>> Distortion Near Bends
When design holes and cutouts, you should keep the distance from the edge of the hole(or cutout) to the start of the inside bend radius at least 2 times the material thickness. The holes or cutouts will distort during the sheet metal bending process if the distance is too close. If you must have holes close to the bend, then the holes or cutouts should be extended beyond the bend line (across the bend line).
>> Bend Radius
In your sheet metal design, the inside bend radius should be equal to material thickness. If the radius is less than the material thickness, soft metal will have material flow problem while hard metal will have fracturing problem.
The bend radius should, if possible, be kept the same for all radiuses in the part to minimize set up changes
>> Critical Dimensions
Only the truly critical dimensions should be highlighted. The manufacturing cost will increase dramatically if you place excessive high tolerances or redundant critical dimensions.
>> Flange Dimensions (also called form height to thickness ratio)
The flange length is the distance from the bend to the edge of the part or to another bend.
The flange length must be longer than 1/2 of the Vee die opening. This is because the flange must bridge across the Vee die in the bending process. As a rule of thumb, the flange length should be at least 4 times the material thickness plus the bending radius. Shorter flange lengths requires extra cost and could cause distortions in the part or damage to tooling or operator due to slippage.
>> Bend Deductions
Sheet metal stretches when it is bent. Bend deductions tell how much the metal will stretch. This number depends on the material thickness, the bend radius, and the bend angle. But this is usually handled by sheet metal fabrication shops, you as a designer usually don’t need to worry about it.