A special consideration of sheet metal formability is in the application of cold rolled sheet metals in the
production of food and beverage cans. Cold rolling significantly reduces the percent elongation to failure of a sheet
metal, but cold rolling per se may not necessarily hinder complex shape forming provided special incremental
forming methods are used. Thus, for example, heavily cold rolled AA3104 aluminium alloy sheet used in beverage
can making may have a 1-2 percent elongation, yet for the manufacture of a beverage can body it is drawn, redrawn,
wall ironed in stages, and flanged without difficulty, many of these operations could be considered
The principal problem with the conventional tensile test for gauging the formability of sheet metals revolves
around tensile instability, as is especially the case with cold rolled tempers. An early solution to resolving this
problem involved a tensile testing technique supplemented by continuous bending under tension (CBT) of the
plastically deforming metal, whereby the sheet was wrapped between three rollers that moved continuously over the
gage length of the sheet tensile specimen (Figure 3) until failure occurred. Used on a variety of ferrous and
nonferrous sheet metals in a range of thicknesses and tempers, the total elongation to failure increased dramatically,
depending on the necking susceptibility