What is a U bend?
A U bend forms a channel: two parallel bends in the same direction with a flat bottom between them. It is the most common section in sheet metal work, and almost all of its problems come from the bottom width being too narrow for the tooling or the flanges being too short to seat.
What tooling does a U bend need?
A single-V die and a straight punch for the common case, with the opening following the eight times rule. The bottom width of the channel has to be at least the minimum flange the opening allows, otherwise the flat will not sit on the die shoulders.
| Check | Rule of thumb | If it fails |
|---|---|---|
| Die opening | 8t mild, 10t stainless, 6t aluminium | Angle and radius both drift |
| Bottom width | ≥ V/2 + t (minimum flange) | The flat drops into the die |
| Punch width | Fits inside the channel with clearance | Sidewalls collide with the punch |
| Tonnage | Within machine and tooling rating | Tooling chips or the ram stalls |
Why does my U bend come out with different angles?
Three usual causes: the two bends are not the same depth, the sheet is not square to the bend line, or springback differs along the length. Check the angle at both ends of each bend, then in the middle, to tell which one you have.
How do I bend a narrow U?
When the bottom width is below the minimum flange the opening allows, the answers are a narrower opening with a matching punch tip, a two-hit method with a relieved punch, or redesigning the part. Narrow U sections are where standard tooling runs out.
Related technical pages
Press brake dies
Single-V, 2V and multi-V die types for channel work.
Minimum flange calculator
The shortest flange a given opening can form.
Gooseneck vs straight punch
When the channel walls need punch relief.
Z bending
The offset cousin of the U bend, and its clearance problems.
Next step
Send the channel section and material and we will confirm the opening, punch and tonnage.
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