Active Mixing of Disparate Inks for Multimaterial 3D Printing

Abstract

Three-dimensional printing of multi-material parts relies upon efficient mixing of the ink components and a rapid response to composition changes. However, at low Reynolds numbers and large Peclet numbers, mixing disparate viscosity and density inks poses a challenge. In this study, the performance of active micromixers for disparate non-Newtonian inks is evaluated using both This article is protected by copyright. All rights reserved.2 experiments and computational fluid dynamics simulations. The mixing efficiencies are compared with scaling relationships for active micromixers. Using detailed simulation results, multiple factors are identified that can impact the micromixer response time during a composition change. Lastly, an active micromixer is proposed and evaluated to efficiently mix arbitrary multi-material ink compositions and produce fine composition gradients within printed parts.

Direct ink writing advances in multi-material structures for a sustainable future

“…For instance, work with platelet-based materials suggests that platelet roughness at a submicron level can have a large contribution to the mechanical response of composites. 71,72 It can be more difficult to manipulate structure at the microlevel and this may require modications of the printing system as in the use of magnetic elds to manipulate particle orientation 63 or systems designed to actively mix 43,44 the cartridge in situ during printing while controlling the feeding of the different components to enable compositional variations along the structure 73,74 (Fig. 3).…”

“…1). Modications of the extrusion system by using microuidic printheads allows to switch 41,42 or mix 43,44 (Fig. 1) different materials in a single pass.…”

3D Printing of Compositional Gradients Using the Microfluidic Circuit Analogy

“…However, multimaterial printing demonstrations have largely been limited to structures with binary switching between materials using multiple nozzles, or use nozzles designed for binary switches, leading to abrupt transitions in material properties between regions . 3D printing with functional compositional gradients has more recently emerged, but the gradients have mostly been limited to simple shapes and gradients, or the issue of compositional accuracy has been ignored . Accurate compositional control of complex functionally graded materials is challenging, as the tool paths must be coordinated with the deposition of each component of the multimaterial part.…”

“…A typical multimaterial DIW printer uses two separate ink dispensers joined at a single nozzle junction to simultaneously 3D print two viscoelastic inks through a single nozzle. Some models have been established to help control the printing of viscoelastic inks, but they have not been applicable for use in structures with complex compositional gradients . As illustrated in Figure A, the toolpath of the printer is directly coupled with a desired composition ( Φ ) in order to determine the dispensing rate of each material.…”

“…We used an active mixing system with two PDMS inks for both calibration and test cases to validate the use of our model‐guided profiles for compositional accuracy . One ink was colored with a small amount of blue dye to provide a qualitative visual differentiation of the material composition, as well as a basis for quantification in order to validate the model.…”