Manufacturing & engineering
Bend allowance
Definition
Bend allowance is the length of material used up by a sheet metal bend, measured along the neutral axis between the bend's tangent points. It depends on thickness, bend radius, bend angle, and K-factor, and it decides whether the flat blank folds up to the right size.
Also known as: BA
Updated
Three ways to calculate bends#
Sheet metal CAD lets you choose how bends are calculated. Onshape's sheet metal model offers a K-factor option, a bend allowance option that uses the length of the neutral line arc between the tangent points, and a bend deduction option.
Bend deduction is the related value subtracted from the sum of the outside flange lengths to get the flat length. The right numbers depend on the material, tooling, and shop, so many fabricators give designers their own bend tables instead of generic defaults.
Sources
Related terms
K-factor
The K-factor is the ratio of the neutral axis position to the material thickness in a sheet metal bend. CAD programs use it to calculate bend allowance and the size of the flat pattern.
Flat pattern
A flat pattern is the unfolded 2D shape of a sheet metal part, calculated from its bends, radii, and K-factor or bend table. It is what gets cut from the sheet before the part is formed.
DFM
DFM is the practice of shaping a part so it can be made reliably and economically with the intended process. It covers choices such as wall thickness, draft, tool access, bend radii, hole sizes, and tolerances the supplier can actually hold.