Sep 30, 2015

Determining the proper tonnage for air bending a piece of sheet metal or a heavy plate will depend on a couple of variables. Each aspect of sheet metal bending is important to consider when determining the proper tonnage for the desired bend.

There are a couple of aspects that need to be considered in getting the proper tonnage:
  • Material Type
  • Material Thickness

It is necessary to take into consideration the type of material you are working with. Because most charts are based upon calculations related to air bending mild steel, you need to know how your material will compare to mild steel.  For instance, based on a bending chart created for mild steel, air bending stainless steel will require approximately 150% more tonnage than the chart shows, while aluminum will require approximately 50% less. The thickness or gauge of the material is also crucial because that will determine the opening of the die required and the minimum flange length you can bend over that particular die opening. The opening of the die will also determine the inside radius of the bend.

An example of how to determine the proper tonnage required for a bend (please refer to chart below).


In this scenario we want to air bend ¼” mild steel that is 10 feet long. How much tonnage will it take?

  • First look at the left column and find the thickness of ¼”
  • Follow the line across to the yellow diagonal line that is the optimal situation at 15.5 tons/ft. , then go straight up to see that a 2″ “V” opening is the optimal die opening for ¼” material.

In this instance, our part would require a minimum of 155 tons to bend 10’ of 1/4″ steel with a 2″ “V” opening.  Now go to the top of the chart under the 2″ “V” opening and see that the minimum flange length is 1-3/8″ with a 5/16″ radius.

Please take into account that material today tends to vary greatly in both tensile and yield. For this reason, and for the longevity of your machine, never limit yourself to exactly what tonnage is needed to bend your heaviest part — allow a buffer of 20-30%.

The press brake experts at JMT are happy to answer any questions you may have about metal bending and fabrication. Call 855-Press-Brake (855-773-7727) to speak with someone about your specific metalworking projects, or email


See also:

Press Brake Tonnage Calculator

Press Brake Air-Bending Tonnage Chart

Choosing the Right Press Brake

What to Consider When Buying a Press Brake

JMT Press Brake Product Page


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