Metal deforming – By relatively movable offset tool-faces – With tool motion in fixed path
Reexamination Certificate
2002-05-23
2004-03-16
Jones, David B. (Department: 3725)
Metal deforming
By relatively movable offset tool-faces
With tool motion in fixed path
C072S391800, C029S243518, C029S243530
Reexamination Certificate
active
06705149
ABSTRACT:
FIELD OF THE INVENTION
The present invention is directed to a backup mandrel. More particularly, the present invention is directed to a backup mandrel for attaching a grommet to a washer within an opening in an aircraft panel.
BACKGROUND OF THE INVENTION
An aircraft typically has an outer skin comprised of a plurality of panels. Each panel, in turn, typically comprises a plurality of openings for receiving screws, bolts, rivets or the like (hereinafter fasteners), which are used to fasten the panel to an internal structure of the aircraft. When the panel has been fastened to the internal structure of the aircraft in this way and the panel experiences a force tending to shift the panel, the fasteners exert a corresponding force on the panel openings to prevent the panel from shifting. However, the fasteners are generally comprised of a material that is much stronger than the material of the panel. For example, a typical fastener is comprised of stainless steel or titanium, while a typical panel is comprised of a composite material, such as fiber glass. Consequently, as the fasteners bear against the panel openings, over time the panel openings wear, i.e. become enlarged, resulting in a loose connection between the panel and the internal structure of the aircraft, or worse, the fasteners fracture or delaminate the panel, possibly resulting in the panel disengaging from the internal structure of the aircraft.
To alleviate this problem a metal insert may be affixed within the panel opening. For example,
FIG. 1A
shows a metal grommet
10
inserted into an aircraft panel
12
through a panel opening
14
. A first end
10
A of the grommet
10
abuts a first surface
12
A of the panel
12
, while a washer
16
having an opening
160
abuts a second surface
12
B of the panel
12
. The grommet
10
extends through both the panel opening
14
and the washer opening
160
, such that a second end
10
B of the grommet
10
protrudes from the washer opening
160
. To affix the grommet
10
within the panel opening
14
, the second end
10
B of the grommet
10
is swaged, i.e. flared or bent, towards a recessed area
16
R in the washer
16
until the second end
10
B of the grommet
10
abuts an exposed surface of the washer
16
within the recessed area
16
R, as shown in FIG.
1
B.
FIGS. 2A-2C
show prior art backup mandrels
18
,
18
A and
18
C having shoulders of varying lengths. For clarity and to avoid duplication, a majority of the following description will involve the backup mandrel
18
having a shoulder
21
B. The backup mandrel
18
comprises a nose piece
20
having the shoulder
21
B and a mandrel stem
22
. The mandrel stem
22
comprises a stem head, a stem body and a stem tip. The stem head is larger than a nose piece opening and the stem body and stem tip are smaller than the nose piece opening to allow the stem body and tip to be inserted into the nose piece opening. A first portion of the stem body is housed within the nose piece opening, while a second portion of the stem body and the stem tip protrude from the nose piece opening.
FIGS. 2D-2F
show the prior art backup mandrel
18
being used to affix the grommet
10
within the panel opening
14
. In use, the stem tip, the stem body and the shoulder
21
B are inserted into the grommet
10
until the nose piece
20
abuts the first end
10
A of the grommet
10
and the stem tip and the second portion of the stem body protrude from the second end
10
B of the grommet
10
. The second portion of the stem body and the stem tip are then inserted into an opening in a swage gun
24
. The swage gun
24
comprises a first swage tool
28
, which is moved in a position disposed within an inner diameter of the grommet
10
. Within the swage gun
24
is a plurality of jaws
26
having teeth that removably clampingly engage a plurality of grooves
25
in the stem tip. When the jaws
26
are clampingly engaged with the stem tip, the jaws
26
pull the stem, and therefore the entire backup mandrel
18
towards the swage gun
24
. This motion causes the second end
10
B of the grommet
10
to contact an angled shoulder
30
on the first swage tool
28
.
As shown in
FIG. 2E
, as the second end
10
B of the grommet
10
is pressed against the angled shoulder
30
of the first swage tool
28
, the second end
10
B of the grommet swages, i.e. is bent, in the shape of the angled shoulder
30
. However, as can be seen in
FIG. 2E
, during the swaging, a portion
32
of the inner diameter of the grommet
10
is not supported. As a result, buckling
34
often occurs in the unsupported portion
32
of the grommet
10
. As a result, as the jaws
26
continue to pull the backup mandrel
18
towards the swage gun
24
, the shoulder
21
is often compressed by the buckling
34
. This makes removal of the shoulder
21
B from the grommet
10
after the grommet
10
has been affixed to the panel
12
difficult. In addition, the compression of the shoulder
21
B can cause breakage of the mandrel stem
22
; tearing or delaminating of the panel
12
; or failure of the installed grommet. Also, in some instances the buckling
34
reduces the grommet internal diameter to the point that the fastener intended to be inserted into the grommet
10
, to attach the panel
12
to the internal structure of the aircraft, cannot be inserted through the grommet
10
past the buckling
34
. In such an instance, the grommet
10
must be drilled out of the panel
12
and, if the panel
12
did not suffer any damage, a new grommet
10
must be installed into the panel
12
.
As shown in
FIG. 2F
, when a biasing force that biases the first swage tool
28
towards the grommet
10
is overcome by the force required to further swage the grommet
10
, a further pulling of the backup mandrel
18
towards the swage gun
24
by the jaws
26
causes the first swage tool
28
to retract into the swage gun
24
. When the first swage tool
28
is retracted, a second swage tool
36
is allowed to contact the second end
10
B of the grommet
10
. Thus, as the jaws
26
continue to pull the backup mandrel
18
towards the swage gun
24
, the second swage tool
36
contacts the second end
10
B of the grommet
10
, swaging the second end
10
B of the grommet
10
towards the recessed area
16
R of the washer
16
until the second end
10
B of the grommet
10
contacts the washer
16
.
However, because the backup mandrel
18
does not comprise a force limiting or shock absorbing means, the swaging of the grommet
10
by the first and second swage tools
28
and
36
occurs at full force and very abruptly, i.e. the first and second swage tools
28
and
36
slam into the second end
10
B of the grommet
10
at full force and with considerable shock, causing the first end
10
A of the grommet
10
to forcefully press against the nose piece
20
, often causing dishing
38
(see
FIG. 3C
) in the first end
10
A of the grommet
10
.
The dishing
38
often causes the fastener, which is intended to be inserted into the grommet
10
to attach the panel
12
to the internal structure of the aircraft, to not fit flushly against the first end
10
A of the grommet
10
. As a result, it is difficult to fasten the fastener as far into the internal structure of the aircraft as desired, resulting in a loose connection of the panel
12
to the internal structure of the aircraft. Also, dishing
38
usually causes a collapse of the internal diameter at
10
A end of the grommet
10
, requiring the grommet to be removed from the structure, and replaced.
The backup mandrel
18
also has other disadvantages. For example, if the shoulder
21
B contacts the first swage tool
28
the shoulder
21
B will cause the first swage tool
28
to retract into the swage gun
24
. As such, the length of shoulder
21
is dimensioned such that it does not contact the first swage tool
28
until the first swage tool
28
has swaged the second end
10
B of the grommet
10
by a desired amount. Therefore, the length of the shoulder
21
B is designed such that it is as long as possible without interfering with the first swage
Cobzaru Cristinel O.
Myers Alan
Christie Parker & Hale LLP
Huck Patents, Inc.
Jones David B.
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