Punch assembly for forming a base in a metal beverage can

Details Punch assembly for forming a base in a metal beverage can Punch assembly for forming a base in a metal beverage can

1998-06-11

2002-08-20

Larson, Lowell A. (Department: 3725)

Metal deforming

By use of closed-die and coacting work-forcer

Cup or shell drawing

C072S349000

Reexamination Certificate

active

06434996

ABSTRACT:

FIELD OF THE INVENTION
The present invention is related to light-weighted metal beverage cans and more particularly to an apparatus forming the base of such cans.
BACKGROUND OF THE INVENTION
Light-weighted metal beverage cans and apparatus employed in forming the same are well known in the art. Typically, it is desirable to manufacture metal cans with as little material as possible to reduce the weight of the finished can, while maintaining the structural integrity of the same.
In typical can forming processes, metal stock is manipulated through various stages of a forming apparatus to form the shape and size of the finished can. One of the first steps taken in a can forming process is the placement of the metal stock into a cupping press wherein the metal stock is deformed into the shape of a cup. Next, the cup is conveyed to a wall ironing machine and the deformed metal stock is redrawn to start forming the general shape of the sidewall and base of the finished can. After the metal stock is redrawn, the metal stock is passed through one or more ironing stations wherein the metal stock is more finely and accurately manipulated into the final shape of the finished can. In one of the last forming steps, the metal stock is passed into a bottom forming station wherein the base of the metal can is formed into its final shape.
FIG. 1
shows a metal beverage can
10
. The can sidewall and base have been formed in accordance with the method described above. The shape of the beverage can
10
is well known to those skilled in the art. Generally, the beverage can
10
has a circumferential sidewall
12
having an upper portion
14
and a lower portion
16
. The upper portion
14
of the sidewall
12
is mechanically coupled with a tab end
18
. The lower portion
16
of the sidewall is connected to the base
20
.
FIGS. 2 and 3
show the base
20
in more detail. The base
20
includes a nose portion
22
upon which the beverage can rests when set upright. The nose portion
22
is connected with a relatively concave dome portion
24
by a gradually smooth transition. The nose portion
22
is also connected to the outer profile
26
by a gradually smooth transition. The outer profile
26
is connected to the lower portion
16
of the metal can sidewall
12
by a gradually smooth transition.
FIG. 4
shows a conventional bottom forming station
28
that may be employed to form the base
20
of the metal beverage can
10
. The bottom forming station
28
comprises a ram
30
that is adapted to slide along a relatively horizontal plane from a first position (not shown) to a second position (as shown in FIG.
4
). A punch sleeve
32
and a punch nose
34
are mechanically coupled with the ram
30
.
The punch sleeve
32
and punch nose
34
are adapted to receive a partially formed metal stock
36
. When the ram
30
is at the second position, the punch nose
34
forces the metal stock
36
into engagement with the bottom forming die
38
and ceramic insert
40
under a relatively high impact force, thereby, forming the final shape of the base of the metal can.
The punch sleeve
32
has an outer surface
42
that includes a relatively smooth upper portion
44
that conforms to the shape of the upper portion
14
of the circumferential sidewall
12
of the finished can
10
. The outer surface
42
of the punch sleeve
32
also has a generally curved front portion
46
that conforms to the lower portion
16
of the circumferential sidewall
12
of the finished metal can
10
. The outer surface
42
includes a lower portion
48
that defines a bore
49
and that is adapted to receive and abut with a portion of the punch nose
34
, as described below. The punch sleeve may be made of a steel material, or a carbide material.
The punch nose
34
has an outer surface
52
that includes a protruding portion
54
that conforms to the nose portion
22
of the finished can
10
. A relatively upwardly angled front portion
56
is connected to the protruding portion
54
by a gradually smooth transition and conforms to the outer profile
26
of the finished can
10
. A downwardly angled back portion
58
is connected to the upwardly angled portion
56
at an apex
60
and is adapted to abut with the lower portion
48
of the punch sleeve
32
. The remaining sections of the outer surface
52
of the punch nose
34
are adapted to be slip fit between the punch sleeve
32
and a retaining bolt
62
to maintain the punch nose
34
in an operating position.
The punch nose
34
may be made of a steel material, such as hardened tool steel-M
2
, or a ceramic material. Punch noses that are made of a steel material are typically coated with a chemical material, such as titanium nitride, for various reasons. One reason is that the chemical material provides a “mobile” surface that enables the metal stock to be drawn to form the base of the metal beverage can with a reduced metal thickness as the punch nose impacts the bottom forming die
38
and ceramic insert of the extractor
40
.
In the operating position, the punch nose
34
is placed within the punch sleeve bore
49
such that the punch nose and punch sleeve are securely positioned adjacent one another with a relatively small diametrical clearance —.001 inches. Between punch nose
34
and punch sleeve
32
there is a gap at a location called a split line
64
. This gap may measure about .001 inches. The split line
64
has a junction area
66
, which is the entrance into the split line
64
, proximate the apex
60
of the punch nose
34
and the end of the punch sleeve. In this arrangement, the outer surfaces of the punch sleeve
44
and
46
, and punch nose
54
and
56
form the profile of the can body and base.
It is noted that the sections on the punch sleeve and punch nose that the metal stock is in actual contact with as the base is being formed are called “active locations.” Those sections on the punch sleeve and punch nose that are not in contact with the metal stock as the base is being formed are called “non-active locations.” As shown in
FIG. 4
, the junction area
66
is located along an active location.
Over time, the punch sleeve
32
and punch nose
34
may become misaligned along the junction area
66
. As the metal stock is drawn over a misaligned junction area
66
, stress lines may be formed in the base of the finished metal can. The area around a stress line is likely to corrode and then crack after the beverage can is filled with a liquid. It would, therefore, be desirable to provide an apparatus that reduces the likelihood of stress lines being formed in he base of a finished metal can.
Conventional methods of maintaining the punch nose
34
and punch sleeve
32
in a proper alignment require corresponding punch noses and punch sleeves to be manufactured within substantially tight tolerances. The manufacturing of punch noses and punch sleeves within these tight tolerances is relatively difficult and costly to obtain. It would, therefore, be desirable to provide a base forming apparatus that is relatively more efficient to manufacture.
The chemical coating that is applied over the outer surface of a steel punch nose is likely to crack and dislodge from the punch nose during the base forming operation. The dislodged chemical flakes are likely to accumulate along the junction area
66
and contact the metal stock
36
as the metal stock is drawn. Unfortunately, these chemical flakes scratch the metal stock as the base of the finished metal can is being formed. The area around these scratches is likely to corrode and then crack after the beverage can is filled with a liquid. It would, therefore, be desirable to provide an apparatus that reduces the likelihood of scratches being formed on the base of a metal beverage can.
SUMMARY OF THE INVENTION
A punch sleeve in a bottom forming station for forming a metal beverage can having a sidewall and base portion is provided. The punch sleeve comprises a body having a sidewall that defines a bore for securely receiving a punch nose. The sidewall has a first section that corresponds to the shape of at l

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