Hole drilling elastically deformed superalloy turbine blade

A fixture for drilling a hole in a superalloy turbine blade includes a mount to selectively hold a root of the superalloy turbine blade with the superalloy turbine blade extending from the mount. The fixture may also include an actuator to apply a force to elastically deform at least a portion of the superalloy turbine blade when held by the mount from a relaxed, initial position to an elastically deformed position, the at least a portion of the superalloy turbine blade having a curvature in the elastically deformed position not present in the relaxed, initial position. The fixture may also include a drill guide configured to guide a drilling element into the superalloy turbine blade in the elastically deformed position.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application relates to co-pending U.S. patent application Ser. No. 15/485,505, filed concurrently herewith, and currently pending.

BACKGROUND OF THE INVENTION

The disclosure relates generally to turbine blade machining, and more particularly, to a method and fixture for hole drilling an elastically deformed superalloy turbine blade.

Large turbine blades for power generation turbines can include turbine blades more than one meter in length that are very thin relative to their span and chord, particularly near the trailing edge in radially outer span locations. Such turbine blades can also have curvature in the span-wise and chord-wise directions. Due to the high operating temperatures, turbine blades typically include a number of cooling passages extending therethrough, which are provided, among other reasons, to extend the creep life of the blades. Creep is effectively the long term accumulation of plastic strain that eventually leads to rupture. However, the turbine blade thinness and curvature can make it difficult to fabricate cooling passages or holes within the airfoil of the blade, including span-wise cooling passages that follow the curvature of the airfoil. Methods to fabricate long cooling passages with variable curvature, particularly accurately-placed long variable-curvature passages formed using widely employed shaped tube electrolytic machining (STEM) drilling, have not been developed.

One approach to produce curvilinear holes is to flatten the airfoil of the blade in the region where the hole is required, drill a straight hole and then bend the drilled region into the required curve. This process thus requires plastic deformation and reformation of the airfoil. Advances in turbomachinery technology however have led to the use of more advanced materials such as superalloys like high gamma prime superalloys, which cannot be deformed in this manner. In particular, plastically deforming superalloys, i.e., bending the material such that it does not automatically return to its original state, induces plastic strain and dislocations in the material that are not repaired when the superalloy is bent back into its original position. Conventional materials can be exposed to a high temperature thermal process in order to negate the impact of the strain and dislocations on the creep life. However, with superalloys exposed to a high plastic strain, the high temperature thermal process may generate recrystallized grains, weakening the material. Any manufacturing process that induces plastic strain into a turbine blade will effectively give the creep a head start and reduce the overall life of the blade. Consequently, this approach is inapplicable to current turbine blades that are made of superalloys.

BRIEF DESCRIPTION OF THE INVENTION

A first aspect of the disclosure provides a method including: applying a force to elastically deform at least a portion of a superalloy turbine blade from a relaxed, initial position to an elastically deformed position, the at least a portion of the superalloy turbine blade having a curvature in the elastically deformed position not present in the relaxed, initial position; drilling a hole generally span-wise through the at least a portion of the superalloy turbine blade in the elastically deformed position; and releasing the force, allowing the superalloy turbine blade to return to the relaxed, initial position and the hole to take on a hole curvature within the at least a portion of the superalloy turbine blade.

A second aspect of the disclosure provides a method including: coupling a protective member to a first portion of a superalloy turbine blade; applying a force to the protective member to elastically deform at least a second portion of a superalloy turbine blade from a relaxed, initial position to an elastically deformed position, the at least a second portion of the superalloy turbine blade having a curvature in the elastically deformed position not present in the relaxed, initial position; drilling a hole, using shaped tube electrolytic machining (STEM), generally span-wise through the at least a second portion of the superalloy turbine blade in the elastically deformed position; and releasing the force, allowing the superalloy turbine blade to return to the relaxed, initial position and the hole to take on a hole curvature within the at least a portion of the superalloy turbine blade.

A third aspect of the disclosure provides a fixture for drilling a hole in a superalloy turbine blade, the fixture including: a mount to selectively hold a root of the superalloy turbine blade, the superalloy turbine blade extending from the mount; an actuator to apply a force to elastically deform at least a portion of the superalloy turbine blade when held by the mount from a relaxed, initial position to an elastically deformed position, the at least a portion of the superalloy turbine blade having a curvature in the elastically deformed position not present in the relaxed, initial position; and a drill guide configured to guide a drilling element into the superalloy turbine blade in the elastically deformed position.

DETAILED DESCRIPTION OF THE INVENTION

In addition, several descriptive terms may be used regularly herein, and it should prove helpful to define these terms at the onset of this section. These terms and their definitions, unless stated otherwise, are as follows. As used herein, “downstream” and “upstream” are terms that indicate a direction relative to the flow of a fluid, such as the working fluid through the turbine engine or, for example, the flow of air through the combustor or coolant through one of the turbine's component systems. The term “downstream” corresponds to the direction of flow of the fluid, and the term “upstream” refers to the direction opposite to the flow. The terms “forward” and “aft,” without any further specificity, refer to directions, with “forward” referring to the front or compressor end of the engine, and “aft” referring to the rearward or turbine end of the engine. With regard to turbine blades, the terms “leading” and “trailing” without any further specificity, refer to directions, with “leading” referring to the front, upstream edge of the blade, and “trailing” referring to the rearward, downstream edge of the blade. It is often required to describe parts that are at differing radial positions with regard to a center axis. The term “radial” refers to movement or position perpendicular to an axis. In cases such as this, if a first component resides closer to the axis than a second component, it will be stated herein that the first component is “radially inward” or “inboard” of the second component. If, on the other hand, the first component resides further from the axis than the second component, it may be stated herein that the first component is “radially outward” or “outboard” of the second component. The term “axial” refers to movement or position parallel to an axis. Further, the term “circumferential” refers to movement or position around an axis. It will be appreciated that such terms may be applied in relation to the center axis of the turbine. “Generally span-wise” relates to a direction of drilling relative to a superalloy turbine blade and means mainly through a length of, or mainly longitudinally through, the superalloy turbine blade, perhaps with some radius of curvature in the drilling and perhaps with some offset from an axis of the blade.

As indicated above, the disclosure provides a method and fixture to form cooling passages in a large, superalloy turbine blade, and in particular, an airfoil thereof. The cooling passage may be formed as a hole having long variable-curvature in large, superalloy turbine blades. In the present disclosure, at least a portion of turbine blade is elastically deformed using various types of fixtures followed by drilling of a hole therein to form long cooling passages. Here, the superalloy turbine blades are not permanently or plastically deformed. The elastic deformations allows drilling of a straight or linear hole and/or holes of constant curvature using STEM drilling using known methods. Once the force causing the elastic deformation is removed, the superalloy turbine blade returns to its manufactured state, and the hole in the blade creating the cooling passage has a hole curvature that can be constant or can vary over its length. The methodology enables installation of cooling passages in superalloy turbine blades to enhance their creep life without creating any plastic strain.

Referring to the perspective view ofFIG. 1, a fixture100for drilling a hole in a superalloy turbine blade102according to one embodiment of the disclosure is illustrated. Superalloy turbine blade102may include any now known or later developed form of turbine blade. As noted, teachings of the disclosure are especially applicable to turbine blades102having relatively long lengths, e.g., approximately 1 meter, but may be applied to any length turbine blade. Superalloy turbine blade102may general include: a root104including any now known or later developed structure for mounting turbine blade102in a rotor wheel (not shown) of a turbomachine, an airfoil106and a tip end108. Tip end108may include a tip shroud or cover (not shown). Superalloy turbine blade102may also include a mid-span shroud114, but this is not necessary in all instances. As used herein, “superalloy” refers to a metal alloy having numerous excellent physical characteristics compared to conventional alloys, such as but not limited to a tensile elongation range (based on 2 inch gauge length) of 4% to 15%. Example superalloys may include but are not limited to: nickel or cobalt based superalloys. It is noted that not all of superalloy turbine blade102need be superalloy, but only the portion upon which teachings of the disclosure will be applied.

Continuing withFIG. 1, fixture100includes a mount110to selectively hold root104of superalloy turbine blade102. Superalloy turbine blade102extends from mount110, e.g., in a cantilevered fashion. In one embodiment, mount110may be held in position by a base112upon which other parts of fixture100may also be mounted. Base112may include any form of foundational element, e.g., a metal plate, a stand, a floor, a table, etc., capable of positioning parts of fixture100and to apply forces, as described herein, to superalloy turbine blade102. It is understood, however, that mount110and other parts of fixture100may be separately positioned relative to one another, e.g., using separate floor foundations. In one embodiment, mount110may include a plurality of clamps116to hold root104to base112. Clamps116may include any form of adjustable clamp, e.g., threaded bolts with holding elements, etc. Alternatively, mount110may include any variety of systems to hold superalloy turbine blade102, e.g., a dovetail slot118(FIG. 3) similar to that in a rotor wheel (not shown) in which a dovetail of root104would be mounted.

As shown inFIG. 1and the enlarged perspective view ofFIG. 2, fixture100may also include an actuator120to apply a force F to elastically deform at least a portion of the superalloy turbine blade102when held by mount110. As shown in the schematic plan view ofFIG. 3, force F forces at least a portion122of superalloy turbine blade102from a relaxed, initial position124R to an elastically deformed position124D (in phantom). It is noted that in the relaxed, initial position, superalloy turbine blade102may include curved surfaces or span, such features being its as-built shape. The extent of portion122may depend on, for example, the blade, the actuator use, the amount of force F and where/how force F is applied. According to embodiments of the disclosure, force F may be substantially similar to a force applied to superalloy turbine blade102during operation of the blade in a turbomachine. That is, force F is sufficient to elastically deform the blade (i.e., temporarily deflect it from relaxed, initial position124R) but not permanently bend or permanently deform the blade. Hence, in the elastically deformed position, superalloy turbine blade is not permanently or plastically misshapen or deformed. Further, it will return to relaxed, initial position124R upon release of force F. As shown inFIG. 3, portion(s)122of superalloy turbine blade102has a curvature in elastically deformed position124D not present in relaxed, initial position124R. Further, as shown inFIG. 3, elastically deformed position124D may include a lateral deformation LD perpendicular to a longitudinal axis A of superalloy turbine blade102, and/or a twist R about longitudinal axis A of superalloy turbine blade102. Whether lateral deformation LD and/or rotation R is present in elastically deformed position124D will vary on superalloy turbine blade102shape, size, etc., and how force F is applied (described herein). The force F applicable to each blade to achieve the desired hole curvature will depend on a number of factors such as but not limited to: the superalloy used, the length of the blade, the location of the application of force F, the distribution of force F, and the configuration of portion122in which the hole is desired. As used herein, “hole curvature” may include planar curvature, or non-planar or helical curvature depending on how force F is applied. The amount of curvature in the blade in elastically deformed position124D can be calculated based on the aforementioned force factors and the amount of hole curvature desired in a cooling passage hole to be created in, for example, airfoil106. In the example shown inFIGS. 1-2, portion122includes a length of superalloy turbine blade102extending radially inward from its tip end108, but not an area in airfoil106radially outward from root104. However, portion122can be altered depending on the desired hole curvature.

As shown inFIGS. 1 and 2, fixture100may optionally include a protective member130for coupling to a location on portion122of superalloy turbine blade102at which actuator120engages superalloy turbine blade102. InFIGS. 1 and 2, protective member130includes a block132having an opening134therein configured to seat on tip end108of superalloy turbine blade102, e.g., a shroud thereof. Block132preferably mates with tip end108to protect tip end108and allow transfer of force F to superalloy turbine blade102without damage. Protective member130may include any material capable of withstanding force F, protecting superalloy turbine blade102and withstanding any drilling-related electrolyte, e.g., a strong metal alloy, carbon, ceramic, steel or steel alloy. Protective member130may not be necessary in all instances.

Fixture100also may include a drill guide140configured to guide a drilling element142into superalloy turbine blade102in elastically deformed position124D. In one embodiment, drill guide140is configured to guide drilling element142of a shaped tube electrolytic machining (STEM) system144to form a hole146(FIG. 2). STEM system144may include any now known or later developed system employing an acid electrolytic drilling technique, e.g., for making long precision holes in corrosion resistant superalloys. As understood in the field, STEM system144provides one or more tubular drilling elements through which an electrolyte is passed into the blade. A high current is passed between the conductive blade and the drilling element which acts as an electrode. As the electrolyte passes through the drilling element, a hole shaped like a cross-section of the drilling element is drilled into superalloy turbine blade102, and material is removed by the electrolyte. Drilling element142may be straight, i.e., along a linear path, or curved. In the latter case, STEM system144may drill at a constant radius curvature into the blade.

Fixture100may also include a mechanism to identify whether superalloy turbine blade102is in the desired, elastically deformed position124D. In one embodiment, shown inFIGS. 1 and 2, a sensor150may be provided that is configured to identify that superalloy turbine blade102is in elastically deformed position124D. Sensor150may include any form of electronic sensor capable of positional triggering, e.g., a touch sensor, laser sensor, button sensor, etc. Sensor150may indicate proper positioning in any known fashion, e.g., visible or audible indicator, or an electric signal to a control system of, for example, STEM system144, or actuator120, etc. In operation, superalloy turbine blade102would be elastically deformed using actuator120until sensor150indicated it was in elastically deformed position124D. In alternative embodiment, shown inFIG. 3, rather than sensor150, a positioning element152configured to locate superalloy turbine blade102in elastically deformed position124D may be employed. Positioning element152may be any form of fixed or adjustable stop mounted in a controlled fashion relative to mount110, e.g., on base112. In one embodiment, actuator120may apply force F to elastically deform superalloy turbine blade102until portion122reaches a predetermined distance, e.g., 1 millimeter, from positioning element152, which indicates portion122is in elastically deformed position124D. The predetermined distance can be any distance readily measurable by a user, and can be measured in any known fashion, e.g., ruler, calipers, electronically, etc.

With continuing reference toFIGS. 1 and 2, and alsoFIGS. 4-6, actuator120can take a variety of forms within the scope of the disclosure. InFIGS. 1 and 2, actuator120includes a jack screw160including a selectively rotatable screw162, e.g., a bolt, configured to engage at least portion122of superalloy turbine blade102. Jack screw160may include any form of fixed coupling, e.g., to base112via a support164. Screw162may be rotatably adjusted and therefore length adjusted relative to support164to apply force F to superalloy turbine blade102. Referring to the perspective view ofFIG. 4, in another embodiment, actuator120may include a selectively rotatable, eccentric cam170including a surface172configured to apply force F to at least portion122of superalloy turbine blade102. In another embodiment, shown in the perspective view ofFIG. 5, actuator120may include a selectively rotatable winch174including a flexible cord176coupled to protective member130to apply force F. Flexible cord176may take any form capable of withstanding the tensile forces applied thereto, e.g., a metal cable, chain, etc. Any pulley(s)178required to direct flexible cord176may be employed. Selectively rotatable winch174and/or pulley(s)178may be coupled to base112(not shown) in any manner. Referring to the perspective view shown inFIG. 6, in another embodiment, protective member130may include a first gear180on an exterior surface182thereof, and actuator120may include a selectively rotatable second gear184configured to mesh with first gear180to apply force F to portion122of superalloy turbine blade102. In this case, force F is a rotational force that will rotate portion122of the blade, creating twist R (FIG. 3).

In each of the embodiments ofFIGS. 1, 2 and 4-6, the rotation of the selectively rotatable component of actuator120that causes application of force F can be provided in a number of ways. For example, inFIGS. 1 and 2, screw162includes a bolt head166for turning by a conventional wrench (not shown) or wrench driver. InFIG. 4, a motor186may be coupled to selectively rotatable, eccentric cam170to rotate the cam and apply force F to at least portion122. InFIG. 5, a motor188may be coupled to selectively rotate winch174. InFIG. 6, a handle190is coupled to rotatable second gear184to selectively rotate the second gear and apply force F to at least portion122. Any of the above-described techniques for selectively rotating the requisite part of actuator120may be applied in any embodiment. With further reference to theFIGS. 1, 2, 4 and 5embodiments, in each embodiment, actuator120is shown applying force F to a protective member130. It is emphasized, however, that protective member130may not be necessary in all instances and the force F may be applied directly to portion122.

Referring toFIGS. 7-15, in another embodiment, fixture100may include a pair of clamping members222,224configured to engage superalloy turbine blade102.FIG. 7shows a perspective view of fixture100andFIGS. 8-14show various cross-sectional views of fixture100. Clamping members222,224are movable to apply force F by an actuator220. Clamping members222,224may together in a closed position, shown in the cross-sectional view ofFIG. 9, apply force F to position superalloy turbine blade102in elastically deformed position124D. That is, an interior surface226of one or both clamping members222,224may have a shape, alone or collectively, that elastically deforms superalloy turbine blade102, e.g., by providing surfaces that deform the blade in certain locations and/or pockets that allow the blade to move therein to deform. In operation, superalloy turbine blade102in relaxed, initial position124R is placed within clamping members222,224in an open position thereof, as shown inFIG. 8. Actuator220then forces clamping members222,224to a closed position as shown inFIG. 9to apply force F and elastically deform the blade into elastically deformed position124D. As shown inFIG. 9, in elastically deformed position124D, drill guide140may guide drilling element142of STEM system144to drill hole146into the blade.

In another embodiment, as shown in the cross-sectional view ofFIG. 10, rather than having complex surfaces226that create the elastic deformation, clamping members222,224may generally mimic the blade exterior but be slightly larger. In this case, at least one of clamping member222,224may include an element228configured to apply force F to elastically deform at least portion122of superalloy turbine blade102. Otherwise, clamping members222,224may generally mimic an exterior surface of superalloy turbine blade102. Element228may be, for example, a bump or ridge on surface226. Actuator220may include any of the afore-described mechanisms inFIGS. 1, 2, 4-6, to apply force to one (FIG. 9) or both (FIG. 10) clamping members222,224about superalloy turbine blade102.

Referring to the cross-sectional views ofFIGS. 11 and 12, in another embodiment, a protective member230for coupling at a location232on superalloy turbine blade102may be provided for use with clamping members222,224. In this case, at least one of the clamping members222,224(shown as both) include a recess234to accommodate protective member230. Clamping member(s)222,224may include interior surface226to apply force to protective member230or another location of the blade. Protective member230may include any material capable of withstanding force F and protecting superalloy turbine blade102, e.g., a strong metal alloy, steel or steel alloy. Protective member130may not be necessary in all instances.

With further regard to theFIGS. 7-12embodiments, while clamping members222,224are shown encompassing all of superalloy turbine blade102, it is recognized that clamping members222,224may encompass only that section of the blade necessary to create the desired elastically deformed position124D, e.g., only airfoil106or a part thereof.

FIG. 13shows an enlarged cross-sectional view of another optional embodiment of clamping members222,224. In this embodiment, a sensor240is operatively coupled to at least one of clamping members222,224to identify that superalloy turbine blade102is in elastically deformed position124D. Sensor240may include any form of electronic sensor capable of positional triggering, e.g., a touch sensor, laser sensor, button sensor, etc. Sensor240may indicate proper positioning in any known fashion, e.g., visible or audible indicator, or an electric signal to a control system of, for example, STEM system144(not shown) or actuator220. In operation, superalloy turbine blade102would be elastically deformed using actuator220until sensor240indicated it was in elastically deformed position124D.

FIG. 14shows a partial cross-sectional view andFIG. 15shows a schematic perspective view of a seal250for use with clamping members222,224. As understood, STEM system144disperses a liquid electrolyte as part of the process of drilling hole146. In order to prevent electrolyte from spilling and/or not being recycled in a conventional fashion, seal250may be provided, as shown in the cross-sectional view ofFIG. 14, in at least one of the pair of clamping members222,224for sealing with a surface252of superalloy turbine blade102.FIG. 15illustrates how seal250may extend around an entirety of the blade to prevent liquid electrolyte from passing radially inward along the blade. Here, at least one of the pair of clamping members222,224may include a drain hole254therethrough, i.e., for allowing controlled draining of liquid electrolyte therefrom. Drain hole254could also be fluidly coupled to any now known or later developed form of liquid electrolyte recycling system (not shown) of STEM system144(FIG. 7).

In operation, superalloy turbine blade102is mounted in any one of the afore-described fixtures100. Force F is then applied by fixture100to elastically deform at least portion122of the blade from relaxed, initial position124R (FIG. 3) to elastically deformed position124D (FIG. 3). For example, force F may be applied by applying a pair of clamping members222,224(FIGS. 9-12) to superalloy turbine blade102. As noted, at least one of clamping members222,224may include element228(FIG. 10) configured to apply force F. In this setting, as shown inFIGS. 11 and 12, protective member230may be attached at location232on superalloy turbine blade102, and at least one of clamping members22,224may include recess234to accommodate the protective member. Further, one can ensure superalloy turbine blade102is in elastically deformed position124D prior to the hole drilling by, for example, measuring an amount of deformation using any now known or later developed solution, or sensing a position of the at least a portion of the superalloy turbine blade, e.g., using a sensor240, as shown inFIG. 13, to sense whether elastically deformed position124D has been achieved by applying the pair of clamping members222,224. Further, as shown inFIGS. 14 and 15, seal250may be formed, e.g., mounted or applied, between pair of clamping members222,224and surface252of superalloy turbine blade102, and at least one of clamping members222,224may include drain hole254therethrough to allow liquid electrolyte to drain or be recycled therefrom. In another example, the force may be applied by, as shown inFIGS. 1 and 2, holding first end (root end104) of superalloy turbine blade102in fixture100, and applying force F to a second, opposing end (tip end108) of the blade. Protective member130may be applied to portion122of superalloy turbine blade102, and force F applied to the protective member. In one option, force F, as shown inFIG. 6, may be applied as a turning force to at least portion122of the blade.

As noted, force F is substantially similar to a force applied to superalloy turbine blade102during operation of the superalloy turbine blade in a turbomachine, i.e., it does not permanently deform it. As shown inFIG. 3, elastically deformed position124D may include: lateral deformation LD perpendicular to longitudinal axis A of superalloy turbine blade102and/or a twist R about longitudinal axis A of superalloy turbine blade102. In any event, at least portion122of superalloy turbine blade102has a curvature (SeeFIG. 3) in elastically deformed position124D (FIG. 3) not present in relaxed, initial position124R (FIG. 3). Certain fixtures and actuators may apply force F in a distributed manner along at least portion122of superalloy turbine blade102. For example, fixture100including clamping members222,224may apply a distributed force F, as shown inFIG. 9. Actuators120, as shown inFIGS. 1 and 2, could also be duplicated at select locations along the blade to provide a distributed force. For example,FIG. 16shows a schematic view in which three actuators120, similar to that shown inFIG. 1, are located at a number of locations along at least portion122of superalloy turbine blade102to apply a force F. In this example, actuators120may straighten the blade.

Regardless of how elastically deformed, as shown for example inFIG. 2, a hole146may be drilled generally span-wise through at least portion122of superalloy turbine blade102in elastically deformed position124D. As noted, the hole drilling may include STEM, and may include drilling a straight hole, as shown inFIG. 2, or at a constant radius curvature (CCR), as shown inFIG. 9. While one hole146has been illustrated, it is emphasized that any number of holes146may be drilled either alone or simultaneously.

As shown inFIG. 17, force F is released after the drilling, allowing superalloy turbine blade102to return to relaxed, initial position124R and hole146to take on a hole curvature within at least portion122of the blade. Hole146can be plugged or interconnected to other passages in any known fashion to create a cooling passage260in the blade. As shown inFIG. 17, hole146curvature may vary along at least portion122of the blade.

As described herein, embodiments of the disclosure provide methods and fixtures for elastically deforming superalloy turbine blades while also making them compatible for STEM drilling methods. Consequently, teachings of the disclosure provide for fabrication of long variable curvature cooling passages in large, late stage superalloy turbine blades, providing effective cooling for these blades.