Deep Drawing Defects: Wrinkling, Cracking & Earing

Deep drawing defects are the forming failures — wrinkling, cracking and earing — that appear when material flow, tool geometry or press settings fall out of balance. They show up most on parts with wall thicknesses from 0.15 to 3.0 mm, where the gap between a clean draw and a reject can be a fraction of a millimetre. A deep drawn part that leaves the press with a wrinkle, a crack, or a wavy top edge is more than a scrap part. It is a signal about the process. Most rejects in production trace back to three failure modes: the sheet buckles under compression (wrinkling), it tears under tension (cracking), or it deforms unevenly because the metal is not the same in every direction (earing). Knowing which mode you are looking at changes the fix completely. A single cracked batch can mean a scrapped tool run, a slipped launch date, and a line stopped waiting on replacements; catching the cause early is almost always cheaper than sorting parts after the fact. This guide walks through each defect, why it appears, and the adjustments that stop it — so you can specify and source parts that hold up on the first run.

Wrinkling — compression that went too far

Wrinkling shows up as folds or ripples, most often in the flat flange being drawn inward and sometimes low on the cup wall near the die radius. Wall wrinkling lower down the form usually points the other way — too little hold-down or a ram moving faster than the material can feed — so the same visible symptom can mean opposite problems depending on where it sits. The cause is compressive hoop stress. As the blank is pulled into the die, the outer material is squeezed inward; if nothing holds it flat, it buckles the way a squeezed sheet of paper buckles.

The usual triggers:

• Blank holder force too low. The holder keeps the flange flat. Too little pressure and the flange wrinkles before it can be drawn in.
• Too much unconstrained flange. A large flat blank with a small punch leaves a wide flange that must be controlled over a long travel.
• Thin stock relative to diameter. Thin sheet buckles more easily than thick sheet at the same force.
• Draw ratio pushed past what one stage can hold.
• A lubrication pattern that lets the flange slide instead of being restrained.

What to change first: raise the blank holder force until the flange stays flat, then back off just enough to let the material feed. Add draw beads to the blank holder — they add local restraining force without cranking pressure across the whole flange. If the part still wrinkles, the draw ratio is likely too high for one stroke; split the form into two draws, or start from a smaller blank. Profile rings and a correctly sized die radius also help the material fold in smoothly instead of buckling. Our deep drawing process guide covers how holder force and draw ratio interact on a real press.

Cracking — tension the material could not take

Cracks appear where the metal is stretched hardest: at the punch radius, in the cup wall just above it, and at any redraw transition. The failure is tensile — local stress passed the material’s strength, or the metal ran out of ductility before the form finished. A crack at the punch radius is the classic signature of a corner too sharp for the wall thickness; a crack higher in the wall, or at a redraw shoulder, usually means the reduction per stage was simply too large. Telling the two apart from the fracture location saves a lot of wrong adjustments.

Common causes:

• Punch radius too tight. A sharp corner concentrates stress on a thin band of wall and pulls it into a neck, then a tear.
• Draw ratio too high for the stage. Same root as wrinkling, opposite failure: too much reduction in one step stretches the wall past its limit.
• Insufficient annealing between redraws. Cold work hardens the part; a deep or multi-stage part that is not softened between stages cracks on the next draw.
• Material with low ductility for the job, or inclusions and bad grain that start a tear.
• Poor lubrication at the punch radius, where sliding friction adds to already high tensile load.

First moves: open the punch radius. As a rule the punch corner should be generous relative to wall thickness; a part that cracks at the radius almost always benefits from a larger radius before any other change. Lower the per-stage draw ratio and add a redraw. Schedule an anneal between stages on deep parts. Pick the grade by ductility and drawability, not only by cost — and confirm the mill certificate, because two coils of the same grade can draw differently. Keep the punch radius well lubricated. Material choice is decisive here; our material selection guide lays out how stainless steel, aluminum, brass and copper behave under draw.

Earing — the sheet is not the same in every direction

Earing is the set of lobes or waves around the top edge of a drawn cup. It is not a buckle and not a tear; it is a planned-in defect caused by planar anisotropy. Rolled sheet has a grain direction. Its r-value — how much it thins versus how much it widens under tension — is higher along some directions than others. During drawing the cup grows taller where r is high and stays shorter where r is low, so the rim comes out wavy.

Why it matters beyond looks: those ears have to be trimmed off, which wastes material and adds a trim operation; severe ears can also push the blank off-center in the tool and break dimensional control. Because ears are predictable from the material’s texture, they are also the cheapest defect to design around — a small change to blank shape or grade selection removes them before production starts.

How to keep it down: specify a low planar-anisotropy grade (low Δr). Material supplied with controlled or cross-rolling texture ears far less than single-direction-rolled stock. Pre-notch the blank to a shape that counteracts the ear pattern the grade is known to produce. Always allow trim stock in the blank layout so ears do not become a rejecting condition. If the ears are consistently four-lobed or six-lobed, that pattern tells you exactly which direction the grain is running and lets you rotate or notch the blank accordingly.

At a glance

Defect	Where you see it	Primary cause	First fix
Wrinkling	Flange, lower wall	Compressive buckling, low hold-down	Raise blank holder force, add draw beads
Cracking	Punch radius, upper wall	Tensile overload, tight corner, no anneal	Open punch radius, anneal, lower draw ratio
Earing	Top rim	Planar anisotropy of sheet	Low-Δr grade, blank notch, trim allowance

Stop defects before the tool is cut

Most of these problems are decided at the drawing board, not on the press. Getting these right is what separates a part that draws cleanly from one that needs constant babysitting on the floor:

1. Keep punch and die radii generous relative to wall thickness; tight corners are the single most common crack source.
2. Limit the draw ratio per stage to the material’s limiting draw ratio with margin — our LDR reference lists stainless steel, aluminum and steel values.
3. Call out intermediate annealing on any part that needs two or more redraws.
4. Choose the grade by ductility and drawability, and require a mill certificate.
5. Hold blank thickness tolerance tight; variation shows up as uneven draws.
6. Budget trim allowance for earing on high-anisotropy stock.
7. Write the lubrication specification into the print, not just the shop instructions.
8. Prototype on the actual production material, not a stand-in.
9. For hard or deep geometries, run a trial draw or FEA before committing tool steel — the geometry difficulty guide helps set expectations.
10. Respect the practical floor: our route holds wall thickness from 0.15 mm up, and pushing thinner invites the defects above. The small-part design checklist goes deeper on radii and tolerances.

Frequently Asked Questions

What force makes the flange wrinkle during a deep draw?

Wrinkling is compressive buckling of the sheet, usually in the flange or lower wall.

Direct answer: Raise the blank-holder force so the flange stays flat; that stops the buckling. When the blank holder force is too low, the draw ratio is too high for one stage, or the stock is thin relative to diameter, the inward-squeezed material has nothing to keep it flat and it folds. Raising hold-down pressure, adding draw beads, or splitting the form into two draws usually removes it.

Why do tight punch corners split a drawn cup?

Cracks are tensile failures at the punch radius or in the wall above it.

Direct answer: Open the punch radius and keep the wall-thickness ratio in range so stress does not concentrate. A punch corner that is too sharp for the wall thickness concentrates stress on a thin band and pulls it into a neck, then a tear. Opening the punch radius, annealing between redraws, lowering the per-stage reduction, and keeping the radius well lubricated are the fastest fixes.

Why do drawn cups come out with a wavy top edge, and how is it fixed?

That wavy edge is earing, caused by planar anisotropy — the sheet draws more in some grain directions than others.

Direct answer: That wavy edge is earing from planar anisotropy; control it with low-delta-r sheet and proper blank orientation, then trim. It is controlled by specifying a low-Δr grade, using cross-rolled or balanced material, pre-notching the blank to counter the ear pattern, and allowing trim stock so ears are planned for rather than rejected.

How can deep drawing defects be reduced during part design?

Most defects are set at the design stage.

Direct answer: Keep punch and die radii generous, cap each draw ratio below the material LDR with margin, and specify the right grade. Keep punch and die radii generous, limit each stage’s draw ratio to the material’s LDR with margin, specify intermediate annealing for multi-redraw parts, choose the grade by ductility, hold blank thickness tolerance, and budget trim allowance for earing. Prototyping on the real material and a trial draw before tooling catch most issues early. Our cost guide shows why catching these early also protects unit price.