Method for operating a laser machine tool, and laser machine tool

Abstract

A method for operating a laser machine tool (10), wherein a size of a nozzle opening (20) of a nozzle unit (16) of the laser machine tool (10) is determined on the basis of the measured duration (78).

Description

[0001] Title: Method for operating a laser processing machine and laser processing machine

[0002] Description

[0003] The invention relates to a method for operating a laser processing machine and a laser processing machine.

[0004] Process gases are frequently used during the processing of a workpiece with a laser processing machine. For example, the processing of the workpiece might involve cutting it with a laser beam from the laser processing machine, where the process gas is used as a cutting gas to expel any molten material. Alternatively, the processing of the workpiece might involve creating a weld using the laser beam, where the process gas is used as a shielding gas, for example, to prevent oxidation of the workpiece during the weld process.

[0005] DE 102 02 424 C1 discloses a method for the automatic detection of different cutting nozzles.

[0006] The invention aims to provide a method for operating a laser processing machine and a laser processing machine, each with improved properties, in particular enabling a reliable determination of the size of a nozzle opening.

[0007] The invention solves this problem by providing a method with the features of claim 1 and a laser processing machine with the features of claim 10. Advantageous embodiments and further developments of the invention are set forth in the dependent claims.

[0008] A method according to the invention is designed for operating a laser processing machine for processing a workpiece using a laser beam. During processing, the laser beam and a first process gas exit a nozzle unit and are directed onto the workpiece by means of the nozzle unit. The first process gas is supplied to the nozzle unit via a pressure regulating valve.The method comprises: supplying an inlet of the pressure regulating valve with a second process gas, wherein the second process gas is guided via the pressure regulating valve to the nozzle unit; stopping the supply of the second process gas to the inlet of the pressure regulating valve; measuring a characteristic parameter of a time profile of the outlet pressure, in particular a time interval that elapses until an outlet pressure at an outlet of the pressure regulating valve has fallen from the pressure of the second process gas to a predetermined pressure, in particular the pressure of the first process gas; and determining a size of the nozzle opening based on the characteristic parameter, in particular the measured time interval.

[0009] The characteristic parameter of a time history of the initial pressure can, for example, be a time constant of an exponential pressure drop. This time constant can be determined from the time history of the initial pressure, particularly using an estimation method.

[0010] Advantageously, by pressurizing the inlet of the pressure regulating valve with the second process gas, the nozzle opening size can be determined at a higher pressure compared to the first process gas. This allows for longer time measurements of the pressure drop from the pressure of the second process gas to the pressure of the first process gas. Due to this longer time, the nozzle opening size can be determined with particular precision.

[0011] The laser processing machine can be a laser cutting machine or a laser welding machine. The processing of the workpiece can involve cutting or welding. The laser cutting machine can be designed to generate the laser beam.

[0012] The pressure regulating valve can be pressurized with the first process gas at a pressure of 6 bar. The pressure regulating valve can be pressurized with the second process gas at a pressure of 25 bar.

[0013] The target output pressure could be, for example, 20 bar. The minimum duration could be, for example, 20 seconds.

[0014] The pressure regulating valve can have a single inlet. The inlet of the pressure regulating valve can be supplied with the first process gas and / or the second process gas. The pressure regulating valve can have a single outlet. The outlet of the pressure regulating valve can be connected to the nozzle unit via a gas line, so that a process gas exiting the outlet of the pressure regulating valve is directed to the nozzle unit. The nozzle opening can be circular.

[0015] The first process gas and / or the second process gas can escape from the nozzle opening.

[0016] Determining the nozzle opening size can involve providing a table in which different nozzle opening sizes are assigned discrete time values. The mapping between nozzle opening sizes and time values ​​can be empirically determined for a single machine or for identical machines. This allows the table to establish an empirical relationship between different nozzle opening sizes and time values.

[0017] Determining the size of the nozzle opening can involve reading the nozzle opening size from the table for the measured time period.

[0018] The supply of the second process gas to the inlet of the pressure regulating valve can be stopped when a predetermined target pressure of the second process gas is reached at the outlet of the pressure regulating valve.

[0019] Another aspect of the process may be that cutting problems can be reduced and the risk of machining errors, such as spatter during material processing, can be avoided by using an incorrect nozzle opening size.

[0020] Another aspect may be that the size of the nozzle opening is smaller than the diameter of a pipe that connects the pressure regulating valve to the nozzle unit.

[0021] In a further development of the procedure, the process includes: reading a target size of the nozzle opening and issuing a warning if the deviation between the read target size and the actual nozzle opening exceeds a predefined maximum deviation, for example, a diameter deviation of 0.1 mm (millimeters). Advantageously, this allows verification of whether the nozzle unit is correctly labeled or damaged. The target size can be read by extracting data from an automatic tool changer, particularly a nozzle changer.

[0022] In a further development of the procedure, the process includes: displaying the specific size of the nozzle opening. Advantageously, this allows a user of the laser processing machine to determine whether the correct nozzle unit is connected to the pressure control valve outlet. This display can be provided via a screen on the laser processing machine.

[0023] In a further development of the method, the procedure before measuring the duration includes: positioning the nozzle opening such that no objects are located at a predetermined distance, in particular at a distance of 5 cm, from the nozzle opening. Advantageously, this allows the measured duration to be measured without being affected by disturbances.

[0024] In a further development of the method, the procedure comprises: After stopping the supply of the second process gas to the inlet of the pressure regulating valve, supplying the inlet of the pressure regulating valve with the first process gas, wherein the supply of the first process gas to the inlet is carried out at a lower pressure than the supply of the second process gas; actuating the pressure regulating valve with a predetermined target outlet pressure for a predetermined minimum duration, wherein the predetermined target outlet pressure is greater than the pressure of the first process gas at the inlet of the pressure regulating valve; measuring the outlet pressure at the outlet of the pressure regulating valve during the supply of the first process gas to the inlet and during actuating the pressure regulating valve; determining a pressure reduction that causes a nozzle opening of the nozzle unit at the outlet of the pressure regulating valve;and determining the inlet pressure of the first process gas at the inlet of the pressure regulating valve by adding the determined pressure reduction and the measured outlet pressure at the outlet of the pressure regulating valve.

[0025] Advantageously, the inlet pressure of the first process gas can be determined particularly reliably by measuring the outlet pressure and adding the pressure reduction. In particular, this allows the inlet pressure of the first process gas to be determined without a pressure sensor for measuring the inlet pressure.

[0026] By pressurizing the nozzle unit with the second process gas before pressurizing it with the first process gas, a pressure higher than the inlet pressure of the first process gas is present at the pressure control valve before the outlet pressure of the first process gas is measured. This allows for a more reliable determination of the pressure at the outlet of the pressure control valve when the first process gas is applied. In particular, the pressure of the first process gas at the outlet of the pressure control valve is established from a higher starting point, thus reducing the risk of measurement errors. The pressure reduction can be defined as the difference between the dynamic pressure at the nozzle opening and the hydrostatic pressure. This pressure reduction can be described as a pressure loss.

[0027] Determining the pressure reduction may involve providing a nozzle orifice size.

[0028] Determining the pressure reduction can involve providing a table in which different nozzle orifice sizes are assigned discrete pressure reduction values. The relationship between nozzle orifice sizes and pressure reduction values ​​can be empirically determined for an identical laser processing machine. This allows the table to establish an empirical correlation between nozzle orifice sizes and pressure reduction values.

[0029] Determining the pressure reduction can involve reading the pressure reduction from the table for the provided nozzle opening size.

[0030] The output pressure at the outlet of the pressure regulating valve can also be measured while the inlet is being supplied with the second process gas.

[0031] The pressure control valve can be controlled with the specified target outlet pressure while the inlet of the pressure control valve is being supplied with the first process gas and / or while the inlet of the pressure control valve is being supplied with the second process gas.

[0032] In a further development of the procedure, the process includes: displaying the determined inlet pressure of the first process gas. Advantageously, this allows a user of the laser processing machine to determine whether the inlet pressure is too low or not. The display can be provided via a screen on the laser processing machine.

[0033] In a further development of the method, the procedure includes: outputting a pressure signal if the measured inlet pressure of the first process gas is lower than a predefined minimum pressure. Advantageously, this alerts a user of the laser processing machine to an insufficient inlet pressure of the first process gas. The predefined minimum pressure could be, for example, 4 bar or 5 bar.

[0034] In a further development of the method, the procedure comprises: measuring the supply pressure of the first process gas at a process gas inlet of the laser processing machine; and outputting a wear signal if the deviation between the measured supply pressure and the determined inlet pressure exceeds a predefined maximum pressure deviation, for example, 0.5 bar. Advantageously, this allows verification of whether a fault exists between the process gas inlet of the laser processing machine and the outlet of the pressure regulating valve, for example, in the form of a stuck valve. This makes it possible to determine whether a valve of the laser processing machine, such as the pressure regulating valve, needs to be replaced.

[0035] The laser processing machine can be connected to a pressure source for the first process gas via the process gas inlet. The pressure source can supply the first process gas and / or the second process gas to the laser processing machine.

[0036] In a further development of the method, the procedure prior to measuring the outlet pressure includes: positioning the nozzle opening such that no objects are located within a distance of 5 cm from the nozzle opening. Advantageously, this ensures that the second process gas can flow out of the nozzle opening as freely as possible when the supply of the second process gas to the inlet of the pressure regulating valve is stopped. This allows the outlet pressure to drop particularly quickly from the pressure of the second process gas to the pressure of the first process gas.

[0037] Alternatively, the procedure, prior to measuring the outlet pressure, includes: positioning the nozzle opening at a predetermined distance, particularly no more than 0.7 mm, from a calibration plate. Advantageously, the calibration plate can delay the outflow of the second process gas, thus enabling a particularly precise determination of the pressure reduction. Any surface that is essentially flat and significantly larger than the nozzle opening can be used as a calibration plate.

[0038] In a further development of the method, the procedure is repeated several times. This repetition reduces statistical uncertainties. Particularly preferred is the setting of a different initial pressure in each iteration when the pressure regulating valve is pressurized with the second process gas. This modification of the method reduces systematic uncertainties.

[0039] A laser processing machine according to the invention is designed for processing a workpiece using a laser beam. The laser processing machine is configured to perform a previously described method. The laser processing machine comprises a nozzle unit, a process gas system, and a control unit. The nozzle unit is designed for directing the laser beam and the process gas onto the workpiece. The process gas system is designed for supplying process gas to the nozzle unit. The process gas system includes a pressure control valve with a pressure sensor for measuring the output pressure at the outlet of the pressure control valve. The control unit is designed to measure the time duration and determine the size of the nozzle opening based on the measured time duration.

[0040] Further advantages and advantageous embodiments of the invention can be seen from the figures, their description, and the claims. All features disclosed in the figures, their description, and the claims can be essential to the invention, both individually and in any combination. The figures show:

[0041] Fig. 1 shows a schematic representation of a laser processing machine, and

[0042] Fig. 2 shows a graph of a pressure profile at an output of a pressure control valve of the laser processing machine of Fig. 1 over time.

[0043] Fig. 1 shows a laser processing machine 10. The laser processing machine 10 is designed for processing a workpiece 12 using a laser beam 14 of the laser processing machine 10.

[0044] The laser processing machine 10 is a laser cutting machine and the processing of the workpiece 12 is a cutting of the workpiece 12.

[0045] The laser processing machine 10 has a nozzle unit 16, to which the laser beam 14 and a process gas 18 are supplied for cutting the workpiece 12. The laser beam 14 and the process gas 18 exit from a nozzle opening 20 of the nozzle unit 16.

[0046] The laser beam 14 and the process gas 18 are directed onto the workpiece 12 by means of the nozzle unit 16. The laser beam 14 locally melts the workpiece 12, and the process gas 18 expels the molten material. Simultaneously, the nozzle unit 16 is moved along a direction of movement 22, so that the laser beam 14 and the process gas 18 are guided over the workpiece 12. This creates a cut edge in the workpiece 12. The laser processing machine 10 has a process gas system 24 for supplying the process gas 18 to the nozzle unit 16. The process gas system 24 consists of a plurality of valves and lines.

[0047] The process gas system 24 has a process gas inlet 26 for connecting the laser processing machine 10 to a pressure source 28.

[0048] The pressure source 28 is configured to supply the laser processing machine 10 with a first process gas 30 in the form of compressed air, a second process gas 32 in the form of nitrogen, and a third process gas 34 in the form of oxygen. The first, second, and third process gases 30, 32, 34 are routed from the pressure source 28 to the laser processing machine 10 via separate connecting lines 36. The connecting lines 36 are connected to the process gas inlet 26 of the laser processing machine 10 and to the pressure source 28. The connecting lines 36 extend from the pressure source 28 to the process gas inlet 26.

[0049] The laser processing machine 10 has a control unit 38 for controlling the process gas system 24. The control unit 38 can select the process gas 30, 32, 34 which is supplied to the nozzle unit 16 by controlling the process gas system 24.

[0050] The process gas system 24 has a compressed air line 40 for conveying compressed air 30, a nitrogen line 42 for conveying nitrogen 32 and an oxygen line 44 for conveying oxygen 34.

[0051] The compressed air line 40 carries the compressed air 30 via a compressed air valve module 46 of the process gas system 24. The nitrogen line 42 carries the nitrogen 32 via a nitrogen valve module 48 of the process gas system 24. The oxygen line 44 carries the oxygen 34 via an oxygen valve module 50 of the process gas system 24.

[0052] The compressed air valve module 46, the nitrogen valve module 48, and the oxygen valve module 50 each have a directional control valve (not shown) and a check valve (not shown). Each directional control valve can be controlled by the control unit 38 to introduce or shut off the respective process gas 30, 32, 34. Each check valve prevents process gas from being introduced from the laser processing machine 10 into the pressure source 28. The compressed air line 40 opens into the nitrogen line 42 after the compressed air valve module 46, which in turn opens into a control valve module 52 of the laser processing machine 10. The oxygen line 42 also opens into the control valve module 52.

[0053] The control valve module 52 has a compressed air / nitrogen directional control valve 54 and an oxygen directional control valve 56. The compressed air / nitrogen directional control valve 54 and the oxygen directional control valve 56 can be controlled by the control device 38 to introduce or shut off the respective process gas 30, 32, 34.

[0054] The control valve module 52 has a pressure regulating valve 58. The pressure regulating valve 58 has a single inlet 60, which is connected to the compressed air / nitrogen directional control valve 54 and the oxygen directional control valve 56. The pressure regulating valve 58 has a single outlet 62, which is connected to the nozzle unit 16. The pressure regulating valve 58 has a pressure sensor 64 for measuring an outlet pressure at the outlet 62.

[0055] The control unit 38 is configured to specify a target outlet pressure to the pressure regulating valve 58. The pressure regulating valve 58 opens until the specified target outlet pressure is present at its outlet 62. This allows the control unit 38, together with the pressure regulating valve 58, to control the pressure applied to the nozzle unit 16. The control unit 38 is configured to detect the outlet pressure using the pressure sensor 64, and in particular to record the output pressure curve.

[0056] The laser cutting machine 10 has a nozzle changer (not shown) for replacing the nozzle unit 16 with other nozzle units 16 with different nozzle opening sizes and cross-sectional profiles. This allows the laser cutting machine 10 to be optimally adapted to workpieces of varying thicknesses and materials. The size of the nozzle opening 20 of the exchanged nozzle unit 16 is relevant for the quality of the cut edge. Therefore, it is important to use a nozzle unit 16 with the correct nozzle opening size 20 for the cutting process.

[0057] To measure the size of the nozzle opening 20, the control device 38 controls the nozzle unit 16 in such a way that no objects are arranged at a distance of 5 cm from the nozzle opening 20.

[0058] The control unit 38 then controls the process gas system 24 such that the outlet 62 is supplied with a pressure profile 66 as shown in Fig. 2. In Fig. 2, time 68 is plotted on the X-axis and pressure 70 on the Y-axis. When the control unit 38 opens the nitrogen valve module 48 and the compressed air / nitrogen directional control valve 54 to supply nitrogen 32 to the pressure control valve 58, the nitrogen inlet pressure 72, shown as a dotted line in Fig. 2, is applied to the inlet 60 of the pressure control valve 58.

[0059] If, on the other hand, the control device 38 opens the compressed air valve module 46 and the compressed air / nitrogen directional control valve 54 to supply the pressure control valve 58 with compressed air 30, the compressed air inlet pressure 74 shown in dashed lines in Fig. 2 is applied to the inlet 60 of the pressure control valve 58.

[0060] To measure the size of the nozzle opening 20, the control unit 38 specifies a target outlet pressure of 20 bar to the pressure regulating valve 58 for a period of 20 seconds. Fig. 2 shows the time course 76 of the target outlet pressure. The control unit 38 controls the process gas system 24 such that the inlet 60 of the pressure regulating valve is pressurized with nitrogen 32. When the specified target outlet pressure, as measured by the pressure sensor 64, remains constant at the outlet 62 for a duration of, for example, 0.5 seconds, the control unit 38 stops the pressurization of the pressure regulating valve 58 with nitrogen 32 by closing the nitrogen valve module 48. The control unit 38 then controls the process gas system 24 such that the inlet 60 of the pressure regulating valve 58 is pressurized with compressed air 30. The inlet 60 is pressurized with compressed air 30 at a lower pressure than the inlet 60 is pressurized with nitrogen 32.The process gases 30, 32 flow out of the nozzle opening 20, thereby reducing the output pressure measured by the pressure sensor 64 until a constant level is reached. The control unit 38 measures the output pressure using the pressure sensor 64 and records the output pressure curve 66 shown in Fig. 2.

[0061] The control device 38 measures a time period 78, which elapses until the output pressure has dropped from the pressure of the nitrogen 32 to the pressure of the compressed air 30.

[0062] Control unit 38 is provided with a table in which different time durations are assigned to different nozzle opening sizes. For example, control unit 38 is provided with the following table:

[0063] The values ​​in the table are only examples and must be determined empirically.

[0064] In the illustrated embodiment, the duration is 7.5 seconds, which is why the control device 38 determines a nozzle opening size 20 of 1.2 mm using the table.

[0065] The control unit 38 reads a target size of 1.2 mm for the nozzle opening 20 from the nozzle changer. The read target size and the actual size of the nozzle opening 20 thus match. If the deviation between the read target size of the nozzle opening 20 and the actual size of the nozzle opening 20 exceeds a predefined maximum opening deviation, for example, 0.1 mm, the control unit 38 issues a warning.

[0066] The control unit 38 controls a display of the laser processing machine 10 (not shown) in such a way that the display shows the specific size of the nozzle opening 20.

[0067] This ensures that the workpiece 12 is cut with a correct nozzle opening 20.

[0068] Therefore, one aspect of determining the size of the nozzle opening 20 can be that the size of the nozzle opening 20 is determined when switching between two different process gases with different pressure levels in conjunction with the control behavior of the pressure control valve 58.

[0069] The control device 38 is designed to determine the compressed air inlet pressure 74 at the inlet 60 of the pressure regulating valve 58.

[0070] The control unit 38 is provided with a table that assigns different nozzle opening sizes to different pressure reduction values ​​that a nozzle opening causes at the outlet 62 of the pressure control valve 58. For example, the following table is provided to the control unit 38:

[0071] The values ​​in the table are only examples and must be determined empirically.

[0072] In the illustrated embodiment, the nozzle opening 20 has a size of 1.2 mm, which is why the control device 38 determines a pressure reduction 80 of 0.384 bar using the table. This pressure reduction is achieved by the nozzle opening 20 with a size of 1.2 mm at the outlet 62 of the pressure regulating valve 58. The pressure reduction 80 is shown in Fig. 2.

[0073] If the outlet pressure at the outlet 62 remains constant for a duration of, for example, 0.5 seconds while the pressure regulating valve 58 is pressurized with compressed air 30, the control device 38 measures the outlet pressure of the compressed air 30 using the pressure sensor 64. In the illustrated embodiment, the measured outlet pressure of the compressed air is 304.5 bar.

[0074] The control unit 38 determines the compressed air inlet pressure 74 at the inlet 60 of the pressure regulating valve 58 by adding the determined pressure reduction 80 and the measured outlet pressure of the compressed air 30 at the outlet 62 of the pressure regulating valve 58. In the illustrated embodiment, the determined compressed air inlet pressure 74 is 304.884 bar, see Fig. 2.

[0075] The control unit 38 controls the display (not shown) in such a way that the display shows the determined compressed air inlet pressure 74.

[0076] The control unit 38 outputs a pressure signal when the determined compressed air inlet pressure 74 is less than a predetermined minimum pressure, for example 4.5 bar.

[0077] The laser processing machine 10 has a pressure sensor (not shown) for measuring the compressed air inlet pressure. The control unit is designed to output a wear signal if the deviation between the measured compressed air inlet pressure and the determined compressed air inlet pressure 74 is greater than a predefined maximum pressure deviation, for example 0.5 bar.

Claims

Patent claims 1. Method for operating a laser processing machine (10) for processing a workpiece (12) by means of a laser beam (14), wherein during the processing of the workpiece (12) the laser beam (14) and a first process gas (30) exit from a nozzle unit (16) and are directed onto the workpiece (12) by means of the nozzle unit (16), wherein the first process gas (30) is guided to the nozzle unit (16) via a pressure regulating valve (58), wherein the method comprises: Applying a second process gas (32) to an inlet (60) of the pressure regulating valve (58), wherein the second process gas (32) is led via the pressure regulating valve (58) to the nozzle unit (16), Stopping the application of the second process gas (32) to the inlet (60) of the pressure regulating valve (58), Measuring a characteristic parameter of a time profile of the outlet pressure, in particular a time period (78) that elapses until an outlet pressure at an outlet (62) of the pressure control valve (58) has fallen from the pressure of the second process gas (32) to a predetermined pressure, in particular the pressure of the first process gas (30), and Determining the size of the nozzle opening (20) based on the characteristic parameter, in particular the measured time duration (78).

2. Method according to claim 1, wherein the characteristic parameter is a time constant of an exponential pressure drop and the time constant is determined from the time history of the initial pressure, in particular by means of an estimation method.

3. Method according to claim 1 or 2, wherein the method comprises: reading a target size of the nozzle opening (20) and issuing a warning if a deviation between the read target size of the nozzle opening (20) and the determined size of the nozzle opening (20) is greater than a predetermined maximum opening deviation.

4. Method according to any of the preceding claims, wherein the method comprises: indicating the determined size of the nozzle opening (20).

5. Method according to any of the preceding claims, wherein the method before measuring the time period (78) comprises: positioning the nozzle opening (20) such that no objects are arranged at a predetermined distance, in particular at a distance of 5 cm, from the nozzle opening (20).

6. A method according to any one of the preceding claims, wherein the method comprises: After stopping the supply of the second process gas (32) to the inlet (60) of the pressure control valve (58), supplying the inlet (60) of the pressure control valve (58) with the first process gas (30), wherein the supply of the first process gas (30) to the inlet (60) is at a lower pressure than the supply of the second process gas (32), actuating the pressure control valve (58) with a predetermined setpoint outlet pressure for a predetermined minimum duration, wherein the predetermined setpoint outlet pressure is greater than the pressure of the first process gas (30) at the inlet (60) of the pressure control valve (58), Measuring the outlet pressure at the outlet (62) of the pressure control valve (58) during the application of the first process gas (30) to the inlet (60) and during the actuation of the pressure control valve (58), determining a pressure reduction which causes a nozzle opening (20) of the nozzle unit (16) at the outlet (62) of the pressure control valve (58), and determining an inlet pressure of the first process gas (30) at the inlet (60) of the pressure control valve (58) by adding the determined pressure reduction and the measured outlet pressure at the outlet (62) of the pressure control valve (58).

7. Method according to claim 6, wherein the method comprises: displaying the determined inlet pressure of the first process gas (30).

8. Method according to one of the preceding claims 6 or 7, wherein the method comprises: outputting a pressure signal when the determined input pressure of the first process gas (30) is less than a predetermined minimum pressure.

9. A method according to any one of claims 6 to 8, wherein the method comprises: measuring a supply pressure of the first process gas (30) at a process gas inlet of the laser processing machine (10) and outputting a wear signal when a deviation between the The measured supply pressure and the determined input pressure are greater than a specified maximum pressure deviation.

10. Method according to any one of the preceding claims 6 to 9, wherein the method comprises, prior to measuring the output pressure: positioning the nozzle opening (20) such that no objects are arranged at a predetermined distance, in particular at a distance of 5 cm, from the nozzle opening (20), or wherein the method comprises, prior to measuring the output pressure: positioning the nozzle opening (20) at a predetermined distance, in particular at a distance of at most 0.7 mm, to a calibration plate.

11. A method according to any of the preceding claims, wherein the method is repeated multiple times.

12. Method according to claim 11, wherein when the pressure regulating valve (58) is acted upon with the second process gas (32), a different output pressure is set in each repetition.

13. Laser processing machine (10) for processing a workpiece (12) by means of a laser beam (14), wherein the laser processing machine (10) is configured to perform a method according to one of the preceding claims, wherein the laser processing machine (10) comprises: the nozzle unit (16) for directing the laser beam (14) and the process gas (18) onto the workpiece (12), a process gas system (24) for supplying process gas (18) to the nozzle unit (16), and a control device (38), wherein the process gas system (24) comprises the pressure control valve (58) with a pressure sensor (64) for measuring the output pressure at the outlet (62) of the pressure control valve (58), wherein the control device (38) is configured to measure the time duration (78) and to determine the size of the nozzle opening (20) based on the measured time duration (78).

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