What K-Factor means
When sheet metal is bent, material inside the bend is compressed and material outside is stretched. Somewhere between them sits a plane that is neither — the neutral axis. The K-factor says where that plane sits, as a fraction of the sheet thickness measured from the inside surface.
Why it matters on the shop floor
A K-factor of 0.5 would mean the neutral axis is exactly in the middle of the sheet. In practice it is closer to the inside: for typical air bending of mild steel in a V-die, values cluster around 0.3–0.45, and the number rises as the inside radius grows relative to thickness. That is why a single "standard" K-factor of 0.33 or 0.44 quoted in a textbook will produce flat patterns that are consistently a few tenths of a millimetre out on your own tooling.
In practice
Practically, the K-factor is the bridge between the CAD model and the press brake. If the K-factor in the CAD sheet-metal parameters does not match the tooling that will run the part, the flat pattern is wrong before the first blank is cut — and the error shows up as a dimensional miss after bending, not in the laser nest.
Formula
K = t / T (t = distance from inside surface to neutral axis)Typical air-bending values: soft aluminium 0.38–0.45 · mild steel 0.33–0.42 · stainless 0.35–0.45 · hard grades lower
What to remember
- K-factor is a property of a tooling + material combination, not a universal constant.
- A smaller inside radius relative to thickness pushes the neutral axis inward (lower K).
- Bottoming and coining move the neutral axis outward compared with air bending, so the K-factor changes when the process changes.
- WERIX programmes the K-value its own press brakes produce, so a flat pattern released for production matches the bend result.