Note: Descriptions are shown in the official language in which they were submitted.
CA 02833811 2015-07-03
SELF-DRILLING EXPANSION FASTENER AND METHOD OF FORMING SAME
FIELD OF THE INVENTION
The present invention relates to an expansion fastener integrally formed of a
sheet metal
material, and more particularly to an expansion fastener capable of self-
drilling a hole.
BACKGROUND OF THE INVENTION
An expansion fastening device is usually used to fixedly connect multiple
sheet
workpieces, such as building panels, to one another, and includes a bolt and
an
expansion fastener. Fig. 1 shows a typical conventional expansion fastener 10,
which
includes a barrel body 11 having a plurality of longitudinally extended
elongated slots
12 formed thereon to define a plurality of laterally spaced middle bars 13; a
nut 14
connected to a head of the barrel body 11; and a bottom cover 15 connected to
a bottom
of the barrel body 11. As shown in Fig. 2, a bolt 16 can be extended through
the
bottom cover 15 and the barrel body 11 of the expansion fastener 10 to mesh
with the nut
14. When the barrel body 11 is subjected to a pull, the middle bars 13
are brought to
expand outward and become deformed. The deformed middle bars 13 and the bolt
16
together lock an attached object 17 to a supporting object 18.
The conventional expansion fastener 10 is disadvantageous in terms of
assembling and
installation thereof. First, the nut 14 and the bottom cover 15 are connected
to the
barrel body 11 by welding, which is time and labor consuming to result in high
manufacturing cost of the expansion fastener 10. Second, two steps are
required to
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install the conventional expansion fastener 10 on a sheet workpiece, such as a
panel or a
board. That is, a hole having size corresponding to the expansion fastener 10
must first
be drilled on the supporting object 18; and then, the barrel body 11 is driven
into the
hole with a hammer, for example, so that the barrel body 11 is tightly fitted
in the hole
without the risk of rotating relative to the supporting object 18. The above
installation
is apparently troublesome and consumes a lot of time and labor. It is
therefore
desirable to overcome these disadvantages.
SUMMARY OF THE INVENTION
An aspect of the present inventioli provides a self-drilling expansion
fastener, with
which a user can lock two or more sheet workpieces together with only one
installation
step to largely simplify the working procedure and upgrade the working
efficiency.
Another aspect of the present invention provides a method of integrally
forming a
self-drilling expansion fastener from a sheet metal material through a series
of punching
and stamping procedures, so that the self-drilling expansion fastener can be
easily
manufactured with upgraded production efficiency.
To achieve the above, the self-drilling expansion fastener according to the
present
invention is integrally formed of a sheet metal material for locking two or
more sheet
workpieces together, and includes an expansion structure and a drill structure
located at
a head of the expansion structure. The expansion structure has a plurality of
internal
threads and a plurality of force-distributing bars. The drill structure has a
chip guard for
covering the head of the expansion structure, and a drill forward projected
from the chip
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guard for self-drilling a hole on the sheet workpieces, so that the expansion
structure can
be extended through the sheet workpieces and tightly received in the drilled
hole with
the force-distributing bars fully located behind the sheet workpieces. The
chip guard
features sector-shaped covers overlying respective areas of the head of the
expansion
structure in a manner collectively overlying a substantial entirety thereof.
The drill
features a respective drill bit that is integrally attached to each sector-
shaped cover, is
bent out of plane therefrom on a bend line that lies radially of the expansion
structure,
and resides in a position spanning radially from a center of the head to an
outer
circumference thereof. When an externally threaded element is gradually
screwed deeper
into the expansion structure to mesh with the internal threads, the force-
distributing bars
are brought to expand outward and are finally compressed into a folded state
to thereby
tightly lock the sheet workpieces to one another.
To achieve the above, the method according to the present invention for
integrally
forming a self-drilling expansion fastener includes the following steps:
(a) obtaining a sheet metal material having dimensions required for forming
the
self-drilling expansion fastener, and defining an expansion structure zone and
a drill
structure zone on the obtained sheet metal material;
(b) stamping the expansion structure zone at a specified location, which is
defined as a
thread forming zone, to obtain threads having required dimensions;
(c) punching the expansion structure zone at a specified location, which is
defined as a
barrel body forming zone, to obtain a plurality of force-distributing bars;
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(d) punching the drill structure zone at a predetermined location to
obtain a required chip
guard featuring sector-shaped covers;
(e) punching the drill structure zone at a predetermined location to obtain
a required drill
featuring a respective drill bit integrally attached to each sector-shaped
cover at a radial line
of the respective drill bit; and
(f) stamping the thread forming zone and the barrel body forming zone to
obtain
required configurations for these two zones.
BRIEF DESCRIPTION OF THE DRAWINGS
The structure and the technical means adopted by the present invention to
achieve the
above and other objects can be best understood by referring to the following
detailed
description of the preferred embodiments and the accompanying drawings,
wherein
Fig. 1 is an exploded perspective view of a conventional expansion fastener;
Fig. 2 is a sectional view showing the expansion fastener of Fig. 1 in use;
Fig. 3 is a perspective view of a self-drilling expansion fastener according
to a preferred
embodiment of the present invention;
Fig. 4 is a front plan view of the self-drilling expansion fastener of Fig. 3;
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Fig. 5 is a developed view of the self-drilling expansion fastener of Fig. 3;
Fig. 6 is a cutaway view of the self-drilling expansion fastener of Fig. 3;
Figs. 7A to 7C sequentially show the steps of installing the self-drilling
expansion
fastener of the present invention; and
Figs. 8A to 81 sequentially illustrate the steps included in a method
according to the
present invention for forming the self-drilling expansion fastener.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention will now be described with a preferred embodiment
thereof and
with reference to the accompanying drawings.
Please refer to Figs. 3 to 6. A self-drilling expansion fastener 20 according
to a
preferred embodiment of the present invention is integrally formed of a sheet
metal
material, and includes an expansion structure 21 and a drill structure 30
located at a head
of the expansion structure 21. The expansion structure 21 has a front portion
formed
into an internally threaded body portion 22 and a rear portion formed into a
barrel body
portion 23. The internally threaded body portion 22 is a cylindrical hollow
body and
defines a plurality of internal threads 24.
The barrel body portion 23 is a hexagonal hollow body and internally defines a
hex bore.
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The barrel body portion 23 includes a plurality of laterally spaced force-
distributing bars
25. Once the barrel body portion 23 is subjected to an axial pull, stress
occurs at the
force-distributing bars 25. In other words, the force-distributing bars 25
together form
a weakening zone. In the preferred embodiment as shown in Fig. 5, there are
six
axially extended force-distributing bars 25 being laterally equally spaced on
the barrel
body portion 23, such that a spacing slot 26 is formed between any two
adjacent
force-distributing bars 25. Further, the barrel body portion 23 includes at
least one
retaining wing 27. In the illustrated preferred embodiment, as shown in Fig.
5, there
are two retaining wings 27 formed on the barrel body portion 23 by stamping,
so that
these retaining wings 27 are outward protruded from a wall surface of the
barrel body
portion 23 and are slant at a fixed and oblique angle relative to a horizontal
rear end of
the barrel body portion 23. And, the barrel body portion 23 includes at least
one
stopper 28 formed on the rear end thereof Again, as can be seen in Fig. 5, the
illustrated preferred embodiment of 'he present invention has two
diametrically opposite
stoppers 28, which are respectively upward bent from the rear end of the
barrel body
portion 23 to a sidcwardly projected position.
The drill structure 30 includes a chip guard 31 and a drill 32. As can be seen
in Fig. 3,
the chip guard 31 includes two side covers 33, which are extended from the
internally
threaded body portion 22 and bent toward each other to together cover a front
end of the
internally threaded body portion 22. It is noted two slits 35 are formed at
two lateral
sides of the joint of each side cover 33 and the internally threaded body
portion 22.
The drill 32 consists of two drill bits 34, which are forward projected from
top surfaces
of the two side covers 33.
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As clearly shown in the drawings, the side covers 33 of the chip guard are
sector-shaped
as to overlie respective sector-shaped areas of the expansion structure's
head, whereby
the side covers collectively cover the substantially entire circular area
thereof. Each
respective drill bit is integrally attached to the respective sector-shaped
cover and bent
out of plane therefrom at a radial bend line so as to lie radially of the
expansion
structure in a position spanning from a center of the head to an outer
circumference
thereof. Each drill bit is triangularly shaped. A right angle vertex of the
triangular
drill bit lies centrally of the head. One of the triangular bit's two right
angle sides
extends axially from the right angle vertex to a peak of the drill bit, and
the other of the
triangular bit's two right angle sides extends radially from the right angle
vertex to the
outer circumference of the head. A hypotenuse of the triangular bit slopes
obliquely
between the peak of the drill bit and the outer circumference of the head.
The expansion structure 21 further includes at least one coupling device 40,
which
consists of a lug portion 41 and a notch portion 42 correspondingly located
opposite to
the lug portion 41, such that the lug portion 41 and the notch portion 42 can
be engaged
with and locked to each other.
Figs. 7A to 7C illustrate the steps of installing the self-drilling expansion
fastener 20 on
sheet workpieces. First, as shown in Fig. 7A, apply a rotating force on the
barrel body
portion 23 of the self-drilling expansion fastener 20, so that the drill 32 is
brought to
drill through multiple layers of sheet workpieces, such as an attached object
50 and a
supporting object 51, for the stoppers 28 to tightly press against the
attached object 50.
In addition to the two layers of sheet worpieces shown in the embodiment, more
than
two layers may be fastened by the fastener of the invention. At this point,-
as shown in
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Fig. 7B, the force-distributing bars 25 are located behind the supporting
object 51 and
the retaining wings 27 are embedded in a peripheral wall of the drilled hole
on the
attached object 50, bringing the self-drilling expansion fastener 20 to firmly
associate
with the attached object 50 and the supporting object 51. In practical
installation of the
self-drilling expansion fastener 20, a matching hexagonal tool 54 can be
inserted into the
barrel body portion 23 to facilitate the rotation of the self-drilling
expansion fastener 20,
allowing the drill 32 to drill a hole on the attached object 50 and the
supporting object
51. The chip guard 31 functions to prevent any chips of the workpieces
50, 51 from
getting into the expansion structure 21. Thereafter, as shown in Fig. 7C,
screw an
externally threaded element 52 into the barrel body portion 23 to fully mesh
with the
internal threads 24 in the internally threaded body portion 22. When the
externally
threaded element 52 is gradually screwed deeper into the internally threaded
body
portion 22, the latter is gradually pulled backward to thereby compress the
force-distributing bars 25, bringing the latter to expand outward and finally
be
compressed into a fully folded state. The fully folded force-distributing bars
25 are
now tightly pressed against an inner side of the supporting object 51,
allowing the
self-drilling expansion fastener 20 to firmly lock the attached object 50 to
the supporting
object 51. At this point, the externally threaded element 52 has a front end
extended
beyond the drill 32 by a predetermined length to push open the side covers 33
of the chip
guard 31, so that the drill bits 34 of the drill 32 are separated from one
another.
In brief, the self-drilling expansion fastener 20 according to the present
invention is
integrally formed and has the ability of self-drilling a hole, and can
therefore be
manufactured with fewer components to reduce the production and installation
costs
thereof.
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The self-drilling expansion fastener 20 according to the present invention is
formed of a
sheet metal material through a series of punching and stamping procedures.
Figs. 8A to
81 sequentially illustrate the steps included in a method of the present
invention for
forming the self-drilling expansion fastener 20.
First, as shown in Fig. 8A,
unnecessary portions are removed from a sheet metal raw material to obtain the
sheet
metal material having dimensions for forming the self-drilling expansion
fastener 20; a
reference line "a" is defined to determine an expansion structure zone 60 and
a drill
structure zone 70 on the obtained sheet metal material; and the expansion
structure zone
60 is punched at a specified location to obtain at least one coupling device
61 and at a
rear portion to obtain required stoppers 62. Then, as shown in Fig. 8B, the
expansion
structure zone 60 is stamped at a specified location, which is defined as a
thread forming
zone 64, to obtain required threads 63. Then, as shown in Fig. 8C, the
expansion
structure zone 60 is punched at a predetermined location, which is defined as
a barrel
body forming zone 66, to obtain a plurality of required force-distributing
bars 65; and
the drill structure zone 70 is punched at predetermined locations to obtain
required side
covers 71 and drill bits 72. Each triangular drill bit 72 is integrally
attached to the
respective sector-shaped cover 71 along a radial line thereof that spans from
a radial
center of the sector-shaped cover 71 to a radial terminus thereof. One of the
triangular
bit's two right angle sides is coincident with this radial line of the sector-
shaped cover
71, and the other of triangular bit's two right angle sides extends
perpendicularly from
the triangular bit's right angle vertex at the radial center of the sector-
shaped cover 71 to
a peak of the drill bit. The triangular bit's hypotenuse extends obliquely
from the peak
of the drill bit to the radial terminus of the radial line at which the cover
and bit are
integrally joined. After formation of the side covers and drill bits, as can
be seen in Fig.
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8D, the barrel body forming zone 66 is stamped at predetermined locations to
obtain
required retaining wings 67, and the thread forming zone 64 is punched at
predetermined
locations to obtain slits 73 at joints of the side covers 71 and the thread
forming zone 64.
Then, as shown in Fig. 8E, the stoppers 62, the side covers 71 and drill bits
72 are bent,
so that the side covers 71 together form a required chip guard 74 and the
drill bits 72
together form a required drill 75.
As shown in Figs. 8F to 8H, when the steps shown in Figs. 8A to 8E are
completed, the
thread forming zone 64 and the barrel body forming zone 66 are subjected to a
series of
stamping to respectively obtain a required configuration. For example, the
thread
forming zone 64 is formed into a near-cylindrical hollow body and the barrel
body
forming zone 66 is formed into a hexagonal hollow body internally defining a
hexagonal
bore. Finally, as shown in Fig. 81, when the thread forming zone 64 and the
barrel
body forming zone 66 have been suitably shaped, the coupling devices 61 are
closed to
complete the self-drilling expansion fastener 20 of the present invention.
By forming through a series of prnching and stamping, the self-drilling
expansion
fastener 20 can be easily and quickly completed with largely simplified
procedures,
shortened working time and lowered manufacturing cost.
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