U.S. patent application number 12/147116 was filed with the patent office on 2008-10-23 for multi-section faced shoulderless retractable variable penetration friction stir welding tool.
Invention is credited to Jeffrey J. Bernath, James J. Fisher, Timothy J. Trapp.
Application Number | 20080257936 12/147116 |
Document ID | / |
Family ID | 39711168 |
Filed Date | 2008-10-23 |
United States Patent
Application |
20080257936 |
Kind Code |
A1 |
Trapp; Timothy J. ; et
al. |
October 23, 2008 |
MULTI-SECTION FACED SHOULDERLESS RETRACTABLE VARIABLE PENETRATION
FRICTION STIR WELDING TOOL
Abstract
A method of friction stir welding and a non-consumable
multi-section faced retractable shoulderless variable penetration
friction stir welding tool. The tool includes a substantially
cylindrical body portion, a head portion, and a tip section, each
integral to the tool. The body portion has a longitudinal axis
about which it is rotable, a diameter, a sidewall substantially
parallel to the longitudinal axis, a proximal end, and a distal
end. The head portion is located at the distal end of the body
portion. The head portion includes a multi-section face, having a
first face section and a second face section, that converges to the
tip section. The tool is retractable, reduces overheating, improves
weld quality by reducing internal voids and lack of fusion, and
facilitates variable penetration welds.
Inventors: |
Trapp; Timothy J.;
(Columbus, OH) ; Fisher; James J.; (Columbus,
OH) ; Bernath; Jeffrey J.; (Columbus, OH) |
Correspondence
Address: |
GALLAGHER & DAWSEY CO., L.P.A.
P.O. BOX 785
COLUMBUS
OH
43216
US
|
Family ID: |
39711168 |
Appl. No.: |
12/147116 |
Filed: |
June 26, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11109519 |
Apr 19, 2005 |
7416102 |
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12147116 |
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10970907 |
Oct 22, 2004 |
7234626 |
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11109519 |
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Current U.S.
Class: |
228/2.3 |
Current CPC
Class: |
B23K 20/124 20130101;
B23K 20/1265 20130101; B23K 20/1225 20130101; B23K 20/1255
20130101 |
Class at
Publication: |
228/2.3 |
International
Class: |
B23K 20/12 20060101
B23K020/12 |
Claims
1. A non-consumable multi-section faced retractable shoulderless
variable penetration friction stir welding tool for use in joining
a first workpiece, having a first thickness, and a second
workpiece, having a second thickness, by friction stir welding,
comprising: a substantially cylindrical body portion, a head
portion, and a tip section, each integral to the tool, the body
portion having a longitudinal axis about which it is rotable, a
diameter, a sidewall substantially parallel to the longitudinal
axis, a proximal end, and a distal end; and the head portion
located at the distal end of the body portion having a base with a
diameter substantially equal to the diameter of the body portion
forming a transition between the body portion and the head portion,
and the head portion having a multi-section face with a first face
section nearest the body portion and a second face section nearest
the tip section wherein the multi-section face converges to the tip
section having a diameter and a center wherein the center is
located substantially on the longitudinal axis, a height from the
distal-most portion of the tip section to the base along the
longitudinal axis and the first face section having a first section
horizontal projection component with a magnitude of less than
fifteen percent of the body portion diameter and the first face
section converges at a first face opening angle to the second face
section thereby forming a substantially frustoconical shape.
2. The tool of claim 1, wherein the second face section forms a
substantially frustoconical shape with the second face section
converging to the tip section at a second face opening angle
between approximately 70 degrees and approximately 160 degrees.
3. The tool of claim 1, wherein the first face opening angle is
between approximately 40 degrees and approximately 120 degrees.
4. The tool of claim 1, wherein the first section horizontal
projection component has a magnitude of less than eight percent of
the body portion diameter.
5. The tool of claim 1, wherein the first face section is curved
having a radius of curvature of less than fifteen percent of the
body portion diameter.
6. The tool of claim 1, wherein the portion of the rotating
non-consumable multi-section faced shoulderless variable
penetration friction stir welding tool that is plunged into the
joint is a portion of the head portion such that a portion of the
first face section is within the first and second workpieces and a
portion of the first face section is outside the first and second
workpieces.
7. A non-consumable multi-section faced retractable shoulderless
variable penetration friction stir welding tool for use in joining
a first workpiece, having a first thickness, and a second
workpiece, having a second thickness, by friction stir welding,
comprising: a substantially cylindrical body portion, a head
portion, and a tip section, each integral to the tool, the body
portion having a longitudinal axis about which it is rotable, a
diameter, a sidewall substantially parallel to the longitudinal
axis, a proximal end, and a distal end; and the head portion
located at the distal end of the body portion having a base with a
diameter substantially equal to the diameter of the body portion
forming a transition between the body portion and the head portion,
and the head portion having a multi-section face with a first face
section nearest the body portion and a second face section nearest
the tip section wherein the multi-section face converges to the tip
section having a diameter and a center wherein the center is
located substantially on the longitudinal axis, a height from the
distal-most portion of the tip section to the base along the
longitudinal axis and the first face section having a first section
horizontal projection component with a magnitude of less than
approximately eight percent of the body portion diameter.
8. The tool of claim 7, wherein the second face section forms a
substantially frustoconical shape with the second face section
converging to the tip section at a second face opening angle
between approximately 70 degrees and approximately 160 degrees.
9. The tool of claim 7, wherein the first face section forms a
substantially frustoconical shape with the first face section
converging to the second face section at a first face opening
angle.
10. The tool of claim 9, wherein the first face opening angle is
between approximately 40 degrees and approximately 120 degrees.
11. The tool of claim 7, wherein the first face section is
substantially orthogonal to the longitudinal axis.
12. The tool of claim 11, wherein the first section horizontal
projection component has a magnitude of less than approximately
five percent of the body portion diameter.
13. The tool of claim 7, wherein the first face section is
curved.
14. The tool of claim 7, wherein the portion of the rotating
non-consumable multi-section faced shoulderless variable
penetration friction stir welding tool that is plunged into the
joint is a portion of the head portion such that a portion of the
first face section is within the first and second workpieces and a
portion of the first face section is outside the first and second
workpieces.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a division and claims the benefits of
the previously filed and currently pending U.S. patent application
given Ser. No. 11/109,519, filed on Apr. 19, 2005, which is a
continuation-in-part and claims the benefits of the previously
filed U.S. patent application given Ser. No. 10/970,907, filed on
Oct. 22, 2004, now U.S. Pat. No. 7,234,626, all of which are
incorporated by reference as if completely written herein.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] This invention was not made as part of a federally sponsored
research or development project.
TECHNICAL FIELD
[0003] The present invention relates to the field of friction stir
welding; particularly, to a single piece non-consumable friction
stir welding tool and methods that can perform variable penetration
welds, variable width welds, weld workpieces of differing
thicknesses, weld workpieces having complex curvature, retract from
the weld during welding without producing an exit hole, and improve
the quality of friction stir welds.
BACKGROUND OF THE INVENTION
[0004] Those in the wide ranging materials joining industries have
recognized the benefits of friction stir welding (FSW) since its
invention, only to be precluded from widespread application due to
a number of factors. FSW is a relatively simple method of solid
phase welding developed by The Welding Institute in the early
1990's. The conventional process utilizes a specially shaped
nonconsumable cylindrical tool with a profiled pin, often threaded,
extending from a shoulder of the tool, that is rotated and plunged
into a joint formed by abutting edges of the workpieces that are to
be joined until a surface of the shoulder contacts the surface of
the workpieces. The rotating tool plasticizes a region of the
workpieces around the pin and beneath the shoulder. The tool is
then advanced along the joint. The rotation of the tool develops
frictional heating of the workpieces, from both shoulder friction
and pin friction, as well as adiabatic heating, and the tool forces
plasticized workpiece material from the leading edge of the tool to
the rear of the tool where it consolidates and cools to form a high
quality weld.
[0005] The FSW tool is generally a cylindrical piece with a
shoulder face that meets a pin that projects from the shoulder face
at a right angle, as illustrated in U.S. Pat. Nos. 5,460,317 and
6,029,879. In some instances, the pin actually moves in a
perpendicular direction in an aperture formed in the face of the
shoulder, as illustrated in U.S. Pat. Nos. 5,611,469; 5,697,544;
and 6,053,391. The face of the shoulder may be formed with an
upward dome that is perpendicular to the pin, as illustrated in
U.S. Pat. Nos. 5,611,479; 5,697,544; and 6,053,391. The dome region
and an unobstructed shoulder face to pin interface have been
considered essential for the proper frictional heating of the
workpiece material. Traditional thinking held that the dome region
of the shoulder serves to constrain plasticized material for
consolidation at the trailing edge of the FSW tool so as to prevent
it from extruding out from under the sides of the tool. For
example, U.S. Pat. No. 5,813,592 states at column 1, lines 42-51,
that "In order to achieve a proper consolidation of the weld metal
the probe bottom part (shoulder) must maintain during the whole
welding operation (forward movement) in an intimate contact with
[the] surface of the joined members. If the probe shoulder during
this forward movement even temporarily `lifts` from the surface a
small amount of plasticised welding material will be expelled
behind the probe thus causing occurrence of voids in the weld since
there is no available material to fill the vacant space after the
expelled material." The present invention proves this long-held
belief false.
[0006] Since FSW is a solid-state process, meaning there is no
melting of the materials, many of the problems associated with
other fusion welding methods are avoided, including solidification
cracking, shrinkage, and weld pool positioning and control.
Additionally, FSW minimizes distortion and residual stresses.
Further, since filler materials are not used in FSW, issues
associated with chemical segregation are avoided. Still further,
FSW has enabled the welding of a wide range of alloys that were
previously unweldable. Yet another advantage of FSW is that it does
not have many of the hazards associated with other welding means
such as welding fumes, radiation, high voltage, liquid metals, or
arcing. Additionally, FSW generally has only three process
variables to control (rotation speed, travel speed, and pressure),
whereas fusion welding often has at least twice the number of
process variables (purge gas, voltage, amperage, wire feed speed,
travel speed, shield gas, and arc gap, just to name a few). Perhaps
most importantly, the crushing, stirring, and forging of the
plasticized material by the FSW tool often produces a weld that is
more reliable than conventional welds and maintains material
properties more closely to those of the workpiece properties, often
resulting in twice the fatigue resistance found in fusion
welds.
[0007] Despite all the advantages of FSW, it has only found very
limited commercial application to date due to many difficulties
associated therewith. One early problem associated with
single-piece FSW tools 90, as seen in FIG. 1, was that they leave
an exit hole 80 in the weld 40, as seen in FIG. 5, that must be
filled after completion of the friction stir weld. Such
single-piece FSW tools 90 are also plagued with premature breakage
of the pin 92 during welding, resulting in the pin 92 being
permanently lodged in the weld 40. Such breakage is often
attributed to tool design that has relatively poor heat
distribution and areas of high stress concentration, such as at the
pin 92 to shoulder 91 interface, also known as the transition
region 93, seen in FIG. 1. In an effort to eliminate exit holes 82
the retractable pin tool 95 was developed, as seen in FIG. 2. The
retractable pin tool 95 essentially splits the conventional
shouldered FSW tool 90 into two separate components, namely a
shoulder portion 96 that is hollow and receives the pin 97 that may
extend and retract from the shoulder 96. The independent movement
of the pin 97 permits the pin 97 to be gradually withdrawn from the
weld 40 while the shoulder 96 remains in contact with the
workpieces 10, 20, thereby eliminating the exit hole 80.
[0008] While the retractable pin tool 95 may eliminate the exit
hole 82, it has several drawbacks. The retractable pin tool 95 is
prone to breakage due to the high stress concentrations at the
shoulder 96 to pin 97 interface. The retractable pin tool 95 is
also susceptible to binding between the pin 97 and the shoulder 96
as stirred weld metal can be forced into the gap between the pin 97
and the shoulder 96.
[0009] Another problem with both conventional shouldered FSW tools
90 and retractable pin tools 95 is the overheating caused by the
shoulder 91, 96. During FSW with conventional shouldered FSW tools
90, 95 the weld 40 is repeatedly subjected to the pressure and
rotation of the tool shoulder 91, 96. As a conventional FSW tool
90, 95 traverses a joint 35 the material is first exposed to the
leading edge of the shoulder 91, 96 that is generally exerting a
downward force on the workpieces 10, 20 of several hundred pounds,
often several thousand pounds, and is rotating at RPM's ranging
from under 100 rpm to over 1000 rpm, while traversing the joint 35
rather slowly, generally less than ten inches per minute (IPM),
depending on the materials being joined and their thickness. Taking
for example a simple illustrative case of a conventional tool 90,
95 traversing a joint 35 at 6 IPM and 800 RPM, it takes 10 seconds
to traverse a one inch section of the joint 35 during which 80
revolutions of the tool 90, 95 are made, resulting in 160 exposures
of weld 40 to the shoulder 91, 96 (an exposure at the leading edge
and the trailing edge for each revolution). Such repeated exposure
to the shoulder 91, 96 results in the overheating of the weld 40
and the associated drawbacks. Prior methods and apparatus have
indicated that such top surface friction heating and weld material
containment contributed by the shoulder were essential to FSW. In
fact, the definition of friction stir welding in most welding
references includes the mention of a tool having a pin and a
shoulder, thus a tool lacking a shoulder, or a shoulderless tool,
as in the present invention, is a completely new concept.
[0010] Further, conventional shouldered FSW tools 90 and
retractable pin tools 95 are generally ineffective at joining
workpieces 10, 20 of different thickness, as seen in FIG. 6. This
is due in large part to the fact that such tools 90, 95 are
designed for a specific pin 92, 97 length for a particular material
thickness. Such designs necessitate a unique tool for each
thickness of material to be joined. The retractable pin tool 95 may
reduce the number of tools needed to make welds in materials having
differing thicknesses, but it too is limited in that each
retractable pin tool 95 has a limited useful range established by
the diameter of the shoulder. For instance, if the material is too
thick or thin then under-heating or over-heating will occur.
Additionally, one can easily appreciate that the pin 97 of a
retractable pin tool 95 designed for use in joining 1/8'' thick
sheets will be ineffective and will fail if it is simply further
extended from the shoulder 96 in trying to join 1/2'' thick
plates.
[0011] Additionally, conventional shouldered FSW tools 90 and
retractable pin tools 95 cannot be used in joining workpieces
having more than slight curvature. Such tools 90, 95 provide
inadequate contact, also referred to as lift-off, or result in
gouging of the workpieces, as seen in FIG. 18. Such lift-off and
gouging results in welds having reduced aesthetic qualities that
often require grinding of the surface and diminish the mechanical
properties of the weld.
[0012] Yet another problem associated with conventional shouldered
FSW tools 90 and retractable pin tools 95 is the flow
characteristics imparted on the weld material due to the transition
region 93, labeled in FIG. 1, between the shoulder 91 and the pin
92. The transition region 93 in shouldered tools 90, 95 often
causes dead zones and eddies in the material flow resulting in
subsurface voids and lack of fusion in the weld 40. Such problems
greatly limit the robustness of the conventional tools and methods,
particularly on joints that vary in geometry or heat distribution
due to part shape or tooling.
[0013] A friction stir weld 40 created with conventional shouldered
FSW tools 90, 95 has several distinct regions, as seen in FIG. 3,
where the direction of travel of the tool 90 is into the paper.
First, the metal away from the immediate vicinity of the weld 40
that is not affected by the weld is known as the base metal 50.
Closer to the actual weld 40 is the heat affected zone (HAZ) 60
where the material has experienced a thermal cycle that has
modified the microstructure and/or mechanical properties, yet has
no plastic deformation. Next, closer to the tool 90, 95 is the
thermomechanically affected zone (TMAZ) 70 where the material has
seen limited plastic deformation by the tool 90, 95, and the heat
from the process has also exerted some influence on the material.
With the exception of aluminum, most materials exhibit
recrystallization throughout the TMAZ 70. Aluminum often exhibits
recrystallization in only a portion of the TMAZ, often referred to
as the nugget. Within the TMAZ 70 is the stir zone 75, seen in FIG.
4, having non-uniform grain structure from the violent deformation
that materials in this region undergo while hot. The stir zone 75
has a shoulder region 76 and a pin region 77. The pin region 77 is
that region that has been directly exposed to the pin 92, whereas
the shoulder region 76 is the region just outside of the pin region
77 and below the shoulder 91, 96 of the tool 90, 95. The shoulder
region 76 flares out further away from the pin 92, 97 near the
surface of the workpiece nearest the shoulder 91, 96, due to the
effects of the shoulder 91, 96. This flared-out portion of the
shoulder region 76, or re-stir area, near the surface of the weld
40 is the area most commonly exposed to overheating and the
associated annealing and overageing effects that reduce the weld
properties.
[0014] Additionally, the design of conventional shouldered FSW
tools 90, 95 is prone to excessive wear and poor heat and load
distribution. These problems are largely attributable to the
longstanding belief that FSW tools must have a relatively narrow
pin and wide shoulder.
[0015] Accordingly, the art has needed a tool, and associated
methods, that eliminate the need for a shoulder and thereby
eliminate the multitude of problems associated with the shoulder.
An ideal tool would be simple in design and construction;
inexpensive; allow for retractability during welding thereby
eliminating the exit hole; accommodate joining materials of
differing thicknesses; facilitate variable penetration depth;
improve weld quality by reducing internal voids and lack of fusion;
and eliminate the re-stir area of the stir region. While some of
the prior art devices attempted to improve the state of the art,
none has achieved the unique and novel configurations and
capabilities of the present invention. With these capabilities
taken into consideration, the instant invention addresses many of
the shortcomings of the prior art and offers significant benefits
heretofore unavailable. Further, none of the above inventions and
patents, taken either singly or in combination, is seen to describe
the instant invention as claimed.
SUMMARY OF INVENTION
[0016] In its most general configuration, the present invention
advances the state of the art with a variety of new capabilities
and overcomes many of the shortcomings of prior methods in new and
novel ways. In its most general sense, the present invention
overcomes the shortcomings and limitations of the prior art in any
of a number of generally effective configurations.
[0017] In one of the many preferable configurations, the
non-consumable multi-section faced retractable shoulderless
variable penetration friction stir welding tool includes a
substantially cylindrical body portion, a head portion, and a tip
section, each integral to the tool. The body portion has a
longitudinal axis about which it is rotable, a diameter, a sidewall
substantially parallel to the longitudinal axis, a proximal end,
and a distal end.
[0018] The head portion has a base with a diameter substantially
equal to the diameter of the body portion, thereby forming a
transition between the body portion and the head portion. The head
portion includes a multi-section face that converges to the tip
section. The multi-section face includes at least a first face
section and a section face section. The tool lack of a shoulder in
the traditional sense of friction stir welding therefore has
numerous advantages that have long been overlooked by those in the
FSW industry. Prior methods and apparatus have indicated that top
surface friction heating and weld material containment were
essential to FSW.
[0019] The present invention's elimination, or minimization, of any
portion of the tool that contacts the top surface of either
workpiece away from the point at which the tool enters the
workpiece(s) has several advantages. One such advantage is the
elimination of the primary source of overheating. Additionally,
another advantage of the present tool is the reduction of internal
voids and lack of fusion that are associated with the transition
region between the shoulder and the pin, as well as the transition
from the pin to the pin tip. Further, the present design allows the
use of a single tool in performing welds of varying depth and/or
width, performing welds to join workpieces having differing
thicknesses, performing welds to join workpieces having complex
curvatures, and in retracting the tool to leave a weld free of an
exit hole.
[0020] Numerous variations, modifications, alternatives, and
alterations of the various preferred embodiments, processes, and
methods may be used alone or in combination with one another as
will become more readily apparent to those with skill in the art
with reference to the following detailed description of the
preferred embodiments and the accompanying figures and
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] Without limiting the scope of the present invention as
claimed below and referring now to the drawings and figures:
[0022] FIG. 1 shows a cross-section of a typical conventional
shouldered FSW tool, not to scale;
[0023] FIG. 2 shows a cross-section of a typical conventional
shouldered retractable pin tool, not to scale;
[0024] FIG. 3 shows a cross-section of a first workpiece and a
second workpiece as they are joined by FSW, not to scale;
[0025] FIG. 4 shows an enlarged cross-section of a portion of FIG.
3, not to scale;
[0026] FIG. 5 shows an elevated perspective view of a first and
second workpiece being joined by FSW and the associated exit hole
left by conventional shouldered FSW tools, not to scale;
[0027] FIG. 6 shows a cross-section of a typical conventional
shouldered FSW tool and a first and second workpiece of differing
thicknesses, not to scale;
[0028] FIG. 7 shows a front elevation view of an embodiment of the
tool of the present invention, not to scale;
[0029] FIG. 8 shows a partial cross-section of a joint with the
tool of FIG. 7 joining a first and a second workpiece by FSW, not
to scale;
[0030] FIG. 9 shows a first and a second workpiece configured in a
lap joint, not to scale;
[0031] FIG. 10 shows a first and a second workpiece configured in
butt joint arrangement with a third workpiece below to be joined by
a lap joint;
[0032] FIG. 11 shows a partial cross-section of a joint with an
embodiment of the tool of FIG. 7 joining a first and a second
workpiece by FSW, not to scale;
[0033] FIG. 12 shows a partial cross-section of an embodiment of
the tool of the present invention as it traverses a joint from left
to right while changing from a first penetration depth to a second
penetration depth and then is retracted from the workpieces, not to
scale;
[0034] FIG. 13 shows a front elevation view of an embodiment of the
tool of FIG. 7, not to scale;
[0035] FIG. 14 shows a front elevation view of an embodiment of the
tool of FIG. 7, not to scale;
[0036] FIG. 15 shows a front elevation view of an embodiment of the
tool of FIG. 7, not to scale;
[0037] FIG. 16 shows a front elevation view of an embodiment of the
tool of FIG. 7, not to scale;
[0038] FIG. 17 shows a partial cross-section of a joint with the
tool of FIG. 7 joining a first and a second workpiece of differing
thicknesses by FSW, not to scale;
[0039] FIG. 18 shows a partial cross-section of typical
conventional shouldered FSW tool traversing an undulating joint,
not to scale;
[0040] FIG. 19 shows a partial cross-section of one embodiment of
the tool of FIG. 7 traversing an undulating joint, not to
scale;
[0041] FIG. 20 shows a partial cross-section of a first and a
second workpiece configured in a lap joint being welded by a
typical conventional shouldered FSW tool, not to scale;
[0042] FIG. 21 shows a partial cross-section of a first and a
second workpiece configured in a lap joint being welded by an
embodiment of the present invention, not to scale;
[0043] FIG. 22 shows a partial cross-section of a first and a
second workpiece configured in tee joint arrangement being welded
by an embodiment of the present invention, not to scale;
[0044] FIG. 23 shows a partial cross-section of one embodiment of
the tool traversing an undulating joint, not to scale;
[0045] FIG. 24 shows a partial cross-section of one embodiment of
the tool traversing an undulating joint, not to scale;
[0046] FIG. 25 shows a front elevation view of an embodiment of the
tool of the present invention, not to scale;
[0047] FIG. 26 shows a front elevation view of an embodiment of the
tool of the present invention, not to scale;
[0048] FIG. 27 shows an elevated perspective view of a first and
second workpiece being joined by a tool of the present invention,
not to scale;
[0049] FIG. 28 is a photograph in transverse cross-sectional view,
not to scale, of a weld having an excessive undercut on the
advancing, or left side, and reinforcement and flash on the
retreating side, or right side; and
[0050] FIG. 29 is a photograph in transverse cross-sectional view,
not to scale, of a weld produced with the tool of the present
invention having a minimal undercut on the advancing, or left
side.
DETAILED DESCRIPTION OF THE INVENTION
[0051] The non-consumable multi-section faced retractable
shoulderless variable penetration friction stir welding tool and
methods of friction stir welding of the present invention enable a
significant advance in the state of the art. The preferred
embodiments of the method and apparatus accomplish this by new and
novel methods that are configured in unique and novel ways and
which demonstrate previously unavailable but preferred and
desirable capabilities. The description set forth below in
connection with the drawings is intended merely as a description of
the presently preferred embodiments of the invention, and is not
intended to represent the only form in which the present invention
may be constructed or utilized. The description sets forth the
designs, functions, means, and methods of implementing the
invention in connection with the illustrated embodiments. It is to
be understood, however, that the same or equivalent functions and
features may be accomplished by different embodiments that are also
intended to be encompassed within the spirit and scope of the
invention.
[0052] The present invention includes several methods of friction
stir welding (FSW) and a non-consumable multi-section faced
retractable shoulderless variable penetration friction stir welding
tool 100 for performing the methods. The non-consumable
multi-section faced retractable shoulderless variable penetration
friction stir welding tool 100 is used in joining a first workpiece
10 and a second workpiece 20 with a friction stir weld 40. The tool
100 includes a substantially cylindrical body portion 200, a head
portion 400, and a tip section 500, each integral to the tool 100,
as seen in FIG. 7. The body portion 200 has a longitudinal axis 210
about which it is rotable, a diameter 220, a sidewall 230
substantially parallel to the longitudinal axis 210, a proximal end
240, and a distal end 250.
[0053] The first workpiece 10 has a first thickness 12 and a top
surface 14. Similarly, the second workpiece 20 has a second
thickness 22 and a top surface 24, as seen in FIG. 8. The tool 100
and methods of the present invention work equally as well on butt
joints, as seen in FIG. 5; lap joints, as seen in FIG. 9;
combination butt and lap joints, as seen in FIG. 10; tee joints, as
seen in FIG. 22; corner joints, not illustrated but understood by
one with skill in the art; as well as bead on plate welds to alter
the local characteristics of a plate due to friction stir
processing of the material with the tool.
[0054] Referring again to FIG. 7, the head portion 400 is located
at the distal end 250 of the body portion 200. The head portion 400
has a base 410 with a diameter 420 substantially equal to the
diameter 220 of the body portion 200 thereby forming a transition
300 between the body portion 200 and the head portion 400. The head
portion 400 includes a multi-section face 440, having at least a
first face section 441 nearest the body portion and a second face
section 445 nearest the tip section, labeled in FIG. 8, that
converges to the tip section 500. The tip section 500 has a
diameter 510 and a center 520 wherein the center 520 is located
substantially on the longitudinal axis 210, illustrated in FIGS. 14
and 15. Referring again to FIG. 7, the head portion 400 and the tip
section 500 define a height 430 from the distal-most portion of the
tip section 500 to the base 410 along the longitudinal axis 210.
The transition 300 may incorporate a smooth curve between the body
portion 200 and the head portion 400, but it is not required.
[0055] The substantially equal diameters 220, 420 of the body
portion 200 and the head portion 400, along with the transition 300
therebetween, establish that the present invention lacks a shoulder
as is present in prior art friction stir welding tools 90, 95, as
seen in FIGS. 1 and 2. This lack of a shoulder has numerous
advantages that have long been overlooked by those in the FSW
industry.
[0056] The shoulder 91, 96 of conventional shouldered FSW tools 90
as well as retractable pin tools 95, as seen in FIGS. 1 and 2, is
the source of many problems and confusion in FSW, which have been
previously explained in the Background of the Invention herein. In
short, the present tool 100 does not require a shoulder 91, 96 to
retain the plasticized material of the FSW, contrary to the
teachings of the leaders in the field. Referring to FIG. 11, the
present invention's elimination, or minimization, of any portion of
the tool 100 that contacts the top surface 14, 24 of either
workpieces 10, 20 away from the point at which the tool enters the
workpiece(s) 10, 20 has several advantages.
[0057] One such advantage is the elimination of the primary source
of overheating. Referring again to FIGS. 1-3, during FSW with prior
shouldered FSW tools, the weld 40 is repeatedly subjected to the
pressure and rotation of the tool shoulder 91, 96. As a
conventional FSW tool 90, 95 traverses a joint 35 the material is
first exposed to the leading edge of the shoulder 91, 96 that is
generally exerting a downward force on the workpieces 10, 20 of
several hundred pounds, often several thousand pounds, and is
rotating at several hundred RPM, while traversing the joint rather
slowly, generally less than ten inches per minute (IPM). One with
skill in the art will understand that such characteristics are
dependent on a number of factors including the material being
joined and its thickness. Taking, for example, a simple
illustrative case of a conventional tool 90, 95 traversing a joint
35 at 6 IPM and 800 RPM, it takes 10 seconds to traverse a one inch
section of the joint 35 during which 80 revolutions of the tool 90,
95 are made, resulting in 160 exposures of weld 40 to the shoulder
91, 96 (an exposure at the leading edge and the trailing edge for
each revolution). Such repeated exposure to the shoulder 91, 96
results in the overheating of the weld 40 and the associated
drawbacks, as previously explained. The present invention includes
a method of reducing the amount of overheating experienced by a
friction stir weld 40 by ensuring that while traversing the joint
35 with the rotating tool 100, no portion of the tool 100, or a
minimal portion of the tool 100 substantially smaller than that of
conventional FSW tool, away from the entry penetration of the tool
100 into the workpieces 10, 20, comes in contact with the top
surface 14, 24 of either workpiece 10, 20. Prior methods and
apparatus have indicated that such top surface friction heating and
weld material containment were essential to FSW.
[0058] Another advantage of the present tool 100 and methods is the
reduction of internal voids and lack of fusion that are associated
with the transition region 93, labeled in FIG. 1, between the
shoulder 91, 96 and the pin 92, 97 of traditional friction stir
welding tools 90, 95. As previously discussed in the Background of
the Invention herein, the transition region 93 between the shoulder
91, 96 and the pin 92, 97 is the source of many problems in tool
design and affects the characteristics of the resulting weld. Such
problems are particularly pronounced in conventional retractable
pin tools 95, illustrated in FIG. 2, because the transition region
changes as the pin 97 enters the workpieces 10, 20 or retracts from
the workpieces 10, 20.
[0059] Yet another advantage of the present non-consumable
multi-section faced retractable shoulderless variable penetration
tool 100 and methods of the present invention is that the
elimination of a shoulder 91 allows the use of a single tool 100 in
performing welds 40 of varying depth, performing welds 40 to join
workpieces having differing thicknesses, and in retracting the tool
100 to leave a weld 40 free of an exit hole 80, as seen in FIG. 5.
Conventional single-piece shouldered FSW tools 90, as seen in FIG.
1, have a fixed pin length projecting from the shoulder 91 and
therefore are limited to performing welds of a single penetration
depth. The present tool 100 is designed such that the height 430 of
the head portion 400 may be (i) less than or equal to the lesser of
the first workpiece thickness 12 or the second workpiece thickness
22 such that the entire tip section 500, head portion 400, and a
portion of the body portion 200 are in the friction stir weld 40
during welding, or alternatively (ii) greater than or equal to the
greater of the first workpiece thickness 12 or the second workpiece
thickness 22 such that the entire tip section 500 and a portion of
the head portion 400 are in the friction stir weld 40 during
welding, as seen in FIG. 11. This ability to submerge a portion of
the body portion 200 into the weld 40 permits use of the tool 100
in creating spot welds. Additionally, the tool 100 permits the
joining of a first workpiece 10 and a second workpiece 20 wherein
they have unequal thicknesses 12, 14, as shown in FIG. 17.
[0060] Along with the ability to perform variable depth welds comes
the ability to vary the width of the welds. As one with skill in
the art can appreciate, the further the tool 100 of the present
invention penetrates into the joint 35 the wider the weld 40
becomes. This, along with the ability of the present invention to
be plunged into the joint 35 as it is traversing the joint 35,
permits the economical use of friction stir welding in performing
tack welds. Such tack welds are particularly useful in holding
parts in the tooling.
[0061] Additionally, one with skill in the art can appreciate that
cooperating tools may be used in creating full penetration welds in
thicker workpieces with one tool penetrating half way into the
joint from one side of the joint and a second tool penetrating half
way into the joint from the opposite side of the joint.
[0062] The shoulderless design of the present tool 100 permits the
friction stir welding of workpieces 10, 20 having significant
curvature. In the past conventional shouldered friction stir
welding tools 90, 95 have not been able to join workpieces 10, 20
having more than slight undulation because of shoulder 91, 96
interference. As seen in FIG. 18, while traversing down a slope the
shoulder 91, 96 of conventional tools 90, 95 would lift-off, or
separate from the joint 35, at either the leading edge of the
shoulder 91, 96 or the trailing edge of the shoulder 91, 96
depending on the motion control system. Alternatively, while
traversing down into a valley or up from a valley, the shoulder 91,
96 of conventional tools 90, 95 would gouge into the joint at
either the trailing edge of the shoulder 91, 96 or the leading edge
of the shoulder 91, 96 depending on the motion control system. Such
lift-off and gouging results in welds having reduced aesthetic
qualities that often require grinding of the surface and diminish
the mechanical properties of the weld.
[0063] FIG. 19 illustrates how the present tool 100 eliminates such
gouging and lift-off problems and permits the joining of workpieces
10, 20 having aggressive curvature. Selecting a tool 100 of the
present design such that a portion of the head portion 400, and
therefore a portion of the multi-section face 440, does not
penetrate the joint 35 when joining a flat portion of the
workpieces 10, 20 ensures that the body portion 200 to head portion
400 interface, or transition 300, does not gouge the joint 35,
while the multi-section face 440 remains in contact with the joint
at both the leading and trailing edges of the tool 100. In fact, it
is often preferred to perform the welding operation with a portion
of the first face section 441 within the joint, and thus the first
and second workpieces 10, 20, and a portion of the first face
section 441 outside of the workpieces 10, 20. The curve of FIG. 19
is rather gradual, yet illustrates the point. The tool 100 of the
present invention may be utilized in joining workpieces having
complimentary curves that are much more severe. In fact, the
present tool 100 may be used in configurations where the radius R
of the at least one cooperating curve is less than approximately
two times the diameter 220 of the body portion 200 and greater than
one-half the diameter 220 of the body portion 200. The present tool
100 is illustrated in FIG. 23, with a second face opening angle 620
of 140 degrees, traversing a curve with a radius R equal to twice
the diameter 220 of the body portion 200. Similarly, a tool 100
with a second face opening angle 620 of 70 degrees is shown in FIG.
24 traversing a curve with a radius R equal to approximately
seventy-five percent of the diameter 220 of the body portion
200.
[0064] Still further, another advantage of the present tool 100 is
that it produces wider welds 40 than those produced by conventional
shouldered friction stir welding tools 90, 95 of the same exterior
diameter. FIGS. 20 and 21 illustrate that the lap joint weld width
42, being the width of the weld 40 at the interface between the
first and second workpieces 10, 20, is much greater when using a
tool 100 of the present invention, as seen in FIG. 21, than when
using a conventional tool, as seen in FIG. 20. The improved weld
width 42 is a result of the relatively flat head portion 400, when
compared to prior art shouldered tools 90, 95, and results in more
bonded area between the first and second workpieces 10, 20, and
thus a higher load capacity.
[0065] The relatively flat head portion 400 is also beneficial when
performing welds along tee joints, as seen in FIG. 22, and along
corner joints. The large second face opening angle 620 of the tool
100 results in greater, and more complete, mixing of material
between the first and second workpieces 10, 20. Additionally, the
backing tool 700 may be selected to match the second face opening
angle 620 of the tool 100 so that the face 400 may be parallel to
an edge of the backing tool 700 and either touch the backing tool
700 or come into close proximity thereto, thereby minimizing or
eliminating the potential for dead zones. Further, such a
configuration has the additional benefit of aiding in the root side
fillet/chamfer formation.
[0066] Further, the design of the present invention, namely the
shoulderless transition 300 from the head portion 400 to the body
portion 200, allows the weld penetration depth to change on the
fly. For instance, the tool 100 may first be plunged into the
workpiece(s) 10, 20 to a first penetration depth 82 and travel for
a particular distance (left to right) before further extending, or
retracting, into the workpiece(s) 10, 20 to a second penetration
depth 84, as seen in FIG. 12. It is important to note that the
present tool 100 is capable of entering the joint 35 as it is
moving along the joint 35, and need not be first plunged to a
particular depth and then traversed, as with prior tools. For
instance, the far left tool 100 of FIG. 12 could have started its
descent to the second position from the top surface rather than an
initial depth. This can be particularly advantageous in welding lap
joints, as seen in FIG. 9, and combination butt and lap joints, as
seen in FIG. 10. It is significant to note that the tool 100 of the
present invention is capable of plunging into the joint 35 as it is
moving along the joint 35, it need not be first plunged into a
joint 35 and then moved along the joint 35. Therefore, when joining
the elements of FIG. 10 the tool 100 would first enter the joint 35
between the first and second workpieces 10, 20 to a first depth and
then penetrate to a deeper depth in the vicinity of the third
workpiece 30 so as to not only join the first workpiece 10 to the
second workpiece 20 but to also join each of them to the third
workpiece 30. Such adaptability is not found in the prior art
tools.
[0067] As previously expressed, the head portion 400 includes a
multi-section face 440 that converges to the tip section 500. This
convergence may be in any manner and need not be uniform or
continuous, as seen in FIG. 13. Each section of the multi-section
face 440 has a horizontal projection component, namely a first
section horizontal projection component 442 and a second section
horizontal projection component 446, as seen in FIG. 25. The first
section horizontal projection component 442 represents the
magnitude of the portion of the first face section 441 that is
orthogonal to the longitudinal axis 210. Similarly, the second
section horizontal projection component 446 represents the
magnitude of the portion of the second face section 446 that is
orthogonal to the longitudinal axis 210. The magnitude of the first
section horizontal projection component 442 is less than fifteen
percent of the body portion diameter 220.
[0068] In one embodiment, the second face section 445 forms a
substantially frustoconical shape with the second face section 445
converging to the tip section 500 at a second face opening angle
620, as seen in FIG. 25. The second face opening angle 620 may be
virtually any angle but the range of between approximately 70
degrees and approximately 160 degrees, illustrated in FIG. 15, has
been found to be effective, with the range of approximately 100
degrees and 140 degrees even more preferred. A second face opening
angle 620 of 90 degrees is illustrated in FIG. 14. The relatively
flat head portion 400 and tip section 500 of the present invention
also flies in the face of traditional FSW teachings.
[0069] In a further embodiment, the first face section 610
converges to the second face section 620 at a first face opening
angle 610 to form a substantially frustoconical shape, as seen in
FIG. 25. The first face opening angle 610 may be virtually any
angle. For example, in one embodiment the first face opening angle
is approximately 180 degrees, making the first face section 441
substantially orthogonal to the longitudinal axis 210, as seen in
FIG. 15. In this embodiment the magnitude of the first section
horizontal projection component 442 is less than approximately
eight percent of the body portion diameter 220, and has worked
effectively during experimentation at less than approximately five
percent of the body portion diameter 220. In fact, a magnitude of
the first section horizontal projection component 442 of between
approximately two percent to approximately four percent of the body
portion diameter 220 has been found to be particularly effective
when joining titanium workpieces, while a magnitude of between
approximately four percent to approximately eight percent of the
body portion diameter 220 has been found to be particularly
effective when joining steel workpieces. In an alternative
embodiment the first face opening angle 610 is between
approximately 40 degrees and 120 degrees. In further embodiments
the first face section 441 is curved. One particular curved
embodiment, shown in FIG. 26, has a radius of curvature R of less
than fifteen percent of the body portion diameter 220. Regardless
of the first face opening angle 610 or shape, the magnitude of the
first section horizontal projection component 442 is less than
fifteen percent of the body portion diameter 220, and is generally
selected based upon the material of the workpieces.
[0070] The purpose of the first face 441 is to minimize the
undercut, or under fill, on the advancing side of the tool 100. The
advancing side of the tool 100 is the side of the tool 100 where
the local direction of the multi-section face 440 due to tool
rotation and the direction that the tool 100 is traversing T are in
the same direction. Therefore, the advancing side of the tool 100
in FIG. 27 is the left side of the tool. Alternatively, the
retreating side of the tool 100 is the side of the tool 100 where
the local direction of the multi-section face 440 due to tool
rotation and the direction the tool 100 is traversing T are in the
opposite direction. Therefore, the retreating side of the tool 100
is FIG. 27 is the right side of the tool. Advancing side undercut,
or under fill, is caused when plasticized weld material flows
around the advancing side of the tool 100 and ends up on the
retreating side of the weld in the form of increased local weld
thickness, also referred to as positive reinforcement, or in the
worst case loosely attached flash, thus leaving an area of reduced
weld thickness, or undercut and under fill, on the advancing side
of the weld, as seen in FIG. 28, a cross-sectional photo of a
friction stir weld having undercut on the advancing side. Advancing
side undercut conditions are particularly prevalent when the second
face opening angle 620 is less than 140 degrees. A photograph in
transverse cross-sectional view of a weld produced with the tool
100 of the present invention is shown in FIG. 29 having a minimal
undercut on the advancing, or left side.
[0071] The first face 441 minimizes the undercut by increasing the
amount of plasticized weld material that is dragged around the tool
100 from the retreating side to the advancing side, thereby
infilling the undercut area. The size and configuration of the
first face section 441 play a direct role in reducing the undercut
and on tool 100 performance. The larger the first face section 441
the more plasticized weld material is transferred to the advancing
side, yet a large first face section 441 reduces the robustness of
the tool 100. Therefore, referring again to FIG. 25, the present
invention recognizes this balancing act and has related it to the
first section horizontal projection component 442. It is
preferential to have the magnitude of the first section horizontal
projection component 442 less than fifteen percent of the body
portion diameter 220. Further, the magnitude of the first section
horizontal projection component 442 preferably selected depending
on the material of the workpieces. For example, when joining
titanium workpieces, which do not transfer the heat created during
FSW particularly well, the magnitude of the first section
horizontal projection component 442 may be relatively small because
the plasticized titanium adheres well to the first face section
441. Conversely, when joining steel workpieces, which transfer the
heat created during FSW particularly well, the magnitude of the
first section horizontal projection component 442 must be larger
because the plasticized steel does not adhere well to the first
face section 441. Therefore, the magnitude of first section
horizontal projection component 442 necessary when joining titanium
is roughly fifty percent of the magnitude necessary when joining
steel. For example, a first section horizontal projection component
442 having a magnitude of eight percent, or less, of the body
portion diameter 220 has been found to work particularly well when
joining titanium workpieces, whereas a first section horizontal
projection component 442 having a magnitude of twelve percent, or
less, of the body portion diameter 220 has been found to work
particularly well when joining steel workpieces. In particular, in
the embodiments wherein the first face opening angle 610 is between
approximately 40 degrees and approximately 120 degrees a magnitude
of the first section horizontal projection component 442 of between
approximately two percent to approximately four percent of the body
portion diameter 220 has been found to be particularly effective
when joining titanium workpieces, while a magnitude of between
approximately four percent to approximately eight percent of the
body portion diameter 220 has been found to be particularly
effective when joining steel workpieces. Further, in the
embodiments wherein the first face section 600 is curved
experimentation has shown that a magnitude of the first section
horizontal projection component 442 of between approximately three
percent to approximately six percent of the body portion diameter
220 has been found to be particularly effective when joining
titanium workpieces, while a magnitude of between approximately six
percent to approximately twelve percent of the body portion
diameter 220 has been found to be particularly effective when
joining steel workpieces.
[0072] In one embodiment the tip section 500 is a flat shape 540,
as seen in FIGS. 7 and 15. Alternatively the tip section 500 may be
a curved shape 530, as seen in FIGS. 14 and 11. Still further, the
tip section 500 may by pyramidal in shape, or virtually any other
shape imaginable. Since the head portion 400 converges to the tip
section 500 there will always be tip section diameter 510 at the
interface between the tip section 500 and head portion 400, as seen
in FIGS. 14 and 15. It is at the tip section diameter 510 that the
tip section 500 transitions to the head portion 400. In one
embodiment the tip diameter 510 is less than approximately forty
percent of the body portion diameter 220 or the head portion
diameter 420. Such an aggressive convergence is unlike prior FSW
tools. In some embodiments the tip section 500 continues to
converge at the same angle as the head portion 400 and is therefore
indistinguishable from the head portion 400, as in the case of a
simple cone seen in FIG. 24.
[0073] The multi-section face 440 of the head portion 400 and the
sidewall 230 of the body portion 230 may be substantially smooth or
contain friction and/or plunge control features. For instance, in
one embodiment the multi-section face 440 of the head portion 400
is formed with at least one recess 450, as seen in FIG. 16, to aid
in heat generation; stirring of the weld 40; reduction of surface
flash formation; and improved stability of the tool 100 during the
plunge. Alternatively, the multi-section face 440 may include
projections extending from the multi-section face 440 such as
threads or stipples, as disclosed in the prior art.
[0074] The present tool 100 also eliminates the points of high
stress concentration present in conventional prior art shouldered
tools 90, 95. Typically the pin 92, 97 of conventional prior art
shouldered tools 90, 95 is approximately one-third the diameter of
the overall tool diameter, as seen in FIGS. 1 and 2. This change in
diameter occurs at the shoulder 91, 96 and is a point of
particularly high stress in the pin 92, 97. Obviously, the present
design seen in FIG. 11 does not contain such points of high stress
concentration. Further, the useful life of a tool 100 of the
present design is significantly greater than that of conventional
prior art shouldered tools 90, 95.
[0075] While the disclosure herein refers generally to a first
workpiece 10 and a second workpiece 20, the present invention may
be used in joining more than just two workpieces or in the repair
of a single workpiece. For example, the tool and methods of the
present invention may be used in friction stir processing of a
single workpiece to improve its properties.
[0076] Numerous alterations, modifications, and variations of the
preferred embodiments disclosed herein will be apparent to those
skilled in the art and they are all anticipated and contemplated to
be within the spirit and scope of the instant invention. For
example, although specific embodiments have been described in
detail, those with skill in the art will understand that the
preceding embodiments and variations can be modified to incorporate
various types of substitute and or additional or alternative
materials, relative arrangement of elements, and dimensional
configurations. Accordingly, even though only few variations of the
present invention are described herein, it is to be understood that
the practice of such additional modifications and variations and
the equivalents thereof, are within the spirit and scope of the
invention as defined in the following claims. The corresponding
structures, materials, acts, and equivalents of all means or step
plus function elements in the claims below are intended to include
any structure, material, or acts for performing the functions in
combination with other claimed elements as specifically
claimed.
* * * * *