Punch design and layout becomes more effective with the use of the automatic 2D strip plan, including fold lines. Using this method is very rare in the dies for blanking including hole blanking. This will reduce stress on the springs. Low Strain - Minimal stretch or compression in either the major or minor directions. This subject has been discussed in detail before - try this thread:
I have doubts that your "maths" are accurate. The maths may be unique in that they aren't pulled out of a book but they are just a geometric translation of torque into shear force to give a worst case for thread stripping. Nonetheless your post is very interesting for looking at fundamental concepts, to help the user begin to learn the more complex situation by degrees, with the above links also provided by CoryPad. Placement of 3D folding stages into the strip is a seamless process and the strip can be easily updated to accommodate a reduction or increase in number of stages. In punching, the metal inside the part is removed; in blanking, the metal around the part is removed.
Shown in fig is a rather deep shell that has been drawn from a flat sheet. Any standard catalogue component will also have the correct detail representation within a section view. It's easy to join and it's free. A movable stripper is held by a stripper bolt and a spring. Shearing is a cutting operation used to remove a blank of required dimensions from a large sheet. These forces can be calculated globally for the complete tool or locally for a specific station.