Meaning
Deep drawing of cylindrical metal cups produces non-uniform rim profiles due to variations in directional plastic flow. This variation, quantified as earing height, measures the peak-to-valley difference along the top edge of the formed vessel. It arises from planar anisotropy in the sheet metal, where the material flows more easily in certain crystallographic directions than in others.
Accurate measurement of this height defines the necessary trim allowance for the drawn component.
Forming Anisotropy
Crystallographic texture developed during rolling determines how the metal deforms under tensile stress. Sheet steel and aluminum alloys used for battery housings exhibit different earing height values depending on the cold reduction ratio and annealing temperature. The deformation mechanism involves slip along preferred planes, which causes the material to stretch unevenly.
This behavior produces four or eight ears along the rim.
Production Waste
Uneven rims on drawn cups must be sheared off to create a flat top edge for sealing. Excessive earing height increases the volume of scrap generated during this trimming step. High scrap rates raise the unit cost of battery cans and require more frequent tool maintenance.
This waste reduces the efficiency of high-speed manufacturing lines.
Material Control
Procurement specifications for coil stock restrict the allowable plastic strain ratio variance. Controlling the grain orientation during recrystallization annealing reduces the resulting earing height. Mill operators adjust the hot-rolling finishing temperature to minimize this effect.
