Abstract:
A cooled turbine engine component is made by providing first and second pieces respectively having first and second surfaces. At least one circuit is formed in at least one of the first and second surfaces. A first plurality of apertures is provided in the first piece to form inlets to the at least one circuit. A second plurality of apertures is provided in the second piece to form outlets to the at least one circuit. A combination of the first and second pieces is assembled and integrated.

Description:
U.S. GOVERNMENT RIGHTS 
   The invention was made with U.S. Government support under contract F33615-97-C-2779 awarded by the U.S. Air Force. The U.S. Government has certain rights in the invention. 

   BACKGROUND OF THE INVENTION 
   This invention relates to the manufacture of turbine elements such as airfoils like blades and vanes. More particularly the invention relates to the manufacture of turbine elements via integration of multiple components. 
   A variety of manufacturing techniques are used to make metallic components of gas turbine engines such as blades and vanes. One family of techniques involves investment casting. However, some component materials are not readily susceptible to investment casting. With such materials, machining from ingots or other stock is required. Direct machining imposes severe constraints on the flexibility to machine internal features. Accordingly, it is known to machine components in pieces and then integrate the pieces via diffusion bonding. Examples of diffusion bonding in turbine blade formation (e.g., using Ti-6Al-4V) are found in U.S. Pat. Nos. 5,063,662 and 5,711,068. The &#39;662 patent discloses a detailed process for forming a twisted hollow blade having internal structure. The process involves the diffusion bonding of two blade halves followed by additional deformation and machining. The &#39;068 patent discloses a specific situation in which the two blade halves are cut from a single piece and are diffusion bonded with uncut surfaces facing each other. Nevertheless, there remains room for improvement in the art. 
   SUMMARY OF THE INVENTION 
   One aspect of the invention involves a method for manufacturing a turbine engine component having one or more internal feed passageways, one or more external walls, and one or more outlet passageways. One or more cuts are made in a workpiece to create a plurality of separate subpieces each having one or more cut surfaces. A plurality of apertures are machined in the one or more cut surfaces. A combination of the subpieces or of like subpieces is reassembled and integrated. Internal feed passageways and exterior surfaces of the one or more walls are machined so that at least some of the outlet passageways are formed by combinations of the apertures from separate ones of the subpieces. 
   In various implementations, some of the passageways may be formed by single ones of the apertures. Some of the apertures may form internal connecting passageways between associated pairs of the feed passageways. The cutting may comprise wire electro-discharge machining. At least a first of the cuts may be arcuate. Machining the internal feed passageways may comprise electrochemical machining. The integrating may comprise transient liquid phase (TLP) bonding, diffusion bonding, or at least one of welding and brazing. The component may include an airfoil having a pressure side surface and a suction side surface. A junction between a first of the subpieces and a second of the subpieces may be locally generally parallel to one of the pressure and suction side surfaces. The combination may be assembled to an airfoil end piece and integrated with the airfoil end piece. The airfoil end piece may be machined to form at least one of a vane inboard platform, a vane outboard platform, a blade root structure, and a blade tip shroud. Registration features may be formed and the reassembling may comprise registering the registration features. The workpiece may be a refractory metal alloy. 
   Another aspect involves similarly cutting a plurality of metallic workpieces into first and second subpieces forming first and second cut surfaces on the first and second subpieces, respectively. A plurality of apertures are machined through at least the first cut surface of each first subpiece. Pairs of the first and second subpieces are assembled and integrated. At least one internal passageway is machined transverse to the plurality of apertures in each of the pairs so as to ultimately intersect therewith. There is an external surface machining of each pair. 
   In various implementations, the machining of the at least one internal passageway may be after the integrating. The integrating may consist essentially of TLP bonding or diffusion bonding. The method may be used to form a turbine engine component. The similarly cutting may further cut the plurality of workpieces into a third subpiece. The assembling and integrating may be of trios of the first, second, and third subpieces. The similarly cutting may further cut the plurality of workpieces into a fourth subpiece. The assembling and integrating may be of quartets of the first, second, third, and fourth subpieces. The cutting may comprise making a plurality of substantially nonparallel cuts. 
   Another aspect of the invention involves an article having a metallic wall. At least one non-line-of-sight passageway extends through the wall. An arcuate integration junction is within the wall. 
   In various implementations, the metallic wall may comprise a refractory metal alloy. The article may be a blade outer air seal wherein the junction is parallel to an inboard surface of the seal. 
   The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a view of a turbine element blade precursor. 
       FIG. 2  is an exploded sectional view of the precursor of  FIG. 1 . 
       FIG. 3  is a view of a core subpiece of the precursor of  FIG. 1 . 
       FIG. 4  is a cross-sectional view of the precursor of  FIG. 1  in a reassembled condition. 
       FIG. 5  is a cross-sectional view of an airfoil machined from the reassembled precursor. 
       FIG. 6  is a view of a vane. 
       FIG. 7  is a view of a blade. 
       FIG. 8  is a view of a blade outer air seal (BOAS) precursor. 
       FIG. 9  is a view of a first subpiece of the precursor of  FIG. 8 . 
       FIG. 10  is a sectional view of the precursor of  FIG. 8  in a reassembled condition. 
       FIG. 11  is a sectional view of a BOAS machined from the precursor of  FIG. 8 . 
       FIG. 12  is a view of the BOAS of  FIG. 11 . 
   

   Like reference numbers and designations in the various drawings indicate like elements. 
   DETAILED DESCRIPTION 
     FIG. 1  shows an airfoil precursor block  20  after initial machining stages. The exemplary block  20  may initially be formed as a single-piece right parallelepiped of a metallic material. Exemplary metallic materials are refractory metals and refractory metal-based alloys and combinations of such metals and alloys with refractory metal intermetallics. Exemplary alloys are molybdenum alloys and niobium alloys preferably with intermetallics of molybdenum and niobium, respectively. Exemplary intermetallic contents are greater than 5% by volume (more narrowly, 10-80%, or 20-50%). Exemplary intermetallics are suicides. An exemplary essentially pure molybdenum with molybdenum silicide has a molybdenum silicide content of 10-45%. An exemplary essentially pure niobium with niobium silicide has a molybdenum silicide content of 20-80%. 
   The parallelepiped has axes  500 ,  502 , and  504  which may, for reference, be assigned as X, Y, and Z directions. A central portion  22  of the block is located generally between constant-Z planes  508  and  510  and, ultimately, substantially forms the airfoil of a turbine element such as a blade or vane. An exemplary first of the initial machining stages involves forming registration features to subsequently facilitate the alignment of subpieces cut from the block  20 . In the exemplary embodiment, this machining takes the form of drilling holes into the block. In the exemplary embodiment, the holes are through-holes or bores between opposed faces of the block. Exemplary holes  24  and  26  extend between the constant-X faces of the block and have axes  512  and  514  parallel to the axis  500 . Holes  28  and  30  extend between the constant-Y faces and have axes  516  and  518  parallel to the axis  502 . In the exemplary embodiment, the holes  24 ,  26 ,  28 , and  30  are in portions  32  and  34  outboard of the central portion  22 . During such drilling, the block may be registered in a fixture (not shown) by means of one or more of its faces. 
   A second of the initial machining stages involves cutting the block into the subpieces. This exemplary cutting is performed via wire electro-discharge machining (EDM) process. To facilitate the cutting, the block may be registered in a cutting fixture via the drilled holes. The cutting fixture may securely hold each of the portions of the block that will become the subpieces. In the exemplary embodiment, a first cut  40  extends between the two constant-Y faces and the two constant-Z faces and is a planar cut in a plane  520  parallel to the Z-direction  504 . This exemplary first cut  40  separates a leading subpiece  42  from a remainder of the block (namely from portions  44 ,  46 , and  48  that will become identified as a suction side subpiece; a core subpiece; and a pressure side subpiece, respectively, after second and third cuts). The second cut  54  is arcuate but, in the exemplary embodiment, parallel to the Z-direction  504 . This second cut  54  separates the pressure side subpiece  44  from the remainder of the block  20 . The third cut  56  separates the suction side subpiece  48  from the core subpiece  46 . The exemplary third cut  56  is also arcuate and parallel to the Z-direction  504 . It is noted that the cuts need not be parallel to the Z-direction. Non-parallel cuts could be particularly useful to preform a blade having twist, taper, or other spanwise variance in the shape, size, or orientation of its cross-section. 
     FIG. 2  shows the leading subpiece  42  having a planar cut surface  60  resulting from the first cut  40 . The suction side subpiece  44  has a planar first cut surface  62  resulting from the first cut  40  and a continuously curving concave second cut surface  64  resulting from the second cut  54 . The core subpiece  46  has a planar first cut surface  66  resulting from the first cut  40 , a continuously curving convex second cut surface  68  resulting from the second cut  54  and a continuously curving concave third cut surface  70  resulting from the third cut  56 . The surfaces  68  and  70  meet at junction defining a core subpiece trailing edge  72 . The suction side subpiece  48  has a planar first cut surface  74  resulting from the first cut  40 , a continuously curving convex second cut surface  76  resulting from the second cut  54 , and a continuously curving convex third cut surface  78  resulting from the third cut  56 . 
   With the subpieces disassembled from each other, various features may be machined into their cut surfaces. Prior to the machining, each individual subpiece may be registered in a fixture (not shown) such as via the portions of the registration holes/bores  24 ,  26 ,  28 , and/or  30  located in such subpiece. A drill or milling bit or like machine tool element may be registered off such hole/bores for precise positioning of the features to be machined into the cut surfaces.  FIG. 3  shows the suction side cut surface  68  of the core subpiece  46 . In the exemplary embodiment, a streamwise and spanwise array of individual non-intersecting shallow circuits  100  are machined in the surface  68  to a generally constant shallow depth D 1  ( FIG. 2 ). Each exemplary circuit  100  is formed as a series of three interconnected elongate obround channels  102  (downstream, upstream and intermediate relative to the airfoil section and not to ultimate cooling flow through the circuits). Each channel  102  surrounds a central island  104 . Adjacent channels  102  are interconnected by central gaps  106  in intact portions of the core subpiece defining dividing walls  108  between the channels  102 . Thus, the circuits  100  extend from a downstream leg  110  of the downstream channel, to an upstream leg  112  of the upstream channel. Centrally intersecting each leg  110 , a deeper hole or blind bore  114  ( FIG. 2 ) is drilled. Similar circuits  120  and blind bores  122  may be formed on the suction side cut surface  70 . Other circuit configurations and degrees of interconnectedness are possible as are other numbers and configurations of bores  114  and  122 . As is described in further detail below, ultimately the circuits  100  and  120  will form suction and pressure side wall cooling circuits. 
     FIG. 3  further shows a spanwise series of streamwise elongate slots  130  milled in the suction side cut surface  68 . In the exemplary embodiment, these slots are aligned downstream of associated streamwise groups of the circuits. These slots each have a flat bottom/base with an exemplary shallow depth D 2  and extend from a leading end at a relatively deeper blind bore  132  to a trailing end at the intersection  72  and thus cut through trailing portions of the suction side cut surface  70 . As is described in further detail below, ultimately these slots  130  will help form trailing edge outlet slots. 
   Additional features may be machined into the cut surfaces of the other subpieces  42 ,  44 , and  48 . In the exemplary embodiment, the second cut surface  64  of the suction side subpiece  44  is machined via the drilling of blind bores  140 . Exemplary bores  140  are positioned to align with associated upstream legs  112  of the core subpiece circuits  100 . Similarly, the third cut surface  78  of the suction side subpiece  48  is machined via the drilling of blind bores  150  positioned to align with the upstream legs of associated circuits  120 . Slots  152  are machined in the second cut surface  76  extending through the junction with the third cut surface  78  to align with the slots  130  and form therewith continuous slots upon reassembly. A spanwise series of blind bores  160  are drilled in the cut surface  60  of the leading subpiece  42 . Upon reassembly, these bores  160  align with the first cut surface  66  of the core subpiece  46 . 
   After the machining of features through the cut surfaces, the block may be reassembled. During reassembly, pins  200  may be positioned in the holes  24  and  26  and pins  202  in the holes  28  and  30 . Exemplary pins are short enough so that their ends may become subflush to the associated block faces. The pins are advantageously formed of an alloy or other material suitable for the bonding environment so as to remain intact and constrain (e.g., eliminate or minimize) the relative movement between subpieces. Advantageous material 1) has a melting point and/or strength at the bonding temperature as great as or higher than those of the material being bonded and 2) has a coefficient of thermal expansion close to that of the material. At high bonding temperatures, tungsten may be advantageous because of its high melting point and lack of thermal creep to keep the subpieces from sliding in the bond surface plane. Depending on the subpiece material, the temperature required for bonding, and other bonding environment conditions (oxidation, etc.) other suitable pin alloys could be selected. 
   The reassembled block is placed within a press having opposed pairs of jaws  206  and  208  engaging the block X- and Y-faces to compress the block. The compression is advantageously performed under heating. The compression and heating will initially slightly deform the pieces to permit full remating of the adjacent cut surfaces. If the cuts are constant thickness, the local radii of curvature of two adjacent cut surfaces are mismatched by this thickness. Thus, the deformation may be required to accommodate the mismatch. Where the radii of curvature are large, the mismatch is proportionally insignificant. As the radii decrease, the mismatch may be more significant. It may thus be impractical for the second and third cuts  54  and  56  to parallel the ultimate airfoil suction and pressure side surfaces in low radius of curvature areas such as a leading edge region of the airfoil. Accordingly, the first cut  40  leaves the core subpiece as including only the higher radii of curvature portions of the airfoil contour and thus the core subpiece does not include an airfoil leading edge contour. The heating and compression are advantageously sufficient to diffusion bond the subpieces to each other to reintegrate the assembly. Alternative integrations (e.g., transient liquid phase (TLP) bonding, welding, or brazing) are also possible. 
   For extremely high temperature bonding (e.g., &gt;3000° F., &gt;5 hr, &gt;10 psi), there are few fixture metals that remain stiff and capable of exerting a force to the subpiece assembly to insure bonding. Fixture elements  206  and  208  may be biased by gravity. For example, one may be a large dead-weight applied to the top of the subpiece stack while the other is a support surface. Such a system may be associated with subpiece bond surfaces close to the horizontal. In the exemplary airfoil, using this method may preclude simultaneous bonding of the leading edge subpiece. This may be done in a second bond after an initial first bond of the pressure side, suction side, and center subpieces. 
   After reintegration, an external airfoil contour may be machined and additional internal features may be machined, using the same registration features to maintain location. An exemplary process involves rough machining a suction side surface  250  and a pressure side surface  252  extending between a leading edge  254  and a trailing edge  256 . A major portion of the suction side surface  250  extends parallel to the now-integrated cut surface  64  by a relatively small thickness. A leading portion of the surface  250  is formed along the leading subpiece  42 . The machining of the suction side surface  250  exposes the bores  140  to define outlets on the suction side surface. Similarly, the pressure side surface  252  is spaced apart from the cut surface  78  and exposes the bores  150  and the slots  152 . Internal features may be machined such as feed passageways  260  and  262  and a leading edge cavity  264 . These may be machined through one or both of the Z-faces of the block. In the exemplary embodiment, the feed passageways  260  and  262  are separated by a web  266  and the leading edge cavity  264  is separated from the feed passageway  260  via a web  268 . The cavity  264  and passageway  260  intersect the bore  160  to permit communication therebetween. Additionally, the passageways  260  and  262  intersect various of the bores  114  and  122  and the bore  132  to define inlets to the cooling circuits and trailing edge slots. Additionally, a spanwise and streamwise array of leading edge holes  270  are drilled into the cavity  264 . 
   In ultimate operation of the exemplary airfoil, air may be introduced to one or both of the passageways  260  and  262  (potentially with one feeding the other via impingement through the wall  266  or a turn at one end of the airfoil). From the exemplary feed passageway  260 , air passes through the bores  160  into the cavity  264  and out the holes  270  to cool a leading edge wall portion  272  of the airfoil. Additionally, from the passageways  260  and  262  air enters the cooling circuits through inlets  274  and  275  of the bores  114  and  122  and passes along the circuitous routes of the cooling circuits  100  and  120  exiting the outlets  276  and  277  of the bores  140  and  150  to cool the suction and pressure side airfoil walls  280  and  282 . The circuits are advantageously sufficiently circuitous so that there is no line-of-sight path between each inlet and outlet. Additionally, air entering the trailing edge slots through inlets  285  of the bores  132  cools a trailing portion  286  of the airfoil before exiting outlets  287 . 
   An infinite number of additional variations are possible for airfoil cooling. Cooling circuits may be formed in the suction and pressure side subpieces  44  and  48  instead of in the core subpiece  46 . The circuits may be formed spanning junctions between the core subpiece and the suction and pressure side subpieces (e.g., by having mating halves of patterns on each adjacent cut surface or by having non-mirror-image patterns wherein cooling air passes fully through the circuit defined on one subpiece and then enters the circuit of the mating subpiece). 
   In an exemplary implementation, after the rough machining of the pressure and suction side surfaces and internal features, the central portion  22  may be cut from the outboard portions  32  and  34 . After such cutting, the central portion may be integrated with one or more end pieces for forming end features of the associated turbine element. For example,  FIG. 6  shows end pieces as an inboard platform  290  and an outboard platform  292  at either end of an airfoil  294  manufactured as above to form a vane. This assembly may be integrated via diffusion bonding, welding, brazing, and the like. The end pieces  290  and  292  may be largely pre-formed in final or near final shape or may be near blocks requiring even the rough shaping of features such as mounting features and passageways for communicating with the airfoil passageways  260  and  262 .  FIG. 7  shows an airfoil  300  manufactured as above integrated with an inboard root end piece  302  to form a blade. 
     FIG. 8  shows a blade outer air seal (BOAS) precursor block  350 , having a convex outboard surface  352  and a concave inboard surface  354 . A first exemplary cut  356  divides the block into outboard and inboard subpieces  358  and  360 . Pinning holes  362  may span the cut  356  in similar fashion to those described above. The cut  356  forms a concave cut surface  364  in the outboard subpiece and a convex cut surface  366  in the inboard subpiece.  FIG. 9  Shows the concave surface  364  after the machining of a plurality of elongate rows  368  of circuit channels  370 . Mirror image, out-of-phase, or other complementary features (not shown) may optionally be machined in the convex cut surface  366 . 
     FIG. 10  shows the outline of the BOAS in the precursor. This includes drilled or otherwise machined inlets  380  to the channels and outlets  382  from the channels.  FIGS. 11 and 12  show the BOAS with a thermal barrier coating  390  ( FIG. 11 ), feather seal slots  392  ( FIG. 12 ), and mounting hooks  394  ( FIG. 12 ). 
   One or more embodiments of the present invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. For example, when implemented in creating a replacement for an existing part, details of the existing part may influence details of the particular implementation. The methods may be used to make other components (e.g., integrally bladed or other rotors, case components, combustor components, exhaust components, and the like). In large scale production, individual subpieces from a given block need not be reintegrated with the other subpieces of that block but may be integrated with subpieces from one or more like blocks. The integration may be of pieces not cut from common or like blocks. Accordingly, other embodiments are within the scope of the following claims.