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.

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.