U.S. patent application number 13/625956 was filed with the patent office on 2014-08-28 for aluminum brazing of hollow titanium fan blades.
This patent application is currently assigned to UNITED TECHNOLOGIES CORPORATION. The applicant listed for this patent is UNITED TECHNOLOGIES CORPORATION. Invention is credited to Daniel A. Bales, Thomas J. Watson.
Application Number | 20140241897 13/625956 |
Document ID | / |
Family ID | 50979360 |
Filed Date | 2014-08-28 |
United States Patent
Application |
20140241897 |
Kind Code |
A1 |
Bales; Daniel A. ; et
al. |
August 28, 2014 |
ALUMINUM BRAZING OF HOLLOW TITANIUM FAN BLADES
Abstract
A fan blade includes first and second titanium portions that are
secured to one another with an aluminum alloy braze. A method of
manufacturing a fan blade includes providing first and second
titanium portions, applying an aluminum alloy braze to at least one
of the first and second titanium portions, and heating the fan
blade to melt the aluminum alloy braze and join the first and
second portions to one another to provide a fan blade with an
airfoil exterior contour.
Inventors: |
Bales; Daniel A.; (Avon,
CT) ; Watson; Thomas J.; (South Windsor, CT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
UNITED TECHNOLOGIES CORPORATION; |
|
|
US |
|
|
Assignee: |
UNITED TECHNOLOGIES
CORPORATION
Hartford
CT
|
Family ID: |
50979360 |
Appl. No.: |
13/625956 |
Filed: |
September 25, 2012 |
Current U.S.
Class: |
416/233 ;
228/170; 228/173.1; 228/221; 228/256; 416/241R |
Current CPC
Class: |
B23P 15/04 20130101;
F01D 5/147 20130101; F05D 2220/36 20130101; F04D 29/20 20130101;
F05D 2300/174 20130101; B23K 1/0018 20130101; F05D 2300/173
20130101; F05D 2300/133 20130101; F04D 29/324 20130101; F05D
2230/237 20130101; F04D 29/023 20130101; F04D 29/18 20130101 |
Class at
Publication: |
416/233 ;
416/241.R; 228/256; 228/173.1; 228/170; 228/221 |
International
Class: |
F04D 29/18 20060101
F04D029/18; F04D 29/20 20060101 F04D029/20 |
Claims
1. A fan blade comprising: first and second titanium portions are
secured to one another with an aluminum alloy braze.
2. The fan blade according to claim 1, wherein the first titanium
portion is provided by a forging.
3. The fan blade according to claim 1, wherein the first titanium
portion includes machined ribs.
4. The fan blade according to claim 3, wherein the machined ribs
include undercuts having an arcuate shape.
5. The fan blade according to claim 1, wherein the second titanium
portion is a hot-formed sheet providing a cover.
6. The fan blade according to claim 2, wherein the fan blade has a
blade root defined by the first titanium portion.
7. The fan blade according to claim 6, wherein the fan blade has a
blade tip defined by the first titanium portion.
8. The fan blade according to claim 7, wherein the cover provides
one side of the airfoil.
9. The fan blade according to claim 8, wherein the first titanium
portion includes opposing first and second edges that define the
fan blade leading and trailing edges.
10. A method of manufacturing a fan blade comprising: providing
first and second titanium portions; applying an aluminum alloy
braze to at least one of the first and second titanium portions;
and heating the fan blade to melt the aluminum alloy braze and join
the first and second portions to one another to provide a fan blade
with an airfoil exterior contour.
11. The method according to claim 10, comprising the step of
forging the first titanium portion.
12. The method according to claim 10, comprising the step of
machining the first titanium portion.
13. The method according to claim 10, comprising the step of
applying the aluminum alloy braze before the machining step.
14. The method according to claim 10, comprising the step of
pressing the second titanium portion to produce a cover providing a
side of the airfoil.
15. The method according to claim 14, comprising the step of
pickling the cover.
16. The method according to claim 15, comprising the step of
applying the aluminum alloy braze after pickling the cover.
17. The method according to claim 10, comprising the step of
bagging the first and second titanium portions prior to performing
the heating step.
18. The method according to claim 17, comprising the step of
purging the bag prior to the heating step.
19. The method according to claim 18, comprising the step of
pulling a vacuum on the bag during the heating step.
20. The method according to claim 10, wherein the first titanium
portion provides a root, a tip and leading and trailing edges of
the airfoil exterior contour.
Description
BACKGROUND
[0001] This disclosure relates to hollow fan blades and a method of
brazing the same.
[0002] Titanium-based alloys are widely used for structural
applications in the aerospace industry. These alloys provide good
fatigue properties, erosion benefits relative to aluminum alloys,
and are light weight compared to steel, stainless steels, and
nickel alloys. While significant weight savings can be achieved
with solid titanium components, even greater weight savings can be
achieved using hollow structures.
[0003] It is difficult to create a complicated airfoil shape,
especially a hollow fan blade (HFB). Hollow titanium fan blades are
typically produced by diffusion bonding two machined
cavity-containing plates on the neutral axis, hot forming and
inflating the bonded assembly to achieve its final shape within
complex dies, and finally post-thermal processing the blade's
surface to remove any surface contamination. Much of the part cost
is incurred by the complex bonding and forming process.
[0004] Common practice for joining hollow titanium structures is by
brazing with titanium-nickel-copper alloys or by diffusion bonding.
Brazing titanium with aluminum has been used for decades, but
requires a narrow window of time and temperature. This stems from
the fact that aluminum and titanium can form brittle intermetallic
phases at the joint interface, if line and temperature are not
properly controlled.
SUMMARY
[0005] In one exemplary embodiment, a fan blade includes first and
second titanium portions that are secured to one another with an
aluminum alloy braze.
[0006] In a further embodiment of any of the above, the first
titanium portion is provided by a forging.
[0007] In a further embodiment of any of the above, the first
titanium portion includes machined ribs.
[0008] In a further embodiment of any of the above, the machined
ribs include undercuts that have an arcuate shape.
[0009] In a further embodiment of any of the above, the second
titanium portion is a hot-formed sheet that provides a cover.
[0010] In a further embodiment of any of the above, the fan blade
has a blade root defined by the first titanium portion.
[0011] In a further embodiment of any of the above, the fan blade
has a blade tip defined by the first titanium portion.
[0012] In a further embodiment of any of the above, the cover
provides one side of the airfoil.
[0013] In a further embodiment of any of the above, the first
titanium portion includes opposing first and second edges that
define the fan blade leading and trailing edges.
[0014] In another exemplary embodiment, a method of manufacturing a
fan blade includes providing first and second titanium portions,
applying an aluminum alloy braze to at least one of the first and
second titanium portions, and heating the fan blade to melt the
aluminum alloy braze and join the first and second portions to one
another to provide a fan blade with an airfoil exterior
contour.
[0015] In a further embodiment of any of the above, the method
includes the step of forging the first titanium portion.
[0016] In a further embodiment of any of the above, the method
includes the step of machining the first titanium portion.
[0017] In a further embodiment of any of the above, the method
includes the step of applying the aluminum alloy braze before the
machining step.
[0018] In a further embodiment of any of the above, the method
includes the step of pressing the second titanium portion to
produce a cover that provides a side of the airfoil.
[0019] In a further embodiment of any of the above, the method
includes the step of pickling the cover.
[0020] In a further embodiment of any of the above, the method
includes the step of applying the aluminum alloy braze after
pickling the cover.
[0021] In a further embodiment of any of the above, the method
includes the step of bagging the first and second titanium portions
prior to performing the heating step.
[0022] In a further embodiment of any of the above, the method
includes the step of purging the bag prior to the heating step.
[0023] In a further embodiment of any of the above, the method
includes the step of pulling a vacuum on the bag during the heating
step.
[0024] In a further embodiment of any of the above, the first
titanium portion provides a root, a tip and leading and trailing
edges of the airfoil exterior contour.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] The disclosure can be further understood by reference to the
following detailed description when considered in connection with
the accompanying drawings wherein:
[0026] FIG. 1 is a perspective view of an example brazed titanium
fan blade.
[0027] FIG. 2A is a cross-sectional view of the fan blade shown in
FIG. 1 taken along line 2A-2A.
[0028] FIG. 2B is an exploded enlarged view of a portion of the fan
blade shown in FIG. 2A.
[0029] FIG. 3 is a flow chart depicting an example manufacturing
method for the fan blade.
[0030] FIG. 4 schematically depicts the brazing process.
DETAILED DESCRIPTION
[0031] A fan blade 10 is schematically depicted in FIGS. 1 and 2.
The fan blade 10 includes a root 12 supporting an airfoil 14 that
extends to a tip 16. First and second titanium portions 18, 20 are
brazed to one another to provide an exterior contour 22 of the fan
blade 10.
[0032] In the example, the first titanium portion 18 is provided by
a forged blank that is machined to remove material 24. Ribs 26 are
provided that have undercuts 28 with an arcuate shape and within
the interior of the first titanium portion 18 to reduce weight
while providing fan blade structural integrity, ensuring blade
fatigue life, and supporting the airfoil cover 20. The first
titanium portion 18 provides the root 12 and one side of the
airfoil 14 along with the tip 16. The first portion 18 also
provides first and second edges that define fan blade leading and
trailing edges 17, 19.
[0033] The second titanium portion 20 provides a cover that is
secured over the interior of the first titanium portion 18 by a
braze 34. A titanium cover would be used for its thermal expansion
match with the titanium forging, its superior corrosion resistance
relative to aluminum, its improved stiffness relative to aluminum,
its improved erosion resistance relative to aluminum, and its
improved foreign object debris/impact resistance relative to
aluminum.
[0034] The braze 34 is provided on one or both of the first and
second mating surfaces 30, 32, which are respectively provided by
the first and second titanium portions 18, 20. In one example, the
braze 34 is an aluminum alloy, such as Al--Cu--Mn, having less than
3 wt % copper and less than 5 wt % manganese and having a
solidus-liquidus range within 1175.degree. F.-1225.degree. F. The
aluminum or aluminum alloy chosen for brazing would be pre-placed
onto either the titanium cover or the titanium forging as a photo
etched pre-form or cathodic arc deposited directly onto the
titanium cover or the titanium forging. In one example, the entire
surface of the side of the cover being brazed or the side of the
forging being brazed would be cathodic arc deposited prior to
machining the forging or prior to selective etching the titanium
cover to only provide braze material at areas being joined.
[0035] A method 40 of forming the fan blade 10 is schematically
illustrated at 40. A titanium forging (first titanium portion 18)
is provided, as indicated by block 42. The proposed method of
construction uses a near net shape titanium forging with certified
mechanical properties.
[0036] The titanium forging is machined, as indicated at block 46,
to provide structure similar to that shown in FIGS. 1 and 2, for
example. The fan blade design may be tailored such that no internal
foam inserts would be needed, although inserts may be used if
desired. Prior to machining (in instances where no metallic foam
inserts are used), an aluminum alloy braze may be applied, as
indicated at block 48. Thus, the braze will be provided only on the
raised surfaces, which provides the first mating surface 30,
subsequent to machining.
[0037] A titanium cover (second titanium portion 20) may be
provided, as indicated at block 44. The titanium cover may be hot
formed at processing conditions that ensure maintaining its
certified mechanical properties, while achieving the desired shape
for bonding. Alternatively, or in addition to, an aluminum alloy
braze may be applied, as indicated at block 52, to the titanium
cover subsequent to pickling, as indicated at block 50. Pickling
provides a contaminant-free surface on the cover.
[0038] The cover is arranged over the titanium forging such that
the first and second mating surfaces 30, 32 engage one another. The
assembled fan blade 10 is inserted into a bag 64 (FIG. 4), as
indicated at block 54. The bag is a metallic bag, which may be
constructed from a stainless steel or a nickel alloy foil, for
example, that can be sealed.
[0039] In one example, the sealed bagged fan blade is loaded into a
vacuum compression brazing furnace 62 having a heating element 66,
which is shown in FIG. 4. Oxygen and nitrogen within the bag are
evacuated and the bag is backfilled with argon, as indicated at
block 56. Evacuation and backfilling may be repeated multiple times
to reduce the oxygen and nitrogen to an acceptable concentration
within the bag and within the fan blade's internal cavities.
Following the final evacuation, a negative atmosphere is maintained
within the sealed bag. The magnitude of the bag's internal negative
pressure is such that any positive pressure or vacuum external to
the bag always provides force upon the titanium cover 20 and the
machined fan blade 10 within the bag 64, throughout all subsequent
heating, brazing and cooling.
[0040] Brazing could occur within a vacuum furnace capable of
applying a positive pressure of argon, within an argon retort,
within a furnace capable of maintaining a hard vacuum or within a
vacuum furnace capable of maintaining a partial pressure of argon.
In the first example, vacuum compression brazing furnace 62 is
capable of applying a positive pressure of argon to the bagged fan
blade 10 during heating to melt the aluminum alloy braze material
and during subsequent cooling. If brazing within an argon retort,
such an environment would be free of both oxygen and nitrogen to
the extent acceptable for producing a finished product within the
design criteria but meeting or bettering specified surface
contamination requirements. If in a standard vacuum furnace,
brazing would be accomplished by heating parts in a retort or other
line-of-sight shielding at 5.times.10-4 torr or lower pressure
within a temperature range of 1225.degree. F. to 1290.degree. F.
Regardless of the furnace choice, time between 1175.degree. F. on
heating and 1175.degree. F. on cooling would be controlled to
produce a braze microstructure that conforms to metallurgical
standards established by material characterization testing and fan
blade component testing. Such standards would control amount of
particulate, titanium aluminide, and eutectic intermetallic
structure within the braze. Because the aluminum brazing
temperature is lower than annealing temperatures used for titanium
alloys such as Ti-6-4 and Ti-6-2-4-2, certified mechanical
properties of the fan blade cover 20 and the fan blade forging 18
previously created during prior plate/sheet rolling, fan blade
forging, and associated follow-on heat treatment will be maintained
throughout all aluminum brazing thermal processing. The fan blade
is then finished, if necessary, as indicated at block 60.
[0041] Although an example embodiment has been disclosed, a worker
of ordinary skill in this art would recognize that certain
modifications would come within the scope of the claims. For that
reason, the following claims should be studied to determine their
true scope and content.
* * * * *