Metal Micro-Droplet Based 3D Printing Technology by Lehua Qi & Jun Luo & He Shen & Hongcheng Lian

Author:Lehua Qi & Jun Luo & He Shen & Hongcheng Lian
Language: eng
Format: epub, pdf
ISBN: 9789819909650
Publisher: Springer Nature Singapore

Because the wetting angle between the Pb–Sn alloy liquid and the inner wall of the quartz crucible is about 160° (the metal liquid does not wet the quartz surface), the solid Pb–Sn alloy liquid cannot totally fill the tiny nozzle hole under the effect of surface tension. Therefore, Fig. 5.1b does not perfectly reflect the inner shape of the small nozzle near the nozzle outline. The established nozzle geometry model needs to be further improved hence, after obtaining the internal nozzle profile, the four points near the right side are linearly fitted to obtain a linear profile expression. Then the x coordinate of the nozzle outlet (shown as the rightmost point in Fig. 5.1c) can be calculated by extrapolation using the measured nozzle diameter. In this way, a complete geometry model of the nozzle area can be established.

Several assumptions are made before conducting the simulation of Tin–Lead alloy droplet ejection: (1) Density, viscosity, and surface tension of the liquid metal are considered as constants since the temperature varies only slightly in the droplet ejection process. (2) The liquid flow during ejection is considered to be laminar. (3) The liquid metal is taken as an incompressible Newtonian fluid. That is to say the density, viscosity, and surface tension of the liquid metal are considered to be constant.2.

Determination of the initial and boundary conditions

A 2D axisymmetric model is established to simulate droplet generation, as shown in Fig. 5.2a. Here, the initial zone and mesh conditions are also illustrated. In Fig. 5.2a, the nozzle domain Ω1 has the initial condition of liquid metal. Unstructured meshes are used to adapt to the complex inner surface of the nozzle. A rectangular area directly below the nozzle is the droplet generation domain, which is initialized as the gas domain Ω2. The width and length of this domain are 1 cm and 2 cm, respectively. This droplet generation domain is divided by dense and uniform structured meshes to accurately simulate the change of the droplet contour.

Fig. 5.2Schematic diagram of 2D axisymmetric model and boundary conditions a 2D axisymmetric model of nozzle and droplet generation domains, b boundary conditions

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