Bottoming, also called bottom bending or die bending, is a press-brake method in which the punch drives the sheet all the way down so it conforms to the angle ground into the V-die, rather than stopping it partway as in air bending. Because the material is pressed firmly against both faces of the die at the bottom of the stroke, the bend takes on the die's angle and the inside radius is largely set by the punch nose. This contact forces the metal further past its yield point and reduces the elastic recovery, so springback is much smaller and the finished angle is far more repeatable than air bending.
The trade-off is force. Bottoming typically requires on the order of three to five times the tonnage of air bending the same material in the same die, because the punch must overcome the material's resistance all the way to die contact rather than letting the sheet bridge the opening. The die must also be ground to the target angle (often a degree or two sharper to leave room for the small residual springback), so a bottoming die is less versatile than an air-bending die, which can make many angles from one tool.
In terms of force and precision, bottoming sits squarely between air bending and coining. Air bending uses the least tonnage but gives the loosest angle control and the most springback; coining uses the most tonnage, fully sets the material, and produces the sharpest, most repeatable bends by deliberately thinning the metal at the bend; bottoming achieves tight, consistent angles at moderate tonnage without the extreme pressures of coining.
A practical example: a sheet-metal enclosure that must hold a 90° flange to a fraction of a degree across a long production run is a good candidate for bottoming. The shop grounds the die to roughly 88–89°, the punch bottoms the part each stroke, and the residual springback opens the bend back to 90° consistently — far more reliably than chasing the depth on an air bend where small variations in material strength and thickness shift the angle.
Bottoming also tightens the inside radius compared with air bending. Where an air bend forms a radius set largely by the die opening (often roughly 16% of the V-width), bottoming presses the sheet down onto the punch nose, so the inside radius approaches the punch radius itself — a useful way to achieve a smaller, more controlled radius without resorting to the extreme tonnage of coining. The limits are that the die opening must be matched more closely to the material thickness than in air bending (a common guideline is a V-width around 6 times thickness), and the higher contact pressure makes tool wear and part marking more of a concern, so harder or coated tooling and good lubrication pay off. Because the angle is set by the die rather than by stroke depth, bottoming is also more tolerant of small variations in incoming material, which is exactly why it is favored where repeatable angles matter more than the flexibility of forming many angles from one tool.