Direct ink writing of frontally polymerized thermoset composites
Frontal polymerization (FP) is a self-propagating curing process where a single localized stimulus initiates an exothermic reaction. The released heat drives a curing front through the resin, continuously converting uncured material into a solid as the front advances. We developed a carbon-fiber–reinforced epoxy resin based ink for direct ink writing (DIW) and established radical-induced cationic frontal polymerization (RICFP) as an on-demand curing route for it.
We have extended work life of at least 25 hours, keeping the ink printable for long, uninterrupted print runs. High carbon fiber loading of 15 wt% with high degree of curing (~97%) with low void content. We can complete curing within minutes from a single spot of UV irradiation.
Non-Planar Continuous Envelope Slicing
Additive manufacturing is typically weakest at the layer lines. Non-planar layer lines benefit from increased surface area between layers and therefore increased strength resisting delamination. Continuous non-planar layers require less starting and stopping of material flow. This is critical for rheologically sensitive methods such as direct-ink writing. We have developed a Continuous Envelope Slicing method of additive manufacturing that builds the layers of a part by using the surface geometry of the part to create machine paths to build the part layers.
We have an algorithm to analyze the geometry of a part and produce a toolpath that is sensitive to the surface geometry. It considers convex/concave curvature to ensure tool-speed/material flowrate are accounted for to also ensure even and consistent deposition of material. This toolpath is then tested using commercially available software to check its viability for using a 6-DOF robotic arm.
Additive manufacturing of functional composites
Smart structures and functional devices require coupling of physical properties such as stiffness, damping, conductivity, dielectricity, piezoelectricity, and magnetic properties. Moreover, we require wide range of anisotropic behaviors throughout a structure and device. Although, additive manufacturing provides a platform for printing various geometric features, the conventional printers are limited to small set of materials. We need to customizable 3D printers to print architected microstructures using heterogeneous inks or filaments.
Specially, for functional composites, we study pneumatic-controlled direct ink writing (DIW) printing. The customizable DIW printers can print anisotropic materials using inks from multiple nozzles. Precise control of these ink mixture, printing paths, and speeds enables us to print composites for sensing, processing, and actuation functionalities. We print fiber embedded composites, hydrogels, and LCE to achieve stimuli response to solvents, water, and temperature, respectively. The glass and metallic fibers in elastomeric composites are oriented during printing so that the metamaterial can show directional functions. We also design the anisotropy of LCE by aligning the oligomers by controlling the shear extrusion of nozzle. Additive manufacturing of such logic encoded network is broadly applicable for encoding logic based multistable structures, flexible robotics, and sensor technologies.
Our interests also includes structural composites to rapidly manufacture fiber reinforce composites. Especially, we are studying the frontal polymerization method, an exothermic reaction triggered by an initial stimulus which spontaneously curing the polymer. We aim to develop gradual curing process of this polymers to meet the demand of agile manufacturing and on-site repair works.
