Information
-
Patent Grant
-
6780089
-
Patent Number
6,780,089
-
Date Filed
Tuesday, December 3, 200221 years ago
-
Date Issued
Tuesday, August 24, 200420 years ago
-
Inventors
-
Original Assignees
-
Examiners
- Hail, III; Joseph J.
- Thomas; David B.
Agents
- Ramaswamy; V. G.
- Davidson; James P.
-
CPC
-
US Classifications
Field of Search
US
- 451 28
- 451 29
- 451 36
- 451 64
- 451 99
- 451 113
-
International Classifications
-
Abstract
A system and method of removing a predetermined amount of material from a bottom portion of a dovetail slot in a gas turbine engine disk, including the steps of configuring a designated flow path through the dovetail slot and providing a flow of abrasive media through the flow path a designated number of cycles so that a substantially uniform amount of material is removed from the dovetail slot bottom portion. The method also includes the step of sealing a pressure surface of the dovetail slot to prevent the abrasive media from flowing thereagainst.
Description
BACKGROUND OF THE INVENTION
The present invention relates generally to the repair of a dovetail slot in a gas turbine engine disk and, more particularly, to an apparatus and method of removing a predetermined amount of material from a bottom portion of such dovetail slot.
It has been found that heavily cold worked material and other characteristics having the capability to reduce low cycle fatigue in dovetail slots of gas turbine engine disks, and particularly turbine disks which are rotated, may be caused during generation of such dovetail slots. In particular, the disturbed material may be caused by a dull broach tool during formation of the dovetail slot. Conventional methods of removing such disturbed material include milling the dovetail slot or to broach it again. Each of these processes, however, are useful only so long as the tools employed are sharp. Further, a hand deburr operation is typically required, which inherently involves a high risk of creating tool marks in the highly stressed dovetail area.
It is known in the art to utilize a flow of abrasive material on surfaces of gas turbine engine components in order to polish or provide surface finishing thereof. Such operations involve removing only a minimal amount of material (e.g., on the order of 0.0005 inch or 0.5 mil). An example of one such method is disclosed in U.S. Pat. No. 6,183,347 to Shaw, where a stream of pliant shot in a carrier fluid is discharged at a shallow angle of incidence against a plug and an adjoining surface for selective abrasion to provide a step. It will be appreciated therein that the method described is for the selective surface treating of a workpiece and does not involve the removal of material on the order required to remove a disturbed layer of material or shallow cracks.
While the aforementioned methods of removing disturbed material from a gas turbine engine disk are useful for that particular purpose, it would be desirable for an improved method of removing such disturbed material to be developed which overcomes the limitations noted above. It would also be desirable for an apparatus to be developed which defines a flow path through the dovetail slot in a manner which permit substantially uniform removal of the material in a surface on a bottom portion thereof without affecting the pressure surface portion of the dovetail slot.
BRIEF SUMMARY OF THE INVENTION
In a first exemplary embodiment of the invention, a method of removing a predetermined amount of material from a bottom portion of a dovetail slot in a gas turbine engine disk is disclosed as including the steps of configuring a designated flow path through the dovetail slot and providing a flow of abrasive media through the flow path for a designated number of cycles so that a substantially uniform amount of material is removed from the dovetail slot bottom portion. The method also includes the step of sealing a pressure surface of the dovetail slot to prevent the abrasive media from flowing thereagainst.
In a second exemplary embodiment of the invention, an apparatus for removing a predetermined amount of material from a bottom surface of a dovetail slot in a gas turbine engine disk is disclosed, wherein a longitudinal axis extends through the dovetail slot. The system includes a fixture for providing a flow of abrasive media back and forth through a designated path at a predetermined pressure and flow rate, a cradle for retaining the gas turbine engine disk in position so that the dovetail slot is in flow communication with the designated path, and a device for defining a designated flow path through the dovetail slot for the abrasive media. The flow of abrasive media then removes a substantially uniform amount of material from a bottom surface of the dovetail slot. The designated path of the abrasive flow fixture is configured to enable work on each dovetail slot of the disk to be performed substantially simultaneously.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1
is a cross-sectional view of a turbine disk positioned within an abrasive flow fixture so as to remove material along a bottom portion of the dovetail slots in accordance with the present invention;
FIG. 2
is an enlarged, partial cross-sectional view of the turbine disk positioned within the abrasive flow fixture as depicted in
FIG. 1
;
FIG. 3
is an enlarged, side view of the flow path through a bottom portion of the dovetail slot depicted in
FIGS. 1 and 2
;
FIG. 4
is an enlarged, front view of the flow path through a bottom portion of
FIG. 5
is a partial front view of a turbine disk having a contoured pin member positioned within a dovetail slot in preparation for removal of material along a bottom portion of such dovetail slot;
FIG. 6
is a partial aft view of the turbine disk depicted in
FIG. 5
;
FIG. 7
is a side perspective view of the contoured pin member depicted in
FIGS. 5 and 6
, where an upper portion has been deleted for clarity;
FIG. 8
is a side view of the contoured pin member depicted in
FIG. 7
, where an upper portion has been deleted for clarity;
FIG. 9
is a front view of the contoured pin member depicted in
FIGS. 7 and 8
, where an upper portion has been deleted for clarity;
FIG. 10
is a side perspective view of the contoured pin member depicted in
FIGS. 7-9
with the upper portion included thereon;
FIG. 11
is a side perspective view of a contoured pin having an alternative configuration, where an upper portion has been deleted for clarity;
FIG. 12
is a bottom perspective view of the contoured pin having an alternative configuration depicted in
FIG. 11
, where an upper portion has been deleted for clarity;
FIG. 13
is a side perspective view of the contoured pin depicted in
FIGS. 11 and 12
with an upper portion included thereon; and,
FIG. 14
is a bottom perspective view of the contoured pin depicted in
FIGS. 11-13
with an upper portion included thereon.
DETAILED DESCRIPTION OF THE INVENTION
Referring now to the drawings in detail, wherein identical numerals indicate the same elements throughout the figures,
FIG. 1
depicts a fixture
10
for applying an abrasive flow process to a disk
12
of a gas turbine engine. An exemplary fixture is one known by the name of Spectrum, which is made by Extrudehone Corp. of Irwin, Pa. It will be understood that the abrasive flow process of the present invention may be utilized with a disk of a turbine, compressor or fan of such gas turbine engine, but that disk
12
depicted is a turbine disk. More specifically, disk
12
includes a plurality of circumferentially spaced dovetail slots
14
formed in a periphery thereof, each of which are located between adjacent posts
16
and provided to retain a turbine blade (not shown) having a complementary dovetail section therein (see FIGS.
4
-
6
). Each dovetail slot
14
preferably has a shape generally like a fir tree and includes a pressure face portion
18
and a bottom portion
20
.
In order to remove a predetermined amount of material from a surface
22
of each dovetail slot bottom portion
20
, disk
12
is positioned via a cradle
24
for abrasive flow fixture
10
so that an abrasive media
26
is forced through each dovetail slot
14
as it travels through a designated path
28
. It will be noted from
FIG. 1
that designated path
28
of abrasive flow fixture
10
preferably is circumferential and includes a plurality of branches
30
which are in flow communication with each dovetail slot
14
so that they all may be worked substantially simultaneously. Abrasive media
26
utilized in fixture
10
includes a carrier, such as that identified as model number 995L or 649S by Extrudehone, with grit included therein preferably made of boron carbide, silicon carbide, or industrial diamond. It will be appreciated that abrasive media
26
is forced under a predetermined pressure and flow rate (preferably approximately 500-600 psi at approximately 3-5 cubic inches per second, although the pressure may be higher or lower with a corresponding decrease or increase in flow rate) from a lower portion
34
of abrasive flow fixture
10
through designated path
28
, branches
30
and dovetail slots
14
into an upper portion
36
thereof by a first cylinder (not shown). Thereafter, a second cylinder (not shown) located adjacent upper portion
36
forces abrasive media
26
under the same predetermined pressure and flow rate back through designated path
28
, branches
30
and dovetail slots
14
in the opposite direction to lower portion
34
. It will be understood that the travel of abrasive media
26
from lower portion
34
to upper portion
36
and back to lower portion
34
constitutes one cycle as that term is utilized herein.
With respect to each dovetail slot
14
, a flow path
38
having a longitudinal axis
40
(see
FIG. 3
) is defined through dovetail slot bottom portion
20
which is in flow communication with designated path
28
(as best seen in FIGS.
2
-
4
). In order to define flow path
38
, a device in the form of a plug or pin member
42
having certain predetermined contours is preferably positioned within each dovetail slot
14
. It will be appreciated that flow path
38
does not generally have a uniform cross-section therethrough. More specifically, a bottom surface
44
of pin member
42
includes a substantially arcuate portion
46
for at least part of the axial length thereof so that a variable cross-section exists for flow path
38
along longitudinal axis
40
. Arcuate portion
46
of bottom surface
44
preferably has a designated radius
48
which is proportional to a minimum axial length
50
of dovetail slot bottom portion
22
. A ratio of radius
48
to minimum axial length
50
is preferably in a range of approximately 1.0-1.5 and more preferably in a range of approximately 1.2-1.4.
It will also be seen that bottom surface
44
is preferably arcuate in a circumferential direction (i.e., substantially perpendicular to longitudinal axis
40
) throughout arcuate portion
46
as best seen in FIG.
4
. Accordingly, a circumferential radius
52
exists which is preferably proportional to a circumferential radius
54
for surface
22
of dovetail slot bottom portion
20
. A ratio of radius
52
to radius
54
is preferably in a range of approximately 1.2-1.8 and more preferably in a range of approximately 1.4-1.6.
Substantially planar portions
56
and
58
preferably exist on bottom surface
44
at a forward end
60
and an aft end
62
, respectively, in order to mate with corresponding rabbets
64
and
66
formed on disk
12
. Accordingly, it will be appreciated that while planar portions
56
and
58
may not have equivalent axial lengths, bottom surface
44
is substantially symmetrical thereacross. As seen in an alternate configuration depicted in
FIGS. 11-14
, a pin member
142
may be utilized which has a non-linear, non-symmetrical bottom surface
144
in order to have a desired amount of material removed from bottom surface
22
of dovetail bottom portion
20
.
A minimum cross-section known herein as a critical gap
68
is preferably maintained in flow path
38
so as to ensure the proper flow of abrasive media
26
therethrough. Critical gap
68
may also be defined as a minimum distance between surface
22
of dovetail slot bottom portion
20
and bottom surface
44
of pin member
42
or the difference between a radial height
70
of pin member
42
and a radial height
72
of dovetail slot bottom portion
20
. Critical gap
68
is generally located approximately at a midpoint
71
of flow path
38
and is approximately 50-70% of a gap width
69
at forward and aft ends
60
and
62
. The corresponding cross-section of flow path
38
at midpoint
71
is therefore approximately 30-50% of the cross-section at forward and aft ends
60
and
62
.
Critical gap
68
generally is a function of several parameters, including the material utilized for abrasive media
26
, the predetermined pressure and flow rate at which abrasive media
26
is forced through flow path
38
, and the shape of flow path
38
from both an axial and circumferential perspective. Nevertheless, it has been found for the intended process of removing material from surface
22
of dovetail slot bottom portion
20
that a ratio of radial height
70
to radial height
72
preferably be in a range of approximately 0.75-0.90 and more preferably in a range of approximately 0.80-0.86. Consequently, critical gap
68
will preferably be in a range of approximately 145-220 mils, more preferably in a range of approximately 160-210 mils, and optimally in a range of approximately 170-200 mils.
With respect to pin member
42
, it will be appreciated that it more specifically includes a first portion
74
which extends into dovetail slot bottom portion
20
to define flow path
38
and a second portion
76
which is removably retained in pressure face portion
18
of dovetail slot
14
. First portion
74
has a bottom section
78
which includes bottom surface
44
of pin member
42
. A pair of tapered side walls
80
and
82
are part of bottom section
78
and are configured so as to avoid contact with side surfaces
84
and
86
, respectively, of dovetail slot bottom portion
20
. A middle section
88
extends from a top surface
90
of bottom section
78
, is preferably substantially planar in configuration, and has an axial length
92
. Middle section
88
also preferably includes at least one opening
94
formed therein, the purpose for which will be explained herein. It will be understood that middle section
88
may have other configurations, such as one or more cylinders extending from top surface
90
of bottom section
78
.
First portion
74
further includes a top section
96
oriented substantially perpendicular to middle section
88
so that they together preferably have a substantially T-shaped cross-section. A recessed portion
98
is preferably formed in a top surface
100
of top section
96
so that a gate used in the formation process is provided. In particular, it will be understood that when first portion
74
is formed, such as by investment casting using lost wax process, a gate tail is able to be broken off easily without concern for smoothness since any remaining portion thereof lies beneath top surface
100
. It will be appreciated that the material utilized for first portion
74
is preferably an air-hardened tool steel such as A2, D2 or ductile iron which is heat treated to increase wearability. Other material which may be used for first portion
74
includes cemented tungsten carbide which is molded and sintered. In any case, it is preferred that the material of first portion
74
have a hardness in a range of approximately 25-60 on the Rockwell scale so that it is able to withstand the abrasion from abrasive media
26
flowing through flow path
38
.
Second portion
76
of pin member
42
has a substantially dovetail shape so that it can be easily inserted into pressure face portion
18
of dovetail slot
14
and pin member
42
retained in position. Thus, a pair of grooved portions
77
and
79
are preferably formed on each side thereof, as are a pair flared portions
81
and
83
interposed therewith. Second portion
76
also forms a seal between pressure face portion
18
and bottom portion
20
of dovetail slot, whereby abrasive media
26
is kept away from pressure surface portion
18
. Second portion
76
is generally formed via injection molding and is intended to bond to first portion
74
as shown in
FIG. 10. A
connector portion (not shown) may also be provided which extends through openings
94
of first portion
74
. Second portion
76
is preferably made of a softer material than first portion
74
, such as thermal setting plastic, nylon or urethane, providing it has a hardness with a durometer reading on the Shore scale of approximately D50-90. Accordingly, second portion
76
is able to perform its intended retention and sealing functions without scratching or otherwise marring pressure surface portion
18
.
It will be noted that second portion
76
may include a step
85
located along a forward portion
60
of top surface
87
so as to conform with a corresponding step
102
in each adjacent post
16
of disk
12
. This may also be utilized to confirm that each pin member
42
is properly inserted within dovetail slots
14
during assembly into fixture
10
.
It will be appreciated from the foregoing description of abrasive flow fixture
10
, pin member
42
, and flow path
38
through each dovetail slot
14
that a method of removing a predetermined amount of material from surface
22
of each dovetail slot bottom portion
20
in disk
12
includes the steps of configuring flow path
38
through each dovetail slot
14
and providing a flow of abrasive media
26
through each flow path
38
for a designated number of cycles so that a substantially uniform amount of material is removed from a targeted area of each dovetail slot bottom portion
20
. The method further includes the step of sealing pressure surface portion
18
of each dovetail slot
14
from bottom portion
20
to prevent abrasive media
26
from flowing thereagainst. Both functions are accomplished by inserting second portion
76
of pin member
42
into each dovetail slot
14
. By having pin member
42
contoured properly, areas of reduced cross-section are provided and a minimum or critical gap
42
is maintained in each flow path
38
.
It will be understood that the predetermined amount of material removed from each surface
22
of dovetail slot bottom portion
20
is preferably at least approximately 0.002 inches (2.0 mils), more preferably in a range of approximately 0.002-0.006 inches (2.0-6.0 mils), and optimally in a range of approximately 0.0025-0.0035 inches (2.5-3.5 mils). In order to determine the designated number of cycles required by fixture
10
to remove the predetermined amount of material from each dovetail slot bottom portion, a depth of dovetail slot bottom portion
20
, herein referred to as radial height
72
, is measured prior to providing abrasive media
26
through flow path
38
. After a given number of cycles has been performed by fixture
10
, the depth (radial height
72
) of dovetail slot bottom portion
20
is again measured. This process is repeated until the predetermined amount of material is removed and the number of cycles required is recorded. Even after the designated number of cycles is performed, it is preferred that confirmation be made that at least the predetermined amount of material has been removed. Dovetail slot bottom portion
20
for each dovetail slot
14
may also be shot peened in order to enhance surface
22
after the process of material removal has occurred.
Having shown and described the preferred embodiment of the present invention, further adaptations of the abrasive flow fixture
10
, flow path
38
through dovetail slot bottom portion
20
, and/or pin member
42
may be made and still be within the scope of the invention. Moreover, steps in the method of removing a predetermined amount of material from dovetail slot bottom portion
20
may be altered and still perform the intended function.
Claims
- 1. A method of removing a predetermined amount of material from a bottom portion of a dovetail slot in a gas turbine engine disk, comprising the following steps:(a) configuring a designated flow path through said dovetail slot; and, (b) providing a flow of abrasive media through said flow path a designated number of cycles so that a substantially uniform amount of material is removed from said dovetail slot bottom portion.
- 2. The method of claim 1, further comprising the step of sealing a pressure surface of said dovetail slot to prevent said abrasive media from flowing thereagainst.
- 3. The method of claim 1, further comprising the step of inserting a pin member into said dovetail slot so as to form areas of reduced cross-section in said flow path.
- 4. The method of claim 3, wherein said pin member is retained in a pressure face of said dovetail slot.
- 5. The method of claim 3, further comprising the step of maintaining a minimum gap between a bottom surface of said pin member and a surface of said dovetail slot bottom portion.
- 6. The method of claim 1, further comprising the step of maintaining a minimum cross-section in said flow path.
- 7. The method of claim 1, further comprising the step of measuring a depth for said dovetail slot bottom portion prior to providing said abrasive media through said flow path.
- 8. The method of claim 7, further comprising the step of measuring a depth for said dovetail slot bottom portion after providing said abrasive media through said flow path.
- 9. The method of claim 1, further comprising the step of determining said designated number of cycles required in order for said predetermined amount of material to be removed from said dovetail slot bottom portion.
- 10. The method of claim 1, further comprising the step of confirming that at least said predetermined amount of material is removed from said dovetail slot bottom portion.
- 11. The method of claim 1, further comprising the step of shot peening said dovetail slot bottom portion after said predetermined amount of material is removed therefrom.
- 12. The method of claim 1, wherein said flow path has a variable cross-section along a longitudinal axis through said dovetail slot.
- 13. The method of claim 1, wherein said flow path has a variable cross-section in a direction substantially perpendicular to a longitudinal axis through said dovetail slot.
- 14. The method of claim 1, wherein said predetermined amount of material removed from said dovetail slot bottom portion is at least approximately 2 mils.
- 15. The method of claim 1, wherein said predetermined amount of material is removed from a targeted area in said dovetail slot bottom portion.
- 16. An apparatus for removing a predetermined amount of material from a bottom surface of a dovetail slot in a gas turbine engine disk, wherein a longitudinal axis extends through said dovetail slot, comprising:(a) a fixture for providing a flow of abrasive media back and forth through a designated path at a predetermined pressure and flow rate; (b) a cradle for retaining said gas turbine engine disk in position so that said dovetail slot is in flow communication with said designated path; and, (c) a device for defining a designated flow path through said dovetail slot for said abrasive media; wherein said flow of abrasive media removes a substantially uniform amount of material from a bottom surface of said dovetail slot.
- 17. The apparatus of claim 16, wherein said apparatus seals a pressure face of said dovetail slot from said flow of abrasive media.
- 18. The apparatus of claim 16, wherein said abrasive media flows through said flow path of said dovetail slot for a designated number of cycles.
- 19. The apparatus of claim 16, wherein said predetermined amount of material removed from said dovetail slot bottom surface by said abrasive media is at least approximately 2 mils.
- 20. The apparatus of claim 16, wherein said apparatus provides a minimum cross-section through said designated flow path of said dovetail slot.
- 21. The apparatus of claim 16, wherein said apparatus provides said designated flow path through said dovetail slot with a variable cross-section along said longitudinal axis of said dovetail slot.
- 22. The apparatus of claim 16, wherein said apparatus provides said designated flow path through said dovetail slot with a variable cross-section in a direction substantially perpendicular to said longitudinal axis of said dovetail slot.
- 23. The apparatus of claim 16, wherein designated flow paths through each of said dovetail slots in said disk are in flow communication with said designated path of said abrasive flow fixture so that abrasive media flows therethrough substantially simultaneously.
US Referenced Citations (5)
Foreign Referenced Citations (1)
Number |
Date |
Country |
106507 |
Apr 1984 |
EP |