Digital metal printing by electrohydrodynamic ejection and in-flight melting of microparticles

Metal additive manufacturing (AM) will impact many industries, including those producting of advanced structural, propulsion, electronic, and thermal systems. Many established metal AM processes involve layer-by-layer deposition and selective binding or melting of metal powders. However, these processes do not easily permit multi-material printing or printing directly onto non-planar surfaces. By contrast, AM techniques that deposit metal directly are typically low resolution (e.g., directed energy deposition), or cannot achieve bulk metal properties (e.g., ink-based methods). Here, we present a high resolution direct metal printing method that potentially addresses these limitations. Individual metal microparticles are electrohydrodynamically ejected on-demand from a nozzle-confined meniscus and laser-melted in-flight before landing and solidifying on a substrate. We demonstrate printing of solder and platinum particles ranging in size from 30 to 150 µm and explore the process parameter space as limited by the ejection conditions and the kinetics of melting, impact, and solidification. Our experiments demonstrate process compatibility with a wide range of powder feedstock materials, and tunability of the solidified morphology via the laser processing parameters.