Patent Description:
Lightweight CMC is a highly desirable material for gas turbine engine applications. CMCs exhibit excellent physical, chemical, and mechanical properties at high temperatures and are particularly suited for producing hot section components for gas turbine engines. Gas path components such as turbine blades, seals or shrouds, and combustor panels often include cooling passages for film cooling component surfaces. Cooling holes are typically provided to densified CMC components using machining processes, such as ultrasonic impact grinding, laser hole drilling, or electron beam discharge machining (EDM). These machining processes are time-consuming and cost-intensive and cause fiber breakage, which can weaken the CMC component or expose a surface to environmental attacks.

<CIT> discloses a prior art method for forming a hole in a ceramic matrix composite component as set forth in the preamble of claim <NUM>.

<CIT> discloses prior art needled ceramic matrix composite cooling passages.

In one aspect, there is provided a method for forming a hole in a ceramic matrix composite component as recited in claim <NUM>.

In another aspect, there is provided a tool for forming holes in a ceramic matrix composite component as recited in claim <NUM>.

The present summary is provided only by way of example, and not limitation. Other aspects of the present disclosure will be appreciated in view of the entirety of the present disclosure, including the entire text, claims and accompanying figures.

While the above-identified figures set forth embodiments of the present invention, other embodiments are also contemplated without departing from the scope of the appended claims, 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 appended claims. The figures may not be drawn to scale, and applications and embodiments of the present invention may include features, steps and/or components not specifically shown in the drawings.

The present disclosure is directed to a method of forming cooling holes in a CMC component without causing fiber breakage or damage to the ceramic matrix. As discussed in further detail herein, the method uses guide tubes to precisely locate sacrificial rods in a fiber preform prior to densification. The rods are removed following a densification step, leaving precisely located cooling holes free of fiber breakage and damage to the ceramic matrix. It should be understood that the disclosed method is not limited to the formation of holes capable of carrying a cooling gas but can generally be applied to form passages through fiber-reinforced composite materials. For example, the disclosed method can be used to form retention holes (e.g., bolt holes) or passages for transporting fluids other than cooling air.

<FIG> is a cross-sectional view of assembly <NUM>. First tool component <NUM>, fiber preform <NUM>, second tool component <NUM>, counterbore hole <NUM>, first hole portion <NUM>, second hole portion <NUM>, end <NUM>, hole <NUM>, guide tube <NUM>, and guide tube end <NUM> are shown. Counterbore hole <NUM> is formed in first tool component <NUM> and includes first hole portion <NUM>, second hole portion <NUM>, and end <NUM>. Hole <NUM> is formed through second tool component <NUM>. Fiber preform <NUM> can be formed on first tool component <NUM> to match a shape of first tool component <NUM>. Second tool component <NUM> is positioned over fiber preform <NUM> with holes <NUM> aligned coaxially with counterbore hole <NUM>. Guide tube <NUM> is configured to be received in hole <NUM> and counterbore hole <NUM>. Guide tube end <NUM> is stopped by end <NUM> of first hole portion <NUM>. <FIG> illustrates a first step in a process of forming a cooling hole in CMC component. Specifically, <FIG> illustrates the assembling of first and second tool components <NUM> and <NUM> with fiber preform provided therebetween, and axial aligning hole <NUM> and counterbore hole <NUM> to allow passage of guide tube <NUM>.

First tool component <NUM> and second tool component <NUM> can be molds or shaping structures for fiber preform <NUM>. First tool component <NUM> and second tool component <NUM> can be formed of a material such as carbon, for example, graphite. First tool component <NUM> and second tool component <NUM> can be cast and/or machined with conventional methods and removed without damage to the CMC component. Each of first and second tool components <NUM> and <NUM> can be formed from multiple components. For example, first tool component <NUM> can be a formed in the shape of an airfoil core with one or more components each defining passages within an airfoil. When assembled, second tool component <NUM> can be disposed to fully or substantially surround first tool component <NUM> or can be disposed to fully or substantially cover fiber preform <NUM> positioned on one side of first tool component <NUM>, for example, in the manufacture of a CMC panel or sheet.

First tool component <NUM> includes counterbore hole <NUM>. Counterbore hole <NUM> can be a cylindrical stepped hole having first hole portion <NUM> and second hole portion <NUM>. First and second hole portions <NUM> and <NUM> are coaxial. First hole portion <NUM> has a first diameter d1. Second hole portion <NUM> has a second diameter d2. The second diameter d2 is less than the first diameter d1. First hole portion <NUM> can have a length sufficient to locate an end of guide tube <NUM> in first tool component <NUM>. First hole portion <NUM> can have a substantially flat bottom or end <NUM>, as illustrated. In other examples, end <NUM> of first hole portion can be angled, for example, to match a shape of guide tube end <NUM> of guide tube <NUM>. End <NUM> forms a stop for guide tube <NUM>. Second hole portion <NUM> can be a blind hole formed to a depth sufficient to retain a rod but without extending through a side of first tool component <NUM>. Counterbore hole <NUM> can be drilled with conventional machining methods. Counterbore <NUM> is located and oriented (e.g., angled) to form a desired cooling passage through the CMC component.

Fiber preform <NUM> comprises a plurality of ceramic fibers or fiber tows fibers, which can be woven, non-woven, braided, or selectively placed. For example, fiber preform <NUM> can be formed from a plurality of unidirectional or two-dimensional woven fiber plies or sheets. In other examples, fiber preform <NUM> can be formed from a three-dimensional weave. In some examples, fiber preform <NUM> can additionally include fabric filler materials, e.g., "noodles", and/or chopped fibers. Fiber preform <NUM> can be formed on or around first tool component <NUM>. For example, first tool component <NUM> can be a shape of an airfoil core and fiber preform <NUM> can be wrapped around first tool component <NUM> to form an airfoil. In other examples, fiber preform <NUM> can form a panel (e.g., combustor panel) or segment member such as a blade outer air seal. It should be appreciated that the disclosed method is not limited to aerospace components and can be applied in other fiber-reinforced composite applications. Fiber preform <NUM> can be assembled separately from first and second tool components <NUM> and <NUM> and placed into first and second tool components <NUM> and <NUM> prior to densification. In other examples, fiber preform <NUM> can be formed directly on first tool component <NUM> (e.g., by braiding fiber tows or wrapping fiber plies around a surface of first tool component <NUM> or by fiber layup directly on a surface of first tool component <NUM>). In some examples, fiber preform <NUM> can include a tackifier to help retain a shape of fiber preform <NUM> on first tool component <NUM>. The tackifier material can be burned out prior to or during a densification process. Fiber materials can comprise a material stable at temperatures about <NUM> degrees Celsium. Fibers materials can include, for example, silicon carbide (SiC), carbon (C), silicon oxycarbide (SiOC), silicon nitride (Si<NUM>N<NUM>), silicon carbonitride (SiCN), hafnium carbide (HfC), tantalum carbide (TaC), silicon borocarbonitride (SiBCN), zirconia, alumina, and silicon aluminum carbon nitride (SiAlCN).

Second tool component <NUM> is positioned on or around fiber preform <NUM>, such that fiber preform <NUM> is disposed between first tool component <NUM> and second tool component <NUM>. Second tool component <NUM> can have a shape that conforms to a desired outer shape of preform <NUM>. Second tool component <NUM> can be formed of multiple components, which can be assembled together around fiber preform <NUM> such that an outer surface of preform <NUM> is fully or substantially covered by second tool component <NUM>.

Second tool component <NUM> includes hole <NUM>. Hole <NUM> extends fully through second tool component <NUM>. Hole <NUM> can have a diameter d3 substantially equal to diameter d2 of first hole portion <NUM>. Hole <NUM> is configured to receive guide tube <NUM>. Hole <NUM> is coaxial with counterbore <NUM>. First tool component <NUM> and second tool component <NUM> can include one or more alignment features used to align hole <NUM> with counterbore <NUM> to allow guide tube <NUM> to be received in both hole <NUM> and counterbore <NUM>. For example, first and second tool components <NUM> and <NUM> can be keyed together with dowels and match holes or rectangular slots and matching bosses.

Guide tube <NUM> is a hollow tube with an opening at each end. Guide tube <NUM> is configured to receive a rod in the inner passage of guide tube <NUM>. Guide tube <NUM> forms a sleeve around the rod. An outer diameter d4 of guide tube <NUM> is less than diameters d3 of hole <NUM> and d2 of first hole portion <NUM>. The outer diameter d4 of guide tube <NUM> is greater than diameter d1 of second hole portion <NUM>. As such, guide tube <NUM> cannot be received in second hole portion <NUM> and instead stops at end <NUM> of first hole portion <NUM>. An inner diameter and/or cross-sectional area (shown in <FIG>) of guide tube <NUM> can be substantially equal to or greater than a size of the desired cooling hole. In the disclosed aerospace application examples, cooling holes typically have diameters less than x but it should be understood that the disclosed method can be used to form holes of any size.

Guide tube <NUM> has end <NUM>, which is stopped at end <NUM> of first hole portion <NUM>. Guide tube end <NUM> can be shaped to be able to fit between adjacent fibers or fiber tows of fiber preform <NUM> without catching or pushing fibers and/or fibers tows when being inserted through fiber preform <NUM>. For example, guide tube <NUM> can have a pointed or slanted end similar to a hypodermic needle as illustrated. Guide tube <NUM> can be manufactured of a metal alloy, a nylon, or any other rigid material that is compatible with the CMC material. In some examples, guide tube <NUM> can be a commercially available hypodermic needle. Tube-drawn stainless steel hypodermic needles are available in standard sizes with internal diameters similar to desired cooling hole diameters and with wall thicknesses suitable for forming holes according to the disclosed method.

<FIG> is a cross-sectional view fiber preform <NUM> in the first and second tool components <NUM>, <NUM>, illustrating a step of inserting guide tube <NUM> through hole <NUM> of second tool component <NUM> and into fiber preform <NUM>. As previously discussed, guide tube end <NUM> is shaped to fit between fibers and/or fiber tows and displace fibers and/or fiber tows around guide tube <NUM>, such that a space between fibers and/or fibers tows is expanded to make room for guide tube <NUM> as guide tube <NUM> passes through fiber preform <NUM>. Guide tube end <NUM> and guide tube <NUM> can be received into fiber preform <NUM> without catching or pressing fibers and/or fiber tows into counterbore hole <NUM>.

<FIG> is a cross-sectional view of the fiber preform <NUM> in the first and second tool components <NUM>, <NUM>, illustrating a step of inserting guide tube <NUM> through fiber preform <NUM> and into counterbore hole <NUM> of first tool component <NUM>. As illustrated in <FIG>, guide tube <NUM> can be inserted through fiber preform <NUM> such that fibers and/or fiber tows are not pressed into counterbore <NUM>. Instead, fibers and/or fiber tows are displaced around guide tube <NUM>, primarily within the plane in which they were laid, such that a shape of fiber preform <NUM> is substantially maintained. The fibers of fiber preform <NUM> are not broken by guide tube <NUM>. Guide tube <NUM> can be inserted into first hole portion <NUM> of counterbore hole <NUM> until guide tube <NUM> reaches end <NUM>. In some examples, end <NUM> can be shaped to conform to a shape of end <NUM> of guide tube <NUM> to help secure guide tube <NUM> in counterbore <NUM>.

<FIG> is a cross-sectional view of fiber preform <NUM> in the first and second tool components <NUM>, <NUM>, illustrating a step of inserting rod <NUM> into guide tube <NUM>. Rod <NUM> can be formed from the same material as first and/or second tool components <NUM> and <NUM>, which can be removed from the CMC component following or during a densification step thereby leaving a cooling hole in the CMC component. For example, rod <NUM> can be formed of graphite, which can be burned out in the densification process. Rod <NUM> is shaped and sized to form the desired cooling hole through the CMC component. For example, rod <NUM> can have a circular, rectilinear, oval, racetrack, or other cross-sectional shape. As illustrated in <FIG>, both rod <NUM> and the passage through guide tube <NUM> are cylindrical. In other examples, however, the inner passage through guide tube <NUM> can more generally have a cross-sectional shape matching the cross-sectional shape of rod <NUM>. Similarly, the outer cross-sectional shape of guide tube <NUM> can be cylindrical or can match a cross-sectional shape of rod <NUM>. A cross-sectional area or diameter of rod <NUM> is less than the inner cross-sectional area or diameter of the passage through guide tube <NUM>, such that rod <NUM> is able to be received in guide tube <NUM>.

Rod <NUM> is received in guide tube <NUM> and counterbore <NUM>. Rod <NUM> extends beyond end <NUM> of guide tube <NUM> and into second hole portion <NUM> of guide tube <NUM>. Diameter d2 of second hole portion <NUM> can be slightly larger than an outer diameter of rod <NUM> such that rod <NUM> can be received in second hole portion <NUM>. Second hole portion <NUM> can have a cross-sectional shape matching a cross-sectional shape of rod <NUM>. Second hole portion <NUM> can have a cross-sectional area or diameter d2 that is narrowly larger than a cross-sectional area or diameter of rod <NUM> such that second hole portion <NUM> maintains a position or orientation (e.g., angle) of rod <NUM> and substantially limits side-to-side movement of rod <NUM> within second hole portion <NUM>. In some examples, rod <NUM> can be glued into counterbore <NUM> to retain rod <NUM> in counterbore <NUM>.

<FIG> is a cross-sectional view of fiber preform <NUM> in the first and second tool components <NUM>, <NUM>, illustrating a step of removing guide tube <NUM> from first tool component <NUM> and second tool component <NUM>. Rod <NUM> is retained in first and second tool components <NUM> and <NUM>. The outer diameter or cross-section of guide tube <NUM> can be shaped and sized to allow for easy removal from counterbore <NUM> and hole <NUM>. The inner passage of guide tube <NUM> can be shaped and sized to allow for easy removal of guide tube <NUM> from rod <NUM>. As guide tube <NUM> is removed from first and second tool components <NUM> and <NUM>, fibers and/or fiber tows of fiber preform <NUM> relax toward their initial position and close a gap between rod <NUM> and the fibers and/or fiber tows formed by guide tube <NUM>. The fibers and/or fiber tows can relax to close around rod <NUM>, such that fibers and/or fiber tows contact and enclose the portion of rod <NUM> positioned in fiber preform <NUM>.

<FIG> is a perspective cross-sectional view of fiber preform <NUM> in the first and second tool components <NUM>, <NUM>, illustrating a plurality of cooling holes being formed. <FIG> shows first tool component <NUM>, fiber preform <NUM>, second tool component <NUM>, counterbore holes <NUM>, first hole section <NUM>, second hole section <NUM>, holes <NUM>, rods <NUM>, and holes <NUM>. Holes <NUM> are formed though second tool component <NUM> to provide passages for densifying gases in a densification process. Guide tubes <NUM> have been removed leaving rods <NUM> in place.

Rods <NUM> can be oriented at differing angles through fiber preform <NUM> and can be spaced in varying arrangements. As illustrated in <FIG>, counterbore holes <NUM> can be oriented at differing angles relative to a surface of first tool component <NUM> to which counterbore holes <NUM> open. An orientation of holes <NUM> through second tool component <NUM> can match the orientation of corresponding counterbore holes <NUM>, such that holes <NUM> and counterbore holes <NUM> are coaxial. As shown, counterbore <NUM> can be a blind hole with an end in first tool component <NUM>. Second hole portions <NUM> can be sized to approximately match an outer diameter or cross-sectional area of rods <NUM> to help maintain the orientation of rods <NUM> in fiber preform <NUM>. A gap is formed between the walls of first hole portion <NUM> and rod <NUM> and between the walls of hole <NUM> and rod <NUM> with the removal of guide tube <NUM>. Fibers and/or fiber tows of fiber preform <NUM> have relaxed and closed around rods <NUM>, such that fibers and/or fiber tows contact and enclose the portion of rods <NUM> in fiber preform <NUM>. Rods <NUM> can have a length less than, equal to, or greater than a combined length of the hole formed between an inner most portion of counterbore <NUM> and outer surface of second tool component <NUM>. As such, an end of rod <NUM> can be recessed in hole <NUM>, can be located at the outer surface of second tool component <NUM>, or can extend outward of the outer surface of second tool component <NUM>.

Holes <NUM> can be sized and shaped as appropriate for delivering densifying gases to fiber preform <NUM>. Holes <NUM> can be arranged so as not to interrupt holes <NUM>. Second tool component <NUM> can be fixed relative to first tool component <NUM> via fasteners or retention mechanisms that maintain alignment of holes <NUM> and counterbore holes <NUM> in a densification step.

Fiber preform <NUM> is densified to form the CMC component. Fiber preform <NUM> can be fully or partially densified with a ceramic matrix in second tool component <NUM> via chemical vapor infiltration (CVI). A ceramic matrix material can be, for example, silicon carbide. In some examples, second tool component <NUM> can be removed following partial densification of fiber preform <NUM> or following a densification step sufficient to provide structural rigidity to fiber preform <NUM>. Rods <NUM> can remain in fiber preform <NUM> and first tool component <NUM> through additional densification steps. In some examples, fiber preform <NUM> can be densified through one or more densification processes, such as melt infiltration, slurry infiltration, and CVI. In some examples, an interface coating can be applied to fibers of fiber preform <NUM> via CVI prior to densification.

Rods <NUM> can be removed during or following the densification process. For example, rods <NUM> can be removed via heat, acid, or other methods that do not damage the ceramic material of the CMC component. Cooling holes or passages remain open in the formed CMC component once rods <NUM> are removed.

First tool component <NUM> can be removed from the CMC component following densification. First and second tool components <NUM> and <NUM> can be reused. In embodiments in which the CMC component surrounds first tool component <NUM> in a manner such that first tool component <NUM> cannot be disassembled from the CMC component without damage, first tool component <NUM> can be removed via heat, acid, or other known methods.

<FIG> is a flow chart of a method <NUM> of forming cooling holes in a CMC component as described above and illustrated in <FIG>. First and second tool components <NUM> and <NUM> are formed in step <NUM>. First and second tool components <NUM> and <NUM> can be formed, for example, from a carbon material such as graphite. First and second tool components <NUM> and <NUM> can be cast and/or machined to have a shape matching an outer and/or interior surface of the CMC component. For example, first tool component <NUM> can have a shape of an airfoil core. First tool component <NUM> can have multiple components. For example, each component of first tool component <NUM> can form a different portion (e.g., passage) of the airfoil core. Second tool component <NUM> can have a surface matching a shape of the outer surface of the CMC component opposite the surface of the CMC component adjacent to first tool component <NUM>. Second tool component <NUM> can be formed from multiple components that can be assembled together around fiber preform <NUM>. First and second tool components <NUM> and <NUM> can be manufactured to include one or more alignment features to coaxially locate corresponding holes <NUM> and counterbore hoes <NUM>. One or more retention mechanisms can be used to secure second tool component <NUM> around or to first tool component <NUM> or to secure components of second tool component <NUM> together.

Counterbore holes <NUM> and holes <NUM> are formed in first tool component <NUM> and second tool component <NUM>, respectively, in step <NUM>. Counterbore holes <NUM> and holes <NUM> can be drilled, e.g., via laser drilling or EDM. Counterbore holes <NUM> can be partially drilled into first tool component <NUM> to form blind holes. Holes <NUM> are drilled fully through second tool component <NUM>.

Fiber preform <NUM> is formed in step <NUM>. Fiber preform <NUM> can be formed via two-dimensional or three-dimensional weaving, braiding, or fiber placement. Fiber preform <NUM> can be formed from a braided tube. Fiber preform <NUM> can be formed from a plurality of fiber plies, which can be wrapped around or placed on a surface of first tool component <NUM>. In some examples, a tackifier can be used to help maintain a shape of fiber preform <NUM>. Fiber preform <NUM> can be assembled separate from first tool component <NUM> and applied to first tool component <NUM> following assembly. In other examples, fiber preform <NUM> can be formed directly on first tool component <NUM>.

Second tool component <NUM> is positioned on or around an outer surface of fiber preform <NUM> in step <NUM>. Second tool component <NUM> is assembled with first tool component <NUM> such that holes <NUM> are coaxial or align with counterbore holes <NUM>. First and second tool components <NUM>, <NUM> can include one or more alignment features to facilitate alignment of holes <NUM> and corresponding counterbore holes <NUM>. Second tool component <NUM> can fully or substantially encase fiber preform <NUM>, such that fiber preform <NUM> is fully or substantially disposed between first and second tool components <NUM>, <NUM>. Second tool component <NUM> can be fixed in place relative to first tool component <NUM> and fiber preform <NUM> via one or more retention mechanisms.

Guide tubes <NUM> are inserted through hole <NUM>, fiber preform <NUM>, and counterbore holes <NUM> in step <NUM>. Guide tubes <NUM> are inserted in a manner that causes displacement of fibers and/or fiber tows around guide tubes <NUM> and does not cause breakage of fibers or pressing of fibers and/or fiber tows into counterbore hole <NUM>. Ends <NUM> of guide tubes can have an angled shape like a hypodermic needle to displace fibers and/or fiber tows in fiber preform <NUM>.

Rods <NUM> are inserted into guide tubes <NUM> in step <NUM>. Rods <NUM> are inserted into guide tubes <NUM> and into second hole portion <NUM> of counterbore hole <NUM>. In some examples, rods <NUM> can be glued or otherwise secured in second hole portion <NUM>.

Guide tubes <NUM> are removed from first and second tool components <NUM> and <NUM> in step <NUM>. Guide tubes can be pulled outward away from rods <NUM>, which remain in place. Guide tubes <NUM> can be removed prior to a first densification step.

Fiber preform <NUM> is at least partially densified in step <NUM>. Fiber preform can be densified by one or more densification methods including CVI, melt infiltration, and slurry infiltration.

Second tool component <NUM> is removed from the partially or fully densified fiber preform <NUM> in step <NUM>. Second tool component <NUM> can be removed from fiber preform <NUM>, for example, after partial densification of fiber preform <NUM> via CVI or a partial densification step that provides sufficient rigidity to fiber preform <NUM> to maintain shape during the remaining densification process. Second tool component <NUM> can be mechanically removed from fiber preform <NUM> without damaging the ceramic matrix or fibers. For example, components of second tool component <NUM> can be mechanically separated or pulled away from fiber preform <NUM>. If fiber preform <NUM> has not been fully densified, additional densification steps (<NUM>) can be performed subsequent to removal of second tool component <NUM>.

Rods <NUM> are removed from the CMC component (densified fiber preform <NUM>) in step <NUM>. Rods <NUM> can be removed via heat (e.g., burning out), acid (dissolving), or other methods capable of removing rods <NUM> without damaging the CMC component.

First tool component <NUM> can be removed in step <NUM>. First tool component <NUM> typically can be disassembled from the CMC component for reuse. In other embodiments, first tool component <NUM> can be removed with rods <NUM> via heat, acid, or other methods capable of removing first tool component <NUM> without damaging the CMC component.

Additional densification or application of coatings, such as environmental barrier coatings or thermal barrier coatings can be carried out after first tool component <NUM> and rods <NUM> have been removed from the CMC component. In other examples, coatings can be applied while rods <NUM> and first tool component <NUM> are in place. Finishing machining or other finishing processes may be used to form the final CMC component.

The disclosed method of forming cooling holes in a CMC component is an improvement over conventional machining methods that cause fiber breakage and/or damage to the ceramic matrix. Additionally, the disclosed method does require integrating holes in the fiber layup process. For example, the disclosed method does not require arranging fibers around sacrificial rods during layup or cutting fiber plies. The second tool having holes that are coaxial with counterbore holes in the first tool allows precise placement of a rod within the fiber preform and use of a guide needle helps locate the rods in the counterbore holes and displace fibers in the fiber preform without breakage or pressing fibers into the counterbore hole.

Claim 1:
A method for forming a hole in a ceramic matrix composite component, the method comprising:
providing a first tool component (<NUM>) with a first hole (<NUM>);
providing a fiber preform (<NUM>) of the ceramic matrix composite component on the first tool component (<NUM>);
positioning a second tool component (<NUM>) on the fiber preform (<NUM>), such that the fiber preform (<NUM>) is disposed between the first and second tool components (<NUM>, <NUM>), wherein the second tool component (<NUM>) has a second hole (<NUM>) coaxial with the first hole (<NUM>);
inserting a rod (<NUM>) into the first and second holes (<NUM>, <NUM>) and through the fiber preform (<NUM>); and
performing a densification step of the fiber preform (<NUM>) in the first and second tool components (<NUM>, <NUM>), wherein the fiber preform (<NUM>) is densified with a ceramic matrix,
characterised in that
the method further comprises inserting a guide tube (<NUM>) into the first and second holes (<NUM>, <NUM>) and through the fiber preform (<NUM>).