A draw bead is a raised rib formed into the binder (blank-holder) surface of a draw die, with a matching groove in the opposing surface, that the sheet must bend over and back as it is pulled into the die cavity. Each time the blank passes through the bead it is bent, straightened, re-bent, and re-straightened, and that repeated plastic bending consumes force. The result is a controlled restraining force that holds the sheet back locally, on top of the broad clamping force supplied by the blank holder.
Draw beads exist because flat blank-holder pressure alone is a blunt tool. Hold-down force acts uniformly, but real parts — especially irregular automotive panels — need more restraint in some areas and less in others to flow metal evenly into the cavity. By placing beads only where extra restraint is needed, and sizing them for the right amount, the die designer steers metal flow region by region: more restraint where the wall would otherwise wrinkle from too much loose material, less restraint where the metal must feed freely to avoid splitting.
The restraining force a bead adds depends on its geometry — bead height (depth of engagement), bead radius, and the radii of the entry and exit shoulders — together with material thickness, strength, and lubrication. A taller, sharper bead bends the sheet more severely and restrains harder; a shallow, generous bead restrains gently. Beads can be continuous around a perimeter or segmented, and "lock beads" with deep engagement are used where the metal must be held almost completely.
Practically, draw beads are tuned right alongside blank-holder force and lubrication when balancing a difficult draw. The diagnostic logic is the same as for hold-down: wrinkles in a region call for more local restraint, so a bead is added or made more aggressive there; splits call for less restraint, so a bead is softened or removed. Because beads are machined into the tool, they are usually set during die tryout, where they are progressively reshaped until the part draws in cleanly without wrinkles or tears across its whole shape.
Draw beads do more than simply restrain — they also change the strain the metal sees on its way into the die. Bending and unbending over the bead work-hardens the material and induces some stretch before it ever reaches the part, which can be used deliberately to firm up an otherwise floppy panel and improve its dent resistance and shape control. The cost is that this strain is permanent and the metal that passed through the bead is consumed in the addendum and trimmed off as offal, so beads affect blank size and material utilization, not just flow. Designers therefore weigh bead severity against scrap: a bead aggressive enough to kill wrinkles may force a larger blank. For a typical deep automotive panel, the binder may carry several differently sized beads around its perimeter, lighter where metal must feed and heavier across corners and straight runs where wrinkling would otherwise dominate, all balanced together so the whole panel forms in a single, clean draw.