Abstract: The metal droplet size is mainly determined by the nozzle size in the existing metal drop-on-demand (DOD) technologies. It is hard to spray metal micro droplets with diameter smaller than nozzle diameter by using those technologies. A novel metal droplet generator driven by stress wave is designed and developed to spray metal micro droplets without the limit of the nozzle size. Then the metal micro droplets generation experiment is carried out by using Sn-40%Pb alloy when the heating temperature and coaxial gas flow is about 300 ℃ and more than 6 L/min, respectively. The experiment results show that the average diameter of droplets generated by the stress wave is approximately 60% of the nozzle size and the standard variation of droplet diameter is 9.2 μm when the pulse width is 5 ms, the pulse frequency is 5 Hz, the impact rod stroke is 3 mm and the distance between the vibration rod bottom and nozzle is 1.5 mm. The experiment results show the feasibility of the stress driven DOD generator. The experimental results also show that in the appropriate impact rod stroke range, the size of the droplet diameter increases linearly with the pulse width increases and exponentially decreases with the increase of pulse frequency, showing that it is easy to change the droplet size when the nozzle size is constant using the developed DOD generator. The research provides a novel method for generating droplets of which size is smaller than nozzle size. These works are useful for further application of metal droplet spray technology.

Key words: Drop-on-demand, Microdroplets, Nozzle, Stress wave