Building three-dimensional objects by deposition of molten metal droplets

Purpose - The purpose of this paper is to determine conditions under which good metallurgical bonding was achieved in 3D objects formed by depositing tin droplets layer by layer. Design/methodology/approach - Molten tin droplets (0.18-0.75 mm diameter) were deposited using a pneumatic droplet generator on an aluminum substrate. The primary parameters varied in experiments were those found to most affect bonding between droplets on different layers: droplet temperature (varied from 250 to 325 degrees C) and substrate temperature (varied from 100 to 190 degrees C). Droplet generation frequency was kept low enough (1-10 Hz) that each layer of droplets solidified and cooled down before another molten droplet impinged on it. Findings - in this paper, a one dimensional heat transfer model was used to predict the minimum droplet and substrate temperatures required to remelt a thin layer of the substrate and ensure good bonding of impinging droplets. Cross-sections through samples confirmed that increasing either the droplet temperature or the substrate temperature to the predicted remelting region produces good bonding between deposition layers. Originality/value - This paper used a practical model to provide reasonable prediction of conditions for droplet fusion which is essential to droplet based manufacturing. The feasibility of fabricating 3D metal objects by deposition of molten metal droplets has been well demonstrated.