The K factor is the most important and elusive variable of bending, because it varies both as a function of the material and according to parameters such as angle and tooling. The K factor is defined as the ratio between the material thickness (T) and the neutral fibre axis (t), i.e. the part of the material that bends without being compressed nor elongated.
Bend allowance is a fundamental parameter to calculate sheet elongation. This is defined as the length of the neutral fibre from the beginning to the end of the arc generated by the bend.
To calculate the bend allowance, the K factor and the derived coefficient called the Y factor, insert the thickness and initial length of the sheet into the cells on the left. After bending the sheet, insert the inner radius, and flanges A and B. Bending angle is 90°.