Rotary 3D printer for additive manufacturing of high viscosity filled thermosets

Jada Jackman

doi:10.17918/00011573

Vat-based photopolymerization is commonly restricted to relatively low-viscosity resins because coating and separation forces increase substantially with viscosity, limiting the use of highly filled and mechanically reinforced thermosets. This dissertation introduces a rotary additive-manufacturing platform that replaces the conventional resin vat with continuous slot-die coating on a rotating build plate, followed by spatially controlled ultraviolet photopolymerization. A constant-shear slot-die manifold was incorporated to promote uniform delivery of shear-thinning, non-Newtonian resins, thereby extending projected-light printing to resin formulations that are difficult to process using conventional digital light processing (DLP). This architecture introduces opportunities for continuous production, increased build area, and/or integration with high-viscosity resins, while creating new challenges in resin-film formation, image transformation, motion control, and dimensional accuracy. A prototype printer was designed and constructed with an 880 cm² coating area and a maximum projected irradiance of 12.5 mW/cm². Custom software was developed to transform sliced three-dimensional geometries into projection sequences synchronized with build-plate rotation and to coordinate resin delivery, rotation, vertical displacement, and curing. The system achieved an in-plane pixel resolution of 75.2 [mu]m and a minimum reliable layer thickness of 223 [mu]m. Rotation introduces radial variations in substrate velocity beneath the slot die and in residence time within the fixed projection zone. For Newtonian resins below 500 cP, however, the deposited film leveled to a nearly uniform thickness that was accurately described using the average substrate velocity. The radial variation in curing time produced nonuniform conversion and part warpage. This effect was mitigated by applying a resin-specific radial irradiance gradient based on the measured photopolymerization kinetics. Fourier-transform infrared spectroscopy confirmed that this correction produced a more uniform conversion profile and eliminated the observed warpage. Eight-layer specimens produced by the rotary printer had a measured thickness of 1.716 mm, compared with a predicted thickness of 1.78 mm, and a fractional conversion of 0.57±0.02, compared with 0.58±0.02 for specimens produced by conventional DLP. The mechanical properties of the two sets of specimens were statistically indistinguishable. The processing range of the system was further evaluated using an 8,600 cP BisGMA-BisEMA resin and a strongly shear-thinning DA-2 resin containing 5 wt.% fumed silica, whose low-shear viscosity approached 107 cP. Both formulations were automatically coated, cured, and formed into multilayer components without manual resin spreading. At elevated viscosity, radial thickness variations and pressure limitations in the syringe-based delivery system, rather than failure of the slot-die coating concept, became the primary constraints. These results establish rotary slot-die photopolymerization as a viable route for additive manufacturing with highly viscous and non-Newtonian thermosets and identify the relationships among resin rheology, coating dynamics, spatially varying cure kinetics, and printed-part fidelity.

Rotary 3D printer for additive manufacturing of high viscosity filled thermosets

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Rotary 3D printer for additive manufacturing of high viscosity filled thermosets

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