Method for machining turbine components using reference surfaces - Patent Application 20070122947

Abstract

A method for repairing a turbine blade includes positioning the turbine blade in a system including a machining tool, determining a first distance between a surface of a first PSP attached to a tip shroud of the turbine blade and a reference surface formed in the tip shroud, removing the first PSP from the tip shroud, coupling a second PSP to the tip shroud, and machining a surface of the second PSP using the machining tool, wherein machining the surface of the second PSP includes controlling movement of the machining tool using the reference surface as a reference so that the machined surface of the second PSP is located a first distance from the reference surface.

Description

[Technical Field]

[0001] The field of the disclosure relates generally to turbine blades used with rotary machines, and more particularly to methods of manufacturing and repairing turbine blades having pre-sintered preform layers in which a reference surface is used to machine the pre-sintered preform layers. [Background technology]

[0002] At least some known rotary machines include at least one rotor assembly coupled to a rotor shaft. The rotor assembly includes a plurality of circumferentially spaced blades extending radially outward toward a stationary casing that defines a portion of a hot gas flow path through the rotary machine. A plurality of stationary vanes (or nozzles) are coupled to the casing in a circumferential array such that the stationary vanes extend radially inward into the flow path. The stationary vanes and rotating blades are arranged in alternating rows such that a row of vanes and an immediately downstream row of blades form a "stage" of the rotary machine. The vanes direct the hot gas flow toward a downstream row of buckets where the blades extract energy from the flow, thereby generating the electrical power required to drive the rotor and / or an attached load, such as a generator. For example, without limitation, the rotor assembly may be part of a steam turbine or part of the compressor or turbine section of a gas turbine engine.

[0003] Some turbine hot gas path components can include one or more sheets of material applied over a portion of the underlying component. For example, during pre-sintered preform (PSP) manufacturing, one or more sheets of material are brazed to at least some turbine components, such as shrouded blades or nozzles. The PSP is usually superimposed and brazed onto the component to form an exterior surface. Typically, the sheets are substantially flat or include a curvature that generally resembles the overall geometry of the component surface to which they are attached; however, by pressure, bending, etc., these flat sheets can conform to the underlying component surface during the attachment process.

[0004] At least some gas turbine components include shrouds at the outer ends of the airfoils. The shrouds are typically designed with an interlocking mechanism that allows each component to interlock with its immediately adjacent components when such components are mounted around the turbine disk. This interlocking mechanism helps prevent the airfoils from vibrating, thereby reducing stresses on the components during operation.

[0005] Turbine hot gas path components are typically made from nickel-based superalloys or other high-temperature superalloys designed to retain high strength at high temperatures. However, the materials used in making turbine component shrouds and interlocking mechanisms may not be hard enough to withstand long-term exposure to frictional stresses and / or wear that may occur during turbine engine start-up and shutdown. To improve wear at these locations, hardfaced pre-sintered preforms (PSPs) can be brazed or welded to the components to serve as wear surfaces. The hardfaced material protects each respective component and associated shroud from wear resulting from frictional contact during operation when the turbine component is subjected to centrifugal force, pressure, heat, and / or vibration loads.

[0006] Conventional fabrication and / or reconditioning of turbine components that include hardface PSPs typically requires removing the existing PSP from the component, re-brazing or re-welding a new hardface PSP to the component, and machining the new hardface PSP to a target profile. Machining of the hardface PSP is typically performed using a multi-axis computer numerically controlled (CNC) unit. The CNC unit allows movement of a cutting tool along several axes, including X-, Y-, and Z-axes, as well as a rotational axis. When machining the hardface PSP, the movement of the CNC unit is guided by a coordinate system that relies on data collected from the component to ensure the target profile of the hardface PSP is achieved.

[0007] Typically, a distinct location on a component (e.g., a mid-span shroud) is used as an origin (reference point), and the relative rotation and / or translation of the portion of the component where the hardface PSP is applied (e.g., the tip shroud of an airfoil) is calculated relative to the origin to derive a coordinate system for guiding a CNC unit. The data is collected and stored before removing the existing PSP. After a new hardface PSP is applied, the reference point is probed, and the stored data is analyzed to determine the final translation and rotation derived from the coordinate system transformation to guide the CNC unit in machining the new PSP. Conventional processes such as these can be limited because they rely on the use of reference points that are not located on the portion of the component where the PSP is applied. Thus, the process of deriving translation and rotation data from the coordinate system transformation requires a fairly high degree of accuracy of the same location on the component during initial and final machining, as well as during data storage. Errors in machining hardface PSPs can be amplified due to indirect or inaccurate localization, multiple probing, transformation, and / or data storage errors.

[0008] Therefore, there is a need to simplify the manufacturing and / or reconditioning of turbine components that involve processing pre-sintered preforms so that the process can be reproduced and the above-mentioned problems are reduced and / or eliminated. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] US Patent Application Publication No. 2022 / 0145765 Summary of the Invention

[0010] In one aspect, a method for repairing a turbine blade is provided. The turbine blade includes a tip shroud and a first pre-sintered preform (PSP) attached to the tip shroud. The method includes positioning the turbine blade in a system including a machining tool, determining a first distance between a surface of the first PSP and a reference surface formed in the tip shroud, removing the first PSP from the tip shroud, coupling a second PSP to the tip shroud, and machining the surface of the second PSP using the machining tool, where machining the surface of the second PSP includes controlling movement of the machining tool using the reference surface as a reference so that the machined surface of the second PSP is located the first distance from the reference surface.

[0011] In another aspect, a method for repairing a turbine component is provided. The turbine component includes a first hardened surface structure and a second hardened surface structure. The method includes positioning the turbine component in a system including a machining tool, determining a first distance between a surface of the first hardened surface structure and a reference surface formed in the turbine component, removing the first and second hardened surface structures from the turbine component, bonding a third hardened surface structure to the turbine component, bonding a fourth hardened surface structure to the turbine component, machining the surface of the third hardened surface structure using the machining tool, where machining the surface of the third hardened surface structure includes controlling movement of the machining tool using the reference surface as a reference such that the machined surface of the third hardened surface structure is located the first distance from the reference surface, and machining the surface of the fourth hardened surface structure using the machining tool to a second distance measured between the surfaces of the machined third hardened surface structure and the machined fourth hardened surface structure.

[0012] In another aspect, a method for repairing a turbine blade is provided. The turbine blade includes a tip shroud and first and second pre-sintered preforms (PSPs) attached to the tip shroud. The method includes positioning the turbine blade in a system including a machining tool, controlling the machining tool to machine a reference surface in the tip shroud, removing the first and second PSPs from the tip shroud, coupling third and fourth PSPs to the tip shroud, controlling the machining tool to machine the third PSP using the reference surfaces as a reference, and controlling the machining tool to machine the fourth PSP after machining the third PSP.

[0013] These and other features, aspects, and advantages of the present disclosure will be better understood from the following detailed description when read in conjunction with the accompanying drawings, in which like characters represent like parts throughout. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a schematic diagram of an exemplary rotating machine; [Figure 2] FIG. 2 is a front view of an exemplary turbine blade that may be used with the rotary machine of FIG. 1. [Figure 3] FIG. 3 is a front perspective view of the tip shroud of the turbine blade of FIG. 2. [Figure 4] FIG. 3 is a rear perspective view of the tip shroud of the turbine blade of FIG. 2. [Figure 5] 5 illustrates an exemplary process for manufacturing a turbine blade including a pre-sintered preform attached to the tip shroud of FIGS. 3 and 4. FIG. [Figure 6] FIG. 6 is a schematic diagram of an exemplary system for carrying out the process of FIG. 5. DETAILED DESCRIPTION OF THE INVENTION

[0015] Corresponding reference characters used throughout the drawings indicate corresponding parts. Unless otherwise specified, the drawings provided herein illustrate features of embodiments of the present disclosure. These features are believed to be applicable in a wide variety of systems incorporating one or more embodiments of the present disclosure. Thus, the drawings are not intended to include all conventional features known to those skilled in the art that are required for the practice of the embodiments disclosed herein.

[0016] The embodiments described herein provide a method for manufacturing (e.g., reconditioning) a component used in a rotary machine, such as a blade used in a turbine engine. The turbine blade includes a tip shroud and a first pre-sintered preform (PSP) attached (e.g., brazed or welded) to the tip shroud. A reference surface is formed (e.g., machined) in the tip shroud so that it is oriented substantially parallel to an outer surface defined by the first PSP. The reference surface is used as a reference point for machining a PSP that is subsequently attached to the tip shroud. In particular, the reference surface is located a distance from the outer surface defined by the first PSP. This distance is determined (e.g., may be predetermined, fixed, or determined in situ). The first PSP is then removed during the reconditioning process, for example, if the turbine blade was previously used during operation of the turbine engine and the first PSP experienced operational wear. A second PSP is then coupled to the tip shroud at the same location as the removed first pre-sintered preform. The second PSP is then machined to a target profile such that the second PSP defines the outer surface of the component.

[0017] Advantageously, the datum surface is used as an origin (reference point) during machining of the second PSP to facilitate machining of the second PSP to substantially the same profile as the first PSP. For example, the second PSP is machined so that the outer surface defined by the second PSP substantially coincides with the outer surface defined by the first PSP. Moreover, after machining, the outer surface defined by the second PSP is oriented substantially parallel to the datum surface and is located substantially the same distance from the datum surface as the outer surface defined by the first PSP. Compared to conventional methods of realigning turbine blades having PSPs attached to tip shrouds, the embodiments described herein facilitate reducing errors and increasing accuracy and repeatability when machining PSPs using datum surfaces formed in the tip shroud.

[0018] Unless otherwise specified, terms expressing approximation, such as "generally," "substantially," and "about," used herein indicate that the modified term may apply only to an approximate degree, as recognized by one of ordinary skill in the art, rather than to an absolute or complete degree. Thus, values ​​modified by terms such as "about," "approximately," and "substantially" are not limited to the exact value specified. In at least some cases, approximation terms may correspond to the precision of an instrument for measuring the value. Furthermore, unless otherwise indicated, terms such as "first," "second," and "second" are used herein merely as labels and do not impose any ordering, positioning, or hierarchical requirements on the items they refer to. Furthermore, for example, a reference to a "second" item does not require or exclude the presence of, for example, a "first" item or a lower-numbered item, or a "third" or a higher-numbered item. As used herein, the term "upstream" refers to the forward or inlet end of a rotary machine, and the term "downstream" refers to the downstream or exhaust end of a rotary machine.

[0019] As used herein, the phrases "hardface structure," "pre-sintered preform," or "PSP" refer to a structure, component, or composition that improves the wear resistance of a component to which the hardface structure or PSP is attached (e.g., brazed or welded). The hardface structure or pre-sintered preform may be a sintered powder metallurgy product containing a homogeneous mixture of a superalloy base material and a braze alloy powder. The PSP braze material may include a superalloy. "Superalloy" refers to an alloy that has many superior physical properties compared to conventional alloys, including, but not limited to, high mechanical strength and high thermal creep deformation resistance. Exemplary superalloys include, but are not limited to, iron-based superalloys, nickel-based superalloys, or cobalt-based superalloys. In some examples, the PSP braze material may include, in addition to a base metal, at least one of aluminum (Al), titanium (Ti), chromium (Cr), tungsten (W), molybdenum (Mo), rhenium (Re), tantalum (Ta), silicon (Si), boron (B), or iron (Fe).

[0020] As used herein, the "X-axis," "Y-axis," and "Z-axis" refer to mutually perpendicular axes (i.e., each perpendicular to the other) and are used to describe three-dimensional aspects or orientations. The description of the elements of the subject matter disclosed herein is not limited to the particular axis or axes used to describe the three-dimensional orientation of the elements. In other words, the axes may be interchangeable when referring to three-dimensional aspects of the disclosed subject matter.

[0021] 1 is a schematic diagram of an exemplary rotary machine 110. In the exemplary embodiment, rotary machine 110 is a gas turbine engine. Alternatively, rotary machine 110 may be any other turbine engine and / or rotary machine, including, but not limited to, a steam turbine engine, a gas turbofan aircraft engine, other aircraft engines, a wind turbine, a compressor, and / or a pump. In the exemplary embodiment, gas turbine 110 includes a rotor assembly 112 that includes a shaft 114 and a plurality of axially spaced rotor wheels 118.

[0022] A plurality of rotating blades 120 are coupled to each rotor wheel 118 such that each blade 120 extends radially outward from each respective rotor wheel 118. More specifically, blades 120 are arranged in rows that extend circumferentially around each wheel 118. A plurality of stationary vanes 122 extend circumferentially around shaft 114 such that each row of stationary vanes 122 is between a pair of axially adjacent rows of blades 120. For example, turbine 110 includes a plurality of stages that include rows of stationary vanes 122 and rows of rotating blades 120 extending from rotor wheels 118.

[0023] A compressor 124 is coupled downstream from intake section 123, and a plurality of combustors 126 are coupled circumferentially around rotor assembly 112 such that each combustor 126 is in flow communication with compressor 124. An exhaust section 130 is coupled downstream from turbine 110. Turbine 110 is rotatably coupled to compressor 124 via shaft 114.

[0024] During operation, air at atmospheric pressure is compressed by the compressor 124 and delivered downstream to the combustor 126. The air exiting the compressor is heated by adding fuel to the air and burning the resulting air / fuel mixture. The gas stream resulting from the combustion of the fuel in the combustion stage then expands through the turbine 110 and delivers some of its energy to drive the turbine 110 and a load, such as a generator.

[0025] To generate the required driving torque, turbine 110 consists of one or more stages, each including a row of stationary vanes 122 and a row of rotating blades 120 mounted on rotor wheel 118. Stationary vanes 122 direct incoming gases from the combustion stage onto rotating blades 120, thereby driving rotor wheel 118 and rotor shaft 114.

[0026] 2 is a front view of an exemplary turbine blade 200 that may be used with a rotary machine (e.g., as blade 120 used with rotary machine 110 shown in FIG. 1 ). Additionally or alternatively, turbine blade 200 may be used with other electrically powered turbomachines, including, but not limited to, gas turbofan aircraft engines, other aircraft engines, steam turbines, wind turbines, compressors, fans, and / or pumps. In the exemplary embodiment, each turbine blade 200 in a circumferential row of rotary machine 110 has substantially the same configuration as the other turbine blades in that row. In an alternative embodiment, at least one turbine blade 200 in each row may be different from the remaining blades in that row.

[0027] Turbine blade 200 includes an airfoil portion or airfoil 202 including a leading edge 204 and an opposite trailing edge 206. A pressure sidewall 208 and a suction sidewall 210 each extend from leading edge 204 to trailing edge 206. Turbine blade 200 also includes a root 212 that enables blade 200 to be installed in a rotary machine, such as rotary machine 110 (shown in FIG. 1 ). Root 212 enables, for example, turbine blade 200 to be coupled to turbine rotor wheel 118 of rotary machine 110. In the exemplary embodiment, root 212 is in the form of a dovetail 212. Airfoil 202 and root 212 are separated by a platform 214, which may include an “angel wing” seal (not shown).

[0028] The airfoil 202 extends between a platform 214 and a tip shroud 216 fixedly coupled to the radially outer end of the airfoil 202 opposite the platform 214. The pressure sidewall 208 is generally concave and the suction sidewall 210 is generally convex. As a result, the airfoil 202 has an arcuate profile. The curvatures of the pressure sidewall 208 and the suction sidewall 210 that define the arcuate profile of the airfoil 202 may vary depending on the particular turbine and stage in which the airfoil 202 is intended for use. The present disclosure is not limited to any particular shape of the airfoil 202, and the embodiments disclosed herein are suitable for use with airfoils 202 of various shapes.

[0029] Airfoil 202 also includes a pair of part-span shrouds 218 and 220 that facilitate tuning and / or damping vibration characteristics of airfoil 202 during operation. Part-span shrouds 218 and 220 extend outwardly from airfoil 202 in a mirror image relationship. More specifically, shroud 218 extends outwardly from airfoil pressure sidewall 208, and shroud 220 extends outwardly from airfoil suction sidewall 210. In the exemplary embodiment, part-span shrouds 218 and 220 extend outwardly from their respective sidewalls 208 and 210 at the same radial span. The part-span shrouds 218 and 220 of each circumferential row of turbine blades 200 of each stage of rotary machine 110 may be substantially circumferentially aligned such that each of the shrouds 218 and 220 extends outward from the respective airfoil 202 at the same radial span location. Alternatively, the shrouds 218 and 220 may extend outward from the respective airfoil 202 at different radial span locations. The part-span shrouds 218 and 220 may have the same size and shape and each extend an equal axial distance from the respective sidewalls 208 and 210, or alternatively, the shrouds 218 and 220 may be different shapes and / or sizes from one another.

[0030] As mentioned above, the turbine blade 200 includes a tip shroud 216 coupled to the radially outer end of the airfoil 202. Alternatively, the tip shroud 216 may be integral with the airfoil 202. The tip shroud 216 may generally define the radially outermost portion of the blade 200, with the tip shroud 216 providing a surface area extending substantially perpendicular to the airfoil 202 to cap or cover the tip of the airfoil 202. During operation, the tip shroud 216 engages two adjacent tip shrouds 216 of adjacent blades 200 at opposite ends to form an approximately annular ring or shroud that circumscribes the hot gas path at the stage location of the blade 200. This annular ring contains the expanding gases of the hot path above the airfoil 202 (i.e., does not allow the gases to slide over the ends of the airfoil blades) so that a greater proportion of energy from the working fluid can be converted to mechanical energy by the turbine blade. Thus, tip shrouds generally improve the performance of gas turbines.

[0031] 3 and 4 show tip shroud 216 in more detail. As shown, tip shroud 216 includes a seal rail 222 extending between a first end 224 and a second end 226 of the tip shroud. Alternate embodiments may include more seal rails 222 (e.g., two seal rails 222, three seal rails 222, etc.) or no seal rails 222 at all. As understood in the art, seal rails 222 may have any of a variety of cooling passages (not shown) extending therethrough for cooling tip shroud 216.

[0032] Tip shroud 216 also includes a radially outer surface 228 that lies in an XY plane that includes the X-axis and the Y-axis. Seal rail 222 extends radially outward from radially outer surface 228 in the Z-axis direction. Radially outer surface 228 spans a leading edge portion 230 of tip shroud 216 and a trailing edge portion 232 of tip shroud 216. A leading edge wall 234 surrounds the periphery of leading edge portion 230. A trailing edge wall 236 surrounds the periphery of trailing edge portion 232. Leading edge wall 234 and trailing edge wall 236 each extend downward from radially outer surface 228. Leading edge portion 230 of tip shroud 216 is fixedly coupled to leading edge 204 of airfoil 202. Trailing edge portion 232 of tip shroud 216 is fixedly secured to trailing edge 206 of airfoil 202.

[0033] 3 and 4, blade 200 also includes a hardfacing structure attached to tip shroud 216. The hardfacing structures in the exemplary embodiment are pre-sintered preform structures 238 and 240, also referred to as pre-sintered preforms 238 and 240, or PSPs 238 and 240. PSP 238 is coupled (e.g., brazed or welded) to first end 224 of tip shroud 216, and PSP 240 is coupled (e.g., brazed or welded) to second end 226 of tip shroud 216. Each PSP 238 and 240 functions as a wear component to facilitate improved wear characteristics of tip shroud 216 at first end 224 and second end 226, respectively, thereby facilitating an extended service life for the associated blade 200. In particular, PSP 238 and PSP 240 attached to respective ends 224 and 226 facilitate protecting tip shroud 216 from wear resulting from frictional contact during operation at these locations when tip shroud 216 is subjected to centrifugal forces, pressure, heat, and vibration loads. In some embodiments, each of PSP 238 and PSP 240 is coupled to first end 224 and second end 226, respectively, by brazing.

[0034] Each of the PSPs 238 and 240 has a suitable predetermined shape when attached to the respective ends 224 and 226 of the tip shroud 216. For example, the PSPs 238 and 240 have substantially the same geometric shape as the respective ends 224 and 226 and cover the seal rail 222 at the respective ends 224 and 226. When attached, the PSPs 238 and 240 each define an outer surface 242 and 244, respectively. The outer surfaces 242 and 244 extend substantially parallel to each other and substantially perpendicular to the radially outer surface 228. Thus, the outer surfaces 242 and 244 each lie in a ZY plane that includes the Z-axis and the Y-axis. The PSPs 238 and 240 also have a suitable thickness, measured as the distance in the X-axis direction extending between the respective outer surfaces 242 and 244 and the respective ends 224 and 226 to which the PSPs 238 and 240 are attached.

[0035] After being attached to their respective ends 224 and 226, the PSPs 238 and 240 may be machined to ensure that their respective outer surfaces 242 and 244 are substantially planar and to remove excess material from the PSPs 238 and 240. Machining of the PSPs 238 and 240 may be performed using any now-known or later-developed machining process, such as, but not limited to, electrical discharge machining (EDM), wire EDM, grinding, laser cutting, etc. The machining tool (e.g., the machining tool 602 in FIG. 6 ) is operably coupled to a motion device (e.g., the computer numerical control unit 604 in FIG. 6 ) that communicates with a controller (e.g., the controller 610 in FIG. 6 ). The motion device may be a gantry system, a computer numerically controlled (CNC) machine, a Cartesian robot, or other suitable system that facilitates multi-axis movement of the machining tool. The controller is used to control the multi-axis movement of the motion device to guide the tool path of the machining tool. To further illustrate the invention, the motion device may also be referred to as a CNC unit or CNC system.

[0036] During operation, PSP 238 and PSP 240 may deteriorate or degrade due to exposure to loads (e.g., mechanical, vibration, and / or thermal loads). Reconditioning of blade 200 may include replacing one or both of PSP 238 and / or PSP 240 with new PSP 238 and / or new PSP 240. Typically, the original PSP 238 and / or PSP 240 is removed, and the new PSP 238 and / or PSP 240 is attached (e.g., brazed or welded) to the respective ends 224 and 226 of tip shroud 216. The new PSP 238 and / or PSP 240 is then machined to the target profile (e.g., by flattening the respective outer surfaces 242 and 244 and removing excess material).

[0037] During machining of new PSP 238 and / or PSP 240, the movement of a motion device operably coupled to the machining tool is guided by a coordinate system. In particular, the target profile of PSP 238 and / or PSP 240 references the X, Y, and Z axes and translates to coordinate values ​​in an X, Y, and Z Cartesian coordinate system relative to an origin in the coordinate system. As an example, outer surface 242 and / or outer surface 244 are machined according to Z and Y coordinate values ​​at a fixed X coordinate value relative to the origin. By defining the X, Y, and Z coordinate values ​​of PSP 238 and / or PSP 240, the target profile of PSP 238 and / or PSP 240 can be identified with increased accuracy, and the motion device operably coupled to the machining tool can be guided accordingly.

[0038] 5, a method 300 for manufacturing (e.g., reconditioning) turbine blade 200 (shown in FIG. 2) having tip shroud 216 (shown in FIGS. 3 and 4) is shown. While method 300 is described in the context of reconditioning turbine blade 200, it will be understood that method 300 may also be used in the initial fabrication of turbine blade 200 (e.g., before turbine blade 200 is used with turbine engine 110 during operation).

[0039] Method 300 may be implemented using a system 600 ( FIG. 6 ) including a machining tool (e.g., machining tool 602 of FIG. 6 ) operably coupled to a multi-axis computer numerically controlled (CNC) unit (e.g., CNC unit 604 of FIG. 6 ). System 600 may be referred to herein as a CNC system. In various embodiments, machining tool 602 may be, for example, an electrical discharge machining (EDM) tool, a wire EDM tool, a grinding tool, a laser cutting tool, or the like. CNC systems for use with machining tools are known in the art and are described, for example, in U.S. Pat. No. 7,351,290 (S. Rutkowski et al.), which is incorporated herein by reference in its entirety. The CNC unit (e.g., unit 604) facilitates movement of the machining tool (e.g., machining tool 602) along several X-, Y-, and Z-axes.

[0040] Method 300 will be described with further reference to system 600 shown in Figure 6, which includes a machining tool 602 operably coupled to a CNC unit 604. To begin method 300, turbine blade 200 is placed on, or installed within, CNC unit 604. For example, turbine blade 200 may be placed on a work support 606 of CNC unit 604. Turbine blade 200 loaded onto the work support is represented schematically in Figure 6 by a workpiece 608 positioned on work support 606.

[0041] The CNC unit 604 is operable to move the machining tool 602 relative to the workpiece 608 along one or more of an X-axis, a Y-axis, and a Z-axis. The work support 606 may also be operable to move the workpiece about or along one or more axes relative to the machining tool 602. A sensor 612 (e.g., a contact probe, a camera, or a tool sensor) is mounted within the system 600 (e.g., on the CNC unit 604) to calibrate and / or position the machining tool 602 relative to the workpiece 608. One or more sensors 612 may be included and mounted in the system 600 to enable the system to function as described herein.

[0042] In the exemplary embodiment, system 600 includes a controller 610 communicatively coupled to a machining tool 602, a CNC unit 604, a work support 606, and sensors 612. Controller 610 can communicate with one or more of these components via a communication interface communicatively coupled to one or more of these components. The communication interface may include, but is not limited to, a wired network adapter, a wireless network adapter, a mobile telecommunications adapter, a serial communication adapter, or a parallel communication adapter. The communication interface can receive data signals from or transmit data signals to one or more remote devices, such as machining tool 602, CNC unit 604, work support 606, and / or sensors 612.

[0043] The controller 610, via the processor 614, is operable to control the components of the system 600 (e.g., the machining tool 602, the CNC unit 604, the work support 606, and the sensor 612) by executing instructions stored in a memory device 616 communicatively coupled to the processor 614. The processor 614 may include one or more processing units, such as, for example, a multi-core configuration. The memory device 616 is one or more devices that allow for the storage and retrieval of information, such as executable instructions or other data. The memory device 616 may include one or more computer-readable media, such as, for example, but not limited to, random access memory (RAM), dynamic RAM, static RAM, a solid-state disk, a hard disk, a read-only memory (ROM), erasable programmable ROM, electrically erasable programmable ROM, or non-volatile RAM memory. The above memory types are merely exemplary and thus do not limit the types of memory that may be used to store computer programs.

[0044] The processor 614 may be programmed by encoding operations as one or more executable instructions and providing the executable instructions in the memory device 616. In various embodiments, the processor 614 may be programmed to coordinate and control movement of the CNC unit 604, the machining tool 602, and / or the work support 606 in any one or combination of the X-axis, Y-axis, and Z-axis. In this regard, the processor 614 may be programmed to control multi-axis movement of the machining tool 602 relative to the workpiece 608. The processor 614 may adjust power settings of the machining tool 602, including, for example, adjusting the amount of force (e.g., mechanical and / or electrical) applied by the machining tool 602 to the workpiece 608.

[0045] The memory device 616 may store data related to the operation of the system 600, including, but not limited to, real-time and historical operating parameter values, or any other type of data. The memory device 616 may store instructions executable by the processor 614 to control the CNC unit 604, the work support 606, and / or the machining tool 602, for example, based on a desired shape of the workpiece 608. The desired shape of the workpiece 608 may be defined by a three-dimensional drawing file (e.g., obtained from a CAD / CAM program) stored in the memory device 616. In some embodiments, the memory device 616 may include, but is not limited to, sufficient data, algorithms, and commands to enable the processor 614 to control the components of the system 600 to function as described herein.

[0046] In some embodiments, controller 610 includes a presentation interface 618 coupled to processor 614. Presentation interface 618 presents information, such as a user interface, to an operator of system 600. In one embodiment, presentation interface 618 includes a display adapter (not shown) coupled to a display device (not shown), such as a cathode ray tube (CRT), a liquid crystal display (LCD), an organic light-emitting diode (OLED) display, or an “electronic ink” display. In some embodiments, presentation interface 618 includes one or more display devices. Additionally or alternatively, presentation interface 618 includes an audio output device (not shown), such as, for example, without limitation, an audio adapter, a speaker, or a printer (not shown).

[0047] In some embodiments, controller 610 includes a user input interface 620. In an exemplary embodiment, user input interface 620 is coupled to processor 614 and receives input from an operator. User input interface 620 can include, for example, but is not limited to, a keyboard, a pointing device, a mouse, a stylus, a touch-sensitive panel such as, but not limited to, a touchpad or touchscreen, and / or an audio input interface such as, but not limited to, a microphone. A single component, such as a touchscreen, can function as both the display device of presentation interface 618 and user input interface 620.

[0048] The method 300 includes identifying or determining (302) an initial reference plane (first origin) for the controller 610 to control the movement of the machining tool 602 (e.g., via the CNC unit 604). In order for the controller 610 to control the movement of the machining tool 602 as accurately as possible, the controller needs to know the location of the machining tool with high accuracy. A sensor 612 may be used to determine the reference plane, which may then be processed by the controller 610 to control the movement of the machining tool 602 via the CNC unit 604. The sensor 612 used to determine the reference plane may be, for example, a contact probe. The position of the machining tool 602 can be calibrated to such a probe by noting the probe axis scale position when contact with the probe occurs. From the observed deviation between the programmed position and the actual position, a compensating offset may be determined and stored in the memory device 616 of the controller 610. The offset compensates for the difference between the programmed contact position and the actual contact position of the machining tool 602.

[0049] In the exemplary method 300, determining 302 the initial reference surface includes probing the outer surface of the workpiece 608 in the area to be machined. For example, sensor 612 may be used to probe the outer surface of a PSP of the turbine blade (e.g., outer surface 242 of PSP 238 or outer surface 244 of PSP 240) that will be removed and replaced during reconditioning of turbine blade 200. The probed surface is set by controller 610 as an origin for calibrating the position of machining tool 602 (and a predetermined offset may be applied at this stage, if applicable).

[0050] Method 300 also includes identifying or determining (304) a reference surface on workpiece 608. For example, the reference surface may be defined within tip shroud 216. The reference surface may be formed (e.g., machined) within tip shroud 216 prior to beginning the method, or may be formed during method 300 (e.g., machined using machining tool 602). The reference surface may be identified or determined (304) using sensor 612 (e.g., by probing the reference surface), and this information may be processed by controller 610 to control machining tool 602.

[0051] In the exemplary method 300, a reference surface is formed within tip shroud 216 and oriented substantially parallel to the outer surface of the PSP (e.g., PSP 238 or PSP 240) being probed when determining 302 the reference surface. Referring back to FIGS. 3 and 4 , in the exemplary embodiment, the reference surface is a notch 246 formed in leading edge wall 234. Notch 246 defines a surface oriented substantially parallel to outer surface 244 of PSP 240. Outer surface 244 of PSP 240 serves as the initial reference surface that was previously probed when determining 302 the reference surface.

[0052] Determining 304 the reference plane also includes determining a distance D1, measured in the X-axis direction, between the notch 246 and the outer surface 244 of the PSP 240. Distance D1 may be used by the controller 610 to control the machining tool 602 in subsequent machining, as described below. Distance D1 may be, for example, between about 3 inches and about 5 inches, or, for example, between about 4.0 inches and about 4.2 inches. Distance D1 may vary depending on the component being repaired by the process 300 and the relative dimensions of the component. Orienting the notch 246 substantially parallel to the outer surface 244 and determining the distance D1 between the notch 246 and the outer surface 244 ensures that the spatial relationship between the notch 246 and the new PSP 240 can be easily determined by the controller 610 to control the machining tool 602 to machine the new PSP 240 to a target profile, as described below. It will be appreciated that in an alternative embodiment, when a reference surface is determined (302) as the initial reference surface, the outer surface 242 of the PSP 238 can be probed and a notch (not shown) can be formed in the trailing edge wall 236, which can then be determined (304) as the datum surface.

[0053] In some embodiments, determining 304 the reference surface includes machining a reference surface (e.g., notch 246) in tip shroud 216 after determining 302 the initial reference surface. The reference surface may be machined a predetermined or predefined distance D1 from the determined 302 reference surface. For example, after determining 302 the reference surface, machining tool 602 may be controlled via controller 610 and CNC unit 604 to machine a reference surface (e.g., notch 246) in tip shroud 216 a distance D1 from the initial reference surface (e.g., outer surface 244 of PSP 240). Alternatively, the reference surface may be machined in tip shroud 216, and the distance D1 between the reference surface (e.g., notch 246) and the initial reference surface (e.g., outer surface 244) may then be determined (e.g., by probing the reference surface and measuring the distance D1).

[0054] The method 300 continues by removing (306) from the tip shroud the PSPs that define the outer surface that was previously probed when the reference plane was determined (302). The PSPs may be removed (306) from the tip shroud using a machining tool 602 or by another suitable means. In the exemplary method 300, the PSPs 240 that define the outer surface 244 that was previously probed when the reference plane was determined (302) are removed (306). In some examples, the PSPs 238 that define the outer surface 242 may also be removed (306). Because outer surface 242 of PSP 238 is located a known or predetermined distance D2 from outer surface 244 of PSP 240, measured in the direction of the X-axis, and because outer surfaces 242 and 244 are oriented substantially parallel to one another, the spatial relationship between outer surfaces 242 and 244 is known (e.g., stored in memory device 616), so no additional probing of outer surface 244 is required before removing PSP 238. For example, distance D2 may be defined by a three-dimensional drawing file stored in memory device 616. After PSP 240 is removed (306), optionally, PSP 238, a new PSP 240 is attached (308) (e.g., brazed or welded) to second end 226 of tip shroud 216, and optionally, a new PSP 238 is attached (308) (e.g., brazed or welded) to first end 224 of tip shroud 216.

[0055] The method 300 continues by machining (310) a new PSP 240 attached (308) to the tip shroud 216 to a target profile using a machining tool 602 operably coupled to a controller 610. The target profile is converted to coordinate values ​​that are readily determined by the controller 610 by referencing a reference surface (e.g., notch 246) within the tip shroud 216. Specifically, the target profile of the attached (308) PSP 240 substantially matches the target profile of the previously removed (306) PSP 240. As described above, the target profile is converted to coordinate values ​​that are readily confirmed by the controller 610 using the reference surface (e.g., notch 246) as the origin (reference point) for machining (310). For example, after the PSP 240 is attached (308) and machined (310), the PSP 240 defines an outer surface 244 that substantially matches the outer surface 244 defined by the previously removed (306) PSP 240. That is, the outer surface 244 of the PSP 240 as attached (310) is oriented substantially parallel to and located a precise distance D1 from a reference surface (e.g., notch 246). In this regard, the target profile (e.g., planarization of the outer surface 244) of the previously attached (308) PSP 240 is readily confirmed by probing (e.g., using sensor 612) the reference surface (e.g., notch 246) and using the reference surface as an origin during machining (310). If previously installed (308), new PSP 238 may be machined (312) using distance D2 measured between outer surfaces 242 and 244 of previously removed (306) PSP 238 and PSP 240, respectively. A blend-finish operation may then be performed on previously installed (310) PSP 240 and optionally installed (312) PSP 238 to smooth these newly added components and achieve a finished tip shroud 216 for use in subsequent operation of rotary machine 110.

[0056] Compared to conventional methods for reconditioning turbine blades having tip shrouds with one or more PSP structures, the above-described embodiments offer several advantages. For example, conventional processes allow for the use of portions of the blade (e.g., the part-span shroud) as reference points for machining the PSPs attached to the tip shroud. These reference points are in locations different from the tip shroud, and the coordinate system used to guide the machining tool must be transformed based on the rotation and / or translation of the tip shroud relative to the part-span shroud. These processes also require data storage to enable the transformation of the coordinate system based on these reference points once a new PSP is attached to the tip shroud. These conventional processes are limited by relying on reference points that are not located on the portion of the component to which the PSP is applied, deriving translational and rotational motions from coordinate system transformations that require the same location to be hit during initial and final machining, and storing the data. Machining errors in hardface PSPs can be amplified due to errors in indirect location identification, multiple probing, transformations, and data storage.

[0057] The above-described embodiments overcome the limitations and drawbacks of these conventional processes by forming a reference surface on the tip shroud that is located a known or fixed distance from a new PSP attached to the tip shroud during manufacturing and / or reconditioning. The reference surface is used as an origin in determining coordinate values ​​for subsequent machining of the new PSP (e.g., by forming an outer surface oriented parallel to the reference surface and located a known or fixed distance from the reference surface). Advantages of this embodiment include reducing or eliminating data storage from the machining process and reducing probing and coordinate system transformations from different locations on the turbine blade. These are achieved by using a fixed-distance origin measured at the tip shroud level (e.g., using a reference surface having a Z-axis coordinate at the Z-axis coordinate level of the new PSP). Moreover, because the embodiments described herein use plane-to-plane measurements, coordinate measuring machines (CMMs) and hard gauges can be relied upon for in-process inspection.

[0058] Further aspects of the present disclosure are provided by the subject matter of the following sections.

[0059] Item 1. A method for repairing a turbine blade, the turbine blade including a tip shroud and a first pre-sintered preform (PSP) attached to the tip shroud, the method including: positioning the turbine blade in a system including a machining tool; determining a first distance between a surface of the first PSP and a reference surface formed in the tip shroud; removing the first PSP from the tip shroud; bonding a second PSP to the tip shroud; and machining the surface of the second PSP using the machining tool, wherein machining the surface of the second PSP includes controlling movement of the machining tool using the reference surface as a reference so that the machined surface of the second PSP is located at a first distance from the reference surface.

[0060] Clause 2. The method of clause 1, further comprising using a machining tool to machine a reference surface in the tip shroud such that the reference surface is located a first distance from a surface of the first PSP.

[0061] Clause 3. The method of any one of clauses 1 to 2, wherein determining the first distance includes machining a reference surface in the tip shroud and measuring a distance between the reference surface and a surface of the first PSP.

[0062] Clause 4. The method of any one of clauses 1 to 3, wherein determining the first distance includes determining a predefined first distance and machining a reference surface in the tip shroud the predefined first distance from a surface of the first PSP.

[0063] Clause 5. The method of any one of clauses 1 to 4, wherein coupling the second PSP to the tip shroud includes rigidly coupling the second PSP and the tip shroud together by one of brazing and welding.

[0064] Item 6. The method of any one of items 1 to 5, further comprising: coupling a third PSP to the tip shroud; and, after machining the surface of the second PSP, machining the surface of the third PSP to a second distance measured between the machined surface of the second PSP and the machined surface of the third PSP.

[0065] Item 7. The method of any one of items 1 to 6, wherein machining the surface of the third PSP to a second distance includes machining the surface of the third PSP to a predefined second distance measured between the machined surface of the second PSP and the machined surface of the third PSP.

[0066] Item 8. A method for repairing a turbine component, the turbine component including a first hardened surface structure and a second hardened surface structure, the method including: positioning the turbine component in a system including a machining tool; determining a first distance between a surface of the first hardened surface structure and a reference surface formed in the turbine component; removing the first hardened surface structure and the second hardened surface structure from the turbine component; bonding a third hardened surface structure to the turbine component; bonding a fourth hardened surface structure to the turbine component; machining the surface of the third hardened surface structure using the machining tool, wherein machining the surface of the third hardened surface structure includes controlling movement of the machining tool using the reference surface as a reference such that the machined surface of the third hardened surface structure is located at a first distance from the reference surface; and machining the surface of the fourth hardened surface structure using the machining tool to a second distance measured between the surface of the machined third hardened surface structure and the surface of the machined fourth hardened surface structure.

[0067] Item 9. The method of any one of items 1 to 8, wherein machining the surface of the fourth hardened surface structure includes machining the surface of the fourth hardened surface structure to a second distance substantially equal to a distance measured between the surface of the first hardened surface structure and the surface of the second hardened surface structure.

[0068] Item 10. The method of any one of items 1 to 9, wherein machining the surface of the fourth hardened surface structure to a second distance includes machining the surface of the fourth hardened surface structure to a predefined second distance measured between the machined surface of the third hardened surface structure and the machined surface of the fourth hardened surface structure.

[0069] Clause 11. The method of any one of clauses 1 to 10, further comprising machining a reference surface in the turbine component using a machining tool, wherein machining the reference surface in the turbine component comprises controlling movement of the machining tool using a surface of the first hardened surface structure as a reference.

[0070] Clause 12. The method of any one of clauses 1 to 11, wherein determining the first distance includes machining a reference surface in the turbine component and measuring a distance between the reference surface and a surface of the first hardfacing structure.

[0071] Clause 13. The method of any one of clauses 1 to 12, wherein determining the first distance includes determining a predefined first distance and machining a reference surface in the turbine component the predefined first distance from a surface of the first hardfacing structure.

[0072] Clause 14. The method of any one of clauses 1 to 13, wherein coupling the first hardened surface structure and the second hardened surface structure to the turbine component includes firmly coupling each of the first hardened surface structure and the second hardened surface structure to the turbine component by one of brazing and welding.

[0073] Item 15. A method of repairing a turbine blade, the turbine blade including a tip shroud and a first pre-sintered preform (PSP) and a second PSP attached to the tip shroud, the method including: positioning the turbine blade in a system including a machining tool; controlling the machining tool to machine a reference surface in the tip shroud; removing the first PSP and the second PSP from the tip shroud; coupling a third PSP and a fourth PSP to the tip shroud; controlling the machining tool to machine the third PSP using the reference surfaces as a reference; and controlling the machining tool to machine the fourth PSP after machining the third PSP.

[0074] Item 16. The method of any one of items 1 to 15, wherein controlling the machining tool to machine the reference surface includes controlling the machining tool to machine the reference surface using the surface of the first PSP as a reference.

[0075] Item 17. The method of any one of items 1 to 16, wherein controlling the machining tool to machine the reference surface includes controlling the machining tool to machine the reference surface a first distance from the surface of the first PSP.

[0076] Item 18. The method of any one of items 1 to 17, wherein controlling the machining tool to machine the third PSP includes using the reference surface as a reference and controlling the machining tool to machine the third PSP based on the first distance.

[0077] Item 19. The method of any one of items 1 to 18, wherein controlling the machining tool to machine the third PSP includes controlling the machining tool to machine the third PSP to a first distance from the reference surface.

[0078] Item 20. The method of any one of items 1 to 19, wherein controlling the machining tool to machine the fourth PSP includes controlling the machining tool to machine the fourth PSP based on the distance between the first PSP and the second PSP.

[0079] Exemplary embodiments of turbine blades and methods of manufacturing and repairing turbine blades have been described above in detail. The present disclosure is not limited to the specific embodiments described herein; rather, components of the systems may be utilized independently and separately from other components described herein. For example, methods as disclosed herein may be used in combination with rotating components other than those specifically described herein, and turbine blades may also be used in combination with other rotary machines and methods, and are not limited to practice with only gas turbine engine or steam turbine engine assemblies described herein. Rather, exemplary embodiments may be implemented and utilized in connection with many other rotary machine applications.

[0080] Although specific features of various embodiments of the invention may be shown in some drawings and not in others, this is for convenience only. Moreover, references to "one embodiment" in the above description are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. In accordance with the principles of the invention, any feature of a drawing may be referenced and / or claimed in combination with any feature of any other drawing.

[0081] This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems, and performing any related methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements that do not differ substantially from the literal language of the claims. [Explanation of symbols]

[0082] 110 Rotating Machinery 112 rotor assembly 114 Shaft 118 rotor wheel 120 rotating blades 122 Fixed vane 123 Intake Section 124 Compressor 126 Combustor 130 Exhaust Section 200 turbine blades 202 Airfoil 204 leading edge 206 Trailing edge 208 Pressure sidewall 210 Negative pressure side wall 212 base 214 Platform 216 Tip shroud 218 Part Span Shroud 220 Part Span Shroud 222 Seal Rail 224 first end 226 Second End 228 Radial outer surface 230 leading edge 232 Trailing edge part 234 Leading Edge Wall 236 Trailing edge wall 238 Pre-sintered preform structure, pre-sintered preform, PSP 240 Pre-sintered preform structure, pre-sintered preform, PSP 242 Exterior 244 Exterior 246 Notch 300 Methods and Processes 302 Identifying or determining the initial reference plane 304 Identifying or determining reference planes 306 Removing PSP 308 Installing a new PSP 310 Processing a new PSP 312 Processing new PSPs 600 System 602 Processing tools 604 Computer Numerical Control Unit 606 Work Support Table 608 Processed piece 610 Controller 612 Sensors 614 processor 616 Memory Devices 618 Presentation Interface 620 User Input Interface

Claims

1. A method of repairing a turbine blade (200), the turbine blade (200) including a tip shroud (216) and a first pre-sintered preform (PSP) (238) attached to the tip shroud (216), the method comprising: Positioning the turbine blade (200) in a system (600) including a machining tool (602); determining a first distance between a surface of the first PSP (238) and a reference plane formed within the tip shroud (216); removing the first PSP (238) from the tip shroud (216); coupling a second PSP (240) to the tip shroud (216); machining the surface of the second PSP (240) using the machining tool (602), wherein machining the surface of the second PSP (240) includes controlling movement of the machining tool (602) using the reference plane as a reference so that the machined surface of the second PSP (240) is located at the first distance from the reference plane; A method comprising:

2. 2. The method of claim 1, further comprising: using the machining tool to machine the datum surface in the tip shroud such that the datum surface is located the first distance from a surface of the first PSP.

3. 2. The method of claim 1, wherein determining the first distance comprises machining the datum surface in the tip shroud (216) and measuring a distance between the datum surface and a surface of the first PSP (238).

4. 2. The method of claim 1, wherein determining the first distance comprises determining a predefined first distance and machining the datum surface into the tip shroud (216) the predefined first distance from a surface of the first PSP (238).

5. 2. The method of claim 1, wherein coupling the second PSP to the tip shroud comprises rigidly coupling the second PSP and the tip shroud together by one of brazing and welding.

6. 10. The method of claim 1, further comprising: coupling a third PSP to the tip shroud; and, after machining a surface of the second PSP, machining a surface of the third PSP to a second distance measured between the machined surface of the second PSP and the machined surface of the third PSP.

7. 7. The method of claim 6, wherein machining the surface of the third PSP to the second distance comprises machining the surface of the third PSP to a predefined second distance measured between the machined surface of the second PSP (240) and the machined surface of the third PSP.

8. 1. A method of repairing a turbine component, the turbine component including a first hardface structure and a second hardface structure, the method comprising: Positioning the turbine component in a system (600) including a machining tool (602); determining a first distance between a surface of the first hardfacing structure and a reference surface formed within the turbine component; removing the first hardface structure and the second hardface structure from the turbine component; coupling a third hardface structure to the turbine component and coupling a fourth hardface structure to the turbine component; machining the surface of the third surface-hardened structure using the machining tool (602), wherein machining the surface of the third surface-hardened structure includes controlling movement of the machining tool (602) using the reference surface as a reference so that the machined surface of the third surface-hardened structure is located at the first distance from the reference surface; using the machining tool (602) to machine the surface of the fourth hardened surface structure to a second distance measured between the machined surface of the third hardened surface structure and the machined surface of the fourth hardened surface structure; A method comprising:

9. 9. The method of claim 8, wherein working the surface of the fourth hardened surface structure comprises working the surface of the fourth hardened surface structure to the second distance substantially equal to a distance measured between a surface of the first hardened surface structure and a surface of the second hardened surface structure.

10. 9. The method of claim 8, wherein machining the surface of the fourth hardened surface structure to the second distance comprises machining the surface of the fourth hardened surface structure to a predefined second distance measured between the machined surface of the third hardened surface structure and the machined surface of the fourth hardened surface structure.

11. 10. The method of claim 8, further comprising machining the datum surface in the turbine component using the machining tool (602), wherein machining the datum surface in the turbine component comprises controlling movement of the machining tool (602) using a surface of the first hardened surface structure as a datum.

12. 9. The method of claim 8, wherein determining the first distance comprises machining the datum surface into the turbine component and measuring a distance between the datum surface and a surface of the first hardfacing structure.

13. 9. The method of claim 8, wherein determining the first distance comprises determining a predefined first distance and machining the reference surface into the turbine component the predefined first distance from a surface of the first hardface structure.

14. 9. The method of claim 8, wherein coupling the first hardened surface structure and the second hardened surface structure to the turbine component comprises rigidly coupling each of the first hardened surface structure and the second hardened surface structure to the turbine component by one of brazing and welding.

15. A method of repairing a turbine blade (200), the turbine blade (200) including a tip shroud (216) and a first pre-sintered preform (PSP) (238) and a second PSP (240) attached to the tip shroud (216), the method comprising: Positioning the turbine blade (200) in a system (600) including a machining tool (602); controlling the machining tool (602) to machine a reference surface in the tip shroud (216); removing the first PSP (238) and the second PSP (240) from the tip shroud (216); coupling a third PSP and a fourth PSP to the tip shroud (216); controlling the machining tool (602) to machine the third PSP using the reference surface as a reference; controlling the machining tool (602) to machine the fourth PSP after machining the third PSP; A method comprising:

16. 16. The method of claim 15, wherein controlling the machining tool (602) to machine the reference surface comprises controlling the machining tool (602) to machine the reference surface using a surface of the first PSP (238) as a reference.

17. 17. The method of claim 16, wherein controlling the machining tool (602) to machine the reference surface comprises controlling the machining tool (602) to machine the reference surface a first distance from a surface of the first PSP (238).

18. 18. The method of claim 17, wherein controlling the machining tool (602) to machine the third PSP comprises controlling the machining tool (602) to machine the third PSP based on the first distance using the reference surface as a reference.

19. 20. The method of claim 17, wherein controlling the machining tool (602) to machine the third PSP comprises controlling the machining tool (602) to machine the third PSP to the first distance from the reference plane.

20. 16. The method of claim 15, wherein controlling the machining tool (602) to machine the fourth PSP comprises controlling the machining tool (602) to machine the fourth PSP based on a distance between the first PSP (238) and the second PSP (240).

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