I am into design of a machine, wherein I am bending the sheet metal.

The force that I am required to bend, if its calculated from the basic principles, it gives me
Bending Moment = 1/6 * Stress * Width * (thickness^2).

From Books, I see the Bending Moment = 1/3 * Stress * Width * (thickness^2). TOO high.

Is there any formulae Combining the k-Factor of the sheet metal, which relates the shift of the neutral axis.

Any help is appreciated.

Thanks,