ME-311, IIT Gandhinagar Page 1

Air Vee Bending (AVB)

Aim

To study the Air Vee Bending of metal strips of various materials and compare their springback

with theoretical springback.

Theory of Operation

Springback predictions are important to maintain the geometric tolerance of the

finished part. Springback refers to the elastic recovery of the non-uniformly distributed stresses in a deformed part after the forming load is removed.

In bending the outer fibers will be in tension where as inner fibers will be in compression.

The stress profile looks like as shown in fig given below.

The unloading is always elastic. The loading unloading curve for elasto-plastic deformation looks like in figure give below.

ME-311, IIT Gandhinagar Page 2

The typical stress curve in case of elasto-plastic bending is shown in the part 1 of figure

below. The unloading has been shown in part 2. The unloading is always elastic. The residual stresses are shown in the part 3 of the figure.

The terminology of air vee bending is given below.

Springback can be calculated from the formula

𝑹𝒊

𝑹𝒇= 𝟒

𝒚𝑹𝒊

𝑬𝑻 − 𝟑

𝒚𝑹𝒊

𝑬𝑻 + 𝟏

Procedure

The air vee bending is carried out on simple open die. The bottoming is absent.

The metal strips are placed onto die and punch is used to bend sheets up to desired radius.

The profile of sheet is being traced onto paper. The radius of curvature and bend angle is then measured from the trace on the paper.

Now the punch is released and the final profile is traced on paper.

The final radius of curvature and final bend angle is then measured from the trace on the paper.

Parameters

Ri=initial radius of curvature

Rf=final radius of curvature (after springback)

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βi=initial bend angle

βf=final bend angle (after springback)

θ=springback

Observation Table

Material 1: Aluminum, Thickness = 2.56mm

Sr Punch Stroke (mm) βi βf θ = βf- βi 𝑅𝑖 (mm) 𝑅𝑓 (mm) Rf (expected) (mm)

1 5 17˚45ˊ 15˚25ˊ 2˚20ˊ 26 28 29.585

2 15 51˚20ˊ 50˚50ˊ 30ˊ 14 15 14.979

3 25 86˚25ˊ 82˚40ˊ 3˚45ˊ 12 14 12.712

Material 2: Mild Steel, Thickness = 2.12mm

Sr Punch Stroke (mm) βi βf θ = βf- βi 𝑅𝑖 (mm) 𝑅𝑓 (mm) Rf (expected) (mm)

1 5 18˚25ˊ 14˚30ˊ 3˚55ˊ 29 30 30.259

2 15 55˚05ˊ 49˚15ˊ 5˚50ˊ 13 15 13.247

3 25 86˚55ˊ 81˚30ˊ 5˚25ˊ 12 14 12.210

E Aluminum = 69 GPa

YAluminum = 275 MPa

EMild Steel = 200 GPa

YMild Steel = 245 MPa

Possible Errors

The time for bending was not constant.

Measurement of punch stroke by external scale by manual process.

Inconsistent thickness of metal strips.

Conclusion

The final bend angle after springback is smaller.

The final radius after springback is larger.

-Vrushiket Patil(09003044) Mechanical B’tech 2009

Date: 9 / 9 / 2011