METHOD FOR THE PREPARATION OF ADDITIVES BY MEANS OF DUAL SELECTIVE IRRITATION OF A POWDER BED AND PREHEATING

Description

[0001] The present invention relates to methods for powder bed-based additive manufacturing of a component with dual selective irradiation and integrated preheating, as well as a corresponding device.

[0002] The aforementioned components are preferably intended for use in a turbomachine, preferably in the hot gas path of a stationary gas turbine. The component is preferably made of a superalloy, in particular a nickel- or cobalt-based superalloy. Alternatively, the corresponding component can be another component, such as a high-performance component for applications in aviation or automotive.

[0003] Additive manufacturing processes include, for example, selective laser melting (SLM) or laser sintering (SLS), or electron beam melting (EBM) as powder bed processes. Other additive processes include, for example, directed energy deposition (DED) processes, particularly laser cladding, electron beam or plasma powder welding, wire welding, metallic powder injection molding, so-called sheet lamination processes, or thermal spray processes (VPS, LPPS, GDCS).

[0004] Due to its disruptive potential for industry, generative or additive manufacturing is becoming increasingly interesting for the series production of the above-mentioned turbine components, such as turbine blades or burner components.

[0005] Modern gas turbines are subject to constant improvement to increase their efficiency. However, this leads, among other things, to ever-increasing temperatures in the hot gas path. The metallic materials used for rotor blades, especially in the first stages, are constantly being improved in terms of their strength at high temperatures, creep loading, and thermomechanical fatigue.

[0006] Additive manufacturing processes have proven particularly advantageous for complex or intricately designed components, such as labyrinthine structures, cooling structures, and / or lightweight structures. Additive manufacturing is particularly advantageous due to its particularly short chain of process steps, as a manufacturing or production step of a component can be carried out largely based on a corresponding CAD file and the selection of appropriate manufacturing parameters. The production of gas turbine blades using the described powder bed fusion (PBF) processes advantageously enables the implementation of new geometries, concepts, solutions, and / or designs, which reduces manufacturing costs and assembly and lead times, optimizes the manufacturing process, and can, for example, improve the thermomechanical design or durability of the components.

[0007] Blade components manufactured by conventional means, for example by casting, are significantly inferior to the additive manufacturing route, for example in terms of their design freedom and also in terms of the required lead time and the associated high costs as well as the manufacturing effort.

[0008] A method and a device for the additive manufacturing of components is known, for example, from DE 10 2017 21 37 62 A1. There, a type of dual or synchronous selective melting with different laser beams also takes place, but no preheating as described with reference to the present invention.

[0009] A similar principle of an optical irradiation unit for a system for producing workpieces by irradiating powder layers with laser radiation is known, for example, from EP 2 335 848 A1.

[0010] A method and a device for generative manufacturing with preheating is also known from DE 10 2010 048 335 A1, although no synchronous or dual selective irradiation is used.

[0011] Furthermore, an apparatus for additive manufacturing with electron beam preheating, laser hardening, and corresponding method is known from DE 10 2015 201 637 A1. In particular, electron beam-based preheating is used here, which, however, is used to prevent hot or solidification cracks, and not as described below in connection with the present invention.

[0012] The document DE 10 2014 204 580 A1 describes a device which provides a heating device at least above a component platform for heating a surface of a powder layer to be solidified in segments.

[0013] The documents WO 2013 / 092994 and US2018 / 169946 also belong to the state of the art.

[0014] During the additive manufacturing of a component from a powder bed, i.e., using "powder bed fusion," preheating of the material to be processed is also known to occur by heating a build platform. However, such preheating measures are insufficient, as such platform heating normally only allows preheating temperatures of approximately 200°C and thus cannot significantly contribute to the reduction of residual stresses. Depending on the material used and the powder grain size, heat conduction is insufficient, so that the preheating effect, particularly when processing nickel- or cobalt-based superalloys, decreases significantly with increasing build height. In addition, with these alloys, whose gamma phase (cf."γ") can form a high proportion of so-called (gamma prime) y'-precipitates, which is why these are considered difficult or even impossible to weld and therefore have to be preheated at high temperature but still below the γ / γ'-solvus temperature (i.e. below the onset of γ'-precipitation) in order to promote weldability.

[0015] The common preheating concepts mentioned above cannot achieve a required temperature level, for example between 400 °C and 500 °C, or at least not reliably, across the entire height of the component.

[0016] Even concepts that achieve temperatures of 1000 °C in the build chamber of a corresponding manufacturing facility through inductive heating have the disadvantage of, on the one hand, severe sintering of the surrounding powder. Furthermore, in this case, too, there is insufficient heat conduction, which means that - above a certain component height - the preheating temperature is no longer sufficient to achieve the desired effect.

[0017] It is therefore an object of the present invention to provide means for improved heat management which solves the problems described above, in particular to enable the weldability of nominally difficult or hardly weldable alloys and thereby achieve a significantly improved stress relief and / or a significantly reduced cracking tendency of the processed material.

[0018] This problem is solved by the subject matter of the independent patent claims. Advantageous embodiments are the subject matter of the dependent patent claims.

[0019] One aspect of the present invention relates to a method for powder-bed-based, additive manufacturing of a component, comprising selectively irradiating a layer of a powdered material, whereby the component is built up layer by layer, preferably by selective laser sintering, selective laser melting, or electron beam melting. The irradiation is carried out with a first energy beam and a different second energy beam, wherein the second energy beam surrounds the first energy beam in a ring-shaped manner. This ring-shaped arrangement is to be understood such that either the entire second energy beam can surround the first energy beam in a ring-shaped manner, or merely a beam focus, for example on a corresponding manufacturing or powder surface of the corresponding layer.

[0020] The process further comprises the aselective, non-selective, delocalized, or global irradiation or heating of the layer, whereby a large portion, for example, a predominant or large portion, or the entire production area of the layer is heated to a temperature of at least one-quarter of the temperature experienced by the layer during the described selective irradiation. The latter temperature expediently corresponds to at least one melting temperature of the material used to construct the component. According to the principle of the PBF process, the irradiation, sintering, or melting of the material takes place very locally, for example, in the beam focus and / or in a heat-affected zone.

[0021] In one embodiment, a large part of the layer is heated by the aselective heating to a temperature of at least one third or even almost half the temperature which the layer experiences by the selective irradiation.

[0022] The described process, particularly the combined and targeted application of heat with the aselective heating of the layer, advantageously achieves a reduction in macro-residual stresses, which are inherent in the process and occur in virtually all materials. Furthermore, local preheating as part of the selective irradiation enables the processing of difficult-to-weld nickel-based superalloys, for example, by reducing micro-residual stresses caused by segregation effects. According to the latest findings, cracks caused by such stresses develop during the process primarily because healing of the cracks or backfeeding of the existing melt is no longer possible.

[0023] A superposition of both residual stresses usually leads to a significant occurrence of cracks in a subsequent heat treatment, in particular through so-called "strain age cracking" or "post weld heat treatment cracking" in the alloys or materials mentioned.

[0024] In such (subsequent) post-heat treatments, the actual precipitation for hardening the material can also occur. This is usually superimposed on stress relief, which, without the means of the present invention, would particularly favor macrocracks.

[0025] A simultaneous reduction of macro- and micro-residual stresses through the combination of local and global preheating, as described, has a particularly positive effect on preventing the aforementioned cracking effects. Furthermore, sintering effects are not expected due to the still sufficiently low global preheating temperature. This also partially leads to a significant improvement in surface quality and surface resolution compared to conventional electron beam-based additive processes.

[0026] In one embodiment, the first energy beam represents a reflow laser or first laser, and the second energy beam represents a second, further laser beam, which preferably has a lower radiation intensity than the reflow laser. This embodiment allows for selective irradiation with advantageous heat input into the layer, in particular, reducing a temperature gradient occurring in the layer.

[0027] In one embodiment, the further laser beam causes local heating, in particular preheating of the layer to a temperature of over 400 °C, preferably over 500 °C. This embodiment advantageously allows, in particular, a small volume of material around the processing focus of the first laser or the melting laser to be kept at an elevated temperature, thus advantageously avoiding excessively large temperature gradients.

[0028] In one embodiment, the melting laser and / or the further laser or laser beam have a wavelength in the infrared range.

[0029] In one embodiment, the aselective heating takes place at a temperature between 50 °C and 100 °C below an initial temperature for the formation of phase precipitations, in particular for the formation or precipitation of the gamma prime phase of the material, and additionally optionally at a temperature of 400 °C and 500 °C.

[0030] In this embodiment, the selective heating advantageously takes place sufficiently far away from an operating temperature for the phase precipitation of the gamma-ray phase. The aforementioned operating temperature or initial temperature can designate a temperature above which a thermal expansion coefficient of the material continues to be reduced due to temperature. The temperature to which a large part of the layer is heated across the entire surface is advantageously optimized by this embodiment and coordinated with the selective irradiation of the layer. In particular, the aforementioned temperature is selected high enough to ensure reliable stress relief during and after component construction, while simultaneously preventing precipitation or formation of the gamma-ray phase, which would be detrimental to the structural or welding result during component production.

[0031] In one embodiment, the aselective heating also takes place at a temperature just below the sintering temperature of the material. This embodiment is advantageously consistent with the previously described embodiment and additionally prevents the sintering of material that is not used for the manufactured component and would possibly have to be laboriously removed from cavities or support structures of the component - in sintered form. Below the sintering temperature, it is also normally reliably ensured that the precipitation of a gamma prime phase does not occur.

[0032] In one embodiment, the aselective heating is carried out by inductive heating of a build chamber, e.g. of a corresponding additive manufacturing system, by radiant heating, such as a laser array, an array of laser diodes, an infrared radiator, or by heating a build platform.

[0033] In one embodiment, the aselective heating is performed to preheat the layer. According to this embodiment, the aselective heating can be performed before, but of course also simultaneously with, the selective irradiation step.

[0034] In one embodiment, the aselective heating is carried out simultaneously with the selective irradiation of the layer.

[0035] As described above, aselective heating allows for the reliable prevention of macrocracks and advantageously causes stress relief in the material or in the molten material.

[0036] In one embodiment, the material is a difficult-to-weld alloy, in particular a γ'-hardening nickel- or cobalt-based superalloy.

[0037] In one embodiment, the (finished) manufactured component is subjected to a thermal post-treatment. This post-treatment is preferably provided to effect (additional) stress relaxation and / or to induce precipitation hardening through segregation or formation of the gamma prime phase. The advantages of the invention potentially manifest themselves even without thermal post-treatment, but can occur to a particularly advantageous extent if such a thermal post-treatment is performed.

[0038] In one embodiment, the first energy beam and the second energy beam are directed or focused onto the layer via a common optics or optical unit. In the case of electron beams of the first energy beam and the second energy beam, said optics can also be electron optics.

[0039] In one embodiment, the reflow laser and the further laser are fed to the common optics via a beam splitter or semi-transparent mirror.

[0040] This configuration(s) advantageously allows a particularly simple beam guidance for the selective irradiation or a particularly reliable or reliably synchronous selective irradiation with the first energy beam and the second energy beam.

[0041] A further aspect of the present invention relates to a device for powder bed-based additive manufacturing of a component, which device comprises a construction platform, as well as a coating device, a melting laser, a further laser and a common optics for the melting laser and the further laser, as described above, and wherein the device further comprises a device for aselective heating of the layer, in particular a device for inductive heating of a construction chamber and / or a radiant heater, preferably an infrared radiator. A particular advantage of the described device is that this device or system technology, in contrast to high global preheating temperatures, does not require any significant

[0042] This requires adjustments to the hardware concept within the build space. This advantageously even allows for retrofitting to existing powder-bed-based manufacturing systems or SLM systems.

[0043] Embodiments, features and / or advantages described herein in connection with the method may also relate to the device, and vice versa.

[0044] The term "and / or" as used herein, when used in a series of two or more items, means that any one of the listed items may be used alone, or any combination of two or more of the listed items may be used.

[0045] Further details of the invention are described below with reference to the figures. Figure 1 shows a schematic side view of an apparatus according to an embodiment of the present invention; Figure 2 shows a schematic plan view of two laser beams which are generated using the Figure 1 shown device, and Figure 3 schematically indicates beam intensities of the Figure 2 laser beams shown.

[0046] In the exemplary embodiments and figures, identical or similarly functioning elements may be provided with the same reference numerals. The illustrated elements and their relative sizes are generally not to scale; rather, individual elements may be exaggeratedly thick or oversized for clarity and / or clarity.

[0047] Figure 1 shows a device 1 according to an embodiment of the present invention, which serves for the powder-bed-based, additive production of a component 2 or a component section; in particular for selective laser sintering, selective laser melting, or electron beam melting.

[0048] Component 2 may be a component of a turbomachine, for example a component for the hot gas path of a gas turbine. In particular, the component may designate a rotor or guide vane, a ring segment, a burner part or a burner tip, a shroud, a shield, a heat shield, a nozzle, a seal, a filter, an orifice or lance, a resonator, a plunger or a swirler, or a corresponding transition, insert, or a corresponding retrofit part. Alternatively, the component may designate another component, in particular a component for applications in aviation or automotive.

[0049] The device 1 comprises a build platform 3, which is movable, in particular lowerable, up and down in the vertical z-direction within a build chamber 4. Furthermore, a powder storage device 5 is provided. This comprises a powder chamber 6 for receiving powdered material 7, a powder feed piston 8, which is movable up and down in the z-direction within the powder chamber 6, and a coating device with a doctor blade 9, which is movable back and forth in the y-direction and is designed to transport material 7 contained in the powder chamber 6 to the build chamber 4 and to distribute it evenly in the region of a build zone of the build chamber 4 with a predetermined layer thickness (see reference symbol d).

[0050] Furthermore, the device 1 has a first beam source, which is a reflow laser 11, and a second beam source, which is a further, second laser 12. Furthermore, the device 1 has a common optics or optical unit 13 for the first beam source or the first beam 11 and the second beam source or the second beam 12.

[0051] The first beam source (first energy beam) and the second beam source (second energy beam) are preferably lasers or laser beams, in particular lasers that emit laser beams 14 and 15 with wavelengths in the infrared range, such as Nd-YAG or CO2 lasers or the like (cf. SLM). Alternatively, the aforementioned beam sources / beams can also be particle radiation, such as electron beams (cf. EBM).

[0052] The optics or optical unit 13 comprises a scanner 16 and an F-theta lens 17. Between the first energy beam 11 and the second energy beam 12 and the optical unit 13, a semi-transparent mirror or beam splitter 18 is arranged, which directs the laser beam 14 of the first energy beam 11 and the second energy beam 15 of the preheating laser 12 together to the optical unit 13, from where the energy beams are directed onto the build zone via the scanner 16 and the F-theta lens 17 - based on layer information of a component layer 10 to be produced, which is normally generated by computer-aided modeling from a CAD file using software.

[0053] To produce a component 2 or a component section using the device 1, the build platform 3 is moved in a first step into a position that is below the build by a distance corresponding to the layer thickness d of the component layer 10 to be subsequently generated, wherein the layer thickness d normally lies in a range between 10 and 100 µm, in particular between 20 and 40 µm. The powder feed piston 8 is positioned above the build zone by an analogous distance. The doctor blade 9 is then moved from the Figure 1from the position shown on the far left in dashed lines to the position on the far right, also shown in dashed lines, so that a layer 10 of the powdered component material 7 is evenly distributed on the component platform 3. This layer 10 is then locally fused and solidified in the area of the build-up zone. For this purpose, the beams 14 and 15 are directed onto the beam splitter 18 such that the laser beam or laser focus 14 of the processing laser 11, which is circular in cross-section, is surrounded in a ring by the laser beam 15 of the preheating laser 12 or its focus, as shown in Figure 2 This is achieved here by operating the processing laser 11 in Gaussian mode and the preheating laser 12 in "donut" or "bagel" mode.

[0054] 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 shown in Figure 3 shown schematically in the perspective view.

[0055] The further laser beam 15 preferably effects a selective or local heating, in particular preheating, of each layer 10 to a temperature of at least 400 °C, preferably at least 500 °C. During the construction of the component 2, a heat input of the further laser beam 15 is expediently superimposed with a heat input of the laser beam 14 of the reflow laser 11, so that the melting point of the material 7 can be expediently exceeded and the structure for the component can be solidified.

[0056] The laser beams 14 and 15 are directed jointly from the beam splitter 18 to the optical unit 13, from where they are directed onto the build zone via the scanner 16 and the lens 17. The joint movement of the laser beams 14 and 15 relative to the build zone is (selectively) controlled depending on layer information of the respective component layer 10 to be produced.

[0057] Thanks to the annular 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 not only preheats the powder to be ultimately fused by the laser beam 14, but also partially afterheats it, since the laser beam 15 both precedes and trails the laser beam 14. Accordingly, high temperature gradients during fusion and thus hot cracking are effectively counteracted, whereby the radiation intensities of the laser beams 14 and 15 can be selected independently of one another and thus optimally adapted to the component material 7 to be processed, the layer thickness d to be produced, and the subsequently described aselective, large-area, or global heating.

[0058] This also makes it possible to process component materials that were previously difficult or difficult to weld, such as a γ'-hardening nickel-based superalloy, particularly with a high proportion of γ'-precipitates, to name just one example. To produce the next and subsequent layers, the component platform 3 is lowered again by a layer thickness d, powdered component material 7 is applied, and selectively fused.

[0059] A key advantage of the method according to the invention is, firstly, the previously described avoidance of hot cracking thanks to the flexibly adjustable and local preheating and controlled cooling of the powder to be melted or fused. Secondly, the apparatus design is simple, since the melting laser 11 and the additional laser 12 share the optical unit 13 as well as the beam splitter 18, resulting in comparatively low costs and a small space requirement. Furthermore, coordinating the movements of the laser beams 14 and 15 is also unproblematic, since the movements can always be controlled jointly via the optical unit 13.

[0060] The device 1 further comprises a device 19 for aselectively heating each layer 10. Said device can - as shown - be a radiant heater, such as an infrared radiator or a laser (diode) array. Alternatively, the device 19 can be an inductive heater of the construction chamber 4 or, unlike as shown in Figure 1 , to heat the construction platform 3. Heat that can be introduced into each layer 10 by the device 19 (indicated here by the arrows) preferably heats a large part of the layer 10 in order to prevent (as described above) macrocracks during the production of the component 2 as a whole in conjunction with the synchronous selective irradiation according to the invention.

[0061] In Figure 2The frame around the laser foci of beams 14 and 15 indicates that the present invention advantageously provides a selective or global heating of a large portion of layer 10 or its surface at a temperature T1. According to the present invention, temperature T1 is selected such that it corresponds to at least a quarter of temperature T2 experienced by the respective layer 10 due to the selective irradiation.

[0062] Advantageously, the temperature T2 is locally at least slightly above a sintering or solidus temperature. Preferably, the temperature T2 is at least slightly above a melting temperature of material 7.

[0063] Alternatively, for example, the layer 10 can be aselectively heated to a temperature of at least one third or even almost half of the temperature T2.

[0064] For example, aselective heating can be carried out at a temperature T1 of between 400 °C and 500 °C.

[0065] The aselective heating takes place at a temperature between 50 °C and 100 °C below an initial temperature for the formation of phase precipitations, in particular for the formation of a gamma prime phase (γ / γ' solvus temperature) of the material 7.

[0066] Furthermore, alternatively or additionally, the aselective heating of the majority of the layer 10 preferably takes place below a sintering temperature of the material 7.

[0067] Furthermore, the aselective heating is advantageously carried out to preheat the layer 10 and / or simultaneously with the selective irradiation of the layer 10, as described above.

[0068] The finished component 2 can further be subjected to a thermal post-treatment, for example, to cause stress relaxation and / or precipitation or segregation of alloying elements, such as carbides, nitrides, or intermetallic phases, for hardening (γ'-precipitation). Such a heat treatment can include a so-called solution annealing and one or more subsequent "aging steps," each with a specifically adjusted heating rate, holding time, and cooling rate.

[0069] Furthermore, a so-called "HIP" process ("hot isostatic pressing"), i.e. the application of isostatic mechanical pressure following the additive construction of component 2 and / or the thermal post-treatment, can be used.

Claims

1. Method for the powder bed-based additive manufacturing of a component (2), comprising - selective irradiation of a layer (10) composed of a pulverulent material (7) with a first energy beam (14) and a second energy beam (15), different from the first, wherein the second energy beam (15) ring-shapedly surrounds the first energy beam (14), wherein the first energy beam (14) constitutes a melting laser and the second energy beam (15) constitutes a further laser beam, having a lower radiation intensity than the melting laser, wherein the further laser beam brings about a local heating, in particular preheating, of the layer to a temperature of above 500°C, and - aselective heating of the layer (10), wherein a large portion of the layer (10) is heated to a temperature (T1) of at least one quarter of the temperature (T2) which the layer (10) experiences as a result of the selective irradiation, wherein 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 of the material.

2. Method according to Claim 1, wherein the aselective heating is effected at a temperature of between 400°C and 500°C.

3. Method according to Claim 1 or 2, wherein the aselective heating is effected below a sintering temperature of the material (7).

4. Method according to any of the preceding claims, wherein the aselective heating is effected by an inductive heating of a building chamber (4), a radiant heating facility, in particular infrared emitter, or by way of a heating of a build platform (3).

5. Method according to any of the preceding claims, wherein the aselective heating is carried out for the purpose of preheating the layer (10).

6. Method according to any of the preceding claims, wherein the aselective heating is carried out simultaneously with the selective irradiation of the layer (10).

7. Method according to any of the preceding claims, wherein the material (7) constitutes an alloy which is difficult to weld, in particular a γ'-hardening nickel- or cobalt-based superalloy.

8. Method according to any of the preceding claims, wherein the manufactured component (2) is subjected to a thermal aftertreatment.

9. Method according to any of the preceding claims, wherein the first energy beam (14) and the second energy beam (15) are directed at the layer via a common optical unit (13).

10. Method according to any of the preceding claims, wherein the melting laser (14) and the further laser beam (15) are fed to a common optical unit (13) via a semi-transparent beam splitter (18).

11. Apparatus (1) for the powder bed-based additive manufacturing of a component (2), which apparatus is configured for carrying out a method according to any of the preceding claims and comprises a build platform (3), a coating device (5), a melting laser (11), a further laser (12) and a common optical unit (13) for the melting laser (11) and the further laser (12), and wherein the apparatus (1) furthermore comprises a device (19) for the aselective heating of the layer (10), in particular a device for the inductive heating of a building chamber, a radiant heating facility, preferably an infrared emitter.