Sheet Metal Bending Calculation

Sheet Metal Bending Calculator

Understanding Sheet Metal Bending Calculations

Sheet metal bending is a fundamental process in manufacturing, transforming flat sheets into three-dimensional parts. Achieving precise bends is crucial for product functionality and assembly. This requires accurate calculations to determine the correct flat pattern length of the material before bending, preventing costly errors and material waste.

Key Concepts in Sheet Metal Bending

1. Material Thickness (T)

This is the actual thickness of the sheet metal being bent. It's a critical factor influencing the bend radius and overall dimensions.

2. Inside Bend Radius (IR)

The radius measured on the inside surface of the bent material. This is determined by the tooling (punch radius) and material properties. A common rule of thumb for air bending is to use an inside radius approximately equal to the material thickness.

3. Bend Angle (A)

The angle through which the material is bent. For example, a 90-degree bend creates a right angle. It's important not to confuse this with the included angle, which is the angle between the two flanges after bending (e.g., a 90-degree bend has an included angle of 90 degrees, but the material is bent through 90 degrees).

4. K-Factor (K)

The K-Factor is a ratio that represents the location of the neutral axis within the material's thickness during bending. The neutral axis is the theoretical line within the material that neither stretches nor compresses during the bend. Its position depends on the material type, thickness, and bend radius. Typical K-Factor values range from 0.3 to 0.5, with 0.33 and 0.44 being common defaults. A K-Factor of 0.5 means the neutral axis is exactly in the middle of the material thickness.

5. Bend Allowance (BA)

Bend Allowance is the length of the material along the neutral axis within the bend itself. This is the amount of material that "stretches" or "compresses" to form the bend. It's added to the straight sections of the part to determine the total flat pattern length.

The formula for Bend Allowance is:

BA = (π / 180) * (IR + K * T) * A

• π ≈ 3.14159
• IR = Inside Bend Radius
• K = K-Factor
• T = Material Thickness
• A = Bend Angle in degrees

6. Bend Deduction (BD)

Bend Deduction is the amount of material that needs to be subtracted from the sum of the outside flange lengths (measured to the outside tangent lines or "virtual sharp") to arrive at the correct flat pattern length. It accounts for the material that is effectively "used up" in the bend.

The formula for Bend Deduction is:

BD = 2 * (IR + T) * tan(A / 2) - BA

• tan = Tangent function
• A = Bend Angle in degrees
• IR = Inside Bend Radius
• T = Material Thickness
• BA = Bend Allowance

7. Flat Pattern Length (FPL)

This is the total length of the sheet metal required before any bending operations. It's calculated by summing the straight flange lengths and then adjusting for the bend deduction.

The formula for Flat Pattern Length (for a single bend with two outside flanges L1 and L2) is:

FPL = L1 + L2 - BD

• L1 = Outside Flange Length 1
• L2 = Outside Flange Length 2
• BD = Bend Deduction

Example Calculation

Let's use the following parameters to demonstrate the calculations:

• Material Thickness (T): 1.5 mm
• Inside Bend Radius (IR): 1.5 mm
• Bend Angle (A): 90 degrees
• K-Factor (K): 0.44
• Outside Flange Length 1 (L1): 50 mm
• Outside Flange Length 2 (L2): 50 mm

1. Calculate Bend Allowance (BA):

BA = (π / 180) * (1.5 + 0.44 * 1.5) * 90

BA = (0.017453) * (1.5 + 0.66) * 90

BA = (0.017453) * (2.16) * 90

BA ≈ 3.390 mm

2. Calculate Bend Deduction (BD):

BD = 2 * (1.5 + 1.5) * tan(90 / 2) - 3.390

BD = 2 * (3) * tan(45) - 3.390

BD = 6 * 1 - 3.390

BD ≈ 2.610 mm

3. Calculate Flat Pattern Length (FPL):

FPL = 50 + 50 - 2.610

FPL = 100 - 2.610

FPL ≈ 97.390 mm

Using this calculator, you can quickly determine these critical values for your sheet metal bending projects, ensuring accuracy and efficiency in your manufacturing processes.