Exploration of Metal 3-D Printing Technologies for the Microfabrication of Freeform, Finely Featured, Mesoscaled Structures

Abstract

This paper investigates a mainstream metal 3-D printing technique (i.e., direct metal laser sintering of stainless steel {SS} 316L) and two relatively new metal additive manufacturing methods (i.e., lost-wax casting of sterling silver using digital light projection/stereolithography-printed wax masters, and binder inkjet printing of SS 316L) for the fabrication, using tens-of-microns-sized voxels, of freeform, finely featured, mesoscaled metal structures part of compact systems. Characterization of the 3-D printing methods included assessment of dimensional accuracy and in-plane minimum feature size, measurement of vacuum outgassing, quantification of porosity, and estimation of thermal and electrical properties. The data demonstrate that binder inkjet printing of SS 316L has associated the smallest in-plane offset, out-of-plane offset, and eccentricity of nominally symmetric features while showing ultra-high-vacuum compatibility, low porosity, and intrinsic electrical and thermal properties close to those of bulk metal. Characterization of binder inkjet-printed SS 316L MEMS cantilevers shows repeatable micron-level linear actuation and a near-isotropic Young's modulus of the printed material close to the bulk value. Also, characterization in air at atmospheric pressure and room temperature of binder inkjet-printed SS 316L MEMS corona discharge ionizers with 32 high-aspect-ratio tips (25 tips/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , 5 mm tip height, 141.7 μm ± 3.2 μm tip radii) resulted in 8.7-kV start-up voltage and up to 422 μA total emission current; no evidence of tip degradation was found via optical inspection and device weighting after continuous IV characterization and a 12-h test (300 μA, 13.5 kV). In addition, high-resolution microscopy of binder inkjet-printed SS 316L electrodes part of a novel, compact, multi-electrode harmonized Kingdon ion trap estimates at ~15 μm the maximum height difference between the printed part and the digital model-making possible the implementation of portable, high-resolution mass spectrometers.