Patent Description:
Gas turbine engines, such as those that power modern commercial and military aircraft, generally include a fan section, a compressor section to pressurize an airflow, a combustor section to burn a hydrocarbon fuel in the presence of the pressurized air, and a turbine section to extract energy from the resultant combustion gases. The fan section often utilizes relatively large fan blades of a complicated airfoil shape. Titanium-based alloys provide exceptional fatigue properties, erosion benefits relative to aluminum alloys, and are light weight compared to steel, stainless steels, and nickel alloys. Diffusion bonding may be used for manufacturing hollow, high-temperature alloy components with complex geometries.

Hollow titanium fan blades may be manufactured by diffusion bonding two machined cavity-containing plates on a neutral axis, hot forming, then pressurizing the bonded assembly to achieve its final shape within complex dies. The bonded blade subsequently must be twisted into the proper airfoil configuration, then internally pressurized to expand the relatively thin walls which have collapsed via creep during the prior diffusion bonding steps.

Manufacture of hollow titanium fan blades require substantial investments in equipment and materials and often have limited throughput and yield. Part of the manufacturing challenge is that fusion welding may result in a degradation of ductility, which is a key mechanical property for withstanding a bird impact; as well as degradation of fatigue strength, which is a key mechanical property for an airfoil's extended service life. <CIT>, which discloses the preamble of claim <NUM>, <CIT> and <CIT> disclose fixture assemblies.

In an aspect a fixture assembly is provided according to claim <NUM>.

In another aspect a method of manufacturing a fan blade is disclosed according to claim.

These features and elements as well as the operation of the invention will become more apparent in light of the following description and the accompanying drawings. It should be appreciated, however, the following description and drawings are intended to be exemplary in nature and non-limiting.

The gas turbine engine <NUM> as disclosed herein has a two-spool turbofan that generally incorporates a fan section <NUM>, a compressor section <NUM>, a combustor section <NUM> and a turbine section <NUM>. The fan section <NUM> drives air along a bypass flowpath while the compressor section <NUM> drives air along a core flowpath for compression and communication into the combustor section <NUM> then expansion through the turbine section <NUM>. Although depicted as a turbofan in the disclosed non-limiting embodiment, it should be appreciated that the concepts described herein are not limited only thereto.

The engine <NUM> generally includes a low spool <NUM> and a high spool <NUM> mounted for rotation around an engine central longitudinal axis A relative to an engine static structure <NUM> via several bearing compartments <NUM>. The low spool <NUM> generally includes an inner shaft <NUM> that interconnects a fan <NUM>, a low pressure compressor <NUM> ("LPC") and a low pressure turbine <NUM> ("LPT"). The inner shaft <NUM> drives the fan <NUM> directly or through a geared architecture <NUM> to drive the fan <NUM> at a lower speed than the low spool <NUM>. An exemplary reduction transmission is an epicyclic transmission, namely a planetary or star gear system. The high spool <NUM> includes an outer shaft <NUM> that interconnects a high pressure compressor <NUM> ("HPC") and high pressure turbine <NUM> ("HPT"). A combustor <NUM> is arranged between the HPC <NUM> and the HPT <NUM>. The inner shaft <NUM> and the outer shaft <NUM> are concentric and rotate around the engine central longitudinal axis A which is collinear with their longitudinal axes.

Core airflow is compressed by the LPC <NUM> then the HPC <NUM>, mixed with fuel and burned in the combustor <NUM>, then expanded over the HPT <NUM> and the LPT <NUM>. The turbines <NUM>, <NUM> rotationally drive the respective low spool <NUM> and high spool <NUM> in response to the expansion. The main engine shafts <NUM>, <NUM> are supported at a plurality of points by the bearing compartments <NUM>. It should be appreciated that various bearing compartments <NUM> at various locations may alternatively or additionally be provided.

The fan section <NUM> includes a plurality of circumferentially spaced fan blades <NUM> (<FIG>) which may be made of a high-strength, low weight material such as a titanium alloy, composite material or combinations thereof. In one example, the fan blade <NUM> has a chord of about <NUM> inches (<NUM>) and a span of about <NUM> inches (<NUM>).

With reference to <FIG> and <FIG>, each fan blade <NUM> generally includes an innermost root portion <NUM>, an intermediate portion <NUM>, an airfoil mid-span portion <NUM> and an outermost airfoil portion <NUM>. In one form, the root portion <NUM> defines an attachment such as an inverted fir tree, bulb, or dovetail, so the fan blade <NUM> is slidably received in a complimentary configured recess provided in a fan rotor <NUM>. The intermediate portion <NUM> may be a mechanically attached platform or integral that is generally between the root portion <NUM> and the airfoil mid-span portion <NUM> to define an inner boundary of the air flow path. The airfoil mid-span portion <NUM> defines a blade chord between a leading edge <NUM>, which may include various forward and/or aft sweep configurations, and a trailing edge <NUM>. A concave pressure side <NUM> and a convex suction side <NUM> are defined between the leading edge <NUM> and the trailing edge <NUM>. Although a fan blade <NUM> is illustrated in the disclosed non-limiting embodiment, other hollow structures such as compressor blades, turbofan blades, turboprop propeller blades, tilt rotor props, vanes, struts, and other airfoils may benefit herefrom.

With reference to <FIG>, each fan blade <NUM> is manufactured from a blade body <NUM> and a cover <NUM> that are joined (e.g., brazed, bonded, welded, etc.) to one another to provide an exterior contour <NUM> of the fan blade <NUM> (<FIG>). In the example, the blade body <NUM> is provided by a forged blank that is machined to remove material <NUM>. The ribs <NUM> may be of various configurations such as rib <NUM> (<FIG>) to reduce weight while providing fan blade structural integrity, ensuring blade fatigue life to support the cover <NUM>. The blade body <NUM> provides the root portion <NUM> and one side of the airfoil mid-span portion <NUM> along with the outermost airfoil portion <NUM>. The blade body <NUM> also provides the fan blade leading and trailing edges <NUM>, <NUM>.

The cover <NUM> may be secured to the blade body <NUM> by brazing, welding, bonding or other material or method. The cover <NUM> is typically on the convex side. The cover <NUM> may be manufactured of titanium for its thermal expansion match with the titanium blade body <NUM>. The cover <NUM> may be hot formed at processing conditions that ensure maintaining its certified mechanical properties, while achieving the desired shape for bonding. In one example, the cover <NUM> is about <NUM> to <NUM> thousandths of an inch (<NUM>-<NUM>) in thickness and is superplastically formed to an airfoil shape.

The material <NUM>, for example, braze material or cathodic arc deposited coating is provided on one or both of the first and second mating surfaces <NUM>, <NUM>, which are respectively provided by the blade body <NUM> and the cover <NUM> (<FIG>). The material <NUM> may be pre-placed onto either the titanium blade body <NUM> or the cover <NUM> as a photo etched pre-form or a cathodic arc deposit. In one example, the entire surface <NUM> of the cover <NUM> being joined to the blade body <NUM> would be cathodic arc deposited. In one example, the entire surface of the blade body <NUM> would be cathodic arc coated prior to machining the blade body <NUM> and the material <NUM> would be deposited onto surface <NUM> prior to selective etching the titanium cover <NUM> to only provide material <NUM> at areas being joined.

With reference to <FIG>, a fixture assembly <NUM> for manufacturing the fan blade <NUM> includes a first fixture portion <NUM> and a second fixture portion <NUM> that interfaces with the first fixture portion <NUM>. The airfoil contour of the first fixture portion <NUM> and the second fixture portion <NUM> are generally rectangular with an approximate twist of from about + <NUM> degrees to about - <NUM> degrees (<FIG>). The first fixture portion <NUM> is shaped to the airfoil contour to receive the blade body <NUM>.

The second fixture portion <NUM> is shaped to the airfoil contour to support the cover <NUM> with respect to the blade body <NUM> in response to movement of a sub-fixture <NUM> within the first fixture portion <NUM> which is driven by a multiple of actuators <NUM>. The actuators <NUM> are arranged within the first fixture portion <NUM> such that the sub-fixture <NUM> defines the fusion bond area (<FIG>) to join the cover <NUM> to the blade body <NUM>. In this embodiment, diffusion bonding is utilized along the periphery via the use of a very fine grainsize coating for enhanced bonding and at lower temperatures than otherwise needed. The interior circular and racetrack ribs could be diffusion bonded, brazed, or welded. If diffusion bonded or brazed, the interior circular and racetrack ribs would likely be diffusion bonded or brazed concurrently or sequentially with the periphery diffusion bonding. If welded, the interior circular and racetrack ribs could be done prior to or after the periphery diffusion bond. The sub-fixture <NUM> concentrates the pressure and temperature while preventing distortion during the diffusion bonding operation. A machined recess <NUM> (<FIG>) within the first fixture portion <NUM> receives the sub-fixture <NUM>, provides support for the actuators <NUM>, permits access for gas pressure lines, heating element wires, and sensor wires for thermocouples that provide for real-time monitoring of temperature, gas pressure, and diffusion bonding pressure.

With reference to <FIG>, each of the sub-fixture elements <NUM> includes a heating element <NUM>. In examples, the heating element <NUM> may include a resistance heating element, or other such element that can provide upwards of <NUM> degrees F and is located within a sub-fixture element <NUM> (<FIG>). The heating element <NUM> is be at least partially embedded in a sub-fixture element <NUM> of the sub-fixture <NUM>. The sub-fixture element <NUM> of the sub-fixture <NUM> may be manufactured of a silicon nitride or other heatable material or combination of materials that distributes the heat from the heating elements <NUM>. The sub-fixture <NUM> is formed as a multiple of sub-fixture elements <NUM> to form a segmented 3D heatable and translatable fixture element that heats and applies pressure to the workpiece. Alternatively and not according to the invention, the sub-fixture <NUM> may be formed as a single integral rectilinear shaped element. The heating element <NUM> within the sub-fixture elements <NUM> is generally opposed to a multiple of heating elements <NUM> in the second fixture portion <NUM> to bracket the peripheral fusion bond that joins the cover <NUM> to the blade body <NUM>. That is, the multiple of heating elements <NUM> are opposite the sub-fixture <NUM>. In one example, the internal ribs may be machined to a height below the periphery and in some embodiments need not be bonded, brazed, or welded and the circular ribs and racetrack shaped ribs may be machined to full height and will be bonded, brazed, or welded to the cover at their respective internal locations.

Each actuator <NUM> includes a bellows <NUM> that may be about <NUM> inches (<NUM>) in diameter. The bellows <NUM> includes a threaded attachment <NUM> for installation and removal from the first fixture portion <NUM> and a retainer <NUM> (<FIG>) that is received within a "T" shaped slot <NUM> in the sub-fixture element <NUM> (<FIG>). That is, each of the actuators <NUM> is located between the first fixture portion <NUM> and the sub-fixture element <NUM>. The bellows <NUM> drive the heated sub-fixture elements <NUM> against the titanium blade body <NUM>, thereby causing a protrusion <NUM> of the second fixture portion <NUM> that is opposite the sub-fixture <NUM> to engage the blade cover <NUM> and subsequently diffusion bond the cover <NUM> to the blade body <NUM>.

Each of the actuators <NUM> arc in communication with a control system <NUM>. The control system <NUM> may include at least one processor <NUM> (e.g., a controller, microprocessor, microcontroller, digital signal processor, etc.), memory <NUM>, and an input/output (I/O) subsystem <NUM>. The control system <NUM> may be embodied as any type of computing device (e.g., a tablet computer, smart phone, body-mounted device or wearable device, etc.), a server, an enterprise computer system, a network of computers, a combination of computers and other electronic devices, or other electronic devices. Although not specifically shown, the I/O subsystem <NUM> typically includes, for example, an I/O controller, a memory controller, and one or more I/O ports. The processor <NUM> and the I/O subsystem <NUM> are communicatively coupled to the memory <NUM>. The memory <NUM> may be embodied as any type of computer memory device (e.g., volatile memory such as various forms of random access memory). The I/O subsystem <NUM> may also be communicatively coupled to a number of hardware, firmware, and/or software components, including a data storage device <NUM>, a display <NUM>, and a user interface (UI) subsystem <NUM>. The data storage device <NUM> may include one or more hard drives or other suitable persistent storage devices (e.g., flash memory, memory cards, memory sticks, and/or others). A database <NUM> may reside at least temporarily in the data storage device <NUM> and/or other data storage devices (e.g., data storage devices that are "in the cloud" or otherwise connected to the control system <NUM> by a network).

The control system <NUM> includes other hardware, firmware, and/or software components that are configured to perform the functions disclosed herein, including a temperature sensor <NUM> for each sub-fixture element <NUM> and a pressure sensor <NUM> for each bellows <NUM>. While not specifically shown, the control system <NUM> may include other computing devices (e.g., servers, mobile computing devices, etc.) and computer aided manufacturer (CAM) systems which may be in communication with each other and/or the control system <NUM> via a communication network to perform one or more of the disclosed functions.

With reference to <FIG>, a method <NUM> for manufacturing the fan blade <NUM> is schematically disclosed in terms of a functional block diagram flowchart. It should be appreciated that alternative or additional steps may be provided without departing from the teaching herein.

Initially, the blade body <NUM> is manufactured (step <NUM>). The blade body <NUM> may, for example, be produced as a near-net-shape titanium (e.g., Ti-<NUM>-<NUM>) blade forging (<FIG>). In embodiments, the blade body <NUM> may include a squared off leading edge which is later finished (phantom line <NUM>; <FIG>) to form an aerodynamic leading edge.

Next, the blade body <NUM> is machined (step <NUM>). In one embodiment, the convex suction side <NUM> is machined to form a cavity-back blade blank (<FIG>). The machining forms the ribs <NUM> (<FIG>) to reduce weight while providing fan blade structural integrity, ensuring blade fatigue life to support the cover <NUM>.

Next, the cover <NUM> is formed (step <NUM>). The cover, in one example, may be superplastic formed and chemical milled from titanium (e.g., Ti-<NUM>-<NUM>).

Next, the blade body <NUM> and the cover <NUM> are cleaned (step <NUM>). In one example, the cleaning may include laser cleaning of the bond surfaces.

The material <NUM>, when utilized, is then located on one or both of the first and second mating surfaces <NUM>, <NUM> (step <NUM>).

The cover <NUM> is then located (step <NUM>) into the blade body <NUM> and placed (step <NUM>) within the fixture assembly <NUM>. Initially, the first fixture portion <NUM> and the second fixture portion <NUM> are closed together to enclose the cover <NUM> and the blade body <NUM>. In one example, the first fixture portion <NUM> is moved toward the second fixture portion <NUM> about <NUM>-<NUM> inches (<NUM> - <NUM>). The first fixture portion <NUM>, in one example, may be fixed and remain stationary. The second fixture portion <NUM> may be moved toward the first fixture portion <NUM> to generate a uniform concentrated load, however, further refinement of pressure and temperatures are provided through the sub-fixture <NUM>.

Next, pressure is applied (step <NUM>) to each of the multiple of actuators <NUM> to move the sub-fixture <NUM>. That is, the multiple of actuators <NUM> press the blade body <NUM> into the cover <NUM>. This may be performed while temperature is increased. In one example, the sub-fixture <NUM> may initially be <NUM>-<NUM> inches (<NUM>- <NUM>), and more specifically <NUM>-<NUM> inches (<NUM>-<NUM>) above the surface of the first fixture portion <NUM>. In one example, the sub-fixture <NUM> moves about <NUM> - <NUM> inches (<NUM> - <NUM>). Gas pressure is applied to the bellows <NUM> for each actuator <NUM> to drive the sub-fixture element <NUM> toward the workpiece to provide pressure to the cover <NUM> to achieve diffusion bonding to the blade body <NUM>. The sensors <NUM>, <NUM> permit individual control of each actuator <NUM> to tailor the interface along the periphery of the sub-fixture <NUM> to adjust the peripheral bond. That is, each actuator <NUM> may be individually controlled in temperature and pressure.

The cover <NUM> is then diffusion bonded and/or brazed (step <NUM>) into the blade body <NUM> for the required temperature, time, and pressure. The pre-deposited material <NUM> enables reducing the otherwise elevated temperature processing to a temperature range of <NUM>-<NUM> degrees F (<NUM> - <NUM> degrees Celsius). Alternatively, an adhesive bond or a low temperature bond for composite components may also benefit herefrom to replace an autoclave and/or vacuum bagging. That is, various bonding, brazing, and/or adhesives may benefit herefrom. 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> F (<NUM> degrees C) to about <NUM> degrees F (<NUM> degrees C). 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.

After the required bond temperature, time, and pressure have occurred, each of the multiple of actuators <NUM> is de-pressurized (step <NUM>) and cooled to the required temperature.

The fan blade <NUM> is then unloaded (step <NUM>). Interim inspection (step <NUM>) may then be performed.

Then, the bonded fan blade <NUM> is final machined (step <NUM>) then inspected (step <NUM>).

The fixture and method provide a weight-neutral, cost effective, hollow titanium fan blade that can replace even a hybrid aluminum hollow fan blade. Such can eliminate complex, time consuming, costly processes presently necessary with non-titanium hollow fan blade manufacture. The method is also significantly more environmentally friendly because the reduction in elevated temperature processing time results in less surface contamination that must be removed by acids.

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

A cavity-back fan blade utilizing welding or selective diffusion bonding reduces large-equipment needs, capital expenses, and end-product costs. The fixture assembly <NUM> and method <NUM> for use therewith provides a relatively compact system that can increase the efficiency of <NUM>-D (e.g.. , twisted) cavity-back airfoil production processes via a hybrid process of a diffusion bonded periphery and/or a diffusion bonded or welded interior. This provides, for example, a finished fan blade having greater bird-strike margin, greater fatigue margin, and potentially lighter overall weight.

Although the different non-limiting embodiments have specific illustrated components, the embodiments of this invention are not limited to those particular combinations. It is possible to use some of the components or features from any of the non-limiting embodiments in combination with features or components from any of the other non-limiting embodiments.

It should be appreciated that relative positional terms such as "forward," "aft," "upper," "lower," "above," "below," and the like are with reference to the normal operational attitude of the vehicle and should not be considered otherwise limiting.

It should be appreciated that like reference numerals identify corresponding or similar elements throughout the several drawings. It should also be appreciated that although a particular component arrangement is disclosed in the illustrated embodiment, other arrangements will benefit herefrom.

Although particular step sequences are shown, described, and claimed, it should be appreciated that steps may be performed in any order, separated or combined unless otherwise indicated and will still benefit from the present invention as disclosed in the appended claims.

Claim 1:
A fixture assembly (<NUM>) for manufacturing a fan blade comprising:
a first fixture portion (<NUM>) shaped to an airfoil contour suitable for receiving a blade body (<NUM>);
a second fixture portion (<NUM>) that interfaces with the first fixture portion (<NUM>);
a sub-fixture (<NUM>) movably mounted to the first fixture portion (<NUM>), wherein the sub-fixture (<NUM>) comprises a multiple of sub-fixture elements (<NUM>) and is arranged to define a peripheral diffusion bond to join a cover (<NUM>) to a blade body (<NUM>);
a multiple of actuators (<NUM>) to selectively move the sub-fixture (<NUM>) toward the second fixture portion (<NUM>); the fixture assembly characterised by
a heating element (<NUM>) within each sub-fixture element (<NUM>) of the sub-fixture (<NUM>); and
a control system (<NUM>), wherein each of the multiple of actuators (<NUM>) is in communication with the control system (<NUM>) and is arranged to be individually controlled in temperature and pressure,
wherein each of the multiple of actuators (<NUM>) is located between the first fixture portion (<NUM>) and each sub-fixture element (<NUM>), and each of the multiple of actuators (<NUM>) comprise a bellows (<NUM>) mounted to a sub-fixture element (<NUM>), wherein the second fixture portion (<NUM>) is shaped to an airfoil contour suitable for supporting the cover (<NUM>) with respect to the blade body (<NUM>) in response to movement of the sub-fixture (<NUM>) within the first fixture portion (<NUM>) driven by the multiple of actuators (<NUM>), wherein each of the multiple of actuators (<NUM>) comprise a temperature sensor (<NUM>) and a pressure sensor (<NUM>).