K-factor in Bending

Theory on Bending

When a flat sheet is bent there is no reduction in its width or height, the only change takes place in its length. Therefore if you have to make a bent component, PLUS Bend can tell you what blank size you should start from, so that you get the desired dimensions of the finished component. The starting blank length is also called Flat Length.

The basic information about a bend includes the bend radius, the bend-angle ( BA ), and the material thickness ( T ). It is also useful to refer to the Inside and Outside of a bend, the inside being the side where the punch part of the break tool is used. The bend radius that is specified is the inside bend radius ( R )

During bending the inner surface of the bend is subjected to compression while the outer surface is subjected to tension. However there is layer in between which is free from any forces and thus its length remains the same. This is called the neutral axis ( N.A ). The radius of this layer of metal is called the neutral bend arc radius ( NBAR )and is defined as the inside bend radius plus a percentage( K-factor ) of the metal thickness.

NBAR  =  BR  +  (T * K-factor)

The K-Factor ( K ) depends on the material, the type of bending operation (coining, air-bending),  the ratio of the Bend Radius to the metal thickness ( R/T ) and is typically between 0.3 to 0.5. For most types of steels it is around 0.33 to 0.4

Adding new K factor value in the K factor table

      The k-factor value  for a given material should be fed in to the k-factor table,  this allows the software to use the k-factor value for bending calculations for that particular material. The K-factor should be known for the following cases: 

     K1- k-factor for cases, where  0<R<T.   

     K2- k-factor for cases, where  T<R<3T

     K3- k-factor for cases, where  R>3T

To add a new material in the edit material K-factors dialog go to the new row and feed the material name, material density, material tensile stress and the values of K1, K2, K3. Press the update button

See Also

K-factor calculationBrief Overview of  User Interface