Understanding Sheet Metal Fabrication Basics
All press brakes have rating for a maximum bending pressure, or tonnage. This rating can then be the basis for calculating the press brake's bending capacities. This is done through an understanding of basic factors affecting the formability of metal.
These rules of thumb for press brake forming are based on using mild steel. So now let's look at these bending factors which play a significant role in the press brake's performance.
>> How to Determine Vee Die Opening and Inside Radius?
The rule of thumb of vee die opening for mild steel is 8 times the metal thickness, when the mild steel's thickness if less than one half inch. (0.500'). You should increase the vee die opening to 10 times of the material thickness when the thickness is thicker than 0.500' inch, this is to prevent cracking of the material.
The inside radius of a bend in mild steel is about 0.156' times the vee die opening, regardless of the gauge of the metal being formed. The 0.156' was concluded by measuring formed samples bent over various die openings. For example, if a 1/8' sheet and a 1/4' plate are formed over a 2' vee die, each will have the same inside radius of about 0.312' (0.156 x 2 = 0.312).
>> What Is Spring Back?
Metal formed by an upper and lower die only has three contact points. If metal is pushed into a lower die sufficient to form a specific angle, when the force is released, the angle will open up due to spring back. Normal spring back for mild steel is 2A� to 4A�. If the material is hard, has a higher tensile strength, or a larger than normal inside radius, then the spring back will be even greater.