# Patent

## Title
Method of generating a curved blade retention slot in a turbine disk

## Abstract

A method of forming a curved slot in a turbine disk includes the steps of forming a pre-slot in the turbine disk and finishing the pre-slot to form a slot that receives a portion of a turbine blade. The turbine disk including a first face, an opposing second face, and an outer perimeter surface extending between the first face and the opposing second face. The pre-slot includes a first curved wall and a second curved wall that each extend between the first face and the opposing second face. An intersection between the outer perimeter surface and each of the first curved wall and the second curved wall is defined by a curved line.

## Background
BACKGROUND OF THE INVENTION
This application relates to a method of generating a curved blade retention slot in a turbine disk of a gas turbine engine.
Gas turbine engines generally include turbine rotors having a plurality of removable turbine blades and a plurality of associated static vanes. The turbine blades are mounted on a turbine disk.
FIGS. 1A and 1B show a front view and a side view, respectively, of a related art turbine disk 46 including a plurality of straight slots 48 for mounting turbine blades to a turbine disk 46. The turbine disk 46 includes a first face 53, an opposing second face 55, and an outer perimeter surface 51 that extends between the first face 53 and the opposing second face 55. The straight slots 48 are generally fabricated using a broaching process. A broaching tool makes a pass through the turbine disk 46 to form an initial pre-slot passage in the turbine disk 46. After forming the straight slots 48, an opening 59 of the straight slots 48 on the outer perimeter surface 51 of the turbine disk 46 is defined by two substantially parallel lines 49. Additional broaching tools pass through the passage, enlarging the passage and defining the profile of each of the straight slots 48. A drawback to the broaching process is that it can only form straight slots.
There is a need in the art for a method of generating a curved blade retention slot in a turbine disk of a gas turbine engine that overcomes the drawbacks and shortcomings of the related art.
SUMMARY OF THE INVENTION
A method of forming a curved slot in a turbine disk includes the steps of forming a pre-slot in the turbine disk and finishing the pre-slot to form a slot that receives a portion of a turbine blade. The turbine disk including a first face, an opposing second face, and an outer perimeter surface extending between the first face and the opposing second face. The pre-slot includes a first curved wall and a second curved wall that each extend between the first face and the opposing second face. An intersection between the outer perimeter surface and each of the first curved wall and the second curved wall is defined by a curved line.
In another exemplary embodiment, a method of forming a turbine disk includes the steps of forming a pre-slot in the turbine disk and finishing the pre-slot to form a slot that receives a base of a turbine blade. The turbine disk includes a first face, an opposing second face, and an outer perimeter surface extends between the first face and the opposing second face. The pre-slot includes a first curved wall and a second curved wall that each extend between the first face and the opposing second face. An intersection between the outer perimeter surface and each of the first curved wall and the second curved wall is defined by a curved line. The method further includes the step of inserting the base of the turbine blade into the slot of the turbine disk, and a shape of the slot corresponds to a shape of the base of the turbine blade.
In another exemplary embodiment, a turbine disk includes a body portion including a first face, an opposing second face, and an outer perimeter extending between the first face and the opposing second face. A slot in the body portion extends between the first face and the opposing second face to receive a portion of a turbine blade. The slot defines an opening on the outer perimeter surface, and the opening is defined by two curved lines.
These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1A illustrates a front view of a related turbine disk including a plurality of straight slots;
FIG. 1B illustrates a side view of the related turbine disk including a plurality of straight slots;
FIG. 2 illustrates a simplified cross-sectional view of a standard gas turbine engine;
FIG. 3 illustrates a perspective view of a turbine blade;
FIG. 4A illustrates a front view of a turbine disk including a plurality of curved slots;
FIG. 4B illustrates a side view of the turbine disk including a plurality of curved slots;
FIG. 5 illustrates a front view of the turbine disk with a cup-type forming tool positioned to form a curved pre-slot;
FIG. 6 illustrates a side view of the turbine disk with the cup-type forming tool positioned to form the curved pre-slot;
FIG. 7 illustrates a side view of the turbine disk including curved pre-slots;
FIG. 8 illustrates a bottom view of the cup-type forming tool;
FIG. 9 illustrates several different cup-type forming tools;
FIG. 10 illustrates a front view of the turbine disk showing the curved pre-slot;
FIG. 11 illustrates a step portion added to the cup-type forming tool;
FIG. 12 illustrates a front view of the turbine disk showing the machining of the shape of the curved slots;
FIG. 13 illustrates a side view of the turbine disk showing the machining of the shape of the curved slots;
FIG. 14 illustrates the machining of one side of the curved slot; and
FIG. 15 illustrates the simultaneous machining of both sides of the curved slot.



DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
As shown in FIG. 2, a gas turbine engine 10, such as a turbofan gas turbine engine, is circumferentially disposed about an engine centerline (or axial centerline axis 12). The gas turbine engine 10 includes a fan 14, compressors 16 and 17, a combustion section 18 and turbines 20 and 21. This application extends to engines without a fan, and with more or fewer sections. As is well known in the art, air is compressed in the compressors 16 and 17, mixed with fuel and burned in the combustion section 18, and expanded in turbines 20 and 21. The turbines 20 and 21 include rotors 22 which rotate in response to the expansion, driving the compressors 16 and 17 and the fan 14. The turbines 20 and 21 include alternating rows of metal rotating airfoils or turbine blades 24 and static airfoils or vanes 26. FIG. 2 is schematic, and the turbine blades 24 and the vanes 26 are removable from the rotors 22. It should be understood that this view is included simply to provide a basic understanding of the sections in a gas turbine engine 10 and not to limit the invention. This invention extends to all types of gas turbine engines for all types of applications.
FIG. 3 shows a turbine blade 24. A platform 42 is provided at a radially inner portion of the turbine blade 24, while an airfoil 40 extends radially (as seen from the axial centerline axis 12) outwardly from the platform 42. A curved base 44 located under the platform 42 has an irregular surface including fingers 25 and grooves 23.
FIGS. 4A and 4B show a front view and a side view, respectively, of an exemplary turbine disk 50. The turbine disk 50 includes a first face 84, an opposing second face 86, and an outer perimeter surface 94 that extends between the first face 84 and the opposing second face 86. A plurality of curved blade retention slots 52 extend from the first face 84 and the opposing second face 86 of the turbine disk 50. An opening 98 of the curved slots 52 on the outer perimeter surface 94 of the turbine disk 50 is defined by two substantially curved lines 90. Curved walls 96 that extend from the first face 84 to the opposing second face 86 of the turbine disk 50 define the curved slots 52. In one example, the curved lines 90 are each an arc or a portion of a circle.
Each of the plurality of curved slots 52 receives the curved base 44 of one of the turbine blades 24. Each of the plurality of curved slots 52 is formed by a two step process. In the first step, a curved pre-slot 56 is formed. In the second step, the curved pre-slot 56 is finished to form the curved slot 52. The curved slot 52 includes a plurality of fingers 78 and grooves 80 (as shown in FIG. 12) and has a profile that matches the profile of the curved base 44 of the turbine blade 24.
As shown in FIGS. 5 and 6, in a first step, a cup-type forming tool 54 forms the pre-slot 56 in the turbine disk 50 (as shown in FIG. 7). The first step defines the location of the curved slots 52 and forms the general shape. As shown in FIG. 8, the cup-type forming tool 54 has a generally circular shape and a circumferential portion 58 having a thickness Z. The circumferential portion 58 has an inner diameter Y and an outer diameter X defined from a central axis W of the cup-type forming tool 54. The cup-type forming tool 54 may include a grinding wheel, a plated cubic boron nitride (CBN) wheel, a vitrified cubic boron nitride wheel, an inserted milling cutter or the like. As shown in FIG. 9, the pre-slot 56 can be formed by a variety of different shaped cup-type forming tools 54A, 54B and 54C each having a different thickness Z.
The cup-type forming tool 54 is positioned at a desired location relative to the turbine disk 50. An end surface 62 of the circumferential portion 58, which defines a substantially circular ring, contacts a periphery 64 of the outer perimeter surface 94 of the turbine disk 50 and rotates about the central axis W of the cup-type forming tool 54. The cup-type forming tool 54 is then moved radially inward towards a central axis 66 of the turbine disk 50 to form a u-shaped pre-slot 56 (shown in FIG. 10) that includes substantially arcuate shaped opposing walls. The arcuate shaped pre-slot 56 extends between the faces 84 and 86 of the turbine disk 50 (as shown in FIG. 7). The shape of the pre-slot 56 corresponds to the shape of the portion of the circular circumferential portion 58 of the cup-type forming tool 54 that forms the pre-slot 56. After the pre-slot 56 formed, the cup-type forming tool 54 is removed from the pre-slot 56.
Next, the turbine disk 50 and/or the cup-type forming tool 54 is moved relative to the other to position the cup-type forming tool 54 at a desired location relative to the turbine disk 50. Another pre-slot 56 can then formed in the turbine disk 50. The location of the cup-type forming tool 54 relative to the turbine disk 50 determines the orientation of the curved pre-slots 56 on the turbine disk 50. The diameters X and Y of the cup-type forming tool 54 determine the curvature of the pre-slots 56.
As shown in FIG. 11, in another example, a step portion 68 is positioned on the circumferential portion 58 to add additional contours to the curved pre-slot 56. In one example, the step portion 68 includes a first portion 70, a second portion 72 and a third portion 74. The first portion 70 has a diameter greater than the second portion 72, and the second portion 72 has a diameter greater than the third portion 74.
In a second step, as shown in FIG. 12, the curved pre-slot 56 is finished with a profiled finger type finishing tool 76 to form the curved slots 52. That is, the second step defines the profile of the curved slot 52. The profiled finger type finishing tool 76 may include a plated CBN tool, a vitrified CBN tool, a profiled end mill cutter or the like. As shown in FIG. 13, the finger type finishing tool 76 moves along the curved pre-slot 56 in the path shown in the dashed line to form the final shape of the curved slots 52 that includes the plurality of fingers 78 and the grooves 80. The profiled finger type finishing tool 76 provides the pre-slot 56 with a shape that corresponds to the shape of the curved base 44 of the turbine blade 24. Alternately, multiple tools can be used to achieve the final shape of the slot profile.
In one example shown in FIG. 14, the profile machining can be achieved by machining one side of the curved pre-slot 56 at a time. Alternatively, as shown in FIG. 15, the profile machining can be achieved by simultaneously machining both sides of the curved pre-slot 56 at the same time.
After machining, the curved slots 52 of the turbine disk 50 have the same shape and curvature as the curved base 44 of the turbine blade 24. When the turbine blade 24 is to be installed in the turbine disk 50, the curved base 44 of the turbine blade 24 is aligned with the curved slots 52. The fingers 25 of the turbine blade 24 align with the grooves 80 of the curved slot 52, and the grooves 23 of the turbine blade 24 align with the fingers 78 of the curved slot 52. The turbine blade 24 is then slid relative to the turbine disk 50 to install the turbine blade 24 in the curved slot 52 of the turbine disk 50.
Compared to straight pre-slots of the related prior art, the exemplary curved slots 52 facilitate reducing the stresses on the blade attachment and the curved slots 52, facilitating increasing the retention capability of the turbine blade 24 in the turbine disk 50, and facilitating reducing the size, weight and cost of the gas turbine engine 10.
The foregoing description is only exemplary of the principles of the invention. Many modifications and variations are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than using the example embodiments which have been specifically described. For that reason the following claims should be studied to determine the true scope and content of this invention.

## Claims

1. A method of forming a slot in a turbine disk, the method comprising the steps of:
forming a pre-slot in a turbine disk, the turbine disk including a first face, an opposing second face, and an outer circumferential surface extending between the first face and the opposing second face, and the pre-slot includes a first curved wall and a second curved wall that each extend between the first face and the opposing second face, wherein the step of forming the pre-slot includes rotating a forming tool about a central axis of the forming tool, then moving the forming tool to contact an outer circumferential surface of the turbine disk, and then moving the forming tool in a first direction radially inwards from the outer circumferential surface of the turbine disk and towards a central axis of rotation of the turbine disk to form the pre-slot, and then moving the forming tool radially outward from the pre-slot in a second direction towards the outer circumferential surface of the turbine disk and away from the central axis of rotation of the turbine disk and the pre-slot to remove the forming tool from the pre-slot, wherein the second direction is opposite to the first direction; and
then finishing the pre-slot after the step of forming the pre-slot to form a slot that receives a portion of a turbine blade.

2. The method as recited in claim 1 wherein the step of finishing the pre-slot includes positioning a finishing tool in the pre-slot and forming at least one groove and at least one finger in the pre-slot to form the slot.

3. The method as recited in claim 1 wherein two substantially curved lines define an opening of the slot on the outer circumferential surface of the turbine disk.

4. The method as recited in claim 1 wherein the pre-slot includes a bottom wall, and the first curved wall and the second curved wall are located on opposing sides of the bottom wall, and an entirety of first curved wall and an entirety of the second curved wall are substantially perpendicular to the bottom wall.

5. The method as recited in claim 1 wherein a distance between the first curved wall and the second curved wall defines a width of the pre-slot, and the width is constant for an entire length of the pre-slot and along an entire height of the pre-slot.

6. The method as recited in claim 1 wherein an intersection between the outer circumferential surface with each of the first curved wall and the second curved wall is defined by a curved line.

7. The method as recited in claim 1 wherein a tip of the forming tool includes two portions each having a different diameter.

8. A method of forming a turbine disk, the method comprising the steps of:
forming a pre-slot in a turbine disk, the turbine disk including a first face, an opposing second face, and an outer circumferential surface extending between the first face and the opposing second face, and the pre-slot includes a first curved wall and a second curved wall that each extend between the first face and the opposing second face, wherein a distance between the first curved wall and the second curved wall defines a width of the pre-slot, and a thickness is constant for an entire length of the pre-slot and along an entire height of the pre-slot, and an intersection between the outer circumferential surface and each of the first curved wall and the second curved wall is defined by a curved line, wherein the step of forming the pre-slot includes rotating a forming tool about a central axis of the forming tool, then moving the forming tool contact an outer circumferential surface of the turbine disk, and then moving the forming tool in a first direction radially inwards from the outer circumferential surface of the turbine disk towards a central axis of rotation of the turbine disk to form the pre-slot, and then moving the forming tool radially outward from the pre-slot in a second direction towards the outer circumferential surface of the turbine disk and away from the central axis of rotation of the turbine disk and the pre-slot to remove the forming tool from the pre-slot, wherein the second direction is opposite to the first direction;
then finishing the pre-slot after the step of forming the pre-slot to form a slot that receives a base of a turbine blade; and
inserting the base of the turbine blade into the slot of the turbine disk, wherein a shape of the slot corresponds to a shape of the base of the turbine blade.

9. The method as recited in claim 8 wherein the step of finishing the pre-slot includes positioning a finishing tool in the pre-slot and forming at least one groove and at least one finger in the pre-slot to form the slot.

10. The method as recited in claim 8 wherein the pre-slot includes a bottom wall, and the first curved wall and the second curved wall are located on opposing sides of the bottom wall, and an entirety of first curved wall and an entirety of the second curved wall are substantially perpendicular to the bottom wall.

11. The method as recited in claim 8 wherein a distance between the first curved wall and the second curved wall defines a width of the pre-slot, and the width is constant for an entire length of the pre-slot and along an entire height of the pre-slot.

12. The method as recited in claim 8 wherein an intersection between the outer circumferential surface with each of the first curved wall and the second curved wall is defined by a curved line.

13. The method as recited in claim 8 wherein a tip of the forming tool includes two portions each having a different diameter.

14. A method of forming a slot in a turbine disk, the method comprising the steps of:
forming a pre-slot in a turbine disk, the turbine disk including a first face, an opposing second face, and an outer circumferential surface extending between the first face and the opposing second face, and the pre-slot includes a first curved wall and a second curved wall that each extend between the first face and the opposing second face, wherein the step of forming the pre-slot includes positioning a forming tool relative to the outer circumferential surface of the turbine disk, rotating the forming tool about a central axis of the forming tool, the moving the forming tool to contact the outer circumferential surface of the turbine disk and then radially inwards towards a central axis of the turbine disk to form the pre-slot, and then moving the forming tool radially outward away from the pre-slot to remove the forming tool from the pre-slot wherein the forming tool is a cup having a wall defined by an inner circumferential surface and an outer circumferential surface, and the cup rotates about a central axis to remove a portion of the turbine disk with the wall to define the pre-slot having the shape of the wall and a curvature of the inner circumferential surface and the outer circumferential surface; and
then finishing the pre-slot after the step of forming the pre-slot to form a slot that receives a portion of a turbine blade.

15. The method as recited in claim 14 wherein, during the step of forming the pre-slot when the cup is rotating about the central axis, a portion of the cup is located in the pre-slot and a reminder of the cup is located outside the pre-slot.

16. The method as recited in claim 14 wherein a direction of movement of the cup and the central axis of the cup is perpendicular to the central axis of rotation of the turbine disk.

17. The method as recited in claim 14 wherein the wall of the cup that contacts the turbine blade is spaced away from the central axis of the cup.

18. A method of forming a turbine disk, the method comprising the steps of:
forming a pre-slot in a turbine disk, the turbine disk including a first face, an opposing second face, and an outer circumferential surface extending between the first face and the opposing second face, and the pre-slot includes a first curved wall and a second curved wall that each extend between the first face and the opposing second face, wherein a distance between the first curved wall and the second curved wall defines a width of the pre-slot, and a thickness is constant for an entire length of the pre-slot and along an entire height of the pre-slot, and an intersection between the outer circumferential surface and each of the first curved wall and the second curved wall is defined by a curved line, wherein the step of forming the pre-slot includes positioning a forming tool relative to an outer circumferential surface of a turbine disk, rotating the forming tool about a central axis of the forming tool, then moving the forming tool to contact the outer circumferential surface of the turbine disk and then radially inwards towards a central axis of the turbine disk to form the pre-slot, and then moving the forming tool radially outward away from the pre-slot to remove the forming tool from the pre-slot, wherein the forming tool is a cup having a wall defined by an inner circumferential surface and an outer circumferential surface, and the cup rotates about a central axis to remove a portion of the turbine disk with the wall to define the pre-slot having the shape of the wall and a curvature of the inner circumferential surface and the outer circumferential surface;
then finishing the pre-slot after the step of forming the pre-slot to form a slot that receives a base of a turbine blade; and
inserting the base of the turbine blade into the slot of the turbine disk, wherein a shape of the slot corresponds to a shape of the base of the turbine blade.

19. The method as recited in claim 18 wherein, during the step of forming the pre-slot when the cup is rotating about the central axis, a portion of the cup is located in the pre-slot and a reminder of the cup is located outside the pre-slot.

20. The method as recited in claim 18 wherein a direction of movement of the cup and the central axis of the cup is perpendicular to the central axis of the turbine disk.

21. The method as recited in claim 18 wherein the wall of the cup that contacts the turbine blade is spaced away from the central axis of the cup.