A study on the solidification shapes of molten metal droplet impacting at low weber number

Abstract

In uniform molten metal micro droplet deposition manufacturing (UDDM), the control of droplet solidification shape is essential to meet the forming requirements in different application scenarios to achieve a high forming quality. However, although the prediction of droplet solidification shape has been clearly mastered in a high Weber number application scenario such as thermal spray, droplets generally impact on a substrate at a low Weber number level of 2–10 in UDDM, where the droplet will solidify into various shapes under different processing parameter combinations. Here, to uncover the differentiation mechanism and establish a prediction strategy of the geometric shape of a solidified droplet during print process, the impact events under common forming conditions were systematically investigated by numerical and experimental methods. The solidification shapes of the droplets were roughly assorted into three major categories and a subtype. Results indicate that the solidification shapes are very sensitive to the footprint diameter of the droplet, thereafter an empirical formula for which was derived. On this basis, a mapping of droplet solidification shape to droplet footprint diameter was further developed, which was experimentally verified to be accurate and effective. This work shares a panorama of the solidification shapes of molten droplets impacting at low Weber number. It provides a convenient approach to automatically recognize the contour of a solidified droplet only through measuring the droplet footprint diameter, and more than that, lays a way to artificially tailor the droplet morphology in printing.