UNDERSTANDING PRINT STABILITY IN MATERIAL EXTRUSION ADDITIVE MANUFACTURING OF THERMOSET COMPOSITES

摘要

Over the last several years, rapid progress has been made in 3D printing of thermoset polymer resins. Such materials offer desirable thermal and chemical stability, attractive strength and stiffness, and excellent compatibility with many existing high-performance fibers. Material extrusion additive manufacturing (AM) is an ideal technology to print thermoset-based composites because fibers align during extrusion through the deposition nozzle, thereby enabling the engineer to design fiber orientation into the printed component. Current efforts to scale thermoset AM up to large-scale have shown promise, but have also highlighted issues with print stability. To-date, very little research has focused on understanding how rheological properties of the feedstock dictate the mechanical stability of printed objects. This talk will describe our first efforts in this area by printing tall, thin walls to characterize buckling and yielding due to self-weight. The talk will begin with an overview of thermoset material extrusion AM, including a brief history and the current state of the art in small and large-scale printing. The talk will then describe simple thin-walled test geometry and experimental setup that enable quantitative assessment and monitoring of geometric stability during the printing process using machine vision. Two feed stocks are investigated, each having different rheological properties, and the height at which buckling begins and the height at which full collapse occurs are identified as a function of wall thickness. Complementary rheological characterization shows that collapse of thin printed walls is well predicted by the classical self-weight, elastic buckling model, provided the recovery behavior of the feedstock is accounted for. These tests highlight the importance of understanding recovery in material extrusion AM feedstocks and could lead to the design of better resins and fillers, and could provide guidelines for the selection of successful print parameters for both small and large-scale thermoset AM. The talk will conclude with a brief discussion of next steps and outlook on the future of material extrusion AM of thermoset materials.