U.S. patent application number 16/585754 was filed with the patent office on 2020-04-02 for ultrasonically assisted self-piercing riveting.
The applicant listed for this patent is UT-Battelle, LLC. Invention is credited to Jian Chen, Richard W. Davies, Zhili Feng, Xiaohua Hu, Hui Huang, Xin Sun.
Application Number | 20200101519 16/585754 |
Document ID | / |
Family ID | 69947078 |
Filed Date | 2020-04-02 |
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United States Patent
Application |
20200101519 |
Kind Code |
A1 |
Sun; Xin ; et al. |
April 2, 2020 |
Ultrasonically Assisted Self-Piercing Riveting
Abstract
A method for installing a self-piercing rivet by introducing
acoustic (ultrasonic) vibrational energy is provided. The method
includes positioning multiple workpieces between a blank holder and
a die, applying ultrasonic vibrations to locally soften the
workpieces and driving, using a press tool, the self-piercing rivet
into the workpieces, causing the self-piercing rivet to deform in a
radially outward direction, thereby joining the workpieces together
without thermal processing and without permanent alterations to the
microstructure of the workpiece materials.
Inventors: |
Sun; Xin; (Knoxville,
TN) ; Feng; Zhili; (Knoxville, TN) ; Chen;
Jian; (Knoxville, TN) ; Huang; Hui;
(Knoxville, TN) ; Hu; Xiaohua; (Knoxville, TN)
; Davies; Richard W.; (Knoxville, TN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
UT-Battelle, LLC |
Oak Ridge |
TN |
US |
|
|
Family ID: |
69947078 |
Appl. No.: |
16/585754 |
Filed: |
September 27, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62738514 |
Sep 28, 2018 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B21J 15/025 20130101;
B21J 15/12 20130101 |
International
Class: |
B21J 15/02 20060101
B21J015/02; B21J 15/12 20060101 B21J015/12 |
Goverment Interests
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH AND
DEVELOPMENT
[0002] This invention was made with government support under
Contract No. DE-AC05-00OR22725 awarded by the U.S. Department of
Energy. The government has certain rights in the invention.
Claims
1. A method for installing a self-piercing rivet, the method
comprising: providing a self-piercing rivet tool including a punch
and a die; positioning a plurality of workpieces between the punch
and the die; applying ultrasonic vibrations to the plurality of
workpieces between the punch and the die to locally soften a region
of the plurality of workpieces; and driving, using the punch, a
self-piercing rivet into the softened region of the plurality of
workpieces, and causing the self-piercing rivet to deform in a
radial-outward direction to join the plurality of workpieces
together substantially at ambient temperature.
2. The method of claim 1 wherein the ultrasonic vibrations are
indirectly applied to the plurality of workpieces through vibration
of a portion of the self-piercing rivet tool.
3. The method of claim 1 further including clamping the plurality
of workpieces between a blank holder and the die.
4. The method of claim 1 further including providing an ultrasonic
transducer to apply the ultrasonic vibrations to at least one of
the plurality of workpieces.
5. The method of claim 1 wherein applying ultrasonic vibrations
imparts vibrations in a direction perpendicular to a surface of the
plurality of workpieces.
6. The method of claim 1 wherein applying ultrasonic vibrations
imparts vibrations in a direction parallel to a surface of the
plurality of workpieces.
7. The method of claim 1 wherein applying ultrasonic vibrations
imparts rotational vibrations about an axis that is normal to a
surface of the plurality of workpieces.
8. The method of claim 1 wherein applying ultrasonic vibrations is
performed prior to the step of driving the self-piercing rivet.
9. The method of claim 1 wherein applying ultrasonic vibrations is
performed concurrently with the step of driving the self-piercing
rivet.
10. The method of claim 1 wherein applying ultrasonic vibrations is
performed prior to and concurrently with the step of driving the
self-piercing rivet.
11. A self-piercing rivet tool comprising: a punch and a die which
are operable to drive a self-piercing rivet into a plurality of
workpieces positioned between the punch and the die, the
self-piercing rivet having a hollow leg extending from a head, the
die having a cavity; and an ultrasonic transducer operable to
locally soften a region of the plurality of workpieces positioned
between the punch and the die, wherein the hollow leg of the
self-piercing rivet is deformed in a radial outward direction when
driven into the plurality of workpieces in an axial direction to
join the plurality of workpieces together.
12. The self-piercing rivet tool of claim 11 wherein the ultrasonic
transducer is coupled to the plurality of workpieces through an
ultrasonic horn.
13. The self-piercing rivet tool of claim 11 wherein the ultrasonic
transducer causes the plurality of workpieces to oscillate in a
direction perpendicular to the axial direction.
14. The self-piercing rivet tool of claim 11 wherein the ultrasonic
transducer causes the plurality of workpieces to oscillate in a
direction parallel to the axial direction.
15. The self-piercing rivet tool of claim 11 wherein the ultrasonic
transducer imparts rotational oscillations in the plurality of
workpieces about the axial direction.
16. A method for installing a self-piercing rivet, the method
comprising: providing a self-piercing rivet tool including a punch,
a blank holder, and a die; clamping a plurality of workpieces
between the blank holder and the die, the plurality of workpieces
including an upper sheet and a lower sheet; applying ultrasonic
vibrations to the plurality of workpieces in the region between the
blank holder and the die to locally soften the plurality of
workpieces; and driving, using the punch, a self-piercing rivet
into the softened region of the plurality of workpieces in an axial
direction and causing the self-piercing rivet to deform outwardly
in a radial direction to join the plurality of workpieces
together.
17. The method of claim 16 wherein the ultrasonic vibrations are
indirectly applied to the plurality of workpieces through vibration
of a portion of the self-piercing rivet tool.
18. The method of claim 16 wherein applying ultrasonic vibrations
imparts vibrations in a direction perpendicular to the axial
direction.
19. The method of claim 16 wherein applying ultrasonic vibrations
imparts vibrations in a direction parallel to the axial
direction.
20. The method of claim 16 wherein applying ultrasonic vibrations
imparts rotational vibrations about the axial direction.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Application 62/738,514, filed Sep. 28, 2018, the disclosure of
which is incorporated by reference in its entirety.
FIELD OF THE INVENTION
[0003] The present invention relates to self-piercing riveting
systems to connect a plurality of workpieces with one another.
BACKGROUND OF THE INVENTION
[0004] Self-piercing riveting (SPR) is a cold joining method in
which a rivet 100 is driven by a press tool 102 towards a die 104
to join a top sheet 106 to a bottom sheet 108, shown in FIG. 1. SPR
achieves joining by causing the rivet 100 to flare into the bottom
sheet 108 mechanically, and without thermal input or processing,
which might otherwise degrade the microstructure and properties of
highly engineered structural materials such as high-strength
aluminum and high-strength steel. For example, SPR is widely used
in the automotive industry to join lightweight dissimilar materials
such as aluminum alloy structures, aluminum-steel structures, and
other mixed structures that are difficult to join by resistance
spot welding, which would involve melting and solidification.
[0005] However, SPR is not well suited for joining materials with
low ductility (e.g., magnesium alloys and 700 series aluminum
alloys) or high strength materials (e.g. high strength alloys). For
example, materials having a low ductility and high strength
materials can rupture due to excessive deformations in riveting.
Various thermally-assisted approaches have been attempted using
laser heating, induction heating, and frictional heating to
increase a material's ductility while reducing flow stress. Other
joining methods such as friction stir welding, friction stir spot
welding, friction bit joining, and ultrasonic welding also rely on
significant heating and temperature increases in the bonded region
to soften the workpiece (or base material) to enable bonding.
[0006] In addition to the additional energy associated with these
thermal-based processes, the elevated temperature produced in these
methods can permanently alter a material's microstructure, and
hence degrade the mechanical strength and associated joint
properties. Accordingly, there remains a continued need for an
improved system in which two materials can be SPR-joined at room
temperature, including materials with low ductility and high
strength, optionally without the aid of existing thermal
techniques.
SUMMARY OF THE INVENTION
[0007] A method for installing a self-piercing rivet by introducing
acoustic (ultrasonic) vibrational energy is provided. The method
includes positioning multiple workpieces between a blank holder and
a die, applying ultrasonic vibrations to locally soften the
workpieces and driving, using a press tool, the self-piercing rivet
into the workpieces, causing the self-piercing rivet to deform in a
radially outward direction, thereby joining the workpieces together
without thermal processing and without permanent alterations to the
microstructure of the workpiece materials.
[0008] Embodiments of the present invention include applying
ultrasonic vibrations to the press tool, the blank holder, the die,
and/or the workpiece(s) directly. For example, embodiments include
a transducer to impart ultrasonic vibration on a punch, the
transducer converting electrical energy to ultrasonic vibration at
a desired frequency. High frequency ultrasonic vibrations are
imparted during the riveting process until the two workpieces are
clinched, with the amplitude of vibration optionally in the range
of 2-100 micrometers (.mu.m), optionally 2-40 .mu.m, and the
frequency of vibration greater than 20 kHz, optionally 20 to 80
kHz, further optionally 20 to 60 kHz.
[0009] In one embodiment, continuous ultrasonic vibrations are
applied to the workpiece(s) for at least the length of time that
the press tool drives the rivet into the workpiece(s). In other
embodiments, continuous ultrasonic vibrations are applied to the
workpiece(s) prior to the self-piercing rivet being driven by the
press tool, for example when the workpiece stack is clamped between
the blank holder and the die, but prior to the press tool driving
the rivet. In still other embodiments, continuous ultrasonic
vibrations are applied to the workpiece(s) at least prior to and
while the rivet is driven by the press tool. The ultrasonic
vibrations can be applied in the direction that the rivet is being
driven, perpendicular to the direction that the rivet is being
driven, or rotatively about an axis parallel to the direction that
the rivet is being driven.
[0010] The use of ultrasonic vibrational energy softens the
workpieces, while at generally room temperature, thereby decreasing
the plastic flow stress of the workpiece material, including
materials with high strength and low ductility. The present method
retains the benefits of the SPR process, including the reduction of
processing loads and the improvement of a material's plastic
deformation capability. Different transducers and/or coupling
devices are possible to apply different modes of vibration in which
the direction of the ultrasonic vibration is in principle parallel
to the surface of the workpieces, perpendicular to the surface of
the workpieces, or cyclic with rotation about an axis that is
perpendicular to the surface of the workpieces.
[0011] These and other features of the invention will be more fully
understood and appreciated by reference to the description of the
embodiments and the drawings.
[0012] Before the embodiments of the invention are explained in
detail, it is to be understood that the invention is not limited to
the details of operation or to the details of construction and the
arrangement of the components set forth in the following
description or illustrated in the drawings. The invention may be
implemented in various other embodiments and of being practiced or
being carried out in alternative ways not expressly disclosed
herein. In addition, it is to be understood that the phraseology
and terminology used herein are for the purpose of description and
should not be regarded as limiting. The use of "including" and
"comprising" and variations thereof is meant to encompass the items
listed thereafter and equivalents thereof as well as additional
items and equivalents thereof. Further, enumeration may be used in
the description of various embodiments. Unless otherwise expressly
stated, the use of enumeration should not be construed as limiting
the invention to any specific order or number of components. Nor
should the use of enumeration be construed as excluding from the
scope of the invention any additional steps or components that
might be combined with or into the enumerated steps or
components.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a schematic representation of a prior art
self-piercing rivet for joining multiple workpieces.
[0014] FIG. 2 is a schematic representation of ultrasonic
vibrations imparted on a press tool for a self-piercing rivet.
[0015] FIGS. 3 is a schematic representation of ultrasonic
vibrations imparted on a blank holder for a self-piercing
rivet.
[0016] FIG. 4 is a schematic representation of ultrasonic
vibrations imparted on a die for a self-piercing rivet.
[0017] FIG. 5 is a schematic representation of ultrasonic
vibrations imparted on an upper workpiece for a self-piercing
rivet.
[0018] FIG. 6 is a schematic representation of ultrasonic
vibrations imparted on a lower workpiece for a self-piercing
rivet.
[0019] FIG. 7 is a circuit diagram for a self-piercing rivet tool
in accordance with an embodiment of the present invention.
[0020] FIG. 8 is a first timing diagram for operation of an
ultrasonic transducer and an electrically operated self-piercing
rivet tool.
[0021] FIG. 9 is a second timing diagram for operation of an
ultrasonic transducer and an electrically operated self-piercing
rivet tool.
DETAILED DESCRIPTION OF THE CURRENT EMBODIMENTS
[0022] As discussed herein, the current embodiments generally
relate to a method for installing a self-piercing rivet by
introducing ultrasonic vibrational energy. The method generally
includes positioning multiple workpieces between a blank holder and
a die, applying ultrasonic vibrations to locally soften the
workpieces and driving, using a press tool, the self-piercing rivet
into the workpieces, causing the self-piercing rivet to deform in a
radially outward direction, thereby joining the workpieces together
without thermal processing and without permanent alterations to the
microstructure of the workpiece materials. Each step is separately
discussed below.
[0023] Referring to FIG. 2, positioning multiple workpieces between
portions of a self-piercing rivet tool includes clamping an upper
workpiece 10 and a lower workpiece 12 between a blank holder 14 and
a die 16. The upper and lower workpieces 10, 12 form a stack 18,
with the upper workpiece 10 being closest to the press tool 20 and
the lower workpiece 12 being closest to the die 16. Though not
shown, an optional material can be disposed between the upper
workpiece 10 and the lower workpiece 12. A single self-piercing
rivet 22 is secured within the blank holder 14. The self-piercing
rivet 22 includes a widened head 24 and a partially hollow
cylindrical stem 26 that terminates in a piercing edge 28. The
length of the stem 26 is selected based on the thickness of the
workpiece stack 18. When driven by the press tool 20, the partially
hollow cylindrical stem 26 flares radially outwardly to join the
upper workpiece 10 to the lower workpiece 12, but does not fully
penetrate the workpiece stack 18. The die 16 defines an open die
cavity 30 that faces the self-piercing rivet 22. The blank holder
14 and the die 16 provide a clamping force to retain the workpiece
stack 18 in position.
[0024] Once positioned between portions of a self-piercing rivet
tool, a transducer 40 (shown in FIG. 7) applies ultrasonic
vibrations to the workpiece stack 18, directly or indirectly, to
decrease the plastic flow stress of the workpiece material,
including materials with high strength and low ductility. The
transducer 40 can include a piezo-electric transducer operable to
vibrate at ultrasonic frequencies, for example frequencies of
greater than 20 kHz, further optionally between 20 kHz and 80 kHz,
still further optionally between 20 kHz and 60 kHz, with the
amplitude of vibration optionally in the range of 2-100 .mu.m,
optionally 2-40 .mu.m. In one embodiment, the transducer 40 directs
continuous ultrasonic vibrations to the workpiece stack 18 for at
least the length of time that the press tool 20 drives the rivet 22
into the workpiece stack 18. In other embodiments, continuous
ultrasonic vibrations are applied to the workpiece stack 18 prior
to the self-piercing rivet 22 being driven by the press tool 20,
for example when the workpiece stack 18 is clamped between the
blank holder 14 and the die 16, but prior to the punch tool 20
driving the rivet 22. In still other embodiments, continuous
ultrasonic vibrations are applied to the workpiece stack 18 at
least prior to and while to the rivet 22 is driven by the press
tool 20.
[0025] As shown in FIGS. 2-4, the ultrasonic vibrations can be
applied in the direction that the rivet 22 is being driven,
perpendicular to the direction that the rivet 22 is being driven,
or rotatively about an axis parallel to the driven that the rivet
22 is being driven. FIG. 2 depicts ultrasonic vibrations as
indirectly applied to the upper workpiece 10 through oscillation of
the press tool 20 at ultrasonic frequencies. FIG. 3 depicts
ultrasonic vibrations as indirectly applied to the upper workpiece
10 through oscillation of the blank holder 14, which avoids
softening of the rivet 22. FIG. 4 depicts ultrasonic vibrations as
indirectly applied to the lower workpiece 12 through oscillation of
the die 16, which also avoids softening of the rivet 22. As the
self-piercing rivet 22 is driven into the upper workpiece 10, the
ultrasonic vibrations propagate to the upper or lower workpiece 10,
12 to locally soften these materials in the region directly between
the rivet 22 and the die 16. During insertion, the cylindrical stem
26 deforms in a radially outward direction, but being inserted
without full penetration of the workpiece stack 18.
[0026] As shown in FIGS. 5-6, the self-piercing rivet tool can
include an ultrasonic horn 42 that is coupled to the transducer 40,
transmitting ultrasonic vibrations parallel to its longitudinal
axis, perpendicular to its longitudinal axis, or rotatively about
its longitudinal axis. The longitudinal axis of the horn 42 can be
oriented at an acute angle relative to the workpiece, for example
an angle of between 30.degree. and 60.degree., further optionally
about 45.degree.. The ultrasonic horn 42 includes a tapered
geometry to augment the amplitude of the transducer 40. Optional
geometries include a conical geometry, an exponential geometry, a
stepped geometry, and combinations of the foregoing. At its tapered
end, the horn 42 defines a contact surface for abutting one of the
upper and lower workpieces 10, 12 of the workpiece stack 18. As
shown in FIG. 5, for example, the horn 42 defines a contact surface
for the upper workpiece 10 adjacent the blank holder 14. As
alternatively shown in FIG. 6, for example, the horn 42 defines a
contact surface for the lower workpiece 12 adjacent the die 16. The
horn 42 (and transducer 40) are optionally biased toward the
workpiece stack 18, such that the ultrasonic vibrations propagate
from the transducer 40, through the ultrasonic horn 42 and into the
workpiece stack 18 for reducing the plastic flow stress of the
workpiece stack 18.
[0027] Referring now to FIG. 7, a circuit diagram for an
electrically operated SPR tool in accordance with one embodiment is
illustrated. The self-piercing rivet tool includes a controller 50
for controlling a supply voltage to a press tool 52 through
operation of a first switch S 1. When activated, the first switch
51 closes a relay 54, which causes operation of the press tool 52
in the direction of a die. The controller 50 is also electrically
coupled to a transducer 40 through a second switch S2 for imparting
ultrasonic vibrations to a workpiece stack while clamped between a
blank holder and a die. When activated, the second switch S2
couples the transducer 40 to a DC voltage (Vcc), which cause the
transducer 40, for example a piezo-electric transducer, to vibrate
at ultrasonic frequencies, for example frequencies of at least 20
kHz. In some embodiments, the second switch S2 is activated (in
response to a command to initiate SPR) a predetermined period prior
to activation of the first switch 51, such that the transducer 40
directs continuous ultrasonic vibrations to the workpiece stack
prior to, and optionally during, activation of the first switch 51,
shown in the timing diagram of FIG. 8. In other embodiments, the
first switch 51 and the second switch S2 are activated
simultaneously, such that the transducer 40 directs continuous
ultrasonic vibrations to the workpiece stack only for the length of
time that the press tool 52 drives the rivet into the workpiece
stack, shown in the timing diagram of FIG. 9. In other embodiments
the self-piercing rivet tool is pneumatically driven. The rivet
tool may additionally be operated to remove self-piercing rivets
with a die specifically for that purpose. During and/or prior to
removal, the transducer can reduce the plastic flow stress of the
workpiece material prior substantially as set forth above when
installing a self-piercing rivet.
[0028] To reiterate, embodiments of the present invention include
the application of ultrasonic energy to soften workpieces to
facilitate self-pierce riveting, either by a transducer imposing
ultrasonic vibration to the rivet tool (e.g., die, blank holder,
punch) or directly to the workpiece(s). In some embodiments, high
frequency ultrasonic vibration is introduced during the riveting
process until the two workpieces are clinched. Different
transducers and/or coupling devices are possible to apply different
modes of vibration in which the direction of the ultrasonic
vibration is in principle parallel to the surface of the
workpieces, perpendicular to the surface of the workpieces, or
cyclic with rotation about an axis that is perpendicular to the
surface of the workpieces. The various modes of vibration can be
combined for a given application to maximize the benefits of
acoustic softening in self-piercing riveting operations.
[0029] The above description is that of current embodiments of the
invention. Various alterations and changes can be made without
departing from the spirit and broader aspects of the invention as
defined in the appended claims, which are to be interpreted in
accordance with the principles of patent law including the doctrine
of equivalents. This disclosure is presented for illustrative
purposes and should not be interpreted as an exhaustive description
of all embodiments of the invention or to limit the scope of the
claims to the specific elements illustrated or described in
connection with these embodiments. For example, and without
limitation, any individual element(s) of the described invention
may be replaced by alternative elements that provide substantially
similar functionality or otherwise provide adequate operation. This
includes, for example, presently known alternative elements, such
as those that might be currently known to one skilled in the art,
and alternative elements that may be developed in the future, such
as those that one skilled in the art might, upon development,
recognize as an alternative. Further, the disclosed embodiments
include a plurality of features that are described in concert and
that might cooperatively provide a collection of benefits. The
present invention is not limited to only those embodiments that
include all of these features or that provide all of the stated
benefits, except to the extent otherwise expressly set forth in the
issued claims. Any reference to claim elements in the singular, for
example, using the articles "a," "an," "the" or "said," is not to
be construed as limiting the element to the singular.
* * * * *