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Sheet metal bending

  1. K factor
  2. Neutral axis, Neutral axis offset
  3. Bend allowance
  4. Bend deduction
  • When a piece of metal is being formed,

the inner portion of the bend compresses

while the outer portion expands

​

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1. K – Factor,

  • In sheet metal, the K-factor is the ratio of

the neutral axis to the material thickness.

K = t/T

​

K = 2.5 / 5

​

K = 0.5

L1

L2

OAL

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Radius

Soft / Aluminum

Medium / Steel

Hard / Stainless Steel

Air Bending

 

 

 

0 - MT

0.33

0.38

0.4

Mt. - 3* MT

0.4

0.43

0.45

3*MT - >3* MT

0.5

0.5

0.5

Bottom Bending

 

 

 

0 - MT

0.42

0.44

0.46

MT - 3*MT.

0.46

0.47

0.48

3*T - >3*T

0.5

0.5

0.5

Coining

 

 

 

0 - MT

0.38

0.41

0.44

Mt. - 3*T

0.44

0.46

0.47

3*MT - >3*MT

0.5

0.5

0.5

  • In coining, the angles of the punch and die

determine the angle of the bend in the

metal sheet.

  • in air bending, the bend angle is determined

by how far down vertically the punch presses

into the die.

  • Bottoming is a bending process in which

sheet metal is pressed against a bottom die

featuring a V shape

K – Factor Chart

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2. Neutral axis, Neutral axis offset

Example : Aluminum + 10R + Air bending

​

K = 0.4 & t = ?

K = t/T

​

0.4 = t / 5

​

t = 0.4 X 5

​

t = 2.0

Neutral Axis = 2.5mm

Neutral Axis offset = 2.0mm

The location of the neutral axis varies and is based on the material’s physical properties

and its thickness.

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3. Bend allowance

L1

L2

OAL = L1+BA+L2

OAL = 25 + 19.63+ 25 = 69.63 mm

BA

Bend allowance is defined as the material required to add to the

overall length of the sheet metal in order for it to get cut in the right size

OAL

Bend allowance

= Angle X (ᴫ /180) X (Radius + K factor X MT)

= 90 X (ᴫ/180) X (10 + 0.5 X 5)

= 90 X 0.0174 X 12.5

= 19.63 mm

“BA is the length of the arc on the neutral axis” 

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  •  Bend deduction is the difference between the bend allowance and twice the outside setback.
  •  The material you will have to remove from the total length of the flanges in order to

arrive at the proper length in the flat pattern.

Bend deduction

=  (2 × Outside setback) - Bend allowance

= (2 x 15) – 19.63

= 30 – 19.63

= 10.37 mm

4. Bend Deduction

L1

L2

OAL

BD