The morphology regulation mechanism during coalescence fusion printing of multiple molten droplets

Molten microdroplet printing technology takes the uniform metal droplet as the basic forming unit, and it is a kind of rapid printing technology based on the shape characteristics of the parts to realize the manufacturing parts. This paper is investigated that during the microdroplet 3D printing (three-dimensional printing), electronics is studied based on the coupled level collective integral number method (coupled level set and volume of fluid) and the equivalent heat capacity method. The influence of the regional wettability characteristics of the heterogeneous functional wettability surface and its matching mode on the droplet spreading and coalescence behavior and the phase transition thermal process is explored. The precise regulation mechanism of heterogeneous functional wettability surfaces on the coalescence and forming of molten droplets is revealed. The results show that the wettability matching schemes of dual-functional-region surfaces and spaced multiple functional region surfaces can effectively regulate the dimensionless feature spreading lengths, dimensionless feature average heights, and dimensionless spreading edge spreading uniformities of the double-droplet and multiple droplet simultaneous impingement and coalescence morphologies, respectively. Under the condition of uniform wettability characteristics of the surface, the heat flow density and average temperature inside the molten fluid at the initial stage of the coalescence of double/multiple droplets show more regular symmetrical characteristics. The heat transfer effectiveness at the gap position is low and decreases with the increase in contact angle; when the surfaces are under heterogeneous bifunctional vs spaced multifunctional wettability conditions, the evolution of the overall heat transfer effectiveness of each type of wettability matching scheme increases with the increase in the wall contact angles of the single type of regions. In addition, when the surface wettability matching scheme includes a transition stage from neutral to superlyophobic, the liquid–gas interface is highly susceptible to overcoming the limitation of the energy barrier and thus instability gradually emerges, resulting in fluctuations of the heat transfer characteristics in its domain. The results of this study further enrich the droplet forming law and its phase transition heat transfer mechanism and provide a general strategy for the high-quality and high-effectiveness preparation of complex flexible electronic devices.