Patent Grant
7765658
The invention relates generally to gas turbine engines, and more particularly, to an improved apparatus and method for manufacturing compressor and turbine rotor assemblies as utilized in gas turbine engines.
A compressor or turbine rotor assembly for gas turbine engines, includes a plurality of compressor or turbine blades mounted to the outer periphery of a central rotor. It is important in gas turbine engines that the outer tips of the compressor or turbine blades run very close to surrounding shrouds in order to minimize gas leakage across the tips of the blades. Machining of such compressor or turbine blade tips to the desired outer true tip diameter, is a difficult manufacturing operation because the blades are normally retained with root sections loosely fitting within dovetail grooves in the rotor at the periphery thereof. Prior art fixture tools use radial expansion of resilient materials under axial compression forces for simulating the centrifugal force created during engine operation, to radially position the blades during a machining process. In such a prior art method, it is difficult to accurately control the quantity, acting points, and even distribution of radial forces acting on the individual blades. Therefore, the results are often unsatisfactory. In another prior art machining method, the rotor assembly is rotated at a high speed, resulting in a centrifugal force for positioning the blades within the slots of the rotor in a blade tip machining process. The high speed rotation of the rotor disc during the machining process is however, not desirable due to various concerns such as safety, convenience, cost of the manufacturing process, etc.
Accordingly, there is a need to provide an improved apparatus and method for machining blade tips as used in gas turbine engines.
It is therefore an object of this invention to provide an apparatus and method for machining blade tips of a rotor assembly used for gas turbine engines.
In one aspect, the present invention provides a fixture assembly for positioning a plurality of blades relative to a rotor of a gas turbine engine, the blade being retained therein by loose-fitting dovetail joints. The blades have a dovetail root, an airfoil and a transversely extending platform therebetween. The fixture assembly comprises a support for holding said rotor having the blades mounted thereto, and first and second positioning members. The first positioning member has a blade engagement portion for contacting a first portion of each blade platform protruding axially relative to the rotor. The second positioning member is disposed so as to be on an opposite axial side of the rotor when the rotor is mounted in the support. The second positioning member has a blade engagement portion for contacting a second portion of each blade platform protruding axially relative to the rotor. The second portion of each blade platform is opposite to the first portion. There is a centrally actuatable clamping assembly substantially coaxial to a rotor axis for axially clamping the first and second positioning members together when the rotor is mounted in the support. The first and second positioning members are adapted to transmit a pair of radial forces on the respective first and second portions of each of the blade platforms for radially positioning the blades outwardly against the rotor, thereby simulating a centrifugal force resulting from rotor rotation about said rotor axis.
In another aspect, the present invention provides a fixture assembly for a rotor assembly which includes a rotor disc having an axis of rotation and a plurality of airfoil blades mounted to a periphery of the rotor by respective loose-fitting dovetail joints. The fixture assembly comprises an axle adapted to centrally support the rotor assembly, and first and second clamping members associated with the axle. The clamping members are adapted to be moved towards one another to thereby provide a clamping force therebetween. There are first and second concave assemblies mounted to the axle and positioned such that a central concave surface of each concave assembly faces the rotor. The concave assemblies are disposed on opposite sides of the rotor relative to one another and the first and second concave assemblies each extend from the axle to engage opposite sides of the airfoil blades at respective peripheries of the first and second concave assemblies. The first concave assembly is associated with the first clamping member and the second concave assembly is associated with the second clamping member. When a rotor assembly is installed in the fixture assembly, movement of the clamping members towards one another tends to reduce respective concavities of the first and second concave assemblies and thereby generate an upwardly-directed radial force at the respective peripheries of the first and second concave assemblies in order to radially secure the airfoil blades relative to the rotor disc.
In another aspect, the present invention provides a method of machining rotor assembly blade tip outer diameters. The rotor assembly has an annular array of blades mounted to an outer periphery of a rotor via loose-fitting dovetail joints and the blades each have platforms protruding axially from both sides of the rotor. The method comprises (a) positioning a pair of generally cone-like members which extend from a common axis to a platform engaging surface; (b) positioning the cone-like members with respect to the rotor assembly to locate a portion of each of the cone-like members in a predetermined angular position relative to the blade platforms, one cone-like member on each axial side of the rotor so that opposed sides of each platform are engaged by the first and second cone-like members respectively; (c) radially positioning the blade with respect to the rotor by applying substantially even radial expansion forces to the individual blade platforms by applying an axial compressive on the cone-like members towards one another; and then (d) machining outer tips of the blades.
Further details of these and other aspects of the present invention will be apparent from the detailed description and figures included below.
Reference is now made to the accompanying figures depicting aspects of the present invention, in which:
Referring to
As so mounted upon the rotor 22, the blades 24 are not necessarily disposed in the “running” position, that is, the positions the blades 24 take under centrifugal forces created thereon during operation of the gas turbine engine. Furthermore, the diameter of each of the blade tips 28 relative to a central axis 32 of the rotor 22, varies due to manufacturing tolerance build-up. Therefore, it is desirable to machine the tips 28 when the blades 24 are assembled upon the rotor 22 and held in the “running” position in order to obtain a desired outer diameter of the rotor assembly 20.
In accordance with one embodiment of the present invention, a fixture assembly 40 is contemplated to provide tooling for machining the tips 28 of the rotor assembly 20 in a machining process.
The fixture assembly 40 includes a first disc spring 42 and a second disc spring 44, preferably forming first and second toggle joint devices in order to convert a pair of substantially balanced axial compressive forces into a pair of substantially balanced radial expansion forces acting on opposite axial sides of each blade 24, thereby firmly radially positioning the blade 24 with respect to the rotor 22. The disc springs 42, 44 are preferably similar and therefore only disc spring 42 will be described in detail for convenience of description.
Referring to
It is preferable to provide a resilient layer such as urethane rubber of similar material, on the outer end 58 of each arm 54 in order to ensure firm contact between each arm 54 and the axially protruding portion of the platform 30 of each blade 24. In this embodiment, the resilient layers on the outer ends 58 of the respective arms 54 are connected with the layers on the adjoining arms 54 to form an integral outer ring 60 of resilient material attached to the outer periphery 48 of the disc spring 42. The layer is preferably shaped to complimentarily receive the protruding portions of the blade platforms.
The disc spring 42 further preferably includes an angularity positioning element, for example a small radial recess or slot 62 defined in the inner periphery 46 at a predetermined angular location. This will be further described hereinafter.
Disc springs 42, 44, thus function as toggle joint devices with the outer periphery 48 and the resilient layer 60 thereon in contact with the axial protruding portion of the platform 30 of each blade 24 at the respective opposite sides thereof.
In
In particular, the lifting member 64 which is better illustrated in
The top clamping cover 66 is formed for example, like an inverted bowl having flat upper and lower ends (not indicated) thereof. The top clamping cover 66 defines a shoulder configuration at the lower end thereof similar to the shoulder configuration of the support ring 76, in order to maintain contact with the disc spring 42 at the inner periphery 46 thereof. A ring 82 having an outer diameter slightly greater than the diameter of the inner periphery 46 of the disc spring 42 is preferably attached to the lower end of the top clamping cover 66 using mounting screws (not shown) such that the top clamping cover 66 is detachably attached to the disc spring 42 for convenience of mounting the rotor assembly 22 into the fixture assembly 40. The top clamping cover 66 further includes a central opening 84 with a key slot 86. A plurality of apertures 88 are preferably provided in the top clamping cover 66.
The clamping device 63 further includes a sleeve member 90 which is also shown in
The clamping device 63 is further provided with an actuating screw 106 which extends through the rotor 22 and includes upper and lower threaded sections 108, 110 having complimentary threads with respect to the respective inner threads of the sleeve member 90 and the lifting member 64. The inner threads 92 of the sleeve member 90 and the inner threads 70 of the lifting member 64, as well as the complimentary threads of the respective upper and lower threaded sections 108, 110 are in opposite directions such that when the actuating screw 106 rotates relative to the sleeve member 90 and the lifting member 64, the sleeve member 90 and the lifting member 64 are forced to move towards or away from each other. The actuating screw 106 preferably includes a top head section 112 in a hexagonal configuration, for engagement with a tool (not shown) for turning the actuating screw 106.
A top nut 114 is provided to engage with the outer threads 96 of the sleeve member 90 in order to retain the top clamping cover 66 to move together with the sleeve member 90 towards the lifting member 64. The sleeve member 90 and the cylindrical body 68 of the lifting member 64 have an outer diameter which is significantly smaller than the central bore of the rotor 22, thereby allowing the respective sleeve member 90 and the cylindrical body 68 of the lifting member 64 to be loosely inserted into the central bore of the rotor 22 from opposite sides thereof, which will be further described hereinafter.
The fixture assembly 40 further preferably includes a base structure 116 for operatively supporting the clamping device 63 and for securely supporting the rotor assembly 20 in the fixture assembly 40. The base structure 116 includes for example, a base plate 118 which is illustrated in detail in
The base plate 118 preferably further includes bores 154 located in the grooves of the recess 124 and extending axially through the base plate 118, and channels 156 defined in the bottom of the base plate 118 and extending radially between the individual bores 154 and the outer periphery (not indicated) of the base plate 118, thereby forming fluid passages to discharge the cooling and lubricating fluids from the cavity 120 of the base structure 116 during a machining process.
The base structure 116 further includes a central sleeve 130 which is better illustrated in
The radial flange 132 of the central sleeve 130 preferably further includes an axially extending ring 142 with a plurality of circumferentially spaced slots 144 therein, sized and positioned in accordance with the mating members on, for example, the bottom side of the rotor 22. Those mating members of rotor 22 mate with the rotor of adjacent stages for transferring torque between the adjacent rotors. The mating members are received in the slots 144 when the rotor 22 is supported on the radial flange 132 of the central sleeve 130 such that the angular relationship between the rotor assembly 20 and the base structure 116 is determined.
The base structure 116 is further provided with a central top plate 150 defining a central opening (not indicated) with a key slot (not indicated). The central top plate 150 abuts the top side of the rotor 22 which does not have the mating members, and is secured to the central sleeve 130 at the top end thereof by mounting screws 148 such that the rotor assembly 20 is securely affixed to the base structure 116. The central opening with a key slot of the central top plate 150 allows the sleeve member 90 with attached key 102 to be loosely moveable through the central top plate 150 into the central sleeve 130. Although the rotor assembly 20 is securely affixed to the base structure 116, the disc springs 42, 44 as well as the contacted clamping device 63 which includes the top clamping cover 66 with ring 82, sleeve member 90 and the lifting member 64 with the support ring 76 and ring 78 interconnected by the actuating screw 106, are loosely and operatively retained by the base structure 116 when the disc springs 42, 44 are disposed on the respective bottom and top sides of the rotor assembly 22, prior to a pair of axial forces being applied to the respective disc springs 42, 44. Thus, the disc springs 42, 44 with the clamping device 63 are adjustable about the co-axially positioned central axis 128 of the base plate 118, axis 134 of the central sleeve 130 and axis 32 of the rotor 22. This feature provides an advantage for self-centering of the respective disc springs 42, 44 about the central axis 32 of the rotor 22 in order to ensure appropriate contact with the axially protruding portions of the platform 30 of the blades 24 in compensation for tolerance stackup of both the root assembly 20 and the fixture assembly 40.
The base structure 116 preferably further includes a gauging ring 146 which is secured to the top of the base plate 118 by mounting screws (not shown). The gauging ring 146 is positioned precisely and coaxially with the base plate 118, and has a precisely machined outer periphery with a predetermined diameter thereof in order to provide a measurement reference for the outer diameter of the tips 28 of the blades 24.
As described above, the disc springs 42, 44 function as toggle joint devices with each arm 54 acting as a toggle joint. The working principle of toggle joints are briefly discussed with reverence to
P=F×coefficient, wherein coefficient=cos α/2 sin α.
When the angle α is predetermined, the radial expansion forces which are equivalent to the resistance forces P applied by the toggle joints, can be applied with relative accuracy by controlling the applied axial force F, which can be conveniently achieved by using a torque gauge when applying torque to the actuating screw 106 of
Referring again to
Still referring to
The angular positioning of the respective disc springs 42, 44 with respect to the rotor assembly 20 is automatically completed in the previous mounting steps because of the plurality of angularity positioning elements discussed in the previous paragraph. Nevertheless, in another embodiment of the present invention in which there are no chains of angularity positioning elements provided, efforts must be made at this stage to angularly position the respective disc springs 42, 44 in order to ensure at least each of arms 54 thereof extends toward one blade 24 without interfering with adjacent blades.
An appropriate tool (not shown) is used to firstly apply a small amount of torque to the actuating screw 106 in order to adjust the distance between the lifting member 64 and the clamping top cover 66 into proper axial positions while self-adjusting the respective disc springs 42, 44 such that the outer periphery 48 (see
After the disc springs 42, 44 are properly positioned, a predetermined amount of torque is applied to the actuating screw 106 to apply substantially balanced axial forces to the respective disc springs 42, 44, which convert the axial forces into a pair of substantially balanced radial expansion forces acting on the platform 30 of each blade 24 on the opposite sides thereof, thereby resulting in a total radial expansion force acting substantially through a gravitational center of each blade 24 to radially firmly position the blades 24 with respect to the rotor 22. The tool is generally placed on the machine table, then the various parts are installed and verified for accuracy. The remaining parts of the fixture are then assembled and torque is applied to the top nut 114. The blades are thus centered to ensure that they are tight. At this stage the rotor assembly 20 affixed with the fixture assembly 40, is ready to be placed on a running table, for example, of a grinding machine, for machining the outer tips of the blades 24. Before, during and after the grinding process, the outer diameter of the rotor assembly 20 can be conveniently measured by measurement of the difference between one tip and the outer periphery of the gauging ring 146.
The above description is meant to be exemplary only, and one skilled in the art will recognize that changes may be made to the embodiments described without departure from the scope of the invention disclosed. For example, the disc springs may not include cuts to form individual arms as described in the above embodiments. Nevertheless, disc springs without cuts require more axial compressive forces to overcome the resilient deformation of the material. Generally, the disc springs can be replaced by any concave assemblies or cone-like members. These cone-like members can be made from resilient material such as relatively solid rubber, or can have resilient properties due to the combination of the material and configuration thereof, for example, disc springs with or without cuts. However, the cone-like members can also function properly without being resilient if they are configured as toggle joint devices in which individual arms are pivotally mounted at the inner ends thereof, to an inner ring. The lifting member and the base structure may be of various configurations, provided that the base structure 116 securely supports the rotor 22 and operatively supports the clamping device 63. Other angularity positioning elements which mate with a selected part or parts of the rotor configuration may be provided as an alternative to the slots 144 in the flange 132 of the central sleeve 130 (see
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