U.S. patent application number 09/814583 was filed with the patent office on 2001-11-08 for friction pull plug welding: top hat plug design.
Invention is credited to Cantrell, Mark A., Coletta, Edmond R..
Application Number | 20010038027 09/814583 |
Document ID | / |
Family ID | 26850825 |
Filed Date | 2001-11-08 |
United States Patent
Application |
20010038027 |
Kind Code |
A1 |
Coletta, Edmond R. ; et
al. |
November 8, 2001 |
Friction pull plug welding: top hat plug design
Abstract
Friction Pull Plug Welding is a solid state repair process for
defects up to one inch in length, only requiring single sided
tooling, or outside skin line (OSL), for preferred usage on flight
hardware. The most prevalent defect associated with Friction Pull
Plug Welding (FPPW) was a top side or inside skin line (ISL) lack
of bonding. Bonding was not achieved at this location due to the
reduction in both frictional heat and welding pressure between the
plug and plate at the end of the weld. Thus, in order to eliminate
the weld defects and increase the plug strength at the plug `top` a
small `hat` section is added to the pull plug for added frictional
heating and pressure.
Inventors: |
Coletta, Edmond R.; (New
Orleans, LA) ; Cantrell, Mark A.; (Pearl River,
LA) |
Correspondence
Address: |
GARVEY SMITH NEHRBASS & DOODY, LLC
THREE LAKEWAY CENTER
3838 NORTH CAUSEWAY BLVD., SUITE 3290
METAIRIE
LA
70002
|
Family ID: |
26850825 |
Appl. No.: |
09/814583 |
Filed: |
March 22, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09814583 |
Mar 22, 2001 |
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09545980 |
Apr 10, 2000 |
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6253987 |
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60153750 |
Sep 13, 1999 |
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Current U.S.
Class: |
228/2.3 ;
228/2.1 |
Current CPC
Class: |
B23K 20/12 20130101;
B23K 20/129 20130101; B23K 20/1295 20130101; B23K 20/1265 20130101;
Y10T 29/49746 20150115; Y10T 29/49718 20150115; B23K 20/1255
20130101 |
Class at
Publication: |
228/2.3 ;
228/2.1 |
International
Class: |
B23K 020/12; B23K
037/00 |
Goverment Interests
[0003] The invention described herein was made in the performance
of work under NASA Contract No. NAS8-36200 and is subject to the
provisions of Section 305 of the National Aeronautics and Space Act
of 1958 (42 U.S.C. Section 2457).
Claims
1. A method of friction plug welding repair comprising the steps
of: a) locating a defect in a weld that joins two sections of
material together; b) removing weld material at the defect to form
an opening; c) placing a plug in the opening, wherein the plug has
top and bottom end portions, the top end portion being tapered and
larger in diameter than the opening, wherein the top end portion
has two sections including a gradually tapering section and a
rapidly tapering section, said rapidly tapering section defining
the maximum diameter of the top end portion; d) pulling the bottom
end portion of the plug so that the top end portion of the plug
engages the opening; and e) rotating the plug to heat up the plug
during pulling of step "d".
2. The method of claim 1 wherein in step "c", the plug top end
portions includes two separate sections including a frustoconical
smaller diameter section and a larger diameter section.
3. The method of claim 1 wherein the defect in step "a" is less
than one inch in length.
4. The method of claim 1, further comprising the step of placing a
backing plate member against the sections of material.
5. The method of claim 1 wherein step "b" includes drilling a hole
to form the opening.
6. The method of claim 1 wherein the opening formed in step "b" is
a tapered opening.
7. The method of claim 6 wherein the opening has a maximum
diameter, and the top end portion of the plug has a section with a
diameter larger than said opening maximum diameter.
8. The method of claim 1 wherein the plug top end portion has a
gradually tapering section along a majority of the length of the
top end portion, and a rapidly tapering section of maximum diameter
that extends over a minority of the length of the top end
portion.
9. The method of claim 1 wherein the top end portion includes an
annular curved surface.
10. The method of claim 9 wherein the curved surface has a radius
of less than 1/2 inches.
11. The method of claim 9 wherein the curved surface has a radius
of less than about {fraction (3/16)} inches.
12. A method of friction plug welding repair comprising the steps
of: a) locating a defect in a weld that joins two sections of
material together; b) removing weld material at the defect to form
an opening; c) placing a plug in the opening, the plug having top
and bottom end portions, the top end portion being generally
frustoconically shaped at least in part, the top end portion having
an enlarged diameter tapered portion that is larger in diameter
than the frustoconical section's largest diameter; d) pulling the
bottom end portion of the plug so that the top end portion of the
plug engages the opening; and e) rotating the plug with sufficient
revolutions per unit time that the combined effect of the enlarged
diameter of the plug at the top end and the rotation enables the
plug to heat up the plug top, and wherein the plug top provides
radial and axial pressure.
13. The method of claim 12 wherein the plug is rotated in step "e"
at between 1,000 and 7,000 revolutions per minute.
14. The method of claim 12 wherein the plug is rotated instep "e"
at between 1,000 and 7,000 revolutions per minute.
15. The method of claim 12 wherein the plug is pulled in step "d"
with a tension of between 1,000 and 20,000 pounds.
16. The method of claim 12 wherein the plug is pulled in step "d"
with a tension of between 1,000 and 20,000 pounds.
17. A method of friction plug welding repair comprising the steps
of: a) locating a defect in a weld that joins two sections of
material together; b) removing weld material at the defect to form
an opening; c) placing a tapered plug in the opening, a first end
of the plug having an annular curved portion that defines the
greatest amount of taper per unit length of the plug; d) pulling a
second end portion of plug so that the first end portion of the
plug engages the opening; and e) rotating the plug to heat up the
plug at the first end during the pulling step "d".
18. The method of claim 17 wherein the plug is rotated in step "e"
at between about 1,000 and 7,000 revolutions per minute.
19. The method of claim 17 wherein the plug is rotated in step "e"
at between about 1,000 and 7,000 revolutions per minute.
20. The method of claim 17 wherein the plug is pulled in step "d"
with a tension of between about 1,000 and 20,000 pounds.
21. The method of claim 17 wherein the plug is pulled in step "d"
with a tension of between about 1,000 and 20,000 pounds.
22. A friction pull plug welding apparatus for repairing a defect
in a weld that has been removed, leaving a defect opening in the
weld, comprising; a) a rotary tool; b) a chuck that is supported by
the rotary tool; c) a backing member; d) a pull plug body that fits
the defect opening, wherein the pull plug includes first and second
sections, the first section being sized and shaped to fit through
the defect opening, the second section having a part that is sized
and shaped to not fit through the opening, said second section
including a maximum diameter portion with an annular surface that
rapidly increases in diameter when measured longitudinally and when
compared to the overall length of the pull plug body.
23. The friction pull plug welding apparatus of claim 22 wherein
the rotary tool rotates at between about 4000-6000 revolutions per
minute during use.
24. The friction pull plug welding apparatus of claim 22 wherein
the rotary tool rotates at least about 4000 revolutions per minute
during use.
25. The friction pull plug welding apparatus of claim 22 wherein
the chuck has a tensile strength of at least 1,000 pounds.
26. The friction pull plug welding apparatus of claim 22 wherein
the chuck has a tensile strength of between about 1,000 and 20,000
pounds.
27. The friction pull plug welding apparatus of claim 22 wherein
the chuck and pull plug body are removably connectable.
28. The friction pull plug welding apparatus of claim 22 wherein
the chuck and pull plug body are removably connectable with a
threaded connection.
29. The friction pull plug welding apparatus of claim 22 wherein
the pull plug body annular surface is a curved annular surface.
30. The friction pull plug welding apparatus of claim 22 wherein
the pull plug body annular surface is a curved annular surface
having a cross section with a radius of curvature of less than one
inch.
31. The friction pull plug welding apparatus of claim 22 wherein
the pull plug body annular surface is a curved annular surface
having a cross section with a radius of curvature of about three
sixteenths inches.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The assignee is the owner of a copending patent application
Ser. No. 09/141,294, filed Aug. 26, 1998, entitled "Friction Plug
Welding," and incorporated herein by reference. Forparameters not
mentioned herein, see copending patent application Ser. No.
09/141,294.
[0002] Priority of U.S. Provisional Patent Application Ser. No.
60/153,750, filed Sep. 13, 1999, incorporated herein by reference,
is hereby claimed.
REFERENCE TO A "MICROFICHE APPENDIX"
[0004] Not applicable
BACKGROUND OF THE INVENTION
[0005] 1. Field of the Invention
[0006] The present invention relates to friction welding. More
particularly, the present invention provides an improved method and
apparatus of friction plug welding that employs a specially
configured pull plug that enhances bonding and that is suitable for
flight hardware usage.
[0007] 2. General Background of the Invention
[0008] Friction stir welding (FSW) is a solid state joining process
developed by The Welding Institute (TWI), Cambridge, England and
described in U.S. Pat. No. 5,460,317, incorporated herein by
reference. Also incorporated herein by reference are U.S. Pat. No.
5,718,366 and all references disclosed therein. The following
references are also incorporated herein by reference: U.S. Pat.
Nos. 3,853,258, 3,495,321, 3,234,643, 4,087,038, 3,973,715,
3,848,389; British Patent Specification No. 575,556; SU Patent No.
660,801; German Patent No. 447,084, "New Process to Cut Underwater
Repair Costs", TWI Connect, No. 29, January 1992; "Innovator's
Notebook", Eureka Transfer Technology, October 1991, p. 13;
"Repairing Welds With Friction-Bonded Plugs", NASA Tech. Briefs,
September 1996, p. 95; "Repairing Welds With Friction-BondedPlugs",
Technical Support Package, NASA Tech. Briefs, MFS-30102; "2195
Aluminum-Copper-Lithium Friction Plug Welding Development", AeroMat
'97 Abstract; "Welding, Brazing and Soldering", Friction welding
section: "Joint Design", "Conical Joints", Metals Handbook: Ninth
Edition, Vol. 6, p. 726.
[0009] Friction plug welding (FPW), also referred to as plug
welding and friction taper plug welding (FTPW), is a process in
which initial defective weld material is located, removed and
replaced by a tapered plug, which is friction welded into place.
This process is similar to friction stud welding, in which a plug
is welded to the surface of a plate, end of a rod, or other
material. The primary difference is that FPW is designed to replace
a relatively large volume of material containing a defect whereas
friction stud welding is a surface-joining technique.
[0010] Friction plug welding could be used to repair weld defects
in a wide variety of applications; however, it would most likely be
used where weld strength is critical. This is due to the fact that
manual weld repairs result in strengths much lower than original
weld strengths, as opposed to friction plug welds (FPWs) whose
typical mechanical properties exceed that of the initial weld. In
applications where high strength is not required, manual welding
would be less expensive and would not require specialized
equipment.
[0011] An extension of FPW is known as stitch welding or friction
tapered stitch welding (FTSW) and has been developed to repair
defects longer than what a single plug can eliminate. Stitch
welding is the linear sequential welding of several plugs such that
the last plug weld partially overlaps the previous plug. Defects of
indefinite length can be repaired with this process, limited only
to the time and cost of performing multiple plug welds. These welds
have undergone the same testing procedures as single FPWs,
including NDI and destructive evaluation. The strengths for stitch
welds are similar to those for single plug welds.
[0012] Stagger stitch welding is a process best defined as stitch
welding in a non- linear fashion. Areas wider than one plug length
can be completely covered by staggering plugs side to side as they
progress down the length of an initial weld. This process is being
developed for plug welds whose minor diameter is on the crown side
of the initial weld, and where replacement of the entire initial
weld is desired.
[0013] While friction plug welding might be a preferred method of
repairing defects or strengthening initial welds, there are some
applications where heretofore it has been extremely difficult to
use friction plug welding. The main cause is due to the logistics
of setting up the equipment and/or support tooling to perform
friction plug welding, and the geometry of the workpiece to be
welded.
BRIEF SUMMARY OF THE INVENTION
[0014] The present invention provides an improved method and
apparatus for friction plug welding an article using a plug that
has an improved configuration and geometry that facilitates a good
weld when the plug is pulled.
[0015] With previous pull plug designs (which typically did not
include an angular transition), the plug top usually did not weld
to the plate top in 0.385" gage plate. This lack of bonding
resulted in penetrant, x-ray defects, and ultrasonic indications at
the plug top, ultimately leading to a reduction in tensile
strength. Since a friction pull plug welding (FPPW) process that
produces defects would not be considered for usage on flight
hardware, the defects along the interface have to be
eliminated.
[0016] The "Top Hat" plug design of the present invention ensures
complete bonding between the plug and the plate on the inside skin
line (ISL) side of the weld. The top hat achieves this improvement
through a combined effect of supplying additional material to
frictionally heat at the plug top end portion, as well as providing
additional radial and axial pressure at plug top. Overall weld
quality is significantly improved with the addition of the "Top
Hat" to a plug, through the elimination of all top side defects as
characterized through NDE evaluation (Dye Penetrant, X-Ray, and
Ultrasonic), and through a higher tensile strength weld
interface.
[0017] Listed below are typical and exemplary dimensions of a "top
hat" plug design; a {fraction (3/16)}" radius is utilized in the
curved annular surface transition from the plug body to the "top
hat"; the plug top hat has a diameter of 1.250" to 1.480" extending
out from the body by 0.050" to 0.250"; the plug hat has a thickness
of 0.020", however the thickness can range up to 0.100" thick.
[0018] The present invention includes a method of friction plug
welding an article, comprising several stages. Preferably, the
first stage is making a hole (that is preferably tapered) in the
article to be welded. Machining a tapered hole is not necessarily
required in friction plug push welding where (in certain situations
generally characterized when the article to be welded is softer
(having lower hardness) relative to the harder (having higher
hardness) plug) the plug will form a hole, self bore or embed into
the material either while rotating or not.
[0019] A tapered plug is inserted through the tapered hole. The
plug is then attached to a chuck of a rotary tool or like motor
which can both pull on the tapered plug and rotate it. Some
connector or connection means, such as threads, key grooves, flats,
or locking retention interface, are provided on the tapered plug to
facilitate pulling the plug with the rotary tool.
[0020] The second stage, or heating cycle is always required to
weld the plug to the article. This stage preferably consists of
rotating the plug while pulling (placing the plug in tension
axially) into intimate contact with the hole's surface, or region
surrounding the hole. The typical axial load exerted on the plug
during the heating phase is between about 1000 pounds and 20,000
pounds, preferably between about 6000 pounds and 18,000 pounds,
more preferably 10,000 pounds to 16,000 pounds, and most preferably
12,500 pounds to 15,000 pounds.
[0021] Other forms of heating may also be utilized, including but
not limited to, using electricity to assist in the heating process,
or vibrational energy such as oscillatory rotation rather than the
preferred method of continuous rotation, or lateral, axial or some
combination thereof, rapid displacement (such as ultrasonic
welding) to impart sufficient energy to assist in the heating the
weldment. The plug (preferably tapered, with a taper the same as or
preferably different from the taper of the hole (if it is tapered),
and rotating the plug relative to the part while moving the plug in
the direction such to make contact with the hole's surface, until
contact is made, and forcing the plug into the surface of the hole
by pulling on the plug (imposing a tensile force in the plug in the
plug's axial direction) all while continuously spinning the plug
relative to the article.
[0022] The third stage of the method of the present invention is
the braking stage. This rapid deceleration of rotation, if rotation
is used (or otherwise defined as rapid decline of energy input to
zero or near zero), is necessary to performing a successful weld.
Preferably, the fourth stage which is also referred to as the
forging stage, is a period of cooling in which no further heating
energy is intentionally applied to the weldment and energy in the
form of heat is dissipated. During this stage, it is preferable to
maintain either the same axial tensile load, or a different axial
tensile load whether that be greater or lesser, to cause
densification and or maintain or create a sound metallurgical bond
or weldment. In the current application, although not necessarily
required in other applications, excess sections of the plug are cut
off and material further removed via grinding and sanding to make
it smooth with the initial weldment and/or surrounding materials'
surfaces. The present invention also includes the plug.
[0023] The displacement during heating should be optimized for the
specific plug geometry and hole geometry combination being welded.
Empirical models can be developed to ensure that the heating
displacement is great enough to enact the benefits of the "top
hat", while not producing a weld with defects, such as weld pull
through, lack of bonding, or grain separation.
[0024] In the preferred embodiment of the method of the present
invention, a tapered hole is drilled from one side of the article
being repaired. A tapered plug is then inserted through the tapered
hole, then the plug is attached to a chuck of a motor which can
both pull on the tapered plug and spin it. Some connection means,
such as threads or locking retention interface, are provided on the
tapered plug to facilitate pulling the plug. The plug is pulled
while spun by the motor. Preferably the plug is pulled also after
the spinning stops, with a load the same as or different from the
load while spinning. After the spinning has taken place and the
plug is welded in place, the excess part of the plug is cut off and
the weld machined down to make it smooth. Pulling a tapered plug
during plug welding allows all equipment, including a backing
plate, to be on one side of the article being welded. Pull welding
eliminates the need for large backing structures that must react
high loads associated with friction plug push welding, often
exceeding 10,000 pounds force, while at the same loads deflect an
amount often less than 0.25 inches.
[0025] A hydraulically powered direct drive weld has been used;
however, an electrically powered direct drive, or inertia drive
flywheel weld system may also be used.
[0026] The inventors have discovered that satisfactory welds occur
most frequently when the plug diameter is large enough to maintain
a mechanically stable cool core. For this reason, plug diameters
have continued to increase, and more powerful weld equipment has
been acquired. Techniques have been developed to weld larger
diameter plugs while minimizing the required motor power. One such
discovery entails varying the axial stroke rate during the weld
process to decrease the initial contact friction. In this process,
it is preferable for the plug and article to contact slowly,
thereby reducing the rotational friction at contact. After the
boundary between the plug and article plasticizes, then it is
preferable, although not required, to increase the stroke rate,
thereby increasing the rate of heating at the interface to achieve
weld temperatures. This discovery significantly reduces the
required power to perform welds, and is advantageous in performing
large welds whose power requirement exceeds that which the system
is designed to deliver.
[0027] The inventors have has found that with their current
equipment and process, the preferable operating range at which to
rotate the plug is 4000-6000 rpm prior to contact between the plug
and hole's surface, and it is also preferable to maintain a minimum
of 3000 rpm during the duration of the heating cycle. Successful
welds have been created at much slower speeds, as low as but not
limited to 1000 rpm prior to contact and as high as, but limited
only by the equipment capability, of about 7000 rpm prior to
contact.
[0028] The plug of the present invention preferably has a
connection means comprising a standard external thread. The thread
can be, for example, right-hand 3/4" with 16 threads per inch.
Other methods for holding the plug in the chuck may also include
internal threads and key grooves.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0029] For a further understanding of the nature, objects, and
advantages of the present invention, reference should be had to the
following detailed description, read in conjunction with the
following drawings, wherein like reference numerals denote like
elements and wherein:
[0030] FIG. 1 is a side view of the preferred embodiment of the
apparatus of the present invention illustrating the pull plug
portion that is used as part of the method of the present
invention;
[0031] FIG. 2 is a side view of an alternate embodiment of the
apparatus of the present invention illustrating the pull plug
portion that is used in the method of the present invention;
[0032] FIG. 3 is a fragmentary side view of the pull plug portion
of the preferred embodiment of the apparatus of the present
invention;
[0033] FIG. 4 is a fragmentary side view of the pull plug portion
of the alternate embodiment of the apparatus of the present
invention;
[0034] FIGS. 5 and 6 are side elevational views of pull plugs that
do not include the enlarged annular curved shoulder at one end
portion of the plug;
[0035] FIG. 7 is a side partial sectional elevation view
illustrating the method of the present invention;
[0036] FIG. 8 is another side sectional elevation view illustrating
the method of the present invention;
[0037] FIG. 9 is a sectional view illustrating a lack of bonding
that can occur when a pull plug does not include the improved
configuration of the present invention; and
[0038] FIGS. 10 and 11 are sectional views that illustrate complete
bonding using the preferred embodiment or the alternate embodiment
of the apparatus of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0039] In FIG. 1, the preferred embodiment of the apparatus of the
present invention is designated generally by the numeral 10. FIG. 2
shows an alternate embodiment designated as 10A. In FIG. 1, the
pull plug 10 has a frustoconically shaped section 11 and a
preferably cylindrically shaped, externally threaded shank 12. In
FIG. 2, the pull plug 10A has a longer frustoconical section 13 and
a shank 12 A. Plugs 8 and 9 in FIGS. 5, 6 respectively show plugs
that do not provide the "top hat" of the present invention, namely
the enlarged, curved annular shoulder shown (enlarged) shown in
FIGS. 3 and 4, and designated by the numerals 15, 16, 17. A lack of
complete bonding can occur when using plugs such as 8 and 9. In
FIG. 9, the lack of bonding is illustrated by arrows 30, 31.
[0040] In each of the embodiments of FIGS. 1 and 2, the shank 12 or
12A can be generally cylindrically shaped having a tip 14. External
threads 23 can be provided on each shank 12, 12A. The external
threads 23 on shank 12 or 12A enable a drill, drill chuck or rotary
tool 25 (see FIGS. 7-8) to be fastened to shank 12 so that rotation
and tension can be imparted to plug 10 or 10A.
[0041] The frustoconical sections 11 and 13 are integrally joined
to a "top hat" or enlarged diameter section 15. In FIGS. 1-4 the
enlarged diameter section 15 is defined by a curved annular surface
16 having edge 17. Curved annular surface 16 can be for example a
radius which is generated 360 degrees. Edge 17 defines the largest
diameter of an overall upper or top portion 18 of pull plug 10. The
top portion 18 extends from annular shoulder 19 to edge 17. Lower
portion of each pull plug 10, 10A is designated by the numeral 20
and includes shank 12 and tip 14.
[0042] Using the method of the present invention, a pair of
sections 21,22 that have been welded may possibly have a defect in
the weld. The weld defect is preliminarily located and removed by
drilling, for example. Friction plug welding (FPW) hole geometries
are an important factor to creating a successful weld. The hole 24
is made by mechanically removing the weld bead flush to the top and
bottom sides or the surrounding plate or sheet, drilling a pilot
hole, and counter sinking with a counter sink cutter. The current
included angle is typically 20.degree. to 120.degree., preferably
40.degree. to 90.degree., and most preferably 40.degree. to
60.degree., although it is possible to perform similar welds with
no angle (a straight bored hole), or opposite bored tapers (those
which the taper of the plug and hole are opposing each other). A
dual chamfered hole 24 can be used. Such a dual chamfer arrangement
is disclosed in copending application Ser. No. 60/156,734, entitled
"Friction Pull Plug Welding: Dual Chamfered Plate Hole", which is
incorporated herein by reference. The hole 24 is drilled to a depth
such that the minor diameter is 0.00" to 0.200" greater in diameter
than the diameter of the plug's shaft.
[0043] The major diameter of the plug 10, 10A is typically equal to
or greater than the major diameter of the hole 24. Current shaft
diameters have ranged from 5/8" to 3/4" in diameter; however,
diameters ranging from between 1" and 1.5" are planned. Current
plug major diameters (the diameter on the larger side of the taper)
typically range from 1" to 1.35", but have been made less than 3/4"
and may be made in excess of 1.5". The plug body included angle,
before the annular surface transition to the top hat, ranges from
10.degree. to 90.degree., most preferably between 15.degree. to
60.degree..
[0044] The method of the present invention includes the selection
of a pull plug 10 or 10A that is then placed in the opening 24
formed when the defect is removed. In FIG. 7, a rotary tool 25 is
then attached to the pull plug lower portion 20 at shank 12 (eg. at
threaded connection 23). Tension is applied to the rotary tool,
pulling the connected plug 10 or 10A (see arrow 26, FIGS. 7, 8) so
that its top portion 18 tightly engages the opening 24 that is
formed by the drill at the flaw or defect in the weld. A hydraulic
ram can be used to pull the rotary tool 25, as an example.
[0045] Tension applied to a plug 10, 10A is preferably 6000-18000
lbs, more preferably 10000-15000 lbs, and most preferably
12500-15000 lbs. During the application of such tension, the plug
10 or 10A is preferably rotated (see arrow 27, FIGS. 7-8) at least
4,000 revolutions per minute, more preferably at least 5000 RPM,
most preferably at least 6000 RPM, and perhaps even higher with
proper equipment. The inventors have found that reliability and
robustness increase with increasing RPM.
[0046] The forging phase for typical weld geometry (see FIGS. 1-5)
exerts an axial tensile load of typically 1000 pounds to 20,000
pounds, preferably 6000 pounds to 16,000 pounds, more preferably
8000 pounds to 15,000 pounds, and most preferably 12,000 pounds to
14,000 pounds, as the weld cools. After several seconds, (typically
less than one minute, preferably about 5 seconds), the weld has
cooled sufficiently to remove the tensile load and remove the
tooling and weld equipment.
[0047] The advantage of pulling instead of pushing is that all
equipment can be placed on one side of the object being repaired
(such as the rather large and fragile external tank of the space
shuttle). This makes the logistics of performing a plug weld much
easier in some cases than if standard plug push welding were to be
performed.
[0048] As shown in FIGS. 10 and 11, the enlarged diameter section
15 of top portion 18 ensures complete bonding between the plug 10
and the plate on the inside skin line or ISL side 28 of the weld.
This enlarged diameter section 15 or "top hat" ensures complete
bonding between the plug 10 or 10A and the plate sections 21, 22.
This enlarged diameter section 15 or "top hat" achieves this
improvement through a combined effect of supplying additional
material to frictionally heat up at the plug 10 top portion 18 as
well as providing additional radial and axial pressure at the plug
top portion 18.
[0049] The current equipment and tooling includes a hydraulically
powered direct drive motor 25 to rotate the plug and a suitable
chuck to form an interface between motor 25 and plug 10 or 10A. If
an inertial drive flywheel is instead used to rotate the plug,
perhaps RPM as low as 1000 might produce satisfactory welds.
[0050] The typical maximum temperature for this process, using
typical process parameters, using aluminum alloys is 900.degree. F.
as measured by an embedded thermocouple located within 0.100" from
the original interface at an approximate depth of 33% to 50%
through the substrate's thickness. The first cycle ends after a
pre-programmed time (typically less than 5 seconds, preferably from
0.25 seconds to 2 seconds, more preferably from 0.5 seconds to 2
seconds, and most preferably in about 1 second), displacement
during heating (also referred to as `burn-off`) (typically 0.010
inches to 0.5 inches, preferably 0.150 inches to 0.400 inches, more
preferably 0.200 inches to 0.350 inches, and most preferably 0.250
inches to 0.300 inches), or temperature (typically 500.degree. F.
to 1000.degree. F., preferably 700.degree. F. to 1000.degree. F. as
measured with an imbedded thermocouple within 0.1" of the original
interface buried up to a depth of about 50% through the substrate's
thickness.
[0051] A backing support 29 (also referred to as a pressure foot or
collet) reacts the axial load, and also serves as a restraint to
forge the extruded flash. The depth, diameter and profile of this
support are optimized for each set of conditions, e.g. weld
parameters, plug/hole geometrical design, plate thickness, etc.,
and is important in creating a defect-free weld. In the pull
method, the backing support (also referred to as a pressure foot)
consists of a collet of an appropriate diameter and geometry.
Currently, the diameter of the collet is larger than the shaft of
the plug that passes through it by at least 0.002", typically from
0.002" to 0.400", and preferably from 0.100" to 0.325". The profile
of the collet may include a bevel, taper, groove or other type of
depression to act as a reservoir for plasticized material to flow.
Successful welds have been made with tapered backing supports, with
a taper angle between 0.degree. and 60.degree., most typically
between 20.degree. and 40.degree..
[0052] The present inventors use or contemplate using plug welding
(push and/or pull) with 2195 Al--Cu--Li alloy and 2219 Al--Cu
alloy. Development of plug welding includes plugs (for example) of
extruded Al--Cu--Li 2195 in the T3, T8, and T8 overage condition
welded into (1) Al 2195-T8 sheet, extrusion and plate, (2)
2195-T8/2195-T8 fusion welded sheet, extrusion and plate with Al
4043 filler wire, (3) 2195-T8/2219-T8 fusion welded sheet,
extrusion and plate with Al 4043 filler wire, (4) 2219-T8/2219-T8
fusion welded sheet, extrusion and plate with Al 4043 filler wire,
(5) 2219-T8/2219-T8 fusion welded sheet, extrusion and plate with
Al 2319 filler wire, (6) friction stir welded 2195-T8/2195-T8 sheet
and plate, where all sheets and plates were of thicknesses greater
than 0.12" and no greater than 1.00" and all plugs were a diameter
between 0.500" and 1.500".
[0053] The main application of the Friction Pull Plug Welding Top
Hat Plug Design is for solid state repair welding of welded
pressure vessels utilized in the aerospace industry. This process
would also be useful in any application where a defect free, high
strength, circular weld of up to about 1" diameter is required.
This process could also be readily utilized to repair the Friction
Stir Welding exit keyhole on circumferential welds. Other
applications could be found throughout the automotive, aircraft,
marine, and aerospace industries.
[0054] This application could be utilized in all other alloy
systems or metal matrix composites.
PARTS LIST:
[0055] The following is a list of parts and materials suitable for
use in the present invention:
1 Part Number Description 10 pull plug 10A pull plug 11
frustoconical section 12 shank 13 frustoconical section 14 tip 15
enlarged diameter section 16 curved annular shoulder 17 edge 18 top
portion 19 annular shoulder 20 lower portion 21 plate section 22
plate section 23 threaded section 24 hole 25 rotary tool 26 arrow
27 arrow 28 outside skin line surface 29 backing support 30 arrow
31 arrow
[0056] All measurements disclosed herein are at standard
temperature and pressure, at sea level on Earth, unless indicated
otherwise. All materials used or intended to be used in a human
being are biocompatible, unless indicated otherwise.
[0057] The foregoing embodiments are presented by way of example
only; the scope of the present invention is to be limited only by
the following claims.
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