Patent Application
20130287590
1. Field of the Invention
The present invention relates to a method for producing gas turbine components, in particular aircraft turbine components, preferably low-pressure turbine blades made of a powder which is sintered selectively in layers by locally limited introduction of radiant energy. In addition, the invention relates to an apparatus for producing gas turbine components, in particular according to a corresponding method, and also to a gas turbine blade produced thereby, in particular low-pressure turbine blades made of a TiAl material.
2. Prior Art
What are known as rapid prototyping—or rapid manufacturing—methods, i.e. methods for rapidly producing prototypes or for rapidly producing components, which utilize so-called generative production methods are known from the prior art. In these methods, three-dimensional structures are produced by selectively sintering powder, for example by means of laser or electron beams which are guided over powder arranged in layers. Methods of this type have been proposed for a multiplicity of materials and for an extremely wide variety of components, in particular also aircraft turbine components. Examples of this are named in DE 103 19 494 A1, DE 10 2006 049 216 A1, DE 10 2004 057 865 A1, DE 10 2008 027 315 A1 and DE 109 03 436 C2.
However, the methods and apparatuses described therein have various disadvantages. By way of example, not all the components can be produced from all possible materials, because the nature of the generative production can introduce impurities, which lead to an unfavorable property profile that is unacceptable for the intended use. Particularly in the case of titanium aluminide materials which are to be used, for example, for low-pressure turbine blades in aircraft engines, impurities can lead to instances of embrittlement, which make a use in aircraft turbine construction impossible. In the worst case, the risk of the introduction of impurities correspondingly impedes or prevents a possible use of generative production methods in the production of turbine blades made of titanium aluminides or alloys thereof.
In addition, it must be ensured at the same time that the production outlay remains low in order to achieve economic production of the components. Particularly in generative production methods, long processing times can have the effect that these can no longer be used economically.
It is an object of the present invention, therefore, to provide a method for producing gas turbine components, in particular aircraft turbine components, preferably low-pressure turbine blades made of titanium aluminide materials, which makes it possible to produce a corresponding component with a desired property profile and at the same time is economical.
This object is achieved by a method having the features of claim 1, an apparatus having the features of claim 8 and a gas turbine blade having the features of claim 9 or 10. Advantageous configurations are the subject matter of the dependent claims.
The present invention is based on the concept that an advantageous production of gas turbine components, in particular aircraft turbine components, such as preferably low-pressure turbine blades, made of very reactive materials, for example titanium aluminides, can be effected in a generative production method when it can be ensured that the starting powder used in the generative production method has an appropriate purity. According to the invention, this is achieved by virtue of the fact that the powder production process directly precedes the generative production method, i.e. selective laser or electron beam sintering, it being ensured that the starting powder produced is exposed to no unfavorable ambient atmosphere, which for example contains oxygen, between the powder production and the generative production of the component. This avoids the situation where the powder used, i.e. for example the very reactive titanium aluminides, can react with oxygen from the ambient atmosphere. This in turn has the effect that the powder particles do not form any oxide layers, for example thin aluminum oxide or titanium oxide layers in the case of TiAl, which would then lead to the introduction of oxygen into the component upon sintering of the powder. Accordingly, it is provided that the powder production and the generative component production method are carried out in a defined atmosphere. This can be achieved if both substeps, specifically powder production and generative production method, are carried out in a single housing which can be closed in a gas-tight manner or in two housings which can be connected to one another in a gas-tight manner, such that the powder produced in the first substep no longer has to leave the defined atmosphere before the production of the component. It is thereby possible to produce the powder in a very pure quality and to process it to form a component with a consistent purity by means of the generative production method.
By avoiding exposure of the powder to an ambient atmosphere, and in particular the avoidance of contact between the powder and oxygen or other gases in the normal ambient atmosphere and the associated avoidance of the production of oxide layers or other reaction products, it is also possible to process very fine powder, which in conventional production methods would lead to a high impurity or oxygen content of the component to be produced owing to its high surface area.
For the method according to the invention and a correspondingly designed apparatus, selective laser beam sintering or electron beam sintering can be used as the generative production method.
In both methods, a plurality of radiation beams can be generated at the same time in order to thereby ensure short process times, which increases the economic viability of the method. Moreover, in both types of radiation it is possible to generate radiation with a high power density, so that only short irradiation times are required for the corresponding sintering of the powder. This too promotes the efficiency of the method.
The method can be carried out in a vacuum or in a protective gas atmosphere or in appropriate combinations of vacuum and protective gas atmosphere. By way of example, the electron beam sintering can be effected in a vacuum, while the powder production can be effected in an inert gas atmosphere, in order to provide, through the inert gas, a cooling medium for the powder particles to be cooled for the powder production.
For the method, it is possible to use an extremely wide variety of powders, in particular different metallic powders, where the powder particles can be formed from pure metal or from alloys. The powder can be formed, for example, from titanium aluminide alloys or components for producing titanium aluminide alloys, for example titanium powder, aluminum powder or powder made up of alloying constituents such as niobium or the like. In particular, a plurality of apparatuses can also be provided for powder production, in order to produce different powders. These powder production apparatuses can be provided in a plurality of separate spaces or housings or in a housing with or without corresponding partitions. Possible means of transportation to the site of the generative component production which are closed merely with respect to the ambient atmosphere have to be ensured.
The powder can be mechanically alloyed, i.e. can be appropriately treated with corresponding additional powders. Moreover, a specific grain size distribution can also be set for the powder particles.
The method according to the invention also makes it possible for differently alloyed powder and/or powder set differently in terms of powder size to be provided in different regions in the component to be produced, so that a component with a material gradient may arise.
The powder can be produced differently by known methods. In particular, it is possible to employ atomization of a molten material, for example by rotary atomization.
In the case of an apparatus according to the invention, various devices for powder production and for generatively producing components can be provided in a housing or in housings or spaces connected in a gas-tight manner.
These devices comprise apparatuses for powder production by means of atomization, for example rotary atomizers, corresponding apparatuses for treating the powders, such as sieves and the like, an apparatus for mechanical alloying, i.e. a mixer and the like, and also apparatuses for feeding additional powder from the outside or means for storing powder in the apparatus closed in a gas-tight manner. In addition to the beam-generating apparatus and apparatuses for guiding the beam over a powder layer, an apparatus according to the invention can moreover comprise aids for transporting and handling the powder and also means for feeding gas to and for evacuating the apparatus.
In accordance with the present invention, it is therefore possible to produce gas turbine blades, in particular low-pressure turbine blades made of TiAl materials, which can be formed as hollow blades with an internal supporting structure. These components, which are producible only by generative methods in the case of a complicated cavity structure, can be produced according to the invention from the material TiAl, which is difficult to handle, or TiAl alloys, since fine-grained powders can be used and the production of impurities, in particular the introduction of oxides, is prevented. Accordingly, gas turbine blades produced according to the invention are distinguished by a fine-grained microstructure with a low degree of impurities, in particular a low oxygen content. In addition, the gas turbine blades can have locally different alloy compositions and/or possess grain size distributions. Moreover, corresponding components are distinguished by the avoidance of segregation, as can be observed in components produced by casting.
The invention will be illustrated on the basis of the accompanying drawings, which show, purely schematically, in
Further advantages, characteristics and features of the present invention will become clear in the description of an exemplary embodiment detailed hereinbelow.
The spaces 3 and 4 each have a vacuum pump 5 and 6, such that the spaces 3 and 4 can be pumped out separately from one another. Alternatively, however, provision can be made to provide merely a single pump for pumping out the entire interior of the housing 2.
In addition, provision is made of a plurality of gas feeds 7, 8, 9, which in turn make it possible to separately flood the spaces 3 and 4 with gas. Here, too, provision may be made of only a single gas feed for flooding the entire interior of the housing 2. The flooding with gas can serve merely for cleaning the spaces or for setting an inert gas atmosphere.
The space 4 of the housing 2 is furthermore provided with a melt feed 10 or alternatively an apparatus for melting a metal or an alloy (not shown), which comprises a nozzle device from which the melt for producing powder can emerge. Here, it is possible to use known methods, for example rotary atomization of the melt, in order to produce fine-grained powders.
The thus produced powder can be caught on a table 11, where a pushing device 13 can push the powder off to the side and transport it in the direction of the space 3. In the simplest case, by way of example, the powder situated on the table 11 can be shifted by the pushing device 13 along the table 11 and the connecting plate 22 through the opening 15 in the direction of the powder reservoir 25 in the space 3, in order to be deposited there in the powder reservoir or on the powder reservoir as a powder layer.
The powder reservoir 25 has a double base 26, which is vertically adjustable in accordance with the double-headed arrow, such that, at the start of the process, the double base 26 is moved level with the connecting plate 22 in order to receive a first powder layer.
This first powder layer is locally selectively sintered according to the contour to be produced by an electron or laser beam 24, which is generated by the beam-generating device 23, the electron or laser beam being moved over the powder layer on the double base 26. Where the electron or laser beam impinges on the powder and melts it or starts to melt it, the powder is locally sintered together so that a component 27 is produced. Then, the double base 26 is lowered by a specific height in order to make it possible that the pusher 13 can apply a new powder layer. This powder layer is then correspondingly sintered again by the radiation beams 24 of the laser or electron radiation, and the process is continued until the component 27 to be produced is finished. The component 27 is then situated in a powder bed 28, which is accommodated in the powder reservoir 25. The finished component 27 can be removed from there and can be removed from the housing 2 through an opening 29.
If a specific powder size is to be selected, an opening 21 can be opened in the connecting plate 22 or the table 11, such that the powder 12 passes into a funnel 16 with a sieve 17, through which, however, only the powder having the specific powder size can pass. The powder is then captured in a powder reservoir 18 having a double base 19, which can then be raised in the region of an opening 30 in the connecting plate 22 such that the powder located in the powder reservoir 18 can be raised by means of the double base 19 into the plane of the table 11 or of the connecting plate 22, where it can be shifted by the pusher 13 in the direction of the powder reservoir 25. To this end, provision is made of a hydraulic lifting apparatus 20, which can move the powder reservoir 18 upward, as indicated by the double-headed arrow.
In addition, a charging funnel 14 with a lock, through which additional powder which has been produced externally can be introduced into the apparatus, is provided opposite the opening 30. A gas feed 8 can be connected to the lock in order, for example, to introduce inert gas into the lock region. Similarly, an appropriate vacuum pump (not shown) can be provided in the region of the lock of the inlet funnel 14.
The additional powder which can be introduced into the apparatus 1 by way of the charging funnel 14 can provide for mechanical alloying of the powder, in that alloying constituents are fed from the outside, for example.
In addition, it is also possible to provide powder stores, for example in the space 4 of the housing 2, in which different powders are stored, in order to then mechanically alloy these in a powder mixing apparatus (not shown) in order to thereby be able to produce desired compositions of the powder. Moreover, further apparatuses for powder production and appropriate spaces can be provided.
For the mixing of various powders, both powders of differing chemical composition and also powders of differing grain sizes can be mixed or alloyed.
In this respect, it is not only possible with the apparatus 1 presented to process melts of alloys directly to powders and to use these in the generative production method, but rather it is also possible to realize mechanical alloying of powders of differing grain sizes and/or grain size distributions and also chemical compositions in the apparatus 1.
In particular, it is thereby possible to provide powders which differ in layers, and to thus set gradients in terms of the composition and/or of the grain size in the component 27 to be produced.
The gas feeds 7, 8, 9 and the pumps 5, 6 make it possible to set defined atmospheric conditions in the spaces 3 and 4 of the housing 2, in which case it is also possible to set different atmospheres in the spaces 3 and 4. Thus, in addition to vacuum conditions, it is also possible to create atmospheres with defined gas compositions, for example inert gas atmospheres. In particular, it is possible to set a technically substantially oxygen-free atmosphere in the housing 2, so that the component 27 is not contaminated with undesired oxygen fractions. However, other gases, such as nitrogen, which could lead to the formation of nitrides can also be appropriately excluded, if working in a vacuum or inert gas atmospheres for example.
By setting the atmosphere in a defined manner, it is therefore possible to avoid the presence of impurities in the component produced. At the same time, by using multi-beam devices, i.e. beam-generating apparatuses such as laser or electron beam apparatuses, which can generate a plurality of radiation beams or have high radiation powers, it is possible to achieve a high introduction of energy into the powder, such that the sintering can be realized in very short process times. Accordingly, the method according to the invention can be carried out very efficiently.
In particular, the apparatus and the corresponding method can be used for producing gas turbine blades made of titanium aluminide materials or alloys thereof. Furthermore, it is possible to economically produce hollow blades having complicated cavities, such as cooling ducts, or cavities having complicated supporting structures.
Appropriate grain sizes can be set in the components. Segregation in the case of alloys can also be avoided, and moreover it is possible to produce graduated components having defined compositions in different regions of the blade.
Owing to the method according to the invention, the main blade part 51 can have different compositions in terms of the chemical composition and/or of the grain size distribution, for example in the regions of the partial cavities 56, 57 and 58. The change in the composition can be effected here continuously or gradually, so that a stepless or stepped gradient is established.
Although the present invention has been described in detail with reference to the accompanying examples, it is obvious to a person skilled in the art that the invention is not limited to these examples, but rather that modifications are possible in such a manner that different combinations of the features presented are possible or that individual features can be omitted, without departing from the scope of protection of the accompanying claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2011 008 809.1 | Jan 2011 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/DE2012/000019 | 1/11/2012 | WO | 00 | 7/10/2013 |
