Power Press Tonnage Guide: How to Size the Right Capacity

Tonnage is the single most important spec on a power press, and the easiest to get wrong. Buy too little and you stall on your hardest job. Buy too much and you've spent extra capital and energy you'll never use. Here's how to size it sensibly.

What tonnage really means

Tonnage is the maximum force a press can deliver. The force your job needs depends on what you're doing, punching, blanking, bending, or forging, plus the material and its thickness. The goal is simple: choose a press whose rated tonnage comfortably exceeds your hardest job, with headroom.

Sizing for punching and blanking

For punching or blanking, force rises with the length of cut, the material thickness, and the material's shear strength. The widely used relationship is:

Force = Cut length x Thickness x Shear strength of material.

A longer cut perimeter, thicker stock, or a tougher alloy all push the required tonnage up. Always work from your thickest, toughest part.

Sizing for bending and forming

Bending needs far less force than blanking, but it varies with die opening, material, and bend method (air bending vs bottoming). Forming and deep drawing have their own force profiles. When in doubt, share the part drawing with the manufacturer's engineers.

Sizing for forging

Forging force depends on the projected area of the part and the flow stress of the hot metal. Hotter, softer metal needs less force; larger projected areas need more. This is where talking to an experienced forging-press maker saves expensive mistakes.

Always add headroom

Running a press at 100% of rating every cycle shortens its life and risks overload. A sensible safety margin protects your dies, your accuracy, and your machine.

Birson capacity ranges to self-match: Power presses (H and C frame) 30-300 tons; Friction screw presses 50-800 tons; Forging screw presses 50-1000 tons.

Quick checklist before you buy

• Identified your hardest job (thickest, toughest part)?

• Calculated force for that job?

• Added a safety margin?

• Confirmed the press handles your stroke and bed size, not just tonnage?

Not sure? Send your part drawing to Birson Forgings and our engineers will size the right press.