Magnetohydrodynamic Jet Printing (MJP) is a novel additive manufacturing technique that offers tremendous promise for the fabrication of highly conductive electronic circuits with excellent adhesion on flexible substrates. MJP is an on-demand droplet jetting process in which the fluid is molten metal rather than a conductive nanoparticle ink. The work reported here examines the influence of drop spacing and jetting frequency on line morphology and electrical resistivity. Furthermore, the equivalent wire gauge of printed lines is estimated as a function of the drop volume and drop spacing. Under optimized jetting conditions, electrical resistivity as low as 3.2 ΜΩ cm (equivalent to bulk resistivity) has been achieved in aluminum 4043 alloy printed onto flexible polyimide. Little or no substrate cleaning is needed prior to printing, and post processing steps such as drying and curing are eliminated with this technique. The process uses metal wire as the feedstock material, making it significantly less expensive than conventional nanoparticle ink printing techniques.

This paper demonstrates an easily prepared novel material and approach to producing aligned nickel (Ni) nanowires having unique and customizable structures on a variety of substrates for electronic and magnetic applications. This is a new approach to producing printed metallic Ni structures from precursor materials, and it provides a novel technique for nanowire formation during reduction. This homogeneous solution can be printed in ambient conditions, and it forms aligned elemental Ni nanowires over large areas upon heating in the presence of a magnetic field. The use of templates or subsequent purification are not required. This technique is very flexible, and allows the preparation of unique patterns of nanowires which provides opportunities to produce structures with enhanced anisotropic electrical and magnetic properties. An example of this is the unique fabrication of aligned nanowire grids by overlaying layers of nanowires oriented at different angles with respect to each other. The resistivity of printed and cured films was found to be as low as 560 µΩ∙cm. The saturation magnetization was measured to be 30 emu∙g⁻¹, which is comparable to bulk Ni. Magnetic anisotropy was induced with an axis along the direction of the applied magnetic field, giving soft magnetic properties.

Multi-material inkjet printing has the capability of producing complex functionally graded components; however, material interfaces, rheological constraints, and hardware restrictions inhibit the processability of multi-material components. Ex-situ mixing, mixing on the substrate’s surface, allows for the deposition of combinatorial droplets at precise locations, permitting tailorable material interfaces. Current commercial printing hardware inhibit ex-situ mixing due to the need of multi-resolution deposition printheads. This work looks to address the present hardware constraints for ex-situ mixing by developing an inkjet printer based on a Core XY Fused Filament Fabrication gantry with two independently controlled solenoid valves for microliter deposition. The overall cost to assemble the multi-material multi-resolution printer rivals the cost of current open-source multi-material inkjet printers by 40%, while achieving a positional accuracy of 19 μm and 25 μm in the X and Y axis respectively. Furthermore, multi-resolution drop-on-demand inkjet printing enables the development of combinatorial droplets and multi-material films.