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2 The pit invention relates to the formation of a self-clinching type metal
3 fastener by a progressive forging process.
4 BACKGROUND AND DE$CRIP7ITON OF THE PRIia,IR ART
Internally-threaded, self-cund~irtg type fastener are wdl-known in the art.
6 When inatallod, they provide materials such as poet metal panels with a
threaded
7 structure to receive s straw so that dements can be securod to the panel. A
typical
8 self clinching falter of the standoff type which includes an elongate band
is shown
9 in Figures 3 and 4. The basic structures of this type of thsteners include a
head, a self
clinch groove, a band, and an interns! bore with threads. The fastener is
installed by a
I 1 press and anvil so that the groove receives the cold flow of metal from
the sheet while
12 the polygond head is embeddad into the sheet. These structures secure the
fastener to
13 the sheet rigidly, both axially and rotationally.
I 4 One effective means for producing a self clinching fastener of the above-
I 5 describe type is by a progressive die forging procxas. This process
utilizes sequential
16 punch and die forging to create the head, the clinch groove, the band, and
the internal
17 bore of the fastener from a metal blank or slug. Such a formation process
is described
18 for example in U.S. Patent Application Serial No. 2002/0054806 entitled
"Grooved
19 Nut and Manufacturing Method Thereof' Bled on January 3, 2001 by Sakamura
et al.
and published on May 9, 2002, 'this document discloses the progressive punch
and
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1 die tooling used in this proc~a as exemplified by Figure 3. As shown in this
figure, a
2 horizontally rcapro~ing ram holds a series of punches, each opposite a
respective die
3 providing a aeries of forging stations. The punchy and dies prograsaively
form the
4 basic shape oftha fastener from a blank of metal which is moved between
stations
after each stroke of the ram. The shearing action betvve~ the punch and die of
the
6 final station trims metal from wound the edge of a temporarily formed
araiiar head of
7 the fastener as the blank is pushed through the die by the punch to create
the final
8 polygonal shape.
9 A problan eats with this n~atwi~ttring process, however, because the
shearing process in the last station of the progressive forging leaves an
undesirable
11 upward-facing burr on the top side of the head of the fastener. ~
Furthermore, there is
12 another problem with this 6na1 head trirnrning station in that the scrap
ring which
13 results from cutting the material away from the periphery of the aralar
head to
14 achieve the firu~t polygonal shape often sticks to the face of the trim
die, obaweting
the continuous operation of the progressive forging process. There is
therefore a need
16 in the art to utilize a cold forging process to create a self-clinching
fastener which does
17 not have these deficiencies.
18 ~19,~Y OF
19 The present invention has been devised to curs the above-described problems
of the undesirable nuuaifa~ring burt on the head of the faata~er and to effect
the
21 efTicient ranova! of the trimmed scrap ring at the final station of the
head trimming
22 station of the forging process. ~Acxording to one aspect of the invention,
the ~org<ng
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1 apparatus of the prior art is modified in that the punch and dio tooling in
the head
2 trimming station are reversed in position. That i~ the punch is posisi~ed on
the die
3 block while the die is located on the redprocatiag punch block. This
reverses the
4 direction of relative movement between the fastener and the die so that the
burr is
formed on the underside of the head rather than the top side. This is moro
6 desirable since the underside of the head is embedded into the sheet
material once the
7 fastener is applied to a sheet. The bufr is then not vis~'ble snd cannot
affect the Real
8 appearance of the clinched assembly. Because in the new system the barrel of
the
9 fastener is necessarily held within a cavity of the trim punch at the last
station, an
added reaprocatirtg la~oclc-out pin is employed to eject the part from the
punch and
11 through the opposite aide of the die.
12 Re~nersing the relative dirxtion of movement between the die and the
fastener
13 during head-trimming also leaves the scrap ring wound the outside of the
punch at the
14 final station rather than against the face of the die as in the prior art.
This is
advamageous since the scrap ring then may be quickly and reliably removed from
16 around the trim punch by a stripper sleeve which pushes the scrap ring off
the aid of
17 the trim punch aRer the trim process is completed. This avoids the
unreliable scrap
t 8 removal of the prior art. AdditionaDy, this is also advantageous in
xparating the
19 finished product from the scrap material, whereby also eliminating the need
for costly
sorting or manual inspection operations to remove the scrap from the finished
product.
21 Steps of the forging process of the imrention at the final head-trimnting
station
22 may be further descn'bed as follows. The fastener blank having a tubular
barrel and a
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I teTnporan7y formed cirarlar head is placid into s boro of a punch with the
band of the
2 fastener roaiding in the boro sad an underside of the Grailar head abutting
an end face
3 of the punch. T'he forging apparstua then moves the die toward the top side
of the
4 fastener until a polygonal artting edge of the die shears natal from around
the edges
of the circular head of the fastener blank. Movement of the die steps when the
cutting
b edge lies beyond the punch end face and the underside of the head of the
fastener. At
? this point, a knock-out pin which is reciprocal within the bore of the punch
forceably
8 ejects the fwa through a passage in the die and beyond an opposite side of
the die
9 into a container for completed parts. The forging apparst<ra then moves the
die away
from the punch. Once the die is clear of the punch, a stripper sleeve which is
11 reciprocal about the outside aurthx of the punch moves from a retracted
position over
12 the end of the punch and in doing so ranoves a scrap ring left around the
outside of
13 the punch. Since the orientation ofthe tooWvg is horizontal, the sexap ring
the falls
14 away from the punch by gravity, and may also be assisted by prossurized oil
or air to
ensuro the dowrnvard motion of the scrap ring is achieved. The cycle is then
l6 completed and the trim station is now ready to rocxive the next partially
formed
1 ? fastener blank.
18 The apparatus for performing the inv~a~tive.head-ttin~ming process
comprises a
19 stationary punch having a bore for holding a barrel portion of a fastener
blank, an end
face for supporting an underside of a head portion of the fastener blank when
held in
21 the bore, and a polygonal shank. Tire im~on Rather includes n reciprocal
die having
2Z an internal passage and a trim plats including an aperturo, the trim plate
aperture
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1 having a circutftterattiai polygonal edge closely cornesponding to
dinta>Sions of the
2 shank of the punch for receiving the putsch. The die is moval~e from a
r~racxed
3 position toward a top aide of the fastens blank to an axtended trim position
where the
4 cutting edge lies bayond the punch end face. There is a knock-out pin
reciprocal
within the punch born for ejecting the fastener blank 8~om the bore alts
through the die
6 passage to an opposite aide of the die. A stripper slave slidably mounted to
the
7 outside surface of the punch is taapmcal betvveert rested and extended
positions by
8 a spring-activated mecharomt, the extended position placing a distal end of
the sleeve
9 even w'tth the punch end face for removing a soap ring from the punch. Sinca
the die
is movable in a substantially horimntal plane, the a<xap ring falls away from
the end
11 face of the punch by the force of gravity and can be assisted by
pressurized oil and or
12 air as needed. Other objects and advantages of the present invention will
be readily
13 apparent to those of skill in the art from the following drawings a~
description of the
14 preferred embodiments.
16 Figure 1 is a top diagranunatic view of a prior art multi-station cold
forging
17 apparatus.
18 Figure 2 is a top plan view diagtatr><natically showir4g the cold forging
19 apparatus of the present invention.
Figure 3 is a aide partial cross section view of a fastaur formed by the prior
art
21 method.
22 Figure 4 is a partial cross section view with an enlarged area of a
fas<a~er
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1 produced by the pre:mrt inveatioa
2 Figure 5 is an exploded isometric aa:embly view ofttm various alements of
the
3 present invention corresponding to forging station number six shown in
Figure 2.
4 Figures 6A through 6D aro side elevation partial cut-away views of the cold
forging apparatus of the prexnt inva~tion atwvNng its sequential operation.
6
7 Figure 1 diagrammatically depicts the cold forging apparatus of the prior
art
8 which includes reciprocating punch block 1 1 that holds a series of punches
8 that
4 strokes toward and away from die block 13 that holds a aaioa of dies 9 to
perform a
sequential forging of a metal slug 13 into the general shape of a standard
type self
11 clinching fastener as shown in Figure 3. This prior art apparatus and the
apparatus of
12 the present tion both utilize six forging stations, Sl through S6,
beginning with a
13 first station in which metal slug 1~ has been severed from a rod-like
substrate material
14 17 and ending with the final sixth station whero the cylindrical head is
trinuned to a
I S hexagonal shape on a fully formed part. The slug is sequentially moved
between
I6 stations from one die atvity to the next after each stroke of the punch
block by a
17 transfer mechanism well known in the art (not shown). The invention lies
within the
18 apparatus and operation of the sixth and f nal forn~ing station where the
circular head
19 of the fastens blank is trimmed to a hexagons! shape.
Referring now to Figure 2, the fifth and sucth stations of the present
invention
21 are depicted, stations 1-5 being essentially the same as shown in the prior
art device of
22 Figure I . One of the aspects of the invention is the r~va~sal of punch 8
and die 9
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1 den»ta of tire previous rtations so that the die sssanbhr 12 of the
invention at the
2 sixth station is held by the reap<ocating punch block 11 while the punch
assembly 14
3 is fixed in the stationary die block 13. By rovasarrg the position of these
dements, the
4 direction of the head trimming sheer is reversed. Also, sa will be tirrther
described, the
finished pare is ejected through the punch block rather than filling through
the
6 stationary die block 13 as in the prior art.
7 Charging the direction of trim operation has the bene8aal effect on the
surface
8 charaaeriatics of the fastener head as depicted by Figuros 3 and 4. Aa shown
in Figure
9 3, the prior art method of cold forging shown in figure 1 results in an
upward-facing
trim burr which protrudes from the head of the fastener. This burr is a rough
and
11 sharp edge which is aesihdicaUy w~irsble. Using the apparatus of the
presets
12 invention however the burr, which inevitably results from the die shearing
method of
13 trirnrning the head to its final hexagonal shape, now along the underside
surface
14 of the head of the fastaror. Since after installation the head of the
fastener is
embedded in a substrate material, the trim burr is not visible and the top
surthce of the
16 head of the fastener is flush with the outside surface of the substrate
exhibiting an
17 aesthetically acceptable final appearance after assembly.
18 Referting now to Figure 5, the various el~ts of the invention at the sixth
19 station shown in Figuro 2 aro depicted further including the resulting
finished part 16
and the trim scrap ring i8. Trim die is includes trim plats 2~ that has a
hexagonal
21 opening with a eutang edge along its inside surface. Punch assembly 14
includes a
22 holder 19 that rigidly secures hexagonal punch Z3. The punch assembly
farther
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1 includes a stripper sleeve Z5 snd a lrnock-out pin Zi that aro alidable
within the
2 assembly relative to the fixed punch Z3 and holder 19. Means to effect the
motion of
3 the stripper sleeve and the knock-out pin aro not :ho~m and are wolf within
the
knowledge of one of akin in the art.
Referring now to Figuros 6A through 6D, the four stages of the trim process
6 using the apparatus depictod in >figure 5 aro shown in sequence. Referring
fast to
? Figuro 6A, the ~ blank 16 is delivered by a t:auafar mechanism (not shown)
so
8 that a baml of the resides within the cylindrical bore of a hexagonal punch
23
9 which is rigidly secured within holder 19. The first step in the trim
process begins with
the motion of the die iZ toward the fast. In this position, the underside of
the
11 circular head IS of the fastener blank abuts an end face of the punch.
12 Referring now to Figure 68, the die has moved to the end of its stroke to
the
13 completed trim position. A cutting edge on the trim plate Z? on the facx of
the die has
14 savored a scrap ring 18 from tire fartener blank which is shearod by the
punch 23 from
the circular hcad of the fas<amr to provide a re~lting hexagonal shape. The
16 hexagonal head now resides within a passage of the die beyond a backside of
the trim
17 plate.
18 The next step of the operation of the invention is shown in Figure 6C. The
19 knock-out pin 21 which is preferably apiing-loadad (spring mechanism not
shown) is
released and forceably ejects the finished fastener 16 through the die passage
20 and
21 away from an opposite side of the die falling away by the force of gravity
as depicted
22 by the arrows shown in this figure. It should be noted at this stage that
the scrap ring
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1 18 remains around the outside of the punch Z3.
2 The fowl stage of the operation of thin station is ahovm in Figuro 6D in
which
3 several events occur ainwltaneous)y. While the die 12 is being withdrawn to
its home
4 position, the lrnock-out pin 2i is retracted and stripper sleave t5 is
extended to a point
flush with the ~d face of the punch, forcing the a~xap ring 18 off of the end
of the
6 punch and away from the apparatus by gravity as shown by the arrows.
Thereafter,
7 the stripper sleeve 25 is ~tru~ed to its home position sash with the endface
of holder
8 19. Now the el~ta of the punch assembly are in the same position shown in
1~;gure
9 6A ready to accept the next fa~ener from the transfer mechanism and the
cycle is thus
complete.
11 it should be understood that them may be other modi8~cationa and changes to
12 the present inva~tion that will be obvious to those of skill in the art
from the foregoing
13 descxiption, however, the present im~aon should be limited only by the
following
14 claims and their legal equivalents.
