Meaning
Cold forming process for cylindrical lithium-ion cell housings. A standard 21700 can drawing operation involves stretching a circular blank of nickel plated steel into a cup measuring 21 mm in diameter and 70 mm in length. This specific format demands high dimensional accuracy to ensure the internal electrode assembly fits without excessive void space.
Success depends on the friction between the punch and the sheet material.
Fabrication Sequence
Multi-stage press operations define the geometry. A typical 21700 can drawing setup uses several progressive dies to reduce the diameter while increasing the height. Each stage thins the walls slightly to achieve a uniform thickness across the cylinder.
Material Requirement
Ductility of the base steel limits the maximum draw ratio. High quality nickel plated steel prevents surface micro-cracking during 21700 can drawing. If the plating is brittle it separates from the substrate.
This loss of integrity exposes the steel to electrolyte corrosion.
Dimensional Tolerance
Precision tooling maintains the outer diameter within microns. The height of 21700 can drawing output is trimmed after the final strike to ensure a flat edge for lid welding. Burr formation at the rim interferes with the laser welding process.
Consistency in wall thickness supports uniform heat dissipation during cell operation. The final part must withstand internal pressures generated during fast charging. Each millimetre of height must be perfectly perpendicular to the base to prevent tilted lids.
Thermal expansion coefficients must be considered when matching the can to the header.
