Patent Description:
Diffusion bonding is a common method for creating hollow, high-temperature alloy components with complex geometries. For example, lightweight hollow titanium alloy airfoils (and particularly fan blades) are produced using costly, massive dies and presses. Traditionally, pressure is applied to the entire blade surface and requires wholly reshaping an airfoil from a flat configuration to a <NUM>-dimensional configuration after initial bonding of the flat sheets. This reshaping process imparts internal stresses, distortion, collapsed cavities, and other shortcomings which must be addressed by post-processing, annealing, and the like. Thus a key to successfully manufacturing a finished blade, according to previous methods, is being able to perform the bonding, brazing, and/or welding while ensuring residual stresses induced by thermal mechanical processing steps are properly managed and subsequently relieved without affecting acceptable airfoil dimensions.

Other airfoils can be made from a combination of materials, such as ceramic matrix composites, aluminum alloys, and optionally strengthened by a titanium or nickel sheath subsequently applied adhesively to weaker areas of the blade in order to defend against bird strikes or other foreign object damage (FOD). These complex processes also require substantial investments in equipment and materials and often have limited throughput and yield.

<CIT> discloses prior art tooling associated with diffusion bonding having the features of the preamble to claim <NUM>.

<CIT> discloses a prior art method in which two components are diffusion bonded together.

<CIT> discloses a prior art airfoil for a gas turbine engine and method of manufacturing.

The present invention provides an apparatus as claimed in claim <NUM>.

The present invention provides a method for making a hollow metal blade as claimed in claim <NUM>.

<FIG> is a front exploded view of an embodiment of hollow fan blade assembly <NUM>. Fan blade assembly <NUM> includes cavity-back blade <NUM> and cover <NUM> removed therefrom. Within main cavity <NUM> of cavity-back blade <NUM> are ribs <NUM> having cylindrical portions <NUM>, annular pockets <NUM> within cylindrical portions <NUM>, and linear rib portions <NUM>, some of which connect to cylindrical portions <NUM> at nodes <NUM>. Cavity-back blade <NUM> and cover <NUM> are, e.g., titanium alloys, but are not necessarily so limited. Cavity <NUM> of cavity-back blade <NUM> also can include peripheral recessed portion / cover interface <NUM>, and cavity pockets <NUM> between and around cylindrical rib portions <NUM> and linear rib portions <NUM>.

Annular pockets <NUM> are annular cavities located within cylindrical rib portions <NUM>. Cavity pockets <NUM> extend closer to a perimeter of recessed portion / cover interface <NUM> such that the periphery of recessed portion <NUM> can be narrower than linear rib portions. Any number of linear rib portions <NUM> may include and/or be connected cylindrical rib portions <NUM>. Diameters of cylindrical rib portions <NUM> may vary throughout fan blade assembly <NUM>, for example, based on the structural needs of fan blade <NUM>. Alternatively, diameters of cylindrical portions <NUM> may be mostly or all substantially the same throughout fan blade <NUM>. A height of rib portions <NUM>, <NUM> can also vary throughout blade assembly <NUM>. For example, linear portions of ribs <NUM> that do not include cylindrical portions <NUM>, and that do not reach the periphery of recessed portion <NUM> may be machined down to a third depth, the third depth being deeper than the first depth of the periphery of recessed portion <NUM>, but not as deep as the second depth of cavity pockets <NUM>. As a result, a space can be formed, for example, between cover <NUM> and certain linear rib portions <NUM>, such that cover <NUM> is not in contact therewith.

Linear rib portions <NUM> and/or cylindrical rib portions <NUM> can include tops <NUM> and grooves <NUM>. In this example, grooves <NUM> are grooves or cut-outs in tops <NUM> of one or more linear rib portions <NUM> adjacent to cylindrical portions <NUM>. Grooves <NUM>, where present, extend down a portion of top <NUM> of linear rib portions <NUM> such that grooves <NUM> fluidly connect one or more cavity pockets <NUM>, even when cover <NUM> is in place. As such, most or all cavity pockets <NUM> can be pressurized to the same or similar degrees by introducing inert gas into as few as one cavity pocket <NUM>. For example, to carry out an argon gas pressurization operation, gas can be introduced into a single cavity pocket <NUM> through a hole or passageway <NUM> that extends from the root of the blade into the pocket. The pressurizing gas will then flow into and pressurize all cavity pockets <NUM> of fan blade <NUM> connected by grooves <NUM>.

<FIG> also shows weld apparatus <NUM> for peripherally tack welding cavity back blade <NUM> and cover <NUM> to join <NUM>-dimensional hollow blade assembly <NUM>. Tack welding may be a fusion process or a solid state welding technique. Additionally, <FIG> shows a fusion weld apparatus, such as laser, electron beam, or other fusion welding techniques, for joining cover <NUM> to recessed portion / cover interface <NUM>. Subsequent to welding the periphery, <NUM>-dimensional blade assembly <NUM> is placed in a die assembly according to subsequent figures, in order to diffusion bond, braze, and/or stress-relieve the peripheral weld and blade for use in an engine.

Note that, as all physical objects such as a blade have three dimensions, a "<NUM>-dimensional" hollow blade assembly can be considered one where the desired shape, twist, camber, and other near-final aerodynamic features that define a particular airfoil's performance are already formed into the assembly. This can be distinguished from a generally "flat" blade assembly formed as an intermediary to a traditional diffusion bonding / superplastic forming process, starting with initially flat metal sheets and going through numerous steps to form a final desired airfoil shape that define a particular airfoil's performance in an engine.

Other blade and airfoil geometries suitable for incorporation into the instant disclosure are shown and described in commonly owned <CIT>, filed on August <NUM>,.

<FIG> shows a die apparatus <NUM> for diffusion bonding or brazing a hollow blade such as the example shown in <FIG>. First die half <NUM> and second opposing die half <NUM> receive a <NUM>-dimensional hollow blade (e.g., blade assembly <NUM> from <FIG>) after it has been welded around its perimeter / cover interface (See <FIG>). First and second die halves <NUM>, <NUM> are shaped, for example, to ensure maintaining the <NUM>-dimensional shape of preferably about <NUM>° to about <NUM>° relative to a chordwise direction of the combination of cavity-back blade <NUM> and cover <NUM>. Other features, shown and discussed in this disclosure, permit additional minor shaping to occur with a minimum of residual stresses and deformation.

Conventionally, the two blade parts shown in <FIG> would be placed in a second diffusion bonding machine to impart a final shape after initial bonding as a straight (i.e., flat or untwisted) airfoil shape. In the past, lightweight hollow metal airfoils (and particularly fan blades) have been produced using costly, massive dies and presses. In such an arrangement, two blade halves (each half containing ribs, cavities, and a root) would be placed in a heated press for diffusion bonding as a substantially flat airfoil along its neutral axis, then concurrently heat treated and pre-formed to a <NUM>-dimensional shape in a protective environment, then placed in a <NUM>-dimensional heated die set within a press for final forming the airfoil to its finished shape. This imparts plastic strain, internal distortion, and initial degradation of microstructure and mechanical properties which must be addressed and recovered during post-processing; solution heat treatment, annealing, and the like. Thus a key to successfully manufacturing a finished blade, according to previous methods, is being able to perform the bonding, brazing, and/or welding while ensuring residual stresses induced by thermal mechanical processing steps are properly managed and subsequently relieved without affecting acceptable final airfoil dimensions, mechanical properties, and microstructure.

In contrast, as seen in <FIG>, a plurality of bellows <NUM> can be placed on one or both of the first and second die halves <NUM>, <NUM>, and disposed at least around the peripherally welded interface of the cover and the blade. Bellows <NUM> can generally conform to the shape of annular pockets, cylindrical ribs, or other internal blade features of <FIG>. In the example of <FIG>, bellows <NUM> are placed and secured entirely on the second die half <NUM>. When actuated, some or all of the plurality of bellows <NUM> are arranged in a manner to provide pressure at approximately a <NUM> degree angle to a plane best fitting the surface at each of the plurality of nodes or rib junctions. Each node can be defined by an intersection of two or more rib portions (e.g., cylindrical portions <NUM> and/or linear portions <NUM>) shown in <FIG>.

<FIG>, discussed together, show one example geometry of bellows <NUM> in conjunction with blade assembly <NUM>. The first die half <NUM> and/or the second die half <NUM> includes a plurality of protrusions <NUM> for engaging a hollow portion <NUM> of one or more of the plurality of bellows <NUM>. Retainer <NUM> is disposed annularly between ones of plurality of protrusions <NUM> and the corresponding hollow portion <NUM> of one or more of the plurality of bellows <NUM>. The retainer <NUM> includes at least one knife-edge seal <NUM> for engaging a mating knife edge machined into a recessed flat where a flange of bellows <NUM> resides.

With reference to <FIG> in particular, knife-edge seal <NUM> can be machined into retainer <NUM> and into first die half <NUM> and/or second die half <NUM>, adapted to pinch the flange of bellows <NUM> between to create a leak-free seal. The knife-edge is defined by angle Θ being about <NUM>° relative to a horizontal plane. and angle Φ being about <NUM>° relative to angle Θ. The flange of bellows <NUM> can be provided with a heavy copper-based plating onto one or both surfaces to enhance engagement and subsequent sealing by mating knife-edge(s) <NUM>. Alternatively, a copper gasket (not shown) may be placed between knife-edge(s) <NUM> and the flange of bellows <NUM>.

A plurality of bellows are selectively operated with gas pressure to locally press the cavity-back blade and cover together at strategically placed circular locations (i.e., nodes) about the welded interface of the blade and the cover. This generally can include but is not precisely limited to areas normal to circular rib portions <NUM> (shown in <FIG>).

A recessed catenary <NUM> can additionally or alternatively be disposed above or atop each of the bellows <NUM> between ones of the plurality of protrusions and the corresponding one or more of the plurality of bellows. This recessed catenary <NUM> has the benefit of concentrating the pressure for effecting robust diffusion bonds onto the tops <NUM> of circular ribs <NUM>, while preventing distortion of the cover <NUM> over the interiors of annular pockets <NUM> during the diffusion bonding operation. Referring to <FIG>, recessed catenary <NUM> prevents bellows <NUM> from contacting cover <NUM> over area <NUM>, thus preventing movement of cover <NUM> into annular cavity <NUM>.

Bellows <NUM> can also include various means for generating localized heating at a plurality of interfaces between the blade cover <NUM> and the plurality of nodes (e.g., cylindrical rib portions <NUM>). The heating means can be in electrical or other thermal communication via port <NUM>, or other separate passageway, through one or both of first die half <NUM> and second die half <NUM>. Specific examples are discussed later, but generally the heating means, in the vicinity of bellows hollow portion <NUM>, are sufficient to elevate a temperature of the first and second die halves <NUM>, <NUM> for diffusion bonding, brazing, and/or creep-forming a combination of cavity-back blade <NUM> and cover <NUM>. For a three-dimensional cavity-back blade, this also has the effect of relieving stresses resulting from the initial peripheral weld (shown in <FIG>) while maintaining the desired blade twist angle(s). In the context of titanium alloys, for example, the heating means are sufficient to locally elevate the temperature at the interface to a range of about <NUM>° C (<NUM>° F) to about <NUM>° C (<NUM>° F). To prevent surface contamination during bonding and further facilitate localized bonding and temperature control, the diffusion bonding, brazing, and/or creep-forming operations utilizing bellows <NUM> will be performed in a vacuum, or a vacuum having a partial pressure of inert gas, e.g., argon, relative to an ambient condition. Alternatively, the process can be performed at atmospheric or greater pressures of argon in a vessel.

<FIG> shows details of a first example heating element <NUM> for generating localized heating around a bellows <NUM>. Here, heating element <NUM> includes a circular resistance heating element <NUM> adjacent to one of the plurality of interfaces between cavity-back blade <NUM> and cover <NUM>. Wires <NUM> extend through one of first die half <NUM> and/or second die half <NUM> via conduit <NUM> to provide power for element <NUM>.

<FIG> shows a second example heating element <NUM>', where localized heating is provided by at least one of a quartz heater <NUM> and a light emitting diode <NUM> in electrical communication through one of first die half <NUM> and/or second die half <NUM>, also via wires <NUM> through conduit <NUM>. Note that in <FIG> and <FIG>, ports to pressurize bellows <NUM> are also to be included but are omitted for clarity).

<FIG> shows a sectional view of a cavity-back blade body with the blade cover and bellows-actuated carrier and heater operating at an example interface or node. Similar to <FIG>, the alternate embodiment of <FIG> shows bellows <NUM> in conjunction with blade assembly <NUM>' (peripherally welded combination of cavity-back blade <NUM>' and cover <NUM>'). The first die half (not shown) and/or the second die half <NUM> includes a plurality of protrusions <NUM> for engaging a hollow portion <NUM> of one or more of the plurality of bellows <NUM>. Retainer <NUM> is disposed annularly between ones of plurality of protrusions <NUM> and the corresponding hollow portion <NUM> of one or more of the plurality of bellows <NUM>.

Knife-edge seal <NUM> can be used on bellows retainer <NUM> to pinch the bellows flange against a mating knife edge machined into a recessed flat where the bellows flange resides, thereby creating a seal so bellows <NUM> can be repeatedly pressurized during operation via port <NUM> without leaking. To further facilitate repeated cyclical stresses and pressurization, bellows <NUM> can be provided with a heavy copper-based plating on both surfaces of the flange portion of the bellows onto which the knife edges bite into. When retainer <NUM> is tightened down by fasteners <NUM>, upper and the lower knife-edges <NUM> cut into the copper-based plating.

Gas pressure is applied to bellows hollow portion <NUM> to actuate bellows <NUM>, thus providing movement of carrier <NUM> and integral heating device <NUM>, which ultimately provides pressure to cover <NUM>' to achieve diffusion bonding to tops <NUM> of circular ribs <NUM>'. Similar to other embodiments, this generally can include but is not precisely limited to areas normal to other circular rib portions <NUM>, located both around and inward of the peripheral weld / cover interface (shown in <FIG>).

Recessed catenary <NUM> forms the top of each of bellows <NUM> between ones of the plurality of protrusions <NUM> and the corresponding one or more of the plurality of bellows <NUM>. In this embodiment, the recessed catenary <NUM> ensures an outermost or diametrically outward load path and proper movement of carrier <NUM>, thus enabling delivery of uniform pressure for effecting robust diffusion bonding of cover <NUM>' onto the tops of circular ribs <NUM>'. The rigid structure of the translating ceramic or metallic heating device prevents distortion of the cover <NUM> over the interiors of annular pockets <NUM>' during the operation.

The example configuration of <FIG> can offer additional processing and end product advantages in that the bellows <NUM> is positioned well below the die surface. As such, the bellows can operate at temperatures cooler than the example embodiments shown in <FIG>, <FIG>, <FIG>. This difference has been shown to be on the order of several hundred degrees Fahrenheit. Lower operating temperature of bellows <NUM> enables greater operating pressure for the bellows and in turn, increased diffusion bond pressure to ensure improved contact area between and around mating parts being diffusion bonded (e.g., cover <NUM>' and circular ribs <NUM>'), resulting in improved bond strength. This also offers greater processing flexibility with potentially extended useful life of bellows <NUM>.

Bellows <NUM> can also include various means for generating localized heating at a plurality of interfaces between the blade cover <NUM>' and the plurality of nodes (e.g., cylindrical rib portions <NUM>'). Heating means can include those described with reference to <FIG> and <FIG>, as well as a metal and/or ceramic heater element <NUM>. In the example of electric heating elements, access passage <NUM> through either die half can include suitable wiring for electrical communication. Temperature resistant ceramic (e.g., silicon nitride) carrier <NUM> can hold the heating element(s) in place between bellows <NUM> and blade assembly <NUM>'. In certain embodiments, carrier <NUM> also shields circumferentially fasteners <NUM> which have the effect of interlocking the base of bellows <NUM>.

With respect to a related method, pressure is applied to the entire blade surface and requires shaping an airfoil from a flat configuration to a <NUM>-dimensional configuration. In the primary example of this disclosure, a peripheral weld would initially join a <NUM>-dimensional thin-walled, hot formed or superplastically formed, metal cover engaged into its recessed mating opening in a hollow <NUM>-dimensional machined metal cavity-back blade body, to create the blade assembly. The <NUM>-dimensional welded blade assembly would then be placed within dies with one die-half or both die-halves having a plurality of circular bellows similar to those shown and described, and localized pressure would be provided at thin-ribbed circular nodes (See <FIG>). These small circular bellows are adapted to produce a load at the interface that is sufficient to create a low temperature diffusion bond. At least a portion of the plurality of bellows are arranged in a manner to provide localized pressure to the cover at approximately a <NUM> degree angle to each of a plurality of nodes, (e.g., along a plane best fitting each of the plurality of nodes or rib junctions). Each node can be defined by an intersection of two or more ribs in the cavity-back blade.

During this bonding process, the cover's peripheral weld would be stress relieved and the blade body would be concurrently minimally creep-formed within the dies' <NUM>-dimensional configuration. Upon completion of the bonding/creep-forming/stress relief operation, the blade would be removed from the dies and subsequently CAT-scanned for weld/bond integrity.

A retainer can be positioned annularly between ones of plurality of die protrusions and the corresponding hollow portion of one or more of the plurality of bellows. The retainer optionally includes at least one knife-edge seal adapted to pinch the bellows flange against a mating knife edge machined into a recessed flat where the bellows flange resides. A recessed catenary can be positioned above each of the bellows between ones of the plurality of protrusions and the corresponding one or more of the plurality of bellows.

While the current disclosure focuses on diffusion bonding a <NUM>-dimensional (twisted) cavity-back airfoil blade body and a hot formed or superplastic formed <NUM>-dimensional cover together to create a <NUM>-dimensional (twisted) product, such processing is expected to be adaptable and suitable for diffusion bonding of hollow blades or hollow vanes in a planar (i.e., flat) configuration.

Claim 1:
An apparatus (<NUM>) comprising:
means for peripherally welding a hollow cavity-back blade (<NUM>; <NUM>') and a cover (<NUM>; <NUM>') of the cavity-back blade (<NUM>; <NUM>') to form a <NUM>-dimensional hollow blade assembly (<NUM>; <NUM>');
a first die half (<NUM>) and a second die half (<NUM>; <NUM>) for receiving the <NUM>-dimensional hollow blade assembly (<NUM>; <NUM>');
a plurality of bellows (<NUM>; <NUM>) contained in one or both of the first and second die halves (<NUM>, <NUM>; <NUM>), and configured to be disposed inward of a peripherally welded interface (<NUM>) of the cover (<NUM>; <NUM>') and the cavity-back blade (<NUM>; <NUM>'), wherein at least a portion of the plurality of bellows (<NUM>; <NUM>) are arranged in a manner to provide pressure to the cover (<NUM>; <NUM>'), andthe first die half (<NUM>) or the second die half (<NUM>; <NUM>) includes a plurality of protrusions (<NUM>; <NUM>) for engaging a hollow portion (<NUM>; <NUM>) of one or more of the plurality of bellows (<NUM>; <NUM>); and
a retainer (<NUM>; <NUM>) disposed annularly around ones of the plurality of protrusions (<NUM>; <NUM>) and the corresponding hollow portion (<NUM>; <NUM>) of one or more of the plurality of bellows (<NUM>; <NUM>);
characterised in that:
the retainer (<NUM>; <NUM>) includes at least one knife-edge seal (<NUM>; <NUM>) for engaging a bellows flange against a mating knife edge machined into a recessed flat where the bellows flange resides.