Material deposition unit with multiple material focus zones and deposition welding process

Abstract

The invention relates to a material deposition unit and a method for build-up welding, wherein material focus zones arranged offset from one another are provided.

Description

Laser deposition welding (also laser metal deposition, direct metal deposition (DMD) or direct energy deposition (DED) is a generative manufacturing method for metallic structures.Laser deposition welding is carried out in principle as follows: a melt bath is produced on a component surface by means of a laser. By means of a powder dispensing device, usually in the form of a nozzle, metal powder is introduced automatically. This results in beads or material layers welded to one another, which result in structures on existing base bodies or components.Laser deposition welding makes it possible, for example, to apply 3D structures to existing, possibly even uneven, surfaces. Changes in geometry can be easily implemented in this way. By changing the powder or powder composition, it is possible to change between different materials in a working process. It is also possible to mix the powder used from different materials and thereby produce alloys. To create wear protection layers, it is possible, for example, to feed a matrix material melting in the melt bath in powder form and, in addition, to feed a hard material, which typically does not melt at the temperatures prevailing in the melt bath, likewise in powder form.In laser deposition welding, a material deposition unit is usually used, having a laser unit configured to direct a laser beam onto a workpiece, and having a powder dispensing device configured to dispense powder in directed form onto the workpiece.The powder dispensing device is usually designed in such a way that it dispenses the material powder in the direction of the workpiece via a plurality of powder dispensing units, which can be designed, for example, as powder outlet openings or else as annular gap nozzles. This results in a plurality of powder jets. These powder beams are focused in a material focus zone. The systems hitherto are sensitive with regard to the distance of the powder dispensing device from the workpiece and the combination of the pitch angle distance and the diameter of the material focus.DE 11 2015 001 289 T5 discloses a nozzle for an apparatus for producing a layered object, in which a plurality of powder dispensing units are provided, which are each tiltably fastened to the nozzle, so that a jet angle-and thus a jet focus-of the powder can be changed.It is now the object of the present invention to provide a material deposition unit and a method for laser deposition welding which are particularly flexible and enable a robust process management. This object is achieved by a material deposition unit according to claim 1 and a method for laser deposition welding according to claim 11. Further embodiments of the invention are specified in the dependent claims and in the following description.The material deposition unit according to the invention thus comprises: a laser unit and a powder dispensing device. The laser unit is configured to direct a laser beam along a beam axis extending in a beam direction onto a workpiece and to focus it there. The laser beam focused there generates a melt pool or a melt bath on the workpiece. The powder dispensing device is configured to dispense a material powder, which is typically a metallic powder or comprises such a powder, to the workpiece. Typically, this is realized by a powder gas jet. The powder delivery device comprises a plurality of powder delivery units which are configured to deliver the powder to the workpiece in directed form (for example in the form of a jet or a plurality of jets). According to the invention, the material deposition unit is characterized in that the powder dispensing device comprises at least a first powder dispensing unit and a second powder dispensing unit, which are each configured such that they focus the material powder dispensed by them at a respective first and second material focus zone.The first and second material focus zones are arranged spaced apart from one another in the beam direction. In other words, the regions in which the powder beams emitted by the powder-emitting units are brought together in a focused manner (i.e. the material focus zones of the individual powder-emitting units) are spaced apart from one another along the direction in which the laser beam is directed onto the workpiece. Typically, the material focus zones are incident on the beam axis.It is typically further provided that each of the powder dispensing units has a plurality of powder outlet openings. Accordingly, the first powder dispensing unit typically has a plurality, in particular at least three, first powder outlet openings. The second powder dispensing unit typically has a plurality, in particular at least three, second powder outlet openings.In the respective material focus zone, the individual powder jets from the powder outlet openings are brought together or focused. The individual powder jets thus meet in this zone. For this purpose, the powder dispensing units or the respective powder outlet openings are arranged and configured accordingly. In other words, they are configured such that they emit the powder jets in a correspondingly directed manner.It can typically be provided that the plurality of first powder outlet openings and the plurality of second powder outlet openings each comprise the same number of respective powder outlet openings. In this way, it can be ensured in particular in a simple manner that the same quantity of material is focused in each of the two material focus zones. In addition, direction-independent material focus zones can be created in a simple design.According to the invention, it can further be provided that the first powder outlet openings are configured to emit a powder jet at a first powder feed angle relative to the jet axis in the direction of the first material focus zone and the second powder outlet openings are configured to emit a powder jet at a second powder feed angle relative to the jet axis in the direction of the second material focus zone. Here, the first powder supply angle and the second powder supply angle may be different. This makes it possible, for example, to create an offset arrangement of material focus zones along the beam axis, wherein, however, the powder outlet openings of the first and second types can be arranged at the same height as viewed along the beam axis.However, the first and the second powder feed angle can also be identical and the powder outlet openings can nevertheless be arranged in the same plane along the beam axis, wherein it can then be provided, for example, that the powder outlet openings of the first and second type are arranged at different distances from the beam axis in order to realize the material focus zones spaced apart along the beam axis. For example, the powder outlet openings of the first type can be arranged on a first imaginary circle about the jet axis and the powder outlet openings of the second type can be arranged on a second imaginary circle about the jet axis. Typically, it can generally be provided that the powder outlet openings of the first type all have the same powder feed angle and that the powder outlet openings of the second type likewise all have the same powder feed angle (optionally different from the first).It can be provided in particular that the first powder outlet openings are arranged at a first distance from the beam axis when viewed in a viewing plane running orthogonally to the beam axis and the second powder outlet openings are arranged at a second distance from the beam axis in this viewing plane, which differs from the first distance. The powder outlet openings of the first and second types can lie in the viewing plane when viewed along the beam direction (i.e. lie at the same "height" along the beam axis). Typically, the powder outlet openings of the first type lie on a first imaginary circle around the jet axis and the powder outlet opening of the second type lies on a second imaginary circle around the jet axis.It is also possible for the powder outlet openings of the two types to be arranged in the viewing plane at the same distance from the beam axis or to be arranged in each case on the same imaginary circle around the beam axis. The powder outlet openings can lie in the viewing plane. Typically, the powder outlet openings in this case are designed such that they have different powder feed angles.It can further be provided that the powder outlet openings of the first and second types lie in a first and second plane running orthogonally to the jet axis, wherein the two planes are arranged spaced apart from one another in the jet direction. In other words, it can be provided that the different types of powder outlet openings are arranged at different heights along the jet axis in the jet direction.It can further be provided that the material deposition unit comprises a powder division unit, by means of which a central powder flow is distributed uniformly over the various powder dispensing units or uniformly over the various powder outlet openings.Typically, the material deposition unit is configured such that the powder outlet openings are arranged in a uniformly distributed manner around the jet axis in the circumferential direction. This results in particular in a preferred uniform application behavior of the material deposition unit. According to the invention, it can also be provided that the plurality of first powder outlet openings is connected to a powder source different from the plurality of second powder outlet openings. This is particularly suitable when different powder materials are to be applied in combination. For example, a hard material can thereby be combined with a matrix material, so that wear protection layers can be applied in an advantageous manner. The matrix material is then preferably applied with a different material focus than the hard material particles.The present invention also relates to a method for laser deposition welding, as described above. In this method, a laser beam is focused on a workpiece surface along a beam axis extending in the beam direction. A melt bath is produced by focusing the laser beam. A powder material is supplied to the melt bath via a plurality of powder jets. The method according to the invention is characterized in that a plurality of powder beams is focused in a first material focus zone and a second plurality of powder beams is focused in a second material focus zone, wherein the two material focus zones are arranged spaced apart from one another along the beam axis.In a development according to the invention, it can be provided that a matrix material is supplied to the melt bath via the first plurality of powder jets, wherein this matrix material typically melts in the melt bath (or under the conditions prevailing there) and can be formed, for example, by a metallic material. In this method variant, a hard material is supplied to the melt bath via the second plurality of powder jets, and typically does not melt up in the melt bath (or is selected such that the hard material particles do not melt under the conditions prevailing there, or do not melt until the melt bath has solidified again). This method variant is thereby suitable in particular for producing anti-wear layers.In an advantageous development of the method according to the invention, one of the material deposition units described in this application is used to carry out the method.Further features, possible applications and advantages of the invention are evident from the following description of exemplary embodiments of the invention, which are explained on the basis of the drawing, wherein the features can be essential for the invention both alone and in different combinations, without explicit reference again being made thereto. The following are shown: FIG. 1 shows a material deposition unit according to the invention when irradiating a workpiece; FIG. 2 shows an arrangement according to the invention of powder outlet openings with different powder feed angles; FIG. 3 shows a material deposition unit with two different types of powder outlet openings with the same powder feed angle; and FIG. 4 shows corresponding components and elements in the following figures with the same reference numerals. Variants of corresponding elements are further marked with letters, wherein a reference sign without letters refers to all such variants that are further differentiated by letters. For the sake of better clarity, not all reference numerals are reproduced in all figures.A material deposition unit in FIG. 1 generally has the reference numeral 10.The laser unit 12 is configured in such a way that it directs a laser beam 20 in a beam direction 22 onto a workpiece 24. The jet direction 22 extends along a jet axis 26. The powder dispensing units 16 or powder outlet openings 18 are each configured to dispense a powder 27 in the form of respective powder jets 28 in directed form onto the workpiece 24. In this case, a plurality of first powder outlet openings 18 aare provided in the present case and a plurality of second powder outlet openings 18 b, not shown. First powder jets 28 aemerge from the first powder outlet openings 18 aand second powder jets 28 bemerge from the second powder outlet openings 18 b. The second powder outlet openings 18 bare arranged offset with respect to the first powder outlet openings 18 ain a circumferential direction U about the jet axis 26.The laser beam 20 is focused on the workpiece 24 and forms a melt pool 30 on the workpiece 24 or on the surface 29 thereof. The powder jets 28 aand 28 bor the powder 27 transported through them respectively enter the melt bath 30, wherein powder jets 28 aare focused in a first material focus zone 32 aand the second powder jets 28 bare focused in a second material focus zone 32 b. The material focus zones 32 are located behind the melt pool 30 in the present case along the transport direction of the powder jets 28. Since the laser beam is guided over the workpiece along a movement direction 34, the previously melted melt pool 30 enriched by the powder material 27 and an applied material layer 36 remain solidified.In FIG. 2, the material deposition unit 10 is schematically illustrated as viewed from the workpiece along the beam axis 26.As can be seen in FIG. 2, in the present example the powder outlet openings 18 aof the first type and the powder outlet openings 18 bof the second type lie on a common imaginary circle 38 (the imaginary circle is arranged in this case in a viewing plane 39 which extends orthogonally to the beam axis 26 and in which the powder outlet openings 18 lie). The powder outlet openings 18 are configured in such a way that they have powder feed angles 40, wherein the powder feed angles 40 aof the powder outlet openings 18 aof the first type and the powder feed angles 40 aof the powder outlet openings 18 bof the second type are different. The different powder feed angles 40 result in material focus zones 32 arranged offset along the beam axis. The powder feed angles 40 describe the angle at which the respective powder jets 28 emerging from the outlet openings 18 run to the beam axis 26.In FIG. 3, an alternative material deposition unit 10 is shown, in which the outlet openings 18 aand 18 bof the first second type have the same powder feed angle 40 aand 40 b, respectively. However, in order to realize different material focus zones 32, the powder outlet openings 18 aof the first type and the powder outlet openings 18 bof the second type are arranged on different imaginary circles 38 and 42 around the beam axis 26.A formation of a material deposition unit 10 as shown in FIG. 4 is also possible. In the version of FIG. 4, the material outlet openings are each arranged in two different planes 44 arranged offset with respect to one another in the direction of the beam axis 28. The powder outlet openings are only shown symbolically. In FIG. 4, the material deposition unit 10 is shown in a side view similar to that of FIG. 1.In FIG. 5, a schematic material deposition unit 10 is shown, which comprises a powder division unit 46. The powder dividing unit 46 is configured to uniformly distribute a central powder flow 48 to the powder outlet openings 18. For this purpose, it divides the central powder stream 48 into corresponding partial streams. The central powder stream 48 is supplied to the powder dividing unit 46 from a central powder source 52 as a powder gas stream.In FIG. 6, a schematic material deposition unit 10 is shown, which comprises a first powder division unit 46 aand a second powder division unit 46 b. The powder dividing units 46 are configured to uniformly distribute a first central powder stream 48 aand a second central powder stream 48 a, respectively, to the respective first and second powder outlet openings 18 a, 18 b. For this purpose, they each divide the central powder stream 48 aand 48 bassociated with them into corresponding partial streams 50 aand 50 b, respectively, which in turn are fed to the corresponding first and second powder outlet openings 18 aand 18 b. The central powder streams 48 are fed in each case by a central powder source 52 aand 52 b, respectively, by means of a powder gas stream. In this case, the first powder source 52 aprovides a matrix material in powder form and the second powder source 52 ba hard material. Accordingly, the material deposition unit 10 shown in FIG. 6 is suitable in particular for the production of wear protection layers. It is also conceivable in the variant of FIG. 5 to conduct a mixture of matrix material via the central powder source 52 to the powder outlet openings 18 in order to produce wear protection layers.

Claims

A material deposition unit (10) comprising: a laser unit (12) configured to direct a laser beam (20) onto a workpiece along a beam axis (26) extending in the beam direction (22), and a powder dispensing device (14), wherein the powder dispensing device (14) has a plurality of powder dispensing units (16) configured to dispense powder in directed form onto the workpiece (24), characterized in that the powder dispensing device (14) comprises at least one first powder dispensing unit (16), which in particular has a plurality of first powder outlet openings (18a), having a first material focus zone (32a) and further comprises a second powder dispensing unit (16), which in particular has a plurality of second powder outlet openings (18b), having a second material focus zone (32b), wherein the first and second material focus zones (32a, 32b) are spaced apart from one another in the beam direction (22).The material deposition unit (10) of claim 1, wherein the plurality of first powder exit openings (18a) and the plurality of second powder exit openings (18b) each comprise an equal number of powder exit openings (18).The material deposition unit (10) according to claim 1 or 2, wherein the first powder outlet openings (18a) are configured to emit a powder jet (28a) in each case at a first powder feed angle (40a) relative to the jet axis (26) in the direction of the first material focus zone (32a), and the second powder outlet openings (18b) are configured to emit a powder jet (28b) in each case at a second powder feed angle (40b) relative to the jet axis (26) in the direction of the second material focus zone (32b), wherein the first powder feed angle (40a) and the second powder feed angle (40b) are different.Material deposition unit (10) according to one of the preceding claims, wherein the first powder outlet openings (18a) are configured to emit a powder jet (28a) in each case at a first powder feed angle (40a) relative to the jet axis (26) in the direction of the first material focus zone (32a), and the second powder outlet openings (18b) are configured to emit a powder jet (28b) in each case at a second powder feed angle (40b) relative to the jet axis (26) in the direction of the second material focus zone (32b), wherein the first powder feed angle (40a) and the second powder feed angle (40b) are identical.Material deposition unit (10) according to one of the preceding claims, wherein the first powder outlet openings (18a) are arranged at a first distance from the beam axis (26) when viewed in a viewing plane running orthogonally to the beam axis (26), and the second powder outlet openings (18b) are arranged in this viewing plane at a second distance, which differs from the first distance, from the beam axis (26), in particular wherein the first powder outlet openings (18a) and the second powder outlet openings (18b) are arranged in the viewing plane when viewed along the beam direction.Material deposition unit (10) according to one of Claims 1 to 4, wherein the first powder outlet openings (18a) and the second powder outlet openings (18b), as seen in a viewing plane running orthogonally to the beam axis (26), are arranged in each case at the same distance from the beam axis (26), in particular wherein the first powder outlet openings (18a) and the second powder outlet openings (18b), as seen along the beam direction (22), are situated in the viewing plane.Material deposition unit (10) according to one of the preceding claims, wherein the first powder outlet openings (18a) lie in a first plane (44a) running orthogonally to the beam axis (26), and the second powder outlet openings (18b) lie in a second plane (44b) running orthogonally to the beam axis (26), which is arranged spaced apart from the first plane (44a) in the beam direction (22).Material deposition unit (10) according to one of the preceding claims, wherein it comprises a powder division unit (46) which is designed to uniformly distribute a central powder flow (48) to the powder dispensing units (16), in particular to the powder outlet openings (18).Material deposition unit (10) according to one of the preceding claims, wherein the powder outlet openings (18) are arranged uniformly distributed around the jet axis (26) in the circumferential direction (U).The material deposition unit (10) according to any one of the preceding claims, wherein the plurality of first powder outlet openings (18a) is connected to a different powder source (52) than the plurality of second powder outlet openings (18b).Method for laser deposition welding, wherein a laser beam (20) is focused on a workpiece surface along a beam axis (26) extending in the beam direction (22) in order to produce a melt pool (30), and a powder material is supplied to the melt pool (30) via a plurality of powder beams (28), characterized in that a plurality of first powder beams (28a) is focused in a first material focus zone (32a) and a plurality of second powder beams (28b) is focused in a second material focus zone (32b), wherein the two material focus zones (32) are spaced apart from one another along the beam axis (26).Method according to Claim 12, characterized in that a matrix material is fed to the melt bath via the plurality of first powder jets (28a), and a hard material is fed to the melt bath (30) via the plurality of second powder jets (28b).Method according to one of the two preceding claims, characterized in that a material deposition unit (10) according to one of Claims 1 to 11 is used to carry out the method.

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