U.S. patent application number 12/712423 was filed with the patent office on 2010-07-08 for fastener for attachment by friction stir processing.
This patent application is currently assigned to GM GLOBAL TECHNOLOGY OPERATIONS, INC.. Invention is credited to James F. Hengel, Robin Stevenson, Pei-Chung Wang.
Application Number | 20100172716 12/712423 |
Document ID | / |
Family ID | 39151759 |
Filed Date | 2010-07-08 |
United States Patent
Application |
20100172716 |
Kind Code |
A1 |
Stevenson; Robin ; et
al. |
July 8, 2010 |
Fastener For Attachment By Friction Stir Processing
Abstract
A fastener is provided for attachment to a workpiece by a
friction stir process. The fastener includes a base having an
underside adapted to seat upon the workpiece and a fastener portion
attached to the top side of the base. An anchor portion projects
from the underside of the base and is adapted to be rotated and
advanced at high speed and inserted into the workpiece by friction
stirring of the workpiece. The anchor portion is embedded in the
workpiece upon cooling of the workpiece. The anchor portion has an
indent in the surface thereof enabling the softened stirred
material to flow into the indent and thereby mechanically capture
the anchor portion within the solidified workpiece.
Inventors: |
Stevenson; Robin;
(Bloomfield, MI) ; Wang; Pei-Chung; (Troy, MI)
; Hengel; James F.; (Romeo, MI) |
Correspondence
Address: |
Charles E. Leahy
226 Moran Road
Grosse Pointe Farms
MI
48236
US
|
Assignee: |
GM GLOBAL TECHNOLOGY OPERATIONS,
INC.
Detroit
MI
|
Family ID: |
39151759 |
Appl. No.: |
12/712423 |
Filed: |
February 25, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11469995 |
Sep 5, 2006 |
7695227 |
|
|
12712423 |
|
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Current U.S.
Class: |
411/171 |
Current CPC
Class: |
F16B 37/061
20130101 |
Class at
Publication: |
411/171 |
International
Class: |
F16B 37/06 20060101
F16B037/06 |
Claims
1-12. (canceled)
13. A fastener for attachment to a workpiece, comprising: a base
having an underside adapted to seat upon the workpiece, and a top
side; a fastener portion attached to the top side of the base; an
anchor ring of hollow cylindrical shape projecting from the
underside of the base and adapted to be rotated and advanced at
high speed and inserted into the workpiece upon friction stirring
of the workpiece by the anchor ring, said anchor ring having
indented regions in which the friction stirred material of the
workpiece becomes embedded to thereby anchor the anchor ring in the
workpiece upon cooling of the workpiece; in which the hollow
cylindrical shape is defined by a plurality of annular segments
having voids therebetween forming indents in which the friction
stirred material of the workpiece becomes embedded to thereby
anchor the anchor ring in the workpiece.
14. A fastener for attachment to a workpiece, comprising: a base
having an underside adapted to seat upon the workpiece, and a top
side; a fastener portion attached to the top side of the base; an
anchor ring of hollow cylindrical shape projecting from the
underside of the base and adapted to be rotated and advanced at
high speed and inserted into the workpiece upon friction stirring
of the workpiece by the anchor ring, said anchor ring having
indented regions in which the friction stirred material of the
workpiece becomes embedded to thereby anchor the anchor ring in the
workpiece upon cooling of the workpiece; in which the anchor ring
is a hollow circular cylinder and a plurality of thickened axial
extending pillars are arrayed around the hollow cylinder and the
pillars define the indents.
15-19. (canceled)
Description
FIELD OF THE INVENTION
[0001] The present invention relates to attaching a fastener such
as a screw or a nut to a work piece and more particularly provides
a fastener that is embedded into a work piece by friction stir
processing and is highly resistive to axial extraction and rotation
relative to the work piece.
BACKGROUND OF THE INVENTION
[0002] It is known in the automotive industry and in other
applications to attach a fastener onto a work piece. The fastener,
such as a screw, a nut, a stud, etc., is most conventionally
attached by resistance electric welding, and the fastener may have
small projections that face toward the metal component so that the
electric resistance heating is concentrated at these projections in
order to facilitate the formation of the weld between the fastener
and the metal component. Hence the process is often referred to as
projection welding.
[0003] It has also known that a pair of work pieces, such as metal
sheets, can be joined together by a friction stir rivet process in
which a rivet is spun at high speed and advanced into the work
pieces, thereby causing the a region of the work pieces surrounding
the rivet to be plasticized and then, upon cooling, the rivet is
captured within the cooled metal of the work pieces and thereby
attaches the work pieces together. This friction stir riveting
process is described in U.S. Pat. No. 6,702,535 assigned to the
same assignee as this invention and herein incorporated by
reference.
SUMMARY OF THE INVENTION
[0004] A fastener is provided for attachment to a workpiece by a
friction stir process. The fastener includes a base having an
underside adapted to seat upon the workpiece and a fastener portion
attached to the top side of the base. An anchor portion projects
from the underside of the base and is adapted to be rotated and
advanced at high speed and inserted into the workpiece by friction
stirring of the workpiece. The anchor portion is embedded in the
workpiece upon cooling of the workpiece. The anchor portion has an
indent in the surface thereof enabling the softened stirred
material to flow into the indent and thereby mechanically capture
the anchor portion within the solidified workpiece.
[0005] Further areas of applicability of the present invention will
become apparent from the detailed description provided hereinafter.
It should be understood that the detailed description and specific
examples, while indicating exemplary embodiments of the invention,
are intended for purposes of illustration only and are not intended
to limit the scope of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] The present invention will become more fully understood from
the detailed description and the accompanying drawings,
wherein:
[0007] FIG. 1 is a side elevation view of a fastener according to
the invention;
[0008] FIG. 2 is a section view taken through the fastener of FIG.
1 in the direction of arrows 2-2 of FIG. 1;
[0009] FIG. 3 is a view similar to FIG. 1 but showing the fastener
embedded into a component by friction stir welding;
[0010] FIG. 4 shows a side elevation view of second embodiment of
the invention;
[0011] FIG. 5 shows the second embodiment of the invention embedded
into a workpiece by friction stir welding;
[0012] FIG. 6 shows a side elevation view of a third embodiment of
the invention; and
[0013] FIG. 7 shows a bottom view of the third embodiment of FIG.
6;
[0014] FIG. 8 shows a side elevation view of a fourth embodiment of
the invention; and
[0015] FIG. 9 shows a bottom view of the fourth embodiment of FIG.
8.
DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS
[0016] The following description of certain embodiments is merely
exemplary in nature and is not intended to limit the invention, its
application, or uses.
[0017] Referring to FIG. 1, a fastener 10 is comprised of a base
12, a threaded stud 14, and an anchor 16. The base 12, threaded
stud 14 and anchor 16 are preferably of one-piece manufacture, such
as cold headed or machined, but may be two or more separate pieces
that are joined together.
[0018] The base 12 is a hex shape to enable gripping by a hex
socket. The threaded stud 14 rises from the top surface 20 of the
base 12 and the anchor 16 projects downwardly from the bottom
surface 22 of the base 12.
[0019] The anchor 16 is of a generally solid cylindrical shape,
having a generally circular cross-section, of varying diameter to
develop an enlarged diameter foot portion 24 and a smaller diameter
waist portion 26. The enlarged foot portion 24 has a bottom foot
surface 29. Thus as seen in FIG. 1, an indent region 30 is formed
in what would otherwise be the right cylindrical shape of the
anchor 16. Also some portion of the outer surface 28 of the anchor
16 has a flat portion 32 as is more clearly shown in FIG. 2,
thereby forming an indent region 34 in what would otherwise be a
circular cross-section of the small diameter portion.
[0020] Referring to FIG. 3, it is seen that the fastener 10 has
been attached to a workpiece 36 by friction stir processing. In
friction stir processing, the workpiece 36 is locked in a vise or
otherwise held stationary, while the fastener 10 is locked in a
chuck and rotated at high speed about its central axis 38 while
being advanced toward engagement with the workpiece 36. The
friction heating of the adjoining faces of the fastener 10 and the
workpiece 36 cause softening of the workpiece 36. In FIG. 3 the
friction stirred region within the workpiece is indicated at 40, it
being understood that as the fastener 10 is rotated and advanced
into the workpiece 36, the bottom foot surface 29 of enlarged
diameter of the foot portion 24 will define the outermost
diametrical reach, indicated at 42 of the stirred region. As the
foot portion 24 passes deeper and deeper into the work piece 36,
the softened metal of the work piece 36 is in the form of a right
cylindrical well of softened material of the workpiece. As the foot
portion 24 proceeds, the softened material will back fill around
the smaller diameter waist portion 26 and against the flat portion
32, thus filling into the indents 30 and 34. During the final
stages of insertion, the bottom surface 22 of the base 12 will act
as a lid to force the softened metal of the workpiece 36 to back
fill around the anchor 16, and then the excess material that is
displaced by the volume of the anchor 16 is extruded outwardly to
the outer diameter of the base 12 where it forms an annular ring of
flash 44. This outward extrusion is facilitated by the friction
heating of the material between the bottom surface 22 of the base
12 and the top surface of the workpiece 36.
[0021] As the metals cool and the workpiece material regains its
original strength, the joint is obtained by the mechanical
interference between the anchor 16 and the stirred region 40 of the
workpiece 36. The attachment between the fastener 10 and the
workpiece 36 is made strong by virtue of the mechanical interlock
provided by the shape of the anchor portion 16. In particular, the
deposit of solidified workpiece material into the indent 30 formed
by the difference in diameter between the smaller diameter waist
portion 26 and the enlarged diameter foot portion 24 causes the
anchor portion 16 to be effectively embedded against extraction of
the anchor 16 in the axial direction. Furthermore, the deposit of
solidified workpiece material into the indent 34 formed by the flat
wall 32 of the anchor portion 16 effectively locks the anchor
portion 16 against rotation by torque applied to the fastener
10.
[0022] It will be understood that the softening of the workpiece
and insertion of the anchor portion 16 is enabled by the material
of the anchor portion 16 having a relatively higher metal point
and/or hardness than the metal of the workpiece 36. Thus it is the
material of the workpiece 36 that is subjected to fluid-like motion
such that it may be displaced and induced to flow under the
combined axial and rotary motion of the fastener 10 during the
insertion process. Then upon cessation of stirring and the
associated heat input, the softened material cools, increases in
strength and firmly grips the fastener 10 to produce a high
strength joint between fastener 10 and workpiece 36. Furthermore
under some processing conditions the frictional heat developed may
be sufficient to cause a softening of both the anchor portion 16
and workpiece 36 so that metallurgical bonding occurs, with the
result that the fastener 10 is joined to the workpiece by the
combined effect of both a mechanical embedment of the anchor
portion 16 and a metallurgical bond.
[0023] FIG. 4 shows another embodiment of the invention in which
fastener 50 includes a base 52, threaded stud 54 that rises from
the base 52 and an anchor ring 56 that projects downwardly from the
underside 58 of the base 52. The anchor ring 56 is a hollow
cylinder, annular in shape, and is symmetrical about a central axis
59. The anchor ring 56 has an enlarged foot portion 60 and a
smaller waist portion 62, defining an outer annular indent region
63 and an annular inner indent region 65.
[0024] Referring to FIG. 5, the fastener 50 is friction stir
processed for attachment to a workpiece 64 by rotating the fastener
50 at a high speed and advancing the anchor ring 56 into the
surface of the workpiece 64 to create a region 66 of stirred
softened metal. Upon cooling, the anchor ring 56 is fixedly
attached to the workpiece 64 through the mechanical interference
resulting from the backfilling of the softened metal into the
indents 63 and 65 defined by the smaller diameter waist portion 62.
This locks the anchor ring 56 against axial extraction from the
workpiece 64. Excess material that is displaced by the insertion of
the anchor ring 56 is extruded from beneath the base 52 and forms a
ring of flash 68 around the base 52. It will be understood that the
fastener 50 does not have an indent in the cross section of the
anchor ring 56. However, if desired, fastener 50 may be modified to
provide improved resistance to rotational motion by adding a
structural feature such as the flat 32 of FIG. 1, or by segmenting
the anchor ring as will be discussed below in reference to FIG.
7.
[0025] FIGS. 6 and 7 show another embodiment of the invention in
which fastener 70 includes a nut 72 having an internally threaded
hole 74 and an underside 75. The nut 72 provides a base 76. A
hollow cylindrical structure 77 depends from the base 76 and
includes four arcuate shaped anchor segments 78, 80, 82 and 84 that
are separated from one another by voids 88, 90, 92 and 94 and are
arrayed equidistant around the center axis 93 of the fastener 70.
The voids 88, 90, 92 and 94 define indent regions 95, 96, 97, and
98. The fastener 70 will be rotated at high speed about center axis
93 and advanced toward a workpiece so that the anchor segments 78,
80, 82, and 84 will friction stir and soften the workpiece. The
softened metal will backfill the indents 95, 96, 97 and 98. Upon
cooling, the softened metal regains its initially hard state and
the solidified material residing within the indents 95, 96, 97, and
98 thereby mechanically locks the fastener against rotation by
torque forces applied upon the fastener 70. It will be understood
that the fastener 70 does not have an indent in the axial profile
of the anchor segments that would resist axial pull-out of the
fastener 70 from the workpiece. However, if desired, the fastener
70 may be modified for resistance to axial pull-out by implementing
the narrow-waisted cross section shown in FIG. 4 for the arcuate
sections 78, 80, 82, and 84.
[0026] FIGS. 8 and 9 show yet another embodiment of the invention
in which fastener 100 includes a nut 102 having an internally
threaded hole 104 and an underside 106. The nut 102 provides a base
108 for a hollow cylinder shaped anchor ring 112 that projects
downwardly from the underside 106. The anchor ring 112 has four
enlarged pillar portions 116, 118, 120, and 122 that are arrayed
equidistant around the periphery of the anchor ring 112. The
fastener 100 will be rotated at high speed around its center axis
and axially advanced toward a workpiece so that the anchor ring 112
will friction stir and soften the workpiece. The footprint of the
softened region of workpiece material will be defined by the
pillars 116, 118, 120 and 122 as it is the pillars that define the
outermost and inner most reach of the anchor ring 112. Upon
cooling, the molten metal hardens and the fastener 100 is
mechanically locked against rotation by the solidified material
that has backfilled into outer indent regions 126, 128, 130, and
132 defined between the pillars portions 116, 118, 120 and 122 on
the outermost side of the anchor ring 112. In addition the
solidified material back fills into inner indent regions 134, 136,
138, and 140 defined on the inner surface of the anchor ring 112
between the pillar portions 116, 118, 120 and 122. If desired, the
anchor ring 112 may be modified to incorporate the narrow-waisted
cross section of FIG. 4 to better resist axial pull-out of the
fastener 100.
[0027] The foregoing description of the invention is merely
exemplary in nature and, thus, variations thereof are intended to
be within the scope of the invention. For example, the fastener may
be a rivet, a nut, a threaded screw, or other type of conventional
faster to which an anchor structure is attached for friction stir
embedment into a work piece. And, in view of the forgoing
teachings, a person of skill in the art will appreciate a variety
of structural shapes for the anchor portion that will provide for
highly effective resistance to extraction and resistance to
rotation of the fastener from its friction stir welded attachment
to the work piece. And although the drawings show a metal
workpiece, the workpiece may be a plastic material.
* * * * *