Interactions between molten metal droplets impinging on a solid surface

We photographed molten tin droplets (2.2 mm diameter) landing off-center on a circular splat formed by the impact and solidification of another, identical drop. Final splat shapes were sensitive to the spacing between droplet centers, which was varied from 1.0 to 5.0 mm. We used a three-dimensional model of spreading and solidification to simulate interactions between droplets. The model applied a fixed-grid Eulerian control volume method to solve the fluid dynamics and energy conservation equations. A volume-of-fluid algorithm was used to track free surface deformation. Predictions of droplet shapes during impact from the model agreed well with photographs. By following temperature variations at different points on the surface of the first splat we could identify locations where remelting occurred and the splats fused together. Splat shapes observed in experiments with large tin droplets qualitatively resembled those obtained by plasma-spraying nickel powders on a steel surface.