K-Factor Calculator

K-factor is a ratio that represents the location of the neutral axis relative to the material thickness. It is defined as t/T where t is the distance from the inside surface to the neutral axis and T is the total material thickness. A K-factor of 0.5 means the neutral axis is at the center, while lower values indicate it shifts toward the inside bend. Common values range from 0.25 to 0.50 depending on material type, thickness, and bend radius.

As the inside bend radius increases relative to material thickness (higher R/T ratio), the K-factor increases. Sharp bends with small radii relative to thickness force the neutral axis closer to the inside surface, producing lower K-factors. For R/T ratios below 0.5, K-factors range from 0.27 to 0.40. For larger R/T ratios above 3, K-factors approach 0.50 as the bending becomes more gradual.

Bend allowance is the length of the neutral axis through the bend arc, representing the actual material needed to form the bend. Bend deduction is the amount subtracted from the total flat pattern length to account for the material stretch during bending. Both are derived from the K-factor and are essential for accurate flat pattern development. Bend allowance adds material length while bend deduction subtracts it from the sum of flange lengths.

For mild steel with a 90-degree bend and bend radius equal to material thickness (R/T=1), K-factor is approximately 0.33 to 0.42. Aluminum typically has K-factors of 0.40 to 0.45 due to its greater ductility. Stainless steel, being harder, has lower K-factors around 0.30 to 0.38. Always verify through bend tests for precision work, as actual values vary with tooling, material batch, and grain direction.