U.S. patent application number 14/175664 was filed with the patent office on 2014-08-07 for die condition detection.
This patent application is currently assigned to Henrob Limited. The applicant listed for this patent is Henrob Limited. Invention is credited to Nicholas Richard Clew, Peter John Elliot, Stephen Henry Kaminski.
Application Number | 20140216123 14/175664 |
Document ID | / |
Family ID | 40723232 |
Filed Date | 2014-08-07 |
United States Patent
Application |
20140216123 |
Kind Code |
A1 |
Clew; Nicholas Richard ; et
al. |
August 7, 2014 |
DIE CONDITION DETECTION
Abstract
A die (13, 213, 313) is supported in a die holder (381) such as
a frame or an adapter (18, 518) supported in a frame such that it
is operational use in a material deforming operation. One or both
of the die and the die holder have at least one gas passage which
is substantially closed by at least part of the die. Gas such as
pressurised air is directed into an end of the gas passage opposite
the die via a hose (42, 542) connected to a gas source. If the die
is broken or loose leak paths are available for the escape of gas
past the die to or from atmosphere. A pressure sensor (41)
connected to the hose detects the change in pressure of the gas and
the magnitude of that pressure is used to determine the die
condition. Alternatively a flow rate sensor is used to detect a
change in the flow rate of the gas in order to determine the
condition of the die.
Inventors: |
Clew; Nicholas Richard;
(Farmington Hills, MI) ; Elliot; Peter John;
(Novi, MI) ; Kaminski; Stephen Henry; (Roseville,
MI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Henrob Limited |
Flintshire |
|
GB |
|
|
Assignee: |
Henrob Limited
Flintshire
GB
|
Family ID: |
40723232 |
Appl. No.: |
14/175664 |
Filed: |
February 7, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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12921503 |
Sep 8, 2010 |
8671726 |
|
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PCT/GB2009/000572 |
Mar 3, 2009 |
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14175664 |
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61035208 |
Mar 10, 2008 |
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61114254 |
Nov 13, 2008 |
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Current U.S.
Class: |
72/31.01 |
Current CPC
Class: |
G01M 3/223 20130101;
B21J 15/025 20130101; B21J 15/28 20130101; G01M 3/26 20130101; Y10T
29/49943 20150115; B22F 3/02 20130101; B22F 5/007 20130101; B22F
7/06 20130101; B23Q 17/006 20130101; B33Y 10/00 20141201; B22F
2005/002 20130101; B33Y 80/00 20141201; B23Q 17/0909 20130101; B22F
2998/10 20130101; B21J 15/36 20130101; B22F 3/1055 20130101; B21D
39/031 20130101; B23K 15/0086 20130101; Y10T 29/53065 20150115 |
Class at
Publication: |
72/31.01 |
International
Class: |
B21J 15/28 20060101
B21J015/28 |
Claims
1. A method for detecting the condition of a die for deforming
material, the die having a first surface defining a die cavity in
which material is to be deformed, the method comprising supporting
the die in a die holder such that the die is operational with the
die cavity being exposed for receipt of material and such that at
least one gas passage is defined at least partially by the die
holder, the at least one gas passage extending to a first end
located between the die and the die holder, the first end being
sealed substantially closed by at least a portion of the die,
applying a gas at a pressure and flow rate to the at least one gas
passage, detecting a change in at least one of the pressure or flow
rate of the gas in the at least one gas passage and determining
from the detected change a condition of the die.
2. A method according to claim 1, wherein the die comprises a head
in which the die cavity is defined and a die stem extending from
the head in a direction away from the cavity, further comprising
supporting the die stem in a bore in the die holder and applying
the gas at a second end of the at least one gas passage.
3. A method according to claim 1, wherein there is provided a
further at least one gas passage defined in the die.
4. A method according to claim 1, further comprising using an air
catch sensor to detect the change in pressure of the gas.
5. A method according to claim 1, further comprising directing the
gas to the at least one gas passage via a conduit by connecting an
outlet of the conduit to the at least one gas passage and
connecting an inlet of the conduit to a source of pressurised
gas.
6. A method according to claim 5, further comprising connecting a
sensor to the inlet of the conduit for detecting the change in at
least one of the gas pressure or the flow rate.
7. A method according to claim 1, wherein the die is a riveting die
for upsetting a rivet inserted into the material.
8. A method according to claim 1, wherein the gas is applied to the
at least one gas passage with the die in-situ in apparatus for
deforming material.
9. A method according to claim 1, wherein the at least one gas
passage has a first portion defined by the die holder and a second
portion defined between the die and the die holder, the first end
being defined at the end of the second portion.
10. A method for detecting a loose die, the die being of the kind
for deforming material, the die having a first surface defining a
die cavity in which material is to be deformed, the method
comprising supporting the die in a die holder such that the die is
operational with the die cavity being exposed for receipt of
material and such that at least one gas passage is defined at least
partially by the die holder, the at least one gas passage extending
to a first end located between the die and the die holder, the
first end being sealed substantially closed by at least a portion
of the die, applying a gas at a pressure and flow rate to the at
least one gas passage, detecting a change in at least one of the
pressure or flow rate of the gas in the at least one gas passage
and determining from the detected change whether the die is
loose.
11. A die assembly comprising a die having a first surface defining
a die cavity in which material is to be deformed, a die holder in
which the die is supported such that the die is operational with
the die cavity being exposed for receipt of material, at least one
gas passage is defined at least partially by the die holder, the at
least one gas passage extending to a first end located between the
die and the die holder, the first end being sealed substantially
closed by at least a portion of the die, the conduit having an
outlet in fluid communication with the at least one gas passage and
an inlet connectable to a source of pressurised gas, and a sensor
for detecting the pressure or flow rate of the gas in the at least
one gas passage.
12. A die assembly according to claim 11, wherein the die holder
comprises a die adapter disposed between the die and a support
member.
13. A die assembly according to claim 11, wherein the die holder is
defined by part of a support frame that supports the die.
14. A die assembly according to claim 13, wherein the support
member is part of a support frame.
15. A die assembly according to claim 12, wherein the die adapter
comprises a body having a first end in which the die is supported
and a second end, at least part of the at least one gas passage
extending between the first and second ends.
16. A die assembly according to claim 15, wherein the die comprises
a head in which the die cavity is defined and a stem extending from
the head in a direction away from the die cavity, the stem of the
die being received in a first bore in the first end of the die
adapter body.
17. A die assembly according to claim 16, wherein a first portion
of the at least one gas passage is defined between the stem of the
die and the first bore and a second portion of the at least one gas
passage extends between the outlet of the conduit and the first
portion.
18. A die assembly according to claim 17, wherein the second
portion of the at least one gas passage is in the form of a second
bore.
19. A die assembly according to claim 18, wherein the first and
second bores are substantially cylindrical with the first bore
having diameter that is larger than that of the second bore.
20. A die assembly according to claim 15, wherein the body of the
die adapter has an outwardly extending flange that is seated on the
support member.
Description
FIELD
[0001] The present invention relates to a method for detecting the
condition of a die and also to a die assembly configured to enable
detection of the condition of the die. More particularly, but not
exclusively, the invention relates to detecting the condition of a
die used in a riveting application. The term "condition of the die"
is intended to include, amongst other things, damage of the die, a
loosely fitted die and the complete absence of a die from a die
assembly.
SUMMARY
[0002] In self-piercing riveting a partially hollow rivet of a
particular configuration is inserted into a workpiece such as, for
example, one of more sheets of material without full penetration
such that a deformed end of the rivet remains encapsulated by an
upset annulus of the material. The rivet typically comprises a head
and a partially hollow cylindrical shank that terminates in an
annular piercing edge.
[0003] Self-piercing rivet insertion is generally performed by a
hydraulically, pneumatically or electrically operated rivet setting
tool that is supported by one arm of a C-frame over a suitably
shaped die that is supported by the other arm. The die typically
comprises a head defining a die cavity and a depending stem that is
received in a bore in the arm of the C-frame. As the rivet is
driven into the sheets of material by a punch of the setting tool,
the shank pierces the top sheet and then flares outwardly in the
die such that the sheet material forms an annulus in the die cavity
that encapsulates the shank. The shank of the rivet remains
embedded in the sheet material after the rivet has been set thereby
forming a "button" on one side of the join. Self-piercing riveting
enables sheet material to be joined without the requirement for the
pre-drilling or pre-punching of a hole in the material.
[0004] The insertion force required to pierce the material in
question has to be reacted wholly or at least in part, by the die.
In many applications the magnitude of this force will be high and
the die is therefore subject to very high loading and wear. On this
basis the die needs periodic inspection and replacement. In
practice, dies sometimes crack and/or break into pieces. For
example, all or part of the head of the die may break away from the
stem, or a part of the head may break away with a part of the stem
that is directly under it. The life expectancy of a die is
dependent on many factors including, for example, the number of
riveting cycles to which it is subjected, the rivet setting forces,
the material being riveted, the alignment of the die to the
workpiece and the actuator punch, the amount of joint expansion
into the die cavity, the material properties of the die, the
quality of the surface on which the die is supported in the
C-frame, the degree of retention of the die in the C-frame and
instances of erroneous operation in which the setting tool impacts
directly on the die (this can occur inadvertently, for example,
when the sheet material and/or rivet are not present above the die
either as a result of error or during a test operation).
[0005] In an automated riveting system either the C-frame is moved
by a robotic arm or the workpiece is moved to the setting tool in a
production line environment and a certain amount of quality control
is performed by automatic monitoring of the riveting operation.
Automated process monitoring systems incorporating transducers of
various kinds are currently used in conjunction with riveting
systems to monitor various aspects of the riveting operation
including, in particular, the position of the rivet, the distanced
traveled by the setting tool punch both prior to and during rivet
insertion, and the insertion force applied during rivet setting.
Such monitoring systems can be configured to deduce that a die is
missing by for example detecting when the punch has traveled a
distance above a predetermined threshold (i.e. it has traveled to a
point beyond where the die would ordinarily be present) before it
meets with resistance. However, in instances where a small part of
the die breaks away the fault is not always detectable by the
process monitoring transducers as the damage to the die often does
not significantly affect the distance traveled by the punch or on
the force profile applied by the punch. The faulty die can cause
unsightly distortion of the sheet material around the rivet
insertion location and the strength of the joint may be compromised
as a consequence. Moreover, a die that is loose in the C-frame
cannot be detected with the currently available process monitoring
systems. It will be appreciated that in such circumstances a batch
of faulty joints can be generated before they are inspected and
intercepted. This not only delays the production process but wastes
materials and so there can be a significant cost to the
manufacturer.
[0006] It is known to use air pressure to check for faults in a
die. A sensing head comprising, for example, a disc of nylon with
an open chamber therein is presented over the die cavity such that
it is sealed against it. Pressurised air is supplied into the
sensing head and the pressure of the air in the chamber is detected
by a pressure sensor. If the die is broken air is able to escape
between the seal in the head and the broken face of the die
resulting in a relatively low reading on the pressure sensor.
Similarly, if a die is missing this will be detected by a low
reading on the pressure sensor. A checking system of this kind
works well for dies that are broken or missing but requires
accurate robotic positioning equipment to move the sensing head or
the C-frame to a position where the sensor head is presented and
sealed to the die or at least presented to the die space. Not only
does this require an expensive investment in machinery but it also
introduces delays into the rivet cycle time. The manufacturer has
to balance the quality control benefits provided by performing the
checking process at regular intervals against the time it takes. If
the checking process reveals a broken or missing die then all the
joints performed since the preceding check are potentially faulty
and they either have to be checked or scrapped. It is therefore in
the interest of the manufacturer to perform the checking process at
regular short intervals.
[0007] It is not possible for an air pressure checking system of
the kind described above to detect a die that is in loose
engagement with the C-frame. If a die is loose the mating surfaces
of the underside of the die head and the surface of the arm of the
C-frame against which it bears can become worn or damaged. This
reduces the life expectancy of the die and generally leads to
premature die failure. Moreover, if a loose die is used for an
extended period it can often fall out of the C-frame and unless its
absence is detected immediately the next joint that is made without
the die will generally be so poor that the workpiece may have to be
scrapped.
[0008] It is one object of the present invention, amongst others,
to obviate or mitigate at least one of the aforementioned
disadvantages and to provide for an improved or alternative method
for detecting the condition of a die and to provide for a die
assembly that enables such a method to be performed.
[0009] According to a first aspect of the present invention there
is provided a method for detecting the condition of a die for
deforming material, the die having a first surface defining a die
cavity in which material is to be deformed, the method comprising
supporting the die in a die holder such that the die is operational
with the die cavity being exposed for receipt of material and such
that at least one gas passage is defined at least partially by the
die holder, the at least one gas passage extending to a first end
located between the die and the die holder, the first end being
sealed substantially closed by at least a portion of the die,
applying a gas at a pressure and flow rate to the at least one gas
passage, detecting a change in at least one of the pressure or flow
rate of the gas in the at least one gas passage and determining
from the detected change a condition of the die.
[0010] The gas may be directed into the at least one passage with a
positive gas pressure in which case a change in back pressure is
detected to determine the condition of the die. Alternatively a
negative gas pressure may be applied to the at least one gas
passage and a reduction in the magnitude of the negative pressure
or an increase in flow rate may be detected. In each of the cases
any suitable gas pressure or flow rate sensor may be used.
[0011] By determining the change in the pressure or flow rate in
the at least one gas passage conclusions may be made regarding the
condition of the die. For example, the method may be used to
determine if the die has failed as a result of fracture, cracking
or breakage, it may determine that the die is absent completely,
that the die is not located properly in the holder, or simply that
it is a loose fit in the holder. The method may be performed in
such a manner that the determined condition is either indicative of
the die being present and operational or that it is not operational
in some way. Alternatively, it may be able to make a more refined
statement regarding the die condition by identifying why the die is
not operational e.g. it may determine from the sensed pressure or
flow rate that the die is not present or is broken, or
alternatively that the die is a loose fit in the holder.
[0012] This aspect of the invention relies on using at least one
gas passage in the die holder to apply positive or negative gas
pressure to the first end where the die closes the passage. The
passage may be closed by means of a sealing member of the die and
disposed such that it seals against the die holder (or an
intervening member) or simply by means of a tight engagement (e.g.
a friction fit) between the die and die holder (or an intervening
member). Thus the condition of the die can be determined when it is
in place (or at least should be in place) in the die holder rather
than having to move and present a separate component associated
with a sensor to the die. The pressure or flow rate sensor detects
whether there is a change in pressure or flow rate of the gas flow
delivered from the source as a result of leakages past the die. The
fact that the die serves to close the gas passage means that it
seals or at least partly seals the passage so as to prevent or
restrict the passage of the gas across it. Thus when a die is
correctly fitted to close the passage in the holder the pressure is
relatively high in magnitude (whether positive or negative) and the
flow rate of the gas is relatively low. If the die becomes loose or
damaged, gas may be able to escape past the die more easily, the
pressure is reduced and the flow rate increases. In this case if
positive pressure is applied to the at least one gas passage the
back pressure is reduced or if negative pressure is applied its
magnitude is reduced as a result of gas from the surrounding
environment entering the at least one passage. In this arrangement,
the detection process is not reliant on the presence of a workpiece
over the die to determine the die condition. In is to be understood
that the at least one gas passage may be partially defined between
the die and die holder.
[0013] A statement regarding die condition may be determined from
comparing an absolute value of pressure or flow rate magnitude of
the gas to a predetermined threshold value or simply by detecting a
reduction in the pressure magnitude or flow rate compared to a
previously measured magnitude.
[0014] The gas may be air and the pressure sensor may be an air
catch sensor. There may be a source of gas that is proximate to the
pressure sensor or otherwise. The gas may be directed to or from
the at least one gas passage via a conduit such as, for example, a
flexible hose. Alternatively it may be connected directly to the at
least one gas passage.
[0015] The die may comprise a head defining the die cavity and a
stem extending from the head. The stem of the die may be supported
in the die holder.
[0016] The method may be for detecting the condition of the die in
situ in apparatus for deforming material. The die may be supported
opposite a deforming tool which may be a rivet setting tool, the
rivets being inserted into the material and being upset in the die.
The deforming tool and the die may be for self-piercing riveting in
which the rivets pierce into the material but do not penetrate all
the way therethrough.
[0017] According to a second aspect of the present invention there
is provided a method for detecting a loose die, the die being of
the kind for deforming material, the die having a first surface
defining a die cavity in which material is to be deformed, the
method comprising supporting the die in a die holder such that the
die is operational with the die cavity being exposed for receipt of
material and such that at least one gas passage is defined at least
partially by the die holder, the at least one gas passage extending
to a first end located between the die and the die holder, the
first end being sealed substantially closed by at least a portion
of the die, applying a gas at a pressure and flow rate to the at
least one gas passage, detecting a change in at least one of the
pressure or flow rate of the gas in the at least one gas passage
and determining from the detected change whether the die is
loose.
[0018] According to a third aspect of the present invention there
is provided a die assembly comprising a die having a first surface
defining a die cavity in which material is to be deformed, a die
holder in which the die is supported such that the die is
operational with the die cavity being exposed for receipt of
material, at least one gas passage is defined at least partially by
the die holder, the at least one gas passage extending to a first
end located between the die and the die holder, the first end being
sealed substantially closed by at least a portion of the die, the
conduit having an outlet in fluid communication with the at least
one gas passage and an inlet connectable to a source of pressurised
gas, and a sensor for detecting the pressure or flow rate of the
gas in the at least one gas passage.
[0019] The conduit may be elongate for connection to a remote
pressure source. It may be an integral part of a housing of the
source of pressurised gas or, alternatively, the source of
pressurised gas may be connectable directly or indirectly to the
inlet of the conduit. Similarly the sensor may be connected,
directly or indirectly, to the inlet of the conduit or it may be
connected to any part of the at least one gas passage.
[0020] The sensor may be connectable to a controller that is able
to determine a condition of the die from the detected magnitude of
the pressure or flow rate.
[0021] There may be provided at least one further gas passage that
extends into the die. The further gas passage may extend to a
location that is proximate the die cavity. The die may be a
friction fit or otherwise in a recess in the die holder. The at
least one further gas passage defined in the die may not extend all
the way therethrough and it is closed at its first end by virtue of
being a blind passage. In other words it is closed by a portion of
the die which is not penetrated by the at least one further gas
passage.
[0022] The die holder may be defined by part of a frame that
supports a setting tool. Alternatively, it may comprise a die
adapter between the die and a support member which may be a part of
a frame that supports a setting tool. In either case, the frame may
be a C-frame with a pair of arms, a first arm being disposed over a
second arm in a spaced apart relationship, the first arm supporting
a setting tool and a second arm defining the die holder.
[0023] The die adapter may comprise a body having a first end and a
second end. The die may be supported in the first end and at least
of the at least one gas passage may extend between the first and
second ends.
[0024] The die may comprise a head in which the die cavity is
defined and a stem extending from the head in a direction away from
the die cavity, the stem of the die being received in a first bore
in the first end of the die adapter body.
[0025] A first portion of the at least one gas passage may be
defined between the stem of the die and the first bore and a second
portion of the at least one gas passage extends between the outlet
of the conduit and the first portion.
[0026] The second portion of the at least one gas passage may be in
the form of a second bore.
[0027] The first and second bores may be substantially cylindrical
with the first bore having diameter that is larger than that of the
second bore.
[0028] The body may have a flange for seating on the support
member.
[0029] The second portion of the at least one gas passage may
extend from the second end of the die adapter body to the first
portion of the at least one gas passage and it may extend from the
flange to the first portion. The second portion may comprise a
first part that extends from the second end of the die adapter to
the first portion of the at least one gas passage and a second part
that extends from the flange to the first portion.
[0030] There may be a washer disposed between the die head and the
die holder. The die head may define a second surface, which is
opposite the first surface on which the cavity is defined, the
washer being disposed between the second surface and the die
holder. The second surface may be immediately adjacent to the die
stem. A first surface of the washer may face the second surface of
die head and an opposed second surface may face the die holder. The
facing surfaces may be in contact. One or both of the first and
second surfaces of the washer may define one or more gas paths
which may be in the form of a groove (including a recess or the
like), the gas paths forming at least part of the at least one gas
passage. The washer may have inner and outer peripheral surfaces
that extend between the first and second surfaces. There may be
provided at least one gas path that extends in a radial direction
from the inner peripheral surface towards the outer peripheral
surface. There may be a plurality of such radial gas paths that
extend from the inner peripheral surface to a substantially annular
gas path defined towards the outer peripheral surface.
[0031] In one embodiment, the second surface of the die head may
define one or more gas paths of the kind defined above. In this
particular embodiment the washer need not be present.
[0032] There may be a clearance between die stem and a wall that
defines the at least one gas passage, the clearance may extend
along the length of the die stem so as to provide a gas path. The
clearance may be provided by a flat along the length of the die
stem or, alternatively by a groove defined along the length of an
external surface of the die stem or in the wall that defines the at
least one gas passage in which the die stem is received.
[0033] In one embodiment a sleeve is provided over the outer
periphery of the washer and the die head, the sleeve being
deformable outwardly. In this embodiment the washer may have one or
more gas paths defined on its first surface only. The gas paths may
comprise one or more radial grooves that extend from the inner
peripheral surface to the outer peripheral surface. In the event of
die breakage the sleeve is deformed outwardly by the broken part of
the die so as to provide a clearance between the sleeve and the die
head. In use, this affords a leak path as the gas flows along the
gas path or paths, along the clearance to atmosphere thereby
resulting in a drop in back pressure or an increase in the flow
rate detected by the sensor. Alternatively, in the instance where a
negative suction pressure is applied the gas flows from atmosphere
into the clearance and along the at least one gas passage.
[0034] The die may be fixed in the die holder by means of a fixing
member such as a grub screw or the like. The fixing member is
located in a fixing bore in the die holder which may be in gas
communication with the at least one gas passage such that if the
fixing member is not present or is only loosely fitted the fixing
bore provides a leakage flow path. The amount of leakage determined
from the detected back pressure or flow rate may be of such a value
that it can be attributed to this condition (i.e. the absence or
incorrect fitting of the fixing member).
[0035] In one embodiment the die may comprise at least two
separable parts: a die stem and a collar. The die stem may have a
flange on which the collar is mounted. The collar may have a
depending skirt that extends over at least a part of the depth of
the flange. The die stem may have a gas bleed passage for gas
communication with the at least one gas passage. The gas bleed
passage may extend from an interface between the die holder and the
die to an interface between the die stem and the collar. It may
extend across the depth of the flange. The die stem may have an
upper surface defining a part of the die cavity, the upper surface
may define a die protrusion or nub that serves to guide flaring of
the rivet during deformation. The collar may have an inner annular
surface that defines a part of the die cavity.
BRIEF DESCRIPTION OF THE DRAWINGS
[0036] Specific embodiments of the present invention will now be
described, by way of example only, with reference to the
accompanying drawings in which:
[0037] FIG. 1 is a side view of rivet setting apparatus including a
rivet setting tool supported over a die assembly in a C-frame, in
accordance with the present invention;
[0038] FIG. 2 is a sectioned view through that part of the
apparatus of FIG. 1 that is encircled and labelled A;
[0039] FIG. 3 is a sectioned side view of a die shown with a washer
support in accordance with the present invention;
[0040] FIG. 4 is a perspective view of the washer support of FIG.
3;
[0041] FIG. 5 is a perspective view of an alternative embodiment of
the die in accordance with the present invention;
[0042] FIG. 6 is a sectioned side view of a second alternative
embodiment of a die and support in accordance with the present
invention;
[0043] FIG. 7 is a perspective exploded view of the support of FIG.
6;
[0044] FIG. 8 is a sectioned side view of a third alternative
embodiment of a die and die holder in accordance with the present
invention;
[0045] FIG. 9 is a section side view of a fourth alternative
embodiment of a die in accordance with the present invention;
[0046] FIG. 10 is a perspective view of a C-frame fitted with a die
and die holder in accordance with the present invention;
[0047] FIG. 11 is an enlarged view of the die and die holder of
FIG. 10; and
[0048] FIG. 12 is a sectioned side view of a further alternative
embodiment of a die in accordance with the present invention.
DESCRIPTION
[0049] Referring now to FIG. 1 of the drawings, a rivet setting
tool 10 is mounted on an upper arm 11 of conventional C-frame 12
above a rivet-upsetting die 13 supported in the lower arm 14.
Rivets (not shown in FIG. 1) are inserted by the tool 10 into a
workpiece (not shown) supported over the die 13 as is well known in
the art. The tool 10 is operable such that a lower nose end 15
moves downwards to engage and optionally clamp the workpiece and
then a punch is extended so as to insert the rivet. It is to be
appreciated that whilst the specific embodiment described herein
relates to the insertion of rivets it has application to the
formation of other joints including joints using other fasteners
that are inserted into a work piece using a die such as, for
example, slugs, and also a clinching operation in which a punch of
the setting tool is used directly to deform the material into the
die to form a mechanically interlocked joint which may or may not
then be supplemented with a fastener.
[0050] The C-frame 12 is mounted on a robot manipulator (not shown)
such that it is movable with the tool 10 by the robot towards and
away from the workpiece as required. A mounting bracket 16 is
provided on the C-frame 12 for connection to the robot manipulator.
A suitable rivet delivery system (not shown) is provided and is
designed to supply rivets to the setting tool in a predetermined
and controllable fashion from a bulk source (not shown). This may
be achieved by, for example, using a compressed gas delivery system
that propels the rivets along a tube or track or by a tape drive
system in which rivets are supported in a tape that is wound on a
spool and fed to the setting tool. The tool and feed apparatus are
operated by a controller (not shown in the figures) in the form of
microprocessor-based hardware and operational software. Such rivet
delivery and control systems are well known and will not therefore
be described herein.
[0051] The die 13 shown in FIGS. 1 and 2 is of conventional
configuration but is supported on the lower arm 14 of the C-frame
12 by a die holder adapter 18 that is received in a bore 19 through
the arm 14. The die 13 is generally cylindrical with a head 20
defining an open die cavity 21 for facing the setting tool 10 and a
depending stem 22 that is of reduced diameter compared to the head
20 such that an annular surface 23 extending radially relative to
the central axis of the die is defined on the underside of the head
20. The adapter 18 has a generally cylindrical body with a first
end 25 that is received in a snug fit in the bore 19 in the arm 14
of the C-frame 12 and a second hollow end 26 that receives the die
stem 22 such that the annular surface 23 of the die is seated on an
upper surface 27 of the second end 26. A sealing member such as,
for example, a O-ring or the like may be provided between the
adapter 18 and an upper surface 28 of the surface of the arm 14 in
which the bore 19 is defined. The adapter body has a radially
outward extending flange 29 defined part way along its outer
surface with one of the radially extending faces being seated on
the upper surface 28 of the arm 14 immediately around the bore 19.
The second hollow end 26 is tapered inwardly and terminates in the
annular upper surface 27 on which underside surface 23 of the head
20 is supported. A cylindrical bore 30 extends within the adapter
body from the second end 26 to a position substantially half way
along its length and receives the die stem 22 in a slip fit or
friction fit. The body is also penetrated by two small diameter
passages: a first 31, which extends along a central longitudinal
axis of the body from the first end 25 to the cylindrical bore 30,
and a second 32 that extends radially from the first passage 31 to
the periphery of the flange 29. In each case the passages have
respective enlarged first and second entry ports 33, 34 to allow
connection to a hose for the supply of pressurised air.
[0052] In FIGS. 1 and 2, the first entry port 33 of the die adapter
18 is connected to a pneumatic source 40 and an air catch sensor 41
via a suitable air hose 42. The sensor 41 has an outlet nozzle that
is connected to an inlet end of the hose 42 and delivers air to the
adapter 18. The sensor 41 is operative to detect decreases in the
air pressure flow from the outlet nozzle as a result of the
reduction in back pressure as a result of leakage paths caused by
the absence of all or part of the die 13 in the adapter 18, or
simply by virtue of a loose fitting die. Air catch sensors of this
kind are known in the art and a suitable example for this
application is available from SMC Corporation of Tokyo, Japan such
as, for example, those available under general part no. ISA 2. An
alternative sensor for sensing the flow rate of the gas may be used
instead.
[0053] Under normal operation, when a die 13 is present and secured
in place in the adapter 18 the air catch sensor 41 will detect a
relatively high back pressure in view of the close fit and/or
sealed relationship between the die 13, the adapter 18 and the arm
14 of the C-frame 12. If the die 13 is absent the back-pressure
will be negligible as air is able to leak out through the small
diameter passages 30, 31 to atmosphere. The lack of significant
back-pressure is detected by the sensor 41 and a signal indicative
of the absence of the die 13 is generated and transmitted to the
controller which can issue an alarm. Alternatively, if part of the
die head 20 is missing, the die 13 is only loosely fitted in the
adapter 18, or the adapter 18 is loosely fitted in the bore 19, the
leak flow path is less restricted than normal and a back pressure
of reduced magnitude is sensed. A signal indicative of a broken or
faulty die is then generated and transmitted to the controller so
that a suitable alarm can be generated.
[0054] The configuration of the assembly of the die 13 and the die
holder adapter 18 allows a statement to be made regarding the
condition of the die either by comparing an absolute value of the
sensed back-pressure magnitude with a predetermined threshold value
or simply by detecting a reduction (of a predetermined magnitude)
in the back-pressure compared to a previously measured
magnitude.
[0055] It is to be appreciated that if the bore 19 in the lower arm
14 of the C-frame is modified to provide an air-tight connection
with the end of the hose 42 the die holder adapter 18 may be
eliminated in certain embodiments in which case the lower arm of
the C-frame in the region around the bore 19 serves to hold the die
directly.
[0056] An alternative die arrangement is depicted in FIGS. 3 and 4.
This embodiment can be used with the die adapter 18 of FIGS. 1 and
2 or can be mounted directly into a reduced diameter bore in the
lower arm of the C-frame without an adapter. The die 13 is
supported on an annular washer 50 having an inner edge 51, an outer
peripheral edge 52, an upper surface 53 (for facing the die) that
has a plurality of shallow channels 54, 55 formed therein and a
lower surface 56 for abutment with the adapter 18 or the arm 14 of
the C-frame 11. In the particular embodiment shown in the figures,
there are four substantially radial channels 54 that extend from
the inner edge 51 to a circular channel 55 formed towards the outer
peripheral edge 52 of the washer 50. In use the channels 54, 55 are
in communication with the air supply via the hose 42, the small
diameter passages 31, 32 and bore 30 in the adapter 18 (if present)
and a leak passage or clearance past the die stem. They thus
provide a potential air leak path that runs close to the outer
periphery of the die head 20. If the die 13 is present and its
annular surface 23 is sealed in place against the periphery of the
upper surface 53 of the washer 50 the air channels 54, 55 are
effectively closed by the die as they are not in fluid
communication with the atmosphere and negligible air leakage
occurs. On the other hand, if a fracture takes place at the head 20
of the die 13 in a radial position that is distal from the die stem
22 then, provided the missing part of the die head 20 encompasses
the annular surface 23 on the underside of the die head 20, air can
leak past the die 13 and a reduced back pressure (or an increased
flow rate if a flow rate sensor is used) is detected. Similarly, if
the die is loosely fitted air can leak past resulting in a reduced
back pressure and increase flow rate. It will be appreciated that
the washer 50 may have a similar array of channels 54, 55 formed on
its lower surface 56 if desired so that it does not matter which
way up it is installed. The washer could be retro-fitted or may be
supplied pre-attached to each die.
[0057] In a further die embodiment 113 shown in FIG. 5, the
channels 154, 155 are formed in the annular surface 123 on the
underside of the die head 120. This die 113 may be used with the
adapter 18 or mounted directly into the bore 19 of the C-frame arm
14 as before. In addition, this particular die 113 is shown with a
flat surface 160 along the length of its stem 122. Once the die 113
is supported in the cylindrical bore 30 of the adapter 18 or in the
bore 19 of the C-frame arm 14 the clearance between the flat 160
and the wall of the bore 30 or 19 affords a leak path to allow air
to flow up to the channels 154, 155. This feature may be
incorporated in any of the die embodiments shown in the figures. It
will be appreciated that the flat 160 may be replaced with a
groove, recess, channel or the like in the surface of the stem to
allow for the flow of air.
[0058] The embodiment of FIGS. 6 and 7 comprises a die 213 with a
washer 250 similar to that of FIGS. 3 and 4. However, in this
instance the radial channels 254 in the upper surface of the washer
run between the inner and outer peripheral edges 251, 252 and there
is no circular channel. A thin metallic cylindrical sleeve 270 is
press-fitted over the outer peripheral edges of the washer 250 and
the die head 220 so as to close the channels 254. In the event of
breakage of the die head 220 the sleeve 270 will be deformed
outwards so as to provide a clearance between the die head 220 and
the sleeve 270, thereby allowing a leak path to open. The air leak
path thus travels from the supply, through the hose 42, the small
diameter bores 31, 32 and bore 30 in the adapter 18, the channels
254 in the washer and between the die head 220 and the sleeve 270
(or between the broken parts of the die head). This arrangement has
the benefit that breakage may be detectable even if it does not
extend to the annular surface 223 on the underside of the die head.
Moreover, the sleeve 270 helps to retain the broken die parts and
may serve to prevent the rivet joint from distorting to an extent
where it is unsatisfactory. The sleeve 270 may be replaced by a
tightly wound coil spring or the like.
[0059] In the embodiment of FIG. 8, the die 313 has no stem and the
head 320 is received in a recess 380 in a die holder 381 in a tight
fit such as a friction, press or slip fit. Alternatively or in
addition it may be retained in the recess 380 by a suitable screw.
As before, the die has an upper surface for facing the setting tool
and in which a die cavity 321 is formed. The holder 381 may be an
adapter for fitting in a bore in the C-frame as in the manner of
the embodiment shown in FIGS. 1 and 2 or may, alternatively, be an
integral part of the C-frame. The length of the die holder 381 is
penetrated by a bore 382 that extends between the recess 380 and an
opposite end 383. In use the bore 382 is connected, directly or
indirectly, to pneumatic source and an air catch sensor via a
suitable air hose as in the preceding embodiments. In order to
detect whether die failure has occurred air is directed into the
bore 382 as indicated by the arrow.
[0060] FIG. 9 illustrates an alternative die configuration in which
the die 413 itself is penetrated by a passage for connection to the
sensor. The die may take any suitable form but in this particular
embodiment the die has an elongated head portion 420, an upper
surface of which defines the die cavity 421, and a short stem 422
for receipt in a recess or bore in a die holder (not shown) being
either an adapter or part of the C-frame. A single passage 495
extends up the stem 422 and the head 420 along a longitudinal axis
of the die and terminates a short distance from the die cavity 4.
In use, the passage is in fluid communication with the fluid
passage and/or bore in the die adapter or C-frame and therefore
with the pneumatic source and air catch sensor. More than one
passage 422 may be provided and it will be appreciated that the
precise configuration of the passage or passages may vary. If this
die should fracture in the region around or under the die cavity
421 it will expose the passage or passages in the die thereby
affording leakage. The reduction in back pressure or increase in
flow rate will be detected as before so that a die condition
statement can be made.
[0061] In all embodiments the sensor may located at any convenient
location which may be proximate the die and the die holder or may
be distal therefrom. If the C-frame and setting tool are
robot-mounted it may be convenient for the pressure sensor to be
located outside of the robot cell.
[0062] The source of pressurised gas may be connected directly to a
gas passage in the C-frame or in the die adapter rather than using
an elongate flexible conduit.
[0063] A further alternative embodiment of a die adapter is shown
in FIGS. 10 and 11. In this embodiment the die holder (adapter) 518
is fixed to the lower arm 514 of the C-frame 512 at a bottom flange
529 and extends upwardly to an open end in which the die 513 is
received so as to close the internal gas flow passages (not shown).
The flange 529 has an upper arcuate surface that merges with an
upper end of the die holder 518. The die 513 is retained tightly in
place in the adapter 518 by a grub screw 596 that extends through
the wall of the adapter. Gas in introduced into the adapter 518 at
a side port 534 in the arcuate surface of the flange via a flexible
hose 542 connected thereto. The port 534 is in fluid communication
with the gas passage that extends to the die 513 as before. If the
grub screw 596 is omitted it leaves a gas leakage path to
atmosphere which would be detected by sensing a reduction in the
back pressure or an increase in the gas flow rate. It is to be
understood that the grub screw feature may be used in conjunction
with the die adapters described in preceding embodiments.
[0064] In FIG. 12 there is shown an alternative die embodiment for
insertion into a die holder of any of the kinds described above.
This particular die 613, is in two parts, with a stem 622 having a
radially outwards extending flange 680 that supports an annular
collar 681. An upper surface of the stem 622 and an inner surface
of the collar 681 combine to define the die cavity 621. The collar
681 has a depending skirt 682 that is substantially coterminous
with the depth of the flange 680 and ensures the collar is securely
mounted on the stem 622. In order to detect whether die failure has
occurred gas is directed through a gas passage in the holder and
into a bleed hole 683 defined in the flange 680 of the stem 622.
The bleed hole 683 extends across the depth of the flange 680 from
the interface with the die holder to an interface with the collar
681. The upper surface of the stem 622 may define a protrusion, pip
or nub 684 that is designed to ensure that the rivet is upset
appropriately during rivet insertion and deformation of the
workpiece.
[0065] The two-part die configuration of FIG. 12 is designed
particularly to avoid premature die failure.
[0066] Initial tests conducted by the applicant have established
that being able to detect a loose die and take suitable remedial
action (i.e. tightening, re-fitting or re-sealing the die) has
prolonged the life expectancy of the die considerably and in excess
of expectations.
[0067] In all embodiments described above the pressure sensor or
flow meter sensor may be arranged in line with the hose 42, 542
upstream of the gas passage (or passages) in the die holder or may
be located downstream of the gas passage(s). It the latter case
there may be an outlet port provide in the gas passage to which the
sensor is connected via a flexible conduit if necessary.
[0068] In an alternative arrangement the gas pressure applied is a
negative pressure or suction e.g. by applying a vacuum. In the
event of a leak between the die and the die holder, the magnitude
of the negative pressure decreases and the flow rate increases. An
appropriate sensor may sense either of these.
[0069] It will be appreciated that numerous modifications to the
above described design may be made without departing from the scope
of the invention as defined in the appended claims. For example,
the shape of the die may take any suitable form. The leak paths
afforded by the channels in the embodiments described above may be
provided by any suitable form of grooves in the relevant surfaces
of the washer or die, including recesses or the like. Moreover,
particular shape of the adapter and the passages and bore may take
any suitable form. Furthermore, the die cavity may take any
appropriate form including that suitable for clinching.
* * * * *