Abstract:
A component ( 34 A,  34 B,  34 C) has a core formed of a stack ( 25, 36 ) of sheets ( 20 ) of material with cutouts ( 22 A) aligned to form passages ( 38 ) in the core. An outer casing ( 29 ) spans the stack axially ( 51 ), brackets at least parts of opposed ends of the stack, and holds the sheets together in axial compression ( 46 ). Respective cooperating elements ( 30, 31 ) on the casing and the stack may register the casing with respect to the stack. Pins ( 24 ) in some sheets may engage holes ( 23 ) in adjacent sheets to register the sheets with each other. The casing may be segmented ( 28 A,  28 B,  28 C). A hoop ( 66 ) may be compressed around the segmented casing. A gas turbine fuel injector may be formed of a stack ( 36 ) with an inlet element ( 44 ) compressed ( 46 ) onto the stack by the casing ( 29 ).

Description:
This application is a division of U.S. Pat. No. 8,940,114 filed Apr. 27, 2011 and issued Jan. 27, 2015. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to products with complex internal passages, including gas turbine components. 
     BACKGROUND OF THE INVENTION 
     It is difficult to manufacture components with complex internal geometries. Although precision investment casting is often used to manufacture components with internal cavities, the complexity of the passages is limited by the casting core and the ability to flow material within a mold. Intricate cores are fragile, and may not withstand the casting process. Machining of internal features is usually limited to line-of-sight processes. 
     There are various additive manufacturing techniques such as Direct Laser Metal Sintering (DMLS) that are capable of building components layer-by-layer from sintered powder. Although such techniques are suitable for making prototypes and for limited production, they are not economical for large scale production. Additionally, the surfaces of laser-sintered materials can be unacceptability rough. 
     In stacked laminate construction, a component is constructed from multiple layers of sheet or foil material. Each individual sheet can be easily machined to form cutouts. The component is then built by stacking the sheets. The sheets can be registered with the cutouts aligned to form complex internal geometries. A limitation of the stacked laminate approach is the ability to reliably bond each layer. Some materials such as superalloys Haynes® 230 and 282 that are otherwise desirable are difficult to bond into a laminated structure. This limits the choice of materials that can be used for laminated construction. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is explained in the following description in view of the drawings that show: 
         FIG. 1  is a perspective view of a first sheet of material with a pattern of holes, including two registration holes. 
         FIG. 2  is a perspective view of a second sheet of material with a pattern of holes and two registration pins. 
         FIG. 3  shows stacking of sheets to form a stacked core structure with internal channels. 
         FIG. 4  shows a green-state casing preform surrounding a stacked core structure. 
         FIG. 5  shows the assembly of  FIG. 4  after processing shrinkage of the casing. 
         FIG. 6  shows a fuel injector formed of a stacked core and casing. 
         FIG. 7  shows a casing preform sliding over a stacked core structure to form a fuel injector. 
         FIG. 8  shows the fuel injector formed from  FIG. 7 , including a pressure plate. 
         FIG. 9  shows a fuel injector with air bypass clearance between the casing and the core structure. 
         FIG. 10  shows a cup-shaped casing embodiment with outlets. 
         FIG. 11  shows a segmented casing embodiment. 
         FIG. 12  shows a cup-shaped segmented casing embodiment with hoop. 
         FIG. 13  shows the casing of  FIG. 12  after assembly. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     An aspect of the invention is a product made utilizing a combination of two manufacturing technologies that together provide internal passages in materials that are difficult to fabricate. A component core is made from a series of stacked sheets or foils, and an outer casing is made using a process that compresses the casing on the core. 
       FIG. 1  shows a sheet of material  20 A with cutouts  22 A and registration holes  23 .  FIG. 2  shows a second sheet of material  20 B with corresponding cutouts  22 B and registration pins  24 .  FIG. 3  shows a stack  25  of sheets  20 A- 20 F being assembled. The registration pins  24  fit into the registration holes  24  to register adjacent sheets so that cutouts  22 A align with or overlap the corresponding cutouts  22 B in adjacent sheets to define passages in the stack. Cutout patterns in each sheet may be formed using methods such as drilling/milling, laser cutting, water-jet cutting, stamping, and photochemical machining. 
     The registration pins  24  may be formed by molding, DMLS, or other methods. Alternately, the sheets may be registered in a jig or mold, and may be bonded together by a method such as diffusion bonding or adhesive. Alternately registration holes may be formed through every sheet in the stack  25 , and long registration pins may be inserted through all the sheets. 
       FIG. 4  shows a casing preform  28  that is placed or formed around a core stack  25 . The casing preform may be formed of a material that shrinks during processing. In this context the phrase “shrinks during processing” does not mean simply thermal contraction. It means permanent shrinkage as measured at the same temperature before and after processing. Examples of such materials are ceramic green-bodies and sinterable metal power mixed with a binder such as a polymer. Herein, “green body” or “green state” means a preform prior to processing shrinkage. The preform may be designed and dimensioned to shrink into compression upon the stack  25  as the casing preform is processed. The preform may be manufactured by injection molding or other methods. It may have one or more registration elements  30  that mate with corresponding elements  31  on the stack; for example tongue-and-groove elements. It may have an exterior mounting element(s)  32 . 
       FIG. 5  shows the casing  29  after processing, which reduces its volume, compressing the sheets of the core  25  together, and preventing their separation. The sheets may be bonded together or not, and may be bonded to the casing or not. Sintered metal and ceramic casings may develop a final density close to 100%. The casing may shrink up to about 20%, depending on the material. For sinterable powder materials, the shrinkage amount is largely determined by the particle constituents, their size/shape distribution, and the binder materials and proportion. These parameters may be selected in conjunction with the geometry and dimensions of the preform to produce a desired amount and distribution of compression on the sheets  20 A- 20 F. 
       FIG. 6  shows a gas turbine fuel injector  34 A made of a cylindrical stack  36  of sheets of material  20  in a casing  29 . Cutouts in the sheets align to form internal passages  38  for mixing fuel  40  and air  42 . A fuel and air inlet element  44  may be placed on one end of the stack. The casing  29  may span both the stack  36  and the inlet element  44  such that the casing compresses  46  the inlet element  44  against the stack  36 . The inlet element  44  may be tubular as shown or other shapes, and it may be formed by any method, such as casting or molding. Fuel ports  48  may pass fuel into the mixing passages  38 . Turbulators  50  may be provided in the mixing passages  38  to effectively mix the fuel and air. Stacked core structures for fuel injectors and other components may be designed in various shapes, including cylindrical, barrel-shaped, prismatic polyhedral, and irregular. An axis  51  is defined herein as a geometric central line normal to the planes of the sheets  20 . It may be an axis of rotational symmetry if the stack has such symmetry, but this is not a requirement of the invention. Herein “radial” means in a direction perpendicular to such axis. 
       FIG. 7  shows a geometry that allows the casing preform  28  to slide  52  over the stack  36  and the inlet element  44 . Inwardly extending lips  54  on the top end of the casing preform just clear the outer diameter of the stack  36 . Inwardly extending lips  55  on the bottom end of the preform are not so limited.  FIG. 8  shows the resulting fuel injector  34 B after about 20% shrinkage of the casing. The green body casing may be designed to shrink a given amount such as 18-20% to allow clearance for sliding assembly. The dimensions of the preform may be designed to provide a uniform or non-uniform distribution of compression stresses around the stack  36  and the inlet element  44 . For example, the axial compression  46  may be greater than the radial compression  47 . A pressure plate  56  may be provided to distribute axial force from the lips  55  onto the end of the stack  36 . The pressure plate  56  may be for example at least twice as thick as an average sheet thickness among the sheets of the stack and may be formed of the same or a different material than the other sheets of the stack. 
       FIG. 9  shows a fuel injector embodiment  34 C with an air bypass clearance  58  between the stack  36  and the casing  29  that allows some air  59  to bypass the mixing channels  38  to provide near-wall cooling of the casing  29  or for other purposes. In this embodiment, the casing preform may be designed with an inner diameter large enough to leave the radial clearance  58  after shrinkage. Alternately, a fugitive material may be formed on the outer diameter of the stack, and a casing preform  28  may be bi-cast over the fugitive material, which may be chemically removed after sintering and/or other processing. 
       FIG. 10  shows a cup-shaped casing  29  having a bottom  60  with outlets  62 . These outlets may diverge from the inside to the outside surface of the casing  29  as shown to act as diffusers, and they may have a hexagonal shape as shown. One or more circular arrays of such outlets may be provided, and they may nest in a honeycomb pattern for space efficiency. Such a cup-shaped casing in green-body form may slide over the stacked core as shown in  FIG. 7 . 
       FIG. 11  shows a segmented casing  29  with two or more segments  29 A,  29 B,  29 C rotationally symmetrically spaced around the circumference of the stacked core. Each segment spans a portion of the core. The lips  54 ,  55  may extend inward as far as desired since they do not need to slide over the core as in  FIG. 7 . The segments may fully encircle the sides of the stacked core. However, in the example of  FIG. 11 , each of three segments  29 A,  29 B, and  29 C covers 60 degrees of cylinder, leaving 60 degrees between adjacent segments. 
       FIG. 12  shows a cup-shaped and segmented casing preform  28 , having a bottom  60  with outlets  62  as previously described. Side segments  28 A,  28 B,  28 C are separated by slots  64 . In this example there are four side segments, one of which is hidden. It is suggested that at least 4 segments be provided in this embodiment. This preform  28  can slide over the stacked core by flexing the segments outward, which allows the lips  54  to extend further inward than with a non-flexing preform. One or more hoops  66  may be formed of a material that shrinks during processing, particularly a sinterable material, and especially the same material as the casing. The hoops may be are compressed around the casing during processing in the embodiments of  FIGS. 11 and 12 . Each hoop may be formed into a preform, slipped over the casing preform  28  after assembly of the preform onto the stack, and sintered with the casing or otherwise processed into compression thereon.  FIG. 13  shows a hoop  66  assembled onto the casing  29 . 
     The process herein overcomes limitations associated with poor interfacial bond strength between sheet layers. A stacked sheet core of a component is encased within an outer casing. Precise, three-dimensional features can be produced in both the stacked core and the casing preform. These features may be designed to accurately fixture the components during processing and improve dimensional tolerances. A stacked core of a component can now be made of materials that have excellent heat tolerance or other desirable characteristics, but that are not easily bonded together, such as Haynes 230 and/or 282 superalloys. 
     While various embodiments of the present invention have been shown and described herein, it will be obvious that such embodiments are provided by way of example only. Numerous variations, changes and substitutions may be made without departing from the invention herein. Accordingly, it is intended that the invention be limited only by the spirit and scope of the appended claims.