Press Brake Tonnage Calculator

For a 90° air bend, this tool uses F = Rm × t² ÷ V × (1 + 4 × t ÷ V) in kN per metre of bend, with the tensile strength Rm in N/mm², the thickness t and the die opening V in mm (V in that formula is our reading of the maker’s, as the method below explains). Multiply by the length of the bend in metres. For 3 mm mild steel on a 24 mm die that is 236 kN per metre, about 24 tonnes.

It has only been compared with two makers’ charts, not with measured bends, so read it as an estimate, and one that can read low. At Rm 420 N/mm² the formula is within 5 % of 68 of the 77 figures in the chart it comes from (Bystronic). It sits below that chart in 64 of them, by up to 13 %. Mill scale can add another 5 to 10 %, and plate stronger than you assumed adds more, so in the worst case the real force can be 20 % or more above this figure. WILA’s chart for mild steel runs lower: the formula is a median 7 % above it, and up to 19 % above on a few thin sheets. Stay well inside your machine’s chart and your tools’ limits; do not plan a bend up to the limit on the strength of this figure.

A common starting point (Mate’s table) is 6 × thickness below 2.5 mm, 8 × from 2.5 to under 8 mm, 10 × from 8 to under 10 mm and 12 × from 10 mm. Because the die steps up at those thicknesses, the “usual die” force drops at each step: 2.49 mm on 6 × needs more than 2.5 mm on 8 ×. A wider die lowers the force but raises the inside radius and the shortest flange you can bend. This tool gives no figure under 5 × thickness, where the makers’ charts do not go. Between 5 × and 6 × it gives a figure with a warning: only WILA’s chart reaches there, on a few thin sheets, so do not rely on the figure.

No. WILA says bottoming takes three to five times the air-bending force, and that range is too wide to print one number. Do not scale this figure up and rely on it; use the figures for your own tools and machine.

Not on its own. Bystronic’s tools are marked with a maximum bending force in kN per metre, so compare the per-metre figure with what is marked on your punch and die. The whole-bend figure shares the force along the bend, but a short bend in thick plate puts it all on a short length of tool: it can be well inside the machine’s total and still over the tool’s per-metre limit, and it can damage the tool. Your machine’s own chart and manual, and the tool maker’s limits, govern what they may carry.

Stainless is taken at 1.6 × the mild steel figure (Bystronic, for Rm 650–700 N/mm²); WILA uses 1.5 ×. For aluminium the makers differ more: Bystronic takes 0.65 × for Rm 300 N/mm², WILA takes 0.5 × for soft aluminium and 1.0 × for heat-treated alloys. For a heat-treated alloy use at least the mild steel figure (WILA’s × 1.0). If you know the tensile strength from the mill certificate, choose “Other” and enter it: a stronger alloy needs more. High-strength and wear-resistant plate has its own limits: use the plate maker’s bending data. Mill scale adds a factor of 1.05 to 1.1 on hot-rolled sheet (Bystronic); this tool does not add it.