Nozzle for a laser cutting device, and method for laser cutting a workpiece

Abstract

The invention relates to a nozzle (10) for a laser cutting device, the nozzle comprising a nozzle channel (14) which opens via a nozzle outlet opening (22) into the surroundings and through which a laser beam can pass, the laser beam radiating out of the nozzle (10) in a radiation direction (16) via the nozzle outlet opening (22); at least one cooling channel (30) through which a cooling fluid can flow and which comprises an inflow region (32), a deflection region (34) adjoining the inflow region, and an outflow region (36) adjoining the deflection region (34), cooling fluid flowing in the cooling channel (30) being conducted in the inflow region (32) at least partially in the radiation direction (16), deflected in the deflection region (34) and, thereafter, conducted in the outflow region (36); and a collar (28) which, when correctly mounted, rests against a cutting head, as a result of which the at least one cooling channel (30) in the mounted position can be supplied with cooling fluid from the cutting head.

Description

[0001] NOZZLE FOR A LASER CUTTING DEVICE AND METHOD FOR LASER CUTTING A WORKPIECE

[0002] The invention relates to a nozzle for a laser cutting device and two methods for laser cutting a workpiece.

[0003] During laser cutting, depending on the cutting parameters used, a cutting nozzle is sometimes illuminated by a very large laser beam. This can cause the cutting nozzle to heat up considerably, which can lead to the melting of a very narrow nozzle cross-section and can also negatively impact the accuracy of capacitive distance control. This can be counteracted by actively cooling the cutting nozzle by keeping the nozzle temperature constant. A nozzle that can be cooled with a cooling fluid is known, for example, from EP 3 925 726 A1, CN 210 524 185 U, and JP 2014 136 233 A.

[0004] The object of the present invention is to provide a solution which enables particularly good cooling of a nozzle for a laser cutting device.

[0005] This object is achieved according to the invention 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.

[0006] The invention relates to a nozzle for a laser cutting device, wherein the nozzle can also be referred to as a cutting nozzle. The laser cutting device is designed to provide a laser beam by means of which a workpiece can be cut. The nozzle comprises a nozzle channel, which extends in particular through a nozzle base body of the nozzle. The nozzle channel opens into the environment via a nozzle outlet opening. The provided laser beam can pass through the nozzle channel. The laser beam exits the nozzle in an emission direction via the nozzle outlet opening. In particular, the laser beam can be directed onto the workpiece to be cut by means of the nozzle.

[0007] In addition to the laser beam emitted from the nozzle outlet opening, cutting gas can flow out of the nozzle via the nozzle outlet opening. The flow direction of the cutting gas can coincide with the emission direction of the laser beam. To prevent overheating of the nozzle, the nozzle is provided with at least one cooling channel. A cooling fluid can flow through this cooling channel. The cooling fluid can be water or a gas, such as air, for example. The nozzle can be cooled, in particular, both by the cutting gas flowing in the nozzle channel and by the cooling fluid flowing in the at least one cooling channel.

[0008] The cooling channel has an inflow region, an adjoining deflection region, and an outflow region adjoining the deflection region. The deflection region is arranged downstream of the inflow region in the flow direction of the cooling fluid through the cooling channel, and the outflow region is arranged downstream of the deflection region. Cooling fluid flowing in the cooling channel is guided at least partially in the discharge direction in the inflow region, deflected in the deflection region, and then guided into the outflow region. This means that in the deflection region, by deflecting the cooling fluid, the flow direction of the cooling fluid is changed in relation to the nozzle channel or the laser beam passing through the nozzle channel.By guiding the cooling fluid in the inflow region at least partially in the jet direction, the inflow region of the cooling channel extends radially adjacent to the nozzle channel, starting from a central axis of the nozzle channel, whereby the nozzle can be cooled over a particularly large length region running in the axial direction of the nozzle, in which the inflow region of the cooling channel extends. The at least one cooling channel thus covers the nozzle channel at least partially and radially outwardly over at least one length section.

[0009] The flow direction of the cooling fluid in the inflow region forms an acute angle with the emission direction of the laser beam. In the deflection region, the flow direction of the cooling fluid is deflected, in particular, by an angle of more than 90°. This means that the cooling channel in the deflection region is designed at a particularly acute angle with respect to its longitudinal extent. The cooling fluid guided in the cooling channel can flow out of the cooling channel via the outflow region. In particular, the cooling fluid flows out of the outflow region via an outflow opening with a flow direction that forms an angle of > 90° with the emission direction of the laser beam from the nozzle outlet opening. This can prevent the cooling fluid flowing in the cooling channel from impinging on a laser impact point on the workpiece to be cut, thus influencing the cutting process.In addition, the risk of the cooling fluid mixing with the cutting gas can be kept particularly low.

[0010] The nozzle is further provided with a collar which, when installed as intended, is attached to a cutting head of the laser cutting device. The collar is arranged on the nozzle in particular on a side axially opposite the nozzle outlet opening. The collar can be designed in particular as a flange and provides an end face of the nozzle facing the cutting head in the installed position. The at least one cooling channel can be supplied with cooling fluid from the cutting head in the installed position via the collar which bears against the cutting head. In order to receive the cooling fluid from the cutting head and thus enable the cooling fluid provided by the cutting head to flow into the cooling channel, the cooling channel can be oriented with its inflow region towards the cutting head, in particular with an inflow opening of the cooling channel through which the inflow region opens into the environment.The collar serves primarily as a stop, precisely defining the nozzle's axial position relative to the cutting head. The collar, or rather the entire nozzle face, also serves as the point of heat transfer from the nozzle to potentially cooled components of the cutting head. This allows the nozzle to be cooled in addition to air cooling at particularly high laser power.

[0011] By deflecting the cooling fluid in the deflection region of the cooling channel, the cooling channel has a particularly large axial length in the nozzle, which in turn makes it possible to achieve a particularly large heat exchange surface between the cooling fluid and the nozzle. As a result of this particularly large heat exchange surface, the nozzle can be cooled particularly efficiently by means of the cooling fluid. Furthermore, it is possible for the temperature of the nozzle to be adjusted particularly precisely by means of the cooling fluid flowing in the cooling channel. In a possible development of the invention, it is provided that the nozzle comprises a plurality of cooling channels distributed around a central axis of the nozzle, which cooling channels are completely separated from one another over their entire length. In particular, the respective cooling channels cover the nozzle channel of the nozzle at least in regions and at least in an axial length section in the radially outward direction.The multiple cooling channels are separated from each other along their entire length, preventing mixing of the cooling fluid as long as it flows through the respective cooling channels. The multiple cooling channels can be evenly distributed around the circumference of the nozzle for particularly uniform cooling of the nozzle. In particular, the respective cooling channels can be arranged and configured point-symmetrically to each other. Because the cooling channels are completely separated from each other along their entire length, the respective partial flows of cooling fluid flowing in the cooling channels can be adjusted with particular precision and guided through the main body of the nozzle.

[0012] In a further possible embodiment of the invention, it is provided that the outflow region of the at least one cooling channel runs in such a way that cooling fluid flowing in the outflow region of the cooling channel is guided at least partially against the jet direction. The cooling fluid flows out of the outflow opening arranged at one end of the outflow region in a flow direction, wherein this flow direction encloses an obtuse angle with the jet direction. This means that the flow direction of the cooling fluid, as it flows out of the outflow region via the outflow opening, encloses an angle of > 90° with the jet direction of the laser beam from the nozzle outlet opening. This ensures that the cooling fluid flowing out of the outflow opening from the cooling channel reliably flows away from the workpiece to be cut, and mixing of cutting gas with the cooling fluid can be particularly effectively avoided.This enables a particularly high cutting quality to be achieved for a workpiece cut using the laser cutting device.

[0013] In a further possible embodiment of the invention, the collar is provided with a circumferential annular groove, whereby cooling fluid can flow from the cutting head into the annular groove when installed as intended. In particular, the collar has the annular groove on an end face which, in the installed position, rests against the cutting head. The circumferential annular groove is to be understood as meaning that it runs once around the central axis of the nozzle, in particular around the nozzle channel. It is provided that the at least one cooling channel opens into the annular groove at one end, whereby the cooling fluid can flow from the annular groove into the inflow area of ​​the cooling channel. By means of the annular groove, the cooling fluid is thus distributed among all of the cooling channels of the nozzle, since all of the cooling channels open into the annular groove with their respective inflow areas. The annular groove thus enables the cooling fluid received by the cutting head to be evenly distributed among all of the cooling channels of the nozzle.The annular design of this annular groove enables particularly fast and even distribution of the cooling fluid to the cooling channels. Alternatively, the nozzle can be designed without an annular groove on the collar, particularly if the cutting head has a circumferential annular groove designed to distribute the cooling fluid to the cooling channels when the nozzle collar is in contact with the cutting head.

[0014] In a further possible embodiment of the invention, it is provided that the length of the at least one cooling channel is at least 30%, in particular at least 50%, in particular at least 100% of the length of the nozzle from the collar to the nozzle outlet opening. In particular, the length of the at least one cooling channel can be up to approximately 200% of the length of the nozzle from the collar to the nozzle outlet opening. In this case, the inflow region can extend from the collar to a tip of the nozzle having the nozzle outlet opening, the deflection region in the tip of the nozzle and the outflow region from the tip of the nozzle to the collar. The longer the at least one cooling channel is designed, the larger the heat exchange surface via which heat can be exchanged between the cooling fluid and the nozzle.The larger the heat exchange surface, the more heat the nozzle can absorb via the cooling fluid, allowing the nozzle to be cooled particularly efficiently. The length of the nozzle runs from the collar to the nozzle outlet opening. The length corresponds to the axial distance between the nozzle outlet opening and the nozzle collar.

[0015] In a further possible embodiment of the invention, it is provided that the at least one cooling channel has a fluid guide structure by means of which a flow characteristic of the cooling fluid can be adjusted as it flows through the cooling channel. In particular, the fluid guide structure is arranged in the interior of the at least one cooling channel. The fluid guide structure can be arranged on an inner wall of the cooling channel that delimits the cooling channel. By means of the fluid guide structure, a degree of turbulence of the flow can be adjusted between a laminar flow and a turbulent flow. In particular, the fluid guide structure is designed to increase a degree of turbulence of the cooling fluid in the cooling channel, since with increasing turbulence of the cooling fluid, an improved heat transfer from the nozzle to the cooling fluid can be achieved.

[0016] In a further possible embodiment of the invention, the inflow region and the outflow region are provided by respective bores. This means that during the manufacture of the nozzle, a first bore providing the inflow region is introduced into the nozzle body, and a second bore providing the outflow region is introduced into the nozzle body. Thus, the at least one cooling channel is provided by making the bores in the nozzle body. The at least one cooling channel can thus be introduced into the nozzle particularly easily.

[0017] In a further possible embodiment of the invention, the nozzle base body is designed to be solid in a portion adjacent to the nozzle outlet opening, so that the cooling channel(s) do not extend into this portion of the nozzle base body. For this purpose, the deflection region of the cooling channel(s) is arranged above the solid portion of the nozzle base body in the direction of laser beam emission. In this way, the nozzle can be designed to be slim in the region of the nozzle outlet opening, so that it has a small external interference contour, for example with regard to collisions with tilted, cut workpiece parts. Despite the small outer diameter of the nozzle adjacent to the nozzle outlet opening, the solid portion also makes the nozzle sufficiently stable in the event of collisions. The length of the solid portion in the longitudinal direction of the nozzle is at least 5 mm.To ensure sufficient cooling by the cooling fluid flowing through the cooling channels, the length of the solid section in the longitudinal direction of the nozzle is a maximum of 30%, preferably a maximum of 25%, of the total length of the nozzle. To ensure sufficient stability of the nozzle, the wall thickness of the solid section is never less than 2.5 mm. This ensures that the wall thickness of the nozzle in the solid section is sufficiently large to allow heat dissipation along the nozzle wall toward the cooling channels.

[0018] In a further possible embodiment of the invention, the nozzle channel extending through the nozzle base body is cylindrical and adjacent to the nozzle outlet opening, and in particular has a diameter of between 0.7 mm and 2.0 mm, preferably between 1.4 mm and 2.0 mm. In this way, the nozzle channel forms a parallel-walled reflection section for the laser beam adjacent to the nozzle outlet opening. If the focal point of a laser beam passing through the nozzle lies inside or far below the nozzle, edge regions of the laser beam can be reflected on the inner wall of the nozzle base body as it passes through the reflection section. Compared to a conical inner nozzle contour, this way the absorption of the laser radiation and thus the heating of the nozzle can be reduced.The length of the reflection section in the direction of the nozzle's longitudinal axis is preferably at least 2 mm, and in particular between 3 mm and 4 mm, and is thus large enough to achieve these advantageous effects. If the nozzle channel has a circular cross-section in the reflection section, this advantageously improves the reflection properties in this region of the nozzle. Particularly preferably, the cylindrical reflection section of the nozzle channel is arranged within the solid portion of the nozzle.

[0019] The invention further relates to a first method for laser cutting a workpiece, in which a laser beam is directed onto the workpiece to be cut by means of a laser cutting device. The laser cutting device comprises a nozzle as already described in connection with the nozzle according to the invention. Cooling fluid can be guided to the nozzle by means of a cutting head of the laser cutting device, whereby the cooling fluid can flow through at least one cooling channel of the nozzle during laser cutting of the workpiece. As a result, the nozzle is cooled by means of the cooling fluid flowing in the at least one cooling channel during laser cutting of the workpiece. This makes it particularly easy to avoid local overheating of the nozzle and consequently achieve a particularly high cutting quality for a cut of the workpiece made by the laser cutting device.

[0020] The invention further relates to a second method for laser cutting a workpiece, in which a laser beam is directed onto the workpiece to be cut by means of a laser cutting device. The laser cutting device comprises a nozzle with a nozzle channel which opens into the environment via a nozzle outlet opening. A laser beam can pass through the nozzle channel, wherein the laser beam emits in an emission direction from the nozzle via the nozzle outlet opening. In the method, it is provided that the nozzle is cooled directly and / or indirectly by means of cutting gas as well as by means of a cooling fluid. The cutting gas can flow through the nozzle channel and out of the nozzle via the nozzle outlet opening, in particular onto the workpiece to be cut. In the method, the cooling fluid is guided to the nozzle by means of the laser cutting device, in particular by means of a cutting head.The method further provides that the laser cutting device provides the laser beam with a laser power of at least 6 kW. Furthermore, the cutting gas has a cutting pressure of less than 3 bar, in particular less than 1.5 bar. Furthermore, the distance between a focal plane of the laser beam and the nozzle outlet opening of the nozzle is at least 4 mm, in particular at least 8 mm. The nozzle outlet opening can also be referred to as the nozzle orifice.

[0021] In the second method, it is therefore provided that the laser cutting device provides the laser beam with a particularly high power, as a result of which a particularly large development of heat can occur in the nozzle when the laser beam comes into contact with the nozzle. Because the cutting gas has a particularly low pressure in this method, the cooling effect of the cutting gas alone may not be sufficient for the nozzle given the high heat input. Because the distance between the focal plane of the laser beam and the nozzle outlet opening is at least 4 mm, in particular at least 8 mm, it can happen that certain edge regions of the laser beam impinge on a wall delimiting the nozzle channel, as a result of which heat is introduced into the nozzle.The heat input into the nozzle can be amplified by other factors, such as reflection of the laser beam from the workpiece to be cut and absorption of reflected laser beams by the nozzle. Because the nozzle is additionally cooled directly and / or indirectly by the cooling fluid in this process, overheating of the nozzle, especially local overheating of the nozzle, can be particularly effectively prevented. As a result, local melting of the nozzle can be particularly effectively avoided. Furthermore, particularly high accuracy of capacitive distance control between the laser cutting device and the workpiece can be ensured.

[0022] In this context, a further development of the invention can provide that a laser beam diameter within which 86% of the laser beam power is collected is at least 70%, in particular at least 80%, in particular at least 90% of a narrowest inner diameter of the nozzle and thus of the narrowest inner diameter of the nozzle channel. The larger the laser beam diameter of the laser beam within which 86% of the laser beam power is collected, the larger the outer portion of the circumference of the laser beam that comes into contact with the wall of the nozzle delimiting the nozzle channel and is in particular absorbed by it. The laser beam diameter of the laser beam within which 86% of the laser beam power is collected is also referred to below as the 86% laser beam diameter.Since laser beams often have a Gaussian-shaped intensity distribution around the circumference with an intensity maximum in the center, the power of the laser beam absorbed by the nozzle when the edge region of the laser beam is absorbed by the nozzle wall also increases with an increasing 86% laser beam diameter, and consequently, the heat input into the nozzle increases. The larger the 86% laser beam diameter, the more the nozzle must be cooled to prevent overheating, particularly melting of the nozzle. By using the cooling fluid, which cools the nozzle directly and / or indirectly in addition to the cutting gas, overheating of the nozzle can be particularly effectively prevented, even with large 86% laser beam diameters.

[0023] In a further possible embodiment of the invention, the laser cutting device comprises a nozzle as already described in connection with the nozzle according to the invention for a laser cutting device. Due to the geometry of the at least one cooling channel, the nozzle can thus be cooled particularly efficiently by means of the cooling fluid flowing through the at least one cooling channel, whereby overheating of the nozzle can be particularly reliably prevented.

[0024] 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.

[0025] The drawing shows:

[0026] Fig. 1 is a schematic sectional view of a nozzle for a laser cutting device in a first embodiment; and

[0027] Fig. 2 is a schematic sectional view of the nozzle for the laser cutting device in a second embodiment. Figures 1 and 2 show a respective nozzle 10 for a laser cutting device in different embodiments. The nozzle 10 is designed to be attached to a nozzle holder of a cutting head of the laser cutting device. The nozzle 10 comprises a nozzle base body 12 through which a nozzle channel 14 extends. During operation of the laser cutting device, a laser beam radiates through this nozzle channel 14 in an emission direction 16. The emission direction 16 coincides with a central axis 18 of the nozzle channel 14. The central axis 18 of the nozzle channel 14 is simultaneously the central axis of the entire nozzle 10. The entire nozzle 10 is, in particular, rotationally symmetrical. An axial direction 20 of the nozzle 10 coincides with a longitudinal extension direction of the central axis 18.The radial direction of the nozzle 10 is perpendicular to the axial direction 20 and a circumferential direction of the nozzle 10 runs circularly in the axial direction 20.

[0028] The nozzle channel 14 opens into the environment via a nozzle outlet opening 22. The laser beam can radiate out of the nozzle channel 14 via the nozzle outlet opening 22 in the radiation direction 16, in particular onto the workpiece to be cut by the laser cutting device. In addition, a cutting gas can flow through the nozzle channel 14, which can also flow out of the nozzle channel 14 via the nozzle outlet opening 22. With an end 24 opposite the nozzle outlet opening 22 in the axial direction 20, the nozzle 10 can be attached to the cutting head when used as intended. In particular, the nozzle 10 has a nozzle 26 at the end 24, which can be inserted into an opening in the cutting head. The nozzle 10 also has a collar 28, which rests against the cutting head when the nozzle 26 is inserted into the opening of the cutting head. The collar 28 thus provides an axial stop for the nozzle 10.By means of the collar 28, the nozzle 10 can thus be fixed in its position in the axial direction 20 relative to the cutting head.

[0029] Depending on the cutting process and the parameter window used, nozzles 10 with different nozzle channel 14 diameters can be used. Thus, there may be process windows in which the laser beam within the nozzle 10, with its 86% laser beam diameter, reaches a similar or larger diameter than the nozzle channel 14. The 86% laser beam diameter characterizes a region of the laser beam diameter centered on the central axis of the laser beam and in which 86% of the laser beam's power is concentrated. This means that outside the 86% laser beam diameter, a ring runs around this 86% laser beam diameter, encompassing 14% of the laser beam's power.Depending on the ratio of the 86% laser beam diameter to the diameter of the nozzle channel 14, particularly at a narrowest point of the nozzle channel 14, a portion of the laser power transported by the laser beam can be absorbed by a wall in the nozzle 10 that defines the nozzle channel 14. This means that the nozzle base body 12 absorbs a portion of the laser power of the laser beam. The larger the 86% laser beam diameter of the laser beam compared to the diameter of the nozzle channel 14, the greater the proportion of laser power absorbed by the nozzle base body 12. As a result of the absorption of the laser power, the nozzle base body 12 heats up. This can negatively impact the quality of a cut of the workpiece performed by the laser cutting device.

[0030] In particular, if the laser cutting device provides the laser beam with a laser power of at least 6 kW and / or the cutting gas has a cutting gas pressure of less than 3 bar, in particular less than 1.5 bar, and thus the nozzle 10 cannot be sufficiently cooled by the cutting gas, and a distance of a focal plane of the laser beam to the nozzle outlet opening 22 is at least 4 mm, in particular at least 8 mm, and thus the cross-section of the nozzle channel 14 is illuminated by the laser beam over a particularly large area, since the 86% laser beam diameter covers a particularly large portion of the cross-section of the nozzle channel 14, the nozzle base body 12 can heat up considerably. In order to limit this heating of the nozzle 10, it is provided that the nozzle 10 comprises at least one, in particular several, cooling channels 30.

[0031] In the present case, the nozzle 10, in both embodiments shown in the figures, comprises a plurality of cooling channels 30, which are arranged around the circumference of the nozzle 10 and the nozzle channel 14. In this case, the respective cooling channels 30 adjacent in the circumferential direction are equidistant from one another. In other words, the cooling channels 30 are arranged evenly distributed over the circumference of the nozzle 10. The respective cooling channels 30 are designed to have a cooling fluid flow through them, wherein heat is absorbed by the cooling fluid from the nozzle base body 12, thereby cooling the nozzle 10. In the present case, a gas, in particular air, is used as the cooling fluid. The plurality of cooling channels 30 are separated from one another over their entire length. This means that mixing of the cooling fluid guided in the respective cooling channels 30 does not occur as long as the cooling fluid flows through the respective cooling channels 30.Each of the cooling channels 30 comprises an inflow region 32, a deflection region 34, and an outflow region 36. When flowing through the respective cooling channel 30, the cooling fluid first flows through the inflow region 32, is then deflected in the deflection region 34, and finally flows through the outflow region 36. The cooling fluid flows into the cooling channel 30 via the inflow region 32, and flows out of the cooling channel 30 via the outflow region 36. The respective cooling channels 30 can, as shown in the first embodiment in Fig. 1, open directly into the environment at the collar 28. Alternatively, the collar 28 can, as shown in the second embodiment in Fig. 2, have a circumferential annular groove 38, into which all of the cooling channels 30 and their inflow regions 32 open. The cooling fluid can thus be guided from the cutting head into the annular groove 38 and distributed to all cooling channels 30 by means of the annular groove 38.The cooling fluid thus flows through the annular groove 38 and flows from the annular groove 38 into all cooling channels 30.

[0032] In the respective inflow regions 32, the cooling fluid has a first flow direction 40. In the respective outflow regions 36, the cooling fluid has a second flow direction 42. In particular, the cooling fluid has the first flow direction 40 at least in the region of an inflow opening through which the cooling fluid flows into the inflow region 32 of the respective cooling channel 30, and / or the cooling fluid has the second flow direction 42 at least in the region of an outflow opening through which the cooling fluid flows out of the outflow region 36 of the respective cooling channel 30 into the surroundings of the nozzle 10. The first flow direction 40 has an axial direction component which is greater than 0 and coincides with the jet direction 16. This means that the component of the first flow direction 40 running in the axial direction 20 coincides with the jet direction 16.In the present case, the first flow direction 40 and the jet direction 16 together enclose an acute angle α and thus an angle of less than 90°. The second flow direction 42 can, as shown in Fig. 1, have no directional component running in the axial direction 20 and thus enclose an angle β of approximately 90° with the jet direction 16. Alternatively, the second flow direction 42 can, as shown in Fig. 2, have a directional component running in the axial direction 20, which runs opposite to the jet direction 16. This means that the second

[0033] The flow direction 42 forms an angle ß greater than 90° and thus an obtuse angle with the jet direction 16. The cooling fluid flowing out of the respective outlet openings of the cooling channels 30 is particularly well guided away from the cutting gas flowing out via the nozzle outlet opening 22, thereby minimizing the risk of the cooling fluid mixing with the cutting gas. The risk of the cooling fluid influencing the cut made on the workpiece by the laser cutting device can thus be minimized.

[0034] The cooling fluid is sharply deflected in the deflection region 34. This means that the first flow direction 40 and the second flow direction 42 together enclose an angle y of more than 90° and thus an obtuse angle. If the outflow region 36 of the respective cooling channels 30 extends in such a way that cooling fluid flowing in the outflow region 36 is guided at least partially counter to the jet direction 16, as shown in Fig. 2, then in a longitudinal region 44 of the nozzle 10 extending in the axial direction 20, the cooling fluid is first guided in the first flow direction 40 through the inflow region 32 and then in the second flow direction 42 through the outflow region 36. The cooling fluid thus flows through the longitudinal region 44 twice via each of the cooling channels 30. As a result, a particularly large amount of heat can be absorbed by the cooling fluid from the nozzle 10, in particular in the length region 44. As a result, the nozzle 10 can be cooled particularly well.Due to this double routing of the at least one cooling channel 30 in the length region 44, the cooling channel 30 can have a particularly great length. Depending on the design of the cooling channel 30, it can have a length of at least 30%, in particular at least 50%, in particular at least 100%, in particular up to 200% of the length of the nozzle 10 from the collar 28 to the nozzle outlet opening 22, this length being designated L in Fig. 2.

[0035] To facilitate the introduction of the respective cooling channels 30 into the nozzle base body 12, the respective inflow regions 32 can be provided by a first bore and the respective outflow regions 36 can be provided by a second bore, with the deflection region 34 resulting from the intersection of the first bore and the second bore. By providing the bores, the respective cooling channels 30 can be introduced into the nozzle base body 12 particularly easily.

[0036] In order to be able to adjust the flow properties of the cooling fluid in the respective cooling channels 30 with particular precision, it can be provided that at least one fluid guide structure is arranged in the respective cooling channels 30. By means of the at least one fluid guide structure, a flow property of the cooling fluid can be adjusted as it flows through the cooling channel 30, while the cooling fluid flows along the fluid guide structure.

[0037] For laser cutting of a workpiece, a laser beam can be directed onto the workpiece to be cut using a laser cutting device, wherein the laser cutting device has the nozzle 10 described in connection with Figures 1 and 2. Alternatively, the workpiece can be cut using a laser cutting device which has a different nozzle than the nozzle 10. In this case, the laser beam is directed onto the workpiece to be cut using the laser cutting device. The nozzle 10 of the laser cutting device can be cooled directly and / or indirectly using both cutting gas and the cooling fluid. The cooling fluid can be guided to the nozzle 10 by means of the laser cutting device, in particular by means of the cutting head. The laser cutting device provides the laser beam with a laser power of at least 6 kW.The cutting gas has a cutting gas pressure of less than 3 bar, in particular less than 1.5 bar. The distance between a focal plane of the laser beam and the nozzle outlet opening 22 of the nozzle 10 is at least 4 mm, in particular at least 8 mm. An 86% laser beam diameter of the laser beam provided by the laser cutting device can be at least 70%, in particular at least 80%, in particular at least 90% of a narrowest inner diameter of the nozzle 10.

[0038] The nozzle 10 is a cutting nozzle for a laser cutting device, suitable for use with high laser power and a large illumination of the diameter of the nozzle channel 14 by the laser beam. Large illumination means that the laser beam has a beam diameter similar to the diameter of the nozzle channel 14. This nozzle 10 can be used in particular when cutting is to be carried out with high focal positions, in particular with a focus within the nozzle 10, or particularly low focal positions, a large beam diameter, and / or laser radiation with high divergence. The laser cutting device can be used, in particular, to cut metallic workpieces.

[0039] In laser cutting, increasing laser power from available beam sources results in new ranges of process parameters, particularly process windows, in which an optimal cutting result with fast cutting speed and good cut quality can be achieved. In particular, particularly high or low focus positions can be advantageous for achieving good cut edge qualities. When selecting a very high or very low focus position, the laser beam grazes apertures in the nozzle 10, particularly since the laser beam usually has a Gaussian-like power distribution in the radial direction and thus power components of the laser beam are located at a greater distance from the beam axis. Especially when radiating through the nozzle 10, the laser beam can graze the inner contour of the nozzle 10.While shielding edge radiation from areas of the laser beam can be advantageous for a cutting process, it can lead to heating of the nozzle 10 at high laser power. This heating can negatively impact the achievable cutting edge quality. Therefore, the cooling fluid, for example nitrogen, gas, or a gas-water mixture, is provided for flowing through the nozzle 10 via the cooling channels 30.

[0040] The nozzle 10 described in connection with the figures enables particularly good cooling of the nozzle 10, thereby reducing heating of the nozzle 10 and achieving particularly high cut quality when cutting with high laser power and a high or low focus position. The nozzle 10 is designed such that the cooling fluid, in particular a cooling gas or a cooling gas-water mixture, flows through through-flow bores distributed radially in the nozzle base body 12 and flows out of the nozzle 10 through adjoining outlet bores. The respective inflow regions 32 of the cooling channels 30 are provided by the through-flow bores, and the respective outflow regions 36 of the cooling channels 30 are provided by the outlet bores.The outlet holes are arranged at a different angle to the central axis 18 of the nozzle 10 than the throughflow holes, so that the cooling fluid is deflected at a junction between a throughflow hole and an outlet hole connected to this throughflow hole. In this way, the cooling fluid travels a particularly long path through the nozzle 10, allowing a particularly high cooling effect to be achieved.

[0041] Because the respective outflow regions 36 of cooling channels 30 in the second embodiment shown in Fig. 2 guide the cooling fluid at least partially against the jet direction 16, it can be achieved that cooling fluid flowing out of the cooling channels 30 does not interact with the cutting gas. The cooling fluid is thus kept away from a process zone and thus does not interfere with a cutting process, or only interferes to a very small extent. In particular, the respective outflow regions 36 are designed such that the second flow direction 42 causes the cooling fluid flowing out of the respective cooling channels 30 to flow upward along an outer nozzle surface, in order to thereby exert a cooling effect on the nozzle 10. In this case, the laser beam is directed downwards. In particular, the second flow direction 42 and the jet direction 16 can enclose an angle of at least 105°, in particular an angle between 120° and 150°.

[0042] In the present case, it is provided that eight cooling channels 30 are arranged radially around the central axis 18 of the nozzle 10 in the nozzle base body 12.

[0043] Adjacent to the nozzle outlet opening 22, a cylindrical section 46 is arranged inside the nozzle 10 as shown in Figures 1 and 2 as part of the nozzle channel 14. The cylindrical section 46 has a length of at least 2 mm, in particular between 3 mm and 4 mm. The cylindrical section 46 acts as a reflection section for the laser beam, so that edge regions of the laser beam, which within the cylindrical section 46, with its 86% laser beam diameter, reaches a diameter similar to or larger than that of the nozzle channel 14, can be reflected on the inner wall of the nozzle base body 12. The cylindrical section 46 is arranged in a solid partial region 47 of the nozzle base body 12, into which the cooling channels 30 do not extend. The deflection region 34 of the cooling channels 30 is therefore arranged above the solid partial region 47 in the longitudinal direction of the nozzle 10.The length L1 of the solid portion 47 in the longitudinal direction of the nozzle 10 is at least 5 mm, in particular at least 7 mm, but not more than 30%, preferably not more than 25% of the total length of the nozzle 10. The wall thickness of the solid portion 47 never falls below a value of 2.5 mm. In this way, sufficient heat dissipation from the reflection section 46 via the solid portion 47 to the cooling channels 30 is achieved while maintaining a slim and stable shape of the nozzle 10.

[0044] In the process in which the workpiece is cut using the laser cutting device, the nozzle 10 is actively cooled during laser cutting. Particularly in cutting processes with a low cutting gas pressure within the nozzle 10, the cooling effect of the cutting gas on the nozzle 10 may under certain circumstances be insufficient to dissipate the heat absorbed by the nozzle base body 12 upon absorption or diffuse reflection of the laser beam. In a cutting process with a large illumination of the nozzle 10 by the laser beam and a low cutting gas pressure, when using the described nozzle 10, the cooling fluid flows through or over the nozzle 10 and / or a nozzle holder of the nozzle 10 on the cutting head for additional cooling. There are various options for cooling the nozzle 10, as described below. A water- or oil-flowing nozzle holder can be provided on the cutting head.In this case, cooling water or oil flows through the nozzle holder or mount on the cutting head, thus indirectly cooling the nozzle. This variant allows for a particularly simple cooling design, as cooling water is usually already available for cooling other components on the cutting head. A closed cooling circuit is created, preventing any cooling fluid from escaping when changing the nozzle.

[0045] A nozzle cooled directly with liquid coolant does not have a closed cooling circuit. Furthermore, water or a water / air mixture typically flows through or over the nozzle. Cooling can be achieved through evaporative cooling, with the water ideally evaporating completely. Care must be taken to ensure that no water on the workpiece surface has a negative effect on the cutting process.

[0046] When the nozzle 10 is cooled with a cooling gas, the heat absorbed during the expansion of the cooling gas can be used for cooling. The cooling gas can flow over or through the nozzle 10. If air is used as the cooling fluid, the air can flow through the cooling channels 30 of the nozzle 10 at a volume flow rate of at least 50 liters / minute.

[0047] In particular, in the case of an oxygen flame cut with low cutting gas pressures, which are typically below 3 bar, or in the case of a nitrogen fusion cut with cutting gas pressures of less than 10 bar, sufficient cooling of the nozzle 10 by the cutting gas alone may not be ensured, which is why the cooling channels 30 are provided in the described nozzle 10, through which the cooling fluid can flow, whereby sufficient cooling of the nozzle 10 during laser cutting can be ensured.

[0048] On the one hand, small nozzle diameters may be required on the process side to achieve the highest cutting qualities, and on the other hand, focus positions and focus diameters may be required for laser processing, which lead to a large beam cross-section of the laser beam in the nozzle 10 relative to the nozzle diameter. Furthermore, a multi-part cutting nozzle can be used as the nozzle 10, or the nozzle 10 can have finely structured structures inside, which are designed to increase cutting quality or cutting productivity or to reduce cutting gas consumption. However, due to their thin-walled shape, these nozzle components can potentially be destroyed upon contact with the laser beam. Specifically, very high or very deep focus positions are critical here.Very large focus diameters are critical if a beam waist lies within the nozzle 10; very large divergences are critical if the beam waist lies outside the nozzle 10. The problem of heating up cutting nozzles can be exacerbated by a laser beam that is not exactly centered on the central axis 18 of the nozzle 10, by thermal focus shift, or by operator interventions and thus by parameter changes. Heating up the nozzle 10 can reduce the cutting quality, since with capacitive distance control, the distance between the nozzle 10 and the sheet surface changes. At the very latest, when the nozzle 10 melts, a significant impact on the cutting result can be expected. The disadvantages described can be particularly well avoided by the active cooling of the nozzle 10 described above.

[0049] The cooling effect at the nozzle 10 is achieved in this case by, for example, air from a cutting head being blown into the annular groove 38. From this circumferential annular groove 38 in the nozzle 10, the plurality of cooling channels 30 run towards the underside of the nozzle. By means of the outflow regions 36, the cooling fluid is directed radially or upwardly away from a process zone. The cooling effect is achieved by a particularly long path of the cooling fluid through the cooling channels 30. A large number of cooling channels 30 around the circumference of the nozzle 10 enables particularly high cooling performance. The respective outflow openings of the cooling channels 30 are directed particularly steeply upwards in order to allow the cooling fluid flowing out of the cooling channels 30 to flow along the outside of the nozzle 10.With this alignment of the outlet openings of the respective cooling channel 30, the outside of the nozzle 10 as well as components of the laser cutting device located further upstream, such as a nozzle holder, can also be cooled by the cooling fluid. Furthermore, this keeps the cooling fluid away from the process zone, ensuring a cutting process uninterrupted by the cooling fluid.

[0050] The cooling effect can be further enhanced by spraying a small amount of water into the cooling fluid flow, by increasing the cooling fluid volume flow, by increasing the number of cooling channels 30 around the circumference, and / or by extending the respective cooling channels 30 and thus the respective cooling section. Overall, the invention shows how an air-cooled cutting nozzle and a cutting process can be provided using such a nozzle 10.

[0051] LIST OF REFERENCE SYMBOLS

[0052] 10 nozzle

[0053] 12 nozzle bodies

[0054] 14 nozzle channel

[0055] 16 Beam direction

[0056] 18 Central axis

[0057] 20 axial direction

[0058] 22 Nozzle outlet opening

[0059] 24 End

[0060] 26 nozzles

[0061] 28 collars

[0062] 30 cooling channel

[0063] 32 Inflow area

[0064] 34 Deflection area

[0065] 36 Outflow area

[0066] 38 ring groove

[0067] 40 first flow direction

[0068] 42 second flow direction

[0069] 44 length range

[0070] 46 cylindrical section

[0071] 47 massive sub-area

Claims

PATENT CLAIMS 1. Nozzle (10) for a laser cutting device, with a nozzle channel (14) which opens into the environment via a nozzle outlet opening (22) and which can be irradiated by a laser beam, the laser beam radiating in an irradiation direction (16) from the nozzle (10) via the nozzle outlet opening (22), - at least one cooling channel (30) through which a cooling fluid can flow and which has an inflow region (32), an adjoining deflection region (34) and an outflow region (36) adjoining the deflection region (34), wherein cooling fluid flowing in the cooling channel (30) is guided at least partially in the jet direction (16) in the inflow region (32), is deflected in the deflection region (34) and is then guided in the outflow region (36), a collar (28) which, when installed as intended, is applied to a cutting head, whereby the at least one cooling channel (30) can be supplied with cooling fluid by the cutting head in the installed position.

2. Nozzle (10) according to claim 1, characterized in that the nozzle (10) comprises a plurality of cooling channels (30) distributed around a central axis of the nozzle (10), which are completely separated from one another over their entire length.

3. Nozzle (10) according to claim 1 or 2, characterized in that the outflow region (36) of the at least one cooling channel (30) extends in such a way that cooling fluid flowing in the outflow region (36) of the cooling channel (30) is guided at least partially counter to the jet direction (16).

4. Nozzle (10) according to one of the preceding claims, characterized in that the collar (28) has a circumferential annular groove (38), whereby, when installed as intended, cooling fluid can flow from the cutting head into the annular groove (38), wherein the at least one cooling channel (30) extends at one end into the annular groove (38), whereby the cooling fluid can flow from the annular groove (38) into the inflow area (32) of the cooling channel (30).

5. Nozzle (10) according to one of the preceding claims, characterized in that a length of the at least one cooling channel (30) is at least 30%, in particular at least 50%, in particular at least 100% of the length of the nozzle (10) from the collar (28) to the nozzle outlet opening (22).

6. Nozzle (10) according to one of the preceding claims, characterized in that the at least one cooling channel (30) has a fluid guide structure by means of which a flow property of the cooling fluid can be adjusted when flowing through the cooling channel (30).

7. Nozzle (10) according to one of the preceding claims, characterized in that the inflow region (32) and the outflow region (34) are provided by respective bores.

8. Nozzle (10) according to one of the preceding claims, characterized in that a nozzle base body (12) adjacent to the nozzle outlet opening (22) has a solid partial region (47) into which the at least one cooling channel (30) does not extend.

9. Nozzle (10) according to one of the preceding claims, characterized in that a cylindrical section (46) is arranged adjacent to the nozzle outlet opening (22) in the interior of the nozzle (10) as part of the nozzle channel (14).

10. A method for laser cutting a workpiece, in which a laser beam is directed onto the workpiece to be cut by means of a laser cutting device, wherein the laser cutting device has a nozzle (10) according to one of the preceding claims.

11. A method for laser cutting a workpiece, in which a laser beam is directed onto the workpiece to be cut by means of a laser cutting device, wherein a nozzle (10) of the laser cutting device is cooled directly and / or indirectly by means of cutting gas as well as by means of a cooling fluid and the cooling fluid is guided to the nozzle (10) by means of the laser cutting device, the laser cutting device provides the laser beam with a laser power of at least 6 kW, the cutting gas has a cutting gas pressure of less than 3 bar, in particular less than 1.5 bar, a distance of a focal plane of the laser beam to the nozzle outlet opening (22) of the nozzle (10) is at least 4 mm, in particular at least 8 mm.

12. The method according to claim 11, characterized in that a laser beam diameter within which 86% of the power of the laser beam is collected is at least 70%, in particular at least 80%, in particular at least 90% of a narrowest inner diameter of the nozzle (10).

13. Method according to claim 11 or 12, characterized in that the laser cutting device has a nozzle according to one of claims 1 to 9 as the nozzle (10).

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