Note: Descriptions are shown in the official language in which they were submitted.
CA 02462357 2004-03-24
METHOD AND APPARATUS FOR JOTNING TUBES
Field of the Invention
This invention relates to a method and apparatus for joining tubes. In
particular, this invention relates to a method and apparatus for joining metal
tubes
end-to-end without welding.
Background of the Invention
Metal tubes are used in many applications. A tubular member or frame can be
used to form a support or frame for myriad types of materials, fox example
springs,
cushions, straps, fabric ete. For example, many components of an automobile
are
to constructed from steel tubes. In some cases, the design of the part
requires that tubes
of different diameters be joined end-to-end.
The conventional method of joining metal tubes is by welding. However,
welding is a slow, labour-intensive, inconsistent and dirty process. Further,
the
welding of parts creates quality control concerns, even when welding is
effected by a
15 skilled welder. The effectiveness of a weld is typically assessed visually,
and
problems such as burn-through, metal fatigue in the material surrounding the
weld,
incomplete adhesion due to contaminants on the tubular components and so on,
are
not always avoidable. In applications such as automobile parts, these types of
problems can cause serious safety concerns.
2o It would accordingly be advantageous to provide a method for joining metal
tubes end-to-end without the need for welding, preferably in a single-step
process,
while increasing the strength and consistency of the joints by removing the
element of
judgment and other variables inherent in the welding process.
Summary of the Invention
25 The present invention overcomes these disadvantages by providing a
method and apparatus for joining tubes that is especially suitable for metal
tubes.
According to the method of the invention, a first tubular member having an end
with a
first diameter is interlocked with a second tubular member having an end with
a
second diameter that is larger than the first diameter. In the preferred
embodiment this
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is accomplished in a single operation, thus saving considerable time and cost
relative
to conventional welding operations, while providing a much stronger connection
between the interlocked components.
The invention accomplishes this by curling the joint edge of the larger-
diameter (outer) tube inwardly while curling the joint edge of the smaller-
diameter
(inner) tube outwardly so that the joint edges interlock. In the preferred
embodiment,
the same compression stroke forms a bead about the smaller-diameter tube so
that the
curled edge of the larger-diameter tube is sandwiched between the curled edge
of the
smaller-diameter tube and the bead. In the preferred embodiment the completion
of
1o the stroke clinches the curled edge of the larger-diameter tube between the
bead and
the curled edge of the smaller-diameter tube, forming a secure joint that
prevents both
axial dislodgement and rotation.
In the preferred embodiment the larger-diameter tube is loaded onto a mandrel
for supporting the interior of the larger-diameter tube wall, having an outer
tube seat
at one end for abutting the free end of the larger-diameter tube; an inner
tube seat at
the other end for abutting the j oint end of the smaller-diameter tube in
overlapping
relation to the joint end of the larger-diameter tube; and a constricted
mandrel tip
projecting from the inner tube seat for supporting the interior of the joint
end of the
smaller-diameter tube and guiding the formation of the curled edge. The
smaller-
diameter tube is disposed through a first collar for supporting the outside
wall of the
smaller-diameter tube, and the larger-diameter tube is disposed through a
second
collar for supporting the outside wall of the larger-diameter tube.
Thus, when axially compressed, the joint edges flow into a clearance about the
constricted mandrel tip. In the preferred embodiment the second collar is
provided
with an axial spacer, and as the compression stroke nears completion the
spacer is
retracted to allow material from the smaller-diameter tube wall to form a bead
spaced
from the curled edge of the smaller-diameter tube and clinching the curled
edge of the
larger-diameter tube between the bead and the curled edge of the smaller-
diameter
tube.
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CA 02462357 2004-03-24
The invention thus provides a method of joining an end of a larger-diameter
tube to and end of a smaller-diameter tube, comprising the steps of: a.
supporting;
inner and outer walls of a joint end of the larger-diameter tube and of the
smaller-
diameter tube, b. positioning the joint ends of the larger-diameter tube and
the
smaller-diameter tube in overlapping relation, and c. in any order, or
substantially
simultaneously, curling the joint edge of the larger-diameter tube inwardly
and curling
the joint edge of the smaller-diameter tube outwardly so that the joint edges
interlock.
Other aspects of the method comprise, after or simultaneously with step c;.,
the
step of d. forming a bead about the smaller-diameter tube so that the curled
edge of
l0 the larger-diameter tube is sandwiched between the curled edge of the
smaller-
diameter tube and the bead; and optionally, after or simultaneously with step
d., the
step of e. clinching the curled edge of the larger-diameter tube between the
bead and
the curled edge of the smaller-diameter tube.
The present invention further provides tooling for joining an end of a larger-
15 diameter tube to and end of a smaller-diameter tube, comprising: a collar
for
supporting an outer wall of a joint end of the larger-diameter tube, a collar
for
supporting an outer wall of a joint end of the smaller-diameter tube
comprising a tube
seat for curling an edge of the joint end of the smaller-diameter tube
outwardly, and a
mandrel for supporting an imier wall of a j oint end of the larger-diameter
tube
2o comprising a tip for supporting an inner wall of a joint end of the smaller-
diameter
tube overlapping relation with the larger-diameter tube and a tube seat for
curling an
edge of the joint end of the smaller-diameter tube, whereby axial compression
of the
tubes causes the edge of the joint end of the smaller-diameter tube to curl
outwardly
and causes the edge of the joint end of the larger-diameter tube to curl
inwardly,
25 thereby interlocking the joint ends of the tubes.
In other aspects the tooling of the invention further comprises a spacer ring
disposed between the collars, whereby removal of the spacer ring while
continuing
that axial compression after the joint ends of the tube are interlocked causes
a bead to
form about the smaller-diameter tube.
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CA 02462357 2004-03-24
Brief Description of the Drawings
In drawings which illustrate by way of example only a preferred embodiment
of the invention,
Figure 1 is a perspective view of two tubes before the joining process.
Figure 2 is a perspective view of the tubes of Figure 1 with the smaller-
diameter tube loaded into the first collar and the larger-diameter tube loaded
onto the
mandrel.
Figure 3 is a perspective view of the tubes being compressed during the
joining process.
to Figure 4 is a cutaway elevation showing the tubes after the joining
process.
Figures SA to SF are schematic views showing the steps in the preferred
embodiment of the method of the invention.
Detailed Description of the Invention
Figures 1 to 3 illustrate the components of an apparatus for joining two tubes
15 10, 20. The invention will be described in relation to two tubes 10, 20
having difi:erent
diameters; however, it will be appreciated that only the joint ends 12, 22 of
the tubes
10, 20 need to be of different diameters, and the invention can be implemented
between any two metal tubes that fit together in overlapping relation.
In the preferred embodiment the tooling for the invention, preferably formed
2o from steel or any other material suitable for tooling, comprises a mandrel
30 for
supporting the interior of the wall of the larger-diameter tube 10. The
mandrel 30 has
an outer tube seat 32 at one end for abutting the free end 14 of the larger-
diameter
tube 10; an inner tube seat 34 at the other end preferably having a concave
annulus for
abutting the joint end 22 of the smaller-diameter tube 20 and guiding the
formation of
25 the curled edge; and a constricted mandrel tip 36 projecting from the inner
tube scat
34 for supporting the interior of the joint end 22 of the smaller-diameter
tube 20 when
the joint is formed.
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The smaller-diameter tube 20 is disposed through a first collar 40 for
supporting the outside wall of the smaller-diameter tube 20. In the preferred
embodiment a retractable spacer ring 60 is also provided, preferably formed
from
separable halves 62, 64 in order to allow for retraction of the spacer ring 60
during the
s compression stroke, as described in detail below, and providing a tube seat
66
preferably having a concave annulus for curling the joint end 12 of the larger-
diameter
tube 10, as explained below. The larger-diameter tube 10 is disposed through a
second
collar 50 for supporting the outside wall of the larger-diameter tube 10. The
collars
40, 50 may be formed from halves for easy manufacture and maintenance. The
larger-
l0 diameter tube 10 may be limited in length, because the mandrel 30 must be
retracted
from the tube 10 after joining and there is a practical limit to the length of
a mandrel
30 that will permit retraction. The smaller-diameter tube 20 may be of any
desired
length.
Figures SA to SF illustrate the steps in the preferred embodiment of the
15 method in order to create the joint illustrated in Figure 4. The components
are loaded
into a press (not shown), with the smaller-diameter tube 20 on one side and
the larger-
diameter tube 10 on the other. The mandrel 30 is aligned with the larger-
diameter tube
10, which is in turn aligned with the collar 50. The smaller-diameter tube 20
is aligned
with the collar 40.
2o As shown in Figure SA, as the compression stroke begins the mandrel 30 is
inserted into the larger-diameter tube 10 and the smaller-diameter tube 20 is
inserted
into the collar 50. Figure Sfi shows the mandrel 30 fully inserted into the
larger-
diameter tube 10 and the smaller-diameter tube 20 fully inserted into the
collar '.i0,
and Figure SC shows the mandrel 30 being inserted through the collar 40. As
the
25 compression stroke continues, the larger-diameter tube 10 overlaps the
smaller-
diameter tube 20 and the mandrel tip 36 projects into the smaller-diameter
tube 20.
The joint end 12 of the larger-diameter tube then 10 bottoms out on the tube
seat 66
formed in the spacer ring 6C1 and the smaller-diameter tube 20 bottoms out on
the
inner tube seat 34 of the mandrel 30. As shown in Figure SD, when the joint
end 12 of
3o the larger-diameter tube 10 is compressed against the tube seat 66, the
edge of the
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CA 02462357 2004-03-24
joint end 12 of the tube 10 curls inwardly; likewise, when the joint end 22 of
the
smaller-diameter tube 20 is compressed against the tube seat 34, the edge of
the joint
end 22 of the tube 20 curls outwardly. The tube ends 12., 22 thus interlock.
This
portion of the method of the invention itself interlocks the tubes 10, 20, and
if no
resistance to rotation or axial compression of the two tubes 10, 20 (i.e. the
srnaller-
diameter tube 20 sliding into the larger-diameter tube 10) is required, the
tubes 10, 20
are effectively joined. For this type of joint the retractable spacer 60 is
not required,
and the tube seat 66 for curling the joint end 12 of the larger-diameter tube
10 can be
formed directly into the collar 40.
1 o However, in the preferred embodiment the tubes 10, 20 are further
restrained
against axial slippage and rotation by forming a bead 24 about the smaller-
diameter
tube 20 and compressing the bead 24 against the interlocked edges of the tubes
10, 20.
As shown in Figure SE, as the compression stroke nears completion the halves
62, 64
of the spacer ring 60 are retracted to allow the smaller-diameter tube 20 to
collapse
15 outwardly between the collars 40, 50 to form a bead 24 spaced from the
curled edge of
the smaller-diameter tube 20 (the inside wall of the tube 20 where the bead 24
forms
is supported by the mandrel tip 36, so the tube wall must buckle outwardly).
Figure
SE shows the bead 24 beginning to form. As the compression stroke ends the
collar 40
closes on the bead 24, clinching the curled edge of the larger-diameter tube
10
2o between the bead 24 and the curled edge of the smaller-diameter tube 20, as
shown in
Figure SF. The press is then released and the mandrel 30 retracted to release
the joined
tubes 10, 20 having the joint configuration shown in Figure 4.
It will be appreciated that the compression of the parts is a relative motion,
and
it does not matter whether the smaller-diameter tube 20 is held stationary
while the
25 other components move or the larger-diameter tube 10 is held stationary
while the
other components move, or all parts move in the press.
In the embodiment shown and described, the face of the collar 40 that
squeezes the bead 24 after the spacer ring 60 has been retracted is shown as
planar. It
is possible to provide a concave annulus in the face of the collar 40 that
squeezes the
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bead 24 after the spacer ring 60 is retracted, and this may be desirable if
the shape of
the bead 24 is important.
Various embodiments of the present invention having been thus described in
detail by way of example, it will be apparent to those skilled in the art that
variations
and modifications may be made without departing from the invention. The
invention
includes all such variations and modifications as fall within the scope of the
appended
claims.
