What is air bending?
Air bending is the common press brake method where the punch pushes the sheet only part way into the die, so the metal spans the opening and touches the die only at the two shoulders and the punch tip. The angle is set by how deep the punch goes, not by the tooling profile, which is why one set of tools covers many angles and thicknesses.
What is bottom bending?
Bottom bending drives the sheet fully into the die under full tonnage so the punch bottom and the die shoulders set the angle. The angle comes from the tooling geometry rather than the ram depth, so it is very repeatable, but each thickness and angle needs its own punch and die and the force needed is much higher.
How is coining different from bottom bending?
Coining takes bottom bending to the extreme: enough tonnage to thin the material at the bend so it takes the tooling profile exactly. The radius is very sharp and springback is almost eliminated, but the force is the highest of the three and the tooling wears fastest. On the press brake, coining is recognisable by the tonnage spike and the bright, worked surface at the bend.
| Method | How the angle is set | Force needed | Springback | Tooling flexibility |
|---|---|---|---|---|
| Air bending | Ram depth | Lowest of the three | Largest, must be overbent | One tool set, many angles |
| Bottom bending | Punch and die profile | High | Small, tooling-set | One set per angle and thickness |
| Coining | Punch and die profile, material thinned | Highest | Almost none | One set per profile, fast wear |
Which method should I use?
Air bending is the default for job-shop work because the tonnage is lowest and one die covers a range of thicknesses. Bottom bending earns its force when the angle must repeat tightly across a batch. Coining is reserved for sharp radii or springback that will not come out any other way.
- Air bending: mixed work, thin to medium stock, tonnage-limited machines.
- Bottom bending: production runs where the angle tolerance is tight.
- Coining: sharp-radius brackets, and materials that spring back badly.
- Whatever the method, the V opening still follows the eight times rule for mild steel, ten times for stainless and high-strength steel, and six times for aluminium.
Does air bending really use less force?
Yes, and the difference is large. In air bending the force follows the opening; in bottoming and coining the punch drives the metal into a closing wedge, so the force rises steeply near the end of the stroke. Bottoming the same bend can take three to four times the air bend tonnage, which is why exceeding the machine or tooling rating is the classic bottom-bending failure.
Related technical pages
Press brake tooling guide
The full method comparison, from air bending to coining, in one place.
V-die opening calculator
The opening for each material and thickness, with radius and minimum flange.
Tonnage calculator
Force per metre for air bending, with material multipliers.
Springback guide
Why air bending needs overbending and how to work out the compensation.
Next step
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