A ground-based work of droplet deposition manufacturing toward microgravity: Fine pileup of horizontally ejected metal droplets on vertical substrates

Abstract

Uniform metal micro-droplets deposition manufacturing (MDDM) technology is assumed to be a very promising technique for advancing space manufacturing on account of without using large energy equipment or custom materials. However, the effects of gravity on manufacturing processes remain to be a work-in-progress before MDDM applied in outer space. To intuitively observe the gravity effects in terrestrial environment in the opening phase of the research, we turn the additive direction ninety degrees from upright direction. Therefore, the foremost work is to investigate the deposition process of horizontally ejected droplets on a vertical substrate. Here, freestanding pillar structure (the simplest building block) is planned as fabrication samples. As a prerequisite to printing a freestanding pillar structure, the stable deposition conditions for horizontally ejected droplets are experimentally investigated firstly. To ensure that the pillar behaves a straight profile, the deposition step distance for successive pileup droplets is mathematically modeled. A strategy for the fine pileup of the horizontally ejecting droplets is proposed and identified by experiments. The results suggest that the pileup accuracy mainly depends on the stand-off distance and initial velocity of the droplet. These parameters are normalized as a variable named time consumption for droplet flight, of which the threshold is 5.1 ms. The maximum effective pileup height of droplets decays with the function of pillar height increment and deposition step distance (Δ h/s -1). Finally, structures with high aspect ratio or pillar features are fabricated to verify the formability of the manufacturing process for droplets horizontal deposition. On this basis, toward the application in outer space, an aluminum alloy (aerospace light alloy) structure is built. This work provides meaningful guidance to control the deposition of horizontally ejected droplets and steadily build structures with good appearance on vertical substrates, and laids the foundation for ground research on microgravity-based droplet deposition manufacturing.