The effect of push–pull effect on the liquid bridge pinch-off process in liquid metal drop-on-demand printing

The pinch-off process of liquid bridges in metal droplet-on-demand printing directly determines printing precision and structural quality. Numerical simulations have investigated the regulation mechanism of the liquid bridge necking process by the positive and negative pressure pulses, namely, the “push–pull effect,” generated by electromagnetic actuation on the molten metal. The results show that the positive pressure pulse dominates the initial necking of the liquid bridge through axial stretching effect, while the negative pressure pulse significantly accelerates the necking process of the liquid bridge through a dual strengthening effect, namely, axial reverse stretching and radial shearing effect. The increase in the negative pulse peak causes the upward movement of the pinch-off position and the dynamic evolution of the morphology from inverted cone, cylinder to positive cone. The scaling law of necking velocity under bidirectional drive clarifies the competitive mechanism of surface tension suppressing necking in the early stage and negative pulse-induced curvature instability triggering self-accelerated breakup and the analysis of axial and radial Weber numbers reveals the competition mechanism between inertial force and capillary force. The droplet generation time, velocity, and size can be controlled by the “pulse intensity-duration” collaborative optimization method, which provides a theoretical basis for high-precision electronic printing and microscale metal 3D printing.