Bending flat steel - how can you calculate the shortening?


When bending a flat bar, its length is no longer the original one. How to calculate how much a workpiece will become shorter after bending, and what criteria are decisive for the degree of shortening, is discussed in this article.

bend Deduction

The so-called bending shortening is a technical term that describes the extent of length shortening after bending. Knowing this value is important in order to trim the starting material in the exact length of the molded parts before it is bent. After bending, it should fit exactly, so you have to know the shortening value.

Factors influencing the length shortening

How much a flat steel workpiece shortens during bending depends on a number of factors:

  • plastic deformability of the material under load (ductility)
  • Strength of the material, coatings, roughness of the steel
  • Type of microstructure (ferritic, austenitic or martensitic)
  • Grain size of the microstructure
  • Thickness of flat steel
  • Position of the bend in relation to the rolling direction (during production)
  • Bending technique applied
  • bending radius
  • bending angle

Even if one takes all these factors into account in one calculation, nevertheless occasionally (very slight) deviations can occur. This is hard to avoid in practice.

calculation method

An extended length at a roughly bent 90° angle is calculated in the following way:

Length of the first part + length of the second part + radians ½? (r + ½ t)

where r is the bending radius and t represents the material thickness.

Correction factors calculation

Since in the previous calculation actually the length was calculated from the middle of the workpiece, this deviates at the outer and the inner side, one can count on simple correction methods. However, this is difficult, because with fixed factors, no more accurate results can be achieved.

Calculation at other bending angles

If angles other than 90° are used, the calculation becomes even more complicated. The calculation for angles up to 90° and over 90° is different.

Tips & Tricks

For CAD software, too, you have to enter appropriate shortening values, which have been calculated in advance, so that the software can use them (for material requirements calculations, for example). CAD software can not automatically calculate bending reductions.


Video Board: How To Make Pie Cut Bends