Influence of ultrasonic vibration on molten pool behavior and deposition layer forming morphology for wire and arc additive manufacturing

Ultrasonic assisted metal additive manufacturing is a promising technology with the ability of changing the forming appearance and improving the mechanical properties. To study the influence of assisted ultrasonic vibration (UV) on molten pool behavior and deposition layer forming morphology of wire and arc additive manufacturing (WAAM) parts, a three-dimensional CFD numerical model of the WAAM process with the UV was established, and deposition experiments were carried out. The effect of ultrasonic on pressure field, temperature field and fluid flow in molten pool and appearance of deposition layer were explored. The results showed that assisted high-intensity ultrasonic vibration can significantly change the frequency and amplitude of pressure in molten pool, the cavitation effect strongly affected the grain morphology and size of the deposition layer. The acoustic streaming promoted the flow rate and high-temperature diffusion, which resulted in more uniform temperature distribution and reduced temperature gradient. In addition, many capillary waves appeared on the surface of the molten pool indicating that the surface state of molten pool was also obviously changed by ultrasonic vibration. With the improvement of the wettability and spreading of molten pool by ultrasonic, the width of the deposition layer increased while the height and depth decreased, but the cross section area of deposition layer remained the same. These findings demonstrate the mechanisms of how ultrasonic wave changes the behavior of molten pool and morphology of deposition layer, lay the foundation for further research on performance and morphology control of ultrasonic assisted WAAM.