The calculation formula is as follows:

**L=0.5π ×( R + K coefficient × T) ×(θ/ 90)**

L: Unfold length of sheet metal

R: Inner radius of bend

T: Material thickness

θ: Bending angle

Y factor: a constant determined by the position of the neural bend line. Its default value is 0.5 (the so-called “bend line”).

In the practice of sheet metal design, the commonly used sheet metal flattening calculation formula is based on the K coefficient, which ranges from 0 to 1, indicating the resistance of the material to stretching during bending.

The relationship with the y coefficient is as follows:

Y coefficient = (π / 2) × K coefficient