Note: Descriptions are shown in the official language in which they were submitted.
IRONING DIE FOR IRONING PRESS
DESCRIPTION
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Technical Field
The present invention relates generally to
drawn and ironed containers and more particularly to
an improved ironing die for reducing the sidewall
thic};ness of a cup -to produce a container that has an
integral hottom wall of maximum wall thickness and a
sidewall of minimum wall thickness.
In the formation of a "two-piece" container
it has been customary to utilize a plurality of die `~
assemblies that cooperate with a punch for converting
circular metal discs into finished containers. Usually
this is accomplished in two steps. A circular metal
15 disc is originally drawn into a cup utilizing what is Y
commonly referred to as a cupping machine. The cup
is then transferred to a body maker or press wherein
the cup is converted into the finished container.
One type of body maker that is presently
20 being utllized is produced by Ragsdale Bros., Inc.
which includes a cup redraw assemblyl a plurality of
ironing assemblies and a stripper assembly arranged
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seriatim along a path for a punch. The cups for this
machine are originally formea to have a diameter larger
than the finished internal diameter of the container
and are initially redrawn by the redraw assembly and
the sidewall thereof is then reduced in thickness
between the punch and the plurality of ironing assemblies.
At the end of ~he stroke for the punch, the end wall of
the container is reformed generally to a dome-shaped
configuration and the upper free edge of the container
is then trimmed to a predetermined height and "necked"
and "flanged."
One of the areas that has received a remarkable
degree of attention for obtaining accurate and acceptable
containers is the uniformity of the sidewall thickness
throughout the entire length and diameter thereof. It
will be appreciated that in forming conventional beer
or beverage containers, the stroke of the punch for the
press or body maker must be fairly long and has hereto-
fore created some problems in obtaining a very uniform
wall thickness for each container when operating at
commercial production rates.
Background Prior Art
In order to alleviate some of the problems
in maintaining accurate alignment between the various
ironing rings and the punch, it has been proposed to
utilize floating ironing die assemblies so that the
ironing die can move radially of the path in order to
obtain a more uniform sidewall thickness for the finished
container. An example of such an arrangement is dis-
closed in British Patent No, 724,251, published February
16, 1955, in which the die assemblies are mounted for
radial mo~ement to accommodate misalignment between
the punch and the ironing rings.
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Ironing is a carefully balanced steady state
process up to the point where the edge of the cup enters
the working portion of the die. Most of the time, this
edge is uneven, in magnitude anywhere from a few thou-
sandths of an inch to one-fourth to one-half inch.
Obviously, an uneven edge will disrupt this steady state
ironing process and several types of failures or process
shortcomings show up.
The unevenness of the upper free edge of the
cup or can has two sources. One is the cupping operation
itself, where it is sometimes caused by tooling in-
accuracies or misalignments~ The other source is mis-
alignment of the D&I press. Misalignment causes an
uneven wall thickness around its circumference. The
free edge of the cup or can becomes longer in line with
the thinner wall portion because of the accumulation of
this surplus metal. The unevenness grows progressively
worse as the container moves from one ironing stage to
the next. How to cope with this disruptive imbalance
caused by the uneven edge is a major difficulty in
D&I.
One form of failure caused by the uneven edge
is where the longer portion of the edge will tear off
entirely. Tear-offs can cause jams of the succeeding
cans.
Another very common form, is the punch and
die will be forced into a misaligned position due to
the non-symmetric forces imposed by the uneven edge.
The result is that the longer edge will remain heavier
than the wall thickness prescribed by the undisturbed
tool gap. In turn, this longer, heavier edge may tear
off in the next ironing die.
Another fo~m of failure caused by the uneven
edge is dynamic in origin. Invariably the longer part
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of the edge is thicker than the can wall preceeding it,
therefore, since the can travels at a respectible speed,
upon impact of this unsymmetxic heavy edge on the die,
a sudden tool deflection relative between punch and die
occurs. This can cause either tear~offs of the longer
edge, or smaller type "clip~offs" in the area of the
shorter end of the can.
A further form of process failure is that due
to the dislocation of the die in relation to the punch,
the tools may become damaged~ When the shorter edge
of the cup moves from between the punch and the ironing
die, they may shift sufficiently with respect to each
other so that the area of the punch without a container
wall thereon is actually in surface contact with the
land on the ironing die.
In order to partially alleviate this problem,
a pilot die concept has been develo~ed to support the
can-punch during the disruptive phase and force a certain
degree of ironing of the longer edge. Proceeding in
the direction of the punch travel, the centering pilot
die is placed behind the ironing die and is mounted in
such a way that it forms a rigid assembly with the pre-
ceeding ironing die. Such pilot dies are normally only
paired up with the middle ironing dies and generally
succeed to reduce the thickness of the longer edge to
a level where it will not tear off in the end die.
However, because of the very close tolerances
that are required to obtain container walls of uniform
thickness, this arrangement has been only partially
successful in preventins "clip-offs" during a drawing
and ironing operation~ In order to insure that there is
adequate clearance between the periphery of the container
waIl and the inner opening of the pilot die, the die
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must normally be made slightly larger than the desired
peripheral diameter of the partially formed container
after it has passed through the associated ironing die.
Furthermore, with separate assemblies, the diameter of
the pilot die must be further increased to allow for
inaccuracies in alignment of the various parts.
It can be appreciated that in an arrangement
such as this, it is virtually impossible to ha~ the
openings of the ironing die and,the pilot die exactly
concentric with respect to each other, Thus, it is
virtually impossible to fully accurately align the open-
ings with respect to each other and maintain the openings
in the ironing die and the pilot die exactly concentric
while at the same time providing for sufficient support
with the pilot die to prevent radial shifting of the
punch when an uneven cup is passed through the machine.
Almost universally, ironing dies are usually
shaped with a lead-in conical surface, a narrow land
and an exit conical surface. Ironing is taking place
between the lead-in conical surface and the punch.
Ironing comes theoretically to an end at the beginning
of the land. The effective gap between the internal
diameter of the land and the external diameter of the
punch determines the wall thickness of the can. How-
ever, due to the elasticity of the materials used for
the tools, there still is considerable pressure against
the wall in the gap which is causing friction. Normally,
the axial dimension of the land is preferably maintained
as small as possible and is usually on the order of
30 0.010 to .020 inches in length. The conical exit sur-
face immediately relieves the pressure and friction at
the end of the die.
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Summary of the Invention
According to the present invention, an ironing die is
shaped in a unique configuration, having an integral pilot, so as
to support the cup-punch during the critical phase of ironing
over the uneven edge, thereby resulting in a more uniform thick
wall in the transition to the uneven edge as well as of the longer
part of the edge itself. sy accurately and effectively control-
ling the thickness of the long edge through all stages, that is,
redraw, first, second and third ironing dies, tear~offs and
"clip-offs" are virtually eliminated.
In accordance with the present invention, an ironing die
for use with a punch to reduce the wall thickness of the sidewall
of a metal cup includes a body that has a circular opening extend-
ing from a leading surface to a trailing surface which are sub-
stantially parallel to each other and which extend perpendicular
to the axis of the punch. The opening in the body has a land
spaced from the leading and trailing surfaces which defines a
minimum diameter for the opening and the opening also has a
cylindrical portion between the land and the trailing surface to
guide the cup after a free edge moves past the land. The diameter
of the cylindrical portion should be as close as possible to the
diameter of the ironing land but must be large enough to eliminate
any substantial degree of friction between the peripheral surface
of the cup which is being ironed and the inner surface of the
cylindrical portion.
In a specific embodiment, the ironing land is located
closer to the leading surface than the trailing surface.
As an essential feature of the invention, the diameter
of the cylindrical
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portion between the land and the trialing surface is on
the order of about 1.0001 to about 1.0012 times the
minimum diameter of the land. Preferably, this range
is on the order of 1.0003 to 1~0010 times the minimum
diameter which is defined by the land, Also, the lead
in conical working surface has a small angle of 5 to
15 degrees in relakion to the land. In some instances,
it may also be desirable to have a recess located in the
die for the opening between the cylindrical portion and
the land.
Brief Description of Several Views of Drawings
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Fig. 1 shows a cross section of an ironing die
assembly having the ironing die of the present invention
incorporated therein;
Fig. 2 is an enlarged cross-sectional view of
the profile of the opening in the ironing die;
Fig. 3 is an enlarged fragmentary sectional
view of the joint adjacent the land of the ironing die;
and
Fig. 4 is a view similar to Fig. 2 showing a
slightly modified form of the invention. -~
Detailed Description
While this invention is susceptible of embodi-
ment in many different forms, there is shown in the
drawings and will herein be described in detail pre-
ferred embodiments of the invention with the under-
standing that the present disclosure is to be considered
as an exemplification of the principles of the inven-
tion and is not intended to limit the invention to the
embodiments illustrated.
Fig. 1 of the drawings generally discloses an
ironing die assembly 10 consisting of an ironing die
insert 12 supported in a holder 14 which has an opening
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16 extending therethrough and an enlarged recess 18
surrounding the ope~ing adjacent the leading surface 20
of the assembly into which the ironing die 12 is received
for support thereon.
Usually to reduce the sidewall thickness of a
cup, two or three of such assemblies 10 are spaced along
a path P for a punch and the sidewall of a cup supported
on the punch is reduced in stages to the ultimate thick-
ness for the finished container.
In the past, it has been customary to form the
ironing rings with a very narrow land located generally
in the center of the ironing die opening substantially
e~ually spaced from the opposite or leading and trailing
surfaces of the ironing die, as viewed with respect to
the direction of travel of the punch through the ironing
die assembly. In order to substantially reduce the
amount of friction developed, the land, which actually
controls the wall thickness of the cup in cooperation
with the punch, is usually made as narrow as possible
and in most die assemblies, the areas between the land
and the respective leading and trailing surfaces are
tapered outwardly slightly so as to further reduce the
friction developed during an ironing process.
As was indicated above, when utilizing an
ironing die assembly of this type, when a cup is formed
with a non-uniform wall thickness or when the upper edge
thereof is uneven, during the ironing operation, the
shorter edge of the cup will move past the land on the
ironing die and because of the extreme forces developed
in the ironing operation, the punch and ironing die will
move radially with respect to the axis of the punch and
can cause tear-offs of the longer edge of the uneven free
edge of the cup or clip-offs opposite the long edge. In
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other instances, even when the longer edge of the uneven
cup is not clipped off, the wall thickness thereof will
be greater than the wall thickness of the remainder of
the cup and this situation will be exaggerated as the
cup moves through subsequent ironing dies.
As was indicated above~ to partially alleviate
this problem, it has been proposed to utilize a separate
pilot die assembly adjacent each of the ironing assemblies
on the do~nstream side thereof, as viewed in the direc-
tion of travel of the punch with respect to the ironingdie. However, it has been determined that such arrange-
ment is only partially successful in overcoming the
inherent problems, particularly when producing containers
from cups that have an uneven upper free edge. It has
also been proposed to utilize a pilot die member that
is secured into an enlarged recess adjacent the trailing ;
side of the ironing die holder for supporting, if needed,
the partially ironed cup as it leaves the ironing die.
However, this again has only been partially successful
and past experience has shown that the moment the short
end of an uneven cup passes through the ironing land of
the ironing die, a steady state ironing condition is
lost which many times can result in damage to the die
and/or the punch and can also result in tear-offs and
"clip-offs" which may become trapped in the die assemblies
and cause jams in the succeeding operation.
According to the present invention, the profile
of the opening in the ironing die is constructed in a
fashion so as to constrain the container throughout its
movement through the ironing die to prevent tear-offis
and "clip-offs" and also result in more uniform wall
thickness for the finished drawn and ironed container. ;~
As most clearly shown in Fig. 2 r the profile of the
opening 28 (Fig. 1) within ironing die insert 12 consists
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of a narrow land 30 of minimum axial length to reduce
the frictional forces that must be overcome during an
ironing operation. Land 30 is spaced from leading
surface 32 and trailing surface 34 of the ironing die
and the area or surface 36 of the opening between land
30 and leading surface 32 tapers outwardly slightly to
produce an increasing diameter between the land and
the leading surface and in fact is the working surface
that forces a reduction of the incoming wall thickness
down to the thickness prescribed by the gap (i.e.,
difference between land and punch radius).
According to the present invention, the area
between the trailing surface 34 and land 30 is
cylindrical in shape or has a cylindrical wall portion
38 which has a diameter that is slightly larger than the
diameter of land 30, which is the minimum diameter of
the opening within ironing die insert 12. The land 30
and cylindrical portion 38 are formed on integral body
12 with an inclined portion 42 located therebetween. -
The diameter of cylindrical portion 38 is only
slightly larger than the diameter of land 30 and should
be just large enough to eliminate any substantial amount
of friction between the peripheral surface of the
partially formed cup and the inner surfac of cylindrical
portion 38 while still positively controlling and sup- -` -
porting the cup throughout its movement through the
ironing die. The particular relative dimensions of the -
diameters Dl and D are to some measure a function of the
elasticity of the tooling utilized, particularly the
composite elasticity of the materials for ironing die
assembly 10 and the elasticity of the material for the
punch (not shown) as well as the material for which the
cup is formed. While these parameters have not been
fully developed, it is believed that the diameter D2
should be on the order of about 1.0001 to about 1.0012
times the minimum diameter Dl of the opening within
ironing die insert 12 and :is preferably in the range of
about 1.0003 to 1.0010 times the minimum diameter D1.
While not limiting the invention to exact
dimensions, an example of a specific profile configura-
tion for an ironing die wh:ich has been operated success-
fully when drawing and ironing aluminum cups will now
be given. An ironing die having a thickness of approx-
imately 0.375 inches between the leading surface 32 and
the trailing surface 34 had a land of approximately
0.010 inches located intermediate the leading and
trailing surfaces and the land had a diameter of 2.6025
inches. The trailing edge of the land 30 was located
closer to the leading surface than the trailing surface
and the area between -the land and the leading surface
has an outward taper on the order of 8 degrees per side.
The diameter of the cylinder portion 38 was selected
to be 0.0010 inches greater than the diameter of the
land and had an axial length of approximately 0.200
inches.
Utilizing three of these ironing assemblies
with progressively reducing diameter lands arranged at
axially spaced locations with respect to a movable punch,
more uniform wall thickness was consistently achieved
for the cups that were converted into finished containers
and virtually no tear-offs or "clip-offs" were developed
during the ironing of a cup into a finished container.
In another test using commercial tooling and
the above dimensions, the cylindrical portion 38 was
made 0.0016 inches larger than the diameter of the land
30. Again, more uniform wall thickness was achieved
for the finished containers and less tool wear was
encountered.
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In both examples the need for a pilot die in
the toolpack was eliminated. This resulted in an overall
reduction in cost for the toolpack.
Of course, the respective dimensions could
readily be varied without departing from the spirit of
the invention, For example, if cups having an uneven
edge which would result in a difference of more than
approximately 0.200 inches between the shortest and the
highest point on the uneven edge where encountered, the
length of cylindrical portion 38 could be increased to
insure that the container or partially ironed cup would
be supported within cylindrical portions at all times
when there is any part o~ the upper free edge of the
partially ironed cup within the ironing band 30.
Actual tests have shown that utilizing an
ironing die having an inner surface pro~ile o~ the con-
figuration described above resulted in less tool wear
so that the life of the punch and die was increased sub-
stantially. At the same time, consistently more uniform
wall thickness for each container was achieved.
A slightly modified form of the invention is
illustrated in Fig. 4 and since all elementjs of the
die are identical to the embodiment illustrated in Fig.
2, the same reference numerals have been retained. In
the embodiment illustrated in Fig. 4, opening 28 has a
cut out portion 50 to produce a recess 52 between land
30 and cylindrical portion 38.
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