U.S. patent application number 09/864405 was filed with the patent office on 2001-12-20 for progressively-formed clinch nut.
Invention is credited to McDonough, William P., Ross, Harold D., Swanstrom, Kenneth A..
Application Number | 20010053319 09/864405 |
Document ID | / |
Family ID | 26904333 |
Filed Date | 2001-12-20 |
United States Patent
Application |
20010053319 |
Kind Code |
A1 |
Swanstrom, Kenneth A. ; et
al. |
December 20, 2001 |
Progressively-formed clinch nut
Abstract
A three-sided, progressively-formed threaded fastener is
comprised of a plurality of planar longitudinal faces intersecting
at corner areas. Shank tabs extend downward from the bottom of each
of the faces at the base of the fastener. Threaded regions along
the inside surface of the planar faces are coined indentations
applied during the formation of the fastener. A plurality of
wedge-shaped protrusions extend downward from the corner areas at
the base of the fastener. The combination of shank tabs and
wedge-shaped protrusions form a clinch profile along the bottom of
the fastener so that it may can be affixed to a sheet of metal by
clinch fit.
Inventors: |
Swanstrom, Kenneth A.;
(Doylestown, PA) ; Ross, Harold D.; (Chalfont,
PA) ; McDonough, William P.; (Collegeville,
PA) |
Correspondence
Address: |
Gregory J. Gore
70 W. Oakland Ave., Suite 316
Doylestown
PA
18901
US
|
Family ID: |
26904333 |
Appl. No.: |
09/864405 |
Filed: |
May 25, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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60209628 |
Jun 6, 2000 |
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Current U.S.
Class: |
411/437 |
Current CPC
Class: |
F16B 37/068 20130101;
F16B 37/02 20130101 |
Class at
Publication: |
411/437 |
International
Class: |
F16B 037/16 |
Claims
What is claimed is:
1. A threaded metal fastener, comprising: a tube-like channel
having a polygonal cross-section and being comprised of a plurality
of planar longitudinal faces intersecting at corners; a shank tab
located at the bottom of each of said faces and extending axially
downward from a base of said channel; a plurality of thread regions
comprising longitudinal rows of indentations on an inside surface
of each of said planar faces; a downwardly convergent wedge-shaped
protrusion extending from the bottom of said channel beneath each
corner; and said shank tabs each having angled side edges
convergent upwardly whereby an undercut clinch profile is formed at
the bottom of the channel, said profile providing means to
permanently affix the fastener to a sheet of metal by clinch
fit.
2. The fastener of claim 1, wherein said cross-section is
triangular.
3. The fastener of claim 1, further described as a folded strip of
material having first and second side edges which meet in abutment
along a longitudinal seam.
4. The fastener of claim 3, wherein said first side edge includes a
cutout and said second side edge includes an interlocking clasp tab
corresponding to said cutout whereby said seam is held together by
inserting said clasp tab into said cutout.
5. The method of forming a threaded metal clinch nut, having a
tube-like, elongate channel of polygonal cross-section and a
plurality of substantially planar faces which meet at corners,
comprising the steps of providing an elongate strip of metal;
cutting said strip into fastener blanks with arcuate indentations
in a front surface thereof, said indentations arranged in spaced
longitudinal rows and said blanks each including a shank tab
extending downwardly from a bottom edge thereof beneath each row of
indentations; and folding said strip into a tube-like channel along
longitudinal foldlines located between said rows of indentations
such that wells of said indentations define chordal sections of a
space corresponding to an externally-threaded member.
6. The method of forming a threaded insert of claim 5, wherein a
first edge of said blank includes a clasp tab, and an opposite edge
of said blank includes a cutout corresponding to the shape of said
tab.
7. The method of forming a threaded insert of claim 6, further
including the step of inserting said clasp tab into said cutout to
hold said edges in a fully-folded condition, said edges being in
abutment along a longitudinal seam.
8. The method of forming a threaded insert of claim 5, wherein all
of said fastener blanks remain connected to a common carrier
portion of said strip after formation.
Description
[0001] Priority based upon provisional application Ser. No.
60/209,628 filed on Jun. 6, 2000, entitled "PROGRESSIVELY FORMED
CLINCH NUT" is hereby claimed.
FIELD OF THE INVENTION
[0002] This invention relates to captive, internally threaded
fasteners, more specifically to a clinch nut produced completely by
means of a progressive stamping process. The invention is stamped
and formed from flat coil stock into a fully functional internally
threaded clinch nut that may be supplied in bulk form or on a
reeled carrier strip.
BACKGROUND OF THE INVENTION
[0003] Progressively-formed threaded inserts, an example of which
is shown in U.S. Pat. No. 5,927,920, are known. While this method
of forming a threaded insert is suitable for being fully inserted
into a plastic sheet, it cannot be attached to a metal panel. Other
types of threaded fasteners pressed into metal panels may be joined
by a process known as "clinching" whereby a cold flow of metal
created during the forceful insertion process enters an undercut
groove at the base of the nut. Heretofore a progressively-formed
threaded part having clinch-attachment capabilities is unknown.
[0004] Such a device would be desirable since prior art clinch nuts
are manufactured from a bar stock machining process or a wire
forming process often requiring a costly secondary tapping step.
Bar stock machining processes typically yield 1,000 pieces per hour
with 70% scrap while wire-forming processes typically yield 13,000
pieces per hour with 15% scrap. There is therefore a need in the
art for a clinch nut which may be inexpensively produced
efficiently and with less scrap in the manufacturing process.
SUMMARY OF THE INVENTION
[0005] In order to meet the needs in the art described above, the
present progressively-formed clinch nut invention has been devised.
A three-sided progressively-formed threaded fastener is provided
with wedge-shaped protrusions and angled side edges of shank tabs
that extend from the base of the fastener. The protrusions displace
sheet material into undercuts formed between the shank tabs and the
base of the fastener. These structures provide the clinch
attachment means when the fastener is pressed into a sheet. Except
for the inclusion of these clinch features, the fastener of the
present invention and its method of production is similar to that
disclosed in the above-mentioned U.S. Pat. No. 5,927,920 which is
included herein by reference as though fully set forth.
[0006] More specifically, the applicants have invented a threaded
metal fastener comprising a tube-like channel having a polygonal
cross-section and being comprised of a plurality of planar
longitudinal faces intersecting at corner areas. A plurality of
shank tabs extend downwardly from the bottom of each of the faces
at the base of the channel. A plurality of threaded regions
comprising longitudinal rows of indentations lie on the inside
surface of each of the planar faces. A plurality of wedge-shaped
protrusions extend downward from the corners. This forms a clinch
profile at the bottom of the channel so that the fastener can be
permanently affixed to a sheet of metal by clinch fit. The fastener
has a triangular cross-section and is a folded strip of material
with its first and second side edges meeting in abutment along a
longitudinal seam. The first side edge includes a cutout and the
second side edge includes a corresponding interlocking clasp tab.
The seam is held together by inserting the interlocking side tab
into the cutout.
[0007] The method of forming the present invention comprises
providing an elongate strip of metal, cutting it into fastener
blanks with arcuate indentations in a front surface with the
indentations arranged in spaced longitudinal rows. The blanks each
include shank tabs extending downwardly from a bottom edge. The
method further includes folding the strip into a tube-like channel
along longitudinal foldlines located between the rows of
indentations such that wells of said indentations define chordal
sections of a space corresponding to an externally-threaded member.
A first edge of the blank includes a clasp, and an opposite edge of
the blank includes a cutout corresponding to the shape of the tab.
The clasp is inserted into the cutout to hold the edges in a
fully-folded condition with the edges being in abutment along a
longitudinal seam. The fastener blanks can remain connected to a
common carrier portion of the strip after formation.
[0008] Not only can the present device be produced more efficiently
and less expensively than a machined clinch nut, it provides many
other advantages. For example, the current invention requires a
smaller mounting hole when compared to the prior art resulting in
closer center-line-to-edge distances and less panel distortion.
Over-tightening of the mating screw in the clinch nut will not
damage the threads, since the side walls flex outwardly and
disengage to relieve excess torsional load on the threads prior to
thread damage. Thus, neither the screw nor the clinch nut threads
are damaged. Also, the present invention provides the key features
of the ability to be produced in high volumes at high production
rates with minimal scrap since it can be produced at rates of
21,000 pieces per hour with 15% scrap and no secondary tapping
process. A portion of the scrap can be used as a carrier strip to
facilitate automated installation eliminating the need for an
expensive vibratory feeding bowl. Hence, a clinch nut progressively
formed by die stamping as described herein can be made much less
expensively. Other objects and advantages of the present invention
will be apparent from the following drawings and description of the
preferred embodiment.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is a bottom front right isometric view of the
invention shown in various stages of sequential formation.
[0010] FIG. 2 is a side view of the present invention.
[0011] FIG. 3 is a top perspective view of the present invention
installed in a sheet.
[0012] FIG. 4 is a bottom perspective view of the combination shown
in FIG. 3.
[0013] FIG. 5 is a top view aligned with an insertion hole shown in
dotted lines.
[0014] FIG. 6 is a top perspective view of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0015] FIG. 1 shows the manufacturing progression of the invention.
Flat strip stock 11 is progressively stamped, coined, and then
folded into a polygonal-shaped, internally threaded, channel 9. The
strip of metal is first cut into individual fastener blanks 14,
each blank including a shank tab 3 extending downward from a bottom
edge of the blank. Thread regions are then created in longitudinal
rows divided by foldlines which bound planar faces of the completed
fastener after folding. The blank further includes wedge-shaped
protrusions or teeth 10 which extend from the bottom of the channel
beneath each foldline between the rows of indentations. Thus, the
protrusions will lie directly beneath the resultant corner areas 5
of the fastener. Each shank tab 3 is provided with angled side
edges convergent upwardly so that an undercut clinch profile will
be formed at the bottom of the channel between the shank tab side
edges and the base of the completed fastener.
[0016] In the preferred embodiment, a three-sided fastener is
formed. A three-sided polygon is desirable because it provides the
largest flat area to form the threads 8 and shank tabs 3. A
three-sided polygon also yields the largest bend area 5 to form the
clasp tab 12 and the wedge protrusions 10. The fully formed
fastener 9 can remain on a reeled carrier strip 7 to aid in
orientation and presentation to an automatic installation system
without the need for a vibratory bowl. The thread 8 and thread lead
13 are comprised of three coined patterns oriented to form a free
running thread when formed into the final shape of the fastener
9.
[0017] Referring now to FIG. 2, the fastener 1 of the invention
with an undercut clinch profile 6 on shank tab 3 that provides
means to permanently affix it to a sheet of metal is shown. The
corner areas 5 act as longitudinal strengthening ribs which provide
a means to transmit an installation force from the top of the
fastener 9 to the wedge protrusions 10 just below the corners
without fastener deformation. The keystone shaped clasp tab 12 is
designed to withstand the compression loads of the installation
force and the tensile/expansion loads resultant of the clamp forces
created by a mating screw. The clasp 12 also permits heat treating
the fastener 9 without deformation.
[0018] FIGS. 3 and 4 show the fastener installed into a round hole
2 of sheet 4.
[0019] FIG. 5 shows in dotted lines a hole 2 sized to the tangent
points of the three shank tabs 3. The minimum width of the shank
tabs 3 is dictated by the width of the thread impression 8 as shown
in FIG. 6. The shank tab width can be optimized to result in a
smaller hole than that required by traditional clinch nuts.
Referring further to FIG. 6, the fastener also includes thread lead
13 at the top of the fastener.
[0020] The fastener of the present invention is installed into a
metal sheet, by a simple pressing operation well-known in applying
fasteners to sheets by clinch fit. As the present invention is
pressed into the sheet, the sheet material is displaced by the
wedge protrusions 10 which form teeth located under the three
corner areas 5 of the fastener that bite into the sheet. This
forceful deformation of the sheet by the protrusions displaces
material and forces it into the undercuts 6 between the bottom edge
of the fastener formed by the upwardly-convergent angled side edges
of the shank tabs 3. The cold flow of the material permanently
locks the fastener in place. Referring back to FIG. 5, it will be
apparent that the corners are the areas of greatest diameter of the
fastener and larger than the hole size while the shank tabs will
lie within the diameter of the hole.
[0021] It will be understood by those of ordinary skill in the art
that the main object of the present invention, to include
structures which produce a clinch attachment structure along the
mouth of a progressively-formed folded insert which may be produced
at high production rates with a minimum of scrap, has been
achieved. Other uses, advantages, and modifications to the present
invention will be readily obvious to those of skill in the art,
however, the present invention shall be limited only by the
following claims and their legal equivalents.
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