Volumetric additive manufacturing of polymer structures by holographically projected light fields

Abstract

As additive manufacturing technologies proliferate and mature, overcoming some of their process limitations becomes increasingly important for the continued expansion of practical applications. Two such limitations that arise from layer-based fabrication are slow speed and geometric constraints (which include poor surface quality and challenges fabricating span, cantilever, and overhang elements). Moving beyond point-by-point and layer-by-layer approaches, the ability to generate a complex 3D volume as a unit operation has the potential to overcome these limitations. Since holography has been extensively studied as a means for storage and retrieval of 3D geometrical information, this dissertation explores the use of holographically-shaped light fields for producing three-dimensional structures in a "volume at once" approach. Leveraging advances in spatial light modulator (SLM) technology, phase-controlled light fields are projected into photopolymer resin to cure a desired geometry. By overlapping multiple sub-regions of a single light field within the target volume, the successful fabrication of non-periodic complex 3D geometries is demonstrated by single exposures on timescales of seconds. This dissertation presents a complete prototype platform that makes this approach possible, comprising a suitable hardware configuration along with the computational algorithms necessary to calculate and optimize the required optical fields. A study of the photopolymerization kinetics is also carried out, to determine the boundaries of usable process parameters such as resin absorbance and available light intensity. The results indicate that low-absorbing resins containing ~0.1% photoinitiator, illuminated at modest powers (~10-100 mW) may be used to produce full 3D structures from 1-10 second exposures, with volume build rates exceeding 100 cm3/hr, without layering and with no need for a substrate or support material.