Patent Description:
Gas turbine engines are known and typically include a compressor compressing air and delivering it into a combustor. The air is mixed with fuel in the combustor and ignited. Products of the combustion pass downstream over turbine rotors, driving them to rotate.

It is desirable to ensure that the bulk of the products of combustion pass over turbine blades on the turbine rotor. As such, it is known to provide blade outer air seals radially outwardly of the blades. Blade outer air seals have been proposed made of ceramic matrix composite fiber layers.

Some known methods of forming blade outer air seals of ceramic matrix composite fiber layers use a mandrel.

<CIT> describes extrusion of an endless strip of plastic with a core consisting of a material with greater rigidity. The strip is wound in a hot state onto a pair of mandrels in a helical convolution with oval cross-section. The adjacent convolutions are joined and moved along the mandrels in an axial direction to form an endless hose with oval cross-section, after which the hose is moved forwards over the ends of the mandrels while it is still sufficiently soft to assume a circular cross-section.

<CIT> describes integrally stiffened and formed, load carrying structures comprising a plurality of elongated thin-walled tubes placed co-extensively in a complementary side-by-side fashion which together form a hollow structure having a desired external contour. Integral skins forming the external and internal surfaces of the structure. The structure can be formed with an underlying internal support member spanning the interior of the load carrying structure, thereby connecting opposite sides of the structure together. Also, each of the tubes are wound with fibers in controlled orientations generally paralleling the direction of the loads applied to the tubes to optimize the strength to weight ratio of the tubes.

In a further embodiment of any of the above, a locking pin is inserted into an end of the channel.

In a further embodiment of any of the above, the locking pin is configured to contact the first and second portions and maintain a gap between the first and second portions along the length of the mandrel.

In a further embodiment of any of the above, a second locking pin is inserted into a second end of the channel.

In a further embodiment of any of the above, the end of the channel and the second end of the channel each have an angled surface for engagement with the locking pin and second locking pin.

In a further embodiment of any of the above, a locking wedge is inserted into an end of the channel and configured to maintain a gap between the first and second portions along the length of the mandrel.

In a further embodiment of any of the above, the first and second portions are formed from graphite.

A molding apparatus according to another aspect of the present invention includes a fixture that has a first member and a second member that extend from a base. The first member has a groove and the second member has a fixture pin. A mandrel has a first portion and a second portion. Each of the first and second portion has a dovetail mating surface. The mandrel has first and second locking pins. The mandrel is secured to the fixture by the groove at the first member and by the fixture pin at the second member.

In an embodiment of the above, the fixture pin contacts the second locking pin.

In a further embodiment of any of the above, a space is formed between the mandrel and the base and is configured to receive ceramic matrix composite material when a component is formed about the mandrel.

In a further embodiment of any of the above, the mandrel is configured to provide an inner mold surface and the base is configured to provide an outer mold surface for forming a component.

In a further embodiment of any of the above, the mandrel is formed from graphite.

In a further aspect of the present invention there is provided a method of forming a matrix composite component includes providing a mandrel that has a first portion and a second portion. The first portion includes a first dovetail surface in engagement with a second dovetail surface of the second portion. A locking pin is inserted into an end of the mandrel. A matrix composite laminate is wrapped about the mandrel to form a component. The locking pin is removed. The first portion is removed from a first end of the component and the second portion is removed from a second end of the component.

In an embodiment of the above, the inserting the locking pin comprises forming and maintaining a gap between a first portion inner surface and a second portion inner surface.

In a further embodiment of any of the above, the matrix composite laminate is densified before removing the locking pin.

In a further embodiment of any of the above, the mandrel is mounted to a fixture before the wrapping of the matrix composite laminate.

In a further embodiment of any of the above, the mandrel provides an inner mold surface and the fixture provides an outer mold surface for the matrix composite laminate.

In a further embodiment of any of the above, the component is a blade outer air seal.

"Low corrected fan tip speed" is the actual fan tip speed in ft/sec divided by an industry standard temperature correction of [(Tram °R) / (<NUM> °R)]<NUM>(where °R = K x <NUM>/<NUM>).

<FIG> shows a portion of a turbine section <NUM>, which may be incorporated into a gas turbine engine such as the one shown in <FIG>. However, it should be understood that other sections of the gas turbine engine <NUM> or other gas turbine engines, and even gas turbine engines not having a fan section at all, could benefit from this disclosure.

A turbine blade <NUM> has a radially outer tip <NUM> that is spaced from a blade outer air seal ("BOAS") <NUM>. The BOAS <NUM> may be made up of a plurality of seal segments <NUM> that are circumferentially arranged in an annulus about the central axis A of the engine <NUM>. The BOAS seal segments <NUM> may be monolithic bodies that are formed of a high thermal-resistance, low-toughness material, such as a ceramic matrix composite ("CMC").

The BOAS <NUM> may be mounted to an engine case or structure, such as engine static structure <NUM> via an attachment block <NUM>. The engine structure <NUM> may extend for a full <NUM>° about the engine axis A. The engine structure <NUM> may have a forward hook <NUM> supporting a forward hook <NUM> of the attachment block <NUM>. The engine structure <NUM> may have an aft hook <NUM> supporting an aft hook <NUM> on the attachment block <NUM>. In the illustrated embodiment, engine structure hooks <NUM>, <NUM> face rearwardly, while the attachment block hooks <NUM>, <NUM> face forwardly. It should be understood, however, that the arrangement of some or all of the hooks <NUM>, <NUM>, <NUM>, and <NUM> could be reversed such that hooks <NUM> and/or <NUM> face forwardly and hooks <NUM> and/or <NUM> face rearwardly. In one aspect of this disclosure, the hooks <NUM> and <NUM> face in a common axial direction and the hooks <NUM> and <NUM> face in an opposed axial direction.

<FIG> show an exemplary BOAS seal segment <NUM> of a BOAS <NUM>. The BOAS seal segment <NUM> includes a leading edge <NUM> and a trailing edge <NUM>. The BOAS segment <NUM> includes a forward wall <NUM> and an aft wall <NUM> that extend radially outward from a base portion <NUM> to an outer wall <NUM>. The base portion <NUM> extends between the leading edge <NUM> and the trailing edge <NUM> and defines a gas path on a radially inner side and a non-gas path on a radially outer side. The outer wall <NUM> includes a generally constant thickness and constant position in the radial direction such that an outer surface of the outer wall <NUM> is planar. The forward wall <NUM>, the aft wall <NUM>, the outer wall <NUM>, and the base portion <NUM> define a passage <NUM> for attachment to the attachment block <NUM> (shown in <FIG>). In this disclosure, forward, aft, upstream, downstream, axial, radial, or circumferential is in relation to the engine axis A unless stated otherwise.

The BOAS <NUM> is formed of a ceramic matrix composite ("CMC") material. The BOAS <NUM> is formed of a plurality of CMC laminates. The laminates may be silicon carbide fibers, formed into a woven fabric in each layer. The fibers may be coated by a boron nitride.

CMC components such as a BOAS <NUM> are formed by laying fiber material, such as laminate sheets, in tooling, injecting a liquid resin into the tooling, and curing to form a solid composite component. The component may be densified by adding additional material to further stiffen the laminates. In some more complex components, pre-formed parts are further provided within the tooling before material is put into the tooling. For example, a mandrel may be used to occupy a cavity in the component to prevent material from flowing into the cavity.

<FIG> show a two-piece mandrel <NUM> according to an embodiment. The mandrel <NUM> has a tapered first portion <NUM> and a tapered second portion <NUM>. The first portion <NUM> has an outer surface <NUM> and an inner surface <NUM>. The second portion <NUM> has an outer surface <NUM> and an inner surface <NUM>. In an embodiment, each of the outer and inner surfaces <NUM>, <NUM>, <NUM>, <NUM> is a radial surface. The outer surfaces <NUM>, <NUM> are parallel to one another, and the inner surfaces <NUM>, <NUM> are parallel to one another. The inner surfaces <NUM>, <NUM> are offset relative to the outer surfaces <NUM>, <NUM>. That is, an axis of revolution of the outer surfaces <NUM>, <NUM> is offset from an axis of revolution of the inner surfaces <NUM>, <NUM>. In one example, this offset may be approximated as an angle between a tangent of the inner surfaces <NUM>, <NUM> and a tangent of the outer surfaces <NUM>, <NUM> of between <NUM> and <NUM>°. The first portion <NUM> and second portion <NUM> are opposing radial wedges. The offset axes of the radial inner and outer surfaces results in different heights at each end of each portion. The mandrel <NUM> has a first end <NUM> and a second end <NUM>. The first portion <NUM> has a first height H<NUM> at the first end <NUM> and a second height Hz at the second end <NUM>. The second portion <NUM> is flipped, meaning it has the first height H<NUM> at the second end <NUM> and the second height Hz at the first end <NUM>. In one embodiment, a difference between the first height H<NUM> and the second height H<NUM> is between about <NUM> inches (<NUM>) and <NUM> inches (<NUM>). In a further embodiment, the difference in height between the first height H<NUM> and the second height H<NUM> is about <NUM> inches (<NUM>). The outer surfaces <NUM>, <NUM> are shaped depending on the component they are used to form.

When the first and second portions <NUM>, <NUM> are in a retracted state, as shown in <FIG>, the mandrel <NUM> has a constant cross section along the length. The mandrel <NUM> has a height H along the entire length. When the first and second portions <NUM>, <NUM> are in an expanded state, as shown in <FIG>, a height h is smaller than the height H. This smaller height h when the first and second portions <NUM>, <NUM> are in the retracted state facilitates easy removal of the mandrel <NUM> from the component. The first and second portions <NUM> cannot slide beyond one another past the retracted state.

As shown in <FIG>, the inner surfaces <NUM>, <NUM> slide relative to one another. The first and second portions <NUM>, <NUM> each include dovetail surfaces <NUM>, <NUM> along inner surfaces <NUM>, <NUM>, respectively. In other words, each of the first and second portions <NUM>, <NUM> includes a pair of projections with at least one angled surface. As shown more clearly in <FIG>, the first portion <NUM> includes a pair of projections <NUM> along outside edges, with the dovetail surfaces <NUM> facing inward, or towards one another. The second portion <NUM> includes a pair of projections <NUM> inward of the outside edge, with the dovetail surfaces <NUM> facing outward, or away from one another. The pair of projections <NUM> fits inward of the pair of projections <NUM>, while dovetail surfaces <NUM>, <NUM> contact one another. Although a pair of projections on each portion is illustrated, a single projection may fall within the scope of this disclosure.

In use, the CMC component is formed around the mandrel <NUM>, then the first and second portions <NUM>, <NUM> are slid out opposing ends of the component. The opposing radial wedge shape of the first and second portions <NUM>, <NUM> allows for a mandrel that is easier to remove, because it avoids being locked into the part. The first and second portions <NUM>, <NUM> cannot slide past center in order to have a constant cross section. The dovetail surfaces provide self-centering of the first and second portions when locked for a more precisely controlled tool. Thus, the dovetail surfaces may produce a CMC part with more precisely controlled wall thicknesses.

As shown in <FIG>, the mandrel <NUM> includes a channel <NUM>. The ends of the mandrel <NUM> include a clearance hole <NUM> and angled surfaces <NUM>. In the illustrated embodiment, the channel <NUM> is generally circular in cross section, and the clearance hole <NUM> is generally rectangular. However other shapes of the channel <NUM> and clearance hole <NUM> may be contemplated within the scope of this disclosure.

The channel <NUM> receives a locking pin <NUM>, as shown in <FIG>. The locking pin <NUM> may be inserted into the channel <NUM> from either or both ends of the mandrel <NUM> when the mandrel <NUM> is in the retracted state. As shown, two locking pins <NUM> may be used with the mandrel <NUM>. The locking pin <NUM> includes an elongate body <NUM> and a tab <NUM>. The tab <NUM> improves handling during use. In an embodiment, the elongate body <NUM> is generally cylindrical. In other embodiments, the elongate body <NUM> is generally rectangular or another shape. The elongate body <NUM> is shaped to fit into the channel <NUM>, and the tabs <NUM> fit into the clearance hole <NUM>.

<FIG> shows the pins <NUM> inserted into the channel <NUM>. The first and second portions <NUM>, <NUM> may have angled surfaces <NUM> adjacent the channel <NUM>. These angled surfaces <NUM> engage with the tab <NUM> to force the first and second portions <NUM>, <NUM> away from one another. In some examples, when the pin <NUM> is inserted, a small gap <NUM> is formed between the inner surfaces <NUM>, <NUM>. The dovetail surfaces <NUM>, <NUM> keep the first and second portions <NUM>, <NUM> together while the pin <NUM> is inserted. The locking pins <NUM> are self-centering due to the dovetail surfaces <NUM>, <NUM>. When the locking pins <NUM> are in place, the first and second portions <NUM>, <NUM> are expanded outward, bringing the mandrel <NUM> to its maximum height. This makes the mandrel <NUM> easier to remove once the pin <NUM> is removed.

The mandrel design does not require any threaded parts, making it easier to construct. For example, the mandrel may be formed from graphite for use in high temperature furnaces.

<FIG> show an alternate configuration utilizing a wedge style locking feature in place of the locking pin <NUM>. In this embodiment, the mandrel <NUM> has a rectangular channel <NUM>. A locking wedge <NUM> is inserted into the channel <NUM> to force the dovetail surfaces <NUM>, <NUM> into engagement and form the gap <NUM>. The locking wedge <NUM> extends the full length of the mandrel <NUM>. The locking wedge <NUM> is tapered, such that it has a smaller thickness at a first end <NUM> than at a second end <NUM>. The locking wedge <NUM> is inserted into the mandrel <NUM> with the first end <NUM> first. As the locking wedge <NUM> is pushed further into the channel <NUM> and the thickness of the locking wedge <NUM> increases, the first and second portions <NUM>, <NUM> are forced apart. After the component is formed, the locking wedge <NUM> may be removed by pushing on the first end <NUM> or by pulling on the second end <NUM>. The second end <NUM> may include a puller feature <NUM> to aid in pulling the locking wedge <NUM> from the channel <NUM>.

<FIG> show a molding fixture that uses the mandrel <NUM>. The mandrel <NUM> is mounted in a fixture <NUM>. The fixture <NUM> has a first member <NUM> and a second member <NUM> extending from a base <NUM>. The first member <NUM> includes a groove <NUM>. The mandrel <NUM> with locking pins <NUM> inserted is mounted on the fixture <NUM>. One of the pins 332A fits into the groove <NUM> and is maintained in place by the groove <NUM>. The mandrel <NUM> is rotated about the pin 332A in the groove <NUM> such that the other pin 332B contacts the second member <NUM>. A fixture locking pin <NUM> is inserted into the second member <NUM> to maintain the mandrel <NUM> in place. The fixture locking pin <NUM> is engaged with the locking pin 332B. The fixture locking pin <NUM> is held in place by a combination of friction and spring force.

This mounting arrangement of the mandrel <NUM> in the fixture <NUM> provides clearance about the mandrel <NUM> to form the CMC plies of the component to be formed. In some embodiments, the base <NUM> provides the outer mold line for the component. In such embodiments, the entire gap <NUM> between the mandrel <NUM> and base <NUM> will be filled with CMC plies to form the component. Once the component is formed, the mandrel <NUM> is removed from the fixture <NUM> by removing the fixture locking pin <NUM>.

A method of forming a CMC component includes the steps of providing a mandrel <NUM> having first and second portions <NUM>, <NUM> in a retracted state and inserting locking pins <NUM> into the ends of the mandrel <NUM> to lock the first and second portions in the retracted state. The mandrel may be mounted to a fixture <NUM>. A plurality of CMC laminate layers <NUM> are wrapped about the mandrel <NUM>, as shown in <FIG>. After the CMC laminates <NUM> are wrapped about the mandrel <NUM>, they are solidified into a component <NUM>. In some embodiments, this includes injecting a resin into the fibers. The CMC laminates <NUM> may be silicon carbide fibers, formed into a woven fabric in each layer. The fibers may be coated by a boron nitride.

In some examples, the component is densified. Densification generally includes adding additional material to make the CMC laminates more stiff than their free woven fiber state. The densification process increases the density of the laminate material after assembly. A filler material, such as a silicon carbide matrix material, is injected into the spaces between the fibers in the woven layers.

One hundred percent densification may be defined as the layers being completely saturated with the matrix and about the fibers. One hundred percent densification may be defined as the theoretical upper limit of layers being completely saturated with the matrix and about the fibers, such that no additional material may be deposited. In practice, <NUM>% may be difficult to achieve in practice. The desired amount of densification depends on the particular application.

After the component <NUM> is formed and solidified, the mandrel <NUM> and component <NUM> are removed from the fixture <NUM>. The first and second portions <NUM>, <NUM> of the mandrel <NUM> are moved to the expanded state. The component <NUM> is removed from the mandrel <NUM>. The component may be a BOAS seal segment <NUM> (shown in <FIG>), for example. The mandrel <NUM> may be used to form a CMC material, or may be used to form other matrix composite components, such as organic matrix composite ("OMC") or polymer matrix composite ("PMC") components.

Known mandrels require the component to have a taper to allow the mandrel to be pulled from the part once the curing process is complete. However, such tapers may make the components more complicated. For example, backside sealing of BOAS faces may be more difficult with a tapered surface. The two-piece mandrel allows for a constant fully enclosed cross-section with no taper to be produced in a matrix composite plied component. The constant cross-section may further provide a stronger, more continuous ply construction and reduce the chance of having wrinkles or voids in the plies. The cross-section may also reduce any non-laminated zones, noodles, matrix, or chopped strands. The mandrel may further provide a more uniform hot wall thickness in thermal parts, such as a BOAS. The self-centering pins and dovetail surfaces ensure repeatable results in the manufacturing process. Although a rectangular cross-section mandrel is illustrated, the cross-section could be tubular or another shape.

Claim 1:
A molding apparatus, comprising:
a fixture (<NUM>) having a first member (<NUM>) and a second member (<NUM>) extending from a base (<NUM>), the first member (<NUM>) having a groove (<NUM>) and the second member (<NUM>) having a fixture pin (<NUM>); and
a mandrel (<NUM>) having a first portion (<NUM>) and a second portion (<NUM>), each of the first and second portions (<NUM>, <NUM>) having a dovetail mating surface (<NUM>, <NUM>; <NUM>, <NUM>), characterised in that the mandrel (<NUM>) has first and second locking pins (<NUM>), wherein the mandrel (<NUM>) is secured to the fixture (<NUM>) by the groove (<NUM>) at the first member (<NUM>) and by the fixture pin (<NUM>) at the second member (<NUM>)