Meaning
Sequential metal forming operations that transform flat sheet stock into deep cylindrical containers provide the high volume production method required for lithium ion cell housings. Continuous deep drawing utilizes a series of dies to progressively reduce the diameter and increase the height of a metal cup. This method is distinct from single stage pressing because it maintains a steady flow of material through multiple stations without manual handling between steps.
The process is the standard for manufacturing the cans for 21700 and 4680 cells due to its speed and dimensional consistency. It stops being economical for small batch runs where the cost of the complex progressive die set cannot be recovered.
Material Flow
Plastic deformation moves the metal from the flange into the sidewalls while maintaining a uniform thickness across the entire height of the container. Continuous deep drawing requires a material with high elongation and a favorable plastic strain ratio to prevent tearing at the base. Lubrication plays a central role in reducing the friction between the sheet and the die surface.
If the friction is too high, the force required to pull the metal will exceed the tensile strength of the wall.
Tooling Geometry
Precision engineering of the punch and die radii ensures that the material bends smoothly without wrinkling or thinning excessively. Each stage in continuous deep drawing is designed to work the metal just below its fracture limit. The clearance between the punch and die determines the final wall thickness and the surface quality of the cell case.
Hardened steel or carbide inserts are used to resist the abrasive wear caused by the high speed movement of the metal.
Production Throughput
Automated transfer systems move the parts between stations at rates exceeding one hundred units per minute. Continuous deep drawing allows for the integration of secondary operations like trimming, flanging and bottom stamping within the same machine. This integration reduces the total floor space required for the production line and lowers the energy consumption per part.
If a single station fails, the entire line stops to prevent the production of defective housings. Real time monitoring of press forces detects changes in material properties or tool wear before they lead to catastrophic failure.
