Systems and methods for machining slots in an inner surface of a casing of a gas turbine engine

Abstract

A milling device (74, 96, 134) for machining a slot (45) into an inner surface of a casing (42) for a gas turbine engine (11) is disclosed. The milling device (74, 96, 134) includes a frame assembly (76, 98, 136) including a plurality of structural guides (88, 132) configured to engage a structural feature (66) on the inner surface of the casing (42) to maintain an axial position of the milling device (74, 96, 134) relative to a longitudinal axis (36) of the casing (42). The milling device (74, 96, 134) also includes a milling cutter (78, 100, 138) coupled to the frame assembly (76, 98, 136). The milling device (74, 96, 134) is configured to be displaced relative to the longitudinal axis (36) in a circumferential direction (34) to machine the slot (45) along the inner surface of the casing (42) in the circumferential direction (34) via the milling cutter (78, 100, 138).

Description

BACKGROUND

[0001] The subject matter disclosed herein relates to gas turbine systems, and more particularly, to systems and methods for machining a slot into a casing of a gas turbine system.

[0002] Gas turbines are used to generate electricity for various applications. Typically, they are tested and validated prior to use (e.g., in a power plant). Efficient testing and validation can improve the efficiency and productivity of the gas turbine, as well as the power plant. However, installation of equipment for performing testing and validation on a gas turbine engine can be labor intensive and time consuming. SUMMARY

[0003] The following summarizes certain embodiments commensurate with the scope of the originally claimed subject matter. These embodiments are not intended to limit the scope of the claimed subject matter, but rather these embodiments are intended to provide a brief summary of possible forms of the subject matter. The subject matter can encompass a variety of forms that can be similar or different from the embodiments set forth below.

[0004] In one embodiment, a milling device for machining a slot into an inner surface of a casing for a gas turbine engine is provided. The milling device includes a frame assembly including a plurality of structural guides configured to engage a structural feature on the inner surface of the casing to maintain an axial position of the milling device relative to a longitudinal axis of the casing. The milling device also includes a milling cutter coupled to the frame assembly. The milling device is configured to be displaced in a circumferential direction relative to the longitudinal axis to machine the slot along the inner surface of the casing in the circumferential direction via the milling cutter.

[0005] In another embodiment, a slide block milling device is provided. The slide block milling device includes a frame assembly and a milling cutter coupled to the frame assembly. The slide block milling device also includes a bearing support configured to engage an inner surface of a casing of a gas turbine engine to provide a support force in a direction perpendicular to a longitudinal axis of the casing and to move the milling device in a circumferential direction relative to the longitudinal axis. The slide block milling device is configured to be displaced in the circumferential direction to machine a slot along the inner surface of the casing in the circumferential direction via the milling cutter.

[0006] In another embodiment, a milling system is provided for machining a slot into the inner surface of a gas turbine engine housing. The milling system includes a slide milling device having a frame assembly and a milling cutter. The slide milling device is configured to be displaced in the circumferential direction relative to the longitudinal axis of the housing to machine the slot along the inner surface of the housing in the circumferential direction via the milling cutter, wherein the frame assembly is configured to be interchangeably coupled to different sets of structural guides. Each set of structural guides includes different sizes, shapes, or combinations thereof to enable the slide milling device to engage different structural features on the inner surface of the housing to maintain the axial position of the milling device relative to the longitudinal axis of the housing. The milling system also includes the different sets of structural guides. Attached Figure Description

[0007] These and other features, aspects, and advantages of this subject matter will be better understood when the following detailed description is read with reference to the accompanying drawings, in which the same characters denote the same parts, wherein:

[0008] Figure 1 It is a block diagram of an implementation scheme for a turbine system with an aerodynamic measurement system;

[0009] Figure 2 Is it like this? Figure 1 A cross-sectional side view of an embodiment of a turbine system with an aerodynamic measurement system;

[0010] Figure 3 A perspective view of an embodiment of the inner surface of a portion of the housing (e.g., compressor housing) of a gas turbine engine having multiple circumferential tracks;

[0011] Figure 4 Is Figure 3 A perspective view of an embodiment of a portion of a circumferential track embedded in the inner surface of the housing, taken from line 4-4;

[0012] Figure 5 This is a schematic side view of an implementation of a milling system for machining slots along the inner surface of a housing;

[0013] Figure 6 This is a perspective view of an embodiment of a milling apparatus for machining slots along the inner surface of a housing;

[0014] Figure 7 It is used for machining. Figure 6 Top perspective view of the milling device for the narrow slot;

[0015] Figure 8 It is used for machining. Figure 6 A cross-sectional side view of the milling device for the narrow slot in the middle;

[0016] Figure 9 This is a front perspective view of an embodiment of a milling apparatus for machining slots along the inner surface of a housing;

[0017] Figure 10 It is used for machining. Figure 9 Rear perspective view of the milling device for the narrow slot;

[0018] Figure 11 It is used for machining. Figure 9 Side view of the milling device for the narrow slot;

[0019] Figure 12 yes Figure 9 A side view of a portion of the milling apparatus (e.g., a structural guide); and

[0020] Figure 13 This is a flowchart of a method for machining a slot along the inner surface of a housing using a milling device. Detailed Implementation

[0021] One or more specific embodiments will be described below. To provide a concise description of these embodiments, not all features of the actual implementation may be described in the specification. It should be understood that in the development of any such actual implementation, as in any engineering or design project, many implementation-specific decisions must be made to achieve the developer's specific objectives, such as complying with system-related and business-related constraints, which may vary from implementation to implementation. Furthermore, it should be understood that such development work can be complex and time-consuming, but remains a routine task of design, fabrication, and manufacturing for those skilled in the art who benefit from this disclosure.

[0022] When describing elements of various embodiments of this disclosure, the articles “a,” “an,” “the,” and “the” are intended to mean one or more elements present in the elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that additional elements may be present in addition to the listed elements.

[0023] Embodiments of this disclosure include a milling system for milling slots (e.g., circumferential slots) into an inner surface or diameter of a gas turbine engine housing (e.g., a compressor housing). The slots extend circumferentially relative to the longitudinal axis of the housing or gas turbine engine. The slots are configured to receive a circumferential track defining a cavity for receiving a measurement system (e.g., having multiple sensors) for verifying the operation of the gas turbine engine. The milling system includes a milling device or tool (e.g., a slide milling device or tool) comprising a frame assembly and a milling cutter (e.g., an end mill or drill bit) coupled to the frame assembly. The frame assembly includes or is coupled to a structural guide configured to engage structural features on the inner surface of the housing (e.g., slots or retaining convex angles defining slots for retaining compressor stator blades) to maintain the axial position of the milling device relative to the longitudinal axis. The frame assembly can be interchangeably coupled to different sets of structural guides (e.g., where the size and / or shape of the structural guides vary between sets), wherein each set of structural guides is designed to engage structural features on the inner surface of a housing with different sizes and / or shapes. The milling device is configured to displace circumferentially along the inner surface of the housing (e.g., via force applied by an operator) to machine slots via a milling cutter. In some embodiments, the milling device includes a support member engaging the inner surface of the housing, which provides support force in a direction perpendicular to the longitudinal axis while enabling the slide milling device to move circumferentially. The architecture of the milling device allows it to adapt to and utilize the inner surface of any housing (e.g., a circular or semi-circular housing) of a gas turbine engine with housing features near the area to be milled. The milling device can also precisely align milling tools or cutting tools to create circumferential slots using housing features. The milling device can even be used for damaged, warped, or worn housings. In addition, milling machines are highly transportable due to their small size and light weight, and can be used by a single person to machine slots.

[0024] Switch to the attached image. Figure 1 This is a block diagram of an embodiment of a turbine system 10 having a gas turbine engine 11. For reference, the gas turbine engine 11 may be in the axial direction 30 (e.g., relative to the longitudinal axis 36 of the gas turbine engine 11 or the housing 42, see...). Figure 2The turbine system 10 extends radially toward or away from the longitudinal axis 36 and circumferentially around the longitudinal axis 36 in the radial direction 32. The disclosed turbine system 10 employs a measurement system 13 (e.g., an aerodynamic measurement system), which is made possible by the milling system described in more detail below. The measurement system 13 may include a sensor assembly with multiple sensors that measure various operating parameters used to provide baseline data in verifying the operation of the gas turbine engine 11. The measurement system 13 operates independently of the control system for the gas turbine engine 11. The number of sensors can range from tens to hundreds to thousands. At least some of the sensors may employ optics and / or optical fibers. The measured operating parameters may include blade tip timing (e.g., for displacement, stress, frequency, etc.), blade tip clearance, temperature, dynamic pressure, static pressure, rotor vibration, stall detection, and rotor speed.

[0025] The sensor assembly is disposed within a space or cavity defined by a circumferential track embedded in a circumferential slot along the inner surface or diameter of the housing of the gas turbine engine 11 (e.g., a compressor housing). The circumferential track and slot extend in the circumferential direction 34 relative to the longitudinal axis 36 of the gas turbine engine 11. In some embodiments, the housing may include a plurality of circumferential tracks (and circumferential slots) spaced apart from each other in the axial direction 30. In some embodiments, the measurement system 13 may include a plurality of sensor assemblies, each having a plurality of sensors, wherein the sensor assemblies can be inserted into the plurality of circumferential tracks.

[0026] The circumferential slot needs to have a specific profile to accommodate an embedded sensor track system. The circumferential slot is machined using a milling system (e.g., a slide milling system) that includes a milling device. The milling device utilizes existing housing structural features (e.g., protrusions defining retaining convex angles or slots for holding compressor stator blades) near the area to be milled or machined on the inner surface of the housing as supports for the milling device and guides for the path of the milling device. The milling device includes a frame assembly and milling cutters (e.g., end mills or drills) coupled to the frame assembly. The types of cutters used with the milling device are interchangeable. The frame assembly includes or is coupled to structural guides configured to engage structural features on the inner surface of the housing to maintain the axial position of the milling device relative to the longitudinal axis. The frame assembly can be interchangeably coupled to different sets of structural guides (e.g., where the size and / or shape of the structural guides vary between sets), wherein each set of structural guides is designed to engage structural features on the inner surface of the housing with different sizes and / or shapes. Therefore, milling devices can be used to produce different types of slot profiles. The adaptability of milling devices makes them suitable for damaged, warped, or worn housings. Furthermore, milling devices are configured to be displaced circumferentially along the inner surface of the housing (e.g., by force applied by the operator) to machine slots via a milling cutter. In some embodiments, the milling device includes a support member engaging with the inner surface of the housing, which provides support force in a direction perpendicular to the longitudinal axis while enabling the slide-type milling device to move circumferentially. Milling devices can be used with any type of circular or semi-circular housing (e.g., compressor housings, turbine housings, etc.).

[0027] The turbine system 10 can be driven by liquid or gaseous fuels such as natural gas and / or syngas. As depicted, one or more fuel nozzles 12 allow fuel supply 14 to enter, partially mixing the fuel with air and distributing the fuel and air-fuel mixture to a combustor 16, where further mixing of fuel and air occurs. The air-fuel mixture is burned in a chamber within the combustor 16, producing a hot-pressurized exhaust gas. The combustor 16 guides the exhaust gas through a turbine 18 toward an exhaust outlet 20. As the exhaust gas passes through the turbine 18, the gas drives turbine blades along the axis of the turbine system 10, causing shaft 22 to rotate. As shown, shaft 22 is connected to various components of the turbine system 10, including a compressor 24. Compressor 24 also includes blades coupled to shaft 22. As shaft 22 rotates, the blades within compressor 24 also rotate, thereby compressing air from intake 26 through compressor 24 and compressing the air to fuel nozzles 12 and / or combustor 16. Shaft 22 may also be connected to load 28, which may be a vehicle or stationary load, such as a generator in a power plant or a propulsion unit on an aircraft. Load 28 may include any suitable device capable of being powered by the rotational output of turbine system 10.

[0028] Figure 2 Is it like this? Figure 1 The diagram shows a cross-sectional side view of an embodiment of the gas turbine engine 11. The gas turbine engine 11 has a longitudinal axis 36. In operation, air enters the gas turbine engine 11 through the intake port 26 and is pressurized in the compressor 24. This compressed air is then mixed with gas to be burned in the combustor 16. For example, the fuel nozzle 12 can inject the fuel-air mixture into the combustor 16 at a suitable ratio to achieve optimal combustion, emissions, fuel consumption, and power output. Combustion produces pressurized hot exhaust gas, which then drives the turbine blades 38 in the turbine 18 to rotate the shaft 22, which in turn rotates the compressor 24 and the load 28. The rotation of the turbine blades 38 causes the shaft 22 to rotate, thereby causing the blades 40 (e.g., compressor blades) within the compressor 24 to draw in and pressurize the air received by the intake port 26.

[0029] As depicted, a housing 42 (e.g., a compressor housing) surrounds the blades 40 (and stator blades) of the compressor 24. The housing 42 may include multiple segments (e.g., two halves) that extend together entirely around a longitudinal axis 36 to define the interior of the compressor 24. A circumferential track 44 is embedded in a slot 45 along the inner surface or diameter 46 of the housing 42. The measuring system 13 includes a sensor assembly 48 having multiple sensors disposed within a space or cavity defined between the circumferential track 44 and the inner diameter 46 of the housing 42. The circumferential track 44 is axially 30 positioned between rows of stator blades (not shown) such that the circumferential track 44, and thus the sensors of the sensor assembly 48, are in the plane of the rotating blades 40 (and aligned axially 30 with the rotating blades). The circumferential track 44 extends at least a portion of the inner diameter 46 of the housing 42 in a circumferential direction 34. In some embodiments, the circumferential track 44 extends around the entire inner diameter 46 of the housing 42.

[0030] Figure 3 This is a perspective view of an embodiment of an inner surface 46 of a portion of the housing 42 (e.g., a compressor housing) of a gas turbine engine 11 having multiple circumferential tracks 44. Stator blades and corresponding slots for receiving the stator blades are not shown. In some embodiments, the number of circumferential tracks 44 may correspond to the number of stages of blades 40. In other embodiments, the number of circumferential tracks 44 may be less than or greater than the number of stages of blades 40. As depicted, the circumferential tracks 44 are axially 30 spaced apart from each other relative to the longitudinal axis 36. As described above, the circumferential tracks 44 are axially 30 arranged between rows of stator blades, such that the circumferential tracks 44, and therefore the sensors of the sensor assembly 48, are in the plane of the rotating blades 40 (and aligned axially 30 with the rotating blades). The circumferential tracks 44 extend at least a portion of the inner diameter 46 of the housing 42 in the circumferential direction 34. In some embodiments, the circumferential tracks 44 extend around the entire inner diameter 46 of the housing 42.

[0031] In some embodiments, the circumferential track 44 is a single segment 50, as depicted in circumferential track 52. In other embodiments, the circumferential track 44 may include multiple segments 50, as depicted in circumferential track 54. Each circumferential track 44 includes an opening 56 that allows the sensor of the sensor assembly 48 to face the interior of the compressor 24 (e.g., toward the blades 40) when the sensor assembly 48 is properly inserted into the space defined by the circumferential track 44 and the inner diameter 46 of the housing 42. The opening 56 may include a larger opening 58 and a smaller opening 60 sized for a particular sensor. In some embodiments, the openings 56 may be circumferentially 34-aligned or axially 30-aligned. Figure 4As depicted, a space or cavity 62 is defined between the circumferential track 44 and the inner surface 46 of the housing 42. The sensor assembly 48 can be inserted into and / or removed from the space or cavity 62.

[0032] Figure 5 This is a schematic side view of an embodiment of a milling system 64 (e.g., a machining system) for machining a slot 45 along the inner surface 46 of a housing 42. As depicted, the inner surface 46 of the housing 42 includes structural features 66. These structural features include slots 68 extending in the circumferential direction 34 for retaining stator blades (e.g., compressor stator blades) defined between protrusions 70. The protrusions 70 include retaining convex angles, slots, or recesses 72 for retaining the stator blades within the slots 68. These structural features 66 may vary in size, shape, or spacing from one another. The milling system 64 utilizes the structural features 66 in supporting and guiding the milling system 64 as it machines the slot 45.

[0033] The milling system 64 includes a milling device or tool 74 for machining (e.g., routing, grinding, milling, etc.) a slot 45 (e.g., within a protrusion 70). The milling device 74 includes a frame assembly 76 and a milling cutter or drill bit 78 (e.g., an end mill) coupled to the frame assembly 76 for machining the slot 45. The milling device 74 can be interchangeably coupled to different milling cutters (e.g., roughing end mills, finishing end mills, square end mills, ball end mills, etc.). The milling cutter 78 can be coupled to an electric motor driver coupled to a power source (not shown). As depicted, the frame assembly 76 includes a plate 80 and a pair of guide rails 82 located on the side of the plate 80. The plate 80 is horizontally oriented relative to the pair of guide rails 82 (which extend vertically in the radial direction 32). The milling cutter 78 is coupled to the plate 80. In some embodiments, the position of the milling cutter 78 along the plate 80 can be adjusted (e.g., to change the axial position of the milling cutter 78 relative to the longitudinal axis 36). The dimensions of the frame assembly 76 are adjustable to take into account structural features 66 on the inner surface 46 of the housing 42. In particular, the distance 84 between the guide rails 82 is adjustable to accommodate the width 86 of the protrusion 70. As depicted, the milling device 74 extends above the protrusion 70. In some embodiments, the milling device 74 extends between a plurality of adjacent protrusions 70.

[0034] The milling system 64 includes structural guides 88 coupled to a guide rail 82. The structural guides 88 are configured to engage structural features 66 (e.g., retaining convex angles 72) on protrusions 70 to maintain the axial position of the milling device 74 (e.g., relative to the longitudinal axis 36). As depicted, the structural guides 88 are disposed on the inner surface 90 of the guide rail 82 to engage retaining convex angles 72 disposed on opposite sides of the same protrusion 70. In some embodiments, the structural guides 88 may be disposed on the outer surface of the guide rail 82 or on another portion of the frame assembly 76 to engage corresponding retaining convex angles 72 on different protrusions 70 (e.g., where different protrusions 70 are located on the sides of the machined slots 45 of the protrusions 70). The milling system 64 may include different sets of structural guides 88. Each set of structural guides 88 may be specifically shaped or designed to be different structural features 66 with different dimensions and / or shapes. The milling device 74 may be interchangeably coupled to different sets of structural guides 88. This (along with the adjustability of the frame assembly 76) enables the milling device 74 to be coupled to different structural features 66 on any type of circular or semi-circular housing 42 (including housings with damaged, warped, or worn inner surfaces 46).

[0035] The milling device 74 also includes a frictionless support structure 92 that engages (e.g., contacts) the inner surface 46 of the housing 42 (e.g., the top of the protrusion 70). In some embodiments, the frictionless support structure 92 serves as a support member. The frictionless support structure 92 provides a supporting force in a direction perpendicular to the longitudinal axis 36 (e.g., radial direction 32). Additionally, the frictionless support structure 92 is movable in the circumferential direction 34 along the inner surface 46 of the housing 42 in response to a force applied by the operator (as indicated by arrow 94). Thus, the milling device 74 serves as a slide milling device. The small size and light weight of the milling device 74 allow it to be used by a single person to machine slots 45. In some embodiments, the frictionless support structure 92 may include a spring-loaded frictionless pin (e.g., made of plastic, graphite, or some other frictionless material). As depicted, the frictionless support structure 92 extends from the bottom of the plate 80. In other embodiments, the frictionless support structure 92 may extend from another part of the frame assembly 76 (e.g., guide rail 82).

[0036] Figures 6 to 8 A milling apparatus 96 is depicted for machining a slot 45 along the inner surface 46 of the housing 42. The housing 42 and its features are shown in reference [reference needed]. Figure 5The milling device 96 includes a frame assembly 98 and a milling cutter or drill bit 100 (e.g., an end mill) connected to a machining slot 45 of the frame assembly 98. The milling device 96 can be interchangeably connected to different milling cutters (e.g., roughing end mills, finishing end mills, square end mills, ball end mills, etc.). The milling cutter 100 can be connected to an electric motor driver, which is connected to a power source (not shown) disposed within the housing 102.

[0037] The frame assembly 98 includes a plate or bracket 104 oriented vertically in the radial direction 32. A milling device 96 is coupled to the support plate 104 via the plate 106. A pair of support arms or guide rails 108 are coupled to the plate 104 via a pair of corresponding support brackets 110. The support arms 108 are coupled to the support brackets 110 via fasteners 111 (e.g., bolts). The support arms 108 and support brackets 110 are located on the side of the milling cutter 100 and extend away from the plate 104. The support brackets 110 are coupled to corresponding slots 112 located on the side of the plate 106 within the plate 104 via fasteners (not shown). The width or distance 114 between the support arms 108 can be adjusted by changing the position of the support arms 108 along the slots 112 in the axial direction 30. The support arm 108 also includes a slot 116 that allows the position of the support arm 108 to be adjusted radially 32 relative to the support bracket 110, thereby changing the vertical position of the milling cutter 100 and the depth 118 of the slot 45.

[0038] Each support arm 108 is coupled to a roller 120. A corresponding roller 120 is coupled to the opposing inner surface of each end 122 of the support arm 108. Each support bracket 110 is coupled to a support structure 126. The support structure 126 provides support force in a direction perpendicular to the longitudinal axis 36 (e.g., radial direction 32). Each support structure 126 includes a rod portion 128 and an end portion 130. The rod portion 128 is configured to move in a recess 131 within the support structure 126 in the radial direction 32, allowing the support structure 126 to adjust the height difference of the structural feature 66 along the inner surface 46 of the housing 42 (e.g., in the axial direction). Figure 8As depicted, support structures 126 extend from their respective support brackets 110 at varying lengths to accommodate height differences between adjacent retaining protrusions 72 on the protrusions 70. End portions 130 include flanges or structural guides 132 that engage or fit within the retaining protrusions 72. The flanges 132 enable the milling device 96 to maintain an axial position relative to the longitudinal axis 36. End portions 130 are frictionless. The frictionless end portions 130 (together with the roller 120) allow movement in the circumferential direction 34 along the inner surface 46 of the housing 42 in response to forces applied by the operator. Thus, the milling device 96 functions as a slide-type milling device. The milling device 96 can be interchangeably coupled to different sets of end portions 130. Each set of end portions 130 may include a structural guide 132 whose shape or size is specifically designed to engage structural features 66 of different sizes and / or shapes. This (along with the adjustability of the frame assembly 98) enables the milling device 96 to be coupled to different structural features 66 on any type of circular or semi-circular housing 42 (including housings with damaged, warped, or worn inner surfaces 46).

[0039] Figures 9 to 12 A milling apparatus 134 is depicted for machining a slot 45 along the inner surface 46 of the housing 42. The housing 42 and its features are shown in reference. Figure 5 The milling device 134 includes a frame assembly 136 and a milling cutter or drill bit 138 (e.g., an end mill) coupled to the frame assembly 136 for machining a slot 45. The milling device 134 can be interchangeably coupled to different milling cutters (e.g., roughing end mills, finishing end mills, square end mills, ball end mills, etc.). The milling cutter 138 can be coupled to an electric motor driver connected to a power source (not shown) disposed within the housing 140. The milling device 134 may include one or more shanks 142 for an operator to move the milling device in the circumferential direction 34. One of the shanks 142 may include an actuator 144 (e.g., a trigger) for actuating the milling cutter 138. The milling device 134 may also include an instrument 146 for inspecting the machining of the slot 45.

[0040] The frame assembly 136 includes a pair of rods 148 and a first pair of guide rails 150 and a second pair of guide rails 152 connected (e.g., clamped) to the rods 148 via fasteners 154, 156 (e.g., bolts). The rods 148 extend in an axial direction 30 and the guide rails 150, 152 extend in a circumferential direction 34. The first pair of guide rails 150 are located on the sides of the second pair of guide rails 152. The guide rails 150, 152 are adjustable along the rods 148 in the axial direction 30. This allows the frame assembly 136 to be adjusted along the inner surface 46 of the housing 42 to structural feature 66.

[0041] Plate 158 is connected to a first pair of guide rails 150 via fasteners 160 (e.g., bolts). Plate 162 is connected to plate 158 via a bracket 164, which is fastened to plate 158 via fasteners 166 (e.g., bolts). A milling cutter 138 is connected to an actuator (not shown) within housing 140, which extends through both plates 158, 162. Milling cutter 138 is disposed within a slot 168 on plate 158. Slot 168 extends in the axial direction 30. Each plate 158, 162 is connected to a corresponding threaded socket 170, 172. Threaded sockets 170, 172 are vertically aligned with each other in the axial direction 30. An actuator 174 (e.g., a knob screw) extends through sockets 170, 172. Actuator 174 includes a knob 176 and a threaded portion 178. Threaded portion 178 engages within the threaded portions of sockets 170, 172. Actuation (e.g., rotation) of actuator 174 adjusts the position of plate 162 relative to plate 158 in the axial direction 30, which adjusts the axial position of milling cutter 138 within slot 168.

[0042] like Figure 10 As shown, the milling apparatus 134 includes structural guides 180 coupled to guide rails 152. The number of structural guides 180 on each guide rail 152 can vary (e.g., 2, 3, 4, 5 or more structural guides 180). The structural guides 180 are configured to engage structural features 66 (e.g., retaining convex angles 72) on protrusions 70 to maintain the axial position of the milling apparatus 134 (e.g., relative to the longitudinal axis 36). The structural guides 180 are respectively coupled to bracket supports 182, which are connected to the guide rails 152 via fasteners 184 (e.g., bolts). As depicted, the structural guides 180 are disposed on the outer surface 186 of the guide rail 134 to engage retaining convex angles 72 disposed on the protrusions 70, which are located on the side of the machined slots 45 of the protrusions 70. As depicted, the structural guides 180 have an L-shape. The milling apparatus 134 can be interchangeably coupled to different sets of structural guides 180. Each set of structural guides 180 can be specifically shaped or designed to be different structural features 66 with different dimensions and / or shapes. This (along with the adjustability of the frame assembly 136) allows the milling device to be coupled to different structural features 66 on any type of circular or semi-circular housing 42 (including those housings with damaged, warped, or worn inner surfaces 46).

[0043] The milling apparatus 134 also includes a frictionless support structure 188 that engages (e.g., contacts) the inner surface 46 of the housing 42 (e.g., within the slot 68). The frictionless support structure 188 is a spring-loaded frictionless pin 190 (e.g., made of plastic, graphite, or some other frictionless material). As depicted, the frictionless support structure 188 extends from the bottom surface 192 of the guide rail 152. The frictionless support structure 188 provides a supporting force in a direction perpendicular to the longitudinal axis 36 (e.g., radial direction 32). Furthermore, the frictionless support structure 188 is wear-compensated. Specifically, the spring of the spring-loaded frictionless pin 190 allows the frictionless support structure 188 to wear or be consumed without altering the system settings or accuracy. Further, the frictionless support structure 188 is movable in the circumferential direction 34 along the inner surface 46 of the housing 42 in response to a force applied by the operator. Therefore, the milling apparatus 134 functions as a slide-type milling apparatus. The small size and light weight of the milling device 134 enable the milling device 74 to be used by a single person to machine slots 45.

[0044] Figure 13 This is a flowchart of method 194 for machining a slot along the inner surface of a gas turbine engine housing using a milling apparatus (e.g., milling apparatuses 74, 96, 134). Method 194 includes attaching a structural guide to a frame assembly of the milling apparatus (box 196). As described above, the structural guide enables the milling apparatus to engage structural features on the inner surface of the gas turbine engine housing to maintain the axial position of the milling apparatus (e.g., relative to the longitudinal axis of the housing). In some embodiments, if the structural guide is already attached to the milling apparatus, it can be replaced with another set of structural guides with different sizes and / or shapes. Method 194 also includes adjusting the dimensions of the frame assembly using structural features on the inner surface to attach the milling apparatus to the inner surface of the housing (box 198). Method 194 further includes machining the slot into the inner surface of the housing using the milling apparatus (box 200). The milling apparatus is pushed in the circumferential direction about the inner surface of the housing.

[0045] The technical advantages of the disclosed embodiments include providing a milling apparatus configured to machine circumferential slots along the inner surface of a gas turbine engine casing. The architecture of the milling apparatus allows it to be adapted to and utilized on the inner surface of any gas turbine engine casing (e.g., a circular or semi-circular casing) with casing features near the area to be milled. The milling apparatus also allows for precise alignment of milling tools or cutting tools to create circumferential slots using the casing features. The milling apparatus can even be used for damaged, warped, or worn casings. Furthermore, the milling apparatus is highly transportable due to its small size and light weight, and can be used by a single person to machine slots.

[0046] This written description uses examples to disclose the disclosed subject matter, including best practices, and also enables any person skilled in the art to practice the disclosed subject matter, including making and using any apparatus or system and performing any combination of methods. The patentable scope of the disclosed subject matter is defined by the claims and may include other examples that would occur to a person skilled in the art. Such other examples are contemplated within the scope of the claims if they have structural elements that are not different from the literal language of the claims, or if they include equivalent structural elements that are not substantially different from the literal language of the claims.

Claims

1. A milling device (74, 96, 134) for machining a slot (45) into an inner surface of a casing (42) for a gas turbine engine (11), the milling device comprising: a frame assembly (76, 98, 136) including a plurality of structural guides (88, 132) configured to maintain an axial position of the milling device (74, 96, 134) relative to a longitudinal axis (36) of the casing (42); and a milling cutter (78, 100, 138) coupled to the frame assembly (76, 98, 136); wherein the milling device (74, 96, 134) is configured to be displaced in a circumferential direction (34) relative to the longitudinal axis (36) to machine the slot (45) in the circumferential direction (34) along the inner surface of the casing (42) via the milling cutter (78, 100, 138); wherein the structural guides (88, 132) of the frame assembly (76, 98, 136) are configured to engage a structural feature (66) on the inner surface of the casing (42) to maintain the axial position of the milling device (74, 96, 134) relative to the longitudinal axis (36) of the casing (42); the structural feature (66) on the inner surface of the casing (42) is configured to retain a compressor stator vane; and the milling device (74, 96, 134) utilizes existing casing structural features near the area of the inner surface of the casing (42) to be milled or machined as a support for the milling device (74, 96, 134) and a guide for the path of the milling device (74, 96, 134).

2. The milling device (74, 96, 134) of claim 1, wherein the structural feature (66) on the inner surface of the casing (42) includes a slot (72) extending in a circumferential direction (34).

3. The milling device (74, 96, 134) of claim 1, wherein each structural guide (88, 132) of the plurality of structural guides (88, 132) includes an L-shape.

4. The milling device (74, 96, 134) of claim 1, wherein the frame assembly (76, 98, 136) is adjustable in size and is configured to be interchangeably coupled to different sets of structural guides (88, 132), and each different set of structural guides (88, 132) is configured to engage a different size, shape, or combination thereof, of structural features (66) on the inner surface of the casing (42).

5. The milling device (74, 96, 134) of claim 1, wherein the frame assembly (76, 98, 136) includes a pair of rails (150, 152) coupled to a pair of bars (148), and a position of each rail (150, 152) of the pair of rails (150, 152) is adjustable along a length of the pair of bars (148).

6. The milling device (74, 96, 134) of claim 1, including a plate (158) coupled to the frame assembly (76, 98, 136), wherein the milling cutter (78, 100, 138) is coupled to the frame assembly (76, 98, 136) via the plate (158).

7. The milling device (74, 96, 134) of claim 6, wherein a position of the milling cutter (78, 100, 138) on the plate (158) is adjustable in an axial direction (30) relative to the longitudinal axis (36) of the housing (42).

8. The milling device (74, 96, 134) of claim 1, further comprising: a bearing support configured to interface with an inner surface of a housing (42) of a gas turbine engine (11) to provide a support force in a direction perpendicular to the longitudinal axis (36) of the housing (42) and to move the milling device (74, 96, 134) in a circumferential direction (34) relative to the longitudinal axis (36); and wherein the bearing support is disposed on a surface of the frame assembly (76, 98, 136) facing the inner surface of the housing (42).

9. The milling device (74, 96, 134) of claim 8, wherein the bearing support includes a plurality of spring-loaded pins (190) configured to provide a support force in a direction perpendicular to the longitudinal axis (36) of the housing (42); and wherein each spring-loaded pin (190) of the plurality of spring-loaded pins (190) is frictionless to enable movement of the milling device (74, 96, 134) in the circumferential direction (34).

10. The milling device (74, 96, 134) of claim 1, including a roller (120) to enable movement of the milling device (74, 96, 134) in the circumferential direction (34).

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