U.S. patent application number 10/652532 was filed with the patent office on 2005-03-03 for apparatus and method for friction stir welding using a consumable pin tool.
Invention is credited to Helder, Earl Claude, Subramanian, Pazhayannur Ramanathan, Trapp, Timothy Joseph.
Application Number | 20050045695 10/652532 |
Document ID | / |
Family ID | 34104749 |
Filed Date | 2005-03-03 |
United States Patent
Application |
20050045695 |
Kind Code |
A1 |
Subramanian, Pazhayannur Ramanathan
; et al. |
March 3, 2005 |
Apparatus and method for friction stir welding using a consumable
pin tool
Abstract
The present invention provides a friction stir welding apparatus
operable for welding one or more metals, metal alloys, or other
materials. The friction stir welding apparatus includes a pin tool
holder, a shoulder having a surface coupled to the pin tool holder,
and a pin tool coupled to the pin tool holder, the pin tool at
least partially protruding from the surface of the shoulder,
wherein the pin tool is made of a consumable pin tool material.
Optionally, the shoulder rotates at a predetermined rotational
speed and is retractable into/extendable from the pin tool holder
at a substantially constant rate. Optionally, the shoulder is also
made of a consumable shoulder material that is at least partially
incorporated into the volume of a joint to be welded. The
consumable shoulder material comprises a material that is the same
as, similar to, or dissimilar from one or more materials comprising
a workpiece to be friction stir welded. Preferably, the pin tool
rotates at a predetermined rotational speed and is retractable
into/extendable from the surface of the shoulder at a substantially
constant rate. The consumable pin tool material is at least
partially incorporated into the volume of the joint to be welded.
The consumable pin tool material comprises a material that is the
same as, similar to, or dissimilar from one or more materials
comprising the workpiece to be friction stir welded.
Inventors: |
Subramanian, Pazhayannur
Ramanathan; (Niskayuna, NY) ; Helder, Earl
Claude; (Cincinnati, OH) ; Trapp, Timothy Joseph;
(Upper Arlington, OH) |
Correspondence
Address: |
Paul J. DiConza
GE Global Research Center
1 Research Circle, K-1 3A60
Niskayuna
NY
12309
US
|
Family ID: |
34104749 |
Appl. No.: |
10/652532 |
Filed: |
August 29, 2003 |
Current U.S.
Class: |
228/112.1 ;
148/527 |
Current CPC
Class: |
B23K 20/125 20130101;
B23K 20/128 20130101; B23K 20/1215 20130101; B23K 20/1255
20130101 |
Class at
Publication: |
228/112.1 ;
148/527 |
International
Class: |
B23K 020/12 |
Claims
What is claimed is:
1. A friction stir welding apparatus operable for welding one or
more metals, metal alloys, or other materials, the friction stir
welding apparatus comprising: a pin tool holder; a shoulder having
a surface and an inside diameter; and a pin tool coupled to the pin
tool holder, the pin tool at least partially disposed within the
inside diameter of the shoulder and at least partially protruding
from the surface of the shoulder, wherein the pin tool comprises a
consumable pin tool material.
2. The friction stir welding apparatus of claim 1, wherein the
shoulder rotates at a predetermined rotational speed.
3. The friction stir welding apparatus of claim 1, wherein the
shoulder is retractable into/extendable from the pin tool
holder.
4. The friction stir welding apparatus of claim 3, wherein the
shoulder is retractable into/extendable from the pin tool holder at
a substantially constant rate.
5. The friction stir welding apparatus of claim 1, wherein the
shoulder comprises a consumable shoulder material.
6. The friction stir welding apparatus of claim 5, wherein the
consumable shoulder material is at least partially incorporated
into the volume of a joint to be welded.
7. The friction stir welding apparatus of claim 5, wherein the
consumable shoulder material comprises a material that is the same
as one or more materials comprising a workpiece to be friction stir
welded.
8. The friction stir welding apparatus of claim 5, wherein the
consumable shoulder material comprises a material that is similar
to one or more materials comprising a workpiece to be friction stir
welded.
9. The friction stir welding apparatus of claim 5, wherein the
consumable shoulder material comprises a material that is
dissimilar from one or more materials comprising a workpiece to be
friction stir welded.
10. The friction stir welding apparatus of claim 1, wherein the pin
tool rotates at a predetermined rotational speed.
11. The friction stir welding apparatus of claim 1, wherein the pin
tool is retractable into/extendable from the surface of the
shoulder.
12. The friction stir welding apparatus of claim 11, wherein the
pin tool is retractable into/extendable from the surface of the
shoulder at a substantially constant rate.
13. The friction stir welding apparatus of claim 1, wherein the
consumable pin tool material is at least partially incorporated
into the volume of a joint to be welded.
14. The friction stir welding apparatus of claim 1, wherein the
consumable pin tool material comprises a material that is the same
as one or more materials comprising a workpiece to be friction stir
welded.
15. The friction stir welding apparatus of claim 1, wherein the
consumable pin tool material comprises a material that is similar
to one or more materials comprising a workpiece to be friction stir
welded.
16. The friction stir welding apparatus of claim 1, wherein the
consumable pin tool material comprises a material that is
dissimilar from one or more materials comprising a workpiece to be
friction stir welded.
17. The friction stir welding apparatus of claim 1, wherein the
shoulder has a substantially cylindrical shape.
18. The friction stir welding apparatus of claim 1, wherein the pin
tool has a shape selected from the group consisting of
substantially cylindrical, substantially rod-like, and
substantially conical.
19. The friction stir welding apparatus of claim 1, wherein the pin
tool has a substantially tapered shape comprising a tip radius.
20. The friction stir welding apparatus of claim 1, further
comprising a first axial load feedback controller coupled to the
shoulder, the first axial load feedback controller operable for
controlling a feed rate of the shoulder.
21. The friction stir welding apparatus of claim 20, further
comprising a second axial load feedback controller coupled to the
pin tool, the second axial load feedback controller operable for
controlling a feed rate of the pin tool.
22. The friction stir welding apparatus of claim 21, wherein the
second axial load feedback controller comprises the first axial
load feedback controller.
23. The friction stir welding apparatus of claim 21, wherein the
feed rate of the shoulder is equal to the feed rate of the pin
tool.
24. A friction stir welding apparatus operable for welding one or
more metals, metal alloys, or other materials, the friction stir
welding apparatus comprising: a pin tool holder; a shoulder having
a surface and an inside diameter; and a pin tool coupled to the pin
tool holder, the pin tool at least partially disposed within the
inside diameter of the shoulder and at least partially protruding
from the surface of the shoulder, wherein the pin tool is
retractable into/extendable from the surface of the shoulder, and
wherein the pin tool rotates at a first predetermined rotational
speed, and wherein the pin tool further comprises a consumable pin
tool material.
25. The friction stir welding apparatus of claim 24, wherein the
shoulder rotates at a second predetermined rotational speed.
26. The friction stir welding apparatus of claim 24, wherein the
shoulder is retractable into/extendable from the pin tool
holder.
27. The friction stir welding apparatus of claim 26, wherein the
shoulder is retractable into/extendable from the pin tool holder at
a substantially constant rate.
28. The friction stir welding apparatus of claim 24, wherein the
shoulder comprises a consumable shoulder material.
29. The friction stir welding apparatus of claim 28, wherein the
consumable shoulder material is at least partially incorporated
into the volume of a joint to be welded.
30. The friction stir welding apparatus of claim 28, wherein the
consumable shoulder material comprises a material that is the same
as one or more materials comprising a workpiece to be friction stir
welded.
31. The friction stir welding apparatus of claim 28, wherein the
consumable shoulder material comprises a material that is similar
to one or more materials comprising a workpiece to be friction stir
welded.
32. The friction stir welding apparatus of claim 28, wherein the
consumable shoulder material comprises a material that is
dissimilar from one or more materials comprising a workpiece to be
friction stir welded.
33. The friction stir welding apparatus of claim 24, wherein the
pin tool is retractable into/extendable from the surface of the
shoulder at a substantially constant rate.
34. The friction stir welding apparatus of claim 24, wherein the
consumable pin tool material is at least partially incorporated
into the volume of a joint to be welded.
35. The friction stir welding apparatus of claim 24, wherein the
consumable pin tool material comprises a material that is the same
as one or more materials comprising a workpiece to be friction stir
welded.
36. The friction stir welding apparatus of claim 24, wherein the
consumable pin tool material comprises a material that is similar
to one or more materials comprising a workpiece to be friction stir
welded.
37. The friction stir welding apparatus of claim 24, wherein the
consumable pin tool material comprises a material that is
dissimilar from one or more materials comprising a workpiece to be
friction stir welded.
38. The friction stir welding apparatus of claim 24, wherein the
shoulder has a substantially cylindrical shape.
39. The friction stir welding apparatus of claim 24, wherein the
pin tool has a shape selected from the group consisting of
substantially cylindrical, substantially rod-like, and
substantially conical.
40. The friction stir welding apparatus of claim 24, wherein the
pin tool has a substantially tapered shape comprising a tip
radius.
41. The friction stir welding apparatus of claim 24, further
comprising a first axial load feedback controller coupled to the
shoulder, the first axial load feedback controller operable for
controlling a feed rate of the shoulder.
42. The friction stir welding apparatus of claim 41, further
comprising a second axial load feedback controller coupled to the
pin tool, the second axial load feedback controller operable for
controlling a feed rate of the pin tool.
43. The friction stir welding apparatus of claim 42, wherein the
second axial load feedback controller comprises the first axial
load feedback controller.
44. The friction stir welding apparatus of claim 42, wherein the
feed rate of the shoulder is equal to the feed rate of the pin
tool.
45. A method for friction stir welding one or more metals, metal
alloys, or other materials, the method comprising: providing a pin
tool holder; providing a shoulder having a surface and an inside
diameter; providing a pin tool coupled to the pin tool holder, the
pin tool at least partially disposed within the inside diameter of
the shoulder and at least partially protruding from the surface of
the shoulder, wherein the pin tool comprises a consumable pin tool
material; and incorporating at least a portion of the consumable
pin tool material into the volume of a joint to be welded.
46. The method of claim 45, wherein providing the shoulder further
comprises rotating the shoulder at a predetermined rotational
speed.
47. The method of claim 45, wherein providing the shoulder further
comprises retracting the shoulder into/extending the shoulder from
the pin tool holder.
48. The method of claim 47, wherein providing the shoulder further
comprises retracting the shoulder into/extending the shoulder from
the pin tool holder at a substantially constant rate.
49. The method of claim 45, wherein the shoulder comprises a
consumable shoulder material.
50. The method of claim 49, further comprising incorporating at
least a portion of the consumable shoulder material into the volume
of the joint to be welded.
51. The method of claim 49, wherein the consumable shoulder
material comprises a material that is the same as one or more
materials comprising a workpiece to be friction stir welded.
52. The method of claim 49, wherein the consumable shoulder
material comprises a material that is similar to one or more
materials comprising a workpiece to be friction stir welded.
53. The method of claim 49, wherein the consumable shoulder
material comprises a material that is dissimilar from one or more
materials comprising a workpiece to be friction stir welded.
54. The method of claim 45, wherein providing the pin tool further
comprises rotating the pin tool at a predetermined rotational
speed.
55. The method of claim 45, wherein providing the pin tool further
comprises retracting the pin tool into/extending the pin tool from
the surface of the shoulder.
56. The method of claim 55, wherein providing the pin tool further
comprises retracting the pin tool into/extending the pin tool from
the surface of the shoulder at a substantially constant rate.
57. The method of claim 45, wherein the consumable pin tool
material comprises a material that is the same as one or more
materials comprising a workpiece to be friction stir welded.
58. The method of claim 45, wherein the consumable pin tool
material comprises a material that is similar to one or more
materials comprising a workpiece to be friction stir welded.
59. The method of claim 45, wherein the consumable pin tool
material comprises a material that is dissimilar from one or more
materials comprising a workpiece to be friction stir welded.
60. The method of claim 45, wherein the shoulder has a
substantially cylindrical shape.
61. The method of claim 45, wherein the pin tool has a shape
selected from the group consisting of substantially cylindrical,
substantially rod-like, and substantially conical.
62. The method of claim 45, wherein the pin tool has a
substantially tapered shape comprising a tip radius.
63. The method of claim 45, further comprising receiving a first
axial load feedback from the shoulder and controlling a feed rate
of the shoulder based on the first axial load feedback.
64. The method of claim 63, further comprising receiving a second
axial load feedback from the pin tool and controlling a feed rate
of the pin tool based on the second axial load feedback.
65. The method of claim 64, wherein the second axial load feedback
comprises the axial load feedback.
66. The method of claim 64, wherein the feed rate of the shoulder
is equal to the feed of the pin tool.
Description
FIELD OF THE INVENTION
[0001] The present invention relates generally to an apparatus and
a method for friction stir welding. More specifically, the present
invention relates to an apparatus and a method for friction stir
welding using a consumable pin tool.
BACKGROUND OF THE INVENTION
[0002] Friction stir welding is a solid-state joining technique
that is well known to those of ordinary skill in the art.
Typically, friction stir welding is used to join difficult-to-weld
metals, metal alloys (such as aluminum alloys, titanium alloys,
nickel alloys, and the like), and other materials. For example,
certain aluminum alloys are sensitive in a plasticized
heat-affected zone, where the base metal reaches temperatures
between solidus and liquidus during welding. In this zone, partial
melting at grain boundaries forms a network containing brittle
compounds. As a result, weld ductility is substantially reduced.
Likewise, other conventional joining techniques may create
geometric distortions near a weld joint due to high temperature
gradients induced in a workpiece during welding. These distortions
may cause warping and other dimensional defects in the workpiece,
as well as residual stresses that may cause premature failure by
cracking in the heat-affected zone or weld joint, lamellar tearing,
or by stress-corrosion cracking in some metals and metal alloys. In
addition, some metals, metal alloys, other materials, and types of
weld joints are difficult to join except in a flat position.
[0003] Friction stir welding techniques overcome many of the
problems encountered with other conventional joining techniques. In
friction stir welding, a cylindrical, non-consumable, rotating pin
tool is plunged into a rigidly clamped workpiece and traversed
along the joint to be welded. The pin tool is specially designed to
provide a combination of frictional heat and thermo-mechanical
working to accomplish the weld. As the pin tool is traversed along
the joint to be welded, the plasticized metal, metal alloy, or
other material is transferred from the leading edge of the pin tool
to the trailing edge of the pin tool, forming a strong solid-state
weld joint in the wake of the pin tool. During the friction stir
welding of hard metals and metal alloys, such as steel, titanium
alloys, and nickel alloys, high temperatures are generated in the
pin tool, as well as the pin tool holder. Under such conditions,
pin tool degradation is a serious problem. Pin tool wear and pin
tool debris entrapment are issues that must be addressed in order
to obtain a defect-free weld joint.
[0004] Conventional friction stir welding apparatuses and methods
have been designed, at least in part, to address some of these
problems, with limited success. For example, U.S. Patent
Application No. 2003/0075584 (Sarik et al.) discloses an apparatus
for use in friction stir welding including a friction stir tool,
having a shoulder, a non-consumable welding pin extending downward
centrally from the shoulder, a first workpiece disposed on a
backing workpiece, a second workpiece located a predetermined
distance from the first workpiece on the backing workpiece, and a
transition strip disposed on the backing workpiece between the
first workpiece and the second workpiece, wherein the contact area
or a space between the transition strip and the first workpiece
defines a first interface and the contact area or a space between
the transition strip and the second workpiece defines a second
interface, wherein the non-consumable welding pin is rotated over
the first interface and the second interface to weld the first
workpiece to the second workpiece with the transition strip
material incorporated as part of the weld.
[0005] U.S. Pat. No. 6,543,671 (U.S. Patent Application No.
2003/0042292) (Hatten et al.) discloses a friction stir welding
tool that includes a body having an upper surface defining an
entrance opening and a lower surface, and a pin having a lower
surface defining an exit opening, wherein the pin extends from the
lower surface of the body. The friction stir welding tool also
includes a passageway defined by the body and the pin from the
entrance opening to the exit opening and is capable of allowing a
filler material to pass therethrough. A friction stir welding
method includes applying a frictional heating source to a workpiece
to plasticize a volume of the workpiece and applying the frictional
heating source to a filler material to plasticize the filler
material. The friction stir welding method also includes
introducing the filler material into the volume of the workpiece
and incorporating the filler material into the volume of the
workpiece.
[0006] U.S. Pat. No. 6,206,268 (Mahoney) discloses a friction stir
welding pin having internal flow cavities. The pin is adapted to be
driven by a conventional friction stir welding machine, and may
include external threads for forcing plasticized material toward
the weld root. An internal cavity located along the centerline and
open to the distal end facilitates deformation of the workpiece
material at the weld root. One or more flow channels extending from
the sidewall of the pin to the internal flow cavity induce a
continuous path of plasticized material through the pin. The
internal cavity may include internal threads to further help force
plasticized material toward the weld root. The pin is particularly
useful in welding aluminum workpieces where the tolerance of the
workpiece thickness is not critical.
[0007] In general, conventional friction stir welding apparatuses
and methods fail to address the problem of pin tool degradation. In
some cases, pin tools are manufactured from relatively hard
refractory metal alloys, such as molybdenum alloys, tungsten
alloys, and the like, in order to minimize pin tool degradation.
However, pin tool wear and pin tool debris entrapment still occur,
resulting in weld joints with defects. The present invention
provides friction stir welding apparatuses and methods that address
these problems and issues.
BRIEF SUMMARY OF THE INVENTION
[0008] In various embodiments, the present invention provides
friction stir welding apparatuses and methods that use a consumable
pin tool. The consumable pin tool is manufactured from a material
that is the same as, similar to, or dissimilar from the workpiece
to be friction stir welded. The consumable pin tool is
substantially continuously fed into the joint to be welded and is
incorporated into the weld joint. The feeding of the consumable pin
tool is accomplished using a retractable pin tool holder including
an annular cylindrical shoulder through the center of which the
consumable pin tool is advanced. The shoulder may be consumable or
non-consumable.
[0009] Advantageously, the friction stir welding apparatuses and
methods of the present invention provide a defect-free weld joint,
without entrapped pin tool debris. As a result, the weld joint
demonstrates improved mechanical properties (e.g., mechanical
strength). Because, in one embodiment of the present invention, the
filler material is the same as or similar to the workpiece
material, the weld joint demonstrates improved microstructure.
Because, in another embodiment of the present invention, the filler
material is dissimilar from the workpiece material, the material
chemistry of the substrate may be locally altered and/or a clad
layer or the like may be added. The friction stir welding
apparatuses and methods of the present invention allow for the
welding of complex joints, other than butt-joints, and the welding
of workpieces with less-than-optimal fit-up (e.g., with large joint
gaps or shape mismatches) due to the ability to add filler
material. Finally, the friction stir welding apparatuses and
methods of the present invention provide the ability to locally
increase the thickness of the weld joint, thus increasing joint
efficiency.
[0010] In one embodiment of the present invention, a friction stir
welding apparatus operable for welding one or more metals, metal
alloys, or other materials includes a pin tool holder, a shoulder
having a surface coupled to the pin tool holder, and a pin tool
coupled to the pin tool holder, the pin tool at least partially
protruding from the surface of the shoulder, wherein the pin tool
is made of a consumable pin tool material. Optionally, the shoulder
rotates at a predetermined rotational speed and is retractable
into/extendable from the pin tool holder at a substantially
constant rate. Optionally, the shoulder is also made of a
consumable shoulder material that is at least partially
incorporated into the volume of a joint to be welded. The
consumable shoulder material comprises a material that is the same
as, similar to, or dissimilar from one or more materials comprising
a workpiece to be friction stir welded. Preferably, the pin tool
rotates at a predetermined rotational speed and is retractable
into/extendable from the surface of the shoulder at a substantially
constant rate. The consumable pin tool material is at least
partially incorporated into the volume of the joint to be welded.
The consumable pin tool material comprises a material that is the
same as, similar to, or dissimilar from one or more materials
comprising the workpiece to be friction stir welded. The shoulder
has a substantially cylindrical shape and the pin tool has a
substantially cylindrical, substantially rod-like, or substantially
conical shape. Optionally, the pin tool includes a taper, one or
more truncations, a plurality of threads, and/or a radius tip.
[0011] In another embodiment of the present invention, a friction
stir welding apparatus operable for welding one or more metals,
metal alloys, or other materials includes a pin tool holder, a
shoulder having a surface coupled to the pin tool holder, and a pin
tool coupled to the pin tool holder, the pin tool at least
partially protruding from the surface of the shoulder and
retractable into/extendable from the surface of the shoulder at a
substantially constant rate, wherein the pin tool rotates at a
first predetermined rotational speed, and wherein the pin tool is
made of a consumable pin tool material. Optionally, the shoulder
rotates at a second predetermined rotational speed and is
retractable into/extendable from the pin tool holder at a
substantially constant rate. Optionally, the shoulder is also made
of a consumable shoulder material that is at least partially
incorporated into the volume of a joint to be welded. The
consumable shoulder material comprises a material that is the same
as, similar to, or dissimilar from one or more materials comprising
a workpiece to be friction stir welded. The consumable pin tool
material is at least partially incorporated into the volume of the
joint to be welded. The consumable pin tool material comprises a
material that is the same as, similar to, or dissimilar from one or
more materials comprising the workpiece to be friction stir welded.
The shoulder has a substantially cylindrical shape and the pin tool
has a substantially cylindrical, substantially rodlike, or
substantially conical shape. Optionally, the pin tool includes a
taper, one or more truncations, a plurality of threads, and/or a
radius tip.
[0012] In a further embodiment of the present invention, a method
for friction stir welding one or more metals, metal alloys, or
other materials includes providing a pin tool holder; providing a
shoulder having a surface coupled to the pin tool holder; providing
a pin tool coupled to the pin tool holder, the pin tool at least
partially protruding from the surface of the shoulder, wherein the
pin tool is made of a consumable pin tool material; and
incorporating at least a portion of the consumable pin tool
material into the volume of a joint to be welded. Optionally,
providing the shoulder further includes rotating the shoulder at a
predetermined rotational speed and retracting the shoulder
into/extending the shoulder from the pin tool holder at a
substantially constant rate. Optionally, the shoulder is also made
of a consumable shoulder material and the method further includes
incorporating at least a portion of the consumable shoulder
material into the volume of the joint to be welded. The consumable
shoulder material comprises a material that is the same as, similar
to, or dissimilar from one or more materials comprising a workpiece
to be friction stir welded. Preferably, providing the pin tool
further includes rotating the pin tool at a predetermined
rotational speed and retracting the pin tool into/extending the pin
tool from the surface of the shoulder at a substantially constant
rate. The consumable pin tool material comprises a material that is
the same as, similar to, or dissimilar from one or more materials
comprising the workpiece to be friction stir welded. The shoulder
has a substantially cylindrical shape and the pin tool has a
substantially cylindrical, substantially rod-like, or substantially
conical shape. Optionally, the pin tool includes a taper, one or
more truncations, a plurality of threads, and/or a radius tip.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a cross-sectional side view of one embodiment of
the friction stir welding apparatus of the present invention,
highlighting the configuration and operation of the consumable pin
tool;
[0014] FIG. 2 is a side and end view of a portion of the friction
stir welding apparatus of FIG. 1;
[0015] FIG. 3 is a perspective view of another embodiment of the
consumable pin tool of the present invention; and
[0016] FIG. 4 is a side view of the consumable pin tool of FIG.
3.
DETAILED DESCRIPTION OF THE INVENTION
[0017] Referring to FIGS. 1 and 2, in one embodiment, the friction
stir welding apparatus 10 of the present invention includes a
consumable pin tool 12 that is selectively disposed within a pin
tool holder 14. The pin tool 12 is selectively and continuously
movable between a first, retracted position 12' and a second,
extended position 12". In the second, extended position 12", the
pin tool 12 at least partially protrudes beyond the surface of a
shoulder 16 associated with the pin tool 12 and the pin tool holder
14. Preferably, the pin tool 12 has a substantially cylindrical,
rod-like, or conical shape. For example, the pin tool 12 may have a
substantially pointed shape with a taper of about 45 degrees.
Optionally, the pin tool 12 is threaded and/or incorporates one or
more sharp edges and/or flat surfaces. The pin tool 12 may also be
partially or wholly hollow. In the substantially cylindrical or
rod-like configuration, the initial diameter and length of the pin
tool 12, before being partially or wholly incorporated into a weld,
are about equal to the thickness of the workpiece to be friction
stir welded for a full-penetration weld. For a partial-penetration
weld, the initial diameter and length of the pin tool 12 are
smaller than the thickness of the workpiece to be friction stir
welded. The pin tool 12 is coupled to a drive mechanism 18 via a
stem piece 20. Preferably, the stem piece 20 has a substantially
cylindrical shape, although other suitable shapes may be used. The
drive mechanism 18 is operable for rotating the pin tool 12 and,
optionally, the shoulder 16 about an axis 22 of the pin tool 12,
the shoulder 16, and the pin tool holder 14. Typically, the pin
tool 12 is rotated at a speed of between about 150 rpm and about
1000 rpm during friction stir welding. It should be noted that the
rotational speed is dependent upon the thickness of the workpiece
to be friction stir welded, with thinner sections requiring higher
rotational speeds and thicker sections requiring lower rotational
speeds. The pin tool 12 is made of a material that is the same as,
similar to, or dissimilar from the workpiece to be friction stir
welded. For example, if a metal or metal alloy is to be friction
stir welded, the pin tool 12 may be made of that same metal or
metal alloy, another similar metal or metal alloy, or any other
dissimilar material that provides a desired characteristic when the
material is incorporated into the weld.
[0018] The shoulder 16 comprises an annular structure through which
the pin tool 12 is fed. Preferably, the shoulder 16 has a
substantially cylindrical shape, although other suitable shapes may
be used. The shoulder 16 has an inside diameter that is slightly
larger than the diameter of the pin tool 12 in order to accommodate
the pin tool 12 without restriction and/or binding. The shoulder 16
has an outside diameter that is about two to three times larger
than the diameter of the pin tool 12, although any suitable
dimensions may be used. The shoulder 16 protrudes from the pin tool
holder 14 by about 0.5 inches, although any suitable dimensions may
be used. Preferably, the shoulder 16 is non-consumable and is made
of a refractory alloy (such as a molybdenum-based alloy, a
tungsten-based alloy, or the like). Alternatively, the shoulder 16
is consumable and is made of a material that is the same as,
similar to, or dissimilar from the workpiece to be friction stir
welded. As described above, the shoulder 16 may be rotated about
the axis 22 of the pin tool 12, the shoulder 16, and the pin tool
holder 14. Optionally, the rotation of the shoulder 16 is
independent of the rotation of the pin tool 12. Typically, the
shoulder 16 is rotated at a speed of between 150 rpm and about 1000
rpm during friction stir welding. The shoulder 16 may also be
selectively and continuously retracted into/extended from the pin
tool holder 14, in conjunction with or independent of the
retraction/extension of the pin tool 12.
[0019] The pin tool holder 14 also comprises an annular structure
through which the pin tool 12 is fed. The pin tool holder 14
includes a spindle 24 and a plurality of end sections 26,28
configured to retain and guide the pin tool 12, the drive mechanism
18, the stem piece 20, and the shoulder 16. Preferably, the spindle
24 has a substantially cylindrical shape, although other suitable
shapes may be used. The spindle 24 has an inside diameter that is
slightly larger than the diameter of the pin tool 12 and the drive
mechanism 18 in order to prevent interference. The length of the
spindle 24 is as short as possible in order to prevent spindle
run-out, which may affect positional accuracy, as well as weld
quality/soundness. However, the length of the spindle 24 is long
enough to allow a sufficient length of feedstock (i.e., the pin
tool 12) to be provided in order to produce a weld of useful
continuous length. Preferably, the spindle 24 is made of tool steel
or the like. The inside surface 30 of the spindle and the drive
mechanism 18 and stem piece 20 define one or more channels through
which a cooling fluid flows. The cooling fluid is operable for
cooling the pin tool 12 and/or the shoulder 16 and includes air,
water, cooling oil, or any other suitable cooling fluid.
Preferably, in the case of a consumable pin tool 12, the
temperature of the tip of the pin tool 12 is maintained in a range
in which the pin tool material is substantially plastic. For
example, the temperature of the tip of the pin tool 12 is
maintained in a range of between about 1,650 degrees F. and about
1,990 degrees F. for titanium alloys and about 1,800 degrees F. and
about 2,200 degrees F. for steel and nickel alloys. Likewise, if a
consumable shoulder 16 is used, the temperature of the shoulder 16
is maintained in a range in which the shoulder material is
substantially plastic. For example, the temperature of the shoulder
16 is maintained in a range of between about 1,650 degrees F. and
about 1,990 degrees F. for titanium alloys and about 1,800 degrees
F. and about 2,200 degrees F. for steel and nickel alloys. The
cooling fluid is introduced into the one or more channels via an
exteriormounted shoulder holder cooling device inlet and outlet
(not shown) and a co-axial pin tool inlet 32 disposed in the
spindle 24. In order to contain the cooling fluid within the one or
more channels in the presence of rotating components, one or more
seals 34, such as o-ring seals or the like, are used. Other
suitable cooling mechanisms well known to those of ordinary skill
in the art may also be used.
[0020] Although one preferred embodiment of the friction stir
welding apparatus 10 of the present invention has been illustrated
and described above, it should be noted that any suitable
components or apparatuses that provide a rotating, movable,
consumable pin tool 12 and a rotating or non-rotating, moveable or
nonmoveable, consumable or non-consumable shoulder 16 may be
used.
[0021] As described above, the pin tool 12 is plunged into a
rigidly clamped workpiece and traversed along a joint to be welded.
The pin tool 12 provides a combination of frictional heat and
thermo-mechanical working to accomplish the weld. As the pin tool
12 is traversed along the joint to be welded, the plasticized
metal, metal alloy, or other material is transferred from the
leading edge of the pin tool 12 to the trailing edge of the pin
tool 12, forming a strong solid-state weld joint in the wake of the
pin tool 12. The pin tool 12 is substantially continuously fed into
the joint to be welded and is incorporated into the weld joint as
filler material. Preferably, the pin tool 12 is fed into the joint
to be welded at a rate that is sufficient to fill the joint
preparation (e.g., square groove, V-groove, or J-groove) without
underfill or substantial overfill. Advantageously, the friction
stir welding techniques of the present invention may be used to
apply surfacing welds with relatively little base metal
penetration. It should be noted that the feed rate of the pin tool
12 varies based upon joint type and the material(s) being joined.
Independent axial load feedback control is used for both the pin
tool 12 and the shoulder 16. The pin tool load control is required
to control the feed rate of the pin tool 12 and the shoulder load
control is required to prevent the friction stir welding apparatus
10 from embedding in the workpiece. Typically, the shoulder 16
serves the same function as the shoulders of conventional friction
stir welding apparatuses, namely, providing a continuous forging
action and minimizing flash during friction stir welding. The
shoulder 16 of the present invention also distributes the filler
material evenly within the joint. If a consumable shoulder 16 is
used, the shoulder material is incorporated into the weld joint as
filler material or, alternatively, disposed on the surface of the
weld in a layer.
[0022] Advantageously, the friction stir welding apparatus 10 of
the present invention provides a defect-free weld joint, without
entrapped pin tool debris. As a result, the weld joint demonstrates
improved mechanical properties (e.g., mechanical strength).
Because, in one embodiment of the present invention, the filler
material is the same as or similar to the workpiece material, the
weld joint demonstrates improved microstructure. The localized
plastic deformation and filler material provided by the pin tool 12
lead to a microstructure characterized by relatively small grains
and low porosity. The filler material may also be selected such
that it has intermediate properties relative to two dissimilar
materials to be joined, facilitating friction stir welding.
Because, in another embodiment of the present invention, the filler
material is dissimilar from the workpiece material, the material
chemistry of the substrate may be locally altered and/or a clad
layer or the like may be added using a consumable shoulder 16. In a
further embodiment of the present invention, a filler material may
be selected that has properties that are superior to either of two
dissimilar materials to be joined, providing a joint with superior
properties. The friction stir welding apparatus 10 of the present
invention allows for the welding of complex joints, other than
butt-joints, and the welding of workpieces with less-than-optimal
fit-up (e.g., with large joint gaps or shape mismatches) due to the
ability to add filler material. Finally, the friction stir welding
apparatus 10 of the present invention provides the ability to
locally increase the thickness of the weld joint, thus increasing
joint efficiency.
[0023] Although the present invention has been illustrated and
described with reference to preferred embodiments and examples
thereof, it will be readily apparent to those of ordinary skill in
the art that other embodiments and examples may perform similar
functions and/or achieve similar results. All such equivalent
embodiments and examples are within the spirit and scope of the
present invention and are intended to be covered by the following
claims.
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