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.

What is claimed is: 
     
         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, and   wherein, 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; and   performing 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; and   forming 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.