REVERSE BUBBLE SHELL CONSTRUCT, AND RIVET FORMING METHOD AND TOOLING THEREFOR

Abstract

A rivet forming method includes providing a sheet material with a base thickness, forming the sheet material into a shell, forming a reverse bubble on the shell, forming the shell into a can end, forming the reverse bubble into a rivet button, staking the rivet button to secure a pull tab to the can end, and performing finishing operations on the can end. The reverse bubble provides enhanced rivet forming processes and properties and allows for the use of a metal sheet with a thinner base thickness.

Description

TECHNICAL FIELD

The disclosed and claimed concept relates to can ends and, more particularly, to rivet forming methods for can ends. The disclosed concept also relates to a tooling and machinery for forming rivets.

BACKGROUND ART

Metallic containers (e.g., cans) are structured to hold products such as, for example and without limitation, food and beverages. Generally, a metallic container includes a can body and a can end. The can body typically has a base and a sidewall extending from the base to define a generally enclosed space that is open at one end. The can body is filled with product and the can end is then coupled (e.g., seamed) to the can body at the open end. The container is, in some instances, heated to cook and/or sterilize the contents thereof. This process increases the internal pressure of the container. Further, the container contains, in some instances, a pressurized product such as, but not limited to a carbonated beverage. It will therefore be appreciated that the container must have a minimum strength.

Generally, the strength of the container is related to the thickness of the metal from which the can body and the can end is formed as well as the shape and configuration of various elements of the can body and can end. The present application primarily addresses the can ends rather than the can bodies. The can ends are commonly referred to as “easy open” ends and include a tear panel and an opening device (e.g., a pull tab). The tear panel is defined by a score profile, or score line, on the exterior surface (identified herein as the “public side”) of the can end. The pull tab is attached (e.g., without limitation, riveted) adjacent the tear panel and is structured to be lifted and/or pulled to sever the score line and deflect and/or remove the severable panel, thereby creating an opening for dispensing the contents of the container.

When the can end is made, it originates as a blank, which is cut from a sheet metal product (e.g., without limitation, sheet aluminum, sheet steel). As used herein, a “blank” is a portion of material that is formed into a product. Typically, the blank is formed into a “shell” in a shell press. As used herein, a “shell” is a construct that started as a generally planar blank and which has been subjected to forming operations other than scoring, paneling, rivet forming, and tab staking, as is known The shell is then subsequently further formed into a fully finished can end in a conversion press. That is, further forming operations that convert a shell into a can end include scoring, paneling, rivet forming, and tab staking, as is known. It will be appreciated, however, that it is also possible for the sheet material to be cut and formed into a can end in a single press that performs all of the operations of both a shell press and a conversion press in a single machine (e.g., press).

A shell press and/or a conversion press includes a plurality of tool stations where each station performs a forming operation (or which may include a null station that does not perform a forming operation). In a shell press, the blank moves through successive stations and is formed into the shell. That is, as a non-limiting example, a first station cuts the blank from the sheet material, a second station forms the blank into a cup-like construct with a depending sidewall, a third station forms the depending sidewall into a countersink and a chuck sidewall, and so forth. In a conversion press, the shell is formed into a can end. At least one station forms a “bubble.” A bubble, as used herein, is the construct that is formed into a “rivet button” which, in turn, is formed into the rivet that is staked to attach the pull tab to the can end. As such, the formation of the bubble affects the characteristics of the rivet button and the rivet. As the shell advances from one tool station to the next, conversion operations such as, for example and without limitation, rivet forming, paneling, scoring, embossing, and tab staking (i.e., coupling a tab to the shell via the rivet), are performed until the shell is fully converted into the desired can end and is discharged from the press. Accordingly, a shell/can end is formed in a press having a plurality of stations. The blank is moved intermittently, or as used herein “indexed,” through the plurality of stations, meaning the blank is moved and stops at each station wherein a forming operation is performed (it is understood that some stations are “null” stations that do not perform a forming operation).

In the can-making industry, large volumes of metal are required in order to manufacture a considerable number of cans. Thus, an ongoing objective in the industry is to reduce the amount of metal that is consumed. Efforts are constantly being made, therefore, to reduce the original (i.e., base) thickness or gauge (sometimes referred to as “down-gauging”) of the stock material from which can ends, tabs, and can bodies are made. Presently, can ends are made from sheet metal such as, but not limited to, aluminum and steel as well as alloys including those metals. However, use of a material with a thinner base gauge causes other problems such as, but not limited to, failure (e.g., tearing) of the can end at the rivet and uneven staking and/or overlapping of the rivet with respect to the pull tab. It will therefore be appreciated that as less material (e.g., thinner gauge) is used, problems arise that require the development of unique solutions.

One such example is illustrated in FIGS. 1A and 1B, wherein an expandable bubble 2 construct is formed on a shell 4 as generally disclosed in commonly owned U.S. Pat. Nos. 11,059,091; 11,400,509; and 11,691,193, which are incorporated by reference herein. As shown in FIG. 1A, the expandable bubble 2 is formed in a bubble station 100 (partially shown) including upper and lower tooling assemblies 102, 104. The upper tooling assembly 102 includes an upper cap 106 and an upper punch 108. The lower tooling assembly 104 includes a lower cap 110 and a lower punch 112. The upper cap 106 and the lower cap 110 are structured to move together prior to the upper punch 108 and the lower punch 112 engaging the shell 4. That is, the upper cap 106 and the lower cap 110 together hold, or clamp, the shell 4 as desired. The upper punch 108 includes a generally cylindrical body 120 with a first bubble coining surface 122. The lower punch 112 also includes a body 130 defining a second bubble coining surface 132. In operation, the first bubble coining surface 122 is structured to move between a first position (not shown), wherein the first bubble coining surface 122 is spaced from the second bubble coining surface 132, and the second position shown in FIG. 1A, wherein the first bubble coining surface 122 and the second bubble coining surface 132 engage the shell 4 to form the expandable bubble 2. That is, the tooling coins (i.e., compresses) segments 6, 8 of the shell 4 and creates the upward projection 10 thereby forming the aforementioned expandable bubble 2. Although such expandable bubble 2 has been shown to result in enhanced rivet formation processes and properties, continued room for improvement remains and the quest to reduce metal thickness while maintaining strength and rivet forming consistency continues.

There is, therefore, room for improvement in rivet forming methods and associated tooling.

SUMMARY OF THE INVENTION

These needs, and others, are met by aspects the disclosed concept, which are directed to improved rivet forming methods and tooling as set forth in the drawings, written description and claims herein.

In one exemplary embodiment of the presently disclosed technology, a press structured to form a shell from sheet material comprises a frame and a plurality of forming stations. The plurality of forming stations includes a bubble station. The bubble station includes an upper tooling assembly and a lower tooling assembly. The upper tooling assembly is structured to move between a first position and a second position. The first position is defined where the upper tooling assembly is disengaged from the lower tooling assembly. The second position is defined where the upper tooling assembly is engaged with the lower tooling assembly. The upper tooling assembly and the lower tooling assembly are structured to form a reverse bubble when the upper tooling assembly is in the second position.

In another exemplary embodiment of the presently disclosed technology, a rivet forming method comprises providing a sheet material with a base thickness. The sheet material is formed into a shell. A reverse bubble is formed on the shell. The shell is formed into a can end. The reverse bubble is formed into a rivet button. The rivet button is staked into a rivet to secure a pull tab to the can end.

In a further exemplary embodiment of the presently disclosed technology, a reverse bubble shell construct comprises a shell. A convex sidewall extends upward from the shell. A concave central portion is centrally disposed in the convex sidewall. An annular apex is defined around a perimeter of the concave central portion and comprises a first opposing point disposed oppositely a second opposing point.

BRIEF DESCRIPTION OF THE DRAWINGS

A full understanding of the disclosed concept can be gained from the following description of the preferred embodiments when read in conjunction with the accompanying drawings in which:

FIG. 1A is a cross-sectional view of a portion of a prior art bubble station;

FIG. 1B is a cross-sectional view of an expandable bubble construct formed by the bubble station tooling of FIG. 1A;

FIG. 2A is a partially schematic partially cross-sectional view of a press and bubble station therefor in accordance with a non-limiting embodiment of the disclosed concept;

FIG. 2B is a partially schematic partially cross-sectional view of a press and bubble station therefor in accordance with a non-limiting embodiment of the disclosed concept;

FIG. 3A is a cross-sectional view of a portion of the bubble station of FIG. 2A;

FIG. 3B is a cross-sectional view of a portion of the bubble station of FIG. 2B;

FIG. 3C is a cross-sectional view of reverse bubble shell construct formed by the bubble station tooling of FIG. 3A;

FIG. 4A is a cross-sectional view of a portion of a first rivet station;

FIG. 4B is a cross-sectional view of a rivet button shell construct formed by the first rivet station tooling of FIG. 4A;

FIG. 5A is a cross-sectional view of a portion of a second rivet station;

FIG. 5B is a cross-sectional view of a rivet button shell construct formed by the second rivet station tooling of FIG. 5A;

FIG. 6A is a cross-sectional view of a portion of a third rivet station;

FIG. 6B is a cross-sectional view of a rivet button shell construct formed by the third rivet station tooling of FIG. 6A;

FIG. 7A is cross-sectional view of a portion of a staking station;

FIG. 7B is a cross-sectional view of a rivet formed by the staking station tooling of FIG. 7A, shown affixing a pull tab to a finished can end; and

FIG. 8 is a flow chart of a disclosed method.

DETAILED DESCRIPTION OF THE INVENTION

It will be appreciated that the specific elements illustrated in the figures herein and described in the following specification are simply exemplary embodiments of the disclosed concept, which are provided as non-limiting examples solely for the purpose of illustration. Therefore, specific dimensions, orientations, assembly, number of components used, embodiment configurations and other physical characteristics related to the embodiments disclosed herein are not to be considered limiting on the scope of the disclosed concept.

Directional phrases used herein, such as, for example, clockwise, counterclockwise, left, right, top, bottom, upwards, downwards and derivatives thereof, relate to the orientation of the elements shown in the drawings and are not limiting upon the claims unless expressly recited therein.

As used herein, the singular form of “a,” “an,” and “the” include plural references unless the context clearly dictates otherwise.

As used herein, “structured to [verb]” means that the identified element or assembly has a structure that is shaped, sized, disposed, coupled and/or configured to perform the identified verb. For example, a member that is “structured to move” is movably coupled to another element and includes elements that cause the member to move or the member is otherwise configured to move in response to other elements or assemblies. As such, as used herein, “structured to [verb]” recites structure and not function. Further, as used herein, “structured to [verb]” means that the identified element or assembly is intended to, and is designed to, perform the identified verb. Thus, an element that is merely capable of performing the identified verb but which is not intended to, and is not designed to, perform the identified verb is not “structured to [verb].”

As used herein, the statement that two or more parts or components are “coupled” shall mean that the parts are joined or operate together either directly or indirectly, i.e., through one or more intermediate parts or components, so long as a link occurs. As used herein, “directly coupled” means that two elements are directly in contact with each other. As used herein, “fixedly coupled” or “fixed” means that two components are coupled so as to move as one while maintaining a constant orientation relative to each other. Accordingly, when two elements are coupled, all portions of those elements are coupled.

As used herein, the word “unitary” means a component that is created as a single piece or unit. That is, a component that includes pieces that are created separately and then coupled together as a unit is not a “unitary” component or body.

As used herein, “about” in a phrase such as “disposed about [an element, point or axis]” or “extend about [an element, point or axis]” or “[X] degrees about an [an element, point or axis],” means encircle, extend around, or measured around. When used in reference to a measurement or in a similar manner, “about” means “approximately,” i.e., in an approximate range relevant to the measurement as would be understood by one of ordinary skill in the art.

As used herein, “generally” means “in a general manner” relevant to the term being modified as would be understood by one of ordinary skill in the art.

As used herein, “substantially” means “for the most part” relevant to the term being modified as would be understood by one of ordinary skill in the art.

As used herein, “at” means on and/or near relevant to the term being modified as would be understood by one of ordinary skill in the art.

The following discussion and the Figures refer to a generally cylindrical can end (partially shown in FIG. 7B), however, it is understood that the disclosed concept is also applicable to other can ends of different shapes and sizes than those shown and discussed herein. Further, solely for purposes of illustration, certain non-limiting examples herein refer to dimensions of a can end made from aluminum or aluminum alloys and structured to be coupled to a beverage can; that is, a can structured to contain a beverage such as beer or carbonated beverages, i.e., a “soda” or “pop.” As used herein, such can end is identified as a “beverage container can end.” Similarly, the shell that becomes a “beverage container can end” is, as used herein, a “beverage can shell.” One non-limiting example of a beverage can having a beverage can end is a twelve-ounce beverage can, which is generally well known. It is understood, however, that the disclosed concept is also applicable to can ends made of other materials such as, but not limited to, steel and steel alloys. It is further understood that steel cans and can ends are typically made from material with a base thickness thinner than aluminum can ends. Thus, a steel can end that includes the down-gauging concept disclosed herein would have a thinner base thickness than the dimensions for an aluminum can, as described below, and a thinner base thickness than the metal used to make the can ends that do not include the down-gauging concept disclosed herein.

As is generally known, a can end is structured to be coupled, directly coupled, or fixed in a sealed manner to a can body (not shown) to form a container (not shown).

FIG. 2 shows a press 200 (shown in simplified view in phantom line drawing) including a plurality of stations 202 (some shown schematically) each of which perform a plurality of forming operations on a shell 5 in accordance with non-limiting example embodiments of the disclosed concept. For the purpose of this application, the following stations 202 are identified: a bubble station 302 (FIG. 3A), a first rivet station 402 (FIG. 4A), a second rivet station 502 (FIG. 5A), a third rivet station 602 (FIG. 6A), and a stake station 702 (FIG. 7A). One of the first forming operations includes cutting a blank 3 from a sheet material 1. Thus, there is a blanking station (not shown). Other forming operations form the blank 3 so as to have a countersink, a chuck wall and other elements of a shell 5. It is understood, however, that the reverse bubble 13 construct of the disclosed concept (best shown in FIG. 3B) can be formed at any time prior to forming a rivet, including before the blank 3 is cut from the sheet material 1. Thus, the forming operations that form the reverse bubble 13 can be performed on any of the sheet material 1, the blank 3, or the shell 5. Generally, the discussion below will use the shell 5 as a non-limiting example of a work piece being formed.

Continuing to refer to the non-limiting example of FIG. 2, the shell 5 moves through the press 200 on a conveyor 204 (shown schematically in FIG. 2), that is structured to move with an intermittent, or indexed, motion. In an exemplary embodiment, the conveyor 204 is a belt 206 (shown schematically) including a plurality of recesses (not shown). The belt 206 moves a set distance then stops before moving the set distance again. As the belt 206 moves, a shell 5 is moved sequentially through the stations 202 where, as noted above, each station 202 performs a single forming operation, or a plurality of forming operations, on the shell 5.

The press 200, or stated alternately each station 202 thereof, includes an upper tooling assembly 250 and a lower tooling assembly 252. Each of the upper tooling assembly 250 and a lower tooling assembly 252 for multiple stations 202 are, in an exemplary embodiment, unitary or coupled and support the dies, punches and other elements of each station. In this configuration, the upper tooling assemblies 250 for the stations move at the same time and are driven by a single drive assembly (not shown). For the purpose of identifying specific components, elements of a tooling assembly are also identified as parts of a specific station 202. That is, for example, the upper tooling assembly 350 at the bubble station 302, discussed below, is also identified as the bubble station upper tooling assembly 350. It is understood that any specifically identified upper tooling assembly 250 or lower tooling assembly 252, e.g., without limitation, a “rivet station upper tooling assembly 750,” are generally part of the upper/lower tooling assemblies 250/252, respectively, and the identifier/name merely indicates the nature of the station.

The press 200 further includes a frame 254 and a drive assembly (not shown). In an exemplary embodiment, the lower tooling assembly 252 is fixed to the frame 254 and is substantially and/or generally stationary. The upper tooling assembly 250 is movably coupled to the frame 254 and is structured to move between a first position, wherein the upper tooling assembly 250 is spaced from, or disengaged from, the lower tooling assembly 252, and a second position, wherein the upper tooling assembly 250 is closer to, and in an exemplary embodiment, immediately adjacent or engaged with the lower tooling assembly 252. When the upper tooling assembly 250 is engaged with the lower tooling assembly 252, the shell 5 or other material, is being pressed by the press 200. The lower tooling assembly 252 is, in an exemplary embodiment, coupled, directly coupled, or fixed to the frame 254.

It is understood that, generally, the belt 206 moves when the upper tooling assembly 250 is in (or moving toward or away from) the first position. Conversely, the belt 206 is stationary when the upper tooling assembly 250 is in the second position. As is known, the drive assembly is structured to move the upper tooling assembly 250 between the first and second positions. Further, and as is known, the upper tooling assembly 250 and the lower tooling assembly 252 include separately movable elements (e.g., without limitation, punches, dies, spacers, pads, risers and other sub-elements (collectively hereinafter “sub-elements”)), that are structured to move separately from each other. All elements, however, generally move with the upper tooling assembly 250 between first and second positions. That is, generally, the motions of the sub-elements are relative to each other but as a whole, the upper tooling assembly 250 moves between the first position and the second position as described above. Further, it is understood that the drive assembly includes cams, linkages, and other elements that are structured to move the sub-elements of the upper tooling assembly 250 and the lower tooling assembly 252 in the proper order. That is, selected sub-elements of the upper tooling assembly 250 and the lower tooling assembly 252 are structured to move independently of other selected sub-elements. For example, one selected sub-element is structured to move into, and dwell, at the second position while another sub-element moves into and out of the second position. Such selective motion of the sub-elements is known in the art.

As shown in the enlarged cross-sectional view of FIG. 3A, in accordance with one non-limiting embodiment of the disclosed concept, the upper tooling assembly 350 of the bubble station 302 includes an upper punch 308 and an upper cap 306. The upper punch 308 has a generally cylindrical body 320 and defines a first bubble coining surface 322. The generally cylindrical body 320 defines an opening 326. In the exemplary embodiment, the opening 326 is elongated and extends upward through the first bubble coining surface 322 and at least partially into the upper punch 308. In an exemplary embodiment, the opening 326 may extend entirely through the upper punch 308. Furthermore, in the exemplary embodiment, the opening 326 is centrally defined on the first bubble coining surface 322. The opening 326 is dimensioned to form the central portion 17 of the reverse bubble 13, whereas the opening 326 forms an area of no contact between the shell 5 and the upper tooling assembly 350.

The lower tooling assembly 352 includes a lower punch 312 and a lower cap 310. The lower punch 312 has a generally cylindrical body 330 and a second bubble coining surface 332. The lower punch body 330 further includes a recess 334. In the exemplary embodiment, the recess 334 extends at least partially downward from the second bubble coining surface 332 into the lower punch 312. Furthermore, in the exemplary embodiment, the recess 334 is centrally defined on the second bubble coining surface 332. The recess 334 is dimensioned to form the central portion 17 of the reverse bubble 13, wherein the recess 334 forms an area of no contact between the shell 5 and the lower tooling assembly 352, such that a reverse bubble 13 can be at least partially formed therein. In the exemplary embodiment, the recess 334 of the lower punch 312 is of a greater area than the opening 326 of the upper punch 308. As such, the recess 334 defines the diameter 25 of the annular apex 16 of the reversed bubble 13.

The upper punch 308 is structured to move between a first position (not shown), wherein the upper tooling assembly 350 is spaced from the lower tooling assembly 352, and a second position, shown in FIG. 3A, wherein the upper tooling assembly 350 is closer to, and in the example of FIG. 3A, is adjacent the lower tooling assembly 352 in order to compress or coin the shell 5 between the first and second coining surfaces 322, 332. That is, an arcuate coin area 324 is defined, as shown.

Continuing to refer to FIG. 3A, it will be appreciated that the forming process and associated tooling (e.g., 308, 312) of the disclosed concept is unique and different compared, for example, to the prior art forming process and associated tooling shown in FIG. 1A. That is, unlike the prior art convex upper surface 134 of the body 130 of the lower punch 112 of FIG. 1A, which engages the central portion of the shell 4 to force it upward in the direction of arrow 12 to thereby form a corresponding convex upwardly extending bubble portion 10, the body 330 of the exemplary lower punch 312 instead includes the recess 334 and, therefore, is not structured to, and does not, engage the central portion 17 of the shell 5, as shown in FIG. 3A. Specifically, unlike the prior art forming process depicted in FIG. 1A, in accordance with the disclosed concept the central portion 17 of the shell 5 is not engaged at all by any tooling. This leaves the material thicker in the central portion 17. Furthermore, in operation, the central portion 17 is formed downward in the direction of arrow 15 and into the recess 334 of the lower punch 312, as shown in FIG. 3A. This is precisely the opposite of the prior art tooling and forming method shown and described with respect to FIG. 1A, and thus creates the unique concave downwardly extending central portion 17 resulting in the “reverse bubble” 13 of the disclosed concept.

As shown in FIG. 3B, the reverse bubble 13 includes a convex sidewall 14 with a concave central portion 17 defined centrally therein. The concave central portion 17 is defined within an annular apex 16 defined at a highest point of the convex sidewall 14 relative to the shell 5, wherein the convex sidewall 14 transitions into the concave central portion 17. By way of example, in the illustrated embodiment of FIG. 3B, the concave central portion 17 extends between two opposing points 19, 21 of the annular apex 16 defined between the convex sidewall 14 and the concave central portion 17. The annular apex 16 has a diameter 25, shown in the exemplary embodiment of FIG. 3B as the distance 25, between the first opposing point 19 and the second opposing point 21 of the annular apex 16. In the exemplary embodiment, the reverse bubble 13 is of a uniform shape and thickness around an entire perimeter thereof. The depth 27 of the concave central portion 17 is also shown in FIG. 3B.

As further discussed herein, the reverse bubble 13 results in a number of enhanced rivet properties. As previously discussed, the central portion 17 of the shell 5 is the thickest portion of the shell 5. The concave central portion 17 is thicker than the convex sidewall 14. As the reverse bubble 13 is formed into a rivet button 23 and subsequently a rivet 33, the central portion 17 of the reverse bubble 13 will correspond with a central portion of each of the rivet button 23 and the rivet 33. As such, the central portion of the rivet button 23 and the central portion of the rivet 33 will have a greater tear resistance during the tab staking and finishing operations than traditional bubbles in the can end making process.

As shown in FIGS. 4A, 5A, 6A, a rivet button 23 (FIGS. 4B, 5B, 6B) is formed from the reverse bubble 13 in a plurality of rivet stations 402, 502, 602 in the press 200, discussed above. Three stations are shown and described, although it will be appreciated that embodiments having more, or fewer, than three stations are also within the scope of the disclosed concept. Generally, each of a first, second, and third, rivet station 402, 502, 602, respectively, includes a rivet station upper tooling assembly 450, 550, 650 and a rivet station lower tooling assembly 452, 552, 652. Each rivet station upper tooling assembly 450, 550, 650 includes a rivet station upper cap 406, 506, 606 and a rivet station upper punch 408, 508, 608. Each rivet station lower tooling assembly 452, 552, 652 includes a rivet station lower cap 410, 510, 610 and a rivet station lower punch 412, 512, 612.

Generally, the first rivet station 402, shown in FIG. 4A, forms the reverse bubble 13 shown in FIG. 4B, the second rivet station 502, shown in FIG. 5B, forms the rivet button 23 shown in FIG. 5B, and the third rivet station 602, shown in FIG. 6A, forms the rivet button 23 shown in FIG. 6B. For the purpose of this disclosure, the details of the first rivet station 402, second rivet station 502, and third rivet station 602 are not unique and are similar to those described in commonly owned U.S. Pat. Nos. 11,059,091; 11,400,509; and 11,691,193, which are hereby incorporated by reference as if fully set forth herein.

In an exemplary embodiment, and as shown in FIG. 7A, the press 200 (FIG. 2) includes a staking station 702. As is known, the staking station 702 is structured to couple, directly couple, or fix a tab 50 to the shell 5. The staking station 702 includes a staking station upper tooling assembly 750 and a staking station lower tooling assembly 752. As is known, prior to the staking station 702, a tab 50 is disposed over the rivet button 23 as described above. At the staking station 702, the staking station upper tooling assembly 750 is structured to move between a first position (not shown), wherein the staking station upper tooling assembly 750 is spaced from the staking station lower tooling assembly 752, and the second position shown in FIG. 7A, wherein the staking station upper tooling assembly 750 is adjacent, or immediately adjacent, the staking station lower tooling assembly 752. In this configuration, when the staking station upper tooling assembly 750 is in the second position, the staking station upper tooling assembly 750 and the staking station lower tooling assembly 752 are structured to form a rivet 33 having a diameter, D, larger than rivets (not shown) formed from the same or similar material but using prior art tooling and methods. Further, among other benefits, the relatively larger diameter, D, and improved forming processes and properties of the disclosed rivet 33 result in greater finished residuals with less hinge and rivet tears when opening the can end 70 (FIG. 7B) compared to the known prior art. That is, there is greater overlap, OL, of the rivet 33 with respect to the tab 50, as shown in FIG. 7B. Accordingly, it will be appreciated that the disclosed concept will also allow for the use of material having a thinner base thickness than the prior art thus resulting in less metal consumption overall.

A rivet forming method in accordance with a non-limiting embodiment of the disclosed concept is shown in FIG. 8 and includes: providing 1000 a sheet material with a base thickness, performing 1002 preliminary forming operations on the sheet material to form a shell, forming 1004 a rivet button on the shell, staking 1005 the rivet button, and performing 1006 finishing operations on the can end. Performing 1002 preliminary forming operations on the sheet material to form a shell includes forming a central panel, an annular countersink, a chuck wall, and a curl. Alternately, the method includes providing 1001 a shell having a central panel, an annular countersink, a chuck wall, and a curl. As used herein, “finishing operations” include, but are not limited to, scoring, paneling, inspection, and/or applying coatings and/or other surface treatments.

In an exemplary embodiment, forming 1004 a rivet button on the shell includes forming 1010 a bubble construct on the shell, forming 1020 the bubble with a concave central portion 17 to create a reverse bubble 13, and/or forming 1022 the reverse bubble 13 into a rivet button 23 having a sidewall 24, a generally planar top portion 26, and a peripheral upper edge 28. In an exemplary embodiment, the sidewall 24 of the rivet button 13 is of a greater thickness than the peripheral upper edge 28 and the sidewall 24. As such, when the rivet button 23 is pressed into a rivet 33, the diameter of the rivet 33 can be relatively larger, as previously described, with a lower risk of the rivet 33 tearing when the can end 70 is opened.

Further, in an exemplary embodiment, staking 1005 the rivet button 23 includes providing 1030 a tab 50 with a body having an opening, positioning 1032 the tab 50 over the rivet button with the rivet button extending through the tab opening, forming 1034 the rivet button into the rivet, wherein the rivet has the aforementioned enhanced properties and advantages.

While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of invention which is to be given the full breadth of the claims appended and any and all equivalents thereof.

Claims

1. A press structured to form a shell from sheet material, the press comprising: a frame;a plurality of forming stations including a bubble station, the bubble station including an upper tooling assembly and a lower tooling assembly,wherein the upper tooling assembly is structured to move between a first position, wherein the upper tooling assembly is disengaged from the lower tooling assembly, and a second position, wherein the upper tooling assembly is engaged with the lower tooling assembly, andwherein, when the upper tooling assembly and the lower tooling assembly are in the second position, the upper tooling assembly and the lower tooling assembly are structured to form a reverse bubble.

2. The press of claim 1, wherein the upper tooling assembly includes an upper punch and an upper cap; wherein the upper punch includes a generally cylindrical body defining a first coining surface with an opening; wherein the lower tooling assembly includes a lower punch and a lower cap; wherein the lower punch includes a body defining a second coining surface; wherein the upper punch is structured to move between a first position, wherein the first coining surface is spaced from the second coining surface, and a second position, wherein the first coining surface is immediately adjacent the second coining surface thereby coining a portion of the shell therebetween.

3. The press of claim 2, wherein the opening of the generally cylindrical body defines an area of no contact between the upper tooling assembly and the shell.

4. The press of claim 3, wherein the body of the lower punch includes a recess, and wherein, when the upper punch is in the second position, the central portion of the shell extends into the recessed portion of the lower punch.

5. The press of claim 4, wherein the central portion of the shell has a greater thickness than a portion of the shell between the first coining surface and the second coining surface.

6. The press of claim 1, wherein the plurality of forming stations includes at least one rivet button station structured to form the reverse bubble into a rivet button.

7. The press of claim 6, wherein the plurality of forming stations includes a bubble station, a plurality of rivet button stations and a staking station.

8. The press of claim 6, wherein the plurality of forming stations further includes a staking station; wherein the staking station includes a staking station upper tooling assembly and a staking station lower tooling assembly; wherein the staking station upper tooling assembly is structured to move between a first position, wherein the staking station upper tooling assembly is spaced from the staking station lower tooling assembly, and a second position, wherein the staking station upper tooling assembly is adjacent the staking station lower tooling assembly; and wherein, when the staking station upper tooling assembly is in the second position, the staking station upper tooling assembly and the staking station lower tooling assembly are structured to form a rivet.

9. The press of claim 6, wherein the rivet button comprises a sidewall, a generally planar top portion, and a peripheral upper edge, wherein the generally planar top portion is of a greater thickness than the peripheral upper edge and the sidewall.

10. A rivet forming method, the method comprising: providing a sheet material with a base thickness;forming the sheet material into a shell;forming a reverse bubble on the shell;forming the shell into a can end;forming the reverse bubble into a rivet button;staking the rivet button to secure a pull tab to the can end; andperforming finishing operations on the can end.

11. The method of claim 10, wherein forming the reverse bubble includes forming the bubble with a concave central portion.

12. The method of claim 11, wherein forming the reverse bubble includes forming the concave central portion without engaging the central portion of the shell with any tooling.

13. The method of claim 11, wherein forming the reverse bubble into a rivet button includes forming the rivet button with a sidewall, a generally planar top portion, and a peripheral upper edge.

14. The method of claim 13, wherein the generally planar top portion is of a greater thickness than the peripheral upper edge and the sidewall.

15. The method of claim 10, wherein staking the rivet button includes: providing a tab with a body having an opening;positioning the tab over the rivet button with the rivet button extending through the tab opening; andforming the rivet button into a rivet.

16. A reverse bubble shell construct comprising: a shell;a convex sidewall extending upwardly from the shell;a concave central portion disposed centrally within the convex sidewall;wherein an annular apex is defined around a perimeter of the concave central portion and comprises a first opposing point disposed oppositely a second opposing point.

17. The reverse bubble construct of claim 16, wherein the concave central portion has a diameter measured by the distance between the first opposing point and the second opposing point of the annular apex.

18. The reverse bubble shell construct of claim 16, wherein the central portion has a depth measured by the distance between the top of the annular apex and the bottom of the concave central portion.

19. The reverse bubble shell construct of claim 16, wherein the reverse bubble is thickest at the central portion thereof.

20. The reverse bubble shell construct of claim 16, wherein the shell is thicker at the central portion than the convex sidewall.