U.S. patent application number 10/792409 was filed with the patent office on 2004-11-25 for friction plunge riveting process.
Invention is credited to Stol, Israel, Thomas, Wayne M., Threadgill, Philip L..
Application Number | 20040232209 10/792409 |
Document ID | / |
Family ID | 26699689 |
Filed Date | 2004-11-25 |
United States Patent
Application |
20040232209 |
Kind Code |
A1 |
Stol, Israel ; et
al. |
November 25, 2004 |
Friction plunge riveting process
Abstract
A method of joining a pair of metal components with a rivet
having a hardness that is substantially similar to at least one of
the metal components. The metal components are stack upon each
other and the rivet is rotated and simultaneously plunged in the
metal components under pressure to friction weld and
metallurgically bond the rivet to the metal components.
Inventors: |
Stol, Israel; (Pittsburgh,
PA) ; Thomas, Wayne M.; (Suffolk, GB) ;
Threadgill, Philip L.; (Cambridgeshire, GB) |
Correspondence
Address: |
Daniel C. Abeles, Esq.
Eckert Seamans Cherin & Mellott, LLC
Alcoa Inc.
Alcoa Technical Center, 100 Technical Drive
Alcoa Center
PA
15069-0001
US
|
Family ID: |
26699689 |
Appl. No.: |
10/792409 |
Filed: |
March 3, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10792409 |
Mar 3, 2004 |
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10025402 |
Dec 19, 2001 |
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6769595 |
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60257329 |
Dec 20, 2000 |
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Current U.S.
Class: |
228/112.1 |
Current CPC
Class: |
B23K 20/129 20130101;
B21J 15/027 20130101; B23K 20/127 20130101; B23K 20/12 20130101;
B23K 20/1295 20130101 |
Class at
Publication: |
228/112.1 |
International
Class: |
B23K 020/12 |
Claims
We claim:
1. A method of joining a pair of metal components comprising the
steps of: (a) placing a first metal component having a first
exposed continuous surface and a second metal component having a
second exposed surface in overlapping relationship to each other;
(b) providing a metal rivet having a head and a tip opposite the
head for entering into the first and second components; and (c)
rotating the rivet about its longitudinal axis and simultaneously
plunging the rivet through the first component continuous surface
and into the second component, wherein the hardness of the metal
rivet is substantially similar to the hardness of at least one of
the first and second components, such that the metal of the rivet
and the first and second components plastically deform; and (d)
solidifying the plasticized metal to produce a joint between the
rivet and each of the first and second components.
2. The method of claim 1 wherein the rivet tip is pointed.
3. The method of claim 2 wherein a final position of the rivet tip
is within the second component.
4. The method of claim 2 wherein a final position of the rivet tip
is flush with the second exposed surface.
5. The method of claim 2 wherein a final position of the rivet tip
is exterior to the second component.
6. The method of claim 1 wherein the rivet defines a helical groove
along an exterior surface of the rivet.
7. The method of claim 1 wherein the rivet includes means for
hiding flash produced in the step of plunging and rotating the
rivet.
8. The method of claim 7 wherein the rivet includes a flange and a
lip extending therefrom, the flange and lip thereby defining a
recess for collecting flash between the rivet and the first exposed
surface.
9. The method of claim 1 wherein the rivet tip defines a bore.
10. The method of claim 9 wherein the bore extends partially
through the rivet.
11. The method of claim 9 wherein the bore extends completely
through the rivet.
12. The method of claim 1 wherein the head of the rivet includes
means for engaging another component.
13. The method of claim 1 further comprising joining a third metal
component to the second component by the steps of: (i) positioning
the third component having a third exposed surface in overlapping
relationship to the second exposed surface; (ii) providing another
metal rivet having a head and a tip opposite the head for entering
into the third and second components; and (iii) rotating the other
rivet about its longitudinal axis and simultaneously plunging the
other rivet through the third component exposed surface and into
the second component, wherein the hardness of the other metal rivet
is substantially similar to the hardness of one of the third and
second components.
14. The method of claim 13 wherein steps (c) and (iii) are
performed simultaneously.
15. The method of claim 1 wherein the first and second metal
components and the rivet each comprise aluminum or an aluminum
alloy.
16. The method of claim 15 wherein at least one of the first and
second metal components is a clad product.
17. A composite metal product comprising: a first metal component
having a first exposed surface; a second metal component underlying
the first component; and a metal rivet extending from said first
exposed surface into the second metal component, said rivet being
friction welded to each of said first and second components,
wherein the metal of said rivet has a hardness substantially
similar to at least one of the first and second metal
components.
18. The composite metal product of claim 17 wherein the first metal
and second metal components and the rivet each comprise aluminum or
an aluminum alloy.
19. The composite metal product of claim 18 wherein at least one of
the first and second metal components is a clad product.
20. The composite metal product of claim 17 wherein at least about
50% of the alloying components the first and second components and
the rivet are the same.
21. A system for joining a first metal component to a second metal
component with a rivet, wherein the hardness of the rivet is
substantially similar to the hardness of at least one of the first
and second components, said system comprising: a clamp positioned
on a continuous first exposed surface of the first component for
maintaining the first component adjacent the second component; a
backing anvil for supporting a second exposed surface of the second
component adjacent the first component; and means for rotating and
plunging the rivet through the continuous first exposed surface and
into the second component to produce a region of plasticized metal
between the rivet and each of the first and second components, the
plasticized metal being solidifiable to form a friction weld
between the rivet and each of the first and second components.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. application Ser.
No. 10/025,402 filed Dec. 19, 2001 entitled "Friction Plunge
Riveting" which claims the benefit of U.S. Application No.
60/257,329, filed Dec. 20, 2000 entitled "A Friction Plunge
Riveting Process".
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a process for joining or
riveting two or more pieces of lapped metal together. The method
allows a range of non-ferrous and ferrous metals to be joined,
e.g., aluminum, magnesium, copper, titanium, iron, and their
respective alloys. More particularly, the invention represents an
alternative process for riveting two or more aluminum alloy
products together.
[0004] 2. Prior Art
[0005] Conventional solid-phase welding (friction welding) involves
rubbing two surfaces together under pressure in relative motion for
sufficient time until metal between the two surfaces becomes
thermally softened and in a plastic state. As shown in FIG. 1a,
friction welding commonly involves rotating a first component A
under pressure against a second component B. Alternatively, the
component A may be inserted into a bore defined in the component B
and rotated to produce a joint within the bore. A more recent
development is referred to as "friction plunge welding" which
International Patent Classifications B23k 20/12 and B29c 65/06 on
"Improvements Relating to Friction Welding", describe as being "a
method of operating on a work piece, that method comprising
offering a probe of material harder than the work piece material to
a continuous or substantially continuous or substantially
continuous surface of the work piece; causing relative cyclic
movement between the probe and the work piece while urging the
probe and the work piece together whereby frictional heat is
generated as the probe enters the work piece so as to create a
plasticized region in the work piece material around the probe;
stopping the relative cyclic movement; and allowing the plasticized
material to solidify around the probe." As shown in FIG. 1b,
conventional friction plunge welding involves immersing a
relatively hard material H into a relatively soft material S with
different metal combinations, e.g., steel into aluminum, copper
into aluminum, and the like as described in Connect, September
1993.
[0006] Other mechanisms for joining two or more lapped plates
include friction hydro pillar processing (FHPP) and friction taper
stud welding (FTSW). Each of FHPP and FTSW are employed with a
predrilled hole having a diameter larger than that of the rivet
material for FHPP and one using a tapered drill hole for FTSW.
These conventional spot-based mechanical fastening processes entail
one or more of the following elements: (1) making holes through the
parts to be joined as with all riveting processes (pop rivets,
self-piercing rivets, "blind" rivets); (2) an absence of
metallurgical bonding between the joint parts which makes fastening
fully dependent on mechanical locking; and/or (3) a pronounced
deformation of the parts being joined (e.g., self-piercing rivets
and clinching). Mechanical fastening is also expensive, prone to
seepage of environmental elements (salt water, condensation, and
the like) and often loosens over time. Loosening of fastened joints
may compromise the service performance of the joined
components.
[0007] Accordingly, a need remains for a method of joining or
riveting two or more pieces of lapped metal together wherein the
metals may be the same or different and wherein the rivet used to
join the metal pieces together is not necessarily different from
the metals being joined.
SUMMARY OF THE INVENTION
[0008] This need is met by the method of the present invention
which was conceived by realizing that it is possible to
force-plunge, pierce, penetrate into and metallurgically bond two
or more metal parts lapped or stacked together ("stack ups"), by
striking a balance between (a) a rivet geometry (i.e., tip shape
and diameter and included angle), (b) the strength or hardness of
rivets and parts being joined before and during friction welding,
(c) the melting temperature range of rivets and the parts to be
joined, (d) the respective thicknesses of joined parts, (e) the
rate of heat dissipation into the parts and rivets through
conduction, and (f) other friction welding parameters including
forging and welding force, burn off, revolutions per minute, plunge
rate and the like, all which affect heat generation and the forces
experienced in a given joining region (i.e., between the rivets and
the parts to be joined). While the present invention is
particularly suited for joining metal having no predrilled holes or
apertures, such holes not being required herein, it is to be
understood that the presence of a partially formed hole or a fully
formed hole through at least one of the metal parts being so joined
may be beneficial in increasing the rate of completion of the
method.
[0009] The present invention of friction plunge riveting differs
from conventional uses of friction plunge welding which require
plunging a significantly harder material into a significantly
softer material (e.g., copper or steel into aluminum). The friction
plunge riveting process of the present invention substantially
provides a more homogenous joint region in which the constituent
elements of the rivet and the work piece are made from the same
metal families. For example, two or more aluminum alloy parts (one
or more of which may be substantially pure aluminum) may be joined
with an aluminum alloy rivet. There is no requirement for an
overlap within the same sub-family of alloys. As one representative
example of an interfamily relationship of riveting according to the
present invention, components of Aluminum Association Series (AA)
5xxx alloy may be joined with and AA 7xxx alloy rivet. Preferably,
however, both the work piece materials and the rivet join a work
piece together should have about 50% or greater commonality (or
overlap) in the major alloying components. The present invention
differs from friction plunge welding in that the probe or rivet
used in friction plunge riveting can become partially plasticized
as such, friction plunge riveting is particularly suited for
applications which require the joining of two or more lapped
plates. In such situations, the rivet material may constitute
essentially the same or substantially similar material as the work
pieces being joined or riveted together. For example, friction
plunge riveting of the present invention allows for plunging or
piercing aluminum alloy rivets into an aluminum alloy or
substantially pure aluminum, copper alloy rivets into parts made of
copper alloys or pure copper, magnesium alloy rivets into a
magnesium alloy or pure magnesium component parts, titanium alloy
rivets into a titanium alloy or pure titanium parts, or steel
rivets into steel parts.
[0010] In contrast to the conventional spot-based mechanical
fastening, friction plunge riveting according to the present
invention relies on a metallurgical bond formed between the rivet
and the parts being joined. The riveting process of the present
invention thus a) eliminates the need to machine a hole in the
parts being joined, b) effects a full metallurgical bond between
the rivet and the parts being joined, and c) minimizes deformation
of the parts and/or the rivet unless the deformation is designed
for aesthetic reasons.
[0011] A complete understanding of the invention will be obtained
from the following description when taken in connection with the
accompanying drawing figures wherein like reference characters
identify like parts throughout.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1a is schematic of friction welding according to the
prior art;
[0013] FIG. 1b is schematic of friction plunge welding according to
the prior art;
[0014] FIGS. 2a-2c are cross-sectional views of a pair of metal
work pieces undergoing friction plunge riveting according to the
present invention;
[0015] FIG. 3a is a cross-section view of a friction plunge riveted
joint made in accordance with the present invention, wherein the
rivet creates a raised portion in one of the work pieces;
[0016] FIG. 3b is a cross-section view of a friction plunge riveted
joint made in accordance with the present invention, wherein the
tip of the rivet is flush with the exposed surface of one of the
work pieces;
[0017] FIG. 3c is a cross-section view of a friction plunge riveted
joint made in accordance with the present invention, wherein the
rivet extends through both of the work pieces;
[0018] FIG. 4a is a cross-sectional view of a pair of metal work
pieces undergoing friction plunge riveting according to the present
invention using a clamp and a backing anvil to hold the work pieces
in place;
[0019] FIG. 4a is a cross-sectional view of a pair of metal work
pieces undergoing friction plunge riveting according to the present
invention using a clamp and a backing anvil to hold the work pieces
in place, wherein the anvil defines a rivet tip receiving
recess;
[0020] FIG. 5 is a schematic of a friction plunge riveting
apparatus for practicing the method of the present invention;
[0021] FIGS. 6a-6c are schematics of a pair of metal work pieces
undergoing friction plunge riveting according to the present
invention using a scraper system to remove flash;
[0022] FIGS. 7a-7i show various embodiments of the rivets of the
present invention;
[0023] FIG. 8 is a cross-sectional view of a pair of metal work
pieces undergoing friction plunge riveting using the rivet shown in
FIG. 7g;
[0024] FIGS. 9a-9d are perspective views of other rivets of the
present invention;
[0025] FIGS. 10a and 10b are cross-sectional views of pair of metal
work pieces undergoing friction plunge riveting using a rivet with
a break-away head;
[0026] FIG. 11 is a finishing tool for use with the rivet shown in
FIG. 10b;
[0027] FIG. 12 is a cross-sectional view of a pair of metal work
pieces friction plunge riveted with a rivet which hides flash;
[0028] FIGS. 13a-13c are cross-sectional views of perspective views
of metal work pieces friction plunge riveted with rivets having
alternative heads;
[0029] FIG. 14 is a cross-sectional view of a pair of clad metal
work pieces friction plunge riveted according to the present
invention;
[0030] FIG. 15 is a cross-sectional view of a various work pieces
friction plunge riveted together according to the present
invention; and
[0031] FIGS. 16a and 16b are cross-sectional views of three metal
work pieces undergoing friction plunge riveting according to the
present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0032] For purposes of the description hereinafter, the terms
"upper", "lower", "right", "left", "vertical", "horizontal", "top",
"bottom", and derivatives thereof shall relate to the invention as
it is oriented in the drawing figures. However, it is to be
understood that the invention may assume various alternative
variations and step sequences, except where expressly specified to
the contrary. It is also to be understood that the specific devices
and processes illustrated in the attached drawings, and described
in the following specification, are simply exemplary embodiments of
the invention. Hence, specific dimensions and other physical
characteristics related to the embodiments disclosed herein are not
to be considered as limiting.
[0033] Referring to FIG. 2a, the method of the present invention
includes stacking a first metal component 2 having an exposed,
continuous surface 4 (without a hole predrilled therethrough)
against a second metal component 6 having an exposed surface 8. The
compositions of the first and second metal components 2 and 4 may
be the same or different. A metal rivet 10 having a leading tip 12
and a head 14 is rotated about its longitudinal axis in the
direction of arrow A. The rivet 10 is composed of the same or
different composition as either or both of the first and second
metal components 2 and 6.
[0034] As shown in FIG. 2b, the tip 12 of the rivet 10 is urged
under pressure into the metal of the first component 2 in the
direction of arrow B. The process continues until the rivet 10
extends at least part way into the thickness of the second
component 6 as shown in FIG. 2c. The friction between the rivet 10
and the first and second components 6 causes the metals thereof to
plasticize. The rotation is ceased, and the plasticized metal
solidifies to form a joint 16 between the rivet 10 and each of the
first component 2 and the second component 6. The friction welding
between the rivet 10 and the first component 2 and between the
rivet 10 and the second component 6 causes the formation of flash
18 which escapes from the region of the joint 16 and collects
adjacent the first component exposed surface 4. The flash 18 shown
in FIG. 2c is generally produced in all the embodiments described
herein, however for simplicity, it may not be shown in all the
drawings. The joint 16 is a metallurgical bond between the metal of
the rivet 10 and each of the metals of the first and second
components 2 and 6.
[0035] In the embodiment shown in FIG. 2c, the final location of
tip 12 of the rivet 10 is within the second component 6 such that
the exposed surface 8 of the second component 6 remains unchanged.
FIGS. 3a, 3b, and 3c show alternative final positions for the rivet
tip 12 in the friction plunge riveting process of the present
invention. As shown in FIG. 3a, the rivet 10 may extend so far into
the second component 6 that the tip 12 creates a raised portion 19
on the exposed surface 8 of the second component 6. In FIG. 3b, the
rivet 10 fully penetrates the second component 6 (and is fully
bonded thereto) but the rivet tip 12 remains flush with the exposed
surface 8 of the second component 6. The rivet 12 may spread along
the exposed surface 8 as shown in FIG. 3b. Use of a rivet tip 12
flush with the exposed surface 8 avoids the additional drag
resistance associated with conventional rivets used on the exterior
of transportation vehicles, such as airplanes and truck bodies. A
particular advantage of the use of the present invention in
constructing aircraft skin is that the flush joints produced hereby
reduce or eliminate the shredding of skin in an airplane crash.
Alternatively, as shown in FIG. 3c, the rivet tip 12 may extend
through the exposed surface 8. In this manner, the rivet tip 12 may
have the appearance of a conventional rivet head.
[0036] The friction plunge riveting process of the present
invention preferably is performed by maintaining close contact
between the first and second components 2 and 6. This may be
accomplished by clamping the components 2 and 6 between a backing
anvil 20 and a clamp 22 as shown in FIG. 4a. The backing anvil 20
shown in FIG. 4a is suitable for production for the joint shown in
FIG. 2c and FIG. 3b in which the rivet tip 12 remains within the
thickness of the second component 6 or is flush with the exposed
surface 8 of the second component 6. For the joint shown in FIG.
3b, the backing anvil 20 provides a stop that prevents advance of
the rivet 12 beyond the plane of the exposed surface 8. As shown in
FIG. 4b, when producing the joints shown in FIGS. 3a and 3c, it is
preferred to use a backing anvil 24 that defines a recess 26. The
recess 26 is sized and configured to accommodate the raised portion
19 of the second component 6 as shown in FIG. 3a or the rivet tip
12 as shown in FIG. 3c. In order to avoid uncontrolled separation
between the rivet 12 and the first and second components 2 and 6
due to expulsion of plasticized metal, the recess 26 preferably is
hemispherical and has a diameter D equal to or preferably less than
a diameter d of the rivet tip 12. A hemispherical recess 26 causes
the rivet tip 12 to take on a hemispherical shape when riveting
according to FIG. 3c. In addition, a height h of the recess should
not exceed about one half of the thickness t of the second
component 6. Alternatively, in situations where the rivet 10 has a
relatively constant diameter along its length, the diameter D of
the recess 26 is substantially equal to the rivet diameter d. The
anvil 24 preferably is made of a strong or hard material that can
completely withstand the force and thermal shock associated with
forming the rivet 12 of FIG. 3c. Representative materials include
steel alloys (e.g., tool steel) or ceramic materials (e.g.,
alumina). Other configurations for the recess 26 may be used to
create other shapes for the rivet tip 12 that extends through the
exposed surface 6. Alternative configurations include hexagonal,
round, flat, and hexagonal with a center recess, either hexagonal
or slotted. Raised portions 19 having such alternative shapes can
be produced by plunging the rivet 10 fully through the second
component 6 and deforming the rivet 10 in its plasticized state
into the recess 26 having the desired shape.
[0037] The backing anvil 20 or 24 and clamp 22 shown in FIGS. 4a
and 4b may be constituents of a friction plunge riveting system 30
schematically shown in FIG. 5. The backing anvil 20 or 24 is
supported by a resilient mechanism; such as a spring 32 (or a
pneumatically loaded system or the like) mounted on a lower leg 34
for urging the backing anvil 20 or 26 towards the clamp 22. The
rivet 10 is held and driven by an upper spindle 36 movably
supported by a sleeve 38 fixed to an upper leg 40. The upper
spindle 36 is moveable through the sleeve 38 in the directions of
double arrow D to compensate for varying thicknesses of the first
and second component 2 and 6. The lower leg 34 and upper leg 40 are
mounted to a main support 42 via a connecting axle 44. The
orientations of the lower leg 34 and upper leg 40 may be altered by
rotating the connecting axle 44 in the directions of double arrow
E. A pair of relatively slidable plates 46 and 48 is fixed to the
main support 42 and a beam 50. The main support 42 may be raised or
lowered by sliding the plate 46 relative to the plate 48 in the
directions of double arrow F. The position of the system 30 may be
adjusted by rotating the beam 50 in the directions of double arrow
G or moving the beam 50 in the directions of double arrow H or
both.
[0038] As shown in FIG. 2c, flash 18 may be produced, particularly
on the exposed surface 4 of the first component 2. The flash 18 may
be removed by a scraper system 60 schematically shown in FIGS.
6a-6c. Referring to FIG. 6a, the scraper system may include flash
removing scrapers 62 that also serve to align the rivet 10 in the
location that the joint is to occur. Standoff bearings 64 support
the flash removing scrapers 62 in position adjacent the first
component 2. The flash removing scrapers 62 are releasably engaged
via linking components 66 to the spindle 36. As the spindle 36
rotates and plunges the rivet 10 into the first and second
components 2 and 6, the flash removing scrapers 62 are rotated in a
synchronized manner with the spindle 36. Flash 18 is produced as
shown in FIG. 6b and collects between the flash removing scrapers
62 and the exposed surface 4 of the first component 2. Referring to
FIG. 6c, when riveting is complete, the flash removing scrapers 62
are disengaged from the spindle 36 and are moved away from the
rivet 10 while continuing to rotate thereby knocking the flash 18
away from the location of the joint. The flash 18 may additionally
be blown away with a burst of compressed air or the like.
[0039] The rivet 10 shown in FIG. 10 is shown in detail in FIG. 7a.
Rivet 10 includes slanted sides 72 which make an angle .alpha. with
the centerline L of the rivet 10, with a being up to about
35.degree., preferably about 7.degree. to about 25.degree.. On
suitable diameter d of tip 12 of the rivet 10 is about 10 mm. Rivet
10 is shown as having a rounded tip, but the tip may also be
planar. Other non-limiting examples of rivets are shown in FIGS.
7b-7i. Rivet 80 shown in FIG. 7b includes a cylindrical portion 82
that steps down to a first slanted side 84 which makes an angle
.beta. with the centerline L of the rivet 80 and to a second
slanted side 86 which forms an angle .gamma. with the centerline L
of the rivet 80, with .beta. being greater than angle .gamma.. As
shown in FIG. 7c, rivet 90 includes an integral flange 92 and has a
pointed tip 94. Rivet 100 shown in FIG. 7d is similar to rivet 10
except that rivet 100 has a tip 102 which defines a central opening
104. Another variation of rivet 10 is shown in FIG. 7e as rivet 110
which includes an integral flange 112 having sloping sides 114 and
one or more helical groove(s) 116 defined in the surface. The
helical grooves 116 assist in threading the rivet 110 into a work
piece and act similar to a friction stir welding tool. Rivet 120
shown in FIG. 7f is similar to rivet 110 except that integral
flange 122 has straight sides 124. A partially hollow rivet 130
(similar to rivet 80) with a tip 132 defining a cavity 134 is shown
in FIG. 7g. Rivet 130 displaces less material and requires less
axial force to plunge into work pieces. Alternatively, as shown in
FIGS. 7h and 7i, rivets 140 and 150 define respective bores 142 and
152 through the lengths thereof. Rivets having holes, cavities or
bores typically deform during the friction plunge welding process
yet may hide flash produced during riveting. For example, referring
to FIG. 8, the tip 132 of the rivet 130 may deform such that the
tip 132 is forced back in the opposite direction to the riveting
direction and the cavity 134 widens to provide a mechanical lock in
addition to the metallurgical bond produced during the riveting
process.
[0040] The rivets shown in FIGS. 9a, 9b, 9c, and 9d are configured
to allow for enhanced engagement with the system 30 for rotating
rivet and plunging rivets into work pieces. Rivet 160 shown in FIG.
9a includes an integral flange 162 and a hexagonal head 164.
Referring to FIG. 9b, rivet 165 includes the hexagonal head 164.
Rivet 170 of FIG. 9c includes an integral flange 172 which defines
a hexagonal recess 174, and rivet 175 of FIG. 9d includes integral
flange 176 having a top slotted recess 178. Rivets 160, 165, 170
and 175 are non-limiting examples of rivets configured to engage
with a system that drives the same in a friction plunge riveting
process.
[0041] In another embodiment of the invention shown in FIGS. 10a
and 10b, rivet 180 includes a removable head 182 joined to a main
body 184 via a thinned portion 186. Rivet 180 is plunged into the
first and second components 2 and 6 as described above. However,
when the joint is complete, head 182 removed, i.e. snapped off. In
this manner, once the head 182 is removed from the rivet 180, the
rivet 180 is substantially flush with the exposed surface 4 of the
first component 2. For safety critical applications, the sheared
surface of rivet main body 184 may be friction processed using a
friction-forming tool 188 shown in FIG. 11. The cup-shaped rotary
friction-forming tool 188 defines a recess 189 which receives the
surface of the rivet main body 184 to eliminate or minimize
micro-cracks associated with such sheared surfaces by rotating the
tool in the directions of double arrow I. In addition, the
friction-forming tool 188 can be used as a post-joining, rivet
heading tool or as an alternative to localized machining of a
joined rivet head.
[0042] In another embodiment shown in FIG. 12, the present
invention includes a rivet 190 having an integrally formed flange
192 and annular lip 194. When friction plunge riveted into first
and second components 2 and 6, flange 192 and lip 192 define a
recess 196 into which flash 18 collects thereby hiding flash formed
during the riveting process.
[0043] Alternatively, as shown in FIGS. 13a, 13b, and 13c, the
heads of the rivets may include a portion for engaging with another
component after joining. In FIG. 13a, rivet 200 includes a C-shaped
portion 202. Rivet 204 in FIG. 13b has a threaded shank 206 to
allow an internally threaded component to be threaded thereon. In
FIG. 13c, rivet 210 includes an enlarged head 212 defining a bore
214.
[0044] For certain materials of the first and second components 2
and 6, optional preheating techniques may be employed including (1)
heating the backing anvil 20 or 24 to preheat and preferentially
soften the first and second components 2 and 6, (2) heating the
backing anvil 20 or 24 and the clamp 22 to preheat and locally
soften the first and second components 2 and 6, particularly for
ferrous and certain non-ferrous materials through which induction
through the thickness of the components 2 and 6 may occur, and (3)
a diffused or rastered laser beam or other focused light source to
preheat and condition the first and second components 2 and 6
immediately before the friction plunge riveting process. Such
preheating techniques create a temporary preferential advantage in
relative strengths, namely to soften the first and second
components 2 and 6 such that rivet 10 behaves as a relatively
harder material plunged into relatively softer material. When the
friction plunge riveting process is used to join work pieces which
are not the same but substantially similar, it is preferred that
the rivet material is made of the harder of the two materials being
joined. By controlling the overall surface interface between the
rivet and the work pieces joined, it is possible to augment the
intermixing and interlocking of the material between the rivet and
the work pieces. The friction plunge riveting process of the
present invention can be used to join hard materials to soft
materials or hard materials to hard materials and soft materials to
soft materials. In another embodiment of the invention,
cryogenically cooled soft rivets can be plunged into the same grade
of material or even harder materials that intermix themselves.
[0045] As discussed above, the may be used to join various
materials as the first and second components 2 and 6. Referring to
FIG. 14, the friction plunge riveting process of the present
invention may be used to join a first clad component 220 having
clad layers 222 and 224 to a second clad component 232 having clad
layers 232 and 234. Clad components 220 and 230 may be plate or
sheet product. For clad components having a corrosion resistant
clad layer, such as layer 234, it is preferred that the rivet 10
does not extend through the second component 230. This arrangement
is particularly suited for aircraft skin and marine transportation
components. For example, the first or second components could be
comprised of a 6013-T6 or 7075-T7X aluminum alloy covered with an
1100 aluminum alloy cladding. By maintaining exterior surface 236
of the second component 230 intact, components 220 and 230 are
protected from environmental elements and are resistant to
corrosion and other destructive interactions. For example, as shown
in FIG. 15, aircraft skin component 240 can be friction plunge
riveted to another aircraft skin component 242 and to aircraft
stringer support component 246 without having the rivets 10 exposed
to an exterior surface 248 of the aircraft. The skin components 240
and 242 may have the same or different thicknesses depending on the
need of the particular assembly.
[0046] Referring to FIGS. 16a and 16b, a stack of more than two
components may be friction plunge riveted together. Components 250,
252, and 254 may have the same or different metal compositions. It
may be beneficial to predrill a pilot hole 256 in one component 250
as shown in FIG. 16a. The pilot hole 256 aides in accessing
intermediate component 252 to affect a more rapid efficient joining
of the components. Joints can be made one rivet at a time or
simultaneously using a double-sided friction plunge riveting
machine. With such a device, two friction welded rivets may be
driven opposite each other as a means for joining more than two
components together. Simultaneous double-sided riveting also
provides a balance reactive torque when rotating rivets 10' on
opposite sides of the stack of components 250, 252 and 254.
Frictional heat is generated from either side of the stack. This
increased amount of heat is conducted through the thickness of the
components 250, 252 and 254 to further soften the components 250,
252 and 254 and aid penetration of the rivets 10'. As such,
double-sided friction plunge riveting enables relatively thicker
components to be joined together according to the present
invention. Numerous components may be joined in this manner such as
flexible bus bars, aircraft skins, and structural members.
[0047] The present invention provides significant advances in the
art including the elimination of need for predrilled holes, as is
required with blind riveting, yet produces sufficient frictional
heat to function with smaller diameter, shorter length pilot holes
in appropriate situations. Full metallurgical bonding occurs
between the rivets and the components being joined. Due to the
metallurgical bonding between the rivets and the components being
joined, friction plunge riveting augments the structural
performance of the joint as compared to other riveting processes,
Sealants and/or adhesives at the faying surfaces between the
components may be reduced or eliminated, and the fretting (i.e.,
contact damage from micro-slip between the work pieces and
conventional rivet interface which leads to crack nucleation and
fretting fatigue and fretting corrosion) and loosening of
conventional riveted joints is eliminated
[0048] Larger diameter friction welded rivets may be used and fewer
rivets are required. The process of the present invention may be
operated over a wide range of joining parameters (e.g., forging and
welding force, rotation speeds) while yielding constant results
including a sound metallurgical bond between the rivet and joined
components. The present invention is also uniquely suited for
joining components in restrictive environments, such as in a space
station assembly or underwater.
[0049] In certain applications, the rivets may be manufactured or
treated to provide a differential hardness by such means, including
but not limited to, a) rapidly solidified high temperature
materials, b) aluminum-magnesium-scandium and other metallurgy
alloys that exhibit high strength at high heat, c) metal matrix
composites, d) cold working during manufacture e.g., penning or
cold drawn rivets strengthened with copper or copper alloys, e)
cryogenic treatments, f) rivets manufactured from steel or certain
other metals that produce retained phases rivets to complete the
transformation into martensite prior to hardening and tempering, g)
rivets treated for maximum hardness for heat treated aluminum
alloys, and h) for certain materials, applying the rivet at
sub-zero temperatures. In some applications, a momentary increase
in hardness is desirable. For marine and chemical processing
environments, corrosion resistance may be enhanced by riveting a
hard alloy to a softer, pure aluminum. It is also possible to use a
fully aged hardened rivet material, such as alloy AA7050-T7X into
solution heat-treated and softened parts, such as AA alloy 7055-T4
before allowing the joints to naturally age for up to about 8
weeks. It is anticipated that the resulting joined product will
exhibit the desired combination of both corrosion resistance and
structural performance.
EXAMPLE
[0050] Two sheets of 2 mm thick aluminum alloy AA 6082-T6 (Vickers
Hardness value of 113) were joined together with a cone-shaped
rivet made of 2014-T6 aluminum (Vickers Hardness value of 162). The
rivet had a 10 mm diameter flat tip and an included angle as shown
in FIG. 3a.
[0051] It will be readily appreciated by those skilled in the art
that modifications may be made to the invention without departing
from the concepts disclosed in the foregoing description. Such
modifications are to be considered as included within the following
claims unless the claims, by their language, expressly state
otherwise. Accordingly, the particular embodiments described in
detail herein are illustrative only and are not limiting to the
scope of the invention which is to be given the full breadth of the
appended claims and any and all equivalents thereof.
* * * * *