Method for cutting out a closed contour in a sheet-like workpiece
By reducing the feed rate and laser beam parameters before the cutting endpoint, combined with sensor monitoring, the irregularity problem during the cutting process was solved, and the cutting quality and reliability were improved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- TRUMPF WERKZEUGMASCHINEN GMBH & CO KG
- Filing Date
- 2024-11-27
- Publication Date
- 2026-07-14
AI Technical Summary
When cutting a closed contour, irregularities caused by the tipping of the cut portion, such as material discoloration, molten material splatter, and initial protrusions, affect the cutting quality.
Before the cutting endpoint, the feed rate of the processing head is reduced, and the laser beam is pulsed and its power is reduced. At the same time, distance and optical sensors monitor the complete separation of the cutting endpoint to ensure that the laser beam is accurately shut off.
It reduces material discoloration and initial protrusion in the cutting endpoint area, improves cutting quality and reliability, and avoids unnecessary heat input and material damage.
Smart Images
Figure CN122396563A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to a method for cutting a closed profile in a plate-shaped workpiece by means of a laser beam that moves on the workpiece by means of a processing head. Background Technology
[0002] Such a closed profile can be introduced into a workpiece, for example, as a gap for drilling internal holes. In this case, the useful part is the remaining workpiece, while the cut profile is a scrap part. Conversely, in the opposite case, the cut portion is the useful part, and the remaining residual grille forms a scrap part.
[0003] Here, the machining head's trajectory is typically programmed so that the start and end points of the contour cut are the same. The laser is switched off after reaching the end point. However, the contour has already been cut away before reaching the start point of the laser trajectory. Due to the weight of the cut portions, these portions will tilt downwards while the laser is still active. This results in irregularities on the contour in the areas at the start and end points of the contour cut. These irregularities can include material discoloration or splattering of molten material due to excessive heat input, or contour deformation. These irregularities are undesirable and may require rework of the usable part.
[0004] Therefore, to mitigate these problems, DE 10 2015 221 243 A1 proposes that the laser beam be switched off when the cut portion is tilted after being cut away, i.e., before it reaches the starting point of the cutting trajectory again. However, due to the circular diameter of the laser beam, switching off the laser beam immediately after the contour is cut away may result in the formation of an antegrade bulge, i.e., a small piece of material protruding beyond the cut edge of the contour. If the laser beam is switched off before it reaches the starting point of the cut again, the an antegrade bulge will not be removed by the laser beam. Summary of the Invention
[0005] The purpose of this invention is to provide a method by which irregularities appearing in the region at the cut endpoint when cutting out a closed contour can be further reduced.
[0006] According to the invention, this objective is achieved by a method for cutting a closed contour in a plate-shaped workpiece by means of a laser beam that moves on the workpiece by means of a processing head, characterized in that the feed rate of the processing head is reduced by a predetermined distance before reaching the cutting endpoint of the contour.
[0007] The dependent claims relate to preferred embodiments.
[0008] By reducing the feed rate of the machining head at a predefined distance to the programmed cutting endpoint as described in this application, the cutting front tail (Schneidfrontnachlauf) of laser cutting is reduced, resulting in the cutting front occupying an angle of approximately 90° with the workpiece surface. This can reduce material discoloration in the region of the cutting endpoint. Here, the programmed cutting endpoint can preferably coincide with the starting point of the contour cutting.
[0009] The feed rate can be reduced, for example, 2 mm to 8 mm before reaching the cutting endpoint. Preferably, the feed rate of the machining head can be reduced to 0.5 m / min, and more particularly to 0.1 m / min.
[0010] Preferably, the laser beam can also be pulsed and / or operated at reduced power at a predetermined distance before reaching the cutting endpoint of the contour. This measure will also help to further reduce material discoloration. Here, it has proven advantageous to operate the laser beam at a pulse frequency of 100 Hz and a power between 400 W and 1500 W at a predetermined distance before reaching the cutting endpoint of the contour.
[0011] If the feed rate of the processing head and the pulse frequency and power of the laser beam are reduced simultaneously and linearly, material discoloration can be almost completely avoided by significantly reducing the stretchenenergie of laser cutting.
[0012] Complete separation of the profile can be identified by measuring the distance between the machining head and the workpiece and / or by using an optical sensor device. If the distance measuring device and / or the optical sensor device indicates complete separation, the laser beam can be turned off. This prevents the laser beam from hitting a portion of the workpiece that has been separated and tilted, which could result in molten spatter or profile deformation. For example, the distance between the machining head and the workpiece can be measured capacitively.
[0013] Process reliability can be improved by monitoring contour deflection and triggering laser beam shutdown through both distance measurement and optical inspection. Contour deflection can be reliably identified and the laser beam shut off when the distance between the machining head and the workpiece changes suddenly and the intensity of scattered light detected by the optical sensor changes simultaneously. When using only the distance measurement signal, the laser beam may erroneously shut off, for example, due to vibrations of a plate-like workpiece. To avoid these erroneous shutdowns, scattered light in the region at the cut endpoint can be detected. Since the machining head feed rate decreases in this region, the intensity of scattered light increases. Therefore, the increase in scattered light intensity can be used to confirm contour deflection identified by the increase in the distance measurement signal.
[0014] To avoid initial protrusions at the cut edge, at the start of contour cutting, if the contour is a useful part to be manufactured, the machining head can move the laser beam into the contour perpendicular to the programmed cutting trajectory by a fraction of the laser beam diameter (Bruchteil). Alternatively, if the remaining workpiece is a useful part, the machining head can move the laser beam into the remaining workpiece perpendicular to the programmed cutting trajectory by a fraction of the laser beam diameter, and then move the machining head back to the starting point of the programmed cutting trajectory and cut the contour. The laser beam can be turned off during the return of the machining head to the starting point of the programmed cutting trajectory and then re-energized before the next cut of the contour. This replaces material protrusions, thereby creating small recesses in the cut edge, which are generally more visually acceptable than material protrusions.
[0015] Alternatively or additionally, before complete separation of the contour, if the contour is the useful part to be manufactured, the processing head moves the laser beam into the contour by a portion of the laser beam diameter; or if the remaining workpiece is the useful part, the processing head moves the laser beam into the remaining workpiece by a portion of the laser beam diameter, and then completes the separation of the contour at that position. This measure also creates a small indentation in the cut edge. Here, preferably, the laser beam can be moved into the useful part at a 45° angle 5 mm before reaching the end of the separation. The movement of the laser beam into the useful part can be, for example, 0.1 mm to 0.2 mm, so that the resulting indentation in the cut edge is almost imperceptible.
[0016] The present invention also relates to a laser cutting machine for processing plate-shaped workpieces, the laser cutting machine having a processing head for guiding a laser beam and a control device for adjusting the feed of the processing head and adjusting the laser beam, wherein the laser cutting machine is configured to perform the method according to the present invention.
[0017] In particular, laser cutting machines can be equipped with devices for measuring the distance between the processing head and the workpiece, and with optical sensor devices for detecting scattered light.
[0018] Further features and advantages of the invention can be found in the specification, claims, and drawings. According to the invention, the features mentioned above, as well as those to be further described, can be used individually or in any desired advantageous combination. The illustrated and described embodiments should not be construed as exhaustive, but rather have exemplary characteristics for describing the invention. Attached Figure Description
[0019] Figure 1 A schematic representation of a plate-shaped workpiece with a perforated cutout portion generated by a laser beam is shown; Figure 2 It shows Figure 1 A schematic representation of the start and end of the laser beam cutting of the workpiece's punched and removed portion; Figure 3 A graph showing the distance detection of the cutting head of a laser cutting machine for identifying the cut portion of the punched section is shown; Figure 4 A schematic representation of the laser beam at the start and end of the cutting in the punched section is shown, employing measures to avoid / reduce the starting protrusion in the punched section; and Figure 5 It shows the use of Figure 4 In the case of measures taken, the laser beam is used to cut the entire trajectory of the punched excision section. Detailed Implementation
[0020] Figure 1 A plate-shaped workpiece 10, such as a steel sheet, is shown, from which two circular punched cutouts 11 and 12 have been cut. Furthermore, a laser beam 17 for cutting a third punched cutout 13 in the workpiece 10 is shown. Figure 2 The laser beam 17 is first inserted into the center of the punching and cutting section 13, and then the laser beam 17 is moved outward along the radial trajectory 14 until it reaches the desired outer diameter of the punching and cutting section 13 at point 16. From point 16, the laser beam 17 is guided along the circular trajectory 15 until the material of the punching and cutting section 13 is completely cut off and falls out of the workpiece 10 slightly before reaching point 16.
[0021] Here, at point 16, workpiece 10 experiences a relatively high heat input from laser beam 17, because the laser beam first irradiates point 16 from radial trajectory 14 and then turns from there onto circular trajectory 15. At the end of circular trajectory 15, heat is again introduced by laser beam 17 in the region of point 16. Furthermore, the punched cut section 13 tilts downwards after being cut. This results in irregularities 11.1, 12.1 in the cutting edges 11.2, 12.2 of punched cut sections 11 to 13, as illustrated by the examples of punched cut sections 11 and 12. These irregularities can be material discoloration, molten material spatter, or starting protrusions 18 (…). Figure 2 ).
[0022] To minimize these irregularities 11.1 and 12.1, before the circular trajectory 15 is completed, i.e., before the punched cutting portion 13 is completely cut away, the feed speed of the laser beam 17 is reduced from V to V', as follows: Figure 2 As shown. Preferably, here, the speed V' is only 0.5 m / min. In Figure 2In the greatly enlarged and schematic illustration, the circular cross-section of the laser beam 17 at the starting point of the circular trajectory 15 and the circular cross-section of the laser beam 17' at the ending point of the circular trajectory 15 can be seen. When it reaches position 17', the drilling and cutting portion 13 is completely cut off, and the laser beam 17' can be shut off at this position. However, here, the so-called starting protrusion 18 of the workpiece 10 still exists and protrudes into the drilling and cutting portion 13. This protrusion 18 is caused by the circular cross-sections of the laser beams 17 and 17' and the shut-off of the laser beam 17' before it reaches the starting position 17 again.
[0023] In addition to reducing the feed rate V, the power of the laser beam 17' can be reduced, for example, from 1500 W to 400 W. Furthermore, the pulse frequency of the laser beam 17' can be reduced, for example, from 20000 Hz to 100 Hz. These measures result in a reduction in line energy density, and thus a further reduction in the irregularities 11.1 and 12.1 at the cutting edges 11.2 and 12.2.
[0024] In order to reliably identify the cutting of the punched section 13 and thus enable the laser beam 17' to be switched off in time to prevent unnecessary heat input to the workpiece 10, it is possible to... Figure 3 As shown, the distance 19 between the processing head used to guide the laser beam 17 and the workpiece 10 is monitored in the terminal section of the trajectory 15 of the laser beam 17. When the punching cut-off portion 13 is completely cut off, it falls off the workpiece 10. This increases the distance between the workpiece 10 and the laser processing head. If the distance 19 exceeds the threshold SA, the laser beam 17' is turned off. Here, the distance measurement can be additionally verified by an optical measurement signal. The intensity of the scattered light on the laser trajectory 15 increases as the feed rate is reduced from V to V', which can be detected, for example, by a photodiode. If both the distance 19 increasing above the threshold SA and the increase in the intensity of the scattered light occur, it can be reliably determined that the punching cut-off portion 13 has been cut off, and therefore the laser beam 17' can be turned off. At time t... A That is, the programmed trajectory endpoint of the processing head is reached after the laser beam is turned off.
[0025] Figure 4 and Figure 5 The following measures are shown, through which the following measures can be used to... Figure 2 The initial protrusion 18 in the laser path 15 is reduced to a smaller protrusion 18'. For this purpose, the laser beam 17' is moved into the workpiece 10 in the terminal section 15.1 of the laser path 15 with a stroke d of, for example, 0.1 mm to 0.2 mm. Figure 4 The endpoint position 17' of the laser beam when it is turned off and the reduced starting protrusion 18' are shown. Figure 5The entire programmed laser trajectory 15' is shown, with a terminal section 15.1' extending obliquely into the workpiece 10. The endpoint 20 reached by the laser beam 17' is radially located outside the starting point 16 of the laser trajectory 15'. This creates a small indentation in the workpiece 10. If additionally before starting to cut the circular trajectory 15... Figure 1 Extending the radial laser trajectory 14 shown to the radial distance of point 20 can even completely avoid the starting protrusions 18, 18'.
[0026] In the embodiment shown in the accompanying drawings, workpiece 10 is a useful part, while the punched cutouts 11, 12, and 13 form scrap parts. If the cutouts 11, 12, and 13 are useful parts and the remaining workpiece 10 is scrap, the method according to the invention and various measures for reducing irregularities 11.1 and 12.1 can be similarly performed. In this case, as... Figure 1 As shown, the laser beam 17 is guided radially from the outside onto a circular trajectory 15. To minimize the starting protrusion 18, the laser beam 17 is moved into these useful parts 12 to 13 rather than into the workpiece 10 before the cut-off portions 11, 12, and 13 are cut off. Variations in laser beam parameters (e.g., feed rate, power, and pulse frequency) are independent of which parts are useful. If the cut-off portions 11 to 13 are useful, the identification of the cut-off portions 11 to 13 via distance measurement and optional optical verification, and therefore the automatic shut-off of the laser beam, also remain unchanged.
Claims
1. A method for cutting closed contours (11, 12, 13) in a plate-shaped workpiece (10) by means of a laser beam (17, 17'), said laser beam moving on the workpiece (10) by means of a processing head, characterized in that, The feed rate (V') of the machining head can be reduced by a predetermined distance before reaching the cutting endpoint of the contour (11, 12, 13).
2. The method according to claim 1, characterized in that, The feed rate (V') of the processing head is reduced to 0.5 m / min, and more particularly to 0.1 m / min.
3. The method according to claim 1 or 2, characterized in that, The laser beam (17, 17') will be pulsed and / or operated at reduced power at a predetermined distance before reaching the cutting endpoint of the contour (11, 12, 13).
4. The method according to claim 3, characterized in that, The laser beam (17, 17') operates at a pulse frequency of 100 Hz and a power between 400 W and 1500 W, at a predetermined distance before reaching the cutting endpoint of the contour (11, 12, 13).
5. The method according to any one of the preceding claims, characterized in that, The feed rate (V') of the processing head and the pulse frequency and power of the laser beam (17, 17') are reduced simultaneously and linearly.
6. The method according to any one of the preceding claims, characterized in that, The complete separation of the contours (11, 12, 13) is identified by measuring the distance between the processing head and the workpiece (10) and / or by using an optical sensor device.
7. The method according to claim 6, characterized in that, The distance between the processing head and the workpiece is measured capacitively (19).
8. The method according to claim 6 or 7, characterized in that, When the distance (19) between the processing head and the workpiece (10) suddenly changes and the intensity of the scattered light detected by the optical sensor device changes at the same time, the separation of the contour (11, 12, 13) is detected and the laser beam (17, 17') is turned off.
9. The method according to any one of the preceding claims, characterized in that, At the start of contour cutting (15), if the contour is a useful part to be manufactured, the processing head moves the laser beam (17) into the contour by an amount perpendicular to the programmed cutting trajectory by a portion of the diameter of the laser beam, or if the residual workpiece (10) is a useful part, the processing head moves the laser beam into the residual workpiece by an amount perpendicular to the programmed cutting trajectory by a portion of the diameter of the laser beam, and then moves the processing head back to the starting point of the programmed cutting trajectory (15) and then cuts the contour (13).
10. The method according to any one of the preceding claims, characterized in that, Before the complete separation of the contour (13), if the contour (13) is a useful part to be manufactured, the processing head moves the laser beam (17') into the contour by an amount equal to a portion of the diameter of the laser beam, or if the remaining workpiece (10) is a useful part, the processing head moves the laser beam into the remaining workpiece by an amount equal to a portion of the diameter of the laser beam, and the separation of the contour (13) is completed at that position.
11. The method according to claim 10, characterized in that, Five mm before reaching the end of the cut, the laser beam is moved into the useful element (10, 13) at an angle of 45°.
12. The method according to any one of claims 9 to 11, characterized in that, The laser beam is moved into the useful element (10, 13) at a speed of 0.1 mm to 0.2 mm.
13. A laser cutting machine for processing plate-shaped workpieces (10), the laser cutting machine having a processing head for guiding a laser beam (17, 17') and a control device for adjusting the feed speed (V, V') of the processing head and adjusting the laser beam (17, 17'), characterized in that, The laser cutting machine is configured to perform the method according to any one of claims 1 to 12.
14. The laser cutting machine according to claim 13, characterized in that, The laser cutting machine is equipped with a device for measuring the distance (d) between the processing head and the workpiece (10), and with an optical sensor device for detecting scattered light.