Method for machining a workpiece by means of a laser device, and laser device

Abstract

The invention relates to a method for machining a workpiece (10) by means of a laser device (12), which has a nozzle (16) with a nozzle channel through which a laser beam (14) for machining the workpiece (10) radiates and by means of which cutting gas to be directed onto the workpiece (10) is guided when machining the workpiece (10), in which method the workpiece (10) is machined by means of the laser device (12) in a machining step, which results in the nozzle (16) heating, and, in a non-machining step which follows the machining step and in which machining of the workpiece (10) by means of the laser device (12) ceases, the nozzle (16) is actively cooled by means of cooling gas, by the cooling gas being guided through the nozzle channel.

Description

[0001] METHOD FOR MACHINING A WORKPIECE BY MEANS OF A

[0002] LASER DEVICE AND LASER DEVICE

[0003] The invention relates to a method for machining a workpiece by means of a laser device and to a laser device.

[0004] When edge shaping with a 2D laser cutting machine, strong reflections of a laser beam occur on the rounding surface of a workpiece whose edges are being rounded. The reflected laser radiation hits a laser cutting nozzle of the laser cutting machine or a laser cutting head equipped with the laser cutting nozzle, causing these components to become extremely hot. If this radiation is exposed to the components for too long, a laser cutting unit of the laser cutting machine can be damaged.

[0005] The object of the present invention is to provide a solution by means of which damage to a laser device due to excessive heating as a result of absorption of reflected laser radiation can be avoided.

[0006] The problem is solved by the subject matter of the independent claims. Further possible embodiments of the invention are specified in the subclaims, the description, and the drawings. Features, advantages, and possible embodiments presented in the description for one of the subject matter of the independent claims are to be regarded at least analogously as features, advantages, and possible embodiments of the respective subject matter of the other independent claims, as well as any possible combination of the subject matter of the independent claims, optionally in conjunction with one or more of the subclaims.

[0007] The invention relates to a method for machining a workpiece using a laser device. The workpiece is, in particular, a sheet metal which is machined using the laser device. In particular, the workpiece is machined using the laser device in that a laser beam is directed from the laser device onto the workpiece, whereby the workpiece is changed in its nature or contour as a result of contact with the laser beam. The laser device has a nozzle with a nozzle channel. During machining of the workpiece, the laser beam for machining the workpiece shines through the nozzle channel. Furthermore, a cutting gas to be directed onto the workpiece is guided via the nozzle channel during machining of the workpiece. The nozzle is thus designed to direct the laser beam and the cutting gas onto the workpiece during machining of the workpiece.The nozzle can heat up as a result of portions of the laser beam being reflected by the workpiece. If the nozzle heats up too much due to absorbing the reflected portions of the laser beam, this can lead to damage to the nozzle and cutting unit.

[0008] The method provides for the workpiece to be processed by means of the laser device in one processing step. As a result, the nozzle can heat up. To avoid damage to the nozzle as a result of excessive heating of the nozzle, the method further provides for the nozzle to be actively cooled by means of cooling gas in a non-processing step following the processing step. During the non-processing step, the workpiece is not processed by means of the laser device. Because the workpiece is not processed by means of the laser device in the non-processing step, the laser beam is not reflected by the workpiece in the direction of the nozzle in the non-processing step, so that further absorption of laser radiation by the nozzle is prevented in the non-processing step. Thus, the nozzle does not heat up further in the non-processing step.Instead, the nozzle is actively cooled during the non-processing step using cooling gas by guiding the cooling gas through the nozzle channel. In particular, during active cooling of the nozzle, the cooling gas flows through the nozzle channel at a high volume flow, thereby cooling the nozzle channel particularly quickly and significantly. The temperature of the nozzle can thus be reduced particularly quickly and significantly during the non-processing step, making the nozzle available for another processing step. In particular, the nozzle is actively cooled between two respective processing steps in the non-processing step using the cooling gas, thereby counteracting damage to the nozzle due to an excessively high nozzle temperature.

[0009] The cooling gas can be the same gas that is also used as the cutting gas in the machining step. Alternatively, different gases can be used as the cutting gas and the cooling gas in the process. Although the cutting gas is guided through the nozzle channel during machining of the workpiece, the cooling effect of the cutting gas is not sufficient to prevent the nozzle from heating up to such an extent that it is damaged due to the high temperature. In particular, the cooling gas flows through the nozzle at a higher pressure during the non-machining step than the cutting gas flows through the nozzle channel during the machining step. Thus, the cooling gas can achieve a greater cooling effect than the cutting gas.

[0010] In a possible development of the invention, it is provided that the nozzle is actively cooled by means of the cooling gas during a movement of a processing head of the laser device, which processing head has the nozzle. This means that the nozzle is actively cooled by means of the cooling gas when the processing head is moved from a first position to a second position different from the first position. Thus, an adjustment time for changing the position of the processing head can be used to cool the nozzle by means of the cooling gas. In particular, the processing head is moved between two respective processing steps and thus its position is changed. The time required for moving the processing head can thus be used particularly well to reduce the temperature of the nozzle through active cooling.The nozzle is therefore available for the next processing step very quickly after the laser system's processing head has been moved. This allows a particularly large number of processing steps to be performed consecutively using the nozzle.

[0011] In a further possible embodiment of the invention, it is provided that during the machining step, the cutting gas flows through the nozzle channel at a pressure of less than 0.3 bar, in particular at a pressure of less than 0.05 bar. In certain machining processes in which the workpiece is machined using the laser device, it is advantageous for the machining result if particularly low cutting gas pressures are used. If such a low cutting gas pressure is used during the machining step, it is particularly important that the nozzle is actively cooled by the cooling gas during the non-machining step to prevent overheating of the nozzle.The low cutting gas pressures thus enable particularly good machining results of the workpiece after the machining step, while the active cooling of the nozzle by means of cooling gas during the non-machining step prevents damage to the nozzle due to overheating. In a further possible embodiment of the invention, it is provided that during the non-machining step, the cooling gas flows through the nozzle channel at a pressure of more than 10 bar, in particular at a pressure of more than 20 bar. The cooling gas thus flows through the nozzle channel at a particularly high volume flow due to the high cooling gas pressure, whereby a particularly large amount of heat can be absorbed by the nozzle as the cooling gas flows through the nozzle channel. As a result, the nozzle can be cooled particularly quickly and particularly intensively by means of the cooling gas flowing through the nozzle channel.The risk of overheating of the nozzle during a further processing step following the non-processing step can thus be kept particularly low due to the particularly rapid and strong cooling of the nozzle by means of the cooling gas.

[0012] In a further possible embodiment of the invention, the cutting gas is directed onto the workpiece by means of a chrome-plated nozzle. In other words, the nozzle of the laser device is provided with a chrome coating. This chrome coating on the nozzle results in a particularly large proportion of laser beams reflected from the workpiece in the direction of the nozzle being reflected in turn by the nozzle, and thus none or only a very small proportion of the reflected laser radiation is absorbed by the nozzle. As a result, heat development in the nozzle due to laser beam absorption can be kept particularly low. The chrome-plated design of the nozzle means that the nozzle is provided with the chrome coating at least on its outer surface facing the workpiece surface during machining.Using the chrome-plated nozzle for the processing step ensures that the nozzle only heats up very slightly during the processing step.

[0013] In a further possible embodiment of the invention, it is provided that during the processing step an edge of the workpiece is rounded by means of a defocused laser beam. During the processing step, in particular an edge of the workpiece that has been previously cut by means of the laser device is rounded. For rounding, the defocused laser beam is directed by the laser device onto the edge of the workpiece to be rounded. When edges are rounded using a 2D laser cutting machine, strong reflections of the laser beam occur on a rounding surface of the workpiece because edge rounding is a welding process, in particular a heat conduction welding process. During this process, the component edge of the workpiece to be rounded is melted in a defocused manner and thus rounded. Up to 95 percent, for example around 70 percent, of the laser power is reflected by the workpiece and only a small part (from approx.5 percent), preferably up to about 30 percent. The portion of the laser power reflected by the workpiece can in turn impinge on the nozzle and thereby cause the nozzle to heat up through absorption. The method makes it possible for the edge of the workpiece to be rounded using the defocused laser beam during the processing step and then, through active cooling of the nozzle in the non-processing step, the temperature of the nozzle to be greatly reduced in order to enable a further processing step, in particular further edge rounding, using the nozzle, wherein the risk of damage to the nozzle as a result of overheating is kept particularly low.

[0014] In this context, it can be provided in particular that the following method steps a) to f) are carried out within the scope of the method, whereby these are consecutive method steps which are therefore carried out in the stated order. In the method, in a first method step a), a first cutting line can be cut into the workpiece using the laser beam in a cutting step. This cutting step takes place in particular before the processing step and thus before the edge rounding. During the cutting step, the workpiece is thus cut using the laser device. In a subsequent second method step b), the processing head of the laser device is moved back from an end point of the first cutting line to a starting point of the first cutting line.This means that the position of the processing head of the laser device is moved back from the end point of the first cutting line to the starting point of the first cutting line. In particular, the processing head can be moved back along the first cutting line from the end point to the starting point. This means that the processing head is positioned consistently above the first cutting line during the movement from the end point of the first cutting line to the starting point of the first cutting line. This makes it possible to minimize the risk of completely cut-out sections of the workpiece being tilted by the gas flowing out of the nozzle, regardless of whether it is cutting gas or cooling gas.The method further provides that, in a third method step c), the processing step is carried out in which an edge of the first cutting line of the workpiece created during the cutting process is rounded. Thus, in this processing step, the edge created in the workpiece as a result of the cutting step is rounded. For this purpose, the defocused laser beam can be directed onto the edge of the workpiece to be rounded.

[0015] In a fourth method step d) following the machining step, a second cutting line is cut into the workpiece using the laser beam in a further cutting step. In particular, the starting point of the second cutting line coincides with the end point of the first cutting line. Thus, the further cutting cut continues in the workpiece starting from the first cutting line. Subsequently, in a fifth method step e), the machining head of the laser device is moved back from the end point of the second cutting line to the starting point of the second cutting line, while the nozzle is actively cooled by means of cooling gas during this non-machining step.In the non-machining step, in which the machining head is moved back from the end point of the second cutting line to the starting point of the second cutting line and which follows the machining step, the nozzle is actively cooled to reduce the temperature and prevent damage to the nozzle due to excessive temperature buildup in the nozzle. In particular, it is provided that higher cutting gas pressures are used in the respective cutting steps than in the respective machining steps in which respective edges of the workpiece are rounded. As a result, the nozzle heats up less during the respective cutting steps than during the machining step. Consequently, active cooling of the nozzle immediately after the respective cutting steps is only necessary if the machining step has also been carried out.If only cutting steps and no machining steps were carried out with the low cutting gas pressure, then active cooling of the nozzle using the cooling gas can be omitted.

[0016] The method further provides that, in a sixth method step f), a further processing step is performed, in which an edge of the second cutting line of the workpiece created during cutting is rounded. The further processing step can, in particular, be performed using the same processing parameters as the processing step performed in the third method step c). Thus, a successive cutting and rounding of an entire predetermined cutting contour takes place.

[0017] A concrete example of the process is explained below. For this example, a two-millimeter-thick sheet of CrNi steel can be processed as the workpiece using an 8-kilowatt laser system. In particular, the laser system with the chrome-plated nozzle can be used. This allows the laser radiation reflected from the workpiece and directed to the nozzle to be reflected by the nozzle.

[0018] In this method, a portion of the contour is first cut using the laser, and thus using the laser beam provided by the laser device, in particular approximately 100 to 500 millimeters, in particular 200 to 400 millimeters, preferably 300 millimeters. The cutting head of the laser device, and thus the processing head, is then repositioned to the start of the cut, and the rounding process is started at a cutting gas pressure of 0.02 bar. The edge is now rounded using the defocused laser beam. This heats up the nozzle considerably. The laser is then used again to cut, in particular approximately 100 to 500 millimeters, in particular 200 to 400 millimeters, preferably 300 millimeters. After cutting, the laser is switched off, which means that the laser beam is not provided, and the laser cutting head, which is the processing head, is repositioned to the start of the cut.During the retraction, the nozzle is cooled with maximum gas pressure, especially with a gas pressure of more than 20 bar. Next, the rounding process begins again. This sequence is repeated until all edges on the workpiece are rounded.

[0019] The cooling effect can be increased by reducing the rounding distance along the contour. The optimal rounding length along the contour is approximately 100 to 500 millimeters, in particular 200 to 400 millimeters, and preferably 300 millimeters. This means that the pre-cut is, for example, 300 millimeters long. The laser cutting head is then repositioned by about 300 millimeters at maximum gas pressure, and the nozzle can be cooled. In the next step, the 300 millimeters are rounded, which means that the edge created during the pre-cut is rounded over its entire length. The nozzle heats up again in the process. The cooling effect can be increased by shortening the pre-cut, for example, by half—in this case, 150 millimeters.This means that the return travel for nozzle cooling occurs earlier, or the number of nozzle cooling intervals is increased, and the length of each rounding section during which the nozzle heats up is shortened. Nozzle cooling takes place during the positioning movement of the machining head from the pre-cut to the rounding start position. It is possible that a rounding operation is interrupted if the nozzle becomes too hot. During this interruption of the rounding operation, the nozzle can be cooled with high gas pressure. This means that the nozzle is cooled by a cooling gas, such as nitrogen, flowing into the nozzle channel at a high gas pressure, in particular a pressure of more than 20 bar.

[0020] In a further possible embodiment of the invention, nitrogen or nitrogen gas is passed through the nozzle channel as the cutting gas and / or the cooling gas. In particular, the nitrogen gas can be used both as the cutting gas and as the cooling gas. Alternatively, nitrogen gas can be used either as the cutting gas or as the cooling gas, and a different gas than nitrogen gas can be used for the other application. Nitrogen gas is a particularly cost-effective and environmentally friendly gas. Alternatively or in addition to the use of nitrogen, argon or compressed air, for example, can be used as the cutting gas and / or as the cooling gas.

[0021] In a further possible embodiment of the invention, it is provided that the nozzle is actively cooled by water during the machining step. This can counteract damage to the nozzle as a result of strong heating of the nozzle during the machining step. In order to limit heating of the nozzle during the rounding process, active nozzle cooling with water can be implemented during the rounding process. The water can be guided in special cooling channels of the nozzle, which are different in particular from the nozzle channel. The cooling channels can be closed cooling channels with a supply and return flow. In addition to or as an alternative to water cooling, the nozzle can also be cooled by another gas cooling source, for example using compressed air.

[0022] The invention further relates to a laser device which is configured to machine a workpiece using a method as already described in connection with the method according to the invention for machining a workpiece. In particular, the laser device can be configured to round an edge of the workpiece or to provide it with a chamfer as part of the machining step. The laser device comprises a machining head which is configured to direct a laser beam onto the workpiece for machining the workpiece. This machining head of the laser device in turn comprises a nozzle by means of which the laser beam can be directed onto the workpiece and which has a nozzle channel through which a cutting gas can flow. The cutting gas can be directed onto the workpiece by means of the nozzle.To limit heating of the nozzle due to laser beam absorption of laser beams reflected by the workpiece, the nozzle can be chrome-plated.

[0023] Further features of the invention can be derived from the following description of the figures and from the drawings. The features and combinations of features mentioned above in the description, as well as the features and combinations of features shown below in the description of the figures and / or in the figures alone, can be used not only in the respective combinations specified, but also in other combinations or on their own, without departing from the scope of the invention.

[0024] The drawing shows:

[0025] Fig. 1 is a schematic perspective view of a workpiece machined by means of a laser device.

[0026] Fig. 1 shows a schematic perspective view of a workpiece 10 being machined using a laser device 12. In this case, the laser device 12 is configured to cut the workpiece 10 and to round any cutting edges created on the workpiece 10. To machine the workpiece 10, the laser device 12 can provide a laser beam 14 and direct it onto the workpiece 10. Depending on the set parameters of the laser beam 14, such as power, focus position, and focus diameter, the workpiece 10 is cut using the laser beam 14, or an edge of the workpiece 10 is rounded using the laser beam 14.

[0027] The laser device 12 comprises a processing head 32 with a nozzle 16. The nozzle 16 comprises a nozzle channel (not shown in Fig. 1), through which the laser beam 14 shines for processing the workpiece 10 and by means of which cutting gas can be directed onto the workpiece 10 during processing of the workpiece 10. In particular, the nozzle channel runs centrally through the nozzle 16. In this case, the nozzle 16 is a chrome-plated nozzle.

[0028] The following describes an example process for machining the workpiece 10 using the laser device 12. It is intended that a cutting contour 18 is introduced into the workpiece 10 using the laser device 12, with the respective edges of the cutting contour 18 being rounded. To prevent excessive overheating of the nozzle 16 due to absorption of laser radiation, which has been reflected by the workpiece 10, it is intended that the cutting contour 18 is introduced successively and thus piece by piece into the workpiece 10. For this purpose, in a first cutting step, a first cutting line 20 is cut into the workpiece 10 using the laser beam 14. This first cutting line 20 runs from a first starting point 22 to a first end point 24.After cutting the first cutting line 20 into the workpiece 10, the processing head 32 of the laser device 12, which provides the laser beam 14, is moved back to a first starting position to allow the laser beam 14 to be aligned again by the processing head 32 to the first starting point 22. This is followed by a first processing step in which the edge created during cutting is rounded along the first cutting line 20. The edge is rounded using a defocused laser beam at a cutting gas pressure of less than 0.3 bar, in particular with a cutting gas pressure of less than 0.05 bar, in particular with a cutting gas pressure of 0.02 bar.

[0029] Subsequently, in a second cutting step, a second cutting line 26 is cut into the workpiece 10 using the laser beam 14. A second starting point 28 of the second cutting line 26 coincides with the first end point 24 of the first cutting line 20. This means that the second cutting line 26 adjoins the first cutting line 20. After the second cutting line 26 has been cut, the processing head 32 of the laser device 12 is moved back to a second starting position, from which the second cutting line 26 has been cut by means of the processing head 32. This return movement of the processing head 32 to the second starting position after the second cutting line 26 has been cut constitutes a non-processing step, in which processing of the workpiece 10 using the laser device 12 is omitted.During this non-processing step, the nozzle 16 is actively cooled by means of cooling gas by guiding the cooling gas through the nozzle channel. In this case, the cooling gas flows into the nozzle channel at a pressure of more than 10 bar, in particular at a pressure of more than 20 bar. The cooling gas thus flows through the nozzle channel at a particularly high volume flow, whereby the nozzle 16 is cooled particularly quickly and particularly strongly by means of the cooling gas during the non-processing step. After the processing head 32 has been arranged at the second starting position, the edge created during cutting of the second cutting line 26 can be rounded in a second processing step by guiding the laser beam 14 again along the second cutting line 26. A further cutting line can then be cut at a second end point 30 of the second cutting line 26.The cutting contour 18 is cut successively in the form of several consecutive cutting lines, and the edges created during the cutting process are subsequently rounded in the respective processing steps. In this case, nitrogen gas flows through the nozzle channel of the nozzle 16 as both the cutting gas and the cooling gas.

[0030] To limit or at least contain heating of the nozzle 16 during the respective processing steps, the nozzle 16 can be actively cooled by water during the respective processing steps. The water is guided through at least one cooling channel of the nozzle 16 that is different from the nozzle channel.

[0031] Since higher cutting gas pressures are used for cutting the workpiece 10 than for edge rounding, the nozzle 16 is cooled more effectively during cutting by the cutting gas flowing through the nozzle channel than during edge rounding. The nozzle 16 therefore heats up less during cutting than during edge rounding.

[0032] In order to avoid a collision with components cut out of the workpiece 10, it can be provided that the machining head 32 is only moved above the cutting contour 18 when moving back to the respective starting position.

[0033] In summary, within the scope of the method for machining the workpiece 10, at least one machining step is performed in which the workpiece 10 is machined using the laser device 12, thereby heating the nozzle 16. Within the scope of the machining step, an edge of the workpiece 10 can be rounded or chamfered. Furthermore, the method provides for at least one non-machining step following the at least one machining step, in which machining of the workpiece 10 using the laser device 12 is omitted and in which the nozzle 16 is actively cooled using cooling gas by passing the cooling gas through the nozzle channel.

[0034] The described method is based on the knowledge that laser radiation reflected from the workpiece 10 hits the laser cutting nozzle and thus the nozzle 16 as well as the laser cutting head and thus the processing head 32 of the laser device 12, which is why these components heat up very strongly. If the laser radiation acts on these components for too long, the laser cutting unit and thus the laser device 12 can be damaged. To make matters worse, gas pressures of less than 0.3 bar, typically even 0.02 bar, are used for edge rounding. As a result, there is no or only very little nozzle cooling by convection from the cutting gas. To protect the nozzle 16 from excessive heating, coatings can be applied to a nozzle body of the nozzle 16. Chrome coatings are particularly suitable for this purpose.Another option for reducing the temperature of the nozzle 16 is to use a cooling strategy during the machining process. With this cooling strategy, the nozzle 16 is cooled after a certain time using strong nitrogen gas pressure. The processing is as follows: First, a portion of the cutting contour 18, approximately 300 millimeters long, is cut using the laser beam 14. The laser cutting head is then repositioned to the start of the cut, and the rounding process is started at a gas pressure of less than 0.3 bar, where the gas pressure refers to the cutting gas. The 300 millimeter-long edge is now rounded. This heats up the nozzle 16 considerably. After this, cutting is carried out again with the laser beam 14, approximately 300 millimeters long. After cutting, the laser device 12 is switched off, thus no longer providing the laser beam 14, and the laser cutting head is repositioned to the start of the cut.During the retraction, the nozzle 16 is cooled with maximum nitrogen gas pressure, in particular with a gas pressure of over 20 bar. Next, the rounding process is started again. This sequence is repeated until all edges on a component to be cut from the workpiece 10 are rounded. A combination of the described cooling strategy and the use of a chrome-plated nozzle 16 offers particularly good protection against nozzle heating. In this process, the nozzle 16 is cooled with high nitrogen gas pressure at certain intervals after rounding.

[0035] Overall, the invention shows how nozzle cooling can be implemented during edge rounding.

[0036] 10 Workpiece

[0037] 12 Laser device 14 Laser beam

[0038] 16 nozzle

[0039] 18 Cutting contour

[0040] 20 first cutting line

[0041] 22 first starting point 24 first end point

[0042] 26 second cutting line

[0043] 28 second starting point

[0044] 30 second endpoint

[0045] 32 machining head

Claims

PATENT CLAIMS 1. Method for processing a workpiece (10) using a laser device (12) which has a nozzle (16) with a nozzle channel through which a laser beam (14) shines for processing the workpiece (10) and through which cutting gas is directed towards the workpiece (10) during processing, in which the workpiece (10) is processed in a processing step using the laser device (12), whereby the nozzle (16) heats up, in a subsequent non-processing step in which the workpiece (10) is not processed using the laser device (12), the nozzle (16) is actively cooled by means of cooling gas by passing the cooling gas through the nozzle channel.

2. Method according to claim 1, characterized in that the nozzle (16) is actively cooled by means of the cooling gas during a process of a processing head (32) having the nozzle (16) of the laser device (12).

3. Method according to claim 1 or 2, characterized in that during the processing step the cutting gas flows through the nozzle channel at a pressure of less than 0.3 bar, in particular at a pressure of less than 0.05 bar.

4. Method according to one of the preceding claims, characterized in that during the non-processing step the cooling gas flows through the nozzle channel at a pressure of more than 10 bar, in particular at a pressure of more than 20 bar.

5. Method according to one of the preceding claims, characterized in that the cutting gas is directed onto the workpiece (10) by means of a chrome-plated nozzle (16). Method according to one of the preceding claims, characterized in that in the processing step an edge of the workpiece (10) is rounded by means of a defocused laser beam (14).The method according to claim 6, characterized in that a) in a cutting step a first cutting line (20) is cut into the workpiece (10) by means of the laser beam (14), b) the processing head (32) of the laser device (12) is moved back to a starting point (22) of the first cutting line (20), c) in the processing step an edge of the first cutting line (20) of the workpiece (10) created during cutting is rounded, d) in a further cutting step a second cutting line (26) is cut into the workpiece (10) by means of the laser beam (14), e) the processing head (32) of the laser device (12) is moved back to a starting point (28) of the second cutting line (26), while the nozzle (16) is actively cooled by means of cooling gas in this non-processing step, f) in a further processing step an edge of the second cutting line (26) of the workpiece created during cutting (10) is rounded.A method according to any of the preceding claims, characterized in that nitrogen gas is passed through the nozzle channel as the cutting gas and / or as the cooling gas. A method according to any of the preceding claims, characterized in that the nozzle (16) is actively cooled by water during the processing step. A laser device (12) configured to process a workpiece (10) in a method according to any of the preceding claims.

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