Aluminium stamping: formability and tooling considerations

Most aluminium stamping failures happen in two predictable places, and neither of them is the press. At the sheared edge, where a burr and a work-hardened band give a crack somewhere to start. And at the bend, where aluminium gives back about two and a half times the elastic strain of steel, so a 90° punch angle produces an 87° part that the inspector finds three operations later.

The alloy and temper decide more of the outcome than the press does. 5052-H32 and 3003-H14 cover most brackets, covers and panels; 1100 and 3003 in the annealed temper carry the deeper draws; 6061-T6 belongs on flat parts with holes and a few shallow forms. What follows is the alloy table, the clearance and tonnage arithmetic, the four failures that are specific to aluminium, and the notes that keep a tool from being cut twice.

Which aluminium alloy should a stamped part use?

For a bracket, cover or panel up to about 3 mm, specify 5052-H32 or 3003-H14 and expect to deal with springback rather than with splitting. For a part that has to draw deeper than half its diameter, drop to 3003-O or 1100-O and add stiffness with ribs or a flange, because the strength that makes 5052 useful is the strength that limits its draw.

The strain-hardening exponent n and the plastic strain ratio r explain the table. The exponent n, measured to ASTM E646, tells you how far strain spreads before it localises into a neck: 5052-O runs near 0.27 and 5052-H32 near 0.13, because the H32 temper has already spent part of the hardening capacity at the mill. A part designed on the O-temper value will split in H32 at the same depth.

The plastic strain ratio r is the second. Drawing-quality steel sits at 1.6–2.0, which means the sheet resists thinning and feeds material in from the flange. Aluminium sits near 0.6–0.8, so the flange holds back and the wall thins. On a 3003 cup of 100 mm diameter in 1.5 mm sheet, expect 10–15% wall thinning at the punch nose against roughly 5% on a DC04 cup of the same geometry. That is a design input, not a defect: if the wall cannot lose 15%, the part needs a different alloy or a thicker start gauge.

What die clearance and die surface does aluminium need?

Cut aluminium at 3–6% of thickness per side, with 5% as the working nominal. At 2.0 mm that is 0.06–0.12 mm per side, or 0.12–0.24 mm total. A pierced hole in mild steel runs 3–5% per side and a blanked edge 5–8%, so a tool built for CRCA blanking usually has too much clearance for aluminium and returns a rolled edge, a tall burr and a poor cut face.

The failure from too little clearance is different and more expensive. The punch shears, then drags, then tears; punch load climbs by 20–30%, the punch edge rounds over, and the burnished band on the part grows until the cut face will not take a powder coat without showing the step. On a progressive tool running 5052, punch wear at the corners is the first thing to appear in the maintenance record.

Surface preparation matters more than die steel grade. Aluminium transfers to bare tool steel under pressure, and the transferred layer work-hardens and scratches the next part. Polish draw radii and die entries to a mirror finish, then coat with hard chrome at 5–10 µm, TiN or AlCrN. Keep one set of abrasives and one set of gloves for aluminium; a carbon steel brush that has touched CRCA leaves free iron that shows up as rust spots under the powder coat.

Lubrication closes the gap. Use a mineral or water-based drawing lubricant with anti-galling additives, and keep chlorinated extreme-pressure additives out of the process: they can leave chloride residue in a lap or a hem, and on aluminium that residue promotes pitting under a coating. Apply the lubricant to the die as well as the blank on a deep draw, and clean it off before any pretreatment stage.

How much press force does an aluminium blank need?

Force is perimeter times thickness times shear strength. Aluminium shear strength sits near 0.6 of tensile, so 5052-H32 at 228 MPa tensile shears at about 137 MPa. A blank with a 1,200 mm perimeter in 1.5 mm sheet needs 1,200 × 1.5 × 137 = 246,600 N, or 247 kN, before stripping allowance.

Add 20–30% for stripping and press losses and the job wants about 31 tonne-force, which a 40 T press covers comfortably. The same blank in 1.5 mm CRCA, at a shear strength near 245 MPa, needs 441 kN, or 45 tonne-force. Aluminium needs 56% of the press capacity for the same outline, which is why an aluminium part can often run in a press that is already busy.

Drawing is a separate calculation and it is smaller than most people expect. A 120 mm diameter cup in 1.5 mm 5052-H32 needs π × 120 × 1.5 × 228 = 129 kN of punch force, reduced by a 0.65–0.8 efficiency factor to about 90 kN. The blank holder adds more than the punch on thin aluminium: a 230 mm blank at 1.2 MPa blank-holder pressure carries 50 kN, so the total is around 140 kN, or 14 tonne-force. The press tonnage calculator runs both checks against your own perimeter and blank area.

Blank-holder pressure for aluminium runs 0.7–1.5 MPa, against 1.5–2.5 MPa for steel. Too much pressure thins the flange and starts a split at the die entry; too little lets the flange wrinkle and the wrinkle is pressed into the wall on the next stroke. Set it on the first article and record the value on the tool card.

Where does aluminium stamping fail?

Pickup on the draw wall, tearing at the punch nose, earing and springback account for most aluminium rejects, and each has a physical cause that can be measured.

Pickup and scoring on the draw wall

Aluminium oxide is harder than the die steel it runs against, so the oxide film abrades the die while the metal underneath cold-welds to it. The symptom is a scored wall with a matt, torn appearance and a build-up on the die radius. The fix is a polished, coated die surface plus a lubricant film that survives the contact pressure, not a harder punch.

Tearing at the punch nose

Aluminium tears where the strain path is steepest, which is the punch nose on the first draw. Keep the punch nose radius at 4t or more for 5052 and 6t for a harder temper, keep the first-draw ratio at or below 1.8 for 5052-H32 and 1.9 for 3003-O, and check wall thickness on the first article rather than the last. A wall that has thinned from 1.5 mm to 1.25 mm is a crack that has not opened yet.

Earing and the trim allowance

Rolled aluminium has a crystallographic texture, so a drawn cup is not level. Height varies around the circumference by 2–3% of cup height on 3003 and 5052, with the high points at 0° and 90° to the rolling direction. Two controls: state the rolling direction on the drawing so the tool can be built to it, and put a trim in the sequence. Without a trim, the ear becomes a flange that will not sit flat in the next assembly.

Springback in every formed flange

Covered in the next section, because it is the failure that survives the press and appears at the customer.

How much springback does aluminium carry?

Elastic recovery scales with yield strength divided by elastic modulus. Aluminium at 70 GPa against steel at 210 GPa means an aluminium part recovers three times as much per unit of yield stress, and 5052-H32 carries a yield close to CRCA, so the practical figure is 2.5–3 times the steel springback at the same radius and thickness.

Take a 90° bend at a 4 mm inner radius in 2 mm 5052-H32. The elastic recovery of the bend arc is roughly 3σy R / (E t) = 3 × 193 × 4 / (70,000 × 2) = 0.0165, or 1.5% of the bend angle, about 1.3°. Shop measurement on an air bend runs 1.5–2 times that, because the neutral axis shifts and friction in the die resists the last few degrees. Plan 2–3° of overbend in the tool and confirm on the first article.

Soft tempers behave differently. 1100-H14 at 105 MPa yield recovers at close to the CRCA rate, so a tool built for 1100 will overbend a 5052 part and underbend a 6061-T6 part. That is why the alloy and temper belong on the drawing and on the tool card, not only on the purchase order.

The angle error does not stay at the bend. A hole 40 mm along a flange moves by 40 × tan(2°) = 1.40 mm for every 2° of angular error. If that hole carries a bolt through a clearance hole in a mating part, the assembly either fights or the hole is opened up on site. The springback guide sets out the compensation options, from die angle correction to a restrike station.

What tool features keep an aluminium part in tolerance?

• Corner radii on the blank of at least 0.5t. A sharp corner concentrates shear and starts a corner crack on the first form.
• Die entry radius of 6–10t on a draw, against 4–6t for steel, because aluminium cannot stretch around a tight entry.
• A guided stripper that holds the blank flat through the stroke; aluminium is light enough that a stripping spring will throw the part if it is unbalanced.
• A bottoming pad or restrike station where the bend angle is functional, not cosmetic.
• Hardened, coated draw inserts in a replaceable holder, so pickup can be polished out without rebuilding the die.
• A trim station after the draw for any part that will show a flange edge.

Tooling is quoted separately from the piece price at Ganesh, which keeps the die cost and the conversion cost visible when the volume is still being argued about.

How Ganesh Multitech builds and runs aluminium press tools

The tool room builds 5052-H32 and 3003-H14 draw tools with polished, hard-chrome or AlCrN-coated draw inserts held in replaceable holders, so a pickup mark is polished out on the bench instead of the die block coming off the press. Die entry radii are set at 6–10t on those tools rather than the 4–6t used on steel, and the same shop runs 250 T punching for the heavier 3–4 mm aluminium blank and pierce work, where a 40 T press would be at its limit.

Where the volume does not justify a die, the same alloy is cut on the 12 kW fibre laser with a 40 ft × 16 ft bed and formed on the 200 T 5-axis brake with a 4,450 mm bed to 10 mm. Coated aluminium parts go through seven-tank pretreatment and an 18 ft × 14 ft powder booth, with dry film thickness and cross-hatch adhesion recorded. Formed tolerance is ±0.5 mm typical with tighter features by agreement, and first article inspection and PPAP documentation are available.

Presses run from 20 T to 300 T, custom parts from 0.8 mm to 40 mm, and the plants hold ISO 9001:2015 and ISO 14001:2015 across five units in Mumbai (Vasai) and Nagpur. The customer list includes Mahindra, Mahindra Powerol, Godrej & Boyce, TKE, Eros Elevators, Minda, Gunnebo and Indian Railways.

When an aluminium part should not be stamped

A tool earns its cost when the annual quantity, multiplied by the piece-price saving it creates, exceeds the tool cost plus maintenance. For a few hundred pieces a year the arithmetic rarely closes, and the part should be laser cut and press-braked instead: no die, no tryout, and a design that can still change. The laser cutting aluminium guide covers the edge quality and gas choice for that route.

Stamping is also the wrong route above about 4–5 mm in aluminium. Shear force climbs with thickness and the burr on a thick aluminium edge is difficult to remove without marking the face. Thick aluminium plate is better cut and machined.

We do not solution-treat or age-hardening aluminium, so a 6061 part that needs T6 after forming is not a route we quote; the temper has to come from the mill. We do not run presses above 300 T, and a draw that needs more than that is a different conversation with a different supplier.

What the drawing has to state

• Alloy and temper with the standard reference, for example 5052-H32 to ASTM B209.
• Rolling direction relative to the bend line and to the draw axis.
• The surfaces that stay visible, and the ones the tool is allowed to mark.
• Sheared edge condition: burr side, burr height limit, and whether deburring is in scope.
• Critical dimensions with the tolerance class from ISO 2768-1, plus any tighter callout on hole position and bend angle.
• Blank-holder and lubrication notes if the part is a draw, or a note that the supplier sets them.
• Annual volume and release pattern, so the tool decision can be priced against the piece price.
• Whether the part is welded or riveted after forming, because that changes the flat pattern and the deep drawing rules that apply.

Send the revision, the alloy, the volume and the cosmetic faces through request a quote. The stamping and press tools hub holds the rest of the design guidance for pressed parts.