A review on the deformation mechanism and formability enhancement strategies in incremental sheet forming

The process formability of incremental sheet forming (ISF) is better than the conventional forming processes. Stretching, through-thickness-shear, bending-under-tension (BUT), and compressive forces are the proposed deformation mechanisms for improved formability; however, researchers have not corroborated (on consensus) the relative significance of any one among these. Similarly, researchers observed abrupt fractures (brittle fracture) and fractures preceded by necking (ductile fracture) for different case studies, which initiated a new debate and is still unanswered. Besides, researchers have extended the ISF to energy-assisted ISF to improve the process formability further for materials having a high strength-to-weight ratio. Three prominent energy-assisted ISF are (a) Electric-assisted ISF (E-ISF) works on the principle of lowering the yield stress by raising the temperature and has shown promise for Magnesium and Titanium alloy. (b) The ultrasonic vibration-assisted (UV-ISF) process works on the principle of acoustoplastic softening effect and thus far improved the room temperature material formability while reducing the forming forces. (c) Electromagnetic-assisted ISF (EM-ISF) is a non-contact, high-speed process that utilizes the pulsed magnetic field to apply inertial force, which improves formability by dislocation slips. The EM-ISF and UV-ISF have shown promise to counter the challenges during aluminum alloy forming; however, the work in this regard is still in the initial phase and has not explored its full potential. This study updates the potential research on the current status of the energy-assisted ISF. Different customized testing equipment is discussed that help understand the process mechanism. Microstructural changes in the material occur at normal ISF and with energy-assisted ISF are discussed in detail. Discussion and future work are presented based on the insight from various articles at the end.