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How to Calculate the Bending Force of a Hydraulic Brake Press

Determining the tonnage to apply to your air bend project involves a lot of math. Once you have your blueprint, tooling, and material, now you apply your formulas to calculate the effective tonnage to accomplish your run perfectly on your bending machines. But hand calculations are laborious, appropriating time better spent in the act of fabricating. Fortunately, with a press break tonnage calculator, all you need to do is punch in the known factors and the program will serve up the anticipated tonnage to apply. Keep in mind that these calculations are meant for air bending only. Bottom bending will require about four times the tonnage, and for coining, you should plan for approximately ten times the force you would use for air bends.

Once you've entered your empirical data into the press brake bending chart, consider the following factors, as well:

  • Friction on the Die

    Friction matters, but if you don't know the friction coefficient of the material, don't worry. The calculator defaults to 1.0. Just remember, you may need to increase or decrease tonnage to fine-tune for an unknown friction coefficient.

  • Variable Thickness of Material

    Obviously, you'll know the overall thickness of your material. What you probably won't know is the variation in the thickness across the length and width of the sheet. Sheet and plate metal production processes usually leave some areas a bit thicker than others; it can't be helped.

  • Tensile Strength

    Since tensile strength figures heavily in the outcome of your bend, you want to get as close to the actual PSI as possible. By referring to the Material Strength Chart, you can predict the tensile strength for carbon steel, stainless steel, and aluminum with ease. Always use the maximum tensile value for best results.

  • Capacity of the Tooling

    When forming short parts, keep in mind that the actual tonnage may be fairly low, but the "per foot of bend" may be higher than tool or ram can handle.

    Because variations in actual tensile strength, thickness, and true friction on the die will impact the outcome, a good plan includes a press with a capacity that is at least 20 percent higher than what the chart calculates for your air bends.

  • Hydraulic Press Brake Bending Machine

    If your forming machines are feeling their age or never had the capacity you now need for current projects there are several excellent hydraulic press brake bending machines, along with other precision forming machines to choose from. From gap (C) frames, straight side and hydraulic C frame press bulldozers, to hydraulic ramdozers, whatever your metalwork job requires, there’s a machine for you.