Method and apparatus for laser cutting a workpiece
Patent Information
- Application Number
- PCT/EP2026/054182
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2025-02-28
- Filing Date
- 2026-02-17
- Publication Date
- 2026-09-03
Smart Images
Figure EP2026054182_03092026_PF_FP_ABST
Abstract
Description
[0001] 2024P00051WG
[0002] Applicant:
[0003] TRUMPF Werkzeugmaschinen SE + Co. KG
[0004] Johann-Maus-Str. 2
[0005] 71254 Ditzingen
[0006] Method and device for laser cutting a workpiece
[0007] The present invention relates to a method for machining a metallic, in particular plate-shaped, workpiece by means of a laser beam emerging from a cutting nozzle of a laser processing head, comprising: machining the workpiece along a predetermined cutting contour to separate a workpiece part from a remaining part, checking whether the workpiece part has been completely separated from the remaining part during the machining process, determining that the workpiece part has not been completely separated from the remaining part, and machining the workpiece again by cutting.The invention also relates to a machine for machining a workpiece by cutting, comprising: a machining head for aligning a laser beam emerging from a cutting nozzle onto the workpiece, at least one movement device for generating a relative movement between the machining head and the workpiece, a control device for controlling the at least one movement device for separating a workpiece part from a remaining part by machining the workpiece by cutting along a predetermined cutting contour, as well as an evaluation device configured to check whether the workpiece part has been completely separated from the remaining part during machining, and a distance measuring device for determining the distance between the cutting nozzle and the workpiece part.
[0008] The cutting and machining of metallic workpieces, e.g., sheet metal, can be carried out using thermal or mechanical methods. In thermal machining using a processing beam, for example, a laser beam, a workpiece part is completely separated from a residual part along a cutting contour. The residual part can be a remnant of the workpiece or a remaining lattice of the workpiece, from which the 2024P00051WG
[0009] The workpiece part (good part) is cut free. Alternatively, the cut-free part can be a remnant (waste part), for example, a cutting slug that may be cut free from a good part. The cutting contour used for the free cutting can be a closed cutting contour, but this is not mandatory.
[0010] For example, if an edge of the part to be separated forms an outer edge of the workpiece, the part can be cut free from the remaining grid without cutting a closed cutting contour.
[0011] During cutting processes, especially laser cutting, it is possible that workpiece parts and / or remnants are not completely separated from the remaining workpiece or grid. After separation, they may tilt and become jammed within the remaining workpiece or grid, preventing them from falling out of the workpiece or the workpiece plane. These remaining workpiece parts create an obstruction that interferes with further processing. Unused workpiece parts can damage the laser cutting machine, for example, through collisions between the cutting nozzle or moving support carriages with tilted workpiece parts, or damage automation components. Furthermore, the workpiece may be unintentionally moved or lifted by the interlocking mechanism, compromising the accuracy of the laser cut.
[0012] From DE 102010039525 A1, it is known to scan the workpiece with a distance sensor during and / or after the cutting operation to create a breakthrough, in order to check whether the workpiece has been completely cut through in the area of the breakthrough to be created. If the test result is negative, the cutting operation can be interrupted or the process parameters can be modified.
[0013] Alternatively, DE102011 004117 A1 describes a method for checking whether the workpiece part has been completely separated from the rest of the workpiece during cutting by shining a laser beam pulse onto the workpiece part and detecting the radiation generated by the interaction between the laser beam and the workpiece part. If the workpiece part has not been completely separated, the cutting process can be aborted or resumed completely or only for a portion of the contour to be cut.
[0014] However, during repeated cutting along the specified cutting contour, damage or undesirable discoloration can occur at the edge of the workpiece due to the edge area of the reapplied laser beam or due to slag formation. Movement of the remaining workpiece within the cutting contour forming the cutting gap, caused by the gas pressure of the process gas, can also negatively affect the quality of the resulting cut edges of the workpiece.
[0015] To solve this problem, see DE 102016220459 B3 and in the
[0016] JP 2018 183793 A proposes a laser cutting process in which the workpiece is recut along a further cutting contour laterally offset from the first cutting contour if the workpiece was not completely separated from the rest of the part during the initial cutting process. By appropriately selecting the amount of the lateral offset, damage to the edge of the good part by the laser beam or slag formed during the recutting process is prevented, as are welds and rounding of the circumferential edge of the good part. However, it has been shown that even with the laterally offset recutting, discoloration of the cut edge due to oxidation cannot always be avoided, and that the discoloration can become so severe that the workpiece is scrap.
[0017] Object of the invention
[0018] The present invention is based on the objective of providing an improved method and a machine for the cutting processing of a workpiece using a laser beam, which ensures process reliability in the automated removal of interfering contours that occur when a workpiece part is incompletely separated from a remaining part, and further improves the cut edge uniformity.
[0019] This problem is solved by a method of the type mentioned at the outset, which is characterized by: Repeated cutting of the workpiece along the same or a laterally offset cutting contour, provided that the preceding inspection reveals that the workpiece part has not been completely separated from the remaining part, wherein the cutting contour does not extend completely along the entire contour of the workpiece part during the repeat cutting: During the repeat cutting process, a signal for the distance between the cutting nozzle and the workpiece part is measured according to the invention by means of a capacitive distance measuring device, and the laser beam is switched off as soon as the measured distance measurement signal or a signal derived therefrom exceeds or falls below a predetermined limit value.
[0020] According to the invention, it was discovered that the deterioration of the cut edge quality on the remaining part during subsequent cutting is primarily caused by the laser beam still acting on the cut edge even though the workpiece part has already been separated from the remaining part and has fallen out of it under the influence of gravity. The laser beam, acting along the further contour, leads to undesirable discoloration or rounding of the cut edge, as oxygen from the ambient air can reach the hot cut edge from all sides. This is significantly reduced if the release of the workpiece part from the remaining part during the subsequent cutting process is detected and the laser beam is immediately switched off. The method according to the invention can therefore be used particularly advantageously when the cut-out workpiece part is a scrap piece (cutting slug) and the remaining part is the good part.However, the inventive method is also advantageous in the reverse case, as it prevents the laser beam from striking the workpiece part slipping or falling from the remaining part after the workpiece part (good part) has been freed, thus preventing damage. In the inventive method, a suitable sensor or detector is used to first check whether post-processing is required after the cutting operation to completely separate the workpiece part from the remaining part. If this is the case, a further cutting operation is performed along the same or a laterally offset cutting contour to completely separate the workpiece part from the remaining part and thereby prevent the incompletely cut workpiece part from interfering with further cutting operations.When re-cutting, the cutting contour is either identical to the specified cutting contour or runs parallel to the specified cutting contour with a lateral offset either towards the workpiece part or towards the test part, depending on whether the workpiece part or the remaining part represents the desired good part.
[0021] By precisely switching off the laser beam as soon as the falling of the workpiece part is detected by the distance measuring device during the renewed cutting process, the remaining cut edge of the workpiece part and the remaining part are no longer affected by the laser beam. Oxidation and cut edge discoloration are prevented. Preferably, the laser beam is switched off within a maximum of 50 ms, more preferably within a maximum of 10 ms, after the release of the workpiece part has been detected by the distance measuring device, in order to prevent visible starting marks on the cut edge at the point where the workpiece part is released.
[0022] During repeated cutting operations, the distance between the laser processing head and the workpiece surface is kept constant, and the distance measuring device measures a signal for the distance between the cutting nozzle and the workpiece. The distance measuring device is designed for capacitive detection of the distance between the workpiece and the surface.
[0023] The workpiece (part) and the cutting nozzle are designed as a capacitor that is subjected to an alternating magnetic field. Changing the distance alters the capacitance of this capacitor and thus the resonant frequency of the (LC) resonant circuit of which the described capacitor is a part. From the frequency of the resonant circuit, the distance between the cutting nozzle and the workpiece (part) can be determined using a previously recorded calibration curve, thus generating a distance measurement signal. This distance measurement signal can be used directly to determine when the workpiece part has been released: If the distance measurement signal increases, exceeding a predefined threshold indicates that the workpiece part has fallen out of the remaining workpiece. A decreasing distance measurement signal means that the workpiece part tilted within the remaining workpiece as it was released.In this case, the complete separation of the workpiece part from the remaining part is detected by falling below a limit value for the distance measurement signal.
[0024] A signal derived (mathematically) from the distance measurement signal can also be used to detect the release of the workpiece part, for example, an inverse of it that correlates with the area of the workpiece part under the sensor. This derived signal, like the distance measurement signal, can be compared with predefined limit values.
[0025] In one embodiment of the inventive method, the laser processing head, with the laser beam switched off, can be moved along the predetermined cutting contour or along a further cutting contour laterally offset towards the workpiece before the next cutting operation. This allows the capacitive distance measuring device to measure the distance between the cutting nozzle and the workpiece, thereby recording and storing a height profile of the workpiece along its outer contour. During the next cutting operation, the distance between the cutting nozzle and the previously determined height profile, measured by the capacitive distance measuring device, can then be compared. In this embodiment, the laser beam is only switched off if the difference between the measured distance (A) and the height profile exceeds or falls below a limit value.
[0026] In this process variant, the height profile of a workpiece section that may have tilted in the remaining part is recorded before the next cutting operation. This step is particularly useful if the inner workpiece section 2024P00051WQ
[0027] After the first cut, the workpiece is wedged at a very steep angle within the remaining workpiece. Recording the height profile can also be used to check whether the workpiece part has fallen or is still wedged within the remaining piece. When recutting, the information from the height profile helps to distinguish whether the workpiece part is actually tilting or falling out of the remaining piece, or whether the change in the capacitive distance signal is caused by the angled position of the workpiece part.
[0028] In many cases, the workpiece being recut separates from the rest of the workpiece after the first third of its contour has been cut. The contour of the workpiece then does not need to be traced to its end; instead, the laser processing head can be positioned for the next workpiece immediately after the laser beam is switched off. Besides improving quality, this saves time and thus increases the machine's productivity.
[0029] In the inventive method, achieving good cut edge quality does not necessarily require performing the recutting process along a laterally offset cutting contour. Recutting along the same cutting contour can be advantageous because, when recutting the same contour, the cutting gap is not widened and the flow conditions for the cutting gas change less significantly. Therefore, processing parameters such as laser power, gas pressure, and cutting speed do not need to be changed, which has a beneficial effect on the process reliability of the cutting process.
[0030] The subsequent cutting contour can alternatively be offset laterally towards the workpiece part or the remaining part, depending on whether the workpiece part or the remaining part is to be produced as the good part. This allows the distance of the laser beam to the good part to be increased. By appropriately selecting the amount of the lateral offset, it can be prevented that the circumferential edge of the good part is damaged by the laser beam or by slag during subsequent cutting operations, or that welding or rounding of the circumferential edge of the good part occurs. Preferably, the subsequent cutting contour is offset laterally from the predetermined cutting contour by an amount that is smaller than the cutting gap width of the predetermined cutting contour. If the process gas pressure used during the cutting operation is kept constant, i.e.,Even when used for subsequent cutting operations, typically only a certain degree of offset from the predefined cutting contour is reliably achieved. If the subsequent cutting contour is offset by a distance or amount corresponding to the cutting gap width of the predefined cutting contour, the resulting doubling of the cutting gap width can cause disturbances in cutting quality, potentially leading to process interruption or miscuts. Therefore, the cutting gap width of the predefined cutting contour represents an upper limit for the offset of the subsequent cutting contour.
[0031] In a further embodiment of the inventive method, the distance between the machining head and the workpiece, and thus the distance between the cutting nozzle and the workpiece surface, is increased during the subsequent cutting operation. It has proven advantageous to increase the distance between the cutting nozzle and the workpiece by at least 1.5 mm, preferably at least 2 mm, compared to the first cutting operation of the workpiece portion, as this improves the robustness of the subsequent cutting operation and prevents a collision of the cutting nozzle with a potentially slightly tilted workpiece portion. Increasing the distance is particularly useful in cutting processes where the cutting distance between the machining head and the workpiece is small, as is the case, for example, with cutting processes using a bypass nozzle, where the cutting distance may be reduced.The distance between the machining head or cutting gas nozzle and the workpiece during the subsequent cutting operation is only 0.4 mm. In contrast, the distance between the machining head or the cutting gas nozzle and the workpiece during the subsequent cutting operation can be comparatively large. However, the distance of the cutting nozzle during the subsequent cutting operation should not exceed 35 mm, preferably 25 mm, to ensure sufficiently good signal quality from the distance measuring device and to avoid impairing the effectiveness of the cutting gas. In a further development, increasing the distance involves shifting the focus position of the machining jet towards the workpiece in order to use the same focus position during the subsequent cutting operation as during the initial cutting operation. Typically, for this purpose, the focus position is shifted towards the workpiece by a distance equal to the increase in the distance between the machining head and the workpiece.By maintaining the focus position, a cutting gap can be created during subsequent cutting operations, the width of which essentially corresponds to the width of the cutting gap during the initial cutting operation. To shift the focus position towards the workpiece—without changing the distance between the machining head and the workpiece—a focusing device located in the machining head, such as a focusing lens, can be moved relative to the housing of the machining head.
[0032] In another variant, checking whether the workpiece part has been separated from the remaining part comprises the following steps: shining a preferably pulsed processing beam onto the workpiece at a test position within the specified cutting contour, detecting radiation generated by an interaction between the processing beam and the workpiece, and evaluating the detected radiation to check whether the workpiece part was completely separated from the remaining part during the cutting process. The processing beam used for the test can, in particular, be a laser beam. The method of checking whether the workpiece part has been separated from the remaining part essentially corresponds to the method described in DE 102016 220459 B3 cited above.
[0033] For testing, the machining beam is directed at the workpiece at a test position within the predefined cutting contour, i.e., within the cut-out workpiece section. The radiation generated during this interaction is then used to detect whether the workpiece section has been completely separated from the rest of the workpiece. If the workpiece section is completely separated from the rest of the workpiece, the rest is typically ejected downwards from the machining plane. This means that the machining beam directed at the workpiece at the test position shines into a void formed within the cutting contour, resulting in virtually no interaction between the machining beam and the workpiece and therefore no or only an extremely low radiation intensity being detected.During the irradiation of the processing beam, its intensity can be increased at the test position, and the irradiation can be stopped as soon as it is determined during testing that the workpiece part has not been completely separated from the rest of the workpiece during the cutting process. This ensures, on the one hand, sufficient interaction between the processing beam and the workpiece during irradiation, thus reliably detecting any incomplete separation. On the other hand, the irradiation is stopped as soon as it is detected that the workpiece part has not been completely separated, thereby preventing marking or penetration of the workpiece part by the processing beam.
[0034] It is understood that if the inspection reveals that the workpiece part has been completely separated from the remaining part, the machining of the workpiece will be continued with a new workpiece part.
[0035] After re-cutting a workpiece segment that is not completely separated from the rest of the workpiece, it can be checked again whether the workpiece segment has been completely separated. If the re-check is performed by directing the machining beam onto the workpiece, it can be carried out at the same inspection position as the previous check, but it is also possible to perform the re-check at a different inspection position. If the re-check reveals that the workpiece segment is still not separated from the rest of the workpiece, a further re-cutting step, i.e., another cutting operation, can be performed. This can be done, in particular, along a laterally offset cutting contour, especially if the initial re-cutting operation was performed along the specified cutting contour. This further cutting operation can then be followed by another inspection step, and so on.To prevent an endless loop, an adjustable tolerance threshold can be set, corresponding to a defined number of repetitions of (repeated) cutting machining steps. If the tolerance threshold is exceeded, the machine switches to a pause mode, i.e., the cutting machining of the workpiece is interrupted. Additionally or alternatively, further actions can be performed, such as an audible warning, a message, a real-time image of the machine's machining area, and / or a notification sent to a machine operator's communication device. These further actions can occur upon reaching the first iteration stage, the last iteration stage (i.e., upon exceeding the tolerance threshold), or at any intermediate iteration stage.
[0036] Another aspect of the invention relates to a machine of the type mentioned at the outset for cutting a workpiece, in which the control device is designed or programmed to control at least one movement device, to carry out a further cutting operation on the workpiece along the predetermined cutting contour or along a further cutting contour offset laterally to the predetermined cutting contour, provided that the evaluation device determines during testing that the workpiece part has not been completely separated from the remaining part, and to switch off the laser beam during the further cutting operation as soon as the distance measured by the distance measuring device between the laser cutting nozzle and the workpiece part or a signal derived therefrom exceeds or falls below a limit value.
[0037] The motion device controlled by the control unit can be a motion device for moving the processing head, typically a laser cutting head. Alternatively or additionally, the control unit can control a motion device designed to move the workpiece.
[0038] In a further embodiment, the machine comprises a detector for detecting radiation generated by an interaction between the processing beam and the workpiece, which arises when the preferably pulsed processing beam is directed onto the workpiece at a test position within the predetermined cutting contour, wherein the evaluation device is designed to check, on the basis of the detected radiation, whether the workpiece part was completely separated from the remaining part during the cutting process.
[0039] The control unit is designed to execute an NC (numerical control) machining program in which the cutting contours of the parts to be cut are specified for a workpiece. These cutting contours are determined by communication between the control unit and other machine components, such as the beam source, the distance measuring device, the human-machine interface (HMI), and the programmable logic controller (PLC), using cutting parameters defined for each specified contour. After cutting a part or a cutting contour, the NC machining program may include a waiting period to allow the workpiece to cool before cutting the next part. The test described above can be performed during this waiting period, which may already be scheduled.
[0040] In its simplest form, the detector can be a photodiode that detects or measures the intensity of the radiation reflected back from the workpiece, typically process radiation generated by the interaction of the processing beam with the workpiece, thermal radiation, and / or reflected or scattered processing radiation, especially laser radiation. The detector, e.g., in the form of a photodiode, can be positioned, for example, in the beam source for generating the processing beam, such as a solid-state laser.
[0041] In particular, the detection of laser radiation reflected back from the workpiece has proven advantageous, since in this case the processing beam can be directed with a significantly lower power compared to the detection of process luminescence or thermal radiation, thus preventing damage to the cut-out part during inspection. The latter is especially beneficial when the cut-out part is a good part. Further advantages of the invention will become apparent from the description and the drawings. 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.
[0042] They show:
[0043] Fig. 1 shows a schematic representation of an embodiment of a machine for cutting and machining a workpiece in the form of a laser processing machine.
[0044] Fig. 2 shows a schematic representation of a cutting gap formed in the workpiece during cutting machining,
[0045] Fig. 3 shows a representation of a predetermined cutting contour formed in the workpiece during cutting machining for separating a workpiece part from a remaining part.
[0046] Fig. 4 shows a representation of the specified cutting contour of Fig. 3 as well as another cutting contour that is offset from the specified cutting contour,
[0047] Fig. 5 shows a schematic representation of a cutting nozzle with a distance measuring device, and
[0048] Figs. 6 and 7 show the measured distance between the cutting nozzle and the workpiece during the process. In the following description of the drawings, identical reference numerals are used for identical or functionally equivalent components.
[0049] Fig. 1 shows an exemplary setup of a machine 1 for laser cutting a plate-shaped workpiece 2 (shown with dashed lines) using a laser beam 3. During processing, the workpiece 2 rests on two workpiece support surfaces 4, 5, which in the example shown form the tops of two workpiece tables and define a processing plane E (XY plane of an XYZ coordinate system) for supporting the workpiece 2.
[0050] By means of a conventional movement and holding device 7, which has a drive and clamping devices 8 in the form of clamping jaws for holding the workpiece 2, the workpiece 2 can be moved in a controlled manner on the workpiece support surfaces 4, 5 in a first direction of movement X (hereinafter: X-direction) and moved to a predetermined workpiece position Xw.
[0051] A gap 6 is formed between the two workpiece support surfaces 4, 5. This gap extends in a second direction (hereinafter referred to as the Y-direction) over the entire travel path of a processing head in the form of a laser cutting head 9, which aligns and focuses the laser beam 3 onto the workpiece 2. The laser cutting head 9 can be moved within the gap 6 in the Y-direction by means of a driven carriage 11, which serves as a motion device and is guided on a stationary portal 10. In the example shown, the laser cutting head 9 can also be moved within the gap 6 in the X-direction and can be moved in the X-direction by means of an additional motion device 12 attached to the carriage 11, for example in the form of a linear drive.With the aid of the successive motion devices 11, 12, the laser cutting head 9 can be positioned at a desired cutting head position Xs, Ys within the gap 6 in both the X and Y directions. Two support carriages 13a, 13b are arranged within the gap 6, each extending over the entire width b of the gap 6 and being controlled and independently movable within the gap 6 in the Y direction. Additionally, in the example shown, the laser cutting head 9 can be moved along a third direction of movement Z (direction of gravity, hereinafter: Z-direction) by means of a further motion device 12a, which is based on the first motion device in the form of the carriage 11, in order to adjust the distance between a cutting nozzle 9a of the laser cutting head 9 and the surface of the workpiece 2, or to position the laser cutting head 9 at a desired cutting head position Zs or Ys.to position at a desired distance in the Z direction relative to the workpiece support plane (machining plane) E.
[0052] The support slides 13a, 13b can each be moved to a desired position YUA, YUB in the Y-direction within the gap 6 in order to support the workpiece 2 and workpiece parts 17 to be cut free from the workpiece 2 or cut during machining by means of a support surface 14a, 14b attached to the respective support slide 13a, 13b. In the case shown, the support surface 14a, 14b of each support slide 13a, 13b is flush with the workpiece support surfaces 4, 5 in the Z-direction, i.e., the support surfaces 14a, 14b are located in the support plane E for the workpiece 2.
[0053] To control the cutting process, machine 1 has a control unit 15, which coordinates the movements of the workpiece 2, the laser cutting head 9, and the support slides 13a, 13b in order to set a desired workpiece position Xw, a desired cutting head position Xs, Ys, Zs, and a desired position YUA, YUB of the support slides 13a, 13b, in order to enable the cutting of a predefined cutting contour 18a and, if necessary, to support the workpiece in the area of the gap 6. The movement of the first support slide 13a can be synchronous with or independent of the second support slide 13b. The control unit 15 also serves to control a beam source 31 in the form of a laser beam source.
[0054] In the example shown in Fig. 1, a covering element 16a, 16b is attached to each of the outer edges of the support surfaces 14a, 14b, which extend in the X direction and face away from each other, to cover the gap 6 outside the cutting area formed between the support slides 13a, 13b. The covering elements 16a, 16b extend over the entire width b of the gap 6 and are moved along with the support slides 13a, 13b in the Y direction.
[0055] When cutting away a workpiece part 17 from workpiece 2, more precisely from a remaining part 19 of workpiece 2, the last connection between the workpiece part 17 and the remaining part 19 is severed at a cutting position FP. For this purpose, the two support slides 13a, 13b can be moved closer together so that there is only a very small gap or no gap at all between them in the Y-direction.
[0056] Fig. 2 shows a detail of workpiece 2 from Fig. 1 in a sectional view, in which a cutting gap 26 with a cutting gap width B is shown, which forms along the predetermined cutting contour 18a in the workpiece 2. The cutting gap width B of the cutting gap 26 is determined by process parameters such as cutting gas pressure, feed rate, laser power, etc. Provided that the cutting process shown in Fig. 1 is carried out correctly, the workpiece part 17 is completely separated from the remaining part (remaining grid) 19 at the clearance position FP along the predetermined cutting contour 18a. The workpiece part 17 is subsequently removed from the workpiece plane E, for example by moving the two support slides 13a, 13b in opposite directions in the gap 6, so that the workpiece part 17 is no longer supported and falls downwards into the gap 6, where the workpiece part 17 can be ejected from the machine 1 by means of devices not described in detail.
[0057] To verify whether the workpiece part 17 was actually separated from the remaining part 19 during the cutting process, a test or test step is carried out, as described in DE 102016 220459 B3 cited above, which is illustrated in more detail below with reference to Fig. 3. Fig. 3 shows a top view of the workpiece 2, from which a circular workpiece part 17 is cut out along the cutting contour 18a. To verify whether the workpiece part 17 was completely separated from the remaining part 19 and thus from the 2024P00051WQ
[0058] Once the processing plane E has fallen downwards, the laser cutting head 9 is positioned by means of the two motion devices 11, 12 and / or the workpiece 2 is positioned by means of the motion and holding device 7 such that the laser beam 3 used for processing is oriented essentially perpendicular to the surface of the workpiece 2 and shines onto the workpiece part 17 at a test position 21. If a part that has not been completely cut out is located at the test position 21, for example the workpiece part 17 shown in Fig. 3, the laser beam 3 interacts with the workpiece part 17, thereby generating radiation 27, which is indicated in Fig. 3.
[0059] The radiation 27 generated during the interaction with the laser beam 3, which may consist of process luminescence, thermal radiation due to the heating of the workpiece 2, and / or back-reflected laser radiation, is detected by a detector 22 (see Fig. 1), for example, in the form of a photodiode. If the workpiece part 17 has been completely cut away, the detector 22 will detect no or only a negligible intensity of the radiation 27 generated during the interaction. An evaluation unit 28 (see Fig. 1) uses the detected radiation 27 to check whether the workpiece part 17 has fallen downwards out of the workpiece plane E. For this check, the intensity of the detected radiation 27 can, for example, be compared with an intensity threshold value.If the intensity of the detected radiation 27 is below the intensity threshold, it is assumed that the part 17 has fallen downwards from the workpiece plane E, so that practically no interaction occurs between the laser beam 3 and the part 17 at the test position 21.
[0060] If the inspection reveals that the workpiece part 17 has not been completely separated from the remaining part 19, a second cutting operation is performed. As can be seen in Fig. 4 and Fig. 2, the second cutting operation can either be performed along the same cutting contour 18a as in the first machining step, meaning the cutting contours can be identical for both the initial and subsequent cutting operations. Alternatively, the second cutting operation can be performed along a further cutting contour 18b, which runs parallel to the cutting contour 18a and is offset laterally to the predetermined cutting contour 18a, specifically by a constant amount V in the direction of the remaining part 19, since the cut-out workpiece part 17 is a good part.If, on the other hand, the workpiece part 17 represents a waste part (“cutting slug”), the further cutting contour 18b is offset laterally to the specified cutting contour 18a in the direction of the workpiece part 17.
[0061] The offset V of the subsequent cutting contour 18b is selected such that the processing beam 3 striking the workpiece 2 for cutting the subsequent cutting contour 18b does not strike the edge 25 of the workpiece part 17 (good part) or only strikes it at the outer edge of the intensity I distribution (Gaussian profile) shown in Fig. 2, so that the edge 25 of the workpiece part 17 is not damaged by the laser beam 3 during the subsequent cutting. The offset V can be, in particular, more than approximately 2% or more than 5% of the cutting gap width B of the predetermined cutting contour 18a and is typically selected to be less than the cutting gap width B of the cutting gap 26 along the predetermined cutting contour 18a.
[0062] As can be seen from Fig. 4, the further cutting contour 18b does not extend over the entire length, but only along a section 29 of the predetermined cutting contour 18a. At the end of section 29, the capacitive distance measuring device 20 detected that the distance between the cutting nozzle and the workpiece part fell below or exceeded a predetermined limit value and the laser beam 3 was switched off immediately, within a maximum of 50 ms, in particular within 10 ms.
[0063] The distance measuring device 20 is shown schematically in Fig. 5. The distance measuring device 20 generates a potential difference between the metallic nozzle body of the cutting nozzle 9a and the also metallic workpiece 2 or workpiece part 17, so that an electric field E is formed between the two, the field lines of which are sketched in Fig. 5. Depending on the distance A between the cutting nozzle 9a and the workpiece part 17, the position of the field lines E changes and thus the capacitance between the workpiece part 17 and the cutting nozzle 9a changes. The workpiece 2 or workpiece part 17 and the cutting gas nozzle 9a constitute a capacitor which is subjected to an alternating field by means of a voltage source of the distance measuring device 20 and whose capacitance varies depending on the distance.The capacitor thus formed is part of an (LC) resonant circuit whose distance-dependent oscillation frequency is detected by the distance measuring device 20 in order to relate the measured frequency to a distance A between the laser cutting nozzle 9a and the workpiece 2 or the workpiece part 17, based on a previously determined characteristic curve. When the workpiece part 17 is released and falls, this is detected by the distance measuring device 20 by a change in the oscillation frequency.
[0064] During the subsequent cutting process, the cutting nozzle 9a is held at a constant distance from the top of the workpiece 2, and a distance measurement signal is detected by the distance measuring device 20. The distance measurement signal is shown in Figures 6 and 7 over the course of the process. In a verification device, which can be part of the distance measuring device 20 or the control device 15 (control computer) of the laser cutting machine 1, the distance measurement signal determined by the distance measuring device 20 is compared with a limit value G1, G2. If the distance measurement signal determined by the distance measuring device 20 increases abruptly during the subsequent cutting process, as shown in Figure 6, it can be concluded that the workpiece part 17 has been completely separated from the remaining part 19 and has tipped or fallen out of the remaining part 19.As soon as the distance measurement signal exceeds a limit value G1, the laser beam 3 is switched off by the distance measuring device 20 or the control unit 15. This prevents discoloration or slag adhesion to the remaining cut edge 25 when the cutting contour 18a or 18b is subsequently traversed. If the distance measurement signal determined by the distance measuring device 20 drops abruptly during the next cutting step, as shown in Fig. 7, this indicates that the workpiece part 17 has been completely separated from the remaining part 19 and has tilted towards the cutting nozzle 9a. As soon as the distance measurement signal falls below a limit value G2, the laser beam 3 is switched off by the distance measuring device 20 or the control unit 15, thus preventing further damage.
[0065] that the laser beam 3 acts on the tilted workpiece part 17 and thereby damages it.
[0066] Instead of the distance measurement signal, a derived signal can also be used to detect the release of the workpiece part 17, for example, an inverse of the distance measurement signal that correlates with the area of the workpiece part 17 under the sensor, i.e., the cutting nozzle 9a. This derived signal, like the distance measurement signal, can be compared with predefined limit values.
[0067] The distance measuring device 20 can also be used to determine a height profile of a workpiece part 17 tilted in the remaining part 19 before the next cutting operation. For this purpose, the laser processing head 9, with the laser beam switched off, is moved along the predetermined cutting contour 18a or along a further cutting contour laterally offset towards the workpiece part 17 before the next cutting operation. The capacitive distance measuring device measures the distance A between the cutting nozzle 9a and the workpiece part 17, thus recording and storing a height profile of the workpiece part 17 along its outer contour. During the next cutting operation, the distance A between the cutting nozzle 9a and the workpiece part, measured by the capacitive distance measuring device 20, is then compared with the previously determined distance measurement at the same point on the height profile.If the difference in the distance measurements exceeds a predetermined limit, the laser beam 3 is switched off.
[0068] After the second cutting operation, a further check can be performed to determine whether workpiece part 17 has been completely separated from the remaining part 19. If the second check reveals that part 17, 19 has not been completely cut free, another cutting operation can be performed, followed by a further inspection step. It is understood that, to prevent an endless loop, a termination criterion should be provided so that machine 1 pauses after a predetermined number of repetitions of the cutting operation and inspection. 2024P00051WQ
[0069] During subsequent cutting operations, the distance A between the laser cutting head 9 and the workpiece 2 can be increased to improve the robustness and process reliability of the cutting process. This has proven particularly advantageous in cutting processes using a bypass nozzle, where the distance A between the laser cutting head 9 or nozzle 9a and the workpiece 2 is very small, for example, only about 0.4 mm. For subsequent cutting operations, the distance A can be increased to, for example, 4 mm.
[0070] To maintain the focus position of the laser beam 3 relative to the workpiece 2 despite the increased distance A, the focus position is shifted towards the workpiece 2 as the distance A is increased. For this purpose, a focusing lens can be moved within the laser cutting head 9, for example. This ensures that the subsequent cutting operation is performed with essentially the same kerf width B as the initial cutting operation.
[0071] It is understood that the above-described methods for checking the cutting process, although described in connection with a laser cutting machine 1, can also be carried out on other machine tools, for example, on machines that combine a punching function with a laser cutting function. 2024P00051WQ
[0072] List of reference signs
[0073] 1 laser cutting machine
[0074] 2 (Remaining) workpiece
[0075] 3 Laser beam
[0076] 4, 5 workpiece support surfaces
[0077] 6 columns
[0078] 7 Movement and holding device
[0079] 8 Clamping device
[0080] 9 Laser cutting head
[0081] 9a Cutting nozzle
[0082] 10 Portal
[0083] 11 sleds
[0084] 12,12a Movement facilities
[0085] 13a, 13b Support sled
[0086] 14a, 14b Support surfaces
[0087] 15 Control unit
[0088] 17 workpiece part
[0089] 16a, 16b Covering elements
[0090] 18a, 18b cutting contour, further cutting contour 19 remaining part
[0091] 20 Distance measuring device
[0092] 21 test position
[0093] 22 Detector
[0094] 25 Cutting edge
[0095] 26 cutting gap
[0096] 27 Radiation
[0097] 28 Evaluation unit
[0098] 29 Contour section
[0099] 31 Laser beam source
Claims
- 23 - 2024P00051WO Claims 1. Method for cutting and machining a particularly plate-shaped, metallic workpiece (2) by means of a laser beam (3) emerging from a cutting nozzle (9a) of a laser processing head (9), comprising: a) Cutting machining of the workpiece (2) along a predetermined cutting contour (18a) to separate a workpiece part (17) from a residual part (19), as well as b) Check whether the workpiece part (17) was completely separated from the remaining part (19) during the cutting process, c) Determine that the workpiece part (17) has not been completely separated from the remaining part (19), d) re-cutting the workpiece (2) along the specified cutting contour (18a) or along a laterally offset further cutting contour (18b), characterized in that during the repeated cutting process, a signal for the distance (A) between the cutting nozzle (9a) and the workpiece part (17) is measured by means of a capacitive distance measuring device (20) and the laser beam (3) is switched off as soon as the distance measurement signal or a signal derived therefrom exceeds or falls below a predetermined limit value.
2. Method according to claim 1, wherein the laser beam is switched off within a maximum of 50 ms, in particular within 10 ms, as soon as the distance measurement signal or the derived signal exceeds or falls below the specified limit value.
3. Method according to claim one of the preceding claims, wherein - the laser processing head (9) with the laser beam (3) switched off is moved along the specified cutting contour (18a) or along a further cutting contour (18b) laterally offset towards the workpiece part (17) before the next cutting process and the distance (A) between the cutting nozzle (9a) and the workpiece part (17) is measured by means of the capacitive distance measuring device (20) and a height profile is thus recorded, - during the renewed cutting process, the distance (A) between the cutting nozzle (9a) and the workpiece part (17) is measured using the capacitive distance measuring device (20) and compared with the previously determined height profile, and - the laser beam (3) is switched off as soon as the difference between the measured distance (A) and the height profile exceeds or falls below a limit value.
4. Method according to one of the preceding claims, wherein the further cutting contour (18b) is laterally offset from the predetermined cutting contour (18a) by an amount (V) which is smaller than a cutting gap width (B) of the predetermined cutting contour (18a).
5. Method according to one of the preceding claims, wherein during the subsequent cutting operation the distance (A) of the nozzle to the surface of the workpiece (2) is at least 1.5 mm, preferably at least 2 mm greater than during the first cutting operation.
6. Method according to claim 5, wherein when increasing the distance (A) the focus position (ZF) of the laser beam (3) is shifted towards the workpiece (2) in order to use the same focus position (ZF) during the subsequent cutting operation as during the cutting operation.
7. Method according to one of the preceding claims, wherein the distance of the nozzle to the surface of the workpiece (2) during the re-cutting operation is a maximum of 35 mm, in particular a maximum of 25 mm.
8. A method according to any of the preceding claims, wherein checking whether the workpiece part (17) has been separated from the remaining part (19) comprises the following steps: Direction of a preferably pulsed processing beam (3) onto the workpiece (2) at a test position (21) within the specified cutting contour (18a), - Detecting radiation (27) generated by an interaction between the processing beam (3) and the workpiece (2), as well as - Evaluating the detected radiation (27) to check whether the workpiece part (17) was completely separated from the remaining part (19) during cutting processing.
9. Machine (1) for cutting and machining a particularly plate-shaped, metallic workpiece (2), comprising: - a processing head (9) for aligning a laser beam (3) emerging from a cutting nozzle (9a) onto the workpiece (2), - at least one motion device (7, 11, 12) for generating a relative motion between the machining head (9) and the workpiece (2), as well as - a control device (15) for controlling the at least one motion device (7, 11, 12) for separating a workpiece part (17) from a residual part (19) by cutting the workpiece (2) along a predetermined cutting contour (18a), - an evaluation device (28) configured to check whether the workpiece part (17) has been completely separated from the remaining part (19) during cutting, wherein the control device (15) is configured to control at least one movement device (7, 11, 12) to perform a further cutting operation on the workpiece (2) along the specified cutting contour (18a) or along a further cutting contour (18b) offset laterally to the specified cutting contour (18b), provided that the evaluation device (28) determines during the check that the workpiece part (17) has not been completely separated from the remaining part (19), - a distance measuring device (20) configured to measure a signal for the distance (A) between the cutting nozzle (9a) and the workpiece part (17), characterized in that the control device (15) is designed to switch off the laser beam (3) during renewed cutting processing,- 26 - 2024P00051WO as soon as the distance measurement signal measured by the distance measuring device (20) or a signal derived therefrom exceeds or falls below a limit value.
10. Machine according to claim 9, further comprising: a detector (22) for detecting radiation (27) generated by an interaction between the processing beam (3) and the workpiece (2), which arises when the preferably pulsed processing beam (3) is directed onto the workpiece (2) at a test position (21) within the predetermined cutting contour (18a), wherein the evaluation device (28) is designed to check, on the basis of the detected radiation (27), whether the workpiece part (17) was completely separated from the remaining part (19) during cutting processing.