Magnetic field mediated droplet deposition on curve surfaces

• First comprehensive study of magnetic mediated droplet deposition on curved surfaces. • Lorentz force acts as tunable damping mechanism constraining droplet motion. • Three distinct solidified morphologies observed: regular, bulged, and dimpled shapes. • Predictive scaling law developed coupling magnetic field and surface geometry effects. Precise control of liquid metal droplet deposition on curved surfaces is critical for advanced manufacturing, including droplet-based 3D printing and thermal spray coating, yet the governing mechanisms remain poorly understood. This study provides the first comprehensive analysis of how vertical magnetic fields regulate droplet spreading and solidification on concave and convex spherical surfaces. A coupled Volume-of-Fluid and enthalpy-porosity model is employed to track transient fluid flow and phase change in tin droplet deposition. The applied magnetic field induces a Lorentz force that functions as a controllable damping mechanism, progressively suppressing radial motion and reducing maximum spreading. The maximum area spreading factor α m decreases linearly with diameter ratio D* over −0.33 ≤ D* ≤ +0.33. Droplet impacting concave surfaces exhibits larger spreading compared to those on convex surfaces under identical conditions. The competition among Lorentz, inertial, gravitational, viscous, and surface tension forces leads to three distinct fully solidified droplet morphologies: regular, bulged, and dimpled droplets. A predictive scaling relationship successfully correlates magnetic field effects with surface geometry, most useful in process optimization. These results establish the first quantitative framework for magnetic control of droplet deposition on non-planar surfaces, with direct applications in droplet-based 3D printing, thermal spray coating, and functional surface manufacturing where precise morphological control is critical.