U.S. patent application number 12/589917 was filed with the patent office on 2010-05-06 for necking die with shortened land and method of die necking.
Invention is credited to Jeffrey Edward Geho.
Application Number | 20100107719 12/589917 |
Document ID | / |
Family ID | 42128167 |
Filed Date | 2010-05-06 |
United States Patent
Application |
20100107719 |
Kind Code |
A1 |
Geho; Jeffrey Edward |
May 6, 2010 |
Necking die with shortened land and method of die necking
Abstract
The exemplary embodiments provide a die set comprising a
knockout punch and a necking die for necking-in a metal container
preform. In an axial direction from front to back of the die, the
die has an inwardly tapering in-feed surface, a forming radius, a
generally cylindrical land having a die bore diameter, a discharge
surface and a relief surface having a diameter larger than the die
bore diameter. The land has an axial length of less than 0.1 inch.
It is believed that such a length limits the number of metal
contacts with the land (rebounds between the knockout punch and the
land) to one or two as a metal container preform is necked in the
die in conjunction with a knockout punch having a punch diameter
that provides a gap between the knockout punch and the land. While
the gap may be larger than the topwall thickness of the metal of
the preform within the gap, it may alternatively be the same as, or
smaller than, the thickness (by up to 10%), to effect re-resizing
of the container wall. The exemplary embodiments also provide a
method of necking a container preform using such a die.
Inventors: |
Geho; Jeffrey Edward;
(Aurora, IL) |
Correspondence
Address: |
Christopher C. Dunham;c/o Cooper & Dunham LLP
20th Floor, 30 Rockefeller Plaza
New York
NY
10112
US
|
Family ID: |
42128167 |
Appl. No.: |
12/589917 |
Filed: |
October 30, 2009 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
61197976 |
Oct 31, 2008 |
|
|
|
Current U.S.
Class: |
72/370.02 ;
72/467; 72/470 |
Current CPC
Class: |
B21D 45/02 20130101;
B21D 51/2638 20130101; B21D 51/2615 20130101 |
Class at
Publication: |
72/370.02 ;
72/467; 72/470 |
International
Class: |
B21D 41/04 20060101
B21D041/04; B21D 37/10 20060101 B21D037/10 |
Claims
1. A necking die set for necking-in a metal container preform,
which die set comprises a knockout punch having a generally
cylindrical surface and a die having, in an axial direction from
front to back of the die, an inwardly tapering in-feed surface, a
forming radius, a generally cylindrical land defining a die bore
diameter, a discharge surface following said land, and a relief
surface having a diameter larger than the die bore diameter,
wherein the land has an axial length that is less than 0.1
inch.
2. The die set of claim 1, wherein said axial length of the land
limits a number of metal contacts with the land to one or two as a
metal container preform is necked in the die in co-operation with
said knockout punch.
3. The die set of claim 1, wherein said axial length is from 0.010
to 0.0950 inches.
4. The die set of claim 1, wherein said axial length is from 0.0127
to 0.0827 inches.
5. The die set of claim 1, wherein said knockout punch has an outer
diameter and said die has a bore diameter effective to leave a gap
therebetween, said gap being greater than a top-wall thickness of
said container preform necked in said die set.
6. The die set of claim 1, wherein said knockout punch has an outer
diameter and said die has a bore diameter effective to leave a gap
therebetween, said gap being the same as a top-wall thickness of
said container preform necked in said die set.
7. The die set of claim 1, wherein said knockout punch has an outer
diameter and said die has a bore diameter effective to leave a gap
therebetween, said gap being less than a thickness of a wall of
said container preform to be necked in said die set.
8. The die set of claim 7, wherein said gap is less than said
thickness by an amount of up to 10% of said thickness.
9. The die set of claim 7, wherein said gap is less than said
thickness by an amount of up to 5% of said thickness.
10. The die set of claim 1, wherein dimensioned to neck a container
preform having a top-wall thickness of 0.0058 to 0.010 inch.
11. The die set of claim 1, wherein said forming radius is in a
range of 0.2 and 0.5 inches.
12. A necking die set for necking-in a metal container preform,
which die set comprises a knockout punch having a generally
cylindrical surface and a die having, in an axial direction from
front to back of the die, an inwardly tapering in-feed surface, a
forming radius, a generally cylindrical land defining a die bore
diameter, a discharge surface and a relief surface having a
diameter larger than the die bore diameter, wherein the land has an
axial length that limits the number of metal contacts between with
the land to one.
13. The die set of claim 12, wherein said axial length is from
0.010 to 0.0950 inches.
14. The die set of claim 12, wherein said axial length is from
0.0127 to 0.0827 inches.
15. The die set of claim 12, wherein said knockout punch has an
outer diameter and said die has a bore diameter effective to leave
a gap therebetween, said gap being the same as a thickness of a
wall of said container preform to be necked in said die set.
16. The die set of claim 12, wherein said knockout punch has an
outer diameter and said die has a bore diameter effective to leave
a gap therebetween, said gap being less than a thickness of a wall
of said container preform to be necked in said die set.
17. The die set of claim 16, wherein said gap is less than said
thickness by an amount of up to 10% of said thickness.
18. The die set of claim 16, wherein said gap is less than said
thickness by an amount of up to 5% of said thickness.
19. A necking-in die for said die set of claim 1.
20. A necking-in die for said die set of claim 12.
21. A method of necking-in a metal container preform having a
top-wall thickness, comprising the steps of: directing an open end
of a metal container preform surrounding a cylindrical knockout
punch into an annular necking die to effect necking-in of said
container preform, and then using the knockout punch and optionally
pressurized gas to knock out the container body preform from the
die; wherein the method includes providing said die with, or
selecting said die to have, a land having an axial length effective
to limit a number of contacts between said container preform with
said land during said necking step to one or two.
22. The method of claim 21, wherein said axial length of said land
is made to be less than 0.1 inch.
23. The method of claim 21, wherein said axial length of said land
is made to be from 0.010 to 0.0950 inches.
24. The method of claim 21, wherein said axial length of said land
is made to be from 0.0127 to 0.0827 inches.
25. The method of claim 21, wherein said die and said knockout
punch are made to form a gap between said knockout punch and said
land that is greater than said thickness of said metal by an amount
in a range of 0.0005 to 0.001 inches.
26. The method of claim 21, wherein said die and said knockout
punch are made to form a gap between said knockout punch and said
land that is the same as or less than said top-wall thickness of
said container preform.
27. The method of claim 26, wherein said gap is less than said
top-wall thickness by up to 10% of said thickness.
28. The method of claim 26, wherein said gap is less than said
top-wall thickness by up to 5% of said thickness.
29. The method of claim 21, wherein an aluminum alloy is selected
for said container body preform.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims the priority right of co-pending
U.S. provisional patent application Ser. No. 61/197,976 filed on
Oct. 31, 2008 by applicants named herein. The disclosure of the
aforesaid provisional patent application is specifically
incorporated herein in its entirety by this reference.
BACKGROUND OF THE INVENTION
[0002] I. Field of the Invention
[0003] This invention relates to the shaping of metal containers by
means of a succession of necking steps using dies that gradually
modify the container walls into a desired finished shape. More
particularly, the invention relates to the design of dies to
improve die necking operations and to methods of die necking.
[0004] II. BACKGROUND ART
[0005] Thin walled metal foodstuff containers, beverage cans,
aerosol canisters, and other such containers for consumer or
industrial products are often provided with inwardly- or
outwardly-flared walls for aesthetic reasons or for reasons of
practicality or economy. For example, beverage can bodies are often
provided with an inward flare adjacent to their upper ends
primarily to reduce the size of the required metal end closure
walls. Such end closure walls are necessarily made of a metal of a
much thicker gauge than that required for the walls of the
container bodies, so any reduction in their size results in a
considerable saving of metal. Containers of this kind are often
made from rolled metal sheet that is cut into blanks, cupped, drawn
and ironed to elongate the side walls, and then finally trimmed to
produce a straight-walled open-ended container body pre-form. Such
container body pre-forms are then provided with flared ends or
other shapes of the above-mentioned kind by a process known as die
necking whereby the open end of a tubular pre-form is forced into a
succession of shaped annular dies of ever-decreasing diameter until
the desired size reduction of the tubular wall at the open end is
achieved. A large number of small changes of diameter are carried
out in order to avoid metal buckling, ripping or tearing that
generally occurs if abrupt size changes are attempted in a single
step. More details of a typical necking operation may be obtained
from U.S. Pat. No. 5,497,900 issued to Caleffi et al. on Mar. 12,
1996 and from PCT publication WO 2007/136608 A2, published on Nov.
29, 2007 (the disclosures of which documents are specifically
incorporated herein by reference).
[0006] The necking dies work in conjunction with
correspondingly-sized knockout punches that fit within the central
openings of the dies and help to support and shape the container
pre-forms to be necked. The purpose of the die is to reduce the
diameter of the opening and impart a shape that is aesthetically
pleasing at the top portion of the container pre-form. The purpose
of the knockout punches is to control the metal by diverting it
back towards the die so that the size reduction of a particular die
necking stage is not larger than intended, to prevent failures of
buckling in the neck, and to knock the container pre-form out of
the die after shaping has been accomplished in that stage.
[0007] As the container pre-form is forced into the die,
considerable friction is generated even though a lubricant is
usually present on the die and metal surfaces. The friction thus
generated hinders the smooth shaping operation and increases the
risk of metal buckling. It also limits the degree of necking (the
extent by which the open end may be necked-in at each necking step)
because the container pre-form can sustain only a certain maximum
axial load without deformation, and a greater degree of necking-in
requires a greater degree of axial load regardless of the generated
friction. Therefore, increased friction detracts from the axial
load that can be applied to necking-in.
[0008] U.S. Pat. No. 5,711,178 which issued to Hogendoorn et al. on
Jan. 27, 1998 discloses a die for use in a die-necking process of a
metal body. The die is designed to reduce axial force needed in the
die necking steps.
[0009] U.S. Pat. No. 4,881,394 which issued to Jansen on Nov. 21,
1989 and U.S. Pat. No. 5,168,742 which issued to Heyes et al. on
Dec. 8, 1992 may also relate to the minimization of axial force,
but these patents relate to ironing dies which are quite different
from necking dies.
[0010] It would therefore be advantageous to provide alternative
ways of reducing the amount of friction generated between the metal
pre-form and a necking die without compromising a desired shaping
operation.
SUMMARY OF THE EXEMPLARY EMBODIMENTS
[0011] One exemplary embodiment of the invention provides a necking
die set for necking-in a metal container preform. The die set
comprises a knockout punch having a generally cylindrical surface
and a die having, in an axial direction from front to back of the
die, an inwardly tapering in-feed surface, a forming radius, a
generally cylindrical land defining a die bore diameter, a
discharge surface following the land, and a relief surface having a
diameter larger than the die bore diameter. The land has an axial
length of less than 0.1 inch. This dimension limits the number of
metal contacts with the land to one or two as a metal container
preform is necked in the die in co-operation with the knockout
punch.
[0012] The axial length of the land is preferably from 0.010 to
0.0950 inches, and still more preferably from 0.0127 to 0.0827
inches.
[0013] The knockout punch preferably has an outer diameter and the
die preferably has a bore diameter effective to leave a gap
therebetween, the gap being greater than the top-wall thickness of
a container preform necked in the die set. Alternatively, the gap
may be the same as the top-wall thickness or less than the top-wall
thickness, to effect re-drawing of the container preform during the
necking step. When the gap is less than the top-wall thickness, the
gap is preferably up to 10% smaller than the thickness of the
top-wall, and more preferably up to 5% smaller.
[0014] The container preform may preferably have a top-wall
thickness of 0.0058 to 0.010 inch, and the die may preferably have
a forming radius of 0.2 and 0.5 inches.
[0015] Another exemplary embodiment provides a necking die set for
necking-in a metal container preform. The die set comprises a
knockout punch having a generally cylindrical surface and a die
having, in an axial direction from front to back of the die, an
inwardly tapering in-feed surface, a forming radius, a generally
cylindrical land defining a die bore diameter, a discharge surface
and a relief surface having a diameter larger than the die bore
diameter. The land has an axial length that limits the number of
metal contacts to one.
[0016] The exemplary embodiments also extend to dies designed for
use in the aforesaid die sets.
[0017] Another exemplary embodiment provides a method of necking-in
a metal container preform having a top-wall thickness. The method
includes the steps of directing an open end of a metal container
preform surrounding a cylindrical knockout punch into an annular
necking die to effect necking-in of the container preform, and then
using the knockout punch and optionally pressurized gas to knock
out the container body preform from the die. The method also
includes providing the die with, or selecting the die to have, a
land having an axial length effective to limit a number of contacts
between the container preform with the land during the necking step
to one or two. The distance between the land and the knockout punch
is also preferably reduced to cause a resizing or redistribution of
metal of the necked-in part of the container wall.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 is a cross-section of one form of necking die and
knockout punch combination showing surfaces normally provided
within such a die;
[0019] FIG. 2 is an enlargement of part of the cross-section of
FIG. 1 showing the parts within the dashed-line circle of FIG.
1;
[0020] FIG. 3 is a view similar to FIG. 2, but also showing part of
a wall of a container body pre-form inserted into the die;
[0021] FIG. 4 is an enlargement of the land region of the die of
FIG. 3 showing points of metal contact with the land;
[0022] FIG. 5 is a view similar to FIG. 4 according to an exemplary
embodiment, showing a modification of the region of the land to
minimize metal contact;
[0023] FIGS. 6A and 6B are exaggerated schematic views showing a
prior art die (FIG. 6A) and a die according to an exemplary
embodiment (FIG. 6B); and
[0024] FIG. 7 is a view similar to FIG. 5 but showing a further
alternative exemplary embodiment.
DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS
[0025] In the following, for the sake of simplicity, reference is
made to a "container" rather than a "container body pre-form",
although the latter is generally intended.
[0026] FIGS. 1 and 2 of the accompanying drawings show a necking-in
die set 10 comprising a combination of a die 11 and a knockout
punch 12. This combination is shown in cross-section but is
generally symmetrical about an axial centerline (central axis 14).
The die has a front 16 at the left hand side of the drawing (where
the container is inserted during necking) and a rear 17 at the
right hand side. In a direction front to back of the die 11, the
internal surfaces of the die are made up of an inwardly-tapering
in-feed surface 20, a forming radius 21 (sometimes referred to as
an inflection point), an annular land 22 having a surface that is
parallel to the axial centerline 14 and a specific bore diameter
D.sub.1, a discharge surface 23 at the rear end of the land, and a
relief surface 24 (often referred to as a cut-back surface) of
greater diameter D.sub.2 than the land. Knockout punch 12 fits
within the central opening or bore of the annular die and is
generally cylindrical in shape with a diameter D.sub.3. This
diameter is typically 0.001 to 0.002 inch smaller than the bore
diameter D.sub.1 minus twice the thickness of the metal 25 (see
FIG. 3) forming the top of the container wall undergoing the die
necking stage under consideration (the so-called top-wall
thickness). Because of this smaller diameter D.sub.3, there is a
spacing or degree of free play between the wall of the container
and the opposing land 22 and knockout punch 12 during a die necking
step. For aluminum beverage containers, the top wall of the
un-necked container will generally range between 0.0058 and 0.010
inch, depending on whether the container body is intended for an
aluminum beverage can or an aluminum bottle.
[0027] During neck forming, as represented in FIG. 3, the die is
usually held stationary and the open end 26 of a container 27 is
pushed into the die. The open end 26 is guided into the die by the
in-feed surface 20 which causes a reduction of diameter of the
container and provides the container body with a desired shoulder
shape 30. The wall of the container passes the forming radius 21 of
the die (where bending commences), contacts the knockout punch 12
and is fed into the die bore formed by land 22 to form a neck-in
portion 31 of reduced diameter. This operation is assisted by the
knockout punch 12 which is moved in the same direction as the
container and at approximately the same speed during this stage of
the operation. At the end of the necking step, the knockout punch
12 is reversed in direction and, usually assisted by pressurized
air introduced into the container through a central channel (not
shown) in the knockout punch, is used to push the container out of
the die. A step 28 of enlarged diameter formed on the knockout
punch 12 contacts the open end of the container to effect this
pushing step. The discharge surface 23 at the end of the land 22,
being ramped, aids the removal of the necked-in portion 31 of the
container from the die without damaging the surface coating (if
any) provided on the outer surface of the container. This may be
necessary as the container may have a slightly larger diameter than
the bore diameter at the land 22, particularly at the open end
where there is often an outward flare, as shown.
[0028] As previously mentioned, and as shown more clearly in the
still further enlarged view of FIG. 4, the spacing between the
outer surface of the knockout punch 12 and the adjacent surface of
the land 22 is preferably slightly greater than the thickness of
the metal of the container wall at this stage of the operation
(usually between 0.0005 inch to 0.001 inch greater) so that the
metal does not wedge itself in the gap between the die and the
knockout punch (which could result in axial collapse of the
container). As the metal forced into the die passes the forming
radius 21, it first contacts the outer surface of the knockout
punch 12, and is then diverted back into contact with the surface
of the land 22 (shown as "Contact 1" in the drawing). The metal is
then diverted back again into contact with the knockout punch 12,
and is once again diverted back into contact with the land 22
("Contact 2"). This kind of rebound of the metal between the
knockout punch and the land may occur several more times or, after
the second contact, the metal may stay in continuous contact with
the knockout punch before the metal passes the land and enters the
gap 33 between the knockout punch 12 and the relief surface 24.
Alternatively, in some instances, the metal may remain in
continuous contact with the land 22, or there may be a mix of
rebounds and continuous contact. As previously mentioned, at this
stage of the necking operation, the knockout punch 12 moves in the
same direction as the container wall 25 (from front to back of the
die, as indicated by the arrow) and offers no real resistance to
the movement of the metal since the knockout punch is moved at
approximately the same speed as, or faster than, the metal and no
resistive friction is developed. However, friction is generated at
the positions where the metal contacts the surface of the land 22
and the friction increases with the number of contacts (or area of
contact) between the metal and the land. As the friction increases,
the force or axial loading required to push the container into the
die increases, and there is a greater chance of the container
jamming in the die or buckling under the pushing force.
[0029] An exemplary embodiment of the present invention minimizes
the friction generated in this way by reducing the axial length of
the land below the minimum length conventionally employed (about
0.1 inch). This decreases the number of times the metal contacts
the surface of the land 22 and/or decreases the area of contact.
Ideally, the land is made so short that there is only one contact
of the metal with the land, but as many as two metal contacts may
be accepted. This is illustrated schematically in FIG. 5 of the
accompanying drawings. This limited number of contacts reduces the
friction, which will in turn reduce the axial load required to push
the container into the die during necking.
[0030] It may be possible to determine the number of contacts made
with the land by microscopic examination of the land surface of a
well-used die since the contacts change the surface appearance or
physical wear on the land surface, which appear as surface bands.
Moreover, a test die made of a tough transparent material, e.g.
polycarbonate or other strong polymer, may be used to allow visual
observation of movements of the container wall during the
necking-in process.
[0031] The axial length of the land 22 required to produce the
desired reduction in friction is a function of the forming radius
21, the metal properties of the top wall of the container, the top
wall thickness of the un-necked container body (generally 0.0058 to
0.010 inch), and the clearance between the knockout punch and the
land. For most applications using aluminum can body stock (e.g.
container bodies made of alloys AA3004, AA3014, X319, X343, etc.)
the forming radius 21 will fall between 0.2 and 0.5 inches, and the
knockout punch and die clearance over metal (the metal being at the
gauge to which it thickens in that stage of the necking operation)
will fall between 0.0005 and 0.001 inch per side. In such
circumstances, the preferred land lengths will be within the range
of 0.027 and 0.060 inch in axial length. It should be noted that
the length of the land is the length of the portion that is
parallel to the central axis 14 and does not include any part of
the discharge surface 23 or the forming radius 21. The preferred
working range for the length of the land is 0.010 to 0.0950 inch,
and generally an amount less than 0.1 inch. These dimensions are
normally suitable for all conventional necking speeds and stroke
lengths.
[0032] Table 1 below shows the land lengths that are optimum for
achieving a single contact with the die land.
TABLE-US-00001 TABLE 1 FORMING MINIMUM MAXIMUM RADIUS LAND LENGTH
LAND LENGTH (inch) (inch) (inch) 0.01 0.0127 0.0129 0.1 0.0217
0.0341 0.2 0.027 0.0421 0.3 0.0314 0.0484 0.5 0.0385 0.0583 0.8
0.0468 0.0701 1.0 0.0515 0.0767 1.2 0.0558 0.0827
[0033] Thus, it can be seen from the above table that, for forming
radii below 1.2 inch, the land preferably has a minimum length
above about 0.1 inch and a maximum length below about 0.095 inch,
and preferably below 0.09 inch.
[0034] FIGS. 6A and 6B are somewhat exaggerated schematic views
illustrating the difference between conventional necking dies and
those of some of the exemplary embodiments. Thus, it will be seen
that in the exemplary embodiments illustrated by FIG. 6B, the land
22 is much shorter than that in the conventional die design
illustrated in FIG. 6A.
[0035] The inventor has also surprisingly found that, when the
length of the land is shortened in the indicated manner, the free
play or spacing conventionally provided between the container wall
and the confronting surfaces of the land 22 and knockout punch 12
may be eliminated without increasing friction unacceptably and
without increasing any tendency of the container to jam in the die.
This was evident by the fact that containers necked in this way did
not collapse during the necking step, even when provided with a
weakened mid section (e.g. a narrow waist). It is also noted that,
when the free play or spacing is eliminated, or the spacing between
land and knockout punch is made slightly less than the thickness of
the adjacent container wall (top-wall thickness), the metal in the
container wall may be redistributed or "re-sized" to eliminate or
reduce circumferential irregularities of thickness that may build
up as the container is necked-in. Indeed, the wall thickness after
the neck reduction may be reduced in this process by 10% or less,
and preferably 5% or less, when compared to an equivalently necked
container where conventional free play or spacing is provided. This
wall thickness reduction produces an even wall-smoothing effect.
This advantage can be achieved without further modifying the land,
i.e. while maintaining the flat cross-sectional profile of the
surface of the land 22, as shown. It is theorized that, although
the re-sizing of the container wall can accomplished in this way,
this can be done without significant increases in friction because
the re-sizing of the metal takes place to only over a short axial
distance due to the reduced length of the land.
[0036] This embodiment is illustrated in FIG. 7 of the accompanying
drawings, from which it can be seen that the gap between the
knockout punch 12 and the land 22 is the same as the adjacent
topwall thickness of the container 27. Again, there is just one
contact, but the container remains in contact with the land 22 over
substantially the entire length of the land. Essentially, metal
rebound between the knockout punch and the land has been
eliminated, but the area of metal contact (compared to a
conventional die) has been reduced.
* * * * *