Method for operating a laser processing machine and laser processing machine

Abstract

Method for operating a laser processing machine (10) in which an inlet pressure of a process gas (30) at an inlet (60) of a pressure control valve (58) of the laser processing machine (10) is determined by adding a pressure reduction and an outlet pressure measured at an outlet (62) of the pressure control valve (58).

Description

[0001] The invention relates to a method for operating a laser processing machine and a laser processing machine.

[0002] 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.

[0003] DE 10 2009 053 815 B4 describes a test run for valves of a service brake system of a vehicle.

[0004] 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 reliable determination of an input pressure of a process gas.

[0005] 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.

[0006] A method according to the invention is designed for operating a laser processing machine for processing a workpiece using a laser beam from the laser processing machine. During processing of the workpiece, the laser beam and a first process gas emerge from 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 procedure comprises: pressurizing the inlet of the pressure control valve with the first process gas; actuating the pressure control 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 control valve; measuring an outlet pressure at an outlet of the pressure control valve during the pressurization of the inlet with the first process gas and during actuating the pressure control valve; determining a pressure reduction that causes a nozzle opening of the nozzle unit at the outlet of the pressure control valve; and determining an inlet pressure of the first process gas at the inlet of the pressure control valve by adding the previously determined pressure reduction and the measured outlet pressure at the outlet of the pressure control valve.

[0007] 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.

[0008] 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.

[0009] Another aspect of applying the second process gas to the nozzle unit before applying the first process gas may be that this enables or greatly simplifies the determination of other parameters important for processing, such as determining the size of the nozzle opening.

[0010] 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.

[0011] The first process gas can be compressed air. The second process gas can be nitrogen. 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.

[0012] The target output pressure could be, for example, 20 bar. The minimum duration could be, for example, 20 seconds.

[0013] 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 routed to the nozzle unit.

[0014] The nozzle opening can be circular.

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

[0016] The pressure reduction can be the magnitude of the difference between the dynamic pressure at the nozzle opening and the hydrostatic pressure. This pressure reduction can also be referred to as pressure loss.

[0017] Determining the pressure reduction may involve providing a nozzle orifice size.

[0018] Determining the pressure reduction can be achieved by providing a table that maps different nozzle orifice sizes to discrete pressure reduction values. The mapping between nozzle orifice sizes and pressure reduction values ​​can be empirically determined for the laser processing machine. This allows the table to establish an empirical relationship between nozzle orifice sizes and pressure reduction values. In addition to the nozzle orifice, other parameters of the laser processing machine can be considered when determining the pressure reduction values. Such parameters might include the type of pressure control valve, the hose length between the pressure control valve and the nozzle, the type of cutting unit, and the nozzle type. Once created, the table can be used for all identical laser processing machines.

[0019] Determining the pressure reduction can involve reading the pressure reduction from the table for the provided nozzle opening size.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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 less than a predefined minimum pressure. Advantageously, this can alert 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.

[0025] 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.

[0026] 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.

[0027] In a further development of the method, the procedure before measuring the outlet pressure includes: positioning the nozzle opening so 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.

[0028] 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.

[0029] In a further development of the method, the procedure before determining the pressure reduction comprises: before pressurizing the inlet of the pressure regulating valve with the first process gas; pressurizing an inlet of the pressure regulating valve with a second process gas, wherein the second process gas is fed via the pressure regulating valve to the nozzle unit, wherein the pressurization of the inlet with the second process gas occurs at a higher pressure than the pressurization of the inlet with the first process gas; stopping the pressurization of the inlet of the pressure regulating valve with the second process gas; after pressurizing the inlet (60) of the pressure regulating valve (58) with the first process gas;Measuring a characteristic parameter of a time-dependent output pressure profile, in particular the time it takes for the output pressure at the pressure control valve to drop from the pressure of the second process gas to the pressure of the first process gas, and determining the nozzle opening size based on this characteristic parameter, especially the measured time. The pressure reduction is then determined based on the previously determined nozzle opening size. The characteristic parameter of a time-dependent output pressure profile could, for example, be a time constant of an exponential pressure drop.

[0030] 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.

[0031] Determining the nozzle opening size can be accomplished by providing a table in which different nozzle opening sizes are assigned to discrete time values. The relationship between the nozzle opening sizes and the time values ​​can be empirically determined. This allows the table to establish an empirical connection between different nozzle opening sizes and time values.

[0032] Determining the size of the nozzle opening can involve reading the nozzle opening size from the table for the measured time period.

[0033] Another aspect of the process may be that cutting problems can be reduced and the risk of processing errors, such as spatter during material preparation, can be avoided by using an incorrect nozzle opening size or incorrect gas pressure.

[0034] 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.

[0035] 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 opening deviation, for example, a diameter deviation of 0.1 mm (millimeters). Advantageously, this allows verification of the correct labeling of the nozzle unit. The target size can be read by extracting data from an automatic tool changer, particularly a nozzle changer.

[0036] 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.

[0037] In a further development of the method, the procedure before measuring the duration includes: positioning the nozzle opening such that no objects are located within a distance of 5 cm from the nozzle opening. Advantageously, this allows the measured duration to be measured without being affected by disturbances.

[0038] 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 outlet pressure at the outlet of the pressure control valve. The control unit is configured to determine the pressure reduction and to ascertain the inlet pressure of the process gas.

[0039] 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: Fig. 1 a schematic representation of a laser processing machine, and Fig. 2. A graph of a pressure profile at an output of a pressure control valve of the laser processing machine of Fig. 1 over time.

[0040] Fig. Figure 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.

[0041] The laser processing machine 10 is a laser cutting machine and the processing of the workpiece 12 is a cutting of the workpiece 12.

[0042] 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.

[0043] 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.

[0044] 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 is formed from a plurality of valves and lines.

[0045] The process gas system 24 has a process gas inlet 26 for connecting the laser processing machine 10 to a pressure source 28.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] The compressed air line 40 leads from the compressed air valve module 46 into the nitrogen line 42, which in turn leads into a control valve module 52 of the laser processing machine 10. The oxygen line 42 also leads into the control valve module 52.

[0052] 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 means of the control device 38 to introduce or shut off the respective process gas 30, 32, 34.

[0053] 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.

[0054] 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.

[0055] 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. This allows the laser cutting machine 10 to be optimally adapted to workpieces of varying thicknesses. The size of the nozzle opening 20 of the exchanged nozzle unit 16 is relevant to 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.

[0056] 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.

[0057] The control unit 38 then controls the process gas system 24 such that the output 62 is connected to a Fig. The pressure curve shown in diagram 2 is subjected to 66. Fig.2 represents time 68 on the X-axis and pressure 70 on the Y-axis.

[0058] When the control device 38 opens the nitrogen valve module 48 and the compressed air / nitrogen directional control valve 54 to supply the pressure regulating valve 58 with nitrogen 32, the Fig. 2. Nitrogen inlet pressure 72 shown in dotted lines at the inlet 60 of the pressure regulating valve 58.

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

[0060] To measure the size of the nozzle opening 20, the control device 38 specifies a target output pressure of 20 bar to the pressure control valve 58 for a period of 20 seconds. Fig.Figure 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. If the predetermined 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. 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 outlet 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 takes the reading into account. Fig. 2 shows the course of the initial pressure 66.

[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 durations are assigned to different nozzle opening sizes. For example, control unit 38 is provided with the following table: Nozzle opening size Duration 0.8 mm 15.5 seconds 1.0 mm 12.0 seconds 1.2 mm 8.0 seconds 1.4 mm 6.0 seconds 1.7 mm 5.0 seconds 2.0 mm 4.0 seconds 2.3 mm 3.5 seconds 2.7 mm 3.0 seconds

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

[0064] In the illustrated embodiment, the duration is 8.0 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. This means the read target size and the actual size of the nozzle opening 20 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: Nozzle opening size Pressure reduction 0.8 mm 0.30 bar 1.0 mm 0.34 bar 1.2 mm 0.39 bar 1.4 mm 0.47 bar 1.7 mm 0.64 bar 2.0 mm 0.85 bar 2.3 mm 1.16 bar 2.7 mm 1.70 bar

[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 0.39 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. Fig. 2 shown.

[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 30 is 4.5 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 of the compressed air 30 is 4.89 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 specified 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. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2009 053 815 B4

[0003]

Claims

[1] Method for operating a laser processing machine (10) for processing a workpiece (12) using 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 the first process gas (30) to the inlet (60) of the pressure regulating valve (58), - Controlling the pressure control valve (58) 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 (30) at the inlet (60) of the pressure control valve (58), - Measuring an output pressure at an output (62) of the pressure control valve (58) during the application of the first process gas (30) to the input (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 regulating 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). [2] Method according to claim 1, - the procedure includes: displaying the determined inlet pressure of the first process gas (30). [3] Method according to any of the preceding claims, - wherein the procedure comprises: outputting a pressure signal when the determined input pressure of the first process gas (30) is less than a predetermined minimum pressure. [4] Method according to any of the preceding claims, - wherein the method comprises: measuring a supply pressure of the first process gas (30) at a process gas inlet (60) of the laser processing machine (10) and outputting a wear signal when a deviation between the measured supply pressure and the determined inlet pressure is greater than a predetermined maximum pressure deviation. [5] Method according to any of the preceding claims, - wherein the procedure before measuring the output pressure comprises: positioning the nozzle opening (20) such that no objects are arranged at a distance of 5 cm from the nozzle opening (20), or - wherein the procedure, prior to measuring the output pressure, comprises: positioning the nozzle opening (20) at a predetermined distance, in particular at a distance of no more than 0.7 mm, to a calibration plate. [6] Method according to any of the preceding claims, - the procedure includes, prior to determining the pressure reduction: - before pressurizing the inlet (60) of the pressure regulating valve (58) with the first process gas (30), pressurizing an inlet (60) of the pressure regulating valve (58) with a second process gas (32), wherein the second process gas (32) is directed via the pressure regulating valve (58) to the nozzle unit (16), wherein the pressurization of the inlet (60) with the second process gas (32) takes place at a higher pressure than the pressurization of the inlet (60) with the first process gas (02), - Stopping the application of the second process gas (32) to the inlet (60) of the pressure regulating valve (58), - after pressurizing the inlet (60) of the pressure control valve (58) with the first process gas (30), measuring a characteristic parameter of a time profile of the outlet pressure, in particular a time period (78) that elapses until the outlet pressure at the outlet (62) of the pressure control valve (58) has fallen from the pressure of the second process gas (32) to the pressure of the first process gas (30), and determining a size of the nozzle opening (20) based on the characteristic parameter, in particular the measured time period (78), - where the pressure reduction is determined based on the determined size of the nozzle opening (20). [7] Method according to claim 6, - wherein the procedure includes: 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 specified maximum opening deviation. [8] Method according to one of the preceding claims 6 or 7, - the procedure includes: displaying the specified size of the nozzle opening (20). [9] Method according to any one of claims 6 to 8 above, - wherein the procedure before measuring the time duration (78) comprises: positioning the nozzle opening (20) such that no objects are arranged at a distance of 5 cm from the nozzle opening (20). [10] Laser processing machine (10) for processing a workpiece (12) using 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) includes the pressure control valve (58) with a pressure sensor (64) for measuring the outlet pressure at the outlet (62) of the pressure control valve (58), - wherein the control device (38) is configured to determine the pressure reduction and to determine the inlet pressure of the process gas (18).

Images