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Air Bending

Cálculo de dobras

The aim of air bending is never allow the material to touch the bottom of die, the material stay in touch with the die set by 3 points, on both sides of die set and on the radius of punch.
This process is versatile besides being economic given the possibility of performing any angle between 180° up to the set die angle.
Since the contact between the tools and material is small then the force required will be small as well.
Theoretically, the internal radius is for the open (V) of the die set, that is, the bigger opening of the set die the bigger the internal radius will be.
The air bending is one of the process which better correct the effects caused by the elastic phase of the material.
However, any ram variation could result in variations of the angle bending, that´s why the equipment as its tools must be in perfect conditions.
The calculus for air bending is done by using these formulas below:
In order to find the necessary bending force by meter ( F – ton/m)
F = {[1 + (4 . S / V)] . S 2 . R . L} / V
F = Bending force (ton/m);
S = Thickness (mm);
V = Bending Channel open (mm);
R = Material loads limits (kgf/mm 2;
L = bending length (m).

Note1 – It understood that material loads limits is the rupture tension (tensile strength) as each mechanical properties of each material.
b) To find the internal radius (Ri – mm) knowing the open  “V”
Ri = V / 6
c) To find the open  (V – mm) knowing the radius“Ri”
V = Ri . 6
Important: It´s recommended  a minimum“Ri” equal S . 1,15.
d) To find the minimum external edge ( B-mm)
( Only for 90° bending)
B = 0,7 . V
Where:
B = Minimum edge (mm);
Then, V = B / 0,7
Note2: All the results are theoretical due to several conditions that might directly influence in the results, such as elastic effect of the material, temperature, equipments and tools conditions.
Note3: The formulas showed does not assist for works where are required the contact of the punch with the bottom of die since these sort of works requires a bending force superior than air bending.