Acoustophoretic Liquefaction For 3D Printing Viscosity Nanoparticle Suspensions
Acoustophoretic Liquefaction For 3D Printing Viscosity Nanoparticle Suspensions
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An acoustic liquefaction approach to enhance the flow of yield stress fluids during Digital Light Processing (DLP)-based 3D printing is reported. This enhanced flow enables processing of ultrahigh-viscosity resins (μapp > 3700 Pa s at shear rates γ = 0.01 s–1) based on silica particles in a silicone photopolymer. Numerical simulations of the acousto–mechanical coupling in the DLP resin feed system at different agitation frequencies predict local resin flow velocities exceeding 100 mm s–1 at acoustic transduction frequencies of 110 s–1. Under these conditions, highly loaded particle suspensions (weight fractions, ϕ = 0.23) can be printed successfully in complex geometries. Such mechanically reinforced composites possess a tensile toughness 2000% greater than the neat photopolymer. Beyond an increase in processible viscosities, acoustophoretic liquefaction DLP (AL-DLP) creates a transient reduction in apparent viscosity that promotes resin recirculation and decreases viscous adhesion. As a result, acoustophoretic liquefaction Digital Light Processing (AL-DLP) improves the printed feature resolution by more than 25%, increases printable object sizes by over 50 times, and can build parts >3 × faster when compared to conventional methodologies.
An acoustic liquefaction approach to enhance the flow of yield stress fluids during Digital Light Processing (DLP)-based 3D printing is reported. This enhanced flow enables processing of ultrahigh-viscosity resins (μapp > 3700 Pa s at shear rates γ = 0.01 s–1) based on silica particles in a silicone photopolymer. Numerical simulations of the acousto–mechanical coupling in the DLP resin feed system at different agitation frequencies predict local resin flow velocities exceeding 100 mm s–1 at acoustic transduction frequencies of 110 s–1. Under these conditions, highly loaded particle suspensions (weight fractions, ϕ = 0.23) can be printed successfully in complex geometries. Such mechanically reinforced composites possess a tensile toughness 2000% greater than the neat photopolymer. Beyond an increase in processible viscosities, acoustophoretic liquefaction DLP (AL-DLP) creates a transient reduction in apparent viscosity that promotes resin recirculation and decreases viscous adhesion. As a result, acoustophoretic liquefaction Digital Light Processing (AL-DLP) improves the printed feature resolution by more than 25%, increases printable object sizes by over 50 times, and can build parts >3 × faster when compared to conventional methodologies.
Published 1 paper as the 1st author on Advanced Materials
Presented at MRS Fall 2022
AL-DLP of highly viscous composite resins. a) Schematic of AL-DLP 3D printing hardware. b) Demonstration of acoustophoretic liquefaction using a highly viscoelastic suspension (ϕ = 0.15) that flows under high-shear-rate conditions but remains static under low-shear-rate conditions (ambient). c) Schematic of “overcuring” in conventional DLP printing of high-viscosity resins where sub-gelation photoexposures result in undesired solidification and loss of resolution over successive layers.
Mechanical and rheological properties of composite resins. a) Average uniaxial tensile tests of the molded silicone at volume fractions, ϕ from 0 to 0.15 (N ≥ 3), and printed silicones at ϕ = 0.15 under conventional DLP and with acoustophoretic liquefaction (N = 3). b) Average shear dependent viscosity of the different ϕ silica–silicone suspensions (N = 3), and ϕ = 0.15 Carreau model fitted result. c) Relative viscosity of the composite resins relative to the neat resin as a function of volume fraction at different shear rates.
Optical behavior of composite resins. a) Absorption of the silica–silicone suspensions with different ϕ. b) Average cure depth as a function of exposure dose (N = 7) with corresponding fits. c) Scattering of the silica–silicone suspensions with different ϕ, when excited by 405 nm. d) Laser scanning microscopy of an array of printed rings from a scattering resin (ϕ = 0.15) under a single photoexposure (He = 505 mJ/cm2, λ = 405 nm). e) Average profile (N = 9) of printed rings (ϕ = 0.15) compared to the target profile of the illuminated photopattern. The bounding lines represent standard deviation.
Viscous adhesion and delamination from the build window in AL-DLP. a) The separation process for a printed cylinder of radius, r, depending on whether the ultimate strength of the material exceeds the viscous adhesion to the build window. b) The change in printable length scale (print area increase) for the composite material (ϕ = 0.15) and neat polymer (ϕ = 0) as a function of applied shear rate based this criterion for separation.
Resin flow under acoustic stimulation. a) Total displacement of the resin tray under different frequencies of vibration, measured by confocal sensor. b) The maximum velocity in the x-direction of the resin under different frequencies of vibration by simulation. c) COMSOL simulation result of resin flow (the magnified arrows on the top right represent the direction and magnitude of velocity of the resin near the printed area).
Printed resolution. a) Comparing the surface of printed negative features (500 µm square well) by conventional DLP and with ≈110 s–1 acoustophoretic liquefaction from ϕ = 0.15 resin. b) Printed thin positive features in 2D (ϕ = 0.15). c) Printed resolution of a semisphere with dimples (ϕ = 0.15).
Final Setup
Confocal Chromatic Measuring System
Control system of the acoustophoretic liquefaction. a) The magnetic encoder in the printer. b) The control box for the printer.
Without Acoustophoretic Liquefaction - Fail
With Acoustophoretic Liquefaction - Success
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