Mastering Bending and Unfolding Techniques: Tips and Tricks

Bending allowance table

Double-layer bending allowance table

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

Bending allowance table for different bending angles

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.