Plastic article or earthenware shaping or treating: apparatus – Shaping or casting surface
Reexamination Certificate
2000-08-11
2002-08-13
Mackey, James P. (Department: 1722)
Plastic article or earthenware shaping or treating: apparatus
Shaping or casting surface
C425S390000, C425S403000, C425SDIG004
Reexamination Certificate
active
06431850
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to tooling used to manufacture lightweight fan blades used in gas turbine engines.
BACKGROUND OF THE INVENTION
Gas turbines include, but are not limited to, gas turbine power generation equipment and gas turbine aircraft engines. A gas turbine includes a core engine having a high pressure compressor to compress the air flow entering the core engine, a combustor in which a mixture of fuel and the compressed air is burned to generate a propulsive gas flow, and a high pressure turbine which is rotated by the propulsive gas flow and which is connected by a larger diameter shaft to drive the high pressure compressor. A typical front fan gas turbine aircraft engine adds a low pressure turbine (located aft of the high pressure turbine) which is connected by a smaller diameter coaxial shaft to drive a front fan (located forward of the high pressure compressor) and to drive an optional low pressure compressor (located between the front fan and the high pressure compressor). The low pressure compressor sometimes is called a booster compressor or simply a booster.
The fan and the high and low pressure compressors and turbines have airfoils each including an airfoil portion attached to a shank portion. Rotor blades are those airfoils which are attached to a rotating gas turbine rotor disc. Stator vanes are stationary airfoils which are attached to a non-rotating gas turbine stator casing. Typically, there are alternating circumferential rows of radially-outwardly extending rotor blades and radially-inwardly extending stator vanes. When present, a first and/or last row of stator vanes (also called inlet and outlet guide vanes) may have their radially-inward ends also attached to a non-rotating gas turbine stator casing. Counter-rotating “stator” vanes are also known.
Conventional airfoil designs used in the compressor section at the engine typically have airfoil portions that are made entirely of metal, such as titanium, or are made entirely of a composite. A “composite” is defined to be a material having any (metal or non-metal) fiber filament embedded in any (metal or non-metal) matrix binder, but the term “composite” does not include a metal fiber embedded in a metal matrix. The term “metal” includes alloys such as titanium Alloy 6-2-4-2. An example of a composite is a material having graphite filaments embedded in an epoxy resin.
The all-metal blades, including costly wide-chord hollow blades, are heavier in weight which results in lower fuel performance and require sturdier blade attachments, while the lighter all-composite blades are more susceptible to damage from bird ingestion events. Known hybrid blades include a composite blade having an airfoil shape which is covered by a surface cladding (with only the blade tip and the leading and trailing edge portions of the surface cladding comprising a metal) for erosion and foreign object impacts. The fan blades typically are the largest (and therefore the heaviest) blades in a gas turbine aircraft engine, and the front fan blades are usually the first to be impacted by foreign objects such as birds.
Recent improvements have resulted in lighter-weight gas turbine blades, and especially a gas turbine aircraft engine fan blade that is comprised of a combination of metal and lightweight materials. These blades have been made lighter by removing metal from the pressure side of the blade. In order to retain the aerodynamic characteristics of the blade, the removed metal is replaced by the lightweight material. Restoring the aerodynamic characteristics to the blade by adding the lightweight material to replace the removed metal involves the use of specialized tooling. However, the specialized tooling that includes a special caul sheet currently used in the process of adding lightweight material to the pressure side of the fan blade in order to restore aerodynamic characteristics requires that an effective seal be formed against the blade pressure side by the caul sheet. The caul sheet currently used in the process of adding the lightweight material relies on an O-ring to form the seal with the pressure side of the blade. However, the O-ring can cause the caul sheet to stand off from the pressure side of the blade. The result is that there is a lack of good contact between the caul sheet and the pressure surface, and a step is formed in the molded surface of the lightweight material that can rise above the pressure surface up to the diameter of the O-ring. This step is undesirable, as it adversely affects the aerodynamics of the pressure side of the blade. It is time consuming to and very difficult to remove this step from the lightweight material, as the material is also very tough. What is needed is better method using improved tooling for adding lightweight material to a blade.
SUMMARY OF THE INVENTION
A flexible tool is formed to fit over the pressure or concave side of a metallic airfoil that includes a lightweight material component for a gas turbine engine during fabrication of the airfoil. Typically the airfoil is a metallic fan blade. The metallic fan blade includes pockets or cavities that have been machined into the blade in order to reduce the weight of the blade. The tool is a flexible body manufactured from sheets of composite material and includes an integral elastomeric seal.
The flexible tool is formed by laying up thin sheets of composite material that includes fiber over a metallic master tool. As used herein, composite material is material formed from sheets of plastic resin matrix material having a fiber reinforcement, in which the fiber reinforcement may be unidirectional or bidirectional (woven). This material is sometimes referred to as prepreg. The metallic master tool has a profile that matches the profile of the pressure side of the fan blade, but includes a plurality of slots that are located at positions that correspond to locations along the perimeter of the fan blade, that is, positions just beyond the leading edge, trailing edge or tip end. As used herein, matching the profile of the pressure side of the fan blade means that the metallic tool has a surface that substantially corresponds to the contours, dimensions and curvatures as the pressure side of a corresponding metallic fan blade that is manufactured without cavities. The slot positions correspond to preselected positions, which allow the flexible caul sheet and seal to be correctly assembled to the blade. The slot depth may vary, but need only be sufficiently deep to allow the layers of composite material to be laid into them, thus forming lugs that positively locate the flexible caul sheet when it is placed on to the concave (pressure) side of the blade.
The elastomeric material is partially cured and is placed along the tool within an area inside the outline of the blade, which is permanently marked on the tool, such as by scribing the tool surface. Thus, the elastomeric material is placed on the tool inside of markings that correspond to the perimeter of the blade. The sheets of composite material are laid up to achieve a predetermined thickness over the elastomeric material, over the tool surface in the region outlining the blade and into the slots on the tooling surface. The predetermined thickness provides a predetermined stiffness so that the flexible tool will not deform when lightweight a material is injected under pressure into the pockets of the blade beneath the tool. The tool also includes at least one injection port corresponding to a pocket or cavity so that the lightweight material can be injected through the tool into the blade pockets. Additional ports, each corresponding to a pocket, may be added as required. A surround frame for added local stiffness is assembled from sheets of composite material and is separated from the flexible tool using a TEFLON® (polytetrafluoroethylene—PTFE) film. The surround frame extends around the perimeter of the blade outline on the tooling surface so that it overlies the partially cured elastomer and the sheets of composite material.
The meta
Evans Charles Richard
Tyler Robert Paul
Del Sole Joseph S.
Mackey James P.
Maria Carmen Santa
McNees Wallace & Nurick
Narciso David L.
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