Z-CHANNEL CREATION IN WOVEN PREFORM BY INCORPORATION OF PIN FEATURES INTO PREFORM TOOLING

A tooling assembly for debulking a fibrous preform includes a first tooling fixture comprising a plurality of receiving holes, and a second tooling fixture comprising a plurality of pins projecting toward the first tooling fixture, each of the plurality of pins corresponding to and extending towards one of the plurality of receiving holes. The second tooling fixture is engageable with the first tooling fixture to define an inner volume therebetween, the inner volume configured to support the preform during debulking while a compressive force is applied thereto.

BACKGROUND

The present invention relates to the fabrication of ceramic matrix composites (CMCs) and, more particularly, to CMCs having improved properties for operating in gas turbine engines.

In the processing of CMCs, there is a need to infiltrate matrix within and around fibrous tows to replace pore volume with dense matrix material. In a woven system, large voids often exist between adjacent tows of a preform. Such voids can become large defects after infiltration of the composite that are detrimental to composite properties. The pore network through a woven system is often highly tortuous for infiltrating reactant vapors, which leads to uneven deposition through the thickness of the preform. The formation of z-channels can create more direct pathways for reactant gases, which can facilitate more even matrix infiltration. Thus, means for creating z-channels in preforms are desirable.

SUMMARY

A tooling assembly for debulking a fibrous preform includes a first tooling fixture comprising a plurality of receiving holes, and a second tooling fixture comprising a plurality of pins projecting toward the first tooling fixture, each of the plurality of pins corresponding to and extending towards one of the plurality of receiving holes. The second tooling fixture is engageable with the first tooling fixture to define an inner volume therebetween, the inner volume configured to support the preform during debulking while a compressive force is applied thereto.

A method of preparing a fibrous preform for use in a ceramic matrix composite includes debulking the fibrous preform by supporting the preform with a first tooling fixture, the first tooling fixture including a plurality of receiving holes, engaging a second tooling fixture with the first tooling fixture such that the preform is disposed therebetween, and applying a compressive force to the preform. Engaging the second tooling fixture with the first tooling fixture causes a plurality of pins projecting from the first tooling fixture to extend through a thickness of the preform.

DETAILED DESCRIPTION

This disclosure presents means for perforating a fibrous ceramic preform prior to densification (e.g., via chemical vapor infiltration—CVI). More specifically, perforation can be performed during a debulking process. Multiple embodiments of combined perforating/debulking tooling can be used to create z-channels through the thickness of the preform, such that separate tooling is advantageously not required. Z-channels facilitate access to the interior of the preform by reactant vapors such that matrix deposits in a more even manner compared to non-perforated preforms.

FIG.1is a simplified cross-sectional illustration of tooling assembly10supporting preform12. Tooling assembly10is more specifically a debulking tooling assembly used to shape/mold preform12while preform12is compressed by one or a combination of mechanical or vacuum pressure. Debulking helps reduce voids and remove gases within preform12and can be performed incrementally as layers are added to preform12, and/or in a dedicated debulking step prior to matrix formation. Preform12can be formed from one or more layers of a ceramic (e.g., silicon carbide—SiC) fabric in a woven architecture such as plain, harness (e.g., 3, 5, 8, etc.), twill, braid, tape layup, or non-symmetric to name a few non-limiting examples. Non-woven architectures (e.g., chopped, felted, etc.) are also contemplated herein. The fabric can be dry, stabilized, or a pre-preg material.

As shown, tooling assembly10includes male (i.e., perforating) tooling fixture14and female (i.e., receiving) tooling fixture16. Male tooling fixture14includes multiple pins18extending away from backplate20. Pins18can be arranged as an array of rows and columns and can have uniform or varied lengths with respect to other pins18, as is discussed below with respect toFIGS.3A-3C. Pins18can be monolithically formed with, or removably attached to backplate20depending on the embodiment, as is discussed in greater detail below. Female tooling fixture16includes baseplate22with receiving holes24corresponding to respective pins18on male tooling fixture14. Holes24can be sized to receive respective pins18when pins18are inserted through preform12, as is shown inFIG.2. Tooling fixtures14and16can be formed from a metallic material, a hardened polymer (e.g., plastic), or ceramic, to name a few non-limiting examples.

FIG.2is a simplified cross-sectional illustration of tooling assembly10in an assembled/engaged state around preform12. In the assembled state, fixtures14and16are configured to at least partially enclose preform12within fixed inner volume26. Although not shown inFIG.2, fixtures14and16can be held together via clamps or other suitable means of securing one to the other. Pins18are inserted completely through the thickness of preform12such that the tips/ends extend partially into respective holes24. When male tooling fixture14and pins18are removed from preform12, z-channels will have been formed at the locations of each pin18.

In one example, a non-debulked or partially debulked preform12can be placed within tooling assembly10, and a mechanical compressive force exerted on preform12as fixtures14and16are secured together. This can at least nominally reduce the thickness of preform12. In another example, a vacuum can be generated within inner volume26to compress and debulk preform12. In yet another example, a combination of mechanical and vacuum pressure can be used to debulk preform12. In any case, z-channels are formed during debulking by pins18. Pins18are inserted in such manner as to maximize the pushing away of individual fibers of perform12, and to minimize the breaking of such fibers. Accordingly, formation of z-channels with pins18during debulking can be less destructive than methods such as laser drilling, as well as needling processes that occur in dedicated steps, requiring additional handling of preform12.

FIG.3A,3B, and3Care simplified side views of alternative male tooling fixtures14A,14B, and14C respectively. More specifically,FIG.3Ashows an individual pin18A extending from backplate20A. Pin18A has a length LA extending from base28A to oppositely disposed tip30A. Pin18A is configured with a generally uniformly cylindrical portion over a majority of length LA and a relatively short taper near tip30A such that tip30A is pointed. In the embodiment shown, tooling fixture14A can be monolithically formed (e.g., additively manufactured, 3D printed, etc.) such that pins18A and backplate20A are formed from the same material (e.g., metal, polymer, etc.). Length LA can be uniform across all pins18A in an exemplary embodiment.

FIG.3Bshows individual pin18B extending from mounting boss32B on backplate20B. As such, pin18B can be removably attached to backplate20B via threaded or other engagement with mounting boss32B. Base28B can be defined as the portion of pin18B immediately extending away from mounting boss32B, although some of pin18B can extend into mounting boss32B. Pin18B has an exposed length LB extending from base28B to oppositely disposed tip30B. LB can, in some embodiments, be less than LA due to the inclusion of mounting boss32B, while in other embodiments, pin18B can be elongated such that LB is generally equal to LA. Length LB can be uniform across all pins18B in an exemplary embodiment. Like pin18A, pin18B can be mostly cylindrical with a short taper to form a point at tip30B. Pin18B can be formed from the same material as backplate20B, or from a different material. For example, both can be formed from a hardened polymer material, or pin18B can be formed from a hardened polymer or ceramic, while backplate20B can be formed from metal. Removable pins18B are individually replaceable in case of damage to certain pins18B after repeated insertion into ceramic preform. Select pins18B can also be removed to vary the pattern of pins18B, for example by decreasing the total number of pins18B to increase pin-to-pin spacing. In this manner, male tooling fixture14B can be customizable on a per-preform basis.

FIG.3Cshows multiple individual pins18C of varied lengths, LC1, LC2, and LC3. More specifically, pins18C are removably attached to backplate20C via mounting bosses32C, and the exposed length between base28C and tip30C of each pin18C varies such that LC3is greater than LC2, and LC2is greater than LC1. Male tooling fixture14C can be preferable where the thickness of preform12increases and/or decreases across a given preform area.

FIG.4is a simplified cross-sectional view of alternative tooling assembly110for use with non-linear/non-planar preforms112. Preform112can be substantially similar to preform12, except that preform112is curved. In one embodiment, preform112can be used to form an airfoil (e.g., for a blade or vane) of a gas turbine engine. Like tooling assembly10, tooling assembly110can be a debulking tooling assembly including male tooling fixture114and female tooling fixture116, each having curvature corresponding to preform112. Male tooling fixture114includes pins118extending from backplate120. To facilitate insertion and removal of pins118into/from preform112, male tooling fixture114includes multiple smaller backplate sections134, each with a subset of pins118. As such, each section can be put into place and secured to adjacent sections for debulking, then individually removed. This permits pins118to be oriented generally normal to the surface of preform112. Female tooling fixture116can include holes124corresponding to and configured to receive the tips of pins118. In the embodiment shown, female tooling fixture can be a mandrel.

Tooling assembly110operates substantially similarly to tooling assembly10, applying a mechanical compressive force, and/or supporting preform112while a vacuum is applied. Tooling assembly110can be all or partially formed from metal, hardened polymer material, or ceramic. Like pins18A and18B, pins118can be monolithically formed with backplate120or removably attached thereto (e.g., via mounting bosses). Pins118can be the same material as backplate120, or a different material. Pins118can further be mostly cylindrical with a short taper to form a pointed tip.

After debulking, preforms12,112can be removed from respective tooling assemblies10,110to undergo further processing. In some embodiment, preforms12,112can be transferred to graphite tooling assemblies for interface coating (IFC) deposition via CVI and/or densification (i.e., matrix formation) via CVI. Densification is carried out until the resulting CMC has reached the desired residual porosity. In an alternative embodiment, densification can include other methodologies such as, but not limited to, melt infiltration and polymer infiltration and pyrolysis (PIP).

A CMC component formed with the disclosed tooling assemblies can be incorporated into aerospace, maritime, or industrial equipment, to name a few, non-limiting examples.

Discussion of Possible Embodiments

A tooling assembly for debulking a fibrous preform includes a first tooling fixture comprising a plurality of receiving holes, and a second tooling fixture comprising a plurality of pins projecting toward the first tooling fixture, each of the plurality of pins corresponding to and extending towards one of the plurality of receiving holes. The second tooling fixture is engageable with the first tooling fixture to define an inner volume therebetween, the inner volume configured to support the preform during debulking while a compressive force is applied thereto.

In the above tooling assembly, the second tooling fixture can be further engageable with the first tooling fixture such that the plurality of pins extend through the thickness of the preform and at least partially into respective ones of the plurality of receiving holes.

In any of the above tooling assemblies, a length of each of the plurality of pins can be uniform across the second tooling fixture.

In any of the above tooling assemblies, one pin of the plurality of pins can have a first length, and a second pin of the plurality of pins can have a second length greater than the first length.

In any of the above tooling assemblies, the second tooling fixture can further include a backplate.

In any of the above tooling assemblies, each of the plurality of pins can be removably attached to the backplate via a mounting boss.

In any of the above tooling assemblies, the plurality of pins can be monolithically formed with the backplate.

In any of the above tooling assemblies, the backplate can be formed from a first material, and the plurality of pins can be formed from a second material, the second material being different than the first material.

In any of the above tooling assemblies, each of the backplate and the plurality of pins can be formed from the same material.

In any of the above tooling assemblies, the first tooling fixture and the backplate of the second tooling fixture can be curved.

In any of the above tooling assemblies, the backplate can include a plurality of sections, each of the plurality of sections including a subset of the plurality of pins.

In any of the above tooling assemblies, the first tooling fixture can be a mandrel.

In any of the above tooling assemblies, each of the plurality of pins can be cylindrical with a pointed tip.

A method of preparing a fibrous preform for use in a ceramic matrix composite includes debulking the fibrous preform by supporting the preform with a first tooling fixture, the first tooling fixture including a plurality of receiving holes, engaging a second tooling fixture with the first tooling fixture such that the preform is disposed therebetween, and applying a compressive force to the preform. Engaging the second tooling fixture with the first tooling fixture causes a plurality of pins projecting from the first tooling fixture to extend through a thickness of the preform.

In the above method, engaging the second tooling fixture with the first tooling fixture can further cause the plurality of pins to extend at least partially into respective ones of the plurality of receiving holes.

In any of the above methods, the compressive force can include one or a combination of mechanical pressure and vacuum pressure.

In any of the above methods, debulking can further include after applying the compressive force to the preform, removing the second tooling fixture such that a plurality of z- channels is formed through the thickness of the preform.

Any of the above methods can further include densifying the preform using one or a combination of chemical vapor infiltration, chemical vapor deposition, polymer infiltration and pyrolysis, and melt infiltration.

In any of the above methods, the preform can be formed from silicon carbide.

In any of the above methods, the first tooling fixture, the second tooling fixture, and the preform can be curved.