written 4.9 years ago by | • modified 4.6 years ago |
Fig. bending terminology.
Bending is the process in which a straight length is transformed into a curved length.
During bending, the outer surface of the material is under tension and inner under compression.
Parameters to be considered while designing bending die.
a) Bend radius (rb) :
It is the radius of curvature on inside surface on the bend.
If the bend radius is very small, then outer surface of material cracks due to higher tension.
To prevent the damage the bend radius should not be less than 0.8 mm.
b) Bend allowance (B) :
The length of the bend area which is more than blank length before bending is known as bend allowance.
Bend allowance is calculated using
B = $\alpha$ ( r + k)
Where, B = Bend allowance
$\alpha$ = Bend angle in radius
R = inside bend radius
K = Distance of neutral axis from inside surface of the bend.
c) Bending pressure or bending force (f)
Bending force depends on the stock thickness, bend length, die opening width and type of bend.
For r = bending
F =$\frac{ k.l. 6_ut . t^2}{w}$
Where,
l = length of bend
6ut = ultimate tensile strength
T = Blank thickness
K = Dia opening factor ( 1.2 to 1.33 )
W = width of die opening
W = $R_1$ + $R_2$ + C
Where, c = t = clearance
$R_1$ = punch edge radius.
$R_2$ = die edge radius.