DIN 6935 Bend Allowance Calculator — Cold Bending of Flat Steel

Here's a 90° bend in 2 mm mild steel, with a 4 mm inside radius. The tool says it's OK.

Now make the exact same bend in aluminium 6061-T6. It fails. The outside of the bend will crack.

This is the MechanixCalc sheet metal calculator. It works out the flat blank you need to cut, and it checks the bend radius and the springback. It also covers punching and deep drawing. Let's go through it, step by step.

When sheet metal bends, the outside is stretched and the inside is squeezed. Somewhere in between, one layer keeps its length. That is the neutral axis.

It sits at K times the thickness from the inside, and its length is your flat blank. If the bend is too tight for the material, the stretched outside cracks.

Step one is the material. Mild steel, 2 mm thick. The material sets the stiffness and the strength, and that drives the springback.

The temper matters most. It isn't picked yet, so the tool assumes full-hard, the strictest case. The verdict is CHECK, in amber.

Set the temper to soft, annealed. Now the sheet can bend as tight as half its thickness, and the verdict turns green. It's OK.

Step two is the bend itself. A 4 mm inside radius, bent to 90°. The K-factor of 0.4 puts the neutral axis at 40 % of the thickness.

The two flanges are 50 and 80 mm long. So the flat blank you cut is 125.54 mm. That's shorter than the two flanges added up.

Step three shows the checks. The radius over the thickness, R over t, is 2, and soft steel only needs 0.5. Springback is just 0.54°. So this bend is OK.

Now switch the material to aluminium 6061-T6, and keep the same 4 mm radius.

This alloy needs a radius of at least 3 times its thickness. At R over t of 2, it FAILS, too tight. The outside of the bend will crack.

So open the radius up to 6 mm. R over t is now 3, exactly on the minimum. The verdict is CHECK, in amber. Right on the limit.

Go to 9 mm, and the verdict turns green. The flat blank gets a little shorter, at 123.39 mm.

Step four is springback. With the bigger radius, the part springs back 4.42° when the press opens. So you bend it to 94.64°, to land on 90°.

Springback and the minimum radius are engineering estimates. And the page labels them that way.

DIN 6935 gives a K-factor for this R over t, 0.488. Apply it, and the flat blank becomes 123.67 mm.

Punching is its own module. A 20 mm hole in 2 mm steel needs 4.1 tonnes of press force. On a 200 tonne press, that's only 2 %.

Put the same hole on a small 4 tonne press, and it needs 103 % of its rating. That's OVER CAPACITY. Don't run it.

Deep drawing turns a flat blank into a cup. A 60 mm cup, 30 deep, from a 108 mm blank, draws in a single hit. The draw ratio is 1.8, under the limit of 2.1.

Make the cup 40 deep, and the same blank comes up 6.89 mm short. The tool says BLANK TOO SMALL.

What the tool does not check is listed too: hole-to-bend distance, press-brake force, grain direction and more. So silence never reads as a pass.

Every input, every formula and every check goes into a PDF report. A report your reviewer can follow.

That's a bent part, checked. Try it on your own parts, on MechanixCalc.com.