Design and Operation of a Droplet Deposition System for Freeform Fabrication of Metal Parts

A droplet generator has been designed and built to make wax and tin alloy droplets for freeform fabrication. The linear stability theory of liquid jets for forming droplets is first reviewed. The analytical formula for predicting droplet size and breakup length at optimal conditions are then developed. The suitability of the formulas to be used for the present droplet deposition system is studied by comparing its prediction with the more accurate numerical results and previously published experimental data. Only the suitable formulation is adopted for the design and operation of the droplet generator system. Experiments have been conducted at a wide range of operating conditions including different nozzle sizes, jet velocities, and frequencies. Good agreements are found between the predictions based on the adopted analytical formulation and the experimental results. It has been found that using the present design and procedure recommended, the droplet sizes can be controlled having a size deviation of less than 3 percent and the shape variation of the deposited layer can be managed within 3 percent of its deposited width.