Method for determining cut quality and processing machine

Abstract

The invention relates to a method for determining a cut quality at at least one cut edge (17) of a preferably plate-shaped workpiece (8), comprising: forming the at least one cut edge (17) on the workpiece (8), preferably by means of a laser beam (6), capturing image data (B) of the at least one cut edge (17), and determining the cut quality at the at least one cut edge (17) on the basis of the captured image data (B). In the method, in an edge region (14) of the workpiece (8) adjacent to an outer edge (8a) of the workpiece (8), at least one recess (15) is cut into the workpiece (8) and the cut quality is determined at a cut edge (17) of the at least one recess (15). The invention also relates to a processing machine.

Description

[0001] Method for determining cutting quality and processing machine

[0002] The present invention relates to a method for determining the cut quality at at least one cutting edge of a preferably plate-shaped workpiece, comprising: forming the at least one cutting edge on the workpiece, preferably by means of a laser beam, acquiring image data of the at least one cutting edge, and determining the cut quality at the at least one cutting edge based on the acquired image data. The invention also relates to a processing machine for cutting a workpiece, in particular a laser processing machine, preferably for carrying out the method, comprising: a cutting head, in particular a laser cutting head, for forming at least one cutting edge on the workpiece.

[0003] From DE 10 2019 209 088 A1, a method for evaluating a laser-cut edge of a workpiece is known, comprising: capturing image data of the laser-cut edge and its surroundings, e.g., using a camera of a mobile device. Following processing of the workpiece, the quality of the resulting cut edge is determined by capturing the image data. The image data representing the quality of the cut edge are added to a data record of the current workpiece processing. The data records of workpiece processing are stored in a database to improve a process parameter algorithm.

[0004] DE 10 2018 216 873 A1 describes a method and a device for processing a workpiece with a laser cutting machine, in which the quality of the resulting cut edge is also determined after processing the workpiece, for which a measuring device can be used.

[0005] Object of the invention

[0006] The invention is based on the objective of providing a method for determining a cutting quality and a processing machine in which the cutting quality can be determined automatically before and / or during the cutting process.

[0007] Subject matter of the invention

[0008] This task is solved by a method of the type mentioned above, in which at least one recess is cut into the workpiece in an edge area adjacent to an outer edge of the workpiece and the cut quality is determined at a cutting edge of the at least one recess.

[0009] In the method according to the invention, at least one recess is cut in an edge region of the workpiece that is not intended for cutting. This edge region typically forms a portion of a residual grid frame, which, after the cutting of the workpiece is complete, forms part of a residual grid that is disposed of. Therefore, cutting the recess in the edge region of the workpiece does not restrict the nesting of the workpiece parts in a machining area of ​​the workpiece intended for cutting. However, the recess should extend from the outer edge deep enough into the workpiece or into the edge region of the workpiece to produce a clean cut, allowing for the most precise possible determination of the cut quality at the cut edge of the recess.

[0010] When cutting the recess in the edge area, a cutting slug is formed, which is separated from the workpiece. The workpiece support is designed in such a way that the cutting slug can fall downwards due to gravity, exposing the cut edge of the recess so that image data of the exposed cut edge can be captured. If the workpiece rests on multiple support ridges, it is advantageous for the cutting slug to be located between the support ridges or to rest on only one of them, so that it can fall unhindered. In the method described here, the cut quality is therefore not determined at the cut part, i.e., at the cutting slug, but at the outer edge of the (remaining) workpiece or the recess, which makes no difference for determining the cut quality.

[0011] On machining centers with automated part removal, a cut part can be automatically removed from the workpiece and fed to an image acquisition device, for example, by automatically holding it in front of a camera. This is not possible with a non-automated machining center. In this case, a test part would have to be nested onto the workpiece for manual inspection, which increases machine time and material consumption. Alternatively, the cut quality could be checked with the first part produced during the cutting process. In both cases, the inspection would have to be carried out manually by holding the respective part in front of a camera, which increases personnel requirements and would not typically be performed automatically for every workpiece.Using the method described here, the cutting quality can also be automatically assessed on processing machines that do not have automated part removal.

[0012] In the case of a sheet-like workpiece, the outer edge is typically the long or short side of the rectangular or, if applicable, square sheet. For a tubular workpiece, such as a pipe or a tubular profile (e.g., an L-profile or a T-profile), the outer edge is an end face. The recess is typically cut at a precisely defined point along the outer edge of the workpiece, where a precise cut is made.

[0013] In principle, the determination of cutting quality or quality inspection can be activated either on the machining center or in the programming system. Upon order acceptance, each workpiece can be assigned an attribute indicating that it must be inspected for cutting quality or that certain quality standards must be met. After capturing the image data of the cutting edge, the image analysis can be performed either locally on the machining center or externally, e.g., in the cloud. The results, possibly including the optimization of machining parameters, are sent back to the machining center and transferred to the manufacturing execution system (MES) for documentation.

[0014] In one variant, the edge area extends no more than 1 cm, preferably no more than 5 mm, into the workpiece from its outer edge. As described above, the cutting of the recess should have as little impact as possible on the nesting or machining of the workpiece. This is achieved by ensuring that the edge area, and thus the recess, extends only a short distance into the workpiece. The extent of the edge area is measured perpendicular to the respective outer edge. The workpiece itself has significantly larger dimensions than the edge area. A plate-shaped workpiece typically has a width or extent between opposing outer edges that is on the order of more than one hundred times the extent or width of the edge area.

[0015] In another variant, the image data of the cutting edge is captured by an image acquisition device, preferably a camera (with lens), which is aligned with the outer edge of the workpiece. The camera has a field of view that captures at least a portion of the outer edge of the workpiece in which the recess is formed. For this purpose, the image acquisition device or the camera can, for example, be positioned or mounted laterally to the workpiece at approximately the level of a support surface when working with a plate-shaped workpiece.

[0016] The image acquisition device serves to capture image data in the form of one or more images of the cut edge of the recess or its surroundings. The image data can be processed using suitable image processing to determine the cutting quality. For example, the image data can be segmented for this purpose, as described in the aforementioned DE 10 2019 209 088 A1, which is incorporated in its entirety by reference into this application. Based on the image data, the processing or laser parameters can be adjusted and, if necessary, optimized before or during the cutting process of the workpiece (su).

[0017] In another variant, the position of the workpiece's outer edge is detected before the recess is created. The workpiece's outer edge can be probed or detected in various ways. For example, the outer edge's position can be detected using a distance sensor, particularly a capacitive distance sensor, which measures the distance between a laser processing head and the workpiece. In this case, the workpiece's outer edge can be detected when the measured distance to the workpiece increases abruptly. Alternatively, a laser test pulse or a sequence of laser test pulses can be used to detect the workpiece's outer edge. These pulses are directed onto the workpiece, and their reflection is measured. If no reflection of the laser radiation or of a particular laser test pulse is measured, it is assumed that the workpiece's outer edge has been reached or exceeded.Capturing the flat workpiece from above, for example using another camera, also makes it possible to detect the position of the workpiece's outer edge. Knowing the position of the workpiece's outer edge simplifies cutting the recess, as the laser beam can be switched on at the position of the outer edge or at a small distance from it to cut the recess.

[0018] In a preferred embodiment of this variant, a distance between the position of the workpiece's outer edge and the image acquisition device is determined, and preferably, a scale for the image data of the laser-cut edge determined by the image acquisition device is calculated based on this distance. Knowing the distance between the workpiece's outer edge and the image acquisition device or camera can be used to appropriately adjust the depth of field of the camera or lens to obtain a high-resolution image of the cut edge. A scale can also be calculated in the captured image or image data based on this distance. In this way, the size of geometric features of the cut edge, such as the burr height, can be determined as an absolute value in the captured image or image data.

[0019] In another variant, the recess is cut before the workpiece is machined in a designated cutting area. In this variant, the recess is cut into the raw workpiece or sheet metal before it is machined. Cutting the recess is therefore typically the first cutting operation performed on the workpiece on the machine designated for this purpose. The area designated for cutting the recess is located within the workpiece's outer edge, which is not intended for cutting operations.

[0020] If the cutting quality is determined before the actual cutting of the workpiece, it can be checked and, if necessary, adjusted or optimized before the cutting process begins. It is possible to cut several recesses into the workpiece before the actual cutting process to determine and verify the improvement achieved with each optimization step before the cutting process starts. Typically, the cutting parameters are kept constant or adjusted to the geometry of the contour created on the workpiece's outer edge during the cutting process. However, it is also possible to selectively change individual machining parameters during the cutting process to determine the impact of these changes on the cutting quality and optimize it accordingly.

[0021] In another variant, the workpiece is machined in the designated cutting area, and the cutting process is interrupted to cut the recess. In this variant, which can be performed as an alternative or in addition to the variant described above, the cut quality is checked during the cutting process. Here, too, the check of the cut quality can be followed by automated optimization of the cut quality by appropriately adjusting the machining or cutting parameters. In a further development of this variant, the cutting process of the workpiece is interrupted at a predetermined machining point and / or after the occurrence of an event affecting the cut quality in order to determine it. The determination or...Cutting quality can also be checked during the cutting process, for example at a predetermined point in time when a certain percentage of the cutting process is complete. For example, the predetermined point in time could be at 50% of the total machining time of the workpiece, or at a predetermined point in time.

[0022] The processing point can be reached when, for example, 50% of the workpiece parts have been cut. It is also possible that the cutting process is interrupted if an event occurs that (potentially) affects the cut quality, such as a miscut, a collision between the nozzle of a machining head and the workpiece, or exceeding a contamination detection threshold.

[0023] In another variant, several cutouts are made at the same position or at laterally offset positions on the outer edge of the workpiece to determine the cut quality multiple times. As described above, it can be advantageous or even necessary to cut several cutouts in the edge region of the same workpiece to determine the cut quality at each individual cutout. The cut edge of each cutout must be captured by the image acquisition device. The position at which the cutout is made in the workpiece is understood to be the center position, i.e., the position at which the cutout has half its length along the outer edge of the workpiece. It is possible to cut two or more cutouts at the same position on the outer edge of the workpiece, so that the cutouts overlap. In this case, the depth or...The extent of a subsequently cut recess from the outer edge into the workpiece is greater than that of a previously cut recess. Therefore, to capture the image data of the cut edges, it may be necessary to adjust or change the depth of field of the image acquisition device. Alternatively, two or more recesses are cut laterally offset into the workpiece; these typically do not overlap.

[0024] In another variant, the image acquisition device and / or the workpiece are moved to capture image data of the cut edges of at least two recesses with laterally offset positions. It is possible to move the image acquisition device along the outer edge of the workpiece for this purpose. However, it is generally more advantageous for the image acquisition device to remain stationary while the workpiece is moved. For a plate-shaped workpiece that can be moved, for example, by a pallet changer, the workpiece can be shifted a sufficient distance—approximately 10 cm, for instance—to cut the recesses at laterally offset positions.

[0025] Generally, it is advantageous if the cutout or the cut edge formed during the cutting process has a sufficient length or extent along the outer edge of the workpiece, on the order of at least one centimeter, and usually several centimeters, to allow for a high degree of precision in determining the cut quality. The cutout or cut edge preferably has a straight section that is aligned parallel to the outer edge of the workpiece and can be captured by the camera. In this case, a typically elongated or rectangular cutout is created in the workpiece. However, the cutout or cut edge can, in principle, have any shape or geometry, e.g., a zigzag curve or similar. As described above, when cutting the cutout, it may be necessary to...Processing parameters can be changed in order to determine the cutting quality using one and the same cutting edge under different processing parameters.

[0026] Another aspect of the invention relates to a machining machine of the type mentioned at the outset, further comprising: an image acquisition device, preferably a camera, which is preferably aligned with an outer edge of the workpiece to acquire image data of the at least one cutting edge formed in an edge region adjacent to an outer edge of the workpiece by cutting at least one recess, and an evaluation device configured to determine the cutting quality at the cutting edge of the recess. The machining machine has the advantages described above in connection with the method.

[0027] The workpiece is machined by means of a cutting head, preferably a laser cutting head. The cutting head generates a thermal cutting beam, which is directed at the workpiece to perform the cutting operation. For this purpose, the cutting head and the workpiece are moved relative to each other. The workpiece is typically a plate-shaped workpiece, such as a sheet of metal, but it can also be a tubular workpiece. The cutting beam can, in particular, be a laser beam.

[0028] The method described above for determining cut quality can, in principle, be performed on any type of processing machine, regardless of its level of automation. Besides a flatbed laser machine, the processing machine could, for example, be a combined punching / laser machine, a tube cutting machine, etc. Automated cut quality testing allows multiple workpieces to be processed sequentially on a flatbed laser machine without any deviations in the cutting process going undetected and resulting in significant scrap. In addition to quality testing, automated cut quality optimization can also be performed.

[0029] Further advantages of the invention will become apparent from the description and the drawing. Likewise, the features mentioned above and those listed below can be used individually or in any combination. The embodiments shown and described are not to be understood as an exhaustive list, but rather serve as examples for illustrating the invention. The following are shown:

[0030] Fig. 1 shows a schematic representation of an embodiment of a processing machine for cutting a workpiece in the form of a laser processing machine.

[0031] Fig. 2a shows a schematic representation of an edge area of ​​the workpiece when cutting a recess,

[0032] Fig. 2b shows a schematic representation of a top view of the workpiece with a camera to capture a cutting edge of the recess, as well as

[0033] Fig. 2c is a schematic representation analogous to Fig. 2b, in which the workpiece has a further, laterally offset recess.

[0034] In the following description of the drawings, identical reference symbols are used for identical or functionally equivalent components.

[0035] Fig. 1 shows a CCh laser cutting machine 1 for laser cutting with a CO2 laser resonator 2, a laser processing head 4 and a workpiece support 5. A laser beam 6 generated by the laser resonator 2 is guided to the laser processing head 4 by means of a beam guide 3 of (not shown) deflecting mirrors and focused in this and aligned perpendicular to the surface 8a of a workpiece 8 with the help of mirrors (also not shown), i.e. the beam axis (optical axis) of the laser beam 6 runs perpendicular to the workpiece 8.

[0036] For laser cutting, or the cutting process of the workpiece 8, the laser beam 6 is first used to pierce the workpiece 8, i.e., the workpiece 8 is melted or oxidized at a single point, and the resulting molten material is blown out. Subsequently, the laser beam 6 is moved across the workpiece 8, creating a cutting gap 9 through which the laser beam 6 cuts the workpiece 8. Both the piercing and laser cutting processes can be enhanced by the addition of a gas. Oxygen, nitrogen, compressed air, and / or application-specific gases can be used as cutting gases 10. The gas ultimately used depends on the materials being cut and the required quality of the workpiece 8. Any particles and gases produced can be extracted from an extraction chamber 12 using an extraction device 11.A schematically represented programmable numerical control device 13 controls all essential functions of the laser cutting machine 1, for example the movement of the laser processing head 4 when a processing program is executed on it.

[0037] To determine or evaluate the cut quality during laser cutting of workpiece 8, it is necessary to create a cut edge on the workpiece 8. For this purpose, the following procedure is described: First, a recess 15 is cut into the workpiece 8 in an edge region 14 adjacent to an outer edge 8a of the workpiece 8 using the laser beam 6, as shown in Fig. 2a. During the cutting of the recess 15, a cutting slug 16 is separated from the workpiece 4. As can also be seen in Fig. 2a, the cutting slug 16 falls downwards out of the support plane of the workpiece 4 after separation. The workpiece support 5 has a plurality of spaced-apart support ridges between which the cutting slug 16 falls downwards. In this way, a cut edge 17 of the recess 15 is exposed.

[0038] The cutting edge 17 is captured by an image acquisition device 18 in the form of a camera (with a corresponding lens), as can be seen in Fig. 2b. The image acquisition device 18 is aligned with the outer edge 8a of the workpiece 8, so that the recess 15 and thus also the cutting edge 17 lie within the field of view of the image acquisition device 18, indicated by dashed lines in Fig. 2b. It is understood that the entire recess 15 does not necessarily have to be within the field of view; rather, for determining the cutting quality, it may be sufficient if only a portion of the recess 15 or the cutting edge 17 is captured by the image acquisition device 18. In the example shown, the image acquisition device 18 captures image data B of the cutting edge 17, at least in a section of the cutting edge 17 that runs parallel to the outer edge 8a of the workpiece 8.Based on the captured image data B of the cutting edge 17, the cutting quality at the cutting edge 17 is determined by means of an evaluation unit 19, which in the example shown forms part of the control unit 13. For this purpose, the evaluation unit 19 performs image processing as described, for example, in DE 10 2019 209 088 A1.

[0039] The recess 17 is located at position P xThe cut is made approximately in the middle of the outer edge 8a of the workpiece 8 and, in the example shown, has a length in the direction of the outer edge 8a of the workpiece 8 that is on the order of several centimeters. The outer edge 8a of the workpiece 8 runs in the X-direction of an XYZ coordinate system. The edge region 14, in which the recess 17 is cut, extends, in the example shown, from the outer edge 8a of the workpiece 8 in a direction perpendicular to the outer edge 8a, i.e., in the Y-direction, over a width b of no more than 1 cm, in the example shown, no more than 5 mm.

[0040] Before cutting the recess 17, a position Py of the outer edge 8a of the workpiece 8 is detected or probed, for which, for example, a capacitive distance measuring device integrated into the laser cutting machine 1 can be used. Since the image acquisition device 18 is stationary, a distance A between the outer edge 8a of the workpiece 8 and the image acquisition device 18 can be determined in this way. Based on the distance A, a scale is calculated for the image data B of the cutting edge 17 determined by the image acquisition device 18 in order to determine the size of geometric features of the cutting edge 17 as an absolute value.

[0041] The edge region 14 is not intended for cutting the workpiece 8. The nesting of workpiece parts that are cut during the cutting of the workpiece 8 takes place in a machining area 20 located within the edge region 14. In the example shown, the recess 17 extends over almost the entire width b of the edge region 14 and has a depth of approximately 4 mm.

[0042] In the example shown in Fig. 2b, the recess 15 in the edge region 14 of the workpiece 8 is formed before the workpiece 8 is machined in the machining area 20; that is, the recess 15 is cut into the raw sheet metal. Based on the cut quality determined in the manner described above, the numerical control device 13 can, if necessary, adjust the machining parameters(s) to optimize the cut quality.

[0043] It is also possible, as an alternative or additional step to determining the cutting quality before machining the workpiece 8, to interrupt the machining process in order to determine the cutting quality. If a recess 15 has already been cut into the workpiece 8 before machining, it is necessary to cut a further recess 15a into the workpiece for this purpose, as shown in Fig. 2c. Since the recess 15 already has a depth in the Y-direction that corresponds approximately to the width b of the edge region 14, it is not practical in the example shown to cut the further recess 15a overlapping with the recess 15 into the workpiece 8. In the example shown in Fig. 2c, the further recess 15a was therefore cut at a laterally offset position P. X ' to the recess 15 cut into the workpiece 8 so that the two recesses 15, 15a do not overlap.

[0044] To acquire image data B of the further recess 15a using the stationary image acquisition device 18, the workpiece 8 is moved in the X-direction, i.e., in the direction of the outer edge 8a, in the example shown in Fig. 2c. A pallet changer can be used for this purpose, which serves to load and unload the laser processing machine 1 with workpieces 8.

[0045] As can also be seen in Fig. 2c, the cutting process was interrupted after cutting a first workpiece part 21, which remains connected to the rest of the workpiece 8 via a bridge or microjoint. The cutting process was interrupted because an event affecting the cut quality occurred during the cutting of the first workpiece part 21, namely a collision between the nozzle of the laser cutting head 4 and the top surface 8a of the workpiece 8. It is understood that the cutting process can also be interrupted in the event of other potentially affecting the cut quality. It is also possible to interrupt the cutting process at a predetermined point in time to determine or check the cut quality. For example, this could be a point in time when 50% of the processing time for the cutting of the workpiece 8 has been reached.

Claims

Patent claims 1. Method for determining a cutting quality at at least one cutting edge (17, 17a) of a preferably plate-shaped workpiece (8), comprising: Forming at least one cutting edge (17, 17a) on the workpiece (8), preferably by means of a laser beam (6), Acquisition of image data (B) of the at least one cutting edge (17, 17a), and determination of the cutting quality at the at least one cutting edge (17, 17a) based on the acquired image data (B), characterized in that at least one recess (15, 15a) is cut into the workpiece (8) in an edge region (14) of the workpiece (8) which borders an outer edge (8a) of the workpiece (8) and the cutting quality is determined at a cutting edge (17, 17a) of the at least one recess (15, 15a).

2. Method according to claim 1, wherein the edge region (14) extends from the outer edge (8a) of the workpiece (8) by no more than 1 cm, preferably by no more than 5 mm into the workpiece (8).

3. Method according to claim 1 or 2, wherein the image data (B) of the cutting edge (17, 17a) are captured by an image capture device (18), preferably by a camera, which is aligned with the outer edge (8a) of the workpiece (8).

4. Method according to one of the preceding claims, wherein a position (P) is created before the recess (15, 15a) is formed. y ) the outer edge (8a) of the workpiece (8) is detected.

5. Method according to claim 4, wherein a distance (A) between the position (P y) the outer edge (8a) of the workpiece (8) and the image acquisition device (18) is determined and preferably a scale for the image data (B) of the cutting edge (17, 17a) determined by the image acquisition device (18) is calculated on the basis of the distance (A).

6. Method according to one of the preceding claims, wherein the recess (15, 15a) is cut before the workpiece (8) is machined in a machining area (20) provided for cutting.

7. Method according to one of the preceding claims, wherein the workpiece (8) is machined in the machining area (20) provided for cutting and wherein the cutting machining is interrupted in order to cut the recess (15, 15a).

8. Method according to claim 7, wherein the cutting machining of the workpiece (8) is interrupted at a predetermined machining time and / or after the occurrence of an event potentially influencing the cutting quality in order to determine the cutting quality.

9. Method according to one of the preceding claims, wherein several recesses (15, 15a) are provided at the same position (P) for repeatedly determining the cutting quality x ) or at laterally offset positions (P x , P x ) are cut at the outer edge (8a) of the workpiece (8).

10. Method according to claim 9, wherein the image data (B) of cut edges (17, 17a) of at least two recesses (15, 15a) with laterally offset positions (P) are used to capture the image data (B) of cut edges (17, 17a) of at least two recesses (15, 15a). x , P x ) the image acquisition device (18) and / or the workpiece (8) are moved.

11. Processing machine for cutting a workpiece (8), in particular a laser processing machine (1), preferably for carrying out the method according to one of the preceding claims, comprising: a cutting head, in particular a laser cutting head (4), for forming at least one cutting edge (17, 17a) on the workpiece (8), characterized by an image acquisition device (18), preferably a camera, which is preferably directed towards an outer edge (8a) of the workpiece (8) in order to acquire image data (B) of the at least one cutting edge (17, 17a) which is formed in an edge region (14) adjacent to the outer edge (8a) of the workpiece (8). Cutting of at least one recess (15, 15a) is formed, as well as an evaluation device (19) which is designed to determine the cutting quality at the cutting edge (17, 17a) of the recess (15, 15a).

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