U.S. patent application number 10/565610 was filed with the patent office on 2006-10-26 for blind fastener and method of setting.
This patent application is currently assigned to NEWFRY LLC. Invention is credited to Stephen John Morris, Daniel R. Smith.
Application Number | 20060236739 10/565610 |
Document ID | / |
Family ID | 27772565 |
Filed Date | 2006-10-26 |
United States Patent
Application |
20060236739 |
Kind Code |
A1 |
Smith; Daniel R. ; et
al. |
October 26, 2006 |
Blind fastener and method of setting
Abstract
There is disclosed herein a method of connecting together at
least two workpieces (30, 32) using a blind rivet (10), which
comprises the steps of biasing a blind side end face of a blind
rivet (10) against a workpiece (30) and subsequently effecting
rotation (41) of the blind rivet (10) whilst in abutment with the
workpiece (30) to create a heat weakened region of the workpiece
through which the blind rivet (10) can subsequently be inserted by
a biasing force less than a biasing force normally required to
effect piercing of the workpiece (30, 32) by such a blind rivet
(10).
Inventors: |
Smith; Daniel R.;
(Worcestershire, GB) ; Morris; Stephen John;
(Sutton Coldfield, GB) |
Correspondence
Address: |
HARNESS, DICKEY & PIERCE, P.L.C.
P.O. BOX 828
BLOOMFIELD HILLS
MI
48303
US
|
Assignee: |
NEWFRY LLC
1207 Drummond Plaza
Newark
DE
19711
|
Family ID: |
27772565 |
Appl. No.: |
10/565610 |
Filed: |
July 16, 2004 |
PCT Filed: |
July 16, 2004 |
PCT NO: |
PCT/EP04/07915 |
371 Date: |
January 23, 2006 |
Current U.S.
Class: |
72/67 |
Current CPC
Class: |
B21C 37/298 20130101;
B21J 15/027 20130101 |
Class at
Publication: |
072/067 |
International
Class: |
B21B 1/00 20060101
B21B001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 24, 2003 |
GB |
0317307.7 |
Claims
1. A method of connecting together at least two workpieces using a
blind rivet comprising the steps of positioning the at least two
workpieces in abutment; positioning a blind side end face of a
blind rivet against a first one of said workpieces and applying a
biasing force thereto to maintain said rivet in engagement with
said workpiece; rotating said rivet at a speed whilst maintaining
said biasing force thereon; utilizing said biasing force to drive
said rotating blind rivet through the resultant heat weakened
workpieces; stopping rotation of said inserted rivet and setting
said blind rivet to compress the workpieces between a deformed
portion of the rivet body and a flange portion.
2. A method as claimed in claim 1 wherein said rivet is rotated at
a speed of at least 200 rpm.
3. A method as claimed in claim 1 wherein said biasing force is
determined to be less than that required to force the blind rivet
through the non-weakened workpiece.
4. A method as claimed in claim 1 wherein said biasing force is
between 2 kN and 10 kN.
5. A method as claimed in claim 4 wherein said biasing force is
between 4 kN and 8 kN.
6. A method as claimed in claim 1 wherein said rivet is rotated at
a speed of between 300 rpm and 1000 rpm.
7. A method as claimed in claim 1 using a blind rivet wherein said
blind side end face comprises an abrasive surface.
8. A method as claimed in claim 1 using a blind rivet having a
blind side end face with a workpiece engaging portion having a
contact area less than the cross sectional area of the rivet.
9. A method as claimed in claim 8 using a blind rivet with a
tapered or frusto-conical blind side end face.
10. A method as claimed in claim 1 wherein the step of rotating and
setting the blind rivet is carried out using the same tool.
11. A blind rivet for use in the method as claimed in claim 1
having a parabolically curved blind side end face disposed
co-axially with a longitudinal axis of said rivet.
12. A blind rivet for use in the method as claimed in claim 1
having a frusto-conical blind side end face disposed co-axially
with a longitudinal axis of said rivet.
13. A blind rivet as claimed in claim 12 having an elongate
cylindrical projection extending co-axially from said
frusto-conical end face.
14. A blind rivet as claimed in claim 11 comprising an open ended
rivet body and wherein said blind side end face is formed on a
mandrel head extending beyond said rivet body.
15. A blind rivet as claimed in claim 11 comprising a closed end
blind rivet wherein said blind side end face is formed on said
closed end of said rivet body.
16. A blind rivet as claimed in claim 11 wherein said blind side
end face is formed with an abrasive surface.
17. A blind rivet as claimed in claim 16 wherein said abrasive
surface comprises a coating of abrasive material.
18. A blind rivet comprising a workpiece engaging blind side end
face, wherein said end face is provided with an abrasive
surface.
19. (canceled)
Description
[0001] The present invention relates to blind fasteners of the type
that can be inserted through a workpiece and secured therein by a
setting operation carried out from one side of such workpiece. More
particularly this invention is directed to a blind fastener
ublising a pull mandrel to effect the setting operation by
compressing and deforming the tubular body of the fastener to
compress such workpiece between the deformed part of the body and a
radially extending flange arid an improved method of setting such
fastener and connecting workpieces thereby. Wherein numerous
variants of the blind fastener are known, the most commonly
available will be in the blind rivet, as example of which is such
as that sold by the Applicant under their registered trade mark
POP.RTM..
[0002] Conventional blind rivets are used in areas where access to
both sides of an appropriate workpiece to be secured is difficult
or not possible. The conventional blind rivet is then inserted
through pre-formed holes in the workpiece or workpieces whereby the
rivet body is subsequently compressed by a compressive force
applied to the mandrel of such rivet causing the rivet body to
expand within the hole and to also form a compressed joint on the
blind side of the workpiece which compresses the workpiece between
such deformed body and the mandrel head. Since the rivet body is
compressed by the mandrel, the rivet body expands within the hole
and a robust joint is achieved and the workpiece parts are pulled
into intimate contact with each other. Conventional blind rivets
require previously prepared holes in the workpiece materials. This
results in frequent instances in which these holes are larger than
those specified for good blind rivet practice, which can be caused
due to difficulties in hole alignment and/or as a result of the
cumulation of hole tolerances. This is particularly common with
large workpieces of relatively thin material, such as employed in
automotive bodies. In addition, conventional blind rivets can have
difficulty in achieving the necessary hole filling and clamping
performance in larger holes and there is also an attendent
difficulty in insertion of the rivet through the workpiece material
due to the holes over-lapping one another. If the rivets cannot
achieve good hole filling and clamping, especially where the joint
is subjected to vibration or deflection, the workplece parts can
begin to move relative to one another resulting in squeaks and
rattles or even to distortion of the holes.
[0003] One attempt to address such problem has been the development
of a self-drilling blind rivet such as that disclosed in an earlier
British patent held by the Applicant, GB Patent No 1484259. Here,
the blind rivet is provided with an appropriate drill-point
incorporated into the mandrel head which is rapidly rotated and
brought into contact with the workpieces to effect a drilling
operation to cut through the workpiece. Once a hole has been
drilled using this self-drilling blind rivet it can then be pushed
through such hole and set in a conventional manner. However, a
major draw back of such self drilling blind rivets is that they are
expensive to manufacture, requiring a specialised cutting edge
formed onto the mandrel head and further require the use of
expensive application tools. Additional disadvantages of such
self-drilling blind rivets is that during the drilling operations
small chips from the drilling is generated which, if produced in a
sealed container or difficult to access area, may result in debris
remaining in the finished article.
[0004] Secondly, after setting of the self-drilling blind rivets,
the protruding drill point remains on the retained mandrel head,
creating a sharp and potentially dangerous projection which could,
in many instances, present a hazard.
[0005] As a further alternative to using blind rivets for holding
workpieces together which require preformed holes, there has been
developed self-piercing rivets which are characterised by their
semi tubular form and which may be used to secure two workpieces
together in the absence of any pre-prepared holes. These
self-piercing rivets necessitate access to both sides of the
workpiece whereby it is then possible to arrange for a single rivet
to be forced through a first workpiece and into, but not through,
the second workpiece material and to be expanded therein to secure
together the two workpieces. Such operation however does
necessitate that the workpiece materials are securely clamped
together prior to the setting operation (thereby necessitating
access to both sides of the workpiece) whilst it Is also very
difficult to determine whether or not a good joint has been created
since there is no visible means of detecting whether sufficient
deformation of the self-piercing has occurred within the lower
workpiece material thickness. Also, where a workpiece thickness is
thin, and normally below 1 mm, or a combined thickness of less than
2mm, self-piercing rivets have difficulty in achieving a
satisfactory joint without piercing through these materials. The
self-piercing rivets are also not applicable if non-metallic, and
particularly plastic materials, are used.
[0006] It is therefore an object of the present invention to
provide a method of securing together two or more workplaces by use
of a blind fastener without the need of preformed holes and in a
manner which alleviates the aforementioned problems within the art.
A further object is to provide a blind fastener for use in such a
novel method.
[0007] According to the present Invention there is now provided a
method of connecting together at least two workpieces using a blind
rivet which comprises the steps of firstly positioning the at least
two workpieces in abutment, positioning a blind side end face of a
blind rivet against a first one of said workpieces and applying a
biasing force thereto to maintain the rivet in engagement with the
workpiece, rotating the rivet at a speed whilst maintaining the
biasing force thereon, thus utilising the biasing force to drive
the rotating blind rivet through the resultant heat weakened
workpieces, stopping rotation of the inserted rivet and setting the
blind rivet to compress the workpieces between a deformed portion
of the rivet body and a flange portion thereof. The frictional
resistance to rotation of the rivet body abutting the workpiece
when held in abutment thereof generates a local heat around the
area of contact serving to weaken the workpiece and allowing the
biasing force to be sufficient to force the blind rivet through
such weakened material, thereby minimising the force necessary to
force the rivet through a workpiece and reducing and alleviating
the possibility of deformation of the workpiece in the area of
insertion of the rivet.
[0008] Preferably, the rivet is rotated at a speed of at least 200
rpm.
[0009] Preferably, the biasing force is predetermined so as to be
less than that required to force the blind rivet through the non
weakened workpiece and will usually be between 2 kN and 10 kN (kilo
Newton) and preferably this biasing force is between 4 kN and 8 kN
for low carbon steel workpieces. For aluminium, this biasing force
may be between 2 kN and 6 kN.
[0010] These forces are insufficient to effect normal displacement
of a blind rivet through conventional workpieces.
[0011] Preferably, the speed of rotation of the rivet in abutment
with the workpiece will be between 300 rpm and 1,000 rpm.
[0012] To increase the frictional resistance between the rotating
rivet and the workpiece, the method may employ use of a blind rivet
wherein the blind side end face comprises an abrasive surface,
which may serve to Increase frictional engagement and heat
generation by such relative rotation.
[0013] Preferably, the method will employ the use of a blind rivet
having a blind side end face with a workpiece engaging portion
having a contact area less than the cross sectional area of the
rivet thereby increasing the pressure exerted by the rivet on the
workpiece via the biasing force. Such a blind rivet will usually be
provided with a tapered or frusto-conical blind side end face.
[0014] It is preferred that the step of rotating and subsequently
setting the blind rivet can be carried out using the same tool, a
specialised rotational blind rivet setting tool. This allows a one
step insertion and setting operation significantly reducing the
time and hence associated costs in connecting together two
workpieces as compared to the previous method of firstly
pre-drilling a hole then inserting and setting the blind rivet.
[0015] Further, according to the present invention there is also
provided a blind rivet for use in the aforementioned method having
a parabolically curved blind side end face disposed co-axially with
a longitudinal axis of the rivet. Alternatively, there is also
provided a blind rivet for use in the aforementioned method having
a frusto-conical blind side end face disposed co-axially with the
longitudinal axis of the rivet, preferably having an elongate
cylindrical projection extending co-axially from such
frusto-conical end face.
[0016] Either of these blind rivets may comprise either an open
ended rivet body wherein the blind side end face is formed on a
mandrel head extending beyond such rivet body, or alternatively may
comprise a closed end blind rivet wherein the blind side end face
is formed on the closed end of the rivet body. In either case, the
blind side end face may be formed with an abrasive surface so as to
enhance frictional resistance when rotated against a workpiece.
This abrasive surface would preferably comprise a coating of
abrasive material.
[0017] Still further according to the present invention there is a
provided a blind rivet comprising a workpiece engaging blind side
end face wherein such end face is provided with an abrasive
surface.
[0018] A preferred embodiment of the present invention will now be
described, by way of example only, with reference to the following
illustrative drawings in which:--
[0019] FIG. 1 is a side elevation schematically illustrating the
rotation and insertion of a blind rivet according to the present
invention; and
[0020] FIG. 2 is a side view of the blind rivet of FIG. 1 in a set
configuration; and
[0021] FIG. 3 is a side view of three variant designs of blind
rivet for insertion using the method shown and described with
reference to in FIG. 1; and
[0022] FIG. 4 is a side elevation of a blind rivet setting tool
utilising the method of the present Invention.
[0023] The present invention is directed to a specific and novel
means of inserting blind fasteners, and particularly blind rivets,
into workpiece materials without pre-prepared holes. In its
simplest form, this is achieved by utilising the rivets to generate
its own hole by rotating the rivet and simultaneously applying
pressure to the rivet against the workpiece. Rotation of the rivet
results in the generation of heat by virtue of work done overcoming
the friction between the rivet and the surface of the workpiece,
whereby the heat will soften or reduce the strength of the
workpiece material locally to the area of contact such that the
rivet can then be inserted under a much lower load through the
weakened workpiece. This can be achieved by using an attachment to
a static multi-head rivet setting machine or by a special purpose
hand-held tool that combines both a means of rotating the rivet and
also a means of subsequently setting such blind rivet.
[0024] Referring now to FIG. 1, the basic operation and principle
of the present invention is now shown. A conventional blind rivet
(10) is shown comprising a substantially cylindrical tubular body
(12) disposed concentrically about a rivet axis (A) and having a
uniform external diameter. A front end of such rivet body is
provided with a radially extending flange portion (14) having a
greater external diameter than that of the body (12). This flange
portion forms a radial shoulder portion (16) extending
substantially perpendicular to the rivet axis (A). A rivet mandrel
(18) comprises a cylindrical mandrel stem (20) which passes through
the cylindrical body (12) so as to be substantially coaxial about
the rivet axis (A) and which is usually received in a close
frictional fit within the internal diameter of the rivet body. A
remote end of the mandrel (18) is provided with a mandrel head (22)
having a greater diameter than the mandrel stem and which mandrel
head diameter is substantially equal to or slightly greater than
the external diameter of the rivet body (10). A shoulder portion is
formed between the mandrel head and the mandrel stem (20) which
then sits and abuts with the longitudinally facing tail end portion
(24) of the rivet body (12) remote from the mandrel head (14). This
Is a standard blind rivet configuration and is readily understood
by those skilled in the art and need not be described in any great
detail herein. The mandrel stem (18) is further provided with a
weakened or narrow neck portion by which the mandrel stem can be
broken during the setting operation at a predetermined position
under a predetermined load. The setting operation will briefly be
described below.
[0025] Blind rivets (10) of this type are used for connecting
together two or more workpieces whereby access to a remote or blind
side of such workpiece is often difficult or not permitted. An
example of such an inaccessible workpiece would be the connection
of a first workpiece in the form of a rung or tread of a ladder to
an aluminium box section as part of a domestic step ladder
assembly. The box section does not permit access to its interior
surface and thus any fastener can only be secured from external
engagement. This is schematically illustrated in FIG. 1 whereby the
ladder tread is shown schematically as workpiece (30) and thus box
section is shown in part section by reference numeral (32).
[0026] Once the first workpiece (30) has been positioned and
correctly aligned relative to the second inaccessible workpiece
(32) the blind side of the rivet (10), notably in this embodiment,
the mandrel head (22), is moved into engagement with the first
workpiece (30) and an appropriate engagement force Is applied
thereto and illustrated schematically by arrow (40) so as to force
the rivet head (22) into engagement with the workpiece (30). The
engagement force applied to the rivet which effectively serves as a
biasing force to maintain the rivet in engagement with the
workpiece, is predetermined so as to be sufficient to allow the
rivet to be subsequently forced through the workpiece when weakened
as will be described below, but is insufficient to effect
displacement of the blind rivet through the workpiece in an
unweakened condition. It is also preferred that the biasing force
is pre-selected such that unwarranted deformation of the workplece
in the region of the blind rivet is avoided. For this reason, it is
preferred that the biasing force will be between 2 kN and 10 kN.
Preferably this biasing force is between 4 kN and 8 kN and will, of
course, vary for different workpiece materials. For examples, for
aluminium workpieces the biasing force may be in the range of 2 kN
and 6 kN whereby for plastic material such biasing forces may
reside In the range of 2 kN and 4 kN. Obviously, different
materials and grades of materials and thickness will dictate the
choice of rotational speed and biasing force.
[0027] In the embodiment shown in FIG. 1 the mandrel head (22) has
been modified so as to be suitable for appropriate blind spin
riveting. Effectively, a contact projection (42) having a smaller
cross sectional end face than the cross sectional area of the
entire mandrel head is provided. Obviously, the smaller the cross
sectional area of contact between the blind rivet and the workpiece
will increase the pressure being applied by the rivet (10) on that
workpiece. In this embodiment a remote end projection (42) is
provided having a cross sectional area of between 10% and 50% of
the overall cross sectional area of the mandrel head.
[0028] Once the mandrel head has been bought into frictional
engagement with the workpiece it is then caused to rotate at a
speed of at least 200 rpm revolutions per minute (illustrated by
arrow 41 in FIG. 1). The actual speed of rotation is dependent on
the materials being used in both the rivet and the workpiece and
may be anywhere between the range of 300 rpm and 1000 rpm and
preferably between the range of 400 rpm and 800 rpm. The higher the
speed of rotation then the greater the heat generation due to the
frictional resistance between the mandrel head of the rivet and the
workpiece. More surprising to the applicant is that whilst high
speed rotation is effective in generating sufficient heat so as to
provide appropriate weakening of the workpieces, similar
satisfactory weakening of the workpiece can be achieved at much
lower rotational speeds of as low as 200 rpm.
[0029] The resultant heat generated by rotation of the rivet will
serve to soften or reduce the strength of the workplece material
(30) in an area locally to engagement with the rivet such that the
rivet can then be Inserted through this weakened material under a
much lower insertion force than normally required to punch through
the workpieces. Due to the close proximity and engagement between
the workpiece (30) and the workpiece (32) such heat transfer is
propagated by conduction between the two workpieces serving to
weaken both the outer workplece (30) and the inner workpiece (32)
allowing the rivet to be forced through this weakened material in a
self-piercing operation. This piercing operation is enhanced by the
high pressure exerted by the small area of contact between the
rivet body and the workpieces.
[0030] Once the mandrel head (22) has pierced both workpieces (30,
32) the insertion force (40) serves to continue moving the blind
rivet (10) through the newly formed hole in these workplaces until
the shoulder (16) of the flange portion (14) abuts with the outer
workpiece (30) as shown in FIG. 2. In this position the rivet can
be set in a conventional blind rivet setting operation by firstly
discontinuing rotation of the rivet body (12) and then applying a
setting force (46) (as shown in FIG. 1) to the mandrel stem (20)
whilst utilising an appropriate setting tool to maintain the flange
portion (14) in engagement with the workpiece (30). This setting
force then exerts a compressive force, through the mandrel head
(22), onto the tail end portion of the rivet body until such time
as the rivet body (12) collapses under such compressive force in a
conventional manner forming a deformed portion (50) of the rivet
body on the blind side of the workpieces (30, 32) serving to
compress the workpieces (30) and (32) between such deformed portion
(50) and the flange portion (14) as is conventional for blind
rivets of this type. Continued application of a setting force (46)
will cause an increase in stress on the mandrel stem (20) since no
further displacement of the mandrel head will be permissible due to
the resistance incurred by the rear part of the workpieces (32),
until such time that the mandrel stem breaks at a predetermined
break neck portion (not shown) as is conventional. Once the rivet
(10) has been set in this standard manner, the mandrel head may be
ejected from the rivet body (12) or retained therein, dependent on
the specific nature and design of the blind rivet employed. Both
options are again conventional within the art of blind rivets and
are considered incorporated within this broad inventive
concept.
[0031] A particular advantage of the method of setting blind rivets
in this manner is that the insertion force (40) that needs to be
applied to the rivet so as to force it through the workpieces (30)
and (32) is considerably reduced in comparison to that that would
be associated if no weakening of the workpieces had been achieved
by heating resultant from such rivet rotation. This significantly
reduces and alleviates deformation of the workplaces in the region
of the set rivet which is highly undesirable in those fields where
such blind rivets are used, particularly within the automotive
industry.
[0032] In addition, the preferred invention it is preferable to use
an appropriate setting tool which is capable of both rotating the
blind rivet and undertaking the conventional blind rivet setting
operation once inserted through the workpiece. However, the current
invention is equally applicable to utilisation of a dedicated
rotary tool to first permit rotation and insertion of the blind
rivet into the workpiece following which a second and distinct
blind rivet setting tool can then be employed to undertake the
setting operation.
[0033] It has further been determined that specific designs of
blind rivets prove advantageous in use in this spin rivet setting
operation. Referring to FIG. 3, there are shown three blind rivet
variants (70, 80, 90) whose specific design configurations exhibit
specific spin rivet setting characteristics, each of which are
beneficial to specific operations. In particular, the workpiece
engaging end faces of the rivets (70, 80, 90), which In this
embodiment comprises the mandrel heads (22), are provided with a
unique profile each of which have specific beneficial functions
when used in spin riveting. The mandrel head (22) of rivet (70) is
provided with a generally parabolically curved end face and, in
this specific embodiment, a hyperbolically curve cross sectional
profile. This provides for a very small initial area of contact
between the rivet head and the workpiece during the initial
rotatable engagement therebetween whereby the shape generated by
such hyperbolic curve will give initially a focus to generating
heat at its point of contact, followed by a rapid insertion as the
relative softened workpiece material passes over the curved surface
in a manner similar to the way an armaments bullet passes through
material. This piercing action is enhanced by the extremely high
pressure exerted from a minimal force applied to the rivet during
insertion resultant from the small area of contact between the
workpiece and this rivet. This type of rivet is particularly
suitable for more ductile thin sheet materials such as certain
forms of rigid plastic, eg. glass reinforced materials.
[0034] The embodiment shown as rivet (80) Is provided with a
truncated conical mandrel head which will result in heat generation
over a wider point area, thus softening the workpiece material over
a larger area, and which will also continue to generate heat
resultant from rotation of the rivet, resultant from subsequent
engagement of the conical surface (81) engaging the side edges of
the workpiece during the passage of this conical face of the
mandrel head (22) therethrough. This type of rivet is particularly
beneficial and suitable for use in thicker, less ductile, materials
and also suitable for softer plastic materials.
[0035] The embodiment shown as rivet (90) corresponds substantially
to that illustrated in FIG. 1, but is further provided with a
mandrel head having a substantially conical outer surface (91) with
a central coaxial truncated portion (92) which is normally of
cylindrical configuration. This truncated central portion (92) can
be used to generate a local heat source or even a molten metal
point and is particularly suitable for thicker less ductile sheet
material. Again, the conical outer portion of the mandrel head (91)
will continue to generate heat as it passes through and engages the
workpiece about the periphery of the formed hole therethrough as
rotation of the rivet is continued during such insertion.
[0036] Whilst these specific rivet designs are beneficial for use
in this spin riveting method previously described, they are not
essential to its operation and any form of mandrel head is capable
of generating heat through rotational engagement with the workpiece
to provide a softening of such workpiece allowing the rivet to be
driven therethrough at lower forces than would normally be
associated and necessary to cause penetration.
[0037] An additional feature of the present invention can be a
provision of an appropriate abrasive surface on the mandrel head or
workpiece engaging end of the rivet body so as to increase the
frictional resistance against rotation of the rivet during the
setting operation to thereby significantly Increase the heat
generation. The abrasive surface further serves to abrade, erode
and cause zones of weakness to be generated in the workpieces to
again aid in insertion of the rivet therethrough. An example of
such an abrasive surface could be the mounting of a relatively hard
material such as carborundum or diamond dust onto the mandrel head
or could simply be achieved by producing a work hardened mandrel
head having appropriate hatching or other roughening of the
external surface thereof. Since the mandrel and hence mandrel head
are separate constructions to the rivet body, different materials
can be used to achieve a different surface texture finish and
hardness of the mandrel head to enhance the frictional resistance
and thus heating effect during rotation, without impact on the
ductility or strength of the rivet body necessary to effect
appropriate collapse and setting.
[0038] Referring now to FIG. 4, there is shown a schematic
illustration of a static blind rivet insertion tool mounted in
conjunction with a conventional "C" frame. Such "C" frame (60) is
of conventional design having one arm (62) of such "C" frame
supporting the rotatable rivet setting head (64) with the second,
lower arm (66) of such "C" providing appropriate support for a
plurality of workpieces (schematically illustrated at (68)). Since
such static rivet insertion tools are employed on production lines,
it is possible to connect these to conventional blind rivet feed
mechanisms (70) which are standard within the art and need not be
described In any great detail herein save to explain that they are
capable of carrying a plurality of blind rivets (74) from a
conventional vibrator bowl feeder along a conventional braceway via
an escapement to such rivet feed mechanism so as to be easily
accessible by the setting head (64) in a normal manner. The setting
head (64) will be conventionally driven by pressurised air using a
conventional main ram (76) for appropriate progressive insertion.
The rotary setting head (64) will provide a combined means of
effecting rotation of the blind rivet prior to the setting
operation, with the main ram (76) providing an appropriate
insertion force maintaining the rivet in frictional engagement with
the workpiece (68) as previously described. Once the rivet (74) has
been inserted through the workpiece by combined application of
rotary and progressive force thereon as previously described, the
setting head is then restrained from further displacement while an
effective blind rivet setting operation is carried out in a
conventional manner.
[0039] A specific example of a blind rivet setting tool capable of
effecting both rotation and subsequent setting of a blind rivet in
the method previously described is clearly described in the
Applicants earlier British Patent No. GB 1,484,259 which, by
reference hereto, is considered to incorporate the technical
description and drawings of the specific tool disclosed in that
earlier publication into the current specification in its entirety
and need not be described In detail herein. However, this example
of a rotatable blind rivet setting tool is provided by way of
example only and it will be appreciated that many variants are
possible. Such combined rotary setting tool simply requires that
conventional setting tool configuration of nosepiece and mandrel
engaging jaws are rotatable prior to setting displacement of the
mandrel engaging jaws during the setting operation. In addition,
the manual or hand held setting tool illustrated in UK Patent No.
GB 1,484,259 allows the operator to apply sufficient insertion
force to maintain blind rivet engagement with the workpiece to
create the frictional forces during rotation thereof, although It
will be appreciated that where a stationery rivet setting structure
used, such as that shown in FIG. 4, appropriate hydraulic or
electronic driven motor means may be sufficient to apply the
insertion force to the setting tool.
[0040] In addition. It is to be recognised that the current
invention is not limited to the specific design of blind rivet
described herein. In particular, the current invention is equally
applicable to any form of blind fastener and may specifically
include other types of blind rivet such as closed end blind rivets,
whereby the mandrel head does not extend beyond the longitudinal
tail end face of the rivet body, but is retained therein. In such
embodiment, the closed end face of the tail end of such blind rivet
then provides a contact surface for frictional engagement with the
workpiece during rotation whereby such frictional engagement will
generate sufficient heat to allow the rivet to be driven through
the softened workpiece. Here, the end face could be simply flat and
perpendicular to the rivet axis or may be tapered or profiled
similar to the mandrel head profiles shown in FIG. 3. Where the
mandrel head is retained within the rivet body, then frictional
engagement between the mandrel and the rivet body will often be
sufficient to transmit the rotational force through the mandrel
stem to the rivet body during rotation against the workpiece.
However, such engagement between the mandrel stem and the rivet
body can be enhanced by providing the internal cross sectional
profile of the rivet body and the external cross sectional profile
of the mandrel stem with a geometric design so as to provide
positive rather than frictional engagement between the mandrel stem
and the rivet body during rotation. For example, the mandrel stem
may be squared to be received within a square aperture of
corresponding shape and size of the rivet body. Similarly, the
cross sectional profile of the mandrel stem may be geometrically
profiled so as to be triangular, square or some other form of
geometric shape and to provide a better positive engagement between
the gripping jaws of the rivet setting tool and the mandrel stem
such gripping tool is employed to apply a rotational force to
effect rotation of the blind rivet for use in the method previously
described.
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