Bend Allowance Formula: Calculator & Charts

What Is Bend Allowance?

The concept of bending allowance is as follows: when a sheet of metal is bent, it has three dimensions – two outer dimensions (L1 and L2) and one thickness dimension (T).

It is important to note that the sum of L1 and L2 is greater than the unfolded length (L), and the difference between the two is known as the bending allowance (K).

Hence, the unfolded length of a bend can be calculated as L = L1 + L2 – K.

Related reading:

Bend Allowance Formula

Bend Allowance Formula for Steel

How was the formula for bend allowance created? And how do you calculate bend allowance?

Bend allowance is dependent on the inside formed radius. The lower V die opening determines the inside radius (I.R.) of a formed part. The inside radius for mild steel is 5/32 x lower V die opening (W) when the punch radius is less than 5/32 x W.

If I.R.< Material Thickness (t)

BA=3.1416180×(I.R.+t3)×A

If I.R.> 2 x Material Thickness (t)

BA=3.1416180×(I.R.+t2)×A

Where A= (180 – Bend Included Angle)

If the inside radius is equal to t or 2t, or between t and 2t, the bend allowance is calculated by interpolating the bend allowance values from the two formulas mentioned above.

Bend allowance calculation formula

Besides, to calculate this bending allowance, you can also use the following formula:

BA=A×π180×(R+K×T)
  • BA – Bend Allowance
  • A – bend angle in deg
  • R – inside bend radius in m
  • K – constant
  • T – material thickness in m

This formula considers the diverse geometries and properties of the parts to be formed.

The material thickness (T), bending angle (A), inner bending radius (R), and K-factor of the material to be bent are the most critical factors in this calculation.

As evident from the above formula, calculating the bending allowance is a simple process.

You can determine the bending allowance by substituting the aforementioned values into the formula.

When the bending angle is 90°, the bending allowance formula can be simplified as follows:

BA=π2(R+K×T)

Note: The K-factor for most standard materials and thicknesses typically falls between 0 and 0.5.

You can accurately calculate the value of the K-factor using the following K-factor calculator:

Bend Allowance Formula for Aluminum

The bending allowance for an aluminum plate is 1.6 times the material thickness subtracted from the sum of two bending lengths.

The formula for calculating the bending of an aluminum plate is L = L1 + L2 – 1.6T, where T represents the thickness of the aluminum plate, L1 and L2 are the two bending lengths, and 1.6T represents the bending allowance.

This value is an empirical value established during production.

To determine the expanded size of the aluminum plate, subtract 1.6 times the material thickness from the sum of the two bending lengths.

It’s important to note that this formula is only applicable to aluminum plates with a bending opening of 6 times the thickness of the aluminum plate.

Bend Allowance Calculator

The bending allowance calculator provided below simplifies the process of calculating the bending allowance value.

Bend Allowance Chart

The bending allowance table is a convenient resource that lists the thickness, bending radius, bending angle, bending allowance, or bending deduction values of common materials in a tabular format.

This information is stored in a designated location, making it easy to access and select when needed.

Further reading:

The tables below provide bending allowances for iron, aluminum, and copper respectively, for reference. They allow you to determine the required bend allowances for different material thicknesses easily.

(1) Bending allowance chart for cold rolled steel sheet SPCC (electro-galvanized sheet SECC)

TVAngle0.60.811.21.522.533.544.55Shortest size
V4900.91.42.8
V41200.7
V41500.2
V6901.51.72.154.5
V61200.70.861
V61500.20.30.4
V7901.61.82.12.45
V71200.80.91
V71500.30.30.3
V8901.61.92.22.55.5
V8300.30.340.40.5
V8450.60.70.81
V86011.11.31.5
V81200.80.91.11.3
V81500.30.30.20.5
V10902.73.27
V101201.31.6
V101500.50.5
V12902.83.654.58.5
V12300.50.60.7
V124511.31.5
V12601.722.4
V121201.41.72
V121500.50.60.7
V14904.310
V141202.1
V141500.7
V16904.5511
V161202.2
V161500.8
V18904.613
V181202.3
V181500.8
V20904.85.16.614
V201202.33.3
V201500.81.1
V25905.76.4717.5
V251202.83.13.4
V25150111.2
V32907.58.222
V321204
V321501.4
V40908.79.428
V401204.34.6
V401501.51.6

(2) Bending allowance chart for aluminum plate

TVAngle0.60.811.21.522.533.544.55Shortest size
V41.42.8
V61.64.5
V71.61.85
V81.82.43.15.5
V102.43.27
V122.43.28.5
V143.210
V163.244.811
V184.813
V204.814
V254.85.4617.5
V326.36.922

(3) Bending allowance chart for copper plate

Angle0.60.811.21.522.533.544.55Shortest size
903.65.26.88.428
120
150

(4) Amada bending allowance chart

MATERIALSPCCSUSAl
(LY12)
SECC
TΔTΔKΔTΔKΔTΔKΔTΔK
T=0.6 1.25 1.26    
T=0.80.181.420.151.45  0.091.51
T=1.00.251.750.201.800.301.700.381.62
T=1.20.451.950.252.150.501.900.431.97
T=1.40.642.16      
T=1.50.642.360.502.500.702.30  
T=1.6      0.692.51
T=1.80.653.00      
T=1.90.603.20      
T=2.00.653.350.503.500.973.030.813.19
T=2.50.804.200.854.151.383.62  
T=3.01.005.00 5.201.404.60  
T=3.2      1.295.11
T=4.01.206.801.007.00    
T=5.02.207.802.207.80    
T=6.02.209.80      

Note:

  • The V12 coefficient for 2mm C profile is 3.65 and that for other 2mm plates is 3.5). The edge folding bend allowance for 2mm plate is 1.4;
  • The bend allowance for 6mm copper plate is 10.3;
  • The bend allowance for 8mm copper plate is12.5;
  • The bend allowance for 10mm copper plate is 15;
  • The bend allowance for 12mm copper plate is 17;
  • The bend allowance for 3.0 stainless steel with V25 die is 6;
  • The bend allowance for 3.0 stainless steel with V20 die is 5.5;
  • (The copper bars exceeding 6mm all use the bending allowance of V40 lower die)
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Shane
Author

Shane

Founder of MachineMFG

As the founder of MachineMFG, I have dedicated over a decade of my career to the metalworking industry. My extensive experience has allowed me to become an expert in the fields of sheet metal fabrication, machining, mechanical engineering, and machine tools for metals. I am constantly thinking, reading, and writing about these subjects, constantly striving to stay at the forefront of my field. Let my knowledge and expertise be an asset to your business.

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