Repair or remanufacture of blade platform for a gas turbine engine

Abstract

A method of remanufacturing a turbine blade having a platform includes placing a puck against a surface of the platform. The method may include electrical discharge machining an interface between the puck and the platform and brazing the puck to the platform. A total radial thickness of a finally remanufactured platform of the remanufactured turbine blade is greater than an initial radial thickness of the platform before remanufacturing the turbine blade.

Claims

1. A method of remanufacturing a turbine blade having a platform, the method comprising: placing a puck against a surface of the platform; electrical discharge machining an interface between the puck and the platform; and brazing the puck to the platform, wherein a total radial thickness of a finally remanufactured platform of the remanufactured turbine blade is greater than an initial radial thickness of the platform before remanufacturing the turbine blade.

2. The method according to claim 1, wherein the surface of the platform is a radially inward facing surface on an underplatform of the platform.

3. The method according to claim 2, wherein an entirety of the puck is disposed radially inward of a gas path side of the platform.

4. The method according to claim 1, wherein a gap between the puck and the platform is less than 0.005 (0.127 mm) after electrical discharge machining.

5. The method according to claim 1, further comprising installing the finally remanufactured turbine blade into a turbine engine.

6. The method according to claim 1, further comprising manufacturing the puck from a braze presintered preform (PSP).

7. The method according to claim 1, further comprising manufacturing the puck by casting the puck.

8. The method according to claim 1, further comprising tack welding the puck to the platform prior to brazing the puck to the platform.

9. The method according to claim 1, further comprising machining an underside of the platform to remove a crack from the platform and form the surface of the platform.

10. The method according to claim 9, wherein the underside of the platform is machined to remove the crack without penetrating through a gas path surface of the platform.

11. The method according to claim 1, further comprising coating the brazed puck.

12. The method according to claim 1, wherein a full perimeter of the puck is surrounded by the platform.

13. The method according to claim 1, wherein a radially inward side of the puck includes at least one of a turbulator, a rib, or dimples.

14. The method according to claim 1, wherein the electrical discharge machining is configured to remove material from the platform.

15. A method of remanufacturing a platform of a turbine blade, comprising: machining a surface of the platform to form a machined surface area of the platform, the platform having a machined radial thickness that is less than an initial radial thickness of the platform; forming a puck so that the puck has a shape that matches the machined surface area and forms an interference gap with the machined surface area that is no larger than 0.005 (0.127 mm); locating the puck against the machined surface area; and attaching the puck to the platform, wherein the machined radial thickness and a puck radial thickness together are greater than the initial radial thickness of the platform when remanufacturing of the platform is complete.

16. The method according to claim 15, wherein forming the puck includes one of: electrical discharge machining the puck via the platform, co-electrical discharge machining the puck and the platform, and electrical discharge machining the platform via the puck.

17. The method according to claim 15, wherein attaching the puck to the platform includes brazing the puck to the platform.

18. The method according to claim 17, wherein a full perimeter of the puck is surrounded by the platform.

19. The method according to claim 15, wherein the surface of the platform is a radially inward facing surface on an underplatform of the platform and the puck is disposed entirely radially inward of a gas path side of the platform.

20. A method of remanufacturing a platform of a turbine blade, comprising: removing material from a radially inward facing surface of the platform to remove a crack from the platform and form a recess in the platform, a full perimeter of the recess being surrounded by the platform; placing a puck against the recess; electrical discharge machining the puck so that the puck has a shape that matches the recess with an interference gap that is no larger than 0.005 (0.127 mm); brazing the puck within the recess, wherein a total radial thickness of a finally remanufactured platform of the remanufactured turbine blade is greater than an initial radial thickness of the platform before remanufacturing the turbine blade.

Description

DRAWINGS

(1) Various features will become apparent to those skilled in the art from the following detailed description of the disclosed non-limiting form. In order that the disclosure may be well understood, there will now be described various forms thereof, given by way of example, reference being made to the accompanying drawings, in which:

(2) FIG. 1 is a schematic cross-section of one example gas turbine engine;

(3) FIG. 2 is a schematic view of an example gas turbine engine in an industrial gas turbine environment;

(4) FIG. 3 is an enlarged schematic cross-section of a turbine section of the engine;

(5) FIG. 4 is an enlarged perspective view of a turbine rotor and single representative rotor blade of the engine;

(6) FIG. 5 is an expanded view of an underplatform region of the rotor blade;

(7) FIG. 6 is a flowchart illustrating a method to repair/remanufacture a platform of a turbine blade according to one disclosed non-limiting form;

(8) FIG. 7 is a perspective view of an example puck that is EDM to increase the thickness of the turbine blade platform;

(9) FIG. 8 is a perspective view of an underplatform region of the turbine blade with a puck according to one disclosed non-limiting form;

(10) FIG. 9 is a perspective view of an underplatform region of the turbine blade with a puck according to another disclosed non-limiting form;

(11) FIG. 10 is a perspective view of an underplatform region of the turbine blade with a puck according to another disclosed non-limiting form; and

(12) FIG. 11 is a perspective view of an underplatform region of the turbine blade with a puck according to another disclosed non-limiting form.

(13) The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way.

DETAILED DESCRIPTION

(14) The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features.

(15) FIG. 1 schematically illustrates a gas turbine engine 20. The gas turbine engine 20 generally includes a compressor section 24, a combustor section 26, a turbine section 28, a power turbine section 30, and an exhaust section 32. The engine 20 may be installed within a ground-mounted enclosure 40 (FIG. 2) typical of an industrial gas turbine (IGT). Although depicted as specific engine architecture in the disclosed non-limiting form, it should be understood that the concepts described herein are not limited to only such architecture as the teachings may be applied to other gas turbine architectures.

(16) The compressor section 24, the combustor section 26, and the turbine section 28 are collectively referred to as a gas generator that is operable to drive the power turbine section 30. The power turbine section 30 drives an output shaft 34 to power a generator 36 or other system. In one disclosed non-limiting form, the power turbine section 30 includes a free turbine with no physical connection between the gas generator and the power turbine section 30. The generated power is a thereby a result of mass flow capture by the otherwise free power turbine.

(17) With reference to FIG. 3, an enlarged schematic view of a portion of the turbine section 28 is shown by way of example; however, other engine sections will also benefit herefrom. A full ring shroud assembly 60 mounted to an engine case structure 36 supports a Blade Outer Air Seal (BOAS) assembly 62 with a multiple of circumferentially distributed BOAS 64 proximate to a rotor assembly 66 (one schematically shown). The full ring shroud assembly 60 and the BOAS assembly 62 are axially disposed between a forward stationary vane ring 68 and an aft stationary vane ring 70. Each vane ring 68, 70 includes an array of vanes 72, 74 that extend between a respective inner vane platform 76, 78, and an outer vane platform 80, 82. The outer vane platforms 80, 82 are attached to the engine case structure 36.

(18) The rotor assembly 66 includes an array of blades 84 (one shown in FIG. 4) circumferentially disposed around a disk 86. Each blade 84 includes a root 88, a platform 90, and an airfoil 92. Each blade root 88 is received within a rim 94 of the disk 86 such that the airfoils 92 extend radially outward so that a tip 96 of each airfoil 92 is adjacent the BOAS assembly 62. The blades 84 are typically manufactured of, for example, a Nickel Alloy.

(19) Combustion gases produced in the combustor section 26 (indicated schematically by arrow C) expand in the turbine section 28 and produce pressure gradients, temperature gradients, and vibrations. The turbine components in the turbine section 28 are thereby subject to thermal-mechanical fatigue that, over time, may generate cracks in these components.

(20) With reference to FIG. 5, the platform 90 generally separates the root 88 and the airfoil 92 to define an inner boundary of the core gas path. The airfoil 92 defines a blade chord between a leading edge 98, which may include various forward and/or aft sweep configurations, and a trailing edge 100. A first airfoil sidewall 102 that may be convex to define a suction side, and a second airfoil sidewall 104 that may be concave to define a pressure side are joined at the leading edge 98 and at the axially spaced trailing edge 100. The platform 90 includes a gas path side 106 adjacent to the airfoil 92 and a non-gas path side 108 adjacent to the root 88. Here, the non-gas path side 108 of the platform 90 generally below the second airfoil sidewall 104 is referred to as the underplatform 110.

(21) Thermal-mechanical fatigue cracks may occur on the underplatform 110 and can be removed via machining. This machining, however, thins the platform 90, and applicant has determined that the frequency and amplitude of occurrence of such cracks resulting from use subsequent to such machining is related to the thickness of the platform 90. The thickness of the platform 90, in an exemplary form may range from about 0.100-0.200 inches (2.5-5.1 mm), depending in part upon casting and/or previous repairs.

(22) With reference to FIG. 6, one disclosed non-limiting form of a repair method 200 initially includes manufacture of a puck 120 (FIG. 7; step 202). The puck 120 may be machined, cast, or otherwise manufactured from, for example, a superalloy with grains that will be aligned with the engine axis A. Alternatively, the puck 120 may be manufactured from braze presintered preform (PSP). Such initial manufacture provides a puck 120 with dimensions that are close to the underplatform pocket formed by blade 84.

(23) The puck 120, in this disclosed non-limiting form, is generally semi-circular in shape with an arcuate side 122 that closely fits adjacent to the blade root 88 and a straight side 124 that generally aligns with an edge 90A (FIG. 5) of the platform 90. The puck 120 includes end sections 126, 128 that may be clipped or otherwise shaped for engagement within the underplatform 110 pocket of the non-gas path side 108 (FIG. 7). In this disclosed non-limiting form, the puck 120 is has a thickness of about 0.030-0.375 (0.762-9.525 mm).

(24) Next, the puck 120 is subject to Electrical discharge machining (EDM) (step 204). Electrical discharge machining (EDM) is a highly accurate method of machining metal materials in which material is removed from the workpiece by a series of rapidly recurring current discharges between two electrodes separated by a dielectric liquid, and subject to an electric voltage. One electrode is referred to as the tool-electrode, or simply, the tool, while the other is referred to as the workpiece-electrode, or workpiece. Generally, the tool serves as a working electrode to facilitate removal of material from the workpiece. Here, the polarity is reversed from normal EDM operation such that the blade 84 is the working electrode and the puck 120 is the machined part. That is, the underplatform 110 of the blade 84 (the tool), electro discharge machines the puck 120 (the workpiece).

(25) The puck 120 is plunged into the underplatform 110 to remove material from the puck 120 until both parts create a near perfect fit one to another. Such a near perfect fit enhances braze strength, as it is desired for braze faying surfaces to have a gap no larger than about 0.005 (0.127 mm). That is, the puck 120 is initially cast and/or machined to be close to the dimension of the area of the underplatform 110, then subjected to the reverse EDM process to obtain a close-fitting gap therebetween. Trials have shown a finished gap of about 0.0005-0.0045 (0.0127-0.1143 mm).

(26) Next, the puck 120 and the underplatform 110 area are weld prepared (step 206). Weld preparation includes, but is not limited to, for example, degreasing, fluoride-ion cleaning, grit blast, hydrogen furnace clean, vacuum clean and/or others.

(27) Next, the EDM machined platform puck 120 is then located in the blade underplatform 110 pocket and tack welded thereto (step 208). It should be appreciated that various methods may be alternatively or additionally provided to affix the puck 120 to the underplatform 110 so as to facilitate brazing (step 210).

(28) A braze slurry is then applied around a perimeter of the puck 120 and subsequently brazed via the application of heat to the blade 84, puck 120, and braze slurry (step 210). The braze slurry flows over and around the puck 120 to join the puck 120 to the underplatform 110. Since brazing does not melt the base metal of the joint, brazing allows much tighter control over tolerances and produces a clean joint with minimal-if-any need for secondary finishing. Additionally, dissimilar metals and non-metals (i.e. metalized ceramics) can be brazed. That is, the puck 120 may be manufactured of a material dissimilar to that of the blade 84.

(29) The braze slurry is readily received into the close finished gap interface between the platform puck 120 and the underplatform 110 via capillary action to provide an effective braze therebetween. That is, the reverse EDM interface provides a close-fitting interface that facilitates a high strength brazed interface and does not further reduce the thickness of the platform 90.

(30) Finally, the finished braze B may be blended and coated to form a desired profile (step 212; FIG. 8). The blend may be performed by hand and/or by machine operations.

(31) With reference to FIG. 9, the platform puck 120 can replicate the OEM shape of the underplatform, or incorporate improved cooling and/or strengthening features such as chevron-shaped turbulators 300, a multiple of ribs 400 (FIG. 10), a multiple of dimples 500 (FIG. 11) or other such features. The features facilitate turbulation of a cooling airflow to further control the thermal effects on the turbine blade 84.

(32) The method 200 provides a repair to a small portion of the component to increase platform thickness with the remainder being identical to an OEM component. The Reverse EDM machining also facilitates a relatively rapid repair.

(33) The use of the terms a, an, the, and similar are to be construed to cover both the singular and the plural, unless otherwise indicated herein or specifically contradicted by context. The modifier about used in connection with a quantity is inclusive of the stated value and has the meaning dictated by the context (e.g., it includes the degree of error associated with measurement of the particular quantity). All ranges disclosed herein are inclusive of the endpoints, and the endpoints are independently combinable with each other. 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.

(34) Although the different non-limiting forms have specific illustrated components, the forms 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 forms in combination with features or components from any of the other non-limiting forms.

(35) 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 form, other arrangements will benefit herefrom.

(36) Unless otherwise expressly indicated herein, all numerical values indicating mechanical/thermal properties, compositional percentages, dimensions and/or tolerances, or other characteristics are to be understood as modified by the word about or approximately in describing the scope of the present disclosure. This modification is desired for various reasons including industrial practice, manufacturing technology, and testing capability.

(37) The description of the disclosure is merely exemplary in nature and, thus, variations that do not depart from the substance of the disclosure are intended to be within the scope of the disclosure. Such variations are not to be regarded as a departure from the spirit and scope of the disclosure.

(38) As used herein, the phrase at least one of A, B, and C should be construed to mean a logical (A OR B OR C), using a non-exclusive logical OR, and should not be construed to mean at least one of A, at least one of B, and at least one of C.