Deep drawing turns a flat blank into a hollow cup by pulling it through a die with a punch. Whether a given cup can be drawn in one hit, or needs several, is a planning question you answer before any die is built. The two levers are how much you reduce the diameter per stage and how you control material flow.
The plan answers four things: the blank size, how many draw stages, the punch and die radii at each stage, and the blank-holder strategy that keeps the flange from wrinkling without tearing the wall.
For a simple cylindrical cup, the blank diameter is found by equating the surface area of the flat blank to the surface area of the finished cup (the deep-draw process is essentially constant in thickness for first-order planning). For a plain cup of diameter d and height h, a common estimate is blank diameter ≈ √(d² + 4·d·h), adjusted for the corner radius on taller or sharper-cornered cups.
Add trim allowance because the rim of a drawn cup is rarely uniform — earing and draw-in leave a wavy edge that gets trimmed to the lowest valley. The Blank Development tool helps develop blank sizes, and Sheet Weight converts the blank into material per part for costing.
The draw reduction ratio compares the blank diameter to the cup diameter; the percent reduction is how much the diameter shrinks in a stage. Every material has a limiting draw ratio (LDR) — the most it can be reduced in a single draw before the wall tears. Exceed it and you split parts no matter how perfect the setup.
First draws are typically the most aggressive the material allows; each subsequent redraw must be gentler because the metal has already work-hardened. The Draw Reduction tool computes the ratio and percent reduction for each stage so you can check them against material limits.
When the total reduction from blank to final cup exceeds what one stage can do, split it into a first draw plus one or more redraws. Plan a decreasing reduction per stage and consider an annealing step between draws if the material work-hardens enough to lose ductility.
Ironing is a separate operation that thins and smooths the wall by squeezing it through a clearance smaller than the stock thickness — used to control wall thickness and height. Distinguish it from drawing: drawing reduces diameter, ironing reduces wall thickness.
Punch and die radii that are too small concentrate stress and tear the wall; too large and the flange wrinkles for lack of support. Plan generous-but-controlled radii, then refine. Lubrication on the flange and die reduces the friction the wall has to overcome and is the cheapest, most reversible lever you have.
Blank-holder force and draw beads govern how freely the flange feeds in. Too little restraint wrinkles; too much tears. Plan to start moderate and tune — the Draw Troubleshooter walks the wrinkle-versus-tear decision once the die is running.
Develop the blank size with trim allowance; compute the total reduction and compare to the material’s single-stage limit; stage into draw and redraws if needed with decreasing reduction; set radii and a starting blank-holder strategy; and add ironing only if wall thickness or height demands it. Treat the formulas here as standard planning estimates — confirm material-specific limits and final geometry through tryout.
draw_reduction calculator · draw_troubleshooter calculator · blank_development calculator · sheet_weight calculator