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INPUT   DATA

♥ EXAMPLE Of Input/Output

Title

Material Thickness, T		length
Bend Radius, R		length
Bend Angle, A		°

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OUTPUT   VARIABLES   &   GRAPHS

VARIABLES	Values	Units
♦ Bend Allowance, BA		length
♦Bend Deduction, BD		length
♦Outside mold line, X		length
♦ Inside mold line, Y		length

Bend Deduction & Allowance In Sheet Metal Forming

When a sheet is bent in a press brake, the region of the sheet close to and in touch with the punch elongates. The material is stretched beyond its yield point but below its ultimate tensile strength. Thus, if you compare the sheet length after bending with the initial flat length you will find that they are different. If you don't compensate for this variation, the final product will not have accurate dimensions. It is often required to know the amount of material that needs to be removed from the flat to compensate for the elongation that occurs during the forming process. This amount of shortening is termed Bend Deduction, and a common method of estimating it is via the equations below:

where
     BD = bend deduction or setback
     BA = bend allowance, length along the neutral axis of the bent section
     OSSB = OutSideSetBack = X
     X = distance from outside mold line (heel of angle) to tangent point
     Y = distance from inside mold line to tangent point
     A = angle of bend
     R = radius bend
     T = thickness of material

All lengths are in the same units usually inches or centimeters.

Tips

    ◊ Use link EXAMPLE Of Input/Output  to demo data entry expectations and results; you may edit & use it as starting point

BIBLIOGRAPHY

• Walsh RA; Handbook Of Machining And Metalworking Calculations; McGraw Hill, New York, 2001, Chapter 6.
• Diegel, L; The fine art of sheet metal bending; Aukland, New Zealand; www.massey.ac.nz/~odiegel/bendworks/.
• The Precision Sheet Metal Chronicle, issue 1, vol 8, 2005, www.asmachronicle.com.