Meaning
Metalforming technology transforms flat sheet blanks into hollow three-dimensional vessels through the mechanical action of a punch driving the stock into a die cavity. Deep drawing relies on radial drawing tension and tangential compression forces to reshape the metal while maintaining wall thickness within strict dimensional tolerances. Cylindrical or rectangular hollow components emerge from successive press strokes that induce plastic deformation beyond the yield point of the raw material.
Tooling geometry determines the success of the operation, requiring precise radii on the punch and die shoulders to prevent tearing or wrinkling. This specific manufacturing method governs the production of battery cans and prismatic cell housings where structural integrity and hermetic sealing protect internal electrochemistry. Operations stop applying when depth equals or exceeds the blank diameter, a threshold that demands redrawing stages or alternative fabrication routes to avoid catastrophic material failure.
Blank Hold
Radial restraining pressure applied to the flange prevents wrinkling while the punch advances the material into the die opening. Excessive holder force restricts material flow and causes bottom fracture during the stroke, whereas insufficient pressure permits buckling along the wall profile. Operators calculate optimal tonnage requirements using blank thickness, material tensile strength, and projected surface area to set hydraulic cushions accurately.
Adjusting this clamping force throughout the cycle controls friction and accommodates work hardening as the alloy flows inward.
Draw Ratio
Principal geometric evaluation compares the initial blank diameter against the punch diameter to predict formability limits for a given alloy grade. Primary reductions typically allow a diameter decrease between fifty and sixty percent in the initial forming step without intermediate annealing. Subsequent redraw operations achieve smaller diameter reductions incrementally because cold work exhausts ductility and raises yield strength.
Higher ratios demand superior lubricant performance to manage extreme interface pressures between the sheet metal and the tool faces.
Wall Thinning
Localized stretching occurs near the punch radius where tensile stresses peak during bottom corners formation. Tooling designers specify clearance values slightly exceeding the sheet thickness to compensate for springback and metal thickening at the flange periphery. Uncontrolled thinning compromises structural safety margins in high-pressure lithium-ion cell cases by creating weak spots vulnerable to internal pressure swelling.
Alloy composition dictates the allowable elongation limit before microvoids coalesce into visible splits under tensile loads.
