How to Prevent Wrinkling in Deep Drawing

Direct answer: Wrinkling in deep drawing is a buckling failure of the sheet. The flange of the blank is pushed inward by the punch, and because the circumference of the blank is larger than the circumference of the drawn cup, the flange material is compressed tangentially. When that compressive stress exceeds the sheet’s resistance to buckling, waves form at the rim (flange wrinkling) or propagate into the wall (wall wrinkling). You prevent it by controlling the eight variables below — above all blank holder force, draw ratio, tool radii and material anisotropy — and you cure it by diagnosing which variable is out of range before touching the tool.

What Causes Wrinkling in Deep Drawing?

During the draw, the flange experiences a radial tensile stress (pulling material toward the die cavity) combined with a tangential compressive stress (the circumference is shrinking). Thin material under tangential compression behaves like a column under compression: below a critical stress it is stable, above it, it buckles into waves. The metal does not disappear — it folds. Whether the fold stays in the flange or gets pulled into the wall depends on where and when the restraint is lost. Eight process and tooling variables set that critical stress:

1. Blank Holder Force

The blank holder (pressure pad) presses the flange against the die face, generating the friction that resists tangential buckling. Too little force and the flange lifts and waves; too much and the material cannot flow inward, the wall thins and tears at the punch radius. For a new draw die, start around 20–30% of the calculated drawing force for mild steel and tune during tryout. Use nitrogen, hydraulic or servo cushions where you need a repeatable, adjustable pressure profile; a constant-force holder tuned for one stroke depth will not control a part with a varying flange area.

2. Draw Ratio

The drawing ratio m = d/D (product diameter over blank diameter) measures how much the blank must shrink. The smaller m is, the higher the tangential compression on the flange and the harder it is to stop wrinkling without tearing. Every material has a practical limiting drawing ratio for a single operation — for low-carbon steel, roughly m ≈ 0.50–0.55 (a depth-to-diameter ratio around 0.9–1.0 for a plain cup). If your part needs a deeper single draw than that, add a redraw operation instead of fighting the material.

3. Die and Punch Radius

The die entry radius controls how the flange bends into the cavity and how long the blank holder keeps control of the material. A radius that is too small raises bending stress and can split the wall; one that is too large lets the flange escape the blank holder early, and the unsupported material wrinkles into the wall. Start from roughly 6–10 × sheet thickness for the die radius on steel cups and 4–8 × thickness for the punch radius, then verify by tryout. Punch and die must also be polished in the drawing direction to avoid pickup that disturbs material flow.

4. Material Anisotropy

Sheet metal is not uniform: rolling creates directionality. The normal anisotropy ratio r (Lankford coefficient) describes the sheet’s resistance to thinning versus in-plane contraction — higher r means better wrinkle resistance because the material prefers to thicken rather than buckle. Deep-drawing grades are selected for formability and consistent r values: DC04/DC06 or SPCE for steel, 5052-O for aluminium, and deep-drawing-quality 304 for stainless. If a marginal grade wrinkles on every hit, a better grade usually solves it at lower cost than reworking the tool.

5. Lubrication

Lubrication has two opposing jobs. On the die radius and punch, low friction lets the wall slide and reduces tearing risk. On the flange side, some friction is desirable: it is what lets the blank holder restrain the material. Uneven or excessive flange lubrication therefore promotes wrinkling, while too little lubrication promotes tearing. Use a controlled, uniform film of the correct drawing lubricant for the material (drawing oil, dry-film or polymer coating), and keep the application consistent from part to part.

6. Sheet Thickness

Wrinkle resistance scales strongly with thickness: a thicker sheet has a much higher buckling stress in the flange, which is why thin parts wrinkle long before thick ones under the same holder force. Thickness tolerances matter — a coil at the low end of its tolerance band behaves like a different material. If thin-gauge parts wrinkle intermittently, check the incoming thickness and consider specifying a tighter tolerance or a higher-strength grade that allows the same part at the same gauge.

7. Blank Geometry

The shape and size of the blank decide how evenly the flange is loaded. A perfectly round blank for a cylindrical cup loads symmetrically; an asymmetrical or oversized blank loads the holder unevenly, and the lightly loaded zone wrinkles first. Trim the blank to the smallest workable outline, balance the material flow, and for irregular parts use a developed blank shape rather than a rectangle or circle of convenience.

8. Drawing Speed

Speed changes the strain rate and, through friction work, the temperature at the die radius. On most steels the effect is modest; on aluminium, austenitic stainless and coated sheets it can shift the process into tearing or wrinkling. Keep the press speed and cushion timing constant during tryout so that only one variable changes at a time, and record the production speed in the process sheet — a tool validated at 10 strokes per minute may behave differently at 25.

How to Diagnose Wrinkling

Look at where the wave is, not just that it exists:

• Uniform waves at the outer rim of the flange — the blank holder is not clamping hard enough (force too low, cushion pressure lost, or holder not touching early enough).
• Wrinkles pulled into the wall — restraint is lost before the end of the stroke: draw ratio too aggressive, die radius too large, or draw beads missing/too shallow.
• Wrinkling on one side of the part only — the tool is not parallel (holder or die face out of level), the blank is off-centre, or the cushion is uneven. Check with pressure-sensitive film before changing forces.
• Fine wrinkles around a small corner radius or feature — local material surplus: the surrounding geometry is feeding more material into the feature than it can absorb; add a local bead or change the blank outline.

Teardown inspection helps: stop the press at the bottom of the stroke and check where the flange first lifts from the holder. That point is where the wrinkle starts.

How to Correct the Tooling

Work in this order so you change one variable at a time:

1. Verify the press and cushion are delivering the nominal force. A dying nitrogen cushion or a leaking hydraulic circuit reproduces wrinkling overnight on a tool that was fine the day before.
2. Increase blank holder force in small steps (5–10%) until the rim wave disappears or the wall starts thinning — whichever comes first.
3. Add or deepen draw beads when force alone tears the part before it stops wrinkling. Start shallow; a bead that is too deep turns a wrinkle problem into a split problem.
4. Re-check the die entry radius and gap. Blend the radius larger only if the wall shows burnish or tearing; reduce it (or add a small step/bead at the entry) if the flange escapes early.
5. Fix parallelism and alignment — re-grind and re-fit the holder if pressure film shows one side carrying the load.
6. Change the process inputs last: lubrication type and quantity, blank outline, material grade or thickness, then draw speed.
7. If the draw ratio is beyond the material’s LDR, stop tuning and add a redraw operation. No amount of holder force makes a physically impossible single draw stable.

Case Example

A cylindrical motor housing drawn from 1.2 mm DC04 showed rim wrinkling on the first 40 parts of a tryout. The draw ratio was acceptable (m ≈ 0.58), and the die entry radius was generous (≈ 8 × t). Pressure-sensitive film showed the cushion carrying only 60% of the nominal force on one quadrant because a nitrogen cushion had lost charge. After recharging and equalising the cushion, the rim wave disappeared at the same force setting. The follow-up improvement was a shallow draw bead, added to widen the process window before production release. The lesson: measure the machine before modifying the tool.

Engineering Checklist

• Draw ratio m = d/D above the material’s single-operation limit? If not, plan a redraw.
• Blank holder force set from the flange area and material, with a repeatable cushion?
• Die entry radius in the 6–10 × t starting range; punch radius 4–8 × t?
• Tool faces parallel; cushion force verified with pressure film at tryout?
• Draw beads sized to restrain flow without over-stretching?
• Material grade with adequate r value and consistent thickness tolerance?
• Uniform, correct lubricant application — not over-lubricated on the flange?
• Blank outline trimmed to balance material flow?
• Press speed and cushion timing recorded as process parameters?
• First articles and the process sheet reviewed together before production release?

Deep Drawing Service at Balford

Balford designs and builds deep drawing tooling in-house and runs presses from 25 t to 350 t, with progressive-die capability for high volumes and single-hit tooling for prototypes and medium runs. Our engineers apply the same diagnosis sequence above during DFM and tool tryout — see our deep drawing metal stamping capability for press range and part-size limits. Related engineering guides: deep drawn vs progressive die stamping, deep drawing aluminium parts, and deep drawn solenoid valve housings.

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