METHOD FOR ADDITIVE MANUFACTURING BY MEANS OF DUAL SELECTIVE IRRADIATION OF A POWDER BED AND PREHEATING

Abstract

A method and device for powder bed additive manufacturing of a component includes the selective irradiation of a layer made of a powder material with a first energy beam and a second energy beam, that is different from the first, wherein the second energy beam annularly surrounds the first energy beam, and the aselective heating of the layer, wherein a large part of the layer is heated to a temperature that is at least one quarter of the temperature that the layer is heated to as a result of the selective irradiation.

Claims

1. A method for powder bed-based additive manufacturing of a component, comprising: selective irradiation of a layer composed of a pulverulent material with a first energy beam and a second energy beam, different than the first energy beam, wherein the second energy beam surrounds the first energy beam in a ring-shape, and aselective heating of the layer, wherein a large portion of the layer is heated to a temperature of at least one quarter of the temperature which the layer experiences as a result of the selective irradiation.

2. The method as claimed in claim 1, wherein the first energy beam comprises a melting laser and the second energy beam comprises a further laser beam, having a lower radiation intensity than the melting laser.

3. The method as claimed in claim 2, wherein the further laser beam brings about a local heating of the layer to a temperature of above 500° C.

4. The method as claimed in claim 1, wherein the aselective heating is effected at a temperature of between 400° C. and 500° C. and/or between 50° C. and 100° C. below an initial temperature for formation of phase precipitates.

5. The method as claimed in claim 1, wherein the aselective heating is effected below a sintering temperature of the pulverulent material.

6. The method as claimed in claim 1, wherein the aselective heating is effected by an inductive heating of a building chamber, a radiant heating facility, an infrared emitter, or by way of a heating of a build platform.

7. The method as claimed in claim 1, wherein the aselective heating is carried out for a purpose of preheating the layer.

8. The method as claimed in claim 1, wherein the aselective heating is carried out simultaneously with the selective irradiation of the layer.

9. The method as claimed in claim 1, wherein the pulverulent material constitutes an alloy which is difficult to weld.

10. The method as claimed in claim 1, wherein the manufactured component is subjected to a thermal aftertreatment.

11. The method as claimed in claim 1, wherein the first energy beam and the second energy beam are directed at the layer via a common optical unit.

12. The method as claimed in claim 2, wherein the melting laser and the further laser beam are fed to a common optical unit via a semi-transparent beam splitter.

13. An apparatus for powder bed-based additive manufacturing of a component, which apparatus is configured for carrying out a method as claimed in claim 1, comprising: a build platform, a coating device, a melting laser, a further laser, and a common optical unit for the melting laser and the further laser, and a device for the aselective heating of the layer.

14. The method as claimed in claim 3, wherein the local heating comprises preheating.

15. The method as claimed in claim 4, wherein the aselective heating is effected for formation of a gamma prime phase of the pulverulent material.

16. The method as claimed in claim 9, wherein the alloy comprises a γ′-hardening nickel- or cobalt-based superalloy.

17. The apparatus as claimed in claim 13, wherein the device for the aselective heating of the layer comprises a device for inductive heating of a building chamber, a radiant heating facility, or an infrared emitter.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0044] FIG. 1 shows a schematic side view of an apparatus in accordance with one embodiment of the present invention;

[0045] FIG. 2 indicates a schematic plan view of two laser beams which are generated using the apparatus illustrated in FIG. 1 and

[0046] FIG. 3 schematically indicates beam intensities of the laser beams illustrated in FIG. 2.

DETAILED DESCRIPTION OF INVENTION

[0047] In the exemplary embodiments and figures, identical or identically acting elements may each be provided with the same reference signs. The illustrated elements and their size relationships among one another should not be regarded as true to scale, in principle; rather, individual elements may be illustrated with exaggerated thickness or size dimension in order to enable better illustration and/or in order to afford a better understanding.

[0048] FIG. 1 shows an apparatus 1 in accordance with one embodiment of the present invention, which serves for the powder bed-based additive manufacturing of a component 2 or of a component portion; in particular for selective laser sintering, selective laser melting or electron beam melting.

[0049] The component 2 can be a component of a turbomachine, for example a component for the hot gas path of a gas turbine. In particular, the component can denote a rotor blade or guide vane, a ring segment, a burner part or a burner tip, a shroud, a screen, a heat shield, a nozzle, a seal, a filter, an orifice or lance, a resonator, a piston or a swirler, or a corresponding transition, insert, or a corresponding retrofit part. Alternatively, the component can denote some other component, in particular a component for applications in aeronautics or in automobility.

[0050] The apparatus 1 comprises a build platform 3, which is movable, in particular lowerable, in a vertical z-direction up and down within a building chamber 4. Furthermore, a powder supply 5 is provided. The latter comprises a powder chamber 6 for accommodating pulverulent material 7, a powder feed piston 8, which is movable in the z-direction up and down within the powder chamber 6, and a coating device with a squeegee 9, which is movable back and forth in the y-direction and designed to transport material 7 contained in the powder chamber 6 to the building chamber 4 and to distribute it uniformly with a predetermined layer thickness (cf. reference sign d) in the region of a construction zone of the building chamber 4.

[0051] Furthermore, the apparatus 1 has a first beam source, preferably a melting laser 11, and a second beam source, for example a further, second, laser 12. Furthermore, the apparatus 1 has a common optical unit or optical element 13 for the first beam source or the first beam 11 and the second beam source or the second beam 12.

[0052] The first beam source (first energy beam) and the second beam source (second energy beam) are preferably in each case lasers or laser beams, in particular such lasers which emit laser beams 14 and 15 having wavelengths in the infrared range, such as, for example, Nd-Yag- or CO.sub.2 lasers or the like (cf. SLM). Alternatively, the aforementioned beam sources/beams can also be particle radiation, such as electron beams (cf. EBM).

[0053] The optical unit or optical element 13 comprises a scanner 16 and an F-theta lens 17. Arranged between the first energy beam 11 and the second energy beam 12 and the optical element 13 is a semi-transparent mirror or beam splitter 18, which directs the laser beam 14 of the first energy beam 11 and of the second energy beam 15 of the preheating laser 12 jointly to the optical element 13, from where the energy beams are directed at the construction zone via the scanner 16 and the F-theta lens 17—on the basis of layer information of a component layer 10 to be manufactured, which information is normally generated using software by means of computer-aided modeling from a CAD file.

[0054] In order to manufacture a component 2 or a component portion using the apparatus 1, in a first step the build platform 3 is moved into a position which lies below the construction by an amount corresponding to the layer thickness d of the component layer 10 that is subsequently to be generated, wherein the layer thickness d normally lies in a range of between 10 and 100 μm, in particular between 20 and 40 μm. The powder feed piston 8 is positioned above the construction zone by an analogous amount. Afterward, the squeegee 9, proceeding from the position illustrated by dashed lines at the far left in FIG. 1, is moved into the far right position, likewise illustrated in a dashed manner, with the result that a layer 10 of the pulverulent component material 7 is distributed uniformly on the component platform 3. Subsequently, this layer 10 is locally melted and solidified in the region of the construction zone. For this purpose, the beams 14 and 15 are directed at the beam splitter 18 in such a way that the cross-sectionally circular laser beam or laser focus 14 of the processing laser 11 is surrounded ring-shapedly by the laser beam 15 of the preheating laser 12 or the focus thereof, as is illustrated schematically in FIG. 2. In the present case, this is achieved by operating the processing laser 11 in the Gaussian mode and the preheating laser 12 in the “donut mode” or “bagel mode”.

[0055] In this case, the radiation intensity of the laser beam 14 of the melting laser 11 is preferably significantly higher than that of the laser beam 15 of the further laser 12, as is shown schematically in the perspective illustration in FIG. 3.

[0056] The further laser beam 15 preferably brings about selective or local heating, in particular preheating, of each layer 10 to a temperature of at least 400° C., preferably of at least 500° C. During the construction of the component 2, a heat input of the further laser beam 15 is expediently superposed with a heat input of the laser beam 14 of the melting laser 11, such that the melting point of the material 7 can expediently be exceeded and the structure for the component can be solidified.

[0057] The laser beams 14 and 15, proceeding from the beam splitter 18, are directed jointly to the optical element 13, from where they are directed at the construction zone via the scanner 16 and the lens 17. In this case, the joint movement of the laser beams 14 and 15 relative to the construction zone is controlled (selectively) depending on layer information of the component layer 10 to be manufactured in each case.

[0058] Thanks to the ring-shaped arrangement of the laser beam 15 of the preheating laser 12 around the laser beam 14 of the processing laser 11, the laser beam 15 subjects the powder that is ultimately to be melted by the laser beam 14 to not only preheating but in part also post-heating, since the laser beam 15 both leads and lags behind the laser beam 14. Accordingly, high temperature gradients during the melting and thus hot cracking are effectively counteracted, wherein the radiation intensities of the laser beams 14 and 15 can be chosen independently of one another and can thus be optimally adapted to the component material 7 to be processed, the layer thickness d to be produced, and to the aselective, large-area or global heating described below.

[0059] Consequently, even the processing of component materials which are difficult to weld or hitherto have been scarcely weldable or not weldable at all is possible, such as the processing of a γ′-hardening nickel-base superalloy, in particular with a high proportion of γ′-precipitates, to mention just one example. In order to produce the next and succeeding layers, the component platform 3 is in each case lowered once again by a layer thickness d, and pulverulent component material 7 is applied and selectively melted.

[0060] One major advantage of the method according to the invention consists, firstly, in the above-described avoidance of hot cracking thanks to the flexibly adjustable and also local preheating and controlled cooling of the powder to be melted or the melted powder. Secondly, however, the equipment set-up is also simple since the melting laser 11 and the further laser 12 jointly utilize the optical element 13 and likewise the beam splitter 18, which results in comparatively low costs and a small space requirement. Furthermore, the coordination of the movements of the laser beams 14 and 15 is also unproblematic since the control of the movements can also always be effected jointly by way of the optical element 13.

[0061] The apparatus 1 furthermore has a device 19 for the aselective heating of each layer 10. The aforementioned device can concern—as illustrated—a radiant heating facility, such as an infrared emitter or a laser (diode) array. Alternatively, the device 19 can involve an inductive heating of the building chamber 4 or, unlike the illustration in FIG. 1, a heating of the build platform 3. Heat that can be input in each layer 10 by the device 19 (indicated by the arrows in the present case) preferably heats a large portion of the layer 10 in order (as described above) to prevent macrocracks during the manufacture of the component 2 as a whole in interaction with the synchronous selective irradiation according to the invention.

[0062] In FIG. 2, the frame around the laser foci of the beams 14 and 15 indicates that the present invention advantageously implements an aselective or global heating of a large portion of the layer 10 or the layer surface thereof at a temperature T1. In accordance with the present invention, the temperature T1 is chosen in such a way that it corresponds to at least one quarter of the temperature T2 which the respective layer 10 experiences as a result of the selective irradiation.

[0063] Expediently, the temperature T2 is locally at least just above a sintering or solidus temperature. Preferably, the temperature T2 is at least just above a melting point of the material 7.

[0064] Alternatively, for example, the layer 10 can be aselectively heated to a temperature of at least one third or even just below half of the temperature T2.

[0065] By way of example, the aselective heating can be effected at a temperature T1 of between 400° C. and 500° C.

[0066] Alternatively or additionally, the aselective heating is effected at a temperature of between 50° C. and 100° C. below an initial temperature for the formation of phase precipitates, in particular for the formation of a gamma prime phase (γ/γ′ solvus temperature) of the material 7.

[0067] Furthermore alternatively or additionally, the aselective heating of the large portion of the layer 10 is preferably effected below a sintering temperature of the material 7.

[0068] Furthermore, the aselective heating is advantageously effected for preheating the layer 10 and/or simultaneously with the selective irradiation of the layer 10, as described above.

[0069] The completed component 2 can furthermore be subjected to a thermal aftertreatment in order to bring about for example a stress relaxation and/or precipitation or segregation of alloying elements, such as carbides, nitrides or intermetallic phases, for the purpose of hardening (γ′ precipitation). Such a heat treatment can comprise a so-called solution heat treatment and one or more subsequent “ripening steps” with in each case a specifically set heating rate, holding time and cooling rate.

[0070] Furthermore, it is possible to use a so-called “HIP” process (“hot isostatic pressing”), i.e. the use of isostatic mechanical pressure after the additive construction of the component 2 and/or the thermal aftertreatment.