laser cutting machine 12 (see 1 ) actually set focus position 68 is adjusted. If a combination of process parameters that impairs the cutting quality is detected and corrected, this can be output by the laser cutting machine 12 in the form of a message, for example.

5 12 schematically shows the beam path through the focusing optics 26 and the cutting nozzle 34 of the cutting head 18 4 after setting the focal position 68 of the focus 70 by the machine control 30. According to the illustration shown, the focal position 68 has been enlarged by the focusing system 26 along the laser beam axis 50 and counter to a laser beam propagation direction. In other words, the focus 70 was further spaced from the metallic workpiece 14 or the nozzle orifice 38 .

The laser beam 22 overlaps the cutting nozzle 32 in the overlapping area 72, whereby the low-energy edge area of the laser beam 22 is retained by the cutting nozzle 34. The nozzle orifice 38 acts as an optical screen, as a result of which the cutting quality in the cutting gap 76 can be increased.

According to the embodiment shown, it is also provided that the cutting gas pressure of the cutting gas 28 is adapted to the changed opening diameter of the nozzle opening 38 in order to ensure a constant volume flow for reliable blowing of melt or slag out of the cutting gap 76 . This can be done, for example, by lowering the cutting gas pressure.

6 shows a schematic process sequence of a cutting process 78 according to the invention with adjustment of the focus position 68 (see 3 until 5 ). In a first method step “Providing an orifice diameter” 80, the orifice diameter of the nozzle orifice 38 is provided. The mouth diameter is preferably measured. In a subsequent method step "Focus setting" 82, the focus position 68 of the focus 70 (see 3 until 5 ) set in accordance with the invention predetermined ratio to the mouth diameter.

Reference List

10

Arrangement;

12

laser cutting machine;

14

Workpiece;

16

laser beam generators;

18

cutting head;

20

workpiece support;

22

Laser beam;

24

deflection mirror;

26

focusing optics;

28

cutting gas;

30

machine control;

32

cutting contour;

34

cutting nozzle;

36

measurement setup;

38

nozzle orifice;

40

measuring device;

42

Inner surface;

44

reflected radiation;

46

further deflection mirror;

48

Camera;

50

laser beam axis;

50a

extension of the laser beam axis 50;

52

focusing optical system;

54

Filter;

56

positioning system;

58

lighting source;

60

another semi-transparent mirror;

62

illumination radiation;

64

Illustration;

66

evaluation unit;

68

focal position;

70

Focus;

72

overlap area;

74

cutting ray;

76

kerf;

78

cutting process;

80

providing a muzzle diameter;

82

focus adjustment.

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• WO 2020162823 A2 [0006]
• WO 200243453 A1 [0006]
• DE 102008058422 A1 [0007]
• DE 102018129407 A1 [0008]
• WO 2012107331 A1 [0009]
• WO 2013186317 A1 [0010]

Claims (14)

Cutting method (78) for laser beam flame cutting of metallic, in particular plate-shaped, workpieces (14) with a laser cutting machine (12); characterized in that a focus (70) of a laser beam (22) is arranged above a nozzle orifice (38) of a cutting nozzle (34); and a focus position (68) of the focus (70) of the laser cutting machine (12) along a laser beam axis (50) of the laser beam (22) is set in a predetermined ratio to an orifice diameter of the nozzle orifice (38). Cutting method (78) according to claim 1 , characterized in that for different values of the mouth diameter a respective ratio between the focus position (68) and the mouth diameter is stored in a machine control (30) of the laser cutting machine (12). Cutting method (78) according to claim 1 or 2 , characterized in that the mouth diameter is measured and the focus position (68) is set as a function of the measured mouth diameter. Cutting method (78) according to claim 3 , characterized in that the mouth diameter is measured manually by applying a measuring device. Cutting method (78) according to claim 3 or 4 , characterized in that an image (64), in particular a camera image, of the nozzle orifice (38) is evaluated to measure the orifice diameter. Cutting method (78) according to one of claims 3 until 5 , characterized in that the mouth diameter is measured cyclically. Cutting method (78) according to one of claims 3 until 5 , characterized in that the mouth diameter is measured continuously. Cutting method (78) according to one of Claims 6 or 7 , characterized in that the focus position (68) is set cyclically. Cutting method (78) according to one of the preceding claims, characterized in that the focus position (68) is set automatically by the machine control (30). Cutting method (78) according to one of the preceding claims, characterized in that the focus position (68) is set immediately before and/or during a cutting process of the laser beam flame cutting, in particular by the machine control (30). Cutting method (78) according to one of the preceding claims, characterized in that the nozzle opening (38) is widened by the laser beam (22) of the laser cutting machine (12), in particular immediately before the opening diameter is measured. Cutting method (78) according to claim 11 , characterized in that the mouth diameter is widened by a maximum of one millimeter. Cutting method (78) according to one of the preceding claims, characterized in that a cutting gas pressure is set as a function of the, in particular measured, orifice diameter. Cutting method (78) according to Claim 13 , characterized in that the cutting gas pressure is reduced with increasing orifice diameter.

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