Patent Description:
Ceramic matrix composite components, such as those formed of silicon carbide, are commonly used in high-temperature environments because they can withstand temperatures up to <NUM>°F (<NUM>). Such components can still benefit from additional cooling to prevent component degradation. One way to provide additional cooling is through the incorporation of internal cooling channels into the component. The structure of many composite components can make adding such features somewhat difficult when using traditional fabrication processes.

<CIT> discloses a method for forming a hole within a ceramic matrix composite component according to the preamble of claim <NUM>.

A method of forming a ceramic matrix composite component is as defined in claim <NUM>.

While the above-identified figures set forth one or more embodiments of the present disclosure, other embodiments are also contemplated, as noted in the discussion. In all cases, this disclosure presents the invention by way of representation and not limitation. It should be understood that numerous other modifications and embodiments can be devised by those skilled in the art, which fall within the scope of the principles of the invention. The figures may not be drawn to scale, and applications and embodiments of the present invention may include features and components not specifically shown in the drawings.

This disclosure presents composite component with internal, fluidly-connected cavities, and a method of forming that composite component. The method includes wrapping multiple mandrels each with at least one fiber sheet. Each mandrel has openings or cut-outs that can serve as a template for creating corresponding holes in these fiber sheets. holes can be formed by removal of material (e.g., cutting or punching an opening in the sheet) or by pushing a pin through the thickness of the sheet and into the mandrel opening. Two wrapped mandrels are placed together and aligned such that the holes in each sheet face and are aligned with one another. The mandrels are then overwrapped with at least one further sheet securing the wrapped mandrels in place. The resulting preform structure can undergo matrix formation and mandrel removal to become a composite component with elongate cavities fluidly connected at least in part by passages formed by the aligned holes within the fiber sheets.

<FIG> is a flowchart illustrating selected steps <NUM>-<NUM> of method <NUM>, used to form a composite component. In an exemplary embodiment, the component is a ceramic matrix composite (CMC) component. <FIG> is a simplified illustration of mandrel <NUM> used in method <NUM>. <FIG>, <FIG> are simplified cross-sectional views of alternate embodiments of a fiber preform. Steps <NUM>-<NUM> are described below in combination with <FIG>.

At step <NUM>, each mandrel <NUM> is wrapped with at least one composite fiber sheet <NUM> (shown in <FIG> and <FIG>). As used herein, the term "sheet" can be interchangeable with terms such as "ply" and "fabric". Each sheet <NUM> (or <NUM> in <FIG>) can be formed from braided or woven ceramic fibers or tows arranged in a uni- or multidirectional manner. Exemplary sheets <NUM>, <NUM> can have <NUM>-harness, <NUM>-harness, plain, or twill weave patterns. The ceramic fibers can be formed from silicon carbide or other suitable ceramic materials. Each sheet <NUM>, <NUM> can have a thickness ranging from <NUM> to <NUM> (<NUM> inches to <NUM> inches).

As shown in <FIG>, each mandrel <NUM> includes one or more openings <NUM>. Openings <NUM> can be rounded (e.g., circular, elliptical, etc.), have straight sides (e.g., diamond, square, etc.) or a combination of the two. Openings <NUM> can further be generally uniform in size and shape, as shown in <FIG>, or can vary along a given mandrel <NUM>. Most generally, openings <NUM> are formed at locations and in shapes selected to promote a desired fluid flow volume and patterns between open or hollow spaces in the final component defined during manufacture by the respective locations of adjacent mandrels. A sheet <NUM> is wrapped around a respective mandrel <NUM> such that it at least fully circumscribes the mandrel (i.e., opposite ends of sheet <NUM> touch or overlap slightly). In an alternative embodiment, however, it may only be necessary to cover an area including openings <NUM>, but otherwise not fully circumscribe the mandrel <NUM> with the one or more sheets <NUM>.

At step <NUM>, and once sheet <NUM> is wrapped around or otherwise secured to mandrel <NUM>, sections of sheet <NUM> corresponding to the underlying openings <NUM> of mandrel <NUM> are manipulated to form holes <NUM>. In one embodiment, holes <NUM> can be formed by completely removing sections (i.e., portions lesser than the whole) of sheet <NUM> by, for example, cutting through the fibers of sheet <NUM> with a sharp tool or laser, or by using a punching tool. Each hole <NUM> can generally be formed to match the geometry of the underlying mandrel opening <NUM>.

In an alternative embodiment, holes <NUM> can be formed by pushing pin <NUM> (shown in <FIG>) through a section of sheet <NUM> corresponding to an opening <NUM> in mandrel <NUM>. As used herein, the term "pin" can be interchangeable with terms such as "needle," "rod," "tube," or "wire. " Pin <NUM> can be inserted into sheet <NUM> such that it generally does not damage (e.g., puncture or break) individual fibers, rather, fibers are pushed aside to accommodate the pin. This differs from cutting or punching through sheet <NUM> which breaks fibers so that a section of sheet <NUM> is separated and removed. Using a pin may be preferable if greater continuity (e.g., lack of breakage) of fibers within individual sheets <NUM> is desired for enhanced mechanical and/or thermal properties. One or more pins <NUM> can be used to create holes <NUM>. In some cases, pin(s) <NUM> can create a hole <NUM> but be removed prior to subsequent processing. In other cases, however, individual pins <NUM> can be pushed into sheet <NUM> at the desired location of holes <NUM> and remain embedded throughout subsequent steps of method <NUM>. The latter may prevent the fibers from moving back into the region of holes <NUM> during, for example, matrix formation discussed below. In another alternative embodiment, one or more pins <NUM> can be formed as a part of mandrel <NUM> (as protrusions, bumps, bosses, etc.) in a manner similar to the arrangement of openings <NUM>. In such an embodiment, a sheet <NUM> can be pushed down onto the protrusions and wrapped as desired.

At step <NUM>, and once the desired holes <NUM> are formed in each sheet <NUM> of each mandrel <NUM>, mandrels <NUM> are brought together and aligned such that the holes <NUM> of the first sheet <NUM> on the first mandrel <NUM> are aligned with holes <NUM> on the second sheet <NUM> of the second mandrel <NUM>. This alignment can, as in the embodiment illustrated in <FIG>, be achieved when openings <NUM> of adjacent mandrels are aligned. In other embodiments, as illustrated in <FIG>, the shaping or angle of holes <NUM> can result in alignment of holes <NUM> requiring that openings <NUM> of adjacent mandrels be relatively displaced or offset. Once aligned, mandrels <NUM> are overwrapped by at least one additional sheet <NUM> which surrounds both mandrels <NUM> to form fiber preform <NUM>.

<FIG> is a cross-sectional view of preform <NUM> including a first mandrel <NUM> wrapped with a first sheet <NUM>, a second mandrel <NUM> wrapped with a second sheet <NUM>, and overwrapped with a third sheet <NUM>. Preform <NUM> extends along longitudinal axis A. It should be understood that either/both mandrels <NUM> can be wrapped with more than one sheet <NUM>, and the overwrap can additionally/alternatively include more than one sheet <NUM> based on, for example, the desired thickness of the corresponding regions of the final component. Further, although represented with varied hatching for easier visualization of the individual sheets <NUM>, sheets <NUM> can be formed from the same material and/or have the same thickness, or vary in material and/or thickness. As can be seen in <FIG>, a pair of aligned holes <NUM> form a channel <NUM>.

<FIG> is an enlarged view of area A4 of <FIG> showing an individual channel <NUM>. With reference to <FIG>, holes <NUM> are aligned such that channel <NUM> is generally orthogonal (i.e., angle θ = <NUM>°) to axis A. Such channel orientation can be achieved by forming pairs of holes <NUM> at the same location on the respective mandrels <NUM>. Additionally, channels <NUM> can have a generally cylindrical cross-sectional shape when each hole <NUM> in a respective pair has the same area as the corresponding hole <NUM>. Other cross-sectional shapes (e.g., frustoconical) are contemplated herein.

<FIG> is a cross-sectional view of alternative preform <NUM>. <FIG> is an enlarged view of area A6 of <FIG> showing an individual channel <NUM> of preform <NUM>. Preform <NUM> is substantially similar to preform <NUM>, except for the shape and orientation of channels <NUM>. As shown, channels <NUM> extend at a non-orthogonal angle with respect to axis A. More specifically, angle Θ is greater than <NUM>°, and can alternatively be less than <NUM>° in another embodiment. Angled channels <NUM> can be achieved by staggering/offsetting each hole <NUM> in a respective pair of holes <NUM>. Channels <NUM> are also shown as having a frustoconical cross-sectional shape, which can be achieved by making one hole <NUM> in a respective pair of holes <NUM> larger in at least one dimension than the corresponding hole <NUM>. Other cross-sectional shapes (e.g., cylindrical) are contemplated herein. Angled and/or frustoconical channels can promote directional flow (e.g., for vortex formation) to improve cooling.

The size of each hole <NUM> and/or <NUM> can range from <NUM> to <NUM> (<NUM> inches to <NUM> inches). As used herein, size can refer to a major dimension, such as radius for circular and elliptical holes <NUM>, <NUM>, or length of a straight segment for shapes such as square, rectangular, diamond, etc..

At step <NUM>, preform <NUM>, <NUM> undergoes matrix formation and densification using a chemical vapor infiltration or deposition (CVI or CVD) process. During densification, sheets <NUM>,<NUM> are infiltrated by reactant vapors, and a gaseous precursor deposits on the fibers. The matrix material can be a silicon carbide or other suitable ceramic material. Densification is carried out until the resulting CMC has reached the desired residual porosity. Mandrels <NUM>, <NUM> can also be physically or chemically removed post-densification, as well as any pins, if used, inserted in sheets <NUM>, <NUM>. Removing mandrels <NUM>, <NUM> and pins <NUM> leaves cavities and passages within the finished workpiece for cooling airflow.

<FIG> is a cross-sectional view of component <NUM>, a CMC airfoil, formed using method <NUM>. Component <NUM> extends longitudinally along axis A, which can be the same as the longitudinal axis of preform <NUM>, <NUM>. Component <NUM> includes leading edge <NUM>, trailing edge <NUM>, pressure side <NUM>, and suction side <NUM>. A leading edge cavity <NUM> is and trailing edge cavity <NUM> are defined by outer wall <NUM> and dividing wall <NUM>. Each of leading edge cavity <NUM> and trailing edge cavity <NUM> represent the space at least partially occupied by mandrels <NUM>, <NUM> during component preforming. Walls <NUM> and <NUM> are formed by the various sheets <NUM>, <NUM> wrapped around mandrels <NUM>, <NUM>. Any of walls <NUM> and <NUM> can have a wall thickness ranging from <NUM> to <NUM> (<NUM> inches to <NUM> inches). Crossover channels <NUM> (only one is shown) in dividing wall <NUM> is equivalent to channels <NUM>, <NUM> of preform <NUM>, <NUM>. In operation of component <NUM>, a cooling airflow can be supplied to leading edge cavity <NUM> and/or trailing edge cavity <NUM> from an external source, and the cooling airflow can pass from the receiving cavity to the other cavity via crossover channels <NUM>.

Method <NUM> discussed above can include additional steps (inter-step or post processing) not shown in <FIG>. For example, after step <NUM>, various post-processing steps can be performed, such as the application of one or more protective coatings, such an environmental and/or thermal barrier coatings. A bond coat can also be applied to facilitate bonding between the CMC and protective coating. Other protective coatings, especially those suitable for use in a gas turbine engine environment, are contemplated herein. Various inter-step processes can also be performed, such as the application of a tackifier to sheets <NUM>, <NUM> prior to or just after wrapping on mandrels <NUM>. Other inter-step processes like surface preparation and cleaning are contemplated herein.

Claim 1:
A method of forming a ceramic matrix composite component having an internal cooling circuit, the method comprising:
wrapping at least a first sheet (<NUM>; <NUM>) around a first mandrel (<NUM>; <NUM>);
wrapping at least a second sheet (<NUM>; <NUM>) around a second mandrel (<NUM>; <NUM>);
creating a first plurality of holes (<NUM>; <NUM>) in the first sheet (<NUM>; <NUM>) corresponding to a plurality of openings (<NUM>; <NUM>) in the first mandrel (<NUM>; <NUM>);
creating a second plurality of holes (<NUM>; <NUM>) in the second sheet (<NUM>; <NUM>) corresponding to a plurality of openings (<NUM>; <NUM>) in the second mandrel (<NUM>; <NUM>);
aligning the first mandrel (<NUM>; <NUM>) and the second mandrel (<NUM>; <NUM>);
wrapping at least a third sheet (<NUM>; <NUM>) around both the first mandrel (<NUM>; <NUM>) and second mandrel (<NUM>; <NUM>) to form a preform (<NUM>; <NUM>), the preform (<NUM>; <NUM>) comprising each of the first sheet (<NUM>; <NUM>), the second sheet (<NUM>; <NUM>), and the third sheet (<NUM>; <NUM>); and
densifying the preform (<NUM>; <NUM>), wherein the first sheet (<NUM>; <NUM>), second sheet (<NUM>; <NUM>), and third sheet (<NUM>; <NUM>) are formed from a ceramic fiber material;
characterized in that the step of aligning the first mandrel (<NUM>; <NUM>) and the second mandrel (<NUM>; <NUM>) is carried out such that the first plurality of holes (<NUM>; <NUM>) face and are aligned with the second plurality of holes (<NUM>; <NUM>) forming a corresponding plurality of open channels (<NUM>; <NUM>).