Bending is a common metalworking technique to process sheet metal. It is usually done by hand on a box and pan brake, or industrially on a brake press or machine brake. Typical products that are made like this are boxes such as electrical enclosures, rectangular ductwork, and some firearm parts such as the receiver of the AKM AK-47 variant.

 

Usually bending has to overcome both tensile stresses as well as compressive stresses. When bending is done, the residual stresses make it spring back towards its original position, so we have to overbend the sheet metal keeping in mind the residual stresses.

 

When sheet metal is bent, it stretches in length. The bend deduction is the amount the sheet metal will stretch when bent as measured from the outside. A bend has a radius. The term bend radius refers to the inside radius. The bend radius depends upon the dies used, the metal properties, and the metal thickness.

 

Many software packages refer to the K-factor for bending sheet metal. K-factor is a ratio that represents the location of the neutral sheet with respect to the inside thickness of the sheet metal part. The bend allowance is the length of the arc of the neutral axis between the tangent points of a bend in any material.

 

BD = 2*(R + T) - BA

BA = π*(R + K*T)*A/180

K = (180 * BA)/(π*A*T) - R/T

 

where:

 

BA = bend allowance

R = inside bend radius

K = K-Factor, which is t / T

T = material thickness

t = distance from inside face to neutral sheet

A = bend angle in degrees (the angle through which the material is bent)

 

 

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