What Is Bend Relief and When Does a Sheet Metal Part Need It?

Bend relief is a small notch or cutout at the end of a bend line that stops the material from tearing where the bend meets an adjacent edge or feature. You need it any time a bend doesn't run the full width of the part. Skip it on a partial-width bend and the corner where the bend line ends cracks, distorts, or wrinkles instead of forming a clean line.

Why the corner is the problem

A press brake bends by applying a line load along the full length of the bend die. When that bend line runs edge to edge across the part, the material at the ends is free to move, because there's nothing constraining it sideways. But when a bend only covers part of the width, like a tab or a flange that stops short of the part's edge, the material at the end of the bend is still attached to unbent material on either side.

That attached material resists the stretching happening at the bend, and the stress concentrates right at the transition point. Depending on the material and how tight the bend is, that concentration shows up as a visible crack, a rounded-over corner that never quite conforms to the die, or a wrinkle where the material buckled trying to accommodate the mismatch.

Relief cuts remove that constraint. A rectangular or radiused notch cut into the material right where the bend line ends gives the material somewhere to go instead of tearing.

Where you actually need it

Any bend that terminates inside the part's boundary needs relief at the termination point. That covers a flange narrower than the piece it's formed from, a lanced tab, or a bend that stops at an internal cutout. A bend that runs the full width of a rectangular blank, edge to edge, generally doesn't need it, since there's no attached material at the ends fighting against it.

The other place it matters is where two bend lines meet or nearly meet, like the corners of a formed box. Without relief there, the material has to stretch in two directions at once right at the corner. That's a reliable way to get a tear or a heavily distorted corner even in ductile material.

Getting the size right

Relief cut too small doesn't do its job, because the remaining material still fights the bend. Relief cut too large removes structural material you needed, or leaves a sharp notch corner that becomes its own stress riser.

A common rule of thumb is a relief width and depth on the order of the material thickness, with the corner of the notch relieved by a small radius rather than left sharp. The exact number depends on the material's ductility and the bend radius. If you're pushing a tight bend in a less ductile alloy, size the relief generously and verify on a first article rather than guessing tight.

Where this fits DigiForge's process

DigiForge's sheet metal service handles laser cutting, press-brake forming and PEM hardware insertion, in cold rolled steel, galvanized steel, aluminum 5052 and 6061, and stainless 304 and 316, cut to plus or minus 0.13 mm and bent to plus or minus 0.5 degrees. Relief geometry gets cut in the same laser operation as the rest of the profile, so it doesn't add cost or lead time. The lead time is 2 weeks either way.

What does cost you is skipping it and finding a torn corner on the first bent part. Add relief anywhere a bend line ends short of an edge. If you're not sure the size is right for your material, ask before the parts get formed rather than after.