Note: Descriptions are shown in the official language in which they were submitted.
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TITLE OF THE INVENTION
CLINCHING TOOL, DIE AND METHOD FOR USE THEREOF
FIELD OF THE INVENTION
The present invention relates to clinching tools, dies and methods of their
use.
More specifically the present invention relates to punch and die assemblies
for
mechanically interconnecting ductile sheets of material of various
thicknesses.
BACKGROUND OF THE INVENTION
The process of clinching two metals together is a prior art that has been in
the
public domain for many years, however the existing art pertains to clinch
joining
relatively thin sheet materials, such as those used in the automotive and the
durable goods (ranges, refrigerators) industries. These materials are thinner
gauge, normally up to 1/8 inch (10 gauge) thickness.
The prior art reveals single stroke and double stroke methods for mechanically
interconnecting sheets materials. The single stroke, for the most part,
utilise
expandable or multiple component dies. The multiple component dies are quite
complicated, but are normally required to allow for material displacement to
form the mechanical interconnection, without causing extremely high tooling
material stresses and premature tooling failure. Double stroke methods
typically include a die having a moveable anvil which, following a first step
drawing an amount of the sheets being interconnected into the. die, pushes the
drawn material out the die prior to a subsequent compression step creating the
mechanical . interlock.
SUMMARY OF THE INVENTION
In order to address the above and other drawbacks of the prior art, there is
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disclosed a die for use. with a punch for mechanically interconnecting a
plurality
of sheets of a ductile material. The die comprises a die cavity comprising a
closed end. An inner surface of the closed end has a raised surface profile.
There is also disclosed a clinching tool for mechanically interconnecting at
least
two stacked sheets of a ductile material. The clinching tool comprise a punch,
a
die comprising a die cavity, a closed end of the cavity having a raised
surface
profile, and a controllable source of pressure between the punch and the die.
When the source of pressure is applied between the punch and die, the punch
draws a clinch volume of the sheets. substantially completely into the die
cavity.
Additionally, there is disclosed a method for mechanically interconnecting at
least two stacked sheets of a ductile material. The method comprises the steps
of providing a die comprising a die cavity, a closed end of the cavity having
a
raised surface profile, drawing a clinch volume of the at least two sheets
into
the die cavity, the clinch volume being deformed by the die such that adjacent
sheets mechanically interconnect, and stripping the sheets from the die.
Furthermore, there is disclosed a mechanically interconnected stack of ductile
sheets. The stack comprises at least one region of deformation, wherein each
of the sheets is deformed in the region of deformation, each of the
deformations interacting together to form a mechanical bond and a protrusion
on a first surface of the stack in the region of deformation, the protrusion
comprising a curved depression towards a centre thereof.
There is also disclosed a one piece die for use with a punch for mechanically
interconnecting at least two sheets of a ductile material. The die comprises a
die cavity comprising a sidewall and a bottom wall, the bottom wall defining a
raised surface within the cavity.
Additionally, there is disclosed a die for use with a punch for mechanically
interconnecting at least two sheets of a ductile material. The die comprises a
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die cavity comprising a sidewall and a bottom wall, the bottom wall defining a
curved surface within the cavity.
BRIEF DESCRIPTION OF THE DRAWINGS
Having thus generally described the nature of the invention, reference will
now
be made to the accompanying drawings, showing, by way of illustration an
illustrative embodiment thereof, and in which:
Figure 1 provides a front perspective view of a clinching tool in accordance
with
an illustrative embodiment of the present invention;
Figure 2 provides a top perspective view of a clinching tool detailing the
punch
and die mechanisms in accordance with an illustrative embodiment of the
present invention;
Figure 3A provides a front perspective view of a punch in accordance with an
illustrative embodiment of the present invention;
Figure 3B provides a front perspective view of a punch in accordance with an
alternative illustrative embodiment of the present invention;
Figure 4 provides a front perspective view of a die in accordance with an
illustrative embodiment of the present invention;
Figure 5A provides a sectional view of a punch and die in accordance with an
illustrative embodiment of the present invention;
Figure 5B provides a detailed sectional view of a die cavity in accordance
with
an illustrative embodiment of the present invention;
Figure 6A provides a sectional view of a punch and die with a pair of sheets
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placed there between in accordance with an illustrative embodiment of the
present invention;
Figure 6B provides a sectional view of a punch and die with a pair of sheets
drawn into the die cavity in accordance with an illustrative embodiment of the
present invention; and
Figure 7 provides a detailed front perspective sectional view of a clinch in
accordance with an illustrative embodiment of the present invention.
DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS
Referring now to Figure 1, a clinching tool, generally referred to using the
reference numeral 10, and in accordance with an illustrative embodiment of the
present invention will now be described. The clinching tool 10 comprises a
vertically mounted hydraulic cylinder 12 supported at an upper end 14 to a
framework,16 manufactured from heavy structural steel or the like. A ram 18
exits a lower end 20 of the hydraulic cylinder 12 and is adapted for vertical
movement relative to same. A controllable source of hydraulic fluid and
pressure 22 is interconnected with the cylinder 12 via a control valve
mechanism 24 and. a pair of hoses 26, 28. As known in the art, the ram 18
reciprocates. relative to the lower end 20 of the cylinder 14 by controlling
the
direction of flow of pressurised hydraulic fluid using a control valve 24. In
this
regard, the control valve 24 is equipped with a control lever 30 for manually
controlling the direction of flow of hydraulic fluid.
Note that although the clinching tool 10 has been described using a
hydraulically actuated cylinder 12 and ram 18, other types of reciprocating
presses, for example pneumatic or mechanical presses, could also be used.
Still referring to Figure 1, a die anvil (or bed) 32 is secured to the
framework 16
below the hydraulic cylinder 12 and ram 18 assembly. Referring now to Figure
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2 in addition to Figure 1, a punch 34 is removeably secured to an end 36 of
the
ram 18 and moves with the ram 18 relative to a die 38. The die 38 is held
securely yet removeably in the die anvil 32 illustratively using a collet type
mount.
Referring now to Figure 3A, the punch 34, which may be constructed for
example of heat treated D2 tool steel, powdered metallurgical tool steel (PM
tool steel, such as Vanadis 6 ), or other materials of the like, is presented
in
this illustrative embodiment as having a circular cross section. It should be
understood that, although the present illustrative embodiment discloses a
punch having generally circular cross sections, other cross sections, for
example square, rectangular or oblong, would also provide suitable punch
shapes.
Still referring to Figure 3A, punch 34 comprises an elongated punch tip 40 of
circular cross section extending downwardly from a flat annular punch shoulder
42. A punch base 44, comprising an inverted frustum portion 46 and a
cylindrical portion 48 extends upwardly and outwardly therefrom. A threaded
punch fastening post 50 which is smaller than the cylindrical section 48 of
the
punch base 44 is integrally attached thereto thus defining an annular shelf 52
at
their juncture. Referring back to Figure 2, as will now be apparent to one of
ordinary skill in the art, the punch 34 is secured to the ram 18 simply by
inserting the threaded punch fastening post 50 into a threaded opening (not
shown) machined into the end 36 of the ram 18 and tightening the punch 34
.25 until the annular shelf 52 is resting tightly against the end 36 of the
ram 18.
While securely fastened to the ram 18, the punch 34 remains easily accessible
and quickly interchangeable.
Referring back to Figure 3A, the punch tip 40 comprises a convex or rounded
tip end surface 54, which facilitates penetration of the punch tip 40 into the
stacked sheets to be clinched (not shown), thus relieving excess tooling
material stresses and reducing the likelihood of premature tooling failure.
The
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addition of the rounded tip end surface 54 improves the drawing of material
into
the die by reducing the shearing action of the punch tip 40. This attribute is
particularly advantageous when clinching thick materials, namely in the range
of about 0.25 to about 1.00 inch (about 6.3 mm to about 25.4 mm) thick sheet
stacks, but can also be useful for clinching thinner materials as reduced
clinching pressures are inherently required to complete the same task. In the
present illustrative embodiment the punch tip 40 at the rounded tip end
surface
54 has a diameter of about 0.716 inches (about 18.2 mm) at the rounded tip
end surface 54 of the punch tip 40 is illustratively machined with a convex
profile having a radius of about 3 inches (about 76.2 mm).
Still referring to Figure 3A, the punch tip 40 is illustratively frustum
shaped,
whereby the outer peripheral wall 56 of the punch tip 40 is tapered towards
the
rounded tip end surface 54. Illustratively, the diameter of the punch tip 40
decreases linearly as one moves away from the punch shoulder 42 towards the
tip end surface 54, which facilitates the removal of the punch tip 40 from
clinched sheets once a clinch has been formed. In an illustrative embodiment
of
the present invention, the outer peripheral wall 56 forms an angle of about 0
to
about 6 with the longitudinal axis of the punch 34. In an alternative
illustrative
embodiment of the present invention, the outer peripheral wall 56 forms an
angle of about 2 to about 4 with the longitudinal axis of the punch 34. In
still a
further alternative illustrative embodiment of the present invention, the
outer
peripheral wall 56 forms an angle of about 3 with the longitudinal axis of
the
punch 34.
Referring now to Figure 3B, in an alternative illustrative embodiment of the
present invention the punch 34 is comprised of a punch tip 40 machined such
that the outer peripheral wall 56 has a ridged (or stepped) profile comprised
of
two or more concentric disk portions as in 58. The concentric disk portions as
in
58 are of decreasing diameter as one moves away from the punch shoulder 42
towards the tip end surface 54.
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Referring now to Figure 4 and Figure 5A, the die 38 is also presented in this
illustrative embodiment as having a cylindrical symmetry. The die is
manufactured, for example, from heat treated D2 tool steel, powdered
metallurgical tool steel (PM tool steel, such as Vanadis 4 ) or the like. The
die
38 comprises a die cavity 60 comprising an open end 62 and a closed end 64.
An inner surface 66 of the closed end 64 has a raised surface profile,
illustratively curved and convex, and having a radius R of about 1.35 inches
(about 35 mm). Illustratively, the die 38, further comprises a dowel hole 68
in a
base end 70 thereof. A dowel 72, which forms part of the die anvil 32, is
centred and aligned with the punch tip 40, and serves to guide and align the
die
38. A set of die anvil walls 74, as discussed above in this illustrative
embodiment comprising a collet style mounting, tightly accepts the die 38;
thereby securing the die 38 in place while allowing the die 38 to be easily
interchanged. The die anvil 32 is in turn secured to a clinching base 76, or
table, by a suitable fastening means, illustratively a set of bolts 78 which
are
inserted and tightened into threaded openings 80 in the base 76.
Referring back to Figure 2, in an alternative illustrative embodiment of the
present invention, the die anvil 32 further comprises a stripping mechanism 82
comprised of a stripper 84 mounted to a base 86 using a hinge mechanism 88
around which the stripper 84 can pivot. The stripping mechanism 82 facilitates
removal of clinched sheets from the clinching tool 10.
Referring now to Figure 5A, the raised surface profile of the inner surface 66
of
the closed end 64 comprises a rounded annular depression 90 at its periphery
and a convex or domed protrusion 92 towards the centre of the surface 66. The
raised surface profile of the surface 66 facilitates movement of the ductile
metal
sheets within the die cavity 60 during clinching (as discussed hereinbelow),
relieving excess tooling material stresses and thereby reducing the likelihood
of
premature tooling failure. This attribute is useful when clinching thick
materials,
namely in the range of about 0.25 inch to about 1.00 inch (about 6.3 mm to
about 25.4 mm) thick sheet stacks, but can also be useful for clinching
thinner
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materials.
Still further in accordance with an illustrative embodiment of the present
invention, the die cavity 60 is of a slight frustum shape where a cavity
peripheral wall 94 tapering inwards from the open end 62 to the closed end 64.
Illustratively, a circular cross section of the die cavity 60 decreases
linearly from
the open end 62 to the closed end 64. The frustum shape of the die cavity 60
facilitates the removal of the clinched sheets from the die cavity 60 once the
clinch is formed. In an illustrative embodiment of the present invention, the
cavity peripheral wall 94 forms an angle of about 0 to about 6 with the
longitudinal axis of the die 38. In an alternative illustrative embodiment of
the
present- invention, the die peripheral wall 94 forms an angle of about 2 to
about
4 with the longitudinal axis of the die 38. In still a further alternative
illustrative
embodiment of the present invention, the cavity peripheral wall 94 forms an
angle of about 3 with the longitudinal axis of the die 38.
Still referring to Figure 5A, the open end 62 of the die cavity 60 comprises a
rounded shoulder 96. The rounded shoulder 96 provides for smoother.
penetration of the ductile metal sheets into the die cavity 60 during a
clinching
action.
Referring now to Figure 5B, the height Z, of the raised surface profile of the
surface 66 of the closed end 64 is illustratively between 25% and 35% of the
maximum depth Z2 of the die cavity 60.
Referring to Figure 6A, in order to clinch sheets of ductile material, the
sheets
(A & B) are positioned side by side and placed between the punch 34 and die
38. Referring now to Figure 6B, as the punch 34 is lowered by the ram 18, the
punch tip 40 makes contact with a first sheet A. Continued downward motion of
the punch 34 forces the punch tip 40 into the first ductile sheet A and a
second
ductile sheet B causing material from the ductile sheets A and B to move into
the die cavity 60. As the rounded tip end surface 54 reaches the level of the
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open end 62 of the die 38 a clinching action takes place, wherein a clinch
volume of the material of the ductile sheets A and B is drawn into the die
cavity
60 through the die opening 32. As the rounded tip end surface 54 enters the
die
cavity 60, the ductile sheets A and B are compressed between the rounded tip
end surface 54 and the raised surface profile 66, thereby causing the material
of the ductile sheets A and B to be deformed, this creating a mechanical
interlock between the ductile sheets A and B in the region of the clinch.
Still referring to Figure 6, the punch shoulder 42 serves to prevent necking
(over drawing of the ductile sheets A and B) due to over travel of the punch
34
and to limit the penetration of the punch tip 40 into the material of the
sheets A
and B. The punch shoulder 42 also helps to some degree to force the material
of the sheets A and B into the die cavity 60, thereby improving the quality of
the
clinch. Once the clinch is formed, the clinching action is reversed, and the
punch tip 40 extracted from the clinch form in the sheets'A and B. The clinch
fastened sheets A and B are then removed from the clinching tool 10.
Note that although the above illustrative embodiment has been illustrated
using
a pair of. sheets A and B, the present invention could also be used for clinch
fastening more than two (2) sheets.
Referring now to Figure 7, a typical cross section of a sample clinch 92
reveals,
in an illustrative embodiment of the present invention, a punch cavity 94 on a
first side of the sheets defined by an inverted thimble like volume with a
circular
opening 96 and a rounded closed face 98. A lower face 100 of the sheet A and
an upper face 102 of the sheet B are generally smooth and in contact, and
follow the profile of the punch tip (40 in Figure 3A) in the region of the
clinch 92.
This maintains a substantially constant thickness of the sheet A along the
rounded closed face 98. A bottom surface 104 of the sheet B has substantially
the same shape as the profile of the die cavity (60 in Figure 6). Superior
clinches are those where the ductile of material of sheets A and B are
deformed in a manner that a mechanical interlock is formed between the
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sheets below a lower surface 106 of the sheet in closest proximity to the die
(in
the case at hand, sheet B). In this regard, those clinches where a diameter D
of.
the lower face 100 of the first sheet A is greater than the diameter D' of the
clinch in the second sheet B provide such a mechanical interlock (i.e. a
bulge.
formed in the ductile material of the first sheet A in the region of the
clinch
interlocks with a corresponding bulge formed in the ductile material of the
second sheet B).
In order to examine the suitably of punch/die combinations, punches and dies
having different diameters and depths were tested using samples of copper
sheets, each of the sheets having a thickness of about 0.380 inches (about 9.7
mm) for a total composite thickness of about 0.760 inches (about 19.3 mm).
TABLE 1 provides an overview of the test results.
TABLE 1
PUNCH DIE RATING
0.794" (20.2 mm) diameter 1.24" (31.5 mm) diameter
Flat nose 0.33" (8.4 mm) depth Passable*
0.794" (20.2 mm) diameter 1.300" (33 mm) diameter
Flat nose , 0.375 (9.5 mm) depth Very Good
0.748" (19 mm) diameter 1.24" (31.5 mm) diameter
1" (25.4 mm) radius on nose 0.295" (7.5 mm) depth Passable*
0.748" (19 mm) diameter 1.24" (31.5 mm) diameter
1" (25.4 mm) radius on nose 0.33" (8.4 mm) depth . Failed**
0.748" (19 mm) diameter 1.300" (33 mm) diameter
1" (25.4 mm) radius on nose 0.375 (9.5 mm) depth Passable*
0.704" (17.9 mm) diameter 1.24" (31.5 mm) diameter
Flat nose 0.295" (7.5 mm) depth Very Good
0.704" (17.9 mm) diameter 1.24" (31.5 mm) diameter
Flat nose 0.33" (8.4 mm) depth Very Good
0.704" (17.9 mm) diameter 1.24" (31.5 mm) diameter
Flat nose 0.33" (8.4 mm) depth Excellent
0.724" (18.4 mm) diameter 1.24" (31.5 mm) diameter Good
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3" (76.2 mm) radius on nose 0.33" (8.4 mm) depth
0.724" (18.4 mm) diameter 1.24" (31.5 mm) diameter
3" (76.2 mm) radius on nose 0.33" (8.4 mm) depth Good
3 Step 1.24" (31.5 mm) diameter
3" (76.2 mm) radius on nose 0.295" (7.5 mm) depth Passable***
3 Step 1.24" (31.5 mm) diameter
3" (76.2 mm) radius on nose 0.33" (8.4 mm) depth Passable***
*clinch outside of die **not enough clinch ***die not completely filled
Note that in the above table, depth refers to the deepest (or lowest) point in
the
die.
While this invention has been described with reference to the illustrative
embodiments, this description is not intended to be construed to a limiting
sense. Various modifications or combinations of the illustrative embodiments,
as well as other embodiments of the invention, will be apparent to persons
skilled in the art upon reference to the description. It is therefore intended
that
the described invention encompass any such modifications or embodiments.
