Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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This invention relates to the production of blanks and shaped
articles such as elongated, thin wall shells and, more par~icularly, to
a method and apparatus for forming elongated, tapered wall shells useful
in the fabrication of cartridge cases and the like.
In the prior art, generally the fabrication of tapered wall
shells, such as those used for forming into cartridge cases, has required
a series of steps or h~s required complicated machines which permit the
fabrication of the shell in a single operation. United States Patent
3,g84,259 and United States Patent 3,498,221 illustrate a typical series
of steps used to form the tapered wall shell and a cartridge case there-
from. United States Patent 3,088,225 discloses a method for forming
a tapered wall shell in a single continuous operation. However, this
patent requires triaxial forces, e.g. use of a cushion, to ensure ductility
and to control flow of metal in the blank.
The present invention includes a method and apparatus for
producing blanks and forming shaped articles such as elongated, thin
walled shells having relatively thick integral ends thereon. A simple,
double action draw press may be used, for example.
According to one aspect o the inven~ion there is provided
a method of forming an elongated, unitary shell having a thin side wall
and relatively thick end integral therewith, the shell formed from a
substantially circular blank cut from sheet material, the method comprising
the steps of: ~a~ providing a blank in a blank holder on a die having
an effective entrance aperture and an effective exit aperture, the entrance
aperture having an extent substantially commensurate in size with the
size of the blank to be drawn, said die having a cavity, the walls of which
converge inwardly from said entrance aperture to said e~ective exit
aperture, said wall defined by an arc of a sector of a circle, said arc
passing from the entrance aperture to the exit aperture, said sector having
an angle in the range of 12 to 34, said circle having its center located
in substantially the same plane as said effective exit aperture; and tb~
displacing said blank through said die by action of a punch to form said
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shell.
According to another aspect of the inv~ntion there is
provided a method of forming elongated, unitary shell having a thin
wall and a relatively thick end, the shell formed from sheet material,
the method comprising the steps of: ta) supporting the sheet material on
a blanking die having a substantially circular entrance aperture, an
exit aperture and an inwardly converging transition zone extending from
thc entrance aperture to the exit aperture; (b) punching a blank from the
sheet material using a cylindrical blanking punch axially alignqd with said
blanking die and having a cross-sectional area less than the cross-sectional
area of the entrance aperture, the punching being effected by displacing
the blnnking punch into the entrance aperture, the transition zone controlling
the motion of the blank on shearing from the sheet material and permitting
the blanking punch to maintain engagement with the blank as it is moved
through the blanking die to the exit aperture; (c) providing a combination ;~draw and ironing die in axial alignment with the exit aperture of the
blanking die to receive the blank ~herefrom, the draw and ironing die having
an effective entrance aperture and an effective exit aperture, the draw
and ironing die entrance aperture having an extent substantially commensurate ~:in size with the size of the blank to be drawn and having a cavity, the walls
of which converge inwardly from draw and ironing die entrance aperture to
the effective exit aperture, said wall defined by an arc of a sector of a
circle, said arc passing from the entrance aperture to the exit aper~ure,
said sector having an angle in the range of 12 to 34, said circle having
i~s center located in substantially the same plane as said effective exit
aperture; and (d) displacing said blank through the combination draw and
forming die by action of a punch to form said thin walled shell.
According to a further aspect of the invention there is provided
in the method of forming a cartridge case from an elongated, unitary shell
having a thin side wall and a relatively thick end integral there~ith, the
shell formed from a substantially circular blank, the steps comprising:
(a) providing a blank in a blank holder on a die having an effective
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entrance aperture and an effective exit apeTture, the entrance aperture
having an extent substantially commensurate in size with the size of the
blank to be drawn, said die having a cavity, the walls of which converge
inwardly from said entrance aperture to said effective exit aperture, said
wall defined by an arc of a sector of a circle, said arc passing from the
entrance aperture to the exit aperture, said sector having an angle in the
range o 12 to 34, said circle having its center located in substantially the
same plane as said effective exit aperture; and tb) displacing said blank
through said die by action of a punch to form said shell.
According to yet another aspect of the invention there is provided
in the method of forming a cartridge case from an elongated, tapered wall
shell having a relatively thick end integral therewith, the shell formed
from a substantially circular blank cut from sheet material, the steps
comprising: (a) supporting the sheet material on a blanking die having a
substantially circular entrance aperture, an exit aperture and an inwardly
converging transition zone extending from the entrance aperture to the
exit aperture; (b) punching a blank from the sheet material using a
cylindrical blanking punch axially aligned with said blanking die and
having a cross-sectional area less than the cross-sectional area of the
entrance aperture, the punching being effected by displacing the blanking
punch into the entrance aperture, the transition zone controlling the
motion of the blank on shearing from the sheet material and permitting the
blanking punch to maintain engagement with the blank as it is moved
through the blanking die to the exit aperture; (c) providing a combination
dra~ and ironing die in axial alignment with the exit aperture of the -
blanking die to receive the blank therefrom, the draw and ironing die
having an effective entrance aperture and an effective exit aperture, the
draw and ironing die entrance aperture having an extent substantially
commensurate in size with the size of the blank to be drawn and having a
cavity, the walls of which converge inwardly from draw and ironing die
entrance aperture to the effective exit aperture, said wall de~ined by an
arc of a sector of a circle, said arc passing from the entrance aperture to
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the exit aperture, said sector having an angle in the ra~ge o 12
to 34J said circle having its center located in substantially the Same
plane as said effective exit aperture; and (d) displacing said blank
through the combination draw and forming die by action of a punch to form
said thin walled shell.
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In the accompanying drawings:
Figure 1 is a simplified diagrammatic view, partially
in cross section, including a cylindrical blanking punch and die
assembly with sheet material therebetween in accordance with one
embodiment of the invention.
Figure 2 is a view similar to that shown in Figure 1
showing a blank cut from the sheet material in accordance with
the invention.
Figure 3 is a view similar to that shown in Figure 2
showing a partially formed shell.
Figure 4 shows a tapered wall shell formed by a punch
and die in accordance with the present invention.
Referring now more specifically to Figure 1, there is
shown a novel combination of blanking punch and die assembly
generally referred to as 10 and 20, respectively. ~ workpiece
30, e.g. sheet material, is shown between blanking punch 10 and ;;
die 20. For purposes of illustration, blanking punch 10 and die
20 are shown as substantially circular in cross section. Blanking
die 20 has an entrance aperture 21 and an exit aperture 22 and an
inwardly converging transition zone 23 extending from entrance
aperture 21 to exit aperture 22. Preferably, transition zone 23
is substantially conical in shape as depicted in Figure 1.
Blanking punch 10 can be substantially cylindrical and can
accolNmodate a punch 50 which in cooperation with a die (not shown
in Figure 1) can form a blank into a cup shaped article in one
continuous operation.
Blanking die 20 has aperture 21 axially aligned with
blanking punch 10 substantially as shown in Figure 1. Entrance
aperture 21 has an effective extent larger than the cross-sectional
area of blanking punch 10. When the blanking punch and die are
circular, preferably, aperture 21 has a radius 15 to 25% of the
sheet material 30 greater than the radius of blanking punch 10.
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In addition, typically exit aperture 22 o die 20 has an extent
greater than the cross-sectional area of the blanking punch,
depending largely on the thickness of workpiece 30. For an
entrance aperture having a diameter of 3.235 inches (82.169 mm)
and a sheet thickness of 0.625 inch (15.875 mm), typically exit
aperture 22 would have a diameter of about 3.231 inches (82.067
mm).
By effective extent it is meant that entrance aperture
21 is such that upon displacing blanking punch 10 lineally
towards blanking die 20l blank 32 is cut or sheared from work-
piece 30, Figure 2. The blank has a slightly curved configura-
tion. It will be understood that the curved configuration is
obtained by providing the clearance between blanking punch and
blanking die, as noted hereinabove. Further, it will be under-
stood that in conventional blanking punch and die assemblies, the
clearance is less than those set forth above and typically have a
difference of about 8~ of the sheet material.
If blank 32 is cut from the workpiece by a conventional
blanking punch and die assembly, the sheared edge often exhibits
what is referred to as secondary fractures. Secondary fractures
often result in laps in the wall of the formed article, e.g.
utensils, cartridge cases and the like, during the draw and
ironing operation and, of course, must be avoided since they
provide weak areas in the wall. ~owever, when the blank is cut
from the workpiece in accordance with the present invention, the
sheared edge is substantially free of secondary fractures.
In addition to providing a blank which is curved, the
blanking punch and die of the present invention cooperate to cut
or shear blank 32 from sheet 30 in a way which results in blank
top 6~ having a dimension commensurate in size with the size of
blanking punch 10 and blank bottom 66 having a dimension comrnen-
surate in size with the extent of entrance aperture 21. It is
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believed that shearing the blank -from the workpiece in this way
aids in ensuring the absence of secondary fractures and the ;~
resulting formation of laps in the subsequent forming operations.
It should be understood that in a conventional blanking
die, the blank tends to shoot ahead of the blanking punch on
being sheared or cut from the workpiece. When the blank is ;
permitted to move ahead of the blanking punch, it can become
misali~ned in the die for the next step, e.g. draw and ironing
die, resulting in the formation of a nonsymmetrical cup shaped
article. However, by providing transition zone 23 ln the blank-
ing die in accordance with the principles of the present invention,
the motion of the blank, upon being sheared from the workpiece,
is restricted thereby ensuring that the blank remains in contact -~
with the blanking punch and that it does not become misaligned
with respect to positioning thereof for the next forming opera- `~
tion.
Another aspect of the present invention includes the
formation of elongated, thin walled shells such as tapered wall ~-
shells 80, Figure 4. That is, the present invention includes a
blanking operation substantially as described above and the ~ !
formation of the elongated, tapered wall shell in one continuous
operation. The shells can have a -tapered wall or a substantially
uniformly thick wall depending on the shape of the punch used.
If the shells have a tapered wall for forming into cartridge
cases, a typical thickness at the mouth of the shell for a 30 mm
cartridge would be about 0.03 inch (0.762 mm~. Similarly for a
20 mm cartridge, the shell would have a thickness of about 0~02
inch (0.508 mm~ at its mouth. It will be appreciated that
formation of the shell in one continuous operation eliminates ~
many steps including preforming and cupping operations thereby ~ `
permitting the formation of cartridge cases, for example, in a
highly economical manner. Figures 2, 3 and 4 depict combination
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draw and ironing die 100 and tapered punch 50 used in forming the
elongated, tapered wall shell. It will be seen from an inspec-
tion of Figures 2, 3 and 4 that the blanking die exit aperture 22
can be used as a blank holder for draw and ironing die 100.
Draw and ironing is used herein in its ordinary sense.
That is, ~he term draw refers to an operation where a ~lat blank
is turned upwardly at its peripheral margin and simultaneously
smoothed by use of a punch and die to form a cup shaped article.
The term ironing refers to an operation wherein the wall of the
cup shaped article is elongated by reducing the thic~ness of the
wall and without appreciable reduction in the diameter of the cup ;
shaped article. It will be noted that in drawing, the wall of
the cup shaped article is also elongated but the diameter of the
cup is reduced. By reference to "combination draw and ironing",
it is meant that a large part of the drawing operation and the
ironing operation take place substantially simultaneously in
die 100.
Combination draw and ironing die 100 also has an
entrance aperture 102, an exit aperture 104 and a die cavity 106
defined by wall 108. From Figure 2 it will be noted that entrance
aperture 102 has an effective extent substantially commensurate
in size with the size of blank 32. Also, it will be noted that
wall 108 defining die cavity 106 converges inwardly and connects
entrance aperture 102 and exit aperture 104. Wall 108 of die
caVity 106 has a contoured shape which, along with tapered punch
50 permits the formation of elongated tapered wall shell 80 from
blank 32 in one continuous operation. Wall 108 is defined by an
arc of a sector of a circle, the arc passing from entrance
aperture 102 to exit aperture 104. The sector has an an~le A
(Figure 4) in the range of 12 to 34 and preferably the center
of the circle of which the sector is a part has a center located
in substantially the same plane as effective exit aperture 104,
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as shown in Figure 4. It should be noted that exit aperture 10
also has an effective extent ~hich controls the outside dimen-
sions of the elongated tapered wall shell. The cross-sectional
configuration of tapered punch 50 controls the inside dimensions
of the shell. In addition, the amount of taper in the wall of
the shell is controlled by the taper of the punch.
In the present invention, the diameter of blank 32 and
therefore the extent of entrance aperture 102 of die 100 is
determined largely by the height of the tapered wall shell. That ::
is, because the amount or volume of material in head 82 of the
shell 80 is constant for a particular size of exit aperture 104, -
additional material in the blank is utilized in producing longer
or higher walls on the shells. Thus, the extent or size of
entrance aperture 102 is fixed in this way. ~lso, the size of
the exit aperture is fixed by the outside diameter of the tapered -
wall shell which in the instance of cartridge cases would depend
on the caliber desired. ~hus, entrance aperture 102 and exit
aperture 104 are determined and can be connected by the arc of a
sector of a circle whose center should be in substantially the
same plane as exit aperture 104 (Figure 4). The sector has a
preferred angle in the range of 18 to 26. ~ith respect to the
thickness of the blank, it is determined largely by thickness
desired in head 82 of the tapered wall shell. Head 82 has a
thickness substantially the sarne as the starting blank in most
cases. However, in some instances, the thickness of head 82 can
be slightly thicker than the blank.
I~hen it is desired to fabricate cartridge cases, the
tapered wall shell formed as above may be subject to additional
operations including trimming, providing a head, pocket, vent and
extractor grooye.
The present invention is highly advantageous in that by
use of the novel blanking punch and die assembly blanks can be
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cut or sheared from sheet material which blanks, by ~irtue of the
blanking die, are positioned symmetrically in a highly consistent
basis for forming into shaped articles in subsequent steps. In
addition, the present invention is advantageous in that blanking
and forming of elongated tapered wall shells can be performed in
one continuous operation in a double action press.
By use of the apparatus described, tapered wall,
elongated cylindrical shells were produced from aluminum alloys
7475 and 5454 and from brass and mild steel. The brass had a
composition of 70 wt.% copper and 30 wt.% zinc. The metal blanks
and the tapered wall shell were produced in a single continuous
action. The blanks, which were cut from sheet and used for
aluminum and brass shells, had a diameter of 0.900 inch (22.860
mm) and a thickness of 0.200 inch (5.080 mm). The elongated,
tapered wall shells made from aluminum and brass had a wall
thickness at the mouth of the shell oE 0.022 inch (0.5588 mm).
The shells had a length of about 1.40 inch (35.560 mm) and an
outside diameter of 0.550 inch (13.970 mm), providing a length to
diameter ratio of 2.55:1. The angle of the arc sector for the
combination draw-ironing die was 22. It was found that the mild
steel was much more difficult to form into tapered wall shells
because of the reIatively high yieId strength. However, using
steel sheet having a thickness of 0.115 inch (2.921 mm), a
tapered wall shell having a length of about 0.85 inch (21.590 mm)
was produced. It will be understood that a steel blank having a
greater thickness as well as a larger blank diameter can be used
in order to form a deeper shell. However, in the case of higher
yield stren~th steel, higher press tonnage is required.
Various modifications may be made in the invention
without departing from the spirit thereof, or the scope of the
claims, and therefore, the exact form shown is to be taken as
illustrative only and not in a limiting sense, and it is desired
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that only such limitations shall be placed thereon as are imposed
by the prior art, or are specifically set forth in the appended
claims.
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