U.S. patent application number 11/055368 was filed with the patent office on 2006-08-10 for friction stir nut and method of joining therewith.
Invention is credited to Robin Stevenson, Pei-Chung Wang.
Application Number | 20060175381 11/055368 |
Document ID | / |
Family ID | 36778941 |
Filed Date | 2006-08-10 |
United States Patent
Application |
20060175381 |
Kind Code |
A1 |
Wang; Pei-Chung ; et
al. |
August 10, 2006 |
Friction stir nut and method of joining therewith
Abstract
A friction stir nut is disclosed. The friction stir nut includes
a body, a cap, and an anti-rotation feature. The body has an
elongated cylindrical shank extending between a first end and a
second end, the cap being disposed at the second end, and the
anti-rotation feature being disposed at the cap and/or an outer
surface of the body. The body and cap have a blind axial hole
extending from the first end to the second end, the first end being
blind and the second end being open. The outer surface of the first
end has a flat surface oriented substantially perpendicular to the
axis of the shank, and the body has a cylindrical wall thickness
suitable for receiving internal threads. In response to a mandrel
tool friction stir welding the friction stir nut to a workpiece and
then being extracted, uniform internal threads result at the body.
The anti-rotation feature bonds to the workpiece by metallurgical
bonding and/or mechanical bonding.
Inventors: |
Wang; Pei-Chung; (Troy,
MI) ; Stevenson; Robin; (Bloomfield, MI) |
Correspondence
Address: |
GENERAL MOTORS CORPORATION;LEGAL STAFF
MAIL CODE 482-C23-B21
P O BOX 300
DETROIT
MI
48265-3000
US
|
Family ID: |
36778941 |
Appl. No.: |
11/055368 |
Filed: |
February 10, 2005 |
Current U.S.
Class: |
228/112.1 ;
228/2.1 |
Current CPC
Class: |
F16B 29/00 20130101;
B29C 66/1122 20130101; B29C 65/069 20130101; Y10T 428/31678
20150401; Y10T 428/2495 20150115; B29C 65/0672 20130101; B29C
65/602 20130101; B23K 20/1245 20130101; B29C 66/8322 20130101; B29C
66/21 20130101; B29C 66/5326 20130101; B21J 15/043 20130101; B21J
15/027 20130101 |
Class at
Publication: |
228/112.1 ;
228/002.1 |
International
Class: |
B23K 20/12 20060101
B23K020/12 |
Claims
1. A friction stir nut suitable for friction stir welding to a
workpiece via a mandrel tool, the friction stir nut comprising: a
body having an elongated cylindrical shank extending between a
first end and a second end; a cap at the second end; and an
anti-rotation feature at the cap, at an outer surface of the body,
or at both; wherein the body and cap have a blind axial hole
extending from the first end to the second end, the first end being
blind and the second end being open, the outer surface of the first
end having a flat surface oriented substantially perpendicular to
the axis of the shank; wherein the body has a cylindrical wall
thickness suitable for receiving internal threads; and wherein in
response to the mandrel tool friction stir welding the friction
stir nut to the workpiece and then the mandrel tool being extracted
from the friction stir nut, uniform internal threads result at the
body, and the anti-rotation feature bonds to the workpiece by
metallurgical bonding, mechanical bonding, or both.
2. The friction stir nut of claim 1, wherein: the body comprises a
first portion and a second portion; the first portion has a first
nominal cylindrical wall thickness suitable for receiving internal
threads; the second portion has a second nominal cylindrical wall
thickness that is less than the first nominal cylindrical wall
thickness; the first portion is proximate the first end and the
second portion is proximate the second end; and in response to the
mandrel tool friction stir welding the friction stir nut to the
workpiece and then the mandrel tool being pulled, the second
portion of the body buckles at an opposite side of the workpiece to
that of the cap.
3. The friction stir nut of claim 2, wherein: in response to the
mandrel tool being inserted into the body, internal threads are
received at the first portion; and in response to the mandrel tool
being extracted from the friction stir nut, uniform internal
threads result at the first portion.
4. The friction stir nut of claim 1, wherein: the anti-rotation
feature at the cap comprises a scalloped section at the perimeter
of the cap, a projection at the underside of the cap, a recess at
the underside of the cap, a through-hole at the cap, or any
combination comprising at least one of the foregoing features.
5. The friction stir nut of claim 1, wherein: the anti-rotation
feature at an outer surface of the body comprises a projection, a
recess, a knurl, or any combination comprising at least one of the
foregoing features.
6. The friction stir nut of claim 1, further comprising: internal
threads at the body.
7. The friction stir nut of claim 1, wherein: the body and cap
comprise an iron-based alloy.
8. The friction stir nut of claim 1, wherein: the body and cap
comprise a material having a higher melting point than that of the
material of the workpiece.
9. The friction stir nut of claim 1, wherein: the flat surface
oriented substantially perpendicular to the axis of the shank is
perpendicular to within plus-or-minus two degrees thereof.
10. The friction stir nut of claim 9, wherein: the flat surface has
a diameter equal to or greater than about 80% of the outside
diameter of the first end of the body.
11. The friction stir nut of claim 2, wherein: the second portion
has a compressive strength less than the compressive strength of
the first portion.
12. A friction stir rivet nut suitable for friction stir welding to
a workpiece via a mandrel tool, the friction stir rivet nut
comprising: a body having an elongated cylindrical shank extending
between a first end and a second end, the body comprising a first
portion proximate the first end and a second portion proximate the
second end, the first portion having a first nominal cylindrical
wall thickness, the second portion having a second nominal
cylindrical wall thickness that is less than the first nominal
cylindrical wall thickness; a cap at the second end; and an
anti-rotation feature at the cap, at an outer surface of the body,
or at both; wherein the body and cap have a blind axial hole
extending from the first end to the second end, the first end being
blind and the second end being open, the first end having internal
threads, the outer end surface of the first end having a flat
surface oriented substantially perpendicular to the axis of the
shank.
13. The friction stir rivet nut of claim 12, wherein: in response
to the mandrel tool friction stir welding the friction stir rivet
nut to the workpiece and then the mandrel tool being pulled, the
second portion of the body buckles at an opposite side of the
workpiece to that of the cap.
14. The friction stir rivet nut of claim 12, wherein: in response
to the mandrel tool friction stir welding the friction stir rivet
nut to the workpiece and then the mandrel tool being extracted from
the friction stir rivet nut, uniform internal threads result at the
body, and the anti-rotation feature bonds to the workpiece by
metallurgical bonding, mechanical bonding, or both.
15. The friction stir rivet nut of claim 12, wherein: the
anti-rotation feature comprises a recess, a projection, a hole, or
any combination comprising at least one of the foregoing
features.
16. A method of friction stir welding a friction stir rivet nut to
workpieces via a mandrel, comprising: threadably engaging the
mandrel with the rivet nut, the rivet nut comprising: a body having
a first end and a second end and a cap at the second end, the body
having a first portion proximate the first end and a second portion
proximate the second end, the first portion having a first nominal
cylindrical wall thickness suitable for receiving internal threads,
the second portion having a second nominal cylindrical wall
thickness that is less than the first nominal cylindrical wall
thickness, the outer end of the first end having a flat surface
that extends over equal to or greater than about 80% of the
effective outer diameter of the first end; positioning the rivet
nut at a point of engagement of the workpieces; rotating the
mandrel about its rotational axis, driving the rivet nut toward and
into the workpieces such that resultant frictional heating between
the rivet nut and the workpieces causes the materials of the
workpieces to soften at a process temperature thereby providing a
friction stirred displaceable path for the rivet nut to traverse,
and driving the rivet nut along the displaceable path until the cap
is seated against or partially into the workpieces; stopping
further rotation of the mandrel and allowing the workpieces and
rivet nut to cool below the process temperature, thereby permitting
the softened workpieces to harden; axially loading the mandrel with
sufficient force such that the second portion of the body buckles
at an opposite side of the workpieces to that of the cap; and
rotationally extracting the mandrel such that uniform internal
threads result at the first portion.
17. The method of claim 16, wherein the rivet nut further comprises
an anti-rotation feature at the cap, at an outer surface of the
body, or at both, the method further comprising: in response to the
mandrel being rotationally extracted from the rivet nut, the
workpieces being held together at the point of engagement by the
stirred, intermingled materials of the workpieces, the differential
thermal contraction of the workpieces and the rivet nut, the
mechanical interference between the anti-rotation feature and the
workpieces, the mechanical loading between the buckled second
portion of the body and the workpieces, or any combination
comprising at least one of the foregoing.
18. The method of claim 16, wherein: the rotating comprises
rotating the mandrel at equal to or less than about 12,000
revolutions per minute; and the driving comprises driving the rivet
nut at a rate equal to or greater than about 6 millimeters per
minute and equal to or less than about 150 millimeters per
minute.
19. The method of claim 16, wherein the causing the materials of
the workpieces to soften at a process temperature comprises:
causing the materials to soften at a process temperature that is
substantially lower than the melting temperature of the rivet
nut.
20. The method of claim 16, wherein the driving the rivet nut into
the workpieces comprises: driving the rivet nut absent a
preexisting hole in the workpieces.
21. The method of claim 16, wherein: the resultant frictional
heating is initiated by the friction stir interaction between the
flat surface of the first end of the rivet nut and the workpieces;
and the driving displaces material of the workpieces along the
displaceable path in such a manner as to reduce the tendency for
the displaced material to penetrate the region between the
workpieces as the rivet nut is driven into the workpieces.
Description
BACKGROUND OF THE INVENTION
[0001] The present disclosure relates generally to friction
stirring and a method of joining therewith, particularly to a
friction stir nut and a friction stir rivet nut, and a method of
joining therewith.
[0002] Friction stir welding (FSW) is a method used to join metal
workpieces that generally uses a cylindrical shouldered tool with a
profiled pin that is rotated at the joint line between two
workpieces while being traversed along the joint line. The rotary
motion of the tool generates frictional heat that serves to soften
and plasticize the workpieces. As the pin moves laterally, the
softened material, contributed by both workpieces, intermingles in
the wake of the traversing pin and cools and hardens due to the
absence of further frictional stirring, creating a bond between the
two workpieces.
[0003] Recent advances in friction stir processes have extended the
FSW technique to friction stir riveting (FSR), where a stir rivet
is rotated and advanced into an arrangement of workpieces to be
joined such that the material of the workpieces plasticizes around
the rivet during the friction stirring, and then hardens around the
rivet when the body of the rivet stops rotating and the workpieces
and rivet are allowed to cool.
[0004] Both of the aforementioned processes result in a bonded
workpieces. However, in some instances it may be desirable to both
bond the workpieces and provide a means for receiving additional
hardware. Accordingly, there is a need in the art to further
advance the technology of friction stir bonding in a manner that
offers opportunities for the addition of supplementary features and
capabilities through the use of additional hardware at the point of
bonding.
BRIEF DESCRIPTION OF THE INVENTION
[0005] Embodiments of the invention include a friction stir nut
suitable for friction stir welding to a workpiece via a mandrel
tool. The friction stir nut includes a body, a cap, and an
anti-rotation feature. The body has an elongated cylindrical shank
extending between a first end and a second end, the cap being
disposed at the second end, and the anti-rotation feature being
disposed at the cap, at an outer surface of the body, or at both.
The body and cap have a blind axial hole extending from the first
end to the second end, the first end being blind and the second end
being open. The outer surface of the first end has a flat surface
oriented substantially perpendicular to the axis of the shank, and
the body has a cylindrical wall thickness suitable for receiving
internal threads. In response to the mandrel tool friction stir
welding the friction stir nut to the workpiece and then the mandrel
tool being extracted from the friction stir nut, uniform internal
threads result at the body, and the anti-rotation feature bonds to
the workpiece by metallurgical bonding, mechanical bonding, or
both.
[0006] Other embodiments of the invention include a friction stir
rivet nut suitable for friction stir welding to a workpiece via a
mandrel tool. The friction stir rivet nut includes a body, a cap,
and an anti-rotation feature. The body has an elongated cylindrical
shank extending between a first end and a second end, a first
portion proximate the first end, and a second portion proximate the
second end. The first portion has a first nominal cylindrical wall
thickness, and the second portion has a second nominal cylindrical
wall thickness that is less than the first nominal cylindrical wall
thickness. The cap is disposed at the second end, and the
anti-rotation feature is disposed at the cap, at an outer surface
of the body, or at both. The body and cap have a blind axial hole
extending from the first end to the second end, the first end being
blind and the second end being open. The first end has internal
threads, and the outer end surface of the first end has a flat
surface oriented substantially perpendicular to the axis of the
shank.
[0007] Further embodiments of the invention include a method of
friction stir welding an embodiment of the aforementioned friction
stir rivet nut to workpieces via a mandrel. The mandrel is
threadably engaged with the rivet nut, the rivet nut is positioned
at a point of engagement of the workpieces, the mandrel is rotated
about its rotational axis, and the rivet nut driven toward and into
the workpieces such that resultant frictional heating between the
rivet nut and the workpieces causes the materials of the workpieces
to soften at a process temperature thereby providing a friction
stirred displaceable path for the rivet nut to traverse. The rivet
nut is driven along the displaceable path until the cap is seated
against or partially into the workpieces. Further rotation of the
mandrel is stopped and the workpieces and rivet nut are allowed to
cool below the process temperature, thereby permitting the softened
workpieces to harden. The mandrel is axially loaded with sufficient
force such that the second portion of the body buckles at an
opposite side of the workpieces to that of the cap, and the mandrel
is rotationally extracted such that uniform internal threads result
at the first portion.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] Referring to the exemplary drawings wherein like elements
are numbered alike in the accompanying Figures:
[0009] FIGS. 1 and 2 depict in cross section longitudinal view
exemplary friction stir rivet nuts in accordance with embodiments
of the invention; and
[0010] FIGS. 3A-F depict an exemplary friction stir riveting method
in accordance with embodiments of the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0011] Embodiments of the invention disclose a friction stir nut
and a friction stir rivet nut having a body with an elongated
cylindrical shank and a cap at one end. The body and cap have an
axial blind hole extending from the cap (the open end) to the end
of the shank (the blind end). The outer end of the body at the
blind end has a flat surface that engages the workpieces to be
joined, thereby providing a friction stir surface that has a
reduced tendency to undesirably displace the softened friction
stirred material sideways in the joint between the workpieces. The
shank of the body may have internal threads in place prior to
friction stir welding, or may have a suitable wall thickness for
receiving internal threads via a tapping operation during and/or
subsequent to friction stir welding. In a friction stir nut, the
nominal cylindrical wall thickness of the body may be uniform,
whereas in a friction stir rivet nut, the nominal cylindrical wall
thickness is reduced in a region proximate the cap, thereby
enabling a pulling operation on the body to buckle the cylindrical
wall of the body on an opposite side of the workpieces to that of
the cap. The method of joining two or more workpieces using the
friction stir nut or friction stir rivet nut may be accomplished in
the absence of a preexisting hole in the workpieces to be
joined.
[0012] FIG. 1 depicts a cross section view of an exemplary
embodiment of a friction stir nut 100 having a body 105 with an
elongated cylindrical shank (generally depicted by numeral 105)
extending between a first end 110 and a second end 115, and a cap
120 at the second end 115. As used herein, reference numeral 100
refers to both a friction stir nut and a friction stir rivet nut,
with the distinction between the two being more specifically
described later. The body 105 and/or cap 120 may have anti-rotation
features, such as scallops 125, projections 130, recesses 135,
through holes 140 (best seen by referring to FIG. 2), or any
combination of the foregoing. While the shapes of the anti-rotation
features are depicted circular, they may be of any shape suitable
for the purposes disclosed herein, such as geometrical indentation
recesses and associated geometrical elevated features from a
knurling operation for example. Accordingly, a combination of
projections 130 and recesses 135 is herein considered
representative of a knurl. While FIGS. 1 and 2 depict anti-rotation
features 130, 135 and 140 only in certain areas, it will be
appreciated that these features may be uniformly placed around the
body 105 and cap 120, may be non-uniformly placed, may be all of
one type, or may be of mixed types. For example, the anti-rotation
features at the cap 120 may include one or multiple scalloped
sections 125 at the perimeter of the cap 120, projections 130 at
the underside of the cap 120, recesses 135 at the underside of the
cap 120, and/or through-holes 140 at the cap. Similarly, the
anti-rotation features at an outer surface of the body 105 may
include one or multiple projections 130, recesses 135, and/or a
knurl 130, 135. The body 105 and cap 120 have a blind axial hole
145 extending from the first end 110 to the second end 115, the
first end 110 being blind and the second end 115 being open. The
outer end surface of the first end 110 has a flat surface 150
oriented substantially perpendicular to the axis 155 of the shank
105. In an embodiment, the flat surface 150 of rivet nut 100 is
flat to within plus-or-minus two degrees of perpendicular relative
to axis 155.
[0013] Referring now to FIGS. 1 and 2 in combination, body 105 has
a cylindrical wall thickness "t" suitable for receiving internal
threads 160, which may be cut into body 105 prior to friction stir
welding, or cut via a tapping operation during or subsequent to
friction stir welding, which will be discussed in more detail
later. As can be seen in FIG. 2, the flat surface 150 may only be a
portion of the available flat surface from outside diameter D of
body 105. In an embodiment, the flat surface 150 has a diameter
equal to or greater than about 80% of diameter D.
[0014] In an embodiment of a friction stir rivet nut 100, where it
is desirable for the body to buckle during a pulling operation
thereby providing a rivet-like compressive load on the workpieces,
the body 105 includes a first portion 165 and a second portion 170.
The first portion 165 has a first nominal cylindrical wall
thickness "t" suitable for receiving internal threads, and the
second portion 170 has a second nominal cylindrical wall thickness
"d" that is less than the first nominal cylindrical wall thickness,
thereby resulting in the second portion 170 having a compressive
strength that is less than the compressive strength of the first
portion 165. The first portion 165 is proximate the first end 110
and the second portion 170 is proximate the second end 115. In
response to a mandrel tool 210, best seen by referring to FIG. 3,
friction stir welding the friction stir rivet nut 100 to the
workpieces 200, and then the mandrel tool 210 being pulled (see
description relating to FIG. 3D), the second portion 170 of the
body 105 buckles at an opposite side of the workpiece to that of
the cap 120. As will now be appreciated, a friction stir rivet nut
differs from a friction stir nut by the presence of the second
portion 170 having a nominal wall thickness "d" that is allowed to
buckle to provide a rivet-like compressive load on the workpieces
200.
[0015] Referring now to FIGS. 3A-F, six exemplary frames of a
method for friction stir welding a friction stir rivet nut 100 to
workpieces 200 via a mandrel tool 210 are depicted. Workpieces 200
may be a sheet 202 placed on top of a tubular structure 204 for
example, may be a single part for example, may be a solid block of
metal such as aluminum for example, or may be any other set of
materials desired to be and suitable to be friction stir welded
using a friction stir nut or friction stir rivet nut 100. In all
embodiments of FIGS. 3A-F, workpieces 200 are supported in a
suitable fashion.
[0016] In FIG. 3A, the mandrel 210 is threadably engaged with the
rivet nut 100 and positioned at the desired point of engagement
with the workpieces 200. While not shown, it will be appreciated
that mandrel 210 is connected to a rotary machine for providing the
desired rotation and driving action for friction stir welding. In
an embodiment, mandrel 210 is driven at a rotational speed of about
12,000 revolutions per minute (rpm), and at an axial downward speed
of about 12 millimeters per minute (mm/min).
[0017] In FIG. 3B, mandrel 210 is rotated 215 about its rotational
axis, which is the same as axis 155, and the rivet nut 100 is
driven toward and into the workpieces 200 such that resultant
frictional heating between the rivet nut 100 and the workpieces
200, and more particularly frictional heating initiated by the
friction stir interaction between the flat surface 150 of the rivet
nut 100 and the workpieces 200, causes the materials of the
workpieces 200 to soften at a friction stir process temperature,
thereby providing a friction stirred displaceable path for the
rivet nut 100 to traverse. In an embodiment, the friction stir
process temperature is greater than 20 deg-C. and less than or
equal to the melt temperature of the workpieces 200. Where the
workpieces 200 are aluminum, the process temperature is less than
or equal to about 660 deg-C., for example, and in an embodiment
where the workpieces 200 are thermoplastic, the process temperature
is less than the melt temperature of the respective thermoplastic.
The rivet nut 100 is driven along this displaceable path until the
cap 120 is seated against or partially embedded into the workpieces
200. In this manner of friction stirring, the rivet nut 100 may be
driven into workpieces 200 absent a preexisting hole in the
workpieces 200. While it may be possible to rotate and drive rivet
nut 100 at sufficient speed and rate to cause melting of workpieces
200, it is contemplated that rotating and driving rivet nut 100 to
cause softening of workpieces 200 is sufficient for producing a
suitable joint. In an embodiment, mandrel 210 is rotated at a speed
of about 12,000 rpm and is driven at a rate of equal to or greater
than about 6 mm/min and equal to or less than about 150 mm/min.
However, it is contemplated that rotational speeds of equal to or
less than about 12,000 rpm may be suitable for the purposes
disclosed herein. As a result of the rotational speed in
combination with the drive rate, the friction heating initiated
between the flat surface 150 of rivet nut 100 and the surface of
workpiece 202, a friction stir process temperature is established
that results in the softening of workpieces 200, and preferably but
not necessarily results in softening without melting. As discussed
previously, the process temperature is that temperature between
room temperature and the melt temperature of workpieces 200 at
which the workpieces 200 are soft enough to provide a displaceable
friction stir path for rivet 100 to traverse. In an embodiment, the
process temperature is substantially less than the melt temperature
of rivet nut 100.
[0018] In an embodiment, and with reference still to FIG. 3B,
mandrel 210 drives rivet nut 100 toward workpieces 200 until the
underside of cap 120 is in loaded contact with the topside surface
of workpiece 202, resulting in friction stirring and partial
penetration of cap 120 into the surface of workpiece 202, holds the
12,000 rpm rotation of mandrel 210 for a defined period of time,
such as two seconds for example, and then stops further rotation to
allow workpieces 200 and rivet nut 100 to cool below the process
temperature. During the cooling, the softened workpieces 200
harden.
[0019] In an alternative embodiment, mandrel 210 is held at the
12,000 rpm rotation for a defined period of time subsequent to the
underside of cap 120 being seated against the topside surface of
workpiece 202, and is then stopped to allow workpieces 200 and
rivet nut 100 to cool below the process temperature.
[0020] In FIG. 3C, rotation of the mandrel 210 is stopped to allow
the workpieces 200 and rivet nut 100 to cool below the process
temperature, thereby permitting the softened workpieces 200 to
harden. During the hardening phase, the flowable friction stir
material that has flowed into and around the anti-rotation features
125, 130, 135, 140 of rivet nut 100 also hardens, thereby providing
a mechanical engagement between rivet nut 100 and workpieces 200
that resists an applied torque on rivet nut 100 about axis 155.
[0021] In FIG. 3D, and subsequent to hardening, the mandrel 210 is
axially loaded in tension (pulled upward) 220 with sufficient force
such that the second portion 170 of the body buckles 225 (best seen
by referring to FIGS. 3E and F) at an opposite side of the
workpieces 200 to that of the cap 120.
[0022] In FIG. 3E, the mandrel 210 is rotationally extracted from
the rivet nut 100 such that uniform internal threads 160 result at
the first portion 165 of the body 105. In an embodiment, mandrel
210 is of a machine tap construction such that threads are cut into
the first portion 165 during the phase depicted in FIG. 3A, and
then cleaned out during the phase depicted in FIG. 3E. In another
embodiment, first portion 165 has pre-tapped internal threads (see
FIG. 2 in comparison to FIG. 1) that are cleaned out during the
phase depicted in FIG. 3E. In this manner, any damage at the
internals threads 160, resulting from the thermal and/or mechanical
stress of the friction stir process depicted in FIGS. 3A and B
and/or the pulling process depicted in FIG. 3D, is corrected for by
the machine tap construction of the mandrel 210 in response to its
being rotationally extracted during the phase depicted in FIG. 3E.
In response to friction stir welding the rivet nut 100 to the
workpieces 200 and then extracting the mandrel 210 from the rivet
nut 100, not only do uniform internal threads 160 result at the
body 105, but also the anti-rotation feature 125, 130, 135, 140
bonds to the workpieces 200 by metallurgical bonding, mechanical
bonding, or both, thereby providing sufficient anti-rotation for
the insertion of a mechanical fastener 230, as depicted in FIG. 3F.
Also, in response to the mandrel 210 being rotationally extracted
from the rivet nut 100, the workpieces 200 are held together at the
point of engagement by the stirred, intermingled softened materials
of the workpieces 200, the differential thermal contraction of the
workpieces 200 and the rivet nut 100, the mechanical interference
between the anti-rotation feature 125, 130, 135, 140 and the
workpieces 200, the mechanical loading between the buckled 225
second portion 170 of the body 105 and the workpieces 200, or any
combination of the foregoing.
[0023] During the friction stir welding of rivet nut 100 to
workpieces 200, it is contemplated that the closer the diameter of
flat surface 150 is to the diameter D of the body 105, the less the
tendency will be to displace the softened friction stirred material
sideways into the joint between the workpieces. The use of flat
surface 150 provides an effective way of initiating and generating
frictional heating as the rotating flat surface 150 of rivet nut
100 is driven into workpieces 200, and the use of a 100% flat
surface 150 provides an effective way of reducing the tendency for
the displaced material along the displaceable path to penetrate the
region between workpieces 200 at the faying surfaces as rivet nut
100 is driven into and through workpieces 200. Notwithstanding this
consideration however, it is contemplated that a flat surface
diameter equal to or greater than about 80% of diameter D is
sufficient. In an embodiment, rivet nut 100 is selected to be
copper, titanium, iron, or any alloy having at least one of the
foregoing materials. If the rivet nut 100 is steel, it is
preferable to use low or medium carbon steel. However, for
embodiments of the invention absent a thinned down second portion
170, high carbon steel may be applicable. As used herein, medium
carbon steel refers to a steel having equal to or greater than
about 0.29 weight % carbon and equal to or less than about 0.53
weight % carbon, and high carbon steel refers to a steel having
equal to or greater than about 0.55 weight % carbon and equal to or
less than about 0.95 weight % carbon. In an embodiment having a
thinned down second portion 170, steel having a carbon content of
equal to or less than 0.4 weight % carbon is preferred, and steel
having a carbon content of equal to or less than 0.25 weight %
carbon is more preferred.
[0024] In accordance with embodiments of the invention, it is
contemplated that 3 mm thick workpieces 202 and 204 made of 5052
aluminum may be successfully joined. However, it is also
contemplated that embodiments of the invention also offer
opportunities for joining dissimilar materials including but not
limited to: composites to aluminum; polymers to aluminum; and,
aluminum to magnesium. For a composite to aluminum, or a polymer to
aluminum joint, it is contemplated that the aluminum be mounted
below the composite or polymer so that the buckling of rivet nut
100 during the pulling operation may engage the aluminum as it is
buckled, while the composite or polymer is held by the cap 120 of
body 105, and thus subjected to a lower, less localized stress.
[0025] As disclosed, some embodiments of the invention may include
some of the following advantages: the ability to join workpieces
together and provide a threaded insert (nut) in the absence of a
preexisting hole, thereby minimizing clearance, tolerance, fit-up
and alignment issues, particularly for multi-member stack-ups;
improved flow control of the displaced material that reduces its
tendency to penetrate the joint area between the workpieces,
thereby reducing the likelihood of the displaced material forcing
the workpieces apart as it cools and hardens, leaving a large gap
therebetween; the ability to provide a friction stirred riveted
assembly with a means for receiving a fastener; the ability to
provide a solid block of aluminum, such as an aluminum engine block
of a vehicle, with a friction stirred threaded insert made of
steel; and, the opportunity for friction stir joining dissimilar
materials while also providing a means for receiving a fastener at
the point of engagement.
[0026] While the invention has been described with reference to
exemplary embodiments, it will be understood by those skilled in
the art that various changes may be made and equivalents may be
substituted for elements thereof without departing from the scope
of the invention. In addition, many modifications may be made to
adapt a particular situation or material to the teachings of the
invention without departing from the essential scope thereof.
Therefore, it is intended that the invention not be limited to a
particular embodiment disclosed as the best or only mode
contemplated for carrying out this invention, but that the
invention will include all embodiments falling within the scope of
the appended claims. Moreover, the use of the terms first, second,
etc. do not denote any order or importance, but rather the terms
first, second, etc. are used to distinguish one element from
another. Furthermore, the use of the terms a, an, etc. do not
denote a limitation of quantity, but rather denote the presence of
at least one of the referenced item.
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