Can manufacture

Abstract

A method and apparatus are disclosed which are suitable for use in the manufacture of two-piece metal containers. In particular, a press is disclosed which makes cup sections from metal sheet using a combination of drawing and stretching operations. The cups resulting from the press have the advantage of having a base thickness that is thinner relative to the ingoing gauge of the metal sheet.

1 . A method for manufacture of a metal cup from a metal sheet, the method comprising the following operations:
 i. a drawing operation comprising drawing the metal sheet into a cup having a sidewall and an integral base;   ii. a stretching operation performed on the cup, the operation comprising clamping an annular region on the base of the cup to define an enclosed portion, and deforming and stretching at least part of the base that lies within the enclosed portion to thereby increase the surface area and reduce the thickness of the base, the annular clamping adapted to restrict or prevent metal flow from the clamped region into the enclosed portion during this stretching operation;   the drawing and stretching operations performed in a common press.   
     
     
         2 . The method as claimed in  claim 1 , wherein the drawing operation comprises locating the metal sheet between a draw punch and a draw die, and moving either or both of the draw punch and draw die towards each other such that the draw punch extends through the draw die to thereby draw the metal sheet into the cup, the annular clamping during the stretching operation comprising clamping the annular region on the base of the cup between the draw punch and a clamping element disposed on the opposite side of the cup to the draw punch. 
     
     
         3 . The method as claimed in  claim 2 , wherein the stretching operation comprises using a stretch punch disposed on the opposite side of the cup to the draw punch and moving either or both of the stretch punch and clamped cup towards each other to deform and stretch at least part of the base that lies within the enclosed portion. 
     
     
         4 . The method as claimed in  claim 1 , wherein the stretching operation comprises deforming and stretching at least part of the base that lies within the enclosed portion into a domed profile. 
     
     
         5 . A press for manufacture of a metal cup from a metal sheet, the press comprising:
 i. means for drawing the metal sheet into a cup having a sidewall and an integral base;   ii. a clamping element for clamping the drawn cup during a stretching operation, the clamping element adapted to clamp an annular region on the base of the drawn cup to define an enclosed portion;   iii. a stretch tool adapted to deform and stretch at least part of the base that lies within the enclosed portion in the stretching operation to thereby increase the surface area and reduce the thickness of the base, the clamping element further adapted to restrict or prevent metal flow from the clamped region into the enclosed portion during the stretching operation.   
     
     
         6 . The press as claimed in  claim 5 , wherein the means for drawing the metal sheet comprises a draw punch and a draw die, either or both of the draw punch and draw die being moveable towards each other such that the draw punch may extend through the draw die to draw the metal sheet into the cup, the clamping element disposed on the opposite side of the cup to the draw punch such that in use during the stretching operation the clamping element clamps the annular region of the base between the clamping element and the draw punch. 
     
     
         7 . The press as claimed in  claim 6 , wherein the stretch tool comprises a stretch punch disposed on the opposite side of the cup to the draw punch, either or both the stretch punch and combination of draw punch and clamping element being moveable towards each other such that in use the stretch punch deforms and stretches at least part of the base that lies within the enclosed portion. 
     
     
         8 . The press as claimed in either of  claim 6 , wherein the draw punch is provided with a recess or bore to enable the stretch tool to extend all or partly within the recess or bore during the stretching operation. 
     
     
         9 . A container comprising:
 a circumferential sidewall defining an end; and   a bottom portion enclosing the end of the circumferential sidewall, wherein a material of the bottom portion is stretched relative to the circumferential sidewall to form a thinner preselected profile.   
     
     
         10 . The container of  claim 9 , wherein the thinned preselected profile is a dome. 
     
     
         11 . The container of  claim 10 , wherein the material of the container at or about the dome has a substantially uniform thickness. 
     
     
         12 . The container of  claim 10 , wherein the container is formed from a blank of material;
 wherein the blank of material has a base gauge prior to being formed; wherein, after being formed, the material of the container at or about the dome has a thickness; and wherein the thickness of the material at or about the dome is less than the base gauge.   
     
     
         13 . The container of  claim 12 , wherein the thickness of the material at or about the dome is about 0.0003 inch to about 0.003 inch thinner than the base gauge. 
     
     
         14 . The container of  claim 9 , wherein the container is formed from a blank of material;
 and wherein the blank of material has a preformed dome portion.   
     
     
         15 . The container of  claim 9 , wherein the container is a can body. 
     
     
         16 . The container of  claim 9 , wherein the container is a cup.