SPRINGBACK OF SHEET METAL AFTER PLANE STRAIN STRETCH-BENDING

For the springback problem of sheet metal stretch-bending, a mathematical model was proposed based on Hill’s yielding criterion, exponential hardening and plane strain assumption. The model was validated by a stretch-bending example. The effects of stretching force per unit width, die profile radius, friction and anisotropy on the springback were studied. The results from the proposed model indicate that only if the shift distance of neutral surface exceeds one-fourth of sheet thickness, the increase of stretching force can control the springback effectively. Furthermore, the larger the bending radius, the more effective the increase of binder force in controling the sheet springback. However, the stretching force cannot increase without limit. Its calculation criterion is that the effective strain at the outer sheet layer is not greater than the material limit strain. It also shows that with the increase of stretching force, the friction has much larger influence on the sheet springback. Besides, the anisotropy also has effect on the sheet springback of stretch-bending. Comparison with FE simulation results shows that the predicted results by the mathematical model consist well with those by FEM.