Effects of ultrasonic vibration on deformation mechanism of incremental point-forming process

Abstract Incremental sheet forming (ISF) is a promising manufacturing process in which flat metal sheets are gradually formed into 3D shapes using a generic forming tool. To further improve the forming accuracy and formability, an ultrasonic-assisted incremental forming process has been proposed. This study aims to explore how the superposition of ultrasonic vibration affects the contact behavior and material deformation mechanism during ISF process. First, finite element (FE) simulations were conducted using LS-DYNA to investigate the effects of ultrasonic vibration on a point-forming process. In particular, changes of vibration amplitude (5 µm, 10 µm and 20 µm), tool diameter (10 mm and 20 mm) and material type (AA1050 and AA5052) on forming forces and strain evolution have been presented. This leads to the discussion on the softening mechanism of the formed material. It was found that forming forces reduced considerably with increasing vibration amplitude, especially at later stage. However, the influences of tool size on forming force under ultrasonic (US) condition is two-sided. In terms of material type, softening effect is more profound for materials with larger yield strength. Besides, it was found that the effective plastic strain increases as the increase of the vibration amplitude. Larger tool diameter results in more uniform distribution of effective strain and higher formability. It was suggested that US vibration is a very promising strategy to promote ISF to satisfy industrial requirements.