U.S. patent application number 13/630598 was filed with the patent office on 2013-02-07 for integrally rotating machinery and method and apparatus for achieving the same.
The applicant listed for this patent is Paul S. Prevey, III. Invention is credited to Paul S. Prevey, III.
Application Number | 20130034448 13/630598 |
Document ID | / |
Family ID | 38023752 |
Filed Date | 2013-02-07 |
United States Patent
Application |
20130034448 |
Kind Code |
A1 |
Prevey, III; Paul S. |
February 7, 2013 |
Integrally Rotating Machinery and Method and Apparatus for
Achieving the Same
Abstract
An article formed with blading members comprising a rotor a a
plurality of blading members integrally formed with the rotor
wherein each blading member having continuous zones of compressive
residual stress on the pressure side and the suction side and
extending substantially along the perimeter and extending inwards,
towards the center of each blading member, and wherein the
continuous zones of compressive residual stress have an improved
surface finish.
Inventors: |
Prevey, III; Paul S.;
(Cincinnati, OH) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Prevey, III; Paul S. |
Cincinnati |
OH |
US |
|
|
Family ID: |
38023752 |
Appl. No.: |
13/630598 |
Filed: |
September 28, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11546970 |
Oct 12, 2006 |
7805972 |
|
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13630598 |
|
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60726038 |
Oct 12, 2005 |
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Current U.S.
Class: |
416/241R |
Current CPC
Class: |
B23P 6/002 20130101;
B23P 9/02 20130101; B24B 39/00 20130101; Y10T 29/49336 20150115;
F04D 29/324 20130101; Y10T 29/47 20150115; B23P 15/006
20130101 |
Class at
Publication: |
416/241.R |
International
Class: |
F01D 5/14 20060101
F01D005/14 |
Goverment Interests
ACKNOWLEDGMENT OF FEDERAL GRANTS
[0002] The U.S. Government may have certain rights in this
invention pursuant to contract number F33615-03-C-5207 awarded by
the U.S. Department of the Air Force.
Claims
1. An article having blading members comprising: a rotor having a
plurality of blading members integrally formed with said rotor,
each said blading member having a pressure side and a suction side
in opposition to one another and a perimeter defined by a leading
edge, trailing edge, and a tip of said blading member; wherein said
blading members have continuous zones of compressive residual
stress on said pressure side and said suction side of each blading
member, said continuous zones of compressive residual stress
extending substantially along said perimeter of said blading member
and extending inwards, towards the center of said blading member;
wherein said continuous zones of compressive residual stress have
an improved surface finish.
2. The article of claim 1 wherein said improved surface finish is
in the range of about 5 .mu.in. to about 20 .mu.in
3. The article of claim 1 wherein said continuous compressive zones
of compressive residual stress extend substantially through the
thickness of the blading member.
4. The article of claim 1 wherein said continuous compressive zones
of compressive residual stress operate to offset areas of residual
tensile stress and high applied stresses that occur during
operation of the blading member.
5. The article of claim 1 wherein said continuous compressive zones
of compressive residual stress operate to mitigate foreign object
damage during operation of the blading member.
6. The article of claim 1 wherein said continuous compressive zones
of compressive residual stress has an associated cold work on the
order of less than about 5%.
7. The article of claim 1 wherein said continuous compressive zones
of compressive residual stress has an associated cold work on the
order of less than about 3.5%.
Description
[0001] This application is a divisional application of and claims
benefit of U.S. patent application Ser. No. 12/806,767 filed Aug.
20, 2010, which is a divisional application of and claims benefit
of U.S. patent application Ser. No. 11/546,970, filed Oct. 12, 2006
(now U.S. Pat. No. 7,805,972, issued Oct. 5, 2010), which claims
benefit of U.S. Provisional Application No. 60/726,038, filed Oct.
12, 2005.
TECHNICAL FIELD
[0003] The present invention relates generally to rotating turbo
machinery, and, more specifically, to an integrally bladed rotor or
disk having improved fatigue performance, greater foreign object
damage tolerance, and increased resistance to stress related
failure mechanisms due to the introduction of compressive residual
stresses through burnishing and a method and apparatus for
producing the same.
BACKGROUND
[0004] The high vibratory and tensile stresses experienced by
rotating turbo machinery in operation, particularly the blading
members of the fan, compressor, and turbine stages in gas turbine
engines, make such components susceptible to high cycle fatigue
(HCF) and other stress related failure mechanisms such as stress
corrosion cracking (SCC). HCF and SCC ultimately limit the service
life of these components as prolonged exposure to such extreme
operating conditions leads to the development of fatigue cracks in
areas of the component subject to high operational stresses. The
fatigue life of a component is further limited by the occurrence of
foreign object damage (FOD). FOD locations act as stress risers or
stress concentrators that hasten the development and propagation of
fatigue cracks. FOD, especially along the leading and trailing
edges of blading members, significantly reduces the service life of
aerospace components.
[0005] The potentially catastrophic effects of HCF and FOD require
that fatigue-life limited components be periodically inspected for
both cracks and FOD. Any damage or cracking found during inspection
is assessed and the component is retired from service due to the
extent of the damage or else repaired and returned to service. The
inspection of parts and the retirement of parts from service
adversely impacts both flight readiness and maintenance costs of
the aircraft.
[0006] Integrally formed components, such as rotors integrally
formed with blading members, also known in the industry as blisks
(bladed-disks), blings (bladed-rings), and IBRs (Integrally Bladed
Rotors), incur significant maintenance and repair costs due to
stress related failure mechanisms and FOD. This is a direct result
of their integral or unitary design as opposed to more traditional
rotating turbo machinery, such as bladed rotors, where individual
components of the construct, such as individual blading members,
can be separately removed and repaired or replaced when damage is
discovered or the component has reached its predetermined service
life.
[0007] FOD and stress related cracking in a single blading member
of an integrally formed component may directly impact the integrity
of the entire component. Because the integrally formed blading
members are not readily removable or replaceable in the event of
such damage, an entire integrally bladed rotor may be withdrawn
from service due to damage confined to a single blading member. The
repair and/or replacement of such a complex component is expensive,
both monetarily and from a flight readiness perspective.
[0008] The need to replace or repair integrally bladed rotating
turbo machinery may be significantly reduced if the fatigue
strength, FOD tolerance, and resistance to stress-related failure
mechanisms of new, serviced, and repaired components can be
improved or restored to the as-manufactured condition. Common
methods of improving the fatigue strength and foreign object damage
tolerance of aerospace components include the introduction of
residual compressive stresses in critical areas susceptible to
damage and fatigue failure such as the edges and tips of blading
members. Introducing compressive residual stresses improves the
fatigue properties and foreign object damage tolerance of both new
and repaired blading members. This decreases operation and
maintenance costs and increases the flight readiness of the
aircraft in which the component is employed.
[0009] One method currently used to introduce compressive residual
stresses in the blading members of integrally bladed rotating turbo
machinery is laser shock peening (LSP) as disclosed in U.S. Pat.
No. 6,541,733. LSP uses a high-power laser system to impart
compressive residual stresses at discrete locations on both sides
of the integrally formed airfoil or blading member. However, LSP
processing each blade of an integrally bladed rotor is labor
intensive, time consuming, and expensive.
[0010] Burnishing, also referred to as deep rolling, is an equally
effective, less expensive, and more time efficient alternative to
LSP for inducing compressive residual stresses in the surface of a
part. Burnishing, particularly ball burnishing as disclosed in U.S.
Pat. Nos. 5,826,453, 6,415,486, and 6,622,570, has been shown to
effectively increase the fatigue strength and FOD tolerance of
aerospace components, such as airfoils and turbine disks, and to
substantially mitigate or eliminate stress-induced failure
mechanisms.
[0011] While burnishing is generally well suited for aerospace
applications, the geometrical complexity and unitary design of some
aerospace components, such as integrally bladed rotors, does not
readily permit the use of current, commercially available
burnishing tools to introduce compressive residual stresses in the
individual, integrally formed blading members. As a practical
matter, the complex shape of the blading members and the narrow
spacing between individual blading members of the integrally bladed
rotor does not provide adequate clearance to permit the use of
current tool designs to accomplish the introduction of compressive
residual stress.
[0012] Accordingly, a need exists for an efficient and cost
effective method of imparting residual compressive stresses in the
individual blading members of integrally bladed rotating turbo
machinery to either improve or restore the fatigue performance
and/or resistance to stress related failure mechanisms of the
blading members thereof.
DISCLOSURE OF THE INVENTION
[0013] A rotor integrally formed with blading members for a turbine
or turbo machinery having improved fatigue performance, FOD
tolerance, and resistance to stress-related failure mechanisms is
produced by introducing compressive residual stresses in the
surface of the individual blading members. The rotor is mounted on
the worktable of a CNC machine tool. A caliper burnishing tool is
positioned relative to the individual blading member to be treated.
The geometry of the burnishing tool is such that it can be
positioned relative to the blading member to be treated without
contacting or otherwise interfering with adjacent blading members.
The blading member is burnished introducing compressive residual
stresses in the surface of the blading member. The burnishing tool
is withdrawn and the rotor is rotated such that a subsequent
blading member may be treated.
[0014] One embodiment of the present invention is a rotor
integrally formed with blading members having improved, fatigue
performance and increased tolerance to FOD as a result of
compressive residual stresses introduced in individual blading
members by burnishing.
[0015] In another embodiment, the present invention is a method for
improving the fatigue performance and FOD tolerance of a rotor
integrally formed with blading members by introducing compressive
residual stresses in the blading members of the rotor by
burnishing.
[0016] In another embodiment, the present invention is an apparatus
for inducing compressive residual stresses in blading members
integrally formed with a rotor thereby improving the fatigue
performance and FOD tolerance of the rotor. The apparatus consists
of two burnishing elements oriented in opposition to one another
such that a blading member may be disposed therebetween. This
facilitates the simultaneous introduction of compressive residual
stresses on both surfaces of the blading member. The burnishing
elements are disposed in contoured caliper arms that conform to the
complex geometry of the blading member and permit the in situ
treatment of individual blading members of a rotor.
[0017] Other aspects, advantages and embodiments of the invention
will be apparent from the following description and the appended
claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] These and other features, aspects, and advantages of the
present invention will become better understood with regard to the
following description, appended claims, and accompanying drawings
where:
[0019] FIG. 1 is a schematic illustration of a rotor integrally
formed with blading members treated according to the current
invention.
[0020] FIG. 2 is a schematic drawing of one embodiment of the
burnishing tool that is a subject of the present invention.
[0021] FIG. 3 is a schematic drawing of another embodiment of the
burnishing tool that is a subject of the present invention.
[0022] FIG. 4 is a flow chart of the method for improving the
resistance to stress-related failure mechanisms of a rotor
integrally formed with blading members.
[0023] FIG. 5 is a schematic drawing illustrating a preferred
embodiment of the method of the current invention.
[0024] FIG. 6 is a schematic drawing showing a prior art
caliper-type burnishing tool.
[0025] FIG. 7 is a schematic drawing showing the apparatus of the
present invention having contoured interior surfaces.
BEST MODE FOR CARRYING OUT THE INVENTION
[0026] The present invention relates to rotating turbo machinery
integrally formed with blading members having improved or restored
resistance to fatigue, FOD, and stress-related failure mechanisms.
As shown in FIG. 1, the rotor 100 consists of a central disk 102
integrally formed with blading members 104 spaced about the
periphery and extending radially outward from the center 106 of the
rotor. The blading members 104 are defined by a leading edge 108, a
trailing edge 110, a tip 112, a pressure side 122, and a suction
side 124.
[0027] Using a burnishing process, compressive residual stresses
are induced in the blading members 104 of the rotor 100 in
continuous compressive zones 114, on both the pressure side 122 and
the suction side 124, along the leading edge 108, trailing edge
110, or tip 112, and combinations thereof, in locations on the
blading member where damage and failures are known to occur. The
continuous compressive zones 114 wherein compressive residual
stresses are induced are identified by operational experience of
the component, testing, or mathematical modeling of the residual
and applied stress state of the component, and combinations
thereof. The location and shape of the continuous compressive zones
114 are designed to offset areas of residual tensile stress and
high applied stress or to mitigate FOD known to occur in the
general area through operational experience. In one embodiment, the
compressive residual stresses extend substantially through the
thickness of the blading members from both the pressure side 122
and the suction side 124 such that the entire cross section of the
blading member is under compressive stress.
[0028] In a preferred embodiment of the invention, the compressive
residual stresses induced in the blading members 104 of the rotor
100 have an associated cold work on the order of less than about
5%, preferably less than about 3.5%, in order to create thermally
and mechanically stable compressive residual stresses.
[0029] In another preferred embodiment of the invention, the
continuous zones of compressive residual stress 114 have an
improved surface finish as a result of the burnishing method used
to induce the residual compressive stresses, which, in turn,
benefits the aerodynamic efficiency of the blading members 104. The
improved surface finish is in the range of about 5 .mu.in. to 20
.mu.in., depending on the alloy from which the blading members 104
are manufactured and the characteristics of the burnishing tooling
used. Common alloys used in this type of aerospace application
include, but are not limited to, titanium alloys, stainless steels,
and nickel-base alloys.
[0030] For purposes of the current invention, prior to burnishing,
the rotor 100 may be in the as-manufactured condition, such as a
new rotor or a rotor at an intermediate manufacturing step or a
rotor with no operational service time. Alternatively, the rotor
100 may have been previously fielded and therefore subject to
reduced performance due to operational stress and/or FOD.
[0031] A preferred embodiment of the apparatus of the present
invention is shown in FIG. 2. The apparatus 200 is a
caliper-burnishing tool configured as a second-class lever with a
first caliper arm 202 and a second caliper arm 204 in pivotal
opposition to one another about a pivot point 206. The anterior
surfaces of the first caliper arm 202 and the second caliper arm
204 are shaped to facilitate insertion of each caliper arm between
the blading member being treated and adjacent blading members. In
addition, the interior surfaces of the first caliper arm 202 and
the second caliper arm 204 are contoured to conform to the complex
surface geometry of the blading member being treated.
[0032] The benefit of the curved interior surfaces of the first
caliper arm 202 and the second caliper arm 204 is shown in FIG. 6.
FIG. 6 shows a conventional straight-armed caliper burnishing tool
602 positioned relative to an airfoil 600 shown in cross section.
The airfoil 600 has a complex, curved geometry in the chord-wise
direction. The burnishing elements of the conventional
straight-armed caliper tool 602 are unable to contact all points
along the curved surface of the airfoil 600 without the caliper arm
also contacting the airfoil 600 and potentially damaging the
airfoil 600. As shown in FIG. 7, the apparatus 200 of the subject
invention is shown wherein the caliper arms 202 and 204 comprise
curved interior surfaces 604 that operate to facilitate the
treatment of the entire curved surface of the airfoil 600 by
maintaining sufficient clearance between the caliper arms 202 and
204 and the airfoil 600 thereby reducing the risk of damage to the
airfoil 600.
[0033] Referring again to FIG. 2, the pivot point 206 is attached
to a base 208, which, in turn, is attached to a tool holder 210
that facilitates insertion of the apparatus 200 into the chuck of a
CNC machine tool or other positioning device including, but not
limited to, robotic positioning devices.
[0034] The first caliper arm 202 and the second caliper arm 204 are
pivoted about the pivot point 206 by an actuator 212 located below
the pivot point 206. The actuator 212 mechanically links the first
caliper arm 202 and the second caliper arm 204 via the linkage 214.
The actuator 212 may be selected from the following list including,
but not limited to, hydraulic cylinders, pneumatic cylinders,
electromagnetic solenoids, and mechanical actuators such as
springs.
[0035] The first caliper arm 202 and second caliper arm 204 each
have burnishing elements 216 oriented in opposition to one another
on the interior surface 604 (FIG. 7) of each caliper arm and
disposed within sockets 222 distally located from the pivot point
206. Preferably the burnishing elements 216 are in the form of
burnishing balls for providing single point burnishing and the
sockets 222 are sized and shaped, such as being spherical, to
receive the burnishing elements 216. In a preferred embodiment, the
sockets 222 are provided with a constant volume flow of fluid via
fluid supply lines 218. The constant volume flow of fluid serves to
suspend each of the burnishing elements 216 over the surface of
their respective socket 222 on a thin film of fluid thereby
creating a hydrostatic bearing.
[0036] In another preferred embodiment of the present invention the
apparatus 200 is configured as a first-class lever, as shown in
FIG. 3. In this configuration the pivot point 206 is attached to a
yoke 224 such that the first caliper arm 202 and the second caliper
arm 204 may pivot with respect to each other and the yoke 224. The
yoke 224 is attached to the base 208, which, in turn, is attached
to a tool holder 210.
[0037] Referring again to FIG. 2 to illustrate the operability of a
preferred embodiment of the apparatus, the apparatus 200 is
positioned around a workpiece, such as the blading member 104 of an
integrally bladed rotor 100 as shown in FIG. 1, so that the first
caliper arm 202 and the second caliper arm 204 are positioned
relative to the surfaces of the workpiece (such as the airfoil 600
as shown in FIG. 7) to be treated. A constant volume supply of
fluid is provided to the sockets 222 such that the burnishing
elements 216 are fluidly supported over the surface of the socket.
The actuator 212 is then activated retracting the linkage 214 and
advancing the first caliper arm 202 and the second caliper arm 204
towards one another. The workpiece is impinged between the
burnishing elements 216. With the burnishing elements 216 in
contact with the workpiece, the caliper tool 200 is moved along the
surface of the workpiece imparting compressive residual stresses on
both sides of the workpiece and substantially through the cross
sectional area (thickness T, FIG. 7) of the workpiece. The caliper
tool 200 may be advanced along the workpiece in a predetermined
pattern thereby imparting the desired amount of residual
compressive stress. The depth and magnitude of the induced
compressive residual stress relative to locations on the workpiece
are preferably precisely and continuously controlled by adjusting
the force by which the actuator 212 impinges the burnishing
elements 216 against the workpiece as the caliper tool traverses
the surface of the workpiece in a predetermined pattern under CNC
control.
[0038] It should be obvious to one skilled in the art that the
burnishing elements 216 may also be pinch-peening elements,
indenting elements, coining elements, or roller elements, all of
which may be used to induce residual compressive stress in the
surface of a blading member.
[0039] The method of the present invention may be carried out in a
series of steps as shown in FIG. 4. In a first step 401, the rotor
integrally formed with blading members is mounted on a fixturing
device. As shown in FIG. 5, the fixturing device 504, which is
positioned on the x-y table (not shown) of a CNC machine tool, such
as a vertical mill, permits the precise positioning of the rotor
502 with respect to a caliper-burnishing tool 506 held in the chuck
508 of the machine tool. More specifically, the fixturing device
504 allows for the rotation of the rotor 502 about its normal axis
of rotation (the z-axis of FIG. 5) while simultaneously
facilitating the rotation of the combination of the rotor 502 and
the fixturing device about the x-axis as indicated in the figure.
Orientation of the fixturing device 504 and rotor 502 in the x-y
plane relative to the caliper-burnishing tool 506 is controlled by
the x-y table of the CNC machine tool on which the fixturing device
504 is mounted. The relative positioning of the caliper burnishing
tool 506 and the fixturing device 504 along the z-axis is
controlled by advancing and retracting the chuck 508 of the CNC
machine tool in the direction of the z-axis as well as rotating the
fixturing device 504 in the y-z plane. Rotation of the rotor 502,
rotation of the fixturing device 504 in the y-z plane, and
positioning of the caliper-burnishing tool 506 are accomplished
under CNC control.
[0040] In a second step 402, a computer program is used in
conjunction with the CNC controls of the machine tool to
automatically carry out the treatment operation on each of the
integrally formed blading members of the rotor. Steps 403 through
408 are accomplished under computer control using CNC code. In a
first program step 403, the program rotates the rotor into position
such that the proper profile of the blading member is presented to
the caliper tool to facilitate treatment of an individual
integrally-formed blading member. Referring again to FIG. 5, this
is accomplished by rotating the fixturing device 504 in the y-z
plane and rotating the rotor 502 about its axis of rotation until
the proper profile of an individual blading member is presented to
the caliper-burnishing tool 506. The proper profile is obtained
when the stacking axis of the individual integrally-formed blading
member is aligned with the z-axis of the machine tool.
[0041] Returning to FIG. 4, in the next program step 404, the
caliper tool is lowered into position and inserted between adjacent
blading members such that the caliper arms of the tool are located
on either side of the blading member being treated. This step is
illustrated in FIG. 5. The specific shape of the caliper arms
permits the tool to be positioned in this manner without damaging
or otherwise interfering with adjacent blading members while the
contoured interior surfaces of each caliper arm permit the tool to
be positioned in close proximity to the surface of the blading
member being treated without damaging the blading member.
[0042] In a third program step 405 following insertion of the
caliper tool, the burnishing process begins. It is during this step
that the caliper tool closes around the blading member such that
the burnishing elements of each caliper arm are in contact with
opposing surfaces of the blading member. The hydraulic cylinder is
actuated to impinge the burnishing elements against both sides of
the blading member, thereby imparting residual compressive
stresses. The force exerted by the tool against the surface of the
blading member is regulated by the pressure of hydraulic fluid
supplied to the hydraulic cylinder, which, in turn, is regulated by
the CNC program. This permits the pressure exerted against the
surface of the blading member, and therefore the induced residual
compressive stress, to be precisely controlled and adjusted in
conjunction with the position of the treatment apparatus.
[0043] In a subsequent program step 406, a predetermined residual
compressive stress pattern is imparted in the surface of the
blading member by moving both the caliper tool and the rotor
relative to one another in a continuous operation. During this step
the CNC positioning controls are utilized to precisely control the
positioning of both the caliper tool and the rotor. The burnishing
elements, which are essentially hydrostatic bearings, in
combination with the precision CNC program controls, permit the
caliper tool to smoothly and accurately follow the unique contours
of the individual blading members, thereby producing the desired
residual compressive stress pattern.
[0044] In the fifth program step 407, following the treatment of a
single blading member, the tool is withdrawn from the rotor. In a
final program step 408, the process is repeated until the desired
residual compressive stress patterns have been induced in each of
the integrally formed blading members on the rotor.
[0045] In a preferred embodiment, the compressive stress pattern
imparted provides a compressive residual stress zone that extends
along a portion or extends substantially along the entire
perimeter, such as the entire leading edge 108, trailing edge 110,
and tip 112 (FIG. 1), and inwards towards the center C of the
blading member 104.
[0046] Referring to FIG. 1, another embodiment of the invention is
an article 100, such as a rotor, having a plurality of blading
members 104 each having a pressure side 122, a suction side 124 in
opposition to one another and a perimeter defined by a leading edge
108, a trailing edge 110, and a tip 112. At least one blading
member 104 has continuous zones of compressive residual stress on
its pressure side 122 and its suction side 124 such that the
continuous zones of compressive residual stress extend
substantially along the perimeter and extend inwards in a direction
generally towards the center C. It should now be apparent that the
article formed such as by the method and apparatus described above
(unlike articles formed using laser shocking methods or shot
peening methods that produce a plurality of discrete points of
compression) has continuous zones of compressive residual stress
thereby improving the surface finish of the part and possibly
reducing the potential for stress induced damage.
[0047] It should be apparent to one skilled in the art that the
method and apparatus described herein may also be used to introduce
compressive residual stresses in blading members removably
connected to a central rotor such as that commonly used in rotating
turbines and turbo machinery.
[0048] A principle advantage of the apparatus is the ability to
introduce beneficial compressive residual stresses in the
individual blading members of an integrally bladed component using
a mechanical surface treatment such as burnishing. The
configuration of the apparatus permits treatment of individual
blading members without interfering with or damaging adjacent
blading members. Further, the contoured interior surfaces of the
caliper arms permit the treatment of curved or complex airfoil
surfaces without the risk of damage to the individual airfoil being
treated.
[0049] Another advantage of the present invention is a low cost
method of improving the resistance of an integrally bladed rotating
component to stress-induced failure mechanisms such as FOD,
fatigue, and stress corrosion cracking through the introduction of
beneficial compressive residual stresses by a mechanical surface
treatment such as burnishing. The method reduces overall
manufacturing costs compared to currently employed methods of
inducing compressive residual stresses in the blading members of
integrally formed rotating components and improves manufacturing
throughput.
[0050] Another advantage of the present invention is an integrally
bladed rotating component with improved resistance to
stress-related failure mechanisms such as FOD, fatigue, and stress
corrosion cracking through the introduction of beneficial
compressive residual stress by mechanical surface treatment such as
burnishing.
[0051] While the method and apparatus described herein constitute
preferred embodiments of the invention, it is to be understood that
the invention is not limited to the precise method and apparatus,
and that changes may be made therein without departing from the
scope of the invention which is defined in the appended claims.
* * * * *