Sheet Metal K-Factor Physics: How Press Brakes Deform the Neutral Axis

In precision sheet metal fabrication, developing an accurate flat pattern blank is the difference between a high-tolerance enclosure and scrapped raw material. When sheet metal is formed on a CNC press brake, material outside the neutral axis stretches under tension, while material inside compresses.

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1. Mathematical Derivations of Bend Mechanics

The neutral axis represents the transition layer where longitudinal stress is zero. Its location is defined by the K-factor:

$$K = rac{t}{T}$$

Where $t$ is the distance from the inside surface to the neutral plane, and $T$ is the total material thickness.

The developed Bend Allowance ($BA$) is given by:

$$BA = rac{\pi}{180} \cdot (R + K \cdot T) \cdot lpha$$

Where $R$ is the inside bend radius and $lpha$ is the bend angle in degrees.

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2. Interactive Fabrication Calculators & Engineering Hub

• Calculate exact bend deductions and flat blank expansions instantly with our Sheet Metal K-Factor Calculator.
• Verify 2D and 3D DXF/DWG flat patterns directly in browser memory using the CAD DWG Version Checker.
• Review sheet metal unfolding capabilities across SolidWorks, Inventor, and FreeCAD in the CAD Software Comparison Matrix.
• Explore step-by-step diagnostic workflows at CAD Technical Guides.
• Visit the primary portal at CADGuide.tools.

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3. Empirical Tooling Selection Rules

• Air Bending Mild Steel ($R/T < 1.0$): Use $K pprox 0.33$.
• Air Bending Stainless Steel ($R/T = 1.0 - 2.0$): Use $K pprox 0.38 - 0.42$.
• Bottom Bending All Alloys: The neutral axis moves outward due to coining forces, resulting in $K pprox 0.45 - 0.48$.