K Factor Calculator
Determine the K-factor for sheet metal bending, crucial for accurately calculating bend allowance and deduction.
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Understanding K-Factor in Sheet Metal Bending
In sheet metal fabrication, precision is everything. When a flat piece of metal is bent, the material on the outside of the bend stretches, while the material on the inside compresses. Somewhere between these two surfaces lies a "neutral axis" where the material is neither stretched nor compressed. The K-Factor is a numerical representation of the location of this neutral axis, and it is crucial for accurately calculating the flat pattern length of a bent part.
What is K-Factor?
The K-Factor is a ratio that defines the position of the neutral axis relative to the material thickness. It is expressed by the formula:
K-Factor = t / T- t: The distance from the inside face of the bend to the neutral axis.
- T: The total thickness of the sheet metal.
The K-Factor value is always less than 0.5. A value of 0.5 would imply the neutral axis is exactly in the middle of the material, which is physically impossible as metal must compress on the inside. A "perfect" material might have a K-Factor of 0.4468. Softer materials have a smaller K-Factor (e.g., 0.33 for soft aluminum) because the neutral axis shifts closer to the inside surface, while harder materials have a larger K-Factor (e.g., 0.48 for hard steel).
Why is K-Factor Important? (Bend Allowance)
The primary use of the K-Factor is to calculate the Bend Allowance (BA). Bend Allowance is the length of the arc of the neutral axis. To get the total flat length of a part, you add the lengths of the flat legs to the Bend Allowance.
The formula for Bend Allowance is:
BA = Angle * (π/180) * (Radius + K-Factor * Thickness)Where 'Angle' is the bend angle in degrees, and 'Radius' is the inside bend radius.
Practical Example
Imagine you need to create a 90-degree bend in a piece of 0.060-inch thick aluminum (a soft material). You plan to use an inside bend radius of 0.120 inches. A typical K-Factor for soft aluminum is 0.33.
- Angle (A): 90°
- Inside Bend Radius (R): 0.120 in
- Material Thickness (T): 0.060 in
- K-Factor (K): 0.33
Calculating the Bend Allowance:
- BA = 90 * (π/180) * (0.120 + 0.33 * 0.060)
- BA = 1.5708 * (0.120 + 0.0198)
- BA = 1.5708 * (0.1398)
- BA ≈ 0.2196 inches
This means the length of the material along the neutral axis in the bend itself is 0.2196 inches. This value is then used with the leg lengths to determine the total length of the flat piece before bending.
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