This thesis investigates the feasibility of rapid prototyping by the deposition of molten metal droplets. Issues, including generation of uniform molten metal droplets of various metals using a pneumatic droplet generator, deposition of droplets, formation of vertical columns, and fabrication of 3D objects by successively dispensing molten metal droplets are explored. Fundamental physics related to these processes has also been studied.

Primary parameters affecting the generation of single uniform molten metal droplets were nozzle size, opening time of solenoid valve, and supply pressure. Oxidation of molten metal also had a significant impact on the generation of metal droplets. Stable production of uniform metal droplets using tin and zinc was achieved while continuous generation of aluminum droplets was not reliable.

Droplet temperature, substrate temperature, and deposition frequency were discovered to have the strongest effect on the formation of vertical columns built with metal droplets landing sequentially on top of each other. A one-dimensional steady state conductive heat transfer model as well as a transient model in a column was developed to predict the temperature profile of the column. Droplet coalescence was best achieved when the tip temperature of a column was maintained at the melting point of the metal. Deposition frequency should be decreased as column height increases to hold the tip temperature constant.

Impinging molten droplets could fuse with the pre-deposited material via substrate remelting under appropriate temperature conditions. A one-dimensional model was used to predict the minimum droplet and substrate temperatures required for droplets to remelt a thin layer of the underlying substrate and fuse with it. Freestanding 3D objects of various geometries were fabricated by depositing tin and zinc droplets layer by layer while attempts to build 3D components using aluminum droplets were unsuccessful due to the difficulties in producing aluminum droplets continuously because aluminum oxidizes much faster than tin or zinc.