Bending Aluminum Sheet

Aluminum alloys for brake forming

5052-H32: The most common brake-formed aluminum. Excellent formability, good corrosion resistance, moderate strength (31 ksi yield). Standard for enclosures, brackets, HVAC components, marine panels, and any application where the part will be bent, welded, and possibly anodized. Bends to 1t radius (inside radius = material thickness) without cracking in most orientations. This is the default — if the drawing says "aluminum" without specifying a grade, most shops assume 5052-H32.

6061-T6: Higher strength (40 ksi yield) but less formable than 5052. Cracks at tight bend radii, especially across the grain. Minimum bend radius: 2t for material under 0.125", 2.5–3t for thicker stock. Common for structural brackets, equipment frames, and components that need strength after forming. If the part needs tight bends AND 6061 strength, specify 6061-T4 (solution treated, not aged) — it bends like 5052 and can be aged to T6 after forming.

3003-H14: The easiest aluminum to bend. Softer than 5052 (21 ksi yield), bends to 0.5t radius without cracking. Used for ductwork, light-duty enclosures, trim, and decorative panels where strength isn't critical. Welds and anodizes well.

5083-H116: Marine-grade aluminum. Higher strength than 5052 (33 ksi yield) with excellent saltwater corrosion resistance. Bends similarly to 5052 — 1t radius minimum. Used for boat hulls, marine hardware, and military vehicle armor.

2024-T3: Aerospace aluminum. Very difficult to brake form — cracks easily at any bend radius tighter than 3–4t. If you must bend 2024, do it in the -O (annealed) condition and heat treat after forming. Most aerospace 2024 parts are machined, not formed.

Minimum bend radius

The minimum inside bend radius before cracking depends on alloy, temper, thickness, and grain direction:

3003-H14: 0t (can fold flat) in material under 0.060". 0.5t for 0.060–0.125". 1t for thicker.

5052-H32: 1t for material up to 0.125". 1.5t for 0.125–0.250". 2t for 0.250"+.

6061-T6: 2t for material up to 0.090". 2.5t for 0.090–0.125". 3t for 0.125–0.250". Higher for thicker material.

6061-T4: 1t for material up to 0.125". 1.5t for thicker.

These are "with the grain" radii — bending parallel to the rolling direction. Bending across the grain allows 15–25% tighter radii. When possible, orient bends across the grain on the flat pattern. If the part has bends in both directions, use the tighter requirement for the with-grain bends.

Grain direction on sheet: The rolling direction runs along the length of the sheet as delivered from the mill. It's often not marked — ask the supplier, or look for the long dimension of the sheet (typically the rolling direction). On critical parts, specify "grain direction parallel to [dimension]" on the drawing.

Springback

Aluminum springs back more than mild steel after bending. The amount depends on alloy, temper, thickness, bend radius, and die opening:

5052-H32: 2–4° springback on a 90° bend in standard die openings. Higher springback at tighter radii and in thicker material.

6061-T6: 4–8° springback. This is significant — an uncorrected 90° bend in 6061-T6 comes out at 82–86°. The CNC controller compensates, but the operator needs to verify with a protractor on the first piece.

3003-H14: 1–3° springback. The softest common alloy, easiest to hit angle.

CNC press brakes with angle sensing (Amada HG series, TRUMPF TruBend, Bystronic Xpert) measure springback in real time and correct automatically. On older machines without angle sensing, the operator overbends by the springback amount — program a 92° bend to achieve 90° on 5052-H32, for example.

Coining to reduce springback: Bottom bending (coining) applies enough tonnage to plastically deform the material through the full bend zone, reducing springback to near zero. This requires 3–5x more tonnage than air bending and dedicated die angles. Use coining only when angular tolerance demands it (±0.25° or tighter) or when production volume justifies the tooling investment.

Tonnage

Tonnage formula: T = (575 × t² × L × S) / W

Where: T = tonnage, t = material thickness (inches), L = bend length (feet), S = tensile strength (tons/in²), W = die opening (inches).

Quick references for air bending a 10' length in a die opening of 8× material thickness:

3003-H14 (22 ksi tensile): 0.060" = 3 tons. 0.090" = 7 tons. 0.125" = 14 tons. 0.250" = 55 tons.

5052-H32 (33 ksi tensile): 0.060" = 5 tons. 0.090" = 10 tons. 0.125" = 20 tons. 0.250" = 80 tons.

6061-T6 (45 ksi tensile): 0.060" = 7 tons. 0.090" = 14 tons. 0.125" = 28 tons. 0.250" = 110 tons.

Aluminum requires roughly 60% of the tonnage needed for mild steel at the same thickness and length. A shop with a 150-ton brake can handle most aluminum work up to 0.250" × 10'. For 0.375" or thicker aluminum, 250+ ton machines are required.

Common problems

Cracking at bends: Almost always caused by bending with the grain in a hard temper at a radius tighter than the minimum. Solution: orient bends across the grain, use a softer temper (T4 instead of T6), or increase the bend radius. If the part is already laser-cut and can't be re-oriented, anneal the bend zone locally with a heat gun (350–400°F for 30 minutes on 6061) before bending.

Galling and die marks: Aluminum is soft and leaves marks easily. Use urethane die inserts or apply a protective film (PE tape) to the sheet before bending. Chrome-plated tooling reduces galling. For visible/anodized surfaces, this is critical — die marks show through anodize.

Inconsistent springback: Lot-to-lot variation in aluminum mechanical properties causes springback variation. Two sheets of "5052-H32" from different mills can have 25–35 ksi yield strength variation. CNC angle sensing handles this automatically. On manual or non-sensing machines, verify the first piece in every new lot.

Oil-canning on large flat panels: Laser-cut aluminum panels with large flat areas between bends can oil-can (flex and pop). Mitigation: add stiffening ribs, beads, or embosses to the flat areas. Even a shallow 0.020" bead across a flat panel dramatically increases stiffness.

Cost

Aluminum brake forming is fast and cheap. A simple 90° bend in 5052-H32 takes 15–30 seconds per part once set up. Setup time: 15–30 minutes for a single-bend part, 45–90 minutes for a 6+ bend enclosure with stage bending sequence.

Shop rate for brake forming: $60–100/hr. A bracket with 2 bends at 100 pcs: $0.50–1.50 per part in forming cost (not including material or laser cutting the blank). An enclosure with 8 bends at 50 pcs: $3–8 per part in forming cost.

Aluminum sheet cost: 5052-H32 at $3–5/lb, 6061-T6 at $4–7/lb. A 12" × 18" × 0.090" bracket blank weighs roughly 0.5 lb — $1.50–3.50 in material. Combined with laser cutting ($1–3) and forming ($0.50–1.50), total part cost for a simple aluminum bracket: $3–8 per piece at 100 qty.