3D printing of extremely viscous materials using ultrasonic vibrations

Heterogeneous materials used in biomedical, structural and electronics applications contain a high fraction of solids (> 60 vol.%) and exhibit extremely high viscosities (mu > 1000 Pa s), which hinders their 3D printing using existing technologies. This study shows that inducing high-amplitude ultrasonic vibrations within a nozzle imparts sufficient inertial forces to these materials to drastically reduce effective wall friction and flow stresses, enabling their 3D printing with moderate back pressures (< 1 MPa) at high rates and with precise flow control. This effect is utilized to demonstrate the printing of a commercial polymer clay, an aluminum-polymer composite and a stiffened fondant with viscosities up to 14,000 Pa.s with minimal residual porosity at rates comparable to thermoplastic extrusion. This new method can significantly extend the type of materials that can be printed to produce functional parts without relying on special shear/thermal thinning formulations or solvents to lower viscosity of the plasticizing component. The high yield strength of the printed material also allows freeform 3D fabrication with minimal need for supports.