Laser cutting method and laser cutting machine

Abstract

The invention relates to a laser cutting method, to a laser cutting machine, and to a computer program. The aim of the invention is to provide an improved laser cutting method and an improved laser cutting machine. According to the invention, this is achieved by a laser cutting method with the following steps: - a) cutting a workpiece along a cutting line using a high-power laser cutting beam; - b) ascertaining a correct cut or an incorrect cut of the workpiece during the cutting process of the workpiece; - c) scanning the cutting line on the workpiece using a low-power laser scanning beam or an illumination beam and recording scanning data; - d) changing at least one parameter of the laser cutting machine; - repeating steps a) to c); and analyzing the scanning data with respect to the different parameters of the laser cutting machine in a controller.

Description

[0001] Laser cutting process and laser cutting machine

[0002] The invention relates to a laser cutting method, a laser cutting machine and a computer program product according to the preamble of the independent claims.

[0003] The technical field of industrial cutting of various materials using laser radiation is gaining increasing importance. When cutting workpieces made of various materials, laser radiation from a laser cutting machine with high power, usually in the range of several kilowatts, is used. In exceptional cases, it may happen that a workpiece is not completely cut through and the part to be separated remains on the workpiece. An incomplete cut through the workpiece, which does not result in the workpiece being separated along the cutting line or cutting gap, is referred to as a miscut.

[0004] Usually, a faulty cut is detected by the machine operator in a further process step and the defective workpiece is fed to the laser cutting machine for re-cutting. Another possibility is known from the publication DE 102010039525 A1, in which the workpiece is moved over in the area of ​​a breakthrough with a distance sensor, whereby it is checked whether a complete breakthrough or a severing cut has occurred. The workpiece is then fed to the laser cutting machine for re-cutting. One object of the invention is to provide an improved

[0005] Laser cutting processes and improved

[0006] to provide laser cutting machine.

[0007] For this purpose, a laser cutting process is provided with the following process steps

[0008] - a . cutting a workpiece with a high-power laser cutting beam along a cutting line ;

[0009] - b . Detecting a good cut or a faulty cut of the workpiece during cutting of the workpiece ;

[0010] - c . Scanning the cutting line on the workpiece with a low-power laser scanning beam or with an illumination beam and recording scan data;

[0011] - d . Changing at least one parameter of the laser cutting machine ;

[0012] - Repeating process steps a . to c . ; and

[0013] - Evaluating the scan data with respect to the various parameters of the laser cutting machine in a control device; wherein the scanning of the cutting line on the workpiece is carried out with the low-power laser scanning beam during retraction of a laser processing head.

[0014] Furthermore, a laser cutting machine is provided for cutting a workpiece along a cutting line, comprising at least one laser source for generating a high-power laser cutting beam, a camera for detecting a good cut or a faulty cut of the workpiece during cutting of the workpiece, a low-power laser scanning beam from the laser source or an illumination beam from a lighting unit, with a control device which is designed to change at least one parameter of the laser cutting machine and to evaluate scan data of the low-power laser scanning beam or of the illumination beam with regard to the various parameters of the laser cutting machine.

[0015] Furthermore, a computer program product is provided in a control device for carrying out the method.

[0016] Examples of the invention are described in the dependent claims.

[0017] In one example, a good cut or a faulty cut is detected using a camera while the workpiece is being cut. This allows for reliable detection of faulty cuts in real time.

[0018] In a further example, the method step of evaluation comprises determining the positions of a miscut. The method step of cutting the workpiece with the high-power laser cutting beam is then carried out at the determined positions of the miscut. Determining the position of the miscut on the workpiece is useful for setting parameters of the laser cutting machine in order to achieve an improved cutting result. On the other hand, a miscut is eliminated by targeted control of the high-power laser cutting beam exclusively to those positions on the workpiece which are not cut through, thus eliminating the miscut in an economical manner.

[0019] Another example describes the process steps

[0020] - Classifying the scan data recorded with various parameters as a good cut or a faulty cut; - Feeding the scan data classified as a good cut or a faulty cut into the control device;

[0021] - Adjusting at least one of the parameters classified as a good cut on the laser cutting machine by the control device. These process steps enable improved parameter adjustment of the laser cutting machine in an automated manner. As a result of these process steps, the laser cutting machine will exhibit a significantly lower risk of faulty cuts during operation.

[0022] After a miscut is detected, the cutting line on the workpiece is scanned with a low-power laser scanning beam while a laser processing head retracts to cut the workpiece with the high-power laser cutting beam. The scan quickly determines whether a miscut has occurred or whether the miscut was incorrectly detected. It also determines the length and extent of the miscut.

[0023] In another example, at least one parameter of the laser cutting machine is changed from the selection of the focus position, the laser power of the laser cutting machine, the focus diameter, the distance between a laser nozzle and the workpiece, a feed rate of the workpiece, and / or a gas pressure of a shielding gas. By changing or adjusting at least one of the aforementioned parameters, the cutting result of the laser cutting machine is changed.

[0024] Examples of the invention are described in detail below with reference to the figures. Fig. 1 shows an example of a schematic representation of a laser cutting machine,

[0025] Fig. 2 shows a schematic side view of a sensor device with control device of a laser cutting machine with a workpiece machined with a laser beam of the laser cutting machine;

[0026] Fig. 3 shows an exemplary signal curve of a signal of the sensor device, evaluated in the control device, of a cutting line with an area of ​​a good cut and an area of ​​a faulty cut.

[0027] Fig. 1 shows a schematic representation of a laser cutting machine 10 with a laser source 22, a laser processing head 24 and a workpiece support 25. A solid-state laser is preferably used as the laser source 22, the laser radiation being fed to the laser processing head 24 via a laser light cable. A high-power laser cutting beam 16 generated by the laser source 22 is guided to the laser processing head 24 by means of a beam guide 23, where it is focused and aligned perpendicular to the surface of a workpiece 2 with the aid of mirrors. High power here usually describes power in the order of magnitude of several kilowatts. Thus, the beam axis, optical axis, of the laser cutting beam 16 in this example runs perpendicular to the workpiece 2. In the example shown, the laser source 22 is a CO2 laser source.Alternatively, the laser cutting beam 16 can be generated, for example, by a solid-state laser with a corresponding laser source. Similarly, a low-power laser scanning beam is generated and guided to the workpiece 2. Low power typically refers to power levels in the order of several watts or several hundred milliwatts. The laser cutting beam 16 and the laser scanning beam can be provided by the laser source 22 by adjusting the power of the laser source.

[0028] The laser cutting beam 16 is moved over the workpiece 2 so that a continuous cutting gap or cutting line 14 is created, along which the laser cutting beam 16 usually completely cuts through the workpiece 2.

[0029] Laser cutting can be assisted by adding a gas. Oxygen, nitrogen, compressed air, and / or application-specific gases can be used as cutting gases, which are provided in connected cutting gas containers 32. Resulting particles and gases can be extracted by means of an extraction device 33 from a suction chamber (not shown), which is located below the workpiece support 25.

[0030] The laser processing head 24 and the workpiece 2 are moved relative to one another in the laser cutting machine 1. In the example shown, the workpiece 2 rests on the workpiece support 25 during processing, and the laser processing head 24 is moved along three axes X, Y, Z of an XYZ coordinate system. For this purpose, a drive is provided which moves a gantry 30, indicated by a double arrow, which is displaceable in the X direction. The gantry 30 denotes a displaceable frame on the laser cutting machine 10, as shown by way of example in Fig. 1. The laser processing head 24 can be displaced in the Y direction with the aid of a further drive, indicated by a double arrow, in order to reach any processing position B X, Y in the X-direction and in the Y-direction in a working field determined by the displaceability of the laser processing head 24 or by the workpiece 2. At a respective processing position B X , Y, the laser cutting beam 16 has a feed direction V that corresponds to the relative speed between the laser processing head 24 and the workpiece 2. The feed direction V is shown by an arrow on the workpiece 2 in Fig. 1. The laser processing head 24 is also moved in the Z direction, usually when resetting or retracting or approaching cutting positions of the laser processing head 24.

[0031] The laser processing head 24 further comprises a sensor device 1 as described below.

[0032] Fig. 2 shows a schematic side view of a sensor device 1 with a control device 15 connected by signal technology. The sensor device 1 is included in this example by the laser processing head 24. In this example, the sensor device 1 includes an illumination unit 21 for generating and specifically emitting an illumination beam 13 through an optical element 8 to a suitable mirror 7. The mirror 7 directs the illumination beam 13 from the sensor device 1 through a dichroic deflecting mirror 9, a focusing lens 3 and a cutting gas nozzle 6 to a processing area of ​​the workpiece 2. The cutting gas nozzle 6 is included in the laser processing head 24. The illumination beam 13 is reflected at the workpiece 2 and the reflected illumination beam 13 takes the same path back and passes through the mirror 7 to be recorded by a camera 11.As an alternative to the camera 11, photodiodes can be provided which capture the reflected illumination beam 13. In this way, images of the processing area on the workpiece 2 are recorded by the camera 11 or by photodiodes, the processing area essentially containing a cutting line 14 generated with the laser cutting beam 16 with the adjacent workpiece sections. The cutting line 14 is accordingly swept over or scanned and scan data is recorded. The laser cutting beam 16 is fed into the laser processing head 24 via the deflecting mirror 9, through the focusing lens 3 and the cutting gas nozzle 6, from which the laser cutting beam 16 emerges from the laser processing head 24 with high energy, strikes the workpiece 2 and completely cuts the workpiece 2 in a known manner. In an alternative embodiment, the sensor device 1 does not comprise an illumination unit 21 and no optical element 8.In this embodiment, the cutting line 14 and adjacent areas on the workpiece 2 are swept or scanned by a low-power laser scanning beam. The low-power laser scanning beam can be generated in the laser source 22, in which the high-power laser cutting beam 16 is also generated. The laser source 22 then switches from a high-power cutting mode to a low-power scanning mode. Accordingly, in this alternative, the cutting and scanning of the workpiece 2 are carried out sequentially. In particular, in this embodiment, the scanning of the cutting line 14 on the workpiece 2 with the low-power laser scanning beam is carried out while the laser processing head 24 is retracting.First, the workpiece 2 is cut at high power, then switched to low power, with the laser processing head 24 moving back along the cut path on the cutting line 14 and scanning the cutting line 14.

[0033] The laser processing head 24 moves back along the same path it has traveled, usually when a miscut 18 is detected. The laser processing head 24 is stopped, the laser source 22 is set to a low power by the control device 15 so that a laser scanning beam can be provided. The laser scanning beam then scans the cutting line 14, and scan data are recorded and evaluated as described. The scan data are used to determine whether or not a miscut 18 is present. In other words, it is determined whether miscut detection, the determination of the miscut 18, which causes the laser processing head 24 to stop, was carried out correctly. An incorrect determination of a miscut 18 is ruled out with these means. In particular, it can be quickly determined whether a miscut 18 is actually present because the movement patterns of the laser processing head 24 are optimized.A movement of the laser processing head 24 to a starting point for scanning the cutting line 14 after an error has been detected is no longer necessary. In addition, the position of the incorrect cut 18 is determined, after which the laser processing head 24, in cutting mode, precisely controls the position or positions of the incorrect cut 18 and severs the workpiece 2 by cutting again. The laser processing head 24 covers the shortest possible distance when scanning and cutting. Unnecessary power losses due to cutting at incorrect positions are avoided, the workpiece 2 is not heated up unnecessarily and the quality of the cutting result on the workpiece 2 is not unnecessarily impaired. Repeated cutting can lead to unsatisfactory cutting results. Fig. 3 shows an example signal curve of a signal from the sensor device 1, which signal is evaluated in the control device 15, in the upper area of ​​Fig.3 and an associated cutting line 14 in the lower area of ​​Fig. 3. The cutting line 14 is indicated with numerical values ​​in the range of millimeters mm on the horizontal axis. The signals are generated by the photodiodes or the camera 11 with suitable image processing software. The camera 11 usually records the light intensity of a process light at the cutting line 14, which occurs during laser welding when the laser beam interacts with the material of the workpiece 2. It can be seen that the signal runs largely close to the zero line. The associated cutting line 14 on the workpiece 2 runs free of defects, so that the workpiece 2 is severed completely and only as much material is removed as is necessary to severe or cut through the workpiece 2. The area on the workpiece 2 assigned to the low signal is referred to as the good cut 17.The maximum brightness in the area of ​​the cutting gap of the cutting line 14 is used to check whether a luminous phenomenon is present during scanning and to categorize the images as either a separating cut or a good cut or a cut break or a defective cut. For this categorization, a threshold value is defined in the diagram according to Fig. 2. If an intensity feature, the maximum brightness in the area of ​​the cutting gap of the cutting line 14, is below the threshold value, the image is classified as a good cut; if the intensity feature is above the threshold value, the image generated by the camera 11 is categorized or classified as a defective cut. The light intensity signal is referred to as the scan mode signal. On the right-hand side of Fig. 3 it can be seen that the cutting line 14 is disturbed and interrupted; an undesired defective cut 18 has occurred.In the signal curve, the area on the workpiece 2 with a miscut 18 leads to a significant signal increase, recognizable by the signal to the right of the dashed line in Fig. 3. This signal increase is detected by the control device 15 above a threshold value of a light intensity. As described, a good cut 17 or a miscut 18 of the workpiece 2 is determined during cutting of the workpiece 2 and the cutting line 14 on the workpiece 2 can be scanned in different ways, wherein the cutting data and the scan data are recorded. In the example according to Fig. 3, a miscut 18 occurs as described.Parameters of the laser cutting machine 10 are stored in the control device 15, for example the focus position, a laser power of the laser cutting machine 10, the focus diameter, the distance between a laser nozzle, in this case the cutting gas nozzle 6, and the workpiece 2, a feed rate of the laser processing head 24 and a gas pressure of a protective gas. Further parameters of the laser cutting machine 10 can be stored in the control device 15. The parameters or the parameter set of the laser cutting machine 10 are known for the example in Fig. 3 with the incorrect cut 18. Then at least one parameter of the laser cutting machine 10 is changed and the laser cutting method is repeated, with the at least one changed parameter the method steps of cutting, scanning, recording and evaluating the scan data are carried out as described.With the at least one changed parameter, a good cut 17 or a faulty cut 18 can be determined again, the corresponding parameters or the parameter set being assigned to the good cut 17 or the faulty cut. The above method steps are repeated as often as desired, so that a large number of parameter sets are present in the control device 15 and it is known for each parameter set whether a good cut 17 or a faulty cut 18 is achieved with the parameter set and in which section of the cutting line 14 the good cut 17 and the faulty cut 18 are present. For example, after each cutting process, the parameter of the feed rate of the laser processing head 24 is changed. The cutting process with recording or recording of scan data at the changed feed rate is repeated until a faulty cut is detected.Accordingly, the feed rate of the laser processing head 24 at which a miscut occurs is known in the control device 15. The laser cutting machine 10 can then be adjusted such that the feed rate parameter does not exceed the threshold value at which a miscut occurs.

[0034] The scan data relating to the various parameters or parameter sets of the laser cutting machine 10 are evaluated in the control device 15 using suitable software. For example, parameters or parameter sets can be assigned to a good cut 17, while other parameters or parameter sets are assigned to a defective cut 18. The scan data recorded with various parameters are classified as a good cut 17 or a defective cut 18 and stored. In this way, the control device 15 has classes of parameters or parameter sets which are assigned to good cuts 17, and classes which are assigned to defective cuts 18. The data for the positions of the areas not cut through are also assigned to the classes of defective cuts 18. In principle, the parameters which lead to a good cut 17 are automatically set or adjusted on the laser cutting machine 10.In this way, the laser cutting machine 10 is essentially maintained in an operating state that enables good cuts 17 and avoids faulty cuts 18. The laser cutting machine 10 is thus trained, so to speak. Furthermore, the classified data sets can be used to train a machine learning model.

[0035] List of reference symbols

[0036] Sensor device

[0037] workpiece

[0038] Focusing lens

[0039] Focusing device

[0040] Cutting gas nozzle

[0041] Mirror optical element

[0042] Dichroic mirror

[0043] laser cutting machine

[0044] camera

[0045] Lighting beam

[0046] Cutting line

[0047] Control device

[0048] Laser cutting beam

[0049] Good cut

[0050] Miscut

[0051] lighting unit

[0052] Laser source

[0053] Beam guidance

[0054] Laser processing head

[0055] Workpiece support

[0056] Support bar

[0057] portal

[0058] Cutting gas tank

[0059] Suction device

Claims

Patent claims Laser cutting method comprising the following process steps: a. Cutting a workpiece (2) with a high-power laser cutting beam (16) along a cutting line (14); b. Determining a good cut (17) or a failed cut (18) of the workpiece (2) during the cutting of the workpiece (2); c. scanning the cutting line (14) on the workpiece (2) with a low-power laser scan beam or with an illumination beam (13) and recording scan data; d. changing at least one parameter of the laser cutting machine (10); Repeating process steps a. to c.; and evaluating the scan data with respect to the various parameters of the laser cutting machine (10) in a control device (15); wherein the scanning of the cutting line (14) on the workpiece (2) is carried out with the low-power laser scan beam during a retraction of a laser processing head (24). Laser cutting method according to claim 1, characterized by the process step Determining a good cut (17) or a bad cut (18) during the cutting of the workpiece (2) with a camera (11). Laser cutting method according to one of the preceding claims, characterized in that the method step of The evaluation process step comprises determining the positions of a defective cut (18); with the subsequent process step of cutting the workpiece (2) with the high-power laser cutting beam (16) at the determined positions of the defective cut. Laser cutting method according to one of the preceding claims, characterized by the process step Classifying scan data acquired with different parameters into a good cut (17) or a bad cut (18) ; Feeding the scan data classified as a good cut (17) or a bad cut (18) into the control device (15) ; Setting at least one of the parameters classified for a good cut (17) on the laser cutting machine (10) by the control device (15). Laser cutting method according to one of the preceding claims, characterized by the process step Changing at least one parameter of the laser cutting machine (10) from the selection of focus position, laser power of the laser cutting machine (10), focus diameter, the distance between a laser nozzle and the workpiece (2), a feed rate of the laser processing head (24) and / or a gas pressure of a shielding gas. Laser cutting machine (10) for cutting a workpiece (2) along a cutting line (14) with at least one laser source (22) for generating a high-power laser cutting beam (16), a camera (11) for capturing a good cut (17) or a miscut (18) of the workpiece (2) during the cutting of the workpiece (2), a low-power laser scan beam from the laser source (22) or an illumination beam (13) of a lighting unit (21), characterized by a control device (15) which is configured to change at least one parameter of the laser cutting machine (10) and to evaluate scan data of the low-power laser scan beam or the illumination beam (13) with respect to the various parameters of the laser cutting machine (10). Laser cutting machine (10) according to claim 6, characterized in that the control device (15) is configured to classify and store the scan data acquired with different parameters for a good cut (17) or a miscut (18).Laser cutting machine (10) according to claim 6 or 7, characterized in that the control device (15) is configured to set at least one of the parameters classified for a good cut (17) on the laser cutting machine (10). Laser cutting machine (10) according to one of claims 6 to 8, characterized by a control device (15) for evaluating signals from the detector (11) and for setting the power of the laser source (22) to a high power for cutting the workpiece (2) and a low power for scanning the cutting line (14) with the laser scan beam. Laser cutting machine (10) according to one of claims 6 to 8, characterized in that the low-power laser scan beam consists of at least one pulsed laser beam or of a continuous laser beam. Computer program product in a control device (15) for carrying out the method according to one of claims 1 to 5.

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