Sheet metal is forgiving until it is not. A part that violates a handful of well known rules will either cost more than it should or arrive distorted, and the rules are all consequences of the same fact: the brake needs to grip the flange, and material near a bend moves. Designing with them costs nothing and ignoring them costs on every part forever.
Minimum flange length sheet metal parts need
A press brake forms the flange by pressing it into a die, and a flange shorter than roughly the die opening plus the material thickness cannot be gripped, so it either will not form or forms inaccurately. The practical minimum is set by the shop's tooling, which is why it is worth asking rather than applying a generic number. Short flanges are the commonest reason a part comes back with a question.
Holes, slots and how far from a bend
Material stretches near a bend, so a hole placed too close distorts into an oval and pulls the edge. Keep holes at least a few material thicknesses plus the bend radius away from the bend line. Where a hole must be closer, the usual answer is to make it a slot that extends past the bend, or to punch it after forming as a secondary operation.
Bend relief and tearing
Where a bend ends part way across a part, the material at the end of the bend is trying to stretch and tear at the same time. A relief notch at each end of the bend line gives it somewhere to go. Without one the corner tears or bulges, and the part looks like a mistake even though it is exactly what the model asked for.
One thickness, one radius, one finish
Every different material thickness is a setup. Every different bend radius is a tool change. Every different finish is a separate process and a separate lead time. A design that uses one thickness, one radius and one finish throughout will be cheaper than an otherwise identical one that does not, and in most cases the constraint costs nothing functionally.
Questions people ask about sheet metal design
What is the minimum flange length?
It is set by the shop's press brake tooling, roughly the die opening plus the material thickness. Ask the fabricator for their figure rather than using a generic one.
How far should a hole be from a bend?
Far enough that the stretching material does not distort it, which in practice is several material thicknesses plus the bend radius. Closer than that, punch after forming.
What is bend relief?
A small notch at each end of a bend line that lets material move without tearing. Without it, partial bends tear or bulge at the corner.
Why should I use one bend radius throughout?
Because each different radius means a different punch and a tool change at the brake. One radius keeps the part on one setup, which is where the saving is.
Is this sheet metal guide enough to release a drawing from?
It is enough to avoid the four expensive mistakes and not enough to skip the fabricator's own tooling list, and the page says why in its first section: the practical minimum flange length is set by the shop's tooling rather than by a generic number, so it is worth asking. The rules that do travel are here. Keep holes at least a few material thicknesses plus the bend radius from the bend line, or make them slots that extend past it. Put a relief notch at each end of a bend that stops part way across. And hold one thickness, one radius and one finish throughout, because each extra one is a setup, a tool change or a separate lead time.