U.S. patent application number 15/884808 was filed with the patent office on 2018-05-31 for rivets.
The applicant listed for this patent is AVDEL UK LIMITED. Invention is credited to Carl HERSANT.
Application Number | 20180149183 15/884808 |
Document ID | / |
Family ID | 54258701 |
Filed Date | 2018-05-31 |
United States Patent
Application |
20180149183 |
Kind Code |
A1 |
HERSANT; Carl |
May 31, 2018 |
RIVETS
Abstract
A rivet for fastening workpiece members, the rivet including a
body comprising a shank extending in a first, longitudinal
direction and a head extending in a second, substantially
transversal direction, a bore being defined through the shank and
the head of the body; and, a stem comprising a main longitudinal
portion arranged for insertion into said bore, and an enlarged
portion arranged for radially expanding the shank when the enlarged
portion is forced into said bore to fasten the workpiece members;
the rivet being configured for insertion into respective apertures
formed in the workpiece members; and the rivet being further
configured such that when the workpiece members are fastened, the
head of the body of the rivet is displaced relative to the shank to
engage with the stem to lock the stem in place relative to the body
and/or the workpiece members.
Inventors: |
HERSANT; Carl; (Hertford,
GB) |
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Applicant: |
Name |
City |
State |
Country |
Type |
AVDEL UK LIMITED |
Sheffield |
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GB |
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|
Family ID: |
54258701 |
Appl. No.: |
15/884808 |
Filed: |
January 31, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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PCT/EP2016/068943 |
Aug 9, 2016 |
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15884808 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F16B 2019/1009 20130101;
Y10T 29/49945 20150115; F16B 19/1054 20130101; B21J 15/045
20130101 |
International
Class: |
F16B 19/10 20060101
F16B019/10; B21J 15/04 20060101 B21J015/04 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 14, 2015 |
GB |
1514543.6 |
Claims
1. A rivet for fastening workpiece members, the rivet comprising: a
body comprising a shank extending in a first, longitudinal
direction and a head extending in a second, substantially
transversal direction, a bore being defined through the shank and
the head; and, a stem comprising a main longitudinal portion
arranged for insertion into said bore, and an enlarged portion
arranged for radially expanding the shank when the enlarged portion
is forced into said bore to fasten the workpiece members; the rivet
being configured for insertion into respective apertures formed in
the workpiece members; and the rivet being further configured such
that when the workpiece members are fastened, the head of the body
of the rivet undergoes displacement relative to the shank to engage
with the stem to lock the stem in place relative to the body and/or
the workpiece members.
2. A rivet according to claim 1, wherein the main longitudinal
portion of the stem comprises at least one stem locking feature to
facilitate the engaging of the head of the body of the rivet with
the stem.
3. A rivet according to claim 2, wherein the at least one stem
locking feature comprises a stem shoulder and/or a stem groove.
4. A rivet according to claim 1, wherein the head of the body of
the rivet comprises at least one body locking feature to facilitate
the engaging of the head of the body of the rivet with the
stem.
5. A rivet according to claim 4, wherein the at least one body
locking feature comprises an inner body shoulder and/or an inner
body groove.
6. A rivet according to claim 1, wherein said head has an outer
curved or domed profile.
7. A rivet according to claim 6, wherein said head has a flat or
curved underhead contact surface for abutment against a
corresponding respectively flat or curved surface of one of the
workpiece members.
8. A rivet according to claim 1, wherein said displacement
comprises pivoting of at least a portion of the head around a
region of the head constrained between a surface of one of the
workpiece members and an outer rim of a tool for setting the
rivet.
9. A rivet according to claim 1, wherein at least a substantial
portion of the head undergoes yielding to enable said displacement
to lock the stem in place relative to the body and/or the workpiece
members.
10. A rivet according to claim 1, wherein the body is formed as a
single piece and/or is made of steel.
11. A rivet according to claim 10, wherein the steel is in an
annealed condition.
12. A rivet according to claim 1, wherein the stem is formed as a
single piece and/or is made from steel.
13. A rivet according to claim 12, wherein the steel is in a
hardened condition.
14. A rivet according to claim 1, wherein the body shank has a
plain cylindrical outer profile, or is splined.
15. A rivet according to claim 14, wherein the body shank includes
a voided section.
16. A rivet according to claim 1, wherein the enlarged portion of
the stem comprises a tapered section arranged to facilitate the
radial expansion of at least part of the body shank.
17. A workpiece comprising a rivet according to claim 1, wherein
said workpiece further includes a curved surface for abutment with
the head of the body of the rivet.
18. A method of fastening workpiece members using a rivet
comprising a body having a shank extending in a first, longitudinal
direction and a head extending in a second, substantially
transversal direction, a bore being defined through the shank and
the head of the body, and a stem having a main longitudinal portion
arranged for insertion into said bore, and an enlarged portion
arranged for radially expanding the shank, the method comprising:
inserting the rivet into respective apertures formed in the
workpiece members; forcing the enlarged portion into said bore to
fasten the workpiece members; and, displacing the head of the body
of the rivet relative to the shank to engage with the stem to lock
the stem in place relative to the body and/or the workpiece
members.
19. A method according to claim 18, wherein the step of displacing
the head of the body relative to the shank to engage with the stem
to lock the stem in place relative to the body and/or the workpiece
member is performed immediately subsequently to the step of forcing
the enlarged portion into the bore to fasten the workpiece
members.
20. A method according to claim 19, wherein the step of displacing
the head of the body relative to the shank to engage with the stem
to lock the stem in place relative to the body and/or the workpiece
member is performed immediately subsequently to, and as a result of
a continuation of a same action responsible for, the step of
forcing the enlarged portion into the bore to fasten the workpiece
members.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation application of
International Application PCT/EP2016/068943 with an international
filing date of Aug. 9, 2016 which claims priority from United
Kingdom Patent Application No. GB1514543.6, filed Aug. 14, 2015,
the disclosure of which is incorporated herein by reference in its
entirety.
FIELD OF THE INVENTION
[0002] The invention relates to rivets (more accurately, rivet
assemblies), for fastening workpiece members. In particular, it
relates to blind rivets. More particularly, it relates to blind
rivets of the break-stem type. Rivets according to the present
invention are capable of providing locked fastening, i.e. a type of
fastening whereby parts of the rivets are locked together to reduce
or eliminate relative movement between those parts independently or
in addition to interactions due to the fastening itself.
BACKGROUND OF THE INVENTION
[0003] Blind rivet assemblies (henceforth, "rivets") of the type
described in this application are used to fasten together workpiece
members. Workpiece members may, for example, take the form of
sheets of material or interconnecting members, such as tubular
members, which need to be fastened together so that their relative
movement is constrained or prevented.
[0004] To fasten the workpiece members together, a blind rivet is
passed through corresponding apertures in the workpiece members and
then set in position using a tool which applies a pulling force to
a stem component/part of the rivet (henceforth, "stem"). The
pulling force applied to the stem causes deformation of a body
component/part of the rivet (henceforth, "body") on the "blind"
side of the fastener, i.e. on the opposite side of the workpiece
from the side on which the tool is applied. The deformation of the
body typically results in a deformed portion of the body being in
contact with the blind side of the workpiece, while a head of the
body is in contact with the other side of the workpiece. The
workpiece members are thus fastened (i.e. held or clamped together)
by and between the deformed portion of the body and the head of the
body.
[0005] The strength of such a fastening and the ability of a set
rivet to continue constraining relative movement of the workpiece
members can be compromised if, once the rivet has been set, the
body and the stem are able to move relative to each other. For
example, if the rivet is a breakstem rivet (wherein a part of the
stem is broken off in the course of the setting operation so that
the stem protrudes less or does not protrude at all from the body
head), the portion of the stem left in the body may recoil and move
within the body, towards the blind side of the workpiece. The stem
can also be caused to move within the body by vibration of the
workpiece members or continued stress applied to the joint. Even a
small movement of the stem relative to the body can reduce the
effectiveness of the fastening. In some cases, the stem may make
its way completely out of the body. This can in addition
significantly reduce the shear strength of the fastening, i.e. the
ability of the fastener to constrain or prevent movement of the
workpiece members in directions substantially orthogonal to the
longitudinal axis of the fastener.
[0006] Locking features that mitigate the aforementioned problems
in rivets are known and come in several different
configurations.
[0007] Some rivets comprise a shoulder in the body bore which
impacts a mating shoulder on the stem to force material, locally,
to deform radially inwardly into a stem locking groove immediately
below the stem shoulder to form the lock. The strength of this lock
is only sufficient to resist recoil for smaller rivets.
[0008] Other types of internal locks involve a locking "lip" formed
in the head bore. The locking lip is displaced into a locking
groove formed in the stem when the rivet is set. However, these
locks are difficult to form and also have limited strength.
[0009] Other locks may comprise a folding skirt on the stem which
his splayed out by a special lipped nose tip of the placing tool,
and which locks into a counterbore in the top of the rivet body
head. However, these designs cannot be applied to stems of high
hardness, as the folding skirt would become brittle and liable to
wear the corresponding lip of the tool nose tip.
[0010] In at least some embodiments, the invention aims to go some
way towards solving or at least mitigating the problems set out
above.
[0011] In at least some embodiments, the invention aims to provide
a simpler locking blind rivet design compared to the prior art.
[0012] In at least some embodiments, the invention aims to provide
a robust lock suited to relatively large workpiece members which
may require relatively large apertures and rivets comprising stems
having high tensile strength (and thus being particularly prone to
recoiling).
SUMMARY OF THE INVENTION
[0013] According to an embodiment of the invention there is
provided a rivet for fastening workpiece members, the rivet
comprising: a body comprising a shank extending in a first,
longitudinal direction and a head extending in a second,
substantially transversal direction, a bore being defined through
the shank and the head; and a stem comprising a main longitudinal
portion arranged for insertion into said bore, and an enlarged
portion arranged for radially expanding the shank when the enlarged
portion is forced into said bore to fasten the workpiece members;
the rivet being configured for insertion into respective apertures
formed in the workpiece members; and the rivet being further
configured such that when the workpiece members are fastened, the
head of the body of the rivet undergoes displacement relative to
the shank to engage with the stem to lock the stem in place
relative to the body and/or the workpiece members.
[0014] In preferred embodiments, the main longitudinal portion of
the stem comprises at least one stem locking feature to facilitate
the engaging of the head of the body of the rivet with the stem.
The at least one stem locking feature may for example comprises a
stem shoulder and/or a stem groove.
[0015] In preferred embodiments, the head of the body of the rivet
comprises at least one body locking feature to facilitate the
engaging of the head of the body of the rivet with the stem. The at
least one body locking feature may comprise an inner body shoulder
and/or an inner body groove, for instance.
[0016] In some embodiments, the head has an outer curved or domed
profile, and said head optionally has a flat or curved underhead
contact surface for abutment against a corresponding respectively
flat or curved surface of one of the workpiece members.
[0017] Preferably, the displacement of the head comprises pivoting
of at least a portion of the head around a region of the head
constrained between a surface of one of the workpiece members and
an outer rim of a tool for setting the rivet. At least a
substantial portion of the head may undergo yielding to enable said
displacement to lock the stem in place relative to the body and/or
the workpiece members.
[0018] Optionally, the body is formed as a single piece and/or is
made of steel, optionally in an annealed condition. Analogously,
the stem may be formed as a single piece and/or be made from steel,
optionally in a hardened condition.
[0019] The body shank may have a plain cylindrical outer profile,
or be splined. Optionally the body shank may include a voided
section.
[0020] Preferably, the enlarged portion of the stem comprises a
tapered section arranged to facilitate the radial expansion of at
least part of the body shank.
[0021] Optionally, the workpiece comprises a curved surface for
abutment with the head of the body of the rivet.
[0022] According to another embodiment of the invention there is
provided a method of fastening workpiece members using a rivet
comprising a body having a shank extending in a first, longitudinal
direction and a head extending in a second, substantially
transversal direction, a bore being defined through the shank and
the head of the body, and a stem having a main longitudinal portion
arranged for insertion into said bore, and an enlarged portion
arranged for radially expanding the shank, the method comprising:
inserting the rivet into respective apertures formed in the
workpiece members; forcing the enlarged portion into said bore to
fasten the workpiece members; and displacing the head of the body
of the rivet relative to the shank to engage with the stem to lock
the stem in place relative to the body and/or the workpiece
members.
[0023] Preferably, the step of displacing the head of the body
relative to the shank to engage with the stem to lock the stem in
place relative to the body and/or the workpiece member is performed
immediately subsequently, and optionally as a result of a
continuation of a same action responsible for the step of forcing
the enlarged portion into the bore to fasten the workpiece
members.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] Specific embodiments of the invention will now be described
by way of non-limiting examples, in which:
[0025] FIG. 1 illustrates in cross section a rivet assembly
according to an embodiment of the invention;
[0026] FIG. 2 illustrates in cross section the fastener of FIG. 1
after it has been installed in a tool and inserted through
apertures in a workpiece and is at the beginning of a setting
operation. In this figure and FIGS. 3 to 7, the pulling jaws and
some other components of the tool have been omitted for
clarity;
[0027] FIG. 3 illustrates in cross section the fastener of FIGS. 1
and 2 which is part way through the setting operation;
[0028] FIG. 4 illustrates in cross section the fastener of FIGS. 1
to 3 at a later stage in the setting operation;
[0029] FIG. 5 illustrates in cross section the fastener of FIGS. 1
to 4 further through the setting operation;
[0030] FIG. 6 illustrates in cross section the fastener of FIGS. 1
to 5 still further through the setting operation;
[0031] FIG. 7 illustrates in cross section the fastener of FIGS. 1
to 6 when the setting operation has been completed;
[0032] FIG. 8 illustrates in cross section a rivet assembly
according to an embodiment of the invention after it has been
installed in a tool and inserted through apertures in a differently
shaped workpiece and is at the beginning of a setting operation. In
this Figure and FIGS. 9 to 13, the pulling jaws of the tool have
been included;
[0033] FIG. 9 illustrates in cross section the fastener of FIG. 8
which is part way through the setting operation;
[0034] FIG. 10 illustrates in cross section the fastener of FIGS. 8
and 9 at a later stage in the setting operation;
[0035] FIG. 11 illustrates in cross section the fastener of FIGS. 8
to 10 further through the setting operation;
[0036] FIG. 12 illustrates in cross section the fastener of FIGS. 8
to 11 still further through the setting operation; and
[0037] FIG. 13 illustrates in cross section the fastener of FIGS. 8
to 12 when the setting operation has been completed.
DETAILED DESCRIPTION
[0038] The present embodiments represent the best ways currently
known to the applicant of putting the invention into practice, but
they are not the only ways in which this can be achieved. They are
illustrated, and they will now be described, by way of example
only.
[0039] In FIG. 1 a blind breakstem rivet assembly 11 is
illustrated. The fastener 11 includes a body 13 and a stem 15. The
body 13 defines an axial bore along its length, inside which the
stem 15 is received and positioned. The body 13 includes a body
shank 17 and a radially enlarged body head 21.
[0040] The body shank 17 extends substantially in a first
direction, approximately parallel to the axis of the fastener 11,
i.e. approximately parallel to the longitudinal axis of the body 13
and to the longitudinal axis of the stem 15. Prior to setting of
the fastener 11 in a workpiece (i.e. when the fastener 11 is in the
condition illustrated in FIG. 1), the body head 21 is arranged such
that an underhead contact surface 22 of the body head 21 (for
contacting an outer surface of a workpiece such as the workpiece 19
illustrated in FIGS. 2 to 7 or the workpiece 119 illustrated in
FIGS. 8 to 13) lies substantially in one plane, i.e. is
approximately flat. The plane is approximately orthogonal to the
first direction, i.e. approximately orthogonal to the longitudinal
axis of the body 13 and to the longitudinal axis of the stem 15. In
the illustrated example, the body head 21 has a domed outer surface
against which an installation tool will be pushed during setting of
the fastener 11 (see FIGS. 2 to 7 and FIGS. 8 to 13). In other
examples, the body head 21 may have a different outer surface
profile, such as a flat or stepped profile.
[0041] In the described embodiment, the rivet body 13 also includes
a body locking feature 23. As the skilled person will appreciate,
the locking mechanism of the rivet is in addition to the main
fastening mechanism. In the illustrated example, the body locking
feature 23 is a shoulder 23 in the interior of the body 13, i.e. on
the internal wall defining the axial bore of the body 13. The
shoulder 23 is at the transition between a region 29 of reduced
bore diameter at the head end of the body 13 (i.e. the end of the
body 13 where the head 21 is located) and a region 31 of greater
bore diameter closer to the tail end of the body 13 (i.e. the
opposite end of the body 13 from the head end).
[0042] In other examples, the locking feature 23 may take different
forms. The locking feature 23 may for example be a protrusion which
protrudes radially inwardly from the internal wall of the body 13
(i.e. the wall defining the axial bore of the body 13) and extends
for only a short distance along the axis of the body 13. The
protrusion may extend all the way round the circumference of the
bore of body 13, forming a continuous, annular protrusion in a
plane substantially orthogonal to the longitudinal axis of the
fastener 11, or extend only part way round the bore of the body 13.
If the protrusion extends only part way round the bore of the body
13, there may be several protrusions spaced around the
circumference of the bore of body 13.
[0043] The body locking feature 23 is configured (e.g. sized and
shaped) such that it corresponds approximately to a stem locking
feature 25. In the illustrated example, the stem locking feature 25
comprises a shoulder 26 and a groove 28 in the outer surface of the
stem 15. The shoulder 26 extends round the circumference of the
stem 15, forming a continuous, annular shoulder in a plane
substantially orthogonal to the longitudinal axis of the stem 15.
The groove 28 similarly extends round the circumference of the stem
15, forming a continuous annular groove in a plane substantially
orthogonal to the longitudinal axis of the stem 15. The shoulder 26
is at the transition between a region 33 of greater stem diameter
and a region 35 of narrower stem diameter. The groove 28 is in the
region 35 of narrower stem diameter and is of narrower diameter
than the portions of stem 15 axially immediately either side of the
groove 28.
[0044] In other examples, the stem locking feature 25 may take
different forms. The shoulder and/or the groove may, in some
examples, not be continuous, i.e. may extend only part way round
the circumference of the stem 15. In such cases, there may be
several separate shoulders and/or grooves spaced around the
circumference of the stem 15. The separate shoulders and/or grooves
may give the stem locking feature 25 a castellated appearance.
[0045] The stem 15 includes a stem enlarged portion 27. During
installation of the fastener 11 in a workpiece 19 (see FIGS. 2 to 7
and FIGS. 8 to 13), a pulling force is applied to the stem 15 by an
installation tool 51 at the opposite end of the stem 15 from the
enlarged portion 27. The pulling force draws the stem 15 through
the body 13, towards the head end of the body 13 (towards the left
in the examples of FIGS. 1 to 7 and FIGS. 8 to 13). The stem
enlarged portion 27 causes the shank 17 of the body 13 to deform
radially outwardly as the enlarged portion 27 passes through the
shank 17, as illustrated in FIGS. 2 to 7 and FIGS. 8 to 13. This
leads to the formation of a radially enlarged bulb on the blind
side of the workpiece 19 (i.e. the opposite side of the workpiece
19 from the side on which the installation tool 51 is applied). In
the examples illustrated in the Figures, the right-hand side of the
workpiece 19 is the blind side on which the enlarged bulb is
formed.
[0046] FIG. 2 shows the fastener 11 of FIG. 1 after it has been
inserted into a workpiece 19 comprising two workpiece members 191
and 192. A tool 51 is pushed against the body head 21 and will be
used to set the fastener 11 in the workpiece 19 by applying a
pulling force to the stem 15. The skilled person will appreciate
that the invention can be applied to two as well as more than two
workpiece members simultaneously depending on specific
applications.
[0047] FIGS. 3 to 7 illustrate the movements of the body 13, the
stem 15 and the workpiece 19 during the setting operation. In FIG.
3 the stem enlarged portion 27 has been drawn into the shank 17 of
the body 13, causing the radially outward movement of the shank 17
described above. The shoulder 26 of the stem locking feature 25 is
approaching the shoulder 23 that forms the body locking feature 23
in the illustrated example.
[0048] When the stem 15 has been drawn sufficiently far through the
body 13, the stem locking feature 25 and the body locking feature
23 will come into contact with one another. In the illustrated
example, the shoulder 26 of the stem 15 will come into contact with
the shoulder 23 of the body 13. This stage of the setting operation
is illustrated in FIG. 4.
[0049] As the stem 15 is drawn still further through the body 13, a
force is applied to the body locking feature 23 via the stem
locking feature 25. The force applied to the body locking feature
23 promotes displacement/deformation of at least part of the body
13. The verbs "displace" and "deform" (and their derivatives) in
this context mean any "change in shape or form or configuration"
and are intended to include (but are not limited to) the body 13
changing in shape or configuration by rotation or pivoting of one
or more parts of the body 13 relative to other parts of the body;
and one or more parts of the body 13 elongating or contracting,
e.g. by flow of material from one part of the body 13 to another
part of the body 13. As will be described in more detail below, the
displacement/deformation of the body 13 gives rise to a locking
connection between the body 13 and the stem 15.
[0050] In the illustrated example, the shoulder 26 of the stem 15
applies a force to the shoulder 23 of the body 13 as the stem 15 is
pulled by the installation tool. The force causes the body head 21
to deform/displace.
[0051] FIG. 5 illustrates the fastener 11 at a later stage in the
setting process, after the body locking feature 23 and the stem
locking feature 25 have come into contact with each other and the
body head 21 has begun to deform/displace. The force applied to the
body 13 by the stem 15 has caused the body head 21 to pivot about
the point at which the radially enlarged head 21 and the body shank
17 are connected. The head 21 has pivoted such that the radially
outermost part 37 of the head 21 is still in contact with the
workpiece 19, but an underhead recess 39 has been formed, leaving a
gap between the workpiece 19 and part of the underhead contact
surface 22 of the body head 21 that is radially inward of the
radially outermost part 37. The underhead contact surface 22 no
longer lies substantially in one plane, i.e. is no longer
approximately flat.
[0052] Part of the shank 17 has been drawn through the aperture in
the workpiece 19 and out onto the tool-side of the workpiece 19.
This may be as a result of the whole of the shank 17 moving further
towards the tool side of the workpiece 19, or as a result of part
of the shank 17 deforming by elongating, depending on the extent of
deformation of the tail end of the shank 17 through axial
contraction and/or radial expansion.
[0053] When the fastener 11 has reached the stage of installation
illustrated in FIG. 5, the body locking feature 23 (shoulder 23 in
the illustrated example) is the radially innermost part 41 of the
head 21. The shoulder 23 has pivoted about the point at which the
head 21 is connected to the shank 17. The shoulder 23 is still in
contact with the stem locking feature 25 (shoulder 26 in the
illustrated example).
[0054] When the head 21 has pivoted sufficiently relative to the
body shank 17, the head 21 will be prevented by the installation
tool 51 from pivoting further, as will be described in more detail
below. Continued or increased application of force to the stem 15
by the installation tool 51 may thereafter cause other types of
deformation of the head 21 (i.e. distinct from pivoting of the head
21). It may, in particular, cause further displacement/deformation
of the body locking feature 23 (shoulder 23) into the groove 28 on
the stem 15 (if possible), and corresponding deformation of the
head and/or shank material next to the body locking feature 23 to
enable the deformation of the body locking feature 23. This
deformation arises as a consequence of a contact force applied by
the tool 51 to the head 21, wherein the contact force has a
component which acts radially inwardly. Such deformation of the
shoulder 23 to occupy more of the groove 28 is illustrated in FIG.
6.
[0055] There will come a point at which further force applied to
the stem 15 will cause the stem 15 to fracture at a break groove
43. After the stem 15 has fractured, part of the stem 15 is left
within the body 13, and part of the stem 15 is removed by the tool.
The fracturing of the stem 15 at the break groove 43 is illustrated
in FIG. 7. The fracturing of the stem 15 completes the fastener
installation process.
[0056] The deformation of the body 13 (including the pivoting of
the head 21) during setting of the fastener 11 gives rise to
locking engagement of the body locking feature 23 and the stem
locking feature 25. In particular, the deformation of the head 21
causes the shoulder 23 to enter the groove 28 in the outer surface
of the stem 15.
[0057] The engagement of the body locking feature 23 and the stem
locking feature 25 constrains the relative movement of the body 13
and the stem 15. In particular, the fact that the shoulder 23 has
entered the groove 28 limits the extent to which the stem 15 can
slide axially within the bore of the body 13. Thus, the engagement
of the body locking feature 23 and the stem locking feature 25
helps prevent the stem 15 from recoiling out of the body 13 when
the stem 15 fractures at the break groove 43, and/or from being
shaken loose from the body 13 by vibration of the workpiece 19
after the installation process.
[0058] Retaining the stem 15 within the body 13 in this way may
improve the shear strength of the fastener 11, e.g. the ability of
the fastener to constrain sliding of one workpiece member relative
to the other in a direction substantially orthogonal to the
longitudinal axis of the fastener 11, because of the strength of
the material forming the stem 15.
[0059] Retaining the stem 15 within the body 13 may alternatively
or additionally improve the tensile strength of the fastener, e.g.
the ability of the fastener 11 to prevent separation of the
workpiece members in a direction substantially parallel to the
longitudinal axis of the fastener 11.
[0060] As illustrated in FIGS. 2 to 7 and in FIGS. 8 to 13, the
tool 51 for installing the fastener 11 has a contact face 53 (see,
for example, FIG. 2 or FIG. 8). In the illustrated examples, the
contact face 53 is a concave contact face. The approximate radius
of curvature of the contact face 53 is smaller than the approximate
radius of curvature of the outer surface of the body head 21. When
the contact face 53 of the tool 51 is first pressed against the
body head 21, the contact face 53 contacts the body head 21 only on
a first contact ring 55 near the radially outermost portion of the
contact face 53. There is a gap between the radially inward portion
of the contact face 53 and the radially inward portion of the body
head 21, as illustrated in FIGS. 2 to 4 and FIGS. 8 to 11.
[0061] As the tool 51 pulls on the stem 15 to set the fastener 11
in position, the body head 21 pivots, as previously described. As
the body head 21 pivots, the approximate radius of curvature of the
domed body head 21 as a whole decreases, and the radially inward
portion of the body head 21 approaches the radially inward portion
of the contact face 53, closing the gap between the radially inward
portion of the contact face 53 and the radially inward portion of
the body head 21. The body head 21 eventually pivots to such an
extent that the head 21 cannot pivot any further in that direction.
This is because the radially inward portion of the head 21 comes
into contact with the radially inward portion of the contact face
53 on a second contact ring 57, as illustrated in FIG. 5 and FIG.
12.
[0062] When the body head 21 is in contact with the contact face 53
on the second contact ring 57 and the stem 15 is pulled further,
the body head 21 cannot pivot as it did previously. The reaction
force that the second contact ring 57 exerts against the surface of
the body head 21 overcomes the force that tends to pivot the head
21. The reaction force has a component which is radially inward.
The radially inward force applied to the body head 21 helps promote
the deformation (e.g. extension and/or rounding) of the shoulder 23
into the groove 28. In this way, an axial force applied to the stem
15 by the tool 51 gives rise to a radially inward force applied to
the body head 21. The radially inward force promotes deformation of
the body locking feature 23 into the stem locking feature 25,
thereby helping to constrain relative moment of the body 13 and the
stem 15.
[0063] The tool 51 may be arranged such that the second contact
ring 57 is at or near the most radially inward portion 54 of the
contact face 53. Advantageously this may reduce marking of the body
head 21 caused by application of the tool 51 to the fastener 11.
The contact face 53 may include a substantially flat portion at the
most radially inward portion 54, to further minimise marking of the
body head 21 caused by the contact face 53. The contact face 53 may
be arranged such that its inner radius is approximately equal to
the radius of the bore through the body 13 for a given fastener
11.
[0064] As well as improving the strength of the fastening, the
engagement of the body locking feature 23 and the stem locking
feature 25 through the deformation of the body head 21 helps make
the installed fastener more tamper-proof.
[0065] As discussed above, during setting of the fastener 11 in a
workpiece, the domed body head 21 pivots about the point at which
it is connected to the shank 17. As the head 21 pivots, the
approximate radius of curvature of the head 21 as a whole
decreases, and the radially inward portion of the outer surface of
the body head 21 approaches the radially inward portion of the
contact face 53, closing the gap between the radially inward
portion of the contact face 53 and the radially inward portion of
the body head 21. This deformation/displacement of the body head 21
allows the radially outermost part 37 of the head 21 to remain in
contact with the workpiece, maintaining a better seal of the body
head 21 against the workpiece. This effect is particularly
advantageous when the fastener 11 is used with curved workpieces,
as the radially outermost part 37 of the head 21 pivots and stays
in contact with the curved surface of the workpiece.
[0066] In FIGS. 8 to 13 a fastener 11 according to an embodiment of
the invention is shown being set in a flat workpiece 119 rather
than a curved workpiece 19 as illustrated in FIGS. 2 to 7. Indeed,
the fastener 11 may be used with various shapes of workpiece and is
not intended to be limited to use with a curved workpiece or a flat
workpiece.
[0067] The steps of the setting process illustrated in FIGS. 8 to
13 substantially correspond to the steps illustrated in FIGS. 2 to
7. In FIGS. 8 to 13, jaws 59 forming part of the installation tool
51 are shown. The jaws 59 (which were omitted from FIGS. 2 to 7)
are included for illustrative purposes in FIGS. 8 to 13. The jaws
59 are used to grip a pulling portion of the stem 15 and to apply
the pulling force discussed above.
[0068] As noted above, although in the illustrated examples the
body head 21 has a domed outer surface, in other examples, the body
head may have a different profile, such as a flat top. Similarly,
although the illustrated contact face 53 of the installation tool
51 is a concave contact face, in other examples, the contact face
may take a different form, provided that there is a gap between the
radially inward portion of the body head 21 and the radially inward
portion of the contact surface to allow the
displacement/deformation necessary for the locking to take place.
The surface could for example take the form of a conical or
frustoconical surface, or a stepped surface.
[0069] In some embodiments, the shank 17 of the body 13 may include
a voided section which may promote filling of the apertures in the
workpiece members on installation of the fastener 11.
[0070] The materials of the body 13 and the stem 15 may be selected
so that deformation of the body head 21 is promoted and deformation
of the stem 15 is resisted during the setting operation. The body
13 may for example include a relatively soft steel or other
suitable material, and the stem 15 may include a relatively hard
steel or other suitable material.
* * * * *