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Mastering Bending and Unfolding Techniques: Tips and Tricks

Last updated:
August 24, 2023
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Table Of Contents

Bending allowance table

Plate thickness/V-groove widthCold rolled steel plate, galvanized steel plate or aluminum zinc coated steel plate
0.60.81.01.21.5202.53.03.5.04.55.0Minimum sizeremarks
V40.91.4          2.8When the part graphic size is marked with a negative tolerance, the bending allowance value can be increased. For example, the red part in the table can be increased by at least: 2.8:2.82,3.4:3.43 or 3.44, 4.5:4.6, 5.5:5.6
V6 1.51.72.0        4.5
V7  1.82.12.4       5
V8  1.92.22.5       5.5
V10  2.12.32.7       7
V12  2.22.52.83.4      8.5
V14     3.53.8  6.46.8 10
V16    3.13.84.55.0    11
V18    3.34.0      13
V20     4.04.95.1 6.67.27.814
V25     4.45.05.5 6.87.88.317.5
V32     5.05.56.1 8.7   

Double-layer bending allowance table

Cold rolled steel plate, galvanized steel plate or aluminum zinc coated steel plate

AngleMold slot width90°Internal bending angleExternal bending angle180°
Plate thickness
mm
1.5V1033.24.10.75
2.0V123.843.74.61.0
2.5V16454.86.11.25

Bending allowance table for different bending angles

Plate thickness
mm
3045°60°120°135145°
1.00.350.71.11.00.60.4
1.20.40.81.21.00.60.4
1.50.51.01.61.40.90.6
2.00.61.22.01.71.10.7
2.50.81.62.62.21.40.85
3.01.02.23.42.82.01.2
4.0   3.72.41.4

1. Parts process unfolding design example

1.1 Example of right-angle edge bending process unfolding drawing.

1.1.1 Example of one-bend unfolding drawing and calculation formula

  • A, B – length of the workpiece bend
  • P’ – bending allowance for bend (bending allowance: subtract a allowance for each bend)
  • R – bend radius (usually equal to the thickness of the plate)
  • T – material thickness

Unfolding length: L = A + B – P’, i.e., L = 25 + 65 – 5.5 = 84.5

According to Table 1: For a plate thickness of 3 mm, the V25 lower die should be used, with a bending allowance of 5.5.

Note: According to Table 1, different lower dies have different bending allowances, and different plate thicknesses have different bending allowances.

1.1.2 Example of two-bend unfolding drawing and calculation formula

  • A(A1), B – length of the workpiece bend
  • P – bending allowance for bend (bending allowance: subtract an allowance for each bend)
  • R – bend radius (usually equal to the thickness of the plate)
  • T – material thickness

Unfolding length: L = A + T + B – 2xP’, i.e., L = 50 + 2 + 50 – 2×3.4 = 95.6

According to Table 1: For a plate thickness of 2 mm, the V12 lower die should be used, with a bending allowance of 3.4.

Note: According to Table 1, different lower dies have different bending allowances, and different plate thicknesses have different bending allowances.

1.1.3. Example of three-bend unfolding drawing and calculation formula

  • A(A1), B(B1) – length of the workpiece bend
  • P – bending allowance for bend (bending allowance: subtract an allowance for each bend)
  • R – bend radius (usually equal to the thickness of the plate)
  • T – material thickness

Unfolding length: L = A + T + B + T – 3xP’, i.e., L = 50 + 2 + 90 + 2 – 3×3.4 = 133.8

According to Table 1: For a plate thickness of 2 mm, the V12 lower die should be used, with a bending allowance of 3.4.

Note: According to Table 1, different lower dies have different bending allowances, and different plate thicknesses have different bending allowances.

1.1.4. Example of four-bend unfolding drawing and calculation formula

  • A, B(B1) – length of the workpiece bend
  • P – bending allowance for bend (bending allowance: subtract an allowance for each bend)
  • R – bend radius (usually equal to the thickness of the plate)
  • T – material thickness

Unfolding length: L = A + A + B + T + T – 4xP’, i.e., L = 25 + 25 + 100 + 1.5 + 1.5 – 4×2.8 = 141.8

According to Table 1: For a plate thickness of 1.5 mm, the V12 lower die should be used, with a bending allowance of 2.8.

Note: According to Table 1, different lower dies have different bending allowances, and different plate thicknesses have different bending allowances.

1.1.5. Example of six-bend unfolding drawing and calculation formula

  • A(A1), B(B1) – length of the workpiece bend
  • P’ – bending allowance for bend (bending allowance: subtract an allowance for each bend)
  • R – bend radius (usually equal to the thickness of the plate)
  • T – material thickness

Unfolding length: L = A + T + A + T + B + B1 + B1 – 6xP’, i.e., L = 50 + 1.5 + 50 + 1.5 + 150 + 20 + 20 – 6×2.8 = 276.2

According to Table 1: For a plate thickness of 1.5 mm, the V12 lower die should be used, with a bending allowance of 2.8.

Note: According to Table 1, different lower dies have different bending allowances, and different plate thicknesses have different bending allowances.

1.2.1. Examples and Calculation Formulas for 180° Bending Unfolding.

  • A, B – length of the workpiece bend
  • P – flattening radius bending allowance
  • R – bend radius (usually equal to the thickness of the plate)
  • T – material thickness

Unfolding length: L = A + B – P’, i.e., L = 25 + 65 – 1 = 89

According to Table 2: For a plate thickness of 2 mm, the V12 lower die should be used, with a bending allowance of half the plate thickness.

Note: According to Table 2, different lower dies have different bending allowances, and different plate thicknesses have different bending allowances.

1.2.2. Examples and Calculation Formulas for Double-layer Bending Unfolding.

  • A, B – length of the workpiece bend
  • P1 – bending allowance for internal corners
  • P2 – bending allowance for external corners
  • R – bend radius (usually equal to the thickness of the plate)
  • T – material thickness

Unfolding length: L1 = (A-1.5) + (B-1.5) – P1, i.e., L1 = (65-1.5) + (25-1.5) – 3.2 = 83.8

L2 = A + B – P2, i.e., L2 = 65 + 25 – 4.1 = 85.9

L = L1 + L2 – T/2, i.e., L = 83.8 + 85.9 – 0.75 = 168.95

According to Table 2: For a plate thickness of 1.5 mm, the V12 lower die should be used, with a bending allowance of 3.2 for internal corners, 4.1 for external corners, and 0.75 for a 180° angle.

Note: According to Table 2, different lower dies have different bending allowances, and different plate thicknesses have different bending allowances.

1.2.3. Examples and Calculation Formulas for Double-layer Bending Unfolding.

  • A(A1), B1B2- length of the workpiece bend
  • P1 – bending allowance for internal angle
  • P2 – bending allowance for external angle
  • P3 – 90° bending allowance
  • R – bend radius (usually equal to the thickness of the plate)
  • T – material thickness
  • P4 – 180°bending allowance

Unfolding length: L1 = A + B1 – P2, i.e., L1 = 75 + 29 – 4.6 = 99.4

L2 = (A1 – T) + (B1 – T) – P1, i.e., L2 = (37 – 2) + (29 – 2) – 3.7 = 58.7

L3 = L1 + L2 – P3, i.e., L3 = 99.4 + 58.3 – 1 = 156.7

L = 25.5 + L3 – P1, i.e., L = 25.5 + 156.7 – 3.84 = 178.36

According to Table 2: For a plate thickness of 1.5 mm, the V12 lower die should be used, with an internal angle bending allowance of 3.2, an external angle bending allowance of 4.1, and a 180° bending allowance of 0.75.

Note: According to Table 2, different lower dies have different bending allowances, and different plate thicknesses have different bending allowances.

1.2.4. Examples and Calculation Formulas for Double-layer Bending Unfolding.

  • A, A1, A2, B1, B2, L, L1, L2, L3 – length of the workpiece bend
  • P1 – bending allowance for internal angle
  • R – bend radius (usually equal to the thickness of the plate)
  • T – material thickness
  • P2 – bending allowance for external angle

Unfolding length: L1 = (A1-T) + (B2-T) – P1, i.e., L1 = (35-2) + (34-2) – 3.7 = 61.3

L2 = (B1-T) + (A2-T) – P1, i.e., L2 = (50-2) + (34-2) – 3.7 = 76.3

L3 = A + B1 + B2 – 2 x P2, i.e., L3 = 70 + 35 + 50 – 2 x 4.6 = 145.8

L = L1 + L2 + L3 – 2 x P3, i.e., L = 61.3 + 75.3 + 145.8 – 2 x 1 = 281.4

According to Table 2: For a plate thickness of 2 mm, the V12 lower die should be used, with an internal angle bending allowance of 3.7, an external angle bending allowance of 4.6, and a 180° bending allowance of 1.

Note: According to Table 2, different lower dies have different bending allowances, and different plate thicknesses have different bending allowances.

1.3.1. Examples and Calculation Formulas for Special Angle Bending Unfolding.

  • A(A1), B(B1) – length of the workpiece bend
  • P – bending allowance for one-bend angle (varies with the angle)
  • R – bend radius (usually equal to the thickness of the plate)
  • T – material thickness

Unfolding length: L = (A-T) + (B-T) – P’ = A1 + B1 – P’, i.e., L = (66-1) + (26-1) – 2 = 65+25-2 = 88

According to Table 3: For a plate thickness of 2 mm, the V12 lower die should be used, and the bending allowance for a 60° angle is 2.

Note: According to Table 3, the neutral layer should be used as the bending length and width.

1.3.2. Examples and Calculation Formulas for Step Pressing Unfolding.

  • A, B – length of the workpiece bend
  • R – bend radius (usually equal to the thickness of the plate)
  • T – material thickness

Unfolding length: L = A + 1

Note: When the step is equal to two plate thicknesses, add 0.5 for each step, and add 1 for two steps.

1.3.3. Examples and Calculation Formulas for Special Angle Unfolding.

  • A(A1A2A3A4), B – length of the workpiece bend
  • P – bending allowance for a 135° angle
  • R – bend radius (usually equal to the thickness of the plate)
  • T – material thickness

Unfolding length: L = A1 + A2 + A3 + A2 + A4 – P – P

Note: For bending with steps, just subtract two allowances.

According to Table 3: For a plate thickness of 2 mm, the V12 lower die should be used, and the bending allowance for a 135° angle is 1.1.

1.3.4. Examples and Calculation Formulas for Special Angle Unfolding.

  • A(A1A2), B(B1B2) – length of the workpiece bend
  • P1 – bending allowance for a 120° angle
  • P2 – bending allowance for a 145° angle
  • P3 – 90° bending allowance
  • R – bend radius (usually equal to the thickness of the plate)
  • T – material thickness

Note: When the dimension is marked on the outline, it needs to be converted to the neutral layer size when calculating the unfolding length.

Unfolding length: L = A11 + B11 + B21 + A21 – P1 – P2 – P3, i.e., L = 80 + 50 + 103 + 70 – 1.7 – 0.7 – 3.4 = 297.2

According to Table 3: For a plate thickness of 2 mm, the V12 lower die should be used, with a bending allowance of 1.7 for a 120° angle, 0.7 for a 145° angle, and 3.4 for a 90° angle.

Note: According to Table 3, different lower dies have different bending allowances, and different plate thicknesses have different bending allowances.

1.4.1. Examples and Calculation Formulas for Ordinary Flanging Unfolding.

  • A, B, C – length, width, and height of the workpiece bend
  • P – bending allowance
  • R – bend radius (usually equal to the thickness of the plate)
  • H(H1), L(L1) – unfolding length of each side
  • T – material thickness
  • D – bending process gap (usually between 0 and 0.5)

Unfolding length: L1 = A, i.e., L1 = 27

L = A + C – P, i.e., L = 27 + 9 – 3.4 = 32.6

H1 = B – T – D, i.e., H1 = 22 – 2 – 0.2 = 19.8 (Note: D is taken as 0.2)

H = B + C – P, i.e., H = 22 + 9 – 3.4 = 27.6

According to Table 1: For a plate thickness of 2 mm, the V12 lower die should be used, with a bending allowance of 3.4.

Note: According to Table 1, different lower dies have different bending allowances, and different plate thicknesses have different bending allowances.

1.4.2. Examples and Calculation Formulas for Ordinary Door Flanging Unfolding.

  • A, B, C – length, width, and height of the workpiece bend
  • L(L1), H(H1) – unfolding length of each side
  • P – bending allowance for a 90° angle
  • P1 – bending allowance for a 30° angle
  • R – bend radius (usually equal to the thickness of the plate)
  • T – material thickness
  • D – bending process gap (usually between 0 and 0.5)

Unfolding length: L1 = B – T – D, i.e., L1 = 20 – 1.5 – 0.2 = 18.3

L = B + C1 + C2 – P – P1, i.e., L = 20 + 12 + 8.9 – 2.8 – 0.5 = 37.6

H1 = C1 + A – P – D, i.e., H1 = 12 + 35 – 2.8 – 0.2 = 44 (Note: D is taken as 0.2)

H = A + C – P, i.e., H = 35 + 20 – 2.8 = 52.2

According to Table 1: For a plate thickness of 1.5 mm, the V12 lower die should be used, with a bending allowance of 2.8 for a 90° angle and 0.5 for a 30° angle.

Note: According to Table 1, different lower dies have different bending allowances, and different plate thicknesses have different bending allowances.

1.4.3. Examples and Calculation Formulas for Ordinary Flanging Bending and Unfolding.

  • A, B, C – length, width, and height of the workpiece bend
  • P – bending allowance
  • R – bend radius (usually equal to the thickness of the plate)
  • T – material thickness
  • D – bending process gap (usually between 0 and 0.5)

Unfolding length: H1 = B – B1 – D, i.e., H1 = 50 – 12 – 0.3 = 37.7 (Note: D is taken as 0.2)

H2 = B – T – D, i.e., H2 = 50 – 2.5 – 0.3 = 47.2

H = B + C + B1 – 2xP, i.e., H = 50 + 47 + 12 – 2×4.5 = 100

L1 = A + C – T – D – P, i.e., L1 = 55 + 47 – 2.5 – 0.3 – 4.5 = 94.7

L = A + C+ B2 – 2xP, i.e., L = 55 + 47 + 12 – 2×4.5 = 105

According to Table 1: For a plate thickness of 2.5 mm, the V16 lower die should be used, with a bending allowance of 4.5.

Note: According to Table 1, different lower dies have different bending allowances, and different plate thicknesses have different bending allowances.

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