4 mm 6061-T6 aluminium bend allowance and bend deduction
At a 90° bend with an inside radius of 3 × thickness (12.00 mm / 0.4724 in) and K = 0.40, 4 mm 6061-T6 aluminium (4 mm / 0.1575 in) has a bend allowance of 21.36 mm (0.8411 in) and a bend deduction of 10.64 mm (0.4188 in).
| Bend angle | Included angle | BA (mm) | BD (mm) | BA (in) | BD (in) |
|---|---|---|---|---|---|
| 30° | 150° | 7.12 | 1.45 | 0.2804 | 0.0572 |
| 45° | 135° | 10.68 | 2.57 | 0.4205 | 0.1013 |
| 60° | 120° | 14.24 | 4.23 | 0.5607 | 0.1667 |
| 90° | 90° | 21.36 | 10.64 | 0.8411 | 0.4188 |
| 120° | 60° | 28.48 | 26.94 | 1.1214 | 1.0607 |
| 135° | 45° | 32.04 | 45.21 | 1.2616 | 1.7799 |
| Inside radius | R / T | K-factor | BA (mm) | BD (mm) | BA (in) | BD (in) |
|---|---|---|---|---|---|---|
| 8.00 mm | 2 | 0.40 | 15.08 | 8.92 | 0.5937 | 0.3512 |
| 10.00 mm | 2.5 | 0.40 | 18.22 | 9.78 | 0.7174 | 0.3850 |
| 12.00 mm | 3 | 0.40 | 21.36 | 10.64 | 0.8411 | 0.4188 |
| 16.00 mm | 4 | 0.50 | 28.27 | 11.73 | 1.1132 | 0.4616 |
| 20.00 mm | 5 | 0.50 | 34.56 | 13.44 | 1.3605 | 0.5292 |
Practical notes
The angle in these formulas is the bend angle — how far the flange turns away from flat. The included angle between the two flanges is 180° minus the bend angle, so a 90° bend is also 90° included, but a 135° bend leaves a 45° included angle.
K-factor values here come from a generic air-bending table that depends on R/T (about 0.33 below R = T, 0.40 from T to 3T, 0.50 above 3T for 6061-T6 aluminium). They are approximations: tooling, die width, grain and temper all shift the neutral axis. Bend a test strip, measure the flanges and back-calculate K before cutting a production run.
A V-die opening of about 8 × T (32.00 mm / 1.2598 in) is the usual starting point. In air bending the inside radius forms at roughly 13–15% of the die opening for 6061-T6 aluminium, so the radius you actually get depends on the die more than the punch — recompute with that radius if it differs from the R = 3T used above.
Springback for 6061-T6 aluminium at modest radii is typically about 2–5°, increasing as R/T grows; overbend to compensate. It changes the angle, not the bend allowance calculation.
6061-T6 is the least formable alloy here and cracks on the outside of tight bends; 2–3 × T is a typical minimum inside radius, and thicker plate often needs 3 × T or more. If the part needs a tight bend, consider 5052-H32, or bending 6061 in the O or T4 temper and heat-treating afterwards. Bend across the rolling direction where possible and inspect the outside of the bend for orange peel or cracks.
At 4 mm, many shops will not bend 6061-T6 tighter than about 3 × T (12.00 mm / 0.4724 in), which is why this page uses R = 3T; confirm the radius with your fabricator before finalising the flat pattern.
FAQ
What is the bend deduction for 4 mm 6061-T6 aluminium at 90°?
With R = 3T (12.00 mm / 0.4724 in) and K = 0.40, the bend deduction is 10.64 mm (0.4188 in). For a part with two 50 mm flanges measured to the outside, the flat blank is 50 mm + 50 mm − 10.64 mm = 89.36 mm.
What K-factor should I use for 4 mm 6061-T6 aluminium?
For air bending 6061-T6 aluminium at R = 3T, a K-factor of about 0.40 is a typical starting value; below R = T it drops to about 0.33, and above 3 × T it approaches 0.50. Real values depend on tooling and material lot, so confirm with a test bend.
Can 4 mm 6061-T6 aluminium be bent with a tight radius?
Not reliably. 6061-T6 tends to crack on the outside of tight bends; 2–3 × T is a typical minimum inside radius, and thicker plate often needs 3 × T or more. This page uses R = 3 × T (12.00 mm / 0.4724 in) for that reason. For tighter bends use 5052-H32 or bend 6061 in the O/T4 temper and heat-treat afterwards.
Is the angle in the bend allowance formula the bend angle or the included angle?
It is the bend angle, the amount the flange is turned from flat. If your drawing gives the included angle between flanges, use 180° minus that value: a 45° included angle is a 135° bend.
Sources: Bend allowance formula BA = A·(π/180)·(R + K·T); bend deduction BD = 2·tan(A/2)·(R + T) − BA (Machinery's Handbook, sheet metal bending) · Generic air-bending K-factor table by R/T (approximate)
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