Numerical analysis of pileup process in metal microdroplet deposition manufacture

• We established a 3D numerical model of the pileup process in metal microdroplet deposition manufacture.
• The numerical models are validated with experiments.
• The effects of impacting velocity and droplet spacing on the end-shapes of the pileup are examined.
• An appropriate process window for obtaining good metallurgical bonding among droplets were ascertained.

A systematic numerical investigation of the transient transport phenomena during the pileup of molten metal droplets on the substrate is carried out in this paper. The prevailing physical mechanisms of the pileup process, including the bulk liquid, capillarity effects at the liquid–solid interface, heat transfer, and solidification, are identified and quantified numerically. Droplet diameters are from 100 μm to 320 μm, the impact velocities are 1–3 m/s, and the maximum flattening velocity is up to 1.5 times than the impact velocity. These conditions correspond to Re = O(100), We = O(1). The initial substrate temperature is 350 K. The initial droplet temperature of aluminum alloy molten droplets is 960 K. The numerical models are validated with experiments. The comparison between the numerical simulations and the experimental findings shows a good agreement. The effects of impacting velocity and relative distances between two successive molten droplets on the end-shapes of the impact regime are examined in order to describe the pileup process. This understanding is essential to implement effective process control in metal microdroplet deposition manufacture.