As the neutral axis shifts toward the inside surface of the material, more Along the neutral axis, nothing is changing-no expansion, no compression. On the outside of the neutral axis the material is expanding on the inside of the neutral axis the material is compressing. The neutral axis is an area within the bend where the material goes through no physical change during forming. This because the neutral axis shifts closer to the inside surface of the material. Technically, the metal does neither, but instead elongates. Many will say material “grows” or “stretches” as it is bent in a press brake. The final formed dimensions will be greater than the sum total of the outside dimensions of the part as shown on the print-unless some allowance for the bend is taken into account.

When a sheet metal part is bent, it physically gets bigger. Figure 1: The bend allowance calculation always uses the complementary angle.