U.S. patent application number 11/508678 was filed with the patent office on 2008-02-28 for friction stir welding process having enhanced corrosion performance.
This patent application is currently assigned to Lockheed Martin Corporation. Invention is credited to John E. Barnes.
Application Number | 20080047222 11/508678 |
Document ID | / |
Family ID | 39112053 |
Filed Date | 2008-02-28 |
United States Patent
Application |
20080047222 |
Kind Code |
A1 |
Barnes; John E. |
February 28, 2008 |
Friction stir welding process having enhanced corrosion
performance
Abstract
A three dimensional joint is formed by coupling (joining) a
first structural member and a second structural member. This
involves first aligning a first structural member to a second
structural member. The first structural member has a channel with
which to receive a portion of the second structural member. Certain
embodiments may place corrosively inert materials within the mating
surfaces to prevent or inhibit corrosion or oxidation. Once
aligned, the first structural member and second structural member
may be friction stir welded at the channel to plasticize the
material adjacent to the channel of both the first structural
member and the second structural member to form a friction stir
weld joint. Embodiments may then coat the plasticized surfaces of
the FSW joint with cold sprayed materials to inhibit corrosion.
Should a crack occur within either the plasticized or
non-plasticized materials, cold sprayed material may be deposited
within and on the crack to retard or arrest the growth of the
crack.
Inventors: |
Barnes; John E.; (Roswell,
GA) |
Correspondence
Address: |
BRACEWELL & GIULIANI LLP
P.O. BOX 61389
HOUSTON
TX
77208-1389
US
|
Assignee: |
Lockheed Martin Corporation
|
Family ID: |
39112053 |
Appl. No.: |
11/508678 |
Filed: |
August 23, 2006 |
Current U.S.
Class: |
52/693 |
Current CPC
Class: |
B23K 20/1225 20130101;
B23K 2103/10 20180801; B23K 2101/28 20180801; E04C 3/04 20130101;
B23K 20/124 20130101; B23K 20/24 20130101; B23K 20/128 20130101;
E04C 2003/0452 20130101 |
Class at
Publication: |
52/693 |
International
Class: |
E04C 3/02 20060101
E04C003/02 |
Claims
1. A method for joining structure members, comprising: aligning a
first structural member to a second structural member, the first
structural member having a channel to receive a portion of the
second structural member; friction stir welding (FSW) at the
channel to join the first structural member to the second
structural member; cold spraying material on exposed surfaces of an
FSW joint to inhibit corrosion.
2. The method of claim 1, further comprising placing a corrosively
inert material at the channel to inhibit crevice crack
corrosion.
3. The method of claim 2, further comprising preventing moisture
penetration into a FSW joint formed by the first structural member
and the second structural with the corrosively inert material.
4. The method of claim 1, further comprising placing an adhesive
material at the channel, the adhesive material operable to fit the
first structural member to the second structural member prior to
FSW.
5. The method of claim 1, wherein the first structural member and
the second structural member are within a vehicle frame.
6. The method of claim 1, wherein the first structural member and
the second structural member comprise: a box beam; an I-beams; a
double I-beam; or a C-Beam.
7. The method of claim 1, wherein the first structural member and
the second structural member comprise an aluminum alloy.
8. The method of claim 1, further comprising: inserting a male
connector of the first structural member and/or second structural
member into a female receptacle of the second structural member
and/or first structural member; and friction stir welding materials
of the male connector into the female receptacle to create a FSW
coupling.
9. A method for joining structural members, comprising: aligning a
first structural member to a second structural member, the first
structural member having a channel to receive a portion of the
second structural member; inserting a male connector of the first
structural member and/or second structural member into a female
receptacle of the second structural member and/or first structural
member; friction stir welding (FSW) at the channel and a male
connector/female receptacle interface to join the first structural
member to the second structural member; and cold spraying material
on exposed surfaces of an FSW joint to inhibit corrosion.
10. The method of claim 9, further comprising placing a corrosively
inert material at the channel to inhibit crevice crack
corrosion
11. The method of claim 10, further comprising preventing
penetration of contaminates into a friction stir weld joint formed
by the first structural member and the second structural, the
penetration prevented with the corrosively inert material.
12. The method of claim 9, wherein the first structural member and
the second structural member are within a vehicle frame.
13. The method of claim 9, wherein the first structural member and
the second structural member comprise: a box beam; an I-beams; a
double I-beam; or a C-Beam.
14. The method of claim 9, wherein the first structural member and
the second structural member comprise an aluminum alloy.
15. A friction stir weld joint, comprising: a first structural
member, the first structural member having a channel; at least one
second structural member, the channel of the first structural
member receives a portion of the at least one second structural
member, the materials of the first structural member and at least
one second structural member friction stir welded at the interface
of the first structural member and at least one second structural
member at the channel; and cold sprayed material deposited on an
exposed surface of the friction stir welded interface operable to
inhibit corrosion.
16. The friction stir weld joint of claim 15, wherein the channel
is within a horizontal member of the first structural member, the
channel receives a vertical member of the second structural
member.
17. The friction stir weld joint of claim 15, wherein a barrier
material within the channel fills interface cavities at the
friction stir weld joint to prevent contamination from entering the
friction stir weld joint.
18. The friction stir weld joint of claim 16, wherein the barrier
material comprises corrosively inert material.
19. The friction stir weld joint of claim 15, further comprising: a
male connector of the first structural member and/or second
structural member; a female receptacle of the second structural
member and/or first structural member operable to receive the male
connector, the materials of the male connector friction stir welded
into the female receptacle.
20. The friction stir weld joint of claim 15, wherein an adhesive
material at the channel, the male connector, and or the female
receptacle, the adhesive material operable to fit the first
structural member to the second structural member prior to friction
stir welding.
21. The friction stir weld joint of claim 15, wherein the first
structural member and the second structural member are within a
vehicle frame.
22. The friction stir weld joint of claim 15, wherein the first
structural member and the second structural member comprise: a box
beam; an I-beams; a double I-beam; or a C-Beam.
23. The friction stir weld joint of claim 15, wherein the first
structural member and the second structural member comprise an
aluminum alloy.
24. A friction stir weld joint, comprising: a first structural
member, the first structural member having a channel; at least one
second structural member, the channel of the first structural
member receives a mating surface of the at least one second
structural member, the mating surface and/or channel being coated
with corrosively inert material, the materials of the first
structural member and at least one second structural member
friction stir welded at the interface of the first structural
member and at least one second structural member at the channel;
and cold sprayed material deposited on an exposed surface of the
friction stir welded interface operable to inhibit corrosion.
25. A friction stir weld joint, comprising: a first structural
member, the first structural member having a channel; and at least
one second structural member, the channel of the first structural
member receives a mating surface of the at least one second
structural member, the mating surface and/or channel being coated
with corrosively inert material, the materials of the first
structural member and at least one second structural member
friction stir welded at the interface of the first structural
member and at least one second structural member at the
channel.
26. A method for joining structure members, comprising: aligning a
first structural member to a second structural member, the first
structural member having a channel to receive a portion of the
second structural member; placing a corrosively inert material at
the channel to inhibit crevice crack corrosion; and friction stir
welding (FSW) at the channel to join the first structural member to
the second structural member.
27. A method for joining structural members, comprising: aligning a
first structural member to a second structural member, the first
structural member having a channel to receive a mating of the
second structural member; inserting a male connector of the first
structural member and/or second structural member into a female
receptacle of the second structural member and/or first structural
member; placing a corrosively inert material at the channel/mating
surface to inhibit crevice crack corrosion; placing a corrosively
inert material at a male connector/female receptacle interface to
inhibit crevice crack corrosion; friction stir welding (FSW) at the
channel and a male connector/female receptacle interface to join
the first structural member to the second structural member.
28. A method for retarding crack growth within a structural member,
comprising: identifying a crack within the structural member; and
cold spraying material on/within the crack to retard crack
growth.
29. A method for joining a first structural member and a substrate,
comprising: aligning a first structural member to a metallic
substrate, the first structural member having at least one shaped
cavity; and friction stir welding an exterior surface of the
metallic substrate proximate to the at least one shaped cavity to
extrude metallic material to the at least one shaped cavity.
Description
TECHNICAL FIELD OF THE INVENTION
[0001] The present invention relates generally to structural joints
and more particularly a method to join two or more members in
forming a three-dimensional joint.
BACKGROUND OF THE INVENTION
[0002] Structural beams translate stiffness and other mechanical
loads within structures such as buildings, vehicles, and bridges,
etc. In one example, structural beams may be used to translate
loads associated with the wing of an aircraft. These structural
beams may include box beams, I-beams, double I-beams, C-Beams or
other like structures that are efficient load carrying members.
FIGS. 1A and 1B provide a cross section of a typical I-Beam and
C-Beam. Such beams may be used in a variety of applications.
I-Beams may be used for long clear spans requiring heavy loads.
While C-Beams can be used where design and load requirements allow
use of a C-Beam as opposed to an I-Beam, which provides additional
support. Additionally a C-Beam may provide one flush surface not
present in the I-Beam.
[0003] These beams are typically joined together using fasteners.
Structures constructed via bolted and fastened I-beams and C-beams
often have problems translating stiffness and loads with minimal
weight due to moment continuity. This joining method also requires
drilling holes and installing fasteners to attach the members to
one another. Such holes often produce localized stresses and
mechanical loads that the beams must account for. To account for
such localized loads, the structure of the beam may be reinforced
resulting in increased weight and loads to be handled by the
beams.
[0004] Additionally, set up, tooling and the time required to drill
holes may become major drivers in manufacturing as well as issues
in quality assurance. The installation of fasteners is also a
process prone to quality assurance issues. (i.e. insuring that the
proper fasteners are used with the proper torques)
[0005] Friction Stir Welding (FSW) is a joining method, as
illustrated in FIG. 2 which has gained acceptance as a means for
joining panels together. FSW produces a plasticized region 22 of
material by pushing a non-consumable rotating tool 24 into the
material of parts 26A and 26B that are to be welded. Then a central
pin, or probe, 28 followed by the shoulder 30, is brought into
contact with the two parts 26A and 26B to be joined. The rotation
of tool 24 heats up and plasticizes the materials that the tool is
in contact with. As tool 24 moves along the joint line 32, material
from the front of the tool is swept around this plasticized annulus
to the rear, so eliminating the interface.
[0006] There are cost advantages if one applies a simple stiffened
skin structure that may be produced via FSW to the exterior of a
vehicle such as an aircraft. The robustness and automation of the
process is very attractive for manufacturing. However, smaller
complex three dimensional structures, such as aircraft designs,
have not been easily addressed by the application of FSW. The FSW
process works best when two pieces abut one another and are clamped
tightly together. This is most effectively achieved when the two
pieces are forming a single two-dimensional surface. Joining and
properly plasticizing three-dimensional surfaces is difficult. Thus
it has been difficult to apply FSW processing to complex
three-dimensional structures.
[0007] There are problems associated with each of these joining
methods. The requirement to drill holes and install fasteners to
attach beams to one another requires that the fastened beams be
strengthened in order to account for the localized mechanical loads
caused by the fasteners. Additionally, mechanical loads within the
beams may be localized at the fastener site as opposed to being
transferred across the entire joint interface.
[0008] Further limitations and disadvantages of conventional and
traditional joining process and related structures and
functionality will become apparent to one of ordinary skill in the
art through comparison with the present invention described
herein.
SUMMARY OF THE INVENTION
[0009] The present invention provides a means of joining a first
structural member and a second structural member that substantially
addresses the above identified needs as well as others. Embodiments
of the present invention provide a joint formed by coupling
(joining) a first structural member and a second structural member.
This involves first aligning a first structural member to a second
structural member. The first structural member has a channel with
which to receive a portion of the second structural member. Certain
embodiments may place corrosively inert materials within the mating
surfaces to prevent or inhibit corrosion or oxidation. Once
aligned, the first structural member and second structural member
may be friction stir welded at the channel to plasticize the
material adjacent to the channel of both the first structural
member and the second structural member to form a friction stir
weld joint. Embodiments may then coat the plasticized surfaces of
the FSW joint with cold sprayed materials to inhibit corrosion.
Should a crack occur within either the plasticized or
non-plasticized materials, cold sprayed material may be deposited
within and on the crack to retard or arrest the growth of the
crack.
[0010] Another embodiment in the present invention provides a
method for joining structural members. This involves aligning the
first structural member to a second structural member. The first
structural member has a channel with which to receive a portion of
the second structural member. As in the prior embodiment, this
channel serves as a guide with which to position the first
structural member relative to the second structural member. For
example, the first and second structural member may be an I-beam or
C-beam wherein the channel is placed within the horizontal members
and not the vertical webs of the I-beam. Certain embodiments may
place corrosively inert materials within the mating surfaces to
prevent or inhibit corrosion or oxidation. Once fitted together FSW
takes place at the channel to join the first structural member to
the second structural member. This results in plasticizing and
mixing the materials within and adjacent to the channel of both the
first and the second structural member to form a single continuous
joint at the channel. Cold sprayed materials may then coat the
plasticized surfaces of the FSW joint to inhibit corrosion. Should
a crack occur within either the plasticized or non-plasticized
materials, cold sprayed material may be deposited within and on the
crack to retard or arrest the growth of the crack.
[0011] Additional embodiments may place an adhesive or barrier
material that may both assist in fitting the first structural
member to the second structural member prior to the friction stir
weld as well as providing a barrier as the adhesive or barrier
material is extruded into interface cavities at the friction stir
weld joint. This method is particularly useful for structures where
weight is a concern, such as an aircraft using aluminum or aluminum
alloy structural members. By eliminating the need reinforce
structural components due to the coupling of structural members
using traditional fastener methods, the weight associated with
these structural; members may be greatly reduced.
[0012] Another embodiment of the present invention provides a
similar method for joining structural members. Again the first
structural member is aligned and fitted to a second structural
member wherein a channel within the first structural member
receives a portion of the second structural member. In addition to
this channel which may be used to fit the first structural member
to the second structural member a male connector within either the
first structural member and/or second structural member may be
received within a female receptacle of the second structural member
and/or first structural member. This may further facilitate the
setup and alignment process. Certain embodiments may place
corrosively inert materials on the mating surfaces to prevent or
inhibit corrosion or oxidation. The materials of the male connector
and female receptacle may be friction stir welded at the interface
to further enhance the joint coupling the first structural member
to the second structural member. Additionally, adhesive, barrier,
and/or corrosively inert material may be placed at the channel,
male connector, and/or female receptacle to assist in fitting,
preventing contaminants from entering or penetrating the interface
cavities that remain after joining the structural members, and/or
inhibit corrosion.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] For a more complete understanding of the present invention
and the advantages thereof, reference is now made to the following
description taken in conjunction with the accompanying drawings in
which like reference numerals indicate like features and
wherein:
[0014] FIGS. 1A and 1B provide a cross section of a typical I-Beam
and C-Beam;
[0015] FIG. 2 illustrates the Friction Stir Welding (FSW) joining
method;
[0016] FIG. 3 shows a first structural member in the process of
being fitted to a second structural member in accordance with an
embodiment of the present invention;
[0017] FIG. 4 shows a first structural member having a groove or
channel operable to receive and align a second structural member in
accordance with an embodiment of the present invention;
[0018] FIG. 5 provides a schematic diagram of cold spray
process;
[0019] FIG. 6 shows a first structural member joined to a second
structural wherein the FSW joint has been coated with material to
enhance the corrosion resistance of the FSW joint in accordance
with an embodiment of the present invention
[0020] FIG. 7 shows a first structural member having a groove or
channel joined by a FSW to a second structural member in accordance
with an embodiment of the present invention;
[0021] FIG. 8 shows a first structural member and a second
structural member, initially fitted together by male connectors and
female receptacles, and then permanently joined by a FSW to in
accordance with an embodiment of the present invention;
[0022] FIG. 9 shows a first structural member in the process of
being fitted to a second structural member in accordance with an
embodiment of the present invention wherein corrosively inert
material has been placed on the mating surfaces;
[0023] FIG. 10 shows a first structural member having a groove or
channel operable to receive and align a second structural member in
accordance with an embodiment of the present invention wherein
corrosively inert material has been placed on the mating
surfaces;
[0024] FIG. 11 provides a logic flow diagram describing the joining
of a first structural member and a second structural member
initially fitted together and then permanently joined by a FSW to
in accordance with an embodiment of the present invention;
[0025] FIG. 12 provides a second logic flow diagram describing the
joining of a first structural member and a second structural member
initially fitted together and then permanently joined by a FSW to
in accordance with an embodiment of the present invention;
[0026] FIG. 13 shows a structural member having a crack whose
growth is retarded or arrested in accordance with an embodiment of
the present invention;
[0027] FIG. 14 provides a logic flow diagram describing a process
to retard or arrest crack propagation or growth with a structural
member in accordance with an embodiment of the present
invention;
[0028] FIG. 15 depicts an alternative way to form an in situ
fastener provided by embodiments of the present invention employs
friction stir welding; and
[0029] FIG. 16 provides a logic flow diagram in accordance with an
embodiment of the present invention that uses forms an in-situ
extruded fastener to join a first member to a substrate.
DETAILED DESCRIPTION OF THE INVENTION
[0030] Embodiments of the present invention are illustrated in the
FIGS., like numerals being used to refer to like and corresponding
parts of the various drawings.
[0031] The present invention provides a means of joining a first
structural member and a second structural member that substantially
addresses the above identified needs. A three dimensional joint is
formed by coupling (joining) a first structural member and a second
structural member. This involves first aligning a first structural
member to a second structural member. The first structural member
has a channel with which to receive a portion of the second
structural member. Certain embodiments may place corrosively inert
materials within the mating surfaces to prevent or inhibit
corrosion or oxidation. Once aligned, the first structural member
and second structural member may be friction stir welded at the
channel to plasticize the material adjacent to the channel of both
the first structural member and the second structural member to
form a friction stir weld joint. Embodiments may then coat the
plasticized surfaces of the FSW joint with cold sprayed materials
to inhibit corrosion. Should a crack occur within either the
plasticized or non-plasticized materials, cold sprayed material may
be deposited within and on the crack to retard or arrest the growth
of the crack. One method of performing friction stir welding to
join members is disclosed in U.S. patent application Ser. No.
______ entitled "A FRICTION STIR WELDING PROCESS TO JOIN TWO OR
MORE MEMBERS IN FORMING A THREE-DIMENSIONAL JOINT," which is
incorporated by reference in its entirety for all purposes.
[0032] FIG. 3 shows a first structural member. FIG. 3 depicts two
I-beams, 50 and 52. These may be similar to the beams discussed
with reference to FIGS. 1A and 1B. However, unlike the beams of
FIGS. 1A and 1B, I-beam 52 has a channel or groove 54 cut into the
horizontal surface operable to receive a portion of the web 56 of
I-beam 50 within the channel. In so doing, I-beam 50 is aligned to
I-beam 52. FIG. 4 provides a side view of a portion of I-beam 52
wherein grooves 54 have been cut into the horizontal members 58 of
I-beam 52. Channels 54 as previously discussed with respect to FIG.
3 may receive a portion of the member to be joined and aligned.
Additionally channels 54 assist in fitting and holding member 52
and member 50 during the friction stir weld process. This greatly
reduces the time required to setup and align structural members
prior to permanently joining the members.
[0033] FIG. 5 provides a schematic diagram of cold spray process.
In the cold spray process, energy stored in the high pressure
compressed gas supply 52 is used to propel fine particles 54
supplied by a powder feeder 56 at high velocities. The compressed
gas may be fed via heating unit 58 to gun 60 where the gas entrains
particles 54 and exits through nozzle 62 at a high velocity. Powder
particles 54 are accelerated to a certain velocity and heated to a
desired temperature within gun 60. Upon impact with substrate 64
particles 54 are deformed and bond to substrate 64, thus forming
coating 66. With this process a fine balance exist between particle
size, density, temperature, and velocity in achieving a coding
having a desired set of properties.
[0034] Embodiments of the present invention may provide a cold
spray process where a powder, such as a powered metal, is directly
and selectively applied to the exposed surface(s) of the FSW to act
as sacrificial layer to protect the FSW joint depicted in the FIGS.
Additionally, the impact of the powder during the cold spray
process may create a small residual compressive stress which may
add superior mechanical properties when compared to conventionally
welded and aged joints. The cold spray process depicted in FIG. 5
may be used to apply an aluminum powder to the surface of the FSW
joint on both the root and face or just the face as required.
[0035] Through cold spray processes, embodiments of the present
invention can apply corrosion coatings to any configuration of a
FSW joint to effectively protect exposed surfaces of the FSW joint.
For structural members made using 7000 aluminum alloys, this may
reduce or eliminate the need for a thermal treatment after FSW.
This thermal treatment improves the corrosion resistance of 7000
aluminum alloys, but this sacrifices strength within the 7000
aluminum alloys. Applying cold spray materials to the FSW joint
allows the 7000 aluminum alloys to retain their strength while
protecting the weld area through the application of a coating via
cold spray. Embodiments of the present invention may also provide
the ability to apply a layer of a coatings (i.e. Commercially Pure
Aluminum (CP AL)) to a lapping FSW joint prior to FSW. This will
have the result of providing a faying surface that has been
effectively clad. Mixing the CP Al into the joint will not affect
the strength adversely because of the small addition to the
weld.
[0036] The cold spraying process may also be used to form in situ
fasteners to metallic materials such as aluminum through composite.
One such method is disclosed in U.S. patent application Ser. No.
11/279,970 entitled "PERFORATED COMPOSITES FOR JOINING OF METALLIC
AND COMPOSITE MATERIALS," which is incorporated by reference in its
entirety for all purposes. The joint need not be that dissimilar,
nor aluminum. Through cold spray processes, embodiments of the
present invention can deposit powdered metal directly to the
surface of a metal through a hole drilled into the mating member.
This will improve the fatigue resistance of the member which has
not be through drilled (i.e. the metal). Additionally, a friction
stir spot weld of this compacted powder may be performed to further
consolidate the cold spray material and providing better "adhesion"
to the substrate. Both of these methods may be applied to a drilled
hole or channel.
[0037] An alternative way to form an in situ fastener provided by
embodiments of the present invention employs friction stir welding.
By placing a metallic panel (i.e. Al) on top of a panel with a
machined recess such as a hole or channel (could be composite) and
using FSW on the surface of the metal, the resulting void will be
filled by extruded metal. This has been demonstrated in an Aluminum
to composite panel. The main advantage is that the composite can be
processed separate and does not require laying up the composite on
the metal like COMELD. This process will be further discussed with
reference to FIGS. 15 and 16.
[0038] FIGS. 6 and 8 depict a FSW joint such as that discussed in
FIG. 2 or a three-dimensional joint such as that discussed with
reference to FIG. 3 and FIG. 4 may be used as well. To enhance the
corrosion resistance of plasticized region 22 of the FSW joint a
cold spray process such as that discussed with reference FIG. 5 may
be utilized to deposit a sacrificial material such as an aluminum
powder 64 that may bond to the FSW joint surface of the plasticized
region of material. This will allow the aluminum powder 64 to form
a sacrificial layer 76 on the surface of the friction stir weld
joint that corrodes or oxidizes preferentially. Thus, the
sacrificial layer 76 extends the life of the FSW joint.
Additionally, the small residual compressive stresses may be
imparted to the surface of the FSW joint. These compressive
stresses may improve the static and dynamic properties. This
process provides a significant advantage in that cold spray is a
relatively inexpensive process that allows precise deposition of
material 64 where required. Additionally almost any material can be
converted into a powder that can be deposited using cold spray.
When compared to other techniques used to improve the corrosion
performance application of the material over the entire part is
required and does not provide a selective deposition process.
[0039] To further improve the friction stir weld joint of member 50
and 52, an adhesive may be deposited within the channel in order to
assist in the fitting. This adhesive may also form a barrier to
prevent moisture or other contaminants from penetrating the
friction stir weld joint or any spaces (interface cavities) or gaps
left following the joining process.
[0040] FIG. 7 provides an isometric view of two members, 50 and 52,
in the process of forming a FSW joint. Here a portion of structural
member 50 is received within channel 54 cut into the horizontal
component 58 of I-beam 52. As previously stated, adhesive or other
barrier protection material may be placed within the channel to
assist in fitting, at least temporarily, member 50 to member 52
prior to the FSW process. Rotating tool 24 inserts probe 28 into
the member 52 above channel 54. This probe may also extend into the
portion of member 50 contained within channel 54, however this is
not required. Rotation of probe 28 and the shoulder 30 of rotating
tool 24 will plasticize materials region 60. These materials
include both materials within and adjacent to channel 54 from both
structural member 50 and 52. This causes the material adjacent to
the channel to plasticize as rotating tool 24 follow the path of
channel 54. This eliminates the interface and forms a continuous
joint that couples structural member 52 to member 50.
[0041] Unlike prior applications of FSW where two pieces were
abutted against each other and friction stir welded to form a
single continuous panel. Embodiments of the present invention allow
the creation of a three dimensional structure. Additionally, the
application of FSW limits any deformation of the vertical portions
of the members to be joined. Thus preserving the load bearing
capability of the beams.
[0042] FIG. 8 provides an isometric view of two structural members,
structural members 84 and 86. These members are fitted using male
portions 82 of structural members 84 that are received within
female receptacles 86 and 88 of structural members 86. These male
connectors and female receptacles assist in fitting structural
members 84 to structural member 86 prior to the FSW process wherein
the FSW process plasticizes region 90 that includes both the male
connectors and female receptacles, as well as adjacent material
within both structural members to form a continuous joint able to
better distribute mechanical loads between structural member 84 to
structural member 86.
[0043] In the embodiment presented previously, one can deposit the
adhesive or barrier material in the channel 54 of FIGS. 3, 4, and 5
or within receptacle 88 of FIG. 6. This material may then be forced
from the receptacles or channels and into interfacing cavities as
the material is plasticized. This may fill any free space with the
adhesive or barrier material. Filling these spaces prevents
penetration of contaminants such as moisture into the FSW joint.
Such FSW joints are particularly applicable to structural members
made of materials such as aluminum or aluminum alloys used in the
fabrication of aircraft. Embodiments of the present invention
enable the overall structural requirements and weight of the
structural members to be reduced by eliminating localized regions
of high structural load caused by drilling holes or other
traditional fastener methods. Additionally, the mechanical loads
from one structural member may be transferred throughout the
continuous joint as opposed to localized fasteners where the two or
more structural members meet.
[0044] These FSW joints may be subject to crevice corrosion of the
joint surfaces. One embodiment of the present invention addresses
this issue with the addition of a corrosively inert layer applied
prior to the FSW process. As shown in FIG. 9 an aluminum metallic
(or other corrosively inert material) layer may be applied to
selective areas 120 of the components 52 and 50 to be joined. This
aluminum metallic layer may be applied using the cold spray process
such as that discussed with respect to FIG. 5, kinetic
metallization, or other like processes. Through the application of
the material 120 the aluminum alloy structure may be protected from
corrosive attack. This is done in much the same way that cladding
would protect the structure. Cladding is a process where by a sheet
of material such as a pure aluminum layer is roll bonded onto the
surfaces. Addition of the cladding layer to the mating surfaces
shown in FIGS. 9 and 10 as areas 120 will inhibit corrosion from
moisture entrapment to the same degree cladding does. Friction stir
welding through this thin layer of aluminum will not affect the
mechanical properties significantly. Additionally embodiments of
the present invention would enable the use of a post weld aging to
increase the corrosion resistance of the entire structure because
the additive aluminum layer would not be affected by thermal post
processing. Cold spray technologies.
[0045] FIG. 11 provides with a logic flow diagram that may be used
to illustrate various embodiments in the present invention wherein
structural members are joined together using FSW joints. Operations
100 began by first aligning and fitting a first structural member
to a second structural member in Step 110. This may be achieved by
cutting into the first structural member a channel with which to
receive a portion of the second structural member. Alternatively,
or in combination, male connectors of either the first or second
structural member may be aligned to and placed within female
receptacles of the second and/or first structural member to fit
these members together prior to the FSW. In either case, FSW is
performed in Step 112 at the interface of the first and second
structural members to join together the first and second structural
members. In step 114, material that preferentially oxidizes or
corrodes may be deposited using a cold spray process, kinetic
metallization, or other process to the exposed surface(s) of the
structure.
[0046] This will allow in one embodiment, aluminum powder to form a
sacrificial layer on the surface of the FSW joint that corrodes or
oxidizes preferentially. This sacrificial layer extends the life of
the FSW joint. Additionally, the small residual compressive
stresses may be imparted to the surface of the FSW joint. These
compressive stresses may improve the static and dynamic properties.
This process provides a significant advantage in that cold spray is
a relatively inexpensive process that allows precise deposition of
sacrificial material where required. Additionally almost any
material can be converted into a powder that can be deposited using
cold spray. When compared to other techniques used to improve the
corrosion performance application of the material over the entire
part is required and does not provide a selective deposition
process.
[0047] FIG. 12 provides a logic flow diagram that may be used to
illustrate an embodiment of the present invention where structural
members are joined together using FSW joints. Operations 200 begin
by in step 202 corrosively inert materials may be deposited using a
cold spraying process, kinetic metallization, or other like process
on the mating surfaces of the FSW joint. This corrosively inert
material applied prior to the friction stir welding will protect
the structure from corrosive attack in much the same way cladding
does. For example, in one embodiment pure aluminum may be deposited
on the mating surfaces of an aluminum alloy structure to be joined.
This will inhibit corrosion from moisture entrapment to the same
degree that a layer of cladding on the entire structure would.
Additionally, when using a FSW joining process the thin layer of
corrosively inert material will not affect mechanical properties of
the structure significantly. In step 204 a first structural member
may then be aligned to a second structural member where the
corrosively inert materials have been deposited on the mating
surfaces of one or both the first and second structural members. In
step 206 a friction stir welding process may be applied at the
interface to join the first and second structural member.
Optionally in step 208 a sacrificial material may be cold sprayed
or deposited using kinetic metallization on the exposed surfaces of
the FSW joint to further inhibit corrosion.
[0048] In another embodiment of the present invention as
illustrated in FIG. 13, a crack within a Material 220 may be
arrested or retarded using a cold spray process such as that
described with reference to FIG. 5. As shown in FIG. 13 Material
220 has developed a Crack 222. A layer of Material 224 may be
deposited on top of and within Crack 222 to retard or arrest the
growth of Crack 222. Additionally other embodiments of the present
invention may apply a friction stir weld process to plasticize the
material around Crack 222 and then coat the exterior surface with a
corrosion inhibiting material as part of Layer 224.
[0049] FIG. 14 provides a logic flow diagram in accordance with an
embodiment of the present invention wherein cracks within a joined
structure or individual structural member may be arrested or
retarded via the use of cold spray. In Step 242 a crack is
identified within a structural member or joined structural members.
In Step 244 materials as applied using a cold spraying or kinetic
metallization process over the crack. This material may serve to
arrest or retard the growth of the crack. Optionally a friction
stir well process may be applied to the material around the crack
in order to retard the growth of the crack. This may be done prior
to the deposition of the cold spray material or after the cold
spray process to plasticize the materials adjacent to the crack.
The cold spray process can be used to deposit directly to a cracked
surface to effectively stop or delay the crack growth for thousands
of cycles if not permanently. This alloys cracked surfaces to be
repaired on site, in the field with minimal access.
[0050] Additional steps may require the placing of an adhesive or
barrier material within the channel, upon the male connectors, or
within the female receptacles. This adhesive or barrier material
fills interface cavities to prevent contaminants from entering.
[0051] This invention solves prior problems by using the existing
structural members, such as I-beams C-beams, that incorporate
alignment guides (i.e. channels, connectors, and/or receptacles) to
fit and FSW these materials to form three dimensional shapes such
as T-joint configurations. By incorporating a groove or channel
into the horizontal pieces and inserting the vertical pieces into
these alignment guides, both members are joined together without
disturbing the radius of the upstanding channel or groove. This
joint can be further enhanced through the application of an
adhesive or barrier material near the top of the alignment guide
which will allow load transfer of material not joined by the FSW.
The adhesive or barrier material acts to deny penetration into the
joint by moisture or other contaminants. This adhesive facilitates
fitting the parts (i.e. structural members), during setup.
[0052] The T grooved or channel T FSW joint provided by embodiments
of the present invention has many advantages. First the drilling of
holes and fastener installation is eliminated for assembly of
structure members. In so doing, the fatigue lives of the structural
members are extended through the elimination of localized stresses
concentrated by these holes. Stiffness can be distributed over the
entire cross section versus 2 or 3 bolts/fasteners interfaces
enabling lower overall weight of the structural members and
structure. Set up time is reduced by using the adhesive to locate
the mating parts. This reduces or eliminates complex tooling
requirements. Pull off strength and fatigue life in the finished
structure may be improved by the addition of adhesives. The
adhesive also fills the interface cavities disallowing water or
contaminant entrapment. In so doing crevice corrosion is inhibited.
Cold spray and adhesives improve the stiffness and rigidity of the
finished assembly by improving the stiffener effectiveness. Nascent
adhesive from the weld joint also provides a visual indicator that
adhesive materiel is present in the weld joint, thus simplifying
NDE verification.
[0053] FIG. 15 depicts an alternative way to form an in situ
fastener provided by embodiments of the present invention employs
friction stir welding. By placing a metallic panel 252 (i.e. Al) on
top of a panel 254 with machined recess(es) 256 such as a hole or
channel (could be composite) and using FSW process on the exterior
surface of the metallic panel, the resulting void 256 will be
filled by extruded metal. This has been demonstrated in an Aluminum
to composite panel. The main advantage is that the composite can be
processed separate and does not require laying up the composite on
the metal.
[0054] FIG. 16 provides a logic-flow diagram in accordance with an
embodiment of the present invention that uses forms an in-situ
extruded fastener to join a first member to a substrate similar to
that provided in FIG. 15. The first structural member is aligned to
a metallic substrate in step 260 wherein the first structural
member has a number of shaped or tapered cavities. Protective
inserts may be placed within the shaped or tapered cavities. Unlike
prior applications of FSW where two metallic pieces were abutted
against each other and friction stir welded to form a single
continuous panel. Embodiments of the present invention allow the
FSW process to be applied to secure composite and metallic pieces
without the need for additional fasteners--thus reducing part count
and increasing the mechanical bonds. Additionally, the application
of FSW limits any deformation of the vertical portions of the
members to be joined. Thus preserving the load bearing capability
of the beams. In step 262 a FSW tool may be applied to the exterior
surface of the metallic substrate, the voids will be filled by
extruded metal. This has been demonstrated in an Aluminum to
composite panel. The extruded in-situ tapered fasteners which may
be used to secure materials such as composite materials to metallic
materials. This is achieved without the need drill into the
metallic materials. Such an arrangement reduces the setup costs in
time and money that are associated with drilling holes, installing
fasteners and addressing nonconformance. These setup costs have
been determined to be the greatest assembly line cost driver for
some advanced aircraft. Further, the issue of hole alignment to
fasteners is essentially eliminated. Thus reduce the quality
assurance issues associated with nonconformance. By preparing the
composite materials off-line, edge distance concerns are greatly
reduced.
[0055] In summary, embodiments of the present invention provide a
three dimensional joint formed by coupling (joining) a first
structural member and a second structural member. This involves
first aligning a first structural member to a second structural
member. The first structural member has a channel with which to
receive a portion of the second structural member. Once aligned,
the first structural member and second structural member may be
friction stir welded at the channel to plasticize the material
adjacent to the channel of both the first structural member and the
second structural member to form a FSW joint. One embodiment then
coats the plasticized surfaces of the FSW joint with cold sprayed
materials to inhibit corrosion. Another embodiment places
corrosively inert materials within the mating surfaces to prevent
or inhibit corrosion or oxidation. Should a crack occur within
either the plasticized or non-plasticized materials, cold sprayed
material may be deposited within and on the crack to retard or
arrest the growth of the crack.
[0056] Although the present invention is described in detail, it
should be understood that various changes, substitutions and
alterations can be made hereto without departing from the spirit
and scope of the invention as described by the appended claims.
* * * * *